Inhibition of STAT1 methylation is involved in the resistance of hepatitis B virus to Interferon alpha.
As a major therapy for hepatitis B virus (HBV) infection, Interferon alpha (IFN-alpha) triggers intracellular signal transduction including JAK-STAT pathway to produce various antiviral effector mechanisms. However, patients with chronic hepatitis B usually show low response to IFN-alpha treatment and the underlying mechanism remains unclear. In the present study, HepG2 and HepG2.2.15 cells were used to examine the Type I IFN receptors expression, phosphorylation and methylation of STAT1. STAT1-PIAS1 interaction in cells was tested by protein co-immunoprecipitation. The potential improvement of S-adenosylmethionine (SAM) in the antiviral effect of IFN-alpha was also investigated. Our data demonstrated that both chains of the Type I IFN receptors were expressed for a much higher extent in HepG2.2.15 cells than in HepG2 cells. HBV inhibited dramatically the methylation rather than the phosphorylation of STAT1, which was consistent with an increased STAT1-PIAS1 interaction. Combined with IFN-alpha, SAM treatment effectively improved STAT1 methylation and attenuated STAT1-PIAS1 binding, followed by increased PKR and 2',5'-OAS mRNA expression, thus significantly reducing the HBsAg, HBeAg protein levels and HBV DNA load in the supernatant of HepG2.2.15 cells. Less STAT1 methylation and subsequent increased STAT1-PIAS1 interaction are involved in the mechanism of the IFN-alpha-antagonistic activity of HBV. By improving STAT1 methylation, SAM can enhance the antiviral effect of IFN-alpha.
State Key Laboratory of Infectious Disease Diagnosis and Treatment, First Affiliated Hospital, Zhejiang University College of Medicine, 79 Qingchun Road, Hangzhou, Zhejiang 310003, China.
Jie
J
Li
Feng
F
Chen
Min
M
Zheng
Haihong
H
Zhu
Dongjiu
D
Zhao
Weixia
W
Liu
Wei
W
Liu
Zhi
Z
Chen
D002460:Cell Line; D006515:Hepatitis B virus / Q000276:immunology* / Q000472:pathogenicity*; D022781:Hepatocytes / Q000276:immunology* / Q000821:virology*; D006801:Humans; D047468:Immunoprecipitation; D016898:Interferon-alpha / Q000037:antagonists & inhibitors* / Q000276:immunology*; D008745:Methylation; D010766:Phosphorylation; D011485:Protein Binding; D050828:Protein Inhibitors of Activated STAT / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism*; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism
D016898:Interferon-alpha; C106529:PIAS1 protein, human; D050828:Protein Inhibitors of Activated STAT; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D025841:Small Ubiquitin-Related Modifier Proteins; D012436:S-Adenosylmethionine