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 NBT-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 Fyn (FynK^-) were able to exert a dominant negative effect on the scattering 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 regulator of cell dispersion. Expression of SrcK^- did not alter EGF-evoked Shc tyrosine phosphorylation, Shc-Grb2 complex formation and MAPK activation, three elements of the Ras pathway. Furthermore, the expression of Jun-Fos and Slug rescued the block induced by N17Ras but not by SrcK^-, showing that Src kinases and Ras operate in separate pathways. In addition, actinomycin D inhibition of RNA synthesis repressed the ability of the activated mutant L61Ras but not that of F527Src to induce epithelial cell scattering. Since tyrosine phosphorylation of cytoskeleton-associated proteins pp125FAK and cortactin were abolished in 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 cortical cytoskeleton. [ABSTRACT FROM AUTHOR]