TSH-induced Thyroid Peroxidase expression is inhibited by Nitric Oxide involving the Forkhead Factor FoxE1

MONTESINOS, MM; NICOLA JP; NAZAR, M; PEYRET V; LUCERO AM; PELLIZAS CG; MASINI-REPISO AM

Orlando

Congreso; 15th International Thyroid Congress (ITC); 2015

American Thyroid Association

Introduction: Thyroid peroxidase (TPO) is essential for thyroid hormone synthesis mediating the covalent incorporation of iodine into tyrosine residues of thyroglobulin (I- organification) and the coupling of iodotyrosyl residues to form thyroid hormones. Thyrotropin (TSH) is the main hormonal regulator of TPO gene expression. The thyroid transcription factor FoxE1 is crucial for TSH-induced TPO expression. Previous studies have indicated that nitric oxide (NO) represses TSH-induced I- transport and organification in thyroid cells. Moreover, NO donors inhibit TSH-stimulated TPO mRNA expression in the rat thyroid cell line FRTL-5. Here, we aimed to further explore the molecular mechanism underlying the inhibitory effects of NO on TPO expression. Methods: FRTL-5 cells were incubated with the NO donors sodium nitroprusside and S-nitrosoglutathione. TPO and FoxE1 expression was evaluated through western blot, RT/qPCR, and gene reporter assays. FoxE1 binding to TPO promoter was evaluated by gel shift assays and chromatin immunoprecipitation assays. Results: Both NO donors decreased TSH-induced TPO mRNA and protein expression. NO-reduced TPO expression resulted from transcriptional repression of the TPO gene in response to activation of cyclic guanosine monophosphate/soluble guanylate cyclase (cGMP/cGK) pathway. Deletion and mutagenesis analysis of the TPO promoter revealed the FoxE1 binding site Z as mediator of the NO-induced repression of TPO promoter activity. Coincidently, NO donors decreased the TSH-stimulated FoxE1 binding to the TPO promoter. Further characterization of the role of NO on FoxE1 expression revealed that NO donors reduced the TSH-stimulated FoxE1 level by inhibiting FoxE1 gene expression. Interestingly, FoxE1 overexpression prevented the NO donors-inhibited TPO gene expression in response to TSH. Conclusion: We demonstrated that the NO modulation of TPO transcriptional expression involves NO-triggered inhibition of FoxE1 expression which leads to a reduced transactivation of the TSH-stimulated TPO promoter. These results strongly reinforce the regulatory role of NO on thyroid cell function, an observation of potential pathophysiological relevance in human thyroid pathologies associated with chronic NO production.