The NLR protein, NLRC5 is an important regulator of MHC class I gene expression, however, the role of NLRC5 in other innate immune responses is less well defined. In the present study, we report that NLRC5 binds RIG-I and that this interaction is critical for robust antiviral responses against influenza virus. Overexpression of NLRC5 in the human lung epithelial cell line, A549, and normal human bronchial epithelial cells resulted in impaired replication of influenza virus A/Puerto Rico/8/34 virus (PR8) and enhanced IFN-β expression. Influenza virus leads to induction of IFN-β that drives RIG-I and NLRC5 expression in host cells. Our results suggest that NLRC5 extends and stabilizes influenza virus induced RIG-I expression and delays expression of the viral inhibitor protein NS1. We show that NS1 binds to NLRC5 to suppress its function. Interaction domain mapping revealed that NLRC5 interacts with RIG-I via its N-terminal death domain and that NLRC5 enhanced antiviral activity in an leucine-rich repeat domain independent manner. Taken together, our findings identify a novel role for NLRC5 in RIG-I-mediated antiviral host responses against influenza virus infection, distinguished from the role of NLRC5 in MHC class I gene regulation.Keywords: Influenza r Interferon r NLRC5 r NS1 r RIG-I Antiviral Additional supporting information may be found in the online version of this article at the publisher's web-site
IntroductionThe innate immune system relies on pathogen sensors to provide defense against invading pathogens. To detect diverse pathogen-associated molecular patterns (PAMPs), several classes Correspondence: Dr. Priya Ranjan e-mail: pranjan@cdc.gov of pattern-recognition receptors (PRRs) have evolved in mammals including RIG-I-like receptors, Toll-like receptors (TLRs), and nucleotide-binding domain and leucine-rich repeat containing receptors (NLRs) [1][2][3]. Recognition and binding of PRRs to their cognate ligands often result in conformational changes triggering downstream innate immune signaling [4].In recent years, there has been marked progress in our understanding of NLRs as critical regulators of innate and adaptive C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2015. 45: 758-772 Immunity to infection 759 immune responses. Emerging evidence suggests that NLR family members play crucial roles in antiviral responses [5,6]. NLR proteins have a typical tripartite structure: a C-terminal LRR domain that, in most cases, is associated with PAMP sensing, a centrally located nucleotide-triphosphatase (NTPase) (NACHTdomain present in NAIP, CIITA, HET-E, and TP1) domain responsible for self-oligomerization, and an N-terminal effector domain that mediates protein-protein interactions for initiating downstream signaling [5]. Activation of these receptors induces the production of proinflammatory cytokines, in many cases by the formation of high molecular weight complexes called inflammasomes that lead to caspase-1 activation. However, some of the family members such as NL...