Thyroid-specific gene expression is mainly regulated by thyrotropin (TSH). The cell signaling molecule nitric oxide (NO) is involved in diverse biological processes. Our previous reports indicated that the NO donor, sodium nitroprusside (SNP), inhibited TSH-induced iodide uptake and TPO and thyroglobulin mRNA expression in the rat thyroid cell line FRTL-5. This study aimed to analyse the mechanism involved in NO-induced reduction of TPO gene expression in TSH (0.5mIU/mL) stimulated FRTL-5 cells. In transcription assays SNP (200-500ìM,12h) decreased transcriptional activity of the minimal TPO promoter linked to luciferasa reporter gene (p420TPOLuc). It is known that TTF-2 is crucial for TPO gene regulation. The functional activity of 12ZLuc, a construct with 12 tandem repeats of TTF-2 binding site, was decreased by SNP (12h). Preliminary data indicated a reduction of TTF-2 mRNA level (Northern Blot / RT-PCR) in SNP treated cells (100-500ìM,24h). In conclusion, this study revealed for the first time the ability of NO to reduce TPO gene expression at transcriptional level possibly by involving TTF-2. Since TPO is essential for thyroid hormone biosynthesis, these findings could be of pathophysiological interest.
