The Nuclear Factor-kB (NFkB) transcription factors are key regulators of immune response, cell survival, proliferation and gene expression. NFkB transcription factors function as dimers of five different subunits including p65, RelB, c-Rel, p50 and p52. NFkB family is recognized to comprise ubiquitously expressed transcription factors that can be activated in response to different signals. NFkB expression and activity is altered in anaplastic thyroid carcinomas leading to oncogenic activity, although the function of NFkB in normal thyroid physiology has not been explored. The objective of this study was to analyze a possible role of NFkB in the TSH-induced gene expression in the thyroid cell.

We observed a nuclear recruitment of NFkB subunits in response to TSH in FRTL-5 thyroid cells, suggesting NFkB activation. The TSH-induced NFkB activation was PKA dependent. The presence of NFkB inhibitors significantly reduced the TSH-induced expression of the genes involved in thyroid hormone biosynthesis, Na+/I- symporter, thyroperoxidase, DUOX2 and thyroglobulin. The involvement of NFkB in the activation exerted by TSH was mediated by a transcriptional process. Bioinformatical analysis revealed the presence of a NFkB consensus site in the promoter regions of these differentiation genes. Chromatin immunoprecipitation assay confirmed the binding of the NFkB subunit p65 to the promoter region of all these genes. Silencing of p65 expression corroborated its original role in the TSH-induced gene expression. Although the involvement of p65 was clearly demonstrated, the participation of other NFkB members should not be excluded. In conclusion, these findings provide evidence that NFkB could constitute a novel mediator of crucial importance in the TSH-induced gene expression, a relevant finding of potential physiological and pathophysiological implication.