TSH subunit gene promoters from a murine alpha-subunit producing tumor function normally

Area of Science:

• Endocrinology
• Molecular Biology
• Cancer Research

Background:

• The MGH101A tumor model exhibits absent thyrotropin (TSH) beta gene expression and altered thyroid hormone (T3) regulation of the alpha-subunit.
• No differences were found in the promoter structures of alpha and TSH beta subunit genes between MGH101A tumors and expressing thyrotropes.

Purpose of the Study:

• To investigate the molecular defects underlying absent TSH beta gene expression in the MGH101A tumor.
• To compare the promoter activities of TSH beta and alpha subunit genes in MGH101A cells versus normal thyrotropes.
• To determine the role of trans-acting factors and T3 regulation in MGH101A tumor cells.

Main Methods:

• Gene transfection assays using luciferase reporter constructs for TSH beta and alpha promoters.
• Analysis of promoter activity in MGH101A cells, MGH101A tumors, L-cells, and normal thyrotropes.
• DNase I protection assays to identify protein-DNA interactions in promoter regions.

Main Results:

• TSH beta promoter showed minimal expression in MGH101A cells but increased significantly in thyrotropes.
• Alpha gene promoter activity was highest in thyrotropes and MGH101A cells, lower in MGH101A tumors and L-cells.
• T3 treatment did not substantially affect promoter activity in MGH101A cells but inhibited it in thyrotropes.
• DNase I protection revealed absence of TSH beta promoter-interacting factors in MGH101A cells, contrasting with TtT-97 cells.

Conclusions:

• The molecular defects in the MGH101A tumor are attributed to the absence of specific trans-acting factors, not alterations in the primary gene structure.
• These findings highlight the importance of transcription factors in regulating TSH beta and alpha subunit gene expression in thyrotropes.