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Hua AB, Sweasy JB. Functional roles and cancer variants of the bifunctional glycosylase NEIL2. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2024; 65 Suppl 1:40-56. [PMID: 37310399 DOI: 10.1002/em.22555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 05/23/2023] [Accepted: 06/08/2023] [Indexed: 06/14/2023]
Abstract
Over 70,000 DNA lesions occur in the cell every day, and the inability to properly repair them can lead to mutations and destabilize the genome, resulting in carcinogenesis. The base excision repair (BER) pathway is critical for maintaining genomic integrity by repairing small base lesions, abasic sites and single-stranded breaks. Monofunctional and bifunctional glycosylases initiate the first step of BER by recognizing and excising specific base lesions, followed by DNA end processing, gap filling, and finally nick sealing. The Nei-like 2 (NEIL2) enzyme is a critical bifunctional DNA glycosylase in BER that preferentially excises cytosine oxidation products and abasic sites from single-stranded, double-stranded, and bubble-structured DNA. NEIL2 has been implicated to have important roles in several cellular functions, including genome maintenance, participation in active demethylation, and modulation of the immune response. Several germline and somatic variants of NEIL2 with altered expression and enzymatic activity have been reported in the literature linking them to cancers. In this review, we provide an overview of NEIL2 cellular functions and summarize current findings on NEIL2 variants and their relationship to cancer.
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Affiliation(s)
- Anh B Hua
- Department of Cellular and Molecular Medicine, University of Arizona Cancer Center, Tucson, Arizona, USA
| | - Joann B Sweasy
- Department of Cellular and Molecular Medicine, University of Arizona Cancer Center, Tucson, Arizona, USA
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2
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Hayran AB, Liabakk NB, Aas PA, Kusnierczyk A, Vågbø CB, Sarno A, Iveland TS, Chawla K, Zahn A, Di Noia JM, Slupphaug G, Kavli B. RPA guides UNG to uracil in ssDNA to facilitate antibody class switching and repair of mutagenic uracil at the replication fork. Nucleic Acids Res 2024; 52:784-800. [PMID: 38000394 PMCID: PMC10810282 DOI: 10.1093/nar/gkad1115] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 10/27/2023] [Accepted: 11/06/2023] [Indexed: 11/26/2023] Open
Abstract
Activation-induced cytidine deaminase (AID) interacts with replication protein A (RPA), the major ssDNA-binding protein, to promote deamination of cytosine to uracil in transcribed immunoglobulin (Ig) genes. Uracil-DNA glycosylase (UNG) acts in concert with AID during Ig diversification. In addition, UNG preserves genome integrity by base-excision repair (BER) in the overall genome. How UNG is regulated to support both mutagenic processing and error-free repair remains unknown. UNG is expressed as two isoforms, UNG1 and UNG2, which both contain an RPA-binding helix that facilitates uracil excision from RPA-coated ssDNA. However, the impact of this interaction in antibody diversification and genome maintenance has not been investigated. Here, we generated B-cell clones with targeted mutations in the UNG RPA-binding motif, and analysed class switch recombination (CSR), mutation frequency (5' Ig Sμ), and genomic uracil in clones representing seven Ung genotypes. We show that the UNG:RPA interaction plays a crucial role in both CSR and repair of AID-induced uracil at the Ig loci. By contrast, the interaction had no significant impact on total genomic uracil levels. Thus, RPA coordinates UNG during CSR and pre-replicative repair of mutagenic uracil in ssDNA but is not essential in post-replicative and canonical BER of uracil in dsDNA.
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Affiliation(s)
- Abdul B Hayran
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Nina B Liabakk
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Per A Aas
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Anna Kusnierczyk
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
- PROMEC - Proteomics and Modomics Experimental Core Facility at NTNU and the Central Norway Regional Health Authority, NO-7491 Trondheim, Norway
| | - Cathrine B Vågbø
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
- PROMEC - Proteomics and Modomics Experimental Core Facility at NTNU and the Central Norway Regional Health Authority, NO-7491 Trondheim, Norway
| | - Antonio Sarno
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Tobias S Iveland
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
- Cancer Clinic, St. Olav's Hospital, Trondheim University Hospital, NO-7006 Trondheim, Norway
| | - Konika Chawla
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
- BioCore - Bioinformatics Core Facility at NTNU and the Central Norway Regional Health Authority, NO-7491 Trondheim, Norway
| | - Astrid Zahn
- Institut de Recherches Cliniques de Montréal, 110 Av des Pins Ouest, Montréal, QC H2W 1R7, Canada
| | - Javier M Di Noia
- Institut de Recherches Cliniques de Montréal, 110 Av des Pins Ouest, Montréal, QC H2W 1R7, Canada
- Département of Médicine, Université de Montréal H3C 3J7 Montréal, Québec, Canada
| | - Geir Slupphaug
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
- PROMEC - Proteomics and Modomics Experimental Core Facility at NTNU and the Central Norway Regional Health Authority, NO-7491 Trondheim, Norway
- Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim University Hospital, NO-7006 Trondheim, Norway
| | - Bodil Kavli
- Department of Clinical and Molecular Medicine, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
- Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim University Hospital, NO-7006 Trondheim, Norway
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3
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Greenwood SN, Kulkarni RS, Mikhail M, Weiser BP. Replication Protein A Enhances Kinetics of Uracil DNA Glycosylase on ssDNA and Across DNA Junctions: Explored with a DNA Repair Complex Produced with SpyCatcher/SpyTag Ligation. Chembiochem 2023; 24:e202200765. [PMID: 36883884 PMCID: PMC10267839 DOI: 10.1002/cbic.202200765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 03/06/2023] [Accepted: 03/08/2023] [Indexed: 03/09/2023]
Abstract
DNA repair proteins participate in extensive protein-protein interactions that promote the formation of DNA repair complexes. To understand how complex formation affects protein function during base excision repair, we used SpyCatcher/SpyTag ligation to produce a covalent complex between human uracil DNA glycosylase (UNG2) and replication protein A (RPA). Our covalent "RPA-Spy-UNG2" complex could identify and excise uracil bases in duplex areas next to ssDNA-dsDNA junctions slightly faster than the wild-type proteins, but this was highly dependent on DNA structure, as the turnover of the RPA-Spy-UNG2 complex slowed at DNA junctions where RPA tightly engaged long ssDNA sections. Conversely, the enzymes preferred uracil sites in ssDNA where RPA strongly enhanced uracil excision by UNG2 regardless of ssDNA length. Finally, RPA was found to promote UNG2 excision of two uracil sites positioned across a ssDNA-dsDNA junction, and dissociation of UNG2 from RPA enhanced this process. Our approach of ligating together RPA and UNG2 to reveal how complex formation affects enzyme function could be applied to examine other assemblies of DNA repair proteins.
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Affiliation(s)
- Sharon N Greenwood
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
| | - Rashmi S Kulkarni
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
| | - Michel Mikhail
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
- Department of Internal Medicine, Newark Beth Israel Medical Center, Newark, NJ 07112, USA
| | - Brian P Weiser
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
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4
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Sadeghalvad M, Rezaei N. Immunodeficiencies. Clin Immunol 2023. [DOI: 10.1016/b978-0-12-818006-8.00004-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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5
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Gullickson P, Xu YW, Niedernhofer LJ, Thompson EL, Yousefzadeh MJ. The Role of DNA Repair in Immunological Diversity: From Molecular Mechanisms to Clinical Ramifications. Front Immunol 2022; 13:834889. [PMID: 35432317 PMCID: PMC9010869 DOI: 10.3389/fimmu.2022.834889] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Accepted: 03/02/2022] [Indexed: 12/18/2022] Open
Abstract
An effective humoral immune response necessitates the generation of diverse and high-affinity antibodies to neutralize pathogens and their products. To generate this assorted immune repertoire, DNA damage is introduced at specific regions of the genome. Purposeful genotoxic insults are needed for the successful completion of multiple immunological diversity processes: V(D)J recombination, class-switch recombination, and somatic hypermutation. These three processes, in concert, yield a broad but highly specific immune response. This review highlights the importance of DNA repair mechanisms involved in each of these processes and the catastrophic diseases that arise from DNA repair deficiencies impacting immune system function. These DNA repair disorders underline not only the importance of maintaining genomic integrity for preventing disease but also for robust adaptive immunity.
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6
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Signal-on/signal-off bead-based assays for the multiplexed monitoring of base excision repair activities by flow cytometry. Anal Bioanal Chem 2022; 414:2029-2040. [DOI: 10.1007/s00216-021-03849-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 12/03/2021] [Accepted: 12/13/2021] [Indexed: 11/01/2022]
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7
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Alexeeva M, Moen MN, Xu XM, Rasmussen A, Leiros I, Kirpekar F, Klungland A, Alsøe L, Nilsen H, Bjelland S. Intrinsic Strand-Incision Activity of Human UNG: Implications for Nick Generation in Immunoglobulin Gene Diversification. Front Immunol 2021; 12:762032. [PMID: 35003074 PMCID: PMC8730318 DOI: 10.3389/fimmu.2021.762032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Accepted: 11/17/2021] [Indexed: 12/05/2022] Open
Abstract
Uracil arises in cellular DNA by cytosine (C) deamination and erroneous replicative incorporation of deoxyuridine monophosphate opposite adenine. The former generates C → thymine transition mutations if uracil is not removed by uracil-DNA glycosylase (UDG) and replaced by C by the base excision repair (BER) pathway. The primary human UDG is hUNG. During immunoglobulin gene diversification in activated B cells, targeted cytosine deamination by activation-induced cytidine deaminase followed by uracil excision by hUNG is important for class switch recombination (CSR) and somatic hypermutation by providing the substrate for DNA double-strand breaks and mutagenesis, respectively. However, considerable uncertainty remains regarding the mechanisms leading to DNA incision following uracil excision: based on the general BER scheme, apurinic/apyrimidinic (AP) endonuclease (APE1 and/or APE2) is believed to generate the strand break by incising the AP site generated by hUNG. We report here that hUNG may incise the DNA backbone subsequent to uracil excision resulting in a 3´-α,β-unsaturated aldehyde designated uracil-DNA incision product (UIP), and a 5´-phosphate. The formation of UIP accords with an elimination (E2) reaction where deprotonation of C2´ occurs via the formation of a C1´ enolate intermediate. UIP is removed from the 3´-end by hAPE1. This shows that the first two steps in uracil BER can be performed by hUNG, which might explain the significant residual CSR activity in cells deficient in APE1 and APE2.
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Affiliation(s)
- Marina Alexeeva
- Department of Chemistry, Bioscience and Environmental Technology, University of Stavanger, Stavanger, Norway
| | - Marivi Nabong Moen
- Department of Chemistry, Bioscience and Environmental Technology, University of Stavanger, Stavanger, Norway
- Department of Microbiology, Oslo University Hospital, Oslo, Norway
| | - Xiang Ming Xu
- Department of Chemistry, Bioscience and Environmental Technology, University of Stavanger, Stavanger, Norway
| | - Anette Rasmussen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Ingar Leiros
- Department of Chemistry, University of Tromsø-The Arctic University of Norway, Tromsø, Norway
| | - Finn Kirpekar
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Arne Klungland
- Department of Microbiology, Oslo University Hospital, Oslo, Norway
| | - Lene Alsøe
- Department of Clinical Molecular Biology, University of Oslo, Oslo, Norway
- Section of Clinical Molecular Biology, Akershus University Hospital, Lørenskog, Norway
| | - Hilde Nilsen
- Department of Clinical Molecular Biology, University of Oslo, Oslo, Norway
- Section of Clinical Molecular Biology, Akershus University Hospital, Lørenskog, Norway
- *Correspondence: Svein Bjelland, ; Hilde Nilsen,
| | - Svein Bjelland
- Department of Chemistry, Bioscience and Environmental Technology, University of Stavanger, Stavanger, Norway
- Section of Clinical Molecular Biology, Akershus University Hospital, Lørenskog, Norway
- *Correspondence: Svein Bjelland, ; Hilde Nilsen,
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8
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Botvinnik A, Shivam P, Smith Y, Sharma G, Olshevsky U, Moshel O, Manevitch Z, Climent N, Oliva H, Britan-Rosich E, Kotler M. APOBEC3G rescues cells from the deleterious effects of DNA damage. FEBS J 2021; 288:6063-6077. [PMID: 33999509 DOI: 10.1111/febs.16025] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2020] [Revised: 04/25/2021] [Accepted: 05/14/2021] [Indexed: 11/30/2022]
Abstract
Human apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like 3G (hA3G), a member of the APOBEC family, was described as an anti-HIV-1 restriction factor, deaminating reverse transcripts of the HIV-1 genome. Several types of cancer cells that express high levels of A3G, such as diffuse large B-cell lymphoma cells and glioblastomas, show enhanced cell survival after ionizing radiation and chemotherapy treatments. Previously, we showed that hA3G promotes (DNA) double-strand breaks repair in cultured cells and rescues transgenic mice from a lethal dose of ionizing radiation. Here, we show that A3G rescues cells from the detrimental effects of DNA damage induced by ultraviolet irradiation and by combined bromodeoxyuridine and ultraviolet treatments. The combined treatments stimulate the synthesis of cellular proteins, which are exclusively associated with A3G expression. These proteins participate mainly in nucleotide excision repair and homologous recombination DNA repair pathways. Our results implicate A3G inhibition as a potential strategy for increasing tumor cell sensitivity to genotoxic treatments.
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Affiliation(s)
- Alexander Botvinnik
- Department of Pathology and Immunology, The Lautenberg Center for Immunology and Cancer Research, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Pushkar Shivam
- Department of Pathology and Immunology, The Lautenberg Center for Immunology and Cancer Research, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Yoav Smith
- Genomic Data Analysis, Hadassah Medical School, Hebrew University, Jerusalem, Israel
| | - Gunjan Sharma
- Department of Pathology and Immunology, The Lautenberg Center for Immunology and Cancer Research, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Udy Olshevsky
- Department of Pathology and Immunology, The Lautenberg Center for Immunology and Cancer Research, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Ofra Moshel
- Core Research Facility, Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Zakhariya Manevitch
- Core Research Facility, Light Microscopy and Image Analysis Laboratory, Hadassah Medical School, Hebrew University, Jerusalem, Israel
| | - Nuria Climent
- Faculty of Medicine, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS)-AIDS Research Group and HIV Vaccine Development in Catalonia (HIVACAT), Hospital Clínic de Barcelona, University of Barcelona, Barcelona, Spain
| | | | - Elena Britan-Rosich
- Department of Pathology and Immunology, The Lautenberg Center for Immunology and Cancer Research, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Moshe Kotler
- Department of Pathology and Immunology, The Lautenberg Center for Immunology and Cancer Research, The Hebrew University Hadassah Medical School, Jerusalem, Israel
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9
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Prasad R, Yen TJ, Bellacosa A. Active DNA demethylation-The epigenetic gatekeeper of development, immunity, and cancer. ADVANCED GENETICS (HOBOKEN, N.J.) 2021; 2:e10033. [PMID: 36618446 PMCID: PMC9744510 DOI: 10.1002/ggn2.10033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 10/16/2020] [Accepted: 10/16/2020] [Indexed: 01/11/2023]
Abstract
DNA methylation is a critical process in the regulation of gene expression with dramatic effects in development and continually expanding roles in oncogenesis. 5-Methylcytosine was once considered to be an inherited and stably repressive epigenetic mark, which can be only removed by passive dilution during multiple rounds of DNA replication. However, in the past two decades, physiologically controlled DNA demethylation and deamination processes have been identified, thereby revealing the function of cytosine methylation as a highly regulated and complex state-not simply a static, inherited signature or binary on-off switch. Alongside these fundamental discoveries, clinical studies over the past decade have revealed the dramatic consequences of aberrant DNA demethylation. In this review we discuss DNA demethylation and deamination in the context of 5-methylcytosine as critical processes for physiological and physiopathological transitions within three states-development, immune maturation, and oncogenic transformation; and we describe the expanding role of DNA demethylating drugs as therapeutic agents in cancer.
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Affiliation(s)
- Rahul Prasad
- Cancer Epigenetics and Cancer Biology Programs, Fox Chase Cancer CenterPhiladelphiaPennsylvaniaUSA
| | - Timothy J. Yen
- Cancer Epigenetics and Cancer Biology Programs, Fox Chase Cancer CenterPhiladelphiaPennsylvaniaUSA
| | - Alfonso Bellacosa
- Cancer Epigenetics and Cancer Biology Programs, Fox Chase Cancer CenterPhiladelphiaPennsylvaniaUSA
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10
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Perkins JL, Zhao L. The N-terminal domain of uracil-DNA glycosylase: Roles for disordered regions. DNA Repair (Amst) 2021; 101:103077. [PMID: 33640758 DOI: 10.1016/j.dnarep.2021.103077] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Accepted: 02/14/2021] [Indexed: 01/10/2023]
Abstract
The presence of uracil in DNA calls for rapid removal facilitated by the uracil-DNA glycosylase superfamily of enzymes, which initiates the base excision repair (BER) pathway. In humans, uracil excision is accomplished primarily by the human uracil-DNA glycosylase (hUNG) enzymes. In addition to BER, hUNG enzymes play a key role in somatic hypermutation to generate antibody diversity. hUNG has several isoforms, with hUNG1 and hUNG2 being the two major isoforms. Both isoforms contain disordered N-terminal domains, which are responsible for a wide range of functions, with minimal direct impact on catalytic efficiency. Subcellular localization of hUNG enzymes is directed by differing N-terminal sequences, with hUNG1 dedicated to mitochondria and hUNG2 dedicated to the nucleus. An alternative isoform of hUNG1 has also been identified to localize to the nucleus in mouse and human cell models. Furthermore, hUNG2 has been observed at replication forks performing both pre- and post-replicative uracil excision to maintain genomic integrity. Replication protein A (RPA) and proliferating cell nuclear antigen (PCNA) are responsible for recruitment to replication forks via protein-protein interactions with the N-terminus of hUNG2. These interactions, along with protein degradation, are regulated by various post-translational modifications within the N-terminal tail, which are primarily cell-cycle dependent. Finally, translocation on DNA is also mediated by interactions between the N-terminus and DNA, which is enhanced under molecular crowding conditions by preventing diffusion events and compacting tail residues. This review summarizes recent research supporting the emerging roles of the N-terminal domain of hUNG.
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Affiliation(s)
- Jacob L Perkins
- Department of Chemistry and Environmental Toxicology Graduate Program, University of California, Riverside, Riverside, CA 92521, United States
| | - Linlin Zhao
- Department of Chemistry and Environmental Toxicology Graduate Program, University of California, Riverside, Riverside, CA 92521, United States.
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11
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Demirdag YY, Gupta S. Update on Infections in Primary Antibody Deficiencies. Front Immunol 2021; 12:634181. [PMID: 33643318 PMCID: PMC7905085 DOI: 10.3389/fimmu.2021.634181] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Accepted: 01/07/2021] [Indexed: 11/14/2022] Open
Abstract
Bacterial respiratory tract infections are the hallmark of primary antibody deficiencies (PADs). Because they are also among the most common infections in healthy individuals, PADs are usually overlooked in these patients. Careful evaluation of the history, including frequency, chronicity, and presence of other infections, would help suspect PADs. This review will focus on infections in relatively common PADs, discussing diagnostic challenges, and some management strategies to prevent infections.
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Affiliation(s)
- Yesim Yilmaz Demirdag
- Division of Basic and Clinical Immunology, Department of Medicine, University of California, Irvine, Irvine, CA, United States
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12
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Stratigopoulou M, van Dam TP, Guikema JEJ. Base Excision Repair in the Immune System: Small DNA Lesions With Big Consequences. Front Immunol 2020; 11:1084. [PMID: 32547565 PMCID: PMC7272602 DOI: 10.3389/fimmu.2020.01084] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Accepted: 05/05/2020] [Indexed: 12/13/2022] Open
Abstract
The integrity of the genome is under constant threat of environmental and endogenous agents that cause DNA damage. Endogenous damage is particularly pervasive, occurring at an estimated rate of 10,000–30,000 per cell/per day, and mostly involves chemical DNA base lesions caused by oxidation, depurination, alkylation, and deamination. The base excision repair (BER) pathway is primary responsible for removing and repairing these small base lesions that would otherwise lead to mutations or DNA breaks during replication. Next to preventing DNA mutations and damage, the BER pathway is also involved in mutagenic processes in B cells during immunoglobulin (Ig) class switch recombination (CSR) and somatic hypermutation (SHM), which are instigated by uracil (U) lesions derived from activation-induced cytidine deaminase (AID) activity. BER is required for the processing of AID-induced lesions into DNA double strand breaks (DSB) that are required for CSR, and is of pivotal importance for determining the mutagenic outcome of uracil lesions during SHM. Although uracils are generally efficiently repaired by error-free BER, this process is surprisingly error-prone at the Ig loci in proliferating B cells. Breakdown of this high-fidelity process outside of the Ig loci has been linked to mutations observed in B-cell tumors and DNA breaks and chromosomal translocations in activated B cells. Next to its role in preventing cancer, BER has also been implicated in immune tolerance. Several defects in BER components have been associated with autoimmune diseases, and animal models have shown that BER defects can cause autoimmunity in a B-cell intrinsic and extrinsic fashion. In this review we discuss the contribution of BER to genomic integrity in the context of immune receptor diversification, cancer and autoimmune diseases.
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Affiliation(s)
- Maria Stratigopoulou
- Department of Pathology, Lymphoma and Myeloma Center Amsterdam (LYMMCARE), Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands
| | - Tijmen P van Dam
- Department of Pathology, Lymphoma and Myeloma Center Amsterdam (LYMMCARE), Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands
| | - Jeroen E J Guikema
- Department of Pathology, Lymphoma and Myeloma Center Amsterdam (LYMMCARE), Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands
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13
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Iveland TS, Hagen L, Sharma A, Sousa MML, Sarno A, Wollen KL, Liabakk NB, Slupphaug G. HDACi mediate UNG2 depletion, dysregulated genomic uracil and altered expression of oncoproteins and tumor suppressors in B- and T-cell lines. J Transl Med 2020; 18:159. [PMID: 32264925 PMCID: PMC7137348 DOI: 10.1186/s12967-020-02318-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 03/27/2020] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND HDAC inhibitors (HDACi) belong to a new group of chemotherapeutics that are increasingly used in the treatment of lymphocyte-derived malignancies, but their mechanisms of action remain poorly understood. Here we aimed to identify novel protein targets of HDACi in B- and T-lymphoma cell lines and to verify selected candidates across several mammalian cell lines. METHODS Jurkat T- and SUDHL5 B-lymphocytes were treated with the HDACi SAHA (vorinostat) prior to SILAC-based quantitative proteome analysis. Selected differentially expressed proteins were verified by targeted mass spectrometry, RT-PCR and western analysis in multiple mammalian cell lines. Genomic uracil was quantified by LC-MS/MS, cell cycle distribution analyzed by flow cytometry and class switch recombination monitored by FACS in murine CH12F3 cells. RESULTS SAHA treatment resulted in differential expression of 125 and 89 proteins in Jurkat and SUDHL5, respectively, of which 19 were commonly affected. Among these were several oncoproteins and tumor suppressors previously not reported to be affected by HDACi. Several key enzymes determining the cellular dUTP/dTTP ratio were downregulated and in both cell lines we found robust depletion of UNG2, the major glycosylase in genomic uracil sanitation. UNG2 depletion was accompanied by hyperacetylation and mediated by increased proteasomal degradation independent of cell cycle stage. UNG2 degradation appeared to be ubiquitous and was observed across several mammalian cell lines of different origin and with several HDACis. Loss of UNG2 was accompanied by 30-40% increase in genomic uracil in freely cycling HEK cells and reduced immunoglobulin class-switch recombination in murine CH12F3 cells. CONCLUSION We describe several oncoproteins and tumor suppressors previously not reported to be affected by HDACi in previous transcriptome analyses, underscoring the importance of proteome analysis to identify cellular effectors of HDACi treatment. The apparently ubiquitous depletion of UNG2 and PCLAF establishes DNA base excision repair and translesion synthesis as novel pathways affected by HDACi treatment. Dysregulated genomic uracil homeostasis may aid interpretation of HDACi effects in cancer cells and further advance studies on this class of inhibitors in the treatment of APOBEC-expressing tumors, autoimmune disease and HIV-1.
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Affiliation(s)
- Tobias S Iveland
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway.,Cancer Clinic, St. Olav's Hospital, Trondheim, Norway
| | - Lars Hagen
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway.,Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim, Norway.,Proteomics and Modomics Experimental Core, PROMEC, at NTNU and the Central Norway Regional Health Authority, Stjørdal, Norway
| | - Animesh Sharma
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway.,Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim, Norway.,Proteomics and Modomics Experimental Core, PROMEC, at NTNU and the Central Norway Regional Health Authority, Stjørdal, Norway
| | - Mirta M L Sousa
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway.,Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim, Norway
| | - Antonio Sarno
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway.,Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim, Norway
| | - Kristian Lied Wollen
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway
| | - Nina Beate Liabakk
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway.,Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim, Norway
| | - Geir Slupphaug
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health, Norwegian University of Science and Technology, 7491, Trondheim, Norway. .,Clinic of Laboratory Medicine, St. Olav's Hospital, Trondheim, Norway. .,Proteomics and Modomics Experimental Core, PROMEC, at NTNU and the Central Norway Regional Health Authority, Stjørdal, Norway.
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14
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Kim DV, Makarova AV, Miftakhova RR, Zharkov DO. Base Excision DNA Repair Deficient Cells: From Disease Models to Genotoxicity Sensors. Curr Pharm Des 2020; 25:298-312. [PMID: 31198112 DOI: 10.2174/1381612825666190319112930] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 03/13/2019] [Indexed: 12/29/2022]
Abstract
Base excision DNA repair (BER) is a vitally important pathway that protects the cell genome from many kinds of DNA damage, including oxidation, deamination, and hydrolysis. It involves several tightly coordinated steps, starting from damaged base excision and followed by nicking one DNA strand, incorporating an undamaged nucleotide, and DNA ligation. Deficiencies in BER are often embryonic lethal or cause morbid diseases such as cancer, neurodegeneration, or severe immune pathologies. Starting from the early 1980s, when the first mammalian cell lines lacking BER were produced by spontaneous mutagenesis, such lines have become a treasure trove of valuable information about the mechanisms of BER, often revealing unexpected connections with other cellular processes, such as antibody maturation or epigenetic demethylation. In addition, these cell lines have found an increasing use in genotoxicity testing, where they provide increased sensitivity and representativity to cell-based assay panels. In this review, we outline current knowledge about BER-deficient cell lines and their use.
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Affiliation(s)
- Daria V Kim
- Novosibirsk State University, 2 Pirogova St., Novosibirsk 630090, Russian Federation
| | - Alena V Makarova
- RAS Institute of Molecular Genetics, 2 Kurchatova Sq., Moscow 123182, Russian Federation
| | - Regina R Miftakhova
- Kazan Federal University, 18 Kremlevsakaya St., Kazan 420008, Russian Federation
| | - Dmitry O Zharkov
- Novosibirsk State University, 2 Pirogova St., Novosibirsk 630090, Russian Federation.,SB RAS Institute of Chemical Biology and Fu ndamental Medicine, 8 Lavrentieva Ave., Novosibirsk 630090, Russian Federation
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15
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Weiser BP. Analysis of uracil DNA glycosylase (UNG2) stimulation by replication protein A (RPA) at ssDNA-dsDNA junctions. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1868:140347. [PMID: 31866506 DOI: 10.1016/j.bbapap.2019.140347] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Revised: 12/12/2019] [Accepted: 12/17/2019] [Indexed: 12/17/2022]
Abstract
Replication Protein A (RPA) is a single-stranded DNA binding protein that interacts with DNA repair proteins including Uracil DNA Glycosylase (UNG2). Here, I report DNA binding and activity assays using purified recombinant RPA and UNG2. Using synthetic DNA substrates, RPA was found to promote UNG2's interaction with ssDNA-dsDNA junctions regardless of the DNA strand polarity surrounding the junction. RPA stimulated UNG2's removal of uracil bases paired with adenine or guanine in DNA as much as 17-fold when the uracil was positioned 21 bps from ssDNA-dsDNA junctions, and the largest degree of UNG2 stimulation occurred when RPA was in molar excess compared to DNA. I found that RPA becomes sequestered on ssDNA regions surrounding junctions which promotes its spatial targeting of UNG2 near the junction. However, when RPA concentration exceeds free ssDNA, RPA promotes UNG2's activity without spatial constraints in dsDNA regions. These effects of RPA on UNG2 were found to be mediated primarily by interactions between RPA's winged-helix domain and UNG2's N-terminal domain, but when the winged-helix domain is unavailable, a secondary interaction between UNG2's N-terminal domain and RPA can occur. This work supports a widespread role for RPA in stimulating uracil base excision repair.
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Affiliation(s)
- Brian P Weiser
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA.
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16
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Weiser BP, Rodriguez G, Cole PA, Stivers JT. N-terminal domain of human uracil DNA glycosylase (hUNG2) promotes targeting to uracil sites adjacent to ssDNA-dsDNA junctions. Nucleic Acids Res 2019; 46:7169-7178. [PMID: 29917162 PMCID: PMC6101581 DOI: 10.1093/nar/gky525] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 05/24/2018] [Indexed: 01/29/2023] Open
Abstract
The N-terminal domain (NTD) of nuclear human uracil DNA glycosylase (hUNG2) assists in targeting hUNG2 to replication forks through specific interactions with replication protein A (RPA). Here, we explored hUNG2 activity in the presence and absence of RPA using substrates with ssDNA–dsDNA junctions that mimic structural features of the replication fork and transcriptional R-loops. We find that when RPA is tightly bound to the ssDNA overhang of junction DNA substrates, base excision by hUNG2 is strongly biased toward uracils located 21 bp or less from the ssDNA–dsDNA junction. In the absence of RPA, hUNG2 still showed an 8-fold excision bias for uracil located <10 bp from the junction, but only when the overhang had a 5′ end. Biased targeting required the NTD and was not observed with the hUNG2 catalytic domain alone. Consistent with this requirement, the isolated NTD was found to bind weakly to ssDNA. These findings indicate that the NTD of hUNG2 targets the enzyme to ssDNA–dsDNA junctions using RPA-dependent and RPA-independent mechanisms. This structure-based specificity may promote efficient removal of uracils that arise from dUTP incorporation during DNA replication, or additionally, uracils that arise from DNA cytidine deamination at transcriptional R-loops during immunoglobulin class-switch recombination.
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Affiliation(s)
- Brian P Weiser
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
| | - Gaddiel Rodriguez
- Department of Pharmacology & Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Philip A Cole
- Division of Genetics, Department of Medicine and Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School and Brigham and Women's Hospital, Boston, MA 02115, USA
| | - James T Stivers
- Department of Pharmacology & Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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17
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Pilzecker B, Jacobs H. Mutating for Good: DNA Damage Responses During Somatic Hypermutation. Front Immunol 2019; 10:438. [PMID: 30915081 PMCID: PMC6423074 DOI: 10.3389/fimmu.2019.00438] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 02/19/2019] [Indexed: 11/13/2022] Open
Abstract
Somatic hypermutation (SHM) of immunoglobulin (Ig) genes plays a key role in antibody mediated immunity. SHM in B cells provides the molecular basis for affinity maturation of antibodies. In this way SHM is key in optimizing antibody dependent immune responses. SHM is initiated by targeting the Activation-Induced Cytidine Deaminase (AID) to rearranged V(D)J and switch regions of Ig genes. The mutation rate of this programmed mutagenesis is ~10-3 base pairs per generation, a million-fold higher than the non-AID targeted genome of B cells. AID is a processive enzyme that binds single-stranded DNA and deaminates cytosines in DNA. Cytosine deamination generates highly mutagenic deoxy-uracil (U) in the DNA of both strands of the Ig loci. Mutagenic processing of the U by the DNA damage response generates the entire spectrum of base substitutions characterizing SHM at and around the initial U lesion. Starting from the U as a primary lesion, currently five mutagenic DNA damage response pathways have been identified in generating a well-defined SHM spectrum of C/G transitions, C/G transversions, and A/T mutations around this initial lesion. These pathways include (1) replication opposite template U generates transitions at C/G, (2) UNG2-dependent translesion synthesis (TLS) generates transversions at C/G, (3) a hybrid pathway comprising non-canonical mismatch repair (ncMMR) and UNG2-dependent TLS generates transversions at C/G, (4) ncMMR generates mutations at A/T, and (5) UNG2- and PCNA Ubiquitination (PCNA-Ub)-dependent mutations at A/T. Furthermore, specific strand-biases of SHM spectra arise as a consequence of a biased AID targeting, ncMMR, and anti-mutagenic repriming. Here, we review mammalian SHM with special focus on the mutagenic DNA damage response pathways involved in processing AID induced Us, the origin of characteristic strand biases, and relevance of the cell cycle.
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Affiliation(s)
| | - Heinz Jacobs
- Division of Tumor Biology & Immunology, The Netherlands Cancer Institute, Amsterdam, Netherlands
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18
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Smith T, Cunningham-Rundles C. Primary B-cell immunodeficiencies. Hum Immunol 2018; 80:351-362. [PMID: 30359632 DOI: 10.1016/j.humimm.2018.10.015] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 10/05/2018] [Accepted: 10/21/2018] [Indexed: 12/13/2022]
Abstract
Primary B-cell immunodeficiencies refer to diseases resulting from impaired antibody production due to either molecular defects intrinsic to B-cells or a failure of interaction between B-cells and T-cells. Patients typically have recurrent infections and can vary with presentation and complications depending upon where the defect has occurred in B-cell development or the degree of functional impairment. In this review, we describe B-cell specific immune defects categorized by presence or absence of peripheral B-cells, immunoglobulins isotypes and evidence of antibody impairment.
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Affiliation(s)
- Tukisa Smith
- Division of Allergy and Clinical Immunology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, New York, NY 10029-6574, United States; The Rockefeller University, Laboratory of Biochemical Genetics and Metabolism, 1230 York Avenue, Box 179, New York, NY 10065, United States.
| | - Charlotte Cunningham-Rundles
- Division of Allergy and Clinical Immunology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, New York, NY 10029-6574, United States.
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19
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de la Morena MT. Clinical Phenotypes of Hyper-IgM Syndromes. THE JOURNAL OF ALLERGY AND CLINICAL IMMUNOLOGY-IN PRACTICE 2017; 4:1023-1036. [PMID: 27836054 DOI: 10.1016/j.jaip.2016.09.013] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Revised: 09/21/2016] [Accepted: 09/23/2016] [Indexed: 02/05/2023]
Abstract
The primary immunodeficiency (PID) diseases comprise a heterogeneous group of inherited disorders of immune function. Technical advancements in whole-genome, whole-exome, and RNA-sequencing have seen the explosion of genetic discoveries in the field of PIDs. The present review aims to focus on a group of immunodeficiency disorders associated with elevated levels of IgM (hyper IgM; HIGM) and provides a clinical differential diagnosis. Most patients present for evaluation of immunodeficiency due to recurrent infections, and laboratory studies show either a clear isolated elevation of serum immunoglobulin M (IgM) with low or absent IgG, IgA, and IgE. Alternatively, IgM levels may be normal or moderately elevated while other serum immunoglobulins are reported below the norms for age but not absent. Mechanistically, these disorders are recognized as defects in immunoglobulin (Ig) class switch recombination (CSR). Importantly, to safeguard genetic stability, CSR utilizes elements of the DNA repair machinery including multi-protein complexes involved in mismatch repair (MMR). Therefore, it is not uncommon for defects in the DNA repair machinery, to present with laboratory findings of HIGM. This review will discuss clinical phenotypes associated with congenital defects associated with HIGM. Clinical manifestations, relevant immunologic testing, inheritance pattern, molecular diagnosis, presumed pathogenesis, and OMIM number, when annotated are compiled. Accepted therapeutic options, when available, are reviewed for each condition discussed.
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Affiliation(s)
- M Teresa de la Morena
- Division of Allergy and Immunology, Department of Pediatrics and Internal Medicine, University of Texas, Southwestern Medical Center, Dallas, Texas.
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20
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Dysfunctional BLK in common variable immunodeficiency perturbs B-cell proliferation and ability to elicit antigen-specific CD4+ T-cell help. Oncotarget 2016; 6:10759-71. [PMID: 25926555 PMCID: PMC4484417 DOI: 10.18632/oncotarget.3577] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 02/21/2015] [Indexed: 11/25/2022] Open
Abstract
Common Variable Immunodeficiency (CVID) is the most prevalent primary antibody deficiency, and characterized by defective generation of high-affinity antibodies. Patients have therefore increased risk to recurrent infections of the respiratory and intestinal tract. Development of high-affinity antigen-specific antibodies involves two key actions of B-cell receptors (BCR): transmembrane signaling through BCR-complexes to induce B-cell differentiation and proliferation, and BCR-mediated antigen internalization for class-II MHC-mediated presentation to acquire antigen-specific CD4(+) T-cell help.We identified a variant (L3P) in the B-lymphoid tyrosine kinase (BLK) gene of 2 related CVID-patients, which was absent in healthy relatives. BLK belongs to the Src-kinases family and involved in BCR-signaling. Here, we sought to clarify BLK function in healthy human B-cells and its association to CVID.BLK expression was comparable in patient and healthy B-cells. Functional analysis of L3P-BLK showed reduced BCR crosslinking-induced Syk phosphorylation and proliferation, in both primary B-cells and B-LCLs. B-cells expressing L3P-BLK showed accelerated destruction of BCR-internalized antigen and reduced ability to elicit CD40L-expression on antigen-specific CD4(+) T-cells.In conclusion, we found a novel BLK gene variant in CVID-patients that causes suppressed B-cell proliferation and reduced ability of B-cells to elicit antigen-specific CD4(+) T-cell responses. Both these mechanisms may contribute to hypogammaglobulinemia in CVID-patients.
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21
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Horiuchi K, Imai K, Mitsui-Sekinaka K, Yeh TW, Ochs HD, Durandy A, Nonoyama S. Analysis of somatic hypermutations in the IgM switch region in human B cells. J Allergy Clin Immunol 2014; 134:411-9. [DOI: 10.1016/j.jaci.2014.02.043] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2013] [Revised: 02/06/2014] [Accepted: 02/06/2014] [Indexed: 11/16/2022]
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22
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Expression and recruitment of uracil-DNA glycosylase are regulated by E2A during antibody diversification. Mol Immunol 2014; 60:23-31. [DOI: 10.1016/j.molimm.2014.03.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 03/24/2014] [Indexed: 11/20/2022]
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23
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Lühnsdorf B, Epe B, Khobta A. Excision of uracil from transcribed DNA negatively affects gene expression. J Biol Chem 2014; 289:22008-18. [PMID: 24951587 DOI: 10.1074/jbc.m113.521807] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Uracil is an unavoidable aberrant base in DNA, the repair of which takes place by a highly efficient base excision repair mechanism. The removal of uracil from the genome requires a succession of intermediate products, including an abasic site and a single strand break, before the original DNA structure can be reconstituted. These repair intermediates are harmful for DNA replication and also interfere with transcription under cell-free conditions. However, their relevance for cellular transcription has not been proved. Here we investigated the influence of uracil incorporated into a reporter vector on gene expression in human cells. The expression constructs contained a single uracil opposite an adenine (to mimic dUTP misincorporation during DNA synthesis) or a guanine (imitating a product of spontaneous cytosine deamination). We found no evidence for a direct transcription arrest by uracil in either of the two settings because the vectors containing the base modification exhibited unaltered levels of enhanced GFP reporter gene expression at early times after delivery to cells. However, the gene expression showed a progressive decline during subsequent hours. In the case of U:A pairs, this effect was retarded significantly by knockdown of UNG1/2 but not by knockdown of SMUG1 or thymine-DNA glycosylase uracil-DNA glycosylases, proving that it is base excision by UNG1/2 that perturbs transcription of the affected gene. By contrast, the decline of expression of the U:G constructs was not influenced by either UNG1/2, SMUG1, or thymine-DNA glycosylase knockdown, strongly suggesting that there are substantial mechanistic or kinetic differences between the processing of U:A and U:G lesions in cells.
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Affiliation(s)
- Bork Lühnsdorf
- From the Institute of Pharmacy and Biochemistry, Johannes Gutenberg University of Mainz, Staudingerweg 5, 55128 Mainz, Germany
| | - Bernd Epe
- From the Institute of Pharmacy and Biochemistry, Johannes Gutenberg University of Mainz, Staudingerweg 5, 55128 Mainz, Germany
| | - Andriy Khobta
- From the Institute of Pharmacy and Biochemistry, Johannes Gutenberg University of Mainz, Staudingerweg 5, 55128 Mainz, Germany
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24
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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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25
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Association between polymorphism of the DNA repair SMUG1 and UNG genes and age-related macular degeneration. Retina 2014; 34:38-47. [PMID: 23714858 DOI: 10.1097/iae.0b013e31829477d8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
PURPOSE To investigate the association between the g.4235T>C (rs2337395) polymorphism of the UNG gene and the c.-31A>G (rs3087404) polymorphism of the SMUG1 gene and the risk of age-related macular degeneration (AMD), as well as modulation of this association by some environmental and lifestyle factors. METHODS Overall, 272 AMD patients and 105 control subjects were enrolled in this study. Both polymorphisms were genotyped by restriction fragment length polymorphism-polymerase chain reaction (PCR-RFLP). RESULTS The C/C genotype of the g.4235T>C polymorphism of the UNG gene was associated with an increased risk of dry AMD (odds ratio, 2.54), whereas the T/T genotype of this polymorphism decreased such risk (odds ratio, 0.41). The presence of the T allele of the g.4235T>C polymorphism and the A allele of the c.-31A>G polymorphism of the SMUG1 gene (odds ratio, 2.17 and 2.18, respectively) was associated with an increased risk of AMD severity, expressed by the comparison of the frequencies of genotypes in the group of patients with wet AMD versus those with dry AMD. Conversely, the C/C genotype of the g.4235T>C polymorphism, the G/G genotype of the c.-31A>G polymorphism, and the C/C-G/G combined genotype of both polymorphisms had a protective effect (odds ratio, 0.48, 0.46, and 0.18; respectively). CONCLUSION The results obtained suggest the potential role of the g.4235T>C and the c.-31A>G polymorphisms in AMD pathogenesis.
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Routes J, Abinun M, Al-Herz W, Bustamante J, Condino-Neto A, De La Morena MT, Etzioni A, Gambineri E, Haddad E, Kobrynski L, Le Deist F, Nonoyama S, Oliveira JB, Perez E, Picard C, Rezaei N, Sleasman J, Sullivan KE, Torgerson T. ICON: the early diagnosis of congenital immunodeficiencies. J Clin Immunol 2014; 34:398-424. [PMID: 24619621 DOI: 10.1007/s10875-014-0003-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Accepted: 02/17/2014] [Indexed: 01/27/2023]
Abstract
Primary immunodeficiencies are intrinsic defects in the immune system that result in a predisposition to infection and are frequently accompanied by a propensity to autoimmunity and/or immunedysregulation. Primary immunodeficiencies can be divided into innate immunodeficiencies, phagocytic deficiencies, complement deficiencies, disorders of T cells and B cells (combined immunodeficiencies), antibody deficiencies and immunodeficiencies associated with syndromes. Diseases of immune dysregulation and autoinflammatory disorder are many times also included although the immunodeficiency in these disorders are often secondary to the autoimmunity or immune dysregulation and/or secondary immunosuppression used to control these disorders. Congenital primary immunodeficiencies typically manifest early in life although delayed onset are increasingly recognized. The early diagnosis of congenital immunodeficiencies is essential for optimal management and improved outcomes. In this International Consensus (ICON) document, we provide the salient features of the most common congenital immunodeficiencies.
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Affiliation(s)
- John Routes
- Department of Pediatrics, Medical College of Wisconsin, and Children's Research Institute, Milwaukee, WI, 53226-4874, USA,
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27
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Hu Y, Ericsson I, Doseth B, Liabakk NB, Krokan HE, Kavli B. Activation-induced cytidine deaminase (AID) is localized to subnuclear domains enriched in splicing factors. Exp Cell Res 2014; 322:178-92. [DOI: 10.1016/j.yexcr.2014.01.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Revised: 01/02/2014] [Accepted: 01/06/2014] [Indexed: 10/25/2022]
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28
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Gines G, Saint-Pierre C, Gasparutto D. A multiplex assay based on encoded microbeads conjugated to DNA NanoBeacons to monitor base excision repair activities by flow cytometry. Biosens Bioelectron 2014; 58:81-4. [PMID: 24632132 DOI: 10.1016/j.bios.2014.02.040] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 02/03/2014] [Accepted: 02/14/2014] [Indexed: 02/07/2023]
Abstract
We reported here a new assay to detect base excision repair activities from purified enzymes, as well as in cell-free extracts. The multiplex format rests upon the encoding of magnetic beads with the fluorophore Alexa 488, thanks to a fast and original procedure. Fluorescently encoded microbeads are subsequently functionalized by lesion-containing DNA NanoBeacons labeled with the fluorophore/quencher pair Cyanine 5/BHQ2. Probes cleavage, induced by targeted enzymes leads to Cyanine 5 signal enhancement, which is finally quantified by flow cytometry. The multiplex assay was applied to the detection of restriction enzymes activities as well as base excision repair processes. Each test requires only 500fmol of DNA substrate, which constitutes great sensitivity compared to other BER functional assays. The present biosensor is able to detect both uracil DNA N-glycosylase (UNG) and AP-endonuclease 1 (APE1) within few nanograms of nuclear extract. Additionally, we demonstrated that the corresponding assay has potential application in DNA repair inhibitor search. Finally, the current multiplexed tool shows several advantages in comparison to other functional BER assays with no need of electrophoretic separation, straightforward, easy and reproducible functionalization of encoded microbeads and a high stability of DNA probes in cell-free extracts.
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Affiliation(s)
- Guillaume Gines
- Laboratoire des Lésions des Acides Nucléiques, INAC/SCIB UMR_E3 CEA/UJF-Grenoble 1/CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9, France
| | - Christine Saint-Pierre
- Laboratoire des Lésions des Acides Nucléiques, INAC/SCIB UMR_E3 CEA/UJF-Grenoble 1/CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9, France
| | - Didier Gasparutto
- Laboratoire des Lésions des Acides Nucléiques, INAC/SCIB UMR_E3 CEA/UJF-Grenoble 1/CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9, France.
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29
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Wyatt MD. Advances in understanding the coupling of DNA base modifying enzymes to processes involving base excision repair. Adv Cancer Res 2014; 119:63-106. [PMID: 23870509 DOI: 10.1016/b978-0-12-407190-2.00002-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
This chapter describes some of the recent, exciting developments that have characterized and connected processes that modify DNA bases with DNA repair pathways. It begins with AID/APOBEC or TET family members that covalently modify bases within DNA. The modified bases, such as uracil or 5-formylcytosine, are then excised by DNA glycosylases including UNG or TDG to initiate base excision repair (BER). BER is known to preserve genome integrity by removing damaged bases. The newer studies underscore the necessity of BER following enzymes that deliberately damage DNA. This includes the role of BER in antibody diversification and more recently, its requirement for demethylation of 5-methylcytosine in mammalian cells. The recent advances have shed light on mechanisms of DNA demethylation, and have raised many more questions. The potential hazards of these processes have also been revealed. Dysregulation of the activity of base modifying enzymes, and resolution by unfaithful or corrupt means can be a driver of genome instability and tumorigenesis. The understanding of both DNA and histone methylation and demethylation is now revealing the true extent to which epigenetics influence normal development and cancer, an abnormal development.
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Affiliation(s)
- Michael D Wyatt
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina, USA.
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Eldin P, Chazal N, Fenard D, Bernard E, Guichou JF, Briant L. Vpr expression abolishes the capacity of HIV-1 infected cells to repair uracilated DNA. Nucleic Acids Res 2013; 42:1698-710. [PMID: 24178031 PMCID: PMC3919559 DOI: 10.1093/nar/gkt974] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) Vpr protein binds to the cellular uracil–DNA glycosylase UNG2 and induces its degradation through the assembly with the DDB1-CUL4 ubiquitin ligase complex. This interaction counteracts the antiviral activity exerted by UNG2 on HIV-1 gene transcription, as previously reported by us. In this work, we show that Vpr expression in the context of HIV-1 infection markedly decreases UNG2 expression in transformed or primary CD4+ T lymphocytes. We demonstrate for the first time that Vpr-UNG2 interaction significantly impairs the uracil excision activity of infected cells. The loss of uracil excision activity coincides with a significant accumulation of uracilated bases in the genome of infected cells without changes in cell division. Although UNG2 expression and uracil–DNA glycosylase activity are recovered after the peak of retroviral replication, the mutagenic effect of transient DNA uracilation in cycling cells should be taken into account. Therefore, the possible consequences of Vpr-mediated temporary depletion of endogenous nuclear UNG2 and subsequent alteration of the genomic integrity of infected cells need to be evaluated in the physiopathogenesis of HIV infection.
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Affiliation(s)
- Patrick Eldin
- Centre d'étude d'agents Pathogènes et Biotechnologies pour la Santé (CPBS) - UMR 5236-CNRS - Université Montpellier 1 and 2, Montpellier, France and Centre de Biochimie Structurale, INSERM U1054, CNRS UMR5048, Université Montpellier 1 and 2, Montpellier, France
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31
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Capone G, Calabrò M, Lucchese G, Fasano C, Girardi B, Polimeno L, Kanduc D. Peptide matching between Epstein-Barr virus and human proteins. Pathog Dis 2013; 69:205-12. [DOI: 10.1111/2049-632x.12066] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Revised: 07/04/2013] [Accepted: 07/09/2013] [Indexed: 12/26/2022] Open
Affiliation(s)
- Giovanni Capone
- Department of Biosciences, Biotechnologies and Biopharmaceutics; University of Bari; Bari Italy
| | - Michele Calabrò
- Department of Biosciences, Biotechnologies and Biopharmaceutics; University of Bari; Bari Italy
| | - Guglielmo Lucchese
- Brain and Language Laboratory; Cluster of Excellence “Languages of Emotions”; Free University of Berlin; Berlin Germany
| | - Candida Fasano
- Department of Biosciences, Biotechnologies and Biopharmaceutics; University of Bari; Bari Italy
| | - Bruna Girardi
- Section of Gastroenterology; Department of Emergency and Organ Transplantation (DETO); University of Bari; Bari Italy
| | - Lorenzo Polimeno
- Section of Gastroenterology; Department of Emergency and Organ Transplantation (DETO); University of Bari; Bari Italy
| | - Darja Kanduc
- Department of Biosciences, Biotechnologies and Biopharmaceutics; University of Bari; Bari Italy
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Abstract
High frequency of cytidine to thymidine conversions was identified in the genome of several types of cancer cells. In breast cancer cells, these mutations are clustered in long DNA regions associated with single-strand DNA (ssDNA), double-strand DNA breaks (DSB), and genomic rearrangements. The observed mutational pattern resembles the deamination signature of cytidine to uridine carried out by members of the APOBEC3 family of cellular deaminases. Consistently, APOBEC3B (A3B) was recently identified as the mutational source in breast cancer cells. A3G is another member of the cytidine deaminases family predominantly expressed in lymphoma cells, where it is involved in mutational DSB repair following ionizing radiation treatments. This activity provides us with a new paradigm for cancer cell survival and tumor promotion and a mechanistic link between ssDNA, DSBs, and clustered mutations. Cancer Res; 73(12); 3494-8. ©2013 AACR.
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Affiliation(s)
- Roni Nowarski
- Department of Pathology and the Lautenberg Center for General and Tumor Immunology, the Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Moshe Kotler
- Department of Pathology and the Lautenberg Center for General and Tumor Immunology, the Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
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Galashevskaya A, Sarno A, Vågbø CB, Aas PA, Hagen L, Slupphaug G, Krokan HE. A robust, sensitive assay for genomic uracil determination by LC/MS/MS reveals lower levels than previously reported. DNA Repair (Amst) 2013; 12:699-706. [PMID: 23742752 DOI: 10.1016/j.dnarep.2013.05.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 05/06/2013] [Accepted: 05/09/2013] [Indexed: 10/26/2022]
Abstract
Considerable progress has been made in understanding the origins of genomic uracil and its role in genome stability and host defense; however, the main question concerning the basal level of uracil in DNA remains disputed. Results from assays designed to quantify genomic uracil vary by almost three orders of magnitude. To address the issues leading to this inconsistency, we explored possible shortcomings with existing methods and developed a sensitive LC/MS/MS-based method for the absolute quantification of genomic 2'-deoxyuridine (dUrd). To this end, DNA was enzymatically hydrolyzed to 2'-deoxyribonucleosides and dUrd was purified in a preparative HPLC step and analyzed by LC/MS/MS. The standard curve was linear over four orders of magnitude with a quantification limit of 5 fmol dUrd. Control samples demonstrated high inter-experimental accuracy (94.3%) and precision (CV 9.7%). An alternative method that employed UNG2 to excise uracil from DNA for LC/MS/MS analysis gave similar results, but the intra-assay variability was significantly greater. We quantified genomic dUrd in Ung(+/+) and Ung(-/-) mouse embryonic fibroblasts and human lymphoblastoid cell lines carrying UNG mutations. DNA-dUrd is 5-fold higher in Ung(-/-) than in Ung(+/+) fibroblasts and 11-fold higher in UNG2 dysfunctional than in UNG2 functional lymphoblastoid cells. We report approximately 400-600 dUrd per human or murine genome in repair-proficient cells, which is lower than results using other methods and suggests that genomic uracil levels may have previously been overestimated.
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Affiliation(s)
- Anastasia Galashevskaya
- Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, NO-7489 Trondheim, Norway
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34
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Pieper K, Grimbacher B, Eibel H. B-cell biology and development. J Allergy Clin Immunol 2013; 131:959-71. [PMID: 23465663 DOI: 10.1016/j.jaci.2013.01.046] [Citation(s) in RCA: 315] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 01/21/2013] [Accepted: 01/22/2013] [Indexed: 02/06/2023]
Abstract
B cells develop from hematopoietic precursor cells in an ordered maturation and selection process. Extensive studies with many different mouse mutants provided fundamental insights into this process. However, the characterization of genetic defects causing primary immunodeficiencies was essential in understanding human B-cell biology. Defects in pre-B-cell receptor components or in downstream signaling proteins, such as Bruton tyrosine kinase and B-cell linker protein, arrest development at the pre-B-cell stage. Defects in survival-regulating proteins, such as B-cell activator of the TNF-α family receptor (BAFF-R) or caspase recruitment domain-containing protein 11 (CARD11), interrupt maturation and prevent differentiation of transitional B cells into marginal zone and follicular B cells. Mature B-cell subsets, immune responses, and memory B-cell and plasma cell development are disturbed by mutations affecting Toll-like receptor signaling, B-cell antigen receptor coreceptors (eg, CD19), or enzymes responsible for immunoglobulin class-switch recombination. Transgenic mouse models helped to identify key regulatory mechanisms, such as receptor editing and clonal anergy, preventing the activation of B cells expressing antibodies recognizing autoantigens. Nevertheless, the combination of susceptible genetic backgrounds with the rescue of self-reactive B cells by T cells allows the generation of autoreactive clones found in patients with many autoimmune diseases and even in those with primary immunodeficiencies. The rapid progress of functional genomic research is expected to foster the development of new tools that specifically target dysfunctional B lymphocytes to treat autoimmunity, B-cell malignancies, and immunodeficiency.
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Affiliation(s)
- Kathrin Pieper
- Centre of Chronic Immunodeficiency, University Medical Centre Freiburg, Faculty of Biology, Albert-Ludwigs-Universität, Freiburg, Germany
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35
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Abstract
The base excision repair system is vital to the repair of endogenous and exogenous DNA damage. This pathway is initiated by one of several DNA glycosylases that recognizes and excises specific DNA lesions in a coordinated fashion. Methyl-CpG Domain Protein 4 (MBD4) and Thymine DNA Glycosylase (TDG) are the two major G:T glycosylases that remove thymine generated by the deamination of 5-methylcytosine. Both of these glycosylases also remove a variety of other base lesions, including G:U and preferentially act at CpG sites throughout the genome. Many have questioned the purpose of seemingly redundant glycosylases, but new information has emerged to suggest MBD4 and TDG have diverse biological functions. MBD4 has been closely linked to apoptosis, while TDG has been clearly implicated in transcriptional regulation. This article reviews all of these developments, and discusses the consequences of germline and somatic mutations that lead to non-synonymous amino acid substitutions on MBD4 and TDG protein function. In addition, we report the finding of alternatively spliced variants of MBD4 and TDG and the results of functional studies of a tumor-associated variant of MBD4.
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Abstract
The pathogenesis of age-related macular degeneration (AMD) is complex and involves interactions between environmental and genetic factors, with oxidative stress playing an important role inducing damage in biomolecules, including DNA. Therefore, genetic variability in the components of DNA repair systems may influence the ability of the cell to cope with oxidative stress and in this way contribute to the pathogenesis of AMD. However, few reports have been published on this subject so far. We demonstrated that the c.977C>G polymorphism (rs1052133) in the hOGG1 gene and the c.972G>C polymorphism (rs3219489) in the MUTYH gene, the products of which play important roles in the repair of oxidatively damaged DNA, might be associated with the risk of AMD. Oxidative stress may promote misincorporation of uracil into DNA, where it is targeted by several DNA glycosylases. We observed that the g.4235T>C (rs2337395) and c.–32A>G (rs3087404) polymorphisms in two genes encoding such glycosylases, UNG and SMUG1, respectively, could be associated with the occurrence of AMD. Polymorphisms in some other DNA repair genes, including XPD (ERCC2), XRCC1 and ERCC6 (CSB) have also been reported to be associated with AMD. These data confirm the importance of the cellular reaction to DNA damage, and this may be influenced by variability in DNA repair genes, in AMD pathogenesis.
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APOBEC3G enhances lymphoma cell radioresistance by promoting cytidine deaminase-dependent DNA repair. Blood 2012; 120:366-75. [PMID: 22645179 DOI: 10.1182/blood-2012-01-402123] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
APOBEC3 proteins catalyze deamination of cytidines in single-stranded DNA (ssDNA), providing innate protection against retroviral replication by inducing deleterious dC > dU hypermutation of replication intermediates. APOBEC3G expression is induced in mitogen-activated lymphocytes; however, no physiologic role related to lymphoid cell proliferation has yet to be determined. Moreover, whether APOBEC3G cytidine deaminase activity transcends to processing cellular genomic DNA is unknown. Here we show that lymphoma cells expressing high APOBEC3G levels display efficient repair of genomic DNA double-strand breaks (DSBs) induced by ionizing radiation and enhanced survival of irradiated cells. APOBEC3G transiently accumulated in the nucleus in response to ionizing radiation and was recruited to DSB repair foci. Consistent with a direct role in DSB repair, inhibition of APOBEC3G expression or deaminase activity resulted in deficient DSB repair, whereas reconstitution of APOBEC3G expression in leukemia cells enhanced DSB repair. APOBEC3G activity involved processing of DNA flanking a DSB in an integrated reporter cassette. Atomic force microscopy indicated that APOBEC3G multimers associate with ssDNA termini, triggering multimer disassembly to multiple catalytic units. These results identify APOBEC3G as a prosurvival factor in lymphoma cells, marking APOBEC3G as a potential target for sensitizing lymphoma to radiation therapy.
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38
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Torseth K, Doseth B, Hagen L, Olaisen C, Liabakk NB, Græsmann H, Durandy A, Otterlei M, Krokan HE, Kavli B, Slupphaug G. The UNG2 Arg88Cys variant abrogates RPA-mediated recruitment of UNG2 to single-stranded DNA. DNA Repair (Amst) 2012; 11:559-69. [PMID: 22521144 DOI: 10.1016/j.dnarep.2012.03.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2011] [Revised: 03/28/2012] [Accepted: 03/28/2012] [Indexed: 11/26/2022]
Abstract
In human cell nuclei, UNG2 is the major uracil-DNA glycosylase initiating DNA base excision repair of uracil. In activated B cells it has an additional role in facilitating mutagenic processing of AID-induced uracil at Ig loci and UNG-deficient patients develop hyper-IgM syndrome characterized by impaired class-switch recombination and disturbed somatic hypermutation. How UNG2 is recruited to either error-free or mutagenic uracil processing remains obscure, but likely involves regulated interactions with other proteins. The UNG2 N-terminal domain contains binding motifs for both proliferating cell nuclear antigen (PCNA) and replication protein A (RPA), but the relative contribution of these interactions to genomic uracil processing is not understood. Interestingly, a heterozygous germline single-nucleotide variant leading to Arg88Cys (R88C) substitution in the RPA-interaction motif of UNG2 has been observed in humans, but with unknown functional relevance. Here we demonstrate that UNG2-R88C protein is expressed from the variant allele in a lymphoblastoid cell line derived from a heterozygous germ line carrier. Enzyme activity as well as localization in replication foci of UNG2-R88C was similar to that of WT. However, binding to RPA was essentially abolished by the R88C substitution, whereas binding to PCNA was unaffected. Moreover, we show that disruption of the PCNA-binding motif impaired recruitment of UNG2 to S-phase replication foci, demonstrating that PCNA is a major factor for recruitment of UNG2 to unperturbed replication forks. Conversely, in cells treated with hydroxyurea, RPA mediated recruitment of UNG2 to stalled replication forks independently of functional PCNA binding. Modulation of PCNA- versus RPA-binding may thus constitute a functional switch for UNG2 in cells subsequent to genotoxic stress and potentially also during the processing of uracil at the immunoglobulin locus in antigen-stimulated B cells.
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Affiliation(s)
- Kathrin Torseth
- Department of Cancer Research and Molecular Medicine, Faculty of Medicine, the FUGE Proteomics Node, Norwegian University of Science and Technology, N-7006 Trondheim, Norway
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39
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Doseth B, Ekre C, Slupphaug G, Krokan HE, Kavli B. Strikingly different properties of uracil-DNA glycosylases UNG2 and SMUG1 may explain divergent roles in processing of genomic uracil. DNA Repair (Amst) 2012; 11:587-93. [PMID: 22483865 DOI: 10.1016/j.dnarep.2012.03.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Revised: 03/13/2012] [Accepted: 03/13/2012] [Indexed: 12/11/2022]
Abstract
Genomic uracil resulting from spontaneously deaminated cytosine generates mutagenic U:G mismatches that are usually corrected by error-free base excision repair (BER). However, in B-cells, activation-induced cytosine deaminase (AID) generates U:G mismatches in hot-spot sequences at Ig loci. These are subject to mutagenic processing during somatic hypermutation (SHM) and class switch recombination (CSR). Uracil N-glycosylases UNG2 and SMUG1 (single strand-selective monofunctional uracil-DNA glycosylase 1) initiate error-free BER in most DNA contexts, but UNG2 is also involved in mutagenic processing of AID-induced uracil during the antibody diversification process, the regulation of which is not understood. AID is strictly single strand-specific. Here we show that in the presence of Mg2+ and monovalent salts, human and mouse SMUG1 are essentially double strand-specific, whereas UNG2 efficiently removes uracil from both single and double stranded DNA under all tested conditions. Furthermore, SMUG1 and UNG2 display widely different sequence preferences. Interestingly, uracil in a hot-spot sequence for AID is 200-fold more efficiently removed from single stranded DNA by UNG2 than by SMUG1. This may explain why SMUG1, which is not excluded from Ig loci, is unable to replace UNG2 in antibody diversification. We suggest a model for mutagenic processing in which replication protein A (RPA) recruits UNG2 to sites of deamination and keeps DNA in a single stranded conformation, thus avoiding error-free BER of the deaminated cytosine.
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Affiliation(s)
- Berit Doseth
- Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway
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40
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Krokan HE. A life in DNA repair—And beyond. DNA Repair (Amst) 2012; 11:224-35. [DOI: 10.1016/j.dnarep.2011.04.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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41
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Berquist BR, Wilson DM. Pathways for repairing and tolerating the spectrum of oxidative DNA lesions. Cancer Lett 2012; 327:61-72. [PMID: 22353689 DOI: 10.1016/j.canlet.2012.02.001] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 01/26/2012] [Accepted: 02/01/2012] [Indexed: 01/03/2023]
Abstract
Reactive oxygen species (ROS) arise from both endogenous and exogenous sources. These reactive molecules possess the ability to damage both the DNA nucleobases and the sugar phosphate backbone, leading to a wide spectrum of lesions, including non-bulky (8-oxoguanine and formamidopyrimidine) and bulky (cyclopurine and etheno adducts) base modifications, abasic sites, non-conventional single-strand breaks, protein-DNA adducts, and intra/interstrand DNA crosslinks. Unrepaired oxidative DNA damage can result in bypass mutagenesis during genome copying or gene expression, or blockage of the essential cellular processes of DNA replication or transcription. Such outcomes underlie numerous pathologies, including, but not limited to, carcinogenesis and neurodegeneration, as well as the aging process. Cells have adapted and evolved defense systems against the deleterious effects of ROS, and specifically devote a number of cellular DNA repair and tolerance pathways to combat oxidative DNA damage. Defects in these protective pathways trigger hereditary human diseases that exhibit increased cancer incidence, developmental defects, neurological abnormalities, and/or premature aging. We review herein classic and atypical oxidative DNA lesions, outcomes of encountering these damages during DNA replication and transcription, and the consequences of losing the ability to repair the different forms of oxidative DNA damage. We particularly focus on the hereditary human diseases Xeroderma Pigmentosum, Cockayne Syndrome and Fanconi Anemia, which may involve defects in the efficient repair of oxidative modifications to chromosomal DNA.
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Affiliation(s)
- Brian R Berquist
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, 77843, United States
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42
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Wollen Steen K, Doseth B, P. Westbye M, Akbari M, Kang D, Falkenberg M, Slupphaug G. mtSSB may sequester UNG1 at mitochondrial ssDNA and delay uracil processing until the dsDNA conformation is restored. DNA Repair (Amst) 2012; 11:82-91. [DOI: 10.1016/j.dnarep.2011.10.026] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Revised: 10/02/2011] [Accepted: 10/27/2011] [Indexed: 12/11/2022]
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Honjo T, Kobayashi M, Begum N, Kotani A, Sabouri S, Nagaoka H. The AID dilemma: infection, or cancer? Adv Cancer Res 2012; 113:1-44. [PMID: 22429851 DOI: 10.1016/b978-0-12-394280-7.00001-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Activation-induced cytidine deaminase (AID), which is both essential and sufficient for forming antibody memory, is also linked to tumorigenesis. AID is found in many B lymphomas, in myeloid leukemia, and in pathogen-induced tumors such as adult T cell leukemia. Although there is no solid evidence that AID causes human tumors, AID-transgenic and AID-deficient mouse models indicate that AID is both sufficient and required for tumorigenesis. Recently, AID's ability to cleave DNA has been shown to depend on topoisomerase 1 (Top1) and a histone H3K4 epigenetic mark. When the level of Top1 protein is decreased by AID activation, it induces irreversible cleavage in highly transcribed targets. This finding and others led to the idea that there is an evolutionary link between meiotic recombination and class switch recombination, which share H3K4 trimethyl, topoisomerase, the MRN complex, mismatch repair family proteins, and exonuclease 3. As Top1 has recently been shown to be involved in many transcription-associated genome instabilities, it is likely that AID took advantage of basic genome instability or diversification to evolve its mechanism for immune diversity. AID targets are therefore not highly specific to immunoglobulin genes and are relatively abundant, although they have strict requirements for transcription-induced H3K4 trimethyl modification and repetitive sequences prone to forming non-B structures. Inevitably, AID-dependent cleavage takes place in nonimmunoglobulin targets and eventually causes tumors. However, battles against infection are waged in the context of acute emergencies, while tumorigenesis is rather a chronic, long-term process. In the interest of survival, vertebrates must have evolved AID to prevent infection despite its long-term risk of causing tumorigenesis.
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44
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Genetic polymorphisms of the DNA repair gene UNG are associated with the susceptibility of rheumatoid arthritis. Rheumatol Int 2011; 32:3723-7. [DOI: 10.1007/s00296-011-2185-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Accepted: 10/22/2011] [Indexed: 12/19/2022]
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45
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Doseth B, Visnes T, Wallenius A, Ericsson I, Sarno A, Pettersen HS, Flatberg A, Catterall T, Slupphaug G, Krokan HE, Kavli B. Uracil-DNA glycosylase in base excision repair and adaptive immunity: species differences between man and mouse. J Biol Chem 2011; 286:16669-80. [PMID: 21454529 DOI: 10.1074/jbc.m111.230052] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Genomic uracil is a DNA lesion but also an essential key intermediate in adaptive immunity. In B cells, activation-induced cytidine deaminase deaminates cytosine to uracil (U:G mispairs) in Ig genes to initiate antibody maturation. Uracil-DNA glycosylases (UDGs) such as uracil N-glycosylase (UNG), single strand-selective monofunctional uracil-DNA glycosylase 1 (SMUG1), and thymine-DNA glycosylase remove uracil from DNA. Gene-targeted mouse models are extensively used to investigate the role of these enzymes in DNA repair and Ig diversification. However, possible species differences in uracil processing in humans and mice are yet not established. To address this, we analyzed UDG activities and quantities in human and mouse cell lines and in splenic B cells from Ung(+/+) and Ung(-/-) backcrossed mice. Interestingly, human cells displayed ∼15-fold higher total uracil excision capacity due to higher levels of UNG. In contrast, SMUG1 activity was ∼8-fold higher in mouse cells, constituting ∼50% of the total U:G excision activity compared with less than 1% in human cells. In activated B cells, both UNG and SMUG1 activities were at levels comparable with those measured for mouse cell lines. Moreover, SMUG1 activity per cell was not down-regulated after activation. We therefore suggest that SMUG1 may work as a weak backup activity for UNG2 during class switch recombination in Ung(-/-) mice. Our results reveal significant species differences in genomic uracil processing. These findings should be taken into account when mouse models are used in studies of uracil DNA repair and adaptive immunity.
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Affiliation(s)
- Berit Doseth
- Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
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46
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Suspène R, Aynaud MM, Guétard D, Henry M, Eckhoff G, Marchio A, Pineau P, Dejean A, Vartanian JP, Wain-Hobson S. Somatic hypermutation of human mitochondrial and nuclear DNA by APOBEC3 cytidine deaminases, a pathway for DNA catabolism. Proc Natl Acad Sci U S A 2011; 108:4858-63. [PMID: 21368204 PMCID: PMC3064337 DOI: 10.1073/pnas.1009687108] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The human APOBEC3 (A3A-A3H) locus encodes six cytidine deaminases that edit single-stranded DNA, the result being DNA peppered with uridine. Although several cytidine deaminases are clearly restriction factors for retroviruses and hepadnaviruses, it is not known if APOBEC3 enzymes have roles outside of these settings. It is shown here that both human mitochondrial and nuclear DNA are vulnerable to somatic hypermutation by A3 deaminases, with APOBEC3A standing out among them. The degree of editing is much greater in patients lacking the uracil DNA-glycolyase gene, indicating that the observed levels of editing reflect a dynamic composed of A3 editing and DNA catabolism involving uracil DNA-glycolyase. Nonetheless, hyper- and lightly mutated sequences went hand in hand, raising the hypothesis that recurrent low-level mutation by APOBEC3A could catalyze the transition from a healthy to a cancer genome.
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Affiliation(s)
- Rodolphe Suspène
- Institut Pasteur, Molecular Retrovirology Unit, Centre National de la Recherche Scientifique URA3015 and
| | - Marie-Ming Aynaud
- Institut Pasteur, Molecular Retrovirology Unit, Centre National de la Recherche Scientifique URA3015 and
| | - Denise Guétard
- Institut Pasteur, Molecular Retrovirology Unit, Centre National de la Recherche Scientifique URA3015 and
| | - Michel Henry
- Institut Pasteur, Molecular Retrovirology Unit, Centre National de la Recherche Scientifique URA3015 and
| | - Grace Eckhoff
- Institut Pasteur, Molecular Retrovirology Unit, Centre National de la Recherche Scientifique URA3015 and
| | - Agnès Marchio
- Nuclear Organization and Oncogenesis Unit, 75724 Paris cedex 15, France; and
| | - Pascal Pineau
- Nuclear Organization and Oncogenesis Unit, 75724 Paris cedex 15, France; and
| | - Anne Dejean
- Nuclear Organization and Oncogenesis Unit, 75724 Paris cedex 15, France; and
- Institut National de la Santé et de la Recherche Médicale, U579, 75724 Paris cedex 15, France
| | - Jean-Pierre Vartanian
- Institut Pasteur, Molecular Retrovirology Unit, Centre National de la Recherche Scientifique URA3015 and
| | - Simon Wain-Hobson
- Institut Pasteur, Molecular Retrovirology Unit, Centre National de la Recherche Scientifique URA3015 and
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47
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Zeitlin SG, Chapados BR, Baker NM, Tai C, Slupphaug G, Wang JYJ. Uracil DNA N-glycosylase promotes assembly of human centromere protein A. PLoS One 2011; 6:e17151. [PMID: 21399697 PMCID: PMC3047565 DOI: 10.1371/journal.pone.0017151] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Accepted: 01/19/2011] [Indexed: 11/19/2022] Open
Abstract
Uracil is removed from DNA by the conserved enzyme Uracil DNA N-glycosylase (UNG). Previously, we observed that inhibiting UNG in Xenopus egg extracts blocked assembly of CENP-A, a histone H3 variant. CENP-A is an essential protein in all species, since it is required for chromosome segregation during mitosis. Thus, the implication of UNG in CENP-A assembly implies that UNG would also be essential, but UNG mutants lacking catalytic activity are viable in all species. In this paper, we present evidence that UNG2 colocalizes with CENP-A and H2AX phosphorylation at centromeres in normally cycling cells. Reduction of UNG2 in human cells blocks CENP-A assembly, and results in reduced cell proliferation, associated with increased frequencies of mitotic abnormalities and rapid cell death. Overexpression of UNG2 induces high levels of CENP-A assembly in human cells. Using a multiphoton laser approach, we demonstrate that UNG2 is rapidly recruited to sites of DNA damage. Taken together, our data are consistent with a model in which the N-terminus of UNG2 interacts with the active site of the enzyme and with chromatin.
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Affiliation(s)
- Samantha G Zeitlin
- Moores UCSD Cancer Center and Ludwig Institute for Cancer Research, University of California San Diego, La Jolla, California, United States of America.
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Maul RW, Saribasak H, Martomo SA, McClure RL, Yang W, Vaisman A, Gramlich HS, Schatz DG, Woodgate R, Wilson DM, Gearhart PJ. Uracil residues dependent on the deaminase AID in immunoglobulin gene variable and switch regions. Nat Immunol 2011; 12:70-6. [PMID: 21151102 PMCID: PMC3653439 DOI: 10.1038/ni.1970] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Accepted: 11/12/2010] [Indexed: 11/09/2022]
Abstract
Activation-induced deaminase (AID) initiates diversity of immunoglobulin genes through deamination of cytosine to uracil. Two opposing models have been proposed for the deamination of DNA or RNA by AID. Although most data support DNA deamination, there is no physical evidence of uracil residues in immunoglobulin genes. Here we demonstrate their presence by determining the sensitivity of DNA to digestion with uracil DNA glycosylase (UNG) and abasic endonuclease. Using several methods of detection, we identified uracil residues in the variable and switch regions. Uracil residues were generated within 24 h of B cell stimulation, were present on both DNA strands and were found to replace mainly cytosine bases. Our data provide direct evidence for the model that AID functions by deaminating cytosine residues in DNA.
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Affiliation(s)
- Robert W Maul
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
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49
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Wilson DM, Kim D, Berquist BR, Sigurdson AJ. Variation in base excision repair capacity. Mutat Res 2010; 711:100-12. [PMID: 21167187 DOI: 10.1016/j.mrfmmm.2010.12.004] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2010] [Revised: 11/29/2010] [Accepted: 12/07/2010] [Indexed: 01/20/2023]
Abstract
The major DNA repair pathway for coping with spontaneous forms of DNA damage, such as natural hydrolytic products or oxidative lesions, is base excision repair (BER). In particular, BER processes mutagenic and cytotoxic DNA lesions such as non-bulky base modifications, abasic sites, and a range of chemically distinct single-strand breaks. Defects in BER have been linked to cancer predisposition, neurodegenerative disorders, and immunodeficiency. Recent data indicate a large degree of sequence variability in DNA repair genes and several studies have associated BER gene polymorphisms with disease risk, including cancer of several sites. The intent of this review is to describe the range of BER capacity among individuals and the functional consequences of BER genetic variants. We also discuss studies that associate BER deficiency with disease risk and the current state of BER capacity measurement assays.
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Affiliation(s)
- David M Wilson
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States.
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50
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Abstract
In response to an assault by foreign organisms, peripheral B cells can change their antibody affinity and isotype by somatically mutating their genomic DNA. The ability of a cell to modify its DNA is exceptional in light of the potential consequences of genetic alterations to cause human disease and cancer. Thus, as expected, this mechanism of antibody diversity is tightly regulated and coordinated through one protein, activation-induced deaminase (AID). AID produces diversity by converting cytosine to uracil within the immunoglobulin loci. The deoxyuracil residue is mutagenic when paired with deoxyguanosine, since it mimics thymidine during DNA replication. Additionally, B cells can manipulate the DNA repair pathways so that deoxyuracils are not faithfully repaired. Therefore, an intricate balance exists which is regulated at multiple stages to promote mutation of immunoglobulin genes, while retaining integrity of the rest of the genome. Here we discuss and summarize the current understanding of how AID functions to cause somatic hypermutation.
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Affiliation(s)
- Robert W Maul
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
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