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Regulated localization of rab18 to lipid droplets - Effects of lipolytic stimulation and inhibition of lipid droplet catabolism

机译:rab18在脂滴中的定位调控-脂解刺激的作用和脂滴分解代谢的抑制

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摘要

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.
机译:Rab GTPases是膜运输的关键调节剂。在这里,我们研究了Rab蛋白与脂质小滴(LDs),被磷脂单层包围的中性含脂质细胞器(也称为脂质体)的可能关联,传统上认为它们是相对惰性的存储细胞器。尽管我们发现LD和由表达的Rab5,Rab7或Rab11构建体标记的内体区室紧密并置,但这些Rab蛋白并未检测到LD表面本身的标记。相反,定位于LD的GFP-Rab18和免疫电子显微镜显示与单层表面直接缔合。绿色荧光蛋白(GFP)-Rab18标记的LDs在局部区域经历了振荡运动,并在细胞外围和向核周区域发生了偶发的,快速的盐化运动。在脂肪细胞和非脂肪细胞中,Rab18均定位于部分LDs。为了深入了解这种特定的定位,将Rab18与Cav3(DGV)共表达,Cavolin-3的截短突变体显示可抑制脂滴的分解代谢和运动。 GFP-Rab18和mRFP-Cav3(DGV)标记了LD的互斥亚群。此外,在3T3-L1脂肪细胞中,刺激脂肪分解增加了Rab18在LDs上的定位,这种作用被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LD的单层表面。此外,刺激脂解后与LD表面的结合增加,并被小窝蛋白突变体抑制,这表明Rab18的募集受单个LD代谢状态的调节。

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