Hepatocyte Growth Factor/scatter factor-induces phosphorylation of cortactin in A431 cells in a Src kinase-independent manner.

The Hepatocyte Growth Factor receptor transduces proliferating and scattering signals in epithelial and endothelial cells. We have explored potential interactions of the HGF/SF receptor beta-subunit (p145(beta MET)) with F-actin binding partners aiming to identify novel downstream effectors implicated in HGF/SF pluripotent signalling. Cortactin, a p80/85 F-actin binding protein, was found phosphorylated on tyrosine in response to HGF-SF in A431 human epidermoid carcinoma cells, expressing the HGF/SF receptor (c-MET). The HGF/SF receptor was enriched in the detergent-insoluble fraction and was found to co-precipitate with cortactin and to associate in vitro with cortactin. The Grb2 small adapter protein known to associate via its Src homology 2 domain (SH2) with the MET C-terminus, was also associated with cortactin. Transient transfection of A431 cells with dominant-negative Grb2 constructs has revealed that the Grb2-C-SH3 domain possesses a central role in cortactin phosphorylation in response to HGF/SF. Finally, tyrosine phosphorylation of cortactin was found uncoupled of endogenous c-Src kinase activity, thus further supporting the hypothesis that cortactin is a direct target of the MET kinase. We propose that cortactin may constitute a docking site for MET-derived signals within the cytoskeleton.