Oral Presentation Lorne Infection and Immunity 2018

The host anti-viral protein viperin positively augments the dsDNA signalling pathway via a direct interaction with STING (#105)

Keaton M Crosse 1 , Kylie Van der Hoek 2 , Ebony A Monson 1 , Monique L Smith 2 , Michael R Beard 2 , Karla J Helbig 1
  1. Department of Physiology, Anatomy and Microbiology, La Trobe University, Melbourne, VIC, Australia
  2. Department of Molecular and Cellular Biology, Research Centre for Infectious Diseases, University of Adelaide, Adelaide, SA, Australia

Viperin is a unique and highly evolutionarily conserved protein that is able to restrict multiple viruses, via many different mechanisms. Viperin has previously been shown to enhance TLR7/9 signalling in murine plasmacytoid dendritic cells, and here we shown for the first time, that viperin also positively augments the dsDNA signalling pathway. Using luciferase based assays in combination with ectopic expression of viperin and various mutants, we showed that viperin enhances the activity of the IFN-b promoter by 3 fold in the presence of dsDNA stimulation in both Huh-7 and HeLa cell lines, and requires its localisation to the lipid droplet, as well as its enzymatic activity to achieve this. These results were confirmed via dsDNA stimulation of murine embryonic fibroblasts (MEFs), where a 4.5 fold decreased production in IFN-b expression was seen in vip -/- MEF’s in comparison to wild-type. Confocal microscopy in Huh-7 cells revealed that viperin co-localised with both STING and TBK1 in dsDNA stimulated Huh-7 cells, however viperin was only able to be co-immunoprecipitated with STING, and this interaction was dependent on the central viperin region. Further analysis of this interaction in vitro revealed that viperin enhanced K-27-linked ubiquitination of STING, as well as K-63-linked ubiquitination of TBK1; dsDNA stimulated vip -/- MEFs also demonstrated reduced K-63 linked ubiquitination of TBK1 in comparison to wt MEF’s. Proximity-ligation-assays revealed that viperin also interacted with TRAF3 and TRAF6, both known to form signalling complexes with STING and TBK1. Here we show viperin upregulates IFN-b via enhanced activation of STING and TBK1 following detection of dsDNA within a cell. This data implicates viperin as a pivotal protein involved in the control of microorganisms which activate the dsDNA sensing pattern recognition receptors, and its ability to augment early innate signalling pathways may explain viperin’s capacity to restrict multiple viral families.