PAX8 AND TTF-1 ARE INVOLVED IN THE LIPOPOLYSACCHARIDE (LPS) INDUCED STIMULATION OF THYROGLOBULIN (TG) GENE EXPRESSION.

VÉLEZ MARIA LAURA; FOZZATTI LAURA; MONTESINOS MARIA DEL MAR; LUCERO ARIEL MAXIMILIANO; PELLIZAS CLAUDIA GABRIELA; COLEONI, ALDO HECTOR; MASINI-REPISO ANA MARIA

Buenos Aires.

Congreso; 13th INTERNATIONAL THYROID CONGRESS; 2005

Sociedad Latinoamericana de Tiroides (SLAT), AOTA, ATA y ETA.

Bacterial LPS is a potent biological activator with multiple actions. It has been proposed as an etiopathogenic agent agent in TG-induced thyroid autoimmune disease models through an immunostimulatory effect. We previously reported that LPS increased TG level by activation of TG gene expression at transcriptional level in FRTL-5 cells, revealing for the first time tha ability of LPS to directly affect self-protein expression in the thyroid cell. Here we analyzed the molecular mechanism by which LPS modulates TG gene expression in FRTL-5. Our previous data indicated thet LPS (0.01-1ug/ml) increased TSH-induced TG level (immunofluorescence/Western blot). Here we demosntrated that LPS increased TG mRNA expression at 3-6h (Northern blot). Transfections assays evidenced that LPS increased the activity of minimal TG promoter containing TTF-1, TTF2 and Pax-8/TTF-1 (C-site) binding sites. LPS induced a stimulation of a construct containing 5C sites in tandem linked to TATA-box/CAT gene similarly at 24-48h. Transfection of pTG Luc mutated at the Pax8-binding site evidenced no stimulation under LPS treatment. In EMSAs it was observed that LPS increased the binding of proteins to C site. Evidence that LPS was able to increase the formation of Pax8 and TTF-1/C site complexes was obtained by supershifts. EMSAs with mutated oligoC able to bind only Pax8 (Cp) or TTF-1 (Ct), or EMSAs with oligo C, Cp or Ct as cold competitors. Expression of Pax8 and TTF-1 mRNA and protein was also increased by LPS. These findings provide insight into the LPS ability to stimulate antigenic and hormonogenic TG protein, a fact of possible pathophysiological implicance. The LPS-induced transcriptional activation of TG gene could be exerted through  an enhanced C site-mediated transactivation by Pax8 and TTF-1. A novel property of LPS to increase Pax8 and TTF-1 expression was evidenced.