Disease relevance of TJP1

• MDCK cells permanently transformed with Moloney sarcoma virus, which expresses low levels of E-cadherin, displayed clusters of cytoplasmic ZO-1 granules and very little of this protein at the cell surface [1].
• Upon transfection with E-cadherin into Moloney sarcoma virus-MDCK cells, ZO-1 redistributed to E-cadherin-rich lateral plasma membrane but later failed to segregate into mature tight junctions [1].
• Recently, with the use of an ATP depletion-repletion model for ischemia and reperfusion injury in Madin-Darby canine kidney cells, TJ proteins such as zonula occludens-1 (ZO-1) were shown to reversibly form large complexes and associate with cytoskeletal proteins (T. Tsukamoto and S. K. Nigam, J. Biol. Chem. 272: 16133-16139, 1997) [2].

High impact information on TJP1

• 48 h after Ca2+ switch, upon complete polarization of the epithelium, most of the ZO-1 had segregated from lateral E-cadherin and formed a distinct, separate apical ring [1].
• In MDCK cells cultured in low (micromolar) calcium levels, the tight junctional protein Zonula Occludens-1 (ZO-1) is distributed intracellularly in granular clusters, the larger of which codistribute with E-cadherin [1].
• Nuclear accumulation can be stimulated at sites of wounding in cultured epithelial cells, and immunoperoxidase detection of ZO-1 in tissue sections of intestinal epithelial cells reveals nuclear labeling only along the outer tip of the villus [3].
• Since cell-cell contacts are specialized sites for signaling pathways implicated in growth and differentiation, we suggest that the nuclear accumulation of ZO-1 may be relevant for its suggested role in membrane-associated guanylate kinase homologue signal transduction [3].
• We present evidence that under certain conditions of cell growth, ZO-1 can be detected in the nucleus [3].

Biological context of TJP1

• Accordingly, we have sequenced ZO-1 in this cell type, because this protein is involved in the response of the TJ to changes in Ca2+, phosphorylation, and the cytoskeleton [4].
• ZO-1 of MDCK cells comprises 6805 bp with a predicted open reading frame of 1769 amino acids [4].
• Two exonic elements in the flanking constitutive exons control the alternative splicing of the alpha exon of the ZO-1 pre-mRNA [5].
• Staining of the tight junction-associated protein ZO-1 showed that the changes in transepithelial electrical resistance were accompanied by a diffusing of the protein away from cell peripheries and a reconcentration to the tight junction areas following resistance recovery [6].

Anatomical context of TJP1

• Moreover, membrane-associated PKC activity more than doubled during junction assembly, and immunocytochemical analysis revealed a pool of PKC zeta that appeared to colocalize with ZO-1 at the tight junction [7].
• Moreover, the apical structure of filamentous actin (F-actin) was disturbed and tight junction-associated proteins (ZO-1 and occludin) were dispersed along the basolateral membranes [8].
• The C-terminus of Cx43 has been shown to interact with the PDZ2 domain of the tight and adherens junction associated zona occludens 1 (ZO-1) protein [9].

Associations of TJP1 with chemical compounds

• We found two new splicing regions at the proline-rich region: beta had not been reported in human and mouse counterparts, and gamma, which was previously sequenced in human and mouse ZO-1, is now identified as a splicing region [4].
• The mass of this complex and the incorporation of ZO-1 into the Triton X-100-insoluble cytoskeleton were not PKC dependent [7].
• The junction-associated protein zonula occludens-1 (ZO-1) is a member of a family of membrane-associated guanylate kinase homologues thought to be important in signal transduction at sites of cell-cell contact [3].
• In addition, ZO-1 was phosphorylated subsequent to the initiation of cell-cell contact, and treatment with calphostin C prevented approximately 85% of the phosphorylation increase [7].
• The utility for membrane proteins present in small numbers of copies is demonstrated by labeling a glutamate receptor subunit in mouse cerebellar cortex and the ZO-1 protein in tight junctions between MDCK cells [10].

Analytical, diagnostic and therapeutic context of TJP1

• With the information provided by the sequence, Southern blot, and PCR experiments we can predict a single genomic copy of MDCK-ZO-1 that is at least 13.16 kb long [4].
• Immunofluorescence and immunoelectron microscopy confirmed a close association of beta-catenin and ZO-1 at 0 and 2 h after Ca2+ switch [1].
• Immunoprecipitation with ZO-1 antibodies of extracts from cells kept in low calcium and 2 h after shifting to 1.8 mM Ca2+ demonstrated the association of ZO-1 with alpha-, beta-, and gamma-catenins [1].
• Two different antibodies against distinct portions of the ZO-1 polypeptide reveal nuclear staining in subconfluent, but not confluent, cell cultures [3].
• In Galpha(12)-expressing cells, we found that ZO-1 and Galpha(12) co-localize by confocal microscopy and co-immunoprecipitate [11].

References