101
|
Cusanelli E, Chartrand P. Telomeric repeat-containing RNA TERRA: a noncoding RNA connecting telomere biology to genome integrity. Front Genet 2015; 6:143. [PMID: 25926849 PMCID: PMC4396414 DOI: 10.3389/fgene.2015.00143] [Citation(s) in RCA: 133] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 03/25/2015] [Indexed: 12/15/2022] Open
Abstract
Telomeres are dynamic nucleoprotein structures that protect the ends of chromosomes from degradation and activation of DNA damage response. For this reason, telomeres are essential to genome integrity. Chromosome ends are enriched in heterochromatic marks and proper organization of telomeric chromatin is important to telomere stability. Despite their heterochromatic state, telomeres are transcribed giving rise to long noncoding RNAs (lncRNA) called TERRA (telomeric repeat-containing RNA). TERRA molecules play critical roles in telomere biology, including regulation of telomerase activity and heterochromatin formation at chromosome ends. Emerging evidence indicate that TERRA transcripts form DNA-RNA hybrids at chromosome ends which can promote homologous recombination among telomeres, delaying cellular senescence and sustaining genome instability. Intriguingly, TERRA RNA-telomeric DNA hybrids are involved in telomere length homeostasis of telomerase-negative cancer cells. Furthermore, TERRA transcripts play a role in the DNA damage response (DDR) triggered by dysfunctional telomeres. We discuss here recent developments on TERRA's role in telomere biology and genome integrity, and its implication in cancer.
Collapse
Affiliation(s)
- Emilio Cusanelli
- Max F. Perutz Laboratories, Department of Chromosome Biology, University of Vienna Vienna, Austria
| | - Pascal Chartrand
- Department of Biochemistry and Molecular Medicine, Université de Montréal Montréal, QC, Canada
| |
Collapse
|
102
|
Li X, Liu W, Wang H, Yang L, Li Y, Wen H, Ning H, Wang J, Zhang L, Li J, Fan D. Rap1 is indispensable for TRF2 function in etoposide-induced DNA damage response in gastric cancer cell line. Oncogenesis 2015; 4:e144. [PMID: 25821946 PMCID: PMC4491608 DOI: 10.1038/oncsis.2015.1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Revised: 01/19/2015] [Accepted: 01/21/2015] [Indexed: 12/14/2022] Open
Abstract
The telomeric protein TRF2, involving in telomeric and extratelomeric DNA damage response, has been previously reported to facilitate multidrug resistance (MDR) in gastric cancer cells by interfering ATM-dependent DNA damage response induced by anticancer drugs. Rap1 is the TRF2-interacting protein in the shelterin complex. Complex formation between Rap1 and TRF2 is essential for their function in telomere and end protection. Here we focus on the effects of Rap1 on TRF2 function in DNA damage response induced by anticancer drugs. Both Rap1 and TRF2 expression were upregulated in SGC7901 and its MDR variant SGC7901/VCR after etoposide treatment, which was more marked in SGC7901/VCR than in SGC7901. Rap1 silencing by siRNA in SGC7901/VCR partially reversed the etoposide resistance. And Rap1 silencing partially reversed the TRF2-mediated resistance to etoposide in SGC7901. Rap1 silencing did not affect the TRF2 upregulation induced by etoposide, but eliminated the inhibition effect of TRF2 on ATM expression and ATM phosphorylation at serine 1981 (ATM pS1981). Furthermore, phosphorylation of ATM targets, including γH2AX and serine 15 (S15) on p53, were increased in Rap1 silencing cells in response to etoposide. Thus, we confirm that Rap1, interacting with TRF2 in the shelterin complex, also has an important role in TRF2-mediated DNA damage response in gastric cancer cells treated by etoposide.
Collapse
Affiliation(s)
- X Li
- Department of Neurology, Second Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - W Liu
- Department V of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - H Wang
- Department V of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - L Yang
- Department V of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Y Li
- Department V of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - H Wen
- Department V of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - H Ning
- Department V of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - J Wang
- Department V of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - L Zhang
- Department II of Digestive Diseases, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - J Li
- Department of Neurology, Second Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - D Fan
- State Key Laboratory of Cancer Biology and Xijing Hospital of Digestive Diseases, The Fourth Military Medical University, Xi'an, China
| |
Collapse
|
103
|
Ilicheva NV, Podgornaya OI, Voronin AP. Telomere Repeat-Binding Factor 2 Is Responsible for the Telomere Attachment to the Nuclear Membrane. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2015; 101:67-96. [DOI: 10.1016/bs.apcsb.2015.06.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
|
104
|
Zannini L, Delia D, Buscemi G. CHK2 kinase in the DNA damage response and beyond. J Mol Cell Biol 2014; 6:442-57. [PMID: 25404613 PMCID: PMC4296918 DOI: 10.1093/jmcb/mju045] [Citation(s) in RCA: 279] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Revised: 09/17/2014] [Accepted: 09/24/2014] [Indexed: 12/21/2022] Open
Abstract
The serine/threonine kinase CHK2 is a key component of the DNA damage response. In human cells, following genotoxic stress, CHK2 is activated and phosphorylates >20 proteins to induce the appropriate cellular response, which, depending on the extent of damage, the cell type, and other factors, could be cell cycle checkpoint activation, induction of apoptosis or senescence, DNA repair, or tolerance of the damage. Recently, CHK2 has also been found to have cellular functions independent of the presence of nuclear DNA lesions. In particular, CHK2 participates in several molecular processes involved in DNA structure modification and cell cycle progression. In this review, we discuss the activity of CHK2 in response to DNA damage and in the maintenance of the biological functions in unstressed cells. These activities are also considered in relation to a possible role of CHK2 in tumorigenesis and, as a consequence, as a target of cancer therapy.
Collapse
Affiliation(s)
- Laura Zannini
- Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Via Amadeo 42, 20133 Milan, Italy
| | - Domenico Delia
- Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Via Amadeo 42, 20133 Milan, Italy
| | - Giacomo Buscemi
- Department of Biosciences, University of Milan, via Celoria 26, 20133 Milan, Italy
| |
Collapse
|
105
|
El Maï M, Wagner KD, Michiels JF, Ambrosetti D, Borderie A, Destree S, Renault V, Djerbi N, Giraud-Panis MJ, Gilson E, Wagner N. The Telomeric Protein TRF2 Regulates Angiogenesis by Binding and Activating the PDGFRβ Promoter. Cell Rep 2014; 9:1047-60. [PMID: 25437559 DOI: 10.1016/j.celrep.2014.09.038] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 08/26/2014] [Accepted: 09/19/2014] [Indexed: 12/19/2022] Open
Abstract
Telomeric repeat binding factor 2 (TRF2), which plays a central role in telomere capping, is frequently increased in human tumors. We reveal here that TRF2 is expressed in the vasculature of most human cancer types, where it colocalizes with the Wilms' tumor suppressor WT1. We further show that TRF2 is a transcriptional target of WT1 and is required for proliferation, migration, and tube formation of endothelial cells. These angiogenic effects of TRF2 are uncoupled from its function in telomere capping. Instead, TRF2 binds and transactivates the promoter of the angiogenic tyrosine kinase platelet-derived growth factor receptor β (PDGFRβ). These findings reveal an unexpected role of TRF2 in neoangiogenesis and delineate a distinct function of TRF2 as a transcriptional regulator.
Collapse
Affiliation(s)
- Mounir El Maï
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France
| | - Kay-Dietrich Wagner
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France
| | - Jean-François Michiels
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France; Department of Pathology, Le Centre Hospitalier Universitaire de Nice, 06107 Nice, France
| | - Damien Ambrosetti
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France; Department of Pathology, Le Centre Hospitalier Universitaire de Nice, 06107 Nice, France
| | - Arnaud Borderie
- Department of Pathology, Le Centre Hospitalier Universitaire de Nice, 06107 Nice, France
| | - Sandrine Destree
- Department of Pathology, Le Centre Hospitalier Universitaire de Nice, 06107 Nice, France
| | - Valerie Renault
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France
| | - Nadir Djerbi
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France
| | - Marie-Josèphe Giraud-Panis
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France
| | - Eric Gilson
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France; Department of Medical Genetics, Le Centre Hospitalier Universitaire de Nice, 06107 Nice, France.
| | - Nicole Wagner
- Institut for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, 06107 Nice, France.
| |
Collapse
|
106
|
A switch-like dynamic mechanism for the initiation of replicative senescence. FEBS Lett 2014; 588:4369-74. [DOI: 10.1016/j.febslet.2014.09.043] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Accepted: 09/15/2014] [Indexed: 11/23/2022]
|
107
|
Multifunctional role of ATM/Tel1 kinase in genome stability: from the DNA damage response to telomere maintenance. BIOMED RESEARCH INTERNATIONAL 2014; 2014:787404. [PMID: 25247188 PMCID: PMC4163350 DOI: 10.1155/2014/787404] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 07/28/2014] [Accepted: 08/07/2014] [Indexed: 12/19/2022]
Abstract
The mammalian protein kinase ataxia telangiectasia mutated (ATM) is a key regulator of the DNA double-strand-break response and belongs to the evolutionary conserved phosphatidylinositol-3-kinase-related protein kinases. ATM deficiency causes ataxia telangiectasia (AT), a genetic disorder that is characterized by premature aging, cerebellar neuropathy, immunodeficiency, and predisposition to cancer. AT cells show defects in the DNA damage-response pathway, cell-cycle control, and telomere maintenance and length regulation. Likewise, in Saccharomyces cerevisiae, haploid strains defective in the TEL1 gene, the ATM ortholog, show chromosomal aberrations and short telomeres. In this review, we outline the complex role of ATM/Tel1 in maintaining genomic stability through its control of numerous aspects of cellular survival. In particular, we describe how ATM/Tel1 participates in the signal transduction pathways elicited by DNA damage and in telomere homeostasis and its importance as a barrier to cancer development.
Collapse
|
108
|
Bower BD, Griffith JD. TRF1 and TRF2 differentially modulate Rad51-mediated telomeric and nontelomeric displacement loop formation in vitro. Biochemistry 2014; 53:5485-95. [PMID: 25115914 PMCID: PMC4151696 DOI: 10.1021/bi5006249] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
A growing
body of literature suggests that the homologous recombination/repair
(HR) pathway cooperates with components of the shelterin complex to
promote both telomere maintenance and nontelomeric HR. This may be
due to the ability of both HR and shelterin proteins to promote strand
invasion, wherein a single-stranded DNA (ssDNA) substrate base pairs
with a homologous double-stranded DNA (dsDNA) template displacing
a loop of ssDNA (D-loop). Rad51 recombinase catalyzes D-loop formation
during HR, and telomere repeat binding factor 2 (TRF2) catalyzes the
formation of a telomeric D-loop that stabilizes a looped structure
in telomeric DNA (t-loop) that may facilitate telomere protection.
We have characterized this functional interaction in vitro using a fluorescent D-loop assay measuring the incorporation of
Cy3-labeled 90-nucleotide telomeric and nontelomeric substrates into
telomeric and nontelomeric plasmid templates. We report that preincubation
of a telomeric template with TRF2 inhibits the ability of Rad51 to
promote telomeric D-loop formation upon preincubation with a telomeric
substrate. This suggests Rad51 does not facilitate t-loop formation
and suggests a mechanism whereby TRF2 can inhibit HR at telomeres.
We also report a TRF2 mutant lacking the dsDNA binding domain promotes
Rad51-mediated nontelomeric D-loop formation, possibly explaining
how TRF2 promotes nontelomeric HR. Finally, we report telomere repeat
binding factor 1 (TRF1) promotes Rad51-mediated telomeric D-loop formation,
which may facilitate HR-mediated replication fork restart and explain
why TRF1 is required for efficient telomere replication.
Collapse
Affiliation(s)
- Brian D Bower
- Curriculum in Genetics and Molecular Biology, University of North Carolina , Chapel Hill, North Carolina 27599, United States
| | | |
Collapse
|
109
|
Martínez P, Ferrara‐Romeo I, Flores JM, Blasco MA. Essential role for the TRF2 telomere protein in adult skin homeostasis. Aging Cell 2014; 13:656-68. [PMID: 24725274 PMCID: PMC4326939 DOI: 10.1111/acel.12221] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/23/2014] [Indexed: 11/29/2022] Open
Abstract
TRF2 is a component of shelterin, the protein complex that protects the ends of mammalian chromosomes. TRF2 is essential for telomere capping owing to its roles in suppressing an ATM-dependent DNA damage response (DDR) at chromosome ends and inhibiting end-to-end chromosome fusions. Mice deficient for TRF2 are early embryonic lethal. However, the role of TRF2 in later stages of development and in the adult organism remains largely unaddressed, with the exception of liver, where TRF2 was found to be dispensable for maintaining tissue function. Here, we study the impact of TRF2 conditional deletion in stratified epithelia by generating the TRF2∆/∆-K5-Cre mouse model, which targets TRF2 deletion to the skin from embryonic day E11.5. In marked contrast to TRF2 deletion in the liver, TRF2∆/∆-K5-Cre mice show lethality in utero reaching 100% lethality perinataly. At the molecular and cellular level, TRF2 deletion provokes induction of an acute DDR at telomeres, leading to activation of p53 signaling pathways and to programed cell death since the time of Cre expression at E11.5. Unexpectedly, neither inhibition of the NHEJ pathway by abrogation of 53BP1 nor inhibition of DDR by p53 deficiency rescued these severe phenotypes. Instead, TRF2 deletion provokes an extensive epidermal cell death accompanied by severe inflammation already at E16.5 embryos, which are independent of p53. These results are in contrast with conditional deletion of TRF1 and TPP1 in the skin, where p53 deficiency rescued the associated skin phenotypes, highlighting the comparatively more essential role of TRF2 in skin homeostasis.
Collapse
Affiliation(s)
- Paula Martínez
- Telomeres and Telomerase Group Molecular Oncology Program Spanish National Cancer Centre (CNIO) Melchor Fernández Almagro 3E‐28029 Madrid Spain
| | - Iole Ferrara‐Romeo
- Telomeres and Telomerase Group Molecular Oncology Program Spanish National Cancer Centre (CNIO) Melchor Fernández Almagro 3E‐28029 Madrid Spain
| | - Juana M. Flores
- Animal Surgery and Medicine Department Facultad de Veterinaria Complutense University of Madrid 28029Madrid Spain
| | - Maria A. Blasco
- Telomeres and Telomerase Group Molecular Oncology Program Spanish National Cancer Centre (CNIO) Melchor Fernández Almagro 3E‐28029 Madrid Spain
| |
Collapse
|
110
|
Cremona CA, Behrens A. ATM signalling and cancer. Oncogene 2014; 33:3351-60. [PMID: 23851492 DOI: 10.1038/onc.2013.275] [Citation(s) in RCA: 152] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Revised: 05/17/2013] [Accepted: 05/20/2013] [Indexed: 12/12/2022]
Abstract
ATM, the protein kinase mutated in the rare human disease ataxia telangiectasia (A-T), has been the focus of intense scrutiny over the past two decades. Initially this was because of the unusual radiosensitive phenotype of cells from A-T patients, and latterly because investigating ATM signalling has yielded valuable insights into the DNA damage response, redox signalling and cancer. With the recent explosion in genomic data, ATM alterations have been revealed both in the germline as a predisposing factor for cancer and as somatic changes in tumours themselves. Here we review these findings, as well as advances in the understanding of ATM signalling mechanisms in cancer and ATM inhibition as a strategy for cancer treatment.
Collapse
Affiliation(s)
- C A Cremona
- Mammalian Genetics Lab, Cancer Research UK London Research Institute, London, UK
| | - A Behrens
- Mammalian Genetics Lab, Cancer Research UK London Research Institute, London, UK
| |
Collapse
|
111
|
Bai Y, Lathia JD, Zhang P, Flavahan W, Rich JN, Mattson MP. Molecular targeting of TRF2 suppresses the growth and tumorigenesis of glioblastoma stem cells. Glia 2014; 62:1687-98. [PMID: 24909307 DOI: 10.1002/glia.22708] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Revised: 05/23/2014] [Accepted: 05/23/2014] [Indexed: 12/23/2022]
Abstract
Glioblastoma is the most prevalent primary brain tumor and is essentially universally fatal within 2 years of diagnosis. Glioblastomas contain cellular hierarchies with self-renewing glioblastoma stem cells (GSCs) that are often resistant to chemotherapy and radiation therapy. GSCs express high amounts of repressor element 1 silencing transcription factor (REST), which may contribute to their resistance to standard therapies. Telomere repeat-binding factor 2 (TRF2) stablizes telomeres and REST to maintain self-renewal of neural stem cells and tumor cells. Here we show viral vector-mediated delivery of shRNAs targeting TRF2 mRNA depletes TRF2 and REST from GSCs isolated from patient specimens. As a result, GSC proliferation is reduced and the level of proteins normally expressed by postmitotic neurons (L1CAM and β3-tubulin) is increased, suggesting that loss of TRF2 engages a cell differentiation program in the GSCs. Depletion of TRF2 also sensitizes GSCs to temozolomide, a DNA-alkylating agent currently used to treat glioblastoma. Targeting TRF2 significantly increased the survival of mice bearing GSC xenografts. These findings reveal a role for TRF2 in the maintenance of REST-associated proliferation and chemotherapy resistance of GSCs, suggesting that TRF2 is a potential therapeutic target for glioblastoma.
Collapse
Affiliation(s)
- Yun Bai
- Department of Cell Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China; Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, Baltimore, Maryland
| | | | | | | | | | | |
Collapse
|
112
|
Lee K, Gollahon LS. Zscan4 interacts directly with human Rap1 in cancer cells regardless of telomerase status. Cancer Biol Ther 2014; 15:1094-105. [PMID: 24840609 DOI: 10.4161/cbt.29220] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Telomeres are repetitive sequences at the ends of chromosomes protected by DNA binding proteins of the shelterin complex that form capping structures. Through the interaction of shelterin complex-associated proteins, telomere length maintenance is regulated. Recently, the newly identified embryonic stem cell marker, Zinc finger and SCAN domain-containing 4 gene (Zscan4), was shown to be a telomere-associated protein, co-localizing to the shelterin complex. Furthermore, it was shown to play an essential role in genomic stability by regulating telomere elongation. Although it is known that Zscan4 regulates TRF2, POT1b, and Rap1 expression in embryonic stem cells, the relationship and the exact mechanism of action for ZSscan4-mediated telomere maintenance in cancer cells is unknown. In this study, we investigated Zscan4 expression and interactions with Rap1 in telomerase positive (HeLa, MCF7) and ALT pathway (SaOS2, U2OS) cancer cells. Through western, pulldown, siRNA, and overexpression assays we demonstrate, for the first time, that Zscan4 directly associates with Rap1 (physical association protein). Furthermore, by generating truncated versions of Zscan4, we identified its zinc finger domain as the Rap1 binding site. Using bimolecular fluorescence complementation, we further validate this functional interaction in human cancer cells. Our results indicate that Zscan4 functions as a mediator of telomere length through its direct interaction with Rap1, possibly regulating shelterin complex-controlled telomere elongation in both telomerase positive and alternative lengthening of telomere pathways. This direct interaction between Zscan4 and Rap1 may explain how Zscan4 rapidly increases telomere length, yielding important information about the role of these proteins in telomere biology.
Collapse
Affiliation(s)
- Kyungwoo Lee
- Department of Biological Sciences; Texas Tech University; Lubbock, TX USA
| | - Lauren S Gollahon
- Department of Biological Sciences; Texas Tech University; Lubbock, TX USA; Texas Tech University Imaging Center; Lubbock, TX USA
| |
Collapse
|
113
|
Pessina F, Lowndes NF. The RSF1 histone-remodelling factor facilitates DNA double-strand break repair by recruiting centromeric and Fanconi Anaemia proteins. PLoS Biol 2014; 12:e1001856. [PMID: 24800743 PMCID: PMC4011676 DOI: 10.1371/journal.pbio.1001856] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 03/28/2014] [Indexed: 01/18/2023] Open
Abstract
ATM is a central regulator of the cellular responses to DNA double-strand breaks (DSBs). Here we identify a biochemical interaction between ATM and RSF1 and we characterise the role of RSF1 in this response. The ATM-RSF1 interaction is dependent upon both DSBs and ATM kinase activity. Together with SNF2H/SMARCA5, RSF1 forms the RSF chromatin-remodelling complex. Although RSF1 is specific to the RSF complex, SNF2H/SMARCA5 is a catalytic subunit of several other chromatin-remodelling complexes. Although not required for checkpoint signalling, RSF1 is required for efficient repair of DSBs via both end-joining and homology-directed repair. Specifically, the ATM-dependent recruitment to sites of DSBs of the histone fold proteins CENPS/MHF1 and CENPX/MHF2, previously identified at centromeres, is RSF1-dependent. In turn these proteins recruit and regulate the mono-ubiquitination of the Fanconi Anaemia proteins FANCD2 and FANCI. We propose that by depositing CENPS/MHF1 and CENPX/MHF2, the RSF complex either directly or indirectly contributes to the reorganisation of chromatin around DSBs that is required for efficient DNA repair.
Collapse
Affiliation(s)
- Fabio Pessina
- Genome Stability Laboratory, Centre for Chromosome Biology, School of Natural Science, National University of Ireland Galway, Ireland
| | - Noel F. Lowndes
- Genome Stability Laboratory, Centre for Chromosome Biology, School of Natural Science, National University of Ireland Galway, Ireland
| |
Collapse
|
114
|
Nucleolar organization, ribosomal DNA array stability, and acrocentric chromosome integrity are linked to telomere function. PLoS One 2014; 9:e92432. [PMID: 24662969 PMCID: PMC3963894 DOI: 10.1371/journal.pone.0092432] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 02/21/2014] [Indexed: 12/16/2022] Open
Abstract
The short arms of the ten acrocentric human chromosomes share several repetitive DNAs, including ribosomal RNA genes (rDNA). The rDNA arrays correspond to nucleolar organizing regions that coalesce each cell cycle to form the nucleolus. Telomere disruption by expressing a mutant version of telomere binding protein TRF2 (dnTRF2) causes non-random acrocentric fusions, as well as large-scale nucleolar defects. The mechanisms responsible for acrocentric chromosome sensitivity to dysfunctional telomeres are unclear. In this study, we show that TRF2 normally associates with the nucleolus and rDNA. However, when telomeres are crippled by dnTRF2 or RNAi knockdown of TRF2, gross nucleolar and chromosomal changes occur. We used the controllable dnTRF2 system to precisely dissect the timing and progression of nucleolar and chromosomal instability induced by telomere dysfunction, demonstrating that nucleolar changes precede the DNA damage and morphological changes that occur at acrocentric short arms. The rDNA repeat arrays on the short arms decondense, and are coated by RNA polymerase I transcription binding factor UBF, physically linking acrocentrics to one another as they become fusogenic. These results highlight the importance of telomere function in nucleolar stability and structural integrity of acrocentric chromosomes, particularly the rDNA arrays. Telomeric stress is widely accepted to cause DNA damage at chromosome ends, but our findings suggest that it also disrupts chromosome structure beyond the telomere region, specifically within the rDNA arrays located on acrocentric chromosomes. These results have relevance for Robertsonian translocation formation in humans and mechanisms by which acrocentric-acrocentric fusions are promoted by DNA damage and repair.
Collapse
|
115
|
T-oligo as an anticancer agent in colorectal cancer. Biochem Biophys Res Commun 2014; 446:596-601. [PMID: 24632202 DOI: 10.1016/j.bbrc.2014.03.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 03/04/2014] [Indexed: 11/22/2022]
Abstract
In the United States, there will be an estimated 96,830 new cases of colorectal cancer (CRC) and 50,310 deaths in 2014. CRC is often detected at late stages of the disease, at which point there is no effective chemotherapy. Thus, there is an urgent need for effective novel therapies that have minimal effects on normal cells. T-oligo, an oligonucleotide homologous to the 3'-telomere overhang, induces potent DNA damage responses in multiple malignant cell types, however, its efficacy in CRC has not been studied. This is the first investigation demonstrating T-oligo-induced anticancer effects in two CRC cell lines, HT-29 and LoVo, which are highly resistant to conventional chemotherapies. In this investigation, we show that T-oligo may mediate its DNA damage responses through the p53/p73 pathway, thereby inhibiting cellular proliferation and inducing apoptosis or senescence. Additionally, upregulation of downstream DNA damage response proteins, including E2F1, p53 or p73, was observed. In LoVo cells, T-oligo induced senescence, decreased clonogenicity, and increased expression of senescence associated proteins p21, p27, and p53. In addition, downregulation of POT1 and TRF2, two components of the shelterin protein complex which protects telomeric ends, was observed. Moreover, we studied the antiproliferative effects of T-oligo in combination with an EGFR tyrosine kinase inhibitor, Gefitinib, which resulted in an additive inhibitory effect on cellular proliferation. Collectively, these data provide evidence that T-oligo alone, or in combination with other molecularly targeted therapies, has potential as an anti-cancer agent in CRC.
Collapse
|
116
|
Popuri V, Hsu J, Khadka P, Horvath K, Liu Y, Croteau DL, Bohr VA. Human RECQL1 participates in telomere maintenance. Nucleic Acids Res 2014; 42:5671-88. [PMID: 24623817 PMCID: PMC4027191 DOI: 10.1093/nar/gku200] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
A variety of human tumors employ alternative and recombination-mediated lengthening for telomere maintenance (ALT). Human RecQ helicases, such as BLM and WRN, can efficiently unwind alternate/secondary structures during telomere replication and/or recombination. Here, we report a novel role for RECQL1, the most abundant human RecQ helicase but functionally least studied, in telomere maintenance. RECQL1 associates with telomeres in ALT cells and actively resolves telomeric D-loops and Holliday junction substrates. RECQL1 physically and functionally interacts with telomere repeat-binding factor 2 that in turn regulates its helicase activity on telomeric substrates. The telomeric single-stranded binding protein, protection of telomeres 1 efficiently stimulates RECQL1 on telomeric substrates containing thymine glycol, a replicative blocking lesion. Loss of RECQL1 results in dysfunctional telomeres, telomere loss and telomere shortening, elevation of telomere sister-chromatid exchanges and increased aphidicolin-induced telomere fragility, indicating a role for RECQL1 in telomere maintenance. Further, our results indicate that RECQL1 may participate in the same pathway as WRN, probably in telomere replication.
Collapse
Affiliation(s)
- Venkateswarlu Popuri
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA
| | - Joseph Hsu
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA
| | - Prabhat Khadka
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA
| | - Kent Horvath
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA
| | - Yie Liu
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA
| | - Deborah L Croteau
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA
| | - Vilhelm A Bohr
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA
| |
Collapse
|
117
|
Frit P, Barboule N, Yuan Y, Gomez D, Calsou P. Alternative end-joining pathway(s): bricolage at DNA breaks. DNA Repair (Amst) 2014; 17:81-97. [PMID: 24613763 DOI: 10.1016/j.dnarep.2014.02.007] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 02/01/2014] [Accepted: 02/10/2014] [Indexed: 10/25/2022]
Abstract
To cope with DNA double strand break (DSB) genotoxicity, cells have evolved two main repair pathways: homologous recombination which uses homologous DNA sequences as repair templates, and non-homologous Ku-dependent end-joining involving direct sealing of DSB ends by DNA ligase IV (Lig4). During the last two decades a third player most commonly named alternative end-joining (A-EJ) has emerged, which is defined as any Ku- or Lig4-independent end-joining process. A-EJ increasingly appears as a highly error-prone bricolage on DSBs and despite expanding exploration, it still escapes full characterization. In the present review, we discuss the mechanism and regulation of A-EJ as well as its biological relevance under physiological and pathological situations, with a particular emphasis on chromosomal instability and cancer. Whether or not it is a genuine DSB repair pathway, A-EJ is emerging as an important cellular process and understanding A-EJ will certainly be a major challenge for the coming years.
Collapse
Affiliation(s)
- Philippe Frit
- CNRS, IPBS (Institut de Pharmacologie et de Biologie Structurale), BP 64182, 205 route de Narbonne, 31077 Toulouse, Cedex4, France; Université de Toulouse, UPS, IPBS, F-31077 Toulouse, France; Equipe labellisée Ligue Nationale Contre le Cancer, France
| | - Nadia Barboule
- CNRS, IPBS (Institut de Pharmacologie et de Biologie Structurale), BP 64182, 205 route de Narbonne, 31077 Toulouse, Cedex4, France; Université de Toulouse, UPS, IPBS, F-31077 Toulouse, France; Equipe labellisée Ligue Nationale Contre le Cancer, France
| | - Ying Yuan
- CNRS, IPBS (Institut de Pharmacologie et de Biologie Structurale), BP 64182, 205 route de Narbonne, 31077 Toulouse, Cedex4, France; Université de Toulouse, UPS, IPBS, F-31077 Toulouse, France; Equipe labellisée Ligue Nationale Contre le Cancer, France
| | - Dennis Gomez
- CNRS, IPBS (Institut de Pharmacologie et de Biologie Structurale), BP 64182, 205 route de Narbonne, 31077 Toulouse, Cedex4, France; Université de Toulouse, UPS, IPBS, F-31077 Toulouse, France; Equipe labellisée Ligue Nationale Contre le Cancer, France
| | - Patrick Calsou
- CNRS, IPBS (Institut de Pharmacologie et de Biologie Structurale), BP 64182, 205 route de Narbonne, 31077 Toulouse, Cedex4, France; Université de Toulouse, UPS, IPBS, F-31077 Toulouse, France; Equipe labellisée Ligue Nationale Contre le Cancer, France.
| |
Collapse
|
118
|
Chung YL, Pan CH, Liou WH, Sheu MJ, Lin WH, Chen TC, Huang HS, Wu CH. NSC746364, a G-Quadruplex-Stabilizing Agent, Suppresses Cell Growth of A549 Human Lung Cancer Cells Through Activation of the ATR/Chk1-Dependent Pathway. J Pharmacol Sci 2014; 124:7-17. [DOI: 10.1254/jphs.13096fp] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
|
119
|
The ATM-mediated DNA-damage response. Mol Oncol 2013. [DOI: 10.1017/cbo9781139046947.035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
120
|
Panier S, Durocher D. Push back to respond better: regulatory inhibition of the DNA double-strand break response. Nat Rev Mol Cell Biol 2013; 14:661-72. [PMID: 24002223 DOI: 10.1038/nrm3659] [Citation(s) in RCA: 131] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Single DNA lesions such as DNA double-strand breaks (DSBs) can cause cell death or trigger genome rearrangements that have oncogenic potential, and so the pathways that mend and signal DNA damage must be highly sensitive but, at the same time, selective and reversible. When initiated, boundaries must be set to restrict the DSB response to the site of the lesion. The integration of positive and, crucially, negative control points involving post-translational modifications such as phosphorylation, ubiquitylation and acetylation is key for building fast, effective responses to DNA damage and for mitigating the impact of DNA lesions on genome integrity.
Collapse
Affiliation(s)
- Stephanie Panier
- 1] The Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario M5G 1X5, Canada. [2] Present address: DNA Damage Response Laboratory, London Research Institute, Cancer Research UK, Clare Hall, South Mimms, London EN6 3LD, UK
| | | |
Collapse
|
121
|
Lu Y, Wei B, Zhang T, Chen Z, Ye J. How will telomeric complex be further contributed to our longevity? - the potential novel biomarkers of telomere complex counteracting both aging and cancer. Protein Cell 2013; 4:573-81. [PMID: 23864530 DOI: 10.1007/s13238-013-3002-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Accepted: 03/27/2013] [Indexed: 11/29/2022] Open
Abstract
With the smooth move towards the coming expected clinical reports of anticancer pharmaceutical molecules targeting telomeres and telomerase, and also with the exciting success in the extension of lifespan by regulating telomerase activity without increased onset of oncogenesis in laboratory mouse models (Garcia-Cao et al., 2006; Jaskelioff et al., 2011), we are convinced that targeting telomeres based on telomerase will be a potential approach to conquer both aging and cancer and the idea of longevity seems to be no more mysterious. More interestingly, emerging evidences from clinical research reveal that other telomeric factors, like specific telomeric binding proteins and nonspecific telomere associated proteins also show crucial importance in aging and oncogenesis. This stems from their roles in the stability of telomere structure and in the inhibition of DNA damage response at telomeres. Uncapping these proteins from chromosome ends leads to dramatic telomere loss and telomere dysfunction which is more abrupt than those induced by telomerase inactivation. Abnormal expression of these factors results in developmental failure, aging and even oncogenesis evidenced by several experimental models and clinical cases, indicating telomere specific proteins and its associated proteins have complimentary roles to telomerase in telomere protection and controlling cellular fate. Thus, these telomeric factors might be potential clinical biomarkers for early detection or even therapeutic targets of aging and cancer. Future studies to elucidate how these proteins function in telomere protection might benefit patients suffering aging or cancer who are not sensitive to telomerase mediation.
Collapse
Affiliation(s)
- Yiming Lu
- Shanghai Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China
| | | | | | | | | |
Collapse
|
122
|
The telomere deprotection response is functionally distinct from the genomic DNA damage response. Mol Cell 2013; 51:141-55. [PMID: 23850488 DOI: 10.1016/j.molcel.2013.06.006] [Citation(s) in RCA: 113] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 05/13/2013] [Accepted: 06/04/2013] [Indexed: 01/12/2023]
Abstract
Loss of chromosome end protection through telomere erosion is a hallmark of aging and senescence. Here we developed an experimental system that mimics physiological telomere deprotection in human cells and discovered that the telomere deprotection response is functionally distinct from the genomic DNA damage response. We found that, unlike genomic breaks, deprotected telomeres that are recognized as DNA damage but remain in the fusion-resistant intermediate state activate differential ataxia telangiectasia mutated (ATM) signaling where CHK2 is not phosphorylated. Also unlike genomic breaks, we found that deprotected telomeres do not contribute to the G2/M checkpoint and are instead passed through cell division to induce p53-dependent G1 arrest in the daughter cells. Telomere deprotection is therefore an epigenetic signal passed between cell generations to ensure that replication-associated telomere-dependent growth arrest occurs in stable diploid G1 phase cells before genome instability can occur.
Collapse
|
123
|
Kong CM, Lee XW, Wang X. Telomere shortening in human diseases. FEBS J 2013; 280:3180-93. [PMID: 23647631 DOI: 10.1111/febs.12326] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Revised: 04/12/2013] [Accepted: 04/30/2013] [Indexed: 01/22/2023]
Abstract
The discovery of telomeres dates back to the early 20th century. In humans, telomeres are heterochromatic structures with tandem DNA repeats of 5'-TTAGGG-3' at the chromosomal ends. Telomere length varies greatly among species and ranges from 10 to 15 kb in humans. With each cell division, telomeres shorten progressively because of the 'end-replication problem'. Short or dysfunctional telomeres are often recognized as DNA DSBs, triggering cell-cycle arrest and result in cellular senescence or apoptotic cell death. Therefore, telomere shortening serves as an important tumor-suppressive mechanism by limiting cellular proliferative capacity by regulating senescence checkpoint activation. Although telomeres serve as a mitotic clock to cells, they also confer capping on chromosomes, with help from telomere-associated proteins. Over the past decades, many studies of telomere biology have demonstrated that telomeres and telomere-associated proteins are implicated in human genetic diseases. In addition, it has become more apparent that accelerated telomere erosion is associated with a myriad of metabolic and inflammatory diseases. Moreover, critically short or unprotected telomeres are likely to form telomeric fusions, leading to genomic instability, the cornerstone for carcinogenesis. In light of these, this minireview summarizes studies on telomeres and telomere-associated proteins in human diseases. Elucidating the roles of telomeres involved in the mechanisms underlying pathogenesis of these diseases may open up new possibilities for novel molecular targets as well as provide important diagnostic and therapeutic implications.
Collapse
Affiliation(s)
- Chiou Mee Kong
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | | | | |
Collapse
|
124
|
Kalan S, Matveyenko A, Loayza D. LIM Protein Ajuba Participates in the Repression of the ATR-Mediated DNA Damage Response. Front Genet 2013; 4:95. [PMID: 23755068 PMCID: PMC3664778 DOI: 10.3389/fgene.2013.00095] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Accepted: 05/07/2013] [Indexed: 01/06/2023] Open
Abstract
LIM proteins constitute a superfamily characterized by the presence of a LIM domain, known to be involved in protein-protein interactions. Our previous work has implicated members of the Zyxin family of LIM proteins, namely TRIP6 and LPP, in the repression of the DNA damage response (DDR) at telomeres. Here, we describe a role for Ajuba, a closely related LIM molecule, in repressing the ATR-mediated DDR. We found that depletion of Ajuba led to apparent delays in the cell cycle, accompanied with increased Rb phosphorylation, Chk1 phosphorylation, induction of p53, and cell death. Ajuba could be found in a complex with replication protein A (RPA), and its depletion led to RPA phosphorylation, known to be an early event in ATR activation. We propose that Ajuba protects against unscheduled ATR signaling by preventing inappropriate RPA phosphorylation.
Collapse
Affiliation(s)
- Sampada Kalan
- Department of Biological Sciences, Hunter College , New York, NY , USA
| | | | | |
Collapse
|
125
|
The role of ATM in the deficiency in nonhomologous end-joining near telomeres in a human cancer cell line. PLoS Genet 2013; 9:e1003386. [PMID: 23555296 PMCID: PMC3610639 DOI: 10.1371/journal.pgen.1003386] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 01/28/2013] [Indexed: 11/19/2022] Open
Abstract
Telomeres distinguish chromosome ends from double-strand breaks (DSBs) and prevent chromosome fusion. However, telomeres can also interfere with DNA repair, as shown by a deficiency in nonhomologous end joining (NHEJ) and an increase in large deletions at telomeric DSBs. The sensitivity of telomeric regions to DSBs is important in the cellular response to ionizing radiation and oncogene-induced replication stress, either by preventing cell division in normal cells, or by promoting chromosome instability in cancer cells. We have previously proposed that the telomeric protein TRF2 causes the sensitivity of telomeric regions to DSBs, either through its inhibition of ATM, or by promoting the processing of DSBs as though they are telomeres, which is independent of ATM. Our current study addresses the mechanism responsible for the deficiency in repair of DSBs near telomeres by combining assays for large deletions, NHEJ, small deletions, and gross chromosome rearrangements (GCRs) to compare the types of events resulting from DSBs at interstitial and telomeric DSBs. Our results confirm the sensitivity of telomeric regions to DSBs by demonstrating that the frequency of GCRs is greatly increased at DSBs near telomeres and that the role of ATM in DSB repair is very different at interstitial and telomeric DSBs. Unlike at interstitial DSBs, a deficiency in ATM decreases NHEJ and small deletions at telomeric DSBs, while it increases large deletions. These results strongly suggest that ATM is functional near telomeres and is involved in end protection at telomeric DSBs, but is not required for the extensive resection at telomeric DSBs. The results support our model in which the deficiency in DSB repair near telomeres is a result of ATM-independent processing of DSBs as though they are telomeres, leading to extensive resection, telomere loss, and GCRs involving alternative NHEJ.
Collapse
|
126
|
Galati A, Micheli E, Cacchione S. Chromatin structure in telomere dynamics. Front Oncol 2013; 3:46. [PMID: 23471416 PMCID: PMC3590461 DOI: 10.3389/fonc.2013.00046] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 02/21/2013] [Indexed: 11/13/2022] Open
Abstract
The establishment of a specific nucleoprotein structure, the telomere, is required to ensure the protection of chromosome ends from being recognized as DNA damage sites. Telomere shortening below a critical length triggers a DNA damage response that leads to replicative senescence. In normal human somatic cells, characterized by telomere shortening with each cell division, telomere uncapping is a regulated process associated with cell turnover. Nevertheless, telomere dysfunction has also been associated with genomic instability, cell transformation, and cancer. Despite the essential role telomeres play in chromosome protection and in tumorigenesis, our knowledge of the chromatin structure involved in telomere maintenance is still limited. Here we review the recent findings on chromatin modifications associated with the dynamic changes of telomeres from protected to deprotected state and their role in telomere functions.
Collapse
Affiliation(s)
- Alessandra Galati
- Dipartimento di Biologia e Biotecnologie, Istituto Pasteur - Fondazione Cenci Bolognetti, Sapienza Università di Roma Rome, Italy
| | | | | |
Collapse
|
127
|
Smith JA, Park S, Krause JS, Banik NL. Oxidative stress, DNA damage, and the telomeric complex as therapeutic targets in acute neurodegeneration. Neurochem Int 2013; 62:764-75. [PMID: 23422879 DOI: 10.1016/j.neuint.2013.02.013] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Revised: 02/04/2013] [Accepted: 02/08/2013] [Indexed: 01/19/2023]
Abstract
Oxidative stress has been identified as an important contributor to neurodegeneration associated with acute CNS injuries and diseases such as spinal cord injury (SCI), traumatic brain injury (TBI), and ischemic stroke. In this review, we briefly detail the damaging effects of oxidative stress (lipid peroxidation, protein oxidation, etc.) with a particular emphasis on DNA damage. Evidence for DNA damage in acute CNS injuries is presented along with its downstream effects on neuronal viability. In particular, unchecked oxidative DNA damage initiates a series of signaling events (e.g. activation of p53 and PARP-1, cell cycle re-activation) which have been shown to promote neuronal loss following CNS injury. These findings suggest that preventing DNA damage might be an effective way to promote neuronal survival and enhance neurological recovery in these conditions. Finally, we identify the telomere and telomere-associated proteins (e.g. telomerase) as novel therapeutic targets in the treatment of neurodegeneration due to their ability to modulate the neuronal response to both oxidative stress and DNA damage.
Collapse
Affiliation(s)
- Joshua A Smith
- Division of Neurology, Department of Neurosciences, Medical University of South Carolina, 96 Jonathan Lucas St., Clinical Sciences Building Room 309, Charleston, SC 29425, USA.
| | | | | | | |
Collapse
|
128
|
Her YR, Chung IK. p300-mediated acetylation of TRF2 is required for maintaining functional telomeres. Nucleic Acids Res 2013; 41:2267-83. [PMID: 23307557 PMCID: PMC3575801 DOI: 10.1093/nar/gks1354] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The human telomeric protein TRF2 is required to protect chromosome ends by facilitating their organization into the protective capping structure. Post-translational modifications of TRF2 such as phosphorylation, ubiquitination, SUMOylation, methylation and poly(ADP-ribosyl)ation have been shown to play important roles in telomere function. Here we show that TRF2 specifically interacts with the histone acetyltransferase p300, and that p300 acetylates the lysine residue at position 293 of TRF2. We also report that p300-mediated acetylation stabilizes the TRF2 protein by inhibiting its ubiquitin-dependent proteolysis and is required for efficient telomere binding of TRF2. Furthermore, overexpression of the acetylation-deficient mutant, K293R, induces DNA-damage response foci at telomeres, thereby leading to induction of impaired cell growth, cellular senescence and altered cell cycle distribution. A small but significant number of metaphase chromosomes show no telomeric signals at chromatid ends, suggesting an aberrant telomere structure. These findings demonstrate that acetylation of TRF2 by p300 plays a crucial role in the maintenance of functional telomeres as well as in the regulation of the telomere-associated DNA-damage response, thus providing a new route for modulating telomere protection function.
Collapse
Affiliation(s)
- Yoon Ra Her
- Departments of Systems Biology and Integrated Omics for Biomedical Science, WCU Program of Graduate School, Yonsei University, Seoul 120-749, Korea
| | | |
Collapse
|
129
|
Muraki K, Nyhan K, Han L, Murnane JP. Mechanisms of telomere loss and their consequences for chromosome instability. Front Oncol 2012; 2:135. [PMID: 23061048 PMCID: PMC3463808 DOI: 10.3389/fonc.2012.00135] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Accepted: 09/19/2012] [Indexed: 12/17/2022] Open
Abstract
The ends of chromosomes in mammals, called telomeres, are composed of a 6-bp repeat sequence, TTAGGG, which is added on by the enzyme telomerase. In combination with a protein complex called shelterin, these telomeric repeat sequences form a cap that protects the ends of chromosomes. Due to insufficient telomerase expression, telomeres shorten gradually with each cell division in human somatic cells, which limits the number of times they can divide. The extensive cell division involved in cancer cell progression therefore requires that cancer cells must acquire the ability to maintain telomeres, either through expression of telomerase, or through an alternative mechanism involving recombination. It is commonly thought that the source of many chromosome rearrangements in cancer cells is a result of the extensive telomere shortening that occurs prior to the expression of telomerase. However, despite the expression of telomerase, tumor cells can continue to show chromosome instability due to telomere loss. Dysfunctional telomeres in cancer cells can result from oncogene-induced replication stress, which results in double-strand breaks (DSBs) at fragile sites, including telomeres. DSBs near telomeres are especially prone to chromosome rearrangements, because telomeric regions are deficient in DSB repair. The deficiency in DSB repair near telomeres is also an important mechanism for ionizing radiation-induced replicative senescence in normal human cells. In addition, DSBs near telomeres can result in chromosome instability in mouse embryonic stem cells, suggesting that telomere loss can contribute to heritable chromosome rearrangements. Consistent with this possibility, telomeric regions in humans are highly heterogeneous, and chromosome rearrangements near telomeres are commonly involved in human genetic disease. Understanding the mechanisms of telomere loss will therefore provide important insights into both human cancer and genetic disease.
Collapse
Affiliation(s)
- Keiko Muraki
- Department of Radiation Oncology, University of California at San Francisco San Francisco, CA, USA
| | | | | | | |
Collapse
|
130
|
Huda N, Abe S, Gu L, Mendonca MS, Mohanty S, Gilley D. Recruitment of TRF2 to laser-induced DNA damage sites. Free Radic Biol Med 2012; 53:1192-7. [PMID: 22841872 DOI: 10.1016/j.freeradbiomed.2012.07.024] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 07/10/2012] [Accepted: 07/17/2012] [Indexed: 12/18/2022]
Abstract
Several lines of evidence suggest that the telomere-associated protein TRF2 plays critical roles in the DNA damage response. TRF2 is rapidly and transiently phosphorylated by an ATM-dependent pathway in response to DNA damage and this DNA damage-induced phosphoryation is essential for the DNA-PK-dependent pathway of DNA double-strand break repair (DSB). However, the type of DNA damage that induces TRF2 localization to the damage sites, the requirement for DNA damage-induced phosphorylation of TRF2 for its recruitment, as well as the detailed kinetics of TRF2 accumulation at DNA damage sites have not been fully investigated. In order to address these questions, we used an ultrafast femtosecond multiphoton laser and a continuous wave 405-nm single photon laser to induce DNA damage at defined nuclear locations. Our results showed that DNA damage produced by a femtosecond multiphoton laser was sufficient for localization of TRF2 to these DNA damage sites. We also demonstrate that ectopically expressed TRF2 was recruited to DNA lesions created by a 405-nm laser. Our data suggest that ATM and DNA-PKcs kinases are not required for TRF2 localization to DNA damage sites. Furthermore, we found that phosphorylation of TRF2 at residue T188 was not essential for its recruitment to laser-induced DNA damage sites. Thus, we provide further evidence that a protein known to function in telomere maintenance, TRF2, is recruited to sites of DNA damage and plays critical roles in the DNA damage response.
Collapse
Affiliation(s)
- Nazmul Huda
- Indiana University School of Medicine, Department of Medical and Molecular Genetics, Indianapolis, IN 46202, USA
| | | | | | | | | | | |
Collapse
|
131
|
Salewsky B, Schmiester M, Schindler D, Digweed M, Demuth I. The nuclease hSNM1B/Apollo is linked to the Fanconi anemia pathway via its interaction with FANCP/SLX4. Hum Mol Genet 2012; 21:4948-56. [DOI: 10.1093/hmg/dds338] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
|
132
|
Kwon JH, Shin JH, Kim ES, Lee N, Park JY, Koo BS, Hong SM, Park CW, Choi KY. REST-dependent expression of TRF2 renders non-neuronal cancer cells resistant to DNA damage during oxidative stress. Int J Cancer 2012; 132:832-42. [PMID: 22821339 DOI: 10.1002/ijc.27741] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Accepted: 07/02/2012] [Indexed: 11/07/2022]
Abstract
REST is a neuronal gene silencing factor ubiquitously expressed in non-neuronal tissues. REST is additionally believed to serve as a tumor suppressor in non-neuronal cancers. Conversely, recent findings on REST-dependent tumorigenesis in non-neuronal cells consistently suggest a potential role of REST as a tumor promoter. Here, we have uncovered for the first time the mechanism by which REST contributes to cancer cell survival in non-neuronal cancers. We observed abundant expression of REST in various types of non-neuronal cancer cells compared to normal tissues. The delicate roles of REST were further evaluated in HCT116 and HeLa, non-neuronal cancer cell lines expressing REST. REST silencing resulted in decreased cell survival and activation of the DNA damage response (DDR) through a decrease in the level of TRF2, a telomere-binding protein. These responses were correlated with reduced colony formation ability and accelerated telomere shortening in cancer cells upon the stable knockdown of REST. Interestingly, REST was down-regulated under oxidative stress conditions via ubiquitin proteasome system, suggesting that sustainability of REST expression is critical to determine cell survival during oxidative stress in a tumor microenvironment. Our results collectively indicate that REST-dependent TRF2 expression renders cancer cells resistant to DNA damage during oxidative stress, and mechanisms to overcome oxidative stress, such as high levels of REST or the stress-resistant REST mutants found in specific human cancers, may account for REST-dependent tumorigenesis.
Collapse
Affiliation(s)
- Jung-Hee Kwon
- Department of Life Science, Pohang University of Science and Technology, Pohang, Republic of Korea
| | | | | | | | | | | | | | | | | |
Collapse
|
133
|
Thompson LH. Recognition, signaling, and repair of DNA double-strand breaks produced by ionizing radiation in mammalian cells: the molecular choreography. Mutat Res 2012; 751:158-246. [PMID: 22743550 DOI: 10.1016/j.mrrev.2012.06.002] [Citation(s) in RCA: 261] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 06/09/2012] [Accepted: 06/16/2012] [Indexed: 12/15/2022]
Abstract
The faithful maintenance of chromosome continuity in human cells during DNA replication and repair is critical for preventing the conversion of normal diploid cells to an oncogenic state. The evolution of higher eukaryotic cells endowed them with a large genetic investment in the molecular machinery that ensures chromosome stability. In mammalian and other vertebrate cells, the elimination of double-strand breaks with minimal nucleotide sequence change involves the spatiotemporal orchestration of a seemingly endless number of proteins ranging in their action from the nucleotide level to nucleosome organization and chromosome architecture. DNA DSBs trigger a myriad of post-translational modifications that alter catalytic activities and the specificity of protein interactions: phosphorylation, acetylation, methylation, ubiquitylation, and SUMOylation, followed by the reversal of these changes as repair is completed. "Superfluous" protein recruitment to damage sites, functional redundancy, and alternative pathways ensure that DSB repair is extremely efficient, both quantitatively and qualitatively. This review strives to integrate the information about the molecular mechanisms of DSB repair that has emerged over the last two decades with a focus on DSBs produced by the prototype agent ionizing radiation (IR). The exponential growth of molecular studies, heavily driven by RNA knockdown technology, now reveals an outline of how many key protein players in genome stability and cancer biology perform their interwoven tasks, e.g. ATM, ATR, DNA-PK, Chk1, Chk2, PARP1/2/3, 53BP1, BRCA1, BRCA2, BLM, RAD51, and the MRE11-RAD50-NBS1 complex. Thus, the nature of the intricate coordination of repair processes with cell cycle progression is becoming apparent. This review also links molecular abnormalities to cellular pathology as much a possible and provides a framework of temporal relationships.
Collapse
Affiliation(s)
- Larry H Thompson
- Biology & Biotechnology Division, L452, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, United States.
| |
Collapse
|
134
|
Walker JR, Zhu XD. Post-translational modifications of TRF1 and TRF2 and their roles in telomere maintenance. Mech Ageing Dev 2012; 133:421-34. [PMID: 22634377 DOI: 10.1016/j.mad.2012.05.002] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Revised: 04/27/2012] [Accepted: 05/04/2012] [Indexed: 11/29/2022]
Abstract
Telomeres, heterochromatic structures, found at the ends of linear eukaryotic chromosomes, function to protect natural chromosome ends from nucleolytic attack. Human telomeric DNA is bound by a telomere-specific six-subunit protein complex, termed shelterin/telosome. The shelterin subunits TRF1 and TRF2 bind in a sequence-specific manner to double-stranded telomeric DNA, providing a vital platform for recruitment of additional shelterin proteins as well as non-shelterin factors crucial for the maintenance of telomere length and structure. Both TRF1 and TRF2 are engaged in multiple roles at telomeres including telomere protection, telomere replication, sister telomere resolution and telomere length maintenance. Regulation of TRF1 and TRF2 in these various processes is controlled by post-translational modifications, at times in a cell-cycle-dependent manner, affecting key functions such as DNA binding, dimerization, localization, degradation and interactions with other proteins. Here we review the post-translational modifications of TRF1 and TRF2 and discuss the mechanisms by which these modifications contribute to the function of these two proteins.
Collapse
Affiliation(s)
- John R Walker
- Department of Biology, LSB438, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
| | | |
Collapse
|
135
|
Methods of studying telomere damage induced by quadruplex-ligand complexes. Methods 2012; 57:93-9. [PMID: 22410593 DOI: 10.1016/j.ymeth.2012.02.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2011] [Revised: 02/16/2012] [Accepted: 02/20/2012] [Indexed: 01/08/2023] Open
Abstract
The burgeoning knowledge about the structure of telomeres and the roles of various factors involved in telomere maintenance provides several possible targets for pharmacological intervention. To date the area that has received major attention regarding drug discovery is the targeting the telomeric G-quadruplex (G4) structure. G4 ligands were initially designed to counteract telomerase action at telomeres. Surprisingly, their antiproliferative effects can occur in telomerase negative cells and follow kinetics, which cannot be merely explained by telomere shortening, suggesting that these compounds affect other pathways, not necessarily related to telomere biology. Impressively, it has been shown that polyaromatic compounds featuring end-stacking binding properties trigger a strong DNA damage response at telomeres. This is typical of the telomere deprotection occurring during cellular senescence or upon telomere injury. It emerged that the G4-interacting agents are more than simple telomerase inhibitors and that their direct target is rather telomere than telomerase. This review summarizes the most valid experimental approaches for studying the pharmacological telomere damage induced by G4-ligand complexes.
Collapse
|
136
|
Ponsot E, Echaniz-Laguna A, Delis AM, Kadi F. Telomere length and regulatory proteins in human skeletal muscle with and without ongoing regenerative cycles. Exp Physiol 2012; 97:774-84. [PMID: 22366562 DOI: 10.1113/expphysiol.2011.063818] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
New insights suggest the existence of telomere regulatory mechanisms in several adult tissues. In this study, we aimed to assess in vivo telomere length and the presence of specific proteins involved in telomere regulation in a model of human skeletal muscle with (patients with dermatomyosis or polymyositis) and without ongoing regenerative events (healthy subjects). Mean (meanTRF) and minimal telomere (miniTRF) lengths and the expression of telomerase, tankyrase 1, TRF2 (telomeric repeat binding factor 2) and POT1 (protection of telomeres 1) were investigated in skeletal muscle samples from 12 patients (MYO) and 13 healthy subjects (CON). There was no significant shortening of telomeres in skeletal muscle from patients compared with control subjects (MYO, meanTRF length 11.0 ± 1.8 kbp and miniTRF length 4.7 ± 0.8 kbp; CON, meanTRF length 10.4 ± 1.1 kbp and miniTRF length 4.6 ± 0.5 kbp). Theoretically, telomere length can be controlled by endogenous mechanisms. Here, we show for the first time that expression levels of telomerase, tankyrase 1, TRF2 and POT1 were, respectively, six-, seven-, three- and fivefold higher in the nuclear fraction of skeletal muscle of MYO compared with CON (P < 0.05). This suggests the existence of endogenous mechanisms allowing for telomere regulation in skeletal muscle with ongoing cycles of degeneration and regeneration and a model where regulatory factors are possibly involved in the protection of skeletal muscle telomeres.
Collapse
Affiliation(s)
- Elodie Ponsot
- School of Health and Medical Sciences, University of Örebro, 70182 Örebro, Sweden
| | | | | | | |
Collapse
|
137
|
Reynolds GE, Gao Q, Miller D, Snow BE, Harrington LA, Murnane JP. PIF1 disruption or NBS1 hypomorphism does not affect chromosome healing or fusion resulting from double-strand breaks near telomeres in murine embryonic stem cells. DNA Repair (Amst) 2011; 10:1164-73. [PMID: 21945094 DOI: 10.1016/j.dnarep.2011.09.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 08/29/2011] [Accepted: 09/02/2011] [Indexed: 11/26/2022]
Abstract
Telomerase serves to maintain telomeric repeat sequences at the ends of chromosomes. However, telomerase can also add telomeric repeat sequences at DNA double-strand breaks (DSBs), a process called chromosome healing. Here, we employed a method of inducing DSBs near telomeres to query the role of two proteins, PIF1 and NBS1, in chromosome healing in mammalian cells. PIF1 was investigated because the PIF1 homolog in Saccharomyces cerevisiae inhibits chromosome healing, as shown by a 1000-fold increase in chromosome in PIF1-deficient cells. NBS1 was investigated because the functional homolog of NBS1 in S. cerevisiae, Xrs2, is part of the Mre11/Rad50/Xrs2 complex that is required for chromosome healing due to its role in the processing of DSBs and recruitment of telomerase. We found that disruption of mPif1 had no detectable effect on the frequency of chromosome healing at DSBs near telomeres in murine embryonic stem cells. Moreover, the Nbs1(ΔB) hypomorph, which is defective in the processing of DSBs, also had no detectable effect on the frequency of chromosome healing, DNA degradation, or gross chromosome rearrangements (GCRs) that result from telomeric DSBs. Although we cannot rule out small changes in chromosome healing using this system, it is clear from our results that knockout of PIF1 or the Nbs1(ΔB) hypomorph does not result in large differences in chromosome healing in murine cells. These results represent the first genetic assessment of the role of these proteins in chromosome healing in mammals, and suggest that murine cells have evolved mechanisms to ensure the functional redundancy of Pif1 or Nbs1 in the regulation of chromosome healing.
Collapse
Affiliation(s)
- Gloria E Reynolds
- Department of Radiation Oncology, University of California San Francisco, 2340 Sutter Street, San Francisco, CA 94143-1331, United States
| | | | | | | | | | | |
Collapse
|
138
|
Bhatti S, Kozlov S, Farooqi AA, Naqi A, Lavin M, Khanna KK. ATM protein kinase: the linchpin of cellular defenses to stress. Cell Mol Life Sci 2011; 68:2977-3006. [PMID: 21533982 PMCID: PMC11115042 DOI: 10.1007/s00018-011-0683-9] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Revised: 03/24/2011] [Accepted: 03/29/2011] [Indexed: 01/23/2023]
Abstract
ATM is the most significant molecule involved in monitoring the genomic integrity of the cell. Any damage done to DNA relentlessly challenges the cellular machinery involved in recognition, processing and repair of these insults. ATM kinase is activated early to detect and signal lesions in DNA, arrest the cell cycle, establish DNA repair signaling and faithfully restore the damaged chromatin. ATM activation plays an important role as a barrier to tumorigenesis, metabolic syndrome and neurodegeneration. Therefore, studies of ATM-dependent DNA damage signaling pathways hold promise for treatment of a variety of debilitating diseases through the development of new therapeutics capable of modulating cellular responses to stress. In this review, we have tried to untangle the complex web of ATM signaling pathways with the purpose of pinpointing multiple roles of ATM underlying the complex phenotypes observed in AT patients.
Collapse
Affiliation(s)
- Shahzad Bhatti
- Institute of Molecular Biology and Biotechnology, The University of Lahore, 1 Km Raiwind Road, Thokar Niaz Baig, Lahore, Pakistan
| | - Sergei Kozlov
- Queensland Institute of Medical Research, QIMR, 300 Herston Rd, Herston, Brisbane, 4029 Australia
| | - Ammad Ahmad Farooqi
- Institute of Molecular Biology and Biotechnology, The University of Lahore, 1 Km Raiwind Road, Thokar Niaz Baig, Lahore, Pakistan
| | - Ali Naqi
- Institute of Molecular Biology and Biotechnology, The University of Lahore, 1 Km Raiwind Road, Thokar Niaz Baig, Lahore, Pakistan
| | - Martin Lavin
- Queensland Institute of Medical Research, QIMR, 300 Herston Rd, Herston, Brisbane, 4029 Australia
| | - Kum Kum Khanna
- Queensland Institute of Medical Research, QIMR, 300 Herston Rd, Herston, Brisbane, 4029 Australia
| |
Collapse
|
139
|
Yoo HH, Chung IK. Requirement of DDX39 DEAD box RNA helicase for genome integrity and telomere protection. Aging Cell 2011; 10:557-71. [PMID: 21388492 DOI: 10.1111/j.1474-9726.2011.00696.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Human chromosome ends associate with shelterin, a six-protein complex that protects telomeric DNA from being recognized as sites of DNA damage. The shelterin subunit TRF2 has been implicated in the protection of chromosome ends by facilitating their organization into the protective capping structure and by associating with several accessory proteins involved in various DNA transactions. Here we describe the characterization of DDX39 DEAD-box RNA helicase as a novel TRF2-interacting protein. DDX39 directly interacts with the telomeric repeat binding factor homology domain of TRF2 via the FXLXP motif (where X is any amino acid). DDX39 is also found in association with catalytically competent telomerase in cell lysates through an interaction with hTERT but has no effect on telomerase activity. Whereas overexpression of DDX39 in telomerase-positive human cancer cells led to progressive telomere elongation, depletion of endogenous DDX39 by small hairpin RNA (shRNA) resulted in telomere shortening. Furthermore, depletion of DDX39 induced DNA-damage response foci at internal genome as well as telomeres as evidenced by telomere dysfunction-induced foci. Some of the metaphase chromosomes showed no telomeric signal at chromatid ends, suggesting an aberrant telomere structure. Our findings suggest that DDX39, in addition to its role in mRNA splicing and nuclear export, is required for global genome integrity as well as telomere protection and represents a new pathway for telomere maintenance by modulating telomere length homeostasis.
Collapse
Affiliation(s)
- Hyun Hee Yoo
- Departments of Biology and Integrated Omics for Biomedical Science, WCU program of Graduate School, Yonsei University, 134 Shinchon-dong, Seoul, Korea
| | | |
Collapse
|
140
|
Abstract
p53 takes critical part in a number of positive and negative feedback loops to regulate carcinogenesis, aging and other biological processes. Uncapped or dysfunctional telomeres are an endogenous DNA damage that activates ATM kinase (ataxia telangiectasia mutated) and then p53 to induce cellular senescence or apoptosis. Our recent study shows that p53, a downstream effector of the telomere damage signaling, also functions upstream of the telomere-capping protein complex by inhibiting one of its components, TRF2 (telomeric repeat binding factor 2). Since TRF2 inhibition leads to ATM activation, a novel positive feedback loop exists to amplify uncapped telomere-induced, p53-mediated cellular responses. Siah1 (seven in absentia homolog 1), a p53-inducible E3 ubiquitin ligase, plays a key role in this feedback regulation by targeting TRF2 for ubiquitination and proteasomal degradation. Biological significance and therapeutic implications of this study are discussed.
Collapse
Affiliation(s)
- Izumi Horikawa
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | | | | |
Collapse
|
141
|
Ogrunc M, d'Adda di Fagagna F. Never-ageing cellular senescence. Eur J Cancer 2011; 47:1616-22. [PMID: 21561762 PMCID: PMC3135819 DOI: 10.1016/j.ejca.2011.04.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 02/21/2011] [Accepted: 04/01/2011] [Indexed: 12/04/2022]
Abstract
Cellular senescence was historically discovered as a form of cellular ageing of in vitro cultured cells. It has been under the spotlight following the evidence of oncogene-induced senescence in vivo and its role as a potent tumour suppressor mechanism. Presently, a PubMed search using keywords ‘cellular senescence and cancer’ reveals 8398 number of references (by April 2011) showing that while our knowledge of senescence keeps expanding, the complexity of the phenomenon keeps us – researchers in the field of cancer biology – fascinated and busy. In this short review, we summarise the many cellular pathways leading to cellular senescence and we discuss the latest experimental evidence and the questions emerging in the field.
Collapse
Affiliation(s)
- Müge Ogrunc
- IFOM Foundation, FIRC Institute of Molecular Oncology Foundation, Milan, Italy.
| | | |
Collapse
|
142
|
Murnane JP. Telomere dysfunction and chromosome instability. Mutat Res 2011; 730:28-36. [PMID: 21575645 DOI: 10.1016/j.mrfmmm.2011.04.008] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Revised: 04/22/2011] [Accepted: 04/28/2011] [Indexed: 01/07/2023]
Abstract
The ends of chromosomes are composed of a short repeat sequence and associated proteins that together form a cap, called a telomere, that keeps the ends from appearing as double-strand breaks (DSBs) and prevents chromosome fusion. The loss of telomeric repeat sequences or deficiencies in telomeric proteins can result in chromosome fusion and lead to chromosome instability. The similarity between chromosome rearrangements resulting from telomere loss and those found in cancer cells implicates telomere loss as an important mechanism for the chromosome instability contributing to human cancer. Telomere loss in cancer cells can occur through gradual shortening due to insufficient telomerase, the protein that maintains telomeres. However, cancer cells often have a high rate of spontaneous telomere loss despite the expression of telomerase, which has been proposed to result from a combination of oncogene-mediated replication stress and a deficiency in DSB repair in telomeric regions. Chromosome fusion in mammalian cells primarily involves nonhomologous end joining (NHEJ), which is the major form of DSB repair. Chromosome fusion initiates chromosome instability involving breakage-fusion-bridge (B/F/B) cycles, in which dicentric chromosomes form bridges and break as the cell attempts to divide, repeating the process in subsequent cell cycles. Fusion between sister chromatids results in large inverted repeats on the end of the chromosome, which amplify further following additional B/F/B cycles. B/F/B cycles continue until the chromosome acquires a new telomere, most often by translocation of the end of another chromosome. The instability is not confined to a chromosome that loses its telomere, because the instability is transferred to the chromosome donating a translocation. Moreover, the amplified regions are unstable and form extrachromosomal DNA that can reintegrate at new locations. Knowledge concerning the factors promoting telomere loss and its consequences is therefore important for understanding chromosome instability in human cancer.
Collapse
Affiliation(s)
- John P Murnane
- Department of Radiation Oncology, University of California, San Francisco, CA 94143-1331, USA.
| |
Collapse
|
143
|
The telomere binding protein TRF2 induces chromatin compaction. PLoS One 2011; 6:e19124. [PMID: 21526145 PMCID: PMC3079743 DOI: 10.1371/journal.pone.0019124] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Accepted: 03/27/2011] [Indexed: 12/15/2022] Open
Abstract
Mammalian telomeres are specialized chromatin structures that require the telomere binding protein, TRF2, for maintaining chromosome stability. In addition to its ability to modulate DNA repair activities, TRF2 also has direct effects on DNA structure and topology. Given that mammalian telomeric chromatin includes nucleosomes, we investigated the effect of this protein on chromatin structure. TRF2 bound to reconstituted telomeric nucleosomal fibers through both its basic N-terminus and its C-terminal DNA binding domain. Analytical agarose gel electrophoresis (AAGE) studies showed that TRF2 promoted the folding of nucleosomal arrays into more compact structures by neutralizing negative surface charge. A construct containing the N-terminal and TRFH domains together altered the charge and radius of nucleosomal arrays similarly to full-length TRF2 suggesting that TRF2-driven changes in global chromatin structure were largely due to these regions. However, the most compact chromatin structures were induced by the isolated basic N-terminal region, as judged by both AAGE and atomic force microscopy. Although the N-terminal region condensed nucleosomal array fibers, the TRFH domain, known to alter DNA topology, was required for stimulation of a strand invasion-like reaction with nucleosomal arrays. Optimal strand invasion also required the C-terminal DNA binding domain. Furthermore, the reaction was not stimulated on linear histone-free DNA. Our data suggest that nucleosomal chromatin has the ability to facilitate this activity of TRF2 which is thought to be involved in stabilizing looped telomere structures.
Collapse
|
144
|
Subtelomeric regions in mammalian cells are deficient in DNA double-strand break repair. DNA Repair (Amst) 2011; 10:536-44. [PMID: 21466975 DOI: 10.1016/j.dnarep.2011.03.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Revised: 03/02/2011] [Accepted: 03/03/2011] [Indexed: 11/22/2022]
Abstract
We have previously demonstrated that double-strand breaks (DSBs) in regions near telomeres are much more likely to result in large deletions, gross chromosome rearrangements, and chromosome instability than DSBs at interstitial sites within chromosomes. In the present study, we investigated whether this response of subtelomeric regions to DSBs is a result of a deficiency in DSB repair by comparing the frequency of homologous recombination repair (HRR) and nonhomologous end joining (NHEJ) at interstitial and telomeric sites following the introduction of DSBs by I-SceI endonuclease. We also monitored the frequency of small deletions, which have been shown to be the most common mutation at I-SceI-induced DSBs at interstitial sites. We observed no difference in the frequency of small deletions or HRR at interstitial and subtelomeric DSBs. However, the frequency of NHEJ was significantly lower at DSBs near telomeres compared to interstitial sites. The frequency of NHEJ was also lower at DSBs occurring at interstitial sites containing telomeric repeat sequences. We propose that regions near telomeres are deficient in classical NHEJ as a result of the presence of cis-acting telomere-binding proteins that cause DSBs to be processed as though they were telomeres, resulting in excessive resection, telomere loss, and eventual chromosome rearrangements by alternative NHEJ.
Collapse
|
145
|
Diotti R, Loayza D. Shelterin complex and associated factors at human telomeres. Nucleus 2011; 2:119-35. [PMID: 21738835 PMCID: PMC3127094 DOI: 10.4161/nucl.2.2.15135] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2010] [Revised: 02/09/2011] [Accepted: 02/11/2011] [Indexed: 12/17/2022] Open
Abstract
The processes regulating telomere function have major impacts on fundamental issues in human cancer biology. First, active telomere maintenance is almost always required for full oncogenic transformation of human cells, through cellular immortalization by endowment of an infinite replicative potential. Second, the attrition that telomeres undergo upon replication is responsible for the finite replicative life span of cells in culture, a process called senescence, which is of paramount importance for tumor suppression in vivo. The process of telomere-based senescence is intimately coupled to the induction of a DNA damage response emanating from telomeres, which can be elicited by both the ATM and ATR dependent pathways. At telomeres, the shelterin complex is constituted by a group of six proteins which assembles quantitatively along the telomere tract, and imparts both telomere maintenance and telomere protection. Shelterin is known to regulate the action of telomerase, and to prevent inappropriate DNA damage responses at chromosome ends, mostly through inhibition of ATM and ATR. The roles of shelterin have increasingly been associated with transient interactions with downstream factors that are not associated quantitatively or stably with telomeres. Here, some of the important known interactions between shelterin and these associated factors and their interplay to mediate telomere functions are reviewed.
Collapse
Affiliation(s)
- Raffaella Diotti
- Department of Biological Sciences, Hunter College, New York, NY, USA
| | | |
Collapse
|
146
|
Arora R, Brun CMC, Azzalin CM. TERRA: Long Noncoding RNA at Eukaryotic Telomeres. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2011; 51:65-94. [PMID: 21287134 DOI: 10.1007/978-3-642-16502-3_4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Telomeres protect the ends of linear eukaryotic chromosomes from being recognized as DNA double-stranded breaks, thereby maintaining the stability of our genome. The highly heterochromatic nature of telomeres had, for a long time, reinforced the idea that telomeres were transcriptionally silent. Since a few years, however, we know that DNA-dependent RNA polymerase II transcribes telomeric DNA into TElomeric Repeat-containing RNA (TERRA) molecules in a large variety of eukaryotes. In this chapter, we summarize the current knowledge of telomere structure and function and extensively review data accumulated on TERRA biogenesis and regulation. We also discuss putative functions of TERRA in preserving telomere stability and propose future directions for research encompassing this novel and exciting aspect of telomere biology.
Collapse
Affiliation(s)
- Rajika Arora
- Institute of Biochemistry, ETHZ-Eidgenössische Technische Hochschule Zürich, CH-8093, Zürich, Switzerland
| | | | | |
Collapse
|
147
|
Abstract
Telomeres are nucleoprotein structures that protect the ends of human chromosomes through the formation of a 'cap', thus preventing exonucleolytic degradation, inter- and intra-chromosomal fusion, and subsequent chromosomal instability. During aging, telomere shortening correlates with tissue dysfunction and loss of renewal capacity. In human cancer, telomere dysfunction is involved in early chromosome instability, long-term cellular proliferation, and possibly other processes related to cell survival and microenvironment. Telomeres constitute an attractive target for the development of novel small-molecule anti-cancer drugs. In particular, individual protein components of the core telomere higher-order chromatin structure (known as the telosome or 'shelterin' complex) are promising candidate targets for cancer therapy.
Collapse
|
148
|
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;
| |
Collapse
|
149
|
Endt H, Sprung CN, Keller U, Gaipl U, Fietkau R, Distel LV. Detailed analysis of DNA repair and senescence marker kinetics over the life span of a human fibroblast cell line. J Gerontol A Biol Sci Med Sci 2010; 66:367-75. [PMID: 21081476 DOI: 10.1093/gerona/glq197] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
We examined phosphorylation of H2AX, a marker for DNA double-strand breaks over the life of a human fibroblast cell line. This marker was compared with a number of other cellular senescence and DNA repair endpoints. An increase in γH2AX foci number was observed after 24 hours of repair time following DNA damage over the course of fibroblast passaging. Progressive and relatively constant changes in growth retardation, doubling time, and telomere length were also observed. The fraction of cells expressing β-gal, a marker of cellular senescence, increased considerably around the 40th passage as did some other cell morphology endpoints. The detectable γH2AX foci at 24 hours after ionizing radiation were far fewer than the number detected at 1 hour across all passage numbers. We conclude that although residual DNA damage level increases with passage number, it is unlikely to be the result of less efficient DNA repair in the aged fibroblast since most DNA damage is repaired, even at late passages.
Collapse
Affiliation(s)
- Heidrun Endt
- Department of Radiation Oncology, Friedrich-Alexander-University Erlangen-Nuremberg, Universitätsstraße 27, D-91054 Erlangen, Germany
| | | | | | | | | | | |
Collapse
|
150
|
Saliques S, Zeller M, Lorin J, Lorgis L, Teyssier JR, Cottin Y, Rochette L, Vergely C. Telomere length and cardiovascular disease. Arch Cardiovasc Dis 2010; 103:454-9. [PMID: 21074124 DOI: 10.1016/j.acvd.2010.08.002] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 08/19/2010] [Accepted: 08/21/2010] [Indexed: 12/23/2022]
Abstract
Telomeres are structures composed of deoxyribonucleic acid repeats that protect the end of chromosomes, but shorten with each cell division. They have been the subject of many studies, particularly in the field of oncology, and more recently their role in the onset, development and prognosis of cardiovascular disease has generated considerable interest. It has already been shown that these structures may deteriorate at the beginning of the atherosclerotic process, in the onset and development of arterial hypertension or during myocardial infarction, in which their length may be a predictor of outcome. As telomere length by its nature is a marker of cell senescence, it is of particular interest when studying the lifespan and fate of endothelial cells and cardiomyocytes, especially so because telomere length seems to be regulated by various factors notably certain cardiovascular risk factors, such as smoking, sex and obesity that are associated with high levels of oxidative stress. To gain insights into the links between telomere length and cardiovascular disease, and to assess the usefulness of telomere length as a new marker of cardiovascular risk, it seems essential to review the considerable amount of data published recently on the subject.
Collapse
Affiliation(s)
- Sébastien Saliques
- IFR Santé-STIC, UFR de Médecine et Pharmacie, Laboratoire de Physiopathologie et Pharmacologie Cardiovasculaires Expérimentales (LPPCE), Université de Bourgogne, 7, Boulevard Jeanne-d'Arc, 21000 Dijon, France.
| | | | | | | | | | | | | | | |
Collapse
|