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)

1. Protein degradation in rat hepatocytes in stationary monolayer culture was measured as release of radioactive trichloroacetic acid-soluble material from intracellular proteins labelled with [3H]leucine. 2. Glucocorticoids, but not other steroids, stimulated protein breakdown in the hepatocyte monolayers. The effects observed were greater when the cells were preincubated with the hormones, indicating that the stimulation was not immediate. In addition, the stimulation by glucocorticoids persisted for up to 4 h after hormone removal. 3. Cycloheximide and the lysosomotropic agents leupeptin and ammonia effectively blocked glucocorticoid stimulation of protein degradation. 4. Insulin blocked dexamethasone stimulation when added at the same time as the steroid, but not when added 3 h later. 5. Stimulation of protein breakdown by dexamethasone was additive with that by glucagon or dibutyryl cyclic AMP, suggesting that its mechanism of action is different from that of the latter two agents. 6. Total activities of several lysosomal enzymes were unaffected under conditions where protein breakdown was stimulated by either glucagon or dexamethasone. 7. It is suggested that, whereas glucagon, dibutyryl cyclic AMP and insulin modulate protein breakdown in these cells via changes in autophagocytosis, the stimulation by glucocorticoids is exerted independently, perhaps by stimulating the synthesis of membrane proteins essential to the autophagic process.
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PMID:Stimulation by glucocorticoids of protein degradation in hepatocyte monolayers. 627 54

Primary cultures of adult rat hepatocytes incubated (24-72 h) in Waymouth's 752/1 medium, exhibited a marked decline (80-90%) in their ability to incorporate 0.5 mM [1,3-14C]glycerol and 1.0 mM palmitate into glycerolipids. The specific activities of glycerol kinase and sn-glycerol-3-P acyltransferase also showed a time-dependent reduction (30-80%). Phosphatidate phosphohydrolase, diacylglycerol cholinephosphotransferase, and fatty acid-CoA ligase activities were unaffected. Insulin and/or glucagon (10(-8) to 10(-6) M) not only prevented these reductions in hepatocyte monolayer glycerolipid formation and enzyme activities but increased (2-5-fold) the level of these processes. Cycloheximide (1 microM) reduced the insulin- and glucagon-dependent increases in sn-glycerol-3-P acyltransferase and glycerol kinase activity and glycerolipid biosynthesis. There was an excellent correlation (r greater than 0.93) between changes in glycerol kinase and sn-glycerol-3-P acyltransferase activity and the capacity of hepatocyte monolayers to incorporate labeled glycerol into glycerolipids under all conditions studied. Therefore, insulin and glucagon may regulate hepatic glycerolipid biosynthesis in part by maintaining the liver cell's enzymatic rate of glycerolipid biosynthesis.
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PMID:Effects of chronic insulin and glucagon exposure on the biosynthesis of glycerolipids by cultured hepatocytes. 629 87

Rat hearts were perfused for long periods in the presence of 14C-labeled amino acids. From these hearts, postheparin-effluent and a tissue homogenate containing lipoprotein lipase and neutral lipase, respectively, were derived. Lipolytic activity and 14C-labeled protein in both preparations were characterized by affinity chromatography, immunoprecipitation and SDS-polyacrylamide gel electrophoresis. Lipase activity and 14C-labeled protein co-eluted from heparin-Sepharose 4B at 1.2 M NaCl and were inhibited and precipitated by preincubation with anti-lipoprotein lipase gamma-globulins. Gel electrophoresis of both preparations showed the presence of 14C-labeled protein with a molecular weight of 35 000. These data strongly suggest similarity between lipoprotein lipase and neutral lipase and their possible precursor-product relationship and indicate that during perfusion continuous synthesis, secretion and vascular binding of lipase molecules occur. Cycloheximide perfusion induced a dramatic decrease of lipoprotein lipase and neutral lipase activity, indicating a half-life of less than 90 min for both enzymes. Tunicamycin present during perfusion also induced a drop in lipoprotein lipase and tissue neutral lipase activity, indicating that glycosylation is necessary for secretion of lipoprotein lipase. Long-term perfusion of rat hearts in the presence of norepinephrine, glucagon or tyrosine leads to reciprocal alterations in lipoprotein lipase and neutral lipase activities, i.e., lipoprotein lipase activity increased and neutral lipase activity decreased, whereas total lipase activity (lipoprotein lipase + neutral lipase) remained unaltered. During perfusion in the presence of insulin, no net change in lipase activities was observed. Also, insulin did not affect the glucagon-induced inverse effects on either lipase activity. The reciprocal changes in lipase activities occurring during norepinephrine perfusion were hampered by colchicine and propranolol, pointing towards beta-receptor and microtubular mediation of tissue lipase processing and endothelial binding. Our data suggest that the tissue flux and vascular binding of lipase protein may be important sites of hormonal regulation of lipoprotein lipase homeostasis.
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PMID:Effects of hormones, amino acids and specific inhibitors on rat heart heparin-releasable lipoprotein lipase and tissue neutral lipase activities during long-term perfusion. 637 31

A further characterization of endotoxin-induced changes in zinc metabolism provided insight into the possible mediation processes involved. Endotoxin reduced serum zinc levels while elevating zinc associated with hepatic metallothionein (Zn-MT) in control, fasted, and zinc-depleted rats. Unlike zinc, copper in the serum and that associated with metallothionein showed little response to endotoxin. In vitro translation of liver mRNA demonstrated that metallothionein mRNA levels were increased after endotoxin administration to either control or zinc-depleted rats. Cycloheximide fully blocked endotoxin-induced alterations in serum and metallothionein zinc, but actinomycin D was only partially inhibitory. Glucagon might act as the primary mediator for these actinomycin D-insensitive changes. Glucocorticoids might be responsible for the remaining alterations in zinc metabolism because dexamethasone increased 65Zn accumulation in cultured hepatocytes, whereas endotoxin did not. In endotoxin-treated rats, the kidney as well as liver showed increases in metallothionein-zinc and metallothionein-mRNA. Virtually all the effects of endotoxin were mimicked by leukocytic endogenous mediator, implying that it probably represents the initial mediator of endotoxin action on zinc metabolism.
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PMID:Mediation of endotoxin-induced changes in zinc metabolism in rats. 638 45

Acute hormonal effects on the synthesis rate of the cytosolic form of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (GTP), were investigated using rat hepatocytes maintained in short-term suspension culture. Cells were pulse-labeled with [3H]leucine or [35S]methionine and the rate of synthesis of phosphoenolpyruvate carboxykinase was estimated after immunoprecipitation of cell extracts with specific antibodies or following high-resolution two-dimensional gel electrophoresis of cell proteins. Total RNA was also extracted from cultured cells and subsequently translated in a wheat germ cell-free protein-synthesis system, in order to quantify the level of functional mRNA coding for phosphoenolpyruvate carboxykinase. Glucagon, the single most effective inducer, causes a 15--20-fold increase in the level of specific mRNA in 2 h, accompanied by a similar increase in enzyme synthesis rate. The extent of induction is further amplified about threefold when dexamethasone is added to the culture medium. The synergistic action of dexamethasone does not require pre-exposure of the cells to the glucocorticoid, but on the contrary occurs without lag upon simultaneous addition of glucagon and dexamethasone. The induction of phosphoenolpyruvate carboxykinase mRNA by glucagon is markedly depressed in hepatocytes inhibited for protein synthesis by cycloheximide. Cycloheximide-inhibited cells, however, display a considerable induction of the message after joint stimulation with dexamethasone and glucagon. Thus, the synergistic action of dexamethasone does not require concomitant protein synthesis. These data provide indirect evidence for a primary effect of the glucocorticoids on the expression of the phosphoenolpyruvate carboxykinase gene. Besides glucagon and dexamethasone, the thyroid hormones are shown to influence the rate of phosphoenolpyruvate carboxykinase synthesis in isolated liver cells. The stimulatory effect of 3,5,3'-triiodothyronine (T3) is best demonstrated as a twofold increase in relative rate of enzyme synthesis in cells supplied with T3 plus glucagon, as compared to cells challenged with glucagon alone. The effect of T3 relies on a pretranslational mechanism, as shown by a commensurate increase in functional mRNA coding for phosphoenolpyruvate carboxykinase. Dose-response experiments with T3 as well as dexamethasone demonstrate effects at very low hormone levels, consistent with a role for these hormones as physiological modulators of phosphoenolpyruvate carboxykinase expression.
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PMID:Effects of glucagon, dexamethasone and triiodothyronine on phosphoenolpyruvate carboxykinase (GTP) synthesis and mRNA level in rat liver cells. 651 Apr 13

Insulin partially inhibits endogenous protein degradation in isolated hepatocytes. The inhibition seems to specifically affect the lysosomal pathway of degradation, since it is not additive to the effects of lysosome inhibitors such as propylamine and leupeptin. The insulin effect is potentiated by intermediate concentrations of amino acids, but is largely abolished at high amino acid concentrations which suppress degradation maximally, suggesting that the hormone may exert its effect indirectly by acting upon the more basal amino acid control mechanism. Glucagon, which stimulates protein degradation, similarly displays its effect only in the presence of intermediate amino acid concentrations. The insulin inhibition is not affected by the aminotransferase inhibitor, aminooxyacetate, indicating that it is not due to interference with amino acid metabolism. Protein synthesis furthermore does not seem to be required, since a significant insulin effect can be seen in the presence of the protein synthesis inhibitor, cycloheximide. The issue is, however, complicated by the fact that cycloheximide itself inhibits protein degradation to approximately the same extent as does insulin. Insulin stimulates uptake of the amino acid alpha-aminoisobutyrate (AIB), but not the uptake of valine, indicating a specific stimulation of 'A'-type transport. Cycloheximide similarly stimulates AIB uptake, without completely obfuscating the transport effect of insulin. Neither protein synthesis, protein degradation, amino acid transport, nor the effects of insulin were affected by cell-to-substratum anchorage (attachment and spreading) in any detectable way.
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PMID:Effects of insulin and anchorage on hepatocytic protein metabolism and amino acid transport. 702 88

The effects of insulin and insulin-like growth factor-I (IGF-I) on amino acid transport and protein metabolism were compared in myotubes derived from chicken breast muscle satellite cells. Protein synthesis was assessed by continuous labelling with [3H]-tyrosine. Protein degradation was estimated by the release of trichloroacetic acid (TCA) soluble radioactivity by cells which had been previously labelled with [3H]-tyrosine for 3 days. Amino acid transport was measured in myotubes incubated in Dulbecco's modified Eagle's medium (DMEM) 0.5% bovine serum albumin (BSA) with or without insulin or IGF-I. Subsequent [3H]-aminoisobutyric acid (AIB) uptake was then measured in amino acid-free medium. IGF-I was more efficient than insulin at equimolar concentration (3.2 nmol/l) in stimulating protein synthesis (127 and 113% of basal, respectively) and inhibiting protein degradation (32% and 13% inhibition of protein degradation following 4 h incubation). Half maximal effective concentrations for stimulation of AIB uptake were 0.27 +/- 0.03 nmol/l and 34.8 +/- 3.1 nmol/l for IGF-I and insulin respectively, with maximal stimulation of about 340% of basal. Cycloheximide (3.6 mumol/l) diminished IGF-I-stimulated AIB uptake by 55%. Chicken growth hormone had no effect on basal AIB uptake in these cells and neither glucagon nor dexamethasone had an effect on basal or IGF-I-stimulated AIB uptake. This study demonstrates an anabolic effect for IGF-I in myotubes derived from primary chicken satellite cells which is mediated by the type I IGF receptor, since the cation-independent mannose 6-phosphate receptor does not bind IGF-II in chicken cells.
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PMID:Regulation of amino acid transport and protein metabolism in myotubes derived from chicken muscle satellite cells by insulin-like growth factor-I. 825 77

The synthetic glucocorticoid, dexamethasone, and glucagon cooperatively elevated the level of mRNA for the transcription factor CCAAT/enhancer binding protein beta (C/EBP beta) in primary-cultured rat hepatocytes. In response to dexamethasone and/or glucagon, C/EBP beta mRNA started to increase as early as 30 min, reached a maximum within 2 h, and then gradually decreased. The administration of cycloheximide, a protein synthesis inhibitor, led rather to an increase in C/EBP beta mRNA, which suggested that a labile negative protein factor(s) is involved in regulation of the C/EBP beta mRNA level. Cycloheximide further augmented the increases in C/EBP beta mRNA by dexamethasone and/or glucagon. Therefore, C/EBP beta mRNA accumulation in response to these hormones is apparently independent of ongoing protein synthesis. The elevation of the C/EBP beta mRNA level by these hormones was accounted for by increases in the rate of transcription of the C/EBP beta gene, as deduced on nuclear run-on analysis. Gel mobility shift analysis revealed that the DNA-binding activity of C/EBP beta was increased cooperatively by dexamethasone and glucagon. These results suggest that the C/EBP beta gene is primarily induced by glucocorticoids and/or glucagon and that the accumulated C/EBP beta protein is then involved in secondary activation of target genes in response to these hormones in the liver.
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PMID:Induction of the C/EBP beta gene by dexamethasone and glucagon in primary-cultured rat hepatocytes. 883 49

Glucagon stimulates the vesicle trafficking of aquaporin-8 (AQP8) water channels to the rat hepatocyte canalicular membranes, a process thought to be relevant to glucagon-induced bile secretion. In this study, we investigated whether glucagon is able to modulate the gene expression of hepatocyte AQP8. Glucagon was administered to rats at 0.2 mg/100 g body wt ip in 2, 3, or 6 equally spaced doses for 8, 16, and 36 h, respectively. Immunoblotting analysis showed that hepatic 34-kDa AQP8 was significantly increased by 79 and 107% at 16 and 36 h, respectively. Hepatic AQP9 protein expression remained unaltered. AQP8 mRNA expression, assessed by real-time PCR, was not modified over time, suggesting a posttranscriptional mechanism of AQP8 protein increase. Glucagon effects on AQP8 were directly studied in primary cultured rat hepatocytes. Immunoblotting and confocal immunofluorescence microscopy confirmed the specific glucagon-induced AQP8 upregulation. The RNA polymerase II inhibitor actinomycin D was unable to prevent glucagon effect, providing additional support to the nontranscriptional upregulation of AQP8. Cycloheximide also showed no effect, suggesting that glucagon-induced AQP8 expression does not depend on protein synthesis but rather on protein degradation. Inhibitory experiments suggest that a reduced calpain-mediated AQP8 proteolysis could be involved. The action of glucagon on hepatocyte AQP8 was mimicked by dibutyryl cAMP and suppressed by PKA or phosphatidylinositol-3-kinase (PI3K) inhibitors. In conclusion, our data suggest that glucagon induces the gene expression of rat hepatocyte AQP8 by reducing its degradation, a process that involves cAMP-PKA and PI3K signal pathways.
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PMID:Glucagon induces the gene expression of aquaporin-8 but not that of aquaporin-9 water channels in the rat hepatocyte. 1919 45


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