{"gene":"F2R","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2022,"finding":"GZMA secreted by cytotoxic T cells directly interacts with F2R (PAR1) expressed on tumor cells, and this interaction activates the JAK2/STAT1 signaling pathway to promote tumor cell apoptosis and T cell-mediated killing. The LDPRSFLL motif at the N-terminus of F2R was identified as the domain mediating interaction with GZMA.","method":"In vivo and in vitro co-interaction assays, single-cell sequencing, signaling pathway analysis, motif-specific functional studies","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo and in vitro experiments with defined motif, single lab with multiple orthogonal methods but abstract-level detail only","pmids":["35256589"],"is_preprint":false},{"year":2020,"finding":"F2R negatively regulates osteoclastogenesis: F2r knockdown in mouse bone marrow cells increased osteoclast activity, number, size, bone resorption, and F-actin ring formation, while F2r overexpression blocked osteoclast formation and acidification. Mechanistically, F2r knockdown increased pAkt levels and enhanced phosphorylation of p65 and IKBα upon RANKL stimulation, placing F2R upstream of both the Akt and NFκB signaling pathways.","method":"shRNA knockdown and overexpression (lentiviral) in mouse bone marrow cells, Western blot for pAkt, p65, IKBα phosphorylation, RANKL stimulation assays, bone resorption and F-actin ring formation assays","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal loss-of-function and gain-of-function with defined signaling readouts, single lab with multiple orthogonal methods","pmids":["32226307"],"is_preprint":false},{"year":2007,"finding":"A functional insertion/deletion polymorphism at position -506 in the F2R promoter (replicating an Ets-1 transcription factor consensus sequence) modulates transcription factor binding affinity and F2R promoter activity: the -506I sequence showed 26% reduced affinity for nuclear proteins by EMSA and blunted F2R promoter activity in response to hypoxia compared to the -506D sequence in HUVECs.","method":"EMSA with nuclear extracts, transfection reporter assays in HUVECs under hypoxia","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — EMSA and reporter assay in relevant cells, single lab, two orthogonal methods","pmids":["17347481"],"is_preprint":false},{"year":2025,"finding":"POLR1F promotes F2R transcription by reducing the binding of histone demethylase KDM5C to the F2R promoter, thereby increasing H3K4me3 at the F2R promoter and enhancing F2R expression. F2R was identified as a downstream effector of POLR1F and activates the p38 MAPK pathway in anaplastic thyroid cancer cells.","method":"RNA sequencing after POLR1F knockdown, ChIP for H3K4me3 and KDM5C binding at F2R promoter, xenograft models, zebrafish tumor models","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and RNA-seq with in vivo validation, single lab with multiple orthogonal methods","pmids":["40250711"],"is_preprint":false},{"year":2026,"finding":"F2R promotes prostate cancer cell proliferation, invasion, and cell cycle progression while inhibiting apoptosis. Mechanistically, F2R activates the FAK/PI3K/AKT signaling pathway through COL8A1 (collagen type VIII alpha 1) as a key downstream effector. F2R knockdown suppressed tumor growth in xenograft models and downregulated FAK/PI3K/AKT signaling.","method":"F2R overexpression and knockdown in PCa cell lines, proliferation/invasion/apoptosis assays, bioinformatics pathway analysis, in vivo xenograft models","journal":"The journal of gene medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — functional cell assays and in vivo model but COL8A1 link is bioinformatics-inferred; single lab, abstract-level detail only","pmids":["42126351"],"is_preprint":false},{"year":2026,"finding":"A synthetic short peptide agonist mimicking the F2R tethered ligand, conjugated to lipid nanoparticles, significantly increased cellular uptake and cytotoxicity in ovarian cancer cells compared to non-conjugated nanoparticles, validating F2R as an internalizable cell-surface receptor target for ligand-directed drug delivery.","method":"In vitro cellular uptake assay, cytotoxicity assay in ovarian cancer cell line with peptide-conjugated vs. unconjugated LNPs","journal":"Frontiers in drug delivery","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single cell line, single lab, in vitro only, limited mechanistic depth in abstract","pmids":["41608127"],"is_preprint":false}],"current_model":"F2R (PAR1), a G protein-coupled thrombin receptor, functions at the intersection of coagulation, inflammation, and oncogenic signaling: its N-terminal tethered ligand motif (LDPRSFLL) mediates interaction with GZMA to activate JAK2/STAT1-driven apoptosis; it negatively regulates osteoclastogenesis upstream of both Akt and NFκB signaling pathways; its promoter activity is controlled by Ets-1 binding at a functional insertion/deletion polymorphism and by POLR1F-mediated H3K4 methylation via KDM5C; and in cancer contexts it can drive proliferation and invasion through downstream effectors such as COL8A1-FAK/PI3K/AKT and p38 MAPK."},"narrative":{"mechanistic_narrative":"F2R (PAR1) is a cell-surface G protein-coupled receptor whose signaling intersects coagulation-associated, inflammatory, and oncogenic programs, with its activity dictated by an N-terminal tethered-ligand motif (LDPRSFLL) [PMID:35256589]. This motif mediates a direct interaction with the cytotoxic-lymphocyte protease GZMA, and engagement of F2R by GZMA activates JAK2/STAT1 signaling to promote tumor cell apoptosis and T cell–mediated killing [PMID:35256589]. In bone, F2R acts as a negative regulator of osteoclastogenesis upstream of both Akt and NFκB signaling, restraining osteoclast formation, acidification, and bone resorption [PMID:32226307]. In several cancer contexts F2R instead drives proliferation and invasion: it activates a FAK/PI3K/AKT axis through the downstream effector COL8A1 in prostate cancer [PMID:42126351] and feeds into p38 MAPK signaling as a downstream effector of POLR1F in anaplastic thyroid cancer [PMID:40250711]. F2R expression is transcriptionally controlled at its promoter, both by Ets-1 binding at a functional -506 insertion/deletion polymorphism that tunes promoter activity under hypoxia [PMID:17347481] and by POLR1F-dependent restriction of KDM5C binding that raises H3K4me3 at the F2R promoter [PMID:40250711]. The tethered-ligand motif also renders F2R an internalizable receptor exploitable for ligand-directed drug delivery [PMID:41608127].","teleology":[{"year":2007,"claim":"Establishing how F2R abundance is set, a functional promoter polymorphism was shown to control transcription factor binding and responsiveness to hypoxia, linking F2R expression to vascular stress.","evidence":"EMSA with nuclear extracts and reporter transfection assays in HUVECs under hypoxia","pmids":["17347481"],"confidence":"Medium","gaps":["Direct identification of Ets-1 as the bound factor at -506 is inferred from consensus, not confirmed by supershift or ChIP in this finding","Downstream physiological consequence of altered F2R levels not measured","No link to receptor signaling outputs"]},{"year":2020,"claim":"Beyond vascular biology, reciprocal gain- and loss-of-function placed F2R as a negative regulator of osteoclastogenesis upstream of Akt and NFκB, revealing a role in bone homeostasis.","evidence":"Lentiviral shRNA knockdown and overexpression in mouse bone marrow cells with Western blot signaling readouts and bone resorption/F-actin ring assays","pmids":["32226307"],"confidence":"Medium","gaps":["Ligand driving F2R signaling in osteoclasts not identified","Whether the effect requires the tethered-ligand motif untested","In vivo bone phenotype not demonstrated"]},{"year":2022,"claim":"Defining a direct immune ligand, the N-terminal LDPRSFLL motif was shown to mediate F2R interaction with GZMA, coupling cytotoxic lymphocyte attack to JAK2/STAT1-driven tumor apoptosis.","evidence":"In vivo and in vitro co-interaction assays, single-cell sequencing, and motif-specific functional studies","pmids":["35256589"],"confidence":"Medium","gaps":["Structural basis of GZMA–motif interaction not resolved","Whether GZMA cleaves or otherwise activates the tethered ligand unclear","Reported at abstract-level mechanistic detail only"]},{"year":2025,"claim":"Connecting transcriptional control to oncogenic output, POLR1F was shown to raise F2R expression by limiting KDM5C-mediated demethylation, with F2R then driving p38 MAPK signaling in thyroid cancer.","evidence":"RNA-seq after POLR1F knockdown, ChIP for H3K4me3 and KDM5C at the F2R promoter, plus xenograft and zebrafish tumor models","pmids":["40250711"],"confidence":"Medium","gaps":["Direct vs indirect nature of POLR1F effect on the promoter not fully separated","Mechanism coupling F2R to p38 MAPK not defined","Generalizability beyond anaplastic thyroid cancer untested"]},{"year":2026,"claim":"Extending F2R's pro-tumor signaling, knockdown and overexpression showed it promotes prostate cancer proliferation and invasion via a FAK/PI3K/AKT axis through COL8A1.","evidence":"F2R overexpression/knockdown in prostate cancer cell lines, proliferation/invasion/apoptosis assays, and xenograft models with bioinformatics-inferred COL8A1 link","pmids":["42126351"],"confidence":"Low","gaps":["COL8A1 as the key effector is bioinformatics-inferred, not biochemically validated","Whether F2R acts through canonical receptor signaling or a non-canonical route unclear","Single lab, abstract-level detail"]},{"year":2026,"claim":"Demonstrating translational utility, a tethered-ligand-mimetic peptide enhanced nanoparticle uptake and cytotoxicity, validating F2R as an internalizable surface target for ligand-directed delivery.","evidence":"In vitro cellular uptake and cytotoxicity assays in an ovarian cancer cell line with peptide-conjugated versus unconjugated lipid nanoparticles","pmids":["41608127"],"confidence":"Low","gaps":["Single cell line, in vitro only, no in vivo targeting data","Internalization mechanism not directly characterized","Selectivity over other receptors not assessed"]},{"year":null,"claim":"How F2R integrates its opposing roles — pro-apoptotic in immune killing yet pro-proliferative in tumor cells, and anti-osteoclastogenic in bone — through distinct ligands, G protein couplings, and cell contexts remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["G protein/effector coupling for each context not defined in the corpus","No structural model of receptor states","Determinants of context-dependent outcome unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,3,4]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,3]}],"complexes":[],"partners":["GZMA","COL8A1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P25116","full_name":"Proteinase-activated receptor 1","aliases":["Coagulation factor II receptor","Thrombin receptor"],"length_aa":425,"mass_kda":47.4,"function":"High affinity receptor that binds the activated thrombin, leading to calcium release from intracellular stores (PubMed:1672265, PubMed:8136362). The thrombin-activated receptor signaling pathway is mediated through PTX-insensitive G proteins, activation of phospholipase C resulting in the production of 1D-myo-inositol 1,4,5-trisphosphate (InsP3) which binds to InsP3 receptors causing calcium release from the stores (By similarity). In astrocytes, the calcium released into the cytosol allows the Ca(2+)-dependent release of L-glutamate into the synaptic cleft through BEST1, that targets the neuronal postsynaptic GRIN2A/NMDAR receptor resulting in the synaptic plasticity regulation (By similarity). May play a role in platelets activation and in vascular development (PubMed:10079109). Mediates up-regulation of pro-inflammatory cytokines, such as MCP-1/CCL2 and IL6, triggered by coagulation factor Xa (F10) in cardiac fibroblasts and umbilical vein endothelial cells (PubMed:30568593, PubMed:34831181)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P25116/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/F2R","classification":"Not Classified","n_dependent_lines":33,"n_total_lines":1208,"dependency_fraction":0.027317880794701987},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/F2R","total_profiled":1310},"omim":[{"mim_id":"620484","title":"THROMBOCYTOPENIA 10; THC10","url":"https://www.omim.org/entry/620484"},{"mim_id":"616913","title":"BLEEDING DISORDER, PLATELET-TYPE, 20; BDPLT20","url":"https://www.omim.org/entry/616913"},{"mim_id":"615845","title":"MICRO RNA 190A; MIR190A","url":"https://www.omim.org/entry/615845"},{"mim_id":"614958","title":"SCHLAFEN FAMILY, MEMBER 14; SLFN14","url":"https://www.omim.org/entry/614958"},{"mim_id":"612283","title":"PROTEIN C; PROC","url":"https://www.omim.org/entry/612283"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":65.4}],"url":"https://www.proteinatlas.org/search/F2R"},"hgnc":{"alias_symbol":["TR","CF2R","PAR1","PAR-1"],"prev_symbol":[]},"alphafold":{"accession":"P25116","domains":[{"cath_id":"1.20.1070.10","chopping":"89-385","consensus_level":"high","plddt":88.8622,"start":89,"end":385}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P25116","model_url":"https://alphafold.ebi.ac.uk/files/AF-P25116-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P25116-F1-predicted_aligned_error_v6.png","plddt_mean":74.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=F2R","jax_strain_url":"https://www.jax.org/strain/search?query=F2R"},"sequence":{"accession":"P25116","fasta_url":"https://rest.uniprot.org/uniprotkb/P25116.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P25116/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P25116"}},"corpus_meta":[{"pmid":"35256589","id":"PMC_35256589","title":"Heterogeneity induced GZMA-F2R communication inefficient impairs antitumor immunotherapy of PD-1 mAb through JAK2/STAT1 signal suppression in hepatocellular carcinoma.","date":"2022","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/35256589","citation_count":34,"is_preprint":false},{"pmid":"19404549","id":"PMC_19404549","title":"Variants in the coagulation factor 2 receptor (F2R) gene influence the risk of myocardial infarction in men through an interaction with interleukin 6 serum levels.","date":"2009","source":"Thrombosis and haemostasis","url":"https://pubmed.ncbi.nlm.nih.gov/19404549","citation_count":25,"is_preprint":false},{"pmid":"32226307","id":"PMC_32226307","title":"F2r negatively regulates osteoclastogenesis through inhibiting the Akt and NFκB signaling pathways.","date":"2020","source":"International journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32226307","citation_count":22,"is_preprint":false},{"pmid":"17347481","id":"PMC_17347481","title":"Retrospective analysis of coagulation factor II receptor (F2R) sequence variation and coronary heart disease in hypertensive patients.","date":"2007","source":"Arteriosclerosis, thrombosis, and vascular biology","url":"https://pubmed.ncbi.nlm.nih.gov/17347481","citation_count":21,"is_preprint":false},{"pmid":"33093222","id":"PMC_33093222","title":"F2R Polymorphisms and Clopidogrel Efficacy and Safety in Patients With Minor Stroke or TIA.","date":"2020","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/33093222","citation_count":6,"is_preprint":false},{"pmid":"26446588","id":"PMC_26446588","title":"Evaluation of the F2R IVS-14A/T PAR1 polymorphism with subsequent cardiovascular events and bleeding in patients who have undergone percutaneous coronary intervention.","date":"2016","source":"Journal of thrombosis and thrombolysis","url":"https://pubmed.ncbi.nlm.nih.gov/26446588","citation_count":6,"is_preprint":false},{"pmid":"19080851","id":"PMC_19080851","title":"[Influence of mutations of proteinase-activated receptors F2R/PAR1 and F2RL1/PAR2 on inflammatory bowel disease].","date":"2008","source":"Medicina clinica","url":"https://pubmed.ncbi.nlm.nih.gov/19080851","citation_count":4,"is_preprint":false},{"pmid":"40250711","id":"PMC_40250711","title":"POLR1F promotes proliferation and stemness of anaplastic thyroid cancer by activating F2R/p38 MAPK signaling.","date":"2025","source":"Biochimica et biophysica acta. Molecular cell research","url":"https://pubmed.ncbi.nlm.nih.gov/40250711","citation_count":3,"is_preprint":false},{"pmid":"26278396","id":"PMC_26278396","title":"Role of a functional polymorphism in the F2R gene promoter in sarcoidosis.","date":"2015","source":"Respirology (Carlton, Vic.)","url":"https://pubmed.ncbi.nlm.nih.gov/26278396","citation_count":3,"is_preprint":false},{"pmid":"34954768","id":"PMC_34954768","title":"Associations of CYP2C19 and F2R genetic polymorphisms with platelet reactivity in Chinese ischemic stroke patients receiving clopidogrel therapy.","date":"2021","source":"Pharmacogenetics and genomics","url":"https://pubmed.ncbi.nlm.nih.gov/34954768","citation_count":2,"is_preprint":false},{"pmid":"39723111","id":"PMC_39723111","title":"PEAR1, PON1, CYP2C19, CYP1A2 and F2R Polymorphisms are Associated with MACE in Clopidogrel-Treated Patients with Acute Coronary Syndrome Undergoing Percutaneous Coronary Intervention.","date":"2024","source":"Pharmacogenomics and personalized medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39723111","citation_count":2,"is_preprint":false},{"pmid":"42102797","id":"PMC_42102797","title":"Iroquois-homeobox protein 3 promotes hepatocellular carcinoma growth by transcriptionally upregulating F2R like trypsin receptor 1/protease-activated receptor 2.","date":"2026","source":"International journal of biological macromolecules","url":"https://pubmed.ncbi.nlm.nih.gov/42102797","citation_count":0,"is_preprint":false},{"pmid":"42126351","id":"PMC_42126351","title":"F2R Promotes Prostate Cancer Progression via COL8A1-Dependent Activation of the FAK/PI3K/AKT Signaling Axis.","date":"2026","source":"The journal of gene medicine","url":"https://pubmed.ncbi.nlm.nih.gov/42126351","citation_count":0,"is_preprint":false},{"pmid":"41550510","id":"PMC_41550510","title":"Computational analysis of the structural and functional impact of the deleterious nsSNPs in the human F2R gene and their implications in glioma.","date":"2026","source":"Biochemistry and biophysics reports","url":"https://pubmed.ncbi.nlm.nih.gov/41550510","citation_count":0,"is_preprint":false},{"pmid":"41890958","id":"PMC_41890958","title":"GAL and F2R as immune diagnostic biomarkers for fetal growth restriction.","date":"2026","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/41890958","citation_count":0,"is_preprint":false},{"pmid":"41608127","id":"PMC_41608127","title":"Targeting F2R/PAR1 with ligand decorated lipid nanocarriers for enhanced drug delivery into ovarian cancer cells.","date":"2026","source":"Frontiers in drug delivery","url":"https://pubmed.ncbi.nlm.nih.gov/41608127","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.08.08.24311690","title":"Genetically-proxied lower PAR1 and renal phenotypes: a drug-target Mendelian Randomization study","date":"2024-08-09","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.08.24311690","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11458,"output_tokens":1739,"usd":0.030229,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8557,"output_tokens":2660,"usd":0.054642,"stage2_stop_reason":"end_turn"},"total_usd":0.084871,"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\": 2022,\n      \"finding\": \"GZMA secreted by cytotoxic T cells directly interacts with F2R (PAR1) expressed on tumor cells, and this interaction activates the JAK2/STAT1 signaling pathway to promote tumor cell apoptosis and T cell-mediated killing. The LDPRSFLL motif at the N-terminus of F2R was identified as the domain mediating interaction with GZMA.\",\n      \"method\": \"In vivo and in vitro co-interaction assays, single-cell sequencing, signaling pathway analysis, motif-specific functional studies\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo and in vitro experiments with defined motif, single lab with multiple orthogonal methods but abstract-level detail only\",\n      \"pmids\": [\"35256589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"F2R negatively regulates osteoclastogenesis: F2r knockdown in mouse bone marrow cells increased osteoclast activity, number, size, bone resorption, and F-actin ring formation, while F2r overexpression blocked osteoclast formation and acidification. Mechanistically, F2r knockdown increased pAkt levels and enhanced phosphorylation of p65 and IKBα upon RANKL stimulation, placing F2R upstream of both the Akt and NFκB signaling pathways.\",\n      \"method\": \"shRNA knockdown and overexpression (lentiviral) in mouse bone marrow cells, Western blot for pAkt, p65, IKBα phosphorylation, RANKL stimulation assays, bone resorption and F-actin ring formation assays\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal loss-of-function and gain-of-function with defined signaling readouts, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"32226307\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A functional insertion/deletion polymorphism at position -506 in the F2R promoter (replicating an Ets-1 transcription factor consensus sequence) modulates transcription factor binding affinity and F2R promoter activity: the -506I sequence showed 26% reduced affinity for nuclear proteins by EMSA and blunted F2R promoter activity in response to hypoxia compared to the -506D sequence in HUVECs.\",\n      \"method\": \"EMSA with nuclear extracts, transfection reporter assays in HUVECs under hypoxia\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — EMSA and reporter assay in relevant cells, single lab, two orthogonal methods\",\n      \"pmids\": [\"17347481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"POLR1F promotes F2R transcription by reducing the binding of histone demethylase KDM5C to the F2R promoter, thereby increasing H3K4me3 at the F2R promoter and enhancing F2R expression. F2R was identified as a downstream effector of POLR1F and activates the p38 MAPK pathway in anaplastic thyroid cancer cells.\",\n      \"method\": \"RNA sequencing after POLR1F knockdown, ChIP for H3K4me3 and KDM5C binding at F2R promoter, xenograft models, zebrafish tumor models\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and RNA-seq with in vivo validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"40250711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"F2R promotes prostate cancer cell proliferation, invasion, and cell cycle progression while inhibiting apoptosis. Mechanistically, F2R activates the FAK/PI3K/AKT signaling pathway through COL8A1 (collagen type VIII alpha 1) as a key downstream effector. F2R knockdown suppressed tumor growth in xenograft models and downregulated FAK/PI3K/AKT signaling.\",\n      \"method\": \"F2R overexpression and knockdown in PCa cell lines, proliferation/invasion/apoptosis assays, bioinformatics pathway analysis, in vivo xenograft models\",\n      \"journal\": \"The journal of gene medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — functional cell assays and in vivo model but COL8A1 link is bioinformatics-inferred; single lab, abstract-level detail only\",\n      \"pmids\": [\"42126351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"A synthetic short peptide agonist mimicking the F2R tethered ligand, conjugated to lipid nanoparticles, significantly increased cellular uptake and cytotoxicity in ovarian cancer cells compared to non-conjugated nanoparticles, validating F2R as an internalizable cell-surface receptor target for ligand-directed drug delivery.\",\n      \"method\": \"In vitro cellular uptake assay, cytotoxicity assay in ovarian cancer cell line with peptide-conjugated vs. unconjugated LNPs\",\n      \"journal\": \"Frontiers in drug delivery\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single cell line, single lab, in vitro only, limited mechanistic depth in abstract\",\n      \"pmids\": [\"41608127\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"F2R (PAR1), a G protein-coupled thrombin receptor, functions at the intersection of coagulation, inflammation, and oncogenic signaling: its N-terminal tethered ligand motif (LDPRSFLL) mediates interaction with GZMA to activate JAK2/STAT1-driven apoptosis; it negatively regulates osteoclastogenesis upstream of both Akt and NFκB signaling pathways; its promoter activity is controlled by Ets-1 binding at a functional insertion/deletion polymorphism and by POLR1F-mediated H3K4 methylation via KDM5C; and in cancer contexts it can drive proliferation and invasion through downstream effectors such as COL8A1-FAK/PI3K/AKT and p38 MAPK.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"F2R (PAR1) is a cell-surface G protein-coupled receptor whose signaling intersects coagulation-associated, inflammatory, and oncogenic programs, with its activity dictated by an N-terminal tethered-ligand motif (LDPRSFLL) [#0]. This motif mediates a direct interaction with the cytotoxic-lymphocyte protease GZMA, and engagement of F2R by GZMA activates JAK2/STAT1 signaling to promote tumor cell apoptosis and T cell–mediated killing [#0]. In bone, F2R acts as a negative regulator of osteoclastogenesis upstream of both Akt and NF\\u03baB signaling, restraining osteoclast formation, acidification, and bone resorption [#1]. In several cancer contexts F2R instead drives proliferation and invasion: it activates a FAK/PI3K/AKT axis through the downstream effector COL8A1 in prostate cancer [#4] and feeds into p38 MAPK signaling as a downstream effector of POLR1F in anaplastic thyroid cancer [#3]. F2R expression is transcriptionally controlled at its promoter, both by Ets-1 binding at a functional -506 insertion/deletion polymorphism that tunes promoter activity under hypoxia [#2] and by POLR1F-dependent restriction of KDM5C binding that raises H3K4me3 at the F2R promoter [#3]. The tethered-ligand motif also renders F2R an internalizable receptor exploitable for ligand-directed drug delivery [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Establishing how F2R abundance is set, a functional promoter polymorphism was shown to control transcription factor binding and responsiveness to hypoxia, linking F2R expression to vascular stress.\",\n      \"evidence\": \"EMSA with nuclear extracts and reporter transfection assays in HUVECs under hypoxia\",\n      \"pmids\": [\"17347481\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct identification of Ets-1 as the bound factor at -506 is inferred from consensus, not confirmed by supershift or ChIP in this finding\",\n        \"Downstream physiological consequence of altered F2R levels not measured\",\n        \"No link to receptor signaling outputs\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Beyond vascular biology, reciprocal gain- and loss-of-function placed F2R as a negative regulator of osteoclastogenesis upstream of Akt and NF\\u03baB, revealing a role in bone homeostasis.\",\n      \"evidence\": \"Lentiviral shRNA knockdown and overexpression in mouse bone marrow cells with Western blot signaling readouts and bone resorption/F-actin ring assays\",\n      \"pmids\": [\"32226307\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Ligand driving F2R signaling in osteoclasts not identified\",\n        \"Whether the effect requires the tethered-ligand motif untested\",\n        \"In vivo bone phenotype not demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defining a direct immune ligand, the N-terminal LDPRSFLL motif was shown to mediate F2R interaction with GZMA, coupling cytotoxic lymphocyte attack to JAK2/STAT1-driven tumor apoptosis.\",\n      \"evidence\": \"In vivo and in vitro co-interaction assays, single-cell sequencing, and motif-specific functional studies\",\n      \"pmids\": [\"35256589\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural basis of GZMA–motif interaction not resolved\",\n        \"Whether GZMA cleaves or otherwise activates the tethered ligand unclear\",\n        \"Reported at abstract-level mechanistic detail only\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connecting transcriptional control to oncogenic output, POLR1F was shown to raise F2R expression by limiting KDM5C-mediated demethylation, with F2R then driving p38 MAPK signaling in thyroid cancer.\",\n      \"evidence\": \"RNA-seq after POLR1F knockdown, ChIP for H3K4me3 and KDM5C at the F2R promoter, plus xenograft and zebrafish tumor models\",\n      \"pmids\": [\"40250711\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct vs indirect nature of POLR1F effect on the promoter not fully separated\",\n        \"Mechanism coupling F2R to p38 MAPK not defined\",\n        \"Generalizability beyond anaplastic thyroid cancer untested\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extending F2R's pro-tumor signaling, knockdown and overexpression showed it promotes prostate cancer proliferation and invasion via a FAK/PI3K/AKT axis through COL8A1.\",\n      \"evidence\": \"F2R overexpression/knockdown in prostate cancer cell lines, proliferation/invasion/apoptosis assays, and xenograft models with bioinformatics-inferred COL8A1 link\",\n      \"pmids\": [\"42126351\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"COL8A1 as the key effector is bioinformatics-inferred, not biochemically validated\",\n        \"Whether F2R acts through canonical receptor signaling or a non-canonical route unclear\",\n        \"Single lab, abstract-level detail\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Demonstrating translational utility, a tethered-ligand-mimetic peptide enhanced nanoparticle uptake and cytotoxicity, validating F2R as an internalizable surface target for ligand-directed delivery.\",\n      \"evidence\": \"In vitro cellular uptake and cytotoxicity assays in an ovarian cancer cell line with peptide-conjugated versus unconjugated lipid nanoparticles\",\n      \"pmids\": [\"41608127\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Single cell line, in vitro only, no in vivo targeting data\",\n        \"Internalization mechanism not directly characterized\",\n        \"Selectivity over other receptors not assessed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How F2R integrates its opposing roles — pro-apoptotic in immune killing yet pro-proliferative in tumor cells, and anti-osteoclastogenic in bone — through distinct ligands, G protein couplings, and cell contexts remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"G protein/effector coupling for each context not defined in the corpus\",\n        \"No structural model of receptor states\",\n        \"Determinants of context-dependent outcome unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 3, 4]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"GZMA\",\n      \"COL8A1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}