MicroRNA-548 down-regulates host antiviral response via direct targeting of IFN-λ1

Interferon(IFN)-mediated pathways are a crucial part of the cellular response against viral infection.Type III IFNs,which include IFN-λ1,2 and 3,mediate antiviral responses similar to Type I IFNs via a distinct receptor complex.IFN-λ1 is more effective than the other two members.Transcription of IFN-λ1 requires activation of IRF3/7 and nuclear factor-kappa B(NF-κB),similar to the transcriptional mechanism of Type I IFNs.Using reporter assays,we discovered that viral infection in-duced both IFN-λ1 promoter activity and that of the 3′-untranslated region(UTR),indicating that IFN-λ1 expression is also regulated at the post-transcriptional level.After analysis with microRNA(miRNA)prediction programs and 3′UTR targeting site assays,the miR-NA-548 family,including miR-548b-5p,miR-548c-5p,miR-548i,miR-548j,and miR-548n,was identified to target the 3′UTR of IFN-λ1.Further study demonstrated that miRNA-548 mimics down-regulated the expression of IFN-λ1.In contrast,their inhibitors,the complemen-tary RNAs,enhanced the expression of IFN-λ1 and IFN-stimulated genes.Furthermore,miRNA-548 mimics promoted infection by enterovirus-71(EV71)and ve-sicular stomatitis virus(VSV),whereas their inhibitors significantly suppressed the replication of EV71 and VSV.Endogenous miRNA-548 levels were suppressed during viral infection.In conclusion,our results sug-gest that miRNA-548 regulates host antiviral response via direct targeting of IFN-λ1,which may offer a poten-tial candidate for antiviral therapy.

Inducible Rubicon facilitates viral replication by antagonizing interferon production

The RUN domain Beclin-1-interacting cysteine-rich-containing(Rubicon)protein is involved in the maturation step of autophagy and the endocytic pathway as a Beclin-1-binding partner,but little is known regarding the role of Rubicon during viral infection.Here,we performed functional studies of the identified target in interferon(IFN)signaling pathways associated with Rubicon to elucidate the mechanisms of viral resistance to IFN.The Rubicon protein levels were elevated in peripheral blood mononuclear cells,sera and liver tissues from patients with hepatitis B virus(HBV)infection relative to those in healthy individuals.Assays of the overexpression and knockdown of Rubicon showed that Rubicon significantly promoted HBV replication.In addition,Rubicon knockdown resulted in the inhibition of enterovirus 71,influenza A virus and vesicular stomatitis virus.The expression o0f Rubicon led to the suppression of virus-induced type-I interferon(IFN-αand IFN-β)and type-III interferon(IFN-λ1).Translocation of activated IRF3 and IRF7 from the cytoplasm to the nucleus was involved in this process,and the NF-κB essential modulator(NEMO),a key factor in the IFN pathway,was the target with which Rubicon interacted.Our results reveal a previously unrecognized function of Rubicon as a virus-induced protein that binds to NEMO,leading to the inhibition of type-I interferon production.Rubicon thus functions as an important negative regulator of the innate immune response,enhances viral replication and may play a role in viral immune evasion.