Expression of human telomerase catalytic subunit gene in cancerous and precancerous gastric conditions

An overview of the role of telomeres and telomerase in pre‑neoplastic lesions (Review)

Telomeres are tandem repeats of DNA sequences protecting the end of linear chromosomes. Replicative senescence due to telomere attrition is considered a tumor-preventing mechanism in differentiated somatic cells. However, telomere shortening is associated with genome instability and several disease entities. During carcinogenesis, the development of a telomere maintenance mechanism, predominately through the activation of the telomerase enzyme, represents a hallmark of cancer, since it enables cancer cells to avert senescence and divide indefinitely. Although research of the involvement of telomeres and telomerase in various malignant neoplasms has gained a large amount of interest, the timing and relevance of their role in pre-neoplastic lesions remain to be determined. The present narrative review aims to summarize the evidence regarding the role of telomeres and telomerase in pre-neoplasia across different types of tissues.

Phase I trial of intravenous Ad5CRT in patients with liver metastasis of gastrointestinal cancers

We conducted a phase 1 trial for single-dose intravenous Ad5CRT, a replication-defective adenovirus vector expressing HSVtk (herpes simplex virus thymidine kinase) modulated by a specific trans-splicing ribozyme that targets human telomerase reverse transcriptase (hTERT)-encoding RNAs. Dose-limiting toxicities (DLTs) were evaluated in 15 patients at dose levels of 0.1-2 × 10¹² virus particles. Patients well tolerated study treatment. During the DLT evaluation period, none of the 15 patients developed any grade 4 toxicities or treatment discontinuation that was related to agents investigated by this trial. The most frequent treatment-related adverse event was fever/chill (26.7%). Of the 18 patients, no patients achieved a partial or complete response, and the median progression-free survival for 18 patients was 1.1 months (95% CI, 1.0-1.3) and the results suggest no clinical benefit from this treatment. Ad5CRT's circulating virus half-life was approximately 10 min. Maximum tolerated dose was 2 × 10¹² virus particles. Single-dose intravenous Ad5CRT was feasible and well tolerated in patients with gastrointestinal cancer liver metastasis. Ad5CRT did not provide meaningful clinical benefit, and the reason for the lack of efficacy was not entirely clear because no pharmocodynamic assessment was made.

Genetic variants in TERT are associated with risk of gastric cancer in a Chinese Han population

Telomerase reverse transcriptase (TERT) is a gene within the cancer susceptibility region located at Chr5p15.33, which is associated with multiple cancer types. In this study, we validated the association between TERT polymorphisms and gastric cancer (GC) risk with a case-control study in a Chinese Han population. A total of 302 GC patients and 300 control individuals were recruited. We identified three single nucleotide polymorphisms (SNPs) in TERT that were associated with GC. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated in logistic regression models after adjusting for age and gender to assess the association. The minor alleles of three SNPs were associated with increased GC risk inallelic model analysis. For two of the SNPs, rs10069690 and rs2853676,, the dominant and additive model frequencies were higher in GC cases compared to controls. Further haplotype analysis revealed a protective effect of haplotype “CG” of the TERT gene, while the haplotype “TA” increased GC risk.Our resultsprovide new evidence for the association between TERT and GC susceptibility in the Chinese Han population.

Circulating cell-free human telomerase reverse transcriptase mRNA in plasma and its potential diagnostic and prognostic value for gastric cancer

BACKGROUND

Our aims were to detect circulating cell-free human telomerase reverse transcriptase (hTERT) mRNA in the plasma of gastric cancer patients and evaluate its potential diagnostic and prognostic value.

METHODS

Real-time quantitative reverse transcription-polymerase chain reaction was employed to detect circulating cell-free hTERT mRNA from 118 gastric cancer patients, 40 chronic atrophic gastritis (CAG) patients, and 58 healthy controls.

RESULTS

Circulating cell-free hTERT mRNA was detected in all gastric cancer patients, 39 (97.5 %) CAG patients and 56 (96.6 %) healthy control individuals, respectively. However, it was higher in gastric cancer than in CAG and healthy controls (all at P < 0.05). Moreover, its high level was significantly correlated with clinical stages (P < 0.001) and lymph nodes metastasis (P < 0.001). There was no difference between circulating cell-free mRNA and other parameters. The area under the receiver operating characteristic (ROC) curve was 0.891, and the optimal cut-off point was 0.18, providing a sensitivity of 66 % and a specificity of 87 %. The ROC analysis showed that the diagnosis capability of circulating cell-free mRNA was statistically significantly higher than that of carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA19-9), alone [CEA (0.656); CA19-9 (0.722)] or in combination (0.756). Kaplan-Meier analysis demonstrated a correlation between increased circulating cell-free hTERT mRNA and reduced disease-free survival (P < 0.001) and overall survival (P < 0.001). Cox analysis indicated that it was an independent prognostic factor for disease-free survival and overall survival.

CONCLUSIONS

We concluded that circulating cell-free hTERT mRNA might serve as a potential and useful noninvasive tumor marker for gastric cancer.

Role of alternative splicing events in gastric carcinogenesis

Alternative splicing affects many essential biologic processes and is the basis for a number of pathologic conditions, including cancer. Inherited and acquired changes in pre-mRNA splicing have been documented to play a significant role in human disease development. Many cancer-associated genes are regulated by alternative splicing. In this review, we will summarize the evidence supporting the association between alternative splicing and gastric carcinogenesis. The potential significance of alternative splicing events as a target for the diagnosis and treatment of gastric cancer will also be discussed.

Expression of TERT in precancerous gastric lesions compared to gastric cancer

The objective of this study was to determine the levels of TERT mRNA and TERT protein expression in stomach precancerous lesions such as intestinal metaplasia (IM) and gastric ulcer (GU) and compare them to gastric cancer (GC). Real-time PCR was performed to detect TERT mRNA expression levels in 35 biopsies of IM, 30 of GU, and 22 of GC and their respective normal mucosas. TERT protein was detected by immunohistochemistry in 68 samples, 34 of IM, 23 of GU, and 11 of GC. Increased TERT mRNA expression levels were observed in a significant number of cases, i.e., 46% of IM, 50% of GU, and 79% of GC. The relative mean level of TERT mRNA after normalization with the β-actin reference gene and comparison with the respective adjacent normal mucosa was slightly increased in the IM and GU groups, 2.008 ± 2.605 and 2.730 ± 4.120, respectively, but high TERT mRNA expression was observed in the GC group (17.271 ± 33.852). However, there were no statistically significant differences between the three groups. TERT protein-positive immunostaining was observed in 38% of IM, 39% of GU, and 55% of GC. No association of TERT mRNA and protein expression with Helicobacter pylori infection or other clinicopathological variables was demonstrable, except for the incomplete type vs the complete type of IM. This study confirms previous data of the high expression of both TERT mRNA and protein in gastric cancer and also demonstrates this type of changed expression in IM and GU, thus suggesting that TERT expression may be deregulated in precursor lesions that participate in the early stages of gastric carcinogenesis.

Premalignant lesions in gastric cancer

Despite a plateau in incidence, gastric cancer is one of the most common cancers worldwide and causes considerable morbidity and mortality. Premalignant gastric lesions are well known risk factors for the development of intestinal-type gastric adenocarcinomas. In this multistep model of gastric carcinogenesis, Helicobacter pylori causes chronic active inflammation of the gastric mucosa, which slowly progresses through the premalignant stages of atrophic gastritis, intestinal metaplasia, and adenoma/dysplasia to gastric carcinoma. This progression is paralleled by a stepwise accumulation of multiple genetic and epigenetic abnormalities. Detection, treatment, and molecular analyses of premalignant lesions may thus provide a basis for gastric cancer prevention. This review describes an overview of current knowledge on premalignant gastric lesions. It also reviews the issue of surveillance of patients with premalignant lesions in order to improve the survival of patients with gastric cancer.

Intestinal metaplasia: a premalignant lesion involved in gastric carcinogenesis

Despite a plateau in incidence, gastric cancer remains a significant problem globally. The majority of gastric cancer is associated with histologically recognizable premalignant stages as first described by Pelayo Correa in the mid-1970s. The mortality from gastric cancer remains high especially in Western countries where, arguably, the index of suspicion of gastric cancer in patients presenting with upper abdominal symptoms is lower than in high prevalence countries. What is the evidence that intestinal metaplasia (IM) is a premalignant condition? What should the clinician know about IM and the relative risks of progression to gastric cancer? Finally, what are the current and future strategies that may help stratify patients into high risk and low risk for the development of gastric cancer? This review focuses on gastric IM and outlines some of the literature that discusses it as a premalignant condition. It also reviews the issue of surveillance of patients with IM in order to attempt to reduce the significant mortality of gastric cancer by detection of earlier stages of disease which are eminently treatable.

Expression of the full-length telomerase reverse transcriptase (hTERT) transcript in both malignant and normal gastric tissues

Activation of telomerase by the induction of a full-length telomerase reverse transcriptase (hTERT) transcript is a critical step during cellular immortalization and malignant transformation. Telomerase activity or hTERT expression has thus served as diagnostic and/or prognostic markers in different types of human malignancies. In the present study, we investigated the expression of the telomerase components hTERT and telomerase RNA template (hTER) in normal and malignant gastric tissues derived from 37 patients with gastric cancers. Overall hTERT mRNA was detectable in 33/37 (90%) of tumour specimens and 23/37 (62%) of the corresponding normal gastric tissues. Twenty-five of thirty-seven tumours (71%) expressed the full-length hTERT mRNA, and unexpectedly, this full-length transcript was found in 16 of 37 (43%) normal gastric tissues. Immunohistochemical analyses demonstrated a positive hTERT staining in small fractions of normal epithelial cells and in most gastric cancer cells. A close correlation between the presence of a full-length hTERT transcript and the c-MYC oncogene expression was observed in both normal and cancerous gastric specimens. Moreover, the full-length hTERT expression was positively associated with the tumour size in these patients. Similar levels of hTER expression were expressed in tumour and their corresponding normal tissues. The finding that the full-length hTERT transcript was present in both normal and malignant gastric tissues will preclude its use as a gastric cancer marker. Nevertheless, full-length hTERT mRNA expression may indicate a progressive gastric cancer, and its presence in normal gastric mucosa may have an impact on the anti-telomerase strategy for cancer therapeutic purpose.

Telomerase activity is not a key determinant of sensitivity to standard cytotoxic drugs in human esophageal carcinoma cell lines

The aim of the present study was to investigate if basal telomerase activity levels may predict sensitivity to cytotoxic drugs in a panel of human esophageal carcinoma cell lines. The TRAPeze telomerase detection assay was used to investigate telomerase activity in the cell lines. Cytotoxic drug sensitivity for 20 standard cytotoxic agents was assessed using the fluorometric microculture cytotoxicity assay (FMCA). Telomerase activity was detected in all cell lines with a broad range of activity levels. Drug sensitivity also varied considerably between the cell lines. Except for a P value towards a correlation between mitoxantrone and telomerase activity (P=0.054), no statistically significant correlation was found between telomerase activity levels and sensitivity to investigated drugs, including key drugs such as cisplatin (P=0.9), 5-fluorouracil (P=0.8) and doxorubicin (P=0.54). We therefore conclude that basal telomerase activity level is not a key determinant of sensitivity to standard cytotoxic drugs in esophageal carcinoma cell lines.

Detection of telomerase activity in gastric lavage fluid: a novel method to detect gastric cancer

BACKGROUND

Telomerase is a ribonucleoprotein polymerase that is essential for cell immortality. Recent studies have demonstrated that a high percentage of gastric cancer tissue expressed telomerase. This study describes the presence of telomerase activity in gastric lavage fluid in patients with gastric cancer.

METHODS

Gastric lavage fluid was collected during esophageogastroduodenoscopy in 70 patients: 25 with gastric cancer, 25 with peptic ulcer disease, and 20 with normal stomach. The fluid and biopsy samples were analyzed for telomerase activity by a polymerase chain reaction-based telomerase repeat amplification protocol. The findings were related to the histological results.

RESULTS

Telomerase activity was present in 24 of the 25 (96%) gastric cancer tissue and in 7 of the 25 tissue specimens from peptic ulcer or gastritis. In the gastric lavage fluid, telomerase was detected in 20 patients (80%) with gastric cancer, 7 patients (28%) with peptic ulcer, and none in normal subjects (P < 0.001). The sensitivity, specificity, positive predictive value, and negative predictive value of gastric fluid telomerase expression in gastric cancer patients was 80%, 84%, 74%, and 88%, respectively.

CONCLUSIONS

The presence of telomerase activity is present in gastric lavage fluid of patients with gastric cancer as compared to those without, may represent a novel method for diagnosis of gastric cancer.

Pathology and molecular biology of gastric cancer

Several attempts to classify gastric cancer (GCA) have been made over the past decades. Most successful, and widely used, is the classification by Laurén, which distinguishes, by microscopical morphology alone, two main cancer pathogeneses, diffuse (DGCA) and intestinal (IGCA) subtypes, which appear clearly as dissimilar clinical and epidemiological entities. Here we review the main differences in epidemiology, histopathology, and molecular pathology of the two main subtypes of gastric carcinomas based on Laurén classification. In clinical practice, however, clinical staging, particularly in predicting the survival, still remains superior to all classifications of gastric cancer independent of cancer type. The existence of local precursor lesions or conditions of IGCA tumours, i.e. Helicobacter pylori gastritis, atrophic gastritis (AG), intestinal metaplasia (IM), adenoma, dysplasia, and intramucosal neoplasia, is firmly established. The links of DGCA with intestinal-type epithelium, AG or IM are poor, or do not exist. So far, H. pylori gastritis is the only universal precursor condition for DGCA. It implies that AG and achlorhydria are of minor significance and infrequent in the development of DGCA but are important steps in that of IGCA. Despite an increasing body of data, the overall view on molecular pathology of GCA remains fragmentary. No consistent differences in the molecular pathology of GCA subtypes to meet the Laurén classification have been established. With the exception of TP53, no gene mutation occurring regularly in both histological types of GCA has been reported. Chromosomal aberrations and loss of heterozygosity seem to be non-specific and do not follow any consistent route in the progression of GCA. Microsatellite instability is more commonly found in IGCA than in DGCA. The present epigenetic data suggest that most of the decrease (or loss) of gene expression may be explained by promoter hypermethylation which is more often found in IGCA. In DGCA specific genes such as CDH1 are more often hypermethylated. Compared with GCA, in premalignant condition lesions gene mutations and chromosomal aberrations are infrequent. Epigenetic dysregulation might also represent a major mechanism for altered gene expression in premalignant stages in gastric carcinogenesis.

Value of endoscopic methylene blue and Lugol's iodine double staining and detection of GST-Π and telomerase in the early diagnosis of esophageal carcinoma

AIM: To explore the expressions of GST-Π and telomerase activity in esophageal carcinoma and premalignant lesions and to investigate the value of endoscopic methylene blue (MB) and Lugol's iodine double staining.

METHODS: Seventy-two patients with esophagopathy were sprayed endoscopically with MB and Lugol's iodine in proper order and the areas stained blue and brown, and the area between the blue and brown stains were obtained. Depending on the pattern of mucosal staining, biopsy specimen was obtained. GST-Π and telomerase activity in specimens were examined by immunohis-tochemistry and PCR-based silver staining telomeric repeat amplification protocol, respectively.

RESULTS: After MB and Lugol's iodine staining, the area between both the colors was obtained in 64 of the 72 patients and the areas were stained blue and brown in all of the 72 patients. Association test of two simultaneous ordinal categorical data showed a correlation between the esophageal mucosal staining and the esophageal histology (P<0.005). The expression of GST-Π and telomerase activity in esophageal carcinoma and premalignant lesions increased. The expression of GST-Π and telomerase activity in dysplasia and carcinoma was significantly higher than that in normal epithelium (P<0.005). The expression in hyperplasia was slightly higher than that in normal epithelium. With the lesions progressing from low- to moderate- to high-grade dysplasia, the positive rate increased (P<0.025). Expression of GST-Π was correlated with that of telomerase activity in dysplasia and carcinoma (j = 0.4831, P<0.005; j = 0.3031, P<0.025, respectively); but there was no correlation between them in normal epithelium and hyperplasia.

CONCLUSION: The expression of GST-Π and telomerase may be an early event in the carcinogenesis of esophagus. They may play an induced and synergistic role with each other in the carcinogenesis of esophagus. Endoscopic MB and Lugol's iodine double staining and detection of GST-Π and telomerase activity may contribute to the early diagnosis of esophageal carcinoma.

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.

Significance of hTERT, E-Cadherin and Catenin-b expression in stomach mucinous adenocarcinoma

AIM: To study the significance of human telomerase reverse transcriptase (hTERT), E-Cadberin (E-cad) and Catenin-b (b-cat) expression in the tissues of stomach mucinous adenocarcinoma.

METHODS: The expression of hTERT, E-cad and b-cat were detected by immunohistochemical staining and in situ hybridization in 92 cases of stomach mucinous adenocarcinomas.

RESULTS: The expression of hTERT is negative outside and positive inside of mucinous adenocarcinoma cells, and its expression in pure mucinous adenocarcinoma, papillary mucinous adenocarcinoma, signet-ring cell mucinous adenocarcinoma and mixed cell mucinous adenocarcinoma is 88.9%, 85.4%, 100.0% and 95.8% respectively. The expression ratio become higher with the malignant degree, but no significant difference was found (P>0.05). The expression of E-cad is 100.0% in both pure and papillary mucinous adenocarcinoma, but is 38.9% and 62.5% in signet-ring cell and mixed cell mucinous adenocarcinoma respectively, which showed that E-cad expression was decreased with malignant degree (P<0.01).The expression of b-cat was also decreased with malignant degree.

CONCLUSION: The positive level of hTERT, E-cad and b-cat is related to the histopathological types of stomach mucinous adenocarcinoma, and they are important in the judgement of prognosis.

Telomerase activity in proximal and distal gastric neoplastic and preneoplastic lesions using immunohistochemical detection of hTERT

BACKGROUND

The incidence of distal (corpus and antrum) gastric adenocarcinoma is decreasing with a simultaneous increase in incidence of proximal (cardia) adenocarcinoma. Epidemiological studies suggest that they may represent different diseases but corroborative molecular data are scarce. Intestinal metaplasia may have a lower malignant potential in the proximal stomach but regardless of the locations, its specificity as a predictor of carcinoma is low.

AIMS

The aim of this study was to establish whether human telomerase reverse transcriptase expression differs at various points in proximal versus distal gastric carcinogenesis and to test the utility of human telomerase reverse transcriptase expression as a marker of cancer risk in intestinal metaplasia.

MATERIAL AND METHODS

Wax-embedded tissue from proximal and distal stomach including normal mucosa (n=86), intestinal metaplasia (n=83) and carcinoma (n=101) were used and slides were immunostained for human telomerase reverse transcriptase and pRb and scored semi-quantitatively.

RESULTS

The results showed that in both proximal and distal stomach, human telomerase reverse transcriptase expression rates increased from normal mucosa to cancer. High rates of human telomerase reverse transcriptase expression were seen in the proliferative zones of glands in intestinal metaplasia. In both the locations, loss of pRb expression correlated with higher human telomerase reverse transcriptase expression.

CONCLUSIONS

In conclusion, telomerase activity appears to be an early event in both proximal and distal gastric carcinogenesis and human telomerase reverse transcriptase is expressed in intestinal metaplasia. Telomerase re-expression may be facilitated by pRb inactivation.

Expressions of human telomerase reverse transcriptase gene in cancer and pre-cancer tissues of esophagus

AIM: To investigate the expressions of human telomerase reverse transcriptase (hTERT) gene in cancer and pre-cancer tissues of esophagus and its relation with cellular proliferation antigen Ki-67 and to investigate the value of hTERT in early diagnosis for esophageal cancer as well as predication of prognosis.

METHODS: In situ hybridization was adopted to detect the expressions of hTERTmRNA in tissues of esophageal cancer (42 cases), atypical hyperplasia (37 cases), and normal esophagus(12 cases). Ki-67 antigen was detected by immunohistochemical methods.

RESULTS: The positive rates of hTERTmRNA in tissues of normal mucosa, atypical hyperplasia and cancers were 0.0%, 48.6%, and 83.3% while rates of Ki-67 antigen were 0%, 56.8%, and 88.1% respectively. The expressions of hTERTmRNA and Ki-67 were significantly increased in tissues of hyperplasia and cancer, compared with those in the normal tissues (P <0.01); Expressions of hTERTmRNA and Ki-67 antigen between hyperplasia and cancer also had significant differences (P <0.01). Expressions of hTERTmRNA and Ki-67 antigen significantly related to clinical staging of esophageal cancer and metastasis of lymph node (P <0.05). Meanwhile, there was significant relation between expression of hTERTmRNA and Ki-67 antigen (P <0.05).

CONCLUSION: Over-expression of hTERT gene may play an important role during carcinogenesis and progression of esophageal cancer; Expression of hTERTmRNA is relative to cellular proliferating activity. The detection of hTERT will be helpful for early diagnosis and prognosis evaluation of esophageal cancer.

Telomerase activity in tuberculous peritonitis and malignant ascites

AIM

To determine telomerase activity of exfoliated cells in tuberculous peritonitis and malignant ascites, and study the diagnostic value of telomerase activity in differentiating tuberculous peritonitis from malignant ascites.

METHODS

TRAP-PCR-ELISA and TRAP-PCR-silver staining were employed to determine telomerase activity in 18 specimens of malignant ascites and 13 specimens of tuberculous peritonitis. Telomerase activities in tuberculous peritonitis and malignant ascites were analysed.

RESULTS

Telomerase activity in malignant ascites (0.387±0.023)was significantly higher than that in tuberculous peritonitis(0.023±0.004, P<0.01). The positive rate of telomerase activity in malignant ascites was significantly higher than that in tuberculous peritonitis, 88.9% (16/18) vs 7.7% (1/13), P<0.01. The sensitivity, specificity and accuracy of determination of telomerase activity in diagnosis of malignant ascites were 88.9%, 92.3%, and 90.3%, respectively.

CONCLUSION

Telomerase activity is positive in malignant ascites and may serve as a useful indicator for differentiating between tuberculous peritonitis and malignant ascites.

Telomerase as tumor marker

Telomerase, a critical enzyme responsible for continuous cell growth, is repressed in most somatic cells except proliferating progenitor cells and activated lymphocytes, and activated in approximately 85% of human cancer tissues. Telomerase activity is a useful cancer-cell detecting marker in some types of cancers in which almost all cases show telomerase activation. In other types in which telomerase becomes upregulated according to tumor progression, it is a useful prognostic indicator. Detection of human telomerase reverse transcriptase (hTERT) mRNA or protein in various clinical samples is also applicable. However, careful attention should be paid to the false negative results due to the instability of this enzyme or hTERT mRNA and the existence of polymerase chain reaction inhibitors as well as the false-positive results due to the contamination by normal cells with telomerase activity. If these pitfalls are avoided, in situ detection of hTERT mRNA or protein will facilitate the reliability of telomerase as a tumor marker.

Activity and expression of human telomerase in normal and malignant cells in gastric and colon cancer patients

BACKGROUND

The reactivation of telomerase is believed to play an important role in immortalization and carcinogenesis.

OBJECTIVE

To investigate the expression of three components of the telomerase complex (hTR, hTERT and TP1), along with telomerase activity in malignant and normal cells.

METHODS

Cells were isolated from gastric and colon cancer, and from normal mucosa from the stomach and colon of participating patients. Expression of hTERT, hTR and TP1 has been studied by the reverse transcriptase polymerase chain reaction (PCR) technique. The telomerase repeat amplification protocol and PCR enzyme-linked immunosorbent assay were used for analysis of telomerase activity.

RESULTS

All telomerase components were consistently expressed in colon and gastric cancer cells. Neoplastic RNA produced consistently very strong amplification signals either for hTR, hTERT or TP1. The expression of hTR was observed in RNA isolated from all normal mucosa samples and from peripheral blood lymphocytes. The expression of TP1 and hTERT has been found in the majority of normal cells; however, the amplification signals produced were usually much weaker than in malignant cells. The limiting dilution experiments indicated that the cancer cells have at least 100-fold higher telomerase activity and at least 25-fold higher TP1 and hTERT expression in comparison to normal cells.

CONCLUSIONS

It can be concluded that all the cancer cells tested have higher telomerase expression and activity than normal cells. Therefore, telomerase can be a good cancer marker, provided that quantitative analysis is carried out.

Helicobacter pylori infection generated gastric cancer through p53-Rb tumor-suppressor system mutation and telomerase reactivation

AIM

To investigate the relationship between Helicobacter pylori (H.pylori) infection and the expressions of the p53, Rb, c-myc, bcl-2 and hTERT mRNA in a series of diseases from chronic gastritis (CG), intestinal metaplasia type I or II(IMI-II), intestinal metaplasia type III (IMIII), mild or modest dysplasia (DysI-II), severe dysplasia (DysIII) to gastric cancer(GC) and to elucidate the mechanism of gastric carcinogenesis relating to H.pylori infection.

METHODS

272 cases between 1998 and 2001 were available for the study including 42 cases of CG, 46 cases of IMI-II, 25 cases of IMIII, 48 cases of DysI-II, 27 cases of DysIII, 84 cases of GC. H.pylori infection and the expressions of p53, Rb, c-myc, bcl-2 were detected by means of streptavidin-peroxidase (SP) immunohistochemical method. HTERT mRNA was detected by in situ hybridization (ISH).

RESULTS

The expressions of p53, Rb, c-myc, hTERT mRNA and bcl-2 were higher in the GC than in CG, IM, Dys. The expression of c-myc was higher in IMIII with H.pylori infection (10/16) than that without infection (1/9) and the positive rate in DysI-II and DysIII with H.pylori infection was 18/30 and 13/17, respectively, higher than that without infection (4/18 and 3/10, respectively). In our experiment mutated p53 had no association with H.pylori infection, the expression of Rb was associated with H.pylori infection in GC, but the p53-Rb tumor-suppressor system abnormal in DysI-II cases, DysIII and GC cases with H.pylori infection was 21/30, 15/17 and 48/48 respectively, higher than non-infection groups (4/18, 3/10, 28/36). Furthermore the level of hTERT mRNA in GC with H.pylori infection (47/48) was higher than that without infection (30/36), however the relationship between bcl-2 and H.pylori was only in IMIII. C-myc had a close association with hTERT mRNA in DysIII and GC (P=0.0 253,0.0 305 respectively).

CONCLUSION

In the gastric carcinogenesis, H.pylori might cause the severe imbalance of proliferation and apoptosis in the precancerous lesions (IMIII and GysIII) first, leading to p53-Rb tumor-suppressor system mutation and telomerase reactivation, and finally causes gastric cancer.

The significance of human telomerase reverse transcriptase (hTERT) in cancer

Since the discovery of the enzyme telomerase in humans, it has become apparent that it is the most general of tumour markers known, and enormously significant in its potential for diagnostic, prognostic and therapeutic applications. Extensive work has identified three core components of the enzyme, of which the catalytic subunit hTERT (human telomerase reverse transcriptase) appears to be the most important. The aim of this article is to review the current evidence for the function and activity of hTERT in malignant conditions, and to discuss the future possibilities in terms of cancer diagnosis and treatment.