Abstract
NLR family member X1 (NLRX1) is an important member of the NOD-like receptor (NLR) family and plays unique roles in immune system regulation. Patients with hepatitis B virus (HBV) infection are more likely to have the NLRX1 mutation p.Arg707Cys than healthy individuals. It has been reported that NLRX1 increases the infection rate of HBV in HepG2 cells expressing sodium taurocholate cotransporting polypeptide (NTCP). However, the role of NLRX1 mutation (p.Arg707Cys) in hepatitis remains unclear. We constructed Huh7 cells that stably overexpressed NTCP, using LV003 lentivirus. First, wild-type (WT) and mutant (MT) NLRX1 overexpression plasmids were constructed. The MT plasmid contained a point mutation at position 707 of the WT overexpression plasmid. Then, Huh7-NTCP cells were transfected with the WT or MT NLRX1 overexpression plasmid, and subsequent NLRX1 expression was analyzed using real-time quantitative polymerase chain reaction (RT-qPCR) and western blot. HBV RNA levels were determined using RT-qPCR. HBsAg and HBcAg levels were confirmed immunohistochemically. Interferon alpha (IFN-α), interleukin 6 (IL-6), and type I interferon beta (IFN-β) levels were determined using enzyme-linked immunosorbent assay kits. p-p65, p-interferon regulatory factor (IRF) 3, and p-IRF7 expression levels were examined using western blot. The interaction of NLRX1 and retinoic acid-inducible gene (RIG)-1/mitochondrial antiviral signaling (MAVS) protein was confirmed by coimmunoprecipitation. The interaction of NLRX1 with IFN-α, IL-6, or IFN-β was analyzed by dual luciferase reporter gene assay. The levels of HBV RNA, HBsAg, and HBcAg in infected cells transfected with the WT NLRX1 or MT NLRX1 expression plasmid were higher than those in the untransfected control group; and these levels were lower in the cells transfected with MT NLRX1 than in those transfected with WT NLRX1. The levels of IFN-α, IFN-β, IL-6, p-p65, p-IRF3, and p-IRF7 were lower in cells transfected with WT NLRX1 or MT NLRX1 than in control cells. The levels of IFN-β, p-p65, p-IRF3, and p-IRF7 were higher in cells transfected with MT NLRX1 than in those transfected with WT NLRX1. Moreover, NLRX1 competitively inhibited RIG1 binding to MAVS, but the mutation in MT NLRX1 reduced this inhibitory effect. In addition, NLRX1 decreased the promoter activity of IFN-α, IFN-β, and IL-6. Our findings revealed that NLRX1 is a regulatory factor that inhibits the anti-HBV ability of hepatocytes and that the mutation p.Arg707Cys in NLRX1 suppresses HBV infection and activates the IFN/nuclear factor κB pathway.