Telomerase expression in normal endometrium, endometrial hyperplasia, and endometrial adenocarcinoma

Endometrial telomerase activity in women with either endometrial cancer or hyperplasia: A systematic review and meta-analysis

AIM

We performed a systematic review and meta-analysis to assess whether endometrial telomerase activity is associated with endometrial cancer or hyperplasia.

METHODS

PubMed, Web of Science, Embase, Scielo, LILAC, and CNKI databases were searched to obtain relevant literature for articles published through June 2022, following PRISMA guidelines and a registered PROSPERO protocol. We included observational studies reporting endometrial telomerase activity in patients with either endometrial cancer or hyperplasia compared with benign endometrial tissue (control women). The Newcastle-Ottawa Scale was used to evaluate the quality of studies. Data were expressed as the odds ratios (OR) and 95 % confidence intervals (CI). Random effects and inverse variance methods were used to meta-analyze associations. The I² test was used to assess heterogeneity.

RESULTS

There were significant associations between endometrial telomerase activity and either endometrial cancer (20 studies, OR = 10.65, 95 % CI 6.39, 17.75, p = 0.00001, I² = 21 %) or endometrial hyperplasia (nine studies, OR = 3.62, 95 % CI 1.61, 8.13, p = 0.002, I² = 36 %) compared to women without endometrial cancer and hyperplasia. There was not a significant difference in telomerase activity in women with endometrial cancer compared to those with endometrial hyperplasia (seven studies, OR = 1.03; 95 % CI 0.31, 3.37, p = 0.96, I² = 49 %). In subgroup analyses, there were no significant differences in telomerase activity in patients with endometrial cancer by type of observational studies and by countries of the studies.

CONCLUSION

Endometrial telomerase activity is higher in women with either endometrial cancer or endometrial hyperplasia compared to control women without those lesions.

Telomerase and Telomeres in Endometrial Cancer

Telomeres at the termini of human chromosomes are shortened with each round of cell division due to the “end replication problem” as well as oxidative stress. During carcinogenesis, cells acquire or retain mechanisms to maintain telomeres to avoid initiation of cellular senescence or apoptosis and halting cell division by critically short telomeres. The unique reverse transcriptase enzyme complex, telomerase, catalyzes the maintenance of telomeres but most human somatic cells do not have sufficient telomerase activity to prevent telomere shortening. Tissues with high and prolonged replicative potential demonstrate adequate cellular telomerase activity to prevent telomere erosion, and high telomerase activity appears to be a critical feature of most (80–90%) epithelial cancers, including endometrial cancer. Endometrial cancers regress in response to progesterone which is frequently used to treat advanced endometrial cancer. Endometrial telomerase is inhibited by progestogens and deciphering telomere and telomerase biology in endometrial cancer is therefore important, as targeting telomerase (a downstream target of progestogens) in endometrial cancer may provide novel and more effective therapeutic avenues. This review aims to examine the available evidence for the role and importance of telomere and telomerase biology in endometrial cancer.

Implications of telomeres and telomerase in endometrial pathology

BACKGROUND

Eukaryotic chromosomal ends are linear and are protected by nucleoprotein complexes known as telomeres. The complex structural anatomy and the diverse functions of telomeres as well as the unique reverse transcriptase enzyme, telomerase that maintains telomeres are under intensive scientific scrutiny. Both are involved in many human diseases including cancer, but also in ageing and chronic disease such as diabetes. Their intricate involvement in many cellular processes and pathways is being dynamically deciphered in many organs including the endometrium. This review summarizes our current knowledge on the topic of telomeres and telomerase and their potential role in providing plausible explanations for endometrial aberrations related to common gynaecological pathologies.

OBJECTIVE AND RATIONALE

This review outlines the recent major findings in telomere and telomerase functions in the context of endometrial biology. It highlights the contemporary discoveries in hormonal regulation, normal endometrial regeneration, stem cells and common gynaecological diseases such as endometriosis, infertility, recurrent reproductive failure and endometrial cancer (EC).

SEARCH METHODS

The authors carried out systematic PubMed (Medline) and Ovid searches using the key words: telomerase, telomeres, telomere length, human telomerase reverse transcriptase, telomeric RNA component, with endometrium, hormonal regulation, endometrial stem/progenitor cells, endometrial regeneration, endometriosis, recurrent miscarriage, infertility, endometrial hyperplasia, EC and uterine cancer. Publications used in this review date from 1995 until 31st June 2016.

OUTCOMES

The human endometrium is a unique somatic organ, which displays dynamic telomerase activity (TA) related to the menstrual cycle. Telomerase is implicated in almost all endometrial pathologies and appears to be crucial to endometrial stem cells. In particular, it is vital for normal endometrial regeneration, providing a distinct route to formulate possible curative, non-hormonal therapies to treat chronic endometrial conditions. Furthermore, our current understanding of telomere maintenance in EC is incomplete. Data derived from other malignancies on the role of telomerase in carcinogenesis cannot be extrapolated to EC because unlike in other cancers, TA is already present in proliferating healthy endometrial cells.

WIDER IMPLICATIONS

Since telomerase is pivotal to endometrial regeneration, further studies elucidating the role of telomeres, telomerase, their associated proteins and their regulation in normal endometrial regeneration as well as their role in endometrial pathologies are essential. This approach may allow future development of novel treatment strategies that are not only non-hormonal but also potentially curative.

The status of telomerase enzyme activity in benign and malignant gynaecologic pathologies

BACKGROUND

Telomeres are essential for the function and stability of eukaryotic chromosomes. Telomerase consists of three subunits: human telomerase reverse transcriptase (hTERT), human telomerase RNA (hTR), and telomerase protein 1 (TP1). The hTERT subunit determines the activity of telomerase as an enzyme and is detected in most human tumors and regenerative cells. Telomerase activity is a useful cancer-cell detecting marker in some types of cancers.

AIMS

The aim of this study was to assess of telomerase hTERT mRNA in gynaecological tumors for diagnosis of malignancy.

STUDY DESIGN

Cross-sectional study.

METHODS

A total of 55 gynaecologic tumor samples (35 ovarian, 13 endometrial, 6 cervical and 1 placental site trophoblastic tumor tissue) were obtained at the time of surgery. Quantification of hTERT mRNA was performed in a real-time reverse transcriptase polymerase chain reaction (RT-PCR) using the LightCycler TeloTAGGG hTERT Quantification Kit.

RESULTS

It was histopathologically detected that 18 of the tissue samples were malignant and 37 of the samples were benign. 16 of the malignant tissue samples (88.9%) and 3 (8.1%) (endometrial tissue in proliferative phase, mucinous cyst adenoma and endometriosis) of the benign tissue samples were found to be hTERT positive. With the presence of these data, sensitivity and specificity of hTERT for the diagnosis of malignancy were calculated to be 88.9% and 91.9%, respectively.

CONCLUSION

It was suggested that the measurement of telomerase activity in gynaecologic tumors, except for endometrial tissue in the reproductive phase, is a valuable method for pathological investigation.

Molecular targets in gynaecological cancers

The application of high throughput expression profiling and other advanced molecular biology laboratory techniques has revolutionised the management of cancers and is gaining attention in the field of gynaecological cancers. Such new approaches may help to improve our understanding of carcinogenesis and facilitate screening and early detection of gynaecological cancers and their precursors. Individualised prediction of patients' responses to therapy and design of personalised molecular targeted therapy is also possible. The studies of various molecular targets involved in the various signal pathways related to carcinogenesis are particularly relevant to such applications. At the moment, the application of detection and genotyping of human papillomavirus in management of cervical cancer is one of the most well established appliances of molecular targets in gynaecological cancers. Methylation, telomerase and clonality studies are also potentially useful, especially in assisting diagnosis of difficult clinical scenarios. This post-genomic era of clinical medicine will continue to make a significant impact in routine pathology practice. The contribution of pathologists is indispensable in analysis involving tissue microarray. On the other hand, both pathologists and bedside clinicians should be aware of the limitation of these molecular targets. Interpretation must be integrated with clinical and histopathological context to avoid misleading judgement. The importance of quality assurance of all such molecular techniques and their ethical implications cannot be over-emphasised.

Increased telomerase activity and human telomerase reverse transcriptase mRNA expression in the endometrium of patients with endometriosis

BACKGROUND

Endometriosis is considered a frequent, benign disease with the ability to undergo neoplastic processes. The aim of this study was to evaluate the limitless replication potential of the endometrium in patients with endometriosis by examining human telomerase reverse transcriptase (hTERT) mRNA expression and telomerase activity.

METHODS

Endometrium samples from 30 endometriosis patients and 30 patients without endometriosis were obtained via endometrial biopsy. The expression of hTERT mRNA was determined by real-time RT-PCR assay, and telomerase activity was measured by telomerase repeat amplification protocol (TRAP) assay.

RESULTS

The mean normalized hTERT (N hTERT) mRNA level was significantly higher in the endometriosis than in the control group (P = 0.013). The mean hTERT mRNA levels during the proliferative phase and during the secretory phase were higher in the endometriosis group than in the control group, although the difference was only significant for the secretory phase (P = 0.036). We found a prominent difference in endometrial telomerase activity between moderate-to-severe endometriosis and the control group (P = 0.048). The levels of hTERT mRNA and telomerase activity increased as the disease became more severe (P = 0.038, P = 0.016).

CONCLUSIONS

This study showed the overexpression of hTERT mRNA and telomerase activity in the endometrium of endometriosis patients. These finding suggest that replication potential of endometrial cells may have an important role in the pathogenesis of endometriosis.

Estrogen-receptor-dependent regulation of telomerase activity in human endometrial cancer cell lines

OBJECTIVES

Given that prolonged exposure to unopposed estrogen is associated with endometrial cancer development and that the promoter region of the catalytic subunit of the telomerase enzyme, hTERT, contains putative estrogen response elements (EREs), we postulated that estrogen-receptor (ER)-mediated induction of telomerase activity may play an important role in endometrial carcinogenesis.

METHODS

ER-positive and ER-negative endometrial cancer cell lines were used. ER alpha expression was reconstituted in ER-negative cell lines by transient transfection. Telomerase activity was assayed using a PCR-based telomeric repeat amplification protocol (TRAP) after exposure to estradiol (E2). hTERT mRNA expression was assessed by real-time RT-PCR. Gel shift assays using oligonucleotide probes encoding each ERE and transient expression assays using luciferase reporter plasmids containing varying lengths of the 5' promoter region of the hTERT gene were performed.

RESULTS

E2 induced both hTERT gene transcription and telomerase activity in the ER-positive cell lines, but not in the ER-negative cell lines. Transfection of ER alpha into ER-negative cell lines restored E2-induced hTERT gene transcription and telomerase activity. Gel shift assays revealed two EREs in the hTERT promoter that specifically bind to ER alpha. Luciferase assays demonstrated that at least the proximal ERE is responsible for transcriptional activation by ligand-stimulated ER alpha.

CONCLUSIONS

Telomerase activity and hTERT mRNA were increased in response to estrogen in an ER alpha-dependent fashion in endometrial cancer cells. Binding of complexed estrogen with ER alpha to the EREs found within the hTERT promoter suggests a possible mechanism for telomerase induction that may facilitate the malignant transformation of hormone-dependent endometrial cells.

Immunohistochemical Detection of Human Telomerase Reverse Transcriptase (hTERT), Topoisomerase II?? Expression, and Apoptosis in Endometrial Adenocarcinoma and Atypical Hyperplasia

This study evaluated the immunohistochemical expression of human telomerase reverse transcriptase (hTERT) in endometrial carcinoma and atypical endometrial hyperplasia, and related it to the expression of topoisomerase (TP)IIalpha (a proliferation associated enzyme); apoptosis as determined by the frequency of apoptotic bodies (ABI); mitotic counts; and other clinicopathologic variables. Immunoreactivity for hTERT and TPIIalpha as well as ABI were assessed in 57 endometrial samples (12 atypical hyperplasias, 33 endometrioid carcinomas, 12 serous/clear cell carcinomas). hTERT immunoreactivity, TPIIalpha labeling indices (LI), ABI, and ratios of the indices (ABI/TPIIalpha LI) increased from atypical hyperplasias to endometrioid carcinomas to serous/clear cell carcinomas (p < 0.0001 for each variable). hTERT expression increased with ABI (p < 0.0001), TPIIalpha LI (p = 0.0019), ABI/TPIIalpha ratios (p < 0.0001), and grade (p = 0.0005), but not with FIGO stage (p = 0.2775). TPIIalpha LI, ABI, and ratios were related to high grade (p = 0.0001 for each variable), but not with FIGO stage (p = 0.7362, p = 0.7554, and p = 0.7405, respectively). TPIIalpha LI and ABI were significantly correlated in atypical hyperplasias (p = 0.0004), endometrioid carcinomas (p < 0.0001), and serous/clear cell carcinomas (p = 0.024). Immunostaining levels for hTERT were similar in atypical hyperplasias and grade 1 endometrioid carcinomas (p = 0.1956). These results suggest that hTERT expression is closely related to proliferation, apoptosis, and high grade in endometrial carcinomas, reflecting cell cycle deregulation in endometrial carcinogenesis.

Is the telomerase assay useful for screening of endometrial lesions?

Telomerase activation is specifically observed in most cancers but not in normal tissues with some exceptions, such as germ cells or certain tissues with regenerative potential, suggesting a diagnostic opportunity for cancers involving measurement of telomerase activity. Cytologic screening for endometrial cancer has not been well established, due to the complexity of diagnostic criterion. In the present study, we investigated the utility of the telomerase assay for screening endometrial lesions. A total of 100 patients with or without endometrial lesions were examined for telomerase activity by the telomeric repeat amplification protocol (TRAP) assay using endometrial scraping samples and the correlation with cytology was investigated. The TRAP assay revealed frequent telomerase activation in normal endometria at reproductive age, particularly in 67% of proliferative-phase endometria, suggesting that the telomerase assay is not suitable for screening women of reproductive age. However, in postmenopausal women, telomerase activity was rarely detected (8%) in normal endometria, while it was observed in >80% of endometrial cancers or hyperplasias. Interestingly, some cases of endometrial cancer and hyperplasia were misdiagnosed by cytology but correctly detected by the TRAP assay. The sensitivity of the TRAP assay to screen endometrial lesions was 87%, equivalent to that of cytology. Combination of cytology and the TRAP assay increased sensitivity to 100%. We thus concluded that measuring telomerase activity in endometrial scrapings is a useful diagnostic tool for the screening of endometrial lesions in postmenopausal women, particularly when used with cytology to increase screening sensitivity.

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.

Analysis of telomerase as a diagnostic biomarker of cervical dysplasia and carcinoma

Telomerase expression is a potentially important marker of high-grade cervical dysplasia and squamous cell carcinoma (SCC). The routine practice of cervical cytology is limited by problems of false negative diagnoses as well as by poor specificity for clinically significant lesions in patients with low-grade cytologic abnormalities. Telomerase is widely expressed in most SCCs as well as in a high proportion of high-grade squamous intraepithelial lesions. Histochemical studies have confirmed that telomerase is expressed in the lower portions of normal or metaplastic squamous mucosa but that telomerase positive cells extend into the upper epithelial layers in cases of high-grade dysplasia. Since the cervical smear samples the uppermost cell layers of the cervical mucosa, but does not normally include cells derived from the lower layers of the squamous mucosa, the detection of telomerase in exfoliated cells of the cervical smear may have specificity for clinically significant lesions. The analysis of hTR, hTERT, and telomerase activity are complicated by a number of technical factors that may lead to either false negative or false positive test results. Thus, the practical application of telomerase analysis as a diagnostic adjunct for cervical cytopathology may depend on the development of more reliable and sensitive assay systems, possibly formatted for cytochemical applications.

Quantitative analysis of telomerase hTERT mRNA and telomerase activity in endometrioid adenocarcinoma and in normal endometrium

OBJECTIVES

In the current study, the quantitative levels of telomerase hTERT mRNA and the functional telomerase repeat amplification protocol (TRAP) assay were correlated with tumor grade in endometrial carcinomas and with the histologic phase of normal endometrium.

METHODS

Twenty-six samples of endometroid adenocarcinoma and 20 cases of benign endometrium were obtained from hysterectomy specimens. Total RNA was extracted from each tissue sample and used for quantitative real-time RT-PCR of hTERT mRNA and the levels were standardized to the levels of ribosomal RNA. Quantitative determination of telomerase activity was performed by the polymerase chain-based TRAP assay and the levels of expression were defined by the ratio of radioactivity incorporated into the 6-bp telomerase amplification products versus the radioactivity incorporated into an internal standard (telomerase/ITAS x 100 = 1 RU). Statistical analyses were performed using the Fisher exact test or chi2 test, a Wilcoxon rank sum test, and a linear regression analysis.

RESULTS

hTERT mRNA and telomerase activity levels showed a linear association in the study group (P = 0.006, R2 = 0.139). hTERT mRNA levels and telomerase activity levels were significantly higher in endometrial cancer (179 pg/ng rRNA, 44 relative units (RU)) than in normal endometrium (45 pg/ng), (15 RU) (P = 0.009, P = 0.006). In normal endometrium, hTERT mRNA and telomerase activity levels were highest in the proliferative phase (74 pg/ng rRNA, 25 RU) and were relatively low in secretory (13 pg/ng rRNA, 6 RU) and atrophic endometrium (9 pg/ng rRNA, 2 RU).

CONCLUSION

These results suggest that the quantitative analysis of hTERT and telomerase activity may have potential roles as diagnostic or prognostic adjuncts for both premenopausal and postmenopausal patients with endometrial cancer.

A prospective, randomized study of endometrial telomerase during the menstrual cycle

The purpose of this study was to characterize telomerase activity during the menstrual cycle, focusing on the luteal phase. A total of 84 endometrial biopsy samples were obtained from 72 participants. Daily urinary LH testing (OvuQuick, Quidel) was used to establish the day of the LH rise, and participants were randomized to return during the secretory phase. Twelve women returned on the identical day during the luteal phase of a subsequent cycle to allow intercycle comparisons of telomerase activity. Telomerase activity was evaluated using a modified TRAP-eze (Intergen) detection protocol. At the time of each endometrial biopsy, serum estrogen and progesterone were measured. Proliferative phase endometrium showed high telomerase activity. At the onset of the luteal phase telomerase activity was high, but it decreased during the early luteal phase, disappeared by the midluteal phase (6 d after LH surge detected), and then rose to moderate levels in the late luteal phase beginning on luteal d 10. Serum progesterone levels were inversely related to telomerase activity. In conclusion, endometrial telomerase activity is dynamic: high during the proliferative phase but inhibited during the midsecretory phase of the menstrual cycle. The timing of expression coincides with the rise and fall of progesterone levels and the time period of maximal uterine receptivity for embryo implantation. This supports a relationship between sex steroid levels and telomerase regulation.

High telomerase activity is associated with cell cycle deregulation and rapid progression in endometrioid adenocarcinoma of the uterus

Telomerase activity, a mechanism granting cellular immortality, has been detected in most cancer entities, but its association with clinical, histopathologic, and prognostic parameters is not fully understood. We investigated whether quantitative telomerase levels are correlated to established prognostic factors, telomere lengths, cell cycle kinetics, and the clinical course in endometrioid adenocarcinoma of the uterus (EC). A modified telomeric repeat amplification protocol (TRAP) was used to quantify the relative telomerase activity in a series of 53 primary tumors. Mean telomere length was determined by Southern blot analysis. Cell cycle kinetics were studied immunohistochemically on paraffin sections using monoclonal antibodies to 2 distinct proliferation-specific proteins: Ki-67, which is expressed throughout the cell cycle, and a novel cell cycle-associated protein, repp86, the expression of which is restricted to the cell cycle phases S, G2, and M. The ratio of the 2 immunolabeling indices defines the rate of transition through the restriction point. Telomerase activity was detected in 50 of 53 ECs (94%). Its levels correlated significantly with FIGO stage (P =.01) and FIGO grade (P =.003) but not with myometrial invasion. They were weakly associated with the overall proliferative activity (Ki-67, r =.48) but significantly with the repp86 index (r =.64) and even more strongly with the repp86:Ki-67 ratio (r =.77). There was no correlation with mean telomere length. In the group of tumors with high telomerase activity, 5 patients had relapses and 2 died of the disease within a median follow-up period of 29 months. Recurrence showed no relation to FIGO grade and stage. No events were observed in the group with low telomerase activity. In a multivariate model including tumor stage, histopathologic grade, depth of myometrial invasion, and Ki-67 indices, telomerase activity emerged as the only independent predictor of disease progression (P =.0002). It is concluded that beyond a link to proliferation, high telomerase activity reflects a deregulation of the cell cycle associated with an increased rate of cells entering S phase and a higher degree of malignancy. Therefore, quantitative analysis of telomerase activity may be useful for identifying EC patients at high risk for recurrence.

Telomerase, immortality and cancer

Replication of eukaryotic linear chromosomes is incomplete and leaves terminal gaps. The evolutionary widely distributed solution to this "end replication" is twofold: chromosome ends are capped with telomeres, bearing multiple copies of redundant telomeric sequences, and the telomerase enzyme can add (lost) telomeric repeats. Telomerase in humans, as in all mammals, is ubiquitous in all embryonic tissues. In adults, telomerase remains active in germs cells, and, although down-regulated in most somatic tissues, telomerase is active in regenerative tissues and notably, in tumor cells. Telomerase activity is linked to cellular proliferation, and its activation seems to be a mandatory step in carcinogenesis. In contrast to mammals, indeterminately growing multicellular organisms, like fish and crustaceae, maintain unlimited growth potential or 'immortality' in all somatic tissues throughout their entire life. Also this cell immortalization is brought about by maintaining telomerase expression. Disease prognosis for human tumors includes evaluation of cell proliferation, based on the detection of proliferation markers with monoclonal antibodies. The significance of the classical marker Ki-67, and of a novel marker repp-86 are compared with semiquantitative telomerase assays. For tumor therapy, telomerase inhibitors are attractive tools. Results with telomerase knock-out mice have revealed promise, but also risk of this approach. On the other side, telomerase stimulation is attractive for expanding the potential of cellular proliferation in vitro, with possible applications for transplantation of in vitro expanded human cells, for immortalizing primary human cells as improved tissue models, and for the isolation of otherwise intractable products, like genuine human monoclonal antibodies.

Telomerase activity correlates with histo-pathological factors in uterine endometrial carcinoma

Telomerase activity has been implicated in the progression of various human tumors. Our aim was to evaluate telomerase activity and to compare it with histo-pathological factors in uterine endometrial carcinoma, to look for possible correlations. Telomerase activity was measured by dilution analysis using a PCR-based telomeric repeat amplification method and detected in 31 of 35 primary endometrial carcinoma tumor specimens. High telomerase activity, detected after 100-fold dilution of extracts, was identified in 15 specimens. There was no significant correlation between the positive telomerase activity and tumor surgical stage or histo-pathological factors. However, high telomerase activity was significantly correlated with advanced surgical stage and with pelvic lymph node metastasis. Our findings suggest that an increase in telomerase activity may be associated with tumor progression and that its level may have a prognostic value in endometrial carcinoma.

Human telomerase reverse transcriptase as a critical determinant of telomerase activity in normal and malignant endometrial tissues

Telomerase activation is thought to be essential for cellular immortality and oncogenesis. It is observed in most malignant tumors but not in most normal somatic tissues. Normal human endometrium is, however, known to express significant telomerase activity in a menstrual phase-dependent manner. The 3 major subunits composing telomerase have been identified. Using normal and malignant endometrial tissues, we studied how these components are involved in telomerase activation. A total of 23 endometrial cancers and 32 normal human endometria in various menstrual phases as well as cell lines derived from endometrial cancer were examined for the expression of each telomerase subunit using RT-PCR analysis. Telomerase activity in each sample was determined by the TRAP assay, and the correlation between subunit expression and telomerase activity was examined. RT-PCR analysis revealed that telomerase RNA (hTR) and telomerase-associated protein (TP1) mRNA were constitutively expressed in both normal and malignant endometrial tissues. Expression of human telomerase reverse transcriptase (hTERT) mRNA was observed in most endometrial cancers, while that in normal endometrium depended on the phases of menstrual cycles. Proliferative phase normal endometria expressed hTERT mRNA, while secretory phase endometria did not. There was a strong association between telomerase activity and hTERT expression but not TP1 or hTR expression in both normal and tumor tissues. Five telomerase-positive endometrial cancer cell lines expressed each of the telomerase subunits including hTERT, while 2 telomerase-negative normal primary fibroblast cells expressed TP1 mRNA and hTR, but not hTERT mRNA. Our findings suggest that hTERT is a rate-limiting determinant of enzymatic activity of human telomerase. Since some normal tissues with high regenerative potential can express hTERT, special attention should be paid to the clinical use of hTERT inhibitors as anti-cancer drugs.

Analysis of telomerase expression and proliferative activity in the different layers of cyclic endometrium

To gain better insights into cell kinetics under physiological conditions, telomerase activity in the functional and basal layers of cyclic endometrium (n = 33) was compared with the immunostaining of glandular and stromal cells within these layers (n = 25). Two immunohistochemical proliferation markers were used to demarcate cells in the G1 phase of the cell cycle. In contrast to previous expectations, telomerase activity and both glandular and stromal proliferative activities were all significantly higher in the functional than in the basal endometrium (P < 0.002). The course of telomerase activity in the endometrial layers during the ovarian cycle was significantly associated with the proliferative scores for the functional and basal endometrial glands and the functional stroma but not the stromal compartment of the basal layer. Our findings indicate that the telomerase activity in cyclic endometrium is associated with the total number of proliferating glandular and stromal cells in the functional layer. Proliferating daughter cells of telomerase-competent stem cells may account for the lower levels of telomerase detected in normal basal endometrium.

Part I. Telomerase levels in human metastatic brain tumors show four-fold logarithmic variability but no correlation with tumor type or interval to patient demise

Telomerase expression has been found in the majority of human neoplasms at their primary sites and, in some tumor types, has been correlated with patient prognosis. In part one of this two-part study, we investigated whether telomerase was expressed ubiquitously in metastases to the brain and whether varying levels of expression existed or correlated with patient prognosis. A second aim of this study was to acquire data on brain metastases preliminary to the investigation of whether the telomerase assay could be used for the detection of tumor cells in cerebrospinal fluid (CSF). We investigated 35 brain metastases utilizing the sensitive telomeric repeat amplification protocol (TRAP) assay coupled with densitometric quantitation of telomerase levels on frozen, banked tissue specimens. Specimens metastatic to the brain analyzed in this study included melanoma, adenocarcinoma, hepatocellular carcinoma, germ cell neoplasm, squamous cell carcinoma, osteogenic sarcoma, and secondary lymphoma. Telomerase was found in 32 of 35 metastases. Quantitation of the telomerase products showed a fourfold logarithmic variation, following standardization of protein concentrations. Levels of telomerase expression showed no statistical correlation with either tumor subtype or interval from date of procedure to patient demise. Interestingly, in two patients with two metastatic samples each taken at discordant times, the telomerase levels were higher in the metastasis specimen taken closer to the time of demise. This suggests a possible increase in telomerase level within a given patient's neoplasm as the disease became more advanced, although too few cases were available to reach a firm conclusion in this regard. We conclude that most brain metastases express telomerase, albeit at widely varying levels, which are not clearly correlated with patient survival. These results influence the potential utility of telomerase analysis for the detection of small numbers of metastatic tumor cells in CSF, as addressed in the companion manuscript.

Part II. Telomerase expression in cerebrospinal fluid specimens as an adjunct to cytologic diagnosis

The diagnosis of meningeal carcinomatosis hinges on the cytologic examination of cerebrospinal fluid (CSF), which has a known low sensitivity for the identification of malignant cells. Often only 'suspicious' or 'atypical' diagnoses can be rendered, and specimens are commonly unsatisfactory for evaluation due to poor morphologic preservation. Telomerase is widely expressed in most brain metastases, medulloblastomas, lymphomas, oligodendrogliomas, and is expressed focally in glioblastomas. Little is known about the level of telomerase expression in these tumors, except for brain metastases, where a four-fold variation in telomerase levels exists. In our laboratory, as few as ten carcinoma cells can be detected by a sensitive polymerase chain reaction-based assay, the telomeric repeat amplification protocol (TRAP), for telomerase, but it was unclear whether varying levels of telomerase expressed by different types of metastases would influence detection. Using the TRAP protocol, we studied 281 CSF samples from a wide variety of patients with neurologic and non-neurologic conditions for telomerase expression. An adjusted specificity of 90% and a sensitivity of 64% were achieved for detection of malignant cells in CSF by telomerase expression. The TRAP assay for telomerase detection may serve as an adjunct to the traditional examination of CSF. Neither previously documented four-fold variation in the levels of telomerase expression in brain metastases, high CSF protein levels nor high white blood cell counts precluded detection of malignant cells in CSF.

Detection of telomerase expression in fine-needle aspirations and fluids

The cytologic examination of fine-needle aspirates and fluid specimens is plagued by a persistent false negative rate. The rate of false negative results will be decreased if sensitive molecular assays can be developed to detect cytologically malignant cells. The current study investigated telomerase expression as a potential marker of malignancy, using the telomeric repeat amplification protocol (TRAP) in fine-needle aspirates and fluid specimens. TRAP was performed on 24 fine-needle aspirate and 24 fluid specimens from different body sites and of different histological diagnoses. We found that 6 of 12 fine-needle aspirate specimens that were cytologically positive for malignant cells expressed telomerase activity, while no specimens that were cytologically suspicious for malignancy, atypical, or negative tested positive for telomerase activity. Of the fluid specimens, 4 of 6 cytologically positive cases and 1 of 18 cytologically negative cases expressed telomerase. Seven of eight telomerase negative, cytologically positive specimens contained only rare malignant cells in a very bloody background. Peripheral blood contamination is a possible pitfall in the TRAP assay, as applied in the current study, because the assay is standardized to protein concentration that may be derived from lysed red blood cells. We conclude that with further technical refinement, the TRAP assay could become a useful adjunct in the cytologic examination of fine-needle aspirates and fluid samples.

Telomerase expression shows differences across multiple regions of oligodendroglioma versus high grade astrocytomas but shows correlation with Mib-1 labelling

AIMS/BACKGROUND

Telomerase is an enzyme that is expressed in most human neoplasms and is associated with tumour immortality. Determination of the point in neoplastic transformation at which telomerase is expressed may aid the understanding of tumour pathogenesis and progression. Despite numerous reports on telomerase, few studies have investigated its expression in high grade glial tumours. These studies, performed on archival banked, single brain tumour specimens, have shown conflicting results for oligodendrogliomas and unexpectedly negative results for telomerase expression in high grade astrocytomas, with one third to one half of glioblastoma multiformes being negative.

METHODS

34 rapidly banked glioma specimens taken from patients undergoing gross total surgical resection of their tumours were studied. Telomerase expression was assessed across 3-8 sampled regions from each tumour by the telomeric repeat amplification protocol (TRAP) assay. Matched mirror image tissue samples were taken for histological analysis of tissue adequacy, statistical correlation of telomerase with tumour histological features, Mib-1 (a marker for cell cycling) labelling, and p53 immunohistochemistry.

RESULTS

All five well differentiated oligodendrogliomas were homogeneously telomerase negative and two of three untreated anaplastic oligodendrogliomas were homogeneously positive. In contrast, 10 of 14 high grade astrocytomas showed heterogeneity for telomerase expression across the multiple regions sampled. All glioblastoma multiformes and two of three anaplastic astrocytomas showed at least one region positive for telomerase. When test samples were individually assessed in both oligodendrogliomas and high grade astrocytomas, telomerase expression was associated with Mib-1 labelling (p < 0.001). For the entire group, telomerase expression was associated with grade of tumour, age of patient, and vascular endothelial proliferation (all p < 0.001).

CONCLUSIONS

This regional study clarifies that all glioblastoma multiformes are at least focally positive and that telomerase expression correlates with tumour grade in oligodendrogliomas. Homogeneity versus heterogeneity for telomerase expression across multiple regions of oligodendrogliomas versus high grade astrocytomas may provide important preclinical data on the use of antitelomerase agents in these adult glial tumours.