DNA double-strand break response factors influence end-joining features of IgH class switch and general translocation junctions

Abstract

Ig heavy chain (IgH) class switch recombination (CSR) in B lymphocytes switches IgH constant regions to change antibody functions. CSR is initiated by DNA double-strand breaks (DSBs) within a donor IgH switch (S) region and a downstream acceptor S region. CSR is completed by fusing donor and acceptor S region DSB ends by classical nonhomologous end-joining (C-NHEJ) and, in its absence, by alternative end-joining that is more biased to use longer junctional microhomologies (MHs). Deficiency for DSB response (DSBR) factors, including ataxia telangiectasia-mutated (ATM) and 53BP1, variably impair CSR end-joining, with 53BP1 deficiency having the greatest impact. However, studies of potential impact of DSBR factor deficiencies on MH-mediated CSR end-joining have been technically limited. We now use a robust DSB joining assay to elucidate impacts of deficiencies for DSBR factors on CSR and chromosomal translocation junctions in primary mouse B cells and CH12F3 B-lymphoma cells. Compared with wild-type, CSR and c-myc to S region translocation junctions in the absence of 53BP1, and, to a lesser extent, other DSBR factors, have increased MH utilization; indeed, 53BP1-deficient MH profiles resemble those associated with C-NHEJ deficiency. However, translocation junctions between DSB and general DSBs genome-wide are not MH-biased in ATM-deficient versus wild-type CH12F3 cells and are less biased in 53BP1- and C-NHEJ-deficient cells than CSR junctions or to S region translocation junctions. We discuss potential roles of DSBR factors in suppressing increased MH-mediated DSB end-joining and features of S regions that may render their DSBs prone to MH-biased end-joining in the absence of DSBR factors.

DNA-PKcs phosphorylation at the T2609 cluster alters the repair pathway choice during immunoglobulin class switch recombination

“…2A) or increased inter-sister chromatid or inter-chromosomal translocations (between IgH of two homologous chromosomes 12). A similar phenotype has been noted for B cells lacking cNHEJ factors (e.g., Xrcc4 -/- ) or DNA damage response factors ( e.g., Atm -/- and Tpr53BP1 -/- ) (16, 46, 47).…”

How cells ensure correct repair of DNA double-strand breaks

“…The helicase domain of Pol appears to restrict HR and promote A-EJ by removing RPA from resected DNA ends (95). 53BP1 has been shown to act as an important suppressor of A-EJ in B cells (96). This effect of 53BP1 seems to stem from its ability to suppress resection of DSBs.…”

Defective DNA damage repair leads to frequent catastrophic genomic events in murine and human tumors

“…This emphasizes the role of alternative end-joining in catastrophic events in the context of cNHEJ inactivation. Importantly, loss of p53 alone does not alter cNHEJ activity 14,15 .…”

“…This emphasizes the role of alternative end-joining in catastrophic events in the context of cNHEJ inactivation. Importantly, loss of p53 alone does not alter cNHEJ activity 14,15 .Mutational signatures can be used to evaluate deficiencies in specific repair processes. By adapting the method developed by Alexandrov and colleagues to assign specific signatures to mutational processes in human tumors 16 , we identified mutational signatures contributing to somatic mutations in brain tumors developing in BRCA2/p53, Lig4/p53 and XRCC4/p53 deficient mice (Figure 4d).…”