Nishimura H, Saltis J, Habberfield A D, Garty N B, Greenberg A S, Cushman S W, Londos C, Simpson I A
Experimental Diabetes, Metabolism and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 1991 Dec 15;88(24):11500-4. doi: 10.1073/pnas.88.24.11500.
The acute effects of insulin, adenosine, and isoproterenol on the activity, subcellular distribution, and phosphorylation state of the GLUT4 glucose transporter isoform were investigated in rat adipocytes under conditions carefully controlled to monitor changes in cAMP-dependent protein kinase (A-kinase) activity. In contrast to GLUT1, which has not been shown to be phosphorylated even when cells are exposed to any of the above agents, GLUT4 was partially phosphorylated (0.1-0.2 mol/mol) when the activity of the A-kinase was suppressed, and remained unchanged in response to insulin. Isoproterenol elicited a 64% inhibition of insulin-stimulated glucose transport activity in the absence, but not the presence, of adenosine receptor agonists. However, in either the presence or the absence of agonists, A-kinase was activated as assessed by examining the phosphorylation of the major adipocyte A-kinase substrate, perilipin. Similarly, under either condition, phosphorylation of GLUT4 was enhanced 1.4-fold in the intracellular membranes, but no significant change was observed in the plasma membrane. In the absence of adenosine receptor agonists, isoproterenol exerted a small (14%) but significant inhibition of the insulin-induced translocation of GLUT4 but had no effect on the translocation of GLUT1. Thus, changes in the phosphorylation state and/or subcellular distribution of GLUT4 cannot account for the inhibition of insulin-stimulated glucose activity induced by isoproterenol.
在严格控制条件以监测环磷酸腺苷依赖性蛋白激酶（A激酶）活性变化的情况下，研究了胰岛素、腺苷和异丙肾上腺素对大鼠脂肪细胞中GLUT4葡萄糖转运异构体的活性、亚细胞分布及磷酸化状态的急性影响。与GLUT1不同，即使细胞暴露于上述任何一种试剂，GLUT1也未显示出磷酸化，而当A激酶活性受到抑制时，GLUT4会发生部分磷酸化（0.1 - 0.2摩尔/摩尔），并且对胰岛素的反应保持不变。在不存在腺苷受体激动剂的情况下，异丙肾上腺素对胰岛素刺激的葡萄糖转运活性有64%的抑制作用，但在存在腺苷受体激动剂时则无此作用。然而，无论是否存在激动剂，通过检测主要脂肪细胞A激酶底物 perilipin的磷酸化来评估，A激酶均被激活。同样，在这两种情况下，GLUT4在细胞内膜中的磷酸化增强了1.4倍，但在质膜中未观察到显著变化。在不存在腺苷受体激动剂的情况下，异丙肾上腺素对胰岛素诱导的GLUT4转位有轻微（14%）但显著的抑制作用，但对GLUT1的转位没有影响。因此，GLUT4磷酸化状态和/或亚细胞分布的变化不能解释异丙肾上腺素对胰岛素刺激的葡萄糖活性的抑制作用。
