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Zeid D, Mooney-Leber S, Seemiller LR, Goldberg LR, Gould TJ. Terc Gene Cluster Variants Predict Liver Telomere Length in Mice. Cells 2021; 10:2623. [PMID: 34685603 PMCID: PMC8533930 DOI: 10.3390/cells10102623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 09/19/2021] [Accepted: 09/30/2021] [Indexed: 11/16/2022] Open
Abstract
Variants in a gene cluster upstream-adjacent to TERC on human chromosome 3, which includes genes APRM, LRRC31, LRRC34 and MYNN, have been associated with telomere length in several human populations. Currently, the mechanism by which variants in the TERC gene cluster influence telomere length in humans is unknown. Given the proximity between the TERC gene cluster and TERC (~0.05 Mb) in humans, it is speculated that cluster variants are in linkage disequilibrium with a TERC causal variant. In mice, the Terc gene/Terc gene cluster are also located on chromosome 3; however, the Terc gene cluster is located distantly downstream of Terc (~60 Mb). Here, we initially aim to investigate the interactions between genotype and nicotine exposure on absolute liver telomere length (aTL) in a panel of eight inbred mouse strains. Although we found no significant impact of nicotine on liver aTL, this first experiment identified candidate single nucleotide polymorphisms (SNPs) in the murine Terc gene cluster (within genes Lrrc31, Lrriq4 and Mynn) co-varying with aTL in our panel. In a second experiment, we tested the association of these Terc gene cluster variants with liver aTL in an independent panel of eight inbred mice selected based on candidate SNP genotype. This supported our initial finding that Terc gene cluster polymorphisms impact aTL in mice, consistent with data in human populations. This provides support for mice as a model for telomere dynamics, especially for studying mechanisms underlying the association between Terc cluster variants and telomere length. Finally, these data suggest that mechanisms independent of linkage disequilibrium between the Terc/TERC gene cluster and the Terc/TERC gene mediate the cluster's regulation of telomere length.
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Affiliation(s)
- Dana Zeid
- Department of Biobehavioral Health, Penn State University, University Park, PA 16802, USA; (L.R.S.); (L.R.G.); (T.J.G.)
| | - Sean Mooney-Leber
- Department of Psychology, University of Wisconsin-Stevens Point, Stevens Point, WI 54481, USA;
| | - Laurel R. Seemiller
- Department of Biobehavioral Health, Penn State University, University Park, PA 16802, USA; (L.R.S.); (L.R.G.); (T.J.G.)
| | - Lisa R. Goldberg
- Department of Biobehavioral Health, Penn State University, University Park, PA 16802, USA; (L.R.S.); (L.R.G.); (T.J.G.)
| | - Thomas J. Gould
- Department of Biobehavioral Health, Penn State University, University Park, PA 16802, USA; (L.R.S.); (L.R.G.); (T.J.G.)
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Human Telomerase RNA: Telomerase Component or More? Biomolecules 2020; 10:biom10060873. [PMID: 32517215 PMCID: PMC7355840 DOI: 10.3390/biom10060873] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Revised: 06/04/2020] [Accepted: 06/05/2020] [Indexed: 12/16/2022] Open
Abstract
Telomerase is a ribonucleoprotein complex that maintains the lengths of telomeres. Most studies of telomerase function have focused on the involvement of telomerase activation in the immortalization of cancer cells and cellular rejuvenation. However, some studies demonstrated that the results do not meet expectations for telomerase action in telomere maintenance. Recent results give reason to think that major telomerase components-the reverse transcriptase protein subunit and telomerase RNA-may participate in many cellular processes, including the regulation of apoptosis and autophagy, cell survival, pro-proliferative effects, regulation of gene expression, and protection against oxidative stress. However, the difficulties faced by scientist when researching telomerase component functions often reduce confidence in the minor effects observed in experiments. In this review, we focus on the analysis of the functions of telomerase components (paying more attention to the telomerase RNA component), both as a complex and as independent components, providing effects that are not associated with telomerase activity and telomere length maintenance. Despite the fact that the data on alternative roles of telomerase components look illusory, it would be wrong to completely reject the possibility of their involvement in other biological processes excluded from research/discussion. Investigations to improve the understanding of every aspect of the functioning of telomerase components will provide the basis for a more precise development of approaches to regulate cellular homeostasis, which is important for carcinogenesis and aging.
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Grandin N, Pereira B, Cohen C, Billard P, Dehais C, Carpentier C, Idbaih A, Bielle F, Ducray F, Figarella-Branger D, Delattre JY, Sanson M, Lomonte P, Poncet D, Verrelle P, Charbonneau M. The level of activity of the alternative lengthening of telomeres correlates with patient age in IDH-mutant ATRX-loss-of-expression anaplastic astrocytomas. Acta Neuropathol Commun 2019; 7:175. [PMID: 31706351 PMCID: PMC6842523 DOI: 10.1186/s40478-019-0833-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 10/25/2019] [Indexed: 12/25/2022] Open
Abstract
All cancer cells need to maintain functional telomeres to sustain continuous cell division and proliferation. In human diffuse gliomas, functional telomeres are maintained due either to reactivation of telomerase expression, the main pathway in most cancer types, or to activation of a mechanism called the alternative lengthening of telomeres (ALT). The presence of IDH1/2 mutations (IDH-mutant) together with loss of ATRX expression (ATRX-lost) are frequently associated with ALT in diffuse gliomas. However, detection of ALT, and a fortiori its quantification, are rarely, if ever, measured in neuropathology laboratories. We measured the level of ALT activity using the previously described quantitative “C-circle” assay and analyzed it in a well characterized cohort of 104 IDH-mutant and ATRX-lost adult diffuse gliomas. We report that in IDH-mutant ATRX-lost anaplastic astrocytomas, the intensity of ALT was inversely correlated with age (p < 0.001), the younger the patient, the higher the intensity of ALT. Strikingly, glioblastomas having progressed from anaplastic astrocytomas did not exhibit this correlation. ALT activity level in the tumor did not depend on telomere length in healthy tissue cells from the same patient. In summary, we have uncovered the existence, in anaplastic astrocytomas but not in glioblastomas with the same IDH and ATRX mutations, of a correlation between patient age and the level of activity of ALT, a telomerase-independent pathway of telomere maintenance.
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Lv N, Sun M, Liu C, Li J. Design and synthesis of 2-phenylpyrimidine coumarin derivatives as anticancer agents. Bioorg Med Chem Lett 2017; 27:4578-4581. [DOI: 10.1016/j.bmcl.2017.08.044] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2017] [Revised: 08/17/2017] [Accepted: 08/19/2017] [Indexed: 12/12/2022]
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Balc'h EL, Grandin N, Demattei MV, Guyétant S, Tallet A, Pagès JC, Ouaissi M, Lecomte T, Charbonneau M. Measurement of Telomere Length in Colorectal Cancers for Improved Molecular Diagnosis. Int J Mol Sci 2017; 18:ijms18091871. [PMID: 28850092 PMCID: PMC5618520 DOI: 10.3390/ijms18091871] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 08/18/2017] [Accepted: 08/25/2017] [Indexed: 02/06/2023] Open
Abstract
All tumors have in common to reactivate a telomere maintenance mechanism to allow for unlimited proliferation. On the other hand, genetic instability found in some tumors can result from the loss of telomeres. Here, we measured telomere length in colorectal cancers (CRCs) using TRF (Telomere Restriction Fragment) analysis. Telomeric DNA content was also quantified as the ratio of total telomeric (TTAGGG) sequences over that of the invariable Alu sequences. In most of the 125 CRCs analyzed, there was a significant diminution in telomere length compared with that in control healthy tissue. Only 34 tumors exhibited no telomere erosion and, in some cases, a slight telomere lengthening. Telomere length did not correlate with age, gender, tumor stage, tumor localization or stage of tumor differentiation. In addition, while telomere length did not correlate with the presence of a mutation in BRAF (V-raf murine sarcoma viral oncogene homolog B), PIK3CA (phosphatidylinositol 3-kinase catalytic subunit), or MSI status, it was significantly associated with the occurrence of a mutation in KRAS. Interestingly, we found that the shorter the telomeres in healthy tissue of a patient, the larger an increase in telomere length in the tumor. Our study points to the existence of two types of CRCs based on telomere length and reveals that telomere length in healthy tissue might influence telomere maintenance mechanisms in the tumor.
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Affiliation(s)
- Eric Le Balc'h
- CHRU Hôpital de Tours Trousseau, avenue de la République, 37170 Chambray-lès-Tours, France.
| | - Nathalie Grandin
- UMR CNRS 7292, UFR Pharmacy, University of Tours, Parc Grandmont, 31 avenue Monge, 37200 Tours, France.
| | - Marie-Véronique Demattei
- UMR CNRS 7292, UFR Pharmacy, University of Tours, Parc Grandmont, 31 avenue Monge, 37200 Tours, France.
| | - Serge Guyétant
- CHRU Hôpital de Tours Trousseau, avenue de la République, 37170 Chambray-lès-Tours, France.
| | - Anne Tallet
- CHRU Hôpital de Tours Trousseau, avenue de la République, 37170 Chambray-lès-Tours, France.
| | - Jean-Christophe Pagès
- CHRU Hôpital de Tours Trousseau, avenue de la République, 37170 Chambray-lès-Tours, France.
| | - Mehdi Ouaissi
- CHRU Hôpital de Tours Trousseau, avenue de la République, 37170 Chambray-lès-Tours, France.
| | - Thierry Lecomte
- CHRU Hôpital de Tours Trousseau, avenue de la République, 37170 Chambray-lès-Tours, France.
- UMR CNRS 7292, UFR Pharmacy, University of Tours, Parc Grandmont, 31 avenue Monge, 37200 Tours, France.
| | - Michel Charbonneau
- UMR CNRS 7292, UFR Pharmacy, University of Tours, Parc Grandmont, 31 avenue Monge, 37200 Tours, France.
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Detection of the alternative lengthening of telomeres pathway in malignant gliomas for improved molecular diagnosis. J Neurooncol 2017; 135:381-390. [PMID: 28755323 DOI: 10.1007/s11060-017-2585-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 07/23/2017] [Indexed: 12/24/2022]
Abstract
Human malignant gliomas exhibit acquisition of either one of two telomere maintenance mechanisms, resulting from either reactivation of telomerase expression or activation of an alternative lengthening of telomeres (ALT) mechanism. In the present study, we analyzed 63 human malignant gliomas for the presence of ALT-specific extrachromosomal circles of telomeric DNA (C-circles) and measured telomerase expression, telomeric DNA content (Telo/Alu method), and telomeric repeat-containing RNAs (TERRA) levels. We also assessed histomolecular markers routinely used in clinical practice. The presence of C-circles significantly correlated with IDH1/2 mutation, MGMT exon 1 methylation, low Ki-67 immunostaining, increased telomeric DNA content, absence of functional ATRX protein and level of HTERT gene expression. In multivariate analysis, we observed a trend to a correlation between elevated TERRA levels and increased survival. Interestingly, the C-circles assay allowed to detect ALT activation in glioblastomas exhibiting wild-type IDH1/2 and ATRX expression. These results suggest that, after the correlations uncovered here have been confirmed on larger numbers of tumors, telomeric markers might be useful in improving diagnosis. They also point out to the utility of using the specific, sensitive and quantitative C-circle and Telo/Alu assays that can work with as few as 30 ng of tumor DNA.
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Ozturk MB, Li Y, Tergaonkar V. Current Insights to Regulation and Role of Telomerase in Human Diseases. Antioxidants (Basel) 2017; 6:antiox6010017. [PMID: 28264499 PMCID: PMC5384180 DOI: 10.3390/antiox6010017] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 02/16/2017] [Accepted: 02/21/2017] [Indexed: 12/31/2022] Open
Abstract
The telomerase ribonucleoprotein complex has a pivotal role in regulating the proliferation and senescence of normal somatic cells as well as cancer cells. This complex is comprised mainly of telomerase reverse transcriptase (TERT), telomerase RNA component (TERC) and other associated proteins that function to elongate telomeres localized at the end of the chromosomes. While reactivation of telomerase is a major hallmark of most cancers, together with the synergistic activation of other oncogenic signals, deficiency in telomerase and telomeric proteins might lead to aging and senescence-associated disorders. Therefore, it is critically important to understand the canonical as well as non-canonical functions of telomerase through TERT to develop a therapeutic strategy against telomerase-related diseases. In this review, we shed light on the regulation and function of telomerase, and current therapeutic strategies against telomerase in cancer and age-related diseases.
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Affiliation(s)
- Mert Burak Ozturk
- Division of Cancer Genetics and Therapeutics, Laboratory of NFκB Signaling, Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Singapore 138673, Singapore.
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore 117597, Singapore.
| | - Yinghui Li
- Division of Cancer Genetics and Therapeutics, Laboratory of NFκB Signaling, Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Singapore 138673, Singapore.
| | - Vinay Tergaonkar
- Division of Cancer Genetics and Therapeutics, Laboratory of NFκB Signaling, Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Singapore 138673, Singapore.
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore 117597, Singapore.
- Centre for Cancer Biology, University of South Australia and SA Pathology, Adelaide SA 5000, Australia.
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Liu N, Ding D, Hao W, Yang F, Wu X, Wang M, Xu X, Ju Z, Liu JP, Song Z, Shay JW, Guo Y, Cong YS. hTERT promotes tumor angiogenesis by activating VEGF via interactions with the Sp1 transcription factor. Nucleic Acids Res 2016; 44:8693-8703. [PMID: 27325744 PMCID: PMC5062966 DOI: 10.1093/nar/gkw549] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 06/04/2016] [Accepted: 06/07/2016] [Indexed: 12/11/2022] Open
Abstract
Angiogenesis is recognized as an important hallmark of cancer. Although telomerase is thought to be involved in tumor angiogenesis, the evidence and underlying mechanism remain elusive. Here, we demonstrate that human telomerase reverse transcriptase (hTERT) activates vascular epithelial growth factor (VEGF) gene expression through interactions with the VEGF promoter and the transcription factor Sp1. hTERT binds to Sp1 in vitro and in vivo and stimulates angiogenesis in a manner dependent on Sp1. Deletion of the mTert gene in the first generation of Tert null mice compromised tumor growth, with reduced VEGF expression. In addition, we show that hTERT expression levels are positively correlated with those of VEGF in human gastric tumor samples. Together, our results demonstrate that hTERT facilitates tumor angiogenesis by up-regulating VEGF expression through direct interactions with the VEGF gene and the Sp1 transcription factor. These results provide novel insights into hTERT function in tumor progression in addition to its role in telomere maintenance.
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Affiliation(s)
- Ning Liu
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Deqiang Ding
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Wanyu Hao
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Fan Yang
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Xiaoying Wu
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Miao Wang
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Xiaoling Xu
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Zhenyu Ju
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Jun-Ping Liu
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
| | - Zhangfa Song
- Sir Run Run Shaw Hospital, Medical School, Zhejiang University, Hangzhou 310016, China
| | - Jerry W Shay
- University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Yunliang Guo
- Institute of Cerebrovascular Diseases, Affiliated Hospital of Qingdao University, Qingdao 266003, China
| | - Yu-Sheng Cong
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou 311121, China
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9
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Chen Y, Zhang Y. Functional and mechanistic analysis of telomerase: An antitumor drug target. Pharmacol Ther 2016; 163:24-47. [DOI: 10.1016/j.pharmthera.2016.03.017] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 03/29/2016] [Indexed: 01/26/2023]
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Harada G, Pattarawat P, Ito K, Matsumoto T, Hasegawa T, Katakura Y. Lactobacillus brevis T2102 suppresses the growth of colorectal cancer cells by activating SIRT1. J Funct Foods 2016. [DOI: 10.1016/j.jff.2016.01.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
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Akincilar SC, Unal B, Tergaonkar V. Reactivation of telomerase in cancer. Cell Mol Life Sci 2016; 73:1659-70. [PMID: 26846696 PMCID: PMC4805692 DOI: 10.1007/s00018-016-2146-9] [Citation(s) in RCA: 134] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Revised: 01/19/2016] [Accepted: 01/21/2016] [Indexed: 02/06/2023]
Abstract
Activation of telomerase is a critical step in the development of about 85 % of human cancers. Levels of Tert, which encodes the reverse transcriptase subunit of telomerase, are limiting in normal somatic cells. Tert is subjected to transcriptional, post-transcriptional and epigenetic regulation, but the precise mechanism of how telomerase is re-activated in cancer cells is poorly understood. Reactivation of the Tert promoter involves multiple changes which evolve during cancer progression including mutations and chromosomal re-arrangements. Newly described non-coding mutations in the Tert promoter region of many cancer cells (19 %) in two key positions, C250T and C228T, have added another layer of complexity to telomerase reactivation. These mutations create novel consensus sequences for transcription factors which can enhance Tert expression. In this review, we will discuss gene structure and function of Tert and provide insights into the mechanisms of Tert reactivation in cancers, highlighting the contribution of recently identified Tert promoter mutations.
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Affiliation(s)
- Semih Can Akincilar
- Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Proteos, 61, Biopolis Drive, Singapore, 138673, Singapore
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore, 117597, Singapore
| | - Bilal Unal
- Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Proteos, 61, Biopolis Drive, Singapore, 138673, Singapore
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore, 117597, Singapore
| | - Vinay Tergaonkar
- Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Proteos, 61, Biopolis Drive, Singapore, 138673, Singapore.
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore, 117597, Singapore.
- Centre for Cancer Biology, University of South Australia and SA Pathology, Adelaide, Australia.
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Abstract
INTRODUCTION The mouse is an important, though imperfect, organism with which to model human disease and to discover and test novel drugs in a preclinical setting. Many experimental strategies have been used to discover new biological and molecular targets in the mouse, with the hopes of translating these discoveries into novel drugs to treat prostate cancer in humans. Modeling prostate cancer in the mouse, however, has been challenging, and often drugs that work in mice have failed in human trials. AREAS COVERED The authors discuss the similarities and differences between mice and men; the types of mouse models that exist to model prostate cancer; practical questions one must ask when using a mouse as a model; and potential reasons that drugs do not often translate to humans. They also discuss the current value in using mouse models for drug discovery to treat prostate cancer and what needs are still unmet in field. EXPERT OPINION With proper planning and following practical guidelines by the researcher, the mouse is a powerful experimental tool. The field lacks genetically engineered metastatic models, and xenograft models do not allow for the study of the immune system during the metastatic process. There remain several important limitations to discovering and testing novel drugs in mice for eventual human use, but these can often be overcome. Overall, mouse modeling is an essential part of prostate cancer research and drug discovery. Emerging technologies and better and ever-increasing forms of communication are moving the field in a hopeful direction.
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Affiliation(s)
- Kenneth C Valkenburg
- The Johns Hopkins University, The James Buchanan Brady Urological Institute, Department of Urology , 600 North Wolfe Street, Baltimore, MD 21287 , USA
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Gazzaniga FS, Blackburn EH. An antiapoptotic role for telomerase RNA in human immune cells independent of telomere integrity or telomerase enzymatic activity. Blood 2014; 124:3675-84. [PMID: 25320237 PMCID: PMC4263978 DOI: 10.1182/blood-2014-06-582254] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Accepted: 09/26/2014] [Indexed: 01/28/2023] Open
Abstract
Telomerase is a ribonucleoprotein complex that adds telomeric DNA to the ends of linear chromosomes. It contains two core canonical components: the essential RNA component, hTR, which provides the template for DNA synthesis, and the reverse transcriptase protein component, hTERT. Low telomerase activity in circulating peripheral blood mononuclear cells has been associated with a variety of diseases. It is unknown, however, whether telomerase, in addition to its long-term requirement for telomere maintenance, is also necessary for short-term immune cell proliferation and survival. We report that overexpression of enzymatically inactive hTR mutants protected against dexamethasone-induced apoptosis in stimulated CD4 T cells. Furthermore, hTR knockdown reproducibly induced apoptosis in the absence of any detectable telomere shortening or DNA damage response. In contrast, hTERT knockdown did not induce apoptosis. Strikingly, overexpression of hTERT protein caused apoptosis that was rescued by overexpression of enzymatically inactive hTR mutants. Hence, we propose that hTR can function as a noncoding RNA that protects from apoptosis independent of its function in telomerase enzymatic activity and long-term telomere maintenance in normal human immune cells. These results imply that genetic or environmental factors that alter hTR levels can directly affect immune cell function to influence health and disease.
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Affiliation(s)
- Francesca S Gazzaniga
- Department of Biophysics and Biochemistry, University of California, San Francisco, San Francisco, CA
| | - Elizabeth H Blackburn
- Department of Biophysics and Biochemistry, University of California, San Francisco, San Francisco, CA
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Telomerase stimulates ribosomal DNA transcription under hyperproliferative conditions. Nat Commun 2014; 5:4599. [PMID: 25118183 DOI: 10.1038/ncomms5599] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Accepted: 07/07/2014] [Indexed: 12/26/2022] Open
Abstract
In addition to performing its canonical function, Telomerase Reverse Transcriptase (TERT) has been shown to participate in cellular processes independent of telomerase activity. Furthermore, although TERT mainly localizes to Cajal bodies, it is also present within the nucleolus. Because the nucleolus is the site of rDNA transcription, we investigated the possible role of telomerase in regulating RNA polymerase I (Pol I). Here we show that TERT binds to rDNA and stimulates transcription by Pol I during liver regeneration and Ras-induced hyperproliferation. Moreover, the inhibition of telomerase activity by TERT- or TERC-specific RNA interference, the overexpression of dominant-negative-TERT, and the application of the telomerase inhibitor imetelstat reduce Pol I transcription and the growth of tumour cells. In vitro, telomerase can stimulate the formation of the transcription initiation complex. Our results demonstrate how non-canonical features of telomerase may direct Pol I transcription in oncogenic and regenerative hyperproliferation.
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Ramakrishnan SK, Varshney A, Sharma A, Das BC, Yadava PK. Expression of targeted ribozyme against telomerase RNA causes altered expression of several other genes in tumor cells. Tumour Biol 2014; 35:5539-50. [PMID: 24664581 DOI: 10.1007/s13277-014-1729-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 02/04/2014] [Indexed: 01/11/2023] Open
Abstract
Telomeres are tandem repeat sequences present at chromosome end that are synthesized by RNA-protein enzyme called telomerase. The RNA component (TR) serves as template for telomerase reverse transcriptase (TERT) for generating telomere repeats. TERT is overexpressed in actively dividing cells including cancerous cells, absent in differentiated somatic cells whereas human telomerase RNA (hTR) is present in normal as well as in cancer cells. Telomerase overexpression in cancer cells ensures telomere length maintenance that actually provides proliferative advantage to cells. Stable expression of ribozyme against hTR in HeLa cells results in reduction of hTR levels, telomerase activity, and telomere length which is accompanied by altered cell morphology and expression of several specific cellular genes. The altered genes deduced from differentially display PCR and 2D gel electrophoresis upon hTR knockdown have function in ribosome biogenesis, chromatin modulation, cell cycle control, and p63-dependant pathways. Our observations shows hTR participates in diverse cellular functions other than telomere maintenance, validates as a possible drug targets in p53- and pRB-negative status, and indicated possible cross-talks between telomerase and other cellular pathways.
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Affiliation(s)
- Suresh Kumar Ramakrishnan
- Applied Molecular Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
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An investigation of the effects of the core protein telomerase reverse transcriptase on Wnt signaling in breast cancer cells. Mol Cell Biol 2013; 34:280-9. [PMID: 24216762 DOI: 10.1128/mcb.00844-13] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Telomerase canonically maintains telomeres, but recent reports have suggested that the core protein mammalian telomerase reverse transcriptase (TERT) component, together with the chromatin remodeling factor BRG1 and β-catenin, may also bind to and promote expression of Wnt target genes. However, this proposed noncanonical role of TERT in Wnt signaling has been controversial. Here, we investigated the effects of human TERT (hTERT) on Wnt signaling in human breast cancer lines and HeLa cells. We failed to find evidence for physical association of hTERT with BRG1 or β-catenin; instead, we present evidence that anti-FLAG antibody cross-reactivity properties may explain the previously reported interaction of hTERT with β-catenin. Furthermore, altering hTERT levels in four different breast cancer cell lines caused minimal and discordant effects on Wnt target and Wnt pathway gene expression. Although hTERT's role in Wnt signaling was addressed only indirectly, no significant representation of Wnt target genes was detected in chromatin immunoprecipitation-sequencing (ChIP-seq) and chromatin isolation by RNA purification and sequencing (ChIRP-seq) loci cooccupied in HeLa S3 cells by both BRG1 and hTR. In summary, our evidence fails to support the idea of a biologically consistent hTERT interaction with the Wnt pathway in human breast cancer cells, and any detectable influence of hTERT depended on cell type and experimental system.
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Short telomeres are frequent in hereditary breast tumors and are associated with high tumor grade. Breast Cancer Res Treat 2013; 141:231-42. [DOI: 10.1007/s10549-013-2696-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Accepted: 09/02/2013] [Indexed: 01/05/2023]
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18
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Roger L, Jones RE, Heppel NH, Williams GT, Sampson JR, Baird DM. Extensive telomere erosion in the initiation of colorectal adenomas and its association with chromosomal instability. J Natl Cancer Inst 2013; 105:1202-11. [PMID: 23918447 DOI: 10.1093/jnci/djt191] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Telomere shortening, dysfunction, and fusion may facilitate the acquisition of large-scale genomic rearrangements, driving clonal evolution and tumor progression. The relative contribution that telomere dysfunction and/or APC mutation play in the chromosome instability that occurs during colorectal tumorigenesis is not clear. METHODS We used high-resolution telomere length and fusion analysis to analyze 85 adenomatous colorectal polyps obtained from 10 patients with familial adenomatous polyposis and a panel of 50 colorectal carcinomas with patient-matched normal colonic mucosa. Telomerase activity was determined using the telomeric repeat amplification protocol. Array-CGH was used to detect large-scale genomic rearrangements. Pearson correlation and Student t test were used, and all statistical tests were two-sided. RESULTS Despite the presence of telomerase activity, we observed apparent telomere shortening in colorectal polyps that correlated with large-scale genomic rearrangements (P < .0001) but was independent of polyp size and indistinguishable from that observed in colorectal carcinomas (P = .82). We also observed apparent lengthening of telomeres in both polyps and carcinomas. The extensive differences in mean telomere length of up to 4.6kb between patient-matched normal mucosa and polyps were too large to be accounted for by replicative telomere erosion alone. Telomere fusion events were detected in both polyps and carcinomas; the mutational spectrum accompanying fusion was consistent with alternative nonhomologous end joining. CONCLUSIONS Telomere length distributions observed in colorectal polyps reflect the telomere length composition of the normal originating cells from which clonal growth was initiated. Originating cells containing both short telomeres and APC mutations may give rise to polyps that exhibit short telomeres and are prone to telomere dysfunction, driving genomic instability and progression to malignancy. J Natl Cancer Inst;2013;105:1202-1211.
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Affiliation(s)
- Laureline Roger
- Institute of Cancer and Genetics, School of Medicine, Cardiff University, Cardiff, UK
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19
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Telomerase: central regulator of all of the hallmarks of cancer. Trends Biochem Sci 2013; 38:426-34. [PMID: 23932019 DOI: 10.1016/j.tibs.2013.07.001] [Citation(s) in RCA: 180] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Revised: 06/26/2013] [Accepted: 07/01/2013] [Indexed: 12/13/2022]
Abstract
The hallmarks of cancer described by Hanahan and Weinberg are properties that cancer cells must possess for successful transformation. It is believed that each of these hallmarks is independently driven. Although elongation of telomeres is thought to be the prime function of reactivated telomerase reverse transcriptase, this activity does not account for all its effects, such as increasing cell proliferation, resistance to apoptosis, and invasion. Recent studies suggest that the telomerase subunit telomerase reverse transcriptase (TERT) has novel molecular functions including transcriptional regulation and metabolic reprogramming. We summarize these functions and discuss how they could directly regulate the various hallmarks of cancer. Finally, we suggest that therapeutics targeting noncanonical telomerase functions may work better than those that target its role in telomere extension.
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20
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Cai Z, Yan LJ, Ratka A. Telomere Shortening and Alzheimer’s Disease. Neuromolecular Med 2012; 15:25-48. [DOI: 10.1007/s12017-012-8207-9] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Accepted: 11/02/2012] [Indexed: 10/27/2022]
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21
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Kumar M, Witt B, Knippschild U, Koch S, Meena JK, Heinlein C, Weise JM, Krepulat F, Kuchenbauer F, Iben S, Rudolph KL, Deppert W, Günes C. CEBP factors regulate telomerase reverse transcriptase promoter activity in whey acidic protein-T mice during mammary carcinogenesis. Int J Cancer 2012; 132:2032-43. [PMID: 23023397 DOI: 10.1002/ijc.27880] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Accepted: 09/12/2012] [Indexed: 01/17/2023]
Abstract
Telomerase is activated in the majority of invasive breast cancers, but the time point of telomerase activation during mammary carcinogenesis is not clear. We have recently presented a transgenic mouse model to study human telomerase reverse transcriptase (TERT) gene expression in vivo (hTERTp-lacZ). In the present study, hTERTp-lacZxWAP-T bitransgenic mice were generated to analyze the mechanisms responsible for human and mouse TERT upregulation during tumor progression in vivo. We found that telomerase activity and TERT expression were consistently upregulated in SV40-induced invasive mammary tumors compared to normal and hyperplastic tissues and ductal carcinoma in situ (DCIS). Human and mouse TERT genes are regulated similarly in the breast tissue, involving the CEBP transcription factors. Loss of CEBP-α and induction of CEBP-β expression correlated well with the activation of TERT expression in mouse mammary tumors. Transfection of CEBP-α into human or murine cells resulted in TERT repression, whereas knockdown of CEBP-α in primary human mammary epithelial cells resulted in reactivation of endogenous TERT expression and telomerase activity. Conversely, ectopic expression of CEBP-β activated endogenous TERT gene expression. Moreover, ChIP and EMSA experiments revealed binding of CEBP-α and CEBP-β to human TERT-promoter. This is the first evidence indicating that CEBP-α and CEBP-β are involved in TERT gene regulation during carcinogenesis.
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Affiliation(s)
- Mukesh Kumar
- Institute of Molecular Medicine and Max-Planck Research Group on Stem Cell Aging, Ulm, Germany
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22
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Greider CW. Molecular biology. Wnt regulates TERT--putting the horse before the cart. Science 2012; 336:1519-20. [PMID: 22723405 DOI: 10.1126/science.1223785] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Carol W Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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23
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Regulation of the human catalytic subunit of telomerase (hTERT). Gene 2012; 498:135-46. [PMID: 22381618 DOI: 10.1016/j.gene.2012.01.095] [Citation(s) in RCA: 199] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Revised: 01/29/2012] [Accepted: 01/30/2012] [Indexed: 12/12/2022]
Abstract
Over the past decade, there has been much interest in the regulation of telomerase, the enzyme responsible for maintaining the integrity of chromosomal ends, and its crucial role in cellular immortalization, tumorigenesis, and the progression of cancer. Telomerase activity is characterized by the expression of the telomerase reverse transcriptase (TERT) gene, suggesting that TERT serves as the major limiting agent for telomerase activity. Recent discoveries have led to characterization of various interactants that aid in the regulation of human TERT (hTERT), including numerous transcription factors; further supporting the pivotal role that transcription plays in both the expression and repression of telomerase. Several studies have suggested that epigenetic modulation of the hTERT core promoter region may provide an additional level of regulation. Although these studies have provided essential information on the regulation of hTERT, there has been ambiguity of the role of methylation within the core promoter region and the subsequent binding of various activating and repressive agents. As a result, we found it necessary to consolidate and summarize these recent developments and elucidate these discrepancies. In this review, we focus on the co-regulation of hTERT via transcriptional regulation, the presence or absence of various activators and repressors, as well as the epigenetic pathways of DNA methylation and histone modifications.
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24
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Senthilkumar PK, Robertson LW, Ludewig G. PCB153 reduces telomerase activity and telomere length in immortalized human skin keratinocytes (HaCaT) but not in human foreskin keratinocytes (NFK). Toxicol Appl Pharmacol 2011; 259:115-23. [PMID: 22210444 DOI: 10.1016/j.taap.2011.12.015] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Revised: 12/09/2011] [Accepted: 12/14/2011] [Indexed: 02/07/2023]
Abstract
Polychlorinated biphenyls (PCBs), ubiquitous environmental pollutants, are characterized by long term-persistence in the environment, bioaccumulation, and biomagnification in the food chain. Exposure to PCBs may cause various diseases, affecting many cellular processes. Deregulation of the telomerase and the telomere complex leads to several biological disorders. We investigated the hypothesis that PCB153 modulates telomerase activity, telomeres and reactive oxygen species resulting in the deregulation of cell growth. Exponentially growing immortal human skin keratinocytes (HaCaT) and normal human foreskin keratinocytes (NFK) were incubated with PCB153 for 48 and 24days, respectively, and telomerase activity, telomere length, superoxide level, cell growth, and cell cycle distribution were determined. In HaCaT cells exposure to PCB153 significantly reduced telomerase activity, telomere length, cell growth and increased intracellular superoxide levels from day 6 to day 48, suggesting that superoxide may be one of the factors regulating telomerase activity, telomere length and cell growth compared to untreated control cells. Results with NFK cells showed no shortening of telomere length but reduced cell growth and increased superoxide levels in PCB153-treated cells compared to untreated controls. As expected, basal levels of telomerase activity were almost undetectable, which made a quantitative comparison of treated and control groups impossible. The significant down regulation of telomerase activity and reduction of telomere length by PCB153 in HaCaT cells suggest that any cell type with significant telomerase activity, like stem cells, may be at risk of premature telomere shortening with potential adverse health effects for the affected organism.
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Affiliation(s)
- P K Senthilkumar
- Interdisciplinary Graduate Program in Human Toxicology, The University of Iowa, Iowa City, IA 52242-5000, USA
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25
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Bojovic B, Crowe DL. Dysfunctional telomeres promote genomic instability and metastasis in the absence of telomerase activity in oncogene induced mammary cancer. Mol Carcinog 2011; 52:103-17. [PMID: 22086874 DOI: 10.1002/mc.21834] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Revised: 09/08/2011] [Accepted: 10/08/2011] [Indexed: 12/21/2022]
Abstract
Telomerase is a ribonucleoprotein that maintains the ends of chromosomes (telomeres). In normal cells lacking telomerase activity, telomeres shorten with each cell division because of the inability to completely synthesize the lagging strand. Critically shortened telomeres elicit DNA damage responses and limit cellular division and lifespan, providing an important tumor suppressor function. Most human cancer cells express telomerase which contributes significantly to the tumor phenotype. In human breast cancer, telomerase expression is predictive of clinical outcomes such as lymph node metastasis and survival. In mouse models of mammary cancer, telomerase expression is also upregulated. Telomerase overexpression resulted in spontaneous mammary tumor development in aged female mice. Increased mammary cancer also was observed when telomerase deficient mice were crossed with p53 null mutant animals. However, the effects of telomerase and telomere length on oncogene driven mammary cancer have not been completely characterized. To address these issues we characterized neu proto-oncogene driven mammary tumor formation in G1 Terc-/- (telomerase deficient with long telomeres), G3 Terc-/- (telomerase deficient with short telomeres), and Terc+/+ mice. Telomerase deficiency reduced the number of mammary tumors and increased tumor latency regardless of telomere length. Decreased tumor formation correlated with increased apoptosis in Terc deficient tumors. Short telomeres dramatically increased lung metastasis which correlated with increased genomic instability, and specific alterations in DNA copy number and gene expression. We concluded that short telomeres promote metastasis in the absence of telomerase activity in neu oncogene driven mammary tumors.
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Affiliation(s)
- Bojana Bojovic
- University of Illinois Cancer Center, Chicago, Illinois, USA
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26
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Separation of telomerase functions by reverse genetics. Proc Natl Acad Sci U S A 2011; 108:E1363-71. [PMID: 21949400 DOI: 10.1073/pnas.1112414108] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The canonical function of the human telomerase protein (hTERT) is to synthesize telomeric DNA, but it has other biological activities, including enhancing cell proliferation, decreasing apoptosis, regulating DNA damage responses, and increasing cellular proliferative lifespan. The mechanistic relationships among these activities are not understood. We previously demonstrated that ectopic hTERT expression in primary human mammary epithelial cells diminishes their requirement for exogenous mitogens, thus giving them a proliferative advantage in a mitogen-depleted environment. Here, we show that this phenotype is caused by a combination of increased cell division and decreased apoptosis. In addition, we use a panel of hTERT mutants to demonstrate that this enhanced cell proliferation can be uncoupled not only from telomere elongation, but also from other telomerase activities, including cellular lifespan extension and regulation of DNA damage responses. We also find that the proliferative function of hTERT, which requires hTERT catalytic activity, is not caused by increased Wnt signaling, but is accompanied by alterations in key cell cycle regulators and is linked to an hTERT-catalyzed decrease in the levels of the RNA component of mitochondrial RNA processing endoribonuclease. Thus, enhanced cell proliferation is an independent function of hTERT that could provide a new target for the development of anti-telomerase cancer therapeutic agents.
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27
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Hiyama E, Hiyama K. Telomerase detection in the diagnosis and prognosis of cancer. Cytotechnology 2011; 45:61-74. [PMID: 19003244 DOI: 10.1007/s10616-004-5126-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2004] [Accepted: 09/21/2004] [Indexed: 01/27/2023] Open
Abstract
Telomerase, a critical enzyme responsible 'for cellular immortality, is usually repressed in somatic cells except for lymphocytes and self-renewal cells, but is activated in approximately 85% of human cancer tissues. The human telomerase reverse transcriptase (hTERT) is the catalytic component of human telomerase. In cancers in which telomerase activation occurs at the early stages of the disease, telomerase activity and hTERT expression are useful markers for the detection of cancer cells. In other cancers in which telomerase becomes upregulated upon tumor progression, they are useful as prognostic indicators. However, careful attention should be paid to false-negative results caused by the instability of telomerase and of the hTERT mRNA and the presence of PCR inhibitors, as well as to false-positive results caused by the presence of alternatively spliced hTERT mRNA and normal cells with telomerase activity. Recently, methods for the in situ detection of the hTERT mRNA and protein have been developed. These methods should facilitate the unequivocal detection of cancer cells, even in tissues containing a background of normal telomerase-positive cells.
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Affiliation(s)
- Eiso Hiyama
- Natural Science Center for Basic Research and Development, RIRBM, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan,
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28
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Mitchell MA, Johnson JE, Pascarelli K, Beeharry N, Chiourea M, Gagos S, Lev D, von Mehren M, Kipling D, Broccoli D. Doxorubicin resistance in a novel in vitro model of human pleomorphic liposarcoma associated with alternative lengthening of telomeres. Mol Cancer Ther 2010; 9:682-92. [PMID: 20197395 DOI: 10.1158/1535-7163.mct-09-0705] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Soft tissue sarcomas are a diverse set of fatal human tumors where few agents have demonstrable clinical efficacy, with the standard therapeutic combination of doxorubicin and ifosfamide showing only a 25% to 30% response rate in large multi-institutional trials. Although liposarcomas are the most common histologic form of adult soft tissue sarcomas, research in this area is severely hampered by the lack of experimentally tractable in vitro model systems. To this end, here we describe a novel in vitro model for human pleomorphic liposarcoma. The cell line (LS2) is derived from a pleomorphic liposarcoma that uses the alternative lengthening of telomeres (ALT) mechanism of telomere maintenance, which may be important in modulating the response of this tumor type to DNA-damaging agents. We present detailed baseline molecular and genomic data, including genome-wide copy number and transcriptome profiles, for this model compared with its parental tumor and a panel of liposarcomas covering multiple histologies. The model has retained essentially all of the detectable alterations in copy number that are seen in the parental tumor, and shows molecular karyotypic and expression profiles consistent with pleomorphic liposarcomas. We also show the utility of this model, together with two additional human liposarcoma cell lines, to investigate the relationship between topoisomerase 2A expression and the sensitivity of ALT-positive liposarcomas to doxorubicin. This model, together with its associated baseline data, provides a powerful new tool to develop treatments for this clinically poorly tractable tumor and to investigate the contribution that ALT makes to modulating sensitivity to doxorubicin.
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Affiliation(s)
- Marcy A Mitchell
- Department of Laboratory Oncology Research, Curtis and Elizabeth Anderson Cancer Institute, Memorial University Medical Center, Savannah, Georgia 31404, USA
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29
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Abstract
Normal mammalian somatic cells proliferate a finite number of times in vitro before permanently withdrawing from the cell cycle into a cellular state referred to as senescence. Senescence may be triggered by excessive mitogenic stimulation or by various forms of cellular damage including excessive telomere shortening. Over the past decade, there has been continuing accumulation of evidence that senescence occurs in vivo, that it is relevant to aging and that it has a tumor suppressor function. However, the phenotype of senescence has also been found to include a number of puzzling features, including the secretion of proinflammatory factors that may foster tumorigenesis as well as the senescence of neighboring cells. On the basis of these antagonistic pro- and antitumorigenic effects, and of the observation that many viruses have developed proteins that prevent senescence of the cells they infect, it is argued that the primary function of senescence may have been as an antiviral defense mechanism. Recent progress in understanding how tumor cells evade senescence is also reviewed here.
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Affiliation(s)
- Roger R Reddel
- Cancer Research Unit, Children's Medical Research Institute, 214 Hawkesbury Road, Westmead, New South Wales 2145, Australia.
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30
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Capuco AV, Evock-Clover CM, Minuti A, Wood DL. In vivo expansion of the mammary stem/ progenitor cell population by xanthosine infusion. Exp Biol Med (Maywood) 2009; 234:475-82. [PMID: 19176874 DOI: 10.3181/0811-rm-320] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Mammary stem cells provide for growth and maintenance of the mammary gland and are therefore of considerable interest as determinants of productivity and efficiency of dairy animals and as targets of carcinogenesis in humans. Xanthosine treatment was previously shown to promote expansion of hepatic stem cells in vitro. The objective of this study was to determine if in vivo treatment with xanthosine can increase the mammary stem cell population. Xanthosine was infused into the right mammary glands of four female Holstein calves for 5 consecutive days. Immediately after each xanthosine treatment, calves were injected intravenously with 5-bromo-2-deoxyuridine (BrdU). Forty days after the final treatment, calves were euthanized and mammary tissue harvested. BrdU-label retaining epithelial cells (LREC) were detected immunohistochemically and quantified. Retention of BrdU was used as a marker for putative bovine mammary stem cells. Infusion of xanthosine into the bovine mammary gland significantly increased the number of LREC in treated glands compared to contralateral control glands (P < 0.05). LREC averaged 0.4% of epithelial cells in control glands and 0.8% in xanthosine-treated glands. The increase in LREC in xanthosine-treated glands was supported by a concomitant increase in telomerase activity (P < 0.01) and a correlation between LREC and telomerase (P < 0.05; r (2) = 0.7). Data indicate that in vivo treatment with xanthosine can be used to increase the number of mammary stem cells. This is the first demonstration of an in vivo treatment to increase the endogenous population of mammary stem cells, with utility for biomedical research and dairy management.
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Affiliation(s)
- Anthony V Capuco
- Bovine Functional Genomics Laboratory, USDA-ARS, Beltsville, MD 20705.
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31
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Zhong YH, Liao ZK, Zhou FX, Xie CH, Xiao CY, Pan DF, Luo ZG, Liu SQ, Zhou YF. Telomere length inversely correlates with radiosensitivity in human carcinoma cells with the same tissue background. Biochem Biophys Res Commun 2008; 367:84-9. [DOI: 10.1016/j.bbrc.2007.12.078] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2007] [Accepted: 12/11/2007] [Indexed: 10/22/2022]
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32
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Marie-Egyptienne DT, Brault ME, Zhu S, Autexier C. Telomerase inhibition in a mouse cell line with long telomeres leads to rapid telomerase reactivation. Exp Cell Res 2008; 314:668-75. [DOI: 10.1016/j.yexcr.2007.10.020] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Revised: 09/16/2007] [Accepted: 10/26/2007] [Indexed: 11/16/2022]
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33
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Johnson JE, Gettings EJ, Schwalm J, Pei J, Testa JR, Litwin S, von Mehren M, Broccoli D. Whole-genome profiling in liposarcomas reveals genetic alterations common to specific telomere maintenance mechanisms. Cancer Res 2007; 67:9221-8. [PMID: 17909028 DOI: 10.1158/0008-5472.can-07-1133] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Telomere attrition ultimately leads to the activation of protective cellular responses, such as apoptosis or senescence. Impairment of such mechanisms can allow continued proliferation despite the presence of dysfunctional telomeres. Under such conditions, high levels of genome instability are often engendered. Data from both mouse and human model systems indicate that a period of genome instability might facilitate tumorigenesis. Here, we use a liposarcoma model system to assay telomere maintenance mechanism (TMM)-specific genetic alterations. A multiassay approach was used to assess the TMMs active in tumors. Genomic DNA from these samples was then analyzed by high-resolution DNA mapping array to identify genetic alterations. Our data reveal a higher level of genome instability in alternative lengthening of telomere (ALT)-positive tumors compared with telomerase-positive tumors, whereas tumors lacking both mechanisms have relatively low levels of genome instability. The bulk of the genetic changes are amplifications, regardless of the mode of telomere maintenance used. We also identified genetic changes specific to the ALT mechanism (e.g., deletion of chromosome 1q32.2-q44) as well as changes that are underrepresented among ALT-positive tumors, such as amplification of chromosome 12q14.3-q21.2. Taken together, these studies provide insight into the molecular pathways involved in the regulation of ALT and reveal several loci that might be exploited either as prognostic markers or targets of chemotherapeutic intervention.
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Affiliation(s)
- Jay E Johnson
- Department of Laboratory Oncology Research, Curtis and Elizabeth Anderson Cancer Institute, Memorial Health University Medical Center, Savannah, Georgia 31404, USA
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Lacerte A, Korah J, Roy M, Yang XJ, Lemay S, Lebrun JJ. Transforming growth factor-beta inhibits telomerase through SMAD3 and E2F transcription factors. Cell Signal 2007; 20:50-9. [PMID: 17881189 DOI: 10.1016/j.cellsig.2007.08.012] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Accepted: 08/14/2007] [Indexed: 11/30/2022]
Abstract
Cancer arises from multiple genetic changes within the cell, among which constitutive telomerase activity and attainment of immortality are central. Expression of hTERT, the protein component of telomerase, is increased in most cancer cells. Transforming growth factor-beta (TGFbeta), a potent tumor suppressor, has been reported to regulate hTERT expression. We found that TGFbeta represses hTERT expression in normal and cancer cells and that this effect is mediated through Smad3 but also requires Erk1/2, p38 kinase and histone deacetylase activity. Furthermore, we identified four critical E2F transcription factor binding sites within the hTERT gene promoter that confer the TGFbeta response. Finally, using the E2F-1 knockout model, we showed that loss of E2F-1 abolishes TGFbeta inhibition of telomerase expression. These findings highlight the prominent role of TGFbeta in regulating telomerase expression and identify Smad3 and E2F-1 as critical mediators of TGFbeta effects in both normal and cancer cells.
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Affiliation(s)
- Annie Lacerte
- Hormones and Cancer Research Unit, Department of Medicine, Royal Victoria Hospital, McGill University, 687 Pine Avenue West, H3A 1A1, Montreal, Quebec, Canada
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35
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Kedde M, le Sage C, Duursma A, Zlotorynski E, van Leeuwen B, Nijkamp W, Beijersbergen R, Agami R. Telomerase-independent Regulation of ATR by Human Telomerase RNA. J Biol Chem 2006; 281:40503-14. [PMID: 17098743 DOI: 10.1074/jbc.m607676200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human telomerase RNA (hTR), together with the telomerase reverse transcriptase, hTERT, constitute the core components of telomerase that is essential for telomere maintenance. While hTR is ubiquitously expressed, hTERT is normally restricted to germ cells and certain stem cells, but both are often deregulated during tumorigenesis. Here, we investigated the effects of changes in hTR cellular levels. Surprisingly, while inhibition of hTR expression triggers a rapid, telomerase-independent, growth arrest associated with p53 and CHK1 activation, its increased expression neutralizes activation of these pathways in response to genotoxic stress. These hTR effects are mediated through ATR and are sufficiently strong to impair ATR-mediated DNA-damage checkpoint responses. Furthermore, in response to low UV radiation, which activates ATR, endogenous hTR levels increase irrespective of telomerase status. Thus, we uncovered a novel, telomerase-independent, function of hTR that restrains ATR activity and participates in the recovery of cells from UV radiation.
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Affiliation(s)
- Martijn Kedde
- Division of Tumor Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
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36
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Carter RT, Giudice C, Dubielzig RR, Colitz CMH. Telomerase activity with concurrent loss of cell cycle regulation in feline post-traumatic ocular sarcomas. J Comp Pathol 2005; 133:235-45. [PMID: 16154137 DOI: 10.1016/j.jcpa.2005.04.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2004] [Accepted: 04/22/2005] [Indexed: 11/21/2022]
Abstract
Paraffin wax-embedded ocular globes of cats with post-traumatic ocular sarcomas were examined for the presence of TERT, the active subunit of telomerase. The latter is a ribonucleoprotein complex essential for immortalization and expressed by most malignant tumours, germ line cells, lens epithelial cells, and some stem cells. Due to the frequent loss of cell cycle control with the increased expression of telomerase activity, post-traumatic ocular sarcomas were also examined for loss of p16 expression and alterations in p53, the findings being related to mitotic score, tumour grade, and proliferating cell nuclear antigen. These sarcomas expressed telomerase at a high frequency (62.5%); in addition, the majority showed alterations in cell cycle control, as evaluated by lack of p16 immunolabelling (66.7%). Alterations in p53 were the sole mechanism by which cell cycle control was dysregulated in only two tumours expressing TERT (13%). These findings suggest that p16, and not p53, represents the primary mechanism by which post-traumatic ocular sarcomas that express telomerase activity escape cell cycle control.
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Affiliation(s)
- R T Carter
- Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive, Madison, WI 53706, USA
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37
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Abstract
The structures of specific chromosome regions, centromeres and telomeres, present a number of puzzles. As functions performed by these regions are ubiquitous and essential, their DNA, proteins and chromatin structure are expected to be conserved. Recent studies of centromeric DNA from human, Drosophila and plant species have demonstrated that a hidden universal centromere-specific sequence is highly unlikely. The DNA of telomeres is more conserved consisting of a tandemly repeated 6-8 bp Arabidopsis-like sequence in a majority of organisms as diverse as protozoan, fungi, mammals and plants. However, there are alternatives to short DNA repeats at the ends of chromosomes and for telomere elongation by telomerase. Here we focus on the similarities and diversity that exist among the structural elements, DNA sequences and proteins, that make up terminal domains (telomeres and subtelomeres), and how organisms use these in different ways to fulfil the functions of end-replication and end-protection.
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Affiliation(s)
- Edward J Louis
- Department of Genetics, University of Leicester, Leicester UK.
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38
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Cayuela ML, Flores JM, Blasco MA. The telomerase RNA component Terc is required for the tumour-promoting effects of Tert overexpression. EMBO Rep 2005; 6:268-74. [PMID: 15731767 PMCID: PMC1299269 DOI: 10.1038/sj.embor.7400359] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2004] [Revised: 01/11/2005] [Accepted: 01/25/2005] [Indexed: 11/08/2022] Open
Abstract
A role for the telomerase reverse transcriptase subunit (Tert) in tumorigenesis independent of telomere length is emerging. K5-Tert mice, which overexpress Tert in the skin, show increased tumorigenesis and faster wound healing than wild-type controls. Here, we demonstrate that the telomerase RNA component Terc is necessary to mediate these effects of Tert overexpression. In contrast to K5-Tert mice, K5-Tert mice in a Terc-deficient background, K5-Tert/Terc-/-, do not show increased tumorigenesis or increased wound healing compared with wild-type controls. Indeed, K5-Tert/Terc-/- mice show a reduction in tumour growth compared with Terc-/- controls, indicating an inhibitory effect of Tert overexpression in the absence of Terc. These results indicate that the tumour-promoting effects of Tert overexpression require the formation of Tert-Terc complexes. In addition, we show that the increased expression of Tert in the absence of Terc has an inhibitory effect on tumorigenesis, independently of telomere length and telomerase activity. These findings highlight Terc as a target for telomerase-based anticancer therapies.
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Affiliation(s)
- María Luisa Cayuela
- Molecular Oncology Program, Spanish National Cancer Center (CNIO), 28029 Madrid, Spain
| | - Juana M Flores
- Animal Surgery and Medicine Department, Facultad de Veterinaria, Universidad Complutense, 28040 Madrid, Spain
| | - María A Blasco
- Molecular Oncology Program, Spanish National Cancer Center (CNIO), 28029 Madrid, Spain
- Tel: +34 91 732 8031; Fax: +34 91 732 8028; E-mail:
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39
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Johnson JE, Varkonyi RJ, Schwalm J, Cragle R, Klein-Szanto A, Patchefsky A, Cukierman E, von Mehren M, Broccoli D. Multiple Mechanisms of Telomere Maintenance Exist in Liposarcomas. Clin Cancer Res 2005; 11:5347-55. [PMID: 16061847 DOI: 10.1158/1078-0432.ccr-05-0684] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE Telomeres are specialized nucleoprotein complexes that protect and confer stability upon chromosome ends. Loss of telomere function as a consequence of proliferation-associated sequence attrition results in genome instability, which may facilitate carcinogenesis by generating growth-promoting mutations. However, unlimited cellular proliferation requires the maintenance of telomeric DNA; thus, the majority of tumor cells maintain their telomeres either through the activity of telomerase or via a mechanism known as alternative lengthening of telomeres (ALT). Recent data suggest that constitutive telomere maintenance may not be required in all tumor types. Here we assess the role and requirement of telomere maintenance in liposarcoma. EXPERIMENTAL DESIGN Tumor samples were analyzed with respect to telomerase activity, telomere length, and the presence of ALT-specific subcellular structures, ALT-associated promyelocytic leukemia nuclear bodies. This multi-assay assessment improved the accuracy of categorization. RESULTS Our data reveal a significant incidence (24%) of ALT-positive liposarcomas, whereas telomerase is used at a similar frequency (27%). A large number of tumors (49%) do not show characteristics of telomerase or ALT. In addition, telomere length was always shorter in recurrent disease, regardless of the telomere maintenance mechanism. CONCLUSIONS These results suggest that approximately one half of liposarcomas either employ a novel constitutively active telomere maintenance mechanism or lack such a mechanism. Analysis of recurrent tumors suggests that liposarcomas can develop despite limiting or undetectable activity of a constitutively active telomere maintenance mechanism.
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Affiliation(s)
- Jay E Johnson
- Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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40
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Abstract
Telomeres are specialized DNA-protein structures found at the ends of all linear chromosomes. In mammalian cells, they consist of hexanucleotide (TTAGGG) repeats and multiple associated proteins. Telomeres protect the ends of chromosomes and prevent their recognition as DNA breaks. Loss of functional telomere length below a critical threshold can activate programs leading to cell senescence or death. Telomere length represents a balance between the loss of terminal telomeric repeats, which occurs during cell division with incomplete DNA replication, and the addition of telomeric repeats by the unique RNA-dependent DNA polymerase telomerase. Although most somatic cells do not express telomerase, telomerase is induced in lymphocytes at critical stages of development and activation. Telomerase expression thus may prolong the replicative capacity of lymphocytes and thereby enhance their function in immune responses. We have used murine model systems to address two broadly defined questions about lymphocyte telomere biology: how is telomerase physiologically regulated in T cells responding to antigen challenge, and what is the effect of transcriptionally altered telomerase expression on telomere length and, consequently, on immune function?
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Affiliation(s)
- Karen S Hathcock
- Experimental Immunology Branch, National Cancer Institute, Bethesda, MD 20892, USA.
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41
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Ritz JM, Kühle O, Riethdorf S, Sipos B, Deppert W, Englert C, Günes C. A novel transgenic mouse model reveals humanlike regulation of an 8-kbp human TERT gene promoter fragment in normal and tumor tissues. Cancer Res 2005; 65:1187-96. [PMID: 15735002 DOI: 10.1158/0008-5472.can-04-3046] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Telomerase activity is repressed in most human somatic tissues during differentiation processes but strongly up-regulated in most human tumors. Regulation of human telomerase activity primarily occurs at the level of transcriptional initiation of the TERT gene, which encodes the catalytic subunit of telomerase. We have generated a novel transgenic mouse model to study the regulation of the human TERT gene promoter in an in vivo system. For this purpose, we have cloned an 8.0-kbp human TERT promoter fragment in front of the bacterial lacZ reporter gene (hTERTp-lacZ), which encodes the beta-galactosidase enzyme. Expression of the reporter gene was monitored by reverse transcription-PCR analysis, 5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside staining of whole mount preparations, and histologic sections. We find that the activity of the human TERT promoter in most normal mouse tissues recapitulates the expression of the hTERT gene in normal human tissues and is under tighter control when compared with the endogenous mouse TERT gene expression. In testis, where highest lacZ expression was observed, the expression of the reporter gene was restricted to the spermatogonial stem cells and the spermatocytes. Intriguingly, we find increased levels of lacZ expression in mammary tumors of hTERTp-lacZ x p53(+/-) bitransgenic mouse mammary tumor model. Thus, this transgenic mouse model provides a suitable in vivo system to analyze the expression of the human TERT gene under physiologic conditions and during tumorigenesis.
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MESH Headings
- Animals
- DNA-Binding Proteins
- Gene Expression Regulation/genetics
- Genes, Reporter/genetics
- Genes, p53/genetics
- Humans
- Lac Operon/genetics
- Male
- Mammary Neoplasms, Experimental/genetics
- Mammary Neoplasms, Experimental/metabolism
- Mice
- Mice, Inbred BALB C
- Mice, Transgenic
- Models, Animal
- Promoter Regions, Genetic
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- Telomerase/biosynthesis
- Telomerase/genetics
- Testis/physiology
- Up-Regulation
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Affiliation(s)
- Julia M Ritz
- Heinrich-Pette-Institute, Department of Tumor Virology, Hamburg, Germany
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42
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Blasco MA. Mice with bad ends: mouse models for the study of telomeres and telomerase in cancer and aging. EMBO J 2005; 24:1095-103. [PMID: 15775986 PMCID: PMC556402 DOI: 10.1038/sj.emboj.7600598] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2004] [Accepted: 02/04/2005] [Indexed: 12/13/2022] Open
Abstract
Telomeres are capping structures at the ends of eukaryotic chromosomes, which consist of repetitive DNA bound to an array of specialized proteins. Telomeres are part of the constitutive heterochromatin and are subjected to epigenetic modifications. The function of telomeres is to prevent chromosome ends from being detected as damaged DNA. Both the length of telomere repeats and the integrity of the telomere-binding proteins are important for telomere protection. Telomere length is regulated by telomerase, by the telomere-binding proteins, as well as by activities that modify the state of the chromatin. Various mouse models with altered levels of telomerase activity, or mutant for different telomere-binding proteins, have been recently generated. Here, I will discuss how these different mouse models have contributed to our understanding on the role of telomeres and telomerase in cancer and aging.
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Affiliation(s)
- María A Blasco
- Telomeres and Telomerase Group, Molecular Oncology Program, Spanish National Cancer Centre (CNIO), Madrid, Spain.
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43
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Ariel I, Ayesh S, Gofrit O, Ayesh B, Abdul-Ghani R, Pizov G, Smith Y, Sidi AA, Birman T, Schneider T, de Groot N, Hochberg A. Gene expression in the bladder carcinoma rat model. Mol Carcinog 2004; 41:69-76. [PMID: 15378645 DOI: 10.1002/mc.20046] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We investigated gene expression in N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-induced rat bladder carcinoma in order to test its applicability as a model for the study of novel therapeutic modalities, particularly gene therapy. We administered BBN in the drinking water to Wistar rats for up to 30 wk and induced papillary transitional cell carcinoma (TCC), which is similar to the most prevalent type of human bladder cancer. Tumor evolution was similar to that found in previous studies. However, we described the morphological stages according to modern human bladder carcinoma terminology. Our main goal was to examine the expression levels of the H19 gene, of the insulin-like growth factor 2 (Igf2) transcripts expressed from promoters P2 and P3 and of the telomerase subunits that we had previously investigated as tools for targeted gene therapy of bladder cancer. We detected at 30 wk of BBN exposure significant upregulation of these sequences in the rat bladder tumors, similar to our previous findings in human bladder cancer. To reinforce the similarity of this model to the corresponding human disease, we searched for additional tumor-specific genes documented as having altered expression in human bladder carcinoma, using cDNA expression arrays (Clontech). We suggest that BBN-induced rat bladder cancer has morphological, biological, and molecular parallels to human bladder cancer and is an attractive model for studying novel alternatives of therapeutic intervention.
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Affiliation(s)
- Ilana Ariel
- Department of Pathology, Hadassah-Hebrew University Medical Center, Hadassah University Hospital, Mount Scopus, PO Box 24035, Jerusalem IL-91240, Israel
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44
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Todriya TV, Tzander A. Telomerase activity in cells of 9-day-old spleen colonies formed by bone marrow of normal and thymectomized mice. Bull Exp Biol Med 2004; 138:501-3. [PMID: 15723137 DOI: 10.1007/s10517-005-0081-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Telomerase activity was measured in spleen colonies, in progeny of individual 9-day-old splenic CFU formed by the bone marrow from normal (physiological aging) and thymectomized mice. Cells of spleen colonies expressed telomerase activity. No correlation was found between telomerase activity in spleen colony cells and age of animals. Thymectomy of bone marrow donors had no effect on telomerase activity. Our results suggest that the thymus plays a role in cell aging.
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Affiliation(s)
- T V Todriya
- Hematological Research Center, Moscow, Russia.
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45
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Lewis NL, Mullaney M, Mangan KF, Klumpp T, Rogatko A, Broccoli D. Measurable immune dysfunction and telomere attrition in long-term allogeneic transplant recipients. Bone Marrow Transplant 2004; 33:71-8. [PMID: 14704659 DOI: 10.1038/sj.bmt.1704300] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
This study was conducted to determine if the accelerated telomere attrition that occurs as a consequence of allogeneic stem cell transplantation leads to measurable functional defects. Telomere lengths in mononuclear leukocytes obtained from 15 long-term allogeneic stem cell transplant recipients and their respective donors were determined by Southern hybridization and densitometric analysis. Functional assays evaluated the ability of these cells to proliferate in response to a mitogenic stimulus and to differentiate under appropriate cytokine stimulation. Lymphocyte proliferation in response to phytohemagglutinin was determined by measurement of (3)[H]thymidine uptake. The ability of circulating myeloid cells to differentiate was determined after incubation of peripheral blood mononuclear cells with IL-3 and GM-CSF. A total of 13 patients demonstrated telomeric loss, ranging from 0.1 to 3.7 kbp. Strikingly, lymphocytes from 14 of the 15 patients demonstrated a significant decrease in proliferation when compared to their respective donors (68%+/-22, P=0.001). All patients demonstrated at least a 50% decrease in the number of myeloid colony-forming units when compared to their respective donors (P<0.0001). A decreased ability of hematopoietic cells to proliferate and differentiate is phenotypically consistent with an aged immune system. This may correlate with diminished clinically relevant immune responses to infection or vaccination, as seen in the elderly.
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Affiliation(s)
- N L Lewis
- Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
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46
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Razak ZRA, Varkonyi RJ, Kulp-McEliece M, Caslini C, Testa JR, Murphy ME, Broccoli D. p53 differentially inhibits cell growth depending on the mechanism of telomere maintenance. Mol Cell Biol 2004; 24:5967-77. [PMID: 15199150 PMCID: PMC480899 DOI: 10.1128/mcb.24.13.5967-5977.2004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Telomere stabilization is critical for tumorigenesis. A number of tumors and cell lines use a recombination-based mechanism, alternative lengthening of telomeres (ALT), to maintain telomere repeat arrays. Current data suggest that the mutation of p53 facilitates the activation of this pathway. In addition to its functions in response to DNA damage, p53 also acts to suppress recombination, independent of transactivation activity, raising the possibility that p53 might regulate the ALT mechanism via its role as a regulator of recombination. To test the role of p53 in ALT we utilized inducible alleles of human p53. We show that expression of transactivation-incompetent p53 inhibits DNA synthesis in ALT cell lines but does not affect telomerase-positive cell lines. The expression of temperature-sensitive p53 in clonal cell lines results in ALT-specific, transactivation-independent growth inhibition, due in part to the perturbation of S phase. Utilizing chromatin immunoprecipitation assays, we demonstrate that p53 is associated with the telomeric complex in ALT cells. Furthermore, the inhibition of DNA synthesis in ALT cells by p53 requires intact specific DNA binding and suppression of recombination functions. We propose that p53 causes transactivation-independent growth inhibition of ALT cells by perturbing telomeric recombination.
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47
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Oh BK, Lee CH, Park C, Park YN. Telomerase regulation and progressive telomere shortening of rat hepatic stem-like epithelial cells during in vitro aging. Exp Cell Res 2004; 298:445-54. [PMID: 15265692 DOI: 10.1016/j.yexcr.2004.04.032] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2004] [Revised: 04/12/2004] [Indexed: 11/21/2022]
Abstract
Rat hepatic stem-like epithelial cells, LE/2, LE/6, and WB-F344, share some phenotypic properties with oval cells, observed in the early stages of hepatocarcinogenesis. Here, we describe regulations of telomerase and telomere length during in vitro aging of LEs and WB-F344. These cells displayed no apparent aging phenotypes for over 140 passages. Telomerase activity and telomere length of these cells progressively decreased with the passages, and at the late passages, telomere shortening appeared to be reduced as telomerase activity increased. Regulation of TERT and TR, key components of telomerase, was similar to that of the telomerase activity. LEs possessed weak telomerase activity with a slow rate of proliferation compared to WB-F344, and were not tumorigenic, whereas WB-F344 was transformed in vitro from intermediate passage. In conclusion, LEs and WB-F344 have different biochemical properties, and telomerase activation and short telomeres are unlikely necessary for the transformation of WB-F344. TERT and TR seem to be the regulators of the telomerase activity. The relationship between telomere length and telomerase activity suggests that telomerase contributes to the regulation of telomere length in these cells. Our findings provide a better understanding of mechanisms in neoplastic transformation of rat hepatic stem-like epithelial cells.
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Affiliation(s)
- Bong-Kyeong Oh
- Department of Pathology, Center for Chronic Metabolic Disease Research and Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, South Korea
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48
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Meeker AK, Argani P. Telomere shortening occurs early during breast tumorigenesis: a cause of chromosome destabilization underlying malignant transformation? J Mammary Gland Biol Neoplasia 2004; 9:285-96. [PMID: 15557801 DOI: 10.1023/b:jomg.0000048775.04140.92] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Chromosomal instability appears early during breast carcinogenesis and is considered a major driving force in malignant transformation. While current evidence suggests that centrosomal and mitotic checkpoint defects may, in large part, account for numerical chromosomal abnormalities, the mechanisms underlying structural chromosomal abnormalities remain largely unknown. Telomeres stabilize and protect chromosomal termini, but shorten due to cell division and oxidative damage. Moderate telomere shortening signals a tumor suppressive growth arrest in normal cells. Critically short telomeres, in the setting of abrogated DNA damage checkpoints, cause chromosomal instability due to end-to-end chromosomal fusions, subsequent breakage, and rearrangement, resulting in an increased cancer incidence in animal models. Recent results from high resolution in situ telomere length assessment in human breast tissues indicate that significant telomere shortening is prevalent in preinvasive breast lesions (DCIS), as well as focal areas of histologically normal epithelium from which breast carcinoma is thought to arise. Telomere shortening is therefore a strong candidate for the cause of structural chromosome defects that contribute to breast cancer development.
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Affiliation(s)
- Alan K Meeker
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
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49
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Canela A, Martín-Caballero J, Flores JM, Blasco MA. Constitutive expression of tert in thymocytes leads to increased incidence and dissemination of T-cell lymphoma in Lck-Tert mice. Mol Cell Biol 2004; 24:4275-93. [PMID: 15121848 PMCID: PMC400466 DOI: 10.1128/mcb.24.10.4275-4293.2004] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2003] [Revised: 11/23/2003] [Accepted: 01/20/2004] [Indexed: 12/25/2022] Open
Abstract
Here we describe a new mouse model with constitutive expression of the catalytic subunit of telomerase (Tert) targeted to thymocytes and peripheral T cells (Lck-Tert mice). Two independent Lck-Tert mouse lines showed higher incidences of spontaneous T-cell lymphoma than the corresponding age-matched wild-type controls, indicating that constitutive expression of Tert promotes lymphoma. Interestingly, T-cell lymphomas in Lck-Tert mice were more disseminated than those in wild-type controls and affected both lymphoid and nonlymphoid tissues, while nonlymphoid tissues were never affected with lymphoma in age-matched wild-type controls. Importantly, these roles of Tert constitutive expression in promoting tumor progression and dissemination were independent of the role of telomerase in telomere length maintenance, since telomere length distributions on a single-cell basis were identical in Lck-Tert and wild-type thymocytes. Finally, Tert constitutive expression did not interfere with telomere capping in Lck-Tert primary thymocytes, although it resulted in greater chromosomal instability upon gamma irradiation in Lck-Tert primary lymphocytes than in controls, suggesting that Tert overexpression may interfere with the cellular response to DNA damage.
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MESH Headings
- Animals
- Base Sequence
- DNA Damage
- DNA, Complementary/genetics
- DNA-Binding Proteins
- Disease Models, Animal
- Gene Expression
- Lymphocyte Specific Protein Tyrosine Kinase p56(lck)/genetics
- Lymphoma, T-Cell/etiology
- Lymphoma, T-Cell/genetics
- Lymphoma, T-Cell/pathology
- Mice
- Mice, Inbred C57BL
- Mice, Inbred CBA
- Mice, Transgenic
- Promoter Regions, Genetic
- RNA, Messenger/genetics
- T-Lymphocytes/metabolism
- Telomerase/genetics
- Telomere/genetics
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Affiliation(s)
- Andrés Canela
- Telomeres and Telomerase Group, Molecular Oncology Program, Spanish National Cancer Centre (CNIO), 28029 Madrid, Spain
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50
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Yang H, Ou CC, Feldman RI, Nicosia SV, Kruk PA, Cheng JQ. Aurora-A kinase regulates telomerase activity through c-Myc in human ovarian and breast epithelial cells. Cancer Res 2004; 64:463-7. [PMID: 14744757 DOI: 10.1158/0008-5472.can-03-2907] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Aurora-A kinase is frequently overexpressed/activated in human ovarian and breast cancers. A rat mammary tumor model study indicates that alterations of Aurora-A are early events during mammary tumor development (T. M. Goepfert et al., Cancer Res., 62: 4115-4122, 2002), suggesting that Aurora-A plays a pivotal role in transformation. However, the molecular mechanism by which Aurora-A induces ovarian and breast cell transformation remains elusive. Here we show that ectopic expression of Aurora-A induces telomerase activity in human ovarian and breast epithelial cell lines HIOSE118 and MCF-10A. The mRNA and promoter activities of human telomerase reverse transcriptase (hTERT) are stimulated by Aurora-A. Furthermore, we have demonstrated that the c-Myc binding sites of hTERT promoter are required for Aurora-A-induced hTERT promoter activity. Ectopic expression of Aurora-A up-regulates c-Myc. Knockdown of c-Myc by RNA interference attenuates Aurora-A-stimulated hTERT expression and telomerase activity. To our knowledge, these findings demonstrate, for the first time, that Aurora-A induces telomerase activity and hTERT by up-regulation of c-Myc and provides an additional mechanism for the role of Aurora-A in malignant transformation in addition to its cell cycle control.
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Affiliation(s)
- Hua Yang
- Department of Pathology and Molecular Oncology Program, University of South Florida College of Medicine and H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida, USA
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