Acetylated to Death

Science's STKE  16 Mar 2004:
Vol. 2004, Issue 224, pp. tw94-TW94
DOI: 10.1126/stke.2242004TW94

Activation of the protein Bax by cell damage promotes apoptosis and provides an important mechanism for tumor suppression. Ku70 (which was initially identified as a DNA repair protein) sequesters Bax in healthy cells and thereby suppresses Bax-mediated apoptosis. Although cell damage can disrupt the association between Ku70 and Bax, the underlying mechanisms remain unclear. Noting that a C-terminal linker region adjacent to the Bax interaction domain of Ku70 resembled known acetylation sites in other proteins, Cohen et al. probed Ku70 immunoprecipitates with an antibody against acetylated proteins and found that Ku70 was acetylated in vivo. Moreover, Ku70 acetylation increased after treatment of cells with UV radiation. Western analysis of immunoprecipitates indicated that Ku70 interacted with the acetyltransferases CBP [cAMP response element-binding protein (CREB)-binding protein] and PCAF (p300/CBP-associated factor). Recombinant Ku70 served as an in vitro substrate for CBP, PCAF, and P300. Analysis of the acetylation of synthetic peptides identified two lysine residues (K539 and K542) in the linker region likely to serve as in vivo targets for CBP and PCAF. Tandem mass spectrometry analysis confirmed that both residues were acetylated in vivo. Pharmacological analysis indicated that class I/II histone deacetylases (HDACs) and sirtuins deacetylated Ku70. Treatment with HDAC inhibitors blocked the ability of overexpressed Ku70 to inhibit Bax-mediated apoptosis and decreased association of endogenous Ku70 with Bax. Ku70 mutants designed to mimic constitutive acetylation of K539 or K542 were ineffective in suppressing Bax-mediated apoptosis. Thus acetylation of Ku70 appears to be a mechanism whereby cell damage can lead to Bax-mediated apoptosis; this finding substantiates the emerging role of histone acetyltransferases as tumor suppressors.

H. Y. Cohen, S. Lavu, K. J. Bitterman, B. Kekking, T. A. Imahiyerobo, C. Miller, R. Frye, H. Ploegh, B. M. Kessler, D. A. Sinclair, Acetylation of the C terminus of Ku70 by CBP and PCAF controls Bax-mediated apoptosis. Mol. Cell 13, 627-638 (2004). [Online Journal]