title: AMP-activated protein kinase activation increases phosphorylation of glycogen synthase kinase 3beta and thereby reduces cAMP-responsive element transcriptional activity and phosphoenolpyruvate carboxykinase C gene expression in the liver.
abstract: AMP-activated protein kinase (AMPK) activation reportedly suppresses transcriptional activity of the cAMP-responsive element (CRE) in the phosphoenolpyruvate carboxykinase C (PEPCK-C) promoter and reduces hepatic PEPCK-C expression. Although a previous study found TORC2 phosphorylation to be involved in the suppression of AMPK-mediated CRE transcriptional activity, we herein present evidence that glycogen synthase kinase 3beta (GSK3beta) phosphorylation induced by AMPK also plays an important role. We initially found that injecting fasted mice with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) markedly increased Ser-9 phosphorylation of hepatic GSK3beta within 15 min. Stimulation with AICAR or the GSK3beta inhibitor SB-415286 strongly inhibited CRE-containing promoter activity in HepG2 cells. Using the Gal4-based transactivation assay system, the transcriptional activity of cAMP-response element-binding protein (CREB) was suppressed by both AICAR and SB415286, whereas that of TORC2 was repressed significantly by AICAR but very slightly by SB415286. These results show inactivation of GSK3beta to directly inhibit CREB but not TORC2. Importantly, the AICAR-induced suppression of PEPCK-C expression was shown to be blunted by overexpression of GSK3beta(S9G) but not wild-type GSK3beta. In addition, AICAR stimulation decreased, whereas Compound C (AMPK inhibitor) increased CREB phosphorylation (Ser-129) in HepG2 cells. The time-courses of decreased CREB phosphorylation (Ser-129) and increased GSK3beta phosphorylation were very similar. Furthermore, AMPK-mediated GSK3beta phosphorylation was inhibited by an Akt-specific inhibitor in HepG2 cells, suggesting involvement of the Akt pathway. In summary, phosphorylation (Ser-9) of GSK3beta is very likely to be critical for AMPK-mediated PEPCK-C gene suppression. Reduced CREB phosphorylation (Ser-129) associated with inactivation of GSK3beta by Ser-9 phosphorylation may be the major mechanism underlying PEPCK-C gene suppression by AMPK-activating agents such as biguanide.
authors.affiliation: Department of Physiological Chemistry and Metabolism, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan 734-8553.
authors.forename: Nanao
authors.initials: N
authors.lastname: Horike
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Sakoda
authors.forename: Akifumi
authors.initials: A
authors.lastname: Kushiyama
authors.forename: Hiraku
authors.initials: H
authors.lastname: Ono
authors.forename: Midori
authors.initials: M
authors.lastname: Fujishiro
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kamata
authors.forename: Koichi
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Uchijima
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Kurihara
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kurihara
authors.forename: Tomoichiro
authors.initials: T
authors.lastname: Asano
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D005943:Gluconeogenesis; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D051379:Mice; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism*; D010766:Phosphorylation; D012265:Ribonucleotides / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D001645:Biguanides; D017362:Cyclic AMP Response Element-Binding Protein; D047908:Intracellular Signaling Peptides and Proteins; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D055372:AMP-Activated Protein Kinases; C521898:PCK1 protein, human; D010729:Phosphoenolpyruvate Carboxykinase (GTP); C031143:AICA ribonucleotide
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