ER stress and its regulator X-box-binding protein-1 enhance polyIC-induced innate immune response in dendritic cells.

Multiple physiological and pathological conditions interfere with the function of the endoplasmic reticulum (ER). However, much remains unknown regarding the impact of ER stress on inflammatory responses in dendritic cells (DCs) upon the recognition of pathogen molecules. We show that ER stress greatly potentiates the expression of inflammatory cytokines and IFN-β in murine DCs stimulated by polyIC, a synthetic mimic of virus dsRNA. Both toll-like receptor 3 and melanoma differentiation-associated gene-5 are involved in the enhanced IFN-β production, which is associated with increased activation of NF-κB and IRF3 signaling as well as the splicing of X-box-binding protein-1 (XBP-1), an important regulator involved in ER stress response. Surprisingly, silencing of XBP-1 reduces polyIC-stimulated IFN-β expression in the presence or absence of ER stress, indicating that XBP-1 may be essential for polyIC signaling and ER stress-amplified IFN-β production. Overexpression of a spliced form of XBP-1 (XBP-1s) synergistically augments polyIC-induced inflammatory response. For the first time, we show that XBP-1s overexpression-enhanced IFN-β production in DCs markedly suppresses vesicular stomatitis virus infection, revealing a previously unrecognized role for XBP-1 in an antiviral response. Our findings suggest that evolutionarily conserved ER stress response and XBP-1 may function collaboratively with innate immunity to maintain cellular homeostasis.