Abstract
p53 protein is a stress-responsive molecule that is accumulated and activated by X-irradiation and induces a cell cycle arrest or apoptosis. It has been thought that p53 is accumulated by the inhibition of the interaction between p53 and its specific ubiquitin ligase MDM2 caused by the phosphorylation of p53 at Ser15, Thr18, or Ser20. However, the physiological significance of the phosphorylation of each site remains elusive. Therefore, in the present study, we aimed at elucidateing a role of the phosphorylation on X-ray-induced p53 accumulation. First, we constructed ecdyson-inducible vectors containing the mutant p53 gene in which Ser15, Thr18, and Ser20 were substituted by alanine. Then, these vectors were stably transfected into HT1080. The expression of Ala mutant p53 was induced by ponasterone A (PA). In response to 4 Gy of X-rays, every PA-induced mutant p53 protein was accumulated, although the basal levels and the degree of accumulation were slightly different among the clones. These results indicate that other major mechanism than the inhibition of p53-MDM2 binding can be involved in p53 accumulation. [J Radiat Res 44:421 (2003)]
