Coordination of the nuclear and cytoplasmic activities of p53 in response to DNA damage.

The tumor suppressor p53 plays a key role in the cellular response to various stresses. Most previous studies have focused on either the nuclear or cytoplasmic proapoptotic functions of p53, ignoring the combination of both functions. To explore how the two functions of p53 are coordinated in the DNA damage response via computer simulation, we construct a model for the p53 network comprising coupled positive and negative feedback loops involving p53, Mdm2, and Akt, as well as PUMA and Bax. In our model p53 is stabilized and accumulates in the nucleus and cytoplasm upon DNA damage. Nuclear p53 induces expression of Mdm2, PTEN, PUMA, and Bax. Cytoplasmic p53 is then released from the p53.Bcl-xL complex by PUMA to activate Bax directly. We find that the switching between low and high protein levels underlies the decision between cell survival and death. Moreover, a balance between the nuclear and cytoplasmic p53 levels and appropriate levels of Akt and PUMA are required for reliable cell fate decision. Our results indicate that coordination of the transcription-dependent and -independent activities of p53 is important in determining cellular outcomes. These findings advance our understanding of the mechanism for p53-mediated cellular responses and provide clues to p53-based cancer therapy.