IFNß-Induced CXCL10 Chemokine Expression Is Regulated by Pellino3 Ligase in Monocytes and Macrophages.

IFN-I is the key regulatory component activating and modulating the response of innate and adaptive immune system to bacterial as well as viral pathogens. IFN-I promotes the expression of IFN-induced genes (ISG) and, consequently, the production of chemokines, e.g., CXCL10. Those chemokines control migration and localization of immune cells in tissues, and, thus, are critical to the function of the innate immune system during infection. Consequently, the regulation of IFN-I signaling is essential for the proper induction of an immune response. Our previous study has shown that E3 ubiquitin ligase Pellino3 positively regulates IFNß expression and secretion. Herein, we examined the role of Pellino3 ligase in regulating CXCL10 expression in response to IFNß stimulation. Our experiments were carried out on murine macrophage cell line (BMDM) and human monocytes cell line (THP-1) using IFNß as a IFNAR ligand. We demonstrate that Pellino3 is important for IFNß-induced phosphorylation and nuclear translocation of STAT1/STAT2/IRF9 complex which interacts with CXCL10 promoter and enhances its expression. In this study, we characterize a novel molecular mechanism allowing Pellino3-dependent modulation of the IFNß-induced response in BMDM and THP-1 cell lines.

Absence of Mal/TIRAP Results in Abrogated Imidazoquinolinones-Dependent Activation of IRF7 and Suppressed IFNß and IFN-I Activated Gene Production.

Activation of TLR7 by small imidazoquinoline molecules such as R848 or R837 initiates signaling cascades leading to the activation of transcription factors, such as AP-1, NF-κB, and interferon regulatory factors (IRFs) and afterward to the induction of cytokines and anti-viral Type I IFNs. In general, TLRs mediate these effects by utilizing different intracellular signaling molecules, one of them is Mal. Mal is a protein closely related to the antibacterial response, and its role in the TLR7 pathways remains poorly understood. In this study, we show that Mal determines the expression and secretion of IFNß following activation of TLR7, a receptor that recognizes ssRNA and imidazoquinolines. Moreover, we observed that R848 induces Mal-dependent IFNß production via ERK1/2 activation as well as the transcription factor IRF7 activation. Although activation of TLR7 leads to NF-κB-dependent expression of IRF7, this process is independent of Mal. We also demonstrate that secretion of IFNß regulated by TLR7 and Mal in macrophages and dendritic cells leads to the IP-10 chemokine expression. In conclusion, our data demonstrate that Mal is a critical regulator of the imidazoquinolinones-dependent IFNß production via ERK1/2/IRF7 signaling cascade which brings us closer to understanding the molecular mechanism's regulation of innate immune response.