Reduced phosphorylation of AS160 contributes to glucocorticoid-mediated inhibition of glucose uptake in human and murine adipocytes

Excess glucocorticoids induce insulin resistance and reduce glucose uptake although the underlying mechanisms are unclear. Here we demonstrate that Dex (1 μM for 24 h) inhibits basal and insulin (1 nM) stimulated glucose uptake in human and murine adipocytes by 50% with a concomitant reduction in the levels of GLUT1/4 at the plasma membrane but no change in total GLUT1/4 levels. Expression and phosphorylation of proximal insulin signalling molecules (IRS1, PI3K, AKT) was unaffected by Dex as was phosphorylation of mTOR and FOXO1. In contrast, phosphorylation of AKT substrate 160 kDa (AS160) at T642, which is essential for 14-3-3 recruitment and GLUT4 translocation, was reduced by 50% in basal and insulin-stimulated cells and this was mirrored by decreased 14-3-3 association. Co-treatment with the glucocorticoid receptor antagonist RU486 (10 μM) abrogated the Dex effect on AS160-T642 phosphorylation and restored glucose uptake by 80%. These data suggest Dex inhibits glucose uptake in adipocytes, at least in part, by reducing AS160 phosphorylation and interaction with 14-3-3.