A CELL-LINE THAT PRODUCES THE GLYCOPROTEIN HORMONE ALPHA-SUBUNIT CONTAINS SPECIFIC NUCLEAR FACTORS SIMILAR TO THOSE PRESENT IN THYROTROPES

作者：SARAPURA VD^*; WOOD WM; GORDON DF; RIDGWAY EC

来源：Thyroid, 1992, 2(1): 31-38.

DOI：10.1089/thy.1992.2.31

A unique characteristic 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.

• 出版日期1992