Hydrogen peroxide-induced apoptosis in HL-60 cells requires caspase-3 activation.

Apoptosis has been associated with oxidative stress in biological systems. Caspases have been considered to play a pivotal role in the execution phase of apoptosis. However, which caspases function as executioners in reactive oxygen species (ROS)-induced apoptosis is not known. The present study was performed to identify the major caspases acting in ROS-induced apoptosis. Treatment of HL-60 cells with 50 microM hydrogen peroxide (H2O2) for 4 h induced the morphological changes such as condensed and/or fragmented nuclei, increase in caspase-3 subfamily protease activities, reduction of the procaspase-3 and a DNA fragmentation. To determine the role of caspases in H2O2-induced apoptosis, caspase inhibitors, acetyl-Tyr-Val-Ala-Asp-chloromethyl ketone (Ac-YVAD-cmk), acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) and acetyl-Val-Glu-Ile-Asp-aldehyde (Ac-VEID-CHO), selective for caspase-1 subfamily, caspase-3 subfamily and caspase-6, respectively, were loaded into the cells using an osmotic lysis of pinosomes method. Of these caspase inhibitors, only Ac-DEVD-CHO completely blocked morphological changes, caspase-3 subfamily protease activation and DNA ladder formation in H2O2-treated HL-60 cells. This inhibitory effect was dose-dependent. These results suggest that caspase-3, but not caspase-1 is required for commitment to ROS-triggered apoptosis.