A NOVEL RECOGNITION MOTIF FOR PHOSPHATIDYLINOSITOL 3-KINASE BINDING MEDIATES ITS ASSOCIATION WITH THE HEPATOCYTE GROWTH-FACTOR SCATTER FACTOR-RECEPTOR

The pleiotropic effects (mitogenesis, motogenesis, and morphogenesis) elicited by hepatocyte growth factor/scatter factor (HGF/SF) are media ted by the activation of the tyrosine kinase receptor encoded by the M ET proto-oncogene. Following autophosphorylation, the receptor associa tes with the p85/110 phosphatidylinositol (PI) 3-kinase complex in viv o and in vitro. By a combination of two complementary approaches, comp etition with synthetic phosphopeptides and association with Tyr-Phe re ceptor mutants, we have identified Y-1349 and Y-1356 in the HGF/SF rec eptor as the binding sites for PI 3-kinase. Y-1349VHF and Y-1356VNV do not conform to the canonical consensus sequence YXXM for PI 3-kinase binding and thus define YVXV as a novel recognition motif. Y-1349 and Y-1356 are located within the C-terminal portion of the HGF/SF recepto r and are phosphorylation sites. The affinity of the N- and C-terminal src homology region 2 (SH2) domains of p85 for the phosphopeptides in cluding Y-1349 and Y-1356 is 2 orders of magnitude lower than that mea sured for Y-751 in the platelet-derived growth factor receptor binding site. However, the closely spaced duplication of the novel recognitio n motif in the native HGF/SF receptor may allow binding with both SH2 domains of p85, thus generating an efficient docking site for PI 3-kin ase. In agreement with this model, we have observed that a phosphopept ide including both Y-1349 and Y-1356 activates PI 3-kinase in vitro.