BACKGROUND: In the previous studies, we identified that the interferon-gamma activated sequence (GAS) in the 5-flanking region of rat ICAM-1 gene is major element for interferon-y-inducible expression of the gene in rat thyroid cells, FRTL-5. We here, investigated the role of transcriptional coactivators, CBP (CREB binding protein) and CIITA (class II transactivator) in the modulation of the activity of GAS which could interacts with signal transducers and activators of transcription-1 and 3 (STAT1 and STAT3). METHODS: The expression of CBP RNA and protein were quantitated in FRTL-5 after stimulation with interferon-y (IFN-gamma), thyroid stimulating hormone (TSH), forskolin and methimazole. Direct association of CBP with STAT were analyzed by irnmunoprecipitation. The transcriptional roles of CBP and CIITA in the regulation of GAS were assessed by the cotransfection with their expression vectors with reporters; 5-deletion constructs of rat ICAM-1 promoter or 8xGAS-luc constructs, into FRTL-5 thyroid cells. RESULTS: The level of CBP RNA and protein were not changed by the treatment with TSH, IFN-y, forskolin and methimazole in FRTL-5, FRT and BRL liver cells. The CBP could be directly associated with STAT1. Furthernmore, the overexpression of CBP significantly increases the both promoter activities; rat ICAM-1 gene promoter which has GAS element and 8xGAS-luc cassette constructs. However the cotransfection of CI1TA decreased the constitutive and CBP-mediated transactivation of rat ICAM-1 promoter and SxGAS-luc cassette constructs. CONCLUSION: We identified that the two transcriptional coactivators; CBP and CIITA has differential roles in the regulation of transcriptional activity of GAS drived promoter. CBP increases the GAS activity through the direct binding with STATl, but CIITA inhibited the CBP-mediated transactivation of GAS activity.
Animals ; Colforsin ; Intercellular Adhesion Molecule-1 ; Interferon-gamma ; Liver ; Methimazole ; Rats ; RNA ; Thyroid Gland* ; Thyrotropin ; Transcriptional Activation ; Transducers