Cooperative effect of hepatocyte growth factor and fibronectin in anchorage-independent survival of mammary carcinoma cells: Requirement for phosphatidylinositol 3-kinase activity

Anchorage-independent survival and growth are critical characteristics of m alignant cells. We showed previously that the addition of exogenous hepatoc yte growth factor (HGF) and the presence of fibronectin fibrils stimulate a nchorage-independent colony growth of a murine mammary carcinoma, SP1, whic h expresses both HGF and HGF receptor (Met; R, Saulnier et al, Exp, Cell Re s., 222: 360-369, 1996), We now show that tyrosine phosphorylation of Met i n carcinoma cells is augmented by cell adhesion and spreading on fibronecti n substratum. In contrast, detached serum-starved cells exhibit reduced tyr osine phosphorylation of Met and undergo apoptotic cell death within 18-24 h, Under these conditions, the addition of HGF stimulates tyrosine phosphor ylation of Met and restores survival of carcinoma cells. Soluble fibronecti n also stimulates cell survival and shows a cooperative survival response w ith HGF but does not affect tyrosine phosphorylation of Met; these results indicate that fibronectin acts via a pathway independent of Met in detached cells, We demonstrated previously that inhibition of phosphatidylinositol (PI) 3-kinase activity blocks HGF-induced DMA synthesis of carcinoma cells (N. Rahimi et al,, J. Biol. Chem., 271: 24850-24855, 1996). We now show in detached cells a cooperative effect of HGF and FN in the activation of PI 3 -kinase and on the phosphorylation of PKB/Akt at serine 473, PI 3-kinase ac tivity is also required for the HGF- and fibronectin-induced survival respo nses, as well as anchorage-independent colony growth. However, c-Src kinase or MEK1/2 activities are not required for the cell survival effect. Togeth er, these results demonstrate that the PI 3-kinase/Akt pathway is a key eff ector of the HGF- and fibronectin-induced survival response of breast carci noma cells under detached conditions and corroborate an interaction between integrin and HGF/Met signalling pathways in the development of invasive br east cancer.