Src homology 2-containing inositol 5-phosphatase 1 binds to the multifunctional docking site of c-Met and potentiates hepatocyte growth factor-induced branching tubulogenesis

Hepatocyte growth factor (HGF)/scatter factor is a multifunctional cytokine that induces mitogenesis, motility, and morphogenesis in epithelial, endot helial, and neuronal cells. The receptor for HGF/scatter factor was identif ied as c-Met tyrosine kinase, and activation of the receptor induces multip le signaling cascades,To gain further insight into c-Met-mediated multiple events at a molecular level, we isolated several signaling molecules includ ing a novel binding partner of c-Met, SH2 domain-containing inositol 5-phos phatase 1 (SHIP-1), Western blot analysis revealed that SHIP-1 is expressed in the epithelial cell line, Madin-Darby canine kidney (MDCK) cells. SHIP- 1 binds at phosphotyrosine 1356 at the multifunctional docking site. Becaus e a number of signaling molecules such as Grb2, phosphatidylinositol 3-kina se, and Gab1 bind to the multifunctional docking site, we further performed an in vitro competition study using glutathione S-transferase- or His-tagg ed signaling molecules with c-Met tyrosine kinase, Our binding study reveal ed that SHIP-1, (Grb2, and Gab1 bound preferentially over phosphatidylinosi tol 3-kinase. Surprisingly, MDCK cells that overexpress SHIP-1 demonstrated branching tubulogenesis within 2 days after HGF treatment, whereas wild-ty pe MDCK cells showed tubulogenesis only after 6 days following treatment wi thout altering cell scattering or cell growth potency. Furthermore, overexp ression of a mutant SHIP-1 lacking catalytic activity impaired HGF-mediated branching tubulogenesis.