Viperin is a unique and highly evolutionarily conserved host protein that has been shown to restrict multiple viruses, via many presumably unrelated mechanisms. Here we show for the first time, that viperin acts synergistically to enhance the innate immune dsDNA signaling pathway to limit viral infection, providing a more unifying mechanism for the antiviral activity of this protein.
Primary MEFs isolated from viperin knockout mice presented a significant reduction in their ability to express the prominent antiviral cytokine, type-I interferon (IFN), compared to wild-type MEFs, when challenged with endogenous dsDNA. Subsequent assays involving ectopic expression of viperin and various mutants confirmed these findings and identified viperin’s requirement for its localisation to the lipid droplet, as well as its enzymatic activity to significantly enhance the expression of type-I IFN as well as the expression of downstream antiviral effector genes, following detection of aberrant dsDNA. Additionally, viperin was observed to co-localise with the key signaling molecules of the innate immune dsDNA sensing pathway, STING and TBK1, via direct binding to STING; inducing enhanced K-63 linked ubiquitination of TBK1. Finally, we could show that viperin’s interaction with these molecules and augmentation of the dsDNA signaling pathway was functionally relevant through enhanced upregulation of IFN-β in response to Hepatitis B virus infection, resulting in significantly lowered viral levels in an in vitro infection model.
Here we show that viperin facilitates the formation of a signaling enhansosome, to coordinate efficient signal transduction following activation of the dsDNA signaling pathway; which results in an enhanced antiviral state. This data highlights viperin’s pivotal role in innate immunity and may form the foundation of research towards developing adjuvants for small molecule agonist therapies against currently incurable viral infections.