Department of Medical Biology, University of Split, School of Medicine, Split, Šoltanska 2, Split, Croatia.
Service of Endocrinology, Diabetology and Metabolism, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland.
Biochem Pharmacol. 2020 Mar;173:113605. doi: 10.1016/j.bcp.2019.08.007. Epub 2019 Aug 14.
Nuclear factor, erythroid 2-like 2 (Nrf2) is a transcription factor that has been gaining attention in the field of pharmacology and especially in the chemoprevention of diseases such as cancer, metabolic and neurodegenerative diseases, etc. This is because natural compounds such as sulforaphane, which is found in broccoli sprout extracts, can activate Nrf2. The repertoire of the roles of Nrf2 is ever increasing; besides its traditional antioxidant and cytoprotective effects, Nrf2 can have other functions as a transcription factor. We have recently shown that Nrf2 directly regulates the expression of thyroglobulin (Tg), which is the most abundant thyroidal protein and the precursor of thyroid hormones. Two functional binding sites for Nrf2 (antioxidant response elements, AREs) were identified in the regulatory region of the TG gene. Interestingly, we then observed that one of these AREs harbors a rare single-nucleotide polymorphism (SNP). Also recently, we performed the first genome-wide association study (GWAS) for common SNPs that impact the circulating levels of Tg. Based on these investigations, we were triggered (i) to investigate whether common SNPs in the Nrf2 pathway correlate with circulating Tg levels; and (ii) to examine whether the rare SNP in one of the TG regulatory AREs may affect gene expression. To address the first question, we analyzed GWAS data from a general population and its two subpopulations, one with thyroid disease and/or abnormal thyroid function tests and the other without, in which circulating Tg levels had been measured. Statistically significant associations with Tg levels were observed in the genes encoding Nrf2 and Keap1, including, notably, a known functional SNP in the promoter of the gene encoding Nrf2. Regarding the rare SNP (rs778940395) in the proximal ARE of the TG enhancer, luciferase reporter gene expression studies in PCCL3 rat thyroid follicular cells showed that this SNP abrogated the basal and sulforaphane- or TSH-induced luciferase activity, behaving as a complete loss-of-function mutation. Thus, both rare and common genetic variation in the Keap1/Nrf2 pathway can impact TG expression and Tg circulating levels, respectively.
核因子红细胞 2 样 2（Nrf2）是一种转录因子，在药理学领域，特别是在癌症、代谢和神经退行性疾病等疾病的化学预防方面受到越来越多的关注。这是因为天然化合物，如存在于西兰花芽提取物中的萝卜硫素，可以激活 Nrf2。Nrf2 的作用谱不断增加；除了其传统的抗氧化和细胞保护作用外，Nrf2 还可以作为转录因子发挥其他功能。我们最近表明，Nrf2 可以直接调节甲状腺球蛋白（Tg）的表达，Tg 是甲状腺中最丰富的蛋白质，也是甲状腺激素的前体。在 TG 基因的调控区域中鉴定出了两个 Nrf2 的功能结合位点（抗氧化反应元件，AREs）。有趣的是，我们随后观察到其中一个 ARE 含有一个罕见的单核苷酸多态性（SNP）。最近，我们还进行了首次针对影响 Tg 循环水平的常见 SNPs 的全基因组关联研究（GWAS）。基于这些研究，我们受到启发：（i）研究 Nrf2 通路中的常见 SNPs 是否与循环 Tg 水平相关；（ii）研究 TG 调控 ARE 之一中的罕见 SNP 是否可能影响基因表达。为了解决第一个问题，我们分析了来自一般人群及其两个亚群的 GWAS 数据，一个亚群患有甲状腺疾病和/或甲状腺功能测试异常，另一个亚群没有，并且已经测量了循环 Tg 水平。在编码 Nrf2 和 Keap1 的基因中观察到与 Tg 水平有统计学显著关联，包括编码 Nrf2 的基因启动子中的一个已知功能 SNP。关于 TG 增强子近端 ARE 中的罕见 SNP（rs778940395），在 PCCL3 大鼠甲状腺滤泡细胞中的荧光素酶报告基因表达研究表明，该 SNP 消除了基础和萝卜硫素或 TSH 诱导的荧光素酶活性，表现为完全丧失功能的突变。因此，Keap1/Nrf2 通路中的罕见和常见遗传变异均可分别影响 TG 表达和 Tg 循环水平。
