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Hayward B, Kumari D, Santra S, van Karnebeek CDM, van Kuilenburg ABP, Usdin K. All three MutL complexes are required for repeat expansion in a human stem cell model of CAG-repeat expansion mediated glutaminase deficiency. Sci Rep 2024; 14:13772. [PMID: 38877099 PMCID: PMC11178883 DOI: 10.1038/s41598-024-64480-z] [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: 01/09/2024] [Accepted: 06/10/2024] [Indexed: 06/16/2024] Open
Abstract
The Repeat Expansion Diseases (REDs) arise from the expansion of a disease-specific short tandem repeat (STR). Different REDs differ with respect to the repeat involved, the cells that are most expansion prone and the extent of expansion. Furthermore, whether these diseases share a common expansion mechanism is unclear. To date, expansion has only been studied in a limited number of REDs. Here we report the first studies of the expansion mechanism in induced pluripotent stem cells derived from a patient with a form of the glutaminase deficiency disorder known as Global Developmental Delay, Progressive Ataxia, And Elevated Glutamine (GDPAG; OMIM# 618412) caused by the expansion of a CAG-STR in the 5' UTR of the glutaminase (GLS) gene. We show that alleles with as few as ~ 120 repeats show detectable expansions in culture despite relatively low levels of R-loops formed at this locus. Additionally, using a CRISPR-Cas9 knockout approach we show that PMS2 and MLH3, the constituents of MutLα and MutLγ, the 2 mammalian MutL complexes known to be involved in mismatch repair (MMR), are essential for expansion. Furthermore, PMS1, a component of a less well understood MutL complex, MutLβ, is also important, if not essential, for repeat expansion in these cells. Our results provide insights into the factors important for expansion and lend weight to the idea that, despite some differences, the same mechanism is responsible for expansion in many, if not all, REDs.
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Affiliation(s)
- Bruce Hayward
- Section On Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Daman Kumari
- Section On Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Saikat Santra
- Birmingham Women's and Children's NHS Foundation Trust, Birmingham, B15 2TG, UK
| | - Clara D M van Karnebeek
- Emma Center for Personalized Medicine, Departments of Pediatrics and Human Genetics, Amsterdam Gastro-Enterology Endocrinology and Metabolism, Amsterdam UMC, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands
- United for Metabolic Diseases, Amsterdam, The Netherlands
| | - André B P van Kuilenburg
- Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
- Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam, The Netherlands
| | - Karen Usdin
- Section On Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA.
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2
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Hayward B, Kumari D, Santra S, van Karnebeek CD, van Kuilenburg AB, Usdin K. All three MutL complexes are required for repeat expansion in a human stem cell model of CAG-repeat expansion mediated glutaminase deficiency. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.12.26.573357. [PMID: 38260514 PMCID: PMC10802475 DOI: 10.1101/2023.12.26.573357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
The Repeat Expansion Diseases (REDs) arise from the expansion of a disease-specific short tandem repeat (STR). Different REDs differ with respect to the repeat involved, the cells that are most expansion prone and the extent of expansion. Furthermore, whether these diseases share a common expansion mechanism is unclear. To date, expansion has only been studied in a limited number of REDs. Here we report the first studies of the expansion mechanism in induced pluripotent stem cells derived from a patient with a form of the glutaminase deficiency disorder known as Global Developmental Delay, Progressive Ataxia, And Elevated Glutamine (GDPAG; OMIM# 618412) caused by the expansion of a CAG-STR in the 5' UTR of the glutaminase (GLS) gene. We show that alleles with as few as ~120 repeats show detectable expansions in culture despite relatively low levels of R-loops formed at this locus. Additionally, using a CRISPR-Cas9 knockout approach we show that PMS2 and MLH3, the constituents of MutLα and MutLγ, the 2 mammalian MutL complexes known to be involved in mismatch repair (MMR), are essential for expansion. Furthermore, PMS1, a component of a less well understood MutL complex, MutLβ, is also important, if not essential, for repeat expansion in these cells. Our results provide insights into the factors important for expansion and lend weight to the idea that, despite some differences, the same mechanism is responsible for expansion in many, if not all, REDs.
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Affiliation(s)
- Bruce Hayward
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - Daman Kumari
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - Saikat Santra
- Birmingham Women's and Children's NHS Foundation Trust, Birmingham B15 2TG, United Kingdom
| | - Clara D.M. van Karnebeek
- Amsterdam UMC location University of Amsterdam, Departments of Pediatrics and Human Genetics, Emma Center for Personalized Medicine, Amsterdam Gastroenterology Endocrinology Metabolism, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands
- United for Metabolic Diseases, The Netherlands
| | - André B.P. van Kuilenburg
- Amsterdam UMC location University of Amsterdam, Department of Clinical Chemistry, Laboratory Genetic Metabolic Diseases, Amsterdam, The Netherlands
- Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam, The Netherlands
| | - Karen Usdin
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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3
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McLean ZL, Gao D, Correia K, Roy JCL, Shibata S, Farnum IN, Valdepenas-Mellor Z, Kovalenko M, Rapuru M, Morini E, Ruliera J, Gillis T, Lucente D, Kleinstiver BP, Lee JM, MacDonald ME, Wheeler VC, Mouro Pinto R, Gusella JF. Splice modulators target PMS1 to reduce somatic expansion of the Huntington's disease-associated CAG repeat. Nat Commun 2024; 15:3182. [PMID: 38609352 PMCID: PMC11015039 DOI: 10.1038/s41467-024-47485-0] [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: 07/24/2023] [Accepted: 03/30/2024] [Indexed: 04/14/2024] Open
Abstract
Huntington's disease (HD) is a dominant neurological disorder caused by an expanded HTT exon 1 CAG repeat that lengthens huntingtin's polyglutamine tract. Lowering mutant huntingtin has been proposed for treating HD, but genetic modifiers implicate somatic CAG repeat expansion as the driver of onset. We find that branaplam and risdiplam, small molecule splice modulators that lower huntingtin by promoting HTT pseudoexon inclusion, also decrease expansion of an unstable HTT exon 1 CAG repeat in an engineered cell model. Targeted CRISPR-Cas9 editing shows this effect is not due to huntingtin lowering, pointing instead to pseudoexon inclusion in PMS1. Homozygous but not heterozygous inactivation of PMS1 also reduces CAG repeat expansion, supporting PMS1 as a genetic modifier of HD and a potential target for therapeutic intervention. Although splice modulation provides one strategy, genome-wide transcriptomics also emphasize consideration of cell-type specific effects and polymorphic variation at both target and off-target sites.
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Affiliation(s)
- Zachariah L McLean
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA
| | - Dadi Gao
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA
| | - Kevin Correia
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Jennie C L Roy
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
| | - Shota Shibata
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA
| | - Iris N Farnum
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Zoe Valdepenas-Mellor
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Marina Kovalenko
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Manasa Rapuru
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Elisabetta Morini
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
| | - Jayla Ruliera
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Tammy Gillis
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Diane Lucente
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Benjamin P Kleinstiver
- Center for Genomic Medicine and Department of Pathology, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Pathology, Harvard Medical School, Boston, MA, 02115, USA
| | - Jong-Min Lee
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA
| | - Marcy E MacDonald
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA
| | - Vanessa C Wheeler
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA
| | - Ricardo Mouro Pinto
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Neurology, Harvard Medical School, Boston, MA, 02115, USA
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA
| | - James F Gusella
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA.
- Medical and Population Genetics Program, the Broad Institute of M.I.T. and Harvard, Cambridge, MA, 02142, USA.
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, 02115, USA.
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4
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Laverde EE, Polyzos AA, Tsegay PP, Shaver M, Hutcheson JD, Balakrishnan L, McMurray CT, Liu Y. Flap Endonuclease 1 Endonucleolytically Processes RNA to Resolve R-Loops through DNA Base Excision Repair. Genes (Basel) 2022; 14:genes14010098. [PMID: 36672839 PMCID: PMC9859040 DOI: 10.3390/genes14010098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 12/22/2022] [Accepted: 12/23/2022] [Indexed: 12/30/2022] Open
Abstract
Flap endonuclease 1 (FEN1) is an essential enzyme that removes RNA primers and base lesions during DNA lagging strand maturation and long-patch base excision repair (BER). It plays a crucial role in maintaining genome stability and integrity. FEN1 is also implicated in RNA processing and biogenesis. A recent study from our group has shown that FEN1 is involved in trinucleotide repeat deletion by processing the RNA strand in R-loops through BER, further suggesting that the enzyme can modulate genome stability by facilitating the resolution of R-loops. However, it remains unknown how FEN1 can process RNA to resolve an R-loop. In this study, we examined the FEN1 cleavage activity on the RNA:DNA hybrid intermediates generated during DNA lagging strand processing and BER in R-loops. We found that both human and yeast FEN1 efficiently cleaved an RNA flap in the intermediates using its endonuclease activity. We further demonstrated that FEN1 was recruited to R-loops in normal human fibroblasts and senataxin-deficient (AOA2) fibroblasts, and its R-loop recruitment was significantly increased by oxidative DNA damage. We showed that FEN1 specifically employed its endonucleolytic cleavage activity to remove the RNA strand in an R-loop during BER. We found that FEN1 coordinated its DNA and RNA endonucleolytic cleavage activity with the 3'-5' exonuclease of APE1 to resolve the R-loop. Our results further suggest that FEN1 employed its unique tracking mechanism to endonucleolytically cleave the RNA strand in an R-loop by coordinating with other BER enzymes and cofactors during BER. Our study provides the first evidence that FEN1 endonucleolytic cleavage can result in the resolution of R-loops via the BER pathway, thereby maintaining genome integrity.
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Affiliation(s)
- Eduardo E. Laverde
- Biochemistry Ph.D. Program, Florida International University, Miami, FL 33199, USA
| | - Aris A. Polyzos
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Pawlos P. Tsegay
- Biochemistry Ph.D. Program, Florida International University, Miami, FL 33199, USA
| | - Mohammad Shaver
- Department of Biomedical Engineering, Florida International University, Miami, FL 33199, USA
| | - Joshua D. Hutcheson
- Department of Biomedical Engineering, Florida International University, Miami, FL 33199, USA
| | - Lata Balakrishnan
- Department of Biology, Indiana-Purdue University, Indianapolis, IN 46202, USA
| | - Cynthia T. McMurray
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Yuan Liu
- Biochemistry Ph.D. Program, Florida International University, Miami, FL 33199, USA
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA
- Biomolecular Sciences Institute, Florida International University, Miami, FL 33199, USA
- Correspondence:
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5
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Brown RE, Su XA, Fair S, Wu K, Verra L, Jong R, Andrykovich K, Freudenreich CH. The RNA export and RNA decay complexes THO and TRAMP prevent transcription-replication conflicts, DNA breaks, and CAG repeat contractions. PLoS Biol 2022; 20:e3001940. [PMID: 36574440 PMCID: PMC9829180 DOI: 10.1371/journal.pbio.3001940] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Revised: 01/09/2023] [Accepted: 12/01/2022] [Indexed: 12/28/2022] Open
Abstract
Expansion of structure-forming CAG/CTG repetitive sequences is the cause of several neurodegenerative disorders and deletion of repeats is a potential therapeutic strategy. Transcription-associated mechanisms are known to cause CAG repeat instability. In this study, we discovered that Thp2, an RNA export factor and member of the THO (suppressors of transcriptional defects of hpr1Δ by overexpression) complex, and Trf4, a key component of the TRAMP (Trf4/5-Air1/2-Mtr4 polyadenylation) complex involved in nuclear RNA polyadenylation and degradation, are necessary to prevent CAG fragility and repeat contractions in a Saccharomyces cerevisiae model system. Depletion of both Thp2 and Trf4 proteins causes a highly synergistic increase in CAG repeat fragility, indicating a complementary role of the THO and TRAMP complexes in preventing genome instability. Loss of either Thp2 or Trf4 causes an increase in RNA polymerase stalling at the CAG repeats and other genomic loci, as well as genome-wide transcription-replication conflicts (TRCs), implicating TRCs as a cause of CAG fragility and instability in their absence. Analysis of the effect of RNase H1 overexpression on CAG fragility, RNAPII stalling, and TRCs suggests that RNAPII stalling with associated R-loops are the main cause of CAG fragility in the thp2Δ mutants. In contrast, CAG fragility and TRCs in the trf4Δ mutant can be compensated for by RPA overexpression, suggesting that excess unprocessed RNA in TRAMP4 mutants leads to reduced RPA availability and high levels of TRCs. Our results show the importance of RNA surveillance pathways in preventing RNAPII stalling, TRCs, and DNA breaks, and show that RNA export and RNA decay factors work collaboratively to maintain genome stability.
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Affiliation(s)
- Rebecca E. Brown
- Program in Genetics, Tufts University School of Graduate Biomedical Sciences, Boston, Massachusetts, United States of America
| | - Xiaofeng A. Su
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
- David H. Koch Institute for Integrative Cancer Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Stacey Fair
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Katherine Wu
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Lauren Verra
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Robyn Jong
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Kristin Andrykovich
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Catherine H. Freudenreich
- Program in Genetics, Tufts University School of Graduate Biomedical Sciences, Boston, Massachusetts, United States of America
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
- * E-mail:
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6
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Peng S, Guo P, Lin X, An Y, Sze KH, Lau MHY, Chen ZS, Wang Q, Li W, Sun JKL, Ma SY, Chan TF, Lau KF, Ngo JCK, Kwan KM, Wong CH, Lam SL, Zimmerman SC, Tuccinardi T, Zuo Z, Au-Yeung HY, Chow HM, Chan HYE. CAG RNAs induce DNA damage and apoptosis by silencing NUDT16 expression in polyglutamine degeneration. Proc Natl Acad Sci U S A 2021; 118:e2022940118. [PMID: 33947817 PMCID: PMC8126783 DOI: 10.1073/pnas.2022940118] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
DNA damage plays a central role in the cellular pathogenesis of polyglutamine (polyQ) diseases, including Huntington's disease (HD). In this study, we showed that the expression of untranslatable expanded CAG RNA per se induced the cellular DNA damage response pathway. By means of RNA sequencing (RNA-seq), we found that expression of the Nudix hydrolase 16 (NUDT16) gene was down-regulated in mutant CAG RNA-expressing cells. The loss of NUDT16 function results in a misincorporation of damaging nucleotides into DNAs and leads to DNA damage. We showed that small CAG (sCAG) RNAs, species generated from expanded CAG transcripts, hybridize with CUG-containing NUDT16 mRNA and form a CAG-CUG RNA heteroduplex, resulting in gene silencing of NUDT16 and leading to the DNA damage and cellular apoptosis. These results were further validated using expanded CAG RNA-expressing mouse primary neurons and in vivo R6/2 HD transgenic mice. Moreover, we identified a bisamidinium compound, DB213, that interacts specifically with the major groove of the CAG RNA homoduplex and disfavors the CAG-CUG heteroduplex formation. This action subsequently mitigated RNA-induced silencing complex (RISC)-dependent NUDT16 silencing in both in vitro cell and in vivo mouse disease models. After DB213 treatment, DNA damage, apoptosis, and locomotor defects were rescued in HD mice. This work establishes NUDT16 deficiency by CAG repeat RNAs as a pathogenic mechanism of polyQ diseases and as a potential therapeutic direction for HD and other polyQ diseases.
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Affiliation(s)
- Shaohong Peng
- Laboratory of Drosophila Research, The Chinese University of Hong Kong, Hong Kong, China
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Pei Guo
- Department of Chemistry, The Chinese University of Hong Kong, Hong Kong, China
- School of Biology and Biological Engineering, South China University of Technology, Guangzhou 510006, China
| | - Xiao Lin
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Ying An
- Laboratory of Drosophila Research, The Chinese University of Hong Kong, Hong Kong, China
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Kong Hung Sze
- Department of Microbiology, The University of Hong Kong, Hong Kong, China
| | - Matthew Ho Yan Lau
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Hong Kong, China
| | - Zhefan Stephen Chen
- Laboratory of Drosophila Research, The Chinese University of Hong Kong, Hong Kong, China
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Qianwen Wang
- School of Pharmacy, The Chinese University of Hong Kong, Hong Kong, China
| | - Wen Li
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | | | - Sum Yi Ma
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Ting-Fung Chan
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China
- Gerald Choa Neuroscience Centre, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Kwok-Fai Lau
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Jacky Chi Ki Ngo
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Kin Ming Kwan
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China
- Centre for Cell and Developmental Biology, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Chun-Ho Wong
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Steven C Zimmerman
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | | | - Zhong Zuo
- School of Pharmacy, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Ho Yu Au-Yeung
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Hei-Man Chow
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Ho Yin Edwin Chan
- Laboratory of Drosophila Research, The Chinese University of Hong Kong, Hong Kong, China;
- School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
- Gerald Choa Neuroscience Centre, The Chinese University of Hong Kong, Hong Kong, China
- Nexus of Rare Neurodegenerative Diseases, School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, China
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7
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Khristich AN, Mirkin SM. On the wrong DNA track: Molecular mechanisms of repeat-mediated genome instability. J Biol Chem 2020; 295:4134-4170. [PMID: 32060097 PMCID: PMC7105313 DOI: 10.1074/jbc.rev119.007678] [Citation(s) in RCA: 148] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Expansions of simple tandem repeats are responsible for almost 50 human diseases, the majority of which are severe, degenerative, and not currently treatable or preventable. In this review, we first describe the molecular mechanisms of repeat-induced toxicity, which is the connecting link between repeat expansions and pathology. We then survey alternative DNA structures that are formed by expandable repeats and review the evidence that formation of these structures is at the core of repeat instability. Next, we describe the consequences of the presence of long structure-forming repeats at the molecular level: somatic and intergenerational instability, fragility, and repeat-induced mutagenesis. We discuss the reasons for gender bias in intergenerational repeat instability and the tissue specificity of somatic repeat instability. We also review the known pathways in which DNA replication, transcription, DNA repair, and chromatin state interact and thereby promote repeat instability. We then discuss possible reasons for the persistence of disease-causing DNA repeats in the genome. We describe evidence suggesting that these repeats are a payoff for the advantages of having abundant simple-sequence repeats for eukaryotic genome function and evolvability. Finally, we discuss two unresolved fundamental questions: (i) why does repeat behavior differ between model systems and human pedigrees, and (ii) can we use current knowledge on repeat instability mechanisms to cure repeat expansion diseases?
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Affiliation(s)
| | - Sergei M Mirkin
- Department of Biology, Tufts University, Medford, Massachusetts 02155.
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8
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Cinesi C, Yang B, Dion V. GFP Reporters to Monitor Instability and Expression of Expanded CAG/CTG Repeats. Methods Mol Biol 2020; 2056:255-268. [PMID: 31586353 DOI: 10.1007/978-1-4939-9784-8_16] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Expanded CAG/CTG repeats are genetically unstable and, upon expression, cause neurological and neuromuscular diseases. The molecular mechanisms of repeat instability and expression remain poorly understood despite their importance for the pathogenesis of a family of 14 devastating human diseases. This is in part because conventional assays are tedious and time-consuming. Recently, however, GFP-based reporters have been designed to provide a rapid and reliable means of assessing these parameters. Here we provide protocols for quantifying repeat instability and expression using a GFP-based chromosomal reporter and the newly developed ParB/ANCHOR-mediated Inducible Targeting (PInT) and how to validate the results.
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Affiliation(s)
- Cinzia Cinesi
- Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland
| | - Bin Yang
- Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland
| | - Vincent Dion
- Dementia Research Institute, Cardiff University, Cardiff, UK.
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9
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Kaushal S, Freudenreich CH. The role of fork stalling and DNA structures in causing chromosome fragility. Genes Chromosomes Cancer 2019; 58:270-283. [PMID: 30536896 DOI: 10.1002/gcc.22721] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 11/13/2018] [Accepted: 12/03/2018] [Indexed: 12/19/2022] Open
Abstract
Alternative non-B form DNA structures, also called secondary structures, can form in certain DNA sequences under conditions that produce single-stranded DNA, such as during replication, transcription, and repair. Direct links between secondary structure formation, replication fork stalling, and genomic instability have been found for many repeated DNA sequences that cause disease when they expand. Common fragile sites (CFSs) are known to be AT-rich and break under replication stress, yet the molecular basis for their fragility is still being investigated. Over the past several years, new evidence has linked both the formation of secondary structures and transcription to fork stalling and fragility of CFSs. How these two events may synergize to cause fragility and the role of nuclease cleavage at secondary structures in rare and CFSs are discussed here. We also highlight evidence for a new hypothesis that secondary structures at CFSs not only initiate fragility but also inhibit healing, resulting in their characteristic appearance.
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Affiliation(s)
- Simran Kaushal
- Department of Biology, Tufts University, Medford, Massachusetts
| | - Catherine H Freudenreich
- Department of Biology, Tufts University, Medford, Massachusetts.,Program in Genetics, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, Massachusetts
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10
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Intracellular RNA Sensing in Mammalian Cells: Role in Stress Response and Cancer Therapies. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2019; 344:31-89. [DOI: 10.1016/bs.ircmb.2018.08.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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11
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Belotserkovskii BP, Tornaletti S, D'Souza AD, Hanawalt PC. R-loop generation during transcription: Formation, processing and cellular outcomes. DNA Repair (Amst) 2018; 71:69-81. [PMID: 30190235 PMCID: PMC6340742 DOI: 10.1016/j.dnarep.2018.08.009] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
R-loops are structures consisting of an RNA-DNA duplex and an unpaired DNA strand. They can form during transcription upon nascent RNA "threadback" invasion into the DNA duplex to displace the non-template strand. Although R-loops occur naturally in all kingdoms of life and serve regulatory roles, they are often deleterious and can cause genomic instability. Of particular importance are the disastrous consequences when replication forks or transcription complexes collide with R-loops. The appropriate processing of R-loops is essential to avoid a number of human neurodegenerative and other clinical disorders. We provide a perspective on mechanistic aspects of R-loop formation and their resolution learned from studies in model systems. This should contribute to improved understanding of R-loop biological functions and enable their practical applications. We propose the novel employment of artificially-generated stable R-loops to selectively inactivate tumor cells.
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Affiliation(s)
- Boris P Belotserkovskii
- Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA, 94305-5020, United States
| | - Silvia Tornaletti
- Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA, 94305-5020, United States
| | - Alicia D D'Souza
- Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA, 94305-5020, United States
| | - Philip C Hanawalt
- Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA, 94305-5020, United States.
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12
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Cancer therapies activate RIG-I-like receptor pathway through endogenous non-coding RNAs. Oncotarget 2018; 7:26496-515. [PMID: 27034163 PMCID: PMC5041995 DOI: 10.18632/oncotarget.8420] [Citation(s) in RCA: 118] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2016] [Accepted: 03/05/2016] [Indexed: 12/14/2022] Open
Abstract
Emerging evidence indicates that ionizing radiation (IR) and chemotherapy activate Type I interferon (IFN) signaling in tumor and host cells. However, the mechanism of induction is poorly understood. We identified a novel radioprotective role for the DEXH box RNA helicase LGP2 (DHX58) through its suppression of IR-induced cytotoxic IFN-beta [1]. LGP2 inhibits activation of the RIG-I-like receptor (RLR) pathway upon binding of viral RNA to the cytoplasmic sensors RIG-I (DDX58) and MDA5 (IFIH1) and subsequent IFN signaling via the mitochondrial adaptor protein MAVS (IPS1). Here we show that MAVS is necessary for IFN-beta induction and interferon-stimulated gene expression in the response to IR. Suppression of MAVS conferred radioresistance in normal and cancer cells. Germline deletion of RIG-I, but not MDA5, protected mice from death following total body irradiation, while deletion of LGP2 accelerated the death of irradiated animals. In human tumors depletion of RIG-I conferred resistance to IR and different classes of chemotherapy drugs. Mechanistically, IR stimulated the binding of cytoplasmic RIG-I with small endogenous non-coding RNAs (sncRNAs), which triggered IFN-beta activity. We demonstrate that the small nuclear RNAs U1 and U2 translocate to the cytoplasm after IR treatment, thus stimulating the formation of RIG-I: RNA complexes and initiating downstream signaling events. Taken together, these findings suggest that the physiologic responses to radio-/chemo-therapy converge on an antiviral program in recruitment of the RLR pathway by a sncRNA-dependent activation of RIG-I which commences cytotoxic IFN signaling. Importantly, activation of interferon genes by radiation or chemotherapy is associated with a favorable outcome in patients undergoing treatment for cancer. To our knowledge, this is the first demonstration of a cell-intrinsic response to clinically relevant genotoxic treatments mediated by an RNA-dependent mechanism.
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13
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Gudde AEEG, van Heeringen SJ, de Oude AI, van Kessel IDG, Estabrook J, Wang ET, Wieringa B, Wansink DG. Antisense transcription of the myotonic dystrophy locus yields low-abundant RNAs with and without (CAG)n repeat. RNA Biol 2017; 14:1374-1388. [PMID: 28102759 PMCID: PMC5711456 DOI: 10.1080/15476286.2017.1279787] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 12/21/2016] [Accepted: 12/30/2016] [Indexed: 12/20/2022] Open
Abstract
The unstable (CTG·CAG)n trinucleotide repeat in the myotonic dystrophy type 1 (DM1) locus is bidirectionally transcribed from genes with terminal overlap. By transcription in the sense direction, the DMPK gene produces various alternatively spliced mRNAs with a (CUG)n repeat in their 3' UTR. Expression in opposite orientation reportedly yields (CAG)n-repeat containing RNA, but both structure and biologic significance of this antisense gene (DM1-AS) are largely unknown. Via a combinatorial approach of computational and experimental analyses of RNA from unaffected individuals and DM1 patients we discovered that DM1-AS spans >6 kb, contains alternative transcription start sites and uses alternative polyadenylation sites up- and downstream of the (CAG)n repeat. Moreover, its primary transcripts undergo alternative splicing, whereby the (CAG)n segment is removed as part of an intron. Thus, in patients a mixture of DM1-AS RNAs with and without expanded (CAG)n repeat are produced. DM1-AS expression appears upregulated in patients, but transcript abundance remains very low in all tissues analyzed. Our data suggest that DM1-AS transcripts belong to the class of long non-coding RNAs. These and other biologically relevant implications for how (CAG)n-expanded transcripts may contribute to DM1 pathology can now be explored experimentally.
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Affiliation(s)
- Anke E. E. G. Gudde
- Radboud University Medical Center, Department of Cell Biology, Nijmegen, The Netherlands
| | - Simon J. van Heeringen
- Radboud University, Faculty of Science, Department of Molecular Developmental Biology, Radboud Institute for Molecular Life Sciences, Nijmegen, The Netherlands
| | - Amanda I. de Oude
- Radboud University Medical Center, Department of Cell Biology, Nijmegen, The Netherlands
| | | | - Joseph Estabrook
- Department of Molecular Genetics and Microbiology, Center for Neurogenetics, University of Florida College of Medicine, Gainesville, FL, USA
| | - Eric T. Wang
- Department of Molecular Genetics and Microbiology, Center for Neurogenetics, University of Florida College of Medicine, Gainesville, FL, USA
| | - Bé Wieringa
- Radboud University Medical Center, Department of Cell Biology, Nijmegen, The Netherlands
| | - Derick G. Wansink
- Radboud University Medical Center, Department of Cell Biology, Nijmegen, The Netherlands
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14
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Rohilla KJ, Gagnon KT. RNA biology of disease-associated microsatellite repeat expansions. Acta Neuropathol Commun 2017; 5:63. [PMID: 28851463 PMCID: PMC5574247 DOI: 10.1186/s40478-017-0468-y] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 08/22/2017] [Indexed: 12/13/2022] Open
Abstract
Microsatellites, or simple tandem repeat sequences, occur naturally in the human genome and have important roles in genome evolution and function. However, the expansion of microsatellites is associated with over two dozen neurological diseases. A common denominator among the majority of these disorders is the expression of expanded tandem repeat-containing RNA, referred to as xtrRNA in this review, which can mediate molecular disease pathology in multiple ways. This review focuses on the potential impact that simple tandem repeat expansions can have on the biology and metabolism of RNA that contain them and underscores important gaps in understanding. Merging the molecular biology of repeat expansion disorders with the current understanding of RNA biology, including splicing, transcription, transport, turnover and translation, will help clarify mechanisms of disease and improve therapeutic development.
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15
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Polyzos AA, McMurray CT. Close encounters: Moving along bumps, breaks, and bubbles on expanded trinucleotide tracts. DNA Repair (Amst) 2017; 56:144-155. [PMID: 28690053 PMCID: PMC5558859 DOI: 10.1016/j.dnarep.2017.06.017] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Expansion of simple triplet repeats (TNR) underlies more than 30 severe degenerative diseases. There is a good understanding of the major pathways generating an expansion, and the associated polymerases that operate during gap filling synthesis at these "difficult to copy" sequences. However, the mechanism by which a TNR is repaired depends on the type of lesion, the structural features imposed by the lesion, the assembled replication/repair complex, and the polymerase that encounters it. The relationships among these parameters are exceptionally complex and how they direct pathway choice is poorly understood. In this review, we consider the properties of polymerases, and how encounters with GC-rich or abnormal structures might influence polymerase choice and the success of replication and repair. Insights over the last three years have highlighted new mechanisms that provide interesting choices to consider in protecting genome stability.
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Affiliation(s)
- Aris A Polyzos
- MBIB Division, Lawrence Berkeley Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, United States
| | - Cynthia T McMurray
- MBIB Division, Lawrence Berkeley Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, United States.
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16
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Zhang N, Ashizawa T. RNA toxicity and foci formation in microsatellite expansion diseases. Curr Opin Genet Dev 2017; 44:17-29. [PMID: 28208060 DOI: 10.1016/j.gde.2017.01.005] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 01/04/2017] [Accepted: 01/18/2017] [Indexed: 12/11/2022]
Abstract
More than 30 incurable neurological and neuromuscular diseases are caused by simple microsatellite expansions consisted of 3-6 nucleotides. These repeats can occur in non-coding regions and often result in a dominantly inherited disease phenotype that is characteristic of a toxic RNA gain-of-function. The expanded RNA adopts unusual secondary structures, sequesters various RNA binding proteins to form insoluble nuclear foci, and causes cellular defects at a multisystem level. Nuclear foci are dynamic in size, shape and colocalization of RNA binding proteins in different expansion diseases and tissue types. This review sets to provide new insights into the disease mechanisms of RNA toxicity and foci modulation, in light of recent advancement on bi-directional transcription, antisense RNA, repeat-associated non-ATG translation and beyond.
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Affiliation(s)
- Nan Zhang
- Neurosciences Research Program, Houston Methodist Research Institute, Houston, TX 77030, United States; Division of Cell and Molecular Biology, South Kensington Campus, Imperial College London, London SW7 2AZ, UK
| | - Tetsuo Ashizawa
- Neurosciences Research Program, Houston Methodist Research Institute, Houston, TX 77030, United States.
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17
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Richard P, Manley JL. R Loops and Links to Human Disease. J Mol Biol 2016; 429:3168-3180. [PMID: 27600412 DOI: 10.1016/j.jmb.2016.08.031] [Citation(s) in RCA: 125] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 08/26/2016] [Accepted: 08/31/2016] [Indexed: 12/13/2022]
Abstract
Aberrant R-loop structures are increasingly being realized as an important contributor to human disease. R loops, which are mainly co-transcriptional, abundant RNA/DNA hybrids, form naturally and can indeed be beneficial for transcription regulation at certain loci. However, their unwanted persistence elsewhere or in particular situations can lead to DNA double-strand breaks, chromosome rearrangements, and hypermutation, which are all sources of genomic instability. Mutations in genes involved in R-loop resolution or mutations leading to R-loop formation at specific genes affect the normal physiology of the cell. We discuss here the examples of diseases for which a link with R loops has been described, as well as how disease-causing mutations might participate in the development and/or progression of diseases that include repeat-associated conditions, other neurological disorders, and cancers.
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Affiliation(s)
- Patricia Richard
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
| | - James L Manley
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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18
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Shimada MK, Sanbonmatsu R, Yamaguchi-Kabata Y, Yamasaki C, Suzuki Y, Chakraborty R, Gojobori T, Imanishi T. Selection pressure on human STR loci and its relevance in repeat expansion disease. Mol Genet Genomics 2016; 291:1851-69. [PMID: 27290643 DOI: 10.1007/s00438-016-1219-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2015] [Accepted: 05/21/2016] [Indexed: 12/30/2022]
Abstract
Short Tandem Repeats (STRs) comprise repeats of one to several base pairs. Because of the high mutability due to strand slippage during DNA synthesis, rapid evolutionary change in the number of repeating units directly shapes the range of repeat-number variation according to selection pressure. However, the remaining questions include: Why are STRs causing repeat expansion diseases maintained in the human population; and why are these limited to neurodegenerative diseases? By evaluating the genome-wide selection pressure on STRs using the database we constructed, we identified two different patterns of relationship in repeat-number polymorphisms between DNA and amino-acid sequences, although both patterns are evolutionary consequences of avoiding the formation of harmful long STRs. First, a mixture of degenerate codons is represented in poly-proline (poly-P) repeats. Second, long poly-glutamine (poly-Q) repeats are favored at the protein level; however, at the DNA level, STRs encoding long poly-Qs are frequently divided by synonymous SNPs. Furthermore, significant enrichments of apoptosis and neurodevelopment were biological processes found specifically in genes encoding poly-Qs with repeat polymorphism. This suggests the existence of a specific molecular function for polymorphic and/or long poly-Q stretches. Given that the poly-Qs causing expansion diseases were longer than other poly-Qs, even in healthy subjects, our results indicate that the evolutionary benefits of long and/or polymorphic poly-Q stretches outweigh the risks of long CAG repeats predisposing to pathological hyper-expansions. Molecular pathways in neurodevelopment requiring long and polymorphic poly-Q stretches may provide a clue to understanding why poly-Q expansion diseases are limited to neurodegenerative diseases.
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Affiliation(s)
- Makoto K Shimada
- Institute for Comprehensive Medical Science, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, 470-1192, Japan. .,National Institute of Advanced Industrial Science and Technology, 2-3-26 Aomi Koto-ku, Tokyo, 135-0064, Japan. .,Japan Biological Informatics Consortium, 10F TIME24 Building, 2-4-32 Aomi, Koto-ku, Tokyo, 135-8073, Japan.
| | - Ryoko Sanbonmatsu
- Japan Biological Informatics Consortium, 10F TIME24 Building, 2-4-32 Aomi, Koto-ku, Tokyo, 135-8073, Japan
| | - Yumi Yamaguchi-Kabata
- National Institute of Advanced Industrial Science and Technology, 2-3-26 Aomi Koto-ku, Tokyo, 135-0064, Japan.,Tohoku Medical Megabank Organization, Tohoku University, 2-1 Seiryo-machi, Aoba-ku, Sendai, 980-8573, Japan
| | - Chisato Yamasaki
- National Institute of Advanced Industrial Science and Technology, 2-3-26 Aomi Koto-ku, Tokyo, 135-0064, Japan.,Japan Biological Informatics Consortium, 10F TIME24 Building, 2-4-32 Aomi, Koto-ku, Tokyo, 135-8073, Japan
| | - Yoshiyuki Suzuki
- Graduate School of Natural Sciences, Nagoya City University, 1 Yamanohata, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, 467-8501, Japan
| | - Ranajit Chakraborty
- Health Science Center, University of North Texas, 3500 Camp Bowie Blvd., Fort Worth, TX, 76107, USA
| | - Takashi Gojobori
- National Institute of Advanced Industrial Science and Technology, 2-3-26 Aomi Koto-ku, Tokyo, 135-0064, Japan.,Computational Bioscience Research Center, King Abdullah University of Science and Technology, Ibn Al-Haytham Building (West), Thuwal, 23955-6900, Kingdom of Saudi Arabia
| | - Tadashi Imanishi
- National Institute of Advanced Industrial Science and Technology, 2-3-26 Aomi Koto-ku, Tokyo, 135-0064, Japan.,Department of Molecular Life Science, Tokai University School of Medicine, 143 Shimokasuya, Isehara, Kanagawa, 259-1193, Japan
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19
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Chatterjee N, Lin Y, Wilson JH. Mismatch repair enhances convergent transcription-induced cell death at trinucleotide repeats by activating ATR. DNA Repair (Amst) 2016; 42:26-32. [PMID: 27131875 DOI: 10.1016/j.dnarep.2016.03.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Revised: 03/15/2016] [Accepted: 03/16/2016] [Indexed: 01/08/2023]
Abstract
Trinucleotide repeat (TNR) expansion beyond a certain threshold results in some 20 incurable neurodegenerative disorders where disease anticipation positively correlates with repeat length. Long TNRs typically display a bias toward further expansion during germinal transmission from parents to offspring, and then are highly unstable in somatic tissues of affected individuals. Understanding mechanisms of TNR instability will provide insights into disease pathogenesis. Previously, we showed that enhanced convergent transcription at long CAG repeat tracks induces TNR instability and cell death via ATR activation. Components of TC-NER (transcription-coupled nucleotide excision repair) and RNaseH enzymes that resolve RNA/DNA hybrids oppose cell death, whereas the MSH2 component of MMR (mismatch repair) enhances cell death. The exact role of the MMR pathway during convergent transcription-induced cell death at CAG repeats is not well understood. In this study, we show that siRNA knockdowns of MMR components-MSH2, MSH3, MLHI, PMS2, and PCNA-reduce DNA toxicity. Furthermore, knockdown of MSH2, MLH1, and PMS2 significantly reduces the frequency of ATR foci formation. These observations suggest that MMR proteins activate DNA toxicity by modulating ATR foci formation during convergent transcription.
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Affiliation(s)
- Nimrat Chatterjee
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - Yunfu Lin
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Smithville, TX 78957, USA
| | - John H Wilson
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
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20
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Engineered Nucleases and Trinucleotide Repeat Diseases. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016. [DOI: 10.1007/978-1-4939-3509-3_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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21
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Su XA, Dion V, Gasser SM, Freudenreich CH. Regulation of recombination at yeast nuclear pores controls repair and triplet repeat stability. Genes Dev 2015; 29:1006-17. [PMID: 25940904 PMCID: PMC4441049 DOI: 10.1101/gad.256404.114] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Accepted: 04/10/2015] [Indexed: 12/16/2022]
Abstract
Secondary structure-forming DNA sequences such as CAG repeats interfere with replication and repair, provoking fork stalling, chromosome fragility, and recombination. In budding yeast, Su et al. find that expanded CAG repeats are more likely than unexpanded repeats to localize to the nuclear periphery and that the relocation of damage to nuclear pores plays an important role in a naturally occurring repair process. Secondary structure-forming DNA sequences such as CAG repeats interfere with replication and repair, provoking fork stalling, chromosome fragility, and recombination. In budding yeast, we found that expanded CAG repeats are more likely than unexpanded repeats to localize to the nuclear periphery. This positioning is transient, occurs in late S phase, requires replication, and is associated with decreased subnuclear mobility of the locus. In contrast to persistent double-stranded breaks, expanded CAG repeats at the nuclear envelope associate with pores but not with the inner nuclear membrane protein Mps3. Relocation requires Nup84 and the Slx5/8 SUMO-dependent ubiquitin ligase but not Rad51, Mec1, or Tel1. Importantly, the presence of the Nup84 pore subcomplex and Slx5/8 suppresses CAG repeat fragility and instability. Repeat instability in nup84, slx5, or slx8 mutant cells arises through aberrant homologous recombination and is distinct from instability arising from the loss of ligase 4-dependent end-joining. Genetic and physical analysis of Rad52 sumoylation and binding at the CAG tract suggests that Slx5/8 targets sumoylated Rad52 for degradation at the pore to facilitate recovery from acute replication stress by promoting replication fork restart. We thereby confirmed that the relocation of damage to nuclear pores plays an important role in a naturally occurring repair process.
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Affiliation(s)
- Xiaofeng A Su
- Department of Biology, Tufts University, Medford, Massachusetts 02155, USA
| | - Vincent Dion
- Friedrich Miescher Institute for Biomedical Research, CH-4058 Basel, Switzerland
| | - Susan M Gasser
- Friedrich Miescher Institute for Biomedical Research, CH-4058 Basel, Switzerland; Faculty of Natural Sciences, University of Basel, CH-4056 Basel, Switzerland
| | - Catherine H Freudenreich
- Department of Biology, Tufts University, Medford, Massachusetts 02155, USA; Program in Genetics, Tufts University, Medford, Massachusetts 02155, USA;
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22
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Khan N, Kolimi N, Rathinavelan T. Twisting right to left: A…A mismatch in a CAG trinucleotide repeat overexpansion provokes left-handed Z-DNA conformation. PLoS Comput Biol 2015; 11:e1004162. [PMID: 25876062 PMCID: PMC4395422 DOI: 10.1371/journal.pcbi.1004162] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 01/28/2015] [Indexed: 12/02/2022] Open
Abstract
Conformational polymorphism of DNA is a major causative factor behind several incurable trinucleotide repeat expansion disorders that arise from overexpansion of trinucleotide repeats located in coding/non-coding regions of specific genes. Hairpin DNA structures that are formed due to overexpansion of CAG repeat lead to Huntington’s disorder and spinocerebellar ataxias. Nonetheless, DNA hairpin stem structure that generally embraces B-form with canonical base pairs is poorly understood in the context of periodic noncanonical A…A mismatch as found in CAG repeat overexpansion. Molecular dynamics simulations on DNA hairpin stems containing A…A mismatches in a CAG repeat overexpansion show that A…A dictates local Z-form irrespective of starting glycosyl conformation, in sharp contrast to canonical DNA duplex. Transition from B-to-Z is due to the mechanistic effect that originates from its pronounced nonisostericity with flanking canonical base pairs facilitated by base extrusion, backbone and/or base flipping. Based on these structural insights we envisage that such an unusual DNA structure of the CAG hairpin stem may have a role in disease pathogenesis. As this is the first study that delineates the influence of a single A…A mismatch in reversing DNA helicity, it would further have an impact on understanding DNA mismatch repair. When a set of 3 nucleotides in a DNA sequence repeats beyond a certain number, it leads to incurable neurological or neuromuscular disorders. Such DNA sequences tend to form unusual DNA structures comprising of base pairing schemes different from the canonical A…T/G…C base pairs. Influence of such unusual base pairing on the overall 3-dimensional structure of DNA and its impact on the pathogenesis of disorder is not well understood. CAG repeat overexpansion that leads to Huntington’s disorder and several spinocerebellar ataxias forms noncanonical A…A base pair in between canonical C…G and G…C base pairs. However, no detailed structural information is available on the influence of an A…A mismatch on a DNA structure under any sequence context. Here, we have shown for the first time that A…A base pairing in a CAG repeat provokes the formation of left-handed Z-DNA due to the pronounced structural dissimilarity of A…A base pair with G…C base pair, leading to periodic B-Z junction. Thus, these results suggest that formation of periodic B-Z junction may be one of the molecular bases for CAG repeat instability.
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Affiliation(s)
- Noorain Khan
- Department of Biotechnology, Indian Institute of Technology Hyderabad, Kandi, Telangana State, India
| | - Narendar Kolimi
- Department of Biotechnology, Indian Institute of Technology Hyderabad, Kandi, Telangana State, India
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23
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Environmental stress induces trinucleotide repeat mutagenesis in human cells. Proc Natl Acad Sci U S A 2015; 112:3764-9. [PMID: 25775519 DOI: 10.1073/pnas.1421917112] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The dynamic mutability of microsatellite repeats is implicated in the modification of gene function and disease phenotype. Studies of the enhanced instability of long trinucleotide repeats (TNRs)-the cause of multiple human diseases-have revealed a remarkable complexity of mutagenic mechanisms. Here, we show that cold, heat, hypoxic, and oxidative stresses induce mutagenesis of a long CAG repeat tract in human cells. We show that stress-response factors mediate the stress-induced mutagenesis (SIM) of CAG repeats. We show further that SIM of CAG repeats does not involve mismatch repair, nucleotide excision repair, or transcription, processes that are known to promote TNR mutagenesis in other pathways of instability. Instead, we find that these stresses stimulate DNA rereplication, increasing the proportion of cells with >4 C-value (C) DNA content. Knockdown of the replication origin-licensing factor CDT1 eliminates both stress-induced rereplication and CAG repeat mutagenesis. In addition, direct induction of rereplication in the absence of stress also increases the proportion of cells with >4C DNA content and promotes repeat mutagenesis. Thus, environmental stress triggers a unique pathway for TNR mutagenesis that likely is mediated by DNA rereplication. This pathway may impact normal cells as they encounter stresses in their environment or during development or abnormal cells as they evolve metastatic potential.
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24
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Usdin K, House NCM, Freudenreich CH. Repeat instability during DNA repair: Insights from model systems. Crit Rev Biochem Mol Biol 2015; 50:142-67. [PMID: 25608779 DOI: 10.3109/10409238.2014.999192] [Citation(s) in RCA: 127] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The expansion of repeated sequences is the cause of over 30 inherited genetic diseases, including Huntington disease, myotonic dystrophy (types 1 and 2), fragile X syndrome, many spinocerebellar ataxias, and some cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Repeat expansions are dynamic, and disease inheritance and progression are influenced by the size and the rate of expansion. Thus, an understanding of the various cellular mechanisms that cooperate to control or promote repeat expansions is of interest to human health. In addition, the study of repeat expansion and contraction mechanisms has provided insight into how repair pathways operate in the context of structure-forming DNA, as well as insights into non-canonical roles for repair proteins. Here we review the mechanisms of repeat instability, with a special emphasis on the knowledge gained from the various model systems that have been developed to study this topic. We cover the repair pathways and proteins that operate to maintain genome stability, or in some cases cause instability, and the cross-talk and interactions between them.
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Affiliation(s)
- Karen Usdin
- Laboratory of Cell and Molecular Biology, NIDDK, NIH , Bethesda, MD , USA
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25
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Santillan BA, Moye C, Mittelman D, Wilson JH. GFP-based fluorescence assay for CAG repeat instability in cultured human cells. PLoS One 2014; 9:e113952. [PMID: 25423602 PMCID: PMC4244167 DOI: 10.1371/journal.pone.0113952] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 11/03/2014] [Indexed: 12/13/2022] Open
Abstract
Trinucleotide repeats can be highly unstable, mutating far more frequently than point mutations. Repeats typically mutate by addition or loss of units of the repeat. CAG repeat expansions in humans trigger neurological diseases that include myotonic dystrophy, Huntington disease, and several spinocerebellar ataxias. In human cells, diverse mechanisms promote CAG repeat instability, and in mice, the mechanisms of instability are varied and tissue-dependent. Dissection of mechanistic complexity and discovery of potential therapeutics necessitates quantitative and scalable screens for repeat mutation. We describe a GFP-based assay for screening modifiers of CAG repeat instability in human cells. The assay exploits an engineered intronic CAG repeat tract that interferes with expression of an inducible GFP minigene. Like the phenotypes of many trinucleotide repeat disorders, we find that GFP function is impaired by repeat expansion, in a length-dependent manner. The intensity of fluorescence varies inversely with repeat length, allowing estimates of repeat tract changes in live cells. We validate the assay using transcription through the repeat and engineered CAG-specific nucleases, which have previously been reported to induce CAG repeat instability. The assay is relatively fast and should be adaptable to large-scale screens of chemical and shRNA libraries.
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Affiliation(s)
- Beatriz A. Santillan
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Christopher Moye
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - David Mittelman
- Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, Virginia, United States of America
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America
| | - John H. Wilson
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
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Deyle DR, Hansen RS, Cornea AM, Li LB, Burt AA, Alexander IE, Sandstrom RS, Stamatoyannopoulos JA, Wei CL, Russell DW. A genome-wide map of adeno-associated virus-mediated human gene targeting. Nat Struct Mol Biol 2014; 21:969-75. [PMID: 25282150 PMCID: PMC4405182 DOI: 10.1038/nsmb.2895] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 08/27/2014] [Indexed: 02/03/2023]
Abstract
To determine which genomic features promote homologous recombination, we created a genome-wide map of gene targeting sites. We used an adeno-associated virus vector to target identical loci introduced as transcriptionally active retroviral vectors. A comparison of ~2,000 targeted and untargeted sites showed that targeting occurred throughout the human genome and was not influenced by the presence of nearby CpG islands, sequence repeats or DNase I-hypersensitive sites. Targeted sites were preferentially located within transcription units, especially when the target loci were transcribed in the opposite orientation to their surrounding chromosomal genes. We determined the impact of DNA replication by mapping replication forks, which revealed a preference for recombination at target loci transcribed toward an incoming fork. Our results constitute the first genome-wide screen of gene targeting in mammalian cells and demonstrate a strong recombinogenic effect of colliding polymerases.
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Affiliation(s)
- David R Deyle
- Department of Medicine, University of Washington, Seattle, Washington, USA
| | - R Scott Hansen
- Department of Medicine, University of Washington, Seattle, Washington, USA
| | - Anda M Cornea
- Department of Molecular and Cellular Biology, University of Washington, Seattle, Washington, USA
| | - Li B Li
- Department of Medicine, University of Washington, Seattle, Washington, USA
| | - Amber A Burt
- Department of Medicine, University of Washington, Seattle, Washington, USA
| | - Ian E Alexander
- Gene Therapy Research Unit, Children's Medical Research Institute, Westmead, New South Wales, Australia
| | - Richard S Sandstrom
- Department of Genome Sciences, University of Washington, Seattle, Washington, USA
| | | | - Chia-Lin Wei
- Genomic Technologies Department, Joint Genome Institute, Walnut Creek, California, USA
| | - David W Russell
- 1] Department of Medicine, University of Washington, Seattle, Washington, USA. [2] Department of Biochemistry, University of Washington, Seattle, Washington, USA
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Reddy K, Schmidt MHM, Geist JM, Thakkar NP, Panigrahi GB, Wang YH, Pearson CE. Processing of double-R-loops in (CAG)·(CTG) and C9orf72 (GGGGCC)·(GGCCCC) repeats causes instability. Nucleic Acids Res 2014; 42:10473-87. [PMID: 25147206 PMCID: PMC4176329 DOI: 10.1093/nar/gku658] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
R-loops, transcriptionally-induced RNA:DNA hybrids, occurring at repeat tracts (CTG)n, (CAG)n, (CGG)n, (CCG)n and (GAA)n, are associated with diseases including myotonic dystrophy, Huntington's disease, fragile X and Friedreich's ataxia. Many of these repeats are bidirectionally transcribed, allowing for single- and double-R-loop configurations, where either or both DNA strands may be RNA-bound. R-loops can trigger repeat instability at (CTG)·(CAG) repeats, but the mechanism of this is unclear. We demonstrate R-loop-mediated instability through processing of R-loops by HeLa and human neuron-like cell extracts. Double-R-loops induced greater instability than single-R-loops. Pre-treatment with RNase H only partially suppressed instability, supporting a model in which R-loops directly generate instability by aberrant processing, or via slipped-DNA formation upon RNA removal and its subsequent aberrant processing. Slipped-DNAs were observed to form following removal of the RNA from R-loops. Since transcriptionally-induced R-loops can occur in the absence of DNA replication, R-loop processing may be a source of repeat instability in the brain. Double-R-loop formation and processing to instability was extended to the expanded C9orf72 (GGGGCC)·(GGCCCC) repeats, known to cause amyotrophic lateral sclerosis and frontotemporal dementia, providing the first suggestion through which these repeats may become unstable. These findings provide a mechanistic basis for R-loop-mediated instability at disease-associated repeats.
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Affiliation(s)
- Kaalak Reddy
- Department of Genetics, The Hospital for Sick Children, Peter Gilgan Centre for Research & Learning, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada Program of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 0A4, Canada
| | - Monika H M Schmidt
- Department of Genetics, The Hospital for Sick Children, Peter Gilgan Centre for Research & Learning, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada Program of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 0A4, Canada
| | - Jaimie M Geist
- Department of Genetics, The Hospital for Sick Children, Peter Gilgan Centre for Research & Learning, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada Department of Biology, Laurentian University, Sudbury, Ontario P3E 2C6, Canada
| | - Neha P Thakkar
- Department of Genetics, The Hospital for Sick Children, Peter Gilgan Centre for Research & Learning, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada Program of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 0A4, Canada
| | - Gagan B Panigrahi
- Department of Genetics, The Hospital for Sick Children, Peter Gilgan Centre for Research & Learning, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada Program of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 0A4, Canada
| | - Yuh-Hwa Wang
- Department of Biochemistry & Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Christopher E Pearson
- Department of Genetics, The Hospital for Sick Children, Peter Gilgan Centre for Research & Learning, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada Program of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 0A4, Canada
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28
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Convergent transcription through microsatellite repeat tracts induces cell death. Mol Biol Rep 2014; 41:5627-34. [PMID: 25012912 DOI: 10.1007/s11033-014-3432-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 05/24/2014] [Indexed: 10/25/2022]
Abstract
Microsatellite sequences, composed of short tandem repeats and randomly distributed in human genome, can become unstable during various DNA metabolic processes. Expansions of CAG, GAA, CGG and CCTG repeats located in specific genes are responsible for several human disorders. It is known that a major percentage of human genes simultaneously express both sense and antisense transcripts. Recently, we reported that convergent transcription through a CAG95 tract in human cells leads to cell cycle arrest as well as robust apoptosis. In this study, we studied the effects of convergent transcription through other types of repeats, using cell lines that contain substrates with inducible sense and antisense transcription through CGG66, GAA102, or CCTG134 tracts. We found that convergent transcription through all these repeats inhibits cell growth and induces cell death, though more moderately than convergent transcription through a CAG tract. These results suggest that convergent transcription through various types of tandem repeats represent a novel type of stress to cells.
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Abstract
CNG repeats (where N denotes one of the four natural nucleotides) are abundant in the human genome. Their tendency to undergo expansion can lead to hereditary diseases known as TREDs (trinucleotide repeat expansion disorders). The toxic factor can be protein, if the abnormal gene is expressed, or the gene transcript, or both. The gene transcripts have attracted much attention in the biomedical community, but their molecular structures have only recently been investigated. Model RNA molecules comprising CNG repeats fold into long hairpins whose stems generally conform to an A-type helix, in which the non-canonical N-N pairs are flanked by C-G and G-C pairs. Each homobasic pair is accommodated in the helical context in a unique manner, with consequences for the local helical parameters, solvent structure, electrostatic potential and potential to interact with ligands. The detailed three-dimensional profiles of RNA CNG repeats can be used in screening of compound libraries for potential therapeutics and in structure-based drug design. Here is a brief survey of the CNG structures published to date.
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Affiliation(s)
- Agnieszka Kiliszek
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland
| | - Wojciech Rypniewski
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland
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30
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Goula AV, Festenstein R, Merienne K. Tissue-dependent regulation of RNAP II dynamics: the missing link between transcription and trinucleotide repeat instability in diseases? Transcription 2013; 4:172-6. [PMID: 23989661 DOI: 10.4161/trns.25971] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
More than 15 human genetic diseases, including Huntington's disease, result from the expansion of a trinucleotide repeat. The expansions are unstable in specific somatic tissues, which can lead to disease acceleration. Here we discuss the role of transcription elongation in tissue-selective trinucleotide repeat instability.
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Affiliation(s)
- Agathi-Vasiliki Goula
- Programme of Translational Medicine and Neurogenetics; Institute of Genetics and Molecular and Cellular Biology (IGBMC); UMR 7104-CNRS/INSERM/UdS; Illkirch, France
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31
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Repair of chromosomal double-strand breaks by precise ligation in human cells. DNA Repair (Amst) 2013; 12:480-7. [PMID: 23707303 DOI: 10.1016/j.dnarep.2013.04.024] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 04/05/2013] [Accepted: 04/19/2013] [Indexed: 01/19/2023]
Abstract
Double-strand breaks (DSBs), a common type of DNA lesion, occur daily in human cells as a result of both endogenous and exogenous damaging agents. DSBs are repaired in two general ways: by the homology-dependent, error-free pathways of homologous recombination (HR) and by the homology-independent, error-prone pathways of nonhomologous end-joining (NHEJ), with NHEJ predominating in most cells. DSBs with compatible ends can be re-joined in vitro with DNA ligase alone, which raises the question of whether such DSBs require the more elaborate machinery of NHEJ to be repaired in cells. Here we report that chromosomal DSBs with compatible ends introduced by the rare-cutting endonuclease, ISceI, are repaired by precise ligation nearly 100% of the time in human cells. Precise ligation depends on the classical NHEJ components Ku70, XRCC4, and DNA ligase IV, since siRNA knockdowns of these factors significantly reduced the efficiency of precise ligation. Interestingly, knockdown of the tumor suppressors p53 or BRCA1 showed similar effects as the knockdowns of NHEJ factors. In contrast, knockdown of components involved in alternative NHEJ, mismatch repair, nucleotide excision repair, and single-strand break repair did not reduce precise ligation. In summary, our results demonstrate that DSBs in human cells are efficiently repaired by precise ligation, which requires classical NHEJ components and is enhanced by p53 and BRCA1.
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32
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Gaillard H, Herrera-Moyano E, Aguilera A. Transcription-associated genome instability. Chem Rev 2013; 113:8638-61. [PMID: 23597121 DOI: 10.1021/cr400017y] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Hélène Gaillard
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla , Av. Américo Vespucio s/n, 41092 Seville, Spain
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33
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Polak U, McIvor E, Dent SY, Wells RD, Napierala M. Expanded complexity of unstable repeat diseases. Biofactors 2013; 39:164-75. [PMID: 23233240 PMCID: PMC4648362 DOI: 10.1002/biof.1060] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Accepted: 09/19/2012] [Indexed: 11/05/2022]
Abstract
Unstable repeat diseases (URDs) share a common mutational phenomenon of changes in the copy number of short, tandemly repeated DNA sequences. More than 20 human neurological diseases are caused by instability, predominantly, expansion of microsatellite sequences. Changes in the repeat size initiate a cascade of pathological processes, frequently characteristic of a unique disease or a small subgroup of the URDs. Understanding of both the mechanism of repeat instability and molecular consequences of the repeat expansions is critical to developing successful therapies for these diseases. Recent technological breakthroughs in whole genome, transcriptome and proteome analyses will almost certainly lead to new discoveries regarding the mechanisms of repeat instability, the pathogenesis of URDs, and will facilitate development of novel therapeutic approaches. The aim of this review is to give a general overview of unstable repeats diseases, highlight the complexities of these diseases, and feature the emerging discoveries in the field.
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Affiliation(s)
- Urszula Polak
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
- Poznan University of Medical Sciences, Department of Cell Biology, Rokietnicka 5D, 60-806 Poznan, Poland
| | - Elizabeth McIvor
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
| | - Sharon Y.R. Dent
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
| | - Robert D. Wells
- Institute of Biosciences and Technology, assing the University Health Science Center, Center for Genome Research, 2121 West Holcombe Boulevard, Houston, TX 77030, USA
| | - Marek Napierala
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
- Correspondence should be addressed to: Dr. Marek Napierala, University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, SRD 1.134, 1808 Park Road 1C, Smithville, TX 78957, tel. 512-237-6690,
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Goula AV, Stys A, Chan JPK, Trottier Y, Festenstein R, Merienne K. Transcription elongation and tissue-specific somatic CAG instability. PLoS Genet 2012; 8:e1003051. [PMID: 23209427 PMCID: PMC3510035 DOI: 10.1371/journal.pgen.1003051] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Accepted: 09/05/2012] [Indexed: 12/12/2022] Open
Abstract
The expansion of CAG/CTG repeats is responsible for many diseases, including Huntington's disease (HD) and myotonic dystrophy 1. CAG/CTG expansions are unstable in selective somatic tissues, which accelerates disease progression. The mechanisms underlying repeat instability are complex, and it remains unclear whether chromatin structure and/or transcription contribute to somatic CAG/CTG instability in vivo. To address these issues, we investigated the relationship between CAG instability, chromatin structure, and transcription at the HD locus using the R6/1 and R6/2 HD transgenic mouse lines. These mice express a similar transgene, albeit integrated at a different site, and recapitulate HD tissue-specific instability. We show that instability rates are increased in R6/2 tissues as compared to R6/1 matched-samples. High transgene expression levels and chromatin accessibility correlated with the increased CAG instability of R6/2 mice. Transgene mRNA and H3K4 trimethylation at the HD locus were increased, whereas H3K9 dimethylation was reduced in R6/2 tissues relative to R6/1 matched-tissues. However, the levels of transgene expression and these specific histone marks were similar in the striatum and cerebellum, two tissues showing very different CAG instability levels, irrespective of mouse line. Interestingly, the levels of elongating RNA Pol II at the HD locus, but not the initiating form of RNA Pol II, were tissue-specific and correlated with CAG instability levels. Similarly, H3K36 trimethylation, a mark associated with transcription elongation, was specifically increased at the HD locus in the striatum and not in the cerebellum. Together, our data support the view that transcription modulates somatic CAG instability in vivo. More specifically, our results suggest for the first time that transcription elongation is regulated in a tissue-dependent manner, contributing to tissue-selective CAG instability.
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Affiliation(s)
- Agathi-Vasiliki Goula
- Programme of Translational Medicine and Neurogenetics, Institute of Genetics and Molecular and Cellular Biology (IGBMC), UMR 7104-CNRS/INSERM/UdS, Illkirch, France
| | - Agnieszka Stys
- Programme of Translational Medicine and Neurogenetics, Institute of Genetics and Molecular and Cellular Biology (IGBMC), UMR 7104-CNRS/INSERM/UdS, Illkirch, France
| | - Jackson P. K. Chan
- Department of Medicine, Imperial College London, Hammersmith Hospital Campus, London, United Kingdom
| | - Yvon Trottier
- Programme of Translational Medicine and Neurogenetics, Institute of Genetics and Molecular and Cellular Biology (IGBMC), UMR 7104-CNRS/INSERM/UdS, Illkirch, France
| | - Richard Festenstein
- Department of Medicine, Imperial College London, Hammersmith Hospital Campus, London, United Kingdom
| | - Karine Merienne
- Programme of Translational Medicine and Neurogenetics, Institute of Genetics and Molecular and Cellular Biology (IGBMC), UMR 7104-CNRS/INSERM/UdS, Illkirch, France
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35
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Oligodeoxynucleotide binding to (CTG) · (CAG) microsatellite repeats inhibits replication fork stalling, hairpin formation, and genome instability. Mol Cell Biol 2012; 33:571-81. [PMID: 23166299 DOI: 10.1128/mcb.01265-12] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
(CTG)(n) · (CAG)(n) trinucleotide repeat (TNR) expansion in the 3' untranslated region of the dystrophia myotonica protein kinase (DMPK) gene causes myotonic dystrophy type 1. However, a direct link between TNR instability, the formation of noncanonical (CTG)(n) · (CAG)(n) structures, and replication stress has not been demonstrated. In a human cell model, we found that (CTG)(45) · (CAG)(45) causes local replication fork stalling, DNA hairpin formation, and TNR instability. Oligodeoxynucleotides (ODNs) complementary to the (CTG)(45) · (CAG)(45) lagging-strand template eliminated DNA hairpin formation on leading- and lagging-strand templates and relieved fork stalling. Prolonged cell culture, emetine inhibition of lagging-strand synthesis, or slowing of DNA synthesis by low-dose aphidicolin induced (CTG)(45) · (CAG)(45) expansions and contractions. ODNs targeting the lagging-strand template blocked the time-dependent or emetine-induced instability but did not eliminate aphidicolin-induced instability. These results show directly that TNR replication stalling, replication stress, hairpin formation, and instability are mechanistically linked in vivo.
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36
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Lokanga RA, Entezam A, Kumari D, Yudkin D, Qin M, Smith CB, Usdin K. Somatic expansion in mouse and human carriers of fragile X premutation alleles. Hum Mutat 2012; 34:157-66. [PMID: 22887750 DOI: 10.1002/humu.22177] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Accepted: 07/17/2012] [Indexed: 11/10/2022]
Abstract
Repeat expansion diseases result from expansion of a specific tandem repeat. The three fragile X-related disorders (FXDs) arise from germline expansions of a CGG•CCG repeat tract in the 5' UTR (untranslated region) of the fragile X mental retardation 1 (FMR1) gene. We show here that in addition to germline expansion, expansion also occurs in the somatic cells of both mice and humans carriers of premutation alleles. Expansion in mice primarily affects brain, testis, and liver with very little expansion in heart or blood. Our data would be consistent with a simple two-factor model for the organ specificity. Somatic expansion in humans may contribute to the mosaicism often seen in individuals with one of the FXDs. Because expansion risk and disease severity are related to repeat number, somatic expansion may exacerbate disease severity and contribute to the age-related increased risk of expansion seen on paternal transmission in humans. As little somatic expansion occurs in murine lymphocytes, our data also raise the possibility that there may be discordance in humans between repeat numbers measured in blood and that present in brain. This could explain, at least in part, the variable penetrance seen in some of these disorders.
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Affiliation(s)
- Rachel Adihe Lokanga
- Section on Gene Structure and Disease, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892–0830, USA
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Lin Y, Wilson JH. Nucleotide excision repair, mismatch repair, and R-loops modulate convergent transcription-induced cell death and repeat instability. PLoS One 2012; 7:e46807. [PMID: 23056461 PMCID: PMC3463551 DOI: 10.1371/journal.pone.0046807] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Accepted: 09/07/2012] [Indexed: 11/21/2022] Open
Abstract
Expansion of CAG•CTG tracts located in specific genes is responsible for 13 human neurodegenerative disorders, the pathogenic mechanisms of which are not yet well defined. These disease genes are ubiquitously expressed in human tissues, and transcription has been identified as one of the major pathways destabilizing the repeats. Transcription-induced repeat instability depends on transcription-coupled nucleotide excision repair (TC-NER), the mismatch repair (MMR) recognition component MSH2/MSH3, and RNA/DNA hybrids (R-loops). Recently, we reported that simultaneous sense and antisense transcription–convergent transcription–through a CAG repeat not only promotes repeat instability, but also induces a cell stress response, which arrests the cell cycle and eventually leads to massive cell death via apoptosis. Here, we use siRNA knockdowns to investigate whether NER, MMR, and R-loops also modulate convergent-transcription-induced cell death and repeat instability. We find that siRNA-mediated depletion of TC-NER components increases convergent transcription-induced cell death, as does the simultaneous depletion of RNase H1 and RNase H2A. In contrast, depletion of MSH2 decreases cell death. These results identify TC-NER, MMR recognition, and R-loops as modulators of convergent transcription-induced cell death and shed light on the molecular mechanism involved. We also find that the TC-NER pathway, MSH2, and R-loops modulate convergent transcription-induced repeat instability. These observations link the mechanisms of convergent transcription-induced repeat instability and convergent transcription-induced cell death, suggesting that a common structure may trigger both outcomes.
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Affiliation(s)
- Yunfu Lin
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas,United States of America
| | - John H. Wilson
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas,United States of America
- * E-mail:
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38
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Cohen-Carmon D, Meshorer E. Polyglutamine (polyQ) disorders: the chromatin connection. Nucleus 2012; 3:433-41. [PMID: 22892726 DOI: 10.4161/nucl.21481] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Polyglutamine (PolyQ)-related diseases are dominant late-onset genetic disorders that are manifested by progressive neurodegeneration, leading to behavioral and physical impairments. An increased body of evidence suggests that chromatin structure and epigenetic regulation are involved in disease pathology. PolyQ diseases often display an aberrant transcriptional regulation due to the disrupted function of histone-modifying complexes and altered interactions of the polyQ-extended proteins with chromatin-related factors. In this review we describe recent findings relating to the role of chromatin in polyQ diseases. We discuss the involvement of epigenetic-related factors and chromatin structure in genomic instability of CAG repeats; we describe changes in the expression and regulation of chromatin-related enzymes and in the levels and patterns of histone modifications in disease state; we illustrate the potential beneficial effects of different histone deacetylase (HDAC) inhibitors for the treatment of polyQ diseases, and we end by describing the potential use of human pluripotent stem cells and their differentiated derivatives for modeling polyQ diseases in vitro. Taken together, these accumulating studies strongly suggest that disrupted chromatin regulation may be directly involved with the pathophysiology of polyQ-related diseases.
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Affiliation(s)
- Dorit Cohen-Carmon
- Department of Genetics, The Institute of Life Sciences, The Hebrew University of Jerusalem-Edmond J. Safra Campus, Jerusalem, Israel
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39
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Liu G, Leffak M. Instability of (CTG)n•(CAG)n trinucleotide repeats and DNA synthesis. Cell Biosci 2012; 2:7. [PMID: 22369689 PMCID: PMC3310812 DOI: 10.1186/2045-3701-2-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2011] [Accepted: 02/27/2012] [Indexed: 12/21/2022] Open
Abstract
Expansion of (CTG)n•(CAG)n trinucleotide repeat (TNR) microsatellite sequences is the cause of more than a dozen human neurodegenerative diseases. (CTG)n and (CAG)n repeats form imperfectly base paired hairpins that tend to expand in vivo in a length-dependent manner. Yeast, mouse and human models confirm that (CTG)n•(CAG)n instability increases with repeat number, and implicate both DNA replication and DNA damage response mechanisms in (CTG)n•(CAG)n TNR expansion and contraction. Mutation and knockdown models that abrogate the expression of individual genes might also mask more subtle, cumulative effects of multiple additional pathways on (CTG)n•(CAG)n instability in whole animals. The identification of second site genetic modifiers may help to explain the variability of (CTG)n•(CAG)n TNR instability patterns between tissues and individuals, and offer opportunities for prognosis and treatment.
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Affiliation(s)
- Guoqi Liu
- Department of Biochemistry and Molecular Biology, Boonshoft School of Medicine, Wright State University, Dayton, OH 45435, USA.
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40
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Abstract
Alterations in genome sequence and structure contribute to somatic disease, affect the fitness of subsequent generations and drive evolutionary processes. The crucial roles of highly accurate replication and efficient repair in maintaining overall genome integrity are well-known, but the more localized stability costs that are associated with transcribing DNA into RNA molecules are less appreciated. Here we review the diverse ways in which the essential process of transcription alters the underlying DNA template and thereby modifies the genetic landscape.
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Abstract
Myotonic dystrophy type 1 (DM1) is caused by expansion of a CTG repeat in the gene DMPK. The expansion is highly unstable in somatic cells, a feature that may contribute to disease progression. The RNA expressed from the mutant allele exerts a toxic gain of function, due to the presence of an expanded CUG repeat (CUG(exp)). This RNA dominant mechanism is amenable to therapeutic intervention with antisense oligonucleotides (ASOs). For example, CAG-repeat ASOs that bind CUG(exp) RNA are beneficial in DM1 models by altering the protein interactions or metabolism of the toxic RNA. Because CUG(exp) RNA has been shown to aggravate instability of expanded CTG repeats, we studied whether CAG-repeat ASOs may also affect this aspect of DM1. In human cells the instability of (CTG)(800) was suppressed by addition of CAG-repeat ASOs to the culture media. In mice that carry a DMPK transgene the somatic instability of (CTG)(800) was suppressed by direct injection of CAG-repeat ASOs into muscle tissue. These results raise the possibility that early intervention with ASOs to reduce RNA or protein toxicity may have the additional benefit of stabilizing CTG:CAG repeats at subpathogenic lengths.
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Hubert L, Lin Y, Dion V, Wilson JH. Xpa deficiency reduces CAG trinucleotide repeat instability in neuronal tissues in a mouse model of SCA1. Hum Mol Genet 2011; 20:4822-30. [PMID: 21926083 DOI: 10.1093/hmg/ddr421] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Expansion of trinucleotide repeats (TNRs) is responsible for a number of human neurodegenerative disorders. The molecular mechanisms that underlie TNR instability in humans are not clear. Based on results from model systems, several mechanisms for instability have been proposed, all of which focus on the ability of TNRs to form alternative structures during normal DNA transactions, including replication, DNA repair and transcription. These abnormal structures are thought to trigger changes in TNR length. We have previously shown that transcription-induced TNR instability in cultured human cells depends on several genes known to be involved in transcription-coupled nucleotide excision repair (NER). We hypothesized that NER normally functions to destabilize expanded TNRs. To test this hypothesis, we bred an Xpa null allele, which eliminates NER, into the TNR mouse model for spinocerebellar ataxia type 1 (SCA1), which carries an expanded CAG repeat tract at the endogenous mouse Sca1 locus. We find that Xpa deficiency does not substantially affect TNR instability in either the male or female germline; however, it dramatically reduces CAG repeat instability in neuronal tissues-striatum, hippocampus and cerebral cortex-but does not alter CAG instability in kidney or liver. The tissue-specific effect of Xpa deficiency represents a novel finding; it suggests that tissue-to-tissue variation in CAG repeat instability arises, in part, by different underlying mechanisms. These results validate our original findings in cultured human cells and suggest that transcription may induce NER-dependent TNR instability in neuronal tissues in humans.
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Affiliation(s)
- Leroy Hubert
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
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Topoisomerase 1 and single-strand break repair modulate transcription-induced CAG repeat contraction in human cells. Mol Cell Biol 2011; 31:3105-12. [PMID: 21628532 DOI: 10.1128/mcb.05158-11] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Expanded trinucleotide repeats are responsible for a number of neurodegenerative diseases, such as Huntington disease and myotonic dystrophy type 1. The mechanisms that underlie repeat instability in the germ line and in the somatic tissues of human patients are undefined. Using a selection assay based on contraction of CAG repeat tracts in human cells, we screened the Prestwick chemical library in a moderately high-throughput assay and identified 18 novel inducers of repeat contraction. A subset of these compounds targeted pathways involved in the management of DNA supercoiling associated with transcription. Further analyses using both small molecule inhibitors and small interfering RNA (siRNA)-mediated knockdowns demonstrated the involvement of topoisomerase 1 (TOP1), tyrosyl-DNA phosphodiesterase 1 (TDP1), and single-strand break repair (SSBR) in modulating transcription-dependent CAG repeat contractions. The TOP1-TDP1-SSBR pathway normally functions to suppress repeat instability, since interfering with it stimulated repeat contractions. We further showed that the increase in repeat contractions when the TOP1-TDP1-SSBR pathway is compromised arises via transcription-coupled nucleotide excision repair, a previously identified contributor to transcription-induced repeat instability. These studies broaden the scope of pathways involved in transcription-induced CAG repeat instability and begin to define their interrelationships.
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Sundararajan R, Freudenreich CH. Expanded CAG/CTG repeat DNA induces a checkpoint response that impacts cell proliferation in Saccharomyces cerevisiae. PLoS Genet 2011; 7:e1001339. [PMID: 21437275 PMCID: PMC3060079 DOI: 10.1371/journal.pgen.1001339] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Accepted: 02/15/2011] [Indexed: 11/18/2022] Open
Abstract
Repetitive DNA elements are mutational hotspots in the genome, and their instability is linked to various neurological disorders and cancers. Although it is known that expanded trinucleotide repeats can interfere with DNA replication and repair, the cellular response to these events has not been characterized. Here, we demonstrate that an expanded CAG/CTG repeat elicits a DNA damage checkpoint response in budding yeast. Using microcolony and single cell pedigree analysis, we found that cells carrying an expanded CAG repeat frequently experience protracted cell division cycles, persistent arrests, and morphological abnormalities. These phenotypes were further exacerbated by mutations in DSB repair pathways, including homologous recombination and end joining, implicating a DNA damage response. Cell cycle analysis confirmed repeat-dependent S phase delays and G2/M arrests. Furthermore, we demonstrate that the above phenotypes are due to the activation of the DNA damage checkpoint, since expanded CAG repeats induced the phosphorylation of the Rad53 checkpoint kinase in a rad52Δ recombination deficient mutant. Interestingly, cells mutated for the MRX complex (Mre11-Rad50-Xrs2), a central component of DSB repair which is required to repair breaks at CAG repeats, failed to elicit repeat-specific arrests, morphological defects, or Rad53 phosphorylation. We therefore conclude that damage at expanded CAG/CTG repeats is likely sensed by the MRX complex, leading to a checkpoint response. Finally, we show that repeat expansions preferentially occur in cells experiencing growth delays. Activation of DNA damage checkpoints in repeat-containing cells could contribute to the tissue degeneration observed in trinucleotide repeat expansion diseases. Expansion of a CAG/CTG trinucleotide repeat is the causative mutation for multiple neurodegenerative diseases, including Huntington's disease, myotonic dystrophy, and multiple types of spinocerebellar ataxias. Two reasons for the cell death that occurs in these diseases are toxicity of the repeat-containing RNA and of the polyglutamine-containing protein product. Although the expanded repeat can interfere with DNA replication and repair, it was not known whether the presence of the repeat within the DNA causes any additional cellular toxicity. In this study, we show that an expanded CAG/CTG tract placed within the chromosome of the model eukaryote, budding yeast, elicits a cellular response that interferes with cell growth and division. The effect is enhanced when DNA repair pathways, particularly double-strand break repair, are compromised. Moreover, cells experiencing an arrest were more likely to have undergone further repeat expansions. We show that the conserved MRX protein complex locates to the expanded repeat and is required to sense the damage and activate the DNA damage response. Our results suggest that DNA damage at expanded CAG/CTG repeats could contribute to both tissue degeneration and further repeat instability in affected individuals.
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Lin Y, Wilson JH. Transcription-induced DNA toxicity at trinucleotide repeats: double bubble is trouble. Cell Cycle 2011; 10:611-8. [PMID: 21293182 DOI: 10.4161/cc.10.4.14729] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Trinucleotide repeats (TNR) are a blessing and a curse. In coding regions, where they are enriched, short repeats offer the potential for continuous, rapid length variation with linked incremental changes in the activity of the encoded protein, a valuable source of variation for evolution. But at the upper end of these benign and beneficial lengths, trinucleotide repeats become very unstable, with a dangerous bias toward continual expansion, which can lead to neurological diseases in humans. The mechanisms of expansion are varied and the links to disease are complex. Where they have been delineated, however, they have often revealed unexpected, fundamental aspects of the underlying cell biology. Nowhere is this more apparent than in recent studies, which indicate that expanded CAG repeats can form toxic sites in the genome, which can, upon interaction with normal components of DNA metabolism, trigger cell death. Here we discuss the phenomenon of TNR-induced DNA toxicity, with special emphasis on the role of transcription. Transcription-induced DNA toxicity may have profound biological consequences, with particular relevance to repeat-associated neurodegenerative diseases.
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Affiliation(s)
- Yunfu Lin
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX USA.
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Nakamori M, Pearson CE, Thornton CA. Bidirectional transcription stimulates expansion and contraction of expanded (CTG)*(CAG) repeats. Hum Mol Genet 2010; 20:580-8. [PMID: 21088112 DOI: 10.1093/hmg/ddq501] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
More than 12 neurogenetic disorders are caused by unstable expansions of (CTG)•(CAG) repeats. The expanded repeats are unstable in germline and somatic cells, with potential consequences for disease severity. Previous studies have shown that contractions of (CAG)(95) are more frequent when the repeat tract is transcribed. Here we determined whether transcription can promote repeat expansion, using (CTG)•(CAG) repeat tracts in the size range that is typical for myotonic dystrophy type 1. We derived normal human fibroblasts having single-copy genomic integrations of 800 CTG repeats. The repeat tract showed modest instability when it was not transcribed, yielding an estimated mutation rate of 0.28% per generation. Instability was enhanced several-fold by transcription in the forward or reverse transcription, and 30-fold by bidirectional transcription, yielding many expansions and contractions of more than 200 repeats. These results suggest that convergent bidirectional transcription, which has been reported at several disease loci, could contribute to somatic instability of highly expanded (CTG)•(CAG) repeats.
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Affiliation(s)
- Masayuki Nakamori
- Department of Neurology, University of Rochester Medical Center, Rochester, NY 14642, USA
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Reddy K, Tam M, Bowater RP, Barber M, Tomlinson M, Nichol Edamura K, Wang YH, Pearson CE. Determinants of R-loop formation at convergent bidirectionally transcribed trinucleotide repeats. Nucleic Acids Res 2010; 39:1749-62. [PMID: 21051337 PMCID: PMC3061079 DOI: 10.1093/nar/gkq935] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
R-loops have been described at immunoglobulin class switch sequences, prokaryotic and mitochondrial replication origins, and disease-associated (CAG)n and (GAA)n trinucleotide repeats. The determinants of trinucleotide R-loop formation are unclear. Trinucleotide repeat expansions cause diseases including DM1 (CTG)n, SCA1 (CAG)n, FRAXA (CGG)n, FRAXE (CCG)n and FRDA (GAA)n. Bidirectional convergent transcription across these disease repeats can occur. We find R-loops formed when CTG or CGG and their complementary strands CAG or CCG were transcribed; GAA transcription, but not TTC, yielded R-loops. R-loop formation was sensitive to DNA supercoiling, repeat length, insensitive to repeat interruptions, and formed by extension of RNA:DNA hybrids in the RNA polymerase. R-loops arose by transcription in one direction followed by transcription in the opposite direction, and during simultaneous convergent bidirectional transcription of the same repeat forming double R-loop structures. Since each transcribed disease repeat formed R-loops suggests they may have biological functions.
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Affiliation(s)
- Kaalak Reddy
- Program of Genetics & Genome Biology, The Hospital for Sick Children, 101 College Street, East Tower, 15-312 TMDT, Toronto, Ontario M5G 1L7, Canada
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