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)

The cytotoxic and genotoxic effects of glutaraldehyde were studied in vitro in the human TK6 lymphoblast cell line and in primary cultures of rat hepatocytes. TK6 lymphoblasts were exposed to glutaraldehyde for 2 hr in serum-free GSH-free media. Cytotoxic effects were observed at concentrations as low as 10 microM with only 10% cell survival at 20 microM. Alkaline elution studies indicated that glutaraldehyde-induced DNA-protein crosslinking increased linearly over the concentration range from 0 to 25 microM. Glutaraldehyde-induced mutations were assessed at the thymidine kinase locus over the same concentration range and reached a plateau at 10 microM of about six times the background mutant frequency. At equivalent levels of DNA-protein crosslinks and cytolethality, glutaraldehyde was mutagenic at approximately a one-seventh lower concentration than the rodent nasal carcinogen formaldehyde (Craft et al.; Mutation Research 176:147-155, 1987). Glutaraldehyde induced a marginal increase in unscheduled DNA synthesis in the in vitro hepatocyte DNA repair assay, but only at the two highest concentrations of 50 and 100 microM, indicating the induction of some DNA excision-repair activity. These data demonstrate that glutaraldehyde exhibits DNA-reactive genotoxic activity that may involve, at least in part, DNA-protein crosslinking in these cell culture models. These findings suggest the need to examine the potential carcinogenic activity of glutaraldehyde in appropriate inhalation studies.
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PMID:Evaluation of the genotoxic potential of glutaraldehyde. 190 74

Testicular expression of the endogenous FSH beta-subunit (FSH beta) and common alpha-subunit (C alpha) genes, as well as a Herpes simplex virus type 1 thymidine kinase (tk) transgene, driven by a 2.3-kilobase fragment of the bovine GSH beta promoter, were studied at messenger RNA and protein level in normal and transgenic mice. A major 3.8-kb species of FSH beta messenger RNA was demonstrated i the normal mouse testis by Northern hybridization. This was longer than the main 1.7-kb FSH beta transcript detected in the pituitary gland. Reverse transcription-polymerase chain reaction, followed by Southern hybridization, demonstrated FSH beta and tk expression in the pituitary gland and gonads of adult normal and transgenic mice, respectively. The C alpha expression was detected by reverse transcription-polymerase chain reaction in the pituitary gland and testis. During development, testicular transcription of the FSH beta and tk genes was initiated simultaneously a few days after birth. Immunocytochemistry of adult testes showed stage-specific positive reaction with FSH beta, C alpha, and tk antisera in the pachytene spermatocytes and type B spermatogonia, but not in Sertoli cells. Positive reaction with these antisera was also seen in the interstitial tissue. These results demonstrate testicular expression of the endogenous FSH subunit genes and confirm that the testicular expression of the FSH beta /tk transgene reflects or its subunits play a paracrine or autocrine role in the regulation of testicular function.
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PMID:The follicle-stimulating hormone (FSH) beta- and common alpha-subunits are expressed in mouse testis, as determined in wild-type mice and those transgenic for the FSH beta-subunit/herpes simplex virus thymidine kinase fusion gene. 758 5

Glutathione (GSH) is an abundant cellular non-protein sulfhydryl that functions as an important protectant against reactive oxygen species and electrophiles, is involved in the detoxification of xenobiotics, and contributes to the maintenance of cellular redox balance. The rate-limiting enzyme in the de novo synthesis of glutathione is gamma-glutamylcysteine synthetase (GCS), a heterodimer consisting of heavy and light subunits expressing catalytic and regulatory functions, respectively. Exposure of HepG2 cells to beta-naphthoflavone (beta-NF) resulted in a time- and dose-dependent increase in the steady-state mRNA levels for both subunits. In order to identify sequences mediating the constitutive and induced expression of the heavy subunit gene, a series of deletion mutants created from the 5'-flanking region (-3802 to +465) were cloned into a luciferase reporter vector (pGL3-Basic) and transfected into HepG2 cells. Constitutive expression was maximally directed by sequences between -202 and +22 as well as by elements between -3802 to -2752. The former sequence contains a consensus TATA box. Increased luciferase expression following exposure to 10 microM beta-NF was only detected in cells transfected with a reporter vector containing the full-length -3802:+465 fragment. Hence, elements directing constitutive and induced expression of the GCS heavy subunit are present in the distal portion of the 5'-flanking region, between positions -3802 and -2752. Sequence analysis revealed the presence of several putative consensus response elements in this region, including two potential antioxidant response elements (ARE3 and ARE4), separated by 34 base pairs. When cloned into the thymidine kinase-luciferase vector, pT81-luciferase, and transfected into HepG2 cells, both ARE3 and ARE4 increased basal luciferase expression approximately 20-fold. When cloned in tandem in their native arrangement the increase in luciferase activity was in excess of 100-fold, suggesting a strong interaction between the two sequences. Luciferase expression was elevated in beta-NF-treated cells transfected with the ARE4-tk-luciferase vector and all DNA fragments containing ARE4. In contrast, ARE3 did not direct increased luciferase expression in response to beta-NF nor did it significantly modify the magnitude of induction directed by ARE4. The influence of the ARE4 oligonucleotide on constitutive and induced expression was eliminated by introduction of a single base mutation, converting the core ARE sequence in ARE4 from 5'-GTGACTCAGCG-3' to 5'-GGGACTCAGCG-3'. When introduced into the full-length -3802:+465 segment, the same single base mutation also eliminated both functions. Collectively the data indicate that the constitutive and beta-NF-induced expression of the human GCS heavy subunit gene is mediated by a distal ARE sequence containing an embedded tetradecanoylphorbol-13-acetate-responsive element.
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PMID:Constitutive and beta-naphthoflavone-induced expression of the human gamma-glutamylcysteine synthetase heavy subunit gene is regulated by a distal antioxidant response element/TRE sequence. 905 46

In the present study the molecular mechanisms underlying tetradecanoylphorbol-13-acetate (TPA) mediated regulation of the human gamma-glutamyltransferase (GGT) gene were examined. TPA challenge of HeLa cells resulted in an increase of GGT mRNA and enzyme activity. Deletion analysis of the promoter revealed that the -348 to +60 fragment was able to mediate TPA induced expression. Gel shift and supershift analyses showed that TPA treatment increased nuclear protein binding to a putative AP-1 site (-225 to -214) and that c-Jun was part of the complex. This AP-1 element, when cloned either in its native arrangement or as tandem repeat 5' of the minimal thymidine kinase promoter, mediated a significant increase of luciferase activity after TPA treatment of transfected HeLa cells, while its mutated counterpart abolished the induction. The same AP-1 element was able to mediate TPA induced expression in HepG2 cells. Collectively these results indicate that like other GSH metabolising enzymes, GGT too is a target for AP-1 mediated regulation.
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PMID:Phorbol ester regulation of the human gamma-glutamyltransferase gene promoter. 1468 60

The formation of dihydroxythalidomide and glutathione (GSH) conjugate(s) of 5-hydroxythalidomide was investigated in chimeric mice modified with "humanized" liver: novel humanized TK-NOG mice were prepared by the introduction of thymidine kinase, followed by induction with ganciclovir, and human liver cells were transplanted. Following oral administration of racemic thalidomide (100 mg/kg), plasma concentrations of 5-hydroxy- and dihydroxythalidomide were higher in humanized mice than in controls. After administration of 5-hydroxythalidomide (10 mg/kg), higher concentrations of dihydroxythalidomide were detected. These results indicate that livers of humanized mice mediate thalidomide oxidation, leading to catechol and/or the GSH conjugate in vivo and suggest that thalidomide activation occurs.
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PMID:In vivo formation of dihydroxylated and glutathione conjugate metabolites derived from thalidomide and 5-Hydroxythalidomide in humanized TK-NOG mice. 2226 28