Abstract 4873: Functional interactions between lysine 20 methylation and lysine 16 acetylation on histone H4 in DNA damage responses

Abstract

Abstract Individual histone post-translational modifications have been implicated in regulating many cellular events. Modifications can occur at high densities in the N-terminal tail domains of core histones, enabling the possibility that combinations of modifications regulate chromatin processes differently than modifications occurring individually. However, surprisingly little is known about the nature and functions of multi-site histone modification. This study investigates functional interactions between acetylation of lysine 16 (K16ac) and methylation of lysine 20 (K20me), two modifications that frequently occur together on molecules of histone H4. Methylation state-specific binding of p53-binding protein 1 (53BP1) to dimethyl K20 H4 (K20me2) and the formation of 53BP1 nuclear foci near double strand breaks are early events in DNA damage responses (DDR) that provide a platform for the assembly of downstream effectors. Since global levels of K20me2 are relatively stable and are established independently of DNA damage, we propose that reversible changes in the levels of K16ac co-modification act like a dynamic switch to modulate DDR responses mediated by K20me2. Analyses of the interaction of the K20me2 binding domain of 53BP1 with H4 peptides in vitro reveal that K16ac co-modification attenuates specific recognition of K20me1/2 by 53BP1. The possibility that K16ac and K20me2 interact functionally in vivo is demonstrated by our finding that K16 deacetylation accompanies the induction of H2AX phosphorylation, a well-known marker for DDR, following DNA damage by either UV irradiation or bleomycin treatment. Moreover, the effects of expressing K16 mutants of H4 and inhibition of histone deacetylases on 53BP1 foci formation induced by DNA damage are consistent with our hypothesis that K16ac co-modification negatively regulates the formation of 53BP1 foci. DDR mechanisms are frequently deregulated in cancer cells. Further investigation of the role of H4 modifications in DDR will enhance our understanding of how genome integrity is maintained in normal cells and may identify novel targets for future therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4873.