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Kim JJ, Ahn A, Ying JY, Pollens-Voigt J, Ludlow AT. Effect of aging and exercise on hTERT expression in thymus tissue of hTERT transgenic bacterial artificial chromosome mice. GeroScience 2024:10.1007/s11357-024-01319-5. [PMID: 39222198 DOI: 10.1007/s11357-024-01319-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2024] [Accepted: 08/18/2024] [Indexed: 09/04/2024] Open
Abstract
Telomere shortening occurs with aging in immune cells and may be related to immunosenescence. Exercise can upregulate telomerase activity and attenuate telomere shortening in immune cells, but it is unknown if exercise impacts other immune tissues such as the thymus. This study aimed to examine human telomerase reverse transcriptase (hTERT) alternative splicing (AS) in response to aging and exercise in thymus tissue. Transgenic mice with a human TERT bacterial artificial chromosome integrated into its genome (hTERT-BAC) were utilized in two different exercise models. Mice of different ages were assigned to an exercise cage (running wheel) or not for 3 weeks prior to thymus tissue excision. Middle-aged mice (16 months) were exposed or not to treadmill running (30 min at 60% maximum speed) prior to thymus collection. hTERT transcript variants were measured by RT-PCR. hTERT transcripts decreased with aging (r = - 0.7511, p < 0.0001) and 3 weeks of wheel running did not counteract this reduction. The ratio of exons 7/8 containing hTERT to total hTERT transcripts increased with aging (r = 0.3669, p = 0.0423) but 3 weeks of voluntary wheel running attenuated this aging-driven effect (r = 0.2013, p = 0.4719). Aging increased the expression of senescence marker p16 with no impact of wheel running. Thymus regeneration transcription factor, Foxn1, went down with age with no impact of wheel running exercise. Acute treadmill exercise did not induce any significant changes in thymus hTERT expression or AS variant ratio (p > 0.05). In summary, thymic hTERT expression is reduced with aging. Exercise counteracted a shift in hTERT AS ratio with age. Our data demonstrate that aging impacts telomerase expression and that exercise impacts dysregulated splicing that occurs with aging.
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Affiliation(s)
- Jeongjin J Kim
- School of Kinesiology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Alexander Ahn
- School of Kinesiology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Jeffrey Y Ying
- School of Kinesiology, University of Michigan, Ann Arbor, MI, 48109, USA
| | | | - Andrew T Ludlow
- School of Kinesiology, University of Michigan, Ann Arbor, MI, 48109, USA.
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2
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Guo D, Lin S, Wang X, Jiao Z, Li G, An L, Zhang Z, Zhang L. Establishment and Characterization of a Chicken Myoblast Cell Line. Int J Mol Sci 2024; 25:8340. [PMID: 39125909 PMCID: PMC11312951 DOI: 10.3390/ijms25158340] [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: 06/03/2024] [Revised: 07/17/2024] [Accepted: 07/28/2024] [Indexed: 08/12/2024] Open
Abstract
Skeletal muscle, which is predominantly constituted by multinucleated muscle fibers, plays a pivotal role in sustaining bodily movements and energy metabolism. Myoblasts, which serve as precursor cells for differentiation and fusion into muscle fibers, are of critical importance in the exploration of the functional genes associated with embryonic muscle development. However, the in vitro proliferation of primary myoblasts is inherently constrained. In this study, we achieved a significant breakthrough by successfully establishing a chicken myoblast cell line through the introduction of the exogenous chicken telomerase reverse transcriptase (chTERT) gene, followed by rigorous G418-mediated pressure screening. This newly developed cell line, which was designated as chTERT-myoblasts, closely resembled primary myoblasts in terms of morphology and exhibited remarkable stability in culture for at least 20 generations of population doublings without undergoing malignant transformation. In addition, we conducted an exhaustive analysis that encompassed cellular proliferation, differentiation, and transfection characteristics. Our findings revealed that the chTERT-myoblasts had the ability to proliferate, differentiate, and transfect after multiple rounds of population doublings. This achievement not only furnished a valuable source of homogeneous avian cell material for investigating embryonic muscle development, but also provided valuable insights and methodologies for establishing primary cell lines.
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Affiliation(s)
- Dongxue Guo
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
| | - Shudai Lin
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
| | - Xiaotong Wang
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
| | - Zhenhai Jiao
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
| | - Guo Li
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
| | - Lilong An
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
| | - Zihao Zhang
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
| | - Li Zhang
- College of Coastal Agricultural Sciences, Guangdong Ocean University, Zhanjiang 524088, China
- Key Laboratory of Farm Animal Genetic Resources and Germplasm Innovation in Zhanjiang, Guangdong Ocean University, Zhanjiang 524088, China
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3
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Cheng D, Zhang F, Porter KI, Wang S, Zhang H, Davis CJ, Robertson GP, Zhu J. Humanization of the mouse Tert gene reset telomeres to human length. RESEARCH SQUARE 2024:rs.3.rs-3617723. [PMID: 38260456 PMCID: PMC10802727 DOI: 10.21203/rs.3.rs-3617723/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Telomeres undergo shortening with each cell division, serving as biomarkers of human aging, which is characterized by short telomeres and restricted telomerase expression in adult tissues. Contrarily, mice, featuring their longer telomeres and widespread telomerase activity, present limitations as models for understanding telomere-related human biology and diseases. To bridge this gap, we engineered a mouse strain with a humanized mTert gene, hmTert, wherein specific non-coding sequences were replaced with their human counterparts. The hmTert gene, encoding the wildtype mTert protein, was repressed in adult tissues beyond the gonads and thymus, closely resembling the regulatory pattern of the human TERT gene. Remarkably, the hmTert gene rescued telomere dysfunction in late generations of mTert-knockout mice. Through successive intercrosses of Terth/- mice, telomere length progressively declined, stabilizing below 10-kb. Terth/h mice achieved a human-like average telomere length of 10-12 kb, contrasting with the 50-kb length in wildtype C57BL/6J mice. Despite shortened telomeres, Terth/h mice maintained normal body weight and cell homeostasis in highly proliferative tissues. Notably, colonocyte proliferation decreased significantly in Terth/h mice during dextran sodium sulfate-induced ulcerative colitis-like pathology, suggesting limitations on cellular renewal due to short telomeres. Our findings underscore the genetic determination of telomere homeostasis in mice by the Tert gene. These mice, exhibiting humanized telomere homeostasis, serve as a valuable model for exploring fundamental questions related to human aging and cancer.
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Affiliation(s)
- De Cheng
- Department of Pharmaceutical Sciences, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99202, USA
| | - Fan Zhang
- Department of Pharmaceutical Sciences, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99202, USA
| | - Kenneth I. Porter
- Department of Pharmaceutical Sciences, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99202, USA
| | - Shuwen Wang
- Department of Pharmaceutical Sciences, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99202, USA
| | - Hui Zhang
- Department of Pharmaceutical Sciences, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99202, USA
| | - Christopher J. Davis
- Department of Translational Medicine and Physiology, Elson S. Floyd College of Medicine, Washington State University, Spokane, WA 99202, USA
| | - Gavin P. Robertson
- Department of Pharmacology, Pathology, Dermatology, and Surgery, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Jiyue Zhu
- Department of Pharmaceutical Sciences, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99202, USA
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Kouprina N, Larionov V. Transformation-associated recombination (TAR) cloning and its applications for gene function; genome architecture and evolution; biotechnology and biomedicine. Oncotarget 2023; 14:1009-1033. [PMID: 38147065 PMCID: PMC10750837 DOI: 10.18632/oncotarget.28546] [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: 11/16/2023] [Accepted: 11/27/2023] [Indexed: 12/27/2023] Open
Abstract
Transformation-associated recombination (TAR) cloning represents a unique tool to selectively and efficiently recover a given chromosomal segment up to several hundred kb in length from complex genomes (such as animals and plants) and simple genomes (such as bacteria and viruses). The technique exploits a high level of homologous recombination in the yeast Sacharomyces cerevisiae. In this review, we summarize multiple applications of the pioneering TAR cloning technique, developed previously for complex genomes, for functional, evolutionary, and structural studies, and extended the modified TAR versions to isolate biosynthetic gene clusters (BGCs) from microbes, which are the major source of pharmacological agents and industrial compounds, and to engineer synthetic viruses with novel properties to design a new generation of vaccines. TAR cloning was adapted as a reliable method for the assembly of synthetic microbe genomes for fundamental research. In this review, we also discuss how the TAR cloning in combination with HAC (human artificial chromosome)- and CRISPR-based technologies may contribute to the future.
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Affiliation(s)
- Natalay Kouprina
- Developmental Therapeutics Branch, National Cancer Institute, Bethesda, MD 20892, USA
| | - Vladimir Larionov
- Developmental Therapeutics Branch, National Cancer Institute, Bethesda, MD 20892, USA
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Kim JJ, Ahn A, Ying J, Hickman E, Ludlow AT. Exercise as a Therapy to Maintain Telomere Function and Prevent Cellular Senescence. Exerc Sport Sci Rev 2023; 51:150-160. [PMID: 37288975 PMCID: PMC10526708 DOI: 10.1249/jes.0000000000000324] [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] [Indexed: 06/09/2023]
Abstract
Exercise transiently impacts the expression, regulation, and activity of TERT/telomerase to maintain telomeres and protect the genome from insults. By protecting the telomeres (chromosome ends) and the genome, telomerase promotes cellular survival and prevents cellular senescence. By increasing cellular resiliency, via the actions of telomerase and TERT, exercise promotes healthy aging.
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Affiliation(s)
- Jeongjin J Kim
- School of Kinesiology, University of Michigan, Ann Arbor, MI
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Slusher AL, Kim JJJ, Ribick M, Ludlow AT. Acute Exercise Regulates hTERT Gene Expression and Alternative Splicing in the hTERT-BAC Transgenic Mouse Model. Med Sci Sports Exerc 2022; 54:931-943. [PMID: 35135999 PMCID: PMC9117413 DOI: 10.1249/mss.0000000000002868] [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] [Indexed: 11/21/2022]
Abstract
INTRODUCTION Aerobic exercise maintains telomere length through increased human telomerase reverse transcriptase (hTERT) expression and telomerase enzyme activity. The impact of acute exercise on hTERT alternative splicing (AS) is unknown. PURPOSE This study aimed to examine hTERT AS in response to acute treadmill running. METHODS A bacterial artificial chromosome mouse model containing the 54-kilobase hTERT gene locus inserted into its genome (hTERT-BAC) was utilized. The gastrocnemius, left ventricle, and brain were excised before (Pre), upon cessation (Post), and during recovery (1, 24, 48, and 72 h; n = 5/time point) from treadmill running (30 min at 60% maximum speed). Full-length (FL) hTERT and the "minus beta" (-β) AS variant (skips exons 7 and 8 and does not code for active telomerase) were measured by gel-based and droplet digital reverse transcription-polymerase chain reaction methods. SF3B4 and SRSF2 protein expression were measured by Western blotting. RESULTS Compared with Pre, FL hTERT increased at Post before decreasing during recovery in the gastrocnemius (48 and 72 h; P ≤ 0.001) and left ventricle (24 h; P = 0.004). The percentage of FL hTERT in the gastrocnemius also increased during recovery (1 and 72 h; P ≤ 0.017), whereas a decrease was observed in the left ventricle (1, 24, and 48 h; P ≤ 0.041). hTERT decreased in the brain (48 h), whereas FL hTERT percentage remained unaltered. SF3B4 protein expression decreased throughout recovery in the gastrocnemius and tended to be associated with FL hTERT (r = -0.348, P = 0.075) and -β in opposite directions (r = 0.345, P = 0.067). CONCLUSIONS Endurance exercise increased hTERT gene expression, and altered FL hTERT splicing in contractile tissues and may maintain telomere length necessary to improve the function and health of the organism.
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Affiliation(s)
| | - Jeongjin JJ Kim
- School of Kinesiology, University of Michigan, Ann Arbor, MI
| | - Mark Ribick
- School of Kinesiology, University of Michigan, Ann Arbor, MI
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Abstract
Telomeres are non-coding nucleoprotein structures consisting of a highly conserved tandem repeat DNA sequence that caps the ends of chromosomes in eukaryotes. Telomeres confer chromosomal stability, protect the genome from nucleolytic degradation, avoid aberrant recombination and improper repair, and prevent random fusion of chromosomes. The end-replication problem results in telomere shortening with every cell division, eventually leading to cellular senescence and aging. Telomere length (TL) is thereby an ideal candidate for "biological aging." Telomeres possess guanine-rich repeats, which are highly susceptible to oxidative stress. Epidemiological studies have indicated the association of telomere attrition with mortality and various age-related diseases. Micronutrients comprising vitamins and minerals act as potential modulators of stress and can influence TL. Research has indicated that vitamin B12 (B12) regulates oxidative stress and maintains genomic stability, thereby influencing telomere integrity and cellular aging. The deficiency of B12 leads to elevated levels of homocysteine, which reduces the methylation potential and increases oxidative stress, thereby compromising the TL. Telomere shortening and mitochondrial dysfunction are independently linked to aging. However, they are connected through telomerase reverse transcriptase activity, which regulates mitochondrial biogenesis. Further, experimental evidence indicated the positive association of B12 with relative TL and mitochondrial DNA copy number, an indirect index of mitochondrial biogenesis. The present chapter provides some insights into the role of B12 in influencing TL. Exploring their association might open new avenues to understand the pathophysiology of aging and age-related diseases.
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Yang L, Wang B, Jiao X, Zhou C, Chen S, Gao X, Sun W, Song S, Li J, Liu J, Wang Y, Liu P. TAZ maintains telomere length in TNBC cells by mediating Rad51C expression. Breast Cancer Res 2021; 23:89. [PMID: 34488828 PMCID: PMC8422726 DOI: 10.1186/s13058-021-01466-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 08/25/2021] [Indexed: 11/10/2022] Open
Abstract
Background Telomere maintenance is crucial for the unlimited proliferation of cancer cells and essential for the “stemness” of multiple cancer cells. TAZ is more extensively expressed in triple negative breast cancers (TNBC) than in other types of breast cancers, and promotes proliferation, transformation and EMT of cancer cells. It was reported that TAZ renders breast cancer cells with cancer stem cell features. However, whether TAZ regulates telomeres is still unclear. In this study, we explored the roles of TAZ in the regulation of telomere maintenance in TNBC cells. Methods siRNA and shRNA was used to generate TAZ-depleted TNBC cell lines. qPCR and Southern analysis of terminal restriction fragments techniques were used to test telomere length. Co-immunoprecipitation, Western blotting, immunofluorescence, Luciferase reporter assay and Chromatin-IP were conducted to investigate the underlying mechanism. Results By knocking down the expression of TAZ in TNBC cells, we found, for the first time, that TAZ is essential for the maintenance of telomeres in TNBC cells. Moreover, loss of TAZ causes senescence phenotype of TNBC cells. The observed extremely shortened telomeres in late passages of TAZ knocked down cells correlate with an elevated hTERT expression, reductions of shelterin proteins, and an activated DNA damage response pathway. Our data also showed that depletion of TAZ results in overexpression of TERRAs, which are a group of telomeric repeat‐containing RNAs and regulate telomere length and integrity. Furthermore, we discovered that TAZ maintains telomere length of TNBC cells likely by facilitating the expression of Rad51C, a crucial element of homologous recombination pathway that promotes telomere replication. Conclusions This study supports the notion that TAZ is an oncogenic factor in TNBC, and further reveals a novel telomere-related pathway that is employed by TAZ to regulate TNBC. Supplementary Information The online version contains supplementary material available at 10.1186/s13058-021-01466-z.
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Affiliation(s)
- Lu Yang
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Bo Wang
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Xinyan Jiao
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Can Zhou
- Department of Breast Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Su Chen
- Laboratory of Molecular and Cellular Biology, School of Basic Medical Sciences, Henan University School of Medicine, North Jinming Avenue, Kaifeng, 475004, Henan Province, China
| | - Xiaoqian Gao
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Wei Sun
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Shaoran Song
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Juan Li
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Jie Liu
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Yaochun Wang
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China
| | - Peijun Liu
- Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China. .,Key Laboratory for Tumor Precision Medicine of Shaanxi Province, The First Affiliated Hospital of Xi'an Jiaotong University, 277 Yanta Western Rd, Xi'an, 710061, Shaanxi Province, China.
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Xu T, Cheng D, Zhao Y, Zhang J, Zhu X, Zhang F, Chen G, Wang Y, Yan X, Robertson GP, Gaddameedhi S, Lazarus P, Wang S, Zhu J. Polymorphic tandem DNA repeats activate the human telomerase reverse transcriptase gene. Proc Natl Acad Sci U S A 2021; 118:e2019043118. [PMID: 34155099 PMCID: PMC8256013 DOI: 10.1073/pnas.2019043118] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Multiple independent sequence variants of the hTERT locus have been associated with telomere length and cancer risks in genome-wide association studies. Here, we identified an intronic variable number tandem repeat, VNTR2-1, as an enhancer-like element, which activated hTERT transcription in a cell in a chromatin-dependent manner. VNTR2-1, consisting of 42-bp repeats with an array of enhancer boxes, cooperated with the proximal promoter in the regulation of hTERT transcription by basic helix-loop-helix transcription factors and maintained hTERT expression during embryonic stem-cell differentiation. Genomic deletion of VNTR2-1 in MelJuSo melanoma cells markedly reduced hTERT transcription, leading to telomere shortening, cellular senescence, and impairment of xenograft tumor growth. Interestingly, VNTR2-1 lengths varied widely in human populations; hTERT alleles with shorter VNTR2-1 were underrepresented in African American centenarians, indicating its role in human aging. Therefore, this polymorphic element is likely a missing link in the telomerase regulatory network and a molecular basis for genetic diversities of telomere homeostasis and age-related disease susceptibilities.
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Affiliation(s)
- Tao Xu
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
- College of Life Science, Northeast Forestry University, Harbin 150040, China
| | - De Cheng
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
| | - Yuanjun Zhao
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA 17033
| | - Jinglong Zhang
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
| | - Xiaolu Zhu
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
| | - Fan Zhang
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
| | - Gang Chen
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
| | - Yang Wang
- College of Life Science, Northeast Forestry University, Harbin 150040, China
| | - Xiufeng Yan
- College of Life Science, Northeast Forestry University, Harbin 150040, China
- College of Life and Environmental Science, Wenzhou University, Chashan University Town, Wenzhou 325035, China
| | - Gavin P Robertson
- Department of Pharmacology, Pennsylvania State University College of Medicine, Hershey, PA 17033
- Department of Pathology, Pennsylvania State University College of Medicine, Hershey, PA 17033
- Department of Dermatology, Pennsylvania State University College of Medicine, Hershey, PA 17033
- Department of Surgery, Pennsylvania State University College of Medicine, Hershey, PA 17033
| | - Shobhan Gaddameedhi
- Center for Human Health and the Environment, Department of Biological Sciences, North Carolina State University, Raleigh, NC 27606
| | - Philip Lazarus
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
| | - Shuwen Wang
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210
| | - Jiyue Zhu
- College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA 99210;
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10
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Subasri M, Shooshtari P, Watson AJ, Betts DH. Analysis of TERT Isoforms across TCGA, GTEx and CCLE Datasets. Cancers (Basel) 2021; 13:cancers13081853. [PMID: 33924498 PMCID: PMC8070023 DOI: 10.3390/cancers13081853] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 04/01/2021] [Accepted: 04/08/2021] [Indexed: 12/14/2022] Open
Abstract
Reactivation of the multi-subunit ribonucleoprotein telomerase is the primary telomere maintenance mechanism in cancer, but it is rate-limited by the enzymatic component, telomerase reverse transcriptase (TERT). While regulatory in nature, TERT alternative splice variant/isoform regulation and functions are not fully elucidated and are further complicated by their highly diverse expression and nature. Our primary objective was to characterize TERT isoform expression across 7887 neoplastic and 2099 normal tissue samples using The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression Project (GTEx), respectively. We confirmed the global overexpression and splicing shift towards full-length TERT in neoplastic tissue. Stratifying by tissue type we found uncharacteristic TERT expression in normal brain tissue subtypes. Stratifying by tumor-specific subtypes, we detailed TERT expression differences potentially regulated by subtype-specific molecular characteristics. Focusing on β-deletion splicing regulation, we found the NOVA1 trans-acting factor to mediate alternative splicing in a cancer-dependent manner. Of relevance to future tissue-specific studies, we clustered cancer cell lines with tumors from related origin based on TERT isoform expression patterns. Taken together, our work has reinforced the need for tissue and tumour-specific TERT investigations, provided avenues to do so, and brought to light the current technical limitations of bioinformatic analyses of TERT isoform expression.
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Affiliation(s)
- Mathushan Subasri
- Department of Physiology and Pharmacology, The University of Western Ontario, London, ON N6A 5C1, Canada; (M.S.); (A.J.W.)
| | - Parisa Shooshtari
- Ontario Institute for Cancer Research, Toronto, ON M5G 0A3, Canada;
- Department of Pathology and Laboratory Medicine, The University of Western Ontario, London, ON N6A 5C1, Canada
- Department of Computer Science, The University of Western Ontario, London, ON N6A 5C1, Canada
- The Children’s Health Research Institute—Lawson Health Research Institute, London, ON N6C 2R5, Canada
| | - Andrew J. Watson
- Department of Physiology and Pharmacology, The University of Western Ontario, London, ON N6A 5C1, Canada; (M.S.); (A.J.W.)
- The Children’s Health Research Institute—Lawson Health Research Institute, London, ON N6C 2R5, Canada
- Department of Obstetrics and Gynaecology, The University of Western Ontario, London, ON N6A 5C1, Canada
| | - Dean H. Betts
- Department of Physiology and Pharmacology, The University of Western Ontario, London, ON N6A 5C1, Canada; (M.S.); (A.J.W.)
- The Children’s Health Research Institute—Lawson Health Research Institute, London, ON N6C 2R5, Canada
- Department of Obstetrics and Gynaecology, The University of Western Ontario, London, ON N6A 5C1, Canada
- Correspondence: ; Tel.: +1-519-661-2111 (ext. 83786)
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11
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Gupta S, Vanderbilt CM, Lin YT, Benhamida JK, Jungbluth AA, Rana S, Momeni-Boroujeni A, Chang JC, Mcfarlane T, Salazar P, Mullaney K, Middha S, Zehir A, Gopalan A, Bale TA, Ganly I, Arcila ME, Benayed R, Berger MF, Ladanyi M, Dogan S. A Pan-Cancer Study of Somatic TERT Promoter Mutations and Amplification in 30,773 Tumors Profiled by Clinical Genomic Sequencing. J Mol Diagn 2020; 23:253-263. [PMID: 33285287 DOI: 10.1016/j.jmoldx.2020.11.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 10/15/2020] [Accepted: 11/10/2020] [Indexed: 01/20/2023] Open
Abstract
TERT gene promoter mutations are known in multiple cancer types. Other TERT alterations remain poorly characterized. Sequencing data from 30,773 tumors analyzed by a hybridization capture next-generation sequencing assay (Memorial Sloan Kettering Cancer Center Integrated Mutation Profiling of Actionable Cancer Targets) were analyzed for the presence of TERT alterations. Promoter rearrangements (500 bases upstream of the transcriptional start site), hypermethylation (n = 57), and gene expression (n = 155) were evaluated for a subset of cases. Mutually exclusive and recurrent promoter mutations were identified at three hot spots upstream of the transcriptional start site in 11.3% of cases (-124: 74%; -146: 24%; and -138: <2%). Mutually exclusive amplification events were identified in another 2.3% of cases, whereas mutually exclusive rearrangements proximal to the TERT gene were seen in 24 cases. The highest incidence of TERT promoter mutations was seen in cutaneous melanoma (82%), whereas amplification events significantly outnumbered promoter mutations in well-differentiated/dedifferentiated liposarcoma (14.1% versus 2.4%) and adrenocortical carcinoma (13.6% versus 4.5%). Gene expression analysis suggests that the highest levels of gene expression are seen in cases with amplifications and rearrangements. Hypermethylation events upstream of the TERT coding sequence were not mutually exclusive with known pathogenic alterations. Studies aimed at defining the prevalence and prognostic impact of TERT alterations should incorporate other pathogenic TERT alterations as these may impact telomerase function.
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Affiliation(s)
- Sounak Gupta
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Chad M Vanderbilt
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Yun-Te Lin
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Jamal K Benhamida
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Achim A Jungbluth
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Satshil Rana
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | | | - Jason C Chang
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Tiffany Mcfarlane
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Paulo Salazar
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Kerry Mullaney
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Sumit Middha
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Ahmet Zehir
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Anuradha Gopalan
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Tejus A Bale
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Ian Ganly
- Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Maria E Arcila
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Ryma Benayed
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Michael F Berger
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Marc Ladanyi
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Snjezana Dogan
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York.
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12
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in der Stroth L, Tharehalli U, Günes C, Lechel A. Telomeres and Telomerase in the Development of Liver Cancer. Cancers (Basel) 2020; 12:E2048. [PMID: 32722302 PMCID: PMC7464754 DOI: 10.3390/cancers12082048] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 07/16/2020] [Accepted: 07/22/2020] [Indexed: 02/07/2023] Open
Abstract
Liver cancer is one of the most common cancer types worldwide and the fourth leading cause of cancer-related death. Liver carcinoma is distinguished by a high heterogeneity in pathogenesis, histopathology and biological behavior. Dysregulated signaling pathways and various gene mutations are frequent in hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), which represent the two most common types of liver tumors. Both tumor types are characterized by telomere shortening and reactivation of telomerase during carcinogenesis. Continuous cell proliferation, e.g., by oncogenic mutations, can cause extensive telomere shortening in the absence of sufficient telomerase activity, leading to dysfunctional telomeres and genome instability by breakage-fusion-bridge cycles, which induce senescence or apoptosis as a tumor suppressor mechanism. Telomerase reactivation is required to stabilize telomere functionality and for tumor cell survival, representing a genetic risk factor for the development of liver cirrhosis and liver carcinoma. Therefore, telomeres and telomerase could be useful targets in hepatocarcinogenesis. Here, we review similarities and differences between HCC and iCCA in telomere biology.
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Affiliation(s)
- Lena in der Stroth
- Department of Internal Medicine I, University Hospital Ulm, 89081 Ulm, Germany; (L.i.d.S.); (U.T.)
| | - Umesh Tharehalli
- Department of Internal Medicine I, University Hospital Ulm, 89081 Ulm, Germany; (L.i.d.S.); (U.T.)
| | - Cagatay Günes
- Department of Urology, University Hospital Ulm, 89081 Ulm, Germany;
| | - André Lechel
- Department of Internal Medicine I, University Hospital Ulm, 89081 Ulm, Germany; (L.i.d.S.); (U.T.)
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13
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Aging and biomarkers: Transcriptional levels evaluation of Osteopontin/miRNA-181a axis in hepatic tissue of rats in different age ranges. Exp Gerontol 2020; 133:110879. [DOI: 10.1016/j.exger.2020.110879] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 02/07/2020] [Accepted: 02/12/2020] [Indexed: 12/21/2022]
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14
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DNA Hypermethylation Downregulates Telomerase Reverse Transcriptase (TERT) during H. pylori-Induced Chronic Inflammation. JOURNAL OF ONCOLOGY 2019; 2019:5415761. [PMID: 32082377 PMCID: PMC7012206 DOI: 10.1155/2019/5415761] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Revised: 08/29/2019] [Accepted: 09/27/2019] [Indexed: 12/16/2022]
Abstract
Helicobacter pylori infection causes chronic gastritis and is the major risk factor of gastric cancer. H. pylori induces a chronic inflammation-producing reactive oxygen species (ROS) which is a source of chromosome instabilities and contributes to the development of malignancy. H. pylori also promotes DNA hypermethylation, known to dysregulate essential genes that maintain genetic stability. The maintenance of telomere length by telomerase is essential for chromosome integrity. Telomerase reverse transcriptase (TERT) is the catalytic component of telomerase activity and an important target during host-pathogen interaction. We aimed to investigate the consequences of H. pylori on the regulation of TERT gene expression and telomerase activity. In vitro, hTERT mRNA levels and telomerase activity were analysed in H. pylori-infected human gastric epithelial cells. In addition, C57BL/6 and INS-GAS mice were used to investigate the influence of H. pylori-induced inflammation on TERT levels. Our data demonstrated that, in vitro, H. pylori inhibits TERT gene expression and decreases the telomerase activity. The exposure of cells to lycopene, an antioxidant compound, restores TERT levels in infected cells, indicating that ROS are implicated in this downregulation. In vivo, fewer TERT-positive cells are observed in gastric tissues of infected mice compared to uninfected, more predominantly in the vicinity of large aggregates of lymphocytes, suggesting an inflammation-mediated regulation. Furthermore, H. pylori appears to downregulate TERT gene expression through DNA hypermethylation as shown by the restoration of TERT transcript levels in cells treated with 5′-azacytidine, an inhibitor of DNA methylation. This was confirmed in infected mice, by PCR-methylation assay of the TERT gene promoter. Our data unraveled a novel way for H. pylori to promote genome instabilities through the inhibition of TERT levels and telomerase activity. This mechanism could play an important role in the early steps of gastric carcinogenesis.
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15
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Engineering a humanized telomerase reverse transcriptase gene in mouse embryonic stem cells. Sci Rep 2019; 9:9683. [PMID: 31273310 PMCID: PMC6609615 DOI: 10.1038/s41598-019-46160-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 06/24/2019] [Indexed: 12/18/2022] Open
Abstract
Telomerase is expressed in adult mouse, but not in most human, tissues and mouse telomeres are much longer than those in humans. This interspecies difference of telomere homeostasis poses a challenge in modeling human diseases using laboratory mice. Using chromatinized bacterial artificial chromosome reporters, we discovered that the 5′ intergenic region, introns 2 and 6 of human telomerase gene (hTERT) were critical for regulating its promoter in somatic cells. Accordingly, we engineered a humanized gene, hmTert, by knocking-in a 47-kilobase hybrid fragment containing these human non-coding sequences into the mTert locus in mouse embryonic stem cells (mESCs). The hmTert gene, encoding the wildtype mTert protein, was fully functional, as a mESC line with homozygous hmTert alleles proliferated for over 400 population doublings without exhibiting chromosomal abnormalities. Like human ESCs, the engineered mESCs contained high telomerase activity, which was repressed upon their differentiation into fibroblast-like cells in a histone deacetylase-dependent manner. Fibroblast-like cells differentiated from these mESCs contained little telomerase activity. Thus, telomerase in mESCs with the hmTert alleles was subjected to human-like regulation. Our study revealed a novel approach to engineer a humanized telomerase gene in mice, achieving a milestone in creating a mouse model with humanized telomere homeostasis.
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16
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Liu MY, Nemes A, Zhou QG. The Emerging Roles for Telomerase in the Central Nervous System. Front Mol Neurosci 2018; 11:160. [PMID: 29867352 PMCID: PMC5964194 DOI: 10.3389/fnmol.2018.00160] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Accepted: 04/26/2018] [Indexed: 12/11/2022] Open
Abstract
Telomerase, a specialized ribonucleoprotein enzyme complex, maintains telomere length at the 3′ end of chromosomes, and functions importantly in stem cells, cancer and aging. Telomerase exists in neural stem cells (NSCs) and neural progenitor cells (NPCs), at a high level in the developing and adult brains of humans and rodents. Increasing studies have demonstrated that telomerase in NSCs/NPCs plays important roles in cell proliferation, neuronal differentiation, neuronal survival and neuritogenesis. In addition, recent works have shown that telomerase reverse transcriptase (TERT) can protect newborn neurons from apoptosis and excitotoxicity. However, to date, the link between telomerase and diseases in the central nervous system (CNS) is not well reviewed. Here, we analyze the evidence and summarize the important roles of telomerase in the CNS. Understanding the roles of telomerase in the nervous system is not only important to gain further insight into the process of the neural cell life cycle but would also provide novel therapeutic applications in CNS diseases such as neurodegenerative condition, mood disorders, aging and other ailments.
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Affiliation(s)
- Meng-Ying Liu
- Department of Clinical Pharmacology, Pharmacy College, Nanjing Medical University, Nanjing, China.,The Affiliated Hospital of Nanjing University Medical School, Nanjing Drum Tower Hospital, Nanjing, China
| | - Ashley Nemes
- Department of Stem Cell Biology and Regenerative Medicine, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Qi-Gang Zhou
- Department of Clinical Pharmacology, Pharmacy College, Nanjing Medical University, Nanjing, China.,Department of Stem Cell Biology and Regenerative Medicine, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
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17
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Li X, Xu X, Fang J, Wang L, Mu Y, Zhang P, Yao Z, Ma Z, Liu Z. Rs2853677 modulates Snail1 binding to the TERT enhancer and affects lung adenocarcinoma susceptibility. Oncotarget 2018; 7:37825-37838. [PMID: 27191258 PMCID: PMC5122352 DOI: 10.18632/oncotarget.9339] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 04/28/2016] [Indexed: 01/07/2023] Open
Abstract
Genome wide association studies (GWAS) have shown that SNPs in non-coding regions are associated with inherited susceptibility to cancer. The effect of one single SNP, however, is weak. To identify potential co-factors of SNPs, we investigated the underlying mechanism by which SNPs affect lung cancer susceptibility. We found that rs2853677 is located within the Snail1 binding site in a TERT enhancer. This enhancer increases TERT transcription when juxtaposed to the TERT promoter. The binding of Snail1 to the enhancer disrupts enhancer-promoter colocalization and silences TERT transcription. The high risk variant of rs2853677 disrupts the Snail1 binding site and derepresses TERT expression in response to Snail1 upregulation, thus increasing lung adenocarcinoma susceptibility. Our data suggest that Snail1 may be a co-factor of rs2853677 for predicting lung adenocarcinoma susceptibility and prognosis.
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Affiliation(s)
- Xiaoting Li
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China.,Department of Forensic Medicine, Tianjin Medical University, Tianjin, China
| | - Xing Xu
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China
| | - Jiali Fang
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China
| | - Lin Wang
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China
| | - Yanchao Mu
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China
| | - Peng Zhang
- Department of Clinical Laboratory, Tianjin Medical University Cancer Institute and Hospital, Tianjin, China
| | - Zhi Yao
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China.,Key Laboratory of Immune Microenvironment and Disease of the Ministry of Education, Tianjin Medical University, Tianjin, China
| | - Zhenyi Ma
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China
| | - Zhe Liu
- Department of Immunology, Biochemistry and Molecular Biology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Tianjin Key Laboratory of Medical Epigenetics, Tianjin Medical University, Tianjin, China
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18
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Nanoscale Assembly of High-Mobility Group AT-Hook 2 Protein with DNA Replication Fork. Biophys J 2018; 113:2609-2620. [PMID: 29262356 DOI: 10.1016/j.bpj.2017.10.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 08/24/2017] [Accepted: 10/12/2017] [Indexed: 01/31/2023] Open
Abstract
High mobility group AT-hook 2 (HMGA2) protein is composed of three AT-hook domains. HMGA2 expresses at high levels in both embryonic stem cells and cancer cells, where it interacts with and stabilizes replication forks (RFs), resulting in elevated cell proliferation rates. In this study, we demonstrated that HMGA2 knockdown reduces cell proliferation. To understand the features required for interaction between HMGA2 and RFs, we studied the solution structure of HMGA2, free and in complex with RFs, using an integrated host of biophysical techniques. Circular dichroism and NMR experiments confirmed the disordered state of unbound HMGA2. Dynamic light scattering and sedimentation velocity experiments demonstrated that HMGA2 and RF are monodisperse in solution, and form an equimolar complex. Small-angle x-ray scattering studies revealed that HMGA2 binds in a side-by-side orientation to RF where 3 AT-hooks act as a clamp to wrap around a distorted RF. Thus, our data provide insights into how HMGA2 interacts with stalled RFs and the function of the process.
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19
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Qin QP, Meng T, Tan MX, Liu YC, Luo XJ, Zou BQ, Liang H. Synthesis, crystal structure and biological evaluation of a new dasatinib copper(II) complex as telomerase inhibitor. Eur J Med Chem 2018; 143:1597-1603. [DOI: 10.1016/j.ejmech.2017.10.058] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Revised: 09/23/2017] [Accepted: 10/19/2017] [Indexed: 12/20/2022]
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20
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Wang X, Sun L, Sun X, Yu J, Wang K, Wu Y, Gao Q, Zheng J. Antitumor effects of a dual-specific lentiviral vector carrying the Escherichia coli purine nucleoside phosphorylase gene. Int J Oncol 2017; 50:1612-1622. [PMID: 28393254 PMCID: PMC5403222 DOI: 10.3892/ijo.2017.3949] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 03/13/2017] [Indexed: 12/25/2022] Open
Abstract
The Escherichia coli purine nucleoside phosphorylase/Fludarabine phosphate (ePNP/Fludara) suicide system has several drawbacks, such as side-effects and the low efficiency of ePNP expression. In this study, we evaluated the antitumor effects of the dual-specific 8HSEs-hTERTp-ePNP/Fludara suicide system under hyperthermia in vitro and in vivo. Luciferase activities from the 8HSEs‑hTERT and CMV promoters were compared using the dual luciferase assay in SW480 (high hTERT expression) and MKN74 cells (hTERT-negative) in the presence and absence of hyperthermia. Then, we investigated the effects of overexpressing the suicide gene ePNP using 8HSEs‑hTERT-driven lentiviral vectors with Fludara on in vitro cell viability, side-effects, apoptosis, cycle distribution, colony formation and in vivo xenograft tumor growth. At 43˚C, luciferase activity from the 8HSEs‑hTERT promoter was significantly increased in SW480 cells, but not in MKN74 cells. Importantly, luciferase activities from the 8HSEs‑hTERT promoter were much higher than from the CMV promoter in hTERT-expressing SW480 cells under heated conditions. The in vitro quantitative analysis showed a 4-fold higher ePNP protein expression from the 8HSEs‑hTERT promoter at 43˚C than at 37˚C in SW480 cells and the ePNP mRNA expression in SW480 cells at 43˚C was also higher than at 37˚C. Conversely, ePNP mRNA and protein expression were low, almost absent, in hTERT-negative MKN74 cells with or without hyperthermia. After Fludara addition, cell cytotoxicity assays showed that the significant inhibitory effect of the 8HSEs‑hTERTp-ePNP on SW480 cells was dose- and time-dependent with hyperthermia. The 8HSEs‑hTERTp-ePNP/Fludara suicide system significantly inhibited SW480 cell viability, colony formation, cell cycle progression and induced apoptosis in vitro, but also induced significant bystander effects, especially under the heated conditions. At the protein level, the suicide system significantly promoted Bax, caspase-3 and p53 expression and suppressed Bcl-2 expression. In sections from mouse xenografts, TUNEL assays showed that the suicide system reduced xenograft growth and induced SW480 apoptosis. These results indicated that the combinatorial cancer- and heat-specific promoter system has great potential for improving the efficacy of cancer treatment with hyperthermia. The 8HSEs‑hTERTp-ePNP/Fludara system may serve as a powerful strategy for cancer gene therapy combined with hyperthermia.
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Affiliation(s)
- Xiaolong Wang
- Department of Oncology, The Second Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710004, P.R. China
| | - Lei Sun
- Department of General Surgery, The Second Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710004, P.R. China
| | - Xuejun Sun
- Department of General Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Junhui Yu
- Department of General Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Kai Wang
- Department of General Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Yunhua Wu
- Department of General Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Qi Gao
- Department of General Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Jianbao Zheng
- Department of General Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
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21
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Differential decrease in soluble and DNA-bound telomerase in senescent human fibroblasts. Biogerontology 2017; 18:525-533. [DOI: 10.1007/s10522-017-9688-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Accepted: 02/22/2017] [Indexed: 12/14/2022]
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22
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Kim W, Ludlow AT, Min J, Robin JD, Stadler G, Mender I, Lai TP, Zhang N, Wright WE, Shay JW. Regulation of the Human Telomerase Gene TERT by Telomere Position Effect-Over Long Distances (TPE-OLD): Implications for Aging and Cancer. PLoS Biol 2016; 14:e2000016. [PMID: 27977688 PMCID: PMC5169358 DOI: 10.1371/journal.pbio.2000016] [Citation(s) in RCA: 125] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 11/10/2016] [Indexed: 02/07/2023] Open
Abstract
Telomerase is expressed in early human development and then becomes silenced in most normal tissues. Because ~90% of primary human tumors express telomerase and generally maintain very short telomeres, telomerase is carefully regulated, particularly in large, long-lived mammals. In the current report, we provide substantial evidence for a new regulatory control mechanism of the rate limiting catalytic protein component of telomerase (hTERT) that is determined by the length of telomeres. We document that normal, young human cells with long telomeres have a repressed hTERT epigenetic status (chromatin and DNA methylation), but the epigenetic status is altered when telomeres become short. The change in epigenetic status correlates with altered expression of TERT and genes near to TERT, indicating a change in chromatin. Furthermore, we identified a chromosome 5p telomere loop to a region near TERT in human cells with long telomeres that is disengaged with increased cell divisions as telomeres progressively shorten. Finally, we provide support for a role of the TRF2 protein, and possibly TERRA, in the telomere looping maintenance mechanism through interactions with interstitial TTAGGG repeats. This provides new insights into how the changes in genome structure during replicative aging result in an increased susceptibility to age-related diseases and cancer prior to the initiation of a DNA damage signal.
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Affiliation(s)
- Wanil Kim
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Andrew T Ludlow
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Jaewon Min
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Jerome D Robin
- Faculté de Médecine, Tour Pasteur 8éme Étage, Nice, France
| | - Guido Stadler
- Berkeley Lights, Inc., Emeryville, California, United States of America
| | - Ilgen Mender
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Tsung-Po Lai
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Ning Zhang
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Woodring E Wright
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Jerry W Shay
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
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23
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Cheng D, Zhao Y, Wang S, Zhang F, Russo M, McMahon SB, Zhu J. Repression of telomerase gene promoter requires human-specific genomic context and is mediated by multiple HDAC1-containing corepressor complexes. FASEB J 2016; 31:1165-1178. [PMID: 27940549 DOI: 10.1096/fj.201601111r] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Accepted: 11/28/2016] [Indexed: 12/16/2022]
Abstract
The human telomerase reverse transcriptase (hTERT) gene is repressed in most somatic cells, whereas the expression of the mouse mTert gene is widely detected. To understand the mechanisms of this human-specific repression, we constructed bacterial artificial chromosome (BAC) reporters using human and mouse genomic DNAs encompassing the TERT genes and neighboring loci. Upon chromosomal integration, the hTERT, but not the mTert, reporter was stringently repressed in telomerase-negative human cells in a histone deacetylase (HDAC)-dependent manner, replicating the expression of their respective endogenous genes. In chimeric BACs, the mTert promoter became strongly repressed in the human genomic context, but the hTERT promoter was highly active in the mouse genomic context. Furthermore, an unrelated herpes simplex virus-thymidine kinase (HSV-TK) promoter was strongly repressed in the human, but not in the mouse, genomic context. These results demonstrated that the repression of hTERT gene was dictated by distal elements and its chromatin environment. This repression depended on class I HDACs and involved multiple corepressor complexes, including HDAC1/2-containing Sin3B, nucleosome remodeling and histone deacetylase (NuRD), and corepressor of RE1 silencing transcription factor (CoREST) complexes. Together, our data indicate that the lack of telomerase expression in most human somatic cells results from its repressive genomic environment, providing new insight into the mechanism of long-recognized differential telomerase regulation in mammalian species.-Cheng, D., Zhao, Y., Wang, S., Zhang, F., Russo, M., McMahon, S. B., Zhu, J. Repression of telomerase gene promoter requires human-specific genomic context and is mediated by multiple HDAC1-containing corepressor complexes.
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Affiliation(s)
- De Cheng
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, Washington, USA
| | - Yuanjun Zhao
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA; and
| | - Shuwen Wang
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, Washington, USA
| | - Fan Zhang
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, Washington, USA
| | - Mariano Russo
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA; and
| | - Steven B McMahon
- Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
| | - Jiyue Zhu
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, Washington, USA;
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24
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Kang HJ, Cui Y, Yin H, Scheid A, Hendricks WPD, Schmidt J, Sekulic A, Kong D, Trent JM, Gokhale V, Mao H, Hurley LH. A Pharmacological Chaperone Molecule Induces Cancer Cell Death by Restoring Tertiary DNA Structures in Mutant hTERT Promoters. J Am Chem Soc 2016; 138:13673-13692. [PMID: 27643954 DOI: 10.1021/jacs.6b07598] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Activation of human telomerase reverse transcriptase (hTERT) is necessary for limitless replication in tumorigenesis. Whereas hTERT is transcriptionally silenced in normal cells, most tumor cells reactivate hTERT expression by alleviating transcriptional repression through diverse genetic and epigenetic mechanisms. Transcription-activating hTERT promoter mutations have been found to occur at high frequencies in multiple cancer types. These mutations have been shown to form new transcription factor binding sites that drive hTERT expression, but this model cannot fully account for differences in wild-type (WT) and mutant promoter activation and has not yet enabled a selective therapeutic strategy. Here, we demonstrate a novel mechanism by which promoter mutations activate hTERT transcription, which also sheds light on a unique therapeutic opportunity. Promoter mutations occur in a core promoter region that forms tertiary structures consisting of a pair of G-quadruplexes involved in transcriptional silencing. We show that promoter mutations exert a detrimental effect on the folding of one of these G-quadruplexes, resulting in a nonfunctional silencer element that alleviates transcriptional repression. We have also identified a small drug-like pharmacological chaperone (pharmacoperone) molecule, GTC365, that acts at an early step in the G-quadruplex folding pathway to redirect mutant promoter G-quadruplex misfolding, partially reinstate the correct folding pathway, and reduce hTERT activity through transcriptional repression. This transcription-mediated repression produces cancer cell death through multiple routes including both induction of apoptosis through inhibition of hTERT's role in regulating apoptosis-related proteins and induction of senescence by decreasing telomerase activity and telomere length. We demonstrate the selective therapeutic potential of this strategy in melanoma cells that overexpress hTERT.
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Affiliation(s)
- Hyun-Jin Kang
- University of Arizona , College of Pharmacy, 1703 East Mabel Street, Tucson, Arizona 85721, United States
| | - Yunxi Cui
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University , Kent, Ohio 44242, United States
| | - Holly Yin
- Translational Genomics Research Institute , 445 North Fifth Street, Phoenix, Arizona 85004, United States
| | - Amy Scheid
- College of Science, University of Arizona , 1040 East Fourth Street, Tucson, Arizona 85721, United States
| | - William P D Hendricks
- Translational Genomics Research Institute , 445 North Fifth Street, Phoenix, Arizona 85004, United States
| | - Jessica Schmidt
- Department of Dermatology, Mayo Clinic , 13400 East Shea Boulevard, Scottsdale, Arizona 85259, United States
| | - Aleksandar Sekulic
- Department of Dermatology, Mayo Clinic , 13400 East Shea Boulevard, Scottsdale, Arizona 85259, United States
| | - Deming Kong
- State Key Laboratory of Medicinal Chemical Biology, College of Chemistry, Nankai University , Tianjin 300071, People's Republic of China
| | - Jeffrey M Trent
- Translational Genomics Research Institute , 445 North Fifth Street, Phoenix, Arizona 85004, United States
| | - Vijay Gokhale
- BIO5 Institute , 1657 East Helen Street, Tucson, Arizona 85721, United States
| | - Hanbin Mao
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University , Kent, Ohio 44242, United States
| | - Laurence H Hurley
- University of Arizona , College of Pharmacy, 1703 East Mabel Street, Tucson, Arizona 85721, United States.,BIO5 Institute , 1657 East Helen Street, Tucson, Arizona 85721, United States.,Arizona Cancer Center , 1515 North Campbell Avenue, Tucson, Arizona 85724, United States
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25
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Zhang F, Cheng D, Wang S, Zhu J. Human Specific Regulation of the Telomerase Reverse Transcriptase Gene. Genes (Basel) 2016; 7:genes7070030. [PMID: 27367732 PMCID: PMC4962000 DOI: 10.3390/genes7070030] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Revised: 06/15/2016] [Accepted: 06/17/2016] [Indexed: 12/19/2022] Open
Abstract
Telomerase, regulated primarily by the transcription of its catalytic subunit telomerase reverse transcriptase (TERT), is critical for controlling cell proliferation and tissue homeostasis by maintaining telomere length. Although there is a high conservation between human and mouse TERT genes, the regulation of their transcription is significantly different in these two species. Whereas mTERT expression is widely detected in adult mice, hTERT is expressed at extremely low levels in most adult human tissues and cells. As a result, mice do not exhibit telomere-mediated replicative aging, but telomere shortening is a critical factor of human aging and its stabilization is essential for cancer development in humans. The chromatin environment and epigenetic modifications of the hTERT locus, the binding of transcriptional factors to its promoter, and recruitment of nucleosome modifying complexes all play essential roles in restricting its transcription in different cell types. In this review, we will discuss recent progress in understanding the molecular mechanisms of TERT regulation in human and mouse tissues and cells, and during cancer development.
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Affiliation(s)
- Fan Zhang
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, PO Box 1495, Spokane, WA 99210, USA.
| | - De Cheng
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, PO Box 1495, Spokane, WA 99210, USA.
| | - Shuwen Wang
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, PO Box 1495, Spokane, WA 99210, USA.
| | - Jiyue Zhu
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, PO Box 1495, Spokane, WA 99210, USA.
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26
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Transformation-associated recombination (TAR) cloning for genomics studies and synthetic biology. Chromosoma 2016; 125:621-32. [PMID: 27116033 DOI: 10.1007/s00412-016-0588-3] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Revised: 03/22/2016] [Accepted: 03/29/2016] [Indexed: 12/25/2022]
Abstract
Transformation-associated recombination (TAR) cloning represents a unique tool for isolation and manipulation of large DNA molecules. The technique exploits a high level of homologous recombination in the yeast Sacharomyces cerevisiae. So far, TAR cloning is the only method available to selectively recover chromosomal segments up to 300 kb in length from complex and simple genomes. In addition, TAR cloning allows the assembly and cloning of entire microbe genomes up to several Mb as well as engineering of large metabolic pathways. In this review, we summarize applications of TAR cloning for functional/structural genomics and synthetic biology.
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27
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Wang X, Zhou P, Sun X, Wei G, Zhang L, Wang H, Yao J, Jia P, Zheng J. Modification of the hTERT promoter by heat shock elements enhances the efficiency and specificity of cancer targeted gene therapy. Int J Hyperthermia 2016; 32:244-53. [PMID: 26981638 DOI: 10.3109/02656736.2015.1128569] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
PURPOSE One of the current challenges facing cancer gene therapy is the tumour-specific targeting of therapeutic genes. Effective targeting in gene therapy requires accurate spatial and temporal control of gene expression. To develop a sufficient and accurate tumour-targeting method for cancer gene therapy, we have investigated the use of hyperthermia to control the expression of a transgene under the control of the human telomerase reverse transcriptase (hTERT) promoter and eight heat shock elements (8HSEs). MATERIALS AND METHODS Luciferase reporters were constructed by inserting eight HSEs and the hTERT promoter (8HSEs-hTERTp) upstream of the pGL4.20 vector luciferase gene. The luciferase activity of the hTERT promoter and 8HSEs-hTERT promoter were then compared in the presence and absence of heat. The differences in luciferase activity were analysed using dual luciferase assays in SW480 (high hTERT expression), MKN28 and MRC-5 cells (low hTERT expression). The luciferase activity of the Hsp70B promoter was also compared to the 8HSEs-hTERT promoter in the above listed cell lines. Lentiviral vector and heat-induced expression of EGFP expression under the control of the 8HSEs-hTERT promoter in cultured cells and mouse tumour xenografts was measured by reverse transcription polymerase (RT-PCR), Western blot and immunofluorescence assays. RESULTS hTERT promoter activity was higher in SW480 cells than in MKN28 or MRC-5 cells. At 43 °C, the luciferase activity of the 8HSEs-hTERT promoter was significantly increased in SW480 cells, but not in MKN28 or MRC-5 cells. Importantly, the differences in luciferase activity were much more obvious in both high (SW480) and low (MKN28 and MRC-5) hTERT expressing cells when the activity of the 8HSEs-hTERT promoter was compared to the Hsp70B promoter. Moreover, under the control of 8HSEs-hTERT promoter in vitro and in vivo, EGFP expression was obviously increased by heat treatment in SW480 cells but not in MKN28 or MRC-5 cells, nor was expression increased under normal temperature conditions. CONCLUSIONS The hTERT promoter is a potentially powerful tumour-specific promoter and gene therapy tool for cancer treatment. Incorporating heat-inducible therapeutic elements (8HSEs) into the hTERT promoter may enhance the efficiency and specificity of cancer targeting gene therapy under hyperthermic clinical conditions.
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Affiliation(s)
- Xiaolong Wang
- a Department of General Surgery , First Affiliated Hospital of Xi'an Jiaotong University , Xi'an , Shaanxi
| | - PeiHua Zhou
- a Department of General Surgery , First Affiliated Hospital of Xi'an Jiaotong University , Xi'an , Shaanxi
| | - XueJun Sun
- a Department of General Surgery , First Affiliated Hospital of Xi'an Jiaotong University , Xi'an , Shaanxi
| | - GuangBing Wei
- a Department of General Surgery , First Affiliated Hospital of Xi'an Jiaotong University , Xi'an , Shaanxi
| | - Li Zhang
- b Department of General Surgery , Second Affiliated Hospital of Xi'an Jiaotong University , Xi'an , Shaanxi
| | - Hui Wang
- c Shaanxi Provincial People's Hospital , Xi'an , Shaanxi , and
| | - JianFeng Yao
- c Shaanxi Provincial People's Hospital , Xi'an , Shaanxi , and
| | - PengBo Jia
- d First People's Hospital of XianYang City , XianYang , Shaanxi , China
| | - JianBao Zheng
- a Department of General Surgery , First Affiliated Hospital of Xi'an Jiaotong University , Xi'an , Shaanxi
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28
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Cheng D, Zhao Y, Wang S, Jia W, Kang J, Zhu J. Human Telomerase Reverse Transcriptase (hTERT) Transcription Requires Sp1/Sp3 Binding to the Promoter and a Permissive Chromatin Environment. J Biol Chem 2015; 290:30193-203. [PMID: 26487723 DOI: 10.1074/jbc.m115.662221] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Indexed: 12/14/2022] Open
Abstract
The transcription of human telomerase gene hTERT is regulated by transcription factors (TFs), including Sp1 family proteins, and its chromatin environment. To understand its regulation in a relevant chromatin context, we employed bacterial artificial chromosome reporters containing 160 kb of human genomic sequence containing the hTERT gene. Upon chromosomal integration, the bacterial artificial chromosomes recapitulated endogenous hTERT expression, contrary to transient reporters. Sp1/Sp3 expression did not correlate with hTERT promoter activity, and these TFs bound to the hTERT promoters in both telomerase-positive and telomerase-negative cells. Mutation of the proximal GC-box resulted in a dramatic decrease of hTERT promoter activity, and mutations of all five GC-boxes eliminated its transcriptional activity. Neither mutations of GC-boxes nor knockdown of endogenous Sp1 impacted promoter binding by other TFs, including E-box-binding proteins, and histone acetylation and trimethylation of histone H3K9 at the hTERT promoter in telomerase-positive and -negative cells. The result indicated that promoter binding by Sp1/Sp3 was essential, but not a limiting step, for hTERT transcription. hTERT transcription required a permissive chromatin environment. Importantly, our data also revealed different functions of GC-boxes and E-boxes in hTERT regulation; although GC-boxes were essential for promoter activity, factors bound to the E-boxes functioned to de-repress hTERT promoter.
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Affiliation(s)
- De Cheng
- From the Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, Washington 99210
| | - Yuanjun Zhao
- the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, and
| | - Shuwen Wang
- From the Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, Washington 99210
| | - Wenwen Jia
- the School of Life Sciences and Technology, Tongji University, Shanghai 200092, China
| | - Jiuhong Kang
- the School of Life Sciences and Technology, Tongji University, Shanghai 200092, China
| | - Jiyue Zhu
- From the Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, Washington 99210, the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, and
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29
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Zhao X, Ueda Y, Kajigaya S, Alaks G, Desierto MJ, Townsley DM, Dumitriu B, Chen J, Lacy RC, Young NS. Cloning and molecular characterization of telomerase reverse transcriptase (TERT) and telomere length analysis of Peromyscus leucopus. Gene 2015; 568:8-18. [PMID: 25962353 DOI: 10.1016/j.gene.2015.05.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 04/29/2015] [Accepted: 05/05/2015] [Indexed: 01/14/2023]
Abstract
Telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase complex that regulates telomerase activity to maintain telomere length for all animals with linear chromosomes. As the Mus musculus (MM) laboratory mouse has very long telomeres compared to humans, a potential alternative animal model for telomere research is the Peromyscus leucopus (PL) mouse that has telomere lengths close to the human range and has the wild counterparts for comparison. We report the full TERT coding sequence (pTERT) from PL mice to use in the telomere research. Comparative analysis with eight other mammalian TERTs revealed a pTERT protein considerably homologous to other TERTs and preserved all TERT specific-sequence signatures, yet with some distinctive features. pTERT displayed the highest nucleotide and amino acid sequence homology with hamster TERT. Unlike human but similar to MM mice, pTERT expression was detected in various adult somatic tissues of PL mice, with the highest expression in testes. Four different captive stocks of PL mice and wild-captured PL mice each displayed group-specific average telomere lengths, with the longest and shortest telomeres in inbred and outbred stock mice, respectively. pTERT showed considerable numbers of synonymous and nonsynonymous mutations. A pTERT proximal promoter region cloned was homologous among PL and MM mice and rat, but with species-specific features. From PL mice, we further cloned and characterized ribosomal protein, large, P0 (pRPLP0) to use as an internal control for various assays. Peromyscus mice have been extensively used for various studies, including human diseases, for which pTERT and pRPLP0 would be useful tools.
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Affiliation(s)
- Xin Zhao
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA.
| | - Yasutaka Ueda
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Sachiko Kajigaya
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Glen Alaks
- Department of Conservation Science, Chicago Zoological Society, Brookfield, IL, USA
| | - Marie J Desierto
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Danielle M Townsley
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Bogdan Dumitriu
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Jichun Chen
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Robert C Lacy
- Department of Conservation Science, Chicago Zoological Society, Brookfield, IL, USA
| | - Neal S Young
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
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30
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Garbe JC, Vrba L, Sputova K, Fuchs L, Novak P, Brothman AR, Jackson M, Chin K, LaBarge MA, Watts G, Futscher BW, Stampfer MR. Immortalization of normal human mammary epithelial cells in two steps by direct targeting of senescence barriers does not require gross genomic alterations. Cell Cycle 2015; 13:3423-35. [PMID: 25485586 PMCID: PMC4613853 DOI: 10.4161/15384101.2014.954456] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Telomerase reactivation and immortalization are critical for human carcinoma progression. However, little is known about the mechanisms controlling this crucial step, due in part to the paucity of experimentally tractable model systems that can examine human epithelial cell immortalization as it might occur in vivo. We achieved efficient non-clonal immortalization of normal human mammary epithelial cells (HMEC) by directly targeting the 2 main senescence barriers encountered by cultured HMEC. The stress-associated stasis barrier was bypassed using shRNA to p16INK4; replicative senescence due to critically shortened telomeres was bypassed in post-stasis HMEC by c-MYC transduction. Thus, 2 pathologically relevant oncogenic agents are sufficient to immortally transform normal HMEC. The resultant non-clonal immortalized lines exhibited normal karyotypes. Most human carcinomas contain genomically unstable cells, with widespread instability first observed in vivo in pre-malignant stages; in vitro, instability is seen as finite cells with critically shortened telomeres approach replicative senescence. Our results support our hypotheses that: (1) telomere-dysfunction induced genomic instability in pre-malignant finite cells may generate the errors required for telomerase reactivation and immortalization, as well as many additional “passenger” errors carried forward into resulting carcinomas; (2) genomic instability during cancer progression is needed to generate errors that overcome tumor suppressive barriers, but not required per se; bypassing the senescence barriers by direct targeting eliminated a need for genomic errors to generate immortalization. Achieving efficient HMEC immortalization, in the absence of “passenger” genomic errors, should facilitate examination of telomerase regulation during human carcinoma progression, and exploration of agents that could prevent immortalization.
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Key Words
- BaP, benzo(a)pyrene
- CT, cholera toxin
- DDR, DNA damage response
- DMR, differentially methylated regions
- HMEC, human mammary epithelial cells
- OIS, oncogene-induced senescence
- PD, population doublings
- RB, retinoblastoma protein
- TTS, transcription start site
- X, oxytocin
- c-Myc
- carcinogenesis
- genomic instability
- human mammary epithelial cells
- immortalization
- p, passage
- p16INK4a
- p16sh, shRNA to p16INK4A
- senescence
- telomerase
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Affiliation(s)
- James C Garbe
- a Life Sciences Division ; Lawrence Berkeley National Laboratory ; Berkeley , CA USA
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31
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Dvořáčková M, Fojtová M, Fajkus J. Chromatin dynamics of plant telomeres and ribosomal genes. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2015; 83:18-37. [PMID: 25752316 DOI: 10.1111/tpj.12822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 03/03/2015] [Accepted: 03/03/2015] [Indexed: 05/03/2023]
Abstract
Telomeres and genes encoding 45S ribosomal RNA (rDNA) are frequently located adjacent to each other on eukaryotic chromosomes. Although their primary roles are different, they show striking similarities with respect to their features and additional functions. Both genome domains have remarkably dynamic chromatin structures. Both are hypersensitive to dysfunctional histone chaperones, responding at the genomic and epigenomic levels. Both generate non-coding transcripts that, in addition to their epigenetic roles, may induce gross chromosomal rearrangements. Both give rise to chromosomal fragile sites, as their replication is intrinsically problematic. However, at the same time, both are essential for maintenance of genomic stability and integrity. Here we discuss the structural and functional inter-connectivity of telomeres and rDNA, with a focus on recent results obtained in plants.
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Affiliation(s)
- Martina Dvořáčková
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Kamenice 5, 62500, Brno, Czech Republic
- Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61265, Brno, Czech Republic
| | - Miloslava Fojtová
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Kamenice 5, 62500, Brno, Czech Republic
- Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61265, Brno, Czech Republic
| | - Jiří Fajkus
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Kamenice 5, 62500, Brno, Czech Republic
- Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61265, Brno, Czech Republic
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32
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Wang X, Zhou P, Sun X, Zheng J, Wei G, Zhang L, Wang H, Yao J, Lu S, Jia P. Acidified bile acids increase hTERT expression via c-myc activation in human gastric cancer cells. Oncol Rep 2015; 33:3038-44. [PMID: 25873431 DOI: 10.3892/or.2015.3908] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 02/24/2015] [Indexed: 11/06/2022] Open
Abstract
Human telomerase reverse transcriptase (hTERT) is upregulated in most cancer cell types as well in immortalized cells. The underlying mechanism for such upregulation, however, remains largely unknown. We report here that bile acids under acidified media increase hTERT expression via c-myc activation in primary human gastric cancer cell lines. Human gastric cancer MKN28, MGC803 and SGC7901 cells were treated with 100 µM deoxycholic acid (DCA) or chenodeoxycholic acid (CDCA) with or without acidified media in the presence or absence of the c-myc inhibitor 10058-F4 for 24 h. hTERT and c-myc protein levels were determined by western blot analysis. hTERT and c-myc mRNA levels were determined by RT-PCR. The promoter activities of hTERT and c-myc transcription were determined using promoter reporter luciferase assays for both. Telomerase enzyme activity was analyzed by stretch PCR. hTERT mRNA and protein levels were significantly increased by bile acids in acidified media and were accompanied with enhanced telomerase activity. No changes were found at a pH of 7.0 or with acidified media alone. Similarly, the mRNA and protein levels of c-myc were also increased by bile acids in acidified media but not at a pH of 7.0 or with acidified media alone. Importantly, pharmacologic inhibition of c-myc using 10058-F4 prevented hTERT induction by DCA or CDCA in gastric cancer cells under acidic conditions. Bile acids (DCA and CDCA) under acidic conditions increased hTERT expression in human gastric cancer cells by activation of c-myc transcription. This suggests that acidified bile acids may promote tumorigenesis and affect cell ageing via telomerase activation.
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Affiliation(s)
- Xiaolong Wang
- Department of General Surgery, The First Affiliated Hospital of Medical College, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Peihua Zhou
- Department of General Surgery, The First Affiliated Hospital of Medical College, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Xuejun Sun
- Department of General Surgery, The First Affiliated Hospital of Medical College, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Jianbao Zheng
- Department of General Surgery, The First Affiliated Hospital of Medical College, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Guangbing Wei
- Department of General Surgery, The First Affiliated Hospital of Medical College, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Li Zhang
- Department of General Surgery, The Second Affiliated Hospital of the Medical College, Xi'an Jiaotong University, Xi'an, Shaanxi 710004, P.R. China
| | - Hui Wang
- Shaanxi Provincial People's Hospital, Xi'an, Shaanxi 710068, P.R. China
| | - Jianfeng Yao
- Shaanxi Provincial People's Hospital, Xi'an, Shaanxi 710068, P.R. China
| | - Shaoying Lu
- Department of General Surgery, The First Affiliated Hospital of Medical College, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Pengbo Jia
- The First People's Hospital of Xianyang City, Xianyang, Shaanxi 712000, P.R. China
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33
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Hara T, Mizuguchi M, Fujii M, Nakamura M. Krüppel-like factor 2 represses transcription of the telomerase catalytic subunit human telomerase reverse transcriptase (hTERT) in human T cells. J Biol Chem 2015; 290:8758-63. [PMID: 25694435 DOI: 10.1074/jbc.m114.610386] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2014] [Indexed: 11/06/2022] Open
Abstract
In normal human T cells, telomerase activity is strictly regulated. T cells are thought to express telomerase to avoid replicative senescence, unlike most normal somatic cells with definite replicative lifespan. T cells in blood and tissues are usually in a state of quiescence without expression of the limiting catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT). In contrast to activation, repression of hTERT transcription has not been studied well. Our previous studies have found an hTERT promoter element with repressive function. Here we identified KLF2, which represses hTERT transcription by binding to the putative promoter element. KLF2 and hTERT exhibited reciprocal mRNA expression patterns in primary human T cells. In activated T cells, KLF2 binding to the hTERT promoter was eliminated, relieving the repression of hTERT transcription found in resting T cells. Our results suggest that KLF2 is involved in strict repression of hTERT expression through binding to the promoter in primary human T cells.
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Affiliation(s)
- Toshifumi Hara
- From the Human Gene Sciences Center, Tokyo Medical and Dental University, Tokyo 113-8510 and the Division of Virology, Niigata University Graduate School of Medicine and Dental Sciences, Niigata 951-8510, Japan
| | - Mariko Mizuguchi
- From the Human Gene Sciences Center, Tokyo Medical and Dental University, Tokyo 113-8510 and
| | - Masahiro Fujii
- the Division of Virology, Niigata University Graduate School of Medicine and Dental Sciences, Niigata 951-8510, Japan
| | - Masataka Nakamura
- From the Human Gene Sciences Center, Tokyo Medical and Dental University, Tokyo 113-8510 and
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34
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Zhang D, Sun X, Liu J, Xie X, Cui W, Zhu Y. Homocysteine accelerates senescence of endothelial cells via DNA hypomethylation of human telomerase reverse transcriptase. Arterioscler Thromb Vasc Biol 2015; 35:71-8. [PMID: 25359865 DOI: 10.1161/atvbaha.114.303899] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
OBJECTIVE Homocysteine can accelerate the senescence of endothelial progenitor cells or endothelial cells (ECs) via telomerase inactivation and length shortening. However, the underlying mechanism is unclear. Here, we investigated whether homocysteine promotes endothelial senescence by reducing the expression and activity of human telomerase reverse transcriptase (hTERT) by DNA methylation to reduce ECs telomerase activity. APPROACH AND RESULTS When compared with primary human umbilical vein endothelial cells grown under standard conditions, ECs with chronic homocysteine treatment showed accelerated upregulation of p16, p21, and p53, markers of cellular senescence, during 6 to 10 passages. Interestingly, homocysteine-stimulated but not angiotensin II-stimulated ECs senescence could be reversed by hypermethylation induced by folic acid or s-adenosylmethionine supplementation. Meanwhile, homocysteine promoted the shortening of telomere length specifically related to restoration of hTERT transcriptional expression and CCCTC-binding factor binding sites with hTERT promoter hypomethylation, as detected by quantitative real-time polymerase chain reaction, Western blot, methylation-specific polymerase chain reaction, and bisulfite sequencing assay. Electrophoretic mobility shift assay and chromatin immunoprecipitation results showed that homocysteine-reduced telomere activity and homocysteine-induced EC senescence might contribute to hTERT promoter demethylation by increasing CCCTC-binding factor repression and interfering in the SP1 binding to the demethylated hTERT promoter, which might relate with reduced of DNA methyltransferase 1. Furthermore, the CCCTC-binding factor-dependent mechanism of homocysteine-reduced hTERT expression via DNA demethylation was confirmed in aortic endothelia of mice with hyperhomocysteine levels. CONCLUSIONS CCCTC-binding factor and SP1 cross talk may contribute to homocysteine-reduced hTERT DNA methylation and expression in endothelial senescence.
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Affiliation(s)
- Donghong Zhang
- From the Department of Clinical Laboratory, Peking Union Medical College and Peking Union Medical College Hospital, Beijing, China (D.Z., W.C.); Department of Physiology and Pathophysiology, Key Laboratory of Cardiovascular Science of Ministry of Education, Peking University Health Science Center, Beijing, China (W.C.); Cardiovascular Research Center, Shantou University Medical College, Shantou, Guangdong, China (D.Z., J.L., X.X.); and Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin, China (Y.Z.)
| | - Xiaoli Sun
- From the Department of Clinical Laboratory, Peking Union Medical College and Peking Union Medical College Hospital, Beijing, China (D.Z., W.C.); Department of Physiology and Pathophysiology, Key Laboratory of Cardiovascular Science of Ministry of Education, Peking University Health Science Center, Beijing, China (W.C.); Cardiovascular Research Center, Shantou University Medical College, Shantou, Guangdong, China (D.Z., J.L., X.X.); and Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin, China (Y.Z.)
| | - Jianlan Liu
- From the Department of Clinical Laboratory, Peking Union Medical College and Peking Union Medical College Hospital, Beijing, China (D.Z., W.C.); Department of Physiology and Pathophysiology, Key Laboratory of Cardiovascular Science of Ministry of Education, Peking University Health Science Center, Beijing, China (W.C.); Cardiovascular Research Center, Shantou University Medical College, Shantou, Guangdong, China (D.Z., J.L., X.X.); and Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin, China (Y.Z.)
| | - Xina Xie
- From the Department of Clinical Laboratory, Peking Union Medical College and Peking Union Medical College Hospital, Beijing, China (D.Z., W.C.); Department of Physiology and Pathophysiology, Key Laboratory of Cardiovascular Science of Ministry of Education, Peking University Health Science Center, Beijing, China (W.C.); Cardiovascular Research Center, Shantou University Medical College, Shantou, Guangdong, China (D.Z., J.L., X.X.); and Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin, China (Y.Z.)
| | - Wei Cui
- From the Department of Clinical Laboratory, Peking Union Medical College and Peking Union Medical College Hospital, Beijing, China (D.Z., W.C.); Department of Physiology and Pathophysiology, Key Laboratory of Cardiovascular Science of Ministry of Education, Peking University Health Science Center, Beijing, China (W.C.); Cardiovascular Research Center, Shantou University Medical College, Shantou, Guangdong, China (D.Z., J.L., X.X.); and Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin, China (Y.Z.).
| | - Yi Zhu
- From the Department of Clinical Laboratory, Peking Union Medical College and Peking Union Medical College Hospital, Beijing, China (D.Z., W.C.); Department of Physiology and Pathophysiology, Key Laboratory of Cardiovascular Science of Ministry of Education, Peking University Health Science Center, Beijing, China (W.C.); Cardiovascular Research Center, Shantou University Medical College, Shantou, Guangdong, China (D.Z., J.L., X.X.); and Department of Physiology and Pathophysiology, Tianjin Medical University, Tianjin, China (Y.Z.).
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Do telomeres adapt to physiological stress? Exploring the effect of exercise on telomere length and telomere-related proteins. BIOMED RESEARCH INTERNATIONAL 2013; 2013:601368. [PMID: 24455708 PMCID: PMC3884693 DOI: 10.1155/2013/601368] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/13/2013] [Accepted: 11/26/2013] [Indexed: 01/29/2023]
Abstract
Aging is associated with a tissue degeneration phenotype marked by a loss of tissue regenerative capacity. Regenerative capacity is dictated by environmental and genetic factors that govern the balance between damage and repair. The age-associated changes in the ability of tissues to replace lost or damaged cells is partly the cause of many age-related diseases such as Alzheimer's disease, cardiovascular disease, type II diabetes, and sarcopenia. A well-established marker of the aging process is the length of the protective cap at the ends of chromosomes, called telomeres. Telomeres shorten with each cell division and with increasing chronological age and short telomeres have been associated with a range of age-related diseases. Several studies have shown that chronic exposure to exercise (i.e., exercise training) is associated with telomere length maintenance; however, recent evidence points out several controversial issues concerning tissue-specific telomere length responses. The goals of the review are to familiarize the reader with the current telomere dogma, review the literature exploring the interactions of exercise with telomere phenotypes, discuss the mechanistic research relating telomere dynamics to exercise stimuli, and finally propose future directions for work related to telomeres and physiological stress.
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Zhang D, Wen X, Wu W, Xu E, Zhang Y, Cui W. Homocysteine-related hTERT DNA demethylation contributes to shortened leukocyte telomere length in atherosclerosis. Atherosclerosis 2013; 231:173-9. [PMID: 24125430 DOI: 10.1016/j.atherosclerosis.2013.08.029] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 08/16/2013] [Accepted: 08/26/2013] [Indexed: 12/25/2022]
Abstract
AIMS Leukocyte telomere length (LTL) is shortened in patients with clinical atherosclerosis (AS). Here we aimed to explore the contribution of elevated homocysteine (Hcy) level to LTL shortening in AS patients and the underlying mechanism. METHODS Circulating leukocytes were collected from 197 patients with AS and 165 sex- and age-matched healthy subjects for LTL determination. mRNA expression or DNA methylation of human telomerase reverse transcriptase (hTERT) was determined by real-time PCR and methylation-specific PCR assay, respectively. We established a hyperhomocysteinemia (HHcy) mice model to confirm human results. RESULTS Hcy was negatively correlated with LTL shortening in AS patients (r = -0.179, p = 0.015) and controls (r = -0.146, p = 0.031). Serum folate and high-sensitivity C-reactive protein levels significantly interacted with Hcy in LTL shortening. Hcy was related to hTERT mRNA downregulation and promoter demethylation, which combined was associated with LTL shortening in AS patients. Hcy-induced LTL shortening did not differ by sites of AS lesions or infarction. Similar to clinical observations, our HHcy mice model suggested that Hcy induced DNA demethylation and downregulation of mouse TERT and further contributed to LTL shortening. CONCLUSIONS Elevated Hcy level induced DNA demethylation of hTERT and was closely related with hTERT downregulation, which led to LTL shortening in AS. These findings provide novel insights into an epigenetic mechanism for Hcy-related AS.
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Affiliation(s)
- Donghong Zhang
- Department of Clinical Laboratory, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, 1 Shuaifuyuan, Beijing 100730, China
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Hoffmeyer K, Raggioli A, Rudloff S, Anton R, Hierholzer A, Del Valle I, Hein K, Vogt R, Kemler R. Wnt/β-catenin signaling regulates telomerase in stem cells and cancer cells. Science 2012; 336:1549-54. [PMID: 22723415 DOI: 10.1126/science.1218370] [Citation(s) in RCA: 392] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Telomerase activity controls telomere length and plays a pivotal role in stem cells, aging, and cancer. Here, we report a molecular link between Wnt/β-catenin signaling and the expression of the telomerase subunit Tert. β-Catenin-deficient mouse embryonic stem (ES) cells have short telomeres; conversely, ES cell expressing an activated form of β-catenin (β-cat(ΔEx3/+)) have long telomeres. We show that β-catenin regulates Tert expression through the interaction with Klf4, a core component of the pluripotency transcriptional network. β-Catenin binds to the Tert promoter in a mouse intestinal tumor model and in human carcinoma cells. We uncover a previously unknown link between the stem cell and oncogenic potential whereby β-catenin regulates Tert expression, and thereby telomere length, which could be critical in human regenerative therapy and cancer.
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Affiliation(s)
- Katrin Hoffmeyer
- Department of Molecular Embryology, Max Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany
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Ogrocká A, Sýkorová E, Fajkus J, Fojtová M. Developmental silencing of the AtTERT gene is associated with increased H3K27me3 loading and maintenance of its euchromatic environment. JOURNAL OF EXPERIMENTAL BOTANY 2012; 63:4233-41. [PMID: 22511802 PMCID: PMC3398451 DOI: 10.1093/jxb/ers107] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Telomerase, an enzyme responsible for the maintenance of linear chromosome ends, is precisely regulated during plant development. In animals, involvement of the epigenetic state of the telomerase reverse transcriptase (TERT) gene in the complex regulation of telomerase activity has been reported. To reveal whether epigenetic mechanisms participate in the regulation of plant telomerase, the relationship between telomerase activity in tissues of Arabidopsis thaliana and DNA methylation and histone modifications in the A. thaliana TERT (AtTERT) upstream region was studied. As expected, a gradual decrease of telomerase activity during leaf maturation was observed. A different pattern with a more progressive loss of telomerase activity and AtTERT transcription during leaf development was revealed in MET1 gene-knockout mutants. Analysis of DNA methylation in the AtTERT upstream region showed low levels of methylated cytosines without notable differences between telomerase-positive and telomerase-negative wild-type tissues. Surprisingly, a high level of CG methylation was found in the AtTERT coding region, although this type of methylation is a characteristic attribute of constitutively expressed genes. Analysis of chromatin modifications in the AtTERT upstream region and in exon 5 showed increased loading of the H3K27me3 mark in the telomerase-negative mature leaf compared to telomerase-positive seedlings, whereas H3K4me3, H3K9Ac, and H3K9me2 were approximately at the same level. Consistently, the chromatin structure of the AtTERT gene was maintained. These results are discussed in the context of the general involvement of epigenetic mechanisms in the regulation of gene expression and with respect to similar studies performed in animal models.
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Affiliation(s)
- Anna Ogrocká
- CEITEC – Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
| | - Eva Sýkorová
- CEITEC – Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic v.v.i., Královopolská 65, 612 65 Brno, Czech Republic
| | - Jiří Fajkus
- CEITEC – Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic v.v.i., Královopolská 65, 612 65 Brno, Czech Republic
| | - Miloslava Fojtová
- CEITEC – Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
- To whom correspondence should be addressed. E-mail:
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Wanat JJ, Johnson FB. Telomere stability and carcinogenesis: an off-again, on-again relationship. J Clin Invest 2012; 122:1962-5. [PMID: 22622044 DOI: 10.1172/jci63979] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Previous studies in mice have demonstrated antagonistic effects of telomerase loss on carcinogenesis. Telomere attrition can promote genome instability, thereby stimulating initiation of early-stage cancers, but can also inhibit tumorigenesis by promoting permanent cell growth arrest or death. Human cancers likely develop in cell lineages with low levels of telomerase, leading to telomere losses in early lesions, followed by subsequent activation of telomerase. Mouse models constitutively lacking telomerase have thus not addressed how telomere losses within telomerase-proficient cells have an impact on carcinogenesis. Using a novel transgenic mouse model, Begus-Nahrmann et al. demonstrate in this issue of the JCI that transient telomere dysfunction in telomerase-proficient animals is a potent stimulus of tumor formation.
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Affiliation(s)
- Jennifer J Wanat
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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40
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Shi L, Li M, Su B. MCPH1/BRIT1 represses transcription of the human telomerase reverse transcriptase gene. Gene 2012; 495:1-9. [PMID: 22240313 DOI: 10.1016/j.gene.2011.12.053] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 12/19/2011] [Accepted: 12/22/2011] [Indexed: 01/20/2023]
Abstract
MCPH1, a repressor of human telomerase reverse transcriptase (hTERT) function, is implicated in cellular immortalization. But little is known about how MCPH1 represses telomerase activity. In this study, to determine the mechanism by which MCPH1 regulates hTERT gene expression, we examined the role of MCPH1 in regulating the hTERT promoter in vitro. Co-transfection of the hTERT promoter with MCPH1 in Hela cells could inhibit the hTERT promoter activity. The EMSA assay demonstrated that MCPH1 could bind to the proximal hTERT promoter. Overexpression of MCPH1 could repress telomerase activity, and the repression was abolished by knocking down the MCPH1 expression using siRNA in U2OS cells. We propose that MCPH1 functions as a transcriptional repressor of hTERT in vitro. Since the activation of telomerase, widely observed in human tumor cell lines, is a critical step in tumorigenesis, our findings provide new insights into delineating the tumor-suppressing function of MCPH1 through its down-regulation of hTERT/telomerase expression.
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Affiliation(s)
- Lei Shi
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, PR China
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Sirma H, Kumar M, Meena JK, Witt B, Weise JM, Lechel A, Ande S, Sakk V, Guguen-Guillouzo C, Zender L, Rudolph KL, Günes C. The promoter of human telomerase reverse transcriptase is activated during liver regeneration and hepatocyte proliferation. Gastroenterology 2011; 141:326-37, 337.e1-3. [PMID: 21447332 DOI: 10.1053/j.gastro.2011.03.047] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2010] [Revised: 03/01/2011] [Accepted: 03/11/2011] [Indexed: 01/13/2023]
Abstract
BACKGROUND & AIMS Telomerase activity has not been detected in healthy human liver biopsy samples, but it is up-regulated in most human liver tumors. It is not clear whether telomerase is activated in response to acute or chronic liver injury. Telomerase activity is closely associated with expression of its catalytic subunit, telomerase reverse transcriptase (TERT). We analyzed the activity of the human TERT (hTERT) promoter during liver regeneration in vivo and hepatocyte proliferation in vitro. METHODS We used hTERTp-lacZ transgenic mice, which contain an 8.0-kilobase pair fragment of the hTERT gene promoter, to study the role of TERT in liver regeneration following partial hepatectomy. As an in vitro model, we used the HepaRG cell line as a new model system for human hepatocyte proliferation and differentiation. RESULTS Activity of the hTERT promoter increased significantly after partial hepatectomy; it was also induced in hepatocytes, based on immunohistologic analysis. Similar to the in vivo results, telomerase activity and hTERT expression were up-regulated in proliferating HepaRG cells and repressed in response to growth arrest and differentiation. Promoter mapping revealed that a proximal 0.3-kilobase pair fragment contains all elements necessary for regulation of hTERT in HepaRG cells. We identified E2F2 and E2F7 as transcription factors that control the differential expression of hTERT in proliferating hepatocytes, in vitro and in vivo. CONCLUSIONS hTERT is induced in hepatocytes during liver regeneration, indicating a functional role for telomerase in human liver.
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Identification of PITX1 as a TERT suppressor gene located on human chromosome 5. Mol Cell Biol 2011; 31:1624-36. [PMID: 21300782 DOI: 10.1128/mcb.00470-10] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Telomerase, a ribonucleoprotein enzyme that maintains telomere length, is crucial for cellular immortalization and cancer progression. Telomerase activity is attributed primarily to the expression of telomerase reverse transcriptase (TERT). Using microcell-mediated chromosome transfer (MMCT) into the mouse melanoma cell line B16F10, we previously found that human chromosome 5 carries a gene, or genes, that can negatively regulate TERT expression (H. Kugoh, K. Shigenami, K. Funaki, J. Barrett, and M. Oshimura, Genes Chromosome Cancer 36:37-47, 2003). To identify the gene responsible for the regulation of TERT transcription, we performed cDNA microarray analysis using parental B16F10 cells, telomerase-negative B16F10 microcell hybrids with a human chromosome 5 (B16F10MH5), and its revertant clones (MH5R) with reactivated telomerase. Here, we report the identification of PITX1, whose expression leads to the downregulation of mouse tert (mtert) transcription, as a TERT suppressor gene. Additionally, both human TERT (hTERT) and mouse TERT (mtert) promoter activity can be suppressed by PITX1. We show that three and one binding site within the hTERT and mtert promoters, respectively, that express a unique conserved region are responsible for the transcriptional activation of TERT. Furthermore, we showed that PITX1 binds to the TERT promoter both in vitro and in vivo. Thus, PITX1 suppresses TERT transcription through direct binding to the TERT promoter, which ultimately regulates telomerase activity.
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Jia W, Wang S, Horner JW, Wang N, Wang H, Gunther EJ, DePinho RA, Zhu J. A BAC transgenic reporter recapitulates in vivo regulation of human telomerase reverse transcriptase in development and tumorigenesis. FASEB J 2010; 25:979-89. [PMID: 21135040 DOI: 10.1096/fj.10-173989] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Telomerase is tightly regulated in humans relative to mice, owing to the differential regulation of TERT genes. To explore hTERT regulation in vivo, we engineered mice with a 160-kb transgenic bacterial artificial chromosome (BAC) spanning the hTERT locus with a Renilla luciferase (Rluc) cassette downstream of its promoter. Analysis of multiple founder lines revealed that the Rluc expression profile from the transgenic hTERT reporter locus reproduced that of the native hTERT gene in all tissues and organs examined, demonstrating that genetic sequence determined the species-specific developmental regulation of the hTERT gene and that mouse epigenetic and transcription machineries faithfully regulated hTERT transcription. Thus, these mice allowed detailed analyses of developmental hTERT regulation. Both the transgenic hTERT reporter and the endogenous mTERT locus were expressed in early embryonic stages, and their mRNA levels progressively decreased throughout embryonic and postnatal development. Whereas hTERT transcription was much lower than mTERT expression in most organs, it increased significantly during postnatal development of thymus, testis, and ovary. In testis, the Rluc mRNA was enriched in elongating spermatids of seminiferous tubules. In addition, the transcription of transgenic hTERT reporter, but surprisingly not the endogenous mTERT gene, was activated during Wnt1-induced mammary tumorigenesis, allowing the monitoring of tumor development via noninvasive bioluminescent imaging. Collectively, our results demonstrate that the hTERT transgenic reporter system recapitulates the developmental regulation of the hTERT gene in a chromosomal position-independent manner and serves as a legitimate model to explore telomerase regulation in the development of normal and neoplastic tissues in vivo.
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Affiliation(s)
- Wenwen Jia
- Shaanxi Center for Stem Cell Engineering and Technology, College of Veterinary Medicine, Northwest Agriculture and Forestry University, Shaanxi, China
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Fujiki T, Udono M, Kotake Y, Yamashita M, Shirahata S, Katakura Y. NFAT5 regulates transcription of the mouse telomerase reverse transcriptase gene. Exp Cell Res 2010; 316:3342-50. [PMID: 20937271 DOI: 10.1016/j.yexcr.2010.10.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Revised: 09/13/2010] [Accepted: 10/03/2010] [Indexed: 01/29/2023]
Abstract
We aimed to clarify the transcription-regulation mechanisms of the mouse telomerase reverse transcriptase gene (mTERT). First, we searched for the promoter region required for transcriptional activation of mTERT and identified an enhancer cis-element (named mTERT-EE) located between -200 and -179bp of the mouse TERT gene (mTERT). EMSA results suggested that nuclear factor of activated T cells (NFAT) member proteins bind to mTERT-EE. We then identified NFAT5 as the factor binding to mTERT-EE and found that it activates the transcription of the mTERT core promoter. The results that siRNA directed against NFAT5 significantly reduced mTERT expression and mTERT core promoter activity and that the expressions of NFAT5 and mTERT were well correlated in various mouse tissues except liver suggest that NFAT5 dominantly and directly regulates mTERT expression. To clarify their functionality further, we investigated the effect of hypertonic stress, a known stimulus affecting the expression and transcriptional activity of NFAT5, on mTERT expression. The result indicated that hypertonic stress activates mTERT transcription via the activation and recruitment of NFAT5 to the mTERT promoter. These results provide useful information about the transcription-regulation mechanisms of mTERT.
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Affiliation(s)
- Tsukasa Fujiki
- Faculty of Agriculture, Kyushu University, Fukuoka, Japan
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Li K, Zhang J, Ren JJ, Wang Q, Yang KY, Xiong ZJ, Mao YQ, Qi YY, Chen XW, Lan F, Wang XJ, Xiao HY, Lin P, Wei YQ. A novel zinc finger protein Zfp637 behaves as a repressive regulator in myogenic cellular differentiation. J Cell Biochem 2010; 110:352-62. [PMID: 20235149 DOI: 10.1002/jcb.22546] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Zinc finger proteins have been implicated as transcription factors in the differentiation and development of cells and tissues in higher organisms. The classical C2H2 zinc finger motif is one main type of motif of zinc finger proteins. Our previous studies have shown that Zfp637, which comprises six consecutively typical and one atypical C2H2 zinc finger motifs, is highly expressed in undifferentiated or poorly differentiated cell lines, but is moderately or slightly expressed in normal tissues. We have also demonstrated that Zfp637 can promote cell proliferation. However, its role in the regulation of cell differentiation remains unknown. We report here that endogenous Zfp637 as well as mTERT is expressed in proliferating C2C12 myoblasts and that their expression is downregulated during myogenic differentiation. Constitutive expression of Zfp637 in C2C12 myoblasts increased mTERT expression and telomerase activity, and promoted the progression of the cell cycle and cell proliferation. By contrast, endogenous repression of Zfp637 expression by RNA interference downregulated the mTERT gene and the activity of telomerase, and markedly reduced cell proliferation. Overexpression of Zfp637 also inhibited the expression of myogenic differentiation-specific genes such as MyoD and myogenin, and prevented C2C12 myoblast differentiation. Our results suggest that Zfp637 inhibits muscle differentiation through a defect in the cell cycle exit by potentially regulating mTERT expression in C2C12 myoblasts. This may provide a new research line for studying muscle differentiation.
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Affiliation(s)
- Kai Li
- Division of Geriatrics, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, People's Republic of China
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Mathew R, Jia W, Sharma A, Zhao Y, Clarke LE, Cheng X, Wang H, Salli U, Vrana KE, Robertson GP, Zhu J, Wang S. Robust activation of the human but not mouse telomerase gene during the induction of pluripotency. FASEB J 2010; 24:2702-15. [PMID: 20354136 DOI: 10.1096/fj.09-148973] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Pluripotent stem cells (PSCs) express telomerase and have unlimited proliferative potential. To study telomerase activation during reprogramming, 3 classes of embryonic stem cell (ESC)-like clones were isolated from mouse fibroblasts containing a transgenic hTERT reporter. Class I expressed few pluripotency markers, whereas class II contained many, but not Oct4, Nanog, and Sox2. Neither class of cells differentiated efficiently. Class III cells, the fully reprogrammed induced PSCs (iPSCs), expressed all pluripotency markers, formed teratomas indistinguishable from those of mESCs, and underwent efficient osteogenic differentiation in vitro. Interestingly, whereas the endogenous mTERT gene expression was only moderately increased during reprogramming, the hTERT promoter was strongly activated in class II cells and was further elevated in class III cells. Treatment of class II cells with chemical inhibitors of MEKs and glycogen synthase kinase 3 resulted in their further reprogramming into class III cells, accompanied by a strong activation of hTERT promoter. In reprogrammed human cells, the endogenous telomerase level, although variable among different clones, was dramatically elevated. Only in cells with the highest telomerase were telomeres restored to the lengths in hESCs. Our data, for the first time, demonstrated that the hTERT promoter was strongly activated in discrete steps, revealing a critical difference in human and mouse cell reprogramming. Because telomere elongation is crucial for self-renewal of hPSCs and replicative aging of their differentiated progeny, these findings have important implications in the generation and applications of iPSCs.
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Affiliation(s)
- Renjith Mathew
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
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Zhu J, Zhao Y, Wang S. Chromatin and epigenetic regulation of the telomerase reverse transcriptase gene. Protein Cell 2010; 1:22-32. [PMID: 21203995 DOI: 10.1007/s13238-010-0014-1] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2009] [Accepted: 12/03/2009] [Indexed: 01/30/2023] Open
Abstract
Telomerase expression and telomere maintenance are critical for long-term cell proliferation and survival, and they play important roles in development, aging, and cancer. Cumulating evidence has indicated that regulation of the rate-limiting subunit of human telomerase reverse transcriptase gene (hTERT) is a complex process in normal cells and many cancer cells. In addition to a number of transcriptional activators and repressors, the chromatin environment and epigenetic status of the endogenous hTERT locus are also pivotal for its regulation in normal human somatic cells and in tumorigenesis.
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Affiliation(s)
- Jiyue Zhu
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
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Zhao Y, Wang S, Popova EY, Grigoryev SA, Zhu J. Rearrangement of upstream sequences of the hTERT gene during cellular immortalization. Genes Chromosomes Cancer 2010; 48:963-74. [PMID: 19672873 DOI: 10.1002/gcc.20698] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Telomerase expression, resulting from transcriptional activation of the hTERT gene, allows cells to acquire indefinite proliferative potential during cellular immortalization and tumorigenesis. However, mechanisms of hTERT gene activation in many immortal cell lines and cancer cells are poorly understood. Here, we report our studies on hTERT activation using genetically related pairs of telomerase-negative (Tel(-)) and -positive (Tel(+)) fibroblast lines. First, whereas transiently transfected plasmid reporters did not recapitulate the endogenous hTERT promoter, the promoter in chromosomally integrated bacterial artificial chromosome (BAC) reporters was activated in a subset of Tel(+) cells, indicating that activation of the hTERT promoter required native chromatin context and/or distal regulatory elements. Second, the hTERT gene, located near the telomere of chromosome 5p, was translocated in all three Tel(+) cell lines but not in their parental precrisis cells and Tel(-) immortal siblings. The breakage points were mapped to regions upstream of the hTERT promoter, indicating that the hTERT gene was the target of these chromosomal rearrangements. In two Tel(+) cell lines, translocation of the endogenous hTERT gene appeared to be the major mechanism of its activation as the activity of hTERT promoter in many chromosomally integrated BAC reporters, with intact upstream and downstream neighboring loci, remained relatively low. Therefore, our results suggest that rearrangement of upstream sequences is an important new mechanism of hTERT promoter activation during cellular immortalization. The chromosomal rearrangements likely occurred during cellular crisis and facilitated by telomere dysfunction. Such translocations allowed the hTERT promoter to escape from the native condensed chromatin environment.
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Affiliation(s)
- Yuanjun Zhao
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA, USA
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Wang S, Hu C, Zhu J. Distinct and temporal roles of nucleosomal remodeling and histone deacetylation in the repression of the hTERT gene. Mol Biol Cell 2010; 21:821-32. [PMID: 20053684 PMCID: PMC2828968 DOI: 10.1091/mbc.e09-06-0456] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Transcriptional silencing of the hTERT gene during HL60 cell differentiation was a biphasic process. The initial repression was accompanied by the loss of c-Myc binding and disappearance of a nucleosome-free region at the core promoter. The subsequent nucleosomal remodeling and histone modifications at the promoter stabilized this repression. hTERT, the human telomerase reverse transcriptase, is highly expressed in stem cells and embryonic tissues but undetectable in most adult somatic cells. To understand its repression mechanisms in somatic cells, we investigated the endogenous hTERT gene regulation during differentiation of human leukemic HL60 cells. Our study revealed that silencing of the hTERT promoter was a biphasic process. Within 24 h after initiation of differentiation, hTERT mRNA expression decreased dramatically, accompanied by increased expression of Mad1 gene and disappearance of a nucleosome-free region at the hTERT core promoter. Subsequent to this early repression, nucleosomal remodeling continued at the promoter and downstream region for several days, as demonstrated by micrococcal nuclease and restriction enzyme accessibility assays. This later nucleosomal remodeling correlated with stable silencing of the hTERT promoter. Progressive changes of core histone modifications occurred throughout the entire differentiation process. Surprisingly, inhibition of histone deacetylation at the hTERT promoter did not prevent hTERT repression or nucleosomal deposition, indicating that nucleosomal deposition at the core promoter, but not histone deacetylation, was the cause of transcriptional repression. Our data also suggested that succeeding nucleosomal remodeling and histone deacetylation worked in parallel to establish the stable repressive status of hTERT gene in human somatic cells.
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Affiliation(s)
- Shuwen Wang
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
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Abstract
Telomerase is a specialized reverse transcriptase that is responsible for extending and preserving the end of the chromosomes (telomeres). Telomerase plays a key role in regulating the lifespan of mammalian cells and is involved in critical aspects of cellular ageing processes. In this review, we will briefly summarize our current understanding of the functions of telomeres, telomerase and their regulation. Considering that compensatory islet hyperplasia and beta-cell regeneration play important roles in the prevention and/or delay of the onset of overt diabetes, we will also examine current literature regarding the effects of diabetes on telomere shortening and provide insights from our own studies on the role of telomerase in beta-cell regeneration.
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Affiliation(s)
- C W Liew
- Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, MA, USA
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