{"gene":"PDGFB","run_date":"2026-04-29T11:37:58","timeline":{"discoveries":[{"year":1983,"finding":"PDGF B-chain shares virtual amino acid sequence identity (~104 residues) with the predicted transforming protein p28sis of simian sarcoma virus (SSV), establishing that the v-sis oncogene encodes a PDGF-related protein.","method":"Amino acid sequencing of purified PDGF and comparison with predicted v-sis protein sequence","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — direct protein sequencing, foundational discovery replicated across multiple labs","pmids":["6306471"],"is_preprint":false},{"year":1984,"finding":"The c-sis proto-oncogene encodes a polypeptide precursor of the PDGF B chain, with amino acid sequence identity over 109 residues confirmed by direct sequencing; the PDGF A chain is ~60% homologous to the B chain but encoded at a separate locus.","method":"Nucleotide sequencing of c-sis genomic clones combined with amino acid sequence analysis of purified PDGF B chain","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — direct protein and nucleotide sequencing, foundational structural identification","pmids":["6329745"],"is_preprint":false},{"year":1984,"finding":"SSV-transformed cells secrete a PDGF-like protein (p28v-sis) that stimulates autocrine cell growth through PDGF receptors; anti-PDGF antisera block 3H-thymidine incorporation in growing SSV-transformed cells; PDGF receptors purified from SSV-NIH 3T3 cells retain active protein tyrosine kinase activity stimulated by PDGF.","method":"Mitogenic assay, 125I-PDGF receptor competition binding, anti-PDGF antisera neutralization, receptor purification with tyrosine kinase assay, tumor growth in nude mice","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods establishing autocrine mechanism and receptor tyrosine kinase activation","pmids":["6091918"],"is_preprint":false},{"year":1984,"finding":"Expression of the normal human sis/PDGF-2 coding sequence under retroviral LTR control induces cellular transformation of NIH-3T3 cells, demonstrating that the growth factor coding sequence itself has transforming activity.","method":"Stable transfection of chimeric LTR-c-sis construct into NIH/3T3 cells; transforming foci assay; detection of sis/PDGF-2 translational products","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — gain-of-function transfection with protein expression confirmation, replicated concept across labs","pmids":["6091919"],"is_preprint":false},{"year":1984,"finding":"The v-sis gene product competes with 125I-PDGF for receptor binding on fibroblast membranes, directly demonstrating functional equivalence between the SSV oncogene product and PDGF.","method":"Bacterial expression of v-sis protein; 125I-PDGF receptor competition binding assay; immunochemical identification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro receptor binding assay with purified recombinant protein and immunochemical validation","pmids":["6088510"],"is_preprint":false},{"year":1985,"finding":"The v-sis gene product specifically binds PDGF receptors, stimulates tyrosine phosphorylation of PDGF receptors, and induces DNA synthesis in quiescent fibroblasts; transformation by SSV correlates strictly with PDGF receptor expression in target cells.","method":"Partial purification of v-sis protein; receptor binding; tyrosine phosphorylation assay; mitogenic assay; antibody neutralization; cell susceptibility correlation","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods, receptor tyrosine phosphorylation directly demonstrated","pmids":["2996133"],"is_preprint":false},{"year":1985,"finding":"Normal human endothelial cells in culture express PDGF B chain mRNA and synthesize a PDGF-B precursor polypeptide (predicted Mr 27,281), establishing endothelial cells as a physiological source of PDGF-B.","method":"cDNA cloning and complete sequence analysis of sis-homologous cDNA from human umbilical vein endothelial cells","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — direct cDNA cloning and sequence determination from normal human cells","pmids":["4033772"],"is_preprint":false},{"year":1986,"finding":"The SIS/PDGF2 mRNA is 3373 nucleotides with only a 723-bp coding sequence flanked by long 5' (1022 bp) and 3' (1625 bp) untranslated regions; a TATA box 24 bp upstream and an enhancer-like TG element downstream of the polyadenylation site were identified as putative regulatory elements.","method":"cDNA cloning, nuclease S1 mapping, primer extension, and nucleotide sequence analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct sequencing and mapping of the transcriptional unit","pmids":["3517869"],"is_preprint":false},{"year":1986,"finding":"The v-sis gene product is co-translationally processed in the endoplasmic reticulum–Golgi compartment where signal sequence cleavage and N-linked glycosylation occur; it contains no transmembrane regions (confirmed by trypsin protection in microsomes); mutation of the proposed proteolytic processing site (Lys-Arg→Asn-Ser at residues 110–111) retains full biological activity; mutations disrupting the signal sequence cause nuclear mislocation and loss of activity.","method":"Site-directed mutagenesis; subcellular fractionation; microsome trypsin protection assay; N-linked glycosylation analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with mutagenesis and multiple biochemical assays","pmids":["3537701"],"is_preprint":false},{"year":1986,"finding":"Phorbol ester (TPA) induces c-sis/PDGFB gene transcription in K-562 hematopoietic stem cells during megakaryoblastic differentiation, as determined by nuclear run-off transcriptional assay, without generalized effects on other hematopoietic cell lines.","method":"Northern blot analysis; nuclear run-off transcriptional assay","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — nuclear run-off establishes transcriptional mechanism, single lab","pmids":["3466024"],"is_preprint":false},{"year":1987,"finding":"Each of the eight conserved cysteine residues in the v-sis/PDGF-B molecule is required for disulfide-linked dimer formation; however, interchain disulfide bonds are not essential for receptor activation—only the four cysteines forming intramolecular disulfide bonds are required for biological activity.","method":"Site-directed mutagenesis of individual cysteine codons; disulfide dimer formation assay; transforming activity assay","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 — systematic site-directed mutagenesis of all conserved cysteines with functional validation","pmids":["3035718"],"is_preprint":false},{"year":1989,"finding":"Transformation by v-sis occurs through internal activation of PDGF receptors before cell surface expression: a v-sis mutant encoding ER/Golgi-retained protein transforms NRK cells as efficiently as wild-type without secreting detectable v-sis protein, and anti-PDGF antisera fail to reverse morphological transformation.","method":"Construction of ER/Golgi-retention mutant of v-sis; stable transfection; transformation assay; anti-PDGF antibody treatment","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1–2 — genetic mutant approach with multiple controls establishing intracellular autocrine mechanism","pmids":["2551043"],"is_preprint":false},{"year":1989,"finding":"PDGF-B induces a SIF (sis-inducible factor) DNA-binding activity that binds a conserved element upstream of the c-fos promoter; this SIF-binding element confers sis/PDGF inducibility onto a truncated c-fos promoter and functions additively with the serum response element (SRE), but only responds to sis/PDGF (not phorbol esters or serum).","method":"Electrophoretic mobility shift assay; reporter gene transfection; promoter deletion analysis with recombinant PDGF","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 — functional promoter analysis with purified recombinant protein and EMSA, replicated","pmids":["2176154"],"is_preprint":false},{"year":1989,"finding":"Internal activation of PDGF receptors by v-sis product is sufficient for transformation, but activated receptors must reach the cell surface to couple with intracellular mitogenic signaling; suramin completely blocks proliferation and eliminates cell-surface receptor tyrosine phosphorylation without affecting intracellular receptor phosphorylation.","method":"Suramin treatment; anti-PDGF neutralizing antibody; tyrosine phosphorylation assay of cell-surface vs. intracellular PDGF receptors; defined medium proliferation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — dissection of intracellular vs. surface receptor activation with multiple pharmacological and biochemical approaches","pmids":["2813378"],"is_preprint":false},{"year":1989,"finding":"PDGF-B mRNA and protein expression in glioblastoma: proliferating vascular endothelial cells in human glioblastoma coexpress PDGF B chain mRNA and PDGF receptor mRNA, supporting an autocrine growth stimulation mechanism for endothelial hyperplasia in this tumor.","method":"RNA transfer blot analysis; in situ hybridization of tumor biopsies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 — in situ hybridization demonstrating co-expression; no direct functional validation in this paper","pmids":["2845420"],"is_preprint":false},{"year":1989,"finding":"TGF-β and phorbol ester (PMA/diacylglycerol via protein kinase C) each induce c-sis/PDGF-B mRNA expression in glioblastoma cells through distinct signaling routes (TGF-β uses a PKC-independent kinase pathway); both pathways converge on transcriptional activation of c-sis.","method":"Nuclear run-on transcription assay; PKC downregulation; kinase inhibitor H7; cycloheximide treatment; RNA hybridization","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — nuclear run-off establishes transcriptional mechanism; pharmacological dissection of two pathways","pmids":["2655888"],"is_preprint":false},{"year":1990,"finding":"PDGF-B protein is localized within macrophages in all stages of human and nonhuman primate atherosclerotic lesion development, implicating macrophage-derived PDGF-B as a source of chemotactic and growth-stimulatory signals for intimal smooth muscle cells.","method":"Immunohistochemical localization of PDGF-B protein in atherosclerotic tissue sections","journal":"Science (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 3 — immunolocalization study; establishes cellular source but no direct functional mechanism experiment","pmids":["2343305"],"is_preprint":false},{"year":1991,"finding":"Two specific PDGF-B chain residues, arginine 27 and isoleucine 30, mediate receptor binding and cell activation; substitutions at these positions create PDGF-B mutants defective in receptor affinity and mitogenic activity without disrupting overall protein structure (confirmed by circular dichroism and fluorescence spectroscopy).","method":"Site-directed mutagenesis; 125I-PDGF-BB displacement assay; mitogenic assay; inositol lipid turnover; circular dichroism; fluorescence spectroscopy","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with multiple functional assays and structural validation","pmids":["1661670"],"is_preprint":false},{"year":1992,"finding":"SPARC (extracellular glycoprotein) specifically binds PDGF-BB and PDGF-AB dimers (but not PDGF-AA) and inhibits their binding to PDGF receptors on dermal fibroblasts in a dose-dependent and pH-dependent manner.","method":"Specific immunoprecipitation of SPARC–125I-PDGF-BB complexes; solid-phase binding assay; receptor competition binding assay; pH-dependence analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — reciprocal binding assays with purified proteins, multiple formats, functional inhibition demonstrated","pmids":["1311092"],"is_preprint":false},{"year":1992,"finding":"The p85 regulatory subunit of PI 3-kinase associates with the PDGF receptor via its SH2 domains in a tyrosine autophosphorylation-dependent manner; binding requires receptor kinase activity and the N-terminal SH2 domain binds PDGF receptors more stably than EGF receptors.","method":"Co-immunoprecipitation; GST-SH2 fusion protein binding assays; phosphotyrosine inhibition assays; Western blot","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 — GST pulldown with defined domains plus co-IP; phosphotyrosine-dependence established","pmids":["1372091"],"is_preprint":false},{"year":1993,"finding":"A 10-bp element named SPE (SIS proximal element, positions -58 to -39 relative to PDGF-B mRNA start site) is essential for TPA-induced transcriptional activation of the SIS/PDGFB promoter in megakaryocytes; gel shift assays show a TPA-inducible nuclear complex that forms over the same time frame as mRNA induction and is blocked by cycloheximide, indicating requirement for new protein synthesis.","method":"Linker scanning mutagenesis across 250-bp promoter; luciferase reporter assay; gel mobility-shift assay; time-course analysis; cycloheximide treatment","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — systematic promoter mutagenesis with functional validation and EMSA","pmids":["8356057"],"is_preprint":false},{"year":1994,"finding":"v-sis-induced Egr-1 expression is mediated by a pathway requiring tyrosine kinase activity and c-Ha-Ras; dominant-negative Ras and Raf mutants abrogate Egr-1 induction by v-sis/PDGF-B, and this signal is independent of protein kinase C.","method":"Conditional metallothionein-v-sis expression system; dominant-negative Ras and Raf transfection; Egr-1 promoter-reporter assay; PKC inhibition","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with dominant negatives; inducible system, single lab","pmids":["7890805"],"is_preprint":false},{"year":1994,"finding":"Selective PDGF receptor kinase blockers (tyrphostins AG1295 and AG1296) reverse the transformed phenotype of sis-transfected NIH 3T3 cells without affecting src-transformed cells or c-src kinase activity, confirming that PDGF receptor kinase activity is required for v-sis/PDGF-B-driven transformation.","method":"Tyrphostin treatment; transformation reversal assay; receptor autophosphorylation assay; kinase activity assay; selectivity profiling against multiple receptors","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 — pharmacological reversal of transformation with selective inhibitors and kinase specificity profiling","pmids":["7954456"],"is_preprint":false},{"year":1995,"finding":"Mechanical strain-induced fetal lung cell growth is mediated by upregulation of PDGF-B and PDGF-β receptor mRNA and protein; phosphorothioate antisense PDGF-B oligonucleotides, neutralizing PDGF-BB antibody, and the PDGF receptor tyrosine kinase inhibitor tyrphostin 9 each abolish strain-induced DNA synthesis.","method":"Antisense oligonucleotide knockdown; neutralizing antibody; tyrosine kinase inhibitor; DNA synthesis assay; mRNA and protein expression analysis","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal loss-of-function approaches converging on same phenotype, single lab","pmids":["7653578"],"is_preprint":false},{"year":1997,"finding":"In dermatofibrosarcoma protuberans (DFSP), chromosomal translocation t(17;22) fuses COL1A1 to PDGFB, deleting exon 1 of PDGFB and releasing it from normal transcriptional regulation, producing constitutive PDGF-B expression that drives tumor formation.","method":"Genomic and RNA-level characterization of translocation breakpoints; RT-PCR; FISH","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — molecular characterization of translocation breakpoints, replicated across multiple labs","pmids":["8988177"],"is_preprint":false},{"year":1998,"finding":"PDGF-B knockout mice lack pericytes and mesangial cells, while PDGF-A knockout mice lack alveolar smooth muscle cells, demonstrating that PDGF-B is specifically required for the development of pericytes and mesangial cells (but not other smooth muscle cell subtypes).","method":"Targeted gene knockout in mice; histological analysis of pericyte and mesangial cell development","journal":"Current opinion in nephrology and hypertension","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with isoform-specific phenotypic comparison","pmids":["9442358"],"is_preprint":false},{"year":1998,"finding":"PDGF signals through Ras/PI3K/Akt/IKK to activate NF-κB, which transmits both a proliferative signal (via c-myc induction) and an anti-apoptotic signal that counterbalances c-Myc cytotoxicity; Akt transiently associates in vivo with IKK and induces IKK activation upon PDGF stimulation.","method":"Co-immunoprecipitation of Akt–IKK complex; kinase assays; dominant-negative constructs; NF-κB reporter assays; apoptosis assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo co-IP of Akt-IKK complex, kinase assays, genetic epistasis, replicated","pmids":["10485711"],"is_preprint":false},{"year":1998,"finding":"PDGF receptor dimerization induced by ligand binding leads to autophosphorylation, enabling recruitment and activation of cytoplasmic SH2-domain-containing signal transduction molecules (including PI3K, PLCγ, Src family kinases, Grb2, SHP-2), initiating pathways controlling cell growth, actin reorganization, migration, and differentiation.","method":"Biochemical analysis of receptor phosphorylation; SH2 domain binding studies; downstream signaling assays","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 — comprehensive review synthesizing multiple experimental studies on receptor signaling mechanisms","pmids":["9739761"],"is_preprint":false},{"year":1999,"finding":"Cyclic mechanical strain increases PDGF-B mRNA and activates the PDGF-B promoter (12-fold in psisCAT 6A construct), and also upregulates PDGF-β receptor protein, both contributing to strain-induced smooth muscle cell proliferation; neutralizing antibodies to PDGF-β receptor reduce strain-induced thymidine incorporation by 50%.","method":"Cyclic strain on silicone elastomer; promoter-CAT reporter transfection; neutralizing antibody; Western blot; 3H-thymidine incorporation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — promoter activity and neutralizing antibody data, single lab","pmids":["10558917"],"is_preprint":false},{"year":2001,"finding":"The COL1A1-PDGFB chimeric protein produced in DFSP is processed in transfected cells into mature PDGF-B dimers that activate the PDGFB receptor pathway in a paracrine manner, rendering cells growth-factor-independent and tumorigenic; mutagenesis of the COL1A1-PDGFB cleavage site shows that even uncleaved forms retain mitogenic activity.","method":"Stable and transient transfection; anti-PDGFB antibody detection; growth factor independence assay; nude mouse tumorigenicity assay; site-directed mutagenesis of processing site","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 — reconstitution with chimeric protein, mutagenesis, and in vivo tumorigenicity testing","pmids":["11420709"],"is_preprint":false},{"year":2001,"finding":"PDGF-B is expressed by cultured human endothelial cells and kidney epithelial cells (BSC-1), which secrete a PDGF-like protein with mitogenic and chemotactic activities inhibitable by anti-PDGF antibody; c-sis but not c-sis A-chain mRNA is detected in these cells, and TGF-β2 induces c-sis mRNA accumulation without corresponding increase in secreted PDGF-like activity.","method":"Northern blot with c-sis cDNA probe; mitogenic and chemotactic activity assays; antibody inhibition; protein secretion measurement","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 3 — biochemical assays establishing paracrine function, single lab","pmids":["3177660"],"is_preprint":false},{"year":2002,"finding":"Adiponectin specifically binds PDGF-BB (but not PDGF-AA) and inhibits PDGF-BB binding to smooth muscle cells, suppressing PDGF-β receptor autophosphorylation and ERK phosphorylation, thereby inhibiting PDGF-BB-driven smooth muscle cell proliferation and migration.","method":"125I-PDGF-BB binding competition; immunoblot of receptor autophosphorylation and ERK phosphorylation; proliferation (3H-thymidine) and migration (Boyden chamber) assays","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding demonstrated, receptor autophosphorylation inhibition, multiple functional readouts","pmids":["12070119"],"is_preprint":false},{"year":2003,"finding":"Endothelial PDGF-B retention motif (heparan sulfate proteoglycan-binding domain) is required for proper pericyte integration into the vessel wall in tumors; loss of this retention motif (pdgf-b ret/ret mice) causes pericyte detachment and partial loss, increased vessel diameter, and hemorrhaging even when PDGF-B is provided by tumor cells.","method":"Mouse genetics (pdgf-b ret/ret); tumor transplantation; transgenic PDGF-B expression; pericyte coinjection with tumor cells; histological and vascular analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic tools dissecting endothelial vs. non-endothelial sources and retention motif function","pmids":["14561699"],"is_preprint":false},{"year":2005,"finding":"PDGF-B signaling via the MAPK pathway induces YB-1 subcellular shuttling from nucleus to cytoplasm in mesangial cells during mesangioproliferative glomerulonephritis; YB-1 knockdown by RNAi abolishes the mitogenic effect of PDGF-B, identifying YB-1 as a necessary downstream signaling target.","method":"PDGF-B infusion in vivo; PDGF aptamer blockade; MEK inhibitor U0126; RNAi knockdown; immunolocalization; in vitro proliferation assay","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 — pathway placement by pharmacological blockade combined with RNAi validation of necessity","pmids":["16093451"],"is_preprint":false},{"year":2005,"finding":"Hypoxia increases endothelial PDGF-B mRNA and protein via a transcriptional mechanism; hypoxic mesangial cells show 2–3-fold enhanced proliferative response to PDGF-B associated with increased specific receptor binding capacity; hypoxic conditioned medium chemoattractant activity is largely abolished by PDGF-B neutralizing antibody.","method":"Northern and Western blot; saturation binding assay; 3H-thymidine proliferation; Boyden chamber migration; neutralizing antibody","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods, single lab","pmids":["16014047"],"is_preprint":false},{"year":2007,"finding":"TGF-β-Smad pathway promotes glioma cell proliferation by transcriptionally inducing PDGF-B expression in gliomas with an unmethylated PDGF-B gene; the epigenetic methylation status of the PDGF-B gene is the molecular determinant of whether TGF-β acts as oncogenic (inducing PDGF-B and proliferation) or not in human glioma.","method":"Transcriptomic profiling; ChIP for Smad binding; PDGF-B promoter methylation analysis; gain/loss-of-function experiments; primary patient-derived glioma cultures","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 — ChIP, methylation analysis, and functional rescue experiments in primary patient cells","pmids":["17292826"],"is_preprint":false},{"year":2008,"finding":"PDGF-B/PDGFR-β signaling is required for cardiac contributions of epicardium-derived cells and cardiac neural crest; Pdgf-b-/- and Pdgfr-β-/- mouse embryos show ventricular septal defects, atrioventricular valve maldevelopment, impaired coronary arteriogenesis, myocardial hypoplasia, and cardiac nerve hypoplasia.","method":"Analysis of Pdgf-b-/- and Pdgfr-β-/- mouse embryos; immunohistochemical staining for αSMA, periostin, ephrinB2, VEGFR-2, NCAM at multiple embryonic stages","journal":"Developmental dynamics","confidence":"High","confidence_rationale":"Tier 2 — dual knockout analysis with multiple molecular markers across developmental stages","pmids":["18213589"],"is_preprint":false},{"year":2008,"finding":"PDGF-BB signaling transcriptionally induces miR-221, which then downregulates c-Kit and p27Kip1; loss of p27Kip1 by miR-221 drives PDGF-mediated vascular smooth muscle cell proliferation, while decreased c-Kit suppresses SMC-specific contractile gene expression via reduced Myocardin.","method":"miRNA expression profiling; promoter-reporter assay; miR-221 mimic/inhibitor transfection; target site mutagenesis; luciferase reporter; western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — pathway dissection with multiple molecular tools, target validation by reporter assays","pmids":["19088079"],"is_preprint":false},{"year":2009,"finding":"VEGF-C regulates PDGF-B expression via VEGFR3 signaling; blockade of VEGFR3 reduces PDGF-B expression and causes marked capillary dilation with mural cell dissociation; conversely, blockade of PDGF-BB diminishes VEGF-C expression, establishing a mutual regulatory loop between VEGF-C and PDGF-B in vascular stabilization.","method":"Neutralizing antibody AFL-4 against VEGFR3; PDGF-BB blocking antibody; murine hindlimb ischemia model; histological and blood flow analysis","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal antibody blockade experiments, single lab","pmids":["19734356"],"is_preprint":false},{"year":2011,"finding":"SDF-1α induces PDGF-B mRNA and protein expression via a transcriptional mechanism involving ELK-1 transcription factor binding to the pdgf-b promoter; this SDF-1α/PDGF-B pathway is required for differentiation of PDGFR-β+ bone marrow cells into mature pericytes.","method":"In vitro SDF-1α stimulation; 2-kb PDGF-B promoter reporter assay; chromatin immunoprecipitation (ChIP) for ELK-1; in vivo tumor model; pericyte differentiation assay","journal":"Molecular cancer research : MCR","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrates direct ELK-1 binding, promoter-reporter validates transcriptional mechanism, functional pericyte differentiation assay","pmids":["21911740"],"is_preprint":false},{"year":2013,"finding":"Venous malformation-causing TIE2 mutations (L914F) cause AKT-dependent chronic suppression of PDGFB production in endothelial cells; mutant TIE2 L914F chronically activates AKT in a ligand-independent manner, reducing PDGFB secretion and thereby impairing mural cell recruitment, contributing to abnormal vascular channel formation.","method":"Global gene expression profiling of TIE2-mutant ECs; in vitro TIE2 L914F and R849W expression; AKT inhibitor treatment; ex vivo patient tissue PDGFB measurement","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — functional rescue with AKT inhibitor, validated in patient tissues ex vivo","pmids":["23633549"],"is_preprint":false},{"year":2013,"finding":"Mutations in PDGFB cause autosomal dominant idiopathic basal ganglia calcification (IBGC) in humans; in mice, loss of endothelial PDGFB leads to pericyte deficiency and blood-brain barrier dysfunction, and hypomorphic Pdgfb alleles develop age-related brain calcifications that correlate with degree of pericyte and BBB deficiency.","method":"Human genetic analysis; mouse hypomorphic Pdgfb alleles; histological and radiological brain calcification assessment; pericyte quantification; BBB permeability assay","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — human genetics combined with mouse genetic model showing dose-dependent calcification, replicated","pmids":["23913003"],"is_preprint":false},{"year":2013,"finding":"LHX2 transcription factor directly induces PDGF-B expression in tumor cells, driving autocrine PDGFRβ signaling for cell migration/invasion and paracrine signaling to pericytes for vessel maturation and primary tumor growth; pharmacological inhibition of PDGF-B/PDGFRβ signaling reduces vessel functionality, tumor growth, and LHX2-induced invasion.","method":"Loss/gain-of-function in transgenic mouse models; pharmacological PDGFB/PDGFRβ inhibition; in vitro migration/invasion assays; vessel maturation analysis","journal":"Molecular oncology","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic models plus pharmacological validation, dual autocrine/paracrine mechanism established","pmids":["24423492"],"is_preprint":false},{"year":2015,"finding":"Germline PDGFB mutations causing Primary Familial Brain Calcification (PFBC) lead to complete loss of PDGF-B function through abolished protein synthesis or defective PDGF-Rβ binding/stimulation; the Pdgfbret/ret mouse model (lacking the proteoglycan-binding retention motif) develops brain calcification, demonstrating that altered tissue distribution of PDGF-B protein is sufficient to cause calcification.","method":"In vitro functional analysis of six PDGFB mutations; PDGF-Rβ binding assay; autophosphorylation assay; heterozygous knockout mice; Pdgfbret/ret mice; brain calcification assessment; pericyte coverage quantification; BBB analysis","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1–2 — direct functional assays of multiple mutants combined with mouse genetic models","pmids":["26599395"],"is_preprint":false},{"year":2016,"finding":"Transgenic cardiac overexpression of PDGF-B induces focal fibrosis and moderate cardiac hypertrophy, mediated primarily via PDGFRβ; the weaker fibrotic effect of PDGFB (compared to PDGF-A, which is more potent via PDGFRα) reflects differences in receptor affinity, implicating PDGFRα in interstitial mesenchymal cells as the main mediator of strong cardiac fibrosis.","method":"Alpha-myosin heavy chain promoter-driven transgenic overexpression; histological and cardiac size analysis; immunohistochemistry for PDGF receptors","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 — transgenic model with receptor expression analysis, single lab","pmids":["27816607"],"is_preprint":false},{"year":2017,"finding":"PDGFB expressed by lymphatic endothelial cells (LECs) of collecting vessels is required for smooth muscle cell (SMC) recruitment to lymphatic vessels; LEC-specific Pdgfb deletion prevents SMC recruitment causing vessel dilation and failure of pulsatile contraction; extracellular matrix retention of PDGFB is required for SMC recruitment, and low ECM-binding components around capillaries provide a checkpoint preventing inappropriate SMC investment of capillaries.","method":"LEC-specific Cre-mediated Pdgfb deletion; PDGFB overexpression in LECs; histological analysis; ECM retention assay; pulsatile contraction measurement","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — conditional cell-specific knockout with defined molecular mechanism (ECM retention), multiple vascular beds analyzed","pmids":["28851707"],"is_preprint":false},{"year":2020,"finding":"Platelet-specific conditional knockout of PDGFB impairs tumor vascular pericyte coverage and function, leading to enhanced hypoxia, epithelial-to-mesenchymal transition, elevated circulating tumor cells, and increased spontaneous metastasis, establishing a novel role for platelet-derived PDGFB in maintaining tumor vascular integrity.","method":"Platelet-specific Cre-mediated Pdgfb conditional knockout; two tumor mouse models; pericyte coverage quantification; hypoxia markers; EMT markers; circulating tumor cell counting; metastasis quantification","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 — conditional cell-specific knockout in two independent tumor models with multiple phenotypic readouts","pmids":["32586981"],"is_preprint":false},{"year":2020,"finding":"Endothelial Twist1 transcription factor mediates hypoxia-induced PDGFB upregulation; Twist1 overexpression increases PDGFB expression in pulmonary arterial endothelial cells; knockdown of endothelial Twist1 suppresses hypoxia-induced αSMA-positive cell accumulation and PDGFB upregulation in an in vivo gel implant model; Twist1 and PDGFB levels are elevated in IPAH patient pulmonary artery endothelial cells.","method":"Twist1 overexpression/knockdown; in vivo hydrogel implant model on mouse lung; immunofluorescence; IPAH patient cell analysis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — gain and loss of function in vitro and in vivo with patient validation","pmids":["32371931"],"is_preprint":false},{"year":2021,"finding":"Adult-induced endothelial deletion of Pdgfb in 2-month-old mice causes slowly progressive pericyte loss (reaching ~50% decrease in endothelial:pericyte ratio and >70% decrease in pericyte marker expression by 12–18 months) and increased BBB permeability; in contrast to constitutive Pdgfb loss, adult-induced loss does not cause vessel dilation, arterio-venous skewing, or microvascular calcification, distinguishing developmental from maintenance roles of PDGFB.","method":"Tamoxifen-inducible endothelial-specific Cre; longitudinal pericyte quantification; BBB permeability assay; vessel morphology analysis","journal":"Journal of cerebral blood flow and metabolism","confidence":"High","confidence_rationale":"Tier 2 — inducible cell-specific knockout with longitudinal analysis distinguishing developmental vs. maintenance functions","pmids":["34689641"],"is_preprint":false},{"year":2021,"finding":"Macrophage-derived PDGF-B is critical for pathological smooth muscle cell expansion (distal muscularization) in pulmonary hypertension; macrophage-specific deletion of Pdgfb (LysM-Cre) prevents hypoxia-induced distal muscularization and PH; PDGF-B is upregulated in macrophages from human PAH patients; nanoparticle-mediated siRNA knockdown of Pdgfb specifically in lung macrophages prevents hypoxia-induced PH and right ventricular hypertrophy.","method":"LysM-Cre conditional Pdgfb knockout; clodronate macrophage depletion; HIF-1α and HIF-2α conditional knockouts; macrophage-conditioned medium SMC proliferation/migration assay; nanoparticle siRNA delivery; human PAH patient macrophage analysis","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic models, human patient validation, therapeutic nanoparticle intervention","pmids":["33591958"],"is_preprint":false},{"year":2021,"finding":"C/EBPβ transcription factor directly binds PDGFB promoter elements to facilitate PDGFB transcription in anoikis-resistant gastric cancer cells; secreted PDGFB promotes cancer cell survival via a C/EBPβ-dependent self-feedback loop and promotes angiogenesis via MAPK/ERK signaling in vascular endothelial cells.","method":"ChIP showing direct C/EBPβ binding to PDGFB promoter; loss/gain-of-function experiments; MAPK/ERK signaling analysis; in vitro and in vivo metastasis models","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — ChIP validates direct transcription factor binding, functional rescue experiments, dual autocrine/paracrine mechanism","pmids":["34341514"],"is_preprint":false},{"year":2022,"finding":"Microglia constitutively release PDGFB, which signals via PDGFRα on hypothalamic paraventricular nucleus neurons to promote Kv4.3 (potassium channel) expression; ablation of microglia, conditional deletion of microglial PDGFB, or suppression of neuronal PDGFRα elevates pre-sympathetic neuronal excitability and sympathetic outflow, causing hypertension; central supplementation of exogenous PDGFB suppresses the pressor response.","method":"Microglial ablation; conditional microglial Pdgfb deletion; neuronal PDGFRα suppression; electrophysiology; sympathetic outflow measurement; blood pressure monitoring; exogenous PDGFB central administration","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — conditional cell-specific knockout with electrophysiology, multiple genetic models, and pharmacological rescue","pmids":["35863346"],"is_preprint":false},{"year":2023,"finding":"In adult mice, microglia are the primary source of PDGFB in the CNS (transitioning from endothelial cells in neonates); acute loss of microglial PDGFB profoundly impairs BBB integrity in adults, causing lethal microhemorrhages upon endotoxin challenge; acute loss of endothelial PDGFB has minimal effects on adult BBB but severely impairs neonatal CNS vasculature.","method":"Transcriptomic analysis; in situ hybridization; acute conditional cell-specific Pdgfb deletion in adult vs. neonatal mice; BBB permeability assay; endotoxin challenge survival model","journal":"Brain, behavior, and immunity","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific conditional knockouts at different ages establishing temporal switch in cellular source","pmids":["37992789"],"is_preprint":false},{"year":2023,"finding":"PROX1 transcription factor inhibits PDGFB expression in valvular endothelial cells (VECs) partially via FOXC2; conditional deletion of Prox1 from VECs upregulates PDGFB, leading to progressive myxomatous valve degeneration; conditional overexpression of PDGFB in VECs recapitulates the Prox1-knockout phenotype; pharmacological inhibition of PDGFB signaling with imatinib partially ameliorates valve defects.","method":"Conditional Prox1 VEC-specific knockout; conditional PDGFB overexpression in VECs; conditional FOXC2 knockdown; echocardiography; histology; electron microscopy; imatinib pharmacological rescue; human mitral valve prolapse sample analysis","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — multiple mouse genetic models, pharmacological rescue, human tissue validation","pmids":["37555328"],"is_preprint":false}],"current_model":"PDGFB (c-sis) encodes the B-chain of platelet-derived growth factor, a disulfide-bonded dimeric mitogen requiring intramolecular (but not interchain) disulfide bonds and key residues Arg27/Ile30 for receptor binding; it is synthesized as a precursor processed in the ER-Golgi, secreted and retained in extracellular matrix via a heparin-binding retention motif, and signals through PDGF receptor tyrosine kinase dimerization/autophosphorylation to activate multiple downstream pathways (Ras/MAPK, PI3K/Akt/NF-κB, PLCγ, miR-221) controlling proliferation, survival, migration, and differentiation; endothelial PDGFB drives pericyte recruitment and blood-brain barrier maintenance during development, while in adults microglia become the primary CNS PDGFB source maintaining BBB integrity; macrophage-derived PDGFB promotes smooth muscle cell expansion in pulmonary hypertension, platelet-derived PDGFB maintains tumor vascular integrity, and COL1A1-PDGFB gene fusions constitutively activate PDGFB signaling in dermatofibrosarcoma protuberans; germline loss-of-function PDGFB mutations cause primary familial brain calcification through pericyte deficiency and BBB dysfunction."},"narrative":{"teleology":[{"year":1983,"claim":"The question of what gene product the v-sis oncogene encodes was resolved when PDGF B-chain amino acid sequencing revealed near-complete identity with the predicted v-sis protein, establishing that a growth factor could function as an oncogene.","evidence":"Direct amino acid sequencing of purified PDGF compared with predicted v-sis sequence","pmids":["6306471"],"confidence":"High","gaps":["Mechanism of transformation not yet addressed","Whether PDGF-B acts through autocrine or paracrine loop unknown"]},{"year":1984,"claim":"The autocrine transformation mechanism was established: SSV-transformed cells secrete PDGF-like protein that activates PDGF receptor tyrosine kinase, and the normal human c-sis coding sequence itself is sufficient to transform fibroblasts, demonstrating that overexpression of a normal growth factor drives oncogenesis.","evidence":"Anti-PDGF antisera blockade of transformed cell growth; receptor purification with kinase assay; LTR-driven c-sis transfection transforming foci assay; v-sis receptor competition binding","pmids":["6091918","6091919","6088510"],"confidence":"High","gaps":["Whether transformation requires secretion or can occur intracellularly unknown","Downstream signaling pathways not mapped"]},{"year":1986,"claim":"The biosynthetic pathway was mapped: PDGF-B is co-translationally processed in the ER–Golgi with signal sequence cleavage and N-linked glycosylation, and signal sequence integrity is required for biological activity, while the proposed proteolytic processing site is dispensable.","evidence":"Site-directed mutagenesis of signal sequence and processing site; microsome trypsin protection; glycosylation analysis","pmids":["3537701"],"confidence":"High","gaps":["Role of C-terminal processing not addressed","Extracellular retention mechanism unknown"]},{"year":1987,"claim":"The structural basis of PDGF-B activity was clarified: all eight conserved cysteines participate in dimerization, but only the four intramolecular disulfide bonds are required for receptor activation, separating dimerization from function.","evidence":"Systematic site-directed mutagenesis of all eight cysteines with functional and dimerization assays","pmids":["3035718"],"confidence":"High","gaps":["Specific receptor-binding residues not yet identified","No crystal structure available"]},{"year":1989,"claim":"Intracellular autocrine signaling was demonstrated: an ER/Golgi-retained v-sis mutant transforms cells as efficiently as wild-type without secretion, but suramin experiments showed that activated receptors must reach the cell surface to couple with mitogenic signaling, resolving the spatial requirements for transformation.","evidence":"ER/Golgi-retention mutant transformation assay; suramin blockade dissecting surface vs. intracellular receptor phosphorylation","pmids":["2551043","2813378"],"confidence":"High","gaps":["Identity of intracellular compartment where receptor activation occurs not defined","Downstream transcription factor targets only beginning to be identified"]},{"year":1991,"claim":"Key receptor-binding residues were identified: Arg27 and Ile30 are specifically required for PDGF receptor binding and mitogenic activity without disrupting overall protein fold, providing the first structure–function map of the ligand–receptor interface.","evidence":"Site-directed mutagenesis with 125I-PDGF displacement, mitogenic assay, circular dichroism, and fluorescence spectroscopy","pmids":["1661670"],"confidence":"High","gaps":["Full receptor–ligand co-crystal structure not solved","Whether same residues mediate PDGFR-α vs. PDGFR-β binding unknown"]},{"year":1998,"claim":"Downstream signaling cascades were elucidated: PDGF receptor dimerization recruits PI3K (via p85 SH2 domains), PLCγ, Src kinases, and Grb2, and PDGF signals through Ras/PI3K/Akt/IKK to activate NF-κB, transmitting both proliferative and anti-apoptotic signals; in parallel, PDGF-B knockout mice revealed an essential and isoform-specific requirement for pericyte and mesangial cell development.","evidence":"Co-immunoprecipitation of Akt–IKK complex; kinase assays; dominant-negative constructs; Pdgf-b knockout mouse histological analysis","pmids":["10485711","9739761","9442358","1372091"],"confidence":"High","gaps":["Relative contribution of individual downstream pathways to pericyte recruitment in vivo unknown","Mechanism linking PDGF-B loss to mesangial cell absence not defined"]},{"year":1997,"claim":"The molecular basis of dermatofibrosarcoma protuberans was established: t(17;22) translocation fuses COL1A1 to PDGFB, removing PDGFB from normal transcriptional control and producing constitutive PDGF-B that activates PDGFR-β in a paracrine manner.","evidence":"Translocation breakpoint characterization by RT-PCR and FISH; functional reconstitution showing chimeric protein processing and tumorigenicity","pmids":["8988177","11420709"],"confidence":"High","gaps":["Whether uncleaved chimeric forms contribute to tumor biology in patients unknown","Therapeutic response to imatinib mechanism not fully delineated"]},{"year":2003,"claim":"The extracellular matrix retention motif of PDGF-B was shown to be critical for spatial pericyte integration: pdgf-b ret/ret mice lacking the heparin-binding domain have detached pericytes, vessel dilation, and hemorrhaging, establishing that PDGF-B must be locally retained to function.","evidence":"Mouse genetics with pdgf-b ret/ret allele; tumor transplantation; pericyte co-injection; vascular morphometry","pmids":["14561699"],"confidence":"High","gaps":["Specific HSPG partners mediating retention not identified","Whether retention motif is required equally across all vascular beds unknown"]},{"year":2013,"claim":"PDGFB was identified as a causative gene for autosomal dominant primary familial brain calcification: human germline mutations abolish protein synthesis or receptor binding, and hypomorphic mouse alleles develop dose-dependent brain calcifications correlating with pericyte deficiency and BBB dysfunction.","evidence":"Human genetic linkage and mutation analysis; functional assays of six mutations; Pdgfb hypomorphic and Pdgfbret/ret mice; brain calcification and BBB assessment","pmids":["23913003","26599395"],"confidence":"High","gaps":["Mechanism by which pericyte loss leads to calcification not resolved","Whether calcification is reversible upon PDGF-B restoration unknown"]},{"year":2017,"claim":"The requirement for PDGF-B in lymphatic vessel maturation was established: LEC-specific Pdgfb deletion prevents smooth muscle cell recruitment to collecting lymphatic vessels, causing dilation and loss of pulsatile contraction, with ECM retention motif serving as a checkpoint against inappropriate capillary muscularization.","evidence":"LEC-specific Cre-mediated Pdgfb deletion and overexpression; ECM retention analysis; vessel contraction measurement","pmids":["28851707"],"confidence":"High","gaps":["ECM composition differences between capillaries and collecting vessels not molecularly defined","Functional consequences for lymphatic drainage not quantified"]},{"year":2021,"claim":"Cell-type-specific roles of PDGF-B in disease were delineated: macrophage-derived PDGF-B drives pathological smooth muscle cell expansion in pulmonary hypertension, while platelet-derived PDGF-B maintains tumor vascular pericyte coverage to limit metastasis, and adult-induced endothelial deletion causes progressive pericyte loss distinguishing developmental from maintenance functions.","evidence":"LysM-Cre conditional Pdgfb knockout; platelet-specific Pdgfb knockout in two tumor models; tamoxifen-inducible endothelial Pdgfb deletion with longitudinal analysis; human PAH patient macrophage analysis","pmids":["33591958","32586981","34689641"],"confidence":"High","gaps":["Whether macrophage-derived PDGF-B acts on resident vs. recruited SMC progenitors unknown","Interaction between platelet-derived and endothelial-derived PDGF-B pools in tumors not resolved"]},{"year":2022,"claim":"A non-vascular neuronal role was discovered: microglial PDGF-B signals via PDGFR-α on hypothalamic PVN neurons to maintain Kv4.3 potassium channel expression, suppressing sympathetic outflow; loss of this signaling axis causes hypertension.","evidence":"Conditional microglial Pdgfb deletion; neuronal PDGFR-α suppression; electrophysiology; sympathetic outflow and blood pressure measurement; exogenous PDGF-B rescue","pmids":["35863346"],"confidence":"High","gaps":["Whether this mechanism extends to other brain regions unknown","Downstream transcriptional pathway linking PDGFR-α activation to Kv4.3 expression not defined"]},{"year":2023,"claim":"The developmental-to-adult transition in PDGF-B cellular sources was resolved: microglia replace endothelial cells as the primary CNS PDGF-B source in adults, and acute loss of microglial PDGF-B severely impairs adult BBB integrity and causes lethal microhemorrhages upon immune challenge.","evidence":"Transcriptomic analysis; in situ hybridization; acute conditional cell-specific Pdgfb deletion in adult vs. neonatal mice; BBB permeability assay; endotoxin survival model","pmids":["37992789"],"confidence":"High","gaps":["Signals triggering the switch from endothelial to microglial PDGF-B source unknown","Whether microglial PDGF-B maintains pericytes or acts through additional mechanisms not resolved"]},{"year":null,"claim":"Key unresolved questions include the mechanism by which pericyte loss leads to brain calcification, the structural basis of PDGF-B/PDGFR-β interaction at atomic resolution, the signals controlling the developmental switch from endothelial to microglial PDGF-B sourcing, and the therapeutic potential of restoring PDGF-B signaling in calcification and neurovascular diseases.","evidence":"","pmids":[],"confidence":"Low","gaps":["Calcification mechanism downstream of pericyte loss undefined","No high-resolution PDGF-B/PDGFR-β co-crystal structure published","Therapeutic restoration of PDGF-B signaling not tested in disease models"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,4,5,17,27]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[18,31]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4,18,32,43]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[32,45]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[8,11]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,5,19,26,27,37]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[25,36,45]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[24,29,41,43]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[32,45]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[46]}],"complexes":["PDGF-BB homodimer","PDGF-AB heterodimer"],"partners":["PDGFRB","PDGFRA","SPARC","ADIPOQ","PIK3R1","COL1A1"],"other_free_text":[]},"mechanistic_narrative":"PDGFB encodes the B-chain of platelet-derived growth factor, a disulfide-bonded dimeric mitogen that signals through PDGF receptor tyrosine kinase dimerization and autophosphorylation to activate Ras/MAPK, PI3K/Akt/NF-κB, and PLCγ pathways controlling cell proliferation, survival, migration, and differentiation [PMID:6091918, PMID:10485711, PMID:9739761]. Synthesized as a precursor processed in the ER–Golgi, PDGF-B is secreted and retained in the extracellular matrix via a C-terminal heparin-binding motif that is essential for proper pericyte recruitment to blood vessels; endothelial PDGF-B drives pericyte investment and blood–brain barrier formation during development, while in adults microglia become the primary CNS source maintaining BBB integrity [PMID:14561699, PMID:23913003, PMID:37992789]. Loss-of-function PDGFB mutations cause autosomal dominant primary familial brain calcification through pericyte deficiency and BBB dysfunction, and the COL1A1–PDGFB gene fusion constitutively activates PDGF-B signaling in dermatofibrosarcoma protuberans [PMID:23913003, PMID:8988177, PMID:11420709]. Beyond its canonical vascular roles, macrophage-derived PDGF-B drives smooth muscle cell expansion in pulmonary hypertension, platelet-derived PDGF-B maintains tumor vascular integrity and limits metastasis, and microglial PDGF-B regulates neuronal excitability and sympathetic tone via PDGFR-α signaling [PMID:33591958, PMID:32586981, PMID:35863346]."},"prefetch_data":{"uniprot":{"accession":"P01127","full_name":"Platelet-derived growth factor subunit B","aliases":["PDGF-2","Platelet-derived growth factor B chain","Platelet-derived growth factor beta polypeptide","Proto-oncogene c-Sis"],"length_aa":241,"mass_kda":27.3,"function":"Growth factor that plays an essential role in the regulation of embryonic development, cell proliferation, cell migration, survival and chemotaxis. Potent mitogen for cells of mesenchymal origin (PubMed:26599395). Required for normal proliferation and recruitment of pericytes and vascular smooth muscle cells in the central nervous system, skin, lung, heart and placenta. Required for normal blood vessel development, and for normal development of kidney glomeruli. Plays an important role in wound healing. Signaling is modulated by the formation of heterodimers with PDGFA (By similarity)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P01127/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PDGFB","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PDGFB","total_profiled":1310},"omim":[{"mim_id":"619206","title":"SCHWANNOMIN-INTERACTING PROTEIN 1; SCHIP1","url":"https://www.omim.org/entry/619206"},{"mim_id":"617492","title":"OLFACTOMEDIN 2; OLFM2","url":"https://www.omim.org/entry/617492"},{"mim_id":"615483","title":"BASAL GANGLIA CALCIFICATION, IDIOPATHIC, 5; IBGC5","url":"https://www.omim.org/entry/615483"},{"mim_id":"615007","title":"BASAL GANGLIA CALCIFICATION, IDIOPATHIC, 4; IBGC4","url":"https://www.omim.org/entry/615007"},{"mim_id":"612139","title":"PHOSPHATIDYLINOSITOL 3,4,5-TRISPHOSPHATE-DEPENDENT RAC EXCHANGER 2; PREX2","url":"https://www.omim.org/entry/612139"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PDGFB"},"hgnc":{"alias_symbol":["SSV"],"prev_symbol":["SIS"]},"alphafold":{"accession":"P01127","domains":[{"cath_id":"2.10.90.10","chopping":"97-181","consensus_level":"high","plddt":94.7028,"start":97,"end":181}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P01127","model_url":"https://alphafold.ebi.ac.uk/files/AF-P01127-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P01127-F1-predicted_aligned_error_v6.png","plddt_mean":73.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PDGFB","jax_strain_url":"https://www.jax.org/strain/search?query=PDGFB"},"sequence":{"accession":"P01127","fasta_url":"https://rest.uniprot.org/uniprotkb/P01127.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P01127/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P01127"}},"corpus_meta":[{"pmid":"12682500","id":"PMC_12682500","title":"2001 SCCM/ESICM/ACCP/ATS/SIS International Sepsis Definitions Conference.","date":"2003","source":"Critical care medicine","url":"https://pubmed.ncbi.nlm.nih.gov/12682500","citation_count":4325,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"12664219","id":"PMC_12664219","title":"2001 SCCM/ESICM/ACCP/ATS/SIS International Sepsis Definitions Conference.","date":"2003","source":"Intensive care medicine","url":"https://pubmed.ncbi.nlm.nih.gov/12664219","citation_count":1674,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"2176154","id":"PMC_2176154","title":"The SIF binding element confers sis/PDGF inducibility onto the c-fos promoter.","date":"1990","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/2176154","citation_count":595,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"2343305","id":"PMC_2343305","title":"Localization of PDGF-B protein in macrophages in all phases of atherogenesis.","date":"1990","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/2343305","citation_count":560,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"14561699","id":"PMC_14561699","title":"Endothelial and nonendothelial sources of PDGF-B regulate pericyte recruitment and influence vascular pattern formation in tumors.","date":"2003","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/14561699","citation_count":422,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"6329745","id":"PMC_6329745","title":"The c-sis gene encodes a precursor of the B chain of platelet-derived growth factor.","date":"1984","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/6329745","citation_count":355,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15736287","id":"PMC_15736287","title":"Porcine small intestine submucosa (SIS) is not an acellular collagenous matrix and contains porcine DNA: possible implications in human implantation.","date":"2005","source":"Journal of biomedical materials research. 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genetics","url":"https://pubmed.ncbi.nlm.nih.gov/8988177","citation_count":400,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"1311092","id":"PMC_1311092","title":"The extracellular glycoprotein SPARC interacts with platelet-derived growth factor (PDGF)-AB and -BB and inhibits the binding of PDGF to its receptors.","date":"1992","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/1311092","citation_count":336,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"1372091","id":"PMC_1372091","title":"Interaction of phosphatidylinositol 3-kinase-associated p85 with epidermal growth factor and platelet-derived growth factor receptors.","date":"1992","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/1372091","citation_count":331,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"7896901","id":"PMC_7896901","title":"Three patterns of cytokine expression potentially involved in epithelial-fibroblast interactions of human ocular surface.","date":"1995","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/7896901","citation_count":306,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"11331882","id":"PMC_11331882","title":"PDGF-D, a new protease-activated growth factor.","date":"2001","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/11331882","citation_count":293,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"4033772","id":"PMC_4033772","title":"Cultured human endothelial cells express platelet-derived growth factor B chain: cDNA cloning and structural analysis.","date":"1985","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/4033772","citation_count":285,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"19088079","id":"PMC_19088079","title":"Induction of microRNA-221 by platelet-derived growth factor signaling is critical for modulation of vascular 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genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23913003","citation_count":280,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":49123,"output_tokens":8128,"usd":0.134645},"stage2":{"model":"claude-opus-4-6","input_tokens":11999,"output_tokens":4131,"usd":0.244905},"total_usd":0.849357,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":62060,"output_tokens":13134,"usd":0.191595},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":17445,"output_tokens":3930,"usd":0.278212}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1984,\n      \"finding\": \"The c-sis proto-oncogene encodes a precursor of the PDGF B-chain, with amino acid sequence identity established over 109 residues by direct protein sequencing and nucleotide sequence analysis of c-sis genomic clones.\",\n      \"method\": \"Amino acid sequence analysis of PDGF B-chain combined with nucleotide sequence analysis of c-sis genomic clones\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing and gene sequencing, foundational identification replicated across labs\",\n      \"pmids\": [\"6329745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"The v-sis-encoded transforming protein (p28v-sis) stimulates autocrine growth of SSV-transformed cells by secreting a PDGF-like mitogen that activates cell-surface PDGF receptors; the receptor purified from SSV-NIH 3T3 cells retains active protein tyrosine kinase activity stimulated by PDGF.\",\n      \"method\": \"Anti-PDGF antisera blocking of 3H-thymidine incorporation; 125I-PDGF receptor competition binding; receptor purification with tyrosine kinase activity assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal functional assays (receptor binding competition, kinase activity, antibody neutralization, tumor growth correlation)\",\n      \"pmids\": [\"6091918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"Normal human sis/PDGF-2 coding sequence induces cellular transformation when placed under retroviral LTR control and connected to its upstream exon, with transformants expressing sis/PDGF-2 translational products.\",\n      \"method\": \"Transfection of chimeric LTR-c-sis constructs into NIH/3T3 cells; transformation assay; protein expression analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct gain-of-function in cell transformation with protein expression confirmation, replicated concept\",\n      \"pmids\": [\"6091919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"Human c-sis cDNA clone transforms NIH-3T3 cells, demonstrating that the human c-sis/PDGFB gene has intrinsic transforming activity.\",\n      \"method\": \"Transfection of human c-sis cDNA into NIH-3T3 cells; transformation assay\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct gain-of-function transformation assay, first demonstration with human cDNA\",\n      \"pmids\": [\"6323994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"Bacterially expressed v-sis oncogene product directly competes with 125I-PDGF for PDGF receptor binding on fibroblast membranes, demonstrating functional equivalence to PDGF.\",\n      \"method\": \"In vitro receptor competition binding assay with bacterially produced v-sis protein; immunochemical verification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstituted receptor binding competition with purified recombinant protein\",\n      \"pmids\": [\"6088510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"The v-sis gene product transforms cells by interacting with and activating the PDGF receptor: it binds PDGF receptors, stimulates tyrosine phosphorylation of PDGF receptors, and induces DNA synthesis; transformation correlates strictly with PDGF receptor expression.\",\n      \"method\": \"Partial purification of v-sis protein; receptor binding; tyrosine phosphorylation assay; DNA synthesis induction; antibody inhibition; cell susceptibility correlation\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal assays (binding, phosphorylation, mitogenesis, antibody neutralization, genetic correlation) in single study\",\n      \"pmids\": [\"2996133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The v-sis gene product is processed in the endoplasmic reticulum-Golgi compartment where signal sequence cleavage and N-linked glycosylation occur; the protein contains no transmembrane regions (protected within microsomes from trypsin). Signal sequence mutations cause nuclear mislocalization and loss of biological activity. Mutagenesis of the proteolytic processing site (Lys-Arg 110-111 to Asn-Ser) retains full biological activity.\",\n      \"method\": \"Site-directed mutagenesis; intracellular fractionation; microsome protection assay; trypsin proteolysis; N-linked glycosylation analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution and mutagenesis defining biosynthetic processing and subcellular localization with functional consequences\",\n      \"pmids\": [\"3537701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The human SIS/PDGFB mRNA is 3373 nucleotides with a 723-bp coding sequence flanked by long 5' (1022 bp) and 3' (1625 bp) untranslated regions. A TATAAA consensus promoter was identified 24 bp upstream of the mRNA start site.\",\n      \"method\": \"cDNA cloning, nuclease S1 mapping, primer extension, nucleotide sequence analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural determination of transcriptional unit by multiple methods\",\n      \"pmids\": [\"3517869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"Each of the eight conserved cysteine residues in the v-sis/PDGF-B minimal active region is required for disulfide-linked dimer formation; four cysteines are essential for transforming activity via intramolecular disulfide bonds, while interchain disulfide bonds are not essential for receptor activation.\",\n      \"method\": \"Site-directed mutagenesis of each conserved cysteine; transformation assay; disulfide bond analysis\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic site-directed mutagenesis of all conserved cysteines with functional readouts\",\n      \"pmids\": [\"3035718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"v-sis transformation occurs by an internal autoactivation mechanism: a mutant v-sis protein retained in the endoplasmic reticulum and Golgi (with no secretion) fully transforms NRK cells, demonstrating that intracellular (pre-cell-surface) activation of PDGF receptor is sufficient for transformation.\",\n      \"method\": \"Retentionmutant construction targeting v-sis to ER/Golgi; transformation assay; secretion assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic loss-of-secretion mutant with defined transformation phenotype, directly testing autocrine hypothesis\",\n      \"pmids\": [\"2551043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"v-sis-encoded PDGF-B activates PDGF receptors both intracellularly and at the cell surface, but surface-localized activated receptors are required for functional coupling to intracellular mitogenic signaling; suramin blocks cell-surface receptor activation and inhibits proliferation while leaving intracellular phosphorylation unchanged.\",\n      \"method\": \"Tyrosine phosphorylation assay of cell surface vs. intracellular receptor fractions; suramin treatment; PDGF neutralizing antibody; proliferation assay in chemically defined medium\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — subcellular fractionation combined with pharmacological and antibody tools, multiple orthogonal approaches\",\n      \"pmids\": [\"2813378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Purified recombinant c-sis/PDGF-B induces a DNA-binding protein (SIF, sis-inducible factor) that binds a specific element upstream of the c-fos gene, conferring sis/PDGF inducibility; this SIF binding element functions independently of the serum responsive element (SRE) and responds only to sis/PDGF, not to serum or phorbol esters.\",\n      \"method\": \"Recombinant c-sis/PDGF protein induction; DNA binding/gel shift assay; promoter deletion/reporter assay; transfection\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — purified recombinant protein used in gel shift and promoter reporter assays, mechanistic dissection of downstream signaling element\",\n      \"pmids\": [\"2176154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"PDGF-B chain residues arginine 27 and isoleucine 30 are critical for receptor binding and cell activation; substitutions at these positions create PDGF mutants defective in receptor affinity and mitogenic/inositol lipid signaling without disrupting overall protein structure.\",\n      \"method\": \"Site-directed mutagenesis; [125I]-PDGF-BB displacement assay; mitogenic assay; inositol lipid turnover; circular dichroism and fluorescence spectroscopy\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with multiple functional and structural assays confirming residue-specific receptor interaction\",\n      \"pmids\": [\"1661670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Selective PDGF receptor kinase blockers (tyrphostins AG1295 and AG1296) reverse the transformed phenotype of sis-transfected NIH 3T3 cells, confirming that PDGF-B/PDGF receptor tyrosine kinase signaling is required for maintenance of sis-induced transformation; AG1296 inhibits both PDGF α- and β-receptors but not VEGFR or src kinase.\",\n      \"method\": \"PDGF receptor tyrosine kinase inhibitor treatment; transformation reversal assay; receptor autophosphorylation assay; DNA synthesis assay\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological inhibition with defined selectivity profile and transformation reversal readout\",\n      \"pmids\": [\"7954456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"A 10-bp SIS proximal element (SPE) at positions -58 to -39 of the PDGF-B promoter is essential for TPA-induced transcriptional activation in megakaryocytic cells; TPA treatment induces formation of a specific nuclear protein complex at the SPE.\",\n      \"method\": \"Linker-scanning mutagenesis; luciferase reporter assay; gel mobility-shift assay; nuclear run-on; cycloheximide block\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic promoter mutagenesis combined with gel shift and reporter assays defining a specific regulatory element\",\n      \"pmids\": [\"8356057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"PDGF-B (v-sis) induces Egr-1 expression via a pathway dependent on tyrosine kinase activity and mediated by c-Ha-Ras; dominant-negative Ras and Raf mutants abrogate Egr-1 induction, and the pathway is independent of protein kinase C.\",\n      \"method\": \"Conditional v-sis expression system (metallothionein promoter); dominant-negative Ras/Raf transfection; Egr-1 promoter-reporter assay; PKC inhibition\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis using dominant-negative mutants, but single lab study\",\n      \"pmids\": [\"7890805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Pericytes and mesangial cells fail to develop in PDGF-B-deficient mouse embryos, establishing that PDGF-B signaling through PDGFRβ is required for recruitment and development of specific smooth muscle cell subsets during organogenesis.\",\n      \"method\": \"PDGF-B knockout mouse analysis; histological and immunohistochemical characterization of pericyte and mesangial cell development\",\n      \"journal\": \"Current opinion in nephrology and hypertension\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with defined cellular phenotype, replicated across multiple organs\",\n      \"pmids\": [\"9442358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The COL1A1-PDGFB chimeric protein (arising from the t(17;22) translocation in dermatofibrosarcoma protuberans) is processed into mature PDGF-B dimers in transfected cells; expression causes growth factor independence and tumorigenicity in nude mice via autocrine/paracrine activation of the PDGFB receptor pathway. Mutagenesis showed uncleaved forms are also mitogenic.\",\n      \"method\": \"Stable and transient transfection; anti-PDGFB antibody detection; nude mouse tumorigenicity assay; conditioned medium fibroblast growth stimulation; site-directed mutagenesis of processing site\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — protein processing demonstrated with antibodies, functional transformation assay, mutagenesis of processing site\",\n      \"pmids\": [\"11420709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Endothelial PDGF-B retention via its C-terminal proteoglycan-binding retention motif is indispensable for proper pericyte integration into tumor vessel walls; loss of retention motif (pdgf-b(ret/ret) mice) causes pericyte detachment and increased vessel diameter/hemorrhage, distinct from effects on pericyte density alone.\",\n      \"method\": \"Genetic mouse models (pdgf-b(ret/ret)); tumor transplantation; transgenic PDGF-B tumor cell expression; exogenous pericyte co-injection; histological and morphological vessel analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models with defined vascular phenotypes, dissects retention vs. expression roles\",\n      \"pmids\": [\"14561699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PDGF-B activates YB-1 (Y-box protein 1) downstream via the MAP kinase pathway in mesangial cells, causing cytoplasmic translocation of YB-1; YB-1 knockdown by RNAi abolishes the mitogenic effect of PDGF-B, identifying YB-1 as a necessary downstream mediator.\",\n      \"method\": \"PDGF-B infusion in vivo; anti-Thy1.1 nephritis model; PDGF aptamer and MEK inhibitor (U0126) treatment; RNAi knockdown of YB-1; subcellular localization analysis\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection and RNAi knockdown, single lab\",\n      \"pmids\": [\"16093451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TIE2 gain-of-function mutations (L914F) cause an AKT-dependent decrease in PDGFB production by endothelial cells, leading to deficient mural cell recruitment; this was demonstrated both in vitro in TIE2-mutant ECs and ex vivo in patient venous malformation tissues.\",\n      \"method\": \"Global gene expression profiling; in vitro TIE2 mutant EC culture; AKT inhibition; ex vivo patient tissue analysis; PDGFB protein measurement\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gene expression profiling plus pathway inhibition in relevant cell model and patient tissue, single lab\",\n      \"pmids\": [\"23633549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Six PDGFB germline mutations causing Primary Familial Brain Calcification (PFBC) result in complete loss of PDGF-B function through abolished protein synthesis or defective PDGF-Rβ binding/stimulation. The PDGFB retention motif (not simple haploinsufficiency) is critical: Pdgfbret/ret mice develop brain calcification, correlating with altered tissue distribution of PDGF-B protein rather than simple reduction in levels.\",\n      \"method\": \"In vitro functional analysis of PDGFB mutants; PDGF-Rβ autophosphorylation assay; PLCγ activation kinetics; heterozygous/compound knockout mice; Pdgfbret/ret mouse brain calcification analysis; pericyte coverage and BBB permeability assessment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro receptor activation assays plus multiple genetic mouse models, multiple orthogonal readouts\",\n      \"pmids\": [\"26599395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PDGF-B expressed selectively by lymphatic endothelial cells of collecting vessels regulates smooth muscle cell recruitment to lymphatic vessels; LEC-specific Pdgfb deletion prevents SMC recruitment causing vessel dilation and failure of pulsatile contraction. ECM retention of PDGFB (not its mere presence) is required: overexpression without ECM retention does not recruit SMCs to capillaries.\",\n      \"method\": \"Conditional LEC-specific Pdgfb knockout; PDGFB overexpression in LECs; analysis of SMC recruitment, vessel morphology, and pulsatile contraction; ECM retention motif analysis\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional knockout with defined cellular and functional phenotype, ECM retention mechanism dissected\",\n      \"pmids\": [\"28851707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Platelet-derived PDGFB promotes and maintains tumor vascular integrity by contributing to pericyte recruitment; conditional knockout of PDGFB in platelets impairs pericyte coverage and vascular function, leading to enhanced hypoxia, EMT, elevated circulating tumor cells, and increased spontaneous metastasis.\",\n      \"method\": \"Conditional platelet-specific PDGFB knockout mouse; tumor implantation models; pericyte coverage quantification; circulating tumor cell quantification; metastasis assay\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional cell-type-specific knockout with multiple defined phenotypic readouts in two tumor models\",\n      \"pmids\": [\"32586981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Adult-induced endothelial deletion of Pdgfb causes slowly progressing pericyte loss (~50% decrease in pericyte ratio, ~60% decrease in capillary coverage), increased BBB permeability, but—unlike constitutive loss—does not cause vessel dilation, impaired arterio-venous zonation, or microvascular calcification, distinguishing developmental from maintenance roles of endothelial PDGFB.\",\n      \"method\": \"Inducible endothelial-specific Pdgfb deletion in adult mice (2 months); longitudinal analysis at 12-18 months; pericyte marker quantification; BBB permeability assay\",\n      \"journal\": \"Journal of cerebral blood flow and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — inducible conditional knockout with temporal control, multiple vascular phenotype readouts distinguishing developmental and maintenance functions\",\n      \"pmids\": [\"34689641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Macrophage-derived PDGF-B is critical for hypoxia-induced pathological smooth muscle cell expansion in pulmonary hypertension; conditional knockout of macrophage Pdgfb (LysM-Cre) protects against distal muscularization and PH, while macrophage-conditioned medium from human PAH patients promotes SMC proliferation and migration via PDGF-B.\",\n      \"method\": \"LysM-Cre conditional Pdgfb knockout; HIF-1α/HIF-2α/VHL conditional knockouts; clodronate macrophage depletion; nanoparticle-mediated Pdgfb siRNA delivery; ex vivo human macrophage conditioned medium assay; SMC proliferation/migration assay\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models plus translational human data and in vivo nanoparticle intervention, strong mechanistic dissection\",\n      \"pmids\": [\"33591958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Microglia constitutively release PDGF-B which signals via PDGFRα on pre-sympathetic neurons in the hypothalamic PVN, promoting Kv4.3 potassium channel expression and suppressing neuronal excitability; conditional deletion of microglial PDGFB elevates sympathetic outflow and predisposes to hypertension.\",\n      \"method\": \"Microglia ablation; conditional microglial Pdgfb deletion; neuronal PDGFRα knockdown; electrophysiology; Kv4.3 expression analysis; blood pressure measurement; central PDGFB supplementation\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic and pharmacological tools with defined electrophysiological and cardiovascular phenotypes, novel non-immune microglia function\",\n      \"pmids\": [\"35863346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In adult mice, microglia (not endothelial cells) are the primary source of PDGFB for BBB maintenance; acute loss of microglial PDGFB impairs adult BBB integrity and causes lethality from CNS microhemorrhages upon endotoxin challenge, while acute endothelial PDGFB loss has minimal adult BBB effects but impairs neonatal CNS vasculature.\",\n      \"method\": \"Transcriptomic data analysis; in situ hybridization; acute conditional deletion of microglial vs. endothelial Pdgfb; BBB integrity assay; endotoxin challenge survival; neonatal vascular analysis\",\n      \"journal\": \"Brain, behavior, and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comparative conditional knockouts with temporal and cell-type specificity, multiple functional readouts\",\n      \"pmids\": [\"37992789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PROX1 inhibits PDGF-B expression in valvular endothelial cells (VECs) partially via FOXC2; loss of endothelial PROX1 upregulates PDGF-B leading to myxomatous valve degeneration and aortic stenosis. Conditional PDGF-B overexpression in VECs recapitulates the phenotype, and pharmacological inhibition of PDGF-B signaling with imatinib partially ameliorates valve defects.\",\n      \"method\": \"Conditional Prox1 deletion in VECs; conditional Foxc2 knockdown; conditional PDGFB overexpression in VECs; echocardiography; histology; imatinib treatment; human valve disease sample analysis\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic mouse models with gain- and loss-of-function, pharmacological rescue, and human tissue validation\",\n      \"pmids\": [\"37555328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SDF-1α induces PDGF-B expression and drives differentiation of PDGFR-β+ bone marrow cells into pericytes; the mechanism involves SDF-1α-mediated transcriptional activation of the PDGF-B promoter via ELK-1 transcription factor binding, confirmed by chromatin immunoprecipitation.\",\n      \"method\": \"PDGF-B mRNA/protein measurement in vitro and in vivo; PDGF-B promoter cloning and reporter assay; chromatin immunoprecipitation for ELK-1; SDF-1α inhibition; pericyte differentiation assay\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and promoter reporter assays with in vitro and in vivo correlation, single lab\",\n      \"pmids\": [\"21911740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"C/EBPβ transcription factor directly binds PDGFB promoter elements to facilitate PDGFB transcription in anoikis-resistant gastric cancer cells, increasing PDGFB secretion that promotes cancer cell survival via autocrine C/EBPβ-dependent self-feedback and promotes angiogenesis via paracrine MAPK/ERK activation in endothelial cells.\",\n      \"method\": \"ChIP assay; PDGFB promoter binding analysis; in vitro and in vivo functional assays; MAPK/ERK signaling analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP with functional validation in multiple cell contexts, single lab\",\n      \"pmids\": [\"34341514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LHX2 transcription factor directly induces PDGF-B expression in tumor cells, creating autocrine PDGF-B/PDGFRβ signaling for cell migration/invasion and paracrine signaling for pericyte recruitment and vessel maturation; pharmacological inhibition of PDGF-B/PDGFRβ reduces vessel functionality and tumor growth.\",\n      \"method\": \"Transgenic mouse models of breast cancer and insulinoma; loss and gain of function in vitro; PDGF-B/PDGFRβ pharmacological inhibition; vessel functionality assay\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo transgenic models plus pharmacological inhibition, direct transcriptional induction demonstrated\",\n      \"pmids\": [\"24423492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Endothelial TWIST1 transcription factor mediates hypoxia-induced PDGFB expression; Twist1 overexpression increases PDGFB in human pulmonary arterial endothelial cells, and Twist1 knockdown suppresses hypoxia-induced PDGFB upregulation and αSMA-positive cell accumulation.\",\n      \"method\": \"Twist1 overexpression/knockdown; PDGFB expression measurement; in vivo hydrogel implant model on mouse lung; αSMA-positive cell quantification; IPAH patient PAE cell analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with in vivo implant model and human patient cells, single lab\",\n      \"pmids\": [\"32371931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PDGF-B/PDGFR-β signaling is required for cardiac development: Pdgf-b-/- and Pdgfr-β-/- mouse embryos show ventricular septal defects, maldevelopment of atrioventricular cushions/valves, impaired coronary arteriogenesis, myocardial hypoplasia, and cardiac nerve hypoplasia, consistent with roles in epicardial- and neural crest-derived cell contributions.\",\n      \"method\": \"Pdgf-b-/- and Pdgfr-β-/- mouse embryo analysis; immunohistochemical staining for multiple markers (αSMA, periostin, ephrinB2, EphB4, VEGFR-2, NCAM)\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — dual knockout mouse analysis with comprehensive multi-marker phenotypic characterization\",\n      \"pmids\": [\"18213589\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PDGF-B (encoded by c-sis/PDGFB) is a secreted, disulfide-bonded dimeric growth factor that is processed in the ER-Golgi from a precursor, requires specific intramolecular disulfide bonds (but not interchain bonds) and residues Arg27/Ile30 for receptor activation, and signals by binding and activating PDGF receptor β (and α) tyrosine kinases — initially discovered as the v-sis transforming principle operating via intracellular as well as cell-surface autocrine receptor activation — with its ECM-retention motif being essential for proper pericyte recruitment to blood and lymphatic vessels; in adult tissues, PDGF-B from endothelial cells (developmentally) and microglia (in adulthood) maintains pericyte coverage and blood-brain barrier integrity, while macrophage- and platelet-derived PDGF-B controls smooth muscle cell recruitment in pulmonary hypertension and tumor vessel stabilization respectively, and downstream PDGF-B signaling proceeds through Ras/MAP kinase pathways to activate transcription factors including Egr-1, YB-1, and SIF/STAT elements.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper and extract discoveries only from KEEP papers.\n\n**Classification notes:**\n- Papers about \"SIS\" as small intestinal submucosa scaffold → EXCLUDE (alias collision)\n- Papers about SSV/v-sis oncogene → KEEP (directly encodes PDGF-B/p28v-sis, foundational mechanism papers)\n- Papers about sepsis definitions (SIRS/PIRO) → EXCLUDE (alias collision with \"SIS\" concept)\n- Papers about cryopreservation SSV method → EXCLUDE\n- Papers about SSV (solid surface vitrification) → EXCLUDE\n- Papers about SSV retrovirus biology (S71 endogenous retrovirus) → EXCLUDE (not about PDGFB protein mechanism)\n- Papers about synaptic vesicles (SSV/LDCV) → EXCLUDE\n- Papers about lncRNA PART1 → EXCLUDE (alt-locus product, lncRNA not PDGFB protein)\n- All other PDGFB canonical protein papers → KEEP\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1983,\n      \"finding\": \"PDGF B-chain shares virtual amino acid sequence identity (~104 residues) with the predicted transforming protein p28sis of simian sarcoma virus (SSV), establishing that the v-sis oncogene encodes a PDGF-related protein.\",\n      \"method\": \"Amino acid sequencing of purified PDGF and comparison with predicted v-sis protein sequence\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing, foundational discovery replicated across multiple labs\",\n      \"pmids\": [\"6306471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"The c-sis proto-oncogene encodes a polypeptide precursor of the PDGF B chain, with amino acid sequence identity over 109 residues confirmed by direct sequencing; the PDGF A chain is ~60% homologous to the B chain but encoded at a separate locus.\",\n      \"method\": \"Nucleotide sequencing of c-sis genomic clones combined with amino acid sequence analysis of purified PDGF B chain\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein and nucleotide sequencing, foundational structural identification\",\n      \"pmids\": [\"6329745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"SSV-transformed cells secrete a PDGF-like protein (p28v-sis) that stimulates autocrine cell growth through PDGF receptors; anti-PDGF antisera block 3H-thymidine incorporation in growing SSV-transformed cells; PDGF receptors purified from SSV-NIH 3T3 cells retain active protein tyrosine kinase activity stimulated by PDGF.\",\n      \"method\": \"Mitogenic assay, 125I-PDGF receptor competition binding, anti-PDGF antisera neutralization, receptor purification with tyrosine kinase assay, tumor growth in nude mice\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods establishing autocrine mechanism and receptor tyrosine kinase activation\",\n      \"pmids\": [\"6091918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"Expression of the normal human sis/PDGF-2 coding sequence under retroviral LTR control induces cellular transformation of NIH-3T3 cells, demonstrating that the growth factor coding sequence itself has transforming activity.\",\n      \"method\": \"Stable transfection of chimeric LTR-c-sis construct into NIH/3T3 cells; transforming foci assay; detection of sis/PDGF-2 translational products\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function transfection with protein expression confirmation, replicated concept across labs\",\n      \"pmids\": [\"6091919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"The v-sis gene product competes with 125I-PDGF for receptor binding on fibroblast membranes, directly demonstrating functional equivalence between the SSV oncogene product and PDGF.\",\n      \"method\": \"Bacterial expression of v-sis protein; 125I-PDGF receptor competition binding assay; immunochemical identification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro receptor binding assay with purified recombinant protein and immunochemical validation\",\n      \"pmids\": [\"6088510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"The v-sis gene product specifically binds PDGF receptors, stimulates tyrosine phosphorylation of PDGF receptors, and induces DNA synthesis in quiescent fibroblasts; transformation by SSV correlates strictly with PDGF receptor expression in target cells.\",\n      \"method\": \"Partial purification of v-sis protein; receptor binding; tyrosine phosphorylation assay; mitogenic assay; antibody neutralization; cell susceptibility correlation\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods, receptor tyrosine phosphorylation directly demonstrated\",\n      \"pmids\": [\"2996133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"Normal human endothelial cells in culture express PDGF B chain mRNA and synthesize a PDGF-B precursor polypeptide (predicted Mr 27,281), establishing endothelial cells as a physiological source of PDGF-B.\",\n      \"method\": \"cDNA cloning and complete sequence analysis of sis-homologous cDNA from human umbilical vein endothelial cells\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct cDNA cloning and sequence determination from normal human cells\",\n      \"pmids\": [\"4033772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The SIS/PDGF2 mRNA is 3373 nucleotides with only a 723-bp coding sequence flanked by long 5' (1022 bp) and 3' (1625 bp) untranslated regions; a TATA box 24 bp upstream and an enhancer-like TG element downstream of the polyadenylation site were identified as putative regulatory elements.\",\n      \"method\": \"cDNA cloning, nuclease S1 mapping, primer extension, and nucleotide sequence analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct sequencing and mapping of the transcriptional unit\",\n      \"pmids\": [\"3517869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The v-sis gene product is co-translationally processed in the endoplasmic reticulum–Golgi compartment where signal sequence cleavage and N-linked glycosylation occur; it contains no transmembrane regions (confirmed by trypsin protection in microsomes); mutation of the proposed proteolytic processing site (Lys-Arg→Asn-Ser at residues 110–111) retains full biological activity; mutations disrupting the signal sequence cause nuclear mislocation and loss of activity.\",\n      \"method\": \"Site-directed mutagenesis; subcellular fractionation; microsome trypsin protection assay; N-linked glycosylation analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis and multiple biochemical assays\",\n      \"pmids\": [\"3537701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"Phorbol ester (TPA) induces c-sis/PDGFB gene transcription in K-562 hematopoietic stem cells during megakaryoblastic differentiation, as determined by nuclear run-off transcriptional assay, without generalized effects on other hematopoietic cell lines.\",\n      \"method\": \"Northern blot analysis; nuclear run-off transcriptional assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — nuclear run-off establishes transcriptional mechanism, single lab\",\n      \"pmids\": [\"3466024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"Each of the eight conserved cysteine residues in the v-sis/PDGF-B molecule is required for disulfide-linked dimer formation; however, interchain disulfide bonds are not essential for receptor activation—only the four cysteines forming intramolecular disulfide bonds are required for biological activity.\",\n      \"method\": \"Site-directed mutagenesis of individual cysteine codons; disulfide dimer formation assay; transforming activity assay\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic site-directed mutagenesis of all conserved cysteines with functional validation\",\n      \"pmids\": [\"3035718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"Transformation by v-sis occurs through internal activation of PDGF receptors before cell surface expression: a v-sis mutant encoding ER/Golgi-retained protein transforms NRK cells as efficiently as wild-type without secreting detectable v-sis protein, and anti-PDGF antisera fail to reverse morphological transformation.\",\n      \"method\": \"Construction of ER/Golgi-retention mutant of v-sis; stable transfection; transformation assay; anti-PDGF antibody treatment\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genetic mutant approach with multiple controls establishing intracellular autocrine mechanism\",\n      \"pmids\": [\"2551043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"PDGF-B induces a SIF (sis-inducible factor) DNA-binding activity that binds a conserved element upstream of the c-fos promoter; this SIF-binding element confers sis/PDGF inducibility onto a truncated c-fos promoter and functions additively with the serum response element (SRE), but only responds to sis/PDGF (not phorbol esters or serum).\",\n      \"method\": \"Electrophoretic mobility shift assay; reporter gene transfection; promoter deletion analysis with recombinant PDGF\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — functional promoter analysis with purified recombinant protein and EMSA, replicated\",\n      \"pmids\": [\"2176154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"Internal activation of PDGF receptors by v-sis product is sufficient for transformation, but activated receptors must reach the cell surface to couple with intracellular mitogenic signaling; suramin completely blocks proliferation and eliminates cell-surface receptor tyrosine phosphorylation without affecting intracellular receptor phosphorylation.\",\n      \"method\": \"Suramin treatment; anti-PDGF neutralizing antibody; tyrosine phosphorylation assay of cell-surface vs. intracellular PDGF receptors; defined medium proliferation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — dissection of intracellular vs. surface receptor activation with multiple pharmacological and biochemical approaches\",\n      \"pmids\": [\"2813378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"PDGF-B mRNA and protein expression in glioblastoma: proliferating vascular endothelial cells in human glioblastoma coexpress PDGF B chain mRNA and PDGF receptor mRNA, supporting an autocrine growth stimulation mechanism for endothelial hyperplasia in this tumor.\",\n      \"method\": \"RNA transfer blot analysis; in situ hybridization of tumor biopsies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — in situ hybridization demonstrating co-expression; no direct functional validation in this paper\",\n      \"pmids\": [\"2845420\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"TGF-β and phorbol ester (PMA/diacylglycerol via protein kinase C) each induce c-sis/PDGF-B mRNA expression in glioblastoma cells through distinct signaling routes (TGF-β uses a PKC-independent kinase pathway); both pathways converge on transcriptional activation of c-sis.\",\n      \"method\": \"Nuclear run-on transcription assay; PKC downregulation; kinase inhibitor H7; cycloheximide treatment; RNA hybridization\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — nuclear run-off establishes transcriptional mechanism; pharmacological dissection of two pathways\",\n      \"pmids\": [\"2655888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"PDGF-B protein is localized within macrophages in all stages of human and nonhuman primate atherosclerotic lesion development, implicating macrophage-derived PDGF-B as a source of chemotactic and growth-stimulatory signals for intimal smooth muscle cells.\",\n      \"method\": \"Immunohistochemical localization of PDGF-B protein in atherosclerotic tissue sections\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — immunolocalization study; establishes cellular source but no direct functional mechanism experiment\",\n      \"pmids\": [\"2343305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"Two specific PDGF-B chain residues, arginine 27 and isoleucine 30, mediate receptor binding and cell activation; substitutions at these positions create PDGF-B mutants defective in receptor affinity and mitogenic activity without disrupting overall protein structure (confirmed by circular dichroism and fluorescence spectroscopy).\",\n      \"method\": \"Site-directed mutagenesis; 125I-PDGF-BB displacement assay; mitogenic assay; inositol lipid turnover; circular dichroism; fluorescence spectroscopy\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with multiple functional assays and structural validation\",\n      \"pmids\": [\"1661670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"SPARC (extracellular glycoprotein) specifically binds PDGF-BB and PDGF-AB dimers (but not PDGF-AA) and inhibits their binding to PDGF receptors on dermal fibroblasts in a dose-dependent and pH-dependent manner.\",\n      \"method\": \"Specific immunoprecipitation of SPARC–125I-PDGF-BB complexes; solid-phase binding assay; receptor competition binding assay; pH-dependence analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reciprocal binding assays with purified proteins, multiple formats, functional inhibition demonstrated\",\n      \"pmids\": [\"1311092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The p85 regulatory subunit of PI 3-kinase associates with the PDGF receptor via its SH2 domains in a tyrosine autophosphorylation-dependent manner; binding requires receptor kinase activity and the N-terminal SH2 domain binds PDGF receptors more stably than EGF receptors.\",\n      \"method\": \"Co-immunoprecipitation; GST-SH2 fusion protein binding assays; phosphotyrosine inhibition assays; Western blot\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — GST pulldown with defined domains plus co-IP; phosphotyrosine-dependence established\",\n      \"pmids\": [\"1372091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"A 10-bp element named SPE (SIS proximal element, positions -58 to -39 relative to PDGF-B mRNA start site) is essential for TPA-induced transcriptional activation of the SIS/PDGFB promoter in megakaryocytes; gel shift assays show a TPA-inducible nuclear complex that forms over the same time frame as mRNA induction and is blocked by cycloheximide, indicating requirement for new protein synthesis.\",\n      \"method\": \"Linker scanning mutagenesis across 250-bp promoter; luciferase reporter assay; gel mobility-shift assay; time-course analysis; cycloheximide treatment\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — systematic promoter mutagenesis with functional validation and EMSA\",\n      \"pmids\": [\"8356057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"v-sis-induced Egr-1 expression is mediated by a pathway requiring tyrosine kinase activity and c-Ha-Ras; dominant-negative Ras and Raf mutants abrogate Egr-1 induction by v-sis/PDGF-B, and this signal is independent of protein kinase C.\",\n      \"method\": \"Conditional metallothionein-v-sis expression system; dominant-negative Ras and Raf transfection; Egr-1 promoter-reporter assay; PKC inhibition\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with dominant negatives; inducible system, single lab\",\n      \"pmids\": [\"7890805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Selective PDGF receptor kinase blockers (tyrphostins AG1295 and AG1296) reverse the transformed phenotype of sis-transfected NIH 3T3 cells without affecting src-transformed cells or c-src kinase activity, confirming that PDGF receptor kinase activity is required for v-sis/PDGF-B-driven transformation.\",\n      \"method\": \"Tyrphostin treatment; transformation reversal assay; receptor autophosphorylation assay; kinase activity assay; selectivity profiling against multiple receptors\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — pharmacological reversal of transformation with selective inhibitors and kinase specificity profiling\",\n      \"pmids\": [\"7954456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Mechanical strain-induced fetal lung cell growth is mediated by upregulation of PDGF-B and PDGF-β receptor mRNA and protein; phosphorothioate antisense PDGF-B oligonucleotides, neutralizing PDGF-BB antibody, and the PDGF receptor tyrosine kinase inhibitor tyrphostin 9 each abolish strain-induced DNA synthesis.\",\n      \"method\": \"Antisense oligonucleotide knockdown; neutralizing antibody; tyrosine kinase inhibitor; DNA synthesis assay; mRNA and protein expression analysis\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal loss-of-function approaches converging on same phenotype, single lab\",\n      \"pmids\": [\"7653578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"In dermatofibrosarcoma protuberans (DFSP), chromosomal translocation t(17;22) fuses COL1A1 to PDGFB, deleting exon 1 of PDGFB and releasing it from normal transcriptional regulation, producing constitutive PDGF-B expression that drives tumor formation.\",\n      \"method\": \"Genomic and RNA-level characterization of translocation breakpoints; RT-PCR; FISH\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — molecular characterization of translocation breakpoints, replicated across multiple labs\",\n      \"pmids\": [\"8988177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PDGF-B knockout mice lack pericytes and mesangial cells, while PDGF-A knockout mice lack alveolar smooth muscle cells, demonstrating that PDGF-B is specifically required for the development of pericytes and mesangial cells (but not other smooth muscle cell subtypes).\",\n      \"method\": \"Targeted gene knockout in mice; histological analysis of pericyte and mesangial cell development\",\n      \"journal\": \"Current opinion in nephrology and hypertension\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with isoform-specific phenotypic comparison\",\n      \"pmids\": [\"9442358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PDGF signals through Ras/PI3K/Akt/IKK to activate NF-κB, which transmits both a proliferative signal (via c-myc induction) and an anti-apoptotic signal that counterbalances c-Myc cytotoxicity; Akt transiently associates in vivo with IKK and induces IKK activation upon PDGF stimulation.\",\n      \"method\": \"Co-immunoprecipitation of Akt–IKK complex; kinase assays; dominant-negative constructs; NF-κB reporter assays; apoptosis assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo co-IP of Akt-IKK complex, kinase assays, genetic epistasis, replicated\",\n      \"pmids\": [\"10485711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PDGF receptor dimerization induced by ligand binding leads to autophosphorylation, enabling recruitment and activation of cytoplasmic SH2-domain-containing signal transduction molecules (including PI3K, PLCγ, Src family kinases, Grb2, SHP-2), initiating pathways controlling cell growth, actin reorganization, migration, and differentiation.\",\n      \"method\": \"Biochemical analysis of receptor phosphorylation; SH2 domain binding studies; downstream signaling assays\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive review synthesizing multiple experimental studies on receptor signaling mechanisms\",\n      \"pmids\": [\"9739761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Cyclic mechanical strain increases PDGF-B mRNA and activates the PDGF-B promoter (12-fold in psisCAT 6A construct), and also upregulates PDGF-β receptor protein, both contributing to strain-induced smooth muscle cell proliferation; neutralizing antibodies to PDGF-β receptor reduce strain-induced thymidine incorporation by 50%.\",\n      \"method\": \"Cyclic strain on silicone elastomer; promoter-CAT reporter transfection; neutralizing antibody; Western blot; 3H-thymidine incorporation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter activity and neutralizing antibody data, single lab\",\n      \"pmids\": [\"10558917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The COL1A1-PDGFB chimeric protein produced in DFSP is processed in transfected cells into mature PDGF-B dimers that activate the PDGFB receptor pathway in a paracrine manner, rendering cells growth-factor-independent and tumorigenic; mutagenesis of the COL1A1-PDGFB cleavage site shows that even uncleaved forms retain mitogenic activity.\",\n      \"method\": \"Stable and transient transfection; anti-PDGFB antibody detection; growth factor independence assay; nude mouse tumorigenicity assay; site-directed mutagenesis of processing site\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstitution with chimeric protein, mutagenesis, and in vivo tumorigenicity testing\",\n      \"pmids\": [\"11420709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PDGF-B is expressed by cultured human endothelial cells and kidney epithelial cells (BSC-1), which secrete a PDGF-like protein with mitogenic and chemotactic activities inhibitable by anti-PDGF antibody; c-sis but not c-sis A-chain mRNA is detected in these cells, and TGF-β2 induces c-sis mRNA accumulation without corresponding increase in secreted PDGF-like activity.\",\n      \"method\": \"Northern blot with c-sis cDNA probe; mitogenic and chemotactic activity assays; antibody inhibition; protein secretion measurement\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — biochemical assays establishing paracrine function, single lab\",\n      \"pmids\": [\"3177660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Adiponectin specifically binds PDGF-BB (but not PDGF-AA) and inhibits PDGF-BB binding to smooth muscle cells, suppressing PDGF-β receptor autophosphorylation and ERK phosphorylation, thereby inhibiting PDGF-BB-driven smooth muscle cell proliferation and migration.\",\n      \"method\": \"125I-PDGF-BB binding competition; immunoblot of receptor autophosphorylation and ERK phosphorylation; proliferation (3H-thymidine) and migration (Boyden chamber) assays\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding demonstrated, receptor autophosphorylation inhibition, multiple functional readouts\",\n      \"pmids\": [\"12070119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Endothelial PDGF-B retention motif (heparan sulfate proteoglycan-binding domain) is required for proper pericyte integration into the vessel wall in tumors; loss of this retention motif (pdgf-b ret/ret mice) causes pericyte detachment and partial loss, increased vessel diameter, and hemorrhaging even when PDGF-B is provided by tumor cells.\",\n      \"method\": \"Mouse genetics (pdgf-b ret/ret); tumor transplantation; transgenic PDGF-B expression; pericyte coinjection with tumor cells; histological and vascular analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic tools dissecting endothelial vs. non-endothelial sources and retention motif function\",\n      \"pmids\": [\"14561699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PDGF-B signaling via the MAPK pathway induces YB-1 subcellular shuttling from nucleus to cytoplasm in mesangial cells during mesangioproliferative glomerulonephritis; YB-1 knockdown by RNAi abolishes the mitogenic effect of PDGF-B, identifying YB-1 as a necessary downstream signaling target.\",\n      \"method\": \"PDGF-B infusion in vivo; PDGF aptamer blockade; MEK inhibitor U0126; RNAi knockdown; immunolocalization; in vitro proliferation assay\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pathway placement by pharmacological blockade combined with RNAi validation of necessity\",\n      \"pmids\": [\"16093451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Hypoxia increases endothelial PDGF-B mRNA and protein via a transcriptional mechanism; hypoxic mesangial cells show 2–3-fold enhanced proliferative response to PDGF-B associated with increased specific receptor binding capacity; hypoxic conditioned medium chemoattractant activity is largely abolished by PDGF-B neutralizing antibody.\",\n      \"method\": \"Northern and Western blot; saturation binding assay; 3H-thymidine proliferation; Boyden chamber migration; neutralizing antibody\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, single lab\",\n      \"pmids\": [\"16014047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TGF-β-Smad pathway promotes glioma cell proliferation by transcriptionally inducing PDGF-B expression in gliomas with an unmethylated PDGF-B gene; the epigenetic methylation status of the PDGF-B gene is the molecular determinant of whether TGF-β acts as oncogenic (inducing PDGF-B and proliferation) or not in human glioma.\",\n      \"method\": \"Transcriptomic profiling; ChIP for Smad binding; PDGF-B promoter methylation analysis; gain/loss-of-function experiments; primary patient-derived glioma cultures\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP, methylation analysis, and functional rescue experiments in primary patient cells\",\n      \"pmids\": [\"17292826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PDGF-B/PDGFR-β signaling is required for cardiac contributions of epicardium-derived cells and cardiac neural crest; Pdgf-b-/- and Pdgfr-β-/- mouse embryos show ventricular septal defects, atrioventricular valve maldevelopment, impaired coronary arteriogenesis, myocardial hypoplasia, and cardiac nerve hypoplasia.\",\n      \"method\": \"Analysis of Pdgf-b-/- and Pdgfr-β-/- mouse embryos; immunohistochemical staining for αSMA, periostin, ephrinB2, VEGFR-2, NCAM at multiple embryonic stages\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — dual knockout analysis with multiple molecular markers across developmental stages\",\n      \"pmids\": [\"18213589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PDGF-BB signaling transcriptionally induces miR-221, which then downregulates c-Kit and p27Kip1; loss of p27Kip1 by miR-221 drives PDGF-mediated vascular smooth muscle cell proliferation, while decreased c-Kit suppresses SMC-specific contractile gene expression via reduced Myocardin.\",\n      \"method\": \"miRNA expression profiling; promoter-reporter assay; miR-221 mimic/inhibitor transfection; target site mutagenesis; luciferase reporter; western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pathway dissection with multiple molecular tools, target validation by reporter assays\",\n      \"pmids\": [\"19088079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"VEGF-C regulates PDGF-B expression via VEGFR3 signaling; blockade of VEGFR3 reduces PDGF-B expression and causes marked capillary dilation with mural cell dissociation; conversely, blockade of PDGF-BB diminishes VEGF-C expression, establishing a mutual regulatory loop between VEGF-C and PDGF-B in vascular stabilization.\",\n      \"method\": \"Neutralizing antibody AFL-4 against VEGFR3; PDGF-BB blocking antibody; murine hindlimb ischemia model; histological and blood flow analysis\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal antibody blockade experiments, single lab\",\n      \"pmids\": [\"19734356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SDF-1α induces PDGF-B mRNA and protein expression via a transcriptional mechanism involving ELK-1 transcription factor binding to the pdgf-b promoter; this SDF-1α/PDGF-B pathway is required for differentiation of PDGFR-β+ bone marrow cells into mature pericytes.\",\n      \"method\": \"In vitro SDF-1α stimulation; 2-kb PDGF-B promoter reporter assay; chromatin immunoprecipitation (ChIP) for ELK-1; in vivo tumor model; pericyte differentiation assay\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrates direct ELK-1 binding, promoter-reporter validates transcriptional mechanism, functional pericyte differentiation assay\",\n      \"pmids\": [\"21911740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Venous malformation-causing TIE2 mutations (L914F) cause AKT-dependent chronic suppression of PDGFB production in endothelial cells; mutant TIE2 L914F chronically activates AKT in a ligand-independent manner, reducing PDGFB secretion and thereby impairing mural cell recruitment, contributing to abnormal vascular channel formation.\",\n      \"method\": \"Global gene expression profiling of TIE2-mutant ECs; in vitro TIE2 L914F and R849W expression; AKT inhibitor treatment; ex vivo patient tissue PDGFB measurement\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional rescue with AKT inhibitor, validated in patient tissues ex vivo\",\n      \"pmids\": [\"23633549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Mutations in PDGFB cause autosomal dominant idiopathic basal ganglia calcification (IBGC) in humans; in mice, loss of endothelial PDGFB leads to pericyte deficiency and blood-brain barrier dysfunction, and hypomorphic Pdgfb alleles develop age-related brain calcifications that correlate with degree of pericyte and BBB deficiency.\",\n      \"method\": \"Human genetic analysis; mouse hypomorphic Pdgfb alleles; histological and radiological brain calcification assessment; pericyte quantification; BBB permeability assay\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human genetics combined with mouse genetic model showing dose-dependent calcification, replicated\",\n      \"pmids\": [\"23913003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LHX2 transcription factor directly induces PDGF-B expression in tumor cells, driving autocrine PDGFRβ signaling for cell migration/invasion and paracrine signaling to pericytes for vessel maturation and primary tumor growth; pharmacological inhibition of PDGF-B/PDGFRβ signaling reduces vessel functionality, tumor growth, and LHX2-induced invasion.\",\n      \"method\": \"Loss/gain-of-function in transgenic mouse models; pharmacological PDGFB/PDGFRβ inhibition; in vitro migration/invasion assays; vessel maturation analysis\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic models plus pharmacological validation, dual autocrine/paracrine mechanism established\",\n      \"pmids\": [\"24423492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Germline PDGFB mutations causing Primary Familial Brain Calcification (PFBC) lead to complete loss of PDGF-B function through abolished protein synthesis or defective PDGF-Rβ binding/stimulation; the Pdgfbret/ret mouse model (lacking the proteoglycan-binding retention motif) develops brain calcification, demonstrating that altered tissue distribution of PDGF-B protein is sufficient to cause calcification.\",\n      \"method\": \"In vitro functional analysis of six PDGFB mutations; PDGF-Rβ binding assay; autophosphorylation assay; heterozygous knockout mice; Pdgfbret/ret mice; brain calcification assessment; pericyte coverage quantification; BBB analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct functional assays of multiple mutants combined with mouse genetic models\",\n      \"pmids\": [\"26599395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Transgenic cardiac overexpression of PDGF-B induces focal fibrosis and moderate cardiac hypertrophy, mediated primarily via PDGFRβ; the weaker fibrotic effect of PDGFB (compared to PDGF-A, which is more potent via PDGFRα) reflects differences in receptor affinity, implicating PDGFRα in interstitial mesenchymal cells as the main mediator of strong cardiac fibrosis.\",\n      \"method\": \"Alpha-myosin heavy chain promoter-driven transgenic overexpression; histological and cardiac size analysis; immunohistochemistry for PDGF receptors\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — transgenic model with receptor expression analysis, single lab\",\n      \"pmids\": [\"27816607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PDGFB expressed by lymphatic endothelial cells (LECs) of collecting vessels is required for smooth muscle cell (SMC) recruitment to lymphatic vessels; LEC-specific Pdgfb deletion prevents SMC recruitment causing vessel dilation and failure of pulsatile contraction; extracellular matrix retention of PDGFB is required for SMC recruitment, and low ECM-binding components around capillaries provide a checkpoint preventing inappropriate SMC investment of capillaries.\",\n      \"method\": \"LEC-specific Cre-mediated Pdgfb deletion; PDGFB overexpression in LECs; histological analysis; ECM retention assay; pulsatile contraction measurement\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional cell-specific knockout with defined molecular mechanism (ECM retention), multiple vascular beds analyzed\",\n      \"pmids\": [\"28851707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Platelet-specific conditional knockout of PDGFB impairs tumor vascular pericyte coverage and function, leading to enhanced hypoxia, epithelial-to-mesenchymal transition, elevated circulating tumor cells, and increased spontaneous metastasis, establishing a novel role for platelet-derived PDGFB in maintaining tumor vascular integrity.\",\n      \"method\": \"Platelet-specific Cre-mediated Pdgfb conditional knockout; two tumor mouse models; pericyte coverage quantification; hypoxia markers; EMT markers; circulating tumor cell counting; metastasis quantification\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional cell-specific knockout in two independent tumor models with multiple phenotypic readouts\",\n      \"pmids\": [\"32586981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Endothelial Twist1 transcription factor mediates hypoxia-induced PDGFB upregulation; Twist1 overexpression increases PDGFB expression in pulmonary arterial endothelial cells; knockdown of endothelial Twist1 suppresses hypoxia-induced αSMA-positive cell accumulation and PDGFB upregulation in an in vivo gel implant model; Twist1 and PDGFB levels are elevated in IPAH patient pulmonary artery endothelial cells.\",\n      \"method\": \"Twist1 overexpression/knockdown; in vivo hydrogel implant model on mouse lung; immunofluorescence; IPAH patient cell analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gain and loss of function in vitro and in vivo with patient validation\",\n      \"pmids\": [\"32371931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Adult-induced endothelial deletion of Pdgfb in 2-month-old mice causes slowly progressive pericyte loss (reaching ~50% decrease in endothelial:pericyte ratio and >70% decrease in pericyte marker expression by 12–18 months) and increased BBB permeability; in contrast to constitutive Pdgfb loss, adult-induced loss does not cause vessel dilation, arterio-venous skewing, or microvascular calcification, distinguishing developmental from maintenance roles of PDGFB.\",\n      \"method\": \"Tamoxifen-inducible endothelial-specific Cre; longitudinal pericyte quantification; BBB permeability assay; vessel morphology analysis\",\n      \"journal\": \"Journal of cerebral blood flow and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — inducible cell-specific knockout with longitudinal analysis distinguishing developmental vs. maintenance functions\",\n      \"pmids\": [\"34689641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Macrophage-derived PDGF-B is critical for pathological smooth muscle cell expansion (distal muscularization) in pulmonary hypertension; macrophage-specific deletion of Pdgfb (LysM-Cre) prevents hypoxia-induced distal muscularization and PH; PDGF-B is upregulated in macrophages from human PAH patients; nanoparticle-mediated siRNA knockdown of Pdgfb specifically in lung macrophages prevents hypoxia-induced PH and right ventricular hypertrophy.\",\n      \"method\": \"LysM-Cre conditional Pdgfb knockout; clodronate macrophage depletion; HIF-1α and HIF-2α conditional knockouts; macrophage-conditioned medium SMC proliferation/migration assay; nanoparticle siRNA delivery; human PAH patient macrophage analysis\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models, human patient validation, therapeutic nanoparticle intervention\",\n      \"pmids\": [\"33591958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C/EBPβ transcription factor directly binds PDGFB promoter elements to facilitate PDGFB transcription in anoikis-resistant gastric cancer cells; secreted PDGFB promotes cancer cell survival via a C/EBPβ-dependent self-feedback loop and promotes angiogenesis via MAPK/ERK signaling in vascular endothelial cells.\",\n      \"method\": \"ChIP showing direct C/EBPβ binding to PDGFB promoter; loss/gain-of-function experiments; MAPK/ERK signaling analysis; in vitro and in vivo metastasis models\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP validates direct transcription factor binding, functional rescue experiments, dual autocrine/paracrine mechanism\",\n      \"pmids\": [\"34341514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Microglia constitutively release PDGFB, which signals via PDGFRα on hypothalamic paraventricular nucleus neurons to promote Kv4.3 (potassium channel) expression; ablation of microglia, conditional deletion of microglial PDGFB, or suppression of neuronal PDGFRα elevates pre-sympathetic neuronal excitability and sympathetic outflow, causing hypertension; central supplementation of exogenous PDGFB suppresses the pressor response.\",\n      \"method\": \"Microglial ablation; conditional microglial Pdgfb deletion; neuronal PDGFRα suppression; electrophysiology; sympathetic outflow measurement; blood pressure monitoring; exogenous PDGFB central administration\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional cell-specific knockout with electrophysiology, multiple genetic models, and pharmacological rescue\",\n      \"pmids\": [\"35863346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In adult mice, microglia are the primary source of PDGFB in the CNS (transitioning from endothelial cells in neonates); acute loss of microglial PDGFB profoundly impairs BBB integrity in adults, causing lethal microhemorrhages upon endotoxin challenge; acute loss of endothelial PDGFB has minimal effects on adult BBB but severely impairs neonatal CNS vasculature.\",\n      \"method\": \"Transcriptomic analysis; in situ hybridization; acute conditional cell-specific Pdgfb deletion in adult vs. neonatal mice; BBB permeability assay; endotoxin challenge survival model\",\n      \"journal\": \"Brain, behavior, and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific conditional knockouts at different ages establishing temporal switch in cellular source\",\n      \"pmids\": [\"37992789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PROX1 transcription factor inhibits PDGFB expression in valvular endothelial cells (VECs) partially via FOXC2; conditional deletion of Prox1 from VECs upregulates PDGFB, leading to progressive myxomatous valve degeneration; conditional overexpression of PDGFB in VECs recapitulates the Prox1-knockout phenotype; pharmacological inhibition of PDGFB signaling with imatinib partially ameliorates valve defects.\",\n      \"method\": \"Conditional Prox1 VEC-specific knockout; conditional PDGFB overexpression in VECs; conditional FOXC2 knockdown; echocardiography; histology; electron microscopy; imatinib pharmacological rescue; human mitral valve prolapse sample analysis\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mouse genetic models, pharmacological rescue, human tissue validation\",\n      \"pmids\": [\"37555328\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PDGFB (c-sis) encodes the B-chain of platelet-derived growth factor, a disulfide-bonded dimeric mitogen requiring intramolecular (but not interchain) disulfide bonds and key residues Arg27/Ile30 for receptor binding; it is synthesized as a precursor processed in the ER-Golgi, secreted and retained in extracellular matrix via a heparin-binding retention motif, and signals through PDGF receptor tyrosine kinase dimerization/autophosphorylation to activate multiple downstream pathways (Ras/MAPK, PI3K/Akt/NF-κB, PLCγ, miR-221) controlling proliferation, survival, migration, and differentiation; endothelial PDGFB drives pericyte recruitment and blood-brain barrier maintenance during development, while in adults microglia become the primary CNS PDGFB source maintaining BBB integrity; macrophage-derived PDGFB promotes smooth muscle cell expansion in pulmonary hypertension, platelet-derived PDGFB maintains tumor vascular integrity, and COL1A1-PDGFB gene fusions constitutively activate PDGFB signaling in dermatofibrosarcoma protuberans; germline loss-of-function PDGFB mutations cause primary familial brain calcification through pericyte deficiency and BBB dysfunction.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PDGF-B is a secreted, disulfide-bonded dimeric growth factor (encoded by the c-sis proto-oncogene) that signals through PDGF receptor tyrosine kinases to drive mesenchymal cell proliferation, recruitment, and differentiation — functioning as the principal paracrine signal for pericyte and smooth muscle cell investment of blood vessels, lymphatic vessels, and cardiac structures [PMID:9442358, PMID:28851707, PMID:18213589]. The mature ligand is processed through the ER–Golgi pathway, requires specific intramolecular disulfide bonds and residues Arg27/Ile30 for receptor binding, and its C-terminal extracellular matrix retention motif is essential for proper spatial presentation: loss of this motif causes pericyte detachment, blood–brain barrier breakdown, and brain calcification in mice and humans with Primary Familial Brain Calcification [PMID:3035718, PMID:1661670, PMID:14561699, PMID:26599395]. During development, endothelial-derived PDGF-B recruits pericytes and mural cells to nascent vessels, whereas in the adult brain microglia become the dominant PDGF-B source maintaining pericyte coverage and BBB integrity, and additionally signal through neuronal PDGFRα to regulate sympathetic tone [PMID:37992789, PMID:35863346, PMID:34689641]. Downstream, PDGF-B engagement of PDGFRβ activates Ras/MAPK cascades leading to induction of transcription factors including Egr-1, YB-1, and SIF/STAT elements, and autocrine PDGF-B/PDGFRβ loops — operating both at the cell surface and intracellularly — underlie v-sis-mediated transformation and contribute to dermatofibrosarcoma protuberans and pulmonary hypertension pathogenesis [PMID:7890805, PMID:16093451, PMID:2176154, PMID:2551043, PMID:11420709, PMID:33591958].\",\n  \"teleology\": [\n    {\n      \"year\": 1984,\n      \"claim\": \"The identity of the PDGF B-chain as the product of the c-sis proto-oncogene established that a normal growth factor gene could serve as a viral oncogene, unifying growth factor biology with oncogene research.\",\n      \"evidence\": \"Direct protein sequencing of PDGF B-chain aligned to c-sis genomic clones; functional equivalence confirmed by receptor binding competition with bacterially expressed v-sis protein\",\n      \"pmids\": [\"6329745\", \"6088510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional structure of PDGF-B/receptor complex not yet determined\", \"Physiological roles beyond mitogenesis unknown\"]\n    },\n    {\n      \"year\": 1984,\n      \"claim\": \"Demonstrating that v-sis/PDGF-B transforms cells through autocrine activation of the PDGF receptor tyrosine kinase established the autocrine oncogene paradigm — that transformation requires receptor expression and is mediated by receptor kinase activity.\",\n      \"evidence\": \"Anti-PDGF antisera block SSV-transformed cell growth; receptor purification shows active tyrosine kinase; normal c-sis cDNA transforms NIH-3T3 cells under LTR control; transformation correlates with PDGF receptor expression\",\n      \"pmids\": [\"6091918\", \"6091919\", \"6323994\", \"2996133\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether intracellular versus surface receptor activation drives transformation was unresolved\", \"Downstream signaling pathways unknown\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Defining the biosynthetic processing route — ER signal peptide cleavage, N-linked glycosylation, and Golgi transit — showed that PDGF-B is a conventional secretory pathway client and that signal sequence integrity, not proteolytic maturation cleavage, is essential for biological activity.\",\n      \"evidence\": \"Site-directed mutagenesis of signal sequence and processing site; microsome protection assays; glycosylation analysis; mRNA structural characterization\",\n      \"pmids\": [\"3537701\", \"3517869\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of C-terminal pro-domain not addressed\", \"Mechanism of dimerization not resolved\"]\n    },\n    {\n      \"year\": 1987,\n      \"claim\": \"Systematic cysteine mutagenesis resolved the disulfide bond requirements: intramolecular disulfide bonds formed by four specific cysteines are essential for transforming activity, while interchain disulfide bonds are dispensable for receptor activation, clarifying how the dimer achieves its active conformation.\",\n      \"evidence\": \"Site-directed mutagenesis of all eight conserved cysteines; transformation assays; disulfide bond analysis\",\n      \"pmids\": [\"3035718\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure needed to assign specific disulfide pairings\", \"Whether non-covalent dimers are physiologically relevant was untested\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"The discovery that an ER/Golgi-retained v-sis mutant (incapable of secretion) fully transforms cells demonstrated that intracellular PDGF receptor activation is sufficient for transformation, while subsequent work showed that surface receptor activation is specifically required for mitogenic signal coupling.\",\n      \"evidence\": \"ER-retention mutant transforms NRK cells without secretion; suramin blocks surface receptor activation and proliferation while leaving intracellular phosphorylation intact\",\n      \"pmids\": [\"2551043\", \"2813378\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which intracellular compartment supports productive signaling was not pinpointed\", \"Whether intracellular activation occurs in non-transformed physiology unknown\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Identification of the sis-inducible factor (SIF/STAT) binding element upstream of c-fos, activated specifically by PDGF-B and independent of the serum response element, revealed the first PDGF-specific transcriptional output and foreshadowed the STAT signaling pathway.\",\n      \"evidence\": \"Purified recombinant PDGF-B induction; gel shift assays; promoter deletion/reporter analysis in transfected cells\",\n      \"pmids\": [\"2176154\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of SIF protein not yet established as STAT family member\", \"Full spectrum of PDGF-specific transcriptional targets unknown\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Pinpointing Arg27 and Ile30 as critical receptor-binding residues — whose mutation ablates receptor affinity without disrupting overall fold — defined the receptor-binding interface of PDGF-B at single-residue resolution.\",\n      \"evidence\": \"Site-directed mutagenesis; 125I-PDGF-BB displacement; mitogenic and inositol lipid assays; CD and fluorescence spectroscopy confirming intact structure\",\n      \"pmids\": [\"1661670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis at atomic level required co-crystal\", \"Differential contributions to PDGFRα vs. PDGFRβ binding not dissected\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating that PDGF-B induces Egr-1 via a Ras/Raf-dependent, PKC-independent pathway, and that selective PDGFR kinase inhibitors reverse sis-transformed phenotype, established the Ras/MAPK cascade as the core downstream signaling axis and validated PDGFR kinase as a druggable target.\",\n      \"evidence\": \"Dominant-negative Ras/Raf epistasis; tyrphostin AG1295/AG1296 inhibition reversing transformation; Egr-1 promoter reporters\",\n      \"pmids\": [\"7890805\", \"7954456\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PI3K and other parallel pathways not yet dissected\", \"In vivo therapeutic validation not performed\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"PDGF-B knockout mice revealed an indispensable developmental role: pericytes and mesangial cells fail to develop, establishing PDGF-B/PDGFRβ as the master pathway for mural cell recruitment during organogenesis.\",\n      \"evidence\": \"PDGF-B knockout mouse analysis with histological and immunohistochemical characterization across organs\",\n      \"pmids\": [\"9442358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type-specific source of PDGF-B in each organ not defined\", \"Whether PDGF-B has adult maintenance roles was unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The C-terminal ECM retention motif was shown to be functionally distinct from overall PDGF-B expression: retention-deficient mice had proper pericyte numbers but impaired pericyte vessel integration, revealing that spatial immobilization of PDGF-B in the ECM is essential for functional vascular assembly.\",\n      \"evidence\": \"pdgf-b(ret/ret) mice; tumor transplantation models; pericyte co-injection rescue experiments; vessel morphometry\",\n      \"pmids\": [\"14561699\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the proteoglycan partners mediating retention not established\", \"Whether retention motif has different roles in different vascular beds unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linking PDGFB loss-of-function mutations to Primary Familial Brain Calcification (PFBC) showed that the retention motif — not simply haploinsufficiency — drives brain calcification, connecting the developmental pericyte recruitment mechanism to a human Mendelian disease.\",\n      \"evidence\": \"Functional analysis of six PFBC-causing PDGFB mutations; PDGFRβ autophosphorylation assays; Pdgfbret/ret mice develop brain calcification; pericyte coverage and BBB assessment\",\n      \"pmids\": [\"26599395\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking pericyte deficiency to calcification not resolved\", \"Whether other PDGFB mutations with partial function cause milder phenotypes untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extending PDGF-B's mural cell recruitment role to the lymphatic system, LEC-specific Pdgfb deletion prevented smooth muscle cell coverage of collecting lymphatic vessels, demonstrating that ECM-retained PDGF-B operates by the same spatial mechanism in lymphatic as in blood vasculature.\",\n      \"evidence\": \"Conditional LEC-specific Pdgfb knockout; PDGFB overexpression without retention motif fails to recruit SMCs; vessel contractility and morphology analysis\",\n      \"pmids\": [\"28851707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether lymphatic SMCs differ in PDGFB dependence from blood vessel pericytes unknown\", \"Compensation by other PDGF family members not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Cell-type-specific knockout of PDGFB in platelets and macrophages revealed distinct pathological contributions: platelet PDGFB maintains tumor vascular integrity and limits metastasis, while macrophage PDGFB drives pathological SMC expansion in pulmonary hypertension.\",\n      \"evidence\": \"Conditional platelet-specific (PF4-Cre) and macrophage-specific (LysM-Cre) Pdgfb knockouts; tumor models with pericyte/metastasis readouts; hypoxia-induced PH models; nanoparticle siRNA delivery; human PAH macrophage conditioned medium\",\n      \"pmids\": [\"32586981\", \"33591958\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other platelet-derived factors compensate over time not addressed\", \"Direct macrophage-to-SMC PDGFB signaling pathway intermediates not fully mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Discovery that microglia constitutively release PDGF-B to regulate hypothalamic neuron excitability via PDGFRα/Kv4.3 revealed an entirely non-vascular, non-immune function of microglial PDGF-B in central autonomic control.\",\n      \"evidence\": \"Microglia ablation; conditional microglial Pdgfb deletion; neuronal PDGFRα knockdown; electrophysiology; blood pressure measurements; central PDGFB supplementation rescue\",\n      \"pmids\": [\"35863346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether microglial PDGF-B regulates other neuronal populations beyond PVN unknown\", \"Molecular mechanism linking PDGFRα to Kv4.3 transcription not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Comparative acute deletion established that microglia — not endothelial cells — are the primary adult source of PDGF-B for BBB maintenance, fundamentally revising the long-held model that endothelial PDGF-B maintains the adult BBB, while endothelial PDGF-B is essential only during neonatal vascular development.\",\n      \"evidence\": \"Acute conditional deletion of microglial vs. endothelial Pdgfb in adults; BBB permeability assays; endotoxin challenge survival; neonatal vascular analysis\",\n      \"pmids\": [\"37992789\", \"34689641\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether microglial PDGF-B acts directly on pericytes or through intermediate signals is unclear\", \"Signals that regulate microglial PDGFB expression in the adult brain not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic-resolution structural basis of PDGF-B/PDGFRβ engagement, the identity of ECM proteoglycans mediating retention motif function in vivo, the mechanism linking pericyte loss to brain calcification in PFBC, and how microglial PDGF-B production is regulated in health and neuroinflammation.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of PDGF-B with PDGFRβ from the timeline\", \"Proteoglycan identity for retention motif unknown\", \"Calcification mechanism downstream of pericyte loss unresolved\", \"Regulation of microglial PDGFB expression not characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [1, 4, 5, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 4, 18, 22, 23]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [18, 21, 22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 5, 11, 13, 15, 19, 26]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [16, 33]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [18, 21, 22]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [17, 25, 30, 31]}\n    ],\n    \"complexes\": [\n      \"PDGF-BB homodimer\"\n    ],\n    \"partners\": [\n      \"PDGFRB\",\n      \"PDGFRA\",\n      \"YBX1\",\n      \"EGR1\",\n      \"ELK1\",\n      \"CEBPB\",\n      \"TWIST1\",\n      \"LHX2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"PDGFB encodes the B-chain of platelet-derived growth factor, a disulfide-bonded dimeric mitogen that signals through PDGF receptor tyrosine kinase dimerization and autophosphorylation to activate Ras/MAPK, PI3K/Akt/NF-κB, and PLCγ pathways controlling cell proliferation, survival, migration, and differentiation [PMID:6091918, PMID:10485711, PMID:9739761]. Synthesized as a precursor processed in the ER–Golgi, PDGF-B is secreted and retained in the extracellular matrix via a C-terminal heparin-binding motif that is essential for proper pericyte recruitment to blood vessels; endothelial PDGF-B drives pericyte investment and blood–brain barrier formation during development, while in adults microglia become the primary CNS source maintaining BBB integrity [PMID:14561699, PMID:23913003, PMID:37992789]. Loss-of-function PDGFB mutations cause autosomal dominant primary familial brain calcification through pericyte deficiency and BBB dysfunction, and the COL1A1–PDGFB gene fusion constitutively activates PDGF-B signaling in dermatofibrosarcoma protuberans [PMID:23913003, PMID:8988177, PMID:11420709]. Beyond its canonical vascular roles, macrophage-derived PDGF-B drives smooth muscle cell expansion in pulmonary hypertension, platelet-derived PDGF-B maintains tumor vascular integrity and limits metastasis, and microglial PDGF-B regulates neuronal excitability and sympathetic tone via PDGFR-α signaling [PMID:33591958, PMID:32586981, PMID:35863346].\",\n  \"teleology\": [\n    {\n      \"year\": 1983,\n      \"claim\": \"The question of what gene product the v-sis oncogene encodes was resolved when PDGF B-chain amino acid sequencing revealed near-complete identity with the predicted v-sis protein, establishing that a growth factor could function as an oncogene.\",\n      \"evidence\": \"Direct amino acid sequencing of purified PDGF compared with predicted v-sis sequence\",\n      \"pmids\": [\"6306471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of transformation not yet addressed\", \"Whether PDGF-B acts through autocrine or paracrine loop unknown\"]\n    },\n    {\n      \"year\": 1984,\n      \"claim\": \"The autocrine transformation mechanism was established: SSV-transformed cells secrete PDGF-like protein that activates PDGF receptor tyrosine kinase, and the normal human c-sis coding sequence itself is sufficient to transform fibroblasts, demonstrating that overexpression of a normal growth factor drives oncogenesis.\",\n      \"evidence\": \"Anti-PDGF antisera blockade of transformed cell growth; receptor purification with kinase assay; LTR-driven c-sis transfection transforming foci assay; v-sis receptor competition binding\",\n      \"pmids\": [\"6091918\", \"6091919\", \"6088510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether transformation requires secretion or can occur intracellularly unknown\", \"Downstream signaling pathways not mapped\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"The biosynthetic pathway was mapped: PDGF-B is co-translationally processed in the ER–Golgi with signal sequence cleavage and N-linked glycosylation, and signal sequence integrity is required for biological activity, while the proposed proteolytic processing site is dispensable.\",\n      \"evidence\": \"Site-directed mutagenesis of signal sequence and processing site; microsome trypsin protection; glycosylation analysis\",\n      \"pmids\": [\"3537701\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of C-terminal processing not addressed\", \"Extracellular retention mechanism unknown\"]\n    },\n    {\n      \"year\": 1987,\n      \"claim\": \"The structural basis of PDGF-B activity was clarified: all eight conserved cysteines participate in dimerization, but only the four intramolecular disulfide bonds are required for receptor activation, separating dimerization from function.\",\n      \"evidence\": \"Systematic site-directed mutagenesis of all eight cysteines with functional and dimerization assays\",\n      \"pmids\": [\"3035718\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific receptor-binding residues not yet identified\", \"No crystal structure available\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"Intracellular autocrine signaling was demonstrated: an ER/Golgi-retained v-sis mutant transforms cells as efficiently as wild-type without secretion, but suramin experiments showed that activated receptors must reach the cell surface to couple with mitogenic signaling, resolving the spatial requirements for transformation.\",\n      \"evidence\": \"ER/Golgi-retention mutant transformation assay; suramin blockade dissecting surface vs. intracellular receptor phosphorylation\",\n      \"pmids\": [\"2551043\", \"2813378\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of intracellular compartment where receptor activation occurs not defined\", \"Downstream transcription factor targets only beginning to be identified\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Key receptor-binding residues were identified: Arg27 and Ile30 are specifically required for PDGF receptor binding and mitogenic activity without disrupting overall protein fold, providing the first structure–function map of the ligand–receptor interface.\",\n      \"evidence\": \"Site-directed mutagenesis with 125I-PDGF displacement, mitogenic assay, circular dichroism, and fluorescence spectroscopy\",\n      \"pmids\": [\"1661670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full receptor–ligand co-crystal structure not solved\", \"Whether same residues mediate PDGFR-α vs. PDGFR-β binding unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Downstream signaling cascades were elucidated: PDGF receptor dimerization recruits PI3K (via p85 SH2 domains), PLCγ, Src kinases, and Grb2, and PDGF signals through Ras/PI3K/Akt/IKK to activate NF-κB, transmitting both proliferative and anti-apoptotic signals; in parallel, PDGF-B knockout mice revealed an essential and isoform-specific requirement for pericyte and mesangial cell development.\",\n      \"evidence\": \"Co-immunoprecipitation of Akt–IKK complex; kinase assays; dominant-negative constructs; Pdgf-b knockout mouse histological analysis\",\n      \"pmids\": [\"10485711\", \"9739761\", \"9442358\", \"1372091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of individual downstream pathways to pericyte recruitment in vivo unknown\", \"Mechanism linking PDGF-B loss to mesangial cell absence not defined\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"The molecular basis of dermatofibrosarcoma protuberans was established: t(17;22) translocation fuses COL1A1 to PDGFB, removing PDGFB from normal transcriptional control and producing constitutive PDGF-B that activates PDGFR-β in a paracrine manner.\",\n      \"evidence\": \"Translocation breakpoint characterization by RT-PCR and FISH; functional reconstitution showing chimeric protein processing and tumorigenicity\",\n      \"pmids\": [\"8988177\", \"11420709\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether uncleaved chimeric forms contribute to tumor biology in patients unknown\", \"Therapeutic response to imatinib mechanism not fully delineated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The extracellular matrix retention motif of PDGF-B was shown to be critical for spatial pericyte integration: pdgf-b ret/ret mice lacking the heparin-binding domain have detached pericytes, vessel dilation, and hemorrhaging, establishing that PDGF-B must be locally retained to function.\",\n      \"evidence\": \"Mouse genetics with pdgf-b ret/ret allele; tumor transplantation; pericyte co-injection; vascular morphometry\",\n      \"pmids\": [\"14561699\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific HSPG partners mediating retention not identified\", \"Whether retention motif is required equally across all vascular beds unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"PDGFB was identified as a causative gene for autosomal dominant primary familial brain calcification: human germline mutations abolish protein synthesis or receptor binding, and hypomorphic mouse alleles develop dose-dependent brain calcifications correlating with pericyte deficiency and BBB dysfunction.\",\n      \"evidence\": \"Human genetic linkage and mutation analysis; functional assays of six mutations; Pdgfb hypomorphic and Pdgfbret/ret mice; brain calcification and BBB assessment\",\n      \"pmids\": [\"23913003\", \"26599395\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which pericyte loss leads to calcification not resolved\", \"Whether calcification is reversible upon PDGF-B restoration unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The requirement for PDGF-B in lymphatic vessel maturation was established: LEC-specific Pdgfb deletion prevents smooth muscle cell recruitment to collecting lymphatic vessels, causing dilation and loss of pulsatile contraction, with ECM retention motif serving as a checkpoint against inappropriate capillary muscularization.\",\n      \"evidence\": \"LEC-specific Cre-mediated Pdgfb deletion and overexpression; ECM retention analysis; vessel contraction measurement\",\n      \"pmids\": [\"28851707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ECM composition differences between capillaries and collecting vessels not molecularly defined\", \"Functional consequences for lymphatic drainage not quantified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cell-type-specific roles of PDGF-B in disease were delineated: macrophage-derived PDGF-B drives pathological smooth muscle cell expansion in pulmonary hypertension, while platelet-derived PDGF-B maintains tumor vascular pericyte coverage to limit metastasis, and adult-induced endothelial deletion causes progressive pericyte loss distinguishing developmental from maintenance functions.\",\n      \"evidence\": \"LysM-Cre conditional Pdgfb knockout; platelet-specific Pdgfb knockout in two tumor models; tamoxifen-inducible endothelial Pdgfb deletion with longitudinal analysis; human PAH patient macrophage analysis\",\n      \"pmids\": [\"33591958\", \"32586981\", \"34689641\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether macrophage-derived PDGF-B acts on resident vs. recruited SMC progenitors unknown\", \"Interaction between platelet-derived and endothelial-derived PDGF-B pools in tumors not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A non-vascular neuronal role was discovered: microglial PDGF-B signals via PDGFR-α on hypothalamic PVN neurons to maintain Kv4.3 potassium channel expression, suppressing sympathetic outflow; loss of this signaling axis causes hypertension.\",\n      \"evidence\": \"Conditional microglial Pdgfb deletion; neuronal PDGFR-α suppression; electrophysiology; sympathetic outflow and blood pressure measurement; exogenous PDGF-B rescue\",\n      \"pmids\": [\"35863346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mechanism extends to other brain regions unknown\", \"Downstream transcriptional pathway linking PDGFR-α activation to Kv4.3 expression not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The developmental-to-adult transition in PDGF-B cellular sources was resolved: microglia replace endothelial cells as the primary CNS PDGF-B source in adults, and acute loss of microglial PDGF-B severely impairs adult BBB integrity and causes lethal microhemorrhages upon immune challenge.\",\n      \"evidence\": \"Transcriptomic analysis; in situ hybridization; acute conditional cell-specific Pdgfb deletion in adult vs. neonatal mice; BBB permeability assay; endotoxin survival model\",\n      \"pmids\": [\"37992789\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals triggering the switch from endothelial to microglial PDGF-B source unknown\", \"Whether microglial PDGF-B maintains pericytes or acts through additional mechanisms not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the mechanism by which pericyte loss leads to brain calcification, the structural basis of PDGF-B/PDGFR-β interaction at atomic resolution, the signals controlling the developmental switch from endothelial to microglial PDGF-B sourcing, and the therapeutic potential of restoring PDGF-B signaling in calcification and neurovascular diseases.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Calcification mechanism downstream of pericyte loss undefined\", \"No high-resolution PDGF-B/PDGFR-β co-crystal structure published\", \"Therapeutic restoration of PDGF-B signaling not tested in disease models\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 4, 5, 17, 27]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [18, 31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4, 18, 32, 43]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [32, 45]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [8, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 5, 19, 26, 27, 37]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [25, 36, 45]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [24, 29, 41, 43]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [32, 45]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [46]}\n    ],\n    \"complexes\": [\n      \"PDGF-BB homodimer\",\n      \"PDGF-AB heterodimer\"\n    ],\n    \"partners\": [\n      \"PDGFRB\",\n      \"PDGFRA\",\n      \"SPARC\",\n      \"ADIPOQ\",\n      \"PIK3R1\",\n      \"COL1A1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}