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-beta (C/EBP-beta) induces gene transcription through a novel IFN response element called the gamma-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-gamma-stimulated pathway that operates C/EBP-beta-regulated gene expression independent of JAK1. We show that ERKs are activated by IFN-gamma to stimulate C/EBP-beta-dependent expression. Sustained ERK activation directly correlated with C/EBP-beta-dependent gene expression in response to IFN-gamma. Mutant MKK1, its inhibitors, and mutant ERK suppressed IFN-gamma-stimulated gene induction through the gamma-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-beta-induced gene expression required STAT1, but not JAK1. A C/EBP-beta mutant lacking the ERK phosphorylation site failed to promote IFN-stimulated gene expression. Thus, our data link C/EBP-beta to IFN-gamma signaling through ERKs.
