AMP-activated Protein Kinase Activation Increases Phosphorylation of Glycogen Synthase Kinase 3β 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 3␤ (GSK3␤) 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 GSK3␤ within 15 min. Stimulation with AICAR or the GSK3␤ 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 GSK3␤ to directly inhibit CREB but not TORC2. Importantly, the AICAR-induced suppression of PEPCK-C expression was shown to be blunted by overexpression of GSK3␤(S9G) but not wild-type GSK3␤. 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 GSK3␤ phosphorylation were very similar. Furthermore, AMPK-mediated GSK3␤ phosphorylation was inhibited by an Akt-specific inhibitor in HepG2 cells, suggesting involvement of the Akt pathway. In summary, phosphorylation (Ser-9) of GSK3␤ is very likely to be critical for AMPK-mediated PEPCK-C gene suppression. Reduced CREB phosphorylation (Ser-129) associated with inactivation of GSK3␤ by Ser-9 phosphorylation may be the major mechanism underlying PEPCK-C gene suppression by AMPK-activating agents such as biguanide.

Carbohydrate Metabolism Is Perturbed in Peroxisome-deficient Hepatocytes Due to Mitochondrial Dysfunction, AMP-activated Protein Kinase (AMPK) Activation, and Peroxisome Proliferator-activated Receptor γ Coactivator 1α (PGC-1α) Suppression

“…Second, phosphorylation of GSK3␤ was increased, which has been reported to contribute to the suppression of PEPCK (42). Several additional mechanisms through which AMPK may suppress gluconeogenic gene expression have been reported, such as phosphorylation of FOXO1 and HNF4␣, but these were not experimentally tested in our model, given the already profound effects on CRTC2 and GSK3␤.…”

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

“…However, further AMPK activation through acute AICAR stimulation resulted in a decrease in glycogen levels in myotubes from control and R225W carriers. While this reduction in glycogen content following acute AICAR treatment may have resulted from the phosphorylation of glycogen synthase kinase by AMPK, it may also be the result of allosteric activation of glycogen phosphorylase by AICAR [26,46,47].…”

AMPK-dependent Repression of Hepatic Gluconeogenesis via Disruption of CREB·CRTC2 Complex by Orphan Nuclear Receptor Small Heterodimer Partner

“…AMPK is activated by physiological stimuli, including exercise, muscle contraction, and hormones, such as adiponectin and leptin, as well as by physiological stresses, glucose deprivation, hypoxia, oxidative stress, and osmotic shock conditions (8,9). In the liver, activation of AMPK suppresses hepatic gluconeogenesis acutely by direct phosphorylation of its substrates, including CREB-binding protein (CBP) (10), CRTC2 (11), and GSK3␤ (glycogen synthase kinase 3␤) (12). Recent studies also suggest that AMPK induces SHP gene expression and inhibits hepatic gluconeogenic gene expression in animal models (13,14).…”