Role of HDACs and SAM in interferon-alpha signaling and epigenetic regulation of anti-HCV gene expression

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease in the United States and is a huge burden on the US healthcare system. The FDA-approved traditional standard of care for HCV is pegylated interferon-alpha (IFNalpha) combined with ribavirin, which is effective in about 50% of patients. The molecular mechanisms involved in resistance to IFNalpha therapy remain unclear. Recent data strongly suggest that histone deacetylases (HDACs) and methylation play critical roles in the regulation of IFNalpha anti-HCV signaling and gene expression. The present work was carried out to elucidate the roles of HDACs and S-adenosylmethionine (SAM) metabolism in regulating IFNalpha anti-HCV signaling in human hepatoma cells.;Impaired SAM metabolism, as a result of increased intracellular S-adenosylhomocysteine, markedly reduced IFNalpha-mediated antiviral gene expression and anti-HCV activity, which correlated with a decrease in STAT phosphorylation and an increase in association between STAT1 and its negative regulator PIAS1. We also showed that impaired SAM metabolism downregulated expression of several HDACs, which may also impact IFNalpha antiviral signaling. Importantly, SAM supplementation restored the antiviral and anti-HCV properties of IFNalpha.;Acrolein, an environmental pollutant, significantly inhibited antiviral gene expression, which correlated to impaired STAT phosphorylation, decreased induction of class I HDAC mRNAs, and reduced HDAC activity in human hepatoma cells. The results presented herein reveal a critical role for HDACs and SAM metabolism in IFNalpha-mediated anti-HCV activity and support the use of SAM and/or inducers of HDACs as adjunct therapy in managing HCV infection.;Inhibition of HDACs, by pharmacologic HDAC inhibitors or siRNA, significantly suppressed IFNalpha-mediated antiviral gene expression and partially reversed the anti-HCV action of IFNalpha in human hepatoma cells. The decrease in antiviral gene expression correlated with decreased retention time of activated STATs in the nucleus, an increase in STAT acetylation, inhibition of the STAT1:HDAC1 complex, and decreased occupancy of STAT1 on antiviral gene promoters. We used siRNA to specifically identify HDACs 1 and 3 as being critical for IFNalpha-mediated anti-HCV activity. Finally, we showed that boosting HDAC gene expression by theophylline supplementation improved IFNalpha-mediated antiviral gene expression and anti-HCV activity, thus supporting the hypothesis that HDACs are critical for IFNalpha anti-HCV signaling.