Critical role of 5′-AMP-activated protein kinase in the stimulation of glucose transport in response to inhibition of oxidative phosphorylation

Abstract

5′-AMP-activated protein kinase (AMPK) functions as an energy sensor to provide metabolic adaptation under conditions of ATP depletion, such as hypoxia and inhibition of oxidative phosphorylation. Whether activation of AMPK is critical for stimulation of glucose transport in response to inhibition of oxidative phosphorylation is unknown. Here we found that treatment of Glut1-expressing Clone 9 cells with sodium azide (5 mM for 2 h) or the AMPK activator 5′-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR, 2 mM for 2 h) stimulated the rate of glucose transport by two- to fourfold. Use of small interference RNA (siRNA) directed against AMPKα1or AMPKα1+ AMPKα2(total AMPKα) resulted in a significant inhibition of the glucose transport response and the content of phosphorylated AMPKα1+ phosphorylated AMPKα2(total p-AMPKα) and phosphorylated acetyl-CoA carboxylase (p-ACC) in response to azide. Transfection with siRNA directed against AMPKα2did not affect the glucose transport response. The efficacy of transfection with siRNAs in reducing AMPK content was confirmed by Western blotting. Incubation of cells with compound C, an inhibitor of AMPK, abrogated the glucose transport response and abolished the increase in total p-AMPK in azide-treated or hypoxia-exposed cells. Simultaneous exposure to azide and AICAR did not augment the rate of transport in response to AICAR alone. There was no evidence of coimmunoprecipitation of total p-AMPKα with Glut1. However, LKB1 was associated with total p-AMPKα. We conclude that activation of AMPK plays both a sufficient and a necessary role in the stimulation of glucose transport in response to inhibition of oxidative phosphorylation.