Goalstone M L, Draznin B
Medical Research Service and the Department of Medicine, Veterans Affairs Medical Center and the University of Colorado Health Sciences Center, Denver, Colorado 80220, USA.
J Biol Chem. 1996 Nov 1;271(44):27585-9. doi: 10.1074/jbc.271.44.27585.
Activation of p21(ras) by GTP loading is a critical step in a cascade of intracellular insulin signaling. Farnesylation of p21(ras) protein is an obligatory event that facilitates Ras migration to the plasma membrane and subsequent activation. Farnesyltransferase (FTase) is a ubiquitous enzyme that catalyzes the lipid modification of p21(ras) by the addition of farnesyl to the C-terminal "CAAX" motif. In vitro and in vivo FTase activities were studied in 3T3-L1 adipocytes in response to insulin challenge. Insulin exerted a biphasic stimulatory effect on FTase activity measured in vitro with a 31% increase at 5 min and a 130% increase at 60 min. Insulin-stimulated farnesylation of p21(ras) pools in vivo correlated with FTase activity seen in vitro by displaying an increase in farnesylated p21(ras) from 40% of total cellular Ras in control cells to 63% by 5 min and 80% by 60 min (p < 0.05) in insulin-treated cells. Insulin challenge of 3T3-L1 adipocytes increased incorporation of tritiated mevalonic acid in p21(ras) in a dose-dependent manner and stimulated a 2-fold increase in phosphorylation of the alpha-subunit of FTase at 5 min and a 4-fold increase at 60 min.
通过加载GTP激活p21(ras)是细胞内胰岛素信号级联反应中的关键步骤。p21(ras)蛋白的法尼基化是一个必要事件，它促进Ras迁移到质膜并随后被激活。法尼基转移酶（FTase）是一种普遍存在的酶，它通过将法尼基添加到C末端的“CAAX”基序来催化p21(ras)的脂质修饰。在3T3-L1脂肪细胞中研究了响应胰岛素刺激时的体外和体内FTase活性。胰岛素对体外测量的FTase活性产生双相刺激作用，5分钟时增加31%，60分钟时增加130%。胰岛素刺激的体内p21(ras)池的法尼基化与体外观察到的FTase活性相关，在胰岛素处理的细胞中，法尼基化的p21(ras)从对照细胞中总细胞Ras的40%增加到5分钟时的63%和60分钟时的80%（p < 0.05）。用胰岛素刺激3T3-L1脂肪细胞以剂量依赖的方式增加了p21(ras)中氚标记甲羟戊酸的掺入，并在5分钟时刺激FTaseα亚基的磷酸化增加2倍，60分钟时增加4倍。
