LIPOPOLYSACCHARIDE (LPS) INCREASES THYROGLOBULIN (TG) GENE EXPRESSION AT TRANSCRIPTIONAL LEVEL BY INVOLVING MEDIATION OF THYROID TRANSCRIPTION FACTORS IN FRTL-5 THYROID CELLS

VÉLEZ MARIA LAURA; KIMURA ETNA; COSTAMAGNA, MARIA EUGENIA; FOZZATTI, LAURA; LUCERO, ARIEL MAXIMILIANO; MASINI-REPISO, ANA MARIA

Carlos Paz, Cordoba.

Congreso; X Congreso de la Sociedad Latinoamericana de Tiroides (SLAT).; 2003

Sociedad Latinoamericana de Tiroides (SLAT).

We have previously reported that bacterial endotoxin LPS modulated iodide uptake and thyroperoxidase and TG mRNA expression in FRTL-5 thyroid cells. The aim of this work was to analyze the action of LPS on TG gene expression in FRTL-5. Treatment of cultured FRTL-5 cells with LPS (0.01-1ug/ml) induced an increased in TG level by immunofluorescence with a maximun at 0.1ug/ml LPS. A significant increase of TG was obtained by Western-blot at 24h and 48h. In cells transfected with minimal TG promoter linked to luciferase (Luc) gene in pGL2-Basic vector, pTG Luc(-168), LPS increased transcriptional activity at 18 and 24 h and decreased it at 48h. Minimal TG promoter contains thyroid transcription factor 1(TTF-1), TTF-2 and Pax-8/TTF-1 (C-site) binding sites. When a Pax-8/C-site-mutated minimal promoter, pTG Luc (-168PMT), was transfected, low Luc activity in basal samples [about 30% pTG Luc (-168)], and lack of response to TSH or LPS were obtained. After transfection of a construct with 5 C-sites in tandem linked to TATA/chloramphenicol acetyltransferase (CAT) gene (5C-CAT), LPS (48h) induced a concentration-dependent activation. These results indicate that the LPS-induced increase of TG involves transcriptional activation of TG gene. The decrease of TG to normal level at 72h of LPS action agrees with the repression of TG promoter at 48h and could involve the suggested feedback suppression of specific thyroid gene transcription by TG. Since C-site activity is dependent of both, TTF-1 and Pax-8, data from Pax-8 site mutated and 5C-CAT constructs support a role of Pax-8 and TTF-1 in LPS action. In conclusion, these results revealed a potential ability of LPS to stimulate TG gene expression at transcriptional level, a finding that could be of pathological significance.