Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To compare the respective sensitivity of two nucleoside kinases, adenosine kinase and thymidine kinase, to oxidative stress, we measured these enzyme activities in cultured aortic endothelial cells exposed for 48 h to various O2 concentrations, and in cell extracts treated with H2O2 or the enzyme system hypoxanthine-xanthine oxidase. Adenosine kinase activity was not significantly influenced by the exposure to hyperoxia, nor by treatment with the enzyme system hypoxanthine-xanthine oxidase or with H2O2. On the other hand, there was a dose-dependent inhibitory effect on thymidine kinase activity resulting from exposure to various O2 concentrations or from treatment with various amounts of xanthine oxidase. Incubation of cell extracts in the presence of H2O2 also resulted in a significant reduction of thymidine kinase activity. These results indicate that thymidine kinase exhibits a selective sensitivity to the toxic effect of O2 concentrations and of O2 intermediates such as H2O2.
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PMID:Differential effects of hyperoxia and hydrogen peroxide on thymidine kinase and adenosine kinase activities of cultured endothelial cells. 299 14

Human diploid fibroblast cells lose replicative potential after a certain number of population doublings. We use this experimental system to investigate the role of oxidative damage in cellular aging. Treating cells with H2O2 at < 300 microM did not affect the viability of the majority of cells when judged by morphology, trypan blue exclusion, and protein synthesis. However, the treatment caused a dose-dependent inhibition of DNA synthesis. After a 2-hr treatment with 200 microM H2O2, the cells failed to respond to a stimulus of serum, platelet-derived growth factor, basic fibroblast growth factor, or epidermal growth factor by synthesizing DNA, and the loss of response could not be recovered by 4 days. Subcultivation showed that, as in senescent cells, division of the treated cells was inhibited. The life-time cumulative growth curve showed that the loss of replication due to H2O2 treatment was cumulative and irreversible. The H2O2 treatment decreased the number of the population doublings in the rest of the life span by 35.3 +/- 10.3%. Enzymatic assays indicated that, like the cells in their senescent state, the treated cells were less able to activate ornithine decarboxylase and thymidine kinase. Furthermore, subcultivation after the H2O2 treatment showed that the cells developed the morphology of senescent cells. In conclusion, sublethal treatment of H2O2 "stunned" F65 cells and caused the cells to enter a state resembling senescence.
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PMID:Senescence-like growth arrest induced by hydrogen peroxide in human diploid fibroblast F65 cells. 818 82

The redox-based regulation of gene expression is one of the fundamental mechanisms of cellular functions, and hydrogen peroxide seems to act as an intracellular second messenger of signal transduction of cytokines. Hydrogen peroxide at non-toxic doses induced the accumulation of mRNA for the early growth response-1 (egr-1) gene in mouse osteoblastic cells. The Egr-1 protein is a transcription factor that binds the GCGGGGGCG sequence and contains a zinc-finger structure that is essential for DNA binding. Egr-1 protein is sensitive to oxidative stress and loses specific DNA-binding activity when exposed to high levels of oxidative stress. Incubating cells with hydrogen peroxide at about 50 microM, however, increased the accumulation of Egr-1 protein, and the Egr-1 product seemed to be functional, judging by its binding activity to the GCGGGGGCG sequence and its ability to activate the chloramphenicol acetyltransferase reporter gene under the control of the human thymidine kinase enhancer containing the Egr-1 binding sequence. It was reported that the activity of Egr-1 protein as a transcription factor was negatively regulated by active oxygens. However, with appropriate concentrations of active oxygen, its capacity to bind a specific DNA sequence and to enhance the transcriptional activity of target genes is thought to be elevated.
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PMID:Functional activation of the egr-1 (early growth response-1) gene by hydrogen peroxide. 868 76

Using RNA interference techniques to knock down key proteins in two major double-strand break (DSB) repair pathways (DNA-PKcs for nonhomologous end joining, NHEJ, and Rad54 for homologous recombination, HR), we investigated the influence of DSB repair factors on radiation mutagenesis at the autosomal thymidine kinase (TK) locus both in directly irradiated cells and in unirradiated bystander cells. We also examined the role of p53 (TP53) in these processes by using cells of three human lymphoblastoid cell lines from the same donor but with differing p53 status (TK6 is p53 wild-type, NH32 is p53 null, and WTK1 is p53 mutant). Our results indicated that p53 status did not affect either the production of radiation bystander mutagenic signals or the response to these signals. In directly irradiated cells, knockdown of DNA-PKcs led to an increased mutant fraction in WTK1 cells and decreased mutant fractions in TK6 and NH32 cells. In contrast, knockdown of DNA-PKcs led to increased mutagenesis in bystander cells regardless of p53 status. In directly irradiated cells, knockdown of Rad54 led to increased induced mutant fractions in WTK1 and NH32 cells, but the knockdown did not affect mutagenesis in p53 wild-type TK6 cells. In all cell lines, Rad54 knockdown had no effect on the magnitude of bystander mutagenesis. Studies with extracellular catalase confirmed the involvement of H2O2 in bystander signaling. Our results demonstrate that DSB repair factors have different roles in mediating mutagenesis in irradiated and bystander cells.
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PMID:Deficiencies of double-strand break repair factors and effects on mutagenesis in directly gamma-irradiated and medium-mediated bystander human lymphoblastoid cells. 1822 Apr 73