{"gene":"CLDN8","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2017,"finding":"CLDN8 transcription is directly activated by androgen receptor (AR): AR binds to the CLDN8 promoter (one binding site identified), two functional androgen-responsive elements were confirmed by reporter assay, and CLDN8 mRNA induction by androgen is blocked by AR inhibitor.","method":"Luciferase reporter assay, ChIP/AR binding site mapping, AR inhibitor blockade of CLDN8 induction","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assay with androgen-responsive element mutagenesis plus AR inhibitor, single lab, two orthogonal methods","pmids":["28474805"],"is_preprint":false},{"year":2017,"finding":"CLDN8 overexpression promotes prostate cancer cell proliferation and migration, while knockdown suppresses these processes; CLDN8 also regulates intracellular signal transduction and stabilizes the cytoskeleton.","method":"CLDN8 overexpression and siRNA knockdown in prostate cancer cell lines with functional readouts (proliferation, migration, cytoskeletal assays)","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss- and gain-of-function experiments, single lab, two orthogonal manipulations","pmids":["28474805"],"is_preprint":false},{"year":2019,"finding":"CLDN8 promotes colorectal cancer cell proliferation, migration, and invasion by activating the MAPK/ERK signaling pathway, upregulating p-ERK and MMP9; MAPK/ERK inhibitor PD98059 blocks these CLDN8-driven effects.","method":"CLDN8 knockdown and overexpression in SW480/HT-29 cells, western blot for p-ERK/MMP9, MAPK inhibitor rescue, in vivo xenograft model","journal":"Cancer management and research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain/loss-of-function plus pharmacological inhibitor rescue, single lab, multiple orthogonal methods","pmids":["31118793"],"is_preprint":false},{"year":2018,"finding":"IL-9 cytokine signaling downregulates CLDN8 expression via miR-21 as an intermediary; anti-IL-9 treatment restores CLDN8 levels and alleviates colitis, placing CLDN8 downstream of the IL-9/miR-21 axis in intestinal barrier regulation.","method":"In vitro cell-based assays (Caco-2, NCM460, SW480), TNBS-induced colitis mouse model, anti-IL-9 mAb treatment with CLDN8 protein/mRNA readout","journal":"Inflammatory bowel diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo models with pathway inhibition, single lab, two orthogonal systems","pmids":["29788092"],"is_preprint":false},{"year":2020,"finding":"Mast cell-derived exosomal miR-223 directly inhibits CLDN8 expression in intestinal epithelial cells, leading to increased epithelial permeability and barrier dysfunction; miR-223 inhibitor reverses the suppression of CLDN8.","method":"Exosome transfer from HMC-1 to intestinal epithelial cell lines (NCM460, HT-29, CaCO2), microarray, miR-223 inhibitor rescue, permeability assay","journal":"Biological research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — exosome transfer plus miRNA inhibitor rescue, single lab, multiple cell lines","pmids":["32209121"],"is_preprint":false},{"year":2020,"finding":"CLDN8 directly interacts with IL-22 protein in colon cancer cell lines, as demonstrated by co-immunoprecipitation; both are target genes of miR-340-5p and their co-expression is regulated by LINC00662 acting as a miR-340-5p sponge to activate ERK signaling.","method":"Co-immunoprecipitation, luciferase reporter assay, RNA pulldown","journal":"Journal of experimental & clinical cancer research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP experiment for CLDN8-IL22 interaction, single lab, no mutagenesis to define binding domain","pmids":["31900207"],"is_preprint":false},{"year":2022,"finding":"SOX9 transcription factor directly represses CLDN8 expression in intestinal epithelial cells; miR-145-5p inhibits SOX9, thereby relieving repression of CLDN8. Promoter hypermethylation of miR-145 in Crohn's disease elevates SOX9 and reduces CLDN8, impairing the intestinal mucosal barrier. miR-145-5p agomir rescue is abrogated in Cldn8-/- mice, confirming epistatic placement of CLDN8 downstream of SOX9.","method":"Dual-luciferase reporter assay, chromatin immunoprecipitation, overexpression/RNA interference, TNBS colitis mouse model, Cldn8 knockout genetic epistasis","journal":"EBioMedicine","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — ChIP, luciferase reporter, genetic epistasis with Cldn8 KO mice, in vivo model, multiple orthogonal methods in one study","pmids":["35124427"],"is_preprint":false},{"year":2019,"finding":"miR-361-5p directly binds the 3'UTR of CLDN8 mRNA and inhibits CLDN8 expression; CLDN8 knockdown phenocopies miR-361-5p overexpression by inhibiting retinoblastoma cell proliferation and inducing apoptosis.","method":"Luciferase reporter assay (3'UTR), CLDN8 siRNA knockdown, cell proliferation and apoptosis assays (CCK-8, EdU, flow cytometry)","journal":"Child's nervous system","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — 3'UTR luciferase plus phenotypic rescue by knockdown, single lab, two orthogonal methods","pmids":["31161266"],"is_preprint":false},{"year":2025,"finding":"IL-4, IL-13, TNF-α and IFN-γ downregulate CLDN8 mRNA expression in HaCaT keratinocytes through activation of the JAK signaling pathway; JAK inhibitor treatment blocks this cytokine-mediated CLDN8 suppression.","method":"Cytokine treatment of HaCaT cells with qPCR for CLDN8, JAK inhibitor co-treatment rescue","journal":"Clinical, cosmetic and investigational dermatology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single pharmacological inhibitor experiment, single lab, single method (qPCR readout)","pmids":["40296865"],"is_preprint":false},{"year":2025,"finding":"hsa-miR-31-3p directly targets the 3'UTR of CLDN8 mRNA, reducing CLDN8 expression; both CLDN8 knockdown and miR-31-3p overexpression impair keratinocyte permeability barrier, and miR-31-3p antagomir in an imiquimod psoriasis mouse model restores CLDN8 expression and ameliorates barrier damage.","method":"3'UTR targeting (bioinformatics + molecular validation), CLDN8 knockdown, miR-31-3p overexpression, antagomir treatment in mouse model, barrier permeability assay","journal":"Biochemistry and biophysics reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo rescue with antagomir, single lab, multiple orthogonal methods","pmids":["40160514"],"is_preprint":false}],"current_model":"CLDN8 is a tight junction protein whose transcription is directly activated by androgen receptor (AR) and repressed by the SOX9 transcription factor (itself controlled by miR-145-5p via promoter methylation); multiple miRNAs (miR-21, miR-223, miR-31-3p, miR-361-5p) post-transcriptionally suppress CLDN8, and downstream of CLDN8, activation of the MAPK/ERK pathway and regulation of MMP9 and cytoskeletal integrity drive cell proliferation, migration, and invasion in cancer contexts, while in epithelial tissues CLDN8 maintains barrier integrity through tight junction formation."},"narrative":{"mechanistic_narrative":"CLDN8 is a tight junction protein that functions as a context-dependent regulator of epithelial barrier integrity and, in cancer settings, of cell proliferation and migration [PMID:28474805, PMID:35124427]. In epithelial tissues including intestinal mucosa and skin, CLDN8 supports permeability barrier function: its loss increases epithelial permeability and barrier dysfunction [PMID:32209121, PMID:40160514], and Cldn8 loss in vivo abrogates rescue of intestinal barrier defects, placing CLDN8 as a downstream effector of mucosal barrier maintenance [PMID:35124427]. CLDN8 expression is tightly controlled at multiple levels — transcriptionally it is directly activated by androgen receptor through functional androgen-responsive elements in its promoter [PMID:28474805] and directly repressed by SOX9 [PMID:35124427], and post-transcriptionally it is suppressed by several miRNAs that bind its 3'UTR, including miR-361-5p and miR-31-3p [PMID:31161266, PMID:40160514], as well as miR-223 and miR-21 acting downstream of inflammatory and exosomal signals [PMID:29788092, PMID:32209121]. Inflammatory cytokine signaling (IL-9 via miR-21; IL-4/IL-13/TNF-α/IFN-γ via JAK) drives CLDN8 downregulation in colitis and skin contexts [PMID:29788092, PMID:40296865]. In colorectal cancer, CLDN8 promotes proliferation, migration and invasion by activating MAPK/ERK signaling and upregulating p-ERK and MMP9 [PMID:31118793]. CLDN8 also physically associates with IL-22 in colon cancer cells [PMID:31900207].","teleology":[{"year":2017,"claim":"Established that CLDN8 is a direct transcriptional target of androgen receptor and is functionally pro-tumorigenic, defining both an upstream regulator and a cellular role in prostate cancer.","evidence":"Luciferase reporter with androgen-responsive element mutagenesis, ChIP/AR binding mapping, AR inhibitor blockade, plus gain/loss-of-function proliferation, migration and cytoskeletal assays in prostate cancer cells","pmids":["28474805"],"confidence":"Medium","gaps":["Mechanism by which CLDN8 stabilizes the cytoskeleton not defined","Signal transduction pathway downstream of CLDN8 in prostate cancer not identified"]},{"year":2018,"claim":"Placed CLDN8 downstream of an inflammatory IL-9/miR-21 axis in intestinal barrier regulation, linking cytokine signaling to CLDN8 suppression.","evidence":"Caco-2/NCM460/SW480 cell assays and TNBS colitis mouse model with anti-IL-9 mAb rescue of CLDN8 levels","pmids":["29788092"],"confidence":"Medium","gaps":["Direct miR-21 binding to CLDN8 3'UTR not shown","Whether CLDN8 restoration alone rescues barrier function not isolated"]},{"year":2019,"claim":"Demonstrated CLDN8 drives colorectal cancer aggressiveness through MAPK/ERK activation, providing a downstream effector pathway for CLDN8's pro-tumor effects.","evidence":"Knockdown/overexpression in SW480/HT-29, western blot for p-ERK/MMP9, PD98059 rescue, and xenograft model","pmids":["31118793"],"confidence":"Medium","gaps":["How a tight junction protein activates ERK mechanistically not resolved","Direct vs indirect regulation of MMP9 unclear"]},{"year":2019,"claim":"Identified miR-361-5p as a direct 3'UTR-binding suppressor of CLDN8 and showed CLDN8 promotes survival in retinoblastoma, extending CLDN8 regulation to a non-epithelial cancer.","evidence":"3'UTR luciferase reporter, CLDN8 siRNA, and CCK-8/EdU/flow cytometry proliferation and apoptosis assays","pmids":["31161266"],"confidence":"Medium","gaps":["Downstream effectors of CLDN8 in retinoblastoma not identified","No in vivo confirmation"]},{"year":2020,"claim":"Showed mast cell exosomal miR-223 directly suppresses CLDN8 to increase epithelial permeability, connecting intercellular exosomal signaling to barrier control.","evidence":"Exosome transfer from HMC-1 to NCM460/HT-29/CaCO2, microarray, miR-223 inhibitor rescue, permeability assay","pmids":["32209121"],"confidence":"Medium","gaps":["Direct miR-223 binding site on CLDN8 not mapped by mutagenesis","In vivo relevance not established"]},{"year":2020,"claim":"Reported a physical CLDN8-IL-22 interaction and a LINC00662/miR-340-5p ceRNA circuit co-regulating both, proposing a non-junctional protein partnership for CLDN8.","evidence":"Co-immunoprecipitation, luciferase reporter, and RNA pulldown in colon cancer cells","pmids":["31900207"],"confidence":"Low","gaps":["Single Co-IP without reciprocal validation or binding-domain mapping","Functional consequence of the CLDN8-IL-22 interaction not defined"]},{"year":2022,"claim":"Defined SOX9 as a direct repressor of CLDN8 and used Cldn8 knockout epistasis to position CLDN8 as the downstream barrier effector of the miR-145-5p/SOX9 axis in Crohn's disease.","evidence":"Dual-luciferase reporter, ChIP, overexpression/RNAi, TNBS colitis model, and miR-145-5p agomir rescue abrogated in Cldn8-/- mice","pmids":["35124427"],"confidence":"High","gaps":["How CLDN8 mechanistically restores barrier integrity at the junction not detailed","Relationship of SOX9 repression to other transcriptional regulators of CLDN8 unexplored"]},{"year":2025,"claim":"Extended cytokine-driven CLDN8 suppression to skin, showing JAK-dependent downregulation by inflammatory cytokines in keratinocytes.","evidence":"Cytokine treatment of HaCaT cells with qPCR and JAK inhibitor co-treatment rescue","pmids":["40296865"],"confidence":"Low","gaps":["Single qPCR readout without protein or barrier-function confirmation","Whether effect is direct or via intermediary miRNAs not addressed"]},{"year":2025,"claim":"Established miR-31-3p as a direct 3'UTR-targeting suppressor of CLDN8 controlling keratinocyte barrier function, with in vivo psoriasis rescue confirming CLDN8's barrier role in skin.","evidence":"3'UTR molecular validation, CLDN8 knockdown, miR-31-3p overexpression, antagomir treatment in imiquimod psoriasis mouse model, barrier permeability assay","pmids":["40160514"],"confidence":"Medium","gaps":["Molecular basis of CLDN8's contribution to keratinocyte permeability barrier not resolved","Whether CLDN8 acts alone or with other claudins in skin not addressed"]},{"year":null,"claim":"How CLDN8 mechanistically transmits signals to the MAPK/ERK pathway and physically organizes tight junctions to control barrier permeability remains unresolved.","evidence":"No structural or biochemical study in the timeline defines CLDN8's junctional assembly or signal-transduction mechanism","pmids":[],"confidence":"Low","gaps":["No structural model of CLDN8","No defined junctional binding partners among claudins/occludins","Mechanistic link between CLDN8 and ERK activation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,6,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,9]}],"pathway":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[6]}],"complexes":[],"partners":["AR","IL22"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P56748","full_name":"Claudin-8","aliases":[],"length_aa":225,"mass_kda":24.8,"function":"Can associate with other claudins to regulate tight junction structural and functional strand dynamics (By similarity). May coassemble with CLDN4 into tight junction strands containing anion-selective channels that convey paracellular chloride permeability in renal collecting ducts (By similarity) (PubMed:36008380). Cannot form tight junction strands on its own (PubMed:36008380)","subcellular_location":"Cell junction, tight junction; Cell membrane","url":"https://www.uniprot.org/uniprotkb/P56748/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CLDN8","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/CLDN8","total_profiled":1310},"omim":[{"mim_id":"617005","title":"CLAUDIN 17; CLDN17","url":"https://www.omim.org/entry/617005"},{"mim_id":"612689","title":"TIGHT JUNCTION PROTEIN 3; TJP3","url":"https://www.omim.org/entry/612689"},{"mim_id":"611232","title":"CLAUDIN 12; CLDN12","url":"https://www.omim.org/entry/611232"},{"mim_id":"611231","title":"CLAUDIN 8; CLDN8","url":"https://www.omim.org/entry/611231"},{"mim_id":"607709","title":"TIGHT JUNCTION PROTEIN 2; TJP2","url":"https://www.omim.org/entry/607709"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"breast","ntpm":64.5},{"tissue":"intestine","ntpm":47.8},{"tissue":"kidney","ntpm":64.7},{"tissue":"salivary gland","ntpm":37.8}],"url":"https://www.proteinatlas.org/search/CLDN8"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P56748","domains":[{"cath_id":"1.20.140.150","chopping":"1-30_73-195","consensus_level":"medium","plddt":88.8274,"start":1,"end":195}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P56748","model_url":"https://alphafold.ebi.ac.uk/files/AF-P56748-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P56748-F1-predicted_aligned_error_v6.png","plddt_mean":80.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CLDN8","jax_strain_url":"https://www.jax.org/strain/search?query=CLDN8"},"sequence":{"accession":"P56748","fasta_url":"https://rest.uniprot.org/uniprotkb/P56748.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P56748/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P56748"}},"corpus_meta":[{"pmid":"31900207","id":"PMC_31900207","title":"LncRNA LINC00662 promotes colon cancer tumor growth and metastasis by competitively binding with miR-340-5p to regulate CLDN8/IL22 co-expression and activating ERK signaling pathway.","date":"2020","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/31900207","citation_count":99,"is_preprint":false},{"pmid":"32209121","id":"PMC_32209121","title":"Mast cells-derived MiR-223 destroys intestinal barrier function by inhibition of CLDN8 expression in intestinal epithelial cells.","date":"2020","source":"Biological research","url":"https://pubmed.ncbi.nlm.nih.gov/32209121","citation_count":73,"is_preprint":false},{"pmid":"28474805","id":"PMC_28474805","title":"CLDN8, an androgen-regulated gene, promotes prostate cancer cell proliferation and migration.","date":"2017","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/28474805","citation_count":36,"is_preprint":false},{"pmid":"31118793","id":"PMC_31118793","title":"CLDN8 promotes colorectal cancer cell proliferation, migration, and invasion by activating MAPK/ERK signaling.","date":"2019","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/31118793","citation_count":30,"is_preprint":false},{"pmid":"29788092","id":"PMC_29788092","title":"Cytokine IL9 Triggers the Pathogenesis of Inflammatory Bowel Disease Through the miR21-CLDN8 Pathway.","date":"2018","source":"Inflammatory bowel diseases","url":"https://pubmed.ncbi.nlm.nih.gov/29788092","citation_count":22,"is_preprint":false},{"pmid":"35124427","id":"PMC_35124427","title":"Hypermethylation of miR-145 promoter-mediated SOX9-CLDN8 pathway regulates intestinal mucosal barrier in Crohn's disease.","date":"2022","source":"EBioMedicine","url":"https://pubmed.ncbi.nlm.nih.gov/35124427","citation_count":18,"is_preprint":false},{"pmid":"31161266","id":"PMC_31161266","title":"MiR-361-5p inhibits cell proliferation and induces cell apoptosis in retinoblastoma by negatively regulating CLDN8.","date":"2019","source":"Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery","url":"https://pubmed.ncbi.nlm.nih.gov/31161266","citation_count":12,"is_preprint":false},{"pmid":"29145422","id":"PMC_29145422","title":"Missense mutation at CLDN8 associated with a high plasma interferon gamma-inducible protein 10 level in methadone-maintained patients with urine test positive for morphine.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/29145422","citation_count":4,"is_preprint":false},{"pmid":"38993257","id":"PMC_38993257","title":"Significance and Possible Biological Mechanism for CLDN8 Downregulation in Kidney Renal Clear Cell Carcinoma Tissues.","date":"2024","source":"World journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/38993257","citation_count":2,"is_preprint":false},{"pmid":"40296865","id":"PMC_40296865","title":"IL-4, IL-13, TNF-α and IFN-γ Downregulate CLDN8 Expression Through Activating JAK Signaling Pathway in HaCaT Cells.","date":"2025","source":"Clinical, cosmetic and investigational dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/40296865","citation_count":1,"is_preprint":false},{"pmid":"38764323","id":"PMC_38764323","title":"CircSCNN1A inhibits the proliferation, migration and invasion of renal cell carcinoma cells by decreasing CLDN8 expression through miR-590-5p.","date":"2024","source":"Genesis (New York, N.Y. : 2000)","url":"https://pubmed.ncbi.nlm.nih.gov/38764323","citation_count":1,"is_preprint":false},{"pmid":"40508219","id":"PMC_40508219","title":"Knockdown of Claudin-8 (CLDN8) Indicates a Link Between Breast Cancer Cell Sensitivity to Chemotherapeutics and Reveals a Potential Use of CLDN8 as a Molecular Diagnostic and Target for Therapy.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40508219","citation_count":1,"is_preprint":false},{"pmid":"40160514","id":"PMC_40160514","title":"Hsa-miR-31-3p targets CLDN8 to compromise skin barrier integrity in psoriasis.","date":"2025","source":"Biochemistry and biophysics reports","url":"https://pubmed.ncbi.nlm.nih.gov/40160514","citation_count":1,"is_preprint":false},{"pmid":"42059166","id":"PMC_42059166","title":"Intestinal barrier dysfunction and differential CLDN8 and MUC1 expression in vedolizumab responsiveness among inflammatory bowel disease patients: a proof-of-concept study.","date":"2026","source":"The Malaysian journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/42059166","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10112,"output_tokens":2482,"usd":0.033783,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9626,"output_tokens":3182,"usd":0.06384,"stage2_stop_reason":"end_turn"},"total_usd":0.097623,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"CLDN8 transcription is directly activated by androgen receptor (AR): AR binds to the CLDN8 promoter (one binding site identified), two functional androgen-responsive elements were confirmed by reporter assay, and CLDN8 mRNA induction by androgen is blocked by AR inhibitor.\",\n      \"method\": \"Luciferase reporter assay, ChIP/AR binding site mapping, AR inhibitor blockade of CLDN8 induction\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assay with androgen-responsive element mutagenesis plus AR inhibitor, single lab, two orthogonal methods\",\n      \"pmids\": [\"28474805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CLDN8 overexpression promotes prostate cancer cell proliferation and migration, while knockdown suppresses these processes; CLDN8 also regulates intracellular signal transduction and stabilizes the cytoskeleton.\",\n      \"method\": \"CLDN8 overexpression and siRNA knockdown in prostate cancer cell lines with functional readouts (proliferation, migration, cytoskeletal assays)\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss- and gain-of-function experiments, single lab, two orthogonal manipulations\",\n      \"pmids\": [\"28474805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CLDN8 promotes colorectal cancer cell proliferation, migration, and invasion by activating the MAPK/ERK signaling pathway, upregulating p-ERK and MMP9; MAPK/ERK inhibitor PD98059 blocks these CLDN8-driven effects.\",\n      \"method\": \"CLDN8 knockdown and overexpression in SW480/HT-29 cells, western blot for p-ERK/MMP9, MAPK inhibitor rescue, in vivo xenograft model\",\n      \"journal\": \"Cancer management and research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain/loss-of-function plus pharmacological inhibitor rescue, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31118793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-9 cytokine signaling downregulates CLDN8 expression via miR-21 as an intermediary; anti-IL-9 treatment restores CLDN8 levels and alleviates colitis, placing CLDN8 downstream of the IL-9/miR-21 axis in intestinal barrier regulation.\",\n      \"method\": \"In vitro cell-based assays (Caco-2, NCM460, SW480), TNBS-induced colitis mouse model, anti-IL-9 mAb treatment with CLDN8 protein/mRNA readout\",\n      \"journal\": \"Inflammatory bowel diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo models with pathway inhibition, single lab, two orthogonal systems\",\n      \"pmids\": [\"29788092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Mast cell-derived exosomal miR-223 directly inhibits CLDN8 expression in intestinal epithelial cells, leading to increased epithelial permeability and barrier dysfunction; miR-223 inhibitor reverses the suppression of CLDN8.\",\n      \"method\": \"Exosome transfer from HMC-1 to intestinal epithelial cell lines (NCM460, HT-29, CaCO2), microarray, miR-223 inhibitor rescue, permeability assay\",\n      \"journal\": \"Biological research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — exosome transfer plus miRNA inhibitor rescue, single lab, multiple cell lines\",\n      \"pmids\": [\"32209121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CLDN8 directly interacts with IL-22 protein in colon cancer cell lines, as demonstrated by co-immunoprecipitation; both are target genes of miR-340-5p and their co-expression is regulated by LINC00662 acting as a miR-340-5p sponge to activate ERK signaling.\",\n      \"method\": \"Co-immunoprecipitation, luciferase reporter assay, RNA pulldown\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP experiment for CLDN8-IL22 interaction, single lab, no mutagenesis to define binding domain\",\n      \"pmids\": [\"31900207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SOX9 transcription factor directly represses CLDN8 expression in intestinal epithelial cells; miR-145-5p inhibits SOX9, thereby relieving repression of CLDN8. Promoter hypermethylation of miR-145 in Crohn's disease elevates SOX9 and reduces CLDN8, impairing the intestinal mucosal barrier. miR-145-5p agomir rescue is abrogated in Cldn8-/- mice, confirming epistatic placement of CLDN8 downstream of SOX9.\",\n      \"method\": \"Dual-luciferase reporter assay, chromatin immunoprecipitation, overexpression/RNA interference, TNBS colitis mouse model, Cldn8 knockout genetic epistasis\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — ChIP, luciferase reporter, genetic epistasis with Cldn8 KO mice, in vivo model, multiple orthogonal methods in one study\",\n      \"pmids\": [\"35124427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"miR-361-5p directly binds the 3'UTR of CLDN8 mRNA and inhibits CLDN8 expression; CLDN8 knockdown phenocopies miR-361-5p overexpression by inhibiting retinoblastoma cell proliferation and inducing apoptosis.\",\n      \"method\": \"Luciferase reporter assay (3'UTR), CLDN8 siRNA knockdown, cell proliferation and apoptosis assays (CCK-8, EdU, flow cytometry)\",\n      \"journal\": \"Child's nervous system\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — 3'UTR luciferase plus phenotypic rescue by knockdown, single lab, two orthogonal methods\",\n      \"pmids\": [\"31161266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IL-4, IL-13, TNF-α and IFN-γ downregulate CLDN8 mRNA expression in HaCaT keratinocytes through activation of the JAK signaling pathway; JAK inhibitor treatment blocks this cytokine-mediated CLDN8 suppression.\",\n      \"method\": \"Cytokine treatment of HaCaT cells with qPCR for CLDN8, JAK inhibitor co-treatment rescue\",\n      \"journal\": \"Clinical, cosmetic and investigational dermatology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single pharmacological inhibitor experiment, single lab, single method (qPCR readout)\",\n      \"pmids\": [\"40296865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"hsa-miR-31-3p directly targets the 3'UTR of CLDN8 mRNA, reducing CLDN8 expression; both CLDN8 knockdown and miR-31-3p overexpression impair keratinocyte permeability barrier, and miR-31-3p antagomir in an imiquimod psoriasis mouse model restores CLDN8 expression and ameliorates barrier damage.\",\n      \"method\": \"3'UTR targeting (bioinformatics + molecular validation), CLDN8 knockdown, miR-31-3p overexpression, antagomir treatment in mouse model, barrier permeability assay\",\n      \"journal\": \"Biochemistry and biophysics reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo rescue with antagomir, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"40160514\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CLDN8 is a tight junction protein whose transcription is directly activated by androgen receptor (AR) and repressed by the SOX9 transcription factor (itself controlled by miR-145-5p via promoter methylation); multiple miRNAs (miR-21, miR-223, miR-31-3p, miR-361-5p) post-transcriptionally suppress CLDN8, and downstream of CLDN8, activation of the MAPK/ERK pathway and regulation of MMP9 and cytoskeletal integrity drive cell proliferation, migration, and invasion in cancer contexts, while in epithelial tissues CLDN8 maintains barrier integrity through tight junction formation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CLDN8 is a tight junction protein that functions as a context-dependent regulator of epithelial barrier integrity and, in cancer settings, of cell proliferation and migration [#1, #6]. In epithelial tissues including intestinal mucosa and skin, CLDN8 supports permeability barrier function: its loss increases epithelial permeability and barrier dysfunction [#4, #9], and Cldn8 loss in vivo abrogates rescue of intestinal barrier defects, placing CLDN8 as a downstream effector of mucosal barrier maintenance [#6]. CLDN8 expression is tightly controlled at multiple levels — transcriptionally it is directly activated by androgen receptor through functional androgen-responsive elements in its promoter [#0] and directly repressed by SOX9 [#6], and post-transcriptionally it is suppressed by several miRNAs that bind its 3'UTR, including miR-361-5p and miR-31-3p [#7, #9], as well as miR-223 and miR-21 acting downstream of inflammatory and exosomal signals [#3, #4]. Inflammatory cytokine signaling (IL-9 via miR-21; IL-4/IL-13/TNF-\\u03b1/IFN-\\u03b3 via JAK) drives CLDN8 downregulation in colitis and skin contexts [#3, #8]. In colorectal cancer, CLDN8 promotes proliferation, migration and invasion by activating MAPK/ERK signaling and upregulating p-ERK and MMP9 [#2]. CLDN8 also physically associates with IL-22 in colon cancer cells [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Established that CLDN8 is a direct transcriptional target of androgen receptor and is functionally pro-tumorigenic, defining both an upstream regulator and a cellular role in prostate cancer.\",\n      \"evidence\": \"Luciferase reporter with androgen-responsive element mutagenesis, ChIP/AR binding mapping, AR inhibitor blockade, plus gain/loss-of-function proliferation, migration and cytoskeletal assays in prostate cancer cells\",\n      \"pmids\": [\"28474805\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which CLDN8 stabilizes the cytoskeleton not defined\", \"Signal transduction pathway downstream of CLDN8 in prostate cancer not identified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Placed CLDN8 downstream of an inflammatory IL-9/miR-21 axis in intestinal barrier regulation, linking cytokine signaling to CLDN8 suppression.\",\n      \"evidence\": \"Caco-2/NCM460/SW480 cell assays and TNBS colitis mouse model with anti-IL-9 mAb rescue of CLDN8 levels\",\n      \"pmids\": [\"29788092\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miR-21 binding to CLDN8 3'UTR not shown\", \"Whether CLDN8 restoration alone rescues barrier function not isolated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated CLDN8 drives colorectal cancer aggressiveness through MAPK/ERK activation, providing a downstream effector pathway for CLDN8's pro-tumor effects.\",\n      \"evidence\": \"Knockdown/overexpression in SW480/HT-29, western blot for p-ERK/MMP9, PD98059 rescue, and xenograft model\",\n      \"pmids\": [\"31118793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a tight junction protein activates ERK mechanistically not resolved\", \"Direct vs indirect regulation of MMP9 unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified miR-361-5p as a direct 3'UTR-binding suppressor of CLDN8 and showed CLDN8 promotes survival in retinoblastoma, extending CLDN8 regulation to a non-epithelial cancer.\",\n      \"evidence\": \"3'UTR luciferase reporter, CLDN8 siRNA, and CCK-8/EdU/flow cytometry proliferation and apoptosis assays\",\n      \"pmids\": [\"31161266\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream effectors of CLDN8 in retinoblastoma not identified\", \"No in vivo confirmation\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed mast cell exosomal miR-223 directly suppresses CLDN8 to increase epithelial permeability, connecting intercellular exosomal signaling to barrier control.\",\n      \"evidence\": \"Exosome transfer from HMC-1 to NCM460/HT-29/CaCO2, microarray, miR-223 inhibitor rescue, permeability assay\",\n      \"pmids\": [\"32209121\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miR-223 binding site on CLDN8 not mapped by mutagenesis\", \"In vivo relevance not established\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Reported a physical CLDN8-IL-22 interaction and a LINC00662/miR-340-5p ceRNA circuit co-regulating both, proposing a non-junctional protein partnership for CLDN8.\",\n      \"evidence\": \"Co-immunoprecipitation, luciferase reporter, and RNA pulldown in colon cancer cells\",\n      \"pmids\": [\"31900207\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation or binding-domain mapping\", \"Functional consequence of the CLDN8-IL-22 interaction not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined SOX9 as a direct repressor of CLDN8 and used Cldn8 knockout epistasis to position CLDN8 as the downstream barrier effector of the miR-145-5p/SOX9 axis in Crohn's disease.\",\n      \"evidence\": \"Dual-luciferase reporter, ChIP, overexpression/RNAi, TNBS colitis model, and miR-145-5p agomir rescue abrogated in Cldn8-/- mice\",\n      \"pmids\": [\"35124427\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CLDN8 mechanistically restores barrier integrity at the junction not detailed\", \"Relationship of SOX9 repression to other transcriptional regulators of CLDN8 unexplored\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended cytokine-driven CLDN8 suppression to skin, showing JAK-dependent downregulation by inflammatory cytokines in keratinocytes.\",\n      \"evidence\": \"Cytokine treatment of HaCaT cells with qPCR and JAK inhibitor co-treatment rescue\",\n      \"pmids\": [\"40296865\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single qPCR readout without protein or barrier-function confirmation\", \"Whether effect is direct or via intermediary miRNAs not addressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established miR-31-3p as a direct 3'UTR-targeting suppressor of CLDN8 controlling keratinocyte barrier function, with in vivo psoriasis rescue confirming CLDN8's barrier role in skin.\",\n      \"evidence\": \"3'UTR molecular validation, CLDN8 knockdown, miR-31-3p overexpression, antagomir treatment in imiquimod psoriasis mouse model, barrier permeability assay\",\n      \"pmids\": [\"40160514\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of CLDN8's contribution to keratinocyte permeability barrier not resolved\", \"Whether CLDN8 acts alone or with other claudins in skin not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CLDN8 mechanistically transmits signals to the MAPK/ERK pathway and physically organizes tight junctions to control barrier permeability remains unresolved.\",\n      \"evidence\": \"No structural or biochemical study in the timeline defines CLDN8's junctional assembly or signal-transduction mechanism\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of CLDN8\", \"No defined junctional binding partners among claudins/occludins\", \"Mechanistic link between CLDN8 and ERK activation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 6, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"AR\",\n      \"IL22\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}