Disease relevance of Gck

• An alternate splice acceptor site in the 4th exon of the glucokinase gene was identified in two glucokinase cDNAs from rat insulinoma tissue [1].
• Glucose phosphorylating activity increased by up to 20-fold in extracts from islets treated with adenoviruses containing the cDNAs encoding either tissue isoform of glucokinase, but such cells exhibited no increase in 2- or 5-[3H]glucose usage, lactate production, glycogen content, or glucose oxidation [2].
• Finally, GK expression was increased in rats with impaired central glucosensing (posthypoglycemia and diet-induced obesity) but was unaffected by a 48-h fast [3].
• The introduction of the glucokinase transgene in insulin receptor null mice did not prevent the development of glycosuria [4].
• Similar promoter activity was also detected in dRLh-84 hepatoma cells, which do not express glucokinase [5].

Psychiatry related information on Gck

• In young animals, food deprivation also: (i) reduced liver GK and PK, (ii) increased kidney PEPCK, (iii) decreased muscle PEPCK and (iv) decreased kidney PDH [6].
• Effect of glycerol on glucokinase activity: loss of cooperative behavior with respect to glucose [7].

High impact information on Gck

• Fetal programming of adult glucose metabolism may operate partly through structural alterations and changes in glucokinase expression in the immediate perivenous region [8].
• Glucokinase and cytosolic phosphoenolpyruvate carboxykinase (GTP) in the human liver. Regulation of gene expression in cultured hepatocytes [9].
• In situ glucose uptake and glucokinase activity of pancreatic islets in diabetic and obese rodents [10].
• Glucose regulates the cellular content of glucokinase in the pancreatic beta cell by altering the level of the enzyme [11].
• Using quantitative histochemical techniques, we investigated basal islet glucose content, islet glucose uptake in situ during acute extreme experimental hyperglycemia, and islet glucokinase activity in several animal models of diabetes and obesity [10].

Chemical compound and disease context of Gck

• Conditional expression of the glucokinase regulatory protein in insulinoma cells, under control of the reverse tetracycline-dependent transactivator, was used to investigate whether expression of this protein de novo would alter the intracellular distribution of glucokinase [12].
• Glucose-induced increases in glucokinase activity are an important element of the beta cell adaptive response to hyperglycemia [11].
• Glucokinase partially purified from transplantable insulinomas or rat liver was inactivated by alloxan with a half-maximal effect at 2-4 microM alloxan [13].
• Glucosamine-induced inhibition of liver glucokinase impairs the ability of hyperglycemia to suppress endogenous glucose production [14].
• Even subphysiological doses of T3 (0.1 microgram/100 g body weight) led to an significant increase in glucokinase mRNA levels (1.5-fold, p less than 0.05) in hypothyroid rats, whereas higher doses (100 micrograms/100 g body weight) restored the mRNA levels to those of euthyroid controls [15].

Biological context of Gck

• Adenovirus-mediated overexpression of GKRP (by up to 2-fold above endogenous levels) increased glucokinase binding and inhibited glucose phosphorylation, glycolysis, and glycogen synthesis over a wide range of concentrations of glucose and sorbitol [16].
• These results indicate that PPAR-gamma can directly activate GK expression in liver and may contribute to improving glucose homeostasis in type 2 diabetes [17].
• Insulin regulation of glucokinase gene expression: evidence against a role for sterol regulatory element binding protein 1 in primary hepatocytes [18].
• These findings are not consistent with the hypothesis that programming results from differential methylation of Gck [19].
• The glucokinase gene is 15.5-kilobases long, appears to be present as a single copy, and contains 10 exons that range in size from 96 to 977 base pairs [20].

Anatomical context of Gck

• Furthermore, troglitazone increased endogenous GK mRNA in primary hepatocytes [17].
• Based on measurement of glucose phosphorylation in intact cells, overexpressed glucokinase is clearly active in a non-islet cell line (CV-1) but not within islet cells [2].
• We concluded that pbetaPCCase might be a novel activator of glucokinase in pancreatic beta cells [21].
• The low affinity glucose-phosphorylating enzyme glucokinase shows the phenomenon of intracellular translocation in beta cells of the pancreas and the liver [22].
• To search for such a protein in pancreatic beta cells, we screened for a cDNA library of the HIT-T15 cell line with the cDNA of glucokinase from rat islet by the yeast two hybrid system [21].

Associations of Gck with chemical compounds

• The role of the regulatory protein of glucokinase in the glucose sensory mechanism of the hepatocyte [16].
• Dual role of phosphofructokinase-2/fructose bisphosphatase-2 in regulating the compartmentation and expression of glucokinase in hepatocytes [23].
• To understand the role of GK in glucoprivic counterregulatory responses, we injected alloxan, a GK inhibitor and toxin, into the third ventricle (3v) to target nearby GK-expressing neurons [24].
• We detected a cDNA encoding the precursor of propionyl-CoA carboxylase beta subunit (pbetaPCCase), and glutathione S-transferase pull-down assay illustrated that pbetaPCCase interacted with recombinant rat islet glucokinase and with glucokinase in rat liver and islet extracts [21].
• Furthermore, glucokinase overexpression enhanced insulin secretion in response to stimulatory glucose or glucose plus arginine by only 36-53% relative to control islets [2].

Physical interactions of Gck

• Despite normal to elevated hexokinase and glucokinase activities in the islets of these glucose-intolerant animals and despite normal mitochondrial binding of the hexokinase isoenzymes, the metabolic response to a high concentration of D-glucose is severely affected, especially in terms of D-[6-14C]glucose oxidation [25].

Regulatory relationships of Gck

• Hepatic glucokinase is inhibited by a 68-kDa glucokinase regulatory protein (GKRP) that is expressed in molar excess [16].
• Substrates and glucagon induced adaptive changes in the mitochondrial glucokinase/GKRP ratio suggesting a regulatory role for GKRP [26].
• In the fasted state, a 3 fold glucokinase overexpression was sufficient to mimic feeding-induced increases in pyruvate kinase and acetyl CoA carboxylase mRNA levels, demonstrating a primary role for glucose metabolism in the regulation of these genes in vivo [27].
• A reconstituted system prepared from RINm5F and HIT cell extracts exhibited a composite concentration-dependency curve of glucose usage and showed substantial inhibition of hexokinase and almost fully expressed glucokinase [28].
• Amylin proved ineffective in suppressing subsequent accumulation of glucokinase mRNA in response to maximal or submaximal doses of insulin [29].

Other interactions of Gck

• We concluded that SREBP-1 is unlikely to be the mediator of the early insulin effect on GK gene transcription [18].
• The insulin-induced increases in the abundance of SREBP-1c and glucokinase mRNAs, both of which were sensitive to a dominant-negative mutant of PI 3-kinase, were blocked in cells in which the insulin-induced tyrosine phosphorylation of IRS-1 was inhibited by IRS-1N or IRS-2N [30].
• In addition, experiments showed that PD98059 decreased by half the increase in glucokinase mRNA brought about by insulin, suggesting a contributory role of the mitogen-activated protein kinase cascade [31].
• To explore the role of PPAR-gamma in glucose sensing of beta-cells, we have dissected the beta-cell-specific glucokinase (betaGK) promoter, which constitutes glucose-sensing apparatus in pancreatic beta-cells, and identified a peroxisomal proliferator response element (PPRE) in the promoter [32].
• Double-label in situ hybridization demonstrated neuron-specific GK mRNA expression in locus ceruleus norepinephrine and in hypothalamic neuropeptide Y, pro-opiomelanocortin, and gamma-aminobutyric acid neurons, but it did not demonstrate this expression in orexin neurons [3].

Analytical, diagnostic and therapeutic context of Gck

• Asparagine-leucine motifs of glucokinase located in the hinge region, as well as in the large domain, were changed by site-directed mutagenesis [33].
• Northern blot reveals that fasting levels of Gck expression are reduced after programming, although this distinction disappears after feeding [19].
• The mRNA levels of glucokinase and of its regulatory protein decreased rapidly after partial hepatectomy to minimum values at 6 hours (15%) and at 12 hours (4%), respectively, returning to normal values at 24 hours and 168 hours, respectively [34].
• GK mRNA was also found in the area postrema/nucleus tractus solitarius region by RT-PCR [3].
• Using the bDNA assay, a sensitive signal amplification technique, we detected relative increases in glucokinase messenger RNA levels of 40.5 +/- 7.5% after 3-h incubation with cAMP [35].

References