Kogai T, Hershman J M, Motomura K, Endo T, Onaya T, Brent G A
The Endocrinology Division, VA Greater Los Angeles Healthcare System and Department of Medicine, UCLA School of Medicine, Los Angeles, California 90073, USA.
Endocrinology. 2001 Aug;142(8):3369-79. doi: 10.1210/endo.142.8.8344.
The absence of TSH-stimulated radioiodide uptake in differentiated thyroid cancer is associated with a high recurrence rate and reduced survival. We studied regulation of the sodium/iodide symporter gene in human papillary thyroid cancer cell lines (BHP) and primary human thyroid cells. BHP cells expressed very low levels of sodium/iodide symporter mRNA and did not concentrate iodide, but iodide uptake was restored to levels seen in FRTL-5 rat thyroid cells by stable transfection of a sodium/iodide symporter cDNA. Sodium/iodide symporter gene expression, therefore, was necessary and sufficient for iodide uptake in BHP cells. We cloned the human sodium/iodide symporter gene 5'-flanking region and analyzed progressive 5'-deletions in transient transfections. We identified a region, -596 to -268, essential to confer full promoter activity in primary normal human thyroid cells. Sodium/iodide symporter promoter activity in four BHP cell lines, however, was markedly reduced, consistent with down-regulation of the endogenous sodium/iodide symporter gene. Nuclear extracts from BHP 2-7 cells had reduced or absent binding to regions of the sodium/iodide symporter promoter shown to be critical for expression, compared with nuclear extracts from FRTL-5 cells. Competition studies indicated that these nuclear proteins were not known thyroid transcription factors. Modifications of the sodium/iodide symporter promoter with demethylation or histone acetylation did not increase sodium/iodide symporter expression, and no deletions of the critical regulatory region were identified in the endogenous gene in BHP cells. Regulation of the sodium/iodide symporter 5'-flanking region in transient transfection paralleled endogenous sodium/iodide symporter expression. Reduced expression of potential novel nuclear factor(s) in these cell lines may contribute to reduced sodium/iodide symporter expression resulting in absence of iodide uptake in some papillary thyroid cancers.
分化型甲状腺癌中缺乏促甲状腺激素刺激的放射性碘摄取与高复发率和生存率降低相关。我们研究了人甲状腺乳头状癌细胞系（BHP）和原代人甲状腺细胞中钠/碘同向转运体基因的调控。BHP细胞表达极低水平的钠/碘同向转运体mRNA且不摄取碘，但通过稳定转染钠/碘同向转运体cDNA，碘摄取恢复到FRTL-5大鼠甲状腺细胞中的水平。因此，钠/碘同向转运体基因表达对于BHP细胞摄取碘是必要且充分的。我们克隆了人钠/碘同向转运体基因的5'侧翼区域，并在瞬时转染中分析了逐步的5'缺失。我们确定了一个区域，-596至-268，对于在原代正常人甲状腺细胞中赋予完全启动子活性至关重要。然而，四个BHP细胞系中的钠/碘同向转运体启动子活性明显降低，这与内源性钠/碘同向转运体基因的下调一致。与FRTL-5细胞的核提取物相比，BHP 2-7细胞的核提取物与钠/碘同向转运体启动子中对表达至关重要的区域的结合减少或缺失。竞争研究表明，这些核蛋白不是已知的甲状腺转录因子。用去甲基化或组蛋白乙酰化修饰钠/碘同向转运体启动子并未增加钠/碘同向转运体表达，并且在BHP细胞的内源性基因中未发现关键调控区域的缺失。瞬时转染中钠/碘同向转运体5'侧翼区域的调控与内源性钠/碘同向转运体表达平行。这些细胞系中潜在新型核因子表达的降低可能导致钠/碘同向转运体表达减少，从而导致一些甲状腺乳头状癌中碘摄取缺失。
