Regulation of fibroblast motility by the protein tyrosine phosphatase PTP-PEST

The protein tyrosine phosphatase PTP-PEST is a cytosolic enzyme that displa ys a remarkable degree of selectivity for tyrosine-phosphorylated p130(Cas) as a substrate, both in vitro and in intact cells, We have investigated th e physiological role of PTP-PEST using Rat1 fibroblast-derived stable cell lines that we have engineered to overexpress PTP-PEST. These cell lines exh ibit normal levels of tyrosine phosphorylation of the majority of proteins but have significantly lower levels of tyrosine phosphorylation of p130(Cas ) than control cells. Initial cellular events occurring following integrin- mediated attachment to fibronectin (cell attachment and spreading) are esse ntially unchanged in cells overexpressing PTP-PEST; similarly, the extent a nd time course of mitogen-activated protein kinase activation in response t o integrin engagement is unchanged. In contrast, the reduced phosphorylatio n state of p130(Cas) is associated with a considerably reduced rate of cell migration and a failure of cells overexpressing PTP-PEST to accomplish the normally observed redistribution of p130(Cas) to the leading edge of migra ting cells. Furthermore, cells overexpressing PTP-PEST demonstrate signific antly reduced levels of association of p130(Cas) with the Crk adaptor prote in. Our results suggest that one physiological role of PTP-PEST is to depho sphorylate p130(Cas), thereby controlling tyrosine phosphorylation dependen t signaling events downstream of p130(Cas) and regulating cell migration.