Ubiquitination and Degradation of Mutant p53

AbstractWhile wild-type p53 is normally a rapidly degraded protein, mutant forms of p53 are stabilized and accumulate to high levels in tumor cells. In this study, we show that mutant and wild-type p53 proteins are ubiquitinated and degraded through overlapping but distinct pathways. While Mdm2 can drive the degradation of both mutant and wild-type p53, our data suggest that the ability of Mdm2 to function as a ubiquitin ligase is less important in the degradation of mutant p53, which is heavily ubiquitinated in an Mdm2-independent manner. Our initial attempts to identify ubiquitin ligases that are responsible for the ubiquitination of mutant p53 have suggested a role for the chaperone-associated ubiquitin ligase CHIP (C terminus of Hsc70-interacting protein), although other unidentified ubiquitin ligases also appear to contribute. The contribution of Mdm2 to the degradation of mutant p53 may reflect the ability of Mdm2 to deliver the ubiquitinated mutant p53 to the proteasome. We are grateful to Arnie Levine, Stjepan Uldrijan, and Mary Hanlon for Mdm2 constructs and to Robert Ludwig for help with experiments. We thank Ron Hay for the HA-tagged ubiquitin constructs, Vishva Dixit for Cop1-specific antibody, Martin Eilers for ARF-BP1-specific antibody, and all the members of the Tumor Suppressor Laboratory for their help and advice during the course of this study.We also thank Cancer Research UK and acknowledge FP6 grant “Active p53” for funding support.