Neumann Susanne, Schuchardt Katrin, Reske Andreas, Reske Alexander, Emmrich Peter, Paschke Ralf
III. Medical Department, University of Leipzig, Leipzig, Germany.
Thyroid. 2004 Feb;14(2):99-111. doi: 10.1089/105072504322880337.
Cold thyroid nodules (CTNs) are characterized by a reduced iodide uptake in comparison to normal thyroid tissue. The sodium iodide symporter (NIS) is the first step in thyroid hormone synthesis and mediates the active iodide transport in the thyroid cells suggesting that decreased iodide uptake could be a result of changes in NIS expression or molecular defects in the NIS gene. In contrast to previous studies, an intraindividual comparison of NIS mRNA expression in CTNs and their corresponding surrounding tissue was performed using direct detection of NIS mRNA. A significant reduction in NIS mRNA expression was detected in 86% of the 14 investigated CTNs. We hypothesized that human sodium iodide symporter (hNIS) transcriptional failure could be caused by primary molecular NIS gene defects and/or methylation of DNA in the NIS promoter. However, no mutation in the NIS cDNA nor in the NIS promoter region upstream up to-443 bp from the ATG start codon was detected. Therefore, primary molecular NIS gene defects were excluded. However, in 50% of CTNs with reduced NIS mRNA expression, the promoter region was hypermethylated. NIS mRNA expression in these hypermethylated CTNs only reached a maximum of 30% of the corresponding surrounding tissue. Hence, methylation of CpG islands in the NIS promotor could be a regulatory mechanism of NIS transcription in CTNs. Immunoblot revealed absent hNIS protein expression in the total cell membrane fraction in 45% of investigated nodules. In the majority of the remaining CTNs NIS protein expression was decreased in the nodule tissue compared to the corresponding surrounding tissue. For investigating protein expression immunhistochemistry has two advantages. First, the whole nodule area can be investigated, and second, NIS expression can be detected in areas where an immunoblot of a cell membrane fraction is negative. Interestingly, immunhistochemistry revealed higher NIS expression in 50% of CTNs compared to their corresponding surrounding tissues and NIS staining was predominantly intracellular. These data demonstrate that NIS protein expression does not reflect NIS mRNA expression. Therefore, factors that affect targeting of NIS to the plasma membrane are likely to be affected.
冷甲状腺结节（CTN）的特征是与正常甲状腺组织相比碘摄取减少。钠碘同向转运体（NIS）是甲状腺激素合成的第一步，介导甲状腺细胞中的活性碘转运，这表明碘摄取减少可能是NIS表达变化或NIS基因分子缺陷的结果。与先前的研究不同，使用NIS mRNA的直接检测对CTN及其相应周围组织中的NIS mRNA表达进行了个体内比较。在14个研究的CTN中，86%检测到NIS mRNA表达显著降低。我们假设人类钠碘同向转运体（hNIS）转录失败可能是由原发性分子NIS基因缺陷和/或NIS启动子中DNA甲基化引起的。然而，在NIS cDNA以及从ATG起始密码子上游至-443 bp的NIS启动子区域均未检测到突变。因此，排除了原发性分子NIS基因缺陷。然而，在50%的NIS mRNA表达降低的CTN中，启动子区域发生了高甲基化。这些高甲基化CTN中的NIS mRNA表达仅达到相应周围组织的30%。因此，NIS启动子中CpG岛的甲基化可能是CTN中NIS转录的一种调节机制。免疫印迹显示，在45%的研究结节中，总细胞膜部分不存在hNIS蛋白表达。在大多数其余的CTN中，与相应的周围组织相比，结节组织中的NIS蛋白表达降低。对于研究蛋白表达，免疫组织化学有两个优点。第一，可以研究整个结节区域，第二，可以在细胞膜部分免疫印迹为阴性的区域检测到NIS表达。有趣的是，免疫组织化学显示，50%的CTN与其相应的周围组织相比，NIS表达更高，且NIS染色主要在细胞内。这些数据表明，NIS蛋白表达并不反映NIS mRNA表达。因此，影响NIS靶向质膜的因素可能受到影响。
