Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00492 (hypoxanthine-guanine phosphoribosyltransferase)
 2,385 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cytotoxicity and DNA lesions induced by methotrexate (MTX) were compared in wild-type, hypoxanthine-guanine phosphoribosyltransferase-deficient (HGPRT-) and thymidine-kinase-deficient (TK-) HL-60 cells. TK- and HGPRT- cells were approximately 10 and 3 times more sensitive to MTX than wild-type cells, respectively. Following incubation with 2 microM MTX for 16 hr, TK- cells showed a significantly higher number of DNA strand breaks. Concomitantly, DNA fragmentation at the nucleosomal linker region was detected more prominently in TK- cells. Although MTX tended to decrease TTP pools similarly in all 3 cells types, the initial TTP level in TK- cells was only about one-fifth of that found in the wild type. These results indicate that the thymidine salvage pathway has a pivotal role in mediating MTX-induced toxicity and DNA lesions.
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PMID:Increased methotrexate-induced DNA strand breaks and cytotoxicity following mutational loss of thymidine kinase. 201 62

Two protocols have been developed, both of which utilize the thymidine analog 5-bromodeoxyuridine (BrdUrd) to induce mutations in mammalian cells in culture (E. R. Kaufman and R. L. Davidson, Proc. Natl. Acad. Sci. USA 75:4982-4986, 1978; E. R. Kaufman, Mol. Cell. Biol. 4:2449-2454, 1984). The first protocol, termed incorporational (INC) mutagenesis, utilizes high concentrations of BrdUrd in the culture medium to generate a high intracellular ratio of BrdUTP/dCTP. The second protocol, termed replicational (REP) mutagenesis, entails the incorporation of BrdUrd into DNA under nonmutagenic conditions, the removal of all BrdUrd from the culture medium, and the subsequent replication of the bromouracil-containing DNA in the presence of high intracellular levels of dTTP and dGTP. Genetic studies using reversion analysis at the hypoxanthine-guanine phosphoribosyltransferase locus were used to determine whether the mechanisms of these two BrdUrd mutagenesis protocols had enough specificity to be distinguishable by their ability to revert various mutants. The results of these studies indicated that (i) mutants induced by INC mutagenesis were induced to revert only by REP mutagenesis and not by INC mutagenesis, (ii) mutants induced by REP mutagenesis were more efficiently reverted by INC mutagenesis than by REP mutagenesis, and (iii) both spontaneous mutants and mutants induced by the chemical mutagen ethyl methanesulfonate showed a high degree of specificity when tested for reversion by the BrdUrd mutagenesis protocols.
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PMID:Reversion analysis of mutations induced by 5-bromodeoxyuridine mutagenesis in mammalian cells. 383 41

The mechanism of action of acivicin and tiazofurin was compared in hepatoma 3924A. The results were evaluated by assessing the impact of these drugs on primary targets, the activities of key enzymes, and on secondary and tertiary targets, the concentrations of pools of ribonucleotides and deoxyribonucleotides. The action of acivicin entails inhibition and inactivation of the key enzymes of glutamine utilization in the biosynthesis of purines and pyrimidines. As a result, the GTP and CTP pools were markedly depleted, whereas those of ATP and UTP were unaffected. Acivicin also markedly decreased the concentrations of all 4 deoxynucleoside triphosphates. The nucleotide pools returned to normal or near normal range within 2 to 3 days after a single acivicin injection. The pharmacologic targets of acivicin in anticancer chemotherapy include prominently the activities of glutamine-utilizing enzymes and the pools of GTP and CTP and all 4 dNTP's. These biochemical targets also serve as indicators of acivicin action in cancer cells. The action of tiazofurin in hepatoma cells entails the primary target, IMP dehydrogenase. The subsequent effects include marked enlargement of IMP and PRPP pools and depletion of the pools of GDP and GTP. The increased IMP concentration selectively inhibited the activities of hypoxanthine-guanine phosphoribosyltransferase, but did not affect that of adenine phosphoribosyltransferase. The markedly decreased GTP pool de-inhibited the activity of AMP deaminase which permitted the channeling of AMP to IMP. An important indicator of tiazofurin action is the prolonged depletion of dGTP pools and similar but less pronounced declines in the pools of dCTP and dATP. In contrast, dTTP pools were increased. The crucial biochemical targets and indicators of tiazofurin action in sensitive cancer cells include inhibition of IMP dehydrogenase, a decrease in the concentrations of GDP, GTP, dGTP, dCTP, dATP and marked rise in the pools of IMP, PRPP and dTTP. Measurements of the molecular targets and indicators of drug action should be helpful in identifying cancer cells and tissues sensitive or resistant to the action of acivicin or tiazofurin. Identification of the targets and indicators should also be helpful in the design of frequency of administration of the drugs in combatting animal and human neoplasia.
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PMID:Control of enzymic programs and nucleotide pattern in cancer cells by acivicin and tiazofurin. 620 92

dCMP-deaminase-deficient V79/dC hamster cells have highly imbalanced deoxyribonucleoside triphosphate (dNTP) pools, i.e. a 17-fold larger dCTP pool, a slightly reduced dTTP and a very low dGTP pool, compared to dCMP-deaminase-proficient V79/p cells. Nevertheless, the two lines showed the same rates of spontaneous mutation at the hprt and ouabain-resistance loci. Analysis of spontaneous hprt mutations indicated an increase in misincorporation of C in V79/dC cells, although it was not statistically significant. When the dCTP pool was further increased fivefold by incubating V79/dC cells with cytidine, C misincorporation increased to 88%, but the mutation frequency remained unchanged. The dNTP pools of V79/dC cells were also altered by treatment with thymidine, or with thymidine plus deoxycytidine. After incubation with thymidine alone, the dCTP pool all but disappeared, whereas it maintained a normal level in the presence of deoxycytidine. In both cases dTTP rose to nmol amounts, and dGTP accumulated. Incubation with 10 mM thymidine was the only treatment that increased the mutation frequency; T misincorporation then accounted for 94% of the base substitutions. In the presence of deoxycytidine the cells had a dTTP/dCTP ratio of 0.04, but 86% of the base substitutions involved C misincorporation and most probably originated from G mis-incorporation caused by excess dGTP. Alterations of RNA splicing and hot spots for base substitutions varied with the imbalance, the latter showed "next-nucleotide effects". Our results suggest that the fidelity of DNA replication in V79 cells is only affected by large changes in the pool and is more sensitive to changes in dGTP than in dCTP or dTTP.
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PMID:Molecular analysis of mutations in the hprt gene of V79 hamster fibroblasts: effects of imbalances in the dCTP, dGTP and dTTP pools. 756 70

Anaphase promoting complex/cyclosome (APC/C)-mediated proteolysis is essential for chromosome segregation, mitotic exit, and G1 entry. Here, we show the importance of APC/C in the control of dTTP pool size in mammalian cells. Two enzymes, thymidine kinase 1 (TK1) and thymidylate kinase (TMPK), involved in dTTP formation are the targets of the APC/C pathway. We demonstrate that TMPK is recognized and degraded by APC/C-Cdc20/Cdh1-mediated pathways from mitosis to the early G1 phase, whereas TK1 is targeted for degradation by APC/C-Cdh1 after mitotic exit. Overexpression of wild-type TK1 and TMPK induces a four- to fivefold increase in the cellular dTTP pool without promoting spontaneous mutations in the hprt (hypoxanthine-guanine phosphoribosyl transferase) gene. In contrast, coexpression of nondegradable TK1 and TMPK expands the dTTP pool size 10-fold accompanied by a drastic dNTP pool imbalance. Most interestingly, disruption of APC/C proteolysis of TK1 and TMPK leads to growth retardation and a striking increase in gene mutation rate. We conclude that down-regulation of dTTP pool size by the APC/C pathway during mitosis and the G1 phase is an essential means to maintain a balanced dNTP pool and to avoid genetic instability.
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PMID:Control of dTTP pool size by anaphase promoting complex/cyclosome is essential for the maintenance of genetic stability. 1610 19