Regulated localization of rab18 to lipid droplets - Effects of lipolytic stimulation and inhibition of lipid droplet catabolism
Regulated localization of rab18 to lipid droplets - Effects of lipolytic stimulation and inhibition of lipid droplet catabolism
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DOI：
10.1074/jbc.m506651200
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发表时间：
2005-12-23
影响因子：
4.8
通讯作者：
Parton, RG
中科院分区：
文献类型：
--
作者：
Martin, S;Driessen, K;Parton, RG
Rab GTP酶是膜交通的重要调节因子。在这里，我们研究了RAB蛋白与脂滴(LDS)的可能联系，LDS是由磷脂单分子层包围的中性含脂细胞器，也称为脂体，传统上被认为是相对惰性的储存细胞器。虽然我们发现LDS与表达的Rab5、Rab7或Rab11构建体标记的内体间隔紧密结合，但这些Rab蛋白没有检测到LD表面本身的标记。相反，GFP-Rab18定位于LDS，免疫电子显微镜显示GFP-Rab18与单层表面直接相关。绿色荧光蛋白(GFP)-Rab18标记的LDS在局部区域发生振荡运动，并在细胞外围和向核周区域发生零星、快速的跳跃运动。在脂肪细胞和非脂肪细胞系中，Rab18都定位于LDS的一个亚群。为了深入了解这个特定的定位，Rab18与Cav3(DGV)共表达，Cav3(DGV)是小窝-3的截断突变体，被证明可以抑制脂滴的分解代谢和运动。GFP-Rab18和MRFP-Cav3(DGV)标记的LDS互斥亚群。此外，在3T3-L1脂肪细胞中，脂解的刺激增加了Rab18对LDS的定位，这一作用被β-肾上腺素能拮抗剂逆转。这些结果表明，Rab蛋白直接定位于LDS的单层表面。此外，在脂解刺激后，与LD表面的结合增加，并被一个小凹突变体抑制，这表明Rab18的招募是由单个LD的代谢状态调节的。
Rab GTPases are crucial regulators of membrane traffic. Here we have examined a possible association of Rab proteins with lipid droplets (LDs), neutral lipid-containing organelles surrounded by a phospholipid monolayer, also known as lipid bodies, which have been traditionally considered relatively inert storage organelles. Although we found close apposition between LDs and endosomal compartments labeled by expressed Rab5, Rab7, or Rab11 constructs, there was no detectable labeling of the LD surface itself by these Rab proteins. In contrast, GFP-Rab18 localized to LDs and immunoelectron microscopy showed direct association with the monolayer surface. Green fluorescent protein (GFP)-Rab18-labeled LDs underwent oscillatory movements in a localized area as well as sporadic, rapid, saltatory movements both in the periphery of the cell and toward the perinuclear region. In both adipocytes and non-adipocyte cell lines Rab18 localized to a subset of LDs. To gain insights into this specific localization, Rab18 was co-expressed with Cav3(DGV), a truncation mutant of caveolin-3 shown to inhibit the catabolism and motility of lipid droplets. GFP-Rab18 and mRFP-Cav3(DGV) labeled mutually exclusive subpopulations of LDs. Moreover, in 3T3-L1 adipocytes, stimulation of lipolysis increased the localization of Rab18 to LDs, an effect reversed by beta-adrenergic antagonists. These results show that a Rab protein localizes directly to the monolayer surface of LDs. In addition, association with the LD surface was increased following stimulation of lipolysis and inhibited by a caveolin mutant suggesting that recruitment of Rab18 is regulated by the metabolic state of individual LDs.