INSULIN REGULATION OF GLUCOSE-6-PHOSPHATE-DEHYDROGENASE GENE-EXPRESSION IS RAPAMYCIN-SENSITIVE AND REQUIRES PHOSPHATIDYLINOSITOL 3-KINASE

Glucose-6-phosphate dehydrogenase (G6PDH) controls the flow of carbon through the pentose phosphate pathway and also produces NADPH needed f or maintenance of reduced glutathione and reductive biosynthesis. Hepa tic expression of G6PDH is known to respond to several dietary and hor monal factors, but the mechanism behind regulation of this expression has not been characterized. We show that insulin similarly induces exp ression of endogenous hepatic G6PDH and a reporter construct containin g 935 base pairs of the G6PDH promoter linked to luciferase in transie nt transfection assays. Using well tested and structurally distinct in hibitors of Ras farnesylation, lovastatin and B581, and a specific inh ibitor of mitogen-activated protein kinase kinase activation, PD 98059 , we show that the Ras/Raf/mitogen-activated protein kinase pathway is not utilized for the insulin-induced stimulation of G6PDH gene expres sion in primary rat hepatocytes, Similarly, using well characterized i nhibitors of phosphatidylinositol 3-kinase, wortmannin and LY 294002, me show that PI 3-kinase activity is necessary for the induction of G6 PDH expression by insulin. Rapamycin, an inhibitor of FRAP protein, wh ich is involved in the activation of pp70 S6 kinase, blocks the insuli n induction of G6PDH, suggesting that SG kinase is also necessary for the insulin induction of G6PDH expression.