One of the functions of the tumor suppressor p53 is as a transcriptional regulator, and this activity is stimulated in response to DNA damage. Among the many types of posttranslational modifications that control p53’s various functions is the addition of poly(ADP-ribose), mediated by poly(ADP-ribose) polymerase 1 (PARP-1), the activity of which is stimulated by DNA damage. Kanai et al. identified the residues in mouse p53 that were the major sites of poly(ADP-ribosyl)ation as Glu255, Asp256, and Glu268 and then studied how expression of a p53 fusion protein in which these residues were changed to alanine (GFP-p53EDE/A) influenced the localization and transcriptional activity of the protein compared with expression of a wild-type GFP p53 fusion protein (GFP-WT p53) in mouse embryo fibroblasts (MEFs) deficient for p53. In p53–/– MEFs, GFP-WT p53 was predominantly nuclear, whereas GFP-p53EDE/A was predominantly cytosolic, even when the cells were subjected to the DNA-damaging agent doxorubicin, which suggests that poly(ADP-ribosyl)ation is important for nuclear accumulation of p53. In response to DNA damage, cells expressing GFP-WT p53 showed increased abundance of p21, which is encoded by a p53-target gene, whereas cells expressing GFP-p53EDE/A did not. Consistent with PARP-1 as the enzyme responsible for the poly(ADP-ribosyl)ation of p53, MEFs deficient for PARP-1 showed decreased stability of p53 and failed to up-regulate p21 in response to DNA damage. In cells in which nuclear export was pharmacologically inhibited, the GFP-p53EDE/A mutant increased the abundance of p21 as effectively as WT p53, thus showing that poly(ADP-ribosyl)ation was not required for transactivation activity but that its effect on transactivation activity of p53 was due to decreased accumulation of p53 in the nucleus. The interaction of tagged Crm1, a nuclear export receptor, with tagged p53 or p53EDE/A was enhanced for the p53EDE/A mutant, suggesting that poly(ADP-ribosyl)ation interferes with the binding of p53 with Crm1. In vitro binding assays with poly(ADP-ribosyl)ated p53 and nonmodified p53 and Crm1 supported this interpretation. Thus, the authors propose a model whereby DNA damage promotes the hyperactivation of PARP-1, which targets p53, and poly(ADP-ribosyl)ated p53 then accumulates in the nucleus because it fails to interact with the nuclear export receptor Crm1.
M. Kanai, K. Hanashiro, S.-H. Kim, S. Hanai, A. H. Boulares, M. Miwa, K. Fukasawa, Inhibition of Crm1-p53 interaction and nuclear export of p53 by poly(ADP-ribosyl)ation. Nat. Cell Biol. 9, 1175-1183 (2007). [PubMed]