TSH SUBUNIT GENE PROMOTERS FROM A MURINE ALPHA-SUBUNIT PRODUCING TUMOR FUNCTION NORMALLY

The murine thyrotropic MGH101A tumor is characterized by absent thyrotropin (TSH) β gene expression and altered thyroid hormone (T3) regulation of the α-subunit. Comparison of the promoter structures of both α and TSHβ subunit genes from MGH101A with the promoter in expressing TtT-97 thyrotropes revealed no detectable differences. Transfection of the TSHβ 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 α 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 TSHβ and α genes, respectively. DNase I protection showed that factors from TtT-97 but not from MGH101A cells interacted with regions in the TSHβ promoter, while nuclear extracts from each tumor demonstrated at least one protein-DNA interaction with the α-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. © 1990.