Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The regulation of synthesis of the gluconeogenic cytosolic enzyme phosphoenolpyruvate carboxykinase (PEPCK) and of tyrosine aminotransferase (TAT) by glucagon and glucocorticoid hormones was studied in hepatocytes maintained in suspension culture for 7 h. Specific antibodies were used to measure relative rates of enzyme synthesis after pulse-labelling of the cells with [3H]leucine or [35S]methionine. Concomitantly, amounts of mRNA were quantified after translation in vitro in a reticulocyte lysate and specific immunoprecipitation of the proteins. Glucagon stimulated the rate of synthesis of PEPCK by 4-6-fold and that of TAT by 6-8-fold in 2h. In contrast, dexamethasone had little effect on PEPCK synthesis, whereas it increased TAT synthesis by 5-9-fold. When used in combination, the two hormones displayed additive effects on TAT synthesis, whereas the glucocorticoid hormone strongly potentiated stimulation of PEPCK synthesis by glucagon. In every instance, changes in rates of synthesis of the two enzymes were totally accounted for by increases in amounts of the corresponding functional mRNA, suggesting a pretranslational site of action for both glucagon and dexamethasone.
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PMID:Pretranslational regulation of tyrosine aminotransferase and phosphoenolpyruvate carboxykinase (GTP) synthesis by glucagon and dexamethasone in adult rat hepatocytes. 285 99

The relationship of hepatic ornithine decarboxylase (ODC) activity to cyclic AMP levels and nutritional status was studied in the pre-weanling rat. Previous studies demonstrated that 2 hr without food causes a loss of hepatic ODC induction after glucagon or catecholamine injection. Isoproterenol or glucagon administration produced increased hepatic cyclic AMP and tyrosine aminotransferase activity which were not prevented by nutritional deprivation. Blockade of hepatic beta 2 receptors by the selective antagonist ICI 118,551 prevented increased cAMP levels and ODC activity after isoproterenol administration. Blockade of beta 1 receptors by atenolol did not prevent increased cAMP levels or ODC induction by isoproterenol although it did block activation of cardiac ODC. The phosphodiesterase inhibitor RO20-1724 increased hepatic cAMP levels as well as ODC and TAT activities, although the increase in ODC activity was attenuated by nutritional deprivation. RO20-1724 also potentiated the induction of hepatic ODC after glucagon or isoproterenol administration. Administration of 8-bromo cAMP elevated hepatic ODC activity regardless of nutritional status but also elevated serum levels of growth hormone and corticosterone. Hepatic ODC induction by glucagon or beta 2 agonists can be dissociated from changes in cAMP levels during nutritional deprivation.
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PMID:Hepatic cyclic AMP generation and ornithine decarboxylase induction by glucagon and beta adrenergic agonists. 286 May 51

A simple yet effective method (iso-density percoll centrifugation) has been developed for consistently preparing isolated rat liver parenchymal cells with over 98% initial viability. The method has been applied to cells isolated by a variety of collagenase digestion techniques. This procedure involves the low-speed centrifugation (50 X g) of the initial cell suspension through a percoll medium having a density of 1.06 g/ml and results in the separation of single and viable parenchymal cells from cell aggregates, debris, and nonparenchymal cells. The enriched parenchymal cells have been shown to be superior to untreated cells by a number of criteria including: preparation homogeneity, cell morphology, maintenance of cytochrome P-450, hormonal responsiveness (measured by the induction of tyrosine aminotransferase after treatment with glucagon or dexamethasone, or both), plasma membrane integrity (determined by both trypan blue exclusion and leakage of glutamic-oxaloacetic transaminase), and the DNA repair capability after treatment with benzo[a]pyrene or 2-acetylaminofluorene.
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PMID:Use of a low-speed, iso-density percoll centrifugation method to increase the viability of isolated rat hepatocyte preparations. 287 Oct 8

The quantitative importance of the individual steps of aromatic amino acid metabolism in rat liver was determined by calculation of the respective Control Coefficients (Strengths). The Control Coefficient of tryptophan 2,3-dioxygenase for tryptophan degradation was determined in a variety of physiological conditions and with a range of activities of tryptophan 2,3-dioxygenase. The Control Coefficient varied from 0.75 with basal enzyme activity to 0.25 after maximal induction of the enzyme by dexamethasone. The remainder of the control for tryptophan degradation was associated with the transport of the amino acid across the plasma membrane, with only very small contributions from kynureninase and kynurenine hydroxylase. The Control Coefficients of tyrosine aminotransferase for tyrosine degradation were approx. 0.70 and 0.20 with basal and dexamethasone-induced tyrosine aminotransferase activities respectively; the Control Coefficients of the transport of the amino acid into the cell were 0.22 and 0.58 respectively. Phenylalanine hydroxylase was found to have a Control Coefficient for the degradation of phenylalanine of approx. 0.50 under conditions of basal enzyme activity; after maximal activation by glucagon, the Control Coefficient decreased to 0.12. The transport of phenylalanine was responsible for the remaining control in the pathway. These results have important implications, directly for the regulation of aromatic amino acid metabolism in the liver, and indirectly for the regulation of neuroamine synthesis in the brain.
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PMID:Quantification of the importance of individual steps in the control of aromatic amino acid metabolism. 287 85

In adrenalectomized rats, diacylglycerol, a potent activator of protein kinase C, specifically enhanced the induction of tyrosine aminotransferase and ornithine decarboxylase by even maximally effective doses of dexamethasone phosphate, but itself had no effect on these enzyme inductions in the absence of glucocorticoid. The amplifications of enzyme induction by diacylglycerol was dose-dependent and the time courses of the amplified inductions were similar to those of the inductions by dexamethasone phosphate alone. Since diacylglycerol did not affect the induction of these enzymes by glucagon and insulin, its amplifying effect seemed to be specific for induction by glucocorticoids.
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PMID:Diacylglycerol amplifies the induction in vivo of tyrosine aminotransferase and ornithine decarboxylase by glucocorticoid. 287

Some effects of culturing adult rat hepatocytes on each of four different substrates--laminin (LN), collagen type I (C-I), collagen type IV (C-IV), and fibronectin (FN)--have been investigated under defined conditions. No differential effect on the attachment of the cells to the various substrates was noted; however, the spreading of hepatocytes shortly after initial plating was most strikingly enhanced by FN, whereas LN exhibited little or no such enhancement. The two collagen substrates enhanced the spreading of hepatocytes more than did LN, but less than FN. The different substrates had no differential effect on the induction of tyrosine aminotransferase by dexamethasone and glucagon for at least the first 10 d in culture. The longevity of the hepatocytes was not changed significantly by any of the substrates, at least through the 14th d of culture. During the culture periods the hepatocytes at high cell density were maintained as confluent monolayers, regardless of the substrate on which they had been cultured. After 14 d of culture, gamma-glutamyltranspeptidase activity was highest in cells cultured on C-IV, and lowest in those on FN. DNA synthesis in cultured hepatocytes at a low cell density was highest in cells cultured on FN, with decreasing levels of this parameter in cells cultured on C-IV, C-I, and LN, respectively. These results demonstrate that specific components of the extracellular matrix modulate both differentiated functions and the replication of hepatocytes cultured in serum-free medium.
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PMID:Effects of extracellular matrix components on the growth and differentiation of cultured rat hepatocytes. 288 70

In adrenalectomized rats, the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) markedly enhanced the inductions of tyrosine aminotransferase (TAT) and ornithine decarboxylase by glucocorticoids, even with sufficient concentration of glucocorticoids to have a maximal effect, whereas it had no effect on TAT activity and increased ornithine decarboxylase activity only slightly in the absence of glucocorticoids. Phorbol derivatives and components of TPA such as 4 beta-phorbol, phorbol 12-tetradecanoate, phorbol 13-acetate, and 4-O-methylphorbol 12-tetradecanoate 13-acetate, which have no tumor-promoting activity or ability to activate protein kinase C, did not have any effect on TAT induction by glucocorticoid. TPA enhanced the induction of TAT by various glucocorticoids but had no effect on induction of TAT by glucagon or insulin and did not enhance the induction of glucose-6-phosphate dehydrogenase by 17 beta-estradiol. These results suggest that TPA specifically enhances the induction of TAT and ornithine decarboxylase by glucocorticoids. Similar effects of TPA on TAT induction by glucocorticoid were observed in primary cultures of adult rat hepatocytes. Another activator of protein kinase C, rac-1,2-dioctanoylglycerol, was also found to have similar effects on the cells.
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PMID:Tumor-promoting phorbol ester amplifies the inductions of tyrosine aminotransferase and ornithine decarboxylase by glucocorticoid. 288 1

Epidermal growth factor (EGF) dose-dependently enhanced the induction of tyrosine aminotransferase and tryptophan oxygenase by glucocorticoids in primary cultures of adult rat hepatocytes without itself having any effect on these enzymes in the absence of glucocorticoids. The amplifications were observed even with dexamethasone at high concentrations (10(-6) M-10(-5) M) that had a maximal effect. EGF had no effect on induction of tyrosine aminotransferase by glucagon or Bt2cAMP. The effect of EGF was also observed in adrenal-ectomized and submaxillary gland-ectomized rats. These results suggest that EGF is an endogenous amplifier of the action of glucocorticoids.
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PMID:Epidermal growth factor as a new regulator of induction of tyrosine aminotransferase and tryptophan oxygenase by glucocorticoids. 288 20

We have found many compounds that amplify the action of glucocorticoid without themselves having any glucocorticoid-like action and have proposed the concept of 'Glucocorticoid Action Biomodulators'. These biomodulators consist of 'Glucorticoid Sensitivity Amplifiers', which greatly amplify the action of glucocorticoid at doses of glucocorticoid that alone have minimal effects, and 'Glucocorticoid Potency Amplifiers', which markedly enhance the effect of glucocorticoid at doses that have maximal effects. Potent activators of protein kinase C, such as 1,2-racemic dioctanoylglycerol, 12-o-tetradecanoyl-phorbol-13-acetate, and epidermal growth factor (EGF), markedly enhanced the induction of tyrosine aminotransferase and ornithine decarboxylase by dexamethasone in adrenalectomized rats in vivo and in primary cultures of adult rat hepatocytes in vitro. They amplified enzyme induction by even a large amount of dexamethasone that had a maximal effect, but had no effect in the absence of glucocorticoid. These modes of amplification show that these compounds are 'Glucocorticoid Potency Amplifiers'. They amplified not only enzyme induction in liver but also growth inhibition by glucocorticoid of solid tumor L5178Y lymphoblasts. They specifically amplified the actions of glucocorticoids and did not amplify the actions of other steroids, such as 17-beta estradiol, glucagon and insulin. The induction of tyrosine aminotransferase by glucocorticoid and its amplification by EGF were both inhibited by 1-(5-iso-quinoline-sulfonyl)-2-methylpiperazine, an inhibitor of protein kinase C, and not by N-[2-(methylamino)-ethyl]-5-isoquinoline-sulfonamide, an inhibitor of cyclic nucleotide dependent protein kinases, suggesting that the induction and the amplification are mediated by protein kinase C.
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PMID:Studies on biomodulators of glucocorticoid actions; the nature and the modes of actions of glucocorticoid potency amplifiers. 289 Feb 79

In the liver of suckling rats, the synthesis of hepatic tyrosine aminotransferase, serine dehydratase, and phosphofructokinase 2 as well as of renal beta-glucosidase is controlled by the circulating concentrations of adrenal and pancreatic hormones. Glucagon is capable of stimulating enzyme synthesis only in the presence of a steroid hormone. Dexamethasone and estradiol have been found to exert a permissive function on the inducibility of the studied enzymes by glucagon. Between the hormones of the adrenal medulla and glucagon antagonistic effects in enzyme induction were observed. Obviously, this antagonism is mediated by the alpha 1-adrenergic signal transferring system. A characteristic age dependence of enzyme induction by dexamethasone has been established. This might be correlated to alterations in the degree of methylation of the respective promoters. The methylation inhibitor 5-azacytidine influences significantly the enzyme induction by glucocorticoid hormones.
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PMID:Interaction of adrenal and pancreatic hormones in the control of hepatic enzymes during development. 289 Feb 81


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