51
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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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52
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Saintamand A, Rouaud P, Garot A, Saad F, Carrion C, Oblet C, Cogné M, Pinaud E, Denizot Y. The IgH 3' regulatory region governs μ chain transcription in mature B lymphocytes and the B cell fate. Oncotarget 2016; 6:4845-52. [PMID: 25742787 PMCID: PMC4467119 DOI: 10.18632/oncotarget.3010] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 12/21/2014] [Indexed: 12/11/2022] Open
Abstract
We report that the IgH 3' regulatory region (3'RR) has no role on μ chain transcription and pre-BCR expression in B cell progenitors. In contrast, analysis of heterozygous IgH aΔ3'RR/bwt mice indicated that the 3'RR controls μ chain transcripts in mature splenocytes and impacts membrane IgM density without obvious effect on BCR signals (colocalisation with lipid rafts and phosphorylation of Erk and Akt after BCR crosslinking). Deletion of the 3'RR modulates the B cell fate to less marginal zone B cells. In conclusion, the 3'RR is dispensable for pre-BCR expression and necessary for optimal commitments toward the marginal zone B cell fate. These results reinforce the concept of a dual regulation of the IgH locus transcription and accessibility by 5' elements at immature B cell stages, and by the 3'RR as early as the resting mature B cell stage and then along further activation and differentiation.
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Affiliation(s)
| | | | | | | | | | | | - Michel Cogné
- CNRS, CRIBL, UMR 7276, Limoges, France.,Université de Limoges, CRIBL, UMR 7276, Limoges, France.,Institut Universitaire de France, Paris, France
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53
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Saintamand A, Vincent-Fabert C, Garot A, Rouaud P, Oruc Z, Magnone V, Cogné M, Denizot Y. Deciphering the importance of the palindromic architecture of the immunoglobulin heavy-chain 3' regulatory region. Nat Commun 2016; 7:10730. [PMID: 26883548 PMCID: PMC4757795 DOI: 10.1038/ncomms10730] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Accepted: 01/15/2016] [Indexed: 01/16/2023] Open
Abstract
The IgH 3' regulatory region (3'RR) controls class switch recombination (CSR) and somatic hypermutation (SHM) in B cells. The mouse 3'RR contains four enhancer elements with hs1,2 flanked by inverted repeated sequences and the centre of a 25-kb palindrome bounded by two hs3 enhancer inverted copies (hs3a and hs3b). hs4 lies downstream of the palindrome. In mammals, evolution maintained this unique palindromic arrangement, suggesting that it is functionally significant. Here we report that deconstructing the palindromic IgH 3'RR strongly affects its function even when enhancers are preserved. CSR and IgH transcription appear to be poorly dependent on the 3'RR architecture and it is more or less preserved, provided 3'RR enhancers are present. By contrast, a ‘palindromic effect' significantly lowers VH germline transcription, AID recruitment and SHM. In conclusion, this work indicates that the IgH 3'RR does not simply pile up enhancer units but also optimally exposes them into a functional architecture of crucial importance. The IgH 3' regulatory region contains an evolutionarily conserved palindromic sequence flanking important enhancer elements. Here the authors show that the palindrome is required for generating antibody diversity.
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Affiliation(s)
| | | | - Armand Garot
- Université de Limoges, CRIBL, UMR CNRS 7276, Limoges 87025, France
| | - Pauline Rouaud
- Université de Limoges, CRIBL, UMR CNRS 7276, Limoges 87025, France
| | - Zeliha Oruc
- Université de Limoges, CRIBL, UMR CNRS 7276, Limoges 87025, France
| | - Virginie Magnone
- CNRS et Université de Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 6097, Sophia Antipolis 06560, France
| | - Michel Cogné
- Université de Limoges, CRIBL, UMR CNRS 7276, Limoges 87025, France.,Institut Universitaire de France, Paris 75231, France
| | - Yves Denizot
- Université de Limoges, CRIBL, UMR CNRS 7276, Limoges 87025, France
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54
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Sequential activation and distinct functions for distal and proximal modules within the IgH 3' regulatory region. Proc Natl Acad Sci U S A 2016; 113:1618-23. [PMID: 26831080 DOI: 10.1073/pnas.1514090113] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
As a master regulator of functional Ig heavy chain (IgH) expression, the IgH 3' regulatory region (3'RR) controls multiple transcription events at various stages of B-cell ontogeny, from newly formed B cells until the ultimate plasma cell stage. The IgH 3'RR plays a pivotal role in early B-cell receptor expression, germ-line transcription preceding class switch recombination, interactions between targeted switch (S) regions, variable region transcription before somatic hypermutation, and antibody heavy chain production, but the functional ranking of its different elements is still inaccurate, especially that of its evolutionarily conserved quasi-palindromic structure. By comparing relevant previous knockout (KO) mouse models (3'RR KO and hs3b-4 KO) to a novel mutant devoid of the 3'RR quasi-palindromic region (3'PAL KO), we pinpointed common features and differences that specify two distinct regulatory entities acting sequentially during B-cell ontogeny. Independently of exogenous antigens, the 3'RR distal part, including hs4, fine-tuned B-cell receptor expression in newly formed and naïve B-cell subsets. At mature stages, the 3'RR portion including the quasi-palindrome dictated antigen-dependent locus remodeling (global somatic hypermutation and class switch recombination to major isotypes) in activated B cells and antibody production in plasma cells.
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55
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Zanotti KJ, Gearhart PJ. Antibody diversification caused by disrupted mismatch repair and promiscuous DNA polymerases. DNA Repair (Amst) 2016; 38:110-116. [PMID: 26719140 PMCID: PMC4740194 DOI: 10.1016/j.dnarep.2015.11.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 11/30/2015] [Indexed: 10/25/2022]
Abstract
The enzyme activation-induced deaminase (AID) targets the immunoglobulin loci in activated B cells and creates DNA mutations in the antigen-binding variable region and DNA breaks in the switch region through processes known, respectively, as somatic hypermutation and class switch recombination. AID deaminates cytosine to uracil in DNA to create a U:G mismatch. During somatic hypermutation, the MutSα complex binds to the mismatch, and the error-prone DNA polymerase η generates mutations at A and T bases. During class switch recombination, both MutSα and MutLα complexes bind to the mismatch, resulting in double-strand break formation and end-joining. This review is centered on the mechanisms of how the MMR pathway is commandeered by B cells to generate antibody diversity.
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Affiliation(s)
- Kimberly J Zanotti
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Patricia J Gearhart
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
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56
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Yeap LS, Hwang JK, Du Z, Meyers RM, Meng FL, Jakubauskaitė A, Liu M, Mani V, Neuberg D, Kepler TB, Wang JH, Alt FW. Sequence-Intrinsic Mechanisms that Target AID Mutational Outcomes on Antibody Genes. Cell 2015; 163:1124-1137. [PMID: 26582132 DOI: 10.1016/j.cell.2015.10.042] [Citation(s) in RCA: 122] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Revised: 09/01/2015] [Accepted: 10/13/2015] [Indexed: 12/27/2022]
Abstract
In activated B lymphocytes, AID initiates antibody variable (V) exon somatic hypermutation (SHM) for affinity maturation in germinal centers (GCs) and IgH switch (S) region DNA breaks (DSBs) for class-switch recombination (CSR). To resolve long-standing questions, we have developed an in vivo assay to study AID targeting of passenger sequences replacing a V exon. First, we find AID targets SHM hotspots within V exon and S region passengers at similar frequencies and that the normal SHM process frequently generates deletions, indicating that SHM and CSR employ the same mechanism. Second, AID mutates targets in diverse non-Ig passengers in GC B cells at levels similar to those of V exons, definitively establishing the V exon location as "privileged" for SHM. Finally, Peyer's patch GC B cells generate a reservoir of V exons that are highly mutated before selection for affinity maturation. We discuss the implications of these findings for harnessing antibody diversification mechanisms.
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Affiliation(s)
- Leng-Siew Yeap
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Joyce K Hwang
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Zhou Du
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Robin M Meyers
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Fei-Long Meng
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Agnė Jakubauskaitė
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Mengyuan Liu
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Vinidhra Mani
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Donna Neuberg
- Department of Biostatistics and Computational Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Thomas B Kepler
- Department of Microbiology, Boston University School of Medicine, Boston, MA 02215, USA
| | - Jing H Wang
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Frederick W Alt
- Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine at Boston Children's Hospital, and Department of Genetics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA.
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57
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Saad F, Saintamand A, Cogné M, Denizot Y. The IgH 3' regulatory region influences lymphomagenesis in Igλ-Myc mice. Oncotarget 2015; 6:20302-11. [PMID: 25980500 PMCID: PMC4653006 DOI: 10.18632/oncotarget.3963] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 04/10/2015] [Indexed: 01/11/2023] Open
Abstract
The IgH 3′regulatory region (3′RR), encompassing the four transcriptional enhancers hs3a-hs1,2-hs3b-hs4, has a key role on class switch recombination, somatic hypermutation, IgH transcription and B-cell fate. In plasma cells, transcribed IgH and IgL loci often colocalized in transcription factories and an IgL transcription defect might translate into lowered IgH transcription. We explored whether the 3′RR would affect lymphomagenesis in Igλ-Myc transgenic mice prone to lymphoproliferations. Breeding Igλ-Myc transgenics in a background deficient for the 3′RR influences lymphomagenesis toward less mature lymphomas (16% vs 54%, p = 0.01, Z test for two population proportions). In a 3′RR-deficient background mature tumors less often expressed the CD43 antigen (54% vs 0%, p = 0.02), a membrane glycoprotein expressed on activated mature B-cells. In contrast, in a 3′RR-deficient background tumors more often expressed the CD5 antigen (32% vs 12%, p = 0.05) that may serve to control autoimmunity and that is suspected to play a role in leukemic transformation. Lymphoma myc transcript levels, the Ki67 index of proliferation, the clonality, the usage of V(D)J segments, and their somatic hypermutation status were not affected in the 3′RR-deficient background. In conclusion, most probably through its action during the maturation process, the 3′RR can influence lymphomagenesis even when not linked with an oncogene.
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Affiliation(s)
- Faten Saad
- CNRS UMR 7276, CRIBL, Université de Limoges, Limoges, France
| | | | - Michel Cogné
- CNRS UMR 7276, CRIBL, Université de Limoges, Limoges, France
| | - Yves Denizot
- CNRS UMR 7276, CRIBL, Université de Limoges, Limoges, France
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58
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Proudhon C, Hao B, Raviram R, Chaumeil J, Skok JA. Long-Range Regulation of V(D)J Recombination. Adv Immunol 2015; 128:123-82. [PMID: 26477367 DOI: 10.1016/bs.ai.2015.07.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Given their essential role in adaptive immunity, antigen receptor loci have been the focus of analysis for many years and are among a handful of the most well-studied genes in the genome. Their investigation led initially to a detailed knowledge of linear structure and characterization of regulatory elements that confer control of their rearrangement and expression. However, advances in DNA FISH and imaging combined with new molecular approaches that interrogate chromosome conformation have led to a growing appreciation that linear structure is only one aspect of gene regulation and in more recent years, the focus has switched to analyzing the impact of locus conformation and nuclear organization on control of recombination. Despite decades of work and intense effort from numerous labs, we are still left with an incomplete picture of how the assembly of antigen receptor loci is regulated. This chapter summarizes our advances to date and points to areas that need further investigation.
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Affiliation(s)
- Charlotte Proudhon
- Department of Pathology, New York University School of Medicine, New York, USA
| | - Bingtao Hao
- Department of Pathology, New York University School of Medicine, New York, USA
| | - Ramya Raviram
- Department of Pathology, New York University School of Medicine, New York, USA
| | - Julie Chaumeil
- Institut Curie, CNRS UMR3215, INSERM U934, Paris, France
| | - Jane A Skok
- Department of Pathology, New York University School of Medicine, New York, USA.
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59
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Amin R, Marfak A, Pangault C, Oblet C, Chanut A, Tarte K, Denizot Y, Cogné M. The class-specific BCR tonic signal modulates lymphomagenesis in a c-myc deregulation transgenic model. Oncotarget 2015; 5:8995-9006. [PMID: 25229630 PMCID: PMC4253413 DOI: 10.18632/oncotarget.2297] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Deregulation of c-myc by translocation onto immunoglobulin (Ig) loci can promote B cell malignant proliferations with phenotypes as diverse as acute lymphoid leukemia, Burkitt lymphoma, diffuse large B cell lymphoma, myeloma… The B cell receptor (BCR) normally providing tonic signals for cell survival and mitogenic responses to antigens, can also contribute to lymphomagenesis upon sustained ligand binding or activating mutations. BCR signaling varies among cell compartments and BCR classes. For unknown reasons, some malignancies associate with expression of either IgM or class-switched Ig. We explored whether an IgA BCR, with strong tonic signaling, would affect lymphomagenesis in c-myc IgH 3′RR transgenic mice prone to lymphoproliferations. Breeding c-myc transgenics in a background where IgM expression was replaced with IgA delayed lymphomagenesis. By comparison to single c-myc transgenics, lymphomas from double mutant animals were more differentiated and less aggressive, with an altered transcriptional program. Larger tumor cells more often expressed CD43 and CD138, which culminated in a plasma cell phenotype in 10% of cases. BCR class-specific signals thus appear to modulate lymphomagenesis and may partly explain the observed association of specific Ig classes with human B cell malignancies of differential phenotype, progression and prognosis.
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Affiliation(s)
- Rada Amin
- Centre National de la Recherche Scientifique, Limoges, France. Université de Limoges, Limoges, France. INSERM UMR U917, Rennes, France
| | | | | | - Christelle Oblet
- Centre National de la Recherche Scientifique, Limoges, France. Université de Limoges, Limoges, France
| | - Aurélie Chanut
- Centre National de la Recherche Scientifique, Limoges, France. Université de Limoges, Limoges, France
| | | | - Yves Denizot
- Centre National de la Recherche Scientifique, Limoges, France. Université de Limoges, Limoges, France
| | - Michel Cogné
- Centre National de la Recherche Scientifique, Limoges, France. Université de Limoges, Limoges, France
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60
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Bonaud A, Lechouane F, Le Noir S, Monestier O, Cogné M, Sirac C. Efficient AID targeting of switch regions is not sufficient for optimal class switch recombination. Nat Commun 2015; 6:7613. [PMID: 26146363 DOI: 10.1038/ncomms8613] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 05/26/2015] [Indexed: 02/07/2023] Open
Abstract
Antibody affinity maturation relies on activation-induced cytidine deaminase (AID)-dependent somatic hypermutation (SHM) of immunoglobulin (Ig) loci. Class switch recombination (CSR) can in parallel occur between AID-targeted, transcribed, spliced and repetitive switch (S) regions. AID thus initiates not only mutations but also double-strand breaks (DSBs). What governs the choice between those two outcomes remains uncertain. Here we explore whether insertion of transcribed intronic S regions in a locus (Igκ) strongly recruiting AID is sufficient for efficient CSR. Although strongly targeted by AID and carrying internal deletions, the knocked-in S regions only undergo rare CSR-like events. This model confirms S regions as exquisite SHM targets, extending AID activity far from transcription initiation sites, and shows that such spliced and repetitive AID targets are not sufficient by themselves for CSR. Beyond transcription and AID recruitment, additional IgH elements are thus needed for CSR, restricting this hazardous gene remodelling to IgH loci.
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Affiliation(s)
- Amélie Bonaud
- Immunology, CNRS UMR 7276, Centre Nationale de la Recherche Scientifique, Université de Limoges, Limoges 87025, France
| | - Fabien Lechouane
- Immunology, CNRS UMR 7276, Centre Nationale de la Recherche Scientifique, Université de Limoges, Limoges 87025, France
| | - Sandrine Le Noir
- Immunology, CNRS UMR 7276, Centre Nationale de la Recherche Scientifique, Université de Limoges, Limoges 87025, France
| | - Olivier Monestier
- Immunology, CNRS UMR 7276, Centre Nationale de la Recherche Scientifique, Université de Limoges, Limoges 87025, France
| | - Michel Cogné
- 1] Immunology, CNRS UMR 7276, Centre Nationale de la Recherche Scientifique, Université de Limoges, Limoges 87025, France. [2] Institut Universitaire de France, Paris 75000, France
| | - Christophe Sirac
- Immunology, CNRS UMR 7276, Centre Nationale de la Recherche Scientifique, Université de Limoges, Limoges 87025, France
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61
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Saintamand A, Rouaud P, Saad F, Rios G, Cogné M, Denizot Y. Elucidation of IgH 3′ region regulatory role during class switch recombination via germline deletion. Nat Commun 2015; 6:7084. [DOI: 10.1038/ncomms8084] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 04/01/2015] [Indexed: 02/06/2023] Open
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62
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Saintamand A, Saad F, Denizot Y. A new 3'RR regulatory role during lymphomagenesis. Cell Cycle 2015; 14:1987-8. [PMID: 25927676 DOI: 10.1080/15384101.2015.1046789] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
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63
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Saintamand A, Saad F, Denizot Y. 3'RR targeting in lymphomagenesis: a promising strategy? Cell Cycle 2015; 14:789-90. [PMID: 25790089 DOI: 10.1080/15384101.2015.1010964] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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64
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Maul RW, Saribasak H, Cao Z, Gearhart PJ. Topoisomerase I deficiency causes RNA polymerase II accumulation and increases AID abundance in immunoglobulin variable genes. DNA Repair (Amst) 2015; 30:46-52. [PMID: 25869824 DOI: 10.1016/j.dnarep.2015.03.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Revised: 03/03/2015] [Accepted: 03/09/2015] [Indexed: 10/23/2022]
Abstract
Activation-induced deaminase (AID) is a DNA cytosine deaminase that diversifies immunoglobulin genes in B cells. Recent work has shown that RNA polymerase II (Pol II) accumulation correlates with AID recruitment. However, a direct link between Pol II and AID abundance has not been tested. We used the DT40 B-cell line to manipulate levels of Pol II by decreasing topoisomerase I (Top1), which relaxes DNA supercoiling in front of the transcription complex. Top1 was decreased by stable transfection of a short hairpin RNA against Top1, which produced an accumulation of Pol II in transcribed genes, compared to cells transfected with sh-control RNA. The increased Pol II density enhanced AID recruitment to variable genes in the λ light chain locus, and resulted in higher levels of somatic hypermutation and gene conversion. It has been proposed by another lab that AID itself might directly suppress Top1 to increase somatic hypermutation. However, we found that in both AID(+/+) and AID(-/-) B cells from DT40 and mice, Top1 protein levels were identical, indicating that the presence or absence of AID did not decrease Top1 expression. Rather, our results suggest that the mechanism for increased diversity when Top1 is reduced is that Pol II accumulates and recruits AID to variable genes.
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Affiliation(s)
- Robert W Maul
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States
| | - Huseyin Saribasak
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States
| | - Zheng Cao
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States
| | - Patricia J Gearhart
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States.
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65
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Overlapping hotspots in CDRs are critical sites for V region diversification. Proc Natl Acad Sci U S A 2015; 112:E728-37. [PMID: 25646473 DOI: 10.1073/pnas.1500788112] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Activation-induced deaminase (AID) mediates the somatic hypermutation (SHM) of Ig variable (V) regions that is required for the affinity maturation of the antibody response. An intensive analysis of a published database of somatic hypermutations that arose in the IGHV3-23*01 human V region expressed in vivo by human memory B cells revealed that the focus of mutations in complementary determining region (CDR)1 and CDR2 coincided with a combination of overlapping AGCT hotspots, the absence of AID cold spots, and an abundance of polymerase eta hotspots. If the overlapping hotspots in the CDR1 or CDR2 did not undergo mutation, the frequency of mutations throughout the V region was reduced. To model this result, we examined the mutation of the human IGHV3-23*01 biochemically and in the endogenous heavy chain locus of Ramos B cells. Deep sequencing revealed that IGHV3-23*01 in Ramos cells accumulates AID-induced mutations primarily in the AGCT in CDR2, which was also the most frequent site of mutation in vivo. Replacing the overlapping hotspots in CDR1 and CDR2 with neutral or cold motifs resulted in a reduction in mutations within the modified motifs and, to some degree, throughout the V region. In addition, some of the overlapping hotspots in the CDRs were at sites in which replacement mutations could change the structure of the CDR loops. Our analysis suggests that the local sequence environment of the V region, and especially of the CDR1 and CDR2, is highly evolved to recruit mutations to key residues in the CDRs of the IgV region.
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66
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Laffleur B, Denis-Lagache N, Péron S, Sirac C, Moreau J, Cogné M. AID-induced remodeling of immunoglobulin genes and B cell fate. Oncotarget 2015; 5:1118-31. [PMID: 24851241 PMCID: PMC4012742 DOI: 10.18632/oncotarget.1546] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Survival and phenotype of normal and malignant B lymphocytes are critically dependent on constitutive signals by the B cell receptor (BCR) for antigen. In addition, either antigen ligation of the BCR or various mitogenic stimuli result in B cell activation and induction of activation-induced deaminase (AID). AID activity can in turn mediate somatic hypermutation (SHM) of immunoglobulin (Ig) V regions and also deeply remodel the Ig heavy chain locus through class switch recombination (CSR) or locus suicide recombination (LSR). In addition to changes linked to affinity for antigen, modifying the class/isotype (i.e. the structure and function) of the BCR or suddenly deleting BCR expression also modulates the fate of antigen-experienced B cells.
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67
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Fagarasan S, Macpherson AJ. The Regulation of IgA Production. Mucosal Immunol 2015. [DOI: 10.1016/b978-0-12-415847-4.00023-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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68
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Serone E, Daleno C, Principi N, Porretti L, Iacoacci V, Gargioli C, Magrini A, Massoud R, D'Addabbo P, Cattalini M, Giambra V, Plebani A, Esposito S, Frezza D. The change in Ig regulation from children to adults disconnects the correlation with the 3'RR hs1.2 polymorphism. BMC Immunol 2014; 15:45. [PMID: 25391515 PMCID: PMC4234878 DOI: 10.1186/s12865-014-0045-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 09/25/2014] [Indexed: 11/10/2022] Open
Abstract
Background In the immune system, the serum levels of immunoglobulin (Ig) increase gradually during ageing. Through B cell development, the Ig heavy chain expression is modulated by a regulatory region at the 3’ of the constant alpha gene (3’RR), in single copy in rodents and, due to a large duplication, in two copies in apes. The human 3’RR1 and 3’RR2 are both characterized by three enhancers, the central of which, namely hs1.2, is highly polymorphic. Human hs1.2 has four different variants with unique binding sites for transcription factors (e.g. NF-kB and SP1) and shows variable allelic frequencies in populations with immune disorders. In previous works, we have reported that in several autoimmune diseases the *2 allele of hs1.2 is genetically associated to high level of IgM in peripheral blood. In subjects with altered levels of circulating Ig, an increased level was associated to *2 allele of hs1.2 and low levels corresponded to high frequency of *1 allele. During ageing there is a physiological increase of Ig concentrations in the serum. Therefore, for this study, we hypothesized that the hs1.2 variants may impact differently the levels of secreted Ig during the growth. Results We have correlated the allelic frequencies of hs1.2 with IgM, IgG and IgA serum concentrations in two cohorts of healthy people of different age and after three years follow-up in children homozygous for the allele. Here we show that when the expression levels of Ig in children are low and medium, the frequencies of *1 and *2 alleles are the same. Instead, when the Ig expression levels are high, there is a significantly higher frequency of the allele *2. The follow-up of children homozygous for *1 and *2 alleles showed that the increase or decrease of circulating Ig was not dependent on the number of circulating mature B cells. Conclusions These data support the idea that under physiologic condition there is a switch of regulative pathways involved in the maturation of Ig during ageing. This mechanism is evidenced by hs1.2 variants that in children but not in adults participate to Ig production, coordinating the three class levels. Electronic supplementary material The online version of this article (doi:10.1186/s12865-014-0045-0) contains supplementary material, which is available to authorized users.
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69
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Chen Z, Ranganath S, Viboolsittiseri SS, Eder MD, Chen X, Elos MT, Yuan S, Yuan S, Hansen E, Wang JH. AID-initiated DNA lesions are differentially processed in distinct B cell populations. THE JOURNAL OF IMMUNOLOGY 2014; 193:5545-56. [PMID: 25339658 DOI: 10.4049/jimmunol.1401549] [Citation(s) in RCA: 13] [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) 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.
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Affiliation(s)
- Zhangguo Chen
- 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
| | - Sheila Ranganath
- Boston Children's Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
| | - Sawanee S Viboolsittiseri
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | - Maxwell D Eder
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | - Xiaomi Chen
- 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
| | - Mihret T Elos
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | - Shunzong Yuan
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | | | - Erica Hansen
- Boston Children's Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
| | - Jing H Wang
- 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
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70
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Inter- and intratumoral heterogeneity of BCL2 correlates with IgH expression and prognosis in follicular lymphoma. Blood Cancer J 2014; 4:e249. [PMID: 25303368 PMCID: PMC4220646 DOI: 10.1038/bcj.2014.67] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 08/20/2014] [Indexed: 11/15/2022] Open
Abstract
Most follicular lymphomas (FLs) are genetically defined by the t(14;18)(q32;q21) translocation that juxtaposes the BCL2 gene to the immunoglobulin heavy chain (IgH) 3' regulatory regions (IgH-3'RRs). Despite this recurrent translocation, FL cases are heterogeneous in terms of intratumoral clonal diversity for acquired mutations and variations in the tumor microenvironment. Here we describe an additional mechanism that contributes to inter- and intratumoral heterogeneity in FLs. By applying a novel single-molecule RNA fluorescence-based in situ hybridization (FISH) technique to detect mRNA molecules of BCL2 and IgH in single cells, we found marked heterogeneity in the number of BCL2 mRNA transcripts within individual lymphoma cells. Moreover, BCL2 mRNA molecules correlated with IgH mRNA molecules in individual cells both in t(14;18) lymphoma cell lines and in patient samples. Consistently, a strong correlation between BCL2 and IgH protein levels was found in a series of 205 primary FL cases by flow cytometry and immunohistochemistry. Inter- and intratumoral heterogeneity of BCL2 expression determined resistance to drugs commonly used in FL treatment and affected overall survival of FL patients. These data demonstrate that BCL2 and IgH expressions are heterogeneous and coregulated in t(14;18)-translocated cells, and determine the response to therapy in FL patients.
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71
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Maul RW, Cao Z, Venkataraman L, Giorgetti CA, Press JL, Denizot Y, Du H, Sen R, Gearhart PJ. Spt5 accumulation at variable genes distinguishes somatic hypermutation in germinal center B cells from ex vivo-activated cells. ACTA ACUST UNITED AC 2014; 211:2297-306. [PMID: 25288395 PMCID: PMC4203944 DOI: 10.1084/jem.20131512] [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] [Indexed: 12/22/2022]
Abstract
Variable (V) genes of immunoglobulins undergo somatic hypermutation by activation-induced deaminase (AID) to generate amino acid substitutions that encode antibodies with increased affinity for antigen. Hypermutation is restricted to germinal center B cells and cannot be recapitulated in ex vivo-activated splenic cells, even though the latter express high levels of AID. This suggests that there is a specific feature of antigen activation in germinal centers that recruits AID to V genes which is absent in mitogen-activated cultured cells. Using two Igh knock-in mouse models, we found that RNA polymerase II accumulates in V regions in B cells after both types of stimulation for an extended distance of 1.2 kb from the TATA box. The paused polymerases generate abundant single-strand DNA targets for AID. However, there is a distinct accumulation of the initiating form of polymerase, along with the transcription cofactor Spt5 and AID, in the V region from germinal center cells, which is totally absent in cultured cells. These data support a model where mutations are prevalent in germinal center cells, but not in ex vivo cells, because the initiating form of polymerase is retained, which affects Spt5 and AID recruitment.
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Affiliation(s)
- Robert W Maul
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224
| | - Zheng Cao
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224
| | | | | | - Joan L Press
- Department of Biology, Brandeis University, Waltham, MA 02454
| | - Yves Denizot
- Centre National de la Recherche Scientifique UMR 7276, Université de Limoges, 87025 Limoges, France
| | - Hansen Du
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224
| | - Ranjan Sen
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224
| | - Patricia J Gearhart
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224
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72
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Targeting the oncogene B lymphoma deregulator IgH 3' regulatory region does not impede the in vivo inflammatory response in mice. Oncoscience 2014; 1:591-8. [PMID: 25594069 PMCID: PMC4278336 DOI: 10.18632/oncoscience.81] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Accepted: 09/14/2014] [Indexed: 01/10/2023] Open
Abstract
The IgH 3′ regulatory region (3′RR), encompassing the four transcriptional enhancers hs3a-hs1,2-hs3b-hs4, is a potent lymphoma oncogene deregulator but its role in B cell-mediated inflammatory responses is unknown. We investigated the 3′RR involvement in the in vivo pristane-induced inflammatory response in BALB/c mice. The lack of the 3′RR in BALB/c mice had no wide effect on the incidence, the kinetic of development and the cellular composition of peritoneal ascites. Ascite pro-inflammatory cytokines levels (IL-6, IL-21, IL-12/23, TNF-α) were unchanged while anti-inflammatory cytokines levels (IL-10, interferon-γ) were slightly increased in 3′RR-deficient BALB/c mice as compared to wt BALB/c mice. In conclusion, the 3′RR is dispensable for the efficient recruitment of immune cells and the normal development of an inflammatory response in the in vivo pristane-induced inflammatory model. The 3′RR might be considered as a potential suitable target for anti-lymphoma pharmacological therapy without potent adverse effect on normal immune and inflammatory responses.
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73
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The functional VNTR of IGH enhancer HS1.2 associates with human longevity and interacts with TNFA promoter diplotype in a population of Central Italy. Gene 2014; 551:201-5. [PMID: 25175451 DOI: 10.1016/j.gene.2014.08.057] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Revised: 08/26/2014] [Accepted: 08/27/2014] [Indexed: 11/22/2022]
Abstract
The dysregulation of both immune and inflammatory responses occurring with aging is believed to substantially contribute to morbidity and mortality in humans. We have already reported the association of the functional Variable Number of Tandem Repeat (VNTR) at the Immunoglobulin heavy chain (IGH) enhancer HS1.2 with Immunoglobulin levels and with several autoimmune diseases. Herein we tested the association of the VNTR at the HS1.2 enhancer with human longevity, also evaluating the possible modulatory effect of TNFA promoter diplotype (rs361525/rs1800629). HS1.2 enhancer genotypes have been determined for 193 unrelated healthy individuals from Central Italy divided into two groups: Group 1 (18-84 yrs, mean age 56.8 ± 19.4) and Group 2 (85-100 yrs, mean age 93.0 ± 3.5). Homozygous subjects for 2 allele were significantly disadvantaged in reaching higher life-expectancy (OR=0.457, p=0.021). A significant interaction between TNFA promoter diplotype status, HS1.2 2/2 genotype and the two Groups was found (p=0.014). Of note, TNFA -308A allele seems to exert a protective effect in HS1.2 2/2 carriers. These results support the hypothesis of an important role of HS1.2 VNTR in the puzzle of the immune-system regulation, evidenced also by the potential interaction with TNFA. Moreover, the previous results showing the association of HS1.2 2 allele with inflammatory phenomena are consistent with the hypothesis that this allele is a detrimental factor in reaching advanced age.
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74
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Marquet M, Garot A, Bender S, Carrion C, Rouaud P, Lecardeur S, Denizot Y, Cogné M, Pinaud E. The Eμ enhancer region influences H chain expression and B cell fate without impacting IgVH repertoire and immune response in vivo. THE JOURNAL OF IMMUNOLOGY 2014; 193:1171-83. [PMID: 24965776 DOI: 10.4049/jimmunol.1302868] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The IgH intronic enhancer region Eμ is a combination of both a 220-bp core enhancer element and two 310-350-bp flanking scaffold/matrix attachment regions named MARsEμ. In the mouse, deletion of the core-enhancer Eμ element mainly affects VDJ recombination with minor effects on class switch recombination. We carried out endogenous deletion of the full-length Eμ region (core plus MARsEμ) in the mouse genome to study VH gene repertoire and IgH expression in developing B-lineage cells. Despite a severe defect in VDJ recombination with partial blockade at the pro-B cell stage, Eμ deletion (core or full length) did not affect VH gene usage. Deletion of this regulatory region induced both a decrease of pre-B cell and newly formed B cell compartments and a strong orientation toward the marginal zone B cell subset. Because Igμ H chain expression was decreased in Eμ-deficient pre-B cells, we propose that modification of B cell homeostasis in deficient animals was caused by "weak" pre-B cell and BCR expression. Besides imbalances in B cell compartments, Ag-specific Ab responses were not impaired in animals carrying the Eμ deletion. In addition to its role in VDJ recombination, our study points out that the full-length Eμ region does not influence VH segment usage but ensures efficient Igμ-chain expression required for strong signaling through pre-B cells and newly formed BCRs and thus participates in B cell inflow and fate.
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Affiliation(s)
- Marie Marquet
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France
| | - Armand Garot
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France
| | - Sébastien Bender
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France; Centre Hospitalier Universitaire Dupuytren, Centre de Référence des Amyloses, 87042 Limoges, France; and
| | - Claire Carrion
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France
| | - Pauline Rouaud
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France
| | - Sandrine Lecardeur
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France
| | - Yves Denizot
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France
| | - Michel Cogné
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France; Institut Universitaire de France, 75005 Paris, France
| | - Eric Pinaud
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7276, Université de Limoges, 87025 Limoges, France;
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75
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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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76
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Dingler FA, Kemmerich K, Neuberger MS, Rada C. Uracil excision by endogenous SMUG1 glycosylase promotes efficient Ig class switching and impacts on A:T substitutions during somatic mutation. Eur J Immunol 2014; 44:1925-35. [PMID: 24771041 PMCID: PMC4158878 DOI: 10.1002/eji.201444482] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Revised: 03/06/2014] [Accepted: 04/15/2014] [Indexed: 12/23/2022]
Abstract
Excision of uracil introduced into the immunoglobulin loci by AID is central to antibody diversification. While predominantly carried out by the UNG uracil‐DNA glycosylase as reflected by deficiency in immunoglobulin class switching in Ung−/− mice, the deficiency is incomplete, as evidenced by the emergence of switched IgG in the serum of Ung−/− mice. Lack of switching in mice deficient in both UNG and MSH2 suggested that mismatch repair initiated a backup pathway. We now show that most of the residual class switching in Ung−/− mice depends upon the endogenous SMUG1 uracil‐DNA glycosylase, with in vitro switching to IgG1 as well as serum IgG3, IgG2b, and IgA greatly diminished in Ung−/−Smug1−/− mice, and that Smug1 partially compensates for Ung deficiency over time. Nonetheless, using a highly MSH2‐dependent mechanism, Ung−/−Smug1−/− mice can still produce detectable levels of switched isotypes, especially IgG1. While not affecting the pattern of base substitutions, SMUG1 deficiency in an Ung−/− background further reduces somatic hypermutation at A:T base pairs. Our data reveal an essential requirement for uracil excision in class switching and in facilitating noncanonical mismatch repair for the A:T phase of hypermutation presumably by creating nicks near the U:G lesion recognized by MSH2.
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77
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Immunoglobulin genes undergo legitimate repair in human B cells not only after cis- but also frequent trans-class switch recombination. Genes Immun 2014; 15:341-6. [PMID: 24848929 DOI: 10.1038/gene.2014.25] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 03/26/2014] [Accepted: 04/14/2014] [Indexed: 12/23/2022]
Abstract
Immunoglobulin (Ig) genes specifically recruit activation-induced deaminase (AID) for 'on-target' DNA deamination, initiating either variable (V) region somatic hypermutation, or double-strand break intermediates of class switch recombination (CSR). Such breaks overwhelmingly undergo legitimate intra-Ig repair rather than rare illegitimate and potentially oncogenic junctions outside of Ig loci. We show that in human B cells, legitimate synapsis and repair efficiently join Ig genes whether physically linked on one chromosome or located apart on both alleles. This indicates mechanisms faithfully recognizing and/or pairing loci with homology in structure and accessibility, thus licensing interchromosomal trans-CSR junctions while usually preventing illegitimate interchromosomal recombination with AID off-target genes. Physical linkage of IgH genes in cis on the same allele just increases the likelihood of legitimate repair by another fourfold. The strongest force driving CSR might thus be recognition of legitimate target genes. Formation of IgH intra-allelic loops along this process would then constitute a consequence rather than a pre-requisite of this gene-pairing process.
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78
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Rouaud P, Saintamand A, Saad F, Carrion C, Lecardeur S, Cogné M, Denizot Y. Elucidation of the enigmatic IgD class-switch recombination via germline deletion of the IgH 3' regulatory region. ACTA ACUST UNITED AC 2014; 211:975-85. [PMID: 24752300 DOI: 10.1084/jem.20131385] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Classical class-switch recombination (cCSR) substitutes the Cμ gene with Cγ, Cε, or Cα, thereby generating IgG, IgE, or IgA classes, respectively. This activation-induced deaminase (AID)-driven process is controlled by the IgH 3' regulatory region (3'RR). Regulation of rare IgD CSR events has been enigmatic. We show that μδCSR occurs in mouse mesenteric lymph node (MLN) B cells and is AID-dependent. AID attacks differ from those in cCSR because they are not accompanied by extensive somatic hypermutation (SHM) of targeted regions and because repaired junctions exhibit features of the alternative end-joining (A-EJ) pathway. In contrast to cCSR and SHM, μδCSR is 3'RR-independent, as its absence affects neither breakpoint locations in Sμ- and Sδ-like (σ(δ)) nor mutation patterns at Sμ-σ(δ) junctions. Although mutations occur in the immediate proximity of the μδ junctions, SHM is absent distal to the junctions within both Sμ and rearranged VDJ regions. In conclusion, μδCSR is active in MLNs, occurs independently of 3'RR-driven assembly, and is even dramatically increased in 3'RR-deficient mice, further showing that its regulation differs from cCSR.
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Affiliation(s)
- Pauline Rouaud
- UMR CNRS 7276, Centre National de la Recherche Scientifique, Université de Limoges, 87025 Limoges, France
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Birshtein BK. Epigenetic Regulation of Individual Modules of the immunoglobulin heavy chain locus 3' Regulatory Region. Front Immunol 2014; 5:163. [PMID: 24795714 PMCID: PMC4000994 DOI: 10.3389/fimmu.2014.00163] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Accepted: 03/27/2014] [Indexed: 11/18/2022] Open
Abstract
The Igh locus undergoes an amazing array of DNA rearrangements and modifications during B cell development. During early stages, the variable region gene is constructed from constituent variable (V), diversity (D), and joining (J) segments (VDJ joining). B cells that successfully express an antibody can be activated, leading to somatic hypermutation (SHM) focused on the variable region, and class switch recombination (CSR), which substitutes downstream constant region genes for the originally used Cμ constant region gene. Many investigators, ourselves included, have sought to understand how these processes specifically target the Igh locus and avoid other loci and potential deleterious consequences of malignant transformation. Our laboratory has concentrated on a complex regulatory region (RR) that is located downstream of Cα, the most 3′ of the Igh constant region genes. The ~40 kb 3′ RR, which is predicted to serve as a downstream major regulator of the Igh locus, contains two distinct segments: an ~28 kb region comprising four enhancers, and an adjacent ~12 kb region containing multiple CTCF and Pax5 binding sites. Analysis of targeted mutations in mice by a number of investigators has concluded that the entire 3′ RR enhancer region is essential for SHM and CSR (but not for VDJ joining) and for high levels of expression of multiple isotypes. The CTCF/Pax5 binding region is a candidate for influencing VDJ joining early in B cell development and serving as a potential insulator of the Igh locus. Components of the 3′ RR are subject to a variety of epigenetic changes during B cell development, i.e., DNAse I hypersensitivity, histone modifications, and DNA methylation, in association with transcription factor binding. I propose that these changes provide a foundation by which regulatory elements in modules of the 3′ RR function by interacting with each other and with target sequences of the Igh locus.
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Affiliation(s)
- Barbara K Birshtein
- Department of Cell Biology, Albert Einstein College of Medicine , Bronx, NY , USA
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80
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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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81
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Abstract
In this review, I discuss the currently available experimental evidence concerning the molecular interactions of the activation-induced cytidine deaminase (AID) with transcription of its target genes. The basic question that underlies the transcription relationship is how the process of somatic hypermutation of Ig genes can be restricted to their variable (V) regions. This hallmark of SHM assures that high affinity antibodies can be created while the biological functions of their constant (C) region are undisturbed. I present a revised model of AID function in somatic hypermutation (SHM): In a B cell that produces AID protein and undergoes mutation of the V regions of the expressed Ig heavy and light chain genes, only some of the transcription complexes initiating at the active V-region promoters are associated with AID. When AID travels with the elongating RNA polymerase (pol), it attracts proteins that cause the pausing/stalling of pol and termination of transcription, followed by termination of SHM. This differential AID loading model would allow the mutating B cell to continue producing full-length Ig proteins that are required to avoid apoptosis by permitting the cell to assemble functional B cell receptors.
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Affiliation(s)
- Ursula Storb
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois, USA.
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Ma B, Osborn MJ, Avis S, Ouisse LH, Ménoret S, Anegon I, Buelow R, Brüggemann M. Human antibody expression in transgenic rats: comparison of chimeric IgH loci with human VH, D and JH but bearing different rat C-gene regions. J Immunol Methods 2013; 400-401:78-86. [PMID: 24184135 DOI: 10.1016/j.jim.2013.10.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 10/18/2013] [Accepted: 10/18/2013] [Indexed: 11/28/2022]
Abstract
Expression of human antibody repertoires in transgenic animals has been accomplished by introducing large human Ig loci into mice and, more recently, a chimeric IgH locus into rats. With human VH, D and JH genes linked to the rat C-region antibody expression was significantly increased, similar to wild-type levels not found with fully human constructs. Here we compare four rat-lines containing the same human VH-region (comprising 22 VHs, all Ds and all JHs in natural configuration) but linked to different rat CH-genes and regulatory sequences. The endogenous IgH locus was silenced by zinc-finger nucleases. After breeding, all lines produced exclusively chimeric human H-chain with near normal IgM levels. However, in two lines poor IgG expression and inefficient immune responses were observed, implying that high expression, class-switching and hypermutation are linked to optimal enhancer function provided by the large regulatory region at the 3' end of the IgH locus. Furthermore, exclusion of Cδ and its downstream interval region may assist recombination. Highly diverse IgG and immune responses similar to normal rats were identified in two strains carrying diverse and differently spaced C-genes.
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Affiliation(s)
- Biao Ma
- Recombinant Antibody Technology Ltd., Cambridge, UK
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