{"gene":"SMAD1","run_date":"2026-06-10T07:46:35","timeline":{"discoveries":[{"year":1996,"finding":"MADR1 (SMAD1) is a downstream mediator of BMP2 receptor signaling: BMP2 (but not TGF-β or activin) rapidly induces SMAD1 phosphorylation, which is required for function (a point mutant that gives a null phenotype in Drosophila is not phosphorylated), and BMP2 treatment results in accumulation of SMAD1 in the nucleus.","method":"Phosphorylation assays, point mutagenesis, subcellular fractionation/immunofluorescence in response to BMP2 vs. TGF-β vs. activin","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct phosphorylation assay combined with loss-of-function mutagenesis and nuclear localization experiment; foundational paper replicated across many subsequent studies","pmids":["8653785"],"is_preprint":false},{"year":1999,"finding":"SMAD1 interacts with the homeodomain transcription factor Hoxc-8 (identified by yeast two-hybrid, confirmed by pull-down and co-IP in COS-1 cells); purified SMAD1 inhibits Hoxc-8 binding to its DNA element (osteopontin promoter) in a concentration-dependent manner, thereby de-repressing BMP-induced gene transcription.","method":"Yeast two-hybrid screen, GST pull-down, co-immunoprecipitation, EMSA/gel-shift assay, luciferase reporter transfection","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (Y2H, pulldown, Co-IP, EMSA, reporter assay) in a single study","pmids":["10224145"],"is_preprint":false},{"year":1999,"finding":"SMAD1 interacts with the transcriptional coactivators p300 and CBP both in vitro and in vivo; the C-terminal half of SMAD1 contains two interaction domains that bind the C-terminal region of p300/CBP; phosphorylation of SMAD1 enhances binding to CBP and further stimulates SMAD1-dependent transcription.","method":"In vitro binding assay, co-immunoprecipitation, transcription reporter assays, phosphorylation-binding correlation","journal":"Biochimica et Biophysica Acta","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal assays (in vitro binding, Co-IP, reporter) in a single study","pmids":["10673036"],"is_preprint":false},{"year":1999,"finding":"The Ras/MEK pathway is partially required for TGF-β- and BMP-induced SMAD1 phosphorylation and transcriptional activity in intestinal epithelial cells; either dominant-negative Ras (RasN17) or the MEK inhibitor PD98059 significantly decreased BMP/TGF-β-induced SMAD1 phosphorylation.","method":"Stable inducible dominant-negative Ras expression, MEK inhibitor (PD98059), endogenous SMAD1 phosphorylation assay, luciferase reporter","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic (dominant-negative) plus pharmacological inhibitor approach with phosphorylation readout, single lab","pmids":["10208426"],"is_preprint":false},{"year":2000,"finding":"Calmodulin directly binds to two conserved regions in SMAD1 and increases SMAD1 activity in Xenopus embryos; calmodulin binding inhibits subsequent ERK2-dependent linker phosphorylation of SMAD1, revealing cross-talk between Ca2+/calmodulin, RTK/ERK, and BMP-SMAD1 pathways.","method":"Binding assays (structure-function), Xenopus embryo gain/loss-of-function, ERK2 phosphorylation assay","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo embryo assay plus biochemical phosphorylation analysis, single lab, two orthogonal approaches","pmids":["11007779"],"is_preprint":false},{"year":2002,"finding":"SANE (Smad1 Antagonistic Effector), a LEM-domain protein, binds to SMAD1/5 and to BMP type I receptors, inhibiting BMP-induced SMAD1 phosphorylation and blocking ligand-dependent nuclear translocation of SMAD1; a SANE mutant that cannot bind SMAD1 fails to inhibit BMP signaling.","method":"Co-immunoprecipitation, Xenopus embryo functional assays, mammalian bone-formation model, nuclear translocation assay, SANE-binding mutant analysis","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — reciprocal Co-IP, mutagenesis of binding interface, phosphorylation assay, nuclear localization, and in vivo rescue in two model systems","pmids":["12393873"],"is_preprint":false},{"year":2003,"finding":"SMAD1 and GATA factors (GATA-1, -5, or -6) assemble together on the intronic BMP-response element (I-BRE) of the Smad7 gene in living cells; GATA-dependent co-occupancy renders I-BRE more responsive to low BMP concentrations than the promoter BRE that relies solely on SMAD1/SMAD4 binding.","method":"Chromatin immunoprecipitation (ChIP), luciferase reporter assays, site-directed mutagenesis of Smad1/Smad4 binding sites","journal":"Molecular and Cellular Biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — ChIP in living cells plus mutagenesis and reporter assays, single lab but multiple orthogonal methods","pmids":["12944489"],"is_preprint":false},{"year":2004,"finding":"SMAD1 interacts with the cytoplasmic domain of CD44 (identified by yeast two-hybrid, confirmed by co-IP); full-length CD44 is required for BMP-7-induced SMAD1 phosphorylation and nuclear translocation—overexpression of a truncated CD44 abolished nuclear SMAD1 translocation—and disruption of extracellular hyaluronan-CD44 interactions (by hyaluronidase) inhibited BMP-7-mediated SMAD1 phosphorylation and SMAD4 nuclear translocation.","method":"Yeast two-hybrid, co-immunoprecipitation, nuclear translocation assay, luciferase reporter (SBE4-luc), hyaluronidase treatment","journal":"The Journal of Cell Biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (Y2H, Co-IP, translocation, reporter) in single study","pmids":["15452148"],"is_preprint":false},{"year":2005,"finding":"Interaction between SMAD1 and CHIP (an E3 ubiquitin ligase) was demonstrated by surface plasmon resonance, suggesting CHIP may mediate SMAD1 degradation.","method":"Surface plasmon resonance (SPR) binding assay","journal":"Colloids and Surfaces B: Biointerfaces","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single biochemical binding method only, no functional validation of degradation","pmids":["15708501"],"is_preprint":false},{"year":2005,"finding":"In cardiomyocytes, SMAD1 signaling mediates BMP2-induced protection against apoptosis during hypoxia-reoxygenation via upregulation of Bcl-xL and β-catenin; transgenic mice with cardiac-specific Smad1 overexpression showed significantly smaller myocardial infarctions and fewer apoptotic cardiomyocyte deaths after ischemia-reperfusion injury.","method":"Cardiac-specific transgenic mouse model, adenoviral gene transfer, TUNEL/DNA ladder apoptosis assay, western blot for Bcl-xL, β-catenin, and caspase-3","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo transgenic model combined with in vitro gain-of-function and defined molecular mediators (Bcl-xL), single lab","pmids":["15911698"],"is_preprint":false},{"year":2006,"finding":"Angiotensin II activates SMAD1 through a Src kinase-dependent mechanism in mesangial cells: Ang II induces phosphorylation of Src and SMAD1; Src inhibitor PP2, dominant-negative Src, or Src siRNA all reduce SMAD1 phosphorylation and type IV collagen synthesis.","method":"Pharmacological Src inhibitor (PP2), dominant-negative Src overexpression, Src siRNA knockdown, western blot for p-Src and p-Smad1, collagen IV assay","journal":"Laboratory Investigation","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — three independent approaches (inhibitor, dominant-negative, siRNA) all converging on Src→SMAD1→ColIV axis","pmids":["16767106"],"is_preprint":false},{"year":2006,"finding":"Nanog physically interacts with SMAD1 and blocks BMP-induced mesoderm differentiation of mouse ES cells by interfering with the recruitment of coactivators to active Smad transcriptional complexes.","method":"Co-immunoprecipitation, ES cell differentiation assays, transcriptional reporter assays","journal":"Proceedings of the National Academy of Sciences USA","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional differentiation assay, single lab","pmids":["16801560"],"is_preprint":false},{"year":2007,"finding":"In SSc fibroblasts, SMAD1 directly binds and activates the CCN2 (CTGF) gene promoter; siRNA-mediated depletion of SMAD1 normalizes CCN2 and collagen production; imatinib mesylate reverses Smad1 pathway activation via blockade of c-Abl.","method":"In vitro and in vivo DNA binding assays, siRNA knockdown, luciferase reporter assay, western blot, immunohistochemistry","journal":"Arthritis and Rheumatism","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct DNA binding assay plus siRNA functional validation plus pharmacological pathway positioning, single lab with multiple methods","pmids":["18668566"],"is_preprint":false},{"year":2008,"finding":"Linker-region sequential phosphorylation of SMAD1 by MAPK and then GSK3 negatively regulates BMP-SMAD1 signaling by directing SMAD1 to the centrosomal region for polyubiquitination and proteasomal degradation; Wnt signaling, via GSK3 inhibition, prolongs the BMP-SMAD1 signal.","method":"Xenopus embryo epistasis experiments, phosphorylation-resistant SMAD1 mutants, proteasome inhibitor assays, centrosome fractionation (reviewed/synthesized from multiple primary papers)","journal":"Current Opinion in Genetics & Development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — review synthesizing multiple primary papers using phosphorylation mutants, centrosomal fractionation, and epistasis; not a primary data paper itself but citing well-established results","pmids":["18590818"],"is_preprint":false},{"year":2010,"finding":"Crystal structure of the SMAD1 MH1 domain bound to a palindromic Smad binding element (SBE) reveals that the N-terminal helix 1 of SMAD1 is dislodged from its intramolecular binding site and adopts a domain-swapped arrangement compared to SMAD3, causing helix 2 to kink away and disabling key DNA backbone contacts; this confers lower overall DNA affinity but increased cooperativity on palindromic elements.","method":"X-ray crystallography, thermal melting analysis, DNA binding assays","journal":"Nucleic Acids Research","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional validation by thermal melting and quantitative DNA binding assays","pmids":["20147459"],"is_preprint":false},{"year":2011,"finding":"In endothelial cells, SnoN directly binds ALK1 at the plasma membrane and facilitates the interaction between ALK1 and SMAD1/5, enhancing SMAD1/5 phosphorylation; disruption of SnoN-SMAD interaction impairs SMAD1/5 activation, upregulates SMAD2/3 activity, and causes defective angiogenesis and arteriovenous malformations.","method":"Co-immunoprecipitation, direct binding assay (SnoN-ALK1 interaction), in vivo embryonic angiogenesis phenotype, SMAD1/5 phosphorylation assay","journal":"The Journal of Cell Biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct binding demonstrated, phosphorylation assay, in vivo phenotypic rescue/mutant analysis, single lab with multiple orthogonal methods","pmids":["24019535"],"is_preprint":false},{"year":2011,"finding":"Endoglin promotes TGF-β/SMAD1 signaling in SSc fibroblasts: endoglin is constitutively found in complexes with ALK1, and siRNA depletion of endoglin inhibits SMAD1 phosphorylation without affecting pSMAD2/3, reducing collagen and CCN2 levels.","method":"Co-immunoprecipitation, siRNA knockdown, western blot for pSMAD1","journal":"Journal of Cellular Physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus siRNA functional validation, single lab","pmids":["21344387"],"is_preprint":false},{"year":2011,"finding":"In the developing lung, SMAD1 (but not SMAD5) in epithelial cells transcriptionally activates Wnt inhibitory factor 1 (Wif1), identified by combined cDNA microarray and ChIP-chip; loss of SMAD1-dependent Wif1 activation results in increased Wnt/β-catenin signaling and specific fetal lung abnormalities.","method":"Conditional knockout mice (lung epithelial-specific Smad1 or Smad5 deletion), cDNA microarray, ChIP-chip, Wnt/β-catenin reporter assays","journal":"Development","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vivo conditional KO combined with genome-wide ChIP and transcriptomics identifying direct target gene, replicated at multiple levels","pmids":["21270055"],"is_preprint":false},{"year":2011,"finding":"Smad1 plays a biphasic role in hematopoiesis: early Smad1 expression is required for hemangioblast commitment from mesoderm, while later Smad1 expression in FLK1+ mesoderm restricts expansion of hematopoietic progenitors; depletion of Smad1 after hemangioblast commitment expands hematopoietic progenitors and correlates with increased nuclear SMAD2 activity, indicating cross-regulation between BMP and TGF-β SMAD pathways.","method":"Conditional/temporal siRNA knockdown in embryoid body cultures, embryonic stem cell differentiation, SMAD2 nuclear activity assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional knockdown with temporal control and mechanistic readout of cross-pathway regulation, single lab","pmids":["21515822"],"is_preprint":false},{"year":2012,"finding":"On genotoxic stress, ATM kinase phosphorylates BMP-activated SMAD1 in the nucleus at Ser239; this disrupts SMAD1 interaction with phosphatase PPM1A (leading to enhanced SMAD1 activation), and activated SMAD1 then interacts with p53 to inhibit MDM2-mediated p53 ubiquitination and degradation.","method":"ATM kinase assay, S239 phosphorylation site mutagenesis, Co-IP (SMAD1-PPM1A, SMAD1-p53), ubiquitination assay, cell proliferation and survival assays, clinical sample analysis","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct kinase assay, site mutagenesis, co-IP of multiple complexes, ubiquitination assay, all in single study","pmids":["22588298"],"is_preprint":false},{"year":2012,"finding":"In macrophages, BMP-6-induced IL-1β expression requires a physical interaction between SMAD1 and the transcription factor PU.1; both the canonical SMAD pathway and non-SMAD ERK/JNK pathways are required, and cross-talk between them is mediated through PU.1-SMAD1 interaction.","method":"Co-immunoprecipitation (PU.1-SMAD1), siRNA knockdown, ERK/JNK pathway inhibitors, luciferase reporter","journal":"Molecular Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus knockdown plus inhibitor studies, single lab","pmids":["21571370"],"is_preprint":false},{"year":2012,"finding":"In mesangial cells, scleraxis physically associates with E12 to bind the SMA promoter E-box; scleraxis also induces BMP4 secretion, which activates SMAD1 to induce smooth muscle α-actin (SMA); Id1, induced by extended AGE treatment, dislodges scleraxis from the SMA promoter, thereby modulating the BMP4-SMAD1-SMA pathway.","method":"Co-immunoprecipitation, chromatin immunoprecipitation, promoter binding assays, overexpression/knockdown, ELISA for BMP4","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ChIP plus functional promoter assays, single lab","pmids":["22474292"],"is_preprint":false},{"year":2013,"finding":"In endothelial cells, oscillatory shear stress (OSS) induces sustained BMPRIB-αvβ3 integrin association; the intracytoplasmic kinase domain of BMPRII mediates this interaction and subsequently activates the Shc/FAK/ERK cascade, leading to SMAD1/5 activation; SMAD1/5 then associates with and activates Runx2, leading to mTOR/p70S6K activation and EC proliferation.","method":"Co-immunoprecipitation, in situ proximity ligation assay, shRNA knockdown of SMAD5, kinase domain deletion analysis, in vivo intra-arterial lentiviral injection","journal":"Journal of Thrombosis and Haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus proximity ligation plus in vivo knockdown with BrdU proliferation readout, single lab","pmids":["23387849"],"is_preprint":false},{"year":2013,"finding":"KSHV LANA protein interacts with SMAD1 (identified as novel binding partner), sustains BMP-activated pSMAD1 in the nucleus, and enhances SMAD1 loading on Id gene promoters, resulting in Id upregulation that drives KSHV-induced oncogenic transformation; genetic/chemical inhibition of BMP-SMAD1-Id pathway blocks the oncogenic phenotype.","method":"Co-immunoprecipitation (LANA-SMAD1), ChIP on Id promoters, genetic inhibition (siRNA), chemical inhibitor, in vivo tumor xenograft","journal":"PLoS Pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ChIP plus functional in vivo oncogenesis assay, single lab","pmids":["25010525"],"is_preprint":false},{"year":2016,"finding":"YAP (yes-associated protein) physically interacts with SMAD1 in neural stem cells and is required for BMP2-induced stabilization and nuclear accumulation of SMAD1; in YAP-deficient NSCs, SMAD1 expression is reduced and astrocytic differentiation is impaired; SMAD1 re-expression in YAP-deficient NSCs partially rescues astrocytic differentiation.","method":"Conditional knockout mice (Yap-nestin, Yap-GFAP), co-immunoprecipitation, western blot, rescue by SMAD1 re-expression","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo conditional KO plus Co-IP plus molecular rescue experiment, single lab with multiple orthogonal methods","pmids":["27381227"],"is_preprint":false},{"year":2017,"finding":"Erythropoietin and erythroferrone suppress hepcidin transcription by targeting SMAD1/5 signaling: EPO treatment reduces liver SMAD1/5 phosphorylation in parallel with hepcidin mRNA reduction in control mice, but fails to suppress hepcidin in hepatocyte-specific Smad1/Smad5 double-knockout mice or SMAD1/5 knockdown cells; SMAD1 and SMAD5 have overlapping (redundant) functions in hepcidin regulation.","method":"Hepatocyte-specific conditional double-knockout mice, EPO/erythroferrone treatment, siRNA knockdown, primary hepatocyte cultures, SMAD1/5 phosphorylation assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo conditional KO plus in vitro siRNA plus primary hepatocyte rescue studies, multiple orthogonal approaches, replicated at multiple levels","pmids":["28438754"],"is_preprint":false},{"year":2018,"finding":"TGF-β induces SMAD1/5 phosphorylation through a novel two-receptor mechanism: TGFBR1 phosphorylates and activates ACVR1 (a second type I receptor), which then phosphorylates SMAD1/5; approximately a quarter of the TGF-β-induced transcriptome depends on SMAD1/5 signaling; TGF-β-induced epithelial-to-mesenchymal transition requires both SMAD3 and SMAD1/5 pathways, with SMAD1/5 being essential for ID1 induction.","method":"Receptor knockdown/knockout, phosphorylation assays, transcriptome analysis (RNA-seq), EMT functional assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — receptor-specific knockouts establishing pathway order, phosphorylation assays, genome-wide transcriptomics, and functional EMT assay; multiple orthogonal methods in single study","pmids":["29376829"],"is_preprint":false},{"year":2019,"finding":"SMAD1 is phosphorylated at Ser239 by ATM in the DNA damage response, and this disrupts SMAD1 interaction with phosphatase PPM1A; conversely, DUSP5 (a dual-specificity phosphatase) promotes osteogenic differentiation by competitively binding SCP1/2 (SMAD1 phosphatases) via its linker region, thereby preventing SCP1/2-mediated SMAD1 dephosphorylation and maintaining SMAD1 activation.","method":"Co-immunoprecipitation (DUSP5-SCP1/2-SMAD1), domain mapping, in vitro dephosphorylation assays, osteogenic differentiation assays, OVX mouse model rescue by Dusp5 overexpression","journal":"Stem Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with domain mapping and functional rescue in vivo, single lab","pmids":["34169608"],"is_preprint":false},{"year":2019,"finding":"Sema4C (semaphorin 4C) reverse signaling co-immunoprecipitates with TGFBRII and BMPR1, eliciting non-conventional TGF-β/BMP receptor activation and selective SMAD1/5 phosphorylation leading to increased ID1/3 expression and invasive gene reprogramming in cancer cells.","method":"Co-immunoprecipitation (Sema4C-TGFBRII-BMPR1), SMAD1/5 phosphorylation assay, gene expression profiling, in vivo metastasis assay","journal":"Science Signaling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus phosphorylation assay plus in vivo metastasis data, single lab","pmids":["31431542"],"is_preprint":false},{"year":2022,"finding":"METTL14-mediated m6A methylation of SMAD1 mRNA promotes its stability; IGF2BP1 is the m6A reader for SMAD1 transcripts; knockdown of METTL14 reduces m6A modification of SMAD1, decreasing SMAD1 protein levels and suppressing osteogenic differentiation.","method":"RIP (RNA immunoprecipitation), MeRIP (m6A-seq), luciferase reporter assay, siRNA knockdown, OVX mouse model","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MeRIP plus RIP plus reporter assay establishing m6A-IGF2BP1-SMAD1 axis, single lab","pmids":["36319624"],"is_preprint":false},{"year":2022,"finding":"Hypoxia-induced ALKBH5 demethylase translocates from nucleus to cytoplasm and demethylates m6A-modified SMAD1 (and SMAD5) mRNAs, enhancing their translation and promoting trophoblast invasion via upregulation of MMP9 and ITGA1.","method":"m6A-seq (m6A-RIP), ALKBH5 subcellular fractionation, knockdown in mouse placenta (trophoblast-specific), western blot for SMAD1/5 protein","journal":"Biochimica et Biophysica Acta – Molecular Cell Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — m6A-seq plus in vivo trophoblast knockdown with functional phenotype, single lab","pmids":["35724807"],"is_preprint":false},{"year":2022,"finding":"SMAD1 mediates BMP-dependent repression of SOX2 by recruiting histone H3K27me3 and DNA methylation at the SOX2 promoter; conversely, TGF-β/activin activates SOX2 through SMAD3-dependent H3K4me3 recruitment, defining a reciprocal epigenetic regulatory axis controlling anchorage-independent survival.","method":"Gene expression profiling, ChIP (H3K27me3, H3K4me3), DNA methylation assay, in vivo intraperitoneal tumor model","journal":"Cell Reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for histone marks plus DNA methylation analysis plus in vivo tumor assay, single lab","pmids":["35905726"],"is_preprint":false},{"year":2024,"finding":"In adult mouse neocortex, BMP2 acts on parvalbumin (PV) interneurons via SMAD1 to control glutamatergic synapse proteins and perineuronal net components; PV-interneuron-specific disruption of BMP2-SMAD1 signaling reduces glutamatergic innervation of PV cells, impairs perineuronal net development and PV cell excitability, disrupts cortical excitation-inhibition balance, and causes spontaneous epileptic seizures.","method":"PV interneuron-specific conditional knockout of SMAD1, electrophysiology, immunohistochemistry, proteomics of synapse proteins, in vivo EEG for seizure detection","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO with electrophysiology, molecular (proteomics, IHC), and in vivo seizure phenotype; multiple orthogonal methods, published in high-impact journal","pmids":["38632412"],"is_preprint":false},{"year":2024,"finding":"High fluid shear stress suppresses endothelial SMAD1/5 signaling via a KLF2-BMPER axis: high FSS elevates KLF2, which transcriptionally induces BMPER (a BMP pathway inhibitor), thereby de-inhibiting AKT and facilitating outward vessel remodeling; endothelial BMPER deletion impairs blood flow recovery.","method":"Surgically induced high-FSS mouse model, endothelial BMPER conditional knockout, SMAD1/5 phosphorylation assay, KLF2 overexpression/knockdown, luciferase reporter","journal":"Nature Cardiovascular Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo mouse model plus conditional KO plus mechanistic reporter assay, single lab","pmids":["39196179"],"is_preprint":false}],"current_model":"SMAD1 is a receptor-activated transcription factor that is phosphorylated at its C-terminal SSXS motif by BMP type I receptors (primarily ALK1/2/3/6) and, via a novel TGFBR1→ACVR1 relay, also by TGF-β stimulation; once phosphorylated, SMAD1 accumulates in the nucleus where it binds DNA through a distinctive domain-swapped MH1 conformation, recruits co-activators (p300/CBP), and cooperates with cell-type-specific DNA-binding partners (Hoxc-8, GATA factors, PU.1, Runx2) to drive transcriptional programs controlling bone formation, hematopoiesis, angiogenesis, iron homeostasis, neuronal excitation-inhibition balance, and organ development; SMAD1 activity is negatively modulated by sequential MAPK and GSK3 linker phosphorylations that direct it to centrosomal proteasomal degradation, by calmodulin binding, by phosphatases SCP1/2 (counteracted by DUSP5), and by m6A mRNA methylation/demethylation; it forms complexes with Nanog, SnoN (at ALK1), SANE, CD44 (cytoplasmic domain), KSHV LANA, and YAP, and integrates upstream inputs from Src, Ras/MEK, ATM (DNA damage), and fluid shear stress."},"narrative":{"mechanistic_narrative":"SMAD1 is a receptor-activated transcription factor that transduces BMP signals into nuclear transcriptional programs governing skeletal, hematopoietic, vascular, neuronal, and iron-homeostatic processes [PMID:8653785, PMID:28438754, PMID:38632412]. BMP2 stimulation, but not TGF-β or activin, rapidly induces SMAD1 phosphorylation that is required for activity and drives its nuclear accumulation [PMID:8653785]; a parallel non-canonical route operates downstream of TGF-β, in which TGFBR1 phosphorylates and activates ACVR1, which in turn phosphorylates SMAD1/5, accounting for a substantial fraction of the TGF-β transcriptome and being essential for ID1 induction and EMT [PMID:29376829]. Once activated, SMAD1 engages DNA through an MH1 domain whose N-terminal helix adopts a domain-swapped conformation that lowers intrinsic affinity but increases cooperativity on palindromic Smad binding elements [PMID:20147459], and it recruits the coactivators p300/CBP in a phosphorylation-enhanced manner [PMID:10673036]. Transcriptional specificity is achieved through cell-type-restricted DNA-binding partners and cofactors—Hoxc-8, GATA factors, PU.1, and Runx2—that direct SMAD1 to context-specific target genes [PMID:10224145, PMID:12944489, PMID:21571370, PMID:23387849], and SMAD1 both activates targets such as CCN2/CTGF, Wif1, and Id genes and represses others such as SOX2 via H3K27me3 and DNA methylation [PMID:18668566, PMID:21270055, PMID:25010525, PMID:35905726]. Signal output is tuned by multiple negative regulators: sequential MAPK then GSK3 linker phosphorylation routes SMAD1 to centrosomal proteasomal degradation [PMID:18590818], calmodulin binding modulates linker phosphorylation [PMID:11007779], and phosphatase balance (PPM1A, SCP1/2 counteracted by DUSP5) and m6A mRNA methylation/demethylation (METTL14/IGF2BP1, ALKBH5) further set SMAD1 levels [PMID:22588298, PMID:34169608, PMID:36319624, PMID:35724807]. Upstream, SMAD1 activation is gated at the receptor and membrane level by CD44, SnoN, endoglin, SANE, and shear-stress–responsive KLF2-BMPER and integrin inputs [PMID:12393873, PMID:15452148, PMID:24019535, PMID:21344387, PMID:39196179], and SMAD1 is integrated with the DNA-damage response through ATM-mediated Ser239 phosphorylation that stabilizes p53 [PMID:22588298]. Physiologically, SMAD1/5 redundantly control hepcidin-mediated iron regulation [PMID:28438754], and SMAD1 in parvalbumin interneurons maintains cortical excitation-inhibition balance, its loss causing epileptic seizures [PMID:38632412].","teleology":[{"year":1996,"claim":"Established SMAD1 as a dedicated, phosphorylation-dependent intracellular effector of BMP receptor signaling, distinguishing it from TGF-β/activin responses.","evidence":"Phosphorylation assays, loss-of-function point mutagenesis, and subcellular fractionation comparing BMP2 vs TGF-β vs activin","pmids":["8653785"],"confidence":"High","gaps":["Did not identify the receptor kinase responsible","Did not map the phosphoacceptor SSXS motif residues directly"]},{"year":1999,"claim":"Defined how phosphorylated SMAD1 achieves transcriptional output by recruiting p300/CBP coactivators and by de-repressing Hoxc-8-occupied promoters, giving the first mechanistic basis for SMAD1-driven gene activation.","evidence":"Yeast two-hybrid, GST pull-down, Co-IP, EMSA, and reporter assays for Hoxc-8 and p300/CBP interactions","pmids":["10224145","10673036"],"confidence":"High","gaps":["Genome-wide target scope not addressed","Stoichiometry of SMAD1-coactivator-partner complexes unresolved"]},{"year":1999,"claim":"Revealed that SMAD1 activation is not purely receptor-driven but is modulated by RTK-linked Ras/MEK signaling, opening the concept of cross-pathway input on SMAD1 phosphorylation.","evidence":"Dominant-negative Ras and MEK inhibitor PD98059 with endogenous phosphorylation and reporter readouts","pmids":["10208426"],"confidence":"Medium","gaps":["Whether MEK acts on the C-terminal or linker phosphosites not distinguished","Single cell-type context (intestinal epithelium)"]},{"year":2000,"claim":"Showed calmodulin directly binds SMAD1 and antagonizes ERK-dependent linker phosphorylation, integrating Ca2+ signaling into the regulation of SMAD1 activity.","evidence":"Structure-function binding assays, Xenopus embryo gain/loss-of-function, and ERK2 phosphorylation assays","pmids":["11007779"],"confidence":"Medium","gaps":["Physiological Ca2+ stimulus that engages this in mammalian cells not defined","Mechanism of how calmodulin occludes linker sites structurally unknown"]},{"year":2002,"claim":"Identified SANE as a receptor-level inhibitor that binds both SMAD1/5 and BMP type I receptors to block phosphorylation and nuclear translocation, defining negative control upstream of SMAD1.","evidence":"Reciprocal Co-IP, binding-mutant analysis, nuclear translocation, and in vivo Xenopus/bone-formation rescue","pmids":["12393873"],"confidence":"High","gaps":["Endogenous tissue contexts where SANE limits BMP signaling not mapped","Structural basis of dual receptor/SMAD binding unresolved"]},{"year":2003,"claim":"Demonstrated that combinatorial co-occupancy with GATA factors sensitizes SMAD1 target elements to low BMP doses, showing how partner transcription factors tune the quantitative BMP response.","evidence":"ChIP in living cells plus binding-site mutagenesis and reporter assays on the Smad7 I-BRE","pmids":["12944489"],"confidence":"High","gaps":["Generality across other BMP targets not tested","Direct SMAD1-GATA physical contact not structurally defined"]},{"year":2004,"claim":"Connected extracellular matrix sensing to SMAD1 activation by showing the CD44 cytoplasmic domain and hyaluronan-CD44 engagement are required for BMP-7-induced SMAD1 phosphorylation and nuclear translocation.","evidence":"Yeast two-hybrid, Co-IP, nuclear translocation, reporter assays, and hyaluronidase treatment","pmids":["15452148"],"confidence":"High","gaps":["How CD44 couples mechanistically to the receptor complex unclear","Whether CD44 dependence is cell-type-specific not resolved"]},{"year":2005,"claim":"Provided first evidence for E3-ligase-mediated turnover of SMAD1 via CHIP binding, pointing toward ubiquitin-dependent control of SMAD1 abundance.","evidence":"Surface plasmon resonance binding assay only","pmids":["15708501"],"confidence":"Low","gaps":["Single binding method without functional degradation assay","No demonstration of in-cell ubiquitination or turnover"]},{"year":2005,"claim":"Established a cytoprotective transcriptional role for SMAD1 in cardiomyocytes by linking it to Bcl-xL/β-catenin upregulation and reduced ischemic apoptosis.","evidence":"Cardiac-specific transgenic mice, adenoviral transfer, TUNEL apoptosis, and western blots for survival mediators","pmids":["15911698"],"confidence":"High","gaps":["Whether SMAD1 directly binds Bcl-xL/β-catenin promoters not shown","Loss-of-function endogenous requirement not tested"]},{"year":2006,"claim":"Extended non-BMP activation of SMAD1 by showing angiotensin II drives SMAD1 phosphorylation through Src kinase to promote collagen IV synthesis, linking SMAD1 to fibrotic signaling.","evidence":"Src inhibitor PP2, dominant-negative Src, and Src siRNA with p-SMAD1 and collagen IV readouts in mesangial cells","pmids":["16767106"],"confidence":"High","gaps":["Whether Src acts on receptor or directly on SMAD1 not resolved","Phosphosite targeted by Src not mapped"]},{"year":2006,"claim":"Showed that pluripotency factor Nanog restrains BMP-driven mesoderm differentiation by binding SMAD1 and blocking coactivator recruitment, defining a stem-cell-specific brake on SMAD1 output.","evidence":"Co-IP, ES cell differentiation, and reporter assays","pmids":["16801560"],"confidence":"Medium","gaps":["Direct competition with p300/CBP not biochemically demonstrated","Interaction interface unmapped"]},{"year":2008,"claim":"Defined the linker-phosphorylation code (MAPK then GSK3) that targets SMAD1 to centrosomal proteasomal degradation and showed Wnt prolongs BMP signaling by inhibiting GSK3, establishing duration control of SMAD1 signaling.","evidence":"Review synthesizing Xenopus epistasis, phospho-resistant mutants, proteasome inhibition, and centrosome fractionation","pmids":["18590818"],"confidence":"Medium","gaps":["Review rather than primary data","Identity of the centrosomal E3 ligase not specified here"]},{"year":2010,"claim":"Provided the structural explanation for SMAD1's distinctive DNA-binding behavior, showing a domain-swapped MH1 conformation that lowers affinity but raises cooperativity on palindromic elements relative to SMAD3.","evidence":"X-ray crystallography of MH1-SBE complex with thermal melting and DNA binding assays","pmids":["20147459"],"confidence":"High","gaps":["Structure of full-length SMAD1 or partner-bound complexes not solved","Functional consequence in cells of cooperativity not directly tested"]},{"year":2011,"claim":"Identified SnoN and endoglin as endothelial receptor-complex factors that selectively promote SMAD1/5 activation at ALK1 and balance it against SMAD2/3, linking SMAD1 to angiogenesis and fibrosis.","evidence":"Co-IP, direct binding assays, siRNA, SMAD1/5 phosphorylation, and in vivo angiogenesis phenotypes","pmids":["24019535","21344387"],"confidence":"High","gaps":["How SnoN/endoglin discriminate SMAD1/5 from SMAD2/3 mechanistically unresolved","Quantitative contribution to AVM pathology incomplete"]},{"year":2011,"claim":"Used conditional knockouts to assign SMAD1 non-redundant developmental roles, including direct Wif1 activation in lung epithelium and biphasic control of hematopoietic progenitor expansion with reciprocal SMAD2 cross-regulation.","evidence":"Lung- and mesoderm-targeted conditional/temporal Smad1 depletion, microarray, ChIP-chip, and Wnt reporter assays","pmids":["21270055","21515822"],"confidence":"High","gaps":["Why SMAD1 but not SMAD5 activates Wif1 not explained","Cross-pathway switch mechanism with SMAD2 incompletely defined"]},{"year":2012,"claim":"Placed SMAD1 within the DNA-damage response by showing ATM phosphorylates it at Ser239, disrupting PPM1A binding and enabling SMAD1 to stabilize p53 against MDM2-mediated degradation.","evidence":"ATM kinase assay, S239 mutagenesis, Co-IP of SMAD1-PPM1A and SMAD1-p53, ubiquitination and survival assays","pmids":["22588298"],"confidence":"High","gaps":["Whether nuclear SMAD1 directly contacts MDM2 or acts via p53 only unclear","Generality across genotoxic stresses not fully tested"]},{"year":2012,"claim":"Expanded the partner repertoire to PU.1 and scleraxis/E12, showing SMAD1 cooperates with lineage transcription factors and integrates non-SMAD ERK/JNK input to drive context-specific genes (IL-1β, SMA).","evidence":"Co-IP, ChIP, promoter assays, knockdown, and pathway inhibitors in macrophages and mesangial cells","pmids":["21571370","22474292"],"confidence":"Medium","gaps":["Direct co-binding on endogenous promoters not structurally resolved","Single-lab, single-context findings"]},{"year":2013,"claim":"Demonstrated mechanotransduction into SMAD1/5 via oscillatory shear stress through BMPRIB-integrin association and a Shc/FAK/ERK cascade feeding into SMAD1/5-Runx2-mTOR-driven endothelial proliferation.","evidence":"Co-IP, proximity ligation assay, shRNA, kinase-domain deletion, and in vivo lentiviral injection","pmids":["23387849"],"confidence":"Medium","gaps":["Direct SMAD1-Runx2 contact not biochemically isolated here","Relative contribution of SMAD1 vs SMAD5 not separated"]},{"year":2013,"claim":"Identified KSHV LANA as a viral hijacker of SMAD1 that sustains nuclear pSMAD1 and enhances loading on Id promoters to drive oncogenic transformation, demonstrating disease exploitation of the BMP-SMAD1-Id axis.","evidence":"Co-IP, ChIP on Id promoters, siRNA/chemical inhibition, and in vivo xenograft","pmids":["25010525"],"confidence":"Medium","gaps":["LANA-SMAD1 binding interface unmapped","Whether LANA blocks SMAD1 degradation or phosphatase access unresolved"]},{"year":2016,"claim":"Showed YAP physically stabilizes SMAD1 and is required for its BMP2-induced nuclear accumulation and astrocytic differentiation of neural stem cells, linking Hippo pathway output to SMAD1 protein levels.","evidence":"Yap conditional knockouts, Co-IP, western blot, and SMAD1 re-expression rescue","pmids":["27381227"],"confidence":"High","gaps":["Mechanism of YAP-mediated stabilization (transcriptional vs post-translational) not fully separated","Direct binding interface unmapped"]},{"year":2017,"claim":"Established SMAD1/5 as the redundant transcriptional node through which erythropoietin and erythroferrone suppress hepcidin, placing SMAD1 at the center of systemic iron homeostasis.","evidence":"Hepatocyte-specific Smad1/Smad5 double-knockout mice, EPO/erythroferrone treatment, siRNA, and primary hepatocyte assays","pmids":["28438754"],"confidence":"High","gaps":["How erythroferrone signal reaches SMAD1/5 at the receptor not fully defined","Individual SMAD1 vs SMAD5 contribution masked by redundancy"]},{"year":2018,"claim":"Discovered a non-canonical TGFBR1→ACVR1 relay that activates SMAD1/5 under TGF-β, revealing that a major share of TGF-β transcriptional and EMT output is SMAD1/5-dependent.","evidence":"Receptor knockdown/knockout, phosphorylation assays, RNA-seq, and EMT functional assays","pmids":["29376829"],"confidence":"High","gaps":["Determinants of when TGF-β engages this relay vs SMAD2/3-only unclear","ACVR1 ligand-independence in this context not fully resolved"]},{"year":2019,"claim":"Defined phosphatase-level control of SMAD1, showing DUSP5 sustains SMAD1 activation by competitively sequestering SCP1/2 to promote osteogenic differentiation.","evidence":"Co-IP with domain mapping, in vitro dephosphorylation assays, osteogenic differentiation, and OVX mouse rescue","pmids":["34169608"],"confidence":"Medium","gaps":["Direct SCP1/2 dephosphorylation site on SMAD1 not mapped here","Single-lab in vivo model"]},{"year":2022,"claim":"Established m6A mRNA modification as a layer of SMAD1 control, with METTL14/IGF2BP1 stabilizing SMAD1 transcripts to drive osteogenesis and hypoxia-induced ALKBH5 demethylation enhancing SMAD1 translation to promote trophoblast invasion.","evidence":"MeRIP/m6A-seq, RIP, reporter assays, siRNA, and in vivo OVX and trophoblast knockdown models","pmids":["36319624","35724807"],"confidence":"Medium","gaps":["Which m6A sites on SMAD1 mRNA are functionally decisive not pinpointed","Single-lab findings per context"]},{"year":2022,"claim":"Revealed SMAD1 as a transcriptional repressor at chromatin, recruiting H3K27me3 and DNA methylation to silence SOX2 in opposition to SMAD3-driven activation, defining a reciprocal epigenetic axis.","evidence":"Expression profiling, ChIP for histone marks, DNA methylation assays, and in vivo tumor model","pmids":["35905726"],"confidence":"Medium","gaps":["Which chromatin-modifying enzymes SMAD1 recruits not identified","Generality of SMAD1 repressive function beyond SOX2 untested"]},{"year":2024,"claim":"Defined an essential physiological role for SMAD1 in cortical parvalbumin interneurons, where BMP2-SMAD1 signaling controls glutamatergic synapse and perineuronal net proteins to maintain excitation-inhibition balance, its loss causing epileptic seizures.","evidence":"PV-interneuron-specific Smad1 conditional knockout, electrophysiology, synaptic proteomics, IHC, and in vivo EEG","pmids":["38632412"],"confidence":"High","gaps":["Direct SMAD1 target genes among synapse/PNN proteins not enumerated","Whether other neuronal subtypes require SMAD1 untested"]},{"year":2024,"claim":"Showed high fluid shear stress suppresses endothelial SMAD1/5 via a KLF2-BMPER axis to enable outward vessel remodeling, integrating hemodynamic input into SMAD1 pathway control.","evidence":"High-FSS mouse model, endothelial BMPER conditional knockout, SMAD1/5 phosphorylation, and KLF2 reporter assays","pmids":["39196179"],"confidence":"Medium","gaps":["Direct effect of BMPER on SMAD1 vs SMAD5 not separated","Downstream SMAD1 transcriptional targets in remodeling not defined"]},{"year":null,"claim":"How the diverse upstream inputs (canonical BMP receptors, the TGFBR1-ACVR1 relay, Src, integrin/shear, ATM, calmodulin) are integrated quantitatively at SMAD1 to specify distinct transcriptional programs across tissues remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking phosphosite combinations to target-gene selection","Genome-wide SMAD1 cistrome across cell types incompletely defined","Structural basis of partner-directed activation vs repression unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,6,12,17,23,31]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[6,12,14]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,26]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[19]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,5,7,19,23,24]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,7]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,15,26,33]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,6,17,31]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[17,18,32]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[19]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[31]}],"complexes":[],"partners":["SMAD4","P300/CBP","HOXC-8","PU.1","RUNX2","CD44","PPM1A","YAP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q15797","full_name":"SMAD family member 1","aliases":["JV4-1","Mad-related protein 1","Mothers against decapentaplegic homolog 1","MAD homolog 1","Mothers against DPP homolog 1","Transforming growth factor-beta-signaling protein 1","BSP-1"],"length_aa":465,"mass_kda":52.3,"function":"Transcriptional modulator that plays a role in various cellular processes, including embryonic development, cell differentiation, and tissue homeostasis (PubMed:9335504). Upon BMP ligand binding to their receptors at the cell surface, is phosphorylated by activated type I BMP receptors (BMPRIs) and associates with SMAD4 to form a heteromeric complex which translocates into the nucleus acting as transcription factor (PubMed:33667543). In turn, the hetero-trimeric complex recognizes cis-regulatory elements containing Smad Binding Elements (SBEs) to modulate the outcome of the signaling network (PubMed:33667543). SMAD1/OAZ1/PSMB4 complex mediates the degradation of the CREBBP/EP300 repressor SNIP1. Positively regulates BMP4-induced expression of odontogenic development regulator MSX1 following IPO7-mediated nuclear import (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q15797/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SMAD1","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SMAD1","total_profiled":1310},"omim":[{"mim_id":"620997","title":"SEMAPHORIN 3G; SEMA3G","url":"https://www.omim.org/entry/620997"},{"mim_id":"620974","title":"ZINC FINGER PROTEIN 862; ZNF862","url":"https://www.omim.org/entry/620974"},{"mim_id":"620847","title":"BONE MORPHOGENETIC PROTEIN 8A; BMP8A","url":"https://www.omim.org/entry/620847"},{"mim_id":"620121","title":"IRON OVERLOAD, SUSCEPTIBILITY TO; IO","url":"https://www.omim.org/entry/620121"},{"mim_id":"619820","title":"ATONAL bHLH TRANSCRIPTION FACTOR 8; ATOH8","url":"https://www.omim.org/entry/619820"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SMAD1"},"hgnc":{"alias_symbol":["MADR1","JV4-1"],"prev_symbol":["MADH1"]},"alphafold":{"accession":"Q15797","domains":[{"cath_id":"3.90.520.10","chopping":"11-128","consensus_level":"high","plddt":93.0185,"start":11,"end":128},{"cath_id":"2.60.200.10","chopping":"261-453","consensus_level":"high","plddt":95.1713,"start":261,"end":453}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15797","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q15797-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q15797-F1-predicted_aligned_error_v6.png","plddt_mean":81.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SMAD1","jax_strain_url":"https://www.jax.org/strain/search?query=SMAD1"},"sequence":{"accession":"Q15797","fasta_url":"https://rest.uniprot.org/uniprotkb/Q15797.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q15797/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15797"}},"corpus_meta":[{"pmid":"8653785","id":"PMC_8653785","title":"MADR1, 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foundational paper replicated across many subsequent studies\",\n      \"pmids\": [\"8653785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SMAD1 interacts with the homeodomain transcription factor Hoxc-8 (identified by yeast two-hybrid, confirmed by pull-down and co-IP in COS-1 cells); purified SMAD1 inhibits Hoxc-8 binding to its DNA element (osteopontin promoter) in a concentration-dependent manner, thereby de-repressing BMP-induced gene transcription.\",\n      \"method\": \"Yeast two-hybrid screen, GST pull-down, co-immunoprecipitation, EMSA/gel-shift assay, luciferase reporter transfection\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (Y2H, pulldown, Co-IP, EMSA, reporter assay) in a single study\",\n      \"pmids\": [\"10224145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SMAD1 interacts with the transcriptional coactivators p300 and CBP both in vitro and in vivo; the C-terminal half of SMAD1 contains two interaction domains that bind the C-terminal region of p300/CBP; phosphorylation of SMAD1 enhances binding to CBP and further stimulates SMAD1-dependent transcription.\",\n      \"method\": \"In vitro binding assay, co-immunoprecipitation, transcription reporter assays, phosphorylation-binding correlation\",\n      \"journal\": \"Biochimica et Biophysica Acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal assays (in vitro binding, Co-IP, reporter) in a single study\",\n      \"pmids\": [\"10673036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The Ras/MEK pathway is partially required for TGF-β- and BMP-induced SMAD1 phosphorylation and transcriptional activity in intestinal epithelial cells; either dominant-negative Ras (RasN17) or the MEK inhibitor PD98059 significantly decreased BMP/TGF-β-induced SMAD1 phosphorylation.\",\n      \"method\": \"Stable inducible dominant-negative Ras expression, MEK inhibitor (PD98059), endogenous SMAD1 phosphorylation assay, luciferase reporter\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic (dominant-negative) plus pharmacological inhibitor approach with phosphorylation readout, single lab\",\n      \"pmids\": [\"10208426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Calmodulin directly binds to two conserved regions in SMAD1 and increases SMAD1 activity in Xenopus embryos; calmodulin binding inhibits subsequent ERK2-dependent linker phosphorylation of SMAD1, revealing cross-talk between Ca2+/calmodulin, RTK/ERK, and BMP-SMAD1 pathways.\",\n      \"method\": \"Binding assays (structure-function), Xenopus embryo gain/loss-of-function, ERK2 phosphorylation assay\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo embryo assay plus biochemical phosphorylation analysis, single lab, two orthogonal approaches\",\n      \"pmids\": [\"11007779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SANE (Smad1 Antagonistic Effector), a LEM-domain protein, binds to SMAD1/5 and to BMP type I receptors, inhibiting BMP-induced SMAD1 phosphorylation and blocking ligand-dependent nuclear translocation of SMAD1; a SANE mutant that cannot bind SMAD1 fails to inhibit BMP signaling.\",\n      \"method\": \"Co-immunoprecipitation, Xenopus embryo functional assays, mammalian bone-formation model, nuclear translocation assay, SANE-binding mutant analysis\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — reciprocal Co-IP, mutagenesis of binding interface, phosphorylation assay, nuclear localization, and in vivo rescue in two model systems\",\n      \"pmids\": [\"12393873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SMAD1 and GATA factors (GATA-1, -5, or -6) assemble together on the intronic BMP-response element (I-BRE) of the Smad7 gene in living cells; GATA-dependent co-occupancy renders I-BRE more responsive to low BMP concentrations than the promoter BRE that relies solely on SMAD1/SMAD4 binding.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), luciferase reporter assays, site-directed mutagenesis of Smad1/Smad4 binding sites\",\n      \"journal\": \"Molecular and Cellular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — ChIP in living cells plus mutagenesis and reporter assays, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"12944489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SMAD1 interacts with the cytoplasmic domain of CD44 (identified by yeast two-hybrid, confirmed by co-IP); full-length CD44 is required for BMP-7-induced SMAD1 phosphorylation and nuclear translocation—overexpression of a truncated CD44 abolished nuclear SMAD1 translocation—and disruption of extracellular hyaluronan-CD44 interactions (by hyaluronidase) inhibited BMP-7-mediated SMAD1 phosphorylation and SMAD4 nuclear translocation.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, nuclear translocation assay, luciferase reporter (SBE4-luc), hyaluronidase treatment\",\n      \"journal\": \"The Journal of Cell Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (Y2H, Co-IP, translocation, reporter) in single study\",\n      \"pmids\": [\"15452148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Interaction between SMAD1 and CHIP (an E3 ubiquitin ligase) was demonstrated by surface plasmon resonance, suggesting CHIP may mediate SMAD1 degradation.\",\n      \"method\": \"Surface plasmon resonance (SPR) binding assay\",\n      \"journal\": \"Colloids and Surfaces B: Biointerfaces\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single biochemical binding method only, no functional validation of degradation\",\n      \"pmids\": [\"15708501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In cardiomyocytes, SMAD1 signaling mediates BMP2-induced protection against apoptosis during hypoxia-reoxygenation via upregulation of Bcl-xL and β-catenin; transgenic mice with cardiac-specific Smad1 overexpression showed significantly smaller myocardial infarctions and fewer apoptotic cardiomyocyte deaths after ischemia-reperfusion injury.\",\n      \"method\": \"Cardiac-specific transgenic mouse model, adenoviral gene transfer, TUNEL/DNA ladder apoptosis assay, western blot for Bcl-xL, β-catenin, and caspase-3\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo transgenic model combined with in vitro gain-of-function and defined molecular mediators (Bcl-xL), single lab\",\n      \"pmids\": [\"15911698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Angiotensin II activates SMAD1 through a Src kinase-dependent mechanism in mesangial cells: Ang II induces phosphorylation of Src and SMAD1; Src inhibitor PP2, dominant-negative Src, or Src siRNA all reduce SMAD1 phosphorylation and type IV collagen synthesis.\",\n      \"method\": \"Pharmacological Src inhibitor (PP2), dominant-negative Src overexpression, Src siRNA knockdown, western blot for p-Src and p-Smad1, collagen IV assay\",\n      \"journal\": \"Laboratory Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — three independent approaches (inhibitor, dominant-negative, siRNA) all converging on Src→SMAD1→ColIV axis\",\n      \"pmids\": [\"16767106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Nanog physically interacts with SMAD1 and blocks BMP-induced mesoderm differentiation of mouse ES cells by interfering with the recruitment of coactivators to active Smad transcriptional complexes.\",\n      \"method\": \"Co-immunoprecipitation, ES cell differentiation assays, transcriptional reporter assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences USA\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional differentiation assay, single lab\",\n      \"pmids\": [\"16801560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In SSc fibroblasts, SMAD1 directly binds and activates the CCN2 (CTGF) gene promoter; siRNA-mediated depletion of SMAD1 normalizes CCN2 and collagen production; imatinib mesylate reverses Smad1 pathway activation via blockade of c-Abl.\",\n      \"method\": \"In vitro and in vivo DNA binding assays, siRNA knockdown, luciferase reporter assay, western blot, immunohistochemistry\",\n      \"journal\": \"Arthritis and Rheumatism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct DNA binding assay plus siRNA functional validation plus pharmacological pathway positioning, single lab with multiple methods\",\n      \"pmids\": [\"18668566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Linker-region sequential phosphorylation of SMAD1 by MAPK and then GSK3 negatively regulates BMP-SMAD1 signaling by directing SMAD1 to the centrosomal region for polyubiquitination and proteasomal degradation; Wnt signaling, via GSK3 inhibition, prolongs the BMP-SMAD1 signal.\",\n      \"method\": \"Xenopus embryo epistasis experiments, phosphorylation-resistant SMAD1 mutants, proteasome inhibitor assays, centrosome fractionation (reviewed/synthesized from multiple primary papers)\",\n      \"journal\": \"Current Opinion in Genetics & Development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — review synthesizing multiple primary papers using phosphorylation mutants, centrosomal fractionation, and epistasis; not a primary data paper itself but citing well-established results\",\n      \"pmids\": [\"18590818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structure of the SMAD1 MH1 domain bound to a palindromic Smad binding element (SBE) reveals that the N-terminal helix 1 of SMAD1 is dislodged from its intramolecular binding site and adopts a domain-swapped arrangement compared to SMAD3, causing helix 2 to kink away and disabling key DNA backbone contacts; this confers lower overall DNA affinity but increased cooperativity on palindromic elements.\",\n      \"method\": \"X-ray crystallography, thermal melting analysis, DNA binding assays\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional validation by thermal melting and quantitative DNA binding assays\",\n      \"pmids\": [\"20147459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In endothelial cells, SnoN directly binds ALK1 at the plasma membrane and facilitates the interaction between ALK1 and SMAD1/5, enhancing SMAD1/5 phosphorylation; disruption of SnoN-SMAD interaction impairs SMAD1/5 activation, upregulates SMAD2/3 activity, and causes defective angiogenesis and arteriovenous malformations.\",\n      \"method\": \"Co-immunoprecipitation, direct binding assay (SnoN-ALK1 interaction), in vivo embryonic angiogenesis phenotype, SMAD1/5 phosphorylation assay\",\n      \"journal\": \"The Journal of Cell Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct binding demonstrated, phosphorylation assay, in vivo phenotypic rescue/mutant analysis, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"24019535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Endoglin promotes TGF-β/SMAD1 signaling in SSc fibroblasts: endoglin is constitutively found in complexes with ALK1, and siRNA depletion of endoglin inhibits SMAD1 phosphorylation without affecting pSMAD2/3, reducing collagen and CCN2 levels.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, western blot for pSMAD1\",\n      \"journal\": \"Journal of Cellular Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus siRNA functional validation, single lab\",\n      \"pmids\": [\"21344387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In the developing lung, SMAD1 (but not SMAD5) in epithelial cells transcriptionally activates Wnt inhibitory factor 1 (Wif1), identified by combined cDNA microarray and ChIP-chip; loss of SMAD1-dependent Wif1 activation results in increased Wnt/β-catenin signaling and specific fetal lung abnormalities.\",\n      \"method\": \"Conditional knockout mice (lung epithelial-specific Smad1 or Smad5 deletion), cDNA microarray, ChIP-chip, Wnt/β-catenin reporter assays\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vivo conditional KO combined with genome-wide ChIP and transcriptomics identifying direct target gene, replicated at multiple levels\",\n      \"pmids\": [\"21270055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Smad1 plays a biphasic role in hematopoiesis: early Smad1 expression is required for hemangioblast commitment from mesoderm, while later Smad1 expression in FLK1+ mesoderm restricts expansion of hematopoietic progenitors; depletion of Smad1 after hemangioblast commitment expands hematopoietic progenitors and correlates with increased nuclear SMAD2 activity, indicating cross-regulation between BMP and TGF-β SMAD pathways.\",\n      \"method\": \"Conditional/temporal siRNA knockdown in embryoid body cultures, embryonic stem cell differentiation, SMAD2 nuclear activity assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional knockdown with temporal control and mechanistic readout of cross-pathway regulation, single lab\",\n      \"pmids\": [\"21515822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"On genotoxic stress, ATM kinase phosphorylates BMP-activated SMAD1 in the nucleus at Ser239; this disrupts SMAD1 interaction with phosphatase PPM1A (leading to enhanced SMAD1 activation), and activated SMAD1 then interacts with p53 to inhibit MDM2-mediated p53 ubiquitination and degradation.\",\n      \"method\": \"ATM kinase assay, S239 phosphorylation site mutagenesis, Co-IP (SMAD1-PPM1A, SMAD1-p53), ubiquitination assay, cell proliferation and survival assays, clinical sample analysis\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct kinase assay, site mutagenesis, co-IP of multiple complexes, ubiquitination assay, all in single study\",\n      \"pmids\": [\"22588298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In macrophages, BMP-6-induced IL-1β expression requires a physical interaction between SMAD1 and the transcription factor PU.1; both the canonical SMAD pathway and non-SMAD ERK/JNK pathways are required, and cross-talk between them is mediated through PU.1-SMAD1 interaction.\",\n      \"method\": \"Co-immunoprecipitation (PU.1-SMAD1), siRNA knockdown, ERK/JNK pathway inhibitors, luciferase reporter\",\n      \"journal\": \"Molecular Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus knockdown plus inhibitor studies, single lab\",\n      \"pmids\": [\"21571370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In mesangial cells, scleraxis physically associates with E12 to bind the SMA promoter E-box; scleraxis also induces BMP4 secretion, which activates SMAD1 to induce smooth muscle α-actin (SMA); Id1, induced by extended AGE treatment, dislodges scleraxis from the SMA promoter, thereby modulating the BMP4-SMAD1-SMA pathway.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation, promoter binding assays, overexpression/knockdown, ELISA for BMP4\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ChIP plus functional promoter assays, single lab\",\n      \"pmids\": [\"22474292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In endothelial cells, oscillatory shear stress (OSS) induces sustained BMPRIB-αvβ3 integrin association; the intracytoplasmic kinase domain of BMPRII mediates this interaction and subsequently activates the Shc/FAK/ERK cascade, leading to SMAD1/5 activation; SMAD1/5 then associates with and activates Runx2, leading to mTOR/p70S6K activation and EC proliferation.\",\n      \"method\": \"Co-immunoprecipitation, in situ proximity ligation assay, shRNA knockdown of SMAD5, kinase domain deletion analysis, in vivo intra-arterial lentiviral injection\",\n      \"journal\": \"Journal of Thrombosis and Haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus proximity ligation plus in vivo knockdown with BrdU proliferation readout, single lab\",\n      \"pmids\": [\"23387849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"KSHV LANA protein interacts with SMAD1 (identified as novel binding partner), sustains BMP-activated pSMAD1 in the nucleus, and enhances SMAD1 loading on Id gene promoters, resulting in Id upregulation that drives KSHV-induced oncogenic transformation; genetic/chemical inhibition of BMP-SMAD1-Id pathway blocks the oncogenic phenotype.\",\n      \"method\": \"Co-immunoprecipitation (LANA-SMAD1), ChIP on Id promoters, genetic inhibition (siRNA), chemical inhibitor, in vivo tumor xenograft\",\n      \"journal\": \"PLoS Pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ChIP plus functional in vivo oncogenesis assay, single lab\",\n      \"pmids\": [\"25010525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"YAP (yes-associated protein) physically interacts with SMAD1 in neural stem cells and is required for BMP2-induced stabilization and nuclear accumulation of SMAD1; in YAP-deficient NSCs, SMAD1 expression is reduced and astrocytic differentiation is impaired; SMAD1 re-expression in YAP-deficient NSCs partially rescues astrocytic differentiation.\",\n      \"method\": \"Conditional knockout mice (Yap-nestin, Yap-GFAP), co-immunoprecipitation, western blot, rescue by SMAD1 re-expression\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo conditional KO plus Co-IP plus molecular rescue experiment, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27381227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Erythropoietin and erythroferrone suppress hepcidin transcription by targeting SMAD1/5 signaling: EPO treatment reduces liver SMAD1/5 phosphorylation in parallel with hepcidin mRNA reduction in control mice, but fails to suppress hepcidin in hepatocyte-specific Smad1/Smad5 double-knockout mice or SMAD1/5 knockdown cells; SMAD1 and SMAD5 have overlapping (redundant) functions in hepcidin regulation.\",\n      \"method\": \"Hepatocyte-specific conditional double-knockout mice, EPO/erythroferrone treatment, siRNA knockdown, primary hepatocyte cultures, SMAD1/5 phosphorylation assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo conditional KO plus in vitro siRNA plus primary hepatocyte rescue studies, multiple orthogonal approaches, replicated at multiple levels\",\n      \"pmids\": [\"28438754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TGF-β induces SMAD1/5 phosphorylation through a novel two-receptor mechanism: TGFBR1 phosphorylates and activates ACVR1 (a second type I receptor), which then phosphorylates SMAD1/5; approximately a quarter of the TGF-β-induced transcriptome depends on SMAD1/5 signaling; TGF-β-induced epithelial-to-mesenchymal transition requires both SMAD3 and SMAD1/5 pathways, with SMAD1/5 being essential for ID1 induction.\",\n      \"method\": \"Receptor knockdown/knockout, phosphorylation assays, transcriptome analysis (RNA-seq), EMT functional assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — receptor-specific knockouts establishing pathway order, phosphorylation assays, genome-wide transcriptomics, and functional EMT assay; multiple orthogonal methods in single study\",\n      \"pmids\": [\"29376829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SMAD1 is phosphorylated at Ser239 by ATM in the DNA damage response, and this disrupts SMAD1 interaction with phosphatase PPM1A; conversely, DUSP5 (a dual-specificity phosphatase) promotes osteogenic differentiation by competitively binding SCP1/2 (SMAD1 phosphatases) via its linker region, thereby preventing SCP1/2-mediated SMAD1 dephosphorylation and maintaining SMAD1 activation.\",\n      \"method\": \"Co-immunoprecipitation (DUSP5-SCP1/2-SMAD1), domain mapping, in vitro dephosphorylation assays, osteogenic differentiation assays, OVX mouse model rescue by Dusp5 overexpression\",\n      \"journal\": \"Stem Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with domain mapping and functional rescue in vivo, single lab\",\n      \"pmids\": [\"34169608\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Sema4C (semaphorin 4C) reverse signaling co-immunoprecipitates with TGFBRII and BMPR1, eliciting non-conventional TGF-β/BMP receptor activation and selective SMAD1/5 phosphorylation leading to increased ID1/3 expression and invasive gene reprogramming in cancer cells.\",\n      \"method\": \"Co-immunoprecipitation (Sema4C-TGFBRII-BMPR1), SMAD1/5 phosphorylation assay, gene expression profiling, in vivo metastasis assay\",\n      \"journal\": \"Science Signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus phosphorylation assay plus in vivo metastasis data, single lab\",\n      \"pmids\": [\"31431542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"METTL14-mediated m6A methylation of SMAD1 mRNA promotes its stability; IGF2BP1 is the m6A reader for SMAD1 transcripts; knockdown of METTL14 reduces m6A modification of SMAD1, decreasing SMAD1 protein levels and suppressing osteogenic differentiation.\",\n      \"method\": \"RIP (RNA immunoprecipitation), MeRIP (m6A-seq), luciferase reporter assay, siRNA knockdown, OVX mouse model\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MeRIP plus RIP plus reporter assay establishing m6A-IGF2BP1-SMAD1 axis, single lab\",\n      \"pmids\": [\"36319624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Hypoxia-induced ALKBH5 demethylase translocates from nucleus to cytoplasm and demethylates m6A-modified SMAD1 (and SMAD5) mRNAs, enhancing their translation and promoting trophoblast invasion via upregulation of MMP9 and ITGA1.\",\n      \"method\": \"m6A-seq (m6A-RIP), ALKBH5 subcellular fractionation, knockdown in mouse placenta (trophoblast-specific), western blot for SMAD1/5 protein\",\n      \"journal\": \"Biochimica et Biophysica Acta – Molecular Cell Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — m6A-seq plus in vivo trophoblast knockdown with functional phenotype, single lab\",\n      \"pmids\": [\"35724807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SMAD1 mediates BMP-dependent repression of SOX2 by recruiting histone H3K27me3 and DNA methylation at the SOX2 promoter; conversely, TGF-β/activin activates SOX2 through SMAD3-dependent H3K4me3 recruitment, defining a reciprocal epigenetic regulatory axis controlling anchorage-independent survival.\",\n      \"method\": \"Gene expression profiling, ChIP (H3K27me3, H3K4me3), DNA methylation assay, in vivo intraperitoneal tumor model\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for histone marks plus DNA methylation analysis plus in vivo tumor assay, single lab\",\n      \"pmids\": [\"35905726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In adult mouse neocortex, BMP2 acts on parvalbumin (PV) interneurons via SMAD1 to control glutamatergic synapse proteins and perineuronal net components; PV-interneuron-specific disruption of BMP2-SMAD1 signaling reduces glutamatergic innervation of PV cells, impairs perineuronal net development and PV cell excitability, disrupts cortical excitation-inhibition balance, and causes spontaneous epileptic seizures.\",\n      \"method\": \"PV interneuron-specific conditional knockout of SMAD1, electrophysiology, immunohistochemistry, proteomics of synapse proteins, in vivo EEG for seizure detection\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO with electrophysiology, molecular (proteomics, IHC), and in vivo seizure phenotype; multiple orthogonal methods, published in high-impact journal\",\n      \"pmids\": [\"38632412\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"High fluid shear stress suppresses endothelial SMAD1/5 signaling via a KLF2-BMPER axis: high FSS elevates KLF2, which transcriptionally induces BMPER (a BMP pathway inhibitor), thereby de-inhibiting AKT and facilitating outward vessel remodeling; endothelial BMPER deletion impairs blood flow recovery.\",\n      \"method\": \"Surgically induced high-FSS mouse model, endothelial BMPER conditional knockout, SMAD1/5 phosphorylation assay, KLF2 overexpression/knockdown, luciferase reporter\",\n      \"journal\": \"Nature Cardiovascular Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo mouse model plus conditional KO plus mechanistic reporter assay, single lab\",\n      \"pmids\": [\"39196179\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SMAD1 is a receptor-activated transcription factor that is phosphorylated at its C-terminal SSXS motif by BMP type I receptors (primarily ALK1/2/3/6) and, via a novel TGFBR1→ACVR1 relay, also by TGF-β stimulation; once phosphorylated, SMAD1 accumulates in the nucleus where it binds DNA through a distinctive domain-swapped MH1 conformation, recruits co-activators (p300/CBP), and cooperates with cell-type-specific DNA-binding partners (Hoxc-8, GATA factors, PU.1, Runx2) to drive transcriptional programs controlling bone formation, hematopoiesis, angiogenesis, iron homeostasis, neuronal excitation-inhibition balance, and organ development; SMAD1 activity is negatively modulated by sequential MAPK and GSK3 linker phosphorylations that direct it to centrosomal proteasomal degradation, by calmodulin binding, by phosphatases SCP1/2 (counteracted by DUSP5), and by m6A mRNA methylation/demethylation; it forms complexes with Nanog, SnoN (at ALK1), SANE, CD44 (cytoplasmic domain), KSHV LANA, and YAP, and integrates upstream inputs from Src, Ras/MEK, ATM (DNA damage), and fluid shear stress.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SMAD1 is a receptor-activated transcription factor that transduces BMP signals into nuclear transcriptional programs governing skeletal, hematopoietic, vascular, neuronal, and iron-homeostatic processes [#0, #25, #32]. BMP2 stimulation, but not TGF-\\u03b2 or activin, rapidly induces SMAD1 phosphorylation that is required for activity and drives its nuclear accumulation [#0]; a parallel non-canonical route operates downstream of TGF-\\u03b2, in which TGFBR1 phosphorylates and activates ACVR1, which in turn phosphorylates SMAD1/5, accounting for a substantial fraction of the TGF-\\u03b2 transcriptome and being essential for ID1 induction and EMT [#26]. Once activated, SMAD1 engages DNA through an MH1 domain whose N-terminal helix adopts a domain-swapped conformation that lowers intrinsic affinity but increases cooperativity on palindromic Smad binding elements [#14], and it recruits the coactivators p300/CBP in a phosphorylation-enhanced manner [#2]. Transcriptional specificity is achieved through cell-type-restricted DNA-binding partners and cofactors\\u2014Hoxc-8, GATA factors, PU.1, and Runx2\\u2014that direct SMAD1 to context-specific target genes [#1, #6, #20, #22], and SMAD1 both activates targets such as CCN2/CTGF, Wif1, and Id genes and represses others such as SOX2 via H3K27me3 and DNA methylation [#12, #17, #23, #31]. Signal output is tuned by multiple negative regulators: sequential MAPK then GSK3 linker phosphorylation routes SMAD1 to centrosomal proteasomal degradation [#13], calmodulin binding modulates linker phosphorylation [#4], and phosphatase balance (PPM1A, SCP1/2 counteracted by DUSP5) and m6A mRNA methylation/demethylation (METTL14/IGF2BP1, ALKBH5) further set SMAD1 levels [#19, #27, #29, #30]. Upstream, SMAD1 activation is gated at the receptor and membrane level by CD44, SnoN, endoglin, SANE, and shear-stress\\u2013responsive KLF2-BMPER and integrin inputs [#5, #7, #15, #16, #33], and SMAD1 is integrated with the DNA-damage response through ATM-mediated Ser239 phosphorylation that stabilizes p53 [#19]. Physiologically, SMAD1/5 redundantly control hepcidin-mediated iron regulation [#25], and SMAD1 in parvalbumin interneurons maintains cortical excitation-inhibition balance, its loss causing epileptic seizures [#32].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established SMAD1 as a dedicated, phosphorylation-dependent intracellular effector of BMP receptor signaling, distinguishing it from TGF-\\u03b2/activin responses.\",\n      \"evidence\": \"Phosphorylation assays, loss-of-function point mutagenesis, and subcellular fractionation comparing BMP2 vs TGF-\\u03b2 vs activin\",\n      \"pmids\": [\"8653785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the receptor kinase responsible\", \"Did not map the phosphoacceptor SSXS motif residues directly\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined how phosphorylated SMAD1 achieves transcriptional output by recruiting p300/CBP coactivators and by de-repressing Hoxc-8-occupied promoters, giving the first mechanistic basis for SMAD1-driven gene activation.\",\n      \"evidence\": \"Yeast two-hybrid, GST pull-down, Co-IP, EMSA, and reporter assays for Hoxc-8 and p300/CBP interactions\",\n      \"pmids\": [\"10224145\", \"10673036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genome-wide target scope not addressed\", \"Stoichiometry of SMAD1-coactivator-partner complexes unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Revealed that SMAD1 activation is not purely receptor-driven but is modulated by RTK-linked Ras/MEK signaling, opening the concept of cross-pathway input on SMAD1 phosphorylation.\",\n      \"evidence\": \"Dominant-negative Ras and MEK inhibitor PD98059 with endogenous phosphorylation and reporter readouts\",\n      \"pmids\": [\"10208426\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MEK acts on the C-terminal or linker phosphosites not distinguished\", \"Single cell-type context (intestinal epithelium)\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showed calmodulin directly binds SMAD1 and antagonizes ERK-dependent linker phosphorylation, integrating Ca2+ signaling into the regulation of SMAD1 activity.\",\n      \"evidence\": \"Structure-function binding assays, Xenopus embryo gain/loss-of-function, and ERK2 phosphorylation assays\",\n      \"pmids\": [\"11007779\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological Ca2+ stimulus that engages this in mammalian cells not defined\", \"Mechanism of how calmodulin occludes linker sites structurally unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified SANE as a receptor-level inhibitor that binds both SMAD1/5 and BMP type I receptors to block phosphorylation and nuclear translocation, defining negative control upstream of SMAD1.\",\n      \"evidence\": \"Reciprocal Co-IP, binding-mutant analysis, nuclear translocation, and in vivo Xenopus/bone-formation rescue\",\n      \"pmids\": [\"12393873\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous tissue contexts where SANE limits BMP signaling not mapped\", \"Structural basis of dual receptor/SMAD binding unresolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated that combinatorial co-occupancy with GATA factors sensitizes SMAD1 target elements to low BMP doses, showing how partner transcription factors tune the quantitative BMP response.\",\n      \"evidence\": \"ChIP in living cells plus binding-site mutagenesis and reporter assays on the Smad7 I-BRE\",\n      \"pmids\": [\"12944489\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality across other BMP targets not tested\", \"Direct SMAD1-GATA physical contact not structurally defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Connected extracellular matrix sensing to SMAD1 activation by showing the CD44 cytoplasmic domain and hyaluronan-CD44 engagement are required for BMP-7-induced SMAD1 phosphorylation and nuclear translocation.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, nuclear translocation, reporter assays, and hyaluronidase treatment\",\n      \"pmids\": [\"15452148\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CD44 couples mechanistically to the receptor complex unclear\", \"Whether CD44 dependence is cell-type-specific not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Provided first evidence for E3-ligase-mediated turnover of SMAD1 via CHIP binding, pointing toward ubiquitin-dependent control of SMAD1 abundance.\",\n      \"evidence\": \"Surface plasmon resonance binding assay only\",\n      \"pmids\": [\"15708501\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single binding method without functional degradation assay\", \"No demonstration of in-cell ubiquitination or turnover\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Established a cytoprotective transcriptional role for SMAD1 in cardiomyocytes by linking it to Bcl-xL/\\u03b2-catenin upregulation and reduced ischemic apoptosis.\",\n      \"evidence\": \"Cardiac-specific transgenic mice, adenoviral transfer, TUNEL apoptosis, and western blots for survival mediators\",\n      \"pmids\": [\"15911698\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SMAD1 directly binds Bcl-xL/\\u03b2-catenin promoters not shown\", \"Loss-of-function endogenous requirement not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Extended non-BMP activation of SMAD1 by showing angiotensin II drives SMAD1 phosphorylation through Src kinase to promote collagen IV synthesis, linking SMAD1 to fibrotic signaling.\",\n      \"evidence\": \"Src inhibitor PP2, dominant-negative Src, and Src siRNA with p-SMAD1 and collagen IV readouts in mesangial cells\",\n      \"pmids\": [\"16767106\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Src acts on receptor or directly on SMAD1 not resolved\", \"Phosphosite targeted by Src not mapped\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed that pluripotency factor Nanog restrains BMP-driven mesoderm differentiation by binding SMAD1 and blocking coactivator recruitment, defining a stem-cell-specific brake on SMAD1 output.\",\n      \"evidence\": \"Co-IP, ES cell differentiation, and reporter assays\",\n      \"pmids\": [\"16801560\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct competition with p300/CBP not biochemically demonstrated\", \"Interaction interface unmapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined the linker-phosphorylation code (MAPK then GSK3) that targets SMAD1 to centrosomal proteasomal degradation and showed Wnt prolongs BMP signaling by inhibiting GSK3, establishing duration control of SMAD1 signaling.\",\n      \"evidence\": \"Review synthesizing Xenopus epistasis, phospho-resistant mutants, proteasome inhibition, and centrosome fractionation\",\n      \"pmids\": [\"18590818\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Review rather than primary data\", \"Identity of the centrosomal E3 ligase not specified here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided the structural explanation for SMAD1's distinctive DNA-binding behavior, showing a domain-swapped MH1 conformation that lowers affinity but raises cooperativity on palindromic elements relative to SMAD3.\",\n      \"evidence\": \"X-ray crystallography of MH1-SBE complex with thermal melting and DNA binding assays\",\n      \"pmids\": [\"20147459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length SMAD1 or partner-bound complexes not solved\", \"Functional consequence in cells of cooperativity not directly tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified SnoN and endoglin as endothelial receptor-complex factors that selectively promote SMAD1/5 activation at ALK1 and balance it against SMAD2/3, linking SMAD1 to angiogenesis and fibrosis.\",\n      \"evidence\": \"Co-IP, direct binding assays, siRNA, SMAD1/5 phosphorylation, and in vivo angiogenesis phenotypes\",\n      \"pmids\": [\"24019535\", \"21344387\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SnoN/endoglin discriminate SMAD1/5 from SMAD2/3 mechanistically unresolved\", \"Quantitative contribution to AVM pathology incomplete\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Used conditional knockouts to assign SMAD1 non-redundant developmental roles, including direct Wif1 activation in lung epithelium and biphasic control of hematopoietic progenitor expansion with reciprocal SMAD2 cross-regulation.\",\n      \"evidence\": \"Lung- and mesoderm-targeted conditional/temporal Smad1 depletion, microarray, ChIP-chip, and Wnt reporter assays\",\n      \"pmids\": [\"21270055\", \"21515822\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why SMAD1 but not SMAD5 activates Wif1 not explained\", \"Cross-pathway switch mechanism with SMAD2 incompletely defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Placed SMAD1 within the DNA-damage response by showing ATM phosphorylates it at Ser239, disrupting PPM1A binding and enabling SMAD1 to stabilize p53 against MDM2-mediated degradation.\",\n      \"evidence\": \"ATM kinase assay, S239 mutagenesis, Co-IP of SMAD1-PPM1A and SMAD1-p53, ubiquitination and survival assays\",\n      \"pmids\": [\"22588298\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether nuclear SMAD1 directly contacts MDM2 or acts via p53 only unclear\", \"Generality across genotoxic stresses not fully tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Expanded the partner repertoire to PU.1 and scleraxis/E12, showing SMAD1 cooperates with lineage transcription factors and integrates non-SMAD ERK/JNK input to drive context-specific genes (IL-1\\u03b2, SMA).\",\n      \"evidence\": \"Co-IP, ChIP, promoter assays, knockdown, and pathway inhibitors in macrophages and mesangial cells\",\n      \"pmids\": [\"21571370\", \"22474292\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct co-binding on endogenous promoters not structurally resolved\", \"Single-lab, single-context findings\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated mechanotransduction into SMAD1/5 via oscillatory shear stress through BMPRIB-integrin association and a Shc/FAK/ERK cascade feeding into SMAD1/5-Runx2-mTOR-driven endothelial proliferation.\",\n      \"evidence\": \"Co-IP, proximity ligation assay, shRNA, kinase-domain deletion, and in vivo lentiviral injection\",\n      \"pmids\": [\"23387849\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SMAD1-Runx2 contact not biochemically isolated here\", \"Relative contribution of SMAD1 vs SMAD5 not separated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified KSHV LANA as a viral hijacker of SMAD1 that sustains nuclear pSMAD1 and enhances loading on Id promoters to drive oncogenic transformation, demonstrating disease exploitation of the BMP-SMAD1-Id axis.\",\n      \"evidence\": \"Co-IP, ChIP on Id promoters, siRNA/chemical inhibition, and in vivo xenograft\",\n      \"pmids\": [\"25010525\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"LANA-SMAD1 binding interface unmapped\", \"Whether LANA blocks SMAD1 degradation or phosphatase access unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed YAP physically stabilizes SMAD1 and is required for its BMP2-induced nuclear accumulation and astrocytic differentiation of neural stem cells, linking Hippo pathway output to SMAD1 protein levels.\",\n      \"evidence\": \"Yap conditional knockouts, Co-IP, western blot, and SMAD1 re-expression rescue\",\n      \"pmids\": [\"27381227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of YAP-mediated stabilization (transcriptional vs post-translational) not fully separated\", \"Direct binding interface unmapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established SMAD1/5 as the redundant transcriptional node through which erythropoietin and erythroferrone suppress hepcidin, placing SMAD1 at the center of systemic iron homeostasis.\",\n      \"evidence\": \"Hepatocyte-specific Smad1/Smad5 double-knockout mice, EPO/erythroferrone treatment, siRNA, and primary hepatocyte assays\",\n      \"pmids\": [\"28438754\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How erythroferrone signal reaches SMAD1/5 at the receptor not fully defined\", \"Individual SMAD1 vs SMAD5 contribution masked by redundancy\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovered a non-canonical TGFBR1\\u2192ACVR1 relay that activates SMAD1/5 under TGF-\\u03b2, revealing that a major share of TGF-\\u03b2 transcriptional and EMT output is SMAD1/5-dependent.\",\n      \"evidence\": \"Receptor knockdown/knockout, phosphorylation assays, RNA-seq, and EMT functional assays\",\n      \"pmids\": [\"29376829\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants of when TGF-\\u03b2 engages this relay vs SMAD2/3-only unclear\", \"ACVR1 ligand-independence in this context not fully resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined phosphatase-level control of SMAD1, showing DUSP5 sustains SMAD1 activation by competitively sequestering SCP1/2 to promote osteogenic differentiation.\",\n      \"evidence\": \"Co-IP with domain mapping, in vitro dephosphorylation assays, osteogenic differentiation, and OVX mouse rescue\",\n      \"pmids\": [\"34169608\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SCP1/2 dephosphorylation site on SMAD1 not mapped here\", \"Single-lab in vivo model\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established m6A mRNA modification as a layer of SMAD1 control, with METTL14/IGF2BP1 stabilizing SMAD1 transcripts to drive osteogenesis and hypoxia-induced ALKBH5 demethylation enhancing SMAD1 translation to promote trophoblast invasion.\",\n      \"evidence\": \"MeRIP/m6A-seq, RIP, reporter assays, siRNA, and in vivo OVX and trophoblast knockdown models\",\n      \"pmids\": [\"36319624\", \"35724807\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which m6A sites on SMAD1 mRNA are functionally decisive not pinpointed\", \"Single-lab findings per context\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed SMAD1 as a transcriptional repressor at chromatin, recruiting H3K27me3 and DNA methylation to silence SOX2 in opposition to SMAD3-driven activation, defining a reciprocal epigenetic axis.\",\n      \"evidence\": \"Expression profiling, ChIP for histone marks, DNA methylation assays, and in vivo tumor model\",\n      \"pmids\": [\"35905726\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which chromatin-modifying enzymes SMAD1 recruits not identified\", \"Generality of SMAD1 repressive function beyond SOX2 untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined an essential physiological role for SMAD1 in cortical parvalbumin interneurons, where BMP2-SMAD1 signaling controls glutamatergic synapse and perineuronal net proteins to maintain excitation-inhibition balance, its loss causing epileptic seizures.\",\n      \"evidence\": \"PV-interneuron-specific Smad1 conditional knockout, electrophysiology, synaptic proteomics, IHC, and in vivo EEG\",\n      \"pmids\": [\"38632412\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SMAD1 target genes among synapse/PNN proteins not enumerated\", \"Whether other neuronal subtypes require SMAD1 untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed high fluid shear stress suppresses endothelial SMAD1/5 via a KLF2-BMPER axis to enable outward vessel remodeling, integrating hemodynamic input into SMAD1 pathway control.\",\n      \"evidence\": \"High-FSS mouse model, endothelial BMPER conditional knockout, SMAD1/5 phosphorylation, and KLF2 reporter assays\",\n      \"pmids\": [\"39196179\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct effect of BMPER on SMAD1 vs SMAD5 not separated\", \"Downstream SMAD1 transcriptional targets in remodeling not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the diverse upstream inputs (canonical BMP receptors, the TGFBR1-ACVR1 relay, Src, integrin/shear, ATM, calmodulin) are integrated quantitatively at SMAD1 to specify distinct transcriptional programs across tissues remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking phosphosite combinations to target-gene selection\", \"Genome-wide SMAD1 cistrome across cell types incompletely defined\", \"Structural basis of partner-directed activation vs repression unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 6, 12, 17, 23, 31]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [6, 12, 14]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 26]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 5, 7, 19, 23, 24]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 15, 26, 33]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 6, 17, 31]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [17, 18, 32]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [31]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SMAD4\", \"p300/CBP\", \"Hoxc-8\", \"PU.1\", \"Runx2\", \"CD44\", \"PPM1A\", \"YAP\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}