Abstract 3935: H3K56 is deacetylated in response to UV-irradiation and recovery of acetylation is regulated by ATR and ATM checkpoint kinases

DNA damage results in cell cycle arrest by checkpoint activation until successful completion of DNA repair. Cell cycle arrest and DNA repair processes involve changes in chromatin architecture, which help access of proteins involved in these processes. After DNA repair, the chromatin structure and cell cycle progression are restored, but the mechanism is largely unknown. Recent studies implicated a role of histone chaperones, CAF1 and ASF1 in DNA damage repair through histone modification as well as histone assembly and disassembly. CAF1 depletion can lead to a G1 and S phase checkpoint response, in an ATR-dependent manner. In yeast, ASF1 chaperone associates with Rtt109 HAT complex which is required for H3K56 acetylation and is important for checkpoint recovery. Recently, Das et. al. showed that mammalian ASF1 interacts with p300/CBP histone acetylase and acetylates H3K56, which is deposited at the damage site in a CAF1-dependent manner. In contrast, Tjeertes et. al. showed that H3K56Ac is present in undamaged cells and is reduced in response to DNA damage. Due to the contradictory nature of H3K56 acetylation from these studies, we wanted to establish a solid foundation related to the nature of this important UV damage response event in human cells. For this, cells were irradiated and the status of H3K56 acetylation was determined immediately and up to 48 hr after UV-irradiation. Our data unambiguously show that in comparison to the steady levels of control actin, H3K56 acetylation decreased gradually and was completely eliminated at 24 hr following 20 J/m2 UV dose. However, H3K56 acetylation exhibited full recovery after 48 hr at 2.5, 5 and 10 J/m2 UV doses. Thus, UV-irradiation causes H3K56 deacetylation, which is promptly restored possibly due to the successful repair and checkpoint recovery. We observed a similar effect on H3K56 deacetylation in response to UV damage using NHF cells. Since, H3K56 acetylation has been implicated in checkpoint recovery after completion of DNA repair, we tested whether H3K56 acetylation/deacetylation is regulated by ATR and ATM checkpoint kinases. Interestingly, in Seckel cells (lower ATR level) H3K56 acetylation is dramatically reduced even in the absence of UV-irradiation suggesting that H3K56 acetylation is regulated by ATR. In contrast, in A-T cells (ATM-deficient), H3K56 acetylation did not change in the absence of UV-irradiation. In A-T cells, H3K56 is deacetylated in response to UV-irradiation as in NHF cells, but the acetylation did not recover after 48 hr post-repair. These data clearly indicate a role of ATR/ATM in recovery of H3K56 acetylation. We propose that H3K56 acetylation presents a histone mark needed for ATR/ATM-mediated checkpoint recovery. (This work was supported by NIH grants CA93413, ES2388 and ES12991) 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 3935.