HuR regulates telomerase activity through TERC methylation

Transcription stress at telomeres leads to cytosolic DNA release and paracrine senescence

Transcription stress has been linked to DNA damage -driven aging, yet the underlying mechanism remains unclear. Here, we demonstrate that Tcea1-/- cells, which harbor a TFIIS defect in transcription elongation, exhibit RNAPII stalling at oxidative DNA damage sites, impaired transcription, accumulation of R-loops, telomere uncapping, chromatin bridges, and genome instability, ultimately resulting in cellular senescence. We found that R-loops at telomeres causally contribute to the release of telomeric DNA fragments in the cytoplasm of Tcea1-/- cells and primary cells derived from naturally aged animals triggering a viral-like immune response. TFIIS-defective cells release extracellular vesicles laden with telomeric DNA fragments that target neighboring cells, which consequently undergo cellular senescence. Thus, transcription stress elicits paracrine signals leading to cellular senescence, promoting aging.

Noncanonical functions of telomerase and telomeres in viruses-associated cancer

The cause of cancer is attributed to the uncontrolled growth and proliferation of cells resulting from genetic changes and alterations in cell behavior, a phenomenon known as epigenetics. Telomeres, protective caps on the ends of chromosomes, regulate both cellular aging and cancer formation. In most cancers, telomerase is upregulated, with the telomerase reverse transcriptase (TERT) enzyme and telomerase RNA component (TERC) RNA element contributing to the maintenance of telomere length. Additionally, it is noteworthy that two viruses, human papillomavirus (HPV) and Epstein-Barr virus (EBV), utilize telomerase for their replication or persistence in infected cells. Also, TERT and TERC may play major roles in cancer not related to telomere biology. They are involved in the regulation of gene expression, signal transduction pathways, cellular metabolism, or even immune response modulation. Furthermore, the crosstalk between TERT, TERC, RNA-binding proteins, and microRNAs contributes to a greater extent to cancer biology. To understand the multifaceted roles played by TERT and TERC in cancer and viral life cycles, and then to develop effective therapeutic strategies against these diseases, are fundamental for this goal. By investigating deeply, the complicated mechanisms and relationships between TERT and TERC, scientists will open the doors to new therapies. In its analysis, the review emphasizes the significance of gaining insight into the multifaceted roles that TERT and TERC play in cancer pathogenesis, as well as their involvement in the viral life cycle for designing effective anticancer therapy approaches.

Fyn-mediated phosphorylation of Menin disrupts telomere maintenance in stem cells

Telomeres protect chromosome ends and determine the replication potential of dividing cells. The canonical telomere sequence TTAGGG is synthesized by telomerase holoenzyme, which maintains telomere length in proliferative stem cells. Although the core components of telomerase are well-defined, mechanisms of telomerase regulation are still under investigation. We report a novel role for the Src family kinase Fyn, which disrupts telomere maintenance in stem cells by phosphorylating the scaffold protein Menin. We found that Fyn knockdown prevented telomere erosion in human and mouse stem cells, validating the results with four telomere measurement techniques. We show that Fyn phosphorylates Menin at tyrosine 603 (Y603), which increases Menin's SUMO1 modification, C-terminal stability, and importantly, its association with the telomerase RNA component (TR). Using mass spectrometry, immunoprecipitation, and immunofluorescence experiments we found that SUMO1-Menin decreases TR's association with telomerase subunit Dyskerin, suggesting that Fyn's phosphorylation of Menin induces telomerase subunit mislocalization and may compromise telomerase function at telomeres. Importantly, we find that Fyn inhibition reduces accelerated telomere shortening in human iPSCs harboring mutations for dyskeratosis congenita.

Molecular hallmarks of ageing in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal, severely debilitating and rapidly progressing disorder affecting motor neurons in the brain, brainstem, and spinal cord. Unfortunately, there are few effective treatments, thus there remains a critical need to find novel interventions that can mitigate against its effects. Whilst the aetiology of ALS remains unclear, ageing is the major risk factor. Ageing is a slowly progressive process marked by functional decline of an organism over its lifespan. However, it remains unclear how ageing promotes the risk of ALS. At the molecular and cellular level there are specific hallmarks characteristic of normal ageing. These hallmarks are highly inter-related and overlap significantly with each other. Moreover, whilst ageing is a normal process, there are striking similarities at the molecular level between these factors and neurodegeneration in ALS. Nine ageing hallmarks were originally proposed: genomic instability, loss of telomeres, senescence, epigenetic modifications, dysregulated nutrient sensing, loss of proteostasis, mitochondrial dysfunction, stem cell exhaustion, and altered inter-cellular communication. However, these were recently (2023) expanded to include dysregulation of autophagy, inflammation and dysbiosis. Hence, given the latest updates to these hallmarks, and their close association to disease processes in ALS, a new examination of their relationship to pathophysiology is warranted. In this review, we describe possible mechanisms by which normal ageing impacts on neurodegenerative mechanisms implicated in ALS, and new therapeutic interventions that may arise from this.

Emerging roles of RNA-binding proteins in fatty liver disease

A rampant and urgent global health issue of the 21st century is the emergence and progression of fatty liver disease (FLD), including alcoholic fatty liver disease and the more heterogenous metabolism-associated (or non-alcoholic) fatty liver disease (MAFLD/NAFLD) phenotypes. These conditions manifest as disease spectra, progressing from benign hepatic steatosis to symptomatic steatohepatitis, cirrhosis, and, ultimately, hepatocellular carcinoma. With numerous intricately regulated molecular pathways implicated in its pathophysiology, recent data have emphasized the critical roles of RNA-binding proteins (RBPs) in the onset and development of FLD. They regulate gene transcription and post-transcriptional processes, including pre-mRNA splicing, capping, and polyadenylation, as well as mature mRNA transport, stability, and translation. RBP dysfunction at every point along the mRNA life cycle has been associated with altered lipid metabolism and cellular stress response, resulting in hepatic inflammation and fibrosis. Here, we discuss the current understanding of the role of RBPs in the post-transcriptional processes associated with FLD and highlight the possible and emerging therapeutic strategies leveraging RBP function for FLD treatment. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Stress, epigenetics, and aging: Unraveling the intricate crosstalk

Aging, as a complex process involving multiple cellular and molecular pathways, is known to be exacerbated by various stresses. Because responses to these stresses, such as oxidative stress and genotoxic stress, are known to interplay with the epigenome and thereby contribute to the development of age-related diseases, investigations into how such epigenetic mechanisms alter gene expression and maintenance of cellular homeostasis is an active research area. In this review, we highlight recent studies investigating the intricate relationship between stress and aging, including its underlying epigenetic basis; describe different types of stresses that originate from both internal and external stimuli; and discuss potential interventions aimed at alleviating stress and restoring epigenetic patterns to combat aging or age-related diseases. Additionally, we address the challenges currently limiting advancement in this burgeoning field.

Targeting the RNA-Binding Protein HuR in Cancer

The RNA-binding protein human antigen R (HuR) is a well-established regulator of gene expression at the posttranscriptional level. Its dysregulation has been implicated in various human diseases, particularly cancer. In cancer, HuR is considered "active" when it shows increased subcellular localization in the cytoplasm, in addition to its normal nuclear localization. Cytoplasmic HuR plays a crucial role in stabilizing and enhancing the translation of prosurvival mRNAs that are involved in stress responses relevant to cancer progression, such as hypoxia, radiotherapy, and chemotherapy. In general, due to HuR's abundance and function in cancer cells compared with normal cells, it is an appealing target for oncology research. Exploiting the principles underlying HuR's role in tumorigenesis and resistance to stressors, targeting HuR has the potential for synergy with existing and novel oncologic therapies. This review aims to explore HuR's role in homeostasis and cancer pathophysiology, as well as current targeting strategies, which include silencing HuR expression, preventing its translocation and dimerization from the nucleus to the cytoplasm, and inhibiting mRNA binding. Furthermore, this review will discuss recent studies investigating the potential synergy between HuR inhibition and traditional chemotherapeutics.

Methylation across the central dogma in health and diseases: new therapeutic strategies

The proper transfer of genetic information from DNA to RNA to protein is essential for cell-fate control, development, and health. Methylation of DNA, RNAs, histones, and non-histone proteins is a reversible post-synthesis modification that finetunes gene expression and function in diverse physiological processes. Aberrant methylation caused by genetic mutations or environmental stimuli promotes various diseases and accelerates aging, necessitating the development of therapies to correct the disease-driver methylation imbalance. In this Review, we summarize the operating system of methylation across the central dogma, which includes writers, erasers, readers, and reader-independent outputs. We then discuss how dysregulation of the system contributes to neurological disorders, cancer, and aging. Current small-molecule compounds that target the modifiers show modest success in certain cancers. The methylome-wide action and lack of specificity lead to undesirable biological effects and cytotoxicity, limiting their therapeutic application, especially for diseases with a monogenic cause or different directions of methylation changes. Emerging tools capable of site-specific methylation manipulation hold great promise to solve this dilemma. With the refinement of delivery vehicles, these new tools are well positioned to advance the basic research and clinical translation of the methylation field.

Counteracting Immunosenescence-Which Therapeutic Strategies Are Promising?

Aging attenuates the overall responsiveness of the immune system to eradicate pathogens. The increased production of pro-inflammatory cytokines by innate immune cells under basal conditions, termed inflammaging, contributes to impaired innate immune responsiveness towards pathogen-mediated stimulation and limits antigen-presenting activity. Adaptive immune responses are attenuated as well due to lowered numbers of naïve lymphocytes and their impaired responsiveness towards antigen-specific stimulation. Additionally, the numbers of immunoregulatory cell types, comprising regulatory T cells and myeloid-derived suppressor cells, that inhibit the activity of innate and adaptive immune cells are elevated. This review aims to summarize our knowledge on the cellular and molecular causes of immunosenescence while also taking into account senescence effects that constitute immune evasion mechanisms in the case of chronic viral infections and cancer. For tumor therapy numerous nanoformulated drugs have been developed to overcome poor solubility of compounds and to enable cell-directed delivery in order to restore immune functions, e.g., by addressing dysregulated signaling pathways. Further, nanovaccines which efficiently address antigen-presenting cells to mount sustained anti-tumor immune responses have been clinically evaluated. Further, senolytics that selectively deplete senescent cells are being tested in a number of clinical trials. Here we discuss the potential use of such drugs to improve anti-aging therapy.

In Vivo Screening Unveils Pervasive RNA-Binding Protein Dependencies in Leukemic Stem Cells and Identifies ELAVL1 as a Therapeutic Target

Acute myeloid leukemia (AML) is fueled by leukemic stem cells (LSC) whose determinants are challenging to discern from hematopoietic stem cells (HSC) or uncover by approaches focused on general cell properties. We have identified a set of RNA-binding proteins (RBP) selectively enriched in human AML LSCs. Using an in vivo two-step CRISPR-Cas9 screen to assay stem cell functionality, we found 32 RBPs essential for LSCs in MLL-AF9;NrasG12D AML. Loss-of-function approaches targeting key hit RBP ELAVL1 compromised LSC-driven in vivo leukemic reconstitution, and selectively depleted primitive malignant versus healthy cells. Integrative multiomics revealed differentiation, splicing, and mitochondrial metabolism as key features defining the leukemic ELAVL1-mRNA interactome with mitochondrial import protein, TOMM34, being a direct ELAVL1-stabilized target whose repression impairs AML propagation. Altogether, using a stem cell-adapted in vivo CRISPR screen, this work demonstrates pervasive reliance on RBPs as regulators of LSCs and highlights their potential as therapeutic targets in AML.

SIGNIFICANCE

LSC-targeted therapies remain a significant unmet need in AML. We developed a stem-cell-adapted in vivo CRISPR screen to identify key LSC drivers. We uncover widespread RNA-binding protein dependencies in LSCs, including ELAVL1, which we identify as a novel therapeutic vulnerability through its regulation of mitochondrial metabolism. This article is highlighted in the In This Issue feature, p. 171.

Post-Transcriptional and Post-Translational Modifications in Telomerase Biogenesis and Recruitment to Telomeres

Telomere length is associated with the proliferative potential of cells. Telomerase is an enzyme that elongates telomeres throughout the entire lifespan of an organism in stem cells, germ cells, and cells of constantly renewed tissues. It is activated during cellular division, including regeneration and immune responses. The biogenesis of telomerase components and their assembly and functional localization to the telomere is a complex system regulated at multiple levels, where each step must be tuned to the cellular requirements. Any defect in the function or localization of the components of the telomerase biogenesis and functional system will affect the maintenance of telomere length, which is critical to the processes of regeneration, immune response, embryonic development, and cancer progression. An understanding of the regulatory mechanisms of telomerase biogenesis and activity is necessary for the development of approaches toward manipulating telomerase to influence these processes. The present review focuses on the molecular mechanisms involved in the major steps of telomerase regulation and the role of post-transcriptional and post-translational modifications in telomerase biogenesis and function in yeast and vertebrates.

Molecular Markers of Telomerase Complex for Patients with Pituitary Adenoma

Pituitary adenoma (PA) is the most common benign tumor of the pituitary gland. The pathogenesis of most PA is considered as a multifactorial process, that involves genetic mutations, alterations in gene transcription, and epigenetic factors. Their interaction promotes tumorigenesis. The processes are increasingly focused on changes in telomere length. Our study enrolled 126 patients with PA and 368 healthy subjects. DNA samples from peripheral blood leukocytes were purified by the DNA salting-out method. The RT-PCR carried out SNPs and relative leukocyte telomere lengths (RLTL). ELISA determined the level of TEP1 in blood serum. Binary logistic regression revealed that TERC rs35073794 is likely associated with increased odds of PA development and macro-PA development. It is also associated with decreased odds of active PA, non-invasive PA, and PA without relapse development. Also, we discovered that PA patients with at least one G allele of the TEP1 gene polymorphism rs1713418 have lower serum TEP1 levels than healthy individuals (p = 0.035). To conclude, the study revealed that TERC rs35073794 might be a potential biomarker for PA development.

Poly (A)-specific ribonuclease (PARN): More than just "mRNA stock clearing"

In eukaryotic cells, the balance between the synthesis and the degradation decides the steady-state levels of messenger RNAs (mRNA). The removal of adenosine residues from the poly(A) tail, called deadenylation, is the first and the most crucial step in the process of mRNA degradation. Poly (A)-specific ribonuclease (PARN) is one such enzyme that catalyses the process of deadenylation. Although PARN has been primarily known as the regulator of the mRNA stability, recent evidence clearly suggests several other functions of PARN, including a role in embryogenesis, oocyte maturation, cell-cycle progression, telomere biology, non-coding RNA maturation and ribosome biogenesis. Also, deregulated PARN activity is shown to be a hallmark of specific disease conditions. Pathogenic variants in the PARN gene have been observed in various cancers and inherited bone marrow failure syndromes. The focus in this review is to highlight the emerging functions of PARN, particularly in the context of human diseases.

Post-transcriptional diversity in riboproteins and RNAs in aging and cancer

Post-transcriptional (PtscM) and post-translational (PtrnM) modifications of nucleotides and amino acids are covalent modifications able to change physio-chemical properties of RNAs and proteins. In the ribosome, the adequate assembly of rRNAs and ribosomal protein subunits in the nucleolus ensures suitable translational activity, with protein synthesis tuned according to intracellular demands of energy production, replication, proliferation, and growth. Disruption in the regulatory control of PtscM and PtrnM can impair ribosome biogenesis and ribosome function. Ribosomal impairment may, in turn, impact the synthesis of proteins engaged in functions as varied as telomere maintenance, apoptosis, and DNA repair, as well as intersect with mitochondria and telomerase activity. These cellular processes often malfunction in carcinogenesis and senescence. Here we discuss regulatory mechanisms of PtscMs and PtrnMs on ribosomal function. We also address chemical modification in rRNAs and their impacts on cellular metabolism, replication control, and senescence. Further, we highlight similarities and differences of PtscMs and PtrnMs in ribosomal intermediates during aging and carcinogenesis. Understanding these regulatory mechanisms may uncover critical steps for the development of more efficient oncologic and anti-aging therapies.

Aging through an epitranscriptomic lens

The mechanistic causes of aging, the time-related decline in function and good health that leads to increased mortality, remain poorly understood. Here we propose that age-dependent alteration of the epitranscriptome, encompassing more than 150 chemically distinct post-transcriptional modifications or editing events, warrants exploration as an important modulator of aging. The epitranscriptome is a potent regulator of RNA function, diverse cellular processes and tissue regenerative capacity. To date, only a few studies link alterations in the epitranscriptome to molecular and physiological changes during aging; however, epitranscriptome dysfunction is associated with and underlies several age-associated pathologies, including cancer and neurodegenerative, cardiovascular and autoimmune diseases. For example, changes in RNA modifications (such as N⁶-methyladenosine and inosine) impact cardiac physiology and are linked to cardiac fibrosis. Although an uncharted research focus, mapping epitranscriptome alterations in the context of aging may elucidate novel predictors of both health and lifespan, and may identify therapeutic targets for attenuating aging and abrogating age-related diseases.

HuB and HuD repress telomerase activity by dissociating HuR from TERC

The ubiquitous RNA-binding protein HuR (ELAVL1) promotes telomerase activity by associating with the telomerase noncoding RNA TERC. However, the role of the neural-specific members HuB, HuC, and HuD (ELAVL2-4) in telomerase activity is unknown. Here, we report that HuB and HuD, but not HuC, repress telomerase activity in human neuroblastoma cells. By associating with AU-rich sequences in TERC, HuB and HuD repressed the assembly of the TERT-TERC core complex. Furthermore, HuB and HuD competed with HuR for binding to TERC and antagonized the function of HuR that was previously shown to enhance telomerase activity to promote cell growth. Our findings reveal a novel mechanism controlling telomerase activity in human neuroblastoma cells that involves a competition between HuR and the related, neural-specific proteins HuB and HuD.

Long non-coding RNAs at work on telomeres: Functions and implications in cancer therapy

Long non-coding RNAs (lncRNAs) are known to regulate various biological processes including cancer. Cancer cells possess limitless replicative potential which is attained by telomere length maintenance while normal somatic cells have a limited lifespan because their telomeres shorten with every cell division ultimately triggering replicative senescence. Two lncRNAs have been observed to play a key role in telomere length maintenance. First is the lncRNA TERC (telomerase RNA component) which functions as a template for telomeric DNA synthesis in association with telomerase reverse transcriptase (TERT) which serves as the catalytic component. Together they constitute the telomerase complex which functions as a reverse transcriptase to elongate telomeres. Second lncRNA that helps in regulating telomere length is the telomeric repeat-containing RNA (TERRA) which is transcribed from the subtelomeric region and extends to the telomeric region. TERC and TERRA exhibit important functions in cancer with implications in precision oncology. In this review, we discuss various aspects of these important lncRNAs in humans and their role in cancer along with recent advancements in their anticancer therapeutic application.

SMUG1 Promotes Telomere Maintenance through Telomerase RNA Processing

Telomerase biogenesis is a complex process where several steps remain poorly understood. Single-strand-selective uracil-DNA glycosylase (SMUG1) associates with the DKC1-containing H/ACA ribonucleoprotein complex, which is essential for telomerase biogenesis. Herein, we show that SMUG1 interacts with the telomeric RNA component (hTERC) and is required for co-transcriptional processing of the nascent transcript into mature hTERC. We demonstrate that SMUG1 regulates the presence of base modifications in hTERC, in a region between the CR4/CR5 domain and the H box. Increased levels of hTERC base modifications are accompanied by reduced DKC1 binding. Loss of SMUG1 leads to an imbalance between mature hTERC and its processing intermediates, leading to the accumulation of 3'-polyadenylated and 3'-extended intermediates that are degraded in an EXOSC10-independent RNA degradation pathway. Consequently, SMUG1-deprived cells exhibit telomerase deficiency, leading to impaired bone marrow proliferation in Smug1-knockout mice.

Interaction between HuR and circPABPN1 Modulates Autophagy in the Intestinal Epithelium by Altering ATG16L1 Translation

Intestinal epithelial autophagy is crucial for host defense against invasive pathogens, and defects in this process occur frequently in patients with inflammatory bowel disease (IBD) and other mucosal disorders, but the exact mechanism that activates autophagy is poorly defined. Here, we investigated the role of RNA-binding protein HuR (human antigen R) in the posttranscriptional control of autophagy-related genes (ATGs) in the intestinal epithelium. We found that targeted deletion of HuR in intestinal epithelial cells (IECs) specifically decreased the levels of ATG16L1 in the intestinal mucosa. Intestinal mucosa from patients with IBD exhibited reduced levels of both HuR and ATG16L1. HuR directly interacted with Atg16l1 mRNA via its 3' untranslated region and enhanced ATG16L1 translation, without affecting Atg16l1 mRNA stability. Circular RNA circPABPN1 blocked HuR binding to Atg16l1 mRNA and lowered ATG16L1 production. HuR silencing in cultured IECs also prevented rapamycin-induced autophagy, which was abolished by overexpressing ATG16L1. These findings indicate that HuR regulates autophagy by modulating ATG16L1 translation via interaction with circPABPN1 in the intestinal epithelium.

Understanding and targeting the disease-related RNA binding protein human antigen R (HuR)

Altered gene expression is a characteristic feature of many disease states such as tumorigenesis, and in most cancers, it facilitates cancer cell survival and adaptation. Alterations in global gene expression are strongly impacted by post-transcriptional gene regulation. The RNA binding protein (RBP) HuR (ELAVL1) is an established regulator of post-transcriptional gene regulation and is overexpressed in most human cancers. In many cancerous settings, HuR is not only overexpressed, but it is "overactive" as denoted by increased subcellular localization within the cytoplasm. This dysregulation of HuR expression and cytoplasmic localization allows HuR to stabilize and increase the translation of various prosurvival messenger RNA (mRNAs) involved in the pathogenesis of numerous cancers and various diseases. Based on almost 20 years of work, HuR is now recognized as a therapeutic target. Herein, we will review the role HuR plays in the pathophysiology of different diseases and ongoing therapeutic strategies to target HuR. We will focus on three ongoing-targeted strategies: (1) inhibiting HuR's translocation from the nucleus to the cytoplasm; (2) inhibiting the ability of HuR to bind target RNA; and (3) silencing HuR expression levels. In an oncologic setting, HuR has been demonstrated to be critical for a cancer cell's ability to survive a variety of cancer relevant stressors (including drugs and elements of the tumor microenvironment) and targeting this protein has been shown to sensitize cancer cells further to insult. We strongly believe that targeting HuR could be a powerful therapeutic target to treat different diseases, particularly cancer, in the near future. This article is categorized under: RNA in Disease and Development > RNA in Disease NRA Turnover and Surveillance > Regulation of RNA Stability Translation > Translation Regulation.

The RXFP3 receptor is functionally associated with cellular responses to oxidative stress and DNA damage

DNA damage response (DDR) processes, often caused by oxidative stress, are important in aging and -related disorders. We recently showed that G protein-coupled receptor (GPCR) kinase interacting protein 2 (GIT2) plays a key role in both DNA damage and oxidative stress. Multiple tissue analyses in GIT2KO mice demonstrated that GIT2 expression affects the GPCR relaxin family peptide 3 receptor (RXFP3), and is thus a therapeutically-targetable system. RXFP3 and GIT2 play similar roles in metabolic aging processes. Gaining a detailed understanding of the RXFP3-GIT2 functional relationship could aid the development of novel anti-aging therapies. We determined the connection between RXFP3 and GIT2 by investigating the role of RXFP3 in oxidative stress and DDR. Analyzing the effects of oxidizing (H₂O₂) and DNA-damaging (camptothecin) stressors on the interacting partners of RXFP3 using Affinity Purification-Mass Spectrometry, we found multiple proteins linked to DDR and cell cycle control. RXFP3 expression increased in response to DNA damage, overexpression, and Relaxin 3-mediated stimulation of RXFP3 reduced phosphorylation of DNA damage marker H2AX, and repair protein BRCA1, moderating DNA damage. Our data suggests an RXFP3-GIT2 system that could regulate cellular degradation after DNA damage, and could be a novel mechanism for mitigating the rate of age-related damage accumulation.

mRNA methylation in cell senescence

Cellular senescence, a developmental program central to normal aging and aging pathologies, is robustly regulated at the post-transcriptional level. This regulation involves the interaction of RNA-binding proteins and noncoding RNAs with senescence-associated messenger RNAs (mRNAs). There is increasing evidence that these associations are modulated by chemical modifications of specific mRNA nucleotides which can enhance or reduce the binding of regulatory factors. Recent technological advances in mass spectrometry, next-generation sequencing, and genome mapping have improved markedly the detection of mRNA modifications. Given the rising interest in the epitranscriptomic control of gene expression in aging, we discuss our incipient understanding of the chemical mRNA modifications, specifically m6 A and m5 C, that influence cellular senescence. This article is categorized under: RNA Export and Localization > RNA Localization RNA Processing > RNA Editing and Modification.

How RNAi machinery enters the world of telomerase

Human telomerase holoenzyme consists of the catalytic component TERT and the template RNA TERC. However, a network of accessory proteins plays key roles in its assembly, localization and stability. Defects in genes involved in telomerase biology affect the renewal of critical stem cell populations and cause disorders such as telomeropathies. Moreover, activation of telomerase in somatic cells allows neoplastic cells to proliferate indefinitely, thus contributing to tumorigenesis. For these reasons, identification of new players involved in telomerase regulation is crucial for the determination of novel therapeutic targets and biomarkers. In the very last years, increasing evidence describes components of the RNAi machinery as a new layer of complexity in human telomerase activity. In this review, we will discuss how AGO2 and other proteins which collaborate with AGO2 in RNAi pathway play a pivotal role in TERC stability and function.

A novel antisense oligonucleotide anchored on the intronic splicing enhancer of hTERT pre-mRNA inhibits telomerase activity and induces apoptosis in glioma cells

INTRODUCTION

Alternative splicing of hTERT pre-mRNA is an important step in the regulation of telomerase activity, but the regulation mechanisms and functions remain unclear.

METHODS

RT-PCR analysis was used to detect hTERT splicing in glioma cell lines and brain tissues. TRAP assay was used to detect the telomerase activity. Then, we designed and synthesized 2'-O-methyl-RNA phosphorothioate AONs and transfected them into glioma cells to detect the changes in telomerase activity. MTT assay, plate colony formation assay, western blotting and Annexin V/PI assay were used to detect cell proliferation and apoptosis. At last, bioinformatics analyses were used to predict the expression and function of splicing protein SRSF2 in gliomas.

RESULTS

hTERT splicing occurs both in glioma cell lines and glioma patients' tissues. The telomerase activity was related to the expression level of the full-length hTERT, rather than the total hTERT transcript level. AON-Ex726 was complementary to the sequence of the intronic splicing enhancer (ISE) in intron six, and significantly altered the splicing pattern of hTERT pre-mRNA, reducing the expression level of the full-length hTERT mRNA and increasing the expression level of the -β hTERT mRNA. After transfection with AON-Ex726, the level of apoptosis was increased, while telomerase activity and cell proliferation were significantly decreased. By bioinformatic predictions, we found the AON-Ex726 anchoring sequence in ISE overlaps the binding site of SRSF2 protein, which is up-regulated during the development of gliomas.

CONCLUSIONS

Our findings provided new targets and important clues for the gene therapy of gliomas by regulating the alternative splicing pattern of hTERT pre-mRNA.