1
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Fiumara M, Ferrari S, Omer-Javed A, Beretta S, Albano L, Canarutto D, Varesi A, Gaddoni C, Brombin C, Cugnata F, Zonari E, Naldini MM, Barcella M, Gentner B, Merelli I, Naldini L. Genotoxic effects of base and prime editing in human hematopoietic stem cells. Nat Biotechnol 2024; 42:877-891. [PMID: 37679541 PMCID: PMC11180610 DOI: 10.1038/s41587-023-01915-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Accepted: 07/26/2023] [Indexed: 09/09/2023]
Abstract
Base and prime editors (BEs and PEs) may provide more precise genetic engineering than nuclease-based approaches because they bypass the dependence on DNA double-strand breaks. However, little is known about their cellular responses and genotoxicity. Here, we compared state-of-the-art BEs and PEs and Cas9 in human hematopoietic stem and progenitor cells with respect to editing efficiency, cytotoxicity, transcriptomic changes and on-target and genome-wide genotoxicity. BEs and PEs induced detrimental transcriptional responses that reduced editing efficiency and hematopoietic repopulation in xenotransplants and also generated DNA double-strand breaks and genotoxic byproducts, including deletions and translocations, at a lower frequency than Cas9. These effects were strongest for cytidine BEs due to suboptimal inhibition of base excision repair and were mitigated by tailoring delivery timing and editor expression through optimized mRNA design. However, BEs altered the mutational landscape of hematopoietic stem and progenitor cells across the genome by increasing the load and relative proportions of nucleotide variants. These findings raise concerns about the genotoxicity of BEs and PEs and warrant further investigation in view of their clinical application.
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Affiliation(s)
- Martina Fiumara
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
- Vita-Salute San Raffaele University, Milan, Italy
| | - Samuele Ferrari
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy.
- Vita-Salute San Raffaele University, Milan, Italy.
| | - Attya Omer-Javed
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Stefano Beretta
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Luisa Albano
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Daniele Canarutto
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
- Vita-Salute San Raffaele University, Milan, Italy
- Pediatric Immunohematology Unit and BMT Program, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Angelica Varesi
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Chiara Gaddoni
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Chiara Brombin
- University Center for Statistics in the Biomedical Sciences, Vita-Salute San Raffaele University, Milan, Italy
| | - Federica Cugnata
- University Center for Statistics in the Biomedical Sciences, Vita-Salute San Raffaele University, Milan, Italy
| | - Erika Zonari
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Matteo Maria Naldini
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Matteo Barcella
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Bernhard Gentner
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - Ivan Merelli
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy
- National Research Council, Institute for Biomedical Technologies, Segrate, Italy
| | - Luigi Naldini
- San Raffaele Telethon Institute for Gene Therapy, IRCCS San Raffaele Scientific Institute, Milan, Italy.
- Vita-Salute San Raffaele University, Milan, Italy.
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2
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Lirussi L, Nilsen HL. DNA Glycosylases Define the Outcome of Endogenous Base Modifications. Int J Mol Sci 2023; 24:10307. [PMID: 37373453 DOI: 10.3390/ijms241210307] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 06/13/2023] [Accepted: 06/16/2023] [Indexed: 06/29/2023] Open
Abstract
Chemically modified nucleic acid bases are sources of genomic instability and mutations but may also regulate gene expression as epigenetic or epitranscriptomic modifications. Depending on the cellular context, they can have vastly diverse impacts on cells, from mutagenesis or cytotoxicity to changing cell fate by regulating chromatin organisation and gene expression. Identical chemical modifications exerting different functions pose a challenge for the cell's DNA repair machinery, as it needs to accurately distinguish between epigenetic marks and DNA damage to ensure proper repair and maintenance of (epi)genomic integrity. The specificity and selectivity of the recognition of these modified bases relies on DNA glycosylases, which acts as DNA damage, or more correctly, as modified bases sensors for the base excision repair (BER) pathway. Here, we will illustrate this duality by summarizing the role of uracil-DNA glycosylases, with particular attention to SMUG1, in the regulation of the epigenetic landscape as active regulators of gene expression and chromatin remodelling. We will also describe how epigenetic marks, with a special focus on 5-hydroxymethyluracil, can affect the damage susceptibility of nucleic acids and conversely how DNA damage can induce changes in the epigenetic landscape by altering the pattern of DNA methylation and chromatin structure.
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Affiliation(s)
- Lisa Lirussi
- Department of Clinical Molecular Biology, Institute of Clinical Medicine, University of Oslo, 0318 Oslo, Norway
- Section of Clinical Molecular Biology (EpiGen), Akershus University Hospital, 1478 Lørenskog, Norway
- Department of Microbiology, Oslo University Hospital, 0424 Oslo, Norway
| | - Hilde Loge Nilsen
- Department of Clinical Molecular Biology, Institute of Clinical Medicine, University of Oslo, 0318 Oslo, Norway
- Department of Microbiology, Oslo University Hospital, 0424 Oslo, Norway
- Unit for Precision Medicine, Akershus University Hospital, 1478 Lørenskog, Norway
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3
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Patlán-Vázquez AG, Ayala-García VM, Vallin C, Cortés J, Vásquez-Morales SG, Robleto EA, Nudler E, Pedraza-Reyes M. Dynamics of Mismatch and Alternative Excision-Dependent Repair in Replicating Bacillus subtilis DNA Examined Under Conditions of Neutral Selection. Front Microbiol 2022; 13:866089. [PMID: 35847079 PMCID: PMC9280176 DOI: 10.3389/fmicb.2022.866089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Accepted: 06/10/2022] [Indexed: 11/13/2022] Open
Abstract
Spontaneous DNA deamination is a potential source of transition mutations. In Bacillus subtilis, EndoV, a component of the alternative excision repair pathway (AER), counteracts the mutagenicity of base deamination-induced mispairs. Here, we report that the mismatch repair (MMR) system, MutSL, prevents the harmful effects of HNO2, a deaminating agent of Cytosine (C), Adenine (A), and Guanine (G). Using Maximum Depth Sequencing (MDS), which measures mutagenesis under conditions of neutral selection, in B. subtilis strains proficient or deficient in MutSL and/or EndoV, revealed asymmetric and heterogeneous patterns of mutations in both DNA template strands. While the lagging template strand showed a higher frequency of C → T substitutions; G → A mutations, occurred more frequently in the leading template strand in different genetic backgrounds. In summary, our results unveiled a role for MutSL in preventing the deleterious effects of base deamination and uncovered differential patterns of base deamination processing by the AER and MMR systems that are influenced by the sequence context and the replicating DNA strand.
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Affiliation(s)
- Adriana G. Patlán-Vázquez
- Division of Natural and Exact Sciences, Department of Biology, University of Guanajuato, Guanajuato, Mexico
| | | | - Carmen Vallin
- School of Life Sciences, University of Nevada, Las Vegas, Las Vegas, NV, United States
| | - Jonathan Cortés
- Biological Research Center, Universidad Autónoma del Estado de Morelos, Cuernavaca, Mexico
| | - Suria G. Vásquez-Morales
- Division of Natural and Exact Sciences, Department of Biology, University of Guanajuato, Guanajuato, Mexico
| | - Eduardo A. Robleto
- School of Life Sciences, University of Nevada, Las Vegas, Las Vegas, NV, United States
| | - Evgeny Nudler
- Howard Hughes Medical Institute, New York University School of Medicine, New York, NY, United States
| | - Mario Pedraza-Reyes
- Division of Natural and Exact Sciences, Department of Biology, University of Guanajuato, Guanajuato, Mexico
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4
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Feng Y, Martin A. Mutagenic repair during antibody diversification: emerging insights. Trends Immunol 2022; 43:604-607. [PMID: 35701290 DOI: 10.1016/j.it.2022.05.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Revised: 05/24/2022] [Accepted: 05/24/2022] [Indexed: 10/18/2022]
Abstract
Deoxyuracils (dUs) produced by activation-induced cytidine deaminase (AID) during antibody diversification are processed by base excision repair (BER) and mismatch repair (MMR) pathways that paradoxically expand this lesion within jawed vertebrate immunoglobulin (Ig) genes. We highlight new findings describing mechanisms that allow B cells to carry out mutagenic DNA repair, an essential process for antibody maturation with implications in cancer pathogenesis.
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Affiliation(s)
- Yuqing Feng
- Department of Immunology, University of Toronto, Toronto, Ontario, Canada
| | - Alberto Martin
- Department of Immunology, University of Toronto, Toronto, Ontario, Canada.
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5
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CNOT6: A Novel Regulator of DNA Mismatch Repair. Cells 2022; 11:cells11030521. [PMID: 35159331 PMCID: PMC8833972 DOI: 10.3390/cells11030521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 01/29/2022] [Accepted: 01/31/2022] [Indexed: 11/16/2022] Open
Abstract
DNA mismatch repair (MMR) is a highly conserved pathway that corrects both base–base mispairs and insertion-deletion loops (IDLs) generated during DNA replication. Defects in MMR have been linked to carcinogenesis and drug resistance. However, the regulation of MMR is poorly understood. Interestingly, CNOT6 is one of four deadenylase subunits in the conserved CCR4-NOT complex and it targets poly(A) tails of mRNAs for degradation. CNOT6 is overexpressed in acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML) and androgen-independent prostate cancer cells, which suggests that an altered expression of CNOT6 may play a role in tumorigenesis. Here, we report that a depletion of CNOT6 sensitizes human U2OS cells to N-methyl-N′nitro-N-nitrosoguanidine (MNNG) and leads to enhanced apoptosis. We also demonstrate that the depletion of CNOT6 upregulates MMR and decreases the mutation frequency in MMR-proficient cells. Furthermore, the depletion of CNOT6 increases the stability of mRNA transcripts from MMR genes, leading to the increased expression of MMR proteins. Our work provides insight into a novel CNOT6-dependent mechanism for regulating MMR.
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6
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Caldecott KW, Ward ME, Nussenzweig A. The threat of programmed DNA damage to neuronal genome integrity and plasticity. Nat Genet 2022; 54:115-120. [PMID: 35145299 DOI: 10.1038/s41588-021-01001-y] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 12/09/2021] [Indexed: 02/08/2023]
Abstract
The neuronal genome is particularly sensitive to loss or attenuation of DNA repair, and many neurological diseases ensue when DNA repair is impaired. It is well-established that the neuronal genome is subjected to stochastic DNA damage, most likely because of extensive oxidative stress in the brain. However, recent studies have identified unexpected high levels of 'programmed' DNA breakage in neurons, which we propose arise during physiological DNA metabolic processes intrinsic to neuronal development, differentiation and maintenance. The role of programmed DNA breaks in normal neuronal physiology and disease remains relatively unexplored thus far. However, bulk and single-cell sequencing analyses of neurodegenerative diseases have revealed age-related somatic mutational signatures that are enriched in regulatory regions of the genome. Here, we explore a paradigm of DNA repair in neurons, in which the genome is safeguarded from erroneous impacts of programmed genome breakage intrinsic to normal neuronal function.
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Affiliation(s)
- Keith W Caldecott
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, UK.
| | - Michael E Ward
- National Institute of Neurological Disorders and Stroke, NIH, Bethesda, MD, USA.
| | - André Nussenzweig
- Laboratory of Genome Integrity, National Cancer Institute, NIH, Bethesda, MD, USA.
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7
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Nambiar TS, Baudrier L, Billon P, Ciccia A. CRISPR-based genome editing through the lens of DNA repair. Mol Cell 2022; 82:348-388. [PMID: 35063100 PMCID: PMC8887926 DOI: 10.1016/j.molcel.2021.12.026] [Citation(s) in RCA: 66] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 12/18/2021] [Accepted: 12/20/2021] [Indexed: 01/22/2023]
Abstract
Genome editing technologies operate by inducing site-specific DNA perturbations that are resolved by cellular DNA repair pathways. Products of genome editors include DNA breaks generated by CRISPR-associated nucleases, base modifications induced by base editors, DNA flaps created by prime editors, and integration intermediates formed by site-specific recombinases and transposases associated with CRISPR systems. Here, we discuss the cellular processes that repair CRISPR-generated DNA lesions and describe strategies to obtain desirable genomic changes through modulation of DNA repair pathways. Advances in our understanding of the DNA repair circuitry, in conjunction with the rapid development of innovative genome editing technologies, promise to greatly enhance our ability to improve food production, combat environmental pollution, develop cell-based therapies, and cure genetic and infectious diseases.
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Affiliation(s)
- Tarun S. Nambiar
- Department of Genetics and Development, Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, NY 10032
| | - Lou Baudrier
- Department of Biochemistry and Molecular Biology, Robson DNA Science Centre, Arnie Charbonneau Cancer Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive N. W., Calgary, Alberta T2N 4N1, Canada
| | - Pierre Billon
- Department of Biochemistry and Molecular Biology, Robson DNA Science Centre, Arnie Charbonneau Cancer Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive N. W., Calgary, Alberta T2N 4N1, Canada,Corresponding authors: ,
| | - Alberto Ciccia
- Department of Genetics and Development, Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, NY 10032,Lead Contact,Corresponding authors: ,
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8
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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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9
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Fuchs RP, Isogawa A, Paulo JA, Onizuka K, Takahashi T, Amunugama R, Duxin JP, Fujii S. Crosstalk between repair pathways elicits double-strand breaks in alkylated DNA and implications for the action of temozolomide. eLife 2021; 10:69544. [PMID: 34236314 PMCID: PMC8289412 DOI: 10.7554/elife.69544] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 07/07/2021] [Indexed: 12/12/2022] Open
Abstract
Temozolomide (TMZ), a DNA methylating agent, is the primary chemotherapeutic drug used in glioblastoma treatment. TMZ induces mostly N-alkylation adducts (N7-methylguanine and N3-methyladenine) and some O6-methylguanine (O6mG) adducts. Current models propose that during DNA replication, thymine is incorporated across from O6mG, promoting a futile cycle of mismatch repair (MMR) that leads to DNA double-strand breaks (DSBs). To revisit the mechanism of O6mG processing, we reacted plasmid DNA with N-methyl-N-nitrosourea (MNU), a temozolomide mimic, and incubated it in Xenopus egg-derived extracts. We have shown that in this system, MMR proteins are enriched on MNU-treated DNA and we observed robust, MMR-dependent, repair synthesis. Our evidence also suggests that MMR, initiated at O6mG:C sites, is strongly stimulated in cis by repair processing of other lesions, such as N-alkylation adducts. Importantly, MNU-treated plasmids display DSBs in extracts, the frequency of which increases linearly with the square of alkylation dose. We suggest that DSBs result from two independent repair processes, one involving MMR at O6mG:C sites and the other involving base excision repair acting at a nearby N-alkylation adduct. We propose a new, replication-independent mechanism of action of TMZ, which operates in addition to the well-studied cell cycle-dependent mode of action.
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Affiliation(s)
- Robert P Fuchs
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, United States
| | - Asako Isogawa
- Cancer Research Center of Marseille, UMR7258, CNRS, Marseille, France
| | - Joao A Paulo
- Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Kazumitsu Onizuka
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
| | | | - Ravindra Amunugama
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, United States
| | - Julien P Duxin
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, United States
| | - Shingo Fujii
- Cancer Research Center of Marseille, UMR7258, CNRS, Marseille, France
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10
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Detection of Genomic Uracil Patterns. Int J Mol Sci 2021; 22:ijms22083902. [PMID: 33918885 PMCID: PMC8070346 DOI: 10.3390/ijms22083902] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 03/28/2021] [Accepted: 04/05/2021] [Indexed: 01/06/2023] Open
Abstract
The appearance of uracil in the deoxyuridine moiety of DNA is among the most frequently occurring genomic modifications. Three different routes can result in genomic uracil, two of which do not require specific enzymes: spontaneous cytosine deamination due to the inherent chemical reactivity of living cells, and thymine-replacing incorporation upon nucleotide pool imbalances. There is also an enzymatic pathway of cytosine deamination with multiple DNA (cytosine) deaminases involved in this process. In order to describe potential roles of genomic uracil, it is of key importance to utilize efficient uracil-DNA detection methods. In this review, we provide a comprehensive and critical assessment of currently available uracil detection methods with special focus on genome-wide mapping solutions. Recent developments in PCR-based and in situ detection as well as the quantitation of genomic uracil are also discussed.
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11
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Tang C, Bagnara D, Chiorazzi N, Scharff MD, MacCarthy T. AID Overlapping and Polη Hotspots Are Key Features of Evolutionary Variation Within the Human Antibody Heavy Chain (IGHV) Genes. Front Immunol 2020; 11:788. [PMID: 32425948 PMCID: PMC7204545 DOI: 10.3389/fimmu.2020.00788] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Accepted: 04/07/2020] [Indexed: 01/09/2023] Open
Abstract
Somatic hypermutation (SHM) of the immunoglobulin variable (IgV) loci is a key process in antibody affinity maturation. The enzyme activation-induced deaminase (AID), initiates SHM by creating C → U mismatches on single-stranded DNA (ssDNA). AID has preferential hotspot motif targets in the context of WRC/GYW (W = A/T, R = A/G, Y = C/T) and particularly at WGCW overlapping hotspots where hotspots appear opposite each other on both strands. Subsequent recruitment of the low-fidelity DNA repair enzyme, Polymerase eta (Polη), during mismatch repair, creates additional mutations at WA/TW sites. Although there are more than 50 functional immunoglobulin heavy chain variable (IGHV) segments in humans, the fundamental differences between these genes and their ability to respond to all possible foreign antigens is still poorly understood. To better understand this, we generated profiles of WGCW hotspots in each of the human IGHV genes and found the expected high frequency in complementarity determining regions (CDRs) that encode the antigen binding sites but also an unexpectedly high frequency of WGCW in certain framework (FW) sub-regions. Principal Components Analysis (PCA) of these overlapping AID hotspot profiles revealed that one major difference between IGHV families is the presence or absence of WGCW in a sub-region of FW3 sometimes referred to as “CDR4.” Further differences between members of each family (e.g., IGHV1) are primarily determined by their WGCW densities in CDR1. We previously suggested that the co-localization of AID overlapping and Polη hotspots was associated with high mutability of certain IGHV sub-regions, such as the CDRs. To evaluate the importance of this feature, we extended the WGCW profiles, combining them with local densities of Polη (WA) hotspots, thus describing the co-localization of both types of hotspots across all IGHV genes. We also verified that co-localization is associated with higher mutability. PCA of the co-localization profiles showed CDR1 and CDR2 as being the main contributors to variance among IGHV genes, consistent with the importance of these sub-regions in antigen binding. Our results suggest that AID overlapping (WGCW) hotspots alone or in conjunction with Polη (WA/TW) hotspots are key features of evolutionary variation between IGHV genes.
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Affiliation(s)
- Catherine Tang
- Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, NY, United States
| | - Davide Bagnara
- Karches Center for Oncology Research, The Feinstein Institute for Medical Research, Northwell Health, Manhasset, NY, United States.,Department of Experimental Medicine, University of Genoa, Genoa, Italy
| | - Nicholas Chiorazzi
- Karches Center for Oncology Research, The Feinstein Institute for Medical Research, Northwell Health, Manhasset, NY, United States
| | - Matthew D Scharff
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY, United States
| | - Thomas MacCarthy
- Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, NY, United States
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12
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Cytosine Methylation Affects the Mutability of Neighboring Nucleotides in Germline and Soma. Genetics 2020; 214:809-823. [PMID: 32079595 DOI: 10.1534/genetics.120.303028] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 02/12/2020] [Indexed: 02/07/2023] Open
Abstract
Methylated cytosines deaminate at higher rates than unmethylated cytosines, and the lesions they produce are repaired less efficiently. As a result, methylated cytosines are mutational hotspots. Here, combining rare polymorphism and base-resolution methylation data in humans, Arabidopsis thaliana, and rice (Oryza sativa), we present evidence that methylation state affects mutation dynamics not only at the focal cytosine but also at neighboring nucleotides. In humans, contrary to prior suggestions, we find that nucleotides in the close vicinity (±3 bp) of methylated cytosines mutate less frequently. Reduced mutability around methylated CpGs is also observed in cancer genomes, considering single nucleotide variants alongside tissue-of-origin-matched methylation data. In contrast, methylation is associated with increased neighborhood mutation risk in A. thaliana and rice. The difference in neighborhood mutation risk is less pronounced further away from the focal CpG and modulated by regional GC content. Our results are consistent with a model where altered risk at neighboring bases is linked to lesion formation at the focal CpG and subsequent long-patch repair. Our findings indicate that cytosine methylation has a broader mutational footprint than is commonly assumed.
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13
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Shen B, Chapman JH, Custance MF, Tricola GM, Jones CE, Furano AV. Perturbation of base excision repair sensitizes breast cancer cells to APOBEC3 deaminase-mediated mutations. eLife 2020; 9:e51605. [PMID: 31904337 PMCID: PMC6961979 DOI: 10.7554/elife.51605] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 01/05/2020] [Indexed: 02/06/2023] Open
Abstract
Abundant APOBEC3 (A3) deaminase-mediated mutations can dominate the mutational landscape ('mutator phenotype') of some cancers, however, the basis of this sporadic vulnerability is unknown. We show here that elevated expression of the bifunctional DNA glycosylase, NEIL2, sensitizes breast cancer cells to A3B-mediated mutations and double-strand breaks (DSBs) by perturbing canonical base excision repair (BER). NEIL2 usurps the canonical lyase, APE1, at abasic sites in a purified BER system, rendering them poor substrates for polymerase β. However, the nicked NEIL2 product can serve as an entry site for Exo1 in vitro to generate single-stranded DNA, which would be susceptible to both A3B and DSBs. As NEIL2 or Exo1 depletion mitigates the DNA damage caused by A3B expression, we suggest that aberrant NEIL2 expression can explain certain instances of A3B-mediated mutations.
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Affiliation(s)
- Birong Shen
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular BiologyNational Institute of Diabetes and Digestive and Kidney Disease, National Institutes of HealthBethesdaUnited States
| | - Joseph H Chapman
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular BiologyNational Institute of Diabetes and Digestive and Kidney Disease, National Institutes of HealthBethesdaUnited States
| | - Michael F Custance
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular BiologyNational Institute of Diabetes and Digestive and Kidney Disease, National Institutes of HealthBethesdaUnited States
| | - Gianna M Tricola
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular BiologyNational Institute of Diabetes and Digestive and Kidney Disease, National Institutes of HealthBethesdaUnited States
| | - Charles E Jones
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular BiologyNational Institute of Diabetes and Digestive and Kidney Disease, National Institutes of HealthBethesdaUnited States
| | - Anthony V Furano
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular BiologyNational Institute of Diabetes and Digestive and Kidney Disease, National Institutes of HealthBethesdaUnited States
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14
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Giovannini S, Weller MC, Repmann S, Moch H, Jiricny J. Synthetic lethality between BRCA1 deficiency and poly(ADP-ribose) polymerase inhibition is modulated by processing of endogenous oxidative DNA damage. Nucleic Acids Res 2019; 47:9132-9143. [PMID: 31329989 PMCID: PMC6753488 DOI: 10.1093/nar/gkz624] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 06/11/2019] [Accepted: 07/12/2019] [Indexed: 01/06/2023] Open
Abstract
Poly(ADP-ribose) polymerases (PARPs) facilitate the repair of DNA single-strand breaks (SSBs). When PARPs are inhibited, unrepaired SSBs colliding with replication forks give rise to cytotoxic double-strand breaks. These are normally rescued by homologous recombination (HR), but, in cells with suboptimal HR, PARP inhibition leads to genomic instability and cell death, a phenomenon currently exploited in the therapy of ovarian cancers in BRCA1/2 mutation carriers. In spite of their promise, resistance to PARP inhibitors (PARPis) has already emerged. In order to identify the possible underlying causes of the resistance, we set out to identify the endogenous source of DNA damage that activates PARPs. We argued that if the toxicity of PARPis is indeed caused by unrepaired SSBs, these breaks must arise spontaneously, because PARPis are used as single agents. We now show that a significant contributor to PARPi toxicity is oxygen metabolism. While BRCA1-depleted or -mutated cells were hypersensitive to the clinically approved PARPi olaparib, its toxicity was significantly attenuated by depletion of OGG1 or MYH DNA glycosylases, as well as by treatment with reactive oxygen species scavengers, growth under hypoxic conditions or chemical OGG1 inhibition. Thus, clinical resistance to PARPi therapy may emerge simply through reduced efficiency of oxidative damage repair.
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Affiliation(s)
- Sara Giovannini
- Institute of Molecular Life Sciences of the University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.,Institute of Molecular Cancer Research of the University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.,Institute of Biochemistry of the Swiss Federal Institute of Technology, Otto-Stern-Weg 3, CH-8093 Zurich, Switzerland
| | - Marie-Christine Weller
- Institute of Molecular Cancer Research of the University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Simone Repmann
- Institute of Molecular Cancer Research of the University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Holger Moch
- Institute of Pathology and Molecular Pathology, University Hospital Zurich, Schmelzbergstrasse 12, CH-8091 Zurich, Switzerland
| | - Josef Jiricny
- Institute of Molecular Life Sciences of the University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.,Institute of Molecular Cancer Research of the University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.,Institute of Biochemistry of the Swiss Federal Institute of Technology, Otto-Stern-Weg 3, CH-8093 Zurich, Switzerland
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15
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Ciccarese S, Burger PA, Ciani E, Castelli V, Linguiti G, Plasil M, Massari S, Horin P, Antonacci R. The Camel Adaptive Immune Receptors Repertoire as a Singular Example of Structural and Functional Genomics. Front Genet 2019; 10:997. [PMID: 31681428 PMCID: PMC6812646 DOI: 10.3389/fgene.2019.00997] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 09/18/2019] [Indexed: 01/08/2023] Open
Abstract
The adaptive immune receptors repertoire is highly plastic, with its ability to produce antigen-binding molecules and select those with high affinity for their antigen. Species have developed diverse genetic and structural strategies to create their respective repertoires required for their survival in the different environments. Camelids, until now, considered as a case of evolutionary innovation because of their only heavy-chain antibodies, represent a new mammalian model particularly useful for understanding the role of diversity in the immune system function. Here, we review the structural and functional characteristics and the current status of the genomic organization of camel immunoglobulins (IG) or antibodies, α/ß and γ/δ T cell receptors (TR), and major histocompatibility complex (MHC). In camelid humoral response, in addition to the conventional antibodies, there are IG with “only-heavy-chain” (no light chain, and two identical heavy gamma chains lacking CH1 and with a VH domain designated as VHH). The unique features of these VHH offer advantages in biotechnology and for clinical applications. The TRG and TRD rearranged variable domains of Camelus dromedarius (Arabian camel) display somatic hypermutation (SHM), increasing the intrinsic structural stability in the γ/δ heterodimer and influencing the affinity maturation to a given antigen similar to immunoglobulin genes. The SHM increases the dromedary γ/δ repertoire diversity. In Camelus genus, the general structural organization of the TRB locus is similar to that of the other artiodactyl species, with a pool of TRBV genes positioned at the 5’ end of three in tandem D-J-C clusters, followed by a single TRBV gene with an inverted transcriptional orientation located at the 3’ end. At the difference of TRG and TRD, the diversity of the TRB variable domains is not shaped by SHM and depends from the classical combinatorial and junctional diversity. The MHC locus is located on chromosome 20 in Camelus dromedarius. Cytogenetic and comparative whole genome analyses revealed the order of the three major regions “Centromere-ClassII-ClassIII-ClassI”. Unexpectedly low extent of polymorphisms and haplotypes was observed in all Old World camels despite different geographic origins.
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Affiliation(s)
| | - Pamela A Burger
- Research Institute of Wildlife Ecology, Vetmeduni Vienna, Vienna, Austria
| | - Elena Ciani
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro," Bari, Italy
| | - Vito Castelli
- Department of Biology, University of Bari "Aldo Moro," Bari, Italy
| | | | - Martin Plasil
- Department of Animal Genetics, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences, Brno, Czechia.,CEITEC-VFU, University of Veterinary and Pharmaceutical Sciences, RG Animal Immunogenomics, Brno, Czechia
| | - Serafina Massari
- Department of Biological and Environmental Science and Technologies, University of Salento, Lecce, Italy
| | - Petr Horin
- Department of Animal Genetics, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences, Brno, Czechia.,CEITEC-VFU, University of Veterinary and Pharmaceutical Sciences, RG Animal Immunogenomics, Brno, Czechia
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16
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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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17
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Tesch VK, IJspeert H, Raicht A, Rueda D, Dominguez-Pinilla N, Allende LM, Colas C, Rosenbaum T, Ilencikova D, Baris HN, Nathrath MHM, Suerink M, Januszkiewicz-Lewandowska D, Ragab I, Azizi AA, Wenzel SS, Zschocke J, Schwinger W, Kloor M, Blattmann C, Brugieres L, van der Burg M, Wimmer K, Seidel MG. No Overt Clinical Immunodeficiency Despite Immune Biological Abnormalities in Patients With Constitutional Mismatch Repair Deficiency. Front Immunol 2018; 9:1506. [PMID: 30013564 PMCID: PMC6036136 DOI: 10.3389/fimmu.2018.01506] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 06/18/2018] [Indexed: 11/13/2022] Open
Abstract
Immunoglobulin class-switch recombination (CSR) and somatic hypermutations (SHMs) are prerequisites for antibody and immunoglobulin receptor maturation and adaptive immune diversity. The mismatch repair (MMR) machinery, consisting of homologs of MutSα, MutLα, and MutSβ (MSH2/MSH6, MLH1/PMS2, and MSH2/MSH3, respectively) and other proteins, is involved in CSR, primarily acting as a backup for nonhomologous end-joining repair of activation-induced cytidine deaminase-induced DNA mismatches and, furthermore, in addition to error-prone polymerases, in the repair of SHM-induced DNA breaks. A varying degree of antibody formation defect, from IgA or selective IgG subclass deficiency to common variable immunodeficiency and hyper-IgM syndrome, has been detected in a small number of patients with constitutional mismatch repair deficiency (CMMRD) due to biallelic loss-of-function mutations in one of the MMR genes (PMS2, MSH6, MLH1, or MSH2). To elucidate the clinical relevance of a presumed primary immunodeficiency (PID) in CMMRD, we systematically collected clinical history and laboratory data of a cohort of 15 consecutive, unrelated patients (10 not previously reported) with homozygous/compound heterozygous mutations in PMS2 (n = 8), MSH6 (n = 5), and MLH1 (n = 2), most of whom manifested with typical malignancies during childhood. Detailed descriptions of their genotypes, phenotypes, and family histories are provided. Importantly, none of the patients showed any clinical warning signs of PID (infections, immune dysregulation, inflammation, failure to thrive, etc.). Furthermore, we could not detect uniform or specific patterns of laboratory abnormalities. The concentration of IgM was increased in 3 out of 12, reduced in 3 out of 12, and normal in 6 out of 12 patients, while concentrations of IgG and IgG subclasses, except IgG4, and of IgA, and specific antibody formation were normal in most. Class-switched B memory cells were reduced in 5 out of 12 patients, and in 9 out of 12 also the CD38hiIgM− plasmablasts were reduced. Furthermore, results of next generation sequencing-based analyses of antigen-selected B-cell receptor rearrangements showed a significantly reduced frequency of SHM and an increased number of rearranged immunoglobulin heavy chain (IGH) transcripts that use IGHG3, IGHG1, and IGHA1 subclasses. T cell subsets and receptor repertoires were unaffected. Together, neither clinical nor routine immunological laboratory parameters were consistently suggestive of PID in these CMMRD patients, but previously shown abnormalities in SHM and rearranged heavy chain transcripts were confirmed.
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Affiliation(s)
- Victoria K Tesch
- Research Unit Pediatric Hematology and Immunology, Division of Pediatric Hematology-Oncology, Department of Pediatrics and Adolescent Medicine, Medical University Graz, Graz, Austria
| | - Hanna IJspeert
- Department of Immunology, Erasmus MC, University Medical Center Rotterdam, Rotterdam, Netherlands
| | - Andrea Raicht
- Research Unit Pediatric Hematology and Immunology, Division of Pediatric Hematology-Oncology, Department of Pediatrics and Adolescent Medicine, Medical University Graz, Graz, Austria
| | - Daniel Rueda
- Hereditary Cancer Laboratory, University Hospital Doce de Octubre, i+12 Research Institute, Madrid, Spain
| | - Nerea Dominguez-Pinilla
- Department of Pediatric Hematology and Oncology, Virgen de la Salud Hospital, Toledo, Spain.,i+12 Research Institute, University Hospital Doce de Octubre, Madrid, Spain
| | - Luis M Allende
- Department of Immunology, University Hospital Doce de Octubre, i+12 Research Institute, Madrid, Spain
| | | | | | - Denisa Ilencikova
- Department of Pediatrics, Comenius University Bratislava, Bratislava, Slovakia
| | - Hagit N Baris
- The Genetics Institute, Rambam Health Care Campus, The Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel
| | - Michaela H M Nathrath
- Pediatric Hematology and Oncology, Klinikum Kassel, Kassel, Germany.,Pediatric Oncology Center, Department of Pediatrics, Technische Universität München, Munich, Germany
| | - Manon Suerink
- Department of Clinical Genetics, Leiden University Medical Center, Leiden, Netherlands
| | | | - Iman Ragab
- Pediatrics Department, Hematology-Oncology Unit, Faculty of Medicine, Ain Shams University, Cairo, Egypt
| | - Amedeo A Azizi
- Department of Pediatrics and Adolescent Medicine, Medical University of Vienna, Vienna, Austria
| | - Soeren S Wenzel
- Division of Human Genetics, Medical University Innsbruck, Innsbruck, Austria
| | - Johannes Zschocke
- Division of Human Genetics, Medical University Innsbruck, Innsbruck, Austria
| | - Wolfgang Schwinger
- Research Unit Pediatric Hematology and Immunology, Division of Pediatric Hematology-Oncology, Department of Pediatrics and Adolescent Medicine, Medical University Graz, Graz, Austria
| | - Matthias Kloor
- Department of Applied Tumor Biology, Institute of Pathology, Medical University Heidelberg, Heidelberg, Germany
| | - Claudia Blattmann
- Department of Hematology, Oncology, and Immunology, Olgahospital Stuttgart, Stuttgart, Germany
| | - Laurence Brugieres
- Department of Pediatric and Adolescent Oncology, Gustave Roussy Cancer Campus, Villejuif, France
| | - Mirjam van der Burg
- Department of Immunology, Erasmus MC, University Medical Center Rotterdam, Rotterdam, Netherlands
| | - Katharina Wimmer
- Division of Human Genetics, Medical University Innsbruck, Innsbruck, Austria
| | - Markus G Seidel
- Research Unit Pediatric Hematology and Immunology, Division of Pediatric Hematology-Oncology, Department of Pediatrics and Adolescent Medicine, Medical University Graz, Graz, Austria
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18
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SAMHD1 enhances immunoglobulin hypermutation by promoting transversion mutation. Proc Natl Acad Sci U S A 2018; 115:4921-4926. [PMID: 29669924 DOI: 10.1073/pnas.1719771115] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Activation-induced deaminase (AID) initiates hypermutation of Ig genes in activated B cells by converting C:G into U:G base pairs. G1-phase variants of uracil base excision repair (BER) and mismatch repair (MMR) then deploy translesion polymerases including REV1 and Pol η, which exacerbates mutation. dNTP paucity may contribute to hypermutation, because dNTP levels are reduced in G1 phase to inhibit viral replication. To derestrict G1-phase dNTP supply, we CRISPR-inactivated SAMHD1 (which degrades dNTPs) in germinal center B cells. Samhd1 inactivation increased B cell virus susceptibility, increased transition mutations at C:G base pairs, and substantially decreased transversion mutations at A:T and C:G base pairs in both strands. We conclude that SAMHD1's restriction of dNTP supply enhances AID's mutagenicity and that the evolution of Ig hypermutation included the repurposing of antiviral mechanisms based on dNTP starvation.
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19
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Liu D, Frederiksen JH, Liberti SE, Lützen A, Keijzers G, Pena-Diaz J, Rasmussen LJ. Human DNA polymerase delta double-mutant D316A;E318A interferes with DNA mismatch repair in vitro. Nucleic Acids Res 2017; 45:9427-9440. [PMID: 28934474 PMCID: PMC5766205 DOI: 10.1093/nar/gkx611] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2016] [Accepted: 07/05/2017] [Indexed: 12/11/2022] Open
Abstract
DNA mismatch repair (MMR) is a highly-conserved DNA repair mechanism, whose primary role is to remove DNA replication errors preventing them from manifesting as mutations, thereby increasing the overall genome stability. Defects in MMR are associated with increased cancer risk in humans and other organisms. Here, we characterize the interaction between MMR and a proofreading-deficient allele of the human replicative DNA polymerase delta, PolδD316A;E318A, which has a higher capacity for strand displacement DNA synthesis than wild type Polδ. Human cell lines overexpressing PolδD316A;E318A display a mild mutator phenotype, while nuclear extracts of these cells exhibit reduced MMR activity in vitro, and these defects are complemented by overexpression or addition of exogenous human Exonuclease 1 (EXO1). By contrast, another proofreading-deficient mutant, PolδD515V, which has a weaker strand displacement activity, does not decrease the MMR activity as significantly as PolδD316A;E318A. In addition, PolδD515V does not increase the mutation frequency in MMR-proficient cells. Based on our findings, we propose that the proofreading activity restricts the strand displacement activity of Polδ in MMR. This contributes to maintain the nicks required for EXO1 entry, and in this manner ensures the dominance of the EXO1-dependent MMR pathway.
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Affiliation(s)
- Dekang Liu
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Jane H Frederiksen
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Sascha E Liberti
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Anne Lützen
- Department of Science, Systems and Models, Roskilde University, Denmark
| | - Guido Keijzers
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Javier Pena-Diaz
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Lene Juel Rasmussen
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
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20
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Thientosapol ES, Sharbeen G, Lau KKE, Bosnjak D, Durack T, Stevanovski I, Weninger W, Jolly CJ. Proximity to AGCT sequences dictates MMR-independent versus MMR-dependent mechanisms for AID-induced mutation via UNG2. Nucleic Acids Res 2017; 45:3146-3157. [PMID: 28039326 PMCID: PMC5389528 DOI: 10.1093/nar/gkw1300] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 12/16/2016] [Indexed: 11/30/2022] Open
Abstract
AID deaminates C to U in either strand of Ig genes, exclusively producing C:G/G:C to T:A/A:T transition mutations if U is left unrepaired. Error-prone processing by UNG2 or mismatch repair diversifies mutation, predominantly at C:G or A:T base pairs, respectively. Here, we show that transversions at C:G base pairs occur by two distinct processing pathways that are dictated by sequence context. Within and near AGCT mutation hotspots, transversion mutation at C:G was driven by UNG2 without requirement for mismatch repair. Deaminations in AGCT were refractive both to processing by UNG2 and to high-fidelity base excision repair (BER) downstream of UNG2, regardless of mismatch repair activity. We propose that AGCT sequences resist faithful BER because they bind BER-inhibitory protein(s) and/or because hemi-deaminated AGCT motifs innately form a BER-resistant DNA structure. Distal to AGCT sequences, transversions at G were largely co-dependent on UNG2 and mismatch repair. We propose that AGCT-distal transversions are produced when apyrimidinic sites are exposed in mismatch excision patches, because completion of mismatch repair would require bypass of these sites.
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Affiliation(s)
- Eddy Sanchai Thientosapol
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
| | - George Sharbeen
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
| | - K K Edwin Lau
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
| | - Daniel Bosnjak
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
| | - Timothy Durack
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
| | - Igor Stevanovski
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
| | - Wolfgang Weninger
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
| | - Christopher J Jolly
- Centenary Institute, Royal Prince Alfred Hospital, Camperdown NSW 2050, and Sydney Medical School, The University of Sydney, Sydney NSW 2006, Australia
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21
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DNA mismatch repair and its many roles in eukaryotic cells. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2017; 773:174-187. [PMID: 28927527 DOI: 10.1016/j.mrrev.2017.07.001] [Citation(s) in RCA: 119] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 07/01/2017] [Accepted: 07/06/2017] [Indexed: 02/06/2023]
Abstract
DNA mismatch repair (MMR) is an important DNA repair pathway that plays critical roles in DNA replication fidelity, mutation avoidance and genome stability, all of which contribute significantly to the viability of cells and organisms. MMR is widely-used as a diagnostic biomarker for human cancers in the clinic, and as a biomarker of cancer susceptibility in animal model systems. Prokaryotic MMR is well-characterized at the molecular and mechanistic level; however, MMR is considerably more complex in eukaryotic cells than in prokaryotic cells, and in recent years, it has become evident that MMR plays novel roles in eukaryotic cells, several of which are not yet well-defined or understood. Many MMR-deficient human cancer cells lack mutations in known human MMR genes, which strongly suggests that essential eukaryotic MMR components/cofactors remain unidentified and uncharacterized. Furthermore, the mechanism by which the eukaryotic MMR machinery discriminates between the parental (template) and the daughter (nascent) DNA strand is incompletely understood and how cells choose between the EXO1-dependent and the EXO1-independent subpathways of MMR is not known. This review summarizes recent literature on eukaryotic MMR, with emphasis on the diverse cellular roles of eukaryotic MMR proteins, the mechanism of strand discrimination and cross-talk/interactions between and co-regulation of MMR and other DNA repair pathways in eukaryotic cells. The main conclusion of the review is that MMR proteins contribute to genome stability through their ability to recognize and promote an appropriate cellular response to aberrant DNA structures, especially when they arise during DNA replication. Although the molecular mechanism of MMR in the eukaryotic cell is still not completely understood, increased used of single-molecule analyses in the future may yield new insight into these unsolved questions.
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22
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Girelli Zubani G, Zivojnovic M, De Smet A, Albagli-Curiel O, Huetz F, Weill JC, Reynaud CA, Storck S. Pms2 and uracil-DNA glycosylases act jointly in the mismatch repair pathway to generate Ig gene mutations at A-T base pairs. J Exp Med 2017; 214:1169-1180. [PMID: 28283534 PMCID: PMC5379981 DOI: 10.1084/jem.20161576] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 12/19/2016] [Accepted: 01/26/2017] [Indexed: 11/06/2022] Open
Abstract
Girelli Zubani et al. show that the Pms2 component of the mismatch repair complex and multiple uracil glycosylases contribute, each with a distinct strand bias, to enlarge the Ig gene mutation spectrum from G-C to A-T bases. During somatic hypermutation (SHM) of immunoglobulin genes, uracils introduced by activation-induced cytidine deaminase are processed by uracil-DNA glycosylase (UNG) and mismatch repair (MMR) pathways to generate mutations at G-C and A-T base pairs, respectively. Paradoxically, the MMR-nicking complex Pms2/Mlh1 is apparently dispensable for A-T mutagenesis. Thus, how detection of U:G mismatches is translated into the single-strand nick required for error-prone synthesis is an open question. One model proposed that UNG could cooperate with MMR by excising a second uracil in the vicinity of the U:G mismatch, but it failed to explain the low impact of UNG inactivation on A-T mutagenesis. In this study, we show that uracils generated in the G1 phase in B cells can generate equal proportions of A-T and G-C mutations, which suggests that UNG and MMR can operate within the same time frame during SHM. Furthermore, we show that Ung−/−Pms2−/− mice display a 50% reduction in mutations at A-T base pairs and that most remaining mutations at A-T bases depend on two additional uracil glycosylases, thymine-DNA glycosylase and SMUG1. These results demonstrate that Pms2/Mlh1 and multiple uracil glycosylases act jointly, each one with a distinct strand bias, to enlarge the immunoglobulin gene mutation spectrum from G-C to A-T bases.
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Affiliation(s)
- Giulia Girelli Zubani
- Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France
| | - Marija Zivojnovic
- Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France
| | - Annie De Smet
- Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France
| | - Olivier Albagli-Curiel
- Institut Cochin, Institut National de la Santé et de la Recherche Médicale U1016, Centre National de la Recherche Scientifique UMR8104, Faculté de Médecine-Site Cochin, Université Paris Descartes, Sorbonne Paris Cité, 75006 Paris, France
| | - François Huetz
- Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France.,Département d'Immunologie, Institut Pasteur, 75015 Paris, France
| | - Jean-Claude Weill
- Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France
| | - Claude-Agnès Reynaud
- Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France
| | - Sébastien Storck
- Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France
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Methot S, Di Noia J. Molecular Mechanisms of Somatic Hypermutation and Class Switch Recombination. Adv Immunol 2017; 133:37-87. [DOI: 10.1016/bs.ai.2016.11.002] [Citation(s) in RCA: 165] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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24
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Grin I, Ishchenko AA. An interplay of the base excision repair and mismatch repair pathways in active DNA demethylation. Nucleic Acids Res 2016; 44:3713-27. [PMID: 26843430 PMCID: PMC4856981 DOI: 10.1093/nar/gkw059] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Accepted: 01/22/2016] [Indexed: 01/02/2023] Open
Abstract
Active DNA demethylation (ADDM) in mammals occurs via hydroxylation of 5-methylcytosine (5mC) by TET and/or deamination by AID/APOBEC family enzymes. The resulting 5mC derivatives are removed through the base excision repair (BER) pathway. At present, it is unclear how the cell manages to eliminate closely spaced 5mC residues whilst avoiding generation of toxic BER intermediates and whether alternative DNA repair pathways participate in ADDM. It has been shown that non-canonical DNA mismatch repair (ncMMR) can remove both alkylated and oxidized nucleotides from DNA. Here, a phagemid DNA containing oxidative base lesions and methylated sites are used to examine the involvement of various DNA repair pathways in ADDM in murine and human cell-free extracts. We demonstrate that, in addition to short-patch BER, 5-hydroxymethyluracil and uracil mispaired with guanine can be processed by ncMMR and long-patch BER with concomitant removal of distant 5mC residues. Furthermore, the presence of multiple mispairs in the same MMR nick/mismatch recognition region together with BER-mediated nick formation promotes proficient ncMMR resulting in the reactivation of an epigenetically silenced reporter gene in murine cells. These findings suggest cooperation between BER and ncMMR in the removal of multiple mismatches that might occur in mammalian cells during ADDM.
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Affiliation(s)
- Inga Grin
- Laboratoire «Stabilité Génétique et Oncogenèse» CNRS, UMR 8200, Univ. Paris-Sud, Université Paris-Saclay, Equipe Labellisée Ligue Contre le Cancer, F-94805 Villejuif, France Gustave Roussy Cancer Campus, F-94805 Villejuif, France SB RAS Institute of Chemical Biology and Fundamental Medicine, 8 Lavrentieva Avenue, Novosibirsk 630090, Russia Department of Natural Sciences, Novosibirsk State University, 2 Pirogova Street, Novosibirsk 630090, Russia
| | - Alexander A Ishchenko
- Laboratoire «Stabilité Génétique et Oncogenèse» CNRS, UMR 8200, Univ. Paris-Sud, Université Paris-Saclay, Equipe Labellisée Ligue Contre le Cancer, F-94805 Villejuif, France Gustave Roussy Cancer Campus, F-94805 Villejuif, France
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25
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Kadyrova LY, Kadyrov FA. Endonuclease activities of MutLα and its homologs in DNA mismatch repair. DNA Repair (Amst) 2016; 38:42-49. [PMID: 26719141 PMCID: PMC4820397 DOI: 10.1016/j.dnarep.2015.11.023] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 08/26/2015] [Accepted: 11/30/2015] [Indexed: 12/28/2022]
Abstract
MutLα is a key component of the DNA mismatch repair system in eukaryotes. The DNA mismatch repair system has several genetic stabilization functions. Of these functions, DNA mismatch repair is the major one. The loss of MutLα abolishes DNA mismatch repair, thereby predisposing humans to cancer. MutLα has an endonuclease activity that is required for DNA mismatch repair. The endonuclease activity of MutLα depends on the DQHA(X)2E(X)4E motif which is a part of the active site of the nuclease. This motif is also present in many bacterial MutL and eukaryotic MutLγ proteins, DNA mismatch repair system factors that are homologous to MutLα. Recent studies have shown that yeast MutLγ and several MutL proteins containing the DQHA(X)2E(X)4E motif possess endonuclease activities. Here, we review the endonuclease activities of MutLα and its homologs in the context of DNA mismatch repair.
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Affiliation(s)
- Lyudmila Y Kadyrova
- Department of Biochemistry and Molecular Biology, Southern Illinois University School of Medicine, Carbondale, IL 62901, USA
| | - Farid A Kadyrov
- Department of Biochemistry and Molecular Biology, Southern Illinois University School of Medicine, Carbondale, IL 62901, USA.
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26
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Bregenhorn S, Kallenberger L, Artola-Borán M, Peña-Diaz J, Jiricny J. Non-canonical uracil processing in DNA gives rise to double-strand breaks and deletions: relevance to class switch recombination. Nucleic Acids Res 2016; 44:2691-705. [PMID: 26743004 PMCID: PMC4824095 DOI: 10.1093/nar/gkv1535] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Accepted: 12/23/2015] [Indexed: 12/24/2022] Open
Abstract
During class switch recombination (CSR), antigen-stimulated B-cells rearrange their immunoglobulin constant heavy chain (CH) loci to generate antibodies with different effector functions. CSR is initiated by activation-induced deaminase (AID), which converts cytosines in switch (S) regions, repetitive sequences flanking the CH loci, to uracils. Although U/G mispairs arising in this way are generally efficiently repaired to C/Gs by uracil DNA glycosylase (UNG)-initiated base excision repair (BER), uracil processing in S-regions of activated B-cells occasionally gives rise to double strand breaks (DSBs), which trigger CSR. Surprisingly, genetic experiments revealed that CSR is dependent not only on AID and UNG, but also on mismatch repair (MMR). To elucidate the role of MMR in CSR, we studied the processing of uracil-containing DNA substrates in extracts of MMR-proficient and –deficient human cells, as well as in a system reconstituted from recombinant BER and MMR proteins. Here, we show that the interplay of these repair systems gives rise to DSBs in vitro and to genomic deletions and mutations in vivo, particularly in an S-region sequence. Our findings further suggest that MMR affects pathway choice in DSB repair. Given its amenability to manipulation, our system represents a powerful tool for the molecular dissection of CSR.
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Affiliation(s)
- Stephanie Bregenhorn
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland Department of Biology, Swiss Federal Institute of Technology (ETH) Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Lia Kallenberger
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Mariela Artola-Borán
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Javier Peña-Diaz
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland University of Copenhagen, Faculty of Health Sciences Center for Healthy Aging, Department of Neuroscience and Pharmacology, Blegdamsvej 3b, DK-2200 Copenhagen N, Denmark
| | - Josef Jiricny
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland Department of Biology, Swiss Federal Institute of Technology (ETH) Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
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27
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Abstract
Species survival depends on the faithful replication of genetic information, which is continually monitored and maintained by DNA repair pathways that correct replication errors and the thousands of lesions that arise daily from the inherent chemical lability of DNA and the effects of genotoxic agents. Nonetheless, neutrally evolving DNA (not under purifying selection) accumulates base substitutions with time (the neutral mutation rate). Thus, repair processes are not 100% efficient. The neutral mutation rate varies both between and within chromosomes. For example it is 10-50 fold higher at CpGs than at non-CpG positions. Interestingly, the neutral mutation rate at non-CpG sites is positively correlated with CpG content. Although the basis of this correlation was not immediately apparent, some bioinformatic results were consistent with the induction of non-CpG mutations by DNA repair at flanking CpG sites. Recent studies with a model system showed that in vivo repair of preformed lesions (mismatches, abasic sites, single stranded nicks) can in fact induce mutations in flanking DNA. Mismatch repair (MMR) is an essential component for repair-induced mutations, which can occur as distant as 5 kb from the introduced lesions. Most, but not all, mutations involved the C of TpCpN (G of NpGpA) which is the target sequence of the C-preferring single-stranded DNA specific APOBEC deaminases. APOBEC-mediated mutations are not limited to our model system: Recent studies by others showed that some tumors harbor mutations with the same signature, as can intermediates in RNA-guided endonuclease-mediated genome editing. APOBEC deaminases participate in normal physiological functions such as generating mutations that inactivate viruses or endogenous retrotransposons, or that enhance immunoglobulin diversity in B cells. The recruitment of normally physiological error-prone processes during DNA repair would have important implications for disease, aging and evolution. This perspective briefly reviews both the bioinformatic and biochemical literature relevant to repair-induced mutagenesis and discusses future directions required to understand the mechanistic basis of this process.
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Affiliation(s)
- Jia Chen
- School of Life Science and Technology, ShanghaiTech University, Building 8, 319 Yueyang Road, Shanghai 200031, China
| | - Anthony V Furano
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Building 8, Room 203, 8 Center Drive, MSC 0830, Bethesda, MD 20892-0830, USA.
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28
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Repmann S, Olivera-Harris M, Jiricny J. Influence of oxidized purine processing on strand directionality of mismatch repair. J Biol Chem 2015; 290:9986-99. [PMID: 25694431 DOI: 10.1074/jbc.m114.629907] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Indexed: 12/23/2022] Open
Abstract
Replicative DNA polymerases are high fidelity enzymes that misincorporate nucleotides into nascent DNA with a frequency lower than [1/10(5)], and this precision is improved to about [1/10(7)] by their proofreading activity. Because this fidelity is insufficient to replicate most genomes without error, nature evolved postreplicative mismatch repair (MMR), which improves the fidelity of DNA replication by up to 3 orders of magnitude through correcting biosynthetic errors that escaped proofreading. MMR must be able to recognize non-Watson-Crick base pairs and excise the misincorporated nucleotides from the nascent DNA strand, which carries by definition the erroneous genetic information. In eukaryotes, MMR is believed to be directed to the nascent strand by preexisting discontinuities such as gaps between Okazaki fragments in the lagging strand or breaks in the leading strand generated by the mismatch-activated endonuclease of the MutL homologs PMS1 in yeast and PMS2 in vertebrates. We recently demonstrated that the eukaryotic MMR machinery can make use also of strand breaks arising during excision of uracils or ribonucleotides from DNA. We now show that intermediates of MutY homolog-dependent excision of adenines mispaired with 8-oxoguanine (G(O)) also act as MMR initiation sites in extracts of human cells or Xenopus laevis eggs. Unexpectedly, G(O)/C pairs were not processed in these extracts and failed to affect MMR directionality, but extracts supplemented with exogenous 8-oxoguanine DNA glycosylase (OGG1) did so. Because OGG1-mediated excision of G(O) might misdirect MMR to the template strand, our findings suggest that OGG1 activity might be inhibited during MMR.
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Affiliation(s)
- Simone Repmann
- From the Institute of Molecular Cancer Research of the University of Zurich and the Swiss Institutes of Technology Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Maite Olivera-Harris
- From the Institute of Molecular Cancer Research of the University of Zurich and the Swiss Institutes of Technology Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Josef Jiricny
- From the Institute of Molecular Cancer Research of the University of Zurich and the Swiss Institutes of Technology Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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29
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Ciccarese S, Vaccarelli G, Lefranc MP, Tasco G, Consiglio A, Casadio R, Linguiti G, Antonacci R. Characteristics of the somatic hypermutation in the Camelus dromedarius T cell receptor gamma (TRG) and delta (TRD) variable domains. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2014; 46:300-13. [PMID: 24836674 DOI: 10.1016/j.dci.2014.05.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Revised: 05/05/2014] [Accepted: 05/05/2014] [Indexed: 05/05/2023]
Abstract
In previous reports, we had shown in Camelus dromedarius that diversity in T cell receptor gamma (TRG) and delta (TRD) variable domains can be generated by somatic hypermutation (SHM). In the present paper, we further the previous finding by analyzing 85 unique spleen cDNA sequences encoding a total of 331 mutations from a single animal, and comparing the properties of the mutation profiles of dromedary TRG and TRD variable domains. The transition preference and the significant mutation frequency in the AID motifs (dgyw/wrch and wa/tw) demonstrate a strong dependence of the enzymes mediating SHM in TRG and TRD genes of dromedary similar to that of immunoglobulin genes in mammals. Overall, results reveal no asymmetry in the motifs targeting, i.e. mutations are equally distributed among g:c and a:t base pairs and replacement mutations are favored at the AID motifs, whereas neutral mutations appear to be more prone to accumulate in bases outside of the motifs. A detailed analysis of clonal lineages in TRG and TRD cDNA sequences also suggests that clonal expansion of mutated productive rearrangements may be crucial in shaping the somatic diversification in the dromedary. This is confirmed by the fact that our structural models, computed by adopting a comparative procedure, are consistent with the possibility that, irrespective of where (in the CDR-IMGT or in FR-IMGT) the diversity was generated by mutations, both clonal expansion and selection seem to be strictly related to an enhanced structural stability of the γδ subunits.
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MESH Headings
- Amino Acid Sequence
- Animals
- Base Sequence
- Camelus/genetics
- Gene Rearrangement, delta-Chain T-Cell Antigen Receptor
- Gene Rearrangement, gamma-Chain T-Cell Antigen Receptor
- Models, Molecular
- Molecular Sequence Data
- Mutation Rate
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Receptors, Antigen, T-Cell, gamma-delta/chemistry
- Receptors, Antigen, T-Cell, gamma-delta/genetics
- Sequence Analysis, DNA
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Affiliation(s)
| | - Giovanna Vaccarelli
- Department of Biology, University of Bari, via E. Orabona 4, 70125 Bari, Italy
| | - Marie-Paule Lefranc
- IMGT, Laboratoire d'ImmunoGénétique Moléculaire, Institut de Génétique Humaine, UPR CNRS 1142, Université Montpellier 2, 34396 Montpellier Cedex 5, France
| | - Gianluca Tasco
- Biocomputing Group, CIRI-Health Science and Technologies/Department of Biology, University of Bologna, via Selmi 3, 40126 Bologna, Italy
| | - Arianna Consiglio
- CNR, Institute for Biomedical Technologies of Bari, via Amendola, 70125 Bari, Italy
| | - Rita Casadio
- Biocomputing Group, CIRI-Health Science and Technologies/Department of Biology, University of Bologna, via Selmi 3, 40126 Bologna, Italy
| | - Giovanna Linguiti
- Department of Biology, University of Bari, via E. Orabona 4, 70125 Bari, Italy
| | - Rachele Antonacci
- Department of Biology, University of Bari, via E. Orabona 4, 70125 Bari, Italy
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30
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Bak ST, Sakellariou D, Pena-Diaz J. The dual nature of mismatch repair as antimutator and mutator: for better or for worse. Front Genet 2014; 5:287. [PMID: 25191341 PMCID: PMC4139959 DOI: 10.3389/fgene.2014.00287] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 08/04/2014] [Indexed: 01/19/2023] Open
Abstract
DNA is constantly under attack by a number of both exogenous and endogenous agents that challenge its integrity. Among the mechanisms that have evolved to counteract this deleterious action, mismatch repair (MMR) has specialized in removing DNA biosynthetic errors that occur when replicating the genome. Malfunction or inactivation of this system results in an increase in spontaneous mutability and a strong predisposition to tumor development. Besides this key corrective role, MMR proteins are involved in other pathways of DNA metabolism such as mitotic and meiotic recombination and processing of oxidative damage. Surprisingly, MMR is also required for certain mutagenic processes. The mutagenic MMR has beneficial consequences contributing to the generation of a vast repertoire of antibodies through class switch recombination and somatic hypermutation processes. However, this non-canonical mutagenic MMR also has detrimental effects; it promotes repeat expansions associated with neuromuscular and neurodegenerative diseases and may contribute to cancer/disease-related aberrant mutations and translocations. The reaction responsible for replication error correction has been the most thoroughly studied and it is the subject to numerous reviews. This review describes briefly the biochemistry of MMR and focuses primarily on the non-canonical MMR activities described in mammals as well as emerging research implicating interplay of MMR and chromatin.
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Affiliation(s)
- Sara Thornby Bak
- Department of Neuroscience and Pharmacology and Center for Healthy Aging, University of Copenhagen Copenhagen, Denmark
| | - Despoina Sakellariou
- Department of Neuroscience and Pharmacology and Center for Healthy Aging, University of Copenhagen Copenhagen, Denmark
| | - Javier Pena-Diaz
- Department of Neuroscience and Pharmacology and Center for Healthy Aging, University of Copenhagen Copenhagen, Denmark
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31
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Processive DNA demethylation via DNA deaminase-induced lesion resolution. PLoS One 2014; 9:e97754. [PMID: 25025377 PMCID: PMC4098905 DOI: 10.1371/journal.pone.0097754] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 04/23/2014] [Indexed: 12/13/2022] Open
Abstract
Base modifications of cytosine are an important aspect of chromatin biology, as they can directly regulate gene expression, while DNA repair ensures that those modifications retain genome integrity. Here we characterize how cytosine DNA deaminase AID can initiate DNA demethylation. In vitro, AID initiated targeted DNA demethylation of methyl CpGs when in combination with DNA repair competent extracts. Mechanistically, this is achieved by inducing base alterations at or near methyl-cytosine, with the lesion being resolved either via single base substitution or a more efficient processive polymerase dependent repair. The biochemical findings are recapitulated in an in vivo transgenic targeting assay, and provide the genetic support of the molecular insight into DNA demethylation. This targeting approach supports the hypothesis that mCpG DNA demethylation can proceed via various pathways and mCpGs do not have to be targeted to be demethylated.
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32
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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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33
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Base excision repair AP endonucleases and mismatch repair act together to induce checkpoint-mediated autophagy. Nat Commun 2014; 4:2674. [PMID: 24154628 PMCID: PMC3826653 DOI: 10.1038/ncomms3674] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 09/26/2013] [Indexed: 12/18/2022] Open
Abstract
Cellular responses to DNA damage involve distinct DNA repair pathways, such as mismatch repair (MMR) and base excision repair (BER). Using Caenorhabditis elegans as a model system, we present genetic and molecular evidence of a mechanistic link between processing of DNA damage and activation of autophagy. Here we show that the BER AP endonucleases APN-1 and EXO-3 function in the same pathway as MMR, to elicit DNA-directed toxicity in response to 5-fluorouracil, a mainstay of systemic adjuvant treatment of solid cancers. Immunohistochemical analyses suggest that EXO-3 generates the DNA nicks required for MMR activation. Processing of DNA damage via this pathway, in which both BER and MMR enzymes are required, leads to induction of autophagy in C. elegans and human cells. Hence, our data show that MMR- and AP endonuclease-dependent processing of 5-fluorouracil-induced DNA damage leads to checkpoint activation and induction of autophagy, whose hyperactivation contributes to cell death.
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Differential expression of APE1 and APE2 in germinal centers promotes error-prone repair and A:T mutations during somatic hypermutation. Proc Natl Acad Sci U S A 2014; 111:9217-22. [PMID: 24927551 DOI: 10.1073/pnas.1405590111] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Somatic hypermutation (SHM) of antibody variable region genes is initiated in germinal center B cells during an immune response by activation-induced cytidine deaminase (AID), which converts cytosines to uracils. During accurate repair in nonmutating cells, uracil is excised by uracil DNA glycosylase (UNG), leaving abasic sites that are incised by AP endonuclease (APE) to create single-strand breaks, and the correct nucleotide is reinserted by DNA polymerase β. During SHM, for unknown reasons, repair is error prone. There are two APE homologs in mammals and, surprisingly, APE1, in contrast to its high expression in both resting and in vitro-activated splenic B cells, is expressed at very low levels in mouse germinal center B cells where SHM occurs, and APE1 haploinsufficiency has very little effect on SHM. In contrast, the less efficient homolog, APE2, is highly expressed and contributes not only to the frequency of mutations, but also to the generation of mutations at A:T base pair (bp), insertions, and deletions. In the absence of both UNG and APE2, mutations at A:T bp are dramatically reduced. Single-strand breaks generated by APE2 could provide entry points for exonuclease recruited by the mismatch repair proteins Msh2-Msh6, and the known association of APE2 with proliferating cell nuclear antigen could recruit translesion polymerases to create mutations at AID-induced lesions and also at A:T bp. Our data provide new insight into error-prone repair of AID-induced lesions, which we propose is facilitated by down-regulation of APE1 and up-regulation of APE2 expression in germinal center B cells.
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35
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Shao H, Baitinger C, Soderblom EJ, Burdett V, Modrich P. Hydrolytic function of Exo1 in mammalian mismatch repair. Nucleic Acids Res 2014; 42:7104-12. [PMID: 24829455 PMCID: PMC4066806 DOI: 10.1093/nar/gku420] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Genetic and biochemical studies have previously implicated exonuclease 1 (Exo1) in yeast and mammalian mismatch repair, with results suggesting that function of the protein in the reaction depends on both its hydrolytic activity and its ability to interact with other components of the repair system. However, recent analysis of an Exo1-E109K knockin mouse has concluded that Exo1 function in mammalian mismatch repair is restricted to a structural role, a conclusion based on a prior report that N-terminal His-tagged Exo1-E109K is hydrolytically defective. Because Glu-109 is distant from the nuclease hydrolytic center, we have compared the activity of untagged full-length Exo1-E109K with that of wild type Exo1 and the hydrolytically defective active site mutant Exo1-D173A. We show that the activity of Exo1-E109K is comparable to that of wild type enzyme in a conventional exonuclease assay and that in contrast to a D173A active site mutant, Exo1-E109K is fully functional in mismatch-provoked excision and repair. We conclude that the catalytic function of Exo1 is required for its participation in mismatch repair. We also consider the other phenotypes of the Exo1-E109K mouse in the context of Exo1 hydrolytic function.
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Affiliation(s)
- Hongbing Shao
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Celia Baitinger
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
| | - Erik J Soderblom
- Proteomics Core Facility, Duke University Medical Center, Durham, NC 27710, USA
| | - Vickers Burdett
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Paul Modrich
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
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Chen J, Miller BF, Furano AV. Repair of naturally occurring mismatches can induce mutations in flanking DNA. eLife 2014; 3:e02001. [PMID: 24843013 PMCID: PMC3999860 DOI: 10.7554/elife.02001] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
'Normal' genomic DNA contains hundreds of mismatches that are generated daily by the spontaneous deamination of C (U/G) and methyl-C (T/G). Thus, a mutagenic effect of their repair could constitute a serious genetic burden. We show here that while mismatches introduced into human cells on an SV40-based episome were invariably repaired, this process induced mutations in flanking DNA at a significantly higher rate than no mismatch controls. Most mutations involved the C of TpC, the substrate of some single strand-specific APOBEC cytidine deaminases, similar to the mutations that can typify the 'mutator phenotype' of numerous tumors. siRNA knockdowns and chromatin immunoprecipitation showed that TpC preferring APOBECs mediate the mutagenesis, and siRNA knockdowns showed that both the base excision and mismatch repair pathways are involved. That naturally occurring mispairs can be converted to mutators, represents an heretofore unsuspected source of genetic changes that could underlie disease, aging, and evolutionary change.DOI: http://dx.doi.org/10.7554/eLife.02001.001.
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Affiliation(s)
- Jia Chen
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, United States
| | - Brendan F Miller
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, United States
| | - Anthony V Furano
- Section on Genomic Structure and Function, Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, United States
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37
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Somatic hypermutation at A/T-rich oligonucleotide substrates shows different strand polarities in Ung-deficient or -proficient backgrounds. Mol Cell Biol 2014; 34:2176-87. [PMID: 24710273 DOI: 10.1128/mcb.01452-13] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
A/T mutations at immunoglobulin loci are introduced by DNA polymerase η (Polη) during an Msh2/6-dependent repair process which results in A's being mutated 2-fold more often than T's. This patch synthesis is initiated by a DNA incision event whose origin is still obscure. We report here the analysis of A/T oligonucleotide mutation substrates inserted at the heavy chain locus, including or not including internal C's or G's. Surprisingly, the template composed of only A's and T's was highly mutated over its entire 90-bp length, with a 2-fold decrease in mutation from the 5' to the 3' end and a constant A/T ratio of 4. These results imply that Polη synthesis was initiated from a break in the 5'-flanking region of the substrate and proceeded over its entire length. The A/T bias was strikingly altered in an Ung(-/-) background, which provides the first experimental evidence supporting a concerted action of Ung and Msh2/6 pathways to generate mutations at A/T bases. New analysis of Pms2(-/-) animals provided a complementary picture, revealing an A/T mutation ratio of 4. We therefore propose that Ung and Pms2 may exert a mutual backup function for the DNA incision that promotes synthesis by Polη, each with a distinct strand bias.
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Franchini DM, Incorvaia E, Rangam G, Coker HA, Petersen-Mahrt SK. Simultaneous in vitro characterisation of DNA deaminase function and associated DNA repair pathways. PLoS One 2013; 8:e82097. [PMID: 24349193 PMCID: PMC3857227 DOI: 10.1371/journal.pone.0082097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 10/25/2013] [Indexed: 02/02/2023] Open
Abstract
During immunoglobulin (Ig) diversification, activation-induced deaminase (AID) initiates somatic hypermutation and class switch recombination by catalysing the conversion of cytosine to uracil. The synergy between AID and DNA repair pathways is fundamental for the introduction of mutations, however the molecular and biochemical mechanisms underlying this process are not fully elucidated. We describe a novel method to efficiently decipher the composition and activity of DNA repair pathways that are activated by AID-induced lesions. The in vitro resolution (IVR) assay combines AID based deamination and DNA repair activities from a cellular milieu in a single assay, thus avoiding synthetically created DNA-lesions or genetic-based readouts. Recombinant GAL4-AID fusion protein is targeted to a plasmid containing GAL4 binding sites, allowing for controlled cytosine deamination within a substrate plasmid. Subsequently, the Xenopus laevis egg extract provides a source of DNA repair proteins and functional repair pathways. Our results demonstrated that DNA repair pathways which are in vitro activated by AID-induced lesions are reminiscent of those found during AID-induced in vivo Ig diversification. The comparative ease of manipulation of this in vitro systems provides a new approach to dissect the complex DNA repair pathways acting on defined physiologically lesions, can be adapted to use with other DNA damaging proteins (e.g. APOBECs), and provide a means to develop and characterise pharmacological agents to inhibit these potentially oncogenic processes.
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Affiliation(s)
- Don-Marc Franchini
- DNA Editing in Immunity and Epigenetics, IFOM-Fondazione Instituto FIRC di Oncologia Molecolare, Milano, Italy
- DNA Editing Lab, Clare Hall Laboratories, London Research Institute, South Mimms, United Kingdom
| | - Elisabetta Incorvaia
- DNA Editing in Immunity and Epigenetics, IFOM-Fondazione Instituto FIRC di Oncologia Molecolare, Milano, Italy
| | - Gopinath Rangam
- DNA Editing in Immunity and Epigenetics, IFOM-Fondazione Instituto FIRC di Oncologia Molecolare, Milano, Italy
- DNA Editing Lab, Clare Hall Laboratories, London Research Institute, South Mimms, United Kingdom
| | - Heather A. Coker
- DNA Editing Lab, Clare Hall Laboratories, London Research Institute, South Mimms, United Kingdom
| | - Svend K. Petersen-Mahrt
- DNA Editing in Immunity and Epigenetics, IFOM-Fondazione Instituto FIRC di Oncologia Molecolare, Milano, Italy
- DNA Editing Lab, Clare Hall Laboratories, London Research Institute, South Mimms, United Kingdom
- * E-mail:
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Perevoztchikova SA, Romanova EA, Oretskaya TS, Friedhoff P, Kubareva EA. Modern aspects of the structural and functional organization of the DNA mismatch repair system. Acta Naturae 2013; 5:17-34. [PMID: 24303200 PMCID: PMC3848065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
This review is focused on the general aspects of the DNA mismatch repair (MMR) process. The key proteins of the DNA mismatch repair system are MutS and MutL. To date, their main structural and functional characteristics have been thoroughly studied. However, different opinions exist about the initial stages of the mismatch repair process with the participation of these proteins. This review aims to summarize the data on the relationship between the two MutS functions, ATPase and DNA-binding, and to systematize various models of coordination between the mismatch site and the strand discrimination site in DNA. To test these models, novel techniques for the trapping of short-living complexes that appear at different MMR stages are to be developed.
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Affiliation(s)
- S. A. Perevoztchikova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1, bld. 40, Moscow, Russia, 119991
| | - E. A. Romanova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1, bld. 40, Moscow, Russia, 119991
| | - T. S. Oretskaya
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1, bld. 40, Moscow, Russia, 119991
- Chemistry Department, Lomonosov Moscow State University, Leninskie Gory, 1, bld. 3, Moscow, Russia, 119991
| | - P. Friedhoff
- Institute of Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany
| | - E. A. Kubareva
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1, bld. 40, Moscow, Russia, 119991
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40
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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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41
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Mechanism of somatic hypermutation at the WA motif by human DNA polymerase η. Proc Natl Acad Sci U S A 2013; 110:8146-51. [PMID: 23630267 DOI: 10.1073/pnas.1303126110] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Somatic hypermutation is programmed base substitutions in the variable regions of Ig genes for high-affinity antibody generation. Two motifs, RGYW and WA (R, purine; Y, pyrimidine; W, A or T), have been found to be somatic hypermutation hotspots. Overwhelming evidence suggests that DNA polymerase η (Pol η) is responsible for converting the WA motif to WG by misincorporating dGTP opposite the templating T. To elucidate the molecular mechanism, crystal structures and kinetics of human Pol η substituting dGTP for dATP in four sequence contexts, TA, AA, GA, and CA, have been determined and compared. The T:dGTP wobble base pair is stabilized by Gln-38 and Arg-61, two uniquely conserved residues among Pol η. Weak base paring of the W (T:A or A:T) at the primer end and their distinct interactions with Pol η lead to misincorporation of G in the WA motif. Between two WA motifs, our kinetic and structural data indicate that A-to-G mutation occurs more readily in the TA context than AA. Finally, Pol η can extend the T:G mispair efficiently to complete the mutagenesis.
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42
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Ghodgaonkar MM, Lazzaro F, Olivera-Pimentel M, Artola-Borán M, Cejka P, Reijns MA, Jackson AP, Plevani P, Muzi-Falconi M, Jiricny J. Ribonucleotides misincorporated into DNA act as strand-discrimination signals in eukaryotic mismatch repair. Mol Cell 2013; 50:323-32. [PMID: 23603115 PMCID: PMC3653069 DOI: 10.1016/j.molcel.2013.03.019] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2012] [Revised: 01/30/2013] [Accepted: 03/14/2013] [Indexed: 11/28/2022]
Abstract
To improve replication fidelity, mismatch repair (MMR) must detect non-Watson-Crick base pairs and direct their repair to the nascent DNA strand. Eukaryotic MMR in vitro requires pre-existing strand discontinuities for initiation; consequently, it has been postulated that MMR in vivo initiates at Okazaki fragment termini in the lagging strand and at nicks generated in the leading strand by the mismatch-activated MLH1/PMS2 endonuclease. We now show that a single ribonucleotide in the vicinity of a mismatch can act as an initiation site for MMR in human cell extracts and that MMR activation in this system is dependent on RNase H2. As loss of RNase H2 in S.cerevisiae results in a mild MMR defect that is reflected in increased mutagenesis, MMR in vivo might also initiate at RNase H2-generated nicks. We therefore propose that ribonucleotides misincoporated during DNA replication serve as physiological markers of the nascent DNA strand.
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Affiliation(s)
- Medini Manohar Ghodgaonkar
- Institute of Molecular Cancer Research of the University of Zurich and ETH Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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43
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Abstract
Base excision repair (BER) corrects DNA damage from oxidation, deamination and alkylation. Such base lesions cause little distortion to the DNA helix structure. BER is initiated by a DNA glycosylase that recognizes and removes the damaged base, leaving an abasic site that is further processed by short-patch repair or long-patch repair that largely uses different proteins to complete BER. At least 11 distinct mammalian DNA glycosylases are known, each recognizing a few related lesions, frequently with some overlap in specificities. Impressively, the damaged bases are rapidly identified in a vast excess of normal bases, without a supply of energy. BER protects against cancer, aging, and neurodegeneration and takes place both in nuclei and mitochondria. More recently, an important role of uracil-DNA glycosylase UNG2 in adaptive immunity was revealed. Furthermore, other DNA glycosylases may have important roles in epigenetics, thus expanding the repertoire of BER proteins.
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Affiliation(s)
- Hans E Krokan
- Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, N-7489 Trondheim, Norway.
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44
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Castillo-Acosta VM, Aguilar-Pereyra F, Bart JM, Navarro M, Ruiz-Pérez LM, Vidal AE, González-Pacanowska D. Increased uracil insertion in DNA is cytotoxic and increases the frequency of mutation, double strand break formation and VSG switching in Trypanosoma brucei. DNA Repair (Amst) 2012; 11:986-95. [DOI: 10.1016/j.dnarep.2012.09.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Revised: 09/18/2012] [Accepted: 09/21/2012] [Indexed: 12/25/2022]
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45
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Peña-Diaz J, Bregenhorn S, Ghodgaonkar M, Follonier C, Artola-Borán M, Castor D, Lopes M, Sartori AA, Jiricny J. Noncanonical mismatch repair as a source of genomic instability in human cells. Mol Cell 2012; 47:669-80. [PMID: 22864113 DOI: 10.1016/j.molcel.2012.07.006] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Revised: 05/19/2012] [Accepted: 06/29/2012] [Indexed: 11/24/2022]
Abstract
Mismatch repair (MMR) is a key antimutagenic process that increases the fidelity of DNA replication and recombination. Yet genetic experiments showed that MMR is required for antibody maturation, a process during which the immunoglobulin loci of antigen-stimulated B cells undergo extensive mutagenesis and rearrangements. In an attempt to elucidate the mechanism underlying the latter events, we set out to search for conditions that compromise MMR fidelity. Here, we describe noncanonical MMR (ncMMR), a process in which the MMR pathway is activated by various DNA lesions rather than by mispairs. ncMMR is largely independent of DNA replication, lacks strand directionality, triggers PCNA monoubiquitylation, and promotes recruitment of the error-prone polymerase-η to chromatin. Importantly, ncMMR is not limited to B cells but occurs also in other cell types. Moreover, it contributes to mutagenesis induced by alkylating agents. Activation of ncMMR may therefore play a role in genomic instability and cancer.
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Affiliation(s)
- Javier Peña-Diaz
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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46
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Saribasak H, Gearhart PJ. Does DNA repair occur during somatic hypermutation? Semin Immunol 2012; 24:287-92. [PMID: 22728014 DOI: 10.1016/j.smim.2012.05.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 05/18/2012] [Indexed: 11/25/2022]
Abstract
Activation-induced deaminase (AID) initiates a flood of DNA damage in the immunoglobulin loci, leading to abasic sites, single-strand breaks and mismatches. It is compelling that some proteins in the canonical base excision and mismatch repair pathways have been hijacked to increase mutagenesis during somatic hypermutation. Thus, the AID-induced mutagenic pathways involve a mix of DNA repair proteins and low fidelity DNA polymerases to create antibody diversity. In this review, we analyze the roles of base excision repair, mismatch repair, and mutagenesis during somatic hypermutation of rearranged variable genes. The emerging view is that faithful base excision repair occurs simultaneously with mutagenesis, whereas faithful mismatch repair is mostly absent.
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Affiliation(s)
- Huseyin Saribasak
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States
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47
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Trypanosomes lacking uracil-DNA glycosylase are hypersensitive to antifolates and present a mutator phenotype. Int J Biochem Cell Biol 2012; 44:1555-68. [PMID: 22728162 DOI: 10.1016/j.biocel.2012.06.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2012] [Revised: 06/04/2012] [Accepted: 06/12/2012] [Indexed: 01/13/2023]
Abstract
Cells contain low amounts of uracil in DNA which can be the result of dUTP misincorporation during replication or cytosine deamination. Elimination of uracil in the base excision repair pathway yields an abasic site, which is potentially mutagenic unless repaired. The Trypanosoma brucei genome presents a single uracil-DNA glycosylase responsible for removal of uracil from DNA. Here we establish that no excision activity is detected on U:G, U:A pairs or single-strand uracil-containing DNA in uracil-DNA glycosylase null mutant cell extracts, indicating the absence of back-up uracil excision activities. While procyclic forms can survive with moderate amounts of uracil in DNA, an analysis of the mutation rate and spectra in mutant cells revealed a hypermutator phenotype where the predominant events were GC to AT transitions and insertions. Defective elimination of uracil via the base excision repair pathway gives rise to hypersensitivity to antifolates and oxidative stress and an increased number of DNA strand breaks, suggesting the activation of alternative DNA repair pathways. Finally, we show that uracil-DNA glycosylase defective cells exhibit reduced infectivity in vivo demonstrating that efficient uracil elimination is important for survival within the mammalian host.
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48
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Peña-Diaz J, Jiricny J. Mammalian mismatch repair: error-free or error-prone? Trends Biochem Sci 2012; 37:206-14. [PMID: 22475811 DOI: 10.1016/j.tibs.2012.03.001] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Revised: 02/15/2012] [Accepted: 03/01/2012] [Indexed: 01/13/2023]
Abstract
A considerable surge of interest in the mismatch repair (MMR) system has been brought about by the discovery of a link between Lynch syndrome, an inherited predisposition to cancer of the colon and other organs, and malfunction of this key DNA metabolic pathway. This review focuses on recent advances in our understanding of the molecular mechanisms of canonical MMR, which improves replication fidelity by removing misincorporated nucleotides from the nascent DNA strand. We also discuss the involvement of MMR proteins in two other processes: trinucleotide repeat expansion and antibody maturation, in which MMR proteins are required for mutagenesis rather than for its prevention.
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Affiliation(s)
- Javier Peña-Diaz
- Institute of Molecular Cancer Research of the University of Zurich, Switzerland
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49
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Xiao Y, Jung C, Marx AD, Winkler I, Wyman C, Lebbink JHG, Friedhoff P, Cristovao M. Generation of DNA nanocircles containing mismatched bases. Biotechniques 2012; 51:259-62, 264-5. [PMID: 21988692 DOI: 10.2144/000113749] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Accepted: 08/25/2011] [Indexed: 11/23/2022] Open
Abstract
The DNA mismatch repair (MMR) system recognizes and repairs errors that escaped the proofreading function of DNA polymerases. To study molecular details of the MMR mechanism, in vitro biochemical assays require specific DNA substrates carrying mismatches and strand discrimination signals. Current approaches used to generate MMR substrates are time-consuming and/or not very flexible with respect to sequence context. Here we report an approach to generate small circular DNA containing a mismatch (nanocircles). Our method is based on the nicking of PCR products resulting in single-stranded 3' overhangs, which form DNA circles after annealing and ligation. Depending on the DNA template, one can generate mismatched circles containing a single hemimethylated GATC site (for use with the bacterial system) and/or nicking sites to generate DNA circles nicked in the top or bottom strand (for assays with the bacterial or eukaryotic MMR system). The size of the circles varied (323 to 1100 bp), their sequence was determined by the template DNA, and purification of the circles was achieved by ExoI/ExoIII digestion and/or gel extraction. The quality of the nanocircles was assessed by scanning-force microscopy and their suitability for in vitro repair initiation was examined using recombinant Escherichia coli MMR proteins.
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Affiliation(s)
- Yu Xiao
- Institute of Biochemistry, Justus-Liebig University, Giessen, Germany
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50
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Roles of endonuclease V, uracil-DNA glycosylase, and mismatch repair in Bacillus subtilis DNA base-deamination-induced mutagenesis. J Bacteriol 2011; 194:243-52. [PMID: 22056936 DOI: 10.1128/jb.06082-11] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The disruption of ung, the unique uracil-DNA-glycosylase-encoding gene in Bacillus subtilis, slightly increased the spontaneous mutation frequency to rifampin resistance (Rif(r)), suggesting that additional repair pathways counteract the mutagenic effects of uracil in this microorganism. An alternative excision repair pathway is involved in this process, as the loss of YwqL, a putative endonuclease V homolog, significantly increased the mutation frequency of the ung null mutant, suggesting that Ung and YwqL both reduce the mutagenic effects of base deamination. Consistent with this notion, sodium bisulfite (SB) increased the Rif(r) mutation frequency of the single ung and double ung ywqL strains, and the absence of Ung and/or YwqL decreased the ability of B. subtilis to eliminate uracil from DNA. Interestingly, the Rif(r) mutation frequency of single ung and mutSL (mismatch repair [MMR] system) mutants was dramatically increased in a ung knockout strain that was also deficient in MutSL, suggesting that the MMR pathway also counteracts the mutagenic effects of uracil. Since the mutation frequency of the ung mutSL strain was significantly increased by SB, in addition to Ung, the mutagenic effects promoted by base deamination in growing B. subtilis cells are prevented not only by YwqL but also by MMR. Importantly, in nondividing cells of B. subtilis, the accumulations of mutations in three chromosomal alleles were significantly diminished following the disruption of ung and ywqL. Thus, under conditions of nutritional stress, the processing of deaminated bases in B. subtilis may normally occur in an error-prone manner to promote adaptive mutagenesis.
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