SRC AND RAS ARE INVOLVED IN SEPARATE PATHWAYS IN EPITHELIAL-CELL SCATTERING

We have demonstrated previously that Src controls the epidermal growth factor (EGF)-induced dispersion of NET-II carcinoma epithelial cells. Here we show that while only Src and Yes were expressed and activated by EGF, microinjected kinase-inactive mutants of Src (SrcK(-)) and Fy n (FynK(-)) were able to exert a dominant-negative effect on the scatt ering response, Both SH2 and SH3 domains of FynK(-) were required for inhibition of cell scattering. Expression of dominant-negative N17Ras also abrogated EGF-induced dispersion, showing that Ras is another reg ulator of cell dispersion. Expression of SrcK(-) did not alter EGF-evo ked She tyrosine phosphorylation, Shc-Grb2 complex formation and MAPK activation, three elements of the Ras pathway. Furthermore, the expres sion of Jun-Fos and Slug rescued the block induced by N17Ras but not b y SrcK(-), showing that Src kinases and Ras operate in separate pathwa ys. In addition, actinomycin D inhibition of RNA synthesis repressed t he ability of the activated mutant L61Ras but not that of F527Src to i nduce epithelial cell scattering. Since tyrosine phosphorylation of cy toskeleton-associated proteins pp125FAK and cortactin were abolished i n EGF-stimulated SrcK(-) cells, we concluded that, in contrast to Ras, Src kinases may control epithelial cell dispersion in the absence of gene expression and by directly regulating the organization of the cor tical cytoskeleton.