Human artificial chromosome carrying 3p21.3-p22.2 region suppresses hTERT transcription in oral cancer cells

Telomerase is a ribonucleoprotein ribonucleic enzyme that elongates telomere repeat sequences at the ends of chromosomes and contributes to cellular immortalization. The catalytic component of telomerase, human telomerase reverse transcriptase (hTERT), has been observed to be reactivated in immortalized cells. Notably, most cancer cells have been found to have active hTERT mRNA transcription, resulting in continuous cell division, which is crucial for malignant transformation. Therefore, discovering mechanisms underlying the regulation of hTERT transcription is an attractive target for cancer-specific treatments.Loss of heterozygosity (LOH) of chromosome 3p21.3 has been frequently observed in human oral squamous cell carcinoma (OSCC). Moreover, we previously reported that HSC3 OSCC microcell hybrid clones with an introduced human chromosome 3 (HSC3#3) showed inhibition of hTERT transcription compared with the parental HSC3 cells. This study examined whether hTERT transcription regulators are present in the 3p21.3 region. We constructed a human artificial chromosome (HAC) vector (3p21.3-HAC) with only the 3p21.3-p22.2 region and performed functional analysis using the 3p21.3-HAC. HSC3 microcell hybrid clones with an introduced 3p21.3-HAC exhibited significant suppression of hTERT transcription, similar to the microcell hybrid clones with an intact chromosome 3. In contrast, HSC3 clones with truncated chromosome 3 with deletion of the 3p21.3 region (3delp21.3) showed no effect on hTERT expression levels. These results provide direct evidence that hTERT suppressor gene(s) were retained in the 3p21.3 region, suggesting that the presence of regulatory factors that control telomerase enzyme activity may be involved in the development of OSCC.

Human telomerase reverse transcriptase (hTERT) synergistic with Sp1 upregulate Gli1 expression and increase gastric cancer invasion and metastasis

Abnormal expression of human telomerase reverse transcriptase (hTERT) has been widely identified in tumors, but the relevant mechanism is not well known. This study aims to investigate the role and mechanism of hTERT in gastric cancer metastasis. Gastric cancer and adjacent non-tumor tissues were collected and the expression levels of hTERT and Gli1 were detected by immunohistochemistry. The results demonstrated that hTERT and Gli1 expression levels in gastric cancer tissue were significantly higher than adjacent non-tumor tissues. Western blot and quantitative real-time PCR were used to an identified expression of the related protein in BGC-823 and SGC-7901 cells. The interactions between hTERT and Sp1 were tested by co-immunoprecipitation experiments. Chromatin immunoprecipitation was performed to confirm that Sp1 and hTERT could bind to the Gli1 promoter. Chromatin reimmunoprecipitation assay further demonstrated that both hTERT and Sp1 bind to the Sp1 site of the Gli1 promoter. Moreover, the hTERT, Sp1, and Gli1 were upregulate was verified in human gastric cancer tissues. These results showed that the expression levels of hTERT in GC tissues were strongly closed to the depth of invasion, lymph node metastasis, TNM (tumor, node, metastasis) stage, and distant metastasis. By combining Sp1 and Gli1 promoter, hTERT upregulated Gli1 expression and promoted invasion and metastasis of GC cells. Overall, these data provide a new molecular mechanism of hTERT to promotes gastric cancer progression. Targeting the hTERT/Sp1/Gli1 axis may represent a new therapeutic strategy.

Promoter CpG methylation inhibits Krüppel-like factor 2 (KLF2)-Mediated repression of hTERT gene expression in human T-cells

Constitutive expression of human telomerase reverse transcriptase (hTERT) with DNA methylation of its promoter is a common phenomenon in tumor cells. We recently found that the transcriptional factor Krüppel-like factor 2 (KLF2) binds to the CpG sequences in the hTERT promoter and inhibits hTERT gene expression in normal resting T-cells. The human T-cell line Kit 225 in the resting phase induced by the deprivation of interleukin (IL)-2 showed no decrease in the expression of hTERT, despite the high expression of KLF2. To elucidate the mechanisms of deregulation of hTERT expression in T-cells, we examined the relationship between DNA methylation and KLF2 binding to the hTERT promoter. The hTERT promoter was methylated in Kit 225 cells, resulting in the inhibition of the binding of KLF2 to the promoter. DNA demethylation by the reagent Zebularine recovered KLF2 binding to the hTERT promoter, followed by the downregulation of its gene expression. These findings indicate that the repressive effect of KLF2 on hTERT gene expression is abolished by DNA methylation in T-cell lines.

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Unlike normal T-cells, the hTERT promoter is highly methylated in a leukemic T-cell line.

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DNA methylation of the promoter induces hTERT gene expression.

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Association between the promoter and the repressor KLF2 is inhibited by DNA methylation.

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Demethylation promotes binding of KLF2 and silencing of hTERT expression.

TERRA Gene Expression in Gastric Cancer: Role of hTERT

PURPOSE

One of the most important serious malignancies is gastric cancer (GC) with a high mortality globally. In this way, beside the environmental factors, genetic parameter has a remarkable effective fluctuation in GC. Correspondingly, telomeres are nucleoprotein structures measuring the length of telomeres and they have special potential in diagnosis of various types of cancers. Defect protection of the telomeric length initiates the instability of the genome during cancer, including gastric cancer. The most common way of maintaining telomere length is the function of the telomerase enzyme that replicates the TTAGGG to the end of the 3' chromosome.

METHODS

In this review, we want to discuss the alterations of hTERT repression on the modification of TERRA gene expression in conjunction with the importance of telomere and telomerase in GC.

RESULTS

The telomerase enzyme contains two essential components called telomerase reverse transcriptase (hTERT) and RNA telomerase (hTR, hTERC). Deregulation of hTERT plays a key role in the multistage process of tumorigenicity and anticancer drug resistance. The direct relationship between telomerase activity and hTERT has led to hTERT to be considered a key target for cancer treatment. Recent results show that telomeres are transcribed into telomeric repeat-containing RNA (TERRA) in mammalian cells and are long noncoding RNAs (lncRNAs) identified in different tissues. In addition, most chemotherapy methods have a lot of side effects on normal cells.

CONCLUSION

Telomere and telomerase are useful therapeutic goal. According to the main roles of hTERT in tumorigenesis, growth, migration, and cancer invasion, hTERT and regulatory mechanisms that control the expression of hTERT are attractive therapeutic targets for cancer treatment.

Clinical value of perioperative levels of DNA and mRNA in plasma of patients with renal cell carcinoma

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Plasma levels of GAPDH cfDNA might be useful as complementary methods for diagnosis and prognosis of renal cell carcinoma.

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Pre and postoperative levels of GAPDH cfDNA were independently associated with OS in renal cell carcinoma.

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hTERT cfRNA was not a marker useful for diagnosis nor prognosis of renal cell cancer.

Introduction

The current challenge on renal cell carcinoma (RCC) is to finding a non-invasive biomarker for improving their diagnostic and therapeutic management. In the present study, we analyzed the clinical value of plasma levels of cell-free DNA (cfDNA) and RNA (cfRNA) of two genes: glyceraldehyde 3-phosphate-dehydrogenase (GAPDH) and human telomerase reverse transcriptase (hTERT).

Materials and methods

We recruited 82 patients with RCC, and 20 healthy subjects. Using RT-PCR techniques, plasma levels of cfDNA and cfRNA from hTERT and GAPDH genes were quantified pre- and post-operatively, and one year after surgery. Relationships between such plasma levels and clinicopathological features and evolution of disease were analyzed.

Results

Levels of GAPDH cfDNA and cfRNA were significantly higher in patients than in healthy subjects. hTERT cfDNA was detected in plasma from 35% of RCC patients and in none healthy subject. At diagnosis, plasma levels of GAPDH cfDNA were higher in advanced pT and TNM stages, and hTERT cfDNA in patients with 3–4 Fuhrman grade and affected lymph nodes. Levels of cfNAs were not related to the presence of metastasis. Following nephrectomy, GAPDH cfDNA levels dropped, and patients with higher levels before and after nephrectomy, showed lower overall survival (OS). However, Cox's multivariate model did not prove any association of the cfNA levels with progression.

Conclusion

Plasma levels of cfDNA from GADPH and hTERT genes were correlated to tumor diagnosis and progression and, thus, such analyses might help to diagnosis and prognosis of RCC patients.

DNA Methylation Profiling of hTERT Gene Alongside with the Telomere Performance in Gastric Adenocarcinoma

PURPOSE

Epigenetic modification including of DNA methylation, histone acetylation, histone methylation, histon phosphorylation and non-coding RNA can impress the gene expression and genomic stability and cause different types of malignancies and also main human disorder. Conspicuously, the epigenetic alteration special DNA methylation controls telomere length, telomerase activity and also function of different genes particularly hTERT expression. Telomeres are important in increasing the lifespan, health, aging, and the development and progression of some diseases like cancer.

METHODS

This review provides an assessment of the epigenetic alterations of telomeres, telomerase and repression of its catalytic subunit, hTERT and function of long non-coding RNAs such as telomeric-repeat containing RNA (TERRA) in carcinogenesis and tumorgenesis of gastric cancer.

RESULTS

hTERT expression is essential and indispensable in telomerase activation through immortality and malignancies and also plays an important role in maintaining telomere length. Telomeres and telomerase have been implicated in regulating epigenetic factors influencing certain gene expression. Correspondingly, these changes in the sub telomere and telomere regions are affected by the shortening of telomere length and increased telomerase activity and hTERT gene expression have been observed in many cancers, remarkably in gastric cancer.

CONCLUSION

Epigenetic alteration and regulation of hTERT gene expression are critical in controlling telomerase activity and its expression. Graphical Abstract.

The proliferative lifespan of adult sheep fibroblasts can be conditionally extended by tetracycline-inducible expression of human telomerase reverse transcriptase

Forced expression of human telomerase reverse transcriptase (hTERT) has been used to immortalize mammalian cells. Here, we report conditional extension of proliferative lifespan of adult sheep somatic cells by introducing tetracycline-inducible (Tet-on) expression of hTERT. After transfecting adult sheep fibroblasts with the vector for Tet-on induced conditional expression of hTERT, we obtained several hTERT-positive clones that exhibited extended-lifespan under the induction of tetracycline analogue, doxycycline. Further assays for a representative cell clone A3h38 indicated that the cells had a much stronger proliferative ability than control primary cells, as assessed by population doubling levels and single-cell cloning efficiency. A3h38 cells could maintain vigorous growth in culture for more than 150 days but they became senescent when hTERT expression was abrogated by withdrawal of doxycycline. Although having undergone long-term culture, the nuclei of A3h38 cells could support higher preimplantation development of somatic cell nuclear transfer embryos than control primary cells. These results demonstrated that conditional expression of hTERT could reversibly extend the lifespan of adult sheep fibroblasts, enhance their proliferation and maintain their ability to be reprogrammed after nuclear transfer. This strategy would also be applicable to many other somatic cell types in more species.

Correlation of human telomerase reverse transcriptase single nucleotide polymorphisms with in vitro fertilisation outcomes

PURPOSE

To explore whether it is possible to predict the number and quality of the embryo using a few particular hTERT SNPs.

METHODS

We included 997 Han Chinese women who were genetically unrelated and underwent assisted reproduction using IVF from September 2014 to December 2015. DNA was genotyped by using TaqMan real-time quantitative PCR.

RESULTS

Among the 997 patients, individuals with the CC genotype of rs2075786 had a significantly lower number of good-quality embryos than those with the TT+TC genotypes. Compared with the CT+CC genotype carriers, patients carrying the TT genotype of rs2853677 had a significantly lower number of oocytes retrieved, mature oocytes and available embryos. Among the 750 patients aged ≤ 35 years, individuals with the AA+AG genotypes of rs2853691 had a significantly higher number of good-quality embryos than those with the GG genotype. The haplotype analysis showed that the TTTG (rs2853672/rs2853669/rs2735940/rs2736108) haplotype was more likely to lead to more than three good-quality embryos in patients aged ≤ 35 years.

CONCLUSIONS

Our study suggests that the hTERT SNP is associated with IVF outcomes.

Alternative splicing of human telomerase reverse transcriptase in gliomas and its modulation mediated by CX-5461

Background

Glioma is a heterogeneous, invasive primary brain tumor with a wide range of patient survival and a lack of reliable prognostic biomarkers. Human telomerase reverse transcriptase (hTERT) has been reported in the presence of multiple transcripts in various tumor systems. The biological function and precise regulatory mechanisms of hTERT transcripts remain uncertain.

Methods

Alternative splicing of hTERT and telomerase activity were examined in 96 glioma specimens, including 38 glioblastomas (GBMs), 23 oligodendrogliomas (ODMs), and 35 oligoastrocytomas (OAMs). The correlation between telomerase activity or hTERT transcripts and patient clinical characteristics was investigated. We examined the regulation of alternative splicing of hTERT and telomerase activity by G-quadruplex stabilizer CX-5461 in GBM cells. The biological effects of CX-5461 on GBM cell lines, including inhibition of cell proliferation, effects on cell cycle/apoptosis, and telomere DNA damage were further explored.

Results

The β splicing was verified in human gliomas and hTERT+β was significantly correlated with higher telomerase activity, higher KPS, larger tumor size, and higher tumor grades. Meanwhile, glioma patients lacking hTERT+β expression or telomerase activity showed a significant survival benefit. Notably, CX-5461 altered hTERT splicing patterns, leading to an increase of hTERT-β transcript and a decrease of hTERT+β transcript expression, which inhibits telomerase activity. In addition, CX-5461 had cytotoxic effects on GBM cells and caused telomere DNA damage response, induced G2/M arrest and apoptosis.

Conclusions

The hTERT+β is verified to be correlated with clinical parameters in gliomas, and could serve as a prognostic marker or possibly therapeutic target for gliomas. CX-5461 can regulate the splicing pattern of hTERT, inhibit telomerase activity, and kill GBM cells.

Quantitative Evaluation of Exon Skipping in Immortalized Muscle Cells In Vitro

Exon skipping through the use of antisense oligonucleotides (AOs) is currently one of the most promising approaches for treating Duchenne muscular dystrophy (DMD). While we now have a number of AO drug candidates in clinical trials, we are still faced with issues of poor or controversial efficacy in some of these drugs. This is the case with eteplirsen, an exon 51-skipping AO that is the first and only FDA-approved drug for DMD to date. Effective procedures must, therefore, be set up for the in vitro screening of potential AOs for DMD treatment. Here, we describe one such procedure using immortalized DMD patient-derived muscle cells. Aside from allowing for the quantitative evaluation of candidate AOs based on their exon skipping efficiency and dystrophin protein rescue levels, these immortalized cells are stable, pure, easy to grow, and not subject to confounding by senescence-related issues. This procedure enables a more reliable screening of AOs prior to their entry in clinical trials and greatly facilitates the search for more efficacious candidate exon skipping AOs for DMD treatment.

hTERT gene polymorphism correlates with the risk and the prognosis of thyroid cancer

OBJECTIVES

The study explored the association between rs10069690C/T and rs2736100G/T of human telomerase reverse transcriptase (hTERT) gene, and the prognosis of thyroid cancer.

METHODS

The study had 452 thyroid cancer patients recruited as case group who hospitalized in Jingzhou Central Hospital from January 2001 to June 2004 and 452 healthy people recruited as control group at the same area. The hTERT gene polymorphisms at rs10069690 C/T and rs2736100 G/T were tested by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The association between patients' life quality and hTERT gene polymorphisms six months after surgery was evaluated based on the Cancer patients' quality of life index rating scale.

RESULTS

There were statistical differences in genotype and allele frequencies of rs10069690 C/T between the case group and control group (both P < 0.05). An association between rs10069690C/T polymorphism and an increased risk of thyroid cancer was shown by logistic regression analysis (CT vs. CC, OR = 1.333, 95%CI = 1.006-1.766, P = 0.045; TT vs. CC, OR = 1.910, 95%CI = 1.084-3.367, P = 0.023; CT + TT vs. CC, OR = 2.246, 95%CI = 1.078-1.840, P = 0.006; T vs. C, OR = 1.376, 95%CI = 1.104-1.715, P = 0.004). Genotype frequency of rs2736100G/T between the two groups had no statistical differences (P > 0.05). After stratification according to age, T stage, tumor size and tumor node metastasis (TNM) stage, the distribution frequencies of CC genotype and CT + TT genotype of rs10069690C/T showed significant difference (P < 0.05). The life quality of patients with CC genotype was better than that of patients with CT $+$ TT genotype. The results of Cox regression model multifactor analysis showed that age, T stage, tumor size and rs10069690C/T were independent risk factors of thyroid cancer prognosis.

CONCLUSIONS

hTERT gene polymorphism at rs10069690C/T is associated with the risk and prognosis of thyroid cancer, but hTERT gene polymorphism at rs2736100G/T is not.

Human telomerase reverse transcriptase (hTERT) promotes cancer invasion by modulating cathepsin D via early growth response (EGR)-1

Human telomerase reverse transcriptase (hTERT) contributes to tumor progression as well as maintaining telomere length, however, the mechanism by which hTERT promotes invasiveness is not yet completely understood. This study aims to unravel the precise mechanism through which hTERT promotes cancer invasion. We established an hTERT-overexpressed immortalized cell line (IHOK/hTERT). In orthotopic xenograft models, IHOK/hTERT harbors higher tumorigenicity than IHOK/Control. IHOK/hTERT showed much higher migration and invasion activities compared to IHOK/Control. IHOK/hTERT co-cultured with fibroblasts displayed increased invasion compared to IHOK/hTERT without fibroblasts. We screened for genes that play an important role in intermodulation between cancer cells and fibroblasts using a microarray and identified fibroblast activation protein (FAP). hTERT knockdown showed decreased expression of FAP and early growth response (EGR)-1, one of the transcriptional regulators of FAP in IHOK/hTERT and oral cancer cell line YD10B. Furthermore, EGR-1 knockdown in IHOK/hTERT and YD10B showed reduced invasion and reduced cathepsin D expression compared to Control-siRNA cells. Taken together, this study provides evidence that hTERT overexpression is responsible for the upregulation of the cysteine protease cathepsin D by regulating EGR-1 to activate invasiveness in cancer progression.

Involvement of transcription repressor Snail in the regulation of human telomerase reverse transcriptase (hTERT) by transforming growth factor-β

Human telomerase reverse transcriptase (hTERT), a catalytic subunit of telomerase, is the primary determinant for telomerase enzyme activity, which has been associated with cellular immortality. Expression of the hTERT gene is regulated by various extracellular (external) stimuli and is aberrantly up-regulated in more than 90% of cancers. Here we show that hTERT gene expression was repressed in response to transforming growth factor-β (TGF-β) by a mechanism dependent on transcription factors Snail and c-Myc. TGF-β activated Snail and down-regulated c-Myc gene expression. In addition, ectopic expression of Snail strongly inhibited hTERT promoter activity, although co-expression of c-Myc abrogated this effect. Chromatin immunoprecipitation (ChIP) analysis revealed that TGF-β decreased c-Myc occupancy and dramatically increased recruitment of Snail to the E-box motifs of the hTERT promoter, thereby repressing hTERT expression. Our findings suggest a dynamic alteration in hTERT promoter occupancy by Snail and c-Myc is the mechanistic basis for TGF-β-mediated regulation of hTERT.

Human telomerase reverse transcriptase is a promising target for cancer inhibition in squamous cell carcinomas

BACKGROUND/AIM

The present study aimed to investigate whether the down-regulation of human telomerase reverse transcriptase (hTERT) may induce an anti-invasive effect in oral squamous cell cancer cell lines.

MATERIALS AND METHODS

A genetically-engineered squamous carcinoma cell line overexpressing hTERT in immortalized oral keratinocytes transfected by human papilloma virus (HPV)-16 E6/E7 (IHOK) was used. In vivo tumorigenicity was examined using an orthotopic xenograft model of nude mice. For evaluating anti-invasive activity by knockdown of hTERT expression, transwell invasion assay and real-time polymerase chain reaction (PCR) for matrix metalloproteinases (MMP) were employed.

RESULTS

The down-regulation of hTERT expression reduced the invasive activity and MMP expression. This result was re-confirmed in the HSC3 oral squamous carcinoma cell line.

CONCLUSION

Targeting hTERT may lead to novel therapeutic approaches.