Caspase 3 is activated through caspase 8 instead of caspase 9 during H 2 O 2 -induced apoptosis in hela cells

Abstract

Oxidative stress is known to be involved in a variety of pathological processes including atherosclerosis, diabetes, and neurodegenerative diseases. Understanding how intracellular signaling pathways respond to oxidative stress will have a significant implication in the therapy of these diseases. In this study, we applied hydrogen peroxide (H 2 O 2 ) to trigger apoptosis and investigated the dynamic activation of various caspases using a FRET technique. We measured the activation dynamics of caspase 3 and caspase 9 based on two reporter systems, SCAT 3 and SCAT 9. We found that caspase 3 activation was earlier than that of caspase 9 following H 2 O 2 treatment. Caspase 3 was activated rapidly, reaching a maximum in 12±3 min, while the average duration of caspase 9 activation was 21±3 min. When cells were pretreated with Z-LEHD-fmk, a caspase 9 specific inhibitor, caspase 3 activation and apoptosis by H 2 O 2 treatment were little affected, although the caspase 9 activation was completely inhibited. When cells were pretreated with Z-DEVD-fmk, a caspase 3 specific inhibitor, the activation of both caspase 3 and caspase 9, as well as apoptosis, were inhibited. When cells were pretreated with Z-IETD-fmk, a caspase 8 specific inhibitor, the activation of caspase 3 and caspase 9 were significantly delayed. Finally, we found that Bax did not translocate from the cytosol to the mitochondrial membrane during H 2 O 2 -induced apoptosis. Our results suggest that, during H H 2 O 2 -induced apoptosis, caspase 3 is activated directly through caspase 8 and is not through the mitochondria-dependent caspase 9 activation. © 2011 S. Karger AG, Basel.