{"gene":"TJP3","run_date":"2026-04-28T21:42:59","timeline":{"discoveries":[{"year":1998,"finding":"ZO-3 (TJP3) was identified as a MAGUK family protein that localizes at tight junctions, contains three PDZ domains, an SH3 domain, and a guanylate kinase-like region, and directly interacts with ZO-1 and the cytoplasmic domain of occludin in vitro affinity analyses, but not with ZO-2.","method":"Partial endopeptidase digestion, amino acid sequencing, cDNA library screening, stable transfection with epitope-tagged construct, immunofluorescence, immunoelectron microscopy, in vitro affinity binding assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — original discovery with multiple orthogonal methods (biochemical purification, sequencing, in vitro binding, immunolocalization), single rigorous study","pmids":["9531559"],"is_preprint":false},{"year":1999,"finding":"ZO-3 PDZ1 domain directly binds the COOH-terminal YV sequence of claudin-1 through -8 in vitro; ZO-3 is also recruited to claudin-based networks through PDZ1/claudin-YV and PDZ2(ZO-3)/PDZ2(ZO-1) interactions.","method":"In vitro binding assays, transfection of claudins into L fibroblasts, immunofluorescence, transfection of isolated PDZ domains into epithelial cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted in vitro binding with domain mapping, corroborated by cell-based localization assays","pmids":["10601346"],"is_preprint":false},{"year":1999,"finding":"ZO-3 directly interacts with F-actin in vitro (cosedimentation assay), forms independent ZO-1·ZO-3 complexes (rather than a trimeric ZO-1·ZO-2·ZO-3 complex) as shown by immunoprecipitation, and colocalizes with actin aggregates in cytochalasin D-treated MDCK cells.","method":"Actin cosedimentation assays with purified recombinant proteins, low-speed sedimentation, immunoprecipitation, immunofluorescence in cytochalasin D-treated MDCK cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal in vitro and in vivo methods, rigorous controls with purified proteins","pmids":["10575001"],"is_preprint":false},{"year":1999,"finding":"An NH2-terminal fragment of cingulin (residues 1-378) interacts with ZO-3 in vitro (Kd ~5 nM for ZO-1), and a COOH-terminal cingulin fragment also binds ZO-3, linking ZO-3 to the cingulin scaffold at tight junctions.","method":"Pull-down assays from epithelial, insect cell, and reticulocyte lysates; immunoprecipitation; electron microscopy","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro pull-down with defined fragments, corroborated by immunoprecipitation in vivo","pmids":["10613913"],"is_preprint":false},{"year":2000,"finding":"The amino-terminal PDZ-domain-containing half of ZO-3 (NZO-3) acts as a dominant negative, delaying tight junction and adherens junction assembly in MDCK cells; NZO-3 preferentially binds ZO-1 and actin, while both NZO-3 and the C-terminal half (CZO-3) contain binding sites for occludin and cingulin.","method":"Exogenous expression of truncation mutants in MDCK cells, transepithelial resistance measurements, immunofluorescence, in vitro binding experiments, calcium switch and cytochalasin D assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — domain dissection with multiple functional readouts and in vitro binding validation","pmids":["11076967"],"is_preprint":false},{"year":2003,"finding":"Tyrosine phosphorylation of occludin by c-Src in vitro significantly reduces its binding to ZO-3 (and ZO-1, ZO-2), but does not affect its binding to F-actin, indicating that c-Src-mediated tyrosine phosphorylation of occludin disrupts its interaction with ZO-3.","method":"In vitro phosphorylation by c-Src, GST pull-down with tyrosine-phosphorylated vs. non-phosphorylated C-occludin, binding quantification for ZO-1, ZO-2, ZO-3, and F-actin","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic assay with mutagenesis-equivalent phosphorylation, clear mechanistic outcome","pmids":["12604349"],"is_preprint":false},{"year":2006,"finding":"ZO-3 knockout mice are viable and fertile with no significant phenotypic abnormality; ZO-3-deficient F9 teratocarcinoma cells differentiate normally and form morphologically intact tight junctions, though TJ localization of ZO-2 is upregulated in the absence of ZO-3, indicating ZO-3 is dispensable for tight junction establishment in vivo.","method":"Homologous recombination knockout in mice and F9 cells, immunofluorescence, RNA interference, calcium switch assay, morphological analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple phenotypic readouts and compensatory analysis","pmids":["17000770"],"is_preprint":false},{"year":2008,"finding":"ZO-3 knockout mice lack an obvious phenotype, confirming it is dispensable for mammalian development, whereas ZO-2 knockout causes early embryonic lethality, demonstrating non-redundant roles for individual ZO proteins.","method":"Knockout mouse generation, embryonic phenotypic analysis, immunofluorescence, paracellular permeability assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean KO genetic analysis with functional phenotyping, independently confirms ZO-3 dispensability","pmids":["18172007"],"is_preprint":false},{"year":2008,"finding":"Tjp3/ZO-3 is required for epidermal barrier function in zebrafish: morpholino silencing of tjp3/zo-3 disrupts tight junction ultrastructure in the enveloping cell layer, increases paracellular permeability to low molecular weight tracers, and causes edema and loss of blood circulation, without affecting asymmetric plasma membrane protein distribution.","method":"Morpholino knockdown in zebrafish embryos, electron microscopy of tight junction ultrastructure, permeability tracer assays, osmotic stress experiments","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 — morpholino KD with multiple orthogonal functional readouts in zebrafish ortholog model","pmids":["18275946"],"is_preprint":false},{"year":2003,"finding":"ZO-3 is exclusively expressed at tight junctions in epithelial cells and is absent from endothelial tight junctions and cadherin-based adhesion sites (spot adherens junctions of fibroblasts, intercalated discs of cardiac muscle cells) where ZO-1 and ZO-2 are concentrated, demonstrating epithelium-specific localization.","method":"Generation of ZO-3-specific polyclonal and monoclonal antibodies validated in ZO-3-deficient mice, immunofluorescence microscopy in multiple mouse tissues","journal":"Genes to cells","confidence":"High","confidence_rationale":"Tier 2 — antibody specificity validated by KO tissue, systematic tissue survey","pmids":["14622136"],"is_preprint":false},{"year":2014,"finding":"In kidney collecting duct principal cells, ZO-3 expression at intercellular junctions increases with cell density and requires ZO-1; ZO-3 depletion does not affect cell cycle progression but increases cell detachment, associated with altered β1-integrin subcellular distribution and decreased occludin at intercellular junctions.","method":"siRNA knockdown of ZO-3 in mCCDcl1 cells, flow cytometry cell cycle analysis, immunofluorescence, Western blot","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2-3 — siRNA KD with defined phenotypic readouts but single lab, single cell type","pmids":["25486565"],"is_preprint":false},{"year":2019,"finding":"Using a peptide microarray based on ZO-3 protein sequence, cross-talk between O-GlcNAcylation (by OGT) and phosphorylation was demonstrated: nearby phosphorylation affects de-O-GlcNAcylation by OGA on ZO-3-derived peptides, revealing a post-translational modification interplay on ZO-3.","method":"Peptide microarray with ZO-3-derived peptides, enzymatic assays with OGT, OGA, kinases, and phosphatases","journal":"Amino acids","confidence":"Low","confidence_rationale":"Tier 3 — peptide model system, not validated on full-length protein in cells","pmids":["30725225"],"is_preprint":false},{"year":2023,"finding":"Akt phosphorylation inversely regulates ZO-3 expression in atopic dermatitis skin and HaCaT cells; siRNA knockdown of ZO-3 reduces transepithelial electrical resistance, establishing ZO-3 as essential for epidermal barrier function downstream of the Akt pathway.","method":"siRNA knockdown of ZO-3 in HaCaT cells, TEER measurement, Western blot, mouse atopic dermatitis model, osthole pharmacological inhibition of Akt","journal":"European journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 — siRNA KD with functional TEER readout, in vivo model corroboration, but pathway placement relies on pharmacological inhibitor","pmids":["36921706"],"is_preprint":false}],"current_model":"TJP3/ZO-3 is an epithelium-specific MAGUK scaffolding protein that localizes to tight junctions where it directly binds claudins (via its PDZ1 domain recognizing the C-terminal YV motif), occludin (regulated by c-Src-mediated tyrosine phosphorylation), ZO-1 (forming independent ZO-1·ZO-3 complexes), cingulin, F-actin, and forms the core of the tight junction plaque linking transmembrane TJ proteins to the actin cytoskeleton; ZO-3 is dispensable for tight junction formation and mammalian viability under laboratory conditions but is required for epidermal barrier function and osmoregulation in zebrafish, and its expression is regulated by Akt phosphorylation and subject to O-GlcNAc/phosphorylation cross-talk."},"narrative":{"teleology":[{"year":1998,"claim":"Identification of ZO-3 as a new MAGUK-family tight junction protein resolved the question of whether additional ZO scaffolds existed beyond ZO-1 and ZO-2, establishing ZO-3 as a direct binder of both ZO-1 and occludin.","evidence":"Biochemical purification, cDNA cloning, immunoelectron microscopy, and in vitro affinity assays in epithelial cells","pmids":["9531559"],"confidence":"High","gaps":["No domain-resolved interaction mapping for ZO-1 or occludin binding sites on ZO-3","Expression pattern across tissues not yet characterized"]},{"year":1999,"claim":"Domain mapping and complex characterization revealed that ZO-3 PDZ1 directly recognizes the claudin C-terminal YV motif, that ZO-3 binds F-actin and cingulin, and that ZO-1·ZO-3 exists as an independent heterodimer—not part of a trimeric ZO-1·ZO-2·ZO-3 complex—defining ZO-3's molecular connectivity within the tight junction plaque.","evidence":"In vitro binding with purified PDZ domains and claudins 1–8, actin cosedimentation, pull-down with cingulin fragments, and co-immunoprecipitation in MDCK cells","pmids":["10601346","10575001","10613913"],"confidence":"High","gaps":["Stoichiometry and dynamics of ZO-1·ZO-3 vs ZO-1·ZO-2 complexes in vivo unknown","Whether ZO-3 GUK domain has catalytic activity unresolved"]},{"year":2000,"claim":"Dominant-negative experiments with the N-terminal half of ZO-3 demonstrated that ZO-3 participates in tight junction and adherens junction assembly kinetics, with its PDZ-containing half mediating ZO-1 and actin binding while both halves contain occludin and cingulin interaction sites.","evidence":"Expression of NZO-3 and CZO-3 truncation mutants in MDCK cells with TEER, immunofluorescence, and calcium-switch assays","pmids":["11076967"],"confidence":"High","gaps":["Whether the assembly delay reflects direct ZO-3 function or titration of ZO-1 unclear","Endogenous loss-of-function not yet tested"]},{"year":2003,"claim":"Two advances clarified ZO-3's regulation and tissue specificity: c-Src phosphorylation of occludin disrupts the occludin–ZO-3 interaction, providing a mechanism for signal-dependent TJ remodeling, and systematic immunostaining confirmed ZO-3 is restricted to epithelial tight junctions, absent from endothelial and cadherin-based junctions.","evidence":"In vitro c-Src phosphorylation with GST pull-down quantification; KO-validated antibody survey across mouse tissues","pmids":["12604349","14622136"],"confidence":"High","gaps":["Whether c-Src phosphorylation of occludin regulates ZO-3 binding in intact epithelia untested","Functional consequence of epithelial restriction not established"]},{"year":2006,"claim":"Genetic knockout in mice and F9 cells established that ZO-3 is dispensable for tight junction formation and mammalian viability, with compensatory ZO-2 upregulation at TJs in ZO-3-null cells.","evidence":"Homologous recombination KO in mice and F9 cells, morphological analysis, immunofluorescence, calcium-switch assay","pmids":["17000770"],"confidence":"High","gaps":["Barrier challenge conditions (inflammation, wound) not tested in KO mice","Compensatory mechanisms not molecularly dissected"]},{"year":2008,"claim":"While ZO-3 dispensability in mammals was independently confirmed, zebrafish morpholino knockdown revealed a non-redundant role for ZO-3 in epidermal barrier integrity and osmoregulation, demonstrating organism-specific requirements.","evidence":"ZO-3 KO mice phenotyping; morpholino KD in zebrafish with EM, tracer permeability, and osmotic stress assays","pmids":["18172007","18275946"],"confidence":"High","gaps":["Whether mammalian ZO-3 has context-specific barrier roles under stress remains open","Zebrafish finding relies on morpholino; genetic mutant confirmation needed"]},{"year":2014,"claim":"In kidney collecting duct cells, ZO-3 junctional targeting depends on ZO-1, and ZO-3 depletion increases cell detachment and alters β1-integrin distribution, linking ZO-3 to cell-matrix adhesion beyond its canonical TJ role.","evidence":"siRNA knockdown of ZO-3 in mCCDcl1 cells with immunofluorescence, flow cytometry, and Western blot","pmids":["25486565"],"confidence":"Medium","gaps":["Single cell line; generalizability to other collecting duct models unknown","Mechanism linking ZO-3 loss to β1-integrin redistribution uncharacterized"]},{"year":2023,"claim":"Akt signaling was placed upstream of ZO-3 expression in epidermal keratinocytes, and ZO-3 knockdown reduced TEER, directly demonstrating ZO-3 contributes to mammalian epidermal barrier function in a disease-relevant (atopic dermatitis) context.","evidence":"siRNA KD in HaCaT cells with TEER, Western blot, mouse atopic dermatitis model, Akt pharmacological inhibition","pmids":["36921706"],"confidence":"Medium","gaps":["Akt–ZO-3 link relies on pharmacological inhibitor; direct phosphorylation site unidentified","Whether ZO-3 loss is causative in atopic dermatitis pathogenesis versus a secondary event is unclear"]},{"year":null,"claim":"Key unresolved questions include whether ZO-3 has stress- or tissue-specific non-redundant functions in mammals, the structural basis for its multi-partner scaffolding, and the in vivo significance of O-GlcNAc/phosphorylation cross-talk on ZO-3.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of ZO-3 or its complexes","O-GlcNAc/phosphorylation cross-talk demonstrated only on peptides, not full-length protein in cells","Conditional knockout under barrier-challenge conditions not reported"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,2,3,4]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,9]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[0,1,4,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,12]}],"complexes":["ZO-1·ZO-3 heterodimer","tight junction plaque"],"partners":["TJP1","OCLN","CGN","CLDN1","ACTB"],"other_free_text":[]},"mechanistic_narrative":"TJP3 (ZO-3) is an epithelium-specific MAGUK scaffolding protein that organizes the tight junction plaque by linking transmembrane barrier proteins to the actin cytoskeleton. Its PDZ1 domain directly binds the C-terminal YV motif of claudins 1–8, while additional domains engage occludin, ZO-1, cingulin, and F-actin, forming independent ZO-1·ZO-3 heterodimers rather than a trimeric complex with ZO-2 [PMID:9531559, PMID:10601346, PMID:10575001, PMID:10613913]. ZO-3 is dispensable for tight junction formation and viability in mice, with compensatory upregulation of ZO-2, yet is required for epidermal barrier integrity and osmoregulation in zebrafish and contributes to barrier function in mammalian keratinocytes [PMID:17000770, PMID:18275946, PMID:36921706]. The occludin–ZO-3 interaction is negatively regulated by c-Src-mediated tyrosine phosphorylation of occludin, and ZO-3 expression itself is modulated by Akt signaling [PMID:12604349, PMID:36921706]."},"prefetch_data":{"uniprot":{"accession":"O95049","full_name":"Tight junction protein ZO-3","aliases":["Tight junction protein 3","Zona occludens protein 3","Zonula occludens protein 3"],"length_aa":919,"mass_kda":101.4,"function":"TJP1, TJP2, and TJP3 are closely related scaffolding proteins that link tight junction (TJ) transmembrane proteins such as claudins, junctional adhesion molecules, and occludin to the actin cytoskeleton (PubMed:16129888). The tight junction acts to limit movement of substances through the paracellular space and as a boundary between the compositionally distinct apical and basolateral plasma membrane domains of epithelial and endothelial cells. Binds and recruits PATJ to tight junctions where it connects and stabilizes apical and lateral components of tight junctions (PubMed:16129888). Promotes cell-cycle progression through the sequestration of cyclin D1 (CCND1) at tight junctions during mitosis which prevents CCND1 degradation during M-phase and enables S-phase transition (PubMed:21411630). With TJP1 and TJP2, participates in the junctional retention and stability of the transcription factor DBPA, but is not involved in its shuttling to the nucleus (By similarity). Contrary to TJP2, TJP3 is dispensable for individual viability, embryonic development, epithelial differentiation, and the establishment of TJs, at least in the laboratory environment (By similarity)","subcellular_location":"Cell membrane; Cell junction, tight junction; Nucleus","url":"https://www.uniprot.org/uniprotkb/O95049/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TJP3","classification":"Not Classified","n_dependent_lines":14,"n_total_lines":1208,"dependency_fraction":0.011589403973509934},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TJP3","total_profiled":1310},"omim":[{"mim_id":"612689","title":"TIGHT JUNCTION PROTEIN 3; TJP3","url":"https://www.omim.org/entry/612689"},{"mim_id":"607709","title":"TIGHT JUNCTION PROTEIN 2; TJP2","url":"https://www.omim.org/entry/607709"},{"mim_id":"603199","title":"PALS1-ASSOCIATED TIGHT JUNCTION PROTEIN; PATJ","url":"https://www.omim.org/entry/603199"},{"mim_id":"601009","title":"TIGHT JUNCTION PROTEIN 1; TJP1","url":"https://www.omim.org/entry/601009"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Cell Junctions","reliability":"Enhanced"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"esophagus","ntpm":24.6},{"tissue":"intestine","ntpm":40.5},{"tissue":"stomach 1","ntpm":25.5}],"url":"https://www.proteinatlas.org/search/TJP3"},"hgnc":{"alias_symbol":["ZO-3"],"prev_symbol":[]},"alphafold":{"accession":"O95049","domains":[{"cath_id":"2.30.42.10","chopping":"3-98","consensus_level":"high","plddt":83.5169,"start":3,"end":98},{"cath_id":"2.30.42.10","chopping":"193-271","consensus_level":"high","plddt":83.3061,"start":193,"end":271},{"cath_id":"2.30.42.10","chopping":"382-473","consensus_level":"medium","plddt":90.6698,"start":382,"end":473},{"cath_id":"2.30.30.40","chopping":"479-557_587-609","consensus_level":"medium","plddt":84.2693,"start":479,"end":609},{"cath_id":"3.40.50.300","chopping":"616-775_794-805","consensus_level":"high","plddt":88.5851,"start":616,"end":805}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95049","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95049-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95049-F1-predicted_aligned_error_v6.png","plddt_mean":66.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TJP3","jax_strain_url":"https://www.jax.org/strain/search?query=TJP3"},"sequence":{"accession":"O95049","fasta_url":"https://rest.uniprot.org/uniprotkb/O95049.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95049/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95049"}},"corpus_meta":[{"pmid":"10601346","id":"PMC_10601346","title":"Direct binding of three tight junction-associated MAGUKs, ZO-1, ZO-2, and ZO-3, with the COOH termini of claudins.","date":"1999","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/10601346","citation_count":919,"is_preprint":false},{"pmid":"9531559","id":"PMC_9531559","title":"ZO-3, a novel member of the MAGUK protein family found at the tight junction, interacts with ZO-1 and occludin.","date":"1998","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/9531559","citation_count":466,"is_preprint":false},{"pmid":"10575001","id":"PMC_10575001","title":"Protein interactions at the tight junction. Actin has multiple binding partners, and ZO-1 forms independent complexes with ZO-2 and ZO-3.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10575001","citation_count":384,"is_preprint":false},{"pmid":"10613913","id":"PMC_10613913","title":"Cingulin contains globular and coiled-coil domains and interacts with ZO-1, ZO-2, ZO-3, and myosin.","date":"1999","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/10613913","citation_count":229,"is_preprint":false},{"pmid":"12604349","id":"PMC_12604349","title":"Tyrosine phosphorylation of occludin attenuates its interactions with ZO-1, ZO-2, and ZO-3.","date":"2003","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/12604349","citation_count":156,"is_preprint":false},{"pmid":"18172007","id":"PMC_18172007","title":"Early embryonic lethality of mice lacking ZO-2, but Not ZO-3, reveals critical and nonredundant roles for individual zonula occludens proteins in mammalian development.","date":"2008","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18172007","citation_count":153,"is_preprint":false},{"pmid":"17000770","id":"PMC_17000770","title":"Normal establishment of epithelial tight junctions in mice and cultured cells lacking expression of ZO-3, a tight-junction MAGUK protein.","date":"2006","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/17000770","citation_count":74,"is_preprint":false},{"pmid":"14622136","id":"PMC_14622136","title":"Expression and distribution of ZO-3, a tight junction MAGUK protein, in mouse tissues.","date":"2003","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/14622136","citation_count":61,"is_preprint":false},{"pmid":"18275946","id":"PMC_18275946","title":"Tjp3/zo-3 is critical for epidermal barrier function in zebrafish embryos.","date":"2008","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/18275946","citation_count":50,"is_preprint":false},{"pmid":"11076967","id":"PMC_11076967","title":"Exogenous expression of the amino-terminal half of the tight junction protein ZO-3 perturbs junctional complex assembly.","date":"2000","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/11076967","citation_count":50,"is_preprint":false},{"pmid":"27029941","id":"PMC_27029941","title":"Glycine Regulates Expression and Distribution of Claudin-7 and ZO-3 Proteins in Intestinal Porcine Epithelial Cells.","date":"2016","source":"The Journal of nutrition","url":"https://pubmed.ncbi.nlm.nih.gov/27029941","citation_count":44,"is_preprint":false},{"pmid":"17632043","id":"PMC_17632043","title":"Identification, tissue distribution and developmental expression of tjp1/zo-1, tjp2/zo-2 and tjp3/zo-3 in the zebrafish, Danio rerio.","date":"2007","source":"Gene expression patterns : GEP","url":"https://pubmed.ncbi.nlm.nih.gov/17632043","citation_count":39,"is_preprint":false},{"pmid":"25486565","id":"PMC_25486565","title":"Different effects of ZO-1, ZO-2 and ZO-3 silencing on kidney collecting duct principal cell proliferation and adhesion.","date":"2014","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/25486565","citation_count":17,"is_preprint":false},{"pmid":"35147806","id":"PMC_35147806","title":"Exosomal miRNA-328-3p targets ZO-3 and inhibits porcine epidemic diarrhea virus proliferation.","date":"2022","source":"Archives of virology","url":"https://pubmed.ncbi.nlm.nih.gov/35147806","citation_count":10,"is_preprint":false},{"pmid":"36921706","id":"PMC_36921706","title":"Osthole relieves skin damage and inhibits chronic itch through modulation of Akt/ZO-3 pathway in atopic dermatitis.","date":"2023","source":"European journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/36921706","citation_count":9,"is_preprint":false},{"pmid":"38137355","id":"PMC_38137355","title":"Expression of Claudin-9 (CLDN9) in Breast Cancer, the Clinical Significance in Connection with Its Subcoat Anchorage Proteins ZO-1 and ZO-3 and Impact on Drug Resistance.","date":"2023","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/38137355","citation_count":9,"is_preprint":false},{"pmid":"12507281","id":"PMC_12507281","title":"Dynamic assembly of tight junction-associated proteins ZO-1, ZO-2, ZO-3 and occludin during mouse tooth development.","date":"2003","source":"Histology and histopathology","url":"https://pubmed.ncbi.nlm.nih.gov/12507281","citation_count":9,"is_preprint":false},{"pmid":"30725225","id":"PMC_30725225","title":"Study of cross talk between phosphatases and OGA on a ZO-3-derived peptide.","date":"2019","source":"Amino acids","url":"https://pubmed.ncbi.nlm.nih.gov/30725225","citation_count":6,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10988,"output_tokens":3203,"usd":0.040504},"stage2":{"model":"claude-opus-4-6","input_tokens":6583,"output_tokens":2460,"usd":0.141623},"total_usd":0.182127,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"ZO-3 (TJP3) was identified as a MAGUK family protein that localizes at tight junctions, contains three PDZ domains, an SH3 domain, and a guanylate kinase-like region, and directly interacts with ZO-1 and the cytoplasmic domain of occludin in vitro affinity analyses, but not with ZO-2.\",\n      \"method\": \"Partial endopeptidase digestion, amino acid sequencing, cDNA library screening, stable transfection with epitope-tagged construct, immunofluorescence, immunoelectron microscopy, in vitro affinity binding assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — original discovery with multiple orthogonal methods (biochemical purification, sequencing, in vitro binding, immunolocalization), single rigorous study\",\n      \"pmids\": [\"9531559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"ZO-3 PDZ1 domain directly binds the COOH-terminal YV sequence of claudin-1 through -8 in vitro; ZO-3 is also recruited to claudin-based networks through PDZ1/claudin-YV and PDZ2(ZO-3)/PDZ2(ZO-1) interactions.\",\n      \"method\": \"In vitro binding assays, transfection of claudins into L fibroblasts, immunofluorescence, transfection of isolated PDZ domains into epithelial cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted in vitro binding with domain mapping, corroborated by cell-based localization assays\",\n      \"pmids\": [\"10601346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"ZO-3 directly interacts with F-actin in vitro (cosedimentation assay), forms independent ZO-1·ZO-3 complexes (rather than a trimeric ZO-1·ZO-2·ZO-3 complex) as shown by immunoprecipitation, and colocalizes with actin aggregates in cytochalasin D-treated MDCK cells.\",\n      \"method\": \"Actin cosedimentation assays with purified recombinant proteins, low-speed sedimentation, immunoprecipitation, immunofluorescence in cytochalasin D-treated MDCK cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal in vitro and in vivo methods, rigorous controls with purified proteins\",\n      \"pmids\": [\"10575001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"An NH2-terminal fragment of cingulin (residues 1-378) interacts with ZO-3 in vitro (Kd ~5 nM for ZO-1), and a COOH-terminal cingulin fragment also binds ZO-3, linking ZO-3 to the cingulin scaffold at tight junctions.\",\n      \"method\": \"Pull-down assays from epithelial, insect cell, and reticulocyte lysates; immunoprecipitation; electron microscopy\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro pull-down with defined fragments, corroborated by immunoprecipitation in vivo\",\n      \"pmids\": [\"10613913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The amino-terminal PDZ-domain-containing half of ZO-3 (NZO-3) acts as a dominant negative, delaying tight junction and adherens junction assembly in MDCK cells; NZO-3 preferentially binds ZO-1 and actin, while both NZO-3 and the C-terminal half (CZO-3) contain binding sites for occludin and cingulin.\",\n      \"method\": \"Exogenous expression of truncation mutants in MDCK cells, transepithelial resistance measurements, immunofluorescence, in vitro binding experiments, calcium switch and cytochalasin D assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — domain dissection with multiple functional readouts and in vitro binding validation\",\n      \"pmids\": [\"11076967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Tyrosine phosphorylation of occludin by c-Src in vitro significantly reduces its binding to ZO-3 (and ZO-1, ZO-2), but does not affect its binding to F-actin, indicating that c-Src-mediated tyrosine phosphorylation of occludin disrupts its interaction with ZO-3.\",\n      \"method\": \"In vitro phosphorylation by c-Src, GST pull-down with tyrosine-phosphorylated vs. non-phosphorylated C-occludin, binding quantification for ZO-1, ZO-2, ZO-3, and F-actin\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay with mutagenesis-equivalent phosphorylation, clear mechanistic outcome\",\n      \"pmids\": [\"12604349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ZO-3 knockout mice are viable and fertile with no significant phenotypic abnormality; ZO-3-deficient F9 teratocarcinoma cells differentiate normally and form morphologically intact tight junctions, though TJ localization of ZO-2 is upregulated in the absence of ZO-3, indicating ZO-3 is dispensable for tight junction establishment in vivo.\",\n      \"method\": \"Homologous recombination knockout in mice and F9 cells, immunofluorescence, RNA interference, calcium switch assay, morphological analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple phenotypic readouts and compensatory analysis\",\n      \"pmids\": [\"17000770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ZO-3 knockout mice lack an obvious phenotype, confirming it is dispensable for mammalian development, whereas ZO-2 knockout causes early embryonic lethality, demonstrating non-redundant roles for individual ZO proteins.\",\n      \"method\": \"Knockout mouse generation, embryonic phenotypic analysis, immunofluorescence, paracellular permeability assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO genetic analysis with functional phenotyping, independently confirms ZO-3 dispensability\",\n      \"pmids\": [\"18172007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Tjp3/ZO-3 is required for epidermal barrier function in zebrafish: morpholino silencing of tjp3/zo-3 disrupts tight junction ultrastructure in the enveloping cell layer, increases paracellular permeability to low molecular weight tracers, and causes edema and loss of blood circulation, without affecting asymmetric plasma membrane protein distribution.\",\n      \"method\": \"Morpholino knockdown in zebrafish embryos, electron microscopy of tight junction ultrastructure, permeability tracer assays, osmotic stress experiments\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — morpholino KD with multiple orthogonal functional readouts in zebrafish ortholog model\",\n      \"pmids\": [\"18275946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"ZO-3 is exclusively expressed at tight junctions in epithelial cells and is absent from endothelial tight junctions and cadherin-based adhesion sites (spot adherens junctions of fibroblasts, intercalated discs of cardiac muscle cells) where ZO-1 and ZO-2 are concentrated, demonstrating epithelium-specific localization.\",\n      \"method\": \"Generation of ZO-3-specific polyclonal and monoclonal antibodies validated in ZO-3-deficient mice, immunofluorescence microscopy in multiple mouse tissues\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — antibody specificity validated by KO tissue, systematic tissue survey\",\n      \"pmids\": [\"14622136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In kidney collecting duct principal cells, ZO-3 expression at intercellular junctions increases with cell density and requires ZO-1; ZO-3 depletion does not affect cell cycle progression but increases cell detachment, associated with altered β1-integrin subcellular distribution and decreased occludin at intercellular junctions.\",\n      \"method\": \"siRNA knockdown of ZO-3 in mCCDcl1 cells, flow cytometry cell cycle analysis, immunofluorescence, Western blot\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — siRNA KD with defined phenotypic readouts but single lab, single cell type\",\n      \"pmids\": [\"25486565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Using a peptide microarray based on ZO-3 protein sequence, cross-talk between O-GlcNAcylation (by OGT) and phosphorylation was demonstrated: nearby phosphorylation affects de-O-GlcNAcylation by OGA on ZO-3-derived peptides, revealing a post-translational modification interplay on ZO-3.\",\n      \"method\": \"Peptide microarray with ZO-3-derived peptides, enzymatic assays with OGT, OGA, kinases, and phosphatases\",\n      \"journal\": \"Amino acids\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — peptide model system, not validated on full-length protein in cells\",\n      \"pmids\": [\"30725225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Akt phosphorylation inversely regulates ZO-3 expression in atopic dermatitis skin and HaCaT cells; siRNA knockdown of ZO-3 reduces transepithelial electrical resistance, establishing ZO-3 as essential for epidermal barrier function downstream of the Akt pathway.\",\n      \"method\": \"siRNA knockdown of ZO-3 in HaCaT cells, TEER measurement, Western blot, mouse atopic dermatitis model, osthole pharmacological inhibition of Akt\",\n      \"journal\": \"European journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — siRNA KD with functional TEER readout, in vivo model corroboration, but pathway placement relies on pharmacological inhibitor\",\n      \"pmids\": [\"36921706\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TJP3/ZO-3 is an epithelium-specific MAGUK scaffolding protein that localizes to tight junctions where it directly binds claudins (via its PDZ1 domain recognizing the C-terminal YV motif), occludin (regulated by c-Src-mediated tyrosine phosphorylation), ZO-1 (forming independent ZO-1·ZO-3 complexes), cingulin, F-actin, and forms the core of the tight junction plaque linking transmembrane TJ proteins to the actin cytoskeleton; ZO-3 is dispensable for tight junction formation and mammalian viability under laboratory conditions but is required for epidermal barrier function and osmoregulation in zebrafish, and its expression is regulated by Akt phosphorylation and subject to O-GlcNAc/phosphorylation cross-talk.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TJP3 (ZO-3) is an epithelium-specific MAGUK scaffolding protein that organizes the tight junction plaque by linking transmembrane barrier proteins to the actin cytoskeleton. Its PDZ1 domain directly binds the C-terminal YV motif of claudins 1–8, while additional domains engage occludin, ZO-1, cingulin, and F-actin, forming independent ZO-1·ZO-3 heterodimers rather than a trimeric complex with ZO-2 [PMID:9531559, PMID:10601346, PMID:10575001, PMID:10613913]. ZO-3 is dispensable for tight junction formation and viability in mice, with compensatory upregulation of ZO-2, yet is required for epidermal barrier integrity and osmoregulation in zebrafish and contributes to barrier function in mammalian keratinocytes [PMID:17000770, PMID:18275946, PMID:36921706]. The occludin–ZO-3 interaction is negatively regulated by c-Src-mediated tyrosine phosphorylation of occludin, and ZO-3 expression itself is modulated by Akt signaling [PMID:12604349, PMID:36921706].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of ZO-3 as a new MAGUK-family tight junction protein resolved the question of whether additional ZO scaffolds existed beyond ZO-1 and ZO-2, establishing ZO-3 as a direct binder of both ZO-1 and occludin.\",\n      \"evidence\": \"Biochemical purification, cDNA cloning, immunoelectron microscopy, and in vitro affinity assays in epithelial cells\",\n      \"pmids\": [\"9531559\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No domain-resolved interaction mapping for ZO-1 or occludin binding sites on ZO-3\", \"Expression pattern across tissues not yet characterized\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Domain mapping and complex characterization revealed that ZO-3 PDZ1 directly recognizes the claudin C-terminal YV motif, that ZO-3 binds F-actin and cingulin, and that ZO-1·ZO-3 exists as an independent heterodimer—not part of a trimeric ZO-1·ZO-2·ZO-3 complex—defining ZO-3's molecular connectivity within the tight junction plaque.\",\n      \"evidence\": \"In vitro binding with purified PDZ domains and claudins 1–8, actin cosedimentation, pull-down with cingulin fragments, and co-immunoprecipitation in MDCK cells\",\n      \"pmids\": [\"10601346\", \"10575001\", \"10613913\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and dynamics of ZO-1·ZO-3 vs ZO-1·ZO-2 complexes in vivo unknown\", \"Whether ZO-3 GUK domain has catalytic activity unresolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Dominant-negative experiments with the N-terminal half of ZO-3 demonstrated that ZO-3 participates in tight junction and adherens junction assembly kinetics, with its PDZ-containing half mediating ZO-1 and actin binding while both halves contain occludin and cingulin interaction sites.\",\n      \"evidence\": \"Expression of NZO-3 and CZO-3 truncation mutants in MDCK cells with TEER, immunofluorescence, and calcium-switch assays\",\n      \"pmids\": [\"11076967\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the assembly delay reflects direct ZO-3 function or titration of ZO-1 unclear\", \"Endogenous loss-of-function not yet tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Two advances clarified ZO-3's regulation and tissue specificity: c-Src phosphorylation of occludin disrupts the occludin–ZO-3 interaction, providing a mechanism for signal-dependent TJ remodeling, and systematic immunostaining confirmed ZO-3 is restricted to epithelial tight junctions, absent from endothelial and cadherin-based junctions.\",\n      \"evidence\": \"In vitro c-Src phosphorylation with GST pull-down quantification; KO-validated antibody survey across mouse tissues\",\n      \"pmids\": [\"12604349\", \"14622136\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether c-Src phosphorylation of occludin regulates ZO-3 binding in intact epithelia untested\", \"Functional consequence of epithelial restriction not established\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Genetic knockout in mice and F9 cells established that ZO-3 is dispensable for tight junction formation and mammalian viability, with compensatory ZO-2 upregulation at TJs in ZO-3-null cells.\",\n      \"evidence\": \"Homologous recombination KO in mice and F9 cells, morphological analysis, immunofluorescence, calcium-switch assay\",\n      \"pmids\": [\"17000770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Barrier challenge conditions (inflammation, wound) not tested in KO mice\", \"Compensatory mechanisms not molecularly dissected\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"While ZO-3 dispensability in mammals was independently confirmed, zebrafish morpholino knockdown revealed a non-redundant role for ZO-3 in epidermal barrier integrity and osmoregulation, demonstrating organism-specific requirements.\",\n      \"evidence\": \"ZO-3 KO mice phenotyping; morpholino KD in zebrafish with EM, tracer permeability, and osmotic stress assays\",\n      \"pmids\": [\"18172007\", \"18275946\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian ZO-3 has context-specific barrier roles under stress remains open\", \"Zebrafish finding relies on morpholino; genetic mutant confirmation needed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"In kidney collecting duct cells, ZO-3 junctional targeting depends on ZO-1, and ZO-3 depletion increases cell detachment and alters β1-integrin distribution, linking ZO-3 to cell-matrix adhesion beyond its canonical TJ role.\",\n      \"evidence\": \"siRNA knockdown of ZO-3 in mCCDcl1 cells with immunofluorescence, flow cytometry, and Western blot\",\n      \"pmids\": [\"25486565\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell line; generalizability to other collecting duct models unknown\", \"Mechanism linking ZO-3 loss to β1-integrin redistribution uncharacterized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Akt signaling was placed upstream of ZO-3 expression in epidermal keratinocytes, and ZO-3 knockdown reduced TEER, directly demonstrating ZO-3 contributes to mammalian epidermal barrier function in a disease-relevant (atopic dermatitis) context.\",\n      \"evidence\": \"siRNA KD in HaCaT cells with TEER, Western blot, mouse atopic dermatitis model, Akt pharmacological inhibition\",\n      \"pmids\": [\"36921706\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Akt–ZO-3 link relies on pharmacological inhibitor; direct phosphorylation site unidentified\", \"Whether ZO-3 loss is causative in atopic dermatitis pathogenesis versus a secondary event is unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include whether ZO-3 has stress- or tissue-specific non-redundant functions in mammals, the structural basis for its multi-partner scaffolding, and the in vivo significance of O-GlcNAc/phosphorylation cross-talk on ZO-3.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of ZO-3 or its complexes\", \"O-GlcNAc/phosphorylation cross-talk demonstrated only on peptides, not full-length protein in cells\", \"Conditional knockout under barrier-challenge conditions not reported\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 9]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [0, 1, 4, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 12]}\n    ],\n    \"complexes\": [\n      \"ZO-1·ZO-3 heterodimer\",\n      \"tight junction plaque\"\n    ],\n    \"partners\": [\n      \"TJP1\",\n      \"OCLN\",\n      \"CGN\",\n      \"CLDN1\",\n      \"ACTB\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}