研究促甲状腺激素中糖蛋白激素α亚基(αGSU)基因的调节机制对于理解功能性促甲状腺激素(TSH)的合成至关重要。这里,我们研究了同源异型结构域转录因子Msx1(Msh同源异型盒1)对促甲状腺激素中αGSU表达的影响。Msx1的瞬时表达抑制了αGSU报告基因的活性,以及其在促甲状腺激素来源的αTSH细胞中的内源性mRNA水平。具有连续缺失构建体的荧光素酶报告基因测定和对序列的仔细检查表明,αGSU启动子中推定的Msx1结合位点(PMS)不负责Msx1介导的转录抑制。我们还鉴定了TATA盒结合蛋白(TBP)作为促甲状腺激素中的相互作用蛋白。TBP与Msx1的相互作用以DNA结合非依赖性方式减弱了Msx1对αGSU基因表达的抑制作用。此外,用突变体Msx1进行的瞬时转染研究表明,TBP和Msx1的相互作用对于Msx1介导的αGSU转录抑制至关重要。这些结果表明,Msx1的功能是αGSU的转录抑制因子,其与TBP的相互作用是Msx1调节αGSU基因表达抑制机制的组成部分。
Studying the regulatory mechanism of the glycoprotein hormone α subunit (
αGSU) gene in thyrotropes is essential for understanding the synthesis of functional thyroid-stimulating hormone (TSH). Here, we investigated the influence of a homeodomain transcription factor Msx1 (Msh homeobox 1) on
αGSU expression in thyrotropes. The transient expression of Msx1 inhibited the activity of an
αGSU reporter gene, as well as its endogenous mRNA level in thyrotrope-derived αTSH cells. Luciferase reporter assays with serial deletion constructs and a close examination of the sequences revealed that the putative Msx1 binding site (PMS) in the
αGSU promoter is not responsible for Msx1-mediated transcriptional repression. We also identified the TATA-box binding protein (TBP) as an interacting protein in thyrotropes. Interaction of TBP with Msx1 attenuates the inhibitory effect of Msx1 on
αGSU gene expression in a DNA binding-independent manner. Furthermore, transient transfection studies with mutant Msx1 revealed that the interaction of TBP and Msx1 is critical for Msx1-mediated transcriptional repression of the αGSU. These results suggest that Msx1 functions as a transcriptional repressor of αGSU and that its interaction with TBP is an integral part of the mechanism by which Msx1 regulates the inhibition of αGSU gene expression.