IL-27 activates MHC class II expression in intestinal epithelial cells via STAT1-dependent class II transactivator (CIITA) induction

Introduction: IL-27 is a Th17-cell inhibiting cytokine produced by antigen presenting cells. We recently demonstrated anti-inflammatory and antibacterial functions for IL-27 in intestinal epithelial cells (IEC) and identified CIITA as IL-27 target gene [1]. Both IL-27 and CIITA have been implicated in the susceptibility to inflammatory bowel diseases and certain autoimmune diseases. Here we aimed to analyze the role of IL-27-induced CIITA expression in IEC. Methods: IL-27-induced gene expression and activated signaling pathways were analyzed by microarray, quantitative PCR and western blot experiments. Gene expression knockdown was performed by reverse siRNA transfection. CIITA promoter analysis was performed by electrophoretic mobility shift assays (EMSA). Results: Stimulation of IEC with IL-27 results in phosphorylation of STAT1, STAT3 and STAT6 transcription factors. IL-27 induces expression of MHC class II transactivator (CIITA) mRNA and protein. Knockdown of STAT1, but not STAT3 or STAT6 expression by siRNA transfection resulted in a complete loss of IL-27-induced CIITA expression. In EMSA experiments, we demonstrated that IL-27-activated STAT1 binds directly to the CIITA promoter thereby inducing CIITA expression. CIITA activation through IL-27 resulted in increased expression of MHC class II encoding HLA genes in IEC. IL-27 induced de novo synthesis of HLA mRNAs that were not detected in unstimulated IEC (HLA-DRA, HLA-DOA). In addition, IL-27 up-regulated HLA genes that were expressed at higher basal levels in IEC (HLA-DOB, HLA-DPA, HLA-DMB). While some HLA genes including HLA-DRA, HLA-DOB and HLA-DMA showed an early up-regulation already after 8 hours of IL-27 stimulation, others including HLA-DQA and HLA-DMB were induced strongly up to 540-fold after 48 hours of IL-27 treatment. Conclusion: We identifed IL-27 as a novel inducer of MHC class II expression in IEC. Given that variants in HLA genes are associated with inflammatory bowel disease and that MHC class II-containing exosomes released by IEC participate in antigen presentation to T cells, our data further support a role for IL-27 in intestinal immunity and intestinal inflammation. References: [1] Diegelmann J, Olszak T, Göke B, Blumberg RS, Brand S. J Biol Chem 2012; 287:286–98.