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Mu Y, Chen Z, Plummer JB, Zelazowska MA, Dong Q, Krug LT, McBride KM. UNG-RPA interaction governs the choice between high-fidelity and mutagenic uracil repair. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.30.591927. [PMID: 38746347 PMCID: PMC11092621 DOI: 10.1101/2024.04.30.591927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Mammalian Uracil DNA glycosylase (UNG) removes uracils and initiates high-fidelity base excision repair to maintain genomic stability. During B cell development, activation-induced cytidine deaminase (AID) creates uracils that UNG processes in an error-prone fashion to accomplish immunoglobulin (Ig) somatic hypermutation (SHM) or class switch recombination (CSR). The mechanism that governs high-fidelity versus mutagenic uracil repair is not understood. The B cell tropic gammaherpesvirus (GHV) encodes a functional homolog of UNG that can process AID induced genomic uracils. GHVUNG does not support hypermutation, suggesting intrinsic properties of UNG influence repair outcome. Noting the structural divergence between the UNGs, we define the RPA interacting motif as the determinant of mutation outcome. UNG or RPA mutants unable to interact with each other, only support high-fidelity repair. In B cells, transversions at the Ig variable region are abated while CSR is supported. Thus UNG-RPA governs the generation of mutations and has implications for locus specific mutagenesis in B cells and deamination associated mutational signatures in cancer.
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2
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Safra M, Werner L, Peres A, Polak P, Salamon N, Schvimer M, Weiss B, Barshack I, Shouval DS, Yaari G. A somatic hypermutation-based machine learning model stratifies individuals with Crohn's disease and controls. Genome Res 2023; 33:71-79. [PMID: 36526432 PMCID: PMC9977146 DOI: 10.1101/gr.276683.122] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Accepted: 12/07/2022] [Indexed: 12/23/2022]
Abstract
Crohn's disease (CD) is a chronic relapsing-remitting inflammatory disorder of the gastrointestinal tract that is characterized by altered innate and adaptive immune function. Although massively parallel sequencing studies of the T cell receptor repertoire identified oligoclonal expansion of unique clones, much less is known about the B cell receptor (BCR) repertoire in CD. Here, we present a novel BCR repertoire sequencing data set from ileal biopsies from pediatric patients with CD and controls, and identify CD-specific somatic hypermutation (SHM) patterns, revealed by a machine learning (ML) algorithm trained on BCR repertoire sequences. Moreover, ML classification of a different data set from blood samples of adults with CD versus controls identified that V gene usage, clusters, or mutation frequencies yielded excellent results in classifying the disease (F1 > 90%). In summary, we show that an ML algorithm enables the classification of CD based on unique BCR repertoire features with high accuracy.
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Affiliation(s)
- Modi Safra
- The Alexander Kofkin Faculty of Engineering, Bar Ilan University, 5290002, Ramat Gan, Israel;,Bar Ilan Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
| | - Lael Werner
- Institute of Gastroenterology, Nutrition and Liver Diseases, Schneider Children's Medical Center of Israel, Petah Tikva 4920235, Israel;,Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Ayelet Peres
- The Alexander Kofkin Faculty of Engineering, Bar Ilan University, 5290002, Ramat Gan, Israel;,Bar Ilan Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
| | - Pazit Polak
- The Alexander Kofkin Faculty of Engineering, Bar Ilan University, 5290002, Ramat Gan, Israel;,Bar Ilan Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
| | - Naomi Salamon
- Pediatric Gastroenterology Unit, Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Ramat Gan 5262100, Israel
| | - Michael Schvimer
- Institute of Pathology, Sheba Medical Center, Ramat Gan 5262100, Israel
| | - Batia Weiss
- Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel;,Pediatric Gastroenterology Unit, Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Ramat Gan 5262100, Israel
| | - Iris Barshack
- Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel;,Institute of Pathology, Sheba Medical Center, Ramat Gan 5262100, Israel
| | - Dror S. Shouval
- Institute of Gastroenterology, Nutrition and Liver Diseases, Schneider Children's Medical Center of Israel, Petah Tikva 4920235, Israel;,Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Gur Yaari
- The Alexander Kofkin Faculty of Engineering, Bar Ilan University, 5290002, Ramat Gan, Israel;,Bar Ilan Institute of Nanotechnology and Advanced Materials, Bar Ilan University, 5290002, Ramat Gan, Israel
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3
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Abstract
Life as we know it, simply would not exist without DNA replication. All living organisms utilize a complex machinery to duplicate their genomes and the central role in this machinery belongs to replicative DNA polymerases, enzymes that are specifically designed to copy DNA. "Hassle-free" DNA duplication exists only in an ideal world, while in real life, it is constantly threatened by a myriad of diverse challenges. Among the most pressing obstacles that replicative polymerases often cannot overcome by themselves are lesions that distort the structure of DNA. Despite elaborate systems that cells utilize to cleanse their genomes of damaged DNA, repair is often incomplete. The persistence of DNA lesions obstructing the cellular replicases can have deleterious consequences. One of the mechanisms allowing cells to complete replication is "Translesion DNA Synthesis (TLS)". TLS is intrinsically error-prone, but apparently, the potential downside of increased mutagenesis is a healthier outcome for the cell than incomplete replication. Although most of the currently identified eukaryotic DNA polymerases have been implicated in TLS, the best characterized are those belonging to the "Y-family" of DNA polymerases (pols η, ι, κ and Rev1), which are thought to play major roles in the TLS of persisting DNA lesions in coordination with the B-family polymerase, pol ζ. In this review, we summarize the unique features of these DNA polymerases by mainly focusing on their biochemical and structural characteristics, as well as potential protein-protein interactions with other critical factors affecting TLS regulation.
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Affiliation(s)
- Alexandra Vaisman
- a Laboratory of Genomic Integrity , National Institute of Child Health and Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Roger Woodgate
- a Laboratory of Genomic Integrity , National Institute of Child Health and Human Development, National Institutes of Health , Bethesda , MD , USA
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4
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van Zelm MC, Bartol SJW, Driessen GJ, Mascart F, Reisli I, Franco JL, Wolska-Kusnierz B, Kanegane H, Boon L, van Dongen JJM, van der Burg M. Human CD19 and CD40L deficiencies impair antibody selection and differentially affect somatic hypermutation. J Allergy Clin Immunol 2014; 134:135-44. [PMID: 24418477 DOI: 10.1016/j.jaci.2013.11.015] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 11/08/2013] [Accepted: 11/08/2013] [Indexed: 10/25/2022]
Abstract
BACKGROUND Individuals with genetic defects in CD40 ligand (CD40L) or B-cell antigen receptor coreceptor molecules CD19 and CD81 suffer from an antibody deficiency. Still, these patients carry low levels of memory B cells and serum antibodies. OBJECTIVE We sought to assess why the remaining memory B cells and antibodies in the blood of these patients do not provide functional immunity. METHODS We included CD19-deficient patients (n = 8), CD40L-deficient patients (n = 8), and healthy controls (n = 50) to perform detailed flow cytometry on blood B cells, molecular analysis of IgA and IgG transcripts, as well as functional analysis of B-cell activation. RESULTS CD19-deficient and CD40L-deficient patients carried reduced numbers of all memory B-cell subsets except CD27(-)IgA(+) B cells. Their immunoglobulin heavy chain class-switched transcripts contained less somatic mutations and reduced usage of IgM-distal IgG2 and IgA2 subclasses. The selection strength of mutations for antigen binding was significantly lower than in controls, whereas selection to maintain superantigen binding was normal. Furthermore, the patients showed impaired selection against inherently autoreactive properties of their immunoglobulins. Somatic hypermutation analysis revealed decreased activation-induced cytidine deaminase and uracil-DNA glycosylase 2 activity in CD40L deficiency and increased uracil-DNA glycosylase 2 but decreased mismatch repair in CD19 deficiency. B-cell activation studies revealed that this was at least in part due to transcriptional regulation of DNA repair genes. CONCLUSIONS This study on CD19 and CD40L deficiencies illustrates that both the B-cell antigen receptor and CD40 signaling pathways are required for the selection of immunoglobulin reactivity. Still, they differentially mediate DNA repair pathways during somatic hypermutation, thereby together shaping the human in vivo antigen-experienced B-cell repertoire.
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Affiliation(s)
- Menno C van Zelm
- Department of Immunology, Erasmus MC, Rotterdam, The Netherlands.
| | | | - Gertjan J Driessen
- Department of Immunology, Erasmus MC, Rotterdam, The Netherlands; Department of Pediatrics, Erasmus MC, Rotterdam, The Netherlands
| | - Françoise Mascart
- Immunobiology Clinic, Hôpital Erasme, and Laboratory of Vaccinology and Mucosal Immunity, Université Libre de Bruxelles, Brussels, Belgium
| | - Ismail Reisli
- Meram Medical Faculty, Department of Pediatric Immunology and Allergy, Necmettin Erbakan University, Konya, Turkey
| | - Jose L Franco
- Group of Primary Immunodeficiencies, University of Antioquia, Medellín, Colombia
| | | | - Hirokazu Kanegane
- Department of Pediatrics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan
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Zhou W, Chen YW, Liu X, Chu P, Loria S, Wang Y, Yen Y, Chou KM. Expression of DNA translesion synthesis polymerase η in head and neck squamous cell cancer predicts resistance to gemcitabine and cisplatin-based chemotherapy. PLoS One 2013; 8:e83978. [PMID: 24376779 PMCID: PMC3869838 DOI: 10.1371/journal.pone.0083978] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 11/11/2013] [Indexed: 01/16/2023] Open
Abstract
Purpose The development of resistance against anticancer drugs has been a persistent clinical problem for the treatment of locally advanced malignancies in the head and neck mucosal derived squamous cell carcinoma (HNSCC). Recent evidence indicates that the DNA translesion synthesis (TLS) polymerase η (Pol η; hRad30a gene) reduces the effectiveness of gemcitabine/cisplatin. The goal of this study is to examine the relationship between the expression level of Pol η and the observed resistance against these chemotherapeutic agents in HNSCC, which is currently unknown. Methods Sixty-four mucosal derived squamous cell carcinomas of head and neck (HNSCC) from 1989 and 2007 at the City of Hope National Medical Center (Duarte, CA) were retrospectively analyzed. Pretreatment samples were immunostained with anti-Pol η antibody and the correlation between the expression level of Pol η and clinical outcomes were evaluated. Forty-nine cases treated with platinum (n=40) or gemcitabine (n=9) based chemotherapy were further examined for Pol η expression level for comparison with patient response to chemotherapy. Results The expression of Pol η was elevated in 67% of the head and neck tumor samples. Pol η expression level was significantly higher in grade 1 to grade 2 tumors (well to moderately differentiated). The overall benefit rate (complete response+ partial response) in patients treated with platinum and gemcitabine based chemotherapy was 79.5%, where low Pol η level was significantly associated with high complete response rate (p=0.03), although not associated with overall survival. Furthermore, no significant correlation was observed between Pol η expression level with gender, age, tobacco/alcohol history, tumor stage and metastatic status. Conclusions Our data suggest that Pol η expression may be a useful prediction marker for the effectiveness of platinum or gemcitabine based therapy for HNSCC.
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Affiliation(s)
- Wendi Zhou
- Department of Pathology, St. Luke’s-Roosevelt Hospital Center, Affiliated Hospital of Columbia University College of Physicians and Surgeons, New York, New York, United States of America
| | - Yih-wen Chen
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
| | - Xiyong Liu
- Department of Molecular Pharmacology, Beckman Research Institute of the City of Hope National Medical Center, Duarte, California, United States of America
| | - Peiguo Chu
- Department of Pathology, City of Hope Comprehensive Cancer Center, Duarte, California, United States of America
| | - Sofia Loria
- Department of Pathology, City of Hope Comprehensive Cancer Center, Duarte, California, United States of America
| | - Yafan Wang
- Department of Molecular Pharmacology, Beckman Research Institute of the City of Hope National Medical Center, Duarte, California, United States of America
| | - Yun Yen
- Department of Molecular Pharmacology, Beckman Research Institute of the City of Hope National Medical Center, Duarte, California, United States of America
- * E-mail: (KMC); (YY)
| | - Kai-Ming Chou
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
- * E-mail: (KMC); (YY)
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Mechanism of somatic hypermutation at the WA motif by human DNA polymerase η. Proc Natl Acad Sci U S A 2013; 110:8146-51. [PMID: 23630267 DOI: 10.1073/pnas.1303126110] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Somatic hypermutation is programmed base substitutions in the variable regions of Ig genes for high-affinity antibody generation. Two motifs, RGYW and WA (R, purine; Y, pyrimidine; W, A or T), have been found to be somatic hypermutation hotspots. Overwhelming evidence suggests that DNA polymerase η (Pol η) is responsible for converting the WA motif to WG by misincorporating dGTP opposite the templating T. To elucidate the molecular mechanism, crystal structures and kinetics of human Pol η substituting dGTP for dATP in four sequence contexts, TA, AA, GA, and CA, have been determined and compared. The T:dGTP wobble base pair is stabilized by Gln-38 and Arg-61, two uniquely conserved residues among Pol η. Weak base paring of the W (T:A or A:T) at the primer end and their distinct interactions with Pol η lead to misincorporation of G in the WA motif. Between two WA motifs, our kinetic and structural data indicate that A-to-G mutation occurs more readily in the TA context than AA. Finally, Pol η can extend the T:G mispair efficiently to complete the mutagenesis.
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Sun Y, Wang C, Wang Y, Zhang T, Ren L, Hu X, Zhang R, Meng Q, Guo Y, Fei J, Li N, Zhao Y. A comprehensive analysis of germline and expressed immunoglobulin repertoire in the horse. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2010; 34:1009-1020. [PMID: 20466019 DOI: 10.1016/j.dci.2010.05.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Revised: 05/02/2010] [Accepted: 05/03/2010] [Indexed: 05/29/2023]
Abstract
Based on the recently released horse genome, we have characterized the genomic organization of the horse Ig gene loci. The horse IgH locus in genomic scaffold Un0011 contains 40 D(H) segments, 8 J(H) segments and 50 V(H) segments. The Igkappa locus contains only a single C(kappa) gene, 5 J(kappa) segments and a 60 V(kappa) segments, whereas the Iglambda locus contains 7 C(lambda) genes each preceded by a J(lambda) gene segment. A total of 110 V(lambda) segments with the same transcriptional polarity as J(lambda)-C(lambda) were identified upstream of the J(lambda)-C(lambda) cluster. However, 34 V(lambda) segments locating downstream of the J(lambda)-C(lambda) cluster showed an opposite transcriptional polarity. Our results reveal that the horse germline V repertoires were more complex than previously estimated. By analyzing the cloned IgH/L cDNA, we further showed that several selected V subgroups were utilized in the expressed V(H), V(kappa), or V(lambda) and a high frequency of nucleotide deletions and insertions were introduced by somatic hypermutation in these expressed V genes.
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Affiliation(s)
- Yi Sun
- State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
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8
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Steele EJ. Mechanism of somatic hypermutation: critical analysis of strand biased mutation signatures at A:T and G:C base pairs. Mol Immunol 2008; 46:305-20. [PMID: 19062097 DOI: 10.1016/j.molimm.2008.10.021] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 10/14/2008] [Indexed: 12/17/2022]
Abstract
The DNA sequence data of the somatic hypermutation (SHM) field published since 1984 has been critically reviewed. The analysis has revealed three strand biased mutation signatures. The first concerns the mutations generated at G:C base pairs in mice genetically deficient in uracil-DNA glycosylase and MSH2-MSH6-mediated mismatch repair. Such mice display the AID deaminase footprint and here C mutations exceed G mutations at least 1.5-fold. This supports earlier and more recent studies claiming that dC-to-dU deaminations occur preferentially in the single stranded DNA regions of the displaced nontranscribed strand (NTS) during transcription. The second concerns the signature generated in immunised mice where G mutations exceed C mutations by at least 1.7-fold. This is a newly identified strand bias which has previously gone undetected. It is consistent with the polynucleotide polymerisation signature of RNA polymerase II copying the template DNA strand carrying AID-mediated lesions generated at C bases, viz. uracils and abasic sites. A reverse transcription step would then need to intervene to fix the mutation pattern in DNA. The third concerns the long recognised strand biased signature generated in normal aged or actively immunised mice whereby A mutations exceed T mutations by two- to three-fold. It is argued that this pattern is best understood as a combination of adenosine-to-inosine (A-to-I) RNA editing followed by a reverse transcription step fixing the A-to-G, as well as A-to-T and A-to-C, as strand biased mutation signatures in DNA. The reasons why the AID-linked RNA polymerase II mutation signature had previously gone undetected are discussed with regard to limitations of standard PCR-based SHM assay techniques. It is concluded that the most economical SHM mechanism involves both DNA and RNA deaminations coupled to a reverse transcription process, most likely involving DNA polymerase eta acting in its reverse transcriptase mode. Experimental approaches to differentiate this RNA-based model from the standard DNA deamination model are discussed.
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Affiliation(s)
- Edward J Steele
- Genomic Interactions Group and CILR, Research School of Biological Sciences, The Institute of Advanced Studies, Australian National University, Canberra, ACT 2601, Australia.
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9
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Cleaver JE. Historical Aspects of Xeroderma Pigmentosum and Nucleotide Excision Repair. MOLECULAR MECHANISMS OF XERODERMA PIGMENTOSUM 2008; 637:1-9. [DOI: 10.1007/978-0-387-09599-8_1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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10
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Analysis of somatic hypermutation in X-linked hyper-IgM syndrome shows specific deficiencies in mutational targeting. Blood 2008; 113:3706-15. [PMID: 19023113 DOI: 10.1182/blood-2008-10-183632] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Subjects with X-linked hyper-IgM syndrome (X-HIgM) have a markedly reduced frequency of CD27(+) memory B cells, and their Ig genes have a low level of somatic hypermutation (SHM). To analyze the nature of SHM in X-HIgM, we sequenced 209 nonproductive and 926 productive Ig heavy chain genes. In nonproductive rearrangements that were not subjected to selection, as well as productive rearrangements, most of the mutations were within targeted RGYW, WRCY, WA, or TW motifs (R = purine, Y = pyrimidine, and W = A or T). However, there was significantly decreased targeting of the hypermutable G in RGYW motifs. Moreover, the ratio of transitions to transversions was markedly increased compared with normal. Microarray analysis documented that specific genes involved in SHM, including activation-induced cytidine deaminase (AICDA) and uracil-DNA glycosylase (UNG2), were up-regulated in normal germinal center (GC) B cells, but not induced by CD40 ligation. Similar results were obtained from light chain rearrangements. These results indicate that in the absence of CD40-CD154 interactions, there is a marked reduction in SHM and, specifically, mutations of AICDA-targeted G residues in RGYW motifs along with a decrease in transversions normally related to UNG2 activity.
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Longo NS, Satorius CL, Plebani A, Durandy A, Lipsky PE. Characterization of Ig gene somatic hypermutation in the absence of activation-induced cytidine deaminase. THE JOURNAL OF IMMUNOLOGY 2008; 181:1299-306. [PMID: 18606684 DOI: 10.4049/jimmunol.181.2.1299] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Somatic hypermutation (SHM) of Ig genes depends upon the deamination of C nucleotides in WRCY (W = A/T, R = A/G, Y = C/T) motifs by activation-induced cytidine deaminase (AICDA). Despite this, a large number of mutations occur in WA motifs that can be accounted for by the activity of polymerase eta (POL eta). To determine whether there are AICDA-independent mutations and to characterize the relationship between AICDA- and POL eta-mediated mutations, 1470 H chain and 1313 kappa- and lambda-chain rearrangements from three AICDA(-/-) patients were analyzed. The Ig mutation frequency of all V(H) genes from AICDA(-/-) patients was 40-fold less than that of normal donors, whereas the mutation frequency of mutated V(H) sequences from AICDA(-/-) patients was 6.8-fold less than that of normal donors. AICDA(-/-) B cells lack mutations in WRCY/RGYW motifs as well as replacement mutations and mutational targeting in complementarity-determining regions. A significantly reduced mutation frequency in WA motifs compared with normal donors and an increased percentage of transitions, which may relate to reduced uracil DNA-glycosylase activity, suggest a role for AICDA in regulating POL eta and uracil DNA-glycosylase activity. Similar results were observed in V(L) rearrangements. The residual mutations were predominantly G:C substitutions, indicating that AICDA-independent cytidine deamination was a likely, yet inefficient, mechanism for mutating Ig genes.
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Affiliation(s)
- Nancy S Longo
- Autoimmunity Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, MD 20892, USA
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12
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Abstract
Xeroderma pigmentosum-variant (XP-V) patients have sun sensitivity and increased skin cancer risk. Their cells have normal nucleotide excision repair, but have defects in the POLH gene encoding an error-prone polymerase, DNA polymerase eta (pol eta). To survey the molecular basis of XP-V worldwide, we measured pol eta protein in skin fibroblasts from putative XP-V patients (aged 8-66 years) from 10 families in North America, Turkey, Israel, Germany, and Korea. Pol eta was undetectable in cells from patients in eight families, whereas two showed faint bands. DNA sequencing identified 10 different POLH mutations. There were two splicing, one nonsense, five frameshift (3 deletion and 2 insertion), and two missense mutations. Nine of these mutations involved the catalytic domain. Although affected siblings had similar clinical features, the relation between the clinical features and the mutations was not clear. POLH mRNA levels were normal or reduced by 50% in three cell strains with undetectable levels of pol eta protein, indicating that nonsense-mediated message decay was limited. We found a wide spectrum of mutations in the POLH gene among XP-V patients in different countries, suggesting that many of these mutations arose independently.
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13
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Cook AJL, Raftery JM, Lau KKE, Jessup A, Harris RS, Takeda S, Jolly CJ. DNA-dependent protein kinase inhibits AID-induced antibody gene conversion. PLoS Biol 2007; 5:e80. [PMID: 17355182 PMCID: PMC1820612 DOI: 10.1371/journal.pbio.0050080] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2006] [Accepted: 01/18/2007] [Indexed: 11/19/2022] Open
Abstract
Affinity maturation and class switching of antibodies requires activation-induced cytidine deaminase (AID)-dependent hypermutation of Ig V(D)J rearrangements and Ig S regions, respectively, in activated B cells. AID deaminates deoxycytidine bases in Ig genes, converting them into deoxyuridines. In V(D)J regions, subsequent excision of the deaminated bases by uracil-DNA glycosylase, or by mismatch repair, leads to further point mutation or gene conversion, depending on the species. In Ig S regions, nicking at the abasic sites produced by AID and uracil-DNA glycosylases results in staggered double-strand breaks, whose repair by nonhomologous end joining mediates Ig class switching. We have tested whether nonhomologous end joining also plays a role in V(D)J hypermutation using chicken DT40 cells deficient for Ku70 or the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Inactivation of the Ku70 or DNA-PKcs genes in DT40 cells elevated the rate of AID-induced gene conversion as much as 5-fold. Furthermore, DNA-PKcs-deficiency appeared to reduce point mutation. The data provide strong evidence that double-strand DNA ends capable of recruiting the DNA-dependent protein kinase complex are important intermediates in Ig V gene conversion.
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Affiliation(s)
- Adam J. L Cook
- Centenary Institute and University of Sydney Faculty of Medicine, Sydney, New South Wales, Australia
| | - Joanna M Raftery
- Centenary Institute and University of Sydney Faculty of Medicine, Sydney, New South Wales, Australia
| | - K. K. Edwin Lau
- Centenary Institute and University of Sydney Faculty of Medicine, Sydney, New South Wales, Australia
| | - Andrew Jessup
- Centenary Institute and University of Sydney Faculty of Medicine, Sydney, New South Wales, Australia
| | - Reuben S Harris
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
- Institute for Molecular Virology, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Shunichi Takeda
- Department of Radiation Genetics, Kyoto University School of Medicine, Kyoto, Japan
| | - Christopher J Jolly
- Centenary Institute and University of Sydney Faculty of Medicine, Sydney, New South Wales, Australia
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14
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Pan-Hammarström Q, Zhao Y, Hammarström L. Class switch recombination: a comparison between mouse and human. Adv Immunol 2007; 93:1-61. [PMID: 17383538 DOI: 10.1016/s0065-2776(06)93001-6] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Humans and mice separated more than 60 million years ago. Since then, evolution has led to a multitude of changes in their genomic sequences. The divergence of genes has resulted in differences both in the innate and adaptive immune systems. In this chapter, we focus on species difference with regard to immunoglobulin class switch recombination (CSR). We have compared the immunoglobulin constant region gene loci from human and mouse, with an emphasis on the switch regions, germ line transcription promoters, and 3' enhancers. We have also compared pathways/factors that are involved in CSR. Although there are remarkable similarities in the cellular machinery involved in CSR, there are also a number of unique features in each species.
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Affiliation(s)
- Qiang Pan-Hammarström
- Department of Laboratory Medicine, Division of Clinical Immunology, Karolinska University Hospital Huddinge, SE-14186 Stockholm, Sweden
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15
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Högerkorp CM, Borrebaeck CAK. The human CD77- B cell population represents a heterogeneous subset of cells comprising centroblasts, centrocytes, and plasmablasts, prompting phenotypical revision. THE JOURNAL OF IMMUNOLOGY 2006; 177:4341-9. [PMID: 16982868 DOI: 10.4049/jimmunol.177.7.4341] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The process of becoming an Ig-producing plasma cell takes the mature B cell through the germinal center, where Ig genes are diversified through somatic hypermutation and class switch recombination. To more clearly define functional characteristics of the germinal center dark zone centroblasts and the light zone centrocytes, we have performed expression analysis of the CD77(+) and CD77(-) populations, because CD77 has been accepted as a discriminator of centroblasts and centrocytes. Our results demonstrated that the CD77(+) and the CD77(-) populations lack functional associated expression programs discriminating the two populations. Both populations are shown to be actively cycling and to share common features associated with cell cycle regulation and DNA maintenance. They are also shown to have an equally active DNA repair program, as well as components involved in somatic hypermutation and class switch recombination. Moreover, the data also demonstrated that the CD77(-) population comprises cells with an already initiated plasma cell differentiation program. Together this demonstrates that CD77 does not discriminate centroblasts and centrocytes and that the CD77(-) population represents a heterogeneous subset of cells, comprising centroblasts, centrocytes, and plasmablast.
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16
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Spencer J, Dunn-Walters DK. Hypermutation at A-T base pairs: the A nucleotide replacement spectrum is affected by adjacent nucleotides and there is no reverse complementarity of sequences flanking mutated A and T nucleotides. THE JOURNAL OF IMMUNOLOGY 2005; 175:5170-7. [PMID: 16210621 DOI: 10.4049/jimmunol.175.8.5170] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Hypermutation is thought to be a two-phase process. The first phase is via the action of activation-induced cytidine deaminase (AID), which deaminates C nucleotides in WRC motifs. This results in the RGYW/WRCY hot spot motifs for mutation from G and C observed in vivo. The resemblance between the hot spot for C mutations and the reverse complement of that for G mutations implies a process acting equally on both strands of DNA. The second phase of hypermutation generates mutations from A and T and exhibits strand bias, with more mutations from A than T. Although this does not concur with the idea of one mechanism acting equally on both strands, it has been suggested that the AT mutator also has a reversible motif; WA/TW. We show here that the motifs surrounding the different substitutions from A vary significantly; there is no single targeting motif for all A mutations. Sequence preferences associated with mutations from A more likely reflect an influence of adjacent nucleotides over what the A mutates "to." This influence tends toward "like" replacements: Purines (A or G) in the 5' position bias toward replacement by another purine (G), whereas replacement with pyrimidines (C or T) is more likely if the preceding base is also a pyrimidine. There is no reverse complementarity in these observations, in that similar influences of nucleotides adjacent to T are not seen. Hence, WA and TW should not be considered as reverse complement hot spot motifs for A and T mutations.
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Affiliation(s)
- Jo Spencer
- Department of Immunobiology, King's College London School of Medicine at Guy's, King's, United Kingdom
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17
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Zan H, Shima N, Xu Z, Al-Qahtani A, Evinger III AJ, Zhong Y, Schimenti JC, Casali P. The translesion DNA polymerase theta plays a dominant role in immunoglobulin gene somatic hypermutation. EMBO J 2005; 24:3757-69. [PMID: 16222339 PMCID: PMC1276717 DOI: 10.1038/sj.emboj.7600833] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Accepted: 09/12/2005] [Indexed: 11/08/2022] Open
Abstract
Immunoglobulin (Ig) somatic hypermutation (SHM) critically underlies the generation of high-affinity antibodies. Mutations can be introduced by error-prone polymerases such as polymerase zeta (Rev3), a mispair extender, and polymerase eta, a mispair inserter with a preference for dA/dT, while repairing DNA lesions initiated by AID-mediated deamination of dC to yield dU:dG mismatches. The partial impairment of SHM observed in the absence of these polymerases led us to hypothesize a main role for another translesion DNA polymerase. Here, we show that deletion in C57BL/6J mice of the translesion polymerase theta, which possesses a dual nucleotide mispair inserter-extender function, results in greater than 60% decrease of mutations in antigen-selected V186.2DJ(H) transcripts and greater than 80% decrease in mutations in the Ig H chain intronic J(H)4-iEmu sequence, together with significant alterations in the spectrum of the residual mutations. Thus, polymerase theta plays a dominant role in SHM, possibly by introducing mismatches while bypassing abasic sites generated by UDG-mediated deglycosylation of AID-effected dU, by extending DNA past such abasic sites and by synthesizing DNA during dU:dG mismatch repair.
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Affiliation(s)
- Hong Zan
- Center for Immunology, School of Medicine and School of Biological Sciences, University of California, Irvine, CA, USA
| | - Naoko Shima
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Zhenming Xu
- Center for Immunology, School of Medicine and School of Biological Sciences, University of California, Irvine, CA, USA
| | - Ahmed Al-Qahtani
- Center for Immunology, School of Medicine and School of Biological Sciences, University of California, Irvine, CA, USA
| | - Albert J Evinger III
- Center for Immunology, School of Medicine and School of Biological Sciences, University of California, Irvine, CA, USA
| | - Yuan Zhong
- Center for Immunology, School of Medicine and School of Biological Sciences, University of California, Irvine, CA, USA
| | - John C Schimenti
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Paolo Casali
- Center for Immunology, School of Medicine and School of Biological Sciences, University of California, Irvine, CA, USA
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18
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Gening LV, Kamensky AA, Levitskaya NG, Petrochenkov AN, Poletaeva II, Tarantul VZ. Enhanced Activity of DNA Polymerase Iota in Mouse Brain Cells Is Associated with Aggressiveness. BIOCHEMISTRY (MOSCOW) 2005; 70:1157-62. [PMID: 16271034 DOI: 10.1007/s10541-005-0240-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Recent studies performed with crude extracts of mouse tissues showed that the activity of DNA-polymerase iota (Pol iota) can be detected only in brain and testis extracts. To assess whether the activity of Pol iota is associated with animal behavior, we determined Pol iota activity in brain extracts of mice of two lines sharply differing in aggressiveness (RSB and RLB). We found that Pol iota activity in the mice with aggressive behavior was three times higher than in the less aggressive mice. The possible relationship between the activity of Pol iota and animal behavior is discussed.
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Affiliation(s)
- L V Gening
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, 123182, Russia
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19
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Mayorov VI, Rogozin IB, Adkison LR, Gearhart PJ. DNA polymerase eta contributes to strand bias of mutations of A versus T in immunoglobulin genes. THE JOURNAL OF IMMUNOLOGY 2005; 174:7781-6. [PMID: 15944281 DOI: 10.4049/jimmunol.174.12.7781] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
DNA polymerase (pol) eta participates in hypermutation of A:T bases in Ig genes because humans deficient for the polymerase have fewer substitutions of these bases. To determine whether polymerase eta is also responsible for the well-known preference for mutations of A vs T on the nontranscribed strand, we sequenced variable regions from three patients with xeroderma pigmentosum variant (XP-V) disease, who lack polymerase eta. The frequency of mutations in the intronic region downstream of rearranged J(H)4 gene segments was similar between XP-V and control clones; however, there were fewer mutations of A:T bases and correspondingly more substitutions of C:G bases in the XP-V clones (p < 10(-7)). There was significantly less of a bias for mutations of A compared with T nucleotides in the XP-V clones compared with control clones, whereas the frequencies for mutations of C and G were identical in both groups. An analysis of mutations in the WA sequence motif suggests that polymerase eta generates more mutations of A than T on the nontranscribed strand. This in vivo data from polymerase eta-deficient B cells correlates well with the in vitro specificity of the enzyme. Because polymerase eta inserts more mutations opposite template T than template A, it would generate more substitutions of A on the newly synthesized strand.
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Affiliation(s)
- Vladimir I Mayorov
- Department of Basic Medical Sciences, Mercer University School of Medicine, Macon, GA 31207, USA
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20
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Zheng NY, Wilson K, Jared M, Wilson PC. Intricate targeting of immunoglobulin somatic hypermutation maximizes the efficiency of affinity maturation. ACTA ACUST UNITED AC 2005; 201:1467-78. [PMID: 15867095 PMCID: PMC2213188 DOI: 10.1084/jem.20042483] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
It is believed that immunoglobulin-variable region gene (IgV) somatic hypermutation (SHM) is initiated by activation-induced cytidine deaminase (AID) upon deamination of cytidine to deoxyuracil. Patch-excision repair of these lesions involving error prone DNA polymerases such as polη causes mutations at all base positions. If not repaired, the deaminated nucleotides on the coding and noncoding strands result in C-to-T and G-to-A exchanges, respectively. Herein it is reported that IgV gene evolution has been considerably influenced by the need to accommodate extensive C deaminations and the resulting accumulation of C-to-T and G-to-A exchanges. Although seemingly counterintuitive, the precise placement of C and G nucleotides causes most C-to-T and G-to-A mutations to be silent or conservative. We hypothesize that without intricate positioning of C and G nucleotides the efficiency of affinity maturation would be significantly reduced due to a dominance of replacements caused by C and G transition mutations. The complexity of these evolved biases in codon use are compounded by the precise concomitant hotspot/coldspot targeting of AID activity and Polη errors to maximize SHM in the CDRs and minimize mutations in the FWRs.
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Affiliation(s)
- Nai-Ying Zheng
- Molecular Immunogenetics Program, The Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
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21
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Revy P, Buck D, le Deist F, de Villartay JP. The Repair of DNA Damages/Modifications During the Maturation of the Immune System: Lessons from Human Primary Immunodeficiency Disorders and Animal Models. Adv Immunol 2005; 87:237-95. [PMID: 16102576 DOI: 10.1016/s0065-2776(05)87007-5] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The immune system is the site of various genotoxic stresses that occur during its maturation as well as during immune responses. These DNA lesions/modifications are primarily the consequences of specific physiological processes such as the V(D)J recombination, the immunoglobulin class switch recombination (CSR), and the generation of somatic hypermutations (SHMs) within Ig variable domains. The DNA lesions can be introduced either by specific factors (RAG1 and RAG2 in the case of V(D)J recombination and AID in the case of CSR and SHM) or during the various phases of cellular proliferation and cellular activation. All these DNA lesions are taken care of by the diverse DNA repair machineries of the cell. Several animal models as well as human conditions have established the critical importance of these DNA lesions/modifications and their repair in the physiology of the immune system. Indeed their defects have consequences ranging from immune deficiency to development of immune malignancy. The survey of human pathology has been highly instrumental in the past in identifying key factors involved in the generation of DNA modifications (AID for the Ig CSR and generation of SHM) or the repair of specific DNA damages (Artemis for V(D)J recombination). Defects in factors involved in the cell cycle checkpoints following DNA damage also have deleterious consequences on the immune system. The continuous survey of human diseases characterized by primary immunodeficiency associated with increased sensitivity to ionizing radiation should help identify other important DNA repair factors essential for the development and maintenance of the immune system.
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Affiliation(s)
- Patrick Revy
- Développement Normal et Pathologique du Système Immunitaire, INSERM U429, Hôpital Necker, Paris, France
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22
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Faili A, Aoufouchi S, Weller S, Vuillier F, Stary A, Sarasin A, Reynaud CA, Weill JC. DNA polymerase eta is involved in hypermutation occurring during immunoglobulin class switch recombination. ACTA ACUST UNITED AC 2004; 199:265-70. [PMID: 14734526 PMCID: PMC2211761 DOI: 10.1084/jem.20031831] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Base substitutions, deletions, and duplications are observed at the immunoglobulin locus in DNA sequences involved in class switch recombination (CSR). These mutations are dependent upon activation-induced cytidine deaminase (AID) and present all the characteristics of the ones observed during V gene somatic hypermutation, implying that they could be generated by the same mutational complex. It has been proposed, based on the V gene mutation pattern of patients with the cancer-prone xeroderma pigmentosum variant (XP-V) syndrome who are deficient in DNA polymerase η (pol η), that this enzyme could be responsible for a large part of the mutations occurring on A/T bases. Here we show, by analyzing switched memory B cells from two XP-V patients, that pol η is also an A/T mutator during CSR, in both the switch region of tandem repeats as well as upstream of it, thus suggesting that the same error-prone translesional polymerases are involved, together with AID, in both processes.
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Affiliation(s)
- Ahmad Faili
- INSERM U373, Faculté de Médecine Necker-Enfants Malades, Université Paris V, France
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23
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Abstract
Activation-induced cytidine deaminase (AID) is an essential enzyme to regulate class switch recombination (CSR), somatic hypermutation (SHM), and gene conversion (GC). AID is known to be required for DNA cleavage of S regions in CSR. However, its molecular mechanism is a focus of extensive debate. RNA editing hypothesis postulates that AID edits yet unknown mRNA to generate specific endonucleases for CSR and SHM. By contrast, DNA deamination hypothesis assumes that AID deaminates cytosine in DNA, followed by DNA cleavage by base excision repair enzymes. We discuss available evidence for the two proposed models. Recent findings, namely requirement of protein synthesis for DNA breakage and dispensability of U removal activity of uracil DNA glycosylase, force us to reconsider DNA deamination hypothesis.
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Affiliation(s)
- Tasuku Honjo
- Department of Medical Chemistry and Molecular Biology, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-Ku, Kyoto 606-8501, Japan.
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24
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Lähdesmäki A, Taylor AMR, Chrzanowska KH, Pan-Hammarström Q. Delineation of the role of the Mre11 complex in class switch recombination. J Biol Chem 2004; 279:16479-87. [PMID: 14747472 DOI: 10.1074/jbc.m312796200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Class switch recombination (CSR) is a region-specific, transcriptionally regulated, nonhomologous recombinational process that is initiated by activation-induced cytidine deaminase (AID). The initial lesions in the switch (S) regions are processed and resolved, leading to a recombination of the two S regions involved. The mechanism involved in the repair and ligation of the broken DNA ends is however still unclear. Here, we describe that switching is less efficient in cells from patients with Mre11 deficiency (Ataxia-Telangiectasia-like disorder, ATLD) and, more importantly, that the switch recombination junctions resulting from the in vivo switching events are aberrant. There was a trend toward an increased usage of microhomology (> or =4 bp) at the switch junctions in both ATLD and Nijmegen breakage syndrome (NBS) patients. However, the DNA ends were not joined as "perfectly" as those from Ataxia-Telangiectasia (A-T) patients and 1-2 bp mutations or insertions were often observed. In switch junctions from ATLD patients, there were fewer base substitutions due to transitions and, most strikingly, the substitutions that occurred most often in controls, C --> T transitions, never occurred at, or close to, the junctions derived from the ATLD patients. In switch junctions from NBS patients, all base substitutions were observed at the G/C nucleotides, and transitions were preferred. These data suggest that the Mre11-Rad50-Nbs1 complex (Mre11 complex) is involved in the nonhomologous end joining pathway in CSR and that Mre11, Nbs1, and protein mutated in ataxia-telangiectasia (ATM) might have both common and independent roles in this process.
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Affiliation(s)
- Aleksi Lähdesmäki
- Division of Clinical Immunology, Department of Laboratory Medicine, Karolinska Institutet at Huddinge Hospital, SE-14186 Stockholm, Sweden
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25
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Franklin A, Milburn PJ, Blanden RV, Steele EJ. Human DNA polymerase‐η, an A‐T mutator in somatic hypermutation of rearranged immunoglobulin genes, is a reverse transcriptase. Immunol Cell Biol 2004; 82:219-25. [PMID: 15061777 DOI: 10.1046/j.0818-9641.2004.01221.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We have proposed previously that error-prone reverse transcription using pre-mRNA of rearranged immunoglobulin variable (IgV) regions as templates is involved in the antibody diversifying mechanism of somatic hypermutation (SHM). As patients deficient in DNA polymerase-eta exhibit an abnormal spectrum of SHM, we postulated that this recently discovered Y-family polymerase is a reverse transcriptase (RT). This possibility was tested using a product-enhanced RT (PERT) assay that uses a real time PCR step with a fluorescent probe to detect cDNA products of at least 27-37 nucleotides. Human pol-eta and two other Y-family enzymes that are dispensable for SHM, human pols-iota and -kappa, copied a heteropolymeric DNA-primed RNA template in vitro under conditions with substantial excesses of template. Repeated experiments gave highly reproducible results. The RT activity detected using one aliquot of human pol-eta was confirmed using a second sample from an independent source. Human DNA pols-beta and -mu, and T4 DNA polymerase repeatedly demonstrated no RT activity. Pol-eta was the most efficient RT of the Y-family enzymes assayed but was much less efficient than an HIV-RT standard in vitro. It is thus feasible that pol-eta acts as both a RNA- and a DNA-dependent DNA polymerase in SHM in vivo, and that Y-family RT activity participates in other mechanisms of physiological importance.
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Affiliation(s)
- Andrew Franklin
- Division of Immunology and Genetics, John Curtin School of Medical Research, Australian National University, GPO Box 334, Canberra, ACT 2601, Australia.
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26
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Steele EJ, Franklin A, Blanden RV. Genesis of the strand‐biased signature in somatic hypermutation of rearranged immunoglobulin variable genes. Immunol Cell Biol 2004; 82:209-18. [PMID: 15061776 DOI: 10.1046/j.0818-9641.2004.01224.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The history and current development of the reverse transcriptase model of somatic hypermutation (RT-model) is reviewed with particular reference to the genesis of strand-biased mutation signatures in rearranged immunoglobulin variable genes (V(D)J). The recent disagreement in the field as to whether strand bias really exists or not has been critically analysed and the confusion traced to the putative presence, in some mutated V(D)J sequence collections, of polymerase chain reaction (PCR)-recombinant artefacts. Recent analysis of somatic hypermutation in xeroderma pigmentosum variant patients, by the group of PJ Gearhart and others, has established that the Y-family translesion DNA repair enzyme, DNA polymerase eta (eta), is responsible for the striking A-T targeted strand-bias mutation signature seen in all mouse and human collections of somatically mutated V(D)J sequences. This evidence, together with our own recent demonstration that human DNA polymerase eta is a reverse transcriptase, leads to the conclusion that the strand-biased A-T mutation signature is caused either by: (i) error-prone DNA-dependent DNA repair synthesis by pol-eta of single-strand nicks preferentially in the non-transcribed strand; and/or (ii) by error-prone cDNA synthesis of the transcribed strand by pol-eta using the pre-mRNA as the copying template, primed by the nicked transcribed DNA strand, followed by replacement of the original transcribed strand by cDNA. Analysis of the total mutation pattern also suggests that the major transitions observed in SHM (A-->G, C-->T and G-->A) can be explained by known RNA editing mechanisms active on pre-mRNA which are then written into cDNA during synthesis of the transcribed strand by error-prone cellular reverse transcriptases such as pol-eta.
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Affiliation(s)
- Edward J Steele
- Division of Immunology and Genetics, John Curtin School of Medical Research, Australian National University, Canberra, ACT 2601, Australia.
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27
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Abstract
Cells have high-fidelity polymerases whose task is to accurately replicate the genome, and low-fidelity polymerases with specialized functions. Although some of these low-fidelity polymerases are exceptional in their ability to replicate damaged DNA and restore the undamaged sequence, they are error prone on undamaged DNA. In fact, these error-prone polymerases are sometimes used in circumstances where the capacity to make errors has a selective advantage. The mutagenic potential of the error-prone polymerases requires that their expression, activity, and access to undamaged DNA templates be regulated. Here we review these specialized polymerases with an emphasis on their biological roles.
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Affiliation(s)
- Alison J Rattray
- Gene Regulation and Chromosome Biology Laboratory, NCI-Frederick, National Cancer Institute, National Institutes of Health, Frederick, Maryland 21702, USA.
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28
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McDonald JP, Frank EG, Plosky BS, Rogozin IB, Masutani C, Hanaoka F, Woodgate R, Gearhart PJ. 129-derived strains of mice are deficient in DNA polymerase iota and have normal immunoglobulin hypermutation. J Exp Med 2003; 198:635-43. [PMID: 12925679 PMCID: PMC2194173 DOI: 10.1084/jem.20030767] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Recent studies suggest that DNA polymerase eta (poleta) and DNA polymerase iota (poliota) are involved in somatic hypermutation of immunoglobulin variable genes. To test the role of poliota in generating mutations in an animal model, we first characterized the biochemical properties of murine poliota. Like its human counterpart, murine poliota is extremely error-prone when catalyzing synthesis on a variety of DNA templates in vitro. Interestingly, when filling in a 1 base-pair gap, DNA synthesis and subsequent strand displacement was greatest in the presence of both pols iota and eta. Genomic sequence analysis of Poli led to the serendipitous discovery that 129-derived strains of mice have a nonsense codon mutation in exon 2 that abrogates production of poliota. Analysis of hypermutation in variable genes from 129/SvJ (Poli-/-) and C57BL/6J (Poli+/+) mice revealed that the overall frequency and spectrum of mutation were normal in poliota-deficient mice. Thus, either poliota does not participate in hypermutation, or its role is nonessential and can be readily assumed by another low-fidelity polymerase.
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Affiliation(s)
- John P McDonald
- Laboratory of Genomic Integrity, Building 6, Room 1A13, NICHD, NIH, 9000 Rockville Pike, Bethesda, MD 20892-2725, USA.
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29
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Reynaud CA, Aoufouchi S, Faili A, Weill JC. What role for AID: mutator, or assembler of the immunoglobulin mutasome? Nat Immunol 2003; 4:631-8. [PMID: 12830138 DOI: 10.1038/ni0703-631] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Activation-induced cytidine deaminase (AID) has been shown to trigger three mechanisms for diversifying immunoglobulin genes--somatic hypermutation, isotype switch recombination and gene conversion--most probably by initiating cytidine deamination at the immunoglobulin locus. Although this deamination process has been shown to be potentially mutagenic by itself, most of the mutations generated in the physiological hypermutation process seem to be created through the AID-mediated assembly of a mutasome complex involving specific repair activities and error-prone DNA polymerases.
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Affiliation(s)
- Claude-Agnès Reynaud
- INSERM U373, Faculté de Médecine Necker-Enfants Malades, 156 rue de Vaugirard, 75730 Paris Cedex 15, France
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30
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Wu X, Feng J, Komori A, Kim EC, Zan H, Casali P. Immunoglobulin somatic hypermutation: double-strand DNA breaks, AID and error-prone DNA repair. J Clin Immunol 2003; 23:235-46. [PMID: 12959216 PMCID: PMC4624321 DOI: 10.1023/a:1024571714867] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Somatic hypermutation (SHM) is critical for antibody affinity maturation and the generation of memory B cells. Somatic mutations consist mainly of single nucleotide changes with rare insertions and deletions. Such changes would be introduced during error-prone repair of lesions involving single-strand DNA breaks (SSBs) or, more likely, double-strand DNA breaks (DSBs), as DSBs occur exclusively in genes that have the potentials to undergo SHM. In the human, such genes include Ig V, BCL6, and c-MYC. In these germline genes, DSBs are blunt. In rearranged Ig V, BCL6, and translocated c-MYC genes, blunt DSBs are processed to yield resected DNA ends. This process is dependent on the expression of activation-induced cytidine deaminase (AID), which is selectively expressed upon CD40-signaling in hypermutating B cells. CD40-induced and AID-dependent free 5'- and 3'-staggered DNA ends critically channel the repair of DSBs through the homologous recombination (HR) repair pathway. During HR, the modulation of critical translesion DNA polymerases, as signaled by cross-linking of the B cell receptor (BCR) for antigen, leads to the insertions of mismatches, i.e., mutations. The nature of DSBs, the possible roles of AID in the modification of DSBs and that of the translesion DNA polymerases zeta and iota in the subsequent repair process that lead to the insertions of mutations are discussed here within the context of an integrated model of SHM.
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Affiliation(s)
- Xiaoping Wu
- Division of Molecular Immunology, Joan and Sanford I. Weill Medical College and Graduate School of Medical Sciences, Cornell University, New York, USA
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31
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Kunkel TA, Pavlov YI, Bebenek K. Functions of human DNA polymerases eta, kappa and iota suggested by their properties, including fidelity with undamaged DNA templates. DNA Repair (Amst) 2003; 2:135-49. [PMID: 12531385 DOI: 10.1016/s1568-7864(02)00224-0] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Human DNA polymerases eta, kappa and iota are template-dependent, Y-family DNA polymerases that have been implicated in translesion DNA synthesis (TLS) in human cells. Here, we briefly review evidence that these exonuclease-deficient polymerases copy undamaged DNA with very low fidelity and unusual error specificity. Based on the base substitution specificity and other biochemical properties of DNA polymerases eta and iota, we consider the possibility that they participate in specialized DNA transactions that repair damaged DNA and/or generate mutations in the variable regions of immunoglobulin genes.
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Affiliation(s)
- Thomas A Kunkel
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
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