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Martin OA, Thomas M, Marquet M, Bruzeau C, Garot A, Brousse M, Bender S, Carrion C, Choi JE, Vuong BQ, Gearhart PJ, Maul RW, Le Noir S, Pinaud E. The IgH Eµ-MAR regions promote UNG-dependent error-prone repair to optimize somatic hypermutation. Front Immunol 2023; 14:1030813. [PMID: 36865553 PMCID: PMC9971809 DOI: 10.3389/fimmu.2023.1030813] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 01/13/2023] [Indexed: 02/16/2023] Open
Abstract
Intoduction Two scaffold/matrix attachment regions (5'- and 3'-MARsEµ ) flank the intronic core enhancer (cEµ) within the immunoglobulin heavy chain locus (IgH). Besides their conservation in mice and humans, the physiological role of MARsEµ is still unclear and their involvement in somatic hypermutation (SHM) has never been deeply evaluated. Methods Our study analyzed SHM and its transcriptional control in a mouse model devoid of MARsEµ , further combined to relevant models deficient for base excision repair and mismatch repair. Results We observed an inverted substitution pattern in of MARsEµ -deficient animals: SHM being decreased upstream from cEµ and increased downstream of it. Strikingly, the SHM defect induced by MARsEµ -deletion was accompanied by an increase of sense transcription of the IgH V region, excluding a direct transcription-coupled effect. Interestingly, by breeding to DNA repair-deficient backgrounds, we showed that the SHM defect, observed upstream from cEµ in this model, was not due to a decrease in AID deamination but rather the consequence of a defect in base excision repair-associated unfaithful repair process. Discussion Our study pointed out an unexpected "fence" function of MARsEµ regions in limiting the error-prone repair machinery to the variable region of Ig gene loci.
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Affiliation(s)
- Ophélie A Martin
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Morgane Thomas
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Marie Marquet
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Charlotte Bruzeau
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Armand Garot
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Mylène Brousse
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Sébastien Bender
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France.,Centre Hospitalier Universitaire Dupuytren, Service d'Immunopathologie, Limoges, France
| | - Claire Carrion
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Jee Eun Choi
- The Graduate Center, The City University of New York, New York, NY, United States
| | - Bao Q Vuong
- The Graduate Center, The City University of New York, New York, NY, United States
| | - Patricia J Gearhart
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Robert W Maul
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Sandrine Le Noir
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
| | - Eric Pinaud
- Laboratoire Contrôle de la Réponse Immune B et des Lymphoproliférations (CRIBL), Université de Limoges, CNRS Unité Mixte de Recherche 7276, Inserm Unité 1262, Limoges, France
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Heltzel JHM, Maul RW, Yang W, Gearhart PJ. Promoter Proximity Defines Mutation Window for V H and V Κ Genes Rearranged to Different J Genes. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2022; 208:2220-2226. [PMID: 35418469 PMCID: PMC9050841 DOI: 10.4049/jimmunol.2101002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Accepted: 02/21/2022] [Indexed: 05/03/2023]
Abstract
Somatic hypermutation induced by activation-induced deaminase (AID) occurs at high densities between the Ig V gene promoter and intronic enhancer, which encompasses DNA encoding the rearranged V gene exon and J intron. It has been proposed that proximity between the promoter and enhancer defines the boundaries of mutation in V regions. However, depending on the J gene used, the distance between the promoter and enhancer is quite variable and may result in differential targeting around the V gene. To examine the effect of distance in mutation accumulation, we sequenced 320 clones containing different endogenous rearranged V genes in the IgH and Igκ loci from Peyer's patch B cells of mice. Clones were grouped by their use of different J genes. Distances between the V gene and enhancer ranged from ∼2.3 kb of intron DNA for rearrangements using J1, ∼2.0 kb for rearrangements using J2, ∼1.6 kb for rearrangements using J3 (H) or 4 (κ), and 1.1 kb for rearrangements using J4 (H) or 5 (κ). Strikingly, >90% of intron mutations occurred within 1 kb downstream of the J gene for both H and κ clones, regardless of which J gene was used. Thus, there is no evidence that the intron sequence or enhancer plays a role in determining the extent of mutation. The results indicate that V region intron mutations are targeted by their proximity to the promoter, suggesting they result from AID interactions with RNA polymerase II over a 1-kb region.
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Affiliation(s)
- Justin H M Heltzel
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD
| | - Robert W Maul
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD
| | - William Yang
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD
| | - Patricia J Gearhart
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD
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3
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Dinesh RK, Barnhill B, Ilanges A, Wu L, Michelson DA, Senigl F, Alinikula J, Shabanowitz J, Hunt DF, Schatz DG. Transcription factor binding at Ig enhancers is linked to somatic hypermutation targeting. Eur J Immunol 2019; 50:380-395. [PMID: 31821534 DOI: 10.1002/eji.201948357] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Revised: 10/05/2019] [Accepted: 12/02/2019] [Indexed: 01/15/2023]
Abstract
Secondary diversification of the Ig repertoire occurs through somatic hypermutation (SHM), gene conversion (GCV), and class switch recombination (CSR)-three processes that are initiated by activation-induced cytidine deaminase (AID). AID targets Ig genes at orders of magnitude higher than the rest of the genome, but the basis for this specificity is poorly understood. We have previously demonstrated that enhancers and enhancer-like sequences from Ig genes are capable of stimulating SHM of neighboring genes in a capacity distinct from their roles in increasing transcription. Here, we use an in vitro proteomics approach to identify E-box, MEF2, Ets, and Ikaros transcription factor family members as potential binders of these enhancers. ChIP assays in the hypermutating Ramos B cell line confirmed that many of these factors bound the endogenous Igλ enhancer and/or the IgH intronic enhancer (Eμ) in vivo. Further investigation using SHM reporter assays identified binding sites for E2A and MEF2B in Eμ and demonstrated an association between loss of factor binding and decreases in the SHM stimulating activity of Eμ mutants. Our results provide novel insights into trans-acting factors that dictate SHM targeting and link their activity to specific DNA binding sites within Ig enhancers.
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Affiliation(s)
- Ravi K Dinesh
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Benjamin Barnhill
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Anoj Ilanges
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Lizhen Wu
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Daniel A Michelson
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Filip Senigl
- Institute of Molecular Genetics, Czech Academy of Sciences, Videnska 1083, CZ-14220, Prague 4, Czech Republic
| | - Jukka Alinikula
- Institute of Biomedicine, University of Turku, Turku, Finland
| | | | - Donald F Hunt
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA.,Department of Pathology, University of Virginia, Charlottesville, VA, USA
| | - David G Schatz
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
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4
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Heltzel JMH, Gearhart PJ. What Targets Somatic Hypermutation to the Immunoglobulin Loci? Viral Immunol 2019; 33:277-281. [PMID: 31770070 DOI: 10.1089/vim.2019.0149] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
One of the most profound enigmas in B cell biology is how activation-induced deaminase (AID) is targeted to a very small region of DNA in the immunoglobulin loci. Two specific regions are singled out: the variable region of 2 kb that contains rearranged genes on the heavy, κ light, and λ light chain loci, and the switch region of ∼4 kb that contains an extensive stretch of G:C rich DNA on the heavy chain locus. Transcription is required for AID recruitment; however, many genes are also highly transcribed and do not undergo the catastrophic mutagenesis that occurs in variable and switch regions. The DNA sequences of these regions cause RNA polymerase II to accumulate for an extended distance of 2-4 kb. The stalled polymerases then recruit the transcription cofactor Spt5, and AID, which deaminates cytosines to uracils in exposed transcription bubbles. Thus, the immunoglobulin loci are unique in that a favorable combination of DNA sequences and 3' transcription enhancers make them the perfect storm for AID-induced somatic hypermutation.
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Affiliation(s)
- Justin M H Heltzel
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Patricia J Gearhart
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
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5
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Enhancers Improve the AID-Induced Hypermutation in Episomal Vector for Antibody Affinity Maturation in Mammalian Cell Display. Antibodies (Basel) 2018; 7:antib7040042. [PMID: 31544892 PMCID: PMC6698961 DOI: 10.3390/antib7040042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2018] [Revised: 12/10/2018] [Accepted: 12/11/2018] [Indexed: 12/03/2022] Open
Abstract
The induction of somatic hypermutation (SHM) in various cell lines by activation-induced cytidine deaminase (AID) has been used in protein-directed selection, especially in antibody affinity maturation. Several antibody affinity maturation systems based on mammalian cells have been developed in recent years, i.e., 293T, H1299, Raji and CHO cells. However, the efficiency of in vitro AID-induced hypermutation is low, restricting the application of such systems. In this study, we examined the role of Ig and Ek enhancers in enhancing SHM in the episomal vector pCEP4 that expresses an anti-high mobility group box 1 (HMGB1) full-length antibody. The plasmid containing the two enhancers exhibited two-fold improvement of mutation rate over pCEP4 in an AID expression H1299 cell line (H1299-AID). With the engineered episomal vector, we improved the affinity of this antibody in H1299-AID cells by 20-fold.
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6
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Castiblanco DP, Norton DD, Maul RW, Gearhart PJ. J H6 downstream intronic sequence is dispensable for RNA polymerase II accumulation and somatic hypermutation of the variable gene in Ramos cells. Mol Immunol 2018; 97:101-108. [PMID: 29625296 DOI: 10.1016/j.molimm.2018.03.031] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Revised: 03/09/2018] [Accepted: 03/30/2018] [Indexed: 02/03/2023]
Abstract
Activation-induced deaminase (AID) introduces nucleotide substitutions within the variable region of immunoglobulin genes to promote antibody diversity. This activity, which is limited to 1.5 kb downstream of the variable gene promoter, mutates both the coding exon and downstream intronic sequences. We recently reported that RNA polymerase II accumulates in these regions during transcription in mice. This build-up directly correlates with the area that is accessible to AID, and manipulation of RNA polymerase II levels alters the mutation frequency. To address whether the intronic DNA sequence by itself can regulate RNA polymerase II accumulation and promote mutagenesis, we deleted 613 bp of DNA downstream of the JH6 intron in the human Ramos B cell line. The loss of this sequence did not alter polymerase abundance or mutagenesis in the variable gene, suggesting that most of the intronic sequence is dispensable for somatic hypermutation.
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Affiliation(s)
- Diana P Castiblanco
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Darrell D Norton
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Robert W Maul
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Patricia J Gearhart
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA.
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7
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Abstract
Enhancers are short noncoding segments of DNA (100-1000 bp) that control the temporal and spatial activity of genes in an orientation-independent manner. They can be separated from their target genes by large distances and are thus known as distal regulatory elements. One consequence of the variability in the distance separating enhancers and their target promoters is that it is difficult to determine which elements are involved in the regulation of a particular gene. Moreover, enhancers can be found in clusters in which multiple regulatory elements control expression of the same target gene. However, little is known about how the individual elements contribute to gene expression. Here, we describe how chromatin conformation promotes and constraints enhancer activity. Further, we discuss enhancer clusters and what is known about the contribution of individual elements to the regulation of target genes. Finally, we examine the reliability of different methods used to identify enhancers.
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Affiliation(s)
- Valentina Snetkova
- Department of Pathology, New York University School of Medicine, 550 First Avenue, MSB 599, New York, NY 10016, USA.,MS 84-171, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Jane A Skok
- Department of Pathology, New York University School of Medicine, 550 First Avenue, MSB 599, New York, NY 10016, USA
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8
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Cui A, Di Niro R, Vander Heiden JA, Briggs AW, Adams K, Gilbert T, O'Connor KC, Vigneault F, Shlomchik MJ, Kleinstein SH. A Model of Somatic Hypermutation Targeting in Mice Based on High-Throughput Ig Sequencing Data. THE JOURNAL OF IMMUNOLOGY 2016; 197:3566-3574. [PMID: 27707999 DOI: 10.4049/jimmunol.1502263] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 08/22/2016] [Indexed: 11/19/2022]
Abstract
Analyses of somatic hypermutation (SHM) patterns in B cell Ig sequences have important basic science and clinical applications, but they are often confounded by the intrinsic biases of SHM targeting on specific DNA motifs (i.e., hot and cold spots). Modeling these biases has been hindered by the difficulty in identifying mutated Ig sequences in vivo in the absence of selection pressures, which skew the observed mutation patterns. To generate a large number of unselected mutations, we immunized B1-8 H chain transgenic mice with nitrophenyl to stimulate nitrophenyl-specific λ+ germinal center B cells and sequenced the unexpressed κ L chains using next-generation methods. Most of these κ sequences had out-of-frame junctions and were presumably uninfluenced by selection. Despite being nonfunctionally rearranged, they were targeted by SHM and displayed a higher mutation frequency than functional sequences. We used 39,173 mutations to construct a quantitative SHM targeting model. The model showed targeting biases that were consistent with classic hot and cold spots, yet revealed additional highly mutable motifs. We observed comparable targeting for functional and nonfunctional sequences, suggesting similar biological processes operate at both loci. However, we observed species- and chain-specific targeting patterns, demonstrating the need for multiple SHM targeting models. Interestingly, the targeting of C/G bases and the frequency of transition mutations at C/G bases was higher in mice compared with humans, suggesting lower levels of DNA repair activity in mice. Our models of SHM targeting provide insights into the SHM process and support future analyses of mutation patterns.
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Affiliation(s)
- Ang Cui
- Interdepartmental Program in Computational Biology and Bioinformatics, Yale University, New Haven, CT 06511
| | - Roberto Di Niro
- Department of Immunology, University of Pittsburgh, Pittsburgh, PA 15213
| | - Jason A Vander Heiden
- Interdepartmental Program in Computational Biology and Bioinformatics, Yale University, New Haven, CT 06511
| | | | | | | | - Kevin C O'Connor
- Department of Neurology, Yale School of Medicine, New Haven, CT 06511.,Human and Translational Immunology Program, Yale School of Medicine, New Haven, CT 06511; and
| | | | - Mark J Shlomchik
- Department of Immunology, University of Pittsburgh, Pittsburgh, PA 15213
| | - Steven H Kleinstein
- Interdepartmental Program in Computational Biology and Bioinformatics, Yale University, New Haven, CT 06511; .,Human and Translational Immunology Program, Yale School of Medicine, New Haven, CT 06511; and.,Departments of Pathology and Immunobiology, Yale School of Medicine, New Haven, CT 06511
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9
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Somatic hypermutation in immunity and cancer: Critical analysis of strand-biased and codon-context mutation signatures. DNA Repair (Amst) 2016; 45:1-24. [DOI: 10.1016/j.dnarep.2016.07.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Accepted: 07/01/2016] [Indexed: 01/01/2023]
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10
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Related Mechanisms of Antibody Somatic Hypermutation and Class Switch Recombination. Microbiol Spectr 2016; 3:MDNA3-0037-2014. [PMID: 26104555 DOI: 10.1128/microbiolspec.mdna3-0037-2014] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The primary antibody repertoire is generated by mechanisms involving the assembly of the exons that encode the antigen-binding variable regions of immunoglobulin heavy (IgH) and light (IgL) chains during the early development of B lymphocytes. After antigen-dependent activation, mature B lymphocytes can further alter their IgH and IgL variable region exons by the process of somatic hypermutation (SHM), which allows the selection of B cells in which SHMs resulted in the production of antibodies with increased antigen affinity. In addition, during antigen-dependent activation, B cells can also change the constant region of their IgH chain through a DNA double-strand-break (DSB) dependent process referred to as IgH class switch recombination (CSR), which generates B cell progeny that produce antibodies with different IgH constant region effector functions that are best suited for a elimination of a particular pathogen or in a particular setting. Both the mutations that underlie SHM and the DSBs that underlie CSR are initiated in target genes by activation-induced cytidine deaminase (AID). This review describes in depth the processes of SHM and CSR with a focus on mechanisms that direct AID cytidine deamination in activated B cells and mechanisms that promote the differential outcomes of such cytidine deamination.
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11
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The 3'-Jα Region of the TCRα Locus Bears Gene Regulatory Activity in Thymic and Peripheral T Cells. PLoS One 2015; 10:e0132856. [PMID: 26177549 PMCID: PMC4503570 DOI: 10.1371/journal.pone.0132856] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2015] [Accepted: 06/18/2015] [Indexed: 11/19/2022] Open
Abstract
Much progress has been made in understanding the important cis-mediated controls on mouse TCRα gene function, including identification of the Eα enhancer and TCRα locus control region (LCR). Nevertheless, previous data have suggested that other cis-regulatory elements may reside in the locus outside of the Eα/LCR. Based on prior findings, we hypothesized the existence of gene regulatory elements in a 3.9-kb region 5’ of the Cα exons. Using DNase hypersensitivity assays and TCRα BAC reporter transgenes in mice, we detected gene regulatory activity within this 3.9-kb region. This region is active in both thymic and peripheral T cells, and selectively affects upstream, but not downstream, gene expression. Together, these data indicate the existence of a novel cis-acting regulatory complex that contributes to TCRα transgene expression in vivo. The active chromatin sites we discovered within this region would remain in the locus after TCRα gene rearrangement, and thus may contribute to endogenous TCRα gene activity, particularly in peripheral T cells, where the Eα element has been found to be inactive.
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de Almeida CR, Hendriks RW, Stadhouders R. Dynamic Control of Long-Range Genomic Interactions at the Immunoglobulin κ Light-Chain Locus. Adv Immunol 2015; 128:183-271. [DOI: 10.1016/bs.ai.2015.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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13
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Chen Z, Wang JH. Generation and repair of AID-initiated DNA lesions in B lymphocytes. Front Med 2014; 8:201-16. [PMID: 24748462 PMCID: PMC4039616 DOI: 10.1007/s11684-014-0324-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 12/30/2013] [Indexed: 01/12/2023]
Abstract
Activation-induced deaminase (AID) initiates the secondary antibody diversification process in B lymphocytes. In mammalian B cells, this process includes somatic hypermutation (SHM) and class switch recombination (CSR), both of which require AID. AID induces U:G mismatch lesions in DNA that are subsequently converted into point mutations or DNA double stranded breaks during SHM/CSR. In a physiological context, AID targets immunoglobulin (Ig) loci to mediate SHM/CSR. However, recent studies reveal genome-wide access of AID to numerous non-Ig loci. Thus, AID poses a threat to the genome of B cells if AID-initiated DNA lesions cannot be properly repaired. In this review, we focus on the molecular mechanisms that regulate the specificity of AID targeting and the repair pathways responsible for processing AID-initiated DNA lesions.
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Affiliation(s)
- Zhangguo Chen
- Integrated Department of Immunology, University of Colorado Anschutz Medical Campus and National Jewish Health, Denver, CO 80206
| | - Jing H. Wang
- Integrated Department of Immunology, University of Colorado Anschutz Medical Campus and National Jewish Health, Denver, CO 80206
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14
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Levin-Klein R, Kirillov A, Rosenbluh C, Cedar H, Bergman Y. A novel pax5-binding regulatory element in the igκ locus. Front Immunol 2014; 5:240. [PMID: 24904588 PMCID: PMC4033077 DOI: 10.3389/fimmu.2014.00240] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Accepted: 05/08/2014] [Indexed: 12/31/2022] Open
Abstract
The Igκ locus undergoes a variety of different molecular processes during B cell development, including V(D)J rearrangement and somatic hypermutations (SHM), which are influenced by cis regulatory regions (RRs) within the locus. The Igκ locus includes three characterized RRs termed the intronic (iEκ), 3′Eκ, and Ed enhancers. We had previously noted that a region of DNA upstream of the iEκ and matrix attachment region (MAR) was necessary for demethylation of the locus in cell culture. In this study, we further characterized this region, which we have termed Dm, for demethylation element. Pre-rearranged Igκ transgenes containing a deletion of the entire Dm region, or of a Pax5-binding site within the region, fail to undergo efficient CpG demethylation in mature B cells in vivo. Furthermore, we generated mice with a deletion of the full Dm region at the endogenous Igκ locus. The most prominent phenotype of these mice is reduced SHM in germinal center B cells in Peyer’s patches. In conclusion, we propose the Dm element as a novel Pax5-binding cis regulatory element, which works in concert with the known enhancers, and plays a role in Igκ demethylation and SHM.
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Affiliation(s)
- Rena Levin-Klein
- Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Hebrew University Medical School , Jerusalem , Israel
| | - Andrei Kirillov
- Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Hebrew University Medical School , Jerusalem , Israel
| | - Chaggai Rosenbluh
- Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Hebrew University Medical School , Jerusalem , Israel
| | - Howard Cedar
- Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Hebrew University Medical School , Jerusalem , Israel
| | - Yehudit Bergman
- Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Hebrew University Medical School , Jerusalem , Israel
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15
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Targeting of somatic hypermutation by immunoglobulin enhancer and enhancer-like sequences. PLoS Biol 2014; 12:e1001831. [PMID: 24691034 PMCID: PMC3972084 DOI: 10.1371/journal.pbio.1001831] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Accepted: 02/21/2014] [Indexed: 11/19/2022] Open
Abstract
Immunoglobulin gene enhancers have a conserved function in targeting somatic hypermutation to immunoglobulin genes, thereby supporting the production of high affinity antibodies. Somatic hypermutation (SH) generates point mutations within rearranged immunoglobulin (Ig) genes of activated B cells, providing genetic diversity for the affinity maturation of antibodies. SH requires the activation-induced cytidine deaminase (AID) protein and transcription of the mutation target sequence, but how the Ig gene specificity of mutations is achieved has remained elusive. We show here using a sensitive and carefully controlled assay that the Ig enhancers strongly activate SH in neighboring genes even though their stimulation of transcription is negligible. Mutations in certain E-box, NFκB, MEF2, or Ets family binding sites—known to be important for the transcriptional role of Ig enhancers—impair or abolish the activity. Full activation of SH typically requires a combination of multiple Ig enhancer and enhancer-like elements. The mechanism is evolutionarily conserved, as mammalian Ig lambda and Ig heavy chain intron enhancers efficiently stimulate hypermutation in chicken cells. Our results demonstrate a novel regulatory function for Ig enhancers, indicating that they either recruit AID or alter the accessibility of the nearby transcription units. During the B cell immune response, immunoglobulin (Ig) genes are subject to a unique mutation process known as somatic hypermutation that allows the immune system to generate high-affinity antibodies. Somatic hypermutation preferentially affects Ig genes, relative to other genes, and this is important in preventing catastrophic levels of general genomic mutations that could lead to B cell cancers. We hypothesized that this preferential targeting of somatic hypermutation is assisted by specific DNA sequences in or near Ig genes that focus the action of the mutation machinery on those genes. In this study, we show that Ig genes across species—from human, mouse, and chicken—do indeed contain such mutation targeting sequences and that they coincide with transcriptional regulatory regions known as enhancers. We show that combinations of Ig enhancers cooperate to achieve strong mutation targeting and that this action depends on well-known transcription factor binding sites in these enhancer elements. Our findings establish an evolutionarily conserved function for enhancers in somatic hypermutation targeting, which operates by a mechanism distinct from the conventional enhancer function of increasing levels of transcription. We propose that combinations of Ig enhancers target somatic mutation to Ig genes by recruiting the mutation machinery and/or by making the Ig genes better substrates for mutation.
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16
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Erratum to: The role of activation-induced deaminase in antibody diversification and genomic instability. Immunol Res 2013. [DOI: 10.1007/s12026-013-8432-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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17
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Wang JH. The role of activation-induced deaminase in antibody diversification and genomic instability. Immunol Res 2013; 55:287-97. [PMID: 22956489 DOI: 10.1007/s12026-012-8369-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
More than a decade ago, activation-induced deaminase (AID) was identified as the initiator for somatic hypermutation (SHM) and class switch recombination (CSR). Since then, tremendous progress has been achieved toward elucidating how AID functions. AID targets the highly repetitive switch regions of the immunoglobulin heavy chain (IgH) locus to induce DNA double-strand breaks (DSBs), which can be rejoined, leading to switch of constant regions of antibody. When targeting to variable region exons of IgH and IgL loci, AID predominantly induces point mutations, termed SHM, resulting in increased affinity of antibody for antigen. While SHM and CSR enhance antibody diversity, AID-initiated DSBs and mutations may predispose B cells to carcinogenesis. This review focuses on the mechanisms that provide the specificity of AID targeting to Ig loci and the role of AID in genomic instability.
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Affiliation(s)
- Jing H Wang
- Integrated Department of Immunology, University of Colorado School of Medicine and National Jewish Health, Denver, CO 80206, USA.
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18
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Chen Z, Viboolsittiseri SS, O'Connor BP, Wang JH. Target DNA sequence directly regulates the frequency of activation-induced deaminase-dependent mutations. THE JOURNAL OF IMMUNOLOGY 2012; 189:3970-82. [PMID: 22962683 DOI: 10.4049/jimmunol.1200416] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Activation-induced deaminase (AID) catalyses class switch recombination (CSR) and somatic hypermutation (SHM) in B lymphocytes to enhance Ab diversity. CSR involves breaking and rejoining highly repetitive switch (S) regions in the IgH (Igh) locus. S regions appear to be preferential targets of AID. To determine whether S region sequence per se, independent of Igh cis regulatory elements, can influence AID targeting efficiency and mutation frequency, we established a knock-in mouse model by inserting a core Sγ1 region into the first intron of proto-oncogene Bcl6, which is a non-Ig target of SHM. We found that the mutation frequency of the inserted Sγ1 region was dramatically higher than that of the adjacent Bcl6 endogenous sequence. Mechanistically, S region-enhanced SHM was associated with increased recruitment of AID and RNA polymerase II, together with Spt5, albeit to a lesser extent. Our studies demonstrate that target DNA sequences influence mutation frequency via regulating AID recruitment. We propose that the nucleotide sequence preference may serve as an additional layer of AID regulation by restricting its mutagenic activity to specific sequences despite the observation that AID has the potential to access the genome widely.
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Affiliation(s)
- Zhangguo Chen
- Integrated Department of Immunology, University of Colorado School of Medicine and National Jewish Health, Denver, CO 80206, USA
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19
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Gramlich HS, Reisbig T, Schatz DG. AID-targeting and hypermutation of non-immunoglobulin genes does not correlate with proximity to immunoglobulin genes in germinal center B cells. PLoS One 2012; 7:e39601. [PMID: 22768095 PMCID: PMC3387148 DOI: 10.1371/journal.pone.0039601] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Accepted: 05/25/2012] [Indexed: 12/21/2022] Open
Abstract
Upon activation, B cells divide, form a germinal center, and express the activation induced deaminase (AID), an enzyme that triggers somatic hypermutation of the variable regions of immunoglobulin (Ig) loci. Recent evidence indicates that at least 25% of expressed genes in germinal center B cells are mutated or deaminated by AID. One of the most deaminated genes, c-Myc, frequently appears as a translocation partner with the Ig heavy chain gene (Igh) in mouse plasmacytomas and human Burkitt's lymphomas. This indicates that the two genes or their double-strand break ends come into close proximity at a biologically relevant frequency. However, the proximity of c-Myc and Igh has never been measured in germinal center B cells, where many such translocations are thought to occur. We hypothesized that in germinal center B cells, not only is c-Myc near Igh, but other mutating non-Ig genes are deaminated by AID because they are near Ig genes, the primary targets of AID. We tested this "collateral damage" model using 3D-fluorescence in situ hybridization (3D-FISH) to measure the distance from non-Ig genes to Ig genes in germinal center B cells. We also made mice transgenic for human MYC and measured expression and mutation of the transgenes. We found that there is no correlation between proximity to Ig genes and levels of AID targeting or gene mutation, and that c-Myc was not closer to Igh than were other non-Ig genes. In addition, the human MYC transgenes did not accumulate mutations and were not deaminated by AID. We conclude that proximity to Ig loci is unlikely to be a major determinant of AID targeting or mutation of non-Ig genes, and that the MYC transgenes are either missing important regulatory elements that allow mutation or are unable to mutate because their new nuclear position is not conducive to AID deamination.
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Affiliation(s)
- Hillary Selle Gramlich
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Tara Reisbig
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - David G. Schatz
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America
- * E-mail:
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20
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Zhou X, Xiang Y, Ding X, Garrard WT. A new hypersensitive site, HS10, and the enhancers, E3' and Ed, differentially regulate Igκ gene expression. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2012; 188:2722-32. [PMID: 22323542 PMCID: PMC3294001 DOI: 10.4049/jimmunol.1102758] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The mouse Igκ gene locus has three known transcriptional enhancers: an intronic enhancer (Ei), a 3' enhancer (E3'), and a further downstream enhancer (Ed). We previously discovered, using the chromosome conformation-capture technique, that Ei and E3' interact with a novel DNA sequence near the 3' end of the Igκ locus, specifically in B cells. In the present investigation, we examined the function of this far downstream element. The sequence is evolutionarily conserved and exhibits a plasmacytoma cell-specific DNase I-hypersensitive site in chromatin, henceforth termed HS10 in the locus. HS10 acts as a coactivator of E3' in transient transfection assays. Although HS10(-/-) mice exhibited normal patterns of B cell development, they were tested further along with E3'(-/-) and Ed(-/-) mice for their Igκ expression levels in plasma cells, as well as for both allelic and isotype exclusion in splenic B cells. HS10(-/-) and Ed(-/-), but not E3'(-/-), mice exhibited 2.5-fold lower levels of Igκ expression in antigenically challenged plasma cells. E3'(-/-) mice, but not HS10(-/-) mice, exhibited impaired IgL isotype and allelic exclusion in splenic B cells. We have suggestive results that Ed may also weakly participate in these processes. In addition, HS10(-/-) mice no longer exhibited regional chromosome interactions with E3', and they exhibited modestly reduced somatic hypermutation in the Jκ-Cκ intronic region in germinal center B cells from Peyer's patches. We conclude that the HS10, E3', and Ed differentially regulate Igκ gene dynamics.
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Affiliation(s)
- Xiaorong Zhou
- Department of Molecular Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9148
- Department of Microbiology and Immunology, Medical School of Nantong University, 19 Qixiu Road, Nantong, Jiangsu 226001, PR China
| | - Yougui Xiang
- Department of Molecular Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9148
| | - Xiaoling Ding
- Department of Molecular Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9148
| | - William T. Garrard
- Department of Molecular Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9148
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21
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Abstract
Antibody maturation requires class switch recombination (CSR) and somatic hypermutation (SHM), both of which are initiated by activation-induced cytidine deaminase (AID). AID deaminates cytosine residues resulting in mismatches that are differentially processed to produce double-strand breaks in Ig switch (S) regions that lead to CSR, or to point mutations in variable (V) exons resulting in SHM. Although AID was first thought to be Ig-specific, recent work indicates that it also targets a diverse group of non-Ig loci, including genes such as Bcl6 and c-myc, whose modification by AID results in lymphoma-associated mutations and translocations. Here, we review the recent literature on AID targeting and the role for transcriptional stalling in recruitment of this enzyme to Ig and non-Ig loci. We propose a model for AID recruitment based on transcriptional stalling, which reconciles several of the key features of SHM, CSR, and lymphoma-associated translocation.
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Affiliation(s)
- Rushad Pavri
- Laboratory of Molecular Immunology, The Rockefeller University, New York, USA
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22
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Kothapalli NR, Norton DD, Fugmann SD. Classical Mus musculus Igκ enhancers support transcription but not high level somatic hypermutation from a V-lambda promoter in chicken DT40 cells. PLoS One 2011; 6:e18955. [PMID: 21533098 PMCID: PMC3080390 DOI: 10.1371/journal.pone.0018955] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2010] [Accepted: 03/21/2011] [Indexed: 01/28/2023] Open
Abstract
Somatic hypermutation (SHM) of immunoglobulin genes is initiated by activation-induced cytidine deaminase (AID) in activated B cells. This process is strictly dependent on transcription. Hence, cis-acting transcriptional control elements have been proposed to target SHM to immunoglobulin loci. The Mus musculus Igκ locus is regulated by the intronic enhancer (iE/MAR) and the 3′ enhancer (3′E), and multiple studies using transgenic and knock-out approaches in mice and cell lines have reported somewhat contradictory results about the function of these enhancers in AID-mediated sequence diversification. Here we show that the M. musculus iE/MAR and 3′E elements are active solely as transcriptional enhancer when placed in the context of the IGL locus in Gallus gallus DT40 cells, but they are very inefficient in targeting AID-mediated mutation events to this locus. This suggests that either key components of the cis-regulatory targeting elements reside outside the murine Igκ transcriptional enhancer sequences, or that the targeting of AID activity to Ig loci occurs by largely species-specific mechanisms.
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Affiliation(s)
- Naga Rama Kothapalli
- Laboratory of Molecular Biology and Immunology, Molecular Immunology Unit, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
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23
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Kothapalli NR, Fugmann SD. Targeting of AID-mediated sequence diversification to immunoglobulin genes. Curr Opin Immunol 2011; 23:184-9. [PMID: 21295456 DOI: 10.1016/j.coi.2010.12.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Revised: 12/07/2010] [Accepted: 12/13/2010] [Indexed: 11/17/2022]
Abstract
Activation-induced cytidine deaminase (AID) is a key enzyme for antibody-mediated immune responses. Antibodies are encoded by the immunoglobulin genes and AID acts as a transcription-dependent DNA mutator on these genes to improve antibody affinity and effector functions. An emerging theme in field is that many transcribed genes are potential targets of AID, presenting an obvious danger to genomic integrity. Thus there are mechanisms in place to ensure that mutagenic outcomes of AID activity are specifically restricted to the immunoglobulin loci. Cis-regulatory targeting elements mediate this effect and their mode of action is probably a combination of immunoglobulin gene specific activation of AID and a perversion of faithful DNA repair towards error-prone outcomes.
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Affiliation(s)
- Naga Rama Kothapalli
- Molecular Immunology Unit, Laboratory of Molecular Biology and Immunology, National Institute on Aging/National Institutes of Health, Biomedical Research Center, 251 Bayview Blvd., Baltimore, MD 21224, USA
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24
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Li F, Yan Y, Pieretti J, Feldman DA, Eckhardt LA. Comparison of identical and functional Igh alleles reveals a nonessential role for Eμ in somatic hypermutation and class-switch recombination. THE JOURNAL OF IMMUNOLOGY 2010; 185:6049-57. [PMID: 20937850 DOI: 10.4049/jimmunol.0902992] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Somatic hypermutation (SHM), coupled with Ag selection, provides a mechanism for generating Abs with high affinity for invading pathogens. Class-switch recombination (CSR) ensures that these Abs attain pathogen-appropriate effector functions. Although the enzyme critical to both processes, activation-induced cytidine deaminase, has been identified, it remains unclear which cis-elements within the Ig loci are responsible for recruiting activation-induced cytidine deaminase and promoting its activity. Studies showed that Ig gene-transcription levels are positively correlated with the frequency of SHM and CSR, making the intronic, transcriptional enhancer Eμ a likely contributor to both processes. Tests of this hypothesis yielded mixed results arising, in part, from the difficulty in studying B cell function in mice devoid of Eμ. In Eμ's absence, V(H) gene assembly is dramatically impaired, arresting B cell development. The current study circumvented this problem by modifying the murine Igh locus through simultaneous insertion of a fully assembled V(H) gene and deletion of Eμ. The behavior of this allele was compared with that of a matched allele carrying the same V(H) gene but with Eμ intact. Although IgH transcription was as great or greater on the Eμ-deficient allele, CSR and SHM were consistently, but modestly, reduced relative to the allele in which Eμ remained intact. We conclude that Eμ contributes to, but is not essential for, these complex processes and that its contribution is not as a transcriptional enhancer but, rather, is at the level of recruitment and/or activation of the SHM/CSR machinery.
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Affiliation(s)
- Fubin Li
- Department of Biological Sciences, Hunter College and Graduate Center, City University of New York, New York, NY 10065, USA
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25
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Abstract
In response to an assault by foreign organisms, peripheral B cells can change their antibody affinity and isotype by somatically mutating their genomic DNA. The ability of a cell to modify its DNA is exceptional in light of the potential consequences of genetic alterations to cause human disease and cancer. Thus, as expected, this mechanism of antibody diversity is tightly regulated and coordinated through one protein, activation-induced deaminase (AID). AID produces diversity by converting cytosine to uracil within the immunoglobulin loci. The deoxyuracil residue is mutagenic when paired with deoxyguanosine, since it mimics thymidine during DNA replication. Additionally, B cells can manipulate the DNA repair pathways so that deoxyuracils are not faithfully repaired. Therefore, an intricate balance exists which is regulated at multiple stages to promote mutation of immunoglobulin genes, while retaining integrity of the rest of the genome. Here we discuss and summarize the current understanding of how AID functions to cause somatic hypermutation.
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Affiliation(s)
- Robert W Maul
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
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26
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Paddock MN, Buelow BD, Takeda S, Scharenberg AM. The BRCT domain of PARP-1 is required for immunoglobulin gene conversion. PLoS Biol 2010; 8:e1000428. [PMID: 20652015 PMCID: PMC2907289 DOI: 10.1371/journal.pbio.1000428] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Accepted: 06/08/2010] [Indexed: 11/18/2022] Open
Abstract
During affinity maturation, genomic integrity is maintained through specific targeting of DNA mutations. The DNA damage sensor PARP-1 helps determine whether a DNA lesion results in faithful or mutagenic repair. Genetic variation at immunoglobulin (Ig) gene variable regions in B-cells is created through a multi-step process involving deamination of cytosine bases by activation-induced cytidine deaminase (AID) and their subsequent mutagenic repair. To protect the genome from dangerous, potentially oncogenic effects of off-target mutations, both AID activity and mutagenic repair are targeted specifically to the Ig genes. However, the mechanisms of targeting are unknown and recent data have highlighted the role of regulating mutagenic repair to limit the accumulation of somatic mutations resulting from the more widely distributed AID-induced lesions to the Ig genes. Here we investigated the role of the DNA damage sensor poly-(ADPribose)-polymerase-1 (PARP-1) in the repair of AID-induced DNA lesions. We show through sequencing of the diversifying Ig genes in PARP-1−/− DT40 B-cells that PARP-1 deficiency results in a marked reduction in gene conversion events and enhanced high-fidelity repair of AID-induced lesions at both Ig heavy and light chains. To further characterize the role of PARP-1 in the mutagenic repair of AID-induced lesions, we performed functional analyses comparing the role of engineered PARP-1 variants in high-fidelity repair of DNA damage induced by methyl methane sulfonate (MMS) and the mutagenic repair of lesions at the Ig genes induced by AID. This revealed a requirement for the previously uncharacterized BRCT domain of PARP-1 to reconstitute both gene conversion and a normal rate of somatic mutation at Ig genes, while being dispensable for the high-fidelity base excision repair. From these data we conclude that the BRCT domain of PARP-1 is required to initiate a significant proportion of the mutagenic repair specific to diversifying antibody genes. This role is distinct from the known roles of PARP-1 in high-fidelity DNA repair, suggesting that the PARP-1 BRCT domain has a specialized role in assembling mutagenic DNA repair complexes involved in antibody diversification. To produce a limitless diversity of antibodies within the constraints of a finite genome, activated B cells introduce random mutations into antibody genes through a process of targeted DNA damage and subsequent mutagenic repair. At the same time, the rest of the genome must be protected from mutagenesis to prevent off-target mutations which can lead to the development of lymphoma or leukemia. How antibody genes are specifically targeted is still largely unknown. A potential player in this process is the DNA-damage-sensing enzyme PARP-1, which recruits DNA repair enzymes to sites of damage. Using a chicken B cell lymphoma cell line because it has only a single PARP isoform and constitutively mutates its antibody genes, we compared the types of mutations accumulated in PARP-1−/− cells to wild type. We found that in cells lacking PARP-1, the major pathway of mutagenic repair was disrupted and fewer mutations than normal were introduced into their antibody genes. To identify what might be important for mutagenesis, we tested different factors for their ability to rescue this mutagenic deficiency and found a role for the BRCT (BRCA1 C-terminal) domain of PARP-1, a consensus protein domain known to be involved in directing protein-protein interactions. Our evidence suggests that PARP-1 may be interacting with another hypothetical protein via its BRCT domain that is required for the mutagenic rather than faithful repair of DNA lesions in the antibody genes.
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Affiliation(s)
- Marcia N. Paddock
- Department of Immunology, University of Washington, Seattle, Washington, United States of America
- Center for Immunity and Immunotherapies, Seattle Children's Hospital Research Institute, Seattle, Washington, United States of America
| | - Ben D. Buelow
- Department of Immunology, University of Washington, Seattle, Washington, United States of America
- Center for Immunity and Immunotherapies, Seattle Children's Hospital Research Institute, Seattle, Washington, United States of America
| | - Shunichi Takeda
- Crest Laboratory, Department of Radiation Genetics, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto, Japan
| | - Andrew M. Scharenberg
- Department of Immunology, University of Washington, Seattle, Washington, United States of America
- Center for Immunity and Immunotherapies, Seattle Children's Hospital Research Institute, Seattle, Washington, United States of America
- * E-mail:
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27
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A coming-of-age story: activation-induced cytidine deaminase turns 10. Nat Immunol 2009; 10:1147-53. [PMID: 19841648 DOI: 10.1038/ni.1799] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The discovery and characterization of activation-induced cytidine deaminase (AID) 10 years ago provided the basis for a mechanistic understanding of secondary antibody diversification and the subsequent generation and maintenance of cellular memory in B lymphocytes, which signified a major advance in the field of B cell immunology. Here we celebrate and review the triumphs in the mission to understand the mechanisms through which AID influences antibody diversification, as well as the implications of AID function on human physiology. We also take time to point out important ongoing controversies and outstanding questions in the field and highlight key experiments and techniques that hold the potential to elucidate the remaining mysteries surrounding this vital protein.
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28
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Kim Y, Tian M. NF-kappaB family of transcription factor facilitates gene conversion in chicken B cells. Mol Immunol 2009; 46:3283-91. [PMID: 19699530 DOI: 10.1016/j.molimm.2009.07.027] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2009] [Accepted: 07/26/2009] [Indexed: 12/21/2022]
Abstract
Activation-induced cytidine deaminase (AID) is critical for immunoglobulin (Ig) diversification in B cells. The majority of evidence supports the model that AID modifies Ig genes at the DNA level by deaminating cytosines into uracils. The mutagenic activity is largely restricted to Ig genes to avoid genomic damage in general, but the underlying mechanism is not understood. We addressed this question in chicken B cell line DT40. We characterized a regulatory region within the Iglambda locus. This regulatory region is important for AID-mediated gene conversion at the Iglambda locus, and is capable of targeting AID activity to ectopic loci. This regulatory region contains binding sites for transcription factors NF-kappaB, Mef2 and octamer binding proteins. Mutation of these binding sites or ablation of NF-kappaB family member, p50 or c-Rel, impairs the AID targeting function of this regulatory region. These results suggest that NF-kappaB family of transcription factors contribute to AID-mediated gene conversion.
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Affiliation(s)
- Yonghwan Kim
- Section of Molecular Genetics and Microbiology, University of Texas at Austin, 1 University Station, Austin, TX 78712, USA
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29
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Blagodatski A, Batrak V, Schmidl S, Schoetz U, Caldwell RB, Arakawa H, Buerstedde JM. A cis-acting diversification activator both necessary and sufficient for AID-mediated hypermutation. PLoS Genet 2009; 5:e1000332. [PMID: 19132090 PMCID: PMC2607555 DOI: 10.1371/journal.pgen.1000332] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2008] [Accepted: 12/09/2008] [Indexed: 12/24/2022] Open
Abstract
Hypermutation of the immunoglobulin (Ig) genes requires Activation Induced cytidine Deaminase (AID) and transcription, but it remains unclear why other transcribed genes of B cells do not mutate. We describe a reporter transgene crippled by hypermutation when inserted into or near the Ig light chain (IgL) locus of the DT40 B cell line yet stably expressed when inserted into other chromosomal positions. Step-wise deletions of the IgL locus revealed that a sequence extending for 9.8 kilobases downstream of the IgL transcription start site confers the hypermutation activity. This sequence, named DIVAC for diversification activator, efficiently activates hypermutation when inserted at non-Ig loci. The results significantly extend previously reported findings on AID-mediated gene diversification. They show by both deletion and insertion analyses that cis-acting sequences predispose neighboring transcription units to hypermutation.
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Affiliation(s)
- Artem Blagodatski
- Institute for Molecular Radiobiology, Helmholtz Center Munich, Neuherberg, Germany
| | - Vera Batrak
- Institute for Molecular Radiobiology, Helmholtz Center Munich, Neuherberg, Germany
| | - Sabine Schmidl
- Institute for Molecular Radiobiology, Helmholtz Center Munich, Neuherberg, Germany
| | - Ulrike Schoetz
- Institute for Molecular Radiobiology, Helmholtz Center Munich, Neuherberg, Germany
| | - Randolph B. Caldwell
- Institute for Molecular Radiobiology, Helmholtz Center Munich, Neuherberg, Germany
| | - Hiroshi Arakawa
- Institute for Molecular Radiobiology, Helmholtz Center Munich, Neuherberg, Germany
| | - Jean-Marie Buerstedde
- Institute for Molecular Radiobiology, Helmholtz Center Munich, Neuherberg, Germany
- * E-mail:
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30
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Xiang Y, Garrard WT. The Downstream Transcriptional Enhancer, Ed, positively regulates mouse Ig kappa gene expression and somatic hypermutation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2008; 180:6725-32. [PMID: 18453592 PMCID: PMC2424255 DOI: 10.4049/jimmunol.180.10.6725] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The mouse Igkappa locus has three known transcriptional enhancers: the matrix association region/intronic enhancer, the 3' enhancer (E3'), and the further downstream enhancer (Ed). Previous studies have shown that both matrix association region/intronic and E3' enhancers are required for maximal gene rearrangement of the locus, and that E3' is also required for maximal expression and somatic hypermutation (SHM). To functionally elucidate Ed in vivo, we generated knockout mice with a targeted germline deletion of Ed. Ed deleted homozygous mice (Ed-/-) have moderately reduced numbers of Igkappa expressing B cells and correspondingly increased numbers of Iglambda expressing B cells in spleen. Ed-/- mice also have decreased Igkappa mRNA expression in resting and T cell-dependent activated splenic B cells and reduced Igkappa chains in sera. However, our analysis indicates that Igkappa gene rearrangement is normal in Ed-/- mice. In addition, our results show that Ed-/- mice exhibit reduced SHM in the Igkappa gene J-C intronic region in germinal center B cells from Peyer's patches. We conclude that Ed positively regulates Igkappa gene expression and SHM, but not gene rearrangement.
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Affiliation(s)
- Yougui Xiang
- Department of Molecular Biology University of Texas, Southwestern Medical Center, Dallas, TX 75390, USA
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31
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Kothapalli N, Norton DD, Fugmann SD. Cutting Edge: A cis-Acting DNA Element Targets AID-Mediated Sequence Diversification to the Chicken Ig Light Chain Gene Locus. THE JOURNAL OF IMMUNOLOGY 2008; 180:2019-23. [DOI: 10.4049/jimmunol.180.4.2019] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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32
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Kim MS, Lim HS, Ahn SJ, Jeong YK, Kim CG, Lee HH. Enhanced expression of EGFP gene in CHSE-214 cells by an ARS element from mud loach (Misgurnus mizolepis). Plasmid 2007; 58:228-39. [PMID: 17586046 DOI: 10.1016/j.plasmid.2007.05.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Revised: 04/16/2007] [Accepted: 05/01/2007] [Indexed: 10/23/2022]
Abstract
The origins of replication are associated with nuclear matrices or are found in close proximity to matrix attachment regions (MARs). In this report, fish MARs were cloned into an autonomously replicating sequence (ARS) cloning vector and were screened for ARS elements in Saccharomyces cerevisiae. Sixteen clones were isolated that were able to grow on the selective plates. In particular, an ARS905 that shows high efficiency among them was selected for this study. Southern hybridization indicated the autonomous replication of the transformation vector containing the ARS905 element. DNA sequences analysis showed that the ARS905 contained two ARS consensus sequences as well as MAR motifs, such as AT tracts, ORI patterns, and ATC tracts. In vitro matrix binding analysis, major matrix binding activity and ARS function coincided in a subfragment of the ARS905. To analyze the effects of ARS905 on expression of a reporter gene, an ARS905(E1158) with ARS activity was inserted into pBaEGFP(+) containing mud loach beta-actin promoter, EGFP as a reporter gene, and SV40 poly(A) signal. The pBaEGFP(+)-ARS905(E1158) was transfected into a fish cell line, CHSE-214. The intensity of EGFP transfected cells was a 7-fold of the control at 11days post-transfection. These results indicate that ARS905 enhances the expression of the EGFP gene and that it should be as a component of expression vectors in further fish biotechnological studies.
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Affiliation(s)
- Moo-Sang Kim
- Department of Aquatic Life Medicine, Pukyong National University, Busan 608-737, Republic of Korea
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Nikolajczyk BS, Sardi SH, Tumang JR, Ganley-Leal LM. Immunoglobulin kappa enhancers are differentially regulated at the level of chromatin structure. Mol Immunol 2007; 44:3407-15. [PMID: 17382392 PMCID: PMC2442924 DOI: 10.1016/j.molimm.2007.02.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2006] [Revised: 02/10/2007] [Accepted: 02/14/2007] [Indexed: 12/19/2022]
Abstract
The kappa intronic and the kappa 3' enhancers synergize to regulate recombination and transcription of the Ig kappa locus. Although these enhancers have overlapping functions, the kappa i enhancer appears to predominate during receptor editing, while the kappa 3' enhancer may be more important for initiating Ig kappa germline transcription to target locus recombination and, later in development, somatic hypermutation. Changes in chromatin structure appear to regulate both enhancers, and previous reports suggest that both enhancers are packaged into an accessible chromatin structure only in B lineage cells. Why these enhancers cannot activate the demethylated, accessible, protein-associated Ig kappa allele in pro-B cells is not known. Furthermore, how the enhancers function to reactivate the locus for receptor editing or to quantitatively promote hypermutation in B cells is vague. Quantitative analysis of Ig enhancer chromatin structure in murine pro-, pre-and splenic B cells demonstrated that the kappa i enhancer maintains a highly accessible chromatin structure under a variety of conditions. This stable chromatin structure mirrored the highly accessible structure characterizing the Ig mu intronic enhancer, despite the fact that Ig mu is activated prior to Ig kappa during B cell development. Surprisingly, parallel analysis of the kappa 3' enhancer demonstrated its accessible chromatin structure is markedly unstable, as characterized by sensitivity to changes in environmental conditions. These data unexpectedly suggest that kappa locus regulation is compartmentalized along the gene in B lineage cells. Furthermore, these findings raise the possibility that environmentally dependent regulation of kappa 3' enhancer structure underlies changes in kappa activation during B cell development.
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Affiliation(s)
- Barbara S Nikolajczyk
- Departments of Microbiology and Medicine, Boston University School of Medicine, Boston, MA 02118, USA.
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Chaudhuri J, Basu U, Zarrin A, Yan C, Franco S, Perlot T, Vuong B, Wang J, Phan RT, Datta A, Manis J, Alt FW. Evolution of the Immunoglobulin Heavy Chain Class Switch Recombination Mechanism. Adv Immunol 2007; 94:157-214. [PMID: 17560275 DOI: 10.1016/s0065-2776(06)94006-1] [Citation(s) in RCA: 195] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
To mount an optimum immune response, mature B lymphocytes can change the class of expressed antibody from IgM to IgG, IgA, or IgE through a recombination/deletion process termed immunoglobulin heavy chain (IgH) class switch recombination (CSR). CSR requires the activation-induced cytidine deaminase (AID), which has been shown to employ single-stranded DNA as a substrate in vitro. IgH CSR occurs within and requires large, repetitive sequences, termed S regions, which are parts of germ line transcription units (termed "C(H) genes") that are composed of promoters, S regions, and individual IgH constant region exons. CSR requires and is directed by germ line transcription of participating C(H) genes prior to CSR. AID deamination of cytidines in S regions appears to lead to S region double-stranded breaks (DSBs) required to initiate CSR. Joining of two broken S regions to complete CSR exploits the activities of general DNA DSB repair mechanisms. In this chapter, we discuss our current knowledge of the function of S regions, germ line transcription, AID, and DNA repair in CSR. We present a model for CSR in which transcription through S regions provides DNA substrates on which AID can generate DSB-inducing lesions. We also discuss how phosphorylation of AID may mediate interactions with cofactors that facilitate access to transcribed S regions during CSR and transcribed variable regions during the related process of somatic hypermutation (SHM). Finally, in the context of this CSR model, we further discuss current findings that suggest synapsis and joining of S region DSBs during CSR have evolved to exploit general mechanisms that function to join widely separated chromosomal DSBs.
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Affiliation(s)
- Jayanta Chaudhuri
- Immunology Program, Memorial Sloan Kettering Cancer Center, New York, New York, USA
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Yang SY, Fugmann SD, Schatz DG. Control of gene conversion and somatic hypermutation by immunoglobulin promoter and enhancer sequences. ACTA ACUST UNITED AC 2006; 203:2919-28. [PMID: 17178919 PMCID: PMC2118177 DOI: 10.1084/jem.20061835] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
It is thought that gene conversion (GCV) and somatic hypermutation (SHM) of immunoglobulin (Ig) genes occur in two steps: the generation of uracils in DNA by activation-induced cytidine deaminase, followed by their subsequent repair by various DNA repair pathways to generate sequence-diversified products. It is not known how either of the two steps is targeted specifically to Ig loci. Because of the tight link between transcription and SHM, we have investigated the role of endogenous Ig light chain (IgL) transcriptional control elements in GCV/SHM in the chicken B cell line DT40. Promoter substitution experiments led to identification of a strong RNA polymerase II promoter incapable of supporting efficient GCV/SHM. This surprising finding indicates that high levels of transcription are not sufficient for robust GCV/SHM in Ig loci. Deletion of the IgL enhancer in a context in which high-level transcription was not compromised showed that the enhancer is not necessary for GCV/SHM. Our results indicate that cis-acting elements are important for Ig gene diversification, and we propose that targeting specificity is achieved through the combined action of several Ig locus elements that include the promoter.
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Affiliation(s)
- Shu Yuan Yang
- Section of Immunobiology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06520, USA
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Abstract
Somatic hypermutation (SHM) introduces mutations in the variable region of immunoglobulin genes at a rate of approximately 10(-3) mutations per base pair per cell division, which is 10(6)-fold higher than the spontaneous mutation rate in somatic cells. To ensure genomic integrity, SHM needs to be targeted specifically to immunoglobulin genes. The rare mistargeting of SHM can result in mutations and translocations in oncogenes, and is thought to contribute to the development of B-cell malignancies. Despite years of intensive investigation, the mechanism of SHM targeting is still unclear. We review and attempt to reconcile the numerous and sometimes conflicting studies on the targeting of SHM to immunoglobulin loci, and highlight areas that hold promise for further investigation.
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Affiliation(s)
- Valerie H Odegard
- VaxInnate Corporation, 300 George Street, Suite 311, New Haven, Connecticut 06511, USA
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