Cadherin mediated cell-cell adhesion is regulated by tyrosine phosphatases in human keratinocytes

Normal Human Keratinocytes express on their cell surface E- and P-cadherins, two Ca2+ dependent homophilic cell adhesion molecules that mediate keratinocyte-keratinocyte adherens junctions. In other cell types, adherens-type junctions are reported to be major subcellular targets for tyrosine specific protein phosphorylation (Volberg et al. (1991) Cell Regul., 2, 105-120) involving tyrosine kinases and tyrosine phosphatases. We investigated the role of tyrosine phosphatases in the regulation of cadherin mediated keratinocyte-keratinocyte adhesion. We report the results of a wide tyrosine phosphatase inhibition using pervanadate, a modified vanadate derivative known to inhibit most tyrosine phosphatases. Keratinocytes treated with pervanadate, exhibit an important change in cellular morphology and cadherins/catenins localization as shown by phase contrast microscopy and immunocytochemistry. In this conditions, cadherins and catenins no longer colocalize with the actin cytoskeleton of cells and the amount of E-cadherin bound to the cytoskeleton decreases. A more intense phosphotyrosine labelling is seen at the edges of the treated cells, suggesting that an increase in the phosphorylation rate of some cadherin-catenin complex proteins induces a diminished intercellular adhesion. Finally immunoprecipitation experiments of the E-cadherin/catenin complex from pervanadate treated keratinocytes reveal an increase in the tyrosine phosphorylation rate of E-cadherin, beta catenin and probably gamma catenin. These data suggest an essential role for the protein tyrosine phosphatases in keratinocyte intercellular junctions.