Autoregulation by iodine of thyroid protein synthesis: influence of iodine on amino acid transport in cultured thyroid cells.
Autoregulation by iodine of thyroid protein synthesis: influence of iodine on amino acid transport in cultured thyroid cells.
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DOI：
10.1210/endo-114-4-1379
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发表时间：
1984-04
期刊：
影响因子：
4.8
通讯作者：
S. Filetti;B. Rapoport
中科院分区：
文献类型：
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作者：
S. Filetti;B. Rapoport
进行研究以确定碘对甲状腺蛋白质合成的抑制作用是否可以通过细胞内氨基酸转运的减少来解释。在原代培养的最初 24 小时内，使用不可代谢氨基酸 [14C] 环亮氨酸作为狗甲状腺细胞中性氨基酸转运 L 系统的探针。环亮氨酸的摄取在长达 30 分钟内呈线性。在所有时间点，在 NaI (10(-4) M) 中预孵育 3 小时的细胞中环亮氨酸转运均减少。在10(-6)、10(-5)和10(-4)M碘化物下，NaI对环亮氨酸转运（10分钟）的抑制（在典型实验中）分别为19%、42%和69%。甲硫咪唑 (3 mM) 与碘化物一起消除了碘化物对环亮氨酸转运的抑制作用，这意味着碘化物有机化的必要性。甲硫咪唑本身并没有显着改变环亮氨酸的转运。 T3、T4、MIT 和 DIT 同样不抑制环亮氨酸转运。 NaI 不会抑制缺乏碘化物组织机制的细胞中的环亮氨酸转运。不同底物浓度下环亮氨酸流入的双倒数图表明，NaI 降低了环亮氨酸转运的最大速度（2.1 与 4.0 nmol min-1 mg Protein-1），而不影响 Km (1 mM)。与流入相反，碘不影响环亮氨酸流出。碘对环亮氨酸转运的抑制作用在去除细胞外碘后是可逆的，并在 24 小时内完全恢复。碘同样抑制[14C]α-甲基氨基异丁酸以及在30mM甲基-α-氨基异丁酸存在下的[14C]α-氨基异丁酸的细胞摄取，其分别是中性氨基酸的A和ASC转运系统的特异性探针。这些数据表明，碘对甲状腺蛋白质合成的自动调节至少部分是通过 A、ASC 和 L 转运系统调节中性氨基酸摄取的最大速度而发生的。
Studies were conducted to determine whether the inhibitory effect of iodine on thyroid protein synthesis could be explained by a reduction in intracellular amino acid transport. The nonmetabolizable amino acid [14C]cycloleucine was used as a probe for the L system of neutral amino acid transport in dog thyroid cells during the initial 24 h of primary culture. Uptake of cycloleucine was linear for up to 30 min. At all time points, cycloleucine transport was reduced in cells preincubated for 3 h in NaI (10(-4) M). Inhibition (in a typical experiment) by NaI of cycloleucine transport (10 min) was 19%, 42%, and 69% at 10(-6), 10(-5), and 10(-4) M iodide, respectively. Methimazole (3 mM) together with iodide abolished the inhibitory effect of iodide on cycloleucine transport, implying the necessity of iodide organification. Methimazole itself did not significantly alter cycloleucine transport. T3, T4, MIT, and DIT similarly did not inhibit cycloleucine transport. NaI did not inhibit cycloleucine transport in cells lacking a mechanism for iodide organification. Double reciprocal plots of cycloleucine influx at different substrate concentrations indicated that NaI decreases the maximum velocity of cycloleucine transport (2.1 vs. 4.0 nmol min-1 mg protein-1) without affecting the Km (1 mM). In contrast to influx, iodine did not affect cycloleucine efflux. The inhibitory action of iodine on cycloleucine transport was reversible after removal of extracellular iodide, with full recovery occurring within 24 h. Iodine similarly inhibited the cellular uptake of [14C] alpha-methylaminoisobutyric acid as well as [14C] alpha-aminoisobutyric acid in the presence of 30 mM methyl-alpha-aminoisobutyric acid, that is of specific probes for the A and ASC transport systems of neutral amino acids, respectively. These data indicate that autoregulation by iodine of thyroid protein synthesis occurs, at least in part, by regulation of the maximum velocity of neutral amino acid uptake via the A, ASC, and L transport systems.