Hepatitis C virus NS5A is not an effective antagonist of the canonical PKR-eIF2α pathway

Abstract

Protein kinase R (PKR) is an antiviral sensor that induces translational shutdown and stress granule (SG) formation through the phosphorylation of eIF2. Although previous studies have proposed that hepatitis C virus (HCV) non-structural protein 5A (NS5A) inhibits PKR dimerization, other studies consistently observe PKR activation and SG formation during HCV infection. To address this discrepancy, we interrogated the ability of NS5A from different genotypes and strains to regulate canonical PKR-eIF2 activation in a variety of cell culture models. Regardless of the genotype or strain tested, HCV NS5A failed to inhibit PKR dimerization or dsRNA-induced PKR activation, nor did it rescue downstream steps in the PKR-eIF2 pathway, such as translation halt and SG formation, in contrast to known viral PKR antagonists. Similarly, NS5A did not antagonise PKR activation when expressed in the context of other HCV non-structural proteins. We also tested the role of the host factor cyclophilin A (CypA), which interacts with both NS5A and PKR. However, the absence of CypA did not affect downstream PKR signaling or the activity of viral PKR antagonists or NS5A. Collectively, these findings indicate that NS5A does not effectively antagonise the PKR-eIF2 pathway and further support previous findings that HCV replication occurs in the presence of an active PKR response.