JUNCTIONAL UVOMORULIN E-CADHERIN AND PHOSPHOTYROSINE-MODIFIED PROTEIN-CONTENT ARE CORRELATED WITH PARACELLULAR PERMEABILITY IN MADIN-DARBY CANINE KIDNEY (MDCK) EPITHELIA

Strains I and II of Madin-Darby canine kidney (MDCK) cells, which differ markedly in transepithelial resistance (R,) and paracellular permeability, have been used to investigate whether differences in the cellular content of uvomorulin/E-cadherin and phosphotyrosine may be correlated with junctional properties. Using immunocytochemistry, the strain T ''tight'' epithelia showed significantly stronger uvomorulin staining at regions of cell-cell contact compared with strain II ''leaky'' MDCK epithelia. In contrast, strain I MDCK cells showed a relatively faint phosphotyrosine staining, distributed evenly throughout the cytoplasm, while strain II MDCK cells displayed intense staining for phosphotyrosine residues in the junctional region and the lateral cell membrane with additional labelling of the cytoplasm. Exposure to vanadate in conjunction with H2O2 (which are potent inhibitors of protein tyrosine phosphatases) resulted in a dramatic increase in phosphotyrosine staining at the intercellular area and, concomitantly, induced changes in cell morphology, a significant decrease in R,, increase in paracellular inulin permeability, and time-dependent disappearance of uvomorulin from the cell-cell contact sites. Moreover, the effects of vanadate/H2O2 treatment were more dramatic in strain II compared with strain I cells, consistent with greater generation of tyrosine-modified protein in strain II cells. An inverse relationship was demonstrated between membrane-associated uvomorulin/E-cadherin and cellular phosphotyrosine content, which varied between the two strains of MDCK cells and when phosphotyrosine was directly manipulated. These data support the hypothesis that regulation of paracellular permeability may result from specific tyrosine phosphorylation of protein components of the junctional complex.