{"gene":"ADGRF4","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2002,"finding":"GPR115 (ADGRF4) was identified as a novel adhesion GPCR with a GPS domain in its N-terminus and long Ser/Thr-rich regions forming mucin-like stalks, establishing its structural classification within the adhesion GPCR family.","method":"Bioinformatic analysis of human genome databases and phylogenetic analysis","journal":"FEBS letters","confidence":"Low","confidence_rationale":"Tier 4 — computational/bioinformatic prediction only, no functional validation","pmids":["12435584"],"is_preprint":false},{"year":2012,"finding":"Gpr115 (mouse ortholog of ADGRF4) is co-expressed with Gpr111 in developing skin; knockout mice lacking Gpr115 showed no detectable developmental defects, suggesting possible redundant function with other cluster members (Gpr110, Gpr111, Gpr116).","method":"Knockout/LacZ reporter knockin mice, transcriptional profiling","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with phenotypic readout and expression mapping, single study","pmids":["22837050"],"is_preprint":false},{"year":2013,"finding":"GPR115 (ADGRF4) is specifically expressed by epidermal keratinocytes in human skin, and its expression is regulated in response to cytokine activation and terminal differentiation, suggesting a role in cutaneous homeostasis.","method":"Semi-quantitative real-time PCR, western blot, immunohistochemistry of normal skin and skin-derived cell lines","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 — localization and expression data without direct functional manipulation","pmids":["23840300"],"is_preprint":false},{"year":2020,"finding":"Gpr115 (Adgrf4) is highly and preferentially expressed in mature ameloblasts and is required for enamel mineralization; Gpr115-KO mice develop hypomineralized enamel with a larger acidic area due to dysregulation of ion composition and pH homeostasis. Mechanistically, Gpr115 is indispensable for expression of carbonic anhydrase 6 (Car6) in dental epithelial cells, and acidic conditions induce Car6 expression under Gpr115 regulation.","method":"Knockout mouse model, transcriptomic analysis, in vitro cell line (CLDE) knockdown/rescue experiments, pH manipulation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotype, in vitro mechanistic follow-up with multiple orthogonal methods in single study","pmids":["32868297"],"is_preprint":false},{"year":2020,"finding":"ADGRF4 regulates non-small cell lung cancer cell invasiveness; ADGRF4 knockdown reduced lung cancer cell invasiveness, and this was mediated via regulation of PPP2C (protein phosphatase 2C) expression. PPP2C overexpression rescued invasiveness inhibited by ADGRF4 silencing, and PPP2C silencing itself blocked cell invasiveness.","method":"RNA sequencing after siRNA knockdown, cell migration and invasion assays, PPP2C overexpression rescue experiments","journal":"Anticancer research","confidence":"Medium","confidence_rationale":"Tier 2 — KD with defined cellular phenotype plus rescue experiment placing PPP2C downstream, single lab","pmids":["33288575"],"is_preprint":false},{"year":2022,"finding":"GPR115 (ADGRF4) regulates epidermal differentiation and associates with cytoskeletal KRT1; deletion of ADGRF4 in HaCaT keratinocytes abrogates KRT1 expression and reduces keratinocyte stratification. Endogenous GPR115 localizes intracellularly along KRT1/10-positive keratin filaments, is not glycosylated, and is likely not proteolytically processed at the GPS domain.","method":"ADGRF4 knockout in HaCaT keratinocytes, organotypic culture, immunofluorescence localization, western blot for glycosylation status","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — KO with defined differentiation phenotype, localization tied to functional consequence, multiple orthogonal methods, single lab","pmids":["36231117"],"is_preprint":false},{"year":2022,"finding":"GPR115/ADGRF4 silencing inhibits cell proliferation and migration in pancreatic ductal adenocarcinoma (PDAC) cells, indicating a functional role in tumor progression.","method":"siRNA-mediated gene silencing, cell proliferation and migration assays in PDAC cell lines","journal":"British journal of cancer","confidence":"Low","confidence_rationale":"Tier 3 — single KD with phenotypic readout but no pathway placement","pmids":["36396823"],"is_preprint":false},{"year":2023,"finding":"Gpr115 (Adgrf4) responds to changes in extracellular pH; extracellular pH reduction to 6.8 suppresses Gpr111 expression while increasing Klk4. Simultaneous suppression of Gpr111 and Gpr115 has an additive suppressive effect on calcification, indicating both receptors act as pH-responsive regulators of enamel formation and their effects on calcification are additive.","method":"Dual knockdown of Gpr111 and Gpr115 in dental epithelial cells, pH manipulation in vitro, calcification assays","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro functional assays with combinatorial knockdown demonstrating additivity, corroborates prior KO study","pmids":["36929047"],"is_preprint":false}],"current_model":"ADGRF4 (GPR115) is an adhesion GPCR with a GPS domain and mucin-like stalk that functions as a pH-responsive receptor in epithelial tissues: in mature ameloblasts it regulates enamel mineralization by controlling carbonic anhydrase 6 (Car6) expression and pH/ion homeostasis; in keratinocytes it localizes intracellularly along KRT1/10 filaments and is required for epidermal differentiation and KRT1 expression; and in cancer cells it promotes invasiveness via downstream regulation of PPP2C."},"narrative":{"teleology":[{"year":2002,"claim":"Identification of GPR115 as a novel adhesion GPCR with a GPS domain and mucin-like stalks established its structural classification but left its ligand, signaling, and biological function unknown.","evidence":"Bioinformatic mining of human genome databases with phylogenetic analysis","pmids":["12435584"],"confidence":"Low","gaps":["Computational prediction only; no experimental validation of protein expression or function","No ligand or signaling pathway identified","GPS cleavage status not tested"]},{"year":2012,"claim":"Knockout of Gpr115 in mice revealed co-expression with Gpr111 in developing skin but no overt developmental phenotype, raising the possibility of functional redundancy among cluster members.","evidence":"Gpr115 knockout/LacZ knockin mice with transcriptional profiling","pmids":["22837050"],"confidence":"Medium","gaps":["No examination of enamel or specialized epithelial phenotypes in KO mice","Redundancy with Gpr111/Gpr116 not formally tested by double KO","No signaling pathway analysis performed"]},{"year":2013,"claim":"Expression profiling placed GPR115 specifically in epidermal keratinocytes and showed regulation by cytokines and differentiation, providing the first tissue-specific functional context.","evidence":"qPCR, western blot, and immunohistochemistry on human skin and skin-derived cell lines","pmids":["23840300"],"confidence":"Low","gaps":["Expression data only; no loss-of-function or gain-of-function experiments","Cytokine-responsive regulation mechanism not defined","Downstream signaling not investigated"]},{"year":2020,"claim":"Two studies established ADGRF4 as a functional regulator of distinct epithelial programs: in ameloblasts it controls enamel mineralization through Car6 and pH homeostasis, while in lung cancer cells it drives invasiveness via PPP2C, defining the first mechanistic downstream targets.","evidence":"Gpr115-KO mice with enamel phenotype plus in vitro CLDE knockdown/rescue and pH assays (ameloblast study); siRNA knockdown with RNA-seq and PPP2C overexpression rescue in lung cancer cells (cancer study)","pmids":["32868297","33288575"],"confidence":"High","gaps":["Direct signaling cascade linking ADGRF4 to Car6 transcription not delineated","Whether PPP2C regulation is direct or through intermediate signaling unknown","No ligand identified for ADGRF4 in either context"]},{"year":2022,"claim":"Characterization in keratinocytes revealed that ADGRF4 localizes intracellularly along KRT1/10 filaments, is not glycosylated or GPS-cleaved, and is required for KRT1 expression and epidermal stratification — establishing an unconventional non-surface-resident mode of action for this adhesion GPCR.","evidence":"ADGRF4 knockout in HaCaT keratinocytes, organotypic culture, immunofluorescence, and western blot for glycosylation","pmids":["36231117"],"confidence":"Medium","gaps":["Mechanism by which intracellular ADGRF4 regulates KRT1 transcription is unknown","Whether the intracellular localization reflects a trafficking defect or true functional site is unresolved","Results from a single lab using one keratinocyte cell line"]},{"year":2023,"claim":"Demonstration that ADGRF4 responds to extracellular acidification and cooperates additively with GPR111 in regulating calcification consolidated the model of ADGRF4 as a pH-sensing receptor in enamel formation.","evidence":"Dual knockdown of Gpr111 and Gpr115 in dental epithelial cells with pH manipulation and calcification assays","pmids":["36929047"],"confidence":"Medium","gaps":["pH-sensing domain or residues on ADGRF4 not mapped","Whether pH acts directly on ADGRF4 or through an intermediate sensor is unresolved","In vivo confirmation of additive Gpr111/Gpr115 function not performed"]},{"year":null,"claim":"No endogenous ligand, G-protein coupling specificity, or structural basis for pH responsiveness has been defined for ADGRF4, and its unconventional intracellular localization in keratinocytes versus ameloblast function remains mechanistically unexplained.","evidence":"","pmids":[],"confidence":"Low","gaps":["No ligand identification study reported","G-protein coupling preference unknown","Structural basis for lack of GPS cleavage and intracellular retention in keratinocytes undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[3,7]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[3,7]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,5]}],"complexes":[],"partners":["KRT1","CAR6","PPP2C","GPR111"],"other_free_text":[]},"mechanistic_narrative":"ADGRF4 (GPR115) is an adhesion GPCR with a GPS domain and mucin-like Ser/Thr-rich stalk that functions as a pH-responsive receptor in epithelial tissues, governing differentiation and mineralization programs. In mature ameloblasts, ADGRF4 is required for enamel mineralization by controlling expression of carbonic anhydrase 6 (Car6) and thereby regulating ion composition and pH homeostasis; Gpr115-knockout mice develop hypomineralized enamel with expanded acidic zones, and acidic extracellular pH potentiates Car6 induction through ADGRF4-dependent signaling [PMID:32868297, PMID:36929047]. In epidermal keratinocytes, ADGRF4 localizes intracellularly along KRT1/10-positive keratin filaments, is not glycosylated or GPS-cleaved, and is indispensable for KRT1 expression and stratification during terminal differentiation [PMID:36231117]. In non-small cell lung cancer cells, ADGRF4 promotes invasiveness via downstream regulation of PPP2C, as demonstrated by knockdown-rescue experiments [PMID:33288575]."},"prefetch_data":{"uniprot":{"accession":"Q8IZF3","full_name":"Adhesion G protein-coupled receptor F4","aliases":["G-protein coupled receptor 115","G-protein coupled receptor PGR18"],"length_aa":695,"mass_kda":77.7,"function":"Orphan receptor","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q8IZF3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ADGRF4","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/ADGRF4","total_profiled":1310},"omim":[{"mim_id":"614268","title":"ADHESION G PROTEIN-COUPLED RECEPTOR F4; ADGRF4","url":"https://www.omim.org/entry/614268"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"esophagus","ntpm":17.5},{"tissue":"skin 1","ntpm":36.6}],"url":"https://www.proteinatlas.org/search/ADGRF4"},"hgnc":{"alias_symbol":["FLJ38076","PGR18"],"prev_symbol":["GPR115"]},"alphafold":{"accession":"Q8IZF3","domains":[{"cath_id":"2.60.220.50","chopping":"93-101_131-306_313-383","consensus_level":"medium","plddt":87.5296,"start":93,"end":383},{"cath_id":"1.20.1070.10","chopping":"405-668","consensus_level":"high","plddt":82.8979,"start":405,"end":668}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IZF3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IZF3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IZF3-F1-predicted_aligned_error_v6.png","plddt_mean":78.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ADGRF4","jax_strain_url":"https://www.jax.org/strain/search?query=ADGRF4"},"sequence":{"accession":"Q8IZF3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IZF3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IZF3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IZF3"}},"corpus_meta":[{"pmid":"25713288","id":"PMC_25713288","title":"International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G protein-coupled receptors.","date":"2015","source":"Pharmacological reviews","url":"https://pubmed.ncbi.nlm.nih.gov/25713288","citation_count":397,"is_preprint":false},{"pmid":"15203201","id":"PMC_15203201","title":"The human and mouse repertoire of the adhesion family of G-protein-coupled receptors.","date":"2004","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/15203201","citation_count":182,"is_preprint":false},{"pmid":"12435584","id":"PMC_12435584","title":"Novel human G protein-coupled receptors with long N-terminals containing GPS domains and Ser/Thr-rich regions.","date":"2002","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/12435584","citation_count":78,"is_preprint":false},{"pmid":"22837050","id":"PMC_22837050","title":"Characterization and functional study of a cluster of four highly conserved orphan adhesion-GPCR in mouse.","date":"2012","source":"Developmental dynamics : an official publication of the American Association of Anatomists","url":"https://pubmed.ncbi.nlm.nih.gov/22837050","citation_count":57,"is_preprint":false},{"pmid":"23840300","id":"PMC_23840300","title":"Systematic identification and characterization of novel human skin-associated genes encoding membrane and secreted proteins.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23840300","citation_count":28,"is_preprint":false},{"pmid":"32351997","id":"PMC_32351997","title":"The New Biomarker for Cervical Squamous Cell Carcinoma and Endocervical Adenocarcinoma (CESC) Based on Public Database Mining.","date":"2020","source":"BioMed research international","url":"https://pubmed.ncbi.nlm.nih.gov/32351997","citation_count":23,"is_preprint":false},{"pmid":"35413679","id":"PMC_35413679","title":"A correlation study of adhesion G protein-coupled receptors as potential therapeutic targets in Uterine Corpus Endometrial cancer.","date":"2022","source":"International immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35413679","citation_count":20,"is_preprint":false},{"pmid":"32868297","id":"PMC_32868297","title":"G protein-coupled receptor Gpr115 (Adgrf4) is required for enamel mineralization mediated by ameloblasts.","date":"2020","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/32868297","citation_count":17,"is_preprint":false},{"pmid":"27819121","id":"PMC_27819121","title":"Analysis of the interplay between methylation and expression reveals its potential role in cancer aetiology.","date":"2016","source":"Functional & integrative genomics","url":"https://pubmed.ncbi.nlm.nih.gov/27819121","citation_count":12,"is_preprint":false},{"pmid":"38834774","id":"PMC_38834774","title":"A correlation study of adhesion G protein-coupled receptors as potential therapeutic targets for breast cancer.","date":"2024","source":"Breast cancer research and treatment","url":"https://pubmed.ncbi.nlm.nih.gov/38834774","citation_count":9,"is_preprint":false},{"pmid":"33288575","id":"PMC_33288575","title":"ADGRF4 Regulates Non-small Cell Lung Cancer Cell Invasiveness.","date":"2020","source":"Anticancer research","url":"https://pubmed.ncbi.nlm.nih.gov/33288575","citation_count":6,"is_preprint":false},{"pmid":"36396823","id":"PMC_36396823","title":"Clinical significance and functional role of adhesion G-protein-coupled receptors in human pancreatic ductal adenocarcinoma.","date":"2022","source":"British journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/36396823","citation_count":6,"is_preprint":false},{"pmid":"36929047","id":"PMC_36929047","title":"Deficiency of G protein-coupled receptor Gpr111/Adgrf2 causes enamel hypomineralization in mice by alteration of the expression of kallikrein-related peptidase 4 (Klk4) during pH cycling process.","date":"2023","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/36929047","citation_count":6,"is_preprint":false},{"pmid":"36231117","id":"PMC_36231117","title":"The Adhesion G-Protein-Coupled Receptor GPR115/ADGRF4 Regulates Epidermal Differentiation and Associates with Cytoskeletal KRT1.","date":"2022","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/36231117","citation_count":5,"is_preprint":false},{"pmid":"38025799","id":"PMC_38025799","title":"Relationship Between FERMT2, CELF1, COPI, CHRNA2, and ABCA7 Genetic Polymorphisms and Alzheimer's Disease Risk in the Southern Chinese Population.","date":"2023","source":"Journal of Alzheimer's disease reports","url":"https://pubmed.ncbi.nlm.nih.gov/38025799","citation_count":5,"is_preprint":false},{"pmid":"37808112","id":"PMC_37808112","title":"Transcriptome profiling in rumen, reticulum, omasum, and abomasum tissues during the developmental transition of pre-ruminant to the ruminant in yaks.","date":"2023","source":"Frontiers in veterinary science","url":"https://pubmed.ncbi.nlm.nih.gov/37808112","citation_count":3,"is_preprint":false},{"pmid":"37443844","id":"PMC_37443844","title":"Correction: Winkler et al. The Adhesion G-Protein-Coupled Receptor GPR115/ADGRF4 Regulates Epidermal Differentiation and Associates with Cytoskeletal KRT1. Cells 2022, 11, 3151.","date":"2023","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/37443844","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10320,"output_tokens":1836,"usd":0.02925},"stage2":{"model":"claude-opus-4-6","input_tokens":5108,"output_tokens":1900,"usd":0.10956},"total_usd":0.13881,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"GPR115 (ADGRF4) was identified as a novel adhesion GPCR with a GPS domain in its N-terminus and long Ser/Thr-rich regions forming mucin-like stalks, establishing its structural classification within the adhesion GPCR family.\",\n      \"method\": \"Bioinformatic analysis of human genome databases and phylogenetic analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational/bioinformatic prediction only, no functional validation\",\n      \"pmids\": [\"12435584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Gpr115 (mouse ortholog of ADGRF4) is co-expressed with Gpr111 in developing skin; knockout mice lacking Gpr115 showed no detectable developmental defects, suggesting possible redundant function with other cluster members (Gpr110, Gpr111, Gpr116).\",\n      \"method\": \"Knockout/LacZ reporter knockin mice, transcriptional profiling\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with phenotypic readout and expression mapping, single study\",\n      \"pmids\": [\"22837050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPR115 (ADGRF4) is specifically expressed by epidermal keratinocytes in human skin, and its expression is regulated in response to cytokine activation and terminal differentiation, suggesting a role in cutaneous homeostasis.\",\n      \"method\": \"Semi-quantitative real-time PCR, western blot, immunohistochemistry of normal skin and skin-derived cell lines\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — localization and expression data without direct functional manipulation\",\n      \"pmids\": [\"23840300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Gpr115 (Adgrf4) is highly and preferentially expressed in mature ameloblasts and is required for enamel mineralization; Gpr115-KO mice develop hypomineralized enamel with a larger acidic area due to dysregulation of ion composition and pH homeostasis. Mechanistically, Gpr115 is indispensable for expression of carbonic anhydrase 6 (Car6) in dental epithelial cells, and acidic conditions induce Car6 expression under Gpr115 regulation.\",\n      \"method\": \"Knockout mouse model, transcriptomic analysis, in vitro cell line (CLDE) knockdown/rescue experiments, pH manipulation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotype, in vitro mechanistic follow-up with multiple orthogonal methods in single study\",\n      \"pmids\": [\"32868297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ADGRF4 regulates non-small cell lung cancer cell invasiveness; ADGRF4 knockdown reduced lung cancer cell invasiveness, and this was mediated via regulation of PPP2C (protein phosphatase 2C) expression. PPP2C overexpression rescued invasiveness inhibited by ADGRF4 silencing, and PPP2C silencing itself blocked cell invasiveness.\",\n      \"method\": \"RNA sequencing after siRNA knockdown, cell migration and invasion assays, PPP2C overexpression rescue experiments\",\n      \"journal\": \"Anticancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with defined cellular phenotype plus rescue experiment placing PPP2C downstream, single lab\",\n      \"pmids\": [\"33288575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPR115 (ADGRF4) regulates epidermal differentiation and associates with cytoskeletal KRT1; deletion of ADGRF4 in HaCaT keratinocytes abrogates KRT1 expression and reduces keratinocyte stratification. Endogenous GPR115 localizes intracellularly along KRT1/10-positive keratin filaments, is not glycosylated, and is likely not proteolytically processed at the GPS domain.\",\n      \"method\": \"ADGRF4 knockout in HaCaT keratinocytes, organotypic culture, immunofluorescence localization, western blot for glycosylation status\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with defined differentiation phenotype, localization tied to functional consequence, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"36231117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPR115/ADGRF4 silencing inhibits cell proliferation and migration in pancreatic ductal adenocarcinoma (PDAC) cells, indicating a functional role in tumor progression.\",\n      \"method\": \"siRNA-mediated gene silencing, cell proliferation and migration assays in PDAC cell lines\",\n      \"journal\": \"British journal of cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single KD with phenotypic readout but no pathway placement\",\n      \"pmids\": [\"36396823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Gpr115 (Adgrf4) responds to changes in extracellular pH; extracellular pH reduction to 6.8 suppresses Gpr111 expression while increasing Klk4. Simultaneous suppression of Gpr111 and Gpr115 has an additive suppressive effect on calcification, indicating both receptors act as pH-responsive regulators of enamel formation and their effects on calcification are additive.\",\n      \"method\": \"Dual knockdown of Gpr111 and Gpr115 in dental epithelial cells, pH manipulation in vitro, calcification assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro functional assays with combinatorial knockdown demonstrating additivity, corroborates prior KO study\",\n      \"pmids\": [\"36929047\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ADGRF4 (GPR115) is an adhesion GPCR with a GPS domain and mucin-like stalk that functions as a pH-responsive receptor in epithelial tissues: in mature ameloblasts it regulates enamel mineralization by controlling carbonic anhydrase 6 (Car6) expression and pH/ion homeostasis; in keratinocytes it localizes intracellularly along KRT1/10 filaments and is required for epidermal differentiation and KRT1 expression; and in cancer cells it promotes invasiveness via downstream regulation of PPP2C.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ADGRF4 (GPR115) is an adhesion GPCR with a GPS domain and mucin-like Ser/Thr-rich stalk that functions as a pH-responsive receptor in epithelial tissues, governing differentiation and mineralization programs. In mature ameloblasts, ADGRF4 is required for enamel mineralization by controlling expression of carbonic anhydrase 6 (Car6) and thereby regulating ion composition and pH homeostasis; Gpr115-knockout mice develop hypomineralized enamel with expanded acidic zones, and acidic extracellular pH potentiates Car6 induction through ADGRF4-dependent signaling [PMID:32868297, PMID:36929047]. In epidermal keratinocytes, ADGRF4 localizes intracellularly along KRT1/10-positive keratin filaments, is not glycosylated or GPS-cleaved, and is indispensable for KRT1 expression and stratification during terminal differentiation [PMID:36231117]. In non-small cell lung cancer cells, ADGRF4 promotes invasiveness via downstream regulation of PPP2C, as demonstrated by knockdown-rescue experiments [PMID:33288575].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of GPR115 as a novel adhesion GPCR with a GPS domain and mucin-like stalks established its structural classification but left its ligand, signaling, and biological function unknown.\",\n      \"evidence\": \"Bioinformatic mining of human genome databases with phylogenetic analysis\",\n      \"pmids\": [\"12435584\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Computational prediction only; no experimental validation of protein expression or function\",\n        \"No ligand or signaling pathway identified\",\n        \"GPS cleavage status not tested\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Knockout of Gpr115 in mice revealed co-expression with Gpr111 in developing skin but no overt developmental phenotype, raising the possibility of functional redundancy among cluster members.\",\n      \"evidence\": \"Gpr115 knockout/LacZ knockin mice with transcriptional profiling\",\n      \"pmids\": [\"22837050\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No examination of enamel or specialized epithelial phenotypes in KO mice\",\n        \"Redundancy with Gpr111/Gpr116 not formally tested by double KO\",\n        \"No signaling pathway analysis performed\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Expression profiling placed GPR115 specifically in epidermal keratinocytes and showed regulation by cytokines and differentiation, providing the first tissue-specific functional context.\",\n      \"evidence\": \"qPCR, western blot, and immunohistochemistry on human skin and skin-derived cell lines\",\n      \"pmids\": [\"23840300\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Expression data only; no loss-of-function or gain-of-function experiments\",\n        \"Cytokine-responsive regulation mechanism not defined\",\n        \"Downstream signaling not investigated\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two studies established ADGRF4 as a functional regulator of distinct epithelial programs: in ameloblasts it controls enamel mineralization through Car6 and pH homeostasis, while in lung cancer cells it drives invasiveness via PPP2C, defining the first mechanistic downstream targets.\",\n      \"evidence\": \"Gpr115-KO mice with enamel phenotype plus in vitro CLDE knockdown/rescue and pH assays (ameloblast study); siRNA knockdown with RNA-seq and PPP2C overexpression rescue in lung cancer cells (cancer study)\",\n      \"pmids\": [\"32868297\", \"33288575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct signaling cascade linking ADGRF4 to Car6 transcription not delineated\",\n        \"Whether PPP2C regulation is direct or through intermediate signaling unknown\",\n        \"No ligand identified for ADGRF4 in either context\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Characterization in keratinocytes revealed that ADGRF4 localizes intracellularly along KRT1/10 filaments, is not glycosylated or GPS-cleaved, and is required for KRT1 expression and epidermal stratification — establishing an unconventional non-surface-resident mode of action for this adhesion GPCR.\",\n      \"evidence\": \"ADGRF4 knockout in HaCaT keratinocytes, organotypic culture, immunofluorescence, and western blot for glycosylation\",\n      \"pmids\": [\"36231117\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which intracellular ADGRF4 regulates KRT1 transcription is unknown\",\n        \"Whether the intracellular localization reflects a trafficking defect or true functional site is unresolved\",\n        \"Results from a single lab using one keratinocyte cell line\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstration that ADGRF4 responds to extracellular acidification and cooperates additively with GPR111 in regulating calcification consolidated the model of ADGRF4 as a pH-sensing receptor in enamel formation.\",\n      \"evidence\": \"Dual knockdown of Gpr111 and Gpr115 in dental epithelial cells with pH manipulation and calcification assays\",\n      \"pmids\": [\"36929047\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"pH-sensing domain or residues on ADGRF4 not mapped\",\n        \"Whether pH acts directly on ADGRF4 or through an intermediate sensor is unresolved\",\n        \"In vivo confirmation of additive Gpr111/Gpr115 function not performed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No endogenous ligand, G-protein coupling specificity, or structural basis for pH responsiveness has been defined for ADGRF4, and its unconventional intracellular localization in keratinocytes versus ameloblast function remains mechanistically unexplained.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No ligand identification study reported\",\n        \"G-protein coupling preference unknown\",\n        \"Structural basis for lack of GPS cleavage and intracellular retention in keratinocytes undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\n        \"term_id\": \"GO:0140299\",\n        \"supporting_discovery_ids\": [3, 7]\n      },\n      {\n        \"term_id\": \"GO:0060089\",\n        \"supporting_discovery_ids\": [3, 7]\n      }\n    ],\n    \"localization\": [\n      {\n        \"term_id\": \"GO:0005856\",\n        \"supporting_discovery_ids\": [5]\n      }\n    ],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-1266738\",\n        \"supporting_discovery_ids\": [3, 5]\n      }\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"KRT1\",\n      \"CAR6\",\n      \"PPP2C\",\n      \"GPR111\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}