LAUSR

Contrary to previous reports, wild-type p53 can interact with p73 to promote cell stress–induced apoptosis. Another look at p53-p73 interactions The transcription factor p53 critically regulates cell survival or death in response to cellular stress. Mutations in p53 are common in cancer and alter its interactions with other proteins and, consequently, with cell fate–specific genes. Mutant p53 binds to and inhibits its family member p73, thereby promoting cell survival instead of cell death in response to cell stress. It was believed that this interaction with p73 was specific to mutant p53. However, Wolf et al. found that wild-type p53 can bind p73 to promote stress-induced cell death. Phosphorylation of wild-type p53 by the cell stress–responsive kinase JNK caused a conformational change that mirrored the regional structure of the mutant and enabled its binding to p73 but, unlike mutant p53, the wild-type protein could still bind to apoptotic gene targets. These findings refine our understanding of p53 interactions and, specifically, p53-p73 coordination in the cell stress response. The transcription factors p53 and p73 are critical to the induction of apoptotic cell death, particularly in response to cell stress that activates c-Jun N-terminal kinase (JNK). Mutations in the DNA-binding domain of p53, which are commonly seen in cancers, result in conformational changes that enable p53 to interact with and inhibit p73, thereby suppressing apoptosis. In contrast, wild-type p53 reportedly does not interact with p73. We found that JNK-mediated phosphorylation of Thr81 in the proline-rich domain (PRD) of p53 enabled wild-type p53, as well as mutant p53, to form a complex with p73. Structural algorithms predicted that phosphorylation of Thr81 exposes the DNA-binding domain in p53 to enable its binding to p73. The dimerization of wild-type p53 with p73 facilitated the expression of apoptotic target genes [such as those encoding p53–up-regulated modulator of apoptosis (PUMA) and Bcl-2-associated X protein (BAX)] and, subsequently, the induction of apoptosis in response to JNK activation by cell stress in various cells. Thus, JNK phosphorylation of mutant and wild-type p53 promotes the formation of a p53/p73 complex that determines cell fate: apoptosis in the context of wild-type p53 or cell survival in the context of the mutant. These findings refine our current understanding of both the mechanistic links between p53 and p73 and the functional role for Thr81 phosphorylation.