Multiple sites of in vivo phosphorylation in the MDM2 oncoprotein cluster within two important functional domains

The MDM2 oncoprotein is a negative regulatory partner of the p53 tumour sup pressor. MDM2 mediates ubiquitination of p53 and targets the protein to the cytoplasm for 26S proteosome-dependent degradation. In this paper, we show that MDM2 is modified in cultured cells by multisite phosphorylation. Dele tion analysis of MDM2 indicated that the sites of modification fall into tw o clusters which map respectively within the N-terminal region encompassing the p53 binding domain and nuclear export sequence, and the central acidic domain that mediates p14(ARF) binding, p53 ubiquitination and cytoplasmic shuttling. The data are consistent with potential regulation of MDM2 functi on by multisite phosphorylation. (C) 2000 Federation of European Biochemica l Societies. Published by Elsevier Science B.V. All rights reserved.