title: Alternative end-joining and classical nonhomologous end-joining pathways repair different types of double-strand breaks during class-switch recombination.
abstract: Classical nonhomologous end-joining (C-NHEJ) and alternative end-joining (A-EJ) are the main DNA double-strand break (DSB) repair pathways when a sister chromatid is not available. However, it is not clear how one pathway is chosen over the other to process a given DSB. To address this question, we studied in mouse splenic B cells and CH12F3 cells how C-NHEJ and A-EJ repair DSBs initiated by the activation-induced deaminase during IgH (Igh) class-switch recombination (CSR). We show in this study that lowering the deamination density at the Igh locus increases DSB resolution by microhomology-mediated repair while decreasing C-NHEJ activity. This process occurs without affecting 53BP1 and γH2AX levels during CSR. Mechanistically, lowering deamination density increases exonuclease I recruitment and single-stranded DNA at the Igh locus and promotes C-terminal binding protein interacting protein and MSH2-dependent DSB repair during CSR. Indeed, reducing activation-induced deaminase levels increases CSR efficiency in C-NHEJ-defective cells, suggesting enhanced use of an A-EJ pathway. Our results establish a mechanism by which C-NHEJ and this C-terminal binding protein interacting protein/MSH2-dependent pathway that relies on microhomology can act concurrently but independently to repair different types of DSBs and reveal that the density of DNA lesions influences the choice of DSB repair pathway during CSR.
authors.affiliation: Division of Gerontology and Geriatric Medicine, Department of Medicine, University of Miami Miller School of Medicine, Miami, FL 33136;
authors.forename: Elena M
authors.initials: EM
authors.lastname: Cortizas
authors.forename: Astrid
authors.initials: A
authors.lastname: Zahn
authors.forename: Maurice E
authors.initials: ME
authors.lastname: Hajjar
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Patenaude
authors.forename: Javier M
authors.initials: JM
authors.lastname: Di Noia
authors.forename: Ramiro E
authors.initials: RE
authors.lastname: Verdun
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D003564:Cytidine Deaminase / Q000235:genetics; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D004268:DNA-Binding Proteins / Q000378:metabolism; D003641:Deamination / Q000235:genetics; D005090:Exodeoxyribonucleases / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D051718:MutS Homolog 2 Protein / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D059767:Recombinational DNA Repair / Q000235:genetics; D000071857:Tumor Suppressor p53-Binding Protein 1; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D006657:Histones; C498302:Trp53bp1 protein, mouse; D000071857:Tumor Suppressor p53-Binding Protein 1; C475961:gamma-H2AX protein, mouse; D000429:Alcohol Oxidoreductases; C096794:C-terminal binding protein; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase; C497173:Msh2 protein, mouse; D051718:MutS Homolog 2 Protein