Telomerase activity and telomere length in women with breast cancer or without malignancy: A systematic review and meta-analysis

AIM

We performed a systematic review and meta-analysis to assess whether telomerase activity and telomere length are associated with breast cancer.

METHODS

PubMed, Web of Science, Embase, LILACS, Scielo, Embase, and CNKI databases were searched to obtain relevant articles published through May 10, 2023, following PRISMA guidelines and a registered PROSPERO protocol (CRD42022335402). We included observational studies reporting telomerase activity or telomere length in patients with breast cancer compared with women with benign lesions or normal tissue (control women). The Newcastle-Ottawa Scale was used to evaluate the quality of studies. Data were expressed as odds ratios (OR) and 95 % confidence intervals (CI). Random effects and inverse variance methods were used to meta-analyze associations. The I2 test was used to assess heterogeneity.

RESULTS

The meta-analysis of telomerase shows significantly greater activity in patients with breast cancer than in those without malignancies (OR = 23.46, 95 % CI 14.07-39.11, p < 0.00001, I2 = 72 %). There were non-significant differences in relative telomere length (OR = 1.16, 95 % CI = 0.90-1.49, p = 0.26, I2 = 86 %) and leukocyte telomere length (OR = 2.32, 95 % CI = 0.89-6.08, p = 0.09, I2 = 98 %) between women with and without breast cancer. In subgroup analyses by world regions of studies, both telomerase activity and telomere length displayed the same trends as in their respective meta-analyses. In sensitivity analyses, variables showed their respective same trends.

CONCLUSION

Telomerase activity is higher in patients with breast cancer than in women without malignancies. There were no significant differences in either relative telomere length or leukocyte telomere length in women with and without breast cancer. PROSPERO protocol CRD42022335402.

Telomere biology disorders may manifest as common variable immunodeficiency (CVID)

Telomere biology disorders (TBD) are caused by germline pathogenic variants in genes related to telomere maintenance and are characterized by critically short telomeres. In contrast to classical dyskeratosis congenita (DC), which is typically diagnosed in infancy, adult or late onset TBD frequently lack the typical DC triad and rather show variable organ manifestations and a cryptic disease course, thus complicating its diagnosis. Common variable immunodeficiency (CVID), on the other hand, is a primary antibody deficiency (PAD) syndrome. PADs are a heterogenous group of diseases characterized by hypogammaglobulinemia which occurs due to dysfunctional B lymphocytes and additional autoimmune and autoinflammatory complications. Genetic screening reveals a monogenic cause in a subset of CVID patients (15-35%). In our study, we screened the exomes of 491 CVID patients for the occurrence of TBD-related variants in 13 genes encoding for telomere/telomerase-associated proteins, which had previously been linked to the disease. We found 110/491 patients (22%) carrying 91 rare candidate variants in these 13 genes. Following the American College of Medical Genetics and Genomics (ACMG) guidelines, we classified two variants as benign, two as likely benign, 64 as variants of uncertain significance (VUS), four as likely pathogenic, and one heterozygous variant in an autosomal recessive disease gene as pathogenic. We performed telomere length measurement in 42 of the 110 patients with candidate variants and CVID. Two of these 42 patients showed significantly shorter telomeres compared to controls in both lymphocytes and granulocytes. Following the evaluation of the published literature and the patient's manifestations, we re-classified two VUS as likely pathogenic variants. Thus, 0.5-1% of all CVID patients in our study carry possibly pathogenic variants in telomere/telomerase-associated genes. Our data adds CVID to the broad clinical spectrum of cryptic adult-onset TBD. As the molecular diagnosis greatly impacts patient management and treatment strategies, we advise inclusion of all TBD-associated genes-despite their low prevalence-into the molecular screening of patients with antibody deficiencies.

Spotlight on hTERT Complex Regulation in Cutaneous T-Cell Lymphomas

As a major cancer hallmark, there is a sustained interest in understanding the telomerase contribution to carcinogenesis in order to therapeutically target this enzyme. This is particularly relevant in primary cutaneous T-cell lymphomas (CTCL), a malignancy showing telomerase dysregulation with few investigative data available. In CTCL, we examined the mechanisms involved in telomerase transcriptional activation and activity regulation. We analyzed 94 CTCL patients from a Franco-Portuguese cohort, as well as 8 cell lines, in comparison to 101 healthy controls. Our results showed that not only polymorphisms (SNPs) located at the promoter of human telomerase reverse transcriptase (hTERT) gene (rs2735940 and rs2853672) but also an SNP located within the coding region (rs2853676) could influence CTCL occurrence. Furthermore, our results sustained that the post-transcriptional regulation of hTERT contributes to CTCL lymphomagenesis. Indeed, CTCL cells present a different pattern of hTERT spliced transcripts distribution from the controls, mostly marked by an increase in the hTERT β+ variants proportion. This increase seems to be associated with CTCL development and progression. Through hTERT splicing transcriptome modulation with shRNAs, we observed that the decrease in the α-β+ transcript induced a decrease in the cell proliferation and tumorigenic capacities of T-MF cells in vitro. Taken together, our data highlight the major role of post-transcriptional mechanisms regulating telomerase non canonical functions in CTCL and suggest a new potential role for the α-β+ hTERT transcript variant.

Association between dietary vitamin C and telomere length: A cross-sectional study

Background

Currently, telomere length is known to reflect the replication potential and longevity of cells, and many studies have reported that telomere length is associated with age-related diseases and biological aging. Studies have also shown that vitamin C acts as an oxidant and free radical scavenger to protect cells from oxidative stress and telomere wear, thus achieving anti-aging effects. At present, there are few and incomplete studies on the relationship between vitamin C and telomere length, so this study aims to explore the relationship between vitamin C and telomere length.

Methods

This study used cross-sectional data from the National Health and Nutrition Examination Surveys (NHANES) database from 1999 to 2002, a total of 7,094 participants were selected from all races in the United States. Male participants accounted for 48.2% and female participants accounted for 51.8%. The correlation between vitamin C and telomere length was assessed using a multiple linear regression model, and the effect of dietary vitamin C on telomere length was obtained after adjusting for confounding factors such as age, gender, race, body mass index (BMI), and poverty income ratio (PIR).

Results

This cross-sectional study showed that vitamin C was positively correlated with telomere length, with greater dietary vitamin C intake associated with longer telomeres (β = 0.03, 95% CI: 0.01-0.05, P = 0.003).

Conclusion

This study shows that vitamin C intake is positively correlated with human telomere length, which is of guiding significance for our clinical guidance on people's health care, but our study need to be confirmed by more in-depth and comprehensive other research results.

Noncanonical Role of Telomerase in Regulation of Microvascular Redox Environment With Implications for Coronary Artery Disease

Telomerase reverse transcriptase (TERT) (catalytic subunit of telomerase) is linked to the development of coronary artery disease (CAD); however, whether the role of nuclear vs. mitchondrial actions of TERT is involved is not determined. Dominant-negative TERT splice variants contribute to decreased mitochondrial integrity and promote elevated reactive oxygen species production. We hypothesize that a decrease in mitochondrial TERT would increase _mtDNA damage, promoting a pro-oxidative redox environment. The goal of this study is to define whether mitochondrial TERT is sufficient to maintain nitric oxide as the underlying mechanism of flow-mediated dilation by preserving _mtDNA integrity.Immunoblots and quantitative polymerase chain reaction were used to show elevated levels of splice variants α- and β-deletion TERT tissue from subjects with and without CAD. Genetic, pharmacological, and molecular tools were used to manipulate TERT localization. Isolated vessel preparations and fluorescence-based quantification of _mtH₂O₂ and NO showed that reduction of TERT in the nucleus increased flow induced NO and decreased _mtH₂O₂ levels, while prevention of mitochondrial import of TERT augmented pathological effects. Further elevated _mtDNA damage was observed in tissue from subjects with CAD and initiation of _mtDNA repair mechanisms was sufficient to restore NO-mediated dilation in vessels from patients with CAD. The work presented is the first evidence that catalytically active mitochondrial TERT, independent of its nuclear functions, plays a critical physiological role in preserving NO-mediated vasodilation and the balance of mitochondrial to nuclear TERT is fundamentally altered in states of human disease that are driven by increased expression of dominant negative splice variants.

Triptolide inhibits human telomerase reverse transcriptase by downregulating translation factors SP1 and c-Myc in Epstein-Barr virus-positive B lymphocytes

Epstein-Barr virus (EBV) mainly causes infectious mononucleosis and is associated with several neoplasms, including Burkitt's lymphoma, nasopharyngeal carcinoma and lymphoproliferative disease. Human telomerase reverse transcriptase (hTERT) regulates enzymatic activity of telomerase and is closely associated with tumorigenesis and senescence evasion. Triptolide (TP) is a diterpenoid triepoxide, with a broad-spectrum anticancer and immunosuppressive bioactivity profile. The present study investigated whether TP inhibited hTERT expression and suppressed its activity. The mRNA and protein levels of hTERT were examined by reverse transcription-quantitative PCR and western blotting. The activity of hTERT promoter was determined by dual-luciferase reporter assay. Cell Counting Kit-8 assays were performed to analyze cell proliferation. The present study used EBV-positive B lymphoma cells as a model system, and the results demonstrated that TP significantly decreased hTERT transcription and protein expression. Mechanistically, TP attenuated the hTERT promoter activity by downregulating the expression levels of specificityprotein 1 and c-Myc transcription factors. Consistently, inhibition of hTERT via shRNA transfection efficiently enhanced the suppression of cell proliferation by TP. Furthermore, TP increased virus latent replication and promoted the lytic cycle of EBV in EBV-positive B lymphoma cells, increasing the number of lytic cells and inhibiting the viability of tumor cells. Taken together, the results of the present study revealed a molecular mechanism of the pharmacological inhibition of tumor cell proliferation by TP, encouraging the translation of TP-based therapeutics in EBV-positive B lymphoma treatment.

Stress signaling and cellular proliferation reverse the effects of mitochondrial mistranslation

Translation fidelity is crucial for prokaryotes and eukaryotic nuclear-encoded proteins; however, little is known about the role of mistranslation in mitochondria and its potential effects on metabolism. We generated yeast and mouse models with error-prone and hyper-accurate mitochondrial translation, and found that translation rate is more important than translational accuracy for cell function in mammals. Specifically, we found that mitochondrial mistranslation causes reduced overall mitochondrial translation and respiratory complex assembly rates. In mammals, this effect is compensated for by increased mitochondrial protein stability and upregulation of the citric acid cycle. Moreover, this induced mitochondrial stress signaling, which enables the recovery of mitochondrial translation via mitochondrial biogenesis, telomerase expression, and cell proliferation, and thereby normalizes metabolism. Conversely, we show that increased fidelity of mitochondrial translation reduces the rate of protein synthesis without eliciting a mitochondrial stress response. Consequently, the rate of translation cannot be recovered and this leads to dilated cardiomyopathy in mice. In summary, our findings reveal mammalian-specific signaling pathways that respond to changes in the fidelity of mitochondrial protein synthesis and affect metabolism.

Therapeutic strategies for targeting telomerase in cancer

Telomere and telomerase play important roles in abnormal cell proliferation, metastasis, stem cell maintenance, and immortalization in various cancers. Therefore, designing of drugs targeting telomerase and telomere is of great significance. Over the past two decades, considerable knowledge regarding telomere and telomerase has been accumulated, which provides theoretical support for the design of therapeutic strategies such as telomere elongation. Therefore, the development of telomere-based therapies such as nucleoside analogs, non-nucleoside small molecules, antisense technology, ribozymes, and dominant negative human telomerase reverse transcriptase are being prioritized for eradicating a majority of tumors. While the benefits of telomere-based therapies are obvious, there is a need to address the limitations of various therapeutic strategies to improve the possibility of clinical applications. In this study, current knowledge of telomere and telomerase is discussed, and therapeutic strategies based on recent research are reviewed.

Telomeres, Telomerase and Ageing

Telomeres are specialised structures at the end of linear chromosomes. They consist of tandem repeats of the hexanucleotide sequence TTAGGG, as well as a protein complex called shelterin. Together, they form a protective loop structure against chromosome fusion and degradation. Shortening or damage to telomeres and opening of the loop induce an uncapped state that triggers a DNA damage response resulting in senescence or apoptosis.Average telomere length, usually measured in human blood lymphocytes, was thought to be a biomarker for ageing, survival and mortality. However, it becomes obvious that regulation of telomere length is very complex and involves multiple processes. For example, the "end replication problem" during DNA replication as well as oxidative stress are responsible for the shortening of telomeres. In contrast, telomerase activity can potentially counteract telomere shortening when it is able to access and interact with telomeres. However, while highly active during development and in cancer cells, the enzyme is down-regulated in most human somatic cells with a few exceptions such as human lymphocytes. In addition, telomeres can be transcribed, and the transcription products called TERRA are involved in telomere length regulation.Thus, telomere length and their integrity are regulated at many different levels, and we only start to understand this process under conditions of increased oxidative stress, inflammation and during diseases as well as the ageing process.This chapter aims to describe our current state of knowledge on telomeres and telomerase and their regulation in order to better understand their role for the ageing process.

Vitamin D status and its management for achieving optimal health benefits in the elderly

INTRODUCTION

Vitamin D deficiency is common, world-wide, but vitamin D repletion throughout life, and into older age, has accepted health benefits for bone. Many mechanisms through which vitamin D also benefits soft tissues are understood, and clinical evidence of such benefits is now accumulating, especially following re-analyses of trial data, which are revealing previously missed health benefits with correction of deficiency.

AREAS COVERED

The sources of vitamin D, its activation, mechanistic effects; problems of trials of supplementation for reducing health risks, the benefits shown for mortality, cardiovascular disease, infection and cancer; the global problem of vitamin D deficiency; age-related reductions in vitamin D efficacy, and currently recommended intakes.

EXPERT COMMENTARY

High prevalence of vitamin D deficiency and insufficiency worldwide have proven ill-effects on health. Governmental efforts to improve population repletion by recommending minimal daily intakes does benefit some but is not effective at the population-level. However, food fortification with vitamin D3, already implemented in some countries, can solve this highly avoidable problem cost-effectively and is probably the best way to abolish vitamin D inadequacy, allowing public health benefits to emerge over time, thereby allowing future research on vitamin D to be directed at emerging issues on vitamin D.

Telomerase level increase is related to n-3 polyunsaturated fatty acid efficacy in first episode schizophrenia: Secondary outcome analysis of the OFFER randomized clinical trial

Schizophrenia is associated with shortening of the lifespan mainly due to cardiovascular events, cancer and chronic obstructive pulmonary disease. Both telomere attrition and decrease of telomerase levels were observed in schizophrenia. Polyunsaturated fatty acids (PUFA) influence multiple biochemical mechanisms which are postulated to accelerate telomere shortening and limit the longevity of patients with schizophrenia. Intervention studies based on add-on therapy with n-3 polyunsaturated fatty acids (n-3 PUFA) in patients with schizophrenia did not assess the changes in telomerase levels. A randomized placebo-controlled trial named OFFER was designed to compare the efficacy of a 26-week intervention composed of either 2.2g/day of n-3 PUFA or olive oil placebo with regard to symptom severity in first-episode schizophrenia patients. The secondary outcome measure of the study was to describe the association between the clinical effect of n-3 PUFA and changes in telomerase levels. Seventy-one patients aged 16-35 were enrolled in the study and randomly assigned to the study arms. The Positive and Negative Syndrome Scale (PANSS) was used to assess the change in symptom severity. Telomerase levels of peripheral blood mononuclear cells (PBMC) were assessed at three points: at baseline and at weeks 8 and 26 of the intervention. A significantly greater increase in PBMC telomerase levels in the intervention group compared to placebo was observed (p<0.001). Changes in telomerase levels significantly and inversely correlated with improvement in depressive symptoms and severity of the illness. The efficacy of a six-month intervention with n-3 PUFA observed in first-episode schizophrenia may be related to an increase in telomerase levels.

Alternative splicing of human telomerase reverse transcriptase in gliomas and its modulation mediated by CX-5461

Background

Glioma is a heterogeneous, invasive primary brain tumor with a wide range of patient survival and a lack of reliable prognostic biomarkers. Human telomerase reverse transcriptase (hTERT) has been reported in the presence of multiple transcripts in various tumor systems. The biological function and precise regulatory mechanisms of hTERT transcripts remain uncertain.

Methods

Alternative splicing of hTERT and telomerase activity were examined in 96 glioma specimens, including 38 glioblastomas (GBMs), 23 oligodendrogliomas (ODMs), and 35 oligoastrocytomas (OAMs). The correlation between telomerase activity or hTERT transcripts and patient clinical characteristics was investigated. We examined the regulation of alternative splicing of hTERT and telomerase activity by G-quadruplex stabilizer CX-5461 in GBM cells. The biological effects of CX-5461 on GBM cell lines, including inhibition of cell proliferation, effects on cell cycle/apoptosis, and telomere DNA damage were further explored.

Results

The β splicing was verified in human gliomas and hTERT+β was significantly correlated with higher telomerase activity, higher KPS, larger tumor size, and higher tumor grades. Meanwhile, glioma patients lacking hTERT+β expression or telomerase activity showed a significant survival benefit. Notably, CX-5461 altered hTERT splicing patterns, leading to an increase of hTERT-β transcript and a decrease of hTERT+β transcript expression, which inhibits telomerase activity. In addition, CX-5461 had cytotoxic effects on GBM cells and caused telomere DNA damage response, induced G2/M arrest and apoptosis.

Conclusions

The hTERT+β is verified to be correlated with clinical parameters in gliomas, and could serve as a prognostic marker or possibly therapeutic target for gliomas. CX-5461 can regulate the splicing pattern of hTERT, inhibit telomerase activity, and kill GBM cells.

The impact of pathogen burden on leukocyte telomere length in the Multi-Ethnic Study of Atherosclerosis

Several infections have been linked to telomere shortening and in some cases these associations have varied by sex. We assessed the association between seropositivity to four persistent pathogens (cytomegalovirus (CMV), herpes simplex virus-1, Helicobacter pylori, Chlamydia pneumoniae), and total pathogen burden on leukocyte telomere length in a diverse US sample. Data came from the Multi-Ethnic Study of Atherosclerosis, a population-based cohort study. We utilized cross-sectional survey data, and biological samples from participants tested for pathogens and telomere length (N = 163). Linear regression was used to examine the association between seropositivity for individual pathogens as well as total pathogen burden and telomere length, adjusting for various confounders. CMV seropositivity and increased total pathogen burden level were significantly associated with shorter telomere length among females (β = -0·1204 (standard error (s.e.) 0·06), P = 0·044) and (β = -0·1057 (s.e. = 0·05), P = 0·033), respectively. There was no statistically significant association among males. Our findings suggest that prevention or treatment of persistent pathogens, in particular CMV, may play an important role in reducing telomere shortening over the life course among women. Future research is needed to confirm these novel findings in larger longitudinal samples.

Implications of telomeres and telomerase in endometrial pathology

BACKGROUND

Eukaryotic chromosomal ends are linear and are protected by nucleoprotein complexes known as telomeres. The complex structural anatomy and the diverse functions of telomeres as well as the unique reverse transcriptase enzyme, telomerase that maintains telomeres are under intensive scientific scrutiny. Both are involved in many human diseases including cancer, but also in ageing and chronic disease such as diabetes. Their intricate involvement in many cellular processes and pathways is being dynamically deciphered in many organs including the endometrium. This review summarizes our current knowledge on the topic of telomeres and telomerase and their potential role in providing plausible explanations for endometrial aberrations related to common gynaecological pathologies.

OBJECTIVE AND RATIONALE

This review outlines the recent major findings in telomere and telomerase functions in the context of endometrial biology. It highlights the contemporary discoveries in hormonal regulation, normal endometrial regeneration, stem cells and common gynaecological diseases such as endometriosis, infertility, recurrent reproductive failure and endometrial cancer (EC).

SEARCH METHODS

The authors carried out systematic PubMed (Medline) and Ovid searches using the key words: telomerase, telomeres, telomere length, human telomerase reverse transcriptase, telomeric RNA component, with endometrium, hormonal regulation, endometrial stem/progenitor cells, endometrial regeneration, endometriosis, recurrent miscarriage, infertility, endometrial hyperplasia, EC and uterine cancer. Publications used in this review date from 1995 until 31st June 2016.

OUTCOMES

The human endometrium is a unique somatic organ, which displays dynamic telomerase activity (TA) related to the menstrual cycle. Telomerase is implicated in almost all endometrial pathologies and appears to be crucial to endometrial stem cells. In particular, it is vital for normal endometrial regeneration, providing a distinct route to formulate possible curative, non-hormonal therapies to treat chronic endometrial conditions. Furthermore, our current understanding of telomere maintenance in EC is incomplete. Data derived from other malignancies on the role of telomerase in carcinogenesis cannot be extrapolated to EC because unlike in other cancers, TA is already present in proliferating healthy endometrial cells.

WIDER IMPLICATIONS

Since telomerase is pivotal to endometrial regeneration, further studies elucidating the role of telomeres, telomerase, their associated proteins and their regulation in normal endometrial regeneration as well as their role in endometrial pathologies are essential. This approach may allow future development of novel treatment strategies that are not only non-hormonal but also potentially curative.

Targeting telomerase and telomeres to enhance ionizing radiation effects in in vitro and in vivo cancer models

One of the hallmarks of cancer consists in the ability of tumor cells to divide indefinitely, and to maintain stable telomere lengths throughout the activation of specific telomere maintenance mechanisms (TMM). Therefore in the last fifteen years, researchers proposed to target telomerase or telomeric structure in order to block limitless replicative potential of cancer cells providing a fascinating strategy for a broad-spectrum cancer therapy. In the present review, we report in vitro and in vivo evidence regarding the use of chemical agents targeting both telomerase or telomere structure and showing promising antitumor effects when used in combination with ionizing radiation (IR). RNA interference, antisense oligonucleotides (e.g., GRN163L), non-nucleoside inhibitors (e.g., BIBR1532) and nucleoside analogs (e.g., AZT) represent some of the most potent strategies to inhibit telomerase activity used in combination with IR. Furthermore, radiosensitizing effects were demonstrated also for agents acting directly on the telomeric structure such as G4-ligands (e.g., RHPS4 and Telomestatin) or telomeric-oligos (T-oligos). To date, some of these compounds are under clinical evaluation (e.g., GRN163L and KML001). Advantages of Telomere/Telomerase Targeting Compounds (T/TTCs) coupled with radiotherapy may be relevant in the treatment of radioresistant tumors and in the development of new optimized treatment plans with reduced dose adsorbed by patients and consequent attenuation of short- end long-term side effects. Pros and cons of possible future applications in cancer therapy based on the combination of T/TCCs and radiation treatment are discussed.

TERT promoter mutations in telomere biology

Telomere repeats at chromosomal ends, critical to genome integrity, are maintained through an elaborate network of proteins and pathways. Shelterin complex proteins shield telomeres from induction of DNA damage response to overcome end protection problem. A specialized ribonucleic protein, telomerase, maintains telomere homeostasis through repeat addition to counter intrinsic shortcomings of DNA replication that leads to gradual sequence shortening in successive mitoses. The biogenesis and recruitment of telomerase composed of telomerase reverse transcriptase (TERT) subunit and an RNA component, takes place through the intricate machinery that involves an elaborate number of molecules. The synthesis of telomeres remains a controlled and limited process. Inherited mutations in the molecules involved in the process directly or indirectly cause telomeropathies. Telomerase, while present in stem cells, is deactivated due to epigenetic silencing of the rate-limiting TERT upon differentiation in most of somatic cells with a few exceptions. However, in most of the cancer cells telomerase reactivation remains a ubiquitous process and constitutes one of the major hallmarks. Discovery of mutations within the core promoter of the TERT gene that create de novo binding sites for E-twenty-six (ETS) transcription factors provided a mechanism for cancer-specific telomerase reactivation. The TERT promoter mutations occur mainly in tumors from tissues with low rates of self-renewal. In melanoma, glioma, hepatocellular carcinoma, urothelial carcinoma and others, the promoter mutations have been shown to define subsets of patients with adverse disease outcomes, associate with increased transcription of TERT, telomerase reactivation and affect telomere length; in stem cells the mutations inhibit TERT silencing following differentiation into adult cells. The TERT promoter mutations cause an epigenetic switch on the mutant allele along with recruitment of pol II following the binding of GABPA/B1 complex that leads to mono-allelic expression. Thus, the TERT promoter mutations hold potential as biomarkers as well as future therapeutic targets.

Telomerase Activation in Hematological Malignancies

Telomerase expression and telomere maintenance are critical for cell proliferation and survival, and they play important roles in development and cancer, including hematological malignancies. Transcriptional regulation of the rate-limiting subunit of human telomerase reverse transcriptase gen (hTERT) is a complex process, and unveiling the mechanisms behind its reactivation is an important step for the development of diagnostic and therapeutic applications. Here, we review the main mechanisms of telomerase activation and the associated hematologic malignancies.

Association Between Human Telomerase Reverse Transcriptase Gene Variations and Risk of Developing Breast Cancer

BACKGROUND

Despite a reduction in the number of deaths from cancers made possible by the development of early detection tests, improvements in treatment, changes in the age distribution of the population, and changes of personal behaviors as a result of awareness, breast cancer remains a major health problem worldwide. Breast cancer is the most common cancer and second leading cause of cancer death in women. Several genetic and environmental factors are known to be involved in breast cancer pathogenesis, but its exact etiology is complicated and is not clearly identified. The structure and integrity of telomeres are pivotal for genome stability, and telomere length is maintained by the expression of the telomerase enzyme. The human telomerase reverse transcriptase (hTERT) gene is a principal functional subunit of the telomerase. Several recent studies have provided evidence that hTERT gene variants may have an important role in cancer development.

METHODS

Three hTERT variants (rs2736100, rs2736098, and rs2853669) were genotyped for 107 breast cancer patients and 110 healthy controls to determine their effect on breast cancer susceptibility.

RESULTS

It was observed that hTERT rs2736098 was associated with breast cancer risk (odds ratio [OR] = 1.88; p = 0.034), while rs2736100 and rs2853669 did not significantly differ between the groups.

CONCLUSIONS

These findings are the first description of hTERT allele distributions in the Turkish population and may contribute to our understanding of breast cancer development. Nevertheless, further large-scale population studies are needed to understand the role of the hTERT polymorphisms and haplotypes in the development of breast cancer.

Role of GLTSCR2 in the regulation of telomerase activity and chromosome stability

Telomerase is essential for regulating telomeres, and its activation is a critical step in cellular immortalization and tumorigenesis. The transcriptional activation of human telomerase reverse transcriptase (hTERT) is critical for telomerase expression. Although several transcriptional activators have been identified, factors responsible for enhancing the hTERT promoter remain to be fully elucidated. In the present study, the role of glioma tumor-suppressor candidate region gene 2 (GLTSCR2) in telomerase regulation was analyzed. A doxycyclin-inducible green fluorescent protein (GFP)-tagged GLTSCR2-expressing adenovirus (Ad‑GLT/GFP) was used for the transduction of SK‑Hep‑1 and T98G cancer cells, and normal human umbilical vein endothelial cells. Changes in telomerase activity using telomere repeat amplification protocol assay were assessed, and the gene expression levels of hTERT were then examined. To investigate chromosome instability and senescence, Giemsa and β-galactosidase staining was performed. The results revealed that overexpression of GLTSCR2 significantly increased telomerase activity in the cancer and normal cell lines. This increase was consistent with increases in the protein and mRNA expression levels of hTERT. In luciferase assays, the hTERT promoter was activated by GLTSCR2. Knockdown of GLTSCR2 led to the downregulation of telomerase activity, abnormal nuclear morphology as a marker of chromosome instability, significant suppression of growth rate, alterations in cellular morphology and, eventually, cellular senescence. Taken together, the results of the present study suggested that GLTSCR2 is crucially involved in the positive regulation of telomerase and chromosome stability.

Telomerase activity and its association with psychological stress, mental disorders, lifestyle factors and interventions: A systematic review

OBJECTIVE

To summarise and discuss the association between telomerase activity and psychological stress, mental disorders and lifestyle factors.

METHOD

A systematic review was carried out to identify prospective or retrospective studies and interventions published up to June 2015 that reported associations between telomerase activity and psychological stress, mental disorders and lifestyle factors. Electronic data bases of PubMed, ProQuest, CINAHL and Google Scholar were searched.

RESULTS

Twenty six studies on humans measured telomerase activity in peripheral blood mononuclear cells (PBMCs) or leukocytes and examined its association with psychological stress, mental disorders and lifestyle factors. Of those studies, three reported significantly decreased telomerase activity in individuals under chronic psychological stress. Interestingly, one of the three studies found that acute laboratory psychological stress significantly increased telomerase activity. Nine studies reported mixed results on association between mental disorders and telomerase activity. Of the nine studies, five reported that major depressive disorder (MDD) was associated with significantly increased telomerase activity. In thirteen out of fourteen studies on lifestyle factors, it was reported that physical exercise, diet micronutrient supplementation, mindfulness meditation, Qigong practice or yoga mediation resulted in increase in telomerase activity. In addition, two studies on animal models showed that depression-like behaviour was associated with decreased hippocampus telomerase activity. Five animal studies showed that physical exercise increased telomerase activity by cell-type-specific and genotype-specific manners.

CONCLUSION

Although multi-facet results were reported on the association between telomerase activity and psychological stress, mental disorders and lifestyle factors, there were some consistent findings in humans such as (1) decreased telomerase activity in individuals under chronic stress, (2) increased telomerase activity in individuals with MDD, and (3) increased telomerase activity in individuals under lifestyle interventions. Animal studies showed that physical exercise increased telomerase activity in specific cell-types. However, the exact mechanisms for the changes in telomerase activity have not been elucidated. We propose conglomerate models connecting chronic psychological stress, depression, mediation and physical exercise to telomerase activation. Several areas for future research are suggested.

Synthetic Bax-Anti Bcl2 combination module actuated by super artificial hTERT promoter selectively inhibits malignant phenotypes of bladder cancer

BACKGROUND

The synthetic biology technology which enhances the specificity and efficacy of treatment is a novel try in biomedical therapy during recent years. A high frequency of somatic mutations was shown in the human telomerase reverse transcriptase (hTERT) promoter in bladder cancer, indicating that a mutational hTERT promoter might be a tumor-specific element for bladder cancer therapy. In our study, we aimed to construct a synthetic combination module driven by a super artificial hTERT promoter and to investigate its influence on the malignant phenotypes of bladder cancer.

METHODS

The dual luciferase assay system was used to verify the driven efficiency and tumor-specificity of the artificial hTERT promoter and to confirm the relationship between ETS-1 and the driven efficiency of the artificial hTERT promoter. CCK-8 assay and MTT assay were used to test the effects of the Bax-Anti Bcl2 combination module driven by the artificial hTERT promoter on cell proliferation. Simultaneously, the cell apoptosis was detected by the caspase 3ELISA assay and the flow cytometry analysis after transfection. The results of CCK-8 assay and MTT assay were analyzed by ANOVA. The independent samples t-test was used to analyze other data.

RESULTS

We demonstrated that the artificial hTERT promoter had a higher driven efficiency which might be regulated by transcription factor ETS-1 in bladder cancer cells, compared with wild-type hTERT promoter. Meanwhile, the artificial hTERT promoter showed a strong tumor-specific effect. The cell proliferation inhibition and apoptosis induction were observed in artificial hTERT promoter- Bax-Anti Bcl2 combination module -transfected bladder cancer 5637 and T24 cells, but not in the module -transfected normal human fibroblasts.

CONCLUSION

This module offers us a useful synthetic biology platform to inhibit the malignant phenotypes of bladder cancer in a more specific and effective way.

Triptolide inhibits transcription of hTERT through down-regulation of transcription factor specificity protein 1 in primary effusion lymphoma cells

Primary effusion lymphoma (PEL) is a rare and aggressive non-Hodgkin's lymphoma. Human telomerase reverse transcriptase (hTERT), a key component responsible for the regulation of telomerase activity, plays important roles in cellular immortalization and cancer development. Triptolide purified from Tripterygium extracts displays a broad-spectrum bioactivity profile, including immunosuppressive, anti-inflammatory, and anti-tumor. In this study, it is investigated whether triptolide reduces hTERT expression and suppresses its activity in PEL cells. The mRNA and protein levels of hTERT were examined by real time-PCR and Western blotting, respectively. The activity of hTERT promoter was determined by Dual luciferase reporter assay. Our results demonstrated that triptolide decreased expression of hTERT at both mRNA and protein levels. Further gene sequence analysis indicated that the activity of hTERT promoter was suppressed by triptolide. Triptolide also reduced the half-time of hTERT. Additionally, triptolide inhibited the expression of transcription factor specificity protein 1(Sp1) in PEL cells. Furthermore, knock-down of Sp1 by using specific shRNAs resulted in down-regulation of hTERT transcription and protein expression levels. Inhibition of Sp1 by specific shRNAs enhanced triptolide-induced cell growth inhibition and apoptosis. Collectively, our results demonstrate that the inhibitory effect of triptolide on hTERT transcription is possibly mediated by inhibition of transcription factor Sp1 in PEL cells.

Silencing of protein kinase D2 induces glioma cell senescence via p53-dependent and -independent pathways

Background

Glioblastoma multiforme (GBM) is a highly aggressive tumor of the central nervous system with a dismal prognosis for affected patients. Aberrant protein kinase C (PKC) signaling has been implicated in gliomagenesis, and a member of the PKC-activated protein kinase D (PRKD) family, PRKD2, was identified as mediator of GBM growth in vitro and in vivo.

Methods

The outcome of PRKD2 silencing and pharmacological inhibition on glioma cell proliferation was established with different glioma cell lines. Western blotting, senescence assays, co-immunoprecipitation, fluorescence activated cell sorting, quantitative PCR, and immunofluorescence microscopy were utilized to analyze downstream signaling.

Results

RNA-interference (21-mer siRNA) and pharmacological inhibition (CRT0066101) of PRKD2 profoundly inhibited proliferation of p53^wt (U87MG, A172, and primary GBM2), and p53^mut (GM133, T98G, U251, and primary Gli25) glioma cells. In a xenograft experiment, PRKD2 silencing significantly delayed tumor growth of U87MG cells. PRKD2 silencing in p53^wt and p53^mut cells was associated with typical hallmarks of senescence and cell cycle arrest in G1. Attenuated AKT/PKB phosphorylation in response to PRKD2 silencing was a common observation made in p53^wt and p53^mut GBM cells. PRKD2 knockdown in p53^wt cells induced upregulation of p53, p21, and p27 expression, decreased phosphorylation of CDK2 and/or CDK4, hypophosphorylation of retinoblastoma protein (pRb), and reduced transcription of E2F1. In p53^mut GM133 and primary Gli25 cells, PRKD2 silencing increased p27 and p15 and reduced E2F1 transcription but did not affect pRb phosphorylation.

Conclusions

PRKD2 silencing induces glioma cell senescence via p53-dependent and -independent pathways.

Mutations in TERT promoter and FGFR3 and telomere length in bladder cancer

Mutations in the promoter of the telomerase reverse transcriptase (TERT) and fibroblast growth factor receptor 3 (FGFR3) genes constitute the most recurrent somatic alterations in urothelial carcinoma of bladder. In this study, we screened DNA from 327 urothelial bladder carcinomas from well-documented patients, with different stages and grades and known TERT promoter mutational status, for FGFR3 alterations and measured relative telomere length (RTL). Although, the frequency of the TERT promoter mutations was higher than those in FGFR3; however, the alterations at the two loci occurred together more frequently than per chance [Odds ratio (OR) = 4.93, 95% CI = 2.72-8.92, p < 0.0001]. While tumors with TERT promoter and FGFR3 mutations had shorter RTL than those without mutations (p < 0.0001), the TERT promoter mutations in conjunction with the common allele of the rs2853669 polymorphism defined sub-group of patients with an observed decreased overall survival (OR = 2.15, 95% CI = 1.00-4.61) and increased recurrence in patients with TaG1+TaG2 disease categories (OR = 3.68, 95%CI = 1.12-12.05). The finding of shorter telomeres in tumors with TERT promoter and/or FGFR3 mutations than without mutations implies mechanistic relevance of telomere biology in cancer progression. The observed association with recurrence and survival shows that the TERT promoter mutations can potentially be used as markers to refine selection of patients for different treatments. The overwhelming frequency of the TERT promoter mutations also represents a case for development of an eventual therapeutic target.

Synthetic miRNA sponges driven by mutant hTERT promoter selectively inhibit the progression of bladder cancer

The mutant promoter of human telomerase reverse transcriptase (hTERT) shows high transcriptional activity in bladder cancer cells. Some up-regulated microRNAs (miRNAs) are reported as oncogenic factors in bladder cancer. Previous studies report that miRNAs can be inhibited by base-pairing interactions. The purpose of this study is to construct a synthetic device driven by mutant hTERT promoter to suppress four up-regulated miRNAs and to verify its effects on phenotypes of bladder cancer cells and human normal cells. Tandem bulged miRNA binding sites targeting oncogenic miRNAs were inserted into the 3' untranslated region (3' UTR) of mutant hTERT promoter-driven Renilla luciferase gene to construct a synthetic tumor-specific device, miRNA sponges. A negative control was generated by using tandem repeated sequences without targeting any known miRNA. Bladder cancer cells (T24, 5637, UM-UC-3) and human fiber cells (HFC) were transfected with devices. Various functional assays were used to detect the effects of this device. The activity of the mutant hTERT promoter detected by luciferase assay was about three times as large as the wild-type hTERT promoter in bladder cancer cells, while it could not be measured in HFC. Other assays indicated that the synthetic device can significantly inhibit cell growth, decrease motility, and induce apoptosis in bladder cancer cells but not in HFC. A synthetic biology platform is employed to construct tumor-specific miRNA sponges that can be used to target oncogenic miRNAs to inhibit the progression of bladder cancer cells without affecting normal cells.

Telomere length in blood cells is related to the chronicity, severity, and recurrence rate of schizophrenia

INTRODUCTION

Telomere shortening is strongly associated with higher mortality rates and has been shown in a number of age-related diseases, such as cardiovascular disorders, diabetes mellitus, Alzheimer's disease, and psychiatric disorders. Oxidative stress is known to induce DNA breaks and genome instability. Telomeric DNA rich in guanosine is particularly sensitive to such oxidative damages. Psychosis is associated with a disequilibrium between free radical production and antioxidative defense. Although telomere attrition has been demonstrated in schizophrenia, no relationship has been reported between telomere length and severity of schizophrenia.

AIM

The aim of the present study was to identify differences in telomere length in peripheral blood cells between patients with chronic schizophrenia (C-SCZ) and early schizophrenia (E-SCZ) and to identify any relationship between telomere length and disease chronicity and severity.

METHODS

Relative average telomere lengths were determined using qPCR assay in patients with E-SCZ (n=42) and C-SCZ (n=44) hospitalized due to schizophrenia exacerbation. E-SCZ was diagnosed when less than 2 years had passed since the beginning of psychotic symptoms. The severity of symptoms was assessed using appropriate scales.

RESULTS

The severity of schizophrenia symptoms, as well as the number of psychotic episodes and hospital admissions, correlated significantly with telomere length in univariate analyses. Regression analysis revealed that a model incorporating study group (E-SCZ or C-ECZ), sex, and age, as well as the combined number of documented psychotic episodes and hospital admissions, can significantly predict the length of telomeres in patients with schizophrenia, with over 50% of variance in telomere length explained by the model (adjusted R (2)=0.512).

CONCLUSION

The results of the current study indicate that the recurrence of psychotic symptoms as well as their intensity and chronicity may be correlated with telomere attrition, which is well known to contribute to the development of premature senescence and age-related diseases.

Telomeres and telomerase in T cells of tumor immunity

Telomeres are specific nucleoprotein structures at the end of a eukaryotic chromosomes characterized by repeats of the sequence TTAGGG and regulated by the enzyme telomerase which prevents their degradation, loss, rearrangement and end-to-end fusion. During activation, T lymphocytes actively divide, albeit through only a finite number of cell divisions due to shortening of telomeres. However, studies have demonstrated that human telomerase reverse transcriptase (hTERT), thought to be the major component regulating telomerase activity, can enhance the proliferation of T cells when overexpressed. There are many treatments for cancers, most of which are targeting the telomere and telomerase of tumor cells. However, the hTERT-transduced T cells improve their potential for proliferation, making them an appropriate cell resource for tumor adoptive immunotherapy, a procedure whereby T cells are isolated from patients, expanded ex vivo and eventually delivered back into the patients, provides a new approach for tumor therapy through improved overall survival rates in cancer patients. In this review, we will focus on the telomerase activity in T cells, the regulation of telomerase activity, and hTERT-transduced T cells used in adoptive immunotherapy for cancer.

Telomere and telomerase biology

Telomeres are the physical ends of eukaryotic linear chromosomes. Telomeres form special structures that cap chromosome ends to prevent degradation by nucleolytic attack and to distinguish chromosome termini from DNA double-strand breaks. With few exceptions, telomeres are composed primarily of repetitive DNA associated with proteins that interact specifically with double- or single-stranded telomeric DNA or with each other, forming highly ordered and dynamic complexes involved in telomere maintenance and length regulation. In proliferative cells and unicellular organisms, telomeric DNA is replicated by the actions of telomerase, a specialized reverse transcriptase. In the absence of telomerase, some cells employ a recombination-based DNA replication pathway known as alternative lengthening of telomeres. However, mammalian somatic cells that naturally lack telomerase activity show telomere shortening with increasing age leading to cell cycle arrest and senescence. In another way, mutations or deletions of telomerase components can lead to inherited genetic disorders, and the depletion of telomeric proteins can elicit the action of distinct kinases-dependent DNA damage response, culminating in chromosomal abnormalities that are incompatible with life. In addition to the intricate network formed by the interrelationships among telomeric proteins, long noncoding RNAs that arise from subtelomeric regions, named telomeric repeat-containing RNA, are also implicated in telomerase regulation and telomere maintenance. The goal for the next years is to increase our knowledge about the mechanisms that regulate telomere homeostasis and the means by which their absence or defect can elicit telomere dysfunction, which generally results in gross genomic instability and genetic diseases.

TERT promoter mutations in cancer development

Human telomerase reverse transcriptase (TERT) encodes a rate-limiting catalytic subunit of telomerase that maintains genomic integrity. TERT expression is mostly repressed in somatic cells with exception of proliferative cells in self-renewing tissues and cancer. Immortality associated with cancer cells has been attributed to telomerase over-expression. The precise mechanism behind the TERT activation in cancers has mostly remained unknown. The newly described germline and recurrent somatic mutations in melanoma and other cancers in the TERT promoter that create de novo E-twenty six/ternary complex factors (Ets/TCF) binding sites, provide an insight into the possible cause of tumor-specific increased TERT expression. In this review we discuss the discovery and possible implications of the TERT promoter mutations in melanoma and other cancers.

Telomerase downregulation induces proapoptotic genes expression and initializes breast cancer cells apoptosis followed by DNA fragmentation in a cell type dependent manner

The aim of the study was to analyze the consequence of silencing genes coding for the key subunits of the telomerase complex, i.e. TERT, TERC and TP1 in human breast cancer MCF7 and MDA-MB-231cells. The transfection was performed using Lipofectamine2000 and pooled siRNAs. The cytotoxic and/or antiproliferative effect of siRNA was measured by the SRB assay, the cell cycle was analysed by flow cytometry and DNA fragmentation by TUNEL analysis. Telomerase activity was assessed by TRAP, followed by PAGE and ELISA assays. Telomerase downregulation was also assessed using qPCR in order to estimate the changes in the expression profile of genes engaged in apoptosis. It was revealed that treatment of breast cancer cells with different siRNAs (100 nM) resulted in a cell type and time-dependent effects. The downregulation of telomerase subunits was followed by reduction of telomerase activity down to almost 60% compared to control cells. However, a significant effect was only observed when the TERT subunit was downregulated. Its silencing resulted in a significant (p<0.05) increase of apoptosis (over 10% in MCF7 and about 5% in MDA-MB-231 cells, corresponding to the Annexin V assay) and DNA fragmentation (almost 30% in MCF7 and over 25% in MDA-MB-231 cells). Interestingly, also several proapoptotic genes were induced after the downregulation of the key telomerase subunit, including Bax, Bik or caspase-1 and caspase-14, as well as NGFR and TNFSF10 which were upregulated twice and more.

Telomerase as a useful target in cancer fighting-the breast cancer case

Telomerase was initially considered as a relevant factor distinguishing cancer from normal cells. During detailed studies, it appeared that its expression and activity is not only limited to cancer cells however, but in this particular cells, the telomerase is much more abundant. Thus, it has become a very promising target for an anticancer therapy. It was revealed in many studies that regulation of telomerase is a multifactorial process in mammalian cells, involving regulation of expression of telomerase subunits coding genes, post-translational protein–protein interactions, and protein phosphorylation. Numerous proto-oncogenes and tumor suppressor genes are engaged in this mechanism, and the complexity of telomerase control is studied in the context of tumor development as well as aging. Additionally, since numerous studies reveal a correlation between short telomeres and increased genome instability or cell mortality, the telomerase control appears to be one of the crucial factors to study in order to improve the cancer diagnostics and therapy or prevention. Interestingly, almost 100 % of adenocarcinoma, including breast cancer cells, expresses telomerase which makes it a good target for telomerase-related therapy. Additionally, telomerase is also supposed to be associated with drug resistance. Thus, targeting the enzyme might result in attenuation of this phenomenon. Moreover, since stem cells existence was reported, it must be considered whether targeting telomerase can bring some serious side effects and result in stem cells viability or their regenerative potential decrease. Thus, we review some molecular mechanisms engaged in therapy based on targeting telomerase in breast cancer cells.

Cytomegalovirus is associated with reduced telomerase activity in the Whitehall II cohort

Telomere length and telomerase activity have received increased attention as markers of cellular aging, but the determinants of inter-individual variation in these markers are incompletely understood. Cytomegalovirus (CMV) infection may be particularly important for telomere and telomerase dynamics due to its dramatic impact on peripheral blood lymphocyte composition, i.e., increasing the number and proportions of highly differentiated T cells that are characterized by shorter telomere length (TL) and lowered telomerase activity (TA). However, the possible relationship between CMV infection and leukocyte TL and TA has not been well-examined in vivo. This study examined the associations of CMV seropositivity and CMV IgG antibodies with leukocyte (TL) and (TA) in a sample of 434 healthy individuals (ages 53-76) from the Whitehall II cohort. Positive CMV serostatus was significantly associated with lower TA among women, and higher CMV IgG antibody levels were associated with lower TA in the overall sample. However, neither CMV seropositivity nor CMV IgG antibody levels (reflecting subclinical reactivation) among the seropositive were significantly associated with TL. These associations were robust to adjustment for age, employment grade, BMI, and smoking status. The results demonstrate that CMV seropositivity and subclinical reactivation predict lower TA. Future longitudinal studies should test whether the association of CMV with lower TA contributes to accelerated telomere shortening over time.

The chromosomal proteins JIL-1 and Z4/Putzig regulate the telomeric chromatin in Drosophila melanogaster

Drosophila telomere maintenance depends on the transposition of the specialized retrotransposons HeT-A, TART, and TAHRE. Controlling the activation and silencing of these elements is crucial for a precise telomere function without compromising genomic integrity. Here we describe two chromosomal proteins, JIL-1 and Z4 (also known as Putzig), which are necessary for establishing a fine-tuned regulation of the transcription of the major component of Drosophila telomeres, the HeT-A retrotransposon, thus guaranteeing genome stability. We found that mutant alleles of JIL-1 have decreased HeT-A transcription, putting forward this kinase as the first positive regulator of telomere transcription in Drosophila described to date. We describe how the decrease in HeT-A transcription in JIL-1 alleles correlates with an increase in silencing chromatin marks such as H3K9me3 and HP1a at the HeT-A promoter. Moreover, we have detected that Z4 mutant alleles show moderate telomere instability, suggesting an important role of the JIL-1-Z4 complex in establishing and maintaining an appropriate chromatin environment at Drosophila telomeres. Interestingly, we have detected a biochemical interaction between Z4 and the HeT-A Gag protein, which could explain how the Z4-JIL-1 complex is targeted to the telomeres. Accordingly, we demonstrate that a phenotype of telomere instability similar to that observed for Z4 mutant alleles is found when the gene that encodes the HeT-A Gag protein is knocked down. We propose a model to explain the observed transcriptional and stability changes in relation to other heterochromatin components characteristic of Drosophila telomeres, such as HP1a.