101
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d'Adda di Fagagna F, Teo SH, Jackson SP. Functional links between telomeres and proteins of the DNA-damage response. Genes Dev 2004; 18:1781-99. [PMID: 15289453 DOI: 10.1101/gad.1214504] [Citation(s) in RCA: 210] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In response to DNA damage, cells engage a complex set of events that together comprise the DNA-damage response (DDR). These events bring about the repair of the damage and also slow down or halt cell cycle progression until the damage has been removed. In stark contrast, the ends of linear chromosomes, telomeres, are generally not perceived as DNA damage by the cell even though they terminate the DNA double-helix. Nevertheless, it has become clear over the past few years that many proteins involved in the DDR, particularly those involved in responding to DNA double-strand breaks, also play key roles in telomere maintenance. In this review, we discuss the current knowledge of both the telomere and the DDR, and then propose an integrated model for the events associated with the metabolism of DNA ends in these two distinct physiological contexts.
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102
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Abstract
The DNA-dependent protein kinase (DNA-PK) plays a critical role in DNA double-strand break (DSB) repair and in V(D)J recombination. DNA-PK also plays a very important role in triggering apoptosis in response to severe DNA damage or critically shortened telomeres. Paradoxically, components of the DNA-PK complex are present at the mammalian telomere where they function in capping chromosome ends to prevent them from being mistaken for double-strand breaks. In addition, DNA-PK appears to be involved in mounting an innate immune response to bacterial DNA and to viral infection. As DNA-PK localizes very rapidly to DNA breaks and phosphorylates itself and other damage-responsive proteins, it appears that DNA-PK serves as both a sensor and a transducer of DNA-damage signals. The many roles of DNA-PK in the mammalian cell are discussed in this review with particular emphasis on recent advances in our understanding of the phosphorylation events that take place during the activation of DNA-PK at DNA breaks.
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Affiliation(s)
- Sandeep Burma
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
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103
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Maser RS, DePinho RA. Telomeres and the DNA damage response: why the fox is guarding the henhouse. DNA Repair (Amst) 2004; 3:979-88. [PMID: 15279784 DOI: 10.1016/j.dnarep.2004.05.009] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
DNA double strand breaks (DSBs) are repaired by an extensive network of proteins that recognize damaged DNA and catalyze its repair. By virtue of their similarity, the normal ends of linear chromosomes and internal DNA DSBs are both potential substrates for DSB repair enzymes. Thus, telomeres, specialized nucleo-protein complexes that cap chromosomal ends, serve a critical function to differentiate themselves from internal DNA strand breaks, and as a result prevent genomic instability that can result from their inappropriate involvement in repair reactions. Telomeres that become critically short due to failure of telomere maintenance mechanisms, or which become dysfunctional by loss of telomere binding proteins, elicit extensive checkpoint responses that in normal cells blocks proliferation. In this situation, the DNA DSB repair machinery plays a major role in responding to these "damaged" telomeres - creating chromosome fusions or capturing telomeres from other chromosomes in an effort to rid the cell of the perceived damage. However, a surprising aspect of telomere maintenance is that many of the same proteins that facilitate this repair of damaged telomeres are also necessary for their proper integrity. Here, we review recent work defining the roles for DSB repair machinery in telomere maintenance and in response to telomere dysfunction.
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Affiliation(s)
- Richard S Maser
- Department of Medical Oncology, Dana-Farber Cancer Institute, Departments of Medicine and Genetics, Harvard Medical School, Boston, MA 02115, USA.
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104
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Myung K, Ghosh G, Fattah FJ, Li G, Kim H, Dutia A, Pak E, Smith S, Hendrickson EA. Regulation of telomere length and suppression of genomic instability in human somatic cells by Ku86. Mol Cell Biol 2004; 24:5050-9. [PMID: 15143195 PMCID: PMC416406 DOI: 10.1128/mcb.24.11.5050-5059.2004] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ku86 plays a key role in nonhomologous end joining in organisms as evolutionarily disparate as bacteria and humans. In eukaryotic cells, Ku86 has also been implicated in the regulation of telomere length although the effect of Ku86 mutations varies considerably between species. Indeed, telomeres either shorten significantly, shorten slightly, remain unchanged, or lengthen significantly in budding yeast, fission yeast, chicken cells, or plants, respectively, that are null for Ku86 expression. Thus, it has been unclear which model system is most relevant for humans. We demonstrate here that the functional inactivation of even a single allele of Ku86 in human somatic cells results in profound telomere loss, which is accompanied by an increase in chromosomal fusions, translocations, and genomic instability. Together, these experiments demonstrate that Ku86, separate from its role in nonhomologous end joining, performs the additional function in human somatic cells of suppressing genomic instability through the regulation of telomere length.
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Affiliation(s)
- Kyungjae Myung
- 6-155 Jackson Hall, Department of Biochemistry, Molecular Biology, and Biophysics, 321 Church St. SE, University of Minnesota Medical School, Minneapolis, MN 55355, USA
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105
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Lee GE, Yu EY, Cho CH, Lee J, Muller MT, Chung IK. DNA-protein kinase catalytic subunit-interacting protein KIP binds telomerase by interacting with human telomerase reverse transcriptase. J Biol Chem 2004; 279:34750-5. [PMID: 15190070 DOI: 10.1074/jbc.m401843200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Telomere homeostasis, a process that is essential for continued cell proliferation and genomic stability, is regulated by endogenous telomerase and a collection of associated proteins. In this paper, a protein called KIP (previously reported as a protein that binds specifically to DNA-dependent protein kinase), has been identified as a telomerase-regulating activity based on the following pieces of evidence. First, complexes between KIP and the catalytic subunit of telomerase (hTERT) were identified using the yeast two-hybrid technique. Second, antibodies specific to KIP immunoprecipitate human telomerase in cell-free extracts. Third, immunolocalization experiments demonstrate that KIP is a nuclear protein that co-localizes with hTERT in cells. Fourth, KIP binds to hTERT both in vitro and in vivo in the absence of human telomerase RNA or telomeric DNA, thus defining the catalytic subunit of telomerase as the site of physical interaction. Fifth, co-immunoprecipitation experiments suggest that KIP-hTERT complexes form readily in cells and that overexpression of KIP in telomerase-positive cells increases endogenous telomerase activity. Finally, continued overexpression of KIP (60 population doublings) resulted in cells with elongated telomeres; thus, KIP directly or indirectly stimulates telomerase activity through hTERT and contributes to telomere lengthening. The collective data in this paper suggest that KIP plays a positive role in telomere length maintenance and/or regulation and may represent a novel target for anti-cancer drug development.
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Affiliation(s)
- Gun Eui Lee
- Department of Biology and Molecular Aging Research Center, Yonsei University, 134 Shinchon-dong, Seoul 120-749, Korea
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106
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Tarsounas M, Muñoz P, Claas A, Smiraldo PG, Pittman DL, Blasco MA, West SC. Telomere maintenance requires the RAD51D recombination/repair protein. Cell 2004; 117:337-47. [PMID: 15109494 DOI: 10.1016/s0092-8674(04)00337-x] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2003] [Revised: 03/02/2004] [Accepted: 03/08/2004] [Indexed: 11/21/2022]
Abstract
The five RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, and XRCC3) are required in mammalian cells for normal levels of genetic recombination and resistance to DNA-damaging agents. We report here that RAD51D is also involved in telomere maintenance. Using immunofluorescence labeling, electron microscopy, and chromatin immunoprecipitation assays, RAD51D was shown to localize to the telomeres of both meiotic and somatic cells. Telomerase-positive Rad51d(-/-) Trp53(-/-) primary mouse embryonic fibroblasts (MEFs) exhibited telomeric DNA repeat shortening compared to Trp53(-/-) or wild-type MEFs. Moreover, elevated levels of chromosomal aberrations were detected, including telomeric end-to-end fusions, a signature of telomere dysfunction. Inhibition of RAD51D synthesis in telomerase-negative immortalized human cells by siRNA also resulted in telomere erosion and chromosome fusion. We conclude that RAD51D plays a dual cellular role in both the repair of DNA double-strand breaks and telomere protection against attrition and fusion.
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MESH Headings
- Animals
- Antibodies, Monoclonal/metabolism
- Blotting, Western
- Cell Line, Transformed
- Cell Transformation, Neoplastic
- Chromatin/metabolism
- Chromosome Aberrations
- DNA Damage
- DNA Repair
- DNA, Cruciform/metabolism
- DNA, Cruciform/ultrastructure
- DNA-Binding Proteins/metabolism
- DNA-Binding Proteins/ultrastructure
- Fibroblasts/metabolism
- HeLa Cells
- Humans
- In Situ Hybridization, Fluorescence
- Male
- Mice
- Mice, Knockout
- Precipitin Tests
- RNA, Small Interfering/metabolism
- Recombination, Genetic
- Spermatocytes/metabolism
- Spermatocytes/ultrastructure
- Telomere/metabolism
- Telomeric Repeat Binding Protein 2/metabolism
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Affiliation(s)
- Madalena Tarsounas
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms, Hertfordshire, EN6 3LD, United Kingdom
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107
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Espejel S, Martín M, Klatt P, Martín-Caballero J, Flores JM, Blasco MA. Shorter telomeres, accelerated ageing and increased lymphoma in DNA-PKcs-deficient mice. EMBO Rep 2004; 5:503-9. [PMID: 15105825 PMCID: PMC1299048 DOI: 10.1038/sj.embor.7400127] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2003] [Revised: 01/26/2004] [Accepted: 02/18/2004] [Indexed: 12/14/2022] Open
Abstract
Non-homologous end joining (NHEJ) is the principal repair mechanism used by mammalian cells to cope with double-strand breaks (DSBs) that continually occur in the genome. One of the key components of the mammalian NHEJ machinery is the DNA-PK complex, formed by the Ku86/70 heterodimer and the DNA-PK catalytic subunit (DNA-PKcs). Here, we report on the detailed life-long follow-up of DNA-PKcs-defective mice. Apart from defining a role of DNA-PKcs in telomere length maintenance in the context of the ageing organism, we observed that DNA-PKcs-defective mice had a shorter life span and showed an earlier onset of ageing-related pathologies than the corresponding wild-type littermates. In addition, DNA-PKcs ablation was associated with a markedly higher incidence of T lymphomas and infections. In conclusion, these data link the dual role of DNA-PKcs in DNA repair and telomere length maintenance to organismal ageing and cancer.
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Affiliation(s)
- Silvia Espejel
- Molecular Oncology Program, Spanish National Cancer Centre (CNIO), Melchor Fernández Almagro 3, E-28029, Madrid, Spain
| | - Marta Martín
- Department of Cell Biology, Physiology and Immunology, and Institute of Biotechnology and Biomedicine, Universitat Autonoma de Barcelona, Barcelona 08193, Spain
| | - Peter Klatt
- Molecular Oncology Program, Spanish National Cancer Centre (CNIO), Melchor Fernández Almagro 3, E-28029, Madrid, Spain
| | - Juan Martín-Caballero
- Molecular Oncology Program, Spanish National Cancer Centre (CNIO), Melchor Fernández Almagro 3, E-28029, Madrid, Spain
| | - Juana M Flores
- Animal Surgery and Medicine Department, Facultad de Veterinaria, Universidad Complutense de Madrid, E-28040, Madrid, Spain
| | - María A Blasco
- Molecular Oncology Program, Spanish National Cancer Centre (CNIO), Melchor Fernández Almagro 3, E-28029, Madrid, Spain
- Tel: +34 917328031; Fax: +34 917328028; E-mail:
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108
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Lieber MR, Karanjawala ZE. Ageing, repetitive genomes and DNA damage. Nat Rev Mol Cell Biol 2004; 5:69-75. [PMID: 14708011 DOI: 10.1038/nrm1281] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The mitochondrial production of reactive oxygen species is inversely proportional to longevity in animals. A key question now is, which molecules, among those that are oxidized, affect the lifespan of the organism most significantly?
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Affiliation(s)
- Michael R Lieber
- University of Southern California Norris Comprehensive Cancer Center, Room 5428, Department of Pathology, 1441 Eastlake Avenue, MC9176, Los Angeles, California 90033, USA.
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109
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Murnane JP, Sabatier L. Chromosome rearrangements resulting from telomere dysfunction and their role in cancer. Bioessays 2004; 26:1164-74. [PMID: 15499579 DOI: 10.1002/bies.20125] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Telomeres play a vital role in protecting the ends of chromosomes and preventing chromosome fusion. The failure of cancer cells to properly maintain telomeres can be an important source of the chromosome instability involved in cancer cell progression. Telomere loss results in sister chromatid fusion and prolonged breakage/fusion/bridge (B/F/B) cycles, leading to extensive DNA amplification and large deletions. These B/F/B cycles end primarily when the unstable chromosome acquires a new telomere by translocation of the ends of other chromosomes. Many of these translocations are nonreciprocal, resulting in the loss of the telomere from the donor chromosome, providing a mechanism for transfer of instability from one chromosome to another until a chromosome acquires a telomere by a mechanism other than nonreciprocal translocation. B/F/B cycles can also result in other forms of chromosome rearrangements, including double-minute chromosomes and large duplications. Thus, the loss of a single telomere can result in instability in multiple chromosomes, and generate many of the types of rearrangements commonly associated with human cancer.
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Affiliation(s)
- John P Murnane
- Radiation Oncology Research Laboratory, University of California, San Francisco, CA 94103, USA.
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110
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Abstract
The protective "cap" that assembles at chromosome ends recruits and controls an intricate network of biochemical activities, each one critical for telomere structure and the maintenance of genomic stability. Recent studies have uncovered the components of telomere caps and have started to define the pathways that lead from telomere dysfunction to chromosomal catastrophe.
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Affiliation(s)
- Miguel Godinho Ferreira
- Telomere Biology Laboratory, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3PX, United Kingdom
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111
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Rebuzzini P, Lisa A, Giulotto E, Mondello C. Chromosomal end-to-end fusions in immortalized mouse embryonic fibroblasts deficient in the DNA-dependent protein kinase catalytic subunit. Cancer Lett 2004; 203:79-86. [PMID: 14670620 DOI: 10.1016/j.canlet.2003.08.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Telomeres constitute the ends of the linear eukaryotic chromosomes and are essential for the maintenance of chromosome stability and genome integrity. One of the consequences of an altered telomere structure is the formation of telomeric fusions (TFs), that is aberrant chromosomes in which two elements are fused at their telomeres. Proteins involved in the non-homologous end joining pathway for the repair of the DNA double strand breaks, as the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), contribute to the formation of a functional telomere. To investigate the role of DNA-PKcs in telomere functionality, we studied the frequency of TFs in mouse embryonic fibroblasts obtained from animals in which the DNA-PKcs gene had been inactivated; the analysis was performed prior and after spontaneous immortalization in culture. Our results suggest that DNA-PKcs deficiency has a limited effect, if any, on TF formation in primary cells, while it further increases chromosomal instability in immortalized cells. In fact, the frequency of TFs was significantly higher in immortalized DNA-PKcs mutant cells compared to wild type cells. Together with TFs, we also found metacentric or submetacentric chromosomes in which no telomeric sequences were detected at the joining site. The frequency of this anomaly, that resembles the Robertsonian translocations observed in wild mice, was independent of the DNA-PKcs genotype. This suggests that the formation of these rearranged chromosomes does not rely on a functional DNA-PKcs.
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Affiliation(s)
- Paola Rebuzzini
- Istituto di Genetica Molecolare, CNR, Via Abbiategrasso 207, 27100 Pavia, Italy
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112
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Abstract
Data have been emerging over the past two decades concerning two phenomena in which important biological effects of ionizing radiation arise in cells that in themselves receive no radiation exposure. In the first, radiation-induced genomic instability, biological effects occur in the progeny of the irradiated cell after many generations of cell division. In the second, radiation-induced bystander effects, they arise in cells that receive no radiation exposure as a consequence of damage signals transmitted from neighboring irradiated cells; transmission may be mediated either by direct intercellular communication through gap junctions, or by factors released into the surrounding medium. In both phenomena, the biological effects appear to be associated with an upregulation of oxidative metabolism. The present paper is designed to review the historical background leading to our current knowledge of these two phenomena, and to indicate some future directions for research that will allow us to assess better their importance in the health effects of exposure to ionizing radiation.
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Affiliation(s)
- John B Little
- Laboratory of Radiobiology, Harvard School of Public Health, 665 Huntington Avenue Boston, MA 02115, USA.
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113
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Krutilina RI, Smirnova AN, Mudrak OS, Pleskach NM, Svetlova MP, Oei SL, Yau PM, Bradbury EM, Zalensky AO, Tomilin NV. Protection of internal (TTAGGG)n repeats in Chinese hamster cells by telomeric protein TRF1. Oncogene 2003; 22:6690-8. [PMID: 14555982 DOI: 10.1038/sj.onc.1206745] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Chinese hamster cells have large interstitial (TTAGGG) bands (ITs) which are unstable and should be protected by an unknown mechanism. Here, we expressed in Chinese hamster V79 cells green fluorescent protein (GFP)-tagged human TRF1, and found that a major fraction of GFP-TRF1 bound to ITs is diffusionally mobile. This fraction strongly decreases after treatment of cells with wortmannin, a protein kinase inhibitor, and this drug also increases the frequency of chromosome aberrations. Ionizing radiation does not induce detectable translocation of GFP-TRF1 to the sites of random double-strand breaks visualized using antibodies against histone gamma-H2AX. TRF1 is known to be eliminated from telomeres by overexpression of tankyrase 1 which induces TRF1 poly(ADP-ribosyl)ation. We transfected V79 cells by plasmid encoding tankyrase 1 and found that the frequency of chromosome rearrangements is increased in these cells independently of their treatment by IR. Taken together, our results suggest that TRF1 is involved in sequence-specific protection of internal nontelomeric (TTAGGG)n repeats.
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Affiliation(s)
- Raisa Ivanovna Krutilina
- Laboratory of Chromosome Stability, Institute of Cytology, Russian Academy of Sciences, 194064 St Petersburg, Russia
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114
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M'kacher R, Bennaceur A, Farace F, Laugé A, Plassa LF, Wittmer E, Dossou J, Violot D, Deutsch E, Bourhis J, Stoppa-Lyonnet D, Ribrag V, Carde P, Parmentier C, Bernheim A, Turhan AG. Multiple molecular mechanisms contribute to radiation sensitivity in mantle cell lymphoma. Oncogene 2003; 22:7905-12. [PMID: 12970738 DOI: 10.1038/sj.onc.1206826] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Mantle cell lymphomas (MCL) are characterized by their aggressive behavior and poor response to chemotherapy regimens. We report here evidence of increased in vitro radiation sensitivity in two cell lines that we have generated from two MCL patients (UPN1 and UPN2). However, despite their increased radiation sensitivity, UPN2 cells were totally resistant to apoptotic cell death, whereas UPN1 cells underwent massive apoptosis 6 h after irradiation. The frequency of induced chromosomal abnormalities was higher in UPN1 as compared to UPN2. Distinct mechanisms have been found to contribute to this phenotype: a major telomere shortening (UPN1 and UPN2), deletion of one ATM allele and a point mutation in the remaining allele in UPN2, mutation of p53 gene (UPN1 and UPN2) with absence of functional p53 as revealed by functional yeast assays. After irradiation, Ku70 levels in UPN1 increased and decreased in UPN2, whereas in the same conditions, DNA-PKcs protein levels decreased in UPN1 and remained unchanged in UPN2. Thus, irradiation-induced apoptotic cell death can occur despite the nonfunctional status of p53 (UPN1), suggesting activation of a unique pathway in MCL cells for the induction of this event. Overall, our study demonstrates that MCL cells show increased radiation sensitivity, which can be the result of distinct molecular events. These findings could clinically be exploited to increase the dismal response rates of MCL patients to the current chemotherapy regimens.
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Affiliation(s)
- R M'kacher
- Department of Medicine, UPRES EA 27-10, Villejuif, France
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115
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Bai Y, Murnane JP. Telomere instability in a human tumor cell line expressing a dominant-negative WRN protein. Hum Genet 2003; 113:337-47. [PMID: 12827497 DOI: 10.1007/s00439-003-0972-y] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2003] [Accepted: 05/12/2003] [Indexed: 11/25/2022]
Abstract
Werner Syndrome (WS) is an autosomal recessive disease characterized by premature aging and chromosome instability. The protein involved in WS, WRN, is a RecQ-type helicase that also has exonuclease activity. WRN has been demonstrated to bind to a variety of other proteins, including RPA, DNA-PKcs, and TRF2, suggesting that WRN is involved in DNA replication, repair, recombination, and telomere maintenance. In culture, WS cells show premature senescence, which can be overcome by transfection with an expression vector containing the gene for the catalytic subunit of telomerase. However, telomerase expression does not eliminate chromosome instability in WS cells, which led to the proposal that telomere loss is not the cause of the high rate of chromosome rearrangements in WS cells. In the present study, we have investigated how a WRN protein containing a dominant-negative mutation (K577M-WRN) influences the stability of telomeres in a human tumor cell line expressing telomerase. The results demonstrate an increased rate of telomere loss and chromosome fusion in cells expressing K577M-WRN. Expression of K577M-WRN results in reduced levels of telomerase activity, however, the absence of detectable changes in average telomere length demonstrates that WRN-associated telomere loss results from stochastic events involving complete telomere loss or loss of telomere capping function. Thus, telomere loss can contribute to chromosome instability in cells deficient in WRN regardless of the expression of telomerase activity.
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Affiliation(s)
- Yongli Bai
- Radiation Oncology Research Laboratory, University of California San Francisco, 1855 Folsom Street, MCB 200, San Francisco, CA 94103, USA
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116
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Abstract
Chromosome ends, or telomeres, are formed by a special chromatin structure that protects them from recombination and degradation, thus preventing end-to-end chromosome fusions and other chromosomal aberrations. The functionality of telomeres, and that of the cellular activity that synthesizes them, telomerase, has been shown to impact on both cancer and aging, as well as on the organismal sensitivity to ionizing radiation. This review focuses on the analysis of different mouse models for proteins that are important for telomere function, which have highlighted the importance of telomeres and telomerase for cancer and aging.
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Affiliation(s)
- María A Blasco
- Department of Immunology and Oncology, National Centre of Biotechnology, Madrid, Spain.
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117
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Karlseder J, Kachatrian L, Takai H, Mercer K, Hingorani S, Jacks T, de Lange T. Targeted deletion reveals an essential function for the telomere length regulator Trf1. Mol Cell Biol 2003; 23:6533-41. [PMID: 12944479 PMCID: PMC193696 DOI: 10.1128/mcb.23.18.6533-6541.2003] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human telomeric DNA binding factor TRF1 (hTRF1) and its interacting proteins TIN2, tankyrase 1 and 2, and PINX1 have been implicated in the regulation of telomerase-dependent telomere length maintenance. Here we show that targeted deletion of exon 1 of the mouse gene encoding Trf1 causes early (day 5 to 6 postcoitus) embryonic lethality. The absence of telomerase did not alter the Terf1(ex1Delta/ex1Delta) lethality, indicating that the phenotype was not due to inappropriate telomere elongation by telomerase. Terf1(ex1Delta/ex1Delta) blastocysts had a severe growth defect of the inner cell mass that was accompanied by apoptosis. However, no evidence was found for telomere uncapping causing this cell death; chromosome spreads of Terf1(ex1Delta/ex1Delta) blastocysts did not reveal chromosome end-to-end fusions, and p53 deficiency only briefly delayed Terf1(ex1Delta/ex1Delta) lethality. These data suggest that murine Trf1 has an essential function that is independent of telomere length regulation.
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Affiliation(s)
- Jan Karlseder
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, NY 10021, USA
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118
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Chakhparonian M, Wellinger RJ. Telomere maintenance and DNA replication: how closely are these two connected? Trends Genet 2003; 19:439-46. [PMID: 12902162 DOI: 10.1016/s0168-9525(03)00135-5] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The maintenance of the DNA at chromosome ends, the telomeres, depends on conventional semiconservative replication and on the action of telomerase, a specialized reverse transcriptase. Current research strongly suggests a regulatory interplay between this conventional semiconservative replication and telomerase, thus ensuring that no sequences are lost at the very ends of the telomeres during replication. Here, we describe recent findings on the interactions between the conventional replication machinery and telomere replication, and we discuss how DNA-integrity checkpoints might impinge on both the processing of the telomeric DNA ends and the establishment of the DNA end structure required for end protection and genome stability.
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Affiliation(s)
- Mikhail Chakhparonian
- Department of Microbiology and Infectiology, Faculty of Medicine, Université de Sherbrooke, 3001 12th Ave N., Sherbrooke (QC), Canada J1H 5N4
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119
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Jaco I, Muñoz P, Goytisolo F, Wesoly J, Bailey S, Taccioli G, Blasco MA. Role of mammalian Rad54 in telomere length maintenance. Mol Cell Biol 2003; 23:5572-80. [PMID: 12897131 PMCID: PMC166323 DOI: 10.1128/mcb.23.16.5572-5580.2003] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The homologous recombination (HR) DNA repair pathway participates in telomere length maintenance in yeast but its putative role at mammalian telomeres is unknown. Mammalian Rad54 is part of the HR machinery, and Rad54-deficient mice show a reduced HR capability. Here, we show that Rad54-deficient mice also show significantly shorter telomeres than wild-type controls, indicating that Rad54 activity plays an essential role in telomere length maintenance in mammals. Rad54 deficiency also resulted in an increased frequency of end-to-end chromosome fusions involving telomeres compared to the controls, suggesting a putative role of Rad54 in telomere capping. Finally, the study of mice doubly deficient for Rad54 and DNA-PKcs showed that telomere fusions due to DNA-PKcs deficiency were not rescued in the absence of Rad54, suggesting that they are not mediated by Rad54 activity.
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Affiliation(s)
- Isabel Jaco
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain, Department of Genetics, Erasmus University, Rotterdam, The Netherlands, Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Purificación Muñoz
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain, Department of Genetics, Erasmus University, Rotterdam, The Netherlands, Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Fermín Goytisolo
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain, Department of Genetics, Erasmus University, Rotterdam, The Netherlands, Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Joanna Wesoly
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain, Department of Genetics, Erasmus University, Rotterdam, The Netherlands, Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Susan Bailey
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain, Department of Genetics, Erasmus University, Rotterdam, The Netherlands, Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Guillermo Taccioli
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain, Department of Genetics, Erasmus University, Rotterdam, The Netherlands, Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - María A. Blasco
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain, Department of Genetics, Erasmus University, Rotterdam, The Netherlands, Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118
- Corresponding author. Mailing address: Department of Immunology and Oncology, Centro Nacional de Biotecnología, Madrid E-28049, Spain. Phone: 34-915854846. Fax: 34-913720493. E-mail:
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120
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Desmaze C, Soria JC, Freulet-Marrière MA, Mathieu N, Sabatier L. Telomere-driven genomic instability in cancer cells. Cancer Lett 2003; 194:173-82. [PMID: 12757975 DOI: 10.1016/s0304-3835(02)00704-8] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Telomeres, the ends of linear chromosomes, play a major role in the maintenance of genome integrity. Telomerase or alternative lengthening of telomeres (ALT) mechanisms exist in most cancer cells in order to stabilize telomere length by the addition of telomeric repeats. Telomere loss can be dramatically mutagenic. Chromosomes lacking one telomere remain unstable until they are capped, generating chromosomal instability, gene amplification via breakage/fusion/bridge (B/F/B) cycles and resulting in chromosome imbalances. The chronology of the occurrence of gene amplification and chromosome imbalances detected in human tumors is still unknown. All of the aberrations that occur prior to, during or after activation of a telomere maintenance mechanism promote the development of cancer.
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Affiliation(s)
- Chantal Desmaze
- CEA-DSV/DRR/LRO, 18 Route du Panorama, 92265 Cedex, Fontenay aux Roses, France
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121
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Reichenbach P, Höss M, Azzalin CM, Nabholz M, Bucher P, Lingner J. A human homolog of yeast Est1 associates with telomerase and uncaps chromosome ends when overexpressed. Curr Biol 2003; 13:568-74. [PMID: 12676087 DOI: 10.1016/s0960-9822(03)00173-8] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Telomeres protect the eukaryotic chromosome ends from degradation and fusion. They are maintained by the ribonucleoprotein telomerase, the core of which is composed of a reverse transcriptase (TERT) and a RNA subunit. In the yeast Saccharomyces cerevisiae, a third critical telomerase subunit, the Ever Shorter Telomeres 1 (EST1) gene product, recruits or activates telomerase at the 3' end of telomeres. Est1p has so far only been known in budding yeast, and mechanisms that mediate telomerase access and activation in other eukaryotes have remained elusive. Here, we use iterative profile searches to identify homologs of yeast Est1p in a large variety of eukaryotes, including human. One of three human homologs, designated human EST1A (hEST1A), is shown to be associated with most or all active telomerase in HeLa cell extracts. Overexpression of hEST1A induces anaphase bridges due to chromosome-end fusions, and telomeric DNA persists at the fusion points. Thus, overexpression of hEST1A affects telomere capping. The identification of EST1 homologs in a large variety of eukaryotes may indicate that the mechanisms of telomere extension are more conserved than anticipated previously.
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Affiliation(s)
- Patrick Reichenbach
- Swiss Institute for Experimental Cancer Research (ISREC), 1066, Epalinges, Switzerland
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122
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Rooney S, Alt FW, Lombard D, Whitlow S, Eckersdorff M, Fleming J, Fugmann S, Ferguson DO, Schatz DG, Sekiguchi J. Defective DNA repair and increased genomic instability in Artemis-deficient murine cells. J Exp Med 2003; 197:553-65. [PMID: 12615897 PMCID: PMC2193825 DOI: 10.1084/jem.20021891] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
In developing lymphocytes, the recombination activating gene endonuclease cleaves DNA between V, D, or J coding and recombination signal (RS) sequences to form hairpin coding and blunt RS ends, which are fused to form coding and RS joins. Nonhomologous end joining (NHEJ) factors repair DNA double strand breaks including those induced during VDJ recombination. Human radiosensitive severe combined immunodeficiency results from lack of Artemis function, an NHEJ factor with in vitro endonuclease/exonuclease activities. We inactivated Artemis in murine embryonic stem (ES) cells by targeted mutation. Artemis deficiency results in impaired VDJ coding, but not RS, end joining. In addition, Artemis-deficient ES cells are sensitive to a radiomimetic drug, but less sensitive to ionizing radiation. VDJ coding joins from Artemis-deficient ES cells, which surprisingly are distinct from the highly deleted joins consistently obtained from DNA-dependent protein kinase catalytic subunit-deficient ES cells, frequently lack deletions and often display large junctional palindromes, consistent with a hairpin coding end opening defect. Strikingly, Artemis-deficient ES cells have increased chromosomal instability including telomeric fusions. Thus, Artemis appears to be required for a subset of NHEJ reactions that require end processing. Moreover, Artemis functions as a genomic caretaker, most notably in prevention of translocations and telomeric fusions. As Artemis deficiency is compatible with human life, Artemis may also suppress genomic instability in humans.
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Affiliation(s)
- Sean Rooney
- Howard Hughes Medical Institute, The Children's Hospital, The Center for Blood Research, Harvard Medical School, Boston, MA 02115, USA
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123
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Abstract
Telomerase activity is necessary to maintain the integrity of telomeres, which in turn prevent chromosome ends from being processed and signaled as damaged DNA. That cancer cells rely on telomerase to maintain functional telomeres and to divide indefinitely has highlighted the potential for developing novel therapeutic approaches that target telomerase.
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Affiliation(s)
- María A Blasco
- Department of Immunology and Oncology, National Centre of Biotechnology, Madrid, Spain.
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124
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Anastasiadou E, Schwaller J. Role of constitutively activated protein tyrosine kinases in malignant myeloproliferative disorders: an update. Curr Opin Hematol 2003; 10:40-8. [PMID: 12483110 DOI: 10.1097/00062752-200301000-00007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Modern molecular technology helped identify more than 10 protein tyrosine kinases related to myeloid malignancies, which allowed the development of small molecule inhibitors targeting deregulated protein tyrosine kinase activity. Protein tyrosine kinase deregulation can occur as a consequence of fusion gene formation because of chromosomal translocations, or as distinct gain-of-function point mutations. Although the tyrosine kinase inhibitor imatinib mesylate (Gleevec) targeting the ABL protein tyrosine kinase has revolutionized current chronic myeloid leukemia therapy, it became rapidly evident that overcoming the multiple cellular resistance mechanisms will be very challenging. To develop efficient therapeutic alternatives, one must understand the complex signal transduction mechanisms involved in transformation by deregulated protein tyrosine kinases. This article reviews the most recently identified molecular mechanisms involved in cell transformation by the BCR/ABL protein tyrosine kinase fusion and presents new members of the increasing family of deregulated protein tyrosine kinases involved in myeloproliferative disorders. In addition, the article discusses new, promising small molecule protein tyrosine kinase inhibitors and the molecular mechanism that may lead to resistance to these drugs. Finally, the article highlights putative alternative strategies that could be used to block signal transduction pathways of deregulated protein tyrosine kinase activity.
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Affiliation(s)
- Ema Anastasiadou
- Harvard Institutes of Medicine, Harvard Medical School, Boston, Massachusetts, USA
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125
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Gladdy RA, Taylor MD, Williams CJ, Grandal I, Karaskova J, Squire JA, Rutka JT, Guidos CJ, Danska JS. The RAG-1/2 endonuclease causes genomic instability and controls CNS complications of lymphoblastic leukemia in p53/Prkdc-deficient mice. Cancer Cell 2003; 3:37-50. [PMID: 12559174 DOI: 10.1016/s1535-6108(02)00236-2] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Double-strand DNA breaks (DSB) induce chromosomal translocations and gene amplification in cell culture, but mechanisms by which DSB cause genomic instability in vivo are poorly understood. We show that RAG-1/2-induced DSB cause IgH/c-Myc translocations in leukemic pro-B cells from p53/Prkdc-deficient mice. Strikingly, these translocations were complex, clonally heterogeneous and amplified. We observed reiterated IgH/c-Myc fusions on dicentric chromosomes, suggesting that amplification occurred by repeated cycles of bridge, breakage and fusion. Leukemogenesis was not mitigated in RAG-2/p53/Prkdc-deficient mice, but leukemic pro-B cells lacked IgH/c-Myc translocations. Thus, global genomic instability conferred by p53/Prkdc disruption efficiently transforms pro-B cells lacking RAG-1/2-induced DSB. Unexpectedly, RAG-2/p53/Prkdc-deficient mice also developed leptomeningeal leukemia, providing a novel spontaneous model for this frequent complication of human lymphoblastic malignancies.
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MESH Headings
- Animals
- Blotting, Northern
- Blotting, Southern
- Cell Transformation, Neoplastic/genetics
- Central Nervous System Diseases/etiology
- Central Nervous System Diseases/pathology
- DNA-Binding Proteins/deficiency
- DNA-Binding Proteins/genetics
- Flow Cytometry
- Gene Amplification/genetics
- Genes, myc/genetics
- Hematopoietic Stem Cell Transplantation
- Hematopoietic Stem Cells/physiology
- Homeodomain Proteins/genetics
- Immunoglobulin Heavy Chains/genetics
- Immunohistochemistry
- In Situ Hybridization, Fluorescence
- Leukemia, Lymphoid/complications
- Leukemia, Lymphoid/genetics
- Leukemia, Lymphoid/physiopathology
- Meningeal Neoplasms/etiology
- Meningeal Neoplasms/genetics
- Mice
- Models, Animal
- Translocation, Genetic
- Tumor Suppressor Protein p53/deficiency
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Affiliation(s)
- Rebecca A Gladdy
- Program in Developmental Biology, The Hospital for Sick Children and Department of Surgery, University of Toronto, Toronto, Ontario, Canada
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126
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Abstract
We review the genes and proteins related to the homologous recombinational repair (HRR) pathway that are implicated in cancer through either genetic disorders that predispose to cancer through chromosome instability or the occurrence of somatic mutations that contribute to carcinogenesis. Ataxia telangiectasia (AT), Nijmegen breakage syndrome (NBS), and an ataxia-like disorder (ATLD), are chromosome instability disorders that are defective in the ataxia telangiectasia mutated (ATM), NBS, and Mre11 genes, respectively. These genes are critical in maintaining cellular resistance to ionizing radiation (IR), which kills largely by the production of double-strand breaks (DSBs). Bloom syndrome involves a defect in the BLM helicase, which seems to play a role in restarting DNA replication forks that are blocked at lesions, thereby promoting chromosome stability. The Werner syndrome gene (WRN) helicase, another member of the RecQ family like BLM, has very recently been found to help mediate homologous recombination. Fanconi anemia (FA) is a genetically complex chromosomal instability disorder involving seven or more genes, one of which is BRCA2. FA may be at least partially caused by the aberrant production of reactive oxidative species. The breast cancer-associated BRCA1 and BRCA2 proteins are strongly implicated in HRR; BRCA2 associates with Rad51 and appears to regulate its activity. We discuss in detail the phenotypes of the various mutant cell lines and the signaling pathways mediated by the ATM kinase. ATM's phosphorylation targets can be grouped into oxidative stress-mediated transcriptional changes, cell cycle checkpoints, and recombinational repair. We present the DNA damage response pathways by using the DSB as the prototype lesion, whose incorrect repair can initiate and augment karyotypic abnormalities.
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Affiliation(s)
- Larry H Thompson
- Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory L-441, P.O. Box 808, Livermore, CA 94551-0808, USA.
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127
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Espejel S, Franco S, Sgura A, Gae D, Bailey SM, Taccioli GE, Blasco MA. Functional interaction between DNA-PKcs and telomerase in telomere length maintenance. EMBO J 2002; 21:6275-87. [PMID: 12426399 PMCID: PMC137185 DOI: 10.1093/emboj/cdf593] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
DNA-PKcs is the catalytic subunit of the DNA-dependent protein kinase (DNA-PK) complex that functions in the non-homologous end-joining of double-strand breaks, and it has been shown previously to have a role in telomere capping. In particular, DNA-PKcs deficiency leads to chromosome fusions involving telomeres produced by leading-strand synthesis. Here, by generating mice doubly deficient in DNA-PKcs and telomerase (Terc(-/-)/DNA-PKcs(-/-)), we demonstrate that DNA-PKcs also has a fundamental role in telomere length maintenance. In particular, Terc(-/-)/DNA-PKcs(-/-) mice displayed an accelerated rate of telomere shortening when compared with Terc(-/-) controls, suggesting a functional interaction between both activities in maintaining telomere length. In addition, we also provide direct demonstration that DNA-PKcs is essential for both end-to-end fusions and apoptosis triggered by critically short telomeres. Our data predict that, in telomerase-deficient cells, i.e. human somatic cells, DNA-PKcs abrogation may lead to a faster rate of telomere degradation and cell cycle arrest in the absence of increased apoptosis and/or fusion of telomere-exhausted chromosomes. These results suggest a critical role of DNA-PKcs in both cancer and aging.
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Affiliation(s)
- Silvia Espejel
- Department of Immunology and Oncology, National Centre of Biotechnology, E-28049 Madrid, Spain, Department of Biology, University of Rome ‘Roma Tre’, Via le Marconi 446, Rome 00146, Italy, Department of Microbiology, Boston University School of Medicine, Boston, MA 02118-2526 and Department of Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA Corresponding author e-mail: S.Espejel, S.Franco and A.Sgura contributed equally to this work
| | - Sonia Franco
- Department of Immunology and Oncology, National Centre of Biotechnology, E-28049 Madrid, Spain, Department of Biology, University of Rome ‘Roma Tre’, Via le Marconi 446, Rome 00146, Italy, Department of Microbiology, Boston University School of Medicine, Boston, MA 02118-2526 and Department of Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA Corresponding author e-mail: S.Espejel, S.Franco and A.Sgura contributed equally to this work
| | - Antonella Sgura
- Department of Immunology and Oncology, National Centre of Biotechnology, E-28049 Madrid, Spain, Department of Biology, University of Rome ‘Roma Tre’, Via le Marconi 446, Rome 00146, Italy, Department of Microbiology, Boston University School of Medicine, Boston, MA 02118-2526 and Department of Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA Corresponding author e-mail: S.Espejel, S.Franco and A.Sgura contributed equally to this work
| | - Darren Gae
- Department of Immunology and Oncology, National Centre of Biotechnology, E-28049 Madrid, Spain, Department of Biology, University of Rome ‘Roma Tre’, Via le Marconi 446, Rome 00146, Italy, Department of Microbiology, Boston University School of Medicine, Boston, MA 02118-2526 and Department of Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA Corresponding author e-mail: S.Espejel, S.Franco and A.Sgura contributed equally to this work
| | - Susan M. Bailey
- Department of Immunology and Oncology, National Centre of Biotechnology, E-28049 Madrid, Spain, Department of Biology, University of Rome ‘Roma Tre’, Via le Marconi 446, Rome 00146, Italy, Department of Microbiology, Boston University School of Medicine, Boston, MA 02118-2526 and Department of Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA Corresponding author e-mail: S.Espejel, S.Franco and A.Sgura contributed equally to this work
| | - Guillermo E. Taccioli
- Department of Immunology and Oncology, National Centre of Biotechnology, E-28049 Madrid, Spain, Department of Biology, University of Rome ‘Roma Tre’, Via le Marconi 446, Rome 00146, Italy, Department of Microbiology, Boston University School of Medicine, Boston, MA 02118-2526 and Department of Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA Corresponding author e-mail: S.Espejel, S.Franco and A.Sgura contributed equally to this work
| | - María A. Blasco
- Department of Immunology and Oncology, National Centre of Biotechnology, E-28049 Madrid, Spain, Department of Biology, University of Rome ‘Roma Tre’, Via le Marconi 446, Rome 00146, Italy, Department of Microbiology, Boston University School of Medicine, Boston, MA 02118-2526 and Department of Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA Corresponding author e-mail: S.Espejel, S.Franco and A.Sgura contributed equally to this work
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128
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Lo AWI, Sabatier L, Fouladi B, Pottier G, Ricoul M, Murnane JP. DNA amplification by breakage/fusion/bridge cycles initiated by spontaneous telomere loss in a human cancer cell line. Neoplasia 2002; 4:531-8. [PMID: 12407447 PMCID: PMC1503667 DOI: 10.1038/sj.neo.7900267] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2002] [Accepted: 07/24/2002] [Indexed: 11/09/2022]
Abstract
The development of genomic instability is an important step in generating the multiple genetic changes required for cancer. One consequence of genomic instability is the overexpression of oncogenes due to gene amplification. One mechanism for gene amplification is the breakage/fusion/bridge (B/F/B) cycle that involves the repeated fusion and breakage of chromosomes following the loss of a telomere. B/F/B cycles have been associated with low-copy gene amplification in human cancer cells, and have been proposed to be an initiating event in high-copy gene amplification. We have found that spontaneous telomere loss on a marker chromosome 16 in a human tumor cell line results in sister chromatid fusion and prolonged periods of chromosome instability. The high rate of anaphase bridges involving chromosome 16 demonstrates that this instability results from B/F/B cycles. The amplification of subtelomeric DNA on the marker chromosome provides conclusive evidence that B/F/B cycles initiated by spontaneous telomere loss are a mechanism for gene amplification in human cancer cells.
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Affiliation(s)
- Anthony W I Lo
- Radiation Oncology Research Laboratory, University of California, 1855 Folsom Street, MCB 200, San Francisco, CA 94103, USA
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129
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Smogorzewska A, Karlseder J, Holtgreve-Grez H, Jauch A, de Lange T. DNA ligase IV-dependent NHEJ of deprotected mammalian telomeres in G1 and G2. Curr Biol 2002; 12:1635-44. [PMID: 12361565 DOI: 10.1016/s0960-9822(02)01179-x] [Citation(s) in RCA: 298] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Telomeres are required to prevent end-to-end chromosome fusions. End-to-end fusions of metaphase chromosomes are observed in mammalian cells with dysfunctional telomeres due to diminished function of telomere-associated proteins and in cells experiencing extensive attrition of telomeric DNA. However, the molecular nature of these fusions and the mechanism by which they occur have not been elucidated. RESULTS We document that telomere fusions resulting from inhibition of the telomere-protective factor TRF2 are generated by DNA ligase IV-dependent nonhomologous end joining (NHEJ). NHEJ gives rise to covalent ligation of the C strand of one telomere to the G strand of another. Breakage of the resulting dicentric chromosomes results in nonreciprocal translocations, a hallmark of human cancer. Telomere NHEJ took place before and after DNA replication, and both sister telomeres participated in the reaction. Telomere fusions were accompanied by active degradation of the 3' telomeric overhangs. CONCLUSIONS The main threat to dysfunctional mammalian telomeres is degradation of the 3' overhang and subsequent telomere end-joining by DNA ligase IV. The involvement of NHEJ in telomere fusions is paradoxical since the NHEJ factors Ku70/80 and DNA-PKcs are present at telomeres and protect chromosome ends from fusion.
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Affiliation(s)
- Agata Smogorzewska
- Laboratory for Cell Biology and Genetics, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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130
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Bundock P, van Attikum H, Hooykaas P. Increased telomere length and hypersensitivity to DNA damaging agents in an Arabidopsis KU70 mutant. Nucleic Acids Res 2002; 30:3395-400. [PMID: 12140324 PMCID: PMC137071 DOI: 10.1093/nar/gkf445] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
We have identified a putative homologue of the KU70 gene (AtKU70) from Arabidopsis thaliana. In order to study its function in plants we have isolated an A.thaliana line that contains a T-DNA inserted into AtKU70. Plants homozygous for this insertion appear normal and are fertile. In other organisms the KU70 gene has been shown to play a role in the repair of DNA damage induced by ionising radiation (IR) and by radiomimetic chemicals such as methylmethane sulfonate (MMS). We show that AtKU70(-/-) plants are hypersensitive to IR and MMS, and thus the AtKU70 gene plays a similar role in DNA repair in plants as in other organisms. The KU70 gene also plays a role in maintaining telomere length. Yeast and mammalian cells deficient for Ku70 have shortened telomeres. When we studied the telomeres in the AtKU70(-/-) plants we found unexpectedly that they were significantly longer (>30 kb) than was found in wild-type plants (2-4 kb). We propose several hypotheses to explain this telomere lengthening in the AtKU70(-/-) plants.
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Affiliation(s)
- Paul Bundock
- Institute of Molecular Plant Sciences, Sectie 2A, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
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131
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DuBois ML, Haimberger ZW, McIntosh MW, Gottschling DE. A quantitative assay for telomere protection in Saccharomyces cerevisiae. Genetics 2002; 161:995-1013. [PMID: 12136006 PMCID: PMC1462171 DOI: 10.1093/genetics/161.3.995] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Telomeres are the protective ends of linear chromosomes. Telomeric components have been identified and described by their abilities to bind telomeric DNA, affect telomere repeat length, participate in telomeric DNA replication, or modulate transcriptional silencing of telomere-adjacent genes; however, their roles in chromosome end protection are not as well defined. We have developed a genetic, quantitative assay in Saccharomyces cerevisiae to measure whether various telomeric components protect chromosome ends from homologous recombination. This "chromosomal cap" assay has revealed that the telomeric end-binding proteins, Cdc13p and Ku, both protect the chromosome end from homologous recombination, as does the ATM-related kinase, Tel1p. We propose that Cdc13p and Ku structurally inhibit recombination at telomeres and that Tel1p regulates the chromosomal cap, acting through Cdc13p. Analysis with recombination mutants indicated that telomeric homologous recombination events proceeded by different mechanisms, depending on which capping component was compromised. Furthermore, we found that neither telomere repeat length nor telomeric silencing correlated with chromosomal capping efficiency. This capping assay provides a sensitive in vivo approach for identifying the components of chromosome ends and the mechanisms by which they are protected.
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Affiliation(s)
- Michelle L DuBois
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue, Seattle, WA 98109-1024, USA
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132
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Wei C, Skopp R, Takata M, Takeda S, Price CM. Effects of double-strand break repair proteins on vertebrate telomere structure. Nucleic Acids Res 2002; 30:2862-70. [PMID: 12087170 PMCID: PMC117051 DOI: 10.1093/nar/gkf396] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Although telomeres are not recognized as double-strand breaks (DSBs), some DSB repair proteins are present at telomeres and are required for telomere maintenance. To learn more about the telomeric function of proteins from the homologous recombination (HR) and non-homologous end joining pathways (NHEJ), we have screened a panel of chicken DT40 knockout cell lines for changes in telomere structure. In contrast to what has been observed in Ku-deficient mice, we found that Ku70 disruption did not result in telomere-telomere fusions and had no effect on telomere length or the structure of the telomeric G-strand overhang. G-overhang length was increased by Rad51 disruption but unchanged by disruption of DNA-PKcs, Mre11, Rad52, Rad54, XRCC2 or XRCC3. The effect of Rad51 depletion was unexpected because gross alterations in telomere structure have not been detected in yeast HR mutants. Thus, our results indicate that Rad51 has a previously undiscovered function at vertebrate telomeres. They also indicate that Mre11 is not required to generate G-overhangs. Although Mre11 has been implicated in overhang generation, overhang structure had not previously been examined in Mre11-deficient cells. Overall our findings indicate that there are significant species-specific differences in the telomeric function of DSB repair proteins.
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Affiliation(s)
- Chao Wei
- Department of Molecular Genetics, Biochemistry and Microbiology, College of Medicine, University of Cincinnati, ML0524, 231 Albert Sabin Way, Cincinnati, OH 45267, USA
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