Caspase-independent cell death by arsenic trioxide in human cervical cancer cells: Reactive oxygen species-mediated poly(ADP-ribose) polymerase-1 activation signals apoptosis-inducing factor release from mitochondria

Although mechanisms of arsenic trioxide (As₂O ₃)-induced cell death have been studied extensively in hematologic cancers, those in solid cancers have yet to be clearly defined. In this study, we showed that the translocation of apoptosis-inducing factor (AIF) from mitochondria to the nucleus is required for As₂O₃-induced cell death in human cervical cancer cells. We also showed that reactive oxygen species (ROS)-mediated poly-(ADP-ribose) polymerase-1 (PARP-1) activation is necessary for AIF release from mitochondria. The treatment of human cervical cancer cells with As₂O₃ induces dissipation of mitochondrial membrane potential (Δψ_m), translocation of AIF from mitochondria to the nucleus, and subsequent cell death. Small interfering RNA targeting of AIF effectively protects cervical cancer cells against As₂O₃-induced cell death. As₂O ₃ also induces an increase of intracellular ROS level and a marked activation of PARP-1. N-acetyl-L-cystein, a thiol-containing antioxidant, completely blocks As₂O₃-induced PARP-1 activation, Δψ_m loss, nuclear translocation of AIF from mitochondria, and the consequent cell death. Furthermore, pretreatment of 1,5- dihydroxyisoquinoline or 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-l(2H)- isoquinolinone, PARP-1 inhibitors, effectively attenuates the loss of Δψ_m, AIF release, and cell death. These data support a notion that ROS-mediated PARP-1 activation signals AIF release from mitochondria, resulting in activation of a caspase-independent pathway of cell death in solid tumor cells by As₂O₃ treatment.