Abstract

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted great attention as a promising anti-cancer reagent. Recombinant soluble TRAIL (rsTRAIL) derivatives induce apoptosis in various cancer cells, but not in most normal cells. However, a number of cancerous cell types are resistant to TRAIL cytotoxicity, limiting its application in cancer therapy. In the present study, we report that actinomycin D (Act D) pretreatment increases apoptosis in human neuroblastoma SH-SY5Y cells treated with rsTRAIL. Both caspase-9 and caspase-7, but not caspase-3, were activated during the apoptosis process. z-VAD-fmk, a pan-caspase inhibitor, only partially suppressed apoptosis of the cells, suggesting that the Act D-enhanced apoptosis of SH-SY5Y occurred via caspase-dependent and -independent manners. In cells pretreated with Act D, we found decreased mitochondrial transmembrane potential, high levels of reactive oxygen species (ROS), and up-regulated apoptotic-inducing factor (AIF). Cell death was blocked in cells stably transfected with AIF-siRNA plasmid. Taken together, these data indicate that Act D sensitizes SH-SY5Y cells to rsTRAIL-induced apoptosis via caspase activation, impairment of the mitochondrial membrane, release of ROS, and up-regulation of AIF expression. This study provides a novel strategy for the therapy of malignant neuroblastoma resistant to rsTRAIL cytotoxicity.