Complementary Functions of the Flippase ATP8B1 and the Floppase ABCB4 in Maintaining Canalicular Membrane Integrity
Complementary Functions of the Flippase ATP8B1 and the Floppase ABCB4 in Maintaining Canalicular Membrane Integrity
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DOI：
10.1053/j.gastro.2011.07.042
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发表时间：
2011-11-01
期刊：
影响因子：
29.4
通讯作者：
Elferink, Ronald P. J. Oude
中科院分区：
文献类型：
--
作者：
Groen, Annemiek;Rodriguez Romero, Marta;Elferink, Ronald P. J. Oude
背景与目的：进行性家族性肝内胆汁淤积症可由ABCB 4或ATP 8B 1突变引起;每种突变编码一种蛋白质，可使磷脂移位，但方向相反。ABCB 4将磷脂酰胆碱从内小叶漂到外小叶，在那里它被胆汁盐提取。ATP 8B 1与辅助蛋白CDC 50 A复合，以相反方向翻转磷脂酰丝氨酸。Abcb 4（-/-）小鼠缺乏胆汁中的磷脂酰胆碱分泌，而Atp 8b 1缺陷小鼠向胆汁中的磷脂酰丝氨酸分泌增加。每种系统都被认为具有保护小管膜免受胆汁盐影响的作用。方法：采用正交试验设计为了研究ABCB 4和ATP 8B 1机制之间的关系，我们在培养的细胞中分别和一起表达转运蛋白，并研究活力和磷脂转运。我们还创建了ABCB 4和ATP 8B 1（双敲除）破坏的小鼠，并研究了喂食胆汁盐的小鼠的胆汁形成和肝损伤。结果：ABCB 4过表达对HEK 293 T细胞有毒性作用，ATP 8B 1-CDC 50 A复合物的共表达可抵消ABCB 4的毒性作用。在Atp 8b 1缺陷小鼠，胆汁盐诱导提取磷脂酰丝氨酸和胞外酶从小管膜，这个过程中没有观察到的双敲除小鼠。结论：ATP 8B 1是肝细胞功能所必需的，特别是在ABCB 4存在的情况下。这很可能是因为ATP 8B 1-CDC 50 A的磷脂酰丝氨酸翻转酶复合物抵消了ABCB 4翻转磷脂酰胆碱时发生的膜不稳定。因此，脂质不对称性对小管膜的完整性很重要; ABCB 4和ATP 8B 1合作保护肝细胞免受胆汁盐的影响。
BACKGROUND & AIMS: Progressive familial intrahepatic cholestasis can be caused by mutations in ABCB4 or ATP8B1; each encodes a protein that translocates phospholipids, but in opposite directions. ABCB4 flops phosphatidylcholine from the inner to the outer leaflet, where it is extracted by bile salts. ATP8B1, in complex with the accessory protein CDC50A, flips phosphatidylserine in the reverse direction. Abcb4(-/-) mice lack biliary secretion of phosphatidylcholine, whereas Atp8b1-deficient mice have increased excretion of phosphatidylserine into bile. Each system is thought to have a role protecting the canalicular membrane from bile salts. METHODS: To investigate the relationship between the mechanisms of ABCB4 and ATP8B1, we expressed the transporters separately and together in cultured cells and studied viability and phospholipid transport. We also created mice with disruptions in ABCB4 and ATP8B1 (double knockouts) and studied bile formation and hepatic damage in mice fed bile salts. RESULTS: Overexpression of ABCB4 was toxic to HEK293T cells; the toxicity was counteracted by coexpression of the ATP8B1-CDC50A complex. In Atp8b1-deficient mice, bile salts induced extraction of phosphatidylserine and ectoenzymes from the canalicular membrane; this process was not observed in the double-knockout mice. CONCLUSIONS: ATP8B1 is required for hepatocyte function, particularly in the presence of ABCB4. This is most likely because the phosphatidylserine flippase complex of ATP8B1-CDC50A counteracts the destabilization of the membrane that occurs when ABCB4 flops phosphatidylcholine. Lipid asymmetry is therefore important for the integrity of the canalicular membrane; ABCB4 and ATP8B1 cooperate to protect hepatocytes from bile salts.