TYROSINE-1356 IN THE CARBOXYL-TERMINAL TAIL OF THE HGF SF RECEPTOR ISESSENTIAL FOR THE TRANSDUCTION OF SIGNALS FOR CELL MOTILITY AND MORPHOGENESIS/

The met proto-oncogene is a receptor tyrosine kinase for hepatocyte gr owth factor/scatter factor (HGF/SF). HGF/SF is a multifunctional cytok ine that stimulates mitogenesis, motility, invasion, and tubulogenesis of a spectrum of epithelial and endothelial cells in culture. Using a chimeric receptor (CSF-MET), containing the extracellular domain of t he colony stimulating factor-1 (CSF-1) receptor fused to the transmemb rane and intracellular domain of the Met receptor, we have previously demonstrated that activation of the Met kinase domain is sufficient to mediate the motility, invasion and morphogenic signals of HGF/SF in M adin-Darby canine kidney epithelial cells (MDCK). In this study we hav e analyzed the role of tyrosine phosphorylation of the Met receptor in the transmission of these signals by site-directed mutagenesis of spe cific tyrosine residues. Mutation of two tyrosine residues (tyrosine 1 234 and tyrosine 1235), involved in activation of the catalytic activi ty of the kinase, abrogates the biological activity of the chimera. In addition, we have identified a single noncatalytic tyrosine residue ( tyrosine 1356) in the carboxyl terminus of the Met receptor, that is e ssential for the biological activity of the chimeric receptor. Mutatio n of tyrosine 1356 to a nonphosphorylatable phenylalanine residue does not affect the exogenous kinase activity of the receptor toward enola se, but it impairs the ability of the mutant protein to associate with the adaptor protein Grb2, and MDCK cells expressing this mutant fail to scatter, invade, and form branching tubules in response to CSF-1. T hese results support a crucial role for tyrosine 1356 in activation of signaling pathways involved in the biological activity of the Met rec eptor in response to HGF/SF.