Inducible GBP5 Mediates The Antiviral Response Via Interferon-related Pathways During Influenza A Virus Infection

Influenza A virus(IAV)is a negative-sense RNA virus of the Orthomyxoviridae family which is the etiological agent of a contagious acute respiratory disease.Some seasonal and rare pandemic virus strains,such as the deadly 1918 H1N1 virus,belong to this family.These viruses are responsible for severe illness and considerable mortality worldwide.Annually,influenza viruses cause 3-5 million severe clinical infections and 250,000-500,000 fatal cases.The outcome of IAV infections is largely determined by the complex interactions between the virus and the innate immune system;therefore,a detailed understanding of the molecular mechanisms involved in innate immune recognition and response can provide a valuable framework for the development of therapeutics.Guanine nucleotide binding proteins(GBPs)are involved in important cellular processes,including signal transduction,translation,vesicle trafficking,and exocytosis.Structurally,GBPs have a molecular weight of 67-73 kDa,display a high degree of homology,and share highly conserved GTP-binding or hydrolysis domains.These GTPases bind phosphoinositides,cardiolipin,soluble NSF attachment protein receptor adaptor proteins,and other p47 IRGs to direct their membrane regulatory activities against compartmentalized bacteria and protozoa.Among them,guanylate binding protein 5(GBP5)belongs to the family of IFN-?-induced p65 GTPases,which has seven members in humans.This family of GBPs was originally identified by the ability of its members to bind to immobilized guanine nucleotides with similar affinities for GTP,GDP,and GMP.GBP5 was reported to be a critical cellular factor in inflammasome assembly.Furthermore,GBP5 has been reported to induce inflammatory cytokines including IL1? and IL18 through the activation of NLRP3 and AIM2.Recently,Kirchhoff group's research shows that GBP5 is expressed in the primary target cells of HIV-1,where it impairs viral infectivity by interfering with the processing and virion incorporation of the viral envelope glycoprotein.In this study,we found that GBP5 expression was significantly elevated in influenza patients and IAV-infected A549 human lung epithelial cells.Further study showed that GBP5 inhibited virus replication by enhancing the expression of virus-induced interferon(IFN)and IFN-related effectors.We also found that GBP5 enhanced endogenous IFN expression by interacting with the NF-?B-essential modulator(NEMO)complex and stimulating NF-?B signaling.Additionally,we found that the expression of proinflammatory factors,such as interleukin(IL)-6,IL-8,tumor necrosis factor-.cyclooxygenase-2,and inducible nitric oxide synthase,was also activated by GBP5.Taken together,our results reveal that GBP5 restricted virus replication through the activation of IFN signaling and proinflammatory factors.