Fujimoto T, Kogo H, Ishiguro K, Tauchi K, Nomura R
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan.
J Cell Biol. 2001 Mar 5;152(5):1079-85. doi: 10.1083/jcb.152.5.1079.
Caveolin-1 and -2 constitute a framework of caveolae in nonmuscle cells. In the present study, we showed that caveolin-2, especially its beta isoform, is targeted to the surface of lipid droplets (LD) by immunofluorescence and immunoelectron microscopy, and by subcellular fractionation. Brefeldin A treatment induced further accumulation of caveolin-2 along with caveolin-1 in LD. Analysis of mouse caveolin-2 deletion mutants revealed that the central hydrophobic domain (residues 87-119) and the NH(2)-terminal (residues 70-86) and COOH-terminal (residues 120-150) hydrophilic domains are all necessary for the localization in LD. The NH(2)- and COOH-terminal domains appeared to be related to membrane binding and exit from ER, respectively, implying that caveolin-2 is synthesized and transported to LD as a membrane protein. In conjunction with recent findings that LD contain unesterified cholesterol and raft proteins, the result implies that the LD surface may function as a membrane domain. It also suggests that LD is related to trafficking of lipid molecules mediated by caveolins.
小窝蛋白-1和-2构成非肌肉细胞中小窝的框架。在本研究中，我们通过免疫荧光、免疫电子显微镜和亚细胞分级分离表明，小窝蛋白-2，尤其是其β亚型，定位于脂滴（LD）表面。布雷菲德菌素A处理导致小窝蛋白-2与小窝蛋白-1在脂滴中进一步积累。对小鼠小窝蛋白-2缺失突变体的分析表明，中央疏水结构域（第87 - 119位氨基酸残基）以及氨基末端（第70 - 86位氨基酸残基）和亲水羧基末端（第120 - 150位氨基酸残基）对于其在脂滴中的定位都是必需的。氨基末端结构域似乎分别与膜结合有关，羧基末端结构域与从内质网排出有关，这意味着小窝蛋白-2作为一种膜蛋白被合成并转运至脂滴。结合最近关于脂滴含有未酯化胆固醇和筏蛋白的研究结果，这一结果表明脂滴表面可能作为一个膜结构域发挥作用。这也表明脂滴与由小窝蛋白介导的脂质分子运输有关。
