Honnor R C, Naghshineh S, Cushman S W, Wolff J, Simpson I A, Londos C
Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Cell Signal. 1992 Jan;4(1):87-98. doi: 10.1016/0898-6568(92)90010-6.
Adenylyl cyclase in rat adipose cells is stimulated by ligands for Rs receptors (e.g. isoproterenol) and inhibited by ligands for Ri receptors (e.g. adenosine). In contrast, Rs receptors mediate inhibition and Ri receptors mediate augmentation of insulin-stimulated glucose transport activity by a process independent of changes in cellular cAMP-dependent protein kinase activity [Kuroda M., Honnor R. C., Cushman S. W., Londos C. and Simpson I. A. (1987) J. biol. Chem. 262, 245-253]. The present study examines the possible role of G-proteins in the regulation of insulin-stimulated glucose transport activity by Rs and Ri receptors. First, conditions were established that permit intoxication of isolated rat adipocytes by cholera and pertussis toxins without compromising cell integrity. Effectiveness of toxin treatment was monitored by examining adenylyl cyclase activity in isolated plasma membranes. Secondly, neither toxin interfered with the ability of a maximal concentration insulin to initiate the glucose transport response. Thirdly, pertussis toxin eliminated the augmenting effects of adenosine on insulin-stimulated glucose transport activity, but enhanced the inhibitory effects of isoproterenol. Findings with ligands for other Ri receptors (nicotinic acid and prostaglandin E2) mirrored those with adenosine. Finally, cholera toxin elicited a modest depression of transport activity, and only in the absence of an Ri ligand (e.g. adenosine). Furthermore, in contrast to the enhanced stimulation of adenylyl cyclase by isoproterenol and GTP, cholera toxin eliminated the inhibitory effect of isoproterenol on transport activity. The augmentative effects of adenosine on transport activity were unchanged. Measurements of (-/+cAMP) cAMP-dependent protein kinase activity ratios reinforce the notion that modulation of glucose transport activity is independent of changes in cAMP. We conclude that regulation of glucose transport activity by Rs and Ri receptors is mediated by the G-proteins, Gs and Gi (or other toxin substrates), respectively. Inasmuch as such regulation occurs at the plasma membrane and appears to be cAMP-independent, it is suggested that glucose transporters may be direct targets for receptor: G-protein interactions.
大鼠脂肪细胞中的腺苷酸环化酶可被Rs受体的配体（如异丙肾上腺素）激活，并被Ri受体的配体（如腺苷）抑制。相反，Rs受体介导抑制作用，而Ri受体通过一个独立于细胞cAMP依赖性蛋白激酶活性变化的过程介导胰岛素刺激的葡萄糖转运活性增强[黑田真、洪诺尔·R·C、库什曼·S·W、伦敦多斯·C和辛普森·I·A（1987年）《生物化学杂志》262卷，245 - 253页]。本研究探讨了G蛋白在Rs和Ri受体对胰岛素刺激的葡萄糖转运活性调节中的可能作用。首先，建立了在不损害细胞完整性的情况下使分离的大鼠脂肪细胞被霍乱毒素和百日咳毒素中毒的条件。通过检测分离的质膜中的腺苷酸环化酶活性来监测毒素处理的有效性。其次，两种毒素均未干扰最大浓度胰岛素引发葡萄糖转运反应的能力。第三，百日咳毒素消除了腺苷对胰岛素刺激的葡萄糖转运活性的增强作用，但增强了异丙肾上腺素的抑制作用。其他Ri受体配体（烟酸和前列腺素E2）的研究结果与腺苷的结果相似。最后，霍乱毒素仅在不存在Ri配体（如腺苷）时才引起转运活性的适度降低。此外，与异丙肾上腺素和GTP对腺苷酸环化酶的增强刺激相反，霍乱毒素消除了异丙肾上腺素对转运活性的抑制作用。腺苷对转运活性的增强作用未改变。对（- / + cAMP）cAMP依赖性蛋白激酶活性比值的测量强化了葡萄糖转运活性调节独立于cAMP变化的观点。我们得出结论，Rs和Ri受体对葡萄糖转运活性的调节分别由G蛋白Gs和Gi（或其他毒素底物）介导。由于这种调节发生在质膜上且似乎不依赖于cAMP，因此提示葡萄糖转运体可能是受体：G蛋白相互作用的直接靶点。
