Hydrogen peroxide induces cell death in human TRAIL-resistant melanoma through intracellular superoxide generation
International Journal of Oncology
Intracellular reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) are thought to mediate apoptosis induced by death receptor ligands, including tumor necrosis factorrelated apoptosis-inducing ligand (TRAIL). However, the role of H 2 O 2 is controversial, since some evidence suggests that H 2 O 2 acts as an anti-apoptotic factor. Here, we show that exogenously applied H 2 O 2 (30-100 µM) induces cell death in TRAIL-resistant human melanoma cells via intracellular superoxide (O 2
... r superoxide (O 2 -) generation. H 2 O 2 induced apoptotic or necrotic cell death, depending on the concentration of the oxidant applied; low concentrations of H 2 O 2 preferentially activated the caspase-dependent apoptotic pathway, while high concentrations of H 2 O 2 induced apoptotic and necrotic cell death in a caspase-independent manner. The H 2 O 2 -induced cell death was associated with increased mitochondrial membrane potential collapse and caspase-3/7 activation and ER stress responses including caspase-12 and X-box-binding protein-1 (XBP-1) activation. H 2 O 2 induced intracellular O 2 generation even within the mitochondria, while TRAIL did not. The superoxide dismutase mimetic antioxidant MnTBaP [Mn (III) tetrakis (4-benzonic acid) porphyrin chloride] inhibited the H 2 O 2 -induced O 2 generation, apoptosis and XBP-1 and caspase-12 activation at comparable concentrations. Importantly, H 2 O 2 treatment caused minimal O 2 generation and apoptosis in normal primary melanocytes. These data show that H 2 O 2 induces endoplasmic reticulum-associated cell death via intracellular O 2 generation and that malignant melanoma cells are more susceptible than normal cells to this oxidative cell death. The findings suggest that H 2 O 2 has therapeutic potential in the treatment of TRAIL-resistant melanoma.