Rab18 localizes to lipid droplets and induces their close apposition to the endoplasmic reticulum-derived membrane
Rab18 localizes to lipid droplets and induces their close apposition to the endoplasmic reticulum-derived membrane
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DOI：
10.1242/jcs.02401
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发表时间：
2005-06-15
影响因子：
4
通讯作者：
Fujimoto, T
中科院分区：
文献类型：
--
作者：
Ozeki, S;Cheng, JL;Fujimoto, T
脂滴（LDs）是储存中性脂质的细胞器，但其调节机制尚不清楚。在本研究中，我们确定Rab 18作为一个LD组件的HepG 2细胞的蛋白质组学分析，并确认其定位免疫组化和蛋白质印迹。野生型和显性活性Rab 18定位于LD，但显性阴性形式没有。内源性Rab 18与脂肪细胞分化相关蛋白（ADRP）在LDs中共存，但两种蛋白的标记强度表现出明显的相互作用。与此观察结果一致，Rab 18的过表达诱导HepG 2和BALB/c 3 T3细胞中LD中ADRP的量减少。此外，Rab 18过表达导致LD与连接到粗糙ER的膜池紧密并列。另外两种降低ADRP的方法，即RNA干扰和布雷菲德菌素A处理，诱导了相同的形态学变化，表明ADRP的降低是LD-ER沉积的原因。根据ER和其他细胞器之间的相似结构，我们建议将与LD并列的ER膜命名为LD相关膜或LAM。目前的结果表明，Rab 18调节LAM的形成，这可能涉及动员储存在LD中的脂质酯。
Lipid droplets (LDs) are organelles that store neutral lipids, but their regulatory mechanism is not well understood. In the present study, we identified Rab18 as an LD component of HepG2 cells by proteomic analysis, and confirmed its localization by immunohistochemistry and western blotting. Wild-type and dominant-active Rab18 localized to LDs but the dominant-negative form did not. Endogenous Rab18 coexisted with adipocyte differentiation-related protein (ADRP) in LDs, but the labeling intensity of the two proteins showed clear reciprocity. Consistent with this observation, overexpression of Rab18 induced a decrease in the amounts of ADRP in LDs in HepG2 and BALB/c 3T3 cells. Furthermore, Rab18 overexpression caused close apposition of LDs to membrane cisternae connected to the rough ER. Two other procedures that decrease ADRP, i.e. RNA interference and brefeldin A treatment, induced the same morphological change, indicating that decrease in ADRP was the cause of the LD-ER apposition. In accordance with similar structures found between ER and other organelles, we propose that the ER membrane apposed to LDs should be named the LD-associated membrane, or LAM. The present results suggested that Rab18 regulates LAM formation, which is likely to be involved in mobilizing lipid esters stored in LDs.