The sodium iodide symporter (NIS) mediates iodide (I(-)) transport in the thyroid gland and other tissues and is of increasing importance as a therapeutic target and nuclear imaging reporter. NIS activity in vitro is currently measured with radiotracers and electrophysiological techniques. We report on the development of a novel live cell imaging assay of NIS activity using the I(-)-sensitive and genetically encodable yellow fluorescent protein (YFP) variant YFP-H148Q/I152L. In FRTL-5 thyrocytes stably expressing YFP-H148Q/I152L, I(-) induced a rapid and reversible decrease in cellular fluorescence characterized by 1) high affinity for extracellular I(-) (35 muM), 2) inhibition by the NIS inhibitor perchlorate, 3) extracellular Na(+) dependence, and 4) TSH dependence, suggesting that fluorescence changes are due to I(-) influx via NIS. Individual cells within a population of FRTL-5 cells exhibited a 3.5-fold variation in the rate of NIS-mediated I(-) influx, illustrating the utility of YFP-H148Q/I152L to detect cell-to-cell difference in NIS activity. I(-) also caused a perchlorate-sensitive decrease in YFP-H148Q/I152L fluorescence in COS-7 cells expressing NIS but not in cells lacking NIS. These results demonstrate that YFP-H148Q/I152L is a sensitive biosensor of NIS-mediated I(-) uptake in thyroid cells and in nonthyroidal cells following gene transfer and suggest that fluorescence detection of cellular I(-) may be a useful tool by which to study the pathophysiology and pharmacology of NIS.

译文

碘化钠同向转运体 (NIS) 介导碘 (I(-)) 在甲状腺和其他组织中的转运,作为治疗靶标和核成像报告基因的重要性日益提高。目前使用放射性示踪剂和电生理技术测量体外的NIS活性。我们报告了使用I(-) 敏感且可遗传编码的黄色荧光蛋白 (YFP) 变体YFP-H148Q/I152L对NIS活性进行新型活细胞成像测定的开发。在稳定表达YFP-H148Q/I152L的FRTL-5甲状腺细胞中,I(-) 诱导细胞荧光的快速和可逆降低,其特征是1) 对细胞外I(-) (35 muM) 的高亲和力,2) NIS抑制剂高氯酸盐的抑制,3) 细胞外Na(+) 依赖性,和4) TSH依赖性,表明荧光变化是由于I(-) 通过NIS流入所致。FRTL-5细胞群内的单个细胞表现出NIS介导的I(-) 流入速率的3.5倍变化,说明YFP-H148Q/I152L用于检测NIS活性的细胞间差异。I(-) 还导致表达NIS的COS-7细胞中YFP-H148Q/I152L荧光的高氯酸盐敏感降低,但在缺乏NIS的细胞中不引起。这些结果表明,YFP-H148Q/I152L是基因转移后甲状腺细胞和非甲状腺细胞中NIS介导的I(-) 摄取的敏感生物传感器,并表明细胞I(-) 的荧光检测可能是研究的有用工具。NIS的病理生理学和药理学。

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