Gustavsson J, Parpal S, Karlsson M, Ramsing C, Thorn H, Borg M, Lindroth M, Peterson K H, Magnusson K E, Strâlfors P
Department of Cell Biology, Department of Medical Microbiology, Faculty of Health Sciences, Linköping University, S-58185 Linköping, Sweden.
FASEB J. 1999 Nov;13(14):1961-71.
The insulin receptor is a transmembrane protein of the plasma membrane, where it recognizes extracellular insulin and transmits signals into the cellular signaling network. We report that insulin receptors are localized and signal in caveolae microdomains of adipocyte plasma membrane. Immunogold electron microscopy and immunofluorescence microscopy show that insulin receptors are restricted to caveolae and are colocalized with caveolin over the plasma membrane. Insulin receptor was enriched in a caveolae-enriched fraction of plasma membrane. By extraction with beta-cyclodextrin or destruction with cholesterol oxidase, cholesterol reduction attenuated insulin receptor signaling to protein phosphorylation or glucose transport. Insulin signaling was regained by spontaneous recovery or by exogenous replenishment of cholesterol. beta-Cyclodextrin treatment caused a nearly complete annihilation of caveolae invaginations as examined by electron microscopy. This suggests that the receptor is dependent on the caveolae environment for signaling. Insulin stimulation of cells prior to isolation of caveolae or insulin stimulation of the isolated caveolae fraction increased tyrosine phosphorylation of the insulin receptor in caveolae, demonstrating that insulin receptors in caveolae are functional. Our results indicate that insulin receptors are localized to caveolae in the plasma membrane of adipocytes, are signaling in caveolae, and are dependent on caveolae for signaling.
胰岛素受体是质膜上的一种跨膜蛋白，它能识别细胞外的胰岛素并将信号传递到细胞信号网络中。我们报告胰岛素受体定位于脂肪细胞质膜的小窝微区并在其中发挥信号传导作用。免疫金电子显微镜和免疫荧光显微镜显示胰岛素受体局限于小窝，并且在质膜上与小窝蛋白共定位。胰岛素受体在富含小窝的质膜组分中富集。通过β - 环糊精提取或胆固醇氧化酶破坏，胆固醇减少会减弱胰岛素受体向蛋白质磷酸化或葡萄糖转运的信号传导。通过自发恢复或外源性补充胆固醇可恢复胰岛素信号传导。电子显微镜检查显示，β - 环糊精处理导致小窝内陷几乎完全消失。这表明受体信号传导依赖于小窝环境。在分离小窝之前对细胞进行胰岛素刺激或对分离的小窝组分进行胰岛素刺激，均可增加小窝内胰岛素受体的酪氨酸磷酸化，表明小窝内的胰岛素受体具有功能。我们的结果表明，胰岛素受体定位于脂肪细胞质膜的小窝，在小窝中发挥信号传导作用，并且信号传导依赖于小窝。
