Ohsaka Y, Tokumitsu Y, Nomura Y
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
FEBS Lett. 1997 Feb 3;402(2-3):246-50. doi: 10.1016/s0014-5793(97)00007-0.
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.
胰岛素通过葡萄糖转运蛋白（GLUT）4转位至大鼠脂肪细胞的质膜部分来增加2-脱氧葡萄糖（2-DG）摄取。胰岛素的刺激作用伴随着质膜部分磷脂酰肌醇（PI）3-激酶免疫反应性p85亚基的增加以及p85亚基酪氨酸磷酸化导致的PI 3-激酶激活。β3-肾上腺素能受体激动剂CL316243（CL）在腺苷脱氨酶（ADA）处理的细胞中抑制了所有胰岛素作用，但在未用ADA处理的细胞中无作用。添加N6-苯基异丙基腺苷可消除CL对GLUT 4转位和PI 3-激酶激活的抑制作用。霍乱毒素处理可显著提高细胞内cAMP水平，抑制质膜部分中GLUT 4和PI 3-激酶水平对胰岛素的升高反应。此外，二丁酰（Bt2）cAMP也损害胰岛素对PI 3-激酶的激活。这些结果表明，在cAMP水平显著升高（约12倍）的情况下，CL抑制胰岛素刺激的葡萄糖转运。在用胰岛素处理细胞后，即使将cAMP、8-溴-cAMP或Bt2 cAMP添加到PI 3-激酶p85亚基的免疫沉淀物中，胰岛素对PI 3-激酶激活的抑制作用仍然存在。这些结果表明，CL至少部分地通过cAMP依赖性机制抑制胰岛素刺激的PI 3-激酶活性，在ADA处理的脂肪细胞中直接发挥cAMP作用，由此抑制PI 3-激酶激活，导致GLUT 4转位减少以及随后对胰岛素的2-DG摄取减少。
