Gene Summary

Gene:TERC; telomerase RNA component
Aliases: TR, hTR, TRC3, DKCA1, PFBMFT2, SCARNA19
Summary:Telomerase is a ribonucleoprotein polymerase that maintains telomere ends by addition of the telomere repeat TTAGGG. The enzyme consists of a protein component with reverse transcriptase activity, and an RNA component, encoded by this gene, that serves as a template for the telomere repeat. Telomerase expression plays a role in cellular senescence, as it is normally repressed in postnatal somatic cells resulting in progressive shortening of telomeres. Deregulation of telomerase expression in somatic cells may be involved in oncogenesis. Studies in mouse suggest that telomerase also participates in chromosomal repair, since de novo synthesis of telomere repeats may occur at double-stranded breaks. Mutations in this gene cause autosomal dominant dyskeratosis congenita, and may also be associated with some cases of aplastic anemia. [provided by RefSeq, Jul 2008]
Databases:OMIM, HGNC, Ensembl, GeneCard, Gene
Source:NCBIAccessed: 20 July, 2015

Cancer Overview

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Literature Analysis

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Tag cloud generated 20 July, 2015 using data from PubMed, MeSH and CancerIndex

Latest Publications: TERC (cancer-related)

Flacco A, Ludovini V, Bianconi F, et al.
MYC and human telomerase gene (TERC) copy number gain in early-stage non-small cell lung cancer.
Am J Clin Oncol. 2015; 38(2):152-8 [PubMed] Related Publications
OBJECTIVES: We investigated the frequency of MYC and TERC increased gene copy number (GCN) in early-stage non-small cell lung cancer (NSCLC) and evaluated the correlation of these genomic imbalances with clinicopathologic parameters and outcome.
MATERIALS AND METHODS: Tumor tissues were obtained from 113 resected NSCLCs. MYC and TERC GCNs were tested by fluorescence in situ hybridization (FISH) according to the University of Colorado Cancer Center (UCCC) criteria and based on the receiver operating characteristic (ROC) classification.
RESULTS: When UCCC criteria were applied, 41 (36%) cases for MYC and 41 (36%) cases for TERC were considered FISH-positive. MYC and TERC concurrent FISH-positive was observed in 12 cases (11%): 2 (17%) cases with gene amplification and 10 (83%) with high polysomy. By using the ROC analysis, high MYC (mean ≥ 2.83 copies/cell) and TERC (mean ≥ 2.65 copies/cell) GCNs were observed in 60 (53.1%) cases and 58 (51.3%) cases, respectively. High TERC GCN was associated with squamous cell carcinoma (SCC) histology (P=0.001). In univariate analysis, increased MYC GCN was associated with shorter overall survival (P=0.032 [UCCC criteria] or P=0.02 [ROC classification]), whereas high TERC GCN showed no association. In multivariate analysis including stage and age, high MYC GCN remained significantly associated with worse overall survival using both the UCCC criteria (P=0.02) and the ROC classification (P=0.008).
CONCLUSIONS: Our results confirm MYC as frequently amplified in early-stage NSCLC and increased MYC GCN as a strong predictor of worse survival. Increased TERC GCN does not have prognostic impact but has strong association with squamous histology.

Akıncılar SC, Low KC, Liu CY, et al.
Quantitative assessment of telomerase components in cancer cell lines.
FEBS Lett. 2015; 589(9):974-84 [PubMed] Related Publications
Besides its canonical function of catalyzing the formation of telomeric repeats, many groups have recently reported non-canonical functions of hTERT in particular, and telomerase in general. Regulating transcription is the central basis of non-canonical functions of telomerase. However, unlike reverse transcriptase activity of telomerase that requires only a few molecules of enzymatically active hTERT, non-canonical functions of hTERT or other telomerase components theoretically require several hundred copies. Here, we provide the first direct quantification of all the telomerase components in human cancer cell lines. We demonstrate that telomerase components do not exist in a 1:1 stoichiometric ratio, and there are several hundred copies of hTERT in cells. This provides the molecular basis of hTERT to function in other signaling cascades, including transcription.

Visnovsky J, Kudela E, Farkasova A, et al.
Amplification of TERT and TERC genes in cervical intraepithelial neoplasia and cervical cancer.
Neuro Endocrinol Lett. 2014; 35(6):518-22 [PubMed] Related Publications
OBJECTIVES: Telomerase is activated in various stages of oncogenesis. For cervical cancer, telomerase is already active in precancerous lesions. In our study we focused on the analysis of the amplification patterns of telomerase genes TERT and TERC.
DESIGN AND SETTING: We included 39 patients in our study between January 2012 and April 2013. Each patient underwent a classical gynaecological examination and a colposcopy. During the colposcopic examination we collected material for a Pap smear, HPV DNA test (HC2) and LBC (LiquiPrep™), and performed punch biopsies for histopathological evaluation. Residual cytologic sample was hybridized with the FISH probe and telomerase genes were analysed.
RESULTS: The amplification of the TERT gene showed us a very similar amplification pattern as TERC and gradually corresponded with both histolopathological (p<0.001) and cytopathological findings (p<0.001). The specificity and sensitivity of TERC gene amplification for the detection of CIN2+ lesions (cut off value 2.3) was 88.2% and 95.5% respectively (PPV 91.3%, NPV 93.8%).
CONCLUSIONS: We identified increasing amplification pattern of telomerase genes in cervical lesions. According to our results telomerase genes could help in the future to determine the malignant potential of cervical lesions and could be tested together with cytology and HPV DNA in order to obtain the highest combined sensitivity and specificity for CIN2+ lesion detection.

Townsley DM, Dumitriu B, Young NS
Bone marrow failure and the telomeropathies.
Blood. 2014; 124(18):2775-83 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Our understanding of the pathophysiology of aplastic anemia is undergoing significant revision, with implications for diagnosis and treatment. Constitutional and acquired disease is poorly delineated, as lesions in some genetic pathways cause stereotypical childhood syndromes and also act as risk factors for clinical manifestations in adult life. Telomere diseases are a prominent example of this relationship. Accelerated telomere attrition is the result of mutations in telomere repair genes and genes encoding components of the shelterin complex and related proteins. Genotype-phenotype correlations show genes responsible for X-linked (DKC1) and severe recessive childhood dyskeratosis congenita, typically with associated mucocutaneous features, and others (TERC and TERT) for more subtle presentation as telomeropathy in adults, in which multiorgan failure may be prominent. Telomerase mutations also are etiologic in familial pulmonary fibrosis and cryptic liver disease. Detection of a telomere disease requires awareness in the clinic, appropriate laboratory testing of telomere content, and genetic sequencing. In treatment decisions, genetic screening of related donors for hematopoietic stem cell transplantation is critical, and androgen therapy may be helpful. Telomeres shorten normally with aging, as well as under environmental circumstances, with regenerative stress and oxidative damage. Telomere biology is complexly related to oncogenesis: telomere attrition is protective by enforcing senescence or apoptosis in cells with a long mitotic history, but telomere loss also can destabilize the genome by chromosome rearrangement and aneuploidy.

Iles MM, Bishop DT, Taylor JC, et al.
The effect on melanoma risk of genes previously associated with telomere length.
J Natl Cancer Inst. 2014; 106(10) [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Telomere length has been associated with risk of many cancers, but results are inconsistent. Seven single nucleotide polymorphisms (SNPs) previously associated with mean leukocyte telomere length were either genotyped or well-imputed in 11108 case patients and 13933 control patients from Europe, Israel, the United States and Australia, four of the seven SNPs reached a P value under .05 (two-sided). A genetic score that predicts telomere length, derived from these seven SNPs, is strongly associated (P = 8.92x10(-9), two-sided) with melanoma risk. This demonstrates that the previously observed association between longer telomere length and increased melanoma risk is not attributable to confounding via shared environmental effects (such as ultraviolet exposure) or reverse causality. We provide the first proof that multiple germline genetic determinants of telomere length influence cancer risk.

Kudela E, Farkasova A, Visnovsky J, et al.
Amplification of 3q26 and 5p15 regions in cervical intraepithelial neoplasia.
Acta Obstet Gynecol Scand. 2014; 93(10):997-1002 [PubMed] Related Publications
OBJECTIVE: To analyze different amplification patterns of 3q26 and 5p15 regions in low-grade and high-grade cervical intraepithelial neoplasia.
DESIGN: Experimental research.
SETTING: Department of Obstetrics and Gynecology at a medical faculty in Slovakia.
POPULATION: A group of 83 patients referred for colposcopic examination.
METHODS: Amplification of 3q26 and 5p15 regions was analyzed on the 100 most atypical cells from a cervical cytology slide by fluorescent in situ hybridization using a multicolor hybridization probe. Chi-squared and Man-Whitney U-tests were used for statistical analysis.
MAIN OUTCOME MEASURES: Liquid-based cytology samples and biopsy samples obtained during colposcopic examination correlated with high-risk human papillomavirus status and with amplification patterns of selected regions analyzed by fluorescent in situ hybridization.
RESULTS: The number of cells with 3q26 and 5p15 gain rises with the severity of the lesion p < 0.01. The sensitivity of 3q26 amplification for CIN2+ lesions was 72.1% (95% confidence interval 56.3-84.7) and specificity was 90.0% (95% confidence interval 76.3-97.1). The sensitivity of 5p15 amplification for CIN2+ lesions was 69.8% (95% confidence interval 53.9-82.8) and specificity was 85.0% (95% confidence interval 70.2-94.3).
CONCLUSION: Evaluation of telomerase components can help in differential diagnosis of low-grade and high-grade cervical lesions and in individualized management of these patients.

Gao T, Wang J, Yang M, Li H
Transcriptome analysis reveals the effect of oral contraceptive use on cervical cancer.
Mol Med Rep. 2014; 10(4):1703-8 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Differentially-expressed genes (DEGs) correlated to oral contraceptives (OCs) were identified by comparing the transcriptomes of cervical cancer patients who have taken OCs and those who have not. Their biological functions and relevance to clinical manifestations were investigated further in order to gain an understanding of the pathogenesis of cervical cancer and provide potential therapeutic targets. Level 3 RNA-sequencing (seq) data for cervical squamous-cell carcinoma and endocervical adenocarcinoma and the clinical information were downloaded from The Cancer Genome Atlas. The present study analyzed the RNA‑seq data and information on OC use of 35 patients [OC users (n=18) and those who have never used OCs (n=17)]. Student's t‑test was used in order to identify DEGs and the false discovery rate (FDR) was estimated by a Beta-Uniform Mixture model, which was adopted in multiple testing corrections. A functional enrichment analysis was performed with the Database for Annotation, Visualization and Integrated Discovery tool and BioCarta. A total of 80 DEGs were identified in OC users while FDR=0.3 was set as the cut-off value. The metabolic process and human telomerase RNA gene transcription were significantly upregulated in DEGs. Furthermore, secreted LY6/PLAUR domain containing 1 was identified to be correlated to the pathological response, while the synapse defective 1 Rho GTPase homolog 2 was found to be significantly associated with the histological grade and overall survival time. In conclusion, present study shed light on the effect of OC use on the oncogenesis of the cervix and may indicate novel approaches for a targeted therapy of cervical cancer.

Campa D, Martino A, Varkonyi J, et al.
Risk of multiple myeloma is associated with polymorphisms within telomerase genes and telomere length.
Int J Cancer. 2015; 136(5):E351-8 [PubMed] Related Publications
Compelling biological and epidemiological evidences point to a key role of genetic variants of the TERT and TERC genes in cancer development. We analyzed the genetic variability of these two gene regions using samples of 2,267 multiple myeloma (MM) cases and 2,796 healthy controls. We found that a TERT variant, rs2242652, is associated with reduced MM susceptibility (OR = 0.81; 95% CI: 0.72-0.92; p = 0.001). In addition we measured the leukocyte telomere length (LTL) in a subgroup of 140 cases who were chemotherapy-free at the time of blood donation and 468 controls, and found that MM patients had longer telomeres compared to controls (OR = 1.19; 95% CI: 0.63-2.24; p(trend)  = 0.01 comparing the quartile with the longest LTL versus the shortest LTL). Our data suggest the hypothesis of decreased disease risk by genetic variants that reduce the efficiency of the telomerase complex. This reduced efficiency leads to shorter telomere ends, which in turn may also be a marker of decreased MM risk.

Li L, Jiang W, Zeng SY, Li L
Prospective study of hTERC gene detection by fluorescence in situ hybridization (FISH) in cervical intraepithelial neoplasia 1 natural prognosis.
Eur J Gynaecol Oncol. 2014; 35(3):289-91 [PubMed] Related Publications
OBJECTIVE: The aim of this study was to evaluate the prognostic significance of human chromosome telomerase gene (hTERC) overexpression in cervical intraepithelial neoplasia grade 1 (CIN1) natural prognosis.
MATERIALS AND METHODS: A total number of 2,499 women aged 30-49 years were screened in a population-based cervical cancer screening study from Jiangxi province rural sites. Pathology as the gold standard, 74 CIN1 patients first diagnosed by pathological examination were studied. They were observed by carrying the hybrid capture2 (HC2) and hTERC genetic testing to understand the baseline. All observed women accepted voluntary follow-up. Follow-up for the first time in the first 12 months after screening included hr-HPV HC-2 testing. The second follow-up after screening the first 24 months, included hr-HPV HC-2, colposcopy + pathological examinations.
RESULTS: Of the 74 CIN1 cases that were followed-up for 24 months, seven cases (9.5%) progressed; 25 cases (33.8%) persisted, and 42 patients (56.7%) regressed. There was significant difference between hTERC amplification positive and negative group (chi2 = 21.07, p < 0.001). The risk of CIN1 persistence and progression in positive group was 3.24 (1.96-5.37) times higher than that in negative group. There was significant difference between hr-HPV persist positive and turn to negative or persistent negative group (chi2 = 7.645, p = 0.006). There was significant difference between hTERC gene and the initial test of hr-HPV both positive and both negative group (chi2 = 4.544, p = 0.033).
CONCLUSION: There was a strong association between prevalence of hTERC gene overexpression and CIN1 natural prognosis. The follow-up results indicated that Hr-HPV required repeat testing and that there was significant difference between hr-HPV persistent positive and turn to negative/persistent negative group (chi2 = 7.645, p = 0.006). hTERC gene overexpression could prognoses cervical intraepithelial neoplasia 1 natural prognosis individually.

Wang X, Liu J, Xi H, Cai L
The significant diagnostic value of human telomerase RNA component (hTERC) gene detection in high-grade cervical lesions and invasive cancer.
Tumour Biol. 2014; 35(7):6893-900 [PubMed] Related Publications
Gains of 3q26 chromosome region, where the human telomerase RNA gene (hTERC) is located, have been previously documented in cervical carcinomas. However, published data on this subject are inconclusive. Therefore, we performed a meta-analysis to evaluate the diagnostic value of hTERC in high-grade cervical lesions and invasive cancer. We searched all the eligible studies through PubMed, EMBASE, and the Cochrane Library database without language limitation. Studies were assessed for quality using quality assessment of diagnostic accuracy studies (QUADAS). Positive likelihood ratio (PLR) and negative likelihood ratio (NLR) were pooled separately and compared with overall accuracy measures of diagnostic odds ratio (DOR) and symmetric summary receiver operating characteristic (SROC). The PLR and NLR and their 95 % confidence interval (CI) were calculated using a fixed effects model according to the Mantel-Haensed method and random effects model based on the work of Der Simonian and laird, respectively. A total of 12 studies were included for the analysis. The pooled sensitivity was 0.81 (95 % CI, 0.80-0.82). The pooled specificity was 0.83 (95 % CI, 0.82-0.84). The DOR estimate was performed, and the result was 17.37. Our meta-analysis showed that the detection of genomic amplification of hTERC is a noninvasive and effective approach for high-grade cervical lesions and invasive cancer.

Ramakrishnan SK, Varshney A, Sharma A, et al.
Expression of targeted ribozyme against telomerase RNA causes altered expression of several other genes in tumor cells.
Tumour Biol. 2014; 35(6):5539-50 [PubMed] Related Publications
Telomeres are tandem repeat sequences present at chromosome end that are synthesized by RNA-protein enzyme called telomerase. The RNA component (TR) serves as template for telomerase reverse transcriptase (TERT) for generating telomere repeats. TERT is overexpressed in actively dividing cells including cancerous cells, absent in differentiated somatic cells whereas human telomerase RNA (hTR) is present in normal as well as in cancer cells. Telomerase overexpression in cancer cells ensures telomere length maintenance that actually provides proliferative advantage to cells. Stable expression of ribozyme against hTR in HeLa cells results in reduction of hTR levels, telomerase activity, and telomere length which is accompanied by altered cell morphology and expression of several specific cellular genes. The altered genes deduced from differentially display PCR and 2D gel electrophoresis upon hTR knockdown have function in ribosome biogenesis, chromatin modulation, cell cycle control, and p63-dependant pathways. Our observations shows hTR participates in diverse cellular functions other than telomere maintenance, validates as a possible drug targets in p53- and pRB-negative status, and indicated possible cross-talks between telomerase and other cellular pathways.

Mohamad Ashari ZS, Sulong S, Hassan R, et al.
Low level of TERC gene amplification between chronic myeloid leukaemia patients resistant and respond to imatinib mesylate treatment.
Asian Pac J Cancer Prev. 2014; 15(4):1863-9 [PubMed] Related Publications
The amplification of telomerase component (TERC) gene could play an important role in generation and treatment of haematological malignancies. This present study was aimed to investigate copy number amplification status of TERC gene in chronic myeloid leukaemia (CML) patients who were being treated with imatinib mesylate (IM). Genomic DNA was extracted from peripheral blood of CML-IM Resistant (n=63), CML-IM Respond (n=63) and healthy individuals (n=30). TERC gene copy number predicted (CNP) and copy number calculated (CNC) were determined based on Taqman® Copy Number Assay. Fluorescence in situ hybridization (FISH) analysis was performed to confirm the normal signal pattern in C4 (calibrator) for TERC gene. Nine of CML patients showed TERC gene amplification (CNP=3), others had 2 CNP. A total of 17 CML patients expressed CNC>2.31 and the rest had 2.31>CNC>1.5. TERC gene CNP value in healthy individuals was 2 and their CNC value showed in range 1.59-2.31. The average CNC TERC gene copy number was 2.07, 1.99 and 1.94 in CML- IM Resistant patients, CML-IM Respond and healthy groups, respectively. No significant difference of TERC gene amplification observed between CML-IM Resistant and CML-IM Respond patients. Low levels of TERC gene amplification might not have a huge impact in haematological disorders especially in terms of resistance towards IM treatment.

Li T, Tang L, Bian D, et al.
Detection of hTERC and c-MYC genes in cervical epithelial exfoliated cells for cervical cancer screening.
Int J Mol Med. 2014; 33(5):1289-97 [PubMed] Related Publications
Cervical cancer is the principal cause of mortality due to cancer in women worldwide. New predictive markers may increase survival rates by improving the treatment of patients at a high risk for cancer. This study was carried out to investigate the amplification of human telomerase RNA component (hTERC) or/and c-MYC in cervical epithelial exfoliated cells for cervical carcinoma screening. We collected 171 specimens. including speciments from normal cervix, benign lesions, cervical intraepithelial neoplasia (CIN)1, CIN2 and CIN3, or carcinoma in situ, as well as invasive cervical squamous cell carcinoma. Fluorescence in situ hybridization (FISH) was performed to detect alterations in hTERC and c-MYC expression. We analyzed the area under the receiver operating characteristic (ROC) curve (AUC), as well as the sensitivity and specificity of single screening and conjoined screening. There was a trend toward an increasing amplification of 2 genes with the increasing severity of cervical lesions. ROC curve analysis demonstrated that the AUC values of the hTERC gene for the screening of different cervical lesions were >0.8. Compared with the hTERC gene, the AUC of the c-MYC gene for the screening of ≥CIN3 was >0.8 and the AUC for the screening of other cervical lesions was >0.7. For the screening of cervical lesions above the grade of benign lesions, cytological diagnosis was superior to the gene detection with significant differences. For the screening of cervical lesions >CIN1, there were no statistically significant differences (P>0.05) between the hTERC gene and cytological diagnosis, whereas the screening results of c-MYC detection and cytological diagnosis differed significantly (P<0.05). For the screening of cervical lesions >CIN2 or >CIN3, the detection of hTERC and c-MYC genes and cytological diagnosis had similar screening results with no statistically significant differences (P>0.05). In conclusion, using FISH to detect the amplification of hTERC or/and c-MYC on cervical epithelial exfoliated cells may be a useful and specific screening method for precancerous lesions.

Earley A, Lamont JL, Dahabreh IJ, et al.
Fluorescence in situ hybridization testing for the diagnosis of high-grade cervical abnormalities: a systematic review.
J Low Genit Tract Dis. 2014; 18(3):218-27 [PubMed] Related Publications
OBJECTIVE: We examined the diagnostic performance of fluorescence in situ hybridization (FISH) tests on cervical cytology for precancerous lesions or cancer on cervical histology.
MATERIALS AND METHODS: A search was conducted in MEDLINE, the Cochrane Central Register of Controlled Trials, and Scopus through September 3, 2013. Eleven studies examined FISH tests for telomerase RNA component gene (TERC), myelocytomatosis oncogene (MYC), or human papillomavirus (HPV) type 16 or 18 in samples exhibiting atypical squamous cells of unknown significance (ASC-US) or low-grade squamous intraepithelial lesions (LSIL). None examined HPV-positive, cytologically normal samples. We extracted data on the sensitivity and specificity for high-grade cervical intraepithelial neoplasia (CIN 2+ or CIN 3+).
RESULTS: Fluorescence in situ hybridization test probes and thresholds varied across studies. Included populations were convenience samples. Only 1 study testing for TERC specified HPV status. In meta-analysis, FISH for TERC in LSIL (9 studies, 1,082 cases) had a summary sensitivity of 0.76 (95% confidence interval = 0.63-0.85) and a summary specificity of 0.78 (95% confidence interval = 0.57-0.91) for CIN 2+. Fluorescence in situ hybridization for TERC in ASC-US (3 studies, 839 cases) showed sensitivities ranging from 0.75 to 1.00 and specificities from 0.87 to 0.93 for CIN 2+. For CIN 3+, sensitivity and specificity appeared similar, although a small number of studies preclude firm conclusions. For FISH tests for HPV, we found only few studies with small sample sizes.
CONCLUSIONS: The evidence on FISH testing is limited given the small number of studies for each cytology subgroup and the lack of studies in well-defined screening contexts stratifying participants by HPV status.

Zhou J, Ding D, Wang M, Cong YS
Telomerase reverse transcriptase in the regulation of gene expression.
BMB Rep. 2014; 47(1):8-14 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Telomerase plays a pivotal role in the pathology of aging and cancer by maintaining genome integrity, controlling cell proliferation, and regulating tissue homeostasis. Telomerase is essentially composed of an RNA component, Telomerase RNA or TERC, which serves as a template for telomeric DNA synthesis, and a catalytic subunit, telomerase reverse transcriptase (TERT). The canonical function of TERT is the synthesis of telomeric DNA repeats, and the maintenance of telomere length. However, accumulating evidence indicates that TERT may also have some fundamental functions that are independent of its enzymatic activity. Among these telomere-independent activities of hTERT, the role of hTERT in gene transcription has been investigated in detail. Transcriptional regulation is a fundamental process in biological systems. Several studies have shown a direct involvement of hTERT in gene transcription. This mini-review will focus on the role of hTERT in gene transcription regulation, and discuss its possible mechanisms.

Li JL, Mazar J, Zhong C, et al.
Genome-wide methylated CpG island profiles of melanoma cells reveal a melanoma coregulation network.
Sci Rep. 2013; 3:2962 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Metastatic melanoma is a malignant cancer with generally poor prognosis, with no targeted chemotherapy. To identify epigenetic changes related to melanoma, we have determined genome-wide methylated CpG island distributions by next-generation sequencing. Melanoma chromosomes tend to be differentially methylated over short CpG island tracts. CpG islands in the upstream regulatory regions of many coding and noncoding RNA genes, including, for example, TERC, which encodes the telomerase RNA, exhibit extensive hypermethylation, whereas several repeated elements, such as LINE 2, and several LTR elements, are hypomethylated in advanced stage melanoma cell lines. By using CpG island demethylation profiles, and by integrating these data with RNA-seq data obtained from melanoma cells, we have identified a co-expression network of differentially methylated genes with significance for cancer related functions. Focused assays of melanoma patient tissue samples for CpG island methylation near the noncoding RNA gene SNORD-10 demonstrated high specificity.

Antoniou KM, Samara KD, Lasithiotaki I, et al.
Differential telomerase expression in idiopathic pulmonary fibrosis and non-small cell lung cancer.
Oncol Rep. 2013; 30(6):2617-24 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Telomerase is a reverse transcriptase ribonucleo-protein (h-TERT) that synthesizes telomeric repeats using its RNA component (h-TERC) as a template. Telomerase dysfunction has been associated with both fibrogenesis and carcinogenesis. In this study, we aimed to evaluate the telomerase mRNA expression levels of both subunits (h-TERT and h-TERC) in lung tissue and bronchoalveolar lavage fluid (BALF) from patients with idiopathic pulmonary fibrosis (IPF) and non-small cell lung cancer (NSCLC), since there are indications of common pathogenetic pathways in these diseases. We prospectively examined lung tissue samples from 29 patients with IPF, 10 patients with NSCLC and 21 controls. Furthermore, we examined BALF samples from 31 patients with NSCLC, 23 patients with IPF and 12 control subjects. The mRNA expression for both h-TERT and h-TERC was measured by real-time RT-PCR. In the lung tissue samples, both h-TERT and h-TERC mRNA expression levels varied among the 3 groups (p=0.036 and p=0.002, respectively). h-TERT mRNA levels in the patients with IPF were lower compared with those in the controls (p=0.009) and patients with NSCLC (p=0.004). h-TERC mRNA levels in the patients with IPF were lower compared with those in the controls (p=0.0005) and patients with NSCLC (p=0.0004). In the BALF samples, h-TERT mRNA expression levels varied among the groups (p=0.012). More specifically, h-TERT mRNA levels in the patients with IPF were higher compared with those in the controls (p=0.03) and patients with NSCLC (p=0.007). The attenuation of telomerase gene expression in IPF in comparison to lung cancer suggests a differential role of this regulatory gene in fibrogenesis and carcinogenesis. Further functional studies are required in order to further elucidate the role of telomerase in these devastating diseases.

El Idrissi M, Hervieu V, Merle P, et al.
Cause-specific telomere factors deregulation in hepatocellular carcinoma.
J Exp Clin Cancer Res. 2013; 32:64 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
BACKGROUND: Among the numerous genetic defects associated with hepatocarcinogenesis, telomere abnormalities appear to play a role both in tumor promotion and maintenance. Telomeres, the chromosome extremities, are protected by specific proteins, the shelterin complex and by additional factors. Besides telomerase dysregulation, expression changes of these telomere factors have been observed in cancers.
METHODS: Here, we tested the hypothesis that such dysregulation might occur in hepatocellular carcinoma (HCC) with specific patterns depending on the cause of HCC. We compared telomere length, telomerase activity (TA), hTERT and telomere genes expression using PCR and Western-blot analyses between non-cirrhotic liver, peritumoral cirrhotic tissue (40 samples) and cancerous tissue (40 samples) derived from 40 patients with HBV-, HCV-, or alcohol-related HCC.
RESULTS: Alterations in TA, hTERT expression and telomere length between non-cirrhotic, cirrhotic, and tumor samples were not significantly influenced by the cause of HCC. In contrast, the expression pattern of hTR, shelterin, and non-shelterin telomere protective factors clearly distinguished the 3 causes of cirrhosis and HCC. For patients with HBV diseased liver, when compared with non-cirrhotic liver, the cirrhotic tissue underexpressed all shelterin and all but HMRE11A and RAD50 non-shelterin telomere factors. For HCV the expression level of POT1, RAP1, Ku80, and RAD50 was higher in cirrhotic than in non-cirrhotic liver samples without evidence for significant transcriptional change for the remaining genes. For alcohol-related liver diseases, the expression level of POT1, RAP1, TIN2, hMRE11A, hMRE11B, Ku70, Ku80, RAD50, TANK1, and PINX1 was higher in cirrhotic than in non-cirrhotic liver samples. For the 3 causes of HCC, there was no significant change in shelterin and non-shelterin gene expression between cirrhosis and HCC samples.
CONCLUSIONS: These results validate our hypotheses and demonstrate that cirrhosis and HCC add-up numerous telomere dysfunctions including numerous cause-specific changes that appear to occur early during the course of the disease.

Wu XQ, Huang C, He X, et al.
Feedback regulation of telomerase reverse transcriptase: new insight into the evolving field of telomerase in cancer.
Cell Signal. 2013; 25(12):2462-8 [PubMed] Related Publications
Telomerase reverse transcriptase (TERT) is the catalytic component of telomerase, especially the rate-limiting determinant of telomerase activity. So far, TERT has been reported to be over-expressed in more than 90% of cancers, thereby playing a critical role in sustained proliferation and survival potentials of various cancer cells. Over the past decade, a comprehensive network of transcription factors has been shown to be involved in the regulation of TERT. Furthermore, accumulating evidence has suggested that TERT could modulate the expression of numerous genes involved in diverse group of cellular processes, including cell cycle regulation and cellular signaling. Therefore, it indicates that TERT is both an effector and a regulator in carcinoma. However, the mechanisms of the interaction between TERT and its target genes are still not fully understood. Thus, it is necessary to consolidate and summarize recent developments of the cross-talk between TERT and related genes in cancer cells or other cells with cancer cell characteristics, and elucidate these relevant mechanisms. In this review, we focus on various signaling pathways and genes that participate in the feedback regulation of TERT and the underlying feedback loop mechanism of TERT, further providing new insights into non-telomeric functions of telomerase and potentially to be used as a novel therapeutic target for cancer.

Theelen W, Litjens RJ, Vinokurova S, et al.
Human papillomavirus multiplex ligation-dependent probe amplification assay for the assessment of viral load, integration, and gain of telomerase-related genes in cervical malignancies.
Hum Pathol. 2013; 44(11):2410-8 [PubMed] Related Publications
We evaluated the reliability of a novel multiplex ligation-dependent probe amplification (MLPA) assay in detecting integration of human papillomavirus (HPV) based on the viral E2/E6 copy number ratio in formalin-fixed and paraffin-embedded cervical lesions. The MLPA results were compared with those of amplification of papillomavirus oncogene transcripts for RNA, detection of integrated papillomavirus sequences for DNA, and HPV fluorescence in situ hybridization (FISH). DNA was isolated from 41 formalin-fixed and paraffin-embedded HPV-positive cervical lesions (cervical intraepithelial neoplasia grade 3 lesions, squamous cell carcinomas, and adenocarcinomas) for MLPA analysis. From 13 matching frozen samples, DNA and RNA were isolated for the detection of integrated papillomavirus sequences and/or the amplification of papillomavirus oncogene transcripts, respectively. Integrated HPV16, HPV18, or both were identified. The MLPA assay detected viral integration in 12 of these 13 cases, and episomal copies also were detected in 7 cases. In 20 of the 24 cases with exclusive viral integration or episomal viral copies as detected by FISH, MLPA confirmed the physical status of the virus. In the cases classified as mixed by FISH, the presence of excess episomal copies complicated the recognition of viral integration by MLPA. Furthermore, the feasibility of detecting gain of the telomerase genes with the HPV MLPA assay was evaluated. The MLPA confirmed the FISH data in 12 of 13 cases in which the status of copy number gain for telomerase RNA component was known. In conclusion, the HPV MLPA assay can be performed on routinely processed cervical lesions for the detection of viral load and HPV integration.

Bollmann FM
Physiological and pathological significance of human telomerase reverse transcriptase splice variants.
Biochimie. 2013; 95(11):1965-70 [PubMed] Related Publications
Human telomerase reverse transcriptase (hTERT) is tightly regulated at various transcriptional and post-transcriptional levels. Alternative splicing of hTERT has been shown in many human tissues and cell lines regardless of telomerase status and may play a role in regulation of telomerase activity and other cellular functions. Catalytically inactive splice variants make up a substantial proportion of total hTERT mRNA and are at least partly translated into protein. Shifts in splicing patterns occur in development, tumorigenesis and in response to exogenous stimuli in a tissue- and cell type-specific manner. This review focuses on prevalence, patterns and regulation of hTERT alternative splicing, describes associations with telomerase activity and telomere length, and discusses the potential significance of hTERT alternative splice variants in cancer as well as possible telomere-independent functions.

Nair V
Latency and tumorigenesis in Marek's disease.
Avian Dis. 2013; 57(2 Suppl):360-5 [PubMed] Related Publications
Despite the remarkable progress in our understanding of Marek's disease (MD) and the causative Marek's disease virus (MDV) biology, a number of major features of this complex viral disease remain unknown. Significant information on critical aspects of virus latency in lymphoid cells, and the virus-host interaction in MDV-induced lymphoma, remains to be identified. Moreover, the nature of the unique milieu of the feather follicle epithelial cell that allows cytolytic infection to continue, despite maintaining the latent infection in the lymphoid cells, is not fully understood. Although there has been significant progress in our understanding of the functions of a number of viral genes in the pathogenesis of the disease, the characteristics of the latent infection, how it differs from tumor phase, and whether latency is a prerequisite for the tumor phase are all important questions still to be answered. Reticuloendotheliosis virus-transformed cell lines have been shown to support MDV latency in a manner almost identical to that seen in MDV-transformed cell lines. There are increasing data on the role of epigenetic regulation, including DNA methylation and histone modifications, in maintaining viral latency. Onset of MD tumor is relatively rapid, and recent studies based on chromosomal integration and T-cell repertoire analysis demonstrated the clonal nature of MD lymphomas. Among the viral determinants of oncogenicity, the basic leucine zipper protein Meq is considered to be the most important and the most extensively studied. Deleting the Meq proteins or abolishing some of the important interactions does affect the oncogenicity of the virus. In addition, the noncoding sequences in the viral genome, such as the viral telomerase RNA and the virus-encoded microRNAs, also have significant influence on MDV-encoded oncogenesis.

López-Romero R, Iglesias-Chiesa C, Alatorre B, et al.
HPV frequency in penile carcinoma of Mexican patients: important contribution of HPV16 European variant.
Int J Clin Exp Pathol. 2013; 6(7):1409-15 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
The role of human papillomavirus (HPV) infection in penile carcinoma (PeC) is currently reported and about half of the PeC is associated with HPV16 and 18. We used a PCR-based strategy by using HPV general primers to analyze 86 penile carcinomas paraffin-embedded tissues. Some clinical data, the histological subtype, growth pattern, and differentiation degree were also collected. The amplified fragments were then sequenced to confirm the HPV type and for HPV16/18 variants. DNA samples were also subjected to relative real time PCR for hTERC gene copy number. Some clinical data were also collected. Global HPV frequency was 77.9%. Relative contributions was for HPV16 (85%), 31 (4.4%), 11 (4.4%), 58, 33, 18, and 59 (1.4% each one). Sequence analysis of HPV16 identified European variants and Asian-American (AAb-c) variants in 92% and in 8% of the samples, respectively. Furthermore hTERC gene amplification was observed in only 17% of the cases. Our results suggest that some members of HPV A9 group (represented by HPV16, 58, and 31) are the most frequent among PeC patients studied with an important contribution from HPV16 European variant. The hTERC gene amplification could be poorly related to penile epithelial tissue.

Rubis B, Holysz H, Gladych M, et al.
Telomerase downregulation induces proapoptotic genes expression and initializes breast cancer cells apoptosis followed by DNA fragmentation in a cell type dependent manner.
Mol Biol Rep. 2013; 40(8):4995-5004 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
The aim of the study was to analyze the consequence of silencing genes coding for the key subunits of the telomerase complex, i.e. TERT, TERC and TP1 in human breast cancer MCF7 and MDA-MB-231cells. The transfection was performed using Lipofectamine2000 and pooled siRNAs. The cytotoxic and/or antiproliferative effect of siRNA was measured by the SRB assay, the cell cycle was analysed by flow cytometry and DNA fragmentation by TUNEL analysis. Telomerase activity was assessed by TRAP, followed by PAGE and ELISA assays. Telomerase downregulation was also assessed using qPCR in order to estimate the changes in the expression profile of genes engaged in apoptosis. It was revealed that treatment of breast cancer cells with different siRNAs (100 nM) resulted in a cell type and time-dependent effects. The downregulation of telomerase subunits was followed by reduction of telomerase activity down to almost 60% compared to control cells. However, a significant effect was only observed when the TERT subunit was downregulated. Its silencing resulted in a significant (p<0.05) increase of apoptosis (over 10% in MCF7 and about 5% in MDA-MB-231 cells, corresponding to the Annexin V assay) and DNA fragmentation (almost 30% in MCF7 and over 25% in MDA-MB-231 cells). Interestingly, also several proapoptotic genes were induced after the downregulation of the key telomerase subunit, including Bax, Bik or caspase-1 and caspase-14, as well as NGFR and TNFSF10 which were upregulated twice and more.

Zheng X, Liang P, Zheng Y, et al.
Clinical significance of hTERC gene detection in exfoliated cervical epithelial cells for cervical lesions.
Int J Gynecol Cancer. 2013; 23(5):785-90 [PubMed] Related Publications
OBJECTIVE: To investigate the clinical significance of abnormal human telomerase RNA gene component (hTERC) gene amplification tested by fluorescence in situ hybridization in cervical lesions.
METHODS: In 373 patients with cytologic abnormalities, high-risk human papilomavirus (HR-HPV) was detected by the hybrid capture II method, and abnormal amplification of the hTERC gene in exfoliated cells was detected by fluorescence in situ hybridization.
RESULTS: Cell smear findings suggested atypical squamous cells in 148 patients, low-grade squamous intraepithelial lesion in 62 patients, and high-grade squamous intraepithelial lesion in 107 patients, squamous cell carcinoma in 56 patients, and cervical biopsy-revealed inflammation in 89 patients, cervical intraepithelial neoplasia (CIN) I in 36 patients, CIN II in 43 patients, CIN III in 129 patients, and infiltrating carcinoma in 76 patients. In the inflammation, CIN I, CIN II, CIN III, and infiltrating carcinoma groups, the infection rates of HR-HPV were 29.21%, 52.78%, 74.42%, 92.25%, and 93.42% (P < 0.01), respectively; the positive rates of hTERC gene amplification were 0.00%, 13.89%, 41.86%, 78.29%, and 89.47% (P < 0.01), respectively. With respect to advanced cervical lesions (≥CIN II), cytology (≥ low-grade squamous intraepithelial lesion), HR-HPV testing, and hTERC testing differed insignificantly in the negative predictive value (P > 0.05), but they differed significantly in the sensitivity, specificity, and positive predictive value (P < 0.01). Among the 3 methods, hTERC testing showed the highest specificity and positive predictive value, and HR-HPV testing showed the highest sensitivity. In 41 patients with untreated CIN I and CIN II, the sensitivity of detection of hTERC gene amplification to predict lesion progression was 88.89%, and the specificity was 93.75%.
CONCLUSION: Detection of abnormal amplification of the hTERC gene can assist in screening cervical lesions and identifying CIN I/II patients with a high progression risk.

Wang YF, Wang XS, Gao SG, et al.
Clinical significance of combined detection of human papilloma virus infection and human telomerase RNA component gene amplification in patients with squamous cell carcinoma of the esophagus in northern China.
Eur J Med Res. 2013; 18:11 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
BACKGROUND: The aim of the study was to test for human papilloma virus (HPV) infection and human telomerase RNA component (hTERC) gene amplification in tissues derived from esophageal cancer, in esophagus displaying atypical hyperplasia and in normal tissue, and to analyze the relationship between them and discuss whether HPV infection and hTERC gene amplification play a role in the duration of survival of esophageal cancer patients.
METHODS: To test for HPV infection, surface plasma resonance was used after extracting and subjecting the DNA to PCR amplification. Measurement of hTERC gene amplification was performed by the fluorescence in situ hybridization technique.
RESULTS: The rates of HPV infection in the normal group, the atypical esophageal hyperplasia group and the cancer group were 0% (0/40), 10.00% (1/10) and 20.65% (19/92), respectively, with a statistically significant difference of P < 0.01. The hTERC gene amplification rate in normal tissue, grade I atypical hyperplastic tissue, grade II/III atypical hyperplastic tissue and esophageal cancer tissue were 0% (0/89), 15.38% (4/26), 47.06% (8/17) and 89.13% (82/92), respectively, with a statistically significant difference of P < 0.01. On follow-up of 92 patients, survival curves of the HPV-positive and HPV-negative groups were not significantly different (P > 0.05). Survival curves of the hTERC gene amplification-positive and hTERC gene amplification-negative groups were statistically significant (P < 0.05). A matching chi-square test showed that there was no correlation between HPV infection and hTERC gene amplification (P > 0.05).
CONCLUSION: HPV infection may be one of many factors contributing to the development of esophageal cancer, but it does not influence prognosis. Amplification of the hTERC gene appears to influence certain features associated with postoperative survival in esophageal carcinoma patients.

Pellatt AJ, Wolff RK, Torres-Mejia G, et al.
Telomere length, telomere-related genes, and breast cancer risk: the breast cancer health disparities study.
Genes Chromosomes Cancer. 2013; 52(7):595-609 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Telomeres are involved in maintaining genomic stability. Previous studies have linked both telomere length (TL) and telomere-related genes with cancer. We evaluated associations between telomere-related genes, TL, and breast cancer risk in an admixed population of US non-Hispanic white (1,481 cases, 1,586 controls) and U.S. Hispanic and Mexican women (2,111 cases, 2,597 controls) from the Breast Cancer Health Disparities Study. TL was assessed in 1,500 women based on their genetic ancestry. TL-related genes assessed were MEN1, MRE11A, RECQL5, TEP1, TERC, TERF2, TERT, TNKS, and TNKS2. Longer TL was associated with increased breast cancer risk [odds ratio (OR) 1.87, 95% confidence interval (CI) 1.38, 2.55], with the highest risk (OR 3.11, 95% CI 1.74, 5.67 p interaction 0.02) among women with high Indigenous American ancestry. Several TL-related single nucleotide polymorphisms had modest association with breast cancer risk overall, including TEP1 rs93886 (OR 0.82, 95% CI 0.70,0.95); TERF2 rs3785074 (OR 1.13, 95% CI 1.03,1.24); TERT rs4246742 (OR 0.85, 95% CI 0.77,0.93); TERT rs10069690 (OR 1.13, 95% CI 1.03,1.24); TERT rs2242652 (OR 1.51, 95% CI 1.11,2.04); and TNKS rs6990300 (OR 0.89, 95% CI 0.81,0.97). Several differences in association were detected by hormone receptor status of tumors. Most notable were associations with TERT rs2736118 (ORadj 6.18, 95% CI 2.90, 13.19) with estrogen receptor negative/progesterone receptor positive (ER-/PR+) tumors and TERT rs2735940 (ORadj 0.73, 95% CI 0.59, 0.91) with ER-/PR- tumors. These data provide support for an association between TL and TL-related genes and risk of breast cancer. The association may be modified by hormone receptor status and genetic ancestry.

Sun XC, Yan JY, Chen XL, et al.
Depletion of telomerase RNA inhibits growth of gastrointestinal tumors transplanted in mice.
World J Gastroenterol. 2013; 19(15):2340-7 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
AIM: To explore effects of telomerase RNA-targeting phosphorothioate antisense oligodeoxynucleotides (PS-ASODN) on growth of human gastrointestinal stromal tumors transplanted in mice.
METHODS: A SCID mouse model for transplantation of human gastrointestinal stromal tumors (GISTs) was established using tumor cells from a patient who was diagnosed with GIST and consequently had been treated with imatinib. GIST cells cultured for 10 passages were used for inoculation into mice. Transfection of PS-ASODN was carried out with Lipotap Liposomal Transfection Reagent. GISTs that subsequently developed in SCID mice were subjected to intra-tumoral injection once daily from day 7 to day 28 post-inoculation, and mice were divided into the following four groups according to treatment: PS-ASODN group (5.00 μmoL/L of oligonucleotide, each mouse received 0.2 mL once daily); imatinib group (0.1 mg/g body weight); liposome negative control group (0.01 mL/g); and saline group (0.01 mL/g). On day 28, the mice were sacrificed, and tumor attributes including weight and longest and shortest diameters were measured. Tumor growth was compared between treatment groups, and telomerase activity was measured by enzyme-linked immunosorbent assay. Apoptosis was examined by flow cytometry. Real-time polymerase chain reaction was used to detect expression of the mRNA encoding the apoptosis inhibition B-cell leukemia/lymphoma 2 (bcl-2) gene.
RESULTS: In the PS-ASODN group, tumor growth was inhibited by 59.437%, which was markedly higher than in the imatinib group (11.071%) and liposome negative control group (2.759%) [tumor inhibition = (mean tumor weight of control group--mean tumor weight of treatment group)/(mean tumor weight of control group) × 100%]. Telomerase activity was significantly lower (P < 0.01) in the PS-ASODN group (0.689 ± 0.158) compared with the imatinib group (1.838 ± 0.241), liposome negative control group (2.013 ± 0.273), and saline group (2.004 ± 0.163). Flow cytometry revealed that the apoptosis rate of tumor cells treated with PS-ASODN was 20.751% ± 0.789%, which was higher (P < 0.01) than that of the imatinib group (1.163% ± 0.469%), liposome negative control group (1.212% ± 0.310%), and saline group (1.172% ± 0.403%). Expression of bcl-2 mRNA in the transplanted GISTs was markedly downregulated (P < 0.01) in the PS-ASODN group (7.245 ± 0.739) compared with the imatinib group (14.153 ± 1.618) and liposome negative control group (16.396 ± 1.351).
CONCLUSION: PS-ASODN can repress GIST growth, mediated perhaps by inhibition of telomerase activity and downregulation of bcl-2 expression.

Listerman I, Sun J, Gazzaniga FS, et al.
The major reverse transcriptase-incompetent splice variant of the human telomerase protein inhibits telomerase activity but protects from apoptosis.
Cancer Res. 2013; 73(9):2817-28 [PubMed] Article available free on PMC after 30/10/2015 Related Publications
Human telomerase reverse transcriptase (hTERT; the catalytic protein subunit of telomerase) is subjected to numerous alternative splicing events, but the regulation and function of these splice variants is obscure. Full-length hTERT includes conserved domains that encode reverse transcriptase activity, RNA binding, and other functions. The major splice variant termed α+β- or β-deletion is highly expressed in stem and cancer cells, where it codes for a truncated protein lacking most of the reverse transcriptase domain but retaining the known RNA-binding motifs. In a breast cancer cell panel, we found that β-deletion was the hTERT transcript that was most highly expressed. Splicing of this transcript was controlled by the splice regulators SRSF11, HNRNPH2, and HNRNPL, and the β-deletion transcript variant was associated with polyribosomes in cells. When ectopically overexpressed, β-deletion protein competed for binding to telomerase RNA (hTR/TERC), thereby inhibiting endogenous telomerase activity. Overexpressed β-deletion protein localized to the nucleus and mitochondria and protected breast cancer cells from cisplatin-induced apoptosis. Our results reveal that a major hTERT splice variant can confer a growth advantage to cancer cells independent of telomere maintenance, suggesting that hTERT makes multiple contributions to cancer pathophysiology.

Chiodi I, Belgiovine C, Zongaro S, et al.
Super-telomeres in transformed human fibroblasts.
Biochim Biophys Acta. 2013; 1833(8):1885-93 [PubMed] Related Publications
Telomere length maintenance is critical for organisms' long-term survival and cancer cell proliferation. Telomeres are kept within species-specific length ranges by the interplay between telomerase activity and telomeric chromatin organization. In this paper, we exploited telomerase immortalized human fibroblasts (cen3tel) that gradually underwent neoplastic transformation during culture propagation to study telomere composition and length regulation during the transformation process. Just after telomerase catalytic subunit (hTERT) expression, cen3tel telomeres shortened despite the presence of telomerase activity. At a later stage and concomitantly with transformation, cells started elongating telomeres, which reached a mean length greater than 100kb in about 900 population doublings. Super-telomeres were stable and compatible with cell growth and tumorigenesis. Telomere extension was associated with increasing levels of telomerase activity that were linked to the deregulation of endogenous telomerase RNA (hTERC) and exogenous telomerase reverse transcriptase (hTERT) expression. Notably, the increase in hTERC levels paralleled the increase in telomerase activity, suggesting that this subunit plays a role in regulating enzyme activity. Telomeres ranging in length between 10 and more than 100kb were maintained in an extendible state although TRF1 and TRF2 binding increased with telomere length. Super-telomeres neither influenced subtelomeric region global methylation nor the expression of the subtelomeric gene FRG1, attesting the lack of a clear-cut relationship between telomere length, subtelomeric DNA methylation and expression in human cells. The cellular levels of the telomeric proteins hTERT, TRF1, TRF2 and Hsp90 rose with transformation and were independent of telomere length, pointing to a role of these proteins in tumorigenesis.

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