Acute regulation by insulin of phosphatidylinositol-3-kinase, Rad, Glut 4, and lipoprotein lipase mRNA levels in human muscle

Abstract

We have investigated the acute regulation by insulin of the mRNA levels of nine genes involved in insulin action, in muscle biopsies obtained before and at the end of a 3-h euglycemic hyperinsulinemic clamp. Using reverse transcription-competitive PCR, we have measured the mRNAs encoding the two insulin receptor variants, the insulin receptor substrate-1, the p85α subunit of phosphatidylinositol-3-kinase, Ras associated to diabetes (RAd), the glucose transporter Glut 4, glycogen synthase, 6-phosphofructo-1- kinase, lipoprotein lipase, and the hormone-sensitive lipase. Insulin infusion induced a significant increase in the mRNA level of Glut 4 (+56±13%), Rad (+96±25%), the p85α subunit of phosphatidylinositol-3- kinase (+92±18%) and a decrease in the lipoprotein lipase mRNA level (- 49±5%), while the abundance of the other mRNAs was unaffected. The relative expression of the two insulin receptor variants was not modified. These results demonstrate an acute coordinated regulation by insulin of the expression of genes coding key proteins involved in its action in human skeletal muscle and suggest that Rad and the p85α regulatory subunit of phosphatidylinositol-3-kinase can be added to the list of the genes controlled by insulin.