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 diff er markedly in transepithelial resistance (R,) and paracellular permea bility, have been used to investigate whether differences in the cellu lar content of uvomorulin/E-cadherin and phosphotyrosine may be correl ated with junctional properties. Using immunocytochemistry, the strain T ''tight'' epithelia showed significantly stronger uvomorulin staini ng at regions of cell-cell contact compared with strain II ''leaky'' M DCK epithelia. In contrast, strain I MDCK cells showed a relatively fa int phosphotyrosine staining, distributed evenly throughout the cytopl asm, while strain II MDCK cells displayed intense staining for phospho tyrosine residues in the junctional region and the lateral cell membra ne with additional labelling of the cytoplasm. Exposure to vanadate in conjunction with H2O2 (which are potent inhibitors of protein tyrosin e phosphatases) resulted in a dramatic increase in phosphotyrosine sta ining at the intercellular area and, concomitantly, induced changes in cell morphology, a significant decrease in R,, increase in paracellul ar inulin permeability, and time-dependent disappearance of uvomorulin from the cell-cell contact sites. Moreover, the effects of vanadate/H 2O2 treatment were more dramatic in strain II compared with strain I c ells, consistent with greater generation of tyrosine-modified protein in strain II cells. An inverse relationship was demonstrated between m embrane-associated uvomorulin/E-cadherin and cellular phosphotyrosine content, which varied between the two strains of MDCK cells and when p hosphotyrosine was directly manipulated. These data support the hypoth esis that regulation of paracellular permeability may result from spec ific tyrosine phosphorylation of protein components of the junctional complex.