Brigitte H. Flannery

Arenaviruses, such as Lassa virus (LASV) and Junin virus (JUNV), cause severe and often lethal hemorrhagic fevers, for which there are no FDA-approved vaccines or effective therapeutics. The viral nucleoprotein (NP) contains a 3′-5′ exoribonuclease (exoN) domain to suppress type I interferon (IFN-I) induction. However, the precise biological roles of the NP exoN during infection remain poorly characterized for highly pathogenic arenaviruses due to biosafety constraints and challenges in generating viable exoN mutants. Utilizing a recombinant tri-segmented Pichinde virus (PICV) vector (rP18tri) suitable for BSL-2 research, we generated two exoN-deficient GFP reporter viruses, (NPm1)-G and (NPm2)-G, by mutating key catalytic residues, and inserted JUNV NP as a transgene within the mutant backbones. All recombinant viruses replicated efficiently in IFN-deficient Vero cells. In IFN-competent A549 cells, all viruses except for the wild-type reporter virus rP18tri-G failed to undergo multicycle replication, consistent with their differential inhibition of IFN-I responses. In contrast to rP18tri-G, which effectively suppressed IFN-I induction throughout the infection time course, exoN-deficient viruses induced robust early IFN-I responses, whereas expressing JUNV NP as a transgene suppressed early IFN-I induction at 16 hpi but failed to sustain suppression at later time points. Further examination during the first round of viral replication in A549 cells demonstrated that the absence of exoN activity is associated with markedly reduced viral gene expression and decreased infectious particle production. Together, these data demonstrate an essential role for NP exoN in mediating IFN-I suppression and suggest its biological functions in viral gene expression and infectious particle production within IFN-competent cells, highlighting its potential as a broad-spectrum therapeutic target.

Current antiviral treatments often target specific viral components, which can lead to the rapid emergence of drug-resistant mutants. Targeting host signaling pathways, including their associated cellular factors, that are important for virus replication is a novel approach toward the development of next-generation antivirals to overcome drug resistance. Various cellular receptor tyrosine kinases (RTKs) have previously been shown to play important roles in mediating viral replication including coronaviruses. In this study, we examined the roles of RTKs in SARS-CoV-2 replication in two cell lines, A549-ACE2 (human lung epithelial cells) and Vero-E6 (African Green Monkey kidney cell), via chemical inhibitors. We showed that the HER2 inhibitor Lapatinib significantly reduced viral replication in both cell lines, the TrkA inhibitor GW441756 was effective only in A549-ACE2 cells, while the EGFR inhibitor Gefitinib had little effect in either cell line. Lapatinib and GW441756 exhibited a high therapeutic index (CC₅₀/EC₅₀ > 10) in A549-ACE2 cells. Time-of-addition experiments indicated that Lapatinib may inhibit the early entry step, whereas GW441756 can affect post-entry steps of the viral life cycle. These findings suggest the important roles of HER2 and TrkA signaling in SARS-CoV-2 infection in human lung epithelial cells and support further investigation of RTK inhibitors as potential COVID-19 treatments.