{"gene":"DDR1","run_date":"2026-04-28T17:46:02","timeline":{"discoveries":[{"year":2006,"finding":"DDR1 forms ligand-independent dimers in the biosynthetic pathway and on the cell surface; the transmembrane leucine zipper (but not the GXXXG motif) is required for collagen-induced signaling, as leucine-zipper mutations abolish kinase activation while still permitting dimerization. Both extracellular and cytoplasmic domains are individually dispensable for dimerization.","method":"Chemical cross-linking, co-immunoprecipitation of differentially tagged DDR1 constructs, TOXCAT bacterial membrane reporter assay, site-directed mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal methods (cross-linking, co-IP, mutagenesis, TOXCAT) in a single rigorous study","pmids":["16774916"],"is_preprint":false},{"year":2007,"finding":"DDR1 exists as a disulfide-linked dimer; cysteines 303 and 348 in the stalk region of the extracellular domain are necessary for dimerization, collagen binding, and kinase activation. Deletion of the discoidin domain does not prevent dimerization, whereas deletion of the stalk region abolishes it.","method":"Non-reducing SDS-PAGE, deletion and point mutagenesis of extracellular domain, collagen-binding and kinase activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with functional assays (collagen binding, kinase activity)","pmids":["18065762"],"is_preprint":false},{"year":2017,"finding":"Collagen activates DDR1 through lateral association of pre-formed DDR1 dimers and trans-phosphorylation between dimers. Receiver dimers (kinase-dead) are phosphorylated by donor DDR1 in a collagen-dependent manner requiring donor kinase activity but not receiver kinase activity; transmembrane domain mutation abolishes trans-phosphorylation, and collagen-binding-deficient DDR1 is recruited into DDR1 signaling clusters.","method":"Co-expression of signalling-incompetent ('receiver') and functional ('donor') DDR1 mutants, enforced covalent dimerization constructs, mutagenesis of transmembrane domain, fluorescence-based clustering assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with multiple engineered mutants and orthogonal approaches in a single rigorous study","pmids":["28590245"],"is_preprint":false},{"year":2004,"finding":"The DDR1 collagen-binding site maps to four surface-exposed loops of the discoidin domain: residues Ser52–Thr57 (loop 1), Arg105–Lys112 (loop 3), and Ser175 (loop 4) are critically required for collagen binding, as determined by alanine-scanning and deletion mutagenesis of GST-fusion discoidin domain proteins in solid-phase collagen-binding assays.","method":"GST-fusion protein expression in insect cells, solid-phase collagen-binding assay, ELISA-based collagen binding, alanine-scanning and deletion mutagenesis, 3D homology modeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis plus in vitro binding assays with multiple mutants","pmids":["15136580"],"is_preprint":false},{"year":2008,"finding":"Collagen stimulation induces rapid aggregation and internalization of DDR1 dimers into early endosomes, preceding receptor activation. Significant FRET signal indicating DDR1 dimerization is present even without collagen; collagen causes clustering and sharp FRET increase in aggregated receptor regions.","method":"FRET microscopy with CFP- and YFP-tagged DDR1 in live cells, internalization kinetics imaging","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 — direct live-cell imaging with FRET and quantitative kinetics","pmids":["19007791"],"is_preprint":false},{"year":2005,"finding":"Collagen-induced DDR1 activation leads to phosphorylation of multiple tyrosine residues; Nck2 and Shp-2 bind DDR1 in a collagen-dependent manner. The Shp-2 binding site was mapped to Tyr-740 within an ITIM-consensus sequence. DDR1 ablation in mouse mammary gland causes delocalized Nck2 expression, linking DDR1-Nck2 interaction to alveologenesis defects.","method":"Phosphopeptide mapping, site-directed mutagenesis, SH2 domain pull-down, co-immunoprecipitation, DDR1-null mouse mammary gland analysis","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1–2 — phosphopeptide mapping with mutagenesis plus in vivo genetic model","pmids":["16337946"],"is_preprint":false},{"year":2001,"finding":"DDR1 regulates smooth muscle cell attachment to collagen, chemotaxis, proliferation, and MMP production. DDR1-null mice show significantly reduced neointimal thickening and collagen deposition after carotid artery injury, establishing DDR1 as a collagen receptor mediating vascular wound repair.","method":"DDR1-knockout mouse model, carotid artery injury model, in vitro smooth muscle cell assays (migration, proliferation, MMP production)","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined cellular and in vivo phenotypic readouts","pmids":["11254672"],"is_preprint":false},{"year":2001,"finding":"Wnt-5a is a co-factor necessary for collagen-induced DDR1 phosphorylation in mammary epithelial cells. Repression of Wnt-5a abolishes DDR1 phosphorylation, impairs cell-collagen interaction, and enhances motility; conversely, Wnt-5a overexpression enables DDR1 phosphorylation in non-Wnt-5a-producing cells. This effect is independent of β-catenin/canonical Wnt signaling.","method":"Antisense repression and overexpression of Wnt-5a, DDR1 phosphorylation assays, collagen binding assays, cell migration assays, β-catenin pathway inhibition","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays, single lab","pmids":["11493640"],"is_preprint":false},{"year":2011,"finding":"DDR1 promotes E-cadherin-mediated cell-cell adhesion and epithelial differentiation by stabilizing E-cadherin at the plasma membrane through inactivation of Cdc42. DDR1 overexpression reduces E-cadherin degradation rate and increases its membrane stability (shown by FRAP/photoconversion); dominant-negative DDR1 has opposite effects.","method":"DDR1 overexpression and knockdown, photobleaching (FRAP) and photoconversion of Eos-E-cadherin, pull-down assays, constitutively active/dominant-negative Cdc42 constructs","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including live-cell FRAP and mutagenesis","pmids":["21289093"],"is_preprint":false},{"year":2018,"finding":"DDR1 identifies BCR as a substrate: nilotinib inhibits DDR1 kinase activity and prevents DDR1-mediated BCR phosphorylation at Tyr177, which is required to maintain β-catenin transcriptional activity necessary for colorectal cancer cell invasion.","method":"Quantitative phosphoproteomics, nilotinib treatment, co-immunoprecipitation, β-catenin reporter assays, invasion assays","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 1–2 — phosphoproteomics substrate identification with functional validation","pmids":["29438985"],"is_preprint":false},{"year":2022,"finding":"DDR1 promotes kidney inflammation and fibrosis via phosphorylation of BCR in renal proximal tubule cells, which increases β-catenin activity and MCP-1 production. DDR1 also activates STAT3 to stimulate TGF-β secretion. DDR1-induced BCR phosphorylation or BCR downregulation both increase MCP-1, indicating BCR acts as a negative regulator downstream of DDR1.","method":"Ddr1-null mouse ischemia/reperfusion model, co-immunoprecipitation, phosphorylation assays, β-catenin reporter, siRNA knockdown","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — genetic KO mouse model plus mechanistic in vitro dissection with multiple methods","pmids":["34941574"],"is_preprint":false},{"year":2021,"finding":"DDR1 extracellular domain (ECD), but not its intracellular kinase domain, is required for immune exclusion in triple-negative breast cancer. DDR1-ECD binding to collagen enforces aligned collagen fibers that obstruct T cell infiltration. Membrane-untethered DDR1-ECD is sufficient to rescue tumor growth in immunocompetent hosts.","method":"Ddr1 knockout mouse tumor models, domain-specific rescue constructs (ECD vs. kinase-dead), ECD-neutralizing antibodies, collagen fiber alignment imaging, T cell infiltration quantification","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — genetic rescue dissection with domain-specific constructs plus antibody perturbation in vivo","pmids":["34732895"],"is_preprint":false},{"year":2022,"finding":"Matrix-metalloprotease-cleaved collagen I (cCol I) activates DDR1-NF-κB-p62-NRF2 signaling to promote pancreatic cancer growth; intact collagen I (iCol I) triggers DDR1 degradation and restrains growth. Inhibition of NF-κB or mitochondrial biogenesis downstream of DDR1 blocks tumorigenesis in wild-type but not MMP-resistant collagen I-expressing mice.","method":"Genetic mouse models with MMP-resistant collagen I, DDR1 knockout/inhibition, NF-κB inhibition, in vivo tumor assays, western blotting for NRF2/p62 pathway","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic mouse models with epistasis establishing pathway order","pmids":["36198801"],"is_preprint":false},{"year":2022,"finding":"DDR1 undergoes stiffness/collagen-stimulated liquid-liquid phase separation (LLPS), co-condensing with LATS1 to competitively inhibit MOB1 binding to LATS1 and thereby suppress LATS1 phosphorylation, leading to YAP activation. The transmembrane domain drives DDR1 droplet formation; the C-terminus is required for co-condensation with LATS1. Single-point C-terminus mutants (H745P, H902P) abolish co-condensation.","method":"VSMCs on polyacrylamide gels of varying stiffness, LLPS assays with purified DDR1 domains, mutagenesis, co-immunoprecipitation/co-condensation assays, SMC-specific Ddr1-KO mice with LATS1 inhibition, YAP activity assays","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1–2 — reconstitution with purified domains, mutagenesis, and in vivo genetic rescue","pmids":["36475898"],"is_preprint":false},{"year":2022,"finding":"ECM stiffness induces DDR1 phosphorylation, oligomerization, and endocytosis in a collagen-independent manner in vascular smooth muscle cells, leading to ERK and p53 pathway activation that represses DNMT1 expression, resulting in a proinflammatory phenotype.","method":"VSMCs on PA gels of varying stiffness, DDR1 phosphorylation/oligomerization/endocytosis assays, ERK and p53 pathway inhibition, DNMT1 expression assays, DDR1 inhibitor treatment in vivo","journal":"Bioactive materials","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vitro and in vivo methods, single lab","pmids":["35386458"],"is_preprint":false},{"year":2015,"finding":"DDR1 constitutively associates with IGF-IR; IGF-I stimulation enhances this interaction and promotes rapid DDR1 tyrosine phosphorylation and co-internalization with IGF-IR into early endosomes. DDR1 is critical for IGF-IR endocytosis, trafficking, and protein expression, as well as IGF-I-induced signaling and biological responses. Reciprocally, IGF-IR is required for collagen-dependent DDR1 phosphorylation.","method":"Co-immunoprecipitation, DDR1 silencing and overexpression, IGF-IR endocytosis/trafficking assays, co-transfection in mouse fibroblasts","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2–3 — reciprocal co-IP plus functional trafficking assays, single lab","pmids":["25840417"],"is_preprint":false},{"year":2019,"finding":"DDR1 drives glioblastoma therapy resistance by associating with a YWHA/14-3-3–BECN1–AKT1 multiprotein complex that promotes pro-survival AKT-MTOR signaling and suppresses autophagy. DDR1 inhibition sensitizes glioblastoma cells to radio- and chemotherapy by inducing autophagic cell death.","method":"Co-immunoprecipitation of multiprotein complex, DDR1 inhibition/knockdown, autophagy flux assays, clonogenic survival after irradiation/chemotherapy","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2–3 — complex identification by co-IP with functional autophagy readout, single lab","pmids":["31117874"],"is_preprint":false},{"year":2013,"finding":"Oligomers of recombinant DDR1-Fc extracellular domain bind collagen with higher affinity than dimeric DDR1-Fc alone. DDR1-Fc oligomerizes upon in vitro collagen binding as shown by AFM. Inhibition of dynamin-mediated endocytosis blocks ligand-induced internalization of DDR1 but does not affect oligomerization.","method":"Solid-phase binding assays, atomic force microscopy, dynamin inhibition, live-cell internalization assays","journal":"Journal of structural biology","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro reconstitution with AFM imaging, single lab","pmids":["23810922"],"is_preprint":false},{"year":2017,"finding":"TM4SF1 colocalizes with and co-immunoprecipitates with DDR1 in pancreatic cancer cells; TM4SF1 silencing reduces DDR1 expression and invadopodia formation, and DDR1 overexpression rescues the inhibitory effects of TM4SF1 silencing on migration, invasion, and MMP2/9 expression.","method":"Co-immunoprecipitation, double immunofluorescence, siRNA knockdown, DDR1 rescue overexpression, invadopodia functional assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP plus rescue experiments, single lab","pmids":["28368050"],"is_preprint":false},{"year":2020,"finding":"Periostin signals through DDR1 to promote cartilage degeneration: genetic deficiency or pharmacological inhibition of DDR1 in mouse chondrocytes blocks periostin-induced MMP-13 expression and collagen/proteoglycan degradation downstream of AKT/β-catenin.","method":"DDR1-knockout mouse chondrocytes, DDR1 pharmacological inhibitor, periostin stimulation assays, MMP-13 expression readout","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — genetic and pharmacological perturbation with defined molecular readout","pmids":["32330138"],"is_preprint":false},{"year":2020,"finding":"LRP-1 interacts with DDR1 at the plasma membrane in colon cancer cells and regulates DDR1 cell-surface levels through endocytosis. LRP-1-mediated DDR1 endocytosis promotes cell cycle progression and decreases apoptosis.","method":"Co-immunoprecipitation, LRP-1 knockdown, DDR1 surface expression quantification, 3D collagen matrix proliferation/apoptosis assays","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 3 — single co-IP plus functional endocytosis assays","pmids":["32582700"],"is_preprint":false},{"year":2022,"finding":"DDR1 promotes YAP/TAZ nuclear localization and transcriptional activity in VSMCs; YAP/TAZ knockdown attenuates DDR1 expression, and YAP/TAZ bind to the Ddr1 promoter in response to collagen or increased substrate stiffness, establishing a DDR1-YAP/TAZ positive feedback loop for DDR1 auto-regulation.","method":"DDR1-KO and WT VSMCs on varied-stiffness substrates, YAP/TAZ nuclear localization assays, ChIP at Ddr1 promoter, YAP/TAZ siRNA knockdown, collagen stimulation","journal":"Matrix biology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP plus genetic KO with functional readout, single lab","pmids":["35562016"],"is_preprint":false},{"year":2023,"finding":"DDR1 interacts with CD44 as a co-receptor that amplifies collagen I-induced DDR1 signaling. Collagen I–DDR1 activation antagonizes Hippo signaling by facilitating PP2AA recruitment to MST1, leading to MST1 dephosphorylation and exaggerated YAP activation, promoting HCC cancer stem cell properties.","method":"Co-immunoprecipitation (DDR1–CD44 and PP2AA–MST1 interactions), in vitro and in vivo DDR1 activation assays, combined DDR1/YAP inhibition experiments","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2–3 — co-IP with pathway dissection and in vivo validation, single lab","pmids":["37117273"],"is_preprint":false},{"year":2022,"finding":"DDR1 promotes intestinal barrier disruption in ulcerative colitis via the NF-κB p65-MLCK-p-MLC2 pathway, leading to tight junction protein degradation and epithelial apoptosis. DDR1 knockout mice show alleviated barrier injury, upregulated tight junction proteins, and reduced proinflammatory cytokines after DSS-induced colitis.","method":"DDR1-knockout and WT mice (DSS colitis model), DDR1 overexpression and shRNA in epithelial cell monolayers, NF-κB p65 inhibition (JSH-23), tight junction protein assays","journal":"Pharmacological research","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse model plus pathway inhibition, single lab","pmids":["35905891"],"is_preprint":false},{"year":2024,"finding":"DDR1 directly interacts with the PAS domain of HIF-1α, suppresses HIF-1α ubiquitination and degradation, and strengthens HIF-1α transcriptional regulation of angiogenesis. DDR1 also promotes actin cytoskeleton reorganization via HIF-1α/RhoA/ROCK1 signaling to enhance gastric cancer metastasis.","method":"Co-immunoprecipitation (DDR1–HIF-1α PAS domain), ubiquitination assays, RhoA/ROCK1 pathway assays, PDX and organoid models with DDR1 inhibition","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2–3 — co-IP with domain specificity plus functional PDX/organoid validation","pmids":["39024501"],"is_preprint":false},{"year":2022,"finding":"DDR1 promotes migration and invasion of breast cancer cells by binding to Src and FAK (co-immunoprecipitation) and activating Src-FAK signaling; inhibition of FAK and Src attenuates DDR1-enhanced migration.","method":"Co-immunoprecipitation of DDR1 with Src and FAK, DDR1 knockdown/overexpression, Src and FAK inhibitor treatment, migration/invasion assays","journal":"Neoplasma","confidence":"Low","confidence_rationale":"Tier 3 — single co-IP plus inhibitor rescue, single lab","pmids":["35818965"],"is_preprint":false},{"year":2021,"finding":"DDR1 instructs breast epithelial stem cell differentiation into basal cells, which in turn stimulate luminal progenitor differentiation via Notch signaling to form lobules in a 3D biomimetic breast tissue model. This establishes DDR1 as the receptor linking ECM collagen signals to multi-lineage stem cell differentiation.","method":"3D biomimetic human breast tissue engineering, DDR1 inhibition/knockdown, Notch pathway inhibition, lineage differentiation assays","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — defined loss-of-function in organotypic 3D model with epistasis (DDR1→basal→Notch→luminal)","pmids":["34893587"],"is_preprint":false},{"year":2023,"finding":"A humanized DDR1 antibody (PRTH-101) binds the discoidin-like (DS-like) domain (not the collagen-binding DS domain) of DDR1 ECD as revealed by 3.15-Å crystal structure of the DDR1-ECD/Fab complex. Mechanistically, PRTH-101 inhibits DDR1 phosphorylation, decreases collagen-mediated cell attachment, and blocks DDR1 shedding from the cell surface.","method":"Crystal structure at 3.15 Å resolution, DDR1 phosphorylation assays, cell attachment assays, DDR1 shedding assays, in vivo tumor model with collagen fiber alignment imaging","journal":"Journal for immunotherapy of cancer","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation across multiple orthogonal assays","pmids":["37328286"],"is_preprint":false}],"current_model":"DDR1 is a collagen-binding receptor tyrosine kinase that exists as pre-formed disulfide-linked dimers on the cell surface; collagen binding induces lateral association of DDR1 dimers, clustering, and trans-phosphorylation between dimers mediated by the transmembrane leucine zipper, with downstream signaling through multiple phosphotyrosine-dependent interactions (including Shp-2 at Y740, Nck2, BCR, Src, FAK, and STAT3) that regulate cell adhesion, migration, MMP production, NF-κB/NRF2 metabolic signaling, YAP/LATS1 mechanotransduction via liquid-liquid phase separation, and ECM remodeling in contexts ranging from fibrosis and vascular injury to cancer progression and immune exclusion."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing DDR1 as a physiologically relevant collagen receptor in vivo: DDR1-null mice showed reduced neointimal thickening after vascular injury, demonstrating that DDR1 mediates smooth muscle cell adhesion, migration, MMP production, and collagen deposition during wound repair.","evidence":"DDR1-knockout mouse carotid artery injury model with in vitro SMC assays","pmids":["11254672"],"confidence":"High","gaps":["Downstream signaling intermediates not identified","Relative contribution of kinase activity vs. ECD-mediated collagen organization unknown"]},{"year":2001,"claim":"Identifying a non-canonical co-factor requirement: Wnt-5a was shown to be necessary for collagen-induced DDR1 phosphorylation in mammary epithelial cells, operating independently of β-catenin, suggesting DDR1 activation is context-dependent.","evidence":"Antisense repression and overexpression of Wnt-5a with DDR1 phosphorylation and cell migration assays","pmids":["11493640"],"confidence":"Medium","gaps":["Mechanism by which Wnt-5a facilitates DDR1 phosphorylation not defined","Not replicated in other cell types","Direct physical interaction between Wnt-5a and DDR1 not demonstrated"]},{"year":2004,"claim":"Mapping the collagen-binding interface: alanine-scanning mutagenesis identified four surface-exposed loops of the discoidin domain essential for collagen binding, providing the first structural map of DDR1 ligand recognition.","evidence":"GST-fusion discoidin domain mutagenesis with solid-phase collagen-binding assays and homology modeling","pmids":["15136580"],"confidence":"High","gaps":["No atomic-resolution structure of the DDR1–collagen complex","Collagen-type selectivity determinants not fully resolved"]},{"year":2005,"claim":"Identifying first proximal signaling effectors: phosphopeptide mapping revealed Nck2 and Shp-2 as collagen-dependent DDR1-binding partners, with Shp-2 binding mapped to Tyr-740 in an ITIM motif, and DDR1-null mammary glands showed mislocalized Nck2.","evidence":"Phosphopeptide mapping, mutagenesis, SH2 pull-downs, co-IP, DDR1-null mouse mammary analysis","pmids":["16337946"],"confidence":"High","gaps":["Functional consequence of Shp-2 recruitment to Y740 on downstream pathways not determined","Additional phosphotyrosine-dependent effectors likely exist"]},{"year":2006,"claim":"Resolving the dimerization mechanism: DDR1 forms ligand-independent dimers in the biosynthetic pathway, and the transmembrane leucine zipper—not the GXXXG motif—is specifically required for collagen-induced kinase activation while being dispensable for dimerization per se.","evidence":"Chemical cross-linking, co-IP of differentially tagged constructs, TOXCAT assay, site-directed mutagenesis","pmids":["16774916"],"confidence":"High","gaps":["Structure of the transmembrane leucine zipper dimer not solved","Mechanism coupling TM conformational change to kinase activation unclear"]},{"year":2007,"claim":"Identifying disulfide bonds that stabilize the dimer: Cys303 and Cys348 in the extracellular stalk were shown to be required for disulfide-linked dimerization, collagen binding, and kinase activation, placing the stalk as a critical structural element.","evidence":"Non-reducing SDS-PAGE, cysteine mutagenesis, collagen binding and kinase activity assays","pmids":["18065762"],"confidence":"High","gaps":["Stalk conformation and its role in transmitting collagen-binding signal to TM domain not structurally resolved"]},{"year":2008,"claim":"Visualizing ligand-induced receptor dynamics: live-cell FRET showed DDR1 dimers exist constitutively, and collagen triggers rapid clustering into aggregates followed by internalization into early endosomes, preceding full kinase activation.","evidence":"CFP/YFP-tagged DDR1 FRET microscopy with internalization kinetics in live cells","pmids":["19007791"],"confidence":"High","gaps":["Whether clustering is necessary for or merely accompanies activation not formally separated"]},{"year":2011,"claim":"Connecting DDR1 to cell–cell adhesion: DDR1 stabilizes E-cadherin at the plasma membrane by inactivating Cdc42, linking collagen sensing to epithelial differentiation and polarity beyond the classical cell–matrix signaling framework.","evidence":"FRAP/photoconversion of Eos-E-cadherin, dominant-negative Cdc42 rescue, DDR1 overexpression/knockdown","pmids":["21289093"],"confidence":"High","gaps":["Kinase-dependence of E-cadherin stabilization not fully tested","Whether Cdc42 inactivation is direct or through an intermediary not defined"]},{"year":2017,"claim":"Establishing the trans-phosphorylation activation model: collagen induces lateral association of pre-formed DDR1 dimers, and kinase-active 'donor' dimers trans-phosphorylate kinase-dead 'receiver' dimers in a TM-domain-dependent manner, definitively resolving the activation mechanism.","evidence":"Co-expression of engineered donor/receiver DDR1 mutants, enforced dimerization constructs, fluorescence clustering assays","pmids":["28590245"],"confidence":"High","gaps":["Stoichiometry of the higher-order signaling cluster not determined","Whether specific dimer–dimer interfaces exist beyond TM contacts is unknown"]},{"year":2018,"claim":"Identifying BCR as a DDR1 substrate: phosphoproteomics revealed DDR1 phosphorylates BCR at Tyr177, maintaining β-catenin transcriptional activity required for colorectal cancer invasion.","evidence":"Quantitative phosphoproteomics with nilotinib treatment, co-IP, β-catenin reporter, invasion assays","pmids":["29438985"],"confidence":"High","gaps":["Whether BCR is a direct kinase substrate or requires an intermediate kinase not formally shown by in vitro kinase assay"]},{"year":2020,"claim":"Expanding the co-receptor repertoire: LRP-1 was shown to interact with DDR1 at the plasma membrane and regulate DDR1 surface levels through endocytosis, linking DDR1 turnover to cell cycle progression.","evidence":"Co-IP, LRP-1 knockdown, DDR1 surface expression quantification, 3D collagen proliferation assays","pmids":["32582700"],"confidence":"Medium","gaps":["Single co-IP without reciprocal or domain-mapping validation","Whether LRP-1 acts as a clearance receptor or signaling partner not resolved"]},{"year":2021,"claim":"Separating kinase-dependent from ECD-dependent functions in vivo: the DDR1 extracellular domain alone—independent of kinase activity—promotes collagen fiber alignment that physically excludes T cells from tumors, establishing a non-catalytic structural role.","evidence":"DDR1-KO tumor models with domain-specific rescue constructs and ECD-neutralizing antibodies in immunocompetent hosts","pmids":["34732895"],"confidence":"High","gaps":["Molecular mechanism by which ECD aligns collagen fibers not defined","Whether ECD oligomerization state affects fiber alignment unknown"]},{"year":2021,"claim":"Linking DDR1 to mammary stem cell fate: DDR1 instructs basal differentiation of breast epithelial stem cells, which in turn drives luminal progenitor differentiation via Notch, establishing a DDR1→ECM→stem cell hierarchy.","evidence":"3D biomimetic breast tissue model with DDR1 inhibition/knockdown and Notch pathway epistasis","pmids":["34893587"],"confidence":"Medium","gaps":["Whether kinase activity or ECD collagen binding drives stem cell differentiation not separated","Relevance to in vivo human mammary development not confirmed"]},{"year":2022,"claim":"Revealing DDR1 as a mechanosensor via phase separation: matrix stiffness and collagen trigger DDR1 liquid–liquid phase separation through its TM domain; DDR1 condensates sequester LATS1 from MOB1, suppressing Hippo signaling and activating YAP in vascular smooth muscle cells.","evidence":"In vitro LLPS reconstitution with purified DDR1 domains, point mutagenesis (H745P, H902P), SMC-specific Ddr1-KO mice, YAP activity assays","pmids":["36475898"],"confidence":"High","gaps":["Whether LLPS occurs under physiological DDR1 expression levels not shown","Contribution of phase separation vs. conventional signaling complexes to YAP activation in vivo not quantified"]},{"year":2022,"claim":"Defining collagen-quality-dependent signaling: MMP-cleaved collagen I activates DDR1→NF-κB→p62→NRF2 signaling promoting pancreatic cancer, whereas intact collagen I triggers DDR1 degradation, revealing that the collagen modification state determines DDR1 signaling outcome.","evidence":"Genetic mouse models with MMP-resistant collagen I, DDR1 KO/inhibition, NF-κB inhibition, epistasis analysis","pmids":["36198801"],"confidence":"High","gaps":["Structural basis for differential DDR1 response to cleaved vs. intact collagen not known","Whether other collagen modifications elicit distinct DDR1 outputs not tested"]},{"year":2022,"claim":"Extending DDR1–BCR–β-catenin axis to kidney fibrosis: DDR1 phosphorylates BCR and activates STAT3 in renal proximal tubule cells, with BCR acting as a negative regulator whose phosphorylation by DDR1 de-represses MCP-1 production and TGF-β secretion.","evidence":"Ddr1-null mouse ischemia/reperfusion model, co-IP, siRNA, β-catenin reporter","pmids":["34941574"],"confidence":"High","gaps":["How BCR phosphorylation converts it from inhibitor to activator of MCP-1 mechanistically unclear"]},{"year":2023,"claim":"Structural basis for therapeutic antibody targeting: a 3.15-Å crystal structure of DDR1-ECD bound to PRTH-101 Fab revealed binding to the DS-like domain (not the collagen-binding DS domain), explaining how the antibody inhibits DDR1 phosphorylation and shedding without directly competing for collagen binding.","evidence":"X-ray crystallography, DDR1 phosphorylation/shedding/cell-attachment assays, in vivo tumor collagen fiber alignment","pmids":["37328286"],"confidence":"High","gaps":["Full-length DDR1 dimer structure still lacking","Whether allosteric inhibition mechanism generalizes to other DDR1 antibodies unknown"]},{"year":2023,"claim":"Identifying CD44 as a DDR1 co-receptor in Hippo suppression: CD44 amplifies collagen-induced DDR1 signaling and facilitates recruitment of PP2AA to MST1 for dephosphorylation, linking DDR1 to YAP activation and cancer stemness in hepatocellular carcinoma.","evidence":"Co-IP of DDR1–CD44 and PP2AA–MST1, combined DDR1/YAP inhibition in vitro and in vivo","pmids":["37117273"],"confidence":"Medium","gaps":["Direct vs. bridged interaction between DDR1 and CD44 not resolved","Whether CD44–DDR1 crosstalk operates in non-cancer contexts unknown"]},{"year":null,"claim":"Key open questions: no full-length DDR1 dimer structure exists; the mechanism by which the ECD organizes collagen fibers independently of kinase activity is unknown; the relative contributions of phase separation versus classical signaling complexes to DDR1-mediated YAP activation in vivo remain unquantified; and how collagen modification state (intact vs. cleaved) differentially engages DDR1 at a structural level is unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["Full-length DDR1 dimer structure","Mechanism of ECD-mediated collagen fiber alignment","In vivo significance of DDR1 LLPS","Structural basis of cleaved vs. intact collagen discrimination"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,5,9,10]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,13,22]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,4,20]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[4,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,5,9,10,13,22]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[6,11,12]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[8]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[9,11,12,16]}],"complexes":[],"partners":["SHP2","NCK2","BCR","LATS1","CD44","IGF1R","LRP1","TM4SF1"],"other_free_text":[]},"mechanistic_narrative":"DDR1 is a collagen-activated receptor tyrosine kinase that transduces extracellular matrix signals into diverse cellular responses including adhesion, migration, ECM remodeling, epithelial differentiation, and mechanotransduction. DDR1 exists as disulfide-linked dimers mediated by stalk-region cysteines (Cys303, Cys348); collagen binding to surface loops of the discoidin domain induces lateral association of pre-formed dimers, clustering, and trans-phosphorylation dependent on the transmembrane leucine zipper, followed by dynamin-mediated endocytosis [PMID:16774916, PMID:18065762, PMID:28590245, PMID:19007791]. Downstream, DDR1 signals through phosphotyrosine-dependent recruitment of Shp-2 (at Y740), Nck2, and BCR, and activates NF-κB–NRF2, STAT3, Src–FAK, and Hippo–YAP pathways—the latter via liquid–liquid phase separation that sequesters LATS1 from MOB1 [PMID:16337946, PMID:29438985, PMID:36475898, PMID:36198801]. The DDR1 extracellular domain independently organizes collagen fiber alignment to exclude T cell infiltration in tumors, while kinase-dependent signaling drives vascular remodeling after injury, kidney fibrosis, and intestinal barrier regulation [PMID:34732895, PMID:11254672, PMID:34941574, PMID:35905891]."},"prefetch_data":{"uniprot":{"accession":"Q08345","full_name":"Epithelial discoidin domain-containing receptor 1","aliases":["CD167 antigen-like family member A","Cell adhesion kinase","Discoidin receptor tyrosine kinase","HGK2","Mammary carcinoma kinase 10","MCK-10","Protein-tyrosine kinase 3A","Protein-tyrosine kinase RTK-6","TRK E","Tyrosine kinase DDR","Tyrosine-protein kinase CAK"],"length_aa":913,"mass_kda":101.1,"function":"Tyrosine kinase that functions as a cell surface receptor for fibrillar collagen and regulates cell attachment to the extracellular matrix, remodeling of the extracellular matrix, cell migration, differentiation, survival and cell proliferation. Collagen binding triggers a signaling pathway that involves SRC and leads to the activation of MAP kinases. Regulates remodeling of the extracellular matrix by up-regulation of the matrix metalloproteinases MMP2, MMP7 and MMP9, and thereby facilitates cell migration and wound healing. Required for normal blastocyst implantation during pregnancy, for normal mammary gland differentiation and normal lactation. Required for normal ear morphology and normal hearing (By similarity). Promotes smooth muscle cell migration, and thereby contributes to arterial wound healing. Also plays a role in tumor cell invasion. 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Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/35054451","citation_count":21,"is_preprint":false},{"pmid":"29859097","id":"PMC_29859097","title":"Selective pharmacological inhibition of DDR1 prevents experimentally-induced glomerulonephritis in prevention and therapeutic regime.","date":"2018","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29859097","citation_count":21,"is_preprint":false},{"pmid":"36356724","id":"PMC_36356724","title":"New target DDR1: A \"double-edged sword\" in solid tumors.","date":"2022","source":"Biochimica et biophysica acta. Reviews on cancer","url":"https://pubmed.ncbi.nlm.nih.gov/36356724","citation_count":20,"is_preprint":false},{"pmid":"33110221","id":"PMC_33110221","title":"Silencing of sinusoidal DDR1 reduces murine liver metastasis by colon carcinoma.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33110221","citation_count":20,"is_preprint":false},{"pmid":"17786934","id":"PMC_17786934","title":"NHERFs, NEP, MAGUKs, and more: interactions that regulate PTEN.","date":"2007","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17786934","citation_count":20,"is_preprint":false},{"pmid":"27729773","id":"PMC_27729773","title":"Andrographolide promotes vincristine-induced SK-NEP-1 tumor cell death via PI3K-AKT-p53 signaling pathway.","date":"2016","source":"Drug design, development and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/27729773","citation_count":20,"is_preprint":false},{"pmid":"36257259","id":"PMC_36257259","title":"DDR1 activation in macrophage promotes IPF by regulating NLRP3 inflammasome and macrophage reaction.","date":"2022","source":"International immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/36257259","citation_count":19,"is_preprint":false},{"pmid":"34263649","id":"PMC_34263649","title":"Nilotinib, a Discoidin domain receptor 1 (DDR1) inhibitor, induces apoptosis and inhibits migration in breast cancer.","date":"2021","source":"Neoplasma","url":"https://pubmed.ncbi.nlm.nih.gov/34263649","citation_count":19,"is_preprint":false},{"pmid":"34837026","id":"PMC_34837026","title":"Curcumin derivative ST09 modulates the miR-199a-5p/DDR1 axis and regulates proliferation and migration in ovarian cancer cells.","date":"2021","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/34837026","citation_count":19,"is_preprint":false},{"pmid":"31746375","id":"PMC_31746375","title":"The synergistic effect of DZ‑NEP, panobinostat and temozolomide reduces clonogenicity and induces apoptosis in glioblastoma cells.","date":"2019","source":"International journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/31746375","citation_count":19,"is_preprint":false},{"pmid":"27642041","id":"PMC_27642041","title":"Compounds from Polyphaga plancyi and their inhibitory activities against JAK3 and DDR1 kinases.","date":"2016","source":"Fitoterapia","url":"https://pubmed.ncbi.nlm.nih.gov/27642041","citation_count":19,"is_preprint":false},{"pmid":"34893587","id":"PMC_34893587","title":"Breast tissue regeneration is driven by cell-matrix interactions coordinating multi-lineage stem cell differentiation through DDR1.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34893587","citation_count":19,"is_preprint":false},{"pmid":"34270989","id":"PMC_34270989","title":"Involvement of miR-199a-3p/DDR1 in vascular endothelial cell senescence in diabetes.","date":"2021","source":"European journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/34270989","citation_count":18,"is_preprint":false},{"pmid":"29952722","id":"PMC_29952722","title":"DDR1 and DDR2 in skin.","date":"2018","source":"Cell adhesion & migration","url":"https://pubmed.ncbi.nlm.nih.gov/29952722","citation_count":18,"is_preprint":false},{"pmid":"23810922","id":"PMC_23810922","title":"Oligomerization of DDR1 ECD affects receptor-ligand binding.","date":"2013","source":"Journal of structural biology","url":"https://pubmed.ncbi.nlm.nih.gov/23810922","citation_count":18,"is_preprint":false},{"pmid":"30783426","id":"PMC_30783426","title":"3D culture enhances chemoresistance of ALL Jurkat cell line by increasing DDR1 expression.","date":"2019","source":"Experimental and therapeutic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30783426","citation_count":18,"is_preprint":false},{"pmid":"37194065","id":"PMC_37194065","title":"Inhibition of discoidin domain receptor (DDR)-1 with nilotinib alters CSF miRNAs and is associated with reduced inflammation and vascular fibrosis in Alzheimer's disease.","date":"2023","source":"Journal of neuroinflammation","url":"https://pubmed.ncbi.nlm.nih.gov/37194065","citation_count":18,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":47979,"output_tokens":6806,"usd":0.123013},"stage2":{"model":"claude-opus-4-6","input_tokens":10567,"output_tokens":4311,"usd":0.240915},"total_usd":0.363928,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"DDR1 forms ligand-independent dimers in the biosynthetic pathway and on the cell surface; the transmembrane leucine zipper (but not the GXXXG motif) is required for collagen-induced signaling, as leucine-zipper mutations abolish kinase activation while still permitting dimerization. Both extracellular and cytoplasmic domains are individually dispensable for dimerization.\",\n      \"method\": \"Chemical cross-linking, co-immunoprecipitation of differentially tagged DDR1 constructs, TOXCAT bacterial membrane reporter assay, site-directed mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods (cross-linking, co-IP, mutagenesis, TOXCAT) in a single rigorous study\",\n      \"pmids\": [\"16774916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"DDR1 exists as a disulfide-linked dimer; cysteines 303 and 348 in the stalk region of the extracellular domain are necessary for dimerization, collagen binding, and kinase activation. Deletion of the discoidin domain does not prevent dimerization, whereas deletion of the stalk region abolishes it.\",\n      \"method\": \"Non-reducing SDS-PAGE, deletion and point mutagenesis of extracellular domain, collagen-binding and kinase activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with functional assays (collagen binding, kinase activity)\",\n      \"pmids\": [\"18065762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Collagen activates DDR1 through lateral association of pre-formed DDR1 dimers and trans-phosphorylation between dimers. Receiver dimers (kinase-dead) are phosphorylated by donor DDR1 in a collagen-dependent manner requiring donor kinase activity but not receiver kinase activity; transmembrane domain mutation abolishes trans-phosphorylation, and collagen-binding-deficient DDR1 is recruited into DDR1 signaling clusters.\",\n      \"method\": \"Co-expression of signalling-incompetent ('receiver') and functional ('donor') DDR1 mutants, enforced covalent dimerization constructs, mutagenesis of transmembrane domain, fluorescence-based clustering assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with multiple engineered mutants and orthogonal approaches in a single rigorous study\",\n      \"pmids\": [\"28590245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The DDR1 collagen-binding site maps to four surface-exposed loops of the discoidin domain: residues Ser52–Thr57 (loop 1), Arg105–Lys112 (loop 3), and Ser175 (loop 4) are critically required for collagen binding, as determined by alanine-scanning and deletion mutagenesis of GST-fusion discoidin domain proteins in solid-phase collagen-binding assays.\",\n      \"method\": \"GST-fusion protein expression in insect cells, solid-phase collagen-binding assay, ELISA-based collagen binding, alanine-scanning and deletion mutagenesis, 3D homology modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis plus in vitro binding assays with multiple mutants\",\n      \"pmids\": [\"15136580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Collagen stimulation induces rapid aggregation and internalization of DDR1 dimers into early endosomes, preceding receptor activation. Significant FRET signal indicating DDR1 dimerization is present even without collagen; collagen causes clustering and sharp FRET increase in aggregated receptor regions.\",\n      \"method\": \"FRET microscopy with CFP- and YFP-tagged DDR1 in live cells, internalization kinetics imaging\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct live-cell imaging with FRET and quantitative kinetics\",\n      \"pmids\": [\"19007791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Collagen-induced DDR1 activation leads to phosphorylation of multiple tyrosine residues; Nck2 and Shp-2 bind DDR1 in a collagen-dependent manner. The Shp-2 binding site was mapped to Tyr-740 within an ITIM-consensus sequence. DDR1 ablation in mouse mammary gland causes delocalized Nck2 expression, linking DDR1-Nck2 interaction to alveologenesis defects.\",\n      \"method\": \"Phosphopeptide mapping, site-directed mutagenesis, SH2 domain pull-down, co-immunoprecipitation, DDR1-null mouse mammary gland analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — phosphopeptide mapping with mutagenesis plus in vivo genetic model\",\n      \"pmids\": [\"16337946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DDR1 regulates smooth muscle cell attachment to collagen, chemotaxis, proliferation, and MMP production. DDR1-null mice show significantly reduced neointimal thickening and collagen deposition after carotid artery injury, establishing DDR1 as a collagen receptor mediating vascular wound repair.\",\n      \"method\": \"DDR1-knockout mouse model, carotid artery injury model, in vitro smooth muscle cell assays (migration, proliferation, MMP production)\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined cellular and in vivo phenotypic readouts\",\n      \"pmids\": [\"11254672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Wnt-5a is a co-factor necessary for collagen-induced DDR1 phosphorylation in mammary epithelial cells. Repression of Wnt-5a abolishes DDR1 phosphorylation, impairs cell-collagen interaction, and enhances motility; conversely, Wnt-5a overexpression enables DDR1 phosphorylation in non-Wnt-5a-producing cells. This effect is independent of β-catenin/canonical Wnt signaling.\",\n      \"method\": \"Antisense repression and overexpression of Wnt-5a, DDR1 phosphorylation assays, collagen binding assays, cell migration assays, β-catenin pathway inhibition\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays, single lab\",\n      \"pmids\": [\"11493640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DDR1 promotes E-cadherin-mediated cell-cell adhesion and epithelial differentiation by stabilizing E-cadherin at the plasma membrane through inactivation of Cdc42. DDR1 overexpression reduces E-cadherin degradation rate and increases its membrane stability (shown by FRAP/photoconversion); dominant-negative DDR1 has opposite effects.\",\n      \"method\": \"DDR1 overexpression and knockdown, photobleaching (FRAP) and photoconversion of Eos-E-cadherin, pull-down assays, constitutively active/dominant-negative Cdc42 constructs\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including live-cell FRAP and mutagenesis\",\n      \"pmids\": [\"21289093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DDR1 identifies BCR as a substrate: nilotinib inhibits DDR1 kinase activity and prevents DDR1-mediated BCR phosphorylation at Tyr177, which is required to maintain β-catenin transcriptional activity necessary for colorectal cancer cell invasion.\",\n      \"method\": \"Quantitative phosphoproteomics, nilotinib treatment, co-immunoprecipitation, β-catenin reporter assays, invasion assays\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — phosphoproteomics substrate identification with functional validation\",\n      \"pmids\": [\"29438985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR1 promotes kidney inflammation and fibrosis via phosphorylation of BCR in renal proximal tubule cells, which increases β-catenin activity and MCP-1 production. DDR1 also activates STAT3 to stimulate TGF-β secretion. DDR1-induced BCR phosphorylation or BCR downregulation both increase MCP-1, indicating BCR acts as a negative regulator downstream of DDR1.\",\n      \"method\": \"Ddr1-null mouse ischemia/reperfusion model, co-immunoprecipitation, phosphorylation assays, β-catenin reporter, siRNA knockdown\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO mouse model plus mechanistic in vitro dissection with multiple methods\",\n      \"pmids\": [\"34941574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDR1 extracellular domain (ECD), but not its intracellular kinase domain, is required for immune exclusion in triple-negative breast cancer. DDR1-ECD binding to collagen enforces aligned collagen fibers that obstruct T cell infiltration. Membrane-untethered DDR1-ECD is sufficient to rescue tumor growth in immunocompetent hosts.\",\n      \"method\": \"Ddr1 knockout mouse tumor models, domain-specific rescue constructs (ECD vs. kinase-dead), ECD-neutralizing antibodies, collagen fiber alignment imaging, T cell infiltration quantification\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic rescue dissection with domain-specific constructs plus antibody perturbation in vivo\",\n      \"pmids\": [\"34732895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Matrix-metalloprotease-cleaved collagen I (cCol I) activates DDR1-NF-κB-p62-NRF2 signaling to promote pancreatic cancer growth; intact collagen I (iCol I) triggers DDR1 degradation and restrains growth. Inhibition of NF-κB or mitochondrial biogenesis downstream of DDR1 blocks tumorigenesis in wild-type but not MMP-resistant collagen I-expressing mice.\",\n      \"method\": \"Genetic mouse models with MMP-resistant collagen I, DDR1 knockout/inhibition, NF-κB inhibition, in vivo tumor assays, western blotting for NRF2/p62 pathway\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic mouse models with epistasis establishing pathway order\",\n      \"pmids\": [\"36198801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR1 undergoes stiffness/collagen-stimulated liquid-liquid phase separation (LLPS), co-condensing with LATS1 to competitively inhibit MOB1 binding to LATS1 and thereby suppress LATS1 phosphorylation, leading to YAP activation. The transmembrane domain drives DDR1 droplet formation; the C-terminus is required for co-condensation with LATS1. Single-point C-terminus mutants (H745P, H902P) abolish co-condensation.\",\n      \"method\": \"VSMCs on polyacrylamide gels of varying stiffness, LLPS assays with purified DDR1 domains, mutagenesis, co-immunoprecipitation/co-condensation assays, SMC-specific Ddr1-KO mice with LATS1 inhibition, YAP activity assays\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstitution with purified domains, mutagenesis, and in vivo genetic rescue\",\n      \"pmids\": [\"36475898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ECM stiffness induces DDR1 phosphorylation, oligomerization, and endocytosis in a collagen-independent manner in vascular smooth muscle cells, leading to ERK and p53 pathway activation that represses DNMT1 expression, resulting in a proinflammatory phenotype.\",\n      \"method\": \"VSMCs on PA gels of varying stiffness, DDR1 phosphorylation/oligomerization/endocytosis assays, ERK and p53 pathway inhibition, DNMT1 expression assays, DDR1 inhibitor treatment in vivo\",\n      \"journal\": \"Bioactive materials\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vitro and in vivo methods, single lab\",\n      \"pmids\": [\"35386458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR1 constitutively associates with IGF-IR; IGF-I stimulation enhances this interaction and promotes rapid DDR1 tyrosine phosphorylation and co-internalization with IGF-IR into early endosomes. DDR1 is critical for IGF-IR endocytosis, trafficking, and protein expression, as well as IGF-I-induced signaling and biological responses. Reciprocally, IGF-IR is required for collagen-dependent DDR1 phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation, DDR1 silencing and overexpression, IGF-IR endocytosis/trafficking assays, co-transfection in mouse fibroblasts\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — reciprocal co-IP plus functional trafficking assays, single lab\",\n      \"pmids\": [\"25840417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DDR1 drives glioblastoma therapy resistance by associating with a YWHA/14-3-3–BECN1–AKT1 multiprotein complex that promotes pro-survival AKT-MTOR signaling and suppresses autophagy. DDR1 inhibition sensitizes glioblastoma cells to radio- and chemotherapy by inducing autophagic cell death.\",\n      \"method\": \"Co-immunoprecipitation of multiprotein complex, DDR1 inhibition/knockdown, autophagy flux assays, clonogenic survival after irradiation/chemotherapy\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — complex identification by co-IP with functional autophagy readout, single lab\",\n      \"pmids\": [\"31117874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Oligomers of recombinant DDR1-Fc extracellular domain bind collagen with higher affinity than dimeric DDR1-Fc alone. DDR1-Fc oligomerizes upon in vitro collagen binding as shown by AFM. Inhibition of dynamin-mediated endocytosis blocks ligand-induced internalization of DDR1 but does not affect oligomerization.\",\n      \"method\": \"Solid-phase binding assays, atomic force microscopy, dynamin inhibition, live-cell internalization assays\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro reconstitution with AFM imaging, single lab\",\n      \"pmids\": [\"23810922\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TM4SF1 colocalizes with and co-immunoprecipitates with DDR1 in pancreatic cancer cells; TM4SF1 silencing reduces DDR1 expression and invadopodia formation, and DDR1 overexpression rescues the inhibitory effects of TM4SF1 silencing on migration, invasion, and MMP2/9 expression.\",\n      \"method\": \"Co-immunoprecipitation, double immunofluorescence, siRNA knockdown, DDR1 rescue overexpression, invadopodia functional assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP plus rescue experiments, single lab\",\n      \"pmids\": [\"28368050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Periostin signals through DDR1 to promote cartilage degeneration: genetic deficiency or pharmacological inhibition of DDR1 in mouse chondrocytes blocks periostin-induced MMP-13 expression and collagen/proteoglycan degradation downstream of AKT/β-catenin.\",\n      \"method\": \"DDR1-knockout mouse chondrocytes, DDR1 pharmacological inhibitor, periostin stimulation assays, MMP-13 expression readout\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and pharmacological perturbation with defined molecular readout\",\n      \"pmids\": [\"32330138\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LRP-1 interacts with DDR1 at the plasma membrane in colon cancer cells and regulates DDR1 cell-surface levels through endocytosis. LRP-1-mediated DDR1 endocytosis promotes cell cycle progression and decreases apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, LRP-1 knockdown, DDR1 surface expression quantification, 3D collagen matrix proliferation/apoptosis assays\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single co-IP plus functional endocytosis assays\",\n      \"pmids\": [\"32582700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR1 promotes YAP/TAZ nuclear localization and transcriptional activity in VSMCs; YAP/TAZ knockdown attenuates DDR1 expression, and YAP/TAZ bind to the Ddr1 promoter in response to collagen or increased substrate stiffness, establishing a DDR1-YAP/TAZ positive feedback loop for DDR1 auto-regulation.\",\n      \"method\": \"DDR1-KO and WT VSMCs on varied-stiffness substrates, YAP/TAZ nuclear localization assays, ChIP at Ddr1 promoter, YAP/TAZ siRNA knockdown, collagen stimulation\",\n      \"journal\": \"Matrix biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus genetic KO with functional readout, single lab\",\n      \"pmids\": [\"35562016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DDR1 interacts with CD44 as a co-receptor that amplifies collagen I-induced DDR1 signaling. Collagen I–DDR1 activation antagonizes Hippo signaling by facilitating PP2AA recruitment to MST1, leading to MST1 dephosphorylation and exaggerated YAP activation, promoting HCC cancer stem cell properties.\",\n      \"method\": \"Co-immunoprecipitation (DDR1–CD44 and PP2AA–MST1 interactions), in vitro and in vivo DDR1 activation assays, combined DDR1/YAP inhibition experiments\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP with pathway dissection and in vivo validation, single lab\",\n      \"pmids\": [\"37117273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR1 promotes intestinal barrier disruption in ulcerative colitis via the NF-κB p65-MLCK-p-MLC2 pathway, leading to tight junction protein degradation and epithelial apoptosis. DDR1 knockout mice show alleviated barrier injury, upregulated tight junction proteins, and reduced proinflammatory cytokines after DSS-induced colitis.\",\n      \"method\": \"DDR1-knockout and WT mice (DSS colitis model), DDR1 overexpression and shRNA in epithelial cell monolayers, NF-κB p65 inhibition (JSH-23), tight junction protein assays\",\n      \"journal\": \"Pharmacological research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse model plus pathway inhibition, single lab\",\n      \"pmids\": [\"35905891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DDR1 directly interacts with the PAS domain of HIF-1α, suppresses HIF-1α ubiquitination and degradation, and strengthens HIF-1α transcriptional regulation of angiogenesis. DDR1 also promotes actin cytoskeleton reorganization via HIF-1α/RhoA/ROCK1 signaling to enhance gastric cancer metastasis.\",\n      \"method\": \"Co-immunoprecipitation (DDR1–HIF-1α PAS domain), ubiquitination assays, RhoA/ROCK1 pathway assays, PDX and organoid models with DDR1 inhibition\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP with domain specificity plus functional PDX/organoid validation\",\n      \"pmids\": [\"39024501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR1 promotes migration and invasion of breast cancer cells by binding to Src and FAK (co-immunoprecipitation) and activating Src-FAK signaling; inhibition of FAK and Src attenuates DDR1-enhanced migration.\",\n      \"method\": \"Co-immunoprecipitation of DDR1 with Src and FAK, DDR1 knockdown/overexpression, Src and FAK inhibitor treatment, migration/invasion assays\",\n      \"journal\": \"Neoplasma\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single co-IP plus inhibitor rescue, single lab\",\n      \"pmids\": [\"35818965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDR1 instructs breast epithelial stem cell differentiation into basal cells, which in turn stimulate luminal progenitor differentiation via Notch signaling to form lobules in a 3D biomimetic breast tissue model. This establishes DDR1 as the receptor linking ECM collagen signals to multi-lineage stem cell differentiation.\",\n      \"method\": \"3D biomimetic human breast tissue engineering, DDR1 inhibition/knockdown, Notch pathway inhibition, lineage differentiation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined loss-of-function in organotypic 3D model with epistasis (DDR1→basal→Notch→luminal)\",\n      \"pmids\": [\"34893587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A humanized DDR1 antibody (PRTH-101) binds the discoidin-like (DS-like) domain (not the collagen-binding DS domain) of DDR1 ECD as revealed by 3.15-Å crystal structure of the DDR1-ECD/Fab complex. Mechanistically, PRTH-101 inhibits DDR1 phosphorylation, decreases collagen-mediated cell attachment, and blocks DDR1 shedding from the cell surface.\",\n      \"method\": \"Crystal structure at 3.15 Å resolution, DDR1 phosphorylation assays, cell attachment assays, DDR1 shedding assays, in vivo tumor model with collagen fiber alignment imaging\",\n      \"journal\": \"Journal for immunotherapy of cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation across multiple orthogonal assays\",\n      \"pmids\": [\"37328286\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DDR1 is a collagen-binding receptor tyrosine kinase that exists as pre-formed disulfide-linked dimers on the cell surface; collagen binding induces lateral association of DDR1 dimers, clustering, and trans-phosphorylation between dimers mediated by the transmembrane leucine zipper, with downstream signaling through multiple phosphotyrosine-dependent interactions (including Shp-2 at Y740, Nck2, BCR, Src, FAK, and STAT3) that regulate cell adhesion, migration, MMP production, NF-κB/NRF2 metabolic signaling, YAP/LATS1 mechanotransduction via liquid-liquid phase separation, and ECM remodeling in contexts ranging from fibrosis and vascular injury to cancer progression and immune exclusion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"DDR1 is a collagen-activated receptor tyrosine kinase that transduces extracellular matrix signals into diverse cellular responses including adhesion, migration, ECM remodeling, epithelial differentiation, and mechanotransduction. DDR1 exists as disulfide-linked dimers mediated by stalk-region cysteines (Cys303, Cys348); collagen binding to surface loops of the discoidin domain induces lateral association of pre-formed dimers, clustering, and trans-phosphorylation dependent on the transmembrane leucine zipper, followed by dynamin-mediated endocytosis [PMID:16774916, PMID:18065762, PMID:28590245, PMID:19007791]. Downstream, DDR1 signals through phosphotyrosine-dependent recruitment of Shp-2 (at Y740), Nck2, and BCR, and activates NF-κB–NRF2, STAT3, Src–FAK, and Hippo–YAP pathways—the latter via liquid–liquid phase separation that sequesters LATS1 from MOB1 [PMID:16337946, PMID:29438985, PMID:36475898, PMID:36198801]. The DDR1 extracellular domain independently organizes collagen fiber alignment to exclude T cell infiltration in tumors, while kinase-dependent signaling drives vascular remodeling after injury, kidney fibrosis, and intestinal barrier regulation [PMID:34732895, PMID:11254672, PMID:34941574, PMID:35905891].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing DDR1 as a physiologically relevant collagen receptor in vivo: DDR1-null mice showed reduced neointimal thickening after vascular injury, demonstrating that DDR1 mediates smooth muscle cell adhesion, migration, MMP production, and collagen deposition during wound repair.\",\n      \"evidence\": \"DDR1-knockout mouse carotid artery injury model with in vitro SMC assays\",\n      \"pmids\": [\"11254672\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling intermediates not identified\", \"Relative contribution of kinase activity vs. ECD-mediated collagen organization unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identifying a non-canonical co-factor requirement: Wnt-5a was shown to be necessary for collagen-induced DDR1 phosphorylation in mammary epithelial cells, operating independently of β-catenin, suggesting DDR1 activation is context-dependent.\",\n      \"evidence\": \"Antisense repression and overexpression of Wnt-5a with DDR1 phosphorylation and cell migration assays\",\n      \"pmids\": [\"11493640\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which Wnt-5a facilitates DDR1 phosphorylation not defined\", \"Not replicated in other cell types\", \"Direct physical interaction between Wnt-5a and DDR1 not demonstrated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Mapping the collagen-binding interface: alanine-scanning mutagenesis identified four surface-exposed loops of the discoidin domain essential for collagen binding, providing the first structural map of DDR1 ligand recognition.\",\n      \"evidence\": \"GST-fusion discoidin domain mutagenesis with solid-phase collagen-binding assays and homology modeling\",\n      \"pmids\": [\"15136580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic-resolution structure of the DDR1–collagen complex\", \"Collagen-type selectivity determinants not fully resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identifying first proximal signaling effectors: phosphopeptide mapping revealed Nck2 and Shp-2 as collagen-dependent DDR1-binding partners, with Shp-2 binding mapped to Tyr-740 in an ITIM motif, and DDR1-null mammary glands showed mislocalized Nck2.\",\n      \"evidence\": \"Phosphopeptide mapping, mutagenesis, SH2 pull-downs, co-IP, DDR1-null mouse mammary analysis\",\n      \"pmids\": [\"16337946\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of Shp-2 recruitment to Y740 on downstream pathways not determined\", \"Additional phosphotyrosine-dependent effectors likely exist\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolving the dimerization mechanism: DDR1 forms ligand-independent dimers in the biosynthetic pathway, and the transmembrane leucine zipper—not the GXXXG motif—is specifically required for collagen-induced kinase activation while being dispensable for dimerization per se.\",\n      \"evidence\": \"Chemical cross-linking, co-IP of differentially tagged constructs, TOXCAT assay, site-directed mutagenesis\",\n      \"pmids\": [\"16774916\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the transmembrane leucine zipper dimer not solved\", \"Mechanism coupling TM conformational change to kinase activation unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identifying disulfide bonds that stabilize the dimer: Cys303 and Cys348 in the extracellular stalk were shown to be required for disulfide-linked dimerization, collagen binding, and kinase activation, placing the stalk as a critical structural element.\",\n      \"evidence\": \"Non-reducing SDS-PAGE, cysteine mutagenesis, collagen binding and kinase activity assays\",\n      \"pmids\": [\"18065762\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stalk conformation and its role in transmitting collagen-binding signal to TM domain not structurally resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Visualizing ligand-induced receptor dynamics: live-cell FRET showed DDR1 dimers exist constitutively, and collagen triggers rapid clustering into aggregates followed by internalization into early endosomes, preceding full kinase activation.\",\n      \"evidence\": \"CFP/YFP-tagged DDR1 FRET microscopy with internalization kinetics in live cells\",\n      \"pmids\": [\"19007791\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether clustering is necessary for or merely accompanies activation not formally separated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connecting DDR1 to cell–cell adhesion: DDR1 stabilizes E-cadherin at the plasma membrane by inactivating Cdc42, linking collagen sensing to epithelial differentiation and polarity beyond the classical cell–matrix signaling framework.\",\n      \"evidence\": \"FRAP/photoconversion of Eos-E-cadherin, dominant-negative Cdc42 rescue, DDR1 overexpression/knockdown\",\n      \"pmids\": [\"21289093\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase-dependence of E-cadherin stabilization not fully tested\", \"Whether Cdc42 inactivation is direct or through an intermediary not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Establishing the trans-phosphorylation activation model: collagen induces lateral association of pre-formed DDR1 dimers, and kinase-active 'donor' dimers trans-phosphorylate kinase-dead 'receiver' dimers in a TM-domain-dependent manner, definitively resolving the activation mechanism.\",\n      \"evidence\": \"Co-expression of engineered donor/receiver DDR1 mutants, enforced dimerization constructs, fluorescence clustering assays\",\n      \"pmids\": [\"28590245\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the higher-order signaling cluster not determined\", \"Whether specific dimer–dimer interfaces exist beyond TM contacts is unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying BCR as a DDR1 substrate: phosphoproteomics revealed DDR1 phosphorylates BCR at Tyr177, maintaining β-catenin transcriptional activity required for colorectal cancer invasion.\",\n      \"evidence\": \"Quantitative phosphoproteomics with nilotinib treatment, co-IP, β-catenin reporter, invasion assays\",\n      \"pmids\": [\"29438985\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether BCR is a direct kinase substrate or requires an intermediate kinase not formally shown by in vitro kinase assay\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Expanding the co-receptor repertoire: LRP-1 was shown to interact with DDR1 at the plasma membrane and regulate DDR1 surface levels through endocytosis, linking DDR1 turnover to cell cycle progression.\",\n      \"evidence\": \"Co-IP, LRP-1 knockdown, DDR1 surface expression quantification, 3D collagen proliferation assays\",\n      \"pmids\": [\"32582700\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single co-IP without reciprocal or domain-mapping validation\", \"Whether LRP-1 acts as a clearance receptor or signaling partner not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Separating kinase-dependent from ECD-dependent functions in vivo: the DDR1 extracellular domain alone—independent of kinase activity—promotes collagen fiber alignment that physically excludes T cells from tumors, establishing a non-catalytic structural role.\",\n      \"evidence\": \"DDR1-KO tumor models with domain-specific rescue constructs and ECD-neutralizing antibodies in immunocompetent hosts\",\n      \"pmids\": [\"34732895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which ECD aligns collagen fibers not defined\", \"Whether ECD oligomerization state affects fiber alignment unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linking DDR1 to mammary stem cell fate: DDR1 instructs basal differentiation of breast epithelial stem cells, which in turn drives luminal progenitor differentiation via Notch, establishing a DDR1→ECM→stem cell hierarchy.\",\n      \"evidence\": \"3D biomimetic breast tissue model with DDR1 inhibition/knockdown and Notch pathway epistasis\",\n      \"pmids\": [\"34893587\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether kinase activity or ECD collagen binding drives stem cell differentiation not separated\", \"Relevance to in vivo human mammary development not confirmed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealing DDR1 as a mechanosensor via phase separation: matrix stiffness and collagen trigger DDR1 liquid–liquid phase separation through its TM domain; DDR1 condensates sequester LATS1 from MOB1, suppressing Hippo signaling and activating YAP in vascular smooth muscle cells.\",\n      \"evidence\": \"In vitro LLPS reconstitution with purified DDR1 domains, point mutagenesis (H745P, H902P), SMC-specific Ddr1-KO mice, YAP activity assays\",\n      \"pmids\": [\"36475898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LLPS occurs under physiological DDR1 expression levels not shown\", \"Contribution of phase separation vs. conventional signaling complexes to YAP activation in vivo not quantified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defining collagen-quality-dependent signaling: MMP-cleaved collagen I activates DDR1→NF-κB→p62→NRF2 signaling promoting pancreatic cancer, whereas intact collagen I triggers DDR1 degradation, revealing that the collagen modification state determines DDR1 signaling outcome.\",\n      \"evidence\": \"Genetic mouse models with MMP-resistant collagen I, DDR1 KO/inhibition, NF-κB inhibition, epistasis analysis\",\n      \"pmids\": [\"36198801\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for differential DDR1 response to cleaved vs. intact collagen not known\", \"Whether other collagen modifications elicit distinct DDR1 outputs not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extending DDR1–BCR–β-catenin axis to kidney fibrosis: DDR1 phosphorylates BCR and activates STAT3 in renal proximal tubule cells, with BCR acting as a negative regulator whose phosphorylation by DDR1 de-represses MCP-1 production and TGF-β secretion.\",\n      \"evidence\": \"Ddr1-null mouse ischemia/reperfusion model, co-IP, siRNA, β-catenin reporter\",\n      \"pmids\": [\"34941574\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How BCR phosphorylation converts it from inhibitor to activator of MCP-1 mechanistically unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Structural basis for therapeutic antibody targeting: a 3.15-Å crystal structure of DDR1-ECD bound to PRTH-101 Fab revealed binding to the DS-like domain (not the collagen-binding DS domain), explaining how the antibody inhibits DDR1 phosphorylation and shedding without directly competing for collagen binding.\",\n      \"evidence\": \"X-ray crystallography, DDR1 phosphorylation/shedding/cell-attachment assays, in vivo tumor collagen fiber alignment\",\n      \"pmids\": [\"37328286\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length DDR1 dimer structure still lacking\", \"Whether allosteric inhibition mechanism generalizes to other DDR1 antibodies unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying CD44 as a DDR1 co-receptor in Hippo suppression: CD44 amplifies collagen-induced DDR1 signaling and facilitates recruitment of PP2AA to MST1 for dephosphorylation, linking DDR1 to YAP activation and cancer stemness in hepatocellular carcinoma.\",\n      \"evidence\": \"Co-IP of DDR1–CD44 and PP2AA–MST1, combined DDR1/YAP inhibition in vitro and in vivo\",\n      \"pmids\": [\"37117273\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs. bridged interaction between DDR1 and CD44 not resolved\", \"Whether CD44–DDR1 crosstalk operates in non-cancer contexts unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions: no full-length DDR1 dimer structure exists; the mechanism by which the ECD organizes collagen fibers independently of kinase activity is unknown; the relative contributions of phase separation versus classical signaling complexes to DDR1-mediated YAP activation in vivo remain unquantified; and how collagen modification state (intact vs. cleaved) differentially engages DDR1 at a structural level is unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length DDR1 dimer structure\", \"Mechanism of ECD-mediated collagen fiber alignment\", \"In vivo significance of DDR1 LLPS\", \"Structural basis of cleaved vs. intact collagen discrimination\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 5, 9, 10]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 13, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 4, 20]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [4, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 5, 9, 10, 13, 22]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [6, 11, 12]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [9, 11, 12, 16]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SHP2\", \"NCK2\", \"BCR\", \"LATS1\", \"CD44\", \"IGF1R\", \"LRP1\", \"TM4SF1\"],\n    \"other_free_text\": []\n  }\n}\n```"}