Thyroid hormone transport by the heterodimeric human system L amino acid transporter
Thyroid hormone transport by the heterodimeric human system L amino acid transporter
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DOI：
10.1210/en.142.10.4339
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发表时间：
2001-10-01
期刊：
影响因子：
4.8
通讯作者：
Visser, TJ
中科院分区：
文献类型：
--
作者：
Friesema, ECH;Docter, R;Visser, TJ
甲状腺激素跨细胞膜的运输是甲状腺激素作用和代谢所必需的。我们研究了人类系统 L 氨基酸转运蛋白（一种由人 4F2 重链和人 LAT1 轻链组成的蛋白质）可能转运碘甲状腺原氨酸的情况。将编码人4F2重链和/或人LAT1轻链的cRNA注射到非洲爪蟾卵母细胞中，2天后与0.01-10μM[I-125]T-4、[I-125]T-3、[I-125]rT(3)或[I-125]3,3'-二碘甲状腺氨酸或与10-100微米 [H-3]精氨酸、[H-3]亮氨酸、[H-3]苯丙氨酸、[H-3]酪氨酸或[H-3]色氨酸。由于人4F2重链与内源爪蟾轻链的二聚化，单独注射人4F2重链cRNA刺激亮氨酸和精氨酸的摄取，但不影响其他配体的摄取。单独注射人 LAT1 轻链 cRNA 不会刺激任何配体的摄取。人 4F2 重链和人 LAT1 轻链的 cRNA 共注射刺激苯丙氨酸 > 酪氨酸 > 亮氨酸 > 色氨酸 (100 mum) 和 3,3'-二碘甲状腺原氨酸 > rT(3) 的摄取，类似于 T-3 > T-4 (10 nM)，在所有情况下均不依赖于 Na+。饱和分析提供表观米氏常数 (K-m) 值，T-4 为 7.9 μM，T-3 为 0.8 μM，rT(3) 为 12.5 μM，3,3'-二碘甲状腺原氨酸为 7.9 μM，亮氨酸为 46 μM，色氨酸为 19 μM。亮氨酸、酪氨酸和色氨酸（10 μM）的摄取被不同的碘甲状腺原氨酸（10 μM）抑制，特别是T-3。反之亦然，与 100 mum 亮氨酸、色氨酸、酪氨酸或苯丙氨酸共孵育时，0.1 mum T-3 的摄取几乎完全被阻断。我们的结果表明，人类异二聚体系统 L 氨基酸转运蛋白对碘甲状腺原氨酸进行立体特异性 Na+ 独立转运。
Transport of thyroid hormone across the cell membrane is required for thyroid hormone action and metabolism. We have investigated the possible transport of iodothyronines by the human system L amino acid transporter, a protein consisting of the human 4F2 heavy chain and the human LAT1 light chain. Xenopus oocytes were injected with the cRNAs coding for human 4F2 heavy chain and/or human LAT1 light chain, and after 2 d were incubated at 25 C with 0.01-10 muM [I-125]T-4, [I-125]T-3, [I-125]rT(3), or [I-125]3,3'-diiodothyronine or with 10-100 muM [H-3]arginine, [H-3]leucine, [H-3]phenylalanine, [H-3]tyrosine, or [H-3]tryptophan. Injection of human 4F2 heavy chain cRNA alone stimulated the uptake of leucine and arginine due to dimerization of human 4F2 heavy chain with an endogenous Xenopus light chain, but did not affect the uptake of other ligands. Injection of human LAT1 light chain cRNA alone did not stimulate the uptake of any ligand. Coinjection of cRNAs for human 4F2 heavy chain and human LAT1 light chain stimulated the uptake of phenylalanine > tyrosine > leucine > tryptophan (100 mum) and of 3,3'-diiodothyronine > rT(3) similar to T-3 > T-4 (10 nM), which in all cases was Na+ independent. Saturation analysis provided apparent Michaelis constant (K-m) values of 7.9 muM for T-4, 0.8 mum for T-3, 12.5 mum for rT(3), 7.9 muM for 3,3'-diiodothyronine, 46 muM for leucine, and 19 muM for tryptophan. Uptake of leucine, tyrosine, and tryptophan (10 muM) was inhibited by the different iodothyronines (10 muM), in particular T-3. Vice versa, uptake of 0.1 mum T-3 was almost completely blocked by coincubation with 100 mum leucine, tryptophan, tyrosine, or phenylalanine.Our results demonstrate stereospecific Na+-independent transport of iodothyronines by the human heterodimeric system L amino acid transporter.