Kanai Y, Segawa H, Miyamoto K i, Uchino H, Takeda E, Endou H
Department of Pharmacology and Toxicology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181, Japan.
J Biol Chem. 1998 Sep 11;273(37):23629-32. doi: 10.1074/jbc.273.37.23629.
A cDNA was isolated from rat C6 glioma cells by expression cloning which encodes a novel Na+-independent neutral amino acid transporter designated LAT1. For functional expression in Xenopus oocytes, LAT1 required the heavy chain of 4F2 cell surface antigen (CD98), a type II membrane glycoprotein. When co-expressed with 4F2 heavy chain, LAT1 transported neutral amino acids with branched or aromatic side chains and did not accept basic amino acids or acidic amino acids. The transport via LAT1 was Na+-independent and sensitive to a system L-specific inhibitor 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid. These functional properties correspond to those of the classically characterized amino acid transport system L, a major nutrient transporter. In in vitro translation, LAT1 was shown to be a nonglycosylated membrane protein consistent with the property of 4F2 light chain, suggesting LAT1 is at least one of the proteins formerly referred to as 4F2 light chain. LAT1 exhibits relatively low but significant amino acid sequence similarity to mammalian cationic amino acid transporters and amino acid permeases of bacteria and yeasts, indicating LAT1 is a new member of the APC superfamily. Because of highly regulated nature and high level of expression in tumor cell lines, LAT1 is thought to be up-regulated to support the high protein synthesis for cell growth and cell activation. The cloning of LAT1 is expected to facilitate the research on the protein-protein interaction in the transporter field and to provide a clue to the search for still unidentified transporters.
通过表达克隆从大鼠C6胶质瘤细胞中分离出一种互补DNA（cDNA），其编码一种名为LAT1的新型非钠依赖性中性氨基酸转运体。为了在非洲爪蟾卵母细胞中进行功能性表达，LAT1需要4F2细胞表面抗原（CD98）的重链，这是一种II型膜糖蛋白。当与4F2重链共表达时，LAT1转运带有支链或芳香族侧链的中性氨基酸，不接受碱性氨基酸或酸性氨基酸。通过LAT1的转运不依赖于钠，且对系统L特异性抑制剂2-氨基双环-（2,2,1）-庚烷-2-羧酸敏感。这些功能特性与经典表征的氨基酸转运系统L（一种主要的营养转运体）的特性相符。在体外翻译中，LAT1被证明是一种非糖基化膜蛋白，这与4F2轻链的特性一致，表明LAT1至少是以前被称为4F2轻链的蛋白质之一。LAT1与哺乳动物阳离子氨基酸转运体以及细菌和酵母的氨基酸通透酶表现出相对较低但显著的氨基酸序列相似性，表明LAT1是APC超家族的一个新成员。由于其高度受调控的性质以及在肿瘤细胞系中的高表达水平，LAT1被认为是上调的，以支持细胞生长和细胞激活所需的高蛋白合成。LAT1的克隆有望促进转运体领域蛋白质 - 蛋白质相互作用的研究，并为寻找仍未鉴定的转运体提供线索。
