INTERFERON REGULATORY FACTORS AND TFIIB COOPERATIVELY REGULATE INTERFERON-RESPONSIVE PROMOTER ACTIVITY IN-VIVO AND IN-VITRO

Interferon regulatory factors (IRFs) bind to the interferon-stimulated response element (ISRE) and regulate interferon- and virus-mediated g ene expression. IRF-1 acts as a transcriptional activator, while IRF-2 acts as a repressor. Here we show that IRF-1 and IRF-2 bind to both c ellular TFIIB, a component of the basal transcription machinery, and r ecombinant TFIIB (rTFIIB) and that this protein-protein interaction fa cilitates binding of IRFs to the ISRE. A functional interaction betwee n TFIIB and IRF was assessed by a newly established in vitro transcrip tion assay in which recombinant IRF-1 (rIRF-1) stimulated transcriptio n specifically from an ISRE-containing template. With this assay we sh ow that rIRF-1 and rTFIIB cooperatively enhance the ISRE promoter in v itro. We found that the activity of an ISRE-containing promoter was co operatively enhanced upon cotransfection of TFIIB and IRF-1 cDNAs into P19 embryonal carcinoma cells, further demonstrating functional inter actions in vivo. The cooperative enhancement by TFIIB and IRF-1 was in dependent of the TATA sequence in the ISRE promoter but dependent on t he initiator sequence (Inr) and was abolished when P19 cells were indu ced to differentiate by retinoic acid treatment. In contrast, cotransf ection of TFIIB and IRF-1 into NIH 3T3 cells resulted in a dose-depend ent repression of promoter activation which occurred in a TATA-depende nt manner. Our results indicate the presence of a cell type-specific f actor that mediates the functional interaction between IRFs and TFIIB and that acts in conjunction with the requirement of TATA and Inr for promoter activation.