BIK polymorphism and proteasome regulation unveil host risk factor for severe influenza.

Influenza A viruses (IAVs) pose a significant public health threat, with host factors playing a crucial role in disease severity. We investigated the role of Bcl-2-interacting killer (BIK) in IAV infection using cellular and mouse models, and influenza-infected human cohort. In airway epithelial cells (AECs), BIK deficiency impaired viral replication, while BIK restoration enhanced it. Conversely, airway-specific BIK overexpression in mice increased viral load, inflammation, and mortality, whereas BIK suppression conferred protection. Critically, a genetic variation (rs738276) in the gene, influencing BIK expression, correlates with altered viral replication in air-liquid interface differentiated primary normal human bronchial epithelial cells and influenza severity in humans. Mechanistically, we demonstrate that IAV nucleoprotein (NP) suppresses β5, a subunit of the proteasome, leading to increased BIK levels and enhanced viral replication. Conversely, β5 treatment dampened BIK levels and protected mice from IAV-induced morbidity and mortality. Furthermore, BIK interacts with NP, disrupting the Bcl-2/NP interaction and promoting viral replication. Our findings uncover an IAV-BIK-β5 axis that governs viral replication, suggesting that targeting BIK or β5 may offer therapeutic strategies against influenza.