1
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Riccio A, Brannon A, Krahn J, Bouvette J, Williams J, Borgnia M, Copeland W. Coordinated DNA polymerization by Polγ and the region of LonP1 regulated proteolysis. Nucleic Acids Res 2024; 52:7863-7875. [PMID: 38932681 PMCID: PMC11260448 DOI: 10.1093/nar/gkae539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Revised: 05/09/2024] [Accepted: 06/10/2024] [Indexed: 06/28/2024] Open
Abstract
The replicative mitochondrial DNA polymerase, Polγ, and its protein regulation are essential for the integrity of the mitochondrial genome. The intricacies of Polγ regulation and its interactions with regulatory proteins, which are essential for fine-tuning polymerase function, remain poorly understood. Misregulation of the Polγ heterotrimer, consisting of (i) PolG, the polymerase catalytic subunit and (ii) PolG2, the accessory subunit, ultimately results in mitochondrial diseases. Here, we used single particle cryo-electron microscopy to resolve the structure of PolG in its apoprotein state and we captured Polγ at three intermediates within the catalytic cycle: DNA bound, engaged, and an active polymerization state. Chemical crosslinking mass spectrometry, and site-directed mutagenesis uncovered the region of LonP1 engagement of PolG, which promoted proteolysis and regulation of PolG protein levels. PolG2 clinical variants, which disrupted a stable Polγ complex, led to enhanced LonP1-mediated PolG degradation. Overall, this insight into Polγ aids in an understanding of mitochondrial DNA replication and characterizes how machinery of the replication fork may be targeted for proteolytic degradation when improperly functioning.
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Affiliation(s)
- Amanda A Riccio
- Mitochondrial DNA Replication group, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - Asia J Brannon
- Mitochondrial DNA Replication group, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - Juno M Krahn
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - Jonathan Bouvette
- Molecular Microscopy Consortium, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - Jason G Williams
- Mass Spectrometry Research and Support Group, Epigenetics and Stem Cell Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - Mario J Borgnia
- Molecular Microscopy Consortium, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - William C Copeland
- Mitochondrial DNA Replication group, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
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2
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Brañas Casas R, Zuppardo A, Risato G, Dinarello A, Celeghin R, Fontana C, Grelloni E, Gilea AI, Viscomi C, Rasola A, Dalla Valle L, Lodi T, Baruffini E, Facchinello N, Argenton F, Tiso N. Zebrafish polg2 knock-out recapitulates human POLG-disorders; implications for drug treatment. Cell Death Dis 2024; 15:281. [PMID: 38643274 PMCID: PMC11032366 DOI: 10.1038/s41419-024-06622-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 03/15/2024] [Accepted: 03/18/2024] [Indexed: 04/22/2024]
Abstract
The human mitochondrial DNA polymerase gamma is a holoenzyme, involved in mitochondrial DNA (mtDNA) replication and maintenance, composed of a catalytic subunit (POLG) and a dimeric accessory subunit (POLG2) conferring processivity. Mutations in POLG or POLG2 cause POLG-related diseases in humans, leading to a subset of Mendelian-inherited mitochondrial disorders characterized by mtDNA depletion (MDD) or accumulation of multiple deletions, presenting multi-organ defects and often leading to premature death at a young age. Considering the paucity of POLG2 models, we have generated a stable zebrafish polg2 mutant line (polg2ia304) by CRISPR/Cas9 technology, carrying a 10-nucleotide deletion with frameshift mutation and premature stop codon. Zebrafish polg2 homozygous mutants present slower development and decreased viability compared to wild type siblings, dying before the juvenile stage. Mutants display a set of POLG-related phenotypes comparable to the symptoms of human patients affected by POLG-related diseases, including remarkable MDD, altered mitochondrial network and dynamics, and reduced mitochondrial respiration. Histological analyses detected morphological alterations in high-energy demanding tissues, along with a significant disorganization of skeletal muscle fibres. Consistent with the last finding, locomotor assays highlighted a decreased larval motility. Of note, treatment with the Clofilium tosylate drug, previously shown to be effective in POLG models, could partially rescue MDD in Polg2 mutant animals. Altogether, our results point at zebrafish as an effective model to study the etiopathology of human POLG-related disorders linked to POLG2, and a suitable platform to screen the efficacy of POLG-directed drugs in POLG2-associated forms.
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Affiliation(s)
| | - Alessandro Zuppardo
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Giovanni Risato
- Department of Biology, University of Padova, Padova, 35131, Italy
- Department of Cardio-Thoraco-Vascular Sciences and Public Health, University of Padova, Padova, 35128, Italy
| | - Alberto Dinarello
- Department of Biology, University of Padova, Padova, 35131, Italy
- Novo Nordisk Foundation Center for Stem Cell Medicine (reNEW), University of Copenhagen, Copenhagen, 2200, Denmark
| | - Rudy Celeghin
- Department of Cardio-Thoraco-Vascular Sciences and Public Health, University of Padova, Padova, 35128, Italy
| | - Camilla Fontana
- Department of Biology, University of Padova, Padova, 35131, Italy
- Department of Animal and Aquatic Sciences, Faculty of Agriculture, Chiang Mai University, Chiang Mai, 50200, Thailand
| | | | - Alexandru Ionut Gilea
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, 43124, Italy
| | - Carlo Viscomi
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Andrea Rasola
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | | | - Tiziana Lodi
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, 43124, Italy
| | - Enrico Baruffini
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, 43124, Italy
| | - Nicola Facchinello
- Neuroscience Institute, Italian Research Council (CNR), 35131, Padova, Italy.
| | | | - Natascia Tiso
- Department of Biology, University of Padova, Padova, 35131, Italy.
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3
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Wu C, Zhu H, Zhang Y, Ding L, Wang J. Interference with mitochondrial metabolism could serve as a potential therapeutic strategy for advanced prostate cancer. PLoS One 2024; 19:e0290753. [PMID: 38598542 PMCID: PMC11006138 DOI: 10.1371/journal.pone.0290753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Accepted: 08/15/2023] [Indexed: 04/12/2024] Open
Abstract
Metabolic reprogramming has been defined as a hallmark of malignancies. Prior studies have focused on the single nucleotide polymorphism (SNP) of POLG2 gene, which is reportedly responsible for encoding mitochondrial DNA genes and is implicated in the material and energy metabolism of tumor cells, whereas its function in prostate cancer has been elusive. Gene expression profile matrix and clinical information were downloaded from TCGA (The Cancer Genome Atlas) data portal, and GSE3325 and GSE8511 were retrieved from GEO (Gene Expression Omnibus) database. We conducted analysis of the relative expression of POLG2, clinical characterization, survival analysis, GO / KEGG and GSEA (Gene Set Enrichment Analysis) enrichment analysis in R and employed STRING portal to acquaint ourselves with the protein-protein interaction (PPI). IHC (Immunohistochemical) profiles of POLG2 protein between normal and cancerous tissues were consulted via HPA (Human protein atlas) database and the immunohistochemical POLG2 were verified between para-cancerous and cancerous tissues in tissue array. At the cellular level, Mitochondrial dysfunction assay, DNA synthesis test, wound healing assay, and invasion assay were implemented to further validate the phenotype of POLG2 knockdown in PCa cell lines. RT-qPCR and western blotting were routinely adopted to verify variations of molecular expression within epithelial mesenchymal transition (EMT). Results showed that POLG2 was over-expressed in most cancer types, and the over-expression of POLG2 was correlated with PCa progression and suggested poor OS (Overall Survival) and PFI (Progress Free Interval). Multivariate analysis showed that POLG2 might be an independent prognostic factor of prostate cancer. We also performed GO/KEGG, GSEA analysis, co-expression genes, and PPI, and observed the metabolism-related gene alterations in PCa. Furthermore, we verified that POLG2 knockdown had an inhibitory effect on mitochondrial function, proliferation, cell motility, and invasion, we affirmed POLG2 could affect the prognosis of advanced prostate cancer via EMT. In summary, our findings indicate that over-expressed POLG2 renders poor prognosis in advanced prostate cancer. This disadvantageous factor can serve as a potential indicator, making it possible to target mitochondrial metabolism to treat advanced prostate cancer.
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Affiliation(s)
- Chuang Wu
- Department of Urology, Jiangsu Province Geriatric Hospital, Nanjing, Jiangsu, China
| | - Huihuang Zhu
- Department of Urology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, China
| | - Yang Zhang
- Department of Urology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, China
| | - Li Ding
- Department of Urology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, China
| | - Junqi Wang
- Department of Urology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, China
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4
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Buchel G, Nayak AR, Herbine K, Sarfallah A, Sokolova VO, Zamudio-Ochoa A, Temiakov D. Structural basis for DNA proofreading. Nat Commun 2023; 14:8501. [PMID: 38151585 PMCID: PMC10752894 DOI: 10.1038/s41467-023-44198-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 12/04/2023] [Indexed: 12/29/2023] Open
Abstract
DNA polymerase (DNAP) can correct errors in DNA during replication by proofreading, a process critical for cell viability. However, the mechanism by which an erroneously incorporated base translocates from the polymerase to the exonuclease site and the corrected DNA terminus returns has remained elusive. Here, we present an ensemble of nine high-resolution structures representing human mitochondrial DNA polymerase Gamma, Polγ, captured during consecutive proofreading steps. The structures reveal key events, including mismatched base recognition, its dissociation from the polymerase site, forward translocation of DNAP, alterations in DNA trajectory, repositioning and refolding of elements for primer separation, DNAP backtracking, and displacement of the mismatched base into the exonuclease site. Altogether, our findings suggest a conserved 'bolt-action' mechanism of proofreading based on iterative cycles of DNAP translocation without dissociation from the DNA, facilitating primer transfer between catalytic sites. Functional assays and mutagenesis corroborate this mechanism, connecting pathogenic mutations to crucial structural elements in proofreading steps.
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Affiliation(s)
- Gina Buchel
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St, Philadelphia, PA, 19107, USA
| | - Ashok R Nayak
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St, Philadelphia, PA, 19107, USA
| | - Karl Herbine
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St, Philadelphia, PA, 19107, USA
| | - Azadeh Sarfallah
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St, Philadelphia, PA, 19107, USA
| | - Viktoriia O Sokolova
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St, Philadelphia, PA, 19107, USA
| | - Angelica Zamudio-Ochoa
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St, Philadelphia, PA, 19107, USA
| | - Dmitry Temiakov
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St, Philadelphia, PA, 19107, USA.
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5
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Wojtaszek JL, Hoff KE, Longley MJ, Kaur P, Andres S, Wang H, Williams R, Copeland W. Structure-specific roles for PolG2-DNA complexes in maintenance and replication of mitochondrial DNA. Nucleic Acids Res 2023; 51:9716-9732. [PMID: 37592734 PMCID: PMC10570022 DOI: 10.1093/nar/gkad679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Revised: 07/13/2023] [Accepted: 08/09/2023] [Indexed: 08/19/2023] Open
Abstract
The homodimeric PolG2 accessory subunit of the mitochondrial DNA polymerase gamma (Pol γ) enhances DNA binding and processive DNA synthesis by the PolG catalytic subunit. PolG2 also directly binds DNA, although the underlying molecular basis and functional significance are unknown. Here, data from Atomic Force Microscopy (AFM) and X-ray structures of PolG2-DNA complexes define dimeric and hexameric PolG2 DNA binding modes. Targeted disruption of PolG2 DNA-binding interfaces impairs processive DNA synthesis without diminishing Pol γ subunit affinities. In addition, a structure-specific DNA-binding role for PolG2 oligomers is supported by X-ray structures and AFM showing that oligomeric PolG2 localizes to DNA crossings and targets forked DNA structures resembling the mitochondrial D-loop. Overall, data indicate that PolG2 DNA binding has both PolG-dependent and -independent functions in mitochondrial DNA replication and maintenance, which provide new insight into molecular defects associated with PolG2 disruption in mitochondrial disease.
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Affiliation(s)
- Jessica L Wojtaszek
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - Kirsten E Hoff
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - Matthew J Longley
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - Parminder Kaur
- Physics Department, North Carolina State University, Raleigh, NC 27695, USA
- Center for Human Health and the Environment, North Carolina State University, Raleigh, NC 27695, USA
| | - Sara N Andres
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - Hong Wang
- Physics Department, North Carolina State University, Raleigh, NC 27695, USA
- Center for Human Health and the Environment, North Carolina State University, Raleigh, NC 27695, USA
- Toxicology Program, North Carolina State University, Raleigh, NC 27695, USA
| | - R Scott Williams
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
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6
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Erdinc D, Macao B, Valenzuela S, Lesko N, Naess K, Peter B, Bruhn H, Wedell A, Wredenberg A, Falkenberg M. The disease-causing mutation p.F907I reveals a novel pathogenic mechanism for POLγ-related diseases. Biochim Biophys Acta Mol Basis Dis 2023:166786. [PMID: 37302426 DOI: 10.1016/j.bbadis.2023.166786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 05/24/2023] [Accepted: 06/07/2023] [Indexed: 06/13/2023]
Abstract
Mutations in the catalytic domain of mitochondrial DNA polymerase γ (POLγ) cause a broad spectrum of clinical conditions. POLγ mutations impair mitochondrial DNA replication, thereby causing deletions and/or depletion of mitochondrial DNA, which in turn impair biogenesis of the oxidative phosphorylation system. We here identify a patient with a homozygous p.F907I mutation in POLγ, manifesting a severe clinical phenotype with developmental arrest and rapid loss of skills from 18 months of age. Magnetic resonance imaging of the brain revealed extensive white matter abnormalities, Southern blot of muscle mtDNA demonstrated depletion of mtDNA and the patient deceased at 23 months of age. Interestingly, the p.F907I mutation does not affect POLγ activity on single-stranded DNA or its proofreading activity. Instead, the mutation affects unwinding of parental double-stranded DNA at the replication fork, impairing the ability of the POLγ to support leading-strand DNA synthesis with the TWINKLE helicase. Our results thus reveal a novel pathogenic mechanism for POLγ-related diseases.
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Affiliation(s)
- Direnis Erdinc
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Gothenburg SE-40530, Sweden
| | - Bertil Macao
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Gothenburg SE-40530, Sweden
| | - Sebastian Valenzuela
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Gothenburg SE-40530, Sweden
| | - Nicole Lesko
- Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm SE-17177, Sweden; Centre for Inherited Metabolic Diseases, Karolinska University Hospital, Stockholm, Sweden
| | - Karin Naess
- Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm SE-17177, Sweden; Centre for Inherited Metabolic Diseases, Karolinska University Hospital, Stockholm, Sweden
| | - Bradley Peter
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Gothenburg SE-40530, Sweden
| | - Helene Bruhn
- Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm SE-17177, Sweden; Centre for Inherited Metabolic Diseases, Karolinska University Hospital, Stockholm, Sweden
| | - Anna Wedell
- Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden; Centre for Inherited Metabolic Diseases, Karolinska University Hospital, Stockholm, Sweden
| | - Anna Wredenberg
- Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm SE-17177, Sweden; Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden.
| | - Maria Falkenberg
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Gothenburg SE-40530, Sweden.
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7
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Park J, Herrmann GK, Mitchell PG, Sherman MB, Yin YW. Polγ coordinates DNA synthesis and proofreading to ensure mitochondrial genome integrity. Nat Struct Mol Biol 2023; 30:812-823. [PMID: 37202477 PMCID: PMC10920075 DOI: 10.1038/s41594-023-00980-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 03/28/2023] [Indexed: 05/20/2023]
Abstract
Accurate replication of mitochondrial DNA (mtDNA) by DNA polymerase γ (Polγ) is essential for maintaining cellular energy supplies, metabolism, and cell cycle control. To illustrate the structural mechanism for Polγ coordinating polymerase (pol) and exonuclease (exo) activities to ensure rapid and accurate DNA synthesis, we determined four cryo-EM structures of Polγ captured after accurate or erroneous incorporation to a resolution of 2.4-3.0 Å. The structures show that Polγ employs a dual-checkpoint mechanism to sense nucleotide misincorporation and initiate proofreading. The transition from replication to error editing is accompanied by increased dynamics in both DNA and enzyme, in which the polymerase relaxes its processivity and the primer-template DNA unwinds, rotates, and backtracks to shuttle the mismatch-containing primer terminus 32 Å to the exo site for editing. Our structural and functional studies also provide a foundation for analyses of Polγ mutation-induced human diseases and aging.
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Affiliation(s)
- Joon Park
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, USA
| | - Geoffrey K Herrmann
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, USA
| | - Patrick G Mitchell
- Division of CryoEM and Bioimaging, Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center National Accelerator Laboratory, Stanford University, Menlo Park, CA, USA
| | - Michael B Sherman
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, USA
| | - Y Whitney Yin
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA.
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, USA.
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA.
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8
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Forslund JME, Stojkovič G, Wanrooij S. Rolling Circle Replication and Bypass of Damaged Nucleotides. Methods Mol Biol 2023; 2615:203-217. [PMID: 36807794 DOI: 10.1007/978-1-0716-2922-2_15] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
Faithful mitochondrial DNA (mtDNA) replication is critical for the proper function of the oxidative phosphorylation system. Problems with mtDNA maintenance, such as replication stalling upon encountering DNA damage, impair this vital function and can potentially lead to disease. An in vitro reconstituted mtDNA replication system can be used to investigate how the mtDNA replisome deals with, for example, oxidatively or UV-damaged DNA. In this chapter, we provide a detailed protocol on how to study the bypass of different types of DNA damage using a rolling circle replication assay. The assay takes advantage of purified recombinant proteins and can be adapted to the examination of various aspects of mtDNA maintenance.
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Affiliation(s)
- Josefin M E Forslund
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Gorazd Stojkovič
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Sjoerd Wanrooij
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden.
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9
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Gupta R, Kanai M, Durham TJ, Tsuo K, McCoy JG, Chinnery PF, Karczewski KJ, Calvo SE, Neale BM, Mootha VK. Nuclear genetic control of mtDNA copy number and heteroplasmy in humans. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.01.19.23284696. [PMID: 36711677 PMCID: PMC9882621 DOI: 10.1101/2023.01.19.23284696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Human mitochondria contain a high copy number, maternally transmitted genome (mtDNA) that encodes 13 proteins required for oxidative phosphorylation. Heteroplasmy arises when multiple mtDNA variants co-exist in an individual and can exhibit complex dynamics in disease and in aging. As all proteins involved in mtDNA replication and maintenance are nuclear-encoded, heteroplasmy levels can, in principle, be under nuclear genetic control, however this has never been shown in humans. Here, we develop algorithms to quantify mtDNA copy number (mtCN) and heteroplasmy levels using blood-derived whole genome sequences from 274,832 individuals of diverse ancestry and perform GWAS to identify nuclear loci controlling these traits. After careful correction for blood cell composition, we observe that mtCN declines linearly with age and is associated with 92 independent nuclear genetic loci. We find that nearly every individual carries heteroplasmic variants that obey two key patterns: (1) heteroplasmic single nucleotide variants are somatic mutations that accumulate sharply after age 70, while (2) heteroplasmic indels are maternally transmitted as mtDNA mixtures with resulting levels influenced by 42 independent nuclear loci involved in mtDNA replication, maintenance, and novel pathways. These nuclear loci do not appear to act by mtDNA mutagenesis, but rather, likely act by conferring a replicative advantage to specific mtDNA molecules. As an illustrative example, the most common heteroplasmy we identify is a length variant carried by >50% of humans at position m.302 within a G-quadruplex known to serve as a replication switch. We find that this heteroplasmic variant exerts cis -acting genetic control over mtDNA abundance and is itself under trans -acting genetic control of nuclear loci encoding protein components of this regulatory switch. Our study showcases how nuclear haplotype can privilege the replication of specific mtDNA molecules to shape mtCN and heteroplasmy dynamics in the human population.
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Affiliation(s)
- Rahul Gupta
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, United States
- Broad Institute of MIT and Harvard, United States
- Analytic and Translational Genetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, United States
| | - Masahiro Kanai
- Broad Institute of MIT and Harvard, United States
- Analytic and Translational Genetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, United States
| | - Timothy J Durham
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, United States
- Broad Institute of MIT and Harvard, United States
| | - Kristin Tsuo
- Broad Institute of MIT and Harvard, United States
- Analytic and Translational Genetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, United States
| | - Jason G McCoy
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, United States
- Broad Institute of MIT and Harvard, United States
| | - Patrick F Chinnery
- Department of Clinical Neurosciences & MRC Mitochondrial Biology Unit, University of Cambridge, United Kingdom
| | - Konrad J Karczewski
- Broad Institute of MIT and Harvard, United States
- Analytic and Translational Genetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, United States
| | - Sarah E Calvo
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, United States
- Broad Institute of MIT and Harvard, United States
| | - Benjamin M Neale
- Broad Institute of MIT and Harvard, United States
- Analytic and Translational Genetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, United States
| | - Vamsi K Mootha
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, United States
- Broad Institute of MIT and Harvard, United States
- Department of Systems Biology, Harvard Medical School, United States
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10
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Karlowicz A, Dubiel AB, Czerwinska J, Bledea A, Purzycki P, Grzelewska M, McAuley RJ, Szczesny RJ, Brzuska G, Krol E, Szczesny B, Szymanski MR. In vitro reconstitution reveals a key role of human mitochondrial EXOG in RNA primer processing. Nucleic Acids Res 2022; 50:7991-8007. [PMID: 35819194 PMCID: PMC9371904 DOI: 10.1093/nar/gkac581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Revised: 06/01/2022] [Accepted: 06/24/2022] [Indexed: 11/12/2022] Open
Abstract
The removal of RNA primers is essential for mitochondrial DNA (mtDNA) replication. Several nucleases have been implicated in RNA primer removal in human mitochondria, however, no conclusive mechanism has been elucidated. Here, we reconstituted minimal in vitro system capable of processing RNA primers into ligatable DNA ends. We show that human 5'-3' exonuclease, EXOG, plays a fundamental role in removal of the RNA primer. EXOG cleaves short and long RNA-containing flaps but also in cooperation with RNase H1, processes non-flap RNA-containing intermediates. Our data indicate that the enzymatic activity of both enzymes is necessary to process non-flap RNA-containing intermediates and that regardless of the pathway, EXOG-mediated RNA cleavage is necessary prior to ligation by DNA Ligase III. We also show that upregulation of EXOG levels in mitochondria increases ligation efficiency of RNA-containing substrates and discover physical interactions, both in vitro and in cellulo, between RNase H1 and EXOG, Pol γA, Pol γB and Lig III but not FEN1, which we demonstrate to be absent from mitochondria of human lung epithelial cells. Together, using human mtDNA replication enzymes, we reconstitute for the first time RNA primer removal reaction and propose a novel model for RNA primer processing in human mitochondria.
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Affiliation(s)
- Anna Karlowicz
- Structural Biology Laboratory, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
| | - Andrzej B Dubiel
- Structural Biology Laboratory, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
| | - Jolanta Czerwinska
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, ul. Pawinskiego 5A, 02-106 Warsaw, Poland.,Faculty of Biology, Institute of Genetics and Biotechnology, University of Warsaw, Warsaw 02-106, Poland
| | - Adela Bledea
- Structural Biology Laboratory, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
| | - Piotr Purzycki
- Structural Biology Laboratory, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
| | - Marta Grzelewska
- Structural Biology Laboratory, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
| | - Ryan J McAuley
- Department of Ophthalmology and Visual Sciences, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA
| | - Roman J Szczesny
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, ul. Pawinskiego 5A, 02-106 Warsaw, Poland
| | - Gabriela Brzuska
- Laboratory of Recombinant Vaccines, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
| | - Ewelina Krol
- Laboratory of Recombinant Vaccines, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
| | - Bartosz Szczesny
- Department of Ophthalmology and Visual Sciences, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA
| | - Michal R Szymanski
- Structural Biology Laboratory, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, University of Gdansk, ul. Abrahama 58, 80-307 Gdansk, Poland
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11
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A new pathogenic POLG variant. Mol Genet Metab Rep 2022; 32:100890. [PMID: 35860755 PMCID: PMC9289853 DOI: 10.1016/j.ymgmr.2022.100890] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 06/22/2022] [Accepted: 06/23/2022] [Indexed: 11/20/2022] Open
Abstract
POLG gene mutations are the most common causes of inherited mitochondrial disorders. The enzyme produced by this gene is responsible for the replication and repair of mitochondrial DNA. To date, around 300 pathogenic variants have been described in this gene. The resulting clinical outcomes of POLG mutations are widely variable in both phenotype and severity. There is considerable overlap in the phenotype of the so-called POLG syndromes with no clear genotype-phenotype correlation. Here we describe a newly discovered pathogenic variant in the POLG gene in a 7-year-old male that died of uncontrollable refractory status epilepticus. Genetic epilepsy panel sequencing identified two variants in the POLG gene, the common p.A467T pathological mutation and a novel p.S809R POLG variant found in trans with the p.A467T POLG that accompanied a severely reduced mitochondrial DNA level in the patient's tissues.
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12
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Sanchez-Contreras M, Sweetwyne MT, Kohrn BF, Tsantilas KA, Hipp MJ, Schmidt EK, Fredrickson J, Whitson JA, Campbell MD, Rabinovitch PS, Marcinek DJ, Kennedy SR. A replication-linked mutational gradient drives somatic mutation accumulation and influences germline polymorphisms and genome composition in mitochondrial DNA. Nucleic Acids Res 2021; 49:11103-11118. [PMID: 34614167 PMCID: PMC8565317 DOI: 10.1093/nar/gkab901] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 09/10/2021] [Accepted: 09/22/2021] [Indexed: 11/22/2022] Open
Abstract
Mutations in mitochondrial DNA (mtDNA) cause maternally inherited diseases, while somatic mutations are linked to common diseases of aging. Although mtDNA mutations impact health, the processes that give rise to them are under considerable debate. To investigate the mechanism by which de novo mutations arise, we analyzed the distribution of naturally occurring somatic mutations across the mouse and human mtDNA obtained by Duplex Sequencing. We observe distinct mutational gradients in G→A and T→C transitions delimited by the light-strand origin and the mitochondrial Control Region (mCR). The gradient increases unequally across the mtDNA with age and is lost in the absence of DNA polymerase γ proofreading activity. In addition, high-resolution analysis of the mCR shows that important regulatory elements exhibit considerable variability in mutation frequency, consistent with them being mutational ‘hot-spots’ or ‘cold-spots’. Collectively, these patterns support genome replication via a deamination prone asymmetric strand-displacement mechanism as the fundamental driver of mutagenesis in mammalian DNA. Moreover, the distribution of mtDNA single nucleotide polymorphisms in humans and the distribution of bases in the mtDNA across vertebrate species mirror this gradient, indicating that replication-linked mutations are likely the primary source of inherited polymorphisms that, over evolutionary timescales, influences genome composition during speciation.
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Affiliation(s)
- Monica Sanchez-Contreras
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | - Mariya T Sweetwyne
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | - Brendan F Kohrn
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | | | - Michael J Hipp
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | - Elizabeth K Schmidt
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | - Jeanne Fredrickson
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | - Jeremy A Whitson
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | - Matthew D Campbell
- Department of Radiology, University of Washington, Seattle, WA 98195, USA
| | - Peter S Rabinovitch
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
| | - David J Marcinek
- Department of Radiology, University of Washington, Seattle, WA 98195, USA
| | - Scott R Kennedy
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA 98195, USA
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13
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Menger KE, Rodríguez-Luis A, Chapman J, Nicholls TJ. Controlling the topology of mammalian mitochondrial DNA. Open Biol 2021; 11:210168. [PMID: 34547213 PMCID: PMC8455175 DOI: 10.1098/rsob.210168] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The genome of mitochondria, called mtDNA, is a small circular DNA molecule present at thousands of copies per human cell. MtDNA is packaged into nucleoprotein complexes called nucleoids, and the density of mtDNA packaging affects mitochondrial gene expression. Genetic processes such as transcription, DNA replication and DNA packaging alter DNA topology, and these topological problems are solved by a family of enzymes called topoisomerases. Within mitochondria, topoisomerases are involved firstly in the regulation of mtDNA supercoiling and secondly in disentangling interlinked mtDNA molecules following mtDNA replication. The loss of mitochondrial topoisomerase activity leads to defects in mitochondrial function, and variants in the dual-localized type IA topoisomerase TOP3A have also been reported to cause human mitochondrial disease. We review the current knowledge on processes that alter mtDNA topology, how mtDNA topology is modulated by the action of topoisomerases, and the consequences of altered mtDNA topology for mitochondrial function and human health.
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Affiliation(s)
- Katja E. Menger
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Alejandro Rodríguez-Luis
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - James Chapman
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Thomas J. Nicholls
- Wellcome Centre for Mitochondrial Research, Biosciences Institute, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
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14
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Butler TJ, Estep KN, Sommers JA, Maul RW, Moore AZ, Bandinelli S, Cucca F, Tuke MA, Wood AR, Bharti SK, Bogenhagen DF, Yakubovskaya E, Garcia-Diaz M, Guilliam TA, Byrd AK, Raney KD, Doherty AJ, Ferrucci L, Schlessinger D, Ding J, Brosh RM. Mitochondrial genetic variation is enriched in G-quadruplex regions that stall DNA synthesis in vitro. Hum Mol Genet 2021; 29:1292-1309. [PMID: 32191790 DOI: 10.1093/hmg/ddaa043] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 01/27/2020] [Accepted: 03/18/2020] [Indexed: 01/08/2023] Open
Abstract
As the powerhouses of the eukaryotic cell, mitochondria must maintain their genomes which encode proteins essential for energy production. Mitochondria are characterized by guanine-rich DNA sequences that spontaneously form unusual three-dimensional structures known as G-quadruplexes (G4). G4 structures can be problematic for the essential processes of DNA replication and transcription because they deter normal progression of the enzymatic-driven processes. In this study, we addressed the hypothesis that mitochondrial G4 is a source of mutagenesis leading to base-pair substitutions. Our computational analysis of 2757 individual genomes from two Italian population cohorts (SardiNIA and InCHIANTI) revealed a statistically significant enrichment of mitochondrial mutations within sequences corresponding to stable G4 DNA structures. Guided by the computational analysis results, we designed biochemical reconstitution experiments and demonstrated that DNA synthesis by two known mitochondrial DNA polymerases (Pol γ, PrimPol) in vitro was strongly blocked by representative stable G4 mitochondrial DNA structures, which could be overcome in a specific manner by the ATP-dependent G4-resolving helicase Pif1. However, error-prone DNA synthesis by PrimPol using the G4 template sequence persisted even in the presence of Pif1. Altogether, our results suggest that genetic variation is enriched in G-quadruplex regions that impede mitochondrial DNA replication.
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Affiliation(s)
- Thomas J Butler
- Translational Gerontology Branch, National Institute on Aging, Baltimore, MD 21224, USA
| | - Katrina N Estep
- Laboratory of Molecular Gerontology, National Institute on Aging, Baltimore, MD 21224, USA
| | - Joshua A Sommers
- Laboratory of Molecular Gerontology, National Institute on Aging, Baltimore, MD 21224, USA
| | - Robert W Maul
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, Baltimore, MD 21224, USA
| | - Ann Zenobia Moore
- Translational Gerontology Branch, National Institute on Aging, Baltimore, MD 21224, USA
| | | | - Francesco Cucca
- Istituto di Ricerca Genetica e Biomedica, Consiglio Nazionale delle Ricerche, Monserrato 09042, Italy
| | - Marcus A Tuke
- Genetics of Complex Traits, University of Exeter Medical School, Exeter EX1 2LU, UK
| | - Andrew R Wood
- Genetics of Complex Traits, University of Exeter Medical School, Exeter EX1 2LU, UK
| | - Sanjay Kumar Bharti
- Laboratory of Molecular Gerontology, National Institute on Aging, Baltimore, MD 21224, USA
| | - Daniel F Bogenhagen
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794-8651, USA
| | - Elena Yakubovskaya
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794-8651, USA
| | - Miguel Garcia-Diaz
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794-8651, USA
| | - Thomas A Guilliam
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton BN1 9RQ, UK
| | - Alicia K Byrd
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Kevin D Raney
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Aidan J Doherty
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton BN1 9RQ, UK
| | - Luigi Ferrucci
- Translational Gerontology Branch, National Institute on Aging, Baltimore, MD 21224, USA
| | - David Schlessinger
- Laboratory of Genetics and Genomics, National Institute on Aging, Baltimore, MD 21224, USA
| | - Jun Ding
- Translational Gerontology Branch, National Institute on Aging, Baltimore, MD 21224, USA
| | - Robert M Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, Baltimore, MD 21224, USA
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15
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Apurinic/Apyrimidinic Endonuclease 2 (APE2): An ancillary enzyme for contextual base excision repair mechanisms to preserve genome stability. Biochimie 2021; 190:70-90. [PMID: 34302888 DOI: 10.1016/j.biochi.2021.07.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 06/29/2021] [Accepted: 07/19/2021] [Indexed: 01/03/2023]
Abstract
The genome of living organisms frequently undergoes various types of modifications which are recognized and repaired by the relevant repair mechanisms. These repair pathways are increasingly being deciphered to understand the mechanisms. Base excision repair (BER) is indispensable to maintain genome stability. One of the enigmatic repair proteins of BER, Apurinic/Apyrimidinic Endonuclease 2 (APE2), like APE1, is truly multifunctional and demonstrates the independent and non-redundant function in maintaining the genome integrity. APE2 is involved in ATR-Chk1 mediated DNA damage response. It also resolves topoisomerase1 mediated cleavage complex intermediate which is formed while repairing misincorporated ribonucleotides in the absence of functional RNase H2 mediated excision repair pathway. BER participates in the demethylation pathway and the role of Arabidopsis thaliana APE2 is demonstrated in this process. Moreover, APE2 is synthetically lethal to BRCA1, BRCA2, and RNase H2, and its homolog, APE1 fails to complement the function. Hence, the role of APE2 is not just an alternate to the repair mechanisms but has implications in diverse functional pathways related to the maintenance of genome integrity. This review analyses genomic features of APE2 and delineates its enzyme function as error-prone as well as efficient and accurate repair protein based on the studies on mammalian or its homolog proteins from model systems such as Arabidopsis thaliana, Schizosaccharomyces pombe, Trypanosoma curzi, Xenopus laevis, Danio rerio, Mus musculus, and Homo sapiens.
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16
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Silva-Pinheiro P, Pardo-Hernández C, Reyes A, Tilokani L, Mishra A, Cerutti R, Li S, Rozsivalova DH, Valenzuela S, Dogan SA, Peter B, Fernández-Silva P, Trifunovic A, Prudent J, Minczuk M, Bindoff L, Macao B, Zeviani M, Falkenberg M, Viscomi C. DNA polymerase gamma mutations that impair holoenzyme stability cause catalytic subunit depletion. Nucleic Acids Res 2021; 49:5230-5248. [PMID: 33956154 PMCID: PMC8136776 DOI: 10.1093/nar/gkab282] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 03/29/2021] [Accepted: 04/08/2021] [Indexed: 01/31/2023] Open
Abstract
Mutations in POLG, encoding POLγA, the catalytic subunit of the mitochondrial DNA polymerase, cause a spectrum of disorders characterized by mtDNA instability. However, the molecular pathogenesis of POLG-related diseases is poorly understood and efficient treatments are missing. Here, we generate the PolgA449T/A449T mouse model, which reproduces the A467T change, the most common human recessive mutation of POLG. We show that the mouse A449T mutation impairs DNA binding and mtDNA synthesis activities of POLγ, leading to a stalling phenotype. Most importantly, the A449T mutation also strongly impairs interactions with POLγB, the accessory subunit of the POLγ holoenzyme. This allows the free POLγA to become a substrate for LONP1 protease degradation, leading to dramatically reduced levels of POLγA in A449T mouse tissues. Therefore, in addition to its role as a processivity factor, POLγB acts to stabilize POLγA and to prevent LONP1-dependent degradation. Notably, we validated this mechanism for other disease-associated mutations affecting the interaction between the two POLγ subunits. We suggest that targeting POLγA turnover can be exploited as a target for the development of future therapies.
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Affiliation(s)
- Pedro Silva-Pinheiro
- MRC/University of Cambridge Mitochondrial Biology Unit, Hills Road, CB2 0XY Cambridge, UK
| | - Carlos Pardo-Hernández
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Medicinaregatan 9A P.O. Box 440, SE405 30 Gothenburg, Sweden
| | - Aurelio Reyes
- MRC/University of Cambridge Mitochondrial Biology Unit, Hills Road, CB2 0XY Cambridge, UK
| | - Lisa Tilokani
- MRC/University of Cambridge Mitochondrial Biology Unit, Hills Road, CB2 0XY Cambridge, UK
| | - Anup Mishra
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Medicinaregatan 9A P.O. Box 440, SE405 30 Gothenburg, Sweden
| | - Raffaele Cerutti
- Department of Neurosciences, University of Padova, via Giustiniani, 2-35128 Padova, Italy
| | - Shuaifeng Li
- Center for Cancer Biology, Life Science of Institution, Zhejiang University, Hangzhou 310058, China
| | - Dieu-Hien Rozsivalova
- Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD) and Center for Molecular Medicine (CMMC), University of Cologne, Joseph-Stelzmann-Strasse 26, 50931 Cologne, Germany
| | - Sebastian Valenzuela
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Medicinaregatan 9A P.O. Box 440, SE405 30 Gothenburg, Sweden
| | - Sukru A Dogan
- Department of Molecular Biology and Genetics, Center for Life Sciences and Technologies, Bogazici University, 34342 Istanbul, Turkey
| | - Bradley Peter
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Medicinaregatan 9A P.O. Box 440, SE405 30 Gothenburg, Sweden
| | - Patricio Fernández-Silva
- Biochemistry and Molecular and Cell Biology Department, University of Zaragoza, C/ Pedro Cerbuna s/n 50.009-Zaragoza, and Biocomputation and Complex Systems Physics Institute (BIFI), C/ Mariano Esquillor, 50.018-Zaragoza, Spain
| | - Aleksandra Trifunovic
- Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD) and Center for Molecular Medicine (CMMC), University of Cologne, Joseph-Stelzmann-Strasse 26, 50931 Cologne, Germany
| | - Julien Prudent
- MRC/University of Cambridge Mitochondrial Biology Unit, Hills Road, CB2 0XY Cambridge, UK
| | - Michal Minczuk
- MRC/University of Cambridge Mitochondrial Biology Unit, Hills Road, CB2 0XY Cambridge, UK
| | - Laurence Bindoff
- Department of Clinical Medicine, University of Bergen, 5007 Bergen, Norway
- Neuro-SysMed, Department of Neurology, Haukeland University Hospital, Jonas Lies vei 65, 5021 Bergen, Norway
| | - Bertil Macao
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Medicinaregatan 9A P.O. Box 440, SE405 30 Gothenburg, Sweden
| | - Massimo Zeviani
- Department of Neurosciences, University of Padova, via Giustiniani, 2-35128 Padova, Italy
- Venetian Institute of Molecular Medicine, via Orus 2-35128 Padova, Italy
| | - Maria Falkenberg
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Medicinaregatan 9A P.O. Box 440, SE405 30 Gothenburg, Sweden
| | - Carlo Viscomi
- Department of Biomedical Sciences, University of Padova, via Ugo Bassi 58/B-35131 Padova, Italy
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17
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Sullivan ED, Longley MJ, Copeland WC. Polymerase γ efficiently replicates through many natural template barriers but stalls at the HSP1 quadruplex. J Biol Chem 2021; 295:17802-17815. [PMID: 33454015 DOI: 10.1074/jbc.ra120.015390] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 10/05/2020] [Indexed: 12/27/2022] Open
Abstract
Faithful replication of the mitochondrial genome is carried out by a set of key nuclear-encoded proteins. DNA polymerase γ is a core component of the mtDNA replisome and the only replicative DNA polymerase localized to mitochondria. The asynchronous mechanism of mtDNA replication predicts that the replication machinery encounters dsDNA and unique physical barriers such as structured genes, G-quadruplexes, and other obstacles. In vitro experiments here provide evidence that the polymerase γ heterotrimer is well-adapted to efficiently synthesize DNA, despite the presence of many naturally occurring roadblocks. However, we identified a specific G-quadruplex-forming sequence at the heavy-strand promoter (HSP1) that has the potential to cause significant stalling of mtDNA replication. Furthermore, this structured region of DNA corresponds to the break site for a large (3,895 bp) deletion observed in mitochondrial disease patients. The presence of this deletion in humans correlates with UV exposure, and we have found that efficiency of polymerase γ DNA synthesis is reduced after this quadruplex is exposed to UV in vitro.
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Affiliation(s)
- Eric D Sullivan
- Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, USA
| | - Matthew J Longley
- Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, USA
| | - William C Copeland
- Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, USA.
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18
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Gustafson MA, Sullivan ED, Copeland WC. Consequences of compromised mitochondrial genome integrity. DNA Repair (Amst) 2021; 93:102916. [PMID: 33087282 DOI: 10.1016/j.dnarep.2020.102916] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Maintenance and replication of the mitochondrial genome (mtDNA) is essential to mitochondrial function and eukaryotic energy production through the electron transport chain. mtDNA is replicated by a core set of proteins: Pol γ, Twinkle, and the single-stranded DNA binding protein. Fewer pathways exist for repair of mtDNA than nuclear DNA, and unrepaired damage to mtDNA may accumulate and lead to dysfunctional mitochondria. The mitochondrial genome is susceptible to damage by both endogenous and exogenous sources. Missense mutations to the nuclear genes encoding the core mtDNA replisome (POLG, POLG2, TWNK, and SSBP1) cause changes to the biochemical functions of their protein products. These protein variants can damage mtDNA and perturb oxidative phosphorylation. Ultimately, these mutations cause a diverse set of diseases that can affect virtually every system in the body. Here, we briefly review the mechanisms of mtDNA damage and the clinical consequences of disease variants of the core mtDNA replisome.
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Affiliation(s)
- Margaret A Gustafson
- Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences (NIEHS), NIH, Research Triangle Park, NC, 27709, USA
| | - Eric D Sullivan
- Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences (NIEHS), NIH, Research Triangle Park, NC, 27709, USA
| | - William C Copeland
- Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences (NIEHS), NIH, Research Triangle Park, NC, 27709, USA.
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19
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Baptiste BA, Baringer SL, Kulikowicz T, Sommers JA, Croteau DL, Brosh RM, Bohr VA. DNA polymerase β outperforms DNA polymerase γ in key mitochondrial base excision repair activities. DNA Repair (Amst) 2021; 99:103050. [PMID: 33540226 PMCID: PMC7887074 DOI: 10.1016/j.dnarep.2021.103050] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 11/13/2020] [Accepted: 01/14/2021] [Indexed: 12/12/2022]
Abstract
DNA polymerase beta (POLβ), well known for its role in nuclear DNA base excision repair (BER), has been shown to be present in the mitochondria of several different cell types. Here we present a side-by-side comparison of BER activities of POLβ and POLγ, the mitochondrial replicative polymerase, previously thought to be the only mitochondrial polymerase. We find that POLβ is significantly more proficient at single-nucleotide gap filling, both in substrates with ends that require polymerase processing, and those that do not. We also show that POLβ has a helicase-independent functional interaction with the mitochondrial helicase, TWINKLE. This interaction stimulates strand-displacement synthesis, but not single-nucleotide gap filling. Importantly, we find that purified mitochondrial extracts from cells lacking POLβ are severely deficient in processing BER intermediates, suggesting that mitochondrially localized DNA POLβ may be critical for cells with high energetic demands that produce greater levels of oxidative stress and therefore depend upon efficient BER for mitochondrial health.
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Affiliation(s)
- Beverly A Baptiste
- Laboratory of Molecular Gerontology, National Institute on Aging, 251 Bayview Blvd., Baltimore, MD, 21224, USA
| | - Stephanie L Baringer
- Laboratory of Molecular Gerontology, National Institute on Aging, 251 Bayview Blvd., Baltimore, MD, 21224, USA
| | - Tomasz Kulikowicz
- Laboratory of Molecular Gerontology, National Institute on Aging, 251 Bayview Blvd., Baltimore, MD, 21224, USA
| | - Joshua A Sommers
- Laboratory of Molecular Gerontology, National Institute on Aging, 251 Bayview Blvd., Baltimore, MD, 21224, USA
| | - Deborah L Croteau
- Laboratory of Molecular Gerontology, National Institute on Aging, 251 Bayview Blvd., Baltimore, MD, 21224, USA
| | - Robert M Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, 251 Bayview Blvd., Baltimore, MD, 21224, USA
| | - Vilhelm A Bohr
- Laboratory of Molecular Gerontology, National Institute on Aging, 251 Bayview Blvd., Baltimore, MD, 21224, USA.
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20
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Luo Y, Ma J, Lu W. The Significance of Mitochondrial Dysfunction in Cancer. Int J Mol Sci 2020; 21:ijms21165598. [PMID: 32764295 PMCID: PMC7460667 DOI: 10.3390/ijms21165598] [Citation(s) in RCA: 140] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2020] [Revised: 07/30/2020] [Accepted: 07/31/2020] [Indexed: 02/06/2023] Open
Abstract
As an essential organelle in nucleated eukaryotic cells, mitochondria play a central role in energy metabolism, maintenance of redox balance, and regulation of apoptosis. Mitochondrial dysfunction, either due to the TCA cycle enzyme defects, mitochondrial DNA genetic mutations, defective mitochondrial electron transport chain, oxidative stress, or aberrant oncogene and tumor suppressor signaling, has been observed in a wide spectrum of human cancers. In this review, we summarize mitochondrial dysfunction induced by these alterations that promote human cancers.
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Affiliation(s)
- Yongde Luo
- School of Pharmaceutical Science, Wenzhou Medical University, Wenzhou 325000, China
- Division of Gastroenterology and Hepatology, Department of Medicine, Stony Brook University, Stony Brook, NY 11794, USA;
- Correspondence: (Y.L.); (W.L.)
| | - Jianjia Ma
- Division of Gastroenterology and Hepatology, Department of Medicine, Stony Brook University, Stony Brook, NY 11794, USA;
| | - Weiqin Lu
- Division of Gastroenterology and Hepatology, Department of Medicine, Stony Brook University, Stony Brook, NY 11794, USA;
- Correspondence: (Y.L.); (W.L.)
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21
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Do Y, Matsuda S, Inatomi T, Nakada K, Yasukawa T, Kang D. The accessory subunit of human DNA polymerase γ is required for mitochondrial DNA maintenance and is able to stabilize the catalytic subunit. Mitochondrion 2020; 53:133-139. [PMID: 32470614 DOI: 10.1016/j.mito.2020.05.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 05/18/2020] [Accepted: 05/22/2020] [Indexed: 01/10/2023]
Abstract
Human DNA polymerase γ (POLG) is a mitochondria-specific replicative DNA polymerase consisting of a single catalytic subunit, POLGα, and a dimeric accessory subunit, POLGβ. To gain a deeper understanding of the role of POLGβ, we knocked out this protein in cultured human cybrid cells and established numerous knockout clones. POLGβ-knockout clones presented a clear phenotype of mitochondrial DNA loss, indicating that POLGβ is necessary for mitochondrial DNA replication. Moreover, POLGβ-knockout cells showed a severe decrease in POLGα levels and acute suppression of POLGβ expression efficiently down-regulated POLGα levels. These results suggest that, in addition to its role as the processivity factor of POLG, POLGβ acts as a POLGα stabilizer, an important role for POLGβ in mitochondrial DNA maintenance.
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Affiliation(s)
- Yura Do
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Shigeru Matsuda
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Teppei Inatomi
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Kazuto Nakada
- Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba-shi, Ibaraki, 305-8572, Japan
| | - Takehiro Yasukawa
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan.
| | - Dongchon Kang
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
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22
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Kaur P, Longley MJ, Pan H, Wang W, Countryman P, Wang H, Copeland WC. Single-molecule level structural dynamics of DNA unwinding by human mitochondrial Twinkle helicase. J Biol Chem 2020; 295:5564-5576. [PMID: 32213598 PMCID: PMC7186178 DOI: 10.1074/jbc.ra120.012795] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Revised: 03/24/2020] [Indexed: 11/06/2022] Open
Abstract
Knowledge of the molecular events in mitochondrial DNA (mtDNA) replication is crucial to understanding the origins of human disorders arising from mitochondrial dysfunction. Twinkle helicase is an essential component of mtDNA replication. Here, we employed atomic force microscopy imaging in air and liquids to visualize ring assembly, DNA binding, and unwinding activity of individual Twinkle hexamers at the single-molecule level. We observed that the Twinkle subunits self-assemble into hexamers and higher-order complexes that can switch between open and closed-ring configurations in the absence of DNA. Our analyses helped visualize Twinkle loading onto and unloading from DNA in an open-ringed configuration. They also revealed that closed-ring conformers bind and unwind several hundred base pairs of duplex DNA at an average rate of ∼240 bp/min. We found that the addition of mitochondrial single-stranded (ss) DNA-binding protein both influences the ways Twinkle loads onto defined DNA substrates and stabilizes the unwound ssDNA product, resulting in a ∼5-fold stimulation of the apparent DNA-unwinding rate. Mitochondrial ssDNA-binding protein also increased the estimated translocation processivity from 1750 to >9000 bp before helicase disassociation, suggesting that more than half of the mitochondrial genome could be unwound by Twinkle during a single DNA-binding event. The strategies used in this work provide a new platform to examine Twinkle disease variants and the core mtDNA replication machinery. They also offer an enhanced framework to investigate molecular mechanisms underlying deletion and depletion of the mitochondrial genome as observed in mitochondrial diseases.
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Affiliation(s)
- Parminder Kaur
- Physics Department, North Carolina State University, Raleigh, North Carolina 27695; Center for Human Health and the Environment, North Carolina State University, Raleigh, North Carolina 27695.
| | - Matthew J Longley
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - Hai Pan
- Physics Department, North Carolina State University, Raleigh, North Carolina 27695
| | - Wendy Wang
- Physics Department, North Carolina State University, Raleigh, North Carolina 27695
| | - Preston Countryman
- Physics Department, North Carolina State University, Raleigh, North Carolina 27695
| | - Hong Wang
- Physics Department, North Carolina State University, Raleigh, North Carolina 27695; Center for Human Health and the Environment, North Carolina State University, Raleigh, North Carolina 27695; Toxicology Program, North Carolina State University, Raleigh, North Carolina 27695
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709.
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23
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Acharya N, Khandagale P, Thakur S, Sahu JK, Utkalaja BG. Quaternary structural diversity in eukaryotic DNA polymerases: monomeric to multimeric form. Curr Genet 2020; 66:635-655. [PMID: 32236653 DOI: 10.1007/s00294-020-01071-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 03/13/2020] [Accepted: 03/24/2020] [Indexed: 12/14/2022]
Abstract
Sixteen eukaryotic DNA polymerases have been identified and studied so far. Based on the sequence similarity of the catalytic subunits of DNA polymerases, these have been classified into four A, B, X and Y families except PrimPol, which belongs to the AEP family. The quaternary structure of these polymerases also varies depending upon whether they are composed of one or more subunits. Therefore, in this review, we used a quaternary structure-based classification approach to group DNA polymerases as either monomeric or multimeric and highlighted functional significance of their accessory subunits. Additionally, we have briefly summarized various DNA polymerase discoveries from a historical perspective, emphasized unique catalytic mechanism of each DNA polymerase and highlighted recent advances in understanding their cellular functions.
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Affiliation(s)
- Narottam Acharya
- Laboratory of Genomic Instability and Diseases, Department of Infectious Disease Biology, Institute of Life Sciences, Bhubaneswar, 751023, India.
| | - Prashant Khandagale
- Laboratory of Genomic Instability and Diseases, Department of Infectious Disease Biology, Institute of Life Sciences, Bhubaneswar, 751023, India
| | - Shweta Thakur
- Laboratory of Genomic Instability and Diseases, Department of Infectious Disease Biology, Institute of Life Sciences, Bhubaneswar, 751023, India
| | - Jugal Kishor Sahu
- Laboratory of Genomic Instability and Diseases, Department of Infectious Disease Biology, Institute of Life Sciences, Bhubaneswar, 751023, India
| | - Bhabasha Gyanadeep Utkalaja
- Laboratory of Genomic Instability and Diseases, Department of Infectious Disease Biology, Institute of Life Sciences, Bhubaneswar, 751023, India
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24
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Abstract
The POLG gene encodes the mitochondrial DNA polymerase that is responsible for replication of the mitochondrial genome. Mutations in POLG can cause early childhood mitochondrial DNA (mtDNA) depletion syndromes or later-onset syndromes arising from mtDNA deletions. POLG mutations are the most common cause of inherited mitochondrial disorders, with as many as 2% of the population carrying these mutations. POLG-related disorders comprise a continuum of overlapping phenotypes with onset from infancy to late adulthood. The six leading disorders caused by POLG mutations are Alpers-Huttenlocher syndrome, which is one of the most severe phenotypes; childhood myocerebrohepatopathy spectrum, which presents within the first 3 years of life; myoclonic epilepsy myopathy sensory ataxia; ataxia neuropathy spectrum; autosomal recessive progressive external ophthalmoplegia; and autosomal dominant progressive external ophthalmoplegia. This Review describes the clinical features, pathophysiology, natural history and treatment of POLG-related disorders, focusing particularly on the neurological manifestations of these conditions.
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25
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Anderson AP, Luo X, Russell W, Yin YW. Oxidative damage diminishes mitochondrial DNA polymerase replication fidelity. Nucleic Acids Res 2020; 48:817-829. [PMID: 31799610 PMCID: PMC6954441 DOI: 10.1093/nar/gkz1018] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 10/12/2019] [Accepted: 11/22/2019] [Indexed: 12/20/2022] Open
Abstract
Mitochondrial DNA (mtDNA) resides in a high ROS environment and suffers more mutations than its nuclear counterpart. Increasing evidence suggests that mtDNA mutations are not the results of direct oxidative damage, rather are caused, at least in part, by DNA replication errors. To understand how the mtDNA replicase, Pol γ, can give rise to elevated mutations, we studied the effect of oxidation of Pol γ on replication errors. Pol γ is a high fidelity polymerase with polymerase (pol) and proofreading exonuclease (exo) activities. We show that Pol γ exo domain is far more sensitive to oxidation than pol; under oxidative conditions, exonuclease activity therefore declines more rapidly than polymerase. The oxidized Pol γ becomes editing-deficient, displaying a 20-fold elevated mutations than the unoxidized enzyme. Mass spectrometry analysis reveals that Pol γ exo domain is a hotspot for oxidation. The oxidized exo residues increase the net negative charge around the active site that should reduce the affinity to mismatched primer/template DNA. Our results suggest that the oxidative stress induced high mutation frequency on mtDNA can be indirectly caused by oxidation of the mitochondrial replicase.
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Affiliation(s)
- Andrew P Anderson
- Quantitative and Computational Biosciences, Baylor College of Medicine, Houston, TX 77030, USA
- Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX 77550, USA
| | - Xuemei Luo
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77550, USA
| | - William Russell
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77550, USA
| | - Y Whitney Yin
- Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX 77550, USA
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX 77550, USA
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26
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Amino and carboxy-terminal extensions of yeast mitochondrial DNA polymerase assemble both the polymerization and exonuclease active sites. Mitochondrion 2019; 49:166-177. [PMID: 31445096 DOI: 10.1016/j.mito.2019.08.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 08/11/2019] [Accepted: 08/19/2019] [Indexed: 11/24/2022]
Abstract
Human and yeast mitochondrial DNA polymerases (DNAPs), POLG and Mip1, are related by evolution to bacteriophage DNAPs. However, mitochondrial DNAPs contain unique amino and carboxyl-terminal extensions that physically interact. Here we describe that N-terminal deletions in Mip1 polymerases abolish polymerization and decrease exonucleolytic degradation, whereas moderate C-terminal deletions reduce polymerization. Similarly, to the N-terminal deletions, an extended C-terminal deletion of 298 amino acids is deficient in nucleotide addition and exonucleolytic degradation of double and single-stranded DNA. The latter observation suggests that the physical interaction between the amino and carboxyl-terminal regions of Mip1 may be related to the spread of pathogenic POLG mutant along its primary sequence.
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27
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Sun X, Johnson J, St John JC. Global DNA methylation synergistically regulates the nuclear and mitochondrial genomes in glioblastoma cells. Nucleic Acids Res 2019; 46:5977-5995. [PMID: 29722878 PMCID: PMC6158714 DOI: 10.1093/nar/gky339] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Accepted: 04/19/2018] [Indexed: 12/12/2022] Open
Abstract
Replication of mitochondrial DNA is strictly regulated during differentiation and development allowing each cell type to acquire its required mtDNA copy number to meet its specific needs for energy. Undifferentiated cells establish the mtDNA set point, which provides low numbers of mtDNA copy but sufficient template for replication once cells commit to specific lineages. However, cancer cells, such as those from the human glioblastoma multiforme cell line, HSR-GBM1, cannot complete differentiation as they fail to enforce the mtDNA set point and are trapped in a ‘pseudo-differentiated’ state. Global DNA methylation is likely to be a major contributing factor, as DNA demethylation treatments promote differentiation of HSR-GBM1 cells. To determine the relationship between DNA methylation and mtDNA copy number in cancer cells, we applied whole genome MeDIP-Seq and RNA-Seq to HSR-GBM1 cells and following their treatment with the DNA demethylation agents 5-azacytidine and vitamin C. We identified key methylated regions modulated by the DNA demethylation agents that also induced synchronous changes to mtDNA copy number and nuclear gene expression. Our findings highlight the control exerted by DNA methylation on the expression of key genes, the regulation of mtDNA copy number and establishment of the mtDNA set point, which collectively contribute to tumorigenesis.
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Affiliation(s)
- Xin Sun
- Centre for Genetic Diseases, Hudson Institute of Medical Research, 27-31 Wright Street, Clayton, VIC 3168, Australia.,Department of Molecular and Translational Sciences, Monash University, 27-31 Wright Street, Clayton, VIC 3168, Australia
| | - Jacqueline Johnson
- Centre for Genetic Diseases, Hudson Institute of Medical Research, 27-31 Wright Street, Clayton, VIC 3168, Australia
| | - Justin C St John
- Centre for Genetic Diseases, Hudson Institute of Medical Research, 27-31 Wright Street, Clayton, VIC 3168, Australia.,Department of Molecular and Translational Sciences, Monash University, 27-31 Wright Street, Clayton, VIC 3168, Australia
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28
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Zhao L. Mitochondrial DNA degradation: A quality control measure for mitochondrial genome maintenance and stress response. Enzymes 2019; 45:311-341. [PMID: 31627882 DOI: 10.1016/bs.enz.2019.08.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Mitochondria play a central role in bioenergetics, and fulfill a plethora of functions in cell signaling, programmed cell death, and biosynthesis of key protein cofactors. Mitochondria harbor their own genomic DNA, which encodes protein subunits of the electron transport chain and a full set of transfer and ribosomal RNAs. Mitochondrial DNA (mtDNA) is essential for cellular and organismal functions, and defects in mitochondrial genome maintenance have been implicated in common human diseases and mitochondrial disorders. mtDNA repair and degradation are known pathways to cope with mtDNA damage; however, molecular factors involved in this process have remained unclear. Such knowledge is fundamental to the understanding of mitochondrial genomic maintenance and pathology, because mtDNA degradation may contribute to the etiology of mtDNA depletion syndromes and to the activation of the innate immune response by fragmented mtDNA. This article reviews the current literature regarding the importance of mitochondrial DNA degradation in mtDNA maintenance and stress response, and the recent progress in uncovering molecular factors involved in mtDNA degradation. These factors include key components of the mtDNA replication machinery, such as DNA polymerase γ, helicase Twinkle, and exonuclease MGME1, as well as a major DNA-packaging protein, mitochondrial transcription factor A (TFAM).
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Affiliation(s)
- Linlin Zhao
- Department of Chemistry, University of California, Riverside, Riverside, CA, United States.
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29
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Hoff KE, DeBalsi KL, Sanchez-Quintero MJ, Longley MJ, Hirano M, Naini AB, Copeland WC. Characterization of the human homozygous R182W POLG2 mutation in mitochondrial DNA depletion syndrome. PLoS One 2018; 13:e0203198. [PMID: 30157269 PMCID: PMC6114919 DOI: 10.1371/journal.pone.0203198] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 08/14/2018] [Indexed: 12/18/2022] Open
Abstract
Mutations in mitochondrial DNA (mtDNA) have been linked to a variety of metabolic, neurological and muscular diseases which can present at any time throughout life. MtDNA is replicated by DNA polymerase gamma (Pol γ), twinkle helicase and mitochondrial single-stranded binding protein (mtSSB). The Pol γ holoenzyme is a heterotrimer consisting of the p140 catalytic subunit and a p55 homodimeric accessory subunit encoded by the nuclear genes POLG and POLG2, respectively. The accessory subunits enhance DNA binding and promote processive DNA synthesis of the holoenzyme. Mutations in either POLG or POLG2 are linked to disease and adversely affect maintenance of the mitochondrial genome, resulting in depletion, deletions and/or point mutations in mtDNA. A homozygous mutation located at Chr17: 62492543G>A in POLG2, resulting in R182W substitution in p55, was previously identified to cause mtDNA depletion and fatal hepatic liver failure. Here we characterize this homozygous R182W p55 mutation using in vivo cultured cell models and in vitro biochemical assessments. Compared to control fibroblasts, homozygous R182W p55 primary dermal fibroblasts exhibit a two-fold slower doubling time, reduced mtDNA copy number and reduced levels of POLG and POLG2 transcripts correlating with the reported disease state. Expression of R182W p55 in HEK293 cells impairs oxidative-phosphorylation. Biochemically, R182W p55 displays DNA binding and association with p140 similar to WT p55. R182W p55 mimics the ability of WT p55 to stimulate primer extension, support steady-state nucleotide incorporation, and suppress the exonuclease function of Pol γin vitro. However, R182W p55 has severe defects in protein stability as determined by differential scanning fluorimetry and in stimulating function as determined by thermal inactivation. These data demonstrate that the Chr17: 62492543G>A mutation in POLG2, R182W p55, severely impairs stability of the accessory subunit and is the likely cause of the disease phenotype.
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Affiliation(s)
- Kirsten E. Hoff
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, DHHS, Research Triangle Park, NC, United States of America
| | - Karen L. DeBalsi
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, DHHS, Research Triangle Park, NC, United States of America
| | - Maria J. Sanchez-Quintero
- Department of Neurology, H. Houston Merritt Neuromuscular Research Center, Columbia University Medical Center, New York, NY, United States of America
| | - Matthew J. Longley
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, DHHS, Research Triangle Park, NC, United States of America
| | - Michio Hirano
- Department of Neurology, H. Houston Merritt Neuromuscular Research Center, Columbia University Medical Center, New York, NY, United States of America
| | - Ali B. Naini
- Department of Neurology, H. Houston Merritt Neuromuscular Research Center, Columbia University Medical Center, New York, NY, United States of America
- Department of Pathology and Cell Biology, Columbia University, New York, NY, United States of America
- Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, New York, NY, United States of America
| | - William C. Copeland
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, DHHS, Research Triangle Park, NC, United States of America
- * E-mail:
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30
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Mitochondrial DNA replication in mammalian cells: overview of the pathway. Essays Biochem 2018; 62:287-296. [PMID: 29880722 PMCID: PMC6056714 DOI: 10.1042/ebc20170100] [Citation(s) in RCA: 100] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 05/18/2018] [Accepted: 05/21/2018] [Indexed: 12/27/2022]
Abstract
Mammalian mitochondria contain multiple copies of a circular, double-stranded DNA genome and a dedicated DNA replication machinery is required for its maintenance. Many disease-causing mutations affect mitochondrial replication factors and a detailed understanding of the replication process may help to explain the pathogenic mechanisms underlying a number of mitochondrial diseases. We here give a brief overview of DNA replication in mammalian mitochondria, describing our current understanding of this process and some unanswered questions remaining.
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31
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Abstract
The mitochondrial genome is a matrilineally inherited DNA that encodes numerous essential subunits of the respiratory chain in all metazoans. As such mitochondrial DNA (mtDNA) sequence integrity is vital to organismal survival, but it has a limited cadre of DNA repair activities, primarily base excision repair (BER). We have known that the mtDNA is significantly oxidized by both endogenous and exogenous sources, but this does not lead to the expected preferential formation of transversion mutations, which suggest a robust base excision repair (BER) system. This year, two different groups reported compelling evidence that what was believed to be exclusively nuclear DNA repair polymerase, POLB, is located in the mitochondria and plays a significant role in mitochondrial BER, mtDNA integrity and mitochondrial function. In this commentary, we review the findings and highlight remaining questions for the field.
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Affiliation(s)
- Brett A Kaufman
- Center for Metabolism and Mitochondrial Medicine, Division of Cardiology, Vascular Medicine Institute, University of Pittsburgh School of Medicine, Pittsburgh PA USA.
| | - Bennett Van Houten
- Hillman Cancer Center, Department of Pharmacology and Chemical Biology, University of Pittsburgh Cancer Institute, Pittsburgh PA USA.
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32
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Çaglayan M, Prasad R, Krasich R, Longley MJ, Kadoda K, Tsuda M, Sasanuma H, Takeda S, Tano K, Copeland WC, Wilson SH. Complementation of aprataxin deficiency by base excision repair enzymes in mitochondrial extracts. Nucleic Acids Res 2017; 45:10079-10088. [PMID: 28973450 PMCID: PMC5622373 DOI: 10.1093/nar/gkx654] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 07/15/2017] [Indexed: 01/08/2023] Open
Abstract
Mitochondrial aprataxin (APTX) protects the mitochondrial genome from the consequence of ligase failure by removing the abortive ligation product, i.e. the 5′-adenylate (5′-AMP) group, during DNA replication and repair. In the absence of APTX activity, blocked base excision repair (BER) intermediates containing the 5′-AMP or 5′-adenylated-deoxyribose phosphate (5′-AMP-dRP) lesions may accumulate. In the current study, we examined DNA polymerase (pol) γ and pol β as possible complementing enzymes in the case of APTX deficiency. The activities of pol β lyase and FEN1 nucleotide excision were able to remove the 5′-AMP-dRP group in mitochondrial extracts from APTX−/− cells. However, the lyase activity of purified pol γ was weak against the 5′-AMP-dRP block in a model BER substrate, and this activity was not able to complement APTX deficiency in mitochondrial extracts from APTX−/−Pol β−/− cells. FEN1 also failed to provide excision of the 5′-adenylated BER intermediate in mitochondrial extracts. These results illustrate the potential role of pol β in complementing APTX deficiency in mitochondria.
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Affiliation(s)
- Melike Çaglayan
- Genome Integrity and Structural Biology Laboratory, DNA Repair and Nucleic Acid Enzymology Group, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
| | - Rajendra Prasad
- Genome Integrity and Structural Biology Laboratory, DNA Repair and Nucleic Acid Enzymology Group, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
| | - Rachel Krasich
- Genome Integrity and Structural Biology Laboratory, Mitochondrial DNA Replication Group, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
| | - Matthew J Longley
- Genome Integrity and Structural Biology Laboratory, Mitochondrial DNA Replication Group, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
| | - Kei Kadoda
- Division of Radiation Life Science, Research Reactor Institute, Kyoto University, Asashiro-Nishi, Kumatori, Osaka 590-0494 Japan
| | - Masataka Tsuda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo, Kyoto 606-8501, Japan
| | - Hiroyuki Sasanuma
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo, Kyoto 606-8501, Japan
| | - Shunichi Takeda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo, Kyoto 606-8501, Japan
| | - Keizo Tano
- Division of Radiation Life Science, Research Reactor Institute, Kyoto University, Asashiro-Nishi, Kumatori, Osaka 590-0494 Japan
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, Mitochondrial DNA Replication Group, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
| | - Samuel H Wilson
- Genome Integrity and Structural Biology Laboratory, DNA Repair and Nucleic Acid Enzymology Group, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
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33
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Young MJ. Off-Target Effects of Drugs that Disrupt Human Mitochondrial DNA Maintenance. Front Mol Biosci 2017; 4:74. [PMID: 29214156 PMCID: PMC5702650 DOI: 10.3389/fmolb.2017.00074] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 10/31/2017] [Indexed: 12/17/2022] Open
Abstract
Nucleoside reverse transcriptase inhibitors (NRTIs) were the first drugs used to treat human immunodeficiency virus (HIV) the cause of acquired immunodeficiency syndrome. Development of severe mitochondrial toxicity has been well documented in patients infected with HIV and administered NRTIs. In vitro biochemical experiments have demonstrated that the replicative mitochondrial DNA (mtDNA) polymerase gamma, Polg, is a sensitive target for inhibition by metabolically active forms of NRTIs, nucleotide reverse transcriptase inhibitors (NtRTIs). Once incorporated into newly synthesized daughter strands NtRTIs block further DNA polymerization reactions. Human cell culture and animal studies have demonstrated that cell lines and mice exposed to NRTIs display mtDNA depletion. Further complicating NRTI off-target effects on mtDNA maintenance, two additional DNA polymerases, Pol beta and PrimPol, were recently reported to localize to mitochondria as well as the nucleus. Similar to Polg, in vitro work has demonstrated both Pol beta and PrimPol incorporate NtRTIs into nascent DNA. Cell culture and biochemical experiments have also demonstrated that antiviral ribonucleoside drugs developed to treat hepatitis C infection act as off-target substrates for POLRMT, the mitochondrial RNA polymerase and primase. Accompanying the above-mentioned topics, this review examines: (1) mtDNA maintenance in human health and disease, (2) reports of DNA polymerases theta and zeta (Rev3) localizing to mitochondria, and (3) additional drugs with off-target effects on mitochondrial function. Lastly, mtDNA damage may induce cell death; therefore, the possibility of utilizing compounds that disrupt mtDNA maintenance to kill cancer cells is discussed.
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Affiliation(s)
- Matthew J Young
- Department of Biochemistry and Molecular Biology, Southern Illinois University School of Medicine, Carbondale, IL, United States
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34
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Chan SSL. Inherited mitochondrial genomic instability and chemical exposures. Toxicology 2017; 391:75-83. [PMID: 28756246 DOI: 10.1016/j.tox.2017.07.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 06/12/2017] [Accepted: 07/24/2017] [Indexed: 12/21/2022]
Abstract
There are approximately 1500 proteins that are needed for mitochondrial structure and function, most of which are encoded in the nuclear genome (Calvo et al., 2006). Each mitochondrion has its own genome (mtDNA), which in humans encodes 13 polypeptides, 22 tRNAs and 2 rRNAs required for oxidative phosphorylation. The mitochondrial genome of humans and most vertebrates is approximately 16.5kbp, double-stranded, circular, with few non-coding bases. Thus, maintaining mtDNA stability, that is, the ability of the cell to maintain adequate levels of mtDNA template for oxidative phosphorylation is essential and can be impacted by the level of mtDNA mutation currently within the cell or mitochondrion, but also from errors made during normal mtDNA replication, defects in mitochondrial quality control mechanisms, and exacerbated by exposures to exogenous and/or endogenous genotoxic agents. In this review, we expand on the origins and consequences of mtDNA instability, the current state of research regarding the mechanisms by which mtDNA instability can be overcome by cellular and chemical interventions, and the future of research and treatments for mtDNA instability.
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Affiliation(s)
- Sherine S L Chan
- Drug Discovery and Biomedical Sciences, College of Pharmacy, Medical University of South Carolina, Charleston, SC 29425, United States; Neuroene Therapeutics, Mt. Pleasant, SC 29464, United States.
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35
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36
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DeBalsi KL, Longley MJ, Hoff KE, Copeland WC. Synergistic Effects of the in cis T251I and P587L Mitochondrial DNA Polymerase γ Disease Mutations. J Biol Chem 2017; 292:4198-4209. [PMID: 28154168 DOI: 10.1074/jbc.m116.773341] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 01/26/2017] [Indexed: 01/28/2023] Open
Abstract
Human mitochondrial DNA (mtDNA) polymerase γ (Pol γ) is the only polymerase known to replicate the mitochondrial genome. The Pol γ holoenzyme consists of the p140 catalytic subunit (POLG) and the p55 homodimeric accessory subunit (POLG2), which enhances binding of Pol γ to DNA and promotes processivity of the holoenzyme. Mutations within POLG impede maintenance of mtDNA and cause mitochondrial diseases. Two common POLG mutations usually found in cis in patients primarily with progressive external ophthalmoplegia generate T251I and P587L amino acid substitutions. To determine whether T251I or P587L is the primary pathogenic allele or whether both substitutions are required to cause disease, we overproduced and purified WT, T251I, P587L, and T251I + P587L double variant forms of recombinant Pol γ. Biochemical characterization of these variants revealed impaired DNA binding affinity, reduced thermostability, diminished exonuclease activity, defective catalytic activity, and compromised DNA processivity, even in the presence of the p55 accessory subunit. However, physical association with p55 was unperturbed, suggesting intersubunit affinities similar to WT. Notably, although the single mutants were similarly impaired, a dramatic synergistic effect was found for the double mutant across all parameters. In conclusion, our analyses suggest that individually both T251I and P587L substitutions functionally impair Pol γ, with greater pathogenicity predicted for the single P587L variant. Combining T251I and P587L induces extreme thermal lability and leads to synergistic nucleotide and DNA binding defects, which severely impair catalytic activity and correlate with presentation of disease in patients.
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Affiliation(s)
- Karen L DeBalsi
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - Matthew J Longley
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - Kirsten E Hoff
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - William C Copeland
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
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DeBalsi KL, Hoff KE, Copeland WC. Role of the mitochondrial DNA replication machinery in mitochondrial DNA mutagenesis, aging and age-related diseases. Ageing Res Rev 2017; 33:89-104. [PMID: 27143693 DOI: 10.1016/j.arr.2016.04.006] [Citation(s) in RCA: 117] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Revised: 04/19/2016] [Accepted: 04/19/2016] [Indexed: 12/19/2022]
Abstract
As regulators of bioenergetics in the cell and the primary source of endogenous reactive oxygen species (ROS), dysfunctional mitochondria have been implicated for decades in the process of aging and age-related diseases. Mitochondrial DNA (mtDNA) is replicated and repaired by nuclear-encoded mtDNA polymerase γ (Pol γ) and several other associated proteins, which compose the mtDNA replication machinery. Here, we review evidence that errors caused by this replication machinery and failure to repair these mtDNA errors results in mtDNA mutations. Clonal expansion of mtDNA mutations results in mitochondrial dysfunction, such as decreased electron transport chain (ETC) enzyme activity and impaired cellular respiration. We address the literature that mitochondrial dysfunction, in conjunction with altered mitochondrial dynamics, is a major driving force behind aging and age-related diseases. Additionally, interventions to improve mitochondrial function and attenuate the symptoms of aging are examined.
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Affiliation(s)
- Karen L DeBalsi
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - Kirsten E Hoff
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
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38
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Lewis SC, Uchiyama LF, Nunnari J. ER-mitochondria contacts couple mtDNA synthesis with mitochondrial division in human cells. Science 2016; 353:aaf5549. [PMID: 27418514 DOI: 10.1126/science.aaf5549] [Citation(s) in RCA: 423] [Impact Index Per Article: 52.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 05/26/2016] [Indexed: 12/17/2022]
Abstract
Mitochondrial DNA (mtDNA) encodes RNAs and proteins critical for cell function. In human cells, hundreds to thousands of mtDNA copies are replicated asynchronously, packaged into protein-DNA nucleoids, and distributed within a dynamic mitochondrial network. The mechanisms that govern how nucleoids are chosen for replication and distribution are not understood. Mitochondrial distribution depends on division, which occurs at endoplasmic reticulum (ER)-mitochondria contact sites. These sites were spatially linked to a subset of nucleoids selectively marked by mtDNA polymerase and engaged in mtDNA synthesis--events that occurred upstream of mitochondrial constriction and division machine assembly. Our data suggest that ER tubules proximal to nucleoids are necessary but not sufficient for mtDNA synthesis. Thus, ER-mitochondria contacts coordinate licensing of mtDNA synthesis with division to distribute newly replicated nucleoids to daughter mitochondria.
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Affiliation(s)
- Samantha C Lewis
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Lauren F Uchiyama
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Jodi Nunnari
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
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39
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Varma H, Faust PL, Iglesias AD, Lagana SM, Wou K, Hirano M, DiMauro S, Mansukani MM, Hoff KE, Nagy PL, Copeland WC, Naini AB. Whole exome sequencing identifies a homozygous POLG2 missense variant in an infant with fulminant hepatic failure and mitochondrial DNA depletion. Eur J Med Genet 2016; 59:540-5. [PMID: 27592148 DOI: 10.1016/j.ejmg.2016.08.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 08/04/2016] [Accepted: 08/31/2016] [Indexed: 11/26/2022]
Abstract
Mitochondrial DNA (mtDNA) depletion syndrome manifests as diverse early-onset diseases that affect skeletal muscle, brain and liver function. Mutations in several nuclear DNA-encoded genes cause mtDNA depletion. We report on a patient, a 3-month-old boy who presented with hepatic failure, and was found to have severe mtDNA depletion in liver and muscle. Whole-exome sequencing identified a homozygous missense variant (c.544C > T, p.R182W) in the accessory subunit of mitochondrial DNA polymerase gamma (POLG2), which is required for mitochondrial DNA replication. This variant is predicted to disrupt a critical region needed for homodimerization of the POLG2 protein and cause loss of processive DNA synthesis. Both parents were phenotypically normal and heterozygous for this variant. Heterozygous mutations in POLG2 were previously associated with progressive external ophthalmoplegia and mtDNA deletions. This is the first report of a patient with a homozygous mutation in POLG2 and with a clinical presentation of severe hepatic failure and mitochondrial depletion.
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Affiliation(s)
- Hemant Varma
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA
| | - Phyllis L Faust
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA
| | - Alejandro D Iglesias
- Division of Medical Genetics, Columbia University, New York Presbyterian Hospital, USA
| | - Stephen M Lagana
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA
| | - Karen Wou
- Division of Genetics, New York Presbyterian Hospital, USA
| | - Michio Hirano
- Department of Neurology, Columbia University Medical Center, USA
| | | | - Mahesh M Mansukani
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA
| | - Kirsten E Hoff
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA
| | - Peter L Nagy
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA.
| | - Ali B Naini
- Department of Pathology and Cell Biology, Columbia University, 630 W, 168th Street, New York, NY 10032, USA; Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, USA.
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40
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Oxidative DNA damage stalls the human mitochondrial replisome. Sci Rep 2016; 6:28942. [PMID: 27364318 PMCID: PMC4929447 DOI: 10.1038/srep28942] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Accepted: 05/31/2016] [Indexed: 12/27/2022] Open
Abstract
Oxidative stress is capable of causing damage to various cellular constituents, including DNA. There is however limited knowledge on how oxidative stress influences mitochondrial DNA and its replication. Here, we have used purified mtDNA replication proteins, i.e. DNA polymerase γ holoenzyme, the mitochondrial single-stranded DNA binding protein mtSSB, the replicative helicase Twinkle and the proposed mitochondrial translesion synthesis polymerase PrimPol to study lesion bypass synthesis on oxidative damage-containing DNA templates. Our studies were carried out at dNTP levels representative of those prevailing either in cycling or in non-dividing cells. At dNTP concentrations that mimic those in cycling cells, the replication machinery showed substantial stalling at sites of damage, and these problems were further exacerbated at the lower dNTP concentrations present in resting cells. PrimPol, the translesion synthesis polymerase identified inside mammalian mitochondria, did not promote mtDNA replication fork bypass of the damage. This argues against a conventional role for PrimPol as a mitochondrial translesion synthesis DNA polymerase for oxidative DNA damage; however, we show that Twinkle, the mtDNA replicative helicase, is able to stimulate PrimPol DNA synthesis in vitro, suggestive of an as yet unidentified role of PrimPol in mtDNA metabolism.
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41
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Young MJ, Copeland WC. Human mitochondrial DNA replication machinery and disease. Curr Opin Genet Dev 2016; 38:52-62. [PMID: 27065468 DOI: 10.1016/j.gde.2016.03.005] [Citation(s) in RCA: 129] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 03/03/2016] [Accepted: 03/08/2016] [Indexed: 12/21/2022]
Abstract
The human mitochondrial genome is replicated by DNA polymerase γ in concert with key components of the mitochondrial DNA (mtDNA) replication machinery. Defects in mtDNA replication or nucleotide metabolism cause deletions, point mutations, or depletion of mtDNA. The resulting loss of cellular respiration ultimately induces mitochondrial genetic diseases, including mtDNA depletion syndromes (MDS) such as Alpers or early infantile hepatocerebral syndromes, and mtDNA deletion disorders such as progressive external ophthalmoplegia, ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy. Here we review the current literature regarding human mtDNA replication and heritable disorders caused by genetic changes of the POLG, POLG2, Twinkle, RNASEH1, DNA2, and MGME1 genes.
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Affiliation(s)
- Matthew J Young
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709, United States
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709, United States.
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42
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Ciesielski GL, Hytönen VP, Kaguni LS. Biolayer Interferometry: A Novel Method to Elucidate Protein-Protein and Protein-DNA Interactions in the Mitochondrial DNA Replisome. Methods Mol Biol 2016; 1351:223-31. [PMID: 26530686 DOI: 10.1007/978-1-4939-3040-1_17] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
A lack of effective treatment for mitochondrial diseases prompts scientists to investigate the molecular processes that underlie their development. The major cause of mitochondrial diseases is dysfunction of the sole mitochondrial DNA polymerase, DNA polymerase γ (Pol γ). The development of treatment strategies will require a detailed characterization of the molecular properties of Pol γ. A novel technique, biolayer interferometry, allows one to monitor molecular interactions in real time, thus providing an insight into the kinetics of the process. Here, we present an application of the biolayer interferometry technique to characterize the fundamental reactions that Pol γ undergoes during the initiation phase of mitochondrial DNA replication: holoenzyme formation and binding to the primer-template.
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Affiliation(s)
- Grzegorz L Ciesielski
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, 33014, Finland
| | - Vesa P Hytönen
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, 33014, Finland
- Fimlab Laboratories, Biokatu 4, Tampere, 33101, Finland
| | - Laurie S Kaguni
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, 33014, Finland.
- Department of Biochemistry and Molecular Biology, Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, 48824, USA.
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Abstract
Mitochondrial DNA is replicated by the nuclear-encoded DNA polymerase γ (pol γ) which is composed of a single 140 kDa catalytic subunit and a dimeric 55 kDa accessory subunit. Mitochondrial DNA is vulnerable to various forms of damage, including several types of oxidative lesions, UV-induced photoproducts, chemical adducts from environmental sources, as well as alkylation and inter-strand cross-links from chemotherapy agents. Although many of these lesions block DNA replication, pol γ can bypass some lesions by nucleotide incorporation opposite a template lesion and further extension of the DNA primer past the lesion. This process of translesion synthesis (TLS) by pol γ can occur in either an error-free or an error-prone manner. Assessment of TLS requires extensive analysis of oligonucleotide substrates and replication products by denaturing polyacrylamide sequencing gels. This chapter presents protocols for the analysis of translesion DNA synthesis.
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44
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Young MJ, Humble MM, DeBalsi KL, Sun KY, Copeland WC. POLG2 disease variants: analyses reveal a dominant negative heterodimer, altered mitochondrial localization and impaired respiratory capacity. Hum Mol Genet 2015; 24:5184-97. [PMID: 26123486 PMCID: PMC4550827 DOI: 10.1093/hmg/ddv240] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Revised: 06/02/2015] [Accepted: 06/22/2015] [Indexed: 01/14/2023] Open
Abstract
Human mitochondrial DNA (mtDNA) is replicated and repaired by the mtDNA polymerase gamma, polγ. Polγ is composed of three subunits encoded by two nuclear genes: (1) POLG codes for the 140-kilodalton (kDa) catalytic subunit, p140 and (2) POLG2 encodes the ∼110-kDa homodimeric accessory subunit, p55. Specific mutations are associated with POLG- or POLG2-related disorders. During DNA replication the p55 accessory subunit binds to p140 and increases processivity by preventing polγ's dissociation from the template. To date, studies have demonstrated that homodimeric p55 disease variants are deficient in the ability to stimulate p140; however, all patients currently identified with POLG2-related disorders are heterozygotes. In these patients, we expect p55 to occur as 25% wild-type (WT) homodimers, 25% variant homodimers and 50% heterodimers. We report the development of a tandem affinity strategy to isolate p55 heterodimers. The WT/G451E p55 heterodimer impairs polγ function in vitro, demonstrating that the POLG2 c.1352G>A/p.G451E mutation encodes a dominant negative protein. To analyze the subcellular consequence of disease mutations in HEK293 cells, we designed plasmids encoding p55 disease variants tagged with green fluorescent protein (GFP). P205R and L475DfsX2 p55 variants exhibit irregular diffuse mitochondrial fluorescence and unlike WT p55, they fail to form distinct puncta associated with mtDNA nucleoids. Furthermore, homogenous preparations of P205R and L475DfsX2 p55 form aberrant reducible multimers. We predict that abnormal protein folding or aggregation or both contribute to the pathophysiology of these disorders. Examination of mitochondrial bioenergetics in stable cell lines overexpressing GFP-tagged p55 variants revealed impaired mitochondrial reserve capacity.
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Affiliation(s)
- Matthew J Young
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - Margaret M Humble
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - Karen L DeBalsi
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - Kathie Y Sun
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, DHHS, Research Triangle Park, NC 27709, USA
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45
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Akhmedov AT, Marín-García J. Mitochondrial DNA maintenance: an appraisal. Mol Cell Biochem 2015; 409:283-305. [DOI: 10.1007/s11010-015-2532-x] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 08/06/2015] [Indexed: 12/13/2022]
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46
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Szymanski MR, Kuznetsov VB, Shumate C, Meng Q, Lee YS, Patel G, Patel S, Yin YW. Structural basis for processivity and antiviral drug toxicity in human mitochondrial DNA replicase. EMBO J 2015; 34:1959-70. [PMID: 26056153 DOI: 10.15252/embj.201591520] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Accepted: 05/18/2015] [Indexed: 11/09/2022] Open
Abstract
The human DNA polymerase gamma (Pol γ) is responsible for DNA replication in mitochondria. Pol γ is particularly susceptible to inhibition by dideoxynucleoside-based inhibitors designed to fight viral infection. Here, we report crystal structures of the replicating Pol γ-DNA complex bound to either substrate or zalcitabine, an inhibitor used for HIV reverse transcriptase. The structures reveal that zalcitabine binds to the Pol γ active site almost identically to the substrate dCTP, providing a structural basis for Pol γ-mediated drug toxicity. When compared to the apo form, Pol γ undergoes intra- and inter-subunit conformational changes upon formation of the ternary complex with primer/template DNA and substrate. We also find that the accessory subunit Pol γB, which lacks intrinsic enzymatic activity and does not contact the primer/template DNA directly, serves as an allosteric regulator of holoenzyme activities. The structures presented here suggest a mechanism for processivity of the holoenzyme and provide a model for understanding the deleterious effects of Pol γ mutations in human disease. Crystal structures of the mitochondrial DNA polymerase, Pol γ, in complex with substrate or antiviral inhibitor zalcitabine provide a basis for understanding Pol γ-mediated drug toxicity.
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Affiliation(s)
- Michal R Szymanski
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Vladmir B Kuznetsov
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Christie Shumate
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Qingchao Meng
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA
| | - Young-Sam Lee
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA
| | - Gayatri Patel
- Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | - Smita Patel
- Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | - Y Whitney Yin
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA
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47
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Lodi T, Dallabona C, Nolli C, Goffrini P, Donnini C, Baruffini E. DNA polymerase γ and disease: what we have learned from yeast. Front Genet 2015; 6:106. [PMID: 25852747 PMCID: PMC4362329 DOI: 10.3389/fgene.2015.00106] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 03/02/2015] [Indexed: 11/16/2022] Open
Abstract
Mip1 is the Saccharomyces cerevisiae DNA polymerase γ (Pol γ), which is responsible for the replication of mitochondrial DNA (mtDNA). It belongs to the family A of the DNA polymerases and it is orthologs to human POLGA. In humans, mutations in POLG(1) cause many mitochondrial pathologies, such as progressive external ophthalmoplegia (PEO), Alpers' syndrome, and ataxia-neuropathy syndrome, all of which present instability of mtDNA, which results in impaired mitochondrial function in several tissues with variable degrees of severity. In this review, we summarize the genetic and biochemical knowledge published on yeast mitochondrial DNA polymerase from 1989, when the MIP1 gene was first cloned, up until now. The role of yeast is particularly emphasized in (i) validating the pathological mutations found in human POLG and modeled in MIP1, (ii) determining the molecular defects caused by these mutations and (iii) finding the correlation between mutations/polymorphisms in POLGA and mtDNA toxicity induced by specific drugs. We also describe recent findings regarding the discovery of molecules able to rescue the phenotypic defects caused by pathological mutations in Mip1, and the construction of a model system in which the human Pol γ holoenzyme is expressed in yeast and complements the loss of Mip1.
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Affiliation(s)
- Tiziana Lodi
- Department of Life Sciences, University of Parma Parma, Italy
| | | | - Cecilia Nolli
- Department of Life Sciences, University of Parma Parma, Italy
| | - Paola Goffrini
- Department of Life Sciences, University of Parma Parma, Italy
| | - Claudia Donnini
- Department of Life Sciences, University of Parma Parma, Italy
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Oliveira MT, Haukka J, Kaguni LS. Evolution of the metazoan mitochondrial replicase. Genome Biol Evol 2015; 7:943-59. [PMID: 25740821 PMCID: PMC4419789 DOI: 10.1093/gbe/evv042] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/26/2015] [Indexed: 01/10/2023] Open
Abstract
The large number of complete mitochondrial DNA (mtDNA) sequences available for metazoan species makes it a good system for studying genome diversity, although little is known about the mechanisms that promote and/or are correlated with the evolution of this organellar genome. By investigating the molecular evolutionary history of the catalytic and accessory subunits of the mtDNA polymerase, pol γ, we sought to develop mechanistic insight into its function that might impact genome structure by exploring the relationships between DNA replication and animal mitochondrial genome diversity. We identified three evolutionary patterns among metazoan pol γs. First, a trend toward stabilization of both sequence and structure occurred in vertebrates, with both subunits evolving distinctly from those of other animal groups, and acquiring at least four novel structural elements, the most important of which is the HLH-3β (helix-loop-helix, 3 β-sheets) domain that allows the accessory subunit to homodimerize. Second, both subunits of arthropods and tunicates have become shorter and evolved approximately twice as rapidly as their vertebrate homologs. And third, nematodes have lost the gene for the accessory subunit, which was accompanied by the loss of its interacting domain in the catalytic subunit of pol γ, and they show the highest rate of molecular evolution among all animal taxa. These findings correlate well with the mtDNA genomic features of each group described above, and with their modes of DNA replication, although a substantive amount of biochemical work is needed to draw conclusive links regarding the latter. Describing the parallels between evolution of pol γ and metazoan mtDNA architecture may also help in understanding the processes that lead to mitochondrial dysfunction and to human disease-related phenotypes.
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Affiliation(s)
- Marcos T Oliveira
- Institute of Biosciences and Medical Technology, University of Tampere, Finland Departamento de Tecnologia, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista "Júlio de Mesquita Filho," Jaboticabal, SP, Brazil
| | - Jani Haukka
- Institute of Biosciences and Medical Technology, University of Tampere, Finland
| | - Laurie S Kaguni
- Institute of Biosciences and Medical Technology, University of Tampere, Finland Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University
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49
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Holt IJ, Speijer D, Kirkwood TBL. The road to rack and ruin: selecting deleterious mitochondrial DNA variants. Philos Trans R Soc Lond B Biol Sci 2015; 369:20130451. [PMID: 24864317 DOI: 10.1098/rstb.2013.0451] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Mitochondria constitute the major energy-producing compartment of the eukaryotic cell. These organelles contain many molecules of DNA that contribute only a handful of proteins required for energy production. Mutations in the DNA of mitochondria were identified as a cause of human disease a quarter of a century ago, and they have subsequently been implicated in ageing. The process whereby deleterious variants come to dominate a cell, tissue or human is the subject of debate. It is likely to involve multiple, often competing, factors, as selection pressures on mitochondrial DNA can be both indirect and intermittent, and are subjected to rapid change. Here, we assess the different models and the prospects for preventing the accumulation of deleterious mitochondrial DNA variants with time.
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Affiliation(s)
- Ian J Holt
- MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, UK
| | - Dave Speijer
- Department of Medical Biochemistry, Academic Medical Centre, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
| | - Thomas B L Kirkwood
- Institute for Ageing and Health, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne NE4 5PL, UK
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50
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Abstract
Mitochondrial DNA is replicated by DNA polymerase γ in concert with accessory proteins such as the mitochondrial DNA helicase, single-stranded DNA binding protein, topoisomerase, and initiating factors. Defects in mitochondrial DNA replication or nucleotide metabolism can cause mitochondrial genetic diseases due to mitochondrial DNA deletions, point mutations, or depletion, which ultimately cause loss of oxidative phosphorylation. These genetic diseases include mitochondrial DNA depletion syndromes such as Alpers or early infantile hepatocerebral syndromes, and mitochondrial DNA deletion disorders, such as progressive external ophthalmoplegia, ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy. This review focuses on our current knowledge of genetic defects of mitochondrial DNA replication (POLG, POLG2, C10orf2, and MGME1) that cause instability of mitochondrial DNA and mitochondrial disease.
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Affiliation(s)
- William C. Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
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