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A cell line that produces the glycoprotein hormone alpha-subunit contains specific nuclear factors similar to those present in thyrotropes.

Abstract
A unique characteristics of thyrotrope-specific gene expression is the coordinated expression and regulation of the alpha- and beta-subunits of TSH. A cell line (alpha TSH) derived from the transplantable mouse thyrotropic tumor MGH101A, which no longer expresses the TSH beta-subunit gene but continues to secrete large amounts of alpha-subunit, was used as a model to study alpha-subunit gene expression independent from the TSH beta-subunit gene and was compared with the expression in TSH-secreting TtT97 tumors. Transient transfection studies showed a striking similarity in the activity of 5' deletions of the mouse alpha-subunit gene promoter in both alpha TSH and TtT97 cells and localized two regions important for expression that spanned 100 base pairs, from -480 to -417 and from -417 to -381. These regions were found to have no activity in nonthyrotrope pituitary GH4 cells and L-cell fibroblasts. Analysis of the alpha-subunit 5' flanking DNA interactions with alpha TSH and TtT97 nuclear extracts showed two DNase I protected sequences, from -474 to -452 and from -447 to -400, both of which colocalized with the functionally important regions. Gel retardation analysis demonstrated the specificity of these interactions, and a similar migration of the DNA-protein complexes suggested that protein factors were similar in the two cell types. We conclude that the nuclear factors necessary for alpha-subunit expression in thyrotropes are retained in alpha TSH cells. Moreover, since alpha TSH cells do not express the TSH beta-subunit gene, the factors that determine the expression of the alpha-subunit may not be sufficient for TSH beta-subunit gene expression.
AuthorsV D Sarapura, W M Wood, D F Gordon, E C Ridgway
JournalThyroid : official journal of the American Thyroid Association (Thyroid) Vol. 2 Issue 1 Pg. 31-8 ( 1992) ISSN: 1050-7256 [Print] United States
PMID1381977 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)
Chemical References
  • Glycoprotein Hormones, alpha Subunit
  • Nuclear Proteins
  • Thyrotropin
  • Luciferases
Topics
  • Animals
  • Basophils (metabolism)
  • Cell Line
  • Gene Expression Regulation
  • Glycoprotein Hormones, alpha Subunit (biosynthesis, genetics)
  • Luciferases (biosynthesis)
  • Mice
  • Nuclear Proteins (isolation & purification, physiology)
  • Thyrotropin (metabolism)
  • Transfection
  • Tumor Cells, Cultured

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