p53 initiates apoptosis by transcriptionally targeting the antiapoptotic protein ARC.

p53 plays an important role in regulating apoptosis. However, the molecular mechanism by which it initiates the apoptotic program still remains to be fully understood. Here, we report that p53 can transcriptionally target the antiapoptotic protein, apoptosis repressor with caspase recruitment domain (ARC). Our results show that reactive oxygen species and anoxia lead to the up-regulation of p53 expression. Concomitantly, ARC is down-regulated at both the protein and mRNA levels. Knockdown of p53 expression can attenuate the decreases in ARC protein and mRNA levels, indicating that ARC down-regulation is a consequence of p53 activation. Strikingly, p53-induced ARC repression occurs in a transcription-dependent manner. We further demonstrate that the p53 up-regulated modulator of apoptosis (PUMA) and Bad are up-regulated in response to the stimulation with reactive oxygen species or anoxia, and p53 is responsible for their up-regulation. ARC can interact with PUMA or Bad via its N terminus. Such an interaction displaces the association of PUMA or Bad with Bcl-2. ARC repression by p53 leads to its failure to counteract the proapoptotic activity of PUMA and Bad. Thus, our data reveal a novel p53 apoptotic pathway in which it initiates apoptosis by transcriptionally repressing ARC.