Department of Nutrition and Metabolism, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan.
Biochem Biophys Res Commun. 2010 Jan 1;391(1):995-9. doi: 10.1016/j.bbrc.2009.12.004. Epub 2009 Dec 5.
In adipocytes and myocytes, insulin stimulation translocates glucose transporter 4 (Glut4) storage vesicles (GSVs) from their intracellular storage sites to the plasma membrane (PM) where they dock with the PM. Then, Glut4 is inserted into the PM and initiates glucose uptake into these cells. Previous studies using chemical inhibitors demonstrated that myosin II participates in fusion of GSVs and the PM and increase in the intrinsic activity of Glut4. In this study, the effect of myosin IIA on GSV trafficking was examined by knocking down myosin IIA expression. Myosin IIA knockdown decreased both glucose uptake and exposures of myc-tagged Glut4 to the cell surface in insulin-stimulated cells, but did not affect insulin signal transduction. Interestingly, myosin IIA knockdown failed to decrease insulin-dependent trafficking of Glut4 to the PM. Moreover, in myosin IIA knockdown cells, insulin-stimulated binding of GSV SNARE protein, vesicle-associated membrane protein 2 (VAMP2) to PM SNARE protein, syntaxin 4 was inhibited. These data suggest that myosin IIA plays a role in insulin-stimulated docking of GSVs to the PM in 3T3-L1 adipocytes through SNARE complex formation.
在脂肪细胞和肌细胞中，胰岛素刺激将葡萄糖转运蛋白 4（Glut4）储存囊泡（GSVs）从其细胞内储存部位转运到质膜（PM），在那里它们与 PM 对接。然后，Glut4 被插入 PM 并开始将葡萄糖摄取到这些细胞中。先前使用化学抑制剂的研究表明，肌球蛋白 II 参与 GSVs 与 PM 的融合以及 Glut4 固有活性的增加。在这项研究中，通过敲低肌球蛋白 IIA 表达来检查肌球蛋白 IIA 对 GSV 运输的影响。肌球蛋白 IIA 敲低降低了胰岛素刺激细胞中葡萄糖摄取和 myc 标记的 Glut4 暴露于细胞表面的水平，但不影响胰岛素信号转导。有趣的是，肌球蛋白 IIA 敲低未能降低胰岛素依赖性 Glut4 向 PM 的运输。此外，在肌球蛋白 IIA 敲低细胞中，胰岛素刺激的 GSV SNARE 蛋白、囊泡相关膜蛋白 2（VAMP2）与 PM SNARE 蛋白、突触融合蛋白 4 的结合受到抑制。这些数据表明，肌球蛋白 IIA 通过 SNARE 复合物形成在 3T3-L1 脂肪细胞中发挥作用，促进胰岛素刺激的 GSV 与 PM 的对接。
