Modulation Of Telomerase Activity Research Articles

Connecting the Dots: Telomere Shortening and Rheumatic Diseases.

Telomeres, repetitive sequences located at the extremities of chromosomes, play a pivotal role in sustaining chromosomal stability. Telomerase is a complex enzyme that can elongate telomeres by appending telomeric repeats to chromosome ends and acts as a critical factor in telomere dynamics. The gradual shortening of telomeres over time is a hallmark of cellular senescence and cellular death. Notably, telomere shortening appears to result from the complex interplay of two primary mechanisms: telomere shelterin complexes and telomerase activity. The intricate interplay of genetic, environmental, and lifestyle influences can perturb telomere replication, incite oxidative stress damage, and modulate telomerase activity, collectively resulting in shifts in telomere length. This age-related process of telomere shortening plays a considerable role in various chronic inflammatory and oxidative stress conditions, including cancer, cardiovascular disease, and rheumatic disease. Existing evidence has shown that abnormal telomere shortening or telomerase activity abnormalities are present in the pathophysiological processes of most rheumatic diseases, including different disease stages and cell types. The impact of telomere shortening on rheumatic diseases is multifaceted. This review summarizes the current understanding of the link between telomere length and rheumatic diseases in clinical patients and examines probable telomere shortening in peripheral blood mononuclear cells and histiocytes. Therefore, understanding the intricate interaction between telomere shortening and various rheumatic diseases will help in designing personalized treatment and control measures for rheumatic disease.

Abstract 6144: A polymorphic TERT tandem repeat creating an expandable intronic G4 quadruplex is associated with TERT expression, relative leukocyte telomere length and cancer risk

Abstract A multi-cancer GWAS region at human chromosome 5p15 encodes telomerase reverse transcriptase (TERT). One of the GWAS signals is rs10069690-T, which creates an alternative intron 4 splicing site, co-producing full-length (FL) and truncated INS1b transcript for dominant-negative telomerase-nonfunctional TERT. A variable number tandem repeat (VNTR6-1, 38 bp repeat unit) within intron 6 remains uncharacterized in relation to GWAS signals and cancer risk. We hypothesized that VNTR6-1 might contribute to GWAS signals represented by rs10069690. We scored VNTR6-1 and rs10069690 in short-read WGS data (n=3,202) from the 1000 Genomes Project with a machine learning model using the GLMnet engine, and in phased long-read assemblies (n=544). We defined two VNTR6-1 groups: Short (24-27 copies) and Long (40.5-66.5 copies); the VNTR6-1-Long group was preferentially linked with rs10069690-T compared to C allele (p=2.53E-13). We show that haplotypes of rs56345976 and rs33961405 alleles can predict VNTR6-1 groups. We imputed VNTR6-1 in UK Biobank controls (n=351,634), PLCO cancer cases and controls (n=100,445), and African Burkitt lymphoma cases (aBL, n=79). Functional studies in aBL tumors revealed a suggestive association between reduced total TERT expression, rs10096690-T (p=0.035) and VNTR6-1-Long (p=0.053). VNTR6-1 forms a G4 quadruplex structure sensitive to G4 stabilizing ligands, altering the ratio between FL-TERT and a dominant-negative TERT-β isoform in isogenic cell lines with/without VNTR6-1. In GTEx and TCGA, several metrics related to cell proliferation and telomerase activity correlated positively with FL-TERT expression and negatively with TERT-β expression. We created a composite marker with 0, 1 or 2 copies of the FL-TERT-associated haplotype (VNTR6-1-Short/rs10069690-C) to capture the effects of these variants that negatively affect TERT expression and telomerase activity. The number of copies of the VNTR6-1/rs10069690 haplotype was associated with relative leukocyte telomere length in UK Biobank controlling for sex and age (β=0.049, p=8.75E-78). This marker was also associated with a reduced risk of bladder and prostate cancer but an increased risk of breast, endometrial, ovarian, thyroid cancer, and glioma in PLCO. Our findings reveal that germline variants VNTR6-1-Long/rs10069690-T underlie the multi-cancer GWAS signal and jointly decrease TERT expression and telomerase activity, potentially reducing the risk of some cancers by limiting cell growth. However, decreased telomerase activity could deregulate stem cell-driven tissue regeneration and genome integrity, increasing the risk of other cancers. Our findings unveil novel mechanisms of cancer susceptibility and propose therapeutic avenues for targeting TERT isoform ratios to modulate telomerase activity and its cellular effects. Citation Format: Oscar Florez-Vargas, Michelle Ho, Max Hogshead, Chia-Han Lee, Kaitlin Forsythe, Brenen Papenberg, Kristine Jones, Wen Luo, Kedest Teshome, Cornelis Blauwendraat, Mikhail Kolmogorov, Stephen J. Chanock, Mitchell J. Machiela, John Schneekloth, Shahinaz Gadalla, Sharon A. Savage, Sam M. Mbulaiteye, Ludmila Prokunina-Olsson. A polymorphic TERT tandem repeat creating an expandable intronic G4 quadruplex is associated with TERT expression, relative leukocyte telomere length and cancer risk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6144.

Retraction: Cytokines Modulate Telomerase Activity in a Human Multiple Myeloma Cell Line.

Retraction: Cytokines Modulate Telomerase Activity in a Human Multiple Myeloma Cell Line.

Activation of telomerase activity and telomere elongation of host cells by Theileria annulata infection.

Theileria annulata-transformed cells share many phenotypes with cancer cells, including uncontrolled proliferation, immortalization, and dissemination. Telomeres are DNA-protein complex at the end of eukaryotic chromosomes that function to maintain genome stability and cell replicative capacity. Telomere length maintenance is primarily dependent on telomerase activity. In up to 90% of human cancer cells, telomerase is reactivated through expression of its catalytic subunit TERT. However, the effect of T. annulata infection on telomere and telomerase activity in bovine cells has not yet been described. In the present study, we confirmed that telomere length and telomerase activity are upregulated after T. annulata infection in three types of cell lines. This change depends on the presence of parasites. After eliminating Theileria from cells with antitheilerial drug buparvaquone, telomerase activity and the expression level of bTERT were decreased. In addition, inhibition of bHSP90 by novobiocin led to decreased AKT phosphorylation levels and telomerase activity, indicating that the bHSP90-AKT complex is a potent factor modulates telomerase activity in T. annulata-infected cells.

Genetic and biochemical interactions of yeast DNA helicases.

DNA helicases function in many types of nucleic acid transactions, and as such, they are vital for genome integrity. Although they are often considered individually, work from many groups demonstrates that these enzymes often genetically and biochemically interact in vivo. Here, we highlight methods to interrogate such interactions among the PIF1 (Pif1 and Rrm3) and RecQ (Hrq1 and Sgs1) family helicases in Saccharomyces cerevisiae. The interactions among these enzymes were investigated in vivo using deletion and inactivation alleles with a gross-chromosomal rearrangement (GCR) assay. Further, wild-type and inactive recombinant proteins were used to determine the effects of the helicases on telomerase activity in vitro. We found that synergistic increases in GCR rates often occur in double vs. single mutants, suggesting that the helicases function in distinct genome integrity pathways. Further, the recombinant helicases can function together in vitro to modulate telomerase activity. Overall, the data suggest that the interactions among the members of these DNA helicase families are multipartite and argue for a comprehensive systems biology approach to fully elucidate the physiological interplay between these enzymes.

Alternative Splicing of Human Telomerase Reverse Transcriptase (hTERT) and Its Implications in Physiological and Pathological Processes.

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.

Structure of human telomerase holoenzyme with bound telomeric DNA.

Telomerase adds telomeric repeats at chromosome ends to compensate for the telomere loss that is caused by incomplete genome end replication1. In humans, telomerase is upregulated during embryogenesis and in cancers, and mutations that compromise the function of telomerase result in disease2. A previous structure of human telomerase at a resolution of 8Å revealed a vertebrate-specific composition and architecture3, comprising a catalytic core that is flexibly tethered to an H and ACA (hereafter, H/ACA) box ribonucleoprotein (RNP) lobe by telomerase RNA. High-resolution structural information is necessary to develop treatments that can effectively modulate telomerase activity as a therapeutic approach against cancers and disease. Here we used cryo-electron microscopy to determine the structure of human telomerase holoenzyme bound to telomeric DNAat sub-4 Å resolution, which reveals crucial DNA- and RNA-binding interfaces in the active site of telomerase as well as the locations of mutations that alter telomerase activity. We identified a histone H2A-H2B dimer within the holoenzyme that was bound to an essential telomerase RNA motif, which suggests a role for histones in the folding and function of telomerase RNA. Furthermore, this structure of a eukaryotic H/ACA RNP reveals the molecular recognition of conserved RNA and protein motifs, as well as interactions that are crucial for understanding the molecular pathology of many mutations that cause disease. Our findings provide thestructural details of the assembly and active site of human telomerase, which paves the way for the development of therapeutic agents that target this enzyme.

HnRNP F/H associate with hTERC and telomerase holoenzyme to modulate telomerase function and promote cell proliferation

Human telomerase RNA component hTERC comprises multiple motifs that contribute to hTERC biogenesis, holoenzyme activity, and enzyme recruitment to telomeres. hTERC contains several guanine tracts (G-tracts) at its 5′-end, but its associated proteins and potential roles in telomerase function are still poorly understood. The heterogeneous nuclear ribonucleoproteins F, H1, and H2 (hnRNP F/H) are splicing factors that preferentially bind to poly(G)-rich sequences RNA. Here, we demonstrate that hnRNP F/H associate with both hTERC and telomerase holoenzyme to regulate telomerase activity. We reveal hnRNP F/H bind to the 5′-end region of hTERC in vitro and in vivo, and identify the first three G-tracts of hTERC and qRRM1 domain of hnRNP F/H are required for their interaction. Furthermore, hnRNP F/H also directly interact with telomerase holoenzyme. Functionally, we show that hnRNP F/H plays important roles in modulating telomerase activity and telomere length. Moreover, hnRNP F/H deletion greatly impair cancer and stem cell proliferation, and induce stem cell senescence, while hnRNP F/H overexpression delay stem cell senescence. Collectively, our findings unveil a novel role of hnRNP F/H as the binding partners of hTERC and telomerase holoenzyme to regulate telomerase function.

Telomeres and Telomerase in Cutaneous Squamous Cell Carcinoma.

The role of telomere biology and telomerase activation in skin cancers has been investigated in melanoma and basal cell carcinoma but limited evidence is available for cutaneous squamous cell carcinoma (cSCC). We will review the current knowledge on the role of telomere and telomerase pathway in cSCC pathogenesis. At the somatic level, both long and short telomere lengths have been described in cSCC. This telomere dichotomy is probably related to two different mechanisms of tumour initiation which determines two tumour subtypes. Telomere shortening is observed during the invasive progression from in situ forms of cSCC, such as Bowen’s disease (BD) and actinic keratosis (AK), to invasive cSCC. At the germline level, controversial results have been reported on the association between constitutive telomere length and risk of cSCC. Approximately 75–85% of cSCC tumours are characterized by a high level of telomerase activity. Telomerase activation has been also reported in AKs and BD and in sun-damaged skin, thus supporting the hypothesis that UV modulates telomerase activity in the skin. Activating TERT promoter mutations have been identified in 32–70% of cSCCs, with the majority showing the UV-signature. No significant correlation was observed between TERT promoter mutations and cSCC clinico-pathological features. However, TERT promoter mutations have been recently suggested to be independent predictors of an adverse outcome. The attention on telomere biology and telomerase activity in cSCC is increasing for the potential implications in the development of effective tools for prognostic assessment and of therapeutic strategies in patients with cutaneous cSCC.

Beta-carotene, telomerase activity and Alzheimer's disease in old age subjects.

Advancing age represents the strongest risk factor for Alzheimer's disease (AD), and the identification of biomarkers able to define what characterizes physiological aging from AD may represent a potential starting point for novel preventive strategies. Among these biomarkers, telomeres seem to be a promising target. Interestingly, high intake of carotenoid-rich food may play a role in protecting telomeres by oxidative stress reduction. Accordingly, low plasma β-carotene concentrations have been found in AD subjects when compared with cognitively healthy subjects. In this study, we aim at investigating the hypothesis that low β-carotene might be associated with markers of accelerated cellular aging, including leucocyte telomere length (LTL) and peripheral mononuclear cell (PBMC) telomerase activity in a cohort of old age subjects. The study was conducted in 68 old age subjects, 37 AD, and 31 age-matched healthy controls. In all subjects, β-carotene plasma level, LTL and peripheral telomerase activity were measured. In all populations, β-carotene significantly and positively (r = 0.320, p = 0.008) correlated with telomerase activity, independent of gender. A model having telomerase activity levels as the dependent variable, and age, gender, smoking habit, and β-carotene as independent variables, confirmed that β-carotene was independently associated with telomerase activity (β = 0.319, p = 0.012). Subjects affected by AD had significantly lower plasmatic levels of β-carotene (448 ± 66mg/ml vs 497 ± 59mg/ml, p = 0.001) and LTL (0.53 ± 0.25 vs 0.69 ± 0.29; p = 0.009) as compared with healthy controls. Β-carotene plasma level was associated with AD diagnosis (OR 0.988; IC95% 0.978-0.997; p = 0.013) independently of age, gender, smoking habit, ApoE genotype, and LTL. Our data show that β-carotene may modulate telomerase activity in old age. Moreover, lower plasma β-carotene levels, correlating with peripheral telomerase activity, are associated with AD diagnosis independent of multiple covariates.

Novel combination of tanshinone I and lenalidomide induces chemo-sensitivity in myeloma cells by modulating telomerase activity and expression of shelterin complex and its associated molecules

Shelterin complex and its associated molecules are imperative for proper functioning and maintenance of human telomeres. These molecules in association with human telomerase have been found altered in most cancers including multiple myeloma thereby proposed them as suitable therapeutic targets. Further, due to aggressive and recurring behavior of myeloma novel, efficacious and safe therapeutic agents for disease prevention are primary requirements for treatment of this disease. This maiden attempt evaluated the anti-proliferative properties of tanshinone I (TanI) alone or in combination with lenalidomide (Len) on myeloma cancer cell lines (RPMI8226 and U226). Further, after drug treatment levels of telomerase activity (TA) and molecular expression (mRNA & protein) of shelterin complex and its associated molecules have also been investigated. Results demonstrated that, TanI significantly inhibited proliferation of myeloma cells in dose and time dependent manner as observed through cytotoxicity assay. Additionally, induction of apoptosis by TanI and in combination with Len was observed in myeloma cells through propidium iodide (PI) staining, annexin V-FITC/PI staining, TUNEL and caspase-3/7 activity assays. Further, drug treatment significantly decreased (p < 0.01) TA and molecular expression of ACD, TERF2IP and TANK1 in comparison to vehicle control (0.1% DMSO) myeloma cells. Thus, this maiden in-vitro study provided initial evidences of therapeutic potential of TanI alone or in combination with chemotherapeutic agent Len as novel anticancer agents in myeloma cells which need further evaluation in future. Lastly, down-regulation of TA and decreased expression of these molecules underscores their potential as plausible therapeutic targets.

Silencing of telomere-binding protein adrenocortical dysplasia (ACD) homolog enhances radiosensitivity in glioblastoma cells

Adrenocortical dysplasia (ACD) is a shelterin protein involved in the maintenance of telomere length and in cancer radioresistance. This study investigated the expression profile of ACD in human gliomas and its role in radioresistance of glioma cells. The expression of ACD was analyzed in 62 different grades of glioma tissues and correlated with prognosis. A radioresistant cell line was generated from U87MG cells. For mechanistic studies, ACD was inhibited by small interfering RNA-targeting ACD and the effect on cell radioresistance, telomerase activity, cyclinD1, caspase-3, hTERT, and BIRC1 was evaluated. Clonogenic assay was performed after irradiation, to investigate the effect of ACD silencing on radiation sensitivity. ACD expression appeared strongly upregulated in higher grade gliomas, and its expression was significantly correlated to grading and poor prognosis. In glioma cell lines, ACD expression pattern was similar to those observed in glioma tissues. In irradiated cells, ACD expression was increased in an ionizing radiation dose-dependent manner. A higher expression of ACD was observed in the radioresistant clones than parental cells. Silencing of ACD led to the enhanced radiation sensitivity, decreased telomerase activity and cyclin D1 expression, reduced expression of BIRC1, and finally to the upregulation of caspase-3. This study represents the first report, which demonstrated the expression pattern of ACD in gliomas and its prognostic value. Our results suggested that ACD is involved in glioblastoma radioresistance, likely through the modulation of telomerase activity, proliferation, and apoptosis. ACD might represent a potential molecular biomarker and a novel therapeutic target in glioblastoma.

Modulation of Telomerase Activity in Cancer Cells by Dietary Compounds: A Review.

Telomerase is expressed in ~90% of human cancer cell lines and tumor specimens, whereas its enzymatic activity is not detectable in most human somatic cells, suggesting that telomerase represents a highly attractive target for selective cancer treatment. Accordingly, various classes of telomerase inhibitors have been screened and developed in recent years. We and other researchers have successfully found that some dietary compounds can modulate telomerase activity in cancer cells. Telomerase inhibitors derived from food are subdivided into two groups: one group directly blocks the enzymatic activity of telomerase (e.g., catechin and sulfoquinovosyldiacylglycerol), and the other downregulates the expression of human telomerase reverse transcriptase (hTERT), the catalytic subunit of human telomerase, via signal transduction pathways (e.g., retinoic acid and tocotrienol). In contrast, a few dietary components, including genistein and glycated lipid, induce cellular telomerase activity in several types of cancer cells, suggesting that they may be involved in tumor progression. This review summarizes the current knowledge about the effects of dietary factors on telomerase regulation in cancer cells and discusses their molecular mechanisms of action.

Metal-Ion-Activated DNAzymes Used for Regulation of Telomerase Activity in Living Cells.

Telomerase is a key regulator in cell metabolism, tissue renewal, and organismal lifespan. Here we develop a simple strategy to modulate cellular telomerase activity, and further control cell fate based on Mg2+ - and Zn2+ -activated DNAzymes in living cells. Through modulation of telomerase activity, we can regulate cell behavior, including cell migration, cell differentiation, cell senescence, and cell cycle. Our work provides a new way to modulate telomerase activity in living cells by using DNAzymes.

Shelterin genes, germ line mutations and chronic lymphocytic leukemia

Telomeres are distinctive DNA-protein structures that cap the ends of linear chromosomes; they are essential to maintain chromosomal integrity and genome stability. Telomeres are composed by tandem repeats of the non-codificante DNA sequence TTAGGG bound by the shelterin complex. It contains six core proteins: telomeric repeat binding factor 1 (TERF1), TERF2, protection of telomeres 1 (POT1), adrenocortical dysplasia homolog (ACD), telomeric repeat-binding factor 2-interacting protein (TERF2IP) and TERF1 interacting nuclear factor 2 (TINF2), which play fundamental roles in telomere protection, chromosomal stability and regulation of telomere length (TL) (1). In addition, the shelterin complex modulates telomerase activity at chromosome ends, recognizes telomeric DNA and remodels it into a t-loop, which protects the 3’ overhang from being recognized as DNA damage. Alterations in the structure and function of any of these proteins may lead to undesirable DNA damage responses that could be associated to a role in tumorigenesis and cancer progression.

Hsp90-binding immunophilin FKBP52 modulates telomerase activity by promoting the cytoplasmic retrotransport of hTERT.

Telomerase is a unique ribonucleoprotein enzyme that is required for continued cell proliferation. To generate catalytically active telomerase, human telomerase reverse transcriptase (hTERT) must translocate to the nucleus and assemble with the RNA component of telomerase. The molecular chaperones heat shock protein 90 (Hsp90) and p23 maintain hTERT in a conformation that enables nuclear translocation. However, the regulatory role of chaperones in nuclear transport of hTERT remains unclear. In this work, we demonstrate that immunophilin FK506-binding protein (FKBP)52 linked the hTERT-Hsp90 complex to the dynein-dynactin motor, thereby promoting the transport of hTERT to the nucleus along microtubules. FKBP52 interacted with the hTERT-Hsp90 complex through binding of the tetratricopeptide repeat domain to Hsp90 and binding of the dynamitin (Dyt) component of the dynein-associated dynactin complex to the peptidyl prolyl isomerase domain. The depletion of FKBP52 inhibited nuclear transport of hTERT, resulting in cytoplasmic accumulation. Cytoplasmic hTERT was rapidly degraded through ubiquitin (Ub)-dependent proteolysis, thereby abrogating telomerase activity. In addition, overexpression of dynamitin, which is known to dissociate the dynein-dynactin motor from its cargoes, reduced telomerase activity. Collectively, these results provide a molecular mechanism by which FKBP52 modulates telomerase activity by promoting dynein-dynactin-dependent nuclear import of hTERT.

Modulation of yeast telomerase activity by Cdc13 and Est1 in vitro.

Telomerase is the enzyme involved in extending telomeric DNA. Control of telomerase activity by modulating its access to chromosome ends is one of the most important fundamental mechanisms. This study established an in vitro yeast telomerase reconstitution system that resembles telomere replication in vivo. In this system, a tailed-duplex DNA formed by telomeric DNA was employed to mimic the structure of telomeres. The core catalytic components of telomerase Est2/Tlc1 RNA were used as the telomeric DNA extension machinery. Using the reconstituted systems, this study found that binding of Cdc13 to telomeric DNA inhibited the access of telomerase to its substrate. The result was further confirmed by a single-molecule approach using the tethered-particle motion (TPM)-based telomerase assay. The findings also showed that the inhibitory effect can be relieved by telomerase-associated protein Est1, consistent with the role of Cdc13 and Est1 in regulating telomere extension in vivo. Significantly, this study found that the DNA binding property of Cdc13 was altered by Est1, providing the first mechanistic evidence of Est1 regulating the access of telomerase to its substrate. Thus, the roles of Cdc13 and Est1 in modulating telomerase activity were clearly defined using the in vitro reconstituted system.

Vascular Actions of Angiotensin 1-7 in the Human Microcirculation: Novel Role for Telomerase.

This study examined vascular actions of angiotensin 1-7 (ANG 1-7) in human atrial and adipose arterioles. The endothelium-derived hyperpolarizing factor of flow-mediated dilation (FMD) switches from antiproliferative nitric oxide (NO) to proatherosclerotic hydrogen peroxide in arterioles from humans with coronary artery disease (CAD). Given the known vasoprotective properties of ANG 1-7, we tested the hypothesis that overnight ANG 1-7 treatment restores the NO component of FMD in arterioles from patients with CAD. Endothelial telomerase activity is essential for preserving the NO component of vasodilation in the human microcirculation; thus, we also tested whether telomerase activity was necessary for ANG 1-7-mediated vasoprotection by treating separate arterioles with ANG 1-7±the telomerase inhibitor 2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid. ANG 1-7 dilated arterioles from patients without CAD, whereas dilation was significantly reduced in arterioles from patients with CAD. In atrial arterioles from patients with CAD incubated with ANG 1-7 overnight, the NO synthase inhibitor NG-nitro-l-arginine methyl ester abolished FMD, whereas the hydrogen peroxide scavenger polyethylene glycol catalase had no effect. Conversely, in vessels incubated with ANG 1-7+2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid, NG-nitro-l-arginine methyl ester had no effect on FMD, but polyethylene glycol catalase abolished dilation. In cultured human coronary artery endothelial cells, ANG 1-7 significantly increased telomerase activity. These results indicate that ANG 1-7 dilates human microvessels, and dilation is abrogated in the presence of CAD. Furthermore, ANG 1-7 treatment is sufficient to restore the NO component of FMD in arterioles from patients with CAD in a telomerase-dependent manner. ANG 1-7 exerts vasoprotection in the human microvasculature via modulation of telomerase activity.

GENO-07A MECHANISM OF MUTANT TERT PROMOTER ACTIVATION SHARED ACROSS CANCER TYPES

The human telomerase is an enzyme critical for maintaining telomere length and chromosomal stability in stem cells. The transcriptional regulation of the telomerase reverse transcriptase (TERT) gene, encoding the catalytic subunit of telomerase, is a rate-limiting step in modulating telomerase activity. Although normally silenced in somatic cells, TERT is aberrantly expressed in 90% of aggressive cancers, highlighting this event as a hallmark of tumorigenesis. Reactivating telomerase helps cells with finite lifespan to achieve limitless proliferative potential and bypass cellular senescence induced by DNA replication-associated telomere shortening. Recently discovered non-coding mutations in the TERT promoter are among the most common genetic alterations observed across multiple cancer types. Specifically, one of two positions, G228A or G250A, is mutated in 20% of medulloblastomas, 44% of hepatocellular carcinomas (HCC), 66% of urothelial carcinomas of the bladder, 71% of melanomas, 78% of oligodendrogliomas, and 83% of primary glioblastomas (GBM). The common mutation sites may create de-novo ETS family transcription factor binding sites, but the precise mechanism of how these mutations confer increased TERT expression has remained elusive. Here, a focused siRNA screen of the many ETS transcription factors expressed in GBM identifies GABPA as the single ETS factor to selectively regulate the mutant but not the wild type TERT promoter. Single molecule binding assays and ChIP-qPCR analysis reveal that GABPA is exclusively recruited to the mutant allele in vitro and in vivo respectively. Furthermore, this allelic recruitment is consistent across four tested cancer types, highlighting a shared mechanism underlying mutant TERT promoter activation. Tandem flanking native ETS motifs critically cooperate with these mutations to activate TERT, likely by facilitating GABP heterotetramer binding. GABP thus directly links TERT promoter mutations to aberrant expression across multiple cancers.

Modulation of telomerase activity in fish muscle by biological and environmental factors

Telomerase expression has long been linked to promotion of tumor growth and cell proliferation in mammals. Interestingly, telomerase activity (TA) has been detected in skeletal muscle for a variety of fish species. Despite this being a unique feature in fish, very few studies have investigated the potential role of TA in muscle. The present study was set to prove the concepts that muscle telomerase in fish is related to body growth, and more specifically, to muscle cell proliferation and apoptosis in vivo. Moreover, muscle TA can be influenced by biotic factors and modulated by environmental stress. Using three fish species, mangrove red snapper (Lutjanus argentimaculatus), orange-spotted grouper (Epinephelus coioides), and marine medaka (Oryzias melastigma), the present work reports for the first time that fish muscle TA was sensitive to the environmental stresses of starvation, foodborne exposure to benzo[a]pyrene, and hypoxia. In marine medaka, muscle TA was coupled with fish growth during early life stages. Upon sexual maturation, muscle TA was confounded by sex (female>male). Muscle TA was significantly correlated with telomerase reverse transcriptase (TERT) protein expression (Pearson correlation r=0.892; p≤0.05), which was coupled with proliferating cell nuclear antigen (PCNA) cell proliferation, but not associated with apoptosis (omBax/omBcl2 ratio) in muscle tissue. The results reported here have bridged the knowledge gap between the existence and function of telomerase in fish muscle. The underlying regulatory mechanisms of muscle TA in fish warrant further exploration for comparison with telomerase regulation in mammals.