Smart E J, Ying Y s, Donzell W C, Anderson R G
Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9039, USA.
J Biol Chem. 1996 Nov 15;271(46):29427-35. doi: 10.1074/jbc.271.46.29427.
Caveolin is a 22-kDa membrane protein found associated with a coat material decorating the inner membrane surface of caveolae. A remarkable feature of this protein is its ability to migrate from caveolae directly to the endoplasmic reticulum (ER) when membrane cholesterol is oxidized. We now present evidence caveolin is involved in transporting newly synthesized cholesterol from the ER directly to caveolae. MA104 cells and normal human fibroblasts transported new cholesterol to caveolae with a half-time of approximately 10 min. The cholesterol then rapidly flowed from caveolae to non-caveolae membrane. Cholesterol moved out of caveolae even when the supply of fresh cholesterol from the ER was interrupted. Treatment of cells with 10 microg/ml progesterone blocked cholesterol movement from ER to caveolae. Simultaneously, caveolin accumulated in the lumen of the ER, suggesting cholesterol transport is linked to caveolin movement. Caveolae fractions from cells expressing caveolin were enriched in cholesterol 3-4-fold, while the same fractions from cells lacking caveolin were not enriched. Cholesterol transport to the cell surface was nearly 4 times more rapid in cells expressing caveolin than in matched cells lacking caveolin.
小窝蛋白是一种22千道尔顿的膜蛋白，发现它与装饰小窝内膜表面的包被物质相关。这种蛋白的一个显著特征是，当膜胆固醇被氧化时，它能够从小窝直接迁移到内质网（ER）。我们现在提供证据表明，小窝蛋白参与将新合成的胆固醇从内质网直接运输到小窝。MA104细胞和正常人成纤维细胞将新胆固醇运输到小窝的半衰期约为10分钟。然后胆固醇迅速从小窝流向非小窝膜。即使内质网新鲜胆固醇的供应被中断，胆固醇也会从小窝中流出。用10微克/毫升孕酮处理细胞可阻断胆固醇从内质网向小窝的移动。同时，小窝蛋白在内质网腔中积累，表明胆固醇运输与小窝蛋白的移动有关。表达小窝蛋白的细胞的小窝组分中胆固醇富集3 - 4倍，而缺乏小窝蛋白的细胞的相同组分则没有富集。在表达小窝蛋白的细胞中，胆固醇向细胞表面的运输速度比缺乏小窝蛋白的匹配细胞快近4倍。
