BRCT-domain protein BRIT1 influences class switch recombination

Abstract

DNA double-strand breaks (DSBs) serve as obligatory intermediates for Ig heavy chain (Igh) class switch recombination (CSR). The mechanisms by which DSBs are resolved to promote long-range DNA end-joining while suppressing genomic instability inherently associated with DSBs are yet to be fully elucidated. Here, we use a targeted short-hairpin RNA screen in a B-cell lymphoma line to identify the BRCT-domain protein BRIT1 as an effector of CSR. We show that conditional genetic deletion of BRIT1 in mice leads to a marked increase in unrepaired Igh breaks and a significant reduction in CSR in ex vivo activated splenic B cells. We find that the C-terminal tandem BRCT domains of BRIT1 facilitate its interaction with phosphorylated H2AX and that BRIT1 is recruited to the Igh locus in an activationinduced cytidine deaminase (AID) and H2AX-dependent fashion. Finally, we demonstrate that depletion of another BRCT-domain protein, MDC1, in BRIT1-deleted B cells increases the severity of CSR defect over what is observed upon loss of either protein alone. Our results identify BRIT1 as a factor in CSR and demonstrate that multiple BRCTdomain proteins contribute to optimal resolution of AID-induced DSBs.class switch recombination | DNA repair | BRCT domains | B cells | MDC1

Microcephalin 1/BRIT1-TRF2 interaction promotes telomere replication and repair, linking telomere dysfunction to primary microcephaly

“…7, top). While MCPH1 has been reported to contribute to C-NHEJ repair at DSBs 17,21 , our data show that MCPH1 loss does not compromise C-NHEJ-mediated repair of dysfunctional telomeres lacking TRF2 (Fig. 4a-c).…”

“…Indeed, MCPH1 recruits the BRCA1-BRCA2-RAD51 complex to DNA damage sites for homology-directed repair (HDR), an error-free pathway that repairs nucleolytically processed DNA ends using homologous sister chromatids as templates 15,17,20 . More recent findings suggest that MCPH1 also participates in classical non-homologous end joining (C-NHEJ)-mediated repair, which ligates two DNA ends with little to no processing 17,21 . The role of MCPH1 in DNA repair, as well as its importance in regulating centrosome integrity and both the intra-S and the G 2 /M cell-cycle checkpoints 15,22 , reflect its importance in maintaining genome stability.…”

Generating and repairing genetically programmed DNA breaks during immunoglobulin class switch recombination

“…BRIT1 is a ubiquitously expressed protein that is rapidly recruited to DSBs after ionizing radiation through its C-terminal BRCT repeat domain, which is necessary for its interaction with phosphorylated H2AX (γH2AX) 112 . As predicted, successful CSR requires BRIT1 interaction with γH2AX at recombining S regions 111 . In addition, the BRIT1-γH2AX pathway is further modulated by the interaction of γH2AX with MDC1 in CSR.…”

“…In addition, the BRIT1-γH2AX pathway is further modulated by the interaction of γH2AX with MDC1 in CSR. Although BRIT1 or MDC1 deficiency alone leads to a moderate reduction in CSR, loss of both BRIT1 and MDC1 together markedly impairs CSR 111 . Thus, BRIT1 likely serves as a scaffold to recruit factors that resolve DSBs at S regions downstream of ATM ( Figure 4 ).…”

“…More recently, BRCT-repeat inhibitor of hTert expression (BRIT1) has been implicated as a novel effector of the DNA repair phase of CSR 111 . BRIT1 is a ubiquitously expressed protein that is rapidly recruited to DSBs after ionizing radiation through its C-terminal BRCT repeat domain, which is necessary for its interaction with phosphorylated H2AX (γH2AX) 112 .…”