Abstract

Dehydroepiandrosterone (DHEA) has been shown to modulate glucose utilization in humans and animals, but the mechanisms of DHEA action have not been clarified. We show that DHEA induces a dose- and time-dependent increase in glucose transport rates in both 3T3-L1 and human adipocytes with maximal effects at 2 h. Exposure of adipocytes to DHEA does not result in changes of total GLUT4 and GLUT1 protein levels. However, it does result in significant increases of these glucose transporters in the plasma membrane. In 3T3-L1 adipocytes, DHEA increases tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2 and stimulates IRS-1- and IRS-2-associated phosphatidylinositol (PI) 3-kinase activity with no effects on either insulin receptor or Akt phosphorylation. In addition, DHEA causes significant increases of cytosolic Ca²⁺ concentrations and a parallel activation of protein kinase C (PKC)-β₂. The effects of DHEA are abrogated by pretreatment of adipocytes with PI 3-kinase and phospholipase Cγ inhibitors, as well as by inhibitors of Ca²⁺-dependent PKC isoforms, including a specific PKC-β inhibitor. Thus, DHEA increases glucose uptake in both human and 3T3-L1 adipocytes by stimulating GLUT4 and GLUT1 translocation to the plasma membrane. PI 3-kinase, phospholipase Cγ, and the conventional PKC-β₂ seem to be involved in DHEA effects.