Telomerase reverse transcriptase regulates microRNAs

Accumulation of TERT in mitochondria exerts two opposing effects on apoptosis

Telomerase reverse transcriptase (TERT) is a protein that catalyzes the reverse transcription of telomere elongation. TERT is also expected to play a non-canonical role beyond telomere lengthening since it localizes not only in the nucleus but also in mitochondria, where telomeres do not exist. Several studies have reported that mitochondrial TERT regulates apoptosis induced by oxidative stress. However, there is still some controversy as to whether mitochondrial TERT promotes or inhibits apoptosis, mainly due to the lack of information on changes in TERT distribution in individual cells over time. Here, we simultaneously detected apoptosis and TERT localization after oxidative stress in individual HeLa cells by live-cell tracking. Single-cell tracking revealed that the stress-induced accumulation of TERT in mitochondria caused apoptosis, but that accumulation increased over time until cell death. The results suggest a new model in which mitochondrial TERT has two opposing effects at different stages of apoptosis: it predetermines apoptosis at the first stage of cell-fate determination, but also delays apoptosis at the second stage. As such, our data support a model that integrates the two opposing hypotheses on mitochondrial TERT's effect on apoptosis. Furthermore, detailed statistical analysis of TERT mutations, which have been predicted to inhibit TERT transport to mitochondria, revealed that these mutations suppress apoptosis independent of mitochondrial localization of TERT. Together, these results imply that the non-canonical functions of TERT affect a wide range of mitochondria-dependent and mitochondria-independent apoptosis pathways.

Relationship between miRNAs polymorphisms and peripheral blood leukocyte DNA telomere length in coke oven workers: A cross-sectional study

OBJECTIVE

The purpose of this study was to investigate the factors affecting telomere length (TL) in coke oven workers by analyzing the interaction between miRNAs polymorphisms and coke oven emissions (COEs) exposure.

METHODS

A total of 544 coke oven workers and 238 healthy controls were recruited. Peripheral blood was collected from the subjects, genomic DNA was extracted, leukocyte TL was detected by real-time quantitative polymerase chain reaction, and fifteen polymorphisms of eight miRNAs were genotyped by flight mass spectrometry.

RESULTS

Statistical analysis showed that the peripheral blood DNA TL in the exposure group was shorter than that in the control group (P < 0.001). Generalized linear model found that COEs-exposure [β (95%CI) = -0.427 (-0.556, -0.299), P < 0.001], genotype CC+CT for miR-612 rs1144925 [β (95%CI) = -0.367 (-0.630, -0.104), P = 0.006], and the interaction of miR-181B1 rs12039395 TT genotype and COEs-exposure [β (95% CI) = 0.564 (0.108, 1.020), P = 0.015] were associated with the shortened TL.

CONCLUSION

COEs-exposure and miR-612 rs1144925 TT could promote telomere shortening in coke oven workers. The interaction of miR-181B1 rs12039395 TT genotype and COEs-exposure could protect telomere. This provides clues for further mechanistic studies between miRNA and telomere damage.

Exosomal telomerase transcripts reprogram the microRNA transcriptome profile of fibroblasts and partially contribute to CAF formation

It is now well accepted that cancer cells change their microenvironment from normal to tumor-supportive state to provide sustained tumor growth, metastasis and drug resistance. These processes are partially carried out by exosomes, nano-sized vesicles secreted from cells, shuttled from donor to recipient cells containing a cargo of nucleic acids, proteins and lipids. By transferring biologically active molecules, cancer-derived exosomes may transform microenvironmental cells to become tumor supportive. Telomerase activity is regarded as a hallmark of cancer. We have recently shown that the transcript of human telomerase reverse transcriptase (hTERT), is packaged in cancer cells derived- exosomes. Following the engulfment of the hTERT transcript into fibroblasts, it is translated into a fully active enzyme [after assembly with its RNA component (hTERC) subunit]. Telomerase activity in the recipient, otherwise telomerase negative cells, provides them with a survival advantage. Here we show that exosomal telomerase might play a role in modifying normal fibroblasts into cancer associated fibroblasts (CAFs) by upregulating \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{\alpha }$$\end{document}αSMA and Vimentin, two CAF markers. We also show that telomerase activity changes the transcriptome of microRNA in these fibroblasts. By ectopically expressing microRNA 342, one of the top identified microRNAs, we show that it may mediate the proliferative phenotype that these cells acquire upon taking-up exosomal hTERT, providing them with a survival advantage.

TERT-Regulation and Roles in Cancer Formation

Telomerase reverse transcriptase (TERT) is a catalytic subunit of telomerase. Telomerase complex plays a key role in cancer formation by telomere dependent or independent mechanisms. Telomere maintenance mechanisms include complex TERT changes such as gene amplifications, TERT structural variants, TERT promoter germline and somatic mutations, TERT epigenetic changes, and alternative lengthening of telomere. All of them are cancer specific at tissue histotype and at single cell level. TERT expression is regulated in tumors via multiple genetic and epigenetic alterations which affect telomerase activity. Telomerase activity via TERT expression has an impact on telomere length and can be a useful marker in diagnosis and prognosis of various cancers and a new therapy approach. In this review we want to highlight the main roles of TERT in different mechanisms of cancer development and regulation.

The TERT copy number gain is sensitive to telomerase inhibitors in human melanoma

Telomerase reverse transcriptase (TERT) copy number gain is frequently observed in Asian melanoma patients. Here, we explored the correlation between TERT copy number and the effect of telomerase inhibitors in melanoma. A total of 78 melanoma cases were enrolled in the study. The TERT copy number was examined by QuantiGene Plex DNA assay. The sensitivity to telomerase inhibitors was evaluated in cell lines and patient-derived xenograft (PDX) models with or without TERT copy number gain. Among the 78 patients, 33.3% showed TERT copy number gain, and the incidence of this gain in acral melanoma (61.5%) was higher than that in other melanoma subtypes (P=0.02). The telomerase inhibitors 6-thio-2'-deoxyguanosine (6-Thio-dG) and epigallocatechin-3-gallate (EGCG) inhibited cell viability and repressed tumor growth in PDX models with TERT copy number gain. TERT copy number gain is frequently observed in Chinese patients with melanoma. Targeting telomerase may benefit melanoma patients with TERT copy number gain.

Telomerase Biogenesis and Activities from the Perspective of Its Direct Interacting Partners

Telomerase reverse transcriptase (TERT)—the catalytic subunit of telomerase—is reactivated in up to 90% of all human cancers. TERT is observed in heterogenous populations of protein complexes, which are dynamically regulated in a cell type- and cell cycle-specific manner. Over the past two decades, in vitro protein–protein interaction detection methods have discovered a number of endogenous TERT binding partners in human cells that are responsible for the biogenesis and functionalization of the telomerase holoenzyme, including the processes of TERT trafficking between subcellular compartments, assembly into telomerase, and catalytic action at telomeres. Additionally, TERT have been found to interact with protein species with no known telomeric functions, suggesting that these complexes may contribute to non-canonical activities of TERT. Here, we survey TERT direct binding partners and discuss their contributions to TERT biogenesis and functions. The goal is to review the comprehensive spectrum of TERT pro-malignant activities, both telomeric and non-telomeric, which may explain the prevalence of its upregulation in cancer.

Telomeres and telomerase in oncogenesis

Telomeres are located at the ends of chromosomes and protect them from degradation. Suppressing the activity of telomerase, a telomere-synthesizing enzyme, and maintaining short telomeres is a protective mechanism against cancer in humans. In most human somatic cells, the expression of telomerase reverse transcriptase (TERT) is repressed and telomerase activity is inhibited. This leads to the progressive shortening of telomeres and inhibition of cell growth in a process called replicative senescence. Most types of primary cancer exhibit telomerase activation, which allows uncontrolled cell proliferation. Previous research indicates that TERT activation also affects cancer development through activities other than the canonical function of mediating telomere elongation. Recent studies have improved the understanding of the structure and function of telomeres and telomerase as well as key mechanisms underlying the activation of TERT and its role in oncogenesis. These advances led to a search for drugs that inhibit telomerase as a target for cancer therapy. The present review article summarizes the organization and function of telomeres, their role in carcinogenesis, and advances in telomerase-targeted therapy.

Telomerase Biology Associations Offer Keys to Cancer and Aging Therapeutics

BACKGROUND

Although telomerase has potential for age-related disease intervention, the overexpression of telomerase in about 90% of cancers, and in HIV virus reservoirs, cautions against se in anti-aging telomerase therapeutics. While multiple reviews document the canonical function of telomerase for maintenance of telomeres, as well as an increasing numbers of reviews that reveal new non-canonical functions of telomerase, there was no systematic review that focuses on the array of associates of the subunit of Telomerase Reverse transcriptase protein (TERT) as pieces of the puzzle to assemble a picture of the how specific TERT complexes uniquely impact aging and age-related diseases and more can be expected.

METHODS

A structured search of bibliographic data on TERT complexes was undertaken using databases from the National Center for Biotechnology Information Pubmed with extensive access to biomedical and genomic information in order to obtain a unique documented and cited overview of TERT complexes that may uniquely impact aging and age-related diseases.

RESULTS

The TERT associations include proper folding, intracellular TERT transport, metabolism, mitochondrial ROS (Reactive Oxygen Species) regulation, inflammation, cell division, cell death, and gene expression, in addition to the well-known telomere maintenance. While increase of cell cycle inhibitors promote aging, in cancer, the cell cycle check-point regulators are ambushed in favor of cell proliferation, while cytoplasmic TERT protects a cell cycle inhibitor in oxidative stress. The oncogene cMyc regulates gene expression for overexpression of TERT, and reduction of cell cycle inhibitors-the perfect storm for cancer promotion. TERT binds with the oncogene RMRP RNA, and TERT-RMRP function can regulate levels of that oncogene RNA, and TERT in a TBN complex can regulate heterochromatin. Telomerase benefit and novel function in neurology and cardiology studies open new anti- aging hope. GV1001, a 16 amino acid peptide of TERT that associates with Heat Shock Proteins (HSP's), bypasses the cell membrane with remarkable anti disease potential.

CONCLUSIONS

TERT "associates" are anti-cancer targets for downregulation, but upregulation in antiaging therapy. The overview revealed that unique TERT associations that impact all seven pillars of aging identified by the Trans-NIH Geroscience Initiative that influence aging and urge research for appropriate targeted telomerase supplements/ stimulation, and inclusion in National Institute on Aging Intervention Testing Program. The preference for use of available "smart drugs", targeted to only cancer, not off-target anti- aging telomerase is implied by the multiplicity of TERT associates functions.

Mechanisms underlying the activation of TERT transcription and telomerase activity in human cancer: old actors and new players

Long-lived species Homo sapiens have evolved robust protection mechanisms against cancer by repressing telomerase and maintaining short telomeres, thereby delaying the onset of the majority of cancer types until post-reproductive age. Indeed, telomerase is silent in most differentiated human cells, predominantly due to the transcriptional repression of its catalytic component telomerase reverse transcriptase (TERT) gene. The lack of telomerase/TERT expression leads to progressive telomere erosion in dividing human cells, whereas critically shortened telomere length induces a permanent growth arrest stage named replicative senescence. TERT/telomerase activation has been experimentally shown to be essential to cellular immortalization and malignant transformation by stabilizing telomere length and erasing the senescence barrier. Consistently, TERT expression/telomerase activity is detectable in up to 90% of human primary cancers. Compelling evidence has also accumulated that TERT contributes to cancer development and progression via multiple activities beyond its canonical telomere-lengthening function. Given these key roles of telomerase and TERT in oncogenesis, great efforts have been made to decipher mechanisms underlying telomerase activation and TERT induction. In the last two decades since the TERT gene and promoter were cloned, the derepression of the TERT gene has been shown to be achieved typically at a transcriptional level through dysregulation of oncogenic factors or signaling, post-transcriptional/translational regulation and genomic amplification. However, advances in high-throughput next-generation sequencing technologies have prompted a revolution in cancer genomics, which leads to the recent discovery that genomic alterations take center stage in activating the TERT gene. In this review article, we summarize critical mechanisms activating TERT transcription, with special emphases on the contribution of TERT promoter mutations and structural alterations at the TERT locus, and briefly discuss the underlying implications of these genomic events-driven TERT hyperactivity in cancer initiation/progression and potential clinical applications as well.

Telomerase Reverse Transcriptase (TERT) in Action: Cross-Talking with Epigenetics

Telomerase, an RNA-dependent DNA polymerase with telomerase reverse transcriptase (TERT) as the catalytic component, is silent due to the tight repression of the TERT gene in most normal human somatic cells, whereas activated only in small subsets of cells, including stem cells, activated lymphocytes, and other highly proliferative cells. In contrast, telomerase activation via TERT induction is widespread in human malignant cells, which is a prerequisite for malignant transformation. It is well established that TERT/telomerase extends telomere length, thereby conferring sustained proliferation capacity to both normal and cancerous cells. The recent evidence has also accumulated that TERT/telomerase may participate in the physiological process and oncogenesis independently of its telomere-lengthening function. For instance, TERT is shown to interact with chromatin remodeling factors and to regulate DNA methylation, through which multiple cellular functions are attained. In the present review article, we summarize the non-canonical functions of TERT with a special emphasis on its cross-talk with epigenetics: How TERT contributes to epigenetic alterations in physiological processes and cancer, and how the aberrant epigenetics in turn facilitate TERT expression and function, eventually promoting cancer either initiation or progression or both. Finally, we briefly discuss clinical implications of the TERT-related methylation.

Contributory role of microRNAs in anti-cancer effects of small molecule inhibitor of telomerase (BIBR1532) on acute promyelocytic leukemia cell line

Telomerase-mediated immortalization and proliferation of tumor cells is a promising anti-cancer treatment strategy and development of potent telomerase inhibitors is believed to open new window of treatments in human malignancies. In the present study, we found that BIBR1532, a small molecule inhibitor of human telomerase, exerted cytotoxic effects on a panel of human cancer cells spanning from solid tumors to hematologic malignancies; however, as compared with solid tumors, leukemic cells were more sensitive to this inhibitor. This was independent of molecular status of p53 in the leukemic cells. The results of a miRNA PCR array revealed that BIBR1532-induced cytotoxic effects in NB4, the most sensitive cell line, was coupled with alteration in a substantial number of cancer-related miRNAs. Interestingly, most of these miRNAs were found to act as tumor suppressors with validated targets in cell cycle or nuclear factor (NF)-κB-mediated apoptosis. In accordance with a bioinformatics analysis, our experimental studies showed that BIBR1532-induced apoptosis is mediated, at least partly, by inhibition of NF-κB. Moreover, we found that the alteration in the expression of miRNAs was coupled with the alteration in the cell cycle progression. To sum up with, a straightforward interpretation of our results is that telomerase inhibition using BIBR1532 not only induced CDKN1A-mediated G1 arrest in NB4, but also resulted in a caspase-3-dependent apoptotic cell death mostly through suppression of NF-κB axis.

Air pollution-induced placental epigenetic alterations in early life: a candidate miRNA approach

Particulate matter (PM) exposure during in utero life may entail adverse health outcomes in later-life. Air pollution's adverse effects are known to alter gene expression profiles, which can be regulated by microRNAs (miRNAs). We investigate the potential influence of air pollution exposure in prenatal life on placental miRNA expression. Within the framework of the ENVIRONAGE birth cohort, we measured the expression of six candidate miRNAs in placental tissue from 210 mother-newborn pairs by qRT-PCR. Trimester-specific PM_2.5 exposure levels were estimated for each mother's home address using a spatiotemporal model. Multiple regression models were used to study miRNA expression and in utero exposure to PM_2.5 over various time windows during pregnancy. The placental expression of miR-21 (−33.7%, 95% CI: −53.2 to −6.2, P = 0.022), miR-146a (−30.9%, 95% CI: −48.0 to −8.1, P = 0.012) and miR-222 (−25.4%, 95% CI: −43.0 to −2.4, P = 0.034) was inversely associated with PM_2.5 exposure during the 2nd trimester of pregnancy, while placental expression of miR-20a and miR-21 was positively associated with 1st trimester exposure. Tumor suppressor phosphatase and tensin homolog (PTEN) was identified as a common target of the miRNAs significantly associated with PM exposure. Placental PTEN expression was strongly and positively associated (+59.6% per 5 µg/m³ increment, 95% CI: 26.9 to 100.7, P < 0.0001) with 3rd trimester PM_2.5 exposure. Further research is required to establish the role these early miRNA and mRNA expression changes might play in PM-induced health effects. We provide molecular evidence showing that in utero PM_2.5 exposure affects miRNAs expression as well as its downstream target PTEN.

Functional relevance of miRNAs in premature ageing

Ageing is a complex biological process characterized by the progressive loss of biological fitness due to the accumulation of macromolecular and cellular damage that affects most living organisms. Moreover, ageing is an important risk factor for many pathologies, including cardiovascular diseases, neurological disorders, and cancer. However, the ageing rate can be modulated by genetic, nutritional, and pharmacological factors, highlighting the concept of "ageing plasticity". Progeroid syndromes are a group of rare genetic diseases that resemble many characteristics of physiological ageing. Accordingly, studies on these diseases have been very useful for gaining mechanistic insights in ageing biology. In recent years, a great effort has been made in ageing research and several works have confirmed that geromiRs, the growing subgroup of miRNAs implicated in ageing, are able to modulate organismal lifespan. However, very little is still known about the impact of miRNA in premature ageing. In this review, we will address the functional relevance of this class of small non-coding RNAs in the regulation of the hallmarks of progeroid syndromes. In addition, we will discuss the potential strategies for managing progeria based on geromiR modulation.

Telomere Length, TERT, and miRNA Expression

It has been proposed that miRNAs are involved in the control of telomeres. We test that hypothesis by examining the association between miRNAs and telomere length (TL). Additionally, we evaluate if genetic variation in telomerase reverse transcriptase (TERT) is associated with miRNA expression levels. We use data from a population-based study of colorectal cancer (CRC), where we have previously shown associations between TL and TERT and CRC, to test associations between TL and miRNA expression and TERT and miRNA expression. To gain insight into functions of miRNAs associated with TERT we tested linear associations between miRNAs and their targeted gene mRNAs. An Agilent platform that contained information on over 2000 miRNAs was used. TL was measured using a multiplexed quantitative PCR (qPCR). RNAseq was used to assess gene expression. Our sample consisted of 1152 individuals with SNP data and miRNA expression data; 363 individuals with both TL and miRNA; and 148 individuals with miRNA and mRNA data. Thirty-three miRNAs were directly associated with TL after adjusting for age and sex (false discovery rate (FDR) of 0.05). TERT rs2736118 was associated with differences in miRNA expression between carcinoma and normal colonic mucosa for 75 miRNAs (FDR <0.05). Genes regulated by these miRNAs, as indicated by mRNA/miRNA associations, were associated with major signaling pathways beyond their TL-related functions, including PTEN, and PI3K/AKT signaling. Our data support a direct association between miRNAs and TL; differences in miRNA expression levels by TERT genotype were observed. Based on miRNA and targeted mRNA associations our data suggest that TERT is involved in non-TL-related functions by acting through altered miRNA expression.

The role of telomeres and telomerase reverse transcriptase isoforms in pluripotency induction and maintenance

Telomeres are linear guanine-rich DNA structures at the ends of chromosomes. The length of telomeric DNA is actively regulated by a number of mechanisms in highly proliferative cells such as germ cells, cancer cells, and pluripotent stem cells. Telomeric DNA is synthesized by way of the ribonucleoprotein called telomerase containing a reverse transcriptase (TERT) subunit and RNA component (TERC). TERT is highly conserved across species and ubiquitously present in their respective pluripotent cells. Recent studies have uncovered intricate associations between telomeres and the self-renewal and differentiation properties of pluripotent stem cells. Interestingly, the past decade's work indicates that the TERT subunit also has the capacity to modulate mitochondrial function, to remodel chromatin structure, and to participate in key signaling pathways such as the Wnt/β-catenin pathway. Many of these non-canonical functions do not require TERT's catalytic activity, which hints at possible functions for the extensive number of alternatively spliced TERT isoforms that are highly expressed in pluripotent stem cells. In this review, some of the established and potential routes of pluripotency induction and maintenance are highlighted from the perspectives of telomere maintenance, known TERT isoform functions and their complex regulation.