Plscr1 inhibits murine norovirus entry.

Noroviruses are a leading cause of gastroenteritis worldwide, yet host factors that restrict norovirus replication are not well understood. By mining both CRISPR activation and CRISPR knockout genome-wide screens, we identified the interferon-stimulated gene Plscr1 as a restriction factor for murine norovirus (MNV). Plscr1 inhibits the fusion of enveloped viruses with endocytic membranes, making its antiviral activity against the nonenveloped MNV surprising. Here, we demonstrate that Plscr1 is both necessary and sufficient to restrict MNV infection in vitro and contributes to the control of colonic infection in mice. Mechanistically, we determined that Plscr1 inhibits MNV entry at a post-attachment step. A single amino acid substitution in the minor capsid protein VP2 confers resistance to Plscr1. Because VP2 delivers viral RNA by puncturing endocytic membranes during calicivirus entry, these findings implicate a late entry step targeted by Plscr1. Our results expand the antiviral activity of PLSCR1 to a nonenveloped virus and identify an unexpected point of convergence between enveloped- and non-enveloped-virus entry pathways.