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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mouse telomerase holoenzyme, which synthesizes telomeric DNA de novo, is a ribonucleoprotein complex that includes the mouse telomerase RNA component (mTERC), mouse telomerase-associated protein (mTEP1) and mouse telomerase reverse transcriptase (mTERT). To determine the role of telomerase in urethane-induced lung tumorigenesis in A/J mice we examined telomerase activity and the expression of each telomerase subunit in 20 tumor samples, harvested at 16, 28, 40 and 50 weeks after urethane treatment. The telomeric repeat amplification protocol assay showed that statistically significant telomerase activation occurred both early and late in tumorigenesis. Semi-quantitative reverse transcription-polymerase chain reaction analysis revealed that mRNA expression levels of mTEP1 and mTERT were up-regulated during tumor progression, while mTERC expression was not significantly different between tumors and normal lung. We further examined mTEP1 protein expression in normal lung tissue and lung tumors; western blot analysis showed preferential expression of mTEP1 protein in lung tumors compared with normal lung and immunohistochemistry revealed that a majority of the adenoma cells were positively stained in the nucleus, whereas only a few of the adjacent normal alveolar cells were immunoreactive. In addition, we investigated DNAs of the 20 tumor samples by single strand conformation polymorphism and sequencing analyses to examine whether alterations of the p53 gene in exons 5-8 were associated with telomerase activity. Although we found one nonsense, two missense, two silent and one simultaneous double mutation at different codons in six late stage tumors, there was no apparent correlation between telomerase activity and p53 mutations. Collectively, these results suggest that mTEP1 as well as mTERT may be involved in the regulation of telomerase activity and that telomerase activation may contribute to lung tumorigenesis in A/J mice independently of p53 gene alterations.
Carcinogenesis 2001 May
PMID:Telomerase activation and p53 mutations in urethane-induced A/J mouse lung tumor development. 1132 94

Telomerase is a ribonucleprotein enzyme that extends telomeric repeats at the end of chromosome DNA. Telomere maintenance by telomerase leads to cellular immortality and carcinogenesis. Telomerase is activated in most malignant tumors while it is usually repressed in normal somati tissues, and telomerase activation is thought to be a critical step for cancer progression. These findings suggest that telomerase is a good target for cancer gene therapy. A variety of molecular technique have been used to inhibit telomerase activity in cancer cells. In this review, I introduce the representative methods which efficently inhibit telomerase activity and may have a potential for clinical application.
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PMID:[Telomerase inhibitor]. 1138 9

Recent molecular evidence suggests that allelic deletions of chromosomes are involved in the carcinogenesis of various neoplasms, including oral squamous cell carcinoma (OSCC). To determine the role of 3p deletions in Japanese OSCC and to define the localization of putative tumor suppressor genes, we initially examined loss of heterozygosity (LOH), using nine microsatellite markers in 36 OSCCs and 28 oral epithelial dysplastic lesions (OEDLs). LOH on chromosome 3p was observed at one or more loci in 72% of OSCCs and 18% of OEDLs. Fourteen (61%) of 23 OSCC patients informative at D3S2450 (3pter-p24.2) showed LOH most frequently, in contrast to OEDL, where LOH was never seen at this locus. Interestingly, we found a significant association between an allelic deletion at this locus and the histologic grade of mode of tumor invasion. Therefore, we also examined allelic deletion on chromosome 3p telomeric to where D3S2450 was located. A common deletion region was identified between D3S2450 and D3S3591. Our results provide evidence for the presence of a tumor suppressor gene in a 0.8-cM region bordered by D3S2450 and D3S3591 at 3p25-p26, which may play a role in carcinogenesis and invasion of OSCC.
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PMID:Frequent loss of heterozygosity at 3p25-p26 is associated with invasive oral squamous cell carcinoma. 1139 37

Telomerase activity is associated with most malignant tumors. To evaluate the role of telomerase reactivation as a diagnostic and prognostic marker in oral carcinogenesis activity was investigated in mortal and immortal cell lines in eight oral leukoplakias (OL) and 46 oral squamous cell carcinomas (OSCC). Activity was also investigated in 13 histopathologically unaffected mucosas from distant sites or tumor-free margins of the same patients using a modified, highly sensitive, non-radioactive telomeric repeat amplification protocol (TRAP). This was correlated with histopathological stages and the clinical course of the disease. 50% of OL and 46% of OSCC showed activity. One patient with positive, high dysplastic OL developed an OSCC 11 month later. One of three specimens of adjacent tissue presented activity and a recurrence occurred after 6 months. Out of 10 tissues of distal normal mucosa, 2 demonstrated activity which could also be proved in the corresponding tumor. Detection of telomerase reactivation may be a novel method for early detection of immortalised cell clones and malignant cells in histopathologically normal oral squamous epithelium.
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PMID:Correlation of telomerase activity, clinical prognosis and therapy in oral carcinogenesis. 1139 40

Telomerase is an enzyme that replaces repetitive (TTAGGG)n sequences on the ends of chromosomes that would otherwise be lost during successive cell divisions. Telomerase activity is closely linked to attainment of cellular immortality, a step in carcinogenesis, while lack of such activity contributes to cellular senescence. Telomerase is activated in more than 85% of malignant tumors. However, with the exception of some self-renewing tissues with high regenerative potential, telomerase activity is usually repressed in normal somatic tissues. Based on these reports, we investigated telomerase activity in gastric mucosal tissues. Telomerase activity is highest in cancer, followed by intestinal metaplasia, chronic gastritis, and normal mucosa. In patients with intestinal-type gastric cancer, telomerase activity was higher in those with intestinal metaplasia and H. pylori infection than in patients without infection. Our results suggest that H. pylori infection may influence telomerase activity in cancer and noncancerous tissue. Genes encoding three major components of human telomerase have been recently cloned. They included those for human telomerase RNA component (hTR), human telomerase reverse transcriptase (hTERT), and telomerase-associated protein 1 (TEP1). More recently, two human telomeric repeat binding factors (TRFs) have also been cloned: TRF1, considered to inhibit the action of telomerase at the telomeric region, and TRF2, believed to prevent fusion of chromosome ends and, in vitro, to remodel linear telomeric DNA into large duplex loops. However, the details of mechanisms regulating telomerase activity are still poorly understood, and specific components or binding proteins that might represent suitable targets for cancer gene therapy have not yet been identified. Therefore, we established quantitative assays using a TaqMan RT-PCR for mRNAs encoding the telomerase components hTR, hTERT, and TEP1, as well as for those encoding TRF1 and TRF2. By using our quantitative assays, we found the following results: 1) Expression of TRF1 and TRF2 mRNA was greater in the normal cells than in human malignant hematopoietic cell lines or in patients with acute leukemia, 2) hTERT mRNA expression showed changes paralleling telomerase activity and became undetectable with HL60 cell differentiation, 3) initially low expression of TRF1 and TRF2 mRNA increased during differentiation. Our results suggest that not only hTERT but also TRF1 and 2 are important regulators of telomerase activity.
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PMID:[Telomerase, cell immortality and cancer]. 1148 65

Using comparative genomic hybridization (CGH) analysis, we, and others, have shown that there is a high and consistent incidence of chromosome 1q copy gain in human hepatocellular carcinoma (HCC). Chromosome 1 rearrangements, that involved peri-centromeric breakpoints, have also been frequently reported in karyotypic studies of HCC. Satellite DNA hypomethylation has been postulated as the mechanism underlying the induction of chromosome 1 peri-centromeric instability in many human cancers and in individuals with the rare recessive disorder ICF (immunodeficiency, centromeric heterochromatin instability, facial anomalies). In this study, we have investigated the role of DNA hypomethylation in 1q copy gain in HCC by examining the methylation status of chromosome 1 heterochromatin DNA (band 1q12). Thirty-six histologically confirmed samples of HCC were studied (24 paired tumor and adjacent nontumorous liver tissues, and 12 tumor only). Hypomethylation of satellite 2 (Sat2) DNA in 1q12 was analyzed by Southern blotting using methyl-sensitive enzyme digestion. In parallel, all cases were analyzed by CGH. A strong correlation between hypomethylated Sat2 sequences and 1q copy gain with a 1q12 breakpoint was found (P < 0.001). We postulate that such hypomethylation alters the interaction between the CpG-rich satellite DNA and chromatin proteins, resulting in heterochromatin decondensation, breakage and aberrant 1q formation. Spectral karyotyping further supported the presence of fragile 1q12 in HCC. Of particular interest was the finding of Sat2 DNA hypomethylation in 5 of 24 adjacent nontumorous liver tissues examined. These tissues showed no evidence of malignancy on histological examination nor did they display any CGH abnormalities. Our findings suggest a role for Sat2 demethylation in the early stages of the stepwise progression of liver carcinogenesis.
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PMID:Hypomethylation of chromosome 1 heterochromatin DNA correlates with q-arm copy gain in human hepatocellular carcinoma. 1148 5

Telomerase enzymatic activity has been detected in most human malignant tumours including hepatocellular carcinoma. In order to assess the cellular source, the topographic distribution, and the chronology of telomerase re-expression during human liver carcinogenesis, an in situ technique derived from the standard TRAP (telomeric repeat amplification protocol) assay was set up that allowed the detection of telomerase enzyme activity at the cellular level on frozen liver tissue sections. In situ TRAP (ISTRAP) was performed on 27 hepatocellular carcinomas (HCCs) and 57 non-tumour livers, including normal liver without HCC, liver samples adjacent to tumour with and without hepatic cirrhosis, and biopsies of chronic hepatitis. In HCC, telomerase was detected in the nuclei of liver tumour cells in 23/27 cases (85%), with a heterogeneous distribution within the tumour. This signal was also detected in clusters of hepatocytes in 16/26 (61%) samples of liver adjacent to HCC, in 10/23 (43%) cases of chronic viral hepatitis without adjacent HCC, and in scattered nuclei of 2/8 histologically normal livers. Comparison of the results obtained with ISTRAP and standard TRAP assays on tissue extracts suggests a gain in sensitivity with the in situ technique. This study confirms that telomerase is expressed in most HCCs and suggests that focal telomerase reactivation is an early event during human liver carcinogenesis. ISTRAP is a sensitive technique that allows the study of telomerase expression in the morphological context.
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PMID:In situ detection of telomerase enzymatic activity in human hepatocellular carcinogenesis. 1152 54

Human telomerase is a specialized reverse transcriptase that catalyses telomeric repeat addition at the ends of chromosomes. Activation of this enzyme is one of the key steps in cell immortalization and carcinogenesis, and one of its components, hTERT, is considered as the rate-limiting factor. While telomerase activity was found to be prognostically relevant in various cancers, results obtained from renal cell carcinomas (RCC) failed to show any correlation with the usual prognostic factors. The aim of the study was to reassess the role of telomerase and its hTERT component in the biological behaviour of RCC using new quantitative techniques, such as the quantitative evaluation of hTERT mRNA level by a real-time RT-PCR procedure and the measuring of telomerase activity by an ELISA TRAP assay. Since experimental evidence supports a relationship between cell proliferation or c-myc expression and telomerase, the proliferation index and c-myc mRNA levels were also studied. Forty-one RCC (29 conventional renal cell carcinomas (CRCC), 10 papillary RCC and two urothelial carcinomas) were studied. In 73% of cases, normalized hTERT mRNA expression was significantly higher in the tumour sample than in the normal tissue. Telomerase activity was detected in 63% of RCC, while corresponding normal tissue was always negative. Analysis of correlations showed firstly that both telomerase activity and hTERT mRNA level were lower in the group of CRCC versus non-CRCC (TRAP: 0.3+/-0.1 versus 0.6+/-0.2, p<0.05; hTERT/PO mRNA: 5+/-3 versus 37+/-8, p<0.001, respectively); secondly, that in the group of CRCC, hTERT mRNA expression level was correlated with the stage of the tumour (p=0.01); and thirdly, that no correlation was observed between c-myc mRNA level and hTERT mRNA level. In conclusion, these results support the involvement of telomerase in RCC and the potential interest of hTERT mRNA quantification.
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PMID:hTERT expression in sporadic renal cell carcinomas. 1159

Up-regulation of telomerase has been reported in many cancers. Our aim was to characterize telomerase activity in various states of the oesophagus to facilitate better understanding of carcinogenesis of oesophageal squamous cell carcinoma. During endoscopic examinations, we obtained 45 Lugol-stained normal epithelia, 31 Lugol-unstained epithelia (14 oesophagitis, 7 mild dysplasia, 5 severe dysplasia and 5 intramucosal cancer) and 9 advanced cancer. Telomerase activity was semi-quantified by a telomeric repeat amplification protocol using enzyme-linked immunosorbent assay, and expression of human telomerase reverse transcriptase mRNA was examined by in situ hybridization. In the Lugol-stained normal epithelia, telomerase activity increased in proportion to the increase of severity of the accompanying lesions, with a rank order of advanced cancer, intramucosal cancer, mild dysplasia and oesophagitis. In the Lugol-unstained lesions and advanced cancer, telomerase activity was highest in advanced cancer. Up-regulation of telomerase in normal squamous epithelium may be a marker of progression of oesophageal squamous cell carcinoma.
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PMID:Telomerase activity of the Lugol-stained and -unstained squamous epithelia in the process of oesophageal carcinogenesis. 1159 73

Strong evidence in favour of the somatic mutation theory of cancer, which states that genomic rearrangements are early and essential events in tumour development, has during the past two decades been obtained from both cytogenetic and molecular genetic studies of neoplastic cells. More than 14,000 neoplasms with acquired clonal chromosome aberrations have been reported; the majority have, however, been haematological malignancies, whereas still little is known about the karyology of the quantitatively more important carcinomas. For oral squamous cell carcinomas (SCC), which constitute a substantial subset of human malignancies, only 63 short-term cultured tumours with karyotypic aberrations have been described. Simple numerical changes, mostly -Y, +Y, or +7, have been detected as the sole anomalies in 19 tumours, but these aberrations are probably not causally related to the neoplastic process. The remaining 44 SCC have had structural changes of varying complexity, often together with numerical aberrations. An assessment of the karyotypic imbalances resulting from these aberrations reveals that chromosomes 9, 13, 18 and Y are recurrently lost, and that deletions frequently involve chromosome arms 3p, 7q, 8p, 11q, 17p and the short arms of all acrocentric chromosomes. The chromosomal breakpoints in structural rearrangements frequently involve the centromeric regions of chromosomes 1, 3, 8, 14 and 15 as well as bands 1p22, 11q13 and 19p13. At least one of these bands has been rearranged in 70% of SCC with structural aberrations and they probably contain loci of importance in oral squamous cell carcinogenesis. A comparison of data obtained from oral and other types of SCC--laryngeal, oesophageal, lung, cervical, and anal canal--indicates that some of the events in the multistep process of SCC development involve the same genetic pathways irrespective of site of origin.
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PMID:Chromosome abnormalities in oral squamous cell carcinomas. 1170 18


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