CTCF primes repressive chromatin for rapid BRCA1/BARD1 recruitment to drive homologous recombination repair of DNA double-strand breaks.

Multifaceted CTCF facilitates double-strand break (DSB) repair via homologous recombination (HR), and BRCA1/BARD1 play key roles in HR. However, whether and how CTCF cooperates with BRCA1/BARD1 for HR remain poorly understood. Here, we show CTCF recruits repressive chromatin proteins, HP1γ, KAP1, SUV39H1, SETDB1, and KDM5A, thereby enabling rapid accumulation of BRCA1/BARD1 at DSBs. CTCF depletion abrogates the enrichment of these repressive chromatin proteins, accompanied by loss of H3K9 methylation/H3K4 demethylation at DSBs, resulting in defective rapid BRCA1/BARD1 recruitment. Deprivation of one component of the repressive chromatin proteins or deregulating H3K9 methylation/H3K4 demethylation compromises the immediate accumulation of the other repressive chromatin proteins as well as BRCA1/BARD1 on DSBs. Consequently, recruitment of the exonucleases EXO1/DNA2 is abrogated, which is causally linked to defective DNA end resection and dysfunctional HR. Collectively, our findings suggest that CTCF establishes a hierarchical recruitment cascade in HR, by coordinating the repressive chromatin assembly and BRCA1/BARD1 recruitment at DSBs, facilitating the exonucleases EXO1/DNA2-mediated extensive DNA resection. Finally, we identify a critical role of CTCF in coupling BRCA1/BARD1 with the HR licensing point, the DNA end resection step, for HR.