The vaccinia virus kelch-like protein C2L affects calcium-independent adhesion to the extracellular matrix and inflammation in a murine intradermal model

Chordate poxviruses encode several uncharacterized POZ-kelch proteins and three of these are present in Vaccinia virus (VV) strain Western Reserve. VV gene C2L is predicted to encode a protein of 512 amino acid residues with a POZ/BTB domain in the N-terminal region and three kelch motifs in the C-terminal half of the protein. We have identified the C2L gene product as an intracellular protein of 56 kDa and constructed and characterized a VV mutant lacking the C2L gene (vΔC2L). Compared to wild-type and revertant viruses, vΔC2L had unaltered growth in vitro, but had a different plaque morphology due to an altered cytopathic effect (CPE) of infected cells. Deleting C2L had no effect on VV-induced formation of actin tails or enhanced cell motility, but affected the development of VV-induced cellular projections and the Ca²⁺-independent cell/ extracellular matrix adhesion late during infection. In an intranasal mouse model, C2L did not contribute to virus virulence. However, in an intradermal mouse model, infection with vΔC2L resulted in larger lesions and more cell infiltration into the infected ears during recovery from infection. Thus, in this model, C2L protein inhibits inflammation and reduces immunopathology. In summary, we found that C2L is not required for virus replication in vitro but contributes to aspects of VV-induced CPE and reduces immunopathology in vivo.