Alternative splicing of the rat sodium/bile acid transporter changes its cellular localization and transport properties.
Alternative splicing of the rat sodium/bile acid transporter changes its cellular localization and transport properties.
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DOI：
10.1073/pnas.200325297
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发表时间：
2000-09
影响因子：
11.1
通讯作者：
K. Lazaridis;P. Tietz;Ting Wu;S. Kip;P. Dawson;N. LaRusso
中科院分区：
文献类型：
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作者：
K. Lazaridis;P. Tietz;Ting Wu;S. Kip;P. Dawson;N. LaRusso
胆汁分泌涉及肝细胞和胆管细胞（肝内胆管的衬里细胞）的结构和功能相互作用。肝细胞主动将胆汁酸分泌到泪小管间隙中，然后胆管细胞以矢量方式将胆汁酸转运穿过其顶部和基底侧质膜。胆汁酸跨大鼠胆管细胞跨上皮转运的第一步是通过Na（+）依赖性胆汁酸转运蛋白（ASBT）的顶端摄取。迄今为止，胆汁酸通过胆管细胞基底外侧膜的专性外排机制的分子基础仍然未知。我们已经确定了外显子2跳过，选择性剪接形式的ASBT，指定的t-ASBT，在大鼠胆管细胞，回肠，和肾脏中表达。选择性剪接引起移码，产生154个氨基酸的蛋白质。抗肽抗体在大鼠胆管细胞、回肠和肾脏中检测到约19 kDa的t-ASBT多肽。t-ASBT特异性定位于胆管细胞的基底外侧区。在非洲爪蟾卵母细胞中的转运研究表明，t-ASBT可以作为胆汁酸流出蛋白发挥作用。因此，选择性剪接改变了ASBT的细胞靶向，改变了其功能特性，并为大鼠胆管细胞和其他胆汁酸转运上皮细胞提供了一种挤出胆汁酸的机制。我们的工作代表了一个例子，其中一个单一的基因似乎编码通过选择性剪接摄取和专性外排载体在胆汁酸转运上皮细胞。
Bile secretion involves the structural and functional interplay of hepatocytes and cholangiocytes, the cells lining the intrahepatic bile ducts. Hepatocytes actively secrete bile acids into the canalicular space and cholangiocytes then transport bile acids in a vectorial manner across their apical and basolateral plasma membranes. The initial step in the transepithelial transport of bile acids across rat cholangiocytes is apical uptake by a Na(+)-dependent bile acid transporter (ASBT). To date, the molecular basis of the obligate efflux mechanism for extrusion of bile acids across the cholangiocyte basolateral membrane remains unknown. We have identified an exon-2 skipped, alternatively spliced form of ASBT, designated t-ASBT, expressed in rat cholangiocytes, ileum, and kidney. Alternative splicing causes a frameshift that produces a 154-aa protein. Antipeptide antibodies detected the approximately 19 kDa t-ASBT polypeptide in rat cholangiocytes, ileum, and kidney. The t-ASBT was specifically localized to the basolateral domain of cholangiocytes. Transport studies in Xenopus oocytes revealed that t-ASBT can function as a bile acid efflux protein. Thus, alternative splicing changes the cellular targeting of ASBT, alters its functional properties, and provides a mechanism for rat cholangiocytes and other bile acid-transporting epithelia to extrude bile acids. Our work represents an example in which a single gene appears to encode via alternative splicing both uptake and obligate efflux carriers in a bile acid-transporting epithelial cell.