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Serrano-León IM, Prieto P, Aguilar M. Telomere and subtelomere high polymorphism might contribute to the specificity of homologous recognition and pairing during meiosis in barley in the context of breeding. BMC Genomics 2023; 24:642. [PMID: 37884878 PMCID: PMC10601145 DOI: 10.1186/s12864-023-09738-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Accepted: 10/12/2023] [Indexed: 10/28/2023] Open
Abstract
Barley (Hordeum vulgare) is one of the most popular cereal crops globally. Although it is a diploid species, (2n = 2x = 14) the study of its genome organization is necessary in the framework of plant breeding since barley is often used in crosses with other cereals like wheat to provide them with advantageous characters. We already have an extensive knowledge on different stages of the meiosis, the cell division to generate the gametes in species with sexual reproduction, such as the formation of the synaptonemal complex, recombination, and chromosome segregation. But meiosis really starts with the identification of homologous chromosomes and pairing initiation, and it is still unclear how chromosomes exactly choose a partner to appropriately pair for additional recombination and segregation. In this work we present an exhaustive molecular analysis of both telomeres and subtelomeres of barley chromosome arms 2H-L, 3H-L and 5H-L. As expected, the analysis of multiple features, including transposable elements, repeats, GC content, predicted CpG islands, recombination hotspots, G4 quadruplexes, genes and targeted sequence motifs for key DNA-binding proteins, revealed a high degree of variability both in telomeres and subtelomeres. The molecular basis for the specificity of homologous recognition and pairing occurring in the early chromosomal interactions at the start of meiosis in barley may be provided by these polymorphisms. A more relevant role of telomeres and most distal part of subtelomeres is suggested.
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Affiliation(s)
- I M Serrano-León
- Plant Breeding Department, Institute for Sustainable Agriculture, Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC), Avenida Menéndez Pidal S/N., Campus Alameda del Obispo, 14004, Córdoba, Spain
| | - P Prieto
- Plant Breeding Department, Institute for Sustainable Agriculture, Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC), Avenida Menéndez Pidal S/N., Campus Alameda del Obispo, 14004, Córdoba, Spain.
| | - M Aguilar
- Área de Fisiología Vegetal, Universidad de Córdoba, Campus de Rabanales, Edif. C4, 3ª Planta, Córdoba, Spain
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2
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Kim MJ, Ko YJ, Yun JH, Lee W. Solution structure of the Myb domain of Terfa derived from Zebrafish interacting with both human and plant telomeric DNA. Biochem Biophys Res Commun 2021; 559:252-258. [PMID: 33984809 DOI: 10.1016/j.bbrc.2021.04.057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Accepted: 04/15/2021] [Indexed: 10/21/2022]
Abstract
Telomeric repeat binding factor a (Terfa) derived from zebrafish is a homologous protein with human telomeric repeat binding factor 2 (TRF2). Terfa is known as a senescence-associated biomarker in various research through the zebrafish animal model. In addition, according to the findings so far, it has been confirmed that human or plant telomere binding proteins bind to telomeric DNA specialized for each species, but, in our result, Terfa shows it strongly binds to both human or plant type telomeric DNA. Here we characterized the DNA binding properties and demonstrate the solution structure of Terfa and identified residues participating in the interaction with both human and plant telomeric DNA. In DNA recognition of human and plant telomere binding proteins, the N-terminal loop and the α-helix 3 part of Myb domain were bound majorly, whereas, in the case of Terfa, the N-terminal loop, the α-helix 1-2 loop, and α-helix 2 of the Myb domain were dominantly bound. Therefore, when Terfa recognizes DNA, it was found that the binding module differs from previously known telomere binding proteins. The comparison of the structure of the telomere binding proteins provides an opportunity to understand more specifically how the structural properties of each telomere binding protein are associated with telomeric DNA binding from an evolutionary point of view.
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Affiliation(s)
- Min-Jung Kim
- PCG-Biotech, Ltd., Yonsei Engineering Research Park, Yonsei University, Seoul, 120-749, Republic of Korea
| | - Yoon-Joo Ko
- Nuclear Magnetic Resonance Laboratory, National Center for Inter-University Research Facilities, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 151-742, South Korea
| | - Ji-Hye Yun
- PCG-Biotech, Ltd., Yonsei Engineering Research Park, Yonsei University, Seoul, 120-749, Republic of Korea.
| | - Weontae Lee
- PCG-Biotech, Ltd., Yonsei Engineering Research Park, Yonsei University, Seoul, 120-749, Republic of Korea; Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul, 120-749, Republic of Korea.
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Keener R, Connelly CJ, Greider CW. Tel1 Activation by the MRX Complex Is Sufficient for Telomere Length Regulation but Not for the DNA Damage Response in Saccharomyces cerevisiae. Genetics 2019; 213:1271-1288. [PMID: 31645360 PMCID: PMC6893380 DOI: 10.1534/genetics.119.302713] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Accepted: 10/17/2019] [Indexed: 12/26/2022] Open
Abstract
Previous models suggested that regulation of telomere length in Saccharomyces cerevisiae by Tel1(ATM) and Mec1(ATR) would parallel the established pathways regulating the DNA damage response. Here, we provide evidence that telomere length regulation differs from the DNA damage response in both the Tel1 and Mec1 pathways. We found that Rad53 mediates a Mec1 telomere length regulation pathway but is dispensable for Tel1 telomere length regulation, whereas in the DNA damage response, Rad53 is regulated by both Mec1 and Tel1 Using epistasis analysis with a Tel1 hypermorphic allele, Tel1-hy909, we found that the MRX complex is not required downstream of Tel1 for telomere elongation but is required downstream of Tel1 for the DNA damage response. Our data suggest that nucleolytic telomere end processing is not a required step for telomerase to elongate telomeres.
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Affiliation(s)
- Rebecca Keener
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
- Biochemistry, Cellular and Molecular Biology Graduate Program, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Carla J Connelly
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Carol W Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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Wallace HA, Rana V, Nguyen HQ, Bosco G. Condensin II subunit NCAPH2 associates with shelterin protein TRF1 and is required for telomere stability. J Cell Physiol 2019; 234:20755-20768. [PMID: 31026066 PMCID: PMC6767372 DOI: 10.1002/jcp.28681] [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: 02/08/2019] [Accepted: 03/19/2019] [Indexed: 12/24/2022]
Abstract
Condensin II subunits are known to be expressed and localized to interphase nuclei of eukaryotic cells. Although some studies have shown that condensin II likely exerts axial compaction forces, organizes chromosome territories, and has possible transcriptional modulatory functions, the full range of condensin II interphase activities are not known. In particular, it is not known if condensin II interphase activities are generally genome‐wide or if they have additional local activities unique to specific chromosomal structures such as telomeres. Here, we find that NCAPH2 interacts with TRF1 and these two proteins co‐localize at telomeres. Depletion of NCAPH2 leads to ATR‐dependent accumulation of 53BP1 and γH2AX DNA damage foci, including damage specific to telomeres. Furthermore, depletion of NCAPH2 results in a fragile telomere phenotype and apparent sister‐telomere fusions only days after NCAPH2 depletion. Taken together these observations suggest that NCAPH2 promotes telomere stability, possibly through a direct interaction with the TRF1 shelterin component, and prevents telomere dysfunction resulting from impaired DNA replication. Because proper telomere function is essential for chromosome integrity these observations reveal a previously unappreciated function for NCAPH2 in ensuring genome and telomere stability.
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Affiliation(s)
| | - Vibhuti Rana
- Department of Genetics, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
| | - Huy Q Nguyen
- Department of Genetics, Harvard Medical School, Boston, Massachusetts
| | - Giovanni Bosco
- Department of Genetics, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
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Kosebent EG, Uysal F, Ozturk S. Telomere length and telomerase activity during folliculogenesis in mammals. J Reprod Dev 2018; 64:477-484. [PMID: 30270279 PMCID: PMC6305847 DOI: 10.1262/jrd.2018-076] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Telomeres are repetitive non-coding DNA sequences located at the ends of chromosomes in eukaryotic cells. Their most important function is to protect chromosome ends from being recognized
as DNA damage. They are also implicated in meiosis and synapse formation. The length of telomeres inevitably shortens at the end of each round of DNA replication and, also, as a consequence
of the exposure to oxidative stress and/or genotoxic agents. The enzyme telomerase contributes to telomere lengthening. It has been reported that telomerase is exclusively expressed in germ
cells, granulosa cells, early embryos, stem cells, and various types of cancerous cells. Granulosa cells undergo many mitotic divisions and either granulosa cells or oocytes are exposed to a
variety of genotoxic agents throughout folliculogenesis; thus, telomerase plays an important role in the maintenance of telomere length. In this review article, we have comprehensively
evaluated the studies focusing on the regulation of telomerase expression and activity, as well as telomere length, during folliculogenesis from primordial to antral follicles, in several
mammalian species including mice, bovines, and humans. Also, the possible relationships between female infertility caused by follicular development defects and alterations in the telomeres
and/or telomerase activity are discussed.
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Affiliation(s)
- Esra Gozde Kosebent
- Department of Histology and Embryology, Akdeniz University School of Medicine, Antalya 07070, Turkey
| | - Fatma Uysal
- Department of Histology and Embryology, Ankara University School of Medicine, Ankara, Turkey
| | - Saffet Ozturk
- Department of Histology and Embryology, Akdeniz University School of Medicine, Antalya 07070, Turkey
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Dechsupa S, Yingsakmongkol W, Limthongkul W, Singhatanadgige W, Honsawek S. Relative telomere length and oxidative DNA damage in hypertrophic ligamentum flavum of lumbar spinal stenosis. PeerJ 2018; 6:e5381. [PMID: 30123710 PMCID: PMC6087619 DOI: 10.7717/peerj.5381] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Accepted: 07/14/2018] [Indexed: 12/27/2022] Open
Abstract
Background Lumbar spinal stenosis (LSS) is a common cause of low back pain with degenerative spinal change in older adults. Telomeres are repetitive nucleoprotein DNA sequences of TTAGGG at the ends of chromosomes. Oxidative stress originates from an imbalance in pro-oxidant and antioxidant homeostasis that results in the production of reactive oxygen species (ROS). The purpose of this study was to investigate relative telomere length (RTL) and oxidative DNA damage in ligamentum flavum (LF) tissue from LSS patients. Methods Forty-eight patients with LSS participated in this study. Genomic DNA from non-hypertrophic and hypertrophic LF tissue were analyzed by real-time polymerase chain reaction for relative telomere length (RTL). 8-hydroxy 2'-deoxygaunosine (8-OHdG) levels were determined by using enzyme-linked immunosorbent assay. We cultivated LF fibroblast cells from patients in different ages (61, 66, and 77 years). After each cultivation cycle, we examined RTL and senescence-associated β-galactosidase (SA-β-gal) expression. Results The hypertrophic LF had significantly lower RTL than non-hypertrophic LF (P = 0.04). The levels of 8-OHdG were significantly higher in hypertrophic LF compared to non-hypertrophic LF (P = 0.02). With advancing cell culture passage, the number of cells in each passage was significantly lower in hypertrophic LF fibroblast cells than non-hypertrophic LF fibroblast cells. When evaluated with SA-β-gal staining, all senescent LF fibroblast cells were observed at earlier passages in hypertrophic LF compared with non-hypertrophic LF fibroblast cells. Discussion Our results showed that patients with LSS displayed an accelerated RTL shortening and high oxidative stress in hypertrophic LF. These findings implied that telomere shortening and oxidative stress may play roles in the pathogenesis of hypertrophic LF in lumbar spinal stenosis.
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Affiliation(s)
- Sinsuda Dechsupa
- Osteoarthritis and Musculoskeleton Research Unit, Department of Biochemistry, Faculty of Medicine, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Chulalongkorn University, Bangkok, Thailand
| | - Wicharn Yingsakmongkol
- Department of Orthopaedics, Faculty of Medicine, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Chulalongkorn University, Bangkok, Thailand
| | - Worawat Limthongkul
- Department of Orthopaedics, Faculty of Medicine, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Chulalongkorn University, Bangkok, Thailand
| | - Weerasak Singhatanadgige
- Department of Orthopaedics, Faculty of Medicine, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Chulalongkorn University, Bangkok, Thailand
| | - Sittisak Honsawek
- Osteoarthritis and Musculoskeleton Research Unit, Department of Biochemistry, Faculty of Medicine, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Chulalongkorn University, Bangkok, Thailand
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Alvero AB, Fishman DA, Qumsiyeh MB, Garg M, Kacinski BM, Sapi E. Telomerase Prolongs the Lifespan of Normal Human Ovarian Surface Epithelial Cells Without Inducing Neoplastic Phenotype. ACTA ACUST UNITED AC 2016; 11:553-61. [PMID: 15582501 DOI: 10.1016/j.jsgi.2004.06.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
OBJECTIVE The aim of this study was to determine the effects of exogenous expression of the catalytic subunit of telomerase (hTERT) on the lifespan, growth characteristics, and tumorigenicity of normal human ovarian surface epithelial (OSE) cells. METHODS Low-passage primary cultures of normal human OSE cells were transfected with hTERT and the resulting cell lines were characterized. RESULTS The ectopic expression of hTERT stabilized the telomeres of the OSE cultures above 8 kb. The hTERT-transfected OSE cell lines grew beyond the normal lifespan seen in OSE cells and propagated in culture for more than 40 passages before senescing. Moreover, the hTERT-transfected cells demonstrated extensive proliferative capacity as evidenced by their ability to continuously grow even when seeded at low dilutions. The morphologic features and normal differentiation patterns seen in normal OSE cells were likewise retained by the hTERT-transfected cells. In addition, the cultures remained responsive to physiologic concentrations of epidermal growth factor and transforming growth factor-beta. Changes associated with neoplastic transformation like anchorage-independent growth, tumorigencity and karyotypic instability were not observed. CONCLUSIONS We were able to show that the ectopic expression of hTERT in normal human OSE: 1) resulted in cultures with greater growth potential and longer lifespan and 2) did not induce a transformed phenotype previously seen in viral oncogene-transfected OSE cells. The established cell lines would not only provide sufficient material for comprehensive studies to investigate the normal physiology of OSE cells, but could also help in the understanding of the early steps of ovarian carcinogenesis.
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Affiliation(s)
- Ayesha B Alvero
- Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
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Kim NK, Zhang Q, Feigon J. Structure and sequence elements of the CR4/5 domain of medaka telomerase RNA important for telomerase function. Nucleic Acids Res 2013; 42:3395-408. [PMID: 24335084 PMCID: PMC3950677 DOI: 10.1093/nar/gkt1276] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Telomerase is a unique reverse transcriptase that maintains the 3' ends of eukaryotic chromosomes by adding tandem telomeric repeats. The RNA subunit (TR) of vertebrate telomerase provides a template for reverse transcription, contained within the conserved template/pseudoknot domain, and a conserved regions 4 and 5 (CR4/5) domain, all essential for catalytic activity. We report the nuclear magnetic resonance (NMR) solution structure of the full-length CR4/5 domain from the teleost fish medaka (Oryzias latipes). Three helices emanate from a structured internal loop, forming a Y-shaped structure, where helix P6 stacks on P5 and helix P6.1 points away from P6. The relative orientations of the three helices are Mg2+ dependent and dynamic. Although the three-way junction is structured and has unexpected base pairs, telomerase activity assays with nucleotide substitutions and deletions in CR4/5 indicate that none of these are essential for activity. The results suggest that the junction is likely to change conformation in complex with telomerase reverse transcriptase and that it provides a flexible scaffold that allows P6 and P6.1 to correctly fold and interact with telomerase reverse transcriptase.
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Affiliation(s)
- Nak-Kyoon Kim
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA, Advanced Analysis Center, Korea Institute of Science and Technology, Seoul, 136-791, Republic of Korea and Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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9
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A trans-spliced telomerase RNA dictates telomere synthesis in Trypanosoma brucei. Cell Res 2013; 23:537-51. [PMID: 23478302 DOI: 10.1038/cr.2013.35] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Telomerase is a ribonucleoprotein enzyme typically required for sustained cell proliferation. Although both telomerase activity and the telomerase catalytic protein component, TbTERT, have been identified in the eukaryotic pathogen Trypanosoma brucei, the RNA molecule that dictates telomere synthesis remains unknown. Here, we identify the RNA component of Trypanosoma brucei telomerase, TbTR, and provide phylogenetic and in vivo evidence for TbTR's native folding and activity. We show that TbTR is processed through trans-splicing, and is a capped transcript that interacts and copurifies with TbTERT in vivo. Deletion of TbTR caused progressive shortening of telomeres at a rate of 3-5 bp/population doubling (PD), which can be rescued by ectopic expression of a wild-type allele of TbTR in an apparent dose-dependent manner. Remarkably, introduction of mutations in the TbTR template domain resulted in corresponding mutant telomere sequences, demonstrating that telomere synthesis in T. brucei is dependent on TbTR. We also propose a secondary structure model for TbTR based on phylogenetic analysis and chemical probing experiments, thus defining TbTR domains that may have important functional implications in telomere synthesis. Identification and characterization of TbTR not only provide important insights into T. brucei telomere functions, which have been shown to play important roles in T. brucei pathogenesis, but also offer T. brucei as an attractive model system for studying telomerase biology in pathogenic protozoa and for comparative analysis of telomerase function with higher eukaryotes.
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Fujimori J, Matsuo T, Shimose S, Kubo T, Ishikawa M, Yasunaga Y, Ochi M. Antitumor effects of telomerase inhibitor TMPyP4 in osteosarcoma cell lines. J Orthop Res 2011; 29:1707-11. [PMID: 21590716 DOI: 10.1002/jor.21451] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2010] [Accepted: 04/20/2011] [Indexed: 02/04/2023]
Abstract
Telomere studies in carcinomas have been extensively reported for prognostic utility and effective methods for targeting telomerase therapy has been described, but efficacy of telomerase inhibitor remained unknown in sarcoma cells. In this study, we investigated the effects of telomerase inhibitor cationic porphyrin TMPyP4 on telomerase activity, telomere length, cell growth, and apoptosis in osteosarcoma cell lines. TMPyP4 significantly inhibited telomerase activity in telomerase positive HOS and Saos-2, but not in MG-63. TMPyP4 significantly induced telomere shortening, and inhibition of the cell growth in HOS and Saos-2 with over 17% apoptosis rates. In terms of MG-63, TMPyP4 did not induce inhibition of both telomerase activity and cell growth, although it induced significant telomere shortening. Telomere length after treatment was 5.60 kb in HOS, 4.00 kb in Saos-2, and 9.89 kb in MG-63. These results may suggest that both telomerase activity loss and sufficient telomere shortening are necessary to inhibit cell growth in telomerase positive osteosarcoma cells. TMPyP4 did not induced telomere shortening but significantly inhibited the growth with 22.6% apoptosis rate in telomerase negative with extremely longer telomere-U2OS, may indicating the antitumor effect of TMPyP4 may be related to DNA damage including telomere dysfunction through G-quadruplex stabilization, independent on telomere length.
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Affiliation(s)
- Jun Fujimori
- Department of Orthopaedic Surgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan.
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Affiliation(s)
- Devanshi Jain
- Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London WC2A 3PX, United Kingdom;
| | - Julia Promisel Cooper
- Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London WC2A 3PX, United Kingdom;
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Tom HIK, Greider CW. A sequence-dependent exonuclease activity from Tetrahymena thermophila. BMC BIOCHEMISTRY 2010; 11:45. [PMID: 21080963 PMCID: PMC2998447 DOI: 10.1186/1471-2091-11-45] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/14/2010] [Accepted: 11/16/2010] [Indexed: 01/15/2023]
Abstract
Background Telomere function requires a highly conserved G rich 3'- overhang. This structure is formed by 5'-resection of the C-rich telomere strand. However, while many nucleases have been suggested to play a role in processing, it is not yet clear which nucleases carry out this 5'-resection. Results We used biochemical purification to identify a sequence-dependent exonuclease activity in Tetrahymena thermophila cell extracts. The nuclease activity showed specificity for 5'-ends containing AA or AC sequences, unlike Exo1, which showed sequence-independent cleavage. The Tetrahymena nuclease was active on both phosphorylated and unphosphorylated substrates whereas Exo1 requires a 5'-phosphate for cleavage. Conclusions The specificities of the enzyme indicate that this novel Tetrahymena exonuclease is distinct from Exo1 and has properties required for 3'-overhang formations at telomeres.
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Affiliation(s)
- Hui-I Kao Tom
- Department of Molecular Biology and Genetics, The Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, USA
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Frías C, Morán A, de Juan C, Ortega P, Fernández-Marcelo T, Sánchez-Pernaute A, Torres AJ, Díaz-Rubio E, Benito M, Iniesta P. Telomere function in colorectal cancer. World J Gastrointest Oncol 2009; 1:3-11. [PMID: 21160767 PMCID: PMC2999092 DOI: 10.4251/wjgo.v1.i1.3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2009] [Revised: 07/06/2009] [Accepted: 07/13/2009] [Indexed: 02/05/2023] Open
Abstract
Colorectal cancer is the third most common form of cancer and the second leading cause of cancer-related death in the western world. Tumour cells acquire the hallmarks of cancer during the carcinogenic selection process. Cell immortality is one of the principal features acquired during this process which involves the stabilization of telomere length. It is achieved mainly, by telomerase activation. Thus, the discovery of telomeres and telomerase allowed an understanding of the mechanisms by which cells can become immortalized. Different studies have shown that tumour cells have shorter telomeres than nontumour cells and have detected telomerase activity in the majority of tumours. Survival studies have determined that telomere maintenance and telomerase activity are associated with poor prognosis. Taking into account all the results achieved by different groups, quantification and evaluation of telomerase activity and measurement of telomere length may be useful methods for additional biologic and prognostic staging of colorectal carcinoma.
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Affiliation(s)
- Cristina Frías
- Cristina Frías, Alberto Morán, Carmen de Juan, Paloma Ortega, Tamara Fernández-Marcelo, Manuel Benito, Pilar Iniesta, Department of Biochemistry and Molecular Biology, Faculty of Pharmacy, Complutense University, 28040-Madrid, Spain
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Arora A, Maiti S. Stability and molecular recognition of quadruplexes with different loop length in the absence and presence of molecular crowding agents. J Phys Chem B 2009; 113:8784-92. [PMID: 19480441 DOI: 10.1021/jp809486g] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
G-quadruplexes are known to be potential targets for therapeutic intervention, thus resulting in development of various quadruplex interacting ligands. However, until now, no systemic study has been performed to understand molecular recognition of quadruplex in the presence of molecular crowding agents mimicking cellular conditions. The stability and molecular recognition of quadruplex can be influenced by loop length. Herein, we attempted to study the interaction of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine (TMPyP4), a well-known G-quadruplex binding ligand with various DNA quadruplexes differing in total loop length and loop arrangement in both the absence and presence of molecular crowding agents. Results obtained from CD studies revealed that longer loops favor mixed and antiparallel conformation in both the absence and presence of 30% ethylene glycol. UV thermal melting studies revealed that the stability and formation of quadruplex increases in the presence of 30% ethylene glycol. Moreover, the binding of TMPyP4 molecule to both of the binding sites in different quadruplexes with total loop length varying from 3 to 9 remains unchanged in both the absence and presence of 30% ethylene glycol. The binding affinity (K(a)) of TMPyP4 was found to be decreased approximately by 1 order for the quadruplex sequences with total loop length varying from 11 to 15 in the presence of molecular crowding agents.
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Affiliation(s)
- Amit Arora
- Institute of Genomics and Integrative Biology, CSIR, Delhi, India
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Park YP, Kim KD, Kang SH, Yoon DY, Park JW, Kim JW, Lee HG. Human telomerase reverse transcriptase (hTERT): a target molecule for the treatment of cisplatin-resistant tumors. Korean J Lab Med 2009; 28:430-7. [PMID: 19127107 DOI: 10.3343/kjlm.2008.28.6.430] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
BACKGROUND Human telomerase reverse transcriptase (hTERT) is a catalytic enzyme that is required for telomerase activity (TA) and cancer progression. Telomerase inhibition or inactivation increases cellular sensitivity to UV irradiation, DNA-damaging agents, the tyrosine kinase inhibitor, imatinib, and pharmacological inhibitors, such as BIBR1532. hTERT is associated with apoptosis. Some patients show drug-resistance during anti-cancer drug treatment and the cancer cell acquire anti-apoptotic mechanism. Therefore, we attempted to study correlation between hTERT and drug-resistance. METHODS To study the correlation between protein level and activity of hTERT and drug-resistance, Western blotting and telomerase repeat amplification protocol (TRAP) assays were performed. To investigate whether hTERT contributes to drug resistance in tumor cells, we transiently decreased hTERT levels using small interfering RNA (siRNA) in T24/R2 cells. RESULTS hTERT knockdown increased Bax translocation into the mitochondria and cytochrome C release into the cytosol. Caspase inhibitors, especially Z-VAD-FMK, rescued this phenomenon, suggesting that the stability or expression of hTERT might be regulated by caspase activity. CONCLUSIONS These data suggest that hTERT might be a target molecule for drug-resistant tumor therapy.
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Affiliation(s)
- Yuk Pheel Park
- Medical Genomic Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, Korea
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16
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Is stem cell chromosomes stability affected by cryopreservation conditions? Cytotechnology 2008; 58:11-6. [PMID: 19002774 DOI: 10.1007/s10616-008-9163-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Accepted: 09/12/2008] [Indexed: 02/06/2023] Open
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Lane AN, Chaires JB, Gray RD, Trent JO. Stability and kinetics of G-quadruplex structures. Nucleic Acids Res 2008; 36:5482-515. [PMID: 18718931 PMCID: PMC2553573 DOI: 10.1093/nar/gkn517] [Citation(s) in RCA: 571] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Revised: 07/26/2008] [Accepted: 07/29/2008] [Indexed: 12/30/2022] Open
Abstract
In this review, we give an overview of recent literature on the structure and stability of unimolecular G-rich quadruplex structures that are relevant to drug design and for in vivo function. The unifying theme in this review is energetics. The thermodynamic stability of quadruplexes has not been studied in the same detail as DNA and RNA duplexes, and there are important differences in the balance of forces between these classes of folded oligonucleotides. We provide an overview of the principles of stability and where available the experimental data that report on these principles. Significant gaps in the literature have been identified, that should be filled by a systematic study of well-defined quadruplexes not only to provide the basic understanding of stability both for design purposes, but also as it relates to in vivo occurrence of quadruplexes. Techniques that are commonly applied to the determination of the structure, stability and folding are discussed in terms of information content and limitations. Quadruplex structures fold and unfold comparatively slowly, and DNA unwinding events associated with transcription and replication may be operating far from equilibrium. The kinetics of formation and resolution of quadruplexes, and methodologies are discussed in the context of stability and their possible biological occurrence.
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Affiliation(s)
- Andrew N Lane
- Structural Biology Program, JG Brown Cancer Center, University of Louisville, KY 40202, USA.
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18
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Hwang JY, Smith S, Ceschia A, Torres-Rosell J, Aragon L, Myung K. Smc5-Smc6 complex suppresses gross chromosomal rearrangements mediated by break-induced replications. DNA Repair (Amst) 2008; 7:1426-36. [PMID: 18585101 DOI: 10.1016/j.dnarep.2008.05.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Revised: 04/30/2008] [Accepted: 05/08/2008] [Indexed: 11/30/2022]
Abstract
Translocations in chromosomes alter genetic information. Although the frequent translocations observed in many tumors suggest the altered genetic information by translocation could promote tumorigenesis, the mechanisms for how translocations are suppressed and produced are poorly understood. The smc6-9 mutation increased the translocation class gross chromosomal rearrangement (GCR). Translocations produced in the smc6-9 strain are unique because they are non-reciprocal and dependent on break-induced replication (BIR) and independent of non-homologous end joining. The high incidence of translocations near repetitive sequences such as delta sequences, ARS, tRNA genes, and telomeres in the smc6-9 strain indicates that Smc5-Smc6 suppresses translocations by reducing DNA damage at repetitive sequences. Synergistic enhancements of translocations in strains defective in DNA damage checkpoints by the smc6-9 mutation without affecting de novo telomere addition class GCR suggest that Smc5-Smc6 defines a new pathway to suppress GCR formation.
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Affiliation(s)
- Ji-Young Hwang
- Genome Instability Section, Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, 49 Convent Drive, Bethesda, MD 20892 USA
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Abstract
The temperature-sensitive phenotypes of yku70Delta and yku80Delta have provided a useful tool for understanding telomere homeostasis. Mutating the helicase domain of the telomerase inhibitor Pif1 resulted in the inactivation of cell cycle checkpoints and the subsequent rescue of temperature sensitivity of the yku70Delta strain. The inactivation of Pif1 in yku70Delta increased overall telomere length. However, the long G-rich, single-stranded overhangs at the telomeres, which are the major cause of temperature sensitivity, were slightly increased. Interestingly, the rescue of temperature sensitivity in strains having both pif1-m2 and yku70Delta mutations depended on the homologous recombination pathway. Furthermore, the BLM/WRN helicase yeast homolog Sgs1 exacerbated the temperature sensitivity of the yku70Delta strain. Therefore, the yKu70-80 heterodimer and telomerase maintain telomere size, and the helicase activity of Pif1 likely also helps to balance the overall size of telomeres and G-rich, single-stranded overhangs in wild-type cells by regulating telomere protein homeostasis. However, the absence of yKu70 may provide other proteins such as those involved in homologous recombination, Sgs1, or Pif1 additional access to G-rich, single-stranded DNA and may determine telomere size, cell cycle checkpoint activation, and, ultimately, temperature sensitivity.
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20
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Yang C, Przyborski S, Cooke MJ, Zhang X, Stewart R, Anyfantis G, Atkinson SP, Saretzki G, Armstrong L, Lako M. A key role for telomerase reverse transcriptase unit in modulating human embryonic stem cell proliferation, cell cycle dynamics, and in vitro differentiation. Stem Cells 2008; 26:850-63. [PMID: 18203676 DOI: 10.1634/stemcells.2007-0677] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Embryonic stem cells (ESC) are a unique cell population with the ability to self-renew and differentiate into all three germ layers. Human ESC express the telomerase reverse transcriptase (TERT) gene and the telomerase RNA (TR) and show telomerase activity, but TERT, TR, and telomerase are all downregulated during the differentiation process. To examine the role of telomerase in human ESC self-renewal and differentiation, we modulated the expression of TERT. Upregulation of TERT and increased telomerase activity enhanced the proliferation and colony-forming ability of human ESC, as well as increasing the S phase of the cell cycle at the expense of a reduced G1 phase. Upregulation of TERT expression was associated with increases in CYCLIN D1 and CDC6 expression, as well as hyperphosphorylation of RB. The differentiated progeny of control ESC showed shortening of telomeric DNA as a result of loss of telomerase activity. In contrast, the differentiated cells from TERT-overexpressing ESC maintained high telomerase activity and accumulated lower concentrations of peroxides than wild-type cells, implying greater resistance to oxidative stress. Although the TERT-overexpressing human ESC are able to form teratoma composed of three germ layers in vivo, their in vitro differentiation to all primitive and embryonic lineages was suppressed. In contrast, downregulation of TERT resulted in reduced ESC proliferation, increased G1, and reduced S phase. Most importantly, downregulation of TERT caused loss of pluripotency and human ESC differentiation to extraembryonic and embryonic lineages. Our results indicate for the first time an important role for TERT in the maintenance of human ESC pluripotency, cell cycle regulation, and in vitro differentiation capacity.
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Affiliation(s)
- Chunbo Yang
- North East Institute for Stem Cell Research, Newcastle upon Tyne NE1 3BZ, United Kingdom
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21
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Abstract
It was in the 1930s that telomeres (from the Greek telos = end and meros = part) were first recognized as essential structures at the ends of the chromosomes and were shown to be important for chromosomal stability (Muller HJ: The remaking of chromosomes. The Collecting Net-Woods Hole 1938: 13: 181-198, McClintock B, The stability of broken ends of chromosomes in Zea mays. Genetics 1041: 26: 234-282). However, it was only in 1978 that the first telomeric sequence was identified -- in the protocoa Tetrahymena, a single cell organism that at a certain stage of development has many identical minichromosomes with twice as many telomeres (Blackburn EH and Gall JG. A tandemly repeated sequence at the termini of the extrachromosomal ribosomal RNA genes in Tetrahymena. J. Mol. Biol. 1978: 120: 33-53.). Today we know that telomeres form specialized, three-dimensional DNA-protein structures and fulfil important capping functions. Besides, telomeric DNA is essential as ''access DNA'' for those cells that are not able to counteract loss of DNA during replication because they do not express telomerase, the enzyme responsible for telomere length maintenance. Since telomerase is mostly found in tumor cells and inhibition correlates with telomere shortening and finally growth inhibition, telomerase and lately also the telomeres themselves have become attractive targets for anti-cancer therapy. This review aims to critically throw light on different therapeutical approaches and comes to the conclusion that telomeres may be the better targets for cancer therapeutics.
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Affiliation(s)
- Petra Boukamp
- Department of Genetics and Skin Carcinogenesis, German Cancer Research Center, Heidelberg, Germany.
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22
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Xin H, Liu D, Wan M, Safari A, Kim H, Sun W, O'Connor MS, Songyang Z. TPP1 is a homologue of ciliate TEBP-beta and interacts with POT1 to recruit telomerase. Nature 2007; 445:559-62. [PMID: 17237767 DOI: 10.1038/nature05469] [Citation(s) in RCA: 391] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Accepted: 11/20/2006] [Indexed: 11/08/2022]
Abstract
Telomere dysfunction may result in chromosomal abnormalities, DNA damage responses, and even cancer. Early studies in lower organisms have helped to establish the crucial role of telomerase and telomeric proteins in maintaining telomere length and protecting telomere ends. In Oxytricha nova, telomere G-overhangs are protected by the TEBP-alpha/beta heterodimer. Human telomeres contain duplex telomeric repeats with 3' single-stranded G-overhangs, and may fold into a t-loop structure that helps to shield them from being recognized as DNA breaks. Additionally, the TEBP-alpha homologue, POT1, which binds telomeric single-stranded DNA (ssDNA), associates with multiple telomeric proteins (for example, TPP1, TIN2, TRF1, TRF2 and RAP1) to form the six-protein telosome/shelterin and other subcomplexes. These telomeric protein complexes in turn interact with diverse pathways to form the telomere interactome for telomere maintenance. However, the mechanisms by which the POT1-containing telosome communicates with telomerase to regulate telomeres remain to be elucidated. Here we demonstrate that TPP1 is a putative mammalian homologue of TEBP-beta and contains a predicted amino-terminal oligonucleotide/oligosaccharide binding (OB) fold. TPP1-POT1 association enhanced POT1 affinity for telomeric ssDNA. In addition, the TPP1 OB fold, as well as POT1-TPP1 binding, seemed critical for POT1-mediated telomere-length control and telomere-end protection in human cells. Disruption of POT1-TPP1 interaction by dominant negative TPP1 expression or RNA interference (RNAi) resulted in telomere-length alteration and DNA damage responses. Furthermore, we offer evidence that TPP1 associates with the telomerase in a TPP1-OB-fold-dependent manner, providing a physical link between telomerase and the telosome/shelterin complex. Our findings highlight the critical role of TPP1 in telomere maintenance, and support a yin-yang model in which TPP1 and POT1 function as a unit to protect human telomeres, by both positively and negatively regulating telomerase access to telomere DNA.
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Affiliation(s)
- Huawei Xin
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
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23
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Chen Y, Fender J, Legassie JD, Jarstfer MB, Bryan TM, Varani G. Structure of stem-loop IV of Tetrahymena telomerase RNA. EMBO J 2006; 25:3156-66. [PMID: 16778765 PMCID: PMC1500990 DOI: 10.1038/sj.emboj.7601195] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2006] [Accepted: 05/15/2006] [Indexed: 12/21/2022] Open
Abstract
Conserved domains within the RNA component of telomerase provide the template for reverse transcription, recruit protein components to the holoenzyme and are required for enzymatic activity. Among the functionally essential domains in ciliate telomerase RNA is stem-loop IV, which strongly stimulates telomerase activity and processivity even when provided in trans. The NMR structure of Tetrahymena thermophila stem-loop IV shows a highly structured distal stem-loop linked to a conformationally flexible template-proximal region by a bulge that severely kinks the entire RNA. Through extensive structure-function studies, we identify residues that contribute to both these structural features and to enzymatic activity, with no apparent effect on the binding of TERT protein. We propose that the bending induced by the GA bulge and the flexibility of the template-proximal region allow positioning of the prestructured apical loop during the catalytic cycle.
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Affiliation(s)
- Yu Chen
- Department of Chemistry, University of Washington, Seattle WA, USA
| | - Jessica Fender
- Department of Chemistry, University of Washington, Seattle WA, USA
| | - Jason D Legassie
- Division of Medicinal Chemistry and Natural Products, University of North Carolina, Chapel Hill, NC, USA
| | - Michael B Jarstfer
- Division of Medicinal Chemistry and Natural Products, University of North Carolina, Chapel Hill, NC, USA
| | - Tracy M Bryan
- Children's Medical Research Institute, Westmead, NSW, Australia
| | - Gabriele Varani
- Department of Chemistry, University of Washington, Seattle WA, USA
- Department of Biochemistry, University of Washington, Seattle WA, USA
- Departments of Chemistry & Biochemistry, University of Washington, Box 351700, Seattle, WA 98185-1700, USA. Tel: +1 206 543 7113; Fax: +1 206 685 8665; E-mail:
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24
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Shay JW, Wright WE. Telomerase therapeutics for cancer: challenges and new directions. Nat Rev Drug Discov 2006; 5:577-84. [PMID: 16773071 DOI: 10.1038/nrd2081] [Citation(s) in RCA: 310] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
It has been approximately a decade since telomerase was described as an almost universal marker for human cancer. Most human tumours not only express telomerase but also have very short telomeres, whereas telomerase activity is either reduced or absent in normal tissues, making the inhibition of telomerase an attractive target for cancer therapeutics. Here we review the current status of telomerase therapeutics and discuss future opportunities and challenges for telomerase research, including a possible relationship with cancer stem cells that could be a source of chemo-/radioresistance development in many advanced cancers.
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Affiliation(s)
- Jerry W Shay
- Department of Cell Biology, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9039, USA.
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25
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Mizuno H, Wu J, Kanamori H, Fujisawa M, Namiki N, Saji S, Katagiri S, Katayose Y, Sasaki T, Matsumoto T. Sequencing and characterization of telomere and subtelomere regions on rice chromosomes 1S, 2S, 2L, 6L, 7S, 7L and 8S. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2006; 46:206-17. [PMID: 16623884 DOI: 10.1111/j.1365-313x.2006.02684.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Telomeres, which are important for chromosome maintenance, are composed of long, repetitive DNA sequences associated with a variety of telomere-binding proteins. We characterized the organization and structure of rice telomeres and adjacent subtelomere regions on the basis of cytogenetic and sequence analyses. The length of the rice telomeres ranged from 5.1 to 10.8 kb, as revealed by both fibre-fluorescent in situ hybridization and terminal restriction-fragment assay. Physical maps of the chromosomal ends were constructed from a fosmid library. This facilitated sequencing of the telomere regions of chromosomes 1S, 2S, 2L, 6L, 7S, 7L and 8S. The resulting sequences contained conserved TTTAGGG telomere repeats, which indicates that the physical maps partly covered the telomere regions of the respective chromosome arms. These repeats were organized in the order of 5'-TTTAGGG-3' from the chromosome-specific region, except in chromosome 7S, in which seven inverted copies also existed in tandem array. Analysis of the telomere-flanking regions revealed the occurrence of deletions, insertions, or chromosome-specific substitutions of single nucleotides within the repeat sequences at the junction between the telomere and subtelomere. The sequences of the 500-kb regions of the seven chromosome ends were analysed in detail. A total of 598 genes were predicted in the telomeric regions. In addition, repetitive sequences derived from various kinds of retrotransposon were identified. No significant evidence for segmental duplication could be detected within or among the subtelomere regions. These results indicate that the rice chromosome ends are heterogeneous in both sequence and characterization.
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Affiliation(s)
- Hiroshi Mizuno
- National Institute of Agrobiological Sciences, 1-2, Kannondai 2-chome, Tsukuba, Ibaraki 305-8602, Japan
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26
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Pavlov YI, Shcherbakova PV, Rogozin IB. Roles of DNA Polymerases in Replication, Repair, and Recombination in Eukaryotes. INTERNATIONAL REVIEW OF CYTOLOGY 2006; 255:41-132. [PMID: 17178465 DOI: 10.1016/s0074-7696(06)55002-8] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The functioning of the eukaryotic genome depends on efficient and accurate DNA replication and repair. The process of replication is complicated by the ongoing decomposition of DNA and damage of the genome by endogenous and exogenous factors. DNA damage can alter base coding potential resulting in mutations, or block DNA replication, which can lead to double-strand breaks (DSB) and to subsequent chromosome loss. Replication is coordinated with DNA repair systems that operate in cells to remove or tolerate DNA lesions. DNA polymerases can serve as sensors in the cell cycle checkpoint pathways that delay cell division until damaged DNA is repaired and replication is completed. Eukaryotic DNA template-dependent DNA polymerases have different properties adapted to perform an amazingly wide spectrum of DNA transactions. In this review, we discuss the structure, the mechanism, and the evolutionary relationships of DNA polymerases and their possible functions in the replication of intact and damaged chromosomes, DNA damage repair, and recombination.
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Affiliation(s)
- Youri I Pavlov
- Eppley Institute for Research in Cancer and Allied Diseases, Departments of Biochemistry and Molecular Biology, and Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805, USA
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27
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Hao LY, Armanios M, Strong MA, Karim B, Feldser DM, Huso D, Greider CW. Short Telomeres, even in the Presence of Telomerase, Limit Tissue Renewal Capacity. Cell 2005; 123:1121-31. [PMID: 16360040 DOI: 10.1016/j.cell.2005.11.020] [Citation(s) in RCA: 216] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2005] [Revised: 10/11/2005] [Accepted: 11/04/2005] [Indexed: 11/30/2022]
Abstract
Autosomal-dominant dyskeratosis congenita is associated with heterozygous mutations in telomerase. To examine the dosage effect of telomerase, we generated a line of mTR+/- mice on the CAST/EiJ background, which has short telomeres. Interbreeding of heterozygotes resulted in progressive telomere shortening, indicating that limiting telomerase compromises telomere maintenance. In later-generation heterozygotes, we observed a decrease in tissue renewal capacity in the bone marrow, intestines, and testes that resembled defects seen in dyskeratosis congenita patients. The progressive worsening of disease with decreasing telomere length suggests that short telomeres, not telomerase level, cause stem cell failure. Further, wild-type mice derived from the late-generation heterozygous parents, termed wt*, also had short telomeres and displayed a germ cell defect, indicating that telomere length determines these phenotypes. We propose that short telomeres in mice that have normal telomerase levels can cause an occult form of genetic disease.
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Affiliation(s)
- Ling-Yang Hao
- Department of Molecular Biology and Genetics, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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28
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Sue SC, Hsiao HH, Chung BCP, Cheng YH, Hsueh KL, Chen CM, Ho CH, Huang TH. Solution structure of the Arabidopsis thaliana telomeric repeat-binding protein DNA binding domain: a new fold with an additional C-terminal helix. J Mol Biol 2005; 356:72-85. [PMID: 16337232 DOI: 10.1016/j.jmb.2005.11.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2005] [Revised: 11/01/2005] [Accepted: 11/03/2005] [Indexed: 01/30/2023]
Abstract
The double-stranded telomeric repeat-binding protein (TRP) AtTRP1 is isolated from Arabidopsis thaliana. Using gel retardation assays, we defined the C-terminal 97 amino acid residues, Gln464 to Val560 (AtTRP1(464-560)), as the minimal structured telomeric repeat-binding domain. This region contains a typical Myb DNA-binding motif and a C-terminal extension of 40 amino acid residues. The monomeric AtTRP1(464-560) binds to a 13-mer DNA duplex containing a single repeat of an A.thaliana telomeric DNA sequence (GGTTTAG) in a 1:1 complex, with a K(D) approximately 10(-6)-10(-7) M. Nuclear magnetic resonance (NMR) examination revealed that the solution structure of AtTRP1(464-560) is a novel four-helix tetrahedron rather than the three-helix bundle structure found in typical Myb motifs and other TRPs. Binding of the 13-mer DNA duplex to AtTRP1(464-560) induced significant chemical shift perturbations of protein amide resonances, which suggests that helix 3 (H3) and the flexible loop connecting H3 and H4 are essential for telomeric DNA sequence recognition. Furthermore, similar to that in hTRF1, the N-terminal arm likely contributes to or stabilizes DNA binding. Sequence comparisons suggested that the four-helix structure and the involvement of the loop residues in DNA binding may be features unique to plant TRPs.
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Affiliation(s)
- Shih-Che Sue
- Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei, Taiwan, ROC
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29
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Mukhopadhyay NK, Gordon GJ, Maulik G, Doerre G, Liu BCS, Bueno R, Sugarbaker DJ, Jaklitsch MT. Histone deacetylation is directly involved in desilencing the expression of the catalytic subunit of telomerase in normal lung fibroblast. J Cell Mol Med 2005; 9:662-9. [PMID: 16202213 PMCID: PMC6741419 DOI: 10.1111/j.1582-4934.2005.tb00496.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The regulation of telomerase expression in normal cells is poorly understood. Moreover, the molecular mechanism underlying tumor-specific expression of telomerase remains unclear. We investigated the link between histone deacetylation and telomerase activity in normal lung and lung tumor cells. Four non-small-cell lung cancer (NSCLC) lines and one normal lung fibroblast line were tested for telomerase activity with or without Trichostatin A(TSA). The telomerase activity and the expression of telomerase associated components were determined by TRAP assay, RT-PCR analysis and Western blot analysis. All 4 NSCLC cell lines exposed to 1 microM TSA for 24 h had no change in telomerase activity or hTERT mRNA level. Telomerase activity was very low in normal lung fibroblasts (mrc-9) until exposed to 1 microM TSA for 24 h, at which time telomerase activity was readily detectable, with concomitant upregulation of hTERT mRNA (10-fold). The level of other telomerase associated components (hTER and TP1) were unaltered. Furthermore, 1 microM TSA exposure for 24 h did not alter the level of c-Myc or p21 mRNA. Immunodetection reveled that hTERT protein expression increased (approximately 6 fold) compared to c-Myc, p21, or gelsolin. The effect of TSA on hTERT expression is independent of DNA methylation as judged by 5-azacytidine (5aza) treatment. TSA effect on mrc-9 cells is unaltered even in the presence of 200 microg/ml cyclohexamide, suggesting a direct inhibition of histone deacetylation. Collectively, our study indicates that inhibition of histone deacetylation selectively regulates the transcriptional derepression of telomerase catalytic subunit in normal lung fibroblast cells compared to lung tumor cells.
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Affiliation(s)
- N K Mukhopadhyay
- Division of Thoracic Surgery, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
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30
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Liao XH, Zhang ML, Yang CP, Xu LX, Zhou JQ. Characterization of recombinant Saccharomyces cerevisiae telomerase core enzyme purified from yeast. Biochem J 2005; 390:169-76. [PMID: 15813705 PMCID: PMC1184572 DOI: 10.1042/bj20050208] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Telomerase is a cellular reverse transcriptase that elongates the single-stranded chromosome ends and oligonucleotides in vivo and in vitro. In Saccharomyces cerevisiae, Est2p (telomerase catalytic subunit) and Tlc1 (telomerase RNA template subunit) constitute the telomerase core complex. We co-overexpressed GST (glutathione S-transferase)-Est2p and Tlc1 in S. cerevisiae, and reconstituted the telomerase activity. The GST-Est2p-Tlc1 complex was partially purified by ammonium sulphate fractionation and affinity chromatography on glutathione beads, and the partially purified telomerase did not contain the other two subunits of the telomerase holoenzyme, Est1p and Est3p. The purified recombinant GST-Est2p-Tlc1 telomerase core complex could specifically add nucleotides on to the single-stranded TG(1-3) primer in a processive manner, but could not translocate to synthesize more than one telomeric repeat. The purified telomerase core complex exhibited different activities when primers were paired with the Tlc1 template at different positions. The procedure of reconstitution and purification of telomerase core enzyme that we have developed now allows for further mechanistic studies of the functions of other subunits of the telomerase holoenzyme as well as other telomerase regulation proteins.
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Affiliation(s)
- Xin-Hua Liao
- Max-Planck Junior Research Group in the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; Graduate School of the Chinese Academy of Sciences, Shanghai, 200031, China
| | - Ming-Liang Zhang
- Max-Planck Junior Research Group in the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; Graduate School of the Chinese Academy of Sciences, Shanghai, 200031, China
| | - Cui-Ping Yang
- Max-Planck Junior Research Group in the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; Graduate School of the Chinese Academy of Sciences, Shanghai, 200031, China
| | - Lu-Xia Xu
- Max-Planck Junior Research Group in the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; Graduate School of the Chinese Academy of Sciences, Shanghai, 200031, China
| | - Jin-Qiu Zhou
- Max-Planck Junior Research Group in the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; Graduate School of the Chinese Academy of Sciences, Shanghai, 200031, China
- To whom correspondence should be addressed (email )
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31
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Buczek P, Orr RS, Pyper SR, Shum M, Ota EKI, Gerum SE, Horvath MP. Binding linkage in a telomere DNA-protein complex at the ends of Oxytricha nova chromosomes. J Mol Biol 2005; 350:938-52. [PMID: 15967465 PMCID: PMC2939017 DOI: 10.1016/j.jmb.2005.05.040] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2005] [Revised: 05/07/2005] [Accepted: 05/16/2005] [Indexed: 11/22/2022]
Abstract
Alpha and beta protein subunits of the telomere end binding protein from Oxytricha nova (OnTEBP) combine with telomere single strand DNA to form a protective cap at the ends of chromosomes. We tested how protein-protein interactions seen in the co-crystal structure relate to DNA binding through use of fusion proteins engineered as different combinations of domains and subunits derived from OnTEBP. Joining alpha and beta resulted in a protein that bound single strand telomere DNA with high affinity (K(D-DNA)=1.4 nM). Another fusion protein, constructed without the C-terminal protein-protein interaction domain of alpha, bound DNA with 200-fold diminished affinity (K(D-DNA)=290 nM) even though the DNA-binding domains of alpha and beta were joined through a peptide linker. Adding back the alpha C-terminal domain as a separate protein restored high-affinity DNA binding. The binding behaviors of these fusion proteins and the native protein subunits are consistent with cooperative linkage between protein-association and DNA-binding equilibria. Linking DNA-protein stability to protein-protein contacts at a remote site may provide a trigger point for DNA-protein disassembly during telomere replication when the single strand telomere DNA must exchange between a very stable OnTEBP complex and telomerase.
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32
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Rodier F, Kim SH, Nijjar T, Yaswen P, Campisi J. Cancer and aging: the importance of telomeres in genome maintenance. Int J Biochem Cell Biol 2005; 37:977-90. [PMID: 15743672 DOI: 10.1016/j.biocel.2004.10.012] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2004] [Revised: 10/02/2004] [Accepted: 10/05/2004] [Indexed: 10/26/2022]
Abstract
Telomeres are the specialized DNA-protein structures that cap the ends of linear chromosomes, thereby protecting them from degradation and fusion by cellular DNA repair processes. In vertebrate cells, telomeres consist of several kilobase pairs of DNA having the sequence TTAGGG, a few hundred base pairs of single-stranded DNA at the 3' end of the telomeric DNA tract, and a host of proteins that organize the telomeric double and single-stranded DNA into a protective structure. Functional telomeres are essential for maintaining the integrity and stability of genomes. When combined with loss of cell cycle checkpoint controls, telomere dysfunction can lead to genomic instability, a common cause and hallmark of cancer. Consequently, normal mammalian cells respond to dysfunctional telomeres by undergoing apoptosis (programmed cell death) or cellular senescence (permanent cell cycle arrest), two cellular tumor suppressor mechanisms. These tumor suppressor mechanisms are potent suppressors of cancer, but recent evidence suggests that they can antagonistically also contribute to aging phenotypes. Here, we review what is known about the structure and function of telomeres in mammalian cells, particularly human cells, and how telomere dysfunction may arise and contribute to cancer and aging phenotypes.
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Affiliation(s)
- Francis Rodier
- Lawrence Berkeley National Laboratory, Life Sciences Division, 1 Cyclotron Rd., Berkeley, CA 94720, USA
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33
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Leeper TC, Varani G. The structure of an enzyme-activating fragment of human telomerase RNA. RNA (NEW YORK, N.Y.) 2005; 11:394-403. [PMID: 15703438 PMCID: PMC1370729 DOI: 10.1261/rna.7222505] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2004] [Accepted: 12/21/2004] [Indexed: 05/21/2023]
Abstract
The ribonucleoprotein enzyme telomerase ensures the stability and fidelity of linear chromosome ends by elongating the telomeric DNA that is lost during each round of DNA replication. All telomerases contain a catalytic protein component homologous to viral reverse transcriptases (TERT) and an RNA (TR) that provides the template sequence, acts as the scaffold for ribonucleoprotein assembly, and activates the enzyme for catalysis. Vertebrate telomerase RNAs contain three highly conserved structural and functional domains: the template domain, the "CR4-CR5" or "activation" domain essential for activation of the enzymatic activity, and a 3'-terminal "box H/ACA"-homology domain responsible for ribonucleprotein assembly and maturation. Here we report the NMR structure of a functionally essential RNA structural element derived from the human telomerase RNA CR4-CR5 domain. This RNA, referred to as hTR J6, forms a stable hairpin interrupted by a single nucleotide bulge and an asymmetric internal loop. Previous work on telomerase has shown that deletion of the hTR J6 asymmetric internal loop results in an RNA incapable of binding the enzymatic protein component of the RNP and therefore an inactive RNP without telomerase activity. We demonstrate here that the J6 internal loop introduces a twist in the RNA structure that may position the entire domain into the catalytic site of the enzyme.
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Affiliation(s)
- Thomas C Leeper
- Department of Biochemistry and Department of Chemistry, University of Washington, Seattle, WA 98195-1700, USA
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34
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Chiang YJ, Hemann MT, Hathcock KS, Tessarollo L, Feigenbaum L, Hahn WC, Hodes RJ. Expression of telomerase RNA template, but not telomerase reverse transcriptase, is limiting for telomere length maintenance in vivo. Mol Cell Biol 2004; 24:7024-31. [PMID: 15282303 PMCID: PMC479722 DOI: 10.1128/mcb.24.16.7024-7031.2004] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Telomerase consists of two essential components, the telomerase RNA template (TR) and telomerase reverse transcriptase (TERT). The haplo-insufficiency of TR was recently shown to cause one form of human dyskeratosis congenita, an inherited disease marked by abnormal telomere shortening. Consistent with this finding, we recently reported that mice heterozygous for inactivation of mouse TR exhibit a similar haplo-insufficiency and are deficient in the ability to elongate telomeres in vivo. To further assess the genetic regulation of telomerase activity, we have compared the abilities of TR-deficient and TERT-deficient mice to maintain or elongate telomeres in interspecies crosses. Homozygous TERT knockout mice had no telomerase activity and failed to maintain telomere length. In contrast, TERT(+/-) heterozygotes had no detectable defect in telomere elongation compared to wild-type controls, whereas TR(+/-) heterozygotes were deficient in telomere elongation. Levels of TERT mRNA in heterozygous mice were one-third to one-half the levels expressed in wild-type mice, similar to the reductions in telomerase RNA observed in TR heterozygotes. These findings indicate that both TR and TERT are essential for telomere maintenance and elongation but that gene copy number and transcriptional regulation of TR, but not TERT, are limiting for telomerase activity under the in vivo conditions analyzed.
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Affiliation(s)
- Y Jeffrey Chiang
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Building 10, 4B36, 9000 Rockville Pike, Bethesda, MD 20892, USA.
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35
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Bao K, Cohen SN. Reverse transcriptase activity innate to DNA polymerase I and DNA topoisomerase I proteins of Streptomyces telomere complex. Proc Natl Acad Sci U S A 2004; 101:14361-6. [PMID: 15353591 PMCID: PMC521936 DOI: 10.1073/pnas.0404386101] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Replication of Streptomyces linear chromosomes and plasmids proceeds bidirectionally from a central origin, leaving recessed 5' termini that are extended by a telomere binding complex. This complex contains both a telomere-protecting terminal protein (Tpg) and a telomere-associated protein that interacts with Tpg and the DNA ends of linear Streptomyces replicons. By using histidine-tagged telomere-associated protein (Tap) as a scaffold, we identified DNA polymerase (PolA) and topoisomerase I (TopA) proteins as other components of the Streptomyces telomere complex. Biochemical characterization of these proteins indicated that both PolA and TopA exhibit highly efficient reverse transcriptase (RT) activity in addition to their predicted functions. Although RT activity innate to other DNA-dependent DNA polymerases has been observed previously, its occurrence in a topoisomerase is unprecedented. Deletion mapping and sequence analysis showed that the RT activity of Streptomcyces TopA resides in a peptide region containing motifs that are absent from most bacterial topoisomerases but are highly conserved in a novel subfamily of eubacterial topoisomerases found largely in Actinobacteria. Within one of these motifs, and essential to the RT function of Streptomyces TopA, is an Asp-Asp doublet sequence required also for the RT activities of human immunodeficiency virus and eukaryotic cell telomerases.
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Affiliation(s)
- Kai Bao
- Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5120, USA
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36
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Dudognon C, Pendino F, Hillion J, Saumet A, Lanotte M, Ségal-Bendirdjian E. Death receptor signaling regulatory function for telomerase: hTERT abolishes TRAIL-induced apoptosis, independently of telomere maintenance. Oncogene 2004; 23:7469-74. [PMID: 15326479 DOI: 10.1038/sj.onc.1208029] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Human telomerase has been implicated in cell immortalization and cancer. Recent works suggest that telomerase confers additional function required for tumorigenesis that does not depend on its ability to maintain telomeres. This new action may influence tumor therapy outcomes by yet unraveled mechanisms. Here, we show that overexpression of the catalytic subunit of telomerase (hTERT) protects a maturation-resistant acute promyelocytic leukemia (APL) cell line from apoptosis induced by the tumor necrosis factor (TNF) or TNF-related apoptosis-inducing ligand (TRAIL) and not from apoptosis induced by chemotherapeutic drugs such as etoposide or cisplatin. Conversely, in these cells, TRAIL-induced cell death is magnified by all-trans retinoic acid (ATRA) treatment, independently of telomerase activity on telomeres. Of note, this response is subordinated neither to maturation nor to telomere shortening. This work underlines that retinoids and death receptor signaling cross-talks offer new perspectives for antitumor therapy.
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Affiliation(s)
- Charles Dudognon
- INSERM U496, Institut d'Hématologie, Hôpital Saint-Louis, 1, Avenue Claude Vellefaux, 75010 Paris, France
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37
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Abstract
Cellular senescence is a signal transduction program leading to irreversible cell cycle arrest. This growth arrest can be triggered by many different mechanisms including recognition by cellular sensors of DNA double-strand breaks leading to the activation of cell cycle checkpoint responses and recruitment of DNA repair foci. Senescence is initiated by the shortening of telomeres (replicative senescence) or by other endogenous and exogenous acute and chronic stress signals (STASIS: stress or aberrant signaling-induced senescence). The process of carcinogenesis involves a series of changes that allow tumor cells to bypass the senescence program. Nevertheless, tumor cells retain the capacity to undergo senescence. Treatment of tumor cells with many conventional anticancer therapies activates DNA damage signaling pathways, which induce apoptosis in some cells and senescence in others. Overexpression of tumor suppressors or inhibition of oncogenes can also induce rapid senescence in tumor cells. Senescent cells, while not dividing, remain metabolically active and produce many secreted factors, some of which stimulate and others inhibit the growth of tumors. The emerging knowledge about the pathways that lead to senescence and determine the pattern of gene expression in senescent cells may lead to more effective treatments for cancer.
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Affiliation(s)
- Jerry W Shay
- The University of Texas Southwestern Medical Center, Department of Cell Biology, 5323 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
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38
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Besker N, Anselmi C, Paparcone R, Scipioni A, Savino M, De Santis P. Systematic search for compact structures of telomeric nucleosomes. FEBS Lett 2003; 554:369-72. [PMID: 14623096 DOI: 10.1016/s0014-5793(03)01193-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Telomeres are structures functionally and structurally distinct from bulk chromatin. They are constituted of highly conserved 5-7 bp tandemly repeated units, organized into nucleosomes with short linkers, whereas the knowledge of the linker histone role in telomeric chromatin is still fragmentary. Experimental evidence suggests the structural organization of telomeric nucleosomes is different from that of the bulk chromatin. This work presents a systematic search of the telomeric nucleosome arrangements. A low-resolution molecular model was used to evaluate the relative nucleosome packing energy. Structures with favorable energy were found, reducing the possible telomeric chromatin conformations to two different three-dimensional folds.
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Affiliation(s)
- Neva Besker
- Dipartimento di Chimica, Università La Sapienza, P.le A. Moro 5, I-0018, Rome, Italy
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39
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Yang SW, Kim DH, Lee JJ, Chun YJ, Lee JH, Kim YJ, Chung IK, Kim WT. Expression of the telomeric repeat binding factor gene NgTRF1 is closely coordinated with the cell division program in tobacco BY-2 suspension culture cells. J Biol Chem 2003; 278:21395-407. [PMID: 12646586 DOI: 10.1074/jbc.m209973200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Telomeres are vital for preserving chromosome integrity during cell division. Several genes encoding potential telomere-binding proteins have recently been identified in higher plants, but nothing is known about their function or regulation during cell division. In this study, we have isolated and characterized a cDNA clone, pNgTRF1, encoding a putative double-stranded telomeric repeat binding factor of Nicotiana glutinosa, a diploid tobacco plant. The predicted protein sequence of NgTRF1 (Mr = 75,000) contains a single Myb-like domain with significant homology to a corresponding motif in human TRF1/Pin2 and TRF2. Gel retardation assays revealed that bacterially expressed full-length NgTRF1 was able to form a specific complex only with probes containing three or more contiguous telomeric TTTAGGG repeats. The Myb-like domain of NgTRF1 is essential, but not sufficient, to bind the telomeric repeat sequence. The glutamine-rich extreme C-terminal region, which does not exist in animal proteins, was additionally required to form a specific telomere-protein complex. The dissociation constant (Kd) of the Myb motif plus the glutamine-rich domain of NgTRF1 to the two-telomeric repeat sequence was evaluated to be 4.5 +/- 0.2 x 10-9 m, which is comparable to that of the Myb domain of human TRF1. Expression analysis showed that NgTRF1 gene activity was inversely correlated with the cell division capacity of tobacco root cells and during the 9-day culture period of BY-2 suspension cells, while telomerase activity was positively correlated with cell division. In synchronized BY-2 cells, NgTRF1 was selectively expressed in G1 phase, whereas telomerase activity peaked in S phase. These findings suggest that telomerase activity and NgTRF1 expression are differentially regulated in an opposing fashion during growth and cell division in tobacco plants. The possible physiological functions of NgTRF1 in tobacco cells are also discussed.
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MESH Headings
- Amino Acid Motifs
- Amino Acid Sequence
- Arabidopsis/genetics
- Base Sequence
- Binding, Competitive
- Blotting, Northern
- Blotting, Southern
- Cell Division
- Cell Nucleus/metabolism
- Cloning, Molecular
- DNA/metabolism
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- G1 Phase
- Gene Deletion
- Gene Expression Regulation
- Gene Library
- Green Fluorescent Proteins
- Humans
- Indomethacin/pharmacology
- Kinetics
- Luminescent Proteins/metabolism
- Models, Genetic
- Molecular Sequence Data
- Mutation
- Nucleic Acid Hybridization
- Polymerase Chain Reaction
- Protein Binding
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- S Phase
- Sequence Homology, Amino Acid
- Species Specificity
- Subcellular Fractions
- Telomerase/metabolism
- Telomere/genetics
- Telomere/metabolism
- Telomeric Repeat Binding Protein 1/biosynthesis
- Telomeric Repeat Binding Protein 1/genetics
- Time Factors
- Nicotiana/genetics
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Affiliation(s)
- Seong Wook Yang
- Department of Biology, College of Science, Yonsei University, Seoul 120-749, Korea
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40
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Leeper T, Leulliot N, Varani G. The solution structure of an essential stem-loop of human telomerase RNA. Nucleic Acids Res 2003; 31:2614-21. [PMID: 12736311 PMCID: PMC156033 DOI: 10.1093/nar/gkg351] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The ribonucleoprotein enzyme telomerase maintains chromosome ends in most eukaryotes and is critical for a cell's genetic stability and its proliferative viability. All telomerases contain a catalytic protein component homologous to viral reverse transcriptases (TERT) and an RNA (TR) that provides the template sequence as well as a scaffold for ribonucleoprotein assembly. Vertebrate telomerase RNAs have three essential domains: the template, activation and stability domains. Here we report the NMR structure of an essential RNA element derived from the human telomerase RNA activation domain. The sequence forms a stem-loop structure stabilized by a GU wobble pair formed by two of the five unpaired residues capping a short double helical region. The remaining three loop residues are in a well-defined conformation and form phosphate-base stacking interactions reminiscent of other RNA loop structures. Mutations of these unpaired nucleotides abolish enzymatic activity. The structure rationalizes a number of biochemical observations, and allows us to propose how the loop may function in the telomerase catalytic cycle. The pre-formed structure of the loop exposes the bases of these three essential nucleotides and positions them to interact with other RNA sequences within TR, with the reverse transcriptase or with the newly synthesized telomeric DNA strand. The functional role of this stem-loop appears to be conserved in even distantly related organisms such as yeast and ciliates.
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Affiliation(s)
- Thomas Leeper
- Department of Biochemistry, University of Washington, Seattle WA 98195-1700, USA
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41
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Kim SH, Parrinello S, Kim J, Campisi J. Mus musculus and Mus spretus homologues of the human telomere-associated protein TIN2. Genomics 2003; 81:422-32. [PMID: 12676566 DOI: 10.1016/s0888-7543(02)00033-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Telomere length is regulated by TRF1, which binds telomeric DNA, and TIN2, which binds TRF1. Laboratory mice (Mus musculus) have long telomeres, although a related mouse species, Mus spretus, has human-sized telomeres. Because differences in TIN2 might explain these differences in telomere length, we cloned cDNAs encoding murine TIN2s and compared their sequence to that of human TIN2. M. musculus (Mm) and M. spretus TIN2s were >95% identical, but shared only 67% identity with human TIN2. An N-terminal truncation, or N-terminal fragment, of MmTIN2 elongated M. spretus telomeres. These findings suggest that mouse TIN2, like human TIN2, negatively regulates telomere length, and that N-terminal perturbations have dominant-negative effects. Our findings suggest that differences in TIN2 cannot explain the telomere length differences among Homo sapiens, M. musculus, and M. spretus. Nonetheless, M. spretus cells appear be a good system for studying the function of mouse telomere-associated proteins.
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Affiliation(s)
- Sahn-ho Kim
- Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
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42
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Bao K, Cohen SN. Recruitment of terminal protein to the ends of Streptomyces linear plasmids and chromosomes by a novel telomere-binding protein essential for linear DNA replication. Genes Dev 2003; 17:774-85. [PMID: 12651895 PMCID: PMC196017 DOI: 10.1101/gad.1060303] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Bidirectional replication of Streptomyces linear plasmids and chromosomes from a central origin produces unpaired 3'-leading-strand overhangs at the telomeres of replication intermediates. Filling in of these overhangs leaves a terminal protein attached covalently to the 5' DNA ends of mature replicons. We report here the essential role of a novel 80-kD DNA-binding protein (telomere-associated protein, Tap) in this process. Biochemical studies, yeast two-hybrid analysis, and immunoprecipitation/immunodepletion experiments indicate that Tap binds tightly to specific sequences in 3' overhangs and also interacts with Tpg, bringing Tpg to telomere termini. Using DNA microarrays to analyze the chromosomes of tap mutant bacteria, we demonstrate that survivors of Tap ablation undergo telomere deletion, chromosome circularization, and amplification of subtelomeric DNA. Microarray-based chromosome mapping at single-ORF resolution revealed common endpoints for independent deletions, identified amplified chromosomal ORFs adjacent to these endpoints, and quantified the copy number of these ORFs. Sequence analysis confirmed chromosome circularization and revealed the insertion of adventitious DNA between joined chromosome ends. Our results show that Tap is required for linear DNA replication in Streptomyces and suggest that it functions to recruit and position Tpg at the telomeres of replication intermediates. They also identify hotspots for the telomeric deletions and subtelomeric DNA amplifications that accompany chromosome circularization.
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Affiliation(s)
- Kai Bao
- Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5120, USA
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43
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Saldanha SN, Andrews LG, Tollefsbol TO. Assessment of telomere length and factors that contribute to its stability. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:389-403. [PMID: 12542689 DOI: 10.1046/j.1432-1033.2003.03410.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Short strands of tandem hexameric repeats known as telomeres cap the ends of linear chromosomes. These repeats protect chromosomes from degradation and prevent chromosomal end-joining, a phenomenon that could occur due to the end-replication problem. Telomeres are maintained by the activity of the enzyme telomerase. The total number of telomeric repeats at the terminal end of a chromosome determines the telomere length, which in addition to its importance in chromosomal stabilization is a useful indicator of telomerase activity in normal and malignant tissues. Telomere length stability is one of the important factors that contribute to the proliferative capacity of many cancer cell types; therefore, the detection and estimation of telomere length is extremely important. Until relatively recently, telomere lengths were analyzed primarily using the standard Southern blot technique. However, the complexities of this technique have led to the search for more simple and rapid detection methods. Improvements such as the use of fluorescent probes and the ability to sort cells have greatly enhanced the ease and sensitivity of telomere length measurements. Recent advances, and the limitations of these techniques are evaluated. Drugs that assist in telomere shortening may contribute to tumor regression. Therefore, factors that contribute to telomere stability may influence the efficiency of the drugs that have potential in cancer therapy. These factors in relation to telomere length are also examined in this analysis.
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Affiliation(s)
- Sabita N Saldanha
- Department of Biology, University of Alabama at Birmingham, AL 35294-1170, USA
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44
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Parenteau J, Wellinger RJ. Differential processing of leading- and lagging-strand ends at Saccharomyces cerevisiae telomeres revealed by the absence of Rad27p nuclease. Genetics 2002; 162:1583-94. [PMID: 12524334 PMCID: PMC1462396 DOI: 10.1093/genetics/162.4.1583] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Saccharomyces cerevisiae strains lacking the Rad27p nuclease, a homolog of the mammalian FEN-1 protein, display an accumulation of extensive single-stranded G-tails at telomeres. Furthermore, the lengths of telomeric repeats become very heterogeneous. These phenotypes could be the result of aberrant Okazaki fragment processing of the C-rich strand, elongation of the G-rich strand by telomerase, or an abnormally high activity of the nucleolytic activities required to process leading-strand ends. To distinguish among these possibilities, we analyzed strains carrying a deletion of the RAD27 gene and also lacking genes required for in vivo telomerase activity. The results show that double-mutant strains died more rapidly than strains lacking only telomerase components. Furthermore, in such strains there is a significant reduction in the signals for G-tails as compared to those detected in rad27delta cells. The results from studies of the replication intermediates of a linear plasmid in rad27delta cells are consistent with the idea that only one end of the plasmid acquires extensive G-tails, presumably the end made by lagging-strand synthesis. These data further support the notion that chromosome ends have differential requirements for end processing, depending on whether the ends were replicated by leading- or lagging-strand synthesis.
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Affiliation(s)
- Julie Parenteau
- Département de Microbiologie et Infectiologie, Faculté de Médecine, Université de Sherbooke, Sherbooke, Quebec J1H 5N4, Canada
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45
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Krtolica A, Campisi J. Cancer and aging: a model for the cancer promoting effects of the aging stroma. Int J Biochem Cell Biol 2002; 34:1401-14. [PMID: 12200035 DOI: 10.1016/s1357-2725(02)00053-5] [Citation(s) in RCA: 203] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The incidence of cancer rises exponentially with age in humans and many other mammalian species. Malignant tumors are caused by an accumulation of oncogenic mutations. In addition, malignant tumorigenesis requires a permissive tissue environment in which mutant cells can survive, proliferate, and express their neoplastic phenotype. We propose that the age-related increase in cancer results from a synergy between the accumulation of mutations and age-related, pro-oncogenic changes in the tissue milieu. Most age-related cancers derive from the epithelial cells of renewable tissues. An important element of epithelial tissues is the stroma, the sub-epithelial layer composed of extracellular matrix and several cell types. The stroma is maintained, remodeled and repaired by resident fibroblasts, supports and instructs the epithelium, and is essential for epithelial function. One change that occurs in tissues during aging is the accumulation of epithelial cells and fibroblasts that have undergone cellular senescence. Cellular senescence irreversibly arrests proliferation in response to damage or stimuli that put cells at risk for neoplastic transformation. Senescent cells secrete factors that can disrupt tissue architecture and/or stimulate nearby cells to proliferate. We therefore speculate that their presence may create a pro-oncogenic tissue environment that synergizes with oncogenic mutations to drive the rise in cancer incidence with age. Recent evidence lends support to this idea, and suggests that senescent stromal fibroblasts may be particularly adept at creating a tissue environment that can promote the development of age-related epithelial cancers.
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Affiliation(s)
- Ana Krtolica
- Lawrence Berkeley National Laboratory, Life Sciences Division, Mailstop 84-171, 1 Cyclotron Road, Berkeley, CA 94720, USA
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46
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Abstract
The continuous growth of advanced malignancies almost universally correlates with the reactivation of telomerase. While there is still a great deal of basic and applied research to be done, telomerase remains a very attractive novel target for cancer therapeutics. In this review, we will discuss the challenges and the pros and cons of the most promising antitelomerase approaches currently being investigated.
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Affiliation(s)
- Jerry W Shay
- The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75309, USA.
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47
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Abstract
Most human cancer cells show signs of genome instability, ranging from elevated mutation rates to gross chromosomal rearrangements and alterations in chromosome number. Little is known about the molecular mechanisms that generate this instability or how it is suppressed in normal cells. Recent studies of the yeast Saccharomyces cerevisiae have begun to uncover the extensive and redundant pathways that keep the rate of genome rearrangements at very low levels. These studies, which we review here, have implicated more than 50 genes in the suppression of genome instability, including genes that function in S-phase checkpoints, recombination pathways, and telomere maintenance. Human homologs of several of these genes have well-established roles as tumor suppressors, consistent with the hypothesis that the mechanisms preserving genome stability in yeast are the same mechanisms that go awry in cancer.
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Affiliation(s)
- Richard D Kolodner
- Ludwig Institute for Cancer Research, Cancer Center and Department of Medicine, CMME3058, 9500 Gilman Drive, University of California-San Diego School of Medicine, La Jolla, CA 92093, USA.
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48
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Cao Y, Li H, Deb S, Liu JP. TERT regulates cell survival independent of telomerase enzymatic activity. Oncogene 2002; 21:3130-8. [PMID: 12082628 DOI: 10.1038/sj.onc.1205419] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2001] [Revised: 01/19/2002] [Accepted: 02/20/2002] [Indexed: 02/08/2023]
Abstract
Human telomerase reverse transcriptase (hTERT), the catalytic subunit of telomerase, plays a pivotal role in the maintenance of telomeres and cell proliferation. Here we report that down-regulation of hTERT induces apoptosis independently of telomerase enzymatic activity in human breast cancer cells. Expression of a hTERT mutant lacking telomerase activity rescues the cells with lowered telomerase without inducing cell death. With similar patterns of subcellular distribution to that of the tumor suppressor protein p53 during mitosis, hTERT interacts with p53 and poly(ADP-ribose) polymerase (PARP). Decreasing p53 expression in intact cells worsens, and increasing p53 prevents, cell death induced by lowering hTERT. Thus, hTERT maintains cell survival and proliferation via both telomerase enzymatic activity-dependent telomere lengthening and enzymatic activity-independent intermolecular interactions involving p53 and PARP.
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Affiliation(s)
- Ying Cao
- Molecular Signaling Laboratory, Baker Medical Research Institute, Commercial Road, Prahran, Victoria 3181, Australia
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49
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Fajkus J, Simícková M, Maláska J. Tiptoeing to chromosome tips: facts, promises and perils of today's human telomere biology. Philos Trans R Soc Lond B Biol Sci 2002; 357:545-62. [PMID: 12028791 PMCID: PMC1692969 DOI: 10.1098/rstb.2001.1053] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The past decade has witnessed an explosion of knowledge concerning the structure and function of chromosome terminal structures-telomeres. Today's telomere research has advanced from a pure descriptive approach of DNA and protein components to an elementary understanding of telomere metabolism, and now to promising applications in medicine. These applications include 'passive' ones, among which the use of analysis of telomeres and telomerase (a cellular reverse transcriptase that synthesizes telomeres) for cancer diagnostics is the best known. The 'active' applications involve targeted downregulation or upregulation of telomere synthesis, either to mortalize immortal cancer cells, or to rejuvenate mortal somatic cells and tissues for cellular transplantations, respectively. This article reviews the basic data on structure and function of human telomeres and telomerase, as well as both passive and active applications of human telomere biology.
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Affiliation(s)
- J Fajkus
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, CZ-612 65 Brno, Czech Republic.
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Yang SW, Jin E, Chung IK, Kim WT. Cell cycle-dependent regulation of telomerase activity by auxin, abscisic acid and protein phosphorylation in tobacco BY-2 suspension culture cells. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 29:617-26. [PMID: 11874574 DOI: 10.1046/j.0960-7412.2001.01244.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Telomerase is a specialized RNA-directed DNA polymerase that adds telomeric repeats onto the ends of linear eukaryotic chromosomes. It was recently reported that the low, basal level of telomerase activity markedly increased at early S-phase of the cell cycle, and auxin further increased the S-phase-specific telomerase activity in tobacco BY-2 cells. In this study we show that abscisic acid (ABA), a phytohormone known to induce the cyclin-dependent protein kinase inhibitor, effectively abolished both the auxin- and S-phase-specific activation of telomerase in a concentration- and time-dependent fashion in synchronized tobacco BY-2 cells. These results suggest that there exists a hormonal cross-talk between auxin and ABA for the regulation of telomerase activity during the cell cycle of tobacco cells. Treatment of synchronized BY-2 cells with the protein kinase inhibitor staurosporine or H-7 effectively prevented the S-phase-specific activation of telomerase activity. By contrast, when okadaic acid or cantharidin, potent inhibitors of protein phosphatase 2A (PP2A), was applied to the cells, the S-phase-specific high level of telomerase activity was continuously maintained in the cell cycle for at least 14 h after release from M-phase arrest. Incubation of tobacco cell extracts with exogenous PP2A rapidly abrogated in vitro telomerase activity, while okadaic acid and cantharidin blocked the action of PP2A, effectively restoring in vitro telomerase activity. Taken together, these findings are discussed in the light of the suggestion that antagonistic functions of auxin and ABA, and reciprocal phosphorylation and dephosphorylation of telomerase complex, are necessarily involved in the cell cycle-dependent modulation of telomerase activity in tobacco cells.
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Affiliation(s)
- Seong Wook Yang
- Department of Biology, College of Science, Yonsei University, Seoul 120-749, Korea
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