Identification of p53 sequence elements that are required for MDM2-mediated nuclear export

It has been demonstrated that MDM2 can differentially regulate subcellular distribution of p53 and its close structural homologue p73. In contrast to MDM2-mediated p53 nuclear export, p73 accumulates in the nucleus as aggrega tes that colocalize with MDM2. Distinct distribution patterns of p53 and p7 3 suggest the existence of unique structural elements in the two homologues that determine their MDM2-mediated relocalization in the cell. Using a ser ies of p53/p73 chimeric proteins, we demonstrate that three regions of p53 are:involved in the regulation of MDM2-mediated nuclear export. The DNA bin ding domain (DBD) is involved in the maintenance of a proper conformation t hat is required for functional activity of the nuclear export sequence (NES ) of p53. The extreme C terminus of p53 harbors several lysine residues who se ubiquitination by MDM2 appears to be the initial event in p53 nuclear ex port, as evidenced by the impaired nucleocytoplasmic shuttling of p53 mutan ts bearing simultaneous substitutions of lysines 370, 372, 373, 381, 382, a nd 386 to arginines (6KR) or alanines (6KA). Finally, the region between th e DBD and the oligomerization domain of p53, specifically lysine 305, also plays a critical role in fully revealing p53NES. We conclude that MDM2-medi ated nuclear export of p53 depends on a series of ubiquitination-induced co nformational changes in the p53 molecule that lead to the activation of p53 NES. In addition, we demonstrate that the p53NES may be activated without n ecessarily disrupting the p53 tetramer.