Multiple tumor suppressor microRNAs regulate telomerase and TCF7, an important transcriptional regulator of the Wnt pathway

Molecular Studies on Plant Telomeres: Expanding Horizons in Plant Biology

The integrity of plant genomes is intricately safeguarded by telomeres, the protective caps located at the ends of the chromosome. This review provides a comprehensive analysis of the molecular mechanisms governing the structure, maintenance, and dynamics of plant telomeres, highlighting their genetic and epigenetic regulation and their pivotal roles in plant development, longevity, stress adaptation, and disease resistance. Recent advancements, such as next-generation sequencing and single-molecule imaging, have revolutionized our understanding of telomere biology, unveiling new insights into telomerase activity and telomere-associated genetic variants. Additionally, the review also discusses the challenges and future directions of telomere research, including the potential applications of telomere biology in plant breeding and genetic engineering.

Simultaneous Down-Regulation of Intracellular MicroRNA-21 and hTERT mRNA Using AS1411-Functionallized Gold Nanoprobes to Achieve Targeted Anti-Tumor Therapy

Telomerase presents over-expression in most cancer cells and has been used as a near-universal marker of cancer. Studies have revealed that inhibiting telomerase activity by utilizing oligonucleotides to down-regulate the expression of intracellular human telomerase reverse-transcriptase (hTERT) mRNA is an effective method of achieving anti-tumor therapy. Considering that oncogenic microRNA-21 has been proven to indirectly up-regulate hTERT expression and drive cancer metastasis and aggression through increased telomerase activity, here, we constructed an AS1411-functionallized oligonucleotide-conjugated gold nanoprobe (Au nanoprobe) to simultaneously down-regulate intracellular microRNA-21 and hTERT mRNA by using anti-sense oligonucleotide technology to explore their targeted anti-tumor therapy effect. In vitro cell studies demonstrated that Au nanoprobes could effectively induce apoptosis and inhibit the proliferation of cancer cells by down-regulating intracellular hTERT activity. In vivo imaging and anti-tumor studies revealed that Au nanoprobes could accumulate at the tumor site and inhibit the growth of MCF-7 tumor xenografted on balb/c nude mice, thus having potential for anti-tumor therapy.

The Effect of Circulating Exosomes Obtained from Young and Old Individuals on the Aging related hTERT and P16 Expression in Hematopoietic Stem Cells

Introduction:

Functional reduction of telomeres can induce DNA damage response through cell cycle checkpoints and contribute to the senescence of stem cells. The effect of exosomes on the aging and rejuvenation of hematopoietic stem cells (HSCs) is not well known. Therefore, the present study is designed to examine the impact of plasma exosomes derived from young and old individuals on hTERT and P16 expression involved in the cellular aging process.

Methods:

Exosomes isolated from four young (Y-Exo) and four old (O-Exo) men were evaluated for CD63 protein expression, morphology, size and zeta potential. HSCs were treated with exosomes, and then, the cell viability and the mRNA expression (hTERT and P16) were evaluated using MTT and qRT-PCR methods, respectively. To measure the hTERT protein level, a western blot technique was performed.

Results:

The gene expression of hTERT was significantly decreased in HSCs treated with 5 μg/ml (O5-Exo) and 10 μg/ml (O10-Exo) doses of exosomes obtained from elderly individuals compared to the cells treated with young exosomes and the untreated HSCs (p < 0.05). In addition, there was a profound elevation of hTERT protein in the HSCs treated with both doses of young exosomes in comparison with the cells treated with both doses of old exosomes (p < 0.05). Moreover, P16 expression was markedly upregulated in the O5-Exo and O10-Exo groups compared to the untreated group (p < 0.05).

Conclusion:

Our findings reinforce the concept that depending on the age of individuals, circulating exosomes may acquire properties that affect the pathways involved in the aging process in HSCs.

The Role of Exogenous microRNAs on Human Health: The Plant-Human Trans-Kingdom Hypothesis

MicroRNAs (miRNAs) are small, endogenous, single-stranded RNAs that act on gene silencing at the post-transcriptional level by binding to a target messenger RNA (mRNA), leading to its degradation or inhibiting translation into functional proteins. The key role of miRNAs in development, proliferation, differentiation andapoptosis has been deeply investigated, revealing that deregulation in their expression is critical in various diseases, such as metabolic disorders and cancer. Since these small molecules initially evolved as a mechanism of protection against viruses and transposable elements, the fascinating hypothesis that they can move between organisms both of the same or different species has been postulated. Trans-kingdom is the term used to define the migration that occurs between species. This mechanism has been well analyzed between plants and their pests, in order to boost defense and increase pathogenicity, respectively. Intriguingly, in the last decades, the plant-human trans-kingdom migration via food intake hypothesis arose. In particular, various studies highlighted the ability of exogenous miRNAs, abundant in the mainly consumed plant-derived food, to enter the human body affecting gene expression. Notably, plant miRNAs can resist the strict conditions of the gastrointestinal tract through a methylation step that occurs during miRNA maturation, conferring high stability to these small molecules. Recent studies observed the anti-tumoral, immune modulator and anti-inflammatory abilities of trans-kingdom interaction between plant and human. Here, we depict the existing knowledge and discuss the fascinating plant-human trans-kingdom interaction, highlighting first the eventual role of plant miRNAs from foods on our somatic gene identity card and then the potential impact of using plant miRNAs as novel therapeutic avenues.

MicroRNAs role in telomere length maintenance and telomerase activity in tumor cells

MiRNAs, a class of non-coding RNA molecules, have emerged as critical modulators of telomere length and telomerase activity by finely tuning the expression of target genes (and not gene targets) within signaling pathways involved in telomere homeostasis. The primary objective of this systematic review was to compile and synthesize the existing body of knowledge on the role, association, and involvement of miRNAs in telomere length. Additionally, the review explored the regulation, function, and activation mechanism of the human telomerase reverse transcriptase (hTERT) gene and telomerase activity in tumor cells. A comprehensive analysis of 47 selected articles revealed 40 distinct miRNAs involved in these processes. These miRNAs were shown to exert their function, in both clinical cases and cell line models, either directly or indirectly, regulating hTERT and telomerase activity through distinct molecular mechanisms. The regulatory roles of these miRNAs significantly affected major cancer phenotypes, with outcomes largely dependent on the tissue type and the cellular actions within the tumor cells, whereby they functioned as oncogenes or tumor suppressors. These findings strongly support the pivotal role of miRNAs in modulating telomere length and telomerase activity, thereby contributing to the intricate and complex regulation of telomere homeostasis in tumor cells. Moreover, they emphasize the potential of targeting miRNAs and key regulatory genes as therapeutic strategies to disrupt cancer cell growth and promote senescence, offering promising avenues for novel cancer treatments.

All-trans-retinoic acid modulates glycolysis via H19 and telomerase: the role of mir-let-7a in estrogen receptor-positive breast cancer cells

BACKGROUND

Breast cancer (BC) is the most commonly diagnosed cancer in women. Treatment approaches that differ between estrogen-positive (ER+) and triple-negative BC cells (TNBCs) and may subsequently affect cancer biomarkers, such as H19 and telomerase, are an emanating delight in BC research. For instance, all-trans-Retinoic acid (ATRA) could represent a potent regulator of these oncogenes, regulating microRNAs, mostly let-7a microRNA (miR-let-7a), which targets the glycolysis pathway, mainly pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA) enzymes. Here, we investigated the potential role of ATRA in H19, telomerase, miR-let-7a, and glycolytic enzymes modulation in ER + and TNBC cells.

METHODS

MCF-7 and MDA-MB-231 cells were treated with 5 µM ATRA and/or 100 nM fulvestrant. Then, ATRA-treated or control MCF-7 cells were transfected with either H19 or hTERT siRNA. Afterward, ATRA-treated or untreated MDA-MB-231 cells were transfected with estrogen receptor alpha ER(α) or beta ER(β) expression plasmids. RNA expression was evaluated by RT‒qPCR, and proteins were assessed by Western blot. PKM2 activity was measured using an NADH/LDH coupled enzymatic assay, and telomerase activity was evaluated with a quantitative telomeric repeat amplification protocol assay. Student's t-test or one-way ANOVA was used to analyze data from replicates.

RESULTS

Our results showed that MCF-7 cells were more responsive to ATRA than MDA-MB-231 cells. In MCF-7 cells, ATRA and/or fulvestrant decreased ER(α), H19, telomerase, PKM2, and LDHA, whereas ER(β) and miR-let-7a increased. H19 or hTERT knockdown with or without ATRA treatment showed similar results to those obtained after ATRA treatment, and a potential interconnection between H19 and hTERT was found. However, in MDA-MB-231 cells, RNA expression of the aforementioned genes was modulated after ATRA and/or fulvestrant, with no significant effect on protein and activity levels. Overexpression of ER(α) or ER(β) in MDA-MB-231 cells induced telomerase activity, PKM2 and LDHA expression, in which ATRA treatment combined with plasmid transfection decreased glycolytic enzyme expression.

CONCLUSIONS

To the best of our knowledge, our study is the first to elucidate a new potential interaction between the estrogen receptor and glycolytic enzymes in ER + BC cells through miR-let-7a.

miRNAs and related genetic biomarkers according to the WHO glioma classification: From diagnosis to future therapeutic targets

In the 2021 WHO classification of Tumors of the Central Nervous System, additional molecular characteristics have been included, defining the following adult-type diffuse glioma entities: Astrocytoma IDH-mutant, Oligodendroglioma IDH-mutant and 1p/19q-codeleted, and Glioblastoma IDH-wildtype. Despite advances in genetic analysis, precision oncology, and targeted therapy, malignant adult-type diffuse gliomas remain "hard-to-treat tumors", indicating an urgent need for better diagnostic and therapeutic strategies. In the last decades, miRNA analysis has been a hotspot for researching and developing diagnostic, prognostic, and predictive biomarkers for various disorders, including brain cancer. Scientific interest has recently been directed towards therapeutic applications of miRNAs, with encouraging results. Databases such as NCBI, PubMed, and Medline were searched for a selection of articles reporting the relationship between deregulated miRNAs and genetic aberrations used in the latest WHO CNS classification. The current review discussed the recommended molecular biomarkers and genetic aberrations based on the 2021 WHO classification in adult-type diffuse gliomas, along with associated deregulated miRNAs. Additionally, the study highlights miRNA-based treatment advancements in adults with gliomas.

Telomerase and hallmarks of cancer: An intricate interplay governing cancer cell evolution

Transformed cells must acquire specific characteristics to be malignant. Weinberg and Hanahan characterize these characteristics as cancer hallmarks. Though these features are independently driven, substantial signaling crosstalk in transformed cells efficiently promotes these feature acquisitions. Telomerase is an enzyme complex that maintains telomere length. However, its main component, Telomere reverse transcriptase (TERT), has been found to interact with various signaling molecules like cMYC, NF-kB, BRG1 and cooperate in transcription and metabolic reprogramming, acting as a strong proponent of malignant features such as cell death resistance, sustained proliferation, angiogenesis activation, and metastasis, among others. It allows cells to avoid replicative senescence and achieve endless replicative potential. This review summarizes both the canonical and noncanonical functions of TERT and discusses how they promote cancer hallmarks. Understanding the role of Telomerase in promoting cancer hallmarks provides vital insight into the underlying mechanism of cancer genesis and progression and telomerase intervention as a possible therapeutic target for cancer treatment. More investigation into the precise molecular mechanisms of telomerase-mediated impacts on cancer hallmarks will contribute to developing more focused and customized cancer treatment methods.

Potential roles of the exosome/microRNA axis in breast cancer

Cancer is one of the most common diseases in the world, and various genetic and environmental factors play a key role in its development. Breast cancer is one of the most common and deadly cancers in women. Exosomes are extracellular vesicles (EVs) with an average size of about 100 nm that contain lipids, proteins, microRNAs (miRNAs), and genetic factors and play a significant role in cell signaling, communication, tumorigenesis, and drug resistance. miRNAs are RNAs with about 22 nucleotides, which are synthesized by RNA polymerase and are involved in regulating gene expression, as well as the prevention or progression of cancer. Many studies have indicated the connection between miRNAs and exosomes. According to their findings, it seems that circulating exosomal miRNAs have not been well evaluated as biomarkers for breast cancer diagnosis or monitoring. Therefore, given the importance of miRNAs in exosomes, the goal of the present study was to clarify the relationship between miRNAs in exosomes and the role they play as biomarkers in breast cancer.

Role of telomere length in human carcinogenesis (Review)

Cancer is considered the most important clinical, social and economic issue regarding cause‑specific disability‑adjusted life years among all human pathologies. Exogenous, endogenous and individual factors, including genetic predisposition, participate in cancer triggering. Telomeres are specific DNA structures positioned at the end of chromosomes and consist of repetitive nucleotide sequences, which, together with shelterin proteins, facilitate the maintenance of chromosome stability, while protecting them from genomic erosion. Even though the connection between telomere status and carcinogenesis has been identified, the absence of a universal or even a cancer‑specific trend renders consent even more complex. It is indicative that both short and long telomere lengths have been associated with a high risk of cancer incidence. When evaluating risk associations between cancer and telomere length, a disparity appears to emerge. Even though shorter telomeres have been adopted as a marker of poorer health status and an older biological age, longer telomeres due to increased cell growth potential are associated with the acquirement of cancer‑initiating somatic mutations. Therefore, the present review aimed to comprehensively present the multifaceted pattern of telomere length and cancer incidence association.

Dysregulation of Serum MicroRNA after Intracerebral Hemorrhage in Aged Mice

Stroke is one of the most common diseases that leads to brain injury and mortality in patients, and intracerebral hemorrhage (ICH) is the most devastating subtype of stroke. Though the prevalence of ICH increases with aging, the effect of aging on the pathophysiology of ICH remains largely understudied. Moreover, there is no effective treatment for ICH. Recent studies have demonstrated the potential of circulating microRNAs as non-invasive diagnostic and prognostic biomarkers in various pathological conditions. While many studies have identified microRNAs that play roles in the pathophysiology of brain injury, few demonstrated their functions and roles after ICH. Given this significant knowledge gap, the present study aims to identify microRNAs that could serve as potential biomarkers of ICH in the elderly. To this end, sham or ICH was induced in aged C57BL/6 mice (18–24 months), and 24 h post-ICH, serum microRNAs were isolated, and expressions were analyzed. We identified 28 significantly dysregulated microRNAs between ICH and sham groups, suggesting their potential to serve as blood biomarkers of acute ICH. Among those microRNAs, based on the current literature, miR-124-3p, miR-137-5p, miR-138-5p, miR-219a-2-3p, miR-135a-5p, miR-541-5p, and miR-770-3p may serve as the most promising blood biomarker candidates of ICH, warranting further investigation.

Immunity-related long noncoding RNA WDFY3-AS2 inhibited cell proliferation and metastasis through Wnt/β-catenin signaling in oral squamous cell carcinoma

OBJECTIVE

Long noncoding RNA WDFY3-AS2 has been shown to play dual roles in the modulation of cancer progression. This study aimed at clarifying the biological role of WDFY3-AS2 as well as the association between WDFY3-AS2 expression, β-catenin expression, and OSCC immunity in oral squamous cell carcinoma (OSCC).

DESIGN

Bioinformatics analyses, CCK8, EdU, wound healing, transwell, RT-qPCR, western blot, immunofluorescence, in situ hybridization, and immunohistochemistry assays were adopted for exploring the role of WDFY3-AS2 in OSCC.

RESULTS

Bioinformatics analyses showed that WDFY3-AS2 conferred a poor prognosis for OSCC patients. Further analyses identified WDFY3-AS2 as an independent prognostic indicator for OSCC. Moreover, silencing WDFY3-AS2 inhibits OSCC cell proliferation, migration and invasion. Gene set enrichment analysis indicated that WDFY3-AS2 participated in the regulation of Wnt signaling. In addition, WDFY3-AS2 expression was positively associated with β-catenin mRNA levels, the key component of Wnt signaling. Interestingly, WDFY3-AS2 knockdown inhibited β-catenin expression and nuclear translocation, thus suppressing OSCC progression through Wnt signaling. Furthermore, WDFY3-AS2 expression correlated with an immunosuppressive phenotype in the tumor immune microenvironment. In situ hybridization and immunohistochemistry verified that WDFY3-AS2 was positively associated with total and nuclear β-catenin protein levels and negatively associated with CD4 expression.

CONCLUSIONS

This study demonstrates that the immunity-associated WDFY3-AS2 augments OSCC proliferation and metastasis through Wnt/β-catenin signaling and may serve as a novel treatment target and a new prognostic factor for OSCC.

Physical Exercise and the Hallmarks of Breast Cancer: A Narrative Review

Growing evidence suggests that, among the different molecular/cellular pathophysiological mechanisms associated with cancer, there are 14 hallmarks that play a major role, including: (i) sustaining proliferative signaling, (ii) evading growth suppressors, (iii) activating invasion and metastasis, (iv) enabling replicative immortality, (v) inducing angiogenesis, (vi) resisting cell death, (vii) reprogramming energy metabolism, (viii) evading immune destruction, (ix) genome instability and mutations, (x) tumor-promoting inflammation, (xi) unlocking phenotypic plasticity, (xii) nonmutational epigenetic reprogramming, (xiii) polymorphic microbiomes, and (xiv) senescent cells. These hallmarks are also associated with the development of breast cancer, which represents the most prevalent tumor type in the world. The present narrative review aims to describe, for the first time, the effects of physical activity/exercise on these hallmarks. In summary, an active lifestyle, and particularly regular physical exercise, provides beneficial effects on all major hallmarks associated with breast cancer, and might therefore help to counteract the progression of the disease or its associated burden.

THOR is a targetable epigenetic biomarker with clinical implications in breast cancer

BACKGROUND

Breast cancer (BC) is the most frequently diagnosed cancer and a leading cause of death among women worldwide. Early BC is potentially curable, but the mortality rates still observed among BC patients demonstrate the urgent need of novel and more effective diagnostic and therapeutic options. Limitless self-renewal is a hallmark of cancer, governed by telomere maintenance. In around 95% of BC cases, this process is achieved by telomerase reactivation through upregulation of the human telomerase reverse transcriptase (hTERT). The hypermethylation of a specific region within the hTERT promoter, termed TERT hypermethylated oncological region (THOR) has been associated with increased hTERT expression in cancer. However, its biological role and clinical potential in BC have never been studied to the best of our knowledge. Therefore, we aimed to investigate the role of THOR as a biomarker and explore the functional impact of THOR methylation status in hTERT upregulation in BC.

RESULTS

THOR methylation status in BC was assessed by pyrosequencing on discovery and validation cohorts. We found that THOR is significantly hypermethylated in malignant breast tissue when compared to benign tissue (40.23% vs. 12.81%, P < 0.0001), differentiating malignant tumor from normal tissue from the earliest stage of disease. Using a reporter assay, the addition of unmethylated THOR significantly reduced luciferase activity by an average 1.8-fold when compared to the hTERT core promoter alone (P < 0.01). To further investigate its biological impact on hTERT transcription, targeted THOR demethylation was performed using novel technology based on CRISPR-dCas9 system and significant THOR demethylation was achieved. Cells previously demethylated on THOR region did not develop a histologic cancer phenotype in in vivo assays. Additional studies are required to validate these observations and to unravel the causality between THOR hypermethylation and hTERT upregulation in BC.

CONCLUSIONS

THOR hypermethylation is an important epigenetic mark in breast tumorigenesis, representing a promising biomarker and therapeutic target in BC. We revealed that THOR acts as a repressive regulatory element of hTERT and that its hypermethylation is a relevant mechanism for hTERT upregulation in BC.

Advances in Bioactivity of MicroRNAs of Plant-Derived Exosome-Like Nanoparticles and Milk-Derived Extracellular Vesicles

MicroRNA (miRNA) is a class of small noncoding RNA involved in physiological and pathological processes via the regulation of gene expression. Naked miRNAs are unstable and liable to degradation by RNases. Exosome-like nanoparticles (ELNs) secreted by plants and extracellular vesicles (EVs) found in milk are abundant in miRNAs, which can be carried by ELNs and EVs to target cells to exert their bioactivities. In this review, we describe the current understanding of miRNAs in plant ELNs and milk EVs, summarize their important roles in regulation of inflammation, intestinal barrier, tumors, and infantile immunological functions, and also discuss the adverse effect of EV miRNAs on human health. Additionally, we prospect recent challenges centered around ELN and EV miRNAs for interventional applications and provide insights of grain-derived ELNs and miRNAs interventional use in human health. Overall, plant ELNs and milk EVs can transfer miRNAs to mitigate the pathological status of recipient cells by mediating the expression of target genes but may also exert some side effects. More studies are required to elucidate the in-depth understanding of potential interventional effects of ELN and EV miRNAs on human health.

NAPRT Expression Regulation Mechanisms: Novel Functions Predicted by a Bioinformatics Approach

The nicotinate phosphoribosyltransferase (NAPRT) gene has gained relevance in the research of cancer therapeutic strategies due to its main role as a NAD biosynthetic enzyme. NAD metabolism is an attractive target for the development of anti-cancer therapies, given the high energy requirements of proliferating cancer cells and NAD-dependent signaling. A few studies have shown that NAPRT expression varies in different cancer types, making it imperative to assess NAPRT expression and functionality status prior to the application of therapeutic strategies targeting NAD. In addition, the recent finding of NAPRT extracellular form (eNAPRT) suggested the involvement of NAPRT in inflammation and signaling. However, the mechanisms regulating NAPRT gene expression have never been thoroughly addressed. In this study, we searched for NAPRT gene expression regulatory mechanisms in transcription factors (TFs), RNA binding proteins (RBPs) and microRNA (miRNAs) databases. We identified several potential regulators of NAPRT transcription activation, downregulation and alternative splicing and performed GO and expression analyses. The results of the functional analysis of TFs, RBPs and miRNAs suggest new, unexpected functions for the NAPRT gene in cell differentiation, development and neuronal biology.

MiR-138-5p Suppresses Cell Growth and Migration in Melanoma by Targeting Telomerase Reverse Transcriptase

Recent evidence suggests the existence of a miRNA regulatory network involving human telomerase reverse transcriptase gene (hTERT), with miR-138-5p playing a central role in many types of cancers. However, little is known about the regulation of hTERT expression by microRNA (miRNAs) in melanocytic tumors. Here, we investigated the effects of miR-138-5p in hTERT regulation in melanoma cells lines. In vitro studies demonstrated higher miR-138-5p and lower hTERT messenger RNA (mRNA) expression in human epidermal melanocytes, compared with melanoma cell lines (A2058, A375, SK-MEL-28) by quantitative polymerase chain reaction (qPCR) observing a negative correlation between them. A2058 melanoma cells were selected to be transfected with miR-138-5p mimic or inhibitor. Using luciferase assay, hTERT was identified as a direct target of this miRNA. Overexpression of miR-138-5p detected by Western blot revealed a decrease in hTERT protein expression (p = 0.012), and qPCR showed a reduction in telomerase activity (p < 0.001). Moreover, suppressions in cell growth (p = 0.035) and migration abilities (p = 0.015) were observed in A2058-transfected cells using thiazolyl blue tetrazolium bromide and flow cytometry, respectively. This study identifies miR-138-5p as a crucial tumor suppressor miRNA involved in telomerase regulation. Targeting it as a combination therapy with immunotherapy or targeted therapies could be used in advanced melanoma treatment; however, more preclinical studies are necessary.

Differential Expression of Non-Coding RNA Signatures in Thyroid Cancer between Two Ethnic Groups

Filipino Americans show higher thyroid cancer recurrence rates compared to European Americans. Although they are likely to die of this malignancy, the molecular mechanism has not yet been determined. Recent studies demonstrated that small non-coding RNAs could be utilized to assess thyroid cancer prognosis in tumor models. The goal of this study is to determine whether microRNA (miRNA) signatures are differentially expressed in thyroid cancer in two different ethnic groups. We also determined whether these miRNA signatures are related to cancer staging. This is a retrospective study of archival samples from patients with thyroid cancer (both sexes) in the pathology division from the last ten years at Loma Linda University School of Medicine, California. Deidentified patient demographics were extracted from the patient chart. Discarded formalin-fixed paraffin-embedded tissues were collected post-surgeries. We determined the differential expressions of microRNA in archival samples from Filipino Americans compared to European Americans using the state-of-the-art technique, HiSeq4000. By ingenuity pathway analysis, we determined miRNA targets and the pathways that those targets are involved in. We validated their expressions by real-time quantitative PCR and correlated them with the clinicopathological status in a larger cohort of miRNA samples from both ethnicities. We identified the differentially upregulated/downregulated miRNA clusters in Filipino Americans compared to European Americans. Some of these miRNA clusters are known to target genes that are linked to cancer invasion and metastasis. In univariate analysis, ethnicity and tumor staging were significant factors predicting miR-4633-5p upregulation. When including these factors in a multivariate logistic regression model, ethnicity and tumor staging remained significant independent predictors of miRNA upregulation, whereas the interaction of ethnicity and tumor staging was not significant. In contrast, ethnicity remained an independent predictor of significantly downregulated miR-491-5p and let-7 family. We provide evidence that Filipino Americans showed differentially expressed tumor-tissue-derived microRNA clusters. The functional implications of these miRNAs are under investigation.

Key miRNAs in Modulating Aging and Longevity: A Focus on Signaling Pathways and Cellular Targets

Aging is a multifactorial procedure accompanied by gradual deterioration of most biological procedures of cells. MicroRNAs (miRNAs) are a class of short non-coding RNAs that post-transcriptionally regulate the expression of mRNAs through sequence-specific binding, and contributing to many crucial aspects of cell biology. Several miRNAs are expressed differently in various organisms through aging. The function of miRNAs in modulating aging procedures has been disclosed recently with the detection of miRNAs that modulate longevity in the invertebrate model organisms, through the IIS pathway. In these model organisms, several miRNAs have been detected to both negatively and positively regulate lifespan via commonly aging pathways. miRNAs modulate age-related procedures and disorders in different mammalian tissues by measuring their tissue-specific expression in older and younger counterparts, including heart, skin, bone, brain, and muscle tissues. Moreover, several miRNAs have been contributed to modulating senescence in different human cells, and the roles of these miRNAs in modulating cellular senescence have allowed illustrating some mechanisms of aging. The review discusses the available data on miRNAs through the aging process and we highlight the roles of miRNAs as aging biomarkers and regulators of longevity in cellular senescence, tissue aging, and organism lifespan.

Exosomes and Micro-RNAs in Aging Process

Exosomes are the main actors of intercellular communications and have gained great interest in the new cell-free regenerative medicine. These nanoparticles are secreted by almost all cell types and contain lipids, cytokines, growth factors, messenger RNA, and different non-coding RNA, especially micro-RNAs (mi-RNAs). Exosomes' cargo is released in the neighboring microenvironment but is also expected to act on distant tissues or organs. Different biological processes such as cell development, growth and repair, senescence, migration, immunomodulation, and aging, among others, are mediated by exosomes and principally exosome-derived mi-RNAs. Moreover, their therapeutic potential has been proved and reinforced by their use as biomarkers for disease diagnostics and progression. Evidence has increasingly shown that exosome-derived mi-RNAs are key regulators of age-related diseases, and their involvement in longevity is becoming a promising issue. For instance, mi-RNAs such as mi-RNA-21, mi-RNA-29, and mi-RNA-34 modulate tissue functionality and regeneration by targeting different tissues and involving different pathways but might also interfere with long life expectancy. Human mi-RNAs profiling is effectively related to the biological fluids that are reported differently between young and old individuals. However, their underlying mechanisms modulating cell senescence and aging are still not fully understood, and little was reported on the involvement of mi-RNAs in cell or tissue longevity. In this review, we summarize exosome biogenesis and mi-RNA synthesis and loading mechanism into exosomes' cargo. Additionally, we highlight the molecular mechanisms of exosomes and exosome-derived mi-RNA regulation in the different aging processes.

Mechanism of Human Telomerase Reverse Transcriptase (hTERT) Regulation and Clinical Impacts in Leukemia

The proliferative capacity and continuous survival of cells are highly dependent on telomerase expression and the maintenance of telomere length. For this reason, elevated expression of telomerase has been identified in virtually all cancers, including leukemias; however, it should be noted that expression of telomerase is sometimes observed later in malignant development. This time point of activation is highly dependent on the type of leukemia and its causative factors. Many recent studies in this field have contributed to the elucidation of the mechanisms by which the various forms of leukemias increase telomerase activity. These include the dysregulation of telomerase reverse transcriptase (TERT) at various levels which include transcriptional, post-transcriptional, and post-translational stages. The pathways and biological molecules involved in these processes are also being deciphered with the advent of enabling technologies such as next-generation sequencing (NGS), ribonucleic acid sequencing (RNA-Seq), liquid chromatography-mass spectrometry (LCMS/MS), and many others. It has also been established that TERT possess diagnostic value as most adult cells do not express high levels of telomerase. Indeed, studies have shown that prognosis is not favorable in patients who have leukemias expressing high levels of telomerase. Recent research has indicated that targeting of this gene is able to control the survival of malignant cells and therefore offers a potential treatment for TERT-dependent leukemias. Here we review the mechanisms of hTERT regulation and deliberate their association in malignant states of leukemic cells. Further, we also cover the clinical implications of this gene including its use in diagnostic, prognostic, and therapeutic discoveries.

Exploring hTERT promoter methylation in cutaneous T-cell lymphomas

Cutaneous T‐cell lymphomas (CTCLs) are telomerase‐positive tumors expressing hTERT, although neither gene rearrangement/amplification nor promoter hotspot mutations could explain the hTERT re‐expression. As the hTERT promoter is rich in CpG, we investigated the contribution of epigenetic mechanisms in its re‐expression. We analyzed hTERT promoter methylation status in CTCL cells compared with healthy cells. Gene‐specific methylation analyses revealed a common methylation pattern exclusively in tumor cells. This methylation pattern encompassed a hypermethylated distal region from −650 to −150 bp and a hypomethylated proximal region from −150 to +150 bp. Interestingly, the hypermethylated region matches with the recently named TERT hypermethylated oncogenic region (THOR). THOR has been associated with telomerase reactivation in many cancers, but it has so far not been reported in cutaneous lymphomas. Additionally, we assessed the effect of THOR on two histone deacetylase inhibitors (HDACi), romidepsin and vorinostat, both approved for CTCL treatment and a DNA methyltransferase inhibitor (DNMTi) 5‐azacytidine, unapproved for CTCL. Contrary to our expectations, the findings reported herein revealed that THOR methylation is relatively stable under these epigenetic drugs' pressure, whereas these drugs reduced the hTERT gene expression.

Telomerase Regulation: A Role for Epigenetics

Simple Summary

Maintenance of telomeres is a fundamental step in human carcinogenesis and is primarily regulated by telomerase and the human telomerase reverse transcriptase gene (TERT). Improved understanding of the transcriptional control of this gene may provide potential therapeutic targets. Epigenetic modifications are a prominent mechanism to control telomerase activity and regulation of the TERT gene. TERT-targeting miRNAs have been widely studied and their function explained through pre-clinical in vivo model-based validation studies. Further, histone deacetylase inhibitors are now in pre and early clinical trials with significant clinical success. Importantly, TERT downregulation through epigenetic modifications including TERT promoter methylation, histone deacetylase inhibitors, and miRNA activity might contribute to clinical study design. This review provides an overview of the epigenetic mechanisms involved in the regulation of TERT expression and telomerase activity.

Abstract

Telomerase was first described by Greider and Blackburn in 1984, a discovery ultimately recognized by the Nobel Prize committee in 2009. The three decades following on from its discovery have been accompanied by an increased understanding of the fundamental mechanisms of telomerase activity, and its role in telomere biology. Telomerase has a clearly defined role in telomere length maintenance and an established influence on DNA replication, differentiation, survival, development, apoptosis, tumorigenesis, and a further role in therapeutic resistance in human stem and cancer cells including those of breast and cervical origin. TERT encodes the catalytic subunit and rate-limiting factor for telomerase enzyme activity. The mechanisms of activation or silencing of TERT remain open to debate across somatic, cancer, and stem cells. Promoter mutations upstream of TERT may promote dysregulated telomerase activation in tumour cells but additional factors including epigenetic, transcriptional and posttranscriptional modifications also have a role to play. Previous systematic analysis indicated methylation and mutation of the TERT promoter in 53% and 31%, respectively, of TERT expressing cancer cell lines supporting the concept of a key role for epigenetic alteration associated with TERT dysregulation and cellular transformation. Epigenetic regulators including DNA methylation, histone modification, and non-coding RNAs are now emerging as drivers in the regulation of telomeres and telomerase activity. Epigenetic regulation may be responsible for reversible silencing of TERT in several biological processes including development and differentiation, and increased TERT expression in cancers. Understanding the epigenetic mechanisms behind telomerase regulation holds important prospects for cancer treatment, diagnosis and prognosis. This review will focus on the role of epigenetics in telomerase regulation.

MicroRNA‑138 modulates glioma cell growth, apoptosis and invasion through the suppression of the AKT/mTOR signalling pathway by targeting CREB1

Alterations in the expression of microRNA (miR)-138 have been demonstrated to result in the development of several malignant tumours. However, the possible function of miR-138 in human glioma cells remains unclear. The present study demonstrated that miR-138 was significantly downregulated in 48 human glioma specimens by quantitative PCR analysis. The upregulation of miR-138 exerted significant antiproliferative and anti-invasive effects on glioma cells and promoted their apoptosis. In addition, cAMP response element-binding protein 1 (CREB1) was confirmed as a direct target gene of miR-138 by luciferase gene reporter assay, and the antitumour effect of miR-138 on glioma cells was significantly reversed by CREB1 overexpression. Moreover, the molecular mechanisms underlying the tumour-suppressive role of miR-138 in malignant glioma may be associated with the dephosphorylation of AKT/mTOR caused by the miR-138 upregulation-induced decrease in CREB1 expression in glioma cells. The results of the present study indicated that miR-138 may affect CREB1/AKT/mTOR signalling to regulate the proliferation, apoptosis and invasion of glioma cells and the malignant progression of glioma, thereby suggesting that miR-138 may be a potential target for the treatment of gliomas.

Modulation of telomerase expression and function by miRNAs: Anti-cancer potential

Telomerase is a nucleoprotein reverse transcriptase that maintains the telomere, a protective structure at the ends of the chromosome, and is active in cancer cells, stem cells, and fetal cells. Telomerase immortalizes cancer cells and induces unlimited cell division by preventing telomere shortening. Immortalized cancer cells have unlimited proliferative potential due to telomerase activity that causes tumorigenesis and malignancy. Therefore, telomerase can be a lucrative anti-cancer target. The regulation of catalytic subunit of telomerase (TERT) determines the extent of telomerase activity. miRNAs, as an endogenous regulator of gene expression, can control telomerase activity by targeting TERT mRNA. miRNAs that have a decreasing effect on TERT translation mediate modulation of telomerase activity in cancer cells by binding to TERT mRNA and regulating TERT translation. In this review, we provide an update on miRNAs that influence telomerase activity by regulation of TERT translation.

Oligonucleotides and microRNAs Targeting Telomerase Subunits in Cancer Therapy

Telomerase provides cancer cells with replicative immortality, and its overexpression serves as a near-universal marker of cancer. Anti-cancer therapeutics targeting telomerase have garnered interest as possible alternatives to chemotherapy and radiotherapy. Oligonucleotide-based therapies that inhibit telomerase through direct or indirect modulation of its subunits, human telomerase reverse transcriptase (hTERT) and human telomerase RNA gene (hTERC), are a unique and diverse subclass of telomerase inhibitors which hold clinical promise. MicroRNAs that play a role in the upregulation or downregulation of hTERT and respective progression or attenuation of cancer development have been effectively targeted to reduce telomerase activity in various cancer types. Tumor suppressor miRNAs, such as miRNA-512-5p, miRNA-138, and miRNA-128, and oncogenic miRNAs, such as miRNA-19b, miRNA-346, and miRNA-21, have displayed preclinical promise as potential hTERT-based therapeutic targets. Antisense oligonucleotides like GRN163L and T-oligos have also been shown to uniquely target the telomerase subunits and have become popular in the design of novel cancer therapies. Finally, studies suggest that G-quadruplex stabilizers, such as Telomestatin, preserve telomeric oligonucleotide architecture, thus inhibiting hTERC binding to the telomere. This review aims to provide an adept understanding of the conceptual foundation and current state of therapeutics utilizing oligonucleotides to target the telomerase subunits, including the advantages and drawbacks of each of these approaches.

Intracellular functions of RNA-binding protein, Musashi1, in stem and cancer cells

RNA-binding protein, musashi1 (MSI1), is a main protein in asymmetric cell division of the sensory organ precursor cells, whereas its expression is reported to be upregulated in cancers. This protein is a critical element in proliferation of stem and cancer stem cells, which acts through Wnt and Notch signaling pathways. Moreover, MSI1 modulates malignancy and chemoresistance of lung cancer cells via activating the Akt signaling. Due to the main role of MSI1 in metastasis and cancer development, MSI1 would be an appropriate candidate for cancer therapy. Downregulation of MSI1 inhibits proliferation of cancer stem cells and reduces the growth of solid tumors in several cancers. On the other hand, MSI1 expression is regulated by microRNAs in such a way that several different tumor suppressor miRNAs negatively regulate oncogenic MSI1 and inhibit migration and tumor metastasis. The aim of this review is summarizing the role of MSI1 in stem cell proliferation and cancer promotion.

Effects of Wnt/β-Catenin Signal Pathway Regulated by miR-342-5p Targeting CBX2 on Proliferation, Metastasis and Invasion of Ovarian Cancer Cells

Objective

This study aimed to investigate the effect of Wnt/β-catenin signal pathway mediated by miR-342-5p targeting CBX2 gene on the proliferation, metastasis, invasion and apoptosis of ovarian cancer cells, and to explore its related regulatory mechanism.

Methods

Human normal ovarian epithelial cell line IOSE80, human ovarian cancer cell line SKOV3 and OVCAR3 were the subjects. Software were used to predict the binding site of miR-342-5p targeting CBX2 gene. The proliferation rate of ovarian cancer cells was detected by MTT method; the cell viability of each group was observed by colony formation test; the apoptosis of cells in each group was detected by flow cytometry; the invasive ability of cells was determined by transwell test, and the migration ability of cells was detected by scratch test. The mRNA expression levels of miR-342-5p, CBX2, Wnt1, β-catenin, C-myc and Cyclin D1 were measured by qRT-PCR. Also, Western blot was used to determine the protein expression levels of CBX2, Wnt1, β-catenin, C-myc and Cyclin D1.

Results

CBX2 was identified as the target gene of miR-342-5p. MTT test results showed that miR-342-5p could significantly inhibit the proliferation of SKOV3 and OVCAR3 cells, colony formation assay results indicated that the viability of SKOV3 and OVCAR3 cells transfected with miR-342-5p decreased significantly, and flow cytometry results suggested that miR-342-5p could promote the apoptosis of SKOV3 and OVCAR3 cells. Also, the results of transwell showed that miR-342-5p could significantly inhibit the invasive ability of SKOV3 and OVCAR3 cells, and the results of scratch assay suggested that miR-342-5p could significantly inhibit the migration of SKOV3 and OVCAR3 cells. Moreover, qRT-PCR and Western blot results indicated that the mRNA and protein expression levels of CBX2, Wnt1, β-catenin, C-myc and Cyclin D1 decreased in SKOV3 and OVCAR3 cells transfected with miR-342-5p, while the mRNA expression levels of miR-342-5p increased significantly (P<0.05).

Conclusion

MiR-342-5p targeted gene is CBX2, which can significantly reduce the proliferation, invasion, migration and viability of ovarian cancer cell lines SKOV3 and OVCAR3, and promote their apoptosis. The mechanism may be related to the mediation of Wnt/β-catenin signal pathway and down-regulation of the related genes expression.

Emerging role of stem cell-derived extracellular microRNAs in age-associated human diseases and in different therapies of longevity

Organismal aging involves the progressive decline in organ function and increased susceptibility to age-associated diseases. This has been associated with the aging of stem cell populations within the body that decreases the capacity of stem cells to self-renew, differentiate, and regenerate damaged tissues and organs. This review aims to explore how aging is associated with the dysregulation of stem cell-derived extracellular vesicles (SCEVs) and their corresponding miRNA cargo (SCEV-miRNAs), which are short non-coding RNAs involved in post-transcriptional regulation of target genes. Recent evidence has suggested that in aging stem cells, SCEV-miRNAs may play a vital role regulating various processes that contribute to aging: cellular senescence, stem cell exhaustion, telomere length, and circadian rhythm. Hence, further clarifying the age-dependent molecular mechanisms through which SCEV-miRNAs exert their downstream effects may inform a greater understanding of the biology of aging, elucidate their role in stem cell function, and identify important targets for future regenerative therapies. Additionally, current studies evaluating therapeutic role of SCEVs and SCEV-miRNAs in treating several age-associated diseases are also discussed.

Diverse regulatory manners of human telomerase reverse transcriptase

Human telomerase reverse transcriptase (hTERT) is the core subunit of human telomerase and plays important roles in human cancers. Aberrant expression of hTERT is closely associated with tumorigenesis, cancer cell stemness maintaining, cell proliferation, apoptosis inhibition, senescence evasion and metastasis. The molecular basis of hTERT regulation is highly complicated and consists of various layers. A deep and full-scale comprehension of the regulatory mechanisms of hTERT is pivotal in understanding the pathogenesis and searching for therapeutic approaches. In this review, we summarize the recent advances regarding the diverse regulatory mechanisms of hTERT, including the transcriptional (promoter mutation, promoter region methylation and histone acetylation), post-transcriptional (mRNA alternative splicing and non-coding RNAs) and post-translational levels (phosphorylation and ubiquitination), which may provide novel perspectives for further translational diagnosis or therapeutic strategies targeting hTERT.

Clinical Significance of Transcription Factor 7 (TCF7) as a Prognostic Factor in Gastric Cancer

Background

Transcription factor 7 (TCF7) plays an essential role in Wnt signaling by interacting with β-catenin. Emerging evidence demonstrates that overexpression of TCF7 promotes progression or correlates with poor progression in several types of cancers, but the functions of TCF7 in gastric cancer (GC) have not been revealed.

Material/Methods

A total of 168 patients with GC who underwent radical surgeries were collected and regarded as the test cohort. The expression of TCF7 in the 168 patients was detected with immunohistochemistry. Moreover, the mRNA levels of TCF7 in 11 pairs of GC and adjacent tissues were detected with quantitative real-time PCR (qRT-PCR). The correlations between TCF7 and the clinicopathological factors were evaluated with the chi-square test, and the prognostic value of TCF7 in GC was investigated with univariate analysis and multivariate analysis.

Results

The mRNA levels of TCF7 in GC tissues were significantly higher than in corresponding tumor adjacent tissues. The patients of low TCF7 expression and high TCF7 expression accounted for 76.79% (129/168) and 23.21% (39/168), respectively. In our experiments, TCF7 was significantly associated with positive lymphatic invasion (P=0.022) and metastasis (P<0.001). The high expression of TCF7 was correlated with low survival rates (P=0.012) and was confirmed as an independent prognostic factor (HR=1.92, 95%CI =1.06–3.47, P=0.031) of GC in multivariate analysis.

Conclusions

TCF7 expression is correlated with metastasis and is an independent prognostic factor of GC. TCF7 detection of GC could help stratify the patients with high risk and guide precise treatment.

Transcription factor 7 functions as an unfavorable prognostic marker of glioblastoma multiforme by promoting proliferation by upregulating c-Myc

Transcription factor 7 (TCF7) is an oncogenic transcription factor in several kinds of cancers. However, the clinical significance of TCF7 in glioblastoma multiforme (GBM) has not been well elucidated. A total of 107 patients with surgical resection of GBM were enrolled in our study. TCF7 expression in these cases was detected by immunohistochemistry and the difference in TCF7 mRNA levels between tumor tissues and adjacent tissues was compared with a real-time PCR. The correlation between TCF7 expression and the clinicopathologic factors was analyzed using the χ-test. Moreover, the prognostic value of TCF7 was evaluated by univariate and multivariate analyses. In addition, the influence of TCF7 on the proliferation of the GBM cell line U251 was detected using an MTT assay after regulating TCF7 and its target gene c-Myc. The high and low expressions of TCF7 accounted for 54.21 and 45.79%, respectively, in all cases. The mRNA level of TCF7 in GBM tissues was markedly higher than that in adjacent tissues, indicating the oncogenic role of TCF7 in GBM. High expression of TCF7 was associated significantly with high Ki67 percentage and the sex of the patients, and it was identified as an independent prognostic factor for patients with GBM. With experiments in vitro, TCF7 was shown to promote cell proliferation by increasing c-Myc expression in GBM. TCF7 could be considered an independent prognostic factor in GBM, and could enhance GBM cell proliferation by upregulating c-Myc, indicating that it may be a potential and promising molecular drug target for GBM.

miRNA-miRNA crosstalk: from genomics to phenomics

The discovery of microRNA (miRNA)-miRNA crosstalk has greatly improved our understanding of complex gene regulatory networks in normal and disease-specific physiological conditions. Numerous approaches have been proposed for modeling miRNA-miRNA networks based on genomic sequences, miRNA-mRNA regulation, functional information and phenomics alone, or by integrating heterogeneous data. In addition, it is expected that miRNA-miRNA crosstalk can be reprogrammed in different tissues or specific diseases. Thus, transcriptome data have also been integrated to construct context-specific miRNA-miRNA networks. In this review, we summarize the state-of-the-art miRNA-miRNA network modeling methods, which range from genomics to phenomics, where we focus on the need to integrate heterogeneous types of omics data. Finally, we suggest future directions for studies of crosstalk of noncoding RNAs. This comprehensive summarization and discussion elucidated in this work provide constructive insights into miRNA-miRNA crosstalk.

New emerging roles of microRNAs in breast cancer

BACKGROUND

MicroRNAs constitute a large family of non-coding RNAs, which actively participate in tumorigenesis by regulating a set of mRNAs of distinct signaling pathways. An altered expression of these molecules has been found in different tumorigenic processes of breast cancer, the most common type of cancer in the female population worldwide.

PURPOSE

The objective of this review is to discuss how miRNAs become master regulators in breast tumorigenesis.

METHODS

An integrative review of miRNAs and breast cancer literature from the last 5 years was done on PubMed. We summarize recent works showing that the defects on the biogenesis of miRNAs are associated with different breast cancer characteristics. Then, we show several examples that demonstrate the link between cellular processes regulated by miRNAs and the hallmarks of breast cancer. Finally, we examine the complexity in the regulation of these molecules as they are modulated by other non-coding RNAs and the clinical applications of miRNAs as they could serve as good diagnostic and classification tools.

CONCLUSION

The information presented in this review is important to encourage new directed studies that consider microRNAs as a good tool to improve the diagnostic and treatment alternatives in breast cancer.

miR-541 suppresses proliferation and invasion of squamous cell lung carcinoma cell lines via directly targeting high-mobility group AT-hook 2

An increasing number of studies have demonstrated that micro-ribonucleic acids (miRNAs) are important tumor suppressors during carcinogenesis. However, the function of miRNA-541 (miR-541) in malignancies, especially lung cancer, has not been widely reported. In this study, miR-541 expression was significantly decreased in squamous cell lung carcinoma (SCLC) cancerous tissue and SCLC cell lines. To analyze miR-541 function in SCLC, we overexpressed miR-541 in SCLC cell lines (SK-MES-1 and H226). According to the CCK8, wound scratch, and transwell invasion assay results, miR-541 overexpression significantly inhibited SCLC cell proliferation, migration, and invasion ability. Next, using RT-PCR, Western blotting, immunocytochemistry, and luciferase assays, HMGA2 was identified, for the first time, as a direct regulatory target of miR-541 in SK-MES-1 and H226 cells. Furthermore, upregulating HMGA2 expression significantly alleviated the suppressive effects of miR-541 on SK-MES-1 and H226 cell proliferation, migration, and invasion. In summary, our study revealed that miR-541 inhibited SCLC proliferation and invasion by directly targeting HMGA2.

MicroRNA Regulation of Telomerase Reverse Transcriptase (TERT): Micro Machines Pull Strings of Papier-Mâché Puppets

Substantial fraction of high-quality information is continuously being added into the existing pool of knowledge related to the biology of telomeres. Based on the insights gleaned from decades of research, it is clear that chromosomal stability needs a highly controlled and dynamic balance of DNA gain and loss in each terminal tract of telomeric repeats. Telomeres are formed by tandem repeats of TTAGGG sequences, which are gradually lost with each round of division of the cells. Targeted inhibition of telomerase to effectively induce apoptosis in cancer cells has attracted tremendous attention and overwhelmingly increasingly list of telomerase inhibitors truthfully advocates pharmacological significance of telomerase. Telomerase reverse transcriptase (TERT) is a multi-talented and catalytically active component of the telomerase-associated protein machinery. Different proteins of telomerase-associated machinery work in a synchronized and orchestrated manner to ensure proper maintenance of telomeric length of chromosomes. Rapidly emerging scientific findings about regulation of TERT by microRNAs has revolutionized our understanding related to the biology of telomeres and telomerase. In this review, we have comprehensively discussed how different miRNAs regulate TERT in different cancers. Use of miRNA-based therapeutics against TERT in different cancers needs detailed research in preclinical models for effective translation of laboratory findings to clinically effective therapeutics.

Mechanisms of human telomerase reverse transcriptase (hTERT) regulation: clinical impacts in cancer

Background

Limitless self-renewal is one of the hallmarks of cancer and is attained by telomere maintenance, essentially through telomerase (hTERT) activation. Transcriptional regulation of hTERT is believed to play a major role in telomerase activation in human cancers.

Main body

The dominant interest in telomerase results from its role in cancer. The role of telomeres and telomere maintenance mechanisms is well established as a major driving force in generating chromosomal and genomic instability. Cancer cells have acquired the ability to overcome their fate of senescence via telomere length maintenance mechanisms, mainly by telomerase activation.

hTERT expression is up-regulated in tumors via multiple genetic and epigenetic mechanisms including hTERT amplifications, hTERT structural variants, hTERT promoter mutations and epigenetic modifications through hTERT promoter methylation. Genetic (hTERT promoter mutations) and epigenetic (hTERT promoter methylation and miRNAs) events were shown to have clinical implications in cancers that depend on hTERT activation. Knowing that telomeres are crucial for cellular self-renewal, the mechanisms responsible for telomere maintenance have a crucial role in cancer diseases and might be important oncological biomarkers. Thus, rather than quantifying TERT expression and its correlation with telomerase activation, the discovery and the assessment of the mechanisms responsible for TERT upregulation offers important information that may be used for diagnosis, prognosis, and treatment monitoring in oncology. Furthermore, a better understanding of these mechanisms may promote their translation into effective targeted cancer therapies.

Conclusion

Herein, we reviewed the underlying mechanisms of hTERT regulation, their role in oncogenesis, and the potential clinical applications in telomerase-dependent cancers.

miR-128 inhibits telomerase activity by targeting TERT mRNA

Telomerase is a unique cellular reverse transcriptase (RT) essential for maintaining telomere stability and required for the unlimited proliferation of cancer cells. The limiting determinant of telomerase activity is the catalytic component TERT, and TERT expression is closely correlated with telomerase activity and cancer initiation and disease progression. For this reason the regulation of TERT levels in the cell is of great importance. microRNAs (miRs) function as an additional regulatory level in cells, crucial for defining expression boundaries, proper cell fate decisions, cell cycle control, genome integrity, cell death and metastasis. We performed an anti-miR library screen to identity novel miRs, which participate in the control of telomerase. We identified the tumor suppressor miR (miR-128) as a novel endogenous telomerase inhibitor and determined that miR-128 significantly reduces the mRNA and protein levels of Tert in a panel of cancer cell lines. We further evaluated the mechanism by which miR-128 regulates TERT and demonstrated that miR-128 interacts directly with the coding sequence of TERT mRNA in both HeLa cells and teratoma cells. Interestingly, the functional miR-128 binding site in TERT mRNA, is conserved between TERT and the other cellular reverse transcriptase encoded by Long Interspersed Elements-1 (LINE-1 or L1), which can also contribute to the oncogenic phenotype of cancer. This finding supports the novel idea that miRs may function in parallel pathways to inhibit tumorigenesis, by regulating a group of enzymes (such as RT) by targeting conserved binding sites in the coding region of both enzymes.

Epigenetic silencing of miR-296 and miR-512 ensures hTERT dependent apoptosis protection and telomere maintenance in basal-type breast cancer cells

The catalytic subunit of the telomerase complex, hTERT, ensures unlimited proliferative potential of cancer cells by maintaining telomere function and protecting from apoptosis. Using a miRNA screening approach we identified miR-296-5p and miR-512-5p as miRNAs that target hTERT in breast cancer cells. Ectopic miR-296-5p and miR-512-5p reduce telomerase activity, drive telomere shortening and cause proliferation defects by enhancing senescence and apoptosis in breast cancer cells. In line with the relevance of hTERT expression for human cancer we found that miR-296-5p and miR-512-5p expression is reduced in human breast cancer. Accordingly, high expression of miR-296-5p and miR-512-5p target genes including hTERT is linked with significantly reduced distant metastasis free survival and relapse free survival of basal type breast cancer patients. This suggests relevance of the identified miRNAs in basal type breast cancer. Epigenetic silencing of miR-296 and miR-512 encoding genes is responsible for low levels of miR-296-5p and miR-512-5p expression in basal type breast cancer cells. Disrupting gene silencing results in a dramatic upregulation of miR-296-5p and miR-512-5p levels leading to reduced hTERT expression and increased sensitivity to the induction of apoptosis. Altogether, our data suggest that epigenetic regulatory circuits in basal type breast cancer may contribute to high hTERT levels by silencing miR-296-5p and miR-512-5p expression, thereby contributing to the aggressiveness of basal type breast cancer.

Profound changes in miRNA expression during cancer initiation by aflatoxin B1 and their abrogation by the chemopreventive triterpenoid CDDO-Im

Aflatoxin B₁ (AFB₁ ) is a potent human and animal hepatocarcinogen. To investigate the effects of aflatoxin on miRNA expression during the initiation phase of carcinogenesis, next-generation sequencing was used to analyze liver tissues from F344 rats exposed to 200 μg/kg per day AFB₁ for 4 week. A panel of miRNAs was identified that was upregulated with AFB₁ treatment compared to controls: rno-miR-434-3p, rno-miR-411-5p, rno-miR-221-3p, rno-miR-127-3p, rno-miR-205, rno-miR-429, rno-miR-34a-5p, rno-miR-181c-3p, rno-miR-200b-3p, and rno-miR-541-5p. Analysis of rat livers exposed to AFB₁ plus the chemopreventive triterpenoid CDDO-Im revealed a striking abrogation of this upregulation. These changes were validated by real-time PCR. We also explored the temporal variation in expression of the candidate miRNAs during the 4-week dosing period. Most of the candidate miRNAs were upregulated at week 1 and increased for the duration of AFB₁ dosing over the 4-week period. Treatment with CDDO-Im ameliorated these effects at all time points. All candidate miRNAs were detectable in serum from aflatoxin treated animals; however, there was no significant difference in expression for 7 of the 11 miRNAs examined. Exposure to AFB₁ upregulated miR-122-5p (fivefold), 34a-5p (13-fold), and 181c-3p (170-fold) compared with controls. The findings from this study give insight into epigenetic changes induced by aflatoxin taking place during the initial step of carcinogenesis.

MiR-138: A promising therapeutic target for cancer

MicroRNAs are small noncoding RNAs which regulate gene expressions at post-transcriptional level by binding to the 3'-untranslated region of target messenger RNAs. Growing evidences highlight their pivotal roles in various biological processes of human cancers. Among them, miR-138, generating from two primary transcripts, pri-miR-138-1 and pri-miR-138-2, expresses aberrantly in different cancers and is extensively studied in cancer network. Importantly, studies have shown that miR-138 acts as a tumor suppressor by targeting many target genes, which are related to proliferation, apoptosis, invasion, and migration. Additionally, some researches also discover that miR-138 can sensitize tumors to chemotherapies. In this review, we summarize the expression of miR-138 on regulatory mechanisms and tumor biological processes, which will establish molecular basis on the usage of miR-138 in clinical applications in the future.

Two White Spot Syndrome Virus MicroRNAs Target the Dorsal Gene To Promote Virus Infection in Marsupenaeus japonicus Shrimp

In eukaryotes, microRNAs (miRNAs) serve as regulators of many biological processes, including virus infection. An miRNA can generally target diverse genes during virus-host interactions. However, the regulation of gene expression by multiple miRNAs has not yet been extensively explored during virus infection. This study found that the Spaztle (Spz)-Toll-Dorsal-antilipopolysaccharide factor (ALF) signaling pathway plays a very important role in antiviral immunity against invasion of white spot syndrome virus (WSSV) in shrimp (Marsupenaeus japonicus). Dorsal, the central gene in the Toll pathway, was targeted by two viral miRNAs (WSSV-miR-N13 and WSSV-miR-N23) during WSSV infection. The regulation of Dorsal expression by viral miRNAs suppressed the Spz-Toll-Dorsal-ALF signaling pathway in shrimp in vivo, leading to virus infection. Our study contributes novel insights into the viral miRNA-mediated Toll signaling pathway during the virus-host interaction.IMPORTANCE An miRNA can target diverse genes during virus-host interactions. However, the regulation of gene expression by multiple miRNAs during virus infection has not yet been extensively explored. The results of this study indicated that the shrimp Dorsal gene, the central gene in the Toll pathway, was targeted by two viral miRNAs during infection with white spot syndrome virus. Regulation of Dorsal expression by viral miRNAs suppressed the Spz-Toll-Dorsal-ALF signaling pathway in shrimp in vivo, leading to virus infection. Our study provides new insight into the viral miRNA-mediated Toll signaling pathway in virus-host interactions.

MicroRNA expression profiles identify disease-specific alterations in systemic lupus erythematosus and primary Sjögren's syndrome

The discovery of microRNAs (miRNAs) and their critical role in genetic control opened new avenues in understanding of various biological processes including immune cell lineage commitment, differentiation, proliferation and apoptosis. However, a given miRNA may have hundreds of different mRNA targets and a target might be regulated by multiple miRNAs, thus the characterisation of dysregulated miRNA expression profiles could give a better insight into the development of immunological disturbances in autoimmune diseases. The aim of our study was to examine the changes in miRNA expression profiles in patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS). Eight SLE patients, 8 pSS patients and 7 healthy subjects were enrolled in the investigation. MiRNAs were isolated from peripheral blood mononuclear cells, and expression patterns were determined with Illumina next-generation sequencing technology. Since the immunopathogenesis of pSS and SLE encompasses pronounced B cell hyperactivity along with specific autoantibody production, we paid a special attention on the association between miRNA expression levels and altered peripheral B cell distribution. In SLE patients 135, while in pSS patients 26 miRNAs showed altered expression. Interestingly, the 25 miRNAs including miR-146a, miR-16 and miR-21, which were over-expressed in pSS patients, were found to be elevated in SLE group, as well. On the contrary, we observed the down-regulation of miR-150-5p, which is a novel and unique finding in pSS. Levels of several miRNAs over-expressed in SLE, were not changed in pSS, such as miR-148a-3p, miR-152, miR-155, miR-223, miR-224, miR-326 and miR-342. Expression levels of miR-223-5p, miR-150-5p, miR-155-5p and miR-342-3p, which miRNAs are potentially linked to B cell functions, showed associations with the B cell proportions within peripheral blood mononuclear cells. The observed differences in miRNA expression profiles and the better understanding of immune regulatory mechanisms of miRNAs may help to elucidate the pathogenesis of SLE and pSS.

Epigenetic perturbation driving asleep telomerase reverse transcriptase: Possible therapeutic avenues in carcinoma

In the last decade, implications of human telomerase reverse transcriptase (hTERT), a component of ribonucleoprotein telomerase in aging, senescence, and stem cell are highly evident. Besides, the activation of hTERT is also being documented several cancer types including carcinoma. The awakening of telomerase during carcinoma initiation and development is being seen with different perspectives including genetic and epigenetic tools and events. In view of several tumor progenitors genes (also referred as epigenetic mediators), telomerase is placed as key enzyme to achieve the carcinoma phenotype and sustain during the progression. It is true that swaying of telomerase in carcinoma could be facilitated with dedicated set of epigenetic modulators and modifiers players. These epigenetic alterations are heritable, potentially reversible, and seen as the epigenetic signature of carcinoma. Several papers converge to suggest that DNA methylation, histone modification, and small non-coding RNAs are the widely appreciated epigenetic changes towards hTERT modulation. In this review, we summarize the contribution of epigenetic factors in the telomerase activation and discuss potential avenues to achieve therapeutic intervention in carcinoma.

TCF7 is suppressed by the androgen receptor via microRNA-1-mediated downregulation and is involved in the development of resistance to androgen deprivation in prostate cancer

BACKGROUND

Resistance to androgen deprivation therapy (ADT) represents a key step in the malignant progression of prostate cancer, and mutation to androgen receptor (AR) is one major driver to an androgen-independent phenotype. However, alternative oncogenic pathways that bypass AR signaling have emerged as an important mechanism promoting resistance to ADT. It is known that AR activation can prevent the interaction between β-catenin and T cell factor/lymphoid enhancer-binding factor (TCF/LEF) family, inhibiting the Wnt signaling pathway. The aim of this study was to determine the role of transcription factor 7 (TCF7), a transcription factor best known as a Wnt effector that forms a complex with β-catenin, in the development of advanced prostate cancer. We further investigated the molecular mechanisms by which TCF7 is induced when AR signaling is inactivated.

METHODS

A novel AR signaling pathway that induces microRNA-1 (miR-1) to suppress metastatic prostate cancer was recently demonstrated (AR-miR-1 signaling axis), and its regulation of Wnt signaling was explored in the current study. Clinical data sets were analyzed for potential targets of AR-miR-1 signaling in the TCF/LEF family, and tissue samples were utilized to validate the relationship. The molecular mechanism and biological functions were demonstrated in prostate cancer cell lines and a mouse xenograft model.

RESULTS

We demonstrated a molecular mechanism of AR signaling suppressing TCF7 partly through miR-1-mediated downregulation. TCF7 exhibited oncogenic properties and compromised the tumor-suppressive effects of miR-1. Our results also showed that overexpression of TCF7 or disruption of miR-1 function promoted androgen-independent proliferation.

CONCLUSIONS

We demonstrated that the AR-miR-1 axis negatively regulates the novel oncogenic factor, TCF7. Dysregulation of TCF7 promoted a survival advantage and resistance to androgen deprivation, suggesting its therapeutic potential for castration-resistant prostate cancer.

miR-138-5p contributes to cell proliferation and invasion by targeting Survivin in bladder cancer cells

Background

Survivin (encoded by the gene BIRC5) plays an important role in the carcinogenesis of bladder cancer. Identifying miRNAs that target Survivin in the setting of bladder cancer will help to develop Survivin-based therapies for bladder cancer.

Methods

The expression levels of miR-138-5p and Survivin protein were measured in 12 resected bladder cancer specimens. The correlation between miR-138-5p and Survivin was further examined by evaluating Survivin expression in human bladder cancer cell lines that either overexpressed or knocked down miR-138-5p. A luciferase reporter assay was performed to test the direct binding of miR-138-5p to the target gene BIRC5. We also investigated the biological role of miR-138-5p targeting to Survivin in bladder cancer cell lines both in vivo and in vitro.

Results

In this study, we found that the Survivin protein was either absent or weakly expressed in normal adjacent tissues and consistently up-regulated in bladder cancer tissues; however, the mRNA levels did not vary as much, suggesting that a post-transcriptional mechanism was involved. Because microRNAs are powerful post-transcriptional regulators of gene expression, we used bioinformatic analyses to search for microRNAs that could potentially target BIRC5 in the setting of bladder cancer. We identified 2 specific targeting sites for miR-138-5p in the 3′ untranslated region (3′-UTR) of BIRC5. We further identified an inverse correlation between miR-138-5p and Survivin protein levels in bladder cancer tissue samples. By overexpressing or knocking down miR-138-5p in bladder cancer cells, we experimentally confirmed that miR-138-5p directly recognizes the 3′-UTR of the BIRC5 transcript and regulates Survivin expression. Furthermore, the biological consequences of the targeting of BIRC5 by miR-138-5p were examined in vitro via cell proliferation and invasion assays and in vivo using a mouse xenograft tumor model. We demonstrated that BIRC5 repression by miR-138-5p suppressed the proliferative and invasive characteristics of bladder cancer cells and that miR-138-5p exerted an anti-tumor effect by negatively regulating BIRC5 in a xenograft mouse model.

Conclusions

Taken together, our findings provide the first clues regarding the role of miR-138-5p as a tumor suppressor in bladder cancer by inhibiting BIRC5 translation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-016-0569-4) contains supplementary material, which is available to authorized users.

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.

MiR-541-3p reverses cancer progression by directly targeting TGIF2 in non-small cell lung cancer

Lung cancer remains a leading cause of cancer-associated mortality worldwide, and non-small lung cancer (NSCLC) is responsible for over 80 % of lung cancer-related deaths. Identifying novel molecular biomarker that can inhibit the progression of lung cancer will facilitate the development of new treatment strategies. Herein, we demonstrated that miR-541-3p is a tumor-suppressor microRNA (miRNA) in NSCLC progression. We found that expression of miR-541-3p was decreased obviously in NSCLC tissues and plasma. Down-regulation of miR-541-3p was associated with TNM stage and postoperative survival. Overexpression of miR-541-3p inhibited the growth and metastasis of NSCLC cells. The TGIF2 was a direct target of miR-541-3p and promoted the growth and metastasis of NSCLC cells. Further study showed that TGIF2 could reverse the inhibitory effect of miR-541-3p on growth and metastasis of NSCLC cells. Taken together, our data highlight the pivotal role of miR-541-3p in the progression of NSCLC. Thus, miR-541-3p may be a potential prognostic marker and of treatment relevance for NSCLC progression intervention.

Regulation of the Telomerase Reverse Transcriptase Subunit through Epigenetic Mechanisms

Chromosome-shortening is characteristic of normal cells, and is known as the end replication problem. Telomerase is the enzyme responsible for extending the ends of the chromosomes in de novo synthesis, and occurs in germ cells as well as most malignant cancers. There are three subunits of telomerase: human telomerase RNA (hTERC), human telomerase associated protein (hTEP1), or dyskerin, and human telomerase reverse transcriptase (hTERT). hTERC and hTEP1 are constitutively expressed, so the enzymatic activity of telomerase is dependent on the transcription of hTERT. DNA methylation, histone methylation, and histone acetylation are basic epigenetic regulations involved in the expression of hTERT. Non-coding RNA can also serve as a form of epigenetic control of hTERT. This epigenetic-based regulation of hTERT is important in providing a mechanism for reversibility of hTERT control in various biological states. These include embryonic down-regulation of hTERT contributing to aging and the upregulation of hTERT playing a critical role in over 90% of cancers. Normal human somatic cells have a non-methylated/hypomethylated CpG island within the hTERT promoter region, while telomerase-positive cells paradoxically have at least a partially methylated promoter region that is opposite to the normal roles of DNA methylation. Histone acetylation of H3K9 within the promoter region is associated with an open chromatin state such that transcription machinery has the space to form. Histone methylation of hTERT has varied control of the gene, however. Mono- and dimethylation of H3K9 within the promoter region indicate silent euchromatin, while a trimethylated H3K9 enhances gene transcription. Non-coding RNAs can target epigenetic-modifying enzymes, as well as transcription factors involved in the control of hTERT. An epigenetics diet that can affect the epigenome of cancer cells is a recent fascination that has received much attention. By combining portions of this diet with epigenome-altering treatments, it is possible to selectively regulate the epigenetic control of hTERT and its expression.