Department of Molecular Biology and Genetics, Bilkent University, 06800 Bilkent, Ankara, Turkey.
Nucleic Acids Res. 2010 Jun;38(10):3172-85. doi: 10.1093/nar/gkq023. Epub 2010 Jan 31.
Activity of the sodium/iodide symporter (NIS) in lactating breast is essential for iodide (I(-)) accumulation in milk. Significant NIS upregulation was also reported in breast cancer, indicating a potential use of radioiodide treatment. All-trans-retinoic acid (tRA) is a potent ligand that enhances NIS expression in a subset of breast cancer cell lines and in experimental breast cancer models. Indirect tRA stimulation of NIS in breast cancer cells is very well documented; however, direct upregulation by tRA-activated nuclear receptors has not been identified yet. Aiming to uncover cis-acting elements directly regulating NIS expression, we screened evolutionary-conserved non-coding genomic sequences for responsiveness to tRA in MCF-7. Here, we report that a potent enhancer in the first intron of NIS mediates direct regulation by tRA-stimulated nuclear receptors. In vitro as well as in vivo DNA-protein interaction assays revealed direct association between retinoic acid receptor-alpha (RARalpha) and retinoid-X-receptor (RXR) with this enhancer. Moreover, using chromatin immunoprecipitation (ChIP) we uncovered early events of NIS transcription in response to tRA, which require the interaction of several novel intronic tRA responsive elements. These findings indicate a complex interplay between nuclear receptors, RNA Pol-II and multiple intronic RAREs in NIS gene, and they establish a novel mechanistic model for tRA-induced gene transcription.
钠/碘转运体 (NIS) 在哺乳期乳腺中的活性对于碘 (I(-)) 在乳汁中的积累至关重要。乳腺癌中也报道了 NIS 的显著上调，表明放射性碘治疗的潜在用途。全反式视黄酸 (tRA) 是一种有效的配体，可增强一部分乳腺癌细胞系和实验性乳腺癌模型中的 NIS 表达。tRA 对乳腺癌细胞中 NIS 的间接刺激已有充分记录；然而，tRA 激活的核受体对其的直接上调尚未确定。为了揭示直接调节 NIS 表达的顺式作用元件，我们在 MCF-7 中筛选了对 tRA 有反应的进化保守非编码基因组序列。在这里，我们报告 NIS 第一个内含子中的一个有效增强子介导了 tRA 刺激的核受体的直接调节。体外和体内 DNA-蛋白质相互作用试验表明，视黄酸受体-α (RARα) 和视黄醇 X 受体 (RXR) 与该增强子直接结合。此外，我们通过染色质免疫沉淀 (ChIP) 发现了 tRA 应答中 NIS 转录的早期事件，这需要几个新的内含子 tRA 反应元件之间的相互作用。这些发现表明核受体、RNA Pol-II 和 NIS 基因中多个内含子 RARE 之间存在复杂的相互作用，并为 tRA 诱导的基因转录建立了新的机制模型。
