NLRX1 Mediates MAVS Degradation To Attenuate the Hepatitis C Virus-Induced Innate Immune Response through PCBP2

Abstract

Activation of innate immunity is essential for host cells to restrict the spread of invading viruses and other pathogens. However, attenuation or termination of signaling is also necessary for preventing immune-mediated tissue damage and spontaneous autoimmunity. Here, we identify NLRX1 as a negative regulator for MAVS-mediated signaling pathway during HCV infection. Depletion of NLRX1 enhances HCV-triggered activation of IFN signaling and causes the suppression of HCV propagation in hepatocytes. NLRX1, a HCV-inducible protein, interacts with MAVS and mediates the K48-linked polyubiquitination and the subsequent degradation of MAVS via proteasomal pathway. Moreover, PCBP2 interacts with NLRX1 to participate in NLRX1-induced degradation of MAVS and inhibition of antiviral responses during HCV infection. Mutagenic analyses further revealed that the NOD domain of NLRX1 is essential for NLRX1 to interact with PCBP2 and subsequently induce MAVS degradation. Our study unlocks a key mechanism of fine tuning of innate immunity by which NLRX1 restrains RLRs-MAVS signaling cascade by recruiting PCBP2 to MAVS for inducing MAVS degradation through the proteasomal pathway. NLRX1, a negative regulator of innate immunity, is a pivotal host factor for HCV to establish persistent infection. Innate immunity needs to be tightly regulated to maximize antiviral response and minimize immune-mediated pathology. Whereas, the underlying mechanisms are poorly understood. In this study, we report that NLRX1 is a proviral host factor for HCV infection and functions as a negative regulator in HCV-triggered innate immune response. NLRX1 recruits PCBP2 to MAVS and induces the K48-linked polyubiquitination and degradation of MAVS, leading to the negative regulation of IFN signaling pathway and promoting HCV infection. Overall, this study provides intriguing insights into how innate immunity is regulated during viral infection.

Analysis of eEF1Bγ interactome in the nuclear fraction of A549 human lung adenocarcinoma cells

“…PCBP2 is a wellknown iron chaperon [21], it participates in regulation of antioxidant defence [22]. It is involved in apoptosis [23] and innate immune response systems [24,25].…”

Nucleotide-binding oligomerization domain-like receptor X1 restricts porcine reproductive and respiratory syndrome virus-2 replication by interacting with viral Nsp9

“…NLRX1 was the first NLR shown to reduce type-I IFN production and facilitate viruses infection, by binding to MAVS (mitochondrial antiviral signaling protein) on mitochondria and STING (stimulator of interferon genes) on endoplasmic reticulum (ER), as demonstrated for Sindbisvirus, HIV-1, HSV-1 and KSHV (Guo et al, 2016;Ma et al, 2017;Moore et al, 2008;Qin et al, 2017). However, all of these functions reported for NLRX1 are not without controversy.…”

“…Nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) X1 (also known as CLR11.3 and NOD9), a member of the NLR family proteins, is initially identified as key mediators of immune defense and inflammation (Arnoult et al, 2009;Coutermarsh-Ott et al, 2016;Eitas et al, 2014;Imbeault et al, 2014;Kang et al, 2015;Kanneganti, 2010;Koblansky et al, 2016;Lupfer and Kanneganti, 2013;Moore et al, 2008;Philipson et al, 2015;Singh et al, 2015;Soares et al, 2014;Tattoli et al, 2016;Ting et al, 2008;Wang et al, 2013). To date, accumulated evidence indicated that NLRX1 inhibits NF-κB (Nuclear factor-kappa B) signaling, inflammasome activation, double-stranded RNA (dsRNA) activated kinase PKR and type I interferon (IFN) production but potentiates reactive oxygen species (ROS) production and autophagy (Abdul-Sater et al, 2010;Allen et al, 2011;Feng et al, 2017;Guo et al, 2016;Hung et al, 2018;Kim et al, 2017;Lei et al, 2012;Moore et al, 2008;O'Neill, 2008;Qin et al, 2017;Stokman et al, 2017;Tattoli et al, 2008;Theus et al, 2017;Xia et al, 2011;Yin et al, 2017;Zeng et al, 2017). Recently, NLRX1 was also identified to facilitate Human Immunodeficiency Virus 1 (HIV-1) (Guo et al, 2016), herpes simplex virus 1 (HSV-1) (Guo et al, 2016), hepatitis C virus (HCV) (Qin et al, 2017) and Kaposi's sarcoma-associated herpesvirus (KSHV) infection, whereas restricts influenza A virus (IAV) (Jawors...…”

“…To date, accumulated evidence indicated that NLRX1 inhibits NF-κB (Nuclear factor-kappa B) signaling, inflammasome activation, double-stranded RNA (dsRNA) activated kinase PKR and type I interferon (IFN) production but potentiates reactive oxygen species (ROS) production and autophagy (Abdul-Sater et al, 2010;Allen et al, 2011;Feng et al, 2017;Guo et al, 2016;Hung et al, 2018;Kim et al, 2017;Lei et al, 2012;Moore et al, 2008;O'Neill, 2008;Qin et al, 2017;Stokman et al, 2017;Tattoli et al, 2008;Theus et al, 2017;Xia et al, 2011;Yin et al, 2017;Zeng et al, 2017). Recently, NLRX1 was also identified to facilitate Human Immunodeficiency Virus 1 (HIV-1) (Guo et al, 2016), herpes simplex virus 1 (HSV-1) (Guo et al, 2016), hepatitis C virus (HCV) (Qin et al, 2017) and Kaposi's sarcoma-associated herpesvirus (KSHV) infection, whereas restricts influenza A virus (IAV) (Jaworska et al, 2014), and hepatitis A virus (HAV) (Feng et al, 2017) replication. These conflicting reports about whether NLRX1 functions as a pro-viral or antiviral factor imply that the role of NLRX1 in viral infection is more complex than previously thought and remains to be clarified.…”

Negative Regulation of Cytosolic Sensing of DNA

“…NLRP6 and NLRP12 suppress NF-κB signaling and are involved in the maintenance of intestinal homeostasis and tumorigenesis (Allen et al, 2012;Anand et al, 2012;Lupfer and Kanneganti, 2013;Zaki et al, 2011)-more recent reports also point to a role for NLRP6 in anti-viral immunity in mouse intestines (Wang et al, 2015b). NLRX1, the only mitochondrially localized member of this family, modulates sensing of dsRNA and virus-induced ROS production (Guo et al, 2016;Ma et al, 2017;Moore et al, 2008;Qin et al, 2017a;Tattoli et al, 2008). In collaboration with IQGAP1, NLRC3 suppresses DNA sensing lymphoid cells, myeloid cells, and epithelial cells through interactions with STING (Tocker et al, 2017;Zhang et al, 2014).…”