Activation of Protein Kinase R (PKR) Plays a Pro-Viral Role in Mammarenavirus Infected Cells

ABSTRACT Many viruses, including mammarenaviruses, have evolved mechanisms to counteract different components of the host cell innate immunity, which is required to facilitate robust virus multiplication. The double strand (ds)RNA sensor protein kinase receptor (PKR) pathway plays a critical role in the cell antiviral response. Whether PKR can restrict the multiplication of the Old World mammarenavirus lymphocytic choriomeningitis virus (LCMV) and the mechanisms by which LCMV may counteract the antiviral functions of PKR have not yet been investigated. Here we present evidence that LCMV infection results in very limited levels of PKR activation, but LCMV multiplication is enhanced in the absence of PKR. In contrast, infection with a recombinant LCMV with a mutation affecting the 3’-5’ exonuclease (ExoN) activity of the viral nucleoprotein (NP) resulted in robust PKR activation in the absence of detectable levels of dsRNA, which was associated with severely restricted virus multiplication that was alleviated in the absence of PKR. However, pharmacological inhibition of PKR activation resulted in reduced levels of LCMV multiplication. These findings uncovered a complex role of the PKR pathway in LCMV-infected cells involving both pro-and anti- viral activities. IMPORTANCE As with many other viruses, the prototypic Old World mammarenavirus lymphocytic choriomeningitis virus (LCMV) can interfere with the host cell innate immune response to infection, which includes the double strand (ds)RNA sensor protein kinase receptor (PKR) pathway. A detailed understanding of LCMV-PKR interactions can provide novel insights about mammarenavirus-host cell interactions and facilitate the development of effective antiviral strategies against human pathogenic mammarenaviruses. In the present work, we present evidence that LCMV multiplication is enhanced in PKR- deficient cells, but pharmacological inhibition of PKR activation unexpectedly resulted in severely restricted propagation of LCMV. Likewise, we document a robust PKR activation in LCMV-infected cells in the absence of detectable levels of dsRNA. Our findings have revealed a complex role of the PKR pathway during LCMV infection and uncovered the activation of PKR as a druggable target for the development of antiviral drugs against human pathogenic mammarenaviruses.