Lack of cell cycle regulation of telomerase activity in human cells.

Conflicting reports have appeared concerning the cell cycle regulation of telomerase activity and its possible repression during quiescence and cell differentiation. We have reexamined these issues in an attempt to uncover the basis for the discrepancies. Variations in extracted telomerase activity during the cell cycle are not observed in cells sorted on the basis of DNA content.

Analysis of the FHIT gene and FRA3B region in sporadic breast cancer, preneoplastic lesions, and familial breast cancer probands.

The FHIT gene, which spans the FRA3B fragile site at chromosome 3p14.2, is a candidate tumor suppressor gene in breast and other cancers. We investigated FHIT and FRA3B for loss of heterozygosity (LOH); homozygous deletions; abnormal transcripts; and acquired/germ-line point mutations in breast cancer cell lines (n = 32), breast epithelial and stromal cell cultures (n = 18), microdissected invasive (n = 16) and ductal in situ carcinomas (n = 6), and their accompanying normal and abnormal epithelial foci (n = 14).

Genomic instability and telomerase activity in human bronchial epithelial cells during immortalization by human papillomavirus-16 E6 and E7 genes.

Human papilloma virus types 16 and 18 contribute to the development of cervical carcinomas in which the E6 and E7 genes are frequently retained and expressed in the tumors. Our study explored the ability of the E6 and/or E7 genes to immortalize normal human bronchial epithelial (NHBE) cells and to reactivate telomerase expression in these cells. We have introduced the human papillomavirus type 16 E6 or E7 genes alone or in combination (E6/E7) into NHBE cells using the retroviral construct pLXSN.

Inhibition of telomerase activity correlates with a decrease in the RNA component of telomerase during differentiation.

In most normal somatic cells the telomeres of human chromosomes shorten with each cell division because of low expression or lack of telomerase activity. Telomerase, a ribonucleoprotein that synthesizes telomeric DNA onto chromosomal ends, is reactivated or upregulated in tumor cells and maintains the stability of telomere length. We previously showed that treatment of HL60 leukemia cells with differentiation-inducing agents resulted in inhibition of telomerase activity.

Telomerase expression in respiratory epithelium during the multistage pathogenesis of lung carcinomas.

To investigate the role of telomerase in the multistage pathogenesis of lung cancer, we examined 205 fresh and archival tissue samples obtained from 40 patients, 34 of whom had invasive lung carcinoma, 5 with carcinoma in situ (CIS) without invasion, and 1 without lung carcinoma. We analyzed samples for telomerase enzyme activity using the semiquantitative PCR-based telomeric repeat amplification protocol assay (131 samples) or by a radioactive in situ hybridization method for expression of the RNA component of human telomerase (hTR; 74 samples). A subset of samples was assayed by both methods, and the correlation was excellent (30 of 36; 83%).

Inhibition of protein phosphatase activity induces p53-dependent apoptosis in the absence of p53 transactivation.

Inhibitors of type 1 and type 2A protein phosphatases were used to examine the involvement of protein phosphorylation in regulating the functions of endogenous p53. Exposure of Balb/c 3T3 cells to okadaic acid, an inhibitor of protein phosphatases 1 and 2A, increased the phosphorylation of p53 without changing p53 levels. Okadaic acid treatment enhanced the binding of p53 to a consensus DNA target sequence and caused a 5-8-fold increase in p53 transcriptional activity.

Cytological detection of telomerase activity using an in situ telomeric repeat amplification protocol assay.

A previously reported highly sensitive assay for measuring telomerase activity on cell and tissue extracts indicates that most human tumor tissues, but not cells adjacent to tumors, have detectable telomerase activity. Although this assay has provided a significant amount of information about the presence or absence of telomerase activity, it does not indicate whether all cells within a tumor have telomerase activity or whether only a subset does. The present report demonstrates the ability to advance this technology to an in situ assay.

The relationship between telomere length and therapy-associated cytogenetic responses in patients with chronic myeloid leukemia.

Background: Chronic myeloid leukemia (CML) is a clonal disease with specific cytogenetic changes involving the Philadelphia (Ph) translocation. The authors examined the relationship between telomere length (terminal restriction fragment [TRF]) and therapy-associated cytogenetic responses in CML patients.

Methods: The authors examined the telomere length and telomerase activity in 44 patients with Ph-positive CML in the chronic phase.

Clinical implications of telomerase activity levels in acute leukemia.

In the present study, we used the telomeric repeat amplification protocol assay, an internal telomerase assay standard, and an automatic DNA sequencer to detect and quantitate telomerase activity in blood samples obtained from normal and acute leukemia patients. Telomerase activity was analyzed in 78 acute leukemia patients and ranged from 0.65 to 147 relative to the internal standard.

Decline in telomerase activity as a measure of tumor cell killing by antineoplastic agents in vitro.

Telomerase activity is frequently associated with the malignant phenotype, and it can be considered an almost ubiquitous tumor marker. In this study, we evaluated telomerase activity in telomerase-positive human tumor cell lines exposed in vitro to antineoplastic agents. The results show that drug-induced cell killing of tumor cells is associated with a decline in detectable telomerase activity.

A survey of telomerase activity in human cancer.

Research on the association of the ribonucleoprotein enzyme, telomerase, with human cancer has expanded rapidly in recent years. Essentially all major types of cancer have been screened and the presence of telomerase activity has been detected in the vast majority of cases. In this article we provide a summary, in table form, of the current data.

Multiple pathways for the regulation of telomerase activity.

The ends of vertebrate chromosome are composed of large tracts of a repeated sequence, TTAGGG, which are known as telomeres. Normal somatic cells progressively lose telomeric repeats with each successive cell division due to incomplete replication. Immortal and cancer cells compensate for telomeric loss by expressing the enzyme telomerase, an RNA-dependent DNA polymerase that maintains telomere length.

Human papillomavirus-16 E6/E7 transfected retinal cell line expresses the Müller cell phenotype.

The introduction of viral transforming genes into mammalian cells has been used in establishing cultures of unlimited lifespan. Although Müller cells, the predominant glial cells in the mammalian retina, have been isolated using a variety of techniques, most of these cultures have limited capacity for cell division and are often contaminated by other cell types especially astrocytes, endothelial cells and microglial cells. We have established pure cultures of retinal cells which express Müller cell characteristics and exhibit unlimited growth in vitro.

Telomerase activity in ordinary meningiomas predicts poor outcome.

Telomerase, the enzyme that stabilizes telomere length, is reactivated with almost all cancer types, and it may be necessary for unlimited cell proliferation. Assessment of malignancy in ordinary meningiomas is inconclusive because no clear-cut correlation exists between aggressive clinical behavior and histological features or karyotypic abnormalities. We analyzed telomerase activity in 52 cases of meningioma by using the highly sensitive telomeric repeat amplification protocol and then compared clinical behavior in telomerase-positive and -negative ordinary meningiomas.

Effect of penclomedine (NSC-338720) on telomere fusions, chromatin blebbing, and cell viability with and without telomerase activity and abrogated p53 function.

Telomeres, or chromosome ends, are essential in maintaining chromosomal integrity. Telomeres consist of a short hexameric sequence, 3'-TTAGGG-5', repeated in tandem arrays added to chromosomes by the ribonucleoprotein enzyme telomerase. In this study, we assessed whether penclomedine, a novel synthetic pyridine compound presently being evaluated in clinical trials for its anticancer activity, influences telomere fusions (chromosome end-to-end associations) and telomerase activity in cells in culture.

Telomerase activity and in situ telomerase RNA expression in malignant and non-malignant lymph nodes.

Aims/background: Telomerase, an enzyme associated with cellular immortality, is expressed by most malignant tumours, but is inactive in normal somatic cells except for male germ cells and proliferating stem cells. Thus, the measurement of telomerase activity in tissue samples may provide useful diagnostic and prognostic information. The aim of this study was to determine whether telomerase expression is useful for the detection of occult malignant cells in lymph nodes.

Telomerase in the early detection of cancer.

Although there is justifiable optimism regarding telomerase activity and early detection of cancer, it is important to point out that there is much that remains to be understood and additional validation studies will be required before knowledge of telomerase activity will be useful in decisions regarding patient management. A key question is whether we will be able to distinguish those cancers that are going to progress from those cancers that are not by detecting telomerase activity. Molecular staging using markers such as telomerase activity in combination with other molecular markers may be particularly useful in this regard.

Telomerase activity and cytogenetic changes in chronic myeloid leukemia with disease progression.

Progressive telomere shortening is thought to be important in the regulation of cellular senescence and that the upregulation or reactivation of telomerase activity may be a critical if not rate limiting step in the development of neoplastic cells. To obtain information about telomeres and telomerase activity in hematopoietic neoplasia at various disease stages, we evaluated 54 samples obtained from 41 patients with chronic myeloid leukemia (CML) using a combination of fluorescent-telomeric repeat amplification protocol and an internal telomerase assay standard. The terminal restriction fragment (TRF) lengths in the blast phase was reduced compared to that in the chronic phase (4.

Telomerase activity is detected in pancreatic cancer but not in benign tumors.

Activation of telomerase and stabilization of telomeres are considered to be necessary for immortalization of human tumor cells. In the present study, telomerase activity was detected in 41 (95%) of 43 pancreatic cancer specimens but was detectable in none of 11 benign pancreatic tumors and only one of 3 pancreatitis samples. Low levels of telomerase activity were detected in 5 (14%) of 36 adjacent "normal" pancreatic tissues.

Telomerase assays in the diagnosis and prognosis of cancer.

Telomerase activity is present in most primary human tumours but not in normal somatic tissues except for proliferative cells of renewal tissues (e.g. crypts of the intestine, basal layer of the epidermis, haemopoietic and inflammatory cells).

Progressive telomere shortening and telomerase reactivation during hepatocellular carcinogenesis.

Telomeres shorten progressively with age in normal somatic cells in culture and in vivo. The maintenance of telomere length is assumed to be an obligatory step in the progression and immortalization of most human tumor cells. To understand the role of telomere dynamics in the development of hepatocellular carcinoma (HCC), we examined the length of terminal restriction fragment (TRF), as an indicator for telomere length, in HCC and surrounding tissues with chronic active hepatitis (CAH) or liver cirrhosis (LC).

Telomerase activity concentrates in the mitotically active segments of human hair follicles.

Telomerase is a ribonucleoprotein enzyme capable of adding hexanucleotide repeats onto the ends of linear chromosomal DNA. Whereas normal somatic cells with a limited replicative capacity fail to express telomerase activity, most immortal eukaryotic cells do. Cells of renewal tissues (e.

Chromosome end-to-end associations and telomerase activity during cancer progression in human cells after treatment with alpha-particles simulating radon progeny.

Chromosome end-to-end associations seen at metaphase involve telomeres and are commonly observed in cells derived from individuals with ataxia telangiectasia and most types of human tumors. The associations may arise because of short telomeres and/or alterations of chromatin structure. There is a growing consensus that telomere length is stabilized by the activity of telomerase in immortal cells; however, it is not clear why some immortal cells display chromosome end-to-end associations.