A thyrotrope-specific variant of Pit-1 transactivates the thyrotropin beta promoter

• Published in: The Journal of biological chemistry 1993-10, Vol.268 (28), p.20818-20824
• Main Authors: HAUGEN, B. R, WOOD, W. M, GORDON, D. F, RIDGWAY, E. C
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Biological and medical sciences; Blotting, Southern; Blotting, Western; Cells, Cultured; DNA, Single-Stranded; DNA-Binding Proteins - genetics; DNA-Binding Proteins - isolation & purification; DNA-Binding Proteins - metabolism; Fundamental and applied biological sciences. Psychology; Mice; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Promoter Regions, Genetic; Ribonucleases - metabolism; RNA, Messenger - metabolism; Thyrotropin - genetics; Transcription Factor Pit-1; Transcription Factors - genetics; Transcription Factors - isolation & purification; Transcription Factors - metabolism; Transcription. Transcription factor. Splicing. Rna processing; Transcriptional Activation; Transfection; Tumor Cells, Cultured
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)36858-9

Thyrotropin (TSH) beta is a subunit of TSH, the expression of which is limited to the thyrotrope cells of the anterior pituitary gland. Tissue-specific expression of the mouse TSH beta gene is conferred by sequences between -270 and -80 of the 5'-flanking region. We have investigated tissue-specific expression of the TSH beta promoter in two thyrotrope-derived cell types: 1) TtT-97 thyrotropic tumors, which express the endogenous TSH beta gene, and 2) an alpha-TSH cell line, which was generated from a thyrotropic tumor that has lost the ability to express the TSH beta gene. The pituitary-specific transcription factor Pit-1 is present in thyrotropes and interacts with three cis-acting elements in the functionally important region of the TSH beta promoter. Pit-1 protein is present in TtT-97 tumor cells but is absent from alpha-TSH cells. Reintroduction of Pit-1 into alpha-TSH cells by transient transfection does not restore TSH beta promoter activity. We have identified an alternately spliced variant of Pit-1, called Pit-1T, the mRNA and protein expression of which is limited to thyrotrope-derived cells. Pit-1T contains a 14-amino acid insert in the transactivation domain due to an alternate 3' splice acceptor site. Transiently transfected Pit-1T increases TSH beta promoter activity in TtT-97 thyrotropic tumor cells, whereas additional Pit-1 has no effect. The alpha-TSH cell line, which lacks all Pit-1 proteins, requires both isoforms in order to stimulate TSH beta promoter activity. These data suggest that Pit-1T is a thyrotrope-specific splice variant of Pit-1 that is required for TSH beta promoter stimulation; furthermore, both Pit-1 and Pit-1T are required for TSH beta promoter activity in thyrotrope cells.