Interferon (IFN)-Induced Protein 35 (IFI35), a Type I Interferon-Dependent Transcript, Upregulates Inflammatory Signaling Pathways by Activating Toll-Like Receptor 3 in Human Mesangial Cells.

BACKGROUND/AIMS: Activation of Toll-like receptor 3 (TLR3) signaling followed by type I interferon (IFN) expression is crucial in antiviral and "pseudoviral" immune reactions in renal mesangial cells (MCs). These reactions are probably involved in the pathogenesis of chronic kidney disease (CKD). However, the role of IFN-induced 35-kDa protein 35 (IFI35), a type I IFN-dependent transcript, in glomerular inflammation is unclear. Here, we aimed to investigate the expression and the role of IFI35 in IFN-ß/retinoic acid-inducible gene-I (RIG-I)/CCL5 and IFN-ß/melanoma differentiation-associated gene 5 (MDA5)/CXCL10 axes in MCs. METHODS: We treated human MCs with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, then analysed the IFI35 expression by reverse transcription-polymerase chain reaction and western blotting. To examine the regulation of IFI35 expression, we subjected MCs to RNA interference (siRNA) against IFN-ß, RIG-I, and MDA5. RESULTS: Activation of TLR3 by poly IC induces the IFI35 expression in MCs. siRNA against IFN-ß inhibited poly IC-induced IFI35 expression. Knockdown of IFI35 resulted in a decrease of poly IC-induced RIG-I and MDA5 protein as well as decreased CCL5 and CXCL10 mRNA and protein expression. However, it did not affect the expression of none of phosphorylated signal transducers or activator of transcription (STAT) 1 protein, or RIG-I and MDA5 in mRNA levels. CONCLUSION: Regional expression of IFI35 and its dysregulation may be involved in the pathogenesis of glomerular inflammation in CKD.

ISG54 and ISG56 are induced by TLR3 signaling in U373MG human astrocytoma cells: possible involvement in CXCL10 expression.

Toll-like receptor (TLR) 3 is a pattern recognition receptor that recognizes double-stranded RNA (dsRNA). TLR3 signaling in astrocytes leads to the expression of interferon-ß (IFN-ß), and IFN-ß regulates immune and inflammatory reactions by inducing IFN-stimulated genes (ISGs). We demonstrated in the present study that polyinosinic-polycytidylic acid (poly IC), an authentic dsRNA, up-regulated the expression of ISG54 and ISG56 in U373MG human astrocytoma cells. This reaction was confirmed to be mediated via the TLR3/IFN-ß pathway. We also found that ISG56 positively regulates the expression of ISG54, retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5). In addition, positive feedback loops were found between ISG54 and ISG56, and also between ISG54 and RIG-I. RNA interference experiments revealed that all of ISG54, ISG56, RIG-I and MDA5 were involved in the poly IC-induced expression of a chemokine CXCL10. These results suggest that ISG54 and ISG56 are involved in the induction of CXCL10 in TLR3/IFN-ß signaling at least partly by co-operating with RIG-I and MDA5. ISG54 and ISG56 may contribute to immune and inflammatory reactions elicited by the TLR3/IFN-ß signaling pathway in astrocytes, and may play an important role both in antiviral immunity and in neuroinflammatory diseases.