51
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Janovič T, Stojaspal M, Veverka P, Horáková D, Hofr C. Human Telomere Repeat Binding Factor TRF1 Replaces TRF2 Bound to Shelterin Core Hub TIN2 when TPP1 Is Absent. J Mol Biol 2019; 431:3289-3301. [DOI: 10.1016/j.jmb.2019.05.038] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 05/22/2019] [Accepted: 05/23/2019] [Indexed: 12/17/2022]
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52
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The role of telomere-binding modulators in pluripotent stem cells. Protein Cell 2019; 11:60-70. [PMID: 31350723 PMCID: PMC6949317 DOI: 10.1007/s13238-019-0651-y] [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] [Received: 04/02/2019] [Accepted: 05/07/2019] [Indexed: 01/24/2023] Open
Abstract
Pluripotent stem cells (PSCs) such as embryonic stem cells (ESCs), ESCs derived by somatic cell nuclear transfer (ntESCs), and induced pluripotent stem cells (iPSCs) have unlimited capacity for self-renewal and pluripotency and can give rise to all types of somatic cells. In order to maintain their self-renewal and pluripotency, PSCs need to preserve their telomere length and homeostasis. In recent years, increasing studies have shown that telomere reprogramming is essential for stem cell pluripotency maintenance and its induced pluripotency process. Telomere-associated proteins are not only required for telomere maintenance in both stem cells, their extra-telomeric functions have also been found to be critical as well. Here, we will discuss how telomeres and telomere-associated factors participate and regulate the maintenance of stem cell pluripotency.
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53
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Episkopou H, Diman A, Claude E, Viceconte N, Decottignies A. TSPYL5 Depletion Induces Specific Death of ALT Cells through USP7-Dependent Proteasomal Degradation of POT1. Mol Cell 2019; 75:469-482.e6. [PMID: 31278054 DOI: 10.1016/j.molcel.2019.05.027] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 04/05/2019] [Accepted: 05/17/2019] [Indexed: 01/11/2023]
Abstract
A significant fraction (∼10%) of cancer cells maintain their telomere length via a telomerase-independent mechanism known as alternative lengthening of telomeres (ALT). There are no known molecular, ALT-specific, therapeutic targets. We have identified TSPYL5 (testis-specific Y-encoded-like protein 5) as a PML body component, co-localizing with ALT telomeres and critical for ALT+ cell viability. TSPYL5 was described as an inhibitor of the USP7 deubiquitinase. We report that TSPYL5 prevents the poly-ubiquitination of POT1-a shelterin component-and protects POT1 from proteasomal degradation exclusively in ALT+ cells. USP7 depletion rescued POT1 poly-ubiquitination and loss, suggesting that the deubiquitinase activates POT1 E3 ubiquitin ligase(s). Similarly, PML depletion suppressed POT1 poly-ubiquitination, suggesting an interplay between USP7 and PML to trigger POT1 degradation in TSPYL5-depleted ALT+ cells. We demonstrate that ALT telomeres need to be protected from POT1 degradation in ALT-associated PML bodies and identify TSPYL5 as an ALT+ cancer-specific therapeutic target.
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Affiliation(s)
- Harikleia Episkopou
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université Catholique de Louvain, Brussels 1200, Belgium
| | - Aurélie Diman
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université Catholique de Louvain, Brussels 1200, Belgium
| | - Eloïse Claude
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université Catholique de Louvain, Brussels 1200, Belgium
| | - Nikenza Viceconte
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université Catholique de Louvain, Brussels 1200, Belgium
| | - Anabelle Decottignies
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université Catholique de Louvain, Brussels 1200, Belgium.
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Grill S, Tesmer VM, Nandakumar J. The N Terminus of the OB Domain of Telomere Protein TPP1 Is Critical for Telomerase Action. Cell Rep 2019; 22:1132-1140. [PMID: 29386102 DOI: 10.1016/j.celrep.2018.01.012] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Revised: 12/19/2017] [Accepted: 01/03/2018] [Indexed: 01/15/2023] Open
Abstract
Telomerase recruitment to telomeres and enzymatic processivity are mediated by TPP1, an essential component of telomere integrity and telomerase function. A surface on the OB domain of TPP1 called the TEL patch is critical for TPP1's telomerase-associated functions. Here, we identify a separate region in the N terminus of the OB domain (termed NOB) of TPP1 that, like the TEL patch, is essential for telomerase repeat addition processivity in vitro as well as telomerase recruitment to telomeres and telomere lengthening in cells. Although well-conserved among most mammalian TPP1 homologs, the NOB region in mice is distinct. Swapping the sequence of human NOB into mouse TPP1 allows it to stimulate human telomerase, qualifying NOB as an important determinant of species specificity for TPP1-telomerase interaction. Our studies show that TPP1 NOB is critical for telomerase function and demonstrate that the telomerase interaction surface on TPP1 is more elaborate than previously appreciated.
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Affiliation(s)
- Sherilyn Grill
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Valerie M Tesmer
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Jayakrishnan Nandakumar
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA.
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55
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Amir M, Ahmad S, Ahamad S, Kumar V, Mohammad T, Dohare R, Alajmi MF, Rehman T, Hussain A, Islam A, Ahmad F, Hassan MI. Impact of Gln94Glu mutation on the structure and function of protection of telomere 1, a cause of cutaneous familial melanoma. J Biomol Struct Dyn 2019; 38:1514-1524. [DOI: 10.1080/07391102.2019.1610500] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Mohd. Amir
- Jamia Millia Islamia, Jamia Nagar, Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
| | - Shahnawaz Ahmad
- Department of Biotechnology, School of Engineering &Technology, IFTM University, Lodhipur-Rajput, Moradabad, Uttar Pradesh, India
| | - Shahzaib Ahamad
- Department of Biotechnology, School of Engineering &Technology, IFTM University, Lodhipur-Rajput, Moradabad, Uttar Pradesh, India
| | - Vijay Kumar
- Amity Institute of Neuropsychology & Neurosciences, Amity University, Noida, Uttar Pradesh, India
| | - Taj Mohammad
- Jamia Millia Islamia, Jamia Nagar, Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
| | - Ravins Dohare
- Jamia Millia Islamia, Jamia Nagar, Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
| | - Mohamed F. Alajmi
- Department of Pharmacognosy, College of Pharmacy, King Saud University, Riyadh, KSA
| | - Tabish Rehman
- Department of Pharmacognosy, College of Pharmacy, King Saud University, Riyadh, KSA
| | - Afzal Hussain
- Department of Pharmacognosy, College of Pharmacy, King Saud University, Riyadh, KSA
| | - Asimul Islam
- Jamia Millia Islamia, Jamia Nagar, Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
| | - Faizan Ahmad
- Jamia Millia Islamia, Jamia Nagar, Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
| | - Md. Imtaiyaz Hassan
- Jamia Millia Islamia, Jamia Nagar, Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
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56
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Nera B, Huang HS, Hendrickson EA, Xu L. Both the classical and alternative non-homologous end joining pathways contribute to the fusion of drastically shortened telomeres induced by TRF2 overexpression. Cell Cycle 2019; 18:880-888. [PMID: 30907229 DOI: 10.1080/15384101.2019.1598724] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
The double-stranded telomeric binding protein TRF2 is expressed in many human cancers at elevated levels. Moreover, experimental overexpression of TRF2 in human cells causes replication stalling in telomeric tracts, which leads to drastic telomere shortening and fusion of deprotected chromosome ends. To understand which end joining pathway is involved in mediating these chromosome fusions, we overexpressed TRF2 in human HCT116 cell lines that were deficient for the DNA Ligase 4 (Lig4)-dependent classical non-homologous end joining (C-NHEJ) or the DNA Ligase 3 (Lig3)-dependent alternative non-homologous end joining (A-NHEJ) pathway. Surprisingly, abrogation of either Lig4 or nuclear Lig3 significantly reduced inter-chromosomal fusion of drastically shortened telomeres, suggesting that both the C-NHEJ and A-NHEJ pathways are involved in mediating this type of fusion. Fusion between deprotected sister chromatids, however, only required the Lig3-dependent A-NHEJ pathway. Interestingly, a previous study reported similar end joining pathway requirements for the fusion of critically shortened telomeres during a telomere attrition-based cellular crisis. We speculate that, as in cellular crisis, the same repair pathway(s) may drive clonal and genomic evolution in human cancers containing elevated TRF2 levels.
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Affiliation(s)
- Bernadette Nera
- a Department of Microbiology and Molecular Genetics , University of California , Davis , CA , USA
| | - Hui-Shun Huang
- a Department of Microbiology and Molecular Genetics , University of California , Davis , CA , USA
| | - Eric A Hendrickson
- b Department of Biochemistry, Molecular Biology and Biophysics , University of Minnesota Medical School , Minneapolis , MN , USA
| | - Lifeng Xu
- a Department of Microbiology and Molecular Genetics , University of California , Davis , CA , USA
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57
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An N-terminal Flag-tag impairs TPP1 regulation of telomerase function. Biochem Biophys Res Commun 2019; 512:230-235. [PMID: 30885434 DOI: 10.1016/j.bbrc.2019.03.050] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 03/08/2019] [Indexed: 10/27/2022]
Abstract
The shelterin protein complex protects natural chromosome ends from being recognized as DNA damage sites and also regulates the synthesis of telomeric repeats by telomerase. TPP1, a shelterin subunit that is essential for telomerase extension of telomeres, has been studied intensively in recent years. Many such studies utilize epitope tagged TPP1, but it is unclear how the tags may affect the multiple cellular functions of TPP1. Here we analyzed the effect of adding a 3x Flag epitope tag to the N- or C-terminus of TPP1. While the position of the tag did not affect TPP1's interaction within the shelterin complex or its localization to telomeres, the N-terminal Flag tag on TPP1 impaired telomerase function, resulting in reduced telomerase processivity in vitro and a failure to stimulate telomere elongation in vivo. The C-terminally Flag-tagged TPP1, in contrast, behaved similarly to untagged TPP1 in all functional aspects examined. These findings suggest that caution is required when utilizing epitope tagged TPP1 to study its regulation of telomerase function.
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58
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Okamoto K, Seimiya H. Revisiting Telomere Shortening in Cancer. Cells 2019; 8:cells8020107. [PMID: 30709063 PMCID: PMC6406355 DOI: 10.3390/cells8020107] [Citation(s) in RCA: 98] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Revised: 01/28/2019] [Accepted: 01/28/2019] [Indexed: 12/21/2022] Open
Abstract
Telomeres, the protective structures of chromosome ends are gradually shortened by each cell division, eventually leading to senescence or apoptosis. Cancer cells maintain the telomere length for unlimited growth by telomerase reactivation or a recombination-based mechanism. Recent genome-wide analyses have unveiled genetic and epigenetic alterations of the telomere maintenance machinery in cancer. While telomerase inhibition reveals that longer telomeres are more advantageous for cell survival, cancer cells often have paradoxically shorter telomeres compared with those found in the normal tissues. In this review, we summarize the latest knowledge about telomere length alterations in cancer and revisit its rationality. Finally, we discuss the potential utility of telomere length as a prognostic biomarker.
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Affiliation(s)
- Keiji Okamoto
- Division of Molecular Biotherapy, Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Koto-ku, Tokyo 135-8550, Japan.
| | - Hiroyuki Seimiya
- Division of Molecular Biotherapy, Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Koto-ku, Tokyo 135-8550, Japan.
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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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Laberthonnière C, Magdinier F, Robin JD. Bring It to an End: Does Telomeres Size Matter? Cells 2019; 8:E30. [PMID: 30626097 PMCID: PMC6356554 DOI: 10.3390/cells8010030] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 01/01/2019] [Accepted: 01/04/2019] [Indexed: 12/22/2022] Open
Abstract
Telomeres are unique nucleoprotein structures. Found at the edge of each chromosome, their main purpose is to mask DNA ends from the DNA-repair machinery by formation of protective loops. Through life and cell divisions, telomeres shorten and bring cells closer to either cell proliferation crisis or senescence. Beyond this mitotic clock role attributed to the need for telomere to be maintained over a critical length, the very tip of our DNA has been shown to impact transcription by position effect. TPE and a long-reach counterpart, TPE-OLD, are mechanisms recently described in human biology. Still in infancy, the mechanism of action of these processes and their respective genome wide impact remain to be resolved. In this review, we will discuss recent findings on telomere dynamics, TPE, TPE-OLD, and lessons learnt from model organisms.
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Affiliation(s)
| | - Frédérique Magdinier
- Aix Marseille Univ, MMG, Marseille Medical Genetics U1251, 13385 Marseille, France.
| | - Jérôme D Robin
- Aix Marseille Univ, MMG, Marseille Medical Genetics U1251, 13385 Marseille, France.
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61
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Ravindranathan A, Cimini B, Diolaiti ME, Stohr BA. Preliminary development of an assay for detection of TERT expression, telomere length, and telomere elongation in single cells. PLoS One 2018; 13:e0206525. [PMID: 30517099 PMCID: PMC6281304 DOI: 10.1371/journal.pone.0206525] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Accepted: 10/15/2018] [Indexed: 02/06/2023] Open
Abstract
The telomerase enzyme enables unlimited proliferation of most human cancer cells by elongating telomeres and preventing replicative senescence. Despite the critical importance of telomerase in cancer biology, challenges detecting telomerase activity and expression in individual cells have hindered the ability to study patterns of telomerase expression and function across heterogeneous cell populations. While sensitive assays to ascertain telomerase expression and function exist, these approaches have proven difficult to implement at the single cell level. Here, we validate in situ RNAscope detection of the telomerase TERT mRNA and couple this assay with our recently described TSQ1 method for in situ detection of telomere elongation. This approach enables detection of TERT expression, telomere length, and telomere elongation within individual cells of the population. Using this assay, we show that the heterogeneous telomere elongation observed across a HeLa cell population is in part driven by variable expression of the TERT gene. Furthermore, we show that the absence of detectable telomere elongation in some TERT-positive cells is the result of inhibition by the telomeric shelterin complex. This combined assay provides a new approach for understanding the integrated expression, function, and regulation of telomerase at the single cell level.
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Affiliation(s)
- Ajay Ravindranathan
- Department of Pathology, University of California, San Francisco, California, United States of America
| | - Beth Cimini
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, United States of America
| | - Morgan E Diolaiti
- Department of Pathology, University of California, San Francisco, California, United States of America
| | - Bradley A Stohr
- Department of Pathology, University of California, San Francisco, California, United States of America
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62
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Polito F, Cucinotta M, Abbritti RV, Brogna A, Pergolizzi S, Tomasello C, Barresi V, Angileri FF, Di Giorgio R, Conti A, La Torre D, Germanò A, Aguennouz M. Silencing of telomere-binding protein adrenocortical dysplasia (ACD) homolog enhances radiosensitivity in glioblastoma cells. Transl Res 2018; 202:99-108. [PMID: 30080989 DOI: 10.1016/j.trsl.2018.07.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 06/23/2018] [Accepted: 07/10/2018] [Indexed: 11/30/2022]
Abstract
Adrenocortical dysplasia (ACD) is a shelterin protein involved in the maintenance of telomere length and in cancer radioresistance. This study investigated the expression profile of ACD in human gliomas and its role in radioresistance of glioma cells. The expression of ACD was analyzed in 62 different grades of glioma tissues and correlated with prognosis. A radioresistant cell line was generated from U87MG cells. For mechanistic studies, ACD was inhibited by small interfering RNA-targeting ACD and the effect on cell radioresistance, telomerase activity, cyclinD1, caspase-3, hTERT, and BIRC1 was evaluated. Clonogenic assay was performed after irradiation, to investigate the effect of ACD silencing on radiation sensitivity. ACD expression appeared strongly upregulated in higher grade gliomas, and its expression was significantly correlated to grading and poor prognosis. In glioma cell lines, ACD expression pattern was similar to those observed in glioma tissues. In irradiated cells, ACD expression was increased in an ionizing radiation dose-dependent manner. A higher expression of ACD was observed in the radioresistant clones than parental cells. Silencing of ACD led to the enhanced radiation sensitivity, decreased telomerase activity and cyclin D1 expression, reduced expression of BIRC1, and finally to the upregulation of caspase-3. This study represents the first report, which demonstrated the expression pattern of ACD in gliomas and its prognostic value. Our results suggested that ACD is involved in glioblastoma radioresistance, likely through the modulation of telomerase activity, proliferation, and apoptosis. ACD might represent a potential molecular biomarker and a novel therapeutic target in glioblastoma.
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Affiliation(s)
- Francesca Polito
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | - Maria Cucinotta
- Department of Clinical and Experimental Medicine, University of Messina, Italy
| | - Rosaria V Abbritti
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | - Anna Brogna
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | - Stefano Pergolizzi
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | - Chiara Tomasello
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | | | - Flavio F Angileri
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | | | - Alfredo Conti
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | - Domenico La Torre
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | - Antonino Germanò
- Department of Biomedical, Dental Sciences and of Morphological and Functional Images, University of Messina, Italy
| | - M'hammed Aguennouz
- Department of Clinical and Experimental Medicine, University of Messina, Italy.
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63
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Kratz K, de Lange T. Protection of telomeres 1 proteins POT1a and POT1b can repress ATR signaling by RPA exclusion, but binding to CST limits ATR repression by POT1b. J Biol Chem 2018; 293:14384-14392. [PMID: 30082315 DOI: 10.1074/jbc.ra118.004598] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2018] [Revised: 08/02/2018] [Indexed: 12/15/2022] Open
Abstract
Comprised of telomeric TTAGGG repeats and shelterin, telomeres ensure that the natural ends of chromosomes remain impervious to the DNA damage response. Telomeres carry a long constitutive 3' overhang that can bind replication protein A (RPA) and activate the ATR Ser/Thr kinase (ATR), which induces cell cycle arrest. A single-stranded (ss) TTAGGG repeat-binding protein in mouse shelterin, POT1a, has been proposed to repress ATR signaling by preventing RPA binding. Repression of ATR at telomeres requires tethering of POT1a to the other shelterin subunits situated on the double-stranded (ds) telomeric DNA. The simplest model of ATR repression, the "tethered exclusion model," suggests that the only critical features of POT1a are its connection to shelterin and its binding to ss telomeric DNA. In agreement with the model, we show here that a shelterin-tethered variant of RPA70 (lacking the ATR recruitment domain) can repress ATR signaling at telomeres that lack POT1a. However, arguing against the tethered exclusion model, the nearly identical POT1b subunit of shelterin has been shown to be much less proficient than POT1a in repression of ATR. We now show that POT1b has the intrinsic ability to fully repress ATR but is prevented from doing so when bound to Ctc1, Stn1, Ten1 (CST), the complex needed for telomere end processing. These results establish that shelterin represses ATR with a tethered ssDNA-binding domain that excludes RPA from the 3' overhang and also reveal an unexpected effect of CST on the ability of POT1b to repress ATR.
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Affiliation(s)
- Katja Kratz
- From the Laboratory for Cell Biology and Genetics, Rockefeller University, New York, New York 10021
| | - Titia de Lange
- From the Laboratory for Cell Biology and Genetics, Rockefeller University, New York, New York 10021
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64
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Smith ED, Garza-Gongora AG, MacQuarrie KL, Kosak ST. Interstitial telomeric loops and implications of the interaction between TRF2 and lamin A/C. Differentiation 2018; 102:19-26. [PMID: 29979997 DOI: 10.1016/j.diff.2018.06.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Revised: 06/11/2018] [Accepted: 06/12/2018] [Indexed: 11/19/2022]
Abstract
The protein-DNA complexes that compose the end of mammalian chromosomes-telomeres-serve to stabilize linear genomic DNA and are involved in cellular and organismal aging. One mechanism that protects telomeres from premature degradation is the formation of structures called t-loops, in which the single-stranded 3' overhang present at the terminal end of telomeres loops back and invades medial double-stranded telomeric DNA. We identified looped structures formed between terminal chromosome ends and interstitial telomeric sequences (ITSs), which are found throughout the human genome, that we have termed interstitial telomeric loops (ITLs). While they form in a TRF2-dependent manner similar to t-loops, ITLs further require the physical interaction of TRF2 with the nuclear intermediate filament protein lamin A/C. Our findings suggest that interactions between telomeres and the nucleoskeleton broadly impact genomic integrity, including telomere stability, chromosome structure, and chromosome fragility. Here, we review the roles of TRF2 and lamin A/C in telomere biology and consider how their interaction may relate telomere homeostasis to cellular and organismal aging.
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Affiliation(s)
- Erica D Smith
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Arturo G Garza-Gongora
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Kyle L MacQuarrie
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; Division of Hematology, Oncology and Stem Cell Transplantation, Ann & Robert H. Lurie Children's Hospital of Chicago, USA
| | - Steven T Kosak
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
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65
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HuR regulates telomerase activity through TERC methylation. Nat Commun 2018; 9:2213. [PMID: 29880812 PMCID: PMC5992219 DOI: 10.1038/s41467-018-04617-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 05/07/2018] [Indexed: 01/21/2023] Open
Abstract
Telomerase consists of the catalytic protein TERT and the RNA TERC. Mutations in TERC are linked to human diseases, but the underlying mechanisms are poorly understood. Here we report that the RNA-binding protein HuR associates with TERC and promotes the assembly of the TERC/TERT complex by facilitating TERC C106 methylation. Dyskeratosis congenita (DC)-related TERC U100A mutation impair the association of HuR with TERC, thereby reducing C106 methylation. Two other TERC mutations linked to aplastic anemia and autosomal dominant DC, G107U, and GC107/108AG, likewise disrupt methylation at C106. Loss-of-HuR binding and hence lower TERC methylation leads to decreased telomerase activity and telomere shortening. Furthermore, HuR deficiency or mutation of mTERC HuR binding or methylation sites impair the renewal of mouse hematopoietic stem cells, recapitulating the bone marrow failure seen in DC. Collectively, our findings reveal a novel function of HuR, linking HuR to telomerase function and TERC-associated DC. Mutations in the RNA component TERC can cause telomerase dysfunction but the underlying mechanisms are largely unknown. Here, the authors show that RNA-binding protein HuR regulates telomerase function by enhancing the methylation of TERC, which is impaired by several disease-relevant TERC mutations.
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66
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Abstract
The ASBMB 2018 Bert and Natalie Vallee award in Biomedical Sciences honors our work on shelterin, a protein complex that helps cells distinguish the chromosome ends from sites of DNA damage. Shelterin protects telomeres from all aspects of the DNA damage response, including ATM and ATR serine/threonine kinase signaling and several forms of double-strand break repair. Today, this six-subunit protein complex could easily be identified in one single proteomics step. But, it took us more than 15 years to piece together the entire shelterin complex, one protein at a time. Although we did a lot of things right, here I tell the story of shelterin's discovery with an emphasis on the things that I got wrong along the way.
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Affiliation(s)
- Titia de Lange
- From the Laboratory for Cell Biology and Genetics, Rockefeller University, New York, New York 10065
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67
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Liu Y, Liu F, Cao Y, Xu H, Wu Y, Wu S, Liu D, Zhao Y, Songyang Z, Ma W. Shwachman-Diamond Syndrome Protein SBDS Maintains Human Telomeres by Regulating Telomerase Recruitment. Cell Rep 2018; 22:1849-1860. [PMID: 29444436 PMCID: PMC5844287 DOI: 10.1016/j.celrep.2018.01.057] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Revised: 12/20/2017] [Accepted: 01/19/2018] [Indexed: 01/15/2023] Open
Abstract
Shwachman-Diamond syndrome (SDS) is a rare pediatric disease characterized by various systemic disorders, including hematopoietic dysfunction. The mutation of Shwachman-Bodian-Diamond syndrome (SBDS) gene has been proposed to be a major causative reason for SDS. Although SBDS patients were reported to have shorter telomere length in granulocytes, the underlying mechanism is still unclear. Here we provide data to elucidate the role of SBDS in telomere protection. We demonstrate that SBDS deficiency leads to telomere shortening. We found that overexpression of disease-associated SBDS mutants or knockdown of SBDS hampered the recruitment of telomerase onto telomeres, while the overall reverse transcriptase activity of telomerase remained unaffected. Moreover, we show that SBDS could specifically bind to TPP1 during the S phase of cell cycle, likely functioning as a stabilizer for TPP1-telomerase interaction. Our findings suggest that SBDS is a telomere-protecting protein that participates in regulating telomerase recruitment.
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Affiliation(s)
- Yi Liu
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Feng Liu
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China.
| | - Yizhao Cao
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Huimin Xu
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Yangxiu Wu
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Su Wu
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Dan Liu
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Yong Zhao
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Zhou Songyang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China; Collaborative Innovation Center for Cancer Medicine, Institute of Healthy Aging Research, Sun Yat-sen University, Guangzhou 510006, China; Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
| | - Wenbin Ma
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Oncology in South China, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China; Collaborative Innovation Center for Cancer Medicine, Institute of Healthy Aging Research, Sun Yat-sen University, Guangzhou 510006, China.
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68
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Kalathiya U, Padariya M, Baginski M. The structurally similar TRFH domain of TRF1 and TRF2 dimers shows distinct behaviour towards TIN2. Arch Biochem Biophys 2018; 642:52-62. [PMID: 29428209 DOI: 10.1016/j.abb.2018.02.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Revised: 02/06/2018] [Accepted: 02/07/2018] [Indexed: 01/25/2023]
Abstract
The telomere repeat binding-factor 1 and 2 (TRF1 and TRF2) proteins of the shelterin complex bind to duplex telomeric DNA as homodimers, and the homodimerization is mediated by their TRFH (TRF-homology) domains. We performed molecular dynamic (MD) simulations of the dimer forms of TRF1TRFH and TRF2TRFH in the presence/absence of the TIN2TBM (TIN2, TRF-interacting nuclear protein 2, TBM, TRF-binding motif) peptide. The MD results suggest that TIN2TBM is necessary to ensure the stability of TRF1TRFH homodimer but not the TRF2TRFH homodimer. In TRF1-TIN2-TRF2 complex, the peptide enhances the protein-protein interactions to yield a stable heterodimer. Both monomers in TRF1TRFH homodimer interact almost equally with the peptide, whereas in TRF2TRFH homodimer, monomer TRF2TRFH(M1) exhibits more dominant interactions than the TRF2TRFH(M2). The common residues of TRF1/2TRFH(M1) that form interactions with TIN2TBM in all peptide-bound systems originate from the H3 (helix) and L3 (loop) regions. Additionally, in the homodimer systems, residues of TRF1/2TRFH(M2) also interact with the peptide. The residue pair E71-K213 is responsible for different conformations of TRF1TRFH homodimers; specifically, this residue pair enhances the protein-peptide/protein interactions in peptide-bound/unbound systems, respectively. TRF1TRFH and TRF2TRFH proteins have a conserved but different interface responsible for the protein-protein/peptide interactions that exist in the corresponding dimers.
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Affiliation(s)
- Umesh Kalathiya
- Department of Pharmaceutical Technology and Biochemistry, Faculty of Chemistry, Gdansk University of Technology, Narutowicza St 11/12, 80-233 Gdansk, Poland.
| | - Monikaben Padariya
- Department of Pharmaceutical Technology and Biochemistry, Faculty of Chemistry, Gdansk University of Technology, Narutowicza St 11/12, 80-233 Gdansk, Poland
| | - Maciej Baginski
- Department of Pharmaceutical Technology and Biochemistry, Faculty of Chemistry, Gdansk University of Technology, Narutowicza St 11/12, 80-233 Gdansk, Poland
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69
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Hu C, Rai R, Huang C, Broton C, Long J, Xu Y, Xue J, Lei M, Chang S, Chen Y. Structural and functional analyses of the mammalian TIN2-TPP1-TRF2 telomeric complex. Cell Res 2017; 27:1485-1502. [PMID: 29160297 PMCID: PMC5717407 DOI: 10.1038/cr.2017.144] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Revised: 09/25/2017] [Accepted: 10/17/2017] [Indexed: 01/09/2023] Open
Abstract
Telomeres are nucleoprotein complexes that play essential roles in protecting chromosome ends. Mammalian telomeres consist of repetitive DNA sequences bound by the shelterin complex. In this complex, the POT1-TPP1 heterodimer binds to single-stranded telomeric DNAs, while TRF1 and TRF2-RAP1 interact with double-stranded telomeric DNAs. TIN2, the linchpin of this complex, simultaneously interacts with TRF1, TRF2, and TPP1 to mediate the stable assembly of the shelterin complex. However, the molecular mechanism by which TIN2 interacts with these proteins to orchestrate telomere protection remains poorly understood. Here, we report the crystal structure of the N-terminal domain of TIN2 in complex with TIN2-binding motifs from TPP1 and TRF2, revealing how TIN2 interacts cooperatively with TPP1 and TRF2. Unexpectedly, TIN2 contains a telomeric repeat factor homology (TRFH)-like domain that functions as a protein-protein interaction platform. Structure-based mutagenesis analyses suggest that TIN2 plays an important role in maintaining the stable shelterin complex required for proper telomere end protection.
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Affiliation(s)
- Chunyi Hu
- State Key Laboratory of Molecular Biology, National Center for Protein Science Shanghai, Shanghai Science Research Center, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, 333 Haike Road, Shanghai 201210, China
| | - Rekha Rai
- Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06510 USA
| | - Chenhui Huang
- Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China
- Shanghai Institute of Precision Medicine, Shanghai 200125, China
| | - Cayla Broton
- Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06510 USA
| | - Juanjuan Long
- State Key Laboratory of Molecular Biology, National Center for Protein Science Shanghai, Shanghai Science Research Center, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, 333 Haike Road, Shanghai 201210, China
| | - Ying Xu
- State Key Laboratory of Molecular Biology, National Center for Protein Science Shanghai, Shanghai Science Research Center, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, 333 Haike Road, Shanghai 201210, China
| | - Jing Xue
- State Key Laboratory of Molecular Biology, National Center for Protein Science Shanghai, Shanghai Science Research Center, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, 333 Haike Road, Shanghai 201210, China
| | - Ming Lei
- Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China
- Shanghai Institute of Precision Medicine, Shanghai 200125, China
- Key laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Sandy Chang
- Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06510 USA
- Department of Pathology, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06510 USA
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06510 USA
| | - Yong Chen
- State Key Laboratory of Molecular Biology, National Center for Protein Science Shanghai, Shanghai Science Research Center, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, 333 Haike Road, Shanghai 201210, China
- School of Life Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210, China
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70
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Erdel F, Kratz K, Willcox S, Griffith JD, Greene EC, de Lange T. Telomere Recognition and Assembly Mechanism of Mammalian Shelterin. Cell Rep 2017; 18:41-53. [PMID: 28052260 DOI: 10.1016/j.celrep.2016.12.005] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Revised: 11/13/2016] [Accepted: 11/30/2016] [Indexed: 11/16/2022] Open
Abstract
Shelterin is a six-subunit protein complex that plays crucial roles in telomere length regulation, protection, and maintenance. Although several shelterin subunits have been studied in vitro, the biochemical properties of the fully assembled shelterin complex are not well defined. Here, we characterize shelterin using ensemble biochemical methods, electron microscopy, and single-molecule imaging to determine how shelterin recognizes and assembles onto telomeric repeats. We show that shelterin complexes can exist in solution and primarily locate telomeric DNA through a three-dimensional diffusive search. Shelterin can diffuse along non-telomeric DNA but is impeded by nucleosomes, arguing against extensive one-dimensional diffusion as a viable assembly mechanism. Our work supports a model in which individual shelterin complexes rapidly bind to telomeric repeats as independent functional units, which do not alter the DNA-binding mode of neighboring complexes but, rather, occupy telomeric DNA in a "beads on a string" configuration.
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Affiliation(s)
- Fabian Erdel
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Katja Kratz
- Laboratory for Cell Biology and Genetics, Rockefeller University, New York, NY 10065, USA
| | - Smaranda Willcox
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Jack D Griffith
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Eric C Greene
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
| | - Titia de Lange
- Laboratory for Cell Biology and Genetics, Rockefeller University, New York, NY 10065, USA.
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71
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Lim CJ, Zaug AJ, Kim HJ, Cech TR. Reconstitution of human shelterin complexes reveals unexpected stoichiometry and dual pathways to enhance telomerase processivity. Nat Commun 2017; 8:1075. [PMID: 29057866 PMCID: PMC5651854 DOI: 10.1038/s41467-017-01313-w] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Accepted: 09/07/2017] [Indexed: 01/24/2023] Open
Abstract
The human shelterin proteins associate with telomeric DNA to confer telomere protection and length regulation. They are thought to form higher-order protein complexes for their functions, but studies of shelterin proteins have been mostly limited to pairs of proteins. Here we co-express various human shelterin proteins and find that they form defined multi-subunit complexes. A complex harboring both TRF2 and POT1 has the strongest binding affinity to telomeric DNA substrates comprised of double-stranded DNA with a 3′ single-stranded extension. TRF2 interacts with TIN2 with an unexpected 2:1 stoichiometry in the context of shelterin (RAP12:TRF22:TIN21:TPP11:POT11). Tethering of TPP1 to the telomere either via TRF2–TIN2 or via POT1 gives equivalent enhancement of telomerase processivity. We also identify a peptide region from TPP1 that is both critical and sufficient for TIN2 interaction. Our findings reveal new information about the architecture of human shelterin and how it performs its functions at telomeres. The human shelterin complex protects telomere ends from being recognized as damaged DNA sites and regulates telomere length in conjunction with telomerase. Here the authors establish the stoichiometries of human shelterin complexes of various compositions and show shelterin provides dual pathways to stimulate telomerase processivity.
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Affiliation(s)
- Ci Ji Lim
- Howard Hughes Medical Institute, University of Colorado BioFrontiers Institute, Boulder, CO, 80309, USA.,Department of Chemistry & Biochemistry, University of Colorado, Boulder, CO, 80309, USA
| | - Arthur J Zaug
- Howard Hughes Medical Institute, University of Colorado BioFrontiers Institute, Boulder, CO, 80309, USA.,Department of Chemistry & Biochemistry, University of Colorado, Boulder, CO, 80309, USA
| | - Hee Jin Kim
- Howard Hughes Medical Institute, University of Colorado BioFrontiers Institute, Boulder, CO, 80309, USA.,Department of Chemistry & Biochemistry, University of Colorado, Boulder, CO, 80309, USA
| | - Thomas R Cech
- Howard Hughes Medical Institute, University of Colorado BioFrontiers Institute, Boulder, CO, 80309, USA. .,Department of Chemistry & Biochemistry, University of Colorado, Boulder, CO, 80309, USA.
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72
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Hayashi MT. Telomere biology in aging and cancer: early history and perspectives. Genes Genet Syst 2017; 92:107-118. [PMID: 28993556 DOI: 10.1266/ggs.17-00010] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The ends of eukaryotic linear chromosomes are protected from undesired enzymatic activities by a nucleoprotein complex called the telomere. Expanding evidence indicates that telomeres have central functions in human aging and tumorigenesis. While it is undoubtedly important to follow current advances in telomere biology, it is also fruitful to be well informed in seminal historical studies for a comprehensive understanding of telomere biology, and for the anticipation of future directions. With this in mind, I here summarize the early history of telomere biology and current advances in the field, mostly focusing on mammalian studies relevant to aging and cancer.
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Affiliation(s)
- Makoto T Hayashi
- Department of Gene Mechanisms, Graduate School of Biostudies/The Hakubi Center for Advanced Research, Kyoto University
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73
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Kim H, Li F, He Q, Deng T, Xu J, Jin F, Coarfa C, Putluri N, Liu D, Songyang Z. Systematic analysis of human telomeric dysfunction using inducible telosome/shelterin CRISPR/Cas9 knockout cells. Cell Discov 2017; 3:17034. [PMID: 28955502 PMCID: PMC5613224 DOI: 10.1038/celldisc.2017.34] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Accepted: 07/27/2017] [Indexed: 01/14/2023] Open
Abstract
CRISPR/Cas9 technology enables efficient loss-of-function analysis of human genes using
somatic cells. Studies of essential genes, however, require conditional knockout (KO)
cells. Here, we describe the generation of inducible CRISPR KO human cell lines for the
subunits of the telosome/shelterin complex, TRF1, TRF2, RAP1, TIN2, TPP1 and POT1, which
directly interact with telomeres or can bind to telomeres through association with other
subunits. Homozygous inactivation of several subunits is lethal in mice, and most
loss-of-function studies of human telomere regulators have relied on RNA
interference-mediated gene knockdown, which suffers its own limitations. Our inducible
CRISPR approach has allowed us to more expediently obtain large numbers of KO cells in
which essential telomere regulators have been inactivated for biochemical and molecular
studies. Our systematic analysis revealed functional differences between human and mouse
telomeric proteins in DNA damage responses, telomere length and metabolic control,
providing new insights into how human telomeres are maintained.
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Affiliation(s)
- Hyeung Kim
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Feng Li
- Key Laboratory of Gene Engineering of the Ministry of Education and State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Quanyuan He
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Tingting Deng
- Key Laboratory of Gene Engineering of the Ministry of Education and State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Jun Xu
- Cell-Based Assay Screening Service Core, Baylor College of Medicine, Houston, TX, USA
| | - Feng Jin
- Department of Molecular and Cellular Biology and Advanced Technology Core, Baylor College of Medicine, Houston, TX, USA
| | - Cristian Coarfa
- Department of Molecular and Cellular Biology and Advanced Technology Core, Baylor College of Medicine, Houston, TX, USA
| | - Nagireddy Putluri
- Department of Molecular and Cellular Biology and Advanced Technology Core, Baylor College of Medicine, Houston, TX, USA
| | - Dan Liu
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA.,Cell-Based Assay Screening Service Core, Baylor College of Medicine, Houston, TX, USA
| | - Zhou Songyang
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA.,Key Laboratory of Gene Engineering of the Ministry of Education and State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
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74
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Feng X, Hsu SJ, Kasbek C, Chaiken M, Price CM. CTC1-mediated C-strand fill-in is an essential step in telomere length maintenance. Nucleic Acids Res 2017; 45:4281-4293. [PMID: 28334750 PMCID: PMC5416890 DOI: 10.1093/nar/gkx125] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Accepted: 02/15/2017] [Indexed: 11/13/2022] Open
Abstract
To prevent progressive telomere shortening as a result of conventional DNA replication, new telomeric DNA must be added onto the chromosome end. The de novo DNA synthesis involves elongation of the G-rich strand of the telomere by telomerase. In human cells, the CST complex (CTC1-STN1-TEN1) also functions in telomere replication. CST first aids in duplication of the telomeric dsDNA. Then after telomerase has extended the G-rich strand, CST facilitates fill-in synthesis of the complementary C-strand. Here, we analyze telomere structure after disruption of human CTC1 and demonstrate that functional CST is essential for telomere length maintenance due to its role in mediating C-strand fill-in. Removal of CTC1 results in elongation of the 3΄ overhang on the G-rich strand. This leads to accumulation of RPA and telomeric DNA damage signaling. G-overhang length increases with time after CTC1 disruption and at early times net G-strand growth is apparent, indicating telomerase-mediated G-strand extension. In contrast, C-strand length decreases continuously, indicating a deficiency in C-strand fill-in synthesis. The lack of C-strand maintenance leads to gradual shortening of the telomeric dsDNA, similar to that observed in cells lacking telomerase. Thus, telomerase-mediated G-strand extension and CST-mediated C-strand fill-in are equally important for telomere length maintenance.
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Affiliation(s)
- Xuyang Feng
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA
| | - Shih-Jui Hsu
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA
| | - Christopher Kasbek
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA
| | - Mary Chaiken
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA
| | - Carolyn M Price
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA
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Abstract
Aberrations in telomere biology are among the earliest events in prostate cancer tumorigenesis and continue during tumour progression. Substantial telomere shortening occurs in prostate cancer cells and high-grade prostatic intraepithelial neoplasia. Not all mechanisms of telomere shortening are understood, but oxidative stress from local inflammation might accelerate prostatic telomere loss. Critically short telomeres can drive the accumulation of tumour-promoting genomic alterations; however, continued telomere erosion is unsustainable and must be mitigated to ensure cancer cell survival and unlimited replication potential. Prostate cancers predominantly maintain telomeres by activating telomerase, but alternative mechanisms of telomere extension can occur in metastatic disease. Telomerase activity and telomere length assessment might be useful in prostate cancer diagnosis and prognosis. Telomere shortening in normal stromal cells has been associated with prostate cancer, whereas variable telomere lengths in prostate cancer cells and telomere shortening in cancer-associated stromal cells correlated with lethal disease. Single-agent telomerase-targeted treatments for solid cancers were ineffective in clinical trials but have not been investigated in prostate cancer and might be useful in combination with established regimens. Telomere-directed strategies have not been explored as extensively. Telomere deprotection strategies have the advantage of being effective in both telomerase-dependent and telomerase-independent cancers. Disruption of androgen receptor function in prostate cancer cells results in telomere dysfunction, indicating telomeres and telomerase as potential therapeutic targets in prostate cancer.
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76
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Yalçin Z, Selenz C, Jacobs JJL. Ubiquitination and SUMOylation in Telomere Maintenance and Dysfunction. Front Genet 2017; 8:67. [PMID: 28588610 PMCID: PMC5440461 DOI: 10.3389/fgene.2017.00067] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 05/10/2017] [Indexed: 12/14/2022] Open
Abstract
Telomeres are essential nucleoprotein structures at linear chromosomes that maintain genome integrity by protecting chromosome ends from being recognized and processed as damaged DNA. In addition, they limit the cell’s proliferative capacity, as progressive loss of telomeric DNA during successive rounds of cell division eventually causes a state of telomere dysfunction that prevents further cell division. When telomeres become critically short, the cell elicits a DNA damage response resulting in senescence, apoptosis or genomic instability, thereby impacting on aging and tumorigenesis. Over the past years substantial progress has been made in understanding the role of post-translational modifications in telomere-related processes, including telomere maintenance, replication and dysfunction. This review will focus on recent findings that establish an essential role for ubiquitination and SUMOylation at telomeres.
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Affiliation(s)
- Zeliha Yalçin
- Department of Molecular Oncology, Netherlands Cancer InstituteAmsterdam, Netherlands
| | - Carolin Selenz
- Department of Molecular Oncology, Netherlands Cancer InstituteAmsterdam, Netherlands
| | - Jacqueline J L Jacobs
- Department of Molecular Oncology, Netherlands Cancer InstituteAmsterdam, Netherlands
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77
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Abstract
Telomerase is an RNA-protein complex that extends the 3' ends of linear chromosomes, using a unique telomerase reverse transcriptase (TERT) and template in the telomerase RNA (TR), thereby helping to maintain genome integrity. TR assembles with TERT and species-specific proteins, and telomerase function in vivo requires interaction with telomere-associated proteins. Over the past two decades, structures of domains of TR and TERT as well as other telomerase- and telomere-interacting proteins have provided insights into telomerase function. A recently reported 9-Å cryo-electron microscopy map of the Tetrahymena telomerase holoenzyme has provided a framework for understanding how TR, TERT, and other proteins from ciliate as well as vertebrate telomerase fit and function together as well as unexpected insight into telomerase interaction at telomeres. Here we review progress in understanding the structural basis of human and Tetrahymena telomerase activity, assembly, and interactions.
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Affiliation(s)
- Henry Chan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
| | - Yaqiang Wang
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
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78
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Control of Cellular Aging, Tissue Function, and Cancer by p53 Downstream of Telomeres. Cold Spring Harb Perspect Med 2017; 7:cshperspect.a026088. [PMID: 28289249 DOI: 10.1101/cshperspect.a026088] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Telomeres, the nucleoprotein complex at the ends of eukaryotic chromosomes, perform an essential cellular role in part by preventing the chromosomal end from initiating a DNA-damage response. This function of telomeres can be compromised as telomeres erode either as a consequence of cell division in culture or as a normal part of cellular ageing in proliferative tissues. Telomere dysfunction in this context leads to DNA-damage signaling and activation of the tumor-suppressor protein p53, which then can prompt either cellular senescence or apoptosis. By culling cells with dysfunctional telomeres, p53 plays a critical role in protecting tissues against the effects of critically short telomeres. However, as telomere dysfunction worsens, p53 likely exacerbates short telomere-driven tissue failure diseases, including pulmonary fibrosis, aplastic anemia, and liver cirrhosis. In cells lacking p53, unchecked telomere shortening drives chromosomal end-to-end fusions and cycles of chromosome fusion-bridge-breakage. Incipient cancer cells confronting these telomere barriers must disable p53 signaling to avoid senescence and eventually up-regulate telomerase to achieve cellular immortality. The recent findings of highly recurrent activating mutations in the promoter for the telomerase reverse transcriptase (TERT) gene in diverse human cancers, together with the widespread mutations in p53 in cancer, provide support for the idea that circumvention of a telomere-p53 checkpoint is essential for malignant progression in human cancer.
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79
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Structural insights into POT1-TPP1 interaction and POT1 C-terminal mutations in human cancer. Nat Commun 2017; 8:14929. [PMID: 28393832 PMCID: PMC5394241 DOI: 10.1038/ncomms14929] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 02/14/2017] [Indexed: 01/01/2023] Open
Abstract
Mammalian shelterin proteins POT1 and TPP1 form a stable heterodimer that protects chromosome ends and regulates telomerase-mediated telomere extension. However, how POT1 interacts with TPP1 remains unknown. Here we present the crystal structure of the C-terminal portion of human POT1 (POT1C) complexed with the POT1-binding motif of TPP1. The structure shows that POT1C contains two domains, a third OB fold and a Holliday junction resolvase-like domain. Both domains are essential for binding to TPP1. Notably, unlike the heart-shaped structure of ciliated protozoan Oxytricha nova TEBPα–β complex, POT1–TPP1 adopts an elongated V-shaped conformation. In addition, we identify several missense mutations in human cancers that disrupt the POT1C–TPP1 interaction, resulting in POT1 instability. POT1C mutants that bind TPP1 localize to telomeres but fail to repress a DNA damage response and inappropriate repair by A-NHEJ. Our results reveal that POT1 C terminus is essential to prevent initiation of genome instability permissive for tumorigenesis. Human telomeres are protected by a specialized shelterin complex composed of six proteins. Here the authors structurally characterize the interaction between the POT1-TPP1 shelterin component and identify mutations associated with genome instability and cancer that disrupt the POT1-TPP1 interaction.
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80
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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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81
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Martínez P, Blasco MA. Telomere-driven diseases and telomere-targeting therapies. J Cell Biol 2017; 216:875-887. [PMID: 28254828 PMCID: PMC5379954 DOI: 10.1083/jcb.201610111] [Citation(s) in RCA: 171] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 01/03/2017] [Accepted: 01/09/2017] [Indexed: 01/19/2023] Open
Abstract
Martínez and Blasco review the molecular mechanisms underlying diseases associated with telomere dysfunction, including telomeropathies, age-related disorders, and cancer. Current and future therapeutic strategies to treat and prevent these diseases, including preclinical development of telomere-targeted therapies using mouse models, are discussed. Telomeres, the protective ends of linear chromosomes, shorten throughout an individual’s lifetime. Telomere shortening is proposed to be a primary molecular cause of aging. Short telomeres block the proliferative capacity of stem cells, affecting their potential to regenerate tissues, and trigger the development of age-associated diseases. Mutations in telomere maintenance genes are associated with pathologies referred to as telomere syndromes, including Hoyeraal-Hreidarsson syndrome, dyskeratosis congenita, pulmonary fibrosis, aplastic anemia, and liver fibrosis. Telomere shortening induces chromosomal instability that, in the absence of functional tumor suppressor genes, can contribute to tumorigenesis. In addition, mutations in telomere length maintenance genes and in shelterin components, the protein complex that protects telomeres, have been found to be associated with different types of cancer. These observations have encouraged the development of therapeutic strategies to treat and prevent telomere-associated diseases, namely aging-related diseases, including cancer. Here we review the molecular mechanisms underlying telomere-driven diseases and highlight recent advances in the preclinical development of telomere-targeted therapies using mouse models.
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Affiliation(s)
- Paula Martínez
- Telomeres and Telomerase Group, Molecular Oncology Program, Spanish National Cancer Centre, Madrid E-28029, Spain
| | - Maria A Blasco
- Telomeres and Telomerase Group, Molecular Oncology Program, Spanish National Cancer Centre, Madrid E-28029, Spain
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82
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Graham MK, Principessa L, Antony L, Meeker AK, Isaacs JT. Low p16 INK4a Expression in Early Passage Human Prostate Basal Epithelial Cells Enables Immortalization by Telomerase Expression Alone. Prostate 2017; 77:374-384. [PMID: 27859428 PMCID: PMC5548187 DOI: 10.1002/pros.23276] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 10/26/2016] [Indexed: 11/09/2022]
Abstract
BACKGROUND There are two principal senescence barriers that must be overcome to successfully immortalize primary human epithelial cells in culture, stress-induced senescence, and replicative senescence. The p16INK4a /retinoblastoma protein (p16/Rb) pathway mediates stress-induced senescence, and is generally upregulated by primary epithelial cells in response to the artificial conditions from tissue culture. Replicative senescence is associated with telomere loss. Following each round of cell division, telomeres progressively shorten. Once telomeres shorten to a critical length, the DNA damage response pathway is activated, and the tumor suppressor p53 pathway triggers replicative senescence. Exogenous expression of telomerase in normal human epithelial cells extends the replicative capacity of cells, and in some cases, immortalizes cells. However reliable immortalization of epithelial cells usually requires telomerase activity coupled with inactivation of the p16/Rb pathway. METHODS A lentiviral vector, pLOX-TERT-iresTK (Addgene #12245), containing a CMV promoter upstream of a bicistronic coding cassette that includes loxP sites flanking the catalytic subunit of human telomerase gene (TERT) and herpes simplex virus type-1 thymidine kinase gene (HSV1-tk) was used to transduce normal prostate basal epithelial cells (PrECs) initiated in cell culture from prostate cancer patients undergoing radical prostatectomies. RESULTS Transduction of early (i.e., <7) passage PrECs with TERT led to successful immortalization. However, attempts to immortalize late (i.e., >7) passage PrECs were unsuccessful. Late passage PrECs, which acquired elevated p16, were unable to overcome the senescence barrier. Immortalized PrECs (TERT-PrECs) retained a normal male karyotype and low p16 expression. Additionally, TERT-PrECs were non-tumorigenic when inoculated into intact male immunodeficient NSG mice. CONCLUSIONS The present studies document that early passage human PrECs have sufficiently low p16 to permit immortalization by TERT expression alone. TERT-PrECs developed using this transduction approach provides an appropriate and experimentally facile model for clarifying the molecular mechanism(s) involved in both immortalization of human PrECs, as well as identifying genetic/epigenetic "drivers" for conversion of these immortalized non-tumorigenic cells into fully lethal prostate cancers. Notably, loxP sites flank the exogenous TERT gene in the TERT-PrECs. Cre recombinase can be used to excise TERT, and resolve whether TERT expression is required for these cells to be fully transformed into lethal cancer. Prostate 77: 374-384, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Mindy Kim Graham
- Department of Pathology, John Hopkins University School of Medicine, Baltimore, Maryland
| | - Lorenzo Principessa
- Chemical Therapeutic Program, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland
| | - Lizamma Antony
- Chemical Therapeutic Program, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland
| | - Alan K. Meeker
- Departments of Pathology, Oncology and Urology, John Hopkins University School of Medicine, Baltimore, Maryland
| | - John T. Isaacs
- Chemical Therapeutic Program, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland
- Correspondence to: Dr. John T. Isaacs, Chemical Therapeutic Program, Bunting-Blaustein CRB1, 1650 Orleans Street, Baltimore, MD 21231.
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83
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Endogenous Telomerase Reverse Transcriptase N-Terminal Tagging Affects Human Telomerase Function at Telomeres In Vivo. Mol Cell Biol 2017; 37:MCB.00541-16. [PMID: 27872149 DOI: 10.1128/mcb.00541-16] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Accepted: 11/15/2016] [Indexed: 12/27/2022] Open
Abstract
Telomerase action at telomeres is essential for the immortal phenotype of stem cells and the aberrant proliferative potential of cancer cells. Insufficient telomere maintenance can cause stem cell and tissue failure syndromes, while increased telomerase levels are associated with tumorigenesis. Both pathologies can arise from only small perturbation of telomerase function. To analyze telomerase at its low endogenous expression level, we genetically engineered human pluripotent stem cells (hPSCs) to express various N-terminal fusion proteins of the telomerase reverse transcriptase from its endogenous locus. Using this approach, we found that these modifications can perturb telomerase function in hPSCs and cancer cells, resulting in telomere length defects. Biochemical analysis suggests that this defect is multileveled, including changes in expression and activity. These findings highlight the unknown complexity of telomerase structural requirements for expression and function in vivo.
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84
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Abstract
Telomere dysfunctions, rendered through replicative attrition of telomeric DNA or due to the removal of shelterin components, are recognized as DNA double-stranded breaks (DSBs) by the DNA damage repair (DDR) pathway. This leads to the activation of DNA damage checkpoint sensors, including the Mre11-Rad50-Nbs1 (MRN) complex, γ-H2AX and 53BP1, the ATM and ATR signal-transducing kinases, and downstream effectors, including Chk1, Chk2, and p53. Robust DNA damage response signals at dysfunctional telomeres, achieved by the complete deletion of TRF2 or by expressing dominant-negative mutant TPP1ΔRD, can be detected by their association with γ-H2AX and 53BP1 forming "telomere dysfunction induced foci (TIFs)." Induction of TIFs at telomeres provides an opportunity to quantify the extent of telomere dysfunction and monitor downstream signaling pathways.
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Affiliation(s)
- Rekha Rai
- Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT, 06520, USA
| | - Sandy Chang
- Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT, 06520, USA.
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85
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Pandita TK. Critical role of the POT1 OB domain in maintaining genomic stability. Oncogene 2016; 36:1908-1910. [PMID: 27869169 DOI: 10.1038/onc.2016.365] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 08/19/2016] [Indexed: 01/14/2023]
Abstract
Oligonucleotide/oligosaccharide-binding (OB) domain-containing proteins have been identified as critical for telomere maintenance, DNA repair, transcription and other DNA metabolism processes. Protection of telomere 1 (POT1), a telomere binding protein, has an OB domain like single-strand binding protein (SSB1). In this issue of Oncogene, Gu et al. present evidence that POT1, like SSB1, is required to maintain genomic stability. This work, in conjunction with results from previous investigators, highlights the importance of POT1 in telomere metabolism. Inactivation of POT1 telomere protective functions in mouse models lacking p53 expression in the breast epithelium unleashes a torrent of DNA damage responses (DDRs) at the telomeres, culminating in karyotypic alterations with massive arrays of telomere fusions. Therefore, POT1 is not only required to promote telomere homeostasis, but also plays an essential role in maintaining a stable genome.
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Affiliation(s)
- T K Pandita
- Department of Radiation Oncology, The Houston Methodist Research Institute, Weill Cornell Medical College, The Houston Methodist Hospital, Houston, TX, USA
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86
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Gu P, Wang Y, Bisht KK, Wu L, Kukova L, Smith EM, Xiao Y, Bailey SM, Lei M, Nandakumar J, Chang S. Pot1 OB-fold mutations unleash telomere instability to initiate tumorigenesis. Oncogene 2016; 36:1939-1951. [PMID: 27869160 PMCID: PMC5383532 DOI: 10.1038/onc.2016.405] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Revised: 08/02/2016] [Accepted: 09/19/2016] [Indexed: 02/06/2023]
Abstract
Chromosomal aberrations are a hallmark of human cancers, with complex cytogenetic rearrangements leading to genetic changes permissive for cancer initiation and progression. Protection of Telomere 1 (POT1) is an essential component of the shelterin complex and functions to maintain chromosome stability by repressing the activation of aberrant DNA damage and repair responses at telomeres. Sporadic and familial mutations in the oligosaccharide-oligonucleotide (OB) folds of POT1 have been identified in many human cancers, but the mechanism underlying how hPOT1 mutations initiate tumorigenesis has remained unclear. Here we show that the human POT1’s OB-folds are essential for the protection of newly replicated telomeres. Oncogenic mutations in hPOT1 OB-fold fail to bind to ss telomeric DNA, eliciting a DNA damage response at telomeres that promote inappropriate chromosome fusions via the mutagenic alternative non-homologous end joining (A-NHEJ) pathway. hPOT1 mutations also result in telomere elongation and the formation of transplantable hematopoietic malignancies. Strikingly, conditional deletion of both mPot1a and p53 in mouse mammary epithelium resulted in development of highly invasive breast carcinomas and the formation of whole chromosomes containing massive arrays of telomeric fusions reminiscent of chromothripsis. Our results reveal that hPOT1 OB-folds are required to protect and prevent newly replicated telomeres from engaging in A-NHEJ mediated fusions that would otherwise promote genome instability to fuel tumorigenesis.
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Affiliation(s)
- P Gu
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Y Wang
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - K K Bisht
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA.,Program in Chemical Biology, University of Michigan, Ann Arbor, MI, USA
| | - L Wu
- Department of GI Medical Oncology, UT MD Anderson Cancer Center, Houston, TX, USA
| | - L Kukova
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - E M Smith
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA.,Program in Chemical Biology, University of Michigan, Ann Arbor, MI, USA
| | - Y Xiao
- Section of Hematology-Oncology, Department of Medicine and Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - S M Bailey
- Department of Environmental & Radiological Health Sciences, Colorado State University, Fort Collins, CO, USA
| | - M Lei
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - J Nandakumar
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA.,Program in Chemical Biology, University of Michigan, Ann Arbor, MI, USA
| | - S Chang
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT, USA.,Department of Pathology, Yale University School of Medicine, New Haven, CT, USA.,Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT, USA
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87
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Structural and functional consequences of a disease mutation in the telomere protein TPP1. Proc Natl Acad Sci U S A 2016; 113:13021-13026. [PMID: 27807141 DOI: 10.1073/pnas.1605685113] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Telomerase replicates chromosome ends to facilitate continued cell division. Mutations that compromise telomerase function result in stem cell failure diseases, such as dyskeratosis congenita (DC). One such mutation (K170Δ), residing in the telomerase-recruitment factor TPP1, provides an excellent opportunity to structurally, biochemically, and genetically dissect the mechanism of such diseases. We show through site-directed mutagenesis and X-ray crystallography that this TPP1 disease mutation deforms the conformation of two critical amino acids of the TEL [TPP1's glutamate (E) and leucine-rich (L)] patch, the surface of TPP1 that binds telomerase. Using CRISPR-Cas9 technology, we demonstrate that introduction of this mutation in a heterozygous manner is sufficient to shorten telomeres in human cells. Our findings rule out dominant-negative effects of the mutation. Instead, these findings implicate reduced TEL patch dosage in causing telomere shortening. Our studies provide mechanistic insight into telomerase-deficiency diseases and encourage the development of gene therapies to counter such diseases.
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88
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Rajavel M, Orban T, Xu M, Hernandez-Sanchez W, de la Fuente M, Palczewski K, Taylor DJ. Dynamic peptides of human TPP1 fulfill diverse functions in telomere maintenance. Nucleic Acids Res 2016; 44:10467-10479. [PMID: 27655633 PMCID: PMC5137443 DOI: 10.1093/nar/gkw846] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 09/12/2016] [Accepted: 09/14/2016] [Indexed: 12/12/2022] Open
Abstract
Telomeres are specialized nucleoprotein complexes that comprise the ends of linear chromosomes. Human telomeres end in a short, single-stranded DNA (ssDNA) overhang that is recognized and bound by two telomere proteins, POT1 and TPP1. Whereas POT1 binds directly to telomere ssDNA, its interaction with TPP1 is essential for localization of POT1 to the telomere. TPP1 also provides enhanced binding and sequence discrimination that regulates POT1-TPP1 interactions exclusively with telomere ssDNA. Finally, TPP1 recruits telomerase, the enzyme responsible for synthesis of telomere DNA, to the telomere. While the oligosaccharide-oligonucleotide-binding (OB)-fold domain of TPP1 has been solved by X-ray crystallography, the molecular interactions within the POT1-TPP1-ssDNA ternary complex and the conformational changes that contribute to its diverse functions remain ambiguous. We employed hydrogen/deuterium exchange combined with mass spectrometry to identify three peptides, all residing within the OB-fold of TPP1, that exhibit altered exchange rates upon complex formation or ssDNA binding. Mutation of these regions combined with functional assays revealed the diverse contributions of each moiety in protein-protein interactions, regulating telomerase activity or DNA-binding. Together, these functional data combined with biophysical analyses and homology modeling provide a molecular understanding of the diverse contributions of TPP1 in telomere maintenance.
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Affiliation(s)
- Malligarjunan Rajavel
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
| | - Tivadar Orban
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
| | - Mengyuan Xu
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
| | - Wilnelly Hernandez-Sanchez
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
| | - Maria de la Fuente
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
| | - Krzysztof Palczewski
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
| | - Derek J Taylor
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA .,Department of Biochemistry, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA
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89
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Hu Y, Shi G, Zhang L, Li F, Jiang Y, Jiang S, Ma W, Zhao Y, Songyang Z, Huang J. Switch telomerase to ALT mechanism by inducing telomeric DNA damages and dysfunction of ATRX and DAXX. Sci Rep 2016; 6:32280. [PMID: 27578458 PMCID: PMC5006076 DOI: 10.1038/srep32280] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 08/04/2016] [Indexed: 12/12/2022] Open
Abstract
Activation of telomerase or alternative lengthening of telomeres (ALT) is necessary for tumours to escape from dysfunctional telomere-mediated senescence. Anti-telomerase drugs might be effective in suppressing tumour growth in approximately 85–90% of telomerase-positive cancer cells. However, there are still chances for these cells to bypass drug treatment after switching to the ALT mechanism to maintain their telomere integrity. But the mechanism underlying this switch is unknown. In this study, we used telomerase-positive cancer cells (HTC75) to discover the mechanism of the telomerase-ALT switch by inducing telomere-specific DNA damage, alpha-thalassemia X-linked syndrome protein (ATRX) knockdown and deletion of death associated protein (DAXX). Surprisingly, two important ALT hallmarks in the ALT-like HTC75 cells were observed after treatments: ALT-associated promyelocytic leukaemia bodies (APBs) and extrachromosomal circular DNA of telomeric repeats. Moreover, knocking out hTERT by utilizing the CRISPR/Cas9 technique led to telomere elongation in a telomerase-independent manner in ALT-like HTC75 cells. In summary, this is the first report to show that inducing telomeric DNA damage, disrupting the ATRX/DAXX complex and inhibiting telomerase activity in telomerase-positive cancer cells lead to the ALT switch.
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Affiliation(s)
- Yang Hu
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China.,Key Laboratory of Reproductive Medicine of Guangdong Province, School of Life Sciences and the First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510275, China
| | - Guang Shi
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China.,Key Laboratory of Reproductive Medicine of Guangdong Province, School of Life Sciences and the First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510275, China
| | - Laichen Zhang
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China
| | - Feng Li
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China
| | - Yuanling Jiang
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China
| | - Shuai Jiang
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China
| | - Wenbin Ma
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China
| | - Yong Zhao
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China
| | - Zhou Songyang
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China.,Key Laboratory of Reproductive Medicine of Guangdong Province, School of Life Sciences and the First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510275, China
| | - Junjiu Huang
- Key Laboratory of Gene Engineering of the Ministry of Education and Institute of Healthy Aging Research, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China.,Key Laboratory of Reproductive Medicine of Guangdong Province, School of Life Sciences and the First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510275, China
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90
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Abstract
Telomerase activity is responsible for the maintenance of chromosome end structures (telomeres) and cancer cell immortality in most human malignancies, making telomerase an attractive therapeutic target. The rationale for targeting components of the telomerase holoenzyme has been strengthened by accumulating evidence indicating that these molecules have extra-telomeric functions in tumour cell survival and proliferation. This Review discusses current knowledge of the biogenesis, structure and multiple functions of telomerase-associated molecules intertwined with recent advances in drug discovery approaches. We also describe the fertile ground available for the pursuit of next-generation small-molecule inhibitors of telomerase.
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Affiliation(s)
- Greg M Arndt
- Australian Cancer Research Foundation (ACRF) Drug Discovery Centre for Childhood Cancer, Children's Cancer Institute Australia, Lowy Cancer Research Centre, University of New South Wales, Randwick, New South Wales 2031, Australia
| | - Karen L MacKenzie
- Personalised Medicine Program, Children's Cancer Institute Australia, Lowy Cancer Research Centre, University of New South Wales, Randwick, New South Wales 2031, Australia
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91
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Hirai Y, Tamura M, Otani J, Ishikawa F. NEK6-mediated phosphorylation of human TPP1 regulates telomere length through telomerase recruitment. Genes Cells 2016; 21:874-89. [DOI: 10.1111/gtc.12391] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2016] [Accepted: 05/31/2016] [Indexed: 12/29/2022]
Affiliation(s)
- Yugo Hirai
- Department of Gene Mechanisms; Graduate School of Biostudies; Kyoto University; Yoshida-Konoe-cho Sakyo-ku Kyoto 606-8501 Japan
| | - Miki Tamura
- Department of Gene Mechanisms; Graduate School of Biostudies; Kyoto University; Yoshida-Konoe-cho Sakyo-ku Kyoto 606-8501 Japan
| | - Junji Otani
- Department of Gene Mechanisms; Graduate School of Biostudies; Kyoto University; Yoshida-Konoe-cho Sakyo-ku Kyoto 606-8501 Japan
| | - Fuyuki Ishikawa
- Department of Gene Mechanisms; Graduate School of Biostudies; Kyoto University; Yoshida-Konoe-cho Sakyo-ku Kyoto 606-8501 Japan
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92
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Abstract
Telomeres are repetitive DNA repeats that cap the ends of all eukaryotic chromosomes. Their proper maintenance is essential for genomic stability and cellular viability. Dysfunctional telomeres could arise through natural attrition of telomeric DNA or due to the removal of shelterin components. These uncapped chromosomal ends are recognized as DSBs by the DDR pathway, leading to the accumulation of DNA damage sensors at telomeres. The association of these DDR proteins with dysfunctional telomeres forms telomere dysfunction induced DNA damage foci (TIFs). Detection of TIFs at telomeres provides an opportunity to quantify the extent of telomere dysfunction and monitor downstream DNA damage signaling pathways. Here we describe a method for the detection of TIFs using a fluorescent in situ hybridization (FISH) approach.
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Affiliation(s)
- Rekha Rai
- Department of Laboratory Medicine, Yale School of Medicine, 330 Cedar St, New Haven, CT, 06520, USA
| | - Sandy Chang
- Department of Laboratory Medicine, Yale School of Medicine, 330 Cedar St, New Haven, CT, 06520, USA. .,Department of Pathology, Yale School of Medicine, 330 Cedar St., New Haven, CT, 06520, USA.
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93
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Bandaria JN, Qin P, Berk V, Chu S, Yildiz A. Shelterin Protects Chromosome Ends by Compacting Telomeric Chromatin. Cell 2016; 164:735-46. [PMID: 26871633 DOI: 10.1016/j.cell.2016.01.036] [Citation(s) in RCA: 117] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Revised: 09/28/2015] [Accepted: 01/22/2016] [Indexed: 12/12/2022]
Abstract
Telomeres, repetitive DNA sequences at chromosome ends, are shielded against the DNA damage response (DDR) by the shelterin complex. To understand how shelterin protects telomere ends, we investigated the structural organization of telomeric chromatin in human cells using super-resolution microscopy. We found that telomeres form compact globular structures through a complex network of interactions between shelterin subunits and telomeric DNA, but not by DNA methylation, histone deacetylation, or histone trimethylation at telomeres and subtelomeric regions. Mutations that abrogate shelterin assembly or removal of individual subunits from telomeres cause up to a 10-fold increase in telomere volume. Decompacted telomeres accumulate DDR signals and become more accessible to telomere-associated proteins. Recompaction of telomeric chromatin using an orthogonal method displaces DDR signals from telomeres. These results reveal the chromatin remodeling activity of shelterin and demonstrate that shelterin-mediated compaction of telomeric chromatin provides robust protection of chromosome ends against the DDR machinery.
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Affiliation(s)
- Jigar N Bandaria
- Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Peiwu Qin
- Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Veysel Berk
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Physics, Stanford University, Stanford, CA 94305, USA
| | - Steven Chu
- Department of Physics, Stanford University, Stanford, CA 94305, USA
| | - Ahmet Yildiz
- Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
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94
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Swanson MJ, Baribault ME, Israel JN, Bae NS. Telomere protein RAP1 levels are affected by cellular aging and oxidative stress. Biomed Rep 2016; 5:181-187. [PMID: 27446538 PMCID: PMC4950791 DOI: 10.3892/br.2016.707] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 06/24/2016] [Indexed: 12/13/2022] Open
Abstract
Telomeres are important for maintaining the integrity of the genome through the action of the shelterin complex. Previous studies indicted that the length of the telomere did not have an effect on the amount of the shelterin subunits; however, those experiments were performed using immortalized cells with stable telomere lengths. The interest of the present study was to observe how decreasing telomere lengths over successive generations would affect the shelterin subunits. As neonatal human dermal fibroblasts aged and their telomeres became shorter, the levels of the telomere-binding protein telomeric repeat factor 2 (TRF2) decreased significantly. By contrast, the levels of one of its binding partners, repressor/activator protein 1 (RAP1), decreased to a lesser extent than would be expected from the decrease in TRF2. Other subunits, TERF1-interacting nuclear factor 2 and protection of telomeres protein 1, remained stable. The decrease in RAP1 in the older cells occurred in the nuclear and cytoplasmic fractions. Hydrogen peroxide (H2O2) stress was used as an artificial means of aging in the cells, and this resulted in RAP1 levels decreasing, but the effect was only observed in the nuclear portion. Similar results were obtained using U251 glioblastoma cells treated with H2O2 or grown in serum-depleted medium. The present findings indicate that TRF2 and RAP1 levels decrease as fibroblasts naturally age. RAP1 remains more stable compared to TRF2. RAP1 also responds to oxidative stress, but the response is different to that observed in aging.
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Affiliation(s)
- Mark J Swanson
- Division of Basic Medical Sciences, Mercer University School of Medicine, Macon, GA 30207, USA; Department of Biochemistry, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ 85308, USA
| | - Michelle E Baribault
- Department of Biochemistry, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ 85308, USA
| | - Joanna N Israel
- Department of Biochemistry, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ 85308, USA
| | - Nancy S Bae
- Department of Biochemistry, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ 85308, USA
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95
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Xu Y, Goldkorn A. Telomere and Telomerase Therapeutics in Cancer. Genes (Basel) 2016; 7:genes7060022. [PMID: 27240403 PMCID: PMC4929421 DOI: 10.3390/genes7060022] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 05/18/2016] [Accepted: 05/20/2016] [Indexed: 12/13/2022] Open
Abstract
Telomerase is a reverse transcriptase capable of utilizing an integrated RNA component as a template to add protective tandem telomeric single strand DNA repeats, TTAGGG, to the ends of chromosomes. Telomere dysfunction and telomerase reactivation are observed in approximately 90% of human cancers; hence, telomerase activation plays a unique role as a nearly universal step on the path to malignancy. In the past two decades, multiple telomerase targeting therapeutic strategies have been pursued, including direct telomerase inhibition, telomerase interference, hTERT or hTERC promoter driven therapy, telomere-based approaches, and telomerase vaccines. Many of these strategies have entered clinical development, and some have now advanced to phase III clinical trials. In the coming years, one or more of these new telomerase-targeting drugs may be expected to enter the pharmacopeia of standard care. Here, we briefly review the molecular functions of telomerase in cancer and provide an update about the preclinical and clinical development of telomerase targeting therapeutics.
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Affiliation(s)
- Yucheng Xu
- Division of Medical Oncology, Department of Medicine, Keck School of Medicine and Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA 90033, USA.
| | - Amir Goldkorn
- Division of Medical Oncology, Department of Medicine, Keck School of Medicine and Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA 90033, USA.
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96
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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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97
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Yin H, Nie L, Zhao F, Zhou H, Li H, Dong X, Zhang H, Wang Y, Shi Q, Li J. De novo assembly and characterization of the Chinese three-keeled pond turtle (Mauremys reevesii) transcriptome: presence of longevity-related genes. PeerJ 2016; 4:e2062. [PMID: 27257545 PMCID: PMC4888314 DOI: 10.7717/peerj.2062] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Accepted: 05/01/2016] [Indexed: 12/20/2022] Open
Abstract
Mauremys reevesii (Geoemydidae) is one of the most common and widespread semi-aquatic turtles in East Asia. The unusually long lifespan of some individuals makes this turtle species a potentially useful model organism for studying the molecular basis of longevity. In this study, pooled total RNA extracted from liver, spleen and skeletal-muscle of three adult individuals were sequenced using Illumina Hiseq 2500 platform. A set of telomere-related genes were found in the transcriptome, including tert, tep1, and six shelterin complex proteins coding genes (trf1, trf2, tpp1, pot1, tin2 and rap1). These genes products protect chromosome ends from deterioration and therefore significantly contribute to turtle longevity. The transcriptome data generated in this study provides a comprehensive reference for future molecular studies in the turtle.
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Affiliation(s)
- Huazong Yin
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Liuwang Nie
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Feifei Zhao
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Huaxing Zhou
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Haifeng Li
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Xianmei Dong
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Huanhuan Zhang
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Yuqin Wang
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Qiong Shi
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
| | - Jun Li
- College of Life Science, Anhui Normal University, Provincial Key Lab of the Conservation and Exploitation Research of Biological Resources in Anhui, Wuhu, Anhui, China
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98
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Stop pulling my strings - what telomeres taught us about the DNA damage response. Nat Rev Mol Cell Biol 2016; 17:364-78. [PMID: 27165790 DOI: 10.1038/nrm.2016.43] [Citation(s) in RCA: 123] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Mammalian cells have evolved specialized mechanisms to sense and repair double-strand breaks (DSBs) to maintain genomic stability. However, in certain cases, the activity of these pathways can lead to aberrant DNA repair, genomic instability and tumorigenesis. One such case is DNA repair at the natural ends of linear chromosomes, known as telomeres, which can lead to chromosome-end fusions. Here, we review data obtained over the past decade and discuss the mechanisms that protect mammalian chromosome ends from the DNA damage response. We also discuss how telomere research has helped to uncover key steps in DSB repair. Last, we summarize how dysfunctional telomeres and the ensuing genomic instability drive the progression of cancer.
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99
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Mullins MR, Rajavel M, Hernandez-Sanchez W, de la Fuente M, Biendarra SM, Harris ME, Taylor DJ. POT1-TPP1 Binding and Unfolding of Telomere DNA Discriminates against Structural Polymorphism. J Mol Biol 2016; 428:2695-708. [PMID: 27173378 DOI: 10.1016/j.jmb.2016.04.031] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 04/20/2016] [Accepted: 04/21/2016] [Indexed: 11/17/2022]
Abstract
Telomeres are nucleoprotein complexes that reside at the ends of linear chromosomes and help maintain genomic integrity. Protection of telomeres 1 (POT1) and TPP1 are telomere-specific proteins that bind as a heterodimer to single-stranded telomere DNA to prevent illicit DNA damage responses and to enhance telomerase-mediated telomere extension. Telomere DNA is guanosine rich and, as such, can form highly stable secondary structures including G-quadruplexes. G-quadruplex DNA folds into different topologies that are determined by several factors including monovalent ion composition and the precise sequence and length of the DNA. Here, we explore the influence of DNA secondary structure on POT1-TPP1 binding. Equilibrium binding assays reveal that the POT1-TPP1 complex binds G-quadruplex structures formed in buffers containing Na(+) with an affinity that is fivefold higher than for G-quadruplex structures formed in the presence of K(+). However, the binding of the second heterodimer is insensitive to DNA secondary structure, presumably due to unfolding resulting from binding of the first POT1-TPP1. We further show that the rate constant for POT1-TPP1-induced unfolding of DNA secondary structure is substantially faster for G-quadruplex topologies formed in the presence of Na(+) ions. When bound to DNA, POT1-TPP1 forms complexes with similar CD spectra and enhances telomerase activity for all DNA substrates tested, regardless of the substrate secondary structure or solution monovalent ion composition. Together, these data indicate that binding of POT1-TPP1 unfolds telomere secondary structure to assist loading of additional heterodimers and to ensure efficient promotion of telomerase-mediated extension.
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Affiliation(s)
- Michael R Mullins
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Malligarjunan Rajavel
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA
| | | | - Maria de la Fuente
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Sherri M Biendarra
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Michael E Harris
- Department of Biochemistry, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Derek J Taylor
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA; Department of Biochemistry, Case Western Reserve University, Cleveland, OH 44106, USA.
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100
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Jones M, Bisht K, Savage SA, Nandakumar J, Keegan CE, Maillard I. The shelterin complex and hematopoiesis. J Clin Invest 2016; 126:1621-9. [PMID: 27135879 DOI: 10.1172/jci84547] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Mammalian chromosomes terminate in stretches of repetitive telomeric DNA that act as buffers to avoid loss of essential genetic information during end-replication. A multiprotein complex known as shelterin prevents recognition of telomeric sequences as sites of DNA damage. Telomere erosion contributes to human diseases ranging from BM failure to premature aging syndromes and cancer. The role of shelterin telomere protection is less understood. Mutations in genes encoding the shelterin proteins TRF1-interacting nuclear factor 2 (TIN2) and adrenocortical dysplasia homolog (ACD) were identified in dyskeratosis congenita, a syndrome characterized by somatic stem cell dysfunction in multiple organs leading to BM failure and other pleiotropic manifestations. Here, we introduce the biochemical features and in vivo effects of individual shelterin proteins, discuss shelterin functions in hematopoiesis, and review emerging knowledge implicating the shelterin complex in hematological disorders.
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