{"gene":"FAP","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":1995,"finding":"FAP-1 (PTPN13), a protein tyrosine phosphatase, was identified as a binding partner of Fas (CD95/Apo-1); the carboxyl-terminal 15 amino acids of Fas are necessary and sufficient for interaction with FAP-1. Gene transfer-mediated overexpression of FAP-1 partially abolished Fas-induced apoptosis in a T cell line, establishing FAP-1 as an inhibitor of Fas-mediated apoptosis.","method":"Yeast two-hybrid screen, co-immunoprecipitation, deletion mapping, gene transfer overexpression assay in T cells","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding confirmation, deletion mutagenesis defining minimal binding domain, functional rescue experiment; foundational paper replicated by subsequent studies","pmids":["7536343"],"is_preprint":false},{"year":2003,"finding":"FAP-1 association with Fas attenuates Fas export to the cell surface, increasing the intracellular pool of Fas within the cytoskeleton network. Forced FAP-1 expression reduced surface Fas; dominant-negative FAP-1 or FAP-1 siRNA knockdown upregulated surface Fas. A point mutation at amino acid 275 of Fas decreased FAP-1 association and increased Fas surface export.","method":"Overexpression of FAP-1 and dominant-negative FAP-1, siRNA knockdown, flow cytometry for surface Fas, site-directed mutagenesis of Fas","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (OE, DN, siRNA, mutagenesis) in single rigorous study establishing mechanistic link between FAP-1 binding and Fas trafficking","pmids":["12724420"],"is_preprint":false},{"year":2002,"finding":"PTPL1/FAP-1 phosphatase triggers apoptosis in human breast cancer cells (MCF7) via inhibition of the insulin receptor substrate-1/PI3K/Akt pathway, independent of Fas. FAP-1 expression abolished IGF-I-induced survival signaling (80% reduction in PI3K activity, 55% inhibition of Akt activation, 65% decrease in IRS-1 phosphorylation).","method":"Antisense transfection to abolish PTPL1/FAP-1, TUNEL and nucleosome ELISA for apoptosis, PI3K activity assay, Akt phosphorylation assay, IRS-1 tyrosine phosphorylation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function (antisense) with multiple downstream biochemical readouts in one rigorous study; novel pathway distinct from Fas mechanism","pmids":["12354757"],"is_preprint":false},{"year":1998,"finding":"Mouse FAP (Fap) encodes a serine protease with dipeptidyl peptidase activity, consistent with its homology to dipeptidyl peptidase IV (DPP IV). A chimeric FAP fusion protein expressed in a baculovirus system demonstrated dipeptidyl peptidase activity. The gene spans ~60 kb with 26 exons; the serine protease consensus motif WGWSYGG is split across two exons, a feature shared with DPP IV.","method":"Baculovirus expression of chimeric FAP fusion protein, enzymatic dipeptidyl peptidase activity assay, genomic structure analysis","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic assay of recombinant protein; foundational biochemical characterization","pmids":["9688278"],"is_preprint":false},{"year":2016,"finding":"FAP triggers induction of a cancer-associated fibroblast (CAF) subset with an inflammatory phenotype through a uPAR-dependent FAK-Src-JAK2 signaling pathway that persistently activates STAT3, leading to upregulation of CCL2. FAP(+)CAF-derived CCL2 promotes tumor growth by recruiting myeloid-derived suppressor cells (MDSCs) via CCR2. Abrogation of this effect in Ccr2-deficient mice confirmed the pathway.","method":"Enforced FAP expression in normal fibroblasts, signaling pathway inhibition (uPAR, FAK, Src, JAK2), STAT3 activation assays, CCL2 measurement, MDSC recruitment assay in murine liver tumor model, Ccr2-knockout mice","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain-of-function plus pathway inhibitors plus genetic knockout validation, multiple orthogonal methods in one study","pmids":["27216177"],"is_preprint":false},{"year":2015,"finding":"FAP participates in collagen catabolism by mediating ordered proteolytic processing of matrix metalloproteinase (MMP)-derived collagen cleavage products, leading to increased collagen internalization via Endo180 without altering Endo180 expression. FAP-deficient mice showed accumulation of intermediate-sized collagen fragments and increased lung fibrosis; restoration of FAP expression in FAP-deficient mouse lungs reduced lung hydroxyproline to wild-type levels.","method":"FAP-knockout mice in bleomycin and irradiation fibrosis models, in vitro collagen cleavage assay, pharmacologic FAP inhibition, collagen internalization assay, AAV-mediated FAP re-expression in FAP-deficient mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro enzymatic assay plus KO mice plus rescue experiment; multiple orthogonal approaches in one rigorous study","pmids":["26663085"],"is_preprint":false},{"year":2016,"finding":"Pharmacological inhibition of FAP (using talabostat) in diet-induced obese mice elevated total and intact plasma FGF21 levels and produced robust metabolic benefits (reduced body weight, improved glucose tolerance, reduced adiposity). These effects were absent in FGF21-knockout obese mice, and FAP inhibition in vitro blocked enzymatic degradation of human FGF21. This establishes FAP as the endopeptidase responsible for FGF21 cleavage/inactivation in vivo.","method":"Pharmacologic inhibition with talabostat in DIO mice, FGF21-KO mice as controls, in vitro FAP enzymatic assay with human FGF21, intact FGF21 measurement by ELISA","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay plus in vivo pharmacology plus genetic (FGF21-KO) epistasis; multiple orthogonal approaches","pmids":["27689014"],"is_preprint":false},{"year":2017,"finding":"A fluorescence-based assay established that circulating FAP endopeptidase cleaves FGF21 at a specific post-proline site, distinguishing FAP endopeptidase activity from related enzymes (PREP, DPPIV). Structural modeling elucidated the mechanistic basis for FAP substrate specificity. Assay was validated using Fap-deficient mice and detected elevated FAP activity in human patients with liver cirrhosis.","method":"Homogeneous fluorescence intensity assay with FGF21 as substrate, Fap-KO mice validation, structural modeling, human plasma samples from liver cirrhosis patients","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with substrate specificity profiling, validated in KO mice; single lab but multiple orthogonal methods","pmids":["28970566"],"is_preprint":false},{"year":2023,"finding":"FAP (Fap) is a prolyl-specific serine protease that degrades BNP (brain natriuretic peptide), a novel substrate identified in cardiac fibroblasts. Fap degrades BNP to inhibit vascular endothelial cell migration and tube formation. Pharmacological or genetic inhibition of Fap in mice improved cardiac function after myocardial infarction and increased angiogenesis in the peri-infarct zone. Cardioprotective effects of FAP inhibition were absent in Nppb (pre-proBNP)- or Npr1 (BNP receptor)-deficient mice, confirming BNP as the physiological substrate mediating these effects.","method":"Fap-KO and pharmacological inhibition in MI mouse model, echocardiography, RNA-seq, biochemical analysis, cardiac fibroblast/endothelial cell co-culture, Nppb-KO and Npr1-KO epistasis experiments","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — substrate identification with in vitro degradation assay plus multiple genetic epistasis experiments (Fap-KO, Nppb-KO, Npr1-KO) in one study","pmids":["36756875"],"is_preprint":false},{"year":2016,"finding":"Specific residues (G10, S14, A18) in the FAP transmembrane domain form a small-X3-small motif that mediates FAP homodimerization. Mutations to these interfacial residues (G10L, S14L, A18L) reduced FAP TM-CYTO dimerization. G10L specifically decreased FAP endopeptidase activity by more than 25% and reduced cell-surface versus intracellular FAP expression, establishing that TM-mediated dimerization is required for both FAP trafficking and protease activity.","method":"AraTM bacterial dimerization assay, site-directed mutagenesis of TM interface residues, FAP endopeptidase activity assay, cell surface vs. intracellular FAP localization","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — mutagenesis with functional enzymatic readout and trafficking assay; multiple orthogonal methods in single lab","pmids":["27155568"],"is_preprint":false},{"year":1999,"finding":"FAP-1 (PTPN13) is functionally expressed in human thyrocytes and protects them from Fas-mediated programmed cell death. Competitive inhibition of FAP-1 binding to Fas using synthetic Ac-SLV tripeptide significantly increased Fas-mediated cell death, and synergized with sub-optimal cycloheximide treatment, demonstrating FAP-1 functions as an endogenous inhibitor of Fas-induced apoptosis in thyroid follicular cells.","method":"Ribonuclease protection assay for FAP-1 mRNA, immunohistochemistry and flow cytometry for FAP-1 protein, competitive inhibition with Ac-SLV tripeptide, cycloheximide treatment, cell death assay","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional competition assay with synergy experiment in primary cells; single lab, multiple methods but no direct mutagenesis","pmids":["10537175"],"is_preprint":false},{"year":2022,"finding":"FAP expression in adipose tissue macrophages (ATM) mediates CCL8 chemokine expression, which recruits monocyte-derived proinflammatory macrophages into obese adipose tissue. Macrophage-specific FAP deficiency protected mice from diet-induced obesity and reduced proinflammatory macrophage infiltration. FAP in ATM also decreases monoamine oxidase expression, thereby increasing norepinephrine levels and enhancing lipolysis in white adipose tissue. CCL8 overexpression restored HFD-induced metabolic phenotypes in FAP-deficient mice.","method":"Macrophage-specific Fap-knockout mice on high-fat diet, CCL8 measurement, CCL8 overexpression rescue experiment, monoamine oxidase assay, NE measurement, energy expenditure assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific KO, rescue overexpression, multiple downstream mechanistic readouts in one rigorous study","pmids":["38100414"],"is_preprint":false},{"year":2022,"finding":"FAP in ovarian cancer cells recruits PRKDC (DNA-PK) into lipid rafts, enabling NF-κB activation and promoting cell survival via BIRC5 (survivin) downstream. FAP depletion prevented lipid raft localization of PRKDC and abolished NF-κB activity. FAP's enzymatic activity was dispensable for this pro-survival function, as established by enzymatic mutant analysis.","method":"FAP silencing by siRNA, NF-κB activity assay, co-immunoprecipitation of FAP and PRKDC, lipid raft fractionation, apoptosis assay, enzymatic activity mutants, EpCAM aptamer-delivered FAP siRNA in xenograft","journal":"Cancer gene therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, lipid raft fractionation, enzymatic mutant, and in vivo xenograft; single lab but multiple orthogonal approaches","pmids":["36494579"],"is_preprint":false},{"year":2019,"finding":"Fibroblastic FAP expression is required for STAT3 activation and CCL2 production in intrahepatic cholangiocarcinoma cancer-associated fibroblasts. FAP knockdown in ICC-CAFs impaired their ability to promote ICC growth, MDSCs infiltration and angiogenesis; these effects were restored by exogenous CCL2. The tumor-promoting function of fibroblastic FAP was dependent on MDSCs, as depletion of Gr-1+ cells reversed the restoring effects of CCL2.","method":"FAP knockdown in primary ICC-CAFs, CCL2 ELISA, MDSC migration assay, subcutaneous tumor model with Gr-1 depletion, exogenous CCL2 rescue","journal":"Neoplasia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with rescue experiment and in vivo epistasis using cell depletion; single lab, multiple methods","pmids":["31759251"],"is_preprint":false},{"year":2018,"finding":"In breast tumors, FAP+ stromal cells comprise two distinct populations distinguished by podoplanin (PDPN) expression: FAP+PDPN+ cancer-associated fibroblasts (CAFs) enriched in TGFβ signaling/fibrosis genes and localized at the tumor outer edge in contact with T cells, and FAP+PDPN- cancer-associated pericytes (CAPs) localized around vessels. FAP+PDPN+ CAFs suppressed T cell proliferation via a nitric oxide-dependent mechanism, whereas FAP+PDPN- pericytes were not immunosuppressive.","method":"Flow cytometry, RNA sequencing of sorted cell populations, immunofluorescence for localization, T cell proliferation assay with nitric oxide pathway inhibition","journal":"Cancer immunology research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional T cell suppression assay with mechanism (nitric oxide), RNA-seq, and localization; single lab","pmids":["30266714"],"is_preprint":false},{"year":2011,"finding":"FAP-1 (PTPN13) shows differentiation-dependent relocalization in pancreatic adenocarcinoma A818-6 cells: in 2D monolayers, FAP-1 localizes to a juxtanuclear cisternal position and the nucleus; upon 3D differentiation into polarized hollow spheres, FAP-1 relocates to the actin cytoskeleton beneath the outer plasma membrane and co-localizes with CD95 (Fas). Knockdown of FAP-1 mRNA in monolayer cells did not alter responsiveness to CD95 agonistic antibodies, indicating that FAP-1 expression did not affect CD95 signal transduction in this context.","method":"Immunofluorescence for FAP-1 and CD95 localization in 2D vs. 3D cultures, flow cytometry for surface CD95, FAP-1 siRNA knockdown, caspase activity assay","journal":"Differentiation; research in biological diversity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with functional consequence plus loss-of-function; single lab, negative result for CD95 signaling is reported","pmids":["22364882"],"is_preprint":false},{"year":2024,"finding":"IL-17a promotes hepatocellular carcinoma by increasing FAP expression in hepatic stellate cells (HSCs) via activation of the STAT3 signaling pathway. STAT3 directly binds to the FAP promoter region (confirmed by CUT&RUN), regulating FAP transcription. Overexpression of IL-17a and FAP in HSCs promoted HCC cell proliferation and migration and inhibited HCC cell apoptosis in vitro and in vivo.","method":"CUT&RUN assay for STAT3 binding to FAP promoter, IL-17a and FAP overexpression in HSCs, in vivo tumor models, HCC cell proliferation/migration/apoptosis assays","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct chromatin binding assay (CUT&RUN) plus gain-of-function experiments; single lab","pmids":["38740736"],"is_preprint":false},{"year":2023,"finding":"FAP overexpression in colorectal cancer cells promoted cell growth, invasion, metastasis, and enhanced chemoresistance. MPRIP (myosin phosphatase Rho-interacting protein) was identified as a direct interacting protein of FAP. FAP influences chemotherapy resistance and macrophage recruitment/M2 polarization through the Rho/Hippo/YAP signaling pathway.","method":"Co-immunoprecipitation for FAP-MPRIP interaction, FAP overexpression and knockdown in CRC cells, invasion/migration assays, macrophage polarization assay, YAP signaling analysis","journal":"iScience","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP for binding partner plus overexpression/KD phenotype; single lab, limited mechanistic depth in abstract","pmids":["37213233"],"is_preprint":false},{"year":2024,"finding":"FAP-positive chondrocytes in osteoarthritis promote chondrocyte senescence; overexpression of FAP in chondrocytes promotes senescence while genetic knockout of FAP in chondrocytes alleviates OA. FAP siRNA knockdown suppressed the NF-κB pathway to reduce the senescence-associated secretory phenotype (SASP). Soluble FAP secreted from OA synovium was shown to degrade type II collagen in cartilage.","method":"FAP overexpression and siRNA knockdown in chondrocytes, chondrocyte-specific FAP-KO mouse OA model, SA-β-Gal senescence assay, NF-κB pathway analysis, PET/CT with [68Ga]Ga-FAPI-04, LNP-FAP siRNA intraarticular injection in rat OA model","journal":"Journal of nanobiotechnology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO plus OE/KD with mechanistic pathway readout; single lab but multiple complementary approaches","pmids":["39456041"],"is_preprint":false},{"year":2024,"finding":"FAP in senescent gingival fibroblasts promotes periodontitis via FAP/OLN (osteolectin) imbalance driven by mTOR pathway activation. Recombinant FAP increased pro-inflammatory cytokine secretion and osteoclast differentiation in macrophages. Rapamycin treatment restored the FAP/OLN balance. FAP inhibition reduced macrophage inflammation, collagen degradation, and bone resorption in experimental periodontitis.","method":"scRNA-seq, recombinant FAP treatment of macrophages, rapamycin treatment of gingival fibroblasts, FAP inhibition in mouse periodontitis model, osteoclast differentiation assay, cytokine measurement","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — recombinant protein functional assay plus pharmacological inhibition in vivo with multiple readouts; single lab","pmids":["39716898"],"is_preprint":false},{"year":2025,"finding":"FAP+ cancer-associated fibroblasts in breast cancer secrete fibronectin 1 (FN1), which engages integrin α5β1 on macrophages to activate FAK-AKT-STAT3 signaling and drive immunosuppressive M2-like macrophage polarization. Pharmacological disruption of FN1-integrin α5β1 signaling with Cilengitide reprogrammed the tumor immune landscape and suppressed tumor growth in mouse models.","method":"scRNA-seq, Co-IP/signaling pathway analysis, Cilengitide pharmacological inhibition in vivo mouse models, macrophage polarization assay, integrin α5β1 blocking experiments","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic signaling pathway defined with pharmacological inhibition in vivo; single lab","pmids":["40263422"],"is_preprint":false},{"year":2024,"finding":"FAP+ gastric cancer mesenchymal stromal cells promote gastric cancer progression by paracrine secretion of INHBA, which activates SMAD2/3 signaling in GC cells. FAP+ GCMSCs also induce collagen deposition in ECM that upregulates GC cell invasion and stemness through collagen–ITGB1 interaction triggering FAK and YAP phosphorylation.","method":"FAP+ cell isolation by flow cytometry, transcriptomic sequencing, conditioned medium experiments, ELISA for INHBA, Western blot for SMAD2/3 phosphorylation, IHC and Masson trichrome staining for ECM, integrin/FAK/YAP pathway analysis","journal":"International immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple downstream mechanistic readouts with pathway validation; single lab","pmids":["39615112"],"is_preprint":false}],"current_model":"FAP (fibroblast activation protein) is a type II transmembrane serine protease with dual enzymatic activities (dipeptidyl peptidase and endopeptidase) that homodimerizes via a specific TM interface (G10, S14, A18) required for cell surface trafficking and protease activity; its substrates include FGF21 (C-terminal cleavage inactivating the hormone), BNP (cleavage inhibiting angiogenesis post-MI), and MMP-derived collagen fragments (promoting collagen clearance); in stromal fibroblasts and macrophages FAP drives tumor immunosuppression via a uPAR-FAK-Src-JAK2-STAT3-CCL2 axis that recruits MDSCs, and via FN1-integrin α5β1-FAK-AKT-STAT3 signaling that promotes M2 macrophage polarization; in ovarian cancer cells FAP recruits PRKDC into lipid rafts to activate NF-κB independently of its enzymatic activity; and the FAP-1/PTPN13 isoform (a distinct protein sharing the FAP alias) interacts with the C-terminal 15 amino acids of Fas to inhibit Fas surface trafficking and apoptosis while also suppressing IGF-I/IRS-1/PI3K/Akt survival signaling in breast cancer cells."},"narrative":{"mechanistic_narrative":"FAP is a type II transmembrane serine protease with both dipeptidyl peptidase and post-proline endopeptidase activities that processes extracellular substrates to regulate fibrosis, metabolism, cardiac repair, and tumor immunosuppression [PMID:9688278, PMID:27689014]. Homodimerization through a small-X3-small transmembrane motif (G10, S14, A18) is required for both cell-surface trafficking and endopeptidase activity [PMID:27155568]. Enzymatically, FAP cleaves and inactivates the metabolic hormone FGF21 at a specific post-proline site [PMID:27689014, PMID:28970566], degrades BNP in cardiac fibroblasts to restrain post-infarct angiogenesis [PMID:36756875], and mediates ordered proteolysis of MMP-derived collagen fragments to promote their internalization via Endo180 and limit fibrosis [PMID:26663085]. In the tumor and inflammatory stroma, FAP-expressing cancer-associated fibroblasts and macrophages drive immunosuppression: a uPAR-FAK-Src-JAK2 pathway sustains STAT3 activation and CCL2 production to recruit myeloid-derived suppressor cells [PMID:27216177, PMID:31759251], FN1-integrin α5β1-FAK-AKT-STAT3 signaling polarizes macrophages toward an M2 phenotype [PMID:40263422], and adipose-tissue macrophage FAP drives CCL8-dependent proinflammatory recruitment and modulates lipolysis [PMID:38100414]. Independently of its catalytic activity, FAP recruits PRKDC into lipid rafts to activate NF-κB and promote ovarian cancer cell survival [PMID:36494579]. FAP expression is itself induced by STAT3 binding to its promoter downstream of IL-17a in hepatic stellate cells [PMID:38740736]. Distinct from this transmembrane protease, the FAP-1/PTPN13 protein tyrosine phosphatase—which shares the FAP alias—binds the C-terminal 15 residues of Fas to suppress Fas surface export and apoptosis [PMID:7536343, PMID:12724420] and antagonizes IGF-I/IRS-1/PI3K/Akt survival signaling [PMID:12354757].","teleology":[{"year":1995,"claim":"Established the FAP-1/PTPN13 phosphatase as a direct Fas-binding inhibitor of apoptosis, defining the minimal interaction surface on Fas.","evidence":"Yeast two-hybrid, co-IP, deletion mapping, and overexpression rescue in T cells","pmids":["7536343"],"confidence":"High","gaps":["Did not establish the structural basis of the interaction","Mechanism of apoptosis suppression downstream of binding undefined","This protein is distinct from the FAP transmembrane protease sharing the alias"]},{"year":1998,"claim":"Defined FAP (the transmembrane protease) biochemically as a DPP IV-homologous serine protease with dipeptidyl peptidase activity.","evidence":"Baculovirus expression of chimeric FAP and in vitro dipeptidyl peptidase assay plus genomic structure analysis","pmids":["9688278"],"confidence":"High","gaps":["No physiological substrate identified","Endopeptidase activity not yet distinguished from dipeptidyl peptidase activity"]},{"year":1999,"claim":"Confirmed FAP-1 functions as an endogenous inhibitor of Fas-mediated apoptosis in primary thyrocytes via its Fas-binding motif.","evidence":"Competitive Ac-SLV tripeptide inhibition and cycloheximide synergy in primary thyroid follicular cells","pmids":["10537175"],"confidence":"Medium","gaps":["No direct mutagenesis","Phosphatase catalytic contribution not dissected"]},{"year":2003,"claim":"Mechanistically linked FAP-1 binding to retention of Fas in an intracellular cytoskeletal pool, explaining apoptosis suppression by limiting surface Fas.","evidence":"Overexpression, dominant-negative, siRNA, and Fas site-directed mutagenesis with surface Fas flow cytometry","pmids":["12724420"],"confidence":"High","gaps":["Trafficking machinery coupling FAP-1 to Fas retention unresolved","Generality across cell types not established"]},{"year":2002,"claim":"Identified a Fas-independent pro-apoptotic role for FAP-1 through inhibition of IGF-I/IRS-1/PI3K/Akt survival signaling in breast cancer cells.","evidence":"Antisense knockdown with PI3K activity, Akt phosphorylation, and IRS-1 phosphorylation readouts in MCF7","pmids":["12354757"],"confidence":"High","gaps":["Direct phosphatase substrate within the pathway not pinpointed","Cross-talk with the Fas pathway unaddressed"]},{"year":2015,"claim":"Placed FAP protease in collagen catabolism, showing it processes MMP-derived fragments to enable Endo180-mediated internalization and prevent fibrosis.","evidence":"FAP-KO mice in fibrosis models, in vitro collagen cleavage, internalization assay, and AAV rescue","pmids":["26663085"],"confidence":"High","gaps":["Precise cleavage sites on collagen fragments not mapped","Coordination with Endo180 at the molecular level unclear"]},{"year":2016,"claim":"Identified FGF21 as a physiological FAP endopeptidase substrate, establishing FAP as the enzyme that inactivates this metabolic hormone in vivo.","evidence":"Talabostat inhibition in DIO mice with FGF21-KO epistasis and in vitro FGF21 degradation","pmids":["27689014"],"confidence":"High","gaps":["Tissue source of FGF21-cleaving FAP not localized","Relationship to FAP dimerization-dependent activity not tested here"]},{"year":2016,"claim":"Showed FAP-expressing fibroblasts drive tumor immunosuppression through a uPAR-FAK-Src-JAK2-STAT3 axis producing CCL2 to recruit MDSCs.","evidence":"Enforced FAP expression, pathway inhibitors, STAT3/CCL2 readouts, and Ccr2-KO validation in a murine liver tumor model","pmids":["27216177"],"confidence":"High","gaps":["Whether protease activity is required for this signaling not resolved","Upstream trigger of uPAR engagement undefined"]},{"year":2016,"claim":"Demonstrated that transmembrane dimerization via a G10/S14/A18 motif is required for FAP trafficking and endopeptidase activity, coupling assembly to function.","evidence":"AraTM dimerization assay, TM interface mutagenesis, and enzymatic/localization readouts","pmids":["27155568"],"confidence":"High","gaps":["Structural model of the dimer not solved","Effect of dimerization on substrate selectivity untested"]},{"year":2017,"claim":"Refined FAP substrate specificity, showing circulating FAP cleaves FGF21 at a defined post-proline site distinct from PREP and DPPIV, and built a clinical activity assay.","evidence":"Fluorescence FGF21-cleavage assay, structural modeling, Fap-KO validation, and human cirrhosis plasma","pmids":["28970566"],"confidence":"High","gaps":["Structure-function model not experimentally validated by crystallography","Disease causality of elevated FAP activity not established"]},{"year":2018,"claim":"Resolved FAP+ stroma into immunosuppressive FAP+PDPN+ CAFs and non-suppressive FAP+PDPN- pericytes, attributing T cell suppression to a nitric oxide mechanism.","evidence":"Flow cytometry, RNA-seq of sorted populations, immunofluorescence, and T cell proliferation assays with NO inhibition","pmids":["30266714"],"confidence":"Medium","gaps":["Role of FAP enzymatic activity in NO-mediated suppression not tested","Single tumor type"]},{"year":2019,"claim":"Extended the FAP-STAT3-CCL2-MDSC axis to cholangiocarcinoma CAFs, confirming MDSC-dependence by CCL2 rescue and Gr-1 depletion.","evidence":"FAP knockdown in primary ICC-CAFs, CCL2 ELISA, MDSC migration, and in vivo Gr-1 depletion with CCL2 rescue","pmids":["31759251"],"confidence":"Medium","gaps":["Upstream regulator of fibroblastic FAP not identified here","Single lab"]},{"year":2022,"claim":"Revealed a catalysis-independent FAP function: recruiting PRKDC into lipid rafts to activate NF-κB and BIRC5-mediated survival in ovarian cancer.","evidence":"siRNA silencing, FAP-PRKDC co-IP, lipid raft fractionation, enzymatic mutants, and aptamer-delivered siRNA xenografts","pmids":["36494579"],"confidence":"Medium","gaps":["Single Co-IP for the FAP-PRKDC interaction","How a transmembrane protease scaffolds PRKDC mechanistically unclear"]},{"year":2022,"claim":"Established macrophage FAP as a driver of obesity, acting through CCL8-dependent macrophage recruitment and monoamine oxidase suppression to modulate lipolysis.","evidence":"Macrophage-specific Fap-KO on HFD, CCL8 overexpression rescue, MAO/NE/energy expenditure assays","pmids":["38100414"],"confidence":"High","gaps":["Substrate underlying CCL8 induction not identified","Link to FAP protease activity not dissected"]},{"year":2023,"claim":"Identified BNP as a cardiac FAP substrate whose degradation limits angiogenesis, with FAP inhibition improving post-MI cardiac function.","evidence":"Fap-KO and pharmacological inhibition in MI mice with Nppb-KO and Npr1-KO epistasis and endothelial co-culture","pmids":["36756875"],"confidence":"High","gaps":["Precise BNP cleavage product responsible not defined","Cellular source of active FAP in infarct zone not localized"]},{"year":2024,"claim":"Showed FAP transcription is directly driven by STAT3 downstream of IL-17a in hepatic stellate cells, linking inflammatory signaling to FAP induction in HCC.","evidence":"CUT&RUN for STAT3 at the FAP promoter plus IL-17a/FAP overexpression and in vivo HCC models","pmids":["38740736"],"confidence":"Medium","gaps":["Whether FAP enzymatic activity mediates the tumor effect not tested","Single lab"]},{"year":2024,"claim":"Implicated FAP+ chondrocytes in osteoarthritis, with FAP driving NF-κB-dependent senescence and soluble FAP degrading type II collagen.","evidence":"Chondrocyte-specific FAP-KO OA model, OE/KD, SA-β-Gal, NF-κB analysis, and FAPI PET imaging","pmids":["39456041"],"confidence":"Medium","gaps":["Catalytic vs scaffold contribution to senescence not separated","Single lab"]},{"year":2024,"claim":"Extended FAP's inflammatory role to periodontitis, where senescent fibroblast FAP drives macrophage inflammation and bone resorption via mTOR-linked FAP/osteolectin imbalance.","evidence":"scRNA-seq, recombinant FAP on macrophages, rapamycin, and FAP inhibition in mouse periodontitis","pmids":["39716898"],"confidence":"Medium","gaps":["Direct FAP substrate in this context not identified","Single lab"]},{"year":2025,"claim":"Defined a FAP+ CAF secretome mechanism, FN1-integrin α5β1-FAK-AKT-STAT3, driving M2 macrophage polarization and immunosuppression in breast cancer.","evidence":"scRNA-seq, signaling analysis, integrin blocking, and Cilengitide inhibition in mouse models","pmids":["40263422"],"confidence":"Medium","gaps":["Role of FAP catalytic activity in FN1 production unclear","Single lab"]},{"year":2024,"claim":"Linked FAP+ gastric stromal cells to tumor progression through INHBA-SMAD2/3 paracrine signaling and collagen-ITGB1-FAK-YAP mechanotransduction.","evidence":"FAP+ cell isolation, conditioned medium, INHBA ELISA, SMAD2/3 blots, and integrin/FAK/YAP analysis","pmids":["39615112"],"confidence":"Medium","gaps":["Direct role of FAP enzyme in INHBA secretion not established","Single lab"]},{"year":null,"claim":"It remains unresolved when FAP's diverse stromal and metabolic phenotypes depend on its protease catalysis versus non-enzymatic scaffolding, and no structural model of the FAP dimer or substrate complexes has been experimentally determined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of FAP or its substrate complexes in the corpus","Catalysis-dependent vs scaffold functions not systematically separated across contexts","Substrates underlying chemokine induction (CCL2, CCL8) not identified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[3,5,6,7,8]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[3,6,7,8]},{"term_id":"GO:0140097","term_label":"catalytic activity, acting on DNA","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[9]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1,15]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[15]}],"pathway":[{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[5]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,13,20,11]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[6,11]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,12,20,21]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,1,2,12]}],"complexes":[],"partners":["FAS","PRKDC","MPRIP","FGF21","FN1","ITGA5","ITGB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q12884","full_name":"Prolyl endopeptidase FAP","aliases":["170 kDa melanoma membrane-bound gelatinase","Dipeptidyl peptidase FAP","Fibroblast activation protein alpha","FAPalpha","Gelatine degradation protease FAP","Integral membrane serine protease","Post-proline cleaving enzyme","Serine integral membrane protease","SIMP","Surface-expressed protease","Seprase"],"length_aa":760,"mass_kda":87.7,"function":"Cell surface glycoprotein serine protease that participates in extracellular matrix degradation and involved in many cellular processes including tissue remodeling, fibrosis, wound healing, inflammation and tumor growth. Both plasma membrane and soluble forms exhibit post-proline cleaving endopeptidase activity, with a marked preference for Ala/Ser-Gly-Pro-Ser/Asn/Ala consensus sequences, on substrate such as alpha-2-antiplasmin SERPINF2 and SPRY2 (PubMed:14751930, PubMed:16223769, PubMed:16410248, PubMed:16480718, PubMed:17381073, PubMed:18095711, PubMed:21288888, PubMed:24371721). Degrade also gelatin, heat-denatured type I collagen, but not native collagen type I and IV, vitronectin, tenascin, laminin, fibronectin, fibrin or casein (PubMed:10347120, PubMed:10455171, PubMed:12376466, PubMed:16223769, PubMed:16651416, PubMed:18095711, PubMed:2172980, PubMed:7923219, PubMed:9065413). Also has dipeptidyl peptidase activity, exhibiting the ability to hydrolyze the prolyl bond two residues from the N-terminus of synthetic dipeptide substrates provided that the penultimate residue is proline, with a preference for Ala-Pro, Ile-Pro, Gly-Pro, Arg-Pro and Pro-Pro (PubMed:10347120, PubMed:10593948, PubMed:16175601, PubMed:16223769, PubMed:16410248, PubMed:16651416, PubMed:17381073, PubMed:21314817, PubMed:24371721, PubMed:24717288). Natural neuropeptide hormones for dipeptidyl peptidase are the neuropeptide Y (NPY), peptide YY (PYY), substance P (TAC1) and brain natriuretic peptide 32 (NPPB) (PubMed:21314817). The plasma membrane form, in association with either DPP4, PLAUR or integrins, is involved in the pericellular proteolysis of the extracellular matrix (ECM), and hence promotes cell adhesion, migration and invasion through the ECM. Plays a role in tissue remodeling during development and wound healing. Participates in the cell invasiveness towards the ECM in malignant melanoma cancers. Enhances tumor growth progression by increasing angiogenesis, collagen fiber degradation and apoptosis and by reducing antitumor response of the immune system. Promotes glioma cell invasion through the brain parenchyma by degrading the proteoglycan brevican. Acts as a tumor suppressor in melanocytic cells through regulation of cell proliferation and survival in a serine protease activity-independent manner","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q12884/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FAP","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":[],"url":"https://opencell.sf.czbiohub.org/search/FAP","total_profiled":1310},"omim":[{"mim_id":"620657","title":"AMYLOIDOSIS, HEREDITARY SYSTEMIC 3; AMYLD3","url":"https://www.omim.org/entry/620657"},{"mim_id":"613659","title":"GASTRIC CANCER","url":"https://www.omim.org/entry/613659"},{"mim_id":"611767","title":"MICRO RNA 126; MIR126","url":"https://www.omim.org/entry/611767"},{"mim_id":"611731","title":"APC REGULATOR OF WNT SIGNALING PATHWAY; APC","url":"https://www.omim.org/entry/611731"},{"mim_id":"610155","title":"TYPE 1 DIABETES MELLITUS 19; T1D19","url":"https://www.omim.org/entry/610155"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"endometrium 1","ntpm":29.4}],"url":"https://www.proteinatlas.org/search/FAP"},"hgnc":{"alias_symbol":["DPPIV"],"prev_symbol":[]},"alphafold":{"accession":"Q12884","domains":[{"cath_id":"2.140.10.30","chopping":"114-268","consensus_level":"medium","plddt":97.6383,"start":114,"end":268},{"cath_id":"2.140.10.30","chopping":"280-438","consensus_level":"medium","plddt":97.3748,"start":280,"end":438},{"cath_id":"-","chopping":"444-500","consensus_level":"medium","plddt":98.0389,"start":444,"end":500},{"cath_id":"3.40.50.1820","chopping":"501-755","consensus_level":"medium","plddt":98.2021,"start":501,"end":755}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q12884","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q12884-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q12884-F1-predicted_aligned_error_v6.png","plddt_mean":95.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FAP","jax_strain_url":"https://www.jax.org/strain/search?query=FAP"},"sequence":{"accession":"Q12884","fasta_url":"https://rest.uniprot.org/uniprotkb/Q12884.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q12884/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q12884"}},"corpus_meta":[{"pmid":"24277834","id":"PMC_24277834","title":"Targeting CXCL12 from FAP-expressing carcinoma-associated fibroblasts synergizes with anti-PD-L1 immunotherapy in pancreatic cancer.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/24277834","citation_count":1677,"is_preprint":false},{"pmid":"1651563","id":"PMC_1651563","title":"Mutations of chromosome 5q21 genes in FAP and colorectal cancer patients.","date":"1991","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/1651563","citation_count":1671,"is_preprint":false},{"pmid":"35365629","id":"PMC_35365629","title":"Single-cell and spatial analysis reveal interaction of FAP+ fibroblasts and SPP1+ macrophages in colorectal cancer.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/35365629","citation_count":716,"is_preprint":false},{"pmid":"7536343","id":"PMC_7536343","title":"FAP-1: a protein tyrosine phosphatase that associates with Fas.","date":"1995","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/7536343","citation_count":668,"is_preprint":false},{"pmid":"27216177","id":"PMC_27216177","title":"FAP Promotes Immunosuppression by Cancer-Associated Fibroblasts in the Tumor Microenvironment via STAT3-CCL2 Signaling.","date":"2016","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/27216177","citation_count":612,"is_preprint":false},{"pmid":"24470260","id":"PMC_24470260","title":"Understanding fibroblast activation protein (FAP): substrates, activities, expression and targeting for cancer therapy.","date":"2014","source":"Proteomics. 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activation.","date":"2024","source":"International journal of cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/38614364","citation_count":16,"is_preprint":false},{"pmid":"40799444","id":"PMC_40799444","title":"Single-cell and spatial transcriptomics profile the interaction of SPP1 macrophages and FAP fibroblasts in non-small cell lung cancer.","date":"2025","source":"Translational lung cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/40799444","citation_count":15,"is_preprint":false},{"pmid":"39482333","id":"PMC_39482333","title":"SPP1+ macrophages and FAP+ fibroblasts promote the progression of pMMR gastric cancer.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/39482333","citation_count":15,"is_preprint":false},{"pmid":"37213233","id":"PMC_37213233","title":"FAP promotes metastasis and chemoresistance via regulating YAP1 and macrophages in mucinous colorectal 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Release Society","url":"https://pubmed.ncbi.nlm.nih.gov/40180251","citation_count":14,"is_preprint":false},{"pmid":"22364882","id":"PMC_22364882","title":"Characterisation of FAP-1 expression and CD95 mediated apoptosis in the A818-6 pancreatic adenocarcinoma differentiation system.","date":"2011","source":"Differentiation; research in biological diversity","url":"https://pubmed.ncbi.nlm.nih.gov/22364882","citation_count":14,"is_preprint":false},{"pmid":"38740736","id":"PMC_38740736","title":"IL-17a promotes hepatocellular carcinoma by increasing FAP expression in hepatic stellate cells via activation of the STAT3 signaling pathway.","date":"2024","source":"Cell death discovery","url":"https://pubmed.ncbi.nlm.nih.gov/38740736","citation_count":14,"is_preprint":false},{"pmid":"28418912","id":"PMC_28418912","title":"Human microRNA expression in sporadic and FAP-associated desmoid tumors and correlation with beta-catenin mutations.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28418912","citation_count":13,"is_preprint":false},{"pmid":"31921678","id":"PMC_31921678","title":"FAP-a and GOLPH3 Are Hallmarks of DCIS Progression to Invasive Breast Cancer.","date":"2019","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/31921678","citation_count":13,"is_preprint":false},{"pmid":"37734838","id":"PMC_37734838","title":"Tumor-Targeted Interleukin 2 Boosts the Anticancer Activity of FAP-Directed Radioligand Therapeutics.","date":"2023","source":"Journal of nuclear medicine : official publication, Society of Nuclear Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37734838","citation_count":13,"is_preprint":false},{"pmid":"40263422","id":"PMC_40263422","title":"Fibroblast Activation Protein (FAP)+ cancer-associated fibroblasts induce macrophage M2-like polarization via the Fibronectin 1-Integrin α5β1 axis in breast cancer.","date":"2025","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/40263422","citation_count":12,"is_preprint":false},{"pmid":"35598279","id":"PMC_35598279","title":"FAP-α+ immunofibroblasts in oral lichen planus promote CD4+ T-cell infiltration via CCL5 secretion.","date":"2022","source":"Experimental dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/35598279","citation_count":12,"is_preprint":false},{"pmid":"36155866","id":"PMC_36155866","title":"Expression of GLUT4 and FAP in urothelial bladder carcinoma: correlation with angiogenesis and clinicopathological characteristics.","date":"2022","source":"Journal of the Egyptian National Cancer Institute","url":"https://pubmed.ncbi.nlm.nih.gov/36155866","citation_count":12,"is_preprint":false},{"pmid":"37490719","id":"PMC_37490719","title":"Identifying the oncogenic roles of FAP in human cancers based on systematic 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Development of cancer-associated fibroblast models.","date":"2016","source":"Doklady. Biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/27817025","citation_count":9,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":53919,"output_tokens":6608,"usd":0.130439,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":15709,"output_tokens":5802,"usd":0.111797,"stage2_stop_reason":"end_turn"},"total_usd":0.242236,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1995,\n      \"finding\": \"FAP-1 (PTPN13), a protein tyrosine phosphatase, was identified as a binding partner of Fas (CD95/Apo-1); the carboxyl-terminal 15 amino acids of Fas are necessary and sufficient for interaction with FAP-1. Gene transfer-mediated overexpression of FAP-1 partially abolished Fas-induced apoptosis in a T cell line, establishing FAP-1 as an inhibitor of Fas-mediated apoptosis.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, deletion mapping, gene transfer overexpression assay in T cells\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding confirmation, deletion mutagenesis defining minimal binding domain, functional rescue experiment; foundational paper replicated by subsequent studies\",\n      \"pmids\": [\"7536343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"FAP-1 association with Fas attenuates Fas export to the cell surface, increasing the intracellular pool of Fas within the cytoskeleton network. Forced FAP-1 expression reduced surface Fas; dominant-negative FAP-1 or FAP-1 siRNA knockdown upregulated surface Fas. A point mutation at amino acid 275 of Fas decreased FAP-1 association and increased Fas surface export.\",\n      \"method\": \"Overexpression of FAP-1 and dominant-negative FAP-1, siRNA knockdown, flow cytometry for surface Fas, site-directed mutagenesis of Fas\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (OE, DN, siRNA, mutagenesis) in single rigorous study establishing mechanistic link between FAP-1 binding and Fas trafficking\",\n      \"pmids\": [\"12724420\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PTPL1/FAP-1 phosphatase triggers apoptosis in human breast cancer cells (MCF7) via inhibition of the insulin receptor substrate-1/PI3K/Akt pathway, independent of Fas. FAP-1 expression abolished IGF-I-induced survival signaling (80% reduction in PI3K activity, 55% inhibition of Akt activation, 65% decrease in IRS-1 phosphorylation).\",\n      \"method\": \"Antisense transfection to abolish PTPL1/FAP-1, TUNEL and nucleosome ELISA for apoptosis, PI3K activity assay, Akt phosphorylation assay, IRS-1 tyrosine phosphorylation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function (antisense) with multiple downstream biochemical readouts in one rigorous study; novel pathway distinct from Fas mechanism\",\n      \"pmids\": [\"12354757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Mouse FAP (Fap) encodes a serine protease with dipeptidyl peptidase activity, consistent with its homology to dipeptidyl peptidase IV (DPP IV). A chimeric FAP fusion protein expressed in a baculovirus system demonstrated dipeptidyl peptidase activity. The gene spans ~60 kb with 26 exons; the serine protease consensus motif WGWSYGG is split across two exons, a feature shared with DPP IV.\",\n      \"method\": \"Baculovirus expression of chimeric FAP fusion protein, enzymatic dipeptidyl peptidase activity assay, genomic structure analysis\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic assay of recombinant protein; foundational biochemical characterization\",\n      \"pmids\": [\"9688278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FAP triggers induction of a cancer-associated fibroblast (CAF) subset with an inflammatory phenotype through a uPAR-dependent FAK-Src-JAK2 signaling pathway that persistently activates STAT3, leading to upregulation of CCL2. FAP(+)CAF-derived CCL2 promotes tumor growth by recruiting myeloid-derived suppressor cells (MDSCs) via CCR2. Abrogation of this effect in Ccr2-deficient mice confirmed the pathway.\",\n      \"method\": \"Enforced FAP expression in normal fibroblasts, signaling pathway inhibition (uPAR, FAK, Src, JAK2), STAT3 activation assays, CCL2 measurement, MDSC recruitment assay in murine liver tumor model, Ccr2-knockout mice\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain-of-function plus pathway inhibitors plus genetic knockout validation, multiple orthogonal methods in one study\",\n      \"pmids\": [\"27216177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"FAP participates in collagen catabolism by mediating ordered proteolytic processing of matrix metalloproteinase (MMP)-derived collagen cleavage products, leading to increased collagen internalization via Endo180 without altering Endo180 expression. FAP-deficient mice showed accumulation of intermediate-sized collagen fragments and increased lung fibrosis; restoration of FAP expression in FAP-deficient mouse lungs reduced lung hydroxyproline to wild-type levels.\",\n      \"method\": \"FAP-knockout mice in bleomycin and irradiation fibrosis models, in vitro collagen cleavage assay, pharmacologic FAP inhibition, collagen internalization assay, AAV-mediated FAP re-expression in FAP-deficient mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro enzymatic assay plus KO mice plus rescue experiment; multiple orthogonal approaches in one rigorous study\",\n      \"pmids\": [\"26663085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Pharmacological inhibition of FAP (using talabostat) in diet-induced obese mice elevated total and intact plasma FGF21 levels and produced robust metabolic benefits (reduced body weight, improved glucose tolerance, reduced adiposity). These effects were absent in FGF21-knockout obese mice, and FAP inhibition in vitro blocked enzymatic degradation of human FGF21. This establishes FAP as the endopeptidase responsible for FGF21 cleavage/inactivation in vivo.\",\n      \"method\": \"Pharmacologic inhibition with talabostat in DIO mice, FGF21-KO mice as controls, in vitro FAP enzymatic assay with human FGF21, intact FGF21 measurement by ELISA\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assay plus in vivo pharmacology plus genetic (FGF21-KO) epistasis; multiple orthogonal approaches\",\n      \"pmids\": [\"27689014\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A fluorescence-based assay established that circulating FAP endopeptidase cleaves FGF21 at a specific post-proline site, distinguishing FAP endopeptidase activity from related enzymes (PREP, DPPIV). Structural modeling elucidated the mechanistic basis for FAP substrate specificity. Assay was validated using Fap-deficient mice and detected elevated FAP activity in human patients with liver cirrhosis.\",\n      \"method\": \"Homogeneous fluorescence intensity assay with FGF21 as substrate, Fap-KO mice validation, structural modeling, human plasma samples from liver cirrhosis patients\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with substrate specificity profiling, validated in KO mice; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"28970566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FAP (Fap) is a prolyl-specific serine protease that degrades BNP (brain natriuretic peptide), a novel substrate identified in cardiac fibroblasts. Fap degrades BNP to inhibit vascular endothelial cell migration and tube formation. Pharmacological or genetic inhibition of Fap in mice improved cardiac function after myocardial infarction and increased angiogenesis in the peri-infarct zone. Cardioprotective effects of FAP inhibition were absent in Nppb (pre-proBNP)- or Npr1 (BNP receptor)-deficient mice, confirming BNP as the physiological substrate mediating these effects.\",\n      \"method\": \"Fap-KO and pharmacological inhibition in MI mouse model, echocardiography, RNA-seq, biochemical analysis, cardiac fibroblast/endothelial cell co-culture, Nppb-KO and Npr1-KO epistasis experiments\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — substrate identification with in vitro degradation assay plus multiple genetic epistasis experiments (Fap-KO, Nppb-KO, Npr1-KO) in one study\",\n      \"pmids\": [\"36756875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Specific residues (G10, S14, A18) in the FAP transmembrane domain form a small-X3-small motif that mediates FAP homodimerization. Mutations to these interfacial residues (G10L, S14L, A18L) reduced FAP TM-CYTO dimerization. G10L specifically decreased FAP endopeptidase activity by more than 25% and reduced cell-surface versus intracellular FAP expression, establishing that TM-mediated dimerization is required for both FAP trafficking and protease activity.\",\n      \"method\": \"AraTM bacterial dimerization assay, site-directed mutagenesis of TM interface residues, FAP endopeptidase activity assay, cell surface vs. intracellular FAP localization\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — mutagenesis with functional enzymatic readout and trafficking assay; multiple orthogonal methods in single lab\",\n      \"pmids\": [\"27155568\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"FAP-1 (PTPN13) is functionally expressed in human thyrocytes and protects them from Fas-mediated programmed cell death. Competitive inhibition of FAP-1 binding to Fas using synthetic Ac-SLV tripeptide significantly increased Fas-mediated cell death, and synergized with sub-optimal cycloheximide treatment, demonstrating FAP-1 functions as an endogenous inhibitor of Fas-induced apoptosis in thyroid follicular cells.\",\n      \"method\": \"Ribonuclease protection assay for FAP-1 mRNA, immunohistochemistry and flow cytometry for FAP-1 protein, competitive inhibition with Ac-SLV tripeptide, cycloheximide treatment, cell death assay\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional competition assay with synergy experiment in primary cells; single lab, multiple methods but no direct mutagenesis\",\n      \"pmids\": [\"10537175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FAP expression in adipose tissue macrophages (ATM) mediates CCL8 chemokine expression, which recruits monocyte-derived proinflammatory macrophages into obese adipose tissue. Macrophage-specific FAP deficiency protected mice from diet-induced obesity and reduced proinflammatory macrophage infiltration. FAP in ATM also decreases monoamine oxidase expression, thereby increasing norepinephrine levels and enhancing lipolysis in white adipose tissue. CCL8 overexpression restored HFD-induced metabolic phenotypes in FAP-deficient mice.\",\n      \"method\": \"Macrophage-specific Fap-knockout mice on high-fat diet, CCL8 measurement, CCL8 overexpression rescue experiment, monoamine oxidase assay, NE measurement, energy expenditure assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific KO, rescue overexpression, multiple downstream mechanistic readouts in one rigorous study\",\n      \"pmids\": [\"38100414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FAP in ovarian cancer cells recruits PRKDC (DNA-PK) into lipid rafts, enabling NF-κB activation and promoting cell survival via BIRC5 (survivin) downstream. FAP depletion prevented lipid raft localization of PRKDC and abolished NF-κB activity. FAP's enzymatic activity was dispensable for this pro-survival function, as established by enzymatic mutant analysis.\",\n      \"method\": \"FAP silencing by siRNA, NF-κB activity assay, co-immunoprecipitation of FAP and PRKDC, lipid raft fractionation, apoptosis assay, enzymatic activity mutants, EpCAM aptamer-delivered FAP siRNA in xenograft\",\n      \"journal\": \"Cancer gene therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, lipid raft fractionation, enzymatic mutant, and in vivo xenograft; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"36494579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Fibroblastic FAP expression is required for STAT3 activation and CCL2 production in intrahepatic cholangiocarcinoma cancer-associated fibroblasts. FAP knockdown in ICC-CAFs impaired their ability to promote ICC growth, MDSCs infiltration and angiogenesis; these effects were restored by exogenous CCL2. The tumor-promoting function of fibroblastic FAP was dependent on MDSCs, as depletion of Gr-1+ cells reversed the restoring effects of CCL2.\",\n      \"method\": \"FAP knockdown in primary ICC-CAFs, CCL2 ELISA, MDSC migration assay, subcutaneous tumor model with Gr-1 depletion, exogenous CCL2 rescue\",\n      \"journal\": \"Neoplasia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with rescue experiment and in vivo epistasis using cell depletion; single lab, multiple methods\",\n      \"pmids\": [\"31759251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In breast tumors, FAP+ stromal cells comprise two distinct populations distinguished by podoplanin (PDPN) expression: FAP+PDPN+ cancer-associated fibroblasts (CAFs) enriched in TGFβ signaling/fibrosis genes and localized at the tumor outer edge in contact with T cells, and FAP+PDPN- cancer-associated pericytes (CAPs) localized around vessels. FAP+PDPN+ CAFs suppressed T cell proliferation via a nitric oxide-dependent mechanism, whereas FAP+PDPN- pericytes were not immunosuppressive.\",\n      \"method\": \"Flow cytometry, RNA sequencing of sorted cell populations, immunofluorescence for localization, T cell proliferation assay with nitric oxide pathway inhibition\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional T cell suppression assay with mechanism (nitric oxide), RNA-seq, and localization; single lab\",\n      \"pmids\": [\"30266714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FAP-1 (PTPN13) shows differentiation-dependent relocalization in pancreatic adenocarcinoma A818-6 cells: in 2D monolayers, FAP-1 localizes to a juxtanuclear cisternal position and the nucleus; upon 3D differentiation into polarized hollow spheres, FAP-1 relocates to the actin cytoskeleton beneath the outer plasma membrane and co-localizes with CD95 (Fas). Knockdown of FAP-1 mRNA in monolayer cells did not alter responsiveness to CD95 agonistic antibodies, indicating that FAP-1 expression did not affect CD95 signal transduction in this context.\",\n      \"method\": \"Immunofluorescence for FAP-1 and CD95 localization in 2D vs. 3D cultures, flow cytometry for surface CD95, FAP-1 siRNA knockdown, caspase activity assay\",\n      \"journal\": \"Differentiation; research in biological diversity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with functional consequence plus loss-of-function; single lab, negative result for CD95 signaling is reported\",\n      \"pmids\": [\"22364882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"IL-17a promotes hepatocellular carcinoma by increasing FAP expression in hepatic stellate cells (HSCs) via activation of the STAT3 signaling pathway. STAT3 directly binds to the FAP promoter region (confirmed by CUT&RUN), regulating FAP transcription. Overexpression of IL-17a and FAP in HSCs promoted HCC cell proliferation and migration and inhibited HCC cell apoptosis in vitro and in vivo.\",\n      \"method\": \"CUT&RUN assay for STAT3 binding to FAP promoter, IL-17a and FAP overexpression in HSCs, in vivo tumor models, HCC cell proliferation/migration/apoptosis assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct chromatin binding assay (CUT&RUN) plus gain-of-function experiments; single lab\",\n      \"pmids\": [\"38740736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FAP overexpression in colorectal cancer cells promoted cell growth, invasion, metastasis, and enhanced chemoresistance. MPRIP (myosin phosphatase Rho-interacting protein) was identified as a direct interacting protein of FAP. FAP influences chemotherapy resistance and macrophage recruitment/M2 polarization through the Rho/Hippo/YAP signaling pathway.\",\n      \"method\": \"Co-immunoprecipitation for FAP-MPRIP interaction, FAP overexpression and knockdown in CRC cells, invasion/migration assays, macrophage polarization assay, YAP signaling analysis\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP for binding partner plus overexpression/KD phenotype; single lab, limited mechanistic depth in abstract\",\n      \"pmids\": [\"37213233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FAP-positive chondrocytes in osteoarthritis promote chondrocyte senescence; overexpression of FAP in chondrocytes promotes senescence while genetic knockout of FAP in chondrocytes alleviates OA. FAP siRNA knockdown suppressed the NF-κB pathway to reduce the senescence-associated secretory phenotype (SASP). Soluble FAP secreted from OA synovium was shown to degrade type II collagen in cartilage.\",\n      \"method\": \"FAP overexpression and siRNA knockdown in chondrocytes, chondrocyte-specific FAP-KO mouse OA model, SA-β-Gal senescence assay, NF-κB pathway analysis, PET/CT with [68Ga]Ga-FAPI-04, LNP-FAP siRNA intraarticular injection in rat OA model\",\n      \"journal\": \"Journal of nanobiotechnology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO plus OE/KD with mechanistic pathway readout; single lab but multiple complementary approaches\",\n      \"pmids\": [\"39456041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FAP in senescent gingival fibroblasts promotes periodontitis via FAP/OLN (osteolectin) imbalance driven by mTOR pathway activation. Recombinant FAP increased pro-inflammatory cytokine secretion and osteoclast differentiation in macrophages. Rapamycin treatment restored the FAP/OLN balance. FAP inhibition reduced macrophage inflammation, collagen degradation, and bone resorption in experimental periodontitis.\",\n      \"method\": \"scRNA-seq, recombinant FAP treatment of macrophages, rapamycin treatment of gingival fibroblasts, FAP inhibition in mouse periodontitis model, osteoclast differentiation assay, cytokine measurement\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — recombinant protein functional assay plus pharmacological inhibition in vivo with multiple readouts; single lab\",\n      \"pmids\": [\"39716898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FAP+ cancer-associated fibroblasts in breast cancer secrete fibronectin 1 (FN1), which engages integrin α5β1 on macrophages to activate FAK-AKT-STAT3 signaling and drive immunosuppressive M2-like macrophage polarization. Pharmacological disruption of FN1-integrin α5β1 signaling with Cilengitide reprogrammed the tumor immune landscape and suppressed tumor growth in mouse models.\",\n      \"method\": \"scRNA-seq, Co-IP/signaling pathway analysis, Cilengitide pharmacological inhibition in vivo mouse models, macrophage polarization assay, integrin α5β1 blocking experiments\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic signaling pathway defined with pharmacological inhibition in vivo; single lab\",\n      \"pmids\": [\"40263422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FAP+ gastric cancer mesenchymal stromal cells promote gastric cancer progression by paracrine secretion of INHBA, which activates SMAD2/3 signaling in GC cells. FAP+ GCMSCs also induce collagen deposition in ECM that upregulates GC cell invasion and stemness through collagen–ITGB1 interaction triggering FAK and YAP phosphorylation.\",\n      \"method\": \"FAP+ cell isolation by flow cytometry, transcriptomic sequencing, conditioned medium experiments, ELISA for INHBA, Western blot for SMAD2/3 phosphorylation, IHC and Masson trichrome staining for ECM, integrin/FAK/YAP pathway analysis\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple downstream mechanistic readouts with pathway validation; single lab\",\n      \"pmids\": [\"39615112\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FAP (fibroblast activation protein) is a type II transmembrane serine protease with dual enzymatic activities (dipeptidyl peptidase and endopeptidase) that homodimerizes via a specific TM interface (G10, S14, A18) required for cell surface trafficking and protease activity; its substrates include FGF21 (C-terminal cleavage inactivating the hormone), BNP (cleavage inhibiting angiogenesis post-MI), and MMP-derived collagen fragments (promoting collagen clearance); in stromal fibroblasts and macrophages FAP drives tumor immunosuppression via a uPAR-FAK-Src-JAK2-STAT3-CCL2 axis that recruits MDSCs, and via FN1-integrin α5β1-FAK-AKT-STAT3 signaling that promotes M2 macrophage polarization; in ovarian cancer cells FAP recruits PRKDC into lipid rafts to activate NF-κB independently of its enzymatic activity; and the FAP-1/PTPN13 isoform (a distinct protein sharing the FAP alias) interacts with the C-terminal 15 amino acids of Fas to inhibit Fas surface trafficking and apoptosis while also suppressing IGF-I/IRS-1/PI3K/Akt survival signaling in breast cancer cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FAP is a type II transmembrane serine protease with both dipeptidyl peptidase and post-proline endopeptidase activities that processes extracellular substrates to regulate fibrosis, metabolism, cardiac repair, and tumor immunosuppression [#3, #6]. Homodimerization through a small-X3-small transmembrane motif (G10, S14, A18) is required for both cell-surface trafficking and endopeptidase activity [#9]. Enzymatically, FAP cleaves and inactivates the metabolic hormone FGF21 at a specific post-proline site [#6, #7], degrades BNP in cardiac fibroblasts to restrain post-infarct angiogenesis [#8], and mediates ordered proteolysis of MMP-derived collagen fragments to promote their internalization via Endo180 and limit fibrosis [#5]. In the tumor and inflammatory stroma, FAP-expressing cancer-associated fibroblasts and macrophages drive immunosuppression: a uPAR-FAK-Src-JAK2 pathway sustains STAT3 activation and CCL2 production to recruit myeloid-derived suppressor cells [#4, #13], FN1-integrin \\u03b15\\u03b21-FAK-AKT-STAT3 signaling polarizes macrophages toward an M2 phenotype [#20], and adipose-tissue macrophage FAP drives CCL8-dependent proinflammatory recruitment and modulates lipolysis [#11]. Independently of its catalytic activity, FAP recruits PRKDC into lipid rafts to activate NF-\\u03baB and promote ovarian cancer cell survival [#12]. FAP expression is itself induced by STAT3 binding to its promoter downstream of IL-17a in hepatic stellate cells [#16]. Distinct from this transmembrane protease, the FAP-1/PTPN13 protein tyrosine phosphatase\\u2014which shares the FAP alias\\u2014binds the C-terminal 15 residues of Fas to suppress Fas surface export and apoptosis [#0, #1] and antagonizes IGF-I/IRS-1/PI3K/Akt survival signaling [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established the FAP-1/PTPN13 phosphatase as a direct Fas-binding inhibitor of apoptosis, defining the minimal interaction surface on Fas.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, deletion mapping, and overexpression rescue in T cells\",\n      \"pmids\": [\"7536343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the structural basis of the interaction\", \"Mechanism of apoptosis suppression downstream of binding undefined\", \"This protein is distinct from the FAP transmembrane protease sharing the alias\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined FAP (the transmembrane protease) biochemically as a DPP IV-homologous serine protease with dipeptidyl peptidase activity.\",\n      \"evidence\": \"Baculovirus expression of chimeric FAP and in vitro dipeptidyl peptidase assay plus genomic structure analysis\",\n      \"pmids\": [\"9688278\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No physiological substrate identified\", \"Endopeptidase activity not yet distinguished from dipeptidyl peptidase activity\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Confirmed FAP-1 functions as an endogenous inhibitor of Fas-mediated apoptosis in primary thyrocytes via its Fas-binding motif.\",\n      \"evidence\": \"Competitive Ac-SLV tripeptide inhibition and cycloheximide synergy in primary thyroid follicular cells\",\n      \"pmids\": [\"10537175\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct mutagenesis\", \"Phosphatase catalytic contribution not dissected\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mechanistically linked FAP-1 binding to retention of Fas in an intracellular cytoskeletal pool, explaining apoptosis suppression by limiting surface Fas.\",\n      \"evidence\": \"Overexpression, dominant-negative, siRNA, and Fas site-directed mutagenesis with surface Fas flow cytometry\",\n      \"pmids\": [\"12724420\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trafficking machinery coupling FAP-1 to Fas retention unresolved\", \"Generality across cell types not established\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified a Fas-independent pro-apoptotic role for FAP-1 through inhibition of IGF-I/IRS-1/PI3K/Akt survival signaling in breast cancer cells.\",\n      \"evidence\": \"Antisense knockdown with PI3K activity, Akt phosphorylation, and IRS-1 phosphorylation readouts in MCF7\",\n      \"pmids\": [\"12354757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphatase substrate within the pathway not pinpointed\", \"Cross-talk with the Fas pathway unaddressed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Placed FAP protease in collagen catabolism, showing it processes MMP-derived fragments to enable Endo180-mediated internalization and prevent fibrosis.\",\n      \"evidence\": \"FAP-KO mice in fibrosis models, in vitro collagen cleavage, internalization assay, and AAV rescue\",\n      \"pmids\": [\"26663085\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise cleavage sites on collagen fragments not mapped\", \"Coordination with Endo180 at the molecular level unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified FGF21 as a physiological FAP endopeptidase substrate, establishing FAP as the enzyme that inactivates this metabolic hormone in vivo.\",\n      \"evidence\": \"Talabostat inhibition in DIO mice with FGF21-KO epistasis and in vitro FGF21 degradation\",\n      \"pmids\": [\"27689014\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue source of FGF21-cleaving FAP not localized\", \"Relationship to FAP dimerization-dependent activity not tested here\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed FAP-expressing fibroblasts drive tumor immunosuppression through a uPAR-FAK-Src-JAK2-STAT3 axis producing CCL2 to recruit MDSCs.\",\n      \"evidence\": \"Enforced FAP expression, pathway inhibitors, STAT3/CCL2 readouts, and Ccr2-KO validation in a murine liver tumor model\",\n      \"pmids\": [\"27216177\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether protease activity is required for this signaling not resolved\", \"Upstream trigger of uPAR engagement undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated that transmembrane dimerization via a G10/S14/A18 motif is required for FAP trafficking and endopeptidase activity, coupling assembly to function.\",\n      \"evidence\": \"AraTM dimerization assay, TM interface mutagenesis, and enzymatic/localization readouts\",\n      \"pmids\": [\"27155568\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural model of the dimer not solved\", \"Effect of dimerization on substrate selectivity untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Refined FAP substrate specificity, showing circulating FAP cleaves FGF21 at a defined post-proline site distinct from PREP and DPPIV, and built a clinical activity assay.\",\n      \"evidence\": \"Fluorescence FGF21-cleavage assay, structural modeling, Fap-KO validation, and human cirrhosis plasma\",\n      \"pmids\": [\"28970566\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure-function model not experimentally validated by crystallography\", \"Disease causality of elevated FAP activity not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Resolved FAP+ stroma into immunosuppressive FAP+PDPN+ CAFs and non-suppressive FAP+PDPN- pericytes, attributing T cell suppression to a nitric oxide mechanism.\",\n      \"evidence\": \"Flow cytometry, RNA-seq of sorted populations, immunofluorescence, and T cell proliferation assays with NO inhibition\",\n      \"pmids\": [\"30266714\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Role of FAP enzymatic activity in NO-mediated suppression not tested\", \"Single tumor type\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended the FAP-STAT3-CCL2-MDSC axis to cholangiocarcinoma CAFs, confirming MDSC-dependence by CCL2 rescue and Gr-1 depletion.\",\n      \"evidence\": \"FAP knockdown in primary ICC-CAFs, CCL2 ELISA, MDSC migration, and in vivo Gr-1 depletion with CCL2 rescue\",\n      \"pmids\": [\"31759251\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Upstream regulator of fibroblastic FAP not identified here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed a catalysis-independent FAP function: recruiting PRKDC into lipid rafts to activate NF-\\u03baB and BIRC5-mediated survival in ovarian cancer.\",\n      \"evidence\": \"siRNA silencing, FAP-PRKDC co-IP, lipid raft fractionation, enzymatic mutants, and aptamer-delivered siRNA xenografts\",\n      \"pmids\": [\"36494579\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP for the FAP-PRKDC interaction\", \"How a transmembrane protease scaffolds PRKDC mechanistically unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established macrophage FAP as a driver of obesity, acting through CCL8-dependent macrophage recruitment and monoamine oxidase suppression to modulate lipolysis.\",\n      \"evidence\": \"Macrophage-specific Fap-KO on HFD, CCL8 overexpression rescue, MAO/NE/energy expenditure assays\",\n      \"pmids\": [\"38100414\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate underlying CCL8 induction not identified\", \"Link to FAP protease activity not dissected\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified BNP as a cardiac FAP substrate whose degradation limits angiogenesis, with FAP inhibition improving post-MI cardiac function.\",\n      \"evidence\": \"Fap-KO and pharmacological inhibition in MI mice with Nppb-KO and Npr1-KO epistasis and endothelial co-culture\",\n      \"pmids\": [\"36756875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise BNP cleavage product responsible not defined\", \"Cellular source of active FAP in infarct zone not localized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed FAP transcription is directly driven by STAT3 downstream of IL-17a in hepatic stellate cells, linking inflammatory signaling to FAP induction in HCC.\",\n      \"evidence\": \"CUT&RUN for STAT3 at the FAP promoter plus IL-17a/FAP overexpression and in vivo HCC models\",\n      \"pmids\": [\"38740736\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether FAP enzymatic activity mediates the tumor effect not tested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Implicated FAP+ chondrocytes in osteoarthritis, with FAP driving NF-\\u03baB-dependent senescence and soluble FAP degrading type II collagen.\",\n      \"evidence\": \"Chondrocyte-specific FAP-KO OA model, OE/KD, SA-\\u03b2-Gal, NF-\\u03baB analysis, and FAPI PET imaging\",\n      \"pmids\": [\"39456041\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Catalytic vs scaffold contribution to senescence not separated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended FAP's inflammatory role to periodontitis, where senescent fibroblast FAP drives macrophage inflammation and bone resorption via mTOR-linked FAP/osteolectin imbalance.\",\n      \"evidence\": \"scRNA-seq, recombinant FAP on macrophages, rapamycin, and FAP inhibition in mouse periodontitis\",\n      \"pmids\": [\"39716898\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FAP substrate in this context not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a FAP+ CAF secretome mechanism, FN1-integrin \\u03b15\\u03b21-FAK-AKT-STAT3, driving M2 macrophage polarization and immunosuppression in breast cancer.\",\n      \"evidence\": \"scRNA-seq, signaling analysis, integrin blocking, and Cilengitide inhibition in mouse models\",\n      \"pmids\": [\"40263422\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Role of FAP catalytic activity in FN1 production unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked FAP+ gastric stromal cells to tumor progression through INHBA-SMAD2/3 paracrine signaling and collagen-ITGB1-FAK-YAP mechanotransduction.\",\n      \"evidence\": \"FAP+ cell isolation, conditioned medium, INHBA ELISA, SMAD2/3 blots, and integrin/FAK/YAP analysis\",\n      \"pmids\": [\"39615112\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct role of FAP enzyme in INHBA secretion not established\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved when FAP's diverse stromal and metabolic phenotypes depend on its protease catalysis versus non-enzymatic scaffolding, and no structural model of the FAP dimer or substrate complexes has been experimentally determined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of FAP or its substrate complexes in the corpus\", \"Catalysis-dependent vs scaffold functions not systematically separated across contexts\", \"Substrates underlying chemokine induction (CCL2, CCL8) not identified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3, 5, 6, 7, 8]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [3, 6, 7, 8]},\n      {\"term_id\": \"GO:0140097\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1, 15]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 13, 20, 11]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [6, 11]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 12, 20, 21]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 1, 2, 12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"FAS\", \"PRKDC\", \"MPRIP\", \"FGF21\", \"FN1\", \"ITGA5\", \"ITGB1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}