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Telomerase
Kinds of Telomerase Terms modified by Telomerase Selected AbstractsTelomerase inhibition by stable RNA interference impairs tumor growth and angiogenesis in glioblastoma xenograftsINTERNATIONAL JOURNAL OF CANCER, Issue 9 2006Roberto Pallini Abstract Telomerase is highly expressed in advanced stages of most cancers where it allows the clonal expansion of transformed cells by counteracting telomere erosion. Telomerase may also contribute to tumor progression through still undefined cell growth-promoting functions. Here, we inhibited telomerase activity in 2 human glioblastoma (GBM) cell lines, TB10 and U87MG, by targeting the catalytic subunit, hTERT, via stable RNA interference (RNAi). Although the reduction in telomerase activity had no effect on GBM cell growth in vitro, the development of tumors in subcutaneously and intracranially grafted nude mice was significantly inhibited by antitelomerase RNAi. The in vivo effect was observed within a relatively small number of population doublings, suggesting that telomerase inhibition may hinder cancer cell growth in vivo prior to a substantial shortening of telomere length. Tumor xenografts that arose from telomerase-inhibited GBM cells also showed a less-malignant phenotype due both to the absence of massive necrosis and to reduced angiogenesis. © 2005 Wiley-Liss, Inc. [source] The telomere length dynamic and methods of its assessmentJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 4 2005Kah-Wai Lin Abstract Human telomeres are composed of long repeating sequences of TTAGGG, associated with a variety of telomere-binding proteins. Its function as an end-protector of chromosomes prevents the chromosome from end-to-end fusion, recombination and degradation. Telomerase acts as reverse transcriptase in the elongation of telomeres, which prevent the loss of telomeres due to the end replication problems. However, telomerase activity is detected at low level in somatic cells and high level in embryonic stem cells and tumor cells. It confers immortality to embryonic stem cells and tumor cells. In most tumor cells, telomeres are extremely short and stable. Telomere length is an important indicator of the telomerase activity in tumor cells and it may be used in the prognosis of malignancy. Thus, the assessment of telomeres length is of great experimental and clinical significance. This review describes the role of telomere and telomerase in cancer pathogenesis and the dynamics of the telomeres length in different cell types. The various methods of measurement of telomeres length, i.e. southern blot, hybridization protection assay, fluorescence in situ hybridization, primed in situ, quantitative PCR and single telomere length analysis are discussed. The principle and comparative evaluation of these methods are reviewed. The detection of G-strand overhang by telomeric-oligonucleotide ligation assay, primer extension/nick translation assay and electron microscopy are briefly discussed. [source] A mutant telomerase defective in nuclear-cytoplasmic shuttling fails to immortalize cells and is associated with mitochondrial dysfunctionAGING CELL, Issue 2 2010Olga A. Kovalenko Summary Telomerase is a reverse transcriptase specialized in telomere synthesis. The enzyme is primarily nuclear where it elongates telomeres, but many reports show that the catalytic component of telomerase (in humans called hTERT) also localizes outside of the nucleus, including in mitochondria. Shuttling of hTERT between nucleus and cytoplasm and vice versa has been reported, and different proteins shown to regulate such translocation. Exactly why telomerase moves between subcellular compartments is still unclear. In this study we report that mutations that disrupt the nuclear export signal (NES) of hTERT render it nuclear but unable to immortalize cells despite retention of catalytic activity in vitro. Overexpression of the mutant protein in primary fibroblasts is associated with telomere-based cellular senescence, multinucleated cells and the activation of the DNA damage response genes ATM, Chk2 and p53. Mitochondria function is also impaired in the cells. We find that cells expressing the mutant hTERT produce high levels of mitochondrial reactive oxygen species and have damage in telomeric and extratelomeric DNA. Dysfunctional mitochondria are also observed in an ALT (alternative lengthening of telomeres) cell line that is insensitive to growth arrest induced by the mutant hTERT showing that mitochondrial impairment is not a consequence of the growth arrest. Our data indicate that mutations involving the NES of hTERT are associated with defects in telomere maintenance, mitochondrial function and cellular growth, and suggest targeting this region of hTERT as a potential new strategy for cancer treatment. [source] Telomerase reverse transcriptase haploinsufficiency and telomere length in individuals with 5p, syndromeAGING CELL, Issue 5 2007Hong-Yan Du Summary Telomerase, which maintains the ends of chromosomes, consists of two core components, the telomerase reverse transcriptase (TERT) and the telomerase RNA (TERC). Haploinsufficiency for TERC or TERT leads to progressive telomere shortening and autosomal dominant dyskeratosis congenita (DC). The clinical manifestations of autosomal dominant DC are thought to occur when telomeres become critically short, but the rate of telomere shortening in this condition is unknown. Here, we investigated the consequences of de novo TERT gene deletions in a large cohort of individuals with 5p, syndrome. The study group included 41 individuals in which the chromosome deletion resulted in loss of one copy of the TERT gene at 5p15.33. Telomere length in peripheral blood cells from these individuals, although within the normal range, was on average shorter than in normal controls. The shortening was more significant in older individuals suggesting an accelerated age-dependent shortening. In contrast, individuals with autosomal dominant DC due to an inherited TERC gene deletion had very short telomeres, and the telomeres were equally short regardless of the age. Although some individuals with 5p, syndrome showed clinical features that were reminiscent of autosomal dominant DC, these features did not correlate with telomere length, suggesting that these were not caused by critically short telomeres. We conclude that a TERT gene deletion leads to slightly shorter telomeres within one generation. However, our results suggest that several generations of TERT haploinsufficiency are needed to produce the very short telomeres seen in patients with DC. [source] PAX5 activates the transcription of the human telomerase reverse transcriptase gene in B cells,THE JOURNAL OF PATHOLOGY, Issue 1 2010Stéphanie Bougel Abstract Telomerase is an RNA-dependent DNA polymerase that synthesizes telomeric DNA. Its activity is not detectable in most somatic cells but it is reactivated during tumorigenesis. In most cancers, the combination of hTERT hypermethylation and hypomethylation of a short promoter region is permissive for low-level hTERT transcription. Activated and malignant lymphocytes express high telomerase activity, through a mechanism that seems methylation-independent. The aim of this study was to determine which mechanism is involved in the enhanced expression of hTERT in lymphoid cells. Our data confirm that in B cells, some T cell lymphomas and non-neoplastic lymph nodes, the hTERT promoter is unmethylated. Binding sites for the B cell-specific transcription factor PAX5 were identified downstream of the ATG translational start site through EMSA and ChIP experiments. ChIP assays indicated that the transcriptional activation of hTERT by PAX5 does not involve repression of CTCF binding. In a B cell lymphoma cell line, siRNA-induced knockdown of PAX5 expression repressed hTERT transcription. Moreover, ectopic expression of PAX5 in a telomerase-negative normal fibroblast cell line was found to be sufficient to activate hTERT expression. These data show that activation of hTERT in telomerase-positive B cells is due to a methylation-independent mechanism in which PAX5 plays an important role. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [source] DNA-Enden: Nur ein Anfang (Nobel-Aufsatz),ANGEWANDTE CHEMIE, Issue 41 2010Prof. Jack W. Szostak Geheimnis gelüftet: Der Medizin-Nobelpreis 2009 wurde für die Lösung eines der großen Rätsel der Biologie vergeben: Wie werden bei der Zellteilung die Chromosomen vervielfältigt und gegen Abbau geschützt? Die Antwort liegt in den Chromosomenenden , den Telomeren , und im Enzym, das diese bildet , der Telomerase. Die Preisträger schildern hier aus erster Hand den Fortgang der Ereignisse. [source] Telomere und Telomerase: Das Ende ist entscheidend (Nobel-Aufsatz),ANGEWANDTE CHEMIE, Issue 41 2010Prof. Elizabeth H. Blackburn Geheimnis gelüftet: Der Medizin-Nobelpreis 2009 wurde für die Lösung eines der großen Rätsel der Biologie vergeben: Wie werden bei der Zellteilung die Chromosomen vervielfältigt und gegen Abbau geschützt? Die Antwort liegt in den Chromosomenenden , den Telomeren , und im Enzym, das diese bildet , der Telomerase. Die Preisträger schildern hier aus erster Hand den Fortgang der Ereignisse. [source] Die Entdeckung der Telomerase: vom Vergnügen, Teile des Puzzles zusammenzufügen (Nobel-Aufsatz),ANGEWANDTE CHEMIE, Issue 41 2010Prof. Carol W. Greider Geheimnis gelüftet: Der Medizin-Nobelpreis 2009 wurde für die Lösung eines der großen Rätsel der Biologie vergeben: Wie werden bei der Zellteilung die Chromosomen vervielfältigt und gegen Abbau geschützt? Die Antwort liegt in den Chromosomenenden , den Telomeren , und im Enzym, das diese bildet , der Telomerase. Die Preisträger schildern hier aus erster Hand den Fortgang der Ereignisse. [source] Telomerase: not just for the elongation of telomeres,BIOESSAYS, Issue 2 2006Rodrigo T. Calado Telomerase RNA component (TERC) and telomerase reverse transcriptase (TERT) function together to elongate telomeres and to protect chromosomal ends. Recent studies have discovered that overexpression of telomerase's TERT subunit promoted epidermal stem-cell mobilization, hair growth and stem-cell proliferation without changes in length of telomeres.1,2 This telomerase functional characteristic is TERC independent and is operated through a mechanism other than telomere elongation. These findings open new doors for future explorations to understand telomerase function and its interaction with other cell components in the regulation of cell senescence and tumorigenesis. BioEssays 28: 109,112, 2006. © 2006 Wiley periodicals, Inc. [source] Androgen ablation therapy for prostate carcinoma suppresses the immunoreactive telomerase subunit hTERTCANCER, Issue 2 2004Kenneth A. Iczkowski M.D. Abstract BACKGROUND Telomerase is a ribonucleoprotein complex that protects the ends of chromosomes from degradation. Its catalytic subunit, hTERT, controls its activity. Prior data in prostate carcinoma cases indicated that immunohistochemical hTERT reactivity increases with tumor grade and may be absent in lower grade cases. The effect of complete androgen ablation (CAA) on tumor hTERT expression was uncertain. METHODS hTERT immunostaining was performed on the cancerous pretreatment biopsy tissue of 30 men who consecutively underwent CAA with bicalutamide and goserelin acetate for 30 days prior to undergoing radical prostatectomy, and on their tumor tissue from radical prostatectomy. As controls, biopsy and prostatectomy samples from 30 untreated men were studied. Nuclear staining was evaluated by two observers, and the change in staining between biopsy and prostatectomy samples was evaluated using the Student t test in both groups. RESULTS The percent of reactive tumor nuclei in treated men declined from 36.7% to 13.2% (P = 0.0001), and declined from 19.8% to 16.1% in untreated men (P = 0.4). The greater mean hTERT reactivity in the treated men's biopsy specimens was attributed to an increased proportion of higher (Gleason score , 7) grade tumors. The decline in hTERT immunostaining remained significant after normalizing it to that of the untreated group (P = 0.002). The original Gleason scores, corresponding declines in the percentage of reactive tumor nuclei, and significance were: Gleason score , 6: 11% (P = 0.03); Gleason score of 7: 23% (P < 0.006); and Gleason score , 8: 46% (P < 0.005) (from a mean 63% to 17%). CONCLUSIONS CAA for prostate carcinoma can be considered an antitelomerase therapy. The steepest reduction in telomerase activity was noted in the highest grade tumors. Cancer 2004;100:294,9. © 2003 American Cancer Society. [source] Overexpression of Human Telomerase RNA in Helicobacter pylori -infected Human Gastric MucosaCANCER SCIENCE, Issue 11 2000Kwon Hur Telomerase, an enzyme associated with cellular immortality and malignancy, plays an important role in cellular immortalization and tumorigenesis. Furthermore, overexpression of the RNA component of the telomerase, called human telomerase RNA (hTR), has been demonstrated in various human cancers as an early event. The pattern of hTR expression following Helicobacter pylori (H. pylori) infection in human gastric mucosa was investigated by a radioactive in situ hybridization (ISH) assay. Paraffin-embedded sections of 50 biopsy specimens taken from the gastric antrum of individual patients infected to different extents with H. pylori, as well as normal gastric mucosa, were studied. In normal gastric mucosa, only weak hTR expression was noted and the expression was limited to basal cells of the gastric glands. However, the degree of hTR expression gradually increased in parallel with the degree of H. pylori infection. The mean scores of gastric mucosa with mild, moderate and severe degrees of H. pylori infection were 2.3, 2.8, and 3.7 times higher than that of normal gastric mucosa, respectively. The results of this study suggested that up-regulation of hTR expression is a frequent and early event associated with H. pylori infection in the gastric mucosa and may play some role in gastric carcinogenesis. Sufficient synthesis of hTR during this early stage may be a prerequisite for telomerase reactivation to occur in gastric cancer. [source] Telomerase: A Dimeric Ménage à TroisCHEMBIOCHEM, Issue 13 2007Jean-Louis Mergny Dr. Core components of an attractive drug target. Cohen et al. have recently demonstrated that the complex of human active telomerase, an almost universal marker for cancer, involves two copies of each of three components (hTR, hTERT and dyskerin). [source] 3134: Identification of potential human corneal endothelial stem-like cell nichesACTA OPHTHALMOLOGICA, Issue 2010G THURET Purpose to study the localization of potential stem-(like) cells in human adult corneal endothelium Methods Fresh (6-12h post mortem) and organ cultured (OC) corneas were studied after flat mount. The whole endothelium and posterior limbus (PL) was observed after triple staining with Trypan blue, Alizarin red and Hoechst 33342, in order to determine cells shape, localization and viability. The level of endothelial cell (EC) differenciation was determined after immunostaining (fluorescence) for ZO-1, Na+/K+ ATPase and COX IV; the cell proliferation status was assessed using Ki67; four markers for stem cells were used: Oct-4, BCRP, Nestin and Telomerase; ability for cell migration was evaluated from Myosin IIA expression Results In several corneas, the nuclei of peripheral EC were centripetally aligned suggesting continuous slow central migration. Numerous small cells with a reduced expression of differenciation markers were accumulated near peripheral Hassall Henle bodies. In these potential niches, cells were distributed in 3-5 layers. A high expression of Myosin II was found in peripheral cells. Ki67+ cells were found in PL and peripheral EC only after OC. None of the 4 stem cell markers was found in EC, and their expression in PL was poorly reliable because of high background noise. Numerous trypan blue positive cells were located at the PL and in the extreme periphery of endothelium Conclusion several strong arguments suggest the location of corneal endothelial stem-like cell niches in endothelial periphery or in the PL, and the capacity of EC to migrate from these niches toward the centre. Trypan blue staining pattern suggests that they could rapidly die in ex vivo corneas, and be therefore hard to indentify [source] Human telomeric G-quadruplex: The current status of telomeric G-quadruplexes as therapeutic targets in human cancerFEBS JOURNAL, Issue 5 2010Stephen Neidle The 3,-ends of human chromosomal DNA terminate in short single-stranded guanine-rich tandem-repeat sequences. In cancer cells, these are associated with the telomere-maintenance enzyme telomerase together with the end-binding protein hPOT1. Small molecules that can compete with these proteins and induce the single-stranded DNA to form quadruplex,ligand complexes are, in effect, able to expose these 3,-ends, which results in the activation of a DNA damage response and selective inhibition of cell growth. Several of these G-quadruplex binding molecules have shown promising anticancer activity in tumour xenograft models, which indicate that the approach may be applicable to the treatment of a wide range of human cancers. This minireview summarizes the available data on these compounds and the challenges posed for drug discovery. [source] Structure of a human telomeric DNA sequence stabilized by 8-bromoguanosine substitutions, as determined by NMR in a K+ solutionFEBS JOURNAL, Issue 14 2007Akimasa Matsugami The structure of human telomeric DNA is controversial; it depends upon the sequence contexts and the methodologies used to determine it. The solution structure in the presence of K+ is particularly interesting, but the structure is yet to be elucidated, due to possible conformational heterogeneity. Here, a unique strategy is applied to stabilize one such structure in a K+ solution by substituting guanosines with 8-bromoguanosines at proper positions. The resulting spectra are cleaner and led to determination of the structure at a high atomic resolution. This demonstrates that the application of 8-bromoguanosine is a powerful tool to overcome the difficulty of nucleic acid structure determination arising from conformational heterogeneity. The obtained structure is a mixed-parallel/antiparallel quadruplex. The structure of telomeric DNA was recently reported in another study, in which stabilization was brought about by mutation and resultant additional interactions [Luu KN, Phan AT, Kuryavyi V, Lacroix L & Patel DJ (2006) Structure of the human telomere in K+ solution: an intramolecular (3+1) G-quadruplex scaffold. J Am Chem Soc 128, 9963,9970]. The structure of the guanine tracts was similar between the two. However, a difference was seen for loops connecting guanine tracts, which may play a role in the higher order arrangement of telomeres. Our structure can be utilized to design a small molecule which stabilizes the quadruplex. This type of molecule is supposed to inhibit a telomerase and thus is expected to be a candidate anticancer drug. [source] Order of genetic events is critical determinant of aberrations in chromosome count and structureGENES, CHROMOSOMES AND CANCER, Issue 4 2004Christine Fauth A sequential acquisition of genetic events is critical in tumorigenesis. A key step is the attainment of infinite proliferative potential. Acquisition of this immortalization requires the activation of telomerase in addition to other activities, including inactivation of TP53 and the retinoblastoma family of tumor-suppressor proteins. However, the importance of the order in which these genetic events occur has not been established. To address this question, we used a panel of normal mammary fibroblasts and endothelial cultures that were immortalized after transduction with the catalytic subunit of telomerase (hTERT) and a temperature-sensitive mutant of the SV40 large-tumor (tsLT) oncoprotein in different orders in early- and late-passage stocks. These lines were maintained in continuous culture for up to 90 passages, equivalent to >300 population doublings (PDs) post-explantation during 3 years of continuous propagation. We karyotyped the cultures at different passages. Cultures that received hTERT first followed by tsLT maintained a near-diploid karyotype for more than 150 PDs. However, in late-passage stocks (>200 PDs), metaphase cells were mostly aneuploid. In contrast, the reverse order of gene transduction resulted in a marked early aneuploidy and chromosomal instability, already visible after 50 PDs. These results suggest that the order of genetic mutations is a critical determinant of chromosome count and structural aberration events. © 2004 Wiley-Liss, Inc. [source] Amplification of the telomerase reverse transcriptase (hTERT) gene in cervical carcinomasGENES, CHROMOSOMES AND CANCER, Issue 3 2002Anju Zhang The expression of telomerase reverse transcriptase (hTERT), the catalytic component of the telomerase complex, is required for activation of telomerase during immortalization and transformation of human cells. However, the biochemical and genetic mechanisms governing hTERT expression remain to be elucidated. In the present study, we examined hTERT amplification as a potential genetic event contributing to telomerase activation in cervical carcinomas. An amplification of the hTERT gene was found in 1/4 cervical cancer cell lines and 21/88 primary tumor samples derived from the patients with cervical carcinomas. An increase in the hTERT copy number was significantly correlated with higher levels of hTERT protein expression. Moreover, the hTERT alterations with the enhanced hTERT expression were exclusively observed in those tumors with high-risk human papillomavirus infection. Taken together, the hTERT gene amplification, directly or indirectly targeted by human papillomavirus, may be one of the driving forces responsible for upregulation of hTERT expression and activation of telomerase in cervical cancers. © 2002 Wiley-Liss, Inc. [source] Clinical implications of telomerase detectionHISTOPATHOLOGY, Issue 6 2001P Matthews Clinical implications of telomerase detection In 1994 a sensitive method for the detection of telomerase was described. This assay, which was based on the polymerase chain reaction, suggested that telomerase activity was associated with immortal and cancer cells. Since then more than a thousand studies have documented the expression and activity of the enzyme in diseased tissues, primarily tumours. This review gives an overview of the biological significance of telomerase expression and methods for detecting its activity. This is followed by an organ system-based discussion of expression in normal tissues and disease states. We finish with speculation as to the future role of telomerase detection in diagnostic histopathology. [source] Prolonged exposure of naïve CD8+ T cells to interleukin-7 or interleukin-15 stimulates proliferation without differentiation or loss of telomere lengthIMMUNOLOGY, Issue 2 2006Diana L. Wallace Summary Interleukin (IL)-7 and IL-15 are cytokines implicated in homeostatic control of the peripheral CD8 T-cell pool. We compared the effects of IL-7 and IL-15 on survival and proliferation of purified human CD8+ T-cell subsets. Low concentrations of either cytokine reduced the spontaneous apoptosis of all subsets, and enhancement of survival corresponded to the extent of Bcl-2 up-regulation. Surprisingly, although minimal proliferation of naïve CD8+ T cells was observed during the first week of culture with cytokines, a marked expansion of these cells occurred at later time points, particularly in response to IL-15. This occurred largely without phenotypic change or acquisition of effector function, indicating a dissociation of differentiation from proliferation. Notably, progression of naïve CD8+ T cells through several cell divisions resulted in up-regulation of telomerase and the maintenance of telomere length. These data show that IL-7 and IL-15 induce cell proliferation and rescue from apoptosis in a concentration, time and subset-dependent manner, and have implications for the homeostatic expansion of the naïve CD8+ T-cell pool. [source] Inhibition of telomerase in the endothelial cells disrupts tumor angiogenesis in glioblastoma xenograftsINTERNATIONAL JOURNAL OF CANCER, Issue 6 2008Maria Laura Falchetti Abstract Tumor angiogenesis is a complex process that involves a series of interactions between tumor cells and endothelial cells (ECs). In vitro, glioblastoma multiforme (GBM) cells are known to induce an increase in proliferation, migration and tube formation by the ECs. We have previously shown that in human GBM specimens the proliferating ECs of the tumor vasculature express the catalytic component of telomerase, hTERT, and that telomerase can be upregulated in human ECs by exposing these cells to GBM in vitro. Here, we developed a controlled in vivo assay of tumor angiogenesis in which primary human umbilical vascular endothelial cells (HUVECs) were subcutaneously grafted with or without human GBM cells in immunocompromised mice as Matrigel implants. We found that primary HUVECs did not survive in Matrigel implants, and that telomerase upregulation had little effect on HUVEC survival. In the presence of GBM cells, however, the grafted HUVECs not only survived in Matrigel implants but developed tubule structures that integrated with murine microvessels. Telomerase upregulation in HUVECs enhanced such effect. More importantly, inhibition of telomerase in HUVECs completely abolished tubule formation and greatly reduced survival of these cells in the tumor xenografts. Our data demonstrate that telomerase upregulation by the ECs is a key requisite for GBM tumor angiogenesis. © 2007 Wiley-Liss, Inc. [source] Loss of RAB25 expression in breast cancerINTERNATIONAL JOURNAL OF CANCER, Issue 12 2006Ji-Ming Cheng Abstract A novel breast cancer cell line (RAO-3) was established by transduction of the Q61L mutant RAS into human mammary epithelial cells that were immortalized with catalytic subunit of telomerase (hTERT). The cells displayed anchorage-independent growth and proliferation, and formed human mammary spindle cell carcinoma when injected into nude mice. Chromosome locus 1q22-23 was partially duplicated and inverted on one of the 3 chromosomes present in the cell line. We report here that mutations of chromosome 1q22-23 locus have resulted in the loss of RAB25 expression in the breast cancer cell line. Transduction of RAB25 into the breast cancer cell line arrests anchorage-independent growth. We have also demonstrated loss of RAB25 in human breast tumor tissue. These data suggest that loss of RAB25 might contribute to tumorigenesis of breast cancer, and RAB25 is likely to be an important factor in the development of breast cancer. RAB25 could be used as biological marker of breast cancer and provides a target for gene replacement therapy. © 2006 Wiley-Liss, Inc. [source] Telomerase activity and telomere length in acute leukemia: correlations with disease progression, subtypes and overall survivalINTERNATIONAL JOURNAL OF LABORATORY HEMATOLOGY, Issue 2 2010Y. WANG Summary The progressive shortening of telomeres and the activation of telomerase are considered to be one of the important mechanisms in cellular immortalization and disease progression. Bone marrow samples were collected from 148 patients with acute leukemia (AL). Based on the stage of the disease, patients were divided into the newly diagnosed group, the relapsed group and the complete remission (CR) group. telomerase activity (TA) was examined by PCR-ELISA, and telomere length (TL) was examined by Southern blot analyses. TA and TL were analyzed in relation to AL stage and subtype. Five-year survival was analyzed using Kaplan,Meier survival curve. TA in AL patients was higher than healthy individuals. TA level was the highest in the relapsed group, followed by the newly diagnosed group, and then the CR group. TA had no difference between acute nonlymphocytic leukemia (ANLL) group and acute lymphocytic leukemia (ALL) group. But TA in group of subtype M3 was lower than other subtypes of ANLL. TL in AL group was shorter than the control group. TL was the shortest in the relapsed group, followed by the newly diagnosed group, and finally the CR group. TL exhibited an inverse correlation with TA. The group of patients with high TA had a significantly poorer five-year-survival than that of low TA group. TA is elevated and TL is shortened in AL patients. There is a significant inverse correlation between TL and TA. Patients in late-stage disease had shorter TL and higher TA than those in early stages. The shortened TL and elevated TA correlated with disease progression and relapse, and they may serve as prognostic factors for AL patients with poor outcome. M3 subtype is special with relative lower TA and long-lasting survival than other subtypes. [source] Telomere Higher-Order Structure and Genomic InstabilityIUBMB LIFE, Issue 8 2003Terace Fletcher Abstract Telomeres, nucleoprotein complexes at the end of eukaryotic chromosomes, have vital roles in chromosome integrity. Telomere chromatin structure is both intricate and dynamic allowing for a variety of responses to several stimuli. A critical determinant in telomere structure is the G-strand overhang. Facilitated by telomeric proteins, the G-strand overhang stabilizes telomere higher-order assemblies most likely by adopting unusual DNA structures. These structures influence activities that occur at the chromosome end. Dysfunctional telomeres induce signals resulting in cell growth arrest or death. To overcome telomere dysfunction, cancer cells activate the DNA polymerase, telomerase. The presence of telomerase at the telomere may establish a particular telomeric state. If the chromosome ends of cancer and normal cells exist in different states, cancer-specific telomere structures would offer a unique chemotherapeutic target. IUBMB Life, 55: 443-449, 2003 [source] The telomere length dynamic and methods of its assessmentJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 4 2005Kah-Wai Lin Abstract Human telomeres are composed of long repeating sequences of TTAGGG, associated with a variety of telomere-binding proteins. Its function as an end-protector of chromosomes prevents the chromosome from end-to-end fusion, recombination and degradation. Telomerase acts as reverse transcriptase in the elongation of telomeres, which prevent the loss of telomeres due to the end replication problems. However, telomerase activity is detected at low level in somatic cells and high level in embryonic stem cells and tumor cells. It confers immortality to embryonic stem cells and tumor cells. In most tumor cells, telomeres are extremely short and stable. Telomere length is an important indicator of the telomerase activity in tumor cells and it may be used in the prognosis of malignancy. Thus, the assessment of telomeres length is of great experimental and clinical significance. This review describes the role of telomere and telomerase in cancer pathogenesis and the dynamics of the telomeres length in different cell types. The various methods of measurement of telomeres length, i.e. southern blot, hybridization protection assay, fluorescence in situ hybridization, primed in situ, quantitative PCR and single telomere length analysis are discussed. The principle and comparative evaluation of these methods are reviewed. The detection of G-strand overhang by telomeric-oligonucleotide ligation assay, primer extension/nick translation assay and electron microscopy are briefly discussed. [source] p16INK4a -mediated suppression of telomerase in normal and malignant human breast cellsAGING CELL, Issue 5 2010Alexey V. Bazarov Summary The cyclin-dependent kinase inhibitor p16INK4a (CDKN2A) is an important tumor suppressor gene frequently inactivated in human tumors. p16 suppresses the development of cancer by triggering an irreversible arrest of cell proliferation termed cellular senescence. Here, we describe another anti-oncogenic function of p16 in addition to its ability to halt cell cycle progression. We show that transient expression of p16 stably represses the hTERT gene, encoding the catalytic subunit of telomerase, in both normal and malignant breast epithelial cells. Short-term p16 expression increases the amount of histone H3 trimethylated on lysine 27 (H3K27) bound to the hTERT promoter, resulting in transcriptional silencing, likely mediated by polycomb complexes. Our results indicate that transient p16 exposure may prevent malignant progression in dividing cells by irreversible repression of genes, such as hTERT, whose activity is necessary for extensive self-renewal. [source] Hot topics in stem cells and self-renewal: 2010AGING CELL, Issue 4 2010Norman E. Sharpless Summary In many tissues, mammalian aging is associated with a decline in the replicative and functional capacity of somatic stem cells and other self-renewing compartments. Understanding the basis of this decline is a major goal of aging research. In particular, therapeutic approaches to ameliorate or reverse the age-associated loss of stem function could be of use in clinical geriatrics. Such approaches include attempts to protect stem cells from age-promoting damage, to ,rejuvenate' stem cells through the use of pharmacologic agents that mitigate aging-induced alterations in signaling, and to replace lost stem cells through regenerative medicine approaches. Some headway has been made in each of these arenas over the last 18 months including advances in the production of donor-specific totipotent stem cells through induced pluripotency (iPS), gains in our understanding of how tumor suppressor signaling is controlled in self-renewing compartments to regulate aging, and further demonstration of extracellular ,milieu' factors that perturb stem cell function with age. This period has also been marked by the recent award of the Nobel Prize in Physiology or Medicine for elucidation of telomeres and telomerase, a topic of critical importance to stem cell aging. [source] Recent advances in vertebrate aging research 2009AGING CELL, Issue 3 2010Steven Austad Summary Among the notable trends seen in this year's highlights in mammalian aging research is an awakening of interest in the assessment of age-related measures of mouse health in addition to the traditional focus on longevity. One finding of note is that overexpression of telomerase extended life and improved several indices of health in mice that had previously been genetically rendered cancer resistant. In another study, resveratrol supplementation led to amelioration of several degenerative conditions without affecting mouse lifespan. A primate dietary restriction (DR) study found that restriction led to major improvements in glucoregulatory status along with provocative but less striking effects on survival. Visceral fat removal in rats improved their survival, although not as dramatically as DR. An unexpected result showing the power of genetic background effects was that DR shortened the lifespan of long-lived mice bearing Prop1df, whereas a previous report in a different background had found DR to extend the lifespan of Prop1df mice. Treatment with the mammalian target of rapamycin (mTOR) inhibitor, rapamycin, enhanced the survival of even elderly mice and improved their vaccine response. Genetic inhibition of a TOR target made female, but not male, mice live longer. This year saw the mTOR network firmly established as a major modulator of mammalian lifespan. [source] A mutant telomerase defective in nuclear-cytoplasmic shuttling fails to immortalize cells and is associated with mitochondrial dysfunctionAGING CELL, Issue 2 2010Olga A. Kovalenko Summary Telomerase is a reverse transcriptase specialized in telomere synthesis. The enzyme is primarily nuclear where it elongates telomeres, but many reports show that the catalytic component of telomerase (in humans called hTERT) also localizes outside of the nucleus, including in mitochondria. Shuttling of hTERT between nucleus and cytoplasm and vice versa has been reported, and different proteins shown to regulate such translocation. Exactly why telomerase moves between subcellular compartments is still unclear. In this study we report that mutations that disrupt the nuclear export signal (NES) of hTERT render it nuclear but unable to immortalize cells despite retention of catalytic activity in vitro. Overexpression of the mutant protein in primary fibroblasts is associated with telomere-based cellular senescence, multinucleated cells and the activation of the DNA damage response genes ATM, Chk2 and p53. Mitochondria function is also impaired in the cells. We find that cells expressing the mutant hTERT produce high levels of mitochondrial reactive oxygen species and have damage in telomeric and extratelomeric DNA. Dysfunctional mitochondria are also observed in an ALT (alternative lengthening of telomeres) cell line that is insensitive to growth arrest induced by the mutant hTERT showing that mitochondrial impairment is not a consequence of the growth arrest. Our data indicate that mutations involving the NES of hTERT are associated with defects in telomere maintenance, mitochondrial function and cellular growth, and suggest targeting this region of hTERT as a potential new strategy for cancer treatment. [source] Developmental differences in the immortalization of lung fibroblasts by telomeraseAGING CELL, Issue 5 2003Nicholas R. Forsyth Summary The role of ambient (21%) and physiological oxygen (2,5%) in the immortalization of fetal vs. adult human lung fibroblasts was examined. Growth in low oxygen and antioxidants extended the lifespan of both fetal and adult strains. As the ectopic expression of telomerase could immortalize adult lung fibroblasts cultured in ambient oxygen, the lifespan-shortening effects of 21% oxygen must have been largely limited to telomeres. By contrast, fetal lung fibroblasts could not be immortalized in ambient oxygen in spite of telomere elongation by telomerase, suggesting more widespread oxidative damage. The long-term culture requirements for the immortalization of WI-38 fetal lung fibroblasts included supplementation with N-(tert) butyl hydroxylamine, dexamethasone, zinc and vitamin B12, in addition to growth in physiological oxygen. The mechanisms regulating telomere shortening remain controversial. The present results suggest that both end-replication and oxidative damage events contribute to telomere shortening in lung fibroblasts in vitro. These observations emphasize the need for better analytical techniques to distinguish whether the correlation of short telomeres with disease and mortality in humans reflects the consequences of increased proliferation, telomere shortening as a result of oxidative damage or some combination of these processes. [source] Hepatitis C virus core protein induces malignant transformation of biliary epithelial cells by activating nuclear factor-,B pathwayJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 7 2010Zhi-Hua Li Abstract Background and Aim:, In an earlier study, we found that hepatitis C virus core protein, HCV-C, participated in the malignant transformation of HCV-C transfected normal human biliary epithelial (hBE) cells by activating telomerase. Here we further investigated the signaling of the malignant transformation. Methods:, Reverse transcription-polymerase chain reaction (RT-PCR), western blotting and immunoprecipitation were used to analyze the expression of HCV-C, human telomerase reverse transcriptase (hTERT), nuclear factor-,B (NF-,B) and NF-,B inhibitor alpha (I,B,) genes and the phosphorylation level of I,B, protein. Electrophoretic mobility shift assays (EMSA) and NF-,B-linked luciferase reporter assays were carried out to measure NF-,B activity. Results:, The expression of HCV-C and hTERT was detected only in HCV-C-transfected hBE (hBE-HCV-C) cells but not in vector-transfected or parental hBE cells. More NF-,B protein accumulated in nuclear extracts of hBE-HCV-C cells rather than in those of control cells, though total NF-,B protein level showed no difference among these cells. DNA binding activity of NF-,B and the NF-,B-linked luciferase activity were much higher in HCV-C-transfected hBE cells than those in vector- or non-transfected hBE cells. In addition, the I,B, phosphorylation level, but not the I,B, mRNA or protein levels, was increased after HCV-C transfection. Conclusions:, Hepatitis C virus core protein activates NF-,B pathway in hBE cells by increasing the phosphorylation of I,B,. The pathway may be responsible for HCV-C-induced malignant transformation of hBE cells. [source] | ||||||||||||||||||||||||||||||||||