151
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Monti V, Giusti M, Bizzaro D, Manicardi GC, Mandrioli M. Presence of a functional (TTAGG)(n) telomere-telomerase system in aphids. Chromosome Res 2011; 19:625-33. [PMID: 21667174 DOI: 10.1007/s10577-011-9222-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Revised: 05/18/2011] [Accepted: 05/20/2011] [Indexed: 11/28/2022]
Abstract
The structure of the telomeres of four aphid species (Acyrthosiphon pisum, Megoura viciae, Myzus persicae and Rhopalosiphum padi) was evaluated by Southern blotting and fluorescent in situ hybridization, revealing that each chromosomal end consists of a (TTAGG)(n) repeat. The presence of a telomerase coding gene has been verified successively in the A. pisum genome, revealing that aphid telomerase shares sequence identity ranging from 12% to 18% with invertebrate and vertebrate homologues, and possesses the two main domains involved in telomerase activity. Interestingly, telomerase expression has been verified in different somatic tissues suggesting that, in aphids, telomerase activity is not as restricted as in human cells. The study of telomeres in a M. persicae strain with a variable chromosome number showed that aphid telomerase can initiate the de novo synthesis of telomere sequences at internal breakpoints, resulting in the stabilization of chromosomal fragments.
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Affiliation(s)
- Valentina Monti
- Dipartimento di Biologia, Università di Modena e Reggio Emilia, Via Campi 213/D, 41125 Modena, Italy
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152
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Lu L, Zhang C, Zhu G, Irwin M, Risch H, Menato G, Mitidieri M, Katsaros D, Yu H. Telomerase expression and telomere length in breast cancer and their associations with adjuvant treatment and disease outcome. Breast Cancer Res 2011; 13:R56. [PMID: 21645396 PMCID: PMC3218945 DOI: 10.1186/bcr2893] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Revised: 04/21/2011] [Accepted: 06/06/2011] [Indexed: 12/16/2022] Open
Abstract
Introduction Telomere length plays important roles in maintaining genome stability and regulating cell replication and death. Telomerase has functions not only to extend telomere length but also to repair DNA damage. Studies have shown that telomerase may increase cancer cell resistance to DNA-damaging anticancer agents; tamoxifen may suppress telomerase expression in breast cancer cells. This study aimed to investigate the role of telomere length and telomerase activity in breast cancer prognosis. Methods qPCR and qRT-PCR were used to analyze telomere length and telomerase expression, respectively, in tumor samples of 348 breast cancer patients. Cox regression analysis was performed to examine telomere length and telomerase expression in association with disease-free survival and cause-specific mortality. Results Telomere length had no relation to tumor features or disease outcomes. Telomerase expression was detected in 53% of tumors. Larger tumors or aggressive disease were more likely to have telomerase expression. Among patients treated with chemotherapy, high telomerase was found to be associated with increased risk of death (hazard ratio (HR) = 3.15; 95% CI: 1.34 to 7.40) and disease recurrence (HR = 2.04; 95% CI: 0.96 to 4.30) regardless of patient age, disease stage, tumor grade, histological type or hormone receptor status. Patients treated with endocrine therapy had different results regarding telomerase: high telomerase appeared to be associated with better survival outcomes. Telomerase expression made no survival difference in patients who received both chemotherapy and endocrine therapy. Conclusions Overall, telomerase expression was not associated with disease outcome, but this finding may be masked by adjuvant treatment. Patients with high telomerase expression responded poorly to chemotherapy in terms of disease-free and overall survival, but fared better if treated with endocrine therapy.
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Affiliation(s)
- Lingeng Lu
- Department of Epidemiology and Public Health, Yale Cancer Center, Yale University School of Medicine, New Haven, CT 06520-8034, USA
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153
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High-mobility group A2 protein modulates hTERT transcription to promote tumorigenesis. Mol Cell Biol 2011; 31:2605-17. [PMID: 21536653 DOI: 10.1128/mcb.05447-11] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The high-mobility group A2 gene (HMGA2) is one of the most frequently amplified genes in human cancers. However, functions of HMGA2 in tumorigenesis are not fully understood due to limited knowledge of its targets in tumor cells. Our study reveals a novel link between HMGA2 and the regulation of human telomerase reverse transcriptase (hTERT), the catalytic subunit of telomerase, which offers critical insight into how HMGA2 contributes to tumorigenesis. The expression of HMGA2 modulates the expression of hTERT, resulting in cells with enhanced telomerase activities and increased telomere length. Treatment with suberoylanilide hydroxamide (SAHA), a histone deacetylase (HDAC) inhibitor, causes dose-dependent hTERT reporter activation, mimicking HMGA2 overexpression. By interacting with Sp1, HMGA2 interferes with the recruitment of HDAC2 to the hTERT proximal promoter, enhancing localized histone H3-K9 acetylation and thereby stimulating hTERT expression and telomerase activity. Moreover, HMGA2 knockdown by short hairpin HMGA2 in HepG2 cells leads to progressive telomere shortening and a concurrent decrease of steady-state hTERT mRNA levels, attenuating their ability to form colonies in soft agar. Importantly, HMGA2 partially replaces the function of hTERT during the tumorigenic transformation of normal human fibroblasts. These findings are potentially clinically relevant, because HMGA2 expression is reported to be upregulated in a number of human cancers as telomere maintenance is essential for tumorigenesis.
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154
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Grach AA. Alternative telomere-lengthening mechanisms. CYTOL GENET+ 2011. [DOI: 10.3103/s0095452711020046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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155
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Eisenberg DTA. An evolutionary review of human telomere biology: the thrifty telomere hypothesis and notes on potential adaptive paternal effects. Am J Hum Biol 2011; 23:149-67. [PMID: 21319244 DOI: 10.1002/ajhb.21127] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2010] [Revised: 08/03/2010] [Accepted: 09/30/2010] [Indexed: 12/14/2022] Open
Abstract
Telomeres, repetitive DNA sequences found at the ends of linear chromosomes, play a role in regulating cellular proliferation, and shorten with increasing age in proliferating human tissues. The rate of age-related shortening of telomeres is highest early in life and decreases with age. Shortened telomeres are thought to limit the proliferation of cells and are associated with increased morbidity and mortality. Although natural selection is widely assumed to operate against long telomeres because they entail increased cancer risk, the evidence for this is mixed. Instead, here it is proposed that telomere length is primarily limited by energetic constraints. Cell proliferation is energetically expensive, so shorter telomeres should lead to a thrifty phenotype. Shorter telomeres are proposed to restrain adaptive immunity as an energy saving mechanism. Such a limited immune system, however, might also result in chronic infections, inflammatory stress, premature aging, and death--a more "disposable soma." With an increased reproductive lifespan, the fitness costs of premature aging are higher and longer telomeres will be favored by selection. Telomeres exhibit a paternal effect whereby the offspring of older fathers have longer telomeres due to increased telomere lengths of sperm with age. This paternal effect is proposed to be an adaptive signal of the expected age of male reproduction in the environment offspring are born into. The offspring of lineages of older fathers will tend to have longer, and thereby less thrifty, telomeres, better preparing them for an environment with higher expected ages at reproduction.
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Affiliation(s)
- Dan T A Eisenberg
- Department of Anthropology, Northwestern University, Evanston, IL 60208-1330, USA.
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156
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Sellmann L, de Beer D, Bartels M, Opalka B, Nückel H, Dührsen U, Dürig J, Seifert M, Siemer D, Küppers R, Baerlocher GM, Röth A. Telomeres and prognosis in patients with chronic lymphocytic leukaemia. Int J Hematol 2011; 93:74-82. [PMID: 21203871 DOI: 10.1007/s12185-010-0750-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Revised: 11/03/2010] [Accepted: 12/13/2010] [Indexed: 11/27/2022]
Abstract
In the present study, telomere length, telomerase activity, the mutation load of immunoglobulin variable heavy chain (IGHV) genes, and established prognostic factors were investigated in 78 patients with chronic lymphocytic leukaemia (CLL) to determine the impact of telomere biology on the pathogenesis of CLL. Telomere length was measured by an automated multi-colour flow-FISH, and an age-independent delta telomere length (ΔTL) was calculated. CLL with unmutated IGHV genes was associated with shorter telomeres (p = 0.002). Furthermore, we observed a linear correlation between the frequency of IGHV gene mutations and elongation of telomeres (r = 0.509, p < 0.001). With respect to prognosis, a threshold ΔTL of -4.2 kb was the best predictor for progression-free and overall survival. ΔTL was not significantly altered over time or with therapy. The correlation between the mutational load in IGHV genes and the ΔTL in CLL might reflect the initial telomere length of the putative cell of origin (pre- versus post-germinal center B cells). In conclusion, the ΔTL is a reliable prognostic marker for patients with CLL. Short telomeres and high telomerase activity as occurs in some patients with CLL with a worse prognosis might be an ideal target for treatment with telomerase inhibitors.
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MESH Headings
- Disease-Free Survival
- Female
- Humans
- Immunoglobulin Heavy Chains/genetics
- Immunoglobulin Variable Region/genetics
- Leukemia, Lymphocytic, Chronic, B-Cell/genetics
- Leukemia, Lymphocytic, Chronic, B-Cell/metabolism
- Leukemia, Lymphocytic, Chronic, B-Cell/mortality
- Leukemia, Lymphocytic, Chronic, B-Cell/pathology
- Leukemia, Lymphocytic, Chronic, B-Cell/therapy
- Male
- Mutation
- Retrospective Studies
- Survival Rate
- Telomere/genetics
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Affiliation(s)
- Ludger Sellmann
- Department of Haematology, University of Duisburg Essen, Essen, Germany.
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157
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Ourliac-Garnier I, Londoño-Vallejo A. Telomere strand-specific length analysis by fluorescent in situ hybridization (Q-CO-FISH). Methods Mol Biol 2011; 735:33-46. [PMID: 21461809 DOI: 10.1007/978-1-61779-092-8_4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The implementation of quantitative approaches in telomere chromosome-oriented FISH (telomeric CO-FISH) allows the assessment of the relative efficiency of lagging versus leading strand telomere replication and thus provides information on the implicated mechanisms. Here, we describe a simple method for telomere strand-specific analyses and discuss its potential applications.
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158
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Xu Y. Chemistry in human telomere biology: structure, function and targeting of telomere DNA/RNA. Chem Soc Rev 2011; 40:2719-40. [DOI: 10.1039/c0cs00134a] [Citation(s) in RCA: 249] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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159
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Ourliac-Garnier I, Londoño-Vallejo A. Telomere length analysis by quantitative fluorescent in situ hybridization (Q-FISH). Methods Mol Biol 2011; 735:21-31. [PMID: 21461808 DOI: 10.1007/978-1-61779-092-8_3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Length is a functional parameter of telomeres, the nucleoprotein structures that protect chromosome ends. The availability of highly specific, high-affinity probes for telomeric repeated sequences allowed the development of quantitative approaches aimed at measuring telomere length directly on chromosomes or in interphase nuclei. Here, we describe a general method for telomere quantitative FISH on metaphase chromosomes and discuss its most common applications in research.
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160
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Yehezkel S, Rebibo-Sabbah A, Segev Y, Tzukerman M, Shaked R, Huber I, Gepstein L, Skorecki K, Selig S. Reprogramming of telomeric regions during the generation of human induced pluripotent stem cells and subsequent differentiation into fibroblast-like derivatives. Epigenetics 2011; 6:63-75. [PMID: 20861676 DOI: 10.4161/epi.6.1.13390] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Human induced pluripotent stem (hiPS) cells provide therapeutic promises, as well as a potent in vitro model for studying biological processes which take place during human embryonic development and subsequent differentiation in normal and disease states. The epigenetic characteristics of iPS cells are reprogrammed to the embryonic state at which they acquire pluripotency. In addition, telomeres in hiPS cell must elongate sufficiently to provide the necessary replicative potential. Recent studies have demonstrated that the epigenetic characteristics of telomeric and subtelomeric regions are pivotal in regulating telomere length. Here we study telomere length, subtelomeric DNA methylation and telomeric-repeat-containing RNA (TERRA) expression in several hiPS cell clones derived from normal neonatal foreskin fibroblasts. We find that telomeres lengthen significantly in hiPS cells in comparison to the parental fibroblast source, and progressively shorten after differentiation back into fibroblast-like cells, concomitantly with telomerase activation and down-regulation, respectively. Subtelomeres in hiPS cells were found to be generally hypermethylated in comparison to the parental source. However bisulfite analysis revealed that at several subtelomeres examined, methylation levels differed between hiPS clones and that both de novo methylation and demethylation processes occurred during telomere reprogramming. Notably, although subtelomeres were in general very highly methylated, TERRA levels were elevated in hiPS cells, albeit to different degrees in the various clones. TERRA elevation may reflect enhanced stability or impaired degradation in hiPS cells, and/or alternatively, increased transcription from the hypomethylated subtelomeres. We suggest that TERRA may play a role in regulation of appropriate telomere function and length in hiPS cells.
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Affiliation(s)
- Shiran Yehezkel
- Molecular Medicine Laboratory, Faculty of Medicine and Research Institute, Rambam Health Care Campus and Rappaport, Technion - Israel Institute of Technology, Haifa, Israel
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161
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Madonna R, De Caterina R, Willerson JT, Geng YJ. Biologic function and clinical potential of telomerase and associated proteins in cardiovascular tissue repair and regeneration. Eur Heart J 2010; 32:1190-6. [PMID: 21148539 DOI: 10.1093/eurheartj/ehq450] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Telomeres comprise long tracts of double-stranded TTAGGG repeats that extend for 9-15 kb in humans. Telomere length is maintained by telomerase, a specialized ribonucleoprotein that prevents the natural ends of linear chromosomes from undergoing inappropriate repair, which could otherwise lead to deleterious chromosomal fusions. During the development of cardiovascular tissues, telomerase activity is strong but diminishes with age in adult hearts. Dysfunction of telomerase is associated with the impairment of tissue repair or regeneration in several pathologic conditions, including heart failure and infarction. Under both physiologic and pathophysiologic conditions, telomerase interacts with promyogenic nuclear transcription factors (e.g. myocardin, serum response factor) to augment the potency of cardiovascular cells during growth, survival, and differentiation. We review recent findings on the biologic function of telomerase and its potential for clinical application in cardiovascular development and repair. Understanding the roles of telomerase and its associated proteins in the functional regulation of cardiovascular cells and their progenitors may lead to new strategies for cardiovascular tissue repair and regeneration.
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Affiliation(s)
- Rosalinda Madonna
- Texas Heart Institute at St. Luke's Episcopal Hospital, Houston, TX, USA
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162
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Mild hyperoxia limits hTR levels, telomerase activity, and telomere length maintenance in hTERT-transduced bone marrow endothelial cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:1142-53. [DOI: 10.1016/j.bbamcr.2010.06.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Revised: 06/28/2010] [Accepted: 06/28/2010] [Indexed: 01/01/2023]
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163
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Maritz MF, Napier CE, Wen VW, MacKenzie KL. Targeting telomerase in hematologic malignancy. Future Oncol 2010; 6:769-89. [PMID: 20465390 DOI: 10.2217/fon.10.42] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Over the past two decades, it has become increasingly apparent that telomerase-mediated telomere maintenance plays a crucial role in hematopoiesis. Supporting evidence is underscored by recent findings of mutations in genes involved in telomerase-mediated telomere maintenance that contribute to the pathogenesis of bone marrow failure syndromes. More recently described telomere-independent functions of telomerase are also likely to contribute to both normal hematopoiesis and hematologic diseases. The high levels of telomerase detected in aggressive leukemias have fueled fervent investigation into diverse approaches to targeting telomerase in hematologic malignancies. Successful preclinical investigations that employed genetic strategies, oligonucleotides, small-molecule inhibitors and immunotherapy have resulted in a rapid translation to clinical trials. Further investigation of telomere-independent functions of telomerase and detailed preclinical studies of telomerase inhibition in both normal and malignant hematopoiesis will be invaluable for refining treatments to effectively and safely exploit telomerase as a therapeutic target in hematologic malignancies.
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Affiliation(s)
- Michelle F Maritz
- Children's Cancer Institute Australia for Medical Research, Lowy Cancer Research Centre, New South Wales, Australia
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164
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Telomere capping in non-dividing yeast cells requires Yku and Rap1. EMBO J 2010; 29:3007-19. [PMID: 20628356 DOI: 10.1038/emboj.2010.155] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Accepted: 06/18/2010] [Indexed: 01/13/2023] Open
Abstract
The assembly of a protective cap onto the telomeres of eukaryotic chromosomes suppresses genomic instability through inhibition of DNA repair activities that normally process accidental DNA breaks. We show here that the essential Cdc13-Stn1-Ten1 complex is entirely dispensable for telomere protection in non-dividing cells. However, Yku and Rap1 become crucially important for this function in these cells. After inactivation of Yku70 in G1-arrested cells, moderate but significant telomere degradation occurs. As the activity of cyclin-dependent kinases (CDK) promotes degradation, these results suggest that Yku stabilizes G1 telomeres by blocking the access of CDK1-independent nucleases to telomeres. The results indeed show that both Exo1 and the Mre11/Rad50/Xrs2 complex are required for telomeric resection after Yku loss in non-dividing cells. Unexpectedly, both asynchronously growing and quiescent G0 cells lacking Rap1 display readily detectable telomere degradation, suggesting an earlier unanticipated function for this protein in suppression of nuclease activities at telomeres. Together, our results show a high flexibility of the telomeric cap and suggest that distinct configurations may provide for efficient capping in dividing versus non-dividing cells.
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165
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Biron-Shental T, Sukenik Halevy R, Goldberg-Bittman L, Kidron D, Fejgin MD, Amiel A. Telomeres are shorter in placental trophoblasts of pregnancies complicated with intrauterine growth restriction (IUGR). Early Hum Dev 2010; 86:451-6. [PMID: 20619976 DOI: 10.1016/j.earlhumdev.2010.06.002] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Revised: 05/30/2010] [Accepted: 06/01/2010] [Indexed: 11/18/2022]
Abstract
OBJECTIVE Telomeres are nucleoprotein structures located at the termini of chromosomes, and protect them from fusion and degradation. Telomeres are progressively shortened with each mitotic cycle and by environmental factors. We hypothesized that antepartum stress can lead to accelerated telomere shortening in placental trophoblasts, and plays a role in intrauterine growth restriction (IUGR). METHODS Placental biopsies were derived from 16 pregnancies complicated with IUGR and from 13 uncomplicated pregnancies. Fluorescence-in-situ protocol was used to determine telomere length. Immunohistochemistry for hTERT was performed to assess telomerase activity. Clinical and histopathological characteristics were collected to ensure that IUGR was secondary to placental insufficiency. Fluorescence-in-situ-hybridization was used to rule out aneuploidy as a reason for shortened telomeres. RESULTS The number and intensity of telomeres staining and telomerase activity were significantly lower in the IUGR placentas. No aneuploidy was detected for the chromosomes checked in the placental biopsies. CONCLUSIONS Telomeres are shorter in trophoblasts of IUGR placentas.
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166
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Wellinger RJ. When the caps fall off: responses to telomere uncapping in yeast. FEBS Lett 2010; 584:3734-40. [PMID: 20600003 DOI: 10.1016/j.febslet.2010.06.031] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Revised: 06/18/2010] [Accepted: 06/21/2010] [Indexed: 12/25/2022]
Abstract
Telomeres protect the ends of linear chromosomes from activities that cause sequence losses or challenge chromosome integrity. Furthermore, these ends must be hidden from detection by the DNA damage recognition and response pathways. In particular, they must not fuse with each other. These fundamental and very first functions attributed to telomeres are also summarized with the term 'chromosome capping'. However, telomeres can become uncapped and the foremost cellular responses to such events aim to restore genome stability in the most conservative fashion possible. I will provide an outline of cellular responses to uncapping in budding yeast and briefly discuss the reverse, namely avoidance mechanisms that prevent telomere formation at inappropriate places.
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Affiliation(s)
- Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, Quebec, Canada.
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167
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Abstract
The budding yeast nucleus, like those of other eukaryotic species, is highly organized with respect to both chromosomal sequences and enzymatic activities. At the nuclear periphery interactions of nuclear pores with chromatin, mRNA, and transport factors promote efficient gene expression, whereas centromeres, telomeres, and silent chromatin are clustered and anchored away from pores. Internal nuclear organization appears to be function-dependent, reflecting localized sites for tRNA transcription, rDNA transcription, ribosome assembly, and DNA repair. Recent advances have identified new proteins involved in the positioning of chromatin and have allowed testing of the functional role of higher-order chromatin organization. The unequal distribution of silent information regulatory factors and histone modifying enzymes, which arises in part from the juxtaposition of telomeric repeats, has been shown to influence chromatin-mediated transcriptional repression. Other localization events suppress unwanted recombination. These findings highlight the contribution budding yeast genetics and cytology have made to dissecting the functional role of nuclear structure.
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Affiliation(s)
- Angela Taddei
- UMR 218, Centre National de la Recherche Scientifique, 26 rue d'Ulm, 75231 Paris Cedex 05, France
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168
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Telomere dysfunction-induced foci arise with the onset of telomeric deletions and complex chromosomal aberrations in resistant chronic lymphocytic leukemia cells. Blood 2010; 116:239-49. [PMID: 20424183 DOI: 10.1182/blood-2009-12-257618] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
In somatic cells, eroded telomeres can induce DNA double-strand break signaling, leading to a form of replicative senescence or apoptosis, both of which are barriers to tumorigenesis. However, cancer cells might display telomere dysfunctions which in conjunction with defects in DNA repair and apoptosis, enables them to circumvent these pathways. Chronic lymphocytic leukemia (CLL) cells exhibit telomere dysfunction, and a subset of these cells are resistant to DNA damage-induced apoptosis and display short telomeres. We show here that these cells exhibit significant resection of their protective telomeric 3' single-stranded overhangs and an increased number of telomere-induced foci containing gammaH2AX and 53BP1. Chromatin immunoprecipitation and immunofluorescence experiments demonstrated increased levels of telomeric Ku70 and phospho-S2056-DNA-PKcs, 2 essential components of the mammalian nonhomologous end-joining DNA repair system. Notably, these CLL cells display deletions of telomeric signals on one or 2 chromatids in parallel with 11q22 deletions, or with 13q14 deletions associated with another chromosomal aberration or with a complex karyotype. Taken together, our results indicate that a subset of CLL cells from patients with an unfavorable clinical outcome harbor a novel type of chromosomal aberration resulting from telomere dysfunction.
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169
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3D Telomere FISH defines LMP1-expressing Reed-Sternberg cells as end-stage cells with telomere-poor 'ghost' nuclei and very short telomeres. J Transl Med 2010; 90:611-9. [PMID: 20142802 DOI: 10.1038/labinvest.2010.2] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In Epstein-Barr virus (EBV) negative Hodgkin's cell lines and classical EBV-negative Hodgkin's lymphoma (HL), Reed-Sternberg cells (RS cells) represent end-stage tumor cells, in which further nuclear division becomes impossible because of sustained telomere loss, shortening and aggregation. However, the three-dimensional (3D) telomere organization in latent membrane protein 1 (LMP1)-expressing RS cells of EBV-associated HL is not known. We performed a 3D telomere analysis after quantitative fluorescent in situ hybridization on 5 mum tissue sections on two LMP1-expressing HL cases and showed highly significant telomere shortening (P<0.0001) and formation of telomere aggregates in RS cells (P<0.0001), when compared with the mononuclear precursor Hodgkin cells (H cells). Telomere-poor or telomere-free 'ghost' nuclei were a regular finding in these RS cells. These nuclei and their telomere content strongly contrasted with the corona of surrounding lymphocytes showing numerous midsized telomere hybridization signals. Both H cells and RS cells of two EBV-negative HL cases analyzed in parallel showed 3D telomere patterns identical to those of LMP1-expressing cases. As a major advance, our 3D nuclear imaging approach allows the visualization of hitherto unknown profound changes in the 3D nuclear telomere organization associated with the transition from LMP1-positive H cells to LMP1-positive RS cells. We conclude that RS cells irrespective of LMP1 expression are end-stage tumor cells in which the extent of their inability to divide further is proportional to the increase of very short telomeres, telomere loss, aggregate formation and the generation of 'ghost' nuclei.
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170
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Rap1 in Candida albicans: an unusual structural organization and a critical function in suppressing telomere recombination. Mol Cell Biol 2009; 30:1254-68. [PMID: 20008550 DOI: 10.1128/mcb.00986-09] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rap1 (repressor activator protein 1) is a conserved multifunctional protein initially identified as a transcriptional regulator of ribosomal protein genes in Saccharomyces cerevisiae but subsequently shown to play diverse functions at multiple chromosomal loci, including telomeres. The function of Rap1 appears to be evolutionarily plastic, especially in the budding yeast lineages. We report here our biochemical and molecular genetic characterizations of Candida albicans Rap1, which exhibits an unusual, miniaturized domain organization in comparison to the S. cerevisiae homologue. We show that in contrast to S. cerevisiae, C. albicans RAP1 is not essential for cell viability but is critical for maintaining normal telomere length and structure. The rap1 null mutant exhibits drastic telomere-length dysregulation and accumulates high levels of telomere circles, which can be largely attributed to aberrant recombination activities at telomeres. Analysis of combination mutants indicates that Rap1 and other telomere proteins mediate overlapping but nonredundant roles in telomere protection. Consistent with the telomere phenotypes of the mutant, C. albicans Rap1 is localized to telomeres in vivo and recognizes the unusual telomere repeat unit with high affinity and sequence specificity in vitro. The DNA-binding Myb domain of C. albicans Rap1 is sufficient to suppress most of the telomere aberrations observed in the null mutant. Notably, we were unable to detect specific binding of C. albicans Rap1 to gene promoters in vivo or in vitro, suggesting that its functions are more circumscribed in this organism. Our findings provide insights on the evolution and mechanistic plasticity of a widely conserved and functionally critical telomere component.
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171
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Suhr ST, Chang EA, Rodriguez RM, Wang K, Ross PJ, Beyhan Z, Murthy S, Cibelli JB. Telomere dynamics in human cells reprogrammed to pluripotency. PLoS One 2009; 4:e8124. [PMID: 19956585 PMCID: PMC2780312 DOI: 10.1371/journal.pone.0008124] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2009] [Accepted: 11/11/2009] [Indexed: 12/30/2022] Open
Abstract
Background Human induced pluripotent stem cells (IPSCs) have enormous potential in the development of cellular models of human disease and represent a potential source of autologous cells and tissues for therapeutic use. A question remains as to the biological age of IPSCs, in particular when isolated from older subjects. Studies of cloned animals indicate that somatic cells reprogrammed to pluripotency variably display telomere elongation, a common indicator of cell “rejuvenation.” Methodology/Principal Findings We examined telomere lengths in human skin fibroblasts isolated from younger and older subjects, fibroblasts converted to IPSCs, and IPSCs redifferentiated through teratoma formation and explant culture. In IPSCs analyzed at passage five (P5), telomeres were significantly elongated in 6/7 lines by >40% and approximated telomere lengths in human embryonic stem cells (hESCs). In cell lines derived from three IPSC-teratoma explants cultured to P5, two displayed telomeres shortened to lengths similar to input fibroblasts while the third line retained elongated telomeres. Conclusions/Significance While these results reveal some heterogeneity in the reprogramming process with respect to telomere length, human somatic cells reprogrammed to pluripotency generally displayed elongated telomeres that suggest that they will not age prematurely when isolated from subjects of essentially any age.
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Affiliation(s)
- Steven T. Suhr
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
| | - Eun Ah Chang
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
| | - Ramon M. Rodriguez
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
| | - Kai Wang
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
| | - Pablo J. Ross
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
- Programa Andaluz de Terapia Celular y Medicina Regenerativa, Andalucía, Spain
| | - Zeki Beyhan
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
| | - Shashanka Murthy
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
| | - Jose B. Cibelli
- Cellular Reprogramming Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan, United States of America
- Programa Andaluz de Terapia Celular y Medicina Regenerativa, Andalucía, Spain
- * E-mail:
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172
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Isken O, Maquat LE. Telomeric RNAs as a novel player in telomeric integrity. F1000 BIOLOGY REPORTS 2009; 1:90. [PMID: 20376293 PMCID: PMC2849317 DOI: 10.3410/b1-90] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Telomeres protect linear chromosome ends from being recognized and processed as double-strand breaks by DNA repair activities. This protective function of telomeres is essential for chromosome stability. Until recently, telomeres have been considered to be transcriptionally silent. This notion was overturned in a series of recent papers that describe the existence of telomeric repeat-containing RNAs (TERRAs) in vertebrates and yeast. Here, we summarize recent developments in this field of telomere research, in particular the possible mechanisms that control TERRA expression.
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Affiliation(s)
- Olaf Isken
- Institute of Virology and Cell Biology, University of Lübeck, 23556 LübeckRatzeburger Allee 160Germany
| | - Lynne E Maquat
- Department of Biochemistry and Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester601 Elmwood Avenue, Box 712, Rochester, NY 14642USA
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173
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Meznikova M, Erdmann N, Allsopp R, Harrington LA. Telomerase reverse transcriptase-dependent telomere equilibration mitigates tissue dysfunction in mTert heterozygotes. Dis Model Mech 2009; 2:620-6. [PMID: 19841238 DOI: 10.1242/dmm.004069] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Autosomal dominant mutations in telomere-associated factors elicit a disease known as dyskeratosis congenita (DKC), and patients suffer proliferative abnormalities associated with telomere erosion. Mice that are heterozygous for telomerase genes (Tert or Terc, hereafter referred to as mTert and mTerc) are useful models of telomerase haploinsufficiency, but do not strictly mimic DKC. In strains with long telomeres (>60 kbp), animals that are heterozygous for mTert undergo telomere erosion for nine generations and remain phenotypically normal. In an mTerc heterozygous strain with short telomeres (<15 kbp), early mortality arises after five to six generations, but dyskeratosis occurs only upon the further loss of mPot1b. We show that prolonged mTert heterozygosity (for greater than ten generations) did not elicit disease, even upon heterozygote interbreeding, and that telomeres reset to wild-type lengths. This lengthening did not occur in nullizygotes, and short telomeres inherited from mTert null parents were rescued only in heterozygous progeny. In the bone marrow, nullizygotes remained competent for radioprotection for three generations. Thus, gradual telomere erosion in the presence of telomerase may enable subsequent telomere extension, similar to that described in budding yeast. We speculate whether such adaptation occurs in normal human cells (or whether it could be induced in DKC-derived cells), and whether it might mitigate the impact of telomerase inhibition upon stem cells during cancer therapy.
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Affiliation(s)
- Marie Meznikova
- Ontario Cancer Institute/Campbell Family Institute for Cancer Research, Toronto, ON, Canada
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174
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Vulliamy TJ. Premature aging. Cell Mol Life Sci 2009; 66:3091-4. [PMID: 19618112 PMCID: PMC11115659 DOI: 10.1007/s00018-009-0091-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Revised: 07/01/2009] [Accepted: 07/02/2009] [Indexed: 10/20/2022]
Affiliation(s)
- Thomas J Vulliamy
- Centre for Paediatrics, Institute of Cell and Molecular Science, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
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175
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Khadaroo B, Teixeira MT, Luciano P, Eckert-Boulet N, Germann SM, Simon MN, Gallina I, Abdallah P, Gilson E, Géli V, Lisby M. The DNA damage response at eroded telomeres and tethering to the nuclear pore complex. Nat Cell Biol 2009; 11:980-7. [PMID: 19597487 DOI: 10.1038/ncb1910] [Citation(s) in RCA: 158] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Accepted: 04/23/2009] [Indexed: 12/11/2022]
Abstract
The ends of linear eukaryotic chromosomes are protected by telomeres, which serve to ensure proper chromosome replication and to prevent spurious recombination at chromosome ends. In this study, we show by single cell analysis that in the absence of telomerase, a single short telomere is sufficient to induce the recruitment of checkpoint and recombination proteins. Notably, a DNA damage response at eroded telomeres starts many generations before senescence and is characterized by the recruitment of Cdc13 (cell division cycle 13), replication protein A, DNA damage checkpoint proteins and the DNA repair protein Rad52 into a single focus. Moreover, we show that eroded telomeres, although remaining at the nuclear periphery, move to the nuclear pore complex. Our results link the DNA damage response at eroded telomeres to changes in subnuclear localization and suggest the existence of collapsed replication forks at eroded telomeres.
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Affiliation(s)
- Basheer Khadaroo
- CNRS, Unité Propre de Recherche 3081, Genome Instability and Carcinogenesis Conventionné par l'Université d'Aix-Marseille 2, 13402 Marseille Cedex 20, France
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176
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Gunisova S, Elboher E, Nosek J, Gorkovoy V, Brown Y, Lucier JF, Laterreur N, Wellinger RJ, Tzfati Y, Tomaska L. Identification and comparative analysis of telomerase RNAs from Candida species reveal conservation of functional elements. RNA (NEW YORK, N.Y.) 2009; 15:546-559. [PMID: 19223441 PMCID: PMC2661832 DOI: 10.1261/rna.1194009] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Accepted: 12/16/2008] [Indexed: 05/27/2023]
Abstract
The RNA component of telomerase (telomerase RNA; TER) varies substantially both in sequence composition and size (from approximately 150 nucleotides [nt] to >1500 nt) across species. This dramatic divergence has hampered the identification of TER genes and a large-scale comparative analysis of TER sequences and structures among distantly related species. To identify by phylogenetic analysis conserved sequences and structural features of TER that are of general importance, it is essential to obtain TER sequences from evolutionarily distant groups of species, providing enough conservation within each group and enough variation among the groups. To this end, we identified TER genes in several yeast species with relatively large (>20 base pairs) and nonvariant telomeric repeats, mostly from the genus Candida. Interestingly, several of the TERs reported here are longer than all other yeast TERs known to date. Within these TERs, we predicted a pseudoknot containing U-A.U base triples (conserved in vertebrates, budding yeasts, and ciliates) and a three-way junction element (conserved in vertebrates and budding yeasts). In addition, we identified a novel conserved sequence (CS2a) predicted to reside within an internal-loop structure, in all the budding yeast TERs examined. CS2a is located near the Est1p-binding bulge-stem previously identified in Saccharomyces cerevisiae. Mutational analyses in both budding yeasts S. cerevisiae and Kluyveromyces lactis demonstrate that CS2a is essential for in vivo telomerase function. The comparative and mutational analyses of conserved TER elements reported here provide novel insights into the structure and function of the telomerase ribonucleoprotein complex.
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177
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De Boeck G, Forsyth RG, Praet M, Hogendoorn PCW. Telomere-associated proteins: cross-talk between telomere maintenance and telomere-lengthening mechanisms. J Pathol 2009; 217:327-44. [PMID: 19142887 DOI: 10.1002/path.2500] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Telomeres, the ends of eukaryotic chromosomes, have been the subject of intense investigation over the last decade. As telomere dysfunction has been associated with ageing and developing cancer, understanding the exact mechanisms regulating telomere structure and function is essential for the prevention and treatment of human cancers and age-related diseases. The mechanisms by which cells maintain telomere lengthening involve either telomerase or the alternative lengthening of the telomere pathway, although specific mechanisms of the latter and the relationship between the two are as yet unknown. Many cellular factors directly (TRF1/TRF2) and indirectly (shelterin-complex, PinX, Apollo and tankyrase) interact with telomeres, and their interplay influences telomere structure and function. One challenge comes from the observation that many DNA damage response proteins are stably associated with telomeres and contribute to several other aspects of telomere function. This review focuses on the different components involved in telomere maintenance and their role in telomere length homeostasis. Special attention is paid to understanding how these telomere-associated factors, and mainly those involved in double-strand break repair, perform their activities at the telomere ends.
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Affiliation(s)
- Gitte De Boeck
- N. Goormaghtigh Institute of Pathology, University Hospital Ghent, De Pintelaan 185, 9000 Ghent, Belgium
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178
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Sampathi S, Bhusari A, Shen B, Chai W. Human flap endonuclease I is in complex with telomerase and is required for telomerase-mediated telomere maintenance. J Biol Chem 2009; 284:3682-90. [PMID: 19068479 PMCID: PMC2635043 DOI: 10.1074/jbc.m805362200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2008] [Revised: 12/08/2008] [Indexed: 11/06/2022] Open
Abstract
Studies from budding yeast and ciliates have suggested that telomerase extension of telomeres requires the conventional DNA replication machinery, yet little is known about how DNA replication proteins regulate telomerase action in higher eukaryotic cells. Here we investigate the role of one of the DNA replication factors, flap endonuclease I (FEN1), in regulating telomerase activity in mammalian cells. FEN1 is a nuclease that plays an important role in DNA replication, repair, and recombination. We show that FEN1 is in complex with telomerase in vivo via telomeric DNA. We further demonstrate that FEN1 deficiency in mouse embryonic fibroblasts leads to an increase in telomere end-to-end fusions. In cancer cells, FEN1 deficiency induces gradual shortening of telomeres but does not alter the single-stranded G-overhangs. This is, to our knowledge, the first evidence that FEN1 and telomerase physically co-exist as a complex and that FEN1 can regulate telomerase activity at telomeres in mammalian cells.
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Affiliation(s)
- Shilpa Sampathi
- Washington, Wyoming, Alaska, Montana, Idaho Medical Education Program, Washington State University, Spokane, Washington 99210, USA
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179
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Capkova Frydrychova R, Biessmann H, Mason JM. Regulation of telomere length in Drosophila. Cytogenet Genome Res 2009; 122:356-64. [PMID: 19188706 DOI: 10.1159/000167823] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/11/2008] [Indexed: 01/20/2023] Open
Abstract
Telomeres in all organisms must perform the same vital functions to ensure cell viability: to act as a protective chromosome cap that distinguishes natural chromosome ends from DNA double strand breaks, and to balance the loss of DNA from the chromosome end due to incomplete DNA replication. Most eukaryotes rely on a specialized reverse transcriptase, telomerase, to generate short repeats at the chromosome end to maintain chromosome length. Drosophila, however, uses retrotransposons that target telomeres. Transposition of these elements may be controlled by small RNAs and spreading of silent chromatin from the telomere associated sequence, both of which limit the retrotransposon expression level. Proteins binding to the retrotransposon array, such as HP1 and PROD, may also modulate transcription. It is not clear however, that simply increasing transcript levels of the telomeric retrotransposons is sufficient to increase transposition. The chromosome cap may control the ability of the telomere-specific elements to attach to chromosome ends. As in other organisms, chromosomes can be elongated by gene conversion. Although the mechanism is not known, HP1, a component of the cap, and the Ku proteins are key components in this pathway.
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Affiliation(s)
- R Capkova Frydrychova
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709-2233, USA
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180
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Luke B, Panza A, Redon S, Iglesias N, Li Z, Lingner J. The Rat1p 5' to 3' exonuclease degrades telomeric repeat-containing RNA and promotes telomere elongation in Saccharomyces cerevisiae. Mol Cell 2009; 32:465-77. [PMID: 19026778 DOI: 10.1016/j.molcel.2008.10.019] [Citation(s) in RCA: 233] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 07/21/2008] [Accepted: 10/28/2008] [Indexed: 10/21/2022]
Abstract
Vertebrate telomeres are transcribed into telomeric repeat-containing RNA (TERRA) that associates with telomeres and may be important for telomere function. Here, we demonstrate that telomeres are also transcribed in Saccharomyces cerevisiae by RNA polymerase II (RNAPII). Yeast TERRA is polyadenylated and stabilized by Pap1p and regulated by the 5' to 3' exonuclease, Rat1p. rat1-1 mutant cells accumulate TERRA and harbor short telomeres because of defects in telomerase-mediated telomere elongation. Overexpression of RNaseH overcomes telomere elongation defects in rat1-1 cells, indicating that RNA/DNA hybrids inhibit telomerase function at chromosome ends in these mutants. Thus, telomeric transcription combined with Rat1p-dependent TERRA degradation is important for regulating telomerase in yeast. Telomere transcription is conserved in different kingdoms of the eukaryotic domain.
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Affiliation(s)
- Brian Luke
- Ecole Polytechnique Fédérale de Lausanne, Swiss Institute for Experimental Cancer Research (ISREC), CH-1066 Epalinges, Switzerland
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181
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Pallardó FV, Markovic J, García JL, Viña J. Role of nuclear glutathione as a key regulator of cell proliferation. Mol Aspects Med 2009; 30:77-85. [PMID: 19232542 DOI: 10.1016/j.mam.2009.01.001] [Citation(s) in RCA: 127] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Glutathione (GSH) is essential for survival of eukaryotic but not in prokaryotic cells. Its functions in nucleated cells are far from being known. In fact GSH plays an important role in cell proliferation. The purpose of the present review is to summarize the relationship between glutathione and the important events that take place in the nucleus during the cell cycle. Most GSH co-localizes with nuclear DNA when cells are proliferating. However, when cells were confluent no differences between nucleus and cytoplasm could be seen. A number of relevant nuclear proteins are strictly dependent on nuclear redox status. For instance, we found that telomerase is regulated by shifts in glutathione redox potential within values similar to those found in vivo, and alterations in telomerase activity are coordinated with changes in critical cell cycle proteins, particularly Id2 and E2F4. More studies are required to establish the role of nuclear glutathione in the epigenetic control of histone function. The information provided in the present review suggests an important role of nuclear glutathione as a key regulator of epigenetic events that may be critical in the regulation of cell proliferation.
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Affiliation(s)
- Federico V Pallardó
- Department of Physiology, Faculty of Medicine, University of Valencia, Av. Blasco Ibañez 15, E-46010 Valencia, Spain; CIBERER, Av. Blasco Ibañez 15, E-46010 Valencia, Spain
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182
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No attenuation of the ATM-dependent DNA damage response in murine telomerase-deficient cells. DNA Repair (Amst) 2008; 8:347-53. [PMID: 19071232 DOI: 10.1016/j.dnarep.2008.11.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2008] [Revised: 11/02/2008] [Accepted: 11/10/2008] [Indexed: 12/19/2022]
Abstract
Inactivation of mammalian telomerase leads to telomere attrition, eventually culminating in uncapped telomeres, which elicit a DNA damage response and cell cycle arrest or death. In some instances, telomerase modulation evokes a response not obviously attributable to changes in telomere length. One such example is the suppression of the DNA damage response (DDR) and changes in histone modification that occur upon repression of the telomerase reverse transcriptase, TERT, in human primary cells [K. Masutomi, R. Possemato, J.M. Wong, J.L. Currier, Z. Tothova, J.B. Manola, S. Ganesan, P.M. Lansdorp, K. Collins and W.C. Hahn, The telomerase reverse transcriptase regulates chromatin state and DNA damage responses, Proc. Natl. Acad. Sci. U.S.A. 102 (2005) 8222-8227]. Here, we evaluate the contribution of TERT to the DDR in murine Tert(-/-) cells without critically shortened telomeres. We treated mTert(-/-) embryonic stem (ES) cells and murine embryonic fibroblasts (MEFs) with etoposide and irradiation, and assessed the status of p53(pS15), 53BP1, ATM(pS1981), SMC1(pS957), and gammaH2AX by indirect immunofluorescence or western blotting. In four independently derived mTert(-/-) ES cell lines, there was no significant difference in the induction of gammaH2AX, 53BP1 foci, or the phosphorylation of ATM targets (ATM, SMC1, p53) between wildtype and mTert(-/-) ES cells and MEFs. A slight difference in post-translational modification of histones H3 and H4 was observed in a subset of mTert(-/-) ES cells, however this difference was reflected in the cellular levels of H3 and H4. Thus, in contrast to previous studies in human cells, the absence of Tert does not overtly affect the ATM-dependent response to DNA damage in murine cells.
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183
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Spliceosomal cleavage generates the 3' end of telomerase RNA. Nature 2008; 456:910-4. [PMID: 19052544 DOI: 10.1038/nature07584] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Accepted: 10/10/2008] [Indexed: 11/08/2022]
Abstract
Telomeres cap the ends of chromosomes and provide a means to complete replication. The DNA portion of telomeres is synthesized by the enzyme telomerase using part of an RNA subunit as a template for reverse transcription. How the mature 3' end of telomerase RNA is generated has so far remained elusive. Here we show that in Schizosaccharomyces pombe telomerase RNA transcripts must be processed to generate functional telomerase. Characterization of the maturation pathway uncovered an unexpected role for the spliceosome, which normally catalyses splicing of pre-messenger RNA. The first spliceosomal cleavage reaction generates the mature 3' end of telomerase RNA (TER1, the functional RNA encoded by the ter1(+) gene), releasing the active form of the RNA without exon ligation. Blocking the first step or permitting completion of splicing generates inactive forms of TER1 and causes progressive telomere shortening. We establish that 3' end processing of TER1 is critical for telomerase function and describe a previously unknown mechanism for RNA maturation that uses the ability of the spliceosome to mediate site-specific cleavage.
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184
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Shakirov EV, Salzberg SL, Alam M, Shippen DE. Analysis of Carica papaya Telomeres and Telomere-Associated Proteins: Insights into the Evolution of Telomere Maintenance in Brassicales. TROPICAL PLANT BIOLOGY 2008; 1:202-215. [PMID: 20664721 PMCID: PMC2909770 DOI: 10.1007/s12042-008-9018-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Telomeres are terminal regions of linear eukaryotic chromosomes that are critical for genome stability and continued cell proliferation. The draft assembly of the papaya genome provides an opportunity to analyze and compare the evolution of telomeric DNA sequence composition and telomere maintenance machinery in this and other organisms of the Brassicales Order, which includes Arabidopsis. Here we investigate telomere size and sequence variation at papaya chromosome ends. As with most other plant species, papaya telomeres consist of TTTAGGG repeats. However, in contrast to members of the closely related Brassicaceae family, telomeres in papaya are ~10-fold longer. Sequence analysis reveals that many centromereproximal telomere repeats in papaya harbor nucleotide substitutions and insertions of Gs and Ts. In contrast, we found very few N-to-C substitutions, and even fewer instances of nucleotide deletion, suggesting that a six-nucleotide telomere repeat is not well tolerated. The papaya genome encodes single-copy sequence homologues of several genes involved in telomere maintenance and chromosome end protection, including the Telomerase Reverse Transcriptase (TERT) and Protection Of Telomeres (POT1). Notably, unlike Arabidopsis, which encodes six Telomere Repeat binding Factor-like (TRFL) proteins that bind double-stranded telomere DNA, papaya appears to encode only two such proteins. Thus, the more streamlined genome of papaya will provide an excellent resource for comparative and functional analysis of telomeres in plants.
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Affiliation(s)
- E. V. Shakirov
- Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128, USA
| | - S. L. Salzberg
- Center for Bioinformatics and Computational Biology, and Department of Computer Science, University of Maryland, 3125 Biomolecular Sciences Bldg, College Park, MD 20742, USA
| | - M. Alam
- Advanced Studies in Genomics, Proteomics and Bioinformatics, and Department of Microbiology, University of Hawaii, Honolulu, HI 96822, USA
| | - D. E. Shippen
- Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128, USA,
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185
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Knecht H, Sawan B, Lichtensztejn D, Lemieux B, Wellinger RJ, Mai S. The 3D nuclear organization of telomeres marks the transition from Hodgkin to Reed-Sternberg cells. Leukemia 2008; 23:565-73. [PMID: 19039323 DOI: 10.1038/leu.2008.314] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
To get an insight into the transition from mononuclear Hodgkin cells (H cells) to diagnostic multinuclear Reed-Sternberg cells (RS cells), we performed an analysis of the three-dimensional (3D) structure of the telomeres in the nuclei of the Hodgkin cell lines HDLM-2, L-428, L-1236 and lymph node biopsies of patients with Hodgkin's disease. Cellular localization of key proteins of the telomere-localized shelterin complex, the mitotic spindle and double-stranded DNA breaks was also analyzed. RS cells show significantly shorter and significantly fewer telomeres in relation to the total nuclear volume when compared with H cells; in particular, telomere-poor 'ghost' nuclei are often adjacent to one or two nuclei displaying huge telomeric aggregates. Shelterin proteins are mainly cytoplasmic in both H and RS cells, whereas double-stranded DNA breaks accumulate in the nuclei of RS cells. In RS cells, multipolar spindles prevent proper chromosome segregation. In conclusion, a process of nuclear disorganization seems to initiate in H cells and further progresses when the cells turn into RS cells and become end-stage tumor cells, unable to divide further because of telomere loss, shortening and aggregate formation, extensive DNA damage and aberrant mitotic spindles that may no longer sustain chromosome segregation. Our findings allow a mechanistic 3D understanding of the transition of H to RS cells.
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Affiliation(s)
- H Knecht
- Département de Médicine, CHUS, Université de Sherbrooke, Sherbrooke, Québec, Canada.
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186
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Mutant telomeric repeats in yeast can disrupt the negative regulation of recombination-mediated telomere maintenance and create an alternative lengthening of telomeres-like phenotype. Mol Cell Biol 2008; 29:626-39. [PMID: 19029249 DOI: 10.1128/mcb.00423-08] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Some human cancers maintain telomeres using alternative lengthening of telomeres (ALT), a process thought to be due to recombination. In Kluyveromyces lactis mutants lacking telomerase, recombinational telomere elongation (RTE) is induced at short telomeres but is suppressed once telomeres are moderately elongated by RTE. Recent work has shown that certain telomere capping defects can trigger a different type of RTE that results in much more extensive telomere elongation that is reminiscent of human ALT cells. In this study, we generated telomeres composed of either of two types of mutant telomeric repeats, Acc and SnaB, that each alter the binding site for the telomeric protein Rap1. We show here that arrays of both types of mutant repeats present basally on a telomere were defective in negatively regulating telomere length in the presence of telomerase. Similarly, when each type of mutant repeat was spread to all chromosome ends in cells lacking telomerase, they led to the formation of telomeres produced by RTE that were much longer than those seen in cells with only wild-type telomeric repeats. The Acc repeats produced the more severe defect in both types of telomere maintenance, consistent with their more severe Rap1 binding defect. Curiously, although telomerase deletion mutants with telomeres composed of Acc repeats invariably showed extreme telomere elongation, they often also initially showed persistent very short telomeres with few or no Acc repeats. We suggest that these result from futile cycles of recombinational elongation and truncation of the Acc repeats from the telomeres. The presence of extensive 3' overhangs at mutant telomeres suggests that Rap1 may normally be involved in controlling 5' end degradation.
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187
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188
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Final checkup of neoplastic DNA replication: Evidence for failure in decision-making at the mitotic cell cycle checkpoint G1/S. Exp Hematol 2008; 36:1403-16. [DOI: 10.1016/j.exphem.2008.07.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2008] [Revised: 07/29/2008] [Accepted: 07/29/2008] [Indexed: 11/24/2022]
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189
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Yehezkel S, Segev Y, Viegas-Péquignot E, Skorecki K, Selig S. Hypomethylation of subtelomeric regions in ICF syndrome is associated with abnormally short telomeres and enhanced transcription from telomeric regions. Hum Mol Genet 2008; 17:2776-89. [PMID: 18558631 DOI: 10.1093/hmg/ddn177] [Citation(s) in RCA: 171] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Telomeres and adjacent subtelomeric regions are packaged as heterochromatin in many organisms. The heterochromatic features include DNA methylation, histones H3-Lys9 (Lysine 9) and H4-Lys20 (Lysine 20) methylation and heterochromatin protein1 alpha binding. Subtelomeric DNA is hypomethylated in human sperm and ova, and these regions are subjected to de novo methylation during development. In mice this activity is carried out by DNA methyltransferase 3b (Dnmt3b). Mutations in DNMT3B in humans lead to the autosomal-recessive ICF (immunodeficiency, centromeric region instability, facial anomalies) syndrome. Here we show that, in addition to several satellite and non-satellite repeats, the subtelomeric regions in lymphoblastoid and fibroblast cells of ICF patients are also hypomethylated to similar levels as in sperm. Furthermore, the telomeres are abnormally short in both the telomerase-positive and -negative cells, and many chromosome ends lack detectable telomere fluorescence in situ hybridization signals from either one or both sister-chromatids. In contrast to Dnmt3a/b(-/-) mouse embryonic stem cells, increased telomere sister-chromatid exchange was not observed in ICF cells. Hypomethylation of subtelomeric regions was associated in the ICF cells with advanced telomere replication timing and elevated levels of transcripts emanating from telomeric regions, known as TERRA (telomeric-repeat-containing RNA) or TelRNA. The current findings provide a mechanistic explanation for the abnormal telomeric phenotype observed in ICF syndrome and highlights the link between TERRA/TelRNA and structural telomeric integrity.
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Affiliation(s)
- Shiran Yehezkel
- Department of Nephrology and Laboratory of Molecular Medicine, Rambam Medical Center and Rappaport Faculty of Medicine and Research Institute, Technion, Haifa 31096, Israel
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190
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Disease-associated human telomerase RNA variants show loss of function for telomere synthesis without dominant-negative interference. Mol Cell Biol 2008; 28:6510-20. [PMID: 18710936 DOI: 10.1128/mcb.00777-08] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Telomerase adds simple-sequence repeats to chromosome ends to offset the terminal sequence loss inherent in each cycle of genome replication. Inherited mutations in genes encoding subunits of the human telomerase holoenzyme give rise to disease phenotypes including hematopoietic failure and pulmonary fibrosis. Disease-associated variants of the human telomerase RNA are expressed in heterozygous combination with wild-type telomerase RNA. Here, we exploit a sensitized human primary cell assay system to investigate the biological function of disease-linked telomerase RNA variants and their impact on the function of coexpressed wild-type telomerase RNA. We find that telomerase RNA variants discovered in patients with dyskeratosis congenita or aplastic anemia show loss of function without any indication of dominant-negative impact on telomere maintenance by the coexpressed wild-type RNA. To reconcile this result with contradictory findings from reconstitution assays in vitro, we demonstrate that the lack of dominant-negative impact on telomere maintenance correlates with physiological assembly of active human telomerase holoenzyme ribonucleoproteins harboring monomers rather than higher-order multimers of telomerase RNA and telomerase reverse transcriptase. These findings support loss of function of telomerase RNA as a general mechanism of human disease.
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191
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Chromosome Fusions following Telomere Loss Are Mediated by Single-Strand Annealing. Mol Cell 2008; 31:463-473. [DOI: 10.1016/j.molcel.2008.05.028] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2007] [Revised: 04/16/2008] [Accepted: 05/29/2008] [Indexed: 11/23/2022]
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192
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Abstract
Telomeres play a central role in cell fate and aging by adjusting the cellular response to stress and growth stimulation on the basis of previous cell divisions and DNA damage. At least a few hundred nucleotides of telomere repeats must "cap" each chromosome end to avoid activation of DNA repair pathways. Repair of critically short or "uncapped" telomeres by telomerase or recombination is limited in most somatic cells and apoptosis or cellular senescence is triggered when too many "uncapped" telomeres accumulate. The chance of the latter increases as the average telomere length decreases. The average telomere length is set and maintained in cells of the germline which typically express high levels of telomerase. In somatic cells, telomere length is very heterogeneous but typically declines with age, posing a barrier to tumor growth but also contributing to loss of cells with age. Loss of (stem) cells via telomere attrition provides strong selection for abnormal and malignant cells, a process facilitated by the genome instability and aneuploidy triggered by dysfunctional telomeres. The crucial role of telomeres in cell turnover and aging is highlighted by patients with 50% of normal telomerase levels resulting from a mutation in one of the telomerase genes. Short telomeres in such patients are implicated in a variety of disorders including dyskeratosis congenita, aplastic anemia, pulmonary fibrosis, and cancer. Here the role of telomeres and telomerase in human aging and aging-associated diseases is reviewed.
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Affiliation(s)
- Geraldine Aubert
- Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
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193
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Li F, Dong J, Pan X, Oum JH, Boeke JD, Lee SE. Microarray-based genetic screen defines SAW1, a gene required for Rad1/Rad10-dependent processing of recombination intermediates. Mol Cell 2008; 30:325-35. [PMID: 18471978 DOI: 10.1016/j.molcel.2008.02.028] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Revised: 01/29/2008] [Accepted: 02/27/2008] [Indexed: 11/18/2022]
Abstract
Elimination of a double-strand break (DSB) flanked by direct repeat sequences is mediated by single-strand annealing (SSA), which relies on a distinct set of gene products involving recombination, mismatch repair, and nucleotide excision repair. Here, we screened for yeast mutants defective in SSA with a plasmid-based SSA assay coupled to a barcode microarray readout. The screen identified Yal027Wp/Saw1 (single-strand annealing weakened 1) and Slx4 besides other known SSA proteins. Saw1 interacts physically with Rad1/Rad10, Msh2/Msh3, and Rad52 proteins, and cells lacking SLX4 or SAW1 accumulate recombination intermediates blocked at the Rad1/Rad10-dependent 3' flap cleavage step. Slx4 and Saw1 also contribute to the integrity of ribosomal DNA arrays. Saw1 mutants that fail to interact with Rad1, but retain interaction with Rad52 and Msh2, are defective in 3' flap removal and SSA repair. Deletion of SAW1 abolished association of Rad1 at SSA intermediates in vivo. We propose that Saw1 targets Rad1/Rad10 to Rad52-coated recombination intermediates.
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Affiliation(s)
- Fuyang Li
- Department of Molecular Medicine and Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, TX 78245, USA
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194
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195
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Mason JM, Frydrychova RC, Biessmann H. Drosophila telomeres: an exception providing new insights. Bioessays 2008; 30:25-37. [PMID: 18081009 DOI: 10.1002/bies.20688] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Drosophila telomeres comprise DNA sequences that differ dramatically from those of other eukaryotes. Telomere functions, however, are similar to those found in telomerase-based telomeres, even though the underlying mechanisms may differ. Drosophila telomeres use arrays of retrotransposons to maintain chromosome length, while nearly all other eukaryotes rely on telomerase-generated short repeats. Regardless of the DNA sequence, several end-binding proteins are evolutionarily conserved. Away from the end, the Drosophila telomeric and subtelomeric DNA sequences are complexed with unique combinations of proteins that also modulate chromatin structure elsewhere in the genome. Maintaining and regulating the transcriptional activity of the telomeric retrotransposons in Drosophila requires specific chromatin structures and, while telomeric silencing spreads from the terminal repeats in yeast, the source of telomeric silencing in Drosophila is the subterminal arrays. However, the subterminal arrays in both species may be involved in telomere-telomere associations and/or communication.
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Affiliation(s)
- James M Mason
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
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196
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Abstract
The ends of eukaryotic chromosomes have long been defined as structures that must avoid being detected as DNA breaks. They are protected from checkpoints, homologous recombination, end-to-end fusions, or other events that normally promote repair of intrachromosomal DNA breaks. This differentiation is thought to be the consequence of a unique organization of chromosomal ends into specialized nucleoprotein complexes called telomeres. However, it is becoming increasingly clear that proteins governing the DNA damage response are intimately involved in the regulation of telomeres, which undergo processing and structural changes that elicit a transient DNA damage response. This suggests that functional telomeres can be recognized as DNA breaks during a temporally limited window, indicating that the difference between a break and a telomere is less defined than previously assumed.
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Affiliation(s)
- Maria Pia Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milan, Italy.
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197
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Gallardo F, Olivier C, Dandjinou AT, Wellinger RJ, Chartrand P. TLC1 RNA nucleo-cytoplasmic trafficking links telomerase biogenesis to its recruitment to telomeres. EMBO J 2008; 27:748-57. [PMID: 18273059 PMCID: PMC2265757 DOI: 10.1038/emboj.2008.21] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2007] [Accepted: 01/21/2008] [Indexed: 01/15/2023] Open
Abstract
The yeast telomerase holoenzyme, which adds telomeric repeats at the chromosome ends, is composed of the TLC1 RNA and the associated proteins Est1, Est2 and Est3. To study the biogenesis of telomerase in endogenous conditions, we performed fluorescent in situ hybridization on the native TLC1 RNA. We found that the telomerase RNA colocalizes with telomeres in G1- to S-phase cells. Strains lacking any one of the Est proteins accumulate TLC1 RNA in their cytoplasm, indicating that a critical stage of telomerase biogenesis could take place outside of the nucleus. We were able to demonstrate that endogenous TLC1 RNA shuttles between the nucleus and the cytoplasm, in association with the Crm1p exportin and the nuclear importins Mtr10p-Kap122p. Furthermore, nuclear retention of the TLC1 RNA is impaired in the absence of yKu70p, Tel1p or the MRX complex, which recruit telomerase to telomeres. Altogether, our results reveal that the nucleo-cytoplasmic trafficking of the TLC1 RNA is an important step in telomere homeostasis, and link telomerase biogenesis to its recruitment to telomeres.
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Affiliation(s)
- Franck Gallardo
- Département de Biochimie, Université de Montréal, Montréal, Quebec, Canada
| | - Catherine Olivier
- Département de Biochimie, Université de Montréal, Montréal, Quebec, Canada
| | - Alain T Dandjinou
- Département de Microbiologie et Infectiologie, Université de Sherbrooke, Sherbrooke, Quebec, Canada
| | - Raymund J Wellinger
- Département de Microbiologie et Infectiologie, Université de Sherbrooke, Sherbrooke, Quebec, Canada
| | - Pascal Chartrand
- Département de Biochimie, Université de Montréal, Montréal, Quebec, Canada
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198
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Abstract
Telomerase is an attractive cancer target as it appears to be required in essentially all tumours for immortalization of a subset of cells, including cancer stem cells. Moreover, differences in telomerase expression, telomere length and cell kinetics between normal and tumour tissues suggest that targeting telomerase would be relatively safe. Clinical trials are ongoing with a potent and specific telomerase inhibitor, GRN163L, and with several versions of telomerase therapeutic vaccines. The prospect of adding telomerase-based therapies to the growing list of new anticancer products is promising, but what are the advantages and limitations of different approaches, and which patients are the most likely to respond?
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Affiliation(s)
- Calvin B Harley
- Geron Corporation, 230 Constitution Drive, Menlo Park, California 94025, USA.
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199
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Chang M, Arneric M, Lingner J. Telomerase repeat addition processivity is increased at critically short telomeres in a Tel1-dependent manner in Saccharomyces cerevisiae. Genes Dev 2007; 21:2485-94. [PMID: 17908934 PMCID: PMC1993878 DOI: 10.1101/gad.1588807] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Telomerase is the ribonucleoprotein enzyme that elongates telomeres to counteract telomere shortening. The core enzyme consists of a reverse transcriptase protein subunit and an RNA subunit. The RNA subunit contains a short region that is used as a template by the reverse transcriptase to add short, tandem, G-rich repeats to the 3' ends of telomeres. By coexpressing two RNA subunits that differ in the telomeric repeat sequence specified and examining the telomere extensions after one cell cycle, we determined that Saccharomyces cerevisiae telomerase can dissociate and reassociate from a given telomere during one cell cycle. We also confirmed that telomerase is nonprocessive in terms of telomeric repeat addition. However, repeat addition processivity is significantly increased at extremely short telomeres, a process that is dependent on the ATM-ortholog Tel1. We propose that this enhancement of telomerase processivity at short telomeres serves to rapidly elongate critically short telomeres.
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Affiliation(s)
- Michael Chang
- Swiss Institute for Experimental Cancer Research (ISREC), CH-1066 Epalinges, Switzerland; École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland; National Centre of Competence in Research (NCCR) “Frontiers in Genetics,” CH-1211 Geneva, Switzerland
| | - Milica Arneric
- Swiss Institute for Experimental Cancer Research (ISREC), CH-1066 Epalinges, Switzerland; École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland; National Centre of Competence in Research (NCCR) “Frontiers in Genetics,” CH-1211 Geneva, Switzerland
| | - Joachim Lingner
- Swiss Institute for Experimental Cancer Research (ISREC), CH-1066 Epalinges, Switzerland; École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland; National Centre of Competence in Research (NCCR) “Frontiers in Genetics,” CH-1211 Geneva, Switzerland
- Corresponding author.E-MAIL ; FAX 41-21-652-69-33
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200
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Azzalin CM, Reichenbach P, Khoriauli L, Giulotto E, Lingner J. Telomeric repeat containing RNA and RNA surveillance factors at mammalian chromosome ends. Science 2007; 318:798-801. [PMID: 17916692 DOI: 10.1126/science.1147182] [Citation(s) in RCA: 939] [Impact Index Per Article: 55.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Telomeres, the DNA-protein complexes located at the end of linear eukaryotic chromosomes, are essential for chromosome stability. Until now, telomeres have been considered to be transcriptionally silent. We demonstrate that mammalian telomeres are transcribed into telomeric repeat-containing RNA (TERRA). TERRA molecules are heterogeneous in length, are transcribed from several subtelomeric loci toward chromosome ends, and localize to telomeres. We also show that suppressors with morphogenetic defects in genitalia (SMG) proteins, which are effectors of nonsense-mediated messenger RNA decay, are enriched at telomeres in vivo, negatively regulate TERRA association with chromatin, and protect chromosome ends from telomere loss. Thus, telomeres are actively transcribed into TERRA, and SMG factors represent a molecular link between TERRA regulation and the maintenance of telomere integrity.
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Affiliation(s)
- Claus M Azzalin
- Swiss Institute for Experimental Cancer Research (ISREC), CH-1066 Epalinges, Switzerland
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