Gordon D F, Wood W M, Ocran K W, Kao M Y, Sarapura V D, Ridgway E C
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262.
Mol Cell Endocrinol. 1990 Jun 18;71(2):93-103. doi: 10.1016/0303-7207(90)90246-5.
The murine thyrotropic MGH101A tumor is characterized by absent thyrotropin (TSH) beta gene expression and altered thyroid hormone (T3) regulation of the alpha-subunit. Comparison of the promoter structures of both alpha and TSH beta subunit genes from MGH101A with the promoter in expressing TtT-97 thyrotropes revealed no detectable differences. Transfection of the TSH beta promoter from MGH101A linked to luciferase showed minimal expression in primary or cloned MGH101A cells, or L-cells. However, a 6- to 10-fold increase in expression was exhibited in transfected thyrotropes. For the alpha gene, promoter activity was highest in thyrotropes and in cloned MGH101A cells, 5-fold lower in MGH101A tumors, and 10-fold lower in L-cells. Both promoters were not substantially affected by T3 treatment in MGH101A cells. In thyrotropes, promoter activity was inhibited 62.5% and 57.7% by 10 nM T3 treatment for the TSH beta and alpha genes, respectively. DNase I protection showed that factors from TtT-97 but not from MGH101A cells interacted with regions in the TSH beta promoter, while nuclear extracts from each tumor demonstrated at least one protein-DNA interaction with the alpha-subunit promoter. These studies suggest that the molecular defects in the MGH101A tumor are related to the absence of trans-acting factors and are not a result of altered primary gene structure.
鼠促甲状腺素瘤MGH101A的特征是促甲状腺素（TSH）β基因表达缺失以及α亚基的甲状腺激素（T3）调节改变。将MGH101A的α和TSHβ亚基基因的启动子结构与表达促甲状腺素的TtT-97细胞中的启动子进行比较，未发现可检测到的差异。将MGH101A的TSHβ启动子与荧光素酶连接进行转染，结果显示在原代或克隆的MGH101A细胞或L细胞中表达极低。然而，在转染的促甲状腺细胞中表达增加了6至10倍。对于α基因，启动子活性在促甲状腺细胞和克隆的MGH101A细胞中最高，在MGH101A肿瘤中低5倍，在L细胞中低10倍。在MGH101A细胞中，两种启动子均未受到T3处理的显著影响。在促甲状腺细胞中，10 nM T3处理分别使TSHβ和α基因的启动子活性抑制62.5%和57.7%。DNase I保护分析表明，TtT-97细胞而非MGH101A细胞的因子与TSHβ启动子区域相互作用，而每个肿瘤的核提取物均显示至少一种蛋白质与α亚基启动子的DNA相互作用。这些研究表明，MGH101A肿瘤中的分子缺陷与反式作用因子的缺失有关，而非初级基因结构改变的结果。
