Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To examine the relationship between structure and function of glucose-6-phosphatase (G6Pase) in fish, we undertook molecular cloning and modulation of G6Pase expression by starvation and refeeding on diets with different nutrient composition in the liver of the carnivorous fish, Sparus aurata. A cDNA encoding the full-length G6Pase catalytic subunit from the liver of S. aurata was isolated. This cDNA encodes a 350-amino acid protein, with low homology to the mammalian G6Pase, although it contains most of the key residues required for catalysis. Based on hydrophobicity and membrane structure prediction, we propose a model containing nine-transmembrane regions for S. aurata G6Pase. Northern blots showed that refeeding after a prolonged starvation rapidly reverses the glucose/glucose-6-phosphate substrate cycle flux in the fish liver through decreased G6Pase expression and strong glucokinase (GK) induction. The effect of refeeding different diets on G6Pase and GK expression, indicated that hepatic intermediary metabolism of fish fed diets with low protein/high carbohydrate diets is impelled towards utilization of dietary carbohydrates, by means of modulation of GK mRNA levels rather than G6Pase expression. These findings challenge the role attributed to dysregulation of G6Pase or GK expression in the low ability of carnivorous fish to metabolise glucose.
Comp Biochem Physiol B Biochem Mol Biol 2004 Jun
PMID:Molecular cloning of hepatic glucose-6-phosphatase catalytic subunit from gilthead sea bream (Sparus aurata): response of its mRNA levels and glucokinase expression to refeeding and diet composition. 1519 69

Effect of vanadyl acetylacetonate (VAc), tungstate and molybdate on gluconeogenesis has been studied in isolated hepatocytes and kidney-cortex tubules. In renal tubules of control and alloxan-diabetic animals, the rank order of the metal-compounds-induced (i) inhibition of glucose formation from alanine+glycerol+octanoate or aspartate+glycerol+octanoate, (ii) decrease in the mitochondrial membrane potential (delta psim), (iii) increase in the hydroxyl free radicals (HFR) generation and (iv) decline in glucose-6-phosphatase activity was the following: VAc > tungstate > molybdate. Moreover, in contrast to VAc, both tungstate and molybdate at 100 microM concentration did not practically decrease glucose production in hepatocytes isolated from diabetic rabbits, and significantly increased the rate of lactate formation in renal tubules. N-acetylcysteine at 2 mM concentration partially attenuated vanadium-induced alterations in glucose formation, delta psim and the cellular glutathione redox state, whereas 0.1 mM melatonin did not abolish vanadium-induced changes in gluconeogenesis despite attenuation of vanadium effects on HFR formation and delta psim decline. However, similarly to control rabbits, following 6 days of intraperitoneal administration of both VAc (1.275 mg V/kg body weight daily) and melatonin (1 mg/kg body weight daily) to alloxan-diabetic animals, vanadium-induced elevated serum creatinine and urea levels were decreased, indicating the beneficial effect of melatonin on diabetes- and vanadium-induced nephrotoxicity in rabbits. As serum glucose levels were also significantly diminished by vanadium+melatonin treatment of diabetic animals, the combination therapy of vanadium compounds and melatonin needs a careful evaluation.
Mol Cell Biochem 2004 Jun
PMID:Differential effects of vanadium, tungsten and molybdenum on inhibition of glucose formation in renal tubules and hepatocytes of control and diabetic rabbits: beneficial action of melatonin and N-acetylcysteine. 1536 81

There has been increasing interest in the value of using soybean to delay or reduce the tumor incidence. This study was undertaken to investigate the possible protective effects of soybean against hepatocarcinogenesis induced by DL-ethionine. Accordingly, we measured biochemical changes occurring in serum and liver of rats treated with DL-ethionine in the presence or absence of soybean. Male albino rats were fed a control diet containing the hepatocarcinogen, DL-ethionine, or the control diet plus soybean 30%, or the control diet plus soybean plus DL-ethionine 0.25% for three months and then returned to a control diet for up to nine months. Rats fed a control diet plus DL-ethionine showed a gradual decrease in liver DNA, RNA, total protein, and liver weight and enzyme activities of liver transaminases (GOT and GPT) and alkaline phosphatase over the 7-month study period. This was followed by a large increase in the liver parameters at the end of the 9(th) month, except for 5'-nucleotidase and glucose-6-phosphatase that showed a large decrease. On the other hand, a gradual increase in the serum enzyme activities of GOT, GPT, 5-nucleotidase, alkaline phosphatase, and in the albumin/globulin (A/G) ratio is observed in the group of rats fed a control diet plus DL-ethionine compared to the control group over 8 months, and this was followed by a large increase in all serum parameters studied at nine-months. The administration of 30% soybean to the rat diet in addition to DL-ethionine maintained all parameters studied at near control values until the end of the 9(th) month. This study suggests that soybean has a protective effect against the hepatocarcinogenesis induced by DL-ethionine.
J Biochem Mol Biol 2004 May 31
PMID:Protective effect of soybean against hepatocarcinogenesis induced by DL-ethionine. 1546 21

Glycogen storage disease type Ia (GSD-Ia) is caused by deleterious mutations in the glucose-6-phosphatase gene (G6PC). A molecular study of this gene was carried out in 11 Argentinean patients from 8 unrelated families. Four missense (p.Gln54Pro, p.Arg83Cys, p.Thr16Arg, and p.Tyr209Cys) and one deletion (c.79delC) mutations have been identified. Two novel mutations, p.Thr16Arg (c.47C>G) located within the amino-terminal domain and p.Tyr209Cys (c.626A>G) situated in the sixth transmembrane helix, were uncovered in this study. Site-directed mutagenesis and transient expression assays demonstrated that both p.Thr16Arg and p.Tyr209Cys mutations abolished enzymatic activity as well as reduced G6Pase stability.
Mol Genet Metab 2004 Nov
PMID:Glycogen storage disease type Ia in Argentina: two novel glucose-6-phosphatase mutations affecting protein stability. 1554

Increase in glucose-6-phosphatase catalytic subunit (G6Pase, G6pc) transcription enhances hepatic glucose production in non-insulin-dependent diabetes mellitus (NIDDM). The fact that carnivorous fish is an alternative model to study NIDDM led us to clone and characterise the first G6pc promoter region reported for fish and non-mammalian animals. The 5'-flanking region of G6pc from gilthead sea bream (Sparus aurata) was isolated by chromosome walking. With SMART RACE-PCR, the transcription start site was located 106 base pairs (bp) upstream of the translational start. Transfection analysis in HepG2 cells located a functional promoter in the 850 bp 5'-flanking isolated fragment (positions -770 to +80 relative to the transcription start). Sequential 5'-deletion analysis of the promoter fragment revealed that a core functional promoter for basal transcription is comprised within the 190 bp upstream of the transcription start site. In vivo, glucose and insulin reduced G6Pase mRNA levels in the fish liver. Transfection experiments in HepG2 cells showed that insulin repressed S. aurata G6pc under high-glucose conditions. Synergistic activation of piscine G6pc promoter was induced by cotransfection with expression plasmids for hepatocyte nuclear factor-4alpha (HNF-4alpha) and peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1alpha). No direct relationship was found between PGC-1alpha coactivation of HNF-4alpha transactivation and the repressive effect of insulin. Interestingly, insulin hardly affected G6pc promoter activity in the absence of glucose, suggesting that a reduced capacity of insulin-dependent repression of piscine G6pc may lead to insulin resistance in carnivorous fish.
J Mol Endocrinol 2004 Dec
PMID:Transcriptional regulation of glucose-6-phosphatase catalytic subunit promoter by insulin and glucose in the carnivorous fish, Sparus aurata. 1559 Oct 35

The objective of the study described here was to analyze in rainbow trout (Oncorhynchus mykiss) the effects of low protein intake on peripheral glucose phosphorylation capacities and gluconeogenic enzymes in kidney and intestine. Fish were food-deprived for 14 days or kept under a low and a high protein intake regime using a pair feeding protocol in order to maintain constant carbohydrate and lipid intakes. We analyzed the effect of protein restriction on (i) hepatic, renal and intestinal fructose-1.6-bisphophatase (FBPase) and glucose-6-phosphatase (G6Pase) enzymes at the molecular and enzymatic levels and (ii) glucose phosphorylation activities (hexokinases) in the liver, peri-visceral adipose tissue, red muscle and white muscle. Irrespective of the nutritional status, we observed the same levels of hexokinase activities in all the tissues studied. Renal G6Pase and FBPase gene expression and activities were not modified among the groups. In contrast, there was increased intestinal FBPase gene expression in fish under a low protein intake and higher G6Pase activities in both groups of fed fish. This result differs from what is observed in rats and suggest a role of intestine in the regulation of postprandial gluconeogenesis in fed trout. In conclusion, our data did not demonstrate any specific effect of low dietary protein intake to either gluconeogenic capacities or glucose phosphorylation capacities in rainbow trout.
Comp Biochem Physiol B Biochem Mol Biol 2005 Feb
PMID:Effects of low protein intake on extra-hepatic gluconeogenic enzyme expression and peripheral glucose phosphorylation in rainbow trout (Oncorhynchus mykiss). 1564 81

Metformin is thought to decrease blood glucose levels by reducing hepatic glucose output. To elucidate the pharmacological action of metformin on hepatic glucose production, we examined its effect on the gene expression of glucose-6-phosphatase (G6Pase), a key enzyme of gluconeogenesis, in H4IIE rat hepatoma cell line by RT-PCR and quantitative real-time PCR. Metformin suppressed dexamethasone/cAMP-induced expression of G6Pase mRNA in a dose dependent manner, its maximum effect being observed at 2 mM (79.3% inhibition, P<0.05). Pretreatment with the PI3-kinase inhibitor wortmannin, the MEK-1 inhibitor PD98059 or the protein kinase C inhibitor GF109203X had no effect on suppressed G6Pase expression by metformin. Moreover, metformin did not stimulate Akt phosphorylation. In the present study, we demonstrate that metformin suppresses G6Pase mRNA expression by a mechanism that is independent of the activation of PI3-kinase, Akt, MAP kinase and protein kinase C pathway in hepatocytes.
Int J Mol Med 2005 Mar
PMID:Metformin-induced suppression of glucose-6-phosphatase expression is independent of insulin signaling in rat hepatoma cells. 1570 36

The aim of this study was to investigate whether the actively wintering American mink Mustela vison is strictly dependent on continuous food availability or if it has evolved physiological adaptations to tolerate nutritional scarcity. Fifty farm-bred male minks were divided into a fed control group and four experimental groups fasted for 2, 3, 5 or 7 days. The rate of weight loss was several-fold higher (1.5-3.2% day(-1)) in the mink than recorded previously in larger carnivores utilizing passive wintering strategies. The minks remained normoglycaemic, although their liver glycogen stores and glucose-6-phosphatase activities decreased during fasting. Adipose tissue constituted approximately 36% of their body mass after 7 days of food deprivation. Intra-abdominal fat, especially retroperitoneal but also mesenteric adipose tissue, were the most important fat depots to be hydrolyzed, but the ability of the mink to utilize its body lipids during fasting may be limited. The increased liver size, hepatic triacylglycerol accumulation and increases in the activities of plasma aminotransferases indicated liver dysfunction. Food deprivation also affected the red blood cell indices, and the blood monocyte and lymphocyte counts decreased suggesting immunosuppression during fasting. The results of the present study suggest that the mink has not evolved sophisticated adaptations to wintertime fasting.
Comp Biochem Physiol A Mol Integr Physiol 2005 Feb
PMID:Adaptations to fasting in the American mink (Mustela vison): carbohydrate and lipid metabolism. 1574 59

Sudden and unexpected infant deaths can be unexplained [sudden infant death syndrome (SIDS)] or explained (non-SIDS) but risk factors including lower birthweight are similar in both groups. Mutations in the glucokinase (GK) gene result in Maturity Onset Diabetes of the Young type 2 (MODY 2) and are associated with lower birthweight. Low hepatic glucose-6-phosphatase (G6PC1) expression occurs in both low birthweight and SIDS infants. We investigated whether polymorphisms are prevalent in the GK and G6PC1 genes in infants who died suddenly and unexpectedly. Mutation analysis was performed by polymerase chain reaction (PCR) and denaturing high-performance liquid chromatography (DHPLC) in samples from 126 infants who died suddenly and unexpectedly (78 SIDS, 48 non-SIDS) and from 70 healthy, living infants. G6PC1 promoter polymorphism significance was investigated by transfection of reporter gene constructs into a H4IIE cell line. Heterozygous GK polymorphisms were identified in 17.9% of SIDS and 20.8% of non-SIDS infants: two rare silent polymorphisms, Y215Y and S263S, in the coding region; a third rare polymorphism, -45G>A, in the hepatic promoter and the most prevalent polymorphism, c.484-29G>C, in a non-coding region upstream from the intron 4-exon 5 junction. A novel heterozygous polymorphism -77G>A in the G6PC1 promoter in 6.3% of non-SIDS and 2.9% of control infants decreased basal G6PC1 promoter activity (p<0.001). We describe three novel polymorphisms in the GK gene, S263S, -45G>A, and a common (14.3%) intronic substitution, c.484-29G>C, in infants who died suddenly and unexpectedly. We identified the first G6PC1 promoter polymorphism, which lowers expression, potentially increasing risk of hypoglycaemia and hence risk of sudden and unexpected death.
J Mol Med (Berl) 2005 Aug
PMID:Identification of novel polymorphisms in the glucokinase and glucose-6-phosphatase genes in infants who died suddenly and unexpectedly. 1591 42

Glucose-6-phosphatase catalyzes the final step in the gluconeogenic and glycogenolytic pathways. Glucocorticoids stimulate glucose-6-phosphatase catalytic subunit (G6Pase) gene transcription and studies performed in H4IIE hepatoma cells demonstrate the presence of a glucocorticoid response unit (GRU) in the proximal G6Pase promoter. In vitro deoxyribonuclease I footprinting analyses show that the glucocorticoid receptor binds to three glucocorticoid response elements (GREs) in the -231 to -129 promoter region and transfection results indicate all three contribute to glucocorticoid induction of G6Pase gene transcription. Furthermore, binding sites for hepatocyte nuclear factor-1 and -4, CRE binding factors, and FKHR (FOXO1a) are required for the full glucocorticoid response. Chromatin immunoprecipitation assays show that dexamethasone treatment stimulates glucocorticoid receptor and FKHR binding to the endogenous G6Pase promoter. Surprisingly, although glucocorticoids stimulate G6Pase gene transcription, deoxyribonuclease I footprinting and transfection analyses demonstrate the presence of a negative GRE and an associated negative accessory factor element in the -271 to -225 promoter region, which inhibit the glucocorticoid response. This appears to be the first report of a promoter that contains both positive and negative GREs, which function within the same cellular environment. We hypothesize that targeted signaling to the negative accessory element within the GRU may provide tight regulation of the glucocorticoid stimulation.
Mol Endocrinol 2005 Dec
PMID:The glucose-6-phosphatase catalytic subunit gene promoter contains both positive and negative glucocorticoid response elements. 1603 30


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>