Chicken Cells Sense Influenza A Virus Infection through MDA5 and CARDIF Signaling Involving LGP2

Abstract

Avian influenza viruses (AIV) raise worldwide veterinary and public health concerns due to their potential for zoonotic transmission. While infection with highly pathogenic AIV results in high mortality in chickens, this is not necessarily the case in wild birds and ducks. It is known that innate immune factors can contribute to the outcome of infection. In this context, retinoic acid-inducible gene I (RIG-I) is the main cytosolic pattern recognition receptor known for detecting influenza A virus infection in mammalian cells. Chickens, unlike ducks, lack RIG-I, yet chicken cells do produce type I interferon (IFN) in response to AIV infection. Consequently, we sought to identify the cytosolic recognition elements in chicken cells. Chicken mRNA encoding the putative chicken analogs of CARDIF and LGP2 (chCARDIF and chLGP2, respectively) were identified. HT7-tagged chCARDIF was observed to associate with mitochondria in chicken DF-1 fibroblasts. The exogenous expression of chCARDIF, as well as of the caspase activation and recruitment domains (CARDs) of the chicken melanoma differentiation-associated protein 5 (chMDA5), strongly activated the chicken IFN-␤ (chIFN-␤) promoter. The silencing of chMDA5, chCARDIF, and chIRF3 reduced chIFN-␤ levels induced by AIV, indicating their involvement in AIV sensing. As with mammalian cells, chLGP2 had opposing effects. While overexpression decreased the activation of the chIFN-␤ promoter, the silencing of endogenous chLGP2 reduced chIFN-␤ induced by AIV. We finally demonstrate that the chMDA5 signaling pathway is inhibited by the viral nonstructural protein 1. In conclusion, chicken cells, including DF-1 fibroblasts and HD-11 macrophage-like cells, employ chMDA5 for sensing AIV.

Different outcomes of infection of chickens and ducks with a duck-origin H9N2 influenza A virus

“…Additionally, RIG-I was highly upregulated in ducks infected with HPAIVs, and slightly upregulated in ducks infected with LPAIVs (Barber et al, 2010). Studies have also demonstrated that the NS1 protein of AIV could inhibit IFNB signaling due to its interaction with MDA5 signaling pathway and RIG-I signaling pathway (Guo et al, 2007;Liniger et al, 2012). According to these reports, different susceptibility of the two species to the suppressive effect of the H9N2 NS1 gene on the IFNB expression may account for different levels of IFNB expression in ducks and chickens, which shared similarities to the results described by Adams et al (2009) despite the fact that our study selected different tissues, different experimental approaches, time points, and LPAIV subtypes.…”

“…Meanwhile, different IFNB expression levels were observed between ducks and chickens. Recent studies have shown that the chicken melanoma differentiationassociated protein 5 (chMDA5) strongly activated chicken IFNB promoter in response to AIV infection (Liniger et al, 2012), while retinoic acid-inducible gene I (RIG-I) present in ducks, which is apparently absent in chickens, played an essential role in the IFNB production triggered by AIV. Additionally, RIG-I was highly upregulated in ducks infected with HPAIVs, and slightly upregulated in ducks infected with LPAIVs (Barber et al, 2010).…”

Chicken STING Mediates Activation of the IFN Gene Independently of the RIG-I Gene

“…Barber and coworkers (17) characterized the function of duck RIG-I and suggested that the lack of RIG-I in chickens results in deficiency of the antiviral innate immune response induced by this pathway. However, Liniger et al (15) suggested that although RIG-I is missing in chicken cells, chicken MDA5 functionally compensates for the absence of RIG-I in sensing AIV.…”

“…MDA5 senses essentially positive-strand RNA viruses, in particular members of the Picornaviridae and Flaviviridae families (12)(13)(14). However, MDA5 also can be triggered by certain negative-strand RNA viruses such as members of the Paramyxoviridae family (13) and avian influenza virus (AIV) (15).…”

Evading innate immunity in nonviral mRNA delivery: don’t shoot the messenger

“…Although LGP2 was initially assumed to negatively regulate RLR-mediated signaling [40,41], more recent studies revealed a positive role for LGP2 in the regulation of type I IFN responses [42]. Nevertheless, experimental data of further studies are still controversial, with both overexpression and knockdown of LGP2 resulting in type I IFN production [43]. Whether LGP2 mediated signaling can be induced by IVT mRNA remains to be established.…”