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)

Activity of replicase complex enzymes involving thymidine kinase (TK), ribonucleotide reductase (RR), DNA-polymerases alpha and beta as well as DNA synthesis and single breaks in DNA were studied during growth of P388 ascites tumor. Under these conditions the rate of DNA synthesis was distinctly decreased via salvage pathway and de novo. Single breaks were not detected in the preexistent DNA within various periods after transplantation of P338 leukemic cells. Retardation of DNA synthesis during tumor growth correlated with a decrease in TK, RR and DNA-polymerase alpha activities, while DNA-polymerase beta activity was markedly increased. Growth of melanoma B16 was accompanied by a decrease in content of ATP, ADP, NAD, phosphocreatine and phosphosaccharides as well as by an increase in the level of inorganic phosphates.
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PMID:[Changes in the replication apparatus and phosphorus-containing metabolite pool in experimental tumors in animals during development]. 181 11

Twenty-four base pairs of the human antioxidant response element (hARE) are required for high basal transcription of the NAD(P)H:quinone oxidoreductase1 (NQO1) gene and its induction in response to xenobiotics and antioxidants. hARE is a unique cis-element that contains one perfect and one imperfect AP1 element arranged as inverse repeats separated by 3 bp, followed by a "GC" box. We report here that Jun, Fos, Fra, and Nrf nuclear transcription factors bind to the hARE. Overexpression of cDNA derived combinations of the nuclear proteins Jun and Fos or Jun and Fra1 repressed hARE-mediated chloramphenicol acetyltransferase (CAT) gene expression in transfected human hepatoblastoma (Hep-G2) cells. Further experiments suggested that this repression was due to overexpression of c-Fos and Fra1, but not due to Jun proteins. The Jun (c-Jun, Jun-B, and Jun-D) proteins in all the possible combinations were more or less ineffective in repression or upregulation of hARE-mediated gene expression. Interestingly, overexpression of Nrf1 and Nrf2 individually in Hep-G2 and monkey kidney (COS1) cells significantly increased CAT gene expression from reporter plasmid hARE-thymidine kinase-CAT in transfected cells that were inducible by beta-naphthoflavone and teri-butyl hydroquinone. These results indicated that hARE-mediated expression of the NQO1 gene and its induction by xenobiotics and antioxidants are mediated by Nrf1 and Nrf2. The hARE-mediated basal expression, however, is repressed by overexpression of c-Fos and Fra1.
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PMID:Nrf1 and Nrf2 positively and c-Fos and Fra1 negatively regulate the human antioxidant response element-mediated expression of NAD(P)H:quinone oxidoreductase1 gene. 896 64

To investigate the potential of murine gamma-herpesvirus 72 thymidine kinase (MHV-72-TK) to act as a suicide gene, we used a mammalian expression vector on rat fibroblastoid cells deficient in the cellular TK gene. Substrate specificity was assessed in vitro in cells with stable expression of MHV-72-TK. The Herpes simplex virus 1-TK (HSV-1-TK) was used as a reference suicide gene. Unlike HSV-1-TK modified cells, which were sensitive to ganciclovir (GCV) (IC50=9.7 microM), cells modified by MHV-72-TK did not show sensitivity to this drug. The use of 3'-azido-3'-deoxythymidine (AZT) and (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) did not affect the growth of cells expressing either MHV-72-TK or HSV-1-TK in the range of concentration used for AZT (0-375 microM) and for BVDU (0-50 microM). In contrast, 5'-fluoro-2'-deoxyuridine (5-FUdR) was extremely cytotoxic and effectively killed MHV-72-TK expressing cells (IC50 value 2.1 microM). This value was 16 times lower than that required to kill cells expressing HSV1-TK. To test whether the bystander effect between two heterologous cell types could be mediated by the MHV-72-TK/5-FUdR system in vitro, cells expressing MHV-72-TK were co-cultured with the tumour fibroblastoid cell line NAD for 48 hours before the drug (10.8 microM) was added. The cell mixtures contained various ratios of cells expressing MHV-72-TK (0 to 50% of total cells). Only 1% of MHV-72-TK-expressing cells were needed to enhance mouse tumour cell killing and to decrease the survival rate to 25.6%. The bystander effect was more pronounced when 10% of cells expressing MHV-72-TK were used, decreasing survival to 17.4%. In parallel, the same concentration of 5-FUdR dose only marginally inhibited tumour cell growth in the absence of exogenous TK activity (84% survival). These results demonstrate the efficiency of MHV-72-TK as a suicide gene when 5-FUdR is used as a prodrug. When sequenced, MHV-72-TK proved to be identical to MHV-68 strain TK.
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PMID:The bystander effect mediated by the new murine gammaherpesvirus 72--thymidine kinase/5'-fluoro-2'-deoxyuridine (MHV72-TK/5-FUdR) system in vitro. 1095 Mar 89

Nucleoside analogs (NAs) have been used extensively in both antitumor and antiviral therapies. Their general mechanism of action has been postulated to result from incorporation into DNA, leading to disruption of DNA synthesis and DNA polymerase inhibition. To further explore the antitumor mechanisms of NAs we have evaluated ganciclovir (GCV), an NA antiviral agent, in herpes simplex virus thymidine kinase (HSV-TK) gene-modified tumor cells. This system allows specific evaluation of the antitumor effects of NAs because the antitumor effect is directly related to the phosphorylation of the prodrug GCV by the HSV-TK enzyme in the gene-modified tumor cells. We demonstrated that GCV incorporates into DNA and inhibits DNA polymerase, as has been observed in HSV-infected cells and with other antitumor NAs in tumor cells. A novel observation is that GCV activates MAP kinase within 1 hour of GCV exposure. This activation directly correlates with cytotoxicity, because inhibition of the MAP kinase extracellular regulated kinase (Erk) by PD98059, reversed GCV-mediated cytotoxicity. This effect appears to be specific to the Erk pathway, because inhibition of the p38 kinase with SB203580 had no effect on cytotoxicity. Further, GCV does not act as a DNA-damaging agent or activate general DNA-repair mechanisms, but does produce a number of metabolic disruptions, including a reversible decrease in NAD levels. These effects appear to be downstream of the earlier activation of Erk in this system, which may be a novel mechanism of action for GCV cytotoxicity in HSV-TK gene-modified tumor cells, and thus, needs to be further evaluated as the mechanism of tumor cell killing by other antitumor NAs.
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PMID:A role for MAP kinase in the antitumor activity of a nucleoside analog. 1191 43

The gene coding for arylformamidase (Afmid, also known as kynurenine formamidase) was inactivated in mice through the removal of a shared bidirectional promoter region regulating expression of the Afmid and thymidine kinase (Tk) genes. Afmid/Tk -deficient mice are known to develop sclerosis of glomeruli and to have an abnormal immune system. Afmid-catalyzed hydrolysis of N-formyl-kynurenine is a key step in tryptophan metabolism and biosynthesis of kynurenine-derived products including kynurenic acid, quinolinic acid, nicotinamide, NAD, and NADP. A disruption of these pathways is implicated in neurotoxicity and immunotoxicity. In wild-type (WT) mice, Afmid-specific activity (as measured by formyl-kynurenine hydrolysis) was 2-fold higher in the liver than in the kidney. Formyl-kynurenine hydrolysis was reduced by approximately 50% in mice heterozygous (HZ) for Afmid/Tk and almost completely eliminated in Afmid/Tk knockout (KO) mice. However, there was 13% residual formyl-kynurenine hydrolysis in the kidney of KO mice, suggesting the existence of a formamidase other than Afmid. Liver and kidney levels of nicotinamide plus NAD/NADP remained the same in WT, HZ and KO mice. Plasma concentrations of formyl-kynurenine, kynurenine, and kynurenic acid were elevated in KO mice (but not HZ mice) relative to WT mice, further suggesting that there must be enzymes other than Afmid (possibly in the kidney) capable of metabolizing formyl-kynurenine into kynurenine. Gradual kidney deterioration and subsequent failure in KO mice is consistent with high levels of tissue-specific Afmid expression in the kidney of WT but not KO mice. On this basis, the most significant function of the kynurenine pathway and Afmid in mice may be in eliminating toxic metabolites and to a lesser extent in providing intermediates for other processes.
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PMID:Effect of arylformamidase (kynurenine formamidase) gene inactivation in mice on enzymatic activity, kynurenine pathway metabolites and phenotype. 1586 19