Non-conservative homologous recombination in human B lymphocytes is promoted by activation-induced cytidine deaminase and transcription

Abstract

During secondary immunoglobulin (Ig) diversification in vertebrates, the sequence of the variable region of Ig genes may be altered by templated or non-templated mechanisms. In both cases, cytidine deamination by activation-induced cytidine deaminase (AID) in the transcribed Ig loci leads to DNA lesions, which are repaired by conservative homologous recombination (HR) during Ig gene conversion, or by non-templated mutagenesis during somatic hypermutation. The molecular basis for the differential use of these two pathways in different species is unclear. While experimental ablation of HR in avian cells performing Ig gene conversion may promote a switch to somatic hypermutation, the activity of HR processes in intrinsically hypermutating mammalian cells has not been measured to date. Employing a functional HR assay in human germinal centre like B cell lines, we detect elevated HR activity that can be enhanced by transcription and AID. Products of such recombination events mostly arise through non-conservative HR pathways, while the activity of conservative HR is low to absent. Our results identify non-conservative HR as a novel DNA transaction pathway promoted by AID and suggest that somatic hypermutation in germinal centre B cells may be based on a physiological suppression of conservative HR.

Mutation in the RNA binding protein TIS11D/ZFP36L2 is associated with the pathogenesis of acute leukemia

“…TIS11D may also be involved in such DNA repair mechanisms, given that it induces a checkpoint reaction and a decrease in p21 expression. DG75 cells, in which both alleles of TIS11D are inactivated, are more prone to homologous recombination than are other B cell-derived cell lines (23). Whether TIS11D is involved in such abnormal DNA repair mechanisms remains to be addressed in future studies.…”

GANP Regulates the Choice of DNA Repair Pathway by DNA-PKcs Interaction in AID-Dependent IgV Region Diversification

“…AID-initiated DNA injuries can be repaired by various pathways (12,(63)(64)(65)(66). AID attacks and creates DNA single-strand breaks, and DSBs result when these occur on the opposite strand within a localized region.…”

Chromosomal Translocations Caused by Either Pol32-Dependent or Pol32-Independent Triparental Break-Induced Replication

“…In this sense, an involvement of BIR-mediated DSB repair pathways in the generation of oncogenic translocations and gene amplifications affecting the immunoglobulin H and c-myc loci in B cells has been suggested (15). The relevance of HR in the development of B cells has become more evident with the publication of several recent works (10,40). Interestingly, a prevalent use of nonconservative HR pathways, such as BIR, in B cells has recently been suggested, implying that they may have a role in the diversification of immunoglobulin genes (40).…”

“…The relevance of HR in the development of B cells has become more evident with the publication of several recent works (10,40). Interestingly, a prevalent use of nonconservative HR pathways, such as BIR, in B cells has recently been suggested, implying that they may have a role in the diversification of immunoglobulin genes (40). This same type of event may cause the genesis of lymphomas by the generation of chromosomal rearrangements when short homologous sequences on different chromosomes are used.…”