Suppression of insulin-stimulated phosphatidylinositol 3-kinase activity by the beta3-adrenoceptor agonist CL316243 in rat adipocytes

• Published in: FEBS letters 1997-02, Vol.402 (2-3), p.246
• Main Authors: Ohsaka, Y, Tokumitsu, Y, Nomura, Y
• Format: Article
• Language: English
• Subjects: Adenosine Deaminase - pharmacology; Adipocytes - metabolism; Adipose Tissue - metabolism; Adrenergic beta-Agonists - pharmacology; Animals; Bucladesine - pharmacology; Cells, Cultured; Cholera Toxin - pharmacology; Cyclic AMP - metabolism; Dioxoles - pharmacology; Epididymis; Glucose Transporter Type 4; Hypoglycemic Agents - pharmacology; Insulin - pharmacology; Kinetics; Male; Monosaccharide Transport Proteins - metabolism; Muscle Proteins; Phenylisopropyladenosine - pharmacology; Phosphatidylinositol 3-Kinases; Phosphotransferases (Alcohol Group Acceptor) - antagonists & inhibitors; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Rats; Rats, Wistar; Receptors, Adrenergic, beta - physiology; Receptors, Adrenergic, beta-3
• ISSN: 0014-5793

Insulin increased 2-deoxyglucose (2-DG) uptake via the translocation of glucose transporter (GLUT) 4 to the plasma membrane fraction in rat adipocytes. The stimulatory actions of insulin were accompanied by both an increase in the immunoreactive p85 subunit of phosphatidylinositol (PI) 3-kinase in the plasma membrane fractions and PI 3-kinase activation by tyrosine phosphorylation of the p85 subunit. The beta3-adrenoceptor agonist CL316243 (CL) suppressed all the insulin actions in adenosine deaminase (ADA)-treated cells, but was without effect in non-ADA-treated cells. The inhibitory effects of CL on GLUT 4 translocation and PI 3-kinase activation were abolished by the addition of N6-phenylisopropyl adenosine. Cholera toxin treatment, which markedly increased intracellular cAMP levels, suppressed increases in the levels of GLUT 4 and PI 3-kinase in the plasma membrane fractions in response to insulin. In addition, dibutyryl (Bt2) cAMP also impaired the activation of PI 3-kinase by insulin. These results indicated that CL suppressed insulin-stimulated glucose transport under conditions where cAMP levels were markedly increased (approximately 12-fold). The inhibitory actions of PI 3-kinase activation by insulin were exerted even when cAMP, 8-bromo-cAMP, or Bt2 cAMP was added to immunoprecipitates of the p85 subunit of PI 3-kinase, after treating the cells with insulin. These results suggest that CL suppressed insulin-stimulated PI 3-kinase activity via a cAMP-dependent mechanism, at least in part, direct cAMP action in ADA-treated adipocytes, by which PI 3-kinase activation was inhibited, resulting in the decrease in GLUT 4 translocation and subsequent 2-DG uptake in response to insulin.