Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hydroxyurea inhibited the growth and DNA synthesis of Toxoplasma gondii growing in human fibroblast cells. A concentration of 18 micrograms/ml totally suppressed plaque formation. The synthesis of T. gondii RNA was not acutely inhibited. The parasite was equally sensitive to hydroxyurea when grown in wild type or hydroxyurea resistant host cells. With the aid of chemical mutagenesis, we isolated a stable hydroxyurea resistant mutant of T. gondii. This mutant showed no increased ability to incorporate [3H]uracil into its pyrimidine deoxynucleotide pool. Hydroxyurea depressed the [3H]uracil labeling of the pyrimidine deoxynucleotide pool in the wild type parasite but not in the mutant, suggesting that the mutant ribonucleotide reductase was resistant to the inhibitory effect of the drug.
Mol Biochem Parasitol 1982 Sep
PMID:Hydroxyurea inhibition of growth and DNA synthesis in Toxoplasma gondii: characterization of a resistant mutant. 618 67

Cell-free DNA synthesis was performed in a lysed cell system from mouse cell cultures. The in vitro reaction was totally inhibited by N-ethylmaleimide but unaffected by hydroxyurea or fluorodeoxyuridine when these compounds were added to the incubation mixture. However, in a preparation obtained from cells which had been blocked by hydroxyurea before lysis, the rate of DNA synthesis was markedly reduced. This effect could not have been caused by the depletion of the precursor pools as all necessary triphosphates were added to the in vitro incubation mixture. Analysis by alkaline density gradients showed that the ligation of primary synthesis products is retarded in hydroxyurea-pretreated lysed cells and that small fragments accumulate. These results suggest that hydroxyurea interferes with the processing of early replication products, preventing the formation of longer intermediates. Its mechanism is either independent from the well-known inhibition of ribonucleoside diphosphate reductase or it may be the result of an as-yet-unknown function of this enzyme in a later step of replication. This observation could help to explain why cells appear to be blocked by hydroxyurea in the early part of the S phase (rather than at the G1/S border proper) and also why DNA repair synthesis is relatively insensitive to the drug.
Mol Cell Biol 1983 Mar
PMID:Does hydroxyurea inhibit DNA replication in mouse cells by more than one mechanism? 622 Nov 89

The inhibitors of DNA synthesis, 5-fluoro-2'-deoxyuridine and hydroxyurea, caused an inhibition of thymidine kinase, replicative DNA polymerase and CDP reductase activities in stimulated lymphocytes when they were exposed to the inhibitors during the early transformation period (0-17 hr). However, the enzyme activities were unaffected when the inhibitors were added to cells stimulated for more than 17 hr. As opposed to these enzymes the deoxycytidylate deaminase activity was unaffected by the inhibitors during the entire transformation period (0-28 hr). This indicates a close regulatory mechanism in lymphocytes between DNA synthesis and induction of enzymes involved in DNA replication. The inhibitory mechanism exerted by the inhibitors is for the moment unknown. It might be independent of the well-known inhibition of the target enzymes, thymidylate synthetase and ribonucleoside diphosphate reductase, since there was no immediate apparent correlation in time between depletion of the pool sizes and the inhibition of the enzyme activities.
Mol Cell Biochem 1984 Jun
PMID:Effect of 5-fluoro-2'-deoxyuridine and hydroxyurea on the phytohemagglutinin-induced increase of thymidine kinase, replicative DNA polymerase, deoxycytidylate deaminase and CDP reductase activities in human lymphocytes. 623 43

Metaphase chromosomes purified from a hydroxyurea-resistant Chinese hamster cell line were able to transform recipient wild-type cells to hydroxyurea resistance at a frequency of 10(-6). Approximately 60% of the resulting transformant clones gradually lost hydroxyurea resistance when cultivated for prolonged periods in the absence of drug. One transformant was subjected to serial selection in higher concentrations of hydroxyurea. The five cell lines generated exhibited increasing relative plating efficiency in the presence of the drug and a corresponding elevation in their cellular content of ribonucleotide reductase. The most resistant cell line had a 163-fold increase in relative plating efficiency and a 120-fold increase in enzyme activity when compared with the wild-type cell line. The highly hydroxyurea-resistant cell lines had strong electron paramagnetic resonance signals characteristic of an elevated level of the free radical present in the M2 subunit of ribonucleotide reductase. Two-dimensional electrophoresis of cell-free extracts from one of the resistant cell lines indicated that a 53,000-dalton protein was present in greatly elevated quantities when compared with the wild-type cell line. These data suggest that the hydroxyurea-resistant cell lines may contain an amplification of the gene for the M2 subunit of ribonucleotide reductase.
Mol Cell Biol 1983 Jun
PMID:Chromosome-mediated gene transfer of hydroxyurea resistance and amplification of ribonucleotide reductase activity. 630 22

Human T leukemic lymphocytes are highly susceptible to growth inhibition by dAdo. We have investigated this phenomenon using analytical DNA flow cytometry. By using (a) bromodeoxyuridine quenching of Hoechst 33342 fluorescence and (b) the drug ICRF-159, a selective G2 - M-blocking agent, we show that dAdo causes a G1 block in cultured T leukemic cells and that cells in the S phase exposed to dAdo are able to complete that S phase, pass through G2 + M, and return to the G1 phase. Centrifugal elutriation was used to enrich cells for various phases of the cell cycles. dAdo caused elevation of the dATP pool to a similar extent in G1, S, and G2 - M-enriched cell fractions, but did not cause a fall in the dCTP pool. These findings indicate that dAdo induces a G1 block via elevation of dATP pools, apparently independently of inhibition of ribonucleotide reductase.
Mol Pharmacol 1984 Sep
PMID:Analytical DNA flow cytometric analysis of deoxyadenosine toxicity in cultured human leukemic lymphoblasts. 633 78

Mammalian ribonucleotide reductase catalyzes the rate-limiting for the de novo synthesis 2'-deoxyribonucleoside 5'-triphosphates. There is some suggestion that this step may also be the rate-limiting step of DNA synthesis. It is apparent that the level of the enzyme, ribonucleotide reductase, varies through the cell cycle and is highest in those tissues with the greatest proliferation rate. This increase in activity is associated with increased protein synthesis. The purified enzyme has been shown to be subject to strict allosteric regulation by the various nucleoside triphosphates and it has been proposed that allosteric regulation plays an important role in the level of ribonucleotide reductase activity which is expressed. All experimental data relating to this point, however, do not support the role of deoxyribonucleoside triphosphates as a major factor in determining cellular reductase activity during normal cell division. Several naturally occurring factors have been isolated from cells which lower ribonucleotide reductase activity in vitro. These factors have been found in tissues of low growth fraction and appear to be absent or low in tissues or high growth fraction such as tumor, regenerating liver and embryonic tissues. The expression of intracellular ribonucleotide reductase activity is therefore controlled at various levels and by various factors and the prevailing mode of regulation may vary throughout the cell cycle transverse and also in the various types of cells.
Mol Cell Biochem 1983
PMID:Regulation of ribonucleotide reductase activity in mammalian cells. 635 95

An RNA-DNA hybridization assay was used to quantitate the ribonucleoside diphosphate reductase mRNA synthesis (nrd mRNA) to show that gene expression was dependent on protein synthesis. The increased nrd mRNA synthesis induced by inhibition of DNA synthesis was eliminated by simultaneous inhibition of protein synthesis. It was further found that protein synthesis is required not only initially but continuously during DNA inhibition for increased expression of nrd mRNA synthesis.
Mol Gen Genet 1984
PMID:Requirement of protein synthesis for the induction of ribonucleoside diphosphate reductase mRNA in Escherichia coli. 636 81

Two mutator genes of mammalian cells were demonstrated. One was associated with the ribonucleoside diphosphate reductase, and the other was associated with an extreme adenosine sensitivity.
Mol Cell Biol 1981 Jun
PMID:Mutator genes of baby hamster kidney cells. 696 10

9-beta-D-Arabinofuranosyl-2-fluoroadenine (2-F-araA) inhibited the growth in vitro of HeLa cells by 50% at a concentration of 0.25 microM and depressed the replication of herpes simplex virus Types 1 and 2 by 99% at 25 microM. The analogue served as a substrate for cytoplasmic but not mitochondrial deoxycytidine (dCyd) kinase partially purified from human peripheral chronic lymphocytic leukemic blast cells. The Km values of dCyd and 2-F-araA for the cytoplasmic enzyme were 5 microM and 213 microM, respectively. However, at concentrations of 0.4 mM, the analogue was phosphorylated 2.9 times faster than dCyd. The 5'-triphosphate of 2-F-araA was examined for its biochemical effects on partially purified ribonucleotide reductase and highly purified DNA alpha- and beta-polymerases from HeLa cells. 2-F-araATP was a potent inhibitor of ribonucleotide reductase; the concentration required for 50% inhibition of ADP reduction (0.3 mM ADP; 5 mM GTP or dGTP) was 1 microM and for CDP reduction (0.15 mM CPD; 5 mM ATP) was 8.5 microM. Furthermore, 2-F-araATP was a competitive inhibition (Ki = 1.2 microM) with respect to dATP (Km = 3.8 microM) of DNA alpha-polymerase, whereas DNA beta-polymerase was relatively insensitive to the drug. The results suggest that the cytotoxic actions of 2-F-araA may be due, in part, to a "self-potentiating" inhibition of DNA synthesis. This is, by inhibiting the formation of competing dATP, 2-F-araATP may potentiate its inhibition of DNA synthesis.
Mol Pharmacol 1982 Mar
PMID:In vitro biological activity of 9-beta-D-arabinofuranosyl-2-fluoroadenine and the biochemical actions of its triphosphate on DNA polymerases and ribonucleotide reductase from HeLa cells. 704 62

Although a number of transfection experiments have suggested potential targets for the action of the E2F1 transcription factor, as is the case for many transcriptional regulatory proteins, the actual targets in their normal chromosomal environment have not been demonstrated. We have made use of a recombinant adenovirus containing the E2F1 cDNA to infect quiescent cells and then measure the activation of endogenous cellular genes as a consequence of E2F1 production. We find that many of the genes encoding S-phase-acting proteins previously suspected to be E2F targets, including DNA polymerase alpha, thymidylate synthase, proliferating cell nuclear antigen, and ribonucleotide reductase, are indeed induced by E2F1. Several other candidates, including the dihydrofolate reductase and thymidine kinase genes, were only minimally induced by E2F1. In addition to the S-phase genes, we also find that several genes believed to play regulatory roles in cell cycle progression, such as the cdc2, cyclin A, and B-myb genes, are also induced by E2F1. Moreover, the cyclin E gene is strongly induced by E2F1, thus defining an autoregulatory circuit since cyclin E-dependent kinase activity can stimulate E2F1 transcription, likely through the phosphorylation and inactivation of Rb and Rb family members. Finally, we also demonstrate that a G1 arrest brought about by gamma irradiation is overcome by the overexpression of E2F1 and that this coincides with the enhanced activation of key target genes, including the cyclin A and cyclin E genes.
Mol Cell Biol 1995 Aug
PMID:Cellular targets for activation by the E2F1 transcription factor include DNA synthesis- and G1/S-regulatory genes. 762 16


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