Role of ISGF3 in modulating the anti-hepatitis B virus activity of interferon-alpha in vitro

Although interferon-alpha (IFN-alpha) is an effective treatment for hepatitis B virus (HBV) infection, its precise mechanism of action has not been identified. In this study, we investigated the role of signal transduction pathways in the activation of anti-HBV responses mediated by IFN-alpha. Using an oligo microarray, we found that four genes in the IFN-alpha signal pathway were markedly upregulated by IFN-alpha in human hepatoma cells regardless of whether they had been transfected with a plasmid containing the HBV genome: signal transducers and activators of transcription 1 (STAT1), interferon regulatory factor-9 (IRF-9, also called ISGF3 gamma or P48), IFN-alpha-inducible protein 15 (IFI-15) and IFN-alpha-inducible protein 6-16 (IFI-6-16). We also investigated the role of IFN-stimulated gene factor3 (ISGF3) complex in IFN-alpha-mediated anti-HBV responses in human hepatoma cells by measuring the mRNA of the three genes within ISGF3 (STAT1, STAT2 and IRF-9) using semiquantitative reverse-transcription PCR (RT-PCR), and expression of the three proteins by western blot, and the mRNA and protein of dsRNA-dependent protein kinase (PKR). STAT1, STAT2, IRF-9 and PKR mRNA as well as protein levels were upregulated by IFN-alpha treatment. When cells were pretreated with genistein, STAT1, STAT2 and IRF-9 mRNA levels remained unchanged after IFN-alpha stimulation, but PKR mRNA levels decreased, and the expression of the STAT1, P-STAT2, IRF-9 and PKR proteins decreased. Levels of HBV DNA decreased in the supernatants of cells treated with IFN-alpha, while ISGF3 levels increased. The quantity of HBV DNA remained unchanged by pretreating with genistein. These observations suggested that the Janus tyrosine kinase-STAT (JAK-STAT) pathway may play a major role in mediating the effects of IFN-alpha against HBV, and that ISGF3 might be a key factor.