CASPASE-DEPENDENT APOPTOSIS OF COS-7 CELLS INDUCED BY BAX OVEREXPRESSION - DIFFERENTIAL-EFFECTS OF BCL-2 AND BCL-X(L) ON BAX-INDUCED CASPASE ACTIVATION AND APOPTOSIS

Bcl-2 family proteins and ICE/CED-3 family proteases (caspases) are re garded as the basic regulators of apoptotic cell death. They are evolu tionarily conserved and implicated in a variety of apoptosis. However, the precise mechanism by which these two families interact to regulat e cell death is not yet known. In this study, we found that the overex pression of the Bcl-2 family member Bar induced apoptotic cell death i n COS-7 cells through the activation of CPP32 (caspase-3)-like proteas es that cleaved the DEVD tetrapeptide. This apoptotic cell death was s uppressed by the viral proteins CrmA and p35, as well as by the chemic ally synthesized caspase inhibitors Z-Asp-CH2-DCB and zVAD-fmk. We als o found that the Bax-induced apoptosis of COS-7 cells was suppressed b y Bcl-x(L) and Bcl-2, though both Bcl-x(L) and Bcl-2 similarly prevent ed etoposide-induced apoptosis in COS-7 cells, In addition, Bcl-x(L) i nhibited the activation of caspase-3-like proteases accompanying Bax-i nduced COS-7 cell death but Bcl-2 did not. These results indicate that the caspase activation is essential for Bax-induced apoptosis, and th at the ability of Bcl-2 and Bcl-x, to prevent the Bax-induced caspase activation and apoptosis in COS-7 cells could be differentially regula ted. Our results also suggest that Bcl-2 family proteins function upst ream of caspase activation and control apoptosis through the regulatio n of caspase activity.