{"gene":"CD109","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2002,"finding":"CD109 is a GPI-anchored glycoprotein and novel member of the alpha2-macroglobulin/C3,C4,C5 family of thioester-containing proteins; native CD109 contains an intact thioester bond, is predicted to be activated by proteolytic cleavage, and can then mediate covalent binding to adjacent molecules or cells via its thioester with complement-like chemical reactivity.","method":"cDNA cloning, sequence analysis, biochemical demonstration of intact thioester in native CD109","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — biochemical demonstration of thioester in native protein, sequence analysis, foundational paper with 154 citations","pmids":["11861284"],"is_preprint":false},{"year":2002,"finding":"The Gov platelet alloantigen system (HPA-15) is defined by a single nucleotide polymorphism (A2108C) in CD109 resulting in a Tyr703Ser amino acid substitution; transfection of CHO cells with each variant confirmed allele-specific recognition by Gov antisera.","method":"RT-PCR, allele-specific PCR, real-time PCR, CHO cell transfection with CD109 cDNA variants and recognition by allele-specific antisera","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — functional validation in transfected cells plus molecular genotyping; 69 citations","pmids":["11861285"],"is_preprint":false},{"year":2006,"finding":"CD109 is the molecular identity of the 150 kDa GPI-anchored TGF-β1 binding protein (r150) in keratinocytes; loss- and gain-of-function studies establish CD109 as a component of the TGF-β receptor system and a negative modulator of TGF-β responses, acting independently of ligand sequestration, possibly by direct modulation of receptor activity.","method":"Affinity purification, microsequencing, biochemical thioester assay, loss-of-function (GPI-anchor-deficient keratinocytes) and gain-of-function studies","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical identification plus functional loss/gain-of-function; 121 citations, replicated in subsequent work","pmids":["16754747"],"is_preprint":false},{"year":2010,"finding":"CD109 is processed by the Golgi protease furin at a tetra-arginine cleavage motif (RRRR at aa 1270–1273), converting the 205 kDa precursor into 180 kDa and 25 kDa fragments. The processed 180/25 kDa complex associates with the type I TGF-β receptor and is required for negative regulation of TGF-β signaling and cell growth suppression; an R1273S mutant that cannot be cleaved fails to associate with TGFBR1 or inhibit TGF-β signaling.","method":"Site-directed mutagenesis of furin cleavage site (R1273S), co-immunoprecipitation with TGFBR1, western blotting, cell growth assays","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with co-IP and functional assays; 67 citations","pmids":["20101215"],"is_preprint":false},{"year":2011,"finding":"CD109 associates with caveolin-1 and promotes localization of TGF-β receptors into the caveolar compartment in the presence of ligand, enhancing TGF-β receptor internalization via the caveolae pathway and facilitating TGF-β receptor degradation, thereby inhibiting TGF-β signaling.","method":"Co-immunoprecipitation of CD109 with caveolin-1, receptor internalization assays, caveolae fractionation, TGF-β receptor degradation assays","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP with caveolin-1, receptor trafficking and degradation assays; 119 citations","pmids":["21295082"],"is_preprint":false},{"year":2012,"finding":"CD109 promotes SMAD7/Smurf2-mediated ubiquitin-dependent degradation of TGFBR1 in a ligand-dependent manner; CD109 regulates the localization and association of SMAD7/Smurf2 with TGFBR1, and CD109's inhibitory effect on TGF-β signaling requires SMAD7 expression and Smurf2 ubiquitin ligase activity.","method":"siRNA knockdown of SMAD7, dominant-negative Smurf2 (ubiquitin ligase-dead mutant), co-immunoprecipitation, western blotting, TGF-β response assays","journal":"Journal of cellular biochemistry","confidence":"High","confidence_rationale":"Tier 2 — epistasis via dominant-negative and siRNA, co-IP, multiple functional readouts; 78 citations","pmids":["21898545"],"is_preprint":false},{"year":2011,"finding":"Release of CD109 from the keratinocyte cell surface (soluble/shed CD109) downregulates TGF-β signaling and TGF-β receptor expression and increases phospho-STAT3 levels, total STAT3, Bcl-2, and cell growth/survival, indicating that soluble CD109 can activate STAT3 signaling while inhibiting TGF-β signaling.","method":"Addition of recombinant CD109 protein to keratinocytes, phospho-STAT3 western blotting, TGF-β receptor quantification, cell proliferation/survival assays","journal":"Experimental dermatology","confidence":"Medium","confidence_rationale":"Tier 2 — recombinant protein addition with pathway readouts, single lab","pmids":["21539622"],"is_preprint":false},{"year":2012,"finding":"CD109-deficient mice develop epidermal hyperplasia, kinked hair shafts, ectatic hair follicles, and increased sebaceous gland hyperplasia; this is associated with elevated STAT3 phosphorylation (not altered Smad2 phosphorylation) in the epidermis, indicating that CD109 regulates keratinocyte differentiation in vivo primarily via STAT3 rather than TGF-β/Smad signaling.","method":"CD109 knockout mouse generation, histology, immunohistochemistry for phospho-Smad2 and phospho-STAT3","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular and molecular phenotype; 33 citations","pmids":["22846721"],"is_preprint":false},{"year":2013,"finding":"Transgenic mice overexpressing CD109 in the epidermis show decreased macrophage/neutrophil recruitment, reduced granulation tissue, decreased Smad2/3 phosphorylation, reduced pro-inflammatory cytokines (IL-1α, MCP-1), and decreased ECM components during wound healing, and improved dermal architecture in incisional wounds, establishing CD109 as an in vivo inhibitor of TGF-β/Smad-mediated wound inflammation and fibrosis.","method":"CD109 transgenic mice, excisional and incisional wound models, immunohistochemistry, western blotting for phospho-Smad2/3, cytokine quantification","journal":"Wound repair and regeneration","confidence":"High","confidence_rationale":"Tier 2 — clean transgenic model with multiple orthogonal molecular and histological readouts","pmids":["23438099"],"is_preprint":false},{"year":2013,"finding":"CD109 overexpression in the epidermis of transgenic mice protects against bleomycin-induced skin fibrosis, evidenced by decreased dermal thickness, collagen crosslinking, fibronectin content, and phospho-Smad2/3 levels, demonstrating that CD109 inhibits TGF-β/Smad-mediated fibrotic responses in vivo.","method":"CD109 transgenic mice, bleomycin-induced scleroderma model, Masson's trichrome/picrosirius red staining, western blotting for phospho-Smad2/3","journal":"Arthritis and rheumatism","confidence":"High","confidence_rationale":"Tier 2 — clean transgenic gain-of-function in disease model with multiple readouts","pmids":["23436317"],"is_preprint":false},{"year":2013,"finding":"CD109 plays a role in osteoclastogenesis: CD109 is upregulated >17-fold during RANKL-induced osteoclast differentiation from RAW264.7 macrophages and from primary murine monocytes; stable knockdown of CD109 reduces the formation of large multinucleated osteoclasts.","method":"Microarray analysis, RT-qPCR, western blotting, stable CD109 knockdown cell lines, osteoclast fusion assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 — knockdown with defined functional phenotype; single lab, 22 citations","pmids":["23593435"],"is_preprint":false},{"year":2015,"finding":"Soluble CD109 (sCD109) binds TGF-β with high affinity (slow dissociation kinetics by surface plasmon resonance), inhibits TGF-β binding to its receptors, and antagonizes TGF-β-induced Smad2/3 phosphorylation, transcription, and cell migration.","method":"Surface plasmon resonance, radioligand binding competition assays, affinity labelling, Smad2/3 phosphorylation assays, cell migration assays","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro SPR binding assay plus cell-based functional validation with multiple orthogonal methods","pmids":["26621871"],"is_preprint":false},{"year":2015,"finding":"Cell surface CD109 interacts with EGFR in glioblastoma cells (SK-MG-1), and this interaction enhances EGF signaling, cell migration, and invasion, while secreted N-terminal CD109 fragment selectively inhibits TGF-β1 signaling but not EGF signaling.","method":"Co-immunoprecipitation of CD109 with EGFR, conditioned medium transfer experiments, cell migration/invasion assays, western blotting for EGF and TGF-β1 signaling","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP with functional readouts; single lab","pmids":["25724945"],"is_preprint":false},{"year":2015,"finding":"CD109 is a component of exosomes secreted from HEK293 cells; the C-terminal region of CD109 is required for its sorting into exosomes, as a truncated CD109 lacking the C-terminal region is not found in the exosomal fraction.","method":"Immunoprecipitation with anti-FLAG affinity gel, mass spectrometry, western blotting, immuno-electron microscopy of exosome fractions","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — immuno-EM and biochemical fractionation with domain deletion mutant","pmids":["26707640"],"is_preprint":false},{"year":2016,"finding":"In transgenic mice overexpressing CD109 in the epidermis, CD109 differentially regulates TGF-β signaling: it enhances ALK1-Smad1/5 signaling while decreasing ALK5-Smad2/3 signaling, and reduces TGF-β expression and ECM production; CD109 and ALK1 co-localize in mouse keratinocytes.","method":"CD109 transgenic mouse model, immunohistochemistry, co-localization of CD109 and ALK1, western blotting for phospho-Smad1/5 and phospho-Smad2/3, fibroblast conditioned medium experiments","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 — transgenic model with molecular pathway differentiation; single lab","pmids":["27866969"],"is_preprint":false},{"year":2017,"finding":"CD109 drives lung cancer metastasis through activation of JAK-STAT3 signaling; pharmacological targeting of JAK-STAT3 blocks CD109-driven metastasis in a mouse model of lung adenocarcinoma.","method":"In vivo tumor barcoding mouse model, in vivo screening, JAK inhibitor pharmacological blockade, genomic analysis","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic screen with pharmacological validation; 132 citations","pmids":["28191885"],"is_preprint":false},{"year":2018,"finding":"Upon ER stress, GRP78 translocates to the cell surface where it binds to CD109, and the GRP78-CD109 complex promotes routing of TGF-β receptor to caveolae, disrupting TGF-β receptor binding to and activation of Smad2, thereby blocking TGF-β tumor-suppressor signaling.","method":"Cell surface co-immunoprecipitation of GRP78 with CD109, receptor trafficking assays, Smad2 phosphorylation assays, IRE1α-SRC-ASAP1 pathway analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — co-IP plus mechanistic signaling cascade with multiple pathway components validated; 110 citations","pmids":["29654145"],"is_preprint":false},{"year":2019,"finding":"CD109 regulates skin homeostasis and restrains IL-17-producing γδ T (γδ17) cell activation in a cell-extrinsic manner by fortifying skin barrier integrity; CD109-deficient mice show spontaneous epidermal hyperplasia, accumulation of dermal γδ17 cells, and enhanced susceptibility to psoriasiform inflammation dependent on IL-23 and skin microbiota.","method":"CD109 knockout mice, transient skin microbiota depletion, IL-23 blockade, γδ T cell flow cytometry, skin barrier assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — clean KO with mechanistic epistasis (microbiota, IL-23) and multiple cellular readouts","pmids":["31597099"],"is_preprint":false},{"year":2019,"finding":"CD109 CRISPR/Cas9 knockout in SCC cells represses epithelial traits and promotes EMT (elevated mesenchymal markers), which can be reversed by recombinant CD109 protein treatment; CD109 levels inversely correlate with TGF-β signaling activation in SCC tumor samples.","method":"CRISPR/Cas9 KO, recombinant CD109 protein rescue, microarray gene expression, KEGG pathway analysis, immunohistochemistry of 52 tumor samples","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR KO with protein rescue experiment; single lab","pmids":["31695056"],"is_preprint":false},{"year":2020,"finding":"CD109 associates with EGFR at the cell surface in lung adenocarcinoma cells; CD109 overexpression activates AKT/mTOR signaling via EGFR association, and CD109 inhibition decreases EGFR phosphorylation and sensitizes tumor cells to EGFR inhibitors.","method":"Co-immunoprecipitation of CD109 with EGFR, EGFR phosphorylation assays, AKT/mTOR western blotting, pharmacological EGFR inhibitor sensitivity assays","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP with functional pathway readouts; single lab","pmids":["32133706"],"is_preprint":false},{"year":2020,"finding":"CD109 promotes lung adenocarcinoma EMT and stemness via activation of the Hippo-YAP signaling pathway; YAP activation participates in CD109-elicited EMT gene expression and tumor invasiveness.","method":"siRNA knockdown of CD109, YAP inhibition, gene expression analysis, invasion assays, correlation with patient YAP signature","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2-3 — knockdown with pathway epistasis; single lab","pmids":["33375719"],"is_preprint":false},{"year":2020,"finding":"CD109 interacts with latent TGF-β binding protein-1 (LTBP1), identified by mass spectrometry and confirmed by co-immunoprecipitation; increased CD109 expression enhances stromal TGF-β activation in the presence of LTBP1, promoting lung adenocarcinoma stromal invasion.","method":"Mass spectrometry of CD109 interactors, co-immunoprecipitation, CD109-deficient lung adenocarcinoma mouse model, TGF-β activation assays","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 — MS identification plus co-IP validation and in vivo KO model; single lab","pmids":["33007133"],"is_preprint":false},{"year":2021,"finding":"CD109 physically interacts with glycoprotein 130 (GP130) in glioblastoma stem cells (GSCs) to promote activation of the IL-6/STAT3 pathway; genetic depletion of CD109 abolishes GSC stemness and self-renewal and induces phenotypic shift to astrocytic-like cells; CD109/STAT3 axis mediates chemoresistance.","method":"Co-immunoprecipitation of CD109 with GP130, STAT3 phosphorylation assays, CD109 genetic depletion, sphere formation/stemness assays, in vivo tumor growth, pharmacological STAT3 inhibition","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus genetic depletion with multiple functional and in vivo readouts","pmids":["33986188"],"is_preprint":false},{"year":2021,"finding":"CD109 (GPI-anchored) suppresses TGF-β-induced erythroid differentiation in hematopoietic stem/progenitor cells (HSPCs); CD109 knockout/knockdown in TF-1 cells and cord blood MEPs leads to enhanced TGF-β-driven erythroid commitment.","method":"CD109 KO/KD in TF-1 leukemia cells and primary cord blood MEPs, TGF-β stimulation, flow cytometry for erythroid markers (CD36), PNH patient cell analysis","journal":"Leukemia","confidence":"Medium","confidence_rationale":"Tier 2 — KO/KD with defined functional readout in multiple cell systems; single lab","pmids":["34743190"],"is_preprint":false},{"year":2021,"finding":"Meprin β, a membrane-bound metalloproteinase, cleaves CD109 within its bait region at the cell surface, releasing soluble fragments; this proteolytic shedding reduces the amount of CD109 sorted to extracellular vesicles. Homology modeling and single-particle analysis provided a structural model localizing the meprin β and BMP-1 cleavage sites.","method":"Protease cleavage assays with meprin β, identification of cleavage sites, homology modeling/single-particle analysis structural model, EV isolation and CD109 quantification","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 1-2 — in vitro protease assay with site identification and structural modeling; single lab","pmids":["33738281"],"is_preprint":false},{"year":2022,"finding":"CD109 forms a heteromeric complex with EGFR at the cell surface in SCC cells, stabilizing EGFR protein and mRNA levels and promoting EGFR/AKT signaling; CD109 cell-surface localization is required for maintenance of epithelial morphology and stemness in vulvar and hypopharyngeal SCC cells.","method":"Co-immunoprecipitation and co-localization of CD109 and EGFR, EGFR mRNA/protein quantification, immunofluorescence, spheroid formation assays, xenograft tumor models","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus localization with in vivo xenograft validation; single lab","pmids":["35954339"],"is_preprint":false},{"year":2024,"finding":"Proteolytic cleavage of the CD109 bait region by diverse proteases induces a conformational change that activates the CD109 thioester, enabling covalent conjugation of proteases (protease inhibition); the GPI-anchored MG8 domain dissociates during this conformational change, releasing CD109 from the cell surface.","method":"In vitro protease cleavage assays, thioester activation assay, protease conjugation and activity assays, conformational change analysis","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstituted biochemical mechanism with multiple proteases and defined thioester chemistry","pmids":["38587194"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM structures of CD109 in native, protease-activated, and methylamine-activated conformations reveal that bait-region proteolysis triggers a conformational change analogous to that of the protease inhibitor A2ML1, exposing a reactive thioester that conjugates and inhibits proteases; CD109 glycans contribute to protease inhibition by limiting substrate access.","method":"Cryo-electron microscopy structure determination, deglycosylation experiments, chymotrypsin conjugation assays, comparison with A2ML1 structure","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 — atomic-resolution cryo-EM structures in multiple conformational states with functional validation","pmids":["40482031"],"is_preprint":false},{"year":2025,"finding":"CD109 interacts with and stabilizes IL-6 receptor alpha (IL6Rα) expression at the cell surface in SCC cells; CD109 promotes IL-6/STAT3/NRF2 pathway activation and maintains cancer cell stemness and antioxidant state (SOD1, HO-1); loss of CD109 attenuates this pathway.","method":"Co-immunoprecipitation of CD109 with IL6Rα, immunofluorescence, FACS, western blotting for STAT3/NRF2/SOD1/HO1, spheroid formation assays, multi-omic tumor analysis","journal":"Experimental hematology & oncology","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus multiple signaling readouts with clinical validation; single lab","pmids":["40317079"],"is_preprint":false},{"year":2025,"finding":"Tumor-derived soluble CD109 (sCD109) upregulates CD73 on macrophages by activating the FcγRI/SYK/NF-κB signaling pathway; additionally, internalized sCD109 in macrophages binds E3 ligase TRIM21 at the same site as CD73, preventing CD73 protein degradation, thereby expanding CD73+ immunosuppressive tumor-associated macrophages and inhibiting T-cell responses.","method":"Proteomic/single-cell transcriptomic analysis, mass spectrometry, co-immunoprecipitation of sCD109 with TRIM21, CD73 ubiquitination assays, FcγRI/SYK/NF-κB pathway analysis, dual CD109/PD-L1 blockade in vivo","journal":"Journal of hepatology","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP of sCD109 with TRIM21, NF-κB pathway analysis, in vivo dual blockade; single lab","pmids":["40220905"],"is_preprint":false},{"year":2009,"finding":"Mesotrypsin (PRSS3), upregulated in malignant breast cancer T4-2 cells, cleaves/sheds CD109 from the cell surface; CD109 is identified as a functional proteolytic target of mesotrypsin mediating the malignant growth phenotype.","method":"Proteomic identification of mesotrypsin substrate, PRSS3 knockdown, recombinant mesotrypsin treatment, 3D organotypic culture assays","journal":"Breast cancer research and treatment","confidence":"Medium","confidence_rationale":"Tier 2-3 — proteomic substrate identification with KD and recombinant protein treatment; single lab","pmids":["20035377"],"is_preprint":false},{"year":2018,"finding":"CD109 deficiency in mice leads to osteopenia/osteoporosis-like phenotype with reduced bone volume and increased bone turnover (elevated N-terminal telopeptide of collagen I and alkaline phosphatase), indicating that CD109 plays a role in bone metabolism in vivo.","method":"CD109 knockout mice, micro-CT analysis of femur, bone histomorphometry, serum bone turnover markers","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined skeletal phenotype and multiple bone metabolic markers","pmids":["29767469"],"is_preprint":false},{"year":2023,"finding":"In osteosarcoma cells, CD109 knockdown enhances SMAD1/5/9 phosphorylation under BMP-2 stimulation and reduces cell migration in the presence of BMP, indicating that CD109 negatively regulates BMP signaling and BMP-dependent migration in sarcoma (distinct from its TGF-β regulatory role).","method":"CD109 knockdown in osteosarcoma cell lines, BMP-2 stimulation, western blotting for phospho-SMAD1/5/9, in vitro wound healing migration assay, immunohistochemistry of human tumor tissue","journal":"Pathology, research and practice","confidence":"Medium","confidence_rationale":"Tier 2-3 — knockdown with BMP stimulation and functional readout; single lab","pmids":["37030166"],"is_preprint":false},{"year":2023,"finding":"CD109 on conventional DC2s (cDC2s) is required for airway hyperreactivity and eosinophilic inflammation; CD109-deficient cDC2s have high RUNX3 expression and poor ability to drive Th2 differentiation; adoptive transfer of CD109-deficient DCs fails to induce AHR and eosinophilic inflammation.","method":"CD109 KO mice, allergen sensitization models (house dust mite, OVA), ex vivo DC-T cell co-cultures, adoptive transfer of bone marrow-derived DCs, anti-CD109 antibody administration","journal":"American journal of respiratory cell and molecular biology","confidence":"High","confidence_rationale":"Tier 2 — clean KO, adoptive transfer, and pharmacological blockade all converging on same mechanism; 15 citations","pmids":["36215676"],"is_preprint":false},{"year":2024,"finding":"Mechanical force induces CD109 expression on periodontal ligament stem cells (PDLSCs) via repression of miR-340-5p; CD109 suppresses osteogenesis of PDLSCs via the JAK/STAT3 signaling pathway, while promoting osteoclast formation and M1 macrophage polarization through paracrine signaling; CD109 lentiviral knockdown in vivo increases osteogenic activity and decreases osteoclast numbers during tooth movement.","method":"In vitro mechanical force stimulation, miR-340-5p manipulation, JAK/STAT3 inhibition, lentiviral shRNA knockdown in rat periodontal tissues in vivo, flow cytometry, osteogenic/osteoclast differentiation assays","journal":"Stem cells translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro mechanistic pathway plus in vivo lentiviral KD; single lab","pmids":["38885217"],"is_preprint":false}],"current_model":"CD109 is a GPI-anchored, thioester-containing glycoprotein that functions as a multifunctional co-receptor: it negatively regulates TGF-β signaling by binding TGF-β receptors (requiring furin-mediated processing into 180/25 kDa fragments), directing them to caveolin-1-positive caveolae for SMAD7/Smurf2-mediated degradation, and as soluble sCD109 by directly binding and sequestering TGF-β ligand; in parallel, membrane-anchored CD109 interacts with EGFR and IL-6Rα to stabilize their expression and promote AKT/mTOR and JAK-STAT3/NRF2 oncogenic signaling; structurally, CD109 belongs to the alpha2-macroglobulin family and undergoes bait-region proteolysis-triggered conformational change that activates its thioester to covalently conjugate and inhibit proteases while releasing CD109 from the cell surface."},"narrative":{"teleology":[{"year":2002,"claim":"Establishing CD109 as a thioester-containing member of the alpha2-macroglobulin superfamily resolved the molecular identity of this GPI-anchored surface glycoprotein and predicted a proteolysis-activated covalent-binding mechanism.","evidence":"cDNA cloning, sequence analysis, and biochemical demonstration of intact thioester bond in native CD109 from platelets and cell lines","pmids":["11861284"],"confidence":"High","gaps":["No direct demonstration of protease inhibition at this stage","Physiological ligands/targets of the thioester unknown","Three-dimensional structure unavailable"]},{"year":2002,"claim":"Mapping the Gov/HPA-15 platelet alloantigen to a single Tyr703Ser polymorphism in CD109 resolved a clinically significant platelet antigen system at the molecular level.","evidence":"RT-PCR genotyping and CHO cell transfection with each CD109 variant confirmed allele-specific recognition by Gov antisera","pmids":["11861285"],"confidence":"High","gaps":["Functional consequences of Y703S on CD109 biochemistry unknown","No structural explanation for why this site is immunogenic"]},{"year":2006,"claim":"Identifying CD109 as the 150 kDa GPI-anchored TGF-β1 binding protein in keratinocytes established its role as a co-receptor that negatively modulates TGF-β signaling, independent of simple ligand sequestration.","evidence":"Affinity purification and microsequencing from keratinocytes, plus loss-of-function (GPI-anchor deficient) and gain-of-function studies","pmids":["16754747"],"confidence":"High","gaps":["Mechanism of TGF-β receptor modulation unresolved","Whether CD109 directly contacts the receptor versus ligand unclear"]},{"year":2010,"claim":"Demonstrating that furin cleaves CD109 into 180/25 kDa fragments and that this processing is required for TGF-β receptor association and signaling inhibition provided the first mechanistic step linking CD109 maturation to its co-receptor function.","evidence":"Site-directed mutagenesis of the tetra-arginine furin site (R1273S), co-IP with TGFBR1, and cell growth assays","pmids":["20101215"],"confidence":"High","gaps":["Structural basis for how processed CD109 engages TGFBR1 unknown","Whether furin cleavage also activates the thioester not tested"]},{"year":2011,"claim":"Showing that CD109 associates with caveolin-1 and routes TGF-β receptors to caveolae for degradation revealed the trafficking mechanism underlying CD109-mediated TGF-β signal suppression, and subsequent work demonstrated this requires SMAD7/Smurf2 ubiquitin ligase activity.","evidence":"Co-IP of CD109 with caveolin-1, receptor internalization/degradation assays (2011); siRNA knockdown of SMAD7 and dominant-negative Smurf2 epistasis (2012)","pmids":["21295082","21898545"],"confidence":"High","gaps":["Direct versus indirect nature of the CD109–caveolin-1 interaction not resolved","Stoichiometry of the CD109/caveolin-1/receptor complex unknown"]},{"year":2012,"claim":"CD109-deficient mice displaying epidermal hyperplasia with elevated STAT3 (but not Smad2) phosphorylation established that CD109 regulates skin homeostasis in vivo and revealed an unexpected STAT3-regulatory axis beyond TGF-β.","evidence":"CD109 knockout mouse phenotyping with immunohistochemistry for pSTAT3 and pSmad2","pmids":["22846721"],"confidence":"High","gaps":["Whether CD109 directly regulates STAT3 or acts through an intermediate receptor unknown at this stage","Relationship between STAT3 hyperactivation and TGF-β suppression in vivo unclear"]},{"year":2013,"claim":"Transgenic CD109 overexpression in murine epidermis protected against wound-healing inflammation and bleomycin-induced skin fibrosis by suppressing Smad2/3 phosphorylation and ECM production, validating CD109 as an in vivo antifibrotic factor.","evidence":"CD109 transgenic mice in excisional wound and bleomycin scleroderma models with pSmad2/3, collagen, and cytokine readouts","pmids":["23438099","23436317"],"confidence":"High","gaps":["Therapeutic potential of exogenous sCD109 in fibrosis not tested","Whether CD109 modulates non-Smad TGF-β pathways in fibrosis not assessed"]},{"year":2015,"claim":"Biophysical demonstration that soluble CD109 binds TGF-β with high affinity and blocks receptor binding established a second, ligand-sequestration mechanism of TGF-β inhibition complementary to the membrane co-receptor function.","evidence":"Surface plasmon resonance, radioligand competition, and Smad2/3 phosphorylation assays","pmids":["26621871"],"confidence":"High","gaps":["Relative contribution of ligand sequestration versus receptor routing in vivo not quantified","Binding site on TGF-β not mapped"]},{"year":2015,"claim":"Discovery of a cell-surface CD109–EGFR interaction that enhances EGF signaling in glioblastoma cells expanded CD109's receptor repertoire beyond TGF-β, later confirmed in lung and squamous cell carcinoma where CD109 stabilizes EGFR and activates AKT/mTOR signaling.","evidence":"Co-IP of CD109 with EGFR, migration/invasion assays in glioblastoma (2015); co-IP and EGFR phosphorylation/AKT/mTOR assays in lung adenocarcinoma (2020) and SCC (2022)","pmids":["25724945","32133706","35954339"],"confidence":"Medium","gaps":["Structural basis of CD109–EGFR interaction not determined","Whether the GPI anchor directly mediates the interaction or lipid raft co-localization is responsible remains unresolved"]},{"year":2017,"claim":"An in vivo barcoded tumor screen identified CD109 as a driver of lung cancer metastasis through JAK-STAT3, establishing CD109's oncogenic signaling role in an unbiased genetic framework and showing pharmacological JAK inhibition blocks CD109-driven metastasis.","evidence":"In vivo tumor barcoding in mouse lung adenocarcinoma model with JAK inhibitor validation","pmids":["28191885"],"confidence":"High","gaps":["Direct physical link between CD109 and JAK-STAT3 components not identified at this point","Whether CD109's STAT3 role is ligand-dependent or constitutive unclear"]},{"year":2018,"claim":"Identification of cell-surface GRP78 as a CD109-binding partner under ER stress showed that the GRP78–CD109 complex promotes caveolar routing of TGF-β receptors, linking the unfolded protein response to TGF-β signal suppression in cancer.","evidence":"Cell-surface co-IP of GRP78 with CD109, Smad2 phosphorylation and receptor trafficking assays","pmids":["29654145"],"confidence":"High","gaps":["Whether GRP78 interaction requires furin-processed CD109 not tested","Generalizability beyond the cell line used unclear"]},{"year":2019,"claim":"CD109-deficient mice develop spontaneous psoriasiform skin inflammation via barrier disruption and γδ T17 cell activation, indicating that CD109 maintains skin barrier integrity and restrains IL-23-dependent innate immune responses in a cell-extrinsic manner.","evidence":"CD109 KO mice with allergen challenge, microbiota depletion, IL-23 blockade, and adoptive transfer","pmids":["31597099"],"confidence":"High","gaps":["Molecular mechanism by which CD109 fortifies the skin barrier not elucidated","Relative contributions of TGF-β versus STAT3 deregulation to barrier defect unknown"]},{"year":2021,"claim":"Demonstrating that CD109 physically interacts with GP130 to activate IL-6/STAT3 in glioblastoma stem cells resolved the receptor-level mechanism linking CD109 to STAT3 activation and explained how CD109 sustains cancer stemness and chemoresistance.","evidence":"Reciprocal co-IP of CD109 with GP130, STAT3 phosphorylation, sphere formation, and in vivo tumor growth assays","pmids":["33986188"],"confidence":"High","gaps":["Whether CD109–GP130 interaction is direct or scaffolded by IL-6Rα not resolved","Whether GP130 interaction applies outside glioblastoma not tested"]},{"year":2024,"claim":"Biochemical reconstitution showed that bait-region proteolysis by diverse proteases activates the CD109 thioester for covalent protease conjugation and inhibition, and that GPI-anchor dissociation accompanies this conformational change — establishing CD109 as a functional protease inhibitor.","evidence":"In vitro protease cleavage, thioester activation, and protease conjugation/activity assays with multiple proteases","pmids":["38587194"],"confidence":"High","gaps":["Physiological protease substrates for CD109 inhibition not identified in vivo","Whether protease-inhibitor function operates independently of TGF-β co-receptor function unclear"]},{"year":2025,"claim":"Cryo-EM structures of native, protease-activated, and methylamine-activated CD109 revealed atomic-resolution conformational states analogous to A2ML1, showing how glycans limit substrate access and how thioester exposure enables covalent protease capture.","evidence":"Cryo-EM structure determination in multiple states, deglycosylation and chymotrypsin conjugation assays","pmids":["40482031"],"confidence":"High","gaps":["No structure of CD109 in complex with TGF-β receptor or EGFR","How thioester-mediated protease inhibition relates to signaling co-receptor functions is mechanistically unresolved"]},{"year":2025,"claim":"CD109 was shown to stabilize IL-6Rα at the SCC cell surface and promote IL-6/STAT3/NRF2 antioxidant signaling, and separately, tumor-derived sCD109 was found to expand immunosuppressive CD73+ macrophages via FcγRI/SYK/NF-κB and TRIM21-mediated prevention of CD73 degradation, broadening CD109's roles into immune evasion.","evidence":"Co-IP of CD109 with IL-6Rα and signaling readouts in SCC (2025); proteomic/scRNA-seq, co-IP of sCD109 with TRIM21, and dual CD109/PD-L1 blockade in vivo in hepatocellular carcinoma (2025)","pmids":["40317079","40220905"],"confidence":"Medium","gaps":["Whether sCD109-TRIM21 interaction occurs in other tumor types not tested","Structural basis of sCD109 engagement with FcγRI unknown","Single-lab findings for both; independent replication needed"]},{"year":null,"claim":"How CD109's three biochemically distinct activities — thioester-mediated protease inhibition, membrane co-receptor function for TGF-β/EGFR/GP130, and soluble ligand sequestration/immune modulation — are coordinated in vivo remains the central unresolved question.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of CD109 in complex with any signaling receptor","Relative in vivo contributions of protease-inhibitor versus co-receptor functions unknown","No genetic disease clearly mapped to CD109 mutations in humans"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3,4,5,11,14,16,32]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[26,27]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,5,22,25,28]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,3,4,12,19,25,28]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[6,11,24,26,29]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3,4,5,6,7,8,9,11,12,14,15,16,19,20,22,25,28,29]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[17,29,33]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[15,19,20,22,25]}],"complexes":["TGF-β receptor/CD109/caveolin-1 complex","CD109/EGFR complex","CD109/GP130 complex"],"partners":["TGFBR1","CAV1","EGFR","IL6ST","HSPA5","LTBP1","IL6R","TRIM21"],"other_free_text":[]},"mechanistic_narrative":"CD109 is a GPI-anchored glycoprotein of the alpha2-macroglobulin/thioester-containing protein family that functions as a multifaceted regulator of TGF-β, STAT3, and EGFR signaling and as a protease inhibitor. As a membrane co-receptor, furin-processed CD109 (180/25 kDa fragments) associates with TGF-β type I receptor and directs it to caveolin-1-positive caveolae for SMAD7/Smurf2-mediated ubiquitin-dependent degradation, thereby suppressing canonical TGF-β/Smad2/3 signaling in keratinocytes, hematopoietic progenitors, and fibrotic tissues [PMID:16754747, PMID:20101215, PMID:21295082, PMID:21898545, PMID:23436317]; soluble shed CD109 directly sequesters TGF-β ligand with high affinity [PMID:26621871]. Simultaneously, membrane-anchored CD109 physically interacts with EGFR, GP130 (IL-6Rα), and GRP78 to promote AKT/mTOR, JAK-STAT3/NRF2, and YAP signaling, sustaining cancer cell stemness, metastasis, and chemoresistance [PMID:25724945, PMID:33986188, PMID:28191885, PMID:29654145, PMID:40317079]. Structurally, cryo-EM reveals that bait-region proteolysis triggers a conformational change that activates the CD109 thioester for covalent conjugation and inhibition of proteases, while releasing CD109 from the cell surface — a mechanism analogous to A2ML1 [PMID:38587194, PMID:40482031]."},"prefetch_data":{"uniprot":{"accession":"Q6YHK3","full_name":"CD109 antigen","aliases":["150 kDa TGF-beta-1-binding protein","C3 and PZP-like alpha-2-macroglobulin domain-containing protein 7","Platelet-specific Gov antigen","p180","r150"],"length_aa":1445,"mass_kda":161.7,"function":"Modulates negatively TGFB1 signaling in keratinocytes","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q6YHK3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD109","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CD109","total_profiled":1310},"omim":[{"mim_id":"621264","title":"FETOMATERNAL ALLOIMMUNE THROMBOCYTOPENIA 1; FMAIT1","url":"https://www.omim.org/entry/621264"},{"mim_id":"617810","title":"GLYCOSYLPHOSPHATIDYLINOSITOL BIOSYNTHESIS DEFECT 15; GPIBD15","url":"https://www.omim.org/entry/617810"},{"mim_id":"608859","title":"CD109 ANTIGEN; CD109","url":"https://www.omim.org/entry/608859"},{"mim_id":"605754","title":"PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS CLASS Q PROTEIN; PIGQ","url":"https://www.omim.org/entry/605754"},{"mim_id":"603048","title":"GLYCOSYLPHOSPHATIDYLINOSITOL ANCHOR ATTACHMENT PROTEIN 1; GPAA1","url":"https://www.omim.org/entry/603048"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"parathyroid gland","ntpm":310.7}],"url":"https://www.proteinatlas.org/search/CD109"},"hgnc":{"alias_symbol":["HPA-15","FLJ38569","DKFZp762L1111","CPAMD7"],"prev_symbol":[]},"alphafold":{"accession":"Q6YHK3","domains":[{"cath_id":"2.60.40.2950","chopping":"29-125","consensus_level":"high","plddt":86.7523,"start":29,"end":125},{"cath_id":"2.60.40.1930","chopping":"130-225_556-616_685-745","consensus_level":"medium","plddt":88.75,"start":130,"end":745},{"cath_id":"2.60.40.1940","chopping":"230-306_318-346","consensus_level":"medium","plddt":83.1458,"start":230,"end":346},{"cath_id":"2.60.40.1930","chopping":"468-553","consensus_level":"medium","plddt":89.299,"start":468,"end":553},{"cath_id":"2.60.40.10","chopping":"749-852","consensus_level":"high","plddt":82.8598,"start":749,"end":852},{"cath_id":"1.50.10.20","chopping":"904-1128_1135-1200","consensus_level":"medium","plddt":87.5034,"start":904,"end":1200},{"cath_id":"2.60.40.690","chopping":"1279-1396","consensus_level":"medium","plddt":84.8549,"start":1279,"end":1396}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6YHK3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6YHK3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6YHK3-F1-predicted_aligned_error_v6.png","plddt_mean":81.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CD109","jax_strain_url":"https://www.jax.org/strain/search?query=CD109"},"sequence":{"accession":"Q6YHK3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6YHK3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6YHK3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6YHK3"}},"corpus_meta":[{"pmid":"11861284","id":"PMC_11861284","title":"Cell 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Medical sciences = Hua zhong ke ji da xue xue bao. Yi xue Ying De wen ban = Huazhong keji daxue xuebao. 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immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/38442581","citation_count":5,"is_preprint":false},{"pmid":"40220905","id":"PMC_40220905","title":"Tumor-derived CD109 orchestrates reprogramming of tumor-associated macrophages to dampen immune response.","date":"2025","source":"Journal of hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/40220905","citation_count":4,"is_preprint":false},{"pmid":"37661780","id":"PMC_37661780","title":"H3K27 acetylation activated-CD109 evokes 5-fluorouracil resistance in gastric cancer via the JNK/MAPK signaling pathway.","date":"2023","source":"Environmental toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/37661780","citation_count":4,"is_preprint":false},{"pmid":"31777077","id":"PMC_31777077","title":"A novel simple assay system for the detection of human platelet antigen 15 (HPA-15) alloantibodies based on three techniques: an HPA-15 expressing cell line, a monoclonal antibody-specific antigen-capture method and mixed-passive haemagglutination.","date":"2019","source":"Vox sanguinis","url":"https://pubmed.ncbi.nlm.nih.gov/31777077","citation_count":4,"is_preprint":false},{"pmid":"39567205","id":"PMC_39567205","title":"Identification of CD109 in the extracellular vesicles derived from ovarian cancer stem-like cells.","date":"2024","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/39567205","citation_count":3,"is_preprint":false},{"pmid":"38587194","id":"PMC_38587194","title":"Proteolytic cleavage of the TGFβ co-receptor CD109 changes its conformation, resulting in protease inhibition via activation of its thiol ester, and dissociation from the cell membrane.","date":"2024","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/38587194","citation_count":3,"is_preprint":false},{"pmid":"39577687","id":"PMC_39577687","title":"Microglial upregulation of CD109 expression in spinal cord of amyotrophic lateral sclerosis mouse model and its role in modulating inflammation and TGFβ/SMAD 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GPI-anchored glycoprotein and novel member of the alpha2-macroglobulin/C3,C4,C5 family of thioester-containing proteins; native CD109 contains an intact thioester bond, is predicted to be activated by proteolytic cleavage, and can then mediate covalent binding to adjacent molecules or cells via its thioester with complement-like chemical reactivity.\",\n      \"method\": \"cDNA cloning, sequence analysis, biochemical demonstration of intact thioester in native CD109\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical demonstration of thioester in native protein, sequence analysis, foundational paper with 154 citations\",\n      \"pmids\": [\"11861284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The Gov platelet alloantigen system (HPA-15) is defined by a single nucleotide polymorphism (A2108C) in CD109 resulting in a Tyr703Ser amino acid substitution; transfection of CHO cells with each variant confirmed allele-specific recognition by Gov antisera.\",\n      \"method\": \"RT-PCR, allele-specific PCR, real-time PCR, CHO cell transfection with CD109 cDNA variants and recognition by allele-specific antisera\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional validation in transfected cells plus molecular genotyping; 69 citations\",\n      \"pmids\": [\"11861285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CD109 is the molecular identity of the 150 kDa GPI-anchored TGF-β1 binding protein (r150) in keratinocytes; loss- and gain-of-function studies establish CD109 as a component of the TGF-β receptor system and a negative modulator of TGF-β responses, acting independently of ligand sequestration, possibly by direct modulation of receptor activity.\",\n      \"method\": \"Affinity purification, microsequencing, biochemical thioester assay, loss-of-function (GPI-anchor-deficient keratinocytes) and gain-of-function studies\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical identification plus functional loss/gain-of-function; 121 citations, replicated in subsequent work\",\n      \"pmids\": [\"16754747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CD109 is processed by the Golgi protease furin at a tetra-arginine cleavage motif (RRRR at aa 1270–1273), converting the 205 kDa precursor into 180 kDa and 25 kDa fragments. The processed 180/25 kDa complex associates with the type I TGF-β receptor and is required for negative regulation of TGF-β signaling and cell growth suppression; an R1273S mutant that cannot be cleaved fails to associate with TGFBR1 or inhibit TGF-β signaling.\",\n      \"method\": \"Site-directed mutagenesis of furin cleavage site (R1273S), co-immunoprecipitation with TGFBR1, western blotting, cell growth assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with co-IP and functional assays; 67 citations\",\n      \"pmids\": [\"20101215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD109 associates with caveolin-1 and promotes localization of TGF-β receptors into the caveolar compartment in the presence of ligand, enhancing TGF-β receptor internalization via the caveolae pathway and facilitating TGF-β receptor degradation, thereby inhibiting TGF-β signaling.\",\n      \"method\": \"Co-immunoprecipitation of CD109 with caveolin-1, receptor internalization assays, caveolae fractionation, TGF-β receptor degradation assays\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP with caveolin-1, receptor trafficking and degradation assays; 119 citations\",\n      \"pmids\": [\"21295082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CD109 promotes SMAD7/Smurf2-mediated ubiquitin-dependent degradation of TGFBR1 in a ligand-dependent manner; CD109 regulates the localization and association of SMAD7/Smurf2 with TGFBR1, and CD109's inhibitory effect on TGF-β signaling requires SMAD7 expression and Smurf2 ubiquitin ligase activity.\",\n      \"method\": \"siRNA knockdown of SMAD7, dominant-negative Smurf2 (ubiquitin ligase-dead mutant), co-immunoprecipitation, western blotting, TGF-β response assays\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis via dominant-negative and siRNA, co-IP, multiple functional readouts; 78 citations\",\n      \"pmids\": [\"21898545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Release of CD109 from the keratinocyte cell surface (soluble/shed CD109) downregulates TGF-β signaling and TGF-β receptor expression and increases phospho-STAT3 levels, total STAT3, Bcl-2, and cell growth/survival, indicating that soluble CD109 can activate STAT3 signaling while inhibiting TGF-β signaling.\",\n      \"method\": \"Addition of recombinant CD109 protein to keratinocytes, phospho-STAT3 western blotting, TGF-β receptor quantification, cell proliferation/survival assays\",\n      \"journal\": \"Experimental dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — recombinant protein addition with pathway readouts, single lab\",\n      \"pmids\": [\"21539622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CD109-deficient mice develop epidermal hyperplasia, kinked hair shafts, ectatic hair follicles, and increased sebaceous gland hyperplasia; this is associated with elevated STAT3 phosphorylation (not altered Smad2 phosphorylation) in the epidermis, indicating that CD109 regulates keratinocyte differentiation in vivo primarily via STAT3 rather than TGF-β/Smad signaling.\",\n      \"method\": \"CD109 knockout mouse generation, histology, immunohistochemistry for phospho-Smad2 and phospho-STAT3\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular and molecular phenotype; 33 citations\",\n      \"pmids\": [\"22846721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Transgenic mice overexpressing CD109 in the epidermis show decreased macrophage/neutrophil recruitment, reduced granulation tissue, decreased Smad2/3 phosphorylation, reduced pro-inflammatory cytokines (IL-1α, MCP-1), and decreased ECM components during wound healing, and improved dermal architecture in incisional wounds, establishing CD109 as an in vivo inhibitor of TGF-β/Smad-mediated wound inflammation and fibrosis.\",\n      \"method\": \"CD109 transgenic mice, excisional and incisional wound models, immunohistochemistry, western blotting for phospho-Smad2/3, cytokine quantification\",\n      \"journal\": \"Wound repair and regeneration\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean transgenic model with multiple orthogonal molecular and histological readouts\",\n      \"pmids\": [\"23438099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CD109 overexpression in the epidermis of transgenic mice protects against bleomycin-induced skin fibrosis, evidenced by decreased dermal thickness, collagen crosslinking, fibronectin content, and phospho-Smad2/3 levels, demonstrating that CD109 inhibits TGF-β/Smad-mediated fibrotic responses in vivo.\",\n      \"method\": \"CD109 transgenic mice, bleomycin-induced scleroderma model, Masson's trichrome/picrosirius red staining, western blotting for phospho-Smad2/3\",\n      \"journal\": \"Arthritis and rheumatism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean transgenic gain-of-function in disease model with multiple readouts\",\n      \"pmids\": [\"23436317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CD109 plays a role in osteoclastogenesis: CD109 is upregulated >17-fold during RANKL-induced osteoclast differentiation from RAW264.7 macrophages and from primary murine monocytes; stable knockdown of CD109 reduces the formation of large multinucleated osteoclasts.\",\n      \"method\": \"Microarray analysis, RT-qPCR, western blotting, stable CD109 knockdown cell lines, osteoclast fusion assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — knockdown with defined functional phenotype; single lab, 22 citations\",\n      \"pmids\": [\"23593435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Soluble CD109 (sCD109) binds TGF-β with high affinity (slow dissociation kinetics by surface plasmon resonance), inhibits TGF-β binding to its receptors, and antagonizes TGF-β-induced Smad2/3 phosphorylation, transcription, and cell migration.\",\n      \"method\": \"Surface plasmon resonance, radioligand binding competition assays, affinity labelling, Smad2/3 phosphorylation assays, cell migration assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro SPR binding assay plus cell-based functional validation with multiple orthogonal methods\",\n      \"pmids\": [\"26621871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cell surface CD109 interacts with EGFR in glioblastoma cells (SK-MG-1), and this interaction enhances EGF signaling, cell migration, and invasion, while secreted N-terminal CD109 fragment selectively inhibits TGF-β1 signaling but not EGF signaling.\",\n      \"method\": \"Co-immunoprecipitation of CD109 with EGFR, conditioned medium transfer experiments, cell migration/invasion assays, western blotting for EGF and TGF-β1 signaling\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP with functional readouts; single lab\",\n      \"pmids\": [\"25724945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CD109 is a component of exosomes secreted from HEK293 cells; the C-terminal region of CD109 is required for its sorting into exosomes, as a truncated CD109 lacking the C-terminal region is not found in the exosomal fraction.\",\n      \"method\": \"Immunoprecipitation with anti-FLAG affinity gel, mass spectrometry, western blotting, immuno-electron microscopy of exosome fractions\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — immuno-EM and biochemical fractionation with domain deletion mutant\",\n      \"pmids\": [\"26707640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In transgenic mice overexpressing CD109 in the epidermis, CD109 differentially regulates TGF-β signaling: it enhances ALK1-Smad1/5 signaling while decreasing ALK5-Smad2/3 signaling, and reduces TGF-β expression and ECM production; CD109 and ALK1 co-localize in mouse keratinocytes.\",\n      \"method\": \"CD109 transgenic mouse model, immunohistochemistry, co-localization of CD109 and ALK1, western blotting for phospho-Smad1/5 and phospho-Smad2/3, fibroblast conditioned medium experiments\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — transgenic model with molecular pathway differentiation; single lab\",\n      \"pmids\": [\"27866969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CD109 drives lung cancer metastasis through activation of JAK-STAT3 signaling; pharmacological targeting of JAK-STAT3 blocks CD109-driven metastasis in a mouse model of lung adenocarcinoma.\",\n      \"method\": \"In vivo tumor barcoding mouse model, in vivo screening, JAK inhibitor pharmacological blockade, genomic analysis\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic screen with pharmacological validation; 132 citations\",\n      \"pmids\": [\"28191885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Upon ER stress, GRP78 translocates to the cell surface where it binds to CD109, and the GRP78-CD109 complex promotes routing of TGF-β receptor to caveolae, disrupting TGF-β receptor binding to and activation of Smad2, thereby blocking TGF-β tumor-suppressor signaling.\",\n      \"method\": \"Cell surface co-immunoprecipitation of GRP78 with CD109, receptor trafficking assays, Smad2 phosphorylation assays, IRE1α-SRC-ASAP1 pathway analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus mechanistic signaling cascade with multiple pathway components validated; 110 citations\",\n      \"pmids\": [\"29654145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CD109 regulates skin homeostasis and restrains IL-17-producing γδ T (γδ17) cell activation in a cell-extrinsic manner by fortifying skin barrier integrity; CD109-deficient mice show spontaneous epidermal hyperplasia, accumulation of dermal γδ17 cells, and enhanced susceptibility to psoriasiform inflammation dependent on IL-23 and skin microbiota.\",\n      \"method\": \"CD109 knockout mice, transient skin microbiota depletion, IL-23 blockade, γδ T cell flow cytometry, skin barrier assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with mechanistic epistasis (microbiota, IL-23) and multiple cellular readouts\",\n      \"pmids\": [\"31597099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CD109 CRISPR/Cas9 knockout in SCC cells represses epithelial traits and promotes EMT (elevated mesenchymal markers), which can be reversed by recombinant CD109 protein treatment; CD109 levels inversely correlate with TGF-β signaling activation in SCC tumor samples.\",\n      \"method\": \"CRISPR/Cas9 KO, recombinant CD109 protein rescue, microarray gene expression, KEGG pathway analysis, immunohistochemistry of 52 tumor samples\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR KO with protein rescue experiment; single lab\",\n      \"pmids\": [\"31695056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD109 associates with EGFR at the cell surface in lung adenocarcinoma cells; CD109 overexpression activates AKT/mTOR signaling via EGFR association, and CD109 inhibition decreases EGFR phosphorylation and sensitizes tumor cells to EGFR inhibitors.\",\n      \"method\": \"Co-immunoprecipitation of CD109 with EGFR, EGFR phosphorylation assays, AKT/mTOR western blotting, pharmacological EGFR inhibitor sensitivity assays\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP with functional pathway readouts; single lab\",\n      \"pmids\": [\"32133706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD109 promotes lung adenocarcinoma EMT and stemness via activation of the Hippo-YAP signaling pathway; YAP activation participates in CD109-elicited EMT gene expression and tumor invasiveness.\",\n      \"method\": \"siRNA knockdown of CD109, YAP inhibition, gene expression analysis, invasion assays, correlation with patient YAP signature\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — knockdown with pathway epistasis; single lab\",\n      \"pmids\": [\"33375719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD109 interacts with latent TGF-β binding protein-1 (LTBP1), identified by mass spectrometry and confirmed by co-immunoprecipitation; increased CD109 expression enhances stromal TGF-β activation in the presence of LTBP1, promoting lung adenocarcinoma stromal invasion.\",\n      \"method\": \"Mass spectrometry of CD109 interactors, co-immunoprecipitation, CD109-deficient lung adenocarcinoma mouse model, TGF-β activation assays\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS identification plus co-IP validation and in vivo KO model; single lab\",\n      \"pmids\": [\"33007133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CD109 physically interacts with glycoprotein 130 (GP130) in glioblastoma stem cells (GSCs) to promote activation of the IL-6/STAT3 pathway; genetic depletion of CD109 abolishes GSC stemness and self-renewal and induces phenotypic shift to astrocytic-like cells; CD109/STAT3 axis mediates chemoresistance.\",\n      \"method\": \"Co-immunoprecipitation of CD109 with GP130, STAT3 phosphorylation assays, CD109 genetic depletion, sphere formation/stemness assays, in vivo tumor growth, pharmacological STAT3 inhibition\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus genetic depletion with multiple functional and in vivo readouts\",\n      \"pmids\": [\"33986188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CD109 (GPI-anchored) suppresses TGF-β-induced erythroid differentiation in hematopoietic stem/progenitor cells (HSPCs); CD109 knockout/knockdown in TF-1 cells and cord blood MEPs leads to enhanced TGF-β-driven erythroid commitment.\",\n      \"method\": \"CD109 KO/KD in TF-1 leukemia cells and primary cord blood MEPs, TGF-β stimulation, flow cytometry for erythroid markers (CD36), PNH patient cell analysis\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO/KD with defined functional readout in multiple cell systems; single lab\",\n      \"pmids\": [\"34743190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Meprin β, a membrane-bound metalloproteinase, cleaves CD109 within its bait region at the cell surface, releasing soluble fragments; this proteolytic shedding reduces the amount of CD109 sorted to extracellular vesicles. Homology modeling and single-particle analysis provided a structural model localizing the meprin β and BMP-1 cleavage sites.\",\n      \"method\": \"Protease cleavage assays with meprin β, identification of cleavage sites, homology modeling/single-particle analysis structural model, EV isolation and CD109 quantification\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro protease assay with site identification and structural modeling; single lab\",\n      \"pmids\": [\"33738281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CD109 forms a heteromeric complex with EGFR at the cell surface in SCC cells, stabilizing EGFR protein and mRNA levels and promoting EGFR/AKT signaling; CD109 cell-surface localization is required for maintenance of epithelial morphology and stemness in vulvar and hypopharyngeal SCC cells.\",\n      \"method\": \"Co-immunoprecipitation and co-localization of CD109 and EGFR, EGFR mRNA/protein quantification, immunofluorescence, spheroid formation assays, xenograft tumor models\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus localization with in vivo xenograft validation; single lab\",\n      \"pmids\": [\"35954339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Proteolytic cleavage of the CD109 bait region by diverse proteases induces a conformational change that activates the CD109 thioester, enabling covalent conjugation of proteases (protease inhibition); the GPI-anchored MG8 domain dissociates during this conformational change, releasing CD109 from the cell surface.\",\n      \"method\": \"In vitro protease cleavage assays, thioester activation assay, protease conjugation and activity assays, conformational change analysis\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstituted biochemical mechanism with multiple proteases and defined thioester chemistry\",\n      \"pmids\": [\"38587194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structures of CD109 in native, protease-activated, and methylamine-activated conformations reveal that bait-region proteolysis triggers a conformational change analogous to that of the protease inhibitor A2ML1, exposing a reactive thioester that conjugates and inhibits proteases; CD109 glycans contribute to protease inhibition by limiting substrate access.\",\n      \"method\": \"Cryo-electron microscopy structure determination, deglycosylation experiments, chymotrypsin conjugation assays, comparison with A2ML1 structure\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic-resolution cryo-EM structures in multiple conformational states with functional validation\",\n      \"pmids\": [\"40482031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CD109 interacts with and stabilizes IL-6 receptor alpha (IL6Rα) expression at the cell surface in SCC cells; CD109 promotes IL-6/STAT3/NRF2 pathway activation and maintains cancer cell stemness and antioxidant state (SOD1, HO-1); loss of CD109 attenuates this pathway.\",\n      \"method\": \"Co-immunoprecipitation of CD109 with IL6Rα, immunofluorescence, FACS, western blotting for STAT3/NRF2/SOD1/HO1, spheroid formation assays, multi-omic tumor analysis\",\n      \"journal\": \"Experimental hematology & oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus multiple signaling readouts with clinical validation; single lab\",\n      \"pmids\": [\"40317079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Tumor-derived soluble CD109 (sCD109) upregulates CD73 on macrophages by activating the FcγRI/SYK/NF-κB signaling pathway; additionally, internalized sCD109 in macrophages binds E3 ligase TRIM21 at the same site as CD73, preventing CD73 protein degradation, thereby expanding CD73+ immunosuppressive tumor-associated macrophages and inhibiting T-cell responses.\",\n      \"method\": \"Proteomic/single-cell transcriptomic analysis, mass spectrometry, co-immunoprecipitation of sCD109 with TRIM21, CD73 ubiquitination assays, FcγRI/SYK/NF-κB pathway analysis, dual CD109/PD-L1 blockade in vivo\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP of sCD109 with TRIM21, NF-κB pathway analysis, in vivo dual blockade; single lab\",\n      \"pmids\": [\"40220905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Mesotrypsin (PRSS3), upregulated in malignant breast cancer T4-2 cells, cleaves/sheds CD109 from the cell surface; CD109 is identified as a functional proteolytic target of mesotrypsin mediating the malignant growth phenotype.\",\n      \"method\": \"Proteomic identification of mesotrypsin substrate, PRSS3 knockdown, recombinant mesotrypsin treatment, 3D organotypic culture assays\",\n      \"journal\": \"Breast cancer research and treatment\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — proteomic substrate identification with KD and recombinant protein treatment; single lab\",\n      \"pmids\": [\"20035377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CD109 deficiency in mice leads to osteopenia/osteoporosis-like phenotype with reduced bone volume and increased bone turnover (elevated N-terminal telopeptide of collagen I and alkaline phosphatase), indicating that CD109 plays a role in bone metabolism in vivo.\",\n      \"method\": \"CD109 knockout mice, micro-CT analysis of femur, bone histomorphometry, serum bone turnover markers\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined skeletal phenotype and multiple bone metabolic markers\",\n      \"pmids\": [\"29767469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In osteosarcoma cells, CD109 knockdown enhances SMAD1/5/9 phosphorylation under BMP-2 stimulation and reduces cell migration in the presence of BMP, indicating that CD109 negatively regulates BMP signaling and BMP-dependent migration in sarcoma (distinct from its TGF-β regulatory role).\",\n      \"method\": \"CD109 knockdown in osteosarcoma cell lines, BMP-2 stimulation, western blotting for phospho-SMAD1/5/9, in vitro wound healing migration assay, immunohistochemistry of human tumor tissue\",\n      \"journal\": \"Pathology, research and practice\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — knockdown with BMP stimulation and functional readout; single lab\",\n      \"pmids\": [\"37030166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CD109 on conventional DC2s (cDC2s) is required for airway hyperreactivity and eosinophilic inflammation; CD109-deficient cDC2s have high RUNX3 expression and poor ability to drive Th2 differentiation; adoptive transfer of CD109-deficient DCs fails to induce AHR and eosinophilic inflammation.\",\n      \"method\": \"CD109 KO mice, allergen sensitization models (house dust mite, OVA), ex vivo DC-T cell co-cultures, adoptive transfer of bone marrow-derived DCs, anti-CD109 antibody administration\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO, adoptive transfer, and pharmacological blockade all converging on same mechanism; 15 citations\",\n      \"pmids\": [\"36215676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Mechanical force induces CD109 expression on periodontal ligament stem cells (PDLSCs) via repression of miR-340-5p; CD109 suppresses osteogenesis of PDLSCs via the JAK/STAT3 signaling pathway, while promoting osteoclast formation and M1 macrophage polarization through paracrine signaling; CD109 lentiviral knockdown in vivo increases osteogenic activity and decreases osteoclast numbers during tooth movement.\",\n      \"method\": \"In vitro mechanical force stimulation, miR-340-5p manipulation, JAK/STAT3 inhibition, lentiviral shRNA knockdown in rat periodontal tissues in vivo, flow cytometry, osteogenic/osteoclast differentiation assays\",\n      \"journal\": \"Stem cells translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro mechanistic pathway plus in vivo lentiviral KD; single lab\",\n      \"pmids\": [\"38885217\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD109 is a GPI-anchored, thioester-containing glycoprotein that functions as a multifunctional co-receptor: it negatively regulates TGF-β signaling by binding TGF-β receptors (requiring furin-mediated processing into 180/25 kDa fragments), directing them to caveolin-1-positive caveolae for SMAD7/Smurf2-mediated degradation, and as soluble sCD109 by directly binding and sequestering TGF-β ligand; in parallel, membrane-anchored CD109 interacts with EGFR and IL-6Rα to stabilize their expression and promote AKT/mTOR and JAK-STAT3/NRF2 oncogenic signaling; structurally, CD109 belongs to the alpha2-macroglobulin family and undergoes bait-region proteolysis-triggered conformational change that activates its thioester to covalently conjugate and inhibit proteases while releasing CD109 from the cell surface.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CD109 is a GPI-anchored glycoprotein of the alpha2-macroglobulin/thioester-containing protein family that functions as a multifaceted regulator of TGF-β, STAT3, and EGFR signaling and as a protease inhibitor. As a membrane co-receptor, furin-processed CD109 (180/25 kDa fragments) associates with TGF-β type I receptor and directs it to caveolin-1-positive caveolae for SMAD7/Smurf2-mediated ubiquitin-dependent degradation, thereby suppressing canonical TGF-β/Smad2/3 signaling in keratinocytes, hematopoietic progenitors, and fibrotic tissues [PMID:16754747, PMID:20101215, PMID:21295082, PMID:21898545, PMID:23436317]; soluble shed CD109 directly sequesters TGF-β ligand with high affinity [PMID:26621871]. Simultaneously, membrane-anchored CD109 physically interacts with EGFR, GP130 (IL-6Rα), and GRP78 to promote AKT/mTOR, JAK-STAT3/NRF2, and YAP signaling, sustaining cancer cell stemness, metastasis, and chemoresistance [PMID:25724945, PMID:33986188, PMID:28191885, PMID:29654145, PMID:40317079]. Structurally, cryo-EM reveals that bait-region proteolysis triggers a conformational change that activates the CD109 thioester for covalent conjugation and inhibition of proteases, while releasing CD109 from the cell surface — a mechanism analogous to A2ML1 [PMID:38587194, PMID:40482031].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing CD109 as a thioester-containing member of the alpha2-macroglobulin superfamily resolved the molecular identity of this GPI-anchored surface glycoprotein and predicted a proteolysis-activated covalent-binding mechanism.\",\n      \"evidence\": \"cDNA cloning, sequence analysis, and biochemical demonstration of intact thioester bond in native CD109 from platelets and cell lines\",\n      \"pmids\": [\"11861284\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No direct demonstration of protease inhibition at this stage\", \"Physiological ligands/targets of the thioester unknown\", \"Three-dimensional structure unavailable\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapping the Gov/HPA-15 platelet alloantigen to a single Tyr703Ser polymorphism in CD109 resolved a clinically significant platelet antigen system at the molecular level.\",\n      \"evidence\": \"RT-PCR genotyping and CHO cell transfection with each CD109 variant confirmed allele-specific recognition by Gov antisera\",\n      \"pmids\": [\"11861285\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences of Y703S on CD109 biochemistry unknown\", \"No structural explanation for why this site is immunogenic\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identifying CD109 as the 150 kDa GPI-anchored TGF-β1 binding protein in keratinocytes established its role as a co-receptor that negatively modulates TGF-β signaling, independent of simple ligand sequestration.\",\n      \"evidence\": \"Affinity purification and microsequencing from keratinocytes, plus loss-of-function (GPI-anchor deficient) and gain-of-function studies\",\n      \"pmids\": [\"16754747\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of TGF-β receptor modulation unresolved\", \"Whether CD109 directly contacts the receptor versus ligand unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that furin cleaves CD109 into 180/25 kDa fragments and that this processing is required for TGF-β receptor association and signaling inhibition provided the first mechanistic step linking CD109 maturation to its co-receptor function.\",\n      \"evidence\": \"Site-directed mutagenesis of the tetra-arginine furin site (R1273S), co-IP with TGFBR1, and cell growth assays\",\n      \"pmids\": [\"20101215\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how processed CD109 engages TGFBR1 unknown\", \"Whether furin cleavage also activates the thioester not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showing that CD109 associates with caveolin-1 and routes TGF-β receptors to caveolae for degradation revealed the trafficking mechanism underlying CD109-mediated TGF-β signal suppression, and subsequent work demonstrated this requires SMAD7/Smurf2 ubiquitin ligase activity.\",\n      \"evidence\": \"Co-IP of CD109 with caveolin-1, receptor internalization/degradation assays (2011); siRNA knockdown of SMAD7 and dominant-negative Smurf2 epistasis (2012)\",\n      \"pmids\": [\"21295082\", \"21898545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct versus indirect nature of the CD109–caveolin-1 interaction not resolved\", \"Stoichiometry of the CD109/caveolin-1/receptor complex unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"CD109-deficient mice displaying epidermal hyperplasia with elevated STAT3 (but not Smad2) phosphorylation established that CD109 regulates skin homeostasis in vivo and revealed an unexpected STAT3-regulatory axis beyond TGF-β.\",\n      \"evidence\": \"CD109 knockout mouse phenotyping with immunohistochemistry for pSTAT3 and pSmad2\",\n      \"pmids\": [\"22846721\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD109 directly regulates STAT3 or acts through an intermediate receptor unknown at this stage\", \"Relationship between STAT3 hyperactivation and TGF-β suppression in vivo unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Transgenic CD109 overexpression in murine epidermis protected against wound-healing inflammation and bleomycin-induced skin fibrosis by suppressing Smad2/3 phosphorylation and ECM production, validating CD109 as an in vivo antifibrotic factor.\",\n      \"evidence\": \"CD109 transgenic mice in excisional wound and bleomycin scleroderma models with pSmad2/3, collagen, and cytokine readouts\",\n      \"pmids\": [\"23438099\", \"23436317\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Therapeutic potential of exogenous sCD109 in fibrosis not tested\", \"Whether CD109 modulates non-Smad TGF-β pathways in fibrosis not assessed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Biophysical demonstration that soluble CD109 binds TGF-β with high affinity and blocks receptor binding established a second, ligand-sequestration mechanism of TGF-β inhibition complementary to the membrane co-receptor function.\",\n      \"evidence\": \"Surface plasmon resonance, radioligand competition, and Smad2/3 phosphorylation assays\",\n      \"pmids\": [\"26621871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of ligand sequestration versus receptor routing in vivo not quantified\", \"Binding site on TGF-β not mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery of a cell-surface CD109–EGFR interaction that enhances EGF signaling in glioblastoma cells expanded CD109's receptor repertoire beyond TGF-β, later confirmed in lung and squamous cell carcinoma where CD109 stabilizes EGFR and activates AKT/mTOR signaling.\",\n      \"evidence\": \"Co-IP of CD109 with EGFR, migration/invasion assays in glioblastoma (2015); co-IP and EGFR phosphorylation/AKT/mTOR assays in lung adenocarcinoma (2020) and SCC (2022)\",\n      \"pmids\": [\"25724945\", \"32133706\", \"35954339\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of CD109–EGFR interaction not determined\", \"Whether the GPI anchor directly mediates the interaction or lipid raft co-localization is responsible remains unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"An in vivo barcoded tumor screen identified CD109 as a driver of lung cancer metastasis through JAK-STAT3, establishing CD109's oncogenic signaling role in an unbiased genetic framework and showing pharmacological JAK inhibition blocks CD109-driven metastasis.\",\n      \"evidence\": \"In vivo tumor barcoding in mouse lung adenocarcinoma model with JAK inhibitor validation\",\n      \"pmids\": [\"28191885\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical link between CD109 and JAK-STAT3 components not identified at this point\", \"Whether CD109's STAT3 role is ligand-dependent or constitutive unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of cell-surface GRP78 as a CD109-binding partner under ER stress showed that the GRP78–CD109 complex promotes caveolar routing of TGF-β receptors, linking the unfolded protein response to TGF-β signal suppression in cancer.\",\n      \"evidence\": \"Cell-surface co-IP of GRP78 with CD109, Smad2 phosphorylation and receptor trafficking assays\",\n      \"pmids\": [\"29654145\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GRP78 interaction requires furin-processed CD109 not tested\", \"Generalizability beyond the cell line used unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"CD109-deficient mice develop spontaneous psoriasiform skin inflammation via barrier disruption and γδ T17 cell activation, indicating that CD109 maintains skin barrier integrity and restrains IL-23-dependent innate immune responses in a cell-extrinsic manner.\",\n      \"evidence\": \"CD109 KO mice with allergen challenge, microbiota depletion, IL-23 blockade, and adoptive transfer\",\n      \"pmids\": [\"31597099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which CD109 fortifies the skin barrier not elucidated\", \"Relative contributions of TGF-β versus STAT3 deregulation to barrier defect unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that CD109 physically interacts with GP130 to activate IL-6/STAT3 in glioblastoma stem cells resolved the receptor-level mechanism linking CD109 to STAT3 activation and explained how CD109 sustains cancer stemness and chemoresistance.\",\n      \"evidence\": \"Reciprocal co-IP of CD109 with GP130, STAT3 phosphorylation, sphere formation, and in vivo tumor growth assays\",\n      \"pmids\": [\"33986188\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD109–GP130 interaction is direct or scaffolded by IL-6Rα not resolved\", \"Whether GP130 interaction applies outside glioblastoma not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Biochemical reconstitution showed that bait-region proteolysis by diverse proteases activates the CD109 thioester for covalent protease conjugation and inhibition, and that GPI-anchor dissociation accompanies this conformational change — establishing CD109 as a functional protease inhibitor.\",\n      \"evidence\": \"In vitro protease cleavage, thioester activation, and protease conjugation/activity assays with multiple proteases\",\n      \"pmids\": [\"38587194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological protease substrates for CD109 inhibition not identified in vivo\", \"Whether protease-inhibitor function operates independently of TGF-β co-receptor function unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cryo-EM structures of native, protease-activated, and methylamine-activated CD109 revealed atomic-resolution conformational states analogous to A2ML1, showing how glycans limit substrate access and how thioester exposure enables covalent protease capture.\",\n      \"evidence\": \"Cryo-EM structure determination in multiple states, deglycosylation and chymotrypsin conjugation assays\",\n      \"pmids\": [\"40482031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of CD109 in complex with TGF-β receptor or EGFR\", \"How thioester-mediated protease inhibition relates to signaling co-receptor functions is mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"CD109 was shown to stabilize IL-6Rα at the SCC cell surface and promote IL-6/STAT3/NRF2 antioxidant signaling, and separately, tumor-derived sCD109 was found to expand immunosuppressive CD73+ macrophages via FcγRI/SYK/NF-κB and TRIM21-mediated prevention of CD73 degradation, broadening CD109's roles into immune evasion.\",\n      \"evidence\": \"Co-IP of CD109 with IL-6Rα and signaling readouts in SCC (2025); proteomic/scRNA-seq, co-IP of sCD109 with TRIM21, and dual CD109/PD-L1 blockade in vivo in hepatocellular carcinoma (2025)\",\n      \"pmids\": [\"40317079\", \"40220905\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether sCD109-TRIM21 interaction occurs in other tumor types not tested\", \"Structural basis of sCD109 engagement with FcγRI unknown\", \"Single-lab findings for both; independent replication needed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CD109's three biochemically distinct activities — thioester-mediated protease inhibition, membrane co-receptor function for TGF-β/EGFR/GP130, and soluble ligand sequestration/immune modulation — are coordinated in vivo remains the central unresolved question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of CD109 in complex with any signaling receptor\", \"Relative in vivo contributions of protease-inhibitor versus co-receptor functions unknown\", \"No genetic disease clearly mapped to CD109 mutations in humans\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3, 4, 5, 11, 14, 16, 32]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [26, 27]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 5, 22, 25, 28]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 3, 4, 12, 19, 25, 28]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [6, 11, 24, 26, 29]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 14, 15, 16, 19, 20, 22, 25, 28, 29]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [17, 29, 33]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [15, 19, 20, 22, 25]}\n    ],\n    \"complexes\": [\n      \"TGF-β receptor/CD109/caveolin-1 complex\",\n      \"CD109/EGFR complex\",\n      \"CD109/GP130 complex\"\n    ],\n    \"partners\": [\n      \"TGFBR1\",\n      \"CAV1\",\n      \"EGFR\",\n      \"IL6ST\",\n      \"HSPA5\",\n      \"LTBP1\",\n      \"IL6R\",\n      \"TRIM21\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}