THE MOTOGENIC AND MITOGENIC RESPONSES TO HGF ARE AMPLIFIED BY THE SHC ADAPTER PROTEIN

The receptor of Hepatocyte Growth Factor-Scatter Factor (HGF) is a tyrosine kinase which regulates cell motility and growth. After ligand-induced tyrosine phosphorylation, the HGF receptor associates with the Shc adaptor, via the SH2 domain. Site-directed mutagenesis of the HGF receptor indicates that phosphotyrosines y(1349)VHV and (YVNV)-V-1356 can work as docking sites for Shc. The K-d of this interaction, measured in real time using synthetic phosphopeptides and recombinant She on a BIAcore biosensor, is 150 nm for both sites. After stimulation of the HGF receptor, Shc is phosphorylated on (YVNV)-V-317, generating an high affinity binding site for Gr62 (K-d = 15 nM). This duplicates the high affinity binding site for Grb2 present on the HGF receptor ((YVNV)-V-1356). Thus HGF stimulation can trigger the Ras pathway by recruiting Gr62 both directly through the receptor, and indirectly, through Site. Overexpression of wild-type She, but not of the Y-317 --> F mutant, enhances cell migration and growth in response to HGF. These data show that Shc is a relevant substrate of the HGF receptor, and works as an 'amplifier' of the motogenic as well as of the mitogenic response.