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)

Nine independently derived clones of mutagenized rat hepatoma cells selected for resistance to 6-mercaptopurine (6-MP) or 6-thioguanine (6-ThioG) have been isolated. Each has severely reduced catalytic activity of hypoxanthine-guanine phosphoribosyltransferase (HPRT) and seven of them possess significantly increased activities of phosphoribosylpyrophosphate (PRPP) synthetase. The degrees of elevations of PRPP synthetase activities do not correlate with the degrees of deficiencies of HPRT activities. The cells from one of these clones, 1020/12, posses 40% of the normal HPRT catalytic activity and overproduce purines. We have extensively examined the cells from this clone. Immunotration studies of 1020/12 cells indicate that there is a mutation in the structural gene for HPRT. Although they possess increased specific catalytic activities of the enzyme. PRPP synthetase, the catalytic parameters, heat stability, and isoelectric pH of PRPP synthetase from 1020/12 cells are indistinguishable from those of the enzyme from wild-type cells. The cause of purine overproduction by 1020/12 cells appears to be the elevated PRPP synthetase activity, rather than a PRPP "sparing" effect stemming from reduced HPRT activity. Support for this idea is provided by the observation that the complete loss of HPRT activity in a clone derived from 1020/12 cells does not further enhance the levels of PRPP synthetase or purine overproduction. We propose that the elevated levels of PRPP synthetase activity in these HPRT deficient cells result from a mutational event in the structural gene for HPRT, and that this causes the disruption of a previously undescribed regulatory function of this gene on the expression of the PRPP synthetase gene.
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PMID:Increased PRPP synthetase activity in cultured rat hepatoma cells containing mutations in the hypoxanthine-guanine phosphoribosyltransferase gene. 17 76

Thymidine kinase-deficient OTT6050 mouse teratocarcinoma cells were fused with hypoxanthine phosphoribosyltransferase-deficient Fu5AH rat hepatoma cells by means of inactivated Sendai virus. The resulting hybrid cells, which were selected in hypoxanthine/aminopterin/thymidine medium, retained almost all of the mouse chromosomes and various numbers of rat chromosomes, and showed many chromosomal rearrangements. The hybrid cells, as well as both parental lines, formed tumors after subcutaneous injection into athymic nude mice. Single rat--mouse hybrid cells from a clonally established subline were transplanted into C57BL6/J mouse blastocysts carrying many genetic markers suitable for the detection of hybrid cell-derived tissue contributions. From 144 blastocysts, each of which was injected with a hybrid cell and then surgically transferred to the uterus of a pseudopregnant foster mother, 62 adult mice developed without any visible coat mosaicism. However, three of these mice showed internal hybrid-cell participation in their livers and a limited number of organs of endomesodermal origin. A tumor classifiable as hemangio endothelioma was found in the liver, the only mosaic tissue, of one of the chimeric mice. Nine different rat-specific enzyme variants were detected in the mosaic organs. A considerable number of variations concerning the presence and quantitative activity of the foreign gene products probably resulted from chromosomal segregation, tissue-specific gene activity, or dosage compensation during differentiation in vivo. Our results demonstrate that cultured malignant rat--mouse hybrid cells differentiate normally and become functionally integrated during development. The appearacne in vivo of certain rat-specific gene products that are not found in the hybrid cells under conditions in vitro indicates differential gene expression of the introduced xenogeneic chromosomes.
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PMID:Xenogeneic gene expression in chimeric mice derived from rat--mouse hybrid cells. 28 11

Nitroarenes are ubiquitous environmental pollutants displaying potent genotoxicity in bacterial and mammalian cells. In this study, 2,4,7-trinitro-9-fluorenone (TNF) was more potent than 1-nitropyrene (1-NP) in eliciting genotoxic responses in 4 mammalian cell lines. All 4 cell types were capable of activating the nitroarenes, since no special incubation conditions were required. Inhibition of normal DNA synthesis and cytotoxicity were significantly increased with TNF in a dose range of 0.2-5 micrograms/ml for human teratocarcinoma (PA1) cells, mouse Sertoli (TM4) cells, rat hepatoma (RL12) cells, and human-Chinese hamster ovary (CHO-K1) cells. For 1-NP, a dose range of 10-20 micrograms/ml was required to achieve comparable results for the respective cell lines. Only the RL12 and CHO-K1 cells showed recovery of normal DNA synthesis when TNF or 1-NP was removed from the medium. The other cell types showed little or no recovery up to 42 h after removal of the nitroarene. In exclusively studying TNF, the induction of sister-chromatid exchanges (SCEs) and a delay in cell cycle as monitored by harlequin chromosomes, were observed at a concentration range of 0.003-0.2 microgram/ml in PA1, TM4, and RL12 cells. In CHO-K1 cells, TNF at 0.001-1 microgram/ml was clearly mutagenic at the hprt locus.
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PMID:Genotoxicity of 1-nitropyrene and 2,4,7-trinitro-9-fluorenone to mammalian cells. 230 77

Segregation of the X-linked mink markers alpha-galactosidase (GLA), phosphoglycerate kinase-1 (PGK1), hypoxanthine phosphoribosyltransferase (HPRT), and glucose-6-phosphate dehydrogenase (G6PD) was analyzed in hybrids of gamma-irradiated mink fibroblasts and Chinese hamster cells and in hybrids of nonirradiated mink fibroblasts and mouse hepatoma cells. Based on this analysis, the order of the four genes is GLA-PGK1-HPRT-G6PD on the mink X chromosome. Cytogenetic analysis of five mink x Chinese hamster hybrid clones containing mink GLA, PGK1, and HPRT, but lacking G6PD, tentatively localized mink G6PD to Xq15.22----qter and also confirmed the gene order as GLA-PGK1-HPRT-G6PD-qter. Comparison of this order with its counterpart in man and the mouse, as well as an analysis of the G-band patterns of their X chromosomes, demonstrated putative similarities between mink and man and differences in the mouse. These differences may be due to a different rate of X-chromosomal rearrangement in mammalian evolution.
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PMID:Subchromosomal localization and order of GLA, PGK1, HPRT, and G6PD loci on the X chromosome of the American mink (Mustela vison). 284 37

Fusion of hypoxanthine phosphoribosyltransferase (HPRT)(-) rat hepatoma cells with HPRT(+) human fibroblasts yielded hybrid clones that grew in HAT selective medium and contained all the rat chromosomes and one to nine human chromosomes. Among the retained chromosomes was the human X chromosome. In all clones backselected in medium containing 8-azaguanine, human X chromosome was absent. Electrophoretic analysis revealed that, without exception, hybrid clones growing in HAT medium had an active HPRT enzyme, either human or rat, or both. When these clones were backselected in 8-azaguanine, they did not show HPRT enzyme activity. Hybrids that contained the human X chromosome also had human glucose-6-phosphate dehydrogenase. The observed reexpression of rat HPRT in hybrid cells derived from HPRT(-) rat cells suggests that a genetic factor from the human cell determined the expression of the rat structural gene for HPRT.
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PMID:Reexpression of the rat hypoxanthine phosphoribosyltransferase gene in rat-human hybrids. 435 57

Tiazofurin, a C-nucleoside, was cytotoxic in hepatoma 3924A cells grown in culture with an LC50 = 7.5 microM. In the culture, a closely linked dose-related response of tumor cell-kill and depletion of GTP pools was observed after tiazofurin treatment. In rats carrying subcutaneously transplanted hepatoma 3924A solid tumors, a single intraperitoneal injection of tiazofurin (200 mg/kg) caused a rapid inhibition of IMP dehydrogenase (EC 1.2.1.14) activity and depleted GDP, GTP, and dGTP pools in the tumor; concurrently, the 5-phosphoribosyl 1-pyrophosphate (PRPP) and IMP pools expanded 8- and 15-fold, respectively. Tiazofurin decreased tumoral IMP dehydrogenase activity and dGTP pools in a dose-dependent manner over a range of 50-200 mg/kg; by contrast, the depletion of GTP and the accumulation of IMP and PRPP pools were near maximum at 50 mg/kg. The increase in PRPP pools may be attributed to an inhibition by IMP of the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8). The IMP dehydrogenase activity and the pools of ribonucleotides returned to the normal range by 24-48 h after the single injection of tiazofurin. However, the markedly depleted dGTP pools remained low for 72 h. Tiazofurin treatment resulted in significant anti-tumor activity in rats inoculated with hepatoma 3924A. The decrease in GTP levels and particularly the sustained depletion in the dGTP pools may explain, in part at least, the chemo-therapeutic action of tiazofurin on hepatoma 3924A. This is the first report showing that a marked therapeutic response was achieved against rapidly growing hepatoma 3924A by treatment with a single anti-metabolite.
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PMID:Modulation of IMP dehydrogenase activity and guanylate metabolism by tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide). 614 52

The rate with which Novikoff rat hepatoma cells took up exogenous hypoxanthine increased sharply towards the end of the logarithmic growth phase, remained high for several hours into the stationary phase, and then decreased again. In an effort to account for these phenomena, several biochemical parameters were monitored during culture growth: the activities of the hypoxanthine transporter, of hypoxanthine phosphoribosyltransferase, and of P-Rib-PP synthetase; and the intracellular concentrations of ATP and P-Rib-PP. All of these parameters remained virtually constant during growth of the culture, except for P-Rib-PP, which increased greater than 10-fold in a pattern similar to that for hypoxanthine uptake. The activities of the transporter, synthetase, and phosphoribosyltransferase remained stable over 7 h of treatment with cycloheximide.
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PMID:The biochemical determinants of hypoxanthine uptake in Novikoff rat hepatoma cells. 618 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

The enzymic capacities of the de novo and the salvage pathways for purine nucleotide synthesis were compared in rat in normal, differentiating, and regenerating liver, and in three hepatomas of widely different growth rates. The activities of the key de novo and salvage enzymes were also determined in mouse lung and Lewis lung carcinoma, in human kidney and liver, and in renal cell carcinoma and hepatocellular carcinomas. A precise and reproducible assay was worked out for measuring the activities of adenine phosphoribosyltransferase (EC 2.4.2.7) and hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8) in crude liver and hepatoma systems. Kinetic studies on the salvage enzymes were carried out in the crude 100,000 X g supernatant fluid from normal liver and rapidly growing hepatoma 3924A. In both tissue extracts, Michaelis-Menten kinetics was observed for adenine phosphoribosyltransferase and HGPRT. The reciprocal plots for 5-phosphoribosyl-1-pyrophosphate (PRPP) of liver and hepatoma enzymes gave apparent KmS of 2 microM for adenine phosphoribosyltransferase and 4 microM for HGPRT, showing two orders of magnitude higher affinities for PRPP than that of the rate-limiting enzyme of de novo purine synthesis, amidophosphoribosyltransferase (EC 2.4.2.14) (Km = 400 to 900 microM). The apparent Km values for adenine of liver and hepatoma adenine phosphoribosyltransferase were 0.6 to 0.9 microM, respectively. For both liver and hepatoma HGPRT, the reciprocal plots for hypoxanthine and guanine yielded the same Km of 3 microM. The specific activities of purine phosphoribosyltransferases were markedly higher than that of amidophosphoribosyltransferase in rat thymus, spleen, testis, bone marrow, colon, liver, kidney cortex, lung, heart, brain, and skeletal muscle, but were lower in the small intestine. In hepatomas and regenerating and differentiating liver, the activities of the salvage enzymes were 2.1- to 32-fold higher than that of amidophosphoribosyltransferase. The purine phosphoribosyltransferase activities were also higher than that of amidophosphoribosyltransferase in Lewis lung carcinoma (8.2- to 32-fold), human renal cell carcinoma (3.5- to 22-fold), and hepatocellular carcinoma (3.4- to 30-fold). The high activities and the high affinity to PRPP of the purine phosphoribosyltransferases might explain the lack of linkage of the behavior of these enzymic activities with proliferation in normal, regenerating, differentiating, or neoplastic tissues. In contrast, the specific activity of the amidophosphoribosyltransferase, which is lower than that of the salvage enzymes, is linked with transformation as it is increased in all examined tumors.4
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PMID:Enzymic capacities of purine de Novo and salvage pathways for nucleotide synthesis in normal and neoplastic tissues. 632 16

The effect of diethylstilbestrol (DES) on sister chromatid exchange (SCE) induction was measured in four cell lines to determine whether metabolic activation of DES is a factor in its genotoxic potential. Two of these, cell lines derived from a human hepatoblastoma (HepG2-GW) and a rat hepatoma (H4-AG), have been shown previously in our laboratory to be capable of metabolizing several procarcinogens to their active forms. DES, in a dose range of 1 X 10(-8) M to 1 X 10(-5) M, increased SCE frequencies by 50 to 60% in both the rat and human hepatoma lines but had no effect on SCE induction in Chinese hamster lung fibroblasts (V79-GW) or human diploid skin fibroblasts (MGH 2C-GW), both of which are nonmetabolizing cell lines. Furthermore, pretreatment of the responsive cell lines (H4-AG and HepG2-GW) with indomethacin, an inhibitor of prostaglandin synthetase-mediated metabolism of DES, effectively prevented the induction of SCE by DES. DES failed to increase the frequency of hypoxanthine-guanine phosphoribosyltransferase locus mutants in H4-AG cells, over a dose range which induced SCE. These observations suggest that DES induces SCE but does not induce gene mutation. These data strongly support growing evidence that metabolic activation of DES may be an important factor in its genotoxic and carcinogenic mechanisms.
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PMID:Induction of sister chromatid exchange by diethylstilbestrol in metabolically competent hepatoma cell lines but not in fibroblasts. 633 58


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