Role of AMP-activated protein kinase in the regulation by glucose of islet beta cell gene expression

Abstract

Elevated glucose concentrations stimulate the transcription of the pre-proinsulin (PPI), L-type pyruvate kinase (L-PK), and other genes in islet beta cells. In liver cells, pharmacological activation by 5-amino-4-imidazolecarboxamide riboside (AICAR) of AMP-activated protein kinase (AMPK), the mammalian homologue of the yeast SNF1 kinase complex, inhibits the effects of glucose, suggesting a key signaling role for this kinase. Here, we demonstrate that AMPK activity is inhibited by elevated glucose concentrations in MIN6 beta cells and that activation of the enzyme with AICAR prevents the activation of the L-PK gene by elevated glucose. Furthermore, microinjection of antibodies to the alpha2- (catalytic) or beta2-subunits of AMPK complex, but not to the alpha1-subunit or extracellular stimulus-regulated kinase, mimics the effects of elevated glucose on the L-PK and PPI promoter activities as assessed by single-cell imaging of promoter luciferase constructs. In each case, injection of antibodies into the nucleus and cytosol, but not the nucleus alone, was necessary, indicating the importance of either a cytosolic phosphorylation event or the subcellular localization of the alpha2-subunits. Incubation with AICAR diminished, but did not abolish, the effect of glucose on PPI transcription. These data suggest that glucose-induced changes in AMPK activity are necessary and sufficient for the regulation of the L-PK gene by the sugar and also play an important role in the regulation of the PPI promoter.

Kinase activity-independent suppression of p73α by AMP-activated kinase α (AMPKα)

“…As reported by others (Salt et al, 1998;Turnley et al, 1999;da Silva Xavier et al, 2000), endogenous AMPKa1 was mainly located in the cytoplasm, whereas AMPKa2 were detected in the nucleus. When cells expressing GFP-p73a were stained with anti-AMPKa1 antibody and Texas Red-conjugated anti-rabbit IgG, AMPKa1 was found in the nucleus with p73a ( Figure 3a).…”

“…Direct regulation of gene transcription by AMPK is likely achieved through the phosphorylation of transcription factors (PPARa, PPARg, HNF4a, ChREBP, HIF-1 and p53), cofactors (p300, PGC-1 and TRIP6) and the basal transcriptional machinery (Pol I) in the nucleus (Lee et al, 2003;Leff, 2003;Bronner et al, 2004;Jones et al, 2005;Solaz-Fuster et al, 2006). Of the catalytic a subunits found in AMPK, a1 is located mainly in the cytoplasm, whereas a2 is detected preferentially in the nucleus (Salt et al, 1998;Turnley et al, 1999;da Silva Xavier et al, 2000), further indicating that the a subunit may modulate AMPK-regulated gene transcription. The suggested role of AMPK in transcriptional regulation also comes from the observation that Snf1, a yeast homolog of AMPK, acts as a histone kinase in cooperation with the histone acetyltransferase Gcn5 (Lo et al, 2001).…”

Serine-385 phosphorylation of inwardly rectifying K+ channel subunit (Kir6.2) by AMP-dependent protein kinase plays a key role in rosiglitazone-induced closure of the KATP channel and insulin secretion in rats

“…For example, an attempt should be made to replicate our results using islets from AMPK −/− mice to verify the role of this important molecule in physiological and pharmacological stimulation of insulin secretion. Previous reports have shown different relationships between the activation of AMPK and glucosestimulated insulin secretion [16][17][18][43][44][45]. However, these differences may be explained in large part by the different glucose concentrations and experimental systems employed in the different studies.…”

Glucose concentration and AMP-dependent kinase activation regulate expression of insulin receptor family members in rat islets and INS-1E beta cells

“…The AMPactivated protein kinase (AMPK) is activated by high AMP and low ATP concentrations. In detail, 5′-AMP allosterically activates AMPK but also activates the upstream AMPK kinase and makes AMPK a worse substrate for protein phosphatases [23,24]. A low cellular glucose concentration leads to depletion of ATP and cellular accumulation of AMP, which then leads to AMPK activation.…”

“…For cellular experiments, AMPK can be activated by 5-amino-4-imidazolecarboxamide riboside (AICAR). AICAR is taken up by cells and converted to its monophosphate, ZMP, which than acts in an AMP-like way on all levels of AMPdependent activation of AMPK [24]. In pancreatic beta cells, activation of AMPK by low glucose or by AICAR decreased the expression of metabolic genes, including solute carrier family 2 (facilitated glucose transporter), member 2 (SLC2A2), aldolase B (ALDOB), liver-type pyruvate kinase (PKLR) or preproinsulin (INS) [24,25].…”