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Programmable C:G to G:C genome editing with CRISPR-Cas9-directed base excision repair proteins. Nat Commun 2021; 12:1384. [PMID: 33654077 PMCID: PMC7925527 DOI: 10.1038/s41467-021-21559-9] [Citation(s) in RCA: 98] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 01/25/2021] [Indexed: 12/26/2022] Open
Abstract
Many genetic diseases are caused by single-nucleotide polymorphisms. Base editors can correct these mutations at single-nucleotide resolution, but until recently, only allowed for transition edits, addressing four out of twelve possible DNA base substitutions. Here, we develop a class of C:G to G:C Base Editors to create single-base genomic transversions in human cells. Our C:G to G:C Base Editors consist of a nickase-Cas9 fused to a cytidine deaminase and base excision repair proteins. Characterization of >30 base editor candidates reveal that they predominantly perform C:G to G:C editing (up to 90% purity), with rAPOBEC-nCas9-rXRCC1 being the most efficient (mean 15.4% and up to 37% without selection). C:G to G:C Base Editors target cytidine in WCW, ACC or GCT sequence contexts and within a precise three-nucleotide window of the target protospacer. We further target genes linked to dyslipidemia, hypertrophic cardiomyopathy, and deafness, showing the therapeutic potential of these base editors in interrogating and correcting human genetic diseases.
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2
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Gujarathi S, Zafar MK, Liu X, Eoff RL, Zheng G. A Facile Semisynthesis and Evaluation of Garcinoic Acid and Its Analogs for the Inhibition of Human DNA Polymerase β. Molecules 2020; 25:E5847. [PMID: 33322249 PMCID: PMC7763917 DOI: 10.3390/molecules25245847] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Accepted: 12/09/2020] [Indexed: 11/17/2022] Open
Abstract
Garcinoic acid has been identified as an inhibitor of DNA polymerase β (pol β). However, no structure-activity relationship (SAR) studies of garcinoic acid as a pol β inhibitor have been conducted, in part due to the lack of an efficient synthetic method for this natural product and its analogs. We developed an efficient semi-synthetic method for garcinoic acid and its analogs by starting from natural product δ-tocotrienol. Our preliminary SAR studies provided a valuable insight into future discovery of garcinoic acid-based pol β inhibitors.
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Affiliation(s)
- Satheesh Gujarathi
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (S.G.); (X.L.)
| | - Maroof Khan Zafar
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (M.K.Z.); (R.L.E.)
| | - Xingui Liu
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (S.G.); (X.L.)
| | - Robert L. Eoff
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (M.K.Z.); (R.L.E.)
| | - Guangrong Zheng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (S.G.); (X.L.)
- Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL 32610, USA
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3
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DNA Polymerase Beta Participates in Mitochondrial DNA Repair. Mol Cell Biol 2017; 37:MCB.00237-17. [PMID: 28559431 DOI: 10.1128/mcb.00237-17] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 05/25/2017] [Indexed: 12/16/2022] Open
Abstract
We have detected DNA polymerase beta (Polβ), known as a key nuclear base excision repair (BER) protein, in mitochondrial protein extracts derived from mammalian tissue and cells. Manipulation of the N-terminal sequence affected the amount of Polβ in the mitochondria. Using Polβ fragments, mitochondrion-specific protein partners were identified, with the interactors functioning mainly in DNA maintenance and mitochondrial import. Of particular interest was the identification of the proteins TWINKLE, SSBP1, and TFAM, all of which are mitochondrion-specific DNA effectors and are known to function in the nucleoid. Polβ directly interacted functionally with the mitochondrial helicase TWINKLE. Human kidney cells with Polβ knockout (KO) had higher endogenous mitochondrial DNA (mtDNA) damage. Mitochondrial extracts derived from heterozygous Polβ mouse tissue and KO cells had lower nucleotide incorporation activity. Mouse-derived Polβ null fibroblasts had severely affected metabolic parameters. Indeed, gene knockout of Polβ caused mitochondrial dysfunction, including reduced membrane potential and mitochondrial content. We show that Polβ is a mitochondrial polymerase involved in mtDNA maintenance and is required for mitochondrial homeostasis.
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Khanra K, Chakraborty A, Bhattacharyya N. HeLa Cells Containing a Truncated Form of DNA Polymerase Beta are More Sensitized to Alkylating Agents than to Agents Inducing Oxidative Stress. Asian Pac J Cancer Prev 2016; 16:8177-86. [PMID: 26745057 DOI: 10.7314/apjcp.2015.16.18.8177] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The present study was aimed at determining the effects of alkylating and oxidative stress inducing agents on a newly identified variant of DNA polymerase beta (polβ Δ208-304) specific for ovarian cancer. Pol β Δ208-304 has a deletion of exons 11-13 which lie in the catalytic part of enzyme. We compared the effect of these chemicals on HeLa cells and HeLa cells stably transfected with this variant cloned into in pcDNAI/neo vector by MTT, colony forming and apoptosis assays. Polβ Δ208-304 cells exhibited greater sensitivity to an alkylating agent and less sensitivity towards H2O2 and UV when compared with HeLa cells alone. It has been shown that cell death in Pol β Δ208-304 transfected HeLa cells is mediated by the caspase 9 cascade. Exon 11 has nucleotidyl selection activity, while exons 12 and 13 have dNTP selection activity. Hence deletion of this part may affect polymerizing activity although single strand binding and double strand binding activity may remain same. The lack of this part may adversely affect catalytic activity of DNA polymerase beta so that the variant may act as a dominant negative mutant. This would represent clinical significance if translated into a clinical setting because resistance to radiation or chemotherapy during the relapse of the disease could be potentially overcome by this approach.
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Affiliation(s)
- Kalyani Khanra
- Department of Biotechnology, Panskura Banamali College; Panskura RS, Purba Medinipur, West Bengal, India E-mail :
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5
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Barakat KH, Gajewski MM, Tuszynski JA. DNA polymerase beta (pol β) inhibitors: a comprehensive overview. Drug Discov Today 2012; 17:913-20. [PMID: 22561893 DOI: 10.1016/j.drudis.2012.04.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Revised: 03/19/2012] [Accepted: 04/19/2012] [Indexed: 11/25/2022]
Abstract
Base excision repair (BER) is the fundamental pathway responsible for the elimination of damaged DNA bases and repair of DNA single-strand breaks generated spontaneously or produced by DNA-damaging agents. Among the essential enzymes that are required to achieve the BER reaction is DNA polymerase beta (pol β), which has been regarded as a potential therapeutic target. More than 60 pol β-inhibitors have been identified so far; however, most of them are either not potent or not specific enough to become a drug. In this article we compile an essential knowledge base regarding the structures, the modes of inhibition and the activities of these pharmacologically interesting molecules.
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Affiliation(s)
- Khaled H Barakat
- Department of Physics, University of Alberta, Edmonton, AB, Canada.
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6
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Goellner EM, Svilar D, Almeida KH, Sobol RW. Targeting DNA polymerase ß for therapeutic intervention. Curr Mol Pharmacol 2012; 5:68-87. [PMID: 22122465 PMCID: PMC3894524] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2010] [Revised: 01/10/2011] [Accepted: 01/15/2011] [Indexed: 05/31/2023]
Abstract
DNA damage plays a causal role in numerous disease processes. Hence, it is suggested that DNA repair proteins, which maintain the integrity of the nuclear and mitochondrial genomes, play a critical role in reducing the onset of multiple diseases, including cancer, diabetes and neurodegeneration. As the primary DNA polymerase involved in base excision repair, DNA polymerase ß (Polß) has been implicated in multiple cellular processes, including genome maintenance and telomere processing and is suggested to play a role in oncogenic transformation, cell viability following stress and the cellular response to radiation, chemotherapy and environmental genotoxicants. Therefore, Polß inhibitors may prove to be effective in cancer treatment. However, Polß has a complex and highly regulated role in DNA metabolism. This complicates the development of effective Polß-specific inhibitors useful for improving chemotherapy and radiation response without impacting normal cellular function. With multiple enzymatic activities, numerous binding partners and complex modes of regulation from post-translational modifications, there are many opportunities for Polß inhibition that have yet to be resolved. To shed light on the varying possibilities and approaches of targeting Polß for potential therapeutic intervention, we summarize the reported small molecule inhibitors of Polß and discuss the genetic, biochemical and chemical studies that implicate additional options for Polß inhibition. Further, we offer suggestions on possible inhibitor combinatorial approaches and the potential for tumor specificity for Polß-inhibitors.
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Affiliation(s)
- Eva M. Goellner
- Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
- University of Pittsburgh Cancer Institute, Hillman Cancer Center, Pittsburgh, PA 15213, USA
| | - David Svilar
- Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
- University of Pittsburgh Cancer Institute, Hillman Cancer Center, Pittsburgh, PA 15213, USA
| | - Karen H. Almeida
- Department of Physical Sciences, Rhode Island College, 600 Mt. Pleasant Ave, Providence, RI 02908-1991, USA
| | - Robert W. Sobol
- Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
- University of Pittsburgh Cancer Institute, Hillman Cancer Center, Pittsburgh, PA 15213, USA
- Department of Human Genetics, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15261, USA
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Barakat K, Tuszynski J. Relaxed complex scheme suggests novel inhibitors for the lyase activity of DNA polymerase beta. J Mol Graph Model 2011; 29:702-16. [DOI: 10.1016/j.jmgm.2010.12.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Revised: 12/02/2010] [Accepted: 12/06/2010] [Indexed: 11/26/2022]
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Neijenhuis S, Verwijs-Janssen M, van den Broek LJ, Begg AC, Vens C. Targeted Radiosensitization of Cells Expressing Truncated DNA Polymerase β. Cancer Res 2010; 70:8706-14. [DOI: 10.1158/0008-5472.can-09-3901] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Zhang Z, Cao X, Xiong N, Wang H, Huang J, Sun S, Liang Z, Wang T. DNA polymerase-β is required for 1-methyl-4-phenylpyridinium-induced apoptotic death in neurons. Apoptosis 2009; 15:105-15. [DOI: 10.1007/s10495-009-0425-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Neijenhuis S, Verwijs-Janssen M, Kasten-Pisula U, Rumping G, Borgmann K, Dikomey E, Begg AC, Vens C. Mechanism of cell killing after ionizing radiation by a dominant negative DNA polymerase beta. DNA Repair (Amst) 2008; 8:336-46. [PMID: 19059500 DOI: 10.1016/j.dnarep.2008.11.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Revised: 11/05/2008] [Accepted: 11/10/2008] [Indexed: 10/21/2022]
Abstract
Several types of DNA lesion are induced after ionizing irradiation (IR) of which double strand breaks (DSBs) are expected to be the most lethal, although single strand breaks (SSBs) and DNA base damages are quantitatively in the majority. Proteins of the base excision repair (BER) pathway repair these numerous lesions. DNA polymerase beta has been identified as a crucial enzyme in BER and SSB repair (SSBR). We showed previously that inhibition of BER/SSBR by expressing a dominant negative DNA polymerase beta (polbetaDN) resulted in radiosensitization. We hypothesized increased kill to result from DSBs arising from unrepaired SSBs and BER intermediates. We find here higher numbers of IR-induced chromosome aberrations in polbetaDN expressing cells, confirming increased DSB formation. These aberrations did not result from changes in DSB induction or repair of the majority of lesions. SSB conversion to DSBs has been shown to occur during replication. We observed an increased induction of chromatid aberrations in polbetaDN expressing cells after IR, suggesting such a replication-dependence of secondary DSB formation. We also observed a pronounced increase of chromosomal deletions, the most likely cause of the increased kill. After H(2)O(2) treatment, polbetaDN expression only resulted in increased chromatid (not chromosome) aberrations. Together with the lack of sensitization to H(2)O(2), these data further suggest that the additional secondarily induced lethal DSBs resulted from repair attempts at complex clustered damage sites, unique to IR. Surprisingly, the polbetaDN induced increase in residual gammaH2AX foci number was unexpectedly low compared with the radiosensitization or induction of aberrations. Our data thus demonstrate the formation of secondary DSBs that are reflected by increased kill but not by residual gammaH2AX foci, indicating an escape from gammaH2AX-mediated DSB repair. In addition, we show that in the polbetaDN expressing cells secondary DSBs arise in a radiation-specific and partly replication-dependent manner.
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Affiliation(s)
- Sari Neijenhuis
- Department of Experimental Therapy, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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Sokhansanj BA, Wilson DM. Estimating the effect of human base excision repair protein variants on the repair of oxidative DNA base damage. Cancer Epidemiol Biomarkers Prev 2006; 15:1000-8. [PMID: 16702383 DOI: 10.1158/1055-9965.epi-05-0817] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Epidemiologic studies have revealed a complex association between human genetic variance and cancer risk. Quantitative biological modeling based on experimental data can play a critical role in interpreting the effect of genetic variation on biochemical pathways relevant to cancer development and progression. Defects in human DNA base excision repair (BER) proteins can reduce cellular tolerance to oxidative DNA base damage caused by endogenous and exogenous sources, such as exposure to toxins and ionizing radiation. If not repaired, DNA base damage leads to cell dysfunction and mutagenesis, consequently leading to cancer, disease, and aging. Population screens have identified numerous single-nucleotide polymorphism variants in many BER proteins and some have been purified and found to exhibit mild kinetic defects. Epidemiologic studies have led to conflicting conclusions on the association between single-nucleotide polymorphism variants in BER proteins and cancer risk. Using experimental data for cellular concentration and the kinetics of normal and variant BER proteins, we apply a previously developed and tested human BER pathway model to (i) estimate the effect of mild variants on BER of abasic sites and 8-oxoguanine, a prominent oxidative DNA base modification, (ii) identify ranges of variation associated with substantial BER capacity loss, and (iii) reveal nonintuitive consequences of multiple simultaneous variants. Our findings support previous work suggesting that mild BER variants have a minimal effect on pathway capacity whereas more severe defects and simultaneous variation in several BER proteins can lead to inefficient repair and potentially deleterious consequences of cellular damage.
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Affiliation(s)
- Bahrad A Sokhansanj
- School of Biomedical Engineering, Science and Health Systems, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA.
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Gening LV, Klincheva SA, Reshetnjak A, Grollman AP, Miller H. RNA aptamers selected against DNA polymerase beta inhibit the polymerase activities of DNA polymerases beta and kappa. Nucleic Acids Res 2006; 34:2579-86. [PMID: 16707660 PMCID: PMC1463896 DOI: 10.1093/nar/gkl326] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
DNA polymerase β (polβ), a member of the X family of DNA polymerases, is the major polymerase in the base excision repair pathway. Using in vitro selection, we obtained RNA aptamers for polβ from a variable pool of 8 × 1012 individual RNA sequences containing 30 random nucleotides. A total of 60 individual clones selected after seven rounds were screened for the ability to inhibit polβ activity. All of the inhibitory aptamers analyzed have a predicted tri-lobed structure. Gel mobility shift assays demonstrate that the aptamers can displace the DNA substrate from the polβ active site. Inhibition by the aptamers is not polymerase specific; inhibitors of polβ also inhibited DNA polymerase κ, a Y-family DNA polymerase. However, the RNA aptamers did not inhibit the Klenow fragment of DNA polymerase I and only had a minor effect on RB69 DNA polymerase activity. Polβ and κ, despite sharing little sequence similarity and belonging to different DNA polymerase families, have similarly open active sites and relatively few interactions with their DNA substrates. This may allow the aptamers to bind and inhibit polymerase activity. RNA aptamers with inhibitory properties may be useful in modulating DNA polymerase actvity in cells.
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Affiliation(s)
- Leonid V. Gening
- Laboratory of Chemical Biology, Department of Pharmacological Sciences, Stony Brook UniversityStony Brook, NY 11794-8651, USA
- Institute of Molecular Genetics, Russian Academy of SciencesMoscow 123182, Russia
| | | | - Anastasia Reshetnjak
- Institute of Molecular Genetics, Russian Academy of SciencesMoscow 123182, Russia
| | - Arthur P. Grollman
- Laboratory of Chemical Biology, Department of Pharmacological Sciences, Stony Brook UniversityStony Brook, NY 11794-8651, USA
| | - Holly Miller
- Laboratory of Chemical Biology, Department of Pharmacological Sciences, Stony Brook UniversityStony Brook, NY 11794-8651, USA
- To whom correspondence should be addressed: Tel: +1 631 444 3080, Fax: +1 631 444 7641;
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13
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Affiliation(s)
- William A Beard
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709-12233, USA
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Neijenhuis S, Begg AC, Vens C. Radiosensitization by a dominant negative to DNA polymerase β is DNA polymerase β-independent and XRCC1-dependent. Radiother Oncol 2005; 76:123-8. [PMID: 16024118 DOI: 10.1016/j.radonc.2005.06.020] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2005] [Revised: 05/13/2005] [Accepted: 06/19/2005] [Indexed: 11/17/2022]
Abstract
BACKGROUND AND PURPOSE DNA base damages and single strand breaks after ionizing radiation are repaired by base excision repair (BER) and single strand break repair (SSBR), with both DNA polymerase beta (polbeta) and XRCC1 playing key roles. We previously showed that a dominant negative to polbeta (polbetaDN) sensitized human tumor cells to ionizing radiation. However, polbeta-deficient cells, in contrast to XRCC1-deficient cells, are not more radiosensitive. The purpose of the present study was to further elucidate the mechanism of action of the polbetaDN to better understand the roles of BER and SSBR in determining radiosensitivity. MATERIALS AND METHODS Mouse embryonic fibroblasts, both polbeta wildtype and knockout, and hamster XRCC1-deficient EM9 cells together with its parental line, were transfected with the polbetaDN. Clones with equal polbetaDN expression levels were selected and used in clonogenic assays to determine radiosensitivity. RESULTS Radiosensitization of polbeta deficient cells by the polbetaDN is shown here, demonstrating inhibition of a polbeta-independent pathway. In addition, we observed radiosensitization of wildtype hamster cells but no radiosensitization of the XRCC1-deficient EM9 cells. CONCLUSIONS The polbetaDN acts independently of polbeta status and inhibits a pathway, which is dependent on XRCC1, consistent with inhibition of BER and/or SSBR. The data further indicate involvement of other polymerases, which are inhibited by polbetaDN. Finally, they demonstrate that inhibition of BER and SSBR can increase radiosensitivity, with potential clinical relevance.
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Affiliation(s)
- Sari Neijenhuis
- Division of Experimental Therapy, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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Canitrot Y, Capp JP, Puget N, Bieth A, Lopez B, Hoffmann JS, Cazaux C. DNA polymerase beta overexpression stimulates the Rad51-dependent homologous recombination in mammalian cells. Nucleic Acids Res 2004; 32:5104-12. [PMID: 15452277 PMCID: PMC521661 DOI: 10.1093/nar/gkh848] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Overexpression of DNA polymerase beta (polbeta), an error-prone DNA repair enzyme, has been shown to result in mutagenesis, aneuploidy and tumorigenesis. To further investigate the molecular basis leading to cancer-associated genetic changes, we examined whether the DNA polbeta could affect homologous recombination (HR). Using mammalian cells carrying an intrachromosomal recombination marker we showed that the DNA polbeta overexpression increased the HR mostly by enhancing gene conversion. Concomitantly, we observed the generation of DNA strand breaks as well as a DNA polbeta-dependent formation of Rad51 foci. The stimulation of HR was abolished by the coexpression of a dominant negative form of Rad51, suggesting that the Rad51 was involved in the increased HR events. The expression of different DNA polbeta mutants lacking polymerase activity did not result in HR stimulation, indicating that the DNA synthesis activity of DNA polbeta was related to this phenotype. These results provide new insights into the molecular mechanisms of the genetic instability observed in DNA polbeta overexpressing tumour cells.
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Affiliation(s)
- Yvan Canitrot
- Genetic Instability and Cancer Group, Institut de Pharmacologie et de Biologie Structurale UMR CNRS 5089, 205 route de Narbonne, 31077 Toulouse, France
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Kedar PS, Kim SJ, Robertson A, Hou E, Prasad R, Horton JK, Wilson SH. Direct interaction between mammalian DNA polymerase beta and proliferating cell nuclear antigen. J Biol Chem 2002; 277:31115-23. [PMID: 12063248 DOI: 10.1074/jbc.m201497200] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proliferating cell nuclear antigen (PCNA) plays an essential role in nucleic acid metabolism as a component of the DNA replication and DNA repair machinery. As such, PCNA interacts with many proteins that have a sequence motif termed the PCNA interacting motif (PIM) and also with proteins lacking a PIM. Three regions in human and rat DNA polymerases beta (beta-pol) that resemble the consensus PIM were identified, and we show here that beta-polymerase and PCNA can form a complex both in vitro and in vivo. Immunoprecipitation experiments, yeast two-hybrid analysis, and overlay binding assays were used to examine the interaction between the two proteins. Competition experiments with synthetic PIM-containing peptides suggested the importance of a PIM in the interaction, and studies of a beta-polymerase PIM mutant, H222A/F223A, demonstrated that this alteration blocked the interaction with PCNA. The results indicate that at least one of the PIM-like sequences in beta-polymerase appears to be a functional PIM and was required in the interaction between beta-polymerase and PCNA.
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Affiliation(s)
- Padmini S Kedar
- Laboratory of Structural Biology, NIEHS/National Institutes of Health, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709, USA
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17
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Vens C, Dahmen-Mooren E, Verwijs-Janssen M, Blyweert W, Graversen L, Bartelink H, Begg AC. The role of DNA polymerase beta in determining sensitivity to ionizing radiation in human tumor cells. Nucleic Acids Res 2002; 30:2995-3004. [PMID: 12087186 PMCID: PMC117058 DOI: 10.1093/nar/gkf403] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Lethal lesions after ionizing radiation are thought to be mainly unrepaired or misrepaired DNA double-strand breaks, ultimately leading to lethal chromosome aberrations. However, studies with radioprotectors and repair inhibitors indicate that single-strand breaks, damaged nucleotides or abasic sites can also influence cell survival. This paper reports on studies to further define the role of base damage and base excision repair on the radiosensitivity of human cells. We retrovirally transduced human tumor cells with a dominant negative form of DNA polymerase beta, comprising the 14 kDa DNA-binding domain of DNA polymerase beta but lacking polymerase function. Radiosensitization of two human carcinoma cell lines, A549 and SQD9, was observed, achieving dose enhancement factors of 1.5-1.7. Sensitization was dependent on expression level of the dominant negative and was seen in both single cell clones and in unselected virally transduced populations. Sensitization was not due to changes in cell cycle distribution. Little or no sensitization was seen in G(1)-enriched populations, indicating cell cycle specificity for the observed sensitization. These results contrast with the lack of effect seen in DNA polymerase beta knockout cells, suggesting that polDN also inhibits the long patch, DNA polymerase beta-independent repair pathway. These data demonstrate an important role for BER in determining sensitivity to ionizing radiation and might help identify targets for radiosensitizing tumor cells.
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Affiliation(s)
- Conchita Vens
- Division of Experimental Therapy and Department of Radiotherapy, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands
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Lavrik OI, Prasad R, Beard WA, Safronov IV, Dobrikov MI, Srivastava DK, Shishkin GV, Wood TG, Wilson SH. dNTP binding to HIV-1 reverse transcriptase and mammalian DNA polymerase beta as revealed by affinity labeling with a photoreactive dNTP analog. J Biol Chem 1996; 271:21891-7. [PMID: 8702991 DOI: 10.1074/jbc.271.36.21891] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The dNTP binding pocket of human immunodeficiency virus type 1 reverse transcriptase (RT) and DNA polymerase beta (beta-pol) were labeled using a photoreactive analog of dCTP, exo-N-[beta-(p-azidotetrafluorobenzamido)-ethyl]-deoxycytidine-5'- triphosphate (FABdCTP). Two approaches of photolabeling were utilized. In one approach, photoreactive FABdCTP and radiolabeled primer-template were UV-irradiated in the presence of each enzyme and resulted in polymerase radiolabeling. In an alternate approach, FABdCTP was first UV-cross-linked to enzyme; subsequently, radiolabeled primer-template was added, and the enzyme-linked dCTP analog was incorporated onto the 3'-end of the radiolabeled primer. The results showed strong labeling of the p66 subunit of RT, with only minor labeling of p51. No difference in the intensity of cross-linking was observed with either approach. FABdCTP cross-linking was increased in the presence of a dideoxyterminated primer-template with RT, but not with beta-pol, suggesting a significant influence of prior primer-template binding on dNTP binding for RT. Mutagenesis of beta-pol residues observed to interact with the incoming dNTP in the crystal structure of the ternary complex resulted in labeling consistent with kinetic characterization of these mutants and indicated specific labeling of the dNTP binding pocket.
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Affiliation(s)
- O I Lavrik
- Novosibirsk Institute of Bioorganic Chemistry, Siberian Division of the Russian Academy of Sciences, 630090 Novosobirsk, Russia
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Chyan YJ, Strauss PR, Wood TG, Wilson SH. Identification of novel mRNA isoforms for human DNA polymerase beta. DNA Cell Biol 1996; 15:653-9. [PMID: 8769567 DOI: 10.1089/dna.1996.15.653] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Recently, we reported the organization of the thirteen exons of the human DNA polymerase beta (beta-pol) gene and the sequences of the exon-intron junctions. Splice variants of human beta-pol mRNA have been postulated to be related to cancer development. Here, we report the characterization of isoforms of human beta-pol mRNA in different cells by reverse transcription polymerase chain reaction (RT-PCR). DNA sequence analysis of RT-PCR products revealed eight alternative splicing mRNA isoforms in the brain cancer cell line, SK-N-MC. These various isoforms were consistent with alternative splicing of four exons (II, IV, V, and VI) and with a 105-nucleotide insertion (exon alpha) between exons VI and VII. We also found an isoform with a 19-nucleotide sequence inserted into the exon IV and V junction, which resulted from usage of a different 3' splice site. Seven of the isoforms resulted in truncated open reading frame (ORF); five corresponded to deduced peptide of amino acids 1-20 of beta-pol and two corresponded to amino acids 1-60 of beta-pol. Only one of the right mRNA isoforms, that with the exon alpha insertion, was in-frame with the entire wild-type ORF resulting in a deduced protein of 370 residues, compared with the wild-type protein of 335 residues and 39 kD. This longer ORF was shown to be capable of encoding a beta-pol protein, larger than wild-type beta-pol, that cross-reacted with beta-pol antibody and exhibited beta-pol enzymatic activity. The mRNA isoform with the exon alpha insertion was not tumor specific because it as detected in low abundance in all cells tested, except the colon cell line CCD18 Co where the isoform was absent. The genomic location of exon alpha is in intron VI, 990 bp upstream of exon VII and flanked by consensus splice sites. Thus, this 105-bp genomic sequence is a beta-pol exon present in a low-abundance beta-pol mRNA isoform capable of encoding an approximately 42-kD beta-pol.
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Affiliation(s)
- Y J Chyan
- Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston 77555-1068, USA
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Doherty AJ, Serpell LC, Ponting CP. The helix-hairpin-helix DNA-binding motif: a structural basis for non-sequence-specific recognition of DNA. Nucleic Acids Res 1996; 24:2488-97. [PMID: 8692686 PMCID: PMC145986 DOI: 10.1093/nar/24.13.2488] [Citation(s) in RCA: 300] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
One, two or four copies of the 'helix-hairpin-helix' (HhH) DNA-binding motif are predicted to occur in 14 homologous families of proteins. The predicted DNA-binding function of this motif is shown to be consistent with the crystallographic structure of rat polymerase beta, complexed with DNA template-primer [Pelletier, H., Sawaya, M.R., Kumar, A., Wilson, S.H. and Kraut, J. (1994) Science 264, 1891-1903] and with biochemical data. Five crystal structures of predicted HhH motifs are currently known: two from rat pol beta and one each in endonuclease III, AlkA and the 5' nuclease domain of Taq pol I. These motifs are more structurally similar to each other than to any other structure in current databases, including helix-turn-helix motifs. The clustering of the five HhH structures separately from other bi-helical structures in searches indicates that all members of the 14 families of proteins described herein possess similar HhH structures. By analogy with the rat pol beta structure, it is suggested that each of these HhH motifs bind DNA in a non-sequence-specific manner, via the formation of hydrogen bonds between protein backbone nitrogens and DNA phosphate groups. This type of interaction contrasts with the sequence-specific interactions of other motifs, including helix-turn-helix structures. Additional evidence is provided that alphaherpesvirus virion host shutoff proteins are members of the polymerase I 5'-nuclease and FEN1-like endonuclease gene family, and that a novel HhH-containing DNA-binding domain occurs in the kinesin-like molecule nod, and in other proteins such as cnjB, emb-5 and SPT6.
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Affiliation(s)
- A J Doherty
- Laboratory of Molecular Biophysics, University of Oxford, UK
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Clairmont CA, Sweasy JB. Dominant negative rat DNA polymerase beta mutants interfere with base excision repair in Saccharomyces cerevisiae. J Bacteriol 1996; 178:656-61. [PMID: 8550496 PMCID: PMC177708 DOI: 10.1128/jb.178.3.656-661.1996] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
DNA polymerase beta is one of the smallest known eukaryotic DNA polymerases. This polymerase has been very well characterized in vitro, but its functional role in vivo has yet to be determined. Using a novel competition assay in Escherichia coli, we isolated two DNA polymerase beta dominant negative mutants. When we overexpressed the dominant negative mutant proteins in Saccharomyces cerevisiae, the cells became sensitive to methyl methanesulfonate. Interestingly, overexpression of the same polymerase beta mutant proteins did not confer sensitivity to UV damage, strongly suggesting that the mutant proteins interfere with the process of base excision repair but not nucleotide excision repair in S. cerevisiae. Our data implicate a role for polymerase IV, the S. cerevisiae polymerase beta homolog, in base excision repair in S. cerevisiae.
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Affiliation(s)
- C A Clairmont
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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Horton JK, Srivastava DK, Zmudzka BZ, Wilson SH. Strategic down-regulation of DNA polymerase beta by antisense RNA sensitizes mammalian cells to specific DNA damaging agents. Nucleic Acids Res 1995; 23:3810-5. [PMID: 7479021 PMCID: PMC307295 DOI: 10.1093/nar/23.19.3810] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Previously, mouse NIH 3T3 cells were stably transfected with human DNA polymerase beta (beta-pol) cDNA in the antisense orientation and under the control of a metallothionein promoter [Zmudzka, B.Z. and Wilson, S.H. (1990) Som. Cell Mol. Gen., 16, 311-320]. To assess the feasibility of enhancing the efficacy of chemotherapy by an antisense approach and to confirm a role for beta-pol in cellular DNA repair, we looked for increased sensitivity to DNA damaging agents under conditions where beta-pol is down-regulated in the antisense cell line. Such a sensitization is anticipated only where beta-pol is rate-limiting in a DNA repair pathway. A number of agents were tested: cis-diamminedichloroplatinum II (cisplatin); 1,3-bis(2-chloroethyl)-1- nitrosourea (BCNU); ionizing radiation and the radio-mimetic drug bleomycin; the bifunctional alkylating agents nitrogen mustard and L-phenylalanine mustard (melphalan); the monofunctional alkylating agent methyl methane sulfonate (MMS) and ultraviolet (UV) radiation. In the cases of cisplatin and UV radiation, a significant enhancement of cytotoxicity was observed. Damage as a result of both of these agents is thought to be repaired by the nucleotide excision repair (NER) pathway. The results suggest that, in this cell line, beta-pol is involved in and is rate-limiting in NER. We propose that down-regulation of beta-pol by antisense approaches might be used to enhance the cytotoxic effects of cisplatin and other DNA damaging chemotherapeutic agents.
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Affiliation(s)
- J K Horton
- Laboratory of Cell Biology, University of Texas Medical Branch, Galveston 77555, USA
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Affiliation(s)
- W A Beard
- Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston 77555-1068, USA
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