Journal of Korean Endocrine Society 2002;17(1):48-56.
Published online February 1, 2002.
Effect of Class 2 Transactivator on Expression of Thyroid Transcription Factor-1 in FRTL-5 Cells.
Won Bae Kim, Tae Yong Kim, Young Joo Park, Jae Joon Koh, Do Joon Park, Bo Youn Cho
1Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine, Korea.
2Department of Internal Medicine, Asan Medical Center, Seoul National University College of Medicine, Korea.
3Seoul Municipal Boramae Hospital, Seoul, Korea.
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
Key Words: gamma-IFN, Class 2 transactivator, Thyroid transcription factor-1, Thyrocyte


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