The Nucleotide-Binding Oligomerization Domain-Like Receptor NLRC5 Is Involved in IFN-Dependent Antiviral Immune Responses

Abstract

Nucleotide-binding oligomerization domain-like receptors (NLRs) are a group of intracellular proteins that mediate recognition of pathogen-associated molecular patterns or other cytosolic danger signals. Mutations in NLR genes have been linked to a variety of inflammatory diseases, underscoring their pivotal role in host defense and immunity. This report describes the genomic organization and regulation of the human NLR family member NLRC5 and aspects of cellular function of the encoded protein. We have analyzed the tissue-specific expression of NLRC5 and have characterized regulatory elements in the NLRC5 promoter region that are responsive to IFN-γ. We show that NLRC5 is upregulated in human fibroblasts postinfection with CMV and demonstrate the role of a JAK/STAT-mediated autocrine signaling loop involving IFN-γ. We demonstrate that overexpression and enforced oligomerization of NLRC5 protein results in activation of the IFN-responsive regulatory promoter elements IFN-γ activation sequence and IFN-specific response element and upregulation of antiviral target genes (e.g., IFN-α, OAS1, and PRKRIR). Finally, we demonstrate the effect of small interfering RNA-mediated knockdown of NLRC5 on a target gene level in the context of viral infection. We conclude that NLRC5 may represent a molecular switch of IFN-γ activation sequence/IFN-specific response element signaling pathways contributing to antiviral defense mechanisms.

Expression regulation and function of NLRC5

“…Consistent with that, the induction of NLRC5 expression by LPS was abrogated in Ifnαr1 -/-bone marrow-derived macrophages (Staehli et al, 2012). NLRC5 promoter region is predicted to have STAT1 and NF-κB binding sites (Kuenzel et al, 2010). Accordingly, NLRC5 induction is reported to be severely reduced in Stat1 -/-BMDMs after treatment of interferons or various stimuli which can induce interferons such as LPS.…”

“…Based on these discoveries, STAT1 is suggested to play an essential role in the regulation of NLRC5 expression (Staehli et al, 2012). NLRC5 has also been observed to be induced by diversifi ed bacteria and virus, or their PAMPs like poly(I:C), CpG and poly(dA:dT) which all can induce type I IFN (Cui et al, 2010;Kuenzel et al, 2010;Staehli et al, 2012;Yao et al, 2012). Therefore, both type I and type II IFN can strongly induce NLRC5 expression through STAT1 dependent pathway.…”

“…While the role of NLRC5 in regulating MHC class I gene expression is well recognized by intensive studies, previous researches suggested that NLRC5 may also regulate innate immune responses through affecting TLR mediated NF-κB activation, type I interferon (IFN)-producing pathways as well as inflammasome activation (Benko et al, 2010;Cui et al, 2010;Neerincx et al, 2010;Davis et al, 2011;Lamkanfi and Kanneganti, 2012).Two studies showed NLRC5 was a positive regulator of type I IFN producing pathway in human fi broblasts and THP-1 cells (Kuenzel et al, 2010;Neerincx et al, 2010). However, NLRC5 was shown to suppress type I IFN production through association with RIG-I and MDA5 (the dsRNA sensors), or inhibit NF-κB pathway through its direct binding with IκB kinase-α (IKK-α) and IKK-β (Cui et al, 2010).…”

Inflammasomes and its importance in viral infections

“…The role of NLRC5 in innate immunity is still not well understood, but it is known to participate in both the innate and adaptive immune responses [96][97][98][99][100]. In HeLa and THP-1 cells, NLRC5 has been demonstrated to positively regulate the IFN pathway, whereas in other models such as HEK 293 cells and RAW 264.7 cells, NLRC5 has been demonstrated to negatively regulate the IFN, NF-jB, and AP-1 pathways [96][97][98]100]. In RAW 264.7 cells, it was demonstrated that the interaction of NLRC5 with IKKa results in the inhibition of its catalytic activity.…”

Ubiquitin in the activation and attenuation of innate antiviral immunity

“…NLRC5 was initially described to enhance IFN-γ and IFN-α expression and inhibit NF-κB and IFN-β, in the latter case through sequestering the activated effector domains of RIG-I and MDA5 (Cui et al, 2010;Kuenzel et al, 2010). NLRC5 has also been shown to bind and inhibit TBK1-mediated IFN-β induction in HEK-293T cells, although NLRC5 −/− mice show relatively normal cytokine responses upon exposure to RLR-, TLR-, and NLR-activating stimuli (Kumar et al, 2011).…”