Telomerase activity in melanoma and non-melanoma skin cancer

Telomerase Reverse Transcriptase Protein Expression Is More Frequent in Acral Lentiginous Melanoma Than in Other Types of Cutaneous Melanoma

CONTEXT.—

Molecularly distinct from cutaneous melanomas arising from sun-exposed sites, acral lentiginous melanomas (ALMs) typically lack ultraviolet-signature mutations, such as telomerase reverse transcriptase (TERT) promoter mutations. Instead, ALMs show a high degree of copy number alterations, often with multiple amplifications of TERT, which are associated with adverse prognosis. The prognostic value of TERT protein expression in acral melanomas, however, is not established.

OBJECTIVE.—

To evaluate the frequency and pattern of TERT immunoreactivity and assess the potential utility of TERT expression as a prognostic indicator in ALMs.

DESIGN.—

TERT expression by immunohistochemistry was analyzed in a series of 57 acral and nonacral melanocytic lesions, including 24 primary and 6 metastatic ALMs. Clinical outcome in patients with ALMs by TERT expression was assessed.

RESULTS.—

TERT expression was more frequent in ALMs than in nonlentiginous acral melanomas and nonacral cutaneous melanomas, and was absent in acral nevi (P = .01). When present, TERT expression in ALMs was cytoplasmic and more intense than TERT expression in other melanocytic lesions (P = .05) with a higher H-score (P = .01). There was a trend toward decreased overall survival in patients with ALMs with TERT immunoreactivity, but it did not reach statistical significance. Furthermore, no correlation was found between TERT expression and disease-specific survival in patients with ALMs.

CONCLUSIONS.—

Although TERT protein expression was frequently detected in both primary and metastatic ALMs, TERT immunoreactivity in ALMs did not correlate with survival in our study. Further studies with larger cohorts are needed to elucidate the prognostic value of TERT expression in ALMs.

Current and Future Trends in Molecular Biomarkers for Diagnostic, Prognostic, and Predictive Purposes in Non-Melanoma Skin Cancer

Skin cancer represents the most common type of cancer among Caucasians and presents in two main forms: melanoma and non-melanoma skin cancer (NMSC). NMSC is an umbrella term, under which basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and Merkel cell carcinoma (MCC) are found along with the pre-neoplastic lesions, Bowen disease (BD) and actinic keratosis (AK). Due to the mild nature of the majority of NMSC cases, research regarding their biology has attracted much less attention. Nonetheless, NMSC can bear unfavorable characteristics for the patient, such as invasiveness, local recurrence and distant metastases. In addition, late diagnosis is relatively common for a number of cases of NMSC due to the inability to recognize such cases. Recognizing the need for clinically and economically efficient modes of diagnosis, staging, and prognosis, the present review discusses the main etiological and pathological features of NMSC as well as the new and promising molecular biomarkers available including telomere length (TL), telomerase activity (TA), CpG island methylation (CIM), histone methylation and acetylation, microRNAs (miRNAs), and micronuclei frequency (MNf). The evaluation of all these aspects is important for the correct management of NMSC; therefore, the current review aims to assist future studies interested in exploring the diagnostic and prognostic potential of molecular biomarkers for these entities.

Telomeres and Telomerase in Cutaneous Squamous Cell Carcinoma

The role of telomere biology and telomerase activation in skin cancers has been investigated in melanoma and basal cell carcinoma but limited evidence is available for cutaneous squamous cell carcinoma (cSCC). We will review the current knowledge on the role of telomere and telomerase pathway in cSCC pathogenesis. At the somatic level, both long and short telomere lengths have been described in cSCC. This telomere dichotomy is probably related to two different mechanisms of tumour initiation which determines two tumour subtypes. Telomere shortening is observed during the invasive progression from in situ forms of cSCC, such as Bowen's disease (BD) and actinic keratosis (AK), to invasive cSCC. At the germline level, controversial results have been reported on the association between constitutive telomere length and risk of cSCC. Approximately 75⁻85% of cSCC tumours are characterized by a high level of telomerase activity. Telomerase activation has been also reported in AKs and BD and in sun-damaged skin, thus supporting the hypothesis that UV modulates telomerase activity in the skin. Activating TERT promoter mutations have been identified in 32⁻70% of cSCCs, with the majority showing the UV-signature. No significant correlation was observed between TERT promoter mutations and cSCC clinico-pathological features. However, TERT promoter mutations have been recently suggested to be independent predictors of an adverse outcome. The attention on telomere biology and telomerase activity in cSCC is increasing for the potential implications in the development of effective tools for prognostic assessment and of therapeutic strategies in patients with cutaneous cSCC.

Correlation of telomere length to malignancy potential in non-melanoma skin cancers

Telomeres are associated with cell fate and aging through their role in the cellular response to stress and growth stimulation resulting from previous cell divisions and DNA damage. Telomere shortening has been observed in most human cancers, and is known to be a feature of malignancy. The aim of this study is to clarify whether telomere length is related to the malignant potential of non-melanoma skin cancers. Telomere length was analyzed using tissue quantitative fluorescence in situ hybridization in 36 non-melanoma skin cancers including basal cell carcinoma (BCC), squamous cell carcinoma (SCC), Bowen's disease (BD) and actinic keratosis (AK), and also in 26 samples of normal-appearing epidermal tissue surrounding or located close to each tumor. The fluorescence intensities of telomeres and centromeres within nuclei were determined, and the telomere-centromere ratio (TCR) was then calculated in each sample. The resulting histograms suggested that the TCR values for each type of tumor cell were distributed in a lower range than those for epidermal cells located close to the corresponding tumor type, and that the TCR values for SCC and BCC cells were distributed in a lower range than those for BD and AK cells. These results were completely consistent with the potential for metastasis and invasion of each tumor type, suggesting that telomere length in non-melanoma skin cancer cells is intrinsically linked to their biological behavior.

Cancer Immune Equilibrium and Schizophrenia Have Similar Interferon-γ, Tumor Necrosis Factor-α, and Interleukin Expression: A Tumor Model of Schizophrenia

For at least a century, a debate has continued as to whether cancer risk is reduced in schizophrenia. Genetic studies have also suggested the 2 conditions may share protein transcriptional pathways. The author predicted that if the pathophysiology of schizophrenia confers protection from cancer, then the immunology of schizophrenia should reflect a state of tumor suppression, ie, the opposite of tumor escape. To examine this possibility, the author performed a literature search for measurements of cytokines in drug-naïve first episode subjects with schizophrenia for comparison with cytokine expression in tumor escape vs tumor suppression. The comparison showed that instead of either tumor suppression or escape, schizophrenia appears to be in a state of tumor equilibrium. Based on this finding, the author hypothesized that the clinical presentation of schizophrenia may involve cell transformation similar to an early stage of cancer initiation or an attenuated tumorigenesis. While this condition could reflect the presence of an actual tumor such as an ovarian teratoma causing anti-NMDA receptor encephalitis, it would only explain a small percentage of cases. To find a more likely tumor model, the author then compared the cytokine profile of schizophrenia to individual cancers and found the best match was melanoma. To demonstrate the viability of the theory, the author compared the hallmarks, emerging hallmarks, and enabling characteristics of melanoma to schizophrenia and found that many findings in schizophrenia are understood if schizophrenia is a condition of attenuated tumorigenesis.

From Normal Skin to Squamous Cell Carcinoma: A Quest for Novel Biomarkers

Squamous cells carcinoma (SCC) is the second most frequent of the keratinocyte-derived malignancies after basal cell carcinoma and is associated with a significant psychosocial and economic burden for both the patient himself and society. Reported risk factors for the malignant transformation of keratinocytes and development of SCC include ultraviolet light exposure, followed by chronic scarring and inflammation, exposure to chemical compounds (arsenic, insecticides, and pesticides), and immune-suppression. Despite various available treatment methods and recent advances in noninvasive or minimal invasive diagnostic techniques, the risk recurrence and metastasis are far from being negligible, even in patients with negative histological margins and lymph nodes. Analyzing normal, dysplastic, and malignant keratinocyte proteome holds special promise for novel biomarker discovery in SCC that could be used in the future for early detection, risk assessment, tumor monitoring, and development of targeted therapeutic strategies.

Telomere length and the risk of cutaneous melanoma and non-melanoma skin cancer: a review of the literature and meta-analysis

There is much evidence supporting the role of telomeres in cancer pathogenesis, however the studies that investigated the association between telomere length and skin cancer risk provided inconsistent results. To help clarify this issue, we performed a systematic review and meta-analysis of published papers on the association between peripheral leukocytes telomere length (PLTL) and the risk of cutaneous melanoma and non-melanoma skin cancer (NMSC). We calculated summary relative risks (SRR) and 95% confidence intervals (95% CI) using random effect models with maximum likelihood estimates, and explored causes of between-studies heterogeneity of risk estimates. We included 1629 cutaneous melanoma and 1439 NMSC from eight independent studies published until March 2015. The SRR of cutaneous melanoma for those in the lowest (vs. highest) category of PLTL distribution was 0.25 (95% CI 0.09-0.67). The results were less clear for NMSC, with two studies reporting no association and one study showing an increase in risk for those in the lowest (vs. highest) category of PLTL distribution. For both cutaneous melanoma and NMSC, the between-studies heterogeneity was large, mainly due to inclusion of hospital-based case-control studies. Our meta-analysis shows evidence of an association between short PLTL and reduced risk for cutaneous melanoma.

Immunohistochemical expression of MCM2 in nonmelanoma epithelial skin cancers

Cutaneous basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) represent 45.5% and 37.02%, respectively, of total malignant skin cancer according to the latest registry of Egyptian National Cancer Institute. Minichromosome maintenance (MCM) proteins are essential replication initiation factors. The current study examined the immunohistochemical expression of MCM2 in normal skin (10 cases), some proliferative skin lesions (6 psoriasis, 2 keratoacanthoma, and 2 seborrheic keratosis), and nonmelanoma epithelial skin cancers (20 BCC and 21 SCC). MCM2 was expressed in basal layer of normal epidermis and upregulated in proliferative skin lesions and nonmelanoma epithelial skin cancers without significant differences between the latter groups (P > 0.05). Mean and median values of MCM2 percentage of expression in BCC were higher than that of SCC (P = 0.004). MCM2 promotes proliferative capacity of the cells manifested by its expression in basal layer of epidermis, hyperproliferative skin lesions, and malignant cutaneous tumors. Proliferative capacity of BCC may be higher than SCC and this does not necessarily reflect aggressive behavior.

Squamous cell carcinoma in a psoriasis patient after multiple courses of phototherapy

The authors present a clinical case study of squamous cell carcinoma in a psoriasis patient after 24 courses of phototherapy (22 courses of PUVA therapy and two courses of mid-wavelength ultraviolet therapy (311 nm)). The malignant neoplasm developed against the background of signs of a chronic photodamage of the skin: lentigo, actinic elastosis, diffuse hyperpigmentation, spotty skin pigmentation.

The secreted protein S100A7 (psoriasin) is induced by telomere dysfunction in human keratinocytes independently of a DNA damage response and cell cycle regulators

Background

Replicative senescence is preceded by loss of repeat sequences of DNA from the telomeres that eventually leads to telomere dysfunction, the accumulation of irreparable DNA double strand breaks and a DNA damage response (DDR). However, we have previously reported that whilst telomere dysfunction in human keratinocytes is associated with a permanent cell cycle arrest, the DDR was very weak and transcriptional profiling also revealed several molecules normally associated with keratinocytes terminal differentiation, including S100A7 (psoriasin).

Results

We show here that S100A7 and the closely related S100A15 (koebnerisin) are not induced by repairable or irreparable DSBs, ruling out the hypotheses that these genes are induced either by the low DDR observed or by non-specific cell cycle arrest. We next tested whether S100A7 was induced by the cell cycle effectors ARF (p14^ARF), CDKN2A (p16^INK4A) and TP53 (p53) and found that, although all induced a similar level of acute and permanent cell cycle arrest to telomere dysfunction, none induced S100A7 (except p53 over-expression at high levels), showing that cell cycle arrest is not sufficient for its induction. The closely related transcript S100A15 was also upregulated by telomere dysfunction, to a similar extent by p16^INK4A and p53 and to a lesser extent by p14^ARF.

Conclusions

Our results show that mere cell cycle arrest, the upregulation of senescence-associated cell cycle effectors and DNA damage are not sufficient for the induction of the S100 transcripts; they further suggest that whilst the induction of S100A15 expression is linked to both telomere-dependent and -independent senescence, S100A7 expression is specifically associated with telomere-dependent senescence in normal keratinocytes. As both S100A7 and S100A15 are secreted proteins, they may find utility in the early detection of human keratinocyte telomere dysfunction and senescence.

TERT promoter mutation is uncommon in acral lentiginous melanoma

BACKGROUND

Melanoma is a heterogeneous group of diseases with distinct sets of genetic changes. Recurrent and mutually exclusive C>T or CC>TT transition mutations were identified in the promoter region of the reverse transcriptase catalytic subunit of the telomerase gene (TERT) in melanoma recently, and it was suggested that they enhanced the expression of TERT gene and played important roles in the melanoma pathogenesis. These mono or di-nucleotide transitions were ultraviolet (UV)-signature mutations.

METHODS

In this study, polymerase chain reaction and direct sequencing of TERT promoter using formalin-fixed and paraffin-embedded tissue was performed to investigate whether these UV-signature mutations were also present in acral lentiginous melanoma.

RESULTS

TERT promoter mutation was identified in only 2 of the 32 cases (6%) of acral lentiginous melanomas while it was identified in 3 of the 9 cases (33%) of non-acral cutaneous melanomas. The difference was statistically significant (p = 0.028).

CONCLUSIONS

The rarity of TERT promoter mutation in the acral lentiginous melanoma was consistent with the supposed role of UV light in the melanoma pathogenesis and also corroborated the view that acral lentiginous melanomas have a different pathogenesis with the melanomas from sun-exposed sites.

Mutations of the TERT promoter are common in basal cell carcinoma and squamous cell carcinoma

Telomerase is frequently expressed in cancer and contributes to carcinogenesis. Two recent publications report the identification of a set of recurrent mutations in melanoma in the promoter of the telomerase reverse transcriptase gene (TERT) that appears to be the result of mutagenesis from ultraviolet (UV) radiation. Both groups reported that the mutations increase the transcription of TERT. This prompted our search for similar mutations in two other UV-related skin cancers, basal cell carcinoma, and squamous cell carcinoma. We found that the activating TERT promoter mutations reported in melanoma are also frequent in squamous cell carcinoma (50%) and basal cell carcinoma, the latter including both sporadic tumors (78%) and tumors from patients with nevoid basal cell carcinoma syndrome (68%). These mutations were found in only 1 of 11 Bowen's disease (squamous cell carcinoma in situ) specimens, and in none of 15 non-malignant skin specimens and 57 blood specimens. The mutations were frequently homozygous or hemizygous, with little or no normal signal at the mutated positions. These data suggest that TERT promoter mutations are the most frequent putative oncogenic mutations in cutaneous cancer.

Squamous cell carcinoma of the skin: Emerging need for novel biomarkers

The incidence of non-melanoma skin cancers (NMSC) is rising worldwide resulting in demand for clinically useful prognostic biomarkers for these malignant tumors, especially for invasive and metastatic cutaneous squamous cell carcinoma (cSCC). Important risk factors for the development and progression of cSCC include ultraviolet radiation, chronic skin ulcers and immunosuppression. Due to the role of cumulative long-term sun exposure, cSCC is usually a disease of the elderly, but the incidence is also growing in younger individuals due to increased recreational exposure to sunlight. Although clinical diagnosis of cSCC is usually easy and treatment with surgical excision curable, it is responsible for the majority of NMSC related deaths. Clinicians treating skin cancer patients are aware that certain cSCCs grow rapidly and metastasize, but the underlying molecular mechanisms responsible for the aggressive progression of a subpopulation of cSCCs remain incompletely understood. Recently, new molecular markers for progression of cSCC have been identified.

Association between TERT-CLPTM1L rs401681[C] allele and NMSC cancer risk: a meta-analysis including 45,184 subjects

Single-nucleotide polymorphism of CLPTM1L-rs401681(C > T) at the 5p15.33 locus is significantly associated with cancer risk as reported in genome-wide association studies, but the reported studies for non-melanoma skin cancer (NMSC) are inconclusive. To assess the association between rs401681[C] allele and NMSC risk, we performed this meta-analysis with four case-control studies involving 5,469 cases and 39,715 controls. Our meta-analysis showed that rs401681[C] allele was associated with NMSC susceptibility in the overall subjects (C vs. T, OR 1.13, 95 % CI 1.07-1.20). In the stratified analysis, the rs401681[C] allele confers susceptibility in Icelanders (C vs. T, OR 1.15, 95 % CI 1.06-1.26) and non-Icelanders (C vs. T, OR 1.13, 95 % CI 1.03-1.24). In the subtype analysis, we found that rs401681[C] allele was a risk factor for BCC, but not SCC in the overall subjects.

Telomerase detection in the diagnosis and prognosis of cancer

Telomerase, a critical enzyme responsible 'for cellular immortality, is usually repressed in somatic cells except for lymphocytes and self-renewal cells, but is activated in approximately 85% of human cancer tissues. The human telomerase reverse transcriptase (hTERT) is the catalytic component of human telomerase. In cancers in which telomerase activation occurs at the early stages of the disease, telomerase activity and hTERT expression are useful markers for the detection of cancer cells. In other cancers in which telomerase becomes upregulated upon tumor progression, they are useful as prognostic indicators. However, careful attention should be paid to false-negative results caused by the instability of telomerase and of the hTERT mRNA and the presence of PCR inhibitors, as well as to false-positive results caused by the presence of alternatively spliced hTERT mRNA and normal cells with telomerase activity. Recently, methods for the in situ detection of the hTERT mRNA and protein have been developed. These methods should facilitate the unequivocal detection of cancer cells, even in tissues containing a background of normal telomerase-positive cells.

Study of telomerase reverse transcriptase (hTERT) expression in normal, aged, and photo-aged skin

BACKGROUND

Telomerase is a ribonucleoprotein enzyme capable of extending chromosome ends with telomeric DNA sequences. It protects the germline and stem cells from senescence by preventing telomere attrition. Cutaneous aging includes intrinsic aging, and photo-aging. Telomere-associated cellular senescence contributes to certain age-related cutaneous disorders, including increased cancer incidence. Premature skin aging in xeroderma pigmentosa (XP) is expected to show increased telomere attrition. We aimed to study human telomerase reverse transcriptase (hTERT) expression in normal, aged and photo-aged skin and to investigate its possible role in the pathogenesis of aging and photo-aging.

METHODS

hTERT expression using immunohistochemistry was studied in 75 subjects comprising four groups: group I, 10 subjects with aged skin; group II, 20 subjects with photo-aging; group III, Five patients with XP; and group IV, 40 subjects comprising the control groups.

RESULTS

We found positive hTERT in normal skin and in the basal and sometimes in supra-basal layers. We reported positive hTERT expression in dermal fibroblasts, histiocytes, and skin appendages (other than hair follicles) in some cases from all the studied groups. Photo-aged and prematurely photo-aged skin showed greater hTERT expression than young and aged skin.

CONCLUSION

Telomeres rather than telomerase are involved in cellular senescence. Yet, telomerase is intimately related to photo-aging in which lifetime cumulative sun exposure is an important factor. However, genetic damage in XP is the decisive factor and not merely ultraviolet exposure.

Combined analysis of cell growth and apoptosis-regulating proteins in HPVs associated anogenital tumors

Background

The clinical course of human papillomavirus (HPV) associated with Bowenoid papulosis and condyloma acuminatum of anogenital tumors are still unknown. Here we evaluated molecules that are relevant to cellular proliferation and regulation of apoptosis in HPV associated anogenital tumors.

Methods

We investigated the levels of telomerase activity, and inhibitor of apoptosis proteins (IAPs) family (c-IAP1, c-IAP2, XIAP) and c-Myc mRNA expression levels in 20 specimens of Bowenoid papulosis and 36 specimens of condyloma acuminatum in anogenital areas. Overall, phosphorylated (p-) AKT, p-ribosomal protein S6 (S6) and p-4E-binding protein 1 (4EBP1) expression levels were examined by immunohistochemistry in anogenital tumors both with and without positive telomerase activity.

Results

Positive telomerase activity was detected in 41.7% of Bowenoid papulosis and 27.3% of condyloma acuminatum compared to normal skin (p < 0.001). In contrast, the expression levels of Bowenoid papulosis indicated that c-IAP1, c-IAP2 and XIAP mRNA were significantly upregulated compared to those in both condyloma acuminatum samples (p < 0.001, p < 0.001, p = 0.022, respectively) and normal skin (p < 0.001, p = 0.002, p = 0.034, respectively). Overall, 30% of Bowenoid papulosis with high risk HPV strongly promoted IAPs family and c-Myc but condyloma acuminatum did not significantly activate those genes. Immunohistochemically, p-Akt and p-S6 expressions were associated with positive telomerase activity but not with p-4EBP1 expression.

Conclusion

Combined analysis of the IAPs family, c-Myc mRNA expression, telomerase activity levels and p-Akt/p-S6 expressions may provide clinically relevant molecular markers in HPV associated anogenital tumors.

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

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

Unusually stable abnormal karyotype in a highly aggressive melanoma negative for telomerase activity

Malignant melanomas are characterized by increased karyotypic complexity, extended aneuploidy and heteroploidy. We report a melanoma metastasis to the peritoneal cavity with an exceptionally stable, abnormal pseudodiploid karyotype as verified by G-Banding, subtelomeric, centromeric and quantitative Fluorescence in Situ Hybridization (FISH). Interestingly this tumor had no detectable telomerase activity as indicated by the Telomere Repeat Amplification Protocol. Telomeric Flow-FISH and quantitative telomeric FISH on mitotic preparations showed that malignant cells had relatively short telomeres. Microsatellite instability was ruled out by the allelic pattern of two major mononucleotide repeats. Our data suggest that a combination of melanoma specific genomic imbalances were sufficient and enough for this fatal tumor progression, that was not accompanied by genomic instability, telomerase activity, or the engagement of the alternative recombinatorial telomere lengthening pathway.

Immunohistochemical localization of telomerase in myomas and in uterine myometrium

Telomerase activity could be a potential marker for the neoplastic process, because it is absent in normal cells and present in tumor cells. Immunohistochemical studies were conducted using samples obtained from 32 uterine myomas, each sample having a size of 3-4 cm and obtained from women between 35 and 45 years of age. These studies also concentrated on fragments of macroscopically unaltered myometrium, collected 3-4 cm from a uterine tumor. Immunohistochemistry was performed using antibody to the catalytic unit of telomerase (hTERT; clone 44F12, NCL-L-hTERT, Novocastra Laboratories, UK). This study aimed at detecting a possible presence of potentially neoplastic cells in the margins of healthy tissue, which was removed together with the primary tumor. The results were classified according to the number of telomerase-positive cells. Tumors of the first group had up to 50% telomerase-positive cells, while their content in the second group exceeded 50%. Our study demonstrated an almost two-fold increase in the number of telomerase-positive tumor cells compared with myometrial cells 3-4 cm from the tumor. Hopefully, investigating the presence of telomerase in both uterine myometrium and myoma could facilitate the diagnosis of the neoplastic process.

The multi-step process of human skin carcinogenesis: A role for p53, cyclin D1, hTERT, p16, and TSP-1

As proposed by Hanahan and Weinberg (2000. Cell 100, 57-70) carcinogenesis requires crucial events such as (i) genomic instability, (ii) cell cycle deregulation, (iii) induction of a telomere length maintenance mechanism, and (iv) an angiogenic switch. By comparing the expression of p53, cyclin D1, p16, hTERT, and TSP-1 in spontaneously regressing keratoacanthoma (KA) as a paradigm of early neoplasia, with malignant invasive cutaneous squamous cell carcinoma (SCC) as a paradigm of advanced tumour development, we are now able to assign the changes in the expression of these proteins to specific stages and allocate them to defined roles in the multi-step process of skin carcinogenesis. We show that mutational inactivation of the p53 gene, and with that the onset of genomic instability is the earliest event. Individual p53-positive cells are already seen in "normal" skin, and 3/5 actinic keratoses (AKs), 5/22 KAs, and 13/23 SCCs contain p53-positive patches. Cell cycle deregulation was indicated by the overexpression of the cell cycle regulator cyclin D1, as well as by the loss of the cell cycle inhibitor p16. Interestingly, overexpression of cyclin D1 - observed in 80% of KAs and SCCs, respectively - showed a cell cycle-independent function in HaCaT cell transplants on nude mice. Cyclin D1 overexpression was associated with a massive inflammatory response, finally leading to tissue destruction. Loss of the cell cycle inhibitor p16, on the other hand, correlated with SCCs. Thus, it is tempting to suggest that overexpression of cyclin D1 is an early change that in addition to growth stimulation leads to an altered epithelial-mesenchymal interaction, while functional p16 is able to control this deregulated growth and needs to be eliminated for malignant progression. Another requirement for uncontrolled growth is the inhibition of telomere erosion by up-regulating telomerase activity. As measured by hTERT protein expression, all of the KAs and SCCs studied were positive, with a similar distribution of the protein in both groups and an expression pattern resembling that of normal epidermis. Thus, telomerase may not need to be increased significantly in skin carcinomas. Finally, we show that the angiogenesis inhibitor TSP-1 is strongly expressed in most KAs, and mainly by the tumour cells, while in SCCs the generally weak expression is restricted to the tumour-stroma. Furthermore, we provide evidence that the loss of a copy of chromosome 15 is responsible for reduced TSP-1 expression and thereby this aberration contributes to tumour vascularisation (i.e. the angiogenic switch) required for malignant growth.

Impairment of the telomere/telomerase system and genomic instability are associated with keratinocyte immortalization induced by the skin human papillomavirus type 38

The skin human papillomavirus (HPV) types belonging to the genus beta of the HPV phylogenetic tree appear to be associated with nonmelanoma skin cancer. We previously showed that the beta HPV type 38 E6 and E7 oncoproteins are able to inactivate the tumor suppressors p53 and retinoblastoma. Here, both viral proteins were expressed in primary human skin keratinocytes in order to study their effects on the telomere/telomerase system. We show that immortalization of skin keratinocytes induced by HPV38 E6/E7 is associated with hTERT gene overexpression. This event is, in part, explained by the accumulation of the p53-related protein, DeltaNp73. Despite elevated levels of hTERT mRNA, the telomerase activity detected in HPV38 E6/E7 keratinocytes was lower than that observed in HPV16 E6/E7 keratinocytes. The low telomerase activation in highly proliferative HPV38 E6/E7 keratinocytes resulted in the presence of extremely short and unstable telomeres. In addition, we observed anaphase bridges, mitotic multipolarity, and dramatic genomic aberrations. Interestingly, the ectopic expression of hTERT prevents both telomere erosion and genomic instability. Thus, we showed that in HPV38 E6/E7 keratinocytes characterized by unscheduled proliferation, suboptimal activation of telomerase and subsequent extensive telomere shortening result in genomic instability facilitating cellular immortalization.

Telomerase activity of basal cell carcinoma in patients living in North Queensland, Australia

Basal cell carcinoma (BCC) is the most common skin cancer in North Queensland, Australia. The role of telomerase in BCC has not been investigated in this region. The objective of the study was to investigate the expression levels of human telomerase reverse transcriptase (hTERT) and telomerase activity in nodular BCCs and superficial BCCs from patients living in North Queensland. Matched tumor and adjacent nontumorous mucosa samples from 12 BCCs (7 nodular and 5 superficial) among 11 male patients were collected. In these samples, RNA was extracted and then transcribed to complementary DNA. Real-time polymerase chain reaction (PCR) was used to quantify the expression levels of hTERT messenger RNA (mRNA). In addition, telomeric repeat amplification protocol assay, a PCR-based method, was performed to detect telomerase activity in tissue extracts from these samples. The findings were correlated with the clinicopathologic features of patients with these tumors. All BCC samples expressed telomerase hTERT mRNA, and 75% (9/12) of the BCC samples showed telomerase activity. The mean level of expression among BCC samples was higher than that among matched nontumor samples (mean, 0.468 versus 0.140; P < .0001). Nodular BCC samples showed higher expression levels of hTERT mRNA as compared with superficial BCC samples (mean, 0.584 versus 0.305; P < .05). There was no significant association between expression of hTERT mRNA and tumor size. In conclusion, this study is the first on telomerase expression in BCC in Queensland as well as the first to analyze telomerase in BCC by quantitative PCR. The results indicate that telomerase alterations have an important role in the pathogenesis of BCCs. A unique finding is that the telomerase expression level in nodular BCCs is different from that in superficial BCCs.

Telomerase expression in sebaceous lesions of the skin

BACKGROUND

Recent studies have demonstrated telomerase expression in ophthalmologic sebaceous carcinoma and have suggested possible diagnostic utility in distinguishing these neoplasms from sebaceous adenomas. The aim of this study was to evaluate telomerase expression via human telomerase reverse transcriptase (hTERT) immunohistochemical staining in a spectrum of sebaceous lesions of the skin.

METHODS

Paraffin-embedded sections from sebaceous hyperplasia (11), nevus sebaceus (22), sebaceous adenoma (19), sebaceoma (11), and sebaceous carcinoma (14) were evaluated for intensity (0 to 3+) and pattern of anti-hTERT staining.

RESULTS

Strong (2 to 3+) hTERT staining was observed in nucleoli of germinative cells and immature sebocytes in all sebaceous lesions, whereas mature sebocytes were negative. The distribution pattern paralleled features seen by routine haematoxylin and eosin-stained sections.

CONCLUSIONS

All hyperplastic and neoplastic sebaceous skin lesions expressed hTERT in this immunohistochemical study. The pattern of staining was predictive of the histologic pattern of the process but does not significantly add to our diagnostic armamentarium of sebaceous lesions.

Telomeres rather than telomerase a key target for anti-cancer therapy?

It was in the 1930s that telomeres (from the Greek telos = end and meros = part) were first recognized as essential structures at the ends of the chromosomes and were shown to be important for chromosomal stability (Muller HJ: The remaking of chromosomes. The Collecting Net-Woods Hole 1938: 13: 181-198, McClintock B, The stability of broken ends of chromosomes in Zea mays. Genetics 1041: 26: 234-282). However, it was only in 1978 that the first telomeric sequence was identified -- in the protocoa Tetrahymena, a single cell organism that at a certain stage of development has many identical minichromosomes with twice as many telomeres (Blackburn EH and Gall JG. A tandemly repeated sequence at the termini of the extrachromosomal ribosomal RNA genes in Tetrahymena. J. Mol. Biol. 1978: 120: 33-53.). Today we know that telomeres form specialized, three-dimensional DNA-protein structures and fulfil important capping functions. Besides, telomeric DNA is essential as ''access DNA'' for those cells that are not able to counteract loss of DNA during replication because they do not express telomerase, the enzyme responsible for telomere length maintenance. Since telomerase is mostly found in tumor cells and inhibition correlates with telomere shortening and finally growth inhibition, telomerase and lately also the telomeres themselves have become attractive targets for anti-cancer therapy. This review aims to critically throw light on different therapeutical approaches and comes to the conclusion that telomeres may be the better targets for cancer therapeutics.

hTERT expression in melanocytic lesions: an immunohistochemical study on paraffin-embedded tissue

BACKGROUND

Telomerase plays a role in the immortalization of cells and carcinogenesis. Previous studies have yielded conflicting results on whether human telomerase RNA (hTER) expression differs in nevi, atypical nevi and melanomas using polymerase chain reaction-based telomeric repeat amplification protocol or in situ hybridization assays. The aim of this study was to evaluate human telomerase reverse transcriptase (hTERT) staining in melanocytic lesions on paraffin-embedded tissues.

METHODS

Paraffin-embedded sections from 12 acquired nevi, seven dysplastic nevi, 11 Spitz nevi, eight primary invasive melanomas, and three metastatic melanomas were studied for staining intensity (0-3+) and percentage of labeled cells with anti-hTERT.

RESULTS

hTERT staining was observed in most cells (>75%), in all but three lesions, and was of greater intensity in the nucleus, especially the nucleolus, compared with the cytoplasm. Spitz nevi tended to have weaker hTERT staining (mean = 1.7) compared with acquired nevi (mean = 2.2), dysplastic nevi (mean = 2.4), primary melanomas (mean = 2.4), or metastatic melanomas (mean = 3).

CONCLUSIONS

Although telomerase activity was weaker in Spitz nevi, there was overlap with other nevi and primary invasive melanomas in our small series. Thus, hTERT expression does not appear to be a reliable adjunct to the histological diagnosis of primary melanocytic lesions.

Telomere-based DNA damage responses: a new approach to melanoma

Melanoma is the most fatal skin cancer, often highly resistant to chemotherapy. Here we show that treatment with an 11-base DNA oligonucleotide homologous to the telomere 3' overhang sequence (T-oligo) induces apoptosis of several established human melanoma cell lines, including the aggressive MM-AN line, whereas normal human melanocytes exposed to the same or higher T-oligo concentrations show only transient cell cycle arrest, implying that malignant cells are more sensitive to T-oligo effects. When MM-AN cells were briefly exposed to T-oligo in culture and injected into the flank or tail vein of SCID mice, eventual tumor volume and number of metastases were reduced 85-95% compared with control mice. Similarly, T-oligos administered intralesionally or systemically selectively inhibited the growth of previously established MM-AN tumor nodules in the flank and peritoneal cavity by 85 to 90% without detectable toxicity. We previously showed that T-oligos act through ATM, p95/Nbs1, E2F1, p16INK4A, p53, and the p53 homologue p73 to modulate downstream effectors and now additionally demonstrate striking down-regulation of the inhibitor of apoptosis protein livin/ML-IAP. We suggest that T-oligo mimics a physiologic DNA damage signal that is frequently masked in malignant cells and thereby activates innate cancer prevention responses. T-oligos may provide a novel therapeutic approach to melanoma.

Melanoma Cells Express Elevated Levels of Phosphorylated Histone H2AX Foci

When human cells sustain a DNA double-strand break (dsb), histone H2AX in chromatin surrounding the DNA break is phosphorylated, marking repair foci. The number of phosphorylated histone H2AX (gammaH2AX) foci approximates the number of dsb present in the cell's nuclear DNA. We observed 0.4 gammaH2AX foci per nucleus in primary human melanocytes. In contrast, in four melanoma cell lines, we detected 7-17 gammaH2AX foci per nucleus, a 17-42 times increase in the basal level of gammaH2AX foci in melanoma cells relative to melanocytes (MC). Thus, untreated melanoma cells express significantly greater numbers of gammaH2AX foci than do untreated MC. Detection and rejoining of ionizing radiation-induced DNA dsb proceeded as rapidly in melanoma cells as in MC. Melanoma cells, however, reduced the number of radiation-induced gammaH2AX foci down only to pre-irradiation levels. Co-localization of the majority of gammaH2AX foci with ataxia telangiectasia mutated, BRCA1, 53BP1, and Nbs1 foci in untreated melanoma cells indicated that the additional foci in melanoma cells were associated with a DNA change that the cells interpret as DNA dsb. Co-localization of gammaH2AX foci with the telomere replication factor 1 protein in untreated melanoma cells indicates that the additional foci in untreated melanoma cells are associated with dysfunctional telomeres that induce a DNA damage stress response.

Telomeres and telomerase: a dual role in hepatocarcinogenesis

Telomere shortening limits the proliferative capacity of primary human cells and restrains the regenerative capacity of organ systems during chronic diseases and aging. Telomere shortening apparently has a dual role in tumor development and progression. On the one hand, it induces chromosomal instability and the initiation of cancer; on the other hand, tumor progression requires stabilization of telomeres. The predominant mechanism of telomere stabilization in tumor cells is the activation of the telomere-synthesizing enzyme telomerase. The potential use of telomerase activators for the treatment of regenerative disorders will ultimately depend on their effects on tumorigenesis. This review focuses on the role of telomere shortening and telomerase in carcinogenesis with a special focus on hepatocellular carcinoma.

Different effects of interferon-alpha on melanoma cell lines: a study on telomerase reverse transcriptase, telomerase activity and apoptosis

BACKGROUND

Although the antiproliferative and proapoptotic effects of interferon (IFN)-alpha are widely recognized, its antitumour mechanisms are not completely known. Recent studies indicate that the derepressed expression of the catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT), and telomerase activity (TA) are involved in the process of human carcinogenesis. Only a few studies have investigated the effects of IFN-alpha on hTERT and TA, with controversial results. Objectives To study the hTERT mRNA expression, TA and apoptosis in human melanoma cells treated with IFN-alpha.

METHODS

Five human melanoma cell lines (Me665/2/21, Me665/2/60, HT-144, SK-Mel-28 and SK-Mel-5) were cultured in standard conditions and treated with 20000 IU mL-1 of human recombinant IFN-alpha-2b. Apoptosis was evaluated as hypodiploid DNA content determined by flow cytometry, caspase-3/7 activity by enzymatic assay, and poly(adenosine diphosphate-ribose) polymerase cleavage by Western blot analysis. IFN-alpha receptor (IFNA-R) and hTERT mRNA expression levels were evaluated by semiquantitative reverse transcription-polymerase chain reaction. TA was evaluated by a polymerase chain reaction-based telomerase repeat amplification protocol assay.

RESULTS

Besides a variable degree of cell proliferation inhibition in all cell lines tested, we found different responses, ranging from no significant effects in SK-Mel-28 cells, to a high degree of apoptosis with no hTERT mRNA expression and TA modification in HT-144 cells, and induction of apoptosis, along with decrease in hTERT mRNA expression and TA in Me665/2/21 cells. No induction of apoptosis was observed in SK-Mel-5 and Me665/2/60 cells, although an early decrease in hTERT mRNA expression, and a minor increase of both hTERT mRNA expression and TA were found, respectively.

CONCLUSIONS

Our results suggest that the effects of IFN-alpha on hTERT and TA can result from the induction of apoptosis, but they can also occur through a direct modulation of hTERT. We hypothesize that, depending on the cellular context rather than the IFNA-R status of the targeted cells, IFN-alpha can elicit an apoptotic cell death; furthermore, different pathways of apoptosis, not necessarily involving telomerase, can be put into motion.

Inhibition of telomerase increases resistance of melanoma cells to temozolomide, but not to temozolomide combined with poly (adp-ribose) polymerase inhibitor

In the present study, we have investigated the influence of telomerase inhibition in chemosensitivity of melanoma cells to temozolomide (TMZ), a methylating agent with promising antitumor activity against metastatic melanoma. In fact, telomerase, a ribonucleoprotein enzyme expressed in the majority of tumors, is presently considered an attractive target for anticancer therapy, with the double aim of reducing tumor growth and increasing chemosensitivity of cancer cells. Susceptibility to TMZ and to other antitumor agents used for treatment of metastatic melanoma was initially assessed in melanoma lines with different basal levels of telomerase activity. Thereafter, chemosensitivity was investigated after inhibition of telomerase by means of stable transfection of a catalytically inactive, dominant-negative mutant of hTERT (DN-hTERT). This study shows for the first time that: a) susceptibility to TMZ of melanoma lines derived from the same patient did not depend on basal telomerase activity; b) inhibition of telomerase by DN-hTERT resulted in reduced growth rate and increased resistance to TMZ and to the chloroethylating agent carmustine, increased sensitivity to cisplatin, and no change in response to tamoxifen or to a selective N3-adenine methylating agent; c) inhibition of poly(ADP-ribose) polymerase (PARP), an enzyme involved in the repair of N-methylpurines, restored sensitivity of DN-hTERT clones to TMZ. These results indicate that a careful selection of the antitumor agent has to be made when antitelomerase therapy is combined with chemotherapy. Moreover, the data presented here suggest that TMZ + PARP inhibitor combination is active against telomerase-suppressed and slowly growing tumors.

Molecular and cellular biology of basal cell carcinoma

The finding of mutations in the PTCH gene in both Gorlin's syndrome and sporadic basal cell carcinomas has significantly advanced our understanding of the molecular defects that lead to the formation of these tumours. Knowledge of the specific molecular and functional changes that have taken place in these tumours will help us devise more defined therapies, as well as give us a better understanding of normal molecular pathways involved in skin development and function. The following is a summary of our current understanding of the molecular and cellular biology of basal cell carcinoma.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Telomerase inhibition and the future management of head-and-neck cancer

Telomeres are tandem repeats of DNA associated with specific proteins. These structures cap eukaryotic chromosomes and maintain the integrity of the chromosome ends. In the germline, telomeres are maintained by the enzyme telomerase, but in normal somatic cells the enzyme's activity is low or undetectable. Human tumours, including squamous-cell carcinoma of the head and neck (SCCHN), need telomerase to maintain telomere function; inhibition of the enzyme can lead to apoptosis. Furthermore, because most tumour cells have very short telomeres, they are more likely to succumb to telomerase inhibition than normal cells. Telomerase is therefore a potential selective anticancer target. The telomere is also involved in the repair of DNA double strand breaks, and telomere dysfunction provokes radiosensitivity. In this review we consider whether manipulation of telomere function may selectively sensitise SCCHN to radiotherapy and discuss the possible pitfalls. We also assess how some conventional treatments may affect the subsequent use of telomerase inhibitors.

Quantitative in situ evaluation of telomeres in fluorescence in situ hybridization-processed sections of cutaneous melanocytic lesions and correlation with telomerase activity

BACKGROUND

Telomere length is correlated with cellular ageing and immortalization processes. In some human cancers telomere length measurement has proved to be of diagnostic and prognostic value. Results comparable with the traditional terminal restriction fragment length determination by Southern blotting have been obtained in metaphase and interphase cells in some studies by fluorescence in situ hybridization (FISH) analysis; FISH additionally allows for the quantification of telomeres at the cellular level.

OBJECTIVES

In this study, 32 melanocytic lesions were analysed by FISH, aiming at investigating possible telomere differences among various benign and malignant lesions and correlation with telomerase activity (TA) level.

METHODS

FISH was performed on paraffin sections from six common naevi, eight Spitz naevi, 12 melanomas, six melanoma metastases and nine control samples of normal skin. Telomere mean maximum diameter (Feret max), area and number per nuclear area were calculated by image analysis on fluorescent images elaborated through KS400 and in situ imaging system (ISIS) for FISH analysis programs. Mean TA level was also calculated in all lesions and correlated with telomere parameters.

RESULTS

Telomere number per nuclear area was significantly lower in melanomas and metastases than in benign common and Spitz naevi and in control skin (7 small middle dot24 +/- 3.3; 6.11 +/- 3 vs. 14.46 +/- 5.6; 16.92 +/- 7.8; and 12.59 +/- 3.4, respectively; P < 0 .001). No significant differences were found for the other telomere parameters. In common and Spitz naevi, telomere number was positively correlated with Feret max (P = 0.046 and P < 0.0001, respectively). TA was significantly higher in melanomas and metastases than in the other groups (70.18 +/- 25.2; 105.07 +/- 30 vs. 2.16 +/- 2.4; 2 .99 +/- 2.1; 2 +/- 1.2, respectively; P< or = 0. 001) and it was inversely correlated with telomere number per nuclear area in melanomas (P = 0.0041). No other significant correlations were found.

CONCLUSIONS

Encouraging results have been obtained from quantitative telomere evaluation in the diagnosis of melanocytic lesions, although an analysis of a larger number of cases would be necessary to provide more reliable data. An extreme shortening of some telomeres probably results in the decrease of telomeric signals and the lower mean number of detectable telomeres in melanomas and metastases. In melanomas, telomere number per nuclear area is also inversely correlated with TA levels. Quantitative FISH of melanocytic lesions could give more specific information at the cellular level in telomere and telomerase fields of investigation.

Clinical utility of telomerase in cancer

This review will focus on the clinical utilities of telomerase for human cancer diagnosis. Much attention has been focused on detection of telomerase activity and its essential components (hTR and hTERT) in cancer and noncancerous tissues. Expression of hTR and hTERT is upregulated in almost all human malignant tumors but not in benign or normal tissues with the exception of germline cells, proliferative stem cells, activated lymphocytes, and certain benign tumors. Thus, telomerase is a useful marker for cancer diagnosis and in some instance as a prognostic indicator of outcome. Telomerase detection in cells derived from breast fine needle aspirates, bronchial washes, and pancreatic juices show high sensitivity and specificity for cancer detection. In tissue samples, the level of telomerase activity is a useful prognostic indicator in certain adult cancers such as gastric and colon cancers and in neuroblastomas. Immunohistochemical detection of hTERT will facilitate exact diagnosis of the telomerase positive cells and expand the application of telomerase in cancer diagnosis.

Telomerase activity in Kaposi's sarcoma, squamous cell carcinoma, and basal cell carcinoma

Patients with acquired immune deficiency syndrome (AIDS) often develop Kaposi's sarcoma (KS), an unusual skin tumor. The malignant nature of KS has long been disputed. Telomerase activity that maintains telomere length and ensures chromosomal stability, a frequently appearing marker in human malignancies, has been proposed to play a critical role in supporting continued cell growth, hence formation of tumors. We examined telomerase activity in tissue extracts from 22 KS, 10 squamous cell carcinoma (SCC), and 22 basal cell carcinoma (BCC) using the telomeric repeat amplification protocol (TRAP). All of the tumor tissues were previously cryopreserved at -80 degrees C. In this study, all tumor samples tested were positive for telomerase activity. Consistent with the presence of the enzyme activity, the skin tumors had relatively long telomeres. Inhibitors in the tissue extracts of some samples needed to be diluted or extracted by phenol before the enzyme activity was detected in the TRAP assay. All KS as well as two other skin carcinoma samples revealed positive telomerase activity. Our finding supports telomerase's role in tumor cell immortality and suggests the true neoplastic nature of KS.

Alterations of telomerase activity and terminal restriction fragment in gastric cancer and its premalignant lesions

AIMS

In order to explore the role of alterations of telomerase activity and terminal restriction fragment (TRF) length in the development and progression of gastric cancer.

METHODS

Telomerase activity was detected in 176 specimens of gastric mucosa obtained through an operation or endoscopical biopsy by using the telomeric repeat amplification protocol (TRAP) assay. Meanwhile, the mean length of TRF was measured with the use of a Southern blot in part of those samples.

RESULTS

Telomerase activity was detected in 14 of 57 (24.6%) chronic atrophy gastritis patients, six of 18 (33.3%) intestinal metaplasia patients, three of eight (37.5%) dysplasia patients and 60 of 65 (92.3%) gastric cancer patients, respectively. Normal gastric mucosa revealed no telomerase activity. No association was found between telomerase activity and any clinicopathological parameters. The mean TRF length was decreased gradually with age in normal mucosa and in gastric cancer tissue. Regression analysis demonstrated that the reduction rate in these tissues was 41 +/- 12 base pairs/year. Among 35 gastric cancers, TRF length was shown to be shorter in 20 cases (57.1%), similar in 12 cases (34.3%) and elongated in three cases (7.6%), compared to the corresponding adjacent tissues. The mean TRF length tended to decrease as the mucosa underwent chronic atrophy gastritis, intestinal metaplasia, dysplasia and into gastric cancer. The mean TRF length in gastric cancer was not statistically correlated with clinicopathological parameters and telomerase activity.

CONCLUSIONS

Our results suggest that telomerase is expressed during the early stage of gastric carcinogenesis, and that the clinical significance of TRF length appears to be limited in gastric cancer.

Possible regulation of telomerase activity by transcription and alternative splicing of telomerase reverse transcriptase in human melanoma

To investigate the regulatory mechanisms of telomerase activity in human melanoma cells, we assessed the enzyme's catalytic activity and the expression of the telomerase subunits, the human telomerase RNA, the human telomerase-associated protein, and the human telomerase reverse transcriptase, in 52 melanoma lesions. Eight normal skin specimens were also studied. Telomerase activity was detected in 84.6% of melanomas, whereas all skin specimens were telomerase negative. Human telomerase-associated protein mRNA and human telomerase RNA were constitutively expressed in all melanoma and skin specimens. Although at a variable level of expression, human telomerase reverse transcriptase mRNA was detected in all but one melanomas, whereas it was never present in skin samples. Reverse transcriptase-polymerase chain reaction experiments were performed using primers within the reverse transcriptase domain of human telomerase reverse transcriptase and revealed the presence of multiple alternatively spliced transcripts in melanoma specimens. Among the 44 telomerase-positive melanomas, one showed the full-length transcript alone whereas in all other specimens a full-length message was present with different combinations of alternatively spliced variants. In these tumors the expression of the full-length transcript was generally equal to or higher than that of the alternatively spliced variants. The ratio full-length transcript to alternatively spliced species ranged from 0.6 to 5.26, with a median value of 1.18. Among the seven telomerase-negative melanomas, one displayed the beta deletion transcript alone, whereas in the remaining six tumors weak expression of the full-length transcript and a more abundant level of alternatively spliced transcripts were found. In these cases human telomerase reverse transcriptase ratio ranged from 0.09 to 1.1, with a median value of 0.40. The results suggest that transcription and alternative splicing of human telomerase reverse transcriptase are regulatory mechanisms controlling telomerase activity in melanoma.

Clinical implications of telomerase detection

In 1994 a sensitive method for the detection of telomerase was described. This assay, which was based on the polymerase chain reaction, suggested that telomerase activity was associated with immortal and cancer cells. Since then more than a thousand studies have documented the expression and activity of the enzyme in diseased tissues, primarily tumours. This review gives an overview of the biological significance of telomerase expression and methods for detecting its activity. This is followed by an organ system-based discussion of expression in normal tissues and disease states. We finish with speculation as to the future role of telomerase detection in diagnostic histopathology.

Construction of neocentromere-based human minichromosomes by telomere-associated chromosomal truncation

Neocentromeres (NCs) are fully functional centromeres that arise ectopically in noncentromeric regions lacking alpha-satellite DNA. Using telomere-associated chromosome truncation, we have produced a series of minichromosomes (MiCs) from a mardel(10) marker chromosome containing a previously characterized human NC. These MiCs range in size from approximately 0.7 to 1.8 Mb and contain single-copy intact genomic DNA from the 10q25 region. Two of these NC-based Mi-Cs (NC-MiCs) appear circular whereas one is linear. All demonstrate stability in both structure and mitotic transmission in the absence of drug selection. Presence of a functional NC is shown by binding a host of key centromere-associated proteins. These NC-MiCs provide direct evidence for mitotic segregation function of the NC DNA and represent examples of stable mammalian MiCs lacking centromeric repeats.

Attenuation of telomerase activity does not increase sensitivity of human melanoma cells to anticancer agents

In tumour cells, replicative immortality is attained through stabilisation of telomeres by telomerase. Recent evidence suggests that telomerase plays an anti-apoptotic role. Since apoptosis is the primary mode of cell death induced by several drugs, telomerase could be involved in determining the chemosensitivity profile of tumour cells. We investigated whether inhibition of telomerase activity through a hammerhead ribozyme targeting the RNA template of telomerase influences the susceptibility of human melanoma cells to a variety of anticancer agents (platinum compounds, taxanes, topoisomerase I inhibitors). The ribozyme sequence was inserted into an expression vector and the JR8 human melanoma cell line was transfected with it. The cell clones obtained showed a reduced telomerase activity. Growth inhibition curves generated after exposure of ribozyme-transfectant clones to individual drugs were superimposable to those obtained from parental cells. Moreover, telomerase inhibition did not promote apoptosis as a cellular response to drug treatment. Overall, our results indicate that downregulation of telomerase activity does not increase the sensitivity of melanoma cells to anticancer drugs.

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.