title: Hepatitis B virus polymerase impairs interferon-α-induced STA T activation through inhibition of importin-α5 and protein kinase C-δ.
abstract: Treatment with exogenous interferon (IFN)-α is not effective in the majority of patients with chronic hepatitis B virus (HBV) infection. Recent evidence suggests that HBV has evolved strategies to block the nuclear translocation of signal transducer and activator of transcription (STAT) 1 to limit IFN-α-induced cellular antiviral responses. However, it remains unclear whether STAT1 translocation is impaired in chronic hepatitis B patients and what mechanisms are involved. Here we report that the expression of HBV polymerase (Pol) in human hepatic cell lines inhibited induction of IFN-stimulated genes and resulted in a weakened antiviral activity of IFN-α. Ectopic expression of Pol suppressed IFN-α-induced STAT1 serine 727 phosphorylation and STAT1/2 nuclear accumulation, whereas STAT1 tyrosine 701 phosphorylation, and STAT1-STAT2 heterodimer formation were not affected. Further studies demonstrated that Pol interacted with the catalytic domain of protein kinase C-δ (PKC-δ) and perturbed PKC-δ phosphorylation and its association with STAT1, which resulted in the suppression of STAT1 Ser727 phosphorylation. Moreover, Pol was found to interfere with nuclear transportation of STAT1/2 by competitively binding to the region of importin-α5 required for STAT1/2 recruitment. Truncation analysis suggested that the terminal protein and RNase H domains of Pol were able to bind to PKC-δ and importin-α5, respectively, and were responsible for the inhibition of IFN-α signaling. More importantly, the inhibition of STAT1 and PKC-δ phosphorylation were confirmed in a hydrodynamic-based HBV mouse model, and the blockage of IFN-α-induced STAT1/2 nuclear translocation was observed in HBV-infected cells from liver biopsies of chronic HBV patients.
  
  
  CONCLUSIONS
  These results demonstrate a role for Pol in HBV-mediated antagonization of IFN-α signaling and provide a possible molecular mechanism by which HBV resists the IFN therapy and maintains its persistence.
authors.affiliation: Key Laboratory of Medical Molecular Virology, Ministry of Education and HealthShanghai Medical College of Fudan University, Shanghai, China.
authors.forename: Jieliang
authors.initials: J
authors.lastname: Chen
authors.forename: Min
authors.initials: M
authors.lastname: Wu
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Zhang
authors.forename: Wen
authors.initials: W
authors.lastname: Zhang
authors.forename: Zhanqing
authors.initials: Z
authors.lastname: Zhang
authors.forename: Lixiang
authors.initials: L
authors.lastname: Chen
authors.forename: Jing
authors.initials: J
authors.lastname: He
authors.forename: Ye
authors.initials: Y
authors.lastname: Zheng
authors.forename: Cuncun
authors.initials: C
authors.lastname: Chen
authors.forename: Fan
authors.initials: F
authors.lastname: Wang
authors.forename: Yunwen
authors.initials: Y
authors.lastname: Hu
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Zhou
authors.forename: Cong
authors.initials: C
authors.lastname: Wang
authors.forename: Yang
authors.initials: Y
authors.lastname: Xu
authors.forename: Mengji
authors.initials: M
authors.lastname: Lu
authors.forename: Zhenghong
authors.initials: Z
authors.lastname: Yuan
mesh_terms: D000818:Animals; D002460:Cell Line; D056945:Hep G2 Cells; D006515:Hepatitis B virus / Q000201:enzymology; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology / Q000627:therapeutic use*; D051379:Mice; D010766:Phosphorylation; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012194:RNA-Directed DNA Polymerase / Q000378:metabolism*; D050794:STAT1 Transcription Factor / Q000037:antagonists & inhibitors / Q000378:metabolism; D050795:STAT2 Transcription Factor / Q000037:antagonists & inhibitors; D018116:Vesiculovirus / Q000187:drug effects; D028901:alpha Karyopherins / Q000037:antagonists & inhibitors*
chemical_list: D016898:Interferon-alpha; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D028901:alpha Karyopherins; D051745:Protein Kinase C-delta; D012194:RNA-Directed DNA Polymerase