DNA-DAMAGE ACTIVATES P53 THROUGH A PHOSPHORYLATION-ACETYLATION CASCADE

Activation of p53-mediated transcription is a critical cellular respon se to DNA damage. p53 stability and site-specific DNA-binding activity and, therefore, transcriptional activity, are modulated by post-trans lational modifications including phosphorylation and acetylation. Here we show that p53 is acetylated in vitro at separate sites by two diff erent histone acetyltransferases (HATs), the coactivators p300 and PCA F. p300 acetylates Lys-382 in the carboxy-terminal region of p53, wher eas PCAF acetylates Lys-320 in the nuclear localization signal. Acetyl ations at either site enhance sequence-specific DNA binding. Using a p olyclonal antisera specific for p53 that is phosphorylated or acetylat ed at specific residues, we show that Lys-382 of human p53 becomes ace tylated and Ser-33 and Ser-37 become phosphorylated in vivo after expo sing cells to UV light or ionizing radiation. In vitro, amino-terminal p53 peptides phosphorylated at Ser-33 and/or at Ser-37 differentially inhibited p53 acetylation by each HAT. These results suggest that DNA damage enhances p53 activity as a transcription factor in part throug h carboxy-terminal acetylation that, in turn, is directed by amino-ter minal phosphorylation.