Type I IFN augments IL-27-dependent TRIM25 expression to inhibit HBV replication

Hepatitis B virus(HBV)can cause chronic hepatitis B,which may lead to cirrhosis and liver cancer.Type I interferon(IFN)is an approved drug for the treatment of chronic hepatitis B.However,the fundamental mechanisms of antiviral action by type I IFN and the downstream signaling pathway are unclear.TRIM25 is an IFN-stimulated gene(ISG)that has an important role in RIG-I ubiquitination and activation.Whether TRIM25 is induced in liver cells by type I IFN to mediate anti-HBV function remains unclear.Here we report that interleukin-27(IL-27)has a critical role in IFN-induced TRIM25 upregulation.TRIM25 induction requires both STAT1 and STAT3.In TRIM25 knockout HepG2 cells,type I IFN production was consistently attenuated and HBV replication was increased,whereas overexpression of TRIM25 in HepG2 cells resulted in elevated IFN production and reduced HBV replication.More interestingly,we found that TRIM25 expression was downregulated in HBV patients and the addition of serum samples from HBV patients could inhibit TRIM25 expression in HepG2 cells,suggesting that HBV might have involved a mechanism to inhibit antiviral ISG expression and induce IFN resistance.Collectively,our results demonstrate that type I IFN-induced TRIM25 is an important factor in inhibiting HBV replication,and the IFN-IL-27-TRIM25 axis may represent a new target for treating HBV infection.

A dual-role of SARS-CoV-2 nucleocapsid protein in regulating innate immune response

The recently emerged severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),which is the causative agent of ongoing global pan demic of COVID-19,may trigger imm uno suppression in the early stage and overactive immune resp onse in the late stage of infection;However,the un derlying mecha nisms are not well understood.Here we dem on strated that the SARS-CoV-2 nucleocapsid(N)protein dually regulated innate immune responses,i.e.,the low-dose N protein suppressed type I interferon(IFN-I)signaling and inflammatory cytokines,whereas high-dose N protein promoted IFN-I signaling and inflammatory cytokines.Mechanistically,the SARS-CoV-2 N protein dually regulated the phosphorylation and nuclear translocation of IRF3,STAT1,and STAT2.Additi on ally,low-dose N protein combined with TRIM25 could suppress the ubiquitination and activatio n of retinoic acidinducible gene I(RIG-I).Our findings revealed a regulatory mechanism of innate immune responses by the SARS-CoV-2 N protein,which would contribute to understanding the pathogenesis of SARS-CoV-2 and other SARS-like coronaviruses,and development of more effective strategies for controlling COVID-19.

Type III interferon-induced CBFβinhibits HBV replication by hijacking HBx

Hepatitis B virus(HBV)and its associated chronic infection remain serious health threats worldwide.However,there is still no impactful approach for clinical treatment of hepatitis B patients.Therefore,developing a better understanding of the interactions between HBV and its host is particularly important.HBV infection has been reported to induce type-III but not type-I or type-II interferon(IFN).In this study,we identified CBFβ,an HIV enhancer,as an HBV restriction factor that is specifically induced by type-III IFN in the early stages of HBV infection.Type-III IFN-induced IL-10 played an important role in the production of CBFβ.Interestingly,the interaction between CBFβ-and HBV-encoded regulatory protein X(HBx)enhanced the stability of CBFβ,but notably blocked HBx-mediated promotion of HBV replication.CBFβexpression was lower in HBV patients than in healthy persons,and the addition of serum from HBV patients inhibited CBFβexpression in HepG2 cells.On the contrary,HBV via HBsAg inhibited type-III IFN-induced CBFβexpression and decreased the anti-HBV activity of type-III IFN,suggesting that HBV inhibits antiviral interferon-stimulated gene(ISG)expression and induces IFN resistance.Collectively,our results demonstrate that type-III IFN-triggered and IL-10-induced CBFβare crucial factors for inhibiting HBV replication,and the HBx–CBFβ–HBsAg axis reveals a new molecular mechanism of interaction between HBV and its hosts.

TRIM25 inhibits HBV replication by promoting HBx degradation and the RIG-I-mediated pgRNA recognition

Background:The hepatitis B virus(HBV)vaccine has been efficiently used for decades.However,hepatocellular carcinoma caused by HBV is still prevalent globally.We previously reported that interferon(IFN)-induced tripartite motif-containing 25(TRIM25)inhibited HBV replication by increasing the IFN expression,and this study aimed to further clarify the anti-HBV mechanism of TRIM25.Methods:The TRIM25-mediated degradation of hepatitis B virus X(HBx)protein was determined by detecting the expression of HBx in TRIM25-overexpressed or knocked-out HepG2 or HepG2-NTCP cells via Western blotting.Co-immunoprecipitation was performed to confirm the interaction between TRIM25 and HBx,and colocalization of TRIM25 and HBx was identified via immunofluorescence;HBV e-antigen and HBV surface antigen were qualified by using an enzyme-linked immunosorbent assay(ELISA)kit from Kehua Biotech.TRIM25 mRNA,pregenomic RNA(pgRNA),and HBV DNA were detected by quantitative real-time polymerase chain reaction.The retinoic acid-inducible gene I(RIG-I)and pgRNA interaction was verified by RNA-binding protein immunoprecipitation assay.Results:We found that TRIM25 promoted HBx degradation,and confirmed that TRIM25 could enhance the K90-site ubiquitination of HBx as well as promote HBx degradation by the proteasome pathway.Interestingly,apart from the Really Interesting New Gene(RING)domain,the SPRY domain of TRIM25 was also indispensable for HBx degradation.In addition,we found that the expression of TRIM25 increased the recognition of HBV pgRNA by interacting with RIG-I,which further increased the IFN production,and SPRY,but not the RING domain is critical in this process.Conclusions:The study found that TRIM25 interacted with HBx and promoted HBx-K90-site ubiquitination,which led to HBx degradation.On the other hand,TRIM25 may function as an adaptor,which enhanced the recognition of pgRNA by RIG-I,thereby further promoting IFN production.Our study can contribute to a better understanding of host-virus interaction.

Hepatitis B virus X protein and its host partners

Hepatitis B virus(HBV)is a widespread human pathogen,especially in China,and is known to cause liver inflammation,cirrhosis,and hepatocellular carcinoma.A total of ten different genotypes of HBV(A–J)have been reported worldwide.HBV has partially double-stranded DNA,and the 3.2-kb viral genome is located in the nucleus of infected hepatocytes.All of the viral RNAs are transcribed from the covalently closed circular DNA(cccDNA),which acts as the transcription template.The seven main proteins of HBV include Core,pre-Core,Small S,Middle S,Large S,Polymerase,and the critical HBV-encoded regulatory protein hepatitis B virus X protein(HBx).HBx is a 154-amino acid(aa)protein that facilitates the efficient replication of HBV by stimulating HBV gene expression from the cccDNA template.However,the mechanism by which HBx interacts with host proteins and facilitates HBV replication is not precisely known.