Mapping BRD1 and HBO1 genomic binding in BRCA1 mutant cells

The BRCA1 tumor suppressor has many functions in DNA damage repair, DNA replication, and beyond. Loss of any of these functions can lead to breast and ovarian carcinogenesis and also therapeutic sensitivity. In this study, we have discovered a novel role for BRCA1 in controlling replication initiation by regulating the bromodomain-protein BRD1 and the histone acetyltransferase HBO1. Specifically, we show that BRCA1 regulates localization of the BRD1-HBO1 complex to replication origins where the complex normally acetylates histone H3 on lysine 14. We performed chromatin-immunoprecipitation seqeuncing (ChIP-seq) for BRD1 and HBO1 in a BRCA1 mutant line (UWB1.289) and demonstrate that BRD1 and HBO1 co-occupy ORC2 binding sites and replication origins. Overall design: UWB1.289 cells were harvested, chromatin prepared, and immunoprecipitation carried out using the Cell Signaling SimpleChIP Enzymatic Chromatin IP Kit following the manufacturer's protocol (Catalog #9003). 5ug chromatin were used per IP. Antibodies for ChIP included HBO1 (Cell Signaling Cat. #58418) and BRD1 (Abcm Cat. #ab181060). For the HBO1 and BRD1 ChIP, Active Motif's spike in controls were used according to the manufacturer's protocol (Cat. #61686 and 53083).