1
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Li P, Gai X, Li Q, Yang Q, Yu X. DNA-PK participates in pre-rRNA biogenesis independent of DNA double-strand break repair. Nucleic Acids Res 2024; 52:6360-6375. [PMID: 38682589 PMCID: PMC11194077 DOI: 10.1093/nar/gkae316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 04/06/2024] [Accepted: 04/16/2024] [Indexed: 05/01/2024] Open
Abstract
Although DNA-PK inhibitors (DNA-PK-i) have been applied in clinical trials for cancer treatment, the biomarkers and mechanism of action of DNA-PK-i in tumor cell suppression remain unclear. Here, we observed that a low dose of DNA-PK-i and PARP inhibitor (PARP-i) synthetically suppresses BRCA-deficient tumor cells without inducing DNA double-strand breaks (DSBs). Instead, we found that a fraction of DNA-PK localized inside of nucleoli, where we did not observe obvious DSBs. Moreover, the Ku proteins recognize pre-rRNA that facilitates DNA-PKcs autophosphorylation independent of DNA damage. Ribosomal proteins are also phosphorylated by DNA-PK, which regulates pre-rRNA biogenesis. In addition, DNA-PK-i acts together with PARP-i to suppress pre-rRNA biogenesis and tumor cell growth. Collectively, our studies reveal a DNA damage repair-independent role of DNA-PK-i in tumor suppression.
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Affiliation(s)
- Peng Li
- Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang, China
- School of Life Sciences, Westlake University, Hangzhou, Zhejiang, China
- Institute of Basic Medical Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang, China
| | - Xiaochen Gai
- Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang, China
- School of Life Sciences, Westlake University, Hangzhou, Zhejiang, China
- Institute of Basic Medical Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang, China
| | - Qilin Li
- Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang, China
- School of Life Sciences, Westlake University, Hangzhou, Zhejiang, China
- Institute of Basic Medical Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang, China
| | - Qianqian Yang
- Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang, China
- School of Life Sciences, Westlake University, Hangzhou, Zhejiang, China
- Institute of Basic Medical Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang, China
| | - Xiaochun Yu
- Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang, China
- School of Life Sciences, Westlake University, Hangzhou, Zhejiang, China
- Institute of Basic Medical Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang, China
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2
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Sun H, Li X, Long Q, Wang X, Zhu W, Chen E, Zhou W, Yang H, Huang C, Deng W, Chen M. TERC promotes non-small cell lung cancer progression by facilitating the nuclear localization of TERT. iScience 2024; 27:109869. [PMID: 38799568 PMCID: PMC11126826 DOI: 10.1016/j.isci.2024.109869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Revised: 03/26/2024] [Accepted: 04/29/2024] [Indexed: 05/29/2024] Open
Abstract
The core of telomerase consists of the protein subunit telomerase reverse transcriptase (TERT) and the telomerase RNA component (TERC). So far, the role of TERC in cancer development has remained elusive. Here, we found TERC expression elevated in non-small cell lung cancer (NSCLC) tissues, which was associated with disease progression and poor prognosis in patients. Using NSCLC cell lines and xenograft models, we showed that knockdown of TERC caused cell cycle arrest, and inhibition of cell proliferation and migration. Mechanistically, TERC was exported to the cytoplasm by nuclear RNA export factor 1 (NXF1), where it mediated the interaction of TERT with other telomerase subunits. Depletion of TERC hindered the assembly and subsequent nuclear localization of the telomerase complex, preventing TERT from functioning in telomere maintenance and transcription regulation. Our findings suggest that TERC is a potential biomarker for NSCLC diagnosis and prognosis and can be a target for NSCLC treatment.
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Affiliation(s)
- Haohui Sun
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Xiaodi Li
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Qian Long
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
- Department of General Surgery, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China
| | - Xiaonan Wang
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Wancui Zhu
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Enni Chen
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Wenhao Zhou
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Han Yang
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Chuyang Huang
- Department of Urology, Shaoyang Central Hospital, University of South China, Shaoyang, Hunan 422000, China
| | - Wuguo Deng
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
| | - Miao Chen
- State Key Laboratory of Oncology in South China and Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong 510060, China
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3
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Bartle L, Wellinger RJ. Methods that shaped telomerase research. Biogerontology 2024; 25:249-263. [PMID: 37903970 PMCID: PMC10998806 DOI: 10.1007/s10522-023-10073-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Accepted: 09/30/2023] [Indexed: 11/01/2023]
Abstract
Telomerase, the ribonucleoprotein (RNP) responsible for telomere maintenance, has a complex life. Complex in that it is made of multiple proteins and an RNA, and complex because it undergoes many changes, and passes through different cell compartments. As such, many methods have been developed to discover telomerase components, delve deep into understanding its structure and function and to figure out how telomerase biology ultimately relates to human health and disease. While some old gold-standard methods are still key for determining telomere length and measuring telomerase activity, new technologies are providing promising new ways to gain detailed information that we have never had access to before. Therefore, we thought it timely to briefly review the methods that have revealed information about the telomerase RNP and outline some of the remaining questions that could be answered using new methodology.
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Affiliation(s)
- Louise Bartle
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Applied Cancer Research Pavilion, 3201 rue Jean-Mignault, Sherbrooke, QC, J1E 4K8, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Applied Cancer Research Pavilion, 3201 rue Jean-Mignault, Sherbrooke, QC, J1E 4K8, Canada.
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4
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Neumann H, Bartle L, Bonnell E, Wellinger RJ. Ratcheted transport and sequential assembly of the yeast telomerase RNP. Cell Rep 2023; 42:113565. [PMID: 38096049 DOI: 10.1016/j.celrep.2023.113565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Revised: 10/04/2023] [Accepted: 11/22/2023] [Indexed: 12/30/2023] Open
Abstract
The telomerase ribonucleoprotein particle (RNP) replenishes telomeric DNA and minimally requires an RNA component and a catalytic protein subunit. However, telomerase RNP maturation is an intricate process occurring in several subcellular compartments and is incompletely understood. Here, we report how the co-transcriptional association of key telomerase components and nuclear export factors leads to an export-competent, but inactive, RNP. Export is dependent on the 5' cap, the 3' extension of unprocessed telomerase RNA, and protein associations. When the RNP reaches the cytoplasm, an extensive protein swap occurs, the RNA is trimmed to its mature length, and the essential catalytic Est2 protein joins the RNP. This mature and active complex is then reimported into the nucleus as its final destination and last processing steps. The irreversible processing events on the RNA thus support a ratchet-type model of telomerase maturation, with only a single nucleo-cytoplasmic cycle that is essential for the assembly of mature telomerase.
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Affiliation(s)
- Hannah Neumann
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Louise Bartle
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada; Research Center on Aging (CdRV), 1036 rue Belvedere Sud, Sherbrooke, QC J1H 4C4, Canada
| | - Erin Bonnell
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada; Research Center on Aging (CdRV), 1036 rue Belvedere Sud, Sherbrooke, QC J1H 4C4, Canada.
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5
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Klump BM, Schmidt JC. Advances in understanding telomerase assembly. Biochem Soc Trans 2023; 51:2093-2101. [PMID: 38108475 PMCID: PMC10754283 DOI: 10.1042/bst20230269] [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: 09/05/2023] [Revised: 11/30/2023] [Accepted: 12/04/2023] [Indexed: 12/19/2023]
Abstract
Telomerase is a complex ribonucleoprotein scaffolded by the telomerase RNA (TR). Telomere lengthening by telomerase is essential to maintain the proliferative potential of stem cells and germ cells, and telomerase is inappropriately activated in the majority of cancers. Assembly of TR with its 12 protein co-factors and the maturation of the 5'- and 3'-ends of TR have been the focus of intense research efforts over the past two decades. High-resolution Cryo-EM structures of human telomerase, high-throughput sequencing of the 3' end of TR, and live cell imaging of various telomerase components have significantly advanced our understanding of the molecular mechanisms that govern telomerase biogenesis, yet many important questions remain unaddressed. In this review, we will summarize these recent advances and highlight the remaining key questions with the ultimate goal of targeting telomerase assembly to suppress telomere maintenance in cancer cells or to promote telomerase activity in patients affected by telomere shortening disorders.
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Affiliation(s)
- Basma M. Klump
- Institute for Quantitative Health Sciences and Engineering, Michigan State University, East Lansing, MI, U.S.A
- College of Osteopathic Medicine, Michigan State University, East Lansing, MI, U.S.A
- Cell and Molecular Biology Graduate Program, College of Natural Sciences, Michigan State University, East Lansing, MI, U.S.A
| | - Jens C. Schmidt
- Institute for Quantitative Health Sciences and Engineering, Michigan State University, East Lansing, MI, U.S.A
- Department of Obstetrics, Gynecology, and Reproductive Biology, Michigan State University, East Lansing, MI, U.S.A
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6
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Davati N, Ghorbani A. Discovery of long non-coding RNAs in Aspergillus flavus response to water activity, CO 2 concentration, and temperature changes. Sci Rep 2023; 13:10330. [PMID: 37365206 DOI: 10.1038/s41598-023-37236-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 06/19/2023] [Indexed: 06/28/2023] Open
Abstract
Although the role of long non-coding RNAs (lncRNAs) in key biological processes in animals and plants has been confirmed for decades, their identification in fungi remains limited. In this study, we discovered and characterized lncRNAs in Aspergillus flavus in response to changes in water activity, CO2 concentration, and temperature, and predicted their regulatory roles in cellular functions. A total of 472 lncRNAs were identified in the genome of A. flavus, consisting of 470 novel lncRNAs and 2 putative lncRNAs (EFT00053849670 and EFT00053849665). Our analysis of lncRNA expression revealed significant differential expression under stress conditions in A. flavus. Our findings indicate that lncRNAs in A. flavus, particularly down-regulated lncRNAs, may play pivotal regulatory roles in aflatoxin biosynthesis, respiratory activities, cellular survival, and metabolic maintenance under stress conditions. Additionally, we predicted that sense lncRNAs down-regulated by a temperature of 30 °C, osmotic stress, and CO2 concentration might indirectly regulate proline metabolism. Furthermore, subcellular localization analysis revealed that up-and down-regulated lncRNAs are frequently localized in the nucleus under stress conditions, particularly at a water activity of 0.91, while most up-regulated lncRNAs may be located in the cytoplasm under high CO2 concentration.
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Affiliation(s)
- Nafiseh Davati
- Department of Food Science and Technology, College of Food Industry, Bu-Ali Sina University, Hamedan, 65167-38695, Iran.
| | - Abozar Ghorbani
- Nuclear Agriculture Research School, Nuclear Science and Technology Research Institute (NSTRI), Karaj, Iran.
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7
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Post-Transcriptional and Post-Translational Modifications in Telomerase Biogenesis and Recruitment to Telomeres. Int J Mol Sci 2023; 24:ijms24055027. [PMID: 36902458 PMCID: PMC10003056 DOI: 10.3390/ijms24055027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Revised: 03/02/2023] [Accepted: 03/03/2023] [Indexed: 03/08/2023] Open
Abstract
Telomere length is associated with the proliferative potential of cells. Telomerase is an enzyme that elongates telomeres throughout the entire lifespan of an organism in stem cells, germ cells, and cells of constantly renewed tissues. It is activated during cellular division, including regeneration and immune responses. The biogenesis of telomerase components and their assembly and functional localization to the telomere is a complex system regulated at multiple levels, where each step must be tuned to the cellular requirements. Any defect in the function or localization of the components of the telomerase biogenesis and functional system will affect the maintenance of telomere length, which is critical to the processes of regeneration, immune response, embryonic development, and cancer progression. An understanding of the regulatory mechanisms of telomerase biogenesis and activity is necessary for the development of approaches toward manipulating telomerase to influence these processes. The present review focuses on the molecular mechanisms involved in the major steps of telomerase regulation and the role of post-transcriptional and post-translational modifications in telomerase biogenesis and function in yeast and vertebrates.
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8
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Pandey S, Hajikazemi M, Zacheja T, Schalbetter S, Baxter J, Guryev V, Hofmann A, Heermann DW, Juranek SA, Paeschke K. Telomerase subunit Est2 marks internal sites that are prone to accumulate DNA damage. BMC Biol 2021; 19:247. [PMID: 34801008 PMCID: PMC8605574 DOI: 10.1186/s12915-021-01167-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Accepted: 10/15/2021] [Indexed: 12/14/2022] Open
Abstract
Background The main function of telomerase is at the telomeres but under adverse conditions telomerase can bind to internal regions causing deleterious effects as observed in cancer cells. Results By mapping the global occupancy of the catalytic subunit of telomerase (Est2) in the budding yeast Saccharomyces cerevisiae, we reveal that it binds to multiple guanine-rich genomic loci, which we termed “non-telomeric binding sites” (NTBS). We characterize Est2 binding to NTBS. Contrary to telomeres, Est2 binds to NTBS in G1 and G2 phase independently of Est1 and Est3. The absence of Est1 and Est3 renders telomerase inactive at NTBS. However, upon global DNA damage, Est1 and Est3 join Est2 at NTBS and telomere addition can be observed indicating that Est2 occupancy marks NTBS regions as particular risks for genome stability. Conclusions Our results provide a novel model of telomerase regulation in the cell cycle using internal regions as “parking spots” of Est2 but marking them as hotspots for telomere addition. Supplementary Information The online version contains supplementary material available at 10.1186/s12915-021-01167-1.
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Affiliation(s)
- Satyaprakash Pandey
- University of Groningen, University Medical Center Groningen, European Research Institute for the Biology of Ageing, 9713 AV, Groningen, Netherlands
| | - Mona Hajikazemi
- Clinic of Internal Medicine III, Oncology, Hematology, Rheumatology and Clinical Immunology, University Hospital Bonn, Bonn, Germany
| | - Theresa Zacheja
- Clinic of Internal Medicine III, Oncology, Hematology, Rheumatology and Clinical Immunology, University Hospital Bonn, Bonn, Germany
| | | | - Jonathan Baxter
- Department of Life Science, University of Sussex, Brighton, UK
| | - Victor Guryev
- University of Groningen, University Medical Center Groningen, European Research Institute for the Biology of Ageing, 9713 AV, Groningen, Netherlands
| | - Andreas Hofmann
- Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 12, 69120, Heidelberg, Germany
| | - Dieter W Heermann
- Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 12, 69120, Heidelberg, Germany
| | - Stefan A Juranek
- Clinic of Internal Medicine III, Oncology, Hematology, Rheumatology and Clinical Immunology, University Hospital Bonn, Bonn, Germany.
| | - Katrin Paeschke
- University of Groningen, University Medical Center Groningen, European Research Institute for the Biology of Ageing, 9713 AV, Groningen, Netherlands. .,Clinic of Internal Medicine III, Oncology, Hematology, Rheumatology and Clinical Immunology, University Hospital Bonn, Bonn, Germany.
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9
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Hirsch AG, Becker D, Lamping JP, Krebber H. Unraveling the stepwise maturation of the yeast telomerase including a Cse1 and Mtr10 mediated quality control checkpoint. Sci Rep 2021; 11:22174. [PMID: 34773052 PMCID: PMC8590012 DOI: 10.1038/s41598-021-01599-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 10/29/2021] [Indexed: 01/17/2023] Open
Abstract
Telomerases elongate the ends of chromosomes required for cell immortality through their reverse transcriptase activity. By using the model organism Saccharomyces cerevisiae we defined the order in which the holoenzyme matures. First, a longer precursor of the telomerase RNA, TLC1 is transcribed and exported into the cytoplasm, where it associates with the protecting Sm-ring, the Est and the Pop proteins. This partly matured telomerase is re-imported into the nucleus via Mtr10 and a novel TLC1-import factor, the karyopherin Cse1. Remarkably, while mutations in all known transport factors result in short telomere ends, mutation in CSE1 leads to the amplification of Y′ elements in the terminal chromosome regions and thus elongated telomere ends. Cse1 does not only support TLC1 import, but also the Sm-ring stabilization on the RNA enableling Mtr10 contact and nuclear import. Thus, Sm-ring formation and import factor contact resembles a quality control step in the maturation process of the telomerase. The re-imported immature TLC1 is finally trimmed into the 1158 nucleotides long mature form via the nuclear exosome. TMG-capping of TLC1 finalizes maturation, leading to mature telomerase.
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Affiliation(s)
- Anna Greta Hirsch
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie Und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, Göttingen, Germany
| | - Daniel Becker
- Philipps-Universität Marburg, Klinik für Dermatologie Und Allergologie, Baldingerstraße, 35043, Marburg, Germany
| | - Jan-Philipp Lamping
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie Und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, Göttingen, Germany
| | - Heike Krebber
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie Und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, Göttingen, Germany.
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10
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Holland CL, Sanderson BA, Titus JK, Weis MF, Riojas AM, Malczewskyj E, Wasko BM, Lewis LK. Suppression of telomere capping defects of Saccharomyces cerevisiae yku70 and yku80 mutants by telomerase. G3-GENES GENOMES GENETICS 2021; 11:6395363. [PMID: 34718547 PMCID: PMC8664480 DOI: 10.1093/g3journal/jkab359] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 09/27/2021] [Indexed: 11/18/2022]
Abstract
The Ku complex performs multiple functions inside eukaryotic cells, including protection of chromosomal DNA ends from degradation and fusion events, recruitment of telomerase, and repair of double-strand breaks (DSBs). Inactivation of Ku complex genes YKU70 or YKU80 in cells of the yeast Saccharomyces cerevisiae gives rise to mutants that exhibit shortened telomeres and temperature-sensitive growth. In this study, we have investigated the mechanism by which overexpression of telomerase suppresses the temperature sensitivity of yku mutants. Viability of yku cells was restored by overexpression of the Est2 reverse transcriptase and TLC1 RNA template subunits of telomerase, but not the Est1 or Est3 proteins. Overexpression of other telomerase- and telomere-associated proteins (Cdc13, Stn1, Ten1, Rif1, Rif2, Sir3, and Sir4) did not suppress the growth defects of yku70 cells. Mechanistic features of suppression were assessed using several TLC1 RNA deletion derivatives and Est2 enzyme mutants. Supraphysiological levels of three catalytically inactive reverse transcriptase mutants (Est2-D530A, Est2-D670A, and Est2-D671A) suppressed the loss of viability as efficiently as the wild-type Est2 protein, without inducing cell senescence. Roles of proteins regulating telomere length were also determined. The results support a model in which chromosomes in yku mutants are stabilized via a replication-independent mechanism involving structural reinforcement of protective telomere cap structures.
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Affiliation(s)
- Cory L Holland
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Brian A Sanderson
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - James K Titus
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Monica F Weis
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Angelica M Riojas
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Eric Malczewskyj
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Brian M Wasko
- Department of Biology and Biotechnology, University of Houston-Clear Lake, Houston, TX, 77058, USA
| | - L Kevin Lewis
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
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11
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Fekete-Szücs E, Rosas Bringas FR, Stinus S, Chang M. Suppression of cdc13-2-associated senescence by pif1-m2 requires Ku-mediated telomerase recruitment. G3-GENES GENOMES GENETICS 2021; 12:6395364. [PMID: 34751785 PMCID: PMC8728030 DOI: 10.1093/g3journal/jkab360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Accepted: 10/08/2021] [Indexed: 11/17/2022]
Abstract
In Saccharomyces cerevisiae, recruitment of telomerase to telomeres requires an interaction between Cdc13, which binds single-stranded telomeric DNA, and the Est1 subunit of telomerase. A second pathway involving an interaction between the yKu complex and telomerase RNA (TLC1) contributes to telomerase recruitment but cannot sufficiently recruit telomerase on its own to prevent replicative senescence when the primary Cdc13-Est1 pathway is abolished—for example, in the cdc13-2 mutant. In this study, we find that mutation of PIF1, which encodes a helicase that inhibits telomerase, suppresses the replicative senescence of cdc13-2 by increasing reliance on the yKu-TLC1 pathway for telomerase recruitment. Our findings reveal new insight into telomerase-mediated telomere maintenance.
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Affiliation(s)
- Enikő Fekete-Szücs
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen 9713 AV, The Netherlands
| | - Fernando R Rosas Bringas
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen 9713 AV, The Netherlands
| | - Sonia Stinus
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen 9713 AV, The Netherlands
| | - Michael Chang
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen 9713 AV, The Netherlands
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12
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Maturation and shuttling of the yeast telomerase RNP: assembling something new using recycled parts. Curr Genet 2021; 68:3-14. [PMID: 34476547 PMCID: PMC8801399 DOI: 10.1007/s00294-021-01210-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 08/24/2021] [Accepted: 08/25/2021] [Indexed: 11/10/2022]
Abstract
As the limiting component of the budding yeast telomerase, the Tlc1 RNA must undergo multiple consecutive modifications and rigorous quality checks throughout its lifecycle. These steps will ensure that only correctly processed and matured molecules are assembled into telomerase complexes that subsequently act at telomeres. The complex pathway of Tlc1 RNA maturation, involving 5'- and 3'-end processing, stabilisation and assembly with the protein subunits, requires at least one nucleo-cytoplasmic passage. Furthermore, it appears that the pathway is tightly coordinated with the association of various and changing proteins, including the export factor Xpo1, the Mex67/Mtr2 complex, the Kap122 importin, the Sm7 ring and possibly the CBC and TREX-1 complexes. Although many of these maturation processes also affect other RNA species, the Tlc1 RNA exploits them in a new combination and, therefore, ultimately follows its own and unique pathway. In this review, we highlight recent new insights in maturation and subcellular shuttling of the budding yeast telomerase RNA and discuss how these events may be fine-tuned by the biochemical characteristics of the varying processing and transport factors as well as the final telomerase components. Finally, we indicate outstanding questions that we feel are important to be addressed for a complete understanding of the telomerase RNA lifecycle and that could have implications for the human telomerase as well.
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13
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Corda Y, Maestroni L, Luciano P, Najem MY, Géli V. Genome stability is guarded by yeast Rtt105 through multiple mechanisms. Genetics 2021; 217:6126811. [PMID: 33724421 DOI: 10.1093/genetics/iyaa035] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 02/03/2021] [Indexed: 12/15/2022] Open
Abstract
Ty1 mobile DNA element is the most abundant and mutagenic retrotransposon present in the genome of the budding yeast Saccharomyces cerevisiae. Protein regulator of Ty1 transposition 105 (Rtt105) associates with large subunit of RPA and facilitates its loading onto a single-stranded DNA at replication forks. Here, we dissect the role of RTT105 in the maintenance of genome stability under normal conditions and upon various replication stresses through multiple genetic analyses. RTT105 is essential for viability in cells experiencing replication problems and in cells lacking functional S-phase checkpoints and DNA repair pathways involving homologous recombination. Our genetic analyses also indicate that RTT105 is crucial when cohesion is affected and is required for the establishment of normal heterochromatic structures. Moreover, RTT105 plays a role in telomere maintenance as its function is important for the telomere elongation phenotype resulting from the Est1 tethering to telomeres. Genetic analyses indicate that rtt105Δ affects the growth of several rfa1 mutants but does not aggravate their telomere length defects. Analysis of the phenotypes of rtt105Δ cells expressing NLS-Rfa1 fusion protein reveals that RTT105 safeguards genome stability through its role in RPA nuclear import but also by directly affecting RPA function in genome stability maintenance during replication.
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Affiliation(s)
- Yves Corda
- CNRS UMR7258, INSERM U1068, Aix-Marseille Université UM105, Institut Paoli-Calmettes, CRCM, Marseille, France.,Equipe Labellisée Ligue Nationale Contre le Cancer, Paris, France
| | - Laetitia Maestroni
- CNRS UMR7258, INSERM U1068, Aix-Marseille Université UM105, Institut Paoli-Calmettes, CRCM, Marseille, France.,Equipe Labellisée Ligue Nationale Contre le Cancer, Paris, France
| | - Pierre Luciano
- CNRS UMR7258, INSERM U1068, Aix-Marseille Université UM105, Institut Paoli-Calmettes, CRCM, Marseille, France.,Equipe Labellisée Ligue Nationale Contre le Cancer, Paris, France
| | - Maria Y Najem
- CNRS UMR7258, INSERM U1068, Aix-Marseille Université UM105, Institut Paoli-Calmettes, CRCM, Marseille, France.,Equipe Labellisée Ligue Nationale Contre le Cancer, Paris, France
| | - Vincent Géli
- CNRS UMR7258, INSERM U1068, Aix-Marseille Université UM105, Institut Paoli-Calmettes, CRCM, Marseille, France.,Equipe Labellisée Ligue Nationale Contre le Cancer, Paris, France
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14
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Li J, Liu X, Yin Z, Hu Z, Zhang KQ. An Overview on Identification and Regulatory Mechanisms of Long Non-coding RNAs in Fungi. Front Microbiol 2021; 12:638617. [PMID: 33995298 PMCID: PMC8113380 DOI: 10.3389/fmicb.2021.638617] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 04/06/2021] [Indexed: 01/04/2023] Open
Abstract
For decades, more and more long non-coding RNAs (lncRNAs) have been confirmed to play important functions in key biological processes of different organisms. At present, most identified lncRNAs and those with known functional roles are from mammalian systems. However, lncRNAs have also been found in primitive eukaryotic fungi, and they have different functions in fungal development, metabolism, and pathogenicity. In this review, we highlight some recent researches on lncRNAs in the primitive eukaryotic fungi, particularly focusing on the identification of lncRNAs and their regulatory roles in diverse biological processes.
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Affiliation(s)
- Juan Li
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming, China
| | - Xiaoying Liu
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming, China
| | - Ziyu Yin
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming, China
| | - Zhihong Hu
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming, China
| | - Ke-Qin Zhang
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming, China
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15
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Abbasi S, Parmar G, Kelly RD, Balasuriya N, Schild-Poulter C. The Ku complex: recent advances and emerging roles outside of non-homologous end-joining. Cell Mol Life Sci 2021; 78:4589-4613. [PMID: 33855626 PMCID: PMC11071882 DOI: 10.1007/s00018-021-03801-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 01/29/2021] [Accepted: 02/24/2021] [Indexed: 12/15/2022]
Abstract
Since its discovery in 1981, the Ku complex has been extensively studied under multiple cellular contexts, with most work focusing on Ku in terms of its essential role in non-homologous end-joining (NHEJ). In this process, Ku is well-known as the DNA-binding subunit for DNA-PK, which is central to the NHEJ repair process. However, in addition to the extensive study of Ku's role in DNA repair, Ku has also been implicated in various other cellular processes including transcription, the DNA damage response, DNA replication, telomere maintenance, and has since been studied in multiple contexts, growing into a multidisciplinary point of research across various fields. Some advances have been driven by clarification of Ku's structure, including the original Ku crystal structure and the more recent Ku-DNA-PKcs crystallography, cryogenic electron microscopy (cryoEM) studies, and the identification of various post-translational modifications. Here, we focus on the advances made in understanding the Ku heterodimer outside of non-homologous end-joining, and across a variety of model organisms. We explore unique structural and functional aspects, detail Ku expression, conservation, and essentiality in different species, discuss the evidence for its involvement in a diverse range of cellular functions, highlight Ku protein interactions and recent work concerning Ku-binding motifs, and finally, we summarize the clinical Ku-related research to date.
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Affiliation(s)
- Sanna Abbasi
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Gursimran Parmar
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Rachel D Kelly
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Nileeka Balasuriya
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Caroline Schild-Poulter
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada.
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16
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Nostramo RT, Hopper AK. A novel assay provides insight into tRNAPhe retrograde nuclear import and re-export in S. cerevisiae. Nucleic Acids Res 2020; 48:11577-11588. [PMID: 33074312 PMCID: PMC7672469 DOI: 10.1093/nar/gkaa879] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Revised: 09/21/2020] [Accepted: 10/07/2020] [Indexed: 12/13/2022] Open
Abstract
In eukaryotes, tRNAs are transcribed in the nucleus and subsequently exported to the cytoplasm where they serve as essential adaptor molecules in translation. However, tRNAs can be returned to the nucleus by the evolutionarily conserved process called tRNA retrograde nuclear import, before relocalization back to the cytoplasm via a nuclear re-export step. Several important functions of these latter two trafficking events have been identified, yet the pathways are largely unknown. Therefore, we developed an assay in Saccharomyces cerevisiae to identify proteins mediating tRNA retrograde nuclear import and re-export using the unique wybutosine modification of mature tRNAPhe. Our hydrochloric acid/aniline assay revealed that the karyopherin Mtr10 mediates retrograde import of tRNAPhe, constitutively and in response to amino acid deprivation, whereas the Hsp70 protein Ssa2 mediates import specifically in the latter. Furthermore, tRNAPhe is re-exported by Crm1 and Mex67, but not by the canonical tRNA exporters Los1 or Msn5. These findings indicate that the re-export process occurs in a tRNA family-specific manner. Together, this assay provides insights into the pathways for tRNAPhe retrograde import and re-export and is a tool that can be used on a genome-wide level to identify additional gene products involved in these tRNA trafficking events.
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Affiliation(s)
- Regina T Nostramo
- Department of Molecular Genetics Center for RNA Biology The Ohio State University, Columbus, OH 43210, USA
| | - Anita K Hopper
- Department of Molecular Genetics Center for RNA Biology The Ohio State University, Columbus, OH 43210, USA
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17
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Vasianovich Y, Bajon E, Wellinger RJ. Telomerase biogenesis requires a novel Mex67 function and a cytoplasmic association with the Sm 7 complex. eLife 2020; 9:60000. [PMID: 33095156 PMCID: PMC7644208 DOI: 10.7554/elife.60000] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2020] [Accepted: 10/22/2020] [Indexed: 12/15/2022] Open
Abstract
The templating RNA is the core of the telomerase reverse transcriptase. In Saccharomyces cerevisiae, the complex life cycle and maturation of telomerase includes a cytoplasmic stage. However, timing and reason for this cytoplasmic passage are poorly understood. Here, we use inducible RNA tagging experiments to show that immediately after transcription, newly synthesized telomerase RNAs undergo one round of nucleo-cytoplasmic shuttling. Their export depends entirely on Crm1/Xpo1, whereas re-import is mediated by Kap122 plus redundant, kinetically less efficient import pathways. Strikingly, Mex67 is essential to stabilize newly transcribed RNA before Xpo1-mediated nuclear export. The results further show that the Sm7 complex associates with and stabilizes the telomerase RNA in the cytoplasm and promotes its nuclear re-import. Remarkably, after this cytoplasmic passage, the nuclear stability of telomerase RNA no longer depends on Mex67. These results underscore the utility of inducible RNA tagging and challenge current models of telomerase maturation.
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Affiliation(s)
- Yulia Vasianovich
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - Emmanuel Bajon
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
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18
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Liu J, Liu JP. A method for efficient quantitative analysis of genomic subtelomere Y' element abundance in yeasts. Yeast 2020; 37:373-388. [PMID: 32639041 DOI: 10.1002/yea.3511] [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] [Received: 04/01/2020] [Revised: 07/01/2020] [Accepted: 07/06/2020] [Indexed: 01/09/2023] Open
Abstract
Subtelomere Y' elements get amplified by homologous recombination in sustaining the survival and division of the budding yeast Saccharomyces cerevisiae. However, current method for measurement of the subtelomere structures uses Southern blotting with labelled specific probes, which is laborious and time-consuming. By multiple sequence alignment analysis of all 19 subtelomere Y' elements across the 13 chromosomes of the sequenced S288C strain deposited in the yeast genome SGD database, we identified 12 consensus and relative longer fragments and 14 pairs of unique primers for real-time quantitative PCR analysis. With a PAC2 or ACT1 located near the centromere of chromosome V and VI as internal controls, these primers were applied to real-time quantitative PCR analysis, so the relative Y' element intensity normalised to that of wild type (WT) cells was calculated for subtelomere Y' element copy numbers across all different chromosomes using the formula: 2^[-((CTmutant Y' - CTmutant control ) - (CTWT Y' - CTWT control ))]. This novel quantitative subtelomere amplification assay across chromosomes by real-time PCR proves to be a much simpler and more sensitive way than the traditional Southern blotting method to analyse the Y' element recombination events in survivors derived from telomerase deficiency or recruitment failure.
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Affiliation(s)
- Jun Liu
- Institute of Ageing Research, College of Medicine, Hangzhou Normal University, Hangzhou, China
| | - Jun-Ping Liu
- Institute of Ageing Research, College of Medicine, Hangzhou Normal University, Hangzhou, China
- Department of Immunology, Faculty of Medicine, Monash University, Prahran, Victoria, Australia
- Hudson Institute of Medical Research, Clayton, Victoria, Australia
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19
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Insights into the structure and function of Est3 from the Hansenula polymorpha telomerase. Sci Rep 2020; 10:11109. [PMID: 32632130 PMCID: PMC7338525 DOI: 10.1038/s41598-020-68107-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2019] [Accepted: 06/19/2020] [Indexed: 12/12/2022] Open
Abstract
Telomerase is a ribonucleoprotein enzyme, which maintains genome integrity in eukaryotes and ensures continuous cellular proliferation. Telomerase holoenzyme from the thermotolerant yeast Hansenula polymorpha, in addition to the catalytic subunit (TERT) and telomerase RNA (TER), contains accessory proteins Est1 and Est3, which are essential for in vivo telomerase function. Here we report the high-resolution structure of Est3 from Hansenula polymorpha (HpEst3) in solution, as well as the characterization of its functional relationships with other components of telomerase. The overall structure of HpEst3 is similar to that of Est3 from Saccharomyces cerevisiae and human TPP1. We have shown that telomerase activity in H. polymorpha relies on both Est3 and Est1 proteins in a functionally symmetrical manner. The absence of either Est3 or Est1 prevents formation of a stable ribonucleoprotein complex, weakens binding of a second protein to TER, and decreases the amount of cellular TERT, presumably due to the destabilization of telomerase RNP. NMR probing has shown no direct in vitro interactions of free Est3 either with the N-terminal domain of TERT or with DNA or RNA fragments mimicking the probable telomerase environment. Our findings corroborate the idea that telomerase possesses the evolutionarily variable functionality within the conservative structural context.
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20
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Garcia PD, Leach RW, Wadsworth GM, Choudhary K, Li H, Aviran S, Kim HD, Zakian VA. Stability and nuclear localization of yeast telomerase depend on protein components of RNase P/MRP. Nat Commun 2020; 11:2173. [PMID: 32358529 PMCID: PMC7195438 DOI: 10.1038/s41467-020-15875-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 03/27/2020] [Indexed: 01/17/2023] Open
Abstract
RNase P and MRP are highly conserved, multi-protein/RNA complexes with essential roles in processing ribosomal and tRNAs. Three proteins found in both complexes, Pop1, Pop6, and Pop7 are also telomerase-associated. Here, we determine how temperature sensitive POP1 and POP6 alleles affect yeast telomerase. At permissive temperatures, mutant Pop1/6 have little or no effect on cell growth, global protein levels, the abundance of Est1 and Est2 (telomerase proteins), and the processing of TLC1 (telomerase RNA). However, in pop mutants, TLC1 is more abundant, telomeres are short, and TLC1 accumulates in the cytoplasm. Although Est1/2 binding to TLC1 occurs at normal levels, Est1 (and hence Est3) binding is highly unstable. We propose that Pop-mediated stabilization of Est1 binding to TLC1 is a pre-requisite for formation and nuclear localization of the telomerase holoenzyme. Furthermore, Pop proteins affect TLC1 and the RNA subunits of RNase P/MRP in very different ways.
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Affiliation(s)
- P Daniela Garcia
- Department of Molecular Biology, Princeton University, Princeton, NJ, 08544, USA
| | - Robert W Leach
- Bioinformatics Group, Genomics Core Facility, Carl Icahn Laboratory, Princeton University, Princeton, New Jersey, 08544, USA
| | - Gable M Wadsworth
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia, 30332, USA
| | - Krishna Choudhary
- Department of Biomedical Engineering and Genome Center, University of California, Davis, California, 95616, USA
- Gladstone Institute of Data Science and Biotechnology, San Francisco, CA, 94158, USA
| | - Hua Li
- Department of Biomedical Engineering and Genome Center, University of California, Davis, California, 95616, USA
| | - Sharon Aviran
- Department of Biomedical Engineering and Genome Center, University of California, Davis, California, 95616, USA
| | - Harold D Kim
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia, 30332, USA
| | - Virginia A Zakian
- Department of Molecular Biology, Princeton University, Princeton, NJ, 08544, USA.
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21
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Lalonde M, Chartrand P. TERRA, a Multifaceted Regulator of Telomerase Activity at Telomeres. J Mol Biol 2020; 432:4232-4243. [PMID: 32084415 DOI: 10.1016/j.jmb.2020.02.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 02/06/2020] [Accepted: 02/10/2020] [Indexed: 02/07/2023]
Abstract
In eukaryotes, telomeres are repetitive sequences at the end of chromosomes, which are maintained in a constitutive heterochromatin state. It is now known that telomeres can be actively transcribed, leading to the production of a telomeric repeat-containing noncoding RNA called TERRA. Due to its sequence complementarity to the telomerase template, it was suggested early on that TERRA could be an inhibitor of telomerase. Since then, TERRA has been shown to be involved in heterochromatin formation at telomeres, to invade telomeric dsDNA and form R-loops, and even to promote telomerase recruitment at short telomeres. All these functions depend on the diverse capacities of this lncRNA to bind various cofactors, act as a scaffold, and promote higher-order complexes in cells. In this review, it will be highlighted as to how these properties of TERRA work together to regulate telomerase activity at telomeres.
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Affiliation(s)
- Maxime Lalonde
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Quebec, Canada
| | - Pascal Chartrand
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Quebec, Canada.
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22
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Sui J, Zhang S, Chen BPC. DNA-dependent protein kinase in telomere maintenance and protection. Cell Mol Biol Lett 2020; 25:2. [PMID: 31988640 PMCID: PMC6969447 DOI: 10.1186/s11658-020-0199-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 01/02/2020] [Indexed: 12/12/2022] Open
Abstract
This review focuses on DNA-dependent protein kinase (DNA-PK), which is the key regulator of canonical non-homologous end-joining (NHEJ), the predominant mechanism of DNA double-strand break (DSB) repair in mammals. DNA-PK consists of the DNA-binding Ku70/80 heterodimer and the catalytic subunit DNA-PKcs. They assemble at DNA ends, forming the active DNA-PK complex, which initiates NHEJ-mediated DSB repair. Paradoxically, both Ku and DNA-PKcs are associated with telomeres, and they play crucial roles in protecting the telomere against fusions. Herein, we discuss possible mechanisms and contributions of Ku and DNA-PKcs in telomere regulation.
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Affiliation(s)
- Jiangdong Sui
- 1Radiation Oncology Center, Chongqing University Cancer Hospital, Chongqing, 400030 China
| | - Shichuan Zhang
- 2Department of Radiation Oncology, Sichuan Cancer Hospital, Chengdu, China
| | - Benjamin P C Chen
- 3Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd., Dallas, TX 75390-9187 USA
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23
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Into the basket and beyond: the journey of mRNA through the nuclear pore complex. Biochem J 2020; 477:23-44. [DOI: 10.1042/bcj20190132] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 11/28/2019] [Accepted: 12/10/2019] [Indexed: 02/06/2023]
Abstract
The genetic information encoded in nuclear mRNA destined to reach the cytoplasm requires the interaction of the mRNA molecule with the nuclear pore complex (NPC) for the process of mRNA export. Numerous proteins have important roles in the transport of mRNA out of the nucleus. The NPC embedded in the nuclear envelope is the port of exit for mRNA and is composed of ∼30 unique proteins, nucleoporins, forming the distinct structures of the nuclear basket, the pore channel and cytoplasmic filaments. Together, they serve as a rather stationary complex engaged in mRNA export, while a variety of soluble protein factors dynamically assemble on the mRNA and mediate the interactions of the mRNA with the NPC. mRNA export factors are recruited to and dissociate from the mRNA at the site of transcription on the gene, during the journey through the nucleoplasm and at the nuclear pore at the final stages of export. In this review, we present the current knowledge derived from biochemical, molecular, structural and imaging studies, to develop a high-resolution picture of the many events that culminate in the successful passage of the mRNA out of the nucleus.
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24
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Lemon LD, Morris DK, Bertuch AA. Loss of Ku's DNA end binding activity affects telomere length via destabilizing telomere-bound Est1 rather than altering TLC1 homeostasis. Sci Rep 2019; 9:10607. [PMID: 31337791 PMCID: PMC6650470 DOI: 10.1038/s41598-019-46840-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Accepted: 07/05/2019] [Indexed: 11/21/2022] Open
Abstract
Saccharomyces cerevisiae telomerase, which maintains telomere length, is comprised of an RNA component, TLC1, the reverse transcriptase, Est2, and regulatory subunits, including Est1. The Yku70/Yku80 (Ku) heterodimer, a DNA end binding (DEB) protein, also contributes to telomere length maintenance. Ku binds TLC1 and telomere ends in a mutually exclusive fashion, and is required to maintain levels and nuclear localization of TLC1. Ku also interacts with Sir4, which localizes to telomeres. Here we sought to determine the role of Ku's DEB activity in telomere length maintenance by utilizing yku70-R456E mutant strains, in which Ku has reduced DEB and telomere association but proficiency in TLC1 and Sir4 binding, and TLC1 nuclear retention. Telomere lengths in a yku70-R456E strain were nearly as short as those in yku∆ strains and shorter than in strains lacking either Sir4, Ku:Sir4 interaction, or Ku:TLC1 interaction. TLC1 levels were decreased in the yku70-R456E mutant, yet overexpression of TLC1 failed to restore telomere length. Reduced DEB activity did not impact Est1's ability to associate with telomerase but did result in decreased association of Est1 with the telomere. These findings suggest Ku's DEB activity maintains telomere length homeostasis by preserving Est1's interaction at the telomere rather than altering TLC1 levels.
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Affiliation(s)
- Laramie D Lemon
- Graduate Program in Integrative Molecular and Biomedical Sciences, Baylor College of Medicine, Houston, TX, 77030, USA
- Department of Pediatrics, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Danna K Morris
- Department of Pediatrics, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Alison A Bertuch
- Graduate Program in Integrative Molecular and Biomedical Sciences, Baylor College of Medicine, Houston, TX, 77030, USA.
- Department of Pediatrics, Baylor College of Medicine, Houston, TX, 77030, USA.
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25
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Becker D, Hirsch AG, Bender L, Lingner T, Salinas G, Krebber H. Nuclear Pre-snRNA Export Is an Essential Quality Assurance Mechanism for Functional Spliceosomes. Cell Rep 2019; 27:3199-3214.e3. [PMID: 31189105 DOI: 10.1016/j.celrep.2019.05.031] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 04/03/2019] [Accepted: 05/09/2019] [Indexed: 02/05/2023] Open
Abstract
Removal of introns from pre-mRNAs is an essential step in eukaryotic gene expression, mediated by spliceosomes that contain snRNAs as key components. Although snRNAs are transcribed in the nucleus and function in the same compartment, all except U6 shuttle to the cytoplasm. Surprisingly, the physiological relevance for shuttling is unclear, in particular because the snRNAs in Saccharomyces cerevisiae were reported to remain nuclear. Here, we show that all yeast pre-snRNAs including U6 undergo a stepwise maturation process after nuclear export by Mex67 and Xpo1. Sm- and Lsm-ring attachment occurs in the cytoplasm and is important for the snRNA re-import, mediated by Cse1 and Mtr10. Finally, nuclear pre-snRNA cleavage and trimethylation of the 5'-cap finalizes shuttling. Importantly, preventing pre-snRNAs from being exported or processed results in faulty spliceosome assembly and subsequent genome-wide splicing defects. Thus, pre-snRNA export is obligatory for functional splicing and resembles an essential evolutionarily conserved quality assurance step.
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Affiliation(s)
- Daniel Becker
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, Göttingen, Germany
| | - Anna Greta Hirsch
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, Göttingen, Germany
| | - Lysann Bender
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, Göttingen, Germany
| | - Thomas Lingner
- Transkriptomanalyselabor, Institut für Entwicklungsbiochemie, Georg-August Universität Göttingen, Göttingen, Germany
| | - Gabriela Salinas
- Transkriptomanalyselabor, Institut für Entwicklungsbiochemie, Georg-August Universität Göttingen, Göttingen, Germany
| | - Heike Krebber
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, Göttingen, Germany.
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26
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Hopper AK, Nostramo RT. tRNA Processing and Subcellular Trafficking Proteins Multitask in Pathways for Other RNAs. Front Genet 2019; 10:96. [PMID: 30842788 PMCID: PMC6391926 DOI: 10.3389/fgene.2019.00096] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Accepted: 01/29/2019] [Indexed: 01/28/2023] Open
Abstract
This article focuses upon gene products that are involved in tRNA biology, with particular emphasis upon post-transcriptional RNA processing and nuclear-cytoplasmic subcellular trafficking. Rather than analyzing these proteins solely from a tRNA perspective, we explore the many overlapping functions of the processing enzymes and proteins involved in subcellular traffic. Remarkably, there are numerous examples of conserved gene products and RNP complexes involved in tRNA biology that multitask in a similar fashion in the production and/or subcellular trafficking of other RNAs, including small structured RNAs such as snRNA, snoRNA, 5S RNA, telomerase RNA, and SRP RNA as well as larger unstructured RNAs such as mRNAs and RNA-protein complexes such as ribosomes. Here, we provide examples of steps in tRNA biology that are shared with other RNAs including those catalyzed by enzymes functioning in 5' end-processing, pseudoU nucleoside modification, and intron splicing as well as steps regulated by proteins functioning in subcellular trafficking. Such multitasking highlights the clever mechanisms cells employ for maximizing their genomes.
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Affiliation(s)
- Anita K Hopper
- Department of Molecular Genetics, Center for RNA Biology, Ohio State University, Columbus, OH, United States
| | - Regina T Nostramo
- Department of Molecular Genetics, Center for RNA Biology, Ohio State University, Columbus, OH, United States
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27
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Viviescas MA, Cano MIN, Segatto M. Chaperones and Their Role in Telomerase Ribonucleoprotein Biogenesis and Telomere Maintenance. CURR PROTEOMICS 2018. [DOI: 10.2174/1570164615666180713103133] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Telomere length maintenance is important for genome stability and cell division. In most
eukaryotes, telomeres are maintained by the telomerase ribonucleoprotein (RNP) complex, minimally
composed of the Telomerase Reverse Transcriptase (TERT) and the telomerase RNA (TER) components.
In addition to TERT and TER, other protein subunits are part of the complex and are involved in
telomerase regulation, assembly, disassembly, and degradation. Among them are some molecular
chaperones such as Hsp90 and its co-chaperone p23 which are found associated with the telomerase
RNP complex in humans, yeast and probably in protozoa. Hsp90 and p23 are necessary for the telomerase
RNP assembly and enzyme activity. In budding yeast, the Hsp90 homolog (Hsp82) is also responsible
for the association and dissociation of telomerase from the telomeric DNA by its direct interaction
with a telomere end-binding protein (Cdc13), responsible for regulating telomerase access to telomeres.
In addition, AAA+ ATPases, such as Pontin and Reptin, which are also considered chaperone-
like proteins, associate with the human telomerase complex by the direct interaction of Pontin with
TERT and dyskerin. They are probably responsible for telomerase RNP assembly since their depletion
impairs the accumulation of the complex. Moreover, various RNA chaperones, are also pivotal in the
assembly and migration of the mature telomerase complex and complex intermediates. In this review,
we will focus on the importance of molecular chaperones for telomerase RNP biogenesis and how they
impact telomere length maintenance and cellular homeostasis.
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Affiliation(s)
- Maria Alejandra Viviescas
- Genetics Department, Biosciences Institute, Sao Paulo State University (UNESP), Botucatu, SP, Brazil
| | | | - Marcela Segatto
- Genetics Department, Biosciences Institute, Sao Paulo State University (UNESP), Botucatu, SP, Brazil
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Laterreur N, Lemieux B, Neumann H, Berger-Dancause JC, Lafontaine D, Wellinger RJ. The yeast telomerase module for telomere recruitment requires a specific RNA architecture. RNA (NEW YORK, N.Y.) 2018; 24:1067-1079. [PMID: 29777050 PMCID: PMC6049500 DOI: 10.1261/rna.066696.118] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 05/17/2018] [Indexed: 06/08/2023]
Abstract
Telomerases are ribonucleoprotein (RNP) reverse transcriptases. While telomerases maintain genome stability, their composition varies significantly between species. Yeast telomerase RNPs contain an RNA that is comparatively large, and its overall folding shows long helical segments with distal functional parts. Here we investigated the essential stem IVc module of the budding yeast telomerase RNA, called Tlc1. The distal part of stem IVc includes a conserved sequence element CS2a and structurally conserved features for binding Pop1/Pop6/Pop7 proteins, which together function analogously to the P3 domains of the RNase P/MRP RNPs. A more proximal bulged stem with the CS2 element is thought to associate with Est1, a telomerase protein required for telomerase recruitment to telomeres. Previous work found that changes in CS2a cause a loss of all stem IVc proteins, not just the Pop proteins. Here we show that the association of Est1 with stem IVc indeed requires both the proximal bulged stem and the P3 domain with the associated Pop proteins. Separating the P3 domain from the Est1 binding site by inserting only 2 base pairs into the helical stem between the two sites causes a complete loss of Est1 from the RNP and hence a telomerase-negative phenotype in vivo. Still, the distal P3 domain with the associated Pop proteins remains intact. Moreover, the P3 domain ensures Est2 stability on the RNP independently of Est1 association. Therefore, the Tlc1 stem IVc recruitment module of the RNA requires a very tight architectural organization for telomerase function in vivo.
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Affiliation(s)
- Nancy Laterreur
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, PRAC, Sherbrooke, Québec J1E 4K8, Canada
| | - Bruno Lemieux
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, PRAC, Sherbrooke, Québec J1E 4K8, Canada
| | - Hannah Neumann
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, PRAC, Sherbrooke, Québec J1E 4K8, Canada
| | | | - Daniel Lafontaine
- Department of Biology, Faculty of Sciences, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, PRAC, Sherbrooke, Québec J1E 4K8, Canada
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29
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Simoneau A, Ricard É, Wurtele H. An interplay between multiple sirtuins promotes completion of DNA replication in cells with short telomeres. PLoS Genet 2018; 14:e1007356. [PMID: 29659581 PMCID: PMC5919697 DOI: 10.1371/journal.pgen.1007356] [Citation(s) in RCA: 6] [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: 07/11/2017] [Revised: 04/26/2018] [Accepted: 04/09/2018] [Indexed: 01/08/2023] Open
Abstract
The evolutionarily-conserved sirtuin family of histone deacetylases regulates a multitude of DNA-associated processes. A recent genome-wide screen conducted in the yeast Saccharomyces cerevisiae identified Yku70/80, which regulate nonhomologous end-joining (NHEJ) and telomere structure, as being essential for cell proliferation in the presence of the pan-sirtuin inhibitor nicotinamide (NAM). Here, we show that sirtuin-dependent deacetylation of both histone H3 lysine 56 and H4 lysine 16 promotes growth of yku70Δ and yku80Δ cells, and that the NAM sensitivity of these mutants is not caused by defects in DNA double-strand break repair by NHEJ, but rather by their inability to maintain normal telomere length. Indeed, our results indicate that in the absence of sirtuin activity, cells with abnormally short telomeres, e.g., yku70/80Δ or est1/2Δ mutants, present striking defects in S phase progression. Our data further suggest that early firing of replication origins at short telomeres compromises the cellular response to NAM- and genotoxin-induced replicative stress. Finally, we show that reducing H4K16ac in yku70Δ cells limits activation of the DNA damage checkpoint kinase Rad53 in response to replicative stress, which promotes usage of translesion synthesis and S phase progression. Our results reveal a novel interplay between sirtuin-mediated regulation of chromatin structure and telomere-regulating factors in promoting timely completion of S phase upon replicative stress.
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Affiliation(s)
- Antoine Simoneau
- Centre de recherche de l’Hôpital Maisonneuve-Rosemont, boulevard de l’Assomption, Montréal, Canada
- Programme de Biologie Moléculaire, Université de Montréal, Montréal, Canada
| | - Étienne Ricard
- Centre de recherche de l’Hôpital Maisonneuve-Rosemont, boulevard de l’Assomption, Montréal, Canada
- Programme de Biologie Moléculaire, Université de Montréal, Montréal, Canada
| | - Hugo Wurtele
- Centre de recherche de l’Hôpital Maisonneuve-Rosemont, boulevard de l’Assomption, Montréal, Canada
- Département de Médecine, Université de Montréal, Montréal, Canada
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30
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Current Perspectives of Telomerase Structure and Function in Eukaryotes with Emerging Views on Telomerase in Human Parasites. Int J Mol Sci 2018; 19:ijms19020333. [PMID: 29364142 PMCID: PMC5855555 DOI: 10.3390/ijms19020333] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 01/10/2018] [Accepted: 01/17/2018] [Indexed: 12/11/2022] Open
Abstract
Replicative capacity of a cell is strongly correlated with telomere length regulation. Aberrant lengthening or reduction in the length of telomeres can lead to health anomalies, such as cancer or premature aging. Telomerase is a master regulator for maintaining replicative potential in most eukaryotic cells. It does so by controlling telomere length at chromosome ends. Akin to cancer cells, most single-cell eukaryotic pathogens are highly proliferative and require persistent telomerase activity to maintain constant length of telomere and propagation within their host. Although telomerase is key to unlimited cellular proliferation in both cases, not much was known about the role of telomerase in human parasites (malaria, Trypanosoma, etc.) until recently. Since telomerase regulation is mediated via its own structural components, interactions with catalytic reverse transcriptase and several factors that can recruit and assemble telomerase to telomeres in a cell cycle-dependent manner, we compare and discuss here recent findings in telomerase biology in cancer, aging and parasitic diseases to give a broader perspective of telomerase function in human diseases.
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31
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Cdc73 suppresses genome instability by mediating telomere homeostasis. PLoS Genet 2018; 14:e1007170. [PMID: 29320491 PMCID: PMC5779705 DOI: 10.1371/journal.pgen.1007170] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Revised: 01/23/2018] [Accepted: 12/25/2017] [Indexed: 12/18/2022] Open
Abstract
Defects in the genes encoding the Paf1 complex can cause increased genome instability. Loss of Paf1, Cdc73, and Ctr9, but not Rtf1 or Leo1, caused increased accumulation of gross chromosomal rearrangements (GCRs). Combining the cdc73Δ mutation with individual deletions of 43 other genes, including TEL1 and YKU80, which are involved in telomere maintenance, resulted in synergistic increases in GCR rates. Whole genome sequence analysis of GCRs indicated that there were reduced relative rates of GCRs mediated by de novo telomere additions and increased rates of translocations and inverted duplications in cdc73Δ single and double mutants. Analysis of telomere lengths and telomeric gene silencing in strains containing different combinations of cdc73Δ, tel1Δ and yku80Δ mutations suggested that combinations of these mutations caused increased defects in telomere maintenance. A deletion analysis of Cdc73 revealed that a central 105 amino acid region was necessary and sufficient for suppressing the defects observed in cdc73Δ strains; this region was required for the binding of Cdc73 to the Paf1 complex through Ctr9 and for nuclear localization of Cdc73. Taken together, these data suggest that the increased GCR rate of cdc73Δ single and double mutants is due to partial telomere dysfunction and that Ctr9 and Paf1 play a central role in the Paf1 complex potentially by scaffolding the Paf1 complex subunits or by mediating recruitment of the Paf1 complex to the different processes it functions in. Maintaining a stable genome is crucial for all organisms, and loss of genome stability has been linked to multiple human diseases, including many cancers. Previously we found that defects in Cdc73, a component of the Paf1 transcriptional elongation complex, give rise to increased genome instability. Here, we explored the mechanism underlying this instability and found that Cdc73 defects give rise to partial defects in maintaining telomeres, which are the specialized ends of chromosomes, and interact with other mutations causing telomere defects. Remarkably, Cdc73 function is mediated through a short central region of the protein that is not a part of previously identified protein domains but targets Cdc73 to the Paf1 complex through interaction with the Ctr9 subunit. Analysis of the other components of the Paf1 complex provides a model in which the Paf1 subunit mediates recruitment of the other subunits to different processes they function in. Together, these data suggest that the mutations in CDC73 and CTR9 found in patients with hyperparathyroidism-jaw tumor syndrome and some patients with Wilms tumors, respectively, may contribute to cancer progression by contributing to genome instability.
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32
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Chen H, Xue J, Churikov D, Hass EP, Shi S, Lemon LD, Luciano P, Bertuch AA, Zappulla DC, Géli V, Wu J, Lei M. Structural Insights into Yeast Telomerase Recruitment to Telomeres. Cell 2017; 172:331-343.e13. [PMID: 29290466 DOI: 10.1016/j.cell.2017.12.008] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 09/27/2017] [Accepted: 12/04/2017] [Indexed: 10/18/2022]
Abstract
Telomerase maintains chromosome ends from humans to yeasts. Recruitment of yeast telomerase to telomeres occurs through its Ku and Est1 subunits via independent interactions with telomerase RNA (TLC1) and telomeric proteins Sir4 and Cdc13, respectively. However, the structures of the molecules comprising these telomerase-recruiting pathways remain unknown. Here, we report crystal structures of the Ku heterodimer and Est1 complexed with their key binding partners. Two major findings are as follows: (1) Ku specifically binds to telomerase RNA in a distinct, yet related, manner to how it binds DNA; and (2) Est1 employs two separate pockets to bind distinct motifs of Cdc13. The N-terminal Cdc13-binding site of Est1 cooperates with the TLC1-Ku-Sir4 pathway for telomerase recruitment, whereas the C-terminal interface is dispensable for binding Est1 in vitro yet is nevertheless essential for telomere maintenance in vivo. Overall, our results integrate previous models and provide fundamentally valuable structural information regarding telomere biology.
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Affiliation(s)
- Hongwen Chen
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 201210 Shanghai, China
| | - Jing Xue
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 201210 Shanghai, China
| | - Dmitri Churikov
- Marseille Cancer Research Center (CRCM), U1068 INSERM, UMR7258 CNRS, Aix Marseille University, Institut Paoli-Calmettes (Equipe labellisée Ligue), 13009 Marseille, France
| | - Evan P Hass
- Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Shaohua Shi
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 201210 Shanghai, China
| | - Laramie D Lemon
- Department of Pediatrics, Baylor College of Medicine, One Baylor Plaza, BCM225, Houston, TX 77030, USA
| | - Pierre Luciano
- Marseille Cancer Research Center (CRCM), U1068 INSERM, UMR7258 CNRS, Aix Marseille University, Institut Paoli-Calmettes (Equipe labellisée Ligue), 13009 Marseille, France
| | - Alison A Bertuch
- Department of Pediatrics, Baylor College of Medicine, One Baylor Plaza, BCM225, Houston, TX 77030, USA
| | - David C Zappulla
- Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Vincent Géli
- Marseille Cancer Research Center (CRCM), U1068 INSERM, UMR7258 CNRS, Aix Marseille University, Institut Paoli-Calmettes (Equipe labellisée Ligue), 13009 Marseille, France
| | - Jian Wu
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 201210 Shanghai, China.
| | - Ming Lei
- Shanghai Institute of Precision Medicine, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China; Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, 200025 Shanghai, China.
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33
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Telomerase RNA Imaging in Budding Yeast and Human Cells by Fluorescent In Situ Hybridization. Methods Mol Biol 2017. [PMID: 29043638 DOI: 10.1007/978-1-4939-7306-4_27] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Telomerase, the enzyme that elongates telomeres in most eukaryotes, is a ribonucleoprotein complex composed of a reverse transcriptase catalytic subunit (TERT in human, Est2 in the budding yeast S. cerevisiae), regulatory factors and a noncoding RNA called hTERC (in human) or TLC1 (in budding yeast). Telomerase trafficking is a major process in the biogenesis and regulation of telomerase action at telomeres. Due to its higher signal-to-noise ratio, imaging of the telomerase RNA moiety is frequently used to determine telomerase intracellular localization. Here we describe how to image telomerase RNA in human and yeast cells using fluorescence in situ hybridization.
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34
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Ouenzar F, Lalonde M, Laprade H, Morin G, Gallardo F, Tremblay-Belzile S, Chartrand P. Cell cycle-dependent spatial segregation of telomerase from sites of DNA damage. J Cell Biol 2017. [PMID: 28637749 PMCID: PMC5551704 DOI: 10.1083/jcb.201610071] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Telomerase can generate a novel telomere at a DNA break, with potentially lethal consequences for the cell. Ouenzar et al. reveal novel roles for Pif1, Rad52, and Siz1-dependent sumoylation in the spatial exclusion of telomerase from sites of DNA repair during the cell cycle. Telomerase can generate a novel telomere at DNA double-strand breaks (DSBs), an event called de novo telomere addition. How this activity is suppressed remains unclear. Combining single-molecule imaging and deep sequencing, we show that the budding yeast telomerase RNA (TLC1 RNA) is spatially segregated to the nucleolus and excluded from sites of DNA repair in a cell cycle–dependent manner. Although TLC1 RNA accumulates in the nucleoplasm in G1/S, Pif1 activity promotes TLC1 RNA localization in the nucleolus in G2/M. In the presence of DSBs, TLC1 RNA remains nucleolar in most G2/M cells but accumulates in the nucleoplasm and colocalizes with DSBs in rad52Δ cells, leading to de novo telomere additions. Nucleoplasmic accumulation of TLC1 RNA depends on Cdc13 localization at DSBs and on the SUMO ligase Siz1, which is required for de novo telomere addition in rad52Δ cells. This study reveals novel roles for Pif1, Rad52, and Siz1-dependent sumoylation in the spatial exclusion of telomerase from sites of DNA repair.
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Affiliation(s)
- Faissal Ouenzar
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Quebec, Canada
| | - Maxime Lalonde
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Quebec, Canada
| | - Hadrien Laprade
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Quebec, Canada
| | - Geneviève Morin
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Quebec, Canada
| | - Franck Gallardo
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Quebec, Canada
| | - Samuel Tremblay-Belzile
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Quebec, Canada
| | - Pascal Chartrand
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Quebec, Canada
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35
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Vasianovich Y, Wellinger RJ. Life and Death of Yeast Telomerase RNA. J Mol Biol 2017; 429:3242-3254. [PMID: 28115201 DOI: 10.1016/j.jmb.2017.01.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Revised: 01/10/2017] [Accepted: 01/14/2017] [Indexed: 12/20/2022]
Abstract
Telomerase reverse transcriptase elongates telomeres to overcome their natural attrition and allow unlimited cellular proliferation, a characteristic shared by stem cells and the majority of malignant cancerous cells. The telomerase holoenzyme comprises a core RNA molecule, a catalytic protein subunit, and other accessory proteins. Malfunction of certain telomerase components can cause serious genetic disorders including dyskeratosis congenita and aplastic anaemia. A hierarchy of tightly regulated steps constitutes the process of telomerase biogenesis, which, if interrupted or misregulated, can impede the production of a functional enzyme and severely affect telomere maintenance. Here, we take a closer look at the budding yeast telomerase RNA component, TLC1, in its long lifetime journey around the cell. We review the extensive knowledge on TLC1 transcription and processing. We focus on exciting recent studies on telomerase assembly, trafficking, and nuclear dynamics, which for the first time unveil striking similarities between the yeast and human telomerase ribonucleoproteins. Finally, we identify questions yet to be answered and new directions to be followed, which, in the future, might improve our knowledge of telomerase biology and trigger the development of new therapies against cancer and other telomerase-related diseases.
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Affiliation(s)
- Yulia Vasianovich
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Applied Cancer Research Pavillion, 3201 rue Jean-Mignault, Sherbrooke, Quebec, J1E 4K8, Canada.
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Applied Cancer Research Pavillion, 3201 rue Jean-Mignault, Sherbrooke, Quebec, J1E 4K8, Canada.
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36
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Larcher MV, Pasquier E, MacDonald RS, Wellinger RJ. Ku Binding on Telomeres Occurs at Sites Distal from the Physical Chromosome Ends. PLoS Genet 2016; 12:e1006479. [PMID: 27930670 PMCID: PMC5145143 DOI: 10.1371/journal.pgen.1006479] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Accepted: 11/14/2016] [Indexed: 01/28/2023] Open
Abstract
The Ku complex binds non-specifically to DNA breaks and ensures repair via NHEJ. However, Ku is also known to bind directly to telomeric DNA ends and its presence there is associated with telomere capping, but avoiding NHEJ. How the complex discriminates between a DNA break and a telomeric extremity remains unknown. Our results using a tagged Ku complex, or a chromosome end capturing method, in budding yeast show that yKu association with telomeres can occur at sites distant from the physical end, on sub-telomeric elements, as well as on interstitial telomeric repeats. Consistent with previous studies, our results also show that yKu associates with telomeres in two distinct and independent ways: either via protein-protein interactions between Yku80 and Sir4 or via direct DNA binding. Importantly, yKu associates with the new sites reported here via both modes. Therefore, in sir4Δ cells, telomere bound yKu molecules must have loaded from a DNA-end near the transition of non-telomeric to telomeric repeat sequences. Such ends may have been one sided DNA breaks that occur as a consequence of stalled replication forks on or near telomeric repeat DNA. Altogether, the results predict a new model for yKu function at telomeres that involves yKu binding at one-sided DNA breaks caused by replication stalling. On telomere proximal chromatin, this binding is not followed by initiation of non-homologous end-joining, but rather by break-induced replication or repeat elongation by telomerase. After repair, the yKu-distal portion of telomeres is bound by Rap1, which in turn reduces the potential for yKu to mediate NHEJ. These results thus propose a solution to a long-standing conundrum, namely how to accommodate the apparently conflicting functions of Ku on telomeres. The Ku complex binds to and mediates the rejoining of two DNA ends that were generated by a double-stranded DNA break in the genome. However, Ku is known to be present at telomeres as well. If it would induce end-to-end joining there, it would create chromosome end-fusions that inevitably will lead to gross chromosome rearrangements and genome instability, common hallmarks for cancer initiation. Our results here show that Ku actually is associated with sites on telomeric regions that are distant from the physical ends of the chromosomes. We propose that this association serves to rescue DNA replication that has difficulty passing through telomeric chromatin. If so called one-sided breaks occur near or in telomeric repeats, they will generate critically short telomeres that need to be elongated. The binding of Ku may thus either facilitate the establishment of a specialized end-copying mechanism, called break induced replication or aid in recruiting telomerase to the short ends. These findings thus propose ways to potential solutions for the major conceptual problem that arose with the finding that Ku is associated with telomeres.
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Affiliation(s)
- Mélanie V. Larcher
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - Emeline Pasquier
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - R. Stephen MacDonald
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - Raymund J. Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
- * E-mail:
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37
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Laprade H, Lalonde M, Guérit D, Chartrand P. Live-cell imaging of budding yeast telomerase RNA and TERRA. Methods 2016; 114:46-53. [PMID: 27474163 DOI: 10.1016/j.ymeth.2016.07.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 07/11/2016] [Accepted: 07/23/2016] [Indexed: 02/02/2023] Open
Abstract
In most eukaryotes, the ribonucleoprotein complex telomerase is responsible for maintaining telomere length. In recent years, single-cell microscopy techniques such as fluorescent in situ hybridization and live-cell imaging have been developed to image the RNA subunit of the telomerase holoenzyme. These techniques are now becoming important tools for the study of telomerase biogenesis, its association with telomeres and its regulation. Here, we present detailed protocols for live-cell imaging of the Saccharomyces cerevisiae telomerase RNA subunit, called TLC1, and also of the non-coding telomeric repeat-containing RNA TERRA. We describe the approach used for genomic integration of MS2 stem-loops in these transcripts, and provide information for optimal live-cell imaging of these non-coding RNAs.
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Affiliation(s)
- Hadrien Laprade
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Qc H3C 3J7, Canada
| | - Maxime Lalonde
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Qc H3C 3J7, Canada
| | - David Guérit
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Qc H3C 3J7, Canada
| | - Pascal Chartrand
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Qc H3C 3J7, Canada.
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38
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Matsuguchi T, Blackburn E. The yeast telomerase RNA, TLC1, participates in two distinct modes of TLC1-TLC1 association processes in vivo. PeerJ 2016; 4:e1534. [PMID: 27004145 PMCID: PMC4800423 DOI: 10.7717/peerj.1534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Accepted: 12/04/2015] [Indexed: 11/23/2022] Open
Abstract
Telomerase core enzyme minimally consists of the telomerase reverse transcriptase domain-containing protein (Est2 in budding yeast S. cerevisiae) and telomerase RNA, which contains the template specifying the telomeric repeat sequence synthesized. Here we report that in vivo, a fraction of S. cerevisiae telomerase RNA (TLC1) molecules form complexes containing at least two molecules of TLC1, via two separable modes: one requiring a sequence in the 3′ region of the immature TLC1 precursor and the other requiring Ku and Sir4. Such physical TLC1-TLC1 association peaked in G1 phase and did not require telomere silencing, telomere tethering to the nuclear periphery, telomerase holoenzyme assembly, or detectable Est2-Est2 protein association. These data indicate that TLC1-TLC1 associations reflect processes occurring during telomerase biogenesis; we propose that TLC1-TLC1 associations and subsequent reorganization may be regulatory steps in telomerase enzymatic activation.
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Affiliation(s)
- Tet Matsuguchi
- Department of Biochemistry and Biophysics, University of California , San Francisco, CA , United States
| | - Elizabeth Blackburn
- Department of Biochemistry and Biophysics, University of California , San Francisco, CA , United States
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39
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Inhibition of telomerase RNA decay rescues telomerase deficiency caused by dyskerin or PARN defects. Nat Struct Mol Biol 2016; 23:286-92. [PMID: 26950371 PMCID: PMC4830462 DOI: 10.1038/nsmb.3184] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Accepted: 02/05/2016] [Indexed: 01/20/2023]
Abstract
Mutations in the human telomerase RNA component (hTR), the telomerase ribonucleoprotein component dyskerin (DKC1) and the poly(A) RNase (PARN) can lead to reduced levels of hTR and to dyskeratosis congenita (DC). However, the enzymes and mechanisms responsible for hTR degradation are unknown. We demonstrate that defects in dyskerin binding lead to hTR degradation by PAPD5-mediated oligoadenylation, which promotes 3'-to-5' degradation by EXOSC10, as well as decapping and 5'-to-3' decay by the cytoplasmic DCP2 and XRN1 enzymes. PARN increased hTR levels by deadenylating hTR, thereby limiting its degradation by EXOSC10. Telomerase activity and proper hTR localization in dyskerin- or PARN-deficient cells were rescued by knockdown of DCP2 and/or EXOSC10. Prevention of hTR RNA decay also led to a rescue of localization of DC-associated hTR mutants. These results suggest that inhibition of RNA decay pathways might be a useful therapy for some telomere pathologies.
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Abstract
Fluorescence microscopy can be used to assess the dynamic localization and intensity of single entities
in vitro or in living cells. It has been applied with aplomb to many different cellular processes and has significantly enlightened our understanding of the heterogeneity and complexity of biological systems. Recently, high-resolution fluorescence microscopy has been brought to bear on telomeres, leading to new insights into telomere spatial organization and accessibility, and into the mechanistic nuances of telomere elongation. We provide a snapshot of some of these recent advances with a focus on mammalian systems, and show how three-dimensional, time-lapse microscopy and single-molecule fluorescence shine a new light on the end of the chromosome.
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Affiliation(s)
- Yahya Benslimane
- Department of Molecular Biology, University of Montreal, Institute for Research in Immunology and Cancer, Montreal, Quebec, Canada
| | - Lea Harrington
- Department of Molecular Biology, University of Montreal, Institute for Research in Immunology and Cancer, Montreal, Quebec, Canada; Department of Biochemistry, University of Montreal, Institute for Research in Immunology and Cancer, Montreal, Quebec, Canada; Department of Medicine, University of Montreal, Institute for Research in Immunology and Cancer, Montreal, Quebec, Canada
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Rubtsova M, Vasilkova D, Naraykina Y, Dontsova O. Peculiarities of Yeasts and Human Telomerase RNAs Processing. Acta Naturae 2016; 8:14-22. [PMID: 28050263 PMCID: PMC5199203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
Abstract
Telomerase is one of the major components of the telomeres -- linear eukaryotic chromosome ends - maintenance system. Linear chromosomes are shortened during each cell division due to the removal of the primer used for DNA replication. Special repeated telomere sequences at the very ends of linear chromosomes prevent the deletion of genome information caused by primer removal. Telomeres are shortened at each replication round until it becomes critically short and is no longer able to protect the chromosome in somatic cells. At this stage, a cell undergoes a crisis and usually dies. Rare cases result in telomerase activation, and the cell gains unlimited proliferative capacity. Special types of cells, such as stem, germ, embryonic cells and cells from tissues with a high proliferative potential, maintain their telomerase activity indefinitely. The telomerase is inactive in the majority of somatic cells. Telomerase activity in vitro requires two key components: telomerase reverse transcriptase and telomerase RNA. In cancer cells, telomerase reactivates due to the expression of the reverse transcriptase gene. Telomerase RNA expresses constitutively in the majority of human cells. This fact suggests that there are alternative functions to telomerase RNA that are unknown at the moment. In this manuscript, we review the biogenesis of yeasts and human telomerase RNAs thanks to breakthroughs achieved in research on telomerase RNA processing by different yeasts species and humans in the last several years.
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Affiliation(s)
- M.P. Rubtsova
- Lomonosov Moscow State University, Chemistry Department, Leninskie gory, 1, bld. 3, Moscow, 119991 , Russia ,Lomonosov Moscow State University, Belozersky Institute of physico-chemical biology, Leninskie gory, 1, bld. 40, Moscow, 119991, Russia
| | - D.P. Vasilkova
- Lomonosov Moscow State University, Chemistry Department, Leninskie gory, 1, bld. 3, Moscow, 119991 , Russia
| | - Yu.V. Naraykina
- Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, bld. 3, Moscow, 143026 , Russia
| | - O.A. Dontsova
- Lomonosov Moscow State University, Chemistry Department, Leninskie gory, 1, bld. 3, Moscow, 119991 , Russia ,Lomonosov Moscow State University, Belozersky Institute of physico-chemical biology, Leninskie gory, 1, bld. 40, Moscow, 119991, Russia ,Lomonosov Moscow State University, Faculty of bioengineering and bioinformatics, Leninskie gory, 1, bld. 73, Moscow, 119991, Russia
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Sloan KE, Gleizes PE, Bohnsack MT. Nucleocytoplasmic Transport of RNAs and RNA-Protein Complexes. J Mol Biol 2015; 428:2040-59. [PMID: 26434509 DOI: 10.1016/j.jmb.2015.09.023] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 09/26/2015] [Accepted: 09/28/2015] [Indexed: 12/15/2022]
Abstract
RNAs and ribonucleoprotein complexes (RNPs) play key roles in mediating and regulating gene expression. In eukaryotes, most RNAs are transcribed, processed and assembled with proteins in the nucleus and then either function in the cytoplasm or also undergo a cytoplasmic phase in their biogenesis. This compartmentalization ensures that sequential steps in gene expression and RNP production are performed in the correct order and it allows important quality control mechanisms that prevent the involvement of aberrant RNAs/RNPs in these cellular pathways. The selective exchange of RNAs/RNPs between the nucleus and cytoplasm is enabled by nuclear pore complexes, which function as gateways between these compartments. RNA/RNP transport is facilitated by a range of nuclear transport receptors and adaptors, which are specifically recruited to their cargos and mediate interactions with nucleoporins to allow directional translocation through nuclear pore complexes. While some transport factors are only responsible for the export/import of a certain class of RNA/RNP, others are multifunctional and, in the case of large RNPs, several export factors appear to work together to bring about export. Recent structural studies have revealed aspects of the mechanisms employed by transport receptors to enable specific cargo recognition, and genome-wide approaches have provided the first insights into the diverse composition of pre-mRNPs during export. Furthermore, the regulation of RNA/RNP export is emerging as an important means to modulate gene expression under stress conditions and in disease.
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Affiliation(s)
- Katherine E Sloan
- Institute for Molecular Biology, Goettingen University Medical Department, 37073 Goettingen, Germany
| | - Pierre-Emmanuel Gleizes
- Laboratoire de Biologie Moléculaire Eucaryote, UMR 5099, Université de Toulouse-Paul Sabatier, CNRS, Toulouse, France
| | - Markus T Bohnsack
- Institute for Molecular Biology, Goettingen University Medical Department, 37073 Goettingen, Germany; Goettingen Centre for Molecular Biosciences, Georg-August-University, 37075 Goettingen, Germany.
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43
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Abstract
In this review, Schmidt and Cech cover human telomerase biogenesis, trafficking, and activation, comparing key aspects with the analogous events in other species. Telomerase is the ribonucleoprotein enzyme that catalyzes the extension of telomeric DNA in eukaryotes. Recent work has begun to reveal key aspects of the assembly of the human telomerase complex, its intracellular trafficking involving Cajal bodies, and its recruitment to telomeres. Once telomerase has been recruited to the telomere, it appears to undergo a separate activation step, which may include an increase in its repeat addition processivity. This review covers human telomerase biogenesis, trafficking, and activation, comparing key aspects with the analogous events in other species.
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Affiliation(s)
- Jens C Schmidt
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Thomas R Cech
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado Boulder, Boulder, Colorado 80309, USA
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Hass EP, Zappulla DC. The Ku subunit of telomerase binds Sir4 to recruit telomerase to lengthen telomeres in S. cerevisiae. eLife 2015. [PMID: 26218225 PMCID: PMC4547093 DOI: 10.7554/elife.07750] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
In Saccharomyces cerevisiae and in humans, the telomerase RNA subunit is bound by Ku, a ring-shaped protein heterodimer best known for its function in DNA repair. Ku binding to yeast telomerase RNA promotes telomere lengthening and telomerase recruitment to telomeres, but how this is achieved remains unknown. Using telomere-length analysis and chromatin immunoprecipitation, we show that Sir4 – a previously identified Ku-binding protein that is a component of telomeric silent chromatin – is required for Ku-mediated telomere lengthening and telomerase recruitment. We also find that specifically tethering Sir4 directly to Ku-binding-defective telomerase RNA restores otherwise-shortened telomeres to wild-type length. These findings suggest that Sir4 is the telomere-bound target of Ku-mediated telomerase recruitment and provide one mechanism for how the Sir4-competing Rif1 and Rif2 proteins negatively regulate telomere length in yeast. DOI:http://dx.doi.org/10.7554/eLife.07750.001 Inside a cell's nucleus, DNA is packaged into structures called chromosomes. The ends of every chromosome are capped by repeating sequences of DNA known as telomeres, which protect the chromosomes from damage. Every time a cell divides, the telomeres shorten. If telomere length falls below a critical level, the cell can die or enter a state in which it can no longer divide. During cell division, an enzyme called telomerase normally restores telomeres to their original length. Telomerase is made up of several proteins and an RNA molecule. In yeast and humans, a protein called Ku is one part of the telomerase enzyme. Ku binds to the RNA subunit of telomerase and helps the enzyme find and interact with the telomeres. Previous research has shown that Ku is unable to work alone to recruit telomerase to the chromosome. A protein called Sir4 binds to telomeres and cells lacking it have short telomeres, but the reason behind this was not known. Hass and Zappulla confirmed previous reports that Ku binds to Sir4 using a biochemical approach. Additional experiments provided genetic evidence that this binding interaction is important for telomerase to lengthen telomeres appropriately. Cells in which the RNA subunit of telomerase is unable to bind effectively to Ku have short telomeres. Hass and Zappulla directly tethered Sir4 to this defective RNA and found this restored the shortened telomeres to a normal length, indicating that Sir4 normally binds Ku to recruit telomerase. Discovering this mode of recruitment also helps to explain how two other telomeric proteins (Rif1 and 2) limit telomere lengthening; they compete with Ku-Sir4 recruitment to form a length-regulating system. Taken together, Hass and Zappulla's results provide strong evidence that Sir4 cooperates with Ku to control the lengthening of chromosome ends. Future research will hopefully reveal the precise space and time requirements for this telomerase-controlling system in yeast. Additionally, because Ku has been reported to be a subunit of human telomerase, future studies could also explore whether human cells use a similar strategy. DOI:http://dx.doi.org/10.7554/eLife.07750.002
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Affiliation(s)
- Evan P Hass
- Department of Biology, Johns Hopkins University, Baltimore, United States
| | - David C Zappulla
- Department of Biology, Johns Hopkins University, Baltimore, United States
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45
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Bajon E, Laterreur N, Wellinger RJ. A Single Templating RNA in Yeast Telomerase. Cell Rep 2015; 12:441-8. [PMID: 26166570 DOI: 10.1016/j.celrep.2015.06.045] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 06/04/2015] [Accepted: 06/13/2015] [Indexed: 12/31/2022] Open
Abstract
The number of essential telomerase components in the active ribonucleoprotein (RNP) has important implications for its mechanism of action yet is by and large unknown. We report that two differentially tagged TLC1 RNAs endogenously expressed in a heterozygous diploid and simultaneously detected via multi-color fluorescence in situ hybridization (FISH) experiments do not co-localize. Probabilistic calculations combined with direct quantification of FISH signals demonstrate that the TLC1 RNA indeed occurs as a single molecule in these RNPs. In addition, two differentially tagged reverse-transcriptase subunits could not be co-immunoprecipitated. These results therefore show that, in yeast cells, telomerase is assembled and matured and occurs as a monomer when not on telomeres. Finally, combining these findings with previous evidence leads us to propose that the enzyme also acts as a monomer when elongating telomeres.
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Affiliation(s)
- Emmanuel Bajon
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, 3201, rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Nancy Laterreur
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, 3201, rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, 3201, rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada.
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46
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Marcomini I, Gasser SM. Nuclear organization in DNA end processing: Telomeres vs double-strand breaks. DNA Repair (Amst) 2015; 32:134-140. [PMID: 26004856 DOI: 10.1016/j.dnarep.2015.04.024] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Many proteins ligands are shared between double-strand breaks and natural chromosomal ends or telomeres. The structural similarity of the 3' overhang, and the efficiency of cellular DNA end degradation machineries, highlight the need for mechanisms that resect selectively to promote or restrict recombination events. Here we examine the means used by eukaryotic cells to suppress resection at telomeres, target telomerase to short telomeres, and process broken ends for appropriate repair. Not only molecular ligands, but the spatial sequestration of telomeres and damage likely ensure that these two very similar structures have very distinct outcomes with respect to the DNA damage response and repair.
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Affiliation(s)
- Isabella Marcomini
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland; Faculty of Natural Sciences, University of Basel, Basel, Switzerland
| | - Susan M Gasser
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland; Faculty of Natural Sciences, University of Basel, Basel, Switzerland.
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47
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Two Routes to Genetic Suppression of RNA Trimethylguanosine Cap Deficiency via C-Terminal Truncation of U1 snRNP Subunit Snp1 or Overexpression of RNA Polymerase Subunit Rpo26. G3-GENES GENOMES GENETICS 2015; 5:1361-70. [PMID: 25911228 PMCID: PMC4502370 DOI: 10.1534/g3.115.016675] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The trimethylguanosine (TMG) caps of small nuclear (sn) RNAs are synthesized by the enzyme Tgs1 via sequential methyl additions to the N2 atom of the m7G cap. Whereas TMG caps are inessential for Saccharomyces cerevisiae vegetative growth at 25° to 37°, tgs1∆ cells that lack TMG caps fail to thrive at 18°. The cold-sensitive defect correlates with ectopic stoichiometric association of nuclear cap-binding complex (CBC) with the residual m7G cap of the U1 snRNA and is suppressed fully by Cbc2 mutations that weaken cap binding. Here, we show that normal growth of tgs1∆ cells at 18° is also restored by a C-terminal deletion of 77 amino acids from the Snp1 subunit of yeast U1 snRNP. These results underscore the U1 snRNP as a focal point for TMG cap function in vivo. Casting a broader net, we conducted a dosage suppressor screen for genes that allowed survival of tgs1∆ cells at 18°. We thereby recovered RPO26 (encoding a shared subunit of all three nuclear RNA polymerases) and RPO31 (encoding the largest subunit of RNA polymerase III) as moderate and weak suppressors of tgs1∆ cold sensitivity, respectively. A structure-guided mutagenesis of Rpo26, using rpo26∆ complementation and tgs1∆ suppression as activity readouts, defined Rpo26-(78-155) as a minimized functional domain. Alanine scanning identified Glu89, Glu124, Arg135, and Arg136 as essential for rpo26∆ complementation. The E124A and R135A alleles retained tgs1∆ suppressor activity, thereby establishing a separation-of-function. These results illuminate the structure activity profile of an essential RNA polymerase component.
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48
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Wu H, Becker D, Krebber H. Telomerase RNA TLC1 shuttling to the cytoplasm requires mRNA export factors and is important for telomere maintenance. Cell Rep 2014; 8:1630-1638. [PMID: 25220466 DOI: 10.1016/j.celrep.2014.08.021] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 07/09/2014] [Accepted: 08/08/2014] [Indexed: 12/23/2022] Open
Abstract
Telomerases protect the ends of linear chromosomes from shortening. They are composed of an RNA (TLC1 in S. cerevisiae) and several proteins. TLC1 undergoes several maturation steps before it is exported into the cytoplasm to recruit the Est proteins for complete assembly. The mature telomerase is subsequently reimported into the nucleus, where it fulfills its function on telomeres. Here, we show that TLC1 export into the cytoplasm requires not only the Ran GTPase-dependent karyopherin Crm1/Xpo1 but also the mRNA export machinery. mRNA export factor mutants accumulate mature and export-competent TLC1 RNAs in their nuclei. Moreover, TLC1 physically interacts with the mRNA transport factors Mex67 and Dbp5/Rat8. Most importantly, we show that the nuclear export of TLC1 is an essential step for the formation of the functional RNA containing enzyme, because blocking TLC1 export in the mex67-5 xpo1-1 double mutant prevents its cytoplasmic maturation and leads to telomere shortening.
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Affiliation(s)
- Haijia Wu
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, 37077 Göttingen, Germany
| | - Daniel Becker
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, 37077 Göttingen, Germany
| | - Heike Krebber
- Abteilung für Molekulare Genetik, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Georg-August Universität Göttingen, 37077 Göttingen, Germany.
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49
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Williams JM, Ouenzar F, Lemon LD, Chartrand P, Bertuch AA. The principal role of Ku in telomere length maintenance is promotion of Est1 association with telomeres. Genetics 2014; 197:1123-36. [PMID: 24879463 PMCID: PMC4125388 DOI: 10.1534/genetics.114.164707] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 05/23/2014] [Indexed: 01/02/2023] Open
Abstract
Telomere length is tightly regulated in cells that express telomerase. The Saccharomyces cerevisiae Ku heterodimer, a DNA end-binding complex, positively regulates telomere length in a telomerase-dependent manner. Ku associates with the telomerase RNA subunit TLC1, and this association is required for TLC1 nuclear retention. Ku-TLC1 interaction also impacts the cell-cycle-regulated association of the telomerase catalytic subunit Est2 to telomeres. The promotion of TLC1 nuclear localization and Est2 recruitment have been proposed to be the principal role of Ku in telomere length maintenance, but neither model has been directly tested. Here we study the impact of forced recruitment of Est2 to telomeres on telomere length in the absence of Ku's ability to bind TLC1 or DNA ends. We show that tethering Est2 to telomeres does not promote efficient telomere elongation in the absence of Ku-TLC1 interaction or DNA end binding. Moreover, restoration of TLC1 nuclear localization, even when combined with Est2 recruitment, does not bypass the role of Ku. In contrast, forced recruitment of Est1, which has roles in telomerase recruitment and activation, to telomeres promotes efficient and progressive telomere elongation in the absence of Ku-TLC1 interaction, Ku DNA end binding, or Ku altogether. Ku associates with Est1 and Est2 in a TLC1-dependent manner and enhances Est1 recruitment to telomeres independently of Est2. Together, our results unexpectedly demonstrate that the principal role of Ku in telomere length maintenance is to promote the association of Est1 with telomeres, which may in turn allow for efficient recruitment and activation of the telomerase holoenzyme.
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Affiliation(s)
- Jaime M Williams
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030
| | - Faissal Ouenzar
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada H3C 3J7
| | - Laramie D Lemon
- Integrative Molecular and Biomedical Sciences Graduate Program, Baylor College of Medicine, Houston, Texas 77030
| | - Pascal Chartrand
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada H3C 3J7
| | - Alison A Bertuch
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030 Integrative Molecular and Biomedical Sciences Graduate Program, Baylor College of Medicine, Houston, Texas 77030 Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030
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50
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The Ku heterodimer: function in DNA repair and beyond. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2014; 763:15-29. [PMID: 25795113 DOI: 10.1016/j.mrrev.2014.06.002] [Citation(s) in RCA: 185] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 06/07/2014] [Accepted: 06/25/2014] [Indexed: 01/11/2023]
Abstract
Ku is an abundant, highly conserved DNA binding protein found in both prokaryotes and eukaryotes that plays essential roles in the maintenance of genome integrity. In eukaryotes, Ku is a heterodimer comprised of two subunits, Ku70 and Ku80, that is best characterized for its central role as the initial DNA end binding factor in the "classical" non-homologous end joining (C-NHEJ) pathway, the main DNA double-strand break (DSB) repair pathway in mammals. Ku binds double-stranded DNA ends with high affinity in a sequence-independent manner through a central ring formed by the intertwined strands of the Ku70 and Ku80 subunits. At the break, Ku directly and indirectly interacts with several C-NHEJ factors and processing enzymes, serving as the scaffold for the entire DNA repair complex. There is also evidence that Ku is involved in signaling to the DNA damage response (DDR) machinery to modulate the activation of cell cycle checkpoints and the activation of apoptosis. Interestingly, Ku is also associated with telomeres, where, paradoxically to its DNA end-joining functions, it protects the telomere ends from being recognized as DSBs, thereby preventing their recombination and degradation. Ku, together with the silent information regulator (Sir) complex is also required for transcriptional silencing through telomere position effect (TPE). How Ku associates with telomeres, whether it is through direct DNA binding, or through protein-protein interactions with other telomere bound factors remains to be determined. Ku is central to the protection of organisms through its participation in C-NHEJ to repair DSBs generated during V(D)J recombination, a process that is indispensable for the establishment of the immune response. Ku also functions to prevent tumorigenesis and senescence since Ku-deficient mice show increased cancer incidence and early onset of aging. Overall, Ku function is critical to the maintenance of genomic integrity and to proper cellular and organismal development.
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