title: AID-initiated DNA lesions are differentially processed in distinct B cell populations.
abstract: Activation-induced deaminase (AID) initiates U:G mismatches, causing point mutations or DNA double-stranded breaks at Ig loci. How AID-initiated lesions are prevented from inducing genome-wide damage remains elusive. A differential DNA repair mechanism might protect certain non-Ig loci such as c-myc from AID attack. However, determinants regulating such protective mechanisms are largely unknown. To test whether target DNA sequences modulate protective mechanisms via altering the processing manner of AID-initiated lesions, we established a knock-in model by inserting an Sγ2b region, a bona fide AID target, into the first intron of c-myc. Unexpectedly, we found that the inserted S region did not mutate or enhance c-myc genomic instability, due to error-free repair of AID-initiated lesions, in Ag-stimulated germinal center B cells. In contrast, in vitro cytokine-activated B cells display a much higher level of c-myc genomic instability in an AID- and S region-dependent manner. Furthermore, we observe a comparable frequency of AID deamination events between the c-myc intronic sequence and inserted S region in different B cell populations, demonstrating a similar frequency of AID targeting. Thus, our study reveals a clear difference between germinal center and cytokine-activated B cells in their ability to develop genomic instability, attributable to a differential processing of AID-initiated lesions in distinct B cell populations. We propose that locus-specific regulatory mechanisms (e.g., transcription) appear to not only override the effects of S region sequence on AID targeting frequency but also influence the repair manner of AID-initiated lesions.
authors.affiliation: Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; and jing.wang@ucdenver.edu zhangguo.chen@ucdenver.edu.
authors.forename: Zhangguo
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Boston Children's Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115.
authors.forename: Sheila
authors.initials: S
authors.lastname: Ranganath
authors.affiliation: Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045;
authors.forename: Sawanee S
authors.initials: SS
authors.lastname: Viboolsittiseri
authors.affiliation: Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045;
authors.forename: Maxwell D
authors.initials: MD
authors.lastname: Eder
authors.affiliation: Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; and.
authors.forename: Xiaomi
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045;
authors.forename: Mihret T
authors.initials: MT
authors.lastname: Elos
authors.affiliation: Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045;
authors.forename: Shunzong
authors.initials: S
authors.lastname: Yuan
authors.forename: Shunzhong
authors.initials: S
authors.lastname: Yuan
authors.affiliation: Boston Children's Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115.
authors.forename: Erica
authors.initials: E
authors.lastname: Hansen
authors.affiliation: Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; and jing.wang@ucdenver.edu zhangguo.chen@ucdenver.edu.
authors.forename: Jing H
authors.initials: JH
authors.lastname: Wang
mesh_terms: D000818:Animals; D016175:B-Lymphocyte Subsets / Q000502:physiology*; D001402:B-Lymphocytes / Q000502:physiology*; D002478:Cells, Cultured; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D004260:DNA Repair / Q000276:immunology; D055879:Gene Knock-In Techniques; D056426:Genetic Loci / Q000235:genetics; D042822:Genomic Instability; D018858:Germinal Center / Q000276:immunology*; D006801:Humans; D007438:Introns / Q000235:genetics; D057507:Mice, 129 Strain; D009154:Mutation / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D027041:Somatic Hypermutation, Immunoglobulin; D013379:Substrate Specificity; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D016207:Cytokines; D016271:Proto-Oncogene Proteins c-myc; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase