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The cytoplasmic LSm1-7 and nuclear LSm2-8 complexes exert opposite effects on Hepatitis B virus biosynthesis and interferon response

ABSTRACT: Viruses employ various strategies to evade innate immunity. Despite many studies on host or viral gene expression, how the cellular proteome responds to internal or external cues, has not been fully investigated. Using a Hepatitis B Virus (HBV) replication model, we performed proteomic analyses of HBV-replicating cells in G1/S and G2/M phases, as a function of IFN-alpha, providing specific information of how HBV infection, in combination with IFN-alpha, alters the hepatocyte proteome. We identified the conserved LSm (Like-Sm1-8) proteins were differentially expressed as a function of HBV replication and IFN-alpha. Specifically, in G2/M, IFN-alpha increased protein level of LSm1, the unique subunit of cytoplasmic LSm1-7 complex involved in mRNA decay. By contrast, IFN-alpha decreased LSm8, the unique subunit of nuclear LSm2-8 complex, a chaperone of U6 spliceosomal RNA. These results suggest cytoplasmic LSm1-7 has antiviral role, whereas nuclear LSm2-8 complex is pro-viral. Employing HBV replication and infection models, siRNA-mediated knockdown of LSm1 increased the level of all viral RNAs. Conversely, knockdown of LSm8 reduced viral RNA levels, dependent on N6-adenosine methylation (m6A) of the epsilon stem-loop at the 5 end of pre-Core/pregenomic (preC/pg) RNA. Methylated RNA immunoprecipitation (MeRIP) assays demonstrated reduced viral RNA methylation upon LSm8 knockdown, dependent on the m6A modification, suggesting the LSm2-8 complex has a role in mediating this modification. Interestingly, splicing inhibitor Cp028 acting upstream of LSm2-8 complex, suppressed levels of viral RNAs without reducing the m6A modification. This observation suggests Cp028 has novel antiviral effects, likely potentiating IFN-alpha -mediated suppression of HBV biosynthesis.

INSTRUMENT(S): Orbitrap Fusion Lumos, Q Exactive HF

ORGANISM(S): Hepatitis B Virus (ncbitaxon:10407)

SUBMITTER: Ourania Andrisani

PROVIDER: MSV000089600 | MassIVE | Fri Jun 03 13:06:00 BST 2022

REPOSITORIES: MassIVE

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Project description:Hepatitis B virus (HBV) causes both acute and chronic liver inflammation. Approximately 600,000 CHB patients each year die of HBV-related diseases such as cirrhosis and liver cancer. Therefore, CHB remains a global health concern. Although there have been anti-HBV agents for treating CHB, they have some limitations including viral-drug resistance and adverse effects. Type III IFN or IFN-λ is promising to use as anti-HBV agents because of its anti-viral activities like type I IFNs. In addition, the expression of its receptor, IFNLR1, is limited only in epithelial cells including hepatocytes. Thus, treatment with IFN-lambda results in less side effects compared to IFN-alpha treatment. IFN-lambdas have been shown to inhibit the replication of several viruses including IAV, DENV, EMCV, HIV, HCV, and HBV; however, there have been no studies on the effects of IFN-λ3, the highest activity among other subtypes, on HBV replication. Therefore, this study aims to determine antiviral activities of IFN-λ3 against HBV replication and to investigate its molecular mechanism responsible for suppressing HBV propagation. The results showed that HBV transcripts and amount of intracellular HBV DNA were decreased in HepG2.2.15 cells, stable HBV-transfected hepatoblastoma cell line, treated with IFN-λ3 in a dose-dependent manner. This indicated that IFN-λ3 could inhibit HBV replication. Next, we performed quantitative proteomics to investigate the proteome changes in HepG2.2.15 treated with IFN-λ3. The proteins that changed their expressions were involved in several biological processes such as defense to viral infection, immune responses, cell-cell adhesion, transcription, translation, and metabolism. We further confirmed the proteomics results by immunoblotting assay. Consistent with MS data, it found that the expression of OAS3, SAMHD1 and STAT1 were increased as a result of IFN-λ3 stimulation. These results indicated that proteomics results were reproducible and reliable. Finally, we proposed 3 possible mechanisms involved in suppressing HBV replication including i.) IFN-λ3 induced anti-viral proteins affecting many steps in HBV life cycle ii.) IFN-λ3 promoted antigen processing and antigen presentation and iii.) IFN-λ3 rescued RIG-I signaling to promote both type I and type III IFN production.

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The cytoplasmic LSm1-7 and nuclear LSm2-8 complexes exert opposite effects on Hepatitis B virus biosynthesis and interferon response

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