Epigenetic and transcriptional regulation of IL-4 induced CCL17 production in human monocytes and murine macrophages
- University of Melbourne, Department of Medicine, Royal Melbourne Hospital.
- Australian Institute for Musculoskeletal Science (AIMSS), The University of Melbourne and Western Health.
Interleukin- 4 (IL4) is an anti- inflammatory cytokine and alternative macrophage activator, recognized as a hallmark cytokine of Th2- associated diseases. On the other hand, granulocyte- macrophage colony stimulating factor (GM-CSF) is a pro-inflammatory hematopoietic cytokine and involved in the development of autoimmune inflammatory diseases, such as rheumatoid arthritis. Despite the opposing inflammatory roles of these two cytokines, GM-CSF and IL4 are used together to enhance in vitro differentiation of monocytes into dendritic cells. We have previously reported that GM-CSF can induce the secretion of chemokine (C-C motif) ligand 17 (CCL17) from monocytes in an interferon regulatory factor 4 (IRF4)-dependent manner. Interestingly, CCL17 is also an upregulated marker of IL4 polarised M2 macrophages. We investigated whether the IL4 induced CCL17 pathway shared any common elements with the established GM-CSF pathway. We report here that, like GM-CSF, IL4 induces CCL17 expression in an IRF4 dependent manner. IL4 also enhances the expression and activity of Jumanji domain-containing protein 3 (JMJD3) demethylase which epigenetically upregulates IRF4 expression. Signal transducer and activator of transcription 6 (STAT6) is activated by IL4, not GM-CSF, and silencing the STAT6 gene led to a decrease in CCL17 formation, as well as that of its upstream regulators, JMJD3 and IRF4. Moreover, IL4 treatment of human monocytes resulted in an increased association of STAT6 to the promoter regions of the CCL17, IRF4 and JMJD3 genes. Thus, despite the different and almost opposing roles GM-CSF and IL4 play in inflammation, these 2 cytokines share a common signaling pathway in regulating CCL17 production in human monocytes and murine macrophages.