IFN-γ-Stimulated Transcriptional Activation by IFN-γ-Activated Transcriptional Element-Binding Factor 1 Occurs via an Inducible Interaction with CAAAT/Enhancer-Binding Protein-β

IFN-γ-activated transcriptional element (GATE)-binding factor 1 (GBF1) was identified as a transactivator that induces gene expression through GATE, a novel IFN-inducible element. Although it can induce gene expression, it is an extremely weak DNA-binding protein on its own. GATE also binds another transcription factor, C/EBP-β. Therefore, we explored whether GBF1 physically interacts with C/EBP-β to induce IFN-γ-regulated transcription. In response to IFN-γ, C/EBP-β undergoes phosphorylation at a critical ERK1/2 phosphorylation motif. Mutational inactivation of this motif and/or interference with the ERK1/2 activation prevented the IFN-γ-induced interactions between GBF1 and C/EBP-β. A 37-aa long peptide derived from the GBF1 protein can associate with C/EBP-β in an IFN-inducible manner. These results identify a converging point for two transactivators that exert their effects through a single response element. Together, our studies identify a novel regulatory mechanism that controls IFN-induced transcription.