Yuan Taichang, Hong Shangyu, Yao Yao, Liao Kan
State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Cell Res. 2007 Sep;17(9):772-82. doi: 10.1038/cr.2007.73.
Caveolae and non-caveolar lipid rafts are two types of membrane lipid microdomains that play important roles in insulin-stimulated glucose uptake in adipocytes. In order to ascertain their specific functions in this process, caveolae were ablated by caveolin-1 RNA interference. In Cav-1 RNAi adipocytes, neither insulin-stimulated glucose uptake nor Glut-4 (glucose transporter 4) translocation to membrane lipid microdomains was affected by the ablation of caveolae. With a modified sucrose density gradient, caveolae and non-caveolar lipid rafts could be separated. In the wild-type 3T3-L1 adipocytes, Glut-4 was found to be translocated into both caveolae and non-caveolar lipid rafts. However, in Cav-1 RNAi adipocytes, Glut-4 was localized predominantly in non-caveolar lipid rafts. After the removal of insulin, caveolae-localized Glut-4 was internalized faster than non-caveolar lipid raft-associated Glut-4. The internalization of Glut-4 from plasma membrane was significantly decreased in Cav-1 RNAi adipocytes. These results suggest that insulin-stimulated Glut-4 translocation and glucose uptake are caveolae-independent events. Caveolae play a role in the internalization of Glut-4 from plasma membrane after the removal of insulin.
小窝和非小窝脂筏是两种膜脂微区，在脂肪细胞胰岛素刺激的葡萄糖摄取中起重要作用。为了确定它们在此过程中的具体功能，通过小窝蛋白-1 RNA干扰消除了小窝。在Cav-1 RNAi脂肪细胞中，小窝的消除既不影响胰岛素刺激的葡萄糖摄取，也不影响葡萄糖转运蛋白4（Glut-4）向膜脂微区的转位。通过改良的蔗糖密度梯度，可以分离小窝和非小窝脂筏。在野生型3T3-L1脂肪细胞中，发现Glut-4转位到小窝和非小窝脂筏中。然而，在Cav-1 RNAi脂肪细胞中，Glut-4主要定位于非小窝脂筏中。去除胰岛素后，定位于小窝的Glut-4比与非小窝脂筏相关的Glut-4内化更快。在Cav-1 RNAi脂肪细胞中，Glut-4从质膜的内化显著减少。这些结果表明，胰岛素刺激的Glut-4转位和葡萄糖摄取是不依赖于小窝的事件。小窝在去除胰岛素后Glut-4从质膜的内化中起作用。
