p53 sites acetylated in vitro by PCAF and p300 are acetylated in vivo in response to DNA damage

The p53 tumor suppressor protein is a sequence-specific transcription facto r that modulates the response of cells to DNA damage. Recent studies sugges t that full transcriptional activity of p53 requires the coactivators CREB binding protein (CBP)/p300 and PCAF. These coactivators interact with each other, and both possess intrinsic histone acetyltransferase activity. Furth ermore, p300 acetylates p53 to activate its sequence-specific DNA binding a ctivity in vitro. In this study, we demonstrate that PCAF also acetylates p 53 in vitro at a lysine residue distinct from that acetylated by p300 and t hereby increases p53's ability to bind to its cognate DNA. site. We have ge nerated antibodies to acetylated p53 peptides at either of the two lysine r esidues that are targeted by PCAF or p300 and have demonstrated that these antibodies are highly specific for both acetylation and the particular site . Using these antibodies, we detect acetylation of these sites in vivo, and interestingly, acetylation at both sites increases in response to DNA-dama ging agents. These data indicate that site-specific acetylation of p53 incr eases under physiological conditions that activate p53 and identify CBP/p30 0 and PCAF as the probable enzymes that modify p53 in vivo.