51
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Feuerhahn S, Chen LY, Luke B, Porro A. No DDRama at chromosome ends: TRF2 takes centre stage. Trends Biochem Sci 2015; 40:275-85. [DOI: 10.1016/j.tibs.2015.03.003] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Revised: 03/06/2015] [Accepted: 03/06/2015] [Indexed: 12/13/2022]
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52
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Salvati E, Rizzo A, Iachettini S, Zizza P, Cingolani C, D'Angelo C, Porru M, Mondello C, Aiello A, Farsetti A, Gilson E, Leonetti C, Biroccio A. A basal level of DNA damage and telomere deprotection increases the sensitivity of cancer cells to G-quadruplex interactive compounds. Nucleic Acids Res 2015; 43:1759-69. [PMID: 25618850 PMCID: PMC4330372 DOI: 10.1093/nar/gkv006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Here, with the aim of obtaining insight into the intriguing selectivity of G-quadruplex (G4) ligands toward cancer compared to normal cells, a genetically controlled system of progressive transformation in human BJ fibroblasts was analyzed. Among the different comparative evaluations, we found a progressive increase of DNA damage response (DDR) markers throughout the genome from normal toward immortalized and transformed cells. More interestingly, sensitivity to G4 ligands strongly correlated with the presence of a basal level of DNA damage, including at the telomeres, where the chromosome ends were exposed to the DDR without concurrent induction of DNA repair activity, as revealed by the lack of 53BP1 recruitment and telomere aberrations. The link between telomere uncapping and the response to G4 stabilization was directly assessed by showing that a partial TRF2 depletion, causing a basal level of telomere localized DDR, rendered telomerized fibroblasts prone to G4-induced telomere damage and anti-proliferative defects. Taken together these data strongly indicate that the presence of a basal level of telomere-associated DDR is a determinant of susceptibility to G4 stabilization.
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Affiliation(s)
- Erica Salvati
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Angela Rizzo
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Sara Iachettini
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Pasquale Zizza
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Chiara Cingolani
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Carmen D'Angelo
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Manuela Porru
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Chiara Mondello
- Istituto di Genetica Molecolare, National Research Council (CNR), Pavia, Italy
| | - Aurora Aiello
- Institute of Cell Biology and Neurobiology (IBCN), CNR Rome, Italy Department of Experimental Oncology, Regina Elena National Cancer Institute, Rome, Italy
| | - Antonella Farsetti
- Institute of Cell Biology and Neurobiology (IBCN), CNR Rome, Italy Department of Experimental Oncology, Regina Elena National Cancer Institute, Rome, Italy
| | - Eric Gilson
- Institute for Research on Cancer and Aging, Nice (IRCAN), CNRS UMR7284/INSERM U1081, University of Nice, Nice, France Department of Medical Genetics, Archet 2 Hospital, CHU of Nice, Nice, France
| | - Carlo Leonetti
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
| | - Annamaria Biroccio
- Experimental Chemotherapy Laboratory, Regina Elena National Cancer Institute, Rome, Italy
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53
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Sui X, Fang Y, Lou H, Wang K, Zheng Y, Lou F, Jin W, Xu Y, Chen W, Pan H, Wang X, Han W. p53 suppresses stress-induced cellular senescence via regulation of autophagy under the deprivation of serum. Mol Med Rep 2014; 11:1214-20. [PMID: 25369834 DOI: 10.3892/mmr.2014.2853] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Accepted: 09/24/2014] [Indexed: 11/06/2022] Open
Abstract
The tumor suppressor p53 is widely known for its ability to induce cell cycle arrest or cell death, therefore preventing neoplastic progression. Previous studies have demonstrated novel roles for p53 in the regulation of autophagy and senescence. p53 can not only exert cell cycle‑arresting and senescence‑promoting or suppressing functions, but can also induce autophagic flux, particularly under conditions of nutrient deprivation. The present study demonstrated that p53 was capable of activating autophagy, which permits cell survival under conditions of serum starvation, and suppresses cellular senescence through inhibition of the mammalian target of rapamycin pathway. These results suggest that active autophagy may be a potential mechanism by which p53 suppresses cellular senescence, in response to serum starvation. The findings of the present study provide a potential mechanism for suppression of senescence by p53.
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Affiliation(s)
- Xinbing Sui
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Yong Fang
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Haizhou Lou
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Kaifeng Wang
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Yu Zheng
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Fang Lou
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Wei Jin
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Yinghua Xu
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Wei Chen
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Hongming Pan
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Xian Wang
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
| | - Weidong Han
- Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang 310016, P.R. China
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54
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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.
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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.
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55
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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]
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56
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Horikawa I, Fujita K, Jenkins LMM, Hiyoshi Y, Mondal AM, Vojtesek B, Lane DP, Appella E, Harris CC. Autophagic degradation of the inhibitory p53 isoform Δ133p53α as a regulatory mechanism for p53-mediated senescence. Nat Commun 2014; 5:4706. [PMID: 25144556 DOI: 10.1038/ncomms5706] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Accepted: 07/15/2014] [Indexed: 02/06/2023] Open
Abstract
Δ133p53α, a p53 isoform that can inhibit full-length p53, is downregulated at replicative senescence in a manner independent of mRNA regulation and proteasome-mediated degradation. Here we demonstrate that, unlike full-length p53, Δ133p53α is degraded by autophagy during replicative senescence. Pharmacological inhibition of autophagy restores Δ133p53α expression levels in replicatively senescent fibroblasts, without affecting full-length p53. The siRNA-mediated knockdown of pro-autophagic proteins (ATG5, ATG7 and Beclin-1) also restores Δ133p53α expression. The chaperone-associated E3 ubiquitin ligase STUB1, which is known to regulate autophagy, interacts with Δ133p53α and is downregulated at replicative senescence. The siRNA knockdown of STUB1 in proliferating, early-passage fibroblasts induces the autophagic degradation of Δ133p53α and thereby induces senescence. Upon replicative senescence or STUB1 knockdown, Δ133p53α is recruited to autophagosomes, consistent with its autophagic degradation. This study reveals that STUB1 is an endogenous regulator of Δ133p53α degradation and senescence, and identifies a p53 isoform-specific protein turnover mechanism that orchestrates p53-mediated senescence.
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Affiliation(s)
- Izumi Horikawa
- 1] Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Bethesda, Maryland 20892-4258, USA [2]
| | - Kaori Fujita
- 1] Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Bethesda, Maryland 20892-4258, USA [2] [3]
| | - Lisa M Miller Jenkins
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Bethesda, Maryland 20892-4258, USA
| | - Yukiharu Hiyoshi
- Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Bethesda, Maryland 20892-4258, USA
| | - Abdul M Mondal
- Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Bethesda, Maryland 20892-4258, USA
| | - Borivoj Vojtesek
- Regional Centre for Applied and Molecular Oncology, Masaryk Memorial Cancer Institute, Zluty Kopec 7, Brno 65653, Czech Republic
| | - David P Lane
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673, Singapore
| | - Ettore Appella
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Bethesda, Maryland 20892-4258, USA
| | - Curtis C Harris
- Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Bethesda, Maryland 20892-4258, USA
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57
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Suico MA, Fukuda R, Miyakita R, Koyama K, Taura M, Shuto T, Kai H. The transcription factor MEF/Elf4 is dually modulated by p53-MDM2 axis and MEF-MDM2 autoregulatory mechanism. J Biol Chem 2014; 289:26143-26154. [PMID: 25081543 DOI: 10.1074/jbc.m114.580209] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myeloid Elf-1-like factor (MEF) or Elf4 is an ETS transcription factor that activates innate immunity-associated genes such as lysozyme (LYZ), human β-defensin 2 (HβD2), and interleukin-8 (IL-8) in epithelial cells and is also known to influence cell cycle progression. MEF is transcriptionally activated by E2F1, but the E2F1-mediated transcriptional activation is inhibited by p53 through E2F1-p53 protein interaction. Although the transcriptional activation of MEF has been investigated in depth, its post-translational regulation is not well explored. By overexpressing MEF cDNA in human cell lines, here we show that MEF protein expression is suppressed by p53. By screening a number of E3 ligases regulated by p53, we found that MDM2 is involved in the effect of p53 on MEF. MDM2 is transcriptionally activated by p53 and interacts with MEF protein to enhance MEF degradation. MDM2 reduces MEF protein expression, as well as stability and function of MEF as transcriptional activator. Furthermore, MDM2 was able to down-regulate MEF in the absence of p53, indicating a p53-independent effect on MEF. Notably, MEF transcriptionally activates MDM2, which was previously demonstrated to be the mechanism by which MEF suppresses the p53 protein. These results reveal that in addition to the potential of MEF to down-regulate p53 by transcriptionally activating E3 ligase MDM2, MEF participates with MDM2 in a novel autoregulatory feedback loop to regulate itself. Taken together with the findings on the effect of p53 on MEF, these data provide evidence that the p53-MDM2-MEF axis is a feedback mechanism that exquisitely controls the balance of these transcriptional regulators.
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Affiliation(s)
- Mary Ann Suico
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan.
| | - Ryosuke Fukuda
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan
| | - Rui Miyakita
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan
| | - Kosuke Koyama
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan
| | - Manabu Taura
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan
| | - Tsuyoshi Shuto
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan
| | - Hirofumi Kai
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan
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58
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Abstract
Telomeres protect chromosome ends from degradation and inappropriate DNA damage response activation through their association with specific factors. Interestingly, these telomeric factors are able to localize outside telomeric regions, where they can regulate the transcription of genes involved in metabolism, immunity and differentiation. These findings delineate a signalling pathway by which telomeric changes control the ability of their associated factors to regulate transcription. This mechanism is expected to enable a greater diversity of cellular responses that are adapted to specific cell types and telomeric changes, and may therefore represent a pivotal aspect of development, ageing and telomere-mediated diseases.
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59
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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.
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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
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60
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Dinami R, Ercolani C, Petti E, Piazza S, Ciani Y, Sestito R, Sacconi A, Biagioni F, le Sage C, Agami R, Benetti R, Mottolese M, Schneider C, Blandino G, Schoeftner S. miR-155 drives telomere fragility in human breast cancer by targeting TRF1. Cancer Res 2014; 74:4145-56. [PMID: 24876105 DOI: 10.1158/0008-5472.can-13-2038] [Citation(s) in RCA: 90] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Telomeres consist of DNA tandem repeats that recruit the multiprotein complex shelterin to build a chromatin structure that protects chromosome ends. Although cancer formation is linked to alterations in telomere homeostasis, there is little understanding of how shelterin function is limited in cancer cells. Using a small-scale screening approach, we identified miR-155 as a key regulator in breast cancer cell expression of the shelterin component TERF1 (TRF1). miR-155 targeted a conserved sequence motif in the 3'UTR of TRF1, resulting in its translational repression. miR-155 was upregulated commonly in breast cancer specimens, as associated with reduced TRF1 protein expression, metastasis-free survival, and relapse-free survival in estrogen receptor-positive cases. Modulating miR-155 expression in cells altered TRF1 levels and TRF1 abundance at telomeres. Compromising TRF1 expression by elevating miR-155 increased telomere fragility and altered the structure of metaphase chromosomes. In contrast, reducing miR-155 levels improved telomere function and genomic stability. These results implied that miR-155 upregulation antagonizes telomere integrity in breast cancer cells, increasing genomic instability linked to poor clinical outcome in estrogen receptor-positive disease. Our work argued that miRNA-dependent regulation of shelterin function has a clinically significant impact on telomere function, suggesting the existence of "telo-miRNAs" that have an impact on cancer and aging.
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Affiliation(s)
- Roberto Dinami
- Telomeres in Cancer and Aging Unit, Dipartimento di Scienze della Vita, SDBM School of Molecular Biomedicine (SDBM), Università degli Studi di Trieste, Trieste; Telomeres in Cancer and Aging Unit
| | | | - Eleonora Petti
- Telomeres in Cancer and Aging Unit, Dipartimento di Scienze della Vita, SDBM School of Molecular Biomedicine (SDBM), Università degli Studi di Trieste, Trieste; Telomeres in Cancer and Aging Unit
| | | | - Yari Ciani
- Bioinformatics and Functional Genomics Unit, and
| | | | | | | | - Carlos le Sage
- Division of Gene Regulation, The Netherlands Cancer Institute, Amsterdam, the Netherlands
| | - Reuven Agami
- Division of Gene Regulation, The Netherlands Cancer Institute, Amsterdam, the Netherlands
| | - Roberta Benetti
- Epigenetics Unit, Laboratorio Nazionale Consorzio Interuniversitario Biotecnologie (LNCIB); Dipartimento di Scienze Mediche e Biologiche, Universita degli Studi di Udine, Udine, Italy; and
| | | | - Claudio Schneider
- Bioinformatics and Functional Genomics Unit, and Dipartimento di Scienze Mediche e Biologiche, Universita degli Studi di Udine, Udine, Italy; and
| | | | - Stefan Schoeftner
- Telomeres in Cancer and Aging Unit, Telomeres in Cancer and Aging Unit,
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61
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Mitchell TRH, Zhu XD. Methylated TRF2 associates with the nuclear matrix and serves as a potential biomarker for cellular senescence. Aging (Albany NY) 2014; 6:248-63. [PMID: 24721747 PMCID: PMC4032793 DOI: 10.18632/aging.100650] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 04/03/2014] [Indexed: 11/25/2022]
Abstract
Methylation of N-terminal arginines of the shelterin component TRF2 is important for cellular proliferation. While TRF2 is found at telomeres, where it plays an essential role in maintaining telomere integrity, little is known about the cellular localization of methylated TRF2. Here we report that the majority of methylated TRF2 is resistant to extraction by high salt buffer and DNase I treatment, indicating that methylated TRF2 is tightly associated with the nuclear matrix. We show that methylated TRF2 drastically alters its nuclear staining as normal human primary fibroblast cells approach and enter replicative senescence. This altered nuclear staining, which is found to be overwhelmingly associated with misshapen nuclei and abnormal nuclear matrix folds, can be suppressed by hTERT and it is barely detectable in transformed and cancer cell lines. We find that dysfunctional telomeres and DNA damage, both of which are potent inducers of cellular senescence, promote the altered nuclear staining of methylated TRF2, which is dependent upon the ATM-mediated DNA damage response. Collectively, these results suggest that the altered nuclear staining of methylated TRF2 may represent ATM-mediated nuclear structural alteration associated with cellular senescence. Our data further imply that methylated TRF2 can serve as a potential biomarker for cellular senescence.
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Affiliation(s)
- Taylor R H Mitchell
- Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1
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62
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Qi J, Kim H, Scortegagna M, Ronai ZA. Regulators and effectors of Siah ubiquitin ligases. Cell Biochem Biophys 2014; 67:15-24. [PMID: 23700162 DOI: 10.1007/s12013-013-9636-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The Siah ubiquitin ligases are members of the RING finger E3 ligases. The Siah E3s are conserved from fly to mammals. Primarily implicated in cellular stress responses, Siah ligases play a key role in hypoxia, through the regulation of HIF-1α transcription stability and activity. Concomitantly, physiological conditions associated with varying oxygen tension often highlight the importance of Siah, as seen in cancer and neurodegenerative disorders. Notably, recent studies also point to the role of these ligases in fundamental processes including DNA damage response, cellular organization and polarity. This review summarizes the current understanding of upstream regulators and downstream effectors of Siah.
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Affiliation(s)
- Jianfei Qi
- Signal Transduction Program, Cancer Center, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA
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63
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Saha B, Zitnik G, Johnson S, Nguyen Q, Risques RA, Martin GM, Oshima J. DNA damage accumulation and TRF2 degradation in atypical Werner syndrome fibroblasts with LMNA mutations. Front Genet 2013; 4:129. [PMID: 23847654 PMCID: PMC3701863 DOI: 10.3389/fgene.2013.00129] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Accepted: 06/16/2013] [Indexed: 02/01/2023] Open
Abstract
Segmental progeroid syndromes are groups of disorders with multiple features suggestive of accelerated aging. One subset of adult-onset progeroid syndromes, referred to as atypical Werner syndrome, is caused by mutations in the LMNA gene, which encodes a class of nuclear intermediate filaments, lamin A/C. We previously described rapid telomere attrition and accelerated replicative senescence in cultured fibroblasts overexpressing mutant lamin A. In this study, we investigated the cellular phenotypes associated with accelerated telomere shortening in LMNA mutant primary fibroblasts. In early passage primary fibroblasts with R133L or L140R LMNA mutations, shelterin protein components were already reduced while cells still retained telomere lengths comparable to those of controls. There was a significant inverse correlation between the degree of abnormal nuclear morphology and the level of TRF2, a shelterin subunit, suggesting a potential causal relationship. Stabilization of the telomeres via the introduction of the catalytic subunit of human telomerase, hTERT (human telomerase reverse transcriptase), did not prevent degradation of shelterin components, indicating that reduced TRF2 in LMNA mutants is not mediated by short telomeres. Interestingly, γ-H2AX foci (reflecting double strand DNA damage) in early passage LMNA mutant primary fibroblasts and LMNA mutant hTERT fibroblasts were markedly increased in non-telomeric regions of DNA. Our results raise the possibility that mutant lamin A/C causes global genomic instability with accumulation of non-telomeric DNA damage as an early event, followed by TRF2 degradation and telomere shortening.
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Affiliation(s)
- Bidisha Saha
- Department of Pathology, University of Washington Seattle, WA, USA
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64
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Yeung F, Ramírez CM, Mateos-Gomez PA, Pinzaru A, Ceccarini G, Kabir S, Fernández-Hernando C, Sfeir A. Nontelomeric role for Rap1 in regulating metabolism and protecting against obesity. Cell Rep 2013; 3:1847-56. [PMID: 23791522 DOI: 10.1016/j.celrep.2013.05.032] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Revised: 04/16/2013] [Accepted: 05/21/2013] [Indexed: 11/15/2022] Open
Abstract
The mammalian telomere-binding protein Rap1 was recently found to have additional nontelomeric functions, acting as a transcriptional cofactor and a regulator of the NF-κB pathway. Here, we assess the effect of disrupting mouse Rap1 in vivo and report on its unanticipated role in metabolic regulation and body-weight homeostasis. Rap1 inhibition causes dysregulation in hepatic as well as adipose function, leading to glucose intolerance, insulin resistance, liver steatosis, and excess fat accumulation. Furthermore, Rap1 appears to play a pivotal role in the transcriptional cascade that controls adipocyte differentiation in vitro. Using a separation-of-function allele, we show that the metabolic function of Rap1 is independent of its recruitment to TTAGGG binding elements found at telomeres and at other interstitial loci. In conclusion, our study underscores an additional function for the most conserved telomere-binding protein, forging a link between telomere biology and metabolic signaling.
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Affiliation(s)
- Frank Yeung
- The Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, Department of Cell Biology, NYU School of Medicine, New York, NY 10016, USA
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65
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Simeonova I, Jaber S, Draskovic I, Bardot B, Fang M, Bouarich-Bourimi R, Lejour V, Charbonnier L, Soudais C, Bourdon JC, Huerre M, Londono-Vallejo A, Toledo F. Mutant mice lacking the p53 C-terminal domain model telomere syndromes. Cell Rep 2013; 3:2046-58. [PMID: 23770245 DOI: 10.1016/j.celrep.2013.05.028] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 04/01/2013] [Accepted: 05/17/2013] [Indexed: 11/29/2022] Open
Abstract
Mutations in p53, although frequent in human cancers, have not been implicated in telomere-related syndromes. Here, we show that homozygous mutant mice expressing p53Δ31, a p53 lacking the C-terminal domain, exhibit increased p53 activity and suffer from aplastic anemia and pulmonary fibrosis, hallmarks of syndromes caused by short telomeres. Indeed, p53Δ31/Δ31 mice had short telomeres and other phenotypic traits associated with the telomere disease dyskeratosis congenita and its severe variant the Hoyeraal-Hreidarsson syndrome. Heterozygous p53+/Δ31 mice were only mildly affected, but decreased levels of Mdm4, a negative regulator of p53, led to a dramatic aggravation of their symptoms. Importantly, several genes involved in telomere metabolism were downregulated in p53Δ31/Δ31 cells, including Dyskerin, Rtel1, and Tinf2, which are mutated in dyskeratosis congenita, and Terf1, which is implicated in aplastic anemia. Together, these data reveal that a truncating mutation can activate p53 and that p53 plays a major role in the regulation of telomere metabolism.
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Affiliation(s)
- Iva Simeonova
- Genetics of Tumor Suppression, Institut Curie, Centre de Recherche, 26 rue d'Ulm, 75248 Paris Cedex 05, France
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66
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Zhang X, Jia D, Liu H, Zhu N, Zhang W, Feng J, Yin J, Hao B, Cui D, Deng Y, Xie D, He L, Li B. Identification of 5-Iodotubercidin as a genotoxic drug with anti-cancer potential. PLoS One 2013; 8:e62527. [PMID: 23667485 PMCID: PMC3646850 DOI: 10.1371/journal.pone.0062527] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Accepted: 03/22/2013] [Indexed: 11/19/2022] Open
Abstract
Tumor suppressor p53, which is activated by various stress and oncogene activation, is a target for anti-cancer drug development. In this study, by screening panels of protein kinase inhibitors and protein phosphatase inhibitors, we identified 5-Iodotubercidin as a strong p53 activator. 5-Iodotubercidin is purine derivative and is used as an inhibitor for various kinases including adenosine kinase. We found that 5-Iodotubercidin could cause DNA damage, verified by induction of DNA breaks and nuclear foci positive for γH2AX and TopBP1, activation of Atm and Chk2, and S15 phosphorylation and up-regulation of p53. As such, 5-Iodotubercidin induces G2 cell cycle arrest in a p53-dependent manner. Itu also induces cell death in p53-dependent and -independent manners. DNA breaks were likely generated by incorporation of 5-Iodotubercidin metabolite into DNA. Moreover, 5-Iodotubercidin showed anti-tumor activity as it could reduce the tumor size in carcinoma xenograft mouse models in p53-dependent and -independent manners. These findings reveal 5-Iodotubercidin as a novel genotoxic drug that has chemotherapeutic potential.
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Affiliation(s)
- Xin Zhang
- Bio-X Institutes, Key Laboratory for the Genetics of Developmental and Neuropsychiatric Disorders, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
| | - Deyong Jia
- Bio-X Institutes, Key Laboratory for the Genetics of Developmental and Neuropsychiatric Disorders, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
| | - Huijuan Liu
- Bio-X Institutes, Key Laboratory for the Genetics of Developmental and Neuropsychiatric Disorders, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
| | - Na Zhu
- Instrumental Analysis Center, Shanghai Jiao Tong University, Shanghai, China
| | - Wei Zhang
- School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Jun Feng
- School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Jun Yin
- School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Bin Hao
- School of Pharmacy, Shanghai Jiao Tong University, Shanghai, China
| | - Daxiang Cui
- Research Institute of Micro/Nano Science and Technology, Shanghai Jiao Tong University, Shanghai, China
| | - Yuezhen Deng
- Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Dong Xie
- Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Lin He
- Bio-X Institutes, Key Laboratory for the Genetics of Developmental and Neuropsychiatric Disorders, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
| | - Baojie Li
- Bio-X Institutes, Key Laboratory for the Genetics of Developmental and Neuropsychiatric Disorders, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
- * E-mail:
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67
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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.
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Affiliation(s)
- Alessandra Galati
- Dipartimento di Biologia e Biotecnologie, Istituto Pasteur - Fondazione Cenci Bolognetti, Sapienza Università di Roma Rome, Italy
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68
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Telomere protection and TRF2 expression are enhanced by the canonical Wnt signalling pathway. EMBO Rep 2013; 14:356-63. [PMID: 23429341 DOI: 10.1038/embor.2013.16] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 12/24/2012] [Accepted: 01/28/2013] [Indexed: 02/06/2023] Open
Abstract
The DNA-binding protein TRF2 is essential for telomere protection and chromosome stability in mammals. We show here that TRF2 expression is activated by the Wnt/β-catenin signalling pathway in human cancer and normal cells as well as in mouse intestinal tissues. Furthermore, β-catenin binds to TRF2 gene regulatory regions that are functional in a luciferase transactivating assay. Reduced β-catenin expression in cancer cells triggers a marked increase in telomere dysfunction, which can be reversed by TRF2 overexpression. We conclude that the Wnt/β-catenin signalling pathway maintains a level of TRF2 critical for telomere protection. This is expected to have an important role during development, adult stem cell function and oncogenesis.
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69
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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.
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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
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70
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Kato M, Nakayama M, Agata M, Yoshida K. Gene expression levels of human shelterin complex and shelterin-associated factors regulated by the topoisomerase II inhibitors doxorubicin and etoposide in human cultured cells. Tumour Biol 2012; 34:723-33. [PMID: 23247865 DOI: 10.1007/s13277-012-0600-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Accepted: 11/16/2012] [Indexed: 02/08/2023] Open
Abstract
Human telomerase reverse transcriptase (hTERT) is responsible for telomere elongation, and its activity is strongly related to the expression level of the hTERT gene; however, the transcriptional regulation of telomeric genes, which play a central role in telomere maintenance and protection by facilitating replication and regulating telomerase access, is poorly understood. In this study, we aimed to reveal the changes in the mRNA expression of six components of the shelterin complex and three shelterin complex-associated factors in topoisomerase II inhibitor-treated human cultured cells. Using a quantitative gene expression analysis, we found that a reduction in telomeric repeat-binding factor 1 (TRF1), protection of telomeres (POT1), and TRF1-interacting ankyrin-related ADP-ribose polymerase 1 (TNKS1) mRNAs was observed in etoposide- and doxorubicin-treated HeLa and U-2 OS cells, while an increased TRF2-interacting telomeric protein (RAP1) mRNA level was observed in U-2 OS cells. Furthermore, doxorubicin suppressed TRF1 and POT1 mRNAs in both Saos-2 and WI-38 cells and increased RAP1 mRNA in WI-38 cells. In agreement with the results obtained in the quantitative gene expression analysis in U-2 OS cells, the topoisomerase II inhibitors negatively and positively regulated the POT1 and RAP1 gene promoters, respectively. Taken together, these results suggest the successful identification of unique topoisomerase II inhibitor-inducible telomeric genes and provide mechanistic insight into the regulation of telomeric gene expression by chemotherapeutic agents.
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Affiliation(s)
- Masahiro Kato
- Department of Life Sciences, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571, Japan
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71
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Hodjat M, Haller H, Dumler I, Kiyan Y. Urokinase receptor mediates doxorubicin-induced vascular smooth muscle cell senescence via proteasomal degradation of TRF2. J Vasc Res 2012; 50:109-23. [PMID: 23172421 DOI: 10.1159/000343000] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Accepted: 08/23/2012] [Indexed: 11/19/2022] Open
Abstract
The anthracycline doxorubicin is a widely used effective anti-cancer drug. However, its application and dosage are severely limited due to its cardiotoxicity. The exact mechanisms of doxorubicin-induced cardiotoxic side effects remain poorly understood. Even less is known about the impact of doxorubicin treatment on vascular damage. We found that low doses of doxorubicin induced a senescent response in human primary vascular smooth muscle cells (VSMC). We observed that expression of urokinase receptor (uPAR) was upregulated in response to doxorubicin. Furthermore, the level of uPAR expression played a decisive role in developing doxorubicin-induced senescence. uPAR silencing in human VSMC by means of RNA interference as well as uPAR knockout in mouse VSMC resulted in abrogation of doxorubicin-induced cellular senescence. On the contrary, uPAR overexpression promoted VSMC senescence. We further found that proteasomal degradation of telomeric repeat binding factor 2 (TRF2) mediates doxorubicin-induced VSMC senescence. Our results demonstrate that uPAR controls the ubiquitin-proteasome system in VSMC and regulates doxorubicin-induced TRF2 ubiquitination and proteasomal degradation via this mechanism. Therefore, VSMC senescence induced by low doses of doxorubicin may contribute to vascular damage upon doxorubicin treatment. uPAR-mediated TRF2 ubiquitination and proteasomal degradation are further identified as a molecular mechanism underlying this process.
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Affiliation(s)
- Mahshid Hodjat
- Nephrology Department, Hannover Medical School, Hannover, Germany
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72
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Tang Y, Horikawa I, Ajiro M, Robles AI, Fujita K, Mondal AM, Stauffer JK, Zheng ZM, Harris CC. Downregulation of splicing factor SRSF3 induces p53β, an alternatively spliced isoform of p53 that promotes cellular senescence. Oncogene 2012; 32:2792-8. [PMID: 22777358 DOI: 10.1038/onc.2012.288] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Most human pre-mRNA transcripts are alternatively spliced, but the significance and fine-tuning of alternative splicing in different biological processes is only starting to be understood. SRSF3 (SRp20) is a member of a highly conserved family of splicing factors that have critical roles in key biological processes, including tumor progression. Here, we show that SRSF3 regulates cellular senescence, a p53-mediated process to suppress tumorigenesis, through TP53 alternative splicing. Downregulation of SRSF3 was observed in normal human fibroblasts undergoing replicative senescence, and was associated with the upregulation of p53β, an alternatively spliced isoform of p53 that promotes p53-mediated senescence. Knockdown of SRSF3 by short interfering RNA (siRNA) in early-passage fibroblasts induced senescence, which was associated with elevated expression of p53β at mRNA and protein levels. Knockdown of p53 partially rescued SRSF3-knockdown-induced senescence, suggesting that SRSF3 acts on p53-mediated cellular senescence. RNA pulldown assays demonstrated that SRSF3 binds to an alternatively spliced exon uniquely included in p53β mRNA through the consensus SRSF3-binding sequences. RNA crosslinking and immunoprecipitation assays (CLIP) also showed that SRSF3 in vivo binds to endogenous p53 pre-mRNA at the region containing the p53β-unique exon. Splicing assays using a transfected TP53 minigene in combination with siRNA knockdown of SRSF3 showed that SRSF3 functions to inhibit the inclusion of the p53β-unique exon in splicing of p53 pre-mRNA. These data suggest that downregulation of SRSF3 represents an endogenous mechanism for cellular senescence that directly regulates the TP53 alternative splicing to generate p53β. This study uncovers the role for general splicing machinery in tumorigenesis, and suggests that SRSF3 is a direct regulator of p53.
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Affiliation(s)
- Y Tang
- Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4258, USA
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73
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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.
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Affiliation(s)
- John R Walker
- Department of Biology, LSB438, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
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74
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Peuscher MH, Jacobs JJL. Posttranslational control of telomere maintenance and the telomere damage response. Cell Cycle 2012; 11:1524-34. [PMID: 22433952 DOI: 10.4161/cc.19847] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Telomeres help maintain genome integrity by protecting natural chromosome ends from being recognized as damaged DNA. When telomeres become dysfunctional, they limit replicative lifespan and prevent outgrowth of potentially cancerous cells by activating a DNA damage response that forces cells into senescence or apoptosis. On the other hand, chromosome ends devoid of proper telomere protection are subject to DNA repair activities that cause end-to-end fusions and, when cells divide, extensive genomic instability that can promote cancer. While telomeres represent unique chromatin structures with important roles in cancer and aging, we have limited understanding of the way telomeres and the response to their malfunction are controlled at the level of chromatin. Accumulating evidence indicates that different types of posttranslational modifications act in both telomere maintenance and the response to telomere uncapping. Here, we discuss the latest insights on posttranslational control of telomeric chromatin, with emphasis on ubiquitylation and SUMOylation events.
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Affiliation(s)
- Marieke H Peuscher
- Division of Molecular Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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75
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Fumagalli M, Rossiello F, Clerici M, Barozzi S, Cittaro D, Kaplunov JM, Bucci G, Dobreva M, Matti V, Beausejour CM, Herbig U, Longhese MP, d'Adda di Fagagna F. Telomeric DNA damage is irreparable and causes persistent DNA-damage-response activation. Nat Cell Biol 2012; 14:355-65. [PMID: 22426077 DOI: 10.1038/ncb2466] [Citation(s) in RCA: 564] [Impact Index Per Article: 47.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Accepted: 02/17/2012] [Indexed: 02/08/2023]
Abstract
The DNA-damage response (DDR) arrests cell-cycle progression until damage is removed. DNA-damage-induced cellular senescence is associated with persistent DDR. The molecular bases that distinguish transient from persistent DDR are unknown. Here we show that a large fraction of exogenously induced persistent DDR markers is associated with telomeric DNA in cultured cells and mammalian tissues. In yeast, a chromosomal DNA double-strand break next to a telomeric sequence resists repair and impairs DNA ligase 4 recruitment. In mammalian cells, ectopic localization of telomeric factor TRF2 next to a double-strand break induces persistent DNA damage and DDR. Linear, but not circular, telomeric DNA or scrambled DNA induces a prolonged checkpoint in normal cells. In terminally differentiated tissues of old primates, DDR markers accumulate at telomeres that are not critically short. We propose that linear genomes are not uniformly reparable and that telomeric DNA tracts, if damaged, are irreparable and trigger persistent DDR and cellular senescence.
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Affiliation(s)
- Marzia Fumagalli
- IFOM Foundation-FIRC Institute of Molecular Oncology Foundation, Milan 20139, Italy
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76
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Abstract
DNA repair activities at DNA double-strand breaks (DSBs) are under control of regulatory ubiquitylation events governed by the RNF8 and RNF168 ubiquitin-ligases. Defects in this regulatory mechanism, as with mutation of other key DNA damage-response factors, lead to genomic instability and cancer, presumably due to impaired repair of DNA lesions. Recent work revealed that RNF8 and RNF168 also play critical roles at natural chromosome ends, when no longer adequately shielded by telomeres. In contrast to repair of DSBs being needed to maintain genome integrity, repair activities at telomeres create chromosome end-to-end fusions that threaten genome integrity. Upon cell division these telomere fusions give rise to genomic alterations and instability via chromosomal missegregration and initiation of breakage-fusion-bridge cycles. Here, I discuss the role of RNF8 at natural chromosome ends and its (potential) consequences.
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Affiliation(s)
- Jacqueline J L Jacobs
- Division of Molecular Genetics, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
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77
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Rai R, Li JM, Zheng H, Lok GTM, Deng Y, Huen MSY, Chen J, Jin J, Chang S. The E3 ubiquitin ligase Rnf8 stabilizes Tpp1 to promote telomere end protection. Nat Struct Mol Biol 2011; 18:1400-7. [PMID: 22101936 DOI: 10.1038/nsmb.2172] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 10/07/2011] [Indexed: 12/16/2022]
Abstract
The mammalian shelterin component TPP1 has essential roles in telomere maintenance and, together with POT1, is required for the repression of DNA damage signaling at telomeres. Here we show that in Mus musculus, the E3 ubiquitin ligase Rnf8 localizes to uncapped telomeres and promotes the accumulation of DNA damage proteins 53Bp1 and γ-H2ax. In the absence of Rnf8, Tpp1 is unstable, resulting in telomere shortening and chromosome fusions through the alternative nonhomologous end-joining (A-NHEJ) repair pathway. The Rnf8 RING-finger domain is essential for Tpp1 stability and retention at telomeres. Rnf8 physically interacts with Tpp1 to generate Ubc13-dependent Lys63 polyubiquitin chains that stabilize Tpp1 at telomeres. The conserved Tpp1 residue Lys233 is important for Rnf8-mediated Tpp1 ubiquitylation and localization to telomeres. Thus, Tpp1 is a newly identified substrate for Rnf8, indicating a previously unrecognized role for Rnf8 in telomere end protection.
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Affiliation(s)
- Rekha Rai
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
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78
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Abstract
Telomeres are coated by shelterin, a six-subunit complex that is required for protection and replication of chromosome ends. The central subunit TIN2, with binding sites to three subunits (TRF1, TRF2, and TPP1), is essential for stability and function of the complex. Here we show that TIN2 stability is regulated by the E3 ligase Siah2. We demonstrate that TIN2 binds to Siah2 and is ubiquitylated in vivo. We show using purified proteins that Siah2 acts as an E3 ligase to directly ubiquitylate TIN2 in vitro. Depletion of Siah2 led to stabilization of TIN2 protein, indicating that Siah2 regulates TIN2 protein levels in vivo. Overexpression of Siah2 in human cells led to loss of TIN2 at telomeres that was dependent on the presence of the catalytic RING domain of Siah2. In contrast to RNAi-mediated depletion of TIN2 that led to loss of TRF1 and TRF2 at telomeres, Siah2-mediated depletion of TIN2 allowed TRF1 and TRF2 to remain on telomeres, indicating a different fate for shelterin subunits when TIN2 is depleted posttranslationally. TPP1 was lost from telomeres, although its protein level was not reduced. We speculate that Siah2-mediated removal of TIN2 may allow dynamic remodeling of the shelterin complex and its associated factors during the cell cycle.
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79
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Joehanes R, Johnson AD, Barb JJ, Raghavachari N, Liu P, Woodhouse KA, O'Donnell CJ, Munson PJ, Levy D. Gene expression analysis of whole blood, peripheral blood mononuclear cells, and lymphoblastoid cell lines from the Framingham Heart Study. Physiol Genomics 2011; 44:59-75. [PMID: 22045913 DOI: 10.1152/physiolgenomics.00130.2011] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Despite a growing number of reports of gene expression analysis from blood-derived RNA sources, there have been few systematic comparisons of various RNA sources in transcriptomic analysis or for biomarker discovery in the context of cardiovascular disease (CVD). As a pilot study of the Systems Approach to Biomarker Research (SABRe) in CVD Initiative, this investigation used Affymetrix Exon arrays to characterize gene expression of three blood-derived RNA sources: lymphoblastoid cell lines (LCL), whole blood using PAXgene tubes (PAX), and peripheral blood mononuclear cells (PBMC). Their performance was compared in relation to identifying transcript associations with sex and CVD risk factors, such as age, high-density lipoprotein, and smoking status, and the differential blood cell count. We also identified a set of exons that vary substantially between participants, but consistently in each RNA source. Such exons are thus stable phenotypes of the participant and may potentially become useful fingerprinting biomarkers. In agreement with previous studies, we found that each of the RNA sources is distinct. Unlike PAX and PBMC, LCL gene expression showed little association with the differential blood count. LCL, however, was able to detect two genes related to smoking status. PAX and PBMC identified Y-chromosome probe sets similarly and slightly better than LCL.
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Affiliation(s)
- Roby Joehanes
- The National Heart, Lung, and Blood Institute's Framingham Heart Study, Framingham, Massachusetts, USA
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80
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Oxidative stress, mitochondrial dysfunction, and aging. JOURNAL OF SIGNAL TRANSDUCTION 2011; 2012:646354. [PMID: 21977319 PMCID: PMC3184498 DOI: 10.1155/2012/646354] [Citation(s) in RCA: 592] [Impact Index Per Article: 45.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 05/15/2011] [Accepted: 08/03/2011] [Indexed: 12/31/2022]
Abstract
Aging is an intricate phenomenon characterized by progressive decline in physiological functions and increase in mortality that is often accompanied by many pathological diseases. Although aging is almost universally conserved among all organisms, the underlying molecular mechanisms of aging remain largely elusive. Many theories of aging have been proposed, including the free-radical and mitochondrial theories of aging. Both theories speculate that cumulative damage to mitochondria and mitochondrial DNA (mtDNA) caused by reactive oxygen species (ROS) is one of the causes of aging. Oxidative damage affects replication and transcription of mtDNA and results in a decline in mitochondrial function which in turn leads to enhanced ROS production and further damage to mtDNA. In this paper, we will present the current understanding of the interplay between ROS and mitochondria and will discuss their potential impact on aging and age-related diseases.
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81
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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.
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Affiliation(s)
- Izumi Horikawa
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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