Liganded T3 receptor β2 inhibits the positive feedback autoregulation of the gene for GATA2, a transcription factor critical for thyrotropin production
Liganded T3 receptor β2 inhibits the positive feedback autoregulation of the gene for GATA2, a transcription factor critical for thyrotropin production
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DOI：
10.1371/journal.pone.0227646
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发表时间：
2020-01-15
期刊：
影响因子：
3.7
通讯作者：
Suda, Takafumi
中科院分区：
文献类型：
--
作者：
Hirahara, Naoko;Nakamura, Hiroko Misawa;Suda, Takafumi
由于甲状腺激素（T3 及其激素原，T4）水平小幅增加，促甲状腺素（促甲状腺激素，TSH）的血清浓度急剧降低；然而，这种关系背后的机制尚不清楚。 TSH 由绒毛膜促性腺激素 a (CGA) 和 β 链 (TSH beta) 组成。两种肽的表达均由转录因子 GATA2 诱导，GATA2 是垂体中促甲状腺素和促性腺素分化的决定因素。我们之前报道过配体 T3 受体 (TR) 通过束缚机制抑制 GATA2 的反式激活活性，并提出这种机制，而不是 TR 与负性 T3 反应元件的结合，是 T3 依赖性抑制 TSH β 和 CGA 基因的基础。 GATA2 基因本身也存在多个 GATA 响应元件 (GATA-RE)，并介导该基因的正反馈自动调节。为了阐明 T3 对这种非线性调节的影响，我们将 GATA2 基因的 -3.9 kb 或 +9.5 kb 处的 GATA-RE 与其 1S 启动子中包含的氯霉素乙酰转移酶报告基因融合。这些构建体与 GATA2 和垂体特异性 TR、TR beta 2 的表达质粒共转染到肾源性 CV1 细胞中。我们发现配体 TR beta 2 抑制 GATA2 诱导的这些报告基因的反式激活。多维输入函数理论揭示配体 TR beta 2 具有经典转录抑制因子的功能。然后，我们研究了 T3 对促性腺激素来源的 Lβ T2 细胞中 GATA2 蛋白和 mRNA 内源表达的影响。在该细胞系中，T3 独立于泛素蛋白酶体系统而减少 GATA2 蛋白。 GATA2 mRNA 被 T3 显着抑制，其浓度对应于中度甲状腺功能减退和甲状腺功能正常。这些结果表明配体 TR beta 2 抑制 GATA2 基因的正反馈自动调节；此外，这种机制在 T3 有效减少 TSH 产生方面发挥着重要作用。
The serum concentration of thyrotropin (thyroid stimulating hormone, TSH) is drastically reduced by small increase in the levels of thyroid hormones (T3 and its prohormone, T4); however, the mechanism underlying this relationship is unknown. TSH consists of the chorionic gonadotropin a (CGA) and the beta chain (TSH beta). The expression of both peptides is induced by the transcription factor GATA2, a determinant of the thyrotroph and gonadotroph differentiation in the pituitary. We previously reported that the liganded T3 receptor (TR) inhibits transactivation activity of GATA2 via a tethering mechanism and proposed that this mechanism, but not binding of TR with a negative T3-responsive element, is the basis for the T3-dependent inhibition of the TSH beta and CGA genes. Multiple GATA-responsive elements (GATA-REs) also exist within the GATA2 gene itself and mediate the positive feedback autoregulation of this gene. To elucidate the effect of T3 on this non-linear regulation, we fused the GATA-REs at -3.9 kb or +9.5 kb of the GATA2 gene with the chloramphenicol acetyltransferase reporter gene harbored in its 1S-promoter. These constructs were co-transfected with the expression plasmids for GATA2 and the pituitary specific TR, TR beta 2, into kidney-derived CV1 cells. We found that liganded TR beta 2 represses the GATA2-induced transactivation of these reporter genes. Multi-dimensional input function theory revealed that liganded TR beta 2 functions as a classical transcriptional repressor. Then, we investigated the effect of T3 on the endogenous expression of GATA2 protein and mRNA in the gonadotroph-derived L beta T2 cells. In this cell line, T3 reduced GATA2 protein independently of the ubiquitin proteasome system. GATA2 mRNA was drastically suppressed by T3, the concentration of which corresponds to moderate hypothyroidism and euthyroidism. These results suggest that liganded TR beta 2 inhibits the positive feedback autoregulation of the GATA2 gene; moreover this mechanism plays an important role in the potent reduction of TSH production by T3.