The multisubstrate adapter Gab1 regulates hepatocyte growth factor (scatter factor)-c-Met signaling for cell survival and DNA repair

Hepatocyte growth factor (scatter factor) (HGF/SF) is a pleiotrophic mediat or of epithelial cell motility, morphogenesis, angiogenesis, and tumorigene sis. HGF/SF protects cells against DNA damage by a pathway from its recepto r c-Met to phosphatidylinositol 3-kinase (PI3K) to c-Akt, resulting in enha nced DNA repair and decreased apoptosis, We now show that protection agains t the DNA-damaging agent adriamycin (ADR; topoisomerase II alpha inhibitor) requires the Grb2-binding site of c-Met, and overexpression of the Grb2-as sociated binder Gab1 (a multisubstrate adapter required for epithelial morp hogenesis) inhibits the ability of EIGF/SF to protect MDCK epithelial cells against ADR, In contrast to Gab1 and its homolog Gab2, overexpression of c -Cbl, another multisubstrate adapter that associates with c-Met, did not af fect protection. Gab1 blocked the ability of HGF/SF to cause the sustained activation of c-Akt and c-Akt signaling (FKHR phosphorylation), The Gab1 in hibition of sustained c-Akt activation and of cell protection did not requi re the Gab1 pleckstrin homology or SHP2 phosphatase-binding domain hut did require the PI3K-binding domain. HGF/SF protection of parental MDCK cells w as blocked by wortmannin, expression of PTEN, and dominant negative mutants of p85 (regulatory subunit of PI3K), Akt, and Pak1; the protection of cell s overexpressing Gab1 was restored by wild-type or activated mutants of p85 , Akt, and Pak1. These findings suggest that the adapter Gab1 may redirect c-Met signaling through PI3g away from a c-Akt/Pak1 cell survival pathway.