Abstract
We investigated whether the snake venom toxin (SVT) from Vipera lebetina turanica enhances the apoptotic cell death ability of tumor necrosis factor (TNF)-related cell death inducing ligand (TRAIL) in the cancer cells. TRAIL inhibited HCT116 cell growth dose dependently, but not in TRAIL resistant HT-29, A549 and HepG2 cells with even higher dose of TRAIL. SVT enhanced expression of cell death receptor (DR) in TRAIL resistant cancer cells in a dose dependent manner but not by TRAIL. Combination of SVT with TRAIL significantly inhibited cell growth of TRAIL resistant HT-29, A549 and HepG2 cells. Consistent with cell growth inhibition, the expression of TRAIL receptors; DR4 and DR5 was significantly increased as well as apoptotic cell death related proteins such as cleaved caspase-3, -8, -9 and Bax. But the expression of survival proteins such as cFLIP, survivin, XIAP and Bcl2 was decreased by the combination treatment of SVT and TRAIL in HCT116 and HT29 cells. Deletion of DR4 or DR5 by small interfering RNA significantly reversed cell growth inhibitory and apoptotic cell death blocking effects of SVT not only in HCT116 but also in HT-29 cells. Pretreatment of JNK inhibitor SP600125 and ROS scavenger N-acetylcysteine reduced the SVT and TRAIL-induced upregulation of DR4 and DR5 expression and apoptotic cell death related protein expression such as caspase-3 and-9 as well as cell growth inhibitory effects. Our results suggested that SVT facilitates TRAIL-induced apoptotic cell death in cancer cells through up-regulation of the TRAIL receptors; DR4 and DR5 via ROS/ JNK pathway signals.
