Retroendocytosis pathway of ABCA1/apoA-I contributes to HDL formation
Retroendocytosis pathway of ABCA1/apoA-I contributes to HDL formation
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DOI：
10.1111/j.1365-2443.2008.01261.x
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发表时间：
2009-02-01
期刊：
影响因子：
2.1
通讯作者：
Ueda, Kazumitsu
中科院分区：
文献类型：
--
作者：
Azuma, Yuya;Takada, Mie;Ueda, Kazumitsu
三磷酸腺苷结合盒蛋白A1(ABCA1)介导细胞内游离胆固醇和磷脂向血浆中的细胞外受体载脂蛋白A-I(apoA-I)转移，形成高密度脂蛋白(HDL)。目前尚不清楚ABCA1的内吞作用和循环在多大程度上有助于高密度脂蛋白的形成。为了解决这个问题，我们在细胞中表达了带有细胞外HA标签或细胞内GFP标签的人ABCA1构建物，并使用该系统来表征ABCA1和apoA-I的内吞和循环。在基础条件下，ABCA1和apoA-I通过clathrin和Rab5介导的途径被内吞，并至少部分通过Rab4介导的途径迅速循环回到细胞表面；大约30%的内吞ABCA1被循环回到细胞表面。当受体介导的内吞作用被抑制时，细胞表面ABCA1的水平增加，apoA-I内化被阻断。在这些条件下，apoA-I介导的胆固醇从积累了脂蛋白来源的胆固醇的细胞中流出减少，而从没有过量胆固醇的细胞中流出增加。这些结果表明，当细胞中积累了过量的脂蛋白胆固醇时，ABCA1/apoA-I的反向内吞途径有助于高密度脂蛋白的形成。
ATP-binding cassette protein A1 (ABCA1) mediates transfer of cellular free cholesterol and phospholipids to apolipoprotein A-I (apoA-I), an extracellular acceptor in plasma, to form high-density lipoprotein (HDL). It is currently unknown to what extent ABCA1 endocytosis and recycling contribute to the HDL formation. To address this issue, we expressed human ABCA1 constructs with either an extracellular HA tag or an intracellular GFP tag in cells, and used this system to characterize endocytosis and recycling of ABCA1 and apoA-I. Under basal conditions, ABCA1 and apoA-I are endocytosed via a clathrin- and Rab5-mediated pathway and recycled rapidly back to the cell surface, at least in part via a Rab4-mediated route; approximately 30% of the endocytosed ABCA1 is recycled back to the cell surface. When receptor-mediated endocytosis is inhibited, the level of ABCA1 at the cell surface increases and apoA-I internalization is blocked. Under these conditions, apoA-I mediated cholesterol efflux from cells that have accumulated lipoprotein-derived cholesterol is decreased, whereas efflux from cells without excess cholesterol is increased. These results suggest that the retroendocytosis pathway of ABCA1/apoA-I contributes to HDL formation when excess lipoprotein-derived cholesterol has accumulated in cells.