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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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Stem cells at odds with telomere maintenance and protection. Trends Cell Biol 2022; 32:527-536. [DOI: 10.1016/j.tcb.2021.12.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/20/2021] [Accepted: 12/22/2021] [Indexed: 11/23/2022]
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Mechanism of Human Telomerase Reverse Transcriptase ( hTERT) Regulation and Clinical Impacts in Leukemia. Genes (Basel) 2021; 12:genes12081188. [PMID: 34440361 PMCID: PMC8392866 DOI: 10.3390/genes12081188] [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: 04/06/2021] [Revised: 05/09/2021] [Accepted: 05/17/2021] [Indexed: 01/03/2023] Open
Abstract
The proliferative capacity and continuous survival of cells are highly dependent on telomerase expression and the maintenance of telomere length. For this reason, elevated expression of telomerase has been identified in virtually all cancers, including leukemias; however, it should be noted that expression of telomerase is sometimes observed later in malignant development. This time point of activation is highly dependent on the type of leukemia and its causative factors. Many recent studies in this field have contributed to the elucidation of the mechanisms by which the various forms of leukemias increase telomerase activity. These include the dysregulation of telomerase reverse transcriptase (TERT) at various levels which include transcriptional, post-transcriptional, and post-translational stages. The pathways and biological molecules involved in these processes are also being deciphered with the advent of enabling technologies such as next-generation sequencing (NGS), ribonucleic acid sequencing (RNA-Seq), liquid chromatography-mass spectrometry (LCMS/MS), and many others. It has also been established that TERT possess diagnostic value as most adult cells do not express high levels of telomerase. Indeed, studies have shown that prognosis is not favorable in patients who have leukemias expressing high levels of telomerase. Recent research has indicated that targeting of this gene is able to control the survival of malignant cells and therefore offers a potential treatment for TERT-dependent leukemias. Here we review the mechanisms of hTERT regulation and deliberate their association in malignant states of leukemic cells. Further, we also cover the clinical implications of this gene including its use in diagnostic, prognostic, and therapeutic discoveries.
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Yang L, Li N, Wang M, Zhang YH, Yan LD, Zhou W, Yu ZQ, Peng XC, Cai J. Tumorigenic effect of TERT and its potential therapeutic target in NSCLC (Review). Oncol Rep 2021; 46:182. [PMID: 34278503 DOI: 10.3892/or.2021.8133] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Accepted: 05/25/2021] [Indexed: 12/24/2022] Open
Abstract
Non‑small cell lung cancer (NSCLC), which accounts for ~85% of all lung cancer cases, is commonly diagnosed at an advanced stage and has a high patient mortality rate. Despite the increasing availability of treatment strategies, the prognosis of patients with NSCLC remains poor, with a low 5‑year survival rate. This poor prognosis may be associated with the tumor heterogeneity of NSCLC, as well as its acquisition and intrinsic resistance to therapeutic drugs. It has been suggested that combination therapy with telomerase inhibition may be an effective strategy for the treatment of drug‑sensitive and drug‑resistant types of cancer. Telomerase is the key enzyme for cell survival, and ~90% of human cancers maintain telomeres by activating telomerase, which is driven by the upregulation of telomerase reverse transcriptase (TERT). Several mechanisms of telomerase reactivation have been described in a variety of cancer types, including TERT promoter mutation, epigenetic modifications via a TERT promoter, TERT amplification, and TERT rearrangement. The aim of the present study was to comprehensively review telomerase activity and its association with the clinical characteristics and prognosis of NSCLC, as well as analyze the potential mechanism via which TERT activates telomerase and determine its potential clinical application in NSCLC. More importantly, current treatment strategies targeting TERT in NSCLC have been summarized with the aim to promote discovery of novel strategies for the future treatment of NSCLC.
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Affiliation(s)
- Liu Yang
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Na Li
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Meng Wang
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Yan-Hua Zhang
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Lu-Da Yan
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Wen Zhou
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Zhi-Qiong Yu
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Xiao-Chun Peng
- Laboratory of Oncology, Center for Molecular Medicine, Yangtze University, Jingzhou, Hubei 434023, P.R. China
| | - Jun Cai
- Department of Oncology, First Affiliated Hospital of Yangtze University, Jingzhou, Hubei 434023, P.R. China
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Zhu X, Xu T, Zhu J. The regulatory function of tandem repeat VNTR2-1 in hTERT gene involves basic Helix-loop-helix family transcription factors. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2021; 62:338-349. [PMID: 34115413 PMCID: PMC9648534 DOI: 10.1002/em.22447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 06/06/2021] [Accepted: 06/09/2021] [Indexed: 06/12/2023]
Abstract
Telomerase is a ribonucleoprotein enzyme that synthesizes telomere end sequence. The expression of hTERT gene, encoding the catalytic subunit of human telomerase, is restricted to highly proliferative tissues and is undetectable in most somatic cells. Abnormal activation of hTERT gene is found in 90% of human tumors. Previously, we identified tandem repeat of 42-bp/unit, VNTR2-1, in intron 2 of the hTERT gene, as a novel regulatory element important for hTERT transcription in cancer cells. In the current study, we found that multiple 42-bp repeats of VNTR2-1 activated luciferase gene in reporter plasmids. Mutation of the predicted cis-regulatory elements within the 42-bp repeats, including a E-box motif, resulted in a partial or complete loss of its enhancer activity. Moreover, MYC family proteins, c-MYC, MAX, and MNT, regulated hTERT gene transcription through both VNTR2-1 and E-boxes at the proximal hTERT promoter. Chromatin segmentation analysis of published ChIP-sequencing data from K562 cells indicated that VNTR2-1 was a bivalent enhancer. In telomerase-expressing human melanoma cell line MelJuSo, deletion of VNTR2-1 caused the hTERT promoter chromatin status to change from an active state to a repressed state, accompanied by increases of H3K27me3 and H3K9me3 marks. Therefore, we provided additional evidence for VNTR2-1 as a functional regulatory element that regulated hTERT expression by MYC family transcription factors. These results have improved our knowledge on the functions of repetitive genomic DNAs and the regulatory mechanisms of human telomerase gene.
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Affiliation(s)
| | | | - Jiyue Zhu
- To whom correspondence should be addressed. Tel: 1-509-368-6565; Fax: 1-509-368-6561; ; 412E Spokane Falls Blvd, PBS323, Spokane, WA, 99202, USA
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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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Plyasova AA, Zhdanov DD. Alternative Splicing of Human Telomerase Reverse Transcriptase (hTERT) and Its Implications in Physiological and Pathological Processes. Biomedicines 2021; 9:526. [PMID: 34065134 PMCID: PMC8150890 DOI: 10.3390/biomedicines9050526] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 05/03/2021] [Accepted: 05/05/2021] [Indexed: 12/24/2022] Open
Abstract
Alternative splicing (AS) of human telomerase catalytic subunit (hTERT, human telomerase reverse transcriptase) pre-mRNA strongly regulates telomerase activity. Several proteins can regulate AS in a cell type-specific manner and determine the functions of cells. In addition to being involved in telomerase activity regulation, AS provides cells with different splice variants that may have alternative biological activities. The modulation of telomerase activity through the induction of hTERT AS is involved in the development of different cancer types and embryos, and the differentiation of stem cells. Regulatory T cells may suppress the proliferation of target human and murine T and B lymphocytes and NK cells in a contact-independent manner involving activation of TERT AS. This review focuses on the mechanism of regulation of hTERT pre-mRNA AS and the involvement of splice variants in physiological and pathological processes.
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Affiliation(s)
| | - Dmitry D. Zhdanov
- Institute of Biomedical Chemistry, Pogodinskaya st 10/8, 119121 Moscow, Russia;
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Myojin Y, Kodama T, Maesaka K, Motooka D, Sato Y, Tanaka S, Abe Y, Ohkawa K, Mita E, Hayashi Y, Hikita H, Sakamori R, Tatsumi T, Taguchi A, Eguchi H, Takehara T. ST6GAL1 Is a Novel Serum Biomarker for Lenvatinib-Susceptible FGF19-Driven Hepatocellular Carcinoma. Clin Cancer Res 2020; 27:1150-1161. [PMID: 33288659 DOI: 10.1158/1078-0432.ccr-20-3382] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 10/27/2020] [Accepted: 11/17/2020] [Indexed: 12/24/2022]
Abstract
PURPOSE Hepatocellular carcinoma (HCC) is characterized by high intertumor heterogeneity of genetic drivers. Two multitarget tyrosine kinase inhibitors (TKI), lenvatinib and sorafenib, are used as standard-of-care chemotherapeutics in patients with advanced HCC, but a stratification strategy has not been established because of a lack of efficacious biomarkers. Therefore, we sought biomarkers that indicate lenvatinib-susceptible HCC. EXPERIMENTAL DESIGN We performed genetic screening of HCC driver genes involved in TKI susceptibility using a novel HCC mouse model in which tumor diversity of genetic drivers was recapitulated. A biomarker candidate was evaluated in human HCC cell lines. Secreted proteins from HCC cells were then screened using mass spectrometry. Serum and tumor levels of the biomarker candidates were analyzed for their association and prediction of overall survival in patients with HCC. RESULTS We found that lenvatinib selectively eliminated FGF19-expressing tumors, whereas sorafenib eliminated MET- and NRAS-expressing tumors. FGF19 levels and lenvatinib susceptibility were correlated in HCC cell lines, and FGF19 inhibition eliminated lenvatinib susceptibility. Lenvatinib-resistant HCC cell lines, generated by long-term exposure to lenvatinib, showed FGF19 downregulation but were resensitized to lenvatinib by FGF19 reexpression. Thus, FGF19 is a tumor biomarker of lenvatinib-susceptible HCC. Proteome and secretome analyses identified ST6GAL1 as a tumor-derived secreted protein positively regulated by FGF19 in HCC cells. Serum ST6GAL1 levels were positively correlated with tumor FGF19 expression in patients with surgically resected HCC. Among patients with serum ST6GAL1-high HCC who underwent TKI therapy, lenvatinib therapy showed significantly better survival than sorafenib. CONCLUSIONS Serum ST6GAL may be a novel biomarker that identifies lenvatinib-susceptible FGF19-driven HCC.
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Affiliation(s)
- Yuta Myojin
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Takahiro Kodama
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Kazuki Maesaka
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Daisuke Motooka
- Genome Information Research Center, Research Institute for Microbial Diseases, Osaka University, Suita, Japan
| | - Yu Sato
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Satoshi Tanaka
- Department of Gastroenterology and Hepatology, National Hospital Organization Osaka National Hospital, Osaka, Japan
| | - Yuichi Abe
- Division of Molecular Diagnostics, Aichi Cancer Center Research Institute, Nagoya, Japan
| | - Kazuyoshi Ohkawa
- Department of Gastroenterology and Hepatology, Osaka International Cancer Institute, Osaka, Japan
| | - Eiji Mita
- Department of Gastroenterology and Hepatology, National Hospital Organization Osaka National Hospital, Osaka, Japan
| | - Yoshito Hayashi
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Hayato Hikita
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Ryotaro Sakamori
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Tomohide Tatsumi
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Ayumu Taguchi
- Division of Molecular Diagnostics, Aichi Cancer Center Research Institute, Nagoya, Japan.,Division of Advanced Cancer Diagnostics, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Hidetoshi Eguchi
- Department of Gastroenterological Surgery, Osaka University Graduate School of Medicine, Suita, Japan
| | - Tetsuo Takehara
- Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Suita, Japan.
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Reverse transcriptase inhibition potentiates target therapy in BRAF-mutant melanomas: effects on cell proliferation, apoptosis, DNA-damage, ROS induction and mitochondrial membrane depolarization. Cell Commun Signal 2020; 18:150. [PMID: 32933538 PMCID: PMC7493390 DOI: 10.1186/s12964-020-00633-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Accepted: 07/23/2020] [Indexed: 12/31/2022] Open
Abstract
Abstract Target therapies based on BRAF and MEK inhibitors (MAPKi) have changed the therapeutic landscape for metastatic melanoma patients bearing mutations in the BRAF kinase. However, the emergence of drug resistance imposes the necessity to conceive novel therapeutic strategies capable to achieve a more durable disease control. In the last years, retrotransposons laying in human genome have been shown to undergo activation during tumorigenesis, where they contribute to genomic instability. Their activation can be efficiently controlled with reverse transcriptase inhibitors (RTIs) frequently used in the treatment of AIDS. These drugs have demonstrated anti-proliferative effects in several cancer models, including also metastatic melanoma. However, to our knowledge no previous study investigated the capability of RTIs to mitigate drug resistance to target therapy in BRAF-mutant melanomas. In this short report we show that the non-nucleoside RTI, SPV122 in combination with MAPKi strongly inhibits BRAF-mutant melanoma cell growth, induces apoptosis, and delays the emergence of resistance to target therapy in vitro. Mechanistically, this combination strongly induces DNA double-strand breaks, mitochondrial membrane depolarization and increased ROS levels. Our results shed further light on the molecular activity of RTI in melanoma and pave the way to their use as a novel therapeutic option to improve the efficacy of target therapy. Video Abstract
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Zhang F, Wang S, Zhu J. ETS variant transcription factor 5 and c-Myc cooperate in derepressing the human telomerase gene promoter via composite ETS/E-box motifs. J Biol Chem 2020; 295:10062-10075. [PMID: 32518154 DOI: 10.1074/jbc.ra119.012130] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2019] [Revised: 06/04/2020] [Indexed: 12/19/2022] Open
Abstract
The human telomerase gene (hTERT) is repressed in most somatic cells. How transcription factors activate the hTERT promoter in its repressive chromatin environment is unknown. Here, we report that the ETS family protein ETS variant transcription factor 5 (ETV5) mediates epidermal growth factor (EGF)-induced hTERT expression in MCF10A cells. This activation required MYC proto-oncogene bHLH transcription factor (c-Myc) and depended on the chromatin state of the hTERT promoter. Using chromatinized bacterial artificial chromosome (BAC) reporters in human fibroblasts, we found that ETV5 and c-Myc/MYC-associated factor X (MAX) synergistically activate the hTERT promoter via two identical, but inverted, composite Ets/E-box motifs enclosing the core promoter. Mutations of Ets or E-box sites in either DNA motif abolished the activation and reduced or eliminated the synergism. ETV5 and c-Myc facilitated each other's binding to the hTERT promoter. ETV5 bound to the hTERT promoter in both telomerase-negative and -positive cells, but it activated the repressed hTERT promoter and altered histone modifications only in telomerase-negative cells. The synergistic ETV5/c-Myc activation disappeared when hTERT promoter repression became relieved because of the loss of distal regulatory elements in chimeric human/mouse BAC reporters. Our results suggest that the binding of c-Myc and ETS family proteins to the Ets/E-box motifs derepresses the hTERT promoter by inducing an active promoter configuration, providing a mechanistic insight into hTERT activation during tumorigenesis.
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Affiliation(s)
- Fan Zhang
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy and Pharmaceutical Sciences, Spokane, Washington, USA
| | - Shuwen Wang
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy and Pharmaceutical Sciences, Spokane, Washington, USA
| | - Jiyue Zhu
- Department of Pharmaceutical Sciences, Washington State University College of Pharmacy and Pharmaceutical Sciences, Spokane, Washington, USA
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