Identification of host cellular factors that regulate human norovirus replication

The human norovirus (HuNoV) is one of the most predominant causes of gastroenteritis, yet no suitable therapeutics are available for its control. Currently, our knowledge of the precise cellular processes that control its replication is limited. In this study, we used the virus replicon system in human gastric tumour (HGT) cells to determine host factors involved in human norovirus replication, and to analyse the adaptive changes required to support its long-term replication in cell culture. First, using a genome-wide microarray screen, we found that the expression of the receptor for type III interferons is suppressed by epigenetic modification of its promoter, and cells lacking the receptor were more permissive for HuNoV replication. Secondly, the role of the heat shock protein 90 (Hsp90) on HuNoV replication was examined. While this molecular chaperone was previously reported to have a proviral effect on murine norovirus infection, in this current study, we observed that inhibition of the protein with small molecule inhibitors resulted in the degradation of key cellular proteins in the innate immune pathway, with a corresponding increase in virus replication in replicon- harbouring cells. Finally, we showed that human norovirus replication requires the activity of COX-1 so that the inhibition of the enzyme with a small molecule inhibitor (SC-560) reduced virus replication. Prostaglandin E2 supplementation abrogated the effect of SC560 on HuNoV replication. We also observed that a prolonged treatment of the replicon-harbouring cells with SC-560 resulted in the generation of a single amino acid mutation, T229A, in the NS1/2 of the replicon. Introduction of this mutation in the wildtype HuNoV replicon conferred resistance to the inhibitory effect from COX- 1 inhibition by SC-560. Altogether, this work provides new insights into the key dynamics of virus-host interactions that determine the outcome of HuNoV infections, and potentially opens novel avenues for their therapeutic control.