{"gene":"PTN","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1989,"finding":"PTN (HBGF-8) was purified to near homogeneity from bovine uterus as a novel 17 kDa heparin-binding growth factor that binds tightly to cation exchange resins and heparin-Sepharose, and stimulates DNA synthesis (3H-thymidine incorporation) in NIH 3T3 fibroblasts with mitogenic activity comparable to aFGF.","method":"Protein purification (heparin-Sepharose affinity chromatography, cation exchange), N-terminal amino acid sequencing, mitogenic assay (3H-thymidine incorporation in NIH 3T3 cells)","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro biochemical purification and functional assay, foundational characterization paper","pmids":["2610682"],"is_preprint":false},{"year":1991,"finding":"PTN (HBNF) was purified to homogeneity from bovine brain and found to have neurotrophic activity for perinatal rat neurons; C-terminally truncated forms (lacking ~14 or ~22 residues) are generated by proteolysis during extraction, comprising major products in the absence of protease inhibitors.","method":"Protein purification (pH 4.5 extraction, ammonium sulfate precipitation, cation exchange, heparin-Sepharose, reverse-phase HPLC), amino acid sequencing, SDS-PAGE","journal":"Growth factors (Chur, Switzerland)","confidence":"High","confidence_rationale":"Tier 1 / Strong — complete biochemical purification and structural characterization with functional neurotrophic activity assay","pmids":["2049182"],"is_preprint":false},{"year":1992,"finding":"Recombinant PTN (HBNF) inhibits infectivity of herpes simplex viruses types 1 and 2 and human cytomegalovirus; carboxymethylated HBNF (which retains heparin-binding but not free basic charge) loses antiviral activity, suggesting the mechanism involves competition for cell-surface heparan sulfate proteoglycan binding.","method":"In vitro antiviral infectivity assay with recombinant HBNF and carboxymethylated HBNF variant","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct in vitro functional assay with chemical modification control, single lab","pmids":["1335242"],"is_preprint":false},{"year":1993,"finding":"The human PTN (HBNF) gene spans at least 42 kb and is organized in 5 exons; alternative splicing at the exon 5 acceptor site generates a variant mRNA with a 3-bp deletion, encoding a protein (des-Ala119-HBNF) lacking one alanine residue, which comprises ~20% of total HBNF protein in bovine brain.","method":"Southern blotting, genomic library screening, cDNA sequencing, protein characterization from bovine brain","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct genomic and protein characterization, single lab with orthogonal methods","pmids":["8484754"],"is_preprint":false},{"year":1999,"finding":"PTN (HARP) forms non-covalent dimers, and dimerization is promoted by heparin and other sulfated glycosaminoglycans (dermatan sulfate, chondroitin sulfate-C); chlorate treatment of cells (which inhibits sulfation) blocks dimer formation; PTN is secreted as a dimer in conditioned medium of NIH-3T3 cells overexpressing PTN.","method":"DSS cross-linking, heparin-Sepharose affinity chromatography, chlorate treatment, conditioned medium analysis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical methods (cross-linking, affinity chromatography, cellular secretion assay), single lab","pmids":["10600521"],"is_preprint":false},{"year":2000,"finding":"A human endogenous retrovirus-like element (HERV-E.PTN) inserted into the PTN gene generates a novel promoter driving PTN expression in choriocarcinoma and trophoblast cells; a Sp1-binding site within the retroviral enhancer (+443 to +486) is essential for this promoter activity, as shown by site-specific mutation abolishing activity and Sp1 overexpression in Drosophila SL2 cells confirming Sp1-dependent activation.","method":"In situ hybridization, transient transfection promoter assays, deletion analysis, EMSA/supershift, site-directed mutagenesis, Sp1 overexpression in SL2 cells","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including mutagenesis, EMSA, and heterologous cell system, single lab","pmids":["10962555"],"is_preprint":false},{"year":2005,"finding":"PTN and SDF-1 expression in dermal fibroblasts is regulated by the AP-1 transcription factor JUN; fibroblast-secreted PTN exerts a mitogenic (proliferative) effect on primary human keratinocytes in a heterologous feeder layer co-culture system; PTN expression is upregulated during cutaneous wound healing in vivo.","method":"Gene expression profiling of Jun-/- vs wild-type MEFs, semi-quantitative RT-PCR, in situ hybridization on skin sections, heterologous feeder layer co-culture keratinocyte proliferation assay, in vivo wound healing model","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO fibroblasts plus functional co-culture assay, single lab","pmids":["15840658"],"is_preprint":false},{"year":2009,"finding":"IFN-γ markedly induces PTN mRNA expression in macrophages through the JAK/STAT1 signaling pathway; a gamma-activated sequence (GAS) at -2086 to -2078 bp in the PTN promoter is essential for IFN-γ-regulated promoter activity; STAT1 (but not STAT3 or p42) is required for PTN expression, as shown by siRNA knockdown; STAT1 and STAT3 bind to the GAS element at the chromatin level.","method":"JAK inhibitor treatment (WHI-P154, ATA), STAT1 phosphorylation assays, PTN promoter deletion analysis, EMSA, supershift assay, ChIP, siRNA knockdown of STAT1/STAT3/p42","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including promoter mutagenesis, ChIP, EMSA, and siRNA, single lab","pmids":["19917672"],"is_preprint":false},{"year":2010,"finding":"Menin represses PTN transcription and indirectly reduces RPTP β/ζ expression; PTN/RPTP β/ζ signaling promotes A549 lung cancer cell migration in conjunction with integrin αvβ3, focal adhesion kinase (FAK), PI3K, and phosphorylated ERK1/2; ectopic menin expression significantly represses PTN-mediated cell migration.","method":"Ectopic menin overexpression, RT-PCR for PTN and RPTP β/ζ, cell migration assay, pathway inhibitor studies (PI3K inhibitor, ERK inhibitor), integrin αvβ3 blocking","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic overexpression with multiple pathway readouts and pharmacological inhibitors, single lab","pmids":["20639902"],"is_preprint":false},{"year":2012,"finding":"Endogenous PTN in mammary epithelial cells (MECs) promotes motility and invasion (but not proliferation) as demonstrated by anti-PTN blocking antibody; PTN inhibits expansion and differentiation of epithelial progenitor cells by disrupting cell-matrix adhesion; in vivo, PTN inhibits ductal outgrowth and branching via inhibition of phospho-ERK1/2 signaling in mammary epithelial cells.","method":"Anti-PTN blocking antibody treatment, real-time impedance monitoring (RTCA), 3D culture mammosphere assay, in vivo mammary gland analysis, Western blotting for phospho-ERK1/2","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — blocking antibody approach with multiple functional readouts in vitro and in vivo, single lab","pmids":["23077670"],"is_preprint":false},{"year":2013,"finding":"PTN activates anaplastic lymphoma kinase (ALK) via 'Ligand Independent Activation': PTN binds and inactivates the phosphatase activity of its receptor RPTPβ/ζ; inactivated RPTPβ/ζ can no longer dephosphorylate phosphotyrosine sites in the ALK activation domain, resulting in ALK autophosphorylation and autoactivation; this PTN/RPTPβ/ζ pathway also coordinately regulates tyrosine phosphorylation of other downstream proteins.","method":"Review/mechanistic synthesis of experimental findings (phosphatase activity assays, tyrosine phosphorylation studies of ALK cited in reviewed papers)","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic model based on cited experimental evidence (phosphatase assays, phosphorylation studies), review paper synthesizing primary data","pmids":["23777859"],"is_preprint":false},{"year":2014,"finding":"PTN is expressed, produced, and secreted by epithelial ovarian cancer (EOC) cells; siRNA-mediated knockdown of PTN or its receptor PTPRZ1 induces significant apoptosis; PTN signaling in EOC cells activates MAPK family members as downstream effectors, as identified by expression profiling of 36 survival-related genes after PTN knockdown.","method":"siRNA knockdown, Western blot, ELISA, cell viability assay, expression profiling of 36 survival genes, computational pathway mapping","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with functional apoptosis readout and pathway profiling, single lab","pmids":["25418856"],"is_preprint":false},{"year":2017,"finding":"In uterine stromal cells, progesterone stimulates PTN expression via cAMP/PKA/C/EBPβ pathway; PTN acts downstream of C/EBPβ to promote decidualization marker expression (Prl8a2, Prl3c1); PTN mediates C/EBPβ regulation of Hand2, a downstream target in uterine stromal cell differentiation.","method":"siRNA knockdown of PTN and C/EBPβ, constitutive PTN activation, PKA inhibitor (H89) treatment, RT-PCR for decidualization markers, progesterone/cAMP treatment of uterine stromal cells","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic (siRNA/overexpression) and pharmacological approaches in primary cells with multiple pathway readouts, single lab","pmids":["28657144"],"is_preprint":false},{"year":2018,"finding":"Adult hippocampal neural stem cells (NSCs) continuously supply PTN as a feedforward signal to newborn neurons; ablation of NSCs or loss of PTN signaling causes defective dendritic development and arborization in newborn neurons.","method":"Cell ablation, retrovirus-mediated single-cell labeling, signaling pathway modulation, morphological analysis of newborn neurons","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — combination of cell ablation, single-cell labeling, and signaling modulation with defined morphological phenotype, replicated with multiple approaches in one study","pmids":["30497772"],"is_preprint":false},{"year":2018,"finding":"Chemotherapy (in TNBC cells) drives upregulation of PTN and PTPRZ1 expression via CDKN1A; elevated PTN/PTPRZ1 promotes chemoresistance by activating the NF-κB pathway, enhancing tumor proliferation and inhibiting apoptosis; siRNA knockdown of PTPRZ1 revealed its role in this pathway.","method":"Microarray analysis, CCK-8 assay, colony formation, apoptosis analysis, siRNA knockdown, pathway inhibition","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with multiple functional assays and pathway identification, single lab","pmids":["30497491"],"is_preprint":false},{"year":2019,"finding":"PTN-PTPRZ signaling promotes oligodendrocyte precursor cell (OPC) differentiation by enhancing tyrosine phosphorylation of AFAP1L2; PTPRZ dephosphorylates AFAP1L2 at tyrosine residues in vitro and in HEK293T cells; PTN-induced AFAP1L2 phosphorylation activates the PI3K-AKT-mTOR pathway; knock-in mice with catalytically inactive PTPRZ (Cys-to-Ser mutation) show enhanced OPC differentiation and earlier remyelination.","method":"Phosphoproteomics in OPC-like OL1 cells, in vitro PTPRZ phosphatase assay, HEK293T overexpression, siRNA knockdown of AFAP1L2, PI3K inhibitor treatment, Cys-to-Ser knock-in mice, cuprizone demyelination model","journal":"Glia","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro phosphatase assay, phosphoproteomics, mutagenesis (CS knock-in), and in vivo validation with multiple orthogonal methods","pmids":["30667096"],"is_preprint":false},{"year":2021,"finding":"PTN promotes neurite outgrowth from dorsal root ganglion (DRG) neurons; shRNA-mediated knockdown of PTN in pancreatic cancer BxPC-3 cells reduces PTN expression and inhibits neurite outgrowth from co-cultured DRG neurons.","method":"Adenovirus-mediated shRNA knockdown, RT-PCR, immunocytochemistry, Western blot, DRG co-culture neurite morphology assay","journal":"World journal of gastroenterology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown with functional co-culture readout, single lab","pmids":["21677838"],"is_preprint":false},{"year":2024,"finding":"PTN secreted by Leydig cells activates syndecan-2 (SDC2) on spermatogonial stem cells (SSCs); SDC2 knockdown impairs SSC proliferation, DNA synthesis, PLZF expression, and downregulates GFRA1 and HIF-1 signaling; exogenous PTN rescues proliferation and GFRA1 expression in SDC2 knockdown SSC lines; protein immunoprecipitation confirmed the PTN-SDC2 interaction.","method":"Single-cell sequencing data analysis, immunofluorescence, STRING prediction, protein immunoprecipitation, SDC2 knockdown, transcriptome analysis, exogenous PTN rescue experiment","journal":"Biological research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for binding, knockdown with functional rescue, multiple readouts, single lab","pmids":["39285301"],"is_preprint":false},{"year":2024,"finding":"Astrocyte-derived PTN promotes hippocampal neurogenesis and cognition by signaling through PTPRZ1 or ALK receptors to activate AKT signaling; conditional deletion of PTN in astrocytes exacerbates neurogenic deficits in demyelinated hippocampus; PTN overexpression in astrocytes reverses neurogenic and cognitive impairments caused by demyelination.","method":"Conditional knockout (astrocyte-specific PTN deletion), PTN overexpression, AKT signaling pathway analysis, neurogenesis assays, behavioral cognitive testing, demyelination model","journal":"Stem cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional genetic ablation and overexpression with defined signaling and behavioral readouts in vivo, multiple orthogonal approaches","pmids":["39729991"],"is_preprint":false},{"year":2024,"finding":"PTN binds to PTPRZ1 receptor on rat bone marrow mesenchymal stem cells (rBMSCs), induces PLCG1 phosphorylation and NCOA3 nuclear translocation, reduces cellular reactive oxygen species (ROS), and thereby promotes osteogenic differentiation and inhibits apoptosis; PTN promotes fracture healing in osteoporotic animals in vivo.","method":"Phosphorylation quantitative proteomics, immunofluorescence, ALP detection, TUNEL assay, RNA sequencing, in vivo fracture healing in osteoporosis rats","journal":"Biomedicines","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphoproteomics with functional validation and in vivo confirmation, single lab","pmids":["40149671"],"is_preprint":false},{"year":2024,"finding":"TRAPPC12 interacts with Mea6/cTAGE5 and together they regulate PTN secretion from oligodendrocyte precursor cells (OPCs); Mea6/cTAGE5 ablation disrupts COPII trafficking components (SEC13, SEC31A, SAR1) and impairs PTN secretion; exogenous PTN supplementation rescues OPC differentiation deficits caused by Mea6 deficiency.","method":"Co-immunoprecipitation (TRAPPC12-Mea6 interaction), conditional knockout (Mea6 cKO in OPCs), COPII component localization/expression analysis, PTN secretion assay, exogenous PTN rescue experiment","journal":"iScience","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP for protein interaction, conditional KO with mechanistic pathway, rescue experiment, multiple orthogonal methods","pmids":["38439956"],"is_preprint":false},{"year":2025,"finding":"PTN secreted by cardiac fibroblasts promotes fibroblast self-proliferation/invasion and stimulates macrophage inflammatory responses (TNF-α, IL-6, Cox-2) through binding to syndecan-4 (SDC4) receptor, contributing to pressure overload-induced hypertrophic cardiomyopathy.","method":"Single-cell RNA-seq analysis (scRNA-seq), CellChat cell-cell interaction analysis, in vitro validation (RT-qPCR, EdU staining, transwell assay), in vivo TAC mouse model (Western blot, immunofluorescence, echocardiography)","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bioinformatics plus in vitro and in vivo validation of PTN-SDC4 axis, single lab","pmids":["39765325"],"is_preprint":false},{"year":2025,"finding":"Excessive PTN released by dysregulated quiescent neural stem cells (qNSCs) contributes to manic-like phenotypes in Shank3-overexpressing mice; pharmacological and molecular inhibition of PTN in qNSCs rescues aberrant neurogenesis and alleviates manic-like social deficits.","method":"Single-cell RNA sequencing (scRNA-seq), pharmacological PTN inhibition, molecular knockdown of PTN in qNSCs, behavioral assays, neurogenesis analysis","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — scRNA-seq plus pharmacological and molecular inhibition with behavioral readout, single lab","pmids":["40069581"],"is_preprint":false},{"year":2025,"finding":"PTN directly binds to SIRT1 and activates AMPK phosphorylation at Thr172, triggering the AMPK-PGC1α axis to reprogram mitochondrial energy metabolism; PTN overexpression reduces mitochondrial oxidative stress and apoptosis in cardiomyocytes treated with doxorubicin.","method":"PTN-SIRT1 binding assay, Western blot for AMPK phosphorylation (Thr172) and PGC1α, PTN overexpression, flow cytometry for ROS/apoptosis, in vivo cardiotoxicity model","journal":"Acta biochimica et biophysica Sinica","confidence":"Low","confidence_rationale":"Tier 3 / Weak — binding and phosphorylation assays described but methods are limited in detail in abstract, single lab, single publication","pmids":["41640280"],"is_preprint":false},{"year":2025,"finding":"Androgen receptor (AR) signaling in prostate stroma controls a PTN-mediated extrinsic signaling pathway that regulates monounsaturated fatty acid (MUFA) phospholipid biosynthesis and GPX4 expression to suppress prostate epithelial ferroptosis after castration.","method":"In vivo analyses in genetically-engineered mice, human organotypic cultures, ferroptosis assays, castration model","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mouse models with orthogonal validation in human organotypic cultures, preprint not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2014,"finding":"CART (cocaine- and amphetamine-regulated transcript) neuropeptide facilitates neurite outgrowth in cortical neurons after oxygen-glucose deprivation through a PTN-dependent pathway; siRNA-mediated PTN knockdown abolishes the CART-stimulated increase in GAP43 protein levels.","method":"siRNA knockdown of PTN, Western blot for GAP43, post-OGD CART treatment, primary mouse cortical neuron culture","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with defined molecular readout (GAP43) linking PTN to neurite outgrowth pathway, single lab","pmids":["25010400"],"is_preprint":false}],"current_model":"PTN (pleiotrophin/HBNF/HBGF-8) is a secreted heparin-binding growth factor that dimerizes upon binding sulfated glycosaminoglycans and signals primarily through its receptor RPTPβ/ζ (PTPRZ1): PTN binding inactivates RPTPβ/ζ phosphatase activity, causing accumulation of phosphotyrosine on downstream substrates including AFAP1L2 (activating PI3K-AKT-mTOR for oligodendrocyte differentiation), ALK (enabling ligand-independent kinase activation), and other effectors, while also engaging SDC2 and SDC4 as co-receptors in stem cell and cardiac contexts; PTN expression is transcriptionally regulated by JUN/AP-1 in fibroblasts, by IFN-γ/JAK/STAT1 in macrophages, and by progesterone/cAMP/PKA/C/EBPβ in uterine stromal cells, and its secretion is controlled by the Mea6/TRAPPC12-COPII trafficking machinery; through these pathways PTN regulates neuronal maturation, oligodendrocyte differentiation, mammary gland development, bone formation, cardiac fibrosis, and stem cell self-renewal."},"narrative":{"mechanistic_narrative":"PTN (pleiotrophin/HBNF/HBGF-8) is a secreted heparin-binding growth factor that signals through receptor protein tyrosine phosphatases and proteoglycan co-receptors to regulate neuronal maturation, glial differentiation, stem cell behavior, and tissue remodeling [PMID:2610682, PMID:2049182, PMID:30667096]. First purified as a 17 kDa heparin-binding mitogen from bovine uterus and as a neurotrophic factor from bovine brain [PMID:2610682, PMID:2049182], PTN binds sulfated glycosaminoglycans and forms non-covalent dimers whose assembly depends on cellular sulfation [PMID:10600521]. Its central signaling logic is the inactivation of the receptor phosphatase RPTPβ/ζ (PTPRZ1): PTN binding blocks phosphatase activity, allowing accumulation of phosphotyrosine on downstream substrates, including the activation domain of ALK (ligand-independent kinase activation) and AFAP1L2, whose phosphorylation drives PI3K-AKT-mTOR signaling and oligodendrocyte precursor differentiation [PMID:23777859, PMID:30667096]. Through PTPRZ1/ALK-AKT signaling, astrocyte- and neural stem cell-derived PTN promotes hippocampal neurogenesis, dendritic development of newborn neurons, and cognition [PMID:30497772, PMID:39729991], while dysregulated PTN release from quiescent neural stem cells produces aberrant neurogenesis and manic-like behavior [PMID:40069581]. PTN also engages syndecan co-receptors in non-neural contexts, activating SDC2 to sustain spermatogonial stem cell proliferation and SDC4 to drive cardiac fibroblast proliferation and macrophage inflammation in pressure-overload cardiomyopathy [PMID:39285301, PMID:39765325], and acts through PTPRZ1 to promote osteogenic differentiation [PMID:40149671]. PTN expression is transcriptionally controlled in a context-specific manner—by AP-1/JUN in fibroblasts, by IFN-γ/JAK/STAT1 in macrophages, and by progesterone/cAMP/PKA/C/EBPβ in uterine stromal cells [PMID:15840658, PMID:19917672, PMID:28657144]—and its regulated secretion from oligodendrocyte precursors requires the TRAPPC12-Mea6/cTAGE5-COPII trafficking machinery [PMID:38439956].","teleology":[{"year":1989,"claim":"Established PTN as a discrete secreted growth factor by purifying it as a heparin-binding mitogen, answering whether the activity was a defined protein.","evidence":"Heparin-Sepharose/cation exchange purification and N-terminal sequencing from bovine uterus with 3H-thymidine mitogenic assay in NIH 3T3 cells","pmids":["2610682"],"confidence":"High","gaps":["No receptor or signaling mechanism identified","Physiological source and target tissue unresolved"]},{"year":1991,"claim":"Showed the same heparin-binding protein has neurotrophic activity, extending PTN function beyond fibroblast mitogenesis and documenting proteolytic C-terminal truncation.","evidence":"Purification from bovine brain, amino acid sequencing, SDS-PAGE, neurotrophic assay on perinatal rat neurons","pmids":["2049182"],"confidence":"High","gaps":["Functional significance of truncated forms unknown","No receptor identified"]},{"year":1993,"claim":"Defined the human gene structure and alternative splicing, establishing PTN protein heterogeneity at the genomic level.","evidence":"Genomic library screening, Southern blotting, cDNA sequencing, protein characterization from bovine brain","pmids":["8484754"],"confidence":"Medium","gaps":["Functional difference between splice variants not tested"]},{"year":1999,"claim":"Resolved the biophysical basis of signaling competence by showing PTN dimerizes in a sulfation-dependent manner.","evidence":"DSS cross-linking, heparin-Sepharose chromatography, chlorate sulfation inhibition, conditioned medium analysis of NIH-3T3 cells","pmids":["10600521"],"confidence":"Medium","gaps":["Link between dimerization state and receptor activation not directly shown","Structural model of the dimer absent"]},{"year":2000,"claim":"Identified an endogenous retroviral promoter as a context-specific driver of PTN expression in trophoblast/choriocarcinoma cells via an Sp1 element.","evidence":"In situ hybridization, promoter deletion assays, EMSA/supershift, site-directed mutagenesis, Sp1 overexpression in Drosophila SL2 cells","pmids":["10962555"],"confidence":"High","gaps":["Relevance to non-trophoblast tissue regulation unclear"]},{"year":2005,"claim":"Placed PTN downstream of AP-1/JUN in fibroblasts and demonstrated a paracrine mitogenic role on keratinocytes during wound healing.","evidence":"Expression profiling of Jun-/- MEFs, RT-PCR, in situ hybridization, feeder-layer keratinocyte co-culture, in vivo wound model","pmids":["15840658"],"confidence":"Medium","gaps":["Receptor mediating keratinocyte response not identified","Direct JUN binding to PTN promoter not shown"]},{"year":2009,"claim":"Defined IFN-γ/JAK/STAT1 as an inducible transcriptional input to PTN in macrophages, mapping a functional GAS element in the promoter.","evidence":"JAK inhibitors, STAT1 phosphorylation assays, promoter deletion, EMSA/supershift, ChIP, siRNA of STAT1/STAT3/p42","pmids":["19917672"],"confidence":"High","gaps":["Downstream consequence of macrophage PTN secretion not addressed"]},{"year":2010,"claim":"Connected PTN/RPTPβ/ζ signaling to cancer cell migration through integrin αvβ3, FAK, PI3K, and ERK, and identified menin as a transcriptional repressor.","evidence":"Menin overexpression, RT-PCR, migration assays, pathway inhibitors, integrin blocking in A549 cells","pmids":["20639902"],"confidence":"Medium","gaps":["Direct menin binding to the PTN locus not shown","Order of integrin/FAK/PI3K events unresolved"]},{"year":2013,"claim":"Articulated the core mechanistic model: PTN inactivates RPTPβ/ζ phosphatase, enabling ligand-independent ALK autophosphorylation and broad downstream tyrosine phosphorylation.","evidence":"Mechanistic synthesis of phosphatase activity and tyrosine phosphorylation studies (review)","pmids":["23777859"],"confidence":"Medium","gaps":["Review synthesis rather than primary data in this entry","Stoichiometry of receptor inactivation not quantified"]},{"year":2012,"claim":"Defined PTN as a negative regulator of mammary epithelial expansion and ductal outgrowth acting via cell-matrix adhesion and ERK suppression, distinguishing motility from proliferation roles.","evidence":"Anti-PTN blocking antibody, RTCA impedance, 3D mammosphere assay, in vivo mammary analysis, phospho-ERK Western blot","pmids":["23077670"],"confidence":"Medium","gaps":["Receptor mediating mammary effects not identified","Mechanism of adhesion disruption unresolved"]},{"year":2014,"claim":"Established PTN/PTPRZ1 as a survival signal in ovarian cancer acting through MAPK effectors.","evidence":"siRNA knockdown of PTN/PTPRZ1, apoptosis assays, ELISA, survival-gene expression profiling","pmids":["25418856"],"confidence":"Medium","gaps":["Direct MAPK activation mechanism downstream of PTPRZ1 not delineated"]},{"year":2014,"claim":"Placed PTN as a required intermediary in CART neuropeptide-driven neurite outgrowth after ischemic stress.","evidence":"siRNA PTN knockdown, GAP43 Western blot, post-OGD CART treatment in cortical neurons","pmids":["25010400"],"confidence":"Medium","gaps":["Receptor coupling CART to PTN expression unknown"]},{"year":2017,"claim":"Integrated PTN into hormonal control of uterine decidualization, acting downstream of progesterone/cAMP/PKA/C/EBPβ to regulate Hand2 and decidual markers.","evidence":"siRNA of PTN/C/EBPβ, constitutive PTN activation, PKA inhibitor, RT-PCR of decidualization markers in uterine stromal cells","pmids":["28657144"],"confidence":"Medium","gaps":["Receptor mediating decidual PTN effects not identified"]},{"year":2018,"claim":"Demonstrated in vivo that neural stem cell-derived PTN is a feedforward signal required for proper dendritic development of newborn neurons.","evidence":"Cell ablation, retroviral single-cell labeling, signaling modulation, morphological analysis in adult hippocampus","pmids":["30497772"],"confidence":"High","gaps":["Receptor on newborn neurons not pinned down in this study"]},{"year":2018,"claim":"Linked chemotherapy-induced PTN/PTPRZ1 upregulation, via CDKN1A, to NF-κB-driven chemoresistance in triple-negative breast cancer.","evidence":"Microarray, CCK-8/colony/apoptosis assays, siRNA of PTPRZ1, pathway inhibition in TNBC cells","pmids":["30497491"],"confidence":"Medium","gaps":["Direct CDKN1A control of PTN transcription not shown"]},{"year":2019,"claim":"Provided the most direct substrate-level mechanism: PTN-PTPRZ signaling drives AFAP1L2 tyrosine phosphorylation and PI3K-AKT-mTOR activation to promote oligodendrocyte differentiation and remyelination.","evidence":"Phosphoproteomics, in vitro PTPRZ phosphatase assay, HEK293T overexpression, AFAP1L2 siRNA, PI3K inhibition, catalytically inactive PTPRZ knock-in mice, cuprizone model","pmids":["30667096"],"confidence":"High","gaps":["Whether AFAP1L2 is a direct or indirect PTPRZ substrate in vivo not fully resolved"]},{"year":2021,"claim":"Showed tumor-cell-derived PTN promotes neurite outgrowth, implicating PTN in cancer-associated neural remodeling.","evidence":"shRNA knockdown in BxPC-3 pancreatic cancer cells, DRG co-culture neurite assay","pmids":["21677838"],"confidence":"Medium","gaps":["Neuronal receptor mediating outgrowth not identified"]},{"year":2024,"claim":"Identified syndecan co-receptors as alternative PTN effectors: SDC2 sustains spermatogonial stem cell self-renewal and SDC4 drives cardiac fibroblast/macrophage inflammatory responses.","evidence":"Co-IP, knockdown with PTN rescue in SSCs; scRNA-seq/CellChat plus in vitro and TAC in vivo validation for SDC4","pmids":["39285301","39765325"],"confidence":"Medium","gaps":["Whether syndecans act independently or as PTPRZ1 co-receptors not resolved","Structural basis of PTN-syndecan binding unknown"]},{"year":2024,"claim":"Extended the PTPRZ1/ALK-AKT axis in vivo to astrocyte-derived PTN regulation of hippocampal neurogenesis and cognition under demyelination.","evidence":"Astrocyte-specific conditional PTN knockout and overexpression, AKT analysis, neurogenesis and behavioral testing in demyelination model","pmids":["39729991"],"confidence":"High","gaps":["Relative contribution of PTPRZ1 versus ALK not dissected"]},{"year":2024,"claim":"Defined the secretory route for PTN, showing TRAPPC12-Mea6/cTAGE5-COPII machinery is required for PTN release from oligodendrocyte precursors.","evidence":"Co-IP of TRAPPC12-Mea6, Mea6 conditional knockout, COPII component analysis, secretion assay, exogenous PTN rescue","pmids":["38439956"],"confidence":"High","gaps":["Whether this trafficking route is PTN-specific or general unresolved"]},{"year":2024,"claim":"Linked PTN-PTPRZ1 signaling to bone formation through PLCG1 phosphorylation, NCOA3 nuclear translocation, and ROS reduction promoting osteogenic differentiation.","evidence":"Phosphoproteomics, immunofluorescence, ALP/TUNEL assays, RNA-seq, in vivo osteoporotic fracture healing","pmids":["40149671"],"confidence":"Medium","gaps":["Direct PTPRZ1 dependence of PLCG1 phosphorylation not formally shown"]},{"year":2025,"claim":"Implicated dysregulated quiescent neural stem cell PTN release in manic-like behavior, identifying excess PTN as a disease-relevant driver of aberrant neurogenesis.","evidence":"scRNA-seq, pharmacological and molecular PTN inhibition, behavioral and neurogenesis analysis in Shank3-overexpressing mice","pmids":["40069581"],"confidence":"Medium","gaps":["Receptor pathway downstream of excess PTN not defined here"]},{"year":2025,"claim":"Proposed a non-receptor-phosphatase mechanism in which PTN binds SIRT1 to activate the AMPK-PGC1α axis and protect cardiomyocytes from oxidative stress.","evidence":"PTN-SIRT1 binding assay, AMPK Thr172/PGC1α Western blot, PTN overexpression, ROS/apoptosis flow cytometry, in vivo cardiotoxicity model","pmids":["41640280"],"confidence":"Low","gaps":["Methods limited in detail and single publication","Direct PTN-SIRT1 binding not independently confirmed","Reconciliation with secreted-ligand biology unclear"]},{"year":2025,"claim":"Connected stromal androgen receptor signaling to PTN as an extrinsic regulator of epithelial ferroptosis via MUFA phospholipid biosynthesis and GPX4.","evidence":"Genetically engineered mice, human organotypic cultures, ferroptosis and castration models (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint not peer-reviewed","Receptor mediating epithelial PTN response not identified"]},{"year":null,"claim":"How PTN partitions signaling among PTPRZ1, ALK, and syndecan co-receptors across cell types, and the structural basis of dimer/glycosaminoglycan-dependent receptor selection, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of a PTN-receptor complex in the corpus","Rules governing receptor choice across tissues unknown","Quantitative contribution of dimerization to signaling not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,15,17,18]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[10,15]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,4,20]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[10,15,18,19]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[13,15,18]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[5,7,12]}],"complexes":[],"partners":["PTPRZ1","ALK","AFAP1L2","SDC2","SDC4","TRAPPC12","SIRT1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P21246","full_name":"Pleiotrophin","aliases":["Heparin-binding brain mitogen","HBBM","Heparin-binding growth factor 8","HBGF-8","Heparin-binding growth-associated molecule","HB-GAM","Heparin-binding neurite outgrowth-promoting factor","HBNF","Heparin-binding neurite outgrowth-promoting factor 1","HBNF-1","Osteoblast-specific factor 1","OSF-1"],"length_aa":168,"mass_kda":18.9,"function":"Secreted growth factor that mediates its signal through cell-surface proteoglycan and non-proteoglycan receptors (PubMed:11278720, PubMed:16814777, PubMed:19141530). Binds cell-surface proteoglycan receptor via their chondroitin sulfate (CS) groups (PubMed:26896299, PubMed:27445335). Thereby regulates many processes like cell proliferation, cell survival, cell growth, cell differentiation and cell migration in several tissues namely neuron and bone (PubMed:11278720, PubMed:1733956, PubMed:1768439, PubMed:19141530, PubMed:19442624, PubMed:27445335, PubMed:30667096). Also plays a role in synaptic plasticity and learning-related behavior by inhibiting long-term synaptic potentiation (By similarity). Binds PTPRZ1, leading to neutralization of the negative charges of the CS chains of PTPRZ1, inducing PTPRZ1 clustering, thereby causing the dimerization and inactivation of its phosphatase activity leading to increased tyrosine phosphorylation of each of the PTPRZ1 substrates like ALK, CTNNB1 or AFAP1L2 in order to activate the PI3K-AKT pathway (PubMed:10706604, PubMed:16814777, PubMed:17681947, PubMed:27445335, PubMed:30667096). Through PTPRZ1 binding controls oligodendrocyte precursor cell differentiation by enhancing the phosphorylation of AFAP1L2 in order to activate the PI3K-AKT pathway (PubMed:27445335, PubMed:30667096). Forms a complex with PTPRZ1 and integrin alpha-V/beta-3 (ITGAV:ITGB3) that stimulates endothelial cell migration through SRC dephosphorylation and activation that consequently leads to ITGB3 'Tyr-773' phosphorylation (PubMed:19141530). In adult hippocampus promotes dendritic arborization, spine development, and functional integration and connectivity of newborn granule neurons through ALK by activating AKT signaling pathway (By similarity). Binds GPC2 and chondroitin sulfate proteoglycans (CSPGs) at the neuron surface, leading to abrogation of binding between PTPRS and CSPGs and neurite outgrowth promotion (By similarity). Binds SDC3 and mediates bone formation by recruiting and attaching osteoblasts/osteoblast precursors to the sites for new bone deposition (By similarity). Binds ALK and promotes cell survival and cell proliferation through MAPK pathway activation (PubMed:11278720). Inhibits proliferation and enhances differentiation of neural stem cells by inhibiting FGF2-induced fibroblast growth factor receptor signaling pathway (By similarity). Mediates regulatory mechanisms in normal hemostasis and in hematopoietic regeneration and in maintaining the balance of myeloid and lymphoid regeneration (By similarity). In addition may play a role in the female reproductive system, auditory response and the progesterone-induced decidualization pathway (By similarity)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P21246/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PTN","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PTN","total_profiled":1310},"omim":[{"mim_id":"612177","title":"RNA, 7SL, CYTOPLASMIC 1; RN7SL1","url":"https://www.omim.org/entry/612177"},{"mim_id":"607113","title":"APOLIPOPROTEIN B mRNA-EDITING ENZYME, CATALYTIC POLYPEPTIDE-LIKE 3G; APOBEC3G","url":"https://www.omim.org/entry/607113"},{"mim_id":"600263","title":"HELICOBACTER PYLORI INFECTION, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/600263"},{"mim_id":"162096","title":"MIDKINE; MDK","url":"https://www.omim.org/entry/162096"},{"mim_id":"162095","title":"PLEIOTROPHIN; PTN","url":"https://www.omim.org/entry/162095"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Endoplasmic reticulum","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":251.8},{"tissue":"parathyroid gland","ntpm":366.1}],"url":"https://www.proteinatlas.org/search/PTN"},"hgnc":{"alias_symbol":["HBNF","HBGF8"],"prev_symbol":["NEGF1"]},"alphafold":{"accession":"P21246","domains":[{"cath_id":"-","chopping":"50-86","consensus_level":"high","plddt":90.1008,"start":50,"end":86},{"cath_id":"-","chopping":"98-139","consensus_level":"high","plddt":86.0469,"start":98,"end":139}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P21246","model_url":"https://alphafold.ebi.ac.uk/files/AF-P21246-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P21246-F1-predicted_aligned_error_v6.png","plddt_mean":75.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PTN","jax_strain_url":"https://www.jax.org/strain/search?query=PTN"},"sequence":{"accession":"P21246","fasta_url":"https://rest.uniprot.org/uniprotkb/P21246.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P21246/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P21246"}},"corpus_meta":[{"pmid":"2610682","id":"PMC_2610682","title":"A novel 17 kD heparin-binding growth factor (HBGF-8) in bovine uterus: purification and N-terminal amino acid sequence.","date":"1989","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/2610682","citation_count":217,"is_preprint":false},{"pmid":"30497772","id":"PMC_30497772","title":"Neural Stem Cells Behave as a Functional Niche for the Maturation of Newborn Neurons through the Secretion of PTN.","date":"2018","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/30497772","citation_count":87,"is_preprint":false},{"pmid":"15840658","id":"PMC_15840658","title":"Increased keratinocyte proliferation by JUN-dependent expression of PTN and SDF-1 in fibroblasts.","date":"2005","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/15840658","citation_count":84,"is_preprint":false},{"pmid":"24694599","id":"PMC_24694599","title":"Functional receptors and intracellular signal pathways of midkine (MK) and pleiotrophin (PTN).","date":"2014","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/24694599","citation_count":76,"is_preprint":false},{"pmid":"1700712","id":"PMC_1700712","title":"Heparin-binding neurotrophic factor (HBNF) and MK, members of a new family of homologous, developmentally regulated proteins.","date":"1990","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/1700712","citation_count":67,"is_preprint":false},{"pmid":"31521692","id":"PMC_31521692","title":"Downregulation of circular RNA circ-LDLRAD3 suppresses pancreatic cancer progression through miR-137-3p/PTN axis.","date":"2019","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31521692","citation_count":61,"is_preprint":false},{"pmid":"31031625","id":"PMC_31031625","title":"Connecting Metainflammation and Neuroinflammation Through the PTN-MK-RPTPβ/ζ Axis: Relevance in Therapeutic Development.","date":"2019","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/31031625","citation_count":59,"is_preprint":false},{"pmid":"1477961","id":"PMC_1477961","title":"Expression of the HBNF (heparin-binding neurite-promoting factor) gene in the brain of fetal, neonatal and adult rat: an in situ hybridization study.","date":"1992","source":"Brain research. 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immunology","url":"https://pubmed.ncbi.nlm.nih.gov/17825221","citation_count":2,"is_preprint":false},{"pmid":"1569513","id":"PMC_1569513","title":"[Clinical pathology of hypopharyngeal cancer--comparison between TN and pTN].","date":"1992","source":"Nihon Jibiinkoka Gakkai kaiho","url":"https://pubmed.ncbi.nlm.nih.gov/1569513","citation_count":2,"is_preprint":false},{"pmid":"38850864","id":"PMC_38850864","title":"Pt-N catalytic centres concisely enhance interfacial charge transfer in amines functionalized Pt@MOFs for selective conversion of CO2 to CH4.","date":"2024","source":"Journal of colloid and interface science","url":"https://pubmed.ncbi.nlm.nih.gov/38850864","citation_count":2,"is_preprint":false},{"pmid":"40643435","id":"PMC_40643435","title":"Targeting the HNRNPA2B1/HDGF/PTN Axis to Overcome Radioresistance in Non-Small Cell Lung Cancer.","date":"2025","source":"Antioxidants & redox 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open","url":"https://pubmed.ncbi.nlm.nih.gov/41483629","citation_count":1,"is_preprint":false},{"pmid":"41640280","id":"PMC_41640280","title":"Cardiac PTN-SIRT1 axis alleviates oxidative stress and promotes mitochondrial energy reprogramming to mitigate doxorubicin-induced cardiotoxicity through AMPK/PGC1α signaling.","date":"2026","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/41640280","citation_count":1,"is_preprint":false},{"pmid":"36949576","id":"PMC_36949576","title":"Pt-N Coordination Rendering the Chemotherapeutic Agent with Photoactivated ROS Generation and Self-Reporting Cell Uptake.","date":"2023","source":"ACS applied bio materials","url":"https://pubmed.ncbi.nlm.nih.gov/36949576","citation_count":1,"is_preprint":false},{"pmid":"27444877","id":"PMC_27444877","title":"Investigating the mechanism of the selective hydrogenation reaction of cinnamaldehyde catalyzed by Ptn clusters.","date":"2016","source":"Journal of molecular 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gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/41693979","citation_count":0,"is_preprint":false},{"pmid":"33116829","id":"PMC_33116829","title":"Long Non-Coding RNA AGAP2-AS1/miR-628-5p/PTN Axis Modulates Proliferation, Migration, Invasion, and Apoptosis of Glioma Cells [Retraction].","date":"2020","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/33116829","citation_count":0,"is_preprint":false},{"pmid":"41615214","id":"PMC_41615214","title":"Deciphering Key Descriptors for Scaling Relationships in Graphene-Supported Ptn Clusters via Machine Learning.","date":"2026","source":"Small (Weinheim an der Bergstrasse, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/41615214","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.06.668974","title":"Dual pathway regulation of castration response and ferroptosis in the prostate 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\"method\": \"Protein purification (heparin-Sepharose affinity chromatography, cation exchange), N-terminal amino acid sequencing, mitogenic assay (3H-thymidine incorporation in NIH 3T3 cells)\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro biochemical purification and functional assay, foundational characterization paper\",\n      \"pmids\": [\"2610682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"PTN (HBNF) was purified to homogeneity from bovine brain and found to have neurotrophic activity for perinatal rat neurons; C-terminally truncated forms (lacking ~14 or ~22 residues) are generated by proteolysis during extraction, comprising major products in the absence of protease inhibitors.\",\n      \"method\": \"Protein purification (pH 4.5 extraction, ammonium sulfate precipitation, cation exchange, heparin-Sepharose, reverse-phase HPLC), amino acid sequencing, SDS-PAGE\",\n      \"journal\": \"Growth factors (Chur, Switzerland)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — complete biochemical purification and structural characterization with functional neurotrophic activity assay\",\n      \"pmids\": [\"2049182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Recombinant PTN (HBNF) inhibits infectivity of herpes simplex viruses types 1 and 2 and human cytomegalovirus; carboxymethylated HBNF (which retains heparin-binding but not free basic charge) loses antiviral activity, suggesting the mechanism involves competition for cell-surface heparan sulfate proteoglycan binding.\",\n      \"method\": \"In vitro antiviral infectivity assay with recombinant HBNF and carboxymethylated HBNF variant\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vitro functional assay with chemical modification control, single lab\",\n      \"pmids\": [\"1335242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The human PTN (HBNF) gene spans at least 42 kb and is organized in 5 exons; alternative splicing at the exon 5 acceptor site generates a variant mRNA with a 3-bp deletion, encoding a protein (des-Ala119-HBNF) lacking one alanine residue, which comprises ~20% of total HBNF protein in bovine brain.\",\n      \"method\": \"Southern blotting, genomic library screening, cDNA sequencing, protein characterization from bovine brain\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct genomic and protein characterization, single lab with orthogonal methods\",\n      \"pmids\": [\"8484754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PTN (HARP) forms non-covalent dimers, and dimerization is promoted by heparin and other sulfated glycosaminoglycans (dermatan sulfate, chondroitin sulfate-C); chlorate treatment of cells (which inhibits sulfation) blocks dimer formation; PTN is secreted as a dimer in conditioned medium of NIH-3T3 cells overexpressing PTN.\",\n      \"method\": \"DSS cross-linking, heparin-Sepharose affinity chromatography, chlorate treatment, conditioned medium analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical methods (cross-linking, affinity chromatography, cellular secretion assay), single lab\",\n      \"pmids\": [\"10600521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A human endogenous retrovirus-like element (HERV-E.PTN) inserted into the PTN gene generates a novel promoter driving PTN expression in choriocarcinoma and trophoblast cells; a Sp1-binding site within the retroviral enhancer (+443 to +486) is essential for this promoter activity, as shown by site-specific mutation abolishing activity and Sp1 overexpression in Drosophila SL2 cells confirming Sp1-dependent activation.\",\n      \"method\": \"In situ hybridization, transient transfection promoter assays, deletion analysis, EMSA/supershift, site-directed mutagenesis, Sp1 overexpression in SL2 cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including mutagenesis, EMSA, and heterologous cell system, single lab\",\n      \"pmids\": [\"10962555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PTN and SDF-1 expression in dermal fibroblasts is regulated by the AP-1 transcription factor JUN; fibroblast-secreted PTN exerts a mitogenic (proliferative) effect on primary human keratinocytes in a heterologous feeder layer co-culture system; PTN expression is upregulated during cutaneous wound healing in vivo.\",\n      \"method\": \"Gene expression profiling of Jun-/- vs wild-type MEFs, semi-quantitative RT-PCR, in situ hybridization on skin sections, heterologous feeder layer co-culture keratinocyte proliferation assay, in vivo wound healing model\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO fibroblasts plus functional co-culture assay, single lab\",\n      \"pmids\": [\"15840658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IFN-γ markedly induces PTN mRNA expression in macrophages through the JAK/STAT1 signaling pathway; a gamma-activated sequence (GAS) at -2086 to -2078 bp in the PTN promoter is essential for IFN-γ-regulated promoter activity; STAT1 (but not STAT3 or p42) is required for PTN expression, as shown by siRNA knockdown; STAT1 and STAT3 bind to the GAS element at the chromatin level.\",\n      \"method\": \"JAK inhibitor treatment (WHI-P154, ATA), STAT1 phosphorylation assays, PTN promoter deletion analysis, EMSA, supershift assay, ChIP, siRNA knockdown of STAT1/STAT3/p42\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including promoter mutagenesis, ChIP, EMSA, and siRNA, single lab\",\n      \"pmids\": [\"19917672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Menin represses PTN transcription and indirectly reduces RPTP β/ζ expression; PTN/RPTP β/ζ signaling promotes A549 lung cancer cell migration in conjunction with integrin αvβ3, focal adhesion kinase (FAK), PI3K, and phosphorylated ERK1/2; ectopic menin expression significantly represses PTN-mediated cell migration.\",\n      \"method\": \"Ectopic menin overexpression, RT-PCR for PTN and RPTP β/ζ, cell migration assay, pathway inhibitor studies (PI3K inhibitor, ERK inhibitor), integrin αvβ3 blocking\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic overexpression with multiple pathway readouts and pharmacological inhibitors, single lab\",\n      \"pmids\": [\"20639902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Endogenous PTN in mammary epithelial cells (MECs) promotes motility and invasion (but not proliferation) as demonstrated by anti-PTN blocking antibody; PTN inhibits expansion and differentiation of epithelial progenitor cells by disrupting cell-matrix adhesion; in vivo, PTN inhibits ductal outgrowth and branching via inhibition of phospho-ERK1/2 signaling in mammary epithelial cells.\",\n      \"method\": \"Anti-PTN blocking antibody treatment, real-time impedance monitoring (RTCA), 3D culture mammosphere assay, in vivo mammary gland analysis, Western blotting for phospho-ERK1/2\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — blocking antibody approach with multiple functional readouts in vitro and in vivo, single lab\",\n      \"pmids\": [\"23077670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PTN activates anaplastic lymphoma kinase (ALK) via 'Ligand Independent Activation': PTN binds and inactivates the phosphatase activity of its receptor RPTPβ/ζ; inactivated RPTPβ/ζ can no longer dephosphorylate phosphotyrosine sites in the ALK activation domain, resulting in ALK autophosphorylation and autoactivation; this PTN/RPTPβ/ζ pathway also coordinately regulates tyrosine phosphorylation of other downstream proteins.\",\n      \"method\": \"Review/mechanistic synthesis of experimental findings (phosphatase activity assays, tyrosine phosphorylation studies of ALK cited in reviewed papers)\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic model based on cited experimental evidence (phosphatase assays, phosphorylation studies), review paper synthesizing primary data\",\n      \"pmids\": [\"23777859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PTN is expressed, produced, and secreted by epithelial ovarian cancer (EOC) cells; siRNA-mediated knockdown of PTN or its receptor PTPRZ1 induces significant apoptosis; PTN signaling in EOC cells activates MAPK family members as downstream effectors, as identified by expression profiling of 36 survival-related genes after PTN knockdown.\",\n      \"method\": \"siRNA knockdown, Western blot, ELISA, cell viability assay, expression profiling of 36 survival genes, computational pathway mapping\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with functional apoptosis readout and pathway profiling, single lab\",\n      \"pmids\": [\"25418856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In uterine stromal cells, progesterone stimulates PTN expression via cAMP/PKA/C/EBPβ pathway; PTN acts downstream of C/EBPβ to promote decidualization marker expression (Prl8a2, Prl3c1); PTN mediates C/EBPβ regulation of Hand2, a downstream target in uterine stromal cell differentiation.\",\n      \"method\": \"siRNA knockdown of PTN and C/EBPβ, constitutive PTN activation, PKA inhibitor (H89) treatment, RT-PCR for decidualization markers, progesterone/cAMP treatment of uterine stromal cells\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (siRNA/overexpression) and pharmacological approaches in primary cells with multiple pathway readouts, single lab\",\n      \"pmids\": [\"28657144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Adult hippocampal neural stem cells (NSCs) continuously supply PTN as a feedforward signal to newborn neurons; ablation of NSCs or loss of PTN signaling causes defective dendritic development and arborization in newborn neurons.\",\n      \"method\": \"Cell ablation, retrovirus-mediated single-cell labeling, signaling pathway modulation, morphological analysis of newborn neurons\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — combination of cell ablation, single-cell labeling, and signaling modulation with defined morphological phenotype, replicated with multiple approaches in one study\",\n      \"pmids\": [\"30497772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Chemotherapy (in TNBC cells) drives upregulation of PTN and PTPRZ1 expression via CDKN1A; elevated PTN/PTPRZ1 promotes chemoresistance by activating the NF-κB pathway, enhancing tumor proliferation and inhibiting apoptosis; siRNA knockdown of PTPRZ1 revealed its role in this pathway.\",\n      \"method\": \"Microarray analysis, CCK-8 assay, colony formation, apoptosis analysis, siRNA knockdown, pathway inhibition\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with multiple functional assays and pathway identification, single lab\",\n      \"pmids\": [\"30497491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PTN-PTPRZ signaling promotes oligodendrocyte precursor cell (OPC) differentiation by enhancing tyrosine phosphorylation of AFAP1L2; PTPRZ dephosphorylates AFAP1L2 at tyrosine residues in vitro and in HEK293T cells; PTN-induced AFAP1L2 phosphorylation activates the PI3K-AKT-mTOR pathway; knock-in mice with catalytically inactive PTPRZ (Cys-to-Ser mutation) show enhanced OPC differentiation and earlier remyelination.\",\n      \"method\": \"Phosphoproteomics in OPC-like OL1 cells, in vitro PTPRZ phosphatase assay, HEK293T overexpression, siRNA knockdown of AFAP1L2, PI3K inhibitor treatment, Cys-to-Ser knock-in mice, cuprizone demyelination model\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro phosphatase assay, phosphoproteomics, mutagenesis (CS knock-in), and in vivo validation with multiple orthogonal methods\",\n      \"pmids\": [\"30667096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PTN promotes neurite outgrowth from dorsal root ganglion (DRG) neurons; shRNA-mediated knockdown of PTN in pancreatic cancer BxPC-3 cells reduces PTN expression and inhibits neurite outgrowth from co-cultured DRG neurons.\",\n      \"method\": \"Adenovirus-mediated shRNA knockdown, RT-PCR, immunocytochemistry, Western blot, DRG co-culture neurite morphology assay\",\n      \"journal\": \"World journal of gastroenterology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown with functional co-culture readout, single lab\",\n      \"pmids\": [\"21677838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PTN secreted by Leydig cells activates syndecan-2 (SDC2) on spermatogonial stem cells (SSCs); SDC2 knockdown impairs SSC proliferation, DNA synthesis, PLZF expression, and downregulates GFRA1 and HIF-1 signaling; exogenous PTN rescues proliferation and GFRA1 expression in SDC2 knockdown SSC lines; protein immunoprecipitation confirmed the PTN-SDC2 interaction.\",\n      \"method\": \"Single-cell sequencing data analysis, immunofluorescence, STRING prediction, protein immunoprecipitation, SDC2 knockdown, transcriptome analysis, exogenous PTN rescue experiment\",\n      \"journal\": \"Biological research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for binding, knockdown with functional rescue, multiple readouts, single lab\",\n      \"pmids\": [\"39285301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Astrocyte-derived PTN promotes hippocampal neurogenesis and cognition by signaling through PTPRZ1 or ALK receptors to activate AKT signaling; conditional deletion of PTN in astrocytes exacerbates neurogenic deficits in demyelinated hippocampus; PTN overexpression in astrocytes reverses neurogenic and cognitive impairments caused by demyelination.\",\n      \"method\": \"Conditional knockout (astrocyte-specific PTN deletion), PTN overexpression, AKT signaling pathway analysis, neurogenesis assays, behavioral cognitive testing, demyelination model\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional genetic ablation and overexpression with defined signaling and behavioral readouts in vivo, multiple orthogonal approaches\",\n      \"pmids\": [\"39729991\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PTN binds to PTPRZ1 receptor on rat bone marrow mesenchymal stem cells (rBMSCs), induces PLCG1 phosphorylation and NCOA3 nuclear translocation, reduces cellular reactive oxygen species (ROS), and thereby promotes osteogenic differentiation and inhibits apoptosis; PTN promotes fracture healing in osteoporotic animals in vivo.\",\n      \"method\": \"Phosphorylation quantitative proteomics, immunofluorescence, ALP detection, TUNEL assay, RNA sequencing, in vivo fracture healing in osteoporosis rats\",\n      \"journal\": \"Biomedicines\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphoproteomics with functional validation and in vivo confirmation, single lab\",\n      \"pmids\": [\"40149671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TRAPPC12 interacts with Mea6/cTAGE5 and together they regulate PTN secretion from oligodendrocyte precursor cells (OPCs); Mea6/cTAGE5 ablation disrupts COPII trafficking components (SEC13, SEC31A, SAR1) and impairs PTN secretion; exogenous PTN supplementation rescues OPC differentiation deficits caused by Mea6 deficiency.\",\n      \"method\": \"Co-immunoprecipitation (TRAPPC12-Mea6 interaction), conditional knockout (Mea6 cKO in OPCs), COPII component localization/expression analysis, PTN secretion assay, exogenous PTN rescue experiment\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP for protein interaction, conditional KO with mechanistic pathway, rescue experiment, multiple orthogonal methods\",\n      \"pmids\": [\"38439956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTN secreted by cardiac fibroblasts promotes fibroblast self-proliferation/invasion and stimulates macrophage inflammatory responses (TNF-α, IL-6, Cox-2) through binding to syndecan-4 (SDC4) receptor, contributing to pressure overload-induced hypertrophic cardiomyopathy.\",\n      \"method\": \"Single-cell RNA-seq analysis (scRNA-seq), CellChat cell-cell interaction analysis, in vitro validation (RT-qPCR, EdU staining, transwell assay), in vivo TAC mouse model (Western blot, immunofluorescence, echocardiography)\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bioinformatics plus in vitro and in vivo validation of PTN-SDC4 axis, single lab\",\n      \"pmids\": [\"39765325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Excessive PTN released by dysregulated quiescent neural stem cells (qNSCs) contributes to manic-like phenotypes in Shank3-overexpressing mice; pharmacological and molecular inhibition of PTN in qNSCs rescues aberrant neurogenesis and alleviates manic-like social deficits.\",\n      \"method\": \"Single-cell RNA sequencing (scRNA-seq), pharmacological PTN inhibition, molecular knockdown of PTN in qNSCs, behavioral assays, neurogenesis analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — scRNA-seq plus pharmacological and molecular inhibition with behavioral readout, single lab\",\n      \"pmids\": [\"40069581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTN directly binds to SIRT1 and activates AMPK phosphorylation at Thr172, triggering the AMPK-PGC1α axis to reprogram mitochondrial energy metabolism; PTN overexpression reduces mitochondrial oxidative stress and apoptosis in cardiomyocytes treated with doxorubicin.\",\n      \"method\": \"PTN-SIRT1 binding assay, Western blot for AMPK phosphorylation (Thr172) and PGC1α, PTN overexpression, flow cytometry for ROS/apoptosis, in vivo cardiotoxicity model\",\n      \"journal\": \"Acta biochimica et biophysica Sinica\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — binding and phosphorylation assays described but methods are limited in detail in abstract, single lab, single publication\",\n      \"pmids\": [\"41640280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Androgen receptor (AR) signaling in prostate stroma controls a PTN-mediated extrinsic signaling pathway that regulates monounsaturated fatty acid (MUFA) phospholipid biosynthesis and GPX4 expression to suppress prostate epithelial ferroptosis after castration.\",\n      \"method\": \"In vivo analyses in genetically-engineered mice, human organotypic cultures, ferroptosis assays, castration model\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mouse models with orthogonal validation in human organotypic cultures, preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CART (cocaine- and amphetamine-regulated transcript) neuropeptide facilitates neurite outgrowth in cortical neurons after oxygen-glucose deprivation through a PTN-dependent pathway; siRNA-mediated PTN knockdown abolishes the CART-stimulated increase in GAP43 protein levels.\",\n      \"method\": \"siRNA knockdown of PTN, Western blot for GAP43, post-OGD CART treatment, primary mouse cortical neuron culture\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with defined molecular readout (GAP43) linking PTN to neurite outgrowth pathway, single lab\",\n      \"pmids\": [\"25010400\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PTN (pleiotrophin/HBNF/HBGF-8) is a secreted heparin-binding growth factor that dimerizes upon binding sulfated glycosaminoglycans and signals primarily through its receptor RPTPβ/ζ (PTPRZ1): PTN binding inactivates RPTPβ/ζ phosphatase activity, causing accumulation of phosphotyrosine on downstream substrates including AFAP1L2 (activating PI3K-AKT-mTOR for oligodendrocyte differentiation), ALK (enabling ligand-independent kinase activation), and other effectors, while also engaging SDC2 and SDC4 as co-receptors in stem cell and cardiac contexts; PTN expression is transcriptionally regulated by JUN/AP-1 in fibroblasts, by IFN-γ/JAK/STAT1 in macrophages, and by progesterone/cAMP/PKA/C/EBPβ in uterine stromal cells, and its secretion is controlled by the Mea6/TRAPPC12-COPII trafficking machinery; through these pathways PTN regulates neuronal maturation, oligodendrocyte differentiation, mammary gland development, bone formation, cardiac fibrosis, and stem cell self-renewal.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PTN (pleiotrophin/HBNF/HBGF-8) is a secreted heparin-binding growth factor that signals through receptor protein tyrosine phosphatases and proteoglycan co-receptors to regulate neuronal maturation, glial differentiation, stem cell behavior, and tissue remodeling [#0, #1, #15]. First purified as a 17 kDa heparin-binding mitogen from bovine uterus and as a neurotrophic factor from bovine brain [#0, #1], PTN binds sulfated glycosaminoglycans and forms non-covalent dimers whose assembly depends on cellular sulfation [#4]. Its central signaling logic is the inactivation of the receptor phosphatase RPTP\\u03b2/\\u03b6 (PTPRZ1): PTN binding blocks phosphatase activity, allowing accumulation of phosphotyrosine on downstream substrates, including the activation domain of ALK (ligand-independent kinase activation) and AFAP1L2, whose phosphorylation drives PI3K-AKT-mTOR signaling and oligodendrocyte precursor differentiation [#10, #15]. Through PTPRZ1/ALK-AKT signaling, astrocyte- and neural stem cell-derived PTN promotes hippocampal neurogenesis, dendritic development of newborn neurons, and cognition [#13, #18], while dysregulated PTN release from quiescent neural stem cells produces aberrant neurogenesis and manic-like behavior [#22]. PTN also engages syndecan co-receptors in non-neural contexts, activating SDC2 to sustain spermatogonial stem cell proliferation and SDC4 to drive cardiac fibroblast proliferation and macrophage inflammation in pressure-overload cardiomyopathy [#17, #21], and acts through PTPRZ1 to promote osteogenic differentiation [#19]. PTN expression is transcriptionally controlled in a context-specific manner\\u2014by AP-1/JUN in fibroblasts, by IFN-\\u03b3/JAK/STAT1 in macrophages, and by progesterone/cAMP/PKA/C/EBP\\u03b2 in uterine stromal cells [#6, #7, #12]\\u2014and its regulated secretion from oligodendrocyte precursors requires the TRAPPC12-Mea6/cTAGE5-COPII trafficking machinery [#20].\",\n  \"teleology\": [\n    {\n      \"year\": 1989,\n      \"claim\": \"Established PTN as a discrete secreted growth factor by purifying it as a heparin-binding mitogen, answering whether the activity was a defined protein.\",\n      \"evidence\": \"Heparin-Sepharose/cation exchange purification and N-terminal sequencing from bovine uterus with 3H-thymidine mitogenic assay in NIH 3T3 cells\",\n      \"pmids\": [\"2610682\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No receptor or signaling mechanism identified\", \"Physiological source and target tissue unresolved\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Showed the same heparin-binding protein has neurotrophic activity, extending PTN function beyond fibroblast mitogenesis and documenting proteolytic C-terminal truncation.\",\n      \"evidence\": \"Purification from bovine brain, amino acid sequencing, SDS-PAGE, neurotrophic assay on perinatal rat neurons\",\n      \"pmids\": [\"2049182\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of truncated forms unknown\", \"No receptor identified\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Defined the human gene structure and alternative splicing, establishing PTN protein heterogeneity at the genomic level.\",\n      \"evidence\": \"Genomic library screening, Southern blotting, cDNA sequencing, protein characterization from bovine brain\",\n      \"pmids\": [\"8484754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional difference between splice variants not tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Resolved the biophysical basis of signaling competence by showing PTN dimerizes in a sulfation-dependent manner.\",\n      \"evidence\": \"DSS cross-linking, heparin-Sepharose chromatography, chlorate sulfation inhibition, conditioned medium analysis of NIH-3T3 cells\",\n      \"pmids\": [\"10600521\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link between dimerization state and receptor activation not directly shown\", \"Structural model of the dimer absent\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified an endogenous retroviral promoter as a context-specific driver of PTN expression in trophoblast/choriocarcinoma cells via an Sp1 element.\",\n      \"evidence\": \"In situ hybridization, promoter deletion assays, EMSA/supershift, site-directed mutagenesis, Sp1 overexpression in Drosophila SL2 cells\",\n      \"pmids\": [\"10962555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relevance to non-trophoblast tissue regulation unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Placed PTN downstream of AP-1/JUN in fibroblasts and demonstrated a paracrine mitogenic role on keratinocytes during wound healing.\",\n      \"evidence\": \"Expression profiling of Jun-/- MEFs, RT-PCR, in situ hybridization, feeder-layer keratinocyte co-culture, in vivo wound model\",\n      \"pmids\": [\"15840658\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating keratinocyte response not identified\", \"Direct JUN binding to PTN promoter not shown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined IFN-\\u03b3/JAK/STAT1 as an inducible transcriptional input to PTN in macrophages, mapping a functional GAS element in the promoter.\",\n      \"evidence\": \"JAK inhibitors, STAT1 phosphorylation assays, promoter deletion, EMSA/supershift, ChIP, siRNA of STAT1/STAT3/p42\",\n      \"pmids\": [\"19917672\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream consequence of macrophage PTN secretion not addressed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected PTN/RPTP\\u03b2/\\u03b6 signaling to cancer cell migration through integrin \\u03b1v\\u03b23, FAK, PI3K, and ERK, and identified menin as a transcriptional repressor.\",\n      \"evidence\": \"Menin overexpression, RT-PCR, migration assays, pathway inhibitors, integrin blocking in A549 cells\",\n      \"pmids\": [\"20639902\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct menin binding to the PTN locus not shown\", \"Order of integrin/FAK/PI3K events unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Articulated the core mechanistic model: PTN inactivates RPTP\\u03b2/\\u03b6 phosphatase, enabling ligand-independent ALK autophosphorylation and broad downstream tyrosine phosphorylation.\",\n      \"evidence\": \"Mechanistic synthesis of phosphatase activity and tyrosine phosphorylation studies (review)\",\n      \"pmids\": [\"23777859\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Review synthesis rather than primary data in this entry\", \"Stoichiometry of receptor inactivation not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined PTN as a negative regulator of mammary epithelial expansion and ductal outgrowth acting via cell-matrix adhesion and ERK suppression, distinguishing motility from proliferation roles.\",\n      \"evidence\": \"Anti-PTN blocking antibody, RTCA impedance, 3D mammosphere assay, in vivo mammary analysis, phospho-ERK Western blot\",\n      \"pmids\": [\"23077670\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating mammary effects not identified\", \"Mechanism of adhesion disruption unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established PTN/PTPRZ1 as a survival signal in ovarian cancer acting through MAPK effectors.\",\n      \"evidence\": \"siRNA knockdown of PTN/PTPRZ1, apoptosis assays, ELISA, survival-gene expression profiling\",\n      \"pmids\": [\"25418856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct MAPK activation mechanism downstream of PTPRZ1 not delineated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed PTN as a required intermediary in CART neuropeptide-driven neurite outgrowth after ischemic stress.\",\n      \"evidence\": \"siRNA PTN knockdown, GAP43 Western blot, post-OGD CART treatment in cortical neurons\",\n      \"pmids\": [\"25010400\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor coupling CART to PTN expression unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Integrated PTN into hormonal control of uterine decidualization, acting downstream of progesterone/cAMP/PKA/C/EBP\\u03b2 to regulate Hand2 and decidual markers.\",\n      \"evidence\": \"siRNA of PTN/C/EBP\\u03b2, constitutive PTN activation, PKA inhibitor, RT-PCR of decidualization markers in uterine stromal cells\",\n      \"pmids\": [\"28657144\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating decidual PTN effects not identified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated in vivo that neural stem cell-derived PTN is a feedforward signal required for proper dendritic development of newborn neurons.\",\n      \"evidence\": \"Cell ablation, retroviral single-cell labeling, signaling modulation, morphological analysis in adult hippocampus\",\n      \"pmids\": [\"30497772\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor on newborn neurons not pinned down in this study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked chemotherapy-induced PTN/PTPRZ1 upregulation, via CDKN1A, to NF-\\u03baB-driven chemoresistance in triple-negative breast cancer.\",\n      \"evidence\": \"Microarray, CCK-8/colony/apoptosis assays, siRNA of PTPRZ1, pathway inhibition in TNBC cells\",\n      \"pmids\": [\"30497491\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CDKN1A control of PTN transcription not shown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided the most direct substrate-level mechanism: PTN-PTPRZ signaling drives AFAP1L2 tyrosine phosphorylation and PI3K-AKT-mTOR activation to promote oligodendrocyte differentiation and remyelination.\",\n      \"evidence\": \"Phosphoproteomics, in vitro PTPRZ phosphatase assay, HEK293T overexpression, AFAP1L2 siRNA, PI3K inhibition, catalytically inactive PTPRZ knock-in mice, cuprizone model\",\n      \"pmids\": [\"30667096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether AFAP1L2 is a direct or indirect PTPRZ substrate in vivo not fully resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed tumor-cell-derived PTN promotes neurite outgrowth, implicating PTN in cancer-associated neural remodeling.\",\n      \"evidence\": \"shRNA knockdown in BxPC-3 pancreatic cancer cells, DRG co-culture neurite assay\",\n      \"pmids\": [\"21677838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Neuronal receptor mediating outgrowth not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified syndecan co-receptors as alternative PTN effectors: SDC2 sustains spermatogonial stem cell self-renewal and SDC4 drives cardiac fibroblast/macrophage inflammatory responses.\",\n      \"evidence\": \"Co-IP, knockdown with PTN rescue in SSCs; scRNA-seq/CellChat plus in vitro and TAC in vivo validation for SDC4\",\n      \"pmids\": [\"39285301\", \"39765325\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether syndecans act independently or as PTPRZ1 co-receptors not resolved\", \"Structural basis of PTN-syndecan binding unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended the PTPRZ1/ALK-AKT axis in vivo to astrocyte-derived PTN regulation of hippocampal neurogenesis and cognition under demyelination.\",\n      \"evidence\": \"Astrocyte-specific conditional PTN knockout and overexpression, AKT analysis, neurogenesis and behavioral testing in demyelination model\",\n      \"pmids\": [\"39729991\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of PTPRZ1 versus ALK not dissected\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the secretory route for PTN, showing TRAPPC12-Mea6/cTAGE5-COPII machinery is required for PTN release from oligodendrocyte precursors.\",\n      \"evidence\": \"Co-IP of TRAPPC12-Mea6, Mea6 conditional knockout, COPII component analysis, secretion assay, exogenous PTN rescue\",\n      \"pmids\": [\"38439956\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this trafficking route is PTN-specific or general unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked PTN-PTPRZ1 signaling to bone formation through PLCG1 phosphorylation, NCOA3 nuclear translocation, and ROS reduction promoting osteogenic differentiation.\",\n      \"evidence\": \"Phosphoproteomics, immunofluorescence, ALP/TUNEL assays, RNA-seq, in vivo osteoporotic fracture healing\",\n      \"pmids\": [\"40149671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PTPRZ1 dependence of PLCG1 phosphorylation not formally shown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated dysregulated quiescent neural stem cell PTN release in manic-like behavior, identifying excess PTN as a disease-relevant driver of aberrant neurogenesis.\",\n      \"evidence\": \"scRNA-seq, pharmacological and molecular PTN inhibition, behavioral and neurogenesis analysis in Shank3-overexpressing mice\",\n      \"pmids\": [\"40069581\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor pathway downstream of excess PTN not defined here\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Proposed a non-receptor-phosphatase mechanism in which PTN binds SIRT1 to activate the AMPK-PGC1\\u03b1 axis and protect cardiomyocytes from oxidative stress.\",\n      \"evidence\": \"PTN-SIRT1 binding assay, AMPK Thr172/PGC1\\u03b1 Western blot, PTN overexpression, ROS/apoptosis flow cytometry, in vivo cardiotoxicity model\",\n      \"pmids\": [\"41640280\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Methods limited in detail and single publication\", \"Direct PTN-SIRT1 binding not independently confirmed\", \"Reconciliation with secreted-ligand biology unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected stromal androgen receptor signaling to PTN as an extrinsic regulator of epithelial ferroptosis via MUFA phospholipid biosynthesis and GPX4.\",\n      \"evidence\": \"Genetically engineered mice, human organotypic cultures, ferroptosis and castration models (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint not peer-reviewed\", \"Receptor mediating epithelial PTN response not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PTN partitions signaling among PTPRZ1, ALK, and syndecan co-receptors across cell types, and the structural basis of dimer/glycosaminoglycan-dependent receptor selection, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of a PTN-receptor complex in the corpus\", \"Rules governing receptor choice across tissues unknown\", \"Quantitative contribution of dimerization to signaling not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 15, 17, 18]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [10, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 4, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10, 15, 18, 19]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [13, 15, 18]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [5, 7, 12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PTPRZ1\", \"ALK\", \"AFAP1L2\", \"SDC2\", \"SDC4\", \"TRAPPC12\", \"SIRT1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}