Stimulation of GLUT1 glucose transporter expression in response to inhibition of oxidative phosphorylation: Role of reduced sulfhydryl groups

Treatment of Clone 9 cells incubated in the absence of serum with 5 mM azide for 24 h results in an 8- and 3-fold induction in GLUT1 mRNA and GLUT1 protein, respectively. To explore the pathways mediating the induction of GLUT1 mRNA, we first examined whether inhibition of oxidative phosphorylation by other agents results to a similar response. Exposure of cells to 5 mu M carbonyl cyanide m-chlorophenylhydrazone (CCCP), 0.15 mu M oligomycin B, or 5 mM azide resulted in near-equivalent increases in GLUT1 mRNA content. The inhibition of oxidative phosphorylation is associated with increased cell lactate content and in extracellular lactate to pyruvate ratio, reflecting a rise in cytosolic NADH/NAD(+) ratio. We next tested the possibility that an increase in cell SH/SS ratio mediates the enhancement of GLUT1 mRNA in response to azide. We show that treatment of cells with 10 mM mercaptoethanol, an agent that increases cell SH/SS ratio, results in a approximate to 6-fold increase in GLUT1 mRNA content. Moreover, incubation of cells in the presence of 0.3 mM diamide, a known intracellular sulfhydryl oxidizing agent, completely abolishes the induction of GLUT1 mRNA by azide. The results suggest that an increase in cell SH/SS ratio plays a critical role in the induction of GLUT1 mRNA in response to inhibition of oxidative phosphorylation.