Telomerase Activity In Human Cancer Research Articles

Inhibition of cell growth and down-regulation of telomerase activity by amygdalin in human cancer cell lines

The purpose of this study was to examine the effect of amygdalin on cell growth and telomerase activity in human cancer and MRC-5 fibroblast cell lines. The level of β-glucosidase activity for releasing cyanide was significantly (P < .05) higher in cancer cell lines (A-549, MDA-MB-231, MCF-7 and U87-MG) than in MRC-5 fibroblasts. Growth rate of cancer cells was apparently inhibited in concentrations above 10 mg/ml amygdalin with senescent-like abnormal morphology. Whereas the effects were absent or marginally detected in MRC-5 fibroblasts. High incidence of β-galactosidase activity was observed in amygdalin-treated cancer cells, compared with that of untreated control while no difference was observed between the control and amygdalin-treated MRC-5 fibroblasts. Furthermore, level of telomerase activity was significantly (P < .05) higher (∼8–13 fold) in cancer cell lines along with high expression of telomerase reverse transcriptase (TERT) and telomerase RNA component (TERC) than in MRC-5 fibroblasts which did not expressed TERT and TERC. However, telomerase activity was significantly (P < .05) down-regulated in amygdalin-treated cancer cells with the decreased expression of TERT and TERC compared with control cancer cells. There were no difference in the telomerase activity between control and amygdalin-treated MRC-5 fibroblasts. Based on these observations, we concluded that amygdalin treatment offers a valuable option for the cancer treatment, causing inhibition of cell growth and down-regulation of telomerase activity in human cancer cell lines by increasing β-glucosidase activity.

Telomerase directly regulates NF-κB-dependent transcription

Although elongation of telomeres is thought to be the prime function of reactivated telomerase in cancers, this activity alone does not account for all of the properties that telomerase reactivation attributes to human cancer cells. Here, we uncover a link between telomerase and NF-κB, a master regulator of inflammation. We observe that while blocking NF-κB signalling can inhibit effects of telomerase overexpression on processes relevant to transformation, increasing NF-κB activity can functionally substitute for reduced telomerase activity. Telomerase directly regulates NF-κB-dependent gene expression by binding to the NF-κB p65 subunit and recruitment to a subset of NF-κB promoters such as those of IL-6 and TNF-α, cytokines that are critical for inflammation and cancer progression. As NF-κB can transcriptionally upregulate telomerase levels, our findings suggest that a feed-forward regulation between them could be the key mechanistic basis for the coexistence of chronic inflammation and sustained telomerase activity in human cancers.

HTERT mRNA Partially Regulates Telomerase Activity in Gastric Adenocarcinoma and Adjacent Normal Gastric Mucosa

The extent to which human telomerase reverse transcriptase (hTERT) mRNA and its splice variants control telomerase activity in human cancers is controversial. Telomerase and hTERT mRNA were assessed quantitatively in paired samples of gastric adenocarcinoma and adjacent normal tissue. Splice variants within the hTERT reverse transcriptase domain (alpha, beta, alphabeta) were detected by RT-PCR. In gastric adenocarcinoma, compared to normal tissue, median telomerase activity increased significantly (from 0 total product generated [tpg; 95% confidence interval CI, 0-2.3] to 16.1 tpg [95% CI, 3.7-97]; P = 0.008) and median hTERT mRNA levels also increased (from 2.21 [95% CI, 1.40-4.62] to 7.08 [95% CI, 3.26-10.8]; P = 0.0054). hTERT mRNA and telomerase activity correlated in normal gastric mucosa (r = 0.819, P = 0.0002). Alpha, beta, and alphabeta deletions were similar in both groups. We conclude that hTERT mRNA partially regulates telomerase activity in normal gastric mucosa and gastric adenocarcinoma. In contrast, hTERT mRNA splicing is not involved in the regulation of enzyme activity.

Telomerase reverse transcriptase gene amplification in hepatocellular carcinoma.

Telomerase activation is essential for the immortality of cancer cells. The expression of telomerase reverse transcriptase (hTERT), the catalytic component of the telomerase complex, regulates telomerase activity in human cancers. Amplification of the hTERT gene, located at chromosome 5p, is thought to be a potential genetic event contributing to telomerase activation in sporadic tumors. The amplification of the hTERT gene was examined in 46 surgically resected hepatocellular carcinomas (HCC) by real-time polymerase chain reaction and the status was compared with the expression of hTERT mRNA and clinicopathological parameters. Amplified hTERT genes were found in 21.7% (10/46) of HCC. The incidence of amplified hTERT genes in poorly differentiated HCC (6/12, 50%) was significantly higher than that in highly to moderately differentiated HCC (4/34, 11.8%; P = 0.012). Tumor size in those cases with hTERT gene amplification was larger compared to those cases with no amplification (P = 0.047). Amplification of the hTERT gene was not observed in non-cancerous tissues. The hTERT mRNA level did not correlate with the number of hTERT genes. Based on these results, it is thought that hTERT gene amplification is a cancer-specific event, and may furthermore contribute to the dedifferentiation and development of HCC. However, hTERT gene overexpression was rarely due to an increased hTERT gene copy number in HCC.

Prognostic significance of telomerase activity in soft tissue sarcomas.

Only few reports on the prognostic significance of telomerase activity in human cancer exist. To find a new prognostic marker in soft tissue tumors, we investigated 60 soft tissue sarcomas of different histology and six benign tumors for telomerase activity. Telomerase activity was measured by using the non-radioactive PCR-based TRAP-assay. PCR products were analyzed on an automated fluorescence sequencer. Tumors of grade-II and grade-III histology showed a significantly poorer prognosis. Both disease-free (p<0.03) and the overall survival (p<0.02) were reduced in the highly malignant sarcoma patients. We found telomerase activity in 38.3% of the cases, there being a correlation with a more aggressive behavior of soft tissue sarcomas. Telomerase activity correlated with the grade of malignancy (p=0.04), but not with sex (p=0.64) or age (p=0. 48) of the patients. The total survival was significantly reduced in patients with telomerase-positive sarcomas (p=0.04). Both of the patients having grade I tumors with telomerase activity died of disease, whereas 10 of 11 patients with telomerase-negative grade I tumors are still alive. Only one of the benign tumors showed telomerase activity. We suggest that telomerase activity is a potential prognostic factor in malignant soft tissue tumors. Despite the histological heterogeneity of soft tissue tumors, single entities should be assessed for telomerase activity.

Telomerase Is Controlled by Protein Kinase Cα in Human Breast Cancer Cells

Telomerase, a specialized RNA-directed DNA polymerase that extends telomeres of eukaryotic chromosomes, is repressed in human somatic tissues and becomes activated during tumor progression in most human cancers. To date, little is known about how telomerase is activated and controlled in cancer, although activation is thought to be involved in cancer cell immortalization. Here, we report that human telomerase-associated protein 1 (hTEP1) and the telomerase catalytic subunit (human telomerase reverse transcriptase (hTERT)) are phosphoproteins and that their phosphorylation is a prerequisite for the activation of telomerase in intact human breast cancer cells. Identified by hTEP1 peptide affinity chromatography, protein kinase Calpha mediates the phosphorylation of hTEP1 and hTERT and induces a marked increase in telomerase activity. Thus, phosphorylation of hTEP1 and hTERT by protein kinase Calpha represents an essential step in the generation of a functional telomerase complex in the initiation and maintenance of telomerase activity in human cancer.

Rapid, quantitative nonisotopic assay for telomerase activity in human tumors

Telomerase is a ribonucleoprotein enzyme that adds TTAGGG repeats onto human telomeres, preventing their shortening. The activation of this enzyme is an important step in cell immortalization and carcinogenesis and seems to represent a new and promising marker in cancer diagnosis and management. Telomerase activity is usually detected in cellular protein extract by the telomeric repeat amplification protocol (TRAP) assay, which can provide only a qualitative (presence/absence) evaluation. Here we present a modification of this method that can provide quantitative information without requiring time-consuming post-PCR procedures such as gel electrophoresis with radioactive materials and autoradiography. The detection and measurement of telomerase activity is performed by evaluating the amount of double-stranded DNA generated in the telomerase reaction and PCR amplification, with the use of the sensitive DNA fluorescent dye PicoGreen. In a subset of tumors, the presence of telomerase activity was confirmed by the conventional TRAP assay. By this method we evaluated telomerase activity in unselected groups of breast (n = 15), ovarian (n = 12), endometrial (n = 12), gastric (n = 20), and renal (n = 12) carcinomas, in meningiomas (n = 8), and in pheochromocitomas (n = 10). The results indicate substantial differences of telomerase activity among cancer groups; however, a large variability among patients of the same group is observed. Kidney, ovarian, and breast carcinomas showed the highest mean values (31.8 +/- 28.9, 29.2 +/- 26.7, and 35.3 +/- 15.9 ng DNA/microg protein, respectively, mean +/- SD), whereas gastric and endometrial cancers had a lower activity (17.2 +/- 8.8 and 13.5 +/- 7.9 ng DNA/microg protein, respectively). Very low or no detectable telomerase activity was found in meningiomas (with the exception of one malignant atypical variant) and pheochromocitomas (9.7 +/- 12.9 and 2.8 +/- 2.1 ng DNA/microg protein, respectively). In conclusion, our method seems to be an accurate and reasonable procedure for measuring telomerase activity in human cancers.

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A survey of telomerase activity in human cancer

Research on the association of the ribonucleoprotein enzyme, telomerase, with human cancer has expanded rapidly in recent years. Essentially all major types of cancer have been screened and the presence of telomerase activity has been detected in the vast majority of cases. In this article we provide a summary, in table form, of the current data.

Telomerase activity in human cancers and its activation during in vivo carcinogenesis

Telomerase activity in human cancers and its activation during in vivo carcinogenesis

Telomerase activity in human cancer.

The chromosome ends are specialized nucleoprotein structures called telomeres, which are essential for stable chromosome maintenance. In tumor-derived cell lines telomeres are maintained by the ribonucleoprotein enzyme telomerase. Telomerase activity is repressed in almost all normal human somatic cells. Due to the end replication problem, progressive telomere shortening occurs in normal somatic cells, leading to a limited replicative capacity and eventually resulting in cellular senescence. In the presence of viral oncogenes or some somatic mutations that block cellular senescence, cells continue to divide and telomere erosion continues. This continuing telomere erosion ultimately leads to the activation of telomerase, a necessary event for the sustained growth of most human tumors.