Characterization of sequence elements involved in p53 stability regulationreveals cell type dependence for p53 degradation

The growth suppressive properties of the tumor suppressor protein p53 are a ctivated upon DNA damage. The activation of p53 is reflected in increased p 53 levels which are, at least in part, the result of an extended half-life of the protein. Although this suggests that stabilization of p53 is an intr insic feature of p53 activation, the mechanisms involved in p53 degradation and stabilization are poorly understood. Here we report on the identificat ion of an internal deletion mutant of wild-type p53, termed Delta 62-96, wh ich can be stably expressed in various cell lines. This deletion mutant has a turnover rate similar to wild-type p53 and its stability is upregulated by treatment with UV light. In cell lines that express endogenous mutant or no p53, however, Delta 62-96 appears to be stable, strongly indicating tha t these cell lines have lost the ability to degrade p53. Further characteri zation of Delta 62-96 by mutational analyses defines sequence and structura l requirements for p53 degradation and indicates that none of the known p53 phosphorylation sites is essential with respect to p53 stability regulatio n upon UV-irradiation.