ASSOCIATION OF THE MULTISUBSTRATE DOCKING PROTEIN GAB1 WITH THE HEPATOCYTE GROWTH-FACTOR RECEPTOR REQUIRES A FUNCTIONAL GRB2 BINDING-SITE INVOLVING TYROSINE-1356

Hepatocyte growth factor/scatter factor is a multifunctional factor th at induces mitogenesis, motility, invasion, and branching tubulogenesi s of several epithelial and endothelial cell lines in culture, The rec eptor for hepatocyte growth factor has been identified as the Mettyros ine kinase, Upon stimulation with hepatocyte growth factor, the Met be ta subunit becomes highly phosphorylated on tyrosine residues, one of which, tyrosine 1356 within the carboxyl terminus, is crucial for diss ociation, motility, and branching tubule formation in Madin-Darby cani ne kidney epithelial cells, Tyrosine 1356 forms a multisubstrate bindi ng site for the Grb2 and She adaptor proteins, the p85 subunit of phos phatidylinositol 3'-kinase, phospholipase C gamma, and a phosphatase, SHP2, To investigate additional signaling molecules that are activated by the Met receptor, we have identified hepatocyte growth factor-indu ced phosphoproteins in tubular epithelial cells, We have established t hat proteins of 100-130 kDa are highly phosphorylated following stimul ation of epithelial cells and that one of these is the Grb2-associated binding protein Gab1, a possible insulin receptor substrate-1-like si gnal transducer, We show that Gab1 is the major substrate for the Met kinase in vitro and in vivo, Association of Gab1 with Met requires a f unctional Grb2 binding site involving tyrosine 1356 and to a lesser ex tent tyrosine 1349, Met receptor mutants that fail to induce branching tubulogenesis are impaired in their ability to interact with Gab1, su ggesting that Gab1 may play a role in these processes.