Pax-8 Is Essential for Regulation of the Thyroglobulin Gene by Transforming Growth Factor- 1

Publisher Website
Google Scholar
Abstract
Transforming growth factor-b1 (TGF-b1) is a multifunctional cy- tokine that is thought to play a major role in the regulation of growth and differentiation of thyroid cells. However, little is known of its detailed mechanisms of action in thyrocytes. We have therefore stud- ied the molecular mechanisms of TGF-b1 action on thyroglobulin (TG) gene expression by focusing our attention on TGF-b1 regulation of thyroid-specific transcription factors. TGF-b1 decreased TG messen- ger RNA (mRNA) expression both in the presence and in the absence of TSH in rat thyroid FRTL-5 cells. Transfected into FRTL-5 cells, the activity of reporter plasmids containing the rat TG promoter ligated to a luciferase gene was significantly suppressed by the addition of TGF-b1. When the nuclear extracts prepared from TGF-b1-treated FRTL-5 cells were used in gel mobility shift assays, the amount of protein-DNA complex formed by Pax-8 was reduced, both in the pres- ence and in the absence of TSH, but protein-DNA complexes formed by thyroid transcription factor-1 (TTF-1) and TTF-2 were not. The suppressive effect of TGF-b1 on Pax-8/DNA complex formation is in part due to the suppression of Pax-8 mRNA and protein levels by TGF-b1. Expressions of Pax-8 mRNA and protein, which were as- sessed by Northern blot and Western blot analyses, respectively, were decreased by TGF-b1 treatment of FRTL-5 cells in a concentration- dependent manner. In a transfection experiment, mutation of the Pax-8-binding site caused a loss of both TGF-b1- and TSH-respon- siveness in TG promoter activity. Overexpression of Pax-8 abolished the TGF-b1 suppression of TG promoter activity. These results in- dicate that TGF-b1 decreases Pax-8 mRNA levels as well as Pax-8 DNA-binding activity, which, at least in part, seems to be involved in the TGF-b1-induced suppression of TG gene expression. (Endocri- nology 142: 267-275, 2001)

This publication has 0 references indexed in Scilit: