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)-a 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-a-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-a. Ectopic expression of Pol suppressed IFN-a-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-d (PKC-d) and perturbed PKC-d 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-a5 required for STAT1/2 recruitment. Truncation analysis suggested that the terminal protein and RNase H domains of Pol were able to bind to PKC-d and importin-a5, respectively, and were responsible for the inhibition of IFN-a signaling. More importantly, the inhibition of STAT1 and PKC-d phosphorylation were confirmed in a hydrodynamicbased HBV mouse model, and the blockage of IFN-a-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-a signaling and provide a possible molecular mechanism by which HBV resists the IFN therapy and maintains its persistence. (HEPATOLOGY 2013;57:470-482) C hronic hepatitis B (CHB) caused by hepatitis B virus (HBV) is a serious health problem worldwide. The mechanism by which chronic infection is established and maintained is unknown but is thought to be due, in part, to a suppressed host immune response. One key component of the host antiviral responses is the interferon (IFN) system. Viral infection of the host initiates the synthesis of type I IFNs, which consist predominantly of IFN-a and IFN-b (IFN-a/b). By binding to type I IFN receptors,

Glucocorticoid-induced S-Adenosylmethionine Enhances the Interferon Signaling Pathway by Restoring STAT1 Protein Methylation in Hepatitis B Virus-infected Cells

“…Conventional use of IFN-␣ has produced encouraging results, with HBeAg loss rates of 20 -50% (27). However, HBV, as a hepatotropic DNA virus, may have a low sensitivity to IFNinduced ISGs and may counteract IFN actions at different levels, including the IFN signal transduction and antiviral functions of ISG products (28). Although the effect of IFN seems indisputable, response rates are unsatisfactory, from a clinical point of view.…”

Human hepatitis B virus surface and e antigens inhibit major vault protein signaling in interferon induction pathways

“…Several HBV proteins have been shown to interfere with the IFN-induced intracellular signal transduction pathways. HBV polymerase (Pol) is able to inhibit IFN-a-induced MyD88 induction and impair IFN-a-induced STAT activation [12]. HBeAg suppresses TLR-induced IFN-b and interferon-stimulated gene (ISG) induction in both parenchymal and nonparenchymal liver cells [3].…”

Hepatitis B Virus Polymerase Localizes to the Mitochondria, and Its Terminal Protein Domain Contains the Mitochondrial Targeting Signal

“…Apobec3G, a host restriction factor, has been shown to interact with Pol in an RNA-independent manner and is packaged into capsids (24). Multiple studies have also linked Pol to host immune modulation by prevention of IRF3 phosphorylation and blocking of translocation of NF-B and STAT1 to the nucleus, which is thought to dampen host innate immune sensing (25)(26)(27).…”