Constitutive and regulated expression of telomerase reverse transcriptase (hTERT) in human lymphocytes

RNA interference-mediated c-MYC inhibition prevents cell growth and decreases sensitivity to radio- and chemotherapy in childhood medulloblastoma cells

BACKGROUND

With current treatment strategies, nearly half of all medulloblastoma (MB) patients die from progressive tumors. Accordingly, the identification of novel therapeutic strategies remains a major goal. Deregulation of c-MYC is evident in numerous human cancers. In MB, over-expression of c-MYC has been shown to cause anaplasia and correlate with unfavorable prognosis.

METHODS

To study the role of c-MYC in MB biology, we down-regulated c-MYC expression by using small interfering RNA (siRNA) and investigated changes in cellular proliferation, cell cycle analysis, apoptosis, telomere maintenance, and response to ionizing radiation (IR) and chemotherapeutics in a representative panel of human MB cell lines expressing different levels of c-MYC (DAOY wild-type, DAOY transfected with the empty vector, DAOY transfected with c-MYC, D341, and D425).

RESULTS

siRNA-mediated c-MYC down-regulation resulted in an inhibition of cellular proliferation and clonogenic growth, inhibition of G1-S phase cell cycle progression, and a decrease in human telomerase reverse transcriptase (hTERT) expression and telomerase activity. On the other hand, down-regulation of c-MYC reduced apoptosis and decreased the sensitivity of human MB cells to IR, cisplatin, and etoposide. This effect was more pronounced in DAOY cells expressing high levels of c-MYC when compared with DAOY wild-type or DAOY cells transfected with the empty vector.

CONCLUSION

In human MB cells, in addition to its roles in growth and proliferation, c-MYC is also a potent inducer of apoptosis. Therefore, targeting c-MYC might be of therapeutic benefit when used sequentially with chemo- and radiotherapy rather than concomitantly.

Regulation of telomerase activity by interferon regulatory factors 4 and 8 in immune cells

Telomerase activity is downregulated in somatic cells but is upregulated during the activation of cells of the immune system. The mechanism of this reactivation is not well understood. In this study, we demonstrated that interferon regulatory factor 4 (IRF-4) and, to a lesser extent, IRF-8 induce telomerase activity. The suppression of IRF-4 results in decreased levels of TERT (telomerase reverse transcriptase) mRNA and telomerase activity and reduces cell proliferation. The overexpression of TERT compensates for this proliferation defect, suggesting that telomerase contributes to the regulation of cell proliferation by IRF-4. The induction of telomerase by IRF-4 and IRF-8 correlates with the activation of the TERT promoter. IRF-4 binds the interferon response-stimulated element and the gamma interferon-activated sequence composite binding site in the TERT core promoter region in vivo. Additionally, the binding of Sp1, Sp3, USF-1, USF-2, and c-Myc to the TERT promoter is elevated in cells expressing IRF-4. IRF-4, but not IRF-8, synergistically cooperates with Sp1 and Sp3 in the activation of the TERT promoter. Collectively, these results indicate that IRF-4 and IRF-8, two lymphoid cell-specific transcription factors, increase telomerase activity by activating TERT transcription in immune cells.

Distribution and prognostic significance of human telomerase reverse transcriptase (hTERT) expression in giant-cell tumor of bone

Giant-cell tumor of bone is considered a benign, locally aggressive and rarely metastasizing neoplasm of bone. Specific microscopic or radiographic findings that reliably predict behavior have remained elusive. However, recent evidence suggests that activity of the telomerase enzyme complex correlates with recurrence in giant-cell tumor, although the subset of cells with telomerase activity in these heterogeneous tumors has not been defined. In the present study, we investigated whether immunostaining for human telomerase reverse transcriptase, a component of the telomerase complex, correlates with outcome in giant-cell tumor and the distribution of telomerase reverse transcriptase staining in these tumors. We analyzed 58 cases of giant-cell tumor for the presence and pattern of telomerase reverse transcriptase immunostaining, presence of soft tissue involvement and the type of initial surgery, and correlated these findings with recurrence-free survival and metastasis-free survival. Specific staining with telomerase reverse transcriptase was present in 20 out of 58 tumors (35%) in the nuclei of mononuclear cells and, occasionally, osteoclast-like giant cells. Furthermore, positive telomerase reverse transcriptase immunohistochemistry correlated with recurrence-free survival (P=0.02), whereas the presence of soft tissue extension (P=0.3) and the type of initial surgery (P=0.2) did not. Only soft-tissue extension significantly correlated with metastasis-free survival (P=0.003). Therefore, telomerase reverse transcriptase expression may predict recurrence in giant-cell tumor insofar as positive immunostaining correlates with shorter recurrence-free survival and may be a useful prognostic marker to stratify patients to more aggressive treatment protocols.

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.

Telomere dysfunction in hypertension

Aging is a major risk factor for hypertension and associated cardiovascular disease. In most proliferative tissues, aging is characterized by shortening of the DNA component of telomeres, the specialized genetic segments that cap the end of eukaryotic chromosomes and protect them from end-to-end fusions. By inducing genomic instability, replicative senescence and apoptosis, telomere shortening is thought to contribute to organismal aging and to the development of age-related diseases. Here, we review animal and human studies that have investigated the possible links between telomere ablation and the pathogenesis of hypertension and related target organ damage. Although evidence is mounting that alterations in telomerase activity and telomere shortening may play a role in the pathogenesis of hypertension, additional studies are required to understand the molecular mechanisms by which telomere dysfunction and hypertension are functionally connected. As our knowledge on this emerging field grows, the challenge will be to ascertain whether all this information might translate into clinical applications.

DNA damage in telomeres and mitochondria during cellular senescence: is there a connection?

Cellular senescence is the ultimate and irreversible loss of replicative capacity occurring in primary somatic cell culture. It is triggered as a stereotypic response to unrepaired nuclear DNA damage or to uncapped telomeres. In addition to a direct role of nuclear DNA double-strand breaks as inducer of a DNA damage response, two more subtle types of DNA damage induced by physiological levels of reactive oxygen species (ROS) can have a significant impact on cellular senescence: Firstly, it has been established that telomere shortening, which is the major contributor to telomere uncapping, is stress dependent and largely caused by a telomere-specific DNA single-strand break repair inefficiency. Secondly, mitochondrial DNA (mtDNA) damage is closely interrelated with mitochondrial ROS production, and this might also play a causal role for cellular senescence. Improvement of mitochondrial function results in less telomeric damage and slower telomere shortening, while telomere-dependent growth arrest is associated with increased mitochondrial dysfunction. Moreover, telomerase, the enzyme complex that is known to re-elongate shortened telomeres, also appears to have functions independent of telomeres that protect against oxidative stress. Together, these data suggest a self-amplifying cycle between mitochondrial and telomeric DNA damage during cellular senescence.

Assessing ageing of individual T lymphocytes: mission impossible?

Effector T lymphocytes are the progeny of a limited number of antigen-specific precursor cells and it has been estimated that clonotypic human T cells may expand million fold on their way reaching high cell numbers that are sufficient for immune protection. Moreover, memory T cell responses are characterized by repetitive expansion of antigen-specific T cell clonotypes, and limitations in the proliferative capacity could lead to immune senescence. Because telomeres progressively shorten as a function of cell division, telomere length is a powerful indicator of the replicative in vivo history of human T lymphocytes. In this review, we summarize observations made over the last decade on telomere length dynamics of well-defined T cell populations derived from healthy donors and patients with infectious disease or cancer. We focus on T cell differentiation, T cell ageing, and natural and vaccine induced immune responses. We also discuss the scientific evidence for in vivo replicative senescence of antigen-specific T cells, and evaluate the available methods for measuring telomere lengths and telomerase activity, and their potential and limitations to increase our understanding of T cell physiology.

Telomeres, senescence, and hematopoietic stem cells

The replicative lifespan of normal somatic cells is restricted by the erosion of telomeres, which are protective caps at the ends of linear chromosomes. The loss of telomeres induces antiproliferative signals that eventually lead to cellular senescence. The enzyme complex telomerase can maintain telomeres, but its expression is confined to highly proliferative cells such as stem cells and tumor cells. The immense regenerative capacity of the hematopoietic system is provided by a distinct type of adult stem cell: hematopoietic stem cells (HSCs). Although blood cells have to be produced continuously throughout life, the HSC pool seems not to be spared by aging processes. Indeed, limited expression of telomerase is not sufficient to prevent telomere shortening in these cells, which is thought ultimately to limit their proliferative capacity. In this review, we discuss the relevance of telomere maintenance for the hematopoietic stem cell compartment and consider potential functions of telomerase in this context. We also present possible clinical applications of telomere manipulation in HSCs and new insights affecting the aging of the hematopoietic stem cell pool and replicative exhaustion.

The HLA A*0201-restricted hTERT(540-548) peptide is not detected on tumor cells by a CTL clone or a high-affinity T-cell receptor

Tumor-associated human telomerase reverse transcriptase (hTERT) is expressed in >85% of human tumors but not in most normal cells. As a result, this antigen has received considerable attention from those interested in cancer immunotherapy. Specifically, there has been strong interest in MHC class I-associated peptides derived from hTERT because these are expressed on the cell surface and thus may enable the targeting of tumor cells. Much of this interest has focused on peptide 540-548, ILAKFLHWL, which was predicted to exhibit the strongest binding to the common HLA A*0201 presenting molecule. The hTERT(540-548) peptide is currently being assessed in therapeutic vaccination trials; however, there is controversy surrounding whether it is naturally processed and presented on the surface of neoplastic cells. Here, we generate two highly sensitive reagents to assess the presentation of hTERT(540-548) on tumor cells: (a) a CD8(+) CTL clone, and (b) a recombinant T-cell receptor (TCR) that binds with picomolar affinity and a half-life exceeding 14 h. This TCR enables the identification of individual HLA A2-hTERT(540-548) complexes on the cell surface. The use of both this TCR and the highly antigen-sensitive CTL clone shows that the hTERT(540-548) peptide cannot be detected on the surface of tumor cells, indicating that this peptide is not a naturally presented epitope. We propose that, in future, rigorous methods must be applied for the validation of peptide epitopes used for clinical applications.

Telomerase in T lymphocytes: use it and lose it?

The enzyme telomerase counteracts telomere loss in proliferating cells and extends their capacity for replication. The importance of telomerase is highlighted by the award of the 2006 Albert Lasker Prize for Basic Medical Research for its discovery. Malignant cells subvert telomerase induction to their advantage, and up-regulation of this enzyme confers these populations with unlimited proliferative potential with obvious detrimental consequences. However this enzyme is also essential for the lifelong maintenance of normal cell populations that have a high rate of turnover. Thymic involution in early adulthood dictates that memory T cell populations have to be maintained by continuous proliferation. This highlights the inherent paradox that telomerase down-regulation in T cells may protect against malignancy yet also lead to replicative exhaustion of repeatedly activated memory T cells. In this article, we review the data on telomerase regulation in T lymphocytes and the implications this has for the maintenance of T cell memory.

Telomere biology and cardiovascular disease

Accumulation of cellular damage with advancing age leads to atherothrombosis and associated cardiovascular disease. Ageing is also characterized by shortening of the DNA component of telomeres, the specialized genetic segments located at the end of eukaryotic chromosomes that protect them from end-to-end fusions. By inducing genomic instability, replicative senescence and apoptosis, shortening of the telomeric DNA is thought to contribute to organismal ageing. In this Review, we discuss experimental and human studies that have linked telomeres and associated proteins to several factors which influence cardiovascular risk (eg, estrogens, oxidative stress, hypertension, diabetes, and psychological stress), as well as to neovascularization and the pathogenesis of atherosclerosis and heart disease. Two chief questions that remain unanswered are whether telomere shortening is cause or consequence of cardiovascular disease, and whether therapies targeting the telomere may find application in treating these disorders (eg, cell "telomerization" to engineer blood vessels of clinical value for bypass surgery, and to facilitate cell-based myocardial regeneration strategies). Given that most research to date has focused on the role of telomerase, it is also of up most importance to investigate whether alterations in additional telomere-associated proteins may contribute to the pathogenesis of cardiovascular disease.

Telomerase immunity from bench to bedside: round one

Telomerase, a reverse transcriptase primarily devoted to the elongation of telomeres in mammalian cells, is also the first bona fide common tumor antigen. In fact, telomerase is over-expressed in > 85% of tumor cells irrespective of origin and histological type. In the past seven years, there has been considerable interest in assessing telomerase as substrate for vaccination in cancer patients to induce CD8 T cell responses. Because the activation of T cells is restricted by the MHC molecules on antigen presenting cells or tumor cells, the identification of telomerase peptides immunogenic for humans is tightly linked with HLA types. To date, a handful of peptides have been identified through a variety of screening procedures, including bioinformatics prediction, in vivo immunization of HLA transgenic mice, in vitro immunization of PBMC from normal donors and cancer patients, and processing in human tumor cells. Currently, there exist putative peptides for five major HLA types (A2, A1, A3, A24 and B7). Due to the complexity of the HLA system, trials have been performed focusing on the most prevalent HLA type, HLA-A2. Here, we summarize this collective effort and highlight results obtained in Phase 1 trials including a Phase 1 trial performed at the UCSD Cancer Center.

Immunity against breast cancer by TERT DNA vaccine primed with chemokine CCL21

Human telomerase reverse transcriptase (TERT) has been considered a potential tumor-associated antigen for active-specific immunotherapy. However, effective specific tumor antigen-specific immunity has been difficult to induce consistently by various TERT vaccine formulations. New adjuvant strategies have been employed, such as utilizing chemokines to attract T cells and antigen-presenting cells. Chemokine adjuvant strategies may enhance tumor antigen-specific immunity induced by vaccines. Therefore, we utilized chemokine ligand 21 (CCL21) as an adjuvant with a xenogeneic TERT DNA vaccine to induce tumor antigen-specific immunity against TERT-expressing breast cancer. The TERT DNA vaccine consisted of a plasmid containing the COOH terminal end of the TERT (cTERT) gene, encapsulated in multilayered liposomes with hemagglutinating virus of Japan coating. We demonstrated that CCL21 treatment before cTERT DNA vaccine, given intramuscularly, induced significantly higher anti-TERT specific cell-mediated immunity compared to cTERT DNA vaccine alone. Effective tumor antigen-specific immunity was shown both in prophylactic and therapeutic regimens against TS/A murine breast cancer. The study demonstrated that CCL21 administration before cTERT DNA vaccination significantly augmented tumor antigen-specific immunity against breast cancer.

The aging process and potential interventions to extend life expectancy

Aging is commonly defined as the accumulation of diverse deleterious changes occurring in cells and tissues with advancing age that are responsible for the increased risk of disease and death. The major theories of aging are all specific of a particular cause of aging, providing useful and important insights for the understanding of age-related physiological changes. However, a global view of them is needed when debating of a process which is still obscure in some of its aspects. In this context, the search for a single cause of aging has recently been replaced by the view of aging as an extremely complex, multifactorial process. Therefore, the different theories of aging should not be considered as mutually exclusive, but complementary of others in the explanation of some or all the features of the normal aging process. To date, no convincing evidence showing the administration of existing "anti-aging" remedies can slow aging or increase longevity in humans is available. Nevertheless, several studies on animal models have shown that aging rates and life expectancy can be modified. The present review provides an overlook of the most commonly accepted theories of aging, providing current evidence of those interventions aimed at modifying the aging process.

Impact of culture conditions on the proliferative lifespan of human T cells in vitro

BACKGROUND

In human T cells, telomerase is transiently expressed upon activation and stimulation and, as shown previously, telomerase levels are able to control the lifespan of T cells. To improve T-cell expansion it is of critical importance to understand the effects of culture parameters on telomerase activity and lifespan.

METHODS

We investigated the influence of culture condition (FCS, human AB serum and autologous serum) and stimulation (PHA/feeder cells, anti-CD3/CD28 beads) on the lifespan, clonogenicity (number of positive wells), cell cycle, telomerase activity and telomere length of T cells in vitro.

RESULTS

The proliferative lifespan of T cells expanded with PHA/feeder cells and autologous serum from different donors was doubled compared with stimulation with PHA/feeder cells and AB serum. No or only a small difference was found for T cells expanded with anti-CD3/CD28 beads and autologous or AB serum. The use of autologous serum also increased the clonogenicity to about three-fold compared with the use of AB serum or FCS, without any signs of differences in the fractions of cycling cells. Interestingly, T cells cultured with autologous serum exhibited a significantly higher telomerase activity at day 6 after stimulation and a reduced decline of telomerase activity compared with cultures with AB serum.

DISCUSSION

The use of autologous serum combined with PHA stimulation and feeder cells remarkably extends the proliferative lifespan and clonogenicity and increases the telomerase activity of human T cells in vitro. This might be useful for applications where large numbers of specific T cells are required.

Human normal T lymphocytes and lymphoid cell lines do express alternative splicing variants of human telomerase reverse transcriptase (hTERT) mRNA

Alternative splicing of telomerase reverse transcriptase (hTERT) mRNA is known to contribute to regulation of telomerase activity in normal and cancerous cells, however, previous studies indicated that normal human T and B cells exhibited constitutive expression of full-length hTERT mRNA without splicing variants and that activation of telomerase upon stimulation of the cells was due to the shuttling of hTERT protein from cytoplasm to nucleus [Proc. Natl. Acad. Sci. USA 96 (1999) 5147; J. Immunol. 166 (2001) 4826]. We found that typical variants of hTERT mRNA were widespread in human lymphocyte-derived cell lines and normal stimulated T cells. In activated T cells, induction of the full-length hTERT mRNA was coupled with increased hTERT protein expression and telomerase activity. Collectively, human normal and malignant lymphocytes, like other human cells, express splicing variants of hTERT mRNA and require transcriptional activation of the hTERT gene to acquire telomerase activity.

Immortalization of Epstein-Barr virus-negative human B lymphocytes with minimal chromosomal instability

The genes required for immortalization of human B cells infected by Epstein-Barr virus are multiple, and the precise mechanism of this process remains to be elucidated. In the present study HPV16 E6 and E7 were retrovirally transduced into human primary B cells stimulated by CD40-CD40L interaction, thereby establishing an Epstein-Barr virus negative immortalized human B cell line, which continued to proliferate for more than 2 years (100 population doublings). The established cell line had a high telomerase activity from the beginning of the culture period, and no shortening of the telomere length was observed. A chromosomal analysis revealed that a large portion of the HPV16E6E7 transduced cells had retained a normal karyotype. Similar to human epithelial cells, human B lymphocytes seem to require two steps for immortalization, namely, the inactivation of the p16/Rb pathway and the activation of telomerase, the latter that can be induced by the CD40-CD40L interaction. Furthermore, using this system, it is possible to analyze the role of individual genes in human B lymphocyte immortalization without the influence of a pre-existing Epstein-Barr virus genome.

In situ detection of hTERT variants in anaplastic large cell lymphoma

The expression of hTERT and its isoforms is difficult to assess in lymphoma tissues with the commonly used reverse transcription-polymerase chain reaction (RT-PCR) methods, because non-neoplastic lymphocytes expressing hTERT are always present in the lymphomatous infiltrates. The present study aimed to investigate hTERT mRNA variants in anaplastic large cell lymphoma (ALCL) (n = 38) with in situ hybridization (ISH), along with the immunodetection of hTERT protein. Probes for the identification of mRNAs containing (Bplus) and lacking (Bdel) exons 7 and 8 of the hTERT mRNA were used. Normal lymphocyte populations equally expressed both Bplus and Bdel mRNAs. Although all ALCL examined were found positive for hTERT expression with RT-PCR, hTERT mRNAs were identified in 68% of these tumors with ISH, with a higher incidence in the group bearing ALK translocations (10 out of 11; 90.9%) compared to the ALK negative group (17 out of 27; 59.3%) (PPearson's = 0.002). The same results were obtained with immunohistochemistry for hTERT. In approximately 50% of cases, only Bplus positive cells were identified, again with a higher incidence in the ALK positive compared to the ALK negative group (PPearson's = 0.016). In conclusion, ISH for hTERT mRNAs appears to be a valuable tool for the investigation of hTERT expression in lymphomas. Aberrations in hTERT variant profiles and a decline in the expression of the B deleted isoform may be associated with the pathogenesis of ALCL, especially with respect to ALK positive tumors.

A major role of PKC theta and NFkappaB in the regulation of hTERT in human T lymphocytes

Expression of the telomerase catalytic subunit (TERT) is the rate-limiting determinant of telomerase activity in most human cells. In this work, we examined the participation of protein kinase C (PKC) in the regulation of hTERT expression in human T lymphocytes. Transient expression assays using luciferase reporter plasmids containing hTERT promoter showed that overexpression of PKC theta, but not the other PKC isoforms, could activate the promoter activity of hTERT in resting T lymphocytes. Among the PKC theta-activated signalings, we presented evidence that the expression of hTERT is mediated through NFkappaB but not through MEK or c-Jun N-terminal kinase pathways. Analysis of the hTERT promoter occupancy in vivo using chromatin immunoprecipitation assays, however, did not detect an increased binding of NFkappaB to the hTERT promoter in the activated T cells, although an increased binding of cMyc and Sp1 was detected. Together with the observation that inhibition of NFkappaB eliminated the induction of cMyc in activated T cells, these results suggest that PKC theta-activated NFkappaB signaling regulates the expression of hTERT via cMyc in human T lymphocytes.

Characterization of novel alternative splicing sites in human telomerase reverse transcriptase (hTERT): analysis of expression and mutual correlation in mRNA isoforms from normal and tumour tissues

Background

Human telomerase reverse transcriptase (hTERT) is a key component for synthesis and maintenance of telomeres on chromosome ends and is required for the continued proliferation of cells. Estimation of hTERT expression therefore has broad relevance in oncology and stem cell research. Several splicing variants of hTERT have been described whose regulated expression contributes to the control of telomerase activity. Knowledge of the different hTERT mRNA isoforms and the ability to distinguish between them is an important issue when evaluating telomerase expression.

Results

By establishing cDNA-clone panels from lung and colon tissues, we could map hTERT clones individually for differences in DNA sequence. This made possible the identification of novel alternatively spliced sites as well as analysis of their frequency and mutual correlation in mRNA isoforms. Ten different alternatively spliced sites were detected, of which six were novel sites resulting from alternative splicing of intron 2 or 14. The majority of hTERT cDNA clones from normal and tumour lung and colon tissues encoded truncated proteins ending close after exon 2 or 6.

Conclusion

The increased complexity in telomerase expression revealed here has implications for our understanding of telomerase regulation and for the choice of suitable methods for addressing hTERT expression.

hTERT immunopositivity patterns in the normal brain and in astrocytic tumors

Accumulating data about the impact of hTERT in astrocytic tumor carcinogenesis and recent evidence about its association with disease outcome prompt the evaluation of this molecule with methods applicable in routine pathology practice. In this study, we investigated hTERT protein expression with immunohistochemistry (IHC) and the NCL-hTERT antibody in 49 astrocytic tumors. Results were validated with the assessment of hTERT mRNA (relative quantification, identification of splice variants, in situ hybridization). Specific nuclear hTERT immunostaining patterns (IPs) were characterized as patterns As (single large dot) and Am (multiple dots) without nucleoplasm staining and pattern B (nucleoplasm staining with or without dots), corresponding to low and high relative hTERT expression values (P<0.0001). Low- and high-grade astrocytic tumors were found positive for hTERT in 74 and 85% of cases, respectively. Heterogeneity in the distribution of hTERT-positive cells was observed in all tumors. The prevailing nuclear IPs differed significantly between pilocytic astrocytomas (pattern As) and the rest of histologic types up to glioblastoma (patterns Am and B) (P<0.0001). The described nuclear IPs were also observed in non-neoplastic cells. Positive endothelial cells were found in astrocytic tumors of all grades, even when tumor cells showed no hTERT immunoreactivity. A subset of mature normal neurons was positive for hTERT (pattern As), suggesting a role for this molecule in neuronal maintenance in the adult brain. The nuclear hTERT IPs described here may reflect the functional status of non-neoplastic brain and neoplastic astrocytic cells and support the model of a continuum in the development of glioblastomas from diffuse fibrillary astrocytomas.

Oncolytic adenovirus that overproduces ADP and replicates selectively in tumors due to hTERT promoter-regulated E4 gene expression

We have constructed a novel oncolytic adenovirus (Ad) vector, named VRX-011, in which the replication of the vector is targeted to cancer cells by the replacement of the wild-type Ad E4 promoter with the human telomerase reverse transcriptase (hTERT) promoter. Genes in the Ad E4 transcription unit are essential for Ad replication; therefore, VRX-011 will grow efficiently only in cells in which the hTERT promoter is active, that is, in a wide range of cancer and immortalized cells but not in most somatic cells. Consistent with these expectations, VRX-011 replicated efficiently in all cancer cell lines examined, while its growth was restricted in various primary and normal cells. VRX-011 overexpresses ADP (also known as E3-11.6K), an Ad protein required for efficient cell lysis and release of virions from cells at late stages of infection. This overexpression enhances cell-to-cell spread and could significantly increase antitumor efficacy. In a xenograft model in nude mice, both intratumoral and intravenous administration of VRX-011 effectively suppressed the growth of subcutaneous Hep3B human liver tumors. Also, intravenous delivery of VRX-011 greatly reduced the number and size of A549 human lung cancer cell nodules in a disseminated lung tumor model in nude mice. Importantly, tail vein administration of different doses of VRX-011 in C57BL/6 mice showed minimal liver toxicity. Considering its broad range of lytic replication in cancer cells, its attenuated phenotype in primary cells, its efficacy in suppressing xenografts, and its low toxicity in mouse liver, VRX-011 is a promising candidate for further evaluation as an anticancer therapeutic.

Receptor Ck-dependent signaling regulates hTERT gene transcription

BACKGROUND

Available evidence suggests that the regulation of telomerase activity primarily depends on the transcriptional control of the human telomerase reverse transcriptase (hTERT) gene. Although several activators and repressors of hTERT gene transcription have been identified, the exact mechanism by which hTERT transcription is repressed in normal cells and activated in cancer cells remains largely unknown. In an attempt to identify possible novel mechanisms involved in the regulation of hTERT transcription, the present study examined the role of Receptor Ck, a cell surface receptor specific for cholesterol, in the transcription of hTERT gene in normal human peripheral blood mononuclear cells.

RESULTS

Activated Receptor Ck was found to down-regulate hTERT mRNA expression by repressing the transcription of c-myc gene. Receptor Ck-dependent signaling was also found to down-regulate the mRNA expression of the gene coding for the ligand inducible transcription factor, peroxisome proliferator-activated receptor gamma (PPARgamma). The ligand activation of PPARgamma resulted in the down-regulation of c-myc and hTERT mRNA expression. By using specific activator and inhibitor of protein kinase C (PKC), it was demonstrated that Receptor Ck dependent down-regulation of hTERT gene transcription involved inhibition of PKC. In addition, 25-hydroxycholesterol was found to contribute to the transcriptional regulation of hTERT gene.

CONCLUSION

Taken together, the findings of this study present evidence for a molecular link between cholesterol-activated Receptor Ck and hTERT transcription, and provide new insights into the regulation of hTERT expression in normal human peripheral blood mononuclear cells.

A Phase I Study of the Optimized Cryptic Peptide TERT572Y in Patients with Advanced Malignancies

OBJECTIVE

It was the aim of this study to evaluate the safety of the optimized cryptic peptide TERT(572Y) in pretreated patients with advanced cancer.

METHODS

Nineteen patients with progressive and chemotherapy-refractory tumors received escalated doses (2-6 mg) of 2 subcutaneous injections of the optimized TERT(572Y) peptide followed by 4 subcutaneous injections of the native TERT(572) peptide every 3 weeks. Both TERT peptides were coinjected with adjuvant Montanide ISA51. Toxicity was evaluated every 3 weeks and peptide-specific CD8+ cells were detected by flow cytometry using TERT(572Y) tetramers.

RESULTS

Fourteen out of 19 patients completed the vaccination program. No grade III/IV toxicity was observed. Grade I anemia was observed in 4 patients and local skin reaction at the injection site in 11 patients. Other nonhematologic toxicities were mild, and no late toxicity was observed after a median postvaccination follow-up period of 10.7 months. There was no dose-limiting toxicity. Peripheral blood TERT(572Y)-specific CD8+ lymphocytes were detected in 13 out of 14 evaluable patients after 2 injections with the optimized TERT(572Y) peptide. There was no complete or partial response, but 4 patients (21%) with persistent TERT(572Y)-specific CD8+ experienced stable disease for a median of 10.5 months.

CONCLUSION

TERT(572Y) peptide vaccine is well tolerated and effective in eliciting specific TERT(572Y) CD8+ lymphocytes in pretreated cancer patients, demonstrating that cryptic peptides could be used in cancer immunotherapy.

A balanced transcription between telomerase and the telomeric DNA-binding proteins TRF1, TRF2 and Pot1 in resting, activated, HTLV-1-transformed and Tax-expressing human T lymphocytes

Background

The functional state of human telomeres is controlled by telomerase and by a protein complex named shelterin, including the telomeric DNA-binding proteins TRF1, TRF2 and Pot1 involved in telomere capping functions. The expression of hTERT, encoding the catalytic subunit of telomerase, plays a crucial role in the control of lymphocyte proliferation by maintaining telomere homeostasis. It has been previously found that hTERT activity is down-regulated by the human T cell leukaemia virus type 1 (HTLV-1) Tax protein in HTLV-1 transformed T lymphocytes. In this study, we have examined the effects of Tax expression on the transcriptional profile of telomerase and of shelterin in human T lymphocytes.

Results

We first provide evidence that the up-regulation of hTERT transcription in activated CD4+ T lymphocytes is associated with a down-regulation of that of TERF1, TERF2 and POT1 genes. Next, the down-regulation of hTERT transcription by Tax in HTLV-1 transformed or in Tax-expressing T lymphocytes is found to correlate with a significant increase of TRF2 and/or Pot1 mRNAs. Finally, ectopic expression of hTERT in one HTLV-1 T cell line induces a marked decrease in the transcription of the POT1 gene. Collectively, these observations predict that the increased transcriptional expression of shelterin genes is minimizing the impact on telomere instability induced by the down-regulation of hTERT by Tax.

Conclusion

These findings support the notion that Tax, telomerase and shelterin play a critical role in the proliferation of HTLV-1 transformed T lymphocytes.

Quantitative and spatial measurements of telomerase reverse transcriptase expression within normal and malignant human breast tissues

The enzyme telomerase catalyzes the de novo synthesis of telomere repeats, thereby maintaining telomere length, which is necessary for unlimited cellular proliferation. Telomerase reverse transcriptase (TERT), the catalytic domain of telomerase, is the rate-limiting factor for telomerase activity and is expressed in virtually all tumors. Thus, TERT has been proposed as a marker with diagnostic and prognostic potential in breast cancer as well as a basis for breast cancer therapeutics. In these contexts, it is important to define the sites and extent of TERT expression in normal and cancerous human breast tissues. In this study, levels of TERT mRNA were measured within a set of 36 breast carcinomas and 5 normal breast samples by quantitative real-time reverse transcription-PCR, and we subsequently identified and characterized the cells expressing TERT mRNA within these tissues using in situ hybridization. The results show that (a) detectable TERT mRNA expression is specific to the epithelial cells; (b) TERT is expressed in both normal and malignant breast tissues; (c) the pattern and level of TERT expression are heterogeneous, with approximately 75% of tumors expressing bulk TERT mRNA levels equal to or less than those within normal breast tissue; and (d) tumors expressing above-normal levels of TERT mRNA are more likely to be histopathologic grade 3 (P = 0.002), contain high fraction of cells in S phase (P = 0.004), and have increased levels of MYC mRNA (P = 0.034).

Role of Smad3 in the regulation of rat telomerase reverse transcriptase by TGFβ

Telomerase is induced in certain pathological conditions such as cancer and tissue injury and repair. This induction in fibroblasts from injured lung is repressed by transforming growth factor beta (TGFbeta) via yet unknown mechanisms. In this study, the role of Smad3 in the inhibition of telomerase reverse transcriptase (TERT) gene transcription by TGFbeta was investigated. The rat TERT (rTERT) gene promoter was cloned by PCR amplification and fused with a luciferase reporter gene. This construct was used to analyse regulation of promoter activity in fibroblasts isolated from bleomycin-injured lung with induced telomerase activity. The results showed that TGFbeta inhibited rTERT transcription while stimulating Smad3 expression. Interestingly, TGFbeta also inhibited the expression of c-myc. Cotransfection with a Smad3 expressing plasmid further repressed rTERT transcription and c-myc expression, while cotransfection with the corresponding antisense Smad3 construct had the opposite effect. Mutation of an E-box in the rTERT promoter suppressed its activity, which could be further reduced by TGFbeta treatment. In contrast, mutation at a Smad binding element enhanced promoter activity whose inhibition was impaired by TGFbeta treatment. Thus TGFbeta inhibition of rTERT gene expression was directly mediated by Smad3 via the Smad binding element, while c-myc appears to primarily regulate its constitutive or induced expression.

Expression of a recombinant vector of a mutant human telomerase reverse transcriptase gene in human bladder cancer cell line T24, and its clinical significance

OBJECTIVE

To construct a mutant enhanced green fluorescence protein (pEGFP) human telomerase reverse transcriptase (hTERT) gene expression vector (pEGFP-hTERT), to observe its expression in transfected human bladder cancer cell line T24 and its role in the molecular regulatory mechanisms of telomerase, and to provide a new target gene for bladder cancer therapy.

MATERIALS AND METHODS

Polymerase chain reaction (PCR) amplification was performed using primers based on the gene sequence of hTERT. The PCR product was cloned into plasmid pGEMT-T Easy and the sequence of mutant hTERT gene analysed. A recombinant mutant hTERT vector (pEGFP-hTERT) was constructed at the EcoR I and Sal I sites of the pEGFP-C1 vector. After transfecting the fusion gene into T24 cells by the method of calcium phosphate-DNA co-precipitation, we detected steady expression of the GFP-hTERT fusion protein by fluorescent-light microscopy. Changes in the proliferation of T24 cells were detected by light microscopy, and beta-galactosidase staining correlated with senescence.

RESULTS

Identification of pEGFP-hTERT by enzyme digestion showed that the mutant hTERT fragment had been cloned into EcoR I and Sal I sites of the pEGFP-C1 vector. Steady expression of GFP-hTERT fusion protein was located in the nucleus of transfected cells. Positive expression senescence-associated beta-galactosidase staining in transfected cells increased gradually with extended cultured time, and their growth was suppressed.

CONCLUSION

The recombinant mutant vector (pEGFP-hTERT) was successfully constructed and expressed steadily in T24 cells. The mutant-type hTERT gene suppresses the proliferation of T24 cells by a competitive effect on telomerase activity. This suggests that the hTERT gene might be a suitable gene target for bladder cancer therapy.

Telomerase reverse transcriptase mRNA expression in peripheral lymphocytes of patients with chronic HBV and HCV infections

Telomerase activity is present at low levels in peripheral lymphocytes (PL) and is upregulated upon activation, possibly protecting PL from telomere shortening. As decreased telomere length is considered a sign of cellular senescence, telomerase may, therefore, play an important role on immune function, organ regeneration and carcinogenesis. So far, quantification of human telomerase reverse transcriptase levels (hTERT) in PL, has not been reported. We determined hTERT mRNA levels in PL of hepatitis B virus (HBV) and hepatitis C virus (HCV) patients, in an attempt to address whether hTERT transcripts in PL are altered in these viral diseases, which are characterized by immune dysfunction and increased incidence of hepatocarcinogenesis. hTERT mRNA levels in PL of HBV (n = 17), HCV (n = 24) patients and healthy controls (n = 22) were quantified by real-time polymerase chain reaction. We observed significantly lower hTERT mRNA levels in HBV and HCV patients compared with healthy individuals (P < 0.05). hTERT mRNA levels were not associated with the patients' clinical status (inactive, hepatitis and cirrhosis). Also no correlation was observed between hTERT mRNA expression, and HBV and HCV replicative activity. In the inactive group (n = 18) we observed a negative correlation between hTERT mRNA expression and disease duration (rs = -0.52, P < 0.03). We performed for the first time an accurate quantification of hTERT mRNA expression in PL of HBV and HCV patients. The observed low levels of hTERT mRNA expression in the above patients may suggest its involvement in the immunopathogenesis of chronic viral hepatitis.

Whether modern cell technologies can break down biological limitations of tissue-specific regeneration of the myocardium

The paper reviews modern concepts of physiological and reparative regeneration of the myocardium as a highly specific and highly differentiated tissue system. Special attention was given to evaluation of the proliferative potential of cardiomyocytes, in particular, to the existence of a population of resident cardiac stem cells in the myocardium. Modern approaches to replenishment of massive cardiomyocyte loss via transplantation and transdifferentiation of adult and embryonic stem cells are discussed and the possibilities of using cell technologies for induction of tissue-specific regeneration of the myocardium are analyzed.

IL-15 Activates Telomerase and Minimizes Telomere Loss and May Preserve the Replicative Life Span of Memory CD8+T Cells In Vitro

The preservation of the replicative life span of memory CD8(+) T cells is vital for long-term immune protection. Although IL-15 plays a key role in the homeostasis of memory CD8(+) T cells, it is unknown whether IL-15 regulates the replicative life span of memory CD8(+) T cells. In this study, we report an analysis of telomerase expression and telomere length in human memory phenotype CD8(+) T cells maintained by IL-15 in vitro. We demonstrate that IL-15 is capable of activating telomerase in memory CD8(+) T cells via Jak3 and PI3K signaling pathways. Furthermore, IL-15 induces a sustained level of telomerase activity over long periods of time, and in turn minimizes telomere loss in memory CD8(+) T cells after substantial cell divisions. These findings suggest that IL-15 activates stable telomerase expression and compensates telomere loss in memory phenotype CD8(+) T cells, and that telomerase may play an important role in memory CD8(+) T cell homeostasis.

Telomerase catalytic subunit in laryngeal carcinogenesis--an immunohistochemical study

We recently demonstrated that (1) telomerase catalytic subunit messenger RNA (mRNA) relative quantities increase progressively with the degree of laryngeal epithelial abnormalities and that (2) telomerase catalytic subunit gene re-expression represents an early event in laryngeal carcinogenesis. The aim of the study was to determine whether telomerase catalytic protein immunohistochemisty reflects telomerase catalytic subunit gene expression in different grades of laryngeal epithelial abnormalities and squamous cell carcinomas of the larynx. Telomerase catalytic protein was analysed immunohistochemically in 106 laryngeal epithelial tissue samples: 10 normal epithelia, 15 squamous cell hyperplasias, 14 basal/parabasal cell hyperplasias, 10 atypical hyperplasias, eight intraepithelial carcinomas and 49 squamous cell carcinomas. At least 200 nuclei of each lesion were quantified per slide and the number of positive signals per nucleus was expressed as a telomerase catalytic protein index. The mean telomerase catalytic protein index increased progressively with the degree of laryngeal epithelial abnormalities: from 0.17 in normal epithelia, 0.44 in squamous cell hyperplasia, 0.54 in basal/parabasal cell hyperplasia, 0.91 in atypical hyperplasia, 1.05 in intraepithelial carcinoma to 0.96 in squamous cell carcinomas. Statistical analysis revealed three different groups of laryngeal epithelial changes according to the number of telomerase catalytic protein signals per nucleus: (1) normal epithelium, (2) regenerative epithelium (squamous cell hyperplasia, basal/parabasal cell hyperplasia), and (3) atypical hyperplasia, intraepithelial carcinoma and squamous cell carcinoma (P<0.0033). Telomerase catalytic protein immunohistochemistry parallels well with telomerase catalytic subunit mRNA relative quantities in laryngeal carcinogenesis. In normal and regenerative laryngeal epithelia, telomerase catalytic protein is present in occasional basal/parabasal nuclei, becomes undetectable with maturation or differentiation of epithelial cells, and reflects the regenerative capacity of squamous epithelium. Nevertheless, several telomerase catalytic protein signals in the majority of nuclei in precancerous lesions, intraepithelial carcinomas and squamous cell carcinomas, are consistent with telomerase catalytic subunit gene re-expression, an early event in laryngeal carcinogenesis.

Telomere loss, senescence, and genetic instability in CD4+ T lymphocytes overexpressing hTERT

Little is known about the long-term consequences of overexpression of the human telomerase reverse transcriptase (hTERT) gene in T lymphocytes. To address this issue, we transduced polyclonal as well as clonally derived populations of naive and memory CD44 T cells from 2 healthy donors (aged 24 and 34 years) with retroviral vectors encoding green fluorescence protein (GFP) and hTERT (GFP-hTERT) or GFP alone. After transduction, cells were sorted on the basis of GFP expression and cultured in vitro until senescence. T cells transduced with hTERT exhibited high stable telomerase activity throughout the culture period. Relative to GFP controls, minor changes in overall gene expression were observed yet the proliferative lifespan of the hTERT-transduced populations was significantly increased and the rate of telomere loss was lower. Nevertheless, hTERT-transduced cells showed progressive telomere loss and had shorter telomeres at senescence than controls (2.3 +/- 0.3 kilobase [kb] versus 3.4 +/- 0.1 kb). Furthermore, a population of cells with 4N DNA consisting of binucleated cells with connected nuclei emerged in the hTERT-transduced cells prior to senescence. We conclude that overexpression of hTERT in CD4+ T cells provides a proliferative advantage independent of the average telomere length but does not prevent eventual genetic instability and replicative senescence.

Human telomerase reverse transcriptase gene expression and the surgical management of suspicious thyroid tumors

PURPOSE

Patients with a preoperative cytologic diagnosis of a suspicious thyroid nodule present a therapeutic dilemma because surgery differs for benign and malignant lesions. To address this issue, several molecular markers, including human telomerase reverse transcriptase (TERT), have been tested as markers of thyroid cancer. Because most studies select cases falling into well-defined categories to test new markers, they may overestimate their discriminatory power when applied to samples that are difficult to classify. Fine-needle aspirates (FNAs) of the thyroid with indeterminate cytology are an example of such cases.

EXPERIMENTAL DESIGN

We examined whether assessing TERT mRNA by reverse transcription-PCR could have improved the surgical management in a cohort of 100 patients undergoing thyroidectomy for indeterminate FNA results.

RESULTS

Ninety percent of 48 cancers were TERT positive, as were 35% of 52 benign lesions. When 10 cases with concomitant lymphocytic thyroiditis were excluded, the overall sensitivity of TERT was 91% (95% confidence interval, 80-98%) and specificity was 79% (64-90%). No clinical or tumor variable contributed to the predictive ability of TERT except for tumor size, which added only marginally. Basing the surgical approach on the TERT assay alone would have reduced lobectomies performed for malignant disease from 11 to 4 cases and reduced total thyroidectomies for benign lesions from to 15 to 9, an overall 50% reduction in suboptimal treatment.

CONCLUSIONS

The overall performance of preoperative differential diagnosis for thyroid tumors with indeterminate FNA results can be substantially improved by the inclusion of molecular markers such as TERT.

Lymphocyte telomere dynamics and telomerase activity in inflammatory bowel disease: effect of drugs and smoking

BACKGROUND

The chromosome instability observed in peripheral blood lymphocytes in ulcerative colitis could be a biomarker of cancer susceptibility.

AIM

To determine whether accelerated telomere shortening could explain chromosome instability and assess the effect of drugs and smoking on telomere dynamics in these cells.

METHODS

Peripheral blood lymphocytes were isolated from ulcerative colitis, Crohn's disease and non-inflammatory bowel disease control patients. Telomere lengths were measured by quantitative real-time polymerase chain reaction. After activation and cell separation, telomerase activity and human telomerase reverse transcriptase messenger ribonucleic acid were measured by telomerase repeat amplification protocol enzyme-linked immunosorbent serological assay and quantitative real-time polymerase chain reaction, respectively.

RESULTS

Age-related telomere loss in peripheral blood lymphocytes was similar in ulcerative colitis, Crohn's disease and control patients. Telomerase activity decreased with age in all groups and correlated positively with telomere length (r = 0.489, P = 0.006). Among Crohn's disease patients, azathioprine was associated with decreased telomerase activity (0.66 vs. 1.54, P = 0.026, P < 0.05) and smoking was associated with decreased human telomerase reverse transcriptase mRNA expression (10.5 vs. 33.3, P = 0.036, P < 0.05).

CONCLUSIONS

Telomere shortening is not accelerated and therefore cannot be the cause of the chromosome instability observed in ulcerative colitis peripheral blood lymphocytes. Azathioprine and cigarette smoking modify telomerase expression in these cells.

Human telomerase catalytic subunit gene re-expression is an early event in oral carcinogenesis

AIMS

Detection of telomerase catalytic subunit (hTERT) mRNA has been used as a surrogate marker for estimation of telomerase activity. The exact role and timing of telomerase re-activation, a key enzyme implicated in cellular immortalization and transformation, in the multistep process of oral carcinogenesis is still unknown. The aim was to test the hypothesis that (i) quantitative rather than qualitative differences exist in the level of hTERT mRNA expression between normal oral mucosa, different grades of oral epithelial abnormalities and squamous cell carcinomas of the oral cavity, and that (ii) hTERT gene re-expression is an important, probably early event in oral carcinogenesis.

METHODS AND RESULTS

The relative quantity of hTERT mRNA was analysed in 45 frozen oral epithelia representing different morphological stages of oral carcinogenesis classified according to the Ljubljana classification and in 37 oral squamous cell carcinomas, using a commercially available LightCycler Telo TAGGG hTERT Quantification kit. hTERT mRNA was not detected in normal or reactive hyperplastic oral epithelia, but was present in 43% of atypical hyperplasias (premalignant lesions), 60% of intraepithelial carcinomas and 68% of oral squamous cell carcinomas. Statistical analysis revealed two groups of oral epithelial changes, with significant differences in the levels of hTERT mRNA expression: 1, normal and reactive hyperplastic oral epithelium, and 2, atypical hyperplasia, intraepithelial carcinomas and squamous cell carcinomas.

CONCLUSION

These data suggest that hTERT gene re-expression represents an early event in the multistep process of oral carcinogenesis, already detectable at the stage of precancerous oral epithelial changes. Nevertheless, other genetic aberrations appear to be necessary for progression of oral epithelial abnormalities towards invasive squamous cell carcinoma.

Telomerase reactivation is an early event in laryngeal carcinogenesis

The exact role and timing of reactivation of telomerase, a key enzyme implicated in cellular immortalization and transformation in the multistep process of laryngeal carcinogenesis, is still unknown. We attempted to (1) determine that quantitative differences exist in the levels of telomerase catalytic subunit (hTERT) mRNA expression among different grades of laryngeal epithelial abnormalities classified according to the Ljubljana classification; (2) determine that telomerase reactivation is an important, most probably early event in laryngeal carcinogenesis; and (3) analyze whether the relative quantity of hTERT mRNA can be used as a molecular biomarker in the early detection of precancerous lesions. The relative quantity of hTERT mRNA, expressed as an hTERT index, was analyzed in 140 frozen laryngeal tissue specimens representing different morphological stages of laryngeal carcinogenesis by using a commercially available LightCycler Telo TAGGG hTERT Quantification kit. The presence and relative quantity of hTERT mRNA in laryngeal epithelium increases progressively with the degree of epithelial abnormalities. hTERT mRNA was detectable in 1/15 normal laryngeal epithelia (7%, mean hTERT index 0.02), 3/15 simple hyperplasias (20%, mean hTERT index 0.09), 10/27 abnormal hyperplasias (37%, mean hTERT index 0.18), 9/12 atypical hyperplasias (75%, mean hTERT index 0.74), 8/9 intraepithelial carcinomas (89%, mean hTERT index 1.82), and 53/62 invasive laryngeal squamous cell carcinomas (85%, mean hTERT index 2.51). Statistical analysis revealed two groups of laryngeal epithelial changes with significant differences in the levels of hTERT mRNA expression (P <.0033): (1) normal and reactive hyperplastic laryngeal epithelium (simple and abnormal hyperplasia) and (2) atypical hyperplasia (precancerous lesion), intraepithelial and invasive laryngeal squamous cell carcinoma. The results of the present study suggest that telomerase reactivation is an early event in laryngeal carcinogenesis, detectable already at the stage of precancerous laryngeal epithelial changes. Nevertheless, other genetic abnormalities appear to be necessary for progression of these epithelial abnormalities toward invasive laryngeal squamous cell carcinoma.

Overexpression of telomerase confers a survival advantage through suppression of TRF1 gene expression while maintaining differentiation characteristics in K562 cells

Leukemic stem cells that expressed endogenous telomerase activity were induced to show overexpression of exogenous hTERT and were analyzed for biological changes in order to assess the possible influence of telomerase gene therapy on the transplantation of normal hematopoietic stem cells. Introduction of hTERT into K562, a telomerase-positive immortal cell line, resulted in a 2.5-fold elevation of telomerase activity and the lengthening of telomeres by 6 kb to 23 kb. Real-time fluorescent PCR, which could perform quantitative analysis of transcripts, revealed a 175-fold increase in hTERT expression, suggesting the posttranscriptional regulation of telomerase. Ectopic expression of hTERT in K562 cells showed a survival advantage during culture in the absence of serum. Expression of mRNA for the telomeric-repeat binding factor 1 (TRF1) and caspase-3 activity were both decreased in hTERT-transfected K562 cells. Transduced cells retained their usual phenotypic characteristics, differentiation ability, and signal transduction response to TPA. These data suggest that ectopic expression of hTERT by normal hematopoietic stem cells may confer a survival advantage without changing their innate biological characteristics.

High vaccination efficiency of low-affinity epitopes in antitumor immunotherapy

Most of the human tumor-associated antigens (TAAs) characterized thus far are derived from nonmutated "self"-proteins. Numerous strategies have been developed to break tolerance to TAAs, combining various forms of antigens with different vectors and adjuvants. However, no study has yet determined how to select epitopes within a given TAA to induce the highest antitumor effector response. We addressed this question by evaluating in HLA-A*0201-transgenic HHD mice the antitumor vaccination efficacy of high- and low-affinity epitopes from the naturally expressed murine telomerase reverse transcriptase (mTERT). Immunity against low-affinity epitopes was induced with heteroclitical variants. We show here that the CTL repertoire against high-affinity epitopes is partially tolerized, while that against low-affinity epitopes is composed of frequent CTLs with high avidity. The high-affinity p797 and p545 mTERT epitopes are not able to protect mice from a lethal challenge with the mTERT-expressing EL4-HHD tumor. In contrast, mice developing CTL responses against the p572 and p988 low-affinity epitopes exhibit potent antitumor immunity and no sign of autoimmune reactivity against TERT-expressing normal tissues. Our results strongly argue for new TAA epitope selection and modification strategies in antitumor immunotherapy applications in humans.

High vaccination efficiency of low-affinity epitopes in antitumor immunotherapy

Most of the human tumor-associated antigens (TAAs) characterized thus far are derived from nonmutated "self"-proteins. Numerous strategies have been developed to break tolerance to TAAs, combining various forms of antigens with different vectors and adjuvants. However, no study has yet determined how to select epitopes within a given TAA to induce the highest antitumor effector response. We addressed this question by evaluating in HLA-A*0201-transgenic HHD mice the antitumor vaccination efficacy of high- and low-affinity epitopes from the naturally expressed murine telomerase reverse transcriptase (mTERT). Immunity against low-affinity epitopes was induced with heteroclitical variants. We show here that the CTL repertoire against high-affinity epitopes is partially tolerized, while that against low-affinity epitopes is composed of frequent CTLs with high avidity. The high-affinity p797 and p545 mTERT epitopes are not able to protect mice from a lethal challenge with the mTERT-expressing EL4-HHD tumor. In contrast, mice developing CTL responses against the p572 and p988 low-affinity epitopes exhibit potent antitumor immunity and no sign of autoimmune reactivity against TERT-expressing normal tissues. Our results strongly argue for new TAA epitope selection and modification strategies in antitumor immunotherapy applications in humans.

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.

Hypermethylation of the hTERT promoter inhibits the expression of telomerase activity in normal oral fibroblasts and senescent normal oral keratinocytes

Telomerase activity in human cells closely correlates with the expression of its catalytic subunit, telomerase reverse transcriptase (hTERT). Previously, we reported the lack of telomerase activity in normal human oral fibroblasts (NHOF) and the diminution of telomerase activity during senescence in normal human oral keratinocytes (NHOK). To investigate the underlying mechanisms of telomerase regulation in both cell types, we analysed the expression, promoter activity, and methylation status of the hTERT gene. The expression of hTERT mRNA diminished in senescent NHOK, but was not detected in NHOF at any stage of replication. An exogenous hTERT promoter was active in NHOF and in senescing NHOK, indicating that the lack of hTERT gene expression resulted from alteration of the endogenous hTERT promoter. Since methylation is involved in the silencing of numerous genes, we carried out DNA methylation assays. The assay revealed that the hTERT promoter was hypermethylated in NHOF and was gradually methylated during senescence in NHOK. Treatment of NHOF and senescent NHOK with the demethylating agent 5-aza-2′-deoxycytidine restored the expression of endogenous hTERT mRNA. Our results suggest that hypermethylation of the hTERT promoter plays a critical role in the negative regulation of telomerase activity in normal human oral cells.

Correlation between expression of human telomerase subunits and telomerase activity in esophageal squamous cell carcinoma

AIM: To investigate telomerase activity and hTERT, TP-1 expression and their relationships in esophageal squamous cell carcinoma (ESCC).

METHODS: Telomerase activity was measured in 60 ESCC tissues using telomeric repeat amplification protocol (TRAP) assay by silver staining. In situ hybridization was used for detecting hTERT and TP-1mRNA.

RESULTS: The telomerase activity was detected in 83.3% of ESCC tissues. The difference of telomerase activity was significant between well and poorly cancer differentiated lesions (P < 0.05). The positive rate of telomerase activity was higher in patients with lymphatic metastasis than in patients without lymphatic metastasis. In cancer tissues hTERT mRNA expression was 75% and TP-1 mRNA expression was 71.7%. The expression of hTERT, TP-1 mRNA in well and poorly differentiated carcinoma was not significant. The expression of hTERT mRNA was correlated with telomerase activity, but TP-1 mRNA expression was not correlated with it.

CONCLUSION: Telomerase activity and hTERT, TP-1 mRNA expression are up-regulated in ESCC. Telomerase activity in ESCC is correlated with lymphatic metastasis and cancer differentiation. Telomerase activity may be used as a prognostic marker in ESCC. hTERT mRNA expression is correlated with telomerase activity. Enhanced hTERT mRNA expression may initially comprehend the telomerase activity level, but it is less sensitive than TRAP assay.

Cellular distribution of telomerase reverse transcriptase in human hepatocellular carcinoma

BACKGROUND AND AIM

Telomerase is the enzyme that synthesizes telomeric DNA, and the activation of telomerase is closely related to cellular immortality. Telomerase activity has been reported in many human cancer tissues and is regulated by the expression of human telomerase reverse transcriptase (hTERT). The aim of the present study was to identify hTERT-expressing cells in human liver tissues and evaluate the feasibility of the hTERT promoter for gene therapy of hepatocellular carcinoma (HCC).

METHODS

The authors examined the cellular distribution of hTERT transcripts in surgically resected HCC by in situ hybridization.

RESULTS

Among 20 samples, hTERT expression was observed in 15 HCC. Transcripts of hTERT were homogenously distributed in the cytoplasm of HCC cells in nine of 15 cases; six of 15 cases displayed a heterogeneous staining pattern. All poorly differentiated HCC that expressed hTERT showed a homogenous pattern of staining. None of the non-cancerous hepatocytes were positive for the transcripts, but infiltrating lymphocytes were faintly stained. The homogenous expression of hTERT was also observed in the vascular invasion of HCC.

CONCLUSIONS

The results indicate that most HCC cells express hTERT RNA and that the promoter is a good candidate as a target for gene therapy. However, careful consideration must be taken concerning the potential effects on lymphocytes.

Telomerase levels control the lifespan of human T lymphocytes

The loss of telomeric DNA with each cell division contributes to the limited replicative lifespan of human T lymphocytes. Although telomerase is transiently expressed in T lymphocytes upon activation, it is insufficient to confer immortality. We have previously shown that immortalization of human CD8+ T lymphocytes can be achieved by ectopic expression of the human telomerase reverse transcriptase (hTERT) gene, which encodes for the catalytic component of the telomerase complex. To study the role of endogenous hTERT in the lifespan of human T cells, we blocked endogenous hTERT expression by ectopic expression of dominant-negative (DN) hTERT. Cells expressing DN-hTERT had a decreased lifespan and showed cytogenetic abnormalities, including chromosome ends without detectable telomeric DNA as well as chromosome fusions. These results indicate that while endogenous hTERT cannot prevent overall telomere shortening, it has a major influence on the longevity of human T cells. Furthermore, we show that up-regulation of hTERT in T cells upon activation decreases over time in culture. Long-term-cultured T cells also show a decreased expression of c-myc upon activation, resulting in less c-myc-induced transcription of hTERT. Moreover, memory T cells, which have expanded in vivo upon antigen encounter, expressed a lower level of hTERT upon activation than naive cells from the same donor. The observed inverse correlation between telomerase levels and replicative history suggests that telomerase levels in T cells are limiting and increasingly insufficient to sustain their proliferation.

Immunosenescence, autoimmunity, and rheumatoid arthritis

Current disease models of autoimmune syndromes, such as rheumatoid arthritis, propose that chronic inflammation is caused by 'forbidden T-cell clones' that recognize disease-inducing antigens and drive tissue-injurious immune reactions. Reappraisal of disease incidence data, however, emphasizes that rheumatoid arthritis is a syndrome of the elderly that occurs with highest likelihood in individuals in whom the processes of T-cell generation and T-cell repertoire formation are compromised. Thymic T-cell production declines rapidly with advancing age. Multiple mechanisms, including antigen-driven clonal expansion and homeostasis-driven autoproliferation of post-thymic T cells, impose replicative stress on T cells and induce the biological program of cellular senescence. T-cell immunosenescence is associated with profound changes in T-cell functional profile and leads to accumulation of CD4+ T cells that have lost CD28 but have gained killer immunoglobulin-like receptors and cytolytic capability and produce large amounts of interferon-gamma. In patients with rheumatoid arthritis, T-cell immunosenescence occurs prematurely, probably due to a deficiency in the ability to generate sufficient numbers of novel T cells. We propose that autoimmunity in rheumatoid arthritis is a consequence of immunodegeneration that is associated with age-inappropriate remodeling of the T-cell pool.

Detection of human telomerase reverse transcriptase mRNA in urine of patients with bladder cancer: evaluation of an emerging tumor marker

OBJECTIVES

To assess the value of the telomerase enzyme as a bladder cancer detection marker, we investigated the expression of the catalytic subunit of the complex (human telomerase reverse transcriptase [hTERT]) in the urine of patients with malignant or benign urinary lesions, as well as of healthy individuals, and compared the results with urine cytology.

METHODS

Spontaneously voided samples were obtained from two groups of subjects: group 1, 146 previously untreated patients with a histologic diagnosis of transitional cell carcinoma or other urothelial neoplasm; and group 2, 128 control individuals, either healthy or with a nonmalignant bladder disease. Total RNA extracts from sedimented urothelial cells were analyzed by a reverse transcriptase-polymerase chain reaction assay for the presence of a 146-bp hTERT transcript. Urine samples were also examined by standard cytology.

RESULTS

Expression of hTERT was detected in 134 (92%) of 146 patients with bladder cancer, and only 64 (44%) yielded a positive result by cytology (P <0.001). The sensitivity advantage of the former technique became particularly evident in the detection of low-grade transitional cell carcinoma (93% versus 28%, P <0.001). Accordingly, the negative predictive value of the molecular assay was markedly greater than the one calculated for cytologic screening (91% versus 60%). On the other hand, both methods were at least 96% specific, with their positive predictive indexes exceeding 94%.

CONCLUSIONS

Our findings suggest that the assessment of hTERT expression in urine sediments represents a reliable tool for the detection of primary urothelial neoplasms, equally specific, yet far more sensitive, than conventional cytology.