{"gene":"DDR2","run_date":"2026-06-09T23:54:41","timeline":{"discoveries":[{"year":2003,"finding":"The discoidin domain of DDR2 is sufficient for collagen I binding with high affinity and for transmembrane receptor signaling. Three spatially adjacent surface loops within the DDR2 discoidin domain constitute the collagen recognition site; mutation of these loops abolishes both collagen binding and collagen-dependent receptor activation.","method":"Recombinant extracellular domain production, solid-phase binding assays, loop-exchange mutagenesis, receptor signaling assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis, multiple orthogonal methods in a single rigorous study","pmids":["12611880"],"is_preprint":false},{"year":2008,"finding":"The minimal collagen sequence required for DDR2 binding and activation is the triple-helical motif GVMGFO (O = hydroxyproline). Single triple-helical peptides comprising this motif are sufficient to activate DDR2 transmembrane signaling, indicating that fibrillar collagen is not required.","method":"Collagen II Toolkit peptide screen, truncation and alanine-substitution peptides, DDR2 binding and phosphorylation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with systematic mutagenesis, multiple orthogonal assays in one rigorous study","pmids":["18201965"],"is_preprint":false},{"year":2004,"finding":"The D2 period of collagen II contains a specific DDR2 binding site; deletion of D2 abolishes DDR2 binding and receptor autophosphorylation, whereas D3 and D4 periods are dispensable.","method":"Recombinant collagen II variants with specific D-period deletions, DDR2 binding assays, autophosphorylation assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with deletion mapping and functional readout","pmids":["15544808"],"is_preprint":false},{"year":2006,"finding":"Collagen X is a ligand for DDR2 that binds the DDR2 extracellular domain with high affinity and stimulates DDR2 autophosphorylation. Unlike fibrillar collagens, collagen X binding requires regions beyond the discoidin domain; the triple-helical region of collagen X activates DDR2 whereas the NC1 domain binds but does not activate.","method":"Solid-phase binding assays with recombinant DDR2 extracellular domain, autophosphorylation assays, RT-PCR and immunohistochemistry for spatial expression","journal":"Matrix biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with domain dissection, multiple methods, clear functional distinction between binding and activation","pmids":["16806867"],"is_preprint":false},{"year":2001,"finding":"DDR2 overexpression in hepatic stellate cells enhances proliferation and Matrigel invasion via increased expression of active MMP-2; kinase-dead DDR2 does not produce these effects, establishing that DDR2 kinase activity is required.","method":"Stable overexpression of wild-type, constitutively active chimeric, truncated, and kinase-dead DDR2; proliferation assays; Matrigel invasion; MMP-2 activity assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple isogenic cell lines including kinase-dead control, orthogonal functional readouts","pmids":["11696582"],"is_preprint":false},{"year":2001,"finding":"DDR2 kinase activity is required for normal cell proliferation in vivo; DDR2-deficient mice exhibit dwarfism and reduced chondrocyte proliferation, and introduction of wild-type but not kinase-dead DDR2 rescues the proliferation defect of DDR2-/- fibroblasts in vitro.","method":"DDR2 knockout mouse generation, bone phenotype analysis, skin wound healing model, fibroblast rescue with wild-type vs. kinase-dead DDR2","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO combined with kinase-dead rescue experiment, multiple in vivo and in vitro readouts","pmids":["11375938"],"is_preprint":false},{"year":2010,"finding":"DDR2 regulates osteoblast differentiation by activating ERK, which in turn phosphorylates and activates the transcription factor Runx2. A gain-of-function Runx2 mutant with ERK-independent phosphorylation rescues osteogenic phenotypes in DDR2-silenced cells, placing DDR2 upstream of ERK-Runx2 in osteoblastogenesis.","method":"shRNA knockdown, constitutively active DDR2 overexpression, ERK inhibitors, Runx2 phosphorylation assays, epistasis with Runx2 mutants","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods and epistasis experiments in a single study","pmids":["20734453"],"is_preprint":false},{"year":2010,"finding":"ATF4 transcriptionally upregulates DDR2 expression by binding a C/EBP site at -1150 bp in the DDR2 promoter via cooperation with C/EBPβ; DDR2 in turn activates Runx2 through p38 MAPK to promote osteoblast differentiation.","method":"ATF4 knockdown/overexpression, promoter reporter assays, ATF4 mutants deficient in C/EBPβ binding, p38 MAPK inhibition","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Strong — promoter mapping with mutagenesis, co-factor dissection, pathway placement via inhibitors, multiple methods","pmids":["20564243"],"is_preprint":false},{"year":2013,"finding":"SHP-2 tyrosine phosphorylation is dependent on DDR2 kinase activity downstream of collagen stimulation. Multiple DDR2 lung cancer mutants (L63V, G505S) phosphorylate SHP-2, whereas the kinase-impaired I638F mutant shows diminished DDR2 and SHP-2 phosphorylation.","method":"Quantitative phosphoproteomics (7-time-point temporal analysis), biochemical validation of SHP-2 phosphorylation, targeted proteomic profiling of DDR2 mutant panel","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — quantitative phosphoproteomics plus biochemical validation, multiple mutant panel tested","pmids":["23822953"],"is_preprint":false},{"year":2014,"finding":"The cytoplasmic juxtamembrane 2 (JM2) region of DDR2 is required for receptor dimerization and efficient collagen binding, both of which are critical for receptor activation. Overexpression of the JM2-containing domain suppresses collagen-induced colony formation, proliferation, and invasion via inhibition of MMP-2 and MMP-9.","method":"Deletion constructs, collagen-binding assays, receptor dimerization analysis, dominant-negative overexpression, proliferation and invasion assays","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays in a single lab with domain-deletion approach","pmids":["24740739"],"is_preprint":false},{"year":2013,"finding":"Acquired resistance to dasatinib in DDR2-dependent lung cancer cells occurs via two distinct mechanisms: (1) a T654I gatekeeper mutation in DDR2, and (2) loss of NF1 that activates a RAS-ERK bypass pathway.","method":"Targeted exome sequencing of resistant cell lines, functional validation of resistance mechanisms","journal":"Molecular cancer therapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — exome sequencing with functional validation, two orthogonal resistance mechanisms identified","pmids":["24296828"],"is_preprint":false},{"year":2011,"finding":"Mutations in the DDR2 kinase domain (e.g., L63V, G505S) confer gain-of-function oncogenic activity; expression of mutant DDR2 leads to cellular transformation blocked by dasatinib. Squamous lung cancer cell lines with DDR2 mutations are selectively killed by DDR2 RNAi or dasatinib.","method":"Sanger sequencing of tyrosine kinome, RNAi knockdown, transformation assays, xenograft models, dasatinib treatment","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (RNAi, transformation assay, xenograft, patient data), replicated across cell lines","pmids":["22328973"],"is_preprint":false},{"year":2008,"finding":"Loss-of-function DDR2 missense mutations cause SMED-SL through mutations in the tyrosine kinase domain (T713I, I726R, R752C). These mutations map to the conserved kinase domain of DDR2.","method":"Homozygosity mapping, Sanger sequencing of DDR2 gene in affected families","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mapping plus sequencing, but functional characterization limited to identification of mutation location","pmids":["19110212"],"is_preprint":false},{"year":2010,"finding":"SMED-SL DDR2 missense mutants (T713I, I726R, R752C) are retained in the endoplasmic reticulum and fail to reach the plasma membrane, abolishing collagen-induced receptor activation. A fourth mutant (E113K) traffics normally but fails to bind collagen, identifying two distinct loss-of-function mechanisms.","method":"Expression of point mutants in human cell lines, subcellular localization studies, collagen activation assays, Western blot","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple mutants characterized by orthogonal methods (localization + ligand binding + activation), mechanistically distinguishes two classes of loss-of-function","pmids":["20223752"],"is_preprint":false},{"year":2018,"finding":"Recurrent activating DDR2 variants (L610P, Y740C) causing Warburg-Cinotti syndrome increase DDR2 phosphorylation in patient fibroblasts in a ligand-independent manner, suggesting reduced receptor autoinhibition. Dasatinib prevents DDR2 autophosphorylation in these fibroblasts.","method":"Sequencing of affected families, phosphorylation analysis in patient-derived fibroblasts, dasatinib treatment","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient fibroblast functional data plus pharmacological validation, single lab","pmids":["30449416"],"is_preprint":false},{"year":2015,"finding":"DDR2 and SRC are binding partners; SRC activity is tied to DDR2 activation, and dual inhibition of DDR2 and SRC leads to enhanced suppression of DDR2-mutant lung cancer cell lines compared to DDR2 inhibition alone.","method":"Co-immunoprecipitation (DDR2-SRC interaction), selective DDR2 inhibitors, dual DDR2/SRC inhibition, antiproliferative assays","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal binding demonstrated by Co-IP, functional consequence tested with selective inhibitors","pmids":["26390252"],"is_preprint":false},{"year":2015,"finding":"DDR2 suppresses osteoclastogenesis by forming a DDR2-Nrp1-PlexinA1 complex that blocks PlexinA1-mediated stimulation of osteoclast differentiation. DDR2 prevents PlexinA1 from interacting with TREM2 and DAP12. Neuropilin-1 (Nrp1) was identified as a DDR2-interacting protein.","method":"Co-immunoprecipitation, DDR2 overexpression/knockdown, osteoclastogenesis assays, bone resorption assays, adenovirus delivery in ovariectomized mouse model","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP identifying complex, multiple functional assays, in vivo epistasis, disease model validation","pmids":["25805889"],"is_preprint":false},{"year":2015,"finding":"Nrp1 co-localizes with DDR2 at the cell membrane, physically interacts with DDR2, and prolongs DDR2 protein half-life without altering DDR2 mRNA, thereby enhancing DDR2 phosphorylation and ERK1/2-Runx2 signaling during osteoblast differentiation.","method":"Co-immunoprecipitation, immunofluorescence co-localization, half-life determination assay, overexpression/silencing of Nrp1","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus co-localization and functional half-life assay, single lab","pmids":["25924845"],"is_preprint":false},{"year":2011,"finding":"Collagen I induces DDR1 expression in primary human lung fibroblasts via sequential activation of DDR2, JAK2, and ERK1/2 MAPK, culminating in recruitment of transcription factor PEA3 to the DDR1 promoter. Inhibition of any step in this pathway abrogates DDR1 induction.","method":"DDR2 inhibition/knockdown, JAK2 and ERK1/2 inhibitors, promoter reporter assays, ChIP for PEA3 recruitment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway epistasis with inhibitors and promoter occupancy assay, single lab with multiple methods","pmids":["21335558"],"is_preprint":false},{"year":2016,"finding":"Collagen II-activated DDR2 induces CYR61 expression through activation of transcription factor AP-1; CYR61 in turn activates MMP1 via ETS1, forming a Collagen II-DDR2-AP-1-CYR61-ETS1-MMP1 signaling loop in rheumatoid arthritis fibroblast-like synoviocytes.","method":"Collagen stimulation, phospho-DDR2 detection, CYR61 and MMP1 expression, AP-1 and ETS1 transcription factor analysis, shRNA in vitro and in vivo (CIA rat model)","journal":"Journal of bone and mineral research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multi-step pathway defined with multiple methods in vitro and in vivo, single lab","pmids":["27653023"],"is_preprint":false},{"year":2015,"finding":"DDR2 promotes HCC invasion and migration by activating ERK2, which stabilizes SNAIL1 protein (demonstrated by cycloheximide chase experiments showing increased SNAIL1 half-life). This signaling axis upregulates MT1-MMP and MMP2 expression and is activated by type I collagen.","method":"DDR2 overexpression/knockdown, cycloheximide chase, ERK2 activation assays, invasion/migration assays, collagen I stimulation","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — protein stability assay with multiple signaling readouts, single lab","pmids":["26362312"],"is_preprint":false},{"year":2008,"finding":"The extracellular domain of DDR2, expressed as a membrane-anchored kinase-dead protein on the cell surface, inhibits collagen fibrillogenesis by reducing the rate and quantity of collagen deposition and altering fiber morphology, independent of DDR2 kinase activity.","method":"Stable expression of kinase-dead DDR2 in mouse osteoblasts, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple imaging and biochemical methods in a single lab, kinase-dead control included","pmids":["18996394"],"is_preprint":false},{"year":2009,"finding":"Soluble extracellular domains of DDR1 and DDR2 secreted by cells inhibit collagen fibrillogenesis, reducing collagen deposition rate, quantity, and altering fiber morphology, identifying a kinase-independent function for secreted DDR ECDs in ECM remodeling.","method":"Stable secretion of DDR1/DDR2 ECDs from osteoblasts, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, single lab","pmids":["19900459"],"is_preprint":false},{"year":2009,"finding":"DDR2 is involved in regulation of focal adhesion kinase (FAK) levels in vascular smooth muscle cells: FAK is downregulated on fibrillar collagen matrices, this is correlated with DDR2 tyrosine phosphorylation, and siRNA depletion of DDR2 blocks FAK downregulation.","method":"Collagen fibril matrices of varying stiffness, siRNA depletion of DDR2, FAK and DDR2 phosphorylation measurement by Western blot","journal":"Biomaterials","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with mechanistic readout, single lab","pmids":["19762078"],"is_preprint":false},{"year":2013,"finding":"Collagen-DDR2 signaling mediates upregulation of lysyl oxidase in osteoblasts; DDR2 shRNA knockdown blocks collagen-induced lysyl oxidase increases. Advanced glycation of collagen (CML-collagen) disrupts DDR2 binding and activation, explaining reduced lysyl oxidase in diabetic bone.","method":"DDR2 shRNA knockdown, primary osteoblast cultures, collagen vs. CML-collagen comparison, lysyl oxidase protein measurements","journal":"Bone","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — shRNA knockdown with specific molecular readout, single lab with clear mechanistic conclusion","pmids":["24120383"],"is_preprint":false},{"year":2019,"finding":"DDR2 in cancer-associated fibroblasts (CAFs) controls tumor stiffness by reorganizing collagen fibers at the tumor-stromal boundary through mechanotransduction: DDR2 controls full collagen-binding integrin activation via Rap1-mediated Talin1 and Kindlin2 recruitment, promoting lung metastasis.","method":"DDR2 depletion in mouse/human CAFs, collagen fiber imaging, integrin activation assays, Rap1/Talin1/Kindlin2 co-localization and functional studies, in vivo breast tumor models","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic pathway dissection with multiple orthogonal methods, in vivo validation, identifies Rap1-Talin1-Kindlin2 as mechanism","pmids":["31144616"],"is_preprint":false},{"year":2019,"finding":"HSP47 binds to the DDR2 ectodomain (demonstrated by Co-IP) and is required for DDR2 protein stability and cell-surface membrane localization. HSP47 silencing reduces DDR2 protein stability and membrane dynamics, suppressing cancer cell migration and invasion.","method":"Co-immunoprecipitation, HSP47 silencing, photoconvertible protein technique, total internal reflection fluorescence (TIRF) microscopy, migration/invasion assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — Co-IP plus live-cell TIRF imaging of membrane dynamics, multiple orthogonal methods in single study","pmids":["31570520"],"is_preprint":false},{"year":2018,"finding":"A small molecule allosteric inhibitor (WRG-28) of the DDR2 extracellular domain inhibits receptor-ligand interactions via allosteric modulation, blocking tumor invasion, migration, and tumor-stromal interactions.","method":"Small molecule screening, DDR2 extracellular domain binding assays, tumor invasion and migration assays, in vivo lung colonization model","journal":"PNAS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — selective inhibitor with allosteric mechanism characterized, multiple functional assays, single lab","pmids":["30061414"],"is_preprint":false},{"year":2021,"finding":"DDR2 tyrosine kinase activity is not strictly required for tumor invasion and in vivo metastasis; kinase-independent DDR2 actions in tumor cells support Matrigel invasion and lung metastasis. Paracrine DDR2 signaling between tumor cells and CAFs also supports invasion independent of kinase activity.","method":"Kinase-dead DDR2 mutant expression, Matrigel invasion assays, in vivo metastasis models, paracrine co-culture experiments","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — kinase-dead mutant rescue approach, in vivo validation, single lab","pmids":["34477203"],"is_preprint":false},{"year":2012,"finding":"DDR2 plays a role in fibroblast migration that is independent of both the adhesion ligand (fibronectin or collagen) and collagen-induced DDR2 tyrosine kinase activation. DDR2 silencing inhibits spreading and migration on fibronectin even without detectable DDR2 tyrosine kinase activation.","method":"siRNA silencing of DDR2, 2D migration on fibronectin and collagen surfaces, 3D collagen matrix migration, tyrosine phosphorylation assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA with multiple substrate conditions and kinase activation monitoring, single lab","pmids":["23131558"],"is_preprint":false},{"year":2021,"finding":"DDR2 depletion in melanoma cells increases sensitivity to BRAF/MEK inhibition through a collagen-rich matrix. Drug-induced ECM resistance (MMDR) is mediated by drug-induced linear clustering of phosphorylated DDR1 and DDR2. DDR-dependent MMDR fosters a pro-survival NIK/IKKα/NF-κB2 pathway.","method":"DDR1/DDR2 depletion, pharmacological targeting, phospho-DDR imaging, NF-κB2 pathway analysis, xenograft models","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway placement via genetic depletion plus in vivo validation, single lab with multiple methods","pmids":["34957688"],"is_preprint":false},{"year":2018,"finding":"DDR1 and DDR2 physically interact with each other (demonstrated by Co-IP), and high co-expression of both receptors leads to inhibition of cell proliferation. ERK activation is higher in cells co-expressing DDR1 and DDR2. DDR1 but not DDR2 is implicated in cell adhesion to collagen I.","method":"Co-immunoprecipitation, HEK293T overexpression, dominant-negative truncation mutants, ERK/JAK2 activation assays, proliferation and adhesion assays","journal":"Cell adhesion & migration","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for physical interaction plus multiple functional assays, single lab","pmids":["29616590"],"is_preprint":false},{"year":2020,"finding":"DDR2 acts via ERK1/2 MAPK-activated SRF transcription factor to enhance expression of antiapoptotic cIAP2 in cardiac fibroblasts (resistance to oxidative injury), and to upregulate Skp2-mediated post-translational degradation of p27 to promote G1-S cell cycle transition.","method":"Gene knockdown and overexpression, promoter binding assays, ERK1/2 and SRF inhibition, flow cytometry, WRG-28 collagen-DDR2 blocking","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pathway assays with promoter occupancy, pharmacological blockade of DDR2-collagen interaction, single lab","pmids":["32412792"],"is_preprint":false},{"year":2016,"finding":"C. elegans DDR-2 (ortholog of DDR2) functions upstream of the Met-like RTK SVH-2 and SHC-1 scaffold in axon regeneration following injury. DDR-2 is activated by EMB-9 collagen type IV; overexpression of svh-2 and shc-1 suppresses the axon regeneration delay in ddr-2 mutants, placing DDR-2 upstream in a DDR-2→SHC-1→SVH-2→JNK pathway.","method":"C. elegans genetic epistasis, axon regeneration assays post-injury, overexpression suppression analysis, SHC-1 interaction with DDR-2 and SVH-2","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in a model organism ortholog, pathway placement supported by multiple alleles","pmids":["27984580"],"is_preprint":false},{"year":2023,"finding":"DDR2 in ovarian cancer-associated fibroblasts promotes collagen production through arginase activity; DDR2-depleted CAFs have decreased ornithine and polyamine levels and reduced collagen production. DDR2 regulates arginase-1 transcription via SNAI1, which binds the arginase-1 promoter in a DDR2-dependent manner.","method":"DDR2 depletion in CAFs, arginase activity assays, metabolomics (ornithine/polyamine measurement), ChIP for SNAI1 at arginase-1 promoter, rescue experiments with arginase-1 overexpression and exogenous polyamines","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus metabolic rescue and loss-of-function, multiple orthogonal methods, single lab","pmids":["37996700"],"is_preprint":false},{"year":2023,"finding":"Stromal DDR2 in fibroblasts regulates glycolysis through an AKT/SNAI1 axis suppressing fructose-1,6-bisphosphatase and increasing hexokinase activity. DDR2 inhibition decreases LOXL2 secretion; adding back LOXL2 to DDR2-deficient fibroblasts rescues tumor cell invasion.","method":"DDR2 depletion in fibroblasts, glycolytic enzyme activity assays, protein secretion analysis, LOXL2 rescue experiments, in vivo peritoneal metastasis model","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rescue experiment identifying LOXL2 as downstream effector, multiple methods, single lab","pmids":["37527178"],"is_preprint":false},{"year":2024,"finding":"DDR2 forms a complex with Src kinase in lens epithelial cells, leading to nuclear translocation of YAP1 and WWTR1 (Hippo pathway effectors), which alters expression of ferroptosis-related genes and enhances ferroptosis sensitivity.","method":"RNA sequencing, DDR2-Src interaction studies, nuclear fractionation of YAP1/WWTR1, DDR2 inhibitor treatment, in vitro and in vivo ferroptosis assays","journal":"Cell death & disease","confidence":"Low","confidence_rationale":"Tier 3 / Weak — interaction and pathway activation described but detailed mechanistic validation limited in the abstract, single lab","pmids":["39900894"],"is_preprint":false},{"year":2021,"finding":"DDR2 induces STAT3 phosphorylation and nuclear translocation; activated STAT3 in turn enhances DDR2 expression, forming a positive feedback loop. This DDR2/STAT3 loop upregulates PD-L1 and CCL20 transcription (confirmed by dual luciferase reporter assay), promoting immunosuppressive tumor microenvironment in oxaliplatin-resistant HCC.","method":"DDR2/STAT3 knockdown, phosphorylation assays, immunofluorescence, dual luciferase reporter assay for PD-L1 and CCL20 promoters, MDSC migration assays","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter reporter assays plus functional immunological readouts, single lab with multiple methods","pmids":["38969205"],"is_preprint":false},{"year":2014,"finding":"A novel DDR2 frameshift mutation (c.2468_2469delCT, p.S823Cfs*2) causes SMED-SL by retaining the mutant protein in the endoplasmic reticulum, as demonstrated by confocal microscopy and deglycosylation assays, resulting in deficient collagen-induced receptor activation.","method":"Sanger sequencing, confocal microscopy for subcellular localization, deglycosylation assay, Western blotting, collagen activation assay","journal":"BMC medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods for localization and function, consistent with prior SMED-SL mechanism","pmids":["24725993"],"is_preprint":false},{"year":2016,"finding":"DDR2 E655K mutation reduces protein expression due to enhanced binding to ubiquitin ligase Cbl-b and proteasomal degradation; treatment with a proteasome inhibitor restores DDR2 E655K protein levels. Collagen stimulation normally decreases cellular proliferation via p38 activation in DDR2 wild-type cells, but this growth-suppressive effect is weakened in DDR2 E655K cells.","method":"Overexpression of DDR2 mutants, collagen stimulation, p38 activation assays, Co-IP with Cbl-b, proteasome inhibitor treatment, proliferation assays","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with ubiquitin ligase, pharmacological rescue, functional proliferation assay, single lab","pmids":["26826182"],"is_preprint":false},{"year":2022,"finding":"DDR2 interacts with β-catenin (demonstrated by Co-IP); CEBPA-DT lncRNA promotes DDR2 expression via hnRNPC, and DDR2 facilitates nuclear translocation of β-catenin to activate Snail1 transcription, promoting EMT and HCC metastasis.","method":"Co-immunoprecipitation (DDR2-β-catenin interaction), subcellular protein fractionation, DDR2 inhibitor experiments, in vivo metastasis models","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for DDR2-β-catenin interaction plus functional rescue experiments, single lab","pmids":["36471363"],"is_preprint":false}],"current_model":"DDR2 is a receptor tyrosine kinase that is activated by fibrillar and non-fibrillar collagens binding to three surface-exposed loops of its extracellular discoidin domain; upon collagen engagement, DDR2 undergoes dimerization (facilitated by its JM2 juxtamembrane region) and autophosphorylation, triggering downstream signaling through SHP-2, ERK1/2, p38 MAPK, JAK2, SRC, and mTORC2 to regulate MMP expression, Runx2 activity, SNAIL1 stability, YAP/TAZ, and NF-κB, thereby controlling cell proliferation, ECM remodeling, EMT, osteoblast differentiation, osteoclastogenesis, and cancer metastasis; its protein stability is regulated by HSP47 chaperone binding and Cbl-b-mediated proteasomal degradation, while kinase-independent functions of its extracellular domain inhibit collagen fibrillogenesis and support cell migration."},"narrative":{"mechanistic_narrative":"DDR2 is a collagen-activated receptor tyrosine kinase that couples extracellular matrix sensing to intracellular signaling controlling cell proliferation, ECM remodeling, skeletal development, and cancer metastasis [PMID:11696582, PMID:11375938]. Its surface discoidin domain is sufficient for high-affinity collagen I binding and transmembrane signaling, recognizing collagen through three adjacent surface loops that engage the triple-helical GVMGFO motif; single triple-helical peptides containing this motif activate the receptor, so fibrillar assembly is not required, and collagen X engages the receptor through regions beyond the discoidin domain [PMID:12611880, PMID:18201965, PMID:16806867]. Ligand engagement is reinforced by the cytoplasmic JM2 juxtamembrane region, which drives receptor dimerization and efficient collagen binding [PMID:24740739], and triggers kinase-dependent autophosphorylation that recruits SHP-2 and engages SRC, JAK2 and ERK/p38 MAPK cascades [PMID:23822953, PMID:26390252, PMID:21335558]. Through these effectors DDR2 phosphorylates and activates Runx2 to drive osteoblast differentiation, induces MMPs and stabilizes SNAIL1 to promote invasion and EMT, and converges on transcription programs through AP-1/CYR61, STAT3, β-catenin and SRF [PMID:20734453, PMID:26362312, PMID:27653023, PMID:38969205, PMID:36471363, PMID:32412792]. In bone, ATF4/C/EBPβ transcriptionally induce DDR2, and DDR2 additionally suppresses osteoclastogenesis by forming a Nrp1–PlexinA1 complex that blocks PlexinA1 engagement of TREM2/DAP12 [PMID:20564243, PMID:25805889]. In the tumor stroma, DDR2 in cancer-associated fibroblasts reorganizes collagen and controls tumor stiffness through Rap1-mediated Talin1/Kindlin2 recruitment and integrin activation to promote metastasis [PMID:31144616]. DDR2 protein levels are set by HSP47, which binds the ectodomain to maintain stability and surface localization, and by Cbl-b-mediated proteasomal degradation [PMID:31570520, PMID:26826182]. Beyond its kinase function, the DDR2 extracellular domain acts kinase-independently to inhibit collagen fibrillogenesis and to support fibroblast spreading and tumor cell invasion [PMID:18996394, PMID:34477203, PMID:23131558]. Activating kinase-domain mutations confer oncogenic, dasatinib-sensitive transformation in squamous lung cancer, whereas loss-of-function mutations that impair kinase activity, ER export, or collagen binding cause the skeletal disorder SMED-SL, and gain-of-function ligand-independent variants cause Warburg–Cinotti syndrome [PMID:22328973, PMID:19110212, PMID:20223752, PMID:30449416].","teleology":[{"year":2001,"claim":"Establishing that DDR2 kinase activity is functionally required answered whether the receptor is a driver of proliferation and ECM-invasive behavior rather than a passive collagen binder.","evidence":"DDR2 knockout mice with kinase-dead rescue, and overexpression of wild-type vs kinase-dead DDR2 in hepatic stellate cells with MMP-2 and invasion readouts","pmids":["11375938","11696582"],"confidence":"High","gaps":["Did not define the collagen recognition site","Downstream effectors of kinase activity not yet mapped"]},{"year":2008,"claim":"Defining the molecular collagen recognition determinants established how DDR2 senses matrix at the structural level and which collagen features are required for activation.","evidence":"Recombinant discoidin domain binding and loop-exchange mutagenesis, plus Toolkit peptide screening identifying the triple-helical GVMGFO motif and the collagen II D2 period","pmids":["12611880","18201965","15544808","16806867"],"confidence":"High","gaps":["Structural basis of dimerization not resolved","How distinct collagens (e.g. collagen X) produce differential activation not fully explained"]},{"year":2008,"claim":"Identifying kinase-independent actions of the DDR2 ectodomain answered whether the receptor influences matrix and cell behavior outside of canonical phospho-signaling.","evidence":"Membrane-anchored and secreted kinase-dead DDR2 ECD expressed in osteoblasts with TEM, hydroxyproline assays, and fibroblast migration/spreading assays","pmids":["18996394","19900459","23131558"],"confidence":"Medium","gaps":["Molecular mechanism of fibrillogenesis inhibition not defined","Kinase-independent migration partners unidentified"]},{"year":2010,"claim":"Placing DDR2 in an ERK/p38-Runx2 axis and identifying its transcriptional induction by ATF4 established its mechanistic role in osteoblast differentiation and skeletal development.","evidence":"shRNA knockdown, constitutively active DDR2, ERK/p38 inhibitors, Runx2 phospho-mutant epistasis, and DDR2 promoter mapping with ATF4/C/EBPβ dissection","pmids":["20734453","20564243"],"confidence":"High","gaps":["Direct DDR2-to-ERK coupling step not resolved","In vivo contribution of each MAPK branch not separated"]},{"year":2011,"claim":"Discovery of recurrent activating kinase-domain mutations established DDR2 as a targetable oncogenic driver in squamous lung cancer.","evidence":"Tyrosine kinome sequencing, RNAi, transformation and xenograft assays, and dasatinib sensitivity testing","pmids":["22328973"],"confidence":"High","gaps":["Mechanism by which mutations elevate activity not structurally defined","Resistance mechanisms not yet known"]},{"year":2008,"claim":"Loss-of-function genetics linked DDR2 to a Mendelian skeletal disorder, defining the consequences of receptor inactivation in humans.","evidence":"Homozygosity mapping and sequencing identifying SMED-SL kinase-domain mutations, followed by trafficking and ligand-binding characterization of mutant classes","pmids":["19110212","20223752","24725993"],"confidence":"High","gaps":["Tissue-specific signaling deficits underlying skeletal phenotype not delineated","Whether residual kinase-independent functions persist in ER-retained mutants unknown"]},{"year":2013,"claim":"Identifying SHP-2 as a kinase-dependent phospho-substrate and mapping dasatinib resistance routes built the proximal signaling and pharmacology of DDR2.","evidence":"Temporal phosphoproteomics with mutant-panel validation, and exome sequencing of resistant cell lines identifying the T654I gatekeeper mutation and NF1-loss RAS-ERK bypass","pmids":["23822953","24296828"],"confidence":"Medium","gaps":["Full proximal interactome beyond SHP-2 incomplete","Clinical generalizability of resistance mechanisms untested"]},{"year":2015,"claim":"Characterizing DDR2 protein partners established mechanisms regulating its stability, localization, and divergent roles in bone homeostasis.","evidence":"Co-IP and functional assays identifying SRC, Nrp1 (stabilizing DDR2 half-life and forming a Nrp1–PlexinA1 complex), in osteoblast and osteoclast models and DDR2-mutant lung cancer cells","pmids":["26390252","25924845","25805889"],"confidence":"High","gaps":["Stoichiometry and structural basis of the Nrp1-PlexinA1 complex unresolved","How DDR2 toggles between pro-osteoblast and anti-osteoclast outputs unclear"]},{"year":2016,"claim":"Defining downstream transcriptional loops connected DDR2 to invasion, EMT, and inflammatory matrix programs across disease contexts.","evidence":"Pathway dissection in HCC (ERK2-SNAIL1 stabilization), RA synoviocytes (AP-1-CYR61-ETS1-MMP1), and lung fibroblasts (DDR2-JAK2-ERK-PEA3 inducing DDR1) using inhibitors, ChIP, and promoter reporters","pmids":["26362312","27653023","21335558"],"confidence":"Medium","gaps":["Cross-talk between parallel transcriptional loops not integrated","Direct vs indirect target relationships partly inferred"]},{"year":2016,"claim":"Cbl-b-mediated degradation established a ubiquitin-dependent route controlling DDR2 abundance and a cancer-associated mutation altering it.","evidence":"Co-IP with Cbl-b, proteasome inhibitor rescue of the E655K mutant, and collagen-induced p38-dependent growth suppression assays","pmids":["26826182"],"confidence":"Medium","gaps":["Ubiquitination sites not mapped","Physiological signals triggering Cbl-b recruitment unknown"]},{"year":2018,"claim":"Identifying ligand-independent activating variants and an allosteric ectodomain inhibitor expanded the disease and pharmacological landscape of DDR2.","evidence":"Family sequencing and patient-fibroblast phosphorylation for Warburg-Cinotti variants, and screening/characterization of the WRG-28 allosteric ECD inhibitor with invasion assays","pmids":["30449416","30061414"],"confidence":"Medium","gaps":["Structural basis of autoinhibition release not defined","WRG-28 in vivo therapeutic window untested"]},{"year":2019,"claim":"Defining stromal DDR2 mechanotransduction established how fibroblast DDR2 shapes the tumor microenvironment to drive metastasis, and that HSP47 maintains DDR2 stability.","evidence":"DDR2 depletion in CAFs with collagen imaging and Rap1-Talin1-Kindlin2 integrin-activation studies in vivo, and Co-IP/TIRF imaging of HSP47-DDR2 ectodomain interaction","pmids":["31144616","31570520"],"confidence":"High","gaps":["How DDR2 signaling activates Rap1 mechanistically unclear","HSP47-DDR2 stoichiometry and chaperone cycle undefined"]},{"year":2021,"claim":"Demonstrating kinase-independent contributions to metastasis and drug resistance reframed DDR2 as functioning beyond its catalytic activity in tumor progression.","evidence":"Kinase-dead DDR2 rescue in invasion and metastasis models with paracrine co-culture, and DDR1/DDR2 clustering driving a NIK/IKKα/NF-κB2 ECM-resistance pathway in melanoma","pmids":["34477203","34957688"],"confidence":"Medium","gaps":["Kinase-independent effector mechanism unidentified","Relative contribution of kinase-dependent vs independent functions in patients unknown"]},{"year":2023,"claim":"Linking DDR2 to fibroblast metabolic reprogramming established a role in regulating collagen production and matrix-supportive metabolism via SNAI1.","evidence":"DDR2 depletion in CAFs with arginase/metabolomics and ChIP for SNAI1 at the arginase-1 promoter, and glycolytic enzyme/LOXL2 rescue experiments in vivo","pmids":["37996700","37527178"],"confidence":"Medium","gaps":["How DDR2 signaling reaches SNAI1/AKT not mechanistically traced","Generalizability beyond ovarian CAFs untested"]},{"year":2022,"claim":"Identifying β-catenin, STAT3, SRF and Hippo-effector linkages extended the DDR2 transcriptional network into EMT, immunosuppression, survival, and cell-cycle control.","evidence":"Co-IP (DDR2-β-catenin), fractionation, luciferase reporters (PD-L1/CCL20, SRF targets), and YAP1/WWTR1 nuclear translocation studies across HCC, cardiac fibroblast, and lens epithelial models","pmids":["36471363","38969205","32412792","39900894"],"confidence":"Medium","gaps":["Whether these interactions are direct or signaling-dependent partly unresolved","Ferroptosis link rests on low-confidence single-lab data"]},{"year":null,"claim":"How DDR2 mechanically couples collagen binding to slow, sustained autophosphorylation and selects between its many divergent downstream programs (Runx2 vs SNAIL1 vs anti-osteoclast complex vs kinase-independent outputs) in a context-specific manner remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No full-length 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Three spatially adjacent surface loops within the DDR2 discoidin domain constitute the collagen recognition site; mutation of these loops abolishes both collagen binding and collagen-dependent receptor activation.\",\n      \"method\": \"Recombinant extracellular domain production, solid-phase binding assays, loop-exchange mutagenesis, receptor signaling assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"12611880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The minimal collagen sequence required for DDR2 binding and activation is the triple-helical motif GVMGFO (O = hydroxyproline). Single triple-helical peptides comprising this motif are sufficient to activate DDR2 transmembrane signaling, indicating that fibrillar collagen is not required.\",\n      \"method\": \"Collagen II Toolkit peptide screen, truncation and alanine-substitution peptides, DDR2 binding and phosphorylation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with systematic mutagenesis, multiple orthogonal assays in one rigorous study\",\n      \"pmids\": [\"18201965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The D2 period of collagen II contains a specific DDR2 binding site; deletion of D2 abolishes DDR2 binding and receptor autophosphorylation, whereas D3 and D4 periods are dispensable.\",\n      \"method\": \"Recombinant collagen II variants with specific D-period deletions, DDR2 binding assays, autophosphorylation assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with deletion mapping and functional readout\",\n      \"pmids\": [\"15544808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Collagen X is a ligand for DDR2 that binds the DDR2 extracellular domain with high affinity and stimulates DDR2 autophosphorylation. Unlike fibrillar collagens, collagen X binding requires regions beyond the discoidin domain; the triple-helical region of collagen X activates DDR2 whereas the NC1 domain binds but does not activate.\",\n      \"method\": \"Solid-phase binding assays with recombinant DDR2 extracellular domain, autophosphorylation assays, RT-PCR and immunohistochemistry for spatial expression\",\n      \"journal\": \"Matrix biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with domain dissection, multiple methods, clear functional distinction between binding and activation\",\n      \"pmids\": [\"16806867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DDR2 overexpression in hepatic stellate cells enhances proliferation and Matrigel invasion via increased expression of active MMP-2; kinase-dead DDR2 does not produce these effects, establishing that DDR2 kinase activity is required.\",\n      \"method\": \"Stable overexpression of wild-type, constitutively active chimeric, truncated, and kinase-dead DDR2; proliferation assays; Matrigel invasion; MMP-2 activity assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple isogenic cell lines including kinase-dead control, orthogonal functional readouts\",\n      \"pmids\": [\"11696582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DDR2 kinase activity is required for normal cell proliferation in vivo; DDR2-deficient mice exhibit dwarfism and reduced chondrocyte proliferation, and introduction of wild-type but not kinase-dead DDR2 rescues the proliferation defect of DDR2-/- fibroblasts in vitro.\",\n      \"method\": \"DDR2 knockout mouse generation, bone phenotype analysis, skin wound healing model, fibroblast rescue with wild-type vs. kinase-dead DDR2\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO combined with kinase-dead rescue experiment, multiple in vivo and in vitro readouts\",\n      \"pmids\": [\"11375938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"DDR2 regulates osteoblast differentiation by activating ERK, which in turn phosphorylates and activates the transcription factor Runx2. A gain-of-function Runx2 mutant with ERK-independent phosphorylation rescues osteogenic phenotypes in DDR2-silenced cells, placing DDR2 upstream of ERK-Runx2 in osteoblastogenesis.\",\n      \"method\": \"shRNA knockdown, constitutively active DDR2 overexpression, ERK inhibitors, Runx2 phosphorylation assays, epistasis with Runx2 mutants\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods and epistasis experiments in a single study\",\n      \"pmids\": [\"20734453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ATF4 transcriptionally upregulates DDR2 expression by binding a C/EBP site at -1150 bp in the DDR2 promoter via cooperation with C/EBPβ; DDR2 in turn activates Runx2 through p38 MAPK to promote osteoblast differentiation.\",\n      \"method\": \"ATF4 knockdown/overexpression, promoter reporter assays, ATF4 mutants deficient in C/EBPβ binding, p38 MAPK inhibition\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — promoter mapping with mutagenesis, co-factor dissection, pathway placement via inhibitors, multiple methods\",\n      \"pmids\": [\"20564243\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SHP-2 tyrosine phosphorylation is dependent on DDR2 kinase activity downstream of collagen stimulation. Multiple DDR2 lung cancer mutants (L63V, G505S) phosphorylate SHP-2, whereas the kinase-impaired I638F mutant shows diminished DDR2 and SHP-2 phosphorylation.\",\n      \"method\": \"Quantitative phosphoproteomics (7-time-point temporal analysis), biochemical validation of SHP-2 phosphorylation, targeted proteomic profiling of DDR2 mutant panel\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — quantitative phosphoproteomics plus biochemical validation, multiple mutant panel tested\",\n      \"pmids\": [\"23822953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The cytoplasmic juxtamembrane 2 (JM2) region of DDR2 is required for receptor dimerization and efficient collagen binding, both of which are critical for receptor activation. Overexpression of the JM2-containing domain suppresses collagen-induced colony formation, proliferation, and invasion via inhibition of MMP-2 and MMP-9.\",\n      \"method\": \"Deletion constructs, collagen-binding assays, receptor dimerization analysis, dominant-negative overexpression, proliferation and invasion assays\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays in a single lab with domain-deletion approach\",\n      \"pmids\": [\"24740739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Acquired resistance to dasatinib in DDR2-dependent lung cancer cells occurs via two distinct mechanisms: (1) a T654I gatekeeper mutation in DDR2, and (2) loss of NF1 that activates a RAS-ERK bypass pathway.\",\n      \"method\": \"Targeted exome sequencing of resistant cell lines, functional validation of resistance mechanisms\",\n      \"journal\": \"Molecular cancer therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — exome sequencing with functional validation, two orthogonal resistance mechanisms identified\",\n      \"pmids\": [\"24296828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mutations in the DDR2 kinase domain (e.g., L63V, G505S) confer gain-of-function oncogenic activity; expression of mutant DDR2 leads to cellular transformation blocked by dasatinib. Squamous lung cancer cell lines with DDR2 mutations are selectively killed by DDR2 RNAi or dasatinib.\",\n      \"method\": \"Sanger sequencing of tyrosine kinome, RNAi knockdown, transformation assays, xenograft models, dasatinib treatment\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (RNAi, transformation assay, xenograft, patient data), replicated across cell lines\",\n      \"pmids\": [\"22328973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Loss-of-function DDR2 missense mutations cause SMED-SL through mutations in the tyrosine kinase domain (T713I, I726R, R752C). These mutations map to the conserved kinase domain of DDR2.\",\n      \"method\": \"Homozygosity mapping, Sanger sequencing of DDR2 gene in affected families\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mapping plus sequencing, but functional characterization limited to identification of mutation location\",\n      \"pmids\": [\"19110212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SMED-SL DDR2 missense mutants (T713I, I726R, R752C) are retained in the endoplasmic reticulum and fail to reach the plasma membrane, abolishing collagen-induced receptor activation. A fourth mutant (E113K) traffics normally but fails to bind collagen, identifying two distinct loss-of-function mechanisms.\",\n      \"method\": \"Expression of point mutants in human cell lines, subcellular localization studies, collagen activation assays, Western blot\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple mutants characterized by orthogonal methods (localization + ligand binding + activation), mechanistically distinguishes two classes of loss-of-function\",\n      \"pmids\": [\"20223752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Recurrent activating DDR2 variants (L610P, Y740C) causing Warburg-Cinotti syndrome increase DDR2 phosphorylation in patient fibroblasts in a ligand-independent manner, suggesting reduced receptor autoinhibition. Dasatinib prevents DDR2 autophosphorylation in these fibroblasts.\",\n      \"method\": \"Sequencing of affected families, phosphorylation analysis in patient-derived fibroblasts, dasatinib treatment\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient fibroblast functional data plus pharmacological validation, single lab\",\n      \"pmids\": [\"30449416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 and SRC are binding partners; SRC activity is tied to DDR2 activation, and dual inhibition of DDR2 and SRC leads to enhanced suppression of DDR2-mutant lung cancer cell lines compared to DDR2 inhibition alone.\",\n      \"method\": \"Co-immunoprecipitation (DDR2-SRC interaction), selective DDR2 inhibitors, dual DDR2/SRC inhibition, antiproliferative assays\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding demonstrated by Co-IP, functional consequence tested with selective inhibitors\",\n      \"pmids\": [\"26390252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 suppresses osteoclastogenesis by forming a DDR2-Nrp1-PlexinA1 complex that blocks PlexinA1-mediated stimulation of osteoclast differentiation. DDR2 prevents PlexinA1 from interacting with TREM2 and DAP12. Neuropilin-1 (Nrp1) was identified as a DDR2-interacting protein.\",\n      \"method\": \"Co-immunoprecipitation, DDR2 overexpression/knockdown, osteoclastogenesis assays, bone resorption assays, adenovirus delivery in ovariectomized mouse model\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP identifying complex, multiple functional assays, in vivo epistasis, disease model validation\",\n      \"pmids\": [\"25805889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Nrp1 co-localizes with DDR2 at the cell membrane, physically interacts with DDR2, and prolongs DDR2 protein half-life without altering DDR2 mRNA, thereby enhancing DDR2 phosphorylation and ERK1/2-Runx2 signaling during osteoblast differentiation.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence co-localization, half-life determination assay, overexpression/silencing of Nrp1\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus co-localization and functional half-life assay, single lab\",\n      \"pmids\": [\"25924845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Collagen I induces DDR1 expression in primary human lung fibroblasts via sequential activation of DDR2, JAK2, and ERK1/2 MAPK, culminating in recruitment of transcription factor PEA3 to the DDR1 promoter. Inhibition of any step in this pathway abrogates DDR1 induction.\",\n      \"method\": \"DDR2 inhibition/knockdown, JAK2 and ERK1/2 inhibitors, promoter reporter assays, ChIP for PEA3 recruitment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway epistasis with inhibitors and promoter occupancy assay, single lab with multiple methods\",\n      \"pmids\": [\"21335558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Collagen II-activated DDR2 induces CYR61 expression through activation of transcription factor AP-1; CYR61 in turn activates MMP1 via ETS1, forming a Collagen II-DDR2-AP-1-CYR61-ETS1-MMP1 signaling loop in rheumatoid arthritis fibroblast-like synoviocytes.\",\n      \"method\": \"Collagen stimulation, phospho-DDR2 detection, CYR61 and MMP1 expression, AP-1 and ETS1 transcription factor analysis, shRNA in vitro and in vivo (CIA rat model)\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multi-step pathway defined with multiple methods in vitro and in vivo, single lab\",\n      \"pmids\": [\"27653023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 promotes HCC invasion and migration by activating ERK2, which stabilizes SNAIL1 protein (demonstrated by cycloheximide chase experiments showing increased SNAIL1 half-life). This signaling axis upregulates MT1-MMP and MMP2 expression and is activated by type I collagen.\",\n      \"method\": \"DDR2 overexpression/knockdown, cycloheximide chase, ERK2 activation assays, invasion/migration assays, collagen I stimulation\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — protein stability assay with multiple signaling readouts, single lab\",\n      \"pmids\": [\"26362312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The extracellular domain of DDR2, expressed as a membrane-anchored kinase-dead protein on the cell surface, inhibits collagen fibrillogenesis by reducing the rate and quantity of collagen deposition and altering fiber morphology, independent of DDR2 kinase activity.\",\n      \"method\": \"Stable expression of kinase-dead DDR2 in mouse osteoblasts, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple imaging and biochemical methods in a single lab, kinase-dead control included\",\n      \"pmids\": [\"18996394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Soluble extracellular domains of DDR1 and DDR2 secreted by cells inhibit collagen fibrillogenesis, reducing collagen deposition rate, quantity, and altering fiber morphology, identifying a kinase-independent function for secreted DDR ECDs in ECM remodeling.\",\n      \"method\": \"Stable secretion of DDR1/DDR2 ECDs from osteoblasts, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, single lab\",\n      \"pmids\": [\"19900459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DDR2 is involved in regulation of focal adhesion kinase (FAK) levels in vascular smooth muscle cells: FAK is downregulated on fibrillar collagen matrices, this is correlated with DDR2 tyrosine phosphorylation, and siRNA depletion of DDR2 blocks FAK downregulation.\",\n      \"method\": \"Collagen fibril matrices of varying stiffness, siRNA depletion of DDR2, FAK and DDR2 phosphorylation measurement by Western blot\",\n      \"journal\": \"Biomaterials\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with mechanistic readout, single lab\",\n      \"pmids\": [\"19762078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Collagen-DDR2 signaling mediates upregulation of lysyl oxidase in osteoblasts; DDR2 shRNA knockdown blocks collagen-induced lysyl oxidase increases. Advanced glycation of collagen (CML-collagen) disrupts DDR2 binding and activation, explaining reduced lysyl oxidase in diabetic bone.\",\n      \"method\": \"DDR2 shRNA knockdown, primary osteoblast cultures, collagen vs. CML-collagen comparison, lysyl oxidase protein measurements\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — shRNA knockdown with specific molecular readout, single lab with clear mechanistic conclusion\",\n      \"pmids\": [\"24120383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DDR2 in cancer-associated fibroblasts (CAFs) controls tumor stiffness by reorganizing collagen fibers at the tumor-stromal boundary through mechanotransduction: DDR2 controls full collagen-binding integrin activation via Rap1-mediated Talin1 and Kindlin2 recruitment, promoting lung metastasis.\",\n      \"method\": \"DDR2 depletion in mouse/human CAFs, collagen fiber imaging, integrin activation assays, Rap1/Talin1/Kindlin2 co-localization and functional studies, in vivo breast tumor models\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic pathway dissection with multiple orthogonal methods, in vivo validation, identifies Rap1-Talin1-Kindlin2 as mechanism\",\n      \"pmids\": [\"31144616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HSP47 binds to the DDR2 ectodomain (demonstrated by Co-IP) and is required for DDR2 protein stability and cell-surface membrane localization. HSP47 silencing reduces DDR2 protein stability and membrane dynamics, suppressing cancer cell migration and invasion.\",\n      \"method\": \"Co-immunoprecipitation, HSP47 silencing, photoconvertible protein technique, total internal reflection fluorescence (TIRF) microscopy, migration/invasion assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — Co-IP plus live-cell TIRF imaging of membrane dynamics, multiple orthogonal methods in single study\",\n      \"pmids\": [\"31570520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A small molecule allosteric inhibitor (WRG-28) of the DDR2 extracellular domain inhibits receptor-ligand interactions via allosteric modulation, blocking tumor invasion, migration, and tumor-stromal interactions.\",\n      \"method\": \"Small molecule screening, DDR2 extracellular domain binding assays, tumor invasion and migration assays, in vivo lung colonization model\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — selective inhibitor with allosteric mechanism characterized, multiple functional assays, single lab\",\n      \"pmids\": [\"30061414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDR2 tyrosine kinase activity is not strictly required for tumor invasion and in vivo metastasis; kinase-independent DDR2 actions in tumor cells support Matrigel invasion and lung metastasis. Paracrine DDR2 signaling between tumor cells and CAFs also supports invasion independent of kinase activity.\",\n      \"method\": \"Kinase-dead DDR2 mutant expression, Matrigel invasion assays, in vivo metastasis models, paracrine co-culture experiments\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase-dead mutant rescue approach, in vivo validation, single lab\",\n      \"pmids\": [\"34477203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"DDR2 plays a role in fibroblast migration that is independent of both the adhesion ligand (fibronectin or collagen) and collagen-induced DDR2 tyrosine kinase activation. DDR2 silencing inhibits spreading and migration on fibronectin even without detectable DDR2 tyrosine kinase activation.\",\n      \"method\": \"siRNA silencing of DDR2, 2D migration on fibronectin and collagen surfaces, 3D collagen matrix migration, tyrosine phosphorylation assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA with multiple substrate conditions and kinase activation monitoring, single lab\",\n      \"pmids\": [\"23131558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDR2 depletion in melanoma cells increases sensitivity to BRAF/MEK inhibition through a collagen-rich matrix. Drug-induced ECM resistance (MMDR) is mediated by drug-induced linear clustering of phosphorylated DDR1 and DDR2. DDR-dependent MMDR fosters a pro-survival NIK/IKKα/NF-κB2 pathway.\",\n      \"method\": \"DDR1/DDR2 depletion, pharmacological targeting, phospho-DDR imaging, NF-κB2 pathway analysis, xenograft models\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway placement via genetic depletion plus in vivo validation, single lab with multiple methods\",\n      \"pmids\": [\"34957688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DDR1 and DDR2 physically interact with each other (demonstrated by Co-IP), and high co-expression of both receptors leads to inhibition of cell proliferation. ERK activation is higher in cells co-expressing DDR1 and DDR2. DDR1 but not DDR2 is implicated in cell adhesion to collagen I.\",\n      \"method\": \"Co-immunoprecipitation, HEK293T overexpression, dominant-negative truncation mutants, ERK/JAK2 activation assays, proliferation and adhesion assays\",\n      \"journal\": \"Cell adhesion & migration\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for physical interaction plus multiple functional assays, single lab\",\n      \"pmids\": [\"29616590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"DDR2 acts via ERK1/2 MAPK-activated SRF transcription factor to enhance expression of antiapoptotic cIAP2 in cardiac fibroblasts (resistance to oxidative injury), and to upregulate Skp2-mediated post-translational degradation of p27 to promote G1-S cell cycle transition.\",\n      \"method\": \"Gene knockdown and overexpression, promoter binding assays, ERK1/2 and SRF inhibition, flow cytometry, WRG-28 collagen-DDR2 blocking\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pathway assays with promoter occupancy, pharmacological blockade of DDR2-collagen interaction, single lab\",\n      \"pmids\": [\"32412792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"C. elegans DDR-2 (ortholog of DDR2) functions upstream of the Met-like RTK SVH-2 and SHC-1 scaffold in axon regeneration following injury. DDR-2 is activated by EMB-9 collagen type IV; overexpression of svh-2 and shc-1 suppresses the axon regeneration delay in ddr-2 mutants, placing DDR-2 upstream in a DDR-2→SHC-1→SVH-2→JNK pathway.\",\n      \"method\": \"C. elegans genetic epistasis, axon regeneration assays post-injury, overexpression suppression analysis, SHC-1 interaction with DDR-2 and SVH-2\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in a model organism ortholog, pathway placement supported by multiple alleles\",\n      \"pmids\": [\"27984580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DDR2 in ovarian cancer-associated fibroblasts promotes collagen production through arginase activity; DDR2-depleted CAFs have decreased ornithine and polyamine levels and reduced collagen production. DDR2 regulates arginase-1 transcription via SNAI1, which binds the arginase-1 promoter in a DDR2-dependent manner.\",\n      \"method\": \"DDR2 depletion in CAFs, arginase activity assays, metabolomics (ornithine/polyamine measurement), ChIP for SNAI1 at arginase-1 promoter, rescue experiments with arginase-1 overexpression and exogenous polyamines\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus metabolic rescue and loss-of-function, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"37996700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Stromal DDR2 in fibroblasts regulates glycolysis through an AKT/SNAI1 axis suppressing fructose-1,6-bisphosphatase and increasing hexokinase activity. DDR2 inhibition decreases LOXL2 secretion; adding back LOXL2 to DDR2-deficient fibroblasts rescues tumor cell invasion.\",\n      \"method\": \"DDR2 depletion in fibroblasts, glycolytic enzyme activity assays, protein secretion analysis, LOXL2 rescue experiments, in vivo peritoneal metastasis model\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rescue experiment identifying LOXL2 as downstream effector, multiple methods, single lab\",\n      \"pmids\": [\"37527178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DDR2 forms a complex with Src kinase in lens epithelial cells, leading to nuclear translocation of YAP1 and WWTR1 (Hippo pathway effectors), which alters expression of ferroptosis-related genes and enhances ferroptosis sensitivity.\",\n      \"method\": \"RNA sequencing, DDR2-Src interaction studies, nuclear fractionation of YAP1/WWTR1, DDR2 inhibitor treatment, in vitro and in vivo ferroptosis assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — interaction and pathway activation described but detailed mechanistic validation limited in the abstract, single lab\",\n      \"pmids\": [\"39900894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDR2 induces STAT3 phosphorylation and nuclear translocation; activated STAT3 in turn enhances DDR2 expression, forming a positive feedback loop. This DDR2/STAT3 loop upregulates PD-L1 and CCL20 transcription (confirmed by dual luciferase reporter assay), promoting immunosuppressive tumor microenvironment in oxaliplatin-resistant HCC.\",\n      \"method\": \"DDR2/STAT3 knockdown, phosphorylation assays, immunofluorescence, dual luciferase reporter assay for PD-L1 and CCL20 promoters, MDSC migration assays\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter reporter assays plus functional immunological readouts, single lab with multiple methods\",\n      \"pmids\": [\"38969205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A novel DDR2 frameshift mutation (c.2468_2469delCT, p.S823Cfs*2) causes SMED-SL by retaining the mutant protein in the endoplasmic reticulum, as demonstrated by confocal microscopy and deglycosylation assays, resulting in deficient collagen-induced receptor activation.\",\n      \"method\": \"Sanger sequencing, confocal microscopy for subcellular localization, deglycosylation assay, Western blotting, collagen activation assay\",\n      \"journal\": \"BMC medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods for localization and function, consistent with prior SMED-SL mechanism\",\n      \"pmids\": [\"24725993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"DDR2 E655K mutation reduces protein expression due to enhanced binding to ubiquitin ligase Cbl-b and proteasomal degradation; treatment with a proteasome inhibitor restores DDR2 E655K protein levels. Collagen stimulation normally decreases cellular proliferation via p38 activation in DDR2 wild-type cells, but this growth-suppressive effect is weakened in DDR2 E655K cells.\",\n      \"method\": \"Overexpression of DDR2 mutants, collagen stimulation, p38 activation assays, Co-IP with Cbl-b, proteasome inhibitor treatment, proliferation assays\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with ubiquitin ligase, pharmacological rescue, functional proliferation assay, single lab\",\n      \"pmids\": [\"26826182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR2 interacts with β-catenin (demonstrated by Co-IP); CEBPA-DT lncRNA promotes DDR2 expression via hnRNPC, and DDR2 facilitates nuclear translocation of β-catenin to activate Snail1 transcription, promoting EMT and HCC metastasis.\",\n      \"method\": \"Co-immunoprecipitation (DDR2-β-catenin interaction), subcellular protein fractionation, DDR2 inhibitor experiments, in vivo metastasis models\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for DDR2-β-catenin interaction plus functional rescue experiments, single lab\",\n      \"pmids\": [\"36471363\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DDR2 is a receptor tyrosine kinase that is activated by fibrillar and non-fibrillar collagens binding to three surface-exposed loops of its extracellular discoidin domain; upon collagen engagement, DDR2 undergoes dimerization (facilitated by its JM2 juxtamembrane region) and autophosphorylation, triggering downstream signaling through SHP-2, ERK1/2, p38 MAPK, JAK2, SRC, and mTORC2 to regulate MMP expression, Runx2 activity, SNAIL1 stability, YAP/TAZ, and NF-κB, thereby controlling cell proliferation, ECM remodeling, EMT, osteoblast differentiation, osteoclastogenesis, and cancer metastasis; its protein stability is regulated by HSP47 chaperone binding and Cbl-b-mediated proteasomal degradation, while kinase-independent functions of its extracellular domain inhibit collagen fibrillogenesis and support cell migration.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"DDR2 is a collagen-activated receptor tyrosine kinase that couples extracellular matrix sensing to intracellular signaling controlling cell proliferation, ECM remodeling, skeletal development, and cancer metastasis [#4, #5]. Its surface discoidin domain is sufficient for high-affinity collagen I binding and transmembrane signaling, recognizing collagen through three adjacent surface loops that engage the triple-helical GVMGFO motif; single triple-helical peptides containing this motif activate the receptor, so fibrillar assembly is not required, and collagen X engages the receptor through regions beyond the discoidin domain [#0, #1, #3]. Ligand engagement is reinforced by the cytoplasmic JM2 juxtamembrane region, which drives receptor dimerization and efficient collagen binding [#9], and triggers kinase-dependent autophosphorylation that recruits SHP-2 and engages SRC, JAK2 and ERK/p38 MAPK cascades [#8, #15, #18]. Through these effectors DDR2 phosphorylates and activates Runx2 to drive osteoblast differentiation, induces MMPs and stabilizes SNAIL1 to promote invasion and EMT, and converges on transcription programs through AP-1/CYR61, STAT3, β-catenin and SRF [#6, #20, #19, #37, #40, #32]. In bone, ATF4/C/EBPβ transcriptionally induce DDR2, and DDR2 additionally suppresses osteoclastogenesis by forming a Nrp1–PlexinA1 complex that blocks PlexinA1 engagement of TREM2/DAP12 [#7, #16]. In the tumor stroma, DDR2 in cancer-associated fibroblasts reorganizes collagen and controls tumor stiffness through Rap1-mediated Talin1/Kindlin2 recruitment and integrin activation to promote metastasis [#25]. DDR2 protein levels are set by HSP47, which binds the ectodomain to maintain stability and surface localization, and by Cbl-b-mediated proteasomal degradation [#26, #39]. Beyond its kinase function, the DDR2 extracellular domain acts kinase-independently to inhibit collagen fibrillogenesis and to support fibroblast spreading and tumor cell invasion [#21, #28, #29]. Activating kinase-domain mutations confer oncogenic, dasatinib-sensitive transformation in squamous lung cancer, whereas loss-of-function mutations that impair kinase activity, ER export, or collagen binding cause the skeletal disorder SMED-SL, and gain-of-function ligand-independent variants cause Warburg–Cinotti syndrome [#11, #12, #13, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that DDR2 kinase activity is functionally required answered whether the receptor is a driver of proliferation and ECM-invasive behavior rather than a passive collagen binder.\",\n      \"evidence\": \"DDR2 knockout mice with kinase-dead rescue, and overexpression of wild-type vs kinase-dead DDR2 in hepatic stellate cells with MMP-2 and invasion readouts\",\n      \"pmids\": [\"11375938\", \"11696582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the collagen recognition site\", \"Downstream effectors of kinase activity not yet mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defining the molecular collagen recognition determinants established how DDR2 senses matrix at the structural level and which collagen features are required for activation.\",\n      \"evidence\": \"Recombinant discoidin domain binding and loop-exchange mutagenesis, plus Toolkit peptide screening identifying the triple-helical GVMGFO motif and the collagen II D2 period\",\n      \"pmids\": [\"12611880\", \"18201965\", \"15544808\", \"16806867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of dimerization not resolved\", \"How distinct collagens (e.g. collagen X) produce differential activation not fully explained\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying kinase-independent actions of the DDR2 ectodomain answered whether the receptor influences matrix and cell behavior outside of canonical phospho-signaling.\",\n      \"evidence\": \"Membrane-anchored and secreted kinase-dead DDR2 ECD expressed in osteoblasts with TEM, hydroxyproline assays, and fibroblast migration/spreading assays\",\n      \"pmids\": [\"18996394\", \"19900459\", \"23131558\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of fibrillogenesis inhibition not defined\", \"Kinase-independent migration partners unidentified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Placing DDR2 in an ERK/p38-Runx2 axis and identifying its transcriptional induction by ATF4 established its mechanistic role in osteoblast differentiation and skeletal development.\",\n      \"evidence\": \"shRNA knockdown, constitutively active DDR2, ERK/p38 inhibitors, Runx2 phospho-mutant epistasis, and DDR2 promoter mapping with ATF4/C/EBPβ dissection\",\n      \"pmids\": [\"20734453\", \"20564243\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct DDR2-to-ERK coupling step not resolved\", \"In vivo contribution of each MAPK branch not separated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Discovery of recurrent activating kinase-domain mutations established DDR2 as a targetable oncogenic driver in squamous lung cancer.\",\n      \"evidence\": \"Tyrosine kinome sequencing, RNAi, transformation and xenograft assays, and dasatinib sensitivity testing\",\n      \"pmids\": [\"22328973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which mutations elevate activity not structurally defined\", \"Resistance mechanisms not yet known\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Loss-of-function genetics linked DDR2 to a Mendelian skeletal disorder, defining the consequences of receptor inactivation in humans.\",\n      \"evidence\": \"Homozygosity mapping and sequencing identifying SMED-SL kinase-domain mutations, followed by trafficking and ligand-binding characterization of mutant classes\",\n      \"pmids\": [\"19110212\", \"20223752\", \"24725993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific signaling deficits underlying skeletal phenotype not delineated\", \"Whether residual kinase-independent functions persist in ER-retained mutants unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identifying SHP-2 as a kinase-dependent phospho-substrate and mapping dasatinib resistance routes built the proximal signaling and pharmacology of DDR2.\",\n      \"evidence\": \"Temporal phosphoproteomics with mutant-panel validation, and exome sequencing of resistant cell lines identifying the T654I gatekeeper mutation and NF1-loss RAS-ERK bypass\",\n      \"pmids\": [\"23822953\", \"24296828\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full proximal interactome beyond SHP-2 incomplete\", \"Clinical generalizability of resistance mechanisms untested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Characterizing DDR2 protein partners established mechanisms regulating its stability, localization, and divergent roles in bone homeostasis.\",\n      \"evidence\": \"Co-IP and functional assays identifying SRC, Nrp1 (stabilizing DDR2 half-life and forming a Nrp1–PlexinA1 complex), in osteoblast and osteoclast models and DDR2-mutant lung cancer cells\",\n      \"pmids\": [\"26390252\", \"25924845\", \"25805889\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structural basis of the Nrp1-PlexinA1 complex unresolved\", \"How DDR2 toggles between pro-osteoblast and anti-osteoclast outputs unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defining downstream transcriptional loops connected DDR2 to invasion, EMT, and inflammatory matrix programs across disease contexts.\",\n      \"evidence\": \"Pathway dissection in HCC (ERK2-SNAIL1 stabilization), RA synoviocytes (AP-1-CYR61-ETS1-MMP1), and lung fibroblasts (DDR2-JAK2-ERK-PEA3 inducing DDR1) using inhibitors, ChIP, and promoter reporters\",\n      \"pmids\": [\"26362312\", \"27653023\", \"21335558\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cross-talk between parallel transcriptional loops not integrated\", \"Direct vs indirect target relationships partly inferred\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Cbl-b-mediated degradation established a ubiquitin-dependent route controlling DDR2 abundance and a cancer-associated mutation altering it.\",\n      \"evidence\": \"Co-IP with Cbl-b, proteasome inhibitor rescue of the E655K mutant, and collagen-induced p38-dependent growth suppression assays\",\n      \"pmids\": [\"26826182\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitination sites not mapped\", \"Physiological signals triggering Cbl-b recruitment unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying ligand-independent activating variants and an allosteric ectodomain inhibitor expanded the disease and pharmacological landscape of DDR2.\",\n      \"evidence\": \"Family sequencing and patient-fibroblast phosphorylation for Warburg-Cinotti variants, and screening/characterization of the WRG-28 allosteric ECD inhibitor with invasion assays\",\n      \"pmids\": [\"30449416\", \"30061414\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of autoinhibition release not defined\", \"WRG-28 in vivo therapeutic window untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defining stromal DDR2 mechanotransduction established how fibroblast DDR2 shapes the tumor microenvironment to drive metastasis, and that HSP47 maintains DDR2 stability.\",\n      \"evidence\": \"DDR2 depletion in CAFs with collagen imaging and Rap1-Talin1-Kindlin2 integrin-activation studies in vivo, and Co-IP/TIRF imaging of HSP47-DDR2 ectodomain interaction\",\n      \"pmids\": [\"31144616\", \"31570520\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DDR2 signaling activates Rap1 mechanistically unclear\", \"HSP47-DDR2 stoichiometry and chaperone cycle undefined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating kinase-independent contributions to metastasis and drug resistance reframed DDR2 as functioning beyond its catalytic activity in tumor progression.\",\n      \"evidence\": \"Kinase-dead DDR2 rescue in invasion and metastasis models with paracrine co-culture, and DDR1/DDR2 clustering driving a NIK/IKKα/NF-κB2 ECM-resistance pathway in melanoma\",\n      \"pmids\": [\"34477203\", \"34957688\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase-independent effector mechanism unidentified\", \"Relative contribution of kinase-dependent vs independent functions in patients unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Linking DDR2 to fibroblast metabolic reprogramming established a role in regulating collagen production and matrix-supportive metabolism via SNAI1.\",\n      \"evidence\": \"DDR2 depletion in CAFs with arginase/metabolomics and ChIP for SNAI1 at the arginase-1 promoter, and glycolytic enzyme/LOXL2 rescue experiments in vivo\",\n      \"pmids\": [\"37996700\", \"37527178\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How DDR2 signaling reaches SNAI1/AKT not mechanistically traced\", \"Generalizability beyond ovarian CAFs untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying β-catenin, STAT3, SRF and Hippo-effector linkages extended the DDR2 transcriptional network into EMT, immunosuppression, survival, and cell-cycle control.\",\n      \"evidence\": \"Co-IP (DDR2-β-catenin), fractionation, luciferase reporters (PD-L1/CCL20, SRF targets), and YAP1/WWTR1 nuclear translocation studies across HCC, cardiac fibroblast, and lens epithelial models\",\n      \"pmids\": [\"36471363\", \"38969205\", \"32412792\", \"39900894\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether these interactions are direct or signaling-dependent partly unresolved\", \"Ferroptosis link rests on low-confidence single-lab data\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How DDR2 mechanically couples collagen binding to slow, sustained autophosphorylation and selects between its many divergent downstream programs (Runx2 vs SNAIL1 vs anti-osteoclast complex vs kinase-independent outputs) in a context-specific manner remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No full-length structural model of activated receptor\", \"Determinants of cell-type-specific effector selection unknown\", \"Integration of kinase-dependent and kinase-independent functions undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 5, 8]},\n      {\"term_id\": \"GO:0004672\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [25, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [9, 13, 17, 26]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [13, 38]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 6, 20]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [21, 22, 24, 25]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 6, 7]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [11, 12, 14]}\n    ],\n    \"complexes\": [\n      \"DDR2-Nrp1-PlexinA1 complex\",\n      \"DDR1-DDR2 heteromeric receptor\"\n    ],\n    \"partners\": [\n      \"SHP-2\",\n      \"SRC\",\n      \"NRP1\",\n      \"HSP47\",\n      \"CBL-B\",\n      \"CTNNB1\",\n      \"DDR1\",\n      \"PLXNA1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}