AMP-activated Protein Kinase Inhibits the Glucose-activated Expression of Fatty Acid Synthase Gene in Rat Hepatocytes

Abstract

Although it is now clearly established that a number of genes involved in glucose and lipid metabolism are up-regulated by high glucose concentrations in both liver and adipose tissue, the signaling pathway arising from glucose to the transcriptional machinery is still poorly understood. We have analyzed the regulation of fatty acid synthase gene expression by glucose in cultured rat hepatocytes. Glucose (25 mM) induces an activation of the transcription of the fatty acid synthase gene, and this effect is markedly reduced by incubation of the cells with okadaic acid, an inhibitor of protein phosphatases 1 and 2A. A similar reduction in glucoseactivated fatty acid synthase gene expression is obtained by incubation with 5-amino-imidazolecarboxamide riboside, a cell-permeable activator of the AMPactivated protein kinase. Taken together, these results indicate that the glucose-induced expression of the fatty acid synthase gene involves a phosphorylation/dephosphorylation mechanism and suggest that the AMP-activated protein kinase plays an important role in this process. This is the first evidence that implicates the AMP-activated protein kinase in the regulation of gene expression. AMP-activated protein kinase is the mammalian analog of SNF1, a kinase involved in yeast in the transcriptional regulation of genes by glucose.Although it is now clearly established that a number of genes involved in glucose and lipid metabolism are up-regulated by high glucose concentrations in both liver and adipose tissue (for review, see Refs. 1 and 2), the signaling pathway arising from glucose to the transcriptional machinery is still poorly understood. There is general agreement on the fact that glucose has to be metabolized to stimulate the transcription of lipogenicrelated genes such as L-pyruvate kinase, fatty acid synthase (FAS), 1 acetyl-CoA carboxylase (ACC), and S14 (3-5). In previous papers, we have proposed that glucose-6-phosphate could be the signal metabolite for the glucose-induced FAS transcription (3, 5, 6) and therefore for other genes belonging to the same class. This hypothesis was challenged by Doiron et al. (7) who proposed that the signal metabolite was xylulose-5-phosphate. However, whatever the metabolite, the link between the glucose signal and the activation of gene transcription remains unknown.Phosphorylation/dephosphorylation processes are one of the major mechanisms involved in the regulation of glucose and lipid metabolism both at the cellular and molecular levels in eukaryotic cells. It is now well established that many transcription factors have their activity regulated by phosphorylation through a modification of their DNA binding activity, their transactivating capacity, or their subcellular localization (8).In cultured hepatocytes, it has been shown that okadaic acid, an inhibitor of phosphatases 1 and 2A led to the inhibition of glucose stimulation of S14 gene transcription (9). Further experiments with calyculin, a much more potent inhibitor of protein phosphatase 1 than okadaic acid, suggest th...

Regulation of gene expression by glucose

“…Glucose-induced activation of FAS gene transcription is markedly reduced by incubation of the cells with okadaic acid, an inhibitor of protein phosphatase 1 and 2A, suggesting that the glucose stimulatory effect could involve a dephosphorylation mechanism (Foretz et al 1998). A similar reduction in glucose-activated FAS gene expression is obtained by incubation with 5-amino-imidazolecarboxamide riboside, a cell-permeable activator of the AMP-activated protein kinase (AMPK; Foretz et al 1998).…”

“…A similar reduction in glucose-activated FAS gene expression is obtained by incubation with 5-amino-imidazolecarboxamide riboside, a cell-permeable activator of the AMP-activated protein kinase (AMPK; Foretz et al 1998). Expression of the S14 and L-pyruvate kinase genes is also down-regulated when AMPK is activated (Leclerc et al 1998).…”

Naturally occurring R225W mutation of the gene encoding AMP-activated protein kinase (AMPK)γ3 results in increased oxidative capacity and glucose uptake in human primary myotubes

“…Incubation medium was then transferred to a 24 dual-well Teflon trapping plate [37] and the reaction terminated by adding 70% perchloric acid (wt/vol.). During 1 h incubation at 25°C, 14 CO 2 was trapped in 1 mol/l sodium hydroxide and quantified by liquid scintillation counting. Incubation medium was left overnight at 4°C and centrifuged at 15,000 g for 5 min, after which the 14 C-labelled acid soluble metabolites were quantified.…”

“…AMPK may also be regulated through the glycogenbinding domain on the β subunit by the content and structure of intracellular glycogen [9]. When stimulated, AMPK acts to restore cellular energy balance by stimulating ATP-producing pathways (glucose uptake, fatty acid oxidation and mitochondrial biogenesis) [10][11][12][13] and inhibiting ATP-consuming pathways (fatty acid synthesis, glycogen synthesis and protein synthesis) [14][15][16][17].…”

Investigating Metformin for Cancer Prevention and Treatment: The End of the Beginning

“…( 4 ). This phenotype would involve downregulation of energy-consuming processes, such as protein synthesis via mTOR inhibition ( 4 , 54-56 ) and fatty acid synthesis via reduction in fatty acid synthase expression ( 57,58 ). A transformed cell adopting an "energy-saving" phenotype is unlikely to behave in an aggressive fashion, so a benefi cial cytostatic effect is plausible.…”