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

The intraperitoneal administration of several substances (biliverdin, heat-killed bacteria and diatomaceous earth) to rats caused the prompt appearance of a mitotic wave in the liver. Autoradiographic analysis of livers of treated animals showed no evidence of [3H]-thymidine uptake by mitotic hepatocytes. In addition, livers from xenobiotic-treated rats showed a very low thymidine kinase activity, close to that found in normal livers. This excludes the possibility that non-cycling cells move to mitosis through the S phase. The results suggest that mitosis could be derived from a hepatocyte subpopulation arrested in the G2 phase of the cell cycle, which is stimulated to divide by the xenobiotics.
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PMID:Evidence for arrested G2 cell subpopulation in rat liver inducible to mitosis. 350 28

The estrogenic action of some persistent organochlorine pesticide residues may play a role in the progression of hormonally responsive tumors of the breast and uterus. The prototypical xenoestrogen o,p'-dichlorodiphenyltrichloroethane (o,p'-DDT) acts by binding and activating the estrogen receptor (ER). The present study focuses attention on the mechanisms through which another organochlorine compound, beta-hexachlorocyclohexane (beta-HCH), exerts estrogen-like effects in human breast cancer cells. Both o,p'DDT and beta-HCH stimulated proliferation in a dose-dependent manner in the ER-positive cell lines MCF-7 and T47D but not in the ER-negative lines MDA-MB231, MDA-MB468, and HS578T. Both compounds produced an increase in the steady state level of pS2 mRNA in MCF-7 cells. These responses were equal in magnitude to the maximal effect of estradiol, and they were inhibited by inclusion of the antiestrogen ICI164384. On the other hand, when tested in a competitive binding assay, beta-HCH did not displace 17beta-[3H]estradiol from the ER even at a concentration that was 40,000-fold higher than the tracer steroid. Furthermore, nuclear retention of the ER during homogenization procedures was induced by a 2- or 24-h treatment of MCF-7 cells with o,p'-DDT and 17beta-estradiol but not by treatment with beta-HCH; this indicates that beta-HCH nether activates the ER, nor is it converted intracellularly to an ER ligand. Transcriptional activation by beta-HCH occurs in estrogen-responsive GH3 rat pituitary tumor cells transfected with a luciferase reporter construct driven by a complex 2500-bp portion of the PRL gene promoter; this trans-activation response is inhibited by inclusion of ICI164384. However, beta-HCH is ineffective in stimulating a reporter construct driven only by a consensus estrogen response element and a minimal promoter derived from the herpes simplex virus thymidine kinase gene. Thus, beta-HCH cannot act on a simple, single estrogen response element; rather, it requires the combinatorial regulation found in a complex promoter. These data are consistent with the notion that beta-HCH stimulation of cell proliferation and gene expression is ER dependent, but its action is not through the classic pathway of binding and activating the ER. beta-HCH may represent a new class of xenobiotic that produces estrogen-like effects through nonclassic mechanisms and, therefore, may be of concern with regard to breast and uterine cancer risk.
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PMID:Novel estrogenic action of the pesticide residue beta-hexachlorocyclohexane in human breast cancer cells. 896 93

The aim of this work was to develop a procedure for the lipid-mediated transfection of DNA into normal adult human hepatocytes in culture. Cells were plated in a serum-free culture medium at various cell densities, on plastic or collagen-coated dishes, both in the absence and in the presence of epidermal growth factor (EGF). The cells were incubated for various periods of time with mixtures of DNA-lipofectin or DNA-3 beta[N-(N',N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-chol) liposomes, and the efficiency of transfection was assessed by measuring the activity of reporter genes, beta-galactosidase or chloramphenicol acetyl-transferase (CAT). For comparison, similar experiments were carried out with human cell lines including HepG2, Caco-2, and WRL68. The efficiency of transfection (in percentage of cells) was not significantly different after transfection with lipofectin or DC-chol and comprised between 0.04 and 1.7% (extreme values) for different cultures. The efficiency of transfection decreased as the age or density of the culture increased and increased in cultures treated with EGF. Direct measurement of the rate of DNA synthesis suggested that the efficiency of transfection was related to the number of cells entering the S phase. Under the same conditions, the efficiency of transfection was one to two orders of magnitude greater in the three cell lines. A plasmid harboring 660 bp of the 5'-flanking region of CYP1A1 (containing two xenobiotic enhancer elements) fused upstream of the promoter of thymidine kinase and the CAT reporter gene was constructed. When this plasmid was transfected in human hepatocytes, CAT activity was induced as expected. We conclude that normal adult human hepatocytes can be transfected with exogenous DNA and that the transfected construct is regulated in the manner expected from in vivo studies.
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PMID:Lipid-mediated transfection of normal adult human hepatocytes in primary culture. 912 68

Dehydroepiandrosterone sulfotransferase (SULT2A1) is a cytosolic enzyme that mediates sulfo-conjugation of endogenous hydroxysteroids (dehydroepiandrosterone, testosterone, bile acids), and diverse xenobiotic compounds. Upon sulfonation, SULT2A1 substrates become polar and water-soluble and thus suitable for rapid excretion. SULT2A1 is abundantly expressed in the liver and intestine. Recent evidence has shown that the ligand-activated vitamin D receptor (VDR) can transcriptionally induce the xenobiotic-metabolizing cytochrome P450 enzymes. Herein, we report that VDR also targets SULT2A1 for transcriptional activation. Vitamin D stimulated endogenous SULT2A1 expression and induced transfected human, mouse, and rat SULT2A1 promoters in liver and intestinal cells upon cotransfection with VDR. An inverted repeat DNA element (IR0), located within -191 to -168 positions of mouse and rat Sult2A1, mediates VDR induction of Sult2A1. DNase1 footprinting, competition EMSA, and antibody supershift assay showed that the IR0 is a binding site for the RXR-alpha/VDR heterodimer. Point mutations within the IR0 prevented RXR/VDR binding and abolished VDR-mediated Sult2A1 induction. The IR0 element conferred VDR responsiveness on a thymidine kinase promoter. Thus, VDR-mediated nuclear signaling may be important in the phase II metabolism involving Sult2A1. The rodent Sult2A1 gene is also induced by the farnesoid X receptor (FXR) and pregnane X receptor (PXR) through the same IR0. In competition transfections, FXR or PXR inhibited VDR induction of the IR0. Competitive functional interactions among VDR, PXR, and FXR suggest that the intracellular hormonal and metabolic milieu may determine the extent to which a specific nuclear receptor pathway would influence steroid/xenobiotic metabolism using dehydroepiandrosterone sulfotransferase.
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PMID:Dehydroepiandrosterone sulfotransferase is a target for transcriptional induction by the vitamin D receptor. 1497 51