Ostermeyer A G, Paci J M, Zeng Y, Lublin D M, Munro S, Brown D A
Department of Biochemistry and Cell Biology, State University of New York at Stony Brook, Stony Brook, New York 11794, USA.
J Cell Biol. 2001 Mar 5;152(5):1071-8. doi: 10.1083/jcb.152.5.1071.
Caveolin-1 is normally localized in plasma membrane caveolae and the Golgi apparatus in mammalian cells. We found three treatments that redirected the protein to lipid storage droplets, identified by staining with the lipophilic dye Nile red and the marker protein ADRP. Caveolin-1 was targeted to the droplets when linked to the ER-retrieval sequence, KKSL, generating Cav-KKSL. Cav-DeltaN2, an internal deletion mutant, also accumulated in the droplets, as well as in a Golgi-like structure. Third, incubation of cells with brefeldin A caused caveolin-1 to accumulate in the droplets. This localization persisted after drug washout, showing that caveolin-1 was transported out of the droplets slowly or not at all. Some overexpressed caveolin-2 was also present in lipid droplets. Experimental reduction of cellular cholesteryl ester by 80% did not prevent targeting of Cav-KKSL to the droplets. Cav-KKSL expression did not grossly alter cellular triacylglyceride or cholesteryl levels, although droplet morphology was affected in some cells. These data suggest that accumulation of caveolin-1 to unusually high levels in the ER causes targeting to lipid droplets, and that mechanisms must exist to ensure the rapid exit of newly synthesized caveolin-1 from the ER to avoid this fate.
在哺乳动物细胞中，小窝蛋白-1通常定位于质膜小窝和高尔基体。我们发现了三种能将该蛋白重定向至脂质储存小滴的处理方法，这些小滴通过亲脂性染料尼罗红和标记蛋白ADRP染色得以识别。当小窝蛋白-1与内质网回收序列KKSL相连生成Cav-KKSL时，它会靶向至小滴。Cav-DeltaN2，一种内部缺失突变体，也会在小滴以及类似高尔基体的结构中积累。第三，用布雷菲德菌素A孵育细胞会导致小窝蛋白-1在小滴中积累。药物洗脱后这种定位仍持续存在，表明小窝蛋白-1从小滴中缓慢转运出来或根本不转运。一些过表达的小窝蛋白-2也存在于脂滴中。通过实验将细胞胆固醇酯降低80%并不能阻止Cav-KKSL靶向至小滴。尽管一些细胞中的小滴形态受到影响，但Cav-KKSL的表达并未显著改变细胞三酰甘油或胆固醇水平。这些数据表明，内质网中异常高水平的小窝蛋白-1积累会导致其靶向脂质小滴，并且必须存在一些机制来确保新合成的小窝蛋白-1迅速从内质网中排出以避免这种情况发生。
