Influenza A Virus Uses PSMA2 for Downregulation of the NRF2-Mediated Oxidative Stress Response.

Influenza A virus (IAV), an obligatory intracellular parasite, uses host cellular molecules to complete its replication cycle and suppress immune responses. Proteasome subunit alpha type 2 (PSMA2) is a cellular protein highly expressed in IAV-infected human lung epithelial A549 cells. PSMA2 is part of the 20S proteasome complex that degrades or recycles defective proteins and involves proteolytic modification of many cellular regulatory proteins. However, the role of PSMA2 in IAV replication is not well understood. In this study, PSMA2 knockdown (KD) in A549 cells caused a significant reduction in extracellular progeny IAV, but intracellular viral protein translation and viral RNA transcription were not affected. This indicates that PSMA2 is a critical host factor for IAV maturation. To better understand the interplay between PSMA2 KD and IAV infection at the proteomic level, we used the SomaScan 1.3K version, which measures 1,307 proteins to analyze alterations induced by these treatments. We found seven cellular signaling pathways, including phospholipase C signaling, Pak signaling, and nuclear factor erythroid 2p45-related factor 2 (NRF2)-mediated oxidative stress response signaling, that were inhibited by IAV infection but significantly activated by PSMA2 KD. Further analysis of NRF2-mediated oxidative stress response signaling indicated IAV inhibits accumulation of reactive oxygen species (ROS), but ROS levels significantly increased during IAV infection in PSMA2 KD cells. However, IAV infection caused significantly higher NFR2 nuclear translocation that was inhibited in PSMA2 KD cells. This indicates that PSMA2 is required for NRF2-mediated ROS neutralization and that IAV uses PSMA2 to escape viral clearance via the NRF2-mediated cellular oxidative response.