Antisense oligonucleotide-mediated inhibition of hTERT, but not hTERC, induces rapid cell growth decline and apoptosis in the absence of telomere shortening in human prostate cancer cells

The regulatory process and practical significance of non-coding RNA in the dissemination of prostate cancer to the skeletal system

Prostate cancer is a major contributor to male cancer-related mortality globally. It has a particular affinity for the skeletal system with metastasis to bones seriously impacting prognosis. The identification of prostate cancer biomarkers can significantly enhance diagnosis and patient monitoring. Research has found that cancer and metastases exhibit abnormal expression of numerous non-coding RNA. Some of these RNA facilitate prostate cancer bone metastasis by activating downstream signaling pathways, while others inhibit this process. Elucidating the functional processes of non-coding RNA in prostate cancer bone metastasis will likely lead to innovative treatment strategies for this malignant condition. In this review, the mechanistic role of the various RNA in prostate cancer is examined. Our goal is to provide a new avenue of approach to the diagnosis and treatment of bone metastasis in this cancer.

Role of p53 transcription factor in determining the efficacy of telomerase inhibitors in cancer treatment

AIM

Telomerase expression is unique to cancer cells, making it a promising target for therapy. However, a major drawback of telomerase inhibition is that it affects cancer cell proliferation only when telomeres shorten, creating a lag phase post-continuous drug treatment. Acute cytotoxicity of telomerase inhibitors is dependent on their ability to induce DNA damage. p53 senses DNA damage and is the primary effector required for sensitizing cells towards apoptosis.

MAIN METHODS

Isogenic p53+/+ and p53-/- ovarian cancer cell lines were generated using the CRISPR/Cas9 system and the anti-cancer effect of telomerase inhibitors MST-312 and BIBR1532 were determined. Flow cytometry, real-time PCR, and western blot were performed to study cell cycle, apoptosis, and gene expression.

KEY FINDINGS

We report that MST-312 exhibits p53-dependent cytotoxicity, while BIBR1532 exhibits p53-independent cytotoxicity. Colony-forming ability also confirms the p53-dependent effect of MST-312. Re-expression of p53 in p53-/- cells could rescue MST-312 sensitivity. In p53+/+ cells, MST-312 causes S phase arrest and activation of p53-dependent target genes like anti-apoptosis markers (Fas and Puma) and cell cycle markers (p21 and cyclinB). In p53-/- cells, MST-312 causes S/G2/M arrest. BIBR1532 induces S/G2/M phase cell cycle arrest irrespective of p53 status. This correlates with the expression of the DNA damage marker (γ-H2AX). Long-term continuous treatment with MST-312 or BIBR1532 results in p53-independent telomere shortening.

SIGNIFICANCE

In summary, we demonstrate that acute anti-cancer effects of MST-312 are dependent on p53 expression. Hence, it is important to consider the p53 expression status in cancer cells when selecting and administering telomerase inhibitors.

Multiple Actions of Telomerase Reverse Transcriptase in Cell Death Regulation

Telomerase reverse transcriptase (TERT), a core part of telomerase, has been known for a long time only for its telomere lengthening function by reverse transcription of RNA template. Currently, TERT is considered as an intriguing link between multiple signaling pathways. The diverse intracellular localization of TERT corresponds to a wide range of functional activities. In addition to the canonical function of protecting chromosome ends, TERT by itself or as a part of the telomerase complex participates in cell stress responses, gene regulation and mitochondria functioning. Upregulation of TERT expression and increased telomerase activity in cancer and somatic cells relate to improved survival and persistence of such cells. In this review, we summarize the data for a comprehensive understanding of the role of TERT in cell death regulation, with a focus on the interaction of TERT with signaling pathways involved in cell survival and stress response.

Many Functions of Telomerase Components: Certainties, Doubts, and Inconsistencies

A growing number of studies have evidenced non-telomeric functions of "telomerase". Almost all of them, however, investigated the non-canonical effects of the catalytic subunit TERT, and not the telomerase ribonucleoprotein holoenzyme. These functions mainly comprise signal transduction, gene regulation and the increase of anti-oxidative systems. Although less studied, TERC (the RNA component of telomerase) has also been shown to be involved in gene regulation, as well as other functions. All this has led to the publication of many reviews on the subject, which, however, are often disseminating personal interpretations of experimental studies of other researchers as original proofs. Indeed, while some functions such as gene regulation seem ascertained, especially because mechanistic findings have been provided, other ones remain dubious and/or are contradicted by other direct or indirect evidence (e.g., telomerase activity at double-strand break site, RNA polymerase activity of TERT, translation of TERC, mitochondrion-processed TERC). In a critical study of the primary evidence so far obtained, we show those functions for which there is consensus, those showing contradictory results and those needing confirmation. The resulting picture, together with some usually neglected aspects, seems to indicate a link between TERT and TERC functions and cellular stemness and gives possible directions for future research.

Telomerase inhibition on acute myeloid leukemia stem cell induced apoptosis with both intrinsic and extrinsic pathways

AIMS

Acute Myeloid Leukemia (AML) is an invasive and lethal blood cancer caused by a rare population of Leukemia Stem Cells (LSCs). Telomerase activation is a limitless self-renewal process in LSCs. Apart from telomerase role in telomere lengthening, telomerase (especially hTERT subunit) inhibits intrinsic-, extrinsic-, and p53- mediated apoptosis pathways. In this study, the effect of Telomerase Inhibition (TI) on intrinsic-, extrinsic-, p53-mediated apoptosis, and DNMT3a and TET epigenetic markers in stem (CD34⁺) and differentiated (CD34^-) AML cells is evaluated.

MAIN METHODS

High-purity CD34⁺ (primary AML and KG-1a) cells were enriched using the Magnetic-Activated Cell Sorting (MACS) system. CD34⁺ and CD34^- (primary AML and KG-1a) cells were treated with BIBR1532 and then, MTT assay, Annexin V/7AAD, Ki-67 assay, Telomere Length (TL) measurement, and transcriptional alterations of p53, hTERT, TET2, DNMT3a were analyzed. Finally, apoptosis-related genes and proteins were studied.

KEY FINDINGS

TI with the IC50 values of 83.5, 33.2, 54.3, and 24.6 μM in CD34⁺ and CD34^- (primary AML and KG-1a) cells significantly inhibited cell proliferation and induced apoptosis. However, TI had no significant effect on TL. The results also suggested TI induced intrinsic-, extrinsic-, and p53-mediated apoptosis. It was shown that the expression levels of DNMT3a and TET2 epigenetic markers were highly increased following TI.

SIGNIFICANCE

In total, it was revealed that TI induced apoptosis through intrinsic, extrinsic, and p53 pathways and increased the expression of DNMT3a and TET2 epigenetic markers.

Obesity and aging: Molecular mechanisms and therapeutic approaches

The epidemic of obesity is a major challenge for health policymakers due to its far-reaching effects on population health and potentially overwhelming financial burden on healthcare systems. Obesity is associated with an increased risk of developing acute and chronic diseases, including hypertension, stroke, myocardial infarction, cardiovascular disease, diabetes, and cancer. Interestingly, the metabolic dysregulation associated with obesity is similar to that observed in normal aging, and substantial evidence suggests the potential of obesity to accelerate aging. Therefore, understanding the mechanism of fat tissue dysfunction in obesity could provide insights into the processes that contribute to the metabolic dysfunction associated with the aging process. Here, we review the molecular and cellular mechanisms underlying both obesity and aging, and how obesity and aging can predispose individuals to chronic health complications. The potential of lifestyle and pharmacological interventions to counter obesity and obesity-related pathologies, as well as aging, is also addressed.

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.

Non-canonical functions of Telomerase Reverse Transcriptase - Impact on redox homeostasis

Telomerase consists of the catalytic subunit Telomerase Reverse Transcriptase (TERT) and the Telomerase RNA Component. Its canonical function is the prevention of telomere erosion. Over the last years it became evident that TERT is also present in tissues with low replicative potential. Important non-canonical functions of TERT are protection against apoptosis and maintenance of the cellular redox homeostasis in cancer as well as in somatic tissues. Intriguingly, TERT and reactive oxygen species (ROS) are interdependent on each other, with TERT being regulated by changes in the redox balance and itself controlling ROS levels in the cytosol and in the mitochondria. The latter is achieved because TERT is present in the mitochondria, where it protects mitochondrial DNA and maintains levels of anti-oxidative enzymes. Since numerous diseases are associated with oxidative stress, increasing the mitochondrial TERT level could be of therapeutic value.

HKR3 regulates cell cycle through the inhibition of hTERT in hepatocellular carcinoma cell lines

Hepatocellular carcinoma is a malignant disease with improved hepatic regeneration and survival, and is activated by human telomere transferase (hTERT). hTERT is expressed during early fetal development and switched off in most adult tissues, but it becomes reactivated in HCC. The exact mechanism regulating these expression changes remains unknown during HCC progress. We evaluated the relationship between hTERT expression and human kruppel-related 3 (HKR3) and cell cycle-related factors in HCC cell lines. Following transfection for hTERT knockdown and HKR3 overexpression, proteomic and transcriptomic analyses related to hTERT were performed using liquid chromatography/mass spectrometry (LC/MS) and RNA sequencing (RNAseq) in HCC cell lines. The expression levels of hTERT, HKR3, and cell cycle-related factors were measured using western blotting, and tumor growth were evaluated via cell proliferation and cell cycle assays. Transcriptomic and proteomic analyses showed that HKR3, hTERT and cyclin-dependent kinase inhibitor 2A (CDKN2A) were correlated. Up-regulation of HKR3 expression decreased hTERT and cyclin activation and suppressed the G1/S phase of the cell cycle through CDKN2A activation. Our results suggest that HKR3 induced regulation of cell cycle through hTERT inhibition and CDKN2A activation. Our results will facilitate further exploration of the pathways regulating human telomerase activity in HCC cell lines.

Screening and Identification of Molecular Targets Involved in Preventing Gastric Precancerous Lesions in Chronic Atrophic Gastritis by Qilianshupi Decoction

Chronic atrophic gastritis (CAG) is a common and possibly precancerous digestive tract disease. Development of drugs with effect of preventing precancerous lesions draws the eyes of global researchers. Qilianshupi decoction (QLSP) is a Traditional Chinese Medicine (TCM) that is commonly used to treat CAG, but few studies have explored the mechanism of QLSP on treating CAG. This study investigated the molecular targets of the component herbs of QLSP in preventing precancerous lesions based on network pharmacology. Network pharmacology analysis revealed that the 6 herbs regulated multiple CAG-related genes, among which the most important were cancer-related pathway (apoptosis, p53, and VEGF) and epithelial cell signaling in Helicobacter pylori infection. Further animal experiments showed that the expression of survivin and p53 in precancerous lesions of CAG rats was significantly increased which was suppressed by QLSP. Moreover, telomerase activity was inhibited in precancerous lesions of CAG rats, and telomere length of gastric mucosa was increased, which was reversed by QLSP. Our results suggest that the components of QLSP prevents gastric precancerous lesions through decreasing the expression of survivin and p53 and regulating telomerase activity and telomere length in CAG.

Dysregulation of H/ACA ribonucleoprotein components in chronic lymphocytic leukemia

Telomeres are protective repeats of TTAGGG sequences located at the end of human chromosomes. They are essential to maintain chromosomal integrity and genome stability. Telomerase is a ribonucleoprotein complex containing an internal RNA template (hTR) and a catalytic subunit (hTERT). The human hTR gene consists of three major domains; among them the H/ACA domain is essential for telomere biogenesis. H/ACA ribonucleoprotein (RNP) complex is composed of four evolutionary conserved proteins, including dyskerin (encoded by DKC1 gene), NOP10, NHP2 and GAR1. In this study, we have evaluated the expression profile of the H/ACA RNP complex genes: DKC1, NOP10, NHP2 and GAR1, as well as hTERT and hTR mRNA levels, in patients with chronic lymphocytic leukemia (CLL). Results were correlated with the number and type of genetic alteration detected by conventional cytogenetics and FISH (fluorescence in situ hybridization), IGHV (immunoglobulin heavy chain variable region) mutational status, telomere length (TL) and clinico-pathological characteristics of patients. Our results showed significant decreased expression of GAR1, NOP10, DKC1 and hTR, as well as increased mRNA levels of hTERT in patients compared to controls (p≤0.04). A positive correlation between the expression of GAR1-NHP2, GAR1-NOP10, and NOP10-NHP2 (p<0.0001), were observed. The analysis taking into account prognostic factors showed a significant increased expression of hTERT gene in unmutated-IGHV cases compared to mutated-CLL patients (p = 0.0185). The comparisons among FISH groups exhibited increased expression of DKC1 in cases with two or more alterations with respect to no abnormalities, trisomy 12 and del13q14, and of NHP2 and NOP10 compared to those with del13q14 (p = 0.03). The analysis according to TL showed a significant increased expression of hTERT (p = 0.0074) and DKC1 (p = 0.0036) in patients with short telomeres compared to those with long TL. No association between gene expression and clinical parameters was found. Our results suggest a role for these telomere associated genes in genomic instability and telomere dysfunction in CLL.

Phosphorothioate‑modified antisense oligonucleotides against human telomerase reverse transcriptase sensitize cancer cells to radiotherapy

Emergence of resistance, unavoidable systemic toxicity and unsatisfactory efficacy arethe main obstacles for traditional cancer therapy. Combination with phosphorothioate modified antisense oligonucleotides (PS‑ASODN) against human telomerase reverse transcriptase (hTERT) may enhance the therapeutic effect of irradiation. However, the effect of PS‑ASODN against hTERT on the anti‑tumor effects of irradiation in liver cancer remain unclear. In the current study, Walker 256 cells were transfected with hTERT PS‑ASODN. Cell proliferation and cell viability were measured using the MTT assay and cell senescence was examined by SA‑β‑gal staining. Telomerase activity was determined by telomeric repeat amplification protocol‑polymerase chain reaction‑ELISA. Cell apoptosis was assayed by flow cytometry and DNA damage was determined by the comet assay.The PS‑ASODN was demonstrated to have an inhibitory effect on cell proliferation and accelerated effect on cell senescence by inhibiting telomerase activity. PS‑ASODN promoted the irradiation‑induced inhibition of cell viability and telomerase activity, and irradiation‑induced DNA damage and cell apoptosis via the activation of apoptosis‑associated proteins. Taken together, these results indicated that combined treatment of PS‑ASODN with irradiation significantly enhanced tumor inhibition. Therefore, PS‑ASODN provides an experimental foundation for gene therapy and is proposed for application in clinical treatment of liver cancer combined with radiotherapy.

Effect of TERT on the growth of fibrosarcoma via caspase-3, survivin and PKB

The present study explored the effect of telomerase reverse transcriptase (TERT) on the growth and apoptosis of fibrosarcoma, and investigated the potential molecular signalling pathways underlying its effect. A plasmid was constructed in order to overexpress TERT and siRNA was used to knockdown TERT. The effect of TERT on fibrosarcoma cells in vitro was studied by performing reverse transcription-quantitative PCR and western blotting to determine the expression of p53, survivin, caspase-3, caspase-7 and PKB. Knockdown of TERT suppressed cell growth, decreased fibrosarcoma volume, decreased survivin and PKB expression, and increased caspase-3 expression. The results of the present study suggest that TERT regulates the growth of fibrosarcoma in vitro and in vivo, and that this is associated with the expression of caspase-3 and survivin, in addition to the PKB signalling pathway.

Biological significance of PinX1 telomerase inhibitor in esophageal carcinoma treatment

In the present study, to investigate the expression of PinX1 gene and its functional effects in human esophageal carcinoma (Eca)-109 cell line, expression vectors of human PinX1 (pEGFP-C3-PinX1) and its small interfering RNA (PinX1-FAM-siRNA) were constructed and transfected into Eca-109 cells using Lipofectamine 2000. Firstly, the mRNA expression level of PinX1 was examined using reverse transcription-polymerase chain reaction (RT-PCR). Once successful transfection was achieved, the effects on the mRNA level of human telomerase reverse transcriptase (hTERT), telomerase activity, cell proliferation and apoptosis were examined by semi-quantitative RT-PCR, stretch PCR, MTT assay and flow cytometry, respectively. Analysis of restriction and sequencing demonstrated that the recombining plasmids were successfully constructed. The results also indicated that transfection with pEGFP-C3-PinX1 and PinX1-FAM-siRNA into Eca-109 cells significantly increased PinX1 mRNA, decreased hTERT mRNA by 29.9% (P<0.05), and significantly reduced telomerase activity (P<0.05), inhibited cell growth, and increased the cell apoptotic index from 19.27±0.76 to 49.73±2%. The transfected PinX1-FAM-SiRNA exhibited PinX1 mRNA expression levels that were significantly decreased by 70% (P<0.05), whereas the remaining characteristics of Eca-109 cells, including cell growth, mRNA level of hTERT, telomerase activity and cell apoptotic index were not altered. Exogenous PinX1 has been demonstrated to be highly expressed in human Eca. PinX1 can inhibit human telomerase activity and the expression of hTERT mRNA, reduce tumor cell growth and induce apoptosis. Notably, these inhibitory functions were inhibited by silencing PinX1 in Eca with PinX1-FAM-siRNA. PinX1 was successfully increased and decreased in the present study, demonstrating that it may be a potential telomerase activity inhibitor. As PinX1 is an endogenous telomerase inhibitor, it may be used as a novel tumor-targeted gene therapy.

New prospects for targeting telomerase beyond the telomere

Telomerase activity is responsible for the maintenance of chromosome end structures (telomeres) and cancer cell immortality in most human malignancies, making telomerase an attractive therapeutic target. The rationale for targeting components of the telomerase holoenzyme has been strengthened by accumulating evidence indicating that these molecules have extra-telomeric functions in tumour cell survival and proliferation. This Review discusses current knowledge of the biogenesis, structure and multiple functions of telomerase-associated molecules intertwined with recent advances in drug discovery approaches. We also describe the fertile ground available for the pursuit of next-generation small-molecule inhibitors of telomerase.

Inhibition of human telomerase reverse transcriptase in vivo and in vitro for retroviral vector-based antisense oligonucleotide therapy in ovarian cancer

Human telomerase is absent in most normal tissues, but is abnormally activated in all major cancer cells. Telomerase enables tumor cells to maintain telomere length, allowing indefinite replicative capacity. Albeit not sufficient in itself to induce neoplasia, telomerase is believed to be necessary for cancer cells to grow without limit. Studies using an antisense oligonucleotide (ASODN) to the RNA component of telomerase or human telomerase reverse transcriptase (hTERT) demonstrate that telomerase in human tumor lines can be blocked in vivo. Inhibition of hTERT led to telomere shortening and cancer cell death, validating telomerase as a target for anticancer genetic therapy. Varieties of approaches for hTERT inhibition have been investigated. The aim of this study was to analyze the biological activity of ASODN to the hTERT mediated by retrovirus vector, which was used as therapy for ovarian tumor. We constructed and characterized a recombinant retrovirus vector with full-length hTERT antisense complementary DNA. The vector was introduced into ES-2 by lipofectamine-mediated gene transfection. The cellular proliferation and telomerase activity of the transformant cells were retarded. The hTERT gene expression and the telomerase activity of the transformant cells were both decreased. The transformant cells show partial reversion of the malignant phenotype. PT67 cells were also transfected with the recombinant vector and virus-producer cells were generated. The retrovirus-containing supernatant effectively inhibited the growth of human ovarian tumor xenografts in mouse models (subcutaneous tumor model), and enhanced the mouse survival time.

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

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

Therapeutic targeting of replicative immortality

One of the hallmarks of malignant cell populations is the ability to undergo continuous proliferation. This property allows clonal lineages to acquire sequential aberrations that can fuel increasingly autonomous growth, invasiveness, and therapeutic resistance. Innate cellular mechanisms have evolved to regulate replicative potential as a hedge against malignant progression. When activated in the absence of normal terminal differentiation cues, these mechanisms can result in a state of persistent cytostasis. This state, termed "senescence," can be triggered by intrinsic cellular processes such as telomere dysfunction and oncogene expression, and by exogenous factors such as DNA damaging agents or oxidative environments. Despite differences in upstream signaling, senescence often involves convergent interdependent activation of tumor suppressors p53 and p16/pRB, but can be induced, albeit with reduced sensitivity, when these suppressors are compromised. Doses of conventional genotoxic drugs required to achieve cancer cell senescence are often much lower than doses required to achieve outright cell death. Additional therapies, such as those targeting cyclin dependent kinases or components of the PI3K signaling pathway, may induce senescence specifically in cancer cells by circumventing defects in tumor suppressor pathways or exploiting cancer cells' heightened requirements for telomerase. Such treatments sufficient to induce cancer cell senescence could provide increased patient survival with fewer and less severe side effects than conventional cytotoxic regimens. This positive aspect is countered by important caveats regarding senescence reversibility, genomic instability, and paracrine effects that may increase heterogeneity and adaptive resistance of surviving cancer cells. Nevertheless, agents that effectively disrupt replicative immortality will likely be valuable components of new combinatorial approaches to cancer therapy.

Antisense oligodeoxynucleotide against human telomerase reverse transcriptase inhibits the proliferation of Eca-109 esophageal carcinoma cells

Previous studies have demonstrated that the growth of tumor cells may be inhibited by antisense oligonucleotides (ASODNs) targeted against human telomerase (hTR) or human telomerase reverse transcriptase (hTERT), resulting in antitumor activity in a wide variety of tumors. However, few studies have investigated the effect of hTERT gene-targeted ASODNs on telomerase activity and cell proliferation in human esophageal cancer. In the present study, an MTT assay was used to determine the growth inhibition rate of Eca-109 cells treated with a hTERT-targeted phosphorothioate-ASODN (PS-ASODN). An inverted microscope was used to observe the morphologic changes of the cells following treatment with 5 μM PS-ASODN for 10 days. Telomerase activity was detected using the silver staining semi-quantitative telomeric repeat amplification protocol (TRAP) assay. Following treatment with the PS-ASODN (1–5 μmol/l), the proliferation of the Eca-109 cells was inhibited. The differences in inhibition rate between the PS-ASODN and blank control groups were statistically significant (P<0.05) when the concentration of the PS-ASODN was ≥2 μmol/l, whereas no statistically significant difference was identified between the non-specific-ASODN and blank control groups. The inhibition rate increased gradually as the concentration of the PS-ASODN increased and with time, suggesting that the PS-ASODN inhibited the growth of Eca-109 cells in a concentration-dependent, time-dependent and sequence-specific manner. The growth rate of the cells incubated with the PS-ASODN was reduced compared with that of the control cells. Cells treated with the PS-ASODN became round, suspended and reduced in size. The PS-ASODN was also found to inhibit telomerase activity. The ability of the PS-ASODN to inhibit the telomerase activity and cell proliferation of the Eca-109 cell line suggests that ASODNs have the potential to be novel therapeutic agents for the treatment of esophageal cancer.

Extracting extra-telomeric phenotypes from telomerase mouse models

Telomerase reverse transcriptase (TERT) is the protein component of telomerase and combined with an RNA molecule, telomerase RNA component, forms the telomerase enzyme responsible for telomere elongation. Telomerase is essential for maintaining telomere length from replicative attrition and thus contributes to the preservation of genome integrity. Although diverse mouse models have been developed and studied to prove the physiological roles of telomerase as a telomere- elongating enzyme, recent studies have revealed non-canonical TERT activities beyond telomeres. To gain insights into the physiological impact of extra-telomeric roles, this review revisits the strategies and phenotypes of telomerase mouse models in terms of the extra-telomeric functions of telomerase.

Noncoding RNAs in prostate cancer: the long and the short of it

As the leading culprit in cancer incidence for American men, prostate cancer continues to pose significant diagnostic, prognostic, and therapeutic tribulations for clinicians. The vast spectrum of disease behavior warrants better molecular classification to facilitate the development of more robust biomarkers that can identify the more aggressive and clinically significant tumor subtypes that require treatment. The untranslated portion of the human transcriptome, namely noncoding RNAs (ncRNA), is emerging as a key player in cancer initiation and progression and boasts many attractive features for both biomarker and therapeutic research. Genetic linkage studies show that many ncRNAs are located in cancer-associated genomic regions that are frequently deleted or amplified in prostate cancer, whereas aberrant ncRNA expression patterns have well-established links with prostate tumor cell proliferation and survival. The dysregulation of pathways controlled by ncRNAs results in a cascade of multicellular events leading to carcinogenesis and tumor progression. The characterization of RNA species, their functions, and their clinical applicability is a major area of biologic and clinical importance. This review summarizes the growing body of evidence, supporting a pivotal role for ncRNAs in the pathogenesis of prostate cancer. We highlight the most promising ncRNA biomarkers for detection and risk stratification and present the state-of-play for RNA-based personalized medicine in treating the "untreatable" prostate tumors.

Effect of targeted silencing of hTERT mRNA by lentivirus-mediated siRNA on A549 lung cancer cells in vitro

In our present study, we took advantage of the characteristics of RNA interference technology, which can efficiently, stably, and specifically silence target genes, and designed a small interfering RNA (siRNA) that could specifically target hTERT mRNA. We used a lentiviral vector (LV) to deliver the hTERT siRNA into telomerase-positive A549 lung cancer cells and investigated the effect of hTERT siRNA on the hTERT mRNA levels, hTERT protein levels, cell proliferation, and apoptosis in the lung cancer cells. The results from quantitative PCR, Western blotting, and the MTT assay showed that the expression levels of both hTERT mRNA and protein in the cells were significantly decreased and that the cell proliferation rate started to significantly slow down at 48 h after transfection with hTERT-LV. Our study demonstrated that siRNA sequences specifically targeting hTERT mRNA, which were packaged into lentivirus particles and then used to transfect the lung cancer cell line A549, can specifically silence the mRNA of the target gene, hTERT, and then reduce the hTERT protein expression level, which, in turn, reduces cell proliferation, inhibits cell growth, and induces apoptosis.

Modulation of telomerase activity and human telomerase reverse transcriptase expression by caspases and bcl-2 family proteins in Cisplatin-induced cell death

BACKGROUND

Human telomerase is a ribonucleoprotein polymerase, which synthesizes telomeric repeat sequences, and human telomerase reverse transcriptase (hTERT) has been identified as the catalytic subunit, as well as the rate-limiting component, of telomerase. In this study, we attempted to identify the modulators of telomerase, and to determine the molecular mechanisms underlying cisplatin-induced apoptosis.

METHODS

To determine the role of telomerase in cisplatin-induced apoptosis, we measured telomerase activity and analyzed apoptosis using PI and trypan blue staining. Also, we inhibited the caspase activations using Z-VAD-fmk to analyze the effects on expression of hTERT protein. Finally, we induced the transient co-expression of the Bcl-2 and Bak genes in HEK293 cells, and then, the telomerase activity and expression of hTERT were evaluated.

RESULTS

In the Bcl-2-overexpressing HeLa cells, telomerase activity was more enhanced, and cell death was reduced to 40-50% that of the mock controls. This finding suggests that Bcl-2-induced telomerase activity exerts an antiapoptotic effect in cisplatin-induced death. As caspase activation was inhibited via Z-VAD-fmk, the hTERT protein was recovered in the mock controls, but not in the Bcl-2-overexpressing cells. This suggests that the expression of hTERT can be regulated by caspases, but Bcl-2 was located within the upstream pathway. Moreover, when the Bcl-2 and Bak genes were co-transfected into the HEK293, both telomerase activity and hTERT protein were prominently reduced.

CONCLUSIONS

Bcl-2-induced telomerase activity inhibits cisplatin-induced apoptosis in HeLa cells, and can be regulated via both caspases and the interaction of Bcl-2 and Bak.

Targeting the telomere and shelterin complex for cancer therapy: current views and future perspectives

Aberrant telomere homeostasis is essential for cell immortality, enabling cells to evade telomere dependent senescence. Disruption of telomere structure and function in cancer cells is highly toxic as shown by detailed pre-clinical evaluation of telomerase inhibitors. Under telomerase inhibition, cells must divide sufficiently frequently to allow one or more telomeres to shorten to an unprotected length. Functioning telomeres are disguised from the DNA damage machinery by DNA remodelling and other activities of the telomere binding complex shelterin. Direct interference with shelterin has been shown to result in cell killing and small molecules directly targeting telomere DNA also have anti-tumour effects partially dependent on shelterin disruption. However, shelterin components have not generally been regarded as therapeutic targets in their own right. In this review, we explore the possibilities for therapeutic targeting of the shelterin complex.

Direct short-term cytotoxic effects of BIBR 1532 on acute promyelocytic leukemia cells through induction of p21 coupled with downregulation of c-Myc and hTERT transcription

Acute promyelocytic leukemia (APL) is characterized by specific t(15;17), distinct morphologic picture, and clinical coagulopathy that contribute to the morbidity and mortality of the disease. This study aims to investigate the effects of antitelomerase compound BIBR1532 on APL cells (NB4). BIBR 1532 exerts a direct short-term growth suppressive effect in a concentration-dependent manner probably through downregulation of c-Myc and hTERT expression. Our results also suggest that induction of p21 and subsequent disturbance of Bax/Bcl-2 balanced ratio as well as decreased telomerase activity may be rational mechanisms for the potent/direct short-term cytotoxicity of high doses of BIBR1532 against NB4 cells.

Telomerase activity in pleural malignant mesotheliomas

New treatments are needed for malignant pleural mesothelioma (MPM), which currently has a poor prognosis. Cellular immortalisation, one of the hallmarks of cancer, depends on the activity of a telomere length maintenance mechanism (TMM) - either telomerase or alternative lengthening of telomeres (ALT). The TMMs are widely regarded as potential targets for cancer therapies and telomerase inhibitors have entered clinical trials. The aim of this study was to determine what proportion of MPMs use ALT and/or telomerase. Forty-three MPMs from 42 patients were examined for telomerase and ALT activity. Telomerase activity was detected by immunoaffinity purification followed by the telomere repeat amplification protocol (TRAP), and ALT activity was determined by the C-circle assay and by assessing telomere lengths using terminal restriction fragment analyses. We found that 43 of 43 MPMs were telomerase-positive[+] and ALT-negative[-]. Therefore, to investigate whether pleural mesothelial cells are unusually susceptible to activation of telomerase, we examined activation of the TMMs in an in vitro model of cellular immortalisation, in which normal pleural mesothelial cells were transduced with simian virus 40 (SV40) oncogenes. We found that normal mesothelial cells were TMM-negative, and that expression of the SV40 oncogenes did not directly activate telomerase or ALT. Immortalisation, which in this experimental system results from additional genetic changes that have not yet been identified, was accompanied by activation of either TMM. Therefore, pleural mesothelial cells are capable of activating either TMM in vitro, and the observation that 100% of MPMs were telomerase[+] suggests that there are factors in vivo that select for telomerase activity during oncogenesis of this tumour type. We conclude that MPM is a tumour that could be considered for anti-telomerase therapy.

Telomerase inhibition strategies by siRNAs against either hTR or hTERT in oral squamous cell carcinoma

Human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT) are considered effective molecular targets for current anticancer therapy. In this study, we investigated the therapeutic effects of targeting hTR and hTERT individually or in combination by recombinant adenovirus-delivered small interfering RNA (siRNA) in oral squamous cell carcinoma (OSCC) Tca8113. Further, we screened the optimal strategy for RNA interference. Our results show that these different recombinant adenoviruses specifically reduced the levels of hTR mRNA, hTERT mRNA, hTERT protein and telomerase activity in Tca8113 cells. Moreover, they successfully inhibited xenograft tumor growth in nude mice. The potency of their antitumor activities was ranked as follows: anti-hTR >anti-hTR+anti-hTERT >anti-hTERT. Therefore, we demonstrated that the siRNA-expressing recombinant adenoviruses were an effective anticancer tool for treatment of OSCC. Furthermore, the anticancer effect of solely targeting hTR was more direct and efficient, compared with the effect of targeting hTR and hTERT in combination, or hTERT exclusively. The mechanism of this anticancer effect in OSCC was not only related to the inhibition of cell proliferation and the induction of cell apoptosis, but might also involve the inhibition of tumor angiogenesis.

Self-organization of G-quadruplex structures in the hTERT core promoter stabilized by polyaminic side chain perylene derivatives

hTERT core promoter regulates telomerase transcription in human cells, thus its structural features are of large interest. We have found that the G-rich hTERT core promoter region, corresponding to the major DNase I hypersensitive site in chromatin organization, contains nine putative G-quadruplex forming sequences (PQS) and is unfavorable for nucleosome formation. Here we show that four PQS are effectively able to form stable parallel intramolecular G-quadruplexes, using PAGE and CD spectroscopy analysis. The PQS-region, as a whole, appears to be organized in three self-interacting G-quadruplexes, probably giving rise to a helicoidal superstructure, as shown by CD and polymerase stop assay. POL-HPDI drugs, that we previously found useful in selectively stabilizing telomeric G-quadruplex, are able to stabilize both the single intramolecular G-quadruplex and the PQS-region superstructure. The features of their induced CD spectra suggest that POL-HPDIs bind to single G-quadruplexes and to whole PQS-region superstructure, mainly by end-stacking interactions.

[Telomeres and telomerase as targeted therapies in cancer treatment]

Advances in chromosome dynamics have increased our understanding of the significant role of telomeres and telomerase in cancer. Telomerase is expressed in almost all cancer cells but is inactive in most normal somatic cells. Therefore, telomerase is an important target for the design of therapeutic agents that might have minimal side effects. Herein, we evaluate current approaches to telomerase/telomere-targeted therapy, discuss the benefits and disadvantages, and speculate on the future direction of telomerase inhibitors as cancer therapeutics.

Telomerase protects adult rodent olfactory ensheathing glia from early senescence

Adult olfactory bulb ensheathing glia (OB-OEG) promote the repair of acute, subacute, and chronic spinal cord injuries and autologous transplantation is a feasible approach. There are interspecies differences between adult rodent and primate OB-OEG related to their longevity in culture. Whereas primate OB-OEG exhibit a relatively long life span, under the same culture conditions rodent OB-OEG divide just three to four times, are sensitive to oxidative stress and become senescent after the third week in vitro. Telomerase is a "physiological key regulator" of the life span of normal somatic cells and also has extratelomeric functions such as increased resistance to oxidative stress. To elucidate whether telomerase has a role in the senescence of rodent OB-OEG, we have introduced the catalytic subunit of telomerase mTERT into cultures of these cells by retroviral infection. Native and modified adult rat OB-OEG behaved as telomerase-competent cells as they divided while expressing mTERT but entered senescence once the gene switched off. After ectopic expression of mTERT, OB-OEG resumed division at a nonsenescent rate, expressed p75 and other OEG markers, and exhibited the morphology of nonsenescent OB-OEG. The nonsenescent period of mTERT-OEG lasted 9weeks and then ectopic mTERT switched off and cells entered senescence again. Our results suggest a role of telomerase in early senescence of adult rodent OB-OEG cultures and a protection from oxidative damage. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

Well-known signaling proteins exert new functions in the nucleus and mitochondria

One distinguishing feature of eukaryotic cells is their compartmentalization into organelles, which all have a unique structural and functional identity. Some proteins are exclusively localized in a single organelle, whereas others are found in more than one. A few proteins, whose function was thought to be completely understood, were only recently found to be present in the mitochondria. Although these proteins come from diverse functional classes, their common new denominator is the regulation of respiratory chain activity. Therefore, this review focuses on new functions of the Signal Transducer and Activator of Transcription 3, originally described as a transcription factor, the most prominent Src kinase family members, Src, Fyn, and Yes, which were so far known as plasma membrane-associated molecular effectors of a variety of extracellular stimuli, the tyrosine phosphatase Shp-2 previously characterized as a modulator of cytosolic signal transduction involved in cell growth, development, inflammation, and chemotaxis, and Telomerase Reverse Transcriptase, the key enzyme preventing telomere erosion in the nucleus. Their unexpected localization in other organelles and regulation of mitochondrial and/or nuclear functions by them adds a new layer of regulatory complexity. This extends the flexibility to cope with changing environmental demands using a limited number of genes and proteins.

Targeting telomerase in hematologic malignancy

Over the past two decades, it has become increasingly apparent that telomerase-mediated telomere maintenance plays a crucial role in hematopoiesis. Supporting evidence is underscored by recent findings of mutations in genes involved in telomerase-mediated telomere maintenance that contribute to the pathogenesis of bone marrow failure syndromes. More recently described telomere-independent functions of telomerase are also likely to contribute to both normal hematopoiesis and hematologic diseases. The high levels of telomerase detected in aggressive leukemias have fueled fervent investigation into diverse approaches to targeting telomerase in hematologic malignancies. Successful preclinical investigations that employed genetic strategies, oligonucleotides, small-molecule inhibitors and immunotherapy have resulted in a rapid translation to clinical trials. Further investigation of telomere-independent functions of telomerase and detailed preclinical studies of telomerase inhibition in both normal and malignant hematopoiesis will be invaluable for refining treatments to effectively and safely exploit telomerase as a therapeutic target in hematologic malignancies.

Formation of a unique end-to-end stacked pair of G-quadruplexes in the hTERT core promoter with implications for inhibition of telomerase by G-quadruplex-interactive ligands

The hTERT core promoter contains a G-rich region of 12 consecutive G-tracts, embracing 3 Sp1 binding sites, and has the potential to form multiple G-quadruplexes. From the 12 runs of guanines, 9 putative hTERT G-quadruplex-forming sequences were selected to assay for G-quadruplex formation and stability using circular dichroism and a Taq polymerase stop assay. Results from biophysical and chemical assays demonstrate an approximate inverse correlation between total loop size and structure stability. Investigation of the full-length hTERT G-rich sequence using a Taq polymerase stop assay and dimethyl sulfate footprinting revealed the formation of a unique end-to-end stacked G-quadruplex structure from this sequence. This structure consists of an all parallel G-quadruplex, formed by four consecutive G-tracts, linked to another, atypical G-quadruplex, formed by two pairs of consecutive G-tracts separated by a 26-base loop. This 26-base loop likely forms a stable hairpin structure, which would explain the unexpected stability of this G-quadruplex. Significantly, the formation of this tandem G-quadruplex structure in the full-length sequence masks all three Sp1 binding sites, which is predicted to produce significant inhibition of hTERT promoter activity. Furthermore, our study implies that inhibition of telomerase activity by some G-quadruplex ligands is not only produced by targeting telomeric G-quadruplexes but also by stabilization of the hTERT promoter G-quadruplexes.

Generation of mesenchymal stromal cells in the presence of platelet lysate: a phenotypic and functional comparison of umbilical cord blood- and bone marrow-derived progenitors

BACKGROUND

Mesenchymal stromal cells are employed in various different clinical settings in order to modulate immune response. However, relatively little is known about the mechanisms responsible for their immunomodulatory effects, which could be influenced by both the cell source and culture conditions.

DESIGN AND METHODS

We tested the ability of a 5% platelet lysate-supplemented medium to support isolation and ex vivo expansion of mesenchymal stromal cells from full-term umbilical-cord blood. We also investigated the biological/functional properties of umbilical cord blood mesenchymal stromal cells, in comparison with platelet lysate-expanded bone marrow mesenchymal stromal cells.

RESULTS

The success rate of isolation of mesenchymal stromal cells from umbilical cord blood was in the order of 20%. These cells exhibited typical morphology, immunophenotype and differentiation capacity. Although they have a low clonogenic efficiency, umbilical cord blood mesenchymal stromal cells may possess high proliferative potential. The genetic stability of these cells from umbilical cord blood was demonstrated by a normal molecular karyotype; in addition, these cells do not express hTERT and telomerase activity, do express p16(ink4a) protein and do not show anchorage-independent cell growth. Concerning alloantigen-specific immune responses, umbilical cord blood mesenchymal stromal cells were able to: (i) suppress T- and NK-lymphocyte proliferation, (ii) decrease cytotoxic activity and (iii) only slightly increase interleukin-10, while decreasing interferon-gamma secretion, in mixed lymphocyte culture supernatants. While an indoleamine 2,3-dioxygenase-specific inhibitor did not reverse mesenchymal stromal cell-induced suppressive effects, a prostaglandin E(2)-specific inhibitor hampered the suppressive effect of both umbilical cord blood- and bone marrow-mesenchymal stromal cells on alloantigen-induced cytotoxic activity. Mesenchymal stromal cells from both sources expressed HLA-G.

CONCLUSIONS

Umbilical cord blood- and bone marrow-mesenchymal stromal cells may differ in terms of clonogenic efficiency, proliferative capacity and immunomodulatory properties; these differences may be relevant for clinical applications.

Nanoparticle mediated delivery of 2'-O-methyl-RNA leads to efficient telomerase inhibition and telomere shortening in human lung cancer cells

A promising approach for treatment of non-small cell lung cancer (NSCLC) is based on the inhibition of telomerase in cancer cells. The antisense oligonucleotide 2'-O-methyl-RNA binding to the RNA component of telomerase acts as a selective telomerase inhibitor. We developed chitosan-coated polylactide-coglycolide (PLGA) nanoparticles to mediate efficient delivery of 2'-O-methyl-RNA into human lung cancer cells. Cellular uptake of the inhibitor mediated by chitosan-coated PLGA nanoparticles was greatly enhanced compared to the uptake of antisense oligonucleotide alone as shown by flow cytometry analysis. Confocal laser scanning microscopy clearly demonstrated internalization of 2'-O-methyl-RNA. 2'-O-methyl-RNA-nanoparticle complexes exhibited nearly no acute cytotoxicity in human lung cancer cells and did not influence the viability of primary tumor lung fibroblasts. Human NSCLC A549 cells treated with 2'-O-methyl-RNA-nanoparticle complexes showed 87% viability compared to untreated control cells. 2'-O-methyl-RNA delivered by nanoparticle complexes inhibited telomerase activity in a sequence-specific manner. During long-term treatment (15 weeks) telomerase activity was continuously reduced by approximately 80%. Furthermore, nanoparticle mediated delivery of 2'-O-methyl-RNA resulted in significant telomere shortening from 5.9kb to 4kb (p=0.008) in A549 cells. In summary, our data demonstrate that nanoparticle mediated delivery of 2'-O-methyl-RNA induces effective telomerase inhibition and telomere shortening in human lung cancer cells and therefore represents a novel and promising strategy for the treatment of lung cancer.

Telomere and telomerase as targets for cancer therapy

Telomere maintenance and telomerase reactivation is essential for the transformation of most human cancer cells. Telomere shortening to the threshold length, mutations of the telomere-associated proteins, and/or telomerase RNA lead to telomeric dysfunction and therefore genomic instability. Telomerase up-regulation in 85% of human cancer cells has become a hallmark of cancers, hence a promising target for anticancer therapy. In this review, we discuss the mechanism of cancer due to telomere dysfunction and the resulting biological effects, the control of telomerase activity, and the new developments in cancer therapies targeting telomere and telomerase.

Targeting the telosome: therapeutic implications

Since telomere integrity is required to guarantee the unlimited replicative potential of cancer cells, telomerase, the enzyme responsible for telomere length maintenance in most human tumors, and lately also telomeres themselves have become extremely attractive targets for new anticancer interventions. At the current status of knowledge, it is still not possible to define the best therapeutic target between telomerase and telomeres. It is noteworthy that interfering with telomeres, through direct targeting of telomeric DNA or proteins involved in the telosome complex, could negatively affect the proliferative potential not only of tumors expressing telomerase activity but also of those that maintain their telomeres through alternative lengthening or still unknown mechanisms. This review presents the different therapeutic approaches proposed thus far and developed in preclinical tumor models and discusses the perspectives for their use in the clinical setting.

Molecular simulations of peptides: a useful tool for the development of new drugs and for the study of molecular recognition

The study of the molecular recognition and self-organization properties of peptides has emerged in recent years as a very active and diverse field of research, ranging from biomedicine to biotechnology and even to material sciences. In the case of biomedicine, peptides can be used as ligands of biological receptors to gain insights into the structural, dynamical, and chemical determinants underlying the formation of complexes and identify new effectors of biological processes of interest. In the case of biotechnology and material science, short sequences have been used to understand the sequence determinants of the formation of ordered supra-molecular structures of nanoscale dimensions. In this work, we will describe our research activities in these two areas of modern chemical biology. In the first part, we will describe the development of a new, specific, potent, and selective anticancer peptide and its use to obtain the information needed to identify a non-peptidic small molecular lead to be used as an inhibitor of cancer growth. In the second part, we will describe the introduction of a new method for the description of the self-organization process at the basis of the growth of ordered supra-molecular structures held together by weak, non-covalent, yet specific interactions.

Quantification of hTERT splice variants in melanoma by SYBR green real-time polymerase chain reaction indicates a negative regulatory role for the beta deletion variant

Telomerase activity is primarily determined by transcriptional regulation of the catalytic subunit, human telomerase reverse transcriptase (hTERT). Several mRNA splice variants for hTERT have been identified, but it is not clear if telomerase activity is determined by the absolute or relative levels of full-length (functional) and variant hTERT transcripts. We have developed an SYBR green-based reverse transcription-quantitative polymerase chain reaction assay for the enumeration of the four common hTERT mRNA variants and correlated these with telomerase activity and telomere length in 24 human melanoma cell lines. All except five of the lines expressed four hTERT transcripts, with an overall significant level of co-occurrence between absolute mRNA levels of full-length alpha+/beta+ hTERT and the three splice variants alpha-/beta+, alpha+/beta-, and alpha-/beta-. On average, alpha+/beta+ made up the majority (48.1%) of transcripts, followed by alpha+/beta- (44.6%), alpha-/beta- (4.4%), and alpha-/beta+ (2.9%). Telomerase activity ranged from 1 to 247 relative telomerase activity and correlated most strongly with the absolute amount of alpha+/beta+ (R = 0.791, P = .000004) and the relative amount of alpha+/beta- (R = -0.465, P = .022). This study shows that telomerase activity in melanoma cells is best determined by the absolute expression of full-length hTERT mRNA and indicates a role for the hTERT beta deletion variant in the negative regulation of enzyme activity.

Immortalization of neural precursors when telomerase is overexpressed in embryonal carcinomas and stem cells

The DNA repair enzyme telomerase maintains chromosome stability by ensuring that telomeres regenerate each time the cell divides, protecting chromosome ends. During onset of neuroectodermal differentiation in P19 embryonal carcinoma (EC) cells three independent techniques (Southern blotting, Q-FISH, and Q-PCR) revealed a catastrophic reduction in telomere length in nestin-expressing neuronal precursors even though telomerase activity remained high. Overexpressing telomerase protein (mTERT) prevented telomere collapse and the neuroepithelial precursors produced continued to divide, but deaggregated and died. Addition of FGF-2 prevented deaggregation, protected the precursors from the apoptotic event that normally accompanies onset of terminal neuronal differentiation, allowed them to evade senescence, and enabled completion of morphological differentiation. Similarly, primary embryonic stem (ES) cells overexpressing mTERT also initiated neuroectodermal differentiation efficiently, acquiring markers of neuronal precursors and mature neurons. ES precursors are normally cultured with FGF-2, and overexpression of mTERT alone was sufficient to allow them to evade senescence. However, when FGF-2 was removed in order for differentiation to be completed most neural precursors underwent apoptosis indicating that in ES cells mTERT is not sufficient allow terminal differentiation of ES neural precursors in vitro. The results demonstrate that telomerase can potentiate the transition between pluripotent stem cell and committed neuron in both EC and ES cells.

TERT promotes cellular and organismal survival independently of telomerase activity

The expression level of the telomerase catalytic subunit (telomerase reverse transcriptase, TERT) positively correlates with cell survival after exposure to several lethal stresses. However, whether the protective role of TERT is independent of telomerase activity has not yet been clearly explored. Here, we genetically evaluated the protective roles of both TERT and telomerase activity against cell death induced by staurosporine (STS) and N-methyl-D-aspartic acid (NMDA). First generation (G1) TERT-deficient mouse embryonic fibroblasts (MEFs) displayed an increased sensitivity to STS, while TERT transgenic MEFs were more resistant to STS-induced apoptosis than wild-type. Deletion of the telomerase RNA component (TERC) failed to alter the sensitivity of TERT transgenic MEFs to STS treatment. Similarly, NMDA-induced excitotoxic cell death of primary neurons was suppressed by TERT, but not by TERC both in vitro and in vivo. Specifically, NMDA accelerated death of TERT-deficient mice, while TERT transgenic mice showed enhanced survival when compared with wild-type littermates after administration of NMDA. In addition, the transgenic expression of TERT protected motor neurons from apoptosis induced by sciatic nerve axotomy. These results indicate that telomerase activity is not essential for the protective function of TERT. This telomerase activity-independent TERT function may contribute to cancer development and aging independently of telomere lengthening.