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)

Although several hypomethylating agents such as 5-azadeoxycytidine and 5-fluorodeoxycytidine have been shown to activate transcription after incorporation into viral or cellular DNA, agents which selectively affect the methylation status of virus-infected cells have not been described. Studies on the antiviral effect of the methyldeoxycytidine (mdCyd) analogue trifluoromethyldeoxycytidine (F3mdCyd) showed significant antiviral activity against herpes simplex virus type 1 (HSV-1). This analogue of both dCyd and dThd is selectively incorporated into the DNA of herpesvirus infected cells due to the unique specificity of the herpesvirus thymidine kinase (TK) because the HSV-1 TK is both a dCyd and dThd kinase. In contrast, the deoxycytidine kinase of uninfected cells preferentially phosphorylates dCyd and has a poor affinity for F3mdCyd. F3mdCyd hemisubstituted M13 DNA displayed the same properties as mdCyd-substituted M13 DNA with respect to cleavage by restriction enzymes, and acted as an efficient template for eukaryotic DNA methyltransferase (S-adenosyl-L-methionine DNA (cytosine-5) methyltransferase: EC 2.1.1.37). Using the persistently infected CEM cell model system, the extent of DNA methylation was shown to increase in a dose-related manner when HSV-1-infected CEM cells were treated with increasing concentrations of F3mdCyd. Higher levels of methylation correlated with significant decreases in HSV-1 titers. Isoschizomer analyses followed by Southern blotting and hybridization with genomic HSV-1 DNA showed that DNA from HSV-1-infected, analogue-treated Vero cells was resistant to cleavage by restriction enzymes at a time when productive virus was not present in culture. We infer from these results that the methylation-like properties of the incorporated F3mdCyd occur concomitantly with, and appear to be involved in, the mechanisms of the analogue's antiviral effect towards HSV-1.
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PMID:Methylation of HSV-1 DNA as a mechanism of viral inhibition: studies of an analogue of methyldeoxycytidine: trifluoromethyldeoxycytidine (F3mdCyd). 138 26

Genome-wide demethylation has been suggested to be a step in carcinogenesis. Evidence for this notion comes from the frequently observed global DNA hypomethylation in tumour cells, and from a recent study suggesting that defects in DNA methylation might contribute to the genomic instability of some colorectal tumour cell lines. DNA hypomethylation has also been associated with abnormal chromosomal structures, as observed in cells from patients with ICF (Immunodeficiency, Centromeric instability and Facial abnormalities) syndrome and in cells treated with the demethylating agent 5-azadeoxycytidine. Here we report that murine embryonic stem cells nullizygous for the major DNA methyltransferase (Dnmt1) gene exhibited significantly elevated mutation rates at both the endogenous hypoxanthine phosphoribosyltransferase (Hprt) gene and an integrated viral thymidine kinase (tk) transgene. Gene deletions were the predominant mutations at both loci. The major cause of the observed tk deletions was either mitotic recombination or chromosomal loss accompanied by duplication of the remaining chromosome. Our results imply an important role for mammalian DNA methylation in maintaining genome stability.
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PMID:DNA hypomethylation leads to elevated mutation rates. 973 4

Tumor suppressor gene inactivation is a crucial event in oncogenesis. Gene inactivation mechanisms include events resulting in loss of heterozygosity (LOH), gene mutation, and transcriptional silencing. The contribution of each of these different pathways varies among tumor suppressor genes and by cancer type. The factors that influence the relative utilization of gene inactivation pathways are poorly understood. In this study, we describe a detailed quantitative analysis of the three major gene inactivation mechanisms for a model gene at two different genomic integration sites in mouse embryonic stem (ES) cells. In addition, we targeted the major DNA methyltransferase gene, Dnmt1, to investigate the relative contribution of DNA methylation to these various competing gene inactivation pathways. Our data show that gene loss is the predominant mode of inactivation of a herpes simplex virus thymidine kinase neomycin phosphotransferase reporter gene (HSV-TKNeo) at the two integration sites tested and that this event is significantly reduced in Dnmt1-deficient cells. Gene silencing by promoter methylation requires Dnmt1, suggesting that the expression of Dnmt3a and Dnmt3b alone in ES cells is insufficient to achieve effective gene silencing. We used a novel assay to show that missense mutation rates are also substantially reduced in Dnmt1-deficient cells. This is the first direct demonstration that DNA methylation affects point mutation rates in mammalian cells. Surprisingly, the fraction of CpG transition mutations was not reduced in Dnmt1-deficient cells. Finally, we show that methyl group-deficient growth conditions do not cause an increase in missense mutation rates in Dnmt1-proficient cells, as predicted by methyltransferase-mediated mutagenesis models. We conclude that Dnmt1 deficiency and the accompanying genomic DNA hypomethylation result in a reduction of three major pathways of gene inactivation in our model system.
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PMID:Reduced rates of gene loss, gene silencing, and gene mutation in Dnmt1-deficient embryonic stem cells. 1160 95