A novel PKB/Akt inhibitor, MK-2206, effectively inhibits insulin-stimulated glucose metabolism and protein synthesis in isolated rat skeletal muscle

Abstract

PKB (protein kinase B), also known as Akt, is a key component of insulin signalling. Defects in PKB activation lead to insulin resistance and metabolic disorders, whereas PKB overactivation has been linked to tumour growth. Small-molecule PKB inhibitors have thus been developed for cancer treatment, but also represent useful tools to probe the roles of PKB in insulin action. In the present study, we examined the acute effects of two allosteric PKB inhibitors, MK-2206 and Akti 1/2 (Akti) on PKB signalling in incubated rat soleus muscles. We also assessed the effects of the compounds on insulin-stimulated glucose uptake, glycogen and protein synthesis. MK-2206 dose-dependently inhibited insulin-stimulated PKB phosphorylation, PKBβ activity and phosphorylation of PKB downstream targets (including glycogen synthase kinase-3α/β, proline-rich Akt substrate of 40 kDa and Akt substrate of 160 kDa). Insulin-stimulated glucose uptake, glycogen synthesis and glycogen synthase activity were also decreased by MK-2206 in a dose-dependent manner. Incubation with high doses of MK-2206 (10 μM) inhibited insulin-induced p70 ribosomal protein S6 kinase and 4E-BP1 (eukaryotic initiation factor 4E-binding protein-1) phosphorylation associated with increased eEF2 (eukaryotic elongation factor 2) phosphorylation. In contrast, Akti only modestly inhibited insulin-induced PKB and mTOR (mammalian target of rapamycin) signalling, with little or no effect on glucose uptake and protein synthesis. MK-2206, rather than Akti, would thus be the tool of choice for studying the role of PKB in insulin action in skeletal muscle. The results point to a key role for PKB in mediating insulin-stimulated glucose uptake, glycogen synthesis and protein synthesis in skeletal muscle.

Effect of L-arginine supplementation on the hepatic phosphatidylinositol 3-kinase signaling pathway and gluconeogenic enzymes in early intrauterine growth-restricted rats

“…Changes in PEPCK mRNA reflect PEPCK activity and the glyconeogenic rate. Studies have shown that decreased PKB protein expression in skeletal muscle inhibits the transport of glucose transporter 4 and reduces insulin-mediated glucose uptake and glycolysis (24,25). In the present study, PKB protein expression was not obviously abnormal until puberty, at which time PKB activation became a serious obstacle to insulin stimulation and then affected the further transmission of insulin signaling.…”

Fucosylated Chondroitin Sulfate from Sea Cucumber in Combination with Rosiglitazone Improved Glucose Metabolism in the Liver of the Insulin-Resistant Mice

“…37) Arcari et al have reported that HFSD downregulated PKB, IRS-2, and PI3K mRNA expression. 38) Gan et al found that the phosphorylation levels of p85-PI3K and PKB decreased in the liver of the insulin-resistant rats.…”

Quercetin, a Lead Compound against Type 2 Diabetes Ameliorates Glucose Uptake via AMPK Pathway in Skeletal Muscle Cell Line

“…Alterations or defects in the insulin signal transduction pathway were found in diabetic patients associated with decreased levels of IRb, IRS-1, and PI3K (Kadowaki, 2000). Moreover, inhibition of PI3K, a key molecule involved in insulin signaling pathway, completely abolished insulin-stimulated uptake of glucose (Lai et al, 2012). Akt or Pkb is an important downstream target of insulin-stimulated glucose transport and metabolism.…”