Mitochondrial superoxide mediates mitochondrial and endoplasmic reticulum dysfunctions in TRAIL-induced apoptosis in Jurkat cells

Reactive oxygen species (ROS), such as superoxide (O-2(center dot-)) and hydrogen peroxide (H2O2), have been reported to be important mediators of the apoptosis induced by death ligands, including Fas, tumor necrosis factor-alpha, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Conversely, there is evidence that H2O2 and prooxidative conditions are protective. Therefore, the roles of ROS in death ligand-induced apoptosis are a matter of debate. In this study, we attempted to define the oxidant species mediating TRAIL-induced apoptosis in human tumor cells. The generation of intracellular O-2(center dot-), but not H2O2, was correlated with apoptosis in the cells. TRAIL treatment resulted in increased mitochondrial O-2(center dot-)-generation and the oxidation of cardiolipin. The O-2(center dot-)-selective scavenger MnTBaP [Mn(III) tetrakis (4-benzoic acid) porphyrin chloride] specifically blocked TRAIL-induced apoptosis and proapoptotic events including mitochondrial membrane collapse and caspase-3/7 activation. TRAIL also induced endoplasmic reticulum (ER) stress responses including caspase-12 activation, while inhibition of caspase-12 prevented the apoptosis. In addition, increased mitochondrial O-2(center dot-) generation by uncoupling of oxidative phosphorylation or inhibition of the electron transport chain amplified the TRAIL-induced apoptosis and proapoptotic events. This amplification was also significantly abolished by MnTBaP treatment. Our data indicate that mitochondrial O-2(center dot-) mediates mitochondrial and ER dysfunctions during TRAIL-induced apoptosis in Jurkat cells. The present findings suggest that pharmacological agents increasing mitochondrial O-2(center dot-) may serve as clinical drugs that amplify TRAIL effectiveness toward cancer cells. (C) 2013 Elsevier Inc. All rights reserved.