Despite many studies on host or viral gene expression, how the cellular proteome responds to internal or external cues during the infection process remains unclear. In this study, we used a Hepatitis B Virus (HBV) replication model and performed proteomic analyses to understand how HBV evades innate immunity as a function of cell cycle progression. Specifically, we performed proteomic analyses of HBV-replicating cells in G1/S and G2/M phases, as a function of IFN-α treatment. We identified that the conserved LSm (Like-Sm1-8) proteins were differentially regulated in HBV replicating cells treated with IFN-α. Specifically, in G2/M phase, IFN-α increased protein level of LSm1, the unique subunit of cytoplasmic LSm1-7 complex involved in mRNA decay. By contrast, IFN-α decreased LSm8, the unique subunit of nuclear LSm2-8 complex, a chaperone of U6 spliceosomal RNA, suggesting the cytoplasmic LSm1-7 complex is antiviral, whereas the nuclear LSm2-8 complex is pro-viral. In HBV replication and infection models, siRNA-mediated knockdown of LSm1 increased all viral RNAs. Conversely, LSm8 knockdown 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 by LSm8 knockdown, dependent on the 5’ m6A modification, suggesting the LSm2-8 complex has a role in mediating this modification. Interestingly, splicing inhibitor Cp028 acting upstream of the LSm2-8 complex suppressed viral RNA levels without reducing the 5’ m6A modification. This observation suggests Cp028 has novel antiviral effects, likely potentiating IFN-α-mediated suppression of HBV biosynthesis.
CITATION STYLE
Rahman, N., Sun, J., Li, Z., Pattnaik, A., Mohallem, R., Wang, M., … Andrisani, O. (2022). The cytoplasmic LSm1-7 and nuclear LSm2-8 complexes exert opposite effects on Hepatitis B virus biosynthesis and interferon responses. Frontiers in Immunology, 13. https://doi.org/10.3389/fimmu.2022.970130
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