TSH subunit gene promoters from a murine alpha-subunit producing tumor function normally.
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.
Gordon
D F
DF
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262.
Wood
W M
WM
Ocran
K W
KW
Kao
M Y
MY
Sarapura
V D
VD
Ridgway
E C
EC
D000818:Animals; D015972:Gene Expression Regulation, Neoplastic; D051379:Mice; D010446:Peptide Fragments / Q000235:genetics; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D013964:Thyroid Neoplasms / Q000032:analysis / Q000235:genetics* / Q000473:pathology; D013972:Thyrotropin / Q000235:genetics* / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000032:analysis / Q000378:metabolism / Q000473:pathology
D010446:Peptide Fragments; D012333:RNA, Messenger; D013972:Thyrotropin