Critical Role for a Central Part of Mdm2 in the Ubiquitylation of p53

Abstract

The stability of the p53 protein is regulated by Mdm2. By acting as an E3 ubiquitin ligase, Mdm2 directs the ubiquitylation of p53 and its subsequent degradation by the 26S proteasome. In contrast, the Mdmx protein, although structurally similar to Mdm2, cannot ubiquitylate or degrade p53 in vivo. To ascertain which domains determine this functional difference between Mdm2 and Mdmx and consequently are essential for p53 ubiquitylation and degradation, we generated Mdm2-Mdmx chimeric constructs. Here we show that, in addition to a fully functional Mdm2 RING finger, an internal domain of Mdm2 (residues 202 to 302) is essential for p53 ubiquitylation. Strikingly, the function of this domain can be fulfilled in trans, indicating that the RING domain and this internal region perform distinct activities in the ubiquitylation of p53.

ACKNOWLEDGMENTS

We thank A. Levine, D. Lane, and M. Oren for anti-Mdm2 antibodies and Mdm2 expression plasmids, and we thank G. Lozano for p53- and mdm2-null cells. We thank S. Grivell for practical assistance in some of the experiments.

This work was supported by grants from the Dutch Cancer Society (grant RUL 2001-2523 to E.M. and R.F.; grant RUL 96-1329 to R.S.) and from the AICR (grant 01-276 to P.D.G.).