51
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Transient induction of telomerase expression mediates senescence and reduces tumorigenesis in primary fibroblasts. Proc Natl Acad Sci U S A 2019; 116:18983-18993. [PMID: 31481614 PMCID: PMC6754593 DOI: 10.1073/pnas.1907199116] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Telomerase is an enzymatic ribonucleoprotein complex that acts as a reverse transcriptase in the elongation of telomeres. Telomerase activity is well documented in embryonic stem cells and the vast majority of tumor cells, but its role in somatic cells remains to be understood. Here, we report an unexpected function of telomerase during cellular senescence and tumorigenesis. We crossed Tert heterozygous knockout mice (mTert +/- ) for 26 generations, during which time there was progressive shortening of telomeres, and obtained primary skin fibroblasts from mTert +/+ and mTert -/- progeny of the 26th cross. As a consequence of insufficient telomerase activities in prior generations, both mTert +/+ and mTert -/- fibroblasts showed comparable and extremely short telomere length. However, mTert -/- cells approached cellular senescence faster and exhibited a significantly higher rate of malignant transformation than mTert +/+ cells. Furthermore, an evident up-regulation of telomerase reverse-transcriptase (TERT) expression was detected in mTert +/+ cells at the presenescence stage. Moreover, removal or down-regulation of TERT expression in mTert +/+ and human primary fibroblast cells via CRISPR/Cas9 or shRNA recapitulated mTert -/- phenotypes of accelerated senescence and transformation, and overexpression of TERT in mTert -/- cells rescued these phenotypes. Taking these data together, this study suggests that TERT has a previously underappreciated, protective role in buffering senescence stresses due to short, dysfunctional telomeres, and preventing malignant transformation.
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52
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Mennie AK, Moser BA, Hoyle A, Low RS, Tanaka K, Nakamura TM. Tpz1 TPP1 prevents telomerase activation and protects telomeres by modulating the Stn1-Ten1 complex in fission yeast. Commun Biol 2019; 2:297. [PMID: 31396577 PMCID: PMC6686008 DOI: 10.1038/s42003-019-0546-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Accepted: 07/15/2019] [Indexed: 12/24/2022] Open
Abstract
In both mammalian and fission yeast cells, conserved shelterin and CST (CTC1-STN1-TEN1) complexes play critical roles in protection of telomeres and regulation of telomerase, an enzyme required to overcome the end replication problem. However, molecular details that govern proper coordination among shelterin, CST, and telomerase have not yet been fully understood. Here, we establish a conserved SWSSS motif, located adjacent to the Lys242 SUMOylation site in the fission yeast shelterin subunit Tpz1, as a new functional regulatory element for telomere protection and telomere length homeostasis. The SWSSS motif works redundantly with Lys242 SUMOylation to promote binding of Stn1-Ten1 at telomere and sub-telomere regions to protect against single-strand annealing (SSA)-dependent telomere fusions, and to prevent telomerase accumulation at telomeres. In addition, we provide evidence that the SWSSS motif defines an unanticipated role of Tpz1 in limiting telomerase activation at telomeres to prevent uncontrolled telomere elongation.
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Affiliation(s)
- Amanda K. Mennie
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, IL 60607 USA
| | - Bettina A. Moser
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, IL 60607 USA
| | - Alice Hoyle
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, IL 60607 USA
| | - Ross S. Low
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, IL 60607 USA
- Present Address: Earlham Institute, Norwich Research Park, Norwich, NR4 7UZ United Kingdom
| | - Katsunori Tanaka
- Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, Sanda, 669-1337 Japan
| | - Toru M. Nakamura
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, IL 60607 USA
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53
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Telomere length and its correlation with gene mutations in chronic lymphocytic leukemia in a Korean population. PLoS One 2019; 14:e0220177. [PMID: 31335885 PMCID: PMC6650075 DOI: 10.1371/journal.pone.0220177] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 07/10/2019] [Indexed: 11/19/2022] Open
Abstract
Telomere length (TL) is a prognostic indicator in Caucasian chronic lymphocytic leukemia (CLL), but its significance in Asian CLL remains unknown. To investigate the prognostic significance of TL and its correlation with cytogenetic aberrations and somatic mutations, we analyzed TL measurements at the cellular level by interphase fluorescence in situ hybridization in patients with CLL in Korea. The present study enrolled 110 patients (41 females and 69 males) diagnosed with CLL according to the World Health Organization criteria (2001-2017). TLs of bone marrow nucleated cells at the single-cell level were measured by quantitative fluorescence in situ hybridization (Q-FISH) in 71 patients. The correlations of TL with clinical characteristics, cytogenetic aberrations, genetic mutations, and overall survival were assessed. The median value of mean TL in CLL patients (T/C ratio 7.46 (range 1.19-18.14) was significantly shorter than that in the normal controls (T/C ratio 15.28 (range 8.59-24.93) (p < 0.001). Shorter TLs were associated with complex karyotypes (p = 0.030), del(11q22) (p = 0.023), presence of deletion and/or mutation in ATM and/or TP53 (p = 0.019), and SH2B3 mutation (p = 0.015). A shorter TL was correlated with lower hemoglobin levels and adverse survival (mean TL < 9.35, p = 0.021). When the proportion of cells with extremely short TLs (< 7.61) was greater than 90%, CLL patients showed poor survival (p = 0.002). Complex karyotypes, TP53 mutation, and the number of mutated genes were determined to be significant adverse variables by multivariable Cox analysis (p = 0.011, p = 0.002, and p = 0.002, respectively). TL was attrited in CLL, and attrited telomeres were correlated with adverse survival and other well-known adverse prognostic factors. We infer that TL is an independent adverse prognostic predictor in Korean CLL.
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54
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Zhou Z, Wang L, Ge F, Gong P, Wang H, Wang F, Chen L, Liu L. Pold3 is required for genomic stability and telomere integrity in embryonic stem cells and meiosis. Nucleic Acids Res 2019; 46:3468-3486. [PMID: 29447390 PMCID: PMC6283425 DOI: 10.1093/nar/gky098] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2017] [Accepted: 02/01/2018] [Indexed: 12/29/2022] Open
Abstract
Embryonic stem cells (ESCs) and meiosis are featured by relatively higher frequent homologous recombination associated with DNA double strand breaks (DSB) repair. Here, we show that Pold3 plays important roles in DSB repair, telomere maintenance and genomic stability of both ESCs and spermatocytes in mice. By attempting to generate Pold3 deficient mice using CRISPR/Cas9 or transcription activator-like effector nucleases, we show that complete loss of Pold3 (Pold3−/−) resulted in early embryonic lethality at E6.5. Rapid DNA damage response and massive apoptosis occurred in both outgrowths of Pold3-null (Pold3−/−) blastocysts and Pold3 inducible knockout (iKO) ESCs. While Pold3−/− ESCs were not achievable, Pold3 iKO led to increased DNA damage response, telomere loss and chromosome breaks accompanied by extended S phase. Meanwhile, loss of Pold3 resulted in replicative stress, micronucleation and aneuploidy. Also, DNA repair was impaired in Pold3+/− or Pold3 knockdown ESCs. Moreover, Pold3 mediates DNA replication and repair by regulating 53BP1, RIF1, ATR and ATM pathways. Furthermore, spermatocytes of Pold3 haploinsufficient (Pold3+/−) mice with increasing age displayed impaired DSB repair, telomere shortening and loss, and chromosome breaks, like Pold3 iKO ESCs. These data suggest that Pold3 maintains telomere integrity and genomic stability of both ESCs and meiosis by suppressing replicative stress.
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Affiliation(s)
- Zhongcheng Zhou
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.,Department of Cell Biology and Genetics, The Key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Lingling Wang
- Department of Cell Biology and Genetics, The Key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Feixiang Ge
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.,Department of Cell Biology and Genetics, The Key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Peng Gong
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.,Department of Cell Biology and Genetics, The Key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Hua Wang
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.,Department of Cell Biology and Genetics, The Key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Feng Wang
- Department of Genetics, School of basic Medical Sciences, Tianjin Medical University, Tianjin 300070, China
| | - Lingyi Chen
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.,Department of Cell Biology and Genetics, The Key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Lin Liu
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.,Department of Cell Biology and Genetics, The Key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
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55
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Combined treatment with emodin and a telomerase inhibitor induces significant telomere damage/dysfunction and cell death. Cell Death Dis 2019; 10:527. [PMID: 31296842 PMCID: PMC6624283 DOI: 10.1038/s41419-019-1768-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 06/23/2019] [Accepted: 06/24/2019] [Indexed: 01/06/2023]
Abstract
G-quadruplex telomeric secondary structures represent natural replication fork barriers and must be resolved to permit efficient replication. Stabilization of telomeric G4 leads to telomere dysfunctions demonstrated by telomere shortening or damage, resulting in genome instability and apoptosis. Chemical compounds targeting G4 structures have been reported to induce telomere disturbance and tumor suppression. Here, virtual screening was performed in a natural compound library using PyRx to identify novel G4 ligands. Emodin was identified as one of the best candidates, showing a great G4-binding potential. Subsequently, we confirmed that emodin could stabilize G4 structures in vitro and trigger telomere dysfunctions including fragile telomeres, telomere loss, and telomeric DNA damage. However, this telomere disturbance could be rescued by subsequent elevation of telomerase activity; in contrast, when we treated the cells with the telomerase inhibitor BIBR1532 upon emodin treatment, permanent telomere disturbance and obvious growth inhibition of 4T1-cell xenograft tumors were observed in mice. Taken together, our results show for the first time that emodin-induced telomeric DNA damage can upregulate telomerase activity, which may weaken its anticancer effect. The combined use of emodin and the telomerase inhibitor synergistically induced telomere dysfunction and inhibited tumor generation.
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56
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Alnafakh RAA, Adishesh M, Button L, Saretzki G, Hapangama DK. Telomerase and Telomeres in Endometrial Cancer. Front Oncol 2019; 9:344. [PMID: 31157162 PMCID: PMC6533802 DOI: 10.3389/fonc.2019.00344] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Accepted: 04/15/2019] [Indexed: 12/11/2022] Open
Abstract
Telomeres at the termini of human chromosomes are shortened with each round of cell division due to the “end replication problem” as well as oxidative stress. During carcinogenesis, cells acquire or retain mechanisms to maintain telomeres to avoid initiation of cellular senescence or apoptosis and halting cell division by critically short telomeres. The unique reverse transcriptase enzyme complex, telomerase, catalyzes the maintenance of telomeres but most human somatic cells do not have sufficient telomerase activity to prevent telomere shortening. Tissues with high and prolonged replicative potential demonstrate adequate cellular telomerase activity to prevent telomere erosion, and high telomerase activity appears to be a critical feature of most (80–90%) epithelial cancers, including endometrial cancer. Endometrial cancers regress in response to progesterone which is frequently used to treat advanced endometrial cancer. Endometrial telomerase is inhibited by progestogens and deciphering telomere and telomerase biology in endometrial cancer is therefore important, as targeting telomerase (a downstream target of progestogens) in endometrial cancer may provide novel and more effective therapeutic avenues. This review aims to examine the available evidence for the role and importance of telomere and telomerase biology in endometrial cancer.
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Affiliation(s)
- Rafah A A Alnafakh
- Liverpool Women's Hospital NHS Foundation Trust, Liverpool, United Kingdom.,Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Meera Adishesh
- Liverpool Women's Hospital NHS Foundation Trust, Liverpool, United Kingdom.,Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Lucy Button
- Liverpool Women's Hospital NHS Foundation Trust, Liverpool, United Kingdom.,Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Gabriele Saretzki
- The Ageing Biology Centre and Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Dharani K Hapangama
- Liverpool Women's Hospital NHS Foundation Trust, Liverpool, United Kingdom.,Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
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57
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Armando RG, Mengual Gomez DL, Maggio J, Sanmartin MC, Gomez DE. Telomeropathies: Etiology, diagnosis, treatment and follow-up. Ethical and legal considerations. Clin Genet 2019; 96:3-16. [PMID: 30820928 DOI: 10.1111/cge.13526] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 02/12/2019] [Accepted: 02/26/2019] [Indexed: 12/13/2022]
Abstract
Telomeropathies involve a wide variety of infrequent genetic diseases caused by mutations in the telomerase maintenance mechanism or the DNA damage response (DDR) system. They are considered a family of rare diseases that often share causes, molecular mechanisms and symptoms. Generally, these diseases are not diagnosed until the symptoms are advanced, diminishing the survival time of patients. Although several related syndromes may still be unrecognized this work describes those that are known, highlighting that because they are rare diseases, physicians should be trained in their early diagnosis. The etiology and diagnosis are discussed for each telomeropathy and the treatments when available, along with a new classification of this group of diseases. Ethical and legal issues related to this group of diseases are also considered.
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Affiliation(s)
- Romina G Armando
- Laboratory of Molecular Oncology, Universidad Nacional de Quilmes, Buenos Aires, Argentina
| | - Diego L Mengual Gomez
- Laboratory of Molecular Oncology, Universidad Nacional de Quilmes, Buenos Aires, Argentina
| | - Julián Maggio
- Laboratory of Molecular Oncology, Universidad Nacional de Quilmes, Buenos Aires, Argentina
| | - María C Sanmartin
- Laboratory of Molecular Oncology, Universidad Nacional de Quilmes, Buenos Aires, Argentina
| | - Daniel E Gomez
- Laboratory of Molecular Oncology, Universidad Nacional de Quilmes, Buenos Aires, Argentina
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58
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Harrington L, Pucci F. In medio stat virtus: unanticipated consequences of telomere dysequilibrium. Philos Trans R Soc Lond B Biol Sci 2019; 373:rstb.2016.0444. [PMID: 29335368 PMCID: PMC5784064 DOI: 10.1098/rstb.2016.0444] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/07/2017] [Indexed: 12/13/2022] Open
Abstract
The integrity of chromosome ends, or telomeres, depends on myriad processes that must balance the need to compact and protect the telomeric, G-rich DNA from detection as a double-stranded DNA break, and yet still permit access to enzymes that process, replicate and maintain a sufficient reserve of telomeric DNA. When unable to maintain this equilibrium, erosion of telomeres leads to perturbations at or near the telomeres themselves, including loss of binding by the telomere protective complex, shelterin, and alterations in transcription and post-translational modifications of histones. Although the catastrophic consequences of full telomere de-protection are well described, recent evidence points to other, less obvious perturbations that arise when telomere length equilibrium is altered. For example, critically short telomeres also perturb DNA methylation and histone post-translational modifications at distal sites throughout the genome. In murine stem cells for example, this dysregulated chromatin leads to inappropriate suppression of pluripotency regulator factors such as Nanog. This review summarizes these recent findings, with an emphasis on how these genome-wide, telomere-induced perturbations can have profound consequences on cell function and fate. This article is part of the theme issue ‘Understanding diversity in telomere dynamics’.
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Affiliation(s)
- Lea Harrington
- Wellcome Trust Centre for Cell Biology, School of Biological Sciences, College of Science and Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, UK
| | - Fabio Pucci
- Wellcome Trust Centre for Cell Biology, School of Biological Sciences, College of Science and Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, UK
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59
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Telomeres in Plants and Humans: Not So Different, Not So Similar. Cells 2019; 8:cells8010058. [PMID: 30654521 PMCID: PMC6356271 DOI: 10.3390/cells8010058] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 01/07/2019] [Accepted: 01/07/2019] [Indexed: 01/01/2023] Open
Abstract
Parallel research on multiple model organisms shows that while some principles of telomere biology are conserved among all eukaryotic kingdoms, we also find some deviations that reflect different evolutionary paths and life strategies, which may have diversified after the establishment of telomerase as a primary mechanism for telomere maintenance. Much more than animals, plants have to cope with environmental stressors, including genotoxic factors, due to their sessile lifestyle. This is, in principle, made possible by an increased capacity and efficiency of the molecular systems ensuring maintenance of genome stability, as well as a higher tolerance to genome instability. Furthermore, plant ontogenesis differs from that of animals in which tissue differentiation and telomerase silencing occur during early embryonic development, and the “telomere clock” in somatic cells may act as a preventive measure against carcinogenesis. This does not happen in plants, where growth and ontogenesis occur through the serial division of apical meristems consisting of a small group of stem cells that generate a linear series of cells, which differentiate into an array of cell types that make a shoot and root. Flowers, as generative plant organs, initiate from the shoot apical meristem in mature plants which is incompatible with the human-like developmental telomere shortening. In this review, we discuss differences between human and plant telomere biology and the implications for aging, genome stability, and cell and organism survival. In particular, we provide a comprehensive comparative overview of telomere proteins acting in humans and in Arabidopsis thaliana model plant, and discuss distinct epigenetic features of telomeric chromatin in these species.
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60
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Amir M, Kumar V, Mohammad T, Dohare R, Hussain A, Rehman MT, Alam P, Alajmi MF, Islam A, Ahmad F, Hassan MI. Investigation of deleterious effects of nsSNPs in the
POT1
gene: a structural genomics‐based approach to understand the mechanism of cancer development. J Cell Biochem 2018; 120:10281-10294. [DOI: 10.1002/jcb.28312] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Accepted: 11/28/2018] [Indexed: 12/18/2022]
Affiliation(s)
- Mohd. Amir
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia New Delhi India
| | - Vijay Kumar
- Amity Institute of Neuropsychology & Neurosciences, Amity University Noida Uttar Pradesh India
| | - Taj Mohammad
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia New Delhi India
| | - Ravins Dohare
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia New Delhi India
| | - Afzal Hussain
- Department of Pharmacognosy College of Pharmacy, King Saud University Riyadh Saudi Arabia
| | - Md. Tabish Rehman
- Department of Pharmacognosy College of Pharmacy, King Saud University Riyadh Saudi Arabia
| | - Perwez Alam
- Department of Pharmacognosy College of Pharmacy, King Saud University Riyadh Saudi Arabia
| | - Mohamed F. Alajmi
- Department of Pharmacognosy College of Pharmacy, King Saud University Riyadh Saudi Arabia
| | - Asimul Islam
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia New Delhi India
| | - Faizan Ahmad
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia New Delhi India
| | - Md. Imtaiyaz Hassan
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia New Delhi India
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61
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Giant tortoise genomes provide insights into longevity and age-related disease. Nat Ecol Evol 2018; 3:87-95. [PMID: 30510174 PMCID: PMC6314442 DOI: 10.1038/s41559-018-0733-x] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 10/25/2018] [Indexed: 12/21/2022]
Abstract
Giant tortoises are among the longest-lived vertebrate animals and, as such, provide an excellent model to study traits like longevity and age-related diseases. However, genomic and molecular evolutionary information on giant tortoises is scarce. Here, we describe a global analysis of the genomes of Lonesome George-the iconic last member of Chelonoidis abingdonii-and the Aldabra giant tortoise (Aldabrachelys gigantea). Comparison of these genomes with those of related species, using both unsupervised and supervised analyses, led us to detect lineage-specific variants affecting DNA repair genes, inflammatory mediators and genes related to cancer development. Our study also hints at specific evolutionary strategies linked to increased lifespan, and expands our understanding of the genomic determinants of ageing. These new genome sequences also provide important resources to help the efforts for restoration of giant tortoise populations.
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62
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Romaniuk A, Paszel-Jaworska A, Totoń E, Lisiak N, Hołysz H, Królak A, Grodecka-Gazdecka S, Rubiś B. The non-canonical functions of telomerase: to turn off or not to turn off. Mol Biol Rep 2018; 46:1401-1411. [PMID: 30448892 DOI: 10.1007/s11033-018-4496-x] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Accepted: 11/12/2018] [Indexed: 12/19/2022]
Abstract
Telomerase is perceived as an immortality enzyme that enables passing the Hayflick limit. Its main function is telomere restoration but only in a limited group of cells, including cancer cells. Since it is found in a vast majority of cancer cells, it became a natural target for cancer therapy. However, it has much more functions than just altering the metabolism of telomeres-it also reveals numerous so-called non-canonical functions. Thus, a question arises whether it is always beneficial to turn it off when planning a cancer strategy and considering potential side effects? The purpose of this review is to discuss some of the recent discoveries about telomere-independent functions of telomerase in the context of cancer therapy and potential side effects.
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Affiliation(s)
- Aleksandra Romaniuk
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, 49 Przybyszewskiego St., 60-355, Poznań, Poland
| | - Anna Paszel-Jaworska
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, 49 Przybyszewskiego St., 60-355, Poznań, Poland
| | - Ewa Totoń
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, 49 Przybyszewskiego St., 60-355, Poznań, Poland
| | - Natalia Lisiak
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, 49 Przybyszewskiego St., 60-355, Poznań, Poland
| | - Hanna Hołysz
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, 49 Przybyszewskiego St., 60-355, Poznań, Poland
| | - Anna Królak
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, 49 Przybyszewskiego St., 60-355, Poznań, Poland
| | | | - Błażej Rubiś
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, 49 Przybyszewskiego St., 60-355, Poznań, Poland.
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63
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Chen B, Zhang Y, Yang Y, Chen S, Xu A, Wu L, Xu S. Involvement of telomerase activity inhibition and telomere dysfunction in silver nanoparticles anticancer effects. Nanomedicine (Lond) 2018; 13:2067-2082. [PMID: 30203702 DOI: 10.2217/nnm-2018-0036] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
AIM To investigate the possible mechanisms of telomerase and telomere underlying the anticancer effects of silver nanoparticles (AgNPs). MATERIALS & METHODS 25nm polyvinylpyrrolidone-coated AgNPs were used. The telomerase activity and telomere function were evaluated. The anticancer effects of AgNPs were gauged with cell viability assay under different statement of telomerase and telomere. RESULTS & CONCLUSION AgNPs could inhibit telomerase activity and lead to telomere shortening and dysfunction. Overexpression of telomerase attenuated the anticancer activity of AgNPs, whereas downregulation of telomerase activity or dysfunction of the telomere enhanced the cytotoxicity of AgNPs in HeLa cells. Our findings provided strong evidence that the anticancer effects of AgNPs were mediated via interference with the telomerase/telomere.
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Affiliation(s)
- Biao Chen
- School of Environmental Science & Optoelectronic Technology, University of Science & Technology of China, Hefei, Anhui, 230026, PR China.,Key Laboratory of High Magnetic Field & Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, PR China
| | - Yajun Zhang
- Key Laboratory of High Magnetic Field & Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, PR China.,Institute of Physical & Information Technology, Anhui University, Hefei, Anhui, 230601, PR China
| | - Yaning Yang
- School of Environmental Science & Optoelectronic Technology, University of Science & Technology of China, Hefei, Anhui, 230026, PR China.,Key Laboratory of High Magnetic Field & Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, PR China
| | - Shaopeng Chen
- Key Laboratory of High Magnetic Field & Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, PR China.,Institute of Physical & Information Technology, Anhui University, Hefei, Anhui, 230601, PR China
| | - An Xu
- School of Environmental Science & Optoelectronic Technology, University of Science & Technology of China, Hefei, Anhui, 230026, PR China.,Key Laboratory of High Magnetic Field & Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, PR China.,Institute of Physical & Information Technology, Anhui University, Hefei, Anhui, 230601, PR China
| | - Lijun Wu
- School of Environmental Science & Optoelectronic Technology, University of Science & Technology of China, Hefei, Anhui, 230026, PR China.,Key Laboratory of High Magnetic Field & Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, PR China.,Key Laboratory of Environmental Toxicology & Pollution Control Technology of Anhui Province, Hefei, Anhui, 230031, PR China.,Institute of Physical & Information Technology, Anhui University, Hefei, Anhui, 230601, PR China
| | - Shengmin Xu
- Key Laboratory of High Magnetic Field & Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, PR China.,Key Laboratory of Environmental Toxicology & Pollution Control Technology of Anhui Province, Hefei, Anhui, 230031, PR China
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Liu H, Xie Y, Zhang Z, Mao P, Liu J, Ma W, Zhao Y. Telomeric Recombination Induced by DNA Damage Results in Telomere Extension and Length Heterogeneity. Neoplasia 2018; 20:905-916. [PMID: 30118998 PMCID: PMC6097467 DOI: 10.1016/j.neo.2018.07.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Revised: 07/20/2018] [Accepted: 07/24/2018] [Indexed: 12/11/2022] Open
Abstract
About 15% of human cancers counteract telomere loss by alternative lengthening of telomeres (ALT), which is attributed to homologous recombination (HR)–mediated events. But how telomeric HR leads to length elongation is poorly understood. Here, we explore telomere clustering and telomeric HR induced by double-stranded breaks (DSBs). We show that telomere clustering could occur at G1 and S phase of cell cycle and that three types of telomeric HR occur based on the manner of telomeric DNA exchange: equivalent telomeric sister chromatin exchange (T-SCE), inequivalent T-SCE, and No-SCE. While inequivalent T-SCE increases telomere length heterogeneity with no net gain of telomere length, No-SCE, which is presumably induced by interchromatid HR and/or break-induced replication, results in telomere elongation. Accordingly, cells subjected to long-term telomeric DSBs display increased heterogeneity of length and longer telomeres. We also demonstrate that DSBs-induced telomere elongation is telomerase independent. Moreover, telomeric recombination induced by DSBs is associated with formation of ALT-associated PML body and C-circle. Thus, DNA damage triggers recombination mediated elongation, leading to the induction of multiple ALT phenotypes.
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Affiliation(s)
- Haiying Liu
- MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, P. R. China; Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, P. R. China
| | - Yujie Xie
- MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, P. R. China; Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, P. R. China
| | - Zepeng Zhang
- MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, P. R. China; Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, P. R. China
| | - Pingsu Mao
- MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, P. R. China; Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, P. R. China
| | - Jingfan Liu
- MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, P. R. China; Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, P. R. China
| | - Wenbin Ma
- MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, P. R. China
| | - Yong Zhao
- MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, P. R. China; Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, P. R. China.
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Armstrong CA, Tomita K. Fundamental mechanisms of telomerase action in yeasts and mammals: understanding telomeres and telomerase in cancer cells. Open Biol 2018; 7:rsob.160338. [PMID: 28330934 PMCID: PMC5376709 DOI: 10.1098/rsob.160338] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 02/20/2017] [Indexed: 12/12/2022] Open
Abstract
Aberrant activation of telomerase occurs in 85–90% of all cancers and underpins the ability of cancer cells to bypass their proliferative limit, rendering them immortal. The activity of telomerase is tightly controlled at multiple levels, from transcriptional regulation of the telomerase components to holoenzyme biogenesis and recruitment to the telomere, and finally activation and processivity. However, studies using cancer cell lines and other model systems have begun to reveal features of telomeres and telomerase that are unique to cancer. This review summarizes our current knowledge on the mechanisms of telomerase recruitment and activation using insights from studies in mammals and budding and fission yeasts. Finally, we discuss the differences in telomere homeostasis between normal cells and cancer cells, which may provide a foundation for telomere/telomerase targeted cancer treatments.
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Affiliation(s)
- Christine A Armstrong
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK
| | - Kazunori Tomita
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK
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66
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Barrientos-Moreno M, Murillo-Pineda M, Muñoz-Cabello AM, Prado F. Histone depletion prevents telomere fusions in pre-senescent cells. PLoS Genet 2018; 14:e1007407. [PMID: 29879139 PMCID: PMC5991667 DOI: 10.1371/journal.pgen.1007407] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 05/09/2018] [Indexed: 12/20/2022] Open
Abstract
Upon telomerase inactivation, telomeres gradually shorten with each cell division until cells enter replicative senescence. In Saccharomyces cerevisiae, the kinases Mec1/ATR and Tel1/ATM protect the genome during pre-senescence by preventing telomere-telomere fusions (T-TFs) and the subsequent genetic instability associated with fusion-bridge-breakage cycles. Here we report that T-TFs in mec1Δ tel1Δ cells can be suppressed by reducing the pool of available histones. This protection associates neither with changes in bulk telomere length nor with major changes in the structure of subtelomeric chromatin. We show that the absence of Mec1 and Tel1 strongly augments double-strand break (DSB) repair by non-homologous end joining (NHEJ), which might contribute to the high frequency of T-TFs in mec1Δ tel1Δ cells. However, histone depletion does not prevent telomere fusions by inhibiting NHEJ, which is actually increased in histone-depleted cells. Rather, histone depletion protects telomeres from fusions by homologous recombination (HR), even though HR is proficient in maintaining the proliferative state of pre-senescent mec1Δ tel1Δ cells. Therefore, HR during pre-senescence not only helps stalled replication forks but also prevents T-TFs by a mechanism that, in contrast to the previous one, is promoted by a reduction in the histone pool and can occur in the absence of Rad51. Our results further suggest that the Mec1-dependent depletion of histones that occurs during pre-senescence in cells without telomerase (tlc1Δ) prevents T-TFs by favoring the processing of unprotected telomeres by Rad51-independent HR. Telomere shortening upon telomerase inactivation leads to an irreversible cell division arrest known as replicative senescence, which is considered as a tumor suppressor mechanism. Since pre-senescence is critical for tissue homeostasis, cells are endowed with recombination mechanisms that facilitate the replication of short telomeres and prevent premature entry into senescence. Consequently, pre-senescent cells divide with critically short telomeres, which have lost most of their shelterin proteins. The tumor suppressor genes ATR and ATM, as well as their yeast homologs Mec1 and Tel1, prevent telomere fusions during pre-senescence by unknown mechanisms. Here we show that the absence of Mec1 and Tel1 strongly augments DSB repair by non-homologous end joining, which might explain the high rate of telomere fusions in mec1Δ tel1Δ cells. Moreover, we show that a reduction in the pool of available histones prevents telomere fusions in mec1Δ tel1Δ cells by stimulating Rad51-independent homologous recombination. Our results suggest that the Mec1-dependent process of histone depletion that accompanies pre-senescence in cells lacking telomerase activity is required to prevent telomere fusions by promoting the processing of unprotected telomeres by recombination instead of non-homologous end joining.
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Affiliation(s)
- Marta Barrientos-Moreno
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), CSIC-University of Seville-University Pablo de Olavide, Seville, Spain
| | - Marina Murillo-Pineda
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), CSIC-University of Seville-University Pablo de Olavide, Seville, Spain
| | - Ana M. Muñoz-Cabello
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), CSIC-University of Seville-University Pablo de Olavide, Seville, Spain
| | - Félix Prado
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), CSIC-University of Seville-University Pablo de Olavide, Seville, Spain
- * E-mail:
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67
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Thompson CAH, Gu A, Yang SY, Mathew V, Fleisig HB, Wong JMY. Transient Telomerase Inhibition with Imetelstat Impacts DNA Damage Signals and Cell-Cycle Kinetics. Mol Cancer Res 2018; 16:1215-1225. [PMID: 29759988 DOI: 10.1158/1541-7786.mcr-17-0772] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 03/20/2018] [Accepted: 04/27/2018] [Indexed: 11/16/2022]
Abstract
Telomerase is the ribonucleoprotein reverse transcriptase that catalyzes the synthesis of telomeres at the ends of linear chromosomes and contributes to proper telomere-loop (T-loop) formation. Formation of the T-loop, an obligate step before cell division can proceed, requires the generation of a 3'-overhang on the G-rich strand of telomeric DNA via telomerase or C-strand specific nucleases. Here, it is discovered that telomerase activity is critical for efficient cell-cycle progression using transient chemical inhibition by the telomerase inhibitor, imetelstat. Telomerase inhibition changed cell cycle kinetics and increased the proportion of cells in G2-phase, suggesting delayed clearance through this checkpoint. Investigating the possible contribution of unstructured telomere ends to these cell-cycle distribution changes, it was observed that imetelstat treatment induced γH2AX DNA damage foci in a subset of telomerase-positive cells but not telomerase-negative primary human fibroblasts. Chromatin-immunoprecipitation with γH2AX antibodies demonstrated imetelstat treatment-dependent enrichment of this DNA damage marker at telomeres. Notably, the effects of telomerase inhibition on cell cycle profile alterations were abrogated by pharmacological inhibition of the DNA-damage-repair transducer, ATM. Also, imetelstat potentiation of etoposide, a DNA-damaging drug that acts preferentially during S-G2 phases of the cell cycle, depends on functional ATM signaling. Thus, telomerase inhibition delays the removal of ATM-dependent DNA damage signals from telomeres in telomerase-positive cancer cells and interferes with cell cycle progression through G2Implications: This study demonstrates that telomerase activity directly facilitates the progression of the cell cycle through modulation of transient telomere dysfunction signals. Mol Cancer Res; 16(8); 1215-25. ©2018 AACR.
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Affiliation(s)
- Connor A H Thompson
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Alice Gu
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Sunny Y Yang
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Veena Mathew
- Terry Fox Laboratory, British Columbia Cancer Research Centre, Vancouver, BC Cancer Agency, British Columbia, Canada
| | - Helen B Fleisig
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Judy M Y Wong
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
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Conklin QA, King BG, Zanesco AP, Lin J, Hamidi AB, Pokorny JJ, Álvarez-López MJ, Cosín-Tomás M, Huang C, Kaliman P, Epel ES, Saron CD. Insight meditation and telomere biology: The effects of intensive retreat and the moderating role of personality. Brain Behav Immun 2018. [PMID: 29518528 DOI: 10.1016/j.bbi.2018.03.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
A growing body of evidence suggests that meditation training may have a range of salubrious effects, including improved telomere regulation. Telomeres and the enzyme telomerase interact with a variety of molecular components to regulate cell-cycle signaling cascades, and are implicated in pathways linking psychological stress to disease. We investigated the effects of intensive meditation practice on these biomarkers by measuring changes in telomere length (TL), telomerase activity (TA), and telomere-related gene (TRG) expression during a 1-month residential Insight meditation retreat. Multilevel analyses revealed an apparent TL increase in the retreat group, compared to a group of experienced meditators, similarly comprised in age and gender, who were not on retreat. Moreover, personality traits predicted changes in TL, such that retreat participants highest in neuroticism and lowest in agreeableness demonstrated the greatest increases in TL. Changes observed in TRGs further suggest retreat-related improvements in telomere maintenance, including increases in Gar1 and HnRNPA1, which encode proteins that bind telomerase RNA and telomeric DNA. Although no group-level changes were observed in TA, retreat participants' TA levels at post-assessment were inversely related to several indices of retreat engagement and prior meditation experience. Neuroticism also predicted variation in TA across retreat. These findings suggest that meditation training in a retreat setting may have positive effects on telomere regulation, which are moderated by individual differences in personality and meditation experience. (ClinicalTrials.gov #NCT03056105).
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Affiliation(s)
- Quinn A Conklin
- Center for Mind and Brain, University of California, Davis, 267 Cousteau Place, Davis, CA 95618, United States; Department of Psychology, University of California, Davis, 135 Young Hall, Davis, CA 95616, United States.
| | - Brandon G King
- Center for Mind and Brain, University of California, Davis, 267 Cousteau Place, Davis, CA 95618, United States; Department of Psychology, University of California, Davis, 135 Young Hall, Davis, CA 95616, United States
| | - Anthony P Zanesco
- Center for Mind and Brain, University of California, Davis, 267 Cousteau Place, Davis, CA 95618, United States; Department of Psychology, University of California, Davis, 135 Young Hall, Davis, CA 95616, United States
| | - Jue Lin
- Department of Biochemistry & Biophysics, University of California, San Francisco, 600 16th St, San Francisco, CA 94158, United States
| | - Anahita B Hamidi
- Center for Mind and Brain, University of California, Davis, 267 Cousteau Place, Davis, CA 95618, United States; Center for Neuroscience, University of California, Davis, 1544 Newton Court, Davis, CA 95618, United States
| | - Jennifer J Pokorny
- Center for Mind and Brain, University of California, Davis, 267 Cousteau Place, Davis, CA 95618, United States
| | | | - Marta Cosín-Tomás
- Unit of Pharmacology, Institute of Biomedicine, University of Barcelona, Barcelona 08028, Spain
| | - Colin Huang
- Department of Biochemistry & Biophysics, University of California, San Francisco, 600 16th St, San Francisco, CA 94158, United States
| | - Perla Kaliman
- Center for Mind and Brain, University of California, Davis, 267 Cousteau Place, Davis, CA 95618, United States; Unit of Pharmacology, Institute of Biomedicine, University of Barcelona, Barcelona 08028, Spain
| | - Elissa S Epel
- Department of Psychiatry, University of California, San Francisco, 401 Parnassus Ave, San Francisco, CA 94131, United States
| | - Clifford D Saron
- Center for Mind and Brain, University of California, Davis, 267 Cousteau Place, Davis, CA 95618, United States; MIND Institute, University of California, Davis Medical Center, 2825 50th St, Sacramento, CA 95817, United States
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69
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Trajano LADSN, Trajano ETL, Silva MADS, Stumbo AC, Mencalha AL, Fonseca ADSD. Genomic stability and telomere regulation in skeletal muscle tissue. Biomed Pharmacother 2018; 98:907-915. [DOI: 10.1016/j.biopha.2018.01.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 12/19/2017] [Accepted: 01/03/2018] [Indexed: 02/07/2023] Open
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70
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TRF1 participates in chromosome end protection by averting TRF2-dependent telomeric R loops. Nat Struct Mol Biol 2018; 25:147-153. [PMID: 29358759 PMCID: PMC5808845 DOI: 10.1038/s41594-017-0021-5] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 11/26/2017] [Indexed: 12/12/2022]
Abstract
The shelterin protein TRF2 assembles protective T loops at chromosome ends by stimulating intramolecular invasion of the telomeric G-rich single-stranded DNA (ssDNA) overhang into the duplex telomeric array. The other shelterin factor, TRF1, is thought to mainly facilitate telomeric dsDNA replication without directly participating in end protection. Here we show that in vitro human TRF2 stimulates invasion of G-rich TERRA-like RNA into telomeric dsDNA, leading to formation of telomeric RNA-DNA hybrids (telR loops). The N-terminal basic domain of TRF2 binds to TERRA-like RNA and enables TRF2 to promote efficient RNA invasion. TRF1, through its N-terminal acidic domain, counteracts TRF2-mediated RNA invasion but not ssDNA invasion. In vivo, when TRF1 is depleted or replaced with a variant lacking the acidic domain, TRF2 induces formation of telR loops, which in turn cause telomere loss. Hence, uncontrolled TRF2 threatens telomere integrity, and TRF1 directly supports end protection by suppressing harmful telR loops.
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71
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Chan FL, Vinod B, Novy K, Schittenhelm RB, Huang C, Udugama M, Nunez-Iglesias J, Lin JI, Hii L, Chan J, Pickett HA, Daly RJ, Wong LH. Aurora Kinase B, a novel regulator of TERF1 binding and telomeric integrity. Nucleic Acids Res 2017; 45:12340-12353. [PMID: 29040668 PMCID: PMC5716096 DOI: 10.1093/nar/gkx904] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Accepted: 09/26/2017] [Indexed: 01/24/2023] Open
Abstract
AURKB (Aurora Kinase B) is a serine/threonine kinase better known for its role at the mitotic kinetochore during chromosome segregation. Here, we demonstrate that AURKB localizes to the telomeres in mouse embryonic stem cells, where it interacts with the essential telomere protein TERF1. Loss of AURKB function affects TERF1 telomere binding and results in aberrant telomere structure. In vitro kinase experiments successfully identified Serine 404 on TERF1 as a putative AURKB target site. Importantly, in vivo overexpression of S404-TERF1 mutants results in fragile telomere formation. These findings demonstrate that AURKB is an important regulator of telomere structural integrity.
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Affiliation(s)
- Foong Lyn Chan
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Benjamin Vinod
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Karel Novy
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Ralf B Schittenhelm
- Monash Biomedical Proteomics Facility & Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Cheng Huang
- Monash Biomedical Proteomics Facility & Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Maheshi Udugama
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Juan Nunez-Iglesias
- Life Sciences Computation Centre, University of Melbourne, Carlton, VIC 3010, Australia
| | - Jane I Lin
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Linda Hii
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Julie Chan
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Hilda A Pickett
- Telomere Length Regulation Group, Children's Medical Research Institute, University of Sydney, Westmead, New South Wales 2145, Australia
| | - Roger J Daly
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
| | - Lee H Wong
- Department of Biochemistry and Molecular Biology, Cancer Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia
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Maicher A, Kupiec M. Rnr1's role in telomere elongation cannot be replaced by Rnr3: a role beyond dNTPs? Curr Genet 2017; 64:547-550. [PMID: 29119271 DOI: 10.1007/s00294-017-0779-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Accepted: 11/03/2017] [Indexed: 11/29/2022]
Abstract
Telomeres, the nucleoprotein complexes at the end of eukaryotic chromosomes, protect them from degradation and ensure the replicative capacity of cells. In most human tumors and in budding yeast, telomere length is maintained by the activity of telomerase, an enzyme that adds dNTPs according to an internal RNA template. The dNTPs are generated with the help of the ribonucleotide reductase (RNR) complex. We have recently generated strains lacking the large subunit of RNR, Rnr1, which were kept viable by the expression of RNR complexes containing the Rnr1 homolog, Rnr3. Interestingly, we found that these Rnr1-deficient strains have short telomeres that are stably maintained, but cannot become efficiently elongated by telomerase. Thus, a basic maintenance of short telomeres is possible under conditions, where Rnr1 activity is absent, but a sustained elongation of short telomeres fully depends on Rnr1 activity. We show that Rnr3 cannot compensate for this telomeric function of Rnr1 even when overall cellular dNTP values are restored. This suggests that Rnr1 plays a role in telomere elongation beyond increasing cellular dNTP levels. Furthermore, our data indicate that telomerase may act in two different modes, one that is capable of coping with the "end-replication problem" and is functional even in the absence of Rnr1 and another required for the sustained elongation of short telomeres, which fully depends on the presence of Rnr1. Supply of dNTPs for telomere elongation is provided by the Mec1ATR checkpoint, both during regular DNA replication and upon replication fork stalling. We discuss the implications of these results on telomere maintenance in yeast and cancer cells.
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Affiliation(s)
- André Maicher
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, 6997801, Israel
| | - Martin Kupiec
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, 6997801, Israel.
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Renault AL, Mebirouk N, Cavaciuti E, Le Gal D, Lecarpentier J, d'Enghien CD, Laugé A, Dondon MG, Labbé M, Lesca G, Leroux D, Gladieff L, Adenis C, Faivre L, Gilbert-Dussardier B, Lortholary A, Fricker JP, Dahan K, Bay JO, Longy M, Buecher B, Janin N, Zattara H, Berthet P, Combès A, Coupier I, Hall J, Stoppa-Lyonnet D, Andrieu N, Lesueur F. Telomere length, ATM mutation status and cancer risk in Ataxia-Telangiectasia families. Carcinogenesis 2017; 38:994-1003. [PMID: 28981872 PMCID: PMC5862273 DOI: 10.1093/carcin/bgx074] [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] [Received: 01/08/2017] [Accepted: 07/08/2017] [Indexed: 11/12/2022] Open
Abstract
Recent studies have linked constitutive telomere length (TL) to aging-related diseases including cancer at different sites. ATM participates in the signaling of telomere erosion, and inherited mutations in ATM have been associated with increased risk of cancer, particularly breast cancer. The goal of this study was to investigate whether carriage of an ATM mutation and TL interplay to modify cancer risk in ataxia-telangiectasia (A-T) families.The study population consisted of 284 heterozygous ATM mutation carriers (HetAT) and 174 non-carriers (non-HetAT) from 103 A-T families. Forty-eight HetAT and 14 non-HetAT individuals had cancer, among them 25 HetAT and 6 non-HetAT were diagnosed after blood sample collection. We measured mean TL using a quantitative PCR assay and genotyped seven single-nucleotide polymorphisms (SNPs) recurrently associated with TL in large population-based studies.HetAT individuals were at increased risk of cancer (OR = 2.3, 95%CI = 1.2-4.4, P = 0.01), and particularly of breast cancer for women (OR = 2.9, 95%CI = 1.2-7.1, P = 0.02), in comparison to their non-HetAT relatives. HetAT individuals had longer telomeres than non-HetAT individuals (P = 0.0008) but TL was not associated with cancer risk, and no significant interaction was observed between ATM mutation status and TL. Furthermore, rs9257445 (ZNF311) was associated with TL in HetAT subjects and rs6060627 (BCL2L1) modified cancer risk in HetAT and non-HetAT women.Our findings suggest that carriage of an ATM mutation impacts on the age-related TL shortening and that TL per se is not related to cancer risk in ATM carriers. TL measurement alone is not a good marker for predicting cancer risk in A-T families.
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Affiliation(s)
- Anne-Laure Renault
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
| | - Noura Mebirouk
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
| | - Eve Cavaciuti
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
| | - Dorothée Le Gal
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
| | - Julie Lecarpentier
- Centre for Cancer Genetic Epidemiology, Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK
| | | | | | - Marie-Gabrielle Dondon
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
| | - Martine Labbé
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
| | - Gaetan Lesca
- CHU de Lyon, Groupement Hospitalier Est, Service de Génétique Médicale, Lyon, France
| | - Dominique Leroux
- CHU de Grenoble, Hôpital Couple-Enfant, Département de Génétique, Grenoble, France
| | - Laurence Gladieff
- Institut Claudius Regaud-IUCT-Oncopole, Service d'Oncologie Médicale, Toulouse, France
| | | | - Laurence Faivre
- Hôpital d'Enfants, Service de Génétique Médicale, Dijon, France
| | | | - Alain Lortholary
- Centre Catherine de Sienne, Service d'Oncologie Médicale, Nantes, France
| | | | - Karin Dahan
- Clinique Universitaire Saint-Luc, Génétique, Bruxelles, Belgium
| | | | | | | | - Nicolas Janin
- Clinique Universitaire Saint-Luc, Génétique, Bruxelles, Belgium
| | | | - Pascaline Berthet
- Centre François Baclesse, Unité de Pathologie Gynécologique, Caen, France
| | - Audrey Combès
- Centre Hospitalier Universitaire de Nîmes, Unité de Génétique Médicale et Cytogénétique, Nîmes, France
| | - Isabelle Coupier
- Hôpital Arnaud de Villeneuve, CHU Montpellier, Service de Génétique Médicale et Oncogénétique, Montpellier, France.,ICM Val d'Aurel, Unité d'Oncogénétique, Montpellier, France
| | | | - Janet Hall
- Centre de Recherche en Cancérologie de Lyon, Lyon, France.,UMR INSERM 1052, Lyon, France.,CNRS 5286, Lyon, France
| | - Dominique Stoppa-Lyonnet
- Service de Génétique, Institut Curie, Paris, France.,INSERM, U830, Paris, France.,Université Paris Descartes, Paris, France
| | - Nadine Andrieu
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
| | - Fabienne Lesueur
- INSERM, U900, Paris, France.,PSL Research University, Paris, France.,Institut Curie, Paris, France.,Mines Paris Tech, Fontainebleau, France
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Maicher A, Gazy I, Sharma S, Marjavaara L, Grinberg G, Shemesh K, Chabes A, Kupiec M. Rnr1, but not Rnr3, facilitates the sustained telomerase-dependent elongation of telomeres. PLoS Genet 2017; 13:e1007082. [PMID: 29069086 PMCID: PMC5673236 DOI: 10.1371/journal.pgen.1007082] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Revised: 11/06/2017] [Accepted: 10/18/2017] [Indexed: 12/25/2022] Open
Abstract
Ribonucleotide reductase (RNR) provides the precursors for the generation of dNTPs, which are required for DNA synthesis and repair. Here, we investigated the function of the major RNR subunits Rnr1 and Rnr3 in telomere elongation in budding yeast. We show that Rnr1 is essential for the sustained elongation of short telomeres by telomerase. In the absence of Rnr1, cells harbor very short, but functional, telomeres, which cannot become elongated by increased telomerase activity or by tethering of telomerase to telomeres. Furthermore, we demonstrate that Rnr1 function is critical to prevent an early onset of replicative senescence and premature survivor formation in telomerase-negative cells but dispensable for telomere elongation by Homology-Directed-Repair. Our results suggest that telomerase has a "basal activity" mode that is sufficient to compensate for the “end-replication-problem” and does not require the presence of Rnr1 and a different "sustained activity" mode necessary for the elongation of short telomeres, which requires an upregulation of dNTP levels and dGTP ratios specifically through Rnr1 function. By analyzing telomere length and dNTP levels in different mutants showing changes in RNR complex composition and activity we provide evidence that the Mec1ATR checkpoint protein promotes telomere elongation by increasing both dNTP levels and dGTP ratios through Rnr1 upregulation in a mechanism that cannot be replaced by its homolog Rnr3. Telomeres protect the ends of eukaryotic chromosomes and as such determine the replicative capacity of a cell. In budding yeast and approximately 80% of human tumors the enzyme telomerase maintains telomere length by adding newly synthesized repeats to telomeres using dNTPs generated by Ribonucleotide reductase (RNR) complexes. Similarly, telomerase activity can restore telomere length after more severe telomere shortenings that result from collapsed replication forks or lead to telomere over-elongation in the absence of negative regulators of telomerase. Here we provide evidence for two activity modes of telomerase that differentially depend on the major RNR subunit Rnr1. We demonstrate that telomere maintenance and a compensation of the "end-replication-problem" is possible under conditions where Rnr1 activity is absent but that a sustained elongation of short telomeres fully depends on Rnr1 activity. We show that the Rnr1-homolog, Rnr3, cannot compensate for this telomeric function of Rnr1 even when overall cellular dNTP values are restored.
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Affiliation(s)
- André Maicher
- Dept. of Molecular Microbiology & Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
| | - Inbal Gazy
- Dept. of Molecular Microbiology & Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
| | - Sushma Sharma
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Lisette Marjavaara
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Gilad Grinberg
- Dept. of Molecular Microbiology & Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
| | - Keren Shemesh
- Dept. of Molecular Microbiology & Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
| | - Andrei Chabes
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
- Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, Sweden
| | - Martin Kupiec
- Dept. of Molecular Microbiology & Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
- * E-mail:
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75
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Wang S, Pike AM, Lee SS, Strong MA, Connelly CJ, Greider CW. BRD4 inhibitors block telomere elongation. Nucleic Acids Res 2017; 45:8403-8410. [PMID: 28854735 PMCID: PMC5737673 DOI: 10.1093/nar/gkx561] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 06/22/2017] [Indexed: 12/25/2022] Open
Abstract
Cancer cells maintain telomere length equilibrium to avoid senescence and apoptosis induced by short telomeres, which trigger the DNA damage response. Limiting the potential for telomere maintenance in cancer cells has been long been proposed as a therapeutic target. Using an unbiased shRNA screen targeting known kinases, we identified bromodomain-containing protein 4 (BRD4) as a telomere length regulator. Four independent BRD4 inhibitors blocked telomere elongation, in a dose-dependent manner, in mouse cells overexpressing telomerase. Long-term treatment with BRD4 inhibitors caused telomere shortening in both mouse and human cells, suggesting BRD4 plays a role in telomere maintenance in vivo. Telomerase enzymatic activity was not directly affected by BRD4 inhibition. BRD4 is in clinical trials for a number of cancers, but its effects on telomere maintenance have not been previously investigated.
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Affiliation(s)
- Steven Wang
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.,Cellular and Molecular Medicine Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Alexandra M Pike
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.,Cellular and Molecular Medicine Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Stella S Lee
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Margaret A Strong
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Carla J Connelly
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Carol W Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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76
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Goto GH, Ogi H, Biswas H, Ghosh A, Tanaka S, Sugimoto K. Two separate pathways regulate protein stability of ATM/ATR-related protein kinases Mec1 and Tel1 in budding yeast. PLoS Genet 2017; 13:e1006873. [PMID: 28827813 PMCID: PMC5578694 DOI: 10.1371/journal.pgen.1006873] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 08/31/2017] [Accepted: 06/15/2017] [Indexed: 11/18/2022] Open
Abstract
Checkpoint signaling requires two conserved phosphatidylinositol 3-kinase-related protein kinases (PIKKs): ATM and ATR. In budding yeast, Tel1 and Mec1 correspond to ATM and ATR, respectively. The Tel2-Tti1-Tti2 (TTT) complex connects to the Rvb1-Rvb2-Tah1-Pih1 (R2TP) complex for the protein stability of PIKKs; however, TTT-R2TP interaction only partially mediates ATM and ATR protein stabilization. How TTT controls protein stability of ATM and ATR remains to be precisely determined. Here we show that Asa1, like Tel2, plays a major role in stabilization of newly synthesized Mec1 and Tel1 proteins whereas Pih1 contributes to Mec1 and Tel1 stability at high temperatures. Although Asa1 and Pih1 both interact with Tel2, no Asa1-Pih1 interaction is detected. Pih1 is distributed in both the cytoplasm and nucleus wheres Asa1 localizes largely in the cytoplasm. Asa1 and Pih1 are required for proper DNA damage checkpoint signaling. Our findings provide a model in which two different Tel2 pathways promote protein stabilization of Mec1 and Tel1 in budding yeast.
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Affiliation(s)
- Greicy H. Goto
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States of America
| | - Hiroo Ogi
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States of America
| | - Himadri Biswas
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States of America
| | - Avik Ghosh
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States of America
| | - Seiji Tanaka
- Division of Microbial Genetics, National Institute of Genetics, and Department of Genetics, School of Life Science, Graduate School for Advanced Studies, (SOKENDAI), Mishima, Shizuoka, Japan
| | - Katsunori Sugimoto
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States of America
- * E-mail:
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77
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Hapangama DK, Kamal A, Saretzki G. Implications of telomeres and telomerase in endometrial pathology. Hum Reprod Update 2017; 23:166-187. [PMID: 27979878 PMCID: PMC5850744 DOI: 10.1093/humupd/dmw044] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 12/02/2016] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Eukaryotic chromosomal ends are linear and are protected by nucleoprotein complexes known as telomeres. The complex structural anatomy and the diverse functions of telomeres as well as the unique reverse transcriptase enzyme, telomerase that maintains telomeres are under intensive scientific scrutiny. Both are involved in many human diseases including cancer, but also in ageing and chronic disease such as diabetes. Their intricate involvement in many cellular processes and pathways is being dynamically deciphered in many organs including the endometrium. This review summarizes our current knowledge on the topic of telomeres and telomerase and their potential role in providing plausible explanations for endometrial aberrations related to common gynaecological pathologies. OBJECTIVE AND RATIONALE This review outlines the recent major findings in telomere and telomerase functions in the context of endometrial biology. It highlights the contemporary discoveries in hormonal regulation, normal endometrial regeneration, stem cells and common gynaecological diseases such as endometriosis, infertility, recurrent reproductive failure and endometrial cancer (EC). SEARCH METHODS The authors carried out systematic PubMed (Medline) and Ovid searches using the key words: telomerase, telomeres, telomere length, human telomerase reverse transcriptase, telomeric RNA component, with endometrium, hormonal regulation, endometrial stem/progenitor cells, endometrial regeneration, endometriosis, recurrent miscarriage, infertility, endometrial hyperplasia, EC and uterine cancer. Publications used in this review date from 1995 until 31st June 2016. OUTCOMES The human endometrium is a unique somatic organ, which displays dynamic telomerase activity (TA) related to the menstrual cycle. Telomerase is implicated in almost all endometrial pathologies and appears to be crucial to endometrial stem cells. In particular, it is vital for normal endometrial regeneration, providing a distinct route to formulate possible curative, non-hormonal therapies to treat chronic endometrial conditions. Furthermore, our current understanding of telomere maintenance in EC is incomplete. Data derived from other malignancies on the role of telomerase in carcinogenesis cannot be extrapolated to EC because unlike in other cancers, TA is already present in proliferating healthy endometrial cells. WIDER IMPLICATIONS Since telomerase is pivotal to endometrial regeneration, further studies elucidating the role of telomeres, telomerase, their associated proteins and their regulation in normal endometrial regeneration as well as their role in endometrial pathologies are essential. This approach may allow future development of novel treatment strategies that are not only non-hormonal but also potentially curative.
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Affiliation(s)
- D K Hapangama
- Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, L8 7SS, UK.,Liverpool Women's Hospital NHS Foundation Trust, Crown Street, Liverpool L8 7SS, UK
| | - A Kamal
- Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, L8 7SS, UK.,The National Center for Early Detection of Cancer, Oncology Teaching Hospital, Baghdad Medical City, Baghdad, Iraq
| | - G Saretzki
- Institute for Ageing and Institute for Cell and Molecular Biosciences, Campus for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, NE4 5PL, UK
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78
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Collin V, Flamand L. HHV-6A/B Integration and the Pathogenesis Associated with the Reactivation of Chromosomally Integrated HHV-6A/B. Viruses 2017; 9:E160. [PMID: 28672870 PMCID: PMC5537652 DOI: 10.3390/v9070160] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 06/21/2017] [Accepted: 06/22/2017] [Indexed: 01/03/2023] Open
Abstract
Unlike other human herpesviruses, human herpesvirus 6A and 6B (HHV-6A/B) infection can lead to integration of the viral genome in human chromosomes. When integration occurs in germinal cells, the integrated HHV-6A/B genome can be transmitted to 50% of descendants. Such individuals, carrying one copy of the HHV-6A/B genome in every cell, are referred to as having inherited chromosomally-integrated HHV-6A/B (iciHHV-6) and represent approximately 1% of the world's population. Interestingly, HHV-6A/B integrate their genomes in a specific region of the chromosomes known as telomeres. Telomeres are located at chromosomes' ends and play essential roles in chromosomal stability and the long-term proliferative potential of cells. Considering that the integrated HHV-6A/B genome is mostly intact without any gross rearrangements or deletions, integration is likely used for viral maintenance into host cells. Knowing the roles played by telomeres in cellular homeostasis, viral integration in such structure is not likely to be without consequences. At present, the mechanisms and factors involved in HHV-6A/B integration remain poorly defined. In this review, we detail the potential biological and medical impacts of HHV-6A/B integration as well as the possible chromosomal integration and viral excision processes.
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Affiliation(s)
- Vanessa Collin
- Division of Infectious and Immune Diseases, CHU de Quebec Research Center-Laval University, Québec, QC G1V 4G2, Canada.
| | - Louis Flamand
- Division of Infectious and Immune Diseases, CHU de Quebec Research Center-Laval University, Québec, QC G1V 4G2, Canada.
- Department of Microbiology, Infectious Disease and Immunology, Faculty of Medicine, Laval University, Québec, QC G1V 0A6, Canada.
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79
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Abstract
Bacteria and viruses possess circular DNA, whereas eukaryotes with typically very large DNA molecules have had to evolve into linear chromosomes to circumvent the problem of supercoiling circular DNA of that size. Consequently, such organisms possess telomeres to cap chromosome ends. Telomeres are essentially tandem repeats of any DNA sequence that are present at the ends of chromosomes. Their biology has been an enigmatic one, involving various molecules interacting dynamically in an evolutionarily well-trimmed fashion. Telomeres range from canonical hexameric repeats in most eukaryotes to unimaginably random retrotransposons, which attach to chromosome ends and reverse-transcribe to DNA in some plants and insects. Telomeres invariably associate with specialised protein complexes that envelop it, also regulating access of the ends to legitimate enzymes involved in telomere metabolism. They also transcribe into repetitive RNA which also seems to be playing significant roles in telomere maintenance. Telomeres thus form the intersection of DNA, protein, and RNA molecules acting in concert to maintain chromosome integrity. Telomere biology is emerging to appear ever more complex than previously envisaged, with the continual discovery of more molecules and interplays at the telomeres. This review also includes a section dedicated to the history of telomere biology, and intends to target the scientific audience new to the field by rendering an understanding of the phenomenon of chromosome end protection at large, with more emphasis on the biology of human telomeres. The review provides an update on the field and mentions the questions that need to be addressed.
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Affiliation(s)
- Shriram Venkatesan
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, 117597 Singapore, Singapore.
| | - Aik Kia Khaw
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, 117597 Singapore, Singapore.
- Clinical Research Unit, Khoo Teck Puat Hospital, 768828 Singapore, Singapore.
| | - Manoor Prakash Hande
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, 117597 Singapore, Singapore.
- Tembusu College, National University of Singapore, 138598 Singapore, Singapore.
- VIT University, Vellore 632014, India.
- Mangalore University, Mangalore 574199, India.
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80
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Zhang T, Zhang Z, Li F, Hu Q, Liu H, Tang M, Ma W, Huang J, Songyang Z, Rong Y, Zhang S, Chen BP, Zhao Y. Looping-out mechanism for resolution of replicative stress at telomeres. EMBO Rep 2017; 18:1412-1428. [PMID: 28615293 DOI: 10.15252/embr.201643866] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 04/29/2017] [Accepted: 05/08/2017] [Indexed: 01/03/2023] Open
Abstract
Repetitive DNA is prone to replication fork stalling, which can lead to genome instability. Here, we find that replication fork stalling at telomeres leads to the formation of t-circle-tails, a new extrachromosomal structure that consists of circular telomeric DNA with a single-stranded tail. Structurally, the t-circle-tail resembles cyclized leading or lagging replication intermediates that are excised from the genome by topoisomerase II-mediated cleavage. We also show that the DNA damage repair machinery NHEJ is required for the formation of t-circle-tails and for the resolution of stalled replication forks, suggesting that NHEJ, which is normally constitutively suppressed at telomeres, is activated in the context of replication stress. Inhibition of NHEJ or knockout of DNA-PKcs impairs telomere replication, leading to multiple-telomere sites (MTS) and telomere shortening. Collectively, our results support a "looping-out" mechanism, in which the stalled replication fork is cut out and cyclized to form t-circle-tails, and broken DNA is religated. The telomere loss induced by replication stress may serve as a new factor that drives replicative senescence and cell aging.
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Affiliation(s)
- Tianpeng Zhang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.,Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha, China
| | - Zepeng Zhang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.,Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha, China
| | - Feng Li
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Qian Hu
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.,Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha, China
| | - Haiying Liu
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.,Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha, China
| | - Mengfan Tang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Wenbin Ma
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Junjiu Huang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Zhou Songyang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Yikang Rong
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Shichuan Zhang
- Department of Radiation Oncology, Sichuan Cancer Hospital, Chengdu, China
| | - Benjamin Pc Chen
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yong Zhao
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China .,Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha, China
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81
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Rice C, Shastrula PK, Kossenkov AV, Hills R, Baird DM, Showe LC, Doukov T, Janicki S, Skordalakes E. Structural and functional analysis of the human POT1-TPP1 telomeric complex. Nat Commun 2017; 8:14928. [PMID: 28393830 PMCID: PMC5394233 DOI: 10.1038/ncomms14928] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Accepted: 02/14/2017] [Indexed: 12/15/2022] Open
Abstract
POT1 and TPP1 are part of the shelterin complex and are essential for telomere length regulation and maintenance. Naturally occurring mutations of the telomeric POT1-TPP1 complex are implicated in familial glioma, melanoma and chronic lymphocytic leukaemia. Here we report the atomic structure of the interacting portion of the human telomeric POT1-TPP1 complex and suggest how several of these mutations contribute to malignant cancer. The POT1 C-terminus (POT1C) forms a bilobal structure consisting of an OB-fold and a holiday junction resolvase domain. TPP1 consists of several loops and helices involved in extensive interactions with POT1C. Biochemical data shows that several of the cancer-associated mutations, partially disrupt the POT1-TPP1 complex, which affects its ability to bind telomeric DNA efficiently. A defective POT1-TPP1 complex leads to longer and fragile telomeres, which in turn promotes genomic instability and cancer.
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Affiliation(s)
- Cory Rice
- The Wistar Institute, 3601 Spruce St, Philadelphia, Pennsylvania 19104, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | | | | | - Robert Hills
- The Wistar Institute, 3601 Spruce St, Philadelphia, Pennsylvania 19104, USA
| | - Duncan M. Baird
- Division of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff CF10 3AT, UK
| | - Louise C. Showe
- The Wistar Institute, 3601 Spruce St, Philadelphia, Pennsylvania 19104, USA
| | - Tzanko Doukov
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, USA
| | - Susan Janicki
- The Wistar Institute, 3601 Spruce St, Philadelphia, Pennsylvania 19104, USA
| | - Emmanuel Skordalakes
- The Wistar Institute, 3601 Spruce St, Philadelphia, Pennsylvania 19104, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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82
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Kang HT, Park JT, Choi K, Kim Y, Choi HJC, Jung CW, Lee YS, Park SC. Chemical screening identifies ATM as a target for alleviating senescence. Nat Chem Biol 2017; 13:616-623. [DOI: 10.1038/nchembio.2342] [Citation(s) in RCA: 91] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Accepted: 12/21/2016] [Indexed: 12/19/2022]
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83
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Vancevska A, Douglass KM, Pfeiffer V, Manley S, Lingner J. The telomeric DNA damage response occurs in the absence of chromatin decompaction. Genes Dev 2017; 31:567-577. [PMID: 28381410 PMCID: PMC5393052 DOI: 10.1101/gad.294082.116] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 02/14/2017] [Indexed: 12/22/2022]
Abstract
Telomeres are specialized nucleoprotein structures that protect chromosome ends from DNA damage response (DDR) and DNA rearrangements. The telomeric shelterin protein TRF2 suppresses the DDR, and this function has been attributed to its abilities to trigger t-loop formation or prevent massive decompaction and loss of density of telomeric chromatin. Here, we applied stochastic optical reconstruction microscopy (STORM) to measure the sizes and shapes of functional human telomeres of different lengths and dysfunctional telomeres that elicit a DDR. Telomeres have an ovoid appearance with considerable plasticity in shape. Examination of many telomeres demonstrated that depletion of TRF2, TRF1, or both affected the sizes of only a small subset of telomeres. Costaining of telomeres with DDR markers further revealed that the majority of DDR signaling telomeres retained a normal size. Thus, DDR signaling at telomeres does not require decompaction. We propose that telomeres are monitored by the DDR machinery in the absence of telomere expansion and that the DDR is triggered by changes at the molecular level in structure and protein composition.
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Affiliation(s)
- Aleksandra Vancevska
- Swiss Institute for Experimental Cancer Research, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Kyle M Douglass
- Institute of Physics, Laboratory of Experimental Biophysics, EPFL, 1015 Lausanne, Switzerland
| | - Verena Pfeiffer
- Swiss Institute for Experimental Cancer Research, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Suliana Manley
- Institute of Physics, Laboratory of Experimental Biophysics, EPFL, 1015 Lausanne, Switzerland
| | - Joachim Lingner
- Swiss Institute for Experimental Cancer Research, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
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84
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Abstract
Telomerase is the essential reverse transcriptase required for linear chromosome maintenance in most eukaryotes. Telomerase supplements the tandem array of simple-sequence repeats at chromosome ends to compensate for the DNA erosion inherent in genome replication. The template for telomerase reverse transcriptase is within the RNA subunit of the ribonucleoprotein complex, which in cells contains additional telomerase holoenzyme proteins that assemble the active ribonucleoprotein and promote its function at telomeres. Telomerase is distinct among polymerases in its reiterative reuse of an internal template. The template is precisely defined, processively copied, and regenerated by release of single-stranded product DNA. New specificities of nucleic acid handling that underlie the catalytic cycle of repeat synthesis derive from both active site specialization and new motif elaborations in protein and RNA subunits. Studies of telomerase provide unique insights into cellular requirements for genome stability, tissue renewal, and tumorigenesis as well as new perspectives on dynamic ribonucleoprotein machines.
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Affiliation(s)
- R Alex Wu
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202; , , ,
| | - Heather E Upton
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202; , , ,
| | - Jacob M Vogan
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202; , , ,
| | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202; , , ,
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85
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Brown JS, O'Carrigan B, Jackson SP, Yap TA. Targeting DNA Repair in Cancer: Beyond PARP Inhibitors. Cancer Discov 2017; 7:20-37. [PMID: 28003236 PMCID: PMC5300099 DOI: 10.1158/2159-8290.cd-16-0860] [Citation(s) in RCA: 429] [Impact Index Per Article: 61.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 11/03/2016] [Accepted: 11/07/2016] [Indexed: 01/14/2023]
Abstract
Germline aberrations in critical DNA-repair and DNA damage-response (DDR) genes cause cancer predisposition, whereas various tumors harbor somatic mutations causing defective DDR/DNA repair. The concept of synthetic lethality can be exploited in such malignancies, as exemplified by approval of poly(ADP-ribose) polymerase inhibitors for treating BRCA1/2-mutated ovarian cancers. Herein, we detail how cellular DDR processes engage various proteins that sense DNA damage, initiate signaling pathways to promote cell-cycle checkpoint activation, trigger apoptosis, and coordinate DNA repair. We focus on novel therapeutic strategies targeting promising DDR targets and discuss challenges of patient selection and the development of rational drug combinations. SIGNIFICANCE Various inhibitors of DDR components are in preclinical and clinical development. A thorough understanding of DDR pathway complexities must now be combined with strategies and lessons learned from the successful registration of PARP inhibitors in order to fully exploit the potential of DDR inhibitors and to ensure their long-term clinical success. Cancer Discov; 7(1); 20-37. ©2016 AACR.
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Affiliation(s)
| | | | - Stephen P Jackson
- The Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
- The Wellcome Trust Sanger Institute, Hinxton, Cambridge, United Kingdom
| | - Timothy A Yap
- Royal Marsden NHS Foundation Trust, London, United Kingdom.
- The Institute of Cancer Research, London, United Kingdom
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86
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Telomere-associated aging disorders. Ageing Res Rev 2017; 33:52-66. [PMID: 27215853 PMCID: PMC9926533 DOI: 10.1016/j.arr.2016.05.009] [Citation(s) in RCA: 98] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Revised: 05/17/2016] [Accepted: 05/19/2016] [Indexed: 01/25/2023]
Abstract
Telomeres are dynamic nucleoprotein-DNA structures that cap and protect linear chromosome ends. Several monogenic inherited diseases that display features of human premature aging correlate with shortened telomeres, and are referred to collectively as telomeropathies. These disorders have overlapping symptoms and a common underlying mechanism of telomere dysfunction, but also exhibit variable symptoms and age of onset, suggesting they fall along a spectrum of disorders. Primary telomeropathies are caused by defects in the telomere maintenance machinery, whereas secondary telomeropathies have some overlapping symptoms with primary telomeropathies, but are generally caused by mutations in DNA repair proteins that contribute to telomere preservation. Here we review both the primary and secondary telomeropathies, discuss potential mechanisms for tissue specificity and age of onset, and highlight outstanding questions in the field and future directions toward elucidating disease etiology and developing therapeutic strategies.
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87
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Heidenreich B, Kumar R. TERT promoter mutations in telomere biology. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2016; 771:15-31. [PMID: 28342451 DOI: 10.1016/j.mrrev.2016.11.002] [Citation(s) in RCA: 130] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 11/10/2016] [Indexed: 02/07/2023]
Abstract
Telomere repeats at chromosomal ends, critical to genome integrity, are maintained through an elaborate network of proteins and pathways. Shelterin complex proteins shield telomeres from induction of DNA damage response to overcome end protection problem. A specialized ribonucleic protein, telomerase, maintains telomere homeostasis through repeat addition to counter intrinsic shortcomings of DNA replication that leads to gradual sequence shortening in successive mitoses. The biogenesis and recruitment of telomerase composed of telomerase reverse transcriptase (TERT) subunit and an RNA component, takes place through the intricate machinery that involves an elaborate number of molecules. The synthesis of telomeres remains a controlled and limited process. Inherited mutations in the molecules involved in the process directly or indirectly cause telomeropathies. Telomerase, while present in stem cells, is deactivated due to epigenetic silencing of the rate-limiting TERT upon differentiation in most of somatic cells with a few exceptions. However, in most of the cancer cells telomerase reactivation remains a ubiquitous process and constitutes one of the major hallmarks. Discovery of mutations within the core promoter of the TERT gene that create de novo binding sites for E-twenty-six (ETS) transcription factors provided a mechanism for cancer-specific telomerase reactivation. The TERT promoter mutations occur mainly in tumors from tissues with low rates of self-renewal. In melanoma, glioma, hepatocellular carcinoma, urothelial carcinoma and others, the promoter mutations have been shown to define subsets of patients with adverse disease outcomes, associate with increased transcription of TERT, telomerase reactivation and affect telomere length; in stem cells the mutations inhibit TERT silencing following differentiation into adult cells. The TERT promoter mutations cause an epigenetic switch on the mutant allele along with recruitment of pol II following the binding of GABPA/B1 complex that leads to mono-allelic expression. Thus, the TERT promoter mutations hold potential as biomarkers as well as future therapeutic targets.
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Affiliation(s)
| | - Rajiv Kumar
- Division of Molecular Genetic Epidemiology; German Consortium for Translational Cancer Research (DKTK), German Cancer Research Center, 69120 Heidelberg, Germany.
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88
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MacNeil DE, Bensoussan HJ, Autexier C. Telomerase Regulation from Beginning to the End. Genes (Basel) 2016; 7:genes7090064. [PMID: 27649246 PMCID: PMC5042394 DOI: 10.3390/genes7090064] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 08/25/2016] [Accepted: 08/26/2016] [Indexed: 12/11/2022] Open
Abstract
The vast body of literature regarding human telomere maintenance is a true testament to the importance of understanding telomere regulation in both normal and diseased states. In this review, our goal was simple: tell the telomerase story from the biogenesis of its parts to its maturity as a complex and function at its site of action, emphasizing new developments and how they contribute to the foundational knowledge of telomerase and telomere biology.
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Affiliation(s)
- Deanna Elise MacNeil
- Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Côte Ste-Catherine Road, Montréal, QC H3T 1E2, Canada.
- Room M-29, Department of Anatomy and Cell Biology, McGill University, 3640 University Street, Montréal, QC H3A 0C7, Canada.
| | - Hélène Jeanne Bensoussan
- Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Côte Ste-Catherine Road, Montréal, QC H3T 1E2, Canada.
- Room M-29, Department of Anatomy and Cell Biology, McGill University, 3640 University Street, Montréal, QC H3A 0C7, Canada.
| | - Chantal Autexier
- Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Côte Ste-Catherine Road, Montréal, QC H3T 1E2, Canada.
- Room M-29, Department of Anatomy and Cell Biology, McGill University, 3640 University Street, Montréal, QC H3A 0C7, Canada.
- Department of Experimental Medicine, McGill University, 1110 Pins Avenue West, Room 101, Montréal, QC H3A 1A3, Canada.
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89
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Abstract
The ATR (ATM and rad3-related) pathway is crucial for proliferation, responding to DNA replication stress and DNA damage. This critical signaling pathway is carefully orchestrated through a multistep process requiring initial priming of ATR prior to damage, recruitment of ATR to DNA damage lesions, activation of ATR signaling, and, finally, modulation of ATR activity through a variety of post-translational modifications. Following activation, ATR functions in several vital cellular processes, including suppression of replication origin firing, promotion of deoxynucleotide synthesis and replication fork restart, prevention of double-stranded DNA break formation, and avoidance of replication catastrophe and mitotic catastrophe. In many cancers, tumor cells have increased dependence on ATR signaling for survival, making ATR a promising target for cancer therapy. Tumor cells compromised in DNA repair pathways or DNA damage checkpoints, cells reliant on homologous recombination, and cells with increased replication stress are particularly sensitive to ATR inhibition. Understanding ATR signaling and modulation is essential to unraveling which tumors have increased dependence on ATR signaling as well as how the ATR pathway can best be exploited for targeted cancer therapy.
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Affiliation(s)
- Stephanie A Yazinski
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, Massachusetts 02129;
| | - Lee Zou
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, Massachusetts 02129; .,Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02115
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90
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Robust reprogramming of Ataxia-Telangiectasia patient and carrier erythroid cells to induced pluripotent stem cells. Stem Cell Res 2016; 17:296-305. [DOI: 10.1016/j.scr.2016.08.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Revised: 07/29/2016] [Accepted: 08/06/2016] [Indexed: 12/18/2022] Open
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91
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Schmidt JC, Zaug AJ, Cech TR. Live Cell Imaging Reveals the Dynamics of Telomerase Recruitment to Telomeres. Cell 2016; 166:1188-1197.e9. [PMID: 27523609 PMCID: PMC5743434 DOI: 10.1016/j.cell.2016.07.033] [Citation(s) in RCA: 124] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2016] [Revised: 06/14/2016] [Accepted: 07/21/2016] [Indexed: 01/22/2023]
Abstract
Telomerase maintains genome integrity by adding repetitive DNA sequences to the chromosome ends in actively dividing cells, including 90% of all cancer cells. Recruitment of human telomerase to telomeres occurs during S-phase of the cell cycle, but the molecular mechanism of the process is only partially understood. Here, we use CRISPR genome editing and single-molecule imaging to track telomerase trafficking in nuclei of living human cells. We demonstrate that telomerase uses three-dimensional diffusion to search for telomeres, probing each telomere thousands of times each S-phase but only rarely forming a stable association. Both the transient and stable association events depend on the direct interaction of the telomerase protein TERT with the telomeric protein TPP1. Our results reveal that telomerase recruitment to telomeres is driven by dynamic interactions between the rapidly diffusing telomerase and the chromosome end.
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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, CO 80309, USA
| | - Arthur J Zaug
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Thomas R Cech
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado Boulder, Boulder, CO 80309, USA.
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92
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Germ line mutations in shelterin complex genes are associated with familial chronic lymphocytic leukemia. Blood 2016; 128:2319-2326. [PMID: 27528712 DOI: 10.1182/blood-2016-01-695692] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 08/08/2016] [Indexed: 12/30/2022] Open
Abstract
Chronic lymphocytic leukemia (CLL) can be familial; however, thus far no rare germ line disruptive alleles for CLL have been identified. We performed whole-exome sequencing of 66 CLL families, identifying 4 families where loss-of-function mutations in protection of telomeres 1 (POT1) co-segregated with CLL. The p.Tyr36Cys mutation is predicted to disrupt the interaction between POT1 and the telomeric overhang. The c.1164-1G>A splice-site, p.Gln358SerfsTer13 frameshift, and p.Gln376Arg missense mutations are likely to impact the interaction between POT1 and adrenocortical dysplasia homolog (ACD), which is a part of the telomere-capping shelterin complex. We also identified mutations in ACD (c.752-2A>C) and another shelterin component, telomeric repeat binding factor 2, interacting protein (p.Ala104Pro and p.Arg133Gln), in 3 CLL families. In a complementary analysis of 1083 cases and 5854 controls, the POT1 p.Gln376Arg variant, which has a global minor allele frequency of 0.0005, conferred a 3.61-fold increased risk of CLL (P = .009). This study further highlights telomere dysregulation as a key process in CLL development.
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93
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Derepression of hTERT gene expression promotes escape from oncogene-induced cellular senescence. Proc Natl Acad Sci U S A 2016; 113:E5024-33. [PMID: 27503890 DOI: 10.1073/pnas.1602379113] [Citation(s) in RCA: 88] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Oncogene-induced senescence (OIS) is a critical tumor-suppressing mechanism that restrains cancer progression at premalignant stages, in part by causing telomere dysfunction. Currently it is unknown whether this proliferative arrest presents a stable and therefore irreversible barrier to cancer progression. Here we demonstrate that cells frequently escape OIS induced by oncogenic H-Ras and B-Raf, after a prolonged period in the senescence arrested state. Cells that had escaped senescence displayed high oncogene expression levels, retained functional DNA damage responses, and acquired chromatin changes that promoted c-Myc-dependent expression of the human telomerase reverse transcriptase gene (hTERT). Telomerase was able to resolve existing telomeric DNA damage response foci and suppressed formation of new ones that were generated as a consequence of DNA replication stress and oncogenic signals. Inhibition of MAP kinase signaling, suppressing c-Myc expression, or inhibiting telomerase activity, caused telomere dysfunction and proliferative defects in cells that had escaped senescence, whereas ectopic expression of hTERT facilitated OIS escape. In human early neoplastic skin and breast tissue, hTERT expression was detected in cells that displayed features of senescence, suggesting that reactivation of telomerase expression in senescent cells is an early event during cancer progression in humans. Together, our data demonstrate that cells arrested in OIS retain the potential to escape senescence by mechanisms that involve derepression of hTERT expression.
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94
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Abstract
Telomeres at chromosome ends are nucleoprotein structures consisting of tandem TTAGGG repeats and a complex of proteins termed shelterin. DNA damage and repair at telomeres is uniquely influenced by the ability of telomeric DNA to form alternate structures including loops and G-quadruplexes, coupled with the ability of shelterin proteins to interact with and regulate enzymes in every known DNA repair pathway. The role of shelterin proteins in preventing telomeric ends from being falsely recognized and processed as DNA double strand breaks is well established. Here we focus instead on recent developments in understanding the roles of shelterin proteins and telomeric DNA sequence and structure in processing genuine damage at telomeres induced by endogenous and exogenous DNA damage agents. We will highlight advances in double strand break repair, base excision repair and nucleotide excision repair at telomeres, and will discuss important questions remaining in the field.
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Affiliation(s)
- Elise Fouquerel
- Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, University of Pittsburgh Cancer Institute Research Pavilion, 5117 Centre Avenue, University of Pittsburgh, Pittsburgh, PA 15213, United States
| | - Dhvani Parikh
- Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, University of Pittsburgh Cancer Institute Research Pavilion, 5117 Centre Avenue, University of Pittsburgh, Pittsburgh, PA 15213, United States
| | - Patricia Opresko
- Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, University of Pittsburgh Cancer Institute Research Pavilion, 5117 Centre Avenue, University of Pittsburgh, Pittsburgh, PA 15213, United States.
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95
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Abstract
Telomeres maintain genomic integrity in normal cells, and their progressive shortening during successive cell divisions induces chromosomal instability. In the large majority of cancer cells, telomere length is maintained by telomerase. Thus, telomere length and telomerase activity are crucial for cancer initiation and the survival of tumors. Several pathways that regulate telomere length have been identified, and genome-scale studies have helped in mapping genes that are involved in telomere length control. Additionally, genomic screening for recurrent human telomerase gene hTERT promoter mutations and mutations in genes involved in the alternative lengthening of telomeres pathway, such as ATRX and DAXX, has elucidated how these genomic changes contribute to the activation of telomere maintenance mechanisms in cancer cells. Attempts have also been made to develop telomere length- and telomerase-based diagnostic tools and anticancer therapeutics. Recent efforts have revealed key aspects of telomerase assembly, intracellular trafficking and recruitment to telomeres for completing DNA synthesis, which may provide novel targets for the development of anticancer agents. Here, we summarize telomere organization and function and its role in oncogenesis. We also highlight genomic mutations that lead to reactivation of telomerase, and mechanisms of telomerase reconstitution and trafficking that shed light on its function in cancer initiation and tumor development. Additionally, recent advances in the clinical development of telomerase inhibitors, as well as potential novel targets, will be summarized.
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96
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Hu X, Liu J, Jun HI, Kim JK, Qiao F. Multi-step coordination of telomerase recruitment in fission yeast through two coupled telomere-telomerase interfaces. eLife 2016; 5. [PMID: 27253066 PMCID: PMC4936895 DOI: 10.7554/elife.15470] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 06/01/2016] [Indexed: 12/22/2022] Open
Abstract
Tightly controlled recruitment of telomerase, a low-abundance enzyme, to telomeres is essential for regulated telomere synthesis. Recent studies in human cells revealed that a patch of amino acids in the shelterin component TPP1, called the TEL-patch, is essential for recruiting telomerase to telomeres. However, how TEL-patch—telomerase interaction integrates into the overall orchestration of telomerase regulation at telomeres is unclear. In fission yeast, Tel1ATM/Rad3ATR-mediated phosphorylation of shelterin component Ccq1 during late S phase is involved in telomerase recruitment through promoting the binding of Ccq1 to a telomerase accessory protein Est1. Here, we identify the TEL-patch in Tpz1TPP1, mutations of which lead to decreased telomeric association of telomerase, similar to the phosphorylation-defective Ccq1. Furthermore, we find that telomerase action at telomeres requires formation and resolution of an intermediate state, in which the cell cycle-dependent Ccq1-Est1 interaction is coupled to the TEL-patch—Trt1 interaction, to achieve temporally regulated telomerase elongation of telomeres. DOI:http://dx.doi.org/10.7554/eLife.15470.001 The genetic blueprints for animals, plants and fungi are mostly contained within long strands of DNA and packaged into more compact thread-like structures called chromosomes. As such, most cells need to duplicate their chromosomes before they divide so that the two new cells each get a complete set of genetic instructions. The machinery that copies DNA is unable to make it to the very ends of the chromosomes. Instead, an enzyme called telomerase adds new DNA to the chromosome ends to prevent them becoming too short. Problems with this process can cause serious issues, such as cell death or cancer, and so the activity of telomerase is carefully controlled. Other proteins guide telomerase to the ends of the chromosome only after the rest of the DNA has been copied. However, scientists do not know exactly how cells correctly time the arrival of telomerase. A group of proteins called shelterin protects the chromosome ends, and studies with human cells have shown that telomerase attaches to a specific patch on one of shelterin proteins, called the TEL-patch, to begin its work. Now, Hu, Liu et al. have identified a similar TEL-patch in a shelterin protein from a type of yeast called fission yeast; this patch is also needed to attach telomerase to the chromosome ends. Further experiments with this yeast then showed that telomerase only arrives at the ends of the chromosomes after two parallel interaction interfaces have formed. Importantly, one of these interactions only takes place after most of the chromosomes are have been copied. As such, this “two-pronged interaction” mechanism ensures that the telomerase enzyme arrives at the end of the chromosomes at the right time. Other similarities between human and fission yeast chromosome ends make it plausible that a comparable process controls the timing of telomerase attachment in human cells. However, more studies will be needed to confirm if this is the case. DOI:http://dx.doi.org/10.7554/eLife.15470.002
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Affiliation(s)
- Xichan Hu
- Department of Biological Chemistry, University of California, Irvine School of Medicine, Irvine, United States
| | - Jinqiang Liu
- Department of Biological Chemistry, University of California, Irvine School of Medicine, Irvine, United States
| | - Hyun-Ik Jun
- Department of Biological Chemistry, University of California, Irvine School of Medicine, Irvine, United States
| | - Jin-Kwang Kim
- Department of Biological Chemistry, University of California, Irvine School of Medicine, Irvine, United States
| | - Feng Qiao
- Department of Biological Chemistry, University of California, Irvine School of Medicine, Irvine, United States
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97
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Sridharan DM, Asaithamby A, Blattnig SR, Costes SV, Doetsch PW, Dynan WS, Hahnfeldt P, Hlatky L, Kidane Y, Kronenberg A, Naidu MD, Peterson LE, Plante I, Ponomarev AL, Saha J, Snijders AM, Srinivasan K, Tang J, Werner E, Pluth JM. Evaluating biomarkers to model cancer risk post cosmic ray exposure. LIFE SCIENCES IN SPACE RESEARCH 2016; 9:19-47. [PMID: 27345199 PMCID: PMC5613937 DOI: 10.1016/j.lssr.2016.05.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 05/11/2016] [Indexed: 06/06/2023]
Abstract
Robust predictive models are essential to manage the risk of radiation-induced carcinogenesis. Chronic exposure to cosmic rays in the context of the complex deep space environment may place astronauts at high cancer risk. To estimate this risk, it is critical to understand how radiation-induced cellular stress impacts cell fate decisions and how this in turn alters the risk of carcinogenesis. Exposure to the heavy ion component of cosmic rays triggers a multitude of cellular changes, depending on the rate of exposure, the type of damage incurred and individual susceptibility. Heterogeneity in dose, dose rate, radiation quality, energy and particle flux contribute to the complexity of risk assessment. To unravel the impact of each of these factors, it is critical to identify sensitive biomarkers that can serve as inputs for robust modeling of individual risk of cancer or other long-term health consequences of exposure. Limitations in sensitivity of biomarkers to dose and dose rate, and the complexity of longitudinal monitoring, are some of the factors that increase uncertainties in the output from risk prediction models. Here, we critically evaluate candidate early and late biomarkers of radiation exposure and discuss their usefulness in predicting cell fate decisions. Some of the biomarkers we have reviewed include complex clustered DNA damage, persistent DNA repair foci, reactive oxygen species, chromosome aberrations and inflammation. Other biomarkers discussed, often assayed for at longer points post exposure, include mutations, chromosome aberrations, reactive oxygen species and telomere length changes. We discuss the relationship of biomarkers to different potential cell fates, including proliferation, apoptosis, senescence, and loss of stemness, which can propagate genomic instability and alter tissue composition and the underlying mRNA signatures that contribute to cell fate decisions. Our goal is to highlight factors that are important in choosing biomarkers and to evaluate the potential for biomarkers to inform models of post exposure cancer risk. Because cellular stress response pathways to space radiation and environmental carcinogens share common nodes, biomarker-driven risk models may be broadly applicable for estimating risks for other carcinogens.
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Affiliation(s)
| | | | - Steve R Blattnig
- Langley Research Center, Langley Research Center (LaRC), VA, United States
| | - Sylvain V Costes
- Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | | | | | | | - Lynn Hlatky
- CCSB-Tufts School of Medicine, Boston, MA, United States
| | - Yared Kidane
- Wyle Science, Technology & Engineering Group, Houston, TX, United States
| | - Amy Kronenberg
- Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - Mamta D Naidu
- CCSB-Tufts School of Medicine, Boston, MA, United States
| | - Leif E Peterson
- Houston Methodist Research Institute, Houston, TX, United States
| | - Ianik Plante
- Wyle Science, Technology & Engineering Group, Houston, TX, United States
| | - Artem L Ponomarev
- Wyle Science, Technology & Engineering Group, Houston, TX, United States
| | - Janapriya Saha
- UT Southwestern Medical Center, Dallas, TX, United States
| | | | | | - Jonathan Tang
- Exogen Biotechnology, Inc., Berkeley, CA, United States
| | | | - Janice M Pluth
- Lawrence Berkeley National Laboratory, Berkeley, CA, United States.
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98
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Pinzaru AM, Hom RA, Beal A, Phillips AF, Ni E, Cardozo T, Nair N, Choi J, Wuttke DS, Sfeir A, Denchi EL. Telomere Replication Stress Induced by POT1 Inactivation Accelerates Tumorigenesis. Cell Rep 2016; 15:2170-2184. [PMID: 27239034 PMCID: PMC6145145 DOI: 10.1016/j.celrep.2016.05.008] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 02/19/2016] [Accepted: 04/22/2016] [Indexed: 01/05/2023] Open
Abstract
Genome sequencing studies have revealed a number of cancer-associated mutations in the telomerebinding factor POT1. Here, we show that when combined with p53 deficiency, depletion of murine POT1a in common lymphoid progenitor cells fosters genetic instability, accelerates the onset, and increases the severity of T cell lymphomas. In parallel, we examined human and mouse cells carrying POT1 mutations found in cutaneous T cell lymphoma (CTCL) patients. Inhibition of POT1 activates ATRdependent DNA damage signaling and induces telomere fragility, replication fork stalling, and telomere elongation. Our data suggest that these phenotypes are linked to impaired CST (CTC1-STN1-TEN1) function at telomeres. Lastly, we show that proliferation of cancer cells lacking POT1 is enabled by the attenuation of the ATR kinase pathway. These results uncover a role for defective telomere replication during tumorigenesis. Pinzaru et al. define a role for POT1 inactivation in the onset of thymic lymphomas. Inhibition of POT1 causes replication defects at telomeres resulting in telomere fragility, replication fork stalling, and genome instability. These results suggest a role of defective telemore replication during tumorigenesis
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Affiliation(s)
- Alexandra M Pinzaru
- Department of Cell Biology, Skirball Institute of Biomolecular Medicine, NYU School of Medicine, New York, NY 10016, USA
| | - Robert A Hom
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA
| | - Angela Beal
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Aaron F Phillips
- Department of Cell Biology, Skirball Institute of Biomolecular Medicine, NYU School of Medicine, New York, NY 10016, USA
| | - Eric Ni
- Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, NY 10016, USA
| | - Timothy Cardozo
- Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, NY 10016, USA
| | - Nidhi Nair
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Jaehyuk Choi
- Departments of Dermatology and Biochemistry and Molecular Genetics, Northwestern University, Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Deborah S Wuttke
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA
| | - Agnel Sfeir
- Department of Cell Biology, Skirball Institute of Biomolecular Medicine, NYU School of Medicine, New York, NY 10016, USA.
| | - Eros Lazzerini Denchi
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA.
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99
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Lee SS, Bohrson C, Pike AM, Wheelan SJ, Greider CW. ATM Kinase Is Required for Telomere Elongation in Mouse and Human Cells. Cell Rep 2015; 13:1623-32. [PMID: 26586427 PMCID: PMC4663052 DOI: 10.1016/j.celrep.2015.10.035] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Revised: 09/11/2015] [Accepted: 10/11/2015] [Indexed: 12/26/2022] Open
Abstract
Short telomeres induce a DNA damage response, senescence, and apoptosis, thus maintaining telomere length equilibrium is essential for cell viability. Telomerase addition of telomere repeats is tightly regulated in cells. To probe pathways that regulate telomere addition, we developed the ADDIT assay to measure new telomere addition at a single telomere in vivo. Sequence analysis showed telomerase-specific addition of repeats onto a new telomere occurred in just 48 hr. Using the ADDIT assay, we found that ATM is required for addition of new repeats onto telomeres in mouse cells. Evaluation of bulk telomeres, in both human and mouse cells, showed that blocking ATM inhibited telomere elongation. Finally, the activation of ATM through the inhibition of PARP1 resulted in increased telomere elongation, supporting the central role of the ATM pathway in regulating telomere addition. Understanding this role of ATM may yield new areas for possible therapeutic intervention in telomere-mediated disease.
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Affiliation(s)
- Stella Suyong Lee
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Craig Bohrson
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Alexandra Mims Pike
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Sarah Jo Wheelan
- Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA
| | - Carol Widney Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
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