The role of ceranib-2 and its nanoform on the decrease of telomerase levels in human non-small cell cancer.

BACKGROUND: Ceranib-2, an acid ceramidase (AC) inhibitor, can inhibit cancer cell proliferation and tumor development. However, poor water solubility and low cellular bioavailability limit its efficacy in cancer treatment. METHODS AND RESULTS: This study aimed to investigate the cell death induced by ceranib-2 and its solid lipid nanoformulation (ceranib-2-SLN) produced by the hot homogenization technique and the synergistic relationship between ceramide and telomerase in vitro and in silico. Furthermore, this study proved the possible mechanism of ceranib-2-induced AC inhibition by in silico studies. The effective cytotoxic concentrations of ceranib-2, telomerase level, and changes in ceramide levels were measured by MTT colorimetric cytotoxicity assay, ELISA, and LC/MS/MS methods, respectively. TEM results showed that ceranib-2-SLN was 13-fold smaller than the size of ceranib-2. Ceranib-2 and ceranib-2-SLN had IC50 concentrations of 31.62 (± 2.1) and 27.69 (± 1.75) µM in A549, and 48.79 (± 1.56) and 67.98 (± 2.33) in Beas-2B cells. These compounds simultaneously increased ceramide levels and decreased telomerase levels in A549 cells. Ceranib-2 increased telomerase levels while decreasing ceramide levels in Beas-2B cells. It was shown how the synergistic impact of ceranib-2-induced ceramide production and ceramide-induced telomerase level reduction on cytotoxicity in A549 cells. CONCLUSIONS: Ceranib-2-SLN was discovered to be more cytotoxic on cancer cells than ceranib-2, suggesting that it could be a promising option for the development of a new anti-cancer agent.

RIOK2 transcriptionally regulates TRiC and dyskerin complexes to prevent telomere shortening.

Telomere shortening is a prominent hallmark of aging and is emerging as a characteristic feature of Myelodysplastic Syndromes (MDS) and Idiopathic Pulmonary Fibrosis (IPF). Optimal telomerase activity prevents progressive shortening of telomeres that triggers DNA damage responses. However, the upstream regulation of telomerase holoenzyme components remains poorly defined. Here, we identify RIOK2, a master regulator of human blood cell development, as a critical transcription factor for telomere maintenance. Mechanistically, loss of RIOK2 or its DNA-binding/transactivation properties downregulates mRNA expression of both TRiC and dyskerin complex subunits that impairs telomerase activity, thereby causing telomere shortening. We further show that RIOK2 expression is diminished in aged individuals and IPF patients, and it strongly correlates with shortened telomeres in MDS patient-derived bone marrow cells. Importantly, ectopic expression of RIOK2 alleviates telomere shortening in IPF patient-derived primary lung fibroblasts. Hence, increasing RIOK2 levels prevents telomere shortening, thus offering therapeutic strategies for telomere biology disorders.

The Impact of the Mediterranean Diet on Telomere Biology: Implications for Disease Management-A Narrative Review.

INTRODUCTION: Telomeres are nucleoprotein complexes at the ends of chromosomes that are under the control of genetic and environmental triggers. Accelerated telomere shortening is causally implicated in the increasing incidence of diseases. The Mediterranean diet has recently been identified as one that confers protection against diseases. This review aimed to identify the effect of each component of the Mediterranean diet on telomere length dynamics, highlighting the underlying molecular mechanisms. METHODS: PubMed was searched to identify relevant studies to extract data for conducting a narrative review. RESULTS: The Mediterranean diet alleviates clinical manifestations in many diseases. Focusing on autoimmune diseases, the Mediterranean diet can be protective by preventing inflammation, mitochondrial malfunction, and abnormal telomerase activity. Also, each Mediterranean diet constituent seems to attenuate aging through the sustenance or elongation of telomere length, providing insights into the underlying molecular mechanisms. Polyphenols, vitamins, minerals, and fatty acids seem to be essential in telomere homeostasis, since they inhibit inflammatory responses, DNA damage, oxidative stress, mitochondrial malfunction, and cell death and induce telomerase activation. CONCLUSIONS: The Mediterranean diet is beneficial for maintaining telomere dynamics and alleviating age-related illnesses. This review provides a comprehensive overview of cross-sectional, observational, and randomized controlled trials regarding the beneficial impact of every constituent in the Mediterranean diet on telomere length and chronic disease management.

Telomere Length, Telomerase Activity, and Vaginal Microbiome in Patients with HPV-Related Precancerous Lesions.

Persistent high-risk human papillomaviruses (HR HPVs) infection leads to the development of squamous intraepithelial lesions in cervical cells that may lead to cancer. The telomere length, telomerase activity, and species composition of the vaginal microbiome may influence the dynamic of changes and the process of carcinogenesis. In the present study, we analyze relative telomere length (RTL), relative hTERT expression (gene for the telomerase component-reverse transcriptase) in cervical smear cells and vaginal microbiomes. Total RNA and DNA were isolated from tissue samples of 109 patients from the following groups: control, carrier, low-grade or high-grade squamous intraepithelial lesion (L SIL and H SIL, respectively), and cancer. The quantitative PCR method was used to measure telomere length and telomerase expression. Vaginal microbiome bacteria were divided into community state types using morphotype criteria. Significant differences between histopathology groups were confirmed for both relative telomere length and relative hTERT expression (p < 0.001 and p = 0.001, respectively). A significant difference in RTL was identified between carriers and H SIL (p adj < 0.001) groups, as well as between carriers and L SIL groups (p adj = 0.048). In both cases, RTL was lower among carriers. The highest relative hTERT expression level was recorded in the H SIL group, and the highest relative hTERT expression level was recorded between carriers and the H SIL group (p adj < 0.001). A correlation between genotype and biocenosis was identified for genotype 16+A (p < 0.001). The results suggest that identification of HPV infection, telomere length assessment, and hTERT expression measurement together may be more predictive than each of these analyses performed separately.

Establishment and Characterization of a Chicken Myoblast Cell Line.

Skeletal muscle, which is predominantly constituted by multinucleated muscle fibers, plays a pivotal role in sustaining bodily movements and energy metabolism. Myoblasts, which serve as precursor cells for differentiation and fusion into muscle fibers, are of critical importance in the exploration of the functional genes associated with embryonic muscle development. However, the in vitro proliferation of primary myoblasts is inherently constrained. In this study, we achieved a significant breakthrough by successfully establishing a chicken myoblast cell line through the introduction of the exogenous chicken telomerase reverse transcriptase (chTERT) gene, followed by rigorous G418-mediated pressure screening. This newly developed cell line, which was designated as chTERT-myoblasts, closely resembled primary myoblasts in terms of morphology and exhibited remarkable stability in culture for at least 20 generations of population doublings without undergoing malignant transformation. In addition, we conducted an exhaustive analysis that encompassed cellular proliferation, differentiation, and transfection characteristics. Our findings revealed that the chTERT-myoblasts had the ability to proliferate, differentiate, and transfect after multiple rounds of population doublings. This achievement not only furnished a valuable source of homogeneous avian cell material for investigating embryonic muscle development, but also provided valuable insights and methodologies for establishing primary cell lines.

Aging, Cancer, and Inflammation: The Telomerase Connection.

Understanding the complex dynamics of telomere biology is important in the strong link between aging and cancer. Telomeres, the protective caps at the end of chromosomes, are central players in this connection. While their gradual shortening due to replication limits tumors expansion by triggering DNA repair mechanisms, it also promotes oncogenic changes within chromosomes, thus sustaining tumorigenesis. The enzyme telomerase, responsible for maintaining telomere length, emerges as a central player in this context. Its expression in cancer cells facilitates the preservation of telomeres, allowing them to circumvent the growth-limiting effects of short telomeres. Interestingly, the influence of telomerase extends beyond telomere maintenance, as evidenced by its involvement in promoting cell growth through alternative pathways. In this context, inflammation accelerates telomere shortening, resulting in telomere dysfunction, while telomere elements also play a role in modulating the inflammatory response. The recognition of this interplay has promoted the development of novel therapeutic approaches centered around telomerase inhibition. This review provides a comprehensive overview of the field, emphasizing recent progress in knowledge and the implications in understanding of cancer biology.

Telomerase Reverse Transcriptase Regulates Intracellular Ca2+ Homeostasis and Mitochondrial Function via the p53/PGC-1α Pathway in HL-1 Cells.

BACKGROUND: Telomere shortening is strongly associated with cardiovascular aging and disease, and patients with shorter telomeres in peripheral blood leukocytes are at higher risk of cardiovascular diseases such as heart failure and atrial fibrillation (AF). Telomerase reverse transcriptase (TERT) maintains telomere length, and overexpression of TERT has been shown to reduce cardiomyocyte apoptosis and myocardial infarct size, and extend the lifespan of aged mice. However, the specific impact of TERT on the electrophysiology of cardiomyocytes remains to be elucidated. The aims of this study were to evaluate the role of TERT in Ca2+ homeostasis and mitochondrial function in atrial myocytes as well as the underlying mechanisms. METHODS: TERT overexpressed and silenced HL-1 cells were constructed with lentiviruses, and the respective empty lentiviral vectors were used as negative controls. Then the patch clamp technique was used to record the electrophysiological characteristics such as cell action potential duration (APD) and L-type Ca2+ currents (ICa,L), flow cytometry was used to detect intracellular Ca2+ concentration and mitochondrial membrane potential (MMP), and the Seahorse assay was used to measure the oxygen consumption rate (OCR). RESULTS: TERT silencing led to intracellular Ca2+ overload, shortened APD, decreased ICa,L current density, altered Ca2+ gating mechanism, decreased MMP and OCR, and increased reactive oxygen species (ROS), whereas TERT overexpression led to the reverse effects. Additionally, TERT silencing resulted in intracellular Ca2+ overload with decreased expression of the SERCA2a, CaV1.2, and NCX1.1, whereas TERT overexpression had opposing effects. Furthermore, we discovered that TERT could regulate the expression of p53 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). The expression of PGC-1α was downregulated by the p53 agonist Tenovin-6 but upregulated by the p53 inhibitor PFTα. The effects of the PGC-1α inhibitor SR-18292 on intracellular Ca2+ and cell electrophysiology were similar to those of silencing TERT, whereas the PGC-1α agonist ZLN005 produced comparable outcomes to TERT overexpression. CONCLUSIONS: TERT silencing-induced Ca2+ overload and mitochondrial dysfunction may be one mechanism of age-related AF. Overexpression of TERT reduced the basis for arrhythmia formation such as AF, suggesting a favorable safety profile for TERT therapy. TERT regulated intracellular Ca2+ homeostasis and mitochondrial function through the p53/PGC-1α pathway. In addition, PGC-1α might be a novel target for AF, suggesting that intervention for AF should be not limited to abnormal cation handling.

Telomerase activity, telomere length, and the euploidy rate of human embryos.

BACKGROUND: Telomeres maintain chromosome stability, while telomerase counteracts their progressive shortening. Telomere length varies between cell types, with leukocyte telomere length (LTL) decreasing with age. Reduced telomerase activity has been linked to reproductive issues in females, such as low pregnancy rates and premature ovarian failure, with recent studies indicating correlations between telomere length in granulosa cells and IVF outcomes. OBJECTIVES: The study aims to explore the relationship between telomere length, telomerase activity, and euploid blastocyst rate in infertile women undergoing IVF/ICSI PGT-A cycles. METHODS: This prospective study involves 108 patients undergoing controlled ovarian stimulation and PGT-A. Telomere length and telomerase activity were measured in peripheral mononuclear cells and granulosa cells (GC), respectively. RESULTS: The telomere repeat copy number to single gene copy number ratio (T/S) results respectively 0.6 ± 0.8 in leukocytes and 0.7 ± 0.9 in GC. An inverse relationship was found between LTL and the patient's age (p < .01). A higher aneuploid rate was noticed in patients with short LTL, with no differences in ovarian reserve markers (p = .15), number of oocytes retrieved (p = .33), and number of MII (p = 0.42). No significant association was noticed between telomere length in GC and patients' age (p = 0.95), in ovarian reserve markers (p = 0.32), number of oocytes retrieved (p = .58), number of MII (p = .74) and aneuploidy rate (p = .65). CONCLUSION: LTL shows a significant inverse correlation with patient age and higher aneuploidy rates. Telomere length in GCs does not correlate with patient age or reproductive outcomes, indicating differential telomere dynamics between leukocytes and granulosa cells.

Exosomes derived from hTERT-immortalized cells delay cellular senescence of human fibroblasts.

hTERT gene therapies hold significant promise for treating age-related diseases. However, further research is required to address the challenges of delivery and ethical considerations. We hypothesized that exosomes derived from hTERT-immortalized cells could function similarly to hTERT gene therapies by maintaining telomere length and attenuating cellular senescence biomarkers. In this study, we overexpressed the hTERT gene in Human Foreskin Fibroblast-1 cells (HFF cells) to produce hTERT-immortalized HFF cells (hT-HFF cells). We then used exosomes derived from these hT-HFF cells to treat human fibroblasts, HFF cells. Our results demonstrated that these exosomes effectively attenuated biomarkers of cellular senescence in HFF cells. Furthermore, analysis revealed that hTERT mRNA was indeed packaged into the exosomes from hT-HFF cells. This mRNA was capable of elongating telomeres and delaying cellular senescence in HFF cells. Therefore, exosomes from hT-HFF cells show potential as a treatment for age-related diseases.

Telomere C-Strand Fill-In Machinery: New Insights into the Human CST-DNA Polymerase Alpha-Primase Structures and Functions.

Telomeres at the end of eukaryotic chromosomes are extended by a specialized set of enzymes and telomere-associated proteins, collectively termed here the telomere "replisome." The telomere replisome acts on a unique replicon at each chromosomal end of the telomeres, the 3' DNA overhang. This telomere replication process is distinct from the replisome mechanism deployed to duplicate the human genome. The G-rich overhang is first extended before the complementary C-strand is filled in. This overhang is extended by telomerase, a specialized ribonucleoprotein and reverse transcriptase. The overhang extension process is terminated when telomerase is displaced by CTC1-STN1-TEN1 (CST), a single-stranded DNA-binding protein complex. CST then recruits DNA polymerase α-primase to complete the telomere replication process by filling in the complementary C-strand. In this chapter, the recent structure-function insights into the human telomere C-strand fill-in machinery (DNA polymerase α-primase and CST) will be discussed.

Tert-expressing cells contribute to salivary gland homeostasis and tissue regeneration after radiation therapy.

Salivary gland homeostasis and regeneration after radiotherapy depend significantly on progenitor cells. However, the lineage of submandibular gland (SMG) progenitor cells remains less defined compared with other normal organs. Here, using a mouse strain expressing regulated CreERT2 recombinase from the endogenous Tert locus, we identify a distinct telomerase-expressing (TertHigh) cell population located in the ductal region of the adult SMG. These TertHigh cells contribute to ductal cell generation during SMG homeostasis and to both ductal and acinar cell renewal 1 year after radiotherapy. TertHigh cells maintain self-renewal capacity during in vitro culture, exhibit resistance to radiation damage, and demonstrate enhanced proliferative activity after radiation exposure. Similarly, primary human SMG cells with high Tert expression display enhanced cell survival after radiotherapy, and CRISPR-activated Tert in human SMG spheres increases proliferation after radiation. RNA sequencing reveals upregulation of "cell cycling" and "oxidative stress response" pathways in TertHigh cells following radiation. Mechanistically, Tert appears to modulate cell survival through ROS levels in SMG spheres following radiation damage. Our findings highlight the significance of TertHigh cells in salivary gland biology, providing insights into their response to radiotherapy and into their use as a potential target for enhancing salivary gland regeneration after radiotherapy.

Optimization of biotransformation processes of Camarosporium laburnicola to improve production yields of potent telomerase activators.

BACKGROUND: Telomerase activators are promising agents for the healthy aging process and the treatment/prevention of short telomere-related and age-related diseases. The discovery of new telomerase activators and later optimizing their activities through chemical and biological transformations are crucial for the pharmaceutical sector. In our previous studies, several potent telomerase activators were discovered via fungal biotransformation, which in turn necessitated optimization of their production. It is practical to improve the production processes by implementing the design of experiment (DoE) strategy, leading to increased yield and productivity. In this study, we focused on optimizing biotransformation conditions utilizing Camarosporium laburnicola, a recently discovered filamentous fungus, to afford the target telomerase activators (E-CG-01, E-AG-01, and E-AG-02). RESULTS: DoE approaches were used to optimize the microbial biotransformation processes of C. laburnicola. Nine parameters were screened by Plackett-Burman Design, and three significant parameters (biotransformation time, temperature, shaking speed) were optimized using Central Composite Design. After conducting validation experiments, we were able to further enhance the production yield of target metabolites through scale-up studies in shake flasks (55.3-fold for E-AG-01, 13-fold for E-AG-02, and 1.96-fold for E-CG-01). CONCLUSION: Following a process optimization study using C. laburnicola, a significant increase was achieved in the production yields. Thus, the present study demonstrates a promising methodology to increase the production yield of potent telomerase activators. Furthermore, C. laburnicola is identified as a potential biocatalyst for further industrial utilization.

Human ARMC6 binds in vitro to both cancer genes and telomeric RNA, favoring G-quadruplex structure recognition.

Armadillo repeat-containing proteins (ARMCs) are a large family found throughout eukaryotes, which play prominent roles in cell adhesion, signaling and cytoskeletal regulation. The ARMC6 protein is highly conserved in primates, including humans, but to date does not have a clear function beyond initial hints of a link to cancer and telomerase activity. We report here in vitro experiments showing ARMC6 binding to DNA promoter sequences from several cancer-related genes (e.g., EGFR, VEGF and c-MYC), and also to the telomeric RNA repeat (TERRA). ARMC6 binding activity appears to recognize G-quadruplex motifs, which are being increasingly implicated as structure-based protein binding sites in chromosome maintenance and repair. In vivo investigation of ARMC6 function revealed that when this protein is overexpressed in human cell lines, there is different expression of genes connected with oncogenic pathways and those implicated in downstream non-canonical telomerase pathways (e.g., VEGF, hTERT, c-MYC, ESM1, MMP3). ARMC6 is already known to interact with human shelterin protein TRF2 and telomerase. The protein binds G-quadruplex structures and does so preferentially to RNA over DNA. As such, this protein may be an example of how a non-canonical nucleic acid structural motif allows mediation between gene regulation and telomeric chromatin rearrangement pathways.

Targeting hTERT Promoter G-Quadruplex DNA Structures with Small-Molecule Ligand to Downregulate hTERT Expression for Triple-Negative Breast Cancer Therapy.

Human telomerase reverse transcriptase (hTERT) may have noncanonical functions in transcriptional regulation and metabolic reprogramming in cancer cells, but it is a challenging target. We thus developed small-molecule ligands targeting hTERT promoter G-quadruplex DNA structures (hTERT G4) to downregulate hTERT expression. Ligand 5 showed high affinity toward hTERT G4 (Kd = 1.1 µM) and potent activity against triple-negative breast cancer cells (MDA-MB-231, IC50 = 1 µM). In cell-based assays, 5 not only exerts markedly inhibitory activity on classical telomere functions including decreased telomerase activity, shortened telomere length, and cellular senescence but also induces DNA damage, acute cellular senescence, and apoptosis. This study reveals that hTERT G4-targeting ligand may cause mitochondrial dysfunction, disrupt iron metabolism and activate ferroptosis in cancer cells. The in vivo antitumor efficacy of 5 was also evaluated in an MDA-MB-231 xenograft mouse model and approximately 78.7% tumor weight reduction was achieved. No observable toxicity against the major organs was observed.

Telomere Elongation During Pre-Implantation Embryo Development.

The primary mechanism of telomere elongation in mammals is reverse transcription by telomerase. An alternative (ALT) pathway elongates telomeres by homologous recombination in some cancer cells and during pre-implantation embryo development, when telomere length increases rapidly within a few cell cycles. The maternal and paternal telomeres in the zygote are genetically and epigenetically distinct, with differences in telomere length and in chromatin packaging. We discuss models for how these asymmetries may contribute to telomere regulation during the earliest embryonic cell cycles and suggest directions for future research.

Using deep learning to decipher the impact of telomerase promoter mutations on the dynamic metastatic morpholome.

Melanoma showcases a complex interplay of genetic alterations and intra- and inter-cellular morphological changes during metastatic transformation. While pivotal, the role of specific mutations in dictating these changes still needs to be fully elucidated. Telomerase promoter mutations (TERTp mutations) significantly influence melanoma's progression, invasiveness, and resistance to various emerging treatments, including chemical inhibitors, telomerase inhibitors, targeted therapy, and immunotherapies. We aim to understand the morphological and phenotypic implications of the two dominant monoallelic TERTp mutations, C228T and C250T, enriched in melanoma metastasis. We developed isogenic clonal cell lines containing the TERTp mutations and utilized dual-color expression reporters steered by the endogenous Telomerase promoter, giving us allelic resolution. This approach allowed us to monitor morpholomic variations induced by these mutations. TERTp mutation-bearing cells exhibited significant morpholome differences from their wild-type counterparts, with increased allele expression patterns, augmented wound-healing rates, and unique spatiotemporal dynamics. Notably, the C250T mutation exerted more pronounced changes in the morpholome than C228T, suggesting a differential role in metastatic potential. Our findings underscore the distinct influence of TERTp mutations on melanoma's cellular architecture and behavior. The C250T mutation may offer a unique morpholomic and systems-driven advantage for metastasis. These insights provide a foundational understanding of how a non-coding mutation in melanoma metastasis affects the system, manifesting in cellular morpholome.

Impact of khat (Catha edulis) and oral contraceptive use on telomerase levels and tumor suppressor genes p53 and p21 in normal subjects and breast cancer patients.

This study aimed to evaluate the effects of oral contraceptive (OC) use, khat chewing, and their combined effect on telomerase level and tumor suppressor genes, p53 and p21 in breast cancer (BC) patients and normal volunteers. 140 Yemeni women aged 25-40 years old enrolled, 60 newly diagnosed pretreated BC patients, and 80 control subjects. Venous blood (5 ml) was collected and the results showed BC patients to have significantly raised levels of telomerase, p53, and p21 compared to the control group. The use of OCs significantly raised telomerase in control group with no effect in BC patients; whereas p53 and p21 were significantly increased in BC patients. On the other hand, khat chewing significantly increased p53 in controls and BC patients, whereas p21 was significantly raised in BC patients. The combined use of OCs and khat chewing significantly increased telomerase and p53 in control group, and significantly increased p53 and p21 in BC patients. Telomerase was shown to be a risk factor (OR 4.4) for BC, and the use of OCs was a high-risk factor for increasing telomerase (OR 27.8) in normal subjects. In contrast, khat chewing was shown to be protective (OR 0.142), and the combined use of OCs and khat chewing decreased the risk factor of telomerase from OR 27.8 to 2.1.

Clonal inactivation of TERT impairs stem cell competition.

Telomerase is intimately associated with stem cells and cancer, because it catalytically elongates telomeres-nucleoprotein caps that protect chromosome ends1. Overexpression of telomerase reverse transcriptase (TERT) enhances the proliferation of cells in a telomere-independent manner2-8, but so far, loss-of-function studies have provided no evidence that TERT has a direct role in stem cell function. In many tissues, homeostasis is shaped by stem cell competition, a process in which stem cells compete on the basis of inherent fitness. Here we show that conditional deletion of Tert in the spermatogonial stem cell (SSC)-containing population in mice markedly impairs competitive clone formation. Using lineage tracing from the Tert locus, we find that TERT-expressing SSCs yield long-lived clones, but that clonal inactivation of TERT promotes stem cell differentiation and a genome-wide reduction in open chromatin. This role for TERT in competitive clone formation occurs independently of both its reverse transcriptase activity and the canonical telomerase complex. Inactivation of TERT causes reduced activity of the MYC oncogene, and transgenic expression of MYC in the TERT-deleted pool of SSCs efficiently rescues clone formation. Together, these data reveal a catalytic-activity-independent requirement for TERT in enhancing stem cell competition, uncover a genetic connection between TERT and MYC and suggest that a selective advantage for stem cells with high levels of TERT contributes to telomere elongation in the male germline during homeostasis and ageing.

LARP3, LARP7, and MePCE are involved in the early stage of human telomerase RNA biogenesis.

Human telomerase assembly is a highly dynamic process. Using biochemical approaches, we find that LARP3 and LARP7/MePCE are involved in the early stage of human telomerase RNA (hTR) and that their binding to RNA is destabilized when the mature form is produced. LARP3 plays a negative role in preventing the processing of the 3'-extended long (exL) form and the binding of LARP7 and MePCE. Interestingly, the tertiary structure of the exL form prevents LARP3 binding and facilitates hTR biogenesis. Furthermore, low levels of LARP3 promote hTR maturation, increase telomerase activity, and elongate telomeres. LARP7 and MePCE depletion inhibits the conversion of the 3'-extended short (exS) form into mature hTR and the cytoplasmic accumulation of hTR, resulting in telomere shortening. Taken together our data suggest that LARP3 and LARP7/MePCE mediate the processing of hTR precursors and regulate the production of functional telomerase.