Telomerase activity and in situ telomerase RNA expression in malignant and non-malignant lymph nodes

Ratiometric fluorescence resonance energy transfer for reliable and sensitive detection of intracellular telomerase RNA via strand displacement reaction amplification

Human telomerase RNA (hTR) is one essential component of telomerase and is overexpressed in tumor cells. Therefore, the reliable and sensitive detection of hTR is essential for the early cancer diagnosis. Herein, to avoid the false positive signals caused by co-existing components in the cell, a ratiometric fluorescence resonance energy transfer (FRET) strategy was developed to achieve reliable detection of intracellular hTR. Manganese dioxide nanosheets (MnO₂NS) with good biocompatibility carry two fluorophore-labelled hairpin DNA probes into the cancer cell and then release the probes via decomposition of MnO₂NS by intracellular L-glutathione reduced (GSH). Then, hTR triggered the cyclic strand displacement reaction (SDR) between two hairpin DNA probes to continuously form DNA duplexes, which made two fluorophores close to each other and led to an effective FRET. Fluorescence imaging demonstrated a higher expression level of hTR in HeLa cells than that in normal HL-7702 cells. The high specificity of hairpin DNA probes and SDR make it easy to discriminate the single-base mutation. Therefore, it provides a highly sensitive, simple and reliable method for the extracellular and intracellular detection of hTR.

In situ imaging of intracellular human telomerase RNA with molecular beacon-functionalized gold nanoparticles

Since the expression level of human telomerase RNA (hTR) in tumor cells is much higher than that in normal cells, the determination of hTR is of prime importance in biological research of tumors. In this work, we report molecular beacon-functionalized gold nanoparticles for hTR imaging in live cells. The molecular beacon has a loop-and-stem structure with hTR recognition sequences and a red fluorophore Cy5. In the presence of hTR, the hTR sequence could be hybridized with the loop of molecular beacon to form a duplex DNA chain and thus the fluorescence state switched from "off" to "on". After co-incubation with cells, the probe could readily permeate into cells, leading to the in situ imaging of intracellular hTR. The proposed approach could be used to differentiate tumor cells from normal ones and assess hTR expression levels in different tumor cells. Furthermore, the proposed approach allowed us to dynamically monitor the expression level of hTR in live cells and holds great potential for application in tumor diagnosis and hTR-related drug delivery.

Sensitive detection of intracellular RNA of human telomerase by using graphene oxide as a carrier to deliver the assembly element of hybridization chain reaction

Since the level of human telomerase RNA (hTR) in tumor cells is higher than that in normal somatic cells, the quantitative assay of hTR is of significant importance in tumor diagnosis. Herein, graphene oxide (GO) was simultaneously exploited as a fluorescence quencher and a carrier of nucleic acid to successfully deliver two hairpin DNA probes of hybridization chain reaction (HCR) into the cancer cell for detecting telomerase RNA based on DNA nanoassembly of HCR. The sticky end of HCR probes could tightly absorb on the surface of GO, resulting in fluorescence quenching of the dye which was tagged at the sticky end of two hairpin probes. When faced with hTR, the fluorescence of DNA probes is subsequently recovered because hTR could trigger HCR to autonomous assembly of a DNA polymer which released from the GO and led to fluorescence recovery. Taking advantage of nucleic acid nanoassembly of HCR, this intracellular HCR strategy creates enormous signal amplification, and enables ultra-sensitive fluorescence imaging of hTR expression. By monitoring fluorescence change, human telomerase RNA could be specifically studied and this method can also be used for detecting single-base mutation. The GO-aided HCR strategy allowed us to sensitively detect hTR in a living cell, which holds great potential for analyzing other low-abundance biomolecules in living cells via HCR.

Sticky-flares for in situ monitoring of human telomerase RNA in living cells

Human telomerase RNA (hTR), a template of telomerase for telomeric repeat synthesis, was used to reflect the telomerase activity and act as a potential target of antitumor therapy. Here, we report a novel DNA-conjugated AuNP probe termed sticky-flares for the in situ detection of intracellular human telomerase RNA. The sticky-flares probe is capable of entering living cells directly without any auxiliary and recognizing the binding domain of human telomerase RNA. On recognition, the fluorophore-modified recognition flares can specifically bind to the target, separate from the sticky-flares and act as a fluorescent reporter to quantify and dynamically profile human telomerase RNA in living cells. We envision that the sticky-flares probe would be a valuable platform to investigate the function and regulation of hTR in antitumor therapy and hTR-related drug invention.

Telomerase RNA Expression and DNA Ploidy as Prognostic Markers of Prostate Carcinomas

Aims and Background

The objective of this study was to determine whether there was a correlation between telomerase RNA expression and DNA ploidy status with clinicopathological parameters and biochemical recurrence after radical prostatectomy.

Study Design

Telomerase RNA expression and DNA ploidy were evaluated in imprint smear samples obtained from 112 prostates after radical prostatectomy. The results were correlated with pathological stage, Gleason score and serum PSA.

Results

Positive telomerse RNA expression was detected in 67.8% of prostate carcinomas. The multiple linear regression model showed a statistically significance increase in telomerase RNA expression with increased Gleason score ( P <0.0001) and preoperative serum PSA values ( P = 0.0125). DNA ploidy status also varied significantly with Gleason score ( P <0.0001) and preoperative serum PSA values ( P = 0.0110). Five patients with diploid tumors and negative telomerase RNA expression developed a recurrence. However, recurrence was associated with DNA aneuploidy ( P = 0.001) as well as with high telomerase RNA overexpression ( P = 0.001).

Conclusions

We conclude that telomerase RNA expression and DNA ploidy could be additional markers in the field of prognosis of prostate carcinomas.

A dual-colored ratiometric-fluorescent oligonucleotide probe for the detection of human telomerase RNA in cell extracts

A dual-colored ratiometric-fluorescent oligonucleotide probe is designed for the detection of human telomerase RNA (hTR) in cell extracts.

Evaluation of telomerase activity in non-genital Bowen's disease

We investigated the level of telomerase activity (TA) in 17 specimens of non-genital Bowen's disease (BD) and in 14 specimens of skin without sun exposure (non-exposed skin) using a non-isotopic PCR-based telomeric repeat amplification protocol (TRAP) assay. Expression of human telomerase reverse transcriptase (hTERT; the catalytic subunit of telomerase) was also evaluated by immunochemistry in the non-genital BD tissues. Moderate to high levels of TA were detected in 41.2% of 17 non-genital BD specimens (P = 0.001). In contrast, TA was not evident in non-exposed skin. Recently, nucleolin was reported to be associated with hTERT, so we used this antibody instead of hTERT antibody. Immunohistochemistry showed that nucleolin expression was associated with high TA levels in non-genital BD. Our results also revealed differences of TA levels among non-genital BD specimens. High levels of TA in those specimens were not age related. Five out of 7 specimens (71.4%) with moderate to high TA levels were from sun-exposed sites, while the remaining 10 specimens with low levels of TA were from non-exposed sites. These results suggested that cellular DNA damage caused by ultraviolet irradiation might be associated with an increase of TA in non-genital BD. Among non-genital BD specimens, 4 out of 17 (23.5%) showed high levels of TA (median relative TA value: 79.8%; P = 0.003), which might be associated with immortalization or transformation to invasive squamous cell carcinoma.

Telomerase activity is a biomarker for high grade malignant peripheral nerve sheath tumors in neurofibromatosis type 1 individuals

Telomerase activity (TA) and the expression of its enzymatic subunits, which have been demonstrated in many tumors, remain poorly investigated in tumors associated with neurofibromatosis type 1 (NF1). In this study, we analysed the association of TA and the expression of telomerase RNA (TR) and telomerase reverse transcriptase (TERT) in 23 malignant peripheral nerve sheath tumors (MPNST) (17 high grade and 6 low grade tumors), 11 plexiform neurofibromas (PNF) and 6 dermal neurofibromas (DNF). TA was studied using telomerase repeat amplification protocol (TRAP) assay and expression of TR and TERT was investigated using reverse transcription PCR (RT-PCR) and real-time PCR. TA was detected in 14 out of 17 (82%) high grade MPNST, whereas all 6 low grade MPNST and 17 benign tumors were telomerase negative. The TERT transcripts were detected in all high grade MPNST, 50% of the low grade MPNST, and 4 benign tumors. However, the expression level of the TERT strikingly correlated with TA and high grade MPNST. Thus, while TERT expression was similar in both low grade MPNST and PNF (P = 0.115), it was significantly higher in high grade MPNST when compared to either low grade MPNST (P = 0.042), PNF (P = 0.001) or DNF tumors (P = 0.010). These findings indicate that TA and expression level of TERT are potential markers for high grade malignancy in NF1 patients.

Telomerase redefined: Integrated regulation of hTR and hTERT for telomere maintenance and telomerase activity

Telomerase activity is dependent on the expression of 2 main core component genes, hTERT, which encodes the catalytic component and hTR (also called TERC), which encodes the RNA component. The correlation between telomerase activity and carcinogenesis has made this molecule of great interest in cancer research, however in order to fully understand the regulation of telomerase the mechanisms controlling both telomerase genes need to be studied. Some of these mechanisms of regulation have begun to emerge, however many more remain to be deciphered. For many years hTERT has been regarded as the limiting component of telomerase and much of the research in this field has focussed on its regulation, however it was clear from an early stage that hTR expression was also tightly regulated in normal cells and disease. More recently evidence from biochemistry, promoter studies and mouse models has been steadily increasing for a role for hTR as a limiting and essential component for telomerase activity and telomere maintenance. Perhaps the time has come to redefine our view of telomerase regulation. Knowledge of the mechanisms controlling both telomerase genes in normal systems and cancer may aid our understanding of the role of telomerase in carcinogenesis or highlight potential areas for therapeutic intervention. Here we review the essential requirement of hTR for telomere maintenance and telomerase activity in normal tissues and disease and focus on recent advances in our understanding of hTR regulation in relation to hTERT.

Detection of human telomerase RNA in the tumour-surrounding mucosa of bladder carcinomas as a marker for premalignant transformation

OBJECTIVES

To investigate tumour tissue and non-malignant tumour-surrounding bladder mucosa (NTSBM) for expression of human telomerase RNA (hTR) as a possible marker for premalignant transformation of urothelial cells.

MATERIAL AND METHODS

From 67 patients with superficial transitional cell carcinoma (TCC), sections with representative tumour tissue and NTSBM were selected for evaluation. Sections with moderate or severe dysplasia were omitted from evaluation. hTR expression was detected with in situ hybridization using a 35S-UTP-labelled riboprobe, and analysed semiquantitatively by counting the hybridization signals.

RESULTS

In 45 of the 67 patients hTR expression was moderate or strong in tumour tissue, and in 20 hTR expression was moderate or strong in NTSBM. Moderate or strong hTR expression was detected in the NTSBM from 19 of 60 patients with pTa/pT1 tumours. Of the 56 patients who were treated conservatively, eight had tumour recurrence, of whom five had moderate or strong hTR expression in the TSBM, compared with only 14 of 48 patients without tumour recurrence.

CONCLUSION

Detecting hTR expression and the morphological distribution of hTR hybridization signals in NTSBM by in situ hybridization might indicate premalignant alterations involved in tumour recurrence.

Nuclear telomerase is less accessible to antibody probing than known nuclear antigens: retrieval with new immunostaining buffer

Telomerase is an important tumor marker but few antibodies to the enzyme have been described or used without difficulty in histochemical detection. Here we report specific detection of the enzyme in cell and tissue preparations using a new monoclonal antibody (mAb 476) and a new antigen-retrieval buffer (Enhancing buffer). When used to detect telomerase under normal immunostaining conditions in HL-60 cells or tissue sections of hepatocellular carcinoma or metastatic choriocarcinoma, unexpectedly, the antibody stained the cytoplasm rather than the nucleus. Nuclear staining, however, was revealed using the Enhancing buffer. Since other nuclear antigens in the HL-60 cell could be stained both ordinarily and in the Enhancing buffer, nuclear telomerase appears to be shrouded by the nuclear matrix or blocked by accessory proteins. The cytoplasmic activity seen in normal buffer but absent largely from the Enhancing buffer may be an artifact or the nascent, "naked" enzyme. With a known cytoplasmic antigen (proteinase-3) chosen arbitrarily for comparison, the antigenicity was found enhanced, instead, by the Enhancing buffer. The mode of action of the Enhancing buffer differs from that of microwave irradiation or the signal amplification (CSA) used by some investigators. The latter was found to enhance the cytoplasmic reactivity rather than the nuclear reactivity of mAb 476.

Estimation of ribosomal RNA transcription rate in situ

Traditionally, the rate of transcription is measured by metabolic labeling (e.g., the run-on assay), which can be carried out only in isolated or cultured cells. It has been difficult if not impossible to assess the rate of transcription of a gene in a specific cell type in situ. We show here that the quantity of 47S precursor ribosomal RNA (pre-rRNA), which correlates positively with the rate of rRNA transcription as measured by the run-on assay, can serve as an indicator for the rate of its transcription. We adopted this method as an in situ hybridization procedure to demonstrate its validity in vivo. The notion of using the quantity of the primary transcript as an indicator of the rate of transcription has the potential application in monitoring the rate of messenger RNA transcription in single cells within a tissue of complex cellular composition.

Strong telomerase activity of B lymphocyte from mesenteric lymph nodes of patients with inflammatory bowel disease

Telomerase acitivity can be induced in human B lymphocytes by in vitro stimulation of their antigen receptors. To determine whether telomerase activity is induced in vivo, we analyzed telomerase activity in B lymphocytes from the mesenteric lymph nodes of patients with inflammatory bowel disease (IBD), whose lymph nodes are well known to be strongly stimulated, and from those of noninflamed controls. Seven IBD patients and 4 noninflamed controls were enrolled. Telomerase activity was assayed by telomeric repeat amplification protocol with minor modifications. The mesenteric lymph nodes from patients with IBD had stronger telomerase activity than those from controls or peripheral mononuclear cells. Isolation of CD19+ B lymphocytes from these lymph nodes showed that this strong activity resides in this lymphocytes subpopulation. This study provides the evidence that telomerase activity is induced in human B lymphocytes in human inflammatory disease.

Telomerase as a prognostic marker in breast cancer: high-throughput tissue microarray analysis of hTERT and hTR

Telomerase activity (TA) has been shown to correlate with poor clinical outcome in various tumour entities, indicating that tumours expressing this enzyme may be more aggressive and that TA may be a useful prognostic marker. For breast cancer, however, TA is a controversial prognostic marker; whereas some studies suggest an association between TA and disease outcome, others do not find this association. This study used tissue microarrays (breast carcinoma prognosis arrays) containing 611 samples (each 0.6 mm in diameter) from the tumour centre of paraffin-embedded breast carcinomas to analyse the catalytic subunit of telomerase, human telomerase reverse-transcriptase (hTERT), and the internal RNA component (hTR), which are the core components of the telomerase holoenzyme complex. hTERT protein expression was obtained by immunohistochemistry (human anti-telomerase antibody Ab-2, Calbiochem), and hTR RNA was measured by radioactive in situ hybridization. hTERT and hTR expression were determined semi-quantitatively and graded (scores 1-4). Clinical data, such as histological subtype, pT stage, tumour diameter, pN stage, BRE grade, tumour-specific survival (in months), patient's age and others, were available for statistical analysis. A statistically significant correlation was found between tumour-specific survival (overall survival) and hTERT expression (p < 0.0001) or hTR expression (p = 0.00110). Tumours with higher scores (scores 3, 4) for hTR and/or hTERT were associated with a worse prognosis. In multivariate analysis, hTERT expression was an independent prognostic factor. Previous studies, focusing on analysis of TA in smaller numbers of fresh-frozen breast carcinomas by the TRAP assay, gave controversial results with respect to TA as a prognostic marker. Using tissue microarrays from 611 breast carcinomas, this study has demonstrated that increased expression levels of the telomerase core components, hTERT and hTR, are associated with lower overall survival. These findings suggest that TA should be included in future validation studies as a prognostic marker in breast cancer.

Telomerase activity detected in oral lichen planus by RNA in situ hybridisation: not a marker for malignant transformation

BACKGROUND

Oral lichen planus (OLP) is a chronic inflammatory condition. Clinically, it is characterised by the presence of a white lace-like lesion on the buccal mucosa, tongue, and gingivae, with erosions and ulceration. The World Health Organisation considers OLP to be a premalignant condition.

AIMS

To investigate expression of the telomerase RNA component (hTR) in OLP compared with normal control buccal mucosa and to assess the possibility of using hTR expression as a marker for malignant transformation in OLP.

METHODS

hTR expression was analysed in 40 cases of OLP and 18 normal control buccal mucosa samples using an RNA in situ hybridisation approach.

RESULTS

Strong hTR RNA expression was seen in the basal, suprabasal, and to a lesser extent in the upper epithelial layers in 36 of the 40 OLP lesions examined. Infiltrating subepithelial lymphocytes in OLP were also shown to express hTR RNA. Weak hTR RNA expression was seen in seven of the 18 normal control buccal mucosa specimens, with expression confined exclusively to the basal layer of the epithelium and absent in the suprabasal and upper layers.

CONCLUSION

The telomerase RNA component hTR is found to be highly expressed in the epithelium of non-dysplastic OLP lesions. It is possible that this high expression is related to the increased cellular proliferation seen in OLP lesions rather than being an indicator of susceptibility to malignancy. Thus, hTR RNA expression may not be a suitable marker for predicting malignant transformation in OLP.

Human telomerase RNA component expression in Spitz nevi, common melanocytic nevi, and malignant melanomas

BACKGROUND

Telomerase is a ribonucleoprotein DNA polymerase that is capable of synthesizing telomeres onto the ends of chromosomes. The cumulative loss of telomerase activity is believed to be associated with cell senescence. Telomerase activity has been shown to be higher in malignant melanomas than in common melanocytic nevi. The aim of the present study was to elucidate the pattern of expression of the human telomerase RNA (hTER) component in routinely processed specimens of Spitz nevi, malignant melanomas, and ordinary melanocytic nevi.

METHODS

Ten specimens of each type of tumor were studied, using an in situ hybridization technique.

RESULTS

All three types of tumors demonstrated moderate to high intensities of hTER expression, usually in more than half of the tumor cells, and the majority of the studied lesions in each group did not show stratification of staining. The hTER component was also detected in the epidermis, sweat glands, and pilosebaceous units.

CONCLUSIONS

hTER levels do not necessarily correlate with the level of telomerase activity, and the level and pattern of hTER expression are not useful as an adjunct to the histologic differential diagnosis of Spitz nevi from melanocytic nevi and malignant melanomas.

Telomerase as a diagnostic and therapeutic target for cancer

Telomerase is a ribonucleoprotein enzyme responsible for the elongation of telomeres at the ends of chromosomes. It is widely expressed in most cancers, while absent from most normal somatic cells. Telomerase is partially responsible for the cellular immortalization that allows human cancers to progress indefinitely. Due to its widespread occurrence in cancer and its crucial role in the maintenance of the tumor, telomerase is an attractive target for cancer diagnosis and treatment.

Estrogen replacement therapy induces telomerase RNA expression in the macaque endometrium

OBJECTIVE

To evaluate the effects of hormonal therapies on the expression of telomerase RNA (TRNA) in the endometrium of ovariectomized female cynomolgus macaques (Macaca fascicularis).

DESIGN

Randomized long-term experimental trial.

SETTING

Animal study at an academic research institution.

PATIENT(S)

Surgically postmenopausal cynomolgus macaques.

INTERVENTION(S)

Treatments were given in the diet for three years and included conjugated equine estrogens (CEE), CEE + medroxyprogesterone acetate (MPA), and tamoxifen, at clinically relevant doses.

MAIN OUTCOME MEASURE(S)

Expression of TRNA within the basal glands, basal stroma, superficial glands, and superficial stroma of the endometrium by radiolabeled in situ hybridization.

RESULT(S)

Conjugated equine estrogens increased glandular TRNA expression, and the addition of MPA decreased this effect. Tamoxifen induced glandular TRNA expression to a lesser degree. Both CEE + MPA and tamoxifen increased stromal TRNA expression. The expression of TRNA in the endometrial glands was always greater than TRNA expression in the stroma. Treatment groups with greater proliferation and progesterone receptor expression also had elevated TRNA; within-group correlations were not significant. No statistically significant difference occurred between the basal and superficial endometrial layers.

CONCLUSION(S)

These results show for the first time a cell-specific hormonal regulation of TRNA in the primate endometrium, with up-regulation of TRNA by treatments associated with increased risk of endometrial cancer in women.

Telomerase: its clinical relevance in the diagnosis of bladder cancer

More than 50 years ago, Papanicolaou recognized the importance of a non-invasive technique for the diagnosis and follow-up of patients with carcinoma of the urinary bladder. Cystoscopy, however, has remained the 'gold standard' since no currently available non-invasive method can compete with cystoscopy's sensitivity and specificity. The detection of the ribonucleoprotein telomerase or the telomerase subunits human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT) in urine samples offer new diagnostic perspectives. The present article presents a review of publications in the literature and evaluates their clinical relevance. The experimental studies reported to date are very promising and show that telomerase exactly fulfils the requirements for a good diagnostic marker for carcinoma of the urinary bladder. The diagnostic application remains in an experimental stage and telomerase is still several steps away for routine use as a clinical parameter. The remaining steps leading to its routine clinical application will be discussed.

Molecular analyses of sentinel lymph nodes: an open question

AIMS

To detect micrometastases in the sentinel lymph nodes (SLN) of melanoma patients the authors analysed 52 lymph nodes (47 SLNs and five non-sentinel) and 17 corresponding primary skin melanomas using reverse transcriptase-polymerase chain reaction assays in paraffin-embedded tissues to detect the mRNAs of tyrosinase, MAGE1, MAGE3, MIA, MART-1 and mRNA coding for telomerase catalytic component.

RESULTS

Our data show that the use of molecular markers for melanoma micrometastases detection in SLN is still in a very preliminary stage. In comparing the molecular analysis results with the pathological staging we did not find any evident correlation with the expression of the analysed genes in SLN. There are no data for judging the prognostic significance of the detection of circulating tumour cells in patients without clinically recognizable metastases. Despite progress in the field with simultaneous detection of several markers it was assumed that tyrosinase mRNA remains the best target for the detection of metastatic melanoma cells.

hTR repressor-related gene on human chromosome 10p15.1

Somatic cells express genes that suppress telomerase activity and these genes may be inactivated in tumour cells. We postulated that cancer cells acquire immortality by activation of telomerase by the loss of such a gene. We have reported recently that a telomerase repressor gene may be located on 10p15.1 by deletion mapping using microcell-mediated chromosome transfer (MMCT), radiated microcell fusion (RMF), fluorescent in situ hybridization (FISH) and STS analysis. To independently confirm this result, we correlated expression of RNA component of telomerase (hTR) as a marker of telomerase expression by in situ hybridization with allelic loss in pulmonary carcinoid tumours. Unlike most malignant tumours, pulmonary carcinoids (which are low-grade malignant tumours) are heterogeneous for telomerase expression. Loss of 5 closely spaced polymorphic markers on 10p15.1, especially D10S1728, were highly correlated with hTR expression. In an additional experiment, 10p15.1 showed higher and more significant correlation than any region of 3p where it has been predicted as another chromosomal location of telomerase repressor with allelic loss of the region. Our findings strongly suggest that 10p15.1 harbours a gene involved in repression of telomerase RNA component in human somatic cells and each putative repressor (on 3p and 10p) may act independently.

Expression of telomerase subunits in normal and neoplastic prostate epithelial cells isolated by laser capture microdissection

BACKGROUND

Vertebrates have special structures at the ends of their chromosomes, known as telomeres, which may provide the chromosomes with stability and protect them from exonucleolytic degradation. The shortening of telomeric DNA with each cell division may lead to cell cycle arrest and/or apoptosis of a normal human somatic cell. Telomerase, an RNA-dependent DNA polymerase, elongates the 3'-ends of telomeric DNA. Thus, the presence of telomerase activity may reflect a cell's potential immortal state. The telomerase complex is comprised of several subunits. In the current study, the authors describe the use of laser capture microdissection (LCM) to procure pure matched tumor and normal cell populations from histologic sections and to determine the expression of telomerase subunits in these purified samples.

METHODS

Pure matched tumor and normal prostate epithelial cells were procured by LCM using fresh frozen tissue samples obtained from patients undergoing radical prostatectomy. RNA was extracted from LCM captured cells, and the subunits for telomerase were assayed by reverse transcriptase-polymerase chain reaction.

RESULTS

In 18 samples that were captured with LCM, only the catalytic subunit of telomerase, or hTERT, was found to be discriminatory between tumor cells (17 of 18 specimens, 94.4%) and nontumor cells (none of 18 specimens). TP1, a protein that has been shown to be associated with telomerase activity, was expressed in 3 of 18 normal cells (16.7%) and 15 of 18 tumor cells (83.3%). The RNA subunit of telomerase, or hTR, was expressed in 10 of 18 normal cells (55.6%) and 18 of 18 tumor cells (100%). There was no apparent correlation between telomerase subunit(s) expression and Gleason sum score.

CONCLUSIONS

Molecular analyses of LCM cells from prostate carcinoma patient samples demonstrated transcriptional up-regulation of all telomerase subunits in the prostatic epithelium. However, only the catalytic subunit of telomerase, hTERT, was found to be discriminatory between neoplastic versus normal cells (94.4% vs. 0%). This finding suggests that the hTERT subunit may be a useful marker for the detection of prostate carcinoma and/or a potential target for therapy.

Telomerase activity as a marker for malignancy in feline tissues

OBJECTIVE

To establish the diagnostic significance of the telomeric repeat amplification protocol (TRAP) assay in detecting feline malignancies.

SAMPLE POPULATION

Solid tissue specimens collected from 33 client-owned cats undergoing diagnostic or therapeutic procedures at the University of Illinois Veterinary Medical Teaching Hospital between July 1997 and September 1999 and an additional 20 tissue samples were collected from 3 clinically normal control cats euthanatized at the conclusion of an unrelated study.

PROCEDURE

The TRAP assay was used for detection of telomerase activity. Each result was compared to its respective histopathologic diagnosis.

RESULTS

Twenty-nine of 31 malignant and 1 of 22 benign or normal tissue samples had telomerase activity, indicating 94% sensitivity and 95% specificity of the TRAP assay in our laboratory.

CONCLUSIONS AND CLINICAL RELEVANCE

The diagnostic significance of telomerase activity has been demonstrated in humans and recently in dogs by our laboratory. We tested feline samples to determine whether similar patterns of telomerase activity exist. On the basis of our results, the TRAP assay may be clinically useful in providing a rapid diagnosis of malignancy in cats. The telomerase enzyme may also serve as a therapeutic target in feline tumors.

Telomerase activity in clinically normal dogs and dogs with malignant lymphoma

OBJECTIVES

To determine whether telomerase activity was present in lymph nodes, buffy coat, and serum samples from dogs with malignant lymphoma (ML) and in liver, lymph node, buffy coat, and serum samples from clinically normal dogs

SAMPLE POPULATION

Tissue specimens and blood samples were obtained from 11 clinically normal adult dogs (age range, 1 to 4 years) and 14 client-owned dogs with ML.

PROCEDURE

The telomere repeat amplification protocol assay was used to quantify telomerase activity in the tissues from clinically normal dogs and dogs with ML.

RESULTS

Of 11 clinically normal dogs, 8 had lymph node samples, 5 had liver samples, and 1 had buffy coat samples with detectable telomerase activity. None of the serum samples from the clinically normal dogs had detectable telomerase activity. Of 14 dogs with ML, 9 had lymph node samples, 3 had buffy coat samples, and 1 had serum samples with measurable telomerase activity.

CONCLUSIONS AND CLINICAL RELEVANCE

Telomerase activity was not specific to tumor cells and overlapped with that found in cells from clinically normal dogs. Telomerase activity in neoplastic lymph nodes was not substantially different from that found in lymph nodes from clinically normal dogs. The determination of telomerase activity cannot be used as a sole diagnostic test for cancer. Therapeutic modalities directed toward the telomerase enzyme may not be feasible in dogs, because somatic tissues from clinically normal dogs possess variable amounts of telomerase activity.

Telomerase activity of the Lugol-stained and -unstained squamous epithelia in the process of oesophageal carcinogenesis

Up-regulation of telomerase has been reported in many cancers. Our aim was to characterize telomerase activity in various states of the oesophagus to facilitate better understanding of carcinogenesis of oesophageal squamous cell carcinoma. During endoscopic examinations, we obtained 45 Lugol-stained normal epithelia, 31 Lugol-unstained epithelia (14 oesophagitis, 7 mild dysplasia, 5 severe dysplasia and 5 intramucosal cancer) and 9 advanced cancer. Telomerase activity was semi-quantified by a telomeric repeat amplification protocol using enzyme-linked immunosorbent assay, and expression of human telomerase reverse transcriptase mRNA was examined by in situ hybridization. In the Lugol-stained normal epithelia, telomerase activity increased in proportion to the increase of severity of the accompanying lesions, with a rank order of advanced cancer, intramucosal cancer, mild dysplasia and oesophagitis. In the Lugol-unstained lesions and advanced cancer, telomerase activity was highest in advanced cancer. Up-regulation of telomerase in normal squamous epithelium may be a marker of progression of oesophageal squamous cell carcinoma.

Preparation of monoclonal antibodies against human telomerase

Telomerase, a ribonucleoprotein enzyme that extends telomeres of eukaryotic chromosomes, consists of the catalytic protein submit telomerase reverse transcriptase (TERT) and a telomerase RNA subunit. Nearly 85% of human tumors have tested positive for high telomerase activity. Telomerase activity is very low or not present in normal cells, whereas it is up-regulated in immortalized cells. Telomerase, partially purified from the breast tumor cell line MCF-7, was used to immunize Balb/C mice. Monoclonal antibodies (MAbs) were prepared by conventional hybridoma technology and screened by enzyme-linked immunoadsorbent assay (ELISA), followed by a polymerase chain reaction (PCR) based telomeric amplification repeat protocol (TRAP) assay to detect binding to or inhibition of telomerase activity. Reactive MAbs were found to be of IgM type by mu specific ELISA. Two MAbs were characterized, one that neutralizes telomerase activity in TRAP assay and the other non-neutralizing. In Western blotting, crude telomerase extract and HIV-1 virus lysate (control) were blotted on nitrocellulose membranes and the strips were treated with both MAbs and a nonrelated HIV polymerase-specific MAb, also IgM type. A band of approx. 65-kDa was detected in extracts of 293 cells with both the MAbs, but no reaction occurred with the HIV polymerase-specific MAb used as control. Similarly, when HIV-1 virus lysate strips were treated with HIV polymerase-specific MAb, a 65-kDa band was detected and no band was observed with either of the hybridoma supernatants. These antibodies may be useful for studying regulatory mechanism of telomerase and inhibition of its activity in vitro and in vivo.

Relationship between telomerase activation and HPV 16/18 oncogene expression in squamous intraepithelial lesions and squamous cell carcinomas of the uterine cervix

SILs (squamous intraepithelial lesions) comprise a wide spectrum of clinically and biologically heterogeneous lesions ranging from benign proliferations to precancerous lesions. Telomerase activation plays a critical role in cellular immortalization and might be important for malignant progression. The viral oncogenes E6 and E7 are the principal transforming genes of high-risk HPVs and are important in HPV-associated immortalization and neoplastic transformation. In this study we investigated the relationship between telomerase activity, telomerase RNA, and HPV 16/18 oncogene expression in low- and high-grade SILs and SCCs (squamous cell carcinomas) of the cervix uteri. Telomerase activity was examined by the TRAP-assay and expression of the telomerase RNA (hTR) and HPV 16/18 E6/E7 oncogenes by RNA/RNA-in situ hybridization (ISH). The associated HPV-type was determined by PCR. Telomerase activity was observed in 25/29 (86%) SCCs, 31/41 (76%) high-grade SILs, 6/14 (43%) low-grade SILs, and 1/28 (3.6%) normal cervical tissues. Expression of hTR and viral oncogenes increased significantly with histopathologic severity of the lesion (p < 0.0001). A correlation was found between telomerase activity and intensity of viral oncogene expression. These findings suggest that telomerase activation occurs early in cervical carcinogenesis and is predominantly found in high-grade SILs and cervical SCCs. Our findings support current experimental data that suggest that telomerase is at least partially activated by viral oncogenes of high-risk HPV types. Telomerase activity with concomitant strong viral oncogene expression might therefore characterize a subset of lesions that are at risk for malignant progression.

Telomerase activity modulation in the prevention of prostate cancer

Telomerase is a ribonucleoprotein that stabilizes chromosomes by maintaining their telomeric ends. Although telomerase is normally expressed in reproductive tissues, it is virtually absent in most normal somatic tissues. During carcinogenesis, cells activate telomerase to protect chromosomal ends from the telomere erosion that occurs with replication. Prevention of telomere loss by activation of telomerase allows for the cellular immortalization that is a characteristic of cancer cells. Recent studies have shown that genetic instability arising from critical telomere shortening is a mechanism through which cancer cells attain multiple genetic aberrations that characterize a malignant clone. Thus, the timing of telomerase activation during carcinogenesis is likely to play an important role in modulating the genetic instability that determines the malignant phenotype. Earlier activation of telomerase should minimize genetic aberrations in neoplastic cells and lead to less aggressive tumors, or may prevent carcinogenesis. In this article, we discuss recent data on telomerase expression in prostate cancer, propose a model that relates the dynamics of telomerase activation to the evolution of different prostatic malignancies, and discuss the potential application of telomerase activation as a strategy for the prevention of prostate cancer.

Expression of telomerase components in oral keratinocytes and squamous cell carcinomas

Telomerase activity was measured using a telomeric repeat amplification protocol (TRAP), and expressions of the telomerase components, telomerase associated protein 1 (hTEP1), human telomerase RNA component (hTR), and human telomerase reverse transcriptase (hTERT) were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) in cultured normal oral keratinocytes and oral squamous cell carcinoma (SCC) cells. Telomerase localization was analyzed by in situ hybridization (ISH) in normal, precancerous and cancerous oral tissues. There was a strong correlation of telomerase activity with the expression levels of hTERT but not with hTEP1 or hTR mRNA in the cultured cells. Not only hTEP1 and hTR but also hTERT expression were detected in the basal cells of normal oral mucosa, and the cells expressing these mRNAs were also seen in the upper layer of leukoplakia of gingiva, and a heterogeneous pattern of expression was observed in the oral SCC tissues. These results indicate that there are at least two steps in the increase of telomerase activity during carcinogenesis in oral squamous cells; a change in distribution of cells expressing these telomerase components and the over-expression of hTERT gene in individual cells.

Telomerase activity and expression of human telomerase RNA component and human telomerase reverse transcriptase in lung carcinomas

The aim of this study was to evaluate the usefulness of determination of telomerase activity and expression of human telomerase RNA component (hTERC) and human telomerase reverse transcriptase (hTERT) for the diagnosis of lung carcinomas. The tissues studied consisted of 115 carcinomas and adjacent nonneoplastic lung, which were removed surgically without previous chemotherapy or radiotherapy. Telomerase activity was determined using a semiquantitative polymerase chain reaction-based telomeric repeat amplification protocol (TRAP) assay. The results obtained were classified into high and low telomerase groups. Localization of expression was examined by using in situ hybridization and immunohistochemistry. The correlation between telomerase activity in lung carcinoma and clinicopathologic features, including prognosis, was investigated. Telomerase activity in lung carcinomas was detected in 107 of 115 (93%) lung carcinomas, but not in any adjacent noncancerous tissues, and was significantly higher in small cell carcinoma than in any other histologic type. This activity also was significantly higher in poorly differentiated than in well-differentiated squamous cell carcinomas and adenocarcinomas. The overall survival rate (P =.020) was significantly lower in the high telomerase group. Messenger RNAs for hTERC and hTERT were mainly detected in the cytoplasm of cancer cells by in situ hybridization, and TERT protein was localized in the nuclei of these cells by immunohistochemical staining. Determinations of telomerase activity by in situ hybridization, immunohistochemistry, and TRAP assay are useful for evaluating the diagnosis and prognosis of lung carcinomas.

Prognostic value of proliferation index and expression of the RNA component of human telomerase (hTR) in papillary meningiomas

Papillary meningioma is a rare subtype of meningioma that often behaves aggressively. In order to characterize factors that may influence this behavior, we chose to compare MIB-1 labeling index (LI) and telomerase RNA localization (hTR) in papillary meningiomas, meningiomas, and atypical meningiomas. LI is now often used to supplement histologic grade in the evaluation of these lesions. More recent studies indicate that increased expression of hTR is detected in many neoplastic cells, and may play an essential role in cell immortalization. The study group consisted of five papillary meningiomas (and a recurrence in one case), 11 conventional meningiomas, and eight atypical meningiomas. Conventional meningiomas showed either negative or 1 + hTR. Atypical meningiomas showed 1 + hTR. Papillary meningiomas showed the highest hTR (five of six, including recurrence, 2-3+ and one 1+). Generally, the LI was very low for conventional meningiomas (< 2%). The LI of atypical meningiomas ranged from 3-19%, mean 12%, and from 5.5-17.5%, mean 11.75% for papillary meningiomas. LI differentiated between meningiomas, and papillary or atypical meningiomas. hTR further delineated papillary (moderate to high) from atypical meningiomas (low). The combined variable of LI and hTR expression could be a useful independent prognostic indicator in patients with papillary meningioma.

Role of telomerase in cell senescence and oncogenesis

The ends of linear chromosomes are capped by specialized nucleoprotein structures termed telomeres. Telomeres comprise tracts of noncoding hexanucleotide repeat sequences that, in combination with specific proteins, protect against degradation, rearrangement, and chromosomal fusion events. Due to the polarity of conventional DNA synthesis, a net loss of telomeric sequences occurs at each cell division. It has been proposed that this cumulative telomeric erosion is a limiting factor in replicative capacity and elicits a signal for the onset of cellular senescence. To proliferate beyond the senescent checkpoint, cells must restore telomere length. This can be achieved by telomerase, an enzyme with reverse-transcriptase activity. This enzyme is absent in differentiated somatic tissues, but telomerase reactivation has been detected in most tumors. Much investigative effort is focusing on telomere dynamics with a view to possible manipulation of cellular proliferative potential. In this article, we review the role of telomeres and telomerase in senescence and tumor progression, and we discuss the potential use of telomerase in diagnosis and treatment.

Clinical usefulness of telomerase assay for the detection of lymph node metastasis in patients with oral malignancy

OBJECTIVE

Telomerase is considered a diagnostic marker of malignancy. We investigated the usefulness of telomerase assay for the detection of lymph node micrometastasis.

METHODS

Sixteen cervical lymph nodes with metastasis of oral cancer and 20 benign lymph nodes were studied. The oral cancer cell line was used to estimate the sensitivity for telomerase assay. Telomerase activity was measured by semiquantitative telomeric repeat amplification protocol.

RESULTS

There was a significant difference between malignant and benign lymph nodes. The telomerase activity of 50 mg of lymph nodes with 103 or more cancer cells differed from that of control lymph nodes. Lymph nodes with 102 or fewer tumor cells expressed similar levels as benign lymph nodes.

CONCLUSIONS

In addition to routine histologic examination, telomerase assay is considered a useful tool for the detection of lymph node metastasis in patients with oral malignancy.

Telomerase expression in uveal melanoma

BACKGROUND/AIMS

Accumulating evidence indicates that telomerase activity is repressed in normal human somatic cells but reactivated in cancers and immortal cells, suggesting that activation of telomerase activity has a role in carcinogenesis and immortalisation. To date, telomerase in uveal melanoma and, whether, it may have a role in the development or progression of these tumours has not been described. The expression patterns and the activity of telomerase were investigated in 14 uveal melanoma and these results were correlated with histological and immunohistological features of these tumours.

METHODS

A modified PCR based telomeric repeat amplification protocol (TRAP) assay was used to demonstrate telomerase activity in 14 uveal melanomas. In addition, in situ hybridisation was used to demonstrate the expression pattern of the telomerase RNA component (hTR) at the single cell level in eight of these globes.

RESULTS

The TRAP assay revealed moderate telomerase activity in all uveal melanomas examined. In situ hybridisation visualised a moderate to high upregulation of hTR in the melanoma cells but not in the admixed reactive cells. There was no correlation among tumour location, cell type, or growth fraction and the amount of telomerase activity. In addition, the cells of the germinative zone of the lens demonstrated a strong hTR expression.

CONCLUSION

Telomerase activity is upregulated in uveal melanomas. The expression of hTR was located to the tumour cells and not the reactive tumour infiltrating cells. Strong telomerase expression was also demonstrated in cells of the germinative zone of the lens.

Telomerase activity in thyroid malignancy

Telomerase activity seems to play a role in the development and pathogenesis of thyroid carcinoma. Its incidence of expression and its application as a tumor marker remain to be elucidated. Thyroid tissues obtained during thyroidectomy from 1996-1998 were rapidly frozen and stored at -80 degrees C until processed. Telomerase activity was determined using telomeric repeat amplification protocol (TRAP). Histology of the tissue examined (67 benign and 59 malignant) was reviewed. Telomerase activity was detected in 15 of 52 papillary carcinomas (29%); 1 of 1 thyroid lymphoma (100%); 1 of 2 anaplastic carcinomas (50%); and 2 of 16 lymphocytic thyroiditis specimens (13%). Telomerase activity was not detectable in 35 normal thyroid, 9 follicular adenoma, 7 nodular hyperplasia, 2 follicular carcinoma, and 2 medullary carcinoma. Lymphocytic thyroiditis was detected in 8 of 37 (22%) apparently normal thyroid tissues adjacent to papillary thyroid carcinoma and telomerase activity was present in 2 of these 8 specimens (25%). In conclusion, telomerase does not appear to be frequently activated in papillary thyroid carcinoma. The association of lymphocytic thyroiditis with papillary thyroid carcinoma may limit its clinical usefulness as a tumor marker.

Telomerase RNA expression during progression of gastric cancer

Telomerase, an enzyme associated with cellular immortality and malignancy, is stringently repressed in most normal somatic cells but is reactivated in malignant tumor cells and immortal cell lines, indicating that activation of telomerase may play an important role in tumorigenesis and immortalization. The pattern of human telomerase RNA (hTR) expression during progression of gastric cancer was investigated by a radioactive in situ hybridization (ISH) assay. Paraffin-embedded sections of 85 archival samples from Korean patients with benign and various malignant stages of gastric carcinomas as well as normal and regenerative tissues were studied. In normal gastric mucosae and regenerative lesions such as chronic peptic ulcer and hyperplastic polyps, only a weak degree of hTR expression was noted, and the expression was limited to basal cells of the gastric glands. Also, a moderate degree of hTR expression was present in the germinal centers of lymphoid follicles present in the submucosa. In tubular adenomas, the degree of hTR expression was also generally weak, but, unlike normal gastric mucosa, the expression was rather diffuse and occasionally focal in distribution. However, moderate to intense and usually diffuse hTR expression was present in all cancerous tissues at different stages. Although some heterogeneity of hTR expression was noted, there was a tendency for intensity of hTR expression to increase gradually as the cancer progressed to a more advanced stage. Our results indicate that upregulation of telomerase expression is associated with gastric cancer development or plays some role in gastric carcinogenesis. Upregulation of hTR expression detected by ISH assay may be a useful marker or tool for the early detection of gastric cancer.

Detection of telomerase in hepatocellular carcinomas using a PCR ELISA assay: comparison with hTR expression

BACKGROUND

While telomerase is undetectable in most normal somatic tissues, telomerase activation has been detected in many immortal cell lines and various cancers.

AIM

To investigate telomerase expression in hepatocellular carcinoma, and to assess the expression of the RNA component of telomerase, hTR.

METHODS

39 hepatocellular carcinomas were studied using a telomerase polymerase chain reaction (PCR) enzyme linked immunosorbent assay, which does not require radioactive PCR amplification and yields a semiquantitative measurement. Expression of hTR was also assessed by a non-radioactive in situ hybridisation procedure. The correlations between these two markers and the clinicopathological data were analysed.

RESULTS

Telomerase activity was detected in 23 of 39 hepatocellular carcinoma specimens (59%). Comparison of hepatocellular carcinoma with and without telomerase expression, or with high and low telomerase (10 cases v 13 cases), showed no differences in the principal clinicopathological data. Although median survival was lower in the group with detectable telomerase activity than in that with undetectable activity (510 v 720 days) the difference was not significant (log-rank test, p = 0.08). hTR expression was detected in 11 of 14 cases of hepatocellular carcinoma tested (78%) and in four of 12 samples of adjacent non-cancerous tissue (33%). Five tumours and four non-cancerous tissues were positive for hTR, whereas no telomerase activity was detected in these.

CONCLUSIONS

The presence of telomerase activity in hepatocellular carcinomas is confirmed. No correlation was observed between clinicopathological data and telomerase expression in hepatocellular carcinoma, but survival seemed better in the absence of telomerase expression. hTR seems to be more widely expressed than telomerase.

Expression of the RNA component of human telomerase (hTR) in prostate cancer, prostatic intraepithelial neoplasia, and normal prostate tissue

Telomerase is a ribonucleoprotein that synthesizes telomeric DNA on chromosomal ends. While telomerase is undetectable in most normal somatic tissues, telomerase activation has been detected by a polymerase chain reaction (PCR)-based assay (TRAP) in many immortal cell lines and various cancers, including prostate cancers. To investigate the role of telomerase in prostate cancer at the cellular level, the expression of one of the ribonucleoprotein complexes, the RNA component of human telomerase (hTR), was studied in normal, preneoplastic, and cancerous prostate tissues using a non-radioactive in situ hybridization procedure. Nine human prostates resected at the time of radical prostatectomy were studied. In each case, archival paraffin-embedded samples from normal tissue, prostatic intraepithelial neoplasia (PIN) lesions, the putative precancerous lesion, and prostate carcinomas were selected for in situ hybridization. hTR mRNA expression was detected in carcinomatous glands of seven out of the nine cancers (75 per cent). Furthermore, in seven out of the eight cases showing PIN lesions, the epithelial cells of PIN foci also expressed hTR mRNA. By contrast, in normal tissue, epithelial cells were negative, whereas hTR mRNA expression was detected in the basal cells. The detection of hTR mRNA in PIN lesions clearly strengthens the link between PIN and carcinomatous glands and suggests that telomerase expression occurs early in prostate carcinogenesis. Furthermore, this study confirms previous experimental data suggesting that the basal cell layer is the stem cell compartment in prostate.

Telomerase activity and in situ telomerase RNA expression in oral carcinogenesis

To investigate the role of telomerase in oral carcinogenesis, we assayed telomerase activity in various oral tissues by a modified telomeric repeat amplification protocol (TRAP) analysis. Also, using digoxigenin-labeled probes, we measured the in situ expression of human telomerase RNA component (hTR) in paired oral squamous cell carcinomas (OSCC) and adjacent non-cancerous matched tissue (NCMT). We detected telomerase activity in three OSCC cell lines, but not in primary oral keratinocytes. In patient samples, most OSCC (36/42, 86%) and oral premalignant lesions (8/12, 67%) possessed telomerase activity. In addition, 6 of 27 (22%) NCMT contained weak telomerase activity. In situ hybridization showed that hTR was expressed in almost all OSCC (23/27, 85%) as well as in the majority of NCMT (20/25, 80%). In most cases, accumulation of hTR was observed both in the nucleus and cytoplasm of epithelial cells. A correlation between hTR expression and more advanced tumor grade was observed. The appearance of telomerase activation and hTR expression during oral carcinogenesis was different. This study indicates that the activation of telomerase is an early and frequent event in OSCC.

Both transcriptional and posttranscriptional mechanisms regulate human telomerase template RNA levels

The human telomerase RNA component (hTR) is present in normal somatic cells at lower levels than in cancer-derived cell lines. To understand the mechanisms regulating hTR levels in different cell types, we have compared the steady-state hTR levels in three groups of cells: (i) normal telomerase-negative human diploid cells; (ii) normal cells transfected with the human telomerase catalytic subunit, hTERT; and (iii) cells immortalized in vitro and cancer cells expressing their own endogenous hTERT. To account for the differences in steady-state hTR levels observed in these cell types, we compared the transcription rate and half-life of hTR in a subset of these cells. The half-life of hTR in telomerase-negative cells is about 5 days and is increased 1.6-fold in the presence of hTERT. The transcription rate of hTR is essentially unchanged in cells expressing exogenous hTERT, and the increased steady-state hTR level appears to be due to the increased half-life. However, the transcription rate of hTR is greatly increased in cells expressing endogenous hTERT, suggesting some overlap in transcriptional regulatory control. We conclude that the higher hTR level in cells expressing an endogenous telomerase can be a result of both increased transcription and a longer half-life and that the longer half-life might be partially a result of protection or stabilization by the telomerase catalytic subunit. The 4-week half-life of hTR in H1299 tumor cells is the longest half-life yet reported for any RNA.

Hodgkin and Reed-Sternberg cells of classical Hodgkin's disease overexpress the telomerase RNA template (hTR)

There is accumulating evidence to suggest that Hodgkin and Reed-Sternberg (HRS) cells represent the malignant cell population in Hodgkin's disease (HD). A recent report that HD tissue is in most instances devoid of telomerase activity was therefore unexpected. Since telomerase activity was determined in whole tissue extracts and HRS cells comprise only a small minority of the cells in the affected tissue, the telomerase activity of the HRS cells might have escaped detection. To test this possibility and to clarify whether HRS cells contain the enzyme telomerase, 13 cases of classical HD were analysed by three different methods. The presence of telomerase was studied at the single cell level by a sensitive radioactive in situ hybridization method employing a probe specific for the telomerase RNA template (hTR). In addition, tissue extracts were studied for telomerase activity by a modified TRAP assay and for hTR by reverse transcription-polymerase chain reaction (RT-PCR). The extractive methods revealed telomerase activity in eight and hTR in all of the 13 HD cases studied. In situ hybridization located large amounts of hTR in the HRS cells of all 13 HD cases and low to medium amounts in some of the non-malignant lymphoid bystander cells. These results indicate that HRS cells constitutively overexpress telomerase and thus use this enzyme for stabilizing their telomeres. This substantiates the malignant nature of HRS cells. Furthermore, the results confirm that normal lymphoid cells can express telomerase. In consequence, methods of measuring telomerase in tissue extracts are not suitable for determining the presence of this molecule in lymphoma cells, since the vast majority of lymphoid neoplasms contain significant amounts of non-neoplastic lymphoid cells.

Progressive increase in telomerase activity from benign melanocytic conditions to malignant melanoma

The expression of telomerase activity and the in situ localization of the human telomerase RNA component (hTR) in melanocytic skin lesions was evaluated in specimens from sixty-three patients. Specimens of melanocytic nevi, primary melanomas and subcutaneous metastases of melanoma were obtained from fifty-eight patients, whereas metastasized lymph nodes were obtained from five patients. Telomerase activity was determined in these specimens by using a Polymerase Chain Reaction-based assay (TRAP). High relative mean telomerase activity levels were detected in metastatic melanoma (subcutaneous metastases = 54.5, lymph node metastases = 56.5). Much lower levels were detected in primary melanomas, which increased with advancing levels of tumor cell penetration (Clark II = 0.02, Clark III = 1.1, and Clark IV = 1.9). Twenty-six formalin-fixed, paraffin-embedded melanocytic lesions were sectioned and analyzed for telomerase RNA with a radioactive in situ hybridization assay. In situ hybridization studies with a probe to the template RNA component of telomerase confirmed that expression was almost exclusively confined to tumor cells and not infiltrating lymphocytes. These results indicate that levels of telomerase activity and telomerase RNA in melanocytic lesions correlate well with clinical stage and could potentially assist in the diagnosis of borderline lesions.

Applications of telomerase research in the fight against cancer

Telomerase, an enzyme that confers immortality upon cells and that is active in the majority of human tumors, has emerged as a powerful new marker and potential prognostic indicator and therapeutic target for cancer. Furthermore, investigations into the biology of telomerase have revealed important clues into the causes of cell death and have made progress toward answering one of the most important questions of cancer research - what gives a tumor cell an advantage over normal cells? In this article, we present the current state of telomerase research and critically assess both its potential and the pitfalls of its application in cancer diagnosis and treatment.