c-Met overexpression contributes to the acquired apoptosis resistance of non-adherent ovarian cancer cells through a cross-talk mediated by phosphatidylinositol 3-kinase and extracellular signal-regulated kinase 1/2

Abstract

Ovarian cancer is the most lethal gynecological cancer mainly due to widespread peritoneal dissemination and malignant ascites. Key to this is the capacity of tumor cells to escape suspension-induced apoptosis (anoikis), which also underlies their resistance to chemotherapy. Here we utilized a non-adherent cell culture model to investigate molecular mechanisms of apoptotic resistance of ovarian cancer cells that may mimic the chemoresistance found in solid tumors. We found that ovarian cancer cells acquired a remarkable resistance to anoikis and apoptosis induced by exposure to clinically relevant doses of two front-line chemotherapeutic drugs cisplatin and paclitaxel when grown in three-dimensional (3D) than monolayer cultures. Inhibition of the hepatocyte growth factor (HGF) receptor c-Met, which is frequently overexpressed in ovarian cancer, by a specific inhibitor or small interfering RNA blocked the acquired anoikis resistance and restored chemosensitivity in 3D, not in 2D cultures. These effects were found to be dependent on both phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular-signal regulated kinase (ERK) 1/2 signaling pathways. Inhibitors of PI3K/Akt abrogated ERK1/2 activation and its associated anoikis resistance in response to HGF, suggesting a signaling relay between these two pathways. Furthermore, we identified, as a mechanism of this cross-talk, a central role of Ras. Interestingly, Ras did not lie upstream of PI3K/Akt, whereas PI3K/Akt signaling to ERK1/2 involved Ras. These findings shed new light on the apoptotic resistance mechanism of non-adherent ovarian cancer ascites cells.