Convergent Transcription of Interferon-stimulated Genes by TNF-α and IFN-α Augments Antiviral Activity against HCV and HEV

IFN-alpha has been used for decades to treat chronic hepatitis B and C, and as an off-label treatment for some cases of hepatitis E virus (HEV) infection. TNF-alpha is another important cytokine involved in inflammatory disease, which can interact with interferon signaling. Because interferon-stimulated genes (ISGs) are the ultimate antiviral effectors of the interferon signaling, this study aimed to understand the regulation of ISG transcription and the antiviral activity by IFN-alpha and TNF-alpha. In this study, treatment of TNF-alpha inhibited replication of HCV by 71 +/- 2.4% and HEV by 41 +/- 4.9%. Interestingly, TNF-alpha induced the expression of a panel of antiviral ISGs (2-11 fold). Blocking the TNF-alpha signaling by Humira abrogated ISG induction and its antiviral activity. Chip-seq data analysis and mutagenesis assay further revealed that the NF-kappa B protein complex, a key downstream element of TNF-alpha signaling, directly binds to the ISRE motif in the ISG promoters and thereby drives their transcription. This process is independent of interferons and JAK-STAT cascade. Importantly, when combined with IFN-alpha, TNF-alpha works cooperatively on ISG induction, explaining their additive antiviral effects. Thus, our study reveals a novel mechanism of convergent transcription of ISGs by TNF-alpha and IFN-alpha, which augments their antiviral activity against HCV and HEV.