NF-kappaB p65 subunit mediates lipopolysaccharide-induced Na+/I- symporter gene expression by involving functional interaction with the paired domain transcription factor PAX8

NICOLA, JP; NAZAR, M; MASCANFRONI, I; PELLIZAS, CG; MASINI-REPISO, AM

MOLECULAR ENDOCRINOLOGY

ENDOCRINE SOC

Año: 2010 vol. 24 p. 1846 - 1862

0888-8809

The Gram-negative bacterial endotoxin lipopolysaccharide (LPS) elicits a variety of biological responses. Na+/I- symporter (NIS)-mediated iodide uptake is the main rate-limiting step in thyroid hormonogenesis. We have recently reported that LPS stimulates thyroid-stimulating hormone (TSH)-induced iodide uptake. Here, we further analyzed the molecular mechanism involved in the LPS-induced NIS expression in FRTL-5 thyroid cells. We observed an increase in TSH-induced NIS mRNA expression in a dose-dependent manner upon LPS treatment. LPS enhance the TSH-stimulated NIS promoter activity denoting the NIS-upstream enhancer region (NUE) as responsible for the stimulatory effects. We characterized a novel putative conserved κB site for the transcription factor NF-κB within NUE region. NUE contains two binding sites for the transcription factor Pax8, main regulator of NIS transcription. It was observed a physical interaction between the NF-κB p65 subunit and Pax8 which appears to be responsible for the synergic effect displayed by these transcription factors on NIS gene transcription. Moreover, functional blockage of NF-κB signaling and site-directed mutagenesis of the κB cis-acting element abrogated LPS stimulation. Silencing expression of p65 confirmed its participation as an effector of LPS-induced NIS stimulation. Furthermore, chromatin immunoprecipitation corroborated that NIS is a novel target gene for p65 transactivation in response to LPS. Moreover, we were able to corroborate the LPS stimulatory effect on thyroid cells in vivo in LPS-treated rats, supporting that thyrocytes are capable to respond to systemic infections. In conclusion, our results reveal a new mechanism involving p65 in the LPS-induced NIS expression, denoting a novel aspect in thyroid cell differentiation.