Src tyrosine kinase but not activated Ras augments sensitivity to taxanes through apoptosis in human adenocarcinoma cells.

We investigated the mechanistic role of Src and Ras, important oncoproteins implicated in the pathogenesis of many human cancers, in taxane-induced apoptosis using v-src or c-H-ras transfected HAG-1 human gallbladder epithelial cells. Compared with the parental HAG-1 cell line, v-src-transfected HAG/src3-1 cells became 6.0-fold and 7.5-fold sensitive to taxotere, and 1.8-fold and 3.9-fold sensitive to taxol, for 2-hour and 24-hour exposures, respectively. By contrast, HAG-1 cells transfected with activated Ras, which acts downstream of Src, acquired approximately 2.7- and 5.0-fold taxotere resistance, and 2.3- and 2.8-fold taxol resistance, for both exposures, respectively. To examine the mechanism(s) whereby Src augments sensitivity to taxanes, we investigated the functional role of Src in taxotere-induced apoptosis. Treatment of HAG/src3-1 cells with taxotere resulted in subsequent induction of apoptotic cell death, whereas apoptosis did not occur in parental or c-H-ras-transfected HAG/ras5-1 cells. Moreover, a protein kinase C (PKC) and a phosphatidylinositol-3 kinase (PI-3 kinase) inhibitors (H-7 and wortmannin, respectively) did not alter either taxotere sensitivity or taxotere-induced apoptosis in these cells. Similarly, non-cytotoxic concentrations of geldanamycin, which destabilizes c-Raf-1 kinase, did not prevent apoptosis in HAG/src3-1 cells. These data indicate that the ability of activated Src to sensitize HAG/src3-1 cells to taxotere might be mediated by apoptotic events occurring through Src to downstream signal transduction pathways, excluding activated Ras, Raf-1 kinase, PI-3 kinase and PKC.