Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ribonucleoprotein enzyme telomerase is a RNA dependent DNA polymerase. The function of telomeres is mediated by the proteins which bind telomeric repeats. The binding of those proteins is sequence specific. We determined the fidelity of the DNA polymerization reaction of human telomerase in order to understand the origin of non-canonical telomeric repeats in human telomeres and to gain insight into the reaction mechanism of telomerase. By cloning and sequencing a large number of in vitro generated telomeric repeats we found the error rate for human telomerase to be approximately 2 x 10(-3) per nucleotide or one non-TTAGGG repeat for every 100 TTAGGG repeats. All the nucleotide changes observed were A --> C changes for a positional error rate of 1.2 x 10(-2). All the other positions had no observed errors for a positional error rate no greater than 1.2 x 10(-3).
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PMID:The fidelity of human telomerase. 864 50

Telomerase is a ribonucleoprotein DNA polymerase that elongates telomeres in eukaryotes. The telomere hypothesis implicates short telomere length and telomerase activation as critical players in cellular immortalization and cancer. In this review, we refine the original telomere hypothesis to address the results of recent studies on telomerase and telomere length regulation.
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PMID:Telomerase and cancer: revisiting the telomere hypothesis. 891 93

Human immunodeficiency virus type-1 (HIV-1) reverse transcriptase (RT) initiates reverse transcription from tRNA(Lys3). HIV-1 RT is a heterodimer consisting of two polypeptides, p66 and p51. In this work, the possible role of each subunit of RT in the interaction with its natural primer tRNA(Lys3) was studied. Two recombinant forms of HIV-1 RT, heterodimer p66/p51 and homodimer p51/p51, were used. Previously we have expressed and purified recombinant RT p51/p51 which possesses DNA polymerase activity [El Dirani-Diab, R., Andreola, M. L., Nevinsky, G., Tharaud, D., Barr, P. J., Litvak, S. & Tarrago-Litvak, L. (1992) FEBS Lett. 301, 23-28]. Here we show that HIV-1 RT p51/p51 displays certain properties very similar to the p66/p51 recombinant enzyme. The homodimer was able to anneal tRNA(Lys3) to the primer-binding site of the HIV-1 RNA template leading to a functional complex capable of synthesizing cDNA. Further, the p51/p51 enzyme behaved like RT p66/p51 concerning the strong inhibition produced by a non-nucleoside RT inhibitor. These data show that for RT p51/p51, one of the subunits of the homodimer adopts a conformation similar to the catalytic subunit (p66) present in the heterodimeric form. Part of this work was devoted to the study of the complex between the recombinant forms of HIV-1 RT and its primer tRNA. Each enzymatic form was cross-linked to tRNA(Lys3) in the presence of a platinum derivative, giving different ribonucleoprotein complexes of molecular masses higher than 100 kDa, suggesting that primer tRNA may interact with both subunits in the heterodimeric enzyme. After RNase A treatment of the complex RT p66/p51 x tRNA, the label was mainly found to migrate with the p66 subunit, although some cross-linking was also found associated to the p51 subunit. These results show that the p66 and p51 subunits of RT interact with tRNA(Lys3). Moreover, cross-linking of tRNA(Lys3) with HIV-1 RT p66/p51 in the presence of a DNA template containing the primer-binding-site sequence yielded an enzymatically active complex.
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PMID:p66/p51 and p51/p51 recombinant forms of reverse transcriptase from human immunodeficiency virus type 1--interactions with primer tRNA(Lys3), initiation of cDNA synthesis, and effect of inhibitors. 949 22

The ends of chromosomes, or telomeres, consist of short repeated sequences that are synthesized by a ribonucleoprotein-DNA polymerase called telomerase. The RNA component of telomerase is essential for enzyme activity. The maintenance of telomere length by telomerase has been proposed to be essential for cellular viability and to play an important role in cellular senescence and immortalization. We are interested in using the mouse as a model system for the study of telomerase. We studied telomerase activity and expression of the mouse telomerase RNA component (mTR) in two different transgenic mouse models of multistage tumorigenesis: models of islet cell carcinoma and squamous cell carcinoma. In both tumour models, telomerase activity was detected only in late-stage tumours, whereas the telomerase RNA was present at higher than normal levels in pre-neoplastic stages and increased further in late-stage tumours. However, the RNA levels did not parallel the amounts of telomerase activity detected, suggesting that regulation of telomerase activity does not correlate with the regulation of its RNA component. These results establish a direct correlation between progression to late-stage tumours and induction of telomerase activity, and suggest that the initial upregulation of telomerase RNA is an early event. To address the role of telomerase during normal mouse development and tumour formation, we have constructed a knockout mouse for the mouse telomerase RNA, mTR-/-. These mice and the cell lines derived from them are telomerase deficient.
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PMID:Mouse models for the study of telomerase. 952 57

The Epstein-Barr virus (EBV) DNA polymerase (pol) mRNA, which contains a noncanonical polyadenylation signal, UAUAAA, is cleaved and polyadenylated inefficiently (S. C. S. Key and J. S. Pagano, Virology 234:147-159, 1997). We postulated that the EBV early proteins SM and M, which appear to act posttranscriptionally and are homologs of herpes simplex virus (HSV) ICP27, might compensate for the inefficient processing of pol pre-mRNA. Here we show that the SM and M proteins interact with each other in vitro. In addition, glutathione S-transferase-SM/M fusion proteins precipitate the heterogeneous ribonucleoprotein (hnRNP) C1 splicing protein. Further, the SM protein is coimmunoprecipitated from SM-expressing cell extracts with an antibody to the hnRNP A1/A2 proteins, which are splicing and nuclear shuttling proteins. Finally, the amount of processed EBV DNA polymerase mRNA was increased three- to fourfold in a HeLa cell line expressing SM; this increase was not due to enhanced transcription. Thus, inefficient processing of EBV pol RNA by cellular cleavage and polyadenylation factors appears to be compensated for and may be regulated by the early EBV protein, SM, perhaps via RNA 3'-end formation.
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PMID:The Epstein-Barr virus (EBV) SM protein enhances pre-mRNA processing of the EBV DNA polymerase transcript. 976 85

The ends of human chromosomes (telomeres) consist of tandem repeats of the sequence TTAGGG. Telomeres lose up to 200 base pairs of DNA per cell division due to the inability of DNA polymerase to completely replicate the chromosomal ends. Chromosomal shortening ultimately leads to senescence and cell death in normal cells. However, some immortal cells do not lose telomeric sequence during DNA replication. Many human carcinoma lines are immortal in vitro, suggesting that these cells have a mechanism for maintaining the ends of their chromosomes. Telomerase is a ribonucleoprotein complex that synthesizes telomeric DNA onto chromosomes using its RNA component as a template. To elucidate potential mechanisms for telomerase regulation, we tested human squamous cell carcinoma lines (SCCs) for telomerase activity. All SCC lines expressed high levels of telomerase activity. Synchronization in specific cell cycle phases caused marked reduction in telomerase activity in G0 and S, but not in G1 or M. Reduction in telomerase activity correlated with induction of Rb protein in these phases. Overexpression of full length Rb resulted in significant downregulation of telomerase activity. However, expression of an Rb N-terminal oligomerization domain deletion construct, a C-terminal DNA binding domain deletion construct, or a pocket domain mutant failed to downregulate telomerase activity. We concluded that functionally intact Rb was required for cell cycle-dependent downregulation of telomerase activity in SCC lines.
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PMID:Intact functional domains of the retinoblastoma gene product (pRb) are required for downregulation of telomerase activity. 1032 Jul 73

Human telomerase is a ribonucleoprotein DNA polymerase which maintains the telomeric region of human chromosomes and has been detected in all types of human cancer tested. We used the telomeric repeat amplification protocol (TRAP) assay to examine 71 non-small cell lung carcinomas (NSCLC) and their adjacent normal tissue. Telomerase activity was detected in 61 (86%) of the 71 NSCLC examined but not in any of the matched normal lung tissues. A significant correlation was found between the presence of telomerase activity and current smoking status at the time of diagnosis (p=0. 0076). In addition, a trend was found between telomerase activity and smoking exposure (p=0.06). Our findings demonstrate that telomerase activity is a common phenomenon in NSCLC cases but not in the normal lung. However, certain cases in former smokers may follow a telomerase independent pathway.
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PMID:Telomerase activity in non-small cell lung carcinomas correlates with smoking status. 1053 80

Telomerase is a ribonucleoprotein DNA polymerase that maintains the telomeric region of chromosomes lost during successive rounds of cell division. We used the telomeric repeat amplification protocol (TRAP) assay to examine telomerase activity in bronchial lavage (BL) samples from individuals undergoing diagnosis of lung cancer. Telomerase activity was detected in 17 (47%) of 36 samples examined. In particular, 16 (70%) of 23 BL specimens obtained from lung cancer patients showed detectable telomerase activity, while only 1 of 13 (8%) specimens obtained from patients without lung cancer demonstrated activity (P=0.00038). Moreover, 9 (90%) of 10 BL specimens, which were cytologically positive for lung cancer, were also positive for telomerase activity, while 7 (54%) of 13 cytologically negative BL specimens for lung cancer showed detectable telomerase activity. Detection of telomerase activity combined with cytology were able to identify 17 (74%) of 23 lung cancer cases whereas cytology alone identified 10 (43%) of 23 such cases (P=0.035). Our findings indicate that telomerase is a specific marker for malignant lung disease and a potential complementary tool to cytology in the diagnosis of certain lung cancer cases.
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PMID:Evaluation of telomerase activity in bronchial lavage as a potential diagnostic marker for malignant lung disease. 1070 7

More than 80% of human malignancies express telomerase activity, while normal somatic tissues in general lack it. During each normal cell division, there is a constant loss of DNA sequences at chromosomal ends, which is due to the 'end-replication problem' of conventional DNA polymerase. Critical shortening of telomeres induces cell cycle arrest and eventually cell death. Telomerase, a ribonucleoprotein complex with a RNA (TR) and a catalytic subunit (TERT) as core components, is able to add reitineratedly telomeric repeat sequences to the very ends of chromosomes. It was suggested that activation of telomerase in tumor cells has a major impact on their continuous growth. Indeed, transfection of TERT constructs into various normal human cell types led to telomere elongation or stabilization and, most importantly, cellular immortalization. Conversely, inhibition of telomerase in tumor cell lines induced growth arrest, at least in first experimental settings. Such initial success implies that drug-mediated abrogation of telomerase action might be an ideal adjuvant treatment for cancer patients. There are, however, legitimate concerns about the generalization of such an approach.
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PMID:Targeted inhibition of telomerase in human cancer: will it be a double-edged sword? 1144 Dec 76

Telomerase is a ribonucleoprotein DNA polymerase that elongates the telomeres of chromosomes to compensate for losses that occur with each round of DNA replication and maintain chromosomal stability. Interleukin 6 (IL-6) and insulin-like growth factor 1 (IGF-1) are proliferative and survival factors for human multiple myeloma (MM) cells. To date, however, the effects of IGF-1 and IL-6 on telomerase activity and associated sequelae in MM cells have not been characterized. In this study, we evaluated the effects of IGF-1 and IL-6 on telomerase activity in MM cell lines (MM.1S, U266, and RPMI 8226), as well as patient MM cells. We show that these cytokines up-regulate telomerase activity without alteration of human telomerase reverse transcriptase (hTERT) protein expression. We also demonstrate that increased telomerase activity triggered by these cytokines is mediated by phosphatidylinositol 3'-kinase (PI3k)/Akt/nuclear factor kappaB (NFkappaB) signaling. We confirm involvement of PI3k/Akt/NFkappaB signaling because the PI3k inhibitors wortmannin and LY294002 or the inhibitor of NFkappaB (IkappaB) kinase inhibitor PS-1145 block constitutive and cytokine-induced up-regulation of telomerase activity. Furthermore, we show that dexamethasone (Dex) reduces telomerase activity through the inhibition of hTERT expression before the induction of apoptosis. Importantly, IGF-1 and IL-6 abrogate Dex-induced down-regulation of telomerase activity and apoptosis. The protective effect of those cytokines against Dex-induced down-regulation of telomerase activity is blocked by both wortmannin and PS-1145, whereas the protection against Dex-induced apoptosis is blocked by wortmannin but not PS-1145. Therefore, our results demonstrate that telomerase activity is related not only to transcriptional regulation of hTERT by NFkappaB but also to posttranscriptional regulation because of phosphorylation of hTERT by Akt kinase. These studies therefore demonstrate that telomerase activity is associated with cell growth, survival, and drug resistance in MM cells.
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PMID:Cytokines modulate telomerase activity in a human multiple myeloma cell line. 1209 3


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