Background. Thyroid peroxidase (TPO) is a central enzyme involved in thyroid hormone biosynthesis and the main microsomal component for thyroid autoimmunity. NF-kB is a critical mediator of the action of the endotoxin lipopolysaccharide (LPS) and other agents. We have proposed that NF-kB regulates thyroid specific gene expression and that LPS induces thyroglobulin and Na+/I- symporter expression.
Objective. To analyze the involvement of NF-kB in the regulation of TPO expression.
Methods. In the FRTL-5 thyroid cell line treated with TSH, LPS or LPS + TSH, protein (Western-blot), mRNA (RT-PCR), 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 (420 bp) was transfected into FRTL-5. LPS enhanced the TSH-stimulated TPO promoter activity. A construct lacking the êB site (-367 bp) showed no response to LPS and reduced activation by TSH. The LPS-induced transcriptional activity was suppressed by a NF-kB inhibitor, BAY, which also repressed TSH-stimulated TPO expression. A similar inhibition was exerted by BAY on the TPO protein and mRNA level induced by LPS. In addition, quantitative ChIP analysis in TSH and LPS-stimulated cells evidenced the recruitment of the NFkB subunit p65 to the kB site in TPO promoter predicted by bioinformatic analysis.
Conclusions. These findings reveal that a novel mechanism involving the NFkB pathway mediates the TSH and LPS-stimulated TPO expression including, at least in part, the transcriptional level. Since NF-kB activation is related to many pathophysiological processes such as inflammation and autoimmunity, this study favors that NF-kB-induced modifications in TPO expression could be implicated in thyroid disease.
