ATP8B1 requires an accessory protein for endoplasmic reticulum exit and plasma membrane lipid flippase activity
ATP8B1 requires an accessory protein for endoplasmic reticulum exit and plasma membrane lipid flippase activity
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DOI：
10.1002/hep.21950
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发表时间：
2008-01-01
期刊：
影响因子：
13.5
通讯作者：
Elferink, Ronald P. J. Oude
中科院分区：
文献类型：
--
作者：
Paulusma, Coen C.;Folmer, Dineke E.;Elferink, Ronald P. J. Oude
ATP8B1突变可导致进行性家族性肝内胆汁淤积症I型和良性复发性肝内胆汁淤积症I型。以前，我们已经表明，在小鼠中，ATP 8B1缺乏导致增强胆汁排泄的磷脂酰丝氨酸，我们假设ATP 8B1是一个翻转酶的磷脂酰丝氨酸。然而，这一功能的直接证据仍然缺乏。在酿酒酵母中，Cdc50p/Lem3p家族的成员对于ATP 8B1同源物的正常功能是必需的。我们研究了该家族的两个人类成员CDC 50 A和CDC 50 B在ATP 8B 1的路由和活动中的作用。当只有ATP 8B1在中国仓鼠卵巢细胞中表达时，该蛋白定位于内质网。与CDC 50蛋白的共表达导致ATP 8B1从内质网到质膜的再定位。仅当ATP 8B1与CDC 50蛋白共表达时，观察到荧光标记的磷脂酰丝氨酸的易位增加250%-500%。重要的是，与单独表达ATP 8B1的细胞相比，共表达ATP 8B1和CDC 50蛋白的细胞中质膜外叶中的天然磷脂酰丝氨酸暴露减少了17%-25%。ATP 8B1和CDC50A在WIF-B9细胞中的共表达导致两种蛋白在小管膜中共定位。结论：我们的数据表明，CDC50蛋白是ATP 8B1运输到质膜的关键因素，因此可能是ATP 8B1相关疾病的重要决定因素。在质膜中，ATP 8B1作为磷脂酰丝氨酸的翻转酶发挥作用。最后，CDC 50 A可能是肝细胞中ATP 8B1的潜在β亚基或伴侣。
Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type I and benign recurrent intrahepatic cholestasis type 1. Previously, we have shown in mice that Atp8b1 deficiency leads to enhanced biliary excretion of phosphatidylserine, and we hypothesized that ATP8B1 is a flippase for phosphatidylserine. However, direct evidence for this function is still lacking. In Saccharomyces cerevisia, members of the Cdc50p/Lem3p family are essential for proper function of the ATP8B1 homologs. We have studied the role of two human members of this family, CDC50A and CDC50B, in the routing and activity of ATP8B1. When only ATP8B1 was expressed in Chinese hamster ovary cells, the protein localized to the endoplasmic reticulum. Coexpression with CDC50 proteins resulted in relocatization of ATP8B1 from the endoplasmic reticulum to the plasma membrane. Only when ATP8B1 was coexpressed with CDC50 proteins was a 250%-500% increase in the translocation of fluorescently labeled phosphatidylserine observed. Importantly, natural phosphatidylserine exposure in the outer leaflet of the plasma membrane was reduced by 17%-25% in cells coexpressing ATP8B1 and CDC50 proteins in comparison with cells expressing ATP8B1 alone. The coexpression of ATP8B1 and CDC50A in WIF-B9 cells resulted in colocatization of both proteins in the canalicular membrane. Conclusion: Our data indicate that CDC50 proteins are pivotal factors in the trafficking of ATP8B1 to the plasma membrane and thus may be essential determinants of ATP8B1-related disease. In the plasma membrane, ATP8B1 functions as a flippase for phosphatidylserine. Finally, CDC50A may be the potential beta-subunit or chaperone for ATP8B1 in hepatocytes.