The Role And Mechanisms Of DEAD-box RNA Helicasc DDX20 On Antiviral Innate Immunity

Viruses are highly parasitic small particles that widely distributed in nature.Therefore,viruses evolve a series of mechanisms to escape and inhibit the host's immune response system because they must use host's energy metabolism system and protein translation system to achieve self-replication.In the long-term struggling with the viruses,the host has also evolved highly complex and sophisticated immune systems and mechanisms to remove pathogens effectively and timely.The DEAD-box(DDX)family is a kind of RNA helicases with a conserved sequence of D(Asp)-E(Glu)-A(Ala)-D(Asp),which is involved in the process of RNA metabolism,including RNA splicing,transcription,transport,translation,degradation and so on.Some members of the DDX family also play important roles in antiviral immunity.For example,DDX41 and DDX58(RIG-I)can recognize viral DNA and RNA,individually,and further trigger the production of type I interferon beta(IFN-?).DDX20 was firstly screened out to have antiviral activity with RNAi library of DDX family members.We found that knockdown of DDX20 upregulated the replication of vesicular stomatitis virus(VSV)and herpes simplex virus type I(HSV-1).However,overexpression of DDX20 significantly inhibited the replications' of VSV and HSV-1.In addition,we constructed DDX20 knockout mice and found that DDX20 also had antiviral effect in vivo.In order to investigate 'the antiviral mechanism of DDX20,we examined the effect of DDX20 on type I interferon(IFN)production.The results showed that DDX20 ectopic expression enhanced the expression of IFN-? and interferon stimulated genes(ISGs).Further analysis found that DDX20 could enhance the interaction between TBK1 and IRF3,promote the phosphorylation level of IRF3 and so that improved the exresssion of IFN-?.Finally,we found that LRSAM1,an E3 ubiquitin ligase,interacted with DDX20 via immunoprecipitation together with mass spectrometry analysis(IP-MS).LRSAMI also promoted the ubiquitination level of DDX20 and further enhanced the phosphorylation of IRF3 together with DDX20.This work will help us to further elucidate the antiviral innate immune mechanisms of the host,and also provide a new target for the development of antiviral drugs.