Proliferation-associated regulation of telomerase activity in human endometrium and its potential implication in early cancer diagnosis

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.

Hormonal regulation of telomerase activity and hTERT expression in steroid-regulated tissues and cancer

Naturally, in somatic cells chromosome ends (telomeres) shorten during each cell division. This process ensures to limit proliferation of somatic cells to avoid malignant proliferation; however, it leads to proliferative senescence. Telomerase contains the reverse transcriptase TERT, which together with the TERC component, is responsible for protection of genome integrity by preventing shortening of telomeres through adding repetitive sequences. In addition, telomerase has non-telomeric function and supports growth factor independent growth. Unlike somatic cells, telomerase is detectable in stem cells, germ line cells, and cancer cells to support self-renewal and expansion. Elevated telomerase activity is reported in almost all of human cancers. Increased expression of hTERT gene or its reactivation is required for limitless cellular proliferation in immortal malignant cells. In hormonally regulated tissues as well as in prostate, breast and endometrial cancers, telomerase activity and hTERT expression are under control of steroid sex hormones and growth factors. Also, a number of hormones and growth factors are known to play a role in the carcinogenesis via regulation of hTERT levels or telomerase activity. Understanding the role of hormones in interaction with telomerase may help finding therapeutical targets for anticancer strategies. In this review, we outline the roles and functions of several steroid hormones and growth factors in telomerase regulation, particularly in hormone regulated cancers such as prostate, breast and endometrial cancer.

The effect of environmental Bisphenol A exposure on breast cancer associated with obesity

Bisphenol A (BPA) is a widely used endocrine disrupter. Its environmental exposure is a causative factor of cell aging via decreasing telomerase activity, thus leading to shortening of telomere length. Epidemiological studies confirm positive associations between BPA exposure and the incidence of obesity and type 2 diabetes (T2DM). Increased urinary BPA levels in obese females are both significantly correlated with shorter relative telomere length and T2DM. BPA is a critically effective endocrine disrupter leading to poor prognosis via the obesity-inflammation-aromatase axis in breast cancer. Environmental BPA exposure contributes to the progression of both estrogen dependent and triple negative breast cancers. BPA is a positive regulator of human telomerase reverse transcriptase (hTERT) and it increases the expression of hTERT mRNA in breast cancer cells. BPA exposure can lead to tamoxifen resistance. Among patients treated with chemotherapy, those with persistent high telomerase activity due to BPA are at higher risk of death.

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.

Mechanisms of human telomerase reverse transcriptase (hTERT) regulation: clinical impacts in cancer

Background

Limitless self-renewal is one of the hallmarks of cancer and is attained by telomere maintenance, essentially through telomerase (hTERT) activation. Transcriptional regulation of hTERT is believed to play a major role in telomerase activation in human cancers.

Main body

The dominant interest in telomerase results from its role in cancer. The role of telomeres and telomere maintenance mechanisms is well established as a major driving force in generating chromosomal and genomic instability. Cancer cells have acquired the ability to overcome their fate of senescence via telomere length maintenance mechanisms, mainly by telomerase activation.

hTERT expression is up-regulated in tumors via multiple genetic and epigenetic mechanisms including hTERT amplifications, hTERT structural variants, hTERT promoter mutations and epigenetic modifications through hTERT promoter methylation. Genetic (hTERT promoter mutations) and epigenetic (hTERT promoter methylation and miRNAs) events were shown to have clinical implications in cancers that depend on hTERT activation. Knowing that telomeres are crucial for cellular self-renewal, the mechanisms responsible for telomere maintenance have a crucial role in cancer diseases and might be important oncological biomarkers. Thus, rather than quantifying TERT expression and its correlation with telomerase activation, the discovery and the assessment of the mechanisms responsible for TERT upregulation offers important information that may be used for diagnosis, prognosis, and treatment monitoring in oncology. Furthermore, a better understanding of these mechanisms may promote their translation into effective targeted cancer therapies.

Conclusion

Herein, we reviewed the underlying mechanisms of hTERT regulation, their role in oncogenesis, and the potential clinical applications in telomerase-dependent cancers.

Low-dose levels of bisphenol A inhibit telomerase via ER/GPR30-ERK signalling, impair DNA integrity and reduce cell proliferation in primary PBMC

Controversy exists about the human health risk of environmental exposure to bisphenol A (BPA). Telomerase activity is emerging both as biomarker and contributing factor for age-related diseases. The effects of BPA exposure at 1–1000 nM on telomerase, DNA integrity and cell proliferation were investigated in PBMC from human donors. Telomerase activity was determined by TRAP-ELISA assay and mRNA expression by qRT-PCR. Mechanistic studies were carried out on the ER/GPR30-ERK pathway using specific inhibitors/antagonists, the comet assay to quantify DNA damage and flow cytometry for cell proliferation. 24 h BPA exposure inhibited telomerase in a non-monotonic pattern with a peak inhibition of 32% at 1 nM (p ≤ 0.01). A significant telomerase inhibition was evident at 1 h after exposure with a minimum at 6 h. Elevated levels of DNA damage frequency and decrease in cell proliferation were evident upon long-term exposure. The results further demonstrate that BPA triggered rapidly an ER/GPR30-ERK transduction pathway that leads to decreased telomerase activity in human PBMC. This is the first study to demonstrate adverse impact of BPA at levels of current human exposure on telomerase in normal cells, mediated by ER/GPR30-ERK. The results suggest a potentially harmful influence of BPA on immune cells and should be addressed in future studies.

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.

Normal human immune cells are sensitive to telomerase inhibition by Brassica-derived 3,3-diindolylmethane,partly mediated via ERα/β-AP1 signaling

SCOPE

Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM) from Brassica plants are regarded as promising anticancer phytochemicals. The enzyme telomerase is a very attractive target for cancer therapeutics; in normal cells such as lymphocytes, it plays a decisive role for cell maintenance. The effect of I3C and DIM on telomerase in normal human immune cells (PBMC) was studied compared to leukaemia cells (HL-60). Signalling of telomerase regulation via estrogen receptor (ER) was addressed.

METHODS AND RESULTS

Short-term treatment with I3C and DIM inhibited telomerase activity in leukaemia cells (>30 μM I3C; >3 μM DIM). In CD3/CD28 activated PBMC, inhibition was stronger, though (>3 μM I3C; >1 μM DIM). DIM long-term treatment resulted in DNA damage induction and proliferation inhibition in PBMC as determined by the comet assay and CFSE staining, respectively. A relevance of ERα/β-AP1 signaling for telomerase inhibition on enzyme activity, but not transcription level became evident indicating a nonclassical mode for ER regulation of telomerase by DIM.

CONCLUSION

Although desired in cancer cells, this study identified a potential adverse impact of I3C and DIM on telomerase action in normal human immune cells, partly mediated by an ER-dependent mechanism. These new findings should be considered for potential chronic high-dose chemoprevention strategies using these compounds.

Human endometrial epithelial telomerase is important for epithelial proliferation and glandular formation with potential implications in endometriosis

STUDY QUESTION

How does regulation of telomerase activity (TA) in human endometrial epithelial cells (EEC) by ovarian hormones impact on telomere lengths (TL) and cell proliferation?

SUMMARY ANSWER

Healthy endometrial epithelial cell proliferation is characterized by high TA and endometrial TL changes according to the ovarian hormone cycle, with shortest TL observed in the progesterone dominant mid-secretory phase, when TA is lowest, implicating progesterone in the negative regulation of TA and TL.

WHAT IS KNOWN ALREADY

Critical shortening of telomeres may result in permanent cell cycle arrest while the enzyme telomerase maintains telomere length (TL) and replicative capacity of cells. Telomerase expression and activity change in the human endometrium with the ovarian hormone cycle, however the effect of this on endometrial TL and cell growth is not known.

STUDY DESIGN, SIZE, DURATION

A prospective observational study, which included endometrial and blood samples collected from 196 women.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We studied endometrial samples from five different groups of women. Endometrial and matched blood TL and circulating steroid hormones were studied in samples collected from 85 women (Group 1). Fresh epithelial and stromal cell isolation and culture in vitro for TL and TA was done on endometrial biopsies collected from a further 74 healthy women not on hormonal therapy (Group 2) and from 5 women on medroxyprogesterone acetate (MPA) for contraception (Group 3). The epithelial TL and telomerase protein expression was examined in active, peritoneal, ectopic endometriotic and matched uterine (eutopic) endometrial samples collected from 10 women with endometriosis (Group 4); the in vivo effect of mifepristone on telomerase protein expression by immunohistochemistry (IHC) was examined in endometrium from 22 healthy women in mid-secretory phase before (n = 8), and after administering 200 mg mifepristone (n = 14) (Group 5). TA was measured by telomere repeat amplification protocol (TRAP) assay; TL by qPCR, and Q-FISH; cell proliferation was assessed by immunoblotting of histone H3 and 3D-culture to assess the ability of EECs to form spheroids; telomerase reverse transcriptase protein levels and Ki-67 (proliferative index) were assessed with IHC.

MAIN RESULTS AND THE ROLE OF CHANCE

Endometrial TLs correlated negatively with serum progesterone levels (n = 58, r = -0.54) and were significantly longer than corresponding blood TLs (4893 ± 929 bp versus 3955 ± 557 bp, P = 0.002) suggesting a tissue-specific regulation. High TA and short TLs were observed in proliferating EECs in vivo and in vitro. During the progesterone dominant mid-secretory phase endometrial TL were significantly shorter compared with the proliferative phase (P = 0.0002). Progestagen treatment suppressed EEC TA in vivo and reduced endometrial TA in explant (P = 0.01) and in vitro cultures (P = 0.02) compared with untreated cells. Mifepristone (progesterone receptor antagonist) increased telomerase protein levels in vivo (P < 0.05). In 2D culture, Imetelstat inhibited EEC TA (P = 0.03), proliferation (P = 0.009) and in 3D culture disrupted endometrial glandular architecture (P = 0.03).

LIMITATIONS, REASONS FOR CAUTION

The in vitro telomerase inhibition data were tested in a mono-cellular system for a short-term. Further confirmation of the results in an in vivo model is necessary. The women in group 2 included a high proportion of women although with a regular menstrual cycle, with an increased BMI (>25) therefore this may affect extrapolation of data to other groups.

WIDER IMPLICATIONS OF THE FINDINGS

The observed effects of telomerase inhibition in vitro on epithelial cell proliferation, suggest that telomerase might be an attractive target in developing new therapies for proliferative disorders of the endometrium, such as endometriosis.

Ovarian stem cells and aging

OBJECTIVE

To review successes to date in the field of ovarian stem cell research and discuss the evidence supporting their potential to rejuvenate the follicular pool during adult life; to present factors that may contribute to their competence; and to address the question of why menopause is an inevitable outcome of advanced age if ovarian stem cells exist.

METHOD

In a review of the literature, relevant articles were identified through a PubMed literature search from inception to July 2010.

RESULTS

The current concept that mammalian ovaries possess a static ovarian reserve is at odds with the experimental results discussed in this review. Ovarian stem cells are likely to be the source of germline stem cells during fetal and adult life, due to their potential to differentiate into competent oocytes given a suitable environment.

CONCLUSIONS

Stem cells in different compartments share properties such as pluripotency, self-renewal, and diminished regenerative potential in old age. Our model of ovarian stem cell aging suggests that menopause is driven by an age-related decline in ovarian stem cell function rather than depletion of a non-renewable follicular reserve. Understanding how ovarian stem cells interact with their surrounding environment moves us a step closer to controlling the female biological clock when it might be clinically desirable.

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.

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.

The PTEN tumor suppressor inhibits telomerase activity in endometrial cancer cells by decreasing hTERT mRNA levels

OBJECTIVES

Loss of PTEN expression is one of the most prevalent and earliest molecular abnormalities associated with endometrial carcinogenesis. Given that PTEN is often absent and telomerase is overexpressed by endometrial cancers, we hypothesize that PTEN signaling is important in telomerase regulation.

METHODS

PTEN expression was reconstituted in the PTEN-null Ishikawa endometrial cancer cells by adenovirus-mediated gene transduction. Cell proliferation was evaluated 12-96 h after infection. Western blot analysis was performed to assess PTEN status and phosphorylated Akt expression. Telomerase activity was determined by the telomeric repeat amplification protocol (TRAP) assay. hTERT mRNA levels were assessed by real-time RT-PCR. Ishikawa cells were also treated with LY294002, a PI3-kinase inhibitor.

RESULTS

Infection of Ishikawa cells by replication-defective recombinant adenovirus expressing wild-type PTEN, but not control adenovirus or adenovirus expressing lipid phosphatase defective PTEN GE mutant, inhibited constitutive Akt activation and suppressed proliferation of Ishikawa cells. Infection by wild-type PTEN adenovirus, but not control adenovirus, inhibited telomerase activity 24 h after infection. This inhibition of telomerase activity was parallel to decreased hTERT mRNA levels. LY294002 treatment resulted in dose-dependent inhibition of Akt activation and cellular proliferation. LY294002 suppressed telomerase activity and decreased hTERT transcript levels in a dose-dependent manner.

CONCLUSIONS

Our data suggest that PTEN may regulate telomerase activity by a novel mechanism in which inhibition of Akt activation by PTEN leads to decreased hTERT mRNA levels. Thus, loss of PTEN may allow endometrial cells to continue to express high levels of telomerase activity, facilitating the neoplastic transformation of the endometrium.

Hormones and growth factors regulate telomerase activity in ageing and cancer

Telomerase is a specialised reverse transcriptase that synthesises and preserves telomeres (the ends of chromosomes), thereby playing a key role in regulating the lifespan of cell proliferation. Telomerase activity is critically involved in cell development, ageing and tumourigenesis. Activation of telomerase to maintain telomeres is required for self renewal and proliferative expansion of a number of cell types, including stem cells, activated lymphocytes and cancerous cells. However, recent studies show that the safeguard mechanisms and the modes of regulation of telomerase are more revealing than thought under various physiological and pathological conditions. Considerable evidence suggests that hormones and growth factors are crucially involved in regulating telomerase activity and gene expression of telomerase reverse transcriptase (TERT). This review briefly summarises our current understanding of how hormones and growth factors regulate the telomerase and telomere network and how deregulation can induce ageing and related diseases such as cancer.

Telomerase Activity as a Potential Diagnostic Marker for Triage of Abnormal Pap Smears

OBJECTIVES

To determine whether there is an association between high levels of telomerase and premalignant cervical disease and to provide a preliminary analysis of telomerase activity as a potential triage strategy.

MATERIALS AND METHODS

Premenopausal women were invited to participate in the study during routine gynecologic visits as well as visits where colposcopy was performed. Samples were taken from the cervix using a broom device and placed in cold phosphate-buffered saline. A total of 92 samples were evaluated. Cells were counted and lysed, and a semiquantitative measure of telomerase activity was determined using a commercially available telomerase enzyme-linked immunosorbent assay kit. The presence of human papillomavirus (HPV) types 16 and 18 was assessed by polymerase chain reaction analysis. One-way analysis of variance was used to test for the association of telomerase activity with cytology, HPV type 16 or 18 status, and colposcopy and/or biopsy findings.

RESULTS

When telomerase levels were analyzed according to Pap smear results, there were no differences among four groups of cytology findings (normal, atypical squamous cells of undetermined significance, low-grade squamous intraepithelial lesion, and high-grade squamous intraepithelial lesion). When colposcopy and/or biopsy results were considered, significantly higher levels of telomerase were detected in cervical intraepithelial neoplasia (CIN) 2,3 samples than in normal Pap smear samples and CIN 1 samples (p = .035). There was no significant difference in telomerase levels between samples that tested positive for HPV type 16 or 18 and those that did not (p = .111).

CONCLUSIONS

Telomerase levels were significantly higher in cytologic samples from women with biopsy-proven CIN 2,3 than in samples from women with normal cytology results or CIN 1. These results warrant larger studies to determine whether telomerase activity may be a useful triage tool for abnormal cytologic findings.

Hypermethylation in promoter region of retinoic acid receptor-beta gene and immunohistochemical findings on retinoic acid receptors in carcinogenesis of endometrium

In the present study, we analyzed the immunohistochemical findings for the RA receptor (RAR), retinoic X receptor (RXR) and hypermethylation of promoter-region CpG island methylation of RAR-beta2. Immunohistochemistry indicated that though RXR-alpha and -gamma were present in endometrial hyperplasia and cancer, other retinoid receptors were only weakly detected. The hypermethylation of RAR-beta2 was found in 75.0% of endometrial hyperplasia samples and 92.2% of carcinomas. No normal endometria had methylation. This evidence may point to one of the reasons why endometrial hyperplasia acquires high proliferative capacity without differentiation, and the hypermethylation of RAR-beta2 may occur in the early stage of endometrial carcinogenesis.

Overexpression of estrogen receptor-alpha gene suppresses gap junctional intercellular communication in endometrial carcinoma cells

Stimulation of the endometrium by estrogens without the differentiating effect of progestins is the primary etiological factor associated with the development of endometrial hyperplasia and adenocarcinoma. However, the correlation between sex steroids and gap junctional intercellular communication (GJIC), which is considered to play an important role in the control of cell growth and differentiation, is not well known in endometrial carcinoma. In this study, we focused on the influence of estrogen and its receptor in connexin (Cx) expression and GJIC in endometrial carcinoma cells, established stable clone IK-ER1 overexpressing ER-alpha to transfect the expression vector and analysed them in various hormonal conditions. The growth of IK-ER1 was accelerated by 17beta-estradiol and the acceleration of the 5-bromo-25-deoxyuridine labeling index was observed. GJIC was assayed by scoring the number of dye-coupled cells after microinjection of single cells with Lucifer-Yellow, and subcellular localization of Cx26 and Cx32 was analysed by immunocytochemistry. In the presence of estradiol, dye-coupled cells of IK-ER1 were significantly reduced compared to those without estradiol and the reduction was completely inhibited by adding ICI182.780, a pure antiestrogen substrate. Cxs were detected as only small spots by immunocytochemistry, and Western blotting showed that the expression was decreased. These results suggest that activation of ER-alpha by estrogen results in tumor progression by stimulating cell growth and suppressing GJIC via suppression of the expression of Cxs in endometrial carcinogenesis.

Expression of uteroglobin in normal and carcinogenic endometrium and influence of hormone replacement therapy

Uteroglobin, first reported in 1968 as a steroid secreted in rabbit uterine fluid during early pregnancy, is a progesterone-regulated and progesterone-binding protein. There is evidence that indicates that uteroglobin is inversely correlated to neoplastic growth but its role to endometrial carcinogenesis is not known. Therefore we analyzed the expression of uteroglobin in 13 normal endometrium, 19 hyperplasia and 21 endometrial carcinoma samples and the relation to estrogen receptor-alpha (ER-alpha) and progesterone receptor (PR) by immunohistochemistry and Western blotting. We also analyzed the expression of uteroglobin in 15 menopausal women who received hormone replacement therapy (HRT). The expression of uteroglobin was higher during the secretory phase than in the proliferative phase; however, it was detected in endometrial hyperplasia as weakly as in the proliferative phase and decreased according to the loss of differentiation in endometrial carcinoma. The results were basically in accord with those for PR; however, the expression of uteroglobin was weak, though PR was most detected in endometrial hyperplasia. In menopausal endometrium, the group treated with estrogen plus progesterone exhibited higher expression of uteroglobin than the group treated only with estrogen. The evidence suggests that uteroglobin expression is regulated by progesterone in the normal endometrium but that the regulation by PR is lost in endometrial hyperplasia and carcinoma according to acquirement of tumorigenesis and that estrogen plus progesterone therapy reduces the risk for endometrial carcinoma by restoring uteroglobin.

Bisphenol A from dental polycarbonate crown upregulates the expression of hTERT

Bisphenol A (BPA) is one of the endocrine-disrupting chemicals (EDCs) that possess estrogen-like biologic activity. Many dental materials have been reported to release BPA. However, there are few reports available on the release of BPA from dental polycarbonates. The purpose of this study was to investigate the release of BPA from dental polycarbonate crowns and to evaluate the estrogenic activity of BPA. Polycarbonate crowns were immersed in five solvents (water, ethanol, n-hepthane, acetic acid, and acetonitrile) at 37 or 65 degrees C for 24 h. The elution from the material was analyzed by high-performance liquid-chromatography (HPLC) and mass-spectrometry (MS) analysis. BPA release was detected corresponding to the degradation of dental polycarbonates under the some storage conditions (ethanol, acetic acid, and acetonitrile). A previous report proved that estrogen increased human telomerase catalytic subunit (hTERT) mRNA, whereas the effect of EDCs on the hTERT promoter has never been reported. The estrogenic activity of BPA was analyzed by luciferase assay with the use of the hTERT promoter. This assay revealed that BPA was a positive regulator of hTERT transcription. In addition, quantitative real-time PCR analysis showed that BPA increased the expression level of hTERT mRNA in MCF7 cells. Herein, it is demonstrated that hTERT is a new target of BPA.

Improved TRAP-silver staining versus conventional radioactive TRAP assays: quantification of telomerase activity during immortalization and in pathological human endometrium

OBJECTIVES

To develop a sensitive telomeric repeat amplification protocol (TRAP)-silver staining assay for telomerase activity quantification.

DESIGN AND METHODS

TRAP assays were performed by using a TRAPeze telomerase kit with or without [alpha-32P]-dCTP. Amplification products were electrophoresed in polyacrylamide gels and detected by autoradiography or a modified silver staining protocol. Telomerase activity was quantified from radioactive counts or optical density of telomerase products from test extracts and controls.

RESULTS

TRAP-silver staining assay was at least as sensitive as radioactive TRAP assay and quantified telomerase activity within linearity from 10 to 3,000 cell equivalents. Both methods quantified a weak telomerase activity in normal endometrial glandular epithelial cells (GEC) and a strong increase in immortalized GEC. In human pathologic endometria (n=24), telomerase activity was correlated with lesion seriousness and distinguished simple hyperplasias from nonhyperplasic or cancerous lesions.

CONCLUSIONS

TRAP-silver staining assay is suitable for cell and tissue telomerase activity routine quantification.

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.

Acceleration of invasive activity via matrix metalloproteinases by transfection of the estrogen receptor-alpha gene in endometrial carcinoma cells

It is well known that the functions of reproductive organs are regulated by sex steroids and their receptors and it is hypothesized that the progression of neoplasms that originate from the reproductive organs is influenced by them. However, the correlation between sex steroids and tumor progression, especially tumor invasion, is not well known in endometrial carcinoma. In our study, we focused on the influence of estrogen and its receptor in invasion and matrix metalloproteinases (MMPs), which are known to be important in tumor invasion, as well as on endometrial carcinoma cells. The growth of Ishikawa cells, to which an estrogen receptor-alpha expressing vector was transfected, was accelerated by 17 beta-estradiol as was the acceleration of the expression of cyclin D1. By invasion assay, in conditions with 17 beta-estradiol, the invasiveness of Ishikawa cells was enhanced. Furthermore, according to the accelerated invasiveness, the expression of MMP-1, -7 and -9 and Ets-1 was enhanced. These results suggest that activation of ER-alpha by estrogen results in tumor progression by stimulating cell growth and invasiveness via acceleration of the expression of MMPs.

Loss of gamma-Catenin expression in squamous differentiation in endometrial carcinomas

Squamous differentiation occurs in 25 to 50% of endometrial endometrioid adenocarcinomas. In this study, we analyzed the immunohistochemical expression and localization of beta- and gamma-catenin, molecular changes in the beta-catenin gene, and the subcellular localization of the desmosomal component protein, desmoplakin, by laser scanning microscopy in 35 endometrial carcinomas with squamous differentiation. In the glandular component, beta-catenin showed nuclear localization in 10 of 35 (28.5%) samples, whereas in the squamous component, nuclear localization was found in 15 of 35 (42.9%). Of the 15 samples that showed nuclear localization of beta-catenin in the squamous component, seven samples (46.7%) did not express gamma-catenin. The phenomenon was not correlated with mutation in exon 3 region of beta-catenin gene. Furthermore, in these samples, there was diffuse cytoplasmic staining for desmoplakin. These observations have not been reported in other tumors. Our results suggest that unique molecular events, i.e., stimulation of beta-catenin and suppression of gamma-catenin expression, occur within endometrial carcinomas with squamous differentiation.

Immunohistochemical detection of telomerase reverse transcriptase in colorectal adenocarcinoma and benign colonic mucosa

Telomerase activity (TA) is increased in human cancers and cell lines and is thought to contribute to their immortality. High TA has been found to correlate with aggressive tumor behavior. The aim of this study was to determine whether increased TA in colorectal carcinoma (CRC) correlates with survival. Formalin-fixed and paraffin-embedded tissue sections from 82 CRC and 6 cases of benign colon with diverticulosis were immunohistochemically stained for telomerase reverse transcriptase (TRT) using the immunoperoxidase method. The percentage of positive nuclei was determined for each case. Survival analysis was performed using the Kaplan-Meier method. TRT immunoreactivity was always nuclear. In normal colonic mucosa, TRT immunoreactivity was detected in the bottom of crypts. However, in normal colon adjacent to CRC, telomerase immunoreactivity was detected throughout the length of the crypts, including the upper third, and frequently in the surface epithelium. Telomerase immunoreactivity in more than 25% of the cancer cell nuclei was associated with significantly poorer patient survival (P = 0.0081). We conclude that increased TA in CRC, as demonstrated by TRT immunostaining, is associated with poorer survival, and that TA is present in normal colonic mucosa and is increased in colonic mucosa near CRC. Additional studies with larger patient samples and multivariate analysis are needed to determine whether TRT expression is an independent prognostic factor in CRC.

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.

Regulation of the human telomerase reverse transcriptase gene

Most somatic human cells lack telomerase activity because they do not express the telomerase reverse transcriptase (hTERT) gene. Conversely, most cancer cells express hTERT and are telomerase positive. For most tumors it is not clear whether hTERT expression is due to their origin from telomerase positive stem cells or to reactivation of the gene during tumorigenesis. Telomerase negative cells lack detectable cytoplasmic and nuclear hTERT transcripts; in telomerase positive cells 0.2 to 6 mRNA molecules/cell can be detected. This suggests that expression is regulated by changes in the rate of hTERT gene transcription. In tumor cell lines hTERT expression behaves like a recessive trait, indicating that lack of expression in normal cells is due to one or several repressors. Studies with monochromosomal hybrids indicate that several chromosomes may code for such repressors. A number of transcription factors, tumor suppressors, cell cycle inhibitors, cell fate determining molecules, hormone receptors and viral proteins have been implicated in the control of hTERT expression; but these studies have not yet provided a clear explanation for the tumor specific expression of the hTERT gene, and the cis-acting elements which are the targets of repression in normal cells still have to be identified.

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.

Suppressed gap junctional intercellular communication in carcinogenesis of endometrium

To examine whether and at which stage of endometrial carcinogenesis decreased connexin expression occurs, we investigated changes in the expression of the gap junction proteins, connexin 26 (Cx26), Cx32 and Cx43, in human endometrial hyperplasia and cancer samples. Forty-eight endometrial tissue samples (15 endometrial hyperplasias and 33 endometrial cancers) were subjected to immunofluorescence and RT-PCR analysis. In endometrial hyperplasia, Cx26 was aberrantly expressed in all samples as revealed immunohistochemically. There was weak or negative expression in 12 samples (80.0%) and diffuse expression in cytoplasm in 3 samples (20.0%). Cx32 expression in those samples was similar to that of Cx26; there was weak or negative expression in 11 samples (73.3%) and diffuse expression in 4 samples (26.7%). In endometrial cancer, Cx26 was expressed weakly or negatively in 25 samples (75.8%), diffusely in 6 samples (18.2%) and normally in 2 samples (6.1%), while Cx32 was expressed weakly or negatively in 26 samples (78.8%), diffusely in 5 samples (15.2%) and normally in 2 samples (6.1%). It was confirmed that weak staining of Cx26 and Cx32 was due to poor expression of their mRNA. All samples showed weak Cx43 protein expression as revealed by immunohistochemical analysis. In the majority of samples, concomitant expression levels of Cx26 and Cx32 protein were observed, confirming our long-term hypothesis that Cx26 and Cx32 are both abnormally regulated in a coordinated fashion in the endometrium. Our results indicate that during endometrial carcinogenesis, loss of gap junctional intercellular communication (GJIC) may occur due to the suppressed expression and the aberrant localization of connexin at relatively early stages.

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.

Changes in expression and subcellular localization of nuclear retinoic acid receptors in human endometrial epithelium during the menstrual cycle

The endometrium is a uniquely dynamic tissue in that it undergoes monthly cycles of proliferation and secretory activity, and is regulated by ovarian steroid hormones. In this study, we focused on retinoic acid receptors (RAR and RXR) which are ligand-dependent transcription factors belonging to the large family of steroid hormones and are expected to affect to cell growth and differentiation in the endometrium. We analysed the expression and subcellular localization of the RA receptors in 57 samples of human endometrium by immunohistochemistry and Western blotting. In the nuclei of the endometrial epithelium, the RA receptors were expressed strongly in the proliferative phase. However, RAR were drastically reduced in the epithelial nuclei during the secretory phase in association with changes in serum oestradiol and in the expression of the oestrogen receptor. The expression of RXR was localized in the epithelial nuclei throughout the menstrual cycle. Confocal laser scanning microscopical observation clearly showed the difference in the localization between RAR and RXR in the secretory phase. Furthermore the findings of immuno-electron microscopy showed pooled RAR around the rough endoplasmic reticulum, suggesting that transport of these receptors to the nuclei is inhibited. These findings suggest that RAR and RXR work mainly in the proliferative phase and that in the endometrium RXR may play a different role to RAR during the secretory phase.

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.

Over-expression of heat shock proteins in carcinogenic endometrium

We have previously shown that the subcellular localization of beta-catenin changes according to the cell proliferation status of the human endometrium, suggesting a role of intercellular transduction in cell growth control in human endometrium not only in the physiological but also in the carcinogenic condition. To further study the possible role of heat shock proteins (HSPs) in growth control, we immunohistochemically analyzed 92 endometrial samples, 30 of normal endometrium, 20 of endometrial hyperplasia and 42 of endometrial cancer, for expression of HSP27, HSP70, HSP90, estrogen receptor (ER) and progesterone receptor. HSP27 and HSP90 were detected in endometrial epithelium strongly in the proliferative phase and weakly in the secretory phase during the menstrual cycle according to the serum estradiol level. However, they were over-expressed in endometrial hyperplasia, especially HSP27. In endometrial cancer, HSP27 expression was heterogenic among the glands and lower than that in the proliferative phase and endometrial hyperplasia. HSP27 over-expression was also observed in samples including endometrial cancer and associated hyperplasia. Results of Western blotting followed those of immunohistochemistry. HSP70 was not changed during the menstrual cycle, as HSP27 and HSP90 were, and was rather stably expressed in endometrial hyperplasia and cancer. Our results suggest that HSP27 and HSP90 contribute to cell proliferation in endometrial epithelium and that over-expression of HSP27 in endometrial hyperplasia occurs as a result of the activated condition of ER, though in cancer it decreases according to the loss of function of ER.

Induction of hTERT expression and telomerase activity by estrogens in human ovary epithelium cells

In mammals, molecular mechanisms and factors involved in the tight regulation of telomerase expression and activity are still largely undefined. In this study, we provide evidence for a role of estrogens and their receptors in the transcriptional regulation of hTERT, the catalytic subunit of human telomerase and, consequently, in the activation of the enzyme. Through a computer analysis of the hTERT 5'-flanking sequences, we identified a putative estrogen response element (ERE) which was capable of binding in vitro human estrogen receptor alpha (ERalpha). In vivo DNA footprinting revealed specific modifications of the ERE region in ERalpha-positive but not ERalpha-negative cells upon treatment with 17beta-estradiol (E2), indicative of estrogen-dependent chromatin remodelling. In the presence of E2, transient expression of ERalpha but not ERbeta remarkably increased hTERT promoter activity, and mutation of the ERE significantly reduced this effect. No telomerase activity was detected in human ovary epithelial cells grown in the absence of E2, but the addition of the hormone induced the enzyme within 3 h of treatment. The expression of hTERT mRNA and protein was induced in parallel with enzymatic activity. This prompt estrogen modulation of telomerase activity substantiates estrogen-dependent transcriptional regulation of the hTERT gene. The identification of hTERT as a target of estrogens represents a novel finding which advances the understanding of telomerase regulation in hormone-dependent cells and has implications for a potential role of hormones in their senescence and malignant conversion.

Telomerase activity in lens epithelial cells of normal and cataractous lenses

Telomerase is a ribonucleoprotein responsible for maintaining telomere length, preventing chromosomal degradation and recombination, and repairing DNA strand breaks. These activities are believed to be important in preventing cell senescence. Telomerase activity is normally found in germinal, neoplastic and stem cells, but not any ocular tissue studied to date. The epithelium of the crystalline lens is comprised of a population of cells with diverse mitotic potential including the germinative epithelium which contains cells with the potential for unlimited replicative capacity, equatorial cells which terminally differentiate into lens fibers, and the central epithelium which are considered to be quiescent and nonreplicative under normal circumstances. We speculated that the germinative region of lens epithelial cells might have telomerase activity, and that dysregulation of its activity might be associated with cataractogenesis. We investigated these hypotheses in lens capsule specimens from normal and cataractous dogs and from cultures of canine lens epithelial cells using standard assays for telomerase activity and telomere length. Telomerase activity was found in normal canine lens epithelial cells in the central, germinative and equatorial regions of the anterior lens capsule at equivalent levels. Similar findings were made in feline and murine lens epithelial cells, indicating that the presence of telomerase activity in the lens was not species specific. Lens fiber cells, corneal epithelium and endothelium and nonpigmented ciliary epithelium were telomerase negative. Telomerase activity and telomere lengths were significantly greater in lens epithelia from cataractous lenses when compared with normal lenses. Since telomerase activity is associated with an immortal phenotype, the presence of telomerase activity in the lens epithelial cells may function to prevent conversion to senescence. It was, therefore, difficult to explain why these cells cannot be passaged more than four times in culture. We found that telomerase activity and telomere lengths gradually decreased with increased passages until telomerase activity was no longer present at passage two. Consistent with these findings, there were no senescent cells present on the lens capsule when the lens was initially dissected for culture, but an increasing number of cells were senescent with each passage, correlating well with the loss of telomerase activity. Telomerase activity is likely important in the germinative epithelium to maintain its proliferative potential and prevent cell senescence. Telomerase may function in the quiescent, central lens to maintain telomeres damaged by oxidative stress and ultraviolet light exposure, thereby preventing accelerated loss of these elements which triggers cell senescence. It remains to be determined if the increase in telomerase activity in lens epithelial cells from cataractous lenses is a primary dysregulation that may have a role in the development of the cataract, or is secondary to cataract formation.

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.

Telomerase activity in gestational trophoblastic disease

AIMS

To investigate the pattern of telomerase activity in hydatidiform mole as compared with normal placenta and choriocarcinoma, and to determine the prognostic significance of telomerase activity in hydatidiform mole.

METHODS

Telomerase activity in 35 cases of hydatidiform mole, 35 normal placentas, one choriocarcinoma sample, and two choriocarcinoma cell lines (JAR, JEG3) was determined using the sensitive polymerase chain reaction based telomeric repeat amplification protocol (TRAP) assay. Two cases of breast carcinoma and two cases of ovarian carcinoma were also included as positive controls in the telomerase assay.

RESULTS

Telomerase activity was detected in 11 of 30 early placentas (36.7%), one of five term placentas (20%), five of 27 hydatidiform moles which regressed spontaneously (18.5%), and six of eight hydatidiform moles which developed persistent trophoblastic disease (75%) (including three which developed metastases). Hydatidiform moles which subsequently developed persistent disease, especially those which metastasised, were more likely to express telomerase activity (p < 0.01). However, there was no significant difference in the frequency of telomerase activity between early placentas and hydatidiform mole. Strong telomerase activity was observed in choriocarcinoma tissue, choriocarcinoma cell lines, and ovarian and breast carcinomas.

CONCLUSIONS

Telomerase activation occurs in hydatidiform mole with a similar incidence to early normal placentas. This supports the concept that hydatidiform mole is essentially an abnormal conceptus. There is an association between telomerase activation and the development of persistent trophoblastic disease. Further study is warrant to confirm the prognostic significance of telomerase activity in hydatidiform mole.

Role of telomerase in cellular proliferation and cancer

Telomerase is a cellular reverse transcriptase that helps to provide genomic stability in highly proliferative normal, immortal, and tumor cells by maintaining the integrity of the chromosome ends, the telomeres. The activity of telomerase is associated with the majority of malignant human cancers. Telomerase or another mechanism for telomere maintenance is required for continuous tumor cell proliferation. Telomerase-positive cells that exit the cell cycle via quiescence downregulate telomerase through a transcriptional repression pathway. In the case of cell cycle exit via terminal differentiation, proteolysis of telomerase may also be involved. In response to mitogenic or growth factor signaling, telomerase-competent quiescent cells reenter the cell cycle and express telomerase activity independent of DNA synthesis. Under normal growth conditions, inhibition of telomerase activity in tumor-derived cells results in continued cell division coupled with telomere shortening, eventually followed by cellular senescence or death. Thus, repression of telomerase activity may be a novel adjuvant therapy for the treatment of human cancer and detection of telomerase activity may be important for cancer diagnostics.

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.

The Clinicopathologic Significance of Unilateral Adrenal Cortical Hyperplasia: Report of an Unusual Case and a Review of the Literature

We report a case of unilateral primary adrenal cortical hyperplasia associated with hyperaldosteromsm in a 39-yr-old Chinese man. The patient presented with hypertension hy pokalemia, primary hyperaldosteronism(1) suppressed renin activity, and was complicated with aortic dissection. The aortic dissection required emergency realignment while unilateral laparoscopic adrenalectomy was performed subsequently Pathologic examination of the adrenal lesion revealed multiple cortical nodules (up to 1 4 cm in diameter). No telomerase activity was detected in the adrenal lesion. A review of the literature showed that unilateral adrenal cortical hyperplasia has a predilection for the left side occurring more often in males. We conclude that unilateral adrenal cortical hyperplasia is a rare but unique entity and that unilateral adrenalectomy is the treatment of choice.

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.

Telomerase in cancer: clinical applications

The biology of telomeres and telomerase has been the subject of intensive investigative effort since it became evident that they play a significant role in two important biological processes, the loss of cellular replicative capacity inherent to organismal ageing and the unrestricted cell proliferation characteristic of carcinogenesis. Telomere shortening in normal cells is a result of DNA replication events, and reduction beyond a critical length is a signal for cellular senescence. One of the cellular mechanisms used to overcome proliferative restriction is the activation of the enzyme telomerase, which replaces the loss of telomeric DNA that occurs at each cell division. Studies have demonstrated that tumours have shorter telomeres than normal tissue and that telomerase is activated in up to 90% of all human cancers while it is present only in a limited range of normal adult tissues. The role of telomerase in the extension of the cellular replicative lifespan has recently been shown by ectopic expression of the enzyme, being consistent with the oncogenesis model whereby the acquisition of an 'immortal' phenotype is a requirement for advanced tumour progression. In this article we review the present knowledge of telomeres and telomerase in cancer and discuss the potential use of this enzyme as a diagnostic and prognostic tumour marker and as a target for cancer therapy.

Telomeres and telomerase in endocrine pathology

Telomeres representing repetitive DNA sequences of chromosome ends are necessary for maintaining chromosomal integrity. The enzyme telomerase synthesizes de novo telomeric repeats and incorporates them onto the DNA 3'-ends of chromosomes. Stability of chromosome ends and activation of telomerase are elementary requirements for cell immortalization and tumor progression. The telomeric length and telomerase activity have been recently studied in several human neoplasms, including those of endocrine tissues. Assessment of telomerase activity may help to distinguish normal or hyperplastic from neoplastic tissues. Inhibition or inactivation of telomerase activity may provide novel strategies for cancer therapy.