Diabetes and Obesity Research Program, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, Sydney, New South Wales 2010, Australia.
J Biol Chem. 2012 Feb 24;287(9):6128-38. doi: 10.1074/jbc.M111.318238. Epub 2011 Dec 29.
Akt plays a major role in insulin regulation of metabolism in muscle, fat, and liver. Here, we show that in 3T3-L1 adipocytes, Akt operates optimally over a limited dynamic range. This indicates that Akt is a highly sensitive amplification step in the pathway. With robust insulin stimulation, substantial changes in Akt phosphorylation using either pharmacologic or genetic manipulations had relatively little effect on Akt activity. By integrating these data we observed that half-maximal Akt activity was achieved at a threshold level of Akt phosphorylation corresponding to 5-22% of its full dynamic range. This behavior was also associated with lack of concordance or demultiplexing in the behavior of downstream components. Most notably, FoxO1 phosphorylation was more sensitive to insulin and did not exhibit a change in its rate of phosphorylation between 1 and 100 nm insulin compared with other substrates (AS160, TSC2, GSK3). Similar differences were observed between various insulin-regulated pathways such as GLUT4 translocation and protein synthesis. These data indicate that Akt itself is a major amplification switch in the insulin signaling pathway and that features of the pathway enable the insulin signal to be split or demultiplexed into discrete outputs. This has important implications for the role of this pathway in disease.
Akt 在肌肉、脂肪和肝脏的胰岛素代谢调节中发挥主要作用。在这里，我们表明在 3T3-L1 脂肪细胞中，Akt 在有限的动态范围内最佳运作。这表明 Akt 是该途径中的一个高度敏感的放大步骤。在具有强大胰岛素刺激的情况下，使用药理学或遗传学操作对 Akt 磷酸化进行大量改变对 Akt 活性的影响相对较小。通过整合这些数据，我们观察到 Akt 活性的半最大值在 Akt 磷酸化的阈值水平达到，相当于其全动态范围的 5-22%。这种行为还与下游成分的行为缺乏一致性或多路复用有关。值得注意的是，FoxO1 磷酸化对胰岛素更敏感，与其他底物（AS160、TSC2、GSK3）相比，其磷酸化率在 1 到 100nm 胰岛素之间没有变化。在各种胰岛素调节途径（如 GLUT4 易位和蛋白质合成）之间也观察到类似的差异。这些数据表明 Akt 本身是胰岛素信号通路中的一个主要放大开关，而该途径的特征使胰岛素信号能够分裂或多路复用成离散的输出。这对该途径在疾病中的作用具有重要意义。
