ERK1 and ERK2 activate CCAAAT/enhancer-binding protein-β-dependent gene transcription in response to interferon-γ

Abstract

Interferons (IFNs) regulate the expression of a number of cellular genes by activating the JAK-STAT pathway. We have recently discovered that CCAAAT/enhancer-binding protein-β (C/EBP-β) induces gene transcription through a novel IFN response element called the γ-IFN-activated transcriptional element (Roy, S. K., Wachira, S. J., Weihua, X., Hu, J., and Kalvakolanu, D. V. (2000) J. Biol. Chem. 275, 12626-12632. Here, we describe a new IFN-γ-stimulated pathway that operates C/EBP-β-regulated gene expression independent of JAK1. We show that ERKs are activated by IFN-γ to stimulate C/EBP-β-dependent expression. Sustained ERK activation directly correlated with C/EBP-βdependent gene expression in response to IFN-γ. Mutant MKK1, its inhibitors, and mutant ERK suppressed IFN-γ stimulated gene induction through the γ-IFN-activated transcriptional element. Ras and Raf activation was not required for this process. Furthermore, Raf-1 phosphorylation negatively correlated with its activity. Interestingly, C/EBP-β-induced gene expression required STAT1, but not JAK1. A C/EBP-β mutant lacking the ERK phosphorylation site failed to promote IFN-stimulated gene expression. Thus, our data link C/EBP-β to IFN-γ signaling through ERKs.