{"gene":"ADGRF4","run_date":"2026-06-09T22:02:41","timeline":{"discoveries":[{"year":2020,"finding":"Gpr115 (Adgrf4) is highly and preferentially expressed in mature ameloblasts and is required for enamel mineralization. Knockout mice develop hypomineralized enamel with a larger acidic area due to dysregulation of ion composition and pH homeostasis. In vitro, Gpr115 is indispensable for expression of carbonic anhydrase 6 (Car6) in dental epithelial cells, and an acidic extracellular condition induces Car6 expression under Gpr115 regulation.","method":"Knockout mouse model (Gpr115-KO), transcriptomic analysis, in vitro dental epithelial cell line (CLDE) assays, gene expression studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype, corroborated by in vitro mechanistic follow-up with multiple orthogonal methods (transcriptomics, cell line experiments, pH manipulation)","pmids":["32868297"],"is_preprint":false},{"year":2022,"finding":"GPR115/ADGRF4 is expressed in suprabasal noncornified keratinocytes of the stratified epidermis. Deletion of ADGRF4 in HaCaT keratinocytes in organotypic culture abrogates KRT1 expression and reduces keratinocyte stratification. Endogenous GPR115 localizes intracellularly along KRT1/10-positive keratin filaments and is not glycosylated and likely not proteolytically processed, indicating a non-canonical intracellular role in epidermal differentiation.","method":"ADGRF4 knockout in HaCaT keratinocytes (organotypic culture), immunofluorescence localization, western blot (glycosylation status), transcriptomic profiling","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined phenotype plus localization data; single lab with two orthogonal methods but no reconstitution or structural validation","pmids":["36231117"],"is_preprint":false},{"year":2020,"finding":"ADGRF4 regulates non-small cell lung cancer cell invasiveness. ADGRF4 knockdown reduced lung cancer cell invasiveness, and this effect was rescued by overexpression of PPP2C (protein phosphatase 2C). PPP2C gene silencing also blocked lung cancer cell invasiveness, placing PPP2C downstream of ADGRF4 in regulation of invasiveness.","method":"siRNA knockdown of ADGRF4, RNA sequencing, cell migration and invasion assays, PPP2C overexpression rescue, PPP2C knockdown","journal":"Anticancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD phenotype with rescue experiment and downstream target identification; single lab, multiple assays","pmids":["33288575"],"is_preprint":false},{"year":2023,"finding":"Gpr115 responds to changes in extracellular pH and regulates enamel pH cycling. Reduction of extracellular pH suppresses Gpr111 expression, while Gpr115 and Gpr111 together suppress calcification in an additive manner in vitro, indicating that both receptors function as pH-responsive molecules in enamel formation.","method":"In vitro pH manipulation assays, dual knockdown of Gpr111 and Gpr115 in dental epithelial cells, calcification assays","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro assays with pH manipulation and dual KD; single lab, functional assays but no reconstitution or structural data","pmids":["36929047"],"is_preprint":false},{"year":2022,"finding":"GPR115 silencing inhibited cell proliferation and migration in pancreatic ductal adenocarcinoma (PDAC) cells, indicating a functional role in tumor progression.","method":"In vitro siRNA silencing, cell proliferation and migration assays","journal":"British journal of cancer","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method (KD + phenotype assay) with no pathway placement beyond the observation","pmids":["36396823"],"is_preprint":false},{"year":2012,"finding":"Gpr115 is co-expressed with Gpr111 in developing skin of mice (shown by LacZ reporter knockin). Loss of Gpr115 function in mice did not result in detectable developmental defects under the conditions tested, suggesting possible functional redundancy with Gpr111.","method":"LacZ reporter knockin mice, knockout mice, transcriptional profiling","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockout mouse model with expression mapping; negative developmental phenotype reported; single lab","pmids":["22837050"],"is_preprint":false}],"current_model":"ADGRF4 (GPR115) is an adhesion GPCR expressed in mature ameloblasts and suprabasal keratinocytes that regulates enamel mineralization by controlling carbonic anhydrase 6 (Car6) expression and pH homeostasis in response to extracellular pH changes, and promotes epidermal differentiation by associating with KRT1/10 keratin filaments intracellularly; in cancer contexts it promotes cell invasiveness and proliferation, at least partly through downstream regulation of PPP2C in lung cancer cells."},"narrative":{"mechanistic_narrative":"ADGRF4 (GPR115) is an adhesion G protein-coupled receptor that functions as a pH-responsive regulator of epithelial mineralization and differentiation [PMID:32868297, PMID:36929047]. In mature ameloblasts it is required for enamel mineralization: its loss produces hypomineralized enamel with an enlarged acidic area reflecting dysregulated ion composition and pH homeostasis, and it is indispensable for acid-inducible expression of carbonic anhydrase 6 (Car6) in dental epithelial cells [PMID:32868297]. Together with the co-expressed receptor Gpr111, ADGRF4 acts as a pH-responsive molecule that suppresses calcification in enamel pH cycling [PMID:36929047]. In stratified epidermis, ADGRF4 is expressed in suprabasal keratinocytes and promotes keratinocyte stratification and KRT1 expression; endogenous protein localizes intracellularly along KRT1/10 keratin filaments and is neither glycosylated nor evidently proteolytically processed, consistent with a non-canonical intracellular role in epidermal differentiation [PMID:36231117]. In cancer, ADGRF4 promotes invasiveness in non-small cell lung cancer cells through downstream regulation of PPP2C, the rescue and silencing of which place PPP2C downstream of the receptor [PMID:33288575]. The receptor signaling mechanism, ligand, and structural basis of pH sensing have not been characterized in the available corpus.","teleology":[{"year":2012,"claim":"Establishing the expression pattern and an initial loss-of-function test asked whether Gpr115 has a non-redundant developmental role, and revealed co-expression with Gpr111 in developing skin with no overt phenotype, raising the hypothesis of functional redundancy.","evidence":"LacZ reporter knockin and knockout mice with transcriptional profiling","pmids":["22837050"],"confidence":"Medium","gaps":["No tissue-specific phenotype identified despite expression mapping","Redundancy with Gpr111 inferred, not directly tested by double knockout"]},{"year":2020,"claim":"A clean knockout defined the first concrete physiological role, showing Gpr115 is required for enamel mineralization and controls Car6 expression and pH homeostasis, establishing it as a pH-linked regulator in ameloblasts.","evidence":"Gpr115-KO mice, transcriptomics, and CLDE dental epithelial cell assays with extracellular pH manipulation","pmids":["32868297"],"confidence":"High","gaps":["The signaling pathway linking the receptor to Car6 transcription is undefined","No ligand or direct pH-sensing mechanism identified"]},{"year":2020,"claim":"Knockdown-and-rescue experiments placed ADGRF4 in a cancer invasiveness pathway, identifying PPP2C as a downstream effector in non-small cell lung cancer.","evidence":"siRNA knockdown, RNA-seq, invasion assays, and PPP2C overexpression rescue plus PPP2C knockdown","pmids":["33288575"],"confidence":"Medium","gaps":["Mechanism connecting ADGRF4 to PPP2C regulation unknown","Single cancer cell context, no in vivo validation"]},{"year":2022,"claim":"Knockout in organotypic keratinocyte culture extended ADGRF4 function to epidermal differentiation and uncovered a non-canonical intracellular keratin-associated localization.","evidence":"ADGRF4 knockout in HaCaT cells, immunofluorescence, western blot for glycosylation, transcriptomic profiling","pmids":["36231117"],"confidence":"Medium","gaps":["How an intracellular receptor lacking glycosylation drives KRT1 expression is unresolved","No reconstitution or structural validation of keratin association"]},{"year":2022,"claim":"A silencing study broadened the cancer role to pancreatic ductal adenocarcinoma, showing effects on proliferation and migration.","evidence":"siRNA silencing with proliferation and migration assays in PDAC cells","pmids":["36396823"],"confidence":"Low","gaps":["Single method without pathway placement","No downstream effector identified in this context"]},{"year":2023,"claim":"Dual knockdown experiments refined the pH-responsive model, showing Gpr115 and Gpr111 additively suppress calcification and both respond to extracellular pH in enamel formation.","evidence":"In vitro pH manipulation and dual Gpr111/Gpr115 knockdown with calcification assays in dental epithelial cells","pmids":["36929047"],"confidence":"Medium","gaps":["Molecular basis of pH sensing not established","Functional interaction between the two receptors not biochemically defined"]},{"year":null,"claim":"The receptor's ligand, signal transduction mechanism, and the structural basis for its pH responsiveness remain unknown.","evidence":"Not addressed in the available corpus","pmids":[],"confidence":"Low","gaps":["No ligand identified","No G protein coupling or downstream signaling cascade defined","No structural model of pH sensing"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,1]}],"complexes":[],"partners":["KRT1","KRT10","GPR111"],"other_free_text":[]}},"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":402,"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":184,"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":58,"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":29,"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":10,"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":8,"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":7,"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":"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":11090,"output_tokens":1533,"usd":0.028133,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8304,"output_tokens":2189,"usd":0.048122,"stage2_stop_reason":"end_turn"},"total_usd":0.076255,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2020,\n      \"finding\": \"Gpr115 (Adgrf4) is highly and preferentially expressed in mature ameloblasts and is required for enamel mineralization. Knockout mice develop hypomineralized enamel with a larger acidic area due to dysregulation of ion composition and pH homeostasis. In vitro, Gpr115 is indispensable for expression of carbonic anhydrase 6 (Car6) in dental epithelial cells, and an acidic extracellular condition induces Car6 expression under Gpr115 regulation.\",\n      \"method\": \"Knockout mouse model (Gpr115-KO), transcriptomic analysis, in vitro dental epithelial cell line (CLDE) assays, gene expression studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular phenotype, corroborated by in vitro mechanistic follow-up with multiple orthogonal methods (transcriptomics, cell line experiments, pH manipulation)\",\n      \"pmids\": [\"32868297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPR115/ADGRF4 is expressed in suprabasal noncornified keratinocytes of the stratified epidermis. Deletion of ADGRF4 in HaCaT keratinocytes in organotypic culture abrogates KRT1 expression and reduces keratinocyte stratification. Endogenous GPR115 localizes intracellularly along KRT1/10-positive keratin filaments and is not glycosylated and likely not proteolytically processed, indicating a non-canonical intracellular role in epidermal differentiation.\",\n      \"method\": \"ADGRF4 knockout in HaCaT keratinocytes (organotypic culture), immunofluorescence localization, western blot (glycosylation status), transcriptomic profiling\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined phenotype plus localization data; single lab with two orthogonal methods but no reconstitution or structural validation\",\n      \"pmids\": [\"36231117\"],\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 effect was rescued by overexpression of PPP2C (protein phosphatase 2C). PPP2C gene silencing also blocked lung cancer cell invasiveness, placing PPP2C downstream of ADGRF4 in regulation of invasiveness.\",\n      \"method\": \"siRNA knockdown of ADGRF4, RNA sequencing, cell migration and invasion assays, PPP2C overexpression rescue, PPP2C knockdown\",\n      \"journal\": \"Anticancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD phenotype with rescue experiment and downstream target identification; single lab, multiple assays\",\n      \"pmids\": [\"33288575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Gpr115 responds to changes in extracellular pH and regulates enamel pH cycling. Reduction of extracellular pH suppresses Gpr111 expression, while Gpr115 and Gpr111 together suppress calcification in an additive manner in vitro, indicating that both receptors function as pH-responsive molecules in enamel formation.\",\n      \"method\": \"In vitro pH manipulation assays, dual knockdown of Gpr111 and Gpr115 in dental epithelial cells, calcification assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro assays with pH manipulation and dual KD; single lab, functional assays but no reconstitution or structural data\",\n      \"pmids\": [\"36929047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPR115 silencing inhibited cell proliferation and migration in pancreatic ductal adenocarcinoma (PDAC) cells, indicating a functional role in tumor progression.\",\n      \"method\": \"In vitro siRNA silencing, cell proliferation and migration assays\",\n      \"journal\": \"British journal of cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method (KD + phenotype assay) with no pathway placement beyond the observation\",\n      \"pmids\": [\"36396823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Gpr115 is co-expressed with Gpr111 in developing skin of mice (shown by LacZ reporter knockin). Loss of Gpr115 function in mice did not result in detectable developmental defects under the conditions tested, suggesting possible functional redundancy with Gpr111.\",\n      \"method\": \"LacZ reporter knockin mice, knockout mice, transcriptional profiling\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockout mouse model with expression mapping; negative developmental phenotype reported; single lab\",\n      \"pmids\": [\"22837050\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ADGRF4 (GPR115) is an adhesion GPCR expressed in mature ameloblasts and suprabasal keratinocytes that regulates enamel mineralization by controlling carbonic anhydrase 6 (Car6) expression and pH homeostasis in response to extracellular pH changes, and promotes epidermal differentiation by associating with KRT1/10 keratin filaments intracellularly; in cancer contexts it promotes cell invasiveness and proliferation, at least partly through downstream regulation of PPP2C in lung cancer cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ADGRF4 (GPR115) is an adhesion G protein-coupled receptor that functions as a pH-responsive regulator of epithelial mineralization and differentiation [#0, #3]. In mature ameloblasts it is required for enamel mineralization: its loss produces hypomineralized enamel with an enlarged acidic area reflecting dysregulated ion composition and pH homeostasis, and it is indispensable for acid-inducible expression of carbonic anhydrase 6 (Car6) in dental epithelial cells [#0]. Together with the co-expressed receptor Gpr111, ADGRF4 acts as a pH-responsive molecule that suppresses calcification in enamel pH cycling [#3]. In stratified epidermis, ADGRF4 is expressed in suprabasal keratinocytes and promotes keratinocyte stratification and KRT1 expression; endogenous protein localizes intracellularly along KRT1/10 keratin filaments and is neither glycosylated nor evidently proteolytically processed, consistent with a non-canonical intracellular role in epidermal differentiation [#1]. In cancer, ADGRF4 promotes invasiveness in non-small cell lung cancer cells through downstream regulation of PPP2C, the rescue and silencing of which place PPP2C downstream of the receptor [#2]. The receptor signaling mechanism, ligand, and structural basis of pH sensing have not been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing the expression pattern and an initial loss-of-function test asked whether Gpr115 has a non-redundant developmental role, and revealed co-expression with Gpr111 in developing skin with no overt phenotype, raising the hypothesis of functional redundancy.\",\n      \"evidence\": \"LacZ reporter knockin and knockout mice with transcriptional profiling\",\n      \"pmids\": [\"22837050\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No tissue-specific phenotype identified despite expression mapping\", \"Redundancy with Gpr111 inferred, not directly tested by double knockout\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A clean knockout defined the first concrete physiological role, showing Gpr115 is required for enamel mineralization and controls Car6 expression and pH homeostasis, establishing it as a pH-linked regulator in ameloblasts.\",\n      \"evidence\": \"Gpr115-KO mice, transcriptomics, and CLDE dental epithelial cell assays with extracellular pH manipulation\",\n      \"pmids\": [\"32868297\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The signaling pathway linking the receptor to Car6 transcription is undefined\", \"No ligand or direct pH-sensing mechanism identified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Knockdown-and-rescue experiments placed ADGRF4 in a cancer invasiveness pathway, identifying PPP2C as a downstream effector in non-small cell lung cancer.\",\n      \"evidence\": \"siRNA knockdown, RNA-seq, invasion assays, and PPP2C overexpression rescue plus PPP2C knockdown\",\n      \"pmids\": [\"33288575\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting ADGRF4 to PPP2C regulation unknown\", \"Single cancer cell context, no in vivo validation\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Knockout in organotypic keratinocyte culture extended ADGRF4 function to epidermal differentiation and uncovered a non-canonical intracellular keratin-associated localization.\",\n      \"evidence\": \"ADGRF4 knockout in HaCaT cells, immunofluorescence, western blot for glycosylation, transcriptomic profiling\",\n      \"pmids\": [\"36231117\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How an intracellular receptor lacking glycosylation drives KRT1 expression is unresolved\", \"No reconstitution or structural validation of keratin association\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A silencing study broadened the cancer role to pancreatic ductal adenocarcinoma, showing effects on proliferation and migration.\",\n      \"evidence\": \"siRNA silencing with proliferation and migration assays in PDAC cells\",\n      \"pmids\": [\"36396823\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single method without pathway placement\", \"No downstream effector identified in this context\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Dual knockdown experiments refined the pH-responsive model, showing Gpr115 and Gpr111 additively suppress calcification and both respond to extracellular pH in enamel formation.\",\n      \"evidence\": \"In vitro pH manipulation and dual Gpr111/Gpr115 knockdown with calcification assays in dental epithelial cells\",\n      \"pmids\": [\"36929047\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of pH sensing not established\", \"Functional interaction between the two receptors not biochemically defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The receptor's ligand, signal transduction mechanism, and the structural basis for its pH responsiveness remain unknown.\",\n      \"evidence\": \"Not addressed in the available corpus\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No ligand identified\", \"No G protein coupling or downstream signaling cascade defined\", \"No structural model of pH sensing\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"KRT1\", \"KRT10\", \"GPR111\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":5,"faith_total":5,"faith_pct":100.0}}