P125 A novel IFN-G-stimulated ATF6/C/EBP-β signaling pathway critical for the induction of autophagy and elimination of bacteria

Abstract

Introduction The IFNs operate a frontline defense against pathogens and neoplastic cells in vivo by controlling the expression of several genes. The Death-Associated Protein Kinase 1 (DAPK1), an IFN-γ induced enzyme, controls cell cycle, apoptosis, autophagy, and tumor metastasis. Previously, we have shown that transcription factor C/EBP-β is required for the basal and IFN-γ-induced expression of DAPK1 . Here, we show that ATF6, an ER stress-induced transcription factor, interacts with C/EBP-β and is obligatory for Dapk1 expression. IFN-stimulated proteolytic processing of ATF6 and ERK1/2-mediated phosphorylation of C/EBP-β are necessary for these interactions. More importantly, IFN- γ -failed to activate autophagy in cells lacking either ATF6 or C/EBP-β. Indeed, the Atf6 −/− mice were highly susceptible to lethal bacterial infections compared to the wildtype mice. The activation of this signaling axis is independent from the IFN-induced JAK-STAT pathways. These studies, for the first time, not only unravel a novel IFN signaling pathway that controls cell growth, autophagy and antibacterial defense but also expand the role of ATF6 beyond ER-stress. Methods Gene knockout mice, ChIP assays, transcription factor activity assays, FRET assays, autophagy assays, lethal infection by bacteria were used in these studies. Results IFN-γ induced the translocation of ATF6 from ER to the Golgi, where it underwent proteolytic activation. Transcriptionally active ATF6 migrated to the nucleus, and bound to the promoter of DAPK1. IFN-γ also caused the activation of the ERK-1/2. The latter phosphorylated C/EBP-β, which then formed a complex with ATF6 and drove gene expression in response to IFN-γ. More importantly, loss of ATF6 or C/EBP-β suppressed IFN-induced autophagy. Mice devoid of the ATF6 gene were highly susceptible to lethal infection by anthrax bacillus. Conclusion IFN-induces a novel signaling pathway that drives autophagy, where in proteolytic cleavage of ATF6 and MAPK-driven phosphorylation of C/EBP-β are critical. Loss of ATF6 increases susceptibility of animals to lethal bacterial infections.