MEKK1 plays a critical role in activating the transcription factor C/EBP-β-dependent gene expression in response to IFN-γ

IFN-γ induces a number of genes to up-regulate cellular responses by using specific transcription factors and the cognate elements. We recently discovered that CCAAT/enhancer-binding protein-β (C/EBP-β) induces gene transcription through an IFN-response element called γ-IFN-activated transcriptional element (GATE). Using mutant cells, chemical inhibitors, and specific dominant negative inhibitors, we show that induction of GATE-driven gene expression depends on MEK1 (mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinase kinase) and ERKs (extracellular signal-regulated protein kinases) but is independent of Raf-1. Interestingly in cells lacking the MEKK1 gene or expressing the dominant negative MEKK1, ERK activation, and GATE dependent gene expression is inhibited. A dominant negative MEKK1 blocks C/EBP-β-driven gene expression stimulated by IFN-γ. These studies describe an IFN-γ-stimulated pathway that involves MEKK1-MEK1-ERK1/2 kinases to regulate C/EBP-β-dependent gene expression.