P53-DEPENDENT DNA DAMAGE-INDUCED APOPTOSIS REQUIRES FAS APO-1-INDEPENDENT ACTIVATION OF CPP32-BETA/

In many cell types, the p53 tumor suppressor protein is required for t he induction of apoptosis by DNA-damaging chemotherapy or radiation. T herefore, identification of the molecular determinants of p53-dependen t cell death may aid in the design of effective therapies of p53-defic ient cancers. We investigated whether p53-dependent apoptosis requires activation of CPP32 beta (caspase 3), a cysteine protease that has be en found to mediate apoptosis in response to ligation of the Fas molec ule or to granzyme B, a component of CTL lytic granules. Irradiation-i nduced apoptosis was associated with p53-dependent activation of CPP32 beta-related proteolysis, and normal thymocytes were protected from i rradiation by Acetyl-Asp-Glu-Val-Asp-CHO (Ac-DEVD-CHO), a specific inh ibitor of CPP32 beta. We next examined whether the Fas system is requi red for p53-dependent apoptosis and whether stimuli that induce activa tion of CPP32 beta induce apoptosis in p53-deficient cells. Thymocytes or activated T cells from Fas-deficient mice were resistant to apopto sis induced by ligation of Fas or CD3, respectively, but remained norm ally susceptible to irradiation. Thymocytes from p53-deficient mice, a lthough resistant to DNA damage, remained sensitive to CPP32 beta-medi ated apoptosis induced by ligation of Fas or CD3, or by exposure to cy totoxic T cells. These results demonstrate that DNA damage-induced apo ptosis of T cells requires p53-mediated activation of CPP32 beta by a mechanism independent of Fas/FasL interactions and suggest that immuno logical or molecular methods of activating CPP32 beta may be effective at inducing apoptosis in p53-deficient cancers that are resistant to conventional chemotherapy or irradiation.