A NOVEL MECHANISM IN THE REGULATION OF THYROID PEROXIDASE EXPRESSION INVOLVING THE NF-κB TRANSCRIPTION FACTOR
NAZAR, M.; Nicola, JP.; Pellizas, CG.; Masini, AM.
FACULTAD DE CIENCIAS QUÍMICAS; UNIVERSIDAD NACIONAL DE CÓRDOBA, ARGENTINA
Background: Thyroid peroxidase (TPO) is a central enzyme involved in thyroid hormone synthesis and the main microsomal component for thyroid autoimmunity. NF-κB is a critical mediator of the action of lipopolysaccharide (LPS) and other agents. We have proposed that NF-κB regulates thyroid specific gene expression and that LPS induces thyroglobulin and Na+/I- symporter expression.
Objective: To analyze the involvement of NF-κB 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 (420 bp) was transfected into FRTL-5. LPS enhanced the TSH-stimulated TPO promoter activity. A construct lacking the κB site showed no response to LPS and reduced activation by TSH. LPS-induced transcriptional activity was suppressed by a NF-κB 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. As well, quantitative ChIP assay in TSH and LPS-stimulated cells evidenced the binding of NFκB subunit p65 to the κB site in TPO promoter.
Conclusions: These findings reveal that a novel mechanism involving the NF-κB pathway mediates the TSH and LPS-stimulated TPO expression including, at least in part, the transcriptional level. Since NF-κB activation is related to many pathophysiological processes such as inflammation and autoimmunity, this study favors that NF-κB-induced modifications in TPO expression could be implicated in thyroid disease.