DNA double-strand break (DSB) repair occurs within chromatin and can be modulated by chromatin modifying enzymes. Here we identify the related human histone deacetylases HDAC1 and HDAC2 as two participants in the DNA-damage response (DDR). We show that acetylation of histone H3 lysine 56 (H3K56) is regulated by HDAC1/2, and that HDAC1/2 are rapidly recruited to DNA-damage sites to promote H3K56 hypo-acetylation. Furthermore, we establish that HDAC1/2-depleted cells are hypersensitive to DNA-damaging agents and exhibit sustained DNA-damage signaling, phenotypes that reflect defective DSB repair, particularly by the pathway of non-homologous end-joining (NHEJ). Collectively, these results demonstrate that HDAC1 and HDAC2 function in the DDR by promoting DSB repair and thus provide important insights into the radio-sensitizing effects of HDAC inhibitors that are being developed as cancer therapies. KeywordsHDAC1; HDAC2; DNA damage; chromatin; non-homologous end-joining Because DNA damage represents a formidable challenge to the integrity of genetic material, cells have evolved multifaceted systems, collectively termed the DNA-damage response (DDR), to detect, signal and repair various types of DNA damage 1 , 2 . DNA double-strand breaks (DSBs) represent one of the most challenging forms of DNA damage which, if left unrepaired, can trigger cellular death and can contribute to human diseases, including cancer 1 . In eukaryotes, DSBs are repaired by two main pathways: non-homologous endjoining (NHEJ), which operates throughout the cell cycle, and homologous recombination (HR) which is limited to S and G2 cell-cycle phases 3 . For NHEJ, the Ku70/Ku80 complex loads onto free DNA ends where it helps recruit the DDR protein kinase DNA-PK (DNAdependent protein kinase) 4 , as well as other factors, including the nuclease Artemis and the ligase IV-XRCC4 complex, which are required for NHEJ to ensue 5 . NHEJ occurs rapidly within cells and mostly requires minimal processing of DNA ends. By contrast, HR requires extensive DNA end-resection to create stretches of single-stranded DNA (ssDNA) that bind factors such as RPA and RAD51 to promote the various steps in HR 3 . Since HR and NHEJ function together during certain phases of the cell cycle, mechanisms must exist to modulate In this study, our previous observation of a decrease of H3K56Ac upon DNA damage prompted us to evaluate the role of HDACs in the DDR. Here, we describe how human HDAC1 and HDAC2 respond to DNA damage and mediate changes in histone acetylation, including H3K56, following DNA-damage induction. Furthermore, by defining the effects of impairing HDAC1/2 function, we establish that these enzymes serve as important components of the DDR by promoting DSB signalling and repair, principally through their requirement for effective NHEJ. Europe PMC Funders Group RESULTS HDAC1 and HDAC2 localize to sites of DNA damageWe previously demonstrated that H3K56Ac levels are reduced by treatments that induce DNA damage, including the drug phleomycin that produces D...

Recognition and repair of damaged DNA occurs within the context of chromatin. The key protein components of chromatin are histones, whose post-translational modifications control diverse chromatin functions. Here, we report our findings from a large-scale screen for DNAdamage-responsive histone modifications in human cells. We have identified specific phosphorylations and acetylations on histone H3 that decrease in response to DNA damage. Significantly, we find that DNA-damage-induced changes in H3S10p, H3S28p and H3.3S31p are a consequence of cell-cycle re-positioning rather than DNA damage per se. In contrast, H3K9Ac and H3K56Ac, a mark previously uncharacterized in human cells, are rapidly and reversibly reduced in response to DNA damage. Finally, we show that the histone acetyl-transferase GCN5/KAT2A acetylates H3K56 in vitro and in vivo. Collectively, our data indicate that though most histone modifications do not change appreciably after genotoxic stress, H3K9Ac and H3K56Ac are reduced in response to DNA damage in human cells.

DNA double-strand breaks (DSBs) are perhaps the most toxic of all DNA lesions, with defects in the DNA damage response to DSBs being associated with various human diseases. Although it is known that DSB repair pathways are tightly regulated by ubiquitylation, we do not yet have a comprehensive understanding of how deubiquitylating enzymes (DUBs) function in DSB responses. Here, by carrying out a multi-dimensional screening strategy for human DUBs, we identify several with hitherto unknown links to DSB repair, the G2/M DNA-damage checkpoint and genome-integrity maintenance. Phylogenetic analyses reveal functional clustering within certain DUB subgroups, suggesting evolutionally conserved functions and/or related modes-of action. Furthermore, we establish that the DUB UCHL5 regulates DSB resection and repair by homologous recombination through protecting its interactor, NFRKB, from degradation. Collectively our findings extend the list of DUBs promoting the maintenance of genome integrity, and highlight their potential as therapeutic targets for cancer.