Detection of telomerase activity in malignant and nonmalignant skin conditions

Cellular proliferation and telomerase activity in CHRF-288-11 cells

Telomerase activity is detected in many immortalized cell lines. Recent studies suggest that terminal differentiation of some of these cell lines is associated with a reduction in telomerase activity. However, the question remains whether the reduction in telomerase activity results from terminal differentiation or from cessation of cellular proliferation. This was explored in the megakaryocytic cell line CHRF-288-11. Cells were treated with phorbol 12-myristate 13-acetate (PMA), which induces terminal differentiation of CHRF-288-11 cells, EGTA, serum depletion, and okadaic acid. All treatments resulted in cessation of proliferation. Except for okadaic acid, these treatments also induced inhibition of telomerase within 7 days. Restoring the original growth conditions of cells treated with PMA, EGTA and serum depletion resulted in the reversal of telomerase inhibition and an acceleration of proliferation. Apparent inhibition of telomerase was observed to follow the cessation of proliferation, whereas enhanced telomerase activity was noted to precede acceleration in proliferation. Thus, telomerase activity usually reflects the proliferative status rather than the differentiated status of CHRF-288-11 cells.

Inhibition of telomerase activity by a cell-penetrating peptide nucleic acid construct in human melanoma cells

We investigated the effect of two peptide nucleic acids (PNAs), which are complementary to the RNA component of human telomerase, on the catalytic activity of the enzyme. PNAs induced a dose-dependent reduction of telomerase activity in cell extracts from human melanoma cell lines and surgical specimens. To down-regulate telomerase in intact cells, we generated a chimeric molecule synthesized by coupling the 13-mer PNA to the Antennapedia peptide. The PNA construct induced a dose- and time-dependent inhibition of telomerase activity. However, a 20-day exposure to the PNA construct only caused a slight increase in melanoma cell doubling time and failed to induce any telomere shortening.

Clonal heterogeneity in telomerase activity and telomere length in tumor-derived cell lines

The ribonucleoprotein, telomerase, is responsible for the maintenance of telomere length in most immortal and cancer cells. Telomerase appears to be a marker of human malignancy with at least 85% of human cancers expressing its activity. In the present study, we examined a series of tumor-derived and in vitro immortalized cell lines for telomerase activity levels, telomere lengths, and expression levels of the RNA and catalytic components of telomerase. We found significant variability in both telomere lengths and telomerase activity in clones from tumor cells. In addition, the levels of telomerase components or telomerase activity were not predictive of telomere length. Data from clonally derived cells suggest that critically shortened telomeres in these tumor-derived cell lines may signal activation of telomerase activity through an increase in the expression of the catalytic subunit of telomerase. Although clones with low telomerase shorten their telomeres over time, their subclones all have high levels of telomerase activity with no telomere shortening. In addition, analysis of early clones for telomerase activity indicates substantial variability, which suggests that activity levels fluctuate in individual cells. Our data imply that cell populations exhibit a cyclic expression of telomerase activity, which may be partially regulated by telomere shortening.

Telomerase activity in melanocytic lesions: A potential marker of tumor biology

Telomerase activation, being a cardinal requirement for immortalization, is a crucial step in the development of malignancy. With a view toward diagnostic and biological aspects in melanocytic neoplasia, we investigated the relative levels of telomerase activity in 72 nevi and 16 malignant melanomas by means of a modified telomeric repeat amplification protocol (TRAP) assay, including an internal amplification standard. We further compared telomerase activity with the expression of two different proliferation-specific proteins, Ki-67 and repp86, a protein expressed exclusively in the cell cycle phases S, G2, and M. Telomerase activity was associated with the overall growth fraction (Ki-67) but showed a closer correlation with the expression of repp86. Both telomerase activity and proliferation indices discriminated clearly between malignant melanomas and nevi, but not between common and dysplastic nevi. Nonetheless, a portion of nevi exhibited markedly elevated telomerase activity levels without proportionally increased proliferation. This was independent of discernible morphological changes. Clinicopathological correlations showed an association between high telomerase activity and early metastatic spread in melanomas, linking telomerase to tumor biology. Our results provide arguments in favor of an occasional progression from nevi to melanomas and imply that proliferation measurements in combination with telomerase assays may help to elicit early malignant transformation that is undetectable by conventional morphology.

Telomerase. A target for anticancer therapy

Telomerase is absent in most normal tissues, but is abnormally reactivated in all major cancer types. Telomerase enables tumor cells to maintain telomere length, allowing indefinite replicative capacity. Albeit not sufficient in itself to induce neoplasia, telomerase is believed to be necessary for cancer cells to grow without limit. The presence of telomerase has been detected in virtually all cancer types including the most prevalent cancers of the prostate, breast, lung, colon, bladder, uterus, ovary, and pancreas as well as in lymphomas, leukemias, and melanomas. In addition, data from cancer patients indicate that telomerase levels correlate with clinical outcome in neuroblastomas, leukemias, and prostate, gastric, and breast cancers. Studies using an antisense to the human telomerase RNA component demonstrate that telomerase in human tumor lines can be blocked ex vivo. In these experiments, telomerase inhibition led to telomere shortening and cancer cell death, validating telomerase as a target for anticancer therapy. Telomerase is a uniquely appealing target for drug discovery because its dichotomic expression in normal versus cancer cells suggests that no serious side effects would result from a treatment abrogating telomerase activity. A variety of approaches to telomerase inhibition are being investigated and are discussed.

Absence of telomerase activity and telemorase catalytic subunit mRNA in melanocyte cultures

The classic model of activation of telomerase, for which activity has been found in most cancers including cutaneous malignant melanoma (CMM), dictates that enzyme activity is generated by pathological reactivation of telomerase in telomerase-negative somatic cells. However, recent data demonstrated physiological up-regulation in some normal cell types when established as proliferating cultures, indicating that, in some cancer types, telomerase is expressed by the process of up-regulation in telomerase-competent precursor cells. In this study, cultures of epidermal melanocytes, progenitor cells of CMM, were established and harvested in the logarithmic phase of growth. Telomerase activity was looked for using a non-isotopic variant of the telomeric repeat amplification protocol, and transcript expression of the hTERT gene, the rate-limiting catalytic telomerase subunit, was investigated by the reverse transcription polymerase chain reaction. Neither telomerase activity nor hTERT mRNA could be detected in proliferating melanocyte cultures. Our in vitro data argue against the model of telomerase as a common biomarker of cell proliferation. The results further suggest that telomerase is tightly controlled in normal melanocytes, and that telomerase is reactivated rather than up-regulated in melanocytic precursors during melanoma initiation or progression.

Telomerase in cutaneous carcinogenesis

Telomerase is a ribonucleoprotein enzyme that catalyses the addition of telomeric repeats to telomeres. Since the shortening of telomeres is thought to act as a mitotic clock, activation of telomerase is crucial for the continued growth of cancer cells. Telomerase is frequently activated in premalignant and malignant skin tumors and even in normal skin from sun-exposed sites. Normal epidermis contains a subpopulation with telomerase activity, although those might not be stem cells. Telomerase activity correlates closely with the expression of human telomerase catalytic subunits. The effects of acute and chronic UV exposure on telomerase activity and their mechanisms should be studied in relevance to UV-carcinogenesis and photoaging.

Influence of aging and cell senescence on telomerase activity in keratinocytes

Telomeres, which exist in eukaryotic chromosome ends in specialized G-rich TTAGGG structure, protect the ends from degradation or fusion. On the other hand, telomerase is a ribonucleoprotein complex enzyme that synthesizes TTAGGG repeat sequences at the ends of eukaryotic chromosomes. Previous studies suggested that telomere length and telomerase activity cooperate in aging and immortalization of cells. Here, we examined telomere length and telomerase activity in keratinocytes from seven human subjects, including a patient with Werner's syndrome. Telomere length in keratinocytes from healthy individuals was shortened with aging. However, telomerase activity from an individual aged 42 years was reduced, compared with that from a 0 year old individual. Passages of keratinocytes reduced telomerase activity significantly in F2 and F3 keratinocytes from 0 and 42 year old individuals. Withdrawal of either EGF or amphiregulin from medium resulted in down-regulation of telomerase activity. These results suggest that telomere length and telomerase activity in primary cultured keratinocytes may be one of the parameters for cell senescence. However, there remain obscure factors such as ultraviolet-B radiation and growth factors.

Telomerase expression in uveal melanoma

BACKGROUND/AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

Inhibition of telomerase activity by a hammerhead ribozyme targeting the RNA component of telomerase in human melanoma cells

Reactivation of telomerase, an RNA-dependent DNA polymerase that synthesizes new telomeric repeats at the end of chromosomes, is a very common feature in human cancers. Telomerase is thought to be essential in maintaining the proliferative capacity of tumor cells and, as a consequence, it could represent an attractive target for new anti-cancer therapies. In this study, we generated a hammerhead ribozyme composed of a catalytic domain with flanking sequences complementary to the RNA component of human telomerase and designed to cleave specifically a site located at the end of the telomerase template sequence. In vitro the ribozyme induced cleavage of a synthetic RNA substrate obtained by cloning a portion of the RNA component of human telomerase. The extent of cleavage was dependent on the ribozyme/substrate ratio as well as the Mg2+ concentration. Moreover, when added to cell extracts from two human melanoma cell lines (JR8 and M14), or three melanoma surgical specimens, the ribozyme inhibited telomerase activity in a concentration- and time-dependent manner. When the ribozyme was delivered to growing JR8 melanoma cells by (N-(1-(2,3 dioleoxyloxy)propil)-N,N,N trimethylammonium methylsulfate-mediated transfer, a marked inhibition of telomerase activity was observed. Next, the ribozyme sequence was cloned in an expression vector and JR8 cells were transfected with it. The cell clones obtained showed a reduced telomerase activity and telomerase RNA levels and expressed the ribozyme. Moreover, ribozyme transfectants had significantly longer doubling times than control cells and showed a dendritic appearance in monolayer culture. No telomere shortening, however, was observed in these clones. Overall, our results indicate that the hammerhead ribozyme is a potentially useful tool for the inactivation of telomerase in human tumors.

Telomerase activity in benign bone tumors and tumor-like lesions

To assess the role and status of telomerase activity in benign bone tumors and tumor-like lesions, we performed telomerase assays in four giant cell tumors of bone, four fibrous dysplasias, three osteochondromas, three aneurysmal bone cysts, two osteoblastomas, one juvenile bone cyst and one myositis ossificans. A very sensitive non-radioactive TRAP assay was applied. Low level activity was detected in 7 of 18 tumor samples (38.9%), and high level activity was not detected in any of the cases. Telomerase activity was observed in all patients with osteochondromas, in two of the three aneurysmal bone cysts, in one of the four giant cell tumors of bone and in one of the four fibrous dysplasias, but not in osteoblastomas, juvenile bone cyst and myositis ossificans. Although the origin of this enzyme is still unclear, it might play a role in precancerous immortalization of benign bone tumors. Other possible reasons explaining the occurrence of telomerase activity, such as migrating lymphocytes or contamination of immortalized non-tumor cells, should not be ruled out. Telomerase activity, however, does exist in those samples having no malignant phenotype, for which reason telomerase assays are not always useful for the clinical and diagnostic approach in benign bone tumors. Determination of the telomerase status in benign lesions may contribute to a better understanding of the regulation mechanism of telomerase activity during progression of bone tumors.

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.

Correlation of the expression of human telomerase subunits with telomerase activity in normal skin and skin tumors

BACKGROUND

Telomerase activation is thought to be crucial for the continued growth or progression of cancer cells. Three major subunits of human telomerase, human telomerase RNA (hTR), telomerase-associated protein (TP1), and human telomerase catalytic subunit (hTERT) have been identified recently. In the current study, the expression of these telomerase subunits was examined in various human skin tumors and in normal skin samples, and the correlation of their expression with telomerase activity was evaluated.

METHODS

Forty-five skin tumors, including benign, premalignant, and malignant tumors, and 19 samples of normal skin were analyzed by reverse transcriptase-polymerase chain reaction for the expression of telomerase subunits and by telomeric repeat amplification protocol assay for telomerase activity.

RESULTS

TP1 expression was found in 43 of 45 skin tumors (95.6%) and in all normal skin samples analyzed. hTR expression was found in 42 of 45 skin tumors (93.3%) and in 18 of 19 normal skin samples (94.7%). In contrast, hTERT expression was detected in 33 of 45 skin tumors (73.3%) and in only 3 of 19 normal skin samples (15.8%). Telomerase activity was positive in 33 of 45 skin tumors (73.3%) and in 3 of 19 normal skin samples (15.8%). All together, 53 of 64 cases (82.8%) were concordant for both results (P < 0.001), i.e., telomerase activity positive and hTERT positive, or telomerase activity negative and hTERT negative.

CONCLUSIONS

Activation of telomerase activity in skin tumors is strongly correlated with hTERT expression.

Prognostic impact of telomerase activity in non-small cell lung cancers

OBJECTIVE

To evaluate the clinical significance of telomerase activity, particularly in terms of prognostic impact, in non-small cell lung cancer (NSCLC).

SUMMARY BACKGROUND DATA

Telomerase activity has been found in various tissues. The activation of telomerase is considered necessary for the immortalization of human tumor cells, including NSCLC.

METHODS

The authors studied 103 NSCLC specimens using a polymerase chain reaction based on a telomeric repeat amplification protocol assay.

RESULTS

Telomerase activity was detected in 85 (82.5%) of 103 NSCLC specimens but in none of the paired normal lung tissue specimens. More cases of positive telomerase activity were observed in the group with advanced disease and in the group with poorly differentiated tumors. Such factors as the mean age at surgery, sex, smoking, histologic type, and size of tumor extension did not correlate with the telomerase activity. The Kaplan-Meier survival curves in all patients with NSCLC demonstrated that patients with telomerase-positive tumors survived for a significantly shorter period than those with a telomerase-negative tumor (p = 0.0058). According to a multivariate analysis, telomerase activity was identified as an independent prognostic factor (RR = 8.62, p = 0.035).

CONCLUSIONS

Telomerase activity was one of the most important prognostic factors in patients with NSCLC, and its potential prognostic implication was independent of tumor stage.

Telomerase activation in colorectal carcinogenesis

Telomerase activity has been detected in germ cells as well as in the developing embryo. Activity is no longer detectable in most somatic cells of the neonate, although low levels of activity persist in regenerative tissues. Telomerase has been found to be reactivated or up-regulated in the majority of cancers. The colorectal adenoma-carcinoma sequence is one of the best-characterized models of multistep tumourigenesis and is thus suitable for determining at which stage telomerase is activated. Telomerase activity was examined by telomeric repeat amplification protocol (TRAP) assay in 96 cases of colorectal tissues, including 50 carcinomas, 31 adenomas, and 15 normal colonic tissues. For each case, histological diagnosis and telomerase activity were determined on consecutive frozen sections. In order to reduce the chance of a false-negative TRAP assay due to RNA degradation, the integrity of rRNA in the tissues was verified in each case. Twenty-five carcinomas, 30 adenomas, and all of the 15 normal colorectal mucosal samples showed no or only partial rRNA degradation and only in these cases was the TRAP assay interpreted. None of the normal tissues exhibited telomerase activity. In contrast, all of the 25 cancers and 47 per cent (14/30) of the adenomas were positive. In adenomas, telomerase activation was highly significantly related to the grade of dysplasia (p< 0.0001). All adenomas which contained high-grade dysplasia revealed telomerase activity, whereas telomerase activity was detectable in only 20 per cent (4/20) of cases with exclusively low-grade dysplasia. These results indicate that telomerase activation, which may be an obligatory step in colorectal carcinogenesis, occurs in the progression from low-grade to high-grade dysplasia in adenomas. Furthermore, in the adenoma-carcinoma sequence, telomerase activation seems to occur later than K- ras mutation but earlier than p53 mutation.

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

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

Telomerase activity in malignant ovarian tumors with deregulation of cell cycle regulatory proteins

Using a semiquantitative telomeric repeat amplification protocol assay, telomerase-positive frequencies and enzyme levels were measured. Out of 95% of 49 human ovarian tumors, the highest level of telomerase activity was observed in malignant tumors. Furthermore, by immunohistochemical staining of cell cycle regulatory proteins (pRB, p16, cyclin D1, cyclin E and p53) at the G1 checkpoint, we evaluated the relation between each protein alterations and the levels of telomerase activity. We could not demonstrate a clear relation with each molecule except for cyclin E, but suggesting that aberrant accumulation of these proteins was considered as a reason for telomerase deregulation, which may play an essential role in the pathway of telomerase regulation.

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.

Interferon-alpha repressed telomerase along with G1-accumulation of Daudi cells

The implications of telomerase on senescence and human carcinogenesis are widely accepted, but the changes of telomerase activity along with cell cycle modulation by anticancer treatment still remain obscure. In this paper, we issued whether the telomerase activity fluctuated along with cell cycle of cultured cancer cells using the antiproliferative effect of interferon-alpha (IFN-alpha). Daudi Burkitt lymphoma cells, treated with IFN-alpha, showed proliferation inhibition and cell cycle arrest at G1. The telomerase activity at 72 h was repressed to about 20% of control cells. Furthermore, after 72 h IFN-alpha treatment, the cells in G1 phase showed the marked decrease of telomerase activity, while cells in S and G2/M still possessed it. Among expressions of telomerase-related genes, only the catalytic subunit of telomerase (hTERT) decreased from 48 h, while the template RNA component (hTERC) and telomerase-associated protein 1 (TEP-1) were not affected. The downregulation of c-Myc preceded the change of hTERT. Moreover, the analysis of cells treated with IFN-alpha for 24 h revealed that cells in G1-to-S transition mainly expressed high hTERT, while S and G2/M cells had higher level of telomerase activity than that of G1 cells. These results indicate that (i) the expression of hTERT precedes the telomerase activity which is higher in S and G2/M phases than G1 phase, (ii) IFN-alpha repressed the telomerase activity in a cell cycle-dependent manner with the downregulation of hTERT.

Telomerase activation and cell proliferation during 7,12-dimethylbenz[a]anthracene-induced hamster cheek pouch carcinogenesis

Telomerase is a ribonucleoprotein complex intimately involved in cell immortalization and carcinogenesis. This enzyme is activated and stabilizes telomere length in almost all types of cancer. Telomerase may be necessary for continuous cell proliferation. In this study, we analyzed telomerase activity in hamster experimental oral lesions (starting from epithelial hyperplasia through dysplasia, carcinoma in situ, and invasive carcinoma) evoked by 7,12-dimethylbenz[a]anthracene, and in normal mucosa. We also analyzed proliferative activity in these lesions by using immunohistochemical analysis and flow cytometry. Histologically normal epithelium expressed weak telomerase activity. The telomerase activity count increased rapidly in the early stage of carcinogenesis and gradually in the late stage. Cell-proliferative activity closely correlated with progression of disease. These findings indicate that telomerase activation is an early event and that increases in telomerase activity upregulate cell proliferation in chemically induced hamster oral carcinogenesis.

Absence of correlation between telomerase activity and hepatic neoplasia in B6C3F1 mice

Telomeres are the physical ends of eukaryotic chromosomes, which maintain chromosome stability and are progressively shortened with aging in somatic cells. The enzyme telomerase elongates telometric DNA and while not usually detectable in human somatic cells is expressed in most human tumors. The present study was conducted to determine if telomerase activity is a marker for spontaneous hepatic neoplastic changes in B6C3F1 mice, a strain frequently used in rodent carcinogenicity studies. Telomerase activity was generally higher in microscopically normal liver tissue from 8-week-old compared to aged mice (110-week-old); however, telomerase activity was not consistently increased in hepatocellular adenomas and carcinomas. It is proposed that, while elevated telomerase activity may modulate human tumor development, modulation of telomerase activity is not a feature of hepatic tumors in B6C3F1 mice and therefore is unlikely to have utility as a molecular marker for hepatic neoplasia in this mouse strain.

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

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

Functional requirement of p23 and Hsp90 in telomerase complexes

Most normal human diploid cells have no detectable telomerase; however, expression of the catalytic subunit of telomerase is sufficient to induce telomerase activity and, in many cases, will bypass normal senescence. We and others have previously demonstrated in vitro assembly of active telomerase by combining the purified RNA component with the reverse transcriptase catalytic component synthesized in rabbit reticulocyte extract. Here we show that assembly of active telomerase from in vitro-synthesized components requires the contribution of proteins present in reticulocyte extracts. We have identified the molecular chaperones p23 and Hsp90 as proteins that bind to the catalytic subunit of telomerase. Blockade of this interaction inhibits assembly of active telomerase in vitro. Also, a significant fraction of active telomerase from cell extracts is associated with p23 and Hsp90. Consistent with in vitro results, inhibition of Hsp90 function in cells blocks assembly of active telomerase. To our knowledge, p23 and Hsp90 are the first telomerase-associated proteins demonstrated to contribute to telomerase activity.

Telomerase targeting in cancer treatment: new developments

Telomerase, a ribonucleoprotein expressed in 85% of advanced cancers but not in most somatic cells, compensates for telomeric DNA erosion and as such stabilizes cell immortality. Telomerase inhibition might restore mortality in tumor cells. Recent progress is illustrated in studies on telomerase and telomere targeting with differentiation induction, reverse transcriptase inhibitors, promoter down regulation, antisense inhibition, and blockage of telomere/telomerase interactions. Also, new developments are described indicating that anti-telomerase treatment can induce apoptosis in tumor cells and can chemosensitize drug-resistant cell lines. Implications of these findings for anti-telomerase-based therapeutic applications, in particular in combination therapies, are discussed. Copyright 1999 Harcourt Publishers Ltd.

Telomerase in kinetoplastid parasitic protozoa

We have identified telomerase activity in extracts of three evolutionarily diverse kinetoplastid species: Trypanosoma brucei, Leishmania major, and Leishmania tarentolae. Telomerase activity was initially detected in extracts from insect form cells of all three kinetoplastid species by using a modification of the one-tube telomere repeat amplification protocol [Kim, N., et al. (1994) Science 266, 2011-2015], although better results were subsequently achieved with the two-tube telomere repeat amplification protocol [Autexier, C., Pruzan, R., Funk, W. & Greider, C. (1996) EMBO J. 15, 5928-5935]. The activity in T. brucei extracts was sufficiently robust to enable its detection in a direct assay of telomerase; enzyme processivity was found to be relatively low. The in vitro properties of telomerase suggest a possible templating domain sequence for the telomerase RNA of T. brucei. Telomerase activity is likely to contribute to telomere maintenance in these parasitic organisms and provides a new target for chemotherapeutic intervention.

Applications of telomerase research in the fight against cancer

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

Activation of telomerase and its association with G1-phase of the cell cycle during UVB-induced skin tumorigenesis in SKH-1 hairless mouse

Telomerase is a ribonucleoprotein enzyme that adds hexanucleotide repeats TTAGGG to the ends of chromosomes. Telomerase activation is known to play a crucial role in cell-immortalization and carcinogenesis. Telomerase is shown to have a correlation with cell cycle progression, which is controlled by the regulation of cyclins, cyclin dependent kinases (cdks) and cyclin dependent kinase inhibitors (cdkis). Abnormal expression of these regulatory molecules may cause alterations in cell cycle with uncontrolled cell growth, a universal feature of neoplasia. Skin cancer is the most prevalent form of cancer in humans and the solar UV radiation is its major cause. Here, we investigated modulation in telomerase activity and protein expression of cell cycle regulatory molecules during the development of UVB-induced tumors in SKH-1 hairless mice. The mice were exposed to 180 mjoules/cm2 UVB radiation, thrice weekly for 24 weeks. The animals were sacrificed at 4 week intervals and the studies were performed in epidermis. Telomerase activity was barely detectable in the epidermis of non-irradiated mouse. UVB exposure resulted in a progressive increase in telomerase activity starting from the 4th week of exposure. The increased telomerase activity either persisted or further increased with the increased exposure. In papillomas and carcinomas the enzyme activity was comparable and was 45-fold higher than in the epidermis of control mice. Western blot analysis showed an upregulation in the protein expression of cyclin D1 and cyclin E and their regulatory subunits cdk4 and cdk2 during the course of UVB exposure and in papillomas and carcinomas. The protein expression of cdk6 and ckis viz. p16/Ink4A, p21/Waf1 and p27/Kip1 did not show any significant change in UVB exposed skin, but significant upregulation was observed both in papillomas and carcinomas. The results suggest that telomerase activation may be involved in UVB-induced tumorigenesis in mouse skin and that increased telomerase activity may be associated with G1 phase of the cell cycle.

Cytostatic concentrations of anticancer agents do not affect telomerase activity of leukaemic cells in vitro

Telomerase, the enzyme that maintains the ends of linear eukaryotic chromosomes, is more active in the majority of malignant tumours than in normal somatic cells. Telomerase plays a key role in the maintenance of chromosomal stability in tumours, but it still remains unknown whether anticancer agents can inhibit telomerase activity. In this study, we evaluated the effect of various anticancer agents (etoposide, cisplatin, irinotecan, mitomycin C and daunorubicin) on the telomerase activity of three human haematopoietic cancer cell lines (Daudi, K562 and U937). A decrease of telomerase activity was not observed in cells treated with IC50 doses of the drugs, except for irinotecan-treated Daudi cells and daunorubicin- and irinotecan-treated U937 cells. Propidium iodide staining disclosed that the cells with decreased telomerase activity were severely damaged. U937 cells exposed to 5 microM (IC90) etoposide showed three different stages of cell viability during treatment. Apoptotic cells with an intact plasma membrane still maintained high telomerase activity, while cells with plasma membrane damage lost telomerase activity. The mRNA of the telomerase catalytic subunit (hTERT) showed a decrease in expression along with the decline of telomerase activity. These results indicate that the concentrations of drugs resulting in cytostatic effects on cells do not affect telomerase activity.

Telomerase activity does not always imply telomere maintenance

The forced expression of the catalytic subunit of human telomerase, hTERT, produces telomerase activity, allows telomere maintenance, and extends the cellular life span of IMR90 human lung fibroblasts. The mutation D869A abolishes both the catalytic activity of hTERT and its ability to extend cellular life span, demonstrating that the immortalizing capabilities of the enzyme are dependent on active catalysis. A second mutant of hTERT was examined that contains three copies of an HA epitope inserted at the C-terminus. This mutant produced telomerase activity in fibroblasts that was virtually indistinguishable from that of wild type telomerase when assayed in vitro. However, the forced expression of this mutant failed to maintain telomeres or extend cellular life span. Our results show that the catalytic activity of hTERT is required for cellular immortalization but that the presence of active telomerase does not necessarily imply telomere maintenance and immortality.

Telomerase components as a diagnostic tool in human oral lesions

Telomerase activity is considered to be a diagnostic marker of malignancy since most malignant cells express this activity and most somatic cells do not. However, the detection of telomerase activity is rather complicated and is affected by many factors. Recently, human telomerase components were cloned and found to consist of 3 subunits. We assessed which component of telomerase best correlates with malignancy in order to study the possibilities for developing a new diagnostic marker. Telomerase activity was measured by a telomeric repeat amplification protocol (TRAP) assay, and the telomerase components hTR, hTRT-mRNA and TP1-mRNA were detected by the reverse transcriptase-polymerase chain reaction (RT-PCR). Twenty-five of 26 oral malignant lesions, 9 of 22 benign lesions and none of 19 normal control tissues exhibited distinct telomerase activity. hTR and TP1-mRNA expression levels were detected in all malignant lesions and normal control tissues and had no significant correlation with the telomerase activity results. In contrast, hTRT-mRNA expression was closely associated with telomerase activity. All lesions expressing hTRT were telomerase positive. In addition, some samples of dysplastic lesions, benign tumors, lichen planus and normal mucosa exhibiting poor telomerase activity revealed weak expression of hTRT. Expression levels of hTRT-mRNA positively correlated with clinical and pathological findings. Detection of hTRT-mRNA by RT-PCR appeared to be more sensitive for telomerase than measurement of telomerase activity by the TRAP assay. Detection of hTRT-mRNA may provide information useful in the diagnosis of oral malignancies.

Advanced laboratory techniques at the Armed Forces Institute of Pathology applicable to diagnosis and research in dermatology

The Armed Forces Institute of Pathology (AFIP) is well known for providing expert pathology in many specialties and educational courses for civilian and military personnel. Some of the departments at the AFIP have also developed expertise in various advanced laboratory techniques for diagnosis and research that are applicable to dermatology and are not available at most medical centers.

Telomerase activity in melanoma and non-melanoma skin cancer

Telomeres are specialized structures consisting of repeat arrays of TTAGGGn located at the ends of chromosomes. They are essential for chromosome stability and, in the majority of normal somatic cells, telomeres shorten with each cell division. Most immortalized cell lines and tumours reactivate telomerase to stabilize the shortening chromosomes. Telomerase activation is regarded as a central step in carcinogenesis and, here, we demonstrate telomerase activation in premalignant skin lesions and also in all forms of skin cancer. Telomerase activation in normal skin was a rare event, and among 16 samples of normal skin (one with a history of chronic sun exposure) 12.5% (2 out of 16) exhibited telomerase activity. One out of 16 (6.25%) benign proliferative lesions, including viral and seborrhoeic wart samples, had telomerase activity. In premalignant actinic keratoses and Bowen's disease, 42% (11 out of 26) of samples exhibited telomerase activity. In the basal cell carcinoma and cutaneous malignant melanoma (CMM) lesions, telomerase was activated in 77% (10 out of 13) and 69% (22 out of 32) respectively. However, only 25% (3 out of 12) of squamous cell carcinomas (SCC) had telomerase activity. With the exception of one SCC sample, telomerase activity in a positive control cell line derived from a fibrosarcoma (HT1080) was not inhibited when mixed with the telomerase-negative SCC or CMM extracts, indicating that, overall, Taq polymerase and telomerase inhibitors were not responsible for the negative results. Mean telomere hybridizing restriction fragment (TRF) analysis was performed in a number of telomerase-positive and -negative samples and, although a broad range of TRF sizes ranging from 3.6 to 17 kb was observed, a relationship between telomerase status and TRF size was not found.

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.

Telomerase is not an epidermal stem cell marker and is downregulated by calcium

The ribonucleoprotein complex telomerase, which was found to be active in germ line, immortal, and tumor cells, and in cells from continuously renewing normal tissues such as epidermis or bone marrow, is thought to be correlated with an indefinite life span. Therefore, it has been postulated that in the normal tissues, telomerase activity may be restricted to stem cells, the possible precursors of tumor cells. Here, we demonstrate that a 56% enriched population of epidermal stem cells exhibited less telomerase activity than the more actively proliferating transit amplifying cells, which are destined to differentiate after a finite number of cell divisions. Thus telomerase is not a stem cell marker. In human epidermis we found a heterogeneous expression of the telomerase RNA component (hTR) within the basal layer, with clusters of hTR-positive cells showing variable activities. Histone-3 expressing S-phase basal cells were distributed evenly, illustrating that hTR upregulation may not strictly be correlated with proliferation. We further show for human epidermal cells that differentiation-dependent downregulation of telomerase correlates with Ca++-induced cell differentiation and that increasing the amount of Ca++ but not Mg++ or Zn++ reduced telomerase activity in a dose-dependent manner in a cell-free system (differentiation-independent). Furthermore, addition of ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid completely reversed this Ca++-induced inhibition. These data indicate that Ca++ is not only an important regulator of epidermal differentiation but also a key regulator of telomerase.

The effect of vitamin E acetate on ultraviolet-induced mouse skin carcinogenesis

Despite the benefits of sunscreens, ultraviolet (UV) exposure can still lead to skin cancer. In this study we investigated the effect of topical application of the antioxidant vitamin E acetate (VEA) on the inhibition of UV-induced carcinogenesis. Hairless SKH-1 mice received 5.2 mg of VEA 30 min before (VEA/UV) or after (UV/ VEA) a single minimal erythemic dose of UV light. Vehicle-control animals received acetone 30 min before UV exposure (Ace/UV). After 24 h, cyclobutane dimer repair was twofold and 1.5-fold greater in the UVNEA and VEA/UV groups, respectively. Expression of p53 protein in the UV/VEA group was maximum at 12 h after UV exposure, whereas in the Ace/UV- and VEA/UV-treated mice, maximum p53 immunostaining was statistically higher at 15 h (P = 0.03). DNA synthesis as determined by 5-bromo-2'-deoxyuridine incorporation was twofold higher after 15 h in all groups but was not statistically different among treatment groups. Protein levels of cyclin D1 and p21 were increased in both VEA groups by 6 h. In addition, VEA treatments delayed tumor formation and yield for the first 20 wk, although this difference was lost by 30 wk. The telomerase activity of carcinomas from the UV/VEA-treated mice was statistically lower than that of the Ace/UV-treated mice (P = 0.05). This study showed that although VEA may mitigate some of the initial events associated with UV irradiation such as DNA damage and p53 expression, it has limited potential in preventing UV-induced proliferation and tumor formation.

Telomerase activity in human chorionic villi and placenta determined by TRAP and in situ TRAP assay

Telomerase activity (TA) was analysed in human chorionic villi and placenta in normal and abnormal pregnancy using the telomeric repeat amplification protocol (TRAP) and in situ TRAP assay. Twenty chorionic villi specimens and 25 placenta specimens from normal pregnancies were examined as well as placenta specimens from 10 cases of intrauterine growth retardation (IUGR; nine asymmetric and one symmetric). TA was detected in 18 of the 20 (90 per cent) chorionic villi specimens and in 18 of the 25 (72 per cent) placenta specimens from normal pregnancy. However, no or only weak TA was exhibited in the placenta specimens of the nine asymmetric IUGR cases. In situ TRAP assay detected TA in trophoblastic cells from normal pregnancy, but not in trophoblastic cells from cases of asymmetric IUGR.

Telomerase activity and human papillomavirus in malignant, premalignant and benign cervical lesions

The purpose of this study was to define a correlation between telomerase activity and human papillomavirus (HPV) in normal control tissue and in benign, premalignant and malignant cervical lesions. Telomerase activity was detectable in 33 out of 34 cases of squamous-cell carcinoma, five out of six cases of microinvasive carcinoma, 8 out of 20 cases and two out of six cases of high- and low-grade squamous intraepithelial lesions (SILs) respectively. The higher frequency of positive telomerase in invasive carcinoma compared with SILs was observed in both HPV-associated and non-associated groups. Whereas 92.6% of HPV-positive and 100% of HPV-negative invasive lesions expressed telomerase, only 50% of HPV-positive and 25% of HPV-negative SILs did. Interestingly, telomerase activity was also detectable in 13 out of 28 cases of benign lesions regardless of the presence of HPV. In conclusion, there may be two roles of telomerase in the cervix. The first one would present in benign lesions; the second is associated with cancer development and activated during the late stage of multistep carcinogenesis in both HPV-positive and -negative groups.

Telomerase activity correlates with growth of transplantable osteosarcomas in rats treated with cis-diammine dichloroplatinum or the angiogenesis inhibitor AGM-1470

To determine the role of telomerase activity in the growth of tumors in rats undergoing chemotherapy, a comparison of the volumes of telomerase-positive transplantable osteosarcomas was made in rats treated with the antineoplastic agent cis-diammine dichloroplatinum (CDDP) or the angiogenesis inhibitor O-(chloroacetylcarbamoyl)fumagillol (AGM-1470). Male F344 rats, 8 weeks old, received transplants of macroscopic lung metastatic nodules into the subcutaneous back space and treatment was started on day 14 thereafter. CDDP was injected i.v. at doses of 0, 0.625, 1.25 and 2.5 mg/kg body weight (b.w.) and AGM-1470 was administered at total doses of 0, 2.5, 5 and 10 mg/kg b.w. over 2 weeks by osmotic pumps, also implanted into the subcutaneous back space, but remote from the transplanted tumors. On day 28, all animals were killed for measurement of transplanted tumor size and determination of telomerase activities by telomeric repeat amplification protocol (TRAP) assay. The results showed telomerase activity to be highly correlated with the treated/non-treated (T/C) tumor size ratio (r = 0.96, P < 0.0001). In a second experiment, CDDP at 2.5 mg/kg b.w. and AGM-1470 at 10 mg/kg b.w., these being the most effective doses, were given as in the first experiment, and animals were serially killed on days 14, 21, 28, 35 and 42. Tumors in rats treated with CDDP and AGM-1470 showed 18.2% and 20.5% of the control telomerase activity on days 35 and 21, respectively, when tumor growth was inhibited. However, on day 42, the activities increased to 46.5% and 92.5%, this correlating with re-growth (r = 0.73, P < 0.0001). These results suggest that decline of telomerase activity may be involved in tumor growth retardation induced by chemotherapeutic agents. This possibility clearly warrants further mechanistic studies.

Telomerase activity in oral lichen planus

The purpose of this study was to determine the expression of telomerase in refractory oral lichen planus. Using a polymerase chain reaction-based telomerase activity assay, we investigated telomerase activity in 20 oral lichen planus specimens (erosive 9, atrophic 11). Telomerase activity was detected in 14 cases (erosive 7, atrophic 7). Furthermore, 13 cases of lichen planus with mild dysplasia proved telomerase-positive in eight specimens and six of seven cases devoid of dysplasia were also positive in the telomerase assay. The data indicate that, in general, telomerase activity might be frequently detectable in OLP. The data also suggest that telomerase activity might not be particularly associated with the premalignant phenotype in OLP.