CCAAT/Enhancer-binding Protein β Mediates Interferon-γ-induced p48 (ISGF3-γ) Gene Transcription in Human Monocytic Cells

Abstract

Previous studies have identified a novel interferon-stimulated response element-like element, termed γ-interferon-activating transcription element, within the interferon-stimulating gene factor-3γ (p48) promoter region that is bound by novel transcription factors in response to stimulation with interferons (IFNs) (Weihua, X., Kolla, V., and Kalvakolanu, D. V. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 103-108). In the present study, we have identified CCAAT/enhancer-binding protein β (C/EBP-β) as one of the γ-interferon-activating transcription element cognate transcription factors by screening a human monophage-derived cDNA library in a yeast one-hybrid system. Electrophoretic mobility shift assay studies suggest that C/EBP-β dynamically regulates p48 gene expression upon IFN-γ stimulation by undergoing changes in its heterodimerization partners. Transient transfection studies demonstrate that overexpression of C/EBP-β strongly enhanced IFN-γ-induced transcription from the p48 promoter. However, deletion mutants of C/EBP-β that lack the N-terminal transactivation domain were unable to stimulate the p48 promoter. Western blotting revealed that C/EBP-β is induced by IFN-γ stimulation in THP-1-derived macrophages. Collectively, these results suggest that C/EBP-β plays an important role in the human IFN-γ signaling pathway by transcriptional regulation of p48 gene expression, an essential component in the IFN signaling pathway.