Interferon inducible protein, viperin, plays an antiviral role during rotavirus infection

Abstract

Rotaviruses (RVs) are a major cause of acute gastroenteritis in children and animals, leading to thousands of deaths annually. RVs form replication complexes termed “viroplasms”, which are cytoplasmic inclusions that serve as the site for viral genome replication and early virion morphogenesis. Viroplasm formation is dependent on recruitment of cellular lipid droplets (LDs). The interferon inducible cellular protein, viperin, is known to localize to both the endoplasmic reticulum and lipid droplet and has been implicated in a wide array of proviral and antiviral interactions with viruses.

This project sought to (i) establish whether viperin colocalizes with characteristic proteins of the viroplasm or LDs during a RV infection and (ii) determine whether changing the expression of viperin effects RV replication kinetics.

While immunofluorescence work conducted here found no evidence of viperin localizing to viroplasms or LDs over the course of a RV infection, viperin overexpression was found to significantly impair RV replication kinetics.

Due to the COVID-19 pandemic, the focus of this project shifted to another line of inquiry. A conserved amino acid sequence (the pLxIS motif) has recently been identified in innate immune pathway adaptor proteins. The pLxIS motif of adaptor proteins recruits and activates the transcription factor interferon regulatory factor 3 (IRF3), an important upregulator of type 1 interferon (IFN) genes. This motif has also been identified in the C terminus of NSP1, the RV protein known to target IRF3 for degradation and thereby suppress an IFN response. Putative work suggests that the pLxIS motif is essential for NSP1-mediated IFN.

This project further sought to (iii) determine when in evolutionary history did pLxIS motifs emerged in innate immune proteins and (iv) evaluate if pLxIS-impaired RVs have impaired replication kinetics or IFN suppression.

Here, the evolutionary origins of the pLxIS motif were examined by analyzing taxonomically diverse sequences from proteins known to contain a pLxIS motif. pLxIS motifs were found to have emerged in mammals and a putative motif was identified in viperin which requires further characterization. pLxIS-impaired RVs were found not to have impaired viral replication. However, the cell line used in this study was found to contain a disrupted IFN pathway and further investigation of the importance of pLxIS motifs in RV infection is warranted.