Telomerase Activity in Hodgkin's Disease

Telomere dynamics in adult hematological malignancies

Telomeres are repetitive DNA sequences protecting physical ends of linear chromosomes against degradation and end-to-end chromosomal fusion. Telomeres shorten with each cell division, which regulates the cellular lifespan in somatic cells and limits their renewal capacity. Cancer cells are often able to overcome this physiological barrier and become immortal with unlimited replicative capacity. In this review, we present current knowledge on the role of telomeres in human aging with a focus on their behavior in hematological malignancies of adults. Associations of telomere length to age-related diseases and to the prevention of telomere shortening are also discussed.

The Transition between Telomerase and ALT Mechanisms in Hodgkin Lymphoma and Its Predictive Value in Clinical Outcomes

Background: We analyzed telomere maintenance mechanisms (TMMs) in lymph node samples from HL patients treated with standard therapy. The TMMs correlated with clinical outcomes of patients. Materials and Methods: Lymph node biopsies obtained from 38 HL patients and 24 patients with lymphadenitis were included in this study. Seven HL cell lines were used as in vitro models. Telomerase activity (TA) was assessed by TRAP assay and verified through hTERT immunofluorescence expression; alternative telomere lengthening (ALT) was also assessed, along with EBV status. Results: Both TA and ALT mechanisms were present in HL lymph nodes. Our findings were reproduced in HL cell lines. The highest levels of TA were expressed in CD30-/CD15- cells. Small cells were identified with ALT and TA. Hodgkin and Reed Sternberg cells contained high levels of PML bodies, but had very low hTERT expression. There was a significant correlation between overall survival (p < 10-3), event-free survival (p < 10-4), and freedom from progression (p < 10-3) and the presence of an ALT profile in lymph nodes of EBV+ patients. Conclusion: The presence of both types of TMMs in HL lymph nodes and in HL cell lines has not previously been reported. TMMs correlate with the treatment outcome of EBV+ HL patients.

Chromosomal Instability in Hodgkin Lymphoma: An In-Depth Review and Perspectives

The study of Hodgkin lymphoma (HL), with its unique microenvironment and long-term follow-up, has provided exceptional insights into several areas of tumor biology. Findings in HL have not only improved our understanding of human carcinogenesis, but have also pioneered its translation into the clinics. HL is a successful paradigm of modern treatment strategies. Nonetheless, approximately 15–20% of patients with advanced stage HL still die following relapse or progressive disease and a similar proportion of patients are over-treated, leading to treatment-related late sequelae, including solid tumors and organ dysfunction. The malignant cells in HL are characterized by a highly altered genomic landscape with a wide spectrum of genomic alterations, including somatic mutations, copy number alterations, complex chromosomal rearrangements, and aneuploidy. Here, we review the chromosomal instability mechanisms in HL, starting with the cellular origin of neoplastic cells and the mechanisms supporting HL pathogenesis, focusing particularly on the role of the microenvironment, including the influence of viruses and macrophages on the induction of chromosomal instability in HL. We discuss the emerging possibilities to exploit these aberrations as prognostic biomarkers and guides for personalized patient management.

The Use of 3D Telomere FISH for the Characterization of the Nuclear Architecture in EBV-Positive Hodgkin's Lymphoma

The 3D nuclear architecture is closely related to cellular functions and chromosomes are organized in distinct territories. Quantitative 3D telomere FISH analysis (3D Q-FISH) and 3D super-resolution imaging (3D-SIM) at a resolution up to 80 nm as well as the recently developed combined quantitative 3D TRF2-telomere immune FISH technique (3D TRF2/Telo-Q-FISH) have substantially contributed to elucidate molecular pathogenic mechanisms of hematological diseases. Here we report the methods we applied to uncover major molecular steps involved in the pathogenesis of EBV-associated Hodgkin's lymphoma. These methods allowed us to identify the EBV-encoded oncoprotein LMP1 as a key element in the formation of Hodgkin (H-cell) and multinucleated Reed-Sternberg cells (RS-cell), the diagnostic tumor cell of classical Hodgkin's lymphoma (cHL). LMP1 mediates multinuclearity through downregulation of shelterin proteins, in particular telomere repeat binding factor 2 (TRF2).

Omacetaxine mepesuccinate induces apoptosis and cell cycle arrest, promotes cell differentiation, and reduces telomerase activity in diffuse large B‑cell lymphoma cells

Clinical studies have demonstrated that omacetaxine mepesuccinate exerts beneficial effects on acute myelogenous leukemia. It has been suggested that omacetaxine mepesuccinate, used alone or with interferon-α or cytarabine, induces remission in patients with chronic myelogenous leukemia. These effects are possibly mediated by its ability to induce apoptosis of leukemia cells and inhibit the activity of telomerase. To determine whether omacetaxine mepesuccinate is beneficial in diffuse large B-cell lymphoma (DLBCL), two DLBCL cell lines [a germinal center B cell-like subtype (GCB) and an activated B cell-like subtype (ABC)] were treated with omacetaxine mepesuccinate at various concentrations for different durations. The present study indicated that omacetaxine mepesuccinate exerts proapoptotic effects in the two cell types in a dose- and time-dependent manner. The ABC subtype demonstrated increased sensitivity compared with the GCB subtype. At 40 ng/ml, omacetaxine mepesuccinate exhibited a marked proapoptotic effect on DLBCL cells compared with the other tumor cells investigated. Furthermore, omacetaxine mepesuccinate induced cell cycle arrest at G₀/G₁ phase, and promoted cell terminal differentiation of pro-B cells. The present study also demonstrated that omacetaxine mepesuccinate exerted its antitumor effect by reducing telomerase activity. In conclusion, the present study demonstrated that omacetaxine mepesuccinate may induce apoptosis and cell cycle arrest, promote cell differentiation, and reduce telomerase activity in DLBCL cells, thus aiding the development of omacetaxine mepesuccinate-based DLBCL therapeutic strategies.

Is chronic asthma associated with shorter leukocyte telomere length at midlife?

RATIONALE

Asthma is prospectively associated with age-related chronic diseases and mortality, suggesting the hypothesis that asthma may relate to a general, multisystem phenotype of accelerated aging.

OBJECTIVES

To test whether chronic asthma is associated with a proposed biomarker of accelerated aging, leukocyte telomere length.

METHODS

Asthma was ascertained prospectively in the Dunedin Multidisciplinary Health and Development Study cohort (n = 1,037) at nine in-person assessments spanning ages 9-38 years. Leukocyte telomere length was measured at ages 26 and 38 years. Asthma was classified as life-course-persistent, childhood-onset not meeting criteria for persistence, and adolescent/adult-onset. We tested associations between asthma and leukocyte telomere length using regression models. We tested for confounding of asthma-leukocyte telomere length associations using covariate adjustment. We tested serum C-reactive protein and white blood cell counts as potential mediators of asthma-leukocyte telomere length associations.

MEASUREMENTS AND MAIN RESULTS

Study members with life-course-persistent asthma had shorter leukocyte telomere length as compared with sex- and age-matched peers with no reported asthma. In contrast, leukocyte telomere length in study members with childhood-onset and adolescent/adult-onset asthma was not different from leukocyte telomere length in peers with no reported asthma. Adjustment for life histories of obesity and smoking did not change results. Study members with life-course-persistent asthma had elevated blood eosinophil counts. Blood eosinophil count mediated 29% of the life-course-persistent asthma-leukocyte telomere length association.

CONCLUSIONS

Life-course-persistent asthma is related to a proposed biomarker of accelerated aging, possibly via systemic eosinophilic inflammation. Life histories of asthma can inform studies of aging.

Aspirin inhibits human telomerase activation in unstable carotid plaques

The activation of telomerase in unstable plaques is an important factor in atherosclerosis, and may be predictive of the risk of cerebrovascular diseases. Human telomerase reverse transcriptase (hTERT) is a subunit of telomerase that is essential for telomerase activation. The aim of the present study was to investigate whether aspirin inhibits the activation of telomerase and hTERT in unstable carotid plaques. Polymorphonuclear neutrophils (PMNs) derived from carotid plaques were isolated from the washing medium of angioplasty balloons, while circulating PMNs, isolated from arterial blood, served as the controls. A polymerase chain reaction-based telomeric repeat amplification protocol (TRAP) enzyme-linked immunosorbent assay (ELISA) was used to measure the telomerase activity in the cells following treatment with aspirin. The mRNA and protein expression of hTERT were detected by a reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis, respectively. The results revealed that the atherosclerotic plaques were positive for telomerase activity, and that aspirin inhibited the telomerase activity of the PMNs derived from the plaques. In addition, aspirin was demonstrated to inhibit the mRNA and protein expression of hTERT through the suppression of hTERT transcriptional activity; however, it had no inhibitory effect on the telomerase activity of the circulating PMNs. Thus, the activation of telomerase in resident PMNs is critical in the instability of carotid plaques. The upregulation of telomerase and hTERT during the progression of atherosclerosis may indicate a role for telomerase in the vascular remodeling that occurs during atherogenesis. Aspirin was demonstrated to inhibit the activation of telomerase via an hTERT-dependent manner in the PMN cells of unstable carotid plaques, and thus hTERT may be considered as a target in the treatment of cerebrovascular diseases.

Three-dimensional Telomere Signatures of Hodgkin- and Reed-Sternberg Cells at Diagnosis Identify Patients with Poor Response to Conventional Chemotherapy

In classic Hodgkin lymphoma (HL) the malignant mononuclear Hodgkin (H) and multinuclear Reed-Sternberg (RS) cells are characterized by a distinct three-dimensional nuclear telomere organization with shortening of the telomere length and the formation of telomeric aggregates. We asked if the severity of these telomere changes correlates with the clinical behavior of the disease. We retrospectively evaluated three-dimensional telomere organization by quantitative fluorescent in situ hybridization (Q-FISH) of diagnostic biopsies from 16 patients who were good responders and compared them with 16 diagnostic biopsies of 10 patients with refractory or relapsing HL (eight initial biopsies, four confirming progressions, and four confirming relapses). The H cells from patients with refractory/relapsing disease contained a significantly higher percentage of very small telomeres (P = .027) and telomere aggregates (P = .032) compared with H cells of patients entering rapid remission. These differences were even more significant (P = .002 and P = .013, respectively) when comparing the eight initial diagnostic biopsies of refractory/relapsing HL with diagnostic biopsies of eight patients with ongoing long-lasting remission (mean of 47 months). This specific three-dimensional telomere Q-FISH signature identifies these highly aggressive mononuclear H cells at the first diagnostic biopsy and thus may offer a new molecular marker to optimize initial treatment.

Telomere dysfunction and its role in haematological cancer

Observations in human tumours, as well as mouse models, have indicated that telomere dysfunction may be a key event driving genomic instability and disease progression in many solid tumour types. In this scenario, telomere shortening ultimately results in telomere dysfunction, fusion and genomic instability, creating the large-scale rearrangements that are characteristic of these tumours. It is now becoming apparent that this paradigm may also apply to haematological malignancies; indeed these conditions have provided some of the most convincing evidence of telomere dysfunction in any malignancy. Telomere length has been shown in several malignancies to provide clinically useful prognostic information, implicating telomere dysfunction in disease progression. In these malignancies extreme telomere shortening, telomere dysfunction and fusion have all been documented and correlate with the emergence of increased genomic complexity. Telomeres may therefore represent both a clinically useful prognostic tool and a potential target for therapeutic intervention.

Telomerase detection in the diagnosis and prognosis of cancer

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

3D structural and functional characterization of the transition from Hodgkin to Reed-Sternberg cells

Recent research using an innovative 3D quantitative FISH approach of nuclear remodelling associated with the transition from mononuclear Hodgkin to diagnostic multinuclear Reed-Sternberg cells revealed profound changes in the 3D nuclear organization of telomeres. Analogous 3D telomere dynamics were identified in Hodgkin's lymphoma derived cell-lines and diagnostic patient biopsies. These changes were observed in both, EBV positive and EBV-negative Hodgkin's lymphoma and independent of the age of the patients at presentation. Compared to mononuclear Hodgkin cells, multinuclear Reed-Sternberg cells are characterized by a highly significant increase of telomere aggregates, often composed of very short telomeres, telomere shortening and loss. RS-cells with telomere free "ghost" nuclei are regularly observed. The telomere protecting shelterin complex appears to be disrupted and deregulation of DNA-repair mechanisms is observed. Our findings are consistent with the hypothesis that distinct 3D telomere changes and shelterin disruption represent a common pathogenetic denominator in the generation of Reed-Sternberg cells.

3D Telomere FISH defines LMP1-expressing Reed-Sternberg cells as end-stage cells with telomere-poor 'ghost' nuclei and very short telomeres

In Epstein-Barr virus (EBV) negative Hodgkin's cell lines and classical EBV-negative Hodgkin's lymphoma (HL), Reed-Sternberg cells (RS cells) represent end-stage tumor cells, in which further nuclear division becomes impossible because of sustained telomere loss, shortening and aggregation. However, the three-dimensional (3D) telomere organization in latent membrane protein 1 (LMP1)-expressing RS cells of EBV-associated HL is not known. We performed a 3D telomere analysis after quantitative fluorescent in situ hybridization on 5 mum tissue sections on two LMP1-expressing HL cases and showed highly significant telomere shortening (P<0.0001) and formation of telomere aggregates in RS cells (P<0.0001), when compared with the mononuclear precursor Hodgkin cells (H cells). Telomere-poor or telomere-free 'ghost' nuclei were a regular finding in these RS cells. These nuclei and their telomere content strongly contrasted with the corona of surrounding lymphocytes showing numerous midsized telomere hybridization signals. Both H cells and RS cells of two EBV-negative HL cases analyzed in parallel showed 3D telomere patterns identical to those of LMP1-expressing cases. As a major advance, our 3D nuclear imaging approach allows the visualization of hitherto unknown profound changes in the 3D nuclear telomere organization associated with the transition from LMP1-positive H cells to LMP1-positive RS cells. We conclude that RS cells irrespective of LMP1 expression are end-stage tumor cells in which the extent of their inability to divide further is proportional to the increase of very short telomeres, telomere loss, aggregate formation and the generation of 'ghost' nuclei.

The 3D nuclear organization of telomeres marks the transition from Hodgkin to Reed-Sternberg cells

To get an insight into the transition from mononuclear Hodgkin cells (H cells) to diagnostic multinuclear Reed-Sternberg cells (RS cells), we performed an analysis of the three-dimensional (3D) structure of the telomeres in the nuclei of the Hodgkin cell lines HDLM-2, L-428, L-1236 and lymph node biopsies of patients with Hodgkin's disease. Cellular localization of key proteins of the telomere-localized shelterin complex, the mitotic spindle and double-stranded DNA breaks was also analyzed. RS cells show significantly shorter and significantly fewer telomeres in relation to the total nuclear volume when compared with H cells; in particular, telomere-poor 'ghost' nuclei are often adjacent to one or two nuclei displaying huge telomeric aggregates. Shelterin proteins are mainly cytoplasmic in both H and RS cells, whereas double-stranded DNA breaks accumulate in the nuclei of RS cells. In RS cells, multipolar spindles prevent proper chromosome segregation. In conclusion, a process of nuclear disorganization seems to initiate in H cells and further progresses when the cells turn into RS cells and become end-stage tumor cells, unable to divide further because of telomere loss, shortening and aggregate formation, extensive DNA damage and aberrant mitotic spindles that may no longer sustain chromosome segregation. Our findings allow a mechanistic 3D understanding of the transition of H to RS cells.

hTERT gene copy number is not associated with hTERT RNA expression or telomerase activity in colorectal cancer

In a majority of malignant human tumors telomerase activity can be detected, suggesting an immortal phenotype. Expression of the reverse transcriptase subunit, hTERT, in the human telomerase complex is required for telomerase activity. The regulation of hTERT, from gene level to a fully functional protein, is still a poorly understood process. Increased copy number of the hTERT gene has been demonstrated in a significant portion of established cell lines and tumors of different origin but its relevance for telomerase activity levels is unclear. In the present study, we examined the hTERT gene copy number using fluorescence in situ hybridization (FISH) in samples from 64 colorectal carcinomas and an increased copy number (> or = 3 hTERT gene copies/nucleus) was observed in 31 cases (48%). No statistical association existed between hTERT gene copy number and hTERT RNA expression or telomerase activity. However, a significant relationship was found between an increase in hTERT gene copy number and p53 protein accumulation (p = 0.002) and aneuploidy (p = 0.036). Only 4 tumors showed microsatellite instability, 3 of which had a normal hTERT gene copy number. The data indicated that the increased copy number of the hTERT gene in colorectal carcinoma was a result of genomic instability with no obvious consequence for telomerase activity levels.

Measles virus: evidence of an association with Hodgkin's disease

The quest for an infectious agent that may account for cases of Hodgkin's disease (HD) especially in young adults has proven vain until lately. We have recently reported findings that suggested the presence of measles virus (MV) antigens and MV RNA in the tissues of patients with HD. Support for an association between MV and HD has been provided by recent epidemiological findings relating the occurrence of HD to exposure to measles in pregnancy and the perinatal period. We now present further evidence of this putative association based on immunohistochemical, reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridisation studies (ISH) on HD tissues. Biopsies from 82 (54.3%) of our cohort of 154 patients showed a positive immunostain with at least two of the anti-measles antibodies used. Latent membrane protein-1 immunostaining for Epstein-Barr virus was positive in 46 (31.1%) of the patients examined. Reverse transcriptase-PCR and ISH for measles RNA were positive in seven and 10 of 28 patients, respectively. Preliminary clinicopathological associations between MV and HD are noted in this study, but no causal relationship can be claimed at this stage.

Immortalization of bovine capillary endothelial cells by hTERT alone involves inactivation of endogenous p16INK4A/pRb

Recent studies show that stable expression of the human telomerase catalytic subunit, hTERT, alone can lead several types of normal human somatic cells to bypass replicative senescence and become immortal. The molecular mechanisms by which telomerase immortalizes cells are not fully understood, although a key function of telomerase is to maintain a critical length of telomeres in order to preserve the stability and integrity of the genome. Here we report that stable transfection of hTERT alone was sufficient to allow bovine capillary endothelial (BCE) cells to bypass senescence and acquire immortality. Surprisingly, telomere lengths in these stable transfectants were progressively shortened during an increasing number of population doublings (PDLs), despite high telomerase activity. The expression of the cyclin-dependent kinase inhibitors (CDKIs) p16INK4A and p21CIP1/WAF1 was concomitantly repressed, and the retinoblastoma protein (pRb) was maintained in a hyperphosphorylated state in the telomerase-expressing cells. Re-expression of p16INK4A in these cells by either treatment with a demethylating agent or by adenovirus-mediated expression reinduced a senescence-like phenotype, suggesting that the inactivation of p16INK4A was due to DNA methylation and was crucial for the immortalization process. In agreement with this finding, the expression levels of the prototypic DNA methyltransferase DNMT1 were elevated in the hTERT-positive cells.

Telomere dynamics in childhood leukemia and solid tumors: a follow-up study

Telomeres of hematopoietic cells shorten with age, possibly contributing to the aging-associated hematopoietic pathology (immunosenescence, malignant transformation). Accelerated telomere shortening is seen with replicative stress, such as during administration of serial chemotherapy cycles for the treatment of childhood cancer. To define the long-term consequences of pediatric cancer treatment on hematopoietic cell telomere length, we undertook a prospective 4-year follow-up study of a 61-patient cohort of pediatric malignancies in a community-based setting. We found that mononuclear cells (MNC) and granulocytes of children with standard-risk acute lymphoblastic leukemia (ALL) suffered minimal telomere shortening throughout therapy (less than 1 kbp; average follow-up, 20 months), while those of children with solid tumors showed greater and more heterogenous telomere attrition (0.5-2.8 kbp, average follow-up, 9 months). In addition, we evaluated the role of telomerase, the enzyme commonly up-regulated in pediatric leukemic and solid tumor cells for telomere length maintenance, as a disease marker. Serial determinations of telomerase in MNC were useful to confirm disease remission in leukemia, but play no role in the follow-up of children with solid tumors.

Telomerase in cancer and aging

The telomere-telomerase hypothesis is the science of cellular aging (senescence) and cancer. The ends of chromosomes, telomeres, count the number of divisions a cell can undergo before entering permanent growth arrest. As divisions are being counted, events occur on the cellular and molecular level, which may either delay or hasten this arrest. As humans age, a particular concern is the accumulation of events that lead to the progression of cancer. Telomerase is a mechanism that most normal cells do not possess, but almost all cancer cells acquire, to overcome their mortality and extend their lifespan. This review aims to provide a comprehensive understanding of the role of telomerase in cancer development, progression, diagnosis, and in the future, treatment. The ultimate goal of telomerase research is to use our understanding to develop anti-telomerase therapies, an almost universal tumor target.

Telomerase regulation and telomere dynamics in germinal centers

Telomere length maintenance, usually executed by telomerase, is a prerequisite for an extended or infinite division potential. Nevertheless most telomerase positive normal cells exhibit telomere shortening. This study details the telomerase expression and telomere dynamics in purified tonsil B cell subsets during the germinal center (GC) reaction. Significant telomere lengthening was observed as naive B cells matured to centroblasts and when centroblasts matured further to centrocytes, resulting in an increase in telomere length of about 4 kbp determined by Southern blotting. Immunopurified cell populations were also studied by fluorescence in situ hybridization and flow cytometry (flow-FISH) confirming that the GC B cells exhibited lengthened telomeres. These data were further verified in unpurified tonsil cells by combining flow-FISH and immunophenotyping using selected surface markers. Centroblasts expressed high levels of telomerase activity, which was increased in centrocytes, whereas resting naive, activated naive and memory B cells were telomerase activity negative. Expression levels of the catalytic subunit (hTERT) RNA paralleled the telomerase activity levels. The unique telomere elongation in GC B cells permits extensive proliferation during the GC reaction and provides the memory cells with a substantial increase in division potential. Understanding the telomere biology of GC cells is important in defining requirements for telomere elongation in vivo, with implications for the normal immune system as well as for lymphomas, and could provide insights into how the division potential of cells can be manipulated in vitro.

Possible immortalization of Hodgkin and Reed-Sternberg cells: telomerase expression, lengthening of telomere, and inhibition of apoptosis by NF-kappaB expression

Telomerase, an enzyme associated with cellular immortality, is expressed on malignant tumor cells. Deregulation of telomerase is thought to facilitate tumorigenesis and cellular immortality by providing cancer cells with unlimited proliferation capacity. Hodgkin and Reed-Sternberg (H&RS) cells are generally considered as neoplastic cells in Hodgkin's disease (HD), however, such cells are only found in a minority of HD lesions. In addition, H&RS cells with mitotic features are rare and mummified forms are occasionally encountered. There are no available data on the relationship between telomerase activity and apoptosis in HD. We studied 14 cases with Hodgkin's disease (mixed cellularity type, nine cases; nodular sclerosis type, five cases) to clarify the relationship between telomerase activity and apoptosis using in situ hybridization of human telomerase reverse transcriptase (hTERT), reverse transcriptase-polymerase chain reaction (RT-PCR) of hTERT, using extracted RNA and immunohistochemistry of nuclear factor-?B (NF-?B), and TdT-mediated dUTP-digoxigenin nick end-labeling (TUNEL) technique for apoptosis. We also analyzed the telomere length, using sorted H&RS cells. TUNEL showed a few apoptotic H&RS cells, but the cells frequently expressed hTERT, as confirmed by ISH and RT-PCR. Lengthening of the telomere of H&RS cells was noted in ten cases. In addition, H&RS cells frequently expressed NF-?B, which is known as an inducible transcription factor and inhibitor of apoptosis. Our findings of telomerase activity in H&RS cells indicate that these cells are neoplastic and are potentially immortal. In addition, NF-?B expression on H&RS cells suggests its possibility in inhibition of apoptosis of these cells.

Telomerase, immortality and cancer

Replication of eukaryotic linear chromosomes is incomplete and leaves terminal gaps. The evolutionary widely distributed solution to this "end replication" is twofold: chromosome ends are capped with telomeres, bearing multiple copies of redundant telomeric sequences, and the telomerase enzyme can add (lost) telomeric repeats. Telomerase in humans, as in all mammals, is ubiquitous in all embryonic tissues. In adults, telomerase remains active in germs cells, and, although down-regulated in most somatic tissues, telomerase is active in regenerative tissues and notably, in tumor cells. Telomerase activity is linked to cellular proliferation, and its activation seems to be a mandatory step in carcinogenesis. In contrast to mammals, indeterminately growing multicellular organisms, like fish and crustaceae, maintain unlimited growth potential or 'immortality' in all somatic tissues throughout their entire life. Also this cell immortalization is brought about by maintaining telomerase expression. Disease prognosis for human tumors includes evaluation of cell proliferation, based on the detection of proliferation markers with monoclonal antibodies. The significance of the classical marker Ki-67, and of a novel marker repp-86 are compared with semiquantitative telomerase assays. For tumor therapy, telomerase inhibitors are attractive tools. Results with telomerase knock-out mice have revealed promise, but also risk of this approach. On the other side, telomerase stimulation is attractive for expanding the potential of cellular proliferation in vitro, with possible applications for transplantation of in vitro expanded human cells, for immortalizing primary human cells as improved tissue models, and for the isolation of otherwise intractable products, like genuine human monoclonal antibodies.

Real-Time Quantitative Telomeric Repeat Amplification Protocol Assay for the Detection of Telomerase Activity2

Background: Telomerase is a ribonucleoprotein enzyme associated with immortalization and transformation of human cells. The telomeric repeat amplification protocol (TRAP) is widely used for the detection of telomerase activity. The TRAP method, although highly sensitive and specific because it includes PCR amplification, is laborious and does not provide precise quantitative information.

Methods: We developed a real-time quantitative TRAP (RTQ-TRAP) system by combining a real-time PCR technique with the conventional TRAP method. Telomerase activity in human tumor cell lines and in 13 lymphoma samples was measured using the RTQ-TRAP assay, and the results obtained from the samples using the RTQ-TRAP method were compared with the conventional TRAP method.

Results: The RTQ-TRAP method was both accurate and reproducible in measuring telomerase activity in a dilution series of protein extracts from HL60 cells. Telomerase activity in 13 lymphoma samples, as determined by the RTQ-TRAP method, was ninefold lower than that measured by the conventional TRAP method. The half-life of telomerase activity in human tumor cells, as determined using RTQ-TRAP, was much shorter than the half-life reported previously.

Conclusions: Our results suggest that the conventional TRAP assay frequently overestimates telomerase activity in tumor samples. The RTQ-TRAP method is thus a useful tool to rapidly and precisely quantify telomerase activity.

Chondrosarcoma is not characterized by detectable telomerase activity

Reactivation of telomerase, an enzyme which elongates human telomeres, is associated with cell immortilization. In approximately 90% of malignant tumours telomerase activity can be demonstrated, whereas in benign tumours it is mostly absent. Chondrosarcomas are relatively rare malignant cartilaginous neoplasms. A small number of chondrosarcomas located centrally in bone arise secondarily to an enchondroma, while the majority of chondrosarcomas developing from the surface arise within the cartilage cap of an osteochondroma. The histological distinction between a benign lesion and low-grade chondrosarcoma is generally considered difficult. To investigate whether the progression towards chondrosarcoma is characterized by reactivation of telomerase activity, this study determined telomerase activity in ten enchondromas, five osteochondromas, and 37 chondrosarcomas using the TRAP assay. In all tumour samples except one, telomerase activity was absent. By adding tumour lysates to the positive control, an increasing inhibition of telomerase activity was found with an increasing chondroid matrix, suggesting that it may contain inhibitory factors. Inhibition due to endogenous RNAse or Taq-polymerase inhibitors was excluded. The lack of detectable telomerase activity in the high-grade component of a dedifferentiated chondrosarcoma without matrix favours the possibility that telomerase is truly absent. Either its true absence or inhibitory effects disabling telomerase detection exclude the telomerase TRAP assay as a diagnostic tool in the differential diagnosis of benign and low-grade malignant cartilaginous tumours.

Telomerase activity is increased and telomere length shortened in T cells from blood of patients with atopic dermatitis and psoriasis

We studied telomerase activity and telomere length in PBMC and purified CD4(+) and CD8(+) T cells from blood obtained from a total of 32 patients with atopic dermatitis, 16 patients with psoriasis, and 30 normal controls. The telomerase activity was significantly increased in PBMC from the patients compared with PBMC from normal donors. This increase was most pronounced in the subpopulation of CD4(+) T cells, which were significantly above the activity of the CD8(+) T cells in atopic dermatitis, psoriasis patients, and control persons. The telomere length was significantly reduced in all T cell subsets from both atopic dermatitis and psoriasis patients compared with normal individuals. Furthermore, the telomere length was found to be significantly shorter in CD4(+) memory T cells compared with the CD4(+) naive T cells, and both of the cell subsets from diseases were shown to be of significantly shorter telomere length than the same cell subsets from normal controls. No significant difference was observed between CD8(+)CD28(-) and CD8(+)CD28(+) T cell populations in both diseases. However, the telomere length of CD8(+)CD28(+) T cells from both diseases was significantly shorter than CD8(+)CD28(+) T cell subsets from normal donors. In conclusion, the increased telomerase activity and shortened telomere length indicates that T lymphocytes in atopic dermatitis and psoriasis are chronically stimulated and have an increased cellular turnover in vivo.

Telomerase activity in chronic lymphoproliferative disorders of B-cell lineage

The progressive shortening of telomeres at each cell division is a key mechanism in controlling cell proliferative capacity. The activation of telomerase, a reverse transcriptase that extends telomere length, potentially leads to unlimited cell proliferation, and is believed to play a critical role in the neoplastic process. High levels of telomerase activity have been demonstrated in almost all solid tumours; however, little data is available concerning its expression in chronic B-cell neoplasms. By using a quantitative polymerase chain reaction-based method we quantified telomerase activity in normal B lymphocytes, and in various B-cell malignancies, including chronic lymphocytic leukaemia (CLL), mantle cell lymphoma (MCL) and hairy cell leukaemia (HCL). Compared to normal B cells, which expressed very low levels of telomerase activity, malignant cells from most of the patients showed a significant increase in telomerase activity, with highest values observed in HCL samples. Moreover, among the CLL and HCL cases, significantly higher levels of telomerase activity were found in patients with progressive disease at 1 year follow-up versus patients with stable disease. These data suggest that telomerase activity might correlate with disease progression.

Hodgkin and Reed-Sternberg cells of classical Hodgkin's disease overexpress the telomerase RNA template (hTR)

There is accumulating evidence to suggest that Hodgkin and Reed-Sternberg (HRS) cells represent the malignant cell population in Hodgkin's disease (HD). A recent report that HD tissue is in most instances devoid of telomerase activity was therefore unexpected. Since telomerase activity was determined in whole tissue extracts and HRS cells comprise only a small minority of the cells in the affected tissue, the telomerase activity of the HRS cells might have escaped detection. To test this possibility and to clarify whether HRS cells contain the enzyme telomerase, 13 cases of classical HD were analysed by three different methods. The presence of telomerase was studied at the single cell level by a sensitive radioactive in situ hybridization method employing a probe specific for the telomerase RNA template (hTR). In addition, tissue extracts were studied for telomerase activity by a modified TRAP assay and for hTR by reverse transcription-polymerase chain reaction (RT-PCR). The extractive methods revealed telomerase activity in eight and hTR in all of the 13 HD cases studied. In situ hybridization located large amounts of hTR in the HRS cells of all 13 HD cases and low to medium amounts in some of the non-malignant lymphoid bystander cells. These results indicate that HRS cells constitutively overexpress telomerase and thus use this enzyme for stabilizing their telomeres. This substantiates the malignant nature of HRS cells. Furthermore, the results confirm that normal lymphoid cells can express telomerase. In consequence, methods of measuring telomerase in tissue extracts are not suitable for determining the presence of this molecule in lymphoma cells, since the vast majority of lymphoid neoplasms contain significant amounts of non-neoplastic lymphoid cells.