Abstact

Bromodomain-containing protein 4 (BRD4) is well characterized as a histone acetyllysine reader that plays critical roles in the regulation of oncogene transcription. Additionally, BRD4 has been shown to be involved in DNA repair and telomere maintenance in a transcriptionally independent manner. Our previous study revealed that BRD4 inhibits non-homologous end-joining (NHEJ) DNA repair by recognizing the histone H2AK5acK9ac hyperacetylation at DSB sites through its tandem bromodomains (BD1 and BD2), resulting in the accumulation of the BRD4-KU80 protein that impedes the assembly of the DNA repair machinery in mitotic deacetylase complex (MiDAC)-deficient cells. Here we report the structural basis for the recognition of H2AK5acK9ac by BD1 and BD1-BD2 domains, respectively. In particular, we show that Leu92 in BD1 is a key determinant of the H2AK5acK9ac specificity over other diacetyllysine marks on H4, and it negatively regulates NHEJ repair to promote genomic instability in MiDAC-deficient cells. These results reveal a previously unrecognized mode of BRD4-histone interaction and its functional consequences that make a meaningful contribution to chromatin biology and DNA repair.