Regulation of the human telomerase reverse transcriptase gene

hTERT promoter polymorphism, -1327C>T, is associated with the risk of epithelial cancer

Telomeres are repetitive nucleotide sequences that cap the end of eukaryotic chromosomes. Attrition of these structures has been associated with carcinogenesis in many tissues, and therefore, they are essential for chromosome stabilization. Telomeres are maintained by telomerase complexes, of which human telomerase reverse transcriptase (hTERT) is an essential component. A functional polymorphism, -1327C>T (rs2735940), located in the promoter of the hTERT gene is associated with telomere length in peripheral blood leukocytes. We hypothesized that this polymorphism might affect susceptibility to various epithelial malignancies. The -1327C>T polymorphism was examined in 1,551 consecutive autopsy cases (mean age, 80.3 years), and we focused on its effect on the risks of overall and each primary malignancies. The polymorphism was further studied in 391 clinical prostate cancer patients who were diagnosed via prostate biopsy, using autopsy cases as controls. In the autopsy cases, the risk of epithelial malignancy, after adjusting for age, sex, smoking, and drinking habits, was significantly lower for the TT genotype than the CC (reference) genotype (adjusted odds ratio = 0.61, 95% CI = 0.42-0.90). Among primary malignancies, latent prostate cancer, colorectal cancer, and lung cancer were the most strongly associated with the polymorphism. In the study using clinical prostate cancer patients, susceptibility to clinical prostate cancer was lower for -1327 T carriers than for -1327 T non-carriers, but this finding was not significant. The data suggest that the hTERT promoter polymorphism, -1327C>T, is an independent factor influencing the risk of various epithelial malignancies in elderly Japanese.

Methylation of the TERT promoter and risk stratification of childhood brain tumours: an integrative genomic and molecular study

BACKGROUND

Identification of robust biomarkers of malignancy and methods to establish disease progression is a major goal in paediatric neuro-oncology. We investigated whether methylation of the TERT promoter can be a biomarker for malignancy and patient outcome in paediatric brain tumours.

METHODS

For the discovery cohort, we used samples obtained from patients with paediatric brain tumours and individuals with normal brain tissues stored at the German Cancer Research Center (Heidelberg, Germany). We used methylation arrays for genome-wide assessment of DNA. For the validation cohort, we used samples obtained from several tissues for which full clinical and follow-up data were available from two hospitals in Toronto (ON, Canada). We did methylation analysis using quantitative Sequenom and pyrosequencing of an identified region of the TERT promoter. We assessed TERT expression by real-time PCR. To establish whether the biomarker could be used to assess and predict progression, we analysed methylation in paired samples of tumours that transformed from low to high grade and from localised to metastatic, and in choroid plexus tumours of different grades. Finally, we investigated overall survival in patients with posterior fossa ependymomas in which the identified region was hypermethylated or not. All individuals responsible for assays were masked to the outcome of the patients.

FINDINGS

Analysis of 280 samples in the discovery cohort identified one CpG site (cg11625005) in which 78 (99%) of 79 samples from normal brain tissues and low-grade tumours were not hypermethylated, but 145 (72%) of 201 samples from malignant tumours were hypermethylated (>15% methylated; p<0.0001). Analysis of 68 samples in the validation cohort identified a subset of five CpG sites (henceforth, upstream of the transcription start site [UTSS]) that was hypermethylated in all malignant paediatric brain tumours that expressed TERT but not in normal tissues that did not express TERT (p<0.0001). UTSS had a positive predictive value of 1.00 (95% CI 0.95-1.00) and a negative predictive value of 0.95 (0.87-0.99). In two paired samples of paediatric gliomas, UTSS methylation increased during transformation from low to high grade; it also increased in two paired samples that progressed from localised to metastatic disease. Two of eight atypical papillomas that had high UTSS methylation progressed to carcinomas, while the other six assessed did not progress or require additional treatment. 5-year overall survival was 51% (95% CI 31-71) for 25 patients with hypermethylated UTSS posterior fossa ependymomas and 95% (86-100) for 20 with non-hypermethylated tumours (p=0.0008). 5-year progression-free survival was 86% (68-100) for the 25 patients with non-hypermethylated UTSS tumours and 30% (10-50) for those with hypermethylated tumours (p=0.0008).

INTERPRETATION

Hypermethylation of the UTSS region in the TERT promoter is associated with TERT expression in cancers. In paediatric brain tumours, UTSS hypermethylation is associated with tumour progression and poor prognosis. This region is easy to amplify, and the assay to establish hypermethylation can be done on most tissues in most clinical laboratories. Therefore the UTSS region is a potentially accessible biomarker for various cancers.

FUNDING

The Canadian Institute of Health Research and the Terry Fox Foundation.

miR-138 overexpression is more powerful than hTERT knockdown to potentiate apigenin for apoptosis in neuroblastoma in vitro and in vivo

Decrease in expression of the tumor suppressor microRNA-138 (miR-138) correlates well with an increase in telomerase activity in many human cancers. The ability of almost all human cancer cells to grow indefinitely is dependent on presence of telomerase activity. The catalytic component of human telomerase reverse transcriptase (hTERT) regulates telomerase activity in most of the human cancers including malignant neuroblastoma. We observed an indirect increase in the expression of miR-138 after the transfection with hTERT short hairpin RNA (shRNA) plasmid in human malignant neuroblastoma SK-N-DZ and SK-N-BE2 cell lines. Transfection with hTERT shRNA plasmid followed by treatment with the flavonoid apigenin (APG) further increased expression of miR-138. Direct transfection with miR-138 mimic was more powerful than transfection with hTERT shRNA plasmid in potentiating efficacy of APG for decreasing cell viability and colony formation capability of both cell lines. Upregulation of miR-138 was also more effective than down regulation of hTERT in enhancing efficacy of APG for induction of apoptosis in malignant neuroblastoma cells in vitro and in vivo. We delineated that apoptosis occurred with induction of molecular components of the extrinsic and intrinsic pathways in SK-N-DZ and SK-N-BE2 cells both in vitro and in vivo. In conclusion, these results demonstrate that direct miR-138 overexpression is more powerful than hTERT down regulation in enhancing pro-apoptotic effect of APG for controlling growth of human malignant neuroblastoma in cell culture and animal models.

Functional haplotypes of the hTERT gene, leukocyte telomere length shortening, and the risk of peripheral arterial disease

BACKGROUND

The development of peripheral arterial disease (PAD) is heterogeneous even in the presence of similar risk factors. Our aim was to determine whether inter-individual differences in leukocyte telomere length contribute to the susceptibility of PAD.

METHODS

A total of 485 patients with PAD (defined by the ankle-brachial index) and 970 age- and gender-matched controls were recruited from seven rural communities in Henan Province in China. The relative leukocyte telomere length was determined by a quantitative PCR-based method. Two common promoter variants of the hTERT gene were genotyped to assess their effects on telomere length and the risk of PAD. In vivo luciferase assay was performed to study the transcriptional activity.

RESULTS

After adjustment for vascular risk factors and genetic variants in the hTERT gene, individuals in the lowest and middle tertiles of telomere length had a significantly higher risk of PAD than did those in the highest tertile (odds ratio [OR] 1.73, 95% confidence interval [CI] 1.29-2.49 in the middle tertile; 3.15, 95%CI 2.31-4.29 in the lowest tertile). Haplotype analysis using the 2 variants (rs2735940 and rs2853669) showed that subjects with the at-risk C-C haplotype had shorter telomere length than those individuals with the T-T haplotype and consistently had 1.30-fold (OR 1.30, 95%CI 1.06-1.58; P=0.005) increased risk for PAD. The C-C haplotype had 43% lowered transcription activity of hTERT promoter (P<0.001).

CONCLUSION

The associations between the functional haplotype of hTERT gene and telomere length and the risk of atherosclerotic PAD suggested that mean leukocyte telomere length may independently serve as a potential predictor of PAD.

Inhibition of Wnt signaling by cucurbitacin B in breast cancer cells: reduction of Wnt-associated proteins and reduced translocation of galectin-3-mediated β-catenin to the nucleus

The cucurbitacins are tetracyclic triterpenes found in plants of the family Cucurbitaceae. Cucurbitacins have been shown to have anti-cancer and anti-inflamatory activities. We investigated the anti-cancer activity of cucurbitacin B extracted from Thai medicinal plant Trichosanthes cucumerina Linn. Cell viability was assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Results indicated that cucurbitacin B from T. cucumerina Linn. has a cytotoxic effect on breast cancer cell lines SKBR-3 and MCF-7 with an IC50 of 4.60 and 88.75 µg/ml, respectively. Growth inhibition was attributed to G2/M phase arrest and apoptosis. Cyclin D1, c-Myc, and β-catenin expression levels were reduced. Western blot analysis showed increased PARP cleavage and decreased Wnt-associated signaling molecules β-catenin, galectin-3, cyclin D1 and c-Myc, and corresponding changes in phosphorylated GSK-3β levels. Cucurbitacin B treatment inhibited translocation to the nucleus of β-catenin and galectin-3. The depletion of β-catenin and galectin-3 in the nucleus was confirmed by cellular protein fractionation. T-cell factor (TCF)/lymphoid enhancer factor (LEF)-dependent transcriptional activity was disrupted in cucurbitacin B treated cells as tested by a TCF reporter assay. The relative luciferase activity was reduced when we treated cells with cucurbitacin B compound for 24 h. Our data suggest that cucurbitacin B may in part induce apoptosis and exert growth inhibitory effect via interruption the Wnt signaling.

Androgen receptor-mediated gene repression

Androgens have an essential role in inducing the genetic program for masculinization during development. Androgens mediate their effect through the androgen receptor (AR), a ligand-controlled transcription factor and regulator of rapid signaling. Inactivated AR results in complete feminization. Androgens are also essential in later life for reproduction, behavior, muscle development, breast, and prostate growth. In general, androgens inhibit breast and promote prostate growth. In the latter context the AR is a major drug target. On the one hand, many insights have been obtained how the AR mediates gene activation on a molecular level. Gene activation is mediated by a battery of factors including coactivators, chromatin remodeling complex proteins and transcription factors which either directly or indirectly interact with the AR at DNA binding sites. On the other hand, there are important AR target genes that are repressed by androgen-bound AR. However, the underlying molecular mechanisms are poorly understood although genes repressed by AR are key factors involved in cell proliferation and invasion. Here, we summarize molecular mechanisms of AR-mediated gene repression, thereby differentiating between direct and indirect DNA/chromatin recruitment and between genomic and non-genomic effects.

Multifaceted suppression of aggressive behavior of thyroid carcinoma by all-trans retinoic acid induced re-differentiation

Since all-trans retinoic acid (ATRA) has shown promising results in differentiation therapy, the present study was designed to investigate the effects of ATRA on thyroid carcinoma and to evaluate the effectiveness of ATRA in redifferentiation induction of thyroid carcinoma. Therefore, we investigated cell growth rate, morphological and nuclear: cytoplasmic ratio, adherent-dependent growth, response to chemotherapy drug following differentiation, T3 and T4 measurement, and critical genes expression pattern. Papillary cell line showed more growth inhibition by ATRA, in addition, mesenchymal and spindle-shape of 8305C cells changed to polygonal. Additionally, high nuclear: cytoplasmic ratio of anaplastic decreased significantly. Redifferentiation significantly suppressed the anchorage-dependent growth in the both cell lines in a dose-dependent manner, potentiated the arsenic trioxide (ATO) effects in anaplastic and papillary cell lines. Furthermore, reduction in the expression of stemness, and invasion related genes was observed in the both cell lines. Altogether, ATRA treatment could hold the aggressive behavior of thyroid carcinoma in restraint and/or potentiate the effect of chemotherapy drug ATO.

Hypomethylated CpG around the transcription start site enables TERT expression and HPV16 E6 regulates TERT methylation in cervical cancer cells

OBJECTIVE

The human papillomavirus (HPV) oncoprotein, E6, activates telomerase reverse transcriptase (TERT) expression and causes cellular immortalization. It remains unclear whether E6 affects TERT transcription by altering DNA methylation profiles. In this study, we explored the methylation status of the TERT promoter in cervical cancer cell lines and its variations after E6 was silenced by RNAi.

METHODS

Three kinds of cervical cell lines (HPV16 positive: CaSki and SiHa; HPV18 positive: HeLa), were taken to analyze the methylation status of the TERT promoter by methylation-specific polymerase chain reaction (MSP) and bisulfite sequencing (BS). Stealth RNAi was transiently transfected to these cell lines to silence the expression of HPV16/18 E6, and the subsequent changes of TERT mRNA levels and TERT promoter DNA methylation were examined.

RESULTS

Hypomethylation of the DNA around the TERT transcription start site (-156 to +162 bp) was functionally related to its transcription. After transfection with Stealth RNAi, the levels of HPV16/18 E6 and TERT mRNA were greatly decreased. The methylated CpG around the transcription start sites in CaSki and SiHa cells were statistically increased (respectively P=0.016, P=0.000). However, there was no significant difference in HeLa cells (P=0.128).

CONCLUSION

Hypomethylated CpG around the transcription start site enables the expression of TERT in cervical cancer cells. Our results show for the first time that HPV16 E6 can promote TERT transcription through demethylating the DNA sequence around the TERT transcription start site in cervical squamous cancer cells.

Human telomerase expression regulation

Since telomerase has been recognized as a relevant factor distinguishing cancer cells from normal cells, it has become a very promising target for anti-cancer therapy. A correlation between short telomere length and increased mortality was revealed in many studies. The telomerase expression/activity appears to be one of the most crucial factors to study to improve cancer therapy and prevention. However, this multisubunit enzymatic complex can be regulated at various levels. Thus, several strategies have been proposed to control telomerase in cancer cells such as anti-sense technology against TR and TERT, ribozymes against TERT, anti-estrogens, progesterone, vitamin D, retinoic acid, quadruplex stabilizers, telomere and telomerase targeting agents, modulation of interaction with other proteins involved in the regulation of telomerase and telomeres, etc. However, the transcription control of key telomerase subunits seems to play the crucial role in whole complexes activity and cancer cells immortality. Thus, the research of telomerase regulation can bring significant insight into the knowledge concerning stem cells metabolism but also ageing. This review summarizes the current state of knowledge of numerous telomerase regulation mechanisms at the transcription level in human that might become attractive anti-cancer therapy targets.

Is telomerase a viable target in cancer?

The ideal cancer treatment would specifically target cancer cells yet have minimal or no adverse effects on normal somatic cells. Telomerase, the ribonucleoprotein reverse transcriptase that maintains the ends of human chromosome, is an attractive cancer therapeutic target for exactly this reason [1]. Telomerase is expressed in more than 85% of cancer cells, making it a nearly universal cancer marker, while the majority of normal somatic cells are telomerase negative. Telomerase activity confers limitless replicative potential to cancer cells, a hallmark of cancer which must be attained for the continued growth that characterizes almost all advanced neoplasms [2]. In this review we will summarize the role of telomeres and telomerase in cancer cells, and how properties of telomerase are being exploited to create targeted cancer therapies including telomerase inhibitors, telomerase-targeted immunotherapies and telomerase-driven virotherapies. A frank and balanced assessment of the current state of telomerase inhibitors with caveats and potential limitations will be included.

Characterization of a cluster of oncogenic mutations in E6 of a human papillomavirus 83 variant isolated from a high-grade squamous intraepithelial lesion

We previously isolated human papillomavirus 83 (HPV83m) from a cervical smear. Sequence analysis of E6 and E7 proteins highlighted five mutations located in the second putative zinc-finger region of E6 (E6m), an important domain for protein-protein or protein-DNA interactions. Here, we show that E6m of HPV83m can trigger human primary cell proliferation and anchorage-independent growth properties, similarly to E6 of HPV16, a high-risk HPV (HR-HPV). Interestingly, we demonstrate that, in contrast to E6 of HPV16, E6m corrupts neither p53 stability nor telomerase activity, but acts as a specific modulator of the transcriptional machinery. By studying E6m reversion mutants, we confirmed the importance of the second zinc-finger domain in triggering the observed upregulation of cell growth and of the transcriptional machinery. Reversion of these mutations in E6m (to yield strain E6r) fully abolished the oncogenic potential of E6m, transforming the phenotype of E6 from a high-risk to a low-risk phenotype. Importantly, our data define the importance of a cluster of mutations in the second zinc finger of E6m in increasing the oncogenic potential of HPV83.

Regulation of hTERT transcription: a target of cellular and viral mechanisms for immortalization and carcinogenesis

A hallmark of human cancer cells is immortal cell growth, which is associated with telomere maintenance by telomerase. The transcriptional regulation of the human telomerase reverse transcriptase (hTERT) gene is a major mechanism that negatively and positively controls telomerase activity in normal and cancer cells, respectively. A growing body of data suggests that various cellular and viral factors and pathways involved in cell senescence, immortalization and carcinogenesis act on the hTERT promoter. The activity of the hTERT promoter is regulated, either directly or through signaling pathways, by oncogene products (e.g., Myc and Ets families) and tumor suppressor proteins (e.g., BRCA1). Endogenous factors involved in the physiological repression of the hTERT gene have also been revealed by chromosome transfer experiments. The integration of viral genomes in the hTERT locus can lead to hTERT activation and telomerase induction. Here, we summarize these findings and pay special attention to recent findings with relevance to the endogenous regulatory mechanisms of hTERT transcription.

Transforming growth factor-β and the hallmarks of cancer

Tumorigenesis is in many respects a process of dysregulated cellular evolution that drives malignant cells to acquire six phenotypic hallmarks of cancer, including their ability to proliferate and replicate autonomously, to resist cytostatic and apoptotic signals, and to induce tissue invasion, metastasis, and angiogenesis. Transforming growth factor-β (TGF-β) is a potent pleiotropic cytokine that functions as a formidable barrier to the development of cancer hallmarks in normal cells and tissues. Paradoxically, tumorigenesis counteracts the tumor suppressing activities of TGF-β, thus enabling TGF-β to stimulate cancer invasion and metastasis. Fundamental gaps exist in our knowledge of how malignant cells overcome the cytostatic actions of TGF-β, and of how TGF-β stimulates the acquisition of cancer hallmarks by developing and progressing human cancers. Here we review the molecular and cellular mechanisms that underlie the ability of TGF-β to mediate tumor suppression in normal cells, and conversely, to facilitate cancer progression and disease dissemination in malignant cells.

The role of telomeres in the ageing of human skin

Skin is a self-renewing tissue that is required to go through extensive proliferation throughout the lifespan of an organism. Telomere shortening acts as a mitotic clock that prevents aberrant proliferation such as cancer. A consequence of this protection is cellular senescence and ageing. The telomerase enzyme complex maintains telomere length in germline cells and in cancer cells. Telomerase is also active in certain somatic cells such as those in the epidermis but is almost undetectable in the dermis. Increasing evidence indicates that telomerase plays a significant role in maintenance of skin function and proliferation. Mutations in telomerase component genes in the disease dyskeratosis congenita result in numerous epidermal abnormalities. Studies also indicate that telomerase activity in epidermal stem cells might have roles that go beyond telomere elongation. Telomeres in skin cells may be particularly susceptible to accelerated shortening because of both proliferation and DNA-damaging agents such as reactive oxygen species. Skin might present an accessible tissue for manipulation of telomerase activity and telomere length with the potential of ameliorating skin diseases associated with ageing.

EGFR overexpression induces activation of telomerase via PI3K/AKT-mediated phosphorylation and transcriptional regulation through Hif1-alpha in a cellular model of oral-esophageal carcinogenesis

Telomerase plays an important role during immortalization and malignant transformation as crucial steps in the development of human cancer. In a cellular model of oral-esophageal carcinogenesis, recapitulating the human disease, immortalization occurred independent of the activation of telomerase but through the recombination-based alternative lengthening of telomeres (ALT). In this stepwise model, additional overexpression of EGFR led to in vitro transformation and activation of telomerase with homogeneous telomere elongation in already immortalized oral squamous epithelial cells (OKF6-D1_dnp53). More interestingly, EGFR overexpression activated the PI3K/AKT pathway. This strongly suggested a role for telomerase in tumor progression in addition to just elongating telomeres and inferring an immortalized state. Therefore, we sought to identify the regulatory mechanisms involved in this activation of telomerase and in vitro transformation induced by EGFR. In the present study we demonstrate that telomerase expression and activity are induced through both direct phosphorylation of hTERT by phospho-AKT as well as PI3K-dependent transcriptional regulation involving Hif1-alpha as a key transcription factor. Furthermore, EGFR overexpression enhanced cell cycle progression and proliferation via phosphorylation and translocation of p21. Whereas immortalization was induced by ALT, in vitro transformation was associated with telomerase activation, supporting an additional role for telomerase in tumor progression besides elongating telomeres.

Telomerase activation in atherosclerosis and induction of telomerase reverse transcriptase expression by inflammatory stimuli in macrophages

OBJECTIVE

Telomerase serves as a critical regulator of tissue renewal. Although telomerase activity is inducible in response to various environmental cues, it remains unknown whether telomerase is activated during the inflammatory remodeling underlying atherosclerosis formation. To address this question, we investigated in the present study the regulation of telomerase in macrophages and during atherosclerosis development in low-density lipoprotein receptor-deficient mice.

METHODS AND RESULTS

We demonstrate that inflammatory stimuli activate telomerase in macrophages by inducing the expression of the catalytic subunit telomerase reverse transcriptase (TERT). Reporter and chromatin immunoprecipitation assays identified a previously unrecognized nuclear factor-κB (NF-κB) response element in the TERT promoter, to which NF-κB is recruited during inflammation. Inhibition of NF-κB signaling completely abolished the induction of TERT expression, characterizing TERT as a bona fide NF-κB target gene. Furthermore, functional experiments revealed that TERT deficiency results in a senescent cell phenotype. Finally, we demonstrate high levels of TERT expression in macrophages of human atherosclerotic lesions and establish that telomerase is activated during atherosclerosis development in low-density lipoprotein receptor-deficient mice.

CONCLUSIONS

These results characterize TERT as a previously unrecognized NF-κB target gene in macrophages and demonstrate that telomerase is activated during atherosclerosis. This induction of TERT expression prevents macrophage senescence and may have important implications for the development of atherosclerosis.

NFAT5 regulates transcription of the mouse telomerase reverse transcriptase gene

We aimed to clarify the transcription-regulation mechanisms of the mouse telomerase reverse transcriptase gene (mTERT). First, we searched for the promoter region required for transcriptional activation of mTERT and identified an enhancer cis-element (named mTERT-EE) located between -200 and -179bp of the mouse TERT gene (mTERT). EMSA results suggested that nuclear factor of activated T cells (NFAT) member proteins bind to mTERT-EE. We then identified NFAT5 as the factor binding to mTERT-EE and found that it activates the transcription of the mTERT core promoter. The results that siRNA directed against NFAT5 significantly reduced mTERT expression and mTERT core promoter activity and that the expressions of NFAT5 and mTERT were well correlated in various mouse tissues except liver suggest that NFAT5 dominantly and directly regulates mTERT expression. To clarify their functionality further, we investigated the effect of hypertonic stress, a known stimulus affecting the expression and transcriptional activity of NFAT5, on mTERT expression. The result indicated that hypertonic stress activates mTERT transcription via the activation and recruitment of NFAT5 to the mTERT promoter. These results provide useful information about the transcription-regulation mechanisms of mTERT.

Beta-lapachone (LAPA) decreases cell viability and telomerase activity in leukemia cells: suppression of telomerase activity by LAPA

Up-regulation of telomerase activity is associated with immortalization and unlimited cell division in most cancer cells. Therefore, telomerase represents a particularly attractive target for anticancer therapy. Recent reports have suggested that beta-lapachone (LAPA), the product of the South American Tabebuia avellanedae tree, inhibits growth of tumor cells. However, the underlying relationship between telomerase activity and apoptosis in response to LAPA exposure in leukemia cells remains poorly understood. In this study, we confirmed that LAPA treatment induces direct cytotoxicity in human leukemia cells (U937, K562, HL60, and THP-1) through activation of caspase-3 and subsequent cleavage of poly(ADP-ribose) polymerase. The observed induction of cell death was associated with decreased telomerase activity, which was ascribed to down-regulation of telomerase reverse transcriptase. Additionally, overexpression of anti-apoptotic Bcl-2 could not overcome the induction of apoptosis or the decreased telomerase activity in response to treatment of U937 cells with LAPA. We conclude that LAPA has a direct cytotoxic effect and the loss of telomerase activity in leukemia cells.

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.

PinX1 inhibits telomerase activity in gastric cancer cells through Mad1/c-Myc pathway

INTRODUCTION

The aim of this study was to investigate the role of Mad1/c-Myc in telomerase regulation in gastric cancer cells in order to gain insight into telomerase activity and to evaluate PinX1 as a putative inhibitor of gastric cancer.

METHODS

PinX1 and PinX1siRNA eukaryotic expression vectors were constructed by recombinant technology and transfected into gastric carcinoma cells using Lipofectamine 2000. Telomerase activity was measured by the telomeric repeat amplification protocol. Apoptosis of gastric cancer cells was analyzed by flow cytometry and transmission electron microscopy. Reverse transcription-polymerase chain reaction and Western blotting were used to assess the expression levels of PinX1 and Mad1/c-Myc.

RESULTS

We found that PinX1-negative gastric cancer cells showed significantly higher telomerase activity than did the PinX1-postive cells. PinX1-transfection reduced telomerase activity in PinX1-negative gastric cancer cells and exhibited an upregulation of Mad1 and downregulation of c-Myc expression. Pinx1 RNAi treatment led to downregulation of Mad1 and upregulation of c-Myc.

CONCLUSION

Suppression of telomerase activity mediated by PinX1 is involved in the Mad1/c-Myc pathway.

Human chromosome 5 carries a transcriptional regulator of human telomerase reverse transcriptase (hTERT)

Telomerase activation is crucial for cells that tend to be immortalized. Increased telomerase activity is correlated with upregulation of telomerase reverse transcriptase (TERT) expression. In most human somatic cells, hTERT expression is suppressed by multiple factors. We have previously shown that human chromosome 5 carries a possible suppressor of mouse tert mtert expression in a mouse melanoma cell line, B16-F10 cells. However, the function of the transcriptional regulator of TERT on this chromosome remains unclear. To examine the functional role of a putative hTERT regulator(s) on this chromosome, we transferred human chromosome 5 in a human melanoma cell line, A2058 cells by microcell-mediated chromosome transfer (MMCT). Microcell hybrid clones with an introduced chromosome 5, but not chromosome 10, showed a remarkable decrease in the growth rate with an obvious cellular morphological alteration and eventually cellular senescence. Moreover, this phenomenon was accompanied by a reduction of hTERT expression and telomerase activity. Most importantly, we found that transcriptional suppression of hTERT by the introduction of chromosome 5 is largely mediated by regulating hTERT promoter activity. Furthermore, the hTERT promoter region between -1623 and -1047 was responsible for this function. These results provide evidence that transcriptional regulator(s) of the hTERT is carried on human chromosome 5 as an endogenous mechanism of hTERT suppression.

Prognostic significance of telomerase polymorphism in non-small cell lung cancer

PURPOSE

Lung cancer is the leading cause of death in oncologic patients of western countries, with very low survival rates. Telomerase main components are the catalytic subunit (hTERT) and the RNA template (hTR). A functional polymorphism in the hTERT gene was found in the promoter region (-1327T/C), and individuals homozygous for the -1327C/C genotype present shorter telomere length compared with T-carrier genotypes. Our purpose was to investigate the potential prognostic role of the hTERT functional genetic variant in non-small cell lung cancer (NSCLC) patients.

EXPERIMENTAL DESIGN

We prospectively conducted a study involving 226 patients with NSCLC treated with a first-line chemotherapeutic standard protocol. A follow-up study was undertaken (median follow-up time, 26 months) to evaluate treatment response and overall survival of NSCLC patients. The hTERT -1327T/C genetic variants were analyzed by allelic discrimination with real-time PCR.

RESULTS

Our results indicate an influence of the telomerase genetic variants in the overall survival of NSCLC patients. Cox regression analysis showed a significantly higher median estimated cumulative survival of 26.5 months in T-carrier patients, compared with that of 19.3 months in CC patients (hazard ratio, 0.52; 95% confidence interval, 0.35-0.77; P = 0.001).

CONCLUSIONS

Telomerase functional polymorphism in the hTERT gene may contribute as a prognostic factor in NSCLC patients. Our findings indicate that hTERT genetic variants, by modulating telomere length, may confer an advantage in chemotherapy response. The assessment of telomerase genetic variants could supplement prognosis of survival in the course of NSCLC and may be a promising molecular marker of treatment response in these patients.

Multiple genetic variants in telomere pathway genes and breast cancer risk

PURPOSE

To explore the etiologic role of genetic variants in telomere pathway genes and breast cancer risk.

METHODS

A population-based case-control study, the Long Island Breast Cancer Study Project, was conducted, and 1,067 cases and 1,110 controls were included in the present study. Fifty-two genetic variants of nine telomere-related genes were genotyped.

RESULTS

Seven single nucleotide polymorphisms (SNP) showed significant case-control differences at the level of P < 0.05. The top three statistically significant SNPs under a dominant model were TERT-07 (rs2736109), TERT-54 (rs3816659), and POT1-03 (rs33964002). The odds ratios (OR) were 1.56 [95% confidence interval (95% CI), 1.22-1.99] for the TERT-07 G-allele, 1.27 (95% CI, 1.05-1.52) for the TERT-54 T-allele, and 0.79 (95% CI, 0.67-0.95) for the POT1-03 A-allele. TERT-67 (rs2853669) was statistically significant under a recessive model; the OR of the CC genotype was 0.69 (95% CI, 0.69-0.93) compared with the T-allele. However, none of the SNPs retained significance after Bonferroni adjustment for multiple testing at the level of P < 0.001 (0.05/52) except for TERT-07. When restricted to Caucasians (94% of the study subjects), a stronger association for the TERT-07 G-allele was observed with an OR of 1.60 (95% CI, 1.24-2.05; P = 0.0002). No effect modifications were found for variant alleles and menopausal status, telomere length, cigarette smoking, body mass index status, and family history of breast cancer risk.

CONCLUSIONS

Four SNPs in the TERT and POT1 genes were significantly related with overall breast cancer risk. This initial analysis provides valuable clues for further exploration of the biological role of telomere pathway genes in breast cancer.

Chromatin and epigenetic regulation of the telomerase reverse transcriptase gene

Telomerase expression and telomere maintenance are critical for long-term cell proliferation and survival, and they play important roles in development, aging, and cancer. Cumulating evidence has indicated that regulation of the rate-limiting subunit of human telomerase reverse transcriptase gene (hTERT) is a complex process in normal cells and many cancer cells. In addition to a number of transcriptional activators and repressors, the chromatin environment and epigenetic status of the endogenous hTERT locus are also pivotal for its regulation in normal human somatic cells and in tumorigenesis.

Evolution in health and medicine Sackler colloquium: Genetic variation in human telomerase is associated with telomere length in Ashkenazi centenarians

Telomere length in humans is emerging as a biomarker of aging because its shortening is associated with aging-related diseases and early mortality. However, genetic mechanisms responsible for these associations are not known. Here, in a cohort of Ashkenazi Jewish centenarians, their offspring, and offspring-matched controls, we studied the inheritance and maintenance of telomere length and variations in two major genes associated with telomerase enzyme activity, hTERT and hTERC. We demonstrated that centenarians and their offspring maintain longer telomeres compared with controls with advancing age and that longer telomeres are associated with protection from age-related diseases, better cognitive function, and lipid profiles of healthy aging. Sequence analysis of hTERT and hTERC showed overrepresentation of synonymous and intronic mutations among centenarians relative to controls. Moreover, we identified a common hTERT haplotype that is associated with both exceptional longevity and longer telomere length. Thus, variations in human telomerase gene that are associated with better maintenance of telomere length may confer healthy aging and exceptional longevity in humans.

Telomeres and telomerase in chronic myeloid leukaemia: impact for pathogenesis, disease progression and targeted therapy

Telomeres are specialized structures localized at the end of human chromosomes. Due to the end replication problem, each cell division results in a loss of telomeric repeats in normal somatic cells. In germ line and stem cells, the multicomponent enzyme telomerase maintains the length of telomere repeats. However, elevated telomerase activity has also been reported in the majority of solid tumours as well as in acute and chronic leukaemia. Chronic myeloid leukaemia (CML) serves as a model disease to study telomere biology in clonal myeloproliferative disorders. In CML, telomere shortening correlates with disease stage, duration of chronic phase (CP), prognosis measured by the Hasford risk score and the response to disease-modifying therapeutics such as the tyrosine kinase inhibitor Imatinib. In addition, telomerase activity (TA) is already increased in CP CML and further upregulated with disease progression to accelerated phase and blast crisis (BC). Furthermore, a correlation of TA with increased genetic instability as well as a shorter survival of the patients has been reported. Here, we review the current state of knowledge of the role of telomere and telomerase biology in CML and discuss the possible impact of novel treatment approaches.

Polymorphisms in telomere maintenance genes and risk of lung cancer

This study was conducted to comprehensively evaluate the associations between polymorphisms in telomere maintenance genes (TERT, TRF1, TNKS1, TRF2, RAP1, and POT1) and lung cancer risk. We captured 35 polymorphisms in the genes and determined their frequencies in 27 healthy Koreans. Ten haplotype-tagging polymorphisms were examined in a case-control study that consisted of 720 lung cancer patients and 720 healthy controls. The TERT rs2735940 g.C > T and rs2736098 g.G > A, and TNKS1 rs6985140 g.A > G were significantly associated with the risk of lung cancer. In the haplotype analysis, the TERT rs2735940T/rs2736098A haplotype (ht4) was associated with a significantly increased risk of lung cancer compared with the rs2735940C/rs2736098G haplotype (adjusted odds ratio, 1.26; 95% confidence interval, 1.07-1.50; P = 0.008). When the TERT ht4 and TNKS1 rs6985140G as risk alleles, the risk of lung cancer increased in a dose-dependent manner as the number of risk alleles increased (P(trend) < 0.001). Subjects with two to four risk alleles were at a significantly increased risk of lung cancer (adjusted odds ratio, 1.67; 95% confidence interval, 1.23-2.27; P = 0.001) compared with subjects with zero risk allele. These findings suggest that genetic variants in the TERT and TNKS1 genes contribute to genetic susceptibility to lung cancer.

Ets2 transcription factor, telomerase activity and breast cancer

1. The enzyme telomerase maintains telomeres (ends of chromosomes) by synthesizing telomeric DNA at each end of the chromosomes. Its association with telomeres has implicated telomerase in cell immortalization. 2. Numerous studies have shown significant levels of telomerase activity in 85% of various types of cancer. Transcriptional control of the catalytic subunit, telomerase reverse transcriptase (TERT), dominates regulation of telomerase. Although several major factors have been identified in regulating TERT, they cannot explain all the transcriptional activity of the hTERT gene. 3. The Ets transcription factor (TF) family is becoming a regular feature in tumourigenesis, particularly in breast cancer. However, the roles and mechanisms of different Ets TFs are largely unknown. 4. The present minireview discusses the research that identified Ets as a regulator of telomerase required for breast cancer cell survival and proliferation, highlighting the discoveries central to understanding the molecular acts used by Ets TFs to mediate TERT gene transcription.

Prognostic relevance of hTERT mRNA expression in ductal adenocarcinoma of the pancreas

Telomerase is thought to play an essential role in tumorigenesis and progression. Its activity is directly correlated with the expression of its catalytic subunit, human telomerase reverse transcriptase (hTERT). A correlation of transcript expression with a poor prognosis has been detected in different human malignancies. However, data on hTERT in pancreatic ductal adenocarcinoma (PDAC) are purely descriptive so far. Therefore, we evaluated the impact of hTERT expression on patients' prognosis. Human telomerase reverse transcriptase mRNA isolates from 56 human microdissected PDAC tissues were analyzed by quantitative reverse transcription-polymerase chain reaction and multivariate Cox regression hazard test. Elevated hTERT transcript levels were measured in 23 of 56 PDAC tissues, 33 patients showed no detectable transcripts. Unexpectedly, a low expression of hTERT mRNA levels was associated with a worse prognosis for overall survival (relative risk = 5.33; P = .013) when compared to high levels, whereas undetectable expression showed an intermediate risk of tumor-related death. These data challenge previous findings outlining hTERT's negative impact on overall survival. The risk pattern obtained in PDAC suggests a more complex regulation of hTERT.

Expansion and characterization of cancer stem-like cells in squamous cell carcinoma of the head and neck

Evidence has accumulated indicating that only a minority of cancer cells with stem cell properties, cancer stem cells (CSCs), are responsible for maintenance and growth of the tumor. CD44 is currently used to identify CSCs as one of the cell surface markers for solid tumors. Here we report the identification, expansion, and characterization of CD44+ cancer stem-like cells from a permanent squamous cell carcinoma of the head and neck (SCCHN) cell line. Under serum-free medium culture conditions, a small population (less than 3%) of CD44+ cells in a permanent cancer cell line was dramatically increased up to around 40%. The CD44+ cell population also showed higher expression of CD133 and ABCG2 as compared with the CD44- cell population. Moreover, CD44+ cells possess not only a marked capacity for forming tumor spheres, proliferation, migration, and invasion in vitro, but also resistance to chemotherapeutic agents. Four genes related to chemoresistance, ABCB1, ABCG2, CYP2C8, and TERT, were up-regulated in a CD44+ cell population. Our findings indicate that a subpopulation of CSCs is maintained in the SCCHN cell line, and the presence of such CSCs has an important clinical implication for head and neck cancer treatment. Further characterization of CSCs may provide new insights for novel therapeutic targets and prognostic markers.

Association of hsp90 to the hTERT promoter is necessary for hTERT expression in human oral cancer cells

Enhanced expression of human telomerase reverse transcriptase (hTERT) occurs frequently during cellular immortalization. The current study was undertaken to determine the mechanism regulating the hTERT promoter activity during cellular immortalization of human oral keratinocytes. Normal human oral keratinocytes (NHOKs) were immortalized with Bmi-1 and the E6 oncoprotein of human papillomavirus type 16 to establish the telomerase-positive HOK-Bmi-1/E6 cell line. Using DNA-protein-binding assay, we found that heat shock protein 90 (hsp90) physically interacts with the hTERT promoter in vitro. The hsp90 interaction with the promoter was detected more strongly in the telomerase-positive HOK-Bmi-1/E6 cells compared with that in senescing NHOK. Chromatin immunoprecipitation confirmed the in vivo interaction between hsp90 and the hTERT promoter in SCC4 cells, a telomerase-positive oral cancer cell line, but not in the NHOK. To determine the physiological significance of this interaction, SCC4 cells were exposed to geldanamycin (GA), a competitive inhibitor of hsp90. GA exposure led to decrease in telomerase activity, hTERT promoter activity and hTERT messenger RNA expression in SCC4 cells, even in the absence of de novo protein synthesis. Also, it abolished the in vivo interaction of the hTERT promoter region with hsp90 but not with Sp1 or c-Myc. These results indicate that physical interaction between hsp90 and the hTERT promoter occurs in telomerase-positive cells but not in normal human cells and is necessary for the enhanced hTERT expression and telomerase activity in cancer cells.

Pectenotoxin-2 represses telomerase activity in human leukemia cells through suppression of hTERT gene expression and Akt-dependent hTERT phosphorylation

In this study, we found that pectenotoxin-2 (PTX-2) decreased cell viability and inhibited telomerase activity with downregulation of hTERT expression in human leukemia cells. PTX-2 treatment also reduced c-Myc and Sp1 gene expression and DNA binding activity. Further chromatin immunoprecipitation assay demonstrated that PTX-2 attenuated the binding of c-Myc and Sp1 to the regulatory regions of hTERT. We also observed that PTX-2 treatment attenuated the phosphorylation of Akt, thereby reducing the phosphorylation and nuclear translocation of hTERT. We concluded that PTX-2 suppressed telomerase activity through the transcriptional and post-translational suppression of hTERT and this process precedes cellular differentiation of human leukemia cells.

Increased copy number of the TERT and TERC telomerase subunit genes in cancer cells

Telomerase is a ribonucleoprotein enzyme complex that adds telomeric repeats to the ends of chromosomes. The core telomerase components are the telomerase reverse transcriptase (TERT) catalytic subunit, and the telomerase RNA (TR) template subunit. In most cancers, telomerase is expressed at levels that are substantially higher than in normal cells. A known consequence of telomerase up-regulation which is considered to play a critical role in oncogenesis is maintenance of telomere length, and thus evasion by cancer cells of the normal limits on proliferation that are associated with the steady decrease in telomere length that accompanies proliferation of normal cells. It has also been suggested that telomerase up-regulation confers other advantages on cancer cells independent of its enzymatic activity. The mechanisms responsible for up-regulation of telomerase in cancer are incompletely understood. Here we review evidence suggesting that this frequently results from increased copy number of the genes encoding telomerase components. The TERT gene is located at human chromosome band 5p15.33, and the telomerase RNA component (TERC) gene that encodes TR is at 3q26.3. Chromosomal gains and gene amplifications involving chromosome arms 5p and 3q are among the most frequent in human tumors. Increased TERT and TERC gene dosage has been detected frequently in a variety of human cancers, and clonal evolution of cells with increased TERT or TERC copy number has been observed, suggesting a growth advantage in cells with increased TERT or TERC gene dosage.

Platycodin D induces apoptosis and decreases telomerase activity in human leukemia cells

Platycodin D (PD) is a major constituent of triterpene saponins found in the root of Platycodon grandiflorum. Recent studies have demonstrated that PD is a potentially interesting candidate for use in cancer chemotherapy. However, the molecular mechanisms responsible for PD-induced telomerase inhibition remain to be poorly known. In this study, we examined the effects of PD treatment on telomerase activity in different human leukemia cell lines. At concentrations between 10 and 20 microM, PD exerted a dose-dependent direct cytotoxic effect and inhibition of telomerase activity via downregulation of hTERT expression. Because c-Myc and Sp1 are known to directly regulate transcription of hTERT, we also evaluated the expression and DNA binding activity of these proteins. PD treatment reduced c-Myc and Sp1 protein levels and DNA binding activities in a dose-dependent manner. We also observed that PD treatment downregulates the activation of Akt, thereby reducing the phosphorylation and nuclear translocation of hTERT. We conclude that PD has direct cytotoxic effect on human leukemia cells and suppresses telomerase activity through transcriptional and posttranslational suppression of hTERT.

Downregulation of miR-138 is associated with overexpression of human telomerase reverse transcriptase protein in human anaplastic thyroid carcinoma cell lines

Alterations of several microRNA (miRNA) have been linked to cancer development and its biology. To search for unique miRNA that might play a role in the development of anaplastic thyroid carcinoma (ATC), we examined the expression of multiple miRNA and their functional effects on target genes in human thyroid carcinoma cell lines. We quantitatively evaluated the expression of multiple miRNA in 10 ATC and five papillary thyroid carcinoma (PTC) cell lines, as well as primary tumors from 11 thyroid carcinoma patients (three ATC and eight PTC), using the stem-loop-mediated reverse transcription real-time polymerase chain reaction method. We also examined the target gene specificity of unique miRNA that showed differences in expression between ATC and PTC cell lines. One miRNA, miR-138, was significantly downregulated in ATC cell lines in comparison with PTC (P < 0.01). Eleven miRNA (including miR-138) potentially targeting the human telomerase reverse transcriptase (hTERT) gene were totally downregulated in both ATC and PTC cell lines in comparison with normal thyroid tissues. A tendency for an inverse correlation between miR-138 and hTERT protein expression was observed in the thyroid cancer cell lines, although this failed to reach significance (r = -0.392, P = 0.148). We demonstrated that overexpression of miR-138 induced a reduction in hTERT protein expression, and confirmed target specificity between miR-138 and the hTERT 3'-untranslated region by luciferase reporter assay. These results suggest that loss of miR-138 expression may partially contribute to the gain of hTERT protein expression in ATC, and that further multiple miRNA targeting hTERT mRNA might be involved in the development of thyroid carcinoma.

Telomerase redefined: Integrated regulation of hTR and hTERT for telomere maintenance and telomerase activity

Telomerase activity is dependent on the expression of 2 main core component genes, hTERT, which encodes the catalytic component and hTR (also called TERC), which encodes the RNA component. The correlation between telomerase activity and carcinogenesis has made this molecule of great interest in cancer research, however in order to fully understand the regulation of telomerase the mechanisms controlling both telomerase genes need to be studied. Some of these mechanisms of regulation have begun to emerge, however many more remain to be deciphered. For many years hTERT has been regarded as the limiting component of telomerase and much of the research in this field has focussed on its regulation, however it was clear from an early stage that hTR expression was also tightly regulated in normal cells and disease. More recently evidence from biochemistry, promoter studies and mouse models has been steadily increasing for a role for hTR as a limiting and essential component for telomerase activity and telomere maintenance. Perhaps the time has come to redefine our view of telomerase regulation. Knowledge of the mechanisms controlling both telomerase genes in normal systems and cancer may aid our understanding of the role of telomerase in carcinogenesis or highlight potential areas for therapeutic intervention. Here we review the essential requirement of hTR for telomere maintenance and telomerase activity in normal tissues and disease and focus on recent advances in our understanding of hTR regulation in relation to hTERT.

Nuclear translocation of telomerase reverse transcriptase and calcium signaling in repression of telomerase activity in human lung cancer cells by fungal immunomodulatory protein from Ganoderma tsugae

Recombinant fungal immunomodulatory protein, reFIP-gts, was cloned from Ganoderma tsugae and purified. In our previous study, it was shown that reFIP-gts has anti-telomerase effects in A549 cells. Here, we proved that reFIP-gts entry into the cell and localization in endoplasmic reticulum can result in ER stress, thereby increasing ER stress markers (CHOP/GADD153) and intracellular calcium release in A549 cells. The use of calcium chelator restores reFIP-gts-mediated reduction in telomerase activity. These results strongly suggest that ER stress induces intracellular calcium release and results in inhibition of telomerase activity. Although reFIP-gts decreased hTERT mRNA level in both A549 and H1299 cells, only the telomerase activity in A549 cells was inhibited. Surprisingly, we found that reFIP-gts induces translocation of hTERT from the nucleus into the cytosol in A549 cells but not in H1299 cells. Using leptomycin B, nuclear export inhibitor, we showed that hTERT is not transported. Using MG132, a proteasome inhibitor, reFIP-gts also prevents hTERT translocation from proteasome degradation. Taken together, these results indicate that reFIP-gts inhibits telomerase activity in lung cancer cells through nuclear export mechanisms, which might be mediated by ER stress-induced intracellular calcium level.

Change of the expression of human telomerase reverse transcriptase mRNA and human telomerase RNA after cisplatin and 5-fluorouracil exposure in head and neck squamous cell carcinoma cell lines

Telomerase activity appears to be associated with cell immortalization and malignant progression. Understanding how telomerase activity is regulated in vivo is important not only for understanding the molecular biology of telomerase but also for the potential clinical application of anticancer drugs. This study evaluated telomerase activity and quantified the expression of human telomerase reverse transcriptase (hTERT) mRNA and human telomerase RNA (hTR) using a real-time reverse transcriptase-polymerase chain reaction (RT-PCR) method before and after the exposure of cisplatin and 5-fluorouracil (5-FU) in two head and neck squamous cell carcinoma (HNSCC) cell lines. Two human HNSCC cell lines (PNUH-12 and SNU-899) were studied. Cell cytotoxicity, the change of telomerase activity, and hTERT mRNA and hTR expression by 5-FU and cisplatin exposure were assessed by MTT assay, TRAP assay, and real-time RT-PCR, respectively. In two cell lines, after cisplatin exposure, the telomerase activity and hTERT mRNA expression decreased, but hTR expression in- creased according to the concentration of drug. However, in both cell lines, the telomerase activity and hTR did not show any significant change after 5-FU treatment, but the expression of hTERT mRNA decreased. These results suggest that there may be other important regulating mechanism except hTERT mRNA as the regulation factor of telomerase activity in HNSCC cell lines.

Tumor-specific activation of human telomerase reverses transcriptase promoter activity by activating enhancer-binding protein-2beta in human lung cancer cells

The up-regulated expression and telomerase activity of human telomerase reverse transcriptase (hTERT) are hallmarks of tumorigenesis. The hTERT promoter has been shown to promote hTERT gene expression selectively in tumor cells but not in normal cells. However, little is known about how tumor cells differentially activate hTERT transcription and induce telomerase activity. In this study, we identified activating enhancer-binding protein-2beta (AP-2beta) as a novel transcription factor that specifically binds to and activates the hTERT promoter in human lung cancer cells. AP-2beta was detected in hTERT promoter DNA-protein complexes formed in nuclear extracts prepared only from lung cancer cells but not from normal cells. We verified the tumor-specific binding activity of AP-2beta for the hTERT promoter in vitro and in vivo and detected high expression levels of AP-2beta in lung cancer cells. We found that ectopic expression of AP-2beta reactivated hTERT promoter-driven reporter green fluorescent protein (GFP) gene and endogenous hTERT gene expression in normal cells, enhanced GFP gene expression in lung cancer cells, and prolonged the life span of primary lung bronchial epithelial cells. Furthermore, we found that inhibition of endogenous AP-2beta expression by AP-2beta gene-specific small interfering RNAs effectively attenuated hTERT promoter-driven GFP expression, suppressed telomerase activity, accelerated telomere shortening, and inhibited tumor cell growth by induction of apoptosis in lung cancer cells. Our results demonstrate the tumor-specific activation of the hTERT promoter by AP-2beta and imply the potential of AP-2beta as a novel tumor marker or a cancer therapeutic target.

Physiologically achievable concentrations of genistein enhance telomerase activity in prostate cancer cells via the activation of STAT3

Telomerase contributes to the infinite replicative potential of cancer cells by conferring proliferation and survival through the regulation of growth factors and apoptotic proteins. Although it is generally known that the phytoestrogen, genistein, has telomerase-repressing and anti-proliferative effects on various cancer cells at pharmacological concentrations, we report here that physiologically achievable concentrations of genistein enhance telomerase activity, the proliferation of human prostate cancer cells and tumor growth in the transgenic adenocarcinoma mouse prostate model. In determining the mechanism for enhanced telomerase activity, we observed that physiological concentrations of genistein activated signal transducers and activators of transcription 3 (STAT3) both in vitro and in vivo and increased STAT3 binding to the telomerase reverse transcriptase promoter in human prostate cancer cells. These results demonstrate for the first time that physiologically achievable concentrations of genistein enhance telomerase reverse transcriptase transcriptional activity in prostate cancer cells via the activation of STAT3. Consequently, these concentrations of genistein will augment the growth of prostate cancer cells that could be detrimental to individuals with prostate cancer and therefore, caution should be exercised when genistein is considered for chemotherapeutic purposes.

Regeneration in pig livers by compensatory hyperplasia induces high levels of telomerase activity

Background

Several highly proliferative human cells transiently activate telomerase, a ribonucleoprotein with reverse transcriptase activity, to counterbalance replication-associated telomere erosion and to increase stress resistance. Quiescent human hepatocytes exhibit very low or undetectable levels of telomerase activity. However, hepatocytes display a remarkable proliferative capability following liver injury. To investigate whether liver regeneration by compensatory hyperplasia is associated with telomerase activation, we measured telomerase activity in pig livers after 70 to 80% partial hepatectomy using a fully quantitative real-time telomeric repeat amplification protocol. In contrast to commonly studied inbred laboratory mouse strains, telomere length and telomerase activity in porcine tissues are comparable to humans.

Results

Following partial hepatectomy, histology revealed mitotic hepatocytes as marker for compensatory hyperplasia. As expected, there was no induction of inflammation. Telomerase activity increased significantly showing the highest levels (5-fold upregulation) in pigs treated with partial hepatectomy and hepatic decompression. Moreover, telomerase activity significantly correlated to the number of mitotic hepatocytes.

Conclusion

Our data demonstrate telomerase activation in liver regeneration by compensatory hyperplasia in a large animal model with telomere biology comparable to humans. Telomerase activation may constitute a mechanism to protect proliferating liver cells against telomere shortening and oxidative stress.

Killing effect of oxymatrine on human gastric cancer cell line MKN45 and its mechanism

AIM: To explore the killing effects of oxymatrine (OM) on human gastric cancer cell line MKN45 and its anti-neoplastic mechanism.

METHODS: Human gastric cancer cell line MKN45 was cultured and then treated with 0.5, 1, 2, 4 and 6 g/L OM. Methylthiazolyl tetrazolium analysis (MTT) was used to observe the killing effect of OM on MKN45 cells. Cell cycle distribution was measured by flow cytometry. The activity of telomerase was detected by polymerase chain reaction (PCR)-enzyme linked immunosorbent assay (ELISA). Reverse transcription (RT)-PCR was employed to examine the expression of hTERT, c-myc, p53 and mad1 genes in MKN45 cells.

RESULTS: OM exhibited dose-dependent killing effects on MKN45 cells and its IC50 was 2.78 g/L. After administration for 48 hours, OM induced an increase of G1/G0-phase cells (62.2% ± 1.3% vs 56.7% ± 4.0%, P < 0.05) and decrease of G2/M-phase cells (5.4% ± 1.1% vs 10.0% ± 2.8%, P < 0.05) at a dose of 2 g/L, and a decrease of S-phase cells (30.5% ± 1.3% vs 33.4% ± 1.2%, P < 0.05) at a dose of 4 g/L. OM inhibited the activity of telomerase in MKN45 cells in a dose-dependent manner. The expression of hTERT gene in MKN45 cells was decreased, but the expression of p53 and mad1 genes were increased. However, and c-myc gene expression had no apparent changes.

CONCLUSION: OM has dose-dependent killing effects on MKN45 cells, and it can inhibit the telomerase activity through hTERT gene and the up-stream regulation genes.

hTERT (-1327)T/C polymorphism is not associated with age-related telomere attrition in peripheral blood

Regulation of the telomerase catalytic subunit, hTERT, is a complex process accomplished on many levels. Transcription of the hTERT gene has been widely studied but less is known about the implication of genetic variations. Recently, a functional T to C transition polymorphism was indicated 1327 bp upstream the hTERT transcription starting site. The (-1327)C/C genotype was associated with shorter telomere length compared to the alternative genotypes in healthy individuals and in coronary artery disease patients. We tested this observation and analysed telomere length and the (-1327)T/C polymorphism in 226 myocardial infarction patients and 444 controls from southern Sweden. No significant difference in telomere length was found among the genotypes after age adjustments in the control group (p=0.794) or in the MI group (p=0.339). Moreover, no increased age-related attrition was observed for the (-1327)C/C genotype as previously indicated, rather a telomere elongation in the control group (p=0.021) not seen in the MI group (p=0.249).

TAK1 represses transcription of the human telomerase reverse transcriptase gene

In human cells, telomerase activity is tightly regulated by the expression of its catalytic subunit, namely, the human telomerase reverse transcriptase (hTERT). However, the molecular mechanisms involved in the regulation of hTERT expression have not been completely clarified. We have previously reported that transforming growth factor beta (TGF-beta) represses the expression of the hTERT gene. In the present study, we demonstrated that TGF-beta-activated kinase 1 (TAK1), originally identified as a mitogen-activated kinase kinase kinase, represses the hTERT core promoter activity in an E-box-independent manner, and it also represses the transcription of the hTERT gene in human lung adenocarcinoma cell line, A549 cells. This TAK1-induced repression was found to be caused by the recruitment of histone deacetylase to Sp1 at the hTERT promoter and a consequent reduction in the amount of acetylated histone H4 at the hTERT promoter. Finally, we demonstrated that TAK1 induces cellular senescence programs in normal human diploid cells. Thus, we assume that TAK1 triggers the repression mechanisms of the hTERT gene as a result of evoking cellular senescence programs. Considered together, TAK1 is thought to play a causative role in the determination of a finite replicative lifespan of normal and cancer cells.

Role of transforming growth factor-beta in cancer progression

Invasion and metastasis are the most lethal characteristics of cancer and the leading causes of cancer-related death. Transforming growth factor (TGF)-beta is a multifunctional cytokine that normally functions to prevent the uncontrolled proliferation of epithelial, endothelial and hematopoietic cells. Quite dichotomously, however, aberrant genetic or epigenetic events often negate the cytostatic function of TGF-beta in these cells, leading to tumor formation. Once freed from the growth-inhibitory effects of TGF-beta, cancer cells acquire the ability to proliferate, invade and metastasize when stimulated by TGF-beta. A thorough understanding of the molecular mechanisms underlying these paradoxical functions of TGF-beta remains elusive. Here, the authors review the tumor-suppressing and -promoting activities of TGF-beta and discuss the potential use and targeting of the TGF-beta-signaling system to prevent the progression and acquisition of metastatic phenotypes by human malignancies.

Mechanism of telomerase activation by v-Rel and its contribution to transformation

Telomerase is activated during the transformation of lymphoid cells and fibroblasts by v-Rel, the oncogenic member of the Rel/NF-kappaB family of transcription factors. v-Rel-transformed cell lines have longer telomeres than untransformed chicken lymphoid cells and have high levels of telomerase activity. v-Rel-mediated activation of telomerase is achieved by multiple mechanisms. The expression of the gene encoding the catalytic subunit of telomerase (TERT) was directly upregulated by v-Rel. Moreover, the expression of v-Rel altered the ratio of alternatively spliced and full-length TERT transcripts in favor of the full-length forms. The activation of telomerase by v-Rel in lymphocytes was also accompanied by inactivation of nuclear inhibitors. The inhibition of telomerase activity in v-Rel-transformed cell lines led to apoptosis within 24 h. The expression of v-Rel in a macrophage cell line resulted in elevated levels of reactive oxygen species (ROS), increased telomerase activity, and increased sensitivity to telomerase inhibitors. In contrast, the ectopic expression of TERT decreased the extent of apoptosis induced by ROS. The activation of telomerase by v-Rel may, therefore, partially protect the transformed cells from apoptosis induced by ROS.