Effect of Class 2 Transactivator on Expression of Thyroid Transcription Factor-1 in FRTL-5 Cells / 대한내분비학회지

ABSTRACT

BACKGROUND: Gamma-interferon (gamma-IFN) is known to suppress thyroperoxidase (TPO), thyroglobulin (Tg), thyrotropin receptor (TSHR) mRNA expression via unclarified mechanism. Thyroid transcription factor-1 (TTF-1) is a nuclear protein involved in the maximal expression and tissue specific expression of thyroid-specific antigens (TPO, Tg, TSHR, NIS) in thyrocytes. Although It's plausible that gamam-IFN induced suppression of thyroid-specific antigen expression may be mediated by decrease of TTF-1 expression, such an effect has not been documented yet. In this study we investigated the effect of gamma-IFN on the expression of TTF-1 in the rat thyroid cell, FRTL-5, and determined whether such an effect is mediated by sclass 2 transactivator (CIITA). METHEODS The mRNA expression of TTF-1 was quantitated by northern blot analysis after treatment of gamma-IFN, and after expression of CIITA in FRTL-5 cells. Four different promoter constructs were made by cloning into the pRSV-luciferase vector, each contained 5'flanking sequence of different lengths (-5.18 kb, -4.11 kb, -1.94 kb, -1.15 kb) of rat TTF-1 gene. Effects of gamma-IFN and CIITA on promoter activities were analyzed by luciferase assay in FRTL-5 cells into which each promoter construct had been transfected by DEAE-dextran method. RESULTS: Steady state TTF-1 mRNA level at 48 h after gamma-IFN treatment (100 U/mL) was significantly decreased from that of the pre-treatment level (1.65+/-0.16 vs. unit, p<0.05). In all 4 promoter constructs gamma-IFN significantly suppressed promoter activities compared to the vector only transfected cells. CIITA expression in FRTL-5 cells significantly decreased the steady state TTF-1 mRNA level when compared to that in mock-transfected cells (1.69+/-0.31 vs. 1.17+/-0.44 arbitrary unit, p<0.05). CIITA expression in FRTL-5 cells caused suppression of promoter activities in -5.18 kb and -4.11 kb constructs, but had no effects on those activities in -1.94 kb; and -1.15 kb constructs. CONCLUSION: gamma-IFN, directly and indirectly via CIITA expression, suppressed the transcription of TTF-1 gene in the FRTL-5 cells. It may be one of the mechanisms involved in the gamma-IFN-induced suppression of thyroid-specific protein expressions in thyrocytes 1.25+/-0.27 arbitrary