c-Src kinase activity is required for hepatocyte growth factor-induced motility and anchorage-independent growth of mammary carcinoma cells

Overexpression and amplification of hepatocyte growth factor (HGF) receptor (Met) have been detected in many types of human cancers, suggesting a crit ical role for Met in growth and development of malignant cells. However, th e molecular mechanism by which Met contributes to tumorigenesis is not well known. The tyrosine kinase c-Src has been implicated as a modulator of cel l proliferation, spreading, and migration; these functions are also regulat ed by Met. To explore whether c-Src kinase is involved in HGF-induced cell growth, a mouse mammary carcinoma cell line (SP1) that co-expresses HGF and Met and a nonmalignant epithelial cell line (Mv1Lu) that expresses Met but not HGF were used. In this study, we have shown that c-Src kinase activity is constitutively elevated in SP1 cells and is induced in response to HGF in Mv1Lu cells. In addition, c-Src kinase associates with Met following sti mulation with HGF, The enhanced activity of c-Src kinase also correlates wi th its ability to associate with Met. Expression of a dominant negative dou ble mutant of c-Src (SRC-RF), lacking both kinase activity (K295R) and a re gulatory tyrosine residue (Y527F), in SP1 cells significantly reduced c-Src kinase activity and strongly blocked HGF-induced motility and colony growt h in soft agar. In contrast, expression of the dominant negative c-Src muta nt had no effect on HGF-induced cell proliferation on plastic. Taken togeth er, our data strongly suggest that HGF-induced association of c-Src with Me t and c-Src activation play a critical role in HGF-induced cell motility an d anchorage-independent growth of mammary carcinomas and further support th e notion that the presence of paracrine and autocrine HGF loops contributes significantly to the transformed phenotype of carcinoma cells.