Telomerase activity is frequently found in metaplastic and malignant human nasopharyngeal tissues

Epstein-Barr virus: more than 50 years old and still providing surprises

It is more than 50 years since the Epstein-Barr virus (EBV), the first human tumour virus, was discovered. EBV has subsequently been found to be associated with a diverse range of tumours of both lymphoid and epithelial origin. Progress in the molecular analysis of EBV has revealed fundamental mechanisms of more general relevance to the oncogenic process. This Timeline article highlights key milestones in the 50-year history of EBV and discusses how this virus provides a paradigm for exploiting insights at the molecular level in the diagnosis, treatment and prevention of cancer.

Synergism of BARF1 with Ras induces malignant transformation in primary primate epithelial cells and human nasopharyngeal epithelial cells

Although it is well known that nasopharyngeal carcinoma (NPC) is closely related with Epstein-Barr virus (EBV), few data are available about which and how EBV-expressed gene is involved in the carcinogenesis of human nasopharyngeal epithelial cells. EBV-encoded BARF1 (BamH I-A right frame 1) gene has been shown to be oncogenic and capable of inducing malignant transformation in BALB/c3T3 and NIH3T3 cells as well as in human B-cell lines Louckes and Akata. It remains unclear, however, whether BARF1 can transform primate or human epithelial cells. Here, we have shown that overexpression of H-Ras gene transformed BARF1-immortalized PATAS cells into malignant cell line. Furthermore, we found that cooperation of BARF1 with H-Ras and SV40 T antigens was sufficient to transform nonmalignant human nasopharyngeal epithelial NP69 cells when serially introduced BARF1 and H-Ras into the SV40 T antigens-immortalized NP69 cells. Taken together, these results demonstrated that the cooperation of BARF1 with Ras suffices to transform primary primate epithelial cell PATAS. Similarly, BARF1 together with H-Ras and SV40 T can transform human epithelial cell NP69, thereby indicating that BARF1 could be involved in the NPC pathogenesis in combination with additional genetic changes.

Upstream stimulatory factor (USF) as a transcriptional suppressor of human telomerase reverse transcriptase (hTERT) in oral cancer cells

Telomerase activity is suppressed in normal human somatic tissues but is activated in cancer cells and immortal cell lines. The reverse transcriptase (RT) subunit human telomerase reverse transcriptase (hTERT) is the key regulator of telomerase activity. The hTERT promoter contains E-box elements and may allow upstream stimulatory factor (USF), a basic helix-loop-helix (bHLH) leucine zipper family proteins, to bind and regulate the expression. In this study, we investigated whether and how USF effect on hTERT. Through luciferase reporter assays, we found that both USF1 and USF2 possess a comparable effect on the inhibition of hTERT expression. Immunoprecipitation (IP) and immunoblotting (IB) analysis reveal that the suppression of hTERT by USF was not through the interaction of USF with c-myc or mad, nor disturbed the cellular protein levels of those. In gel mobility shift and chromatin immunoprecipitation (CHIP) assays, we found that the USF suppression is through direct binding at the E-box site of hTERT promoter and rendering the effect actively. Analysis on clinical normal and tumor tissues reveal that the expression of USF1 and USF2 was lower in the tumor tissues, correlated with hTERT expression and telomerase activity. Taking together, our results demonstrate that USF is a negative transcriptional repressor for hTERT in oral cancer cells. It is possible that USF lose the inhibitory effect on hTERT expression leading to telomerase reactivation and oral carcinogenesis.

Telomerase as an independent prognostic factor in head and neck squamous cell carcinoma

BACKGROUND

Telomerase activity has been found to be associated with many cancers, including head and neck squamous cell carcinoma (HNSCC). We examined the association of telomerase activity with the clinical outcome of patients with HNSCC.

METHODS

A PCR-based enzyme immunoassay method was used to measure telomerase activity in 217 matched (grossly normal and cancerous) tissues from patients with HNSCC. Pearson chi-square test was used to analyze the correlation of telomerase activity with clinicopathologic parameters. Kaplan-Meier method and Cox logistic regression model were used for prognostic analysis.

RESULTS

Of the 217 tissues assayed, 4.1% of the normal and 63.3% of the cancer tissues had high levels of telomerase activity. Telomerase activity was shown to be statistically correlated with extracapsule spreading (ECS) of lymph nodes (p =.005) and overall survival (p =.003). On multivariant analysis, overall stage (p =.007), tumor depth (p =.045), and telomerase activity (p =.008) showed independent variables associated with poor survival.

CONCLUSIONS

Telomerase activity has been shown to be an independent prognostic factor for survival in cases of HNSCC. Telomerase may be a potential molecular target for clinical use in prognostication and therapy in cases of the disease.

Telomeres and telomerase: a dual role in hepatocarcinogenesis

Telomere shortening limits the proliferative capacity of primary human cells and restrains the regenerative capacity of organ systems during chronic diseases and aging. Telomere shortening apparently has a dual role in tumor development and progression. On the one hand, it induces chromosomal instability and the initiation of cancer; on the other hand, tumor progression requires stabilization of telomeres. The predominant mechanism of telomere stabilization in tumor cells is the activation of the telomere-synthesizing enzyme telomerase. The potential use of telomerase activators for the treatment of regenerative disorders will ultimately depend on their effects on tumorigenesis. This review focuses on the role of telomere shortening and telomerase in carcinogenesis with a special focus on hepatocellular carcinoma.

An introduction to telomeres and telomerase

It is now more than a dozen years since the enzyme telomerase was discovered, and since that time, key studies have characterized the structural components of the enzyme and the associated telomeric proteins. Since the original discovery of telomerase, a clear association with cancer has been demonstrated. In normal somatic cells the telomeres at the ends of chromosomes shorten with every cell division, whereas in cancer cells telomere length is often maintained by reactivation of the enzyme telomerase. These discoveries have led to the proposal that telomerase expression can be used as a helpful marker for diagnostic and prognostic purposes in humans. Another area of research that has developed as a result of improving knowledge and understanding of the role of telomerase in malignancy is that of cancer therapeutics. This article is an introduction to the field of telomere and telomerase research, with an introduction to recent attempts to develop novel cancer treatments based on telomerase structure and function.

Molecular biomarkers in HNSCC: prognostic and therapeutic implications

The prognosis of squamous cell carcinoma of head and neck (HNSCC) is influenced by many factors, such as performance status, TNM staging and pathological grading of differentiation. However, these factors are not sufficient for predicting outcome. Therefore, recent research has focused on the identification of molecular biomarkers. These markers help to stage patients in more meaningful prognostic groups and identify high-risk patients who may benefit from a more aggressive treatment approach. They also identify patients who are resistant to radiotherapy or chemotherapy, potentially avoiding the morbidity and cost of ineffective therapies. They can also identify patients with a high risk of recurrence who may benefit from chemoprevention. Finally, these markers may serve as targets for novel therapies, which would eventually change the outcome of HNSCC.

Locally advanced nasopharyngeal cancer

The Head and Neck Cancer Intergroup phase III clinical trial (Int 0099) for patients with locally advanced, squamous cell carcinomas (SCC) of the nasopharynx (or NPC) has been recently completed in the United States. The results of this study have defined the new standard of treatment for the group of patients studied. Patients with untreated, locally advanced stages III and IV NPC were randomized to a conventional course of radiation, or to radiation given concurrently with chemotherapy followed by three courses of combination chemotherapy. The 3-year progression-free survival (PFS) and overall survival (OS) were 24% versus 69% (P < 0.001) and 46% versus 76% (P < 0.001) for the control and experimental groups, respectively. Recent updates of these survival figures show that they have not changed appreciably. The considerable improvement in OS versus PFS for the patient group receiving radiation alone is accounted for primarily by re-treatment with concurrent radiation-chemotherapy, combination chemotherapy, and isolated salvage neck dissections. Highly significant differences in local control (41% vs 14%) and distant metastases (35% vs 13%) were demonstrated in favor of the chemoradiation treatment arm. The median age for these patients was 51 years, with a 2:1 male to female ratio. Although many patients had a significant history of tobacco exposure with or without alcohol use or abuse, only 24% had keratinizing or well-differentiated squamous (World Health Organization I) type tumors. Whether these results can be extrapolated to the more common Asian variety (WHO II and III) of advanced NPC must be addressed in future clinical trials.