Essential Role of Protein Kinase R Antagonism by TRS1 in Human Cytomegalovirus Replication

Abstract

Human cytomegalovirus (HCMV) lacking TRS1 and IRS1 (HCMV[ΔI/ΔT]) cannot replicate in cell culture. Although both proteins can block the protein kinase R (PKR) pathway, they have been reported to have multiple other activities and binding partners. It remains unknown which of these functions are essential for HCMV replication. To investigate this issue, we first identified a TRS1 mutant that is unable to bind to PKR. Like HCMV[ΔI/ΔT], a recombinant HCMV containing this mutant did not replicate in wild-type cells. However, HCMV[ΔI/ΔT] did replicate in cells in which PKR expression was reduced by RNA interference. Moreover, HCMV[ΔI/ΔT] and the recombinant mutant replicated to similar levels as virus containing TRS1 in two different cell lines in which PKR expression was knocked out by CRISPR/Cas9-mediated genome editing. These results demonstrate that the sole essential function of TRS1 in cultured human fibroblasts is to antagonize PKR and that its other activities do not substantially enhance HCMV replication.