REGULATION OF REACTIVE OXYGEN SPECIES-INDUCED APOPTOSIS AND NECROSIS BY CASPASE 3-LIKE PROTEASES

Reactive oxygen species (ROS) and caspases have been implicated as pot ential mediators of cell death. However, their mechanistic relationshi p remains to be elucidated, Here we investigated the roles of caspases in apoptosis and necrosis induced by ROS, generated by the mixture of xanthine and xanthine oxidase (X/XO), A low concentration of XO (0.02 5 U/ml) induced DNA fragmentation with little cellular membrane damage 3 h after treatment, suggesting the induction of apoptosis, The same treatment induced membrane blebbing, a morphological change typical of apoptosis, 15 min after treatment, A high concentration of XO (0.1 U/ ml) damaged cell membranes with little concomitance of DNA fragmention , suggesting the induction of necrosis, ROS also activated caspase 3-l ike proteases and caspase 3 itself together with the release of cytoch rome c which might be the cause of caspase activation. Apoptosis induc ed by low concentrations of XO and necrosis induced by high concentrat ions of XO was inhibited by z-DEVD-CH2F, an irreversible inhibitor of caspase 3. However, rapid induction of membrane blebbing was not inhib ited by z-DEVD-CH2F. These results suggest that both apoptosis and nec rosis could be induced by ROS through the activation of caspase 3-like protease; however, caspase 3 activation is not needed for ROS-induced membrane blebbing.