Tyrosine phosphorylation of p62(Dok) induced by cell adhesion and insulin:possible role in cell migration

Dok, a 62-kDa Ras GTPase-activating protein (ras-GAP)-associated phosphotyr osyl protein, is thought to act as a multiple docking protein downstream of receptor or non-receptor tyrosine kinases, Cell adhesion to extracellular matrix proteins induced marked tyrosine phosphorylation of Dok, This adhesi on-dependent phosphorylation of Dok was mediated, at least in part, by Src family tyrosine kinases, The maximal insulin-induced tyrosine phosphorylati on of Dok required a Src family kinase, A mutant Dok (Dok Delta PH) that la cked its pleckstrin homology domain failed to undergo tyrosine phosphorylat ion in response to cell adhesion or insulin. Furthermore, unlike the wild-t ype protein, Dok Delta PH did not localize to subcellular membrane componen ts. Insulin promoted the association of tyrosine-phosphorylated Dok with th e adapter protein NCK and rasGAP, In contrast, a mutant Dok (DokY361F), in which Tyr361 was replaced by phenylalanine, failed to bind NCK but partiall y retained the ability to bind rasGAP in response to insulin. Overexpressio n of wild-type Dok, but not that of Dok Delta PH or DokY361F, enhanced the cell migratory response to insulin without affecting insulin activation of mitogen-activated protein kinase, These results identify Dok as a signal tr ansducer that potentially links, through its interaction with NCK or rasGAP , cell adhesion and insulin receptors to the machinery that controls cell m otility.