Interaction between Interferon-Stimulated Gene 56 and Melanoma Differentiation-Associated Gene 5 in Toll-Like Receptor 3 Signaling in Normal Human Mesangial Cells

Abstract

Background/Aims: Toll-like receptor 3 (TLR3) is a pathogen recognition receptor against viral double-stranded RNA. TLR3 signaling is important in antiviral responses, but inappropriate TLR3 signaling may be related with inflammatory renal diseases. Interferon (IFN)-stimulated gene 56 (ISG56) is an IFN-inducible gene that encodes a multifunctional protein with 6 tetratricopeptide motifs and is thought to be involved in antiviral reactions, but the role of ISG56 in TLR3 signaling in mesangial cells is not known well. Methods: Normal human mesangial cells were cultured and treated with a synthetic TLR3 ligand polyinosinic-polycytidylic acid, and the expression of ISG56 was analyzed using real-time RT-PCR and Western blot analyses. Using an RNA-interfering technique, involvement of TLR3, IFN-β, melanoma differentiation-associated gene 5 (MDA5) or retinoic acid-inducible gene-I (RIG-I) in ISG56 expression, and of ISG56 in the expression of MDA5, RIG-I, CXCL10 and CCL5 was examined. Results: Treatment of cells with polyinosinic-polycytidylic acid induced ISG56. ISG56 induction was inhibited by knockdown of TLR3 or IFN-β, and knockdown of ISG56 resulted in the decreased expression of MDA5, RIG-I, CXCL10 and CCL5. RNA interference against MDA5 decreased ISG56 expression. Conclusion: ISG56 was induced by TLR3 signaling via newly synthesized IFN-β. ISG56 is involved in the expression of MDA5, RIG-I, CXCL10 and CCL5, and ISG56 and MDA5 may constitute a positive-feedback loop. ISG56 may play a role in immune and inflammatory reactions induced by TLR3 signaling in human mesangial cells.