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Eid MMA, Shimoda M, Singh SK, Almofty SA, Pham P, Goodman MF, Maeda K, Sakaguchi N. Integrity of immunoglobulin variable regions is supported by GANP during AID-induced somatic hypermutation in germinal center B cells. Int Immunol 2017; 29:211-220. [PMID: 28541550 PMCID: PMC5890899 DOI: 10.1093/intimm/dxx032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Accepted: 05/22/2017] [Indexed: 11/13/2022] Open
Abstract
Immunoglobulin affinity maturation depends on somatic hypermutation (SHM) in immunoglobulin variable (IgV) regions initiated by activation-induced cytidine deaminase (AID). AID induces transition mutations by C→U deamination on both strands, causing C:G→T:A. Error-prone repairs of U by base excision and mismatch repairs (MMRs) create transversion mutations at C/G and mutations at A/T sites. In Neuberger’s model, it remained to be clarified how transition/transversion repair is regulated. We investigate the role of AID-interacting GANP (germinal center-associated nuclear protein) in the IgV SHM profile. GANP enhances transition mutation of the non-transcribed strand G and reduces mutation at A, restricted to GYW of the AID hotspot motif. It reduces DNA polymerase η hotspot mutations associated with MMRs followed by uracil-DNA glycosylase. Mutation comparison between IgV complementary and framework regions (FWRs) by Bayesian statistical estimation demonstrates that GANP supports the preservation of IgV FWR genomic sequences. GANP works to maintain antibody structure by reducing drastic changes in the IgV FWR in affinity maturation.
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Affiliation(s)
| | - Mayuko Shimoda
- Department of Immunology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan.,Laboratory of Host Defense, World Premier International Research Center Initiative (WPI) Immunology Frontier Research Center (IFReC).,Department of Host Defense, Research Institute for Microbial Diseases (RIMD), Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Shailendra Kumar Singh
- Laboratory of Host Defense, World Premier International Research Center Initiative (WPI) Immunology Frontier Research Center (IFReC)
| | - Sarah Ameen Almofty
- Laboratory of Immunology, Institute for Research and Medical Consultations (IRMC), University Of Dammam (UOD), PO Box 1982, Dammam 31441, Saudi Arabia
| | - Phuong Pham
- Departments of Biological Sciences and Chemistry, University of Southern California, 1050 Childs Way, University Park, Los Angeles, CA 90089-2910, USA
| | - Myron F Goodman
- Departments of Biological Sciences and Chemistry, University of Southern California, 1050 Childs Way, University Park, Los Angeles, CA 90089-2910, USA
| | - Kazuhiko Maeda
- Laboratory of Host Defense, World Premier International Research Center Initiative (WPI) Immunology Frontier Research Center (IFReC).,Department of Host Defense, Research Institute for Microbial Diseases (RIMD), Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Nobuo Sakaguchi
- World Premier International Research Center Initiative (WPI) Immunology Frontier Research Center, Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan.,Tokyo Metropolitan Institute of Medical Science, 2-1-6, Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan
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Wright BE, Schmidt KH, Minnick MF. Kinetic models reveal the in vivo mechanisms of mutagenesis in microbes and man. Mutat Res 2013; 752:129-137. [PMID: 23274173 PMCID: PMC3631585 DOI: 10.1016/j.mrrev.2012.12.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Revised: 12/14/2012] [Accepted: 12/18/2012] [Indexed: 06/01/2023]
Abstract
This review summarizes the evidence indicating that mutagenic mechanisms in vivo are essentially the same in all living cells. Unique metabolic reactions to a particular environmental stress apparently target specific genes for increased rates of transcription and mutation, resulting in higher mutation rates for those genes most likely to solve the problem. Kinetic models which have demonstrated predictive value are described and are shown to simulate mutagenesis in vivo in Escherichia coli, the p53 tumor suppressor gene, and somatic hypermutation. In all three models, direct correlations are seen between mutation frequencies and transcription rates. G and C nucleosides in single-stranded DNA (ssDNA) are intrinsically mutable, and G and C silent mutations in p53 and in VH framework regions provide compelling evidence for intrinsic mechanisms of mutability, since mutation outcomes are neutral and are not selected. During transcription, the availability of unpaired bases in the ssDNA of secondary structures is rate-limiting for, and determines the frequency of mutations in vivo. In vitro analyses also verify the conclusion that intrinsically mutable bases are in fact located in ssDNA loops of predicted stem-loop structures (SLSs).
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Affiliation(s)
- Barbara E Wright
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, United States.
| | - Karen H Schmidt
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, United States
| | - Michael F Minnick
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, United States
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Duvvuri B, Wu GE. Gene Conversion-Like Events in the Diversification of Human Rearranged IGHV3-23*01 Gene Sequences. Front Immunol 2012; 3:158. [PMID: 22715339 PMCID: PMC3375636 DOI: 10.3389/fimmu.2012.00158] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Accepted: 05/25/2012] [Indexed: 11/13/2022] Open
Abstract
Gene conversion (GCV), a mechanism mediated by activation-induced cytidine deaminase (AID) is well established as a mechanism of immunoglobulin diversification in a few species. However, definitive evidence of GCV-like events in human immunoglobulin genes is scarce. The lack of evidence of GCV in human rearranged immunoglobulin gene sequences is puzzling given the presence of highly similar germline donors and the presence of all the enzymatic machinery required for GCV. In this study, we undertook a computational analysis of rearranged IGHV3-23(*)01 gene sequences from common variable immunodeficiency (CVID) patients, AID-deficient patients, and healthy individuals to survey "GCV-like" activities. We analyzed rearranged IGHV3-23(*)01 gene sequences obtained from total PBMC RNA and single-cell polymerase chain reaction of individual B cell lysates. Our search identified strong evidence of GCV-like activity. We observed that GCV-like tracts are flanked by AID hotspot motifs. Structural modeling of IGHV3-23(*)01 gene sequence revealed that hypermutable bases flanking GCV-like tracts are in the single stranded DNA (ssDNA) of stable stem-loop structures (SLSs). ssDNA is inherently fragile and also an optimal target for AID. We speculate that GCV could have been initiated by the targeting of hypermutable bases in ssDNA state in stable SLSs, plausibly by AID. We have observed that the frequency of GCV-like events is significantly higher in rearranged IGHV3-23-(*)01 sequences from healthy individuals compared to that of CVID patients. We did not observe GCV-like events in rearranged IGHV3-23-(*)01 sequences from AID-deficient patients. GCV, unlike somatic hypermutation (SHM), can result in multiple base substitutions that can alter many amino acids. The extensive changes in antibody affinity by GCV-like events would be instrumental in protecting humans against pathogens that diversify their genome by antigenic shift.
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Affiliation(s)
- Bhargavi Duvvuri
- School of Kinesiology and Health Science, Faculty of Health, York UniversityToronto, ON, Canada
| | - Gillian E. Wu
- School of Kinesiology and Health Science, Faculty of Health, York UniversityToronto, ON, Canada
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Duvvuri B, Duvvuri VR, Wu J, Wu GE. Stabilised DNA secondary structures with increasing transcription localise hypermutable bases for somatic hypermutation in IGHV3-23. Immunogenetics 2012; 64:481-96. [PMID: 22391874 DOI: 10.1007/s00251-012-0607-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Accepted: 02/07/2012] [Indexed: 12/22/2022]
Abstract
Somatic hypermutation (SHM) mediated by activation-induced cytidine deaminase (AID) is a transcription-coupled mechanism most responsible for generating high affinity antibodies. An issue remaining enigmatic in SHM is how AID is preferentially targeted during transcription to hypermutable bases in its substrates (WRC motifs) on both DNA strands. AID targets only single stranded DNA. By modelling the dynamical behaviour of IGHV3-23 DNA, a commonly used human variable gene segment, we observed that hypermutable bases on the non-transcribed strand are paired whereas those on transcribed strand are mostly unpaired. Hypermutable bases (both paired and unpaired) are made accessible to AID in stabilised secondary structures formed with increasing transcription levels. This observation provides a rationale for the hypermutable bases on both the strands of DNA being targeted to a similar extent despite having differences in unpairedness. We propose that increasing transcription and RNAP II stalling resulting in the formation and stabilisation of stem-loop structures with AID hotspots in negatively supercoiled region can localise the hypermutable bases of both strands of DNA, to AID-mediated SHM.
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Affiliation(s)
- Bhargavi Duvvuri
- School of Kinesiology & Health Science, Faculty of Health, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada.
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