Effect Of Interferon-Induced Protein With Tetratricopeptide Repeats 3 On SFTSV Replication And The Underlying Molecular Mechanism

Background and Aims:Severe fever with thrombocytopenia syndrome(SFTS),caused by severe fever with thrombocytopenia syndrome virus(SFTSV),is associated with high mortality rate of the patients.Since the pathogenesis of SFTS is still unclear,the progress in drug development and clinical therapy is very limited.Interferon(IFN),one of the most important effectors of innate immunity,is on the first line of defense against invading pathogens.Activation of type ?IFN signaling pathway leads to expression of a few hundred IFN-stimulated genes(ISGs),including IFN-induced protein with tetratricopeptide repeats 3(IFIT3),which play important roles in antiviral and immunomodulatory responses to viral infection.IFIT3 showed significant antiviral activity during infection of dengue virus and vesicular stomatitis virus.It has also been reported that IFIT3 expression was increased in SFTSV-infected monocytes,indicating that IFIT3 is involved in SFTSV infection.However,the effects of IFIT3 on SFTSV replication and the underlying molecular mechanism remain unclear.This study aimed to investigate the effect of IFIT3 on SFTSV replication in vitro and the underlying molecular mechanism.Methods:1.Expression of IFIT3 was upregulated or down-regulated by IFIT3 plasmid or siRNA transfection into A549 cells,respectively.ITIT3 expression and SFTSV replication were analyzed by real-time PCR or Western Blot.2.Expression of IFIT3 was upregulated or down-regulated by IFIT3 plasmid or siRNA transfection into A549 cells,respectively.The cells were then treated by IFN after infected with SFTSV.SFTSV replication was analyzed by real-time PCR to evaluate the effect of IFIT3 on IFN antiviral activity.Type I IFN signaling pathway was monitored at three levels:p-STAT1(Western Blot),IRSE activity(Dual Luciferase Assay)and ISGs expression(real-time PCR)to evaluate the effect of IFIT3 on IFN signaling pathway.Key molecules involved in IFN production was detected by real-time PCR.Results:The expression of IFIT3 was significantly upregulated by SFTSV infection or IFN treatment in A549 cells.Overexpression of IFIT3 inhibited NS mRNA expression of SFTSV,while down-regulated expression of IFIT3 promoted it.Upregulation of IFIT3 promoted production of IFN?,which increased the level of pSTAT1,the activity of ISRE and the expression of ISGs.Furthermore,overexpressed IFIT3 was associated with increased expression of RIG-I,MDA5 and TLR3,all of which are involved in IFN production.Conclusions:Overexpression of IFIT3 inhibited SFTSV replication,while down-regulated IFIT3 expression promoted SFTSV replication.IFIT3 could increase the expression of RIG-1,MDA5 and TLR3 to promote production of endogenous IFN?,leading to activation of JAK/STAT signaling pathway,increased ISGs expression and consequently inhibited SFTSV replication.Our results indicate that IFIT3 is important to limit spread of SFTSV infection,providing new insights into the role of IFIT3 in innate immune response to viral infection.