SERINC5 Inhibits Influenza Virus Membrane Fusion

SERINC proteins are short for serine incorporator plays a role in the synthesis of serine-containing lipids such as sphingomyelin and phosphatidylserine.SERINC are highly conserved in eukaryotes from yeast(encode one gene)to humans(encode five genes).SERINC homologues share a highly similar topology,they are integral membrane proteins with 9 to 11 membrane spanning regions.Among five SERINC family members SERINC3 and SERINC5 were identified as inhibitors of HIV-1 infectivity of which SERINC5 has a stronger inhibitory activity.Possible mechanisms of fusion inhibition by SERINC5 are an open question.One model is that SERINC5 interacts with Env trimers and inhibits their activity which is supported by the observation that SERINC5 increases the susceptibility of HIV-1 Env to certain antibodies.The other is that virion-incorporated SERINC5 might delay fusion of the virion and target cell membranes.In addition,there is still no reasonable explanation why HIV-1 with VSVG,Ebola GP and some resistant env glycoproteins,but not with sensitive retrovirus pathogens,makes HIV-1 resistant to SERINC5.Therefore,we sought another enveloped virus influenza A virus to investigate whether SERINC5 inhibits influenza infection,as well as the mechanism by which SERINC5 inhibits virus infection and the reasons for the difference.Influenza A virus(IAV)infection is still a major threat to global health.Influenza A virus contains 8 segments of negative single-stranded genomic RNA which encodes for up to 11 proteins.Influenza A virus initiates the infection process with influenza attachment.Influenza hemagglutinin(HA)binds to the target cell via sialic acid linkages on host glycoproteins.After HA-mediated binding to the receptor,virion endocytosis is triggered.Once within endosomes,the low pH activates the M2 ion channel and causes conformational change in HA that drive fusion of the viral and endosomal lipid membranes,viral matrix protein M1 dissociates from the inner membrane to the viral envelope.Fusion of the two membranes release influenza viral ribonucleoproteins(vRNPs)into the cytoplasm and transport to the nucleus for transcription,translation and replication.Here we demonstrate the idea that SERINC5 restricts influenza A virus infection.First,SERINC5 inhibits the infectivity of WSN pseudoparticles with HA/NA.In virus producing cells,the overexpression of SERINC5 did not affect the production of HIV-1 pseudoparticles and the supernatant can detect the incorporation of SERINC5 by ultracentrifugation.Luciferase value was detected in HIV-1 reporter cell lines TZM-BL infected with HIV-1 pseudoparticles,we found that SERINC5 could inhibit the infectivity of HIV-1 pseudoparticles with HA/NA from influenza WSN,suggesting that SERINC5 could inhibits the infection of influenza virus.Moreover,using SERINC5 overexpress or knockout A549 cell lines,we find that SERINC5 can inhibit influenza A virus WSN infection with single cycle or multicycle infection.Further research shows that SERINC5 inhibit influenza infection during early steps of virus entry,which precise influenza virus membrane fusion.Also,we find that SERINC5 can inhibit low N-glycosylation subtypes of influenza HA infectivity indicating that the difference in the inhibitory activity of SERINC5 to different membrane proteins lies in the level of N-glycosylation.From what has been discussed above,we studied the specific role of SERINC5 in the process of influenza virus infection.We proved that SERINC5 can inhibit influenza virus and cell membrane fusion process so as to inhibit influenza virus infection for the first time.We also proved that the differences of inhibitory activity of SERINC5 targeting different membrane protein lies on the levels of N-glycosylation.Which provides further evidence for the research of SERINC5 antiviral mechanisms.And also provides an important reference for the research on mechanism of envelope virus pathogenic and antiviral response.