Zinc Finger CCCH-type Antiviral Protein 1 Restrict The Replication Of Influenza Virus By Positively Regulating The Type ? Interferon

Influenza A viruses(IAVs)cause annual contagious respiratory disease in the humans and other mammals and are responsible for pandemics that result in higher mortality rates.IAV is a member of the orthomyxovirus family.Besides,its genome is composed of eight negative-sense RNA segments,which typically encode 17 viral proteins.The prime target cells of influenza viruses are respiratory epithelial cells.However,the virus can also infect macrophages and dendritic cells of the respiratory tract.The innate immune system recognizes the RNA of IAV through the Toll-like receptors(TLRs),the Nod-like receptors(NLRs),and the recently identified RNA helicases retinoic acid inducible gene-I(RIG-I)and melanoma differentiation-associated gene 5(MDA5).This recognition initiates the production of antiviral effector such as IFN?/?.The expression of IFN?/?controlled by the underlying transcription factors of the IFN regulatory factor(IRF)family,notably IRF3 and IRF7.The secreted IFN?/? binds to the IFN?/? receptors on the cell membrane and initiates the JAK/STAT(Janus protein tyrosine kinase/signal transducers and activators of transcription)signaling cascade.It leads to the induction of IFN-stimulated genes(ISGs)such as MxA,2'-5' oligoadenylate synthetase(OAS)and protein kinase R(PKR)and Zinc-finger CCCH-type antiviral protein 1(ZC3HAV1).The Zinc-finger antiviral protein originally identified from a rat complementary DNA library due to its resistance to the genetically marked murine leukemia viruses.The ZC3HAV1 encodes the ZC3HAV1 protein,an IFN stimulated gene present on the human chromosome 7(7q34)and inhibited the alphaviruses,filoviruses,hepatitis B virus,and retroviruses.ZC3HAV1 directly binds with the viral mRNA,degrades by recruiting the processing exosome,and removes the poly(A)tail of the target mRNA.Moreover,ZC3HAV1 eliminates the cap structure of the target mRNA by recruiting the decapping complex.Consequently,removal of the cap structure exposes the RNA body to the 5'-3' exoribonuclease Xrn1 for degradation.ZC3HAV1 encodes two isoforms,i.e.ZAPS and ZAPL arising from alternative splicing,and differ only at the C-terminus.In the Nterminus domain of ZC3HAV1,there are four CCCH-type-zinc-finger motifs,which can directly bind to the viral RNA.ZAPL,compared to ZAPS is more active against alphaviruses such as Sindbis virus(SINV)and Semliki forest virus(SFV)and has signatures of positive selection.However,ZAPS is highly expressed in response to type I IFN and viral infection compared to ZAPL.The antiviral activity of ZC3HAV1 depends on the presence of a ZAP-responsive element(ZRE)in the viral mRNA.Viruses sensitive to ZC3HAV1 comprise unique ZRE such as murine leukemia viruses(MLV),SINV,Ebola virus(EBOV),HIV-1,and hepatitis B virus(HBV).Presence of ZRE in the viral mRNA does not confirm the sensitivity of the virus to ZC3HAV1.In present thesis,the antiviral role of the ZC3HAV1 protein analyzed against influenza virus by interfering the expression of ZC3HAV1 in A549 cells.Furthermore,the effects of restricted expression of ZC3HAV1 on the innate immune signaling also studied.Effects of ectopic expression on the replication of IAV and innate immunity investigated too.The results in this thesis provide novel functional insights of ZC3HAV1 to inhibit the replication of IAV.It was observed that cells with silenced expression of ZC3HAV1 were unable to restrict the replication of influenza virus.This claim was further confirmed by the measurement of the expression of IFN-?and other cytokines.It was noticed that the ZC3HAV1 knockdown cells have less expression of IFN-?.As the influenza virus is highly sensitive to the antiviral action of IFN-?,so decreased expression of IFN-? ease the virus replication.Moreover,we evaluated the expression of ISGs and found that expression of MxA has significantly reduced in A549 ZC3HAV1 knockdown cells in response to influenza A virus,as MxA induction is dependent on the expression of type I IFN or type III IFN.Knocking down the expression of ZC3HAV1 resulted in the curtailed expression of IRF3,TNF,and IL-6 in response to influenza A virus infection which are key innate immune regulators.Moreover,exogenous expression of ZC3HAV1 in A549 cells induced the higher level of IFN-? and MxA mRNA after infection with influenza A virus.A549 cells expressing ZC3HAV1 showed substantial suppression of influenza A virus replication.Similarly,the expression of ZC3HAV1 vigorously enhanced the gene expression programs mediated by IRF3 including the genes encoding type I IFN,MxA,proinflammatory cytokines IL-6,and TNF.Data of this study reveal that ZC3HAV1 concisely involved in antiviral innate immune responses against influenza virus.According to the findings,ZC3HAV1 may have an important role in host defense against many other viruses known to activate IRF3 signaling such as hepatitis C virus(HCV)and Japanese encephalitis virus(JEV).Taken together,ZC3HAV1 can restrict the replication of influenza virus by enhancing the expression IFN-P expression through IRF3 signaling.This study expands the information concerning with versatile nature of the ZC3HAV1 and highlight its indispensable antiviral role against influenza A virus.