Telomere length and telomerase activity in malignant lymphomas at diagnosis and relapse

Telomere length maintenance, in the vast majority of cases executed by telomerase, is a prerequisite for long-term proliferation. Most malignant tumours, including lymphomas, are telomerase-positive and this activity is a potential target for future therapeutic interventions since inhibition of telomerase has been shown to result in telomere shortening and cell death in vitro. One prerequisite for the suitability of anti-telomerase drugs in treating cancer is that tumours exhibit shortened telomeres compared to telomerase-positive stem cells. A scenario is envisioned where the tumour burden is reduced using conventional therapy whereafter remaining tumour cells are treated with telomerase inhibitors. In evaluating the realism of such an approach it is essential to know the effects on telomere status by traditional therapeutic regimens. We have studied the telomere lengths in 47 diagnostic lymphomas and a significant telomere shortening was observed compared to benign lymphoid tissues. In addition, telomere length and telomerase activity were studied in consecutive samples from patients with relapsing non-Hodgkin's lymphomas. Shortened, unchanged and elongated telomere lengths were observed in the relapse samples. The telomere length alterations found in the relapsing lymphomas appeared to be independent of telomerase and rather represented clonal selection random at the telomere length level. These data indicate that anti-telomerase therapy would be suitable in only a fraction of malignant lymphomas.     

Telomere length maintenance in aging and carcinogenesis

Normal somatic cells have a finite number of divisions, a limited capacity to proliferate. Human telomeres, the long DNA TTAGGG repeats at the ends of chromosomes, are considered a molecular clock marker. The gradual and progressive telomere shortening at each replicative cycle is associated, through the activation of pRB and p53 pathways and genomic instability, to the replicative senescence, a non-dividing state and widespread cell death. Activation of telomere maintenance [telomerase; or alternative lengthening of telomeres mechanisms (ALT), or other adaptive responses] can revert this program. Although not completely known, several mechanisms and modulating agents may be able to up and down-regulate telomere length and its maintenance. Chemopreventive therapies for the up-regulation of telomerase activity, able to prolong the life of cell cultures in a phenotypically youthful state, could have important applications in research and medicine. On the contrary the therapeutic down-regulation of telomerase activity may be used in cancer therapy. Telomerase expression per se is not oncogenic, but telomere shortening and maintenance seem to be crucial events in tumor formation. Thus a particular focus has been pointed out relatively to the immortalization of normal or potential pre-cancerous cells. With the extension of life span the probability to get in contact with carcinogens increases, genetic instability, oncogene activation and/or onco-suppressor gene inactivation (i.e. p53, pRB, ras): the cancer transformation can be then induced in predisposed cells, depending on their genetic context, by the activation of telomere maintenance. Pharmacological intervention may be able to modulate the rate of living, by increasing life span of few specific target cells, or decreasing it in proliferating . Because of the unknown state of the enormous cell number of the human organism, is it safe to extend the human life span by therapeutic agents?     

食管上皮癌变过程中端粒长度、hTERT含量的定量研究

目的:研究端粒DNA长度、hTERT蛋白定量表达与食管上皮细胞癌变的关系。方法:对84例食管上皮脱落细胞分别应用流式荧光原位杂交检测端粒DNA长度,细胞免疫荧光流式定量法检测hTERT蛋白含量。结果:①正常食管上皮脱落细胞组、重度增生组和癌组增殖指数(PI)分别为11.51±4.08,19.04±5.39和29.46±5.50,癌组细胞增殖活性显著高于重度增生组(P<0.01),重度增生组高于正常组(P<0.01),PI值与细胞学分级呈正相关(r=0.80,P<0.01)。②正常食管上皮脱落细胞组、重度增生组和癌组的端粒长度Q-FISH值分别为50.83±8.86、36.96±8.02和27.81±6.59,癌组端粒长度明显短于重度增生组(P<0.01),重度增生组短于正常组(P<0.01)。端粒长度与细胞学分级呈负相关(r=-0.73,P<0.01)。③正常组、重度增生组和癌组hTERT蛋白荧光指数(FI)分别为0.95±0.14、1.47±0.22和1.75±0.19,癌组hTERT蛋白含量高于重度增生组(P<0.01),重度增生组高于正常组(P<0.01)。hTERT含量与细胞学分级呈正相关(r=0.81,P<0.01)。重度增生组和癌组hTERT蛋白阳性表达率分别为91.43%(32/35)和96.77%(30/31),二者都明显高于正常组(P<0.01)。结论:端粒DNA长度缩短、hTERT蛋白含量升高与食管上皮癌变密切相关。     

Telomere length abnormalities occur early in the initiation of epithelial carcinogenesis.

PURPOSE: Telomeres help maintain chromosomal integrity. Dysfunctional telomeres can cause genetic instability in vitro and an increased cancer incidence in telomerase knock out mouse models. We recently reported that telomere shortening was a prevalent alteration in human prostate, pancreas, and breast cancer precursor lesions. In the present study, we address whether the previous findings are broadly applicable to human epithelial cancer precursors in general. EXPERIMENTAL DESIGN: Surgical specimens of epithelial cancer precursor lesions from the urinary bladder, esophagus, large intestine, oral cavity, and uterine cervix were examined using a recently developed technique for direct in situ telomere length assessment in formalin-fixed human tissue specimens. RESULTS: Widespread telomere length abnormalities were nearly universal (97.1% of cases) in the preinvasive stages of human epithelial carcinogenesis in all sites examined in this series, with telomere shortening the predominant abnormality (88.6% of cases). CONCLUSIONS: Telomere length abnormalities appear to be one of the earliest and most prevalent genetic alterations acquired in the multistep process of malignant transformation. These findings support a model whereby telomere dysfunction induces chromosomal instability as an initiating event in many, perhaps most, human epithelial cancers. Together with previous findings from the prostate and pancreas, the percentage of intraepithelial neoplasia lesions showing telomere length abnormalities is 95.6%. The implications of these findings include the potential that telomere length assessment in situ may be a widely useful biomarker for monitoring disease prevention strategies and for improved early diagnosis.     

Telomere length and telomerase subunits as diagnostic and prognostic biomarkers in Barrett carcinoma

BACKGROUND: Maintenance of telomeres has been identified as an essential regulator of proliferative capacity and genomic integrity in malignant tumors. The authors evaluated telomere length and telomerase subunits, hTR and hTERT, as prognostic markers in patients with Barrett carcinoma. METHODS: Telomere length was measured by Southern blot analysis and hTR expression and hTERT expression by real-time polymerase chain reaction in both cancer tissue and adjacent noncancerous Barrett mucosa in resection specimens from 46 patients with Barrett carcinoma (International Union Against Cancer [UICC] stages I-III). The median follow-up time of the surviving patients was 79 months. RESULTS: Cancer tissue expressed more hTERT-mRNA than noncancerous mucosa (P < .05). Telomere lengths in cancer tissue and in noncancerous mucosa increased with higher pT category (P = .08 and P = .05, respectively). Twenty-one patients who died of tumor recurrence showed significantly longer telomeres in cancer tissue compared with 25 patients without tumor-related deaths (P < .05). Telomere length in both cancer tissue and in noncancerous mucosa and the telomere-length ratio cancer:noncancerous tissue were correlated with overall survival. In multivariate analysis, the telomere-length ratio proved to be an independent prognostic parameter (P < .02; relative risk of death 3.4; confidence interval, 1.3-8.9). Ten patients with telomere-length ratios >1.17 had a significantly poorer overall survival compared with 36 patients with telomere-length ratios 相似文献   

Telomere length and radiosensitivity in human fibroblast clones immortalized by ectopic telomerase expression

Telomeres, the ends of eukaryotic chromosomes, have a variable length among individuals and cell types. While studies in telomerase-deficient mice and cells showed an inverse correlation between telomere length and radiosensitivity, it is less clear whether this remains true in telomerase-proficient cells. To gain insight into this topic, we studied radiosensitivity in three telomerase immortalized fibroblast clones derived from the same cell line and characterized by different telomere length. In two clones, cen3tel4 and cen3tel5, the mean terminal restriction fragment length was approximately 13 and 10 kb, respectively and in the third clone, cen3pci16, it was approximately 4 kb, which is lower than in senescent fibroblasts. To test radiosensitivity, we determined survival to gamma-rays and the induction of chromosomal aberrations after irradiation. Neither the LD50, the gamma-ray dose that reduces survival to 50%, nor the frequency of aberrations detected in the three cell lines showed an inverse correlation with telomere length. In particular, the cen3pci16 cells, which have very short telomeres, did not show a higher sensitivity to irradiation or a greater frequency of chromosomal abnormalities compared to the other two cell lines. Our results suggest that, in the presence of telomerase activity, short telomeres are stabilized and do not cause an increase in radiosensitivity.     

Telomere length and telomerase activity in non-small cell lung cancer prognosis: clinical usefulness of a specific telomere status

Background

Considering previous data and the need to incorporate new biomarkers for the prognosis of solid tumours into the clinic, our aim in this work consists of evaluating the potential clinical use of telomeres and telomerase in non-small cell lung cancer (NSCLC).

Methods

Telomere status was established by determination of telomere length using the Terminal Restriction Fragment length method, and telomerase activity by the Telomeric Repeat Amplification Protocol in 142 NSCLCs and their corresponding control samples, obtained from patients submitted to surgery. Group-oriented curves for disease-free survival were calculated according to the Kaplan-Meier method considering telomere length, T/N ratio (telomere length in tumour to control tissue) and telomerase activity.

Results

Overall, tumours had significantly shorter telomeres compared with telomeres in control tissues (P = 0.027). More than 80 % of NSCLCs displayed telomerase activity. Regarding prognosis studies, patients whose tumours showed a mean telomere length (MTL) <7.29 Kb or T/N ratio <0.97 showed a significantly poor clinical evolution (P = 0.034 and P = 0.040, respectively). As result of a Cox multivariate analysis including pathologic state and lymph node dissemination, the MTL and T/N ratio emerged as independent significant prognostic factors.

Conclusions

Telomerase activity was identified as a marker of poor prognosis. The novel finding of this study is the independent prognosis role of a specific telomere status in NSCLC patients. According to our results, telomere function may emerge as a useful molecular tool that allow to select groups of NSCLC patients with different clinical evolution, in order to establish personalized therapy protocols.     

胃粘膜脱落细胞端粒酶活性研究

目的　探讨胃镜直视下刷取胃粘膜脱落细胞中端粒酶活性对胃癌的诊断价值。方法　采用TRAP PCR ELISA法对 5 6例胃组织和胃粘膜刷落细胞进行端粒酶活性的分析。结果　胃癌组端粒酶活性水平 (平均A值 0 .745 )明显高于胃炎组 (平均A值 0 .0 6 8)。端粒酶活性水平在胃刷落细胞中与组织的是相近的。端粒酶在胃癌组的阳性率为90 % ,明显高于胃刷落细胞涂片的阳性率 (6 6 .7% )、血CEA的阳性率 (5 6 .7% )。同时还测得 75 %的胃粘膜不典型增生者端粒酶活性水平也显著升高。结论　胃镜直视下刷取胃粘膜脱落细胞中端粒酶活性测定可作为诊断胃癌有效而敏感的方法。     

Telomere lengths and telomerase activity in dog tissues: a potential model system to study human telomere and telomerase biology

Studies on telomere and telomerase biology are fundamental to the understanding of aging and age-related diseases such as cancer. However, human studies have been hindered by differences in telomere biology between humans and the classical murine animal model system. In this paper, we describe basic studies of telomere length and telomerase activity in canine normal and neoplastic tissues and propose the dog as an alternative model system. Briefly, telomere lengths were measured in normal canine peripheral blood mononuclear cells (PBMCs), a range of normal canine tissues, and in a panel of naturally occurring soft tissue tumours by terminal restriction fragment (TRF) analysis. Further, telomerase activity was measured in canine cell lines and multiple canine tissues using a combined polymerase chain reaction/enzyme-linked immunosorbent assay method. TRF analysis in canine PBMCs and tissues demonstrated mean TRF lengths to range between 12 and 23 kbp with heterogeneity in telomere lengths being observed in a range of normal somatic tissues. In soft tissue sarcomas, two subgroups were identified with mean TRFs of 22.2 and 18.2 kbp. Telomerase activity in canine tissue was present in tumour tissue and testis with little or no activity in normal somatic tissues. These results suggest that the dog telomere biology is similar to that in humans and may represent an alternative model system for studying telomere biology and telomerase-targeted anticancer therapies.     

Telomere length and the risk of lung cancer

Telomeres play a key role in the maintenance of chromosome integrity and stability. There is growing evidence that short telomeres induce chromosome instability and thereby promote the development of cancer. We investigated the association of telomere length and the risk of lung cancer. Relative telomere length in peripheral blood lymphocytes was measured by quantitative polymerase chain reaction in 243 lung cancer patients and 243 healthy controls that were frequency-matched for age, sex and smoking status. Telomere length was significantly shorter in lung cancer patients than in controls (mean ± standard deviation: 1.59 ± 0.75 versus 2.16 ± 1.10, P  < 0.0001). When the subjects were categorized into quartiles based on telomere length, the risk of lung cancer was found to increase as telomere length shortened ( P _trend < 0.0001). In addition, when the median of telomere length was used as the cutoff between long and short telomeres, individuals with short telomeres were at a significantly higher risk of lung cancer than those with long telomeres (adjusted odds ratio = 3.15, 95% confidence interval = 2.12–4.67, P  < 0.0001). When the cases were categorized by tumor histology, the effect of short telomere length on the risk of lung cancer was more pronounced in patients with small cell carcinoma than in those with squamous cell carcinoma and adenocarcinoma ( P =  0.001, test for homogeneity). These findings suggest that shortening of the telomeres may be a risk factor for lung cancer, and therefore, the presence of shortened telomeres may be used as a marker for susceptibility to lung cancer. ( Cancer Sci 2008; 99: 1385–1389)     

Telomere length heterogeneity and chromosome instability

Chromosome aberrations are the hallmark of cancer cells. Although a few specific chromosome aberrations are frequently detected in some types of cancer, the majority of karyotypic abnormalities tend to differ between different histological types and between individuals with the same type of cancer. Recent work indicates that telomeres may be directly involved in shaping the karyotypes of tumor cells. In particular, the heterogeneity of telomere lengths within cells may have direct influence on the frequency with which chromosomes engage in telomeric fusions and in subsequent breakage-fusion-bridge cycles. Since telomere length distribution among chromosome arms is a polymorphic trait, difference in distributions between individuals may account, at least in part, for the karyotypic differences found among tumors of the same type. Conversely, if single telomere lengths happen to be inherited, the segregation of particularly short telomeres in families may increase the incidence of specific chromosome aberrations during tumor evolution, and perhaps contribute, along with other factors, to cancer pre-disposition.     

Analysis of telomerase activity and telomere length in bone and soft tissue tumors

Telomerase activation is prevalent in most epithelial tumors, and may be a critical step in cellular immortalization and carcinogenesis. However, telomerase activity in tumors of mesenchymal origin is not well understood. In the present study, we examined telomerase activity in clinical samples from osteosarcoma and soft tissue sarcoma and representative sarcoma cell lines (HOS, OST and Saos2), using the telomeric repeat amplification protocol (TRAP) assay. The cell lines HOS and OST were telomerase-positive, but Saos2 cells lacked telomerase activity and hTERT mRNA expression. Treatment of Saos2 cells with the demethylating agent 5-aza-2'-deoxy-cytidine, alone or together with the histone deacetylase inhibitor tricostatin A, did not induce hTERT mRNA expression. Twenty-six of the 83 sarcoma samples (31.3%) were telomerase-positive [bone sarcoma, 15 of 42 samples (35.7%); soft tissue sarcoma, 11 of 41 samples (26.8%)], whereas neither benign tumors nor normal bone tissue expressed telomerase activity. There was no significant correlation between histological type, tumor staging and telomerase activity. However, patients with telomerase-positive tumors had significantly shorter survival than those with telomerase-negative tumors. There was heterogeneity in telomere length (range, 6-18 kb) among the tumors examined, but there was no significant difference in length between telomerase-positive and -negative tumors. Thus, these mesenchymal tumors comprise heterologous groups, some positive and some negative for telomerase, with long and short telomeres, suggesting multiple carcinogenesis pathways. The present results indicate that telomerase activation is not prevalent in mesenchymal tumors and is not a critical determinant of telomere length, but it may be a prognostic indicator of mesenchymal tumors.     

Dynamics of telomere's length and telomerase activity in Philadelphia chromosome negative myeloproliferative neoplasms

Telomere exhaustion and increased telomerase activity are associated with the acquisition of aggressive molecular events in a variety of haematological malignancies. In Philadelphia chromosome negative myeloproliferative neoplasms (Ph^negMPN's), telomere dynamics during clonal evolution of these diseases have not yet been fully elucidated. Herein we demonstrated that telomere shortening is a global phenomenon in Ph^negMPN's, irrespective of disease phenotype, treatment administration and JAK2V617F mutational status but the presence of additional cytogenetic abnormalities further affects them. Consistent with the above finding, TA was upregulated in CD34+ haemopoietic progenitors from almost all Ph^negMPN subgroups compared to healthy donors. Moreover, TL below the cut-off value of 27% could predict disease progression in Ph^negMPN patients (PFS at 5 years 39% vs 81%). Thus, TL emerges as a new prognostic marker in Ph^negMPN, reflecting probably the genetic instability of highly proliferating MPN clones.     

Experimental chemical carcinogenesis in the stomach and colon

Experimental chemical carcinogenesis in the digestive tract is reviewed, mainly on the basis of information obtained in the laboratories of the National Cancer Center Research Institute. It is generally accepted that cancer is the outcome of DNA damage, resulting in mutation, loss, amplification and recombination of genes. Gastric cancer is no exception. It was shown very early that cancer of the glandular stomach can be produced in rats by administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a widely used mutagen. However, this depends on the genotype. Whereas the ACI rat is susceptible to MNNG, the Buffalo rat is resistant and this is a dominantly inherited trait. Genes responsible for the sensitivity to gastric cancer induction are at present under investigation by linkage analysis of rat genome markers. With regard to cancer in humans, our finding that cooked proteinaceous foods can give rise to a series of heterocyclic amines (HCAs) is of major significance. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), one of the most abundant, causes colon cancers in male rats, whereas in females it induces breast cancers. The colon cancers induced by PhIP feature a deletion of G as represented by 5-GGGA-3-->5-GGA-3 in the Apc gene, resulting in a truncated Apc molecule. Microsatellite mutations have also been found in PhIP-induced colon tumors, as in human hereditary non-polyposis colorectal cancer cases. Similarly to the case of gastric cancer production by MNNG, there is a genetic component and F344 rats are more susceptible to PhIP colon carcinogenesis than the ACI/N strain and the gene responsible is being sought. Since carcinogenesis proceeds with accumulation of genetic alteration, often involving genomic instability, exposure to any kind of carcinogenic substances, either xeno- or autobiotics, needs to be reduced as far as possible, taking account of inconvenience at the individual and socio-economical levels.      

Risk analysis of carcinogenesis in the remnant stomach with measurement of ornithine decarboxylase activity

Gastric ornithine decarboxylase (ODC) activity was measured as a biomarker of tumor-promoting activity in the remnant stomach of rats and humans. Gastrectomy of Wistar rats utilizing the Billroth I method caused a significantly high induction of ODC, and use of the Billroth II method caused a significantly higher induction of ODC than the Billroth I method. In humans, ODC activity of remnant gastric cancer tissue, normal-appearing mucosa of remnant gastric cancer patient, and remnant gastric mucosa without cancer after the Billroth II method were significantly higher than that of normal gastric mucosa without gastrectomy. ODC activity of remnant gastric mucosa without cancer after the Billroth II method was significantly higher than that after the Billroth I method. Risk of carcinogenesis was high in the remnant stomach, especially after the Billroth II method. © 1994 Wiley-Liss, Inc.