ABSTRACT
PURPOSE: Reactive oxygen species have been recognized as a common signaling mediator in diverse stimuli-induced apoptosis and hydrogen peroxide is a natural one of those reactive oxygen species. This study was performed to investigate the role of caspases in hydrogen peroxide-induced apoptosis of HL 60 cells. METHODS: Apoptosis was induced in HL 60 cells by treating 50microM hydrogen peroxide for 2, 4, and 6 hrs and induction of apoptosis was confirmed by flow cytometry and DNA fragmentation analysis. Caspase substrate assay was used to show the activity of caspases and then protein levels of caspase and its substrate were analyzed using immunoblotting. RESULTS: During the apoptosis, caspase substrates assay showed the increased activity of caspase-3, -7, -10, but not that of caspase-8 nor caspase-9, and immunoblotting analysis showed decreasing procaspase-3 protein with the progression of apoptosis. Furthermore, with progression of apoptosis, analysis of caspase substrates showed retinoblastoma protein decreased while cleaved 89kD fragment of poly (ADP-ribosyl) polymerase protein increased. CONCLUSION: These results suggest that hydrogen peroxide-induced apoptosis in HL 60 cells is not associated with the activation of caspase-8 nor caspase-9. Rather, caspase-3 is directly activated and responsible for hydrogen peroxide-induced apoptosis of HL 60 cells.