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

Protein kinase R (PKR) serves as an antiviral sensor, triggering translational inhibition and stress granule (SG) formation through the phosphorylation of eIF2. Despite earlier studies suggesting that hepatitis C virus (HCV) non-structural protein 5A (NS5A) hinders PKR dimerization, other research consistently shows PKR activation and SG formation during HCV infection.

To clarify this inconsistency, researchers examined NS5A's ability to regulate the canonical PKR-eIF2 pathway across various cell culture models, using different HCV genotypes and strains. Regardless of the genotype or strain, HCV NS5A did not inhibit PKR dimerization or the activation of PKR mediated by double-stranded RNA, nor did it restore crucial downstream steps in the pathway, such as translation halt and SG formation.

Unlike recognized viral PKR antagonists, HCV NS5A did not exhibit this antagonistic effect. Moreover, NS5A did not block PKR activation when co-expressed with other HCV non-structural proteins. Researchers also investigated the role of the host factor cyclophilin A (CypA), which associates with both NS5A and PKR. However, the absence of CypA did not impact downstream PKR signaling or the functionality of viral PKR antagonists or NS5A.

In summary, these results indicate that NS5A fails to effectively antagonize the PKR-eIF2 pathway, reinforcing the notion that HCV replication can occur despite the presence of an active PKR response.