Murine double minute (MDM2) blocks p53-coactivator interaction, a new mechanism for inhibition of p53-dependent gene expression

The ability of the p53 tumor suppressor to induce cell cycle arrest and cel l death is closely regulated under normal conditions. The transcriptional a ctivity of p53 is negatively controlled by murine double minute (MDM2). p53 requires the coactivator CREB-binding protein (CBP), or its structural hom olog, p300, to stimulate transcription of responsive genes. Here we find th at the transactivation domain of p53 selectively interacts with the N- and C-terminal regions of CBP/p300. A mutant CBP lacking the N terminus failed to stimulate p53-dependent transactivation. In both p53 null Saos2 cells, a nd in UV-irradiated MCF7 cells, we observed that MDM2 associates with the N -terminal region of CBP/p300. Because p53 interacts with both MDM2 and CBP/ p300 through its trans-activation domain, we examined the role of MDM2 in p 53-coactivator interactions. MDM2 blocked CBP/p300 recruitment in vitro and inhibited the interaction of the transactivating region of p53 with both t he N- or C-terminal regions of CBP/p300 in a mammalian two-hybrid assay. Th ese observations suggest that MDM2 may be inhibiting p53 trans-activation b y shielding its activation domain from the coactivators, a new mechanism fo r the inhibition of p53-dependent gene expression.