Thyroperoxidase gene expression is stimulated by lipopolysaccharide (LPS) at transcriptional level by involving a differential regulation of TTF-1 and TTF-2 factors. Evidence for the toll-like receptor 4 mediation

VÉLEZ ML; NICOLA JP; FOZZATTI L; LUCERO AM; MONTESINOS, MM; PELLIZAS CG; MASINI-REPISO AM

Santiago de Chile

Congreso; XII Latin American Thyroid Congress (LATS); 2007

Sociedad Latinoamericana de Tiroides (LATS)

 LPS is a gene inductor mainly acting on immune cells through Toll-like receptor (TLR) 4. It has  been suggested that LPS plays an etiopathogenic role in autoimmunity. Thyroid-specific gene  expression is regulated by TSH mainly involving cAMP pathway and TTF-1, TTF-2 and Pax8  factors. We previously reported that LPS increases thyroglobulin (TG) expression in FRTL-5 thyroid cells. The aim of this study was to analyze the effect of LPS on TPO expression and the mechanism involved in FRTL-5 cells. LPS increased the TSH-induced TPO mRNA expression (RT-PCR,Northern blot;12h,2.2-fold,P<0.01). In transfection assays we evidenced that LPS increased the activity of minimal TPO promoter containing the sites: A and B which bind TTF-1, Z, TTF-2 and C, TTF-1 and Pax8(pTPOLuc;24/48h,1.6/2.1-fold,P<0.01). Constructs with Z and C(pZCLuc) or C(pCLuc) showed no response to LPS. Since A is not crucial for TPO promoter expression, this finding revealed the importance of B. LPS stimulated the activity of the constructs with 12Z (p12xZLuc;48h,1.8-fold,P<0.05) or BZ(pBZLuc;48h,1.6-fold,P<0.05), evidencing a cooperation among Z sites and between Z and B. By EMSAs we demonstrated that LPS increased the binding of TTF-2 to Z and TTF-1 to B. We observed that LPS did not alter TTF-2 level. Contrarily, we previously found that LPS augmented TTF-1 expression. LPS increased the dibutyryl cAMP(cAMP analog)-induced TPO promoter activity(24h,2.1-fold,P<0.01). LPS-stimulatory action on TSH-activated TPO promoter was abolished in the presence of a blocking anti-TLR4 antibody in the medium. This study provides evidence that bacterial LPS increases TPO gene expression by a mechanism of transcriptional activation involving TTF-1 and TTF-2. The action of LPS in TSH- or cAMP-stimulated cells suggests a crosstalk between the signaling pathways induced by LPS and TSH/cAMP. It is revealed, for the first time, a role of TLR4 in mediating the LPS-induced thyroid-specific gene expression. On the basis of the functional and antigenic properties of TPO, these findings could be of pathophysiological implication.