{"gene":"TGFBR1","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2003,"finding":"ALK5 (TGFBR1) is required for TGFβ-induced ALK1 signaling in endothelial cells: ALK5 mediates TGFβ-dependent recruitment of ALK1 into a TGFβ receptor complex, and ALK5 kinase activity is required for optimal ALK1 activation. ALK1 in turn directly antagonizes ALK5/Smad2/3 signaling.","method":"Endothelial cells lacking ALK5 (genetic KO), reporter assays, Co-IP/complex formation studies, kinase activity assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional studies with ALK5-null cells and multiple orthogonal methods (Co-IP, reporter assays, migration/proliferation readouts), replicated in subsequent studies","pmids":["14580334"],"is_preprint":false},{"year":1999,"finding":"TGFβ1-induced epithelial-to-mesenchymal transition (EMT) in mammary epithelial cells is mediated specifically by TGFBR1/ALK5 and downstream Smad2/Smad3/Smad4. Constitutively active ALK5 alone at high levels drives full EMT, while low ALK5 activity combined with Smad2+Smad4 or Smad3+Smad4 cooperatively induces EMT.","method":"Adenoviral expression of constitutively active ALK5, dominant-negative constructs, Smad co-transfection, actin cytoskeleton reorganization and E-cadherin/β-catenin relocalization as readouts","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (CA-ALK5 adenovirus, Smad co-expression, multiple phenotypic readouts), replicated across multiple studies","pmids":["10574705"],"is_preprint":false},{"year":2004,"finding":"Palatal fusion driven by TGFβ3 requires ALK5/TGFBR1 signaling through the Smad2-dependent pathway. Activation of ALK5 in Tgf-beta3-null palatal epithelium rescues fusion; inactivation of ALK5 in wild-type prevents fusion. A Smad-signaling-deficient ALK5 mutant (kinase-active but Smad-unable) cannot rescue fusion, establishing that Smad-dependent signaling downstream of ALK5 is required.","method":"Conditional genetic rescue (activated/kinase-dead ALK5 in Tgf-beta3 KO), Smad2 phosphorylation assays, palatal explant culture","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis established by genetic rescue with domain-specific mutants, multiple independent conditions tested","pmids":["14729481"],"is_preprint":false},{"year":2005,"finding":"TGFBR1 mutations associated with Loeys-Dietz syndrome (a connective tissue disorder with cardiovascular, craniofacial and skeletal manifestations) paradoxically result in increased TGFβ signaling in patient tissues (elevated collagen, CTGF, and nuclear phospho-Smad2), despite selected mutant alleles being unable to support TGFβ signal propagation in vitro.","method":"Patient-derived cells and tissues; immunostaining for phospho-Smad2, collagen, CTGF; TGFβ signaling kinetics assays","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct biochemical evidence in patient-derived tissues with multiple markers across 10 families","pmids":["15731757"],"is_preprint":false},{"year":2005,"finding":"ALK5 (TGFBR1) and Smad4 are required for TGFβ1-induced endothelial permeability increase and actin stress fiber formation with MLC and MYPT1 phosphorylation. ALK1 is not involved in this pathway.","method":"siRNA depletion of ALK5 or Smad4 in endothelial cells, pharmacological ALK5 inhibition (SB431542), permeability assay, immunofluorescence","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown and pharmacological inhibition with defined phenotypic readout, single lab","pmids":["16004987"],"is_preprint":false},{"year":2005,"finding":"The TGFBR1*6A polymorphism (9-bp in-frame deletion in exon 1) is somatically acquired in cancers, and the signal peptide sequence (not the mature receptor) determines its altered signaling. TGFBR1*6A may convert TGFβ growth-inhibitory signals into growth-stimulatory signals in breast and colorectal cancer cells.","method":"In vitro translation assays for signal sequence cleavage site determination, stable transfection of MCF-7 cells, TGFβ-dependent proliferation assays","journal":"JAMA","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro translation + cell-based functional assay, single lab, two orthogonal methods","pmids":["16204663"],"is_preprint":false},{"year":2006,"finding":"ALK5 (TGFBR1) expression in blood vessels is restricted to medial and adventitial layers but is absent from intimal endothelium (where ALK1 predominates). ALK5-null embryos have defects in vascular smooth muscle layer formation but intact vascular lumen formation, in contrast to the severe lumen dilation seen in ALK1-null mice, demonstrating distinct non-overlapping functions.","method":"Alk5-lacZ knockin reporter mice, in situ hybridization/lacZ staining, comparison with Alk5-null and Alk1-null phenotypes","journal":"Laboratory investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct reporter knockin localization with genetic KO phenotypic comparison, establishes cell-type-specific roles","pmids":["16344855"],"is_preprint":false},{"year":2008,"finding":"TGFβ-stimulated phosphorylation of Smad1 and Smad5 (canonically associated with BMP signaling) requires the kinase activity AND specifically the L45 loop motif of ALK5/TGFBR1, as shown by shRNA-resistant ALK5 mutants and in vitro kinase assays. This non-canonical Smad1/5 phosphorylation by ALK5 is essential for TGFβ-stimulated cell migration.","method":"shRNA-resistant ALK5 L45-loop mutants in ALK5-depleted cells, in vitro kinase assays, Smad1/5 co-depletion studies, migration assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay + domain-specific mutagenesis + functional migration readout, single lab with multiple orthogonal methods","pmids":["19096363"],"is_preprint":false},{"year":2008,"finding":"In human chondrocytes, ALK5 forms complexes with ALK1, TGFBR2, endoglin, and betaglycan. Both ALK1 and ALK5 are required for TGFβ-induced Smad1/5 phosphorylation, while only ALK5 is essential for TGFβ-induced Smad3 phosphorylation. ALK1 inhibits while ALK5 potentiates Smad3-driven transcription and expression of PAI-1, fibronectin, and type II collagen.","method":"Affinity labeling/immunoprecipitation, Western blot, promoter/luciferase assays, Smad phosphorylation assays, varying ALK1/ALK5 expression levels","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus multiple functional readouts (reporter, phospho-Smad, ECM gene expression), single lab","pmids":["18333754"],"is_preprint":false},{"year":2008,"finding":"ALK5/TGFBR1 phosphorylates the endoglin cytoplasmic domain basally at serines 646 and 649. Loss of phosphorylation at S646 abrogates endoglin-mediated inhibition of Smad1/5/8 signaling in response to TGFβ and endothelial cell migration, while loss of both S646 and S649 eliminates endoglin-mediated inhibition of Smad1/5/8 in response to BMP-9.","method":"Site-directed mutagenesis of endoglin phosphorylation sites, Smad1/5/8 reporter assays, endothelial migration assays","journal":"Carcinogenesis","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of specific phosphorylation sites with defined signaling and functional readouts, single lab","pmids":["20042635"],"is_preprint":false},{"year":2008,"finding":"Constitutively activated ALK5 (ALK5L193A,P194A,T204D) directed to embryonic myocardium arrests cardiac looping morphogenesis, causes linear/dilated/hypoplastic heart tube, and induces premature expression of the CDK inhibitor p21, establishing an ALK5-sensitive pathway in cardiac morphogenesis and proliferation control.","method":"Cardiac-specific transgenic mice with constitutively active ALK5, morphological analysis, p21/Nkx2.5/dHAND expression analysis","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, cardiac-specific transgenic with defined phenotype and molecular readout","pmids":["9676193"],"is_preprint":false},{"year":2008,"finding":"ALK5/TGFBR1 regulates tooth initiation and early mandible patterning through a pathway independent of TGFBR2. Neural crest-specific Alk5 knockout causes defects not seen in Tgfbr2 knockout, including delayed tooth initiation and altered expression of Msx1, Bmp4, Bmp2, Pax9, Alx4, Lhx6/7 and Gsc. ALK5 controls CNC cell survival through Gsc regulation.","method":"Conditional knockout (Wnt1-Cre;Alk5fl/fl vs Wnt1-Cre;Tgfbr2fl/fl), comparative phenotypic analysis, gene expression analysis (in situ hybridization, RT-PCR)","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — side-by-side genetic comparison of Alk5 and Tgfbr2 KOs establishing receptor-specific pathway, multiple molecular and phenotypic readouts","pmids":["18572160"],"is_preprint":false},{"year":2009,"finding":"Tgfbr1 haploinsufficiency reduces Smad2 and Smad3 phosphorylation and increases cyclin D1 expression and cellular proliferation in colonic epithelium, establishing that TGFBR1 acts as a dose-dependent tumor suppressor in the intestine through Smad-mediated growth control.","method":"Tgfbr1+/- mice crossed with ApcMin/+ mice; intestinal tumor counting, Smad phosphorylation Western blots, cyclin D1 immunohistochemistry, BrdU proliferation assays","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in vivo with multiple molecular mechanism readouts (Smad phosphorylation, cyclin D1, proliferation)","pmids":["19147584"],"is_preprint":false},{"year":2009,"finding":"TGFβ1 and TGFBR1 are expressed in secreting ameloblasts, and activated TGFBR1 specifically promotes MMP20 mRNA expression (but not KLK4) in ameloblast-lineage cells, establishing a TGFβ/TGFBR1→MMP20 axis in amelogenesis.","method":"Immunohistochemistry in developing teeth, constitutively active TGFBR1 vector transfection into ALC cells, RT-PCR for MMP20 and KLK4","journal":"Anatomical record","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — constitutively active receptor transfection with specific gene expression readout, single lab, single method","pmids":["19462458"],"is_preprint":false},{"year":2010,"finding":"ALK5 signaling in lung epithelium controls Clara cell differentiation. Deletion of Alk5 in embryonic lung epithelium blocks Clara cell differentiation and inhibits Hes1 expression. Mechanistically, ALK5 regulates Hes1 expression by inhibiting Pten, which in turn activates ERK and AKT phosphorylation.","method":"Conditional Alk5 KO (Gata5-Cre), lung epithelial cell in vitro experiments, Pten/ERK/AKT pathway analysis, Hes1 expression","journal":"Development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined cellular phenotype plus in vitro mechanistic pathway analysis, single lab","pmids":["20147383"],"is_preprint":false},{"year":2015,"finding":"Neuropilin-1 (Nrp1) suppresses the stalk-cell phenotype in angiogenesis by limiting Smad2/3 activation through both ALK1 and ALK5. Notch downregulates Nrp1, thereby relieving inhibition of ALK1 and ALK5 to drive stalk-cell behavior, placing ALK5 downstream of the Dll4/Notch/Nrp1 axis in tip-stalk cell specification.","method":"Genetic manipulation of Nrp1 in endothelial cells, Smad2/3 phosphorylation assays, angiogenic sprouting assays in vivo and in vitro","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple readouts placing ALK5 in the Notch-Nrp1 pathway, replicated with multiple orthogonal approaches","pmids":["26081042"],"is_preprint":false},{"year":2016,"finding":"GDF-15 inhibits CXCL1-induced β2-integrin activation and neutrophil recruitment via the ALK5 (TGF-βRI)/TGF-βRII heterodimer. Mechanistically, GDF-15 and TGFβ1 inhibit integrin activation by blocking Rap-1 activation in a CalDAG-GEF1 and Cdc42-dependent manner.","method":"Conditional gene inactivation of ALK5 or TGFBR2 in neutrophils; small-molecule inhibitors, antibodies, siRNA; intravital microscopy; β2-integrin activation assays; Rap-1 activity assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional genetic KO in neutrophils combined with pharmacological and siRNA approaches, in vivo and in vitro, multiple orthogonal methods","pmids":["27235139"],"is_preprint":false},{"year":2016,"finding":"Smooth muscle cell-specific deletion of Tgfbr1 in adult mice causes rapid and severe aortic aneurysm (100% penetrance). Loss of TGFBR1 activates TGFBR2-ERK signaling and upregulates angiotensin-converting enzyme; inhibiting ERK phosphorylation or blocking the AngII/AT1R pathway prevents aneurysmal degeneration, placing TGFBR1 upstream of ERK and AngII/AT1R in aortic wall homeostasis.","method":"Inducible SMC-specific Cre-loxP knockout (Myh11-Cre), ERK inhibitor treatment, AT1R blocker treatment, aortic histology and molecular analysis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — inducible cell-type-specific KO with pharmacological pathway rescue experiments defining specific downstream signals","pmids":["27739498"],"is_preprint":false},{"year":2016,"finding":"ALK5 controls mesodermal progenitor fate in the lung: Alk5 deletion in mesodermal progenitors inhibits αSMA+ myofibroblast differentiation and increases lipofibroblasts. This is mediated through direct and indirect modulation of PDGFRα, PPARγ, PRRX1, and ZFP423 signaling.","method":"Conditional Alk5 KO in lung mesoderm, cell lineage analysis, gene expression analysis of downstream pathway components","journal":"BMC biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined cell fate phenotype and identification of downstream transcription factors/receptors, single lab","pmids":["26984772"],"is_preprint":false},{"year":2017,"finding":"TGFβ1 stimulates collagen deposition by mesenchymal stromal cells via the ALK5/Smad3 signaling pathway, and ALK5 inhibition with galunisertib ameliorates myelofibrosis in MPL and JAK2 mouse models.","method":"ALK5 inhibitor treatment in vitro and in vivo (MPL and JAK2 murine MF models), Smad3 phosphorylation assays, collagen I and III measurement","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition in both in vitro and in vivo models with defined molecular pathway readout, single lab","pmids":["28405618"],"is_preprint":false},{"year":2018,"finding":"CYLD deubiquitinase loss promotes ALK5 stabilization (increased protein stability) in oral squamous cell carcinoma, leading to enhanced TGFβ signaling (increased Smad3 phosphorylation) and cell invasion. ALK5 inhibitor completely blocks the invasive phenotype induced by CYLD knockdown.","method":"siRNA knockdown of CYLD, ALK5 protein stability assays, Smad3 phosphorylation Western blot, invasion assays, ALK5 inhibitor rescue","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with pharmacological rescue, protein stability assay, multiple functional readouts, single lab","pmids":["29235674"],"is_preprint":false},{"year":2018,"finding":"Pericyte ALK5 controls brain endothelial morphogenesis through a TIMP3-dependent mechanism: ALK5-depleted pericytes downregulate TIMP3, leading to elevated perivascular MMP activity, endothelial hyperproliferation, reduced pericyte coverage, and germinal matrix hemorrhage. TIMP3 administration rescues endothelial morphogenesis in ALK5 pericyte mutants.","method":"Conditional Alk5 KO in pericytes, TIMP3 protein administration rescue, MMP activity assays, histological analysis of brain microvessels","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional cell-type-specific KO with protein-level rescue (TIMP3 administration), defining a specific molecular pathway (ALK5→TIMP3→MMP activity)","pmids":["29456135"],"is_preprint":false},{"year":2019,"finding":"ALK5 (TGFBR1) inactivation in the mouse uterus leads to metastatic endometrial adenocarcinoma that is estrogen-dependent and requires prior mating (postpartum context), establishing that TGFβ signaling through TGFBR1/ALK5 in the endometrium is required for endometrial homeostasis, tumor suppression, and postpartum repair.","method":"Conditional Alk5 KO in uterus (progesterone receptor Cre), histopathology, ERα and PR immunostaining, metastasis analysis","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional cell-type-specific KO with defined tumor and metastasis phenotype and molecular characterization of hormone receptor status","pmids":["30655341"],"is_preprint":false},{"year":2019,"finding":"GDNF directly binds ALK5/TGFBR1 at His39 and Asp76 residues to activate hepatic stellate cells via Smad2/3 signaling (not via GFRα1), promoting liver fibrosis. This binding was determined by surface plasmon resonance, molecular docking, mutagenesis, and co-immunoprecipitation.","method":"Surface plasmon resonance, molecular docking, mutagenesis of ALK5 binding residues, Co-IP, adenoviral GDNF overexpression/CRISPR silencing in mice, primary HSC activation assays","journal":"Gut","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct binding characterized by SPR + mutagenesis of specific residues + Co-IP + in vivo genetic models, multiple orthogonal methods","pmids":["31171625"],"is_preprint":false},{"year":2019,"finding":"ALK5 signaling mediates neurogenesis and functional recovery after cerebral ischemia/reperfusion in rats via Gadd45b. ALK5 regulates Gadd45b protein levels through Smad2/3 phosphorylation, and ALK5 directly co-immunoprecipitates with Gadd45b.","method":"Lentiviral ALK5 KD/overexpression in vivo, Smad2/3 phosphorylation assays, co-immunoprecipitation of ALK5 and Gadd45b, axonal/dendritic plasticity assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus in vivo gain/loss of function with defined molecular (Smad2/3, Gadd45b) and functional (neurogenesis) readouts, single lab","pmids":["31043581"],"is_preprint":false},{"year":2020,"finding":"TP-008, a selective chemical probe for ALK4 and ALK5, potently inhibits ALK5 kinase activity and strongly abrogates phosphorylation of SMAD2 in cells, confirming that ALK5 kinase activity is directly responsible for SMAD2 phosphorylation.","method":"Kinase selectivity profiling, cellular SMAD2 phosphorylation assays with TP-008 and matched negative control compound","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — selective chemical probe with matched negative control, cellular SMAD2 assay, single paper","pmids":["32176847"],"is_preprint":false},{"year":2021,"finding":"ALK5 acts as a mechanoreceptor in endothelial cells to drive EndMT in response to disturbed shear stress through an ALK5-Shc signaling pathway, independent of other mechanosensors. Depletion of ALK5 abrogates shear stress-induced EndMT, and genetic targeting of endothelial Shc reduces EndMT and atherosclerosis in areas of disturbed flow.","method":"ALK5 depletion in endothelial cells, tensional force and flow reconstitution experiments, endothelial-specific Shc gene targeting in atherosclerosis model, EndMT marker analysis","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Strong — reconstitution experiments plus genetic targeting in vivo with defined pathway (Alk5-Shc) and functional/disease readout, multiple orthogonal methods","pmids":["34244146"],"is_preprint":false},{"year":2021,"finding":"GDF-8 stimulates trophoblast cell invasion by upregulating MMP2 expression via the ALK5-SMAD2/3 signaling pathway. MMP9 expression is not affected by GDF-8. Knockdown of MMP2 attenuates GDF-8-induced invasiveness.","method":"siRNA knockdown of ALK5, SMAD2, SMAD3 in HTR-8/SVneo cells, MMP2/MMP9 expression assays, invasion assays","journal":"Reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA-mediated knockdown of receptor and pathway components with specific gene expression and functional invasion readouts, single lab","pmids":["34432647"],"is_preprint":false},{"year":2022,"finding":"Simultaneous muscle-specific knockout of Tgfbr1 and Acvr1b (but not either alone) induces substantial myofiber hypertrophy via increased Akt and p70S6K phosphorylation and reduced E3 ligase expression, demonstrating synergistic roles of these two TGFβ type I receptors in regulating muscle fiber size and regeneration.","method":"Single and double conditional KO mice (Tgfbr1 and Acvr1b), phospho-Akt/p70S6K Western blots, E3 ligase expression, satellite cell and macrophage quantification, cardiotoxin injury model","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with single vs. double KO comparison, multiple molecular pathway readouts, replicated across different functional contexts","pmids":["35323108"],"is_preprint":false},{"year":2022,"finding":"Mitochondrial dysfunction induces enhanced ALK5-SMAD2 signaling through MAPKs-mediated phosphorylation of SMAD2 with mitochondrial localization of SMAD2, leading to retinal arteriovenous malformations. Pharmacological blockade of ALK5 or genetic SMAD2 deficiency prevents retinal vascular malformations in mitochondrial dysfunction mouse models.","method":"Endothelial-specific KO of TFAM, COX10, or TRX2; single-cell RNA-seq; pharmacological ALK5 inhibition; SMAD2 genetic KO rescue; phospho-SMAD2 localization studies","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — three independent genetic models plus pharmacological and genetic rescue, scRNA-seq pathway analysis, multiple orthogonal methods","pmids":["36496409"],"is_preprint":false},{"year":2022,"finding":"CD147 directly binds ALK5, promoting ALK5 activation and endocytosis, leading to SMAD2/3 phosphorylation and nuclear translocation. N-glycosylation of CD147 (by GNT-V) under high glucose conditions prevents its ubiquitin-proteasome degradation, sustaining ALK5 activation and cardiac fibrosis in diabetic cardiomyopathy.","method":"Co-IP of CD147 and ALK5, AAV9-mediated cardiac-specific CD147 silencing/overexpression, endocytosis assays, SMAD2/3 phosphorylation/nuclear translocation, glycosylation manipulation","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional in vivo AAV knockdown/overexpression and mechanistic endocytosis assays, single lab","pmids":["36594096"],"is_preprint":false},{"year":2023,"finding":"RCN3 promotes fibroblast activation and lung fibrosis through a TGFβ1-RCN3-TGFBR1 positive feedback loop: TGFβ1 upregulates RCN3, which detains EZH2 in the cytoplasm via RCN3-EZH2 interaction, releasing EZH2-H3K27me3 epigenetic repression of TGFBR1 to sustain TGFBR1 expression.","method":"BioID protein interaction assay, RCN3-EZH2 Co-IP, epigenetic (H3K27me3) analysis of TGFBR1 promoter, fibroblast-selective Rcn3 KD mouse model, bleomycin fibrosis model","journal":"Respiratory research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — BioID + Co-IP + epigenetic promoter analysis + in vivo KD model, single lab, multiple orthogonal methods","pmids":["37710230"],"is_preprint":false},{"year":2023,"finding":"NRP1 interacts with TGFBR2 through their cytoplasmic domains, activating the TGFBR1/TGFBR2 complex, which facilitates macropinocytosis-mediated KSHV internalization into mesenchymal stem cells via Cdc42 and Rac1.","method":"Co-IP of NRP1 and TGFBR2, NRP1 KO and overexpression in MSCs, KSHV infection assays, macropinocytosis assays, Cdc42/Rac1 activity measurements","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with domain-level analysis, genetic KO/OE, pathway (Cdc42/Rac1) functional readouts, single lab","pmids":["37224259"],"is_preprint":false},{"year":2020,"finding":"LPAR5 (lysophosphatidic acid receptor 5) transactivates TGFBR1 to stimulate mRNA expression of GAG biosynthesis genes XYLT1 and CHST3 in vascular smooth muscle cells. This LPAR5-to-TGFBR1 transactivation occurs through a ROCK-dependent pathway, and ROS/Akt signaling are not involved.","method":"Pharmacological inhibition of LPAR5 and TGFBR1, ROCK inhibitor experiments, XYLT1/CHST3 mRNA expression assays, ROS and Akt pathway analysis in VSMCs","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection of GPCR-to-TGFBR1 transactivation pathway with multiple inhibitor combinations, single lab","pmids":["32920014"],"is_preprint":false},{"year":1999,"finding":"Multiple self-healing squamous epithelioma (MSSE) maps to chromosome 9q22-q31, and genetic mapping excluded XPA and PTCH as causative genes, narrowing the interval. TGFBR1 (also known as MSSE/ESS1 by alias) was later identified as the MSSE gene through loss-of-function mutations.","method":"Linkage analysis, haplotype analysis, SSCP, DNA sequencing of candidate genes in MSSE families","journal":"Human genetics","confidence":"Low","confidence_rationale":"Tier 4 / Weak — genetic mapping study excluding candidates, not directly establishing TGFBR1 function; connection to TGFBR1 as MSSE gene established in later work","pmids":["9439661"],"is_preprint":false},{"year":2020,"finding":"Loss-of-function mutations in TGFBR1 cause MSSE (Ferguson-Smith disease/multiple self-healing squamous epithelioma) in a digenic manner requiring permissive variants at a second linked locus on chromosome 9q. The spectrum of TGFBR1 mutations in MSSE differs from those in Loeys-Dietz syndrome.","method":"Haplotype analysis, mutation screening in MSSE families, review of families with both MSSE and Loeys-Dietz syndrome","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — genetic evidence across multiple families establishing digenic inheritance, but mechanistic biochemical data not directly provided in this paper","pmids":["33256177"],"is_preprint":false},{"year":2017,"finding":"Lumican C-terminal peptide LumC13 binds directly to ALK5/TGFBR1, forming a stable complex. Computational design of LumC13 derivatives identified minimal residues required for stable lumican/ALK5 complex formation, and these peptides promote corneal epithelial cell migration and wound healing.","method":"In silico binding modeling, in vitro cell migration assays, in vivo corneal wound healing, computational derivative design with experimental validation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — computational binding characterization validated in vitro and in vivo, but no direct high-resolution structural or biophysical binding measurement reported in abstract","pmids":["28181591"],"is_preprint":false},{"year":2021,"finding":"TGFβ1 induces ZIP8 expression via the ALK5-Smad2/3 signaling pathway in vascular endothelial cells, with Smad3-mediated induction occurring with or without p38 MAPK co-activation. This upregulation of ZIP8 increases intracellular cadmium accumulation and potentiates cadmium cytotoxicity.","method":"ALK5 inhibitor (SB431542), Smad2/3 knockdown, p38 MAPK inhibitor, ZIP8 expression assays, cadmium uptake and cytotoxicity assays in endothelial cells","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and siRNA-mediated dissection of pathway components with defined molecular and functional readouts, single lab","pmids":["35008873"],"is_preprint":false}],"current_model":"TGFBR1/ALK5 is a transmembrane serine/threonine kinase receptor that, upon TGFβ ligand binding (and transphosphorylation by TGFBR2), canonically phosphorylates Smad2 and Smad3 to drive transcriptional responses including EMT, fibrosis, and growth inhibition; it also non-canonically phosphorylates Smad1/5 through its L45 loop to promote cell migration, recruits ALK1 into receptor complexes to enable opposing ALK1-Smad1/5 signaling, phosphorylates the endoglin cytoplasmic domain to regulate Smad1/5/8 activity, and functions as a mechanosensor in endothelial cells to drive EndMT via a Shc-dependent pathway, while its activity is regulated post-translationally by CYLD-mediated ubiquitination (affecting stability), CD147-mediated endocytosis, and EZH2-H3K27me3 epigenetic control of its own expression."},"narrative":{"mechanistic_narrative":"TGFBR1 (ALK5) is the type I transmembrane serine/threonine kinase receptor that transduces TGFβ-family ligand signals into canonical Smad-dependent transcriptional programs governing epithelial-mesenchymal transition, tissue morphogenesis, fibrosis, and growth control [PMID:10574705, PMID:14729481, PMID:32176847]. Within the receptor complex it cooperates with TGFBR2 and accessory receptors and, in endothelial and chondrocyte contexts, recruits ALK1 and assembles with endoglin and betaglycan; ALK5 kinase activity is required for optimal ALK1 activation, and ALK1-Smad1/5 signaling reciprocally antagonizes the ALK5-Smad2/3 axis [PMID:14580334, PMID:18333754]. Its principal catalytic output is phosphorylation of Smad2 and Smad3, demonstrated directly with selective kinase inhibition, driving EMT, collagen and ECM gene expression (PAI-1, fibronectin, type II collagen), and growth-inhibitory responses [PMID:10574705, PMID:18333754, PMID:32176847]. Beyond this canonical axis ALK5 phosphorylates Smad1 and Smad5 through its kinase activity and L45 loop to promote cell migration, and basally phosphorylates the endoglin cytoplasmic domain at serines 646/649 to regulate Smad1/5/8 output [PMID:19096363, PMID:20042635]. ALK5 acts as a dose-dependent tumor suppressor in intestine, uterus, and squamous epithelium through Smad-mediated growth control, with haploinsufficiency raising cyclin D1 and proliferation [PMID:19147584, PMID:30655341]; loss of TGFBR1 can paradoxically unleash TGFBR2-ERK and angiotensin signaling, producing aortic aneurysm [PMID:27739498]. In endothelium ALK5 functions as a mechanoreceptor that drives EndMT under disturbed shear stress via an ALK5-Shc pathway [PMID:34244146]. Receptor abundance and activity are controlled post-translationally and epigenetically: CYLD deubiquitinase loss stabilizes ALK5 to enhance invasion [PMID:29235674], CD147 binds and promotes ALK5 activation and endocytosis [PMID:36594096], and a TGFβ1-RCN3 loop relieves EZH2-H3K27me3 repression of the TGFBR1 promoter to sustain its expression [PMID:37710230]. Germline and somatic TGFBR1 mutations cause Loeys-Dietz syndrome, where mutant alleles paradoxically yield elevated tissue TGFβ signaling [PMID:15731757], and loss-of-function mutations cause multiple self-healing squamous epithelioma (Ferguson-Smith disease) in a digenic manner [PMID:33256177].","teleology":[{"year":1999,"claim":"Established that TGFβ-induced EMT in epithelial cells is channeled specifically through ALK5 and its downstream Smad2/3/Smad4 module, defining the receptor's core transcriptional effector pathway.","evidence":"Adenoviral constitutively active ALK5 and dominant-negative constructs with Smad co-expression and cytoskeletal/E-cadherin readouts in mammary epithelial cells","pmids":["10574705"],"confidence":"High","gaps":["Did not resolve which target genes mediate the cytoskeletal reorganization","Cooperative thresholds defined in vitro, not in vivo"]},{"year":2003,"claim":"Resolved how ALK5 integrates with ALK1 in endothelium, showing ALK5 kinase activity recruits and activates ALK1, which then opposes ALK5-Smad2/3 signaling — a reciprocal balance controlling endothelial behavior.","evidence":"ALK5-null endothelial cells, Co-IP complex formation, reporter and kinase assays","pmids":["14580334"],"confidence":"High","gaps":["Stoichiometry of the ALK5/ALK1 complex not defined","How the balance is set in different vascular beds unclear"]},{"year":2004,"claim":"Demonstrated by domain-specific genetic rescue that Smad-dependent (not merely kinase) signaling downstream of ALK5 is required for a developmental fusion event, separating ALK5 kinase activity from its Smad-coupling function.","evidence":"Conditional rescue with activated/kinase-dead and Smad-deficient ALK5 mutants in Tgfβ3-null palatal explants","pmids":["14729481"],"confidence":"High","gaps":["Smad-independent ALK5 outputs in this tissue not characterized"]},{"year":2005,"claim":"Connected TGFBR1 to human disease, showing Loeys-Dietz mutations paradoxically increase tissue TGFβ signaling despite reduced signal propagation in vitro, and that a cancer-associated 6A polymorphism can convert growth-inhibitory into growth-stimulatory signaling.","evidence":"Patient-derived tissues with phospho-Smad2/collagen/CTGF staining; in vitro translation and TGFβ proliferation assays in transfected cells","pmids":["15731757","16204663"],"confidence":"High","gaps":["Mechanism reconciling reduced receptor activity with elevated tissue signaling unresolved","6A signal-peptide effect on receptor processing not structurally defined"]},{"year":2006,"claim":"Defined non-overlapping in vivo roles by mapping ALK5 to medial/adventitial vascular layers and showing ALK5-null vascular smooth muscle defects distinct from ALK1-null lumen defects.","evidence":"Alk5-lacZ knockin reporter mice with comparative Alk5-null and Alk1-null phenotype analysis","pmids":["16344855"],"confidence":"High","gaps":["Cell-type-specific contribution of ALK5 to SMC formation not dissected at the molecular level"]},{"year":2008,"claim":"Expanded ALK5's catalytic repertoire beyond Smad2/3 by showing its kinase activity and L45 loop phosphorylate Smad1/5 to drive migration, and that it directly phosphorylates the endoglin cytoplasmic tail to set Smad1/5/8 output.","evidence":"shRNA-resistant L45-loop ALK5 mutants with in vitro kinase and migration assays; site-directed mutagenesis of endoglin S646/S649 with Smad1/5/8 reporters","pmids":["19096363","20042635","18333754"],"confidence":"High","gaps":["Structural basis of L45-mediated substrate selection not solved","Physiological contexts where Smad1/5 branch dominates not mapped"]},{"year":2009,"claim":"Established TGFBR1 as a dose-dependent intestinal tumor suppressor, linking receptor gene dosage to Smad phosphorylation, cyclin D1 levels, and proliferation.","evidence":"Tgfbr1+/- ; ApcMin/+ mice with tumor counts, Smad phospho-blots, cyclin D1 IHC, BrdU assays","pmids":["19147584"],"confidence":"High","gaps":["Threshold of receptor activity defining tumor suppression vs promotion not quantified"]},{"year":2010,"claim":"Identified receptor-specific developmental functions of ALK5 distinct from TGFBR2, including neural-crest patterning via Gsc and lung Clara cell differentiation via a Pten/ERK/AKT-Hes1 mechanism.","evidence":"Side-by-side Wnt1-Cre Alk5 vs Tgfbr2 conditional KOs and Gata5-Cre lung KO with pathway and gene-expression analyses","pmids":["18572160","20147383"],"confidence":"High","gaps":["How ALK5 signals independently of TGFBR2 in these tissues mechanistically unclear","Pten regulation by ALK5 not biochemically defined"]},{"year":2016,"claim":"Showed ALK5 loss in vascular smooth muscle drives aneurysm by de-repressing TGFBR2-ERK and AngII/AT1R signaling, revealing a homeostatic restraint function whose loss redirects signaling pathologically.","evidence":"Inducible Myh11-Cre Tgfbr1 KO with ERK-inhibitor and AT1R-blocker rescue, aortic histology","pmids":["27739498"],"confidence":"High","gaps":["Direct molecular link between ALK5 loss and ERK activation not defined","Relationship to Loeys-Dietz aneurysm mechanism unresolved"]},{"year":2016,"claim":"Extended ALK5 signaling into immune and angiogenic contexts, mediating GDF-15 suppression of integrin activation in neutrophils and placing ALK5 downstream of Dll4/Notch/Nrp1 in tip-stalk cell specification.","evidence":"Conditional neutrophil ALK5 KO with Rap-1 assays; Nrp1 genetic manipulation with Smad2/3 and sprouting readouts","pmids":["27235139","26081042"],"confidence":"High","gaps":["Whether these effects are Smad-dependent or Smad-independent not fully resolved"]},{"year":2019,"claim":"Identified novel ligands and effectors of ALK5, including direct GDNF binding at His39/Asp76 to activate hepatic stellate cells, and Gadd45b coupling in post-ischemic neurogenesis.","evidence":"SPR, molecular docking, residue mutagenesis and Co-IP for GDNF; lentiviral ALK5 manipulation with Co-IP and Smad2/3 assays for Gadd45b","pmids":["31171625","31043581"],"confidence":"High","gaps":["Whether GDNF-ALK5 signaling requires TGFBR2 not addressed","Structural detail of GDNF-ALK5 interface beyond docking lacking"]},{"year":2021,"claim":"Established ALK5 as a mechanoreceptor in endothelium that drives EndMT under disturbed shear stress through an ALK5-Shc pathway promoting atherosclerosis, identifying a non-ligand-driven activation mode.","evidence":"ALK5 depletion, force/flow reconstitution, and endothelial Shc genetic targeting in an atherosclerosis model","pmids":["34244146"],"confidence":"High","gaps":["How mechanical force activates ALK5 biochemically not defined","Relationship between mechano-activation and ligand-dependent activation unclear"]},{"year":2022,"claim":"Defined post-translational and stress-driven control of ALK5: CYLD loss stabilizes the receptor to enhance invasion, CD147 binds to promote its activation and endocytosis, and mitochondrial dysfunction amplifies ALK5-SMAD2 signaling via MAPKs.","evidence":"CYLD siRNA with stability and invasion assays; CD147 Co-IP and AAV cardiac models with endocytosis readouts; endothelial TFAM/COX10/TRX2 KOs with ALK5 inhibition and SMAD2 rescue","pmids":["29235674","36594096","36496409"],"confidence":"High","gaps":["Direct ubiquitination sites on ALK5 not mapped","How CD147 binding promotes kinase activation mechanistically unclear"]},{"year":2023,"claim":"Uncovered epigenetic control of TGFBR1 expression itself, where a TGFβ1-RCN3 feedback loop sequesters EZH2 in the cytoplasm to relieve H3K27me3 repression of the TGFBR1 promoter, sustaining fibrosis.","evidence":"BioID, RCN3-EZH2 Co-IP, H3K27me3 promoter analysis, fibroblast Rcn3 KD bleomycin model","pmids":["37710230"],"confidence":"Medium","gaps":["Generality of this loop beyond lung fibroblasts unknown","Direct EZH2 occupancy dynamics at the TGFBR1 promoter not time-resolved"]},{"year":2020,"claim":"Linked TGFBR1 loss-of-function to multiple self-healing squamous epithelioma, establishing a digenic inheritance requiring permissive variants at a second 9q locus and distinguishing its mutation spectrum from Loeys-Dietz syndrome.","evidence":"Haplotype and mutation screening across MSSE families with review of co-occurring Loeys-Dietz cases","pmids":["33256177","9439661"],"confidence":"Medium","gaps":["Identity of the required second 9q locus not established","Mechanistic explanation for tissue-restricted skin phenotype lacking"]},{"year":null,"claim":"How ALK5's distinct activation modes (ligand binding, mechanical force, GPCR transactivation) and its multiple substrate branches (Smad2/3, Smad1/5, endoglin, Shc) are selected and integrated within a single cell remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model integrating substrate selection across conditions","Quantitative rules governing canonical vs non-canonical output unknown","Crosstalk between mechano- and ligand-driven activation not defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[7,9,25]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[7,9,25]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,26]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[26]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[23,30,26]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,8,25]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,11,6]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[3,17,22,35]}],"complexes":["TGFBR1/TGFBR2 receptor complex","ALK5/ALK1/endoglin/betaglycan complex"],"partners":["TGFBR2","ALK1","ENDOGLIN","SHC","CD147","GDNF","GADD45B","SMAD3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P36897","full_name":"TGF-beta receptor type-1","aliases":["Activin A receptor type II-like protein kinase of 53kD","Activin receptor-like kinase 5","ALK-5","ALK5","Serine/threonine-protein kinase receptor R4","SKR4","TGF-beta type I receptor","Transforming growth factor-beta receptor type I","TGF-beta receptor type I","TbetaR-I"],"length_aa":503,"mass_kda":56.0,"function":"Transmembrane serine/threonine kinase forming with the TGF-beta type II serine/threonine kinase receptor, TGFBR2, the non-promiscuous receptor for the TGF-beta cytokines TGFB1, TGFB2 and TGFB3. Transduces the TGFB1, TGFB2 and TGFB3 signal from the cell surface to the cytoplasm and is thus regulating a plethora of physiological and pathological processes including cell cycle arrest in epithelial and hematopoietic cells, control of mesenchymal cell proliferation and differentiation, wound healing, extracellular matrix production, immunosuppression and carcinogenesis (PubMed:33914044). The formation of the receptor complex composed of 2 TGFBR1 and 2 TGFBR2 molecules symmetrically bound to the cytokine dimer results in the phosphorylation and the activation of TGFBR1 by the constitutively active TGFBR2. Activated TGFBR1 phosphorylates SMAD2 which dissociates from the receptor and interacts with SMAD4. The SMAD2-SMAD4 complex is subsequently translocated to the nucleus where it modulates the transcription of the TGF-beta-regulated genes. This constitutes the canonical SMAD-dependent TGF-beta signaling cascade. Also involved in non-canonical, SMAD-independent TGF-beta signaling pathways. For instance, TGFBR1 induces TRAF6 autoubiquitination which in turn results in MAP3K7 ubiquitination and activation to trigger apoptosis. Also regulates epithelial to mesenchymal transition through a SMAD-independent signaling pathway through PARD6A phosphorylation and activation","subcellular_location":"Cell membrane; Cell junction, tight junction; Cell surface; Membrane raft","url":"https://www.uniprot.org/uniprotkb/P36897/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TGFBR1","classification":"Not Classified","n_dependent_lines":99,"n_total_lines":1208,"dependency_fraction":0.08195364238410596},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/TGFBR1","total_profiled":1310},"omim":[{"mim_id":"620961","title":"SORTING NEXIN 25; SNX25","url":"https://www.omim.org/entry/620961"},{"mim_id":"619656","title":"LOEYS-DIETZ SYNDROME 6; LDS6","url":"https://www.omim.org/entry/619656"},{"mim_id":"619516","title":"BIFUNCTIONAL APOPTOSIS REGULATOR; BFAR","url":"https://www.omim.org/entry/619516"},{"mim_id":"617888","title":"ZINC FINGER PROTEIN 580; ZNF580","url":"https://www.omim.org/entry/617888"},{"mim_id":"617168","title":"AORTIC ANEURYSM, FAMILIAL THORACIC 10; AAT10","url":"https://www.omim.org/entry/617168"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Primary cilium","reliability":"Approved"},{"location":"Primary cilium tip","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TGFBR1"},"hgnc":{"alias_symbol":["ALK-5","ACVRLK4","ALK5","TBRI","TBR-i"],"prev_symbol":["MSSE","ESS1"]},"alphafold":{"accession":"P36897","domains":[{"cath_id":"2.10.60.10","chopping":"33-100","consensus_level":"high","plddt":88.1381,"start":33,"end":100},{"cath_id":"3.30.200.20","chopping":"189-282","consensus_level":"medium","plddt":87.7114,"start":189,"end":282},{"cath_id":"1.10.510.10","chopping":"286-503","consensus_level":"medium","plddt":95.7594,"start":286,"end":503}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P36897","model_url":"https://alphafold.ebi.ac.uk/files/AF-P36897-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P36897-F1-predicted_aligned_error_v6.png","plddt_mean":84.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TGFBR1","jax_strain_url":"https://www.jax.org/strain/search?query=TGFBR1"},"sequence":{"accession":"P36897","fasta_url":"https://rest.uniprot.org/uniprotkb/P36897.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P36897/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P36897"}},"corpus_meta":[{"pmid":"15731757","id":"PMC_15731757","title":"A 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ALK1 in turn directly antagonizes ALK5/Smad2/3 signaling.\",\n      \"method\": \"Endothelial cells lacking ALK5 (genetic KO), reporter assays, Co-IP/complex formation studies, kinase activity assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional studies with ALK5-null cells and multiple orthogonal methods (Co-IP, reporter assays, migration/proliferation readouts), replicated in subsequent studies\",\n      \"pmids\": [\"14580334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"TGFβ1-induced epithelial-to-mesenchymal transition (EMT) in mammary epithelial cells is mediated specifically by TGFBR1/ALK5 and downstream Smad2/Smad3/Smad4. Constitutively active ALK5 alone at high levels drives full EMT, while low ALK5 activity combined with Smad2+Smad4 or Smad3+Smad4 cooperatively induces EMT.\",\n      \"method\": \"Adenoviral expression of constitutively active ALK5, dominant-negative constructs, Smad co-transfection, actin cytoskeleton reorganization and E-cadherin/β-catenin relocalization as readouts\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (CA-ALK5 adenovirus, Smad co-expression, multiple phenotypic readouts), replicated across multiple studies\",\n      \"pmids\": [\"10574705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Palatal fusion driven by TGFβ3 requires ALK5/TGFBR1 signaling through the Smad2-dependent pathway. Activation of ALK5 in Tgf-beta3-null palatal epithelium rescues fusion; inactivation of ALK5 in wild-type prevents fusion. A Smad-signaling-deficient ALK5 mutant (kinase-active but Smad-unable) cannot rescue fusion, establishing that Smad-dependent signaling downstream of ALK5 is required.\",\n      \"method\": \"Conditional genetic rescue (activated/kinase-dead ALK5 in Tgf-beta3 KO), Smad2 phosphorylation assays, palatal explant culture\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis established by genetic rescue with domain-specific mutants, multiple independent conditions tested\",\n      \"pmids\": [\"14729481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"TGFBR1 mutations associated with Loeys-Dietz syndrome (a connective tissue disorder with cardiovascular, craniofacial and skeletal manifestations) paradoxically result in increased TGFβ signaling in patient tissues (elevated collagen, CTGF, and nuclear phospho-Smad2), despite selected mutant alleles being unable to support TGFβ signal propagation in vitro.\",\n      \"method\": \"Patient-derived cells and tissues; immunostaining for phospho-Smad2, collagen, CTGF; TGFβ signaling kinetics assays\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct biochemical evidence in patient-derived tissues with multiple markers across 10 families\",\n      \"pmids\": [\"15731757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ALK5 (TGFBR1) and Smad4 are required for TGFβ1-induced endothelial permeability increase and actin stress fiber formation with MLC and MYPT1 phosphorylation. ALK1 is not involved in this pathway.\",\n      \"method\": \"siRNA depletion of ALK5 or Smad4 in endothelial cells, pharmacological ALK5 inhibition (SB431542), permeability assay, immunofluorescence\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown and pharmacological inhibition with defined phenotypic readout, single lab\",\n      \"pmids\": [\"16004987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The TGFBR1*6A polymorphism (9-bp in-frame deletion in exon 1) is somatically acquired in cancers, and the signal peptide sequence (not the mature receptor) determines its altered signaling. TGFBR1*6A may convert TGFβ growth-inhibitory signals into growth-stimulatory signals in breast and colorectal cancer cells.\",\n      \"method\": \"In vitro translation assays for signal sequence cleavage site determination, stable transfection of MCF-7 cells, TGFβ-dependent proliferation assays\",\n      \"journal\": \"JAMA\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro translation + cell-based functional assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"16204663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ALK5 (TGFBR1) expression in blood vessels is restricted to medial and adventitial layers but is absent from intimal endothelium (where ALK1 predominates). ALK5-null embryos have defects in vascular smooth muscle layer formation but intact vascular lumen formation, in contrast to the severe lumen dilation seen in ALK1-null mice, demonstrating distinct non-overlapping functions.\",\n      \"method\": \"Alk5-lacZ knockin reporter mice, in situ hybridization/lacZ staining, comparison with Alk5-null and Alk1-null phenotypes\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct reporter knockin localization with genetic KO phenotypic comparison, establishes cell-type-specific roles\",\n      \"pmids\": [\"16344855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"TGFβ-stimulated phosphorylation of Smad1 and Smad5 (canonically associated with BMP signaling) requires the kinase activity AND specifically the L45 loop motif of ALK5/TGFBR1, as shown by shRNA-resistant ALK5 mutants and in vitro kinase assays. This non-canonical Smad1/5 phosphorylation by ALK5 is essential for TGFβ-stimulated cell migration.\",\n      \"method\": \"shRNA-resistant ALK5 L45-loop mutants in ALK5-depleted cells, in vitro kinase assays, Smad1/5 co-depletion studies, migration assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay + domain-specific mutagenesis + functional migration readout, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"19096363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In human chondrocytes, ALK5 forms complexes with ALK1, TGFBR2, endoglin, and betaglycan. Both ALK1 and ALK5 are required for TGFβ-induced Smad1/5 phosphorylation, while only ALK5 is essential for TGFβ-induced Smad3 phosphorylation. ALK1 inhibits while ALK5 potentiates Smad3-driven transcription and expression of PAI-1, fibronectin, and type II collagen.\",\n      \"method\": \"Affinity labeling/immunoprecipitation, Western blot, promoter/luciferase assays, Smad phosphorylation assays, varying ALK1/ALK5 expression levels\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus multiple functional readouts (reporter, phospho-Smad, ECM gene expression), single lab\",\n      \"pmids\": [\"18333754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ALK5/TGFBR1 phosphorylates the endoglin cytoplasmic domain basally at serines 646 and 649. Loss of phosphorylation at S646 abrogates endoglin-mediated inhibition of Smad1/5/8 signaling in response to TGFβ and endothelial cell migration, while loss of both S646 and S649 eliminates endoglin-mediated inhibition of Smad1/5/8 in response to BMP-9.\",\n      \"method\": \"Site-directed mutagenesis of endoglin phosphorylation sites, Smad1/5/8 reporter assays, endothelial migration assays\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of specific phosphorylation sites with defined signaling and functional readouts, single lab\",\n      \"pmids\": [\"20042635\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Constitutively activated ALK5 (ALK5L193A,P194A,T204D) directed to embryonic myocardium arrests cardiac looping morphogenesis, causes linear/dilated/hypoplastic heart tube, and induces premature expression of the CDK inhibitor p21, establishing an ALK5-sensitive pathway in cardiac morphogenesis and proliferation control.\",\n      \"method\": \"Cardiac-specific transgenic mice with constitutively active ALK5, morphological analysis, p21/Nkx2.5/dHAND expression analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, cardiac-specific transgenic with defined phenotype and molecular readout\",\n      \"pmids\": [\"9676193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ALK5/TGFBR1 regulates tooth initiation and early mandible patterning through a pathway independent of TGFBR2. Neural crest-specific Alk5 knockout causes defects not seen in Tgfbr2 knockout, including delayed tooth initiation and altered expression of Msx1, Bmp4, Bmp2, Pax9, Alx4, Lhx6/7 and Gsc. ALK5 controls CNC cell survival through Gsc regulation.\",\n      \"method\": \"Conditional knockout (Wnt1-Cre;Alk5fl/fl vs Wnt1-Cre;Tgfbr2fl/fl), comparative phenotypic analysis, gene expression analysis (in situ hybridization, RT-PCR)\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — side-by-side genetic comparison of Alk5 and Tgfbr2 KOs establishing receptor-specific pathway, multiple molecular and phenotypic readouts\",\n      \"pmids\": [\"18572160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Tgfbr1 haploinsufficiency reduces Smad2 and Smad3 phosphorylation and increases cyclin D1 expression and cellular proliferation in colonic epithelium, establishing that TGFBR1 acts as a dose-dependent tumor suppressor in the intestine through Smad-mediated growth control.\",\n      \"method\": \"Tgfbr1+/- mice crossed with ApcMin/+ mice; intestinal tumor counting, Smad phosphorylation Western blots, cyclin D1 immunohistochemistry, BrdU proliferation assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in vivo with multiple molecular mechanism readouts (Smad phosphorylation, cyclin D1, proliferation)\",\n      \"pmids\": [\"19147584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TGFβ1 and TGFBR1 are expressed in secreting ameloblasts, and activated TGFBR1 specifically promotes MMP20 mRNA expression (but not KLK4) in ameloblast-lineage cells, establishing a TGFβ/TGFBR1→MMP20 axis in amelogenesis.\",\n      \"method\": \"Immunohistochemistry in developing teeth, constitutively active TGFBR1 vector transfection into ALC cells, RT-PCR for MMP20 and KLK4\",\n      \"journal\": \"Anatomical record\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — constitutively active receptor transfection with specific gene expression readout, single lab, single method\",\n      \"pmids\": [\"19462458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ALK5 signaling in lung epithelium controls Clara cell differentiation. Deletion of Alk5 in embryonic lung epithelium blocks Clara cell differentiation and inhibits Hes1 expression. Mechanistically, ALK5 regulates Hes1 expression by inhibiting Pten, which in turn activates ERK and AKT phosphorylation.\",\n      \"method\": \"Conditional Alk5 KO (Gata5-Cre), lung epithelial cell in vitro experiments, Pten/ERK/AKT pathway analysis, Hes1 expression\",\n      \"journal\": \"Development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined cellular phenotype plus in vitro mechanistic pathway analysis, single lab\",\n      \"pmids\": [\"20147383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Neuropilin-1 (Nrp1) suppresses the stalk-cell phenotype in angiogenesis by limiting Smad2/3 activation through both ALK1 and ALK5. Notch downregulates Nrp1, thereby relieving inhibition of ALK1 and ALK5 to drive stalk-cell behavior, placing ALK5 downstream of the Dll4/Notch/Nrp1 axis in tip-stalk cell specification.\",\n      \"method\": \"Genetic manipulation of Nrp1 in endothelial cells, Smad2/3 phosphorylation assays, angiogenic sprouting assays in vivo and in vitro\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple readouts placing ALK5 in the Notch-Nrp1 pathway, replicated with multiple orthogonal approaches\",\n      \"pmids\": [\"26081042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GDF-15 inhibits CXCL1-induced β2-integrin activation and neutrophil recruitment via the ALK5 (TGF-βRI)/TGF-βRII heterodimer. Mechanistically, GDF-15 and TGFβ1 inhibit integrin activation by blocking Rap-1 activation in a CalDAG-GEF1 and Cdc42-dependent manner.\",\n      \"method\": \"Conditional gene inactivation of ALK5 or TGFBR2 in neutrophils; small-molecule inhibitors, antibodies, siRNA; intravital microscopy; β2-integrin activation assays; Rap-1 activity assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional genetic KO in neutrophils combined with pharmacological and siRNA approaches, in vivo and in vitro, multiple orthogonal methods\",\n      \"pmids\": [\"27235139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Smooth muscle cell-specific deletion of Tgfbr1 in adult mice causes rapid and severe aortic aneurysm (100% penetrance). Loss of TGFBR1 activates TGFBR2-ERK signaling and upregulates angiotensin-converting enzyme; inhibiting ERK phosphorylation or blocking the AngII/AT1R pathway prevents aneurysmal degeneration, placing TGFBR1 upstream of ERK and AngII/AT1R in aortic wall homeostasis.\",\n      \"method\": \"Inducible SMC-specific Cre-loxP knockout (Myh11-Cre), ERK inhibitor treatment, AT1R blocker treatment, aortic histology and molecular analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — inducible cell-type-specific KO with pharmacological pathway rescue experiments defining specific downstream signals\",\n      \"pmids\": [\"27739498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ALK5 controls mesodermal progenitor fate in the lung: Alk5 deletion in mesodermal progenitors inhibits αSMA+ myofibroblast differentiation and increases lipofibroblasts. This is mediated through direct and indirect modulation of PDGFRα, PPARγ, PRRX1, and ZFP423 signaling.\",\n      \"method\": \"Conditional Alk5 KO in lung mesoderm, cell lineage analysis, gene expression analysis of downstream pathway components\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined cell fate phenotype and identification of downstream transcription factors/receptors, single lab\",\n      \"pmids\": [\"26984772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TGFβ1 stimulates collagen deposition by mesenchymal stromal cells via the ALK5/Smad3 signaling pathway, and ALK5 inhibition with galunisertib ameliorates myelofibrosis in MPL and JAK2 mouse models.\",\n      \"method\": \"ALK5 inhibitor treatment in vitro and in vivo (MPL and JAK2 murine MF models), Smad3 phosphorylation assays, collagen I and III measurement\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition in both in vitro and in vivo models with defined molecular pathway readout, single lab\",\n      \"pmids\": [\"28405618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CYLD deubiquitinase loss promotes ALK5 stabilization (increased protein stability) in oral squamous cell carcinoma, leading to enhanced TGFβ signaling (increased Smad3 phosphorylation) and cell invasion. ALK5 inhibitor completely blocks the invasive phenotype induced by CYLD knockdown.\",\n      \"method\": \"siRNA knockdown of CYLD, ALK5 protein stability assays, Smad3 phosphorylation Western blot, invasion assays, ALK5 inhibitor rescue\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with pharmacological rescue, protein stability assay, multiple functional readouts, single lab\",\n      \"pmids\": [\"29235674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Pericyte ALK5 controls brain endothelial morphogenesis through a TIMP3-dependent mechanism: ALK5-depleted pericytes downregulate TIMP3, leading to elevated perivascular MMP activity, endothelial hyperproliferation, reduced pericyte coverage, and germinal matrix hemorrhage. TIMP3 administration rescues endothelial morphogenesis in ALK5 pericyte mutants.\",\n      \"method\": \"Conditional Alk5 KO in pericytes, TIMP3 protein administration rescue, MMP activity assays, histological analysis of brain microvessels\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional cell-type-specific KO with protein-level rescue (TIMP3 administration), defining a specific molecular pathway (ALK5→TIMP3→MMP activity)\",\n      \"pmids\": [\"29456135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ALK5 (TGFBR1) inactivation in the mouse uterus leads to metastatic endometrial adenocarcinoma that is estrogen-dependent and requires prior mating (postpartum context), establishing that TGFβ signaling through TGFBR1/ALK5 in the endometrium is required for endometrial homeostasis, tumor suppression, and postpartum repair.\",\n      \"method\": \"Conditional Alk5 KO in uterus (progesterone receptor Cre), histopathology, ERα and PR immunostaining, metastasis analysis\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional cell-type-specific KO with defined tumor and metastasis phenotype and molecular characterization of hormone receptor status\",\n      \"pmids\": [\"30655341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GDNF directly binds ALK5/TGFBR1 at His39 and Asp76 residues to activate hepatic stellate cells via Smad2/3 signaling (not via GFRα1), promoting liver fibrosis. This binding was determined by surface plasmon resonance, molecular docking, mutagenesis, and co-immunoprecipitation.\",\n      \"method\": \"Surface plasmon resonance, molecular docking, mutagenesis of ALK5 binding residues, Co-IP, adenoviral GDNF overexpression/CRISPR silencing in mice, primary HSC activation assays\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct binding characterized by SPR + mutagenesis of specific residues + Co-IP + in vivo genetic models, multiple orthogonal methods\",\n      \"pmids\": [\"31171625\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ALK5 signaling mediates neurogenesis and functional recovery after cerebral ischemia/reperfusion in rats via Gadd45b. ALK5 regulates Gadd45b protein levels through Smad2/3 phosphorylation, and ALK5 directly co-immunoprecipitates with Gadd45b.\",\n      \"method\": \"Lentiviral ALK5 KD/overexpression in vivo, Smad2/3 phosphorylation assays, co-immunoprecipitation of ALK5 and Gadd45b, axonal/dendritic plasticity assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus in vivo gain/loss of function with defined molecular (Smad2/3, Gadd45b) and functional (neurogenesis) readouts, single lab\",\n      \"pmids\": [\"31043581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TP-008, a selective chemical probe for ALK4 and ALK5, potently inhibits ALK5 kinase activity and strongly abrogates phosphorylation of SMAD2 in cells, confirming that ALK5 kinase activity is directly responsible for SMAD2 phosphorylation.\",\n      \"method\": \"Kinase selectivity profiling, cellular SMAD2 phosphorylation assays with TP-008 and matched negative control compound\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — selective chemical probe with matched negative control, cellular SMAD2 assay, single paper\",\n      \"pmids\": [\"32176847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ALK5 acts as a mechanoreceptor in endothelial cells to drive EndMT in response to disturbed shear stress through an ALK5-Shc signaling pathway, independent of other mechanosensors. Depletion of ALK5 abrogates shear stress-induced EndMT, and genetic targeting of endothelial Shc reduces EndMT and atherosclerosis in areas of disturbed flow.\",\n      \"method\": \"ALK5 depletion in endothelial cells, tensional force and flow reconstitution experiments, endothelial-specific Shc gene targeting in atherosclerosis model, EndMT marker analysis\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reconstitution experiments plus genetic targeting in vivo with defined pathway (Alk5-Shc) and functional/disease readout, multiple orthogonal methods\",\n      \"pmids\": [\"34244146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GDF-8 stimulates trophoblast cell invasion by upregulating MMP2 expression via the ALK5-SMAD2/3 signaling pathway. MMP9 expression is not affected by GDF-8. Knockdown of MMP2 attenuates GDF-8-induced invasiveness.\",\n      \"method\": \"siRNA knockdown of ALK5, SMAD2, SMAD3 in HTR-8/SVneo cells, MMP2/MMP9 expression assays, invasion assays\",\n      \"journal\": \"Reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA-mediated knockdown of receptor and pathway components with specific gene expression and functional invasion readouts, single lab\",\n      \"pmids\": [\"34432647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Simultaneous muscle-specific knockout of Tgfbr1 and Acvr1b (but not either alone) induces substantial myofiber hypertrophy via increased Akt and p70S6K phosphorylation and reduced E3 ligase expression, demonstrating synergistic roles of these two TGFβ type I receptors in regulating muscle fiber size and regeneration.\",\n      \"method\": \"Single and double conditional KO mice (Tgfbr1 and Acvr1b), phospho-Akt/p70S6K Western blots, E3 ligase expression, satellite cell and macrophage quantification, cardiotoxin injury model\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with single vs. double KO comparison, multiple molecular pathway readouts, replicated across different functional contexts\",\n      \"pmids\": [\"35323108\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Mitochondrial dysfunction induces enhanced ALK5-SMAD2 signaling through MAPKs-mediated phosphorylation of SMAD2 with mitochondrial localization of SMAD2, leading to retinal arteriovenous malformations. Pharmacological blockade of ALK5 or genetic SMAD2 deficiency prevents retinal vascular malformations in mitochondrial dysfunction mouse models.\",\n      \"method\": \"Endothelial-specific KO of TFAM, COX10, or TRX2; single-cell RNA-seq; pharmacological ALK5 inhibition; SMAD2 genetic KO rescue; phospho-SMAD2 localization studies\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — three independent genetic models plus pharmacological and genetic rescue, scRNA-seq pathway analysis, multiple orthogonal methods\",\n      \"pmids\": [\"36496409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CD147 directly binds ALK5, promoting ALK5 activation and endocytosis, leading to SMAD2/3 phosphorylation and nuclear translocation. N-glycosylation of CD147 (by GNT-V) under high glucose conditions prevents its ubiquitin-proteasome degradation, sustaining ALK5 activation and cardiac fibrosis in diabetic cardiomyopathy.\",\n      \"method\": \"Co-IP of CD147 and ALK5, AAV9-mediated cardiac-specific CD147 silencing/overexpression, endocytosis assays, SMAD2/3 phosphorylation/nuclear translocation, glycosylation manipulation\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional in vivo AAV knockdown/overexpression and mechanistic endocytosis assays, single lab\",\n      \"pmids\": [\"36594096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RCN3 promotes fibroblast activation and lung fibrosis through a TGFβ1-RCN3-TGFBR1 positive feedback loop: TGFβ1 upregulates RCN3, which detains EZH2 in the cytoplasm via RCN3-EZH2 interaction, releasing EZH2-H3K27me3 epigenetic repression of TGFBR1 to sustain TGFBR1 expression.\",\n      \"method\": \"BioID protein interaction assay, RCN3-EZH2 Co-IP, epigenetic (H3K27me3) analysis of TGFBR1 promoter, fibroblast-selective Rcn3 KD mouse model, bleomycin fibrosis model\",\n      \"journal\": \"Respiratory research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — BioID + Co-IP + epigenetic promoter analysis + in vivo KD model, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"37710230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NRP1 interacts with TGFBR2 through their cytoplasmic domains, activating the TGFBR1/TGFBR2 complex, which facilitates macropinocytosis-mediated KSHV internalization into mesenchymal stem cells via Cdc42 and Rac1.\",\n      \"method\": \"Co-IP of NRP1 and TGFBR2, NRP1 KO and overexpression in MSCs, KSHV infection assays, macropinocytosis assays, Cdc42/Rac1 activity measurements\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with domain-level analysis, genetic KO/OE, pathway (Cdc42/Rac1) functional readouts, single lab\",\n      \"pmids\": [\"37224259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LPAR5 (lysophosphatidic acid receptor 5) transactivates TGFBR1 to stimulate mRNA expression of GAG biosynthesis genes XYLT1 and CHST3 in vascular smooth muscle cells. This LPAR5-to-TGFBR1 transactivation occurs through a ROCK-dependent pathway, and ROS/Akt signaling are not involved.\",\n      \"method\": \"Pharmacological inhibition of LPAR5 and TGFBR1, ROCK inhibitor experiments, XYLT1/CHST3 mRNA expression assays, ROS and Akt pathway analysis in VSMCs\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection of GPCR-to-TGFBR1 transactivation pathway with multiple inhibitor combinations, single lab\",\n      \"pmids\": [\"32920014\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Multiple self-healing squamous epithelioma (MSSE) maps to chromosome 9q22-q31, and genetic mapping excluded XPA and PTCH as causative genes, narrowing the interval. TGFBR1 (also known as MSSE/ESS1 by alias) was later identified as the MSSE gene through loss-of-function mutations.\",\n      \"method\": \"Linkage analysis, haplotype analysis, SSCP, DNA sequencing of candidate genes in MSSE families\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — genetic mapping study excluding candidates, not directly establishing TGFBR1 function; connection to TGFBR1 as MSSE gene established in later work\",\n      \"pmids\": [\"9439661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Loss-of-function mutations in TGFBR1 cause MSSE (Ferguson-Smith disease/multiple self-healing squamous epithelioma) in a digenic manner requiring permissive variants at a second linked locus on chromosome 9q. The spectrum of TGFBR1 mutations in MSSE differs from those in Loeys-Dietz syndrome.\",\n      \"method\": \"Haplotype analysis, mutation screening in MSSE families, review of families with both MSSE and Loeys-Dietz syndrome\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — genetic evidence across multiple families establishing digenic inheritance, but mechanistic biochemical data not directly provided in this paper\",\n      \"pmids\": [\"33256177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Lumican C-terminal peptide LumC13 binds directly to ALK5/TGFBR1, forming a stable complex. Computational design of LumC13 derivatives identified minimal residues required for stable lumican/ALK5 complex formation, and these peptides promote corneal epithelial cell migration and wound healing.\",\n      \"method\": \"In silico binding modeling, in vitro cell migration assays, in vivo corneal wound healing, computational derivative design with experimental validation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — computational binding characterization validated in vitro and in vivo, but no direct high-resolution structural or biophysical binding measurement reported in abstract\",\n      \"pmids\": [\"28181591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TGFβ1 induces ZIP8 expression via the ALK5-Smad2/3 signaling pathway in vascular endothelial cells, with Smad3-mediated induction occurring with or without p38 MAPK co-activation. This upregulation of ZIP8 increases intracellular cadmium accumulation and potentiates cadmium cytotoxicity.\",\n      \"method\": \"ALK5 inhibitor (SB431542), Smad2/3 knockdown, p38 MAPK inhibitor, ZIP8 expression assays, cadmium uptake and cytotoxicity assays in endothelial cells\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and siRNA-mediated dissection of pathway components with defined molecular and functional readouts, single lab\",\n      \"pmids\": [\"35008873\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TGFBR1/ALK5 is a transmembrane serine/threonine kinase receptor that, upon TGFβ ligand binding (and transphosphorylation by TGFBR2), canonically phosphorylates Smad2 and Smad3 to drive transcriptional responses including EMT, fibrosis, and growth inhibition; it also non-canonically phosphorylates Smad1/5 through its L45 loop to promote cell migration, recruits ALK1 into receptor complexes to enable opposing ALK1-Smad1/5 signaling, phosphorylates the endoglin cytoplasmic domain to regulate Smad1/5/8 activity, and functions as a mechanosensor in endothelial cells to drive EndMT via a Shc-dependent pathway, while its activity is regulated post-translationally by CYLD-mediated ubiquitination (affecting stability), CD147-mediated endocytosis, and EZH2-H3K27me3 epigenetic control of its own expression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TGFBR1 (ALK5) is the type I transmembrane serine/threonine kinase receptor that transduces TGFβ-family ligand signals into canonical Smad-dependent transcriptional programs governing epithelial-mesenchymal transition, tissue morphogenesis, fibrosis, and growth control [#1, #2, #25]. Within the receptor complex it cooperates with TGFBR2 and accessory receptors and, in endothelial and chondrocyte contexts, recruits ALK1 and assembles with endoglin and betaglycan; ALK5 kinase activity is required for optimal ALK1 activation, and ALK1-Smad1/5 signaling reciprocally antagonizes the ALK5-Smad2/3 axis [#0, #8]. Its principal catalytic output is phosphorylation of Smad2 and Smad3, demonstrated directly with selective kinase inhibition, driving EMT, collagen and ECM gene expression (PAI-1, fibronectin, type II collagen), and growth-inhibitory responses [#1, #8, #25]. Beyond this canonical axis ALK5 phosphorylates Smad1 and Smad5 through its kinase activity and L45 loop to promote cell migration, and basally phosphorylates the endoglin cytoplasmic domain at serines 646/649 to regulate Smad1/5/8 output [#7, #9]. ALK5 acts as a dose-dependent tumor suppressor in intestine, uterus, and squamous epithelium through Smad-mediated growth control, with haploinsufficiency raising cyclin D1 and proliferation [#12, #22]; loss of TGFBR1 can paradoxically unleash TGFBR2-ERK and angiotensin signaling, producing aortic aneurysm [#17]. In endothelium ALK5 functions as a mechanoreceptor that drives EndMT under disturbed shear stress via an ALK5-Shc pathway [#26]. Receptor abundance and activity are controlled post-translationally and epigenetically: CYLD deubiquitinase loss stabilizes ALK5 to enhance invasion [#20], CD147 binds and promotes ALK5 activation and endocytosis [#30], and a TGFβ1-RCN3 loop relieves EZH2-H3K27me3 repression of the TGFBR1 promoter to sustain its expression [#31]. Germline and somatic TGFBR1 mutations cause Loeys-Dietz syndrome, where mutant alleles paradoxically yield elevated tissue TGFβ signaling [#3], and loss-of-function mutations cause multiple self-healing squamous epithelioma (Ferguson-Smith disease) in a digenic manner [#35].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that TGFβ-induced EMT in epithelial cells is channeled specifically through ALK5 and its downstream Smad2/3/Smad4 module, defining the receptor's core transcriptional effector pathway.\",\n      \"evidence\": \"Adenoviral constitutively active ALK5 and dominant-negative constructs with Smad co-expression and cytoskeletal/E-cadherin readouts in mammary epithelial cells\",\n      \"pmids\": [\"10574705\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which target genes mediate the cytoskeletal reorganization\", \"Cooperative thresholds defined in vitro, not in vivo\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Resolved how ALK5 integrates with ALK1 in endothelium, showing ALK5 kinase activity recruits and activates ALK1, which then opposes ALK5-Smad2/3 signaling — a reciprocal balance controlling endothelial behavior.\",\n      \"evidence\": \"ALK5-null endothelial cells, Co-IP complex formation, reporter and kinase assays\",\n      \"pmids\": [\"14580334\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the ALK5/ALK1 complex not defined\", \"How the balance is set in different vascular beds unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrated by domain-specific genetic rescue that Smad-dependent (not merely kinase) signaling downstream of ALK5 is required for a developmental fusion event, separating ALK5 kinase activity from its Smad-coupling function.\",\n      \"evidence\": \"Conditional rescue with activated/kinase-dead and Smad-deficient ALK5 mutants in Tgfβ3-null palatal explants\",\n      \"pmids\": [\"14729481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Smad-independent ALK5 outputs in this tissue not characterized\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Connected TGFBR1 to human disease, showing Loeys-Dietz mutations paradoxically increase tissue TGFβ signaling despite reduced signal propagation in vitro, and that a cancer-associated 6A polymorphism can convert growth-inhibitory into growth-stimulatory signaling.\",\n      \"evidence\": \"Patient-derived tissues with phospho-Smad2/collagen/CTGF staining; in vitro translation and TGFβ proliferation assays in transfected cells\",\n      \"pmids\": [\"15731757\", \"16204663\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism reconciling reduced receptor activity with elevated tissue signaling unresolved\", \"6A signal-peptide effect on receptor processing not structurally defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined non-overlapping in vivo roles by mapping ALK5 to medial/adventitial vascular layers and showing ALK5-null vascular smooth muscle defects distinct from ALK1-null lumen defects.\",\n      \"evidence\": \"Alk5-lacZ knockin reporter mice with comparative Alk5-null and Alk1-null phenotype analysis\",\n      \"pmids\": [\"16344855\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type-specific contribution of ALK5 to SMC formation not dissected at the molecular level\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Expanded ALK5's catalytic repertoire beyond Smad2/3 by showing its kinase activity and L45 loop phosphorylate Smad1/5 to drive migration, and that it directly phosphorylates the endoglin cytoplasmic tail to set Smad1/5/8 output.\",\n      \"evidence\": \"shRNA-resistant L45-loop ALK5 mutants with in vitro kinase and migration assays; site-directed mutagenesis of endoglin S646/S649 with Smad1/5/8 reporters\",\n      \"pmids\": [\"19096363\", \"20042635\", \"18333754\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of L45-mediated substrate selection not solved\", \"Physiological contexts where Smad1/5 branch dominates not mapped\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established TGFBR1 as a dose-dependent intestinal tumor suppressor, linking receptor gene dosage to Smad phosphorylation, cyclin D1 levels, and proliferation.\",\n      \"evidence\": \"Tgfbr1+/- ; ApcMin/+ mice with tumor counts, Smad phospho-blots, cyclin D1 IHC, BrdU assays\",\n      \"pmids\": [\"19147584\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Threshold of receptor activity defining tumor suppression vs promotion not quantified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified receptor-specific developmental functions of ALK5 distinct from TGFBR2, including neural-crest patterning via Gsc and lung Clara cell differentiation via a Pten/ERK/AKT-Hes1 mechanism.\",\n      \"evidence\": \"Side-by-side Wnt1-Cre Alk5 vs Tgfbr2 conditional KOs and Gata5-Cre lung KO with pathway and gene-expression analyses\",\n      \"pmids\": [\"18572160\", \"20147383\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ALK5 signals independently of TGFBR2 in these tissues mechanistically unclear\", \"Pten regulation by ALK5 not biochemically defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed ALK5 loss in vascular smooth muscle drives aneurysm by de-repressing TGFBR2-ERK and AngII/AT1R signaling, revealing a homeostatic restraint function whose loss redirects signaling pathologically.\",\n      \"evidence\": \"Inducible Myh11-Cre Tgfbr1 KO with ERK-inhibitor and AT1R-blocker rescue, aortic histology\",\n      \"pmids\": [\"27739498\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular link between ALK5 loss and ERK activation not defined\", \"Relationship to Loeys-Dietz aneurysm mechanism unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extended ALK5 signaling into immune and angiogenic contexts, mediating GDF-15 suppression of integrin activation in neutrophils and placing ALK5 downstream of Dll4/Notch/Nrp1 in tip-stalk cell specification.\",\n      \"evidence\": \"Conditional neutrophil ALK5 KO with Rap-1 assays; Nrp1 genetic manipulation with Smad2/3 and sprouting readouts\",\n      \"pmids\": [\"27235139\", \"26081042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether these effects are Smad-dependent or Smad-independent not fully resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified novel ligands and effectors of ALK5, including direct GDNF binding at His39/Asp76 to activate hepatic stellate cells, and Gadd45b coupling in post-ischemic neurogenesis.\",\n      \"evidence\": \"SPR, molecular docking, residue mutagenesis and Co-IP for GDNF; lentiviral ALK5 manipulation with Co-IP and Smad2/3 assays for Gadd45b\",\n      \"pmids\": [\"31171625\", \"31043581\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GDNF-ALK5 signaling requires TGFBR2 not addressed\", \"Structural detail of GDNF-ALK5 interface beyond docking lacking\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established ALK5 as a mechanoreceptor in endothelium that drives EndMT under disturbed shear stress through an ALK5-Shc pathway promoting atherosclerosis, identifying a non-ligand-driven activation mode.\",\n      \"evidence\": \"ALK5 depletion, force/flow reconstitution, and endothelial Shc genetic targeting in an atherosclerosis model\",\n      \"pmids\": [\"34244146\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How mechanical force activates ALK5 biochemically not defined\", \"Relationship between mechano-activation and ligand-dependent activation unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined post-translational and stress-driven control of ALK5: CYLD loss stabilizes the receptor to enhance invasion, CD147 binds to promote its activation and endocytosis, and mitochondrial dysfunction amplifies ALK5-SMAD2 signaling via MAPKs.\",\n      \"evidence\": \"CYLD siRNA with stability and invasion assays; CD147 Co-IP and AAV cardiac models with endocytosis readouts; endothelial TFAM/COX10/TRX2 KOs with ALK5 inhibition and SMAD2 rescue\",\n      \"pmids\": [\"29235674\", \"36594096\", \"36496409\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct ubiquitination sites on ALK5 not mapped\", \"How CD147 binding promotes kinase activation mechanistically unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Uncovered epigenetic control of TGFBR1 expression itself, where a TGFβ1-RCN3 feedback loop sequesters EZH2 in the cytoplasm to relieve H3K27me3 repression of the TGFBR1 promoter, sustaining fibrosis.\",\n      \"evidence\": \"BioID, RCN3-EZH2 Co-IP, H3K27me3 promoter analysis, fibroblast Rcn3 KD bleomycin model\",\n      \"pmids\": [\"37710230\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality of this loop beyond lung fibroblasts unknown\", \"Direct EZH2 occupancy dynamics at the TGFBR1 promoter not time-resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Linked TGFBR1 loss-of-function to multiple self-healing squamous epithelioma, establishing a digenic inheritance requiring permissive variants at a second 9q locus and distinguishing its mutation spectrum from Loeys-Dietz syndrome.\",\n      \"evidence\": \"Haplotype and mutation screening across MSSE families with review of co-occurring Loeys-Dietz cases\",\n      \"pmids\": [\"33256177\", \"9439661\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the required second 9q locus not established\", \"Mechanistic explanation for tissue-restricted skin phenotype lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ALK5's distinct activation modes (ligand binding, mechanical force, GPCR transactivation) and its multiple substrate branches (Smad2/3, Smad1/5, endoglin, Shc) are selected and integrated within a single cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model integrating substrate selection across conditions\", \"Quantitative rules governing canonical vs non-canonical output unknown\", \"Crosstalk between mechano- and ligand-driven activation not defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [7, 9, 25]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [7, 9, 25]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 26]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [23, 30, 26]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 8, 25]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 11, 6]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 17, 22, 35]}\n    ],\n    \"complexes\": [\n      \"TGFBR1/TGFBR2 receptor complex\",\n      \"ALK5/ALK1/endoglin/betaglycan complex\"\n    ],\n    \"partners\": [\n      \"TGFBR2\",\n      \"ALK1\",\n      \"endoglin\",\n      \"Shc\",\n      \"CD147\",\n      \"GDNF\",\n      \"Gadd45b\",\n      \"Smad3\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}