hAda3 regulates p14ARF-induced p53 acetylation and senescence.

Acetylation is thought to be a key event for p53 activation. We demonstrate that p14ARF-induced senescence of human mammary epithelial cells (MEC) is associated with p53 acetylation and requires hAda3, a component of histone acetyltransferase complexes and a p53 transcriptional coactivator. Expression of the N-terminal domain of hAda3 that binds p53 but not p300 blocked p14ARF-induced p53 acetylation and protected MECs from senescence. Consistent with these findings, the human papillomavirus 16 E6 mutant Y54D, which selectively targets hAda3 but not p53 for degradation and protects MECs from p14ARF-induced senescence, inhibited p53 acetylation. In H1299 cells, hAda3 overexpression increased p300-mediated p53 acetylation, which conversely decreased following small interfering RNA (siRNA) knockdown of hAda3. Moreover, depletion of hAda3 by siRNA inhibited endogenous p53 acetylation and accumulation of p21cip1 in response to ectopic p14ARF. These studies reveal that, in addition to its known ability to inhibit Mdm2-mediated p53 degradation, p14ARF signals through hAda3 to stimulate p53 acetylation and the induction of cell senescence.