Dehydroepiandrosterone Stimulates Glucose Uptake in Human and Murine Adipocytes by Inducing GLUT1 and GLUT4 Translocation to the Plasma Membrane Sebastio Perrini, 1 Annalisa Natalicchio, 1 Luigi Laviola, 1 Gaetana Belsanti, 1 Carmela Montrone, 1 Angelo Cignarelli, 1 Vincenza Minielli, 2 Maria Grano, 2 Giovanni De Pergola, 1 Riccardo Giorgino, 1 and Francesco Giorgino 1 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 trans- porters 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 recep- tor or Akt phosphorylation. In addition, DHEA causes significant increases of cytosolic Ca 2 concentrations and a parallel activation of protein kinase C (PKC)- 2 . The effects of DHEA are abrogated by pretreatment of adipocytes with PI 3-kinase and phospholipase C inhib- itors, as well as by inhibitors of Ca 2 -dependent PKC isoforms, including a specific PKC- 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 C, and the conventional PKC- 2 seem to be involved in DHEA effects. Diabetes 53:41–52, 2004 I nsulin enhances the rates of glucose transport in adipocytes by stimulating the translocation of the GLUT4 and, to a lesser extent, GLUT1 glucose transporters from specific intracellular membrane compartments to the plasma membrane (1). The cascade of signaling events involved in glucose transporter relocal- ization to the cell surface in response to insulin is triggered by an increase in insulin receptor tyrosine kinase activity followed by tyrosine phosphorylation of the insulin recep- tor substrate (IRS) proteins and activation of a complex network of downstream molecules, including phosphati- dylinositol (PI) 3-kinase and other protein kinases such as the serine/threonine kinase Akt/protein kinase B (PKB) and PKC-/ (1,2). In addition to insulin, multiple other hormones or phys- iologic conditions are capable of stimulating GLUT4 trans- location to the cell surface and glucose uptake. For example, exercise induces GLUT4 translocation and glu- cose transport in skeletal muscle through an insulin- independent pathway (3). Also, introduction of GTP analogs, such as GTPS, into 3T3-L1 adipocytes and activation of  1 -adrenergic or endothelin A receptors result in enhanced glucose uptake rates independent of insulin (4 – 6). Some of the signaling mechanisms that mediate these metabolic responses are similar to those utilized by insulin, whereas others are clearly distinct. For instance, the stimulation of glucose uptake and glucose transporter translocation to the cell surface that occurs in adipocytes treated with arachidonic acid, peroxisome proliferator– activated receptor  agonists, or vanadate compounds seems to involve specific and insulin-independent signal- ing molecules (7–9). Dehydroepiandrosterone (DHEA) and its metabolite DHEA sulfate are the most abundant circulating adrenal steroids in humans. Other than their role as precursors of sex steroid hormones, their physiologic functions remain unclear. A progressive decrease in circulating levels of DHEA with age has long been recognized, with peak levels occurring between the third and fourth decades of life and decreasing progressively thereafter by 90% after the age of 85 (10). The decline in circulating DHEA levels occur- ring with aging has been linked to the gradually increasing prevalence of atherosclerosis, obesity, and diabetes in elderly individuals. In the early 1980s, Coleman et al. (11–13) reported that dietary administration of DHEA to db/db mice induced remission of hyperglycemia and largely corrected insulin resistance in these animals. More recently, DHEA was shown to protect against the devel- opment of visceral obesity and muscle insulin resistance in rats fed a high-fat diet (14). Other recent studies have demonstrated that DHEA increases glucose uptake rates in human fibroblasts and rat adipocytes and have sug- From the 1 Department of Emergency and Organ Transplantation, Section on Internal Medicine, Endocrinology and Metabolic Diseases, Bari, Italy; and the 2 Department of Human Anatomy and Histology, University of Bari, Bari, Italy. Address correspondence and reprint requests to Francesco Giorgino, MD, PhD, Department of Emergency and Organ Transplantation, Section on Internal Medicine, Endocrinology and Metabolic Diseases, University of Bari, Piazza Giulio Cesare, 11, I-70124 Bari, Italy. E-mail: f.giorgino@endo.uniba.it. Received for publication 31 January 2003 and accepted in revised form 24 September 2003. DHEA, dehydroepiandrosterone; DMEM, Dulbecco’s modified Eagle’s me- dium; ERK, extracellular signal–related kinase; IRS, insulin receptor sub- strate; LDM, low-density microsome; MAP, mitogen-activated protein; MEK, MAP/ERK kinase; PI, phosphatidylinositol; PIP 3 , PI trisphosphate; PKB, protein kinase B; PKC, protein kinase C; PLC, phospholipase C; PM, plasma membrane; PMSF, phenylmethylsulfonyl fluoride. © 2004 by the American Diabetes Association. DIABETES, VOL. 53, JANUARY 2004 41