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Sako A, Matsuse M, Saenko V, Tanaka A, Otsubo R, Morita M, Kuba S, Nishihara E, Suzuki K, Ogi T, Kawakami A, Mitsutake N. TERT promoter mutations increase tumor aggressiveness by altering TERT mRNA splicing in papillary thyroid carcinoma. J Clin Endocrinol Metab 2024:dgae220. [PMID: 38576411 DOI: 10.1210/clinem/dgae220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 03/11/2024] [Accepted: 04/03/2024] [Indexed: 04/06/2024]
Abstract
CONTEXT Telomerase reverse transcriptase promoter (TERT-p) mutations, which upregulate TERT expression, are strongly associated with tumor aggressiveness and worse prognosis in papillary thyroid carcinomas (PTCs). TERT expression is also observed in a proportion of PTCs without TERT-p mutations, but such tumors show less aggressiveness and better prognosis compared with TERT-p mutation-positive tumors. OBJECTIVE TERT has multiple splicing variants whose relationships with the TERT-p status and clinicopathological characteristics remain poorly understood. We examined the relationship between the TERT-p mutational status, the TERT splicing pattern, and clinicopathological features. METHODS We investigated the expression of two major variants, α deletion (dA) and β deletion (dB), in a series of 207 PTCs operated between November 2001 and March 2020 in Nagasaki University Hospital and Kuma Hospital. RESULTS The TERT-p mutations were found in 33 cases, and among 174 mutation-negative cases, 24 showed TERT expression. All cases were classified into three groups: the TERT-p mutation-negative/expression-negative group (mut-/exp-), the TERT-p mutation-negative/expression-positive group (mut-/exp+), and the TERT-p mutation-positive group (mut+/exp+). The +A + B/dB ratio in mut+/exp + was significantly higher than that in mut-/exp + PTCs. Analysis with clinicopathological data revealed that +A + B expression was associated with higher PTC aggressiveness, whereas dB expression counteracted this effect. Functional in vitro study demonstrated that dB strongly inhibited cell growth, migration, and clonogenicity, suggesting its tumor suppressive role. CONCLUSION These results provide evidence that the TERT-p mutations alter the expression of different TERT splice variants, which, in turn, associates with different tumor aggressiveness.
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Affiliation(s)
- Ayaka Sako
- Department of Radiation Medical Sciences, Atomic Bomb Disease Institute, Nagasaki University
- Department of Endocrinology and Metabolism, Graduate School of Biomedical Sciences, Nagasaki University
| | - Michiko Matsuse
- Department of Radiation Medical Sciences, Atomic Bomb Disease Institute, Nagasaki University
| | - Vladimir Saenko
- Department of Radiation Molecular Epidemiology, Atomic Bomb Disease Institute, Nagasaki University
| | - Aya Tanaka
- Department of Surgical Oncology, Graduate School of Biomedical Sciences, Nagasaki University
| | - Ryota Otsubo
- Department of Surgical Oncology, Graduate School of Biomedical Sciences, Nagasaki University
| | - Michi Morita
- Department of Surgery, Graduate School of Biomedical Sciences, Nagasaki University
| | - Sayaka Kuba
- Department of Surgery, Graduate School of Biomedical Sciences, Nagasaki University
| | | | - Keiji Suzuki
- Department of Radiation Medical Sciences, Atomic Bomb Disease Institute, Nagasaki University
| | - Tomoo Ogi
- Department of Genetics, Research Institute of Environmental Medicine, Nagoya University
| | - Atsushi Kawakami
- Department of Immunology and Rheumatology, Graduate School of Biomedical Sciences, Nagasaki University
| | - Norisato Mitsutake
- Department of Radiation Medical Sciences, Atomic Bomb Disease Institute, Nagasaki University
- Department of Radiation Molecular Epidemiology, Atomic Bomb Disease Institute, Nagasaki University
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Jahan J, Joshi S, Oca IMD, Toelle A, Lopez-Yang C, Chacon CV, Beyer AM, Garcia CA, Jarajapu YP. The role of telomerase reverse transcriptase in the mitochondrial protective functions of Angiotensin-(1-7) in diabetic CD34 + cells. Biochem Pharmacol 2024; 222:116109. [PMID: 38458330 PMCID: PMC11007670 DOI: 10.1016/j.bcp.2024.116109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 01/08/2024] [Accepted: 03/05/2024] [Indexed: 03/10/2024]
Abstract
Angiotensin (Ang)-(1-7) stimulates vasoprotective functions of diabetic (DB) CD34+ hematopoietic stem/progenitor cells partly by decreasing reactive oxygen species (ROS), increasing nitric oxide (NO) levels and decreasing TGFβ1 secretion. Telomerase reverse transcriptase (TERT) translocates to mitochondria and regulates ROS generation. Alternative splicing of TERT results in variants α-, β- and α-β-TERT, which may oppose functions of full-length (FL) TERT. This study tested if the protective functions of Ang-(1-7) or TGFβ1-silencing are mediated by mitoTERT and that diabetes decreases FL-TERT expression by inducing splicing. CD34+ cells were isolated from the peripheral blood mononuclear cells of nondiabetic (ND, n = 68) or DB (n = 74) subjects. NO and mitoROS levels were evaluated by flow cytometry. TERT splice variants and mitoDNA-lesions were characterized by qPCR. TRAP assay was used for telomerase activity. Decoy peptide was used to block mitochondrial translocation (mitoXTERT). TERT inhibitor or mitoXTERT prevented the effects of Ang-(1-7) on NO or mitoROS levels in DB-CD34+ cells. FL-TERT expression and telomerase activity were lower and mitoDNA-lesions were higher in DB cells compared to ND and were reversed by Ang-(1-7) or TGFβ1-silencing. The prevalence of TERT splice variants, with predominant β-TERT expression, was higher and the expression of FL-TERT was lower in DB cells (n = 25) compared to ND (n = 30). Ang-(1-7) or TGFβ1-silencing decreased TERT-splicing and increased FL-TERT. Blocking of β-splicing increased FL-TERT and protected mitoDNA in DB-cells. The findings suggest that diabetes induces TERT-splicing in CD34+ cells and that β-TERT splice variant largely contributes to the mitoDNA oxidative damage.
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Affiliation(s)
- Jesmin Jahan
- Department of Pharmaceutical Sciences, College of Health Professions, North Dakota State University, Fargo, ND, USA
| | - Shrinidh Joshi
- Department of Pharmaceutical Sciences, College of Health Professions, North Dakota State University, Fargo, ND, USA
| | | | - Andrew Toelle
- Department of Pharmaceutical Sciences, College of Health Professions, North Dakota State University, Fargo, ND, USA
| | | | | | - Andreas M Beyer
- Department of Medicine and Physiology, Medical College of Wisconsin, Milwaukee, WI, USA
| | | | - Yagna Pr Jarajapu
- Department of Pharmaceutical Sciences, College of Health Professions, North Dakota State University, Fargo, ND, USA.
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Pérez-López FR, Ulloque-Badaracco JR, López-Baena MT, Yuan J, Alarcón-Braga EA, Benites-Zapata VA. Endometrial telomerase activity in women with either endometrial cancer or hyperplasia: A systematic review and meta-analysis. Maturitas 2023; 174:57-66. [PMID: 37295252 DOI: 10.1016/j.maturitas.2023.05.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Revised: 04/24/2023] [Accepted: 05/06/2023] [Indexed: 06/12/2023]
Abstract
AIM We performed a systematic review and meta-analysis to assess whether endometrial telomerase activity is associated with endometrial cancer or hyperplasia. METHODS PubMed, Web of Science, Embase, Scielo, LILAC, and CNKI databases were searched to obtain relevant literature for articles published through June 2022, following PRISMA guidelines and a registered PROSPERO protocol. We included observational studies reporting endometrial telomerase activity in patients with either endometrial cancer or hyperplasia compared with benign endometrial tissue (control women). The Newcastle-Ottawa Scale was used to evaluate the quality of studies. Data were expressed as the odds ratios (OR) and 95 % confidence intervals (CI). Random effects and inverse variance methods were used to meta-analyze associations. The I2 test was used to assess heterogeneity. RESULTS There were significant associations between endometrial telomerase activity and either endometrial cancer (20 studies, OR = 10.65, 95 % CI 6.39, 17.75, p = 0.00001, I2 = 21 %) or endometrial hyperplasia (nine studies, OR = 3.62, 95 % CI 1.61, 8.13, p = 0.002, I2 = 36 %) compared to women without endometrial cancer and hyperplasia. There was not a significant difference in telomerase activity in women with endometrial cancer compared to those with endometrial hyperplasia (seven studies, OR = 1.03; 95 % CI 0.31, 3.37, p = 0.96, I2 = 49 %). In subgroup analyses, there were no significant differences in telomerase activity in patients with endometrial cancer by type of observational studies and by countries of the studies. CONCLUSION Endometrial telomerase activity is higher in women with either endometrial cancer or endometrial hyperplasia compared to control women without those lesions.
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Affiliation(s)
- Faustino R Pérez-López
- University of Zaragoza Faculty of Medicine, Domingo Miral s/n, Zaragoza 50009, Spain; Aragón Health Research Institute, San Juan Bosco 13, Zaragoza 50009, Spain.
| | | | | | - Junhua Yuan
- Special Medicine Department, School of Basic Medicine, Qingdao University, Qingado, China
| | - Esteban A Alarcón-Braga
- Escuela de Medicina, Universidad Peruana de Ciencias Aplicadas, Lima, Peru; Sociedad Científica de Estudiantes de Medicina, Escuela de Medicina, Universidad Peruana de Ciencias Aplicadas, Lima, Peru
| | - Vicente A Benites-Zapata
- Unidad de Investigación para la Generación y Síntesis de Evidencias en Salud, Vicerrectorado de Investigación, Universidad San Ignacio de Loyola, Lima, Peru
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A View on Uterine Leiomyoma Genesis through the Prism of Genetic, Epigenetic and Cellular Heterogeneity. Int J Mol Sci 2023; 24:ijms24065752. [PMID: 36982825 PMCID: PMC10056617 DOI: 10.3390/ijms24065752] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Revised: 03/07/2023] [Accepted: 03/15/2023] [Indexed: 03/19/2023] Open
Abstract
Uterine leiomyomas (ULs), frequent benign tumours of the female reproductive tract, are associated with a range of symptoms and significant morbidity. Despite extensive research, there is no consensus on essential points of UL initiation and development. The main reason for this is a pronounced inter- and intratumoral heterogeneity resulting from diverse and complicated mechanisms underlying UL pathobiology. In this review, we comprehensively analyse risk and protective factors for UL development, UL cellular composition, hormonal and paracrine signalling, epigenetic regulation and genetic abnormalities. We conclude the need to carefully update the concept of UL genesis in light of the current data. Staying within the framework of the existing hypotheses, we introduce a possible timeline for UL development and the associated key events—from potential prerequisites to the beginning of UL formation and the onset of driver and passenger changes.
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Cytogenomic Profile of Uterine Leiomyoma: In Vivo vs. In Vitro Comparison. Biomedicines 2021; 9:biomedicines9121777. [PMID: 34944592 PMCID: PMC8698342 DOI: 10.3390/biomedicines9121777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 11/15/2021] [Accepted: 11/23/2021] [Indexed: 11/16/2022] Open
Abstract
We performed a comparative cytogenomic analysis of cultured and uncultured uterine leiomyoma (UL) samples. The experimental approach included karyotyping, aCGH, verification of the detected chromosomal abnormalities by metaphase and interphase FISH, MED12 mutation analysis and telomere measurement by Q-FISH. An abnormal karyotype was detected in 12 out of 32 cultured UL samples. In five karyotypically abnormal ULs, MED12 mutations were found. The chromosomal abnormalities in ULs were present mostly by complex rearrangements, including chromothripsis. In both karyotypically normal and abnormal ULs, telomeres were ~40% shorter than in the corresponding myometrium, being possibly prerequisite to chromosomal rearrangements. The uncultured samples of six karyotypically abnormal ULs were checked for the detected chromosomal abnormalities through interphase FISH with individually designed DNA probe sets. All chromosomal abnormalities detected in cultured ULs were found in corresponding uncultured samples. In all tumors, clonal spectra were present by the karyotypically abnormal cell clone/clones which coexisted with karyotypically normal ones, suggesting that chromosomal abnormalities acted as drivers, rather than triggers, of the neoplastic process. In vitro propagation did not cause any changes in the spectrum of the cell clones, but altered their ratio compared to uncultured sample. The alterations were unique for every UL. Compared to its uncultured counterpart, the frequency of chromosomally abnormal cells in the cultured sample was higher in some ULs and lower in others. To summarize, ULs are characterized by both inter- and intratumor genetic heterogeneity. Regardless of its MED12 status, a tumor may be comprised of clones with and without chromosomal abnormalities. In contrast to the clonal spectrum, which is unique and constant for each UL, the clonal frequency demonstrates up or down shifts under in vitro conditions, most probably determined by the unequal ability of cells with different genetic aberrations to exist outside the body.
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Zadeh Fakhar HB, Zali H, Rezaie-Tavirani M, Darkhaneh RF, Babaabasi B. Proteome profiling of low grade serous ovarian cancer. J Ovarian Res 2019; 12:64. [PMID: 31315664 PMCID: PMC6637464 DOI: 10.1186/s13048-019-0535-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 06/28/2019] [Indexed: 12/20/2022] Open
Abstract
Background Serous carcinoma, the subtype of ovarian cancer has the highest occurrence and mortality in women. Proteomic profiling using mass spectrometry (MS) has been used to detect biomarkers in tissue s obtained from patients with ovarian cancer. Thus, this study aimed at analyzing the interactome (protein-protein interaction (PPI)) and (MS) data to inspect PPI networks in patients with Low grade serous ovarian cancer. Methods For proteome profiling in Low grade serous ovarian cancer, 2DE and mass spectrometry were used. Differentially expressed proteins which had been determined in Low grade serous ovarian cancer and experimental group separately were integrated with PPI data to construct the (QQPPI) networks. Results Six Hub-bottlenecks proteins with significant centrality values, based on centrality parameters of the network (Degree and between), were found including Transgelin (TAGLN), Keratin (KRT14), Single peptide match to actin, cytoplasmic 1(ACTB), apolipoprotein A-I (APOA1), Peroxiredoxin-2 (PRDX2), and Haptoglobin (HP). Discussion This study showed these six proteins were introduced as hub-bottleneck protein. It can be concluded that regulation of gene expression can have a critical role in the pathology of Low-grade serous ovarian cancer.
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Affiliation(s)
| | - Hakimeh Zali
- Proteomics Research Center, School of Advanced Technologies in Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | | | | | - Babak Babaabasi
- Department of Genetics, Reproductive Biomedicine Research Center, Royan Institute, ACECR, Tehran, Iran
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Jie MM, Chang X, Zeng S, Liu C, Liao GB, Wu YR, Liu CH, Hu CJ, Yang SM, Li XZ. Diverse regulatory manners of human telomerase reverse transcriptase. Cell Commun Signal 2019; 17:63. [PMID: 31186051 PMCID: PMC6560729 DOI: 10.1186/s12964-019-0372-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Accepted: 05/17/2019] [Indexed: 12/22/2022] Open
Abstract
Human telomerase reverse transcriptase (hTERT) is the core subunit of human telomerase and plays important roles in human cancers. Aberrant expression of hTERT is closely associated with tumorigenesis, cancer cell stemness maintaining, cell proliferation, apoptosis inhibition, senescence evasion and metastasis. The molecular basis of hTERT regulation is highly complicated and consists of various layers. A deep and full-scale comprehension of the regulatory mechanisms of hTERT is pivotal in understanding the pathogenesis and searching for therapeutic approaches. In this review, we summarize the recent advances regarding the diverse regulatory mechanisms of hTERT, including the transcriptional (promoter mutation, promoter region methylation and histone acetylation), post-transcriptional (mRNA alternative splicing and non-coding RNAs) and post-translational levels (phosphorylation and ubiquitination), which may provide novel perspectives for further translational diagnosis or therapeutic strategies targeting hTERT.
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Affiliation(s)
- Meng-Meng Jie
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China
| | - Xing Chang
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China
| | - Shuo Zeng
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China
| | - Cheng Liu
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China
| | - Guo-Bin Liao
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China
| | - Ya-Ran Wu
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China
| | - Chun-Hua Liu
- Teaching evaluation center of Third Military Medical University (Army Medical University), Chongqing, 400038, China
| | - Chang-Jiang Hu
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China
| | - Shi-Ming Yang
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China.
| | - Xin-Zhe Li
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University (Army Medical University), Chongqing, 400037, China.
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Abstract
Telomeres are specialised structures at the end of linear chromosomes. They consist of tandem repeats of the hexanucleotide sequence TTAGGG, as well as a protein complex called shelterin. Together, they form a protective loop structure against chromosome fusion and degradation. Shortening or damage to telomeres and opening of the loop induce an uncapped state that triggers a DNA damage response resulting in senescence or apoptosis.Average telomere length, usually measured in human blood lymphocytes, was thought to be a biomarker for ageing, survival and mortality. However, it becomes obvious that regulation of telomere length is very complex and involves multiple processes. For example, the "end replication problem" during DNA replication as well as oxidative stress are responsible for the shortening of telomeres. In contrast, telomerase activity can potentially counteract telomere shortening when it is able to access and interact with telomeres. However, while highly active during development and in cancer cells, the enzyme is down-regulated in most human somatic cells with a few exceptions such as human lymphocytes. In addition, telomeres can be transcribed, and the transcription products called TERRA are involved in telomere length regulation.Thus, telomere length and their integrity are regulated at many different levels, and we only start to understand this process under conditions of increased oxidative stress, inflammation and during diseases as well as the ageing process.This chapter aims to describe our current state of knowledge on telomeres and telomerase and their regulation in order to better understand their role for the ageing process.
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Zhdanov DD, Plyasova AA, Gladilina YA, Pokrovsky VS, Grishin DV, Grachev VA, Orlova VS, Pokrovskaya MV, Alexandrova SS, Lobaeva TA, Sokolov NN. Inhibition of telomerase activity by splice-switching oligonucleotides targeting the mRNA of the telomerase catalytic subunit affects proliferation of human CD4 + T lymphocytes. Biochem Biophys Res Commun 2019; 509:790-796. [PMID: 30612734 DOI: 10.1016/j.bbrc.2018.12.186] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2018] [Accepted: 12/31/2018] [Indexed: 02/08/2023]
Abstract
Telomerase activity is regulated at the mRNA level by alternative splicing (AS) of its catalytic subunit hTERT. The aim of this study was to define the ability of splice-switching oligonucleotides (SSOs) that pair with hTERT pre-mRNA to induce AS and inhibit telomerase activity in human CD4+ T lymphocytes. SSOs that blocked the binding of a single splicing regulatory protein, SRp20 or SRp40, to its site within intron 8 of hTERT pre-mRNA demonstrated rather moderate capacities to induce AS and inhibit telomerase. However, a SSO that blocked the interaction of both SRp20 and SRp40 proteins with pre-mRNA was the most active. Cultivation of lymphocytes with spliced hTERT and inhibited telomerase resulted in the reduction of proliferative activity without significant induction of cell death. These results should facilitate further investigation of telomerase activity regulation, and antitelomerase SSOs could become promising agents for antiproliferative cell therapy.
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Affiliation(s)
- Dmitry D Zhdanov
- Institute of Biomedical Chemistry, 10/8 Pogodinskaya st, 119121, Moscow, Russia; Рeoples' Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Street, 117198, Moscow, Russia.
| | - Anna A Plyasova
- Institute of Biomedical Chemistry, 10/8 Pogodinskaya st, 119121, Moscow, Russia
| | - Yulia A Gladilina
- Institute of Biomedical Chemistry, 10/8 Pogodinskaya st, 119121, Moscow, Russia
| | - Vadim S Pokrovsky
- Institute of Biomedical Chemistry, 10/8 Pogodinskaya st, 119121, Moscow, Russia; Рeoples' Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Street, 117198, Moscow, Russia; N.N. Blokhin Cancer Research Center, 24 Kashirskoe Shosse, 115478, Moscow, Russia
| | - Dmitry V Grishin
- Institute of Biomedical Chemistry, 10/8 Pogodinskaya st, 119121, Moscow, Russia
| | - Vladimir A Grachev
- Рeoples' Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Street, 117198, Moscow, Russia
| | - Valentina S Orlova
- Рeoples' Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Street, 117198, Moscow, Russia
| | | | | | - Tatiana A Lobaeva
- Рeoples' Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Street, 117198, Moscow, Russia
| | - Nikolay N Sokolov
- Institute of Biomedical Chemistry, 10/8 Pogodinskaya st, 119121, Moscow, Russia
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NOVA1 directs PTBP1 to hTERT pre-mRNA and promotes telomerase activity in cancer cells. Oncogene 2018; 38:2937-2952. [PMID: 30568224 PMCID: PMC6474811 DOI: 10.1038/s41388-018-0639-8] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 10/24/2018] [Accepted: 12/04/2018] [Indexed: 11/09/2022]
Abstract
Alternative splicing is dysregulated in cancer cells, driving the production of isoforms that allow tumor cells to survive and continuously proliferate. Part of the reactivation of telomerase involves the splicing of hTERT transcripts to produce full-length (FL) TERT. Very few splicing factors to date have been described to interact with hTERT and promote the production of FL TERT. We recently described one such splicing factor, NOVA1, that acts as an enhancer of FL hTERT splicing, increases telomerase activity, and promotes telomere maintenance in cancer cells. NOVA1 is expressed primarily in neurons and is involved in neurogenesis. In the present studies, we describe that polypyrimidine-tract binding proteins (PTBPs), which are also typically involved in neurogenesis, are also participating in the splicing of hTERT to FL in cancer. Knockdown experiments of PTBP1 in cancer cells indicate that PTBP1 reduces hTERT FL splicing and telomerase activity. Stable knockdown of PTBP1 results in progressively shortened telomere length in H1299 and H920 lung cancer cells. RNA pulldown experiments reveal that PTBP1 interacts with hTERT pre-mRNA in a NOVA1 dependent fashion. Knockdown of PTBP1 increases the expression of PTBP2 which also interacts with NOVA1, potentially preventing the association of NOVA1 with hTERT pre-mRNA. These new data highlight that splicing in cancer cells is regulated by competition for splice sites and that combinations of splicing factors interact at cis regulatory sites on pre-mRNA transcripts. By employing hTERT as a model gene, we show the coordination of the splicing factors NOVA1 and PTBP1 in cancer by regulating telomerase that is expressed in the vast majority of cancer cell types.
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Contact-independent suppressive activity of regulatory T cells is associated with telomerase inhibition, telomere shortening and target lymphocyte apoptosis. Mol Immunol 2018; 101:229-244. [PMID: 30025223 DOI: 10.1016/j.molimm.2018.07.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2018] [Revised: 07/02/2018] [Accepted: 07/11/2018] [Indexed: 02/08/2023]
Abstract
Regulatory T cells (Tregs) play a fundamental role in the maintenance of immunological tolerance by suppressing effector target T, B and NK lymphocytes. Contact-dependent suppression mechanisms have been well-studied, though contact-independent Treg activity is not fully understood. In the present study, we showed that human native Tregs, as well as induced ex vivo Tregs, can cause in vitro telomere-dependent senescence in target T, B and NK cells in a contact-independent manner. The co-cultivation of target cells with Tregs separated through porous membranes induced alternative splicing of the telomerase catalytic subunit hTERT (human Telomerase Reverse Transcriptase), which suppressed telomerase activity. Induction of the hTERT splicing variant was associated with increased expression of the apoptotic endonuclease EndoG, a splicing regulator. Inhibited telomerase in target cells co-cultivated with Tregs for a long period of time led to a decrease in their telomere lengths, cell cycle arrest, conversion of the target cells to replicative senescence and apoptotic death. Induced Tregs showed the ability to up-regulate EndoG expression, TERT alternative splicing and telomerase inhibition in mouse T, B and NK cells after in vivo administration. The results of the present study describe a novel mechanism of contact-independent Treg cell suppression that induces telomerase inhibition through the EndoG-provoked alternative splicing of hTERT and converts cells to senescence and apoptosis phenotypes.
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Armstrong CA, Tomita K. Fundamental mechanisms of telomerase action in yeasts and mammals: understanding telomeres and telomerase in cancer cells. Open Biol 2018; 7:rsob.160338. [PMID: 28330934 PMCID: PMC5376709 DOI: 10.1098/rsob.160338] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 02/20/2017] [Indexed: 12/12/2022] Open
Abstract
Aberrant activation of telomerase occurs in 85–90% of all cancers and underpins the ability of cancer cells to bypass their proliferative limit, rendering them immortal. The activity of telomerase is tightly controlled at multiple levels, from transcriptional regulation of the telomerase components to holoenzyme biogenesis and recruitment to the telomere, and finally activation and processivity. However, studies using cancer cell lines and other model systems have begun to reveal features of telomeres and telomerase that are unique to cancer. This review summarizes our current knowledge on the mechanisms of telomerase recruitment and activation using insights from studies in mammals and budding and fission yeasts. Finally, we discuss the differences in telomere homeostasis between normal cells and cancer cells, which may provide a foundation for telomere/telomerase targeted cancer treatments.
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Affiliation(s)
- Christine A Armstrong
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK
| | - Kazunori Tomita
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK
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Zhdanov DD, Gladilina YA, Orlova VS, Grishin DV, Pokrovskaya MV, Aleksandrova SS, Podobed OV, Sokolov NN. Induction of Telomerase Catalytic Subunit Alternative Splicing by Apoptotic Endonuclease G in Mouse and Rat Lymphocytes. ACTA ACUST UNITED AC 2018. [DOI: 10.1134/s1990519x18030124] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Zhdanov DD, Gladilina YA, Grishin DV, Pokrovsky VS, Pokrovskaya MV, Aleksandrova SS, Sokolov NN. Apoptotic Endonuclease EndoG Induces Alternative Splicing of Telomerase TERT Catalytic Subunit, Caspase-2, DNase I, and BCL-x in Human, Murine, and Rat CD4+ T Lymphocytes. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2018. [DOI: 10.1134/s1068162018010181] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Induction of Alternative Splicing and Inhibition of Activity of Telomerase Catalytic Subunit by Apoptotic Endonuclease EndoG in Human T, B, and NK Cells. Bull Exp Biol Med 2018; 164:478-482. [PMID: 29504103 DOI: 10.1007/s10517-018-4016-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Indexed: 10/17/2022]
Abstract
The effect of apoptotic endonuclease EndoG on alternative splicing of mRNA of human telomerase catalytic subunit hTERT (human telomerase reverse transcriptase) and telomerase activity in normal human lymphocytes were studied. Human CD4+, CD8+, B, and NK cells were transfected with a plasmid pEndoG-GFP containing EndoG gene or control plasmid pGFP. The levels of mRNA of EndoG or hTERT splicing variants were analyzed by real-time PCR. Protein content was assessed by Western blotting. Telomerase activity was measured by the telomere repeats amplification protocol. EndoG overexpression reduced the expression of active full-length hTERT and increased the expression of inactive splice variant. Shifted balance of hTERT splice variants in cells led to a significant decrease in telomerase activity within 72 h after transfection.
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16
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Sun B, Zheng YL. Simultaneous Quantification of Multiple Alternatively Spliced mRNA Transcripts Using Droplet Digital PCR. Methods Mol Biol 2018; 1768:387-400. [PMID: 29717455 DOI: 10.1007/978-1-4939-7778-9_22] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Currently there is no sensitive, precise, and reproducible method to quantitate alternative splicing of mRNA transcripts. Droplet digital™ PCR (ddPCR™) analysis allows for accurate digital counting for quantification of gene expression. Human telomerase reverse transcriptase (hTERT) is one of the essential components required for telomerase activity and for the maintenance of telomeres. Several alternatively spliced forms of hTERT mRNA in human primary and tumor cells have been reported in the literature. Using one pair of primers and two probes for hTERT, four alternatively spliced forms of hTERT (α-/β+, α+/β- single deletions, α-/β- double deletion, and nondeletion α+/β+) were accurately quantified through a novel analysis method via data collected from a single ddPCR reaction. In this chapter, we describe this ddPCR method that enables direct quantitative comparison of four alternatively spliced forms of the hTERT messenger RNA without the need for internal standards or multiple pairs of primers specific for each variant, eliminating the technical variation due to differential PCR amplification efficiency for different amplicons and the challenges of quantification using standard curves. This simple and straightforward method should have general utility for quantifying alternatively spliced gene transcripts.
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Affiliation(s)
- Bing Sun
- Georgetown University, Washington, DC, USA
| | - Yun-Ling Zheng
- Georgetown University, Washington, DC, USA. .,Cancer Prevention and Control Program, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC, USA.
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17
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Zhdanov DD, Pokrovsky VS, Orlova EV, Orlova VS, Pokrovskaya MV, Aleksandrova SS, Sokolov NN. Intracellular Localization of Apoptotic Endonuclease EndoG and Splice-Variants of Telomerase Catalytic Subunit hTERT. BIOCHEMISTRY (MOSCOW) 2017; 82:894-905. [PMID: 28941457 DOI: 10.1134/s0006297917080041] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The activity of telomerase catalytic subunit hTERT (human telomerase reverse transcriptase) can be regulated by alternative splicing of its mRNA. The mechanism of hTERT splicing is not understood in detail. Apoptotic endonuclease EndoG is known to participate in this process. In the present work, the intracellular colocalization and mRNA levels of EndoG and hTERT splice-variants in normal and apoptotic cancer cells were studied. We found that the development of apoptosis increased the expression of EndoG and changed the ratio of hTERT splice-variants, which decreased the telomerase activity in the cells. The development of apoptosis was accompanied by changes in the amount of mRNA and in the localization of EndoG and hTERT splice-variants in the cytoplasm, nuclei, and mitochondria of the cells. The suppression of EndoG expression using RNA interference prevented induction of the α+β- splice-variant of hTERT and inhibition of the telomerase activity. A high degree of the intracellular colocalization of EndoG and hTERT was shown. The changes in the expression and localization of EndoG corresponded with changes in the amount and localization of hTERT splice-variants. These data confirm the participation of EndoG in the alternative splicing of mRNA of the telomerase catalytic subunit and in regulation of the telomerase activity.
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Affiliation(s)
- D D Zhdanov
- Orekhovich Institute of Biomedical Chemistry, Moscow, 119121, Russia.
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18
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Zhdanov DD, Vasina DA, Grachev VA, Orlova EV, Orlova VS, Pokrovskaya MV, Alexandrova SS, Sokolov NN. Alternative splicing of telomerase catalytic subunit hTERT generated by apoptotic endonuclease EndoG induces human CD4 + T cell death. Eur J Cell Biol 2017; 96:653-664. [PMID: 28886883 DOI: 10.1016/j.ejcb.2017.08.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 08/24/2017] [Accepted: 08/30/2017] [Indexed: 02/08/2023] Open
Abstract
Telomerase activity is regulated by alternative splicing of its catalytic subunit human Telomerase Reverse Transcriptase (hTERT) mRNA. Induction of a non-active spliced hTERT leads to inhibition of telomerase activity. However, very little is known about the mechanism of hTERT mRNA alternative splicing. The aim of this study was to determine the role of the apoptotic endonuclease EndoG in alternative splicing of hTERT and telomerase activity. A strong correlation was identified between EndoG expression levels and hTERT splice variants in human CD4+ and CD8+ T lymphocytes. Overexpression of EndoG in CD4+ T cells down-regulated the expression of the active full-length hTERT variant and up-regulated expression of the non-active spliced variant. A reduction in full-length hTERT transcripts down-regulated telomerase activity. Long-term in vitro cultivation of EndoG-overexpressing CD4+ T cells led to dramatically shortened telomeres, conversion of cells into a replicative senescence state, and activation of the BCL2/BAX-associated apoptotic pathway finally leading to cell death. These data indicated the participation of EndoG in alternative mRNA splicing of the telomerase catalytic subunit hTERT, regulation of telomerase activity and determination of cell fate.
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Affiliation(s)
- Dmitry D Zhdanov
- Laboratory of Medical Biotechnology, Institute of Biomedical Chemistry, Moscow, Russia; Peoples Friendship University of Russia, Moscow, Russia.
| | | | | | - Elena V Orlova
- Institute of Theoretical and Experimental Biophysics, Puschino, Moscow region, Russia
| | | | - Marina V Pokrovskaya
- Laboratory of Medical Biotechnology, Institute of Biomedical Chemistry, Moscow, Russia
| | | | - Nikolai N Sokolov
- Laboratory of Medical Biotechnology, Institute of Biomedical Chemistry, Moscow, Russia
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19
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Hapangama DK, Kamal A, Saretzki G. Implications of telomeres and telomerase in endometrial pathology. Hum Reprod Update 2017; 23:166-187. [PMID: 27979878 PMCID: PMC5850744 DOI: 10.1093/humupd/dmw044] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 12/02/2016] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Eukaryotic chromosomal ends are linear and are protected by nucleoprotein complexes known as telomeres. The complex structural anatomy and the diverse functions of telomeres as well as the unique reverse transcriptase enzyme, telomerase that maintains telomeres are under intensive scientific scrutiny. Both are involved in many human diseases including cancer, but also in ageing and chronic disease such as diabetes. Their intricate involvement in many cellular processes and pathways is being dynamically deciphered in many organs including the endometrium. This review summarizes our current knowledge on the topic of telomeres and telomerase and their potential role in providing plausible explanations for endometrial aberrations related to common gynaecological pathologies. OBJECTIVE AND RATIONALE This review outlines the recent major findings in telomere and telomerase functions in the context of endometrial biology. It highlights the contemporary discoveries in hormonal regulation, normal endometrial regeneration, stem cells and common gynaecological diseases such as endometriosis, infertility, recurrent reproductive failure and endometrial cancer (EC). SEARCH METHODS The authors carried out systematic PubMed (Medline) and Ovid searches using the key words: telomerase, telomeres, telomere length, human telomerase reverse transcriptase, telomeric RNA component, with endometrium, hormonal regulation, endometrial stem/progenitor cells, endometrial regeneration, endometriosis, recurrent miscarriage, infertility, endometrial hyperplasia, EC and uterine cancer. Publications used in this review date from 1995 until 31st June 2016. OUTCOMES The human endometrium is a unique somatic organ, which displays dynamic telomerase activity (TA) related to the menstrual cycle. Telomerase is implicated in almost all endometrial pathologies and appears to be crucial to endometrial stem cells. In particular, it is vital for normal endometrial regeneration, providing a distinct route to formulate possible curative, non-hormonal therapies to treat chronic endometrial conditions. Furthermore, our current understanding of telomere maintenance in EC is incomplete. Data derived from other malignancies on the role of telomerase in carcinogenesis cannot be extrapolated to EC because unlike in other cancers, TA is already present in proliferating healthy endometrial cells. WIDER IMPLICATIONS Since telomerase is pivotal to endometrial regeneration, further studies elucidating the role of telomeres, telomerase, their associated proteins and their regulation in normal endometrial regeneration as well as their role in endometrial pathologies are essential. This approach may allow future development of novel treatment strategies that are not only non-hormonal but also potentially curative.
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Affiliation(s)
- D K Hapangama
- Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, L8 7SS, UK.,Liverpool Women's Hospital NHS Foundation Trust, Crown Street, Liverpool L8 7SS, UK
| | - A Kamal
- Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, L8 7SS, UK.,The National Center for Early Detection of Cancer, Oncology Teaching Hospital, Baghdad Medical City, Baghdad, Iraq
| | - G Saretzki
- Institute for Ageing and Institute for Cell and Molecular Biosciences, Campus for Ageing and Vitality, Newcastle University, Newcastle upon Tyne, NE4 5PL, UK
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20
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Zhdanov DD, Vasina DA, Orlova EV, Orlova VS, Pokrovskaya MV, Aleksandrova SS, Sokolov NN. Apoptotic endonuclease EndoG regulates alternative splicing of human telomerase catalytic subunit hTERT. BIOCHEMISTRY MOSCOW-SUPPLEMENT SERIES B-BIOMEDICAL CHEMISTRY 2017. [DOI: 10.1134/s1990750817020135] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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21
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Lai AG, Pouchkina-Stantcheva N, Di Donfrancesco A, Kildisiute G, Sahu S, Aboobaker AA. The protein subunit of telomerase displays patterns of dynamic evolution and conservation across different metazoan taxa. BMC Evol Biol 2017; 17:107. [PMID: 28441946 PMCID: PMC5405514 DOI: 10.1186/s12862-017-0949-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 04/04/2017] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Most animals employ telomerase, which consists of a catalytic subunit known as the telomerase reverse transcriptase (TERT) and an RNA template, to maintain telomere ends. Given the importance of TERT and telomere biology in core metazoan life history traits, like ageing and the control of somatic cell proliferation, we hypothesised that TERT would have patterns of sequence and regulatory evolution reflecting the diverse life histories across the Animal Kingdom. RESULTS We performed a complete investigation of the evolutionary history of TERT across animals. We show that although TERT is almost ubiquitous across Metazoa, it has undergone substantial sequence evolution within canonical motifs. Beyond the known canonical motifs, we also identify and compare regions that are highly variable between lineages, but show conservation within phyla. Recent data have highlighted the importance of alternative splice forms of TERT in non-canonical functions and although animals may share some conserved introns, we find that the selection of exons for alternative splicing appears to be highly variable, and regulation by alternative splicing appears to be a very dynamic feature of TERT evolution. We show that even within a closely related group of triclad flatworms, where alternative splicing of TERT was previously correlated with reproductive strategy, we observe highly diverse splicing patterns. CONCLUSIONS Our work establishes that the evolutionary history and structural evolution of TERT involves previously unappreciated levels of change and the emergence of lineage specific motifs. The sequence conservation we describe within phyla suggests that these new motifs likely serve essential biological functions of TERT, which along with changes in splicing, underpin diverse functions of TERT important for animal life histories.
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Affiliation(s)
- Alvina G Lai
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
| | | | | | - Gerda Kildisiute
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
| | - Sounak Sahu
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
| | - A Aziz Aboobaker
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
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22
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Vasina DA, Zhdanov DD, Orlova EV, Orlova VS, Pokrovskaya MV, Aleksandrova SS, Sokolov NN. Apoptotic endonuclease EndoG inhibits telomerase activity and induces malignant transformation of human CD4+ T cells. BIOCHEMISTRY (MOSCOW) 2017; 82:24-37. [DOI: 10.1134/s0006297917010035] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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23
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Zhdanov DD, Vasina DA, Orlova VS, Gotovtseva VY, Bibikova MV, Pokrovsky VS, Pokrovskayaa MV, Aleksandrova SS, Sokolov NN. Apoptotic endonuclease EndoG induces alternative splicing of telomerase catalytic subunit hTERT and death of tumor cells. BIOCHEMISTRY MOSCOW-SUPPLEMENT SERIES B-BIOMEDICAL CHEMISTRY 2016. [DOI: 10.1134/s1990750816040090] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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24
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Plumbagin triggers DNA damage response, telomere dysfunction and genome instability of human breast cancer cells. Biomed Pharmacother 2016; 82:256-68. [DOI: 10.1016/j.biopha.2016.05.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 05/04/2016] [Accepted: 05/04/2016] [Indexed: 12/21/2022] Open
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25
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Telomerase: The Devil Inside. Genes (Basel) 2016; 7:genes7080043. [PMID: 27483324 PMCID: PMC4999831 DOI: 10.3390/genes7080043] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 07/23/2016] [Accepted: 07/25/2016] [Indexed: 01/04/2023] Open
Abstract
High telomerase activity is detected in nearly all human cancers but most human cells are devoid of telomerase activity. There is well-documented evidence that reactivation of telomerase occurs during cellular transformation. In humans, tumors can rely in reactivation of telomerase or originate in a telomerase positive stem/progenitor cell, or rely in alternative lengthening of telomeres, a telomerase-independent telomere-length maintenance mechanism. In this review, we will focus on the telomerase positive tumors. In this context, the recent findings that telomerase reverse transcriptase (TERT) promoter mutations represent the most common non-coding mutations in human cancer have flared up the long-standing discussion whether cancer originates from telomerase positive stem cells or telomerase reactivation is a final step in cellular transformation. Here, we will discuss the pros and cons of both concepts in the context of telomere length-dependent and telomere length-independent functions of telomerase. Together, these observations may provoke a re-evaluation of telomere and telomerase based therapies, both in telomerase inhibition for cancer therapy and telomerase activation for tissue regeneration and anti-ageing strategies.
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26
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Rousseau P, Khondaker S, Zhu S, Lauzon C, Mai S, Autexier C. An intact putative mouse telomerase essential N-terminal domain is necessary for proper telomere maintenance. Biol Cell 2016; 108:96-112. [PMID: 26787169 DOI: 10.1111/boc.201500089] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 01/14/2016] [Indexed: 12/15/2022]
Abstract
BACKGROUND INFORMATION Naturally occurring telomerase reverse transcriptase (TERT) isoforms may regulate telomerase activity, and possibly function independently of telomeres to modulate embryonic stem (ES) cell self-renewal and differentiation. RESULTS We report the characterisation of two novel mouse TERT (mTERT) splice variants, Ins-i1[1-102] (Insi1 for short) and Del-e12[1-40] (Dele12 for short) that have not been previously described. Insi1 represents an in-frame insertion of nucleotides 1-102 from intron 1, encoding a 34 amino acid insertion at amino acid 73. Based on known functions of this region in human and Tetrahymena TERTs, the insertion interrupts the RNA interaction domain 1 implicated in low-affinity RNA binding and the telomerase essential N-terminal domain implicated in DNA substrate interactions. Dele12 contains a 40 nucleotide deletion of exon 12 which generates a premature stop codon, and possible protein lacking the C-terminus. We found Insi1 expressed in adult mouse brain and kidney and Dele12 expressed in adult mouse ovary. Dele12 was inactive in vitro and in mTERT(-/-) ES cells and Insi1 retained 26-48% of telomerase activity reconstituted by wild-type mTERT in vitro and in mTERT(-/-) ES cells. The Insi1 variant exhibited reduced DNA substrate binding in vitro and both variants exhibited a reduction in binding the telomerase RNA, mTR, when expressed in mTERT(-/-) ES cells. Stable expression of Dele12 in the mouse fibroblast CB17 cell line inhibited telomerase activity and slowed cell growth, suggesting a potential dominant-negative effect. Levels of signal-free ends, representing short telomeres, and end-to-end fusions were higher in mTERT(-/-) ES cells expressing mTERT-Insi1 and mTERT-Dele12, compared with levels observed in mTERT(-/-) ES cells expressing wild-type mTERT. In addition, in mTERT(-/-) cells expressing mTERT-Insi1, we observed chromosomes that were products of repeated breakage-bridge-fusion cycles and other telomere dysfunction-related aberrations. CONCLUSION AND SIGNIFICANCE An intact mTERT N-terminus which contributes to mTR binding, DNA binding and telomerase activity is necessary for elongation of short telomeres and the maintenance of functional telomeres. It is reasonable to speculate that relative levels of mTERT-Insi1 may regulate telomere function in specific tissues.
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Affiliation(s)
- Philippe Rousseau
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, H3T 1E2, Canada
| | - Shanjadia Khondaker
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, H3T 1E2, Canada.,Division of Experimental Medicine, McGill University, Montréal, Québec, Canada
| | - Shusen Zhu
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, H3T 1E2, Canada
| | - Catherine Lauzon
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, H3T 1E2, Canada
| | - Sabine Mai
- Manitoba Institute of Cell Biology, University of Manitoba, Manitoba, R3E 0V9, Canada
| | - Chantal Autexier
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, H3T 1E2, Canada.,Division of Experimental Medicine, McGill University, Montréal, Québec, Canada.,Department of Anatomy and Cell Biology, McGill University, Montréal, Québec, Canada
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27
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Melicher D, Buzas EI, Falus A. Genetic and epigenetic trends in telomere research: a novel way in immunoepigenetics. Cell Mol Life Sci 2015; 72:4095-109. [PMID: 26190020 PMCID: PMC11113282 DOI: 10.1007/s00018-015-1991-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Revised: 06/25/2015] [Accepted: 07/10/2015] [Indexed: 01/09/2023]
Abstract
Telomeres are protective heterochromatic structures that cap the end of linear chromosomes and play a key role in preserving genomic stability. Telomere length represents a balance between processes that shorten telomeres during cell divisions with incomplete DNA replication and the ones that lengthen telomeres by the action of telomerase, an RNA-protein complex with reverse transcriptase activity which adds telomeric repeats to DNA molecule ends. Telomerase activity and telomere length have a crucial role in cellular ageing and in the pathobiology of several human diseases attracting intense research. The last few decades have witnessed remarkable advances in our understanding about telomeres, telomere-associated proteins, and the biogenesis and regulation of the telomerase holoenzyme complex, as well as about telomerase activation and the telomere-independent functions of telomerase. Emerging data have revealed that telomere length can be modified by genetic and epigenetic factors, sex hormones, reactive oxygen species and inflammatory reactions. It has become clear that, in order to find out more about the factors influencing the rate of telomere attrition in vivo, it is crucial to explore both genetic and epigenetic mechanisms. Since the telomere/telomerase assembly is under the control of multiple epigenetic influences, the unique design of twin studies could help disentangle genetic and environmental factors in the functioning of the telomere/telomerase system. It is surprising that the literature on twin studies investigating this topic is rather scarce. This review aims to provide an overview of some important immune response- and epigenetics-related aspects of the telomere/telomerase system demanding more research, while presenting the available twin data published in connection with telomere research so far. By emphasising what we know and what we still do not know in these areas, another purpose of this review is to urge more twin studies in telomere research.
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Affiliation(s)
- Dora Melicher
- Department of Genetics, Cell and Immunobiology, Semmelweis University, Budapest, Hungary
| | - Edit I Buzas
- Department of Genetics, Cell and Immunobiology, Semmelweis University, Budapest, Hungary
| | - Andras Falus
- Department of Genetics, Cell and Immunobiology, Semmelweis University, Budapest, Hungary.
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28
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Maida Y, Masutomi K. Telomerase reverse transcriptase moonlights: Therapeutic targets beyond telomerase. Cancer Sci 2015; 106:1486-92. [PMID: 26331588 PMCID: PMC4714691 DOI: 10.1111/cas.12806] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 08/25/2015] [Accepted: 08/26/2015] [Indexed: 12/26/2022] Open
Abstract
Telomeres, the repetitive sequences at chromosomal ends, protect intact chromosomes. Telomeres progressively shorten through successive rounds of cell divisions, and critically shortened telomeres trigger senescence and apoptosis. The enzyme that elongates telomeres and maintains their structure is known as telomerase. The catalytic subunit of this enzyme (telomerase reverse transcriptase [TERT]) is expressed at a high level in malignant cells, but at a very low level in normal cells. Although telomerase activity was long believed to be the only function of TERT, emerging evidence indicates that TERT plays roles beyond telomeres. For example, TERT contributes to stem cell maintenance and cell reprogramming processes in a manner independent of its canonical function. Even some types of splice variants that lack the telomerase catalytic domains exhibit the functions in a manner that does not depend on telomerase activity. We recently demonstrated that the RNA-dependent RNA polymerase (RdRP) activity of TERT is involved in regulation of gene silencing and heterochromatic transcription. Moreover, TERT RdRP activity is mediated by a newly identified complex, distinct from the authentic telomerase complex, that plays a role in cancer stem cells in a telomere maintenance independent manner. TERT has attracted interest as a molecular target for anticancer treatment, but previous efforts aimed at developing novel therapeutic strategies focused only on the canonical function of TERT. However, accumulating evidence about the non-canonical functions of TERT led us to speculate that the functions other than telomerase might be therapeutic targets as well. In this review, we discuss the non-canonical functions of TERT and their potential applications for anticancer treatment.
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Affiliation(s)
- Yoshiko Maida
- Division of Cancer Stem Cell, National Cancer Center Research Institute, Tokyo, Japan
| | - Kenkichi Masutomi
- Division of Cancer Stem Cell, National Cancer Center Research Institute, Tokyo, Japan
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29
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Sun B, Tao L, Zheng YL. Simultaneous quantification of alternatively spliced transcripts in a single droplet digital PCR reaction. Biotechniques 2014; 56:319-25. [PMID: 24924392 DOI: 10.2144/000114179] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2014] [Accepted: 05/05/2014] [Indexed: 11/23/2022] Open
Abstract
Human telomerase reverse transcriptase (hTERT) is an essential component required for telomerase activity and telomere maintenance. Several alternatively spliced forms of hTERT mRNA have been reported in human primary and tumor cells. Currently, however, there is no sensitive and accurate method for the simultaneous quantification of multiple alternatively spliced RNA transcripts, such as in the case of hTERT. Here we show droplet digital PCR (ddPCR) provides sensitive, simultaneous digital quantification in a single reaction of two alternatively spliced single deletion hTERT transcripts (α-/β+ and α+/β-) as well as the opportunity to manually quantify non-deletion (α+/β+) and double deletion (α-/β-) transcripts. Our ddPCR method enables direct comparison among four alternatively spliced mRNAs without the need for internal standards or multiple primer pairs specific for each variant as real-time PCR (qPCR) requires, thus eliminating potential variation due to differences in PCR amplification efficiency.
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Affiliation(s)
- Bing Sun
- Cancer Prevention and Control Program, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC
| | - Lian Tao
- Cancer Prevention and Control Program, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC
| | - Yun-Ling Zheng
- Cancer Prevention and Control Program, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC
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30
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Bollmann FM. Physiological and pathological significance of human telomerase reverse transcriptase splice variants. Biochimie 2013; 95:1965-70. [DOI: 10.1016/j.biochi.2013.07.031] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Accepted: 07/29/2013] [Indexed: 12/22/2022]
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31
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Gómez DLM, Farina HG, Gómez DE. Telomerase regulation: a key to inhibition? (Review). Int J Oncol 2013; 43:1351-6. [PMID: 24042470 DOI: 10.3892/ijo.2013.2104] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 07/05/2013] [Indexed: 11/06/2022] Open
Abstract
Telomerase has been recognized as a common factor in most tumor cells, and in turn a distinctive feature with respect to non-malignant cells. This feature has made telomerase a promising target for cancer therapy. Telomerase studies revealed that it is a multi-subunit complex possessing different levels of regulation, including control of expression, phosphorylation state, assembly and transportation to sites of activity. Thus, we emphasize that targeting telomerase expression or activity is not the only way to shorten telomeres, induce cell senescence and apoptosis. Therefore, there are multiple sites capable of allowing the modulation of its enzymatic activity. In the development of strategies based on the regulation of telomerase activity the understanding of the mechanisms regulating their subunits is essential. Based on this, in this review we summarize the current state of knowledge of some regulatory mechanisms of the components of the telomerase complex, and hypothetize their potential therapeutic application against cancer.
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Affiliation(s)
- Diego L Mengual Gómez
- Laboratory of Molecular Oncology, Science and Technology Department, National University of Quilmes, Buenos Aires, Argentina
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32
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Listerman I, Sun J, Gazzaniga FS, Lukas JL, Blackburn EH. The major reverse transcriptase-incompetent splice variant of the human telomerase protein inhibits telomerase activity but protects from apoptosis. Cancer Res 2013; 73:2817-28. [PMID: 23610451 DOI: 10.1158/0008-5472.can-12-3082] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Human telomerase reverse transcriptase (hTERT; the catalytic protein subunit of telomerase) is subjected to numerous alternative splicing events, but the regulation and function of these splice variants is obscure. Full-length hTERT includes conserved domains that encode reverse transcriptase activity, RNA binding, and other functions. The major splice variant termed α+β- or β-deletion is highly expressed in stem and cancer cells, where it codes for a truncated protein lacking most of the reverse transcriptase domain but retaining the known RNA-binding motifs. In a breast cancer cell panel, we found that β-deletion was the hTERT transcript that was most highly expressed. Splicing of this transcript was controlled by the splice regulators SRSF11, HNRNPH2, and HNRNPL, and the β-deletion transcript variant was associated with polyribosomes in cells. When ectopically overexpressed, β-deletion protein competed for binding to telomerase RNA (hTR/TERC), thereby inhibiting endogenous telomerase activity. Overexpressed β-deletion protein localized to the nucleus and mitochondria and protected breast cancer cells from cisplatin-induced apoptosis. Our results reveal that a major hTERT splice variant can confer a growth advantage to cancer cells independent of telomere maintenance, suggesting that hTERT makes multiple contributions to cancer pathophysiology.
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Affiliation(s)
- Imke Listerman
- Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California, USA
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Palma M, Parker A, Hojjat-Farsangi M, Forster J, Kokhaei P, Hansson L, Osterborg A, Mellstedt H. Telomere length and expression of human telomerase reverse transcriptase splice variants in chronic lymphocytic leukemia. Exp Hematol 2013; 41:615-26. [PMID: 23548418 DOI: 10.1016/j.exphem.2013.03.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 03/14/2013] [Accepted: 03/21/2013] [Indexed: 01/15/2023]
Abstract
Telomerase activity and telomere length (TL) are prognostic markers in chronic lymphocytic leukemia (CLL). The rate-limiting component of telomerase is human telomerase reverse transcriptase (hTERT), for which multiple transcripts exist. Two splicing sites, α and β, have been described that generate deleted transcripts. Only the full-length (FL; α⁺β⁺) transcript translates into a functional protein. The aim of this work was to characterize hTERT splice variants in CLL in relation to disease activity, clinical stage, immunoglobulin heavy chain variable (IGHV) genes mutational status, and TL. Real-time polymerase chain reaction assays were validated for quantification of the hTERT transcripts with either α deletion (del-α; α⁻β⁺)), β deletion (del-β; α⁺β⁻) or both α and β deletions (del-αβ; α⁻β⁻). The splice variant expression pattern was studied in 97 patients with CLL, 6 healthy control subjects, and one CD34 cell sample. TL was assessed with real-time polymerase chain reaction in 71 of 97 samples. Thirty-two percent of the cases did not express any of the splice variants. Average FL expression was 5.5-fold higher in IGHV-unmutated (n = 35) compared with mutated (n = 59) patients (p < 0.0001). FL levels correlated directly with the percentage of IGHV homology (r = 0.34; p = 0.0007) and inversely with TL (r = -0.44; p = 0.0001). Overall, FL expression correlated significantly with that of the other splice variants. All transcripts were more frequently expressed in progressive compared with nonprogressive patients (p < 0.0001 for FL and del-α; p = 0.01 for del-β; and p = 0.006 for del-αβ). This study provides a detailed insight into the hTERT transcript pattern in CLL, highlighting the necessity of subgrouping patients according to IGHV mutation status when analyzing hTERT expression.
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Affiliation(s)
- Marzia Palma
- Immune and Gene Therapy Laboratory, Department of Oncology and Pathology, Cancer Centre Karolinska, Karolinska Institutet, Stockholm, Sweden.
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Alternatively spliced telomerase reverse transcriptase variants lacking telomerase activity stimulate cell proliferation. Mol Cell Biol 2012; 32:4283-96. [PMID: 22907755 DOI: 10.1128/mcb.00550-12] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Eight human and six chicken novel alternatively spliced (AS) variants of telomerase reverse transcriptase (TERT) were identified, including a human variant (Δ4-13) containing an in-frame deletion which removed exons 4 through 13, encoding the catalytic domain of telomerase. This variant was expressed in telomerase-negative normal cells and tissues as well as in transformed telomerase-positive cell lines and cells which employ an alternative method to maintain telomere length. The overexpression of the Δ4-13 variant significantly elevated the proliferation rates of several cell types without enhancing telomerase activity, while decreasing the endogenous expression of this variant by use of small interfering RNA (siRNA) technology reduced cell proliferation. The expression of the Δ4-13 variant stimulated Wnt signaling. In chicken cells, AS TERT variants containing internal deletions or insertions that eliminated or reduced telomerase activity also enhanced cell proliferation. This is the first report that naturally occurring AS TERT variants which lack telomerase activity stimulate cell proliferation.
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Hrdličková R, Nehyba J, Lim SL, Grützner F, Bose HR. Insights into the evolution of mammalian telomerase: platypus TERT shares similarities with genes of birds and other reptiles and localizes on sex chromosomes. BMC Genomics 2012; 13:216. [PMID: 22655747 PMCID: PMC3546421 DOI: 10.1186/1471-2164-13-216] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Accepted: 05/04/2012] [Indexed: 01/05/2023] Open
Abstract
Background The TERT gene encodes the catalytic subunit of the telomerase complex and is responsible for maintaining telomere length. Vertebrate telomerase has been studied in eutherian mammals, fish, and the chicken, but less attention has been paid to other vertebrates. The platypus occupies an important evolutionary position, providing unique insight into the evolution of mammalian genes. We report the cloning of a platypus TERT (OanTERT) ortholog, and provide a comparison with genes of other vertebrates. Results The OanTERT encodes a protein with a high sequence similarity to marsupial TERT and avian TERT. Like the TERT of sauropsids and marsupials, as well as that of sharks and echinoderms, OanTERT contains extended variable linkers in the N-terminal region suggesting that they were present already in basal vertebrates and lost independently in ray-finned fish and eutherian mammals. Several alternatively spliced OanTERT variants structurally similar to avian TERT variants were identified. Telomerase activity is expressed in all platypus tissues like that of cold-blooded animals and murine rodents. OanTERT was localized on pseudoautosomal regions of sex chromosomes X3/Y2, expanding the homology between human chromosome 5 and platypus sex chromosomes. Synteny analysis suggests that TERT co-localized with sex-linked genes in the last common mammalian ancestor. Interestingly, female platypuses express higher levels of telomerase in heart and liver tissues than do males. Conclusions OanTERT shares many features with TERT of the reptilian outgroup, suggesting that OanTERT represents the ancestral mammalian TERT. Features specific to TERT of eutherian mammals have, therefore, evolved more recently after the divergence of monotremes.
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Affiliation(s)
- Radmila Hrdličková
- Section of Molecular Genetics and Microbiology, School of Biological Science, University of Texas at Austin, 78712-1095, USA
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Cifuentes-Rojas C, Shippen DE. Telomerase regulation. Mutat Res 2012; 730:20-7. [PMID: 22032831 PMCID: PMC3256259 DOI: 10.1016/j.mrfmmm.2011.10.003] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Revised: 09/15/2011] [Accepted: 10/12/2011] [Indexed: 02/05/2023]
Abstract
The intimate connection between telomerase regulation and human disease is now well established. The molecular basis for telomerase regulation is highly complex and entails multiple layers of control. While the major target of enzyme regulation is the catalytic subunit TERT, the RNA subunit of telomerase is also implicated in telomerase control. In addition, alterations in gene dosage and alternative isoforms of core telomerase components have been described. Finally, telomerase localization, recruitment to the telomere and enzymology at the chromosome terminus are all subject to modulation. In this review we summarize recent advances in understanding fundamental mechanisms of telomerase regulation.
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Affiliation(s)
| | - Dorothy E. Shippen
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128
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Wojtyla A, Gladych M, Rubis B. Human telomerase activity regulation. Mol Biol Rep 2010; 38:3339-49. [PMID: 21086176 PMCID: PMC3085100 DOI: 10.1007/s11033-010-0439-x] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Accepted: 11/08/2010] [Indexed: 01/27/2023]
Abstract
Telomerase has been recognized as a relevant factor distinguishing cancer cells from normal cells. Thus, it has become a very promising target for anticancer therapy. The cell proliferative potential can be limited by replication end problem, due to telomeres shortening, which is overcome in cancer cells by telomerase activity or by alternative telomeres lengthening (ALT) mechanism. However, this multisubunit enzymatic complex can be regulated at various levels, including expression control but also other factors contributing to the enzyme phosphorylation status, assembling or complex subunits transport. Thus, we show that the telomerase expression targeting cannot be the only possibility to shorten telomeres and induce cell apoptosis. It is important especially since the transcription expression is not always correlated with the enzyme activity which might result in transcription modulation failure or a possibility for the gene therapy to be overcome. This review summarizes the current state of knowledge of numerous telomerase regulation mechanisms that take place after telomerase subunits coding genes transcription. Thus we show the possible mechanisms of telomerase activity regulation which might become attractive anticancer therapy targets.
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Affiliation(s)
- Aneta Wojtyla
- Department of Clinical Chemistry and Molecular Diagnostics, Poznan University of Medical Sciences, Przybyszewskiego 49 St, 60-355 Poznan, Poland
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Strati A, Papoutsi Z, Lianidou E, Moutsatsou P. Effect of ellagic acid on the expression of human telomerase reverse transcriptase (hTERT) alpha+beta+ transcript in estrogen receptor-positive MCF-7 breast cancer cells. Clin Biochem 2009; 42:1358-62. [PMID: 19501078 DOI: 10.1016/j.clinbiochem.2009.05.017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Revised: 05/25/2009] [Accepted: 05/29/2009] [Indexed: 11/24/2022]
Abstract
OBJECTIVES To evaluate the potential of ellagic acid to inhibit the expression of human telomerase reverse transcriptase (hTERT) alpha+beta+ splice variant in MCF-7 breast cancer cells. DESIGN AND METHODS MCF-7 cells were incubated with ellagic acid (10(-)(9) M-10(-5) M) in the absence and in the presence of 17beta-estradiol (10(-8) M), a known inducer of hTERT transcription, and hTERT alpha+beta+ mRNA expression was quantified by real-time RT-PCR. 17beta-estradiol and ICI182780, a known estrogen antagonist, served as positive and negative controls respectively. RESULTS Ellagic acid, when alone, increased hTERT alpha+beta+ mRNA while its coexistence with 17beta-estradiol reduced significantly the 17beta-estradiol-induced increase in hTERT alpha+beta+ mRNA, implicating thus both its estrogenic and anti-estrogenic effects in breast cancer cells. CONCLUSIONS The potential of ellagic acid to down-regulate the 17beta-estradiol-induced hTERT alpha+beta+ mRNA expression may be a mechanism via which ellagic acid exerts, at least in part, its chemopreventive effects in breast cancer.
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Affiliation(s)
- Areti Strati
- Laboratory of Analytical Chemistry, Department of Chemistry, University of Athens, Athens, 15771, Greece
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Proctor A, Brownhill SC, Burchill SA. The promise of telomere length, telomerase activity and its regulation in the translocation-dependent cancer ESFT; clinical challenges and utility. Biochim Biophys Acta Mol Basis Dis 2009; 1792:260-74. [PMID: 19264125 DOI: 10.1016/j.bbadis.2009.02.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2009] [Revised: 02/19/2009] [Accepted: 02/20/2009] [Indexed: 01/12/2023]
Abstract
The Ewing's sarcoma family of tumours (ESFT) are diagnosed by EWS-ETS gene translocations. The resulting fusion proteins play a role in both the initiation and maintenance of these solid aggressive malignant tumours, suppressing cellular senescence and increasing cell proliferation and survival. EWS-ETS fusion proteins have altered transcriptional activity, inducing expression of a number of different target genes including telomerase. Up-regulation of hTERT is most likely responsible for the high levels of telomerase activity in primary ESFT, although telomerase activity and expression of hTERT are not predictive of outcome. However levels of telomerase activity in peripheral blood may be useful to monitor response to some therapeutics. Despite high levels of telomerase activity, telomeres in ESFT are frequently shorter than those of matched normal cells. Uncertainty about the role that telomerase and regulators of its activity play in the maintenance of telomere length in normal and cancer cells, and lack of studies examining the relationship between telomerase activity, regulators of its activity and their clinical significance in patient samples have limited their introduction into clinical practice. Studies in clinical samples using standardised assays are critical to establish how telomerase and regulators of its activity might best be exploited for patient benefit.
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Affiliation(s)
- Andrew Proctor
- Cancer Research UK Clinical Centre, Leeds Institute of Molecular Medicine, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK
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RNA interference-mediated c-MYC inhibition prevents cell growth and decreases sensitivity to radio- and chemotherapy in childhood medulloblastoma cells. BMC Cancer 2009; 9:10. [PMID: 19134217 PMCID: PMC2648994 DOI: 10.1186/1471-2407-9-10] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Accepted: 01/10/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND With current treatment strategies, nearly half of all medulloblastoma (MB) patients die from progressive tumors. Accordingly, the identification of novel therapeutic strategies remains a major goal. Deregulation of c-MYC is evident in numerous human cancers. In MB, over-expression of c-MYC has been shown to cause anaplasia and correlate with unfavorable prognosis. METHODS To study the role of c-MYC in MB biology, we down-regulated c-MYC expression by using small interfering RNA (siRNA) and investigated changes in cellular proliferation, cell cycle analysis, apoptosis, telomere maintenance, and response to ionizing radiation (IR) and chemotherapeutics in a representative panel of human MB cell lines expressing different levels of c-MYC (DAOY wild-type, DAOY transfected with the empty vector, DAOY transfected with c-MYC, D341, and D425). RESULTS siRNA-mediated c-MYC down-regulation resulted in an inhibition of cellular proliferation and clonogenic growth, inhibition of G1-S phase cell cycle progression, and a decrease in human telomerase reverse transcriptase (hTERT) expression and telomerase activity. On the other hand, down-regulation of c-MYC reduced apoptosis and decreased the sensitivity of human MB cells to IR, cisplatin, and etoposide. This effect was more pronounced in DAOY cells expressing high levels of c-MYC when compared with DAOY wild-type or DAOY cells transfected with the empty vector. CONCLUSION In human MB cells, in addition to its roles in growth and proliferation, c-MYC is also a potent inducer of apoptosis. Therefore, targeting c-MYC might be of therapeutic benefit when used sequentially with chemo- and radiotherapy rather than concomitantly.
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Quantification of hTERT splice variants in melanoma by SYBR green real-time polymerase chain reaction indicates a negative regulatory role for the beta deletion variant. Neoplasia 2008; 10:1131-7. [PMID: 18813352 DOI: 10.1593/neo.08644] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Revised: 07/18/2008] [Accepted: 07/18/2008] [Indexed: 11/18/2022] Open
Abstract
Telomerase activity is primarily determined by transcriptional regulation of the catalytic subunit, human telomerase reverse transcriptase (hTERT). Several mRNA splice variants for hTERT have been identified, but it is not clear if telomerase activity is determined by the absolute or relative levels of full-length (functional) and variant hTERT transcripts. We have developed an SYBR green-based reverse transcription-quantitative polymerase chain reaction assay for the enumeration of the four common hTERT mRNA variants and correlated these with telomerase activity and telomere length in 24 human melanoma cell lines. All except five of the lines expressed four hTERT transcripts, with an overall significant level of co-occurrence between absolute mRNA levels of full-length alpha+/beta+ hTERT and the three splice variants alpha-/beta+, alpha+/beta-, and alpha-/beta-. On average, alpha+/beta+ made up the majority (48.1%) of transcripts, followed by alpha+/beta- (44.6%), alpha-/beta- (4.4%), and alpha-/beta+ (2.9%). Telomerase activity ranged from 1 to 247 relative telomerase activity and correlated most strongly with the absolute amount of alpha+/beta+ (R = 0.791, P = .000004) and the relative amount of alpha+/beta- (R = -0.465, P = .022). This study shows that telomerase activity in melanoma cells is best determined by the absolute expression of full-length hTERT mRNA and indicates a role for the hTERT beta deletion variant in the negative regulation of enzyme activity.
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Canis familiaris telomerase reverse transcriptase undergoes alternative splicing. Mamm Genome 2008; 19:647-53. [PMID: 18836773 DOI: 10.1007/s00335-008-9144-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2008] [Accepted: 09/05/2008] [Indexed: 10/21/2022]
Abstract
The enzyme telomerase is essential for cell proliferation and tumorigenesis. Telomerase reverse transcriptase (TERT) represents the catalytic subunit of the enzyme. In humans, TERT expression is regulated by several different mechanisms, including alternative splicing. Canis familiaris TERT (dogTERT) has been shown to have a high level of sequence similarity with human TERT, indicating that the dog may represent a suitable animal model for telomerase studies. In the present report we sought to investigate whether dogTERT undergoes alternative splicing. During the analysis of canine mammary tissues (both tumor and paired adjacent to the tumor normal tissues) for dogTERT expression by RT-PCR, we identified eight samples-one tumor and seven adjacent normal-which gave PCR products of unexpected sizes. DNA sequencing revealed two insertions (175 and 28 bp long) and two deletions (17 and 32 bp long), which were encountered in different combinations and gave rise to five different transcripts. The generation of all variants could be explained by the employment of alternative splicing sites within dogTERT genomic sequences. The 175-bp and 28-bp insertions, identified between exons 7 and 8 and between 8 and 9, respectively, constituted unspliced sequences of introns 7 and 8, respectively. Both deletions originated from exon 8 sequence removals due to alternative splicing. All five variants encoded truncated proteins, which lacked essential motifs for reverse transcription and might have thus lost their ability to compose active telomerase enzymes. This is the first identification of alternative splicing events within dogTERT. The results presented here may provide the basis for more thorough studies on the regulation of telomerase activity in canine normal and cancer cells.
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Wang Y, Kowalski J, Tsai HL, Marik R, Prasad N, Somervell H, Lo PK, Sangenario LE, Dyrskjot L, Orntoft TF, Westra WH, Meeker AK, Eshleman JR, Umbricht CB, Zeiger MA. Differentiating alternative splice variant patterns of human telomerase reverse transcriptase in thyroid neoplasms. Thyroid 2008; 18:1055-63. [PMID: 18816183 PMCID: PMC2857449 DOI: 10.1089/thy.2008.0101] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
BACKGROUND Although fine-needle aspiration (FNA) biopsy of thyroid nodules is very sensitive in detecting thyroid malignancy, it remains ambiguous in 20-30% of cases. Current biomarkers for thyroid cancer lack either the sensitivity or specificity to substantially address this clinical problem. The aim of this study was to investigate the gene expression patterns of human telomerase reverse transcriptase (hTERT) alternative splice variants in benign and malignant thyroid tumors in an attempt to find a more reliable biomarker in the differential diagnosis of thyroid nodules. METHODS One hundred and thirty-three thyroid tumors from eight histopathological tumor types were collected from patients undergoing thyroid surgery at Johns Hopkins Hospital. Gene expression patterns of hTERT alternative splice variants were investigated in the tumors by nested reverse transcriptase-PCR. Telomerase enzyme activity was evaluated in a subset of 16 samples associated with the different hTERT patterns. Association of c-myc expression and hTERT patterns was also examined. RESULTS Malignant thyroid tumors exhibited a greater proportion of the active full-length hTERT transcript (0.57 +/- 0.15) than inactive splice variants, alpha(-) (0.13 +/- 0.02), or beta(-)/alpha(-)beta(-) deletion transcripts (0.30 +/- 0.11; p < 0.001). The opposite was observed in benign tumors, which exhibited greater proportions of beta(-)/alpha(-)beta(-) deletion transcripts (0.64 +/- 0.08) than either the full-length (0.19 +/- 0.06) or alpha(-) deletion transcripts (0.17 +/- 0.02; p < 0.001). Similar results were observed among a diagnostically challenging subset of 50 thyroid tumors that were suspicious for malignancy on FNA. Further, increased telomerase enzymatic activity was only associated with expression of the full-length hTERT isoform. In contrast, c-myc expression, which has been implicated in hTERT regulation, correlated with overall hTERT transcription without specificity for expression of the full-length isoform. CONCLUSIONS These differences in gene expression patterns of hTERT alternative splice variants may provide a useful adjunct to FNA diagnosis of suspicious thyroid tumors.
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Affiliation(s)
- Yongchun Wang
- Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Jeanne Kowalski
- Division of Oncology Biostatistics, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Hua-Ling Tsai
- Division of Oncology Biostatistics, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Radharani Marik
- Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Nijaguna Prasad
- Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Helina Somervell
- Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Pang-Kuo Lo
- Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Lauren E. Sangenario
- Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Lars Dyrskjot
- Molecular Diagnostic Laboratory, Department of Clinical Biochemistry, Aarhus University Hospital, Skejby, Denmark
| | - Torben F. Orntoft
- Molecular Diagnostic Laboratory, Department of Clinical Biochemistry, Aarhus University Hospital, Skejby, Denmark
| | - William H. Westra
- Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Alan K. Meeker
- Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - James R. Eshleman
- Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
- Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Christopher B. Umbricht
- Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland
- Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
- Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
| | - Martha A. Zeiger
- Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland
- Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, Maryland
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Madej P, Plewka A, Madej JA, Dzimira S, Nowak M, Plewka D, Nowaczyk G. Immunohistochemical localization of telomerase in myomas and in uterine myometrium. Pathol Res Pract 2008; 204:637-42. [PMID: 18584973 DOI: 10.1016/j.prp.2008.02.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2007] [Revised: 02/02/2008] [Accepted: 02/12/2008] [Indexed: 10/21/2022]
Abstract
Telomerase activity could be a potential marker for the neoplastic process, because it is absent in normal cells and present in tumor cells. Immunohistochemical studies were conducted using samples obtained from 32 uterine myomas, each sample having a size of 3-4 cm and obtained from women between 35 and 45 years of age. These studies also concentrated on fragments of macroscopically unaltered myometrium, collected 3-4 cm from a uterine tumor. Immunohistochemistry was performed using antibody to the catalytic unit of telomerase (hTERT; clone 44F12, NCL-L-hTERT, Novocastra Laboratories, UK). This study aimed at detecting a possible presence of potentially neoplastic cells in the margins of healthy tissue, which was removed together with the primary tumor. The results were classified according to the number of telomerase-positive cells. Tumors of the first group had up to 50% telomerase-positive cells, while their content in the second group exceeded 50%. Our study demonstrated an almost two-fold increase in the number of telomerase-positive tumor cells compared with myometrial cells 3-4 cm from the tumor. Hopefully, investigating the presence of telomerase in both uterine myometrium and myoma could facilitate the diagnosis of the neoplastic process.
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Affiliation(s)
- Paweł Madej
- Department of Gynaecological Endocrinology, Medical University of Silesia, Poland.
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Mantripragada KK, Caley M, Stephens P, Jones CJ, Kluwe L, Guha A, Mautner V, Upadhyaya M. Telomerase activity is a biomarker for high grade malignant peripheral nerve sheath tumors in neurofibromatosis type 1 individuals. Genes Chromosomes Cancer 2008; 47:238-46. [PMID: 18069666 DOI: 10.1002/gcc.20525] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Telomerase activity (TA) and the expression of its enzymatic subunits, which have been demonstrated in many tumors, remain poorly investigated in tumors associated with neurofibromatosis type 1 (NF1). In this study, we analysed the association of TA and the expression of telomerase RNA (TR) and telomerase reverse transcriptase (TERT) in 23 malignant peripheral nerve sheath tumors (MPNST) (17 high grade and 6 low grade tumors), 11 plexiform neurofibromas (PNF) and 6 dermal neurofibromas (DNF). TA was studied using telomerase repeat amplification protocol (TRAP) assay and expression of TR and TERT was investigated using reverse transcription PCR (RT-PCR) and real-time PCR. TA was detected in 14 out of 17 (82%) high grade MPNST, whereas all 6 low grade MPNST and 17 benign tumors were telomerase negative. The TERT transcripts were detected in all high grade MPNST, 50% of the low grade MPNST, and 4 benign tumors. However, the expression level of the TERT strikingly correlated with TA and high grade MPNST. Thus, while TERT expression was similar in both low grade MPNST and PNF (P = 0.115), it was significantly higher in high grade MPNST when compared to either low grade MPNST (P = 0.042), PNF (P = 0.001) or DNF tumors (P = 0.010). These findings indicate that TA and expression level of TERT are potential markers for high grade malignancy in NF1 patients.
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Saleh S, Lam AKY, Ho YH. Real-time PCR quantification of human telomerase reverse transcriptase (hTERT) in colorectal cancer. Pathology 2008; 40:25-30. [PMID: 18038311 DOI: 10.1080/00313020701716425] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
AIMS Human telomerase reverse transcriptase (hTERT) is believed to a reliable marker for telomerase activity. The expression of telomerase activity has not been investigated in a consecutive series of patients with colorectal adenocarcinoma in North Queensland. The objective of this study was to evaluate the significance of hTERT mRNA expression in colorectal adenocarcinoma in North Queensland. METHODS Matched samples of tumour and adjacent non-tumorous mucosa samples from 53 colorectal carcinomas and nine colorectal adenomas were collected. In all these samples, RNA was extracted and then transcribed to cDNA. Real-time polymerase chain reaction (RT-PCR) was used to quantitate expression the level of hTERT mRNA. The findings were correlated with the clinicopathological features of patients with these tumours prospectively collected into a computerised database. RESULTS hTERT mRNA was expressed in all tumour samples. The level of expression in the colorectal adenocarcinomas was significantly higher than the corresponding non-tumorous mucosa (p = 0.009, t-test). The level of expression in the adenocarcinomas was slightly higher than those of adenomas, but the difference was not statistically significant. A higher level of hTERT expression was often noted in the adenocarcinomas arising from the left colon and rectum when compared with those from the right colon (p = 0.029). CONCLUSIONS Colorectal adenocarcinoma revealed expression of telomerase hTERT mRNA, which was detected quantitatively by real-time PCR. hTERT could be a potential biomarker for colorectal cancer. The difference between proximal and distal colorectum in hTERT expression could account for their known different clinical behaviour.
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Affiliation(s)
- Said Saleh
- Department of Surgery (School of Medicine) and North Queensland Centre for Cancer Research (Australian Institute of Tropical Medicine), James Cook University, Townsville, Australia
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Li W, Li L, Liu Z, Liu C, Liu Z, Strååt K, Björkholm M, Jia J, Xu D. Expression of the full-length telomerase reverse transcriptase (hTERT) transcript in both malignant and normal gastric tissues. Cancer Lett 2007; 260:28-36. [PMID: 18037230 DOI: 10.1016/j.canlet.2007.10.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2007] [Revised: 10/11/2007] [Accepted: 10/15/2007] [Indexed: 12/12/2022]
Abstract
Activation of telomerase by the induction of a full-length telomerase reverse transcriptase (hTERT) transcript is a critical step during cellular immortalization and malignant transformation. Telomerase activity or hTERT expression has thus served as diagnostic and/or prognostic markers in different types of human malignancies. In the present study, we investigated the expression of the telomerase components hTERT and telomerase RNA template (hTER) in normal and malignant gastric tissues derived from 37 patients with gastric cancers. Overall hTERT mRNA was detectable in 33/37 (90%) of tumour specimens and 23/37 (62%) of the corresponding normal gastric tissues. Twenty-five of thirty-seven tumours (71%) expressed the full-length hTERT mRNA, and unexpectedly, this full-length transcript was found in 16 of 37 (43%) normal gastric tissues. Immunohistochemical analyses demonstrated a positive hTERT staining in small fractions of normal epithelial cells and in most gastric cancer cells. A close correlation between the presence of a full-length hTERT transcript and the c-MYC oncogene expression was observed in both normal and cancerous gastric specimens. Moreover, the full-length hTERT expression was positively associated with the tumour size in these patients. Similar levels of hTER expression were expressed in tumour and their corresponding normal tissues. The finding that the full-length hTERT transcript was present in both normal and malignant gastric tissues will preclude its use as a gastric cancer marker. Nevertheless, full-length hTERT mRNA expression may indicate a progressive gastric cancer, and its presence in normal gastric mucosa may have an impact on the anti-telomerase strategy for cancer therapeutic purpose.
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Affiliation(s)
- Wenjuan Li
- Department of Microbiology, School of Medicine, Shandong University, Jinan 250012, PR China.
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Gabet AS, Accardi R, Bellopede A, Popp S, Boukamp P, Sylla BS, Londoño-Vallejo JA, Tommasino M. Impairment of the telomere/telomerase system and genomic instability are associated with keratinocyte immortalization induced by the skin human papillomavirus type 38. FASEB J 2007; 22:622-32. [PMID: 17898088 DOI: 10.1096/fj.07-8389com] [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] [Indexed: 01/27/2023]
Abstract
The skin human papillomavirus (HPV) types belonging to the genus beta of the HPV phylogenetic tree appear to be associated with nonmelanoma skin cancer. We previously showed that the beta HPV type 38 E6 and E7 oncoproteins are able to inactivate the tumor suppressors p53 and retinoblastoma. Here, both viral proteins were expressed in primary human skin keratinocytes in order to study their effects on the telomere/telomerase system. We show that immortalization of skin keratinocytes induced by HPV38 E6/E7 is associated with hTERT gene overexpression. This event is, in part, explained by the accumulation of the p53-related protein, DeltaNp73. Despite elevated levels of hTERT mRNA, the telomerase activity detected in HPV38 E6/E7 keratinocytes was lower than that observed in HPV16 E6/E7 keratinocytes. The low telomerase activation in highly proliferative HPV38 E6/E7 keratinocytes resulted in the presence of extremely short and unstable telomeres. In addition, we observed anaphase bridges, mitotic multipolarity, and dramatic genomic aberrations. Interestingly, the ectopic expression of hTERT prevents both telomere erosion and genomic instability. Thus, we showed that in HPV38 E6/E7 keratinocytes characterized by unscheduled proliferation, suboptimal activation of telomerase and subsequent extensive telomere shortening result in genomic instability facilitating cellular immortalization.
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Affiliation(s)
- Anne-Sophie Gabet
- Infections and Cancer Biology Group, International Agency for Research on Cancer, World Health Organization, 150 Cours Albert Thomas, 69372 Lyon, France
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Molecular cloning and characterization of the zebrafish (Danio rerio) telomerase catalytic subunit (telomerase reverse transcriptase, TERT). J Mol Neurosci 2007; 34:63-75. [PMID: 18157659 DOI: 10.1007/s12031-007-0072-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2007] [Accepted: 08/08/2007] [Indexed: 01/11/2023]
Abstract
Telomerase is an enzyme composed of a catalytic subunit (TERT) and RNA template (TR), which specifically elongates telomeres and prevents cellular senescence. Although telomerase cannot be detected in most human somatic tissues, including the nervous system, it can be detected in teleost tissues. To facilitate the investigation of telomerase function in the teleost visual system, the coding sequence of zebrafish TERT is revealed and cloned. Immunoblot, immunohistochemistry, reverse transcription polymerase chain reaction (RT-PCR), and telomeric repeats amplification protocol (TRAP) assay are used to assess the expression of telomerase at mRNA, protein, and functional levels in zebrafish retina. Based on the amino acid sequence of mouse TERT, a full-length telomerase reverse transcriptase cDNA of zebrafish has been isolated and cloned. The deduced protein sequence contains 1,091 amino acid residues and a predicted molecular mass of 126 kDa. Multiple alignment shows that the protein sequence contains the conserved motifs and residues found in TERT of other species. RT-PCR and TRAP assay has detected TERT mRNA expression and telomerase activity, respectively, in all tissues examined, including the retina and the brain. The presence of telomerase activity indicates that a fully functional form of telomerase can be found in the retina. Immunohistochemistry reveals that most neurons in zebrafish retina express TERT in the cell nucleus. The presence of telomerase in different tissues may be associated with the indeterminate growth of teleost. However, teleost retinal neurons are post-mitotic and do not further divide under normal situation. The expression of telomerase activity and TERT in retina implies that telomerase has functions other than the elongation of telomere. These findings could provide new insights on telomerase function in the nervous system.
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