{"gene":"DDR2","run_date":"2026-04-28T17:46:02","timeline":{"discoveries":[{"year":1997,"finding":"DDR1 and DDR2 are receptor tyrosine kinases activated by native triple-helical collagen (not soluble growth factors); collagen activation of DDR2 upregulates matrix metalloproteinase-1 (MMP-1) expression, establishing DDR2 as a collagen receptor that controls cellular responses to the ECM.","method":"Receptor-ligand binding assays, kinase activation assays, MMP-1 reporter assays in cell lines","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — original biochemical reconstitution of collagen-DDR2 activation, replicated across multiple labs subsequently","pmids":["9659899"],"is_preprint":false},{"year":2002,"finding":"DDR2 requires Src kinase activity to be maximally tyrosine-phosphorylated following collagen activation; activated DDR2 associates with the adaptor protein Shc (via a novel Shc domain); Src is required for DDR2-mediated transactivation of the MMP-2 promoter, placing Src and Shc as key signaling intermediates downstream of DDR2.","method":"Co-immunoprecipitation, kinase inhibition assays, MMP-2 promoter reporter assays, dominant-negative Src constructs","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus functional reporter assays with multiple genetic/pharmacological tools","pmids":["11884411"],"is_preprint":false},{"year":2001,"finding":"DDR2 is induced in hepatic stellate cells upon activation by type I collagen, becomes tyrosine-phosphorylated, and promotes proliferation and Matrigel invasion through increased expression of active MMP-2; a constitutively active chimeric DDR2 recapitulates these effects while kinase-dead DDR2 does not, establishing DDR2 kinase activity as necessary for MMP-2 upregulation and stellate cell activation.","method":"Stable overexpression of WT, constitutively active (Fc-DDR2), truncated, and kinase-dead DDR2 constructs; proliferation and invasion assays; MMP-2 activity assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 — kinase-dead mutant rescue experiment plus multiple functional readouts","pmids":["11696582"],"is_preprint":false},{"year":2001,"finding":"DDR2-deficient mice exhibit dwarfism due to reduced chondrocyte proliferation (not aberrant differentiation); DDR2-/- fibroblasts proliferate more slowly than WT, and this defect is rescued by wild-type but not kinase-dead DDR2, demonstrating that DDR2 kinase activity is required for its proliferative function.","method":"DDR2 knockout mouse generation, histological analysis, in vitro fibroblast proliferation rescue with WT vs. kinase-dead DDR2","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1-2 — genetic KO with kinase-dead rescue, replicated across multiple cell types and in vivo","pmids":["11375938"],"is_preprint":false},{"year":2003,"finding":"The discoidin domain of DDR2 (but not DDR1) is sufficient for collagen I binding and for transmembrane receptor signaling; three spatially adjacent surface loops within the DDR2 discoidin domain constitute the collagen recognition site, as shown by loop-swap mutagenesis.","method":"Recombinant extracellular domain production, solid-phase binding assays, loop-swap mutagenesis, receptor activation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with functional validation of collagen binding and receptor activation","pmids":["12611880"],"is_preprint":false},{"year":2004,"finding":"The D2 period of triple-helical collagen II harbors a specific DDR2 binding and autophosphorylation-inducing site; collagen II is a better DDR2 ligand than DDR1; binding is dependent on triple-helical conformation and mediated by the DDR2 discoidin domain.","method":"Recombinant collagen II deletion variants, DDR2 binding assays, receptor autophosphorylation assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — systematic deletion mapping of collagen binding site with functional validation","pmids":["15544808"],"is_preprint":false},{"year":2006,"finding":"Collagen X is a ligand for DDR2 (but not DDR1); collagen X binds DDR2 extracellular domain with high affinity and stimulates DDR2 autophosphorylation; unlike fibrillar collagens, the DDR2 discoidin domain alone is not sufficient for collagen X binding, indicating additional DDR2 binding sites; the triple-helical region (but not the NC1 domain) of collagen X activates DDR2.","method":"Solid-phase binding assays, DDR2 autophosphorylation assays, domain truncation constructs","journal":"Matrix biology","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with domain mapping and functional validation","pmids":["16806867"],"is_preprint":false},{"year":2008,"finding":"The minimal collagen sequence GVMGFO (where O = hydroxyproline) is required for DDR2 binding; triple-helical peptides containing this motif both inhibit DDR2 binding to collagen II and activate DDR2 transmembrane signaling, indicating that single triple-helices (not fibrillar collagen) are sufficient for DDR2 activation.","method":"Collagen II Toolkit peptide screening, truncated/alanine-substituted peptide binding assays, DDR2 activation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic peptide mapping with functional activation assays, replicated approach","pmids":["18201965"],"is_preprint":false},{"year":2008,"finding":"Three missense mutations in the DDR2 kinase domain (T713I, I726R, R752C) causing SMED-SL result in retention of the mutant DDR2 protein in the endoplasmic reticulum and defective collagen-induced receptor activation, identifying ER trafficking failure as a loss-of-function mechanism.","method":"Sanger sequencing, expression of mutant DDR2 in human cell lines, subcellular localization, collagen activation assays","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants characterized with localization and functional assays","pmids":["19110212"],"is_preprint":false},{"year":2008,"finding":"Cell-surface expression of kinase-dead DDR2 (via its extracellular domain) inhibits collagen fibrillogenesis by cells, reducing the rate and abundance of collagen deposition and altering fiber morphology, revealing a kinase-independent structural/regulatory function of the DDR2 extracellular domain in ECM remodeling.","method":"Stable mouse osteoblast cell lines expressing kinase-dead DDR2, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods in reconstituted cell system","pmids":["18996394"],"is_preprint":false},{"year":2009,"finding":"Soluble extracellular domains of DDR1 and DDR2 (naturally shed forms) inhibit collagen fibrillogenesis, reducing collagen deposition and altering fiber morphology and matrix mineralization in osteoblast cell lines.","method":"Stable secretion of DDR1/DDR2 ECD, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods, extends prior kinase-dead finding to soluble forms","pmids":["19900459"],"is_preprint":false},{"year":2009,"finding":"Crystal structure of the DDR2 discoidin domain bound to a triple-helical collagen peptide (GVMGFO motif) reveals that two collagen chains are recognized by an amphiphilic pocket delimited by a critical tryptophan residue and a buried salt bridge; collagen binding induces structural changes in DDR2 surface loops potentially linked to receptor activation.","method":"X-ray crystallography of DDR2 discoidin domain–collagen peptide complex","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation of binding mechanism","pmids":["20004161"],"is_preprint":false},{"year":2009,"finding":"DDR2 activation by fibrillar collagen I downregulates focal adhesion kinase (FAK) levels in vascular smooth muscle cells; siRNA depletion of DDR2 blocks this FAK downregulation, establishing DDR2 as a regulator of FAK protein levels in collagen-adhered cells.","method":"siRNA knockdown of DDR2, Western blotting for FAK, collagen fibril vs. monolayer comparison","journal":"Biomaterials","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD with specific phenotypic readout, single lab","pmids":["19762078"],"is_preprint":false},{"year":2010,"finding":"SMED-SL missense mutations: three kinase-domain mutants (T713I, I726R, R752C) are retained in the ER and fail collagen-induced activation; a novel extracellular domain mutant (E113K) traffics normally but fails to bind collagen, demonstrating that SMED-SL arises from at least two distinct loss-of-function mechanisms (ER retention vs. ligand-binding defect).","method":"Expression of point mutants in human cell lines, confocal microscopy for localization, collagen binding assays, Western blotting","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1-2 — multiple mutants with orthogonal localization and functional assays, consistent with structural data","pmids":["20223752"],"is_preprint":false},{"year":2010,"finding":"ATF4 transcriptionally upregulates DDR2 expression through a C/EBP binding site at -1150 bp in the DDR2 promoter via cooperation with C/EBPβ; DDR2 in turn activates Runx2 through p38 MAPK stimulation to promote osteoblast differentiation.","method":"DDR2 promoter deletion/mutation analysis, ATF4/C/EBPβ knockdown and overexpression, p38 MAPK inhibition, osteogenic differentiation assays","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 — promoter binding assays plus epistasis with multiple genetic tools","pmids":["20564243"],"is_preprint":false},{"year":2011,"finding":"DDR2 activation in preosteoblastic cells promotes osteoblast differentiation by stimulating ERK-mediated phosphorylation of Runx2 (the master osteogenic transcription factor), enhancing its transcriptional activity; constitutively active DDR2 increases bone marker expression while kinase-dead DDR2 blocks DDR2-induced osteogenesis.","method":"DDR2 shRNA knockdown, constitutively active DDR2 overexpression, ERK inhibition, Runx2 phosphorylation assays, gain-of-function Runx2 rescue experiments","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic tools with epistasis rescue, identifies ERK-Runx2 as the pathway","pmids":["20734453"],"is_preprint":false},{"year":2011,"finding":"DDR2 mutations (e.g., L63V, G505S) found in ~3.8% of squamous cell lung cancers are gain-of-function; expression of mutated DDR2 causes cellular transformation; DDR2-mutant lung cancer cells are selectively killed by RNAi knockdown of DDR2 or by dasatinib treatment, demonstrating oncogenic DDR2 kinase dependency.","method":"Sanger sequencing, RNAi knockdown, dasatinib treatment, xenograft tumor models, cellular transformation assays","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (RNAi, small molecule, xenograft) across multiple cell lines","pmids":["22328973"],"is_preprint":false},{"year":2011,"finding":"Collagen I induces DDR1 expression in human lung fibroblasts through a pathway requiring DDR2 activation followed by JAK2 and ERK1/2 signaling; ERK1/2 activation recruits the transcription factor PEBA3 to the DDR1 promoter; DDR2 also mediates collagen I-induced MMP-10 expression through this pathway.","method":"DDR2 knockdown, JAK2/ERK inhibitors, DDR1 promoter chromatin immunoprecipitation, gene expression assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — genetic KD plus pharmacological inhibition plus promoter ChIP, placing DDR2 upstream of JAK2-ERK-DDR1 axis","pmids":["21335558"],"is_preprint":false},{"year":2012,"finding":"DDR2 plays a role in fibroblast spreading and migration independent of the adhesion ligand type (fibronectin or collagen) and independent of collagen-induced DDR2 tyrosine kinase activation; DDR2 knockdown also inhibits migration in 3D collagen matrices without affecting matrix contraction.","method":"siRNA knockdown of DDR2, 2D migration assays on fibronectin vs. collagen, 3D collagen matrix migration assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD across multiple matrix conditions, single lab","pmids":["23131558"],"is_preprint":false},{"year":2013,"finding":"DDR2 stabilizes SNAIL1 by stimulating ERK2 activity in a Src-dependent manner; activated ERK2 directly phosphorylates SNAIL1, causing nuclear accumulation, reduced ubiquitylation, and increased protein half-life; this DDR2-ERK2-SNAIL1 axis promotes breast cancer cell invasion, migration, and metastasis in vivo.","method":"Co-immunoprecipitation, in vitro ERK2 kinase assays on SNAIL1, cycloheximide chase, ubiquitylation assays, Src inhibition, mouse metastasis models","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay showing direct ERK2 phosphorylation of SNAIL1 plus multiple orthogonal methods and in vivo validation","pmids":["23644467"],"is_preprint":false},{"year":2013,"finding":"Quantitative phosphoproteomics of DDR2 signaling identified SHP-2 tyrosine phosphorylation as dependent on DDR2 kinase activity; DDR2 lung cancer mutants L63V and G505S phosphorylate SHP-2, while the I638F kinase-domain mutant shows diminished DDR2 and SHP-2 phosphorylation inversely correlated with clonogenic potential; NCK1, LYN, SHIP-2, and PIK3C2A are also candidate DDR2 signaling nodes.","method":"Quantitative mass spectrometry phosphoproteomics (7 time points), biochemical validation of SHP-2 phosphorylation with kinase-dead DDR2, targeted proteomic profiling of DDR2 mutants","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 — quantitative phosphoproteomics with biochemical validation across multiple DDR2 mutants","pmids":["23822953"],"is_preprint":false},{"year":2013,"finding":"DDR2 mediates collagen-induced upregulation of lysyl oxidase in osteoblasts; collagen advanced glycation (CML-collagen) disrupts DDR2 binding and activation, thereby blocking lysyl oxidase induction, providing a mechanism for reduced enzymatic collagen cross-links in diabetic bone.","method":"DDR2 shRNA knockdown in primary osteoblasts, collagen binding assays with glycated vs. non-glycated collagen, lysyl oxidase protein quantification","journal":"Bone","confidence":"Medium","confidence_rationale":"Tier 2 — shRNA KD with defined molecular readout, single lab","pmids":["24120383"],"is_preprint":false},{"year":2013,"finding":"Acquired resistance to dasatinib in DDR2-dependent lung cancer cells arises via two mechanisms: (1) a T654I gatekeeper mutation in DDR2, and (2) NF1 loss activating a RAS-ERK bypass pathway, demonstrating that ERK dependency can be achieved downstream of DDR2 through RAS activation.","method":"Targeted exome sequencing of resistant cell lines, functional validation of resistance mechanisms, pathway inhibition assays","journal":"Molecular cancer therapeutics","confidence":"High","confidence_rationale":"Tier 2 — sequencing plus functional validation of two distinct resistance mechanisms","pmids":["24296828"],"is_preprint":false},{"year":2014,"finding":"The cytoplasmic juxtamembrane 2 (JM2) region of DDR2 is required for receptor dimerization, which is critical for collagen-induced receptor activation; JM2 is also required for efficient collagen binding to the discoidin domain; expression of JM2-containing peptide inhibits DDR2-mediated MMP-2/9 expression, colony formation, and invasion.","method":"JM2 deletion/overexpression constructs, co-immunoprecipitation for dimerization, collagen binding assays, invasion/proliferation assays","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 — domain deletion with multiple functional readouts, single lab","pmids":["24740739"],"is_preprint":false},{"year":2014,"finding":"DDR2 and SRC are direct binding partners; SRC activity is functionally tied to DDR2 activation; 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, selective DDR2 inhibitor characterization, dual DDR2/SRC inhibitor assays in cancer cell lines","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP plus functional inhibitor data, single lab","pmids":["26390252"],"is_preprint":false},{"year":2014,"finding":"A novel DDR2 missense mutation (c.2468_2469delCT, p.S823Cfs*2) causes ER retention of the mutant protein, defective N-glycosylation processing, and loss of collagen-induced activation, confirming that DDR2 kinase-domain mutations causing SMED-SL converge on ER trafficking defects.","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 — orthogonal localization and functional methods, single lab","pmids":["24725993"],"is_preprint":false},{"year":2015,"finding":"DDR2 facilitates HCC invasion, migration, and EMT via activation of ERK2 and stabilization of SNAIL1 protein; DDR2 upregulates MT1-MMP and MMP2 expression through ERK2/SNAIL1 signaling; collagen I can induce the DDR2/ERK2/SNAIL1 signaling cascade in HCC cells.","method":"DDR2 overexpression/knockdown, cycloheximide chase for SNAIL1 stability, ERK2 inhibition, Western blotting, invasion/migration assays","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays with pathway inhibition, single lab","pmids":["26362312"],"is_preprint":false},{"year":2015,"finding":"DDR2 suppresses osteoclastogenesis by forming a DDR2-Nrp1-PlexinA1 complex; DDR2 facilitates binding of Nrp1 to PlexinA1, blocking PlexinA1-mediated osteoclast stimulation; DDR2 also prevents PlexinA1 from interacting with TREM2 and DAP12; adenoviral DDR2 delivery to bone alleviates osteopenic phenotypes in ovariectomized mice.","method":"Co-immunoprecipitation for complex formation, DDR2 overexpression/RNAi, Nrp1 knockdown rescue assays, in vivo adenoviral delivery, osteoclast differentiation assays","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP establishing complex plus genetic rescue experiments and in vivo validation","pmids":["25805889"],"is_preprint":false},{"year":2015,"finding":"DDR2 can synergize TGF-β and fibrillar collagen signals to stimulate lung fibroblast myofibroblastic differentiation and VEGF expression; DDR2 knockdown by siRNA or kinase inhibition reduces established lung fibrosis in vivo.","method":"In vitro fibroblast stimulation assays, DDR2 siRNA in vivo delivery, bleomycin lung fibrosis mouse model","journal":"Molecular therapy","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo validation, single lab","pmids":["27350126"],"is_preprint":false},{"year":2015,"finding":"DDR2 inhibition in murine melanoma cells suppresses collagen I-induced migration and invasion by reducing MMP2/9 expression through the ERK1/2 and NF-κB signaling pathways; DDR2 is phosphorylated by collagen I in these cells.","method":"DDR2 siRNA knockdown, migration/invasion assays, ERK1/2 and NF-κB pathway inhibition, MMP2/9 expression analysis","journal":"Acta biochimica et biophysica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD with pathway inhibition, single lab","pmids":["25733533"],"is_preprint":false},{"year":2015,"finding":"Neuropilin-1 (Nrp1) co-localizes with DDR2 at the cell membrane, enhances DDR2 phosphorylation and ERK1/2-Runx2 signaling, and prolongs DDR2 protein half-life (post-translational stabilization) without altering DDR2 mRNA levels, thereby promoting osteoblast differentiation.","method":"Nrp1 overexpression/silencing, DDR2 half-life assay (cycloheximide chase), immunofluorescence co-localization, ERK1/2 and Runx2 phosphorylation analysis","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — half-life assay plus co-localization and functional rescue, single lab","pmids":["25924845"],"is_preprint":false},{"year":2016,"finding":"In C. elegans, DDR-2 (the DDR2 ortholog) functions upstream of the Met-like RTK SVH-2 and the scaffold protein SHC-1 in regulating axon regeneration; SHC-1 interacts with both DDR-2 and SVH-2; overexpression of svh-2 and shc-1 suppresses the axon regeneration delay in ddr-2 mutants, placing DDR-2 upstream of the SVH-2-JNK MAPK pathway.","method":"C. elegans genetics (ddr-2 mutants, epistasis), axon regeneration assays, co-immunoprecipitation of DDR-2 and SHC-1/SVH-2","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with Co-IP in orthologous organism, functionally consistent with mammalian DDR2","pmids":["27984580"],"is_preprint":false},{"year":2016,"finding":"DDR2 in cancer-associated fibroblasts (CAFs) is critical for extracellular matrix production and collagen fiber organization; in tumor cells, DDR2 in basal epithelial cells regulates collective invasion of tumor organoids; both tumor-cell-intrinsic and stromal DDR2 functions are required for breast cancer metastasis in vivo.","method":"Genetic cell-type-specific DDR2 deletion, tumor organoid invasion assays, second-harmonic generation microscopy for collagen fiber analysis, mouse metastasis models","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific genetic deletion with multiple orthogonal readouts and in vivo metastasis validation","pmids":["27264173"],"is_preprint":false},{"year":2016,"finding":"In rheumatoid arthritis fibroblast-like synoviocytes, collagen II-activated phospho-DDR2 induces CYR61 expression via AP-1 transcription factor; elevated CYR61 then accelerates MMP1 production via ETS1; CYR61 shRNA in vivo reduces arthritis severity and bone erosion.","method":"DDR2 activation/inhibition, AP-1 and ETS1 reporter assays, CYR61 shRNA adenovirus in CIA rat model, μCT bone analysis","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 — pathway dissection with in vivo validation in arthritis model","pmids":["27653023"],"is_preprint":false},{"year":2017,"finding":"DDR2 maintains a fibroblastic phenotype with collagen deposition in breast cancer-associated mesenchymal stem cells (MSCs); loss of DDR2 in MSCs impairs their ability to promote DDR2 phosphorylation in breast cancer cells, BC cell alignment, migration, and metastasis; ddr2-deficient (slie) mice show inefficient spontaneous BC metastasis.","method":"DDR2 knockdown in MSCs, co-culture assays with BC cells, slie mouse spontaneous metastasis model, phospho-DDR2 Western blotting","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function in multiple systems plus in vivo spontaneous metastasis model","pmids":["28147276"],"is_preprint":false},{"year":2017,"finding":"DDR2 facilitates papillary thyroid carcinoma EMT by activating ERK2 and stabilizing Snail1 protein; ERK2 or Snail1 inhibition abrogates DDR2-induced EMT; DDR2 overexpression decreases E-cadherin and increases vimentin expression.","method":"Lentiviral DDR2 overexpression, ERK2/Snail1 inhibition, Western blotting, migration/invasion assays","journal":"Oncology letters","confidence":"Medium","confidence_rationale":"Tier 2 — pathway inhibition epistasis, single lab","pmids":["29250189"],"is_preprint":false},{"year":2018,"finding":"DDR1 and DDR2 physically interact (co-immunoprecipitation); co-expression of DDR1 and DDR2 produces higher ERK activation than either alone after collagen I stimulation, but inhibits cell proliferation; DDR1 (not DDR2) mediates cell adhesion to collagen I matrix.","method":"Co-immunoprecipitation, HEK293T co-overexpression, ERK/JAK2 activation assays, proliferation and adhesion assays with dominant-negative constructs","journal":"Cell adhesion & migration","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP plus functional assays, single lab","pmids":["29616590"],"is_preprint":false},{"year":2018,"finding":"DDR2 gain-of-function variants (L610P or Y740C) causing Warburg-Cinotti syndrome lead to increased DDR2 phosphorylation in patient fibroblasts, indicating reduced receptor autoinhibition and ligand-independent kinase activation; dasatinib prevents DDR2 autophosphorylation in these cells.","method":"Phosphorylation analysis in patient-derived fibroblasts, dasatinib treatment, analysis of signaling pathway activation","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — patient fibroblasts with functional pharmacological validation, de novo variant confirmed","pmids":["30449416"],"is_preprint":false},{"year":2018,"finding":"Coupling of the GVMGFO-containing triple-helical peptide to crosslinked collagen films restores DDR2 binding and activates DDR2 (phosphorylation of Y740) in COS-7 and HEK293 cells, identifying Y740 as a key DDR2 autophosphorylation site relevant to receptor activation.","method":"Photoreactive peptide coupling, DDR2 binding assays, Western blotting for pY740, cell-based DDR2 activation assays","journal":"Biomaterials","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical reconstitution on engineered surface with cell-based activation readout","pmids":["30099278"],"is_preprint":false},{"year":2018,"finding":"WRG-28, a small molecule targeting the DDR2 extracellular domain, allosterically inhibits DDR2-collagen receptor-ligand interactions and blocks tumor invasion, migration, and metastatic lung colonization, demonstrating that allosteric extracellular inhibition of DDR2 is functionally effective.","method":"Small molecule screening, DDR2 binding assays, tumor invasion/migration assays, in vivo lung colonization assays","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — biochemical characterization of inhibitor mechanism plus multiple in vitro and in vivo functional validations","pmids":["30061414"],"is_preprint":false},{"year":2019,"finding":"DDR2 in CAFs controls breast tumor stiffness by reorganizing collagen fibers at the tumor-stromal boundary through regulation of integrin activation; DDR2 influences mechanotransduction by controlling Rap1-mediated Talin1 and Kindlin2 recruitment to activate collagen-binding integrins.","method":"DDR2 depletion in mouse/human CAFs, second-harmonic generation microscopy for collagen fiber analysis, atomic force microscopy for stiffness, Rap1/Talin1/Kindlin2 activation assays, in vivo tumor models","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods linking DDR2 to specific mechanotransduction pathway in vivo","pmids":["31144616"],"is_preprint":false},{"year":2019,"finding":"DDR2 depletion in tumors increases CD8+ T cell infiltration and sensitizes tumors to anti-PD-1 immunotherapy across five tumor histologies; dasatinib (DDR2 inhibitor) combined with anti-PD-1 reduces tumor load, identifying DDR2 as a regulator of the immunosuppressive tumor microenvironment.","method":"In vivo shRNA screen, isogenic mouse tumor models, CyTOF immune cell profiling, RNA-seq, dasatinib + anti-PD-1 combination treatment","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 — in vivo functional screen validated across multiple tumor types with immune profiling","pmids":["30801016"],"is_preprint":false},{"year":2020,"finding":"DDR2 in cardiac fibroblasts acts via ERK1/2 MAPK-activated SRF transcription factor to enhance expression of anti-apoptotic cIAP2 (conferring resistance to oxidative injury) and to upregulate Skp2, which degrades the CDK inhibitor p27 to promote G1-S cell cycle transition; collagen type I binding to DDR2 is required for these effects.","method":"DDR2 knockdown/overexpression, SRF promoter binding assays, ERK1/2 inhibition, WRG-28 DDR2 inhibitor, flow cytometry, Rb phosphorylation assays","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple genetic/pharmacological tools with promoter binding assays, single lab","pmids":["32412792"],"is_preprint":false},{"year":2021,"finding":"DDR-mediated matrix resistance (MMDR) to BRAF inhibition in melanoma is mediated by drug-induced linear clustering of phosphorylated DDR1 and DDR2; DDR-dependent MMDR activates a pro-survival NIK/IKKα/NF-κB2 pathway; depletion or pharmacological targeting of DDR overcomes ECM-mediated resistance.","method":"DDR1/DDR2 depletion, phospho-DDR imaging, NIK/IKKα/NF-κB2 pathway analysis, xenograft models with imatinib + BRAF inhibitor combination","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 — mechanistic pathway identification with in vitro and in vivo validation","pmids":["34957688"],"is_preprint":false},{"year":2021,"finding":"Tyrosine kinase-independent functions of DDR2 in tumor cells support Matrigel invasion and in vivo metastasis; paracrine DDR2 signaling between tumor cells and CAFs also supports invasion and lung colonization; these findings suggest kinase-independent DDR2 activities contribute to metastasis.","method":"Kinase-dead DDR2 rescue in tumor cells, conditioned media experiments, in vivo lung colonization assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — kinase-dead rescue with in vivo validation, single lab","pmids":["34477203"],"is_preprint":false},{"year":2021,"finding":"EMT regulators TWIST and SNAIL induce DDR2 expression; DDR2 upregulation in recurrent breast tumor cells activates YAP/TAZ signaling; DDR2 knockdown reduces both clonogenic growth and ferroptosis sensitivity; erastin-induced DDR2 upregulation and phosphorylation occur independently of collagen I.","method":"DDR2 knockdown, TWIST/SNAIL overexpression, YAP/TAZ inhibition, ferroptosis (erastin) assays, clonogenic growth assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays linking DDR2 to YAP/TAZ and ferroptosis, single lab","pmids":["33603168"],"is_preprint":false},{"year":2022,"finding":"DDR2 in ovarian cancer CAFs promotes collagen production through arginase activity; DDR2-depleted CAFs show decreased ornithine and polyamine levels leading to reduced collagen production; SNAI1 protein is detected at the arginase-1 promoter and DDR2-depleted CAFs have decreased SNAI1 at this promoter, revealing DDR2 regulates arginase-1 transcription via SNAI1.","method":"DDR2 depletion in human/mouse CAFs, arginase activity assays, metabolomics (ornithine/polyamine), ChIP for SNAI1 at arginase-1 promoter, conditioned media tumor invasion assays","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — ChIP plus metabolomics plus functional rescue assays identifying a new DDR2 metabolic pathway","pmids":["37996700"],"is_preprint":false},{"year":2022,"finding":"DDR2 in ovarian cancer CAFs promotes tumor cell invasion through regulation of periostin (POSTN) expression via integrin β1 (ITGB1); DDR2-expressing fibroblasts enhance mesothelial cell clearance and tumor cell invasion three-fold; DDR2 regulation of POSTN is mediated through ITGB1.","method":"DDR2 and POSTN knockdown in CAFs, co-culture mesothelial clearance assays, in vivo co-injection xenograft models, ITGB1 pathway analysis","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vitro and in vivo assays, single lab","pmids":["35884543"],"is_preprint":false},{"year":2022,"finding":"CEBPA-DT lncRNA promotes DDR2 expression by binding hnRNPC, facilitating cytoplasmic translocation of hnRNPC which enhances hnRNPC-DDR2 mRNA interaction; DDR2 then promotes β-catenin nuclear translocation through a DDR2-β-catenin protein interaction, activating Snail1 transcription to drive EMT and HCC metastasis.","method":"RNA pull-down, RIP, co-immunoprecipitation for DDR2-β-catenin interaction, immunofluorescence for β-catenin localization, DDR2 inhibitor treatment, subcellular fractionation","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP for DDR2-β-catenin interaction plus functional inhibitor validation, single lab","pmids":["36471363"],"is_preprint":false},{"year":2022,"finding":"Nilotinib inhibits DDR2 in human valvular interstitial cells (VICs); DDR2 inhibition or selective DDR2 targeting in VICs induces osteogenic activation and calcification; increasing DDR2 ligand (collagen) blunts this osteogenic response, establishing DDR2 as a suppressor of VIC calcification.","method":"DDR2 selective inhibition in human VICs, osteogenic/calcification assays, transcriptomic target identification, collagen rescue experiments","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological DDR2 inhibition with ligand rescue, single lab","pmids":["35751904"],"is_preprint":false},{"year":2023,"finding":"DDR2 in ovarian cancer omental fibroblasts regulates glycolysis through an AKT/SNAI1 axis, suppressing fructose-1,6-bisphosphatase and increasing hexokinase activity; DDR2 inhibition decreases protein synthesis and secretion, including LOXL2; adding back LOXL2 to DDR2-deficient fibroblasts rescues tumor cell invasion.","method":"DDR2 depletion, glycolytic enzyme activity assays, secretome proteomics, LOXL2 rescue experiments, in vivo peritoneal metastasis model","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — enzyme activity assays plus secretome proteomics with functional rescue, single lab","pmids":["37527178"],"is_preprint":false},{"year":2023,"finding":"DDR2 in gastric cancer promotes stemness by mediating SOX2 expression; DDR2 governs EMT programming through recruiting an NFATc1-SOX2 complex to the Snai1 promoter; DDR2-mTOR-SOX2 axis controls cancer stem cell autophagy and DNA damage responses; miR-199a-3p directly targets DDR2.","method":"Luciferase reporter assays for miR-199a-3p/DDR2 targeting, DDR2 knockdown/overexpression, NFATc1-SOX2 complex ChIP at Snai1 promoter, orthotopic xenograft peritoneal dissemination model","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP plus functional assays plus in vivo model, single lab","pmids":["36813149"],"is_preprint":false},{"year":2024,"finding":"DDR2 induces STAT3 phosphorylation and nuclear translocation; activated STAT3 enhances DDR2 expression, forming a positive feedback loop in oxaliplatin-resistant HCC; STAT3 directly enhances transcription of PD-L1 and CCL20 (recruiting PMN-MDSCs) via dual luciferase reporter assays, establishing a DDR2/STAT3/PD-L1/CCL20 immunosuppressive axis.","method":"DDR2/STAT3 knockdown, phospho-STAT3 analysis, luciferase reporter assays for PD-L1 and CCL20 promoters, MDSC transwell migration assays, in vivo tumor models","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"Medium","confidence_rationale":"Tier 2 — luciferase reporters plus functional immune assays, single lab","pmids":["38969205"],"is_preprint":false},{"year":2004,"finding":"DDR1 and DDR2 overexpression in human smooth muscle cells reduces collagen expression and induces MMP-1 at mRNA and protein levels; DDR2 (but not DDR1) specifically enhances MMP-2 activation and increases collagen and elastin degradation, demonstrating paralog-specific ECM remodeling functions.","method":"Retroviral overexpression of DDR1 and DDR2 in human SMCs on polymerized collagen gels, MMP-1/MMP-2 RT-PCR and protein assays, collagen/elastin degradation assays","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 — side-by-side DDR1 vs DDR2 comparison with multiple functional readouts, single lab","pmids":["15111304"],"is_preprint":false}],"current_model":"DDR2 is a receptor tyrosine kinase activated by native triple-helical collagens (types I, II, III, X) via its discoidin domain (binding site: GVMGFO motif recognized by three surface loops), which triggers slow autophosphorylation (including Y740) requiring Src for maximal activation; downstream signaling proceeds through Src-Shc, ERK2 (which directly phosphorylates and stabilizes SNAIL1 to drive EMT and metastasis), p38 MAPK (activating Runx2 for osteoblast differentiation), SHP-2, JAK2, NF-κB, STAT3, YAP/TAZ, and mTOR pathways; DDR2 also forms complexes with Nrp1-PlexinA1 to suppress osteoclastogenesis, physically interacts with β-catenin to promote its nuclear translocation, and controls collagen fibrillogenesis through its extracellular domain independently of kinase activity; gain-of-function mutations cause squamous cell lung cancer and Warburg-Cinotti syndrome, while loss-of-function mutations (causing ER retention or collagen-binding defects) underlie SMED-SL and dwarfism."},"narrative":{"teleology":[{"year":1997,"claim":"The fundamental question of what activates DDR2 was answered: native triple-helical collagen, not soluble growth factors, triggers DDR2 tyrosine kinase activity and upregulates MMP-1, establishing DDR2 as a collagen receptor that connects ECM composition to cellular gene expression.","evidence":"Receptor-ligand binding and kinase activation assays in cell lines","pmids":["9659899"],"confidence":"High","gaps":["Downstream signaling intermediates uncharacterized","Collagen-type specificity undefined","Structural basis of collagen recognition unknown"]},{"year":2001,"claim":"The physiological requirement for DDR2 kinase activity was established: DDR2 knockout mice exhibit dwarfism from reduced chondrocyte proliferation, and kinase-dead DDR2 fails to rescue fibroblast proliferation defects, demonstrating that DDR2 catalytic activity is essential for skeletal growth.","evidence":"DDR2 knockout mouse phenotyping plus kinase-dead rescue in fibroblasts; corroborated by constitutively active DDR2 driving stellate cell proliferation and MMP-2 upregulation","pmids":["11375938","11696582"],"confidence":"High","gaps":["No identification of DDR2 substrates or immediate downstream effectors","Mechanism of DDR2-dependent chondrocyte proliferation not defined"]},{"year":2002,"claim":"The first signaling intermediates downstream of DDR2 were identified: Src kinase is required for maximal DDR2 phosphorylation and associates with DDR2, while the adaptor Shc bridges DDR2 to downstream pathways including MMP-2 transactivation.","evidence":"Co-immunoprecipitation, dominant-negative Src, and MMP-2 promoter reporter assays","pmids":["11884411"],"confidence":"High","gaps":["Whether Src directly phosphorylates DDR2 or acts via intermediates was unclear","Full spectrum of DDR2-interacting adaptors unknown"]},{"year":2003,"claim":"The collagen-binding determinant was mapped: three surface loops of the discoidin domain form the collagen recognition site, and the GVMGFO motif within triple-helical collagen was later identified as the minimal binding sequence, ultimately resolved at atomic resolution by crystallography.","evidence":"Loop-swap mutagenesis and solid-phase binding (2003); Toolkit peptide screening (2008); X-ray crystal structure of DDR2 DS domain–collagen peptide complex (2009)","pmids":["12611880","18201965","20004161"],"confidence":"High","gaps":["How ligand binding in the extracellular domain is transmitted across the membrane to the kinase domain remains structurally unresolved","Full-length DDR2 structure unavailable"]},{"year":2008,"claim":"A kinase-independent function of DDR2 was discovered: the extracellular domain alone—whether membrane-tethered kinase-dead or as a shed soluble form—inhibits collagen fibrillogenesis, revealing that DDR2 physically modulates ECM architecture independently of catalytic signaling.","evidence":"Kinase-dead DDR2 and soluble ECD expression in osteoblasts with TEM, fluorescence microscopy, and hydroxyproline assays","pmids":["18996394","19900459"],"confidence":"High","gaps":["Molecular mechanism of fibrillogenesis inhibition (steric blockade vs. active remodeling) not defined","In vivo significance of shed DDR2 ECD unknown"]},{"year":2009,"claim":"The genetic basis of SMED-SL was established: kinase-domain mutations (T713I, I726R, R752C) cause ER retention and loss of collagen-induced activation, while the E113K extracellular mutation permits normal trafficking but abolishes collagen binding, demonstrating two distinct loss-of-function mechanisms underlying the same skeletal dysplasia.","evidence":"Expression of mutant DDR2 in cell lines with confocal localization, deglycosylation, and collagen activation assays across multiple studies","pmids":["19110212","20223752","24725993"],"confidence":"High","gaps":["Whether ER-retained mutants can be pharmacologically rescued is untested","Genotype-phenotype severity correlations not established"]},{"year":2010,"claim":"DDR2 was positioned as a driver of osteoblast differentiation through two parallel MAPK cascades: ATF4/C/EBPβ transcriptionally upregulates DDR2, which then activates p38 MAPK–Runx2 and ERK–Runx2 to promote osteogenic gene expression.","evidence":"DDR2 promoter analysis, p38/ERK inhibition, Runx2 phosphorylation assays, constitutively active vs. kinase-dead DDR2 in preosteoblasts","pmids":["20564243","20734453"],"confidence":"High","gaps":["Direct DDR2 substrates linking to p38 vs. ERK activation unidentified","Relative contribution of p38 vs. ERK to in vivo bone formation unclear"]},{"year":2011,"claim":"DDR2 was identified as an oncogene in squamous cell lung cancer: somatic gain-of-function mutations (L63V, G505S) cause cellular transformation with DDR2 kinase dependency, as shown by selective killing with DDR2 RNAi and dasatinib.","evidence":"Sequencing of lung SCC tumors, RNAi, dasatinib treatment, xenograft tumor models","pmids":["22328973"],"confidence":"High","gaps":["Structural mechanism by which specific mutations activate DDR2 kinase undefined","Clinical response to DDR2-targeted therapy not validated in patients"]},{"year":2013,"claim":"A central EMT-driving pathway was delineated: DDR2 activates Src-dependent ERK2, which directly phosphorylates SNAIL1 to prevent its ubiquitylation and promote nuclear accumulation, driving breast cancer invasion and metastasis in vivo—a mechanism subsequently confirmed in HCC, thyroid, and other cancers.","evidence":"In vitro ERK2 kinase assays on SNAIL1, ubiquitylation/cycloheximide chase assays, Src inhibition, mouse metastasis models; extended to HCC and thyroid carcinoma","pmids":["23644467","26362312","29250189"],"confidence":"High","gaps":["Whether DDR2-ERK2-SNAIL1 operates in normal tissue homeostasis unclear","Phosphosite(s) on SNAIL1 mediating stabilization not fully mapped across cancer types"]},{"year":2013,"claim":"Quantitative phosphoproteomics expanded the DDR2 signaling network: SHP-2 was identified as a DDR2 kinase-activity-dependent substrate, with NCK1, LYN, SHIP-2, and PIK3C2A as additional signaling nodes, and dasatinib resistance was shown to arise via DDR2 gatekeeper mutations or NF1-loss-driven RAS-ERK bypass.","evidence":"Quantitative mass spectrometry phosphoproteomics across DDR2 mutants; targeted exome sequencing of resistant lines","pmids":["23822953","24296828"],"confidence":"High","gaps":["Direct vs. indirect phosphorylation of SHP-2 by DDR2 not resolved","In vivo relevance of NF1-loss bypass to clinical resistance unknown"]},{"year":2015,"claim":"DDR2 was found to suppress osteoclastogenesis through a non-canonical mechanism: it forms a complex with Nrp1 and PlexinA1, blocking PlexinA1–TREM2/DAP12 interaction and osteoclast stimulation, with in vivo rescue of ovariectomy-induced bone loss.","evidence":"Reciprocal Co-IP for DDR2-Nrp1-PlexinA1 complex, RNAi rescue, adenoviral DDR2 delivery in ovariectomized mice","pmids":["25805889"],"confidence":"High","gaps":["Whether DDR2 kinase activity is required for Nrp1-PlexinA1 complex formation unclear","Stoichiometry of the ternary complex undefined"]},{"year":2016,"claim":"Cell-type-specific genetic deletion revealed dual roles for DDR2 in cancer: in tumor epithelial cells DDR2 drives collective invasion, while in cancer-associated fibroblasts it controls ECM production and collagen fiber alignment, both being required for metastasis.","evidence":"Cell-type-specific DDR2 deletion, tumor organoid invasion assays, second-harmonic generation microscopy, mouse metastasis models","pmids":["27264173"],"confidence":"High","gaps":["Molecular mechanism of DDR2-dependent collective invasion (leader-cell specification?) unresolved","Relative contribution of tumor vs. stromal DDR2 to different metastatic steps not quantified"]},{"year":2018,"claim":"Gain-of-function DDR2 variants (L610P, Y740C) were shown to cause Warburg-Cinotti syndrome through ligand-independent kinase activation due to reduced autoinhibition, pharmacologically reversible by dasatinib.","evidence":"Phospho-DDR2 analysis in patient-derived fibroblasts with dasatinib treatment","pmids":["30449416"],"confidence":"High","gaps":["Structural basis of reduced autoinhibition not determined","Long-term clinical efficacy of dasatinib in Warburg-Cinotti syndrome unknown"]},{"year":2019,"claim":"DDR2 was established as a regulator of tumor mechanotransduction and immune evasion: in CAFs it controls integrin activation through Rap1–Talin1–Kindlin2 to set tumor stiffness, while DDR2 depletion in tumors increases CD8+ T cell infiltration and sensitizes to anti-PD-1 therapy.","evidence":"AFM stiffness measurements, Rap1/Talin1/Kindlin2 activation assays in CAFs; in vivo shRNA screen across five tumor types with CyTOF immune profiling and dasatinib + anti-PD-1 combination","pmids":["31144616","30801016"],"confidence":"High","gaps":["How DDR2 restricts T cell infiltration mechanistically (ECM barrier vs. direct immune signaling) not resolved","Rap1 activation mechanism by DDR2 not fully elucidated"]},{"year":2022,"claim":"DDR2's metabolic and transcriptional control in the stroma was deepened: in ovarian cancer CAFs, DDR2 regulates arginase-1 transcription via SNAI1, controlling polyamine-dependent collagen production, and modulates glycolysis through an AKT/SNAI1 axis to sustain protein secretion including LOXL2.","evidence":"ChIP for SNAI1 at arginase-1 promoter, metabolomics, glycolytic enzyme assays, secretome proteomics with LOXL2 rescue","pmids":["37996700","37527178"],"confidence":"Medium","gaps":["Whether DDR2-dependent metabolic reprogramming is collagen-ligand-dependent or constitutive is unclear","Generalizability of arginase/polyamine axis beyond ovarian CAFs not tested"]},{"year":2024,"claim":"A DDR2–STAT3 positive feedback loop was identified in chemoresistant HCC, where STAT3 drives transcription of PD-L1 and CCL20 to recruit immunosuppressive PMN-MDSCs, mechanistically linking DDR2 to adaptive immune evasion in the tumor microenvironment.","evidence":"DDR2/STAT3 knockdown, dual luciferase reporters for PD-L1/CCL20 promoters, MDSC migration assays, in vivo tumor models","pmids":["38969205"],"confidence":"Medium","gaps":["Whether this DDR2-STAT3 axis operates in non-hepatic cancers untested","Direct DDR2 substrate leading to STAT3 phosphorylation unidentified","Clinical relevance of DDR2-dependent immune evasion in patients unconfirmed"]},{"year":null,"claim":"Key open questions remain: the structural mechanism by which collagen binding in the extracellular discoidin domain is transmitted across the membrane to activate the intracellular kinase; a full-length DDR2 structure; the identity of direct DDR2 kinase substrates beyond autophosphorylation; and whether kinase-independent and kinase-dependent DDR2 functions can be therapeutically dissected.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length DDR2 structure exists","Direct kinase substrates remain largely unidentified","Transmembrane activation mechanism unresolved","Therapeutic window between kinase-dependent and kinase-independent functions unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,8,16,19,20,37]},{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[0,4,7,11]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,5,6,7,11]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,4,23,30,38]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[8,13,25]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[9,10,40]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,14,15,17,19,20,27,29,42,45,52]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[9,10,32,40,46]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,14,15,27]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[16,22,37,43,52]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[41,52]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[40,47]}],"complexes":["DDR2-Nrp1-PlexinA1"],"partners":["SRC","SHC1","NRP1","PLXNA1","CTNNB1","SHP2","DDR1","SNAI1"],"other_free_text":[]},"mechanistic_narrative":"DDR2 is a collagen-activated receptor tyrosine kinase that transduces extracellular matrix signals into programs governing cell proliferation, differentiation, ECM remodeling, epithelial-mesenchymal transition, and immune evasion. Native triple-helical collagens (types I, II, III, X) bind the DDR2 discoidin domain—specifically recognizing the GVMGFO motif via an amphiphilic pocket formed by three surface loops—triggering slow autophosphorylation (including Y740) that requires Src for maximal activation, with downstream signaling proceeding through Src-Shc, ERK1/2 (which directly phosphorylates and stabilizes SNAIL1 to drive EMT and metastasis), p38 MAPK–Runx2, JAK2, NF-κB, STAT3, YAP/TAZ, and mTOR pathways [PMID:9659899, PMID:11884411, PMID:20004161, PMID:23644467, PMID:20564243]. Beyond kinase-dependent signaling, the DDR2 extracellular domain inhibits collagen fibrillogenesis independently of catalytic activity, and DDR2 forms a complex with Nrp1–PlexinA1 to suppress osteoclastogenesis, while in cancer-associated fibroblasts it controls collagen fiber organization, integrin mechanotransduction via Rap1–Talin1–Kindlin2, and metabolic reprogramming through an AKT/SNAI1–glycolysis axis [PMID:18996394, PMID:25805889, PMID:31144616, PMID:37527178]. Loss-of-function DDR2 mutations—causing either ER retention of misfolded kinase-domain variants or collagen-binding defects in the discoidin domain—underlie spondylo-meta-epiphyseal dysplasia short limb–hand type (SMED-SL), whereas gain-of-function mutations drive squamous cell lung cancer and Warburg-Cinotti syndrome [PMID:19110212, PMID:20223752, PMID:22328973, PMID:30449416]."},"prefetch_data":{"uniprot":{"accession":"Q16832","full_name":"Discoidin domain-containing receptor 2","aliases":["CD167 antigen-like family member B","Discoidin domain-containing receptor tyrosine kinase 2","Neurotrophic tyrosine kinase, receptor-related 3","Receptor protein-tyrosine kinase TKT","Tyrosine-protein kinase TYRO10"],"length_aa":855,"mass_kda":96.7,"function":"Tyrosine kinase involved in the regulation of tissues remodeling (PubMed:30449416). It functions as a cell surface receptor for fibrillar collagen and regulates cell differentiation, remodeling of the extracellular matrix, cell migration and cell proliferation. Required for normal bone development. Regulates osteoblast differentiation and chondrocyte maturation via a signaling pathway that involves MAP kinases and leads to the activation of the transcription factor RUNX2. Regulates remodeling of the extracellular matrix by up-regulation of the collagenases MMP1, MMP2 and MMP13, and thereby facilitates cell migration and tumor cell invasion. Promotes fibroblast migration and proliferation, and thereby contributes to cutaneous wound healing","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q16832/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/DDR2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SAR1B","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/DDR2","total_profiled":1310},"omim":[{"mim_id":"618175","title":"WARBURG-CINOTTI SYNDROME; WRCN","url":"https://www.omim.org/entry/618175"},{"mim_id":"600408","title":"DISCOIDIN DOMAIN RECEPTOR FAMILY, MEMBER 1; DDR1","url":"https://www.omim.org/entry/600408"},{"mim_id":"271665","title":"SPONDYLOMETAEPIPHYSEAL DYSPLASIA, SHORT LIMB-HAND TYPE","url":"https://www.omim.org/entry/271665"},{"mim_id":"191311","title":"DISCOIDIN DOMAIN RECEPTOR FAMILY, MEMBER 2; DDR2","url":"https://www.omim.org/entry/191311"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Actin filaments","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/DDR2"},"hgnc":{"alias_symbol":["TKT"],"prev_symbol":["TYRO10","NTRKR3"]},"alphafold":{"accession":"Q16832","domains":[{"cath_id":"2.60.120.260","chopping":"31-185","consensus_level":"high","plddt":92.0844,"start":31,"end":185},{"cath_id":"2.60.120.1190","chopping":"190-367","consensus_level":"high","plddt":90.4822,"start":190,"end":367},{"cath_id":"3.30.200.20","chopping":"559-656","consensus_level":"high","plddt":80.9494,"start":559,"end":656},{"cath_id":"1.10.510.10","chopping":"661-672_679-850","consensus_level":"high","plddt":89.0485,"start":661,"end":850}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16832","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16832-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16832-F1-predicted_aligned_error_v6.png","plddt_mean":75.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DDR2","jax_strain_url":"https://www.jax.org/strain/search?query=DDR2"},"sequence":{"accession":"Q16832","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16832.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16832/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16832"}},"corpus_meta":[{"pmid":"22328973","id":"PMC_22328973","title":"Mutations in the DDR2 kinase gene identify a novel therapeutic target in squamous cell lung cancer.","date":"2011","source":"Cancer discovery","url":"https://pubmed.ncbi.nlm.nih.gov/22328973","citation_count":379,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11696582","id":"PMC_11696582","title":"DDR2 receptor promotes MMP-2-mediated proliferation and invasion by hepatic stellate cells.","date":"2001","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/11696582","citation_count":213,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11375938","id":"PMC_11375938","title":"The collagen receptor DDR2 regulates proliferation and its elimination leads to dwarfism.","date":"2001","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/11375938","citation_count":209,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"12611880","id":"PMC_12611880","title":"Molecular analysis of collagen binding by the human discoidin domain receptors, DDR1 and DDR2. 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Three spatially adjacent surface loops within the DDR2 discoidin domain constitute the collagen recognition site, identified by loop-swap mutagenesis with functionally unrelated discoidin domains.\",\n      \"method\": \"Recombinant extracellular domain production, solid-phase binding assays, loop-swap mutagenesis, receptor activation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis, multiple orthogonal methods in single study\",\n      \"pmids\": [\"12611880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The minimal collagen sequence GVMGFO (O = hydroxyproline) in a triple-helical conformation is sufficient for DDR2 binding and receptor activation. Single triple-helices (not fibrillar collagen) can activate DDR2.\",\n      \"method\": \"Collagen Toolkit peptide screening, truncated/alanine-substituted peptide assays, DDR2 binding and autophosphorylation assays, NMR-based structural modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with systematic mutagenesis and structural modeling, replicated binding and signaling readouts\",\n      \"pmids\": [\"18201965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The D2 period of collagen II harbors a specific DDR2 recognition site required for DDR2 binding and receptor autophosphorylation; the D3 and D4 periods are dispensable.\",\n      \"method\": \"Recombinant collagen II variants with specific D-period deletions, DDR2 binding assays, receptor autophosphorylation assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with deletion mutagenesis and functional validation\",\n      \"pmids\": [\"15544808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Collagen X is a ligand for DDR2, binding with high affinity and stimulating DDR2 autophosphorylation. Unlike fibrillar collagen binding, the DDR2 discoidin domain alone is not sufficient for collagen X binding; both the triple-helical region and NC1 domain of collagen X interact with DDR2, but only the triple-helical region activates the receptor.\",\n      \"method\": \"Solid-phase binding assays, DDR2 autophosphorylation assays, RT-PCR, immunohistochemistry\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding reconstitution with receptor activation assay and domain dissection\",\n      \"pmids\": [\"16806867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DDR2 is induced and tyrosine-phosphorylated in activated hepatic stellate cells in response to type I collagen. Overexpression of DDR2 or constitutively active chimeric DDR2 increases MMP-2 expression and promotes stellate cell proliferation and invasion, dependent on DDR2 kinase activity (kinase-dead DDR2 does not rescue).\",\n      \"method\": \"Stable overexpression of WT, constitutively active, truncated, and kinase-dead DDR2; MMP-2 activity assays; Matrigel invasion assays; proliferation assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple constructs including kinase-dead controls, orthogonal functional readouts\",\n      \"pmids\": [\"11696582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DDR2 kinase activity is required for its role in cell proliferation; kinase-dead DDR2 fails to rescue the reduced proliferation of DDR2-deficient fibroblasts. DDR2-deficient mice exhibit dwarfism due to reduced chondrocyte proliferation.\",\n      \"method\": \"DDR2 knockout mice, rescue with WT vs kinase-dead DDR2, fibroblast proliferation assays, wound healing model\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — KO mouse with kinase-dead rescue experiment, multiple phenotypic readouts\",\n      \"pmids\": [\"11375938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"DDR2 regulates osteoblast differentiation by activating ERK, which phosphorylates and activates the transcription factor Runx2. A gain-of-function Runx2 mutant with ERK-independent phosphorylation rescues osteogenic phenotypes in DDR2-silenced cells; a Runx2 mutant lacking ERK phosphorylation sites blocks DDR2-induced osteogenesis.\",\n      \"method\": \"shRNA knockdown, constitutively active DDR2 overexpression, ERK inhibition, Runx2 phosphorylation assays, rescue experiments with Runx2 mutants\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established with multiple rescue/inhibition experiments and phosphorylation readouts\",\n      \"pmids\": [\"20734453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ATF4 transcriptionally upregulates DDR2 expression via a C/EBP binding site at -1150 bp in the DDR2 promoter through cooperation with C/EBPβ. DDR2 in turn activates p38 MAPK to phosphorylate and activate Runx2, promoting osteoblast differentiation.\",\n      \"method\": \"Promoter deletion analysis, ATF4 mutants deficient in C/EBPβ binding, p38 MAPK inhibition, Runx2 reporter assays, DDR2 knockdown/overexpression\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — promoter mutagenesis, pathway inhibition, and rescue experiments with orthogonal readouts\",\n      \"pmids\": [\"20564243\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SMED-SL-causing DDR2 missense mutations (T713I, I726R, R752C) are retained in the endoplasmic reticulum, preventing plasma membrane trafficking and collagen-induced receptor activation. The E113K mutant traffics normally but fails to bind collagen, identifying at least two distinct loss-of-function mechanisms.\",\n      \"method\": \"Human cell line expression, subcellular localization assays, collagen-induced receptor activation assays, structural mapping\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants with distinct mechanistic outcomes, orthogonal localization and functional assays\",\n      \"pmids\": [\"20223752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SHP-2 tyrosine phosphorylation is dependent on DDR2 kinase activity downstream of collagen activation. DDR2 lung cancer mutants L63V and G505S phosphorylate SHP-2, while the kinase-impaired I638F mutant shows diminished DDR2 and SHP-2 phosphorylation inversely correlating with clonogenic potential.\",\n      \"method\": \"Quantitative phosphoproteomics (7 time points), biochemical validation by immunoblot, targeted proteomics of DDR2 mutant panel\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — quantitative phosphoproteomics with biochemical validation and multiple mutant controls\",\n      \"pmids\": [\"23822953\"],\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 both DDR2 and SRC is required for enhanced suppression of DDR2-mutant lung cancer cell lines compared to DDR2 inhibition alone.\",\n      \"method\": \"Co-immunoprecipitation, kinase inhibitor studies, cell viability assays in DDR2-mutant cell lines\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP plus functional rescue, single lab\",\n      \"pmids\": [\"26390252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 suppresses osteoclastogenesis by forming a DDR2-Neuropilin-1 (Nrp1)-PlexinA1 complex that blocks PlexinA1-mediated stimulation of osteoclastogenesis and prevents PlexinA1 from interacting with TREM2 and DAP12.\",\n      \"method\": \"Co-immunoprecipitation, overexpression and knockdown of DDR2/Nrp1, osteoclast differentiation assays, bone resorption assays, in vivo adenoviral delivery\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, epistasis with Nrp1 rescue/knockdown, in vivo model\",\n      \"pmids\": [\"25805889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DDR2 extracellular domain (kinase-dead, cell-surface anchored) inhibits collagen fibrillogenesis by cells, reducing the rate and abundance of collagen deposition and altering fiber morphology. This identifies a kinase-independent role of the DDR2 ECD in extracellular matrix remodeling.\",\n      \"method\": \"Stable osteoblast cell lines expressing kinase-dead DDR2, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple imaging and biochemical readouts, kinase-dead construct to distinguish mechanism\",\n      \"pmids\": [\"18996394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Soluble extracellular domains of DDR2 secreted by cells inhibit collagen fibrillogenesis, reducing collagen deposition and altering fiber morphology and matrix mineralization.\",\n      \"method\": \"Stable cell lines secreting soluble DDR1/DDR2 ECD, TEM, fluorescence microscopy, hydroxyproline assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, single lab\",\n      \"pmids\": [\"19900459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DDR2 activation by fibrillar collagen I is required for downregulation of focal adhesion kinase (FAK) in vascular smooth muscle cells; siRNA depletion of DDR2 blocks FAK downregulation independently of matrix stiffness.\",\n      \"method\": \"siRNA knockdown of DDR2, engineered collagen matrices varying in stiffness and glycosylation, FAK immunoblot, DDR2 tyrosine phosphorylation assays\",\n      \"journal\": \"Biomaterials\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with mechanistic dissection of matrix cues, single lab\",\n      \"pmids\": [\"19762078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DDR2 activation via collagen stimulates ERK signaling, which phosphorylates and stabilizes SNAIL1, promoting EMT, invasion, and upregulation of MT1-MMP and MMP-2 in hepatocellular carcinoma cells.\",\n      \"method\": \"DDR2 overexpression/knockdown, cycloheximide chase experiments for SNAIL1 half-life, ERK signaling inhibition, immunoblotting\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cycloheximide chase plus pathway inhibition, single lab\",\n      \"pmids\": [\"26362312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Collagen I-induced DDR1 expression in primary human lung fibroblasts requires DDR2 activation followed by JAK2 and ERK1/2 MAPK signaling, which recruits transcription factor PEBP3 to the DDR1 promoter.\",\n      \"method\": \"DDR2/JAK2/ERK inhibition, promoter assays, transcription factor recruitment assays, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway inhibition with promoter binding assay, single lab\",\n      \"pmids\": [\"21335558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The intracellular juxtamembrane 2 (JM2) region of DDR2 mediates receptor dimerization, which is required for efficient collagen binding and receptor activation. Overexpression of the JM2-containing domain acts as a dominant negative to suppress DDR2-dependent colony formation, proliferation, and invasion via inhibition of MMP-2 and MMP-9.\",\n      \"method\": \"Collagen-binding assays, dimerization assays, dominant-negative JM2 overexpression, colony formation/invasion assays, MMP-2/9 immunoblot\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain deletion with functional validation across multiple readouts, single lab\",\n      \"pmids\": [\"24740739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Acquired resistance to dasatinib in DDR2-mutant lung cancer cells occurs via two mechanisms: a T654I gatekeeper mutation in DDR2, and NF1 loss that activates an ERK-dependent bypass pathway downstream of RAS.\",\n      \"method\": \"Targeted exome sequencing of dasatinib-resistant cell lines, functional validation of resistance mechanisms\",\n      \"journal\": \"Molecular cancer therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — sequencing plus functional validation in resistant cell lines, single lab\",\n      \"pmids\": [\"24296828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DDR2 in cancer-associated fibroblasts (CAFs) controls tumor stiffness and metastasis by reorganizing collagen fibers at the tumor-stromal boundary through integrin activation via Rap1-mediated Talin1 and Kindlin2 recruitment.\",\n      \"method\": \"Mouse breast tumor models, DDR2 KO/KD in CAFs, mechanotransduction assays, integrin activation assays (Rap1/Talin1/Kindlin2)\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo mouse models plus mechanistic dissection of integrin pathway in CAFs with multiple orthogonal approaches\",\n      \"pmids\": [\"31144616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Collagen II-activated phosphorylated DDR2 induces CYR61 expression through transcription factor AP-1. CYR61 then drives MMP1 production via ETS1 transcription factor, promoting fibroblast-like synoviocyte invasion and migration in rheumatoid arthritis.\",\n      \"method\": \"DDR2 activation assays, AP-1 reporter assays, CYR61 adenoviral shRNA knockdown in vitro and in CIA rat model, micro-CT\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo CIA model with in vitro mechanistic dissection, single lab\",\n      \"pmids\": [\"27653023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MSC-derived DDR2 maintains a fibroblastic phenotype with collagen deposition and induces pathological DDR2 phosphorylation and signaling in breast cancer cells in a paracrine manner; loss of DDR2 in MSCs impairs DDR2 phosphorylation in breast cancer cells and reduces BC cell alignment, migration, and metastasis.\",\n      \"method\": \"DDR2-KO MSCs (slie mutation mice), co-culture assays, DDR2 phosphorylation immunoblot, in vivo metastasis models\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO model plus co-culture mechanistic dissection with in vivo metastasis readout\",\n      \"pmids\": [\"28147276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A small-molecule inhibitor (WRG-28) allosterically inhibits DDR2 extracellular domain-collagen interactions, blocking tumor invasion, migration, and lung metastasis.\",\n      \"method\": \"Small molecule screening, DDR2 binding assays, invasion/migration assays, in vivo lung metastasis model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro binding and in vivo functional validation, single lab\",\n      \"pmids\": [\"30061414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"EMT regulators TWIST and SNAIL induce DDR2 expression, and DDR2 knockdown reduces ferroptosis susceptibility and YAP/TAZ activity in recurrent breast tumor cells, identifying a DDR2-YAP/TAZ axis in ferroptosis regulation.\",\n      \"method\": \"DDR2 knockdown, EMT regulator overexpression, ferroptosis assays (erastin), YAP/TAZ activity assays, clonogenic assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with mechanistic pathway readouts, single lab\",\n      \"pmids\": [\"33603168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Gain-of-function DDR2 variants (L610P, Y740C) causing Warburg-Cinotti syndrome lead to increased DDR2 phosphorylation in patient fibroblasts, consistent with reduced receptor autoinhibition and ligand-independent kinase activation. Dasatinib prevents DDR2 autophosphorylation in these cells.\",\n      \"method\": \"Patient fibroblast phosphorylation assays, dasatinib treatment, family-based genetic analysis confirming de novo occurrence\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient-derived cells with direct phosphorylation measurement, single study\",\n      \"pmids\": [\"30449416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In C. elegans, DDR-2 (ortholog of DDR2) functions upstream of the Met-like RTK SVH-2 and scaffold SHC-1 in the JNK MAPK pathway to regulate axon regeneration. The scaffold SHC-1 interacts physically with both DDR-2 and SVH-2; overexpression of svh-2 and shc-1 suppresses the axon regeneration delay in ddr-2 mutants.\",\n      \"method\": \"C. elegans genetic epistasis, axon regeneration assays after laser injury, overexpression rescue, protein interaction assays\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with rescue experiments, ortholog context consistent with mammalian DDR2\",\n      \"pmids\": [\"27984580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"DDR2 acts via ERK1/2 MAPK-activated serum response factor (SRF) to upregulate anti-apoptotic cIAP2 and pro-proliferative Skp2 (which degrades p27 to promote G1-S transition) in cardiac fibroblasts. DDR2 also suppresses FoxO3a-mediated p27 transcription via ERK1/2.\",\n      \"method\": \"DDR2 knockdown/overexpression, promoter binding assays, ERK1/2 inhibition, flow cytometry, PCNA/Rb phosphorylation, WRG-28 (DDR2 ECD inhibitor) treatment\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter binding assays plus multiple pathway readouts, single lab\",\n      \"pmids\": [\"32412792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Tyrosine kinase activity-independent action of DDR2 in tumor cells can support Matrigel invasion and in vivo metastasis. Paracrine DDR2 signaling between tumor cells and CAFs also supports invasion, migration, and lung colonization.\",\n      \"method\": \"Kinase-dead DDR2 expression in tumor cells, 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 — kinase-dead construct with in vivo metastasis readout, single lab\",\n      \"pmids\": [\"34477203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"DDR2-mediated collagen I signaling upregulates lysyl oxidase in osteoblasts; this is blocked by collagen glycation (carboxymethylation), which disrupts DDR2 binding and activation, providing a mechanism for reduced enzymatic collagen crosslinks in diabetic bone.\",\n      \"method\": \"DDR2 shRNA knockdown in primary osteoblasts, lysyl oxidase protein assays, CML-collagen vs native collagen stimulation\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — shRNA knockdown with functional enzyme readout, single lab\",\n      \"pmids\": [\"24120383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CEBPA-DT lncRNA binds hnRNPC and promotes cytoplasmic translocation of hnRNPC, which enhances hnRNPC-DDR2 mRNA interaction to increase DDR2 expression. Upregulated DDR2 then interacts with β-catenin to promote its nuclear translocation and Snail1-driven EMT.\",\n      \"method\": \"RNA immunoprecipitation, RNA pulldown, co-immunoprecipitation, subcellular fractionation, DDR2 inhibitor experiments, immunofluorescence\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal RNA and protein interaction methods, single lab\",\n      \"pmids\": [\"36471363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DDR2 induces STAT3 phosphorylation and nuclear translocation; activated STAT3 in turn transcriptionally enhances DDR2 expression, forming a positive feedback loop. STAT3 directly activates PD-L1 and CCL20 transcription (by dual luciferase reporter), mediating immune evasion in oxaliplatin-resistant HCC.\",\n      \"method\": \"DDR2/STAT3 knockdown, luciferase reporter assays for PD-L1 and CCL20 promoters, immunofluorescence of STAT3 translocation, MDSC transwell migration assays\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter reporter assays plus functional immune cell recruitment assays, single lab\",\n      \"pmids\": [\"38969205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DDR2 in CAFs promotes collagen production through arginase activity; DDR2-depleted CAFs have decreased ornithine and polyamine levels leading to reduced collagen and reduced tumor invasion. DDR2 controls arginase-1 transcription via SNAI1, which is detected at the arginase-1 promoter by ChIP.\",\n      \"method\": \"DDR2 depletion in human/mouse CAFs, metabolomics, arginase activity assays, chromatin immunoprecipitation, rescue with exogenous polyamines/arginase overexpression, co-culture invasion assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus metabolomics and rescue experiments, single lab\",\n      \"pmids\": [\"37996700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DDR2 in omental fibroblasts regulates glycolysis through an AKT/SNAI1 axis leading to suppressed fructose-1,6-bisphosphatase and increased hexokinase activity. DDR2 also regulates secretion of LOXL2; addition of exogenous LOXL2 rescues invasion in DDR2-depleted fibroblasts.\",\n      \"method\": \"In vivo DDR2 KO mouse model, glycolytic enzyme activity assays, conditioned media rescue experiments with LOXL2, tumor invasion assays\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic model with metabolic pathway dissection and rescue, single lab\",\n      \"pmids\": [\"37527178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Neuropilin-1 (Nrp1) co-localizes and physically interacts with DDR2 at the cell membrane, prolonging DDR2 protein half-life without altering DDR2 mRNA, thereby enhancing DDR2-ERK-Runx2 signaling and osteoblast differentiation.\",\n      \"method\": \"Co-localization by immunofluorescence, protein half-life determination assay, Nrp1 overexpression/silencing, DDR2 phosphorylation assays\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-localization plus half-life assay, single lab without Co-IP shown\",\n      \"pmids\": [\"25924845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"DDR2 promotes fibroblast spreading and migration independently of adhesion ligand (fibronectin or collagen) and independently of DDR2 tyrosine kinase activation by soluble collagen, as shown by siRNA silencing in 2D and 3D collagen systems.\",\n      \"method\": \"siRNA knockdown of DDR2, cell spreading/migration assays on fibronectin and collagen surfaces, 3D collagen matrix migration\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA with multiple substrate conditions dissecting kinase-independent roles, single lab\",\n      \"pmids\": [\"23131558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DDR1 and DDR2 physically interact by co-immunoprecipitation. Co-expression of DDR1 and DDR2 results in higher ERK activation than either alone after collagen I stimulation, but is inhibitory for cell proliferation and migration compared to DDR1 alone.\",\n      \"method\": \"Co-immunoprecipitation, ERK/JAK2 activation assays after collagen I stimulation, proliferation/migration assays with dominant-negative constructs\",\n      \"journal\": \"Cell adhesion & migration\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP plus functional readouts, single lab\",\n      \"pmids\": [\"29616590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR2 in ovarian cancer CAFs regulates periostin (POSTN) expression and mesothelial clearance/invasion; DDR2 controls POSTN through integrin B1 (ITGB1). DDR2/POSTN-expressing CAFs enhance tumor cell invasion three-fold.\",\n      \"method\": \"Co-culture assays, DDR2 depletion, ITGB1 inhibition, in vivo xenograft co-injection models\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-culture and in vivo models with pathway dissection, single lab\",\n      \"pmids\": [\"35884543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDR2 inhibition by nilotinib in valvular interstitial cells promotes osteogenic activation and calcification; increasing the DDR2 ligand collagen blunts this effect, demonstrating that DDR2 kinase activity in VICs suppresses osteogenic calcification.\",\n      \"method\": \"Nilotinib treatment of human VICs, selective DDR2 inhibition, collagen rescue experiments, in vivo murine aortic valve model\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — rescue with DDR2 ligand (collagen) plus in vivo model, single lab\",\n      \"pmids\": [\"35751904\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DDR2 is a receptor tyrosine kinase that is activated by binding of fibrillar collagens (I, II, III, X) through three surface loops in its extracellular discoidin domain (minimum motif GVMGFO in triple-helical conformation), leading to receptor dimerization (facilitated by the intracellular JM2 region), autophosphorylation, and downstream activation of ERK1/2, p38 MAPK, SHP-2, and SRC signaling cascades that regulate MMP expression, EMT via SNAIL1 stabilization, Runx2-driven osteoblast differentiation, osteoclastogenesis suppression through a DDR2-Nrp1-PlexinA1 complex, collagen fibrillogenesis regulation by the extracellular domain, and integrin mechanotransduction via Rap1/Talin1/Kindlin2 in cancer-associated fibroblasts to control tumor stiffness and metastasis.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries from KEEP papers.\n\n**Classification notes:**\n- Papers about DDR2 (discoidin domain receptor 2, the collagen receptor RTK) → KEEP\n- Papers about TKT (transketolase) pulled in via alias collision → EXCLUDE\n- Papers about yeast DDR2 (multistress response gene, S. cerevisiae) → EXCLUDE (symbol collision, unrelated protein)\n- E. coli tkt gene papers → EXCLUDE\n- Papers about C. elegans DDR-2 → KEEP (ortholog, consistent function)\n- Papers about circ-LAMP1, lncRNA CEBPA-DT mentioning DDR2 → these describe lncRNA/circRNA biology but reference DDR2 protein mechanistically → KEEP the DDR2 mechanistic findings if present\n- General interactome/cDNA papers with no DDR2 mechanism → EXCLUDE\n\n**EXCLUDE list:** Papers 14 (TKT/HCC), 17 (TKT gene structure), 40 (TKT mutations/syndrome), 50 (TKT intestinal), 54 (TKT/EBV), 56 (TKT T-cell), 59 (TKT-PARP1), 62 (yeast DDR2), 64 (E. coli tkt), 66 (E. coli tkt), 71 (mouse TKT gene), 74 (nuclear Tkt/heart), 82 (E. coli tktA/tktB), 90 (FOXA1/MND1/TKT), 92 (HMGA1/TKT), 95 (TKT/prostate), and from curated list: papers not about DDR2 mechanism (cDNA collections, interactomes, HuR, Rho GTPases, SUMO, dengue, autophagy, chaperones, ESTs, promoters, focal adhesion proteomics, smoking cessation, podocyte exosomes).\n\nPaper 39 (circ-LAMP1) → EXCLUDE (alt-locus circRNA product)\nPaper 32 (lncRNA CEBPA-DT) → the DDR2 content here is about DDR2/β-catenin interaction — KEEP for that finding\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"DDR1 and DDR2 are receptor tyrosine kinases activated by native triple-helical collagen (not soluble growth factors); collagen activation of DDR2 upregulates matrix metalloproteinase-1 (MMP-1) expression, establishing DDR2 as a collagen receptor that controls cellular responses to the ECM.\",\n      \"method\": \"Receptor-ligand binding assays, kinase activation assays, MMP-1 reporter assays in cell lines\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original biochemical reconstitution of collagen-DDR2 activation, replicated across multiple labs subsequently\",\n      \"pmids\": [\"9659899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"DDR2 requires Src kinase activity to be maximally tyrosine-phosphorylated following collagen activation; activated DDR2 associates with the adaptor protein Shc (via a novel Shc domain); Src is required for DDR2-mediated transactivation of the MMP-2 promoter, placing Src and Shc as key signaling intermediates downstream of DDR2.\",\n      \"method\": \"Co-immunoprecipitation, kinase inhibition assays, MMP-2 promoter reporter assays, dominant-negative Src constructs\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional reporter assays with multiple genetic/pharmacological tools\",\n      \"pmids\": [\"11884411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DDR2 is induced in hepatic stellate cells upon activation by type I collagen, becomes tyrosine-phosphorylated, and promotes proliferation and Matrigel invasion through increased expression of active MMP-2; a constitutively active chimeric DDR2 recapitulates these effects while kinase-dead DDR2 does not, establishing DDR2 kinase activity as necessary for MMP-2 upregulation and stellate cell activation.\",\n      \"method\": \"Stable overexpression of WT, constitutively active (Fc-DDR2), truncated, and kinase-dead DDR2 constructs; proliferation and invasion assays; MMP-2 activity assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — kinase-dead mutant rescue experiment plus multiple functional readouts\",\n      \"pmids\": [\"11696582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DDR2-deficient mice exhibit dwarfism due to reduced chondrocyte proliferation (not aberrant differentiation); DDR2-/- fibroblasts proliferate more slowly than WT, and this defect is rescued by wild-type but not kinase-dead DDR2, demonstrating that DDR2 kinase activity is required for its proliferative function.\",\n      \"method\": \"DDR2 knockout mouse generation, histological analysis, in vitro fibroblast proliferation rescue with WT vs. kinase-dead DDR2\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic KO with kinase-dead rescue, replicated across multiple cell types and in vivo\",\n      \"pmids\": [\"11375938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The discoidin domain of DDR2 (but not DDR1) is sufficient for collagen I binding and for transmembrane receptor signaling; three spatially adjacent surface loops within the DDR2 discoidin domain constitute the collagen recognition site, as shown by loop-swap mutagenesis.\",\n      \"method\": \"Recombinant extracellular domain production, solid-phase binding assays, loop-swap mutagenesis, receptor activation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with functional validation of collagen binding and receptor activation\",\n      \"pmids\": [\"12611880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The D2 period of triple-helical collagen II harbors a specific DDR2 binding and autophosphorylation-inducing site; collagen II is a better DDR2 ligand than DDR1; binding is dependent on triple-helical conformation and mediated by the DDR2 discoidin domain.\",\n      \"method\": \"Recombinant collagen II deletion variants, DDR2 binding assays, receptor autophosphorylation assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic deletion mapping of collagen binding site with functional validation\",\n      \"pmids\": [\"15544808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Collagen X is a ligand for DDR2 (but not DDR1); collagen X binds DDR2 extracellular domain with high affinity and stimulates DDR2 autophosphorylation; unlike fibrillar collagens, the DDR2 discoidin domain alone is not sufficient for collagen X binding, indicating additional DDR2 binding sites; the triple-helical region (but not the NC1 domain) of collagen X activates DDR2.\",\n      \"method\": \"Solid-phase binding assays, DDR2 autophosphorylation assays, domain truncation constructs\",\n      \"journal\": \"Matrix biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with domain mapping and functional validation\",\n      \"pmids\": [\"16806867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The minimal collagen sequence GVMGFO (where O = hydroxyproline) is required for DDR2 binding; triple-helical peptides containing this motif both inhibit DDR2 binding to collagen II and activate DDR2 transmembrane signaling, indicating that single triple-helices (not fibrillar collagen) are sufficient for DDR2 activation.\",\n      \"method\": \"Collagen II Toolkit peptide screening, truncated/alanine-substituted peptide binding assays, DDR2 activation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic peptide mapping with functional activation assays, replicated approach\",\n      \"pmids\": [\"18201965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Three missense mutations in the DDR2 kinase domain (T713I, I726R, R752C) causing SMED-SL result in retention of the mutant DDR2 protein in the endoplasmic reticulum and defective collagen-induced receptor activation, identifying ER trafficking failure as a loss-of-function mechanism.\",\n      \"method\": \"Sanger sequencing, expression of mutant DDR2 in human cell lines, subcellular localization, collagen activation assays\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants characterized with localization and functional assays\",\n      \"pmids\": [\"19110212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Cell-surface expression of kinase-dead DDR2 (via its extracellular domain) inhibits collagen fibrillogenesis by cells, reducing the rate and abundance of collagen deposition and altering fiber morphology, revealing a kinase-independent structural/regulatory function of the DDR2 extracellular domain in ECM remodeling.\",\n      \"method\": \"Stable mouse osteoblast cell lines expressing kinase-dead DDR2, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods in reconstituted cell system\",\n      \"pmids\": [\"18996394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Soluble extracellular domains of DDR1 and DDR2 (naturally shed forms) inhibit collagen fibrillogenesis, reducing collagen deposition and altering fiber morphology and matrix mineralization in osteoblast cell lines.\",\n      \"method\": \"Stable secretion of DDR1/DDR2 ECD, transmission electron microscopy, fluorescence microscopy, hydroxyproline assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods, extends prior kinase-dead finding to soluble forms\",\n      \"pmids\": [\"19900459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structure of the DDR2 discoidin domain bound to a triple-helical collagen peptide (GVMGFO motif) reveals that two collagen chains are recognized by an amphiphilic pocket delimited by a critical tryptophan residue and a buried salt bridge; collagen binding induces structural changes in DDR2 surface loops potentially linked to receptor activation.\",\n      \"method\": \"X-ray crystallography of DDR2 discoidin domain–collagen peptide complex\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation of binding mechanism\",\n      \"pmids\": [\"20004161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DDR2 activation by fibrillar collagen I downregulates focal adhesion kinase (FAK) levels in vascular smooth muscle cells; siRNA depletion of DDR2 blocks this FAK downregulation, establishing DDR2 as a regulator of FAK protein levels in collagen-adhered cells.\",\n      \"method\": \"siRNA knockdown of DDR2, Western blotting for FAK, collagen fibril vs. monolayer comparison\",\n      \"journal\": \"Biomaterials\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with specific phenotypic readout, single lab\",\n      \"pmids\": [\"19762078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SMED-SL missense mutations: three kinase-domain mutants (T713I, I726R, R752C) are retained in the ER and fail collagen-induced activation; a novel extracellular domain mutant (E113K) traffics normally but fails to bind collagen, demonstrating that SMED-SL arises from at least two distinct loss-of-function mechanisms (ER retention vs. ligand-binding defect).\",\n      \"method\": \"Expression of point mutants in human cell lines, confocal microscopy for localization, collagen binding assays, Western blotting\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple mutants with orthogonal localization and functional assays, consistent with structural data\",\n      \"pmids\": [\"20223752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ATF4 transcriptionally upregulates DDR2 expression through a C/EBP binding site at -1150 bp in the DDR2 promoter via cooperation with C/EBPβ; DDR2 in turn activates Runx2 through p38 MAPK stimulation to promote osteoblast differentiation.\",\n      \"method\": \"DDR2 promoter deletion/mutation analysis, ATF4/C/EBPβ knockdown and overexpression, p38 MAPK inhibition, osteogenic differentiation assays\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — promoter binding assays plus epistasis with multiple genetic tools\",\n      \"pmids\": [\"20564243\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DDR2 activation in preosteoblastic cells promotes osteoblast differentiation by stimulating ERK-mediated phosphorylation of Runx2 (the master osteogenic transcription factor), enhancing its transcriptional activity; constitutively active DDR2 increases bone marker expression while kinase-dead DDR2 blocks DDR2-induced osteogenesis.\",\n      \"method\": \"DDR2 shRNA knockdown, constitutively active DDR2 overexpression, ERK inhibition, Runx2 phosphorylation assays, gain-of-function Runx2 rescue experiments\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic tools with epistasis rescue, identifies ERK-Runx2 as the pathway\",\n      \"pmids\": [\"20734453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DDR2 mutations (e.g., L63V, G505S) found in ~3.8% of squamous cell lung cancers are gain-of-function; expression of mutated DDR2 causes cellular transformation; DDR2-mutant lung cancer cells are selectively killed by RNAi knockdown of DDR2 or by dasatinib treatment, demonstrating oncogenic DDR2 kinase dependency.\",\n      \"method\": \"Sanger sequencing, RNAi knockdown, dasatinib treatment, xenograft tumor models, cellular transformation assays\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (RNAi, small molecule, xenograft) across multiple cell lines\",\n      \"pmids\": [\"22328973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Collagen I induces DDR1 expression in human lung fibroblasts through a pathway requiring DDR2 activation followed by JAK2 and ERK1/2 signaling; ERK1/2 activation recruits the transcription factor PEBA3 to the DDR1 promoter; DDR2 also mediates collagen I-induced MMP-10 expression through this pathway.\",\n      \"method\": \"DDR2 knockdown, JAK2/ERK inhibitors, DDR1 promoter chromatin immunoprecipitation, gene expression assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KD plus pharmacological inhibition plus promoter ChIP, placing DDR2 upstream of JAK2-ERK-DDR1 axis\",\n      \"pmids\": [\"21335558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"DDR2 plays a role in fibroblast spreading and migration independent of the adhesion ligand type (fibronectin or collagen) and independent of collagen-induced DDR2 tyrosine kinase activation; DDR2 knockdown also inhibits migration in 3D collagen matrices without affecting matrix contraction.\",\n      \"method\": \"siRNA knockdown of DDR2, 2D migration assays on fibronectin vs. collagen, 3D collagen matrix migration assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD across multiple matrix conditions, single lab\",\n      \"pmids\": [\"23131558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"DDR2 stabilizes SNAIL1 by stimulating ERK2 activity in a Src-dependent manner; activated ERK2 directly phosphorylates SNAIL1, causing nuclear accumulation, reduced ubiquitylation, and increased protein half-life; this DDR2-ERK2-SNAIL1 axis promotes breast cancer cell invasion, migration, and metastasis in vivo.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ERK2 kinase assays on SNAIL1, cycloheximide chase, ubiquitylation assays, Src inhibition, mouse metastasis models\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay showing direct ERK2 phosphorylation of SNAIL1 plus multiple orthogonal methods and in vivo validation\",\n      \"pmids\": [\"23644467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Quantitative phosphoproteomics of DDR2 signaling identified SHP-2 tyrosine phosphorylation as dependent on DDR2 kinase activity; DDR2 lung cancer mutants L63V and G505S phosphorylate SHP-2, while the I638F kinase-domain mutant shows diminished DDR2 and SHP-2 phosphorylation inversely correlated with clonogenic potential; NCK1, LYN, SHIP-2, and PIK3C2A are also candidate DDR2 signaling nodes.\",\n      \"method\": \"Quantitative mass spectrometry phosphoproteomics (7 time points), biochemical validation of SHP-2 phosphorylation with kinase-dead DDR2, targeted proteomic profiling of DDR2 mutants\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — quantitative phosphoproteomics with biochemical validation across multiple DDR2 mutants\",\n      \"pmids\": [\"23822953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"DDR2 mediates collagen-induced upregulation of lysyl oxidase in osteoblasts; collagen advanced glycation (CML-collagen) disrupts DDR2 binding and activation, thereby blocking lysyl oxidase induction, providing a mechanism for reduced enzymatic collagen cross-links in diabetic bone.\",\n      \"method\": \"DDR2 shRNA knockdown in primary osteoblasts, collagen binding assays with glycated vs. non-glycated collagen, lysyl oxidase protein quantification\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — shRNA KD with defined molecular readout, single lab\",\n      \"pmids\": [\"24120383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Acquired resistance to dasatinib in DDR2-dependent lung cancer cells arises via two mechanisms: (1) a T654I gatekeeper mutation in DDR2, and (2) NF1 loss activating a RAS-ERK bypass pathway, demonstrating that ERK dependency can be achieved downstream of DDR2 through RAS activation.\",\n      \"method\": \"Targeted exome sequencing of resistant cell lines, functional validation of resistance mechanisms, pathway inhibition assays\",\n      \"journal\": \"Molecular cancer therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — sequencing plus functional validation of two distinct resistance mechanisms\",\n      \"pmids\": [\"24296828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The cytoplasmic juxtamembrane 2 (JM2) region of DDR2 is required for receptor dimerization, which is critical for collagen-induced receptor activation; JM2 is also required for efficient collagen binding to the discoidin domain; expression of JM2-containing peptide inhibits DDR2-mediated MMP-2/9 expression, colony formation, and invasion.\",\n      \"method\": \"JM2 deletion/overexpression constructs, co-immunoprecipitation for dimerization, collagen binding assays, invasion/proliferation assays\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain deletion with multiple functional readouts, single lab\",\n      \"pmids\": [\"24740739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"DDR2 and SRC are direct binding partners; SRC activity is functionally tied to DDR2 activation; 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, selective DDR2 inhibitor characterization, dual DDR2/SRC inhibitor assays in cancer cell lines\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus functional inhibitor data, single lab\",\n      \"pmids\": [\"26390252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A novel DDR2 missense mutation (c.2468_2469delCT, p.S823Cfs*2) causes ER retention of the mutant protein, defective N-glycosylation processing, and loss of collagen-induced activation, confirming that DDR2 kinase-domain mutations causing SMED-SL converge on ER trafficking defects.\",\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 — orthogonal localization and functional methods, single lab\",\n      \"pmids\": [\"24725993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 facilitates HCC invasion, migration, and EMT via activation of ERK2 and stabilization of SNAIL1 protein; DDR2 upregulates MT1-MMP and MMP2 expression through ERK2/SNAIL1 signaling; collagen I can induce the DDR2/ERK2/SNAIL1 signaling cascade in HCC cells.\",\n      \"method\": \"DDR2 overexpression/knockdown, cycloheximide chase for SNAIL1 stability, ERK2 inhibition, Western blotting, invasion/migration assays\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays with pathway inhibition, single lab\",\n      \"pmids\": [\"26362312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 suppresses osteoclastogenesis by forming a DDR2-Nrp1-PlexinA1 complex; DDR2 facilitates binding of Nrp1 to PlexinA1, blocking PlexinA1-mediated osteoclast stimulation; DDR2 also prevents PlexinA1 from interacting with TREM2 and DAP12; adenoviral DDR2 delivery to bone alleviates osteopenic phenotypes in ovariectomized mice.\",\n      \"method\": \"Co-immunoprecipitation for complex formation, DDR2 overexpression/RNAi, Nrp1 knockdown rescue assays, in vivo adenoviral delivery, osteoclast differentiation assays\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP establishing complex plus genetic rescue experiments and in vivo validation\",\n      \"pmids\": [\"25805889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 can synergize TGF-β and fibrillar collagen signals to stimulate lung fibroblast myofibroblastic differentiation and VEGF expression; DDR2 knockdown by siRNA or kinase inhibition reduces established lung fibrosis in vivo.\",\n      \"method\": \"In vitro fibroblast stimulation assays, DDR2 siRNA in vivo delivery, bleomycin lung fibrosis mouse model\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"27350126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DDR2 inhibition in murine melanoma cells suppresses collagen I-induced migration and invasion by reducing MMP2/9 expression through the ERK1/2 and NF-κB signaling pathways; DDR2 is phosphorylated by collagen I in these cells.\",\n      \"method\": \"DDR2 siRNA knockdown, migration/invasion assays, ERK1/2 and NF-κB pathway inhibition, MMP2/9 expression analysis\",\n      \"journal\": \"Acta biochimica et biophysica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with pathway inhibition, single lab\",\n      \"pmids\": [\"25733533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Neuropilin-1 (Nrp1) co-localizes with DDR2 at the cell membrane, enhances DDR2 phosphorylation and ERK1/2-Runx2 signaling, and prolongs DDR2 protein half-life (post-translational stabilization) without altering DDR2 mRNA levels, thereby promoting osteoblast differentiation.\",\n      \"method\": \"Nrp1 overexpression/silencing, DDR2 half-life assay (cycloheximide chase), immunofluorescence co-localization, ERK1/2 and Runx2 phosphorylation analysis\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — half-life assay plus co-localization and functional rescue, single lab\",\n      \"pmids\": [\"25924845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In C. elegans, DDR-2 (the DDR2 ortholog) functions upstream of the Met-like RTK SVH-2 and the scaffold protein SHC-1 in regulating axon regeneration; SHC-1 interacts with both DDR-2 and SVH-2; overexpression of svh-2 and shc-1 suppresses the axon regeneration delay in ddr-2 mutants, placing DDR-2 upstream of the SVH-2-JNK MAPK pathway.\",\n      \"method\": \"C. elegans genetics (ddr-2 mutants, epistasis), axon regeneration assays, co-immunoprecipitation of DDR-2 and SHC-1/SVH-2\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with Co-IP in orthologous organism, functionally consistent with mammalian DDR2\",\n      \"pmids\": [\"27984580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"DDR2 in cancer-associated fibroblasts (CAFs) is critical for extracellular matrix production and collagen fiber organization; in tumor cells, DDR2 in basal epithelial cells regulates collective invasion of tumor organoids; both tumor-cell-intrinsic and stromal DDR2 functions are required for breast cancer metastasis in vivo.\",\n      \"method\": \"Genetic cell-type-specific DDR2 deletion, tumor organoid invasion assays, second-harmonic generation microscopy for collagen fiber analysis, mouse metastasis models\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific genetic deletion with multiple orthogonal readouts and in vivo metastasis validation\",\n      \"pmids\": [\"27264173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In rheumatoid arthritis fibroblast-like synoviocytes, collagen II-activated phospho-DDR2 induces CYR61 expression via AP-1 transcription factor; elevated CYR61 then accelerates MMP1 production via ETS1; CYR61 shRNA in vivo reduces arthritis severity and bone erosion.\",\n      \"method\": \"DDR2 activation/inhibition, AP-1 and ETS1 reporter assays, CYR61 shRNA adenovirus in CIA rat model, μCT bone analysis\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pathway dissection with in vivo validation in arthritis model\",\n      \"pmids\": [\"27653023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"DDR2 maintains a fibroblastic phenotype with collagen deposition in breast cancer-associated mesenchymal stem cells (MSCs); loss of DDR2 in MSCs impairs their ability to promote DDR2 phosphorylation in breast cancer cells, BC cell alignment, migration, and metastasis; ddr2-deficient (slie) mice show inefficient spontaneous BC metastasis.\",\n      \"method\": \"DDR2 knockdown in MSCs, co-culture assays with BC cells, slie mouse spontaneous metastasis model, phospho-DDR2 Western blotting\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function in multiple systems plus in vivo spontaneous metastasis model\",\n      \"pmids\": [\"28147276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"DDR2 facilitates papillary thyroid carcinoma EMT by activating ERK2 and stabilizing Snail1 protein; ERK2 or Snail1 inhibition abrogates DDR2-induced EMT; DDR2 overexpression decreases E-cadherin and increases vimentin expression.\",\n      \"method\": \"Lentiviral DDR2 overexpression, ERK2/Snail1 inhibition, Western blotting, migration/invasion assays\",\n      \"journal\": \"Oncology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway inhibition epistasis, single lab\",\n      \"pmids\": [\"29250189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DDR1 and DDR2 physically interact (co-immunoprecipitation); co-expression of DDR1 and DDR2 produces higher ERK activation than either alone after collagen I stimulation, but inhibits cell proliferation; DDR1 (not DDR2) mediates cell adhesion to collagen I matrix.\",\n      \"method\": \"Co-immunoprecipitation, HEK293T co-overexpression, ERK/JAK2 activation assays, proliferation and adhesion assays with dominant-negative constructs\",\n      \"journal\": \"Cell adhesion & migration\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP plus functional assays, single lab\",\n      \"pmids\": [\"29616590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DDR2 gain-of-function variants (L610P or Y740C) causing Warburg-Cinotti syndrome lead to increased DDR2 phosphorylation in patient fibroblasts, indicating reduced receptor autoinhibition and ligand-independent kinase activation; dasatinib prevents DDR2 autophosphorylation in these cells.\",\n      \"method\": \"Phosphorylation analysis in patient-derived fibroblasts, dasatinib treatment, analysis of signaling pathway activation\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — patient fibroblasts with functional pharmacological validation, de novo variant confirmed\",\n      \"pmids\": [\"30449416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Coupling of the GVMGFO-containing triple-helical peptide to crosslinked collagen films restores DDR2 binding and activates DDR2 (phosphorylation of Y740) in COS-7 and HEK293 cells, identifying Y740 as a key DDR2 autophosphorylation site relevant to receptor activation.\",\n      \"method\": \"Photoreactive peptide coupling, DDR2 binding assays, Western blotting for pY740, cell-based DDR2 activation assays\",\n      \"journal\": \"Biomaterials\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical reconstitution on engineered surface with cell-based activation readout\",\n      \"pmids\": [\"30099278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"WRG-28, a small molecule targeting the DDR2 extracellular domain, allosterically inhibits DDR2-collagen receptor-ligand interactions and blocks tumor invasion, migration, and metastatic lung colonization, demonstrating that allosteric extracellular inhibition of DDR2 is functionally effective.\",\n      \"method\": \"Small molecule screening, DDR2 binding assays, tumor invasion/migration assays, in vivo lung colonization assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — biochemical characterization of inhibitor mechanism plus multiple in vitro and in vivo functional validations\",\n      \"pmids\": [\"30061414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DDR2 in CAFs controls breast tumor stiffness by reorganizing collagen fibers at the tumor-stromal boundary through regulation of integrin activation; DDR2 influences mechanotransduction by controlling Rap1-mediated Talin1 and Kindlin2 recruitment to activate collagen-binding integrins.\",\n      \"method\": \"DDR2 depletion in mouse/human CAFs, second-harmonic generation microscopy for collagen fiber analysis, atomic force microscopy for stiffness, Rap1/Talin1/Kindlin2 activation assays, in vivo tumor models\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking DDR2 to specific mechanotransduction pathway in vivo\",\n      \"pmids\": [\"31144616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DDR2 depletion in tumors increases CD8+ T cell infiltration and sensitizes tumors to anti-PD-1 immunotherapy across five tumor histologies; dasatinib (DDR2 inhibitor) combined with anti-PD-1 reduces tumor load, identifying DDR2 as a regulator of the immunosuppressive tumor microenvironment.\",\n      \"method\": \"In vivo shRNA screen, isogenic mouse tumor models, CyTOF immune cell profiling, RNA-seq, dasatinib + anti-PD-1 combination treatment\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo functional screen validated across multiple tumor types with immune profiling\",\n      \"pmids\": [\"30801016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"DDR2 in cardiac fibroblasts acts via ERK1/2 MAPK-activated SRF transcription factor to enhance expression of anti-apoptotic cIAP2 (conferring resistance to oxidative injury) and to upregulate Skp2, which degrades the CDK inhibitor p27 to promote G1-S cell cycle transition; collagen type I binding to DDR2 is required for these effects.\",\n      \"method\": \"DDR2 knockdown/overexpression, SRF promoter binding assays, ERK1/2 inhibition, WRG-28 DDR2 inhibitor, flow cytometry, Rb phosphorylation assays\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic/pharmacological tools with promoter binding assays, single lab\",\n      \"pmids\": [\"32412792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDR-mediated matrix resistance (MMDR) to BRAF inhibition in melanoma is mediated by drug-induced linear clustering of phosphorylated DDR1 and DDR2; DDR-dependent MMDR activates a pro-survival NIK/IKKα/NF-κB2 pathway; depletion or pharmacological targeting of DDR overcomes ECM-mediated resistance.\",\n      \"method\": \"DDR1/DDR2 depletion, phospho-DDR imaging, NIK/IKKα/NF-κB2 pathway analysis, xenograft models with imatinib + BRAF inhibitor combination\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway identification with in vitro and in vivo validation\",\n      \"pmids\": [\"34957688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Tyrosine kinase-independent functions of DDR2 in tumor cells support Matrigel invasion and in vivo metastasis; paracrine DDR2 signaling between tumor cells and CAFs also supports invasion and lung colonization; these findings suggest kinase-independent DDR2 activities contribute to metastasis.\",\n      \"method\": \"Kinase-dead DDR2 rescue in tumor cells, conditioned media experiments, in vivo lung colonization assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — kinase-dead rescue with in vivo validation, single lab\",\n      \"pmids\": [\"34477203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"EMT regulators TWIST and SNAIL induce DDR2 expression; DDR2 upregulation in recurrent breast tumor cells activates YAP/TAZ signaling; DDR2 knockdown reduces both clonogenic growth and ferroptosis sensitivity; erastin-induced DDR2 upregulation and phosphorylation occur independently of collagen I.\",\n      \"method\": \"DDR2 knockdown, TWIST/SNAIL overexpression, YAP/TAZ inhibition, ferroptosis (erastin) assays, clonogenic growth assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays linking DDR2 to YAP/TAZ and ferroptosis, single lab\",\n      \"pmids\": [\"33603168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR2 in ovarian cancer CAFs promotes collagen production through arginase activity; DDR2-depleted CAFs show decreased ornithine and polyamine levels leading to reduced collagen production; SNAI1 protein is detected at the arginase-1 promoter and DDR2-depleted CAFs have decreased SNAI1 at this promoter, revealing DDR2 regulates arginase-1 transcription via SNAI1.\",\n      \"method\": \"DDR2 depletion in human/mouse CAFs, arginase activity assays, metabolomics (ornithine/polyamine), ChIP for SNAI1 at arginase-1 promoter, conditioned media tumor invasion assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus metabolomics plus functional rescue assays identifying a new DDR2 metabolic pathway\",\n      \"pmids\": [\"37996700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDR2 in ovarian cancer CAFs promotes tumor cell invasion through regulation of periostin (POSTN) expression via integrin β1 (ITGB1); DDR2-expressing fibroblasts enhance mesothelial cell clearance and tumor cell invasion three-fold; DDR2 regulation of POSTN is mediated through ITGB1.\",\n      \"method\": \"DDR2 and POSTN knockdown in CAFs, co-culture mesothelial clearance assays, in vivo co-injection xenograft models, ITGB1 pathway analysis\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vitro and in vivo assays, single lab\",\n      \"pmids\": [\"35884543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CEBPA-DT lncRNA promotes DDR2 expression by binding hnRNPC, facilitating cytoplasmic translocation of hnRNPC which enhances hnRNPC-DDR2 mRNA interaction; DDR2 then promotes β-catenin nuclear translocation through a DDR2-β-catenin protein interaction, activating Snail1 transcription to drive EMT and HCC metastasis.\",\n      \"method\": \"RNA pull-down, RIP, co-immunoprecipitation for DDR2-β-catenin interaction, immunofluorescence for β-catenin localization, DDR2 inhibitor treatment, subcellular fractionation\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP for DDR2-β-catenin interaction plus functional inhibitor validation, single lab\",\n      \"pmids\": [\"36471363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Nilotinib inhibits DDR2 in human valvular interstitial cells (VICs); DDR2 inhibition or selective DDR2 targeting in VICs induces osteogenic activation and calcification; increasing DDR2 ligand (collagen) blunts this osteogenic response, establishing DDR2 as a suppressor of VIC calcification.\",\n      \"method\": \"DDR2 selective inhibition in human VICs, osteogenic/calcification assays, transcriptomic target identification, collagen rescue experiments\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological DDR2 inhibition with ligand rescue, single lab\",\n      \"pmids\": [\"35751904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DDR2 in ovarian cancer omental fibroblasts regulates glycolysis through an AKT/SNAI1 axis, suppressing fructose-1,6-bisphosphatase and increasing hexokinase activity; DDR2 inhibition decreases protein synthesis and secretion, including LOXL2; adding back LOXL2 to DDR2-deficient fibroblasts rescues tumor cell invasion.\",\n      \"method\": \"DDR2 depletion, glycolytic enzyme activity assays, secretome proteomics, LOXL2 rescue experiments, in vivo peritoneal metastasis model\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — enzyme activity assays plus secretome proteomics with functional rescue, single lab\",\n      \"pmids\": [\"37527178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DDR2 in gastric cancer promotes stemness by mediating SOX2 expression; DDR2 governs EMT programming through recruiting an NFATc1-SOX2 complex to the Snai1 promoter; DDR2-mTOR-SOX2 axis controls cancer stem cell autophagy and DNA damage responses; miR-199a-3p directly targets DDR2.\",\n      \"method\": \"Luciferase reporter assays for miR-199a-3p/DDR2 targeting, DDR2 knockdown/overexpression, NFATc1-SOX2 complex ChIP at Snai1 promoter, orthotopic xenograft peritoneal dissemination model\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus functional assays plus in vivo model, single lab\",\n      \"pmids\": [\"36813149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DDR2 induces STAT3 phosphorylation and nuclear translocation; activated STAT3 enhances DDR2 expression, forming a positive feedback loop in oxaliplatin-resistant HCC; STAT3 directly enhances transcription of PD-L1 and CCL20 (recruiting PMN-MDSCs) via dual luciferase reporter assays, establishing a DDR2/STAT3/PD-L1/CCL20 immunosuppressive axis.\",\n      \"method\": \"DDR2/STAT3 knockdown, phospho-STAT3 analysis, luciferase reporter assays for PD-L1 and CCL20 promoters, MDSC transwell migration assays, in vivo tumor models\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — luciferase reporters plus functional immune assays, single lab\",\n      \"pmids\": [\"38969205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"DDR1 and DDR2 overexpression in human smooth muscle cells reduces collagen expression and induces MMP-1 at mRNA and protein levels; DDR2 (but not DDR1) specifically enhances MMP-2 activation and increases collagen and elastin degradation, demonstrating paralog-specific ECM remodeling functions.\",\n      \"method\": \"Retroviral overexpression of DDR1 and DDR2 in human SMCs on polymerized collagen gels, MMP-1/MMP-2 RT-PCR and protein assays, collagen/elastin degradation assays\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — side-by-side DDR1 vs DDR2 comparison with multiple functional readouts, single lab\",\n      \"pmids\": [\"15111304\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DDR2 is a receptor tyrosine kinase activated by native triple-helical collagens (types I, II, III, X) via its discoidin domain (binding site: GVMGFO motif recognized by three surface loops), which triggers slow autophosphorylation (including Y740) requiring Src for maximal activation; downstream signaling proceeds through Src-Shc, ERK2 (which directly phosphorylates and stabilizes SNAIL1 to drive EMT and metastasis), p38 MAPK (activating Runx2 for osteoblast differentiation), SHP-2, JAK2, NF-κB, STAT3, YAP/TAZ, and mTOR pathways; DDR2 also forms complexes with Nrp1-PlexinA1 to suppress osteoclastogenesis, physically interacts with β-catenin to promote its nuclear translocation, and controls collagen fibrillogenesis through its extracellular domain independently of kinase activity; gain-of-function mutations cause squamous cell lung cancer and Warburg-Cinotti syndrome, while loss-of-function mutations (causing ER retention or collagen-binding defects) underlie SMED-SL and dwarfism.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"DDR2 is a collagen-activated receptor tyrosine kinase that transduces extracellular matrix signals into intracellular programs governing cell proliferation, differentiation, migration, and matrix remodeling. Its extracellular discoidin domain binds fibrillar collagens (I, II, III, X) through three surface loops recognizing a minimal GVMGFO motif in triple-helical conformation, and the intracellular JM2 region mediates receptor dimerization required for autophosphorylation and downstream signaling through ERK1/2, p38 MAPK, SHP-2, SRC, and STAT3 cascades [PMID:12611880, PMID:18201965, PMID:24740739, PMID:23822953]. DDR2 kinase activity drives Runx2-dependent osteoblast differentiation, SNAIL1 stabilization promoting EMT, MMP expression in hepatic stellate cells, and integrin mechanotransduction via Rap1/Talin1/Kindlin2 in cancer-associated fibroblasts controlling tumor stiffness and metastasis [PMID:20734453, PMID:26362312, PMID:11696582, PMID:31144616]. DDR2 also has kinase-independent functions: its extracellular domain inhibits collagen fibrillogenesis, and it supports cell spreading and invasion even when kinase-dead [PMID:18996394, PMID:34477203]. Loss-of-function mutations cause spondylo-meta-epiphyseal dysplasia short limb–hand type (SMED-SL) through ER retention or collagen-binding deficiency, while gain-of-function variants cause Warburg-Cinotti syndrome with ligand-independent receptor activation [PMID:20223752, PMID:30449416].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that DDR2 kinase activity is functionally required: DDR2 knockout mice exhibited dwarfism from reduced chondrocyte proliferation, and kinase-dead DDR2 failed to rescue fibroblast proliferation, proving the kinase domain is essential for DDR2's mitogenic role.\",\n      \"evidence\": \"DDR2 knockout mice with kinase-dead rescue experiments and fibroblast proliferation assays\",\n      \"pmids\": [\"11375938\", \"11696582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Downstream signaling cascade not yet identified at this stage\",\n        \"Whether kinase-independent functions exist was unaddressed\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defining the collagen-binding mechanism: the discoidin domain was shown to be sufficient for high-affinity collagen I binding, with three surface loops constituting the recognition site, establishing the structural basis for DDR2 ligand recognition.\",\n      \"evidence\": \"Recombinant ECD production, solid-phase binding assays, loop-swap mutagenesis\",\n      \"pmids\": [\"12611880\", \"15544808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Minimal collagen motif not yet identified\",\n        \"No crystal structure of the DDR2-collagen complex\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying the minimal collagen recognition motif: GVMGFO in triple-helical conformation was shown to be necessary and sufficient for DDR2 binding and activation, resolving what collagen feature DDR2 senses.\",\n      \"evidence\": \"Collagen Toolkit peptide screening with truncated/alanine-substituted peptides, NMR modeling\",\n      \"pmids\": [\"18201965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Atomic-resolution structure of DDR2 discoidin domain bound to GVMGFO not determined\",\n        \"Whether post-translational collagen modifications modulate binding was unknown\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Discovering kinase-independent functions: the DDR2 extracellular domain—whether membrane-anchored kinase-dead or secreted—inhibited collagen fibrillogenesis, revealing that DDR2 shapes the matrix independently of its catalytic activity.\",\n      \"evidence\": \"Stable cell lines expressing kinase-dead or soluble DDR2 ECD, TEM, hydroxyproline assays\",\n      \"pmids\": [\"18996394\", \"19900459\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular mechanism by which ECD alters fiber assembly not defined\",\n        \"Physiological relevance of shed ECD not tested in vivo\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connecting DDR2 to osteoblast transcriptional programs and disease: DDR2 was shown to activate Runx2 via ERK and p38 MAPK for osteoblast differentiation, and SMED-SL mutations were mechanistically classified into ER-retained and collagen-binding-deficient categories, linking DDR2 loss-of-function to a human skeletal dysplasia.\",\n      \"evidence\": \"Runx2 phosphorylation mutant rescue, ATF4/C/EBPβ promoter analysis, subcellular localization and activation assays of SMED-SL mutants\",\n      \"pmids\": [\"20734453\", \"20564243\", \"20223752\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether ERK vs p38 arms are redundant or context-specific was unclear\",\n        \"No in vivo rescue of SMED-SL phenotype attempted\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Linking DDR2 to EMT: collagen-activated DDR2 was shown to stabilize SNAIL1 via ERK-mediated phosphorylation, promoting EMT, invasion, and MMP upregulation in cancer cells, establishing DDR2 as a collagen-sensing driver of epithelial plasticity.\",\n      \"evidence\": \"Cycloheximide chase for SNAIL1 half-life, ERK inhibition, DDR2 overexpression/knockdown in HCC cells\",\n      \"pmids\": [\"26362312\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct phosphorylation of SNAIL1 by ERK not demonstrated with purified components\",\n        \"In vivo EMT contribution of DDR2 not tested in this study\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Mapping downstream phosphosignaling and identifying pharmacological vulnerabilities: quantitative phosphoproteomics identified SHP-2 as a DDR2-kinase-dependent substrate, and DDR2 lung cancer mutants showed differential signaling, while dasatinib resistance was traced to a DDR2 gatekeeper mutation (T654I) or NF1-loss-mediated ERK bypass.\",\n      \"evidence\": \"7-timepoint quantitative phosphoproteomics, DDR2 mutant panel, exome sequencing of resistant lines\",\n      \"pmids\": [\"23822953\", \"24296828\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether SHP-2 is a direct DDR2 substrate or adapter-mediated was unresolved\",\n        \"Clinical relevance of resistance mechanisms not validated in patients\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defining the dimerization mechanism: the intracellular JM2 region was identified as the DDR2 dimerization interface required for efficient collagen binding and receptor activation, with a JM2-derived dominant-negative blocking MMP-dependent invasion.\",\n      \"evidence\": \"Dimerization assays, collagen-binding assays, dominant-negative JM2 overexpression with colony formation and invasion readouts\",\n      \"pmids\": [\"24740739\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural basis of JM2-mediated dimerization not resolved\",\n        \"Stoichiometry of active receptor complex unknown\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Revealing DDR2's role in bone homeostasis beyond osteoblasts: DDR2 was shown to suppress osteoclastogenesis by forming a DDR2–Nrp1–PlexinA1 complex that sequesters PlexinA1 from TREM2/DAP12, identifying a non-canonical receptor complex function.\",\n      \"evidence\": \"Reciprocal Co-IP, epistasis with Nrp1 rescue/knockdown, osteoclast differentiation assays, in vivo adenoviral delivery\",\n      \"pmids\": [\"25805889\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether DDR2 kinase activity is required for complex formation not tested\",\n        \"In vivo bone mass phenotype of DDR2-Nrp1 double manipulation not assessed\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Gain-of-function DDR2 variants were shown to cause Warburg-Cinotti syndrome through ligand-independent kinase activation, establishing DDR2 as a bidirectional disease gene where both loss and gain of function cause distinct Mendelian disorders.\",\n      \"evidence\": \"Patient fibroblast phosphorylation assays, dasatinib rescue, family-based genetics\",\n      \"pmids\": [\"30449416\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural mechanism of autoinhibition relief not determined\",\n        \"Only two variants characterized; broader allelic series needed\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrating DDR2 as a stromal mechanotransducer in cancer: DDR2 in cancer-associated fibroblasts was shown to control tumor stiffness and metastasis by activating integrin signaling via Rap1-mediated Talin1 and Kindlin2 recruitment, establishing a DDR2–integrin crosstalk axis in the tumor microenvironment.\",\n      \"evidence\": \"DDR2 KO/KD in CAFs, mouse breast tumor models, integrin activation and mechanotransduction assays\",\n      \"pmids\": [\"31144616\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether DDR2-integrin crosstalk operates through direct protein interaction or signaling intermediates is unclear\",\n        \"Relative contribution of DDR2 in tumor cells vs CAFs to metastasis not fully deconvolved\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Expanding DDR2's stromal functions to metabolic control: DDR2 in CAFs was found to regulate collagen production through SNAI1-dependent arginase-1 transcription controlling polyamine biosynthesis, and to reprogram glycolysis through AKT/SNAI1 suppression of fructose-1,6-bisphosphatase, linking DDR2 to metabolic reprogramming of the tumor stroma.\",\n      \"evidence\": \"ChIP at arginase-1 promoter, metabolomics, glycolytic enzyme assays, polyamine/LOXL2 rescue experiments in DDR2-depleted CAFs\",\n      \"pmids\": [\"37996700\", \"37527178\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether metabolic reprogramming requires DDR2 kinase activity or is kinase-independent not tested\",\n        \"Connection between polyamine pathway and collagen deposition remains correlative\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying a DDR2–STAT3 positive feedback loop driving immune evasion: DDR2 induces STAT3 phosphorylation, which transcriptionally upregulates DDR2, PD-L1, and CCL20, mediating MDSC recruitment and drug resistance in hepatocellular carcinoma.\",\n      \"evidence\": \"Dual luciferase reporter assays for PD-L1 and CCL20 promoters, STAT3 nuclear translocation imaging, MDSC transwell migration\",\n      \"pmids\": [\"38969205\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether DDR2 directly phosphorylates STAT3 or acts through JAK intermediates not determined\",\n        \"In vivo immune evasion phenotype not validated with DDR2-specific genetic models\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic structure of DDR2 in complex with collagen, the mechanism by which DDR2 coordinates kinase-dependent and kinase-independent outputs in the same cell, and how DDR2 signaling is differentially deployed in epithelial cells versus stromal fibroblasts to produce context-specific outcomes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of full-length DDR2 or DDR2-collagen complex\",\n        \"Kinase-dependent vs kinase-independent signaling branches not systematically dissected\",\n        \"Cell-type-specific DDR2 interactome not comprehensively mapped\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 5, 6, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11, 12, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 8, 33]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 6, 7, 9, 15, 19, 26, 30]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [12, 13, 28]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 6, 7, 11]}\n    ],\n    \"complexes\": [\n      \"DDR2-Nrp1-PlexinA1\"\n    ],\n    \"partners\": [\n      \"SRC\",\n      \"SHP2\",\n      \"NRP1\",\n      \"PLXNA1\",\n      \"DDR1\",\n      \"SNAI1\",\n      \"RUNX2\",\n      \"CTNNB1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"DDR2 is a collagen-activated receptor tyrosine kinase that transduces extracellular matrix signals into programs governing cell proliferation, differentiation, ECM remodeling, epithelial-mesenchymal transition, and immune evasion. Native triple-helical collagens (types I, II, III, X) bind the DDR2 discoidin domain—specifically recognizing the GVMGFO motif via an amphiphilic pocket formed by three surface loops—triggering slow autophosphorylation (including Y740) that requires Src for maximal activation, with downstream signaling proceeding through Src-Shc, ERK1/2 (which directly phosphorylates and stabilizes SNAIL1 to drive EMT and metastasis), p38 MAPK–Runx2, JAK2, NF-κB, STAT3, YAP/TAZ, and mTOR pathways [PMID:9659899, PMID:11884411, PMID:20004161, PMID:23644467, PMID:20564243]. Beyond kinase-dependent signaling, the DDR2 extracellular domain inhibits collagen fibrillogenesis independently of catalytic activity, and DDR2 forms a complex with Nrp1–PlexinA1 to suppress osteoclastogenesis, while in cancer-associated fibroblasts it controls collagen fiber organization, integrin mechanotransduction via Rap1–Talin1–Kindlin2, and metabolic reprogramming through an AKT/SNAI1–glycolysis axis [PMID:18996394, PMID:25805889, PMID:31144616, PMID:37527178]. Loss-of-function DDR2 mutations—causing either ER retention of misfolded kinase-domain variants or collagen-binding defects in the discoidin domain—underlie spondylo-meta-epiphyseal dysplasia short limb–hand type (SMED-SL), whereas gain-of-function mutations drive squamous cell lung cancer and Warburg-Cinotti syndrome [PMID:19110212, PMID:20223752, PMID:22328973, PMID:30449416].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"The fundamental question of what activates DDR2 was answered: native triple-helical collagen, not soluble growth factors, triggers DDR2 tyrosine kinase activity and upregulates MMP-1, establishing DDR2 as a collagen receptor that connects ECM composition to cellular gene expression.\",\n      \"evidence\": \"Receptor-ligand binding and kinase activation assays in cell lines\",\n      \"pmids\": [\"9659899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling intermediates uncharacterized\", \"Collagen-type specificity undefined\", \"Structural basis of collagen recognition unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The physiological requirement for DDR2 kinase activity was established: DDR2 knockout mice exhibit dwarfism from reduced chondrocyte proliferation, and kinase-dead DDR2 fails to rescue fibroblast proliferation defects, demonstrating that DDR2 catalytic activity is essential for skeletal growth.\",\n      \"evidence\": \"DDR2 knockout mouse phenotyping plus kinase-dead rescue in fibroblasts; corroborated by constitutively active DDR2 driving stellate cell proliferation and MMP-2 upregulation\",\n      \"pmids\": [\"11375938\", \"11696582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No identification of DDR2 substrates or immediate downstream effectors\", \"Mechanism of DDR2-dependent chondrocyte proliferation not defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The first signaling intermediates downstream of DDR2 were identified: Src kinase is required for maximal DDR2 phosphorylation and associates with DDR2, while the adaptor Shc bridges DDR2 to downstream pathways including MMP-2 transactivation.\",\n      \"evidence\": \"Co-immunoprecipitation, dominant-negative Src, and MMP-2 promoter reporter assays\",\n      \"pmids\": [\"11884411\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Src directly phosphorylates DDR2 or acts via intermediates was unclear\", \"Full spectrum of DDR2-interacting adaptors unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The collagen-binding determinant was mapped: three surface loops of the discoidin domain form the collagen recognition site, and the GVMGFO motif within triple-helical collagen was later identified as the minimal binding sequence, ultimately resolved at atomic resolution by crystallography.\",\n      \"evidence\": \"Loop-swap mutagenesis and solid-phase binding (2003); Toolkit peptide screening (2008); X-ray crystal structure of DDR2 DS domain–collagen peptide complex (2009)\",\n      \"pmids\": [\"12611880\", \"18201965\", \"20004161\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ligand binding in the extracellular domain is transmitted across the membrane to the kinase domain remains structurally unresolved\", \"Full-length DDR2 structure unavailable\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"A kinase-independent function of DDR2 was discovered: the extracellular domain alone—whether membrane-tethered kinase-dead or as a shed soluble form—inhibits collagen fibrillogenesis, revealing that DDR2 physically modulates ECM architecture independently of catalytic signaling.\",\n      \"evidence\": \"Kinase-dead DDR2 and soluble ECD expression in osteoblasts with TEM, fluorescence microscopy, and hydroxyproline assays\",\n      \"pmids\": [\"18996394\", \"19900459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of fibrillogenesis inhibition (steric blockade vs. active remodeling) not defined\", \"In vivo significance of shed DDR2 ECD unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The genetic basis of SMED-SL was established: kinase-domain mutations (T713I, I726R, R752C) cause ER retention and loss of collagen-induced activation, while the E113K extracellular mutation permits normal trafficking but abolishes collagen binding, demonstrating two distinct loss-of-function mechanisms underlying the same skeletal dysplasia.\",\n      \"evidence\": \"Expression of mutant DDR2 in cell lines with confocal localization, deglycosylation, and collagen activation assays across multiple studies\",\n      \"pmids\": [\"19110212\", \"20223752\", \"24725993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ER-retained mutants can be pharmacologically rescued is untested\", \"Genotype-phenotype severity correlations not established\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"DDR2 was positioned as a driver of osteoblast differentiation through two parallel MAPK cascades: ATF4/C/EBPβ transcriptionally upregulates DDR2, which then activates p38 MAPK–Runx2 and ERK–Runx2 to promote osteogenic gene expression.\",\n      \"evidence\": \"DDR2 promoter analysis, p38/ERK inhibition, Runx2 phosphorylation assays, constitutively active vs. kinase-dead DDR2 in preosteoblasts\",\n      \"pmids\": [\"20564243\", \"20734453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct DDR2 substrates linking to p38 vs. ERK activation unidentified\", \"Relative contribution of p38 vs. ERK to in vivo bone formation unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"DDR2 was identified as an oncogene in squamous cell lung cancer: somatic gain-of-function mutations (L63V, G505S) cause cellular transformation with DDR2 kinase dependency, as shown by selective killing with DDR2 RNAi and dasatinib.\",\n      \"evidence\": \"Sequencing of lung SCC tumors, RNAi, dasatinib treatment, xenograft tumor models\",\n      \"pmids\": [\"22328973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism by which specific mutations activate DDR2 kinase undefined\", \"Clinical response to DDR2-targeted therapy not validated in patients\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A central EMT-driving pathway was delineated: DDR2 activates Src-dependent ERK2, which directly phosphorylates SNAIL1 to prevent its ubiquitylation and promote nuclear accumulation, driving breast cancer invasion and metastasis in vivo—a mechanism subsequently confirmed in HCC, thyroid, and other cancers.\",\n      \"evidence\": \"In vitro ERK2 kinase assays on SNAIL1, ubiquitylation/cycloheximide chase assays, Src inhibition, mouse metastasis models; extended to HCC and thyroid carcinoma\",\n      \"pmids\": [\"23644467\", \"26362312\", \"29250189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DDR2-ERK2-SNAIL1 operates in normal tissue homeostasis unclear\", \"Phosphosite(s) on SNAIL1 mediating stabilization not fully mapped across cancer types\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Quantitative phosphoproteomics expanded the DDR2 signaling network: SHP-2 was identified as a DDR2 kinase-activity-dependent substrate, with NCK1, LYN, SHIP-2, and PIK3C2A as additional signaling nodes, and dasatinib resistance was shown to arise via DDR2 gatekeeper mutations or NF1-loss-driven RAS-ERK bypass.\",\n      \"evidence\": \"Quantitative mass spectrometry phosphoproteomics across DDR2 mutants; targeted exome sequencing of resistant lines\",\n      \"pmids\": [\"23822953\", \"24296828\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs. indirect phosphorylation of SHP-2 by DDR2 not resolved\", \"In vivo relevance of NF1-loss bypass to clinical resistance unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"DDR2 was found to suppress osteoclastogenesis through a non-canonical mechanism: it forms a complex with Nrp1 and PlexinA1, blocking PlexinA1–TREM2/DAP12 interaction and osteoclast stimulation, with in vivo rescue of ovariectomy-induced bone loss.\",\n      \"evidence\": \"Reciprocal Co-IP for DDR2-Nrp1-PlexinA1 complex, RNAi rescue, adenoviral DDR2 delivery in ovariectomized mice\",\n      \"pmids\": [\"25805889\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DDR2 kinase activity is required for Nrp1-PlexinA1 complex formation unclear\", \"Stoichiometry of the ternary complex undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Cell-type-specific genetic deletion revealed dual roles for DDR2 in cancer: in tumor epithelial cells DDR2 drives collective invasion, while in cancer-associated fibroblasts it controls ECM production and collagen fiber alignment, both being required for metastasis.\",\n      \"evidence\": \"Cell-type-specific DDR2 deletion, tumor organoid invasion assays, second-harmonic generation microscopy, mouse metastasis models\",\n      \"pmids\": [\"27264173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of DDR2-dependent collective invasion (leader-cell specification?) unresolved\", \"Relative contribution of tumor vs. stromal DDR2 to different metastatic steps not quantified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Gain-of-function DDR2 variants (L610P, Y740C) were shown to cause Warburg-Cinotti syndrome through ligand-independent kinase activation due to reduced autoinhibition, pharmacologically reversible by dasatinib.\",\n      \"evidence\": \"Phospho-DDR2 analysis in patient-derived fibroblasts with dasatinib treatment\",\n      \"pmids\": [\"30449416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of reduced autoinhibition not determined\", \"Long-term clinical efficacy of dasatinib in Warburg-Cinotti syndrome unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"DDR2 was established as a regulator of tumor mechanotransduction and immune evasion: in CAFs it controls integrin activation through Rap1–Talin1–Kindlin2 to set tumor stiffness, while DDR2 depletion in tumors increases CD8+ T cell infiltration and sensitizes to anti-PD-1 therapy.\",\n      \"evidence\": \"AFM stiffness measurements, Rap1/Talin1/Kindlin2 activation assays in CAFs; in vivo shRNA screen across five tumor types with CyTOF immune profiling and dasatinib + anti-PD-1 combination\",\n      \"pmids\": [\"31144616\", \"30801016\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DDR2 restricts T cell infiltration mechanistically (ECM barrier vs. direct immune signaling) not resolved\", \"Rap1 activation mechanism by DDR2 not fully elucidated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"DDR2's metabolic and transcriptional control in the stroma was deepened: in ovarian cancer CAFs, DDR2 regulates arginase-1 transcription via SNAI1, controlling polyamine-dependent collagen production, and modulates glycolysis through an AKT/SNAI1 axis to sustain protein secretion including LOXL2.\",\n      \"evidence\": \"ChIP for SNAI1 at arginase-1 promoter, metabolomics, glycolytic enzyme assays, secretome proteomics with LOXL2 rescue\",\n      \"pmids\": [\"37996700\", \"37527178\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether DDR2-dependent metabolic reprogramming is collagen-ligand-dependent or constitutive is unclear\", \"Generalizability of arginase/polyamine axis beyond ovarian CAFs not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A DDR2–STAT3 positive feedback loop was identified in chemoresistant HCC, where STAT3 drives transcription of PD-L1 and CCL20 to recruit immunosuppressive PMN-MDSCs, mechanistically linking DDR2 to adaptive immune evasion in the tumor microenvironment.\",\n      \"evidence\": \"DDR2/STAT3 knockdown, dual luciferase reporters for PD-L1/CCL20 promoters, MDSC migration assays, in vivo tumor models\",\n      \"pmids\": [\"38969205\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this DDR2-STAT3 axis operates in non-hepatic cancers untested\", \"Direct DDR2 substrate leading to STAT3 phosphorylation unidentified\", \"Clinical relevance of DDR2-dependent immune evasion in patients unconfirmed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions remain: the structural mechanism by which collagen binding in the extracellular discoidin domain is transmitted across the membrane to activate the intracellular kinase; a full-length DDR2 structure; the identity of direct DDR2 kinase substrates beyond autophosphorylation; and whether kinase-independent and kinase-dependent DDR2 functions can be therapeutically dissected.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length DDR2 structure exists\", \"Direct kinase substrates remain largely unidentified\", \"Transmembrane activation mechanism unresolved\", \"Therapeutic window between kinase-dependent and kinase-independent functions unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 8, 16, 19, 20, 37]},\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [0, 4, 7, 11]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 5, 6, 7, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 4, 23, 30, 38]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [8, 13, 25]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [9, 10, 40]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 14, 15, 17, 19, 20, 27, 29, 42, 45, 52]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [9, 10, 32, 40, 46]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 14, 15, 27]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [16, 22, 37, 43, 52]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [41, 52]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [40, 47]}\n    ],\n    \"complexes\": [\n      \"DDR2-Nrp1-PlexinA1\"\n    ],\n    \"partners\": [\n      \"SRC\",\n      \"SHC1\",\n      \"NRP1\",\n      \"PLXNA1\",\n      \"CTNNB1\",\n      \"SHP2\",\n      \"DDR1\",\n      \"SNAI1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}