Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.1.49 (phosphoenolpyruvate carboxykinase)
4,654 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nuclei isolated from H4IIE rat hepatoma cells were used in an in vitro run-on assay, with probes directed against various regions of the phosphoenolpyruvate carboxykinase [GTP: oxaloacetate carboxy-lyase (transphosphorylating); EC 4.1.1.32] gene, to analyze whether transcription proceeds uniformly across this gene in response to insulin and cAMP treatment. Fewer polymerase II complexes were associated with the phosphoenolpyruvate carboxykinase gene after insulin treatment, as compared with cAMP-treated cells, but they were distributed uniformly, so insulin does not block transcription at a discrete site, nor does it cause gradual, but progressive, premature termination. The phosphoenolpyruvate carboxykinase primary transcript was synthesized at a rate of about 2500 nucleotides per min in cAMP-treated cells and about 1000 nucleotides per min in insulin-treated cells. Thus insulin retards transcript elongation in comparison with cAMP, but this action does not account for the total effect insulin has on transcription. After insulin treatment, few, if any, nascent transcripts are associated with the first 69 nucleotides of the gene, whereas in cAMP-treated cells the opposite is true. These observations lead us to suggest that both insulin and cAMP exert their primary effects directly at the level of transcription initiation, but in opposite ways.
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PMID:Regulation of phosphoenolpyruvate carboxykinase gene transcription by insulin and cAMP: reciprocal actions on initiation and elongation. 283 22

It is now well established that cAMP induces the transcription rate of the gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) and that this induction is dependent on a nucleotide domain located within the promoter-regulatory region of the gene (Short, J. M., Wynshaw-Boris, A., Short, H. P., and Hanson, R. W. (1986) J. Biol. Chem. 261, 9721-9726). We report here that cAMP also stabilizes phosphoenolpyruvate carboxykinase mRNA against degradation. Using two independent experimental approaches, we show that the half-life of the mRNA for phosphoenolpyruvate carboxykinase is extended when FTO-2B rat hepatoma cells are exposed to dibutyryl cyclic AMP (Bt2cAMP). In the first experiment, the rate of decay of phosphoenolpyruvate carboxykinase mRNA was determined in cells incubated in the presence of insulin, which has been shown to block the transcription rate of the gene for the enzyme. Under these conditions, the half-life of phosphoenolpyruvate carboxykinase mRNA was 30 min. However, in cells incubated in the presence of Bt2cAMP, the mRNA decayed with a half-life of 150 min. In the other experiment, mRNA stability was measured under steady state conditions, utilizing a "pulse-chase" approach. The apparent half-life of phosphoenolpyruvate carboxykinase mRNA increased from 40 min to over 250 min in Bt2cAMP-treated cells. No significant change in the stability of total cellular RNA was noted. Other experiments have shown that the transcription rate of the gene for phosphoenolpyruvate carboxykinase peaks within the first 20 min after exposing the cells to Bt2cAMP and then levels off, while the abundance of the mRNA reaches a maximum at about 90 min and remains at this level thereafter. Thus, the long term effect of cAMP on the expression of the gene coding for phosphoenolpyruvate carboxykinase occurs at least in part, through an alteration in the degradation rate of the mRNA for this enzyme.
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PMID:Cyclic AMP stabilizes the mRNA for phosphoenolpyruvate carboxykinase (GTP) against degradation. 283 95

In summary, the surges of glucagon and epinephrine at birth, coupled with the fall in insulin secretion, are in accord with appropriate receptor changes, as well as genetic ontogenic patterns of enzyme development. Enzyme activities are further stimulated by the hormonal changes at birth; phosphorylase is activated by glucagon and epinephrine, while PEPCK is activated by glucagon and its expression is facilitated by the fall in insulin. In concert, these changes permit rapid activation of catabolic processes and the mobilization and utilization of endogenous fuel stores. Glucose homeostasis is maintained by glycogenolysis and gluconeogenesis supported by the appropriate enzyme inductions. The free fatty acids released, via lipolysis, also serve to sustain gluconeogenesis, since hepatic fatty acid oxidation is necessary for gluconeogenesis by providing the essential cofactors. This framework permits a rational interpretation of the mechanisms underlying the remarkable transition from intrauterine dependence on maternal glucose to extrauterine autonomy of newborn energy integration. This framework can also explain several causes of neonatal hypoglycemia and act as a base for future investigations.
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PMID:Carbohydrate metabolism. 283 6

Plasma insulin (I), glucagon (G) and glucose, hepatic glycogen, fructose 2, 6-bisphosphate (F2, 6-P2), fructose 1, 6-bisphosphate, phosphoenolpyruvate, and some liver key enzymes involved in glycolysis (6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase (6-PF-2kinase/F-2,6-P2ase), activity ratio (velocity at suboptimal substrate concentration/maximum velocity) of pyruvate kinase (PK-L] and in gluconeogenesis (phosphoenolpyruvate carboxykinase activity) have been compared in young (2 months) and old (16 months) rats upon starvation or transition to a high protein (HP) diet. In the 10 and 24 hours after the dietary switch, plasma glucose decreased less and hepatic glycogen was less depleted in the old rats. The ratios of plasma I/G and of hepatic 6-PF-2kinase/F-2,6-P2ase were higher in the old rats and their decrease delayed at both time points, as was the concentration of hepatic F-2,6-P2 and the activity ratio of PK-L (before and after removal of endogenous noncovalent factors). The consistency of these differences indicate that the mechanisms for control of glycolysis/gluconeogenesis are similar in young and old rats, but it appears that in old rats starved or fed HP diet, the switch from glycolysis to gluconeogenesis is delayed. This suggests that as a result of the slowness of the hormonal changes the process of phosphorylation/dephosphorylation, which is so important in the short-term regulation of the glycolysis/gluconeogenesis pathway, may be impaired with age.
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PMID:Age-dependent changes in rat hepatic fructose 2, 6-bisphosphate, 6-phosphofructo-2-kinase/fructose 2, 6-bisphosphatase and pyruvate kinase activity in response to a high protein diet or starvation. 284 Nov 76

Two H4IIE hepatoma cell genes, phosphoenolpyruvate carboxykinase (PEPCK) and gene 33 (g33), are reciprocally regulated by insulin. Quantitation of mRNAPEPCK and mRNAg33 in total RNA isolated from cells treated with insulin showed a 7-fold increase in mRNAg33 amount and a 3-fold decrease of mRNAPEPCK. The cAMP analog 8-(4-chlorophenylthio)-cAMP induced mRNAPEPCK but had no effect on mRNAg33. The responses to various insulins and related molecules showed that the insulin receptor mediates the effects of physiologic concentrations of insulin on each of these genes. This inverse pattern of regulation by insulin was further characterized by determining the transcription rates of both genes in nuclei isolated at various times after the addition of insulin and 8-(4-chlorophenylthio)-cAMP to H4IIE cells. Insulin increased the rate of synthesis of mRNAg33 from 35 to 354 ppm and decreased the synthesis of mRNAPEPCK from 1175 to 109 ppm. These effects of insulin occurred rapidly and reached their maxima by 60 min. In both cases, greater effects were observed as insulin concentrations were increased from 10(-12) to 10(-8) M. Although the effects of insulin were concentration-dependent for both genes, the PEPCK gene was significantly more sensitive to low concentrations of insulin than was gene 33. The reciprocal effects of insulin on the synthesis of mRNAPEPCK and mRNAg33 in H4IIE cells provide a means of investigating how a hormone can exert opposing effects on two genes in the same cell.
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PMID:Reciprocal regulation of gene transcription by insulin. Inhibition of the phosphoenolpyruvate carboxykinase gene and stimulation of gene 33 in a single cell type. 284 5

Hepatoma cells were infected with replication-incompetent murine retroviruses containing the selectable gene for amino-3'-glycosyl phosphotransferase (neo) and/or the nonselectable gene for bovine growth hormone (bGH). Expression of these genes was controlled by the promoter regulatory region of the gene for the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) from the rat, which contains hormone and tissue-specific regulatory elements. Expression of the transduced PEPCK-neo gene was stimulated by Bt2cAMP and glucocorticoids and inhibited by insulin. The amount of RNA which initiated within the retroviral 5' long terminal repeat (5' LTR) was inhibited when internal promoters were present in the retroviral vector. When no internal promoter was present, expression from the 5' LTR was higher and stimulated by glucocorticoids, due to the presence of a glucocorticoid regulatory element in the 5' LTR. Infection of cells with retroviruses altered the basal expression and hormonal regulation of the endogenous PEPCK gene, but had no effect on the expression of the tyrosine aminotransferase gene, which is regulated in a similar manner by cAMP and glucocorticoids. A segment of the PEPCK promoter acted as a hormonally regulated enhancer, bringing the SV40 early promoter under the control of Bt2cAMP. A second, nonselectable gene (PEPCK-bGH), contained in the retroviral vector together with PEPCK-neo, was expressed and regulated appropriately when introduced into hepatoma cells. The proviruses were initially integrated randomly into the host cell genome, but after prolonged selection for expression of the transduced PEPCK-neo gene, cells were selected which contain a predominant site(s) of integration. Among populations of cells, however, the predominant site(s) of proviral integration was different. The selection of cells with a specific site of integration from a population was accelerated by the presence of PEPCK promoter sequences in the provirus. Despite the need to better characterize their effects on the host cell, retroviruses appear to be versatile tools for the specific introduction of regulated genes into cells.
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PMID:Hormonal regulation of chimeric genes containing the phosphoenolpyruvate carboxykinase promoter regulatory region in hepatoma cells infected by murine retroviruses. 284 79

Cyclic AMP plays a major, if not primary, role in the regulation of hepatic gluconeogenesis. The cyclic nucleotide acts on two levels. First, cAMP levels determine the phosphorylation state of key regulatory enzymes including pyruvate kinase and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Regulation of cAMP levels by glucagon, insulin, and catecholamines accounts in large part for minute-to-minute hormonal control of pathway flux in fed animals and during the transition from fed to starved; second, cAMP plays a key role in regulation of gene transcription of phosphoenolpyruvate carboxykinase, pyruvate kinase, glucokinase, and probably 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Cyclic AMP acts to induce synthesis of mRNA for phosphoenolpyruvate carboxykinase and probably fructose 1, 6-bisphosphatase while it suppresses transcription of the genes for pyruvate kinase and glucokinase. Its role in the regulation of gene transcription of the bifunctional enzyme and 6-phosphofructo 1-kinase remains to be defined. Insulin is the most important hormone for restraining the level of cAMP. Insulin acts to oppose the acute actions of cAMP on enzyme phosphorylation, presumably by activating a phosphodiesterase and thereby lowering cAMP levels. Insulin also opposes the action of hormones (alpha-adrenergic agonists, angiotensin, vasopressin) that act in liver via cAMP-independent phosphorylation. However, in the systems in which this has been studied, the cAMP-independent effects on gluconeogenic/glycolytic pathway flux are small in comparison to cAMP-dependent regulation. Insulin also opposes the action of cAMP on gene transcription by an as yet unknown mechanism. This effect does not appear to involve changes in the level of cAMP because the hormone also acts in cultured cells when added alone or in the presence of dexamethasone. The ability of insulin to lower hepatic cAMP levels and to modulate gene expression are important because restoration of acute regulatory hormone responsiveness to starved or diabetic animals could not occur if insulin were unable to lower cAMP levels and be the dominant factor in modulating the gene expression of these key regulatory enzymes. Clearly, the hepatic gluconeogenic/glycolytic pathway undergoes a complex but extremely well-integrated regulation by hormones that accounts in large part for the major role the organ plays in the control of glucose homeostasis.
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PMID:The role of cyclic AMP in rapid and long-term regulation of gluconeogenesis and glycolysis. 285 23

The effect of insulin on the abundance of mRNAs coding for tyrosine aminotransferase (TAT; EC 2.6.1.5), tryptophan oxygenase (TO; EC 1.13.1.12), and P-enolpyruvate carboxykinase(GTP) (PEPCK; EC 4.1.1.32) was examined in primary cultures of adult rat hepatocytes and in FTO-2B rat hepatoma cells by Northern blot analysis using RNA probes made from SP6-cDNAs. Insulin (10(-11)-10(-7) M), which has been reported to induce TAT and decrease the activity of TO, did not change the levels of TAT mRNA and TO mRNA in hepatocytes regardless of the presence of other inducers. In the same cells, dexamethasone increased TAT mRNA up to 19-fold and TO mRNA up to 15-fold, and 8pClPhS-cAMP (CPT-cAMP) raised the level of TAT mRNA up to 36-fold. The abundance of TO mRNA was not altered by CPT-cAMP. In contrast to TAT mRNA and TO mRNA, the level of PEPCK mRNA was dramatically decreased by insulin in the same hepatocytes. The sensitivity to this inhibitory effect of insulin was enhanced by dexamethasone and reduced by CPT-cAMP. FTO-2B hepatoma cells, which do not express detectable levels of TO mRNA, showed responses similar to those of hepatocytes, except that insulin caused a moderate reduction in TAT mRNA, but only in the presence of CPT-cAMP. The PEPCK mRNA in FTO-2B cells was suppressed by insulin in a manner closely resembling the effects in hepatocytes in the present study and in H4IIE hepatoma cells previously reported.
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PMID:Regulation of gene expression in rat hepatocytes and hepatoma cells by insulin: quantitation of messenger ribonucleic acid's coding for tyrosine aminotransferase, tryptophan oxygenase, and phosphoenolpyruvate carboxykinase. 287 68

Glucose transport and metabolism, and the effect of insulin thereon, was studied using suspensions of rat renal tubules enriched in the proximal component. [U-14C]Glucose oxidation is a saturable process (Km 3.1 +/- 0.2 mM; Vmax 14 +/- 0.2 mumole 14CO2 formed/g tissue protein per h). Glucose oxidation and [14C]lactate formation from glucose are inhibited in part by phlorizin and phloretin: the data suggest that the rate-limiting entry of glucose into the cell metabolic pool occurs by both the Na-glucose cotransport system (at the brush border) and the equilibrating, phloretin-sensitive system (at the basal-lateral membrane). Raising external glucose from 5 to 30 mM markedly increases aerobic and anaerobic lactate formation. Gluconeogenesis from lactate is not affected by variations of glucose concentrations. 24 h after streptozotocin administration, aerobic lactate formation is enhanced, as is the uptake of methyl alpha-D-glucoside by the tubules, while anaerobic glycolysis is depressed. Streptozotocin treatment (ST) increases both the Km and Vmax of glucose oxidation; gluconeogenesis and lactate oxidation are not affected. The effect of streptozotocin treatment on lactate formation are abolished by 1 mU/ml insulin. Streptozotocin treatment increases tissue hexokinase activity, decreases glucose-6-phosphatase, but has no significant effect on fructose-1,6-diphosphatase; phosphoenolpyruvate carboxykinase and pyruvate dehydrogenase. The data demonstrate fast streptozotocin-induced changes in cellular enzymes of carbohydrate metabolism. The enhancing effect of streptozotocin on methyl alpha-glucoside uptake is transient: 8 days after administration of the agent, no significant difference from controls is found. It is concluded that under the given experimental conditions insulin enhances the equilibrating glucose entry by the phloretin-sensitive pathway at the basal-lateral membrane, and transiently inhibits the Na-glucose cotransport system.
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PMID:Glucose transport and metabolism in rat renal proximal tubules: multicomponent effects of insulin. 293 29

The activities and zonal distribution of key enzymes of carbohydrate metabolism were studied in livers of diabetic rats. 48 h after alloxan treatment the following alterations were observed, intermediate values being reached after 24 h: Blood glucose, acetoacetate and beta-hydroxybutyrate were increased to more than 500%; liver glycogen was reduced to about 10%. Portal vein insulin was reduced to below 10%, portal glucagon was increased to almost 200%. The glucogenic enzymes phosphoenolpyruvate carboxykinase and glucose-6-phosphatase were enhanced to 320% and 150%, respectively. The glycolytic enzymes glucokinase and pyruvate kinase L (differentiated from the M2 isoenzyme with a specific anti-L-antibody) were lowered to 50% and 75%, respectively. The citrate cycle enzyme succinate dehydrogenase remained unchanged. The normal periportal to perivenous gradient of phosphoenolpyruvate carboxykinase of about 3:1, as measured in microdissected tissue samples, was enhanced to about 4:1 with activities elevated to 230% and 190%, respectively, in the two zones. The normal periportal to perivenous gradient of pyruvate kinase L of about 1:1.7, as determined with the microdissection technique, was reduced to about 1:1.4 with levels lowered to 55% and 45%, respectively, in the two zones. The even zonal distribution of pyruvate kinase M2 remained unaltered.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Metabolic zonation in liver of diabetic rats. Zonal distribution of phosphoenolpyruvate carboxykinase, pyruvate kinase, glucose-6-phosphatase and succinate dehydrogenase. 298 84


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