Wang Huajin, Gilham Dean, Lehner Richard
Department of Cell Biology, and Canadian Institutes of Health Research Group on Molecular and Cell Biology of Lipids, University of Alberta, 328 Heritage Medical Research Centre, Edmonton, Alberta, Canada.
J Biol Chem. 2007 Nov 9;282(45):33218-26. doi: 10.1074/jbc.M706841200. Epub 2007 Sep 11.
The assembly of very low density lipoproteins involves the formation of a primordial, poorly lipidated apoB-containing particle in the endoplasmic reticulum, followed by the addition of neutral lipid from luminal lipid droplets (LLD). However, the lipid and protein compositions of LLD have not been determined. We have isolated LLD from mouse liver microsomes and analyzed their lipid and protein compositions. LLD are variably sized particles relatively poor in triacylglycerol (TG) content when compared with the lipid composition of cytosolic lipid droplets (CLD). They are devoid of apoB, adipophilin, and albumin but contain numerous proteins different from those found on CLD, including TG hydrolase (TGH), carboxylesterase 1 (Ces1), microsomal triglyceride transfer protein (MTP), and apoE. Ectopic expression of TGH in McArdle RH7777 hepatoma cells resulted in decreased cellular TG levels, demonstrating a role for TGH in the mobilization of hepatic neutral lipid stores. The isolation and characterization of LLD provide new supporting evidence for the two-step assembly of very low density lipoproteins.
极低密度脂蛋白的组装过程包括在内质网中形成一个原始的、脂质化程度低的含载脂蛋白B颗粒，随后从内质网腔脂质滴（LLD）中添加中性脂质。然而，LLD的脂质和蛋白质组成尚未确定。我们从小鼠肝脏微粒体中分离出LLD，并分析了它们的脂质和蛋白质组成。与胞质脂质滴（CLD）的脂质组成相比，LLD是大小不一的颗粒，其三酰甘油（TG）含量相对较低。它们不含载脂蛋白B、脂肪亲和素和白蛋白，但含有许多与CLD上发现的蛋白质不同的蛋白质，包括TG水解酶（TGH）、羧酸酯酶1（Ces1）、微粒体甘油三酯转移蛋白（MTP）和载脂蛋白E。在McArdle RH7777肝癌细胞中异位表达TGH导致细胞TG水平降低，证明了TGH在肝脏中性脂质储存动员中的作用。LLD的分离和表征为极低密度脂蛋白的两步组装提供了新的支持证据。
