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 carboxyl-terminal one-third of human topoisomerase II polypeptide expressed in Escherichia coli was used as antigen to generate polyclonal antibodies in rabbits. With the use of antiserum, DNA topoisomerase II levels of phytohemagglutinin-stimulated human lymphocytes were measured by immunoblotting. Our results showed that the increase in intracellular topoisomerase II level paralleled the entry of cells into proliferation. We also found that the increase in the topoisomerase II level resulted from an increase in the amount of topoisomerase II mRNA. The time course study indicated that the appearance of topoisomerase II mRNA was first observed at 36 h after phytohemagglutinin stimulation. The maximal level of topoisomerase II mRNA was seen at 45 h after stimulation. The same RNA blot was rehybridized with a thymidine kinase probe. The maximal level of thymidine kinase mRNA was observed at 39 h after phytohemagglutinin stimulation. In a comparison of the time course of topoisomerase II gene expression with that of [3H]thymidine incorporation and thymidine kinase gene expression, it was found that the expression of the topoisomerase II gene was later than the onset of DNA replication. Thus, this study suggests that topoisomerase I, which is constantly expressed throughout the cell cycle, might participate in the initiation of DNA replication, while topoisomerase II is involved in solving the DNA topological problems accompanying DNA strand separation during DNA replication.
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PMID:Induction of topoisomerase II gene expression in human lymphocytes upon phytohemagglutinin stimulation. 216 62

CPT-11 [7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin ] is a prodrug that is converted to the active metabolite SN-38 by carboxylesterases. In its active form, the drug inhibits topoisomerase I, causes DNA damage, and induces apoptosis. Data in this study show metabolism of CPT-11 to SN-38 (7-ethyl-10-hydroxycamptothecin) by a rabbit liver carboxylesterase in vitro and growth-inhibitory activity of the products of the reaction. Additionally, stable expression of the cDNA encoding this protein in Rh30 human rhabdomyosarcoma cells increased the sensitivity of the cells to CPT-11 8.1-fold. We propose that this prodrug/enzyme combination can be exploited therapeutically in a manner analogous to approaches currently under investigation with the combinations of ganciclovir/herpes simplex virus thymidine kinase and 5-fluorocytosine/cytosine deaminase.
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PMID:Overexpression of a rabbit liver carboxylesterase sensitizes human tumor cells to CPT-11. 942 50

The expression of seven enzymes involved in the biosynthesis of DNA was measured in HL-60 promyelocytic leukemia cells treated with dimethylsulfoxide (DMSO) or all-trans retinoic acid (RA) to gain information on their role in the termination of proliferation in cells undergoing granulocytic differentiation. The steady-state levels of the mRNAs for topoisomerase I, topoisomerase II. DNA polymerase-alpha, thymidylate synthase, thymidine kinase and hypoxanthine-guanine phosphoribosyltransferase progressively declined from day 3 to day 7 of exposure to the polar solvent or the retinoid suggesting that the expression of these enzymes is coordinately regulated. In contrast, a pronounced difference between the two inducers of differentiation occurred in the expression of the mRNA of the M2 subunit of ribonucleotide reductase, with DMSO causing virtually complete inhibition of the expression of the M2 subunit of the enzyme from day 5 through day 7, with no change in the steady-state levels of the mRNA being produced by retinoic acid. Measurement of the enzymatic activities of two of these catalysts, thymidylate synthase and thymidine kinase, in cells exposed to the two inducers of maturation corroborated the findings at the level of the mRNAs, with corresponding decreases in the activity of these enzymes. The findings collectively demonstrate that the down-regulation of the expression of a relatively wide variety of enzymes involved in DNA replication occurs as late events in the granulocytic differentiation of HL-60 cells, ensuring that cellular replication cannot occur in terminally differentiated cells.
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PMID:Regulation of the expression of enzymes involved in the replication of DNA in chemically-induced granulocytic differentiation of HL-60 leukemia cells. 968 95

The expression of a number of housekeeping enzymes of DNA biosynthesis was measured in HL-60 promyelocytic leukemia cells undergoing monocytic/macrophagic differentiation following treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) or 1alpha,25-dihydroxyvitamin D3 (vitamin D3). Progressive decreases in the steady-state levels of the mRNAs for thymidylate synthase, topoisomerase II, and hypoxanthine guanine phosphoribosyltransferase occurred following exposure to TPA or vitamin D3. In contrast, the steady-state levels of the mRNAs for thymidine kinase, topoisomerase I, and DNA polymerase-alpha did not decrease until days 3-5 of treatment with vitamin D3 and then progressively declined thereafter. The mRNAs for thymidine kinase and topoisomerase I decreased slightly and the mRNA for DNA polymerase-alpha by 30-40%, and then remained constant between days 1 to 3 of treatment with the phorbol ester. The M2 subunit of ribonucleotide reductase exhibited an even greater difference, with no change in the steady-state concentration of mRNA over 3 days of exposure to TPA or vitamin D3. On days 5-7 of treatment with vitamin D3, essentially complete loss of the expression of the mRNA for the M2 subunit of ribonucleotide reductase occurred. Measurement of the enzymatic activities of thymidylate synthase and thymidine kinase in cells exposed to either of the inducers of maturation corroborated the findings at the level of the mRNAs, with corresponding decreases in the activity of these enzymes. The results indicate that the down-regulation of the expression of housekeeping enzymes of DNA replication occurs as late events in HL-60 cells undergoing monocytic/macrophagic differentiation, implying that the decreases in their gene expression are the result of the termination of proliferation rather than an initiating event in the cessation of DNA biosynthesis.
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PMID:Regulation of the expression of enzymes involved in the replication of DNA in chemically induced monocytic/macrophagic differentiation of HL-60 leukemia cells. 968 96