Moule S K, Edgell N J, Welsh G I, Diggle T A, Foulstone E J, Heesom K J, Proud C G, Denton R M
Department of Biochemistry, School of Medical Sciences, University Walk Bristol, U.K.
Biochem J. 1995 Oct 15;311 ( Pt 2)(Pt 2):595-601. doi: 10.1042/bj3110595.
We have investigated the signalling pathways involved in the stimulation of glycogen and fatty acid synthesis by insulin in rat fat cells using wortmannin, an inhibitor of phosphatidylinositol 3-kinase, and rapamycin, which blocks activation of p70 ribosomal S6 protein kinase (p70S6K). Insulin produced a decrease in the activity of glycogen synthase kinase-3 which is likely to be important in the observed stimulation of glycogen synthase. Both of these actions were found to be sensitive to inhibition by wortmannin. Activation of three processes is involved in the stimulation of fatty acid synthesis from glucose by insulin, namely glucose uptake, acetyl-CoA carboxylase and pyruvate dehydrogenase. Whereas wortmannin largely abolished the effects of insulin on glucose utilization and acetyl-CoA carboxylase activity, it was without effect on the stimulation of pyruvate dehydrogenase. Although epidermal growth factor stimulated mitogen-activated protein kinase to a greater extent than insulin, it was unable to mimic the effect of insulin on glycogen synthase, glycogen synthase kinase-3, glucose utilization, acetyl-CoA carboxylase or pyruvate dehydrogenase. Rapamycin also failed to have any appreciable effect on stimulation of these parameters by insulin, although it did block the effect of insulin on p70S6K. We conclude that the activity of phosphatidylinositol 3-kinase is required for the effects of insulin on glycogen synthesis, glucose uptake and acetyl-Co-AN carboxylase, but is not involved in signalling to pyruvate dehydrogenase. Activation of mitogen-activated protein kinase or p70S6K, however, does not appear to be sufficient to bring about the stimulation of fatty acid or glycogen synthesis. Altogether is seems likely that at least four distinct signalling pathways are involved in the effects of insulin on rat fat cells.
我们使用磷脂酰肌醇3激酶抑制剂渥曼青霉素和阻断p70核糖体S6蛋白激酶（p70S6K）激活的雷帕霉素，研究了大鼠脂肪细胞中胰岛素刺激糖原和脂肪酸合成所涉及的信号通路。胰岛素使糖原合酶激酶-3的活性降低，这可能在观察到的糖原合酶刺激中起重要作用。发现这两种作用均对渥曼青霉素的抑制敏感。胰岛素刺激葡萄糖合成脂肪酸涉及三个过程的激活，即葡萄糖摄取、乙酰辅酶A羧化酶和丙酮酸脱氢酶。虽然渥曼青霉素在很大程度上消除了胰岛素对葡萄糖利用和乙酰辅酶A羧化酶活性的影响，但对胰岛素刺激丙酮酸脱氢酶没有作用。尽管表皮生长因子比胰岛素更能刺激丝裂原活化蛋白激酶，但它无法模拟胰岛素对糖原合酶、糖原合酶激酶-3、葡萄糖利用、乙酰辅酶A羧化酶或丙酮酸脱氢酶的作用。雷帕霉素对胰岛素刺激这些参数也没有任何明显作用，尽管它确实阻断了胰岛素对p70S6K的作用。我们得出结论，磷脂酰肌醇3激酶的活性是胰岛素对糖原合成、葡萄糖摄取和乙酰辅酶A羧化酶作用所必需的，但不参与向丙酮酸脱氢酶的信号传导。然而，丝裂原活化蛋白激酶或p70S6K的激活似乎不足以刺激脂肪酸或糖原合成。总之，胰岛素对大鼠脂肪细胞的作用似乎至少涉及四条不同的信号通路。
