Background: Thyroid peroxidase (TPO) is a central enzyme involved in thyroid hormone synthesis and the main microsomal component for thyroid autoimmunity. NF-êB is a critical mediator of the action of lipopolysaccharide (LPS). We have proposed that NF-êB regulates thyroid specific gene expression and that LPS induces thyroglobulin and Na+/I- symporter expression.
Objective: To analyze the involvement of NF-êB in regulation of TPO expression.
Methods: FRTL-5 thyroid cells treated with TSH, LPS or LPS + TSH, protein (Western-blot), mRNA (RT-qPCR), promoter activity (luciferase) and ChIP were assayed.
Results: LPS increased TPO expression over the TSH-induced level. An augment of TSH-induced TPO mRNA was also observed. To evaluate transcriptional activity, a construct of TPO promoter was transfected into FRTL-5. LPS enhanced the TSH-stimulated TPO promoter activity. A construct lacking the êB site showed no response to LPS and reduced activation by TSH. LPS-induced transcriptional activity was suppressed by a NF-êB inhibitor, BAY, which also repressed TSH-stimulated TPO expression. BAY exerted a similar inhibition on the TPO protein and mRNA level induced by LPS. As well, quantitative ChIP assay in TSH and LPS-stimulated cells evidenced the NFêB subunit (p65) binding to the êB site in TPO promoter.
Conclusions: These findings reveal that a novel mechanism involving the NF-êB pathway mediates the TSH and LPS-stimulated TPO expression including, at least in part, the transcriptional level. Since NF-êB activation is related to many pathophysiological processes such as inflammation and autoimmunity, this study favors that NF-êB-induced modifications in TPO expression could be implicated in thyroid disease.
