Affinage

TJP3

Tight junction protein ZO-3 · UniProt O95049

Length
919 aa
Mass
101.4 kDa
Annotated
2026-04-28
18 papers in source corpus 13 papers cited in narrative 13 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1998 High

    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

    PMID:9531559

    Open questions at the time
    • No domain-resolved interaction mapping for ZO-1 or occludin binding sites on ZO-3
    • Expression pattern across tissues not yet characterized
  2. 1999 High

    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

    PMID:10575001 PMID:10601346 PMID:10613913

    Open questions at the time
    • 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
  3. 2000 High

    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

    PMID:11076967

    Open questions at the time
    • Whether the assembly delay reflects direct ZO-3 function or titration of ZO-1 unclear
    • Endogenous loss-of-function not yet tested
  4. 2003 High

    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

    PMID:12604349 PMID:14622136

    Open questions at the time
    • Whether c-Src phosphorylation of occludin regulates ZO-3 binding in intact epithelia untested
    • Functional consequence of epithelial restriction not established
  5. 2006 High

    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

    PMID:17000770

    Open questions at the time
    • Barrier challenge conditions (inflammation, wound) not tested in KO mice
    • Compensatory mechanisms not molecularly dissected
  6. 2008 High

    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

    PMID:18172007 PMID:18275946

    Open questions at the time
    • Whether mammalian ZO-3 has context-specific barrier roles under stress remains open
    • Zebrafish finding relies on morpholino; genetic mutant confirmation needed
  7. 2014 Medium

    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

    PMID:25486565

    Open questions at the time
    • Single cell line; generalizability to other collecting duct models unknown
    • Mechanism linking ZO-3 loss to β1-integrin redistribution uncharacterized
  8. 2023 Medium

    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

    PMID:36921706

    Open questions at the time
    • 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

Open questions

Synthesis pass · forward-looking unresolved questions
  • 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.
  • 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

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 5 GO:0008092 cytoskeletal protein binding 2
Localization
GO:0005886 plasma membrane 3 GO:0005856 cytoskeleton 1
Pathway
R-HSA-1500931 Cell-Cell communication 4 R-HSA-162582 Signal Transduction 2
Partners
ACTBCGNCLDN1OCLNTJP1
Complex memberships
ZO-1·ZO-3 heterodimertight junction plaque

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1998 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. Partial endopeptidase digestion, amino acid sequencing, cDNA library screening, stable transfection with epitope-tagged construct, immunofluorescence, immunoelectron microscopy, in vitro affinity binding assays The Journal of cell biology High 9531559
1999 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. In vitro binding assays, transfection of claudins into L fibroblasts, immunofluorescence, transfection of isolated PDZ domains into epithelial cells The Journal of cell biology High 10601346
1999 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. Actin cosedimentation assays with purified recombinant proteins, low-speed sedimentation, immunoprecipitation, immunofluorescence in cytochalasin D-treated MDCK cells The Journal of biological chemistry High 10575001
1999 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. Pull-down assays from epithelial, insect cell, and reticulocyte lysates; immunoprecipitation; electron microscopy The Journal of cell biology High 10613913
2000 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. Exogenous expression of truncation mutants in MDCK cells, transepithelial resistance measurements, immunofluorescence, in vitro binding experiments, calcium switch and cytochalasin D assays The Journal of cell biology High 11076967
2003 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. 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 Biochemical and biophysical research communications High 12604349
2006 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. Homologous recombination knockout in mice and F9 cells, immunofluorescence, RNA interference, calcium switch assay, morphological analysis Molecular and cellular biology High 17000770
2008 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. Knockout mouse generation, embryonic phenotypic analysis, immunofluorescence, paracellular permeability assays Molecular and cellular biology High 18172007
2008 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. Morpholino knockdown in zebrafish embryos, electron microscopy of tight junction ultrastructure, permeability tracer assays, osmotic stress experiments Developmental biology High 18275946
2003 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. Generation of ZO-3-specific polyclonal and monoclonal antibodies validated in ZO-3-deficient mice, immunofluorescence microscopy in multiple mouse tissues Genes to cells High 14622136
2014 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. siRNA knockdown of ZO-3 in mCCDcl1 cells, flow cytometry cell cycle analysis, immunofluorescence, Western blot Cell cycle Medium 25486565
2019 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. Peptide microarray with ZO-3-derived peptides, enzymatic assays with OGT, OGA, kinases, and phosphatases Amino acids Low 30725225
2023 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. siRNA knockdown of ZO-3 in HaCaT cells, TEER measurement, Western blot, mouse atopic dermatitis model, osthole pharmacological inhibition of Akt European journal of pharmacology Medium 36921706

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1999 Direct binding of three tight junction-associated MAGUKs, ZO-1, ZO-2, and ZO-3, with the COOH termini of claudins. The Journal of cell biology 919 10601346
1998 ZO-3, a novel member of the MAGUK protein family found at the tight junction, interacts with ZO-1 and occludin. The Journal of cell biology 466 9531559
1999 Protein interactions at the tight junction. Actin has multiple binding partners, and ZO-1 forms independent complexes with ZO-2 and ZO-3. The Journal of biological chemistry 384 10575001
1999 Cingulin contains globular and coiled-coil domains and interacts with ZO-1, ZO-2, ZO-3, and myosin. The Journal of cell biology 229 10613913
2003 Tyrosine phosphorylation of occludin attenuates its interactions with ZO-1, ZO-2, and ZO-3. Biochemical and biophysical research communications 156 12604349
2008 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. Molecular and cellular biology 153 18172007
2006 Normal establishment of epithelial tight junctions in mice and cultured cells lacking expression of ZO-3, a tight-junction MAGUK protein. Molecular and cellular biology 74 17000770
2003 Expression and distribution of ZO-3, a tight junction MAGUK protein, in mouse tissues. Genes to cells : devoted to molecular & cellular mechanisms 61 14622136
2008 Tjp3/zo-3 is critical for epidermal barrier function in zebrafish embryos. Developmental biology 50 18275946
2000 Exogenous expression of the amino-terminal half of the tight junction protein ZO-3 perturbs junctional complex assembly. The Journal of cell biology 50 11076967
2016 Glycine Regulates Expression and Distribution of Claudin-7 and ZO-3 Proteins in Intestinal Porcine Epithelial Cells. The Journal of nutrition 44 27029941
2007 Identification, tissue distribution and developmental expression of tjp1/zo-1, tjp2/zo-2 and tjp3/zo-3 in the zebrafish, Danio rerio. Gene expression patterns : GEP 39 17632043
2014 Different effects of ZO-1, ZO-2 and ZO-3 silencing on kidney collecting duct principal cell proliferation and adhesion. Cell cycle (Georgetown, Tex.) 17 25486565
2022 Exosomal miRNA-328-3p targets ZO-3 and inhibits porcine epidemic diarrhea virus proliferation. Archives of virology 10 35147806
2023 Osthole relieves skin damage and inhibits chronic itch through modulation of Akt/ZO-3 pathway in atopic dermatitis. European journal of pharmacology 9 36921706
2023 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. Biomedicines 9 38137355
2003 Dynamic assembly of tight junction-associated proteins ZO-1, ZO-2, ZO-3 and occludin during mouse tooth development. Histology and histopathology 9 12507281
2019 Study of cross talk between phosphatases and OGA on a ZO-3-derived peptide. Amino acids 6 30725225