DEAD-box RNA helicase DDX3 is a well-known host factor that inhibits hepatitis B viral proliferation and
boosts innate immune responses via TANK-binding kinase 1 (TBK1)/IKKε-mediated and/or interferon (IFN)-β promoter
stimulator-1 (IPS-1)-mediated IFN-β induction. Previously, we demonstrated the anti-hepatitis B activity of Rg3 via
stimulation of TRAF6/TAK1 degradation and inhibition of JNK/AP-1 signaling. To determine the effects of Rg3 on innate
immunity, an IFN-β promoter assay was performed. Rg3 ameliorated IFN-β expression via upregulation of both the
TBK1/IKKε pathway and DDX3 expression. In addition, Rg3 induced the phosphorylation of IRF3 and its translocation
into nucleus, which is a key molecule to induction of IFN-β expression. To evaluate the molecular mechanism of Rg3 on
DDX3 expression, the DDX3 promoter (-1406/+105) was subjected to luciferase assay and ChIP analysis. p53 phosphorylation
resulted in upregulation of DDX3 expression, which enhanced DDX3 promoter transactivation activity. Transient
transfection with wild-type p53 increased DDX3 promoter activity in Hep3B cells which have null mutant of p53,
whereas knockdown p53 by si-p53 reduced DDX3 promoter activity in HepG2.2.15 and HepG2 cells, respectively. Rg3-
mediated phosphorylation of p53 resulted in inhibition of Akt phosphorylation, which in turn reduced MDM2-mediated
p53 degradation. An Akt inhibitor augmented DDX3 promoter activity and reduced the secretion of hepatitis B surface antigen.
Our data indicate that Rg3 enhances innate immunity by inducing IFN-β expression through upregulation of DDX3
promoter activity via p53-mediated transactivation and activation of the TBK1/IKKε/IRF3 pathway.
Keywords: Akt, DDX3 RNA helicase, Ginsenoside Rg3, Hepatitis B, HepG2.2.15 cells, interferon-β, innate immunity, p53.
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