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

Prognostic Alternative Splicing Signatures in Esophageal Carcinoma

Alternative splicing (AS) is a method of increasing the number of proteins that the genome is capable of coding for, by altering the pre-mRNA during its maturation. This process provides the ability of a broad range of proteins to arise from a single gene. AS events are known to occur in up to 94% of human genes. Cumulative data have shown that aberrant AS functionality is a major factor in human diseases. This review focuses on the contribution made by aberrant AS functionality in the development and progression of esophageal cancer. The changes in the pattern of expression of alternately spliced isoforms in esophageal cancer can be used as diagnostic or prognostic biomarkers. Additionally, these can be used as targets for the development of new treatments for esophageal cancer.

Telomere Length and Oxidative Stress and Its Relation with Metabolic Syndrome Components in the Aging

Simple Summary

A link between telomere length and some age-related diseases has been identified, including metabolic syndrome. So far, there is no mechanism to explain the origin or cause of telomere shortening in this syndrome; however, oxidative stress is a constant factor. Therefore, we reviewed scientific evidence that supported the association between oxidative stress and telomere length dynamics, also examining how each of the metabolic syndrome components individually affects the length. In this regard, there is strong scientific evidence that an increase in the number of metabolic syndrome components is associated with a shorter telomere length, oxidative damage at the lipid and DNA level, and inflammation, as well as its other components, such as obesity, hyperglycemia, and hypertension, while for dyslipidemia, there is a little more discrepancy. The difficulty for the correct treatment of metabolic syndrome lies in its multifactorial nature. Hence, there is a need to carry out more studies on healthy lifestyles during aging to prevent and reduce oxidative damage and telomere wear during aging, and consequently the progression of chronic degenerative diseases, thus improving the living conditions of older people.

Abstract

A great amount of scientific evidence supports that Oxidative Stress (OxS) can contribute to telomeric attrition and also plays an important role in the development of certain age-related diseases, among them the metabolic syndrome (MetS), which is characterised by clinical and biochemical alterations such as obesity, dyslipidaemia, arterial hypertension, hyperglycaemia, and insulin resistance, all of which are considered as risk factors for type 2 diabetes mellitus (T2DM) and cardiovascular diseases, which are associated in turn with an increase of OxS. In this sense, we review scientific evidence that supports the association between OxS with telomere length (TL) dynamics and the relationship with MetS components in aging. It was analysed whether each MetS component affects the telomere length separately or if they all affect it together. Likewise, this review provides a summary of the structure and function of telomeres and telomerase, the mechanisms of telomeric DNA repair, how telomere length may influence the fate of cells or be linked to inflammation and the development of age-related diseases, and finally, how the lifestyles can affect telomere length.

Decreased expression of TERT and telomeric proteins as human ovaries age may cause telomere shortening

OBJECTIVE

Telomeres are repetitive sequences localized at the ends of eukaryotic chromosomes comprising noncoding DNA and telomere-binding proteins. TRF1 and TRF2 both bind to the double-stranded telomeric DNA to regulate its length throughout the lifespan of eukaryotic cells. POT1 interacts with single-stranded telomeric DNA and contributes to protecting genomic integrity. Previous studies have shown that telomeres gradually shorten as ovaries age, coinciding with fertility loss. However, the molecular background of telomere shortening with ovarian aging is not fully understood.

METHODS

The present study aimed to determine the spatial and temporal expression levels of the TERT, TRF1, TRF2, and POT1 proteins in different groups of human ovaries: fetal (n = 11), early postnatal (n = 10), premenopausal (n = 12), and postmenopausal (n = 14). Also, the relative telomere signal intensity of each group was measured using the Q-FISH method.

RESULTS

We found that the telomere signal intensities decreased evenly and significantly from fetal to postmenopausal groups (P < 0.05). The TERT, TRF1, TRF2, and POT1 proteins were localized in the cytoplasmic and nuclear regions of the oocytes, granulosa and stromal cells. Furthermore, the expression levels of these proteins reduced significantly from fetal to postmenopausal groups (P < 0.05).

CONCLUSION

These findings suggest that decreased TERT and telomere-binding protein expression may underlie the telomere shortening of ovaries with age, which may be associated with female fertility loss. Further investigations are required to elicit the molecular mechanisms regulating the gradual decrease in the expression of TERT and telomere-binding proteins in human oocytes and granulosa cells during ovarian aging.

From experimental design to functional gene networks: DNA microarray contribution to skin ageing research

There is no doubt that the DNA microarray-based technology contributed to increase our knowledge of a wide range of processes. However, integrating genes into functional networks, rather than terms describing generic characteristics, remains an important challenge. The highly context-dependent function of a given gene and feedback mechanisms complexify greatly the interpretation of the data. Moreover, it is difficult to determine whether changes in gene expression are the result or the cause of pathologies or physiological events. In both cases, the difficulty relies on the involvement of processes that, at an early stage, can be protective and later on, deleterious because of their runaway. Each individual cell has its own transcription profile that determines its behaviour and its relationships with its neighbours. This is particularly true when a mechanism such as cell cycle is concerned. Another issue concerns the analyses from samples of different donors. Whereas the statistical tools lead to determine common features among groups, they tend to smooth the overall data and consequently, the selected values represent the 'tip of the iceberg'. There is a significant overlap in the set of genes identified in the different studies on skin ageing processes described in the present review. The reason of this overlap is because most of these genes belong to the basic machinery controlling cell growth and arrest. To get a more full picture of these processes, a hard work has still to be done to determine the precise mechanisms conferring the cell type specificity of ageing. Integrative biology applied to the huge amount of existing microarray data should fulfil gaps, through the characterization of additional actors accounting for the activation of specific signalling pathways at crossing points. Furthermore, computational tools have to be developed taking into account that expression values among similar groups may not vary 'by chance' but may reflect, along with other subtle changes, specific features of one given donor. Through a better stratification, these tools will allow to recover genes from the 'bottom of the iceberg'. Identifying these genes should contribute to understand how skin ages among individuals, thus paving the way for personalized skin care.

Adenoviral vectors for prodrug activation-based gene therapy for cancer

Cancer cell heterogeneity is a common feature - both between patients diagnosed with the same cancer and within an individual patient's tumor - and leads to widely different response rates to cancer therapies and the potential for the emergence of drug resistance. Diverse therapeutic approaches have been developed to combat the complexity of cancer, including individual treatment modalities designed to target tumor heterogeneity. This review discusses adenoviral vectors and how they can be modified to replicate in a cancer-specific manner and deliver therapeutic genes under multi-tiered regulation to target tumor heterogeneity, including heterogeneity associated with cancer stem cell-like subpopulations. Strategies that allow for combination of prodrug-activation gene therapy with a novel replication-conditional, heterogeneous tumor-targeting adenovirus are discussed, as are the benefits of using adenoviral vectors as tumor-targeting oncolytic vectors. While the anticancer activity of many adenoviral vectors has been well established in preclinical studies, only limited successes have been achieved in the clinic, indicating a need for further improvements in activity, specificity, tumor cell delivery and avoidance of immunogenicity.

Prognostic significance of telomere maintenance mechanisms in pediatric high-grade gliomas

Children with high-grade glioma, including diffuse intrinsic pontine glioma (DIPG), have a poor prognosis despite multimodal therapy. Identifying novel therapeutic targets is critical to improve their outcome. We evaluated prognostic roles of telomere maintenance mechanisms in children with HGG, including DIPG. A multi-institutional retrospective study was conducted involving 50 flash-frozen HGG (35 non-brainstem; 15 DIPG) tumors from 45 children (30 non-brainstem; 15 DIPG). Telomerase activity, expression of hTERT mRNA (encoding telomerase catalytic component) and TERC (telomerase RNA template) and alternative lengthening of telomeres (ALT) mechanism were assayed. Cox Proportional Hazard regression analyses assessed association of clinical and pathological variables, TERC and hTERT levels, telomerase activity, and ALT use with progression-free or overall survival (OS). High TERC and hTERT expression was detected in 13/28 non-brainstem HGG samples as compared to non-neoplastic controls. High TERC and hTERT expression was identified in 13/15 and 11/15 DIPG samples, respectively, compared to controls. Evidence of ALT was noted in 3/11 DIPG and 10/19 non-brainstem HGG specimens. ALT and telomerase use were identified in 4/19 non-brainstem HGG and 2/11 DIPG specimens. In multivariable analyses, increased TERC and hTERT levels were associated with worse OS in patients with non-brainstem HGG, after controlling for tumor grade or resection extent. Children with HGG and DIPG, have increased hTERT and TERC expression. In children with non-brainstem HGG, increased TERC and hTERT expression levels are associated with a worse OS, making telomerase a promising potential therapeutic target in pediatric HGG.

Human sarcomas are mosaic for telomerase-dependent and telomerase-independent telomere maintenance mechanisms: implications for telomere-based therapies

Telomere shortening necessitates that tumor cells activate a telomere maintenance mechanism (TMM) to support immortalization. Although most tumor cells activate expression of the enzyme telomerase, some cells elongate telomeres in a telomerase-independent manner, termed alternative lengthening of telomeres (ALT). Previous studies have evaluated the presence of telomerase or ALT mechanisms or both in a variety of tumor types. Our studies also show that TMMs are not mutually exclusive in some tumors. In contrast, our IHC analyses of human sarcomas identified a subset of tumors with some cells containing ALT-associated PML bodies, a hallmark of ALT, and separate cells expressing telomerase in the same tumor. By using a second set of human osteosarcomas, we merged IHC and biochemical analyses to characterize more fully the tumor TMM. The IHC data reveal the presence of both telomerase- and ALT-positive tumor cells in samples that demonstrate characteristics of both telomerase and ALT in biochemical assays. These assays, which measure telomere length and telomerase activity of tumor extracts, are conventionally used to classify tumor TMM. Our results suggest that TMM is not a single or perhaps static characteristic of some tumors and that TMM heterogeneity should be considered in tumor stratification. Furthermore, clinical interest in telomere-based therapies may necessitate accurate characterization of tumor TMM before treatment to maximize therapeutic efficacy.

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 expression in the glial scar of rats with spinal cord injury

A rat model of spinal cord injury was established using the weight drop method. A cavity formed 14 days following spinal cord injury, and compact scar tissue formed by 56 days. Enzyme-linked immunosorbent assay and polymerase chain reaction enzyme-linked immunosorbent assay results demonstrated that glial fibrillary acidic protein and telomerase expression increased gradually after injury, peaked at 28 days, and then gradually decreased. Spearman rank correlation showed a positive correlation between glial fibrillary acidic protein expression and telomerase expression in the glial scar. These results suggest that telomerase promotes glial scar formation.

Modulation of telomerase and signal transduction proteins by hexyl-ALA-photodynamic therapy (PDT) in human doxorubicin resistant cancer cell models

AIMS

This study employed a doxorubicin resistant (MES-SA-Dx5) human uterine sarcoma cell line and its counterpart (MES-SA), to elucidate the efficacy of aminolevulinic acid-hexylester (hexyl-ALA) mediated PDT at molecular and transcriptional levels.

METHODS

Hexyl-ALA generated protoporphyrin IX in both cells were determined by molecular probes using Confocal Laser Scanning Microscopy. The hexyl-ALA-PDT induced signal transduction proteins and mode of cell death were quantitated by CASE ELISA assays and DAPI staining. The modulation of hTERT mRNA expression and telomerase activity were investigated by TaqMan real-time PCR and ELISA respectively. Hexyl-ALA-PDT mediated cell migratory effect was determined by wound-healing assay.

RESULTS

The results demonstrated that mitochondria were the major target of hexyl-ALA. At LD(30), hexyl-ALA-PDT significantly provoked an up-regulation of phosphorylated p38MAPK and JNK proteins in both cells. Hexyl-ALA-PDT down-regulated hTERT (a catalytic subunit of telomerase) mRNA expression and showed a strong correlation with diminished telomerase activity in both cells (MES-SA: r(2) = 0.9932; MES-SA-Dx5: r(2) = 0.9775). The suppression of cell migratory effect in both cells was obtained after hexyl-ALA-PDT. Further, 50% and 30% of apoptotic cells were attained at LD(50), for wild-type and drug resistant cells respectively. Unlike the wild-type, a higher PDT dose was crucial to induce apoptosis in the drug resistant cells.

CONCLUSIONS

Our study provides the first evidence that p38MAPK and JNK kinases played a vital role in triggering hexyl-ALA-PDT-induced apoptosis, down-regulated hTERT mRNA expression and telomerase activity in both proposed cells. In vivo studies are worth examining for the benefit of clinical applications in drug resistant cancers and PDT development.

Characterization and fate of telomerase-expressing epithelia during kidney repair

After acute kidney injury, mice with short telomeres develop increased damage with reduced proliferative capacity, which suggests an important role for telomere length in kidney repair. The enzyme telomerase reverse transcriptase (mTert) regulates telomere length; embryonic stem cells and certain adult stem cells express mTert, but whether cells in the adult kidney express mTert and whether these cells play a role in renal repair are unknown. Here, we found that telomerase protein and mRNA were highly enriched in renal papilla, a proposed niche of kidney stem cells. Using mTert-GFP reporter mice, we detected mTert in a subset of papillary epithelial cells comprising the collecting duct predominantly but also the loop of Henle. Approximately 5% of mTert-GFP(+) cells were label retaining, a characteristic of stem cells. mTert mRNA levels increased in renal papilla after ischemia-reperfusion injury, but genetically labeled mTert-expressing papillary cells neither divided nor migrated out of the renal papilla during kidney repair. In summary, these data suggest that cells expressing telomerase reverse transcriptase are not a progenitor-cell population, and they do not play a direct role in kidney repair.

Serum human telomerase reverse transcriptase: a novel biomarker for breast cancer diagnosis

BACKGROUND

Telomerase is a ribonucleoprotein complex composed mainly of a reverse transcriptase catalytic subunit, telomerase reverse transcriptase (hTERT). Expression of hTERT confers telomerase activity, indicating that hTERT is the rate-limiting component of human telomerase. The aim of the present study was to investigate the diagnostic implications of hTERT in the serum of breast cancer patients.

METHODS

The study was conducted on 159 breast cancer patients and 41 healthy volunteers as controls. The evaluation of hTERT, cancer antigen 15.3 and carcinoembryonic antigen were performed by enzyme-linked immunosorbent assay, and analysed for their correlation with the patient's clinicopathological features.

RESULTS

27 of 52 (51.9%) patients with stage I breast cancer, 31 of 40 (77.5%) with stage II and 30 of 34 (88.2%) patients with stage III exhibited elevated hTERT levels. Serum hTERT levels showed significantly higher mean values in patients with breast cancer than healthy individuals. The sensitivity and specificity of hTERT in cancer diagnosis was 68.9 and 83.3%, respectively, which is significantly higher than conventional markers. The expression of serum hTERT was significantly correlated with telomerase activity in breast cancer tissues. Pretreatment serum hTERT levels showed a significant correlation with clinical stage, while correlation with nodal status and tumor size were marginal and no correlation was found with family history and age.

CONCLUSION

Serum hTERT is useful for diagnosing and assessing the clinical stage of breast cancer and is superior to conventional markers. Therefore, serum hTERT could have a potential application as a novel biomarker for breast cancer diagnosis.

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.

The role of telomeres in the ageing of human skin

Skin is a self-renewing tissue that is required to go through extensive proliferation throughout the lifespan of an organism. Telomere shortening acts as a mitotic clock that prevents aberrant proliferation such as cancer. A consequence of this protection is cellular senescence and ageing. The telomerase enzyme complex maintains telomere length in germline cells and in cancer cells. Telomerase is also active in certain somatic cells such as those in the epidermis but is almost undetectable in the dermis. Increasing evidence indicates that telomerase plays a significant role in maintenance of skin function and proliferation. Mutations in telomerase component genes in the disease dyskeratosis congenita result in numerous epidermal abnormalities. Studies also indicate that telomerase activity in epidermal stem cells might have roles that go beyond telomere elongation. Telomeres in skin cells may be particularly susceptible to accelerated shortening because of both proliferation and DNA-damaging agents such as reactive oxygen species. Skin might present an accessible tissue for manipulation of telomerase activity and telomere length with the potential of ameliorating skin diseases associated with ageing.

Posttranscriptional regulation of the telomerase hTERT by gambogic acid in human gastric carcinoma 823 cells

We previously reported that gambogic acid (GA), a natural product, was an effective telomerase inhibitor by repressing hTERT promoter. In this study, posttranscriptional regulation of the telomerase hTERT by GA was investigated in BGC-823 human gastric carcinoma cells. The telomerase activity was detected by PCR-TRAP assay. RT-PCR assay and Western blot were performed to examine the repression of telomerase hTERT and c-Myc after GA or c-Myc-specific siRNA treatment. The results indicated that GA repressed telomerase activity and hTERT transcriptional activity via down-regulation of c-Myc expression in BGC-823 human gastric carcinoma cells. We further observed that hTERT transcriptional activity was not completely blocked by c-Myc-specific siRNA, suggesting that additional factors are involved in the repression of telomerase activity. The results of Western blot and immunoprecipitation assay revealed that GA inhibits the phosphorylation of Akt. The further results also confirmed that celecoxib, an inhibitor of Akt phosphorylation, could significantly repressed telomerase activity alone and enhance the repression of telomerase activity combined with GA. These data suggested that GA inhibits the posttranslational modification of hTERT by inhibiting the phosphorylation of Akt. Collectively, we suggest that GA represses telomerase activity not only by repressing hTERT transcriptional activity via c-Myc but also by posttranslational modification of hTERT via Akt.

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.

The contribution of epidermal stem cells to skin cancer

Tumors arising from the skin are of multiple phenotypes, with differing degrees of malignant potential. In mouse models of skin carcinogenesis, tumors of squamous phenotype are the most common; however, human disease indicates that multiple phenotypes may arise from a common pool of stem cells that are then influenced by epigenetic factors. The use of transgenic and knockout gene technologies with mice is unraveling some of the specific genes regulating fate determination in stem cells other than squamous lineage, including basal cell carcinoma and sebaceous adenomas. The following review examines the evidence for the stem cell origin of epidermal tumors and the contribution of some specific gene families toward stem cell fate decisions during epidermal tumor progression.

hTERT, the catalytic component of telomerase, is downregulated in the haematopoietic stem cells of patients with chronic myeloid leukaemia

Telomere shortening is associated with disease progression in chronic myeloid leukaemia (CML). To investigate the biology and regulation of telomerase in CML, we evaluated expression of the telomerase components, its regulators and several telomeric-associated proteins. Quantitative real-time-polymerase chain reaction (PCR) was used to compare gene expression in the CD34+/leukaemic blast cells of 22 CML patient samples to the CD34+ cell population of healthy individuals. hTERT, the catalytic component of telomerase, was downregulated in eight of 12 chronic phase (CP) patients (P = 0.0387). Furthermore, hTERT was significantly downregulated in two of three patients in accelerated phase (AP) and seven of seven patients in blast crisis (BC), P = 0.0017. Expression of hTR and telomeric-associated proteins TEP1, TRF1, TRF2, tankyrase and PinX1 was high in the majority of CP and AP patients. With the exceptions of TEP1 and hTR, expression of these factors was highest in CP and decreased during disease progression. Expression of c-Myc, a positive regulator of hTERT transcription, correlated with hTERT expression and decreased with disease progression, falling below control levels in BC. hTERT levels were increased in CP patients following successful treatment with imatinib, relative to untreated CP patients. We suggest that reduced hTERT expression directly causes the shortened telomeres observed in CML.

The expression of hTR and hTERT in human breast cancer: correlation with clinico-pathological parameters

BACKGROUND

Telomerase is a ribonucleoprotein enzyme that synthesizes telomeres after cell division and maintains chromosomal stability leading to cellular immortalization. Telomerase has been associated with negative prognostic indicators in some studies. The present study aims to detect any association between telomerase sub-units: hTERT and hTR and the prognostic indicators including tumour's size and grade, nodal status and patient's age.

METHODS

Tumour samples from 46 patients with primary invasive breast cancer and 3 patients with benign tumours were collected. RT-PCR analysis was used for the detection of hTR, hTERT, and PGM1 (as a housekeeping) genes expression.

RESULTS

The expression of hTR and hTERT was found in 31(67.4%) and 38 (82.6%) samples respectively. We observed a significant association between hTR gene expression and younger age at diagnosis (p = 0.019) when comparing patients < or = 40 years with those who are older than 40 years. None of the benign tumours expressed hTR gene. However, the expression of hTERT gene was revealed in 2 samples. No significant association between hTR and hTERT expression and tumour's grade, stage and nodal status was seen.

CONCLUSION

The expression of hTR and hTERT seems to be independent of tumour's stage. hTR expression probably plays a greater role in mammary tumourogenesis in younger women (< or = 40 years) and this may have therapeutic implications in the context of hTR targeting strategies.

The association between telomerase activity and expression of its RNA component (hTR) in breast cancer patients: the importance of DNase treatment

Telomerase is a ribonucleoprotein enzyme that compensates for the telomere length shortening which occurs during the cell cycle. Telomerase activity has been detected in most tumours but not in somatic cells. However, hTR; the RNA component of telomerase; has been reported to be universally expressed in both cancerous and non-cancerous tissues. Tumour samples from 50 patients with primary invasive breast cancer were collected. The TRAP assay was used to detect telomerase activity. RT-PCR on cDNA and DNased cDNA samples and control groups was used to detect the expression of hTR, GAPDH and PGM1 genes. Seventy-two percent of samples showed telomerase activity. DNA contamination was detected in 36 (72%) of RNA samples. Without performing DNase treatment, 49 (98%) of all samples showed hTR expression, but with the application of this strategy, hTR expression decreased from 98% to 64%. A significant association (p < 0.001) between hTR expression and telomerase activity was observed. Among the 32 hTR positive samples, 30 had telomerase activity and among the 18 hTR negative samples, telomerase activity was observed in 6 cases. Thus the application of this strategy could provide an applicable tool to use instead of the TRAP assay thus facilitating telomerase research in cancer genetic investigations.

Telomerase activity in prognostic histopathologic features of melanoma

BACKGROUND

Telomerase activity (TA) is believed to play a role in the regulation of senescence and to limit the number of cell divisions. The deregulation of telomerase appears to contribute to oncogenesis and the formation of immortal cell lines. As a result, it is believed that it could be used as a prognostic marker in melanoma.

METHODS

TA was assayed by the polymerase chain reaction PCR-ELISA-based telomeric repeat amplification protocol (TRAP assay). One hundred and eight samples were distributed in four histological groups: 30 samples from primary cutaneous melanomas, 24 from peritumoural skin sites, 28 from benign melanocytic lesions, and 26 from normal skin sites as a control.

RESULTS

TA was different among the four tested groups (Kruskall-Wallis test p<0.001), and increasing values of TA were observed progressing from normal skin to benign and then to malignant lesions. Among melanoma samples, there was a significant association between TA and ulceration (p=0.025), TA and vascular invasion (p=0.018) and TA and mitotic rate (p=0.029) (Mann-Whitney test). A linear regression analysis showed significant associations between the increase of TA with Breslow thickness (p=0.004) and the presence of satellites (p=0.002).

CONCLUSIONS

We observed that TA had increased from control skin to peritumoural skin, and then to benign melanocytic lesions and finally to melanoma, suggesting tumour progression. TA showed higher values in the presence of some important histopathologic parameters related to poor prognosis in cutaneous melanoma such as ulceration, vascular invasion, satellites, high rates of mitosis, and in thicker tumours.

Repression of telomerase reverse transcriptase mRNA and hTERT promoter by gambogic acid in human gastric carcinoma cells

OBJECTIVES

To investigate the effects and potential mechanisms of gambogic acid (GA), a naturally occurring anticancer agent, on the expression and regulation of telomerase in human gastric carcinoma cells.

METHODS

GA-induced inhibition of cell proliferation was evaluated by the commonly employed MTT assay on two human gastric carcinoma cell lines, MGC-803 and SGC-7901. Telomerase activity and hTERT mRNA expression were determined by telomeric repeat amplication protocol-polymerase chain reaction and reverse transcription-polymerase chain reaction, respectively. The hTERT promoter activity was measured by luciferase assay. The expression of c-MYC, an apoptotic gene that modulates the expression of hTERT promoter, was quantified by Western blotting.

RESULTS

The proliferation of human gastric carcinoma cell lines, MGC-803 and SGC-7901, was significantly inhibited with GA treatment. Both telomerase activity and hTERT mRNA expression were notably decreased in cells treated with GA. The activity of hTERT promoter and the expression of c-MYC were also remarkably decreased in GA-treated cells.

CONCLUSION

This study demonstrated that GA treatment of human gastric carcinoma cell lines, MGC-803 and SGC-7901, significantly reduced the expression of c-MYC in a time- and concentration-dependent manner accompanied with the down-regulation of the hTERT transcription and the ultimate reduction in telomerase activity. Our results indicate that the hTERT is a target of c-MYC activity and identify a feasible mechanism of GA's potent anticancer activity.

Effects of tea polyphenols on telomerase activity of a tongue cancer cell line: a preliminary study

The aim of this study was to determine, at the mRNA and protein levels, whether tea polyphenols (TPs) affect the expression of the human telomerase reverse transcriptase (hTERT) gene in the Tca8113 cancerous cell line. The expression of this gene was determined at the mRNA level by reverse transcription and polymerase chain reaction and at the protein level by Western blotting. The semi-quantitative scores of hTERT mRNA expression were analyzed by one-way analysis of variance. After 72 h of exposure to TPs, the mean (+/-SD) scores of hTERT mRNA expression in TP 0.1g/l, TP 0.05 g/l and a control group were 0.32+/-0.05, 0.41+/-0.04 and 0.72+/-0.05, respectively (P<0.05). The Western blot assay showed that TPs also decreased the expression of hTERT at the protein level. These results indicate that TPs reduce hTERT activity in the human Tca8113 cell line in a time- and dose-dependent manner, disabling telomerase activity and thereby terminating unlimited cancer cell proliferation. These findings suggest a mechanism behind TP's anticancer activity.

Multiple Mechanisms of Telomere Maintenance Exist in Liposarcomas

PURPOSE

Telomeres are specialized nucleoprotein complexes that protect and confer stability upon chromosome ends. Loss of telomere function as a consequence of proliferation-associated sequence attrition results in genome instability, which may facilitate carcinogenesis by generating growth-promoting mutations. However, unlimited cellular proliferation requires the maintenance of telomeric DNA; thus, the majority of tumor cells maintain their telomeres either through the activity of telomerase or via a mechanism known as alternative lengthening of telomeres (ALT). Recent data suggest that constitutive telomere maintenance may not be required in all tumor types. Here we assess the role and requirement of telomere maintenance in liposarcoma.

EXPERIMENTAL DESIGN

Tumor samples were analyzed with respect to telomerase activity, telomere length, and the presence of ALT-specific subcellular structures, ALT-associated promyelocytic leukemia nuclear bodies. This multi-assay assessment improved the accuracy of categorization.

RESULTS

Our data reveal a significant incidence (24%) of ALT-positive liposarcomas, whereas telomerase is used at a similar frequency (27%). A large number of tumors (49%) do not show characteristics of telomerase or ALT. In addition, telomere length was always shorter in recurrent disease, regardless of the telomere maintenance mechanism.

CONCLUSIONS

These results suggest that approximately one half of liposarcomas either employ a novel constitutively active telomere maintenance mechanism or lack such a mechanism. Analysis of recurrent tumors suggests that liposarcomas can develop despite limiting or undetectable activity of a constitutively active telomere maintenance mechanism.

Expression profiles of p63, p53, survivin, and hTERT in skin tumors

BACKGROUND

p63 is a p53 homolog and a marker expressed in replicating keratinocytes. Survivin is a recently characterized inhibitor of apoptosis protein that is abundantly expressed in most solid and hematologic malignancies. Telomerase reverse transcriptase (TERT) is the major determinant of human telomerase activity, and its expression is indicative of unlimited replication. We herein evaluated the expression profiles of p63, p53, survivin, and hTERT in usual skin cancers, including squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) and putative preneoplastic epidermal lesions, including actinic keratosis (AK), Bowen's disease, and porokeratosis.

METHODS

Immunohistochemistry using antibodies against p63, p53, survivin, and hTERT was performed. Semi-quantitative evaluation (-, +, 2+, 3+) was carried out.

RESULTS

BCCs showed diffuse p63 expression and SCCs heterogeneous p63 expression with negativity in terminally differentiated squamous cells. All preneoplastic epidermal lesions showed p63 expression in all cell layers. p53 was found in seven of 10 cases of BCCs, all 10 cases of SCCs, and nine of 10 cases of Bowen's disease. AK and porokeratosis revealed focal to moderate p53 expression. Survivin was found in eight of 10 cases of SCCs and eight of 10 cases of Bowen's disease. Six of 10 cases of BCCs revealed weak survivin positivity. AK and porokeratosis showed survivin expression confined to the basal layer. hTERT expression was found in most cases of skin cancers and preneoplastic lesions.

CONCLUSIONS

p63 expression may be a marker of basal/progenitor cells and a diagnostic marker in skin tumors. p63 expression is not related to p53 expression in these tumors. This study points to a putative role of survivin and hTERT in the development of certain skin cancers. In addition, our data support the concept of porokeratosis being a premalignant condition.

Genetic and epigenetic modulation of telomerase activity in development and disease

Telomerase activity is one of the most important factors that have been linked to multiple developmental processes, including cell proliferation, differentiation, aging and senescence. Dysregulation of telomerase has often been found in developmental abnormalities, such as cancer, loss of function in the hematopoietic system, and low success rate of somatic cloning. A comprehensive network of transcription factors has been shown to be involved in the genetic control of telomerase expression and activity. Epigenetic mechanisms have recently been shown to provide an additional level of regulation, and may be responsible for the diverse expression status of telomerase that is manifested in a tissue and cell-type-dependent manner. This article summarizes the recent developments in the field of telomerase research with a focus on the coregulation of the telomerase gene by both genetic and epigenetic pathways. Developmental consequences of aberrant telomerase activity will also be summarized and discussed.

Telomerase activity and expression of telomerase genes in squamous dysplasia and squamous cell carcinoma of the esophagus

BACKGROUND

Telomerase maintains telomere length and is considered to be necessary for the indefinite proliferation of human cells. Activation of telomerase plays a key role in the malignant transformation process. The aim of this study was to study the regulation of telomerase, and to explore the possibility of telomerase as a biomarker in squamous carcinogenesis of the esophagus.

METHODS

Twenty-nine esophageal squamous cell carcinomas (ESCC) and its corresponding adjacent normal tissues, and 47 epithelial squamous dysplasia tissues were analyzed by the reverse transcriptase-polymerase chain reaction (RT-PCR) technique for the mRNA expression of three major telomerase subunits: human telomerase RNA (hTR), telomerase protein component 1 (TP1), and human telomerase reverse transcriptase (hTERT) and by telomeric repeat amplification protocol assay (TRAP) for telomerase activity.

RESULTS

For the expression of hTR and TP1 mRNA, there were no significant differences among ESCC, dysplasia and normal tissues (P > 0.05). In contrast, hTERT mRNA expression was detected in 28 of 29 ESCC (96.6%), in 23 of 47 dysplasia (48.9%), and only in two of 29 normal tissues (7.5%). Telomerase activity was positive in 25 of 29 ESCC (86.2%), in 21 of 47 (44.7%) epithelial dysplasia tissues, and in none of normal tissue. All together, 95 of 105 cases (90.48%) were concordant for both results, i.e., telomerase activity positive and hTERT positive or telomerase activity negative and hTERT negative tissues, and telomerase activity correlated with hTERT mRNA expression (P < 0.001).

CONCLUSIONS

Higher telomerase activity and hTERT mRNA expression were shown during an early stage in the esophageal carcinogenesis. Activation of telomerase activity was strongly correlated with hTERT mRNA expression, suggesting hTERT is a major regulator of telomerase activity, and telomerase activation may play a critical role in esophageal carcinogenesis. Therefore, telomerase, especially hTERT can be used as a potential molecular biomarker of ESCC.

There is no correlation between c-Myc mRNA expression and telomerase activity in human breast cancer

BACKGROUND: Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal length and stability thus leading to cellular immortalisation. The hTERT (human telomerase reverse transcriptase) subunit seems to be the rate-limiting determinant of telomerase and knowledge of factors controlling hTERT transcription may be useful in therapeutic strategies. The hTERT promoter contains binding sites for c-Myc and there is experimental and in vitro evidence that c-Myc may increase hTERT expression. MATERIALS AND METHODS: RNA was extracted from 18 breast carcinomas and c-Myc mRNA expression was estimated by quantitative reverse transcriptase-PCR (RT-PCR) with Taqman methodology. These tumours had already been analysed for ER and PgR status using ligand-binding assays and had had their DNA ploidy and S-phase fractions measured by flow cytometry. Telomerase activity had already been determined by using a modified telomeric repeat and amplification protocol (TRAP) assay. RESULTS: Telomerase activity ranged from 0 to 246 units of Total Protein Generated (TPG), where one unit of TPG was equal to 600 molecules of telomerase substrate primers extended by at least three telomeric repeats. Median levels of TPG were 60 and mean levels 81. There was no significant correlation between levels of c-Myc mRNA expression, telomerase activity, S phase fraction or PgR. There was a significant negative correlation with ER status. CONCLUSION: Although the hTERT promoter contains potential binding sites for c-Myc oncoprotein, we have found no correlation between c-Myc mRNA levels and telomerase activity.

Biological behavior of keratoacanthoma and squamous cell carcinoma: telomerase activity and COX-2 as potential markers

Distinguishing keratoacanthoma from squamous cell carcinoma is a persistent issue in pathology practice. Solitary keratoacanthoma is a self-limiting lesion as opposed to rather aggressive clinical behavior of squamous cell carcinoma. Several markers were studied to understand their biology and to separate these two lesions on a firm basis, but without much success. In this study, we plan to utilize recent markers such as telomerase activity and cyclooxygenase-2 (COX-2) along with more established marker p53 in understanding the biologic differences between keratoacanthoma and squamous cell carcinoma. We studied 17 well to moderately differentiated squamous cell carcinoma and 24 early proliferative phase keratoacanthoma by immunohistochemistry for the expression of p53 protein, COX-2 and telomerase activity. Higher telomerase activity was found in 11/17 squamous cell carcinoma (65%) compared to 4/24 (17%) of keratoacanthoma. Similarly, stronger expression of p53 and COX-2 was detected in 12 (71%) and 11 (65%) cases of squamous cell carcinoma compared to 2 (8%) and 2 (8%) cases of keratoacanthoma respectively. A highly significant 'P' value was obtained for telomerase activity (0.001), p53 (0.000), and COX-2 (0.001). Telomerase activity, COX-2, and p53 expression provide evidence that keratoacanthoma and squamous cell carcinoma are indeed distinct entities and also help in discriminating these two lesions, which closely resemble each other on conventional morphology. Although these markers present new insights into the biologic variation of keratoacanthoma and squamous cell carcinoma, they are of limited value for routine application in histological distinction of these two lesions. The differential expression of markers also explains the sustained proliferation observed in squamous cell carcinoma, compared to a shorter lifespan and involution in keratoacanthoma.

The effects of oxidative stress on telomerase activity and other stress-related proteins in lens epithelial cells

Telomerase is a ribonucleoprotein complex responsible for maintaining the ends of chromosomes and for repair of DNA strand breaks. While telomerase activity is generally found in cells that have unlimited proliferative potential such as neoplastic cells, germline cells and some stem cells, lens epithelial cells (though not highly proliferative) have telomerase activity. Our previous studies indicated that lens epithelial cells express high levels of telomerase despite their low proliferative potential, thus we hypothesized that telomerase expression protects lens epithelial cells from oxidative stress. We also determined levels of the stress proteins gadd45 and p16 and the stress and proliferation-related protein, proliferating cell nuclear antigen (PCNA). In acute studies, lenses were exposed to TBHP for 0-120 min. In recovery studies, lenses were exposed to TBHP for 1 hr, then allowed to recover for up to 18 hr. In acute studies, telomerase activity was increased, p16 initially decreased then normalized, PCNA levels did not change significantly even in the overnight recovery groups, and gadd45 was decreased in some TBHP exposed groups. In recovery studies, telomerase activity was increased in all groups, gadd45 decreased then became elevated, and p16 levels were decreased at later recovery times. PCNA levels remained constant during the studies, indicating that there was no change in proliferation. These studies showed that elevated telomerase activity did not correlate with increased proliferation in lens epithelial cells; instead, increased telomerase activity was associated with increased levels of the stress-related protein gadd45 only in the later recovery times. These findings support the hypothesis that telomerase plays a protective rather than a proliferative role in lens epithelial cells.

Inhibition of the epidermal growth factor receptor suppresses telomerase activity in HSC-1 human cutaneous squamous cell carcinoma cells

Activation of telomerase, which stabilizes the telomere length of chromosomes, is crucial for the continued growth or progression of cancer cells. In a previous study, we showed that telomerase is frequently activated in skin tumors. Because epidermal growth factor plays an important role during the tumorigenesis of epithelial tissue, we have now examined the role of epidermal growth factor signaling in regulating telomerase activity using HSC-1 human cutaneous squamous cell carcinoma cells. Treatment of HSC-1 cells with AG 1478, an inhibitor of the epidermal growth factor receptor, or with a neutralizing antibody to the epidermal growth factor receptor, significantly suppressed their telomerase activity, in association with inhibiting their growth. The suppression of telomerase activity was obvious at day 3 and was maximal at day 5 after treatment with AG 1478. The suppression of telomerase activity correlated with the decreased expression of human telomerase catalytic subunit (hTERT) mRNA, the rate-limiting determinant of its enzyme activity. The expression of c-Myc and of Sp1 proteins, transcription factors for hTERT, were also suppressed by AG 1478 in HSC-1 cells, but the expression of Ets-2 protein, another transcription factor, was not affected. The expression of Mad-1, a competitor of c-Myc, was increased. Inhibition of ERK, Src, or Akt suppressed telomerase activity in HSC-1 cells, but to a lesser extent than did treatment with AG 1478. Serum starvation suppressed telomerase activity, but addition of epidermal growth factor or transforming growth factor alpha did not increase it, indicating the involvement of other epidermal growth factor receptor ligands in the activation of telomerase in HSC-1 cells. These data indicate that blockade of the epidermal growth factor receptor might be effective in inhibiting telomerase activity of squamous cell carcinomas, which would lead to the suppression of tumor growth.

The mRNA expression of hTERT in human breast carcinomas correlates with VEGF expression

Background

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal stability leading to cellular immortalisation. hTERT (human telomerase reverse transcriptase) is the rate-limiting determinant of telomerase reactivation. Telomerase has been associated with negative prognostic indicators in some studies. The present study aims to detect any correlation between hTERT and the negative prognostic indicators VEGF and PCNA by quantitatively measuring the mRNA expression of these genes in human breast cancer and in adjacent non-cancerous tissue (ANCT).

Materials and methods

RNA was extracted from 38 breast carcinomas and 40 ANCT. hTERT and VEGF165, VEGF189 and PCNA mRNA expressions were estimated by reverse transcriptase-PCR (RT-PCR) and Taqman methodology.

Results

The level of expression of VEGF-165 and PCNA was significantly higher in carcinoma tissue than ANCT (p = 0.02). The ratio of VEGF165/189 expression was significantly higher in breast carcinoma than ANCT (p = 0.025). hTERT mRNA expression correlated with VEGF-189 mRNA (p = 0.008) and VEGF165 (p = 0.07).

Conclusions

hTERT mRNA expression is associated with the expression of the VEGF189 and 165 isoforms. This could explain the poorer prognosis reported in breast tumours expressing high levels of hTERT. The relative expression of the VEGF isoforms is significantly different in breast tumour to ANCT, and this may be important in breast carcinogenesis.

Interaction between HIV-1 Tat and pRb2/p130: a possible mechanism in the pathogenesis of AIDS-related neoplasms

Tat protein is an early nonstructural protein necessary for virus replication, which is secreted by infected cells and taken up by uninfected cells. Extensive evidence indicates that Tat may be a cofactor in the development of AIDS-related neoplasms. The molecular mechanism underlying Tat's oncogenic activity may include deregulation of cellular genes. Among these genes, it has recently been shown that pRb2/p130 oncosuppressor protein is one of the targets in the interaction between HIV gene product Tat and host proteins. However, whether the HIV-1 gene product Tat may inactivate the oncosuppressive function of pRb2/p130 has not yet been elucidated. Here, we show that mRNA levels of pRb2/p130 increase in the presence of Tat, whereas no change in the phosphorylation status of pRb2/p130 is observed. In addition, Tat can inhibit the growth control activity exerted by pRb2/p130 in the T98G cell line. Finally, Tat does not compete with E2F-4 in binding to pRb2/p130. The interaction between Tat and pRb2/p130 seems to result in the deregulation of the control exerted by pRb2/p130 on the cell cycle. Taken together, these results open a window on the role of pRb2/p130 in AIDS-related oncogenesis.

Telomerase activity and telomerase subunit gene expression levels are not related in prostate cancer: a real-time quantification and in situ hybridization study

Because the mechanisms of telomerase activation in prostate cancer are mainly unknown, we investigated the relationships between telomerase activity and expression levels of human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT) mRNA in benign and malignant alterations of the human prostate gland. Using the LightCycler technology, hTERT mRNA expression was quantified in 46 radical prostatectomy and 10 benign prostatic hyperplasia (BPH) cases; hTR expression was quantified in a subset of these tissue samples. Telomerase activity was measured using a quantitative telomeric repeat amplification protocol ELISA assay. Similar to hTR, which was expressed in all tissue samples tested, hTERT mRNA was detected in 98% of the prostate cancer samples and in 30% of the BPH samples. Regarding clinicopathologic variables, telomerase activity was significantly correlated with Gleason score (<7 vs > or =7, p = 0.02). No relationships emerged between normalized hTR or hTERT expression levels and tumor stage, Gleason score, lymph node status, or preoperative serum prostate-specific antigen. Remarkably, one third of all cancer and BPH tissue samples with hTR and hTERT expression lack telomerase activity. Quantitative analyses contradict the assumption that a certain threshold level of hTR or hTERT mRNA is required for telomerase activation, thus indicating that telomerase regulation in prostate cancer occurs more likely on a posttranscriptional level. Nevertheless, the observation that hTR and hTERT mRNA levels are significantly (p < 0.002) correlated suggests some common mechanisms in the up-regulation of hTR and hTERT expression. Because in situ hybridization revealed strong hTERT expression in all cells of the tumor glands but also in high-grade prostatic intraepithelial neoplasia foci, this up-regulation seems to occur early in prostate carcinogenesis.

hTERT mRNA expression correlates with telomerase activity in human breast cancer

AIMS

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal length and stability thus leading to cellular immortalisation. hTERT (human telomerase reverse transcriptase) gene seems to be the rate-limiting determinant of telomerase reactivation. hTERT mRNA expression was reported to correlate with telomerase activity in cell lines and some human tumours. However the correlation between telomerase activity and hTERT mRNA expression has not been previously examined in human breast cancer. The present study aims to quantitatively measure the expression of hTERT mRNA and telomerase activity in human breast cancer and examine the relationship between these parameters. Furthermore the associations with other parameters including estrogen receptor (ER) and progesterone receptor (PgR) status, DNA ploidy, and S-phase fraction (SPF) are also examined.

METHODS

RNA was extracted from 18 breast carcinomas and hTERT mRNA expressions were estimated by reverse transcriptase-PCR (RT-PCR) and Taqman methodology. These tumours had already been analysed for ER and PgR status using ligand-binding assays and had had their DNA ploidy and S-phase fractions measured by flow cytometry. Telomerase activity had already been determined by using a modified telomeric repeat and amplification protocol (TRAP) assay.

RESULTS

The expression of hTERT mRNA in the breast tumours ranged between 1.3 and 2.7 x 10(7) copy numbers per micro g of cellular RNA (the median value was 2.7x10(5) and the mean was 3.1 x 10(6)). Telomerase activity was between 0 and 246 units of Total Protein Generated (TPG), where one unit of TPG was equal to 600 molecules, of telomerase substrate primers extended by at least three telomeric repeats. The median level of TPG was 60 units and the mean level was 81 units). Telomerase activity was found to significantly correlate with hTERT expression (r(s)=0.51112, P=0.0302). There was no significant correlation between hTERT and other parameters.

CONCLUSION

hTERT mRNA expression significantly correlates with telomerase activity in human breast cancer. This is consistent with the hypothesis that hTERT is the catalytic and rate-limiting determinant subunit of the enzyme.

hTERT expression in human breast cancer and non-cancerous breast tissue: correlation with tumour stage and c-Myc expression

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal length and stability thus leading to cellular immortalisation. hTERT (human telomerase reverse transcriptase) gene is the rate-limiting determinant of telomerase reactivation. The present study aims to quantitatively measure the expression of hTERT mRNA in human breast cancer, adjacent non-cancerous tissue (ANCT) and benign breast lesions, examine the association between hTERT and the clinicopathological characteristics of the cancer specimens and to explore the relationship between c-Myc and hTERT expressions. RNA was extracted from 49 breast carcinomas, 46 matched ANCT, and eight fibroadenomas. hTERT and c-Myc mRNA expressions were estimated by reverse transcriptase-PCR (RT-PCR) and Taqman methodology. hTERT mRNA was present in all of the cancerous and most of ANCT specimens with levels being much higher in the cancerous tissue than in ANCT. The ratio of hTERT mRNA in tumour to that in ANCT was 2011 (95% confidence interval 373-10,853, P < 0.0001). There was no significant association between tumour hTERT expression and patient's age, tumour size, grade, nodal metastasis, estrogen receptor (ER) positivity, lymphovascular (LVI) or c-Myc expression. However, there was a weak but significant negative correlation between hTERT expression and progesterone receptor (PR) status (p = 0.04) in tumours. hTERT mRNA expression was also significantly higher in carcinomas (median = 2.61 x 10(6)) than in fibroadenomas (median = 424).We conclude that hTERT mRNA expression is significantly higher in human breast cancer than in non-cancerous breast tissue suggesting that hTERT has a potential role in breast cancer diagnosis. The hTERT mRNA levels in tumour do not seem to be associated with the patient's age or advanced tumour stage. Furthermore, hTERT mRNA expression does not correlate with c-Myc mRNA expression in breast cancer.

Comparative analysis of telomere lengths and erosion with age in human epidermis and lingual epithelium

We investigated progressive telomere shortening in normal human epidermis and lingual epithelium during aging, and attempted, in particular, to ascertain whether the telomere shortening that accompanies aging occurs at the same rate in different tissues. We studied telomeric DNA integrity, and estimated annual telomere loss, in 52 specimens of epidermis and 48 specimens of lingual epithelium collected at autopsy from subjects who had died at ages between 0 and 101 y. Most of the DNA samples were measured twice by southern blot hybridization. In addition, the correlation between telomere lengths in the two types of tissues was examined. The telomere reduction rates in epidermis and lingual epithelium were 36 bp and 30 bp per y, respectively, and these were significantly different. The rates obtained by the second measurements in epidermis and lingual epithelium were 39 and 32 bp per y, respectively, and these were also significantly different. The mean telomere lengths in the epidermis of eight neonates and the lingual epithelium of seven neonates were 13.2+/-1.0 and 13.8+/-1.0 kb, respectively. Comparison of telomere lengths in the two tissues for 41 paired samples showed that the mean telomere length in the epidermis (10.7+/-2.3 kb) was less than that in the lingual epithelium (12.4+/-2.5 kb); however, statistical analysis revealed a very significant relationship between epidermal and lingual epithelial telomere length (r=0.842, p<0.0001). These results indicate that the telomeres in epidermis and lingual epithelium are characterized by tissue-specific loss rates.

Hypermethylation of the human telomerase catalytic subunit (hTERT) gene correlates with telomerase activity

DNA methylation is an epigenetic process involved in embryonic development, differentiation and aging. It is 1 of the mechanisms resulting in gene silencing in carcinogenesis, especially in tumor suppressor genes (e.g., p16, Rb). Telomerase, the DNA polymerase adding TTAGGG repeats to the chromosome end, is involved in the regulation of the replicative life span by maintaining telomere length. This enzyme is activated in germ and stem cells, repressed in normal somatic cells and reactivated in a large majority of tumor cells. The promoter region of the hTERT gene, encoding for the catalytic subunit of human telomerase, has been located in a CpG island and may therefore be regulated at least in part by DNA methylation. We analyzed the methylation status of 27 CpG sites within the hTERT promoter core region by methylation-sensitive single-strand conformation analysis (MS-SSCA) and direct sequencing using bisulfite-modified DNA in 56 human tumor cell lines, as well as tumor and normal tissues from different organs. A positive correlation was observed among hypermethylation of the hTERT promoter, hTERT mRNA expression and telomerase activity (p < 0.00001). Furthermore, this correlation was confirmed in normal tissues where hypermethylation of the hTERT promoter was found exclusively in hTERT-expressing telomerase-positive samples and was absent in telomerase-negative samples (p < 0.00002). Since tumor tissues contain also nonneoplastic stromal elements, we performed microdissection to allow confirmation that the hTERT promoter methylation truly occurred in tumor cells. Our results suggest that methylation may be involved in the regulation of hTERT gene expression. To our knowledge, this is the first gene in which methylation of its promoter sequence has been found to be positively correlated with gene expression.

Telomerase activity and hTERT mRNA expression can be heterogeneous and does not correlate with telomere length in soft tissue sarcomas

In a previous study, we showed that telomerase activity (TA) and human telomerase reverse transcriptase (hTERT) mRNA expression were undetectable in benign mesenchymal lesions and low-grade soft tissue sarcomas (STSs), but detectable in about 50% of intermediate-/high-grade STSs. We wondered if this lack of TA or hTERT mRNA expression could be related to the tumor sample examined and if there was a relationship between the former 2 parameters and telomere length. Two separate tumor samples from 37 STSs were examined for telomerase activity, using the telomerase repeat amplification protocol (TRAP) assay and for hTERT mRNA expression, using RT-PCR. Telomere length was determined in each tumor sample, using the terminal restriction fragments (TRF) technique. Significant variations in telomere length, TA and hTERT mRNA expression between 2 samples of the same tumor were observed in 27%, 11% and 27% of STSs, respectively. Telomere length did not correlate with TA or hTERT mRNA expression. Despite great intratumoral heterogeneity in telomere length, short and long telomeres were more often seen in the low/intermediate-grade and high-grade STS categories, respectively. Few STSs that showed a TRF pattern suggestive of alternative lengthening of telomeres (ALT) may contain ALT subpopulations.

Telomerase activity and Bcl-2 expression in human breast cancer

AIMS

Telomerase is a ribonucleoprotein that synthesizes telomeres and plays an important role in cellular immortalization. Bcl-2 gene encodes for a mitochondrial protein thought to prevent apoptosis of normal cells. We previously reported telomerase activity in 74% of human invasive breast cancers and detected a significant association between telomerase activity and prognostic parameters such as nodal status, tumour size and cellular proliferation. We hypothesized that telomerase reactivation in human breast cancer was associated with increased immunohistochemical expression of Bcl-2.

METHODS

Bcl-2 immunohistochemical expression was determined in 25 infiltrating breast carcinomas with known telomerase activity (17 telomerase-positive and 8 telomerase-negative). The percentage of strongly and moderately stained tumour cells for Bcl-2 was determined by a breast pathologist who was blinded to telomerase data. Fisher's exact test was used to examine the association between telomerase activity and Bcl-2 expression.

RESULTS

The median percentage of strongly stained tumour cells was 50% for telomerase-positive tumours (range, 0--100%) and 45% for telomerase-negative tumours (range, 0--100%). Twelve (70%) of 17 telomerase-positive tumours expressed strong or moderate Bcl-2 staining in >50% of tumour cells compared with six (75%) of eight telomerase-negative tumours (P=1.0).

CONCLUSION

Telomerase reactivation seems to be independent of Bcl-2 protein expression in human breast cancer.

The significance of human telomerase reverse transcriptase (hTERT) in cancer

Since the discovery of the enzyme telomerase in humans, it has become apparent that it is the most general of tumour markers known, and enormously significant in its potential for diagnostic, prognostic and therapeutic applications. Extensive work has identified three core components of the enzyme, of which the catalytic subunit hTERT (human telomerase reverse transcriptase) appears to be the most important. The aim of this article is to review the current evidence for the function and activity of hTERT in malignant conditions, and to discuss the future possibilities in terms of cancer diagnosis and treatment.

Regulation of telomerase during human placental differentiation: a role for TGFbeta1

The transient tumor-like attributes of the first-trimester placenta anchor the developing embryo to the uterine wall thus establishing a vital link between the mother and the fetus. Dysregulation of this invasive behavior and/or controlled proliferation of the placenta is associated with abnormal pregnancies. Several of these diseased states also exhibit aberrant telomerase activity, among other pathophysiological manifestations. Considering the strong correlation between telomerase activity and tumorigenesis, it was of interest to see whether the crucial processes of trophoblast proliferation and differentiation were brought about through the modulation of telomerase. Using two in vitro model systems of trophoblast differentiation, we demonstrate here that telomerase activity is negatively regulated during placental differentiation. We further show that this modulation is at the level of transcription of hTERT. We also propose a role for TGF beta1 in regulating telomerase activity in differentiating trophoblasts by down-regulating the expression of hTERT at the transcriptional level.

Telomerase activity in periampullary tumors correlates with aggressive malignancy

OBJECTIVE

To determine the presence of telomerase activity in a variety of periampullary malignancies and pancreatic diseases and quantify its activity to establish any association with the stage or aggressiveness of malignancy.

SUMMARY BACKGROUND DATA

Progressive shortening of telomeres, repetitive DNA sequences at the ends of chromosomes, plays a role in cell senescence. Telomerase catalyzes conservation of telomeric repeats and may promote cell immortality and hence malignancy. It is absent in normal tissues but upregulated in more than 80% of cancers.

METHODS

Fresh specimens of 62 periampullary tumors were snap-frozen in liquid nitrogen and adjacent tissue was formalin-fixed for histopathology. The telomerase repeat amplification protocol (TRAP) was used to obtain telomerase DNA products. These were separated with gel electrophoresis, stained with SYBR green, and quantified by densitometry. Findings were confirmed with a fluorometric TRAP assay in which fluorescent primers specific for telomerase were selectively amplified in its presence.

RESULTS

Telomerase activity was upregulated in 26 of 33 periampullary malignancies (79%): 17 of 21 pancreatic adenocarcinomas (81%), 2 of 2 cholangiocarcinomas, 2 of 2 duodenal carcinomas, and 5 of 8 ampullary carcinomas (63%). Poorly differentiated periampullary tumors had significantly higher telomerase activity than well-differentiated tumors, and tumors larger than 2 cm had significantly higher telomerase activity than those 2 cm or smaller. Pancreatic ductal adenocarcinomas with lymph node metastases had significantly greater activity than node-negative cancers. Two of 11 intraductal papillary mucinous tumors were positive for telomerase activity, but only in foci of invasive carcinoma. Chronic pancreatitis (n = 7), serous cystadenomas (n = 5), benign mucinous cystic neoplasms (n = 4), neuroendocrine cancer (n = 1), and acinar cell carcinoma (n = 1) had no detectable telomerase activity.

CONCLUSION

Telomerase activity is common in periampullary carcinomas. The magnitude of activity correlates with aggressiveness in pancreatic adenocarcinoma and may prove useful as a molecular index for biologic staging.

Activity, function, and gene regulation of the catalytic subunit of telomerase (hTERT)

Recent interest in the regulation of telomerase, the enzyme that maintains chromosomal termini, has lead to the discovery and characterization of the catalytic subunit of telomerase, hTERT. Many studies have suggested that the transcription of hTERT represents the rate-limiting step in telomerase expression and key roles for hTERT have been implied in cellular aging, immortalization, and transformation. Before the characterization of the promoter of hTERT in 1999, regulatory mechanisms suggested for this gene were limited to speculation. The successful cloning and characterization of the hTERT 5' gene regulatory region has enabled its formal investigation and analysis of potential mechanisms controlling hTERT expression. Although these studies have provided important information about hTERT gene regulation, there has been some confusion regarding the nucleotide boundaries of this region, the location, number, and importance of various transcription factor binding motifs, and the results of promoter activity assays. We feel that this uncertainty, combined with the sheer volume of recent publications on hTERT regulation, calls for consolidation and review. In this analysis we examine recent advances in the regulation of the hTERT gene and attempt to resolve discrepancies resulting from the nearly simultaneous nature of publications in this fast-moving area. Additionally, we aim to summarize the extant knowledge of hTERT gene regulation and its role in important biological processes such as cancer and aging.

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.

Up-regulation of vaults may be necessary but not sufficient for multidrug resistance

Vaults are ribonucleoprotein complexes comprised of the 100 kDa major vault protein (MVP), the 2 high m.w. vault proteins p193 (VPARP) and p240 (TEP1) and an untranslated small RNA (vRNA). Increased levels of MVP, vault-associated vRNA and vaults have been linked directly to non-P-glycoprotein-mediated multidrug resistance (MDR). To further characterize the putative role of vaults in MDR, expression levels of all of the vault proteins were examined in various MDR cell lines. Subcellular fractionation of vault particles revealed that all 3 vault proteins are increased in MDR cells compared to the parental, drug-sensitive cells. Furthermore, protein analysis of subcellular fractions of the drug-sensitive, MVP-transfected AC16 cancer cell line indicated that vault levels are increased, in this stable line. Since TEP1 is shared by both vaults and the telomerase complex, TEP1 protein (and vault) levels were compared with telomerase activity in a variety of cell lines, including various MDR lines. Our studies demonstrate that while vault levels may be a good predictor of drug resistance, their up-regulation alone is not sufficient to confer the drug-resistant phenotype. This implies a requirement of an additional factor(s) for vault-mediated MDR.

Functional and dysfunctional roles of quadruplex DNA in cells

A number of biological roles have been proposed for quadruplex, also referred to as G4 or tetraplex, DNA. The presence of quadruplex DNA may lead to errors in some biological processes and be required in others. Proteins that interact with quadruplex DNA have been identified including those that cause Bloom's and Werner's syndromes. There are small molecules that specifically bind to quadruplex DNA, inhibit telomerase, and are cytotoxic towards tumor cells indicating a role for quadruplex DNA in telomere function. It is now possible to make testable proposals for the possible biological implications of quadruplex DNA in replication, transcription, and recombination as well as possible routes to therapeutic intervention.