Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This paper discussed the significance of the activities of purine and pyrimidine salvage enzymes in cancer cells and the targeting against them of chemotherapy. 1. The activities of salvage enzymes in the rat liver were orders of magnitude higher than those of the rate-limiting enzymes of de novo biosynthesis. A similar relationship was observed in rat hepatomas of different growth rates and in primary colon carcinoma in human. 2. The concentrations of nucleosides and nucleobases were measured in plasma, liver and hepatoma 3924A in the rat. The freeze-clamp method was required to determine the concentrations of these precursors in rat liver and hepatoma in a reliable and precise fashion because ischemia markedly altered the concentrations of nucleosides, nucleobases and, as shown earlier, nucleotides in these tissues. The results indicated that the liver markedly concentrated the purine precursors, hypoxanthine, guanine and adenine, but not thymidine, which was one-third that of the plasma. Uridine and deoxycytidine occurred in the same concentration as in plasma, but cytidine was 3-fold higher in liver. In the hepatoma in comparison to the liver the concentrations of the nucleosides and bases were altered and for some of the changes the enzymic differences between liver and hepatoma appeared to be accountable. 3. Kinetic parameters for purine and pyrimidine synthetic enzymes and for the substrates and co-factors were determined in liver and hepatoma 3924A. When enzymic activities were calculated at the tissue steady-state concentrations of the various ligands, the activities of the salvage enzymes were markedly higher than those of the rate-limiting enzymes. 4. Hepatoma cells were highly sensitive to the action of the transport inhibitor, dipyridamole, in lag and log phases. However, plateau phase cells lost their sensitivity to dipyridamole. 5. Amphotericin B rendered plateau phase cells sensitive to the inhibitory action of dipyridamole for the incorporation of thymidine. 6. Amphotericin B enhanced cytotoxicity of dipyridamole in hepatoma and human colon cancer HT-29 cells. 7. In these studies we discovered the decreased responsiveness to dipyridamole of plateau phase cells and the ability of amphotericin B to restore the sensitivity. Moreover, dipyridamole and amphotericin B were synergistic in their cytotoxic action in rat hepatoma cells and human colon cancer cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Salvage pathways as targets of chemotherapy. 367 9

Uridylate-trapping analogs of D-galactose or D-glucose divert the uridylate moiety of UDPglucose and/or UTP to UDP-sugar analogs that accumulate while the pools of UTP and of related pyrimidine nucleotides are depleted. The uridylate-trapping action of sugar analogs is determined by the enzyme pattern of the target tissue. D-Galactose analogs are preferentially metabolized by hepatoma cells and hepatocytes. TA3-mammary tumor cells are susceptible to the action of D-glucosamine and other D-glucose analogs. A high rate of de novo pyrimidine synthesis and/or an active salvage of extracellular uridine compensate for the uridylate-trapping action of sugar analogs and prevent depletion of UTP pools. Accordingly, synergistic actions are induced by combining sugar analogs, such as D-galactosamine or D-glucosamine, with inhibitors of de novo pyrimidine synthesis, such as lapachol or 6-azauridine. Uridylate-trapping by D-galactosamine, acting on hepatocytes, shifts the balance between uridine consumption and uridine release by the liver and results in a fall of uridine and cytidine concentrations in blood plasma (20). Cultured hepatocytes produce uridine and cytidine. Combination of 5-fluorouridine with sugar analogs results in the formation of fluorinated UDP-sugar analogs in hepatoma cells or in mammary tumor cells. Formation of FUDP-sugar analogs transiently removes intracellular FUTP, but FUDP can be released subsequently in glycosyltransferase reactions (22). Pretreatment of hepatoma cells or of TA3-mammary tumor cells with an uridylate-trapping sugar analog in combination with an inhibitor of de novo pyrimidine synthesis enhances the uptake of 5-fluorouridine, its incorporation into RNA, and its growth inhibitory effect. The chemotherapeutic action of 5-fluorouridine in rats and mice, carrying the AS-30D and the TA3 ascites tumor, respectively, is significantly improved by pretreatment with an amino sugar together with 6-azauridine.
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PMID:Potentiation of antimetabolite action by uridylate trapping. 383 24

The purpose of this investigation was to elucidate the factors that regulate the pattern of gene expression in purine and pyrimidine metabolism in normal liver and hepatoma. For this purpose, the action of a hormone, insulin, and the development of resistance to a chemotherapeutic agent, tiazofurin, were studied. This investigation brought detailed evidence showing that in the rat insulin exerted a profound effect on liver purine and pyrimidine metabolism by regulating the concentrations of nucleotides through controlling the activities of strategic enzymes involved in their biosynthesis. When rats were made diabetic by alloxan treatment, in the average liver cell concentrations of ATP, GTP, UTP and CTP decreased to 66, 62, 54 and 63%, respectively, of those of normal liver. Administration of insulin for 2 days returned the hepatic nucleotide concentrations to normal range; further insulin treatment for an additional 5 days raised the concentrations of ATP, GTP, UTP and CTP to 197, 352, 412 and 792% of values observed in the liver of diabetic rats. In diabetic rats the hepatic activities of OMP decarboxylase, orotate phosphoribosyltransferase, uridine phosphorylase, uridine-cytidine kinase and uracil phosphoribosyltransferase decreased to 44, 48, 70, 36 and 41% of the activities of normal liver. Insulin treatment for 2 days returned activities to normal range. Continued insulin treatment for an additional 5 days increased the enzymic activities to 3.9- to 5.3-fold of those of the liver of the diabetic rats. The regulation by insulin treatment of the activities of enzymes of de novo and salvage synthesis of UMP should explain, in part at least, the decline and increase of the uridylate pool in diabetes and after insulin treatment. In the diabetic rat hepatic CTP synthetase, the rate-limiting enzyme of CTP biosynthesis, decreased to 53% and insulin administration for 2 days restored activity to normal range. Insulin treatment for an additional 5 days increased the synthetase activity to 4-fold of the values of the diabetic liver. Thus, the behavior of liver CTP synthetase activity is tightly linked with that of the CTP pool. In the diabetic rat liver, the activity of IMP dehydrogenase, the rate-limiting enzyme of GTP biosynthesis, decreased to 24% of that of the normal liver. Insulin administration for 2 days returned the activity to normal range, yielding a 4.5-fold increase in the activity from the diabetic to the insulin-treated state.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Regulation of purine and pyrimidine metabolism by insulin and by resistance to tiazofurin. 390 7

An impressive array of evidence has been obtained during the past decade establishing correlations between specific DNA adducts and carcinogenesis. Many of the studies utilized organ specific differences in carcinogenesis to establish the correlations. More recently, we have investigated similar relationships between target and nontarget cell populations within the liver. Chronic exposure to methylating hepatocarcinogens predominantly induces hemangiosarcomas, whereas exposure to ethylating agents causes hepatocellular carcinomas. This cell specificity in carcinogenesis correlates well with the presence of promutagenic DNA adducts. In the case of methylating agents, the nonparenchymal cells accumulate O6-methylguanine whereas the hepatocytes do not. Exposure to ethylating agents leads to accumulation of O4-ethyldeoxythymidine, but not O6-ethyldeoxyguanosine in hepatocytes. These differences reflect the ability of the two cell populations to repair O6-alkylguanine and the extent of purine and pyrimidine alkylation with methylating and ethylating agents. Hepatocytes of rats exposed to diethylnitrosamine for 28 days have four to five times more promutagenic DNA adducts (O6-alkyldeoxyguanosine and O4-alkyldeoxythymidine) than hepatocytes of rats exposed to nearly equimolar doses of dimethylhydrazine. Both O6-methylguanine and O4-methyldeoxythymidine are rapidly repaired by rat hepatocytes, while only O6-ethyldeoxyguanosine is rapidly repaired. Studies comparing the relationship between the induction of gamma-glutamyl transpeptidase-positive foci, hepatocellular carcinoma and promutagenic lesions such as O4-ethyldeoxythymidine will be useful in understanding associations between the molecular dosimetry of DNA adducts, initiation, and progression of hepatocarcinogenesis.
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PMID:Relationships between DNA adduct formation and carcinogenesis. 408 20

A clone of cells in which the regulation of purine metabolism is genetically altered was selected and isolated from chemically mutagenized HTC cells (a line of rat hepatoma cells in continuous culture). The clone, designated MAU V, was selected for increased ability to salvage exogenous purines by isolating it in medium containing methylmercaptopurine ribonucleoside, adenine, and uridine, in which medium wild-type cells cannot divide. We have characterized these cells as having an increased rate of de novo purine biosynthesis, apparently as the result of an altered phosphoribosylpyrophosphate (PRPP) synthetase. The altered enzyme has normal catalytic properties but an altered sensitivity to feedback inhibition by purine and pyrimidine nucleotides. The types of inhibitions (competitive and uncompetitive) exerted by AMP, ADP, and TDP on the wild-type enzyme have been maintained in the altered enzyme, but values for K(i) have been increased by factors of 10, 17.5, and 5, respectively. The specific catalytic activities of AMP: pyrophosphate phosphoribosyltransferase and IMP:pyrophosphate phosphoribosyltransferase are normal. The mutant cell may serve as a model for a specific human disease, one type of dominantly inherited overproduction hyperuricemia.
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PMID:Characterization of a feedback-resistant phosphoribosylpyrophosphate synthetase from cultured, mutagenized hepatoma cells that overproduce purines. 435 85

Carbamoyl-phosphate synthetase II [EC 6.3.5.5] of rat ascites hepatoma cells (AH 13), the first and regulatory enzyme of de novo pyrimidine nucleotide biosynthesis, exists as a multienzyme complex (molecular weight, 870,000) with aspartate carbamoyltransferase [EC 2.1.3.2] and dihydroorotase [EC 3.5.2.3] (Mori, M. & Tatibana, M. (1975) J. Biochem. 78, 239-242). The purified complex was phosphorylated by the catalytic subunit of cAMP-dependent protein kinase [EC 2.7.1.37] of rabbit skeletal muscle. The incorporation of 32Pi was 2.2 mol/mol of the complex. The phosphorylation was completely inhibited by the inhibitor protein of the cAMP-dependent protein kinase. Among the substrates and effectors of the enzyme complex tested, only MgUTP, an allosteric inhibitor of carbamoyl-phosphate synthetase II, strongly inhibited the phosphorylation; this inhibition was due probably to the competition of MgUTP with y inhibited by the inhibitor protein of the cAMP-dependent protein kinase. Among the substrates and effectors of the enzyme complex tested, only MgUTP, an allosteric inhibitor of carbamoyl-phosphate synthetase II, strongly inhibited the phosphorylation; this inhibition was due probably to the competition of MgUTP with y inhibited by the inhibitor protein of the cAMP-dependent protein kinase. Among the substrates and effectors of the enzyme complex tested, only MgUTP, an allosteric inhibitor of carbamoyl-phosphate synthetase II, strongly inhibited the phosphorylation; this inhibition was due probably to the competition of MgUTP with the substrate MgATP for the protein kinase. The complex that was phosphorylated by cAMP-dependent protein kinase was dephosphorylated by phosphoprotein phosphatase [EC 3.1.3.16] of rat skeletal muscle. The complex was also phosphorylated by cAMP-independent protein kinase activity present in the extract of AH 13 cells and dephosphorylated by phosphoprotein phosphatase activity of the same origin. These results suggest that the complex is subject to phosphorylation and dephosphorylation in the living cells. Phosphorylation of the complex by cAMP-dependent protein kinase was associated only with a slight change, albeit definite, in the activity of carbamoyl-phosphate synthetase II under the assay conditions. Thus, the physiological significance of phosphorylation-dephosphorylation remains to be further studied.
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PMID:Phosphorylation and dephosphorylation of carbamoyl-phosphate synthetase II complex of rat ascites hepatoma cells. 611 55

Inorganic pyrophosphatase (EC 3.6.1.1) has been purified to electrophoretic homogeneity from the soluble portion of the cytoplasm of rat Hepatoma 3924A and rat liver. It has a specific activity of 600 to 700 mumol inorganic orthophosphate liberated per min per mg protein at 25 degrees, a value in the same range as the highly purified enzymes from yeast and Escherichia coli. By all criteria applied, the hepatoma inorganic pyrophosphatase is identical with the liver enzyme. It is a dimer with subunits with molecular weights of approximately 30,000 to 33,000 and has a pH optimum of 7.4, a Km for pyrophosphate of 5 microM, and a Ka for Mg2+ of 0.3 mM with a pyrophosphate concentration of 0.2 mM. It is not inhibited by high Mg2+ concentrations up to 20 mM. Other metal ions such as Zn2+ and Ca2+ do not activate. Mn2+ activates to less than 10% that of Mg2+ at 0.6 mM and has no effect at 1 mM or higher. In the presence of optimal (4 mM) Mg2+ concentration, Ca2+, Mn2+, Hg2+, and F- at 0.2 mM inhibited strongly, but Zn2+ at 1 mM was not inhibitory. The enzyme had no phosphatase activity toward any of the purine or pyrimidine nucleoside mono-, di-, and triphosphates or toward p-nitrophenyl phosphate, beta-glycerophosphate, glucose 6-phosphate, or glucose 1-phosphate. Bromo- or iodoacetate at high concentration had no inhibitory effect, but p-chloromercuribenzoate and p-chloromercuriphenylsulfonate inhibited strongly at low concentration. The purified enzyme was very unstable but was protected markedly at or above the pH optimum of 7.4 by cysteine, dithiothreitol, and glutathione.
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PMID:Purification and properties of inorganic pyrophosphatase of rat liver and hepatoma 3924A. 612 58

Carbamoyl-phosphate synthetase II of higher animals, the first enzyme of de novo pyrimidine biosynthesis, forms a multienzyme complex with aspartate carbamoyltransferase and dihydroorotase, the second and third enzymes of the pathway. The hypothesis that the complex serves to channel carbamoyl-phosphate, synthesized by the first enzyme of the complex, to the second enzyme was tested using a highly purified complex preparation from Yoshida ascites hepatoma cells (AH 13). Experimentally, aspartate carbamoyltransferase in the complex was allowed to compete with exogenously added ornithine carbamoyltransferase, another carbamoyl-phosphate-utilizing enzyme, for carbamoyl-phosphate which was either synthesized endogenously or added exogenously. The ratios of amounts of the two enzymic products, carbamoyl-aspartate and citrulline, were compared. In the absence of enzyme stabilizers dimethyl sulfoxide or glycerol, a slight channeling of the intermediate in the complex was observed. The further addition of 5-phosphoribosyl 1-pyrophosphate, MgUTP (positive and negative allosteric effectors of carbamoyl-phosphate synthetase II), 30% (v/v) dimethyl sulfoxide or 30% (w/v) glycerol did not affect the extent of channeling. It was slightly increased in the presence of 7.5% (v/v) dimethyl sulfoxide plus 2.5% (w/v) glycerol. Any shift of the assay temperature, pH or concentration of MgATP or of the enzyme complex resulted in little further increase in the extent of channeling. Even when a larger amount of the enzyme complex was used to approximate physiological conditions, there was no increase in the extent of channeling either without or with allosteric effectors. MgUTP even abolished channeling under these conditions. These results indicate that carbamoyl-phosphate can be channeled in the multienzyme complex of AH 13 cells, but the extent of channeling is very small, contrary to expectation.
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PMID:Studies on channeling of carbamoyl-phosphate in the multienzyme complex that initiates pyrimidine biosynthesis in rat ascites hepatoma cells. 613 83

Rat hepatoma cells that have undergone stepwise selection in increasing concentrations of pyrazofurin have coordinately increased levels of both orotate phosphoribosyltransferase (EC 2.4.2.10) and orotidine-5'-phosphate decarboxylase (EC 4.1.1.23) activity. These two activities catalyze the conversion of orotic acid to UMP in de novo pyrimidine biosynthesis. Cells selected in 50 microM pyrazofurin have over 40 times the wild type level for both activities. A single polypeptide of approximately 55,000 daltons is increased in the resistant cells in amounts corresponding to the increase in the two activities. Resistant cell lines that are grown for extended periods in the absence of pyrazofurin are unstable, losing their elevated levels of both enzyme activities and the increased specific protein. Antibody prepared against a purified protein containing both enzyme activities binds specifically to this increased protein. These results corroborate other evidence indicating the two enzyme activities are contained within a single polypeptide called UMP synthase. Poly(A+) mRNA isolated from wild type and resistant lines was analyzed by in vitro translation for production of UMP synthase protein. Immunoprecipitation of the translation products shows the resistant cells have a 17-fold increase in translatable mRNA activity coding for UMP synthase. The synthase accounts for 0.24% of the total in vitro translation products synthesized with poly(A+) mRNA from the pyrazofurin-resistant cells as opposed to 0.014% with wild type mRNA. A cloned UMP synthase cDNA sequence hybridizes strongly to a 1.8-kilobase mRNA in the resistant cells. This mRNA is only barely detectable in equivalent preparations from wild type cells. Quantitation of the mRNA by dot hybridization techniques indicates a 16-fold increase in UMP synthase mRNA in the resistant cells. Although this increase in mRNA for UMP synthase could explain most of the increased protein, it is not sufficient to totally account for the 40-fold increase in UMP synthase.
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PMID:Increased levels of UMP synthase protein and mRNA in pyrazofurin-resistant rat hepatoma cells. 613 25

On the basis of our observation of the increased specific activities of glutamine-utilizing enzymes in purine and pyrimidine metabolism in hepatoma 3924A, and because the concentration of glutamine is ten times lower in the hepatomas than in the liver, the biochemical pharmacology of the anti-glutamine agent, acivicin, was examined. (1) Acivicin competitively inhibited the activities of amidophosphoribosyl-transferase, CTP synthetase and carbamoyl-phosphate synthetase II from extracts of liver and hepatoma 3924A. (2) In addition to the competitive inhibition exerted by acivicin, evidence was obtained that this drug also irreversibly inactivated in vitro the glutamine-utilizing enzymes. It is particularly relevant for the selectivity of acivicin that the activity of aspartate carbamoyltransferase, an enzyme present in the same complex as carbamoyl-phosphate synthetase II, was not affected by the anti-glutamine agent. (3) Acivicin in vivo brought down the activities of glutamine-utilizing enzymes in a period of 10 min to 1 hr after injection. CTP synthetase activity declined to less than 10% of that observed in the uninjected rats. The decreases were not reversible by various in vitro methods, but in vivo the activities returned to normal range in 72 hr. (4) The activity of aspartate carbamoyltransferase, which exists as a multi-enzyme complex with synthetase II, was not altered by acivicin injection. Similar results were observed in transplantable sarcoma in the rat. (5) The acivicin-induced decrease in enzymic activities could not be restored by purification of the enzymes. (6) In vitro studies indicated that addition of acivicin to liver or hepatoma extracts or purified enzymes rapidly decreased enzymic activities; the activities could not be restored. These results are consistent with an interpretation that acivicin acts either as a tight-binding inhibitor or as an inactivator through alkylation of the enzymes of glutamine utilization. (7) Acivicin in combination with actinomycin provided a synergistic kill of hepatoma cells in tissue culture and also inhibited the growth of transplantable solid hepatoma 3924A in the rat. (8) The synergistic biological results of combination chemotherapy with acivicin and actinomycin can be accounted for by the action of acivicin in inhibiting GMP and CTP synthetases, resulting in a decrease in GTP and CTP content, and by the actinomycin-caused inhibition of RNA polymerase in selectively blocking the utilization of GTP and CTP.
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PMID:Multi-enzyme-targeted chemotherapy by acivicin and actinomycin. 618 Jun 9


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