1
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Antequera-Parrilla P, Castillo-Acosta VM, Bosch-Navarrete C, Ruiz-Pérez LM, González-Pacanowska D. A nuclear orthologue of the dNTP triphosphohydrolase SAMHD1 controls dNTP homeostasis and genomic stability in Trypanosoma brucei. Front Cell Infect Microbiol 2023; 13:1241305. [PMID: 37674581 PMCID: PMC10478004 DOI: 10.3389/fcimb.2023.1241305] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 08/07/2023] [Indexed: 09/08/2023] Open
Abstract
Maintenance of dNTPs pools in Trypanosoma brucei is dependent on both biosynthetic and degradation pathways that together ensure correct cellular homeostasis throughout the cell cycle which is essential for the preservation of genomic stability. Both the salvage and de novo pathways participate in the provision of pyrimidine dNTPs while purine dNTPs are made available solely through salvage. In order to identify enzymes involved in degradation here we have characterized the role of a trypanosomal SAMHD1 orthologue denominated TbHD82. Our results show that TbHD82 is a nuclear enzyme in both procyclic and bloodstream forms of T. brucei. Knockout forms exhibit a hypermutator phenotype, cell cycle perturbations and an activation of the DNA repair response. Furthermore, dNTP quantification of TbHD82 null mutant cells revealed perturbations in nucleotide metabolism with a substantial accumulation of dATP, dCTP and dTTP. We propose that this HD domain-containing protein present in kinetoplastids plays an essential role acting as a sentinel of genomic fidelity by modulating the unnecessary and detrimental accumulation of dNTPs.
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Affiliation(s)
| | - Víctor M. Castillo-Acosta
- Instituto de Parasitología y Biomedicina “López-Neyra, Consejo Superior de Investigaciones Científicas, Parque Tecnológico de Ciencias de la Salud, Granada, Spain
| | | | | | - Dolores González-Pacanowska
- Instituto de Parasitología y Biomedicina “López-Neyra, Consejo Superior de Investigaciones Científicas, Parque Tecnológico de Ciencias de la Salud, Granada, Spain
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2
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Long MJC, Ly P, Aye Y. Still no Rest for the Reductases: Ribonucleotide Reductase (RNR) Structure and Function: An Update. Subcell Biochem 2022; 99:155-197. [PMID: 36151376 DOI: 10.1007/978-3-031-00793-4_5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Herein we present a multidisciplinary discussion of ribonucleotide reductase (RNR), the essential enzyme uniquely responsible for conversion of ribonucleotides to deoxyribonucleotides. This chapter primarily presents an overview of this multifaceted and complex enzyme, covering RNR's role in enzymology, biochemistry, medicinal chemistry, and cell biology. It further focuses on RNR from mammals, whose interesting and often conflicting roles in health and disease are coming more into focus. We present pitfalls that we think have not always been dealt with by researchers in each area and further seek to unite some of the field-specific observations surrounding this enzyme. Our work is thus not intended to cover any one topic in extreme detail, but rather give what we consider to be the necessary broad grounding to understand this critical enzyme holistically. Although this is an approach we have advocated in many different areas of scientific research, there is arguably no other single enzyme that embodies the need for such broad study than RNR. Thus, we submit that RNR itself is a paradigm of interdisciplinary research that is of interest from the perspective of the generalist and the specialist alike. We hope that the discussions herein will thus be helpful to not only those wanting to tackle RNR-specific problems, but also those working on similar interdisciplinary projects centering around other enzymes.
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Affiliation(s)
- Marcus J C Long
- University of Lausanne (UNIL), Lausanne, Switzerland
- Department of Biochemistry, UNIL, Epalinges, Switzerland
| | - Phillippe Ly
- Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland
- EPFL SB ISIC LEAGO, Lausanne, Switzerland
| | - Yimon Aye
- Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland.
- EPFL SB ISIC LEAGO, Lausanne, Switzerland.
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3
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Hoffert KM, Higginbotham KSP, Gibson JT, Oehrle S, Strome ED. Mutations in the S-Adenosylmethionine Synthetase Genes SAM1 and SAM2 Differentially Affect Genome Stability in Saccharomyces cerevisiae. Genetics 2019; 213:97-112. [PMID: 31320408 PMCID: PMC6727793 DOI: 10.1534/genetics.119.302435] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 07/15/2019] [Indexed: 12/20/2022] Open
Abstract
Maintenance of genome integrity is a crucial cellular focus that involves a wide variety of proteins functioning in multiple processes. Defects in many different pathways can result in genome instability, a hallmark of cancer. Utilizing a diploid Saccharomyces cerevisiae model, we previously reported a collection of gene mutations that affect genome stability in a haploinsufficient state. In this work we explore the effect of gene dosage on genome instability for one of these genes and its paralog; SAM1 and SAM2 These genes encode S-Adenosylmethionine (AdoMet) synthetases, responsible for the creation of AdoMet from methionine and ATP. AdoMet is the universal methyl donor for methylation reactions and is essential for cell viability. It is the second most used cellular enzyme substrate and is exceptionally well-conserved through evolution. Mammalian cells express three genes, MAT1A, MAT2A, and MAT2B, with distinct expression profiles and functions. Alterations to these AdoMet synthetase genes, and AdoMet levels, are found in many cancers, making them a popular target for therapeutic intervention. However, significant variance in these alterations are found in different tumor types, with the cellular consequences of the variation still unknown. By studying this pathway in the yeast system, we demonstrate that losses of SAM1 and SAM2 have different effects on genome stability through distinctive effects on gene expression and AdoMet levels, and ultimately separate effects on the methyl cycle. Thus, this study provides insight into the mechanisms by which differential expression of the SAM genes have cellular consequences that affect genome instability.
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Affiliation(s)
- Kellyn M Hoffert
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099
| | - Kathryn S P Higginbotham
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099
| | - Justin T Gibson
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099
| | - Stuart Oehrle
- Waters Field Laboratory, Chemistry Department, Northern Kentucky University, Highland Heights, Kentucky 41099
| | - Erin D Strome
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099
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4
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Schmidt TT, Sharma S, Reyes GX, Gries K, Gross M, Zhao B, Yuan JH, Wade R, Chabes A, Hombauer H. A genetic screen pinpoints ribonucleotide reductase residues that sustain dNTP homeostasis and specifies a highly mutagenic type of dNTP imbalance. Nucleic Acids Res 2019; 47:237-252. [PMID: 30462295 PMCID: PMC6326808 DOI: 10.1093/nar/gky1154] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 10/29/2018] [Indexed: 12/12/2022] Open
Abstract
The balance and the overall concentration of intracellular deoxyribonucleoside triphosphates (dNTPs) are important determinants of faithful DNA replication. Despite the established fact that changes in dNTP pools negatively influence DNA replication fidelity, it is not clear why certain dNTP pool alterations are more mutagenic than others. As intracellular dNTP pools are mainly controlled by ribonucleotide reductase (RNR), and given the limited number of eukaryotic RNR mutations characterized so far, we screened for RNR1 mutations causing mutator phenotypes in Saccharomyces cerevisiae. We identified 24 rnr1 mutant alleles resulting in diverse mutator phenotypes linked in most cases to imbalanced dNTPs. Among the identified rnr1 alleles the strongest mutators presented a dNTP imbalance in which three out of the four dNTPs were elevated (dCTP, dTTP and dGTP), particularly if dGTP levels were highly increased. These rnr1 alleles caused growth defects/lethality in DNA replication fidelity-compromised backgrounds, and caused strong mutator phenotypes even in the presence of functional DNA polymerases and mismatch repair. In summary, this study pinpoints key residues that contribute to allosteric regulation of RNR’s overall activity or substrate specificity. We propose a model that distinguishes between different dNTP pool alterations and provides a mechanistic explanation why certain dNTP imbalances are particularly detrimental.
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Affiliation(s)
- Tobias T Schmidt
- DNA Repair Mechanisms and Cancer, German Cancer Research Center (DKFZ), Heidelberg D-69120, Germany.,Faculty of Bioscience, Heidelberg University, Heidelberg D-69120, Germany
| | - Sushma Sharma
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå SE-901 87 Sweden
| | - Gloria X Reyes
- DNA Repair Mechanisms and Cancer, German Cancer Research Center (DKFZ), Heidelberg D-69120, Germany
| | - Kerstin Gries
- DNA Repair Mechanisms and Cancer, German Cancer Research Center (DKFZ), Heidelberg D-69120, Germany
| | - Maike Gross
- DNA Repair Mechanisms and Cancer, German Cancer Research Center (DKFZ), Heidelberg D-69120, Germany
| | - Boyu Zhao
- DNA Repair Mechanisms and Cancer, German Cancer Research Center (DKFZ), Heidelberg D-69120, Germany.,Faculty of Bioscience, Heidelberg University, Heidelberg D-69120, Germany
| | - Jui-Hung Yuan
- Molecular and Cellular Modeling Group, Heidelberg Institute for Theoretical Studies (HITS), Heidelberg D-69118, Germany
| | - Rebecca Wade
- Molecular and Cellular Modeling Group, Heidelberg Institute for Theoretical Studies (HITS), Heidelberg D-69118, Germany.,Interdisciplinary Center for Scientific Computing (IWR), Heidelberg D-69120, Germany.,Center for Molecular Biology of the University of Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Heidelberg D-69120, Germany
| | - Andrei Chabes
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå SE-901 87 Sweden.,Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå SE-901 87, Sweden
| | - Hans Hombauer
- DNA Repair Mechanisms and Cancer, German Cancer Research Center (DKFZ), Heidelberg D-69120, Germany
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5
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Long MJC, Liu X, Aye Y. Chemical Biology Gateways to Mapping Location, Association, and Pathway Responsivity. Front Chem 2019; 7:125. [PMID: 30949469 PMCID: PMC6437114 DOI: 10.3389/fchem.2019.00125] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Accepted: 02/18/2019] [Indexed: 12/14/2022] Open
Abstract
Here we discuss, how by applying chemical concepts to biological problems, methods have been developed to map spatiotemporal regulation of proteins and small-molecule modulation of proteome signaling responses. We outline why chemical-biology platforms are ideal for such purposes. We further discuss strengths and weaknesses of chemical-biology protocols, contrasting them against classical genetic and biochemical approaches. We make these evaluations based on three parameters: occupancy; functional information; and spatial restriction. We demonstrate how the specific choice of chemical reagent and experimental set-up unite to resolve biological problems. Potential improvements/extensions as well as specific controls that in our opinion are often overlooked or employed incorrectly are also considered. Finally, we discuss some of the latest emerging methods to illuminate how chemical-biology innovations provide a gateway toward information hitherto inaccessible by conventional genetic/biochemical means. Finally, we also caution against solely relying on chemical-biology strategies and urge the field to undertake orthogonal validations to ensure robustness of results.
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Affiliation(s)
| | - Xuyu Liu
- École Polytechnique Fédérale de Lausanne, Institute of Chemical Sciences and Engineering, Lausanne, Switzerland
| | - Yimon Aye
- École Polytechnique Fédérale de Lausanne, Institute of Chemical Sciences and Engineering, Lausanne, Switzerland
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6
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Chen PYT, Funk MA, Brignole EJ, Drennan CL. Disruption of an oligomeric interface prevents allosteric inhibition of Escherichia coli class Ia ribonucleotide reductase. J Biol Chem 2018; 293:10404-10412. [PMID: 29700111 DOI: 10.1074/jbc.ra118.002569] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Revised: 04/17/2018] [Indexed: 11/06/2022] Open
Abstract
Ribonucleotide reductases (RNRs) convert ribonucleotides to deoxynucleotides, a process essential for DNA biosynthesis and repair. Class Ia RNRs require two dimeric subunits for activity: an α2 subunit that houses the active site and allosteric regulatory sites and a β2 subunit that houses the diferric tyrosyl radical cofactor. Ribonucleotide reduction requires that both subunits form a compact α2β2 state allowing for radical transfer from β2 to α2 RNR activity is regulated allosterically by dATP, which inhibits RNR, and by ATP, which restores activity. For the well-studied Escherichia coli class Ia RNR, dATP binding to an allosteric site on α promotes formation of an α4β4 ring-like state. Here, we investigate whether the α4β4 formation causes or results from RNR inhibition. We demonstrate that substitutions at the α-β interface (S37D/S39A-α2, S39R-α2, S39F-α2, E42K-α2, or L43Q-α2) that disrupt the α4β4 oligomer abrogate dATP-mediated inhibition, consistent with the idea that α4β4 formation is required for dATP's allosteric inhibition of RNR. Our results further reveal that the α-β interface in the inhibited state is highly sensitive to manipulation, with a single substitution interfering with complex formation. We also discover that residues at the α-β interface whose substitution has previously been shown to cause a mutator phenotype in Escherichia coli (i.e. S39F-α2 or E42K-α2) are impaired only in their activity regulation, thus linking this phenotype with the inability to allosterically down-regulate RNR. Whereas the cytotoxicity of RNR inhibition is well-established, these data emphasize the importance of down-regulation of RNR activity.
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Affiliation(s)
| | | | - Edward J Brignole
- From the Departments of Chemistry and.,Biology and.,the Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Catherine L Drennan
- From the Departments of Chemistry and .,Biology and.,the Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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7
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Brignole EJ, Tsai KL, Chittuluru J, Li H, Aye Y, Penczek PA, Stubbe J, Drennan CL, Asturias F. 3.3-Å resolution cryo-EM structure of human ribonucleotide reductase with substrate and allosteric regulators bound. eLife 2018; 7:31502. [PMID: 29460780 PMCID: PMC5819950 DOI: 10.7554/elife.31502] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Accepted: 01/15/2018] [Indexed: 12/31/2022] Open
Abstract
Ribonucleotide reductases (RNRs) convert ribonucleotides into deoxyribonucleotides, a reaction essential for DNA replication and repair. Human RNR requires two subunits for activity, the α subunit contains the active site, and the β subunit houses the radical cofactor. Here, we present a 3.3-Å resolution structure by cryo-electron microscopy (EM) of a dATP-inhibited state of human RNR. This structure, which was determined in the presence of substrate CDP and allosteric regulators ATP and dATP, has three α2 units arranged in an α6 ring. At near-atomic resolution, these data provide insight into the molecular basis for CDP recognition by allosteric specificity effectors dATP/ATP. Additionally, we present lower-resolution EM structures of human α6 in the presence of both the anticancer drug clofarabine triphosphate and β2. Together, these structures support a model for RNR inhibition in which β2 is excluded from binding in a radical transfer competent position when α exists as a stable hexamer. Cells often need to make more DNA, for example when they are about to divide or need to repair their genetic information. The building blocks of DNA – also called deoxyribonucleotides – are created through a series of biochemical reactions. Among the enzymes that accomplish these reactions, ribonucleotide reductases (or RNRs, for short) perform a key irreversible step. One prominent class of RNR contains two basic units, named alpha and beta. The active form of these RNRs is made up of a pair of alpha units (α2), which associates with a pair of beta units (β2) to create an α2β2 structure. α2 captures molecules called ribonucleotides and, with the help of β2, converts them to deoxyribonucleotides that after futher processing will be used to create DNA. As RNR produces deoxyribonucleotides, levels of DNA building blocks in the cell rise. To avoid overstocking the cell, RNR contains an ‘off switch’ that is triggered when levels of one of the DNA building blocks, dATP, is high enough to occupy a particular site on the alpha unit. Binding of dATP to this site results in three pairs of alpha units getting together to form a stable ring of six units (called α6). How the formation of this stable α6 ring actually turns off RNR was an open question. Here, Brignole, Tsai et al. use a microscopy method called cryo-EM to reveal the three-dimensional structure of the inactive human RNR almost down to the level of individual atoms. When the alpha pairs form an α6 ring, the hole in the center of this circle is smaller than β2, keeping β2 away from α2. This inaccessibility leads to RNR being switched off. If RNR is inactive, DNA synthesis is impaired and cells cannot divide. In turn, controlling whether or not cells proliferate is key to fighting diseases like cancer (where ‘rogue’ cells keep replicating) or bacterial infections. Certain cancer treatments already target RNR, and create the inactive α6 ring structure. In addition, in bacteria, the inactive form of RNR is different from the human one and forms an α4β4 ring,rather than an α6 ring. Understanding the structure of the human inactive RNR could help scientists to find both new anticancer and antibacterial drugs.
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Affiliation(s)
- Edward J Brignole
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States
| | - Kuang-Lei Tsai
- Department of Integrative Computational and Structural Biology, The Scripps Research Institute, La Jolla, United States
| | - Johnathan Chittuluru
- Department of Integrative Computational and Structural Biology, The Scripps Research Institute, La Jolla, United States
| | - Haoran Li
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, United States
| | - Yimon Aye
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, United States
| | - Pawel A Penczek
- Department of Biochemistry and Molecular Biology, The University of Texas-Houston Medical School, Houston, United States
| | - JoAnne Stubbe
- Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Chemistry, Massachusetts Institute of Technology, Cambridge, United States
| | - Catherine L Drennan
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Chemistry, Massachusetts Institute of Technology, Cambridge, United States
| | - Francisco Asturias
- Department of Integrative Computational and Structural Biology, The Scripps Research Institute, La Jolla, United States
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8
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Teichman SL, Thomson KS, Regnier M. Cardiac Myosin Activation with Gene Therapy Produces Sustained Inotropic Effects and May Treat Heart Failure with Reduced Ejection Fraction. Handb Exp Pharmacol 2017; 243:447-464. [PMID: 27590227 DOI: 10.1007/164_2016_31] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Chronic inotropic therapy is effective for the treatment of heart failure with reduced ejection fraction, but has been limited by adverse long-term safety profiles, development of tolerance, and the need for chronic parenteral administration. A safe and convenient therapeutic agent that produces sustained inotropic effects could improve symptoms, functional capacity, and quality of life. Small amounts of 2-deoxy-adenosine triphosphate (dATP) activate cardiac myosin leading to enhanced contractility in normal and failing heart muscle. Cardiac myosin activation triggers faster myosin crossbridge cycling with greater force generation during each contraction. This paper describes the rationale and results of a translational medicine effort to increase dATP levels using a gene therapy strategy to deliver and upregulate ribonucleotide reductase (R1R2), the enzyme responsible for dATP synthesis, selectively in cardiomyocytes. In small and large animal models of heart failure, a single dose of this gene therapy has led to sustained inotropic effects with a benign safety profile. Further animal studies are appropriate with the goal of testing this agent in patients with heart failure.
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Affiliation(s)
- Sam L Teichman
- BEAT Biotherapeutics Corp, 1380 112th Ave., NE, Suite 200, Seattle, WA, 98004, USA.
| | | | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, WA, USA.,Center for Cardiovascular Biology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA
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9
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Pai CC, Kishkevich A, Deegan RS, Keszthelyi A, Folkes L, Kearsey SE, De León N, Soriano I, de Bruin RAM, Carr AM, Humphrey TC. Set2 Methyltransferase Facilitates DNA Replication and Promotes Genotoxic Stress Responses through MBF-Dependent Transcription. Cell Rep 2017; 20:2693-2705. [PMID: 28903048 PMCID: PMC5608972 DOI: 10.1016/j.celrep.2017.08.058] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Revised: 06/10/2017] [Accepted: 08/17/2017] [Indexed: 11/24/2022] Open
Abstract
Chromatin modification through histone H3 lysine 36 methylation by the SETD2 tumor suppressor plays a key role in maintaining genome stability. Here, we describe a role for Set2-dependent H3K36 methylation in facilitating DNA replication and the transcriptional responses to both replication stress and DNA damage through promoting MluI cell-cycle box (MCB) binding factor (MBF)-complex-dependent transcription in fission yeast. Set2 loss leads to reduced MBF-dependent ribonucleotide reductase (RNR) expression, reduced deoxyribonucleoside triphosphate (dNTP) synthesis, altered replication origin firing, and a checkpoint-dependent S-phase delay. Accordingly, prolonged S phase in the absence of Set2 is suppressed by increasing dNTP synthesis. Furthermore, H3K36 is di- and tri-methylated at these MBF gene promoters, and Set2 loss leads to reduced MBF binding and transcription in response to genotoxic stress. Together, these findings provide new insights into how H3K36 methylation facilitates DNA replication and promotes genotoxic stress responses in fission yeast.
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Affiliation(s)
- Chen-Chun Pai
- CRUK-MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, ORCRB, Roosevelt Drive, Oxford OX3 7DQ, UK.
| | - Anastasiya Kishkevich
- MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6B, UK
| | - Rachel S Deegan
- CRUK-MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, ORCRB, Roosevelt Drive, Oxford OX3 7DQ, UK
| | - Andrea Keszthelyi
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Brighton, Sussex BN1 9RQ, UK
| | - Lisa Folkes
- CRUK-MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, ORCRB, Roosevelt Drive, Oxford OX3 7DQ, UK
| | - Stephen E Kearsey
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
| | - Nagore De León
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
| | - Ignacio Soriano
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
| | | | - Antony M Carr
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Brighton, Sussex BN1 9RQ, UK
| | - Timothy C Humphrey
- CRUK-MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, ORCRB, Roosevelt Drive, Oxford OX3 7DQ, UK.
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10
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Pai CC, Kearsey SE. A Critical Balance: dNTPs and the Maintenance of Genome Stability. Genes (Basel) 2017; 8:genes8020057. [PMID: 28146119 PMCID: PMC5333046 DOI: 10.3390/genes8020057] [Citation(s) in RCA: 98] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 01/24/2017] [Indexed: 01/14/2023] Open
Abstract
A crucial factor in maintaining genome stability is establishing deoxynucleoside triphosphate (dNTP) levels within a range that is optimal for chromosomal replication. Since DNA replication is relevant to a wide range of other chromosomal activities, these may all be directly or indirectly affected when dNTP concentrations deviate from a physiologically normal range. The importance of understanding these consequences is relevant to genetic disorders that disturb dNTP levels, and strategies that inhibit dNTP synthesis in cancer chemotherapy and for treatment of other disorders. We review here how abnormal dNTP levels affect DNA replication and discuss the consequences for genome stability.
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Affiliation(s)
- Chen-Chun Pai
- CRUK-MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, ORCRB, Roosevelt Drive, Oxford OX3 7DQ, UK.
| | - Stephen E Kearsey
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
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11
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Translation of Cardiac Myosin Activation with 2-deoxy-ATP to Treat Heart Failure via an Experimental Ribonucleotide Reductase-Based Gene Therapy. JACC Basic Transl Sci 2016; 1:666-679. [PMID: 28553667 PMCID: PMC5444879 DOI: 10.1016/j.jacbts.2016.07.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Despite recent advances, chronic heart failure remains a significant and growing unmet medical need, reaching epidemic proportions carrying substantial morbidity, mortality, and costs. A safe and convenient therapeutic agent that produces sustained inotropic effects could ameliorate symptoms and improve functional capacity and quality of life. The authors discovered that small amounts of 2-deoxy-ATP (dATP) activate cardiac myosin leading to enhanced contractility in normal and failing heart muscle. Cardiac myosin activation triggers faster myosin cross-bridge cycling with greater force generation during each contraction. They describe the rationale and results of a translational medicine effort to increase dATP levels using a gene therapy strategy that up-regulates ribonucleotide reductase, the rate-limiting enzyme for dATP synthesis, selectively in cardiomyocytes. In small and large animal models of heart failure, a single dose of this gene therapy has led to sustained inotropic effects with no toxicity or safety concerns identified to date. Further animal studies are being conducted with the goal of testing this agent in patients with heart failure.
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12
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Kolwicz SC, Odom GL, Nowakowski SG, Moussavi-Harami F, Chen X, Reinecke H, Hauschka SD, Murry CE, Mahairas GG, Regnier M. AAV6-mediated Cardiac-specific Overexpression of Ribonucleotide Reductase Enhances Myocardial Contractility. Mol Ther 2015; 24:240-250. [PMID: 26388461 DOI: 10.1038/mt.2015.176] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Accepted: 09/10/2015] [Indexed: 12/13/2022] Open
Abstract
Impaired systolic function, resulting from acute injury or congenital defects, leads to cardiac complications and heart failure. Current therapies slow disease progression but do not rescue cardiac function. We previously reported that elevating the cellular 2 deoxy-ATP (dATP) pool in transgenic mice via increased expression of ribonucleotide reductase (RNR), the enzyme that catalyzes deoxy-nucleotide production, increases myosin-actin interaction and enhances cardiac muscle contractility. For the current studies, we initially injected wild-type mice retro-orbitally with a mixture of adeno-associated virus serotype-6 (rAAV6) containing a miniaturized cardiac-specific regulatory cassette (cTnT(455)) composed of enhancer and promotor portions of the human cardiac troponin T gene (TNNT2) ligated to rat cDNAs encoding either the Rrm1 or Rrm2 subunit. Subsequent studies optimized the system by creating a tandem human RRM1-RRM2 cDNA with a P2A self-cleaving peptide site between the subunits. Both rat and human Rrm1/Rrm2 cDNAs resulted in RNR enzyme overexpression exclusively in the heart and led to a significant elevation of left ventricular (LV) function in normal mice and infarcted rats, measured by echocardiography or isolated heart perfusions, without adverse cardiac remodeling. Our study suggests that increasing RNR levels via rAAV-mediated cardiac-specific expression provide a novel gene therapy approach to potentially enhance cardiac systolic function in animal models and patients with heart failure.
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Affiliation(s)
- Stephen C Kolwicz
- Mitochondria and Metabolism Center, University of Washington, Seattle, Washington, USA
| | - Guy L Odom
- Department of Neurology, University of Washington, Seattle, Washington, USA
| | - Sarah G Nowakowski
- Department of Bioengineering, University of Washington, Seattle, Washington, USA
| | - Farid Moussavi-Harami
- Division of Cardiology, Department of Medicine, University of Washington, Seattle, Washington, USA
| | - Xiaolan Chen
- Department of Biochemistry, University of Washington, Seattle, Washington, USA
| | - Hans Reinecke
- Department of Pathology, University of Washington, Seattle, Washington, USA
| | - Stephen D Hauschka
- Department of Biochemistry, University of Washington, Seattle, Washington, USA
| | - Charles E Murry
- Department of Bioengineering, University of Washington, Seattle, Washington, USA; Division of Cardiology, Department of Medicine, University of Washington, Seattle, Washington, USA; Department of Pathology, University of Washington, Seattle, Washington, USA; Center for Cardiovascular Biology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, USA
| | | | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, Washington, USA; Center for Cardiovascular Biology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, USA.
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13
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Aye Y, Li M, Long MJC, Weiss RS. Ribonucleotide reductase and cancer: biological mechanisms and targeted therapies. Oncogene 2014; 34:2011-21. [PMID: 24909171 DOI: 10.1038/onc.2014.155] [Citation(s) in RCA: 276] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Revised: 04/25/2014] [Accepted: 04/26/2014] [Indexed: 12/16/2022]
Abstract
Accurate DNA replication and repair is essential for proper development, growth and tumor-free survival in all multicellular organisms. A key requirement for the maintenance of genomic integrity is the availability of adequate and balanced pools of deoxyribonucleoside triphosphates (dNTPs), the building blocks of DNA. Notably, dNTP pool alterations lead to genomic instability and have been linked to multiple human diseases, including mitochondrial disorders, susceptibility to viral infection and cancer. In this review, we discuss how a key regulator of dNTP biosynthesis in mammals, the enzyme ribonucleotide reductase (RNR), impacts cancer susceptibility and serves as a target for anti-cancer therapies. Because RNR-regulated dNTP production can influence DNA replication fidelity while also supporting genome-protecting DNA repair, RNR has complex and stage-specific roles in carcinogenesis. Nevertheless, cancer cells are dependent on RNR for de novo dNTP biosynthesis. Therefore, elevated RNR expression is a characteristic of many cancers, and an array of mechanistically distinct RNR inhibitors serve as effective agents for cancer treatment. The dNTP metabolism machinery, including RNR, has been exploited for therapeutic benefit for decades and remains an important target for cancer drug development.
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Affiliation(s)
- Y Aye
- 1] Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA [2] Department of Biochemistry, Weill Cornell Medical College, New York, NY, USA
| | - M Li
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA
| | - M J C Long
- Graduate Program in Biochemistry, Brandeis University, Waltham, MA, USA
| | - R S Weiss
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA
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14
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Fleck O, Vejrup-Hansen R, Watson A, Carr AM, Nielsen O, Holmberg C. Spd1 accumulation causes genome instability independently of ribonucleotide reductase activity but functions to protect the genome when deoxynucleotide pools are elevated. J Cell Sci 2013; 126:4985-94. [PMID: 23986475 DOI: 10.1242/jcs.132837] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cullin4, Ddb1 and Cdt2 are core subunits of the ubiquitin ligase complex CRL4(Cdt2), which controls genome stability by targeting Spd1 for degradation during DNA replication and repair in fission yeast. Spd1 has an inhibitory effect on ribonucleotide reductase (RNR), the activity of which is required for deoxynucleotide (dNTP) synthesis. The failure to degrade Spd1 in mutants where CRL4(Cdt2) is defective leads to DNA integrity checkpoint activation and dependency. This correlates with a lower dNTP pool. Pools are restored in a spd1-deleted background and this also suppresses checkpoint activation and dependency. We hypothesized that fission yeast with RNR hyperactivity would display a mutator phenotype on their own, but also possibly repress aspects of the phenotype associated with the inability to target Spd1 for degradation. Here, we report that a mutation in the R1 subunit of ribonucleotide reductase cdc22 (cdc22-D57N), which alleviated allosteric feedback inhibition, caused a highly elevated dNTP pool that was further increased by deleting spd1. The Δspd1 cdc22-D57N double mutant had elevated mutation rates and was sensitive to damaging agents that cause DNA strand breaks, demonstrating that Spd1 can protect the genome when dNTP pools are high. In ddb1-deleted cells, cdc22-D57N also potently elevated RNR activity, but failed to allow cell growth independently of the intact checkpoint. Our results provide evidence that excess Spd1 interferes with other functions in addition to its inhibitory effect on ribonucleotide reduction to generate replication stress and genome instability.
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Affiliation(s)
- Oliver Fleck
- Cell Cycle and Genome Stability Group, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen N, Denmark
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15
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Abstract
Ribonucleotide reductase (RNR) is the only source for de novo production of the four deoxyribonucleoside triphosphate (dNTP) building blocks needed for DNA synthesis and repair. It is crucial that these dNTP pools are carefully balanced, since mutation rates increase when dNTP levels are either unbalanced or elevated. RNR is the major player in this homeostasis, and with its four different substrates, four different allosteric effectors and two different effector binding sites, it has one of the most sophisticated allosteric regulations known today. In the past few years, the structures of RNRs from several bacteria, yeast and man have been determined in the presence of allosteric effectors and substrates, revealing new information about the mechanisms behind the allosteric regulation. A common theme for all studied RNRs is a flexible loop that mediates modulatory effects from the allosteric specificity site (s-site) to the catalytic site for discrimination between the four substrates. Much less is known about the allosteric activity site (a-site), which functions as an on-off switch for the enzyme's overall activity by binding ATP (activator) or dATP (inhibitor). The two nucleotides induce formation of different enzyme oligomers, and a recent structure of a dATP-inhibited α(6)β(2) complex from yeast suggested how its subunits interacted non-productively. Interestingly, the oligomers formed and the details of their allosteric regulation differ between eukaryotes and Escherichia coli. Nevertheless, these differences serve a common purpose in an essential enzyme whose allosteric regulation might date back to the era when the molecular mechanisms behind the central dogma evolved.
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Affiliation(s)
- Anders Hofer
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden.
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16
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Xu X, Page JL, Surtees JA, Liu H, Lagedrost S, Lu Y, Bronson R, Alani E, Nikitin AY, Weiss RS. Broad overexpression of ribonucleotide reductase genes in mice specifically induces lung neoplasms. Cancer Res 2008; 68:2652-60. [PMID: 18413732 DOI: 10.1158/0008-5472.can-07-5873] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Ribonucleotide reductase (RNR) catalyzes the rate-limiting step in nucleotide biosynthesis and plays a central role in genome maintenance. Although a number of regulatory mechanisms govern RNR activity, the physiologic effect of RNR deregulation had not previously been examined in an animal model. We show here that overexpression of the small RNR subunit potently and selectively induces lung neoplasms in transgenic mice and is mutagenic in cultured cells. Combining RNR deregulation with defects in DNA mismatch repair, the cellular mutation correction system, synergistically increased RNR-induced mutagenesis and carcinogenesis. Moreover, the proto-oncogene K-ras was identified as a frequent mutational target in RNR-induced lung neoplasms. Together, these results show that RNR deregulation promotes lung carcinogenesis through a mutagenic mechanism and establish a new oncogenic activity for a key regulator of nucleotide metabolism. Importantly, RNR-induced lung neoplasms histopathologically resemble human papillary adenocarcinomas and arise stochastically via a mutagenic mechanism, making RNR transgenic mice a valuable model for lung cancer.
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Affiliation(s)
- Xia Xu
- Department of Biomedical Sciences, Cornell University, Ithaca, New York 14853, USA
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17
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Yoshio N, Kawai Y, Hori H, Ueda T. Resistance to 9-beta-D-arabinofuranosyl-2-fluoroadenine due to reduced incorporation into DNA from competition by excess deoxyadenosine triphosphate: implications for different sensitivities to nucleoside analogues. Int J Hematol 2005; 81:405-12. [PMID: 16158821 DOI: 10.1532/ijh97.05008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The cytotoxic action of the deoxyadenosine analogue 9-beta-D-arabinofuranosyl-2-fluoroadenine (F-ara-A) depends on the incorporation into DNA after being phosphorylated to F-ara-A triphosphate (F-ara-ATP) by deoxycytidine kinase (dCK). The mechanisms of resistance to F-ara-A were investigated in a newly established variant of L1210 mouse leukemia cells (L1210/F). L1210/F was more than 41-fold more resistant to F-ara-A than the parental cell line and had a 55% lower dCK activity. Interestingly, L1210/F showed a modest level of cross-resistance to deoxycytidine analogues phosphorylated by dCK, for instance, 1-beta-D-arabinofuranosylcytosine (ara-C). The comparative study of F-ara-A and ara-C demonstrated that the difference in the accumulation of their respective triphosphates was minor. In contrast, the incorporation of F-ara-A into DNA was strikingly suppressed compared with that of ara-C. In general, the high natural triphosphate levels interfere with corresponding analogue incorporation into DNA. The deoxyadenosine triphosphate (dATP) and deoxycytidine triphosphate pool sizes in L1210/F cells were increased by 4.9-fold and 1.9-fold, respectively, compared with the parental cells. Treatment with hydroxyurea increased the ratio of F-ara-ATP to dATP 2.1-fold and enhanced the action of F-ara-A in L1210/F. This is the first cell line to show that the profoundly defective incorporation of F-ara-A into DNA during competition with excess dATP confers a high degree of resistance to F-ara-A.
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Affiliation(s)
- Nobuyuki Yoshio
- First Department of Internal Medicine, Faculty of Medical Sciences, University of Fukui, Fukui, Japan
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18
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Hofer A, Schmidt PP, Gräslund A, Thelander L. Cloning and characterization of the R1 and R2 subunits of ribonucleotide reductase from Trypanosoma brucei. Proc Natl Acad Sci U S A 1997; 94:6959-64. [PMID: 9192674 PMCID: PMC21267 DOI: 10.1073/pnas.94.13.6959] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Ribonucleotide reductase (RNR) catalyzes the rate limiting step in the de novo synthesis of deoxyribonucleotides by directly reducing ribonucleotides to the corresponding deoxyribonucleotides. To keep balanced pools of deoxyribonucleotides, all nonviral RNRs studied so far are allosterically regulated. Most eukaryotes contain a class I RNR, which is a heterodimer of two nonidentical subunits called proteins R1 and R2. We have isolated cDNAs encoding the R1 and R2 proteins from Trypanosoma brucei. The amino acid sequence identities with the mouse R1 and R2 subunits are 58% and 63%, respectively. Recombinant active trypanosome R1 and R2 proteins were expressed in Escherichia coli and purified. The R2 protein contains an iron-tyrosyl free radical center verified by EPR spectroscopy and iron analyses. Measurement of cytidine 5'-diphosphate reduction by the trypanosome RNR in the presence of various allosteric effectors showed that the activity is highest with dTTP, dGTP, or dATP and considerably lower with ATP. The effect of dGTP is either activating (alone) or inhibitory (in the presence of ATP). Filter binding studies indicated that there are two classes of allosteric effector binding sites that bind ATP or dATP (low-affinity dATP site) and ATP, dATP, dGTP, or dTTP (high-affinity dATP site), respectively. Therefore, the structural organization of the allosteric sites is very similar to the mammalian RNRs, whereas the allosteric regulation of cytidine 5'-diphosphate reduction is unique. Hopefully, this difference can be used to target the trypanosome RNR for therapeutic purposes.
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Affiliation(s)
- A Hofer
- Department of Medical Biochemistry and Biophysics, Umeâ University, S-901 87 Umeâ, Sweden
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Abstract
In many ways, cervical cancer behaves as a sexually transmitted disease. The major risk factors are multiple sexual partners and early onset of sexual activity. Although high-risk types of human papillomaviruses (HPV) play an important role in the development of nearly all cases of cervical cancer, other sexually transmitted infectious agents may be cofactors. Herpes simplex virus type 2 (HSV-2) is transmitted primarily by sexual contact and therefore has been implicated as a risk factor. Several independent studies suggest that HSV-2 infections correlate with a higher than normal incidence of cervical cancer. In contrast, other epidemiological studies have concluded that infection with HSV-2 is not a major risk factor. Two separate transforming domains have been identified within the HSV-2 genome, but continued viral gene expression apparently is not necessary for neoplastic transformation. HSV infections lead to unscheduled cellular DNA synthesis, chromosomal amplifications, and mutations. These observations suggest that HSV-2 is not a typical DNA tumor virus. It is hypothesized that persistent or abortive infections induce permanent genetic alterations that interfere with differentiation of cervical epithelium and subsequently induce abnormal proliferation. Thus, HSV-2 may be a cofactor in some but not all cases of cervical cancer.
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Affiliation(s)
- C Jones
- Department of Veterinary and Biomedical Sciences, University of Nebraska, Lincoln 68583, USA
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20
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Chakrabarti D, Schuster SM, Chakrabarti R. Cloning and characterization of subunit genes of ribonucleotide reductase, a cell-cycle-regulated enzyme, from Plasmodium falciparum. Proc Natl Acad Sci U S A 1993; 90:12020-4. [PMID: 8265664 PMCID: PMC48117 DOI: 10.1073/pnas.90.24.12020] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Ribonucleotide reductase (EC 1.17.4.1; RNR), a cell-cycle-regulated enzyme, catalyzes the rate-limiting step in the de novo synthesis of deoxyribonucleotides by the reduction of the corresponding ribonucleotides. The important role of the RNR in DNA synthesis and cell division makes this enzyme an excellent target for chemotherapy. However, nothing is known about this enzyme from the malaria parasite Plasmodium falciparum. We have isolated cDNA clones encoding both the large and small RNR subunits. The sequences of full-length clones of the large and small RNR subunits revealed an open reading frame encoding 806 and 349 amino acids, respectively, and showed significant identity with other RNR sequences in the data base. RNA blot analysis showed that the size of the large and small RNR subunit transcripts are 5.4 kb and 2.2 kb, respectively. Both the RNR subunit transcripts fluctuate in level during the cell cycle, reaching a peak preceding maximal DNA synthesis activity. An oligodeoxynucleotide phosphorothioate that is complementary to sequences around the translational initiation codon of the small RNR subunit showed significant inhibition of growth, as measured by the inhibition in DNA synthesis.
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Affiliation(s)
- D Chakrabarti
- Department of Infectious Diseases, University of Florida, Gainesville 32611-0880
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21
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Temperature-sensitive DNA mutant of Chinese hamster ovary cells with a thermolabile ribonucleotide reductase activity. Mol Cell Biol 1990. [PMID: 2233712 DOI: 10.1128/mcb.10.11.5688] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
JB3-B is a Chinese hamster ovary cell mutant previously shown to be temperature sensitive for DNA replication (J. J. Dermody, B. E. Wojcik, H. Du, and H. L. Ozer, Mol. Cell. Biol. 6:4594-4601, 1986). It was chosen for detailed study because of its novel property of inhibiting both polyomavirus and adenovirus DNA synthesis in a temperature-dependent manner. Pulse-labeling studies demonstrated a defect in the rate of adenovirus DNA synthesis. Measurement of deoxyribonucleoside triphosphate (dNTP) pools as a function of time after shift of uninfected cultures from 33 to 39 degrees C revealed that all four dNTP pools declined at similar rates in extracts prepared either from whole cells or from rapidly isolated nuclei. Ribonucleoside triphosphate pools were unaffected by a temperature shift, ruling out the possibility that the mutation affects nucleoside diphosphokinase. However, ribonucleotide reductase activity, as measured in extracts, declined after cell cultures underwent a temperature shift, in parallel with the decline in dNTP pool sizes. Moreover, the activity of cell extracts was thermolabile in vitro, consistent with the model that the JB3-B mutation affects the structural gene for one of the ribonucleotide reductase subunits. The kinetics of dNTP pool size changes after temperature shift are quite distinct from those reported after inhibition of ribonucleotide reductase with hydroxyurea. An indirect effect on ribonucleotide reductase activity in JB3-B has not been excluded since human sequences other than those encoding the enzyme subunits can correct the temperature-sensitive growth defect in the mutant.
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22
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Wojcik BE, Dermody JJ, Ozer HL, Mun B, Mathews CK. Temperature-sensitive DNA mutant of Chinese hamster ovary cells with a thermolabile ribonucleotide reductase activity. Mol Cell Biol 1990; 10:5688-99. [PMID: 2233712 PMCID: PMC361336 DOI: 10.1128/mcb.10.11.5688-5699.1990] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
JB3-B is a Chinese hamster ovary cell mutant previously shown to be temperature sensitive for DNA replication (J. J. Dermody, B. E. Wojcik, H. Du, and H. L. Ozer, Mol. Cell. Biol. 6:4594-4601, 1986). It was chosen for detailed study because of its novel property of inhibiting both polyomavirus and adenovirus DNA synthesis in a temperature-dependent manner. Pulse-labeling studies demonstrated a defect in the rate of adenovirus DNA synthesis. Measurement of deoxyribonucleoside triphosphate (dNTP) pools as a function of time after shift of uninfected cultures from 33 to 39 degrees C revealed that all four dNTP pools declined at similar rates in extracts prepared either from whole cells or from rapidly isolated nuclei. Ribonucleoside triphosphate pools were unaffected by a temperature shift, ruling out the possibility that the mutation affects nucleoside diphosphokinase. However, ribonucleotide reductase activity, as measured in extracts, declined after cell cultures underwent a temperature shift, in parallel with the decline in dNTP pool sizes. Moreover, the activity of cell extracts was thermolabile in vitro, consistent with the model that the JB3-B mutation affects the structural gene for one of the ribonucleotide reductase subunits. The kinetics of dNTP pool size changes after temperature shift are quite distinct from those reported after inhibition of ribonucleotide reductase with hydroxyurea. An indirect effect on ribonucleotide reductase activity in JB3-B has not been excluded since human sequences other than those encoding the enzyme subunits can correct the temperature-sensitive growth defect in the mutant.
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Affiliation(s)
- B E Wojcik
- Department of Biological Science, Hunter College, City University of New York, New York 10021
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