Wells R G, Lee W S, Kanai Y, Leiden J M, Hediger M A
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
J Biol Chem. 1992 Aug 5;267(22):15285-8.
The 4F2 cell surface antigen is a disulfide-linked heterodimer induced during the process of cellular activation and expressed widely in mammalian tissues (Parmacek, M. S., Karpinski, B. A., Gottesdiener, K. M., Thompson, C. B., and Leiden, J. M. (1989) Nucleic Acids Res. 17, 1915-1931). The human heavy chain component, a type II membrane glycoprotein, has 29% identity to the amino acid transport-related protein encoded by the recently cloned rat D2 cDNA. We have demonstrated that Xenopus oocytes injected with in vitro transcribed cRNA from D2 take up cystine and dibasic and neutral amino acids (Wells, R. G., and Hediger, M. A. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 5596-5600). In the present study, we examine the role of the human 4F2 heavy chain in amino acid transport. In vitro transcribed 4F2 cRNA was injected into Xenopus oocytes which were assayed for the uptake of radiolabeled amino acids. Our results show that cRNA from 4F2 stimulates the uptake of dibasic and neutral amino acids into oocytes at levels up to 3-fold higher than for water-injected control oocytes. There is no demonstrable uptake of cystine. Uptake is saturable, with characteristics of high affinity transport, and inhibition data suggest that uptake occurs via a single transporter. Dibasic amino acids are taken up by both 4F2 and D2 cRNA-injected oocytes in a sodium-independent manner. In contrast, 4F2-induced but not D2-induced neutral amino acid uptake has a significant component of sodium dependence. Likewise, neutral amino acids in excess inhibit the 4F2-induced uptake of radiolabeled arginine but not leucine in a sodium-dependent manner. The 4F2-induced uptake we observe most likely represents the activity of a single transport system with some characteristics of systems y+, b0,+, and B0,+. We suggest that 4F2 and D2 represent a new family of proteins which induce amino acid transport with distinct characteristics, possibly functioning as transport activators or regulators.
4F2细胞表面抗原是一种在细胞活化过程中诱导产生的二硫键连接的异二聚体，在哺乳动物组织中广泛表达（帕尔马塞克，M.S.，卡尔平斯基，B.A.，戈特斯迪纳，K.M.，汤普森，C.B.，和莱登，J.M.（1989年）《核酸研究》17，1915 - 1931）。人类重链成分是一种II型膜糖蛋白，与最近克隆的大鼠D2 cDNA编码的氨基酸转运相关蛋白有29%的同源性。我们已经证明，注射了来自D2的体外转录cRNA的非洲爪蟾卵母细胞摄取胱氨酸以及二价和中性氨基酸（韦尔斯，R.G.，和赫迪格，M.A.（1992年）《美国国家科学院院刊》89，5596 - 5600）。在本研究中，我们研究了人类4F2重链在氨基酸转运中的作用。将体外转录的4F2 cRNA注射到非洲爪蟾卵母细胞中，并检测其对放射性标记氨基酸的摄取。我们的结果表明，来自4F2的cRNA刺激二价和中性氨基酸摄取到卵母细胞中的水平比注射水的对照卵母细胞高3倍。没有可证明的胱氨酸摄取。摄取是可饱和的，具有高亲和力转运的特征，并且抑制数据表明摄取是通过单一转运体发生的。二价氨基酸被注射了4F2和D2 cRNA的卵母细胞以不依赖钠的方式摄取。相比之下，4F2诱导而非D2诱导的中性氨基酸摄取有一个显著的依赖钠的成分。同样，过量的中性氨基酸以依赖钠的方式抑制4F2诱导的放射性标记精氨酸的摄取，但不抑制亮氨酸的摄取。我们观察到的4F2诱导的摄取很可能代表了一个具有系统y +、b0，+和B0，+某些特征的单一转运系统的活性。我们认为4F2和D2代表了一类新的蛋白质家族，它们诱导具有不同特征的氨基酸转运，可能作为转运激活剂或调节剂发挥作用。
