REGULATION OF MDM2-DIRECTED DEGRADATION BY THE C-TERMINUS OF P53

The stability of the p53 tumor suppressor protein is regulated by inte raction with Mdm2, the product of a p53-inducible gene. Mdm2-targeted degradation of p53 depends on the interaction between the two proteins and is mediated hv the proteasome. We show here that in addition to t he N-terminal Mdm2 binding domain, the C terminus of p53 participates in the ability of p53 to be degraded by Mdm2. In contrast, alterations in the central DNA binding domain of p53, which change the conformati on of the p53 protein, do not abrogate the sensitivity of the protein to Mdm2-mediated degradation. The importance of the C-terminal oligome rization domain to Mdm2-targeted degradation of p53 is likely to refle ct the importance of oligomerization of the full-length p53 protein fo r interaction with Mdm2, as previously shown in vitro. Interestingly, the extreme C-terminal region of p53, outside the oligomerization doma in, was also shown to be necessary for efficient degradation, and dele tion of this region stabilized the protein without abrogating its abil ity to bind to Mdm2. Mdm2-resistant p53 mutants were not further stabi lized following DNA damage, supporting a role for Mdm2 as the principa l regulator of p53 stability in cells. The extreme C terminus of the p 53 protein has previously been shown to contain several regulatory ele ments, raising the possibility that either allosteric regulation of p5 3 by this domain or interaction between this region and a third protei n plays a role in determining the sensitivity of p53 to Mdm2-directed degradation.