Rauer Christine, Ringseis Robert, Rothe Susanne, Wen Gaiping, Eder Klaus
Institute of Animal Nutrition and Nutrition Physiology, Justus-Liebig-Universität Gießen, Gießen, Germany.
PLoS One. 2014 Mar 13;9(3):e91265. doi: 10.1371/journal.pone.0091265. eCollection 2014.
Sterol regulatory element-binding proteins (SREBPs)-1c and -2, which were initially discovered as master transcriptional regulators of lipid biosynthesis and uptake, were recently identified as novel transcriptional regulators of the sodium-iodide symporter gene in the thyroid, which is essential for thyroid hormone synthesis. Based on this observation that SREBPs play a role for thyroid hormone synthesis, we hypothesized that another gene involved in thyroid hormone synthesis, the thyroid peroxidase (TPO) gene, is also a target of SREBP-1c and -2. Thyroid epithelial cells treated with 25-hydroxycholesterol, which is known to inhibit SREBP activation, had about 50% decreased mRNA levels of TPO. Similarly, the mRNA level of TPO was reduced by about 50% in response to siRNA mediated knockdown of both, SREBP-1 and SREBP-2. Reporter gene assays revealed that overexpression of active SREBP-1c and -2 causes a strong transcriptional activation of the rat TPO gene, which was localized to an approximately 80 bp region in the intron 1 of the rat TPO gene. In vitro- and in vivo-binding of both, SREBP-1c and SREBP-2, to this region in the rat TPO gene could be demonstrated using gel-shift assays and chromatin immunoprecipitation. Mutation analysis of the 80 bp region of rat TPO intron 1 revealed two isolated and two overlapping SREBP-binding elements from which one, the overlapping SRE+609/InvSRE+614, was shown to be functional in reporter gene assays. In connection with recent findings that the rat NIS gene is also a SREBP target gene in the thyroid, the present findings suggest that SREBPs may be possible novel targets for pharmacological modulation of thyroid hormone synthesis.
固醇调节元件结合蛋白（SREBPs）-1c和-2最初被发现是脂质生物合成和摄取的主要转录调节因子，最近被确定为甲状腺中钠碘同向转运体基因的新型转录调节因子，该基因对甲状腺激素合成至关重要。基于SREBPs在甲状腺激素合成中发挥作用这一观察结果，我们推测另一个参与甲状腺激素合成的基因——甲状腺过氧化物酶（TPO）基因，也是SREBP-1c和-2的靶标。用已知可抑制SREBP激活的25-羟基胆固醇处理的甲状腺上皮细胞，其TPO的mRNA水平降低了约50%。同样，响应于siRNA介导的SREBP-1和SREBP-2敲低，TPO 的mRNA水平降低了约50%。报告基因分析表明，活性SREBP-1c和-2的过表达会导致大鼠TPO基因的强烈转录激活，该基因定位于大鼠TPO基因内含子1中大约80 bp的区域。使用凝胶迁移分析和染色质免疫沉淀可以证明SREBP-1c和SREBP-2在体外和体内与大鼠TPO基因的该区域结合。对大鼠TPO内含子1的80 bp区域进行突变分析，发现了两个分离的和两个重叠的SREBP结合元件，其中一个重叠的SRE+609/InvSRE+614在报告基因分析中显示具有功能。结合最近关于大鼠NIS基因也是甲状腺中SREBP靶基因的发现，目前的研究结果表明，SREBPs可能是甲状腺激素合成药理调节的新型靶标。
