Phosphorylation of Ser46 Regulates Apoptosis-inducing Ability of p53
A newly found transcriptional activation domain (43-63) and the proline-rich domain (64-92) have been suggested to be needed for apoptosis induction by p53 because deletion of either of these two domains abolishes this activity. In order to test the possibility that phosphorylation of a specific site in these domains regulates apoptosis-inducing ability of p53, we generated antibodies to recognize 3 potential phosphorylation sites in these domains. We now found that phosphorylation of Ser46 is induced after DNA damage. Particularly, phosphorylation of this site was observed only at the late stage after DNA damage by several different agents, and high dose of gamma-ray or UV was needed compared to Ser15 or Ser20. Moreover, the time course of phosphorylation of Ser46 and apoptosis induction was similar. When p53 mutants which were changed at Ser46 were transfected or microinjected into H1299 cells, apoptosis-inducing ability of S46A or S46del was greatly reduced while that of S46F was increased compared to wild type. However, there were no difference in induction of p21Waf1 between wild-type and these mutants.
Kinase activity to phosphorylate Ser46 was detected from crude cell extracts only after treatment with high dose of DNA-damaging agents. These results suggest an intriguing possibility that phosphorylation of Ser46 regulates the transcriptional activation of apoptosis-inducing genes by p53. We have isolated such a candidate apoptosis-inducing gene which is regulated by phosphorylation of Ser46 of p53. It is p53AIP1 (p53-regulated Apoptosis Inducing Protein 1). Its expression is induced by wild-type p53 and its protein is localized in mitochondria. Ectopic expression of p53AIP1 induces mitochondrial membrane potential change and apoptosis. Interestingly, only the expression of p53AIP1, among many p53-target genes, was consistent to induction of phosphorylation of Ser46 in p53 and apoptosis of cells.
Tomoaki Tanaka, Katsuyuki Tamai1, Hirofumi Arakawa2,, Yusuke Nakamura2, and Yoichi Taya
Biology Div., National Cancer Center Research Inst.,