Abstract
Background RIG-I (retinoic acid inducible gene-I) is one of the key cytosolic pattern recognition receptors (PRRs) for detecting nucleotide pathogen associated molecular patterns (PAMPs) and mediating the induction of type I interferon and inflammatory cytokines in innate immune response. Though the mechanism is well characterized in mammals, the study of the accurate function of RIG-I in teleosts is still in its infancy.Methodology/Principal FindingsTo clarify the functional characterizations of RIG-I in grass carp Ctenopharyngodon idella (CiRIG-I), six representative overexpression plasmids were constructed and transfected into C. idella kidney (CIK) cell lines to obtain stably expressing recombinant proteins, respectively. A virus titer test and 96-well plate staining assay showed that all constructs exhibited the antiviral activity somewhat. The quantitative real-time RT-PCR (qRT-PCR) demonstrated that mRNA expressions of CiIPS-1, CiIFN-I and CiMx2 were regulated by not only virus (GCRV) or viral PAMP (poly(IC)) challenge but also bacterial PAMPs (LPS and PGN) stimulation in the steadily transfected cells. The results showed that the full-length CiRIG-I played a key role in RLR pathway. The repressor domain (RD) exerted an inhibitory function of the signaling channel under all utilized challenges. Caspase activation and recruitment domains (CARDs) showed a positive role in GCRV and poly(I:C) challenge. Helicase motifs were crucial for the signaling pathway upon LPS and PGN stimulation. Interestingly, ΔCARDs (CARDs deleted) showed postive modulation in RIG-I signal transduction.Conclusions/SignificanceThe results provided some novel insights into RIG-I sensing with a strikingly broad regulation in teleosts, responding not only to the dsRNA virus or synthetic dsRNA but also bacterial PAMPs.
Highlights
The innate immune system serves as the first line of protection against invading microbial pathogens through a limited number of germ line-encoded pattern recognition receptors (PRRs) [1]
Antiviral Activity of CiRIG-I and its Domains To clarify the functional characterizations of CiRIG-I, six representative overexpression plasmids were constructed (Fig. 1) for stably expressing recombinant protein in C. idella kidney (CIK) cells, respectively
The cells transfected with pDCARDs, pCARDs-repressor domain (RD) and pCARDs displayed moderate roles of resistance to grass carp reovirus (GCRV)
Summary
The innate immune system serves as the first line of protection against invading microbial pathogens through a limited number of germ line-encoded pattern recognition receptors (PRRs) [1]. The PRRs recognize different but overlapping pathogen-associated molecular patterns (PAMPs), and trigger innate immune responses and subsequent adaptive immunity [2]. Four major classes of PRRs have been identified and classified into transmembrane proteins such as C-type lectin receptors (CLRs) and Toll-like receptors (TLRs), and cytoplasmic proteins such as NOD-like receptors (NLRs) and RIG-I-like receptors (RLRs) [3]. TLRs and RLRs trigger type I interferon (IFN-I), leading to an enhanced antiviral state of host cells [9]. RIG-I (retinoic acid inducible gene-I) is one of the key cytosolic pattern recognition receptors (PRRs) for detecting nucleotide pathogen associated molecular patterns (PAMPs) and mediating the induction of type I interferon and inflammatory cytokines in innate immune response. Though the mechanism is well characterized in mammals, the study of the accurate function of RIG-I in teleosts is still in its infancy
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