Kobayashi Aya, Takanezawa Yasukazu, Hirata Takashi, Shimizu Yuji, Misasa Keiko, Kioka Noriyuki, Arai Hiroyuki, Ueda Kazumitsu, Matsuo Michinori
Laboratory of Cellular Biochemistry, Division of Applied Life Sciences, Kyoto University Graduate School of Agriculture, Kyoto 606-8502, Japan.
J Lipid Res. 2006 Aug;47(8):1791-802. doi: 10.1194/jlr.M500546-JLR200. Epub 2006 May 15.
Cholesterol and phospholipids are essential to the body, but an excess of cholesterol or lipids is toxic and a risk factor for arteriosclerosis. ABCG1, one of the half-type ABC proteins, is thought to be involved in cholesterol homeostasis. To explore the role of ABCG1 in cholesterol homeostasis, we examined its subcellular localization and function. ABCG1 and ABCG1-K120M, a WalkerA lysine mutant, were localized to the plasma membrane in HEK293 cells stably expressing ABCG1 and formed a homodimer. A stable transformant expressing ABCG1 exhibited efflux of cholesterol and choline phospholipids in the presence of BSA, and the cholesterol efflux was enhanced by the presence of HDL, whereas cells expressing ABCG1-K120M did not, suggesting that ATP binding and/or hydrolysis is required for the efflux. Mass and TLC analyses revealed that ABCG1 and ABCA1 secrete several species of sphingomyelin (SM) and phosphatidylcholine (PC), and SMs were preferentially secreted by ABCG1, whereas PCs were preferentially secreted by ABCA1. These results suggest that ABCA1 and ABCG1 mediate the lipid efflux in different mechanisms, in which different species of phospholipids are secreted, and function coordinately in the removal of cholesterol and phospholipids from peripheral cells.
胆固醇和磷脂对身体至关重要，但胆固醇或脂质过量具有毒性，是动脉粥样硬化的一个风险因素。ABCG1是半型ABC蛋白之一，被认为参与胆固醇稳态。为了探究ABCG1在胆固醇稳态中的作用，我们检测了其亚细胞定位和功能。ABCG1和ABCG1-K120M（一种沃克A赖氨酸突变体）在稳定表达ABCG1的HEK293细胞中定位于质膜，并形成同二聚体。在存在牛血清白蛋白（BSA）的情况下，表达ABCG1的稳定转化体表现出胆固醇和胆碱磷脂的流出，高密度脂蛋白（HDL）的存在增强了胆固醇流出，而表达ABCG1-K120M的细胞则没有，这表明流出需要ATP结合和/或水解。质谱和薄层层析（TLC）分析显示，ABCG1和ABCA1分泌几种鞘磷脂（SM）和磷脂酰胆碱（PC），ABCG1优先分泌SM，而ABCA1优先分泌PC。这些结果表明，ABCA1和ABCG1以不同机制介导脂质流出，其中分泌不同种类的磷脂，并在外周细胞胆固醇和磷脂的清除中协同发挥作用。
