The Cytokine IL-1β Activates IFN Response Factor 3 in Human Fetal Astrocytes in Culture

The cytokine IL-1beta is a major activator of primary human fetal astrocytes in culture, leading to the production of a wide range of cytokines and chemokines important in the host defense against pathogens. IL-1beta, like TLR4, signals via the MyD88/IL-1betaR-associated kinase-1 pathway linked to activation of NF-kappaB and AP-1. Recent studies have shown that TLR4 also signals independently of MyD88, resulting in the activation of IFN regulatory factor 3 (IRF3), a transcription factor required for the production of primary antiviral response genes such as IFN-beta. Using a functional genomics approach, we observed that IL-1beta induced in astrocytes a group of genes considered to be IFN-stimulated genes (ISG), suggesting that IL-1beta may also signal via IRF3 in these cells. We now show, using real-time PCR, that in astrocytes IL-1beta induces the expression of IFN-beta, IRF7, CXCL10/IFN-gamma-inducible protein-10, and CCL5/RANTES. Chemokine expression was confirmed by ELISA. We also show that IL-1beta induces phosphorylation and nuclear translocation of IRF3 and delayed phosphorylation of STAT1. The dependency of IFN-beta, IRF7, and CXCL10/IFN-gamma-inducible protein-10 gene expression on IRF3 was confirmed using a dominant negative IRF3-expressing adenovirus. The robust induction by IL-1beta of additional ISG noted on the microarrays, such as STAT1, 2'5'-oligoadenylate synthetase 2, and ISG15, also supports an active signaling role for IL-1beta via this pathway in human fetal astrocytes. These data are the first to show that IL-1beta, in addition to TLRs, can stimulate IRF3, implicating this cytokine as an activator of genes involved in innate antiviral responses in astrocytes.