The nicotinamide phosphoribosyltransferase inhibitor FK866 restricts influenza A virus replication by perturbing viral polymerase activity

Nicotinamide phosphoribosyltransferase (NAMPT), a key rate-limiting enzyme in NAD + synthesis, plays important roles in various physiological and pathological processes. However, the function and underlying mechanisms of NAMPT in influenza A virus (IAV) infection and pathogenesis remain ambiguous. Here, in vitro studies showed that NAMPT had profound effects on the replication of IAV. Treatment with the NAMPT inhibitor FK866 or disruption of NAMPT expression markedly attenuated the replication of various IAV subtypes, including H1N1, H3N2, and H9N2. Additionally, FK866-treated mice exhibited significant resistance to the IAV infection, as evidenced by a lower degree of tissue injury, slower body weight loss, and better survival than untreated animals challenged with IAV. Mechanistically, NAMPT interacted with viral polymerase basic protein 1 (PB1) and promoted the association of PB1 with polymerase acidic protein (PA) and polymerase basic protein 2 (PB2). Inhibition or depletion of NAMPT restrained the activity of viral RNA-dependent RNA polymerase (RdRp), thereby repressing IAV transcription and replication. Furthermore, we identified arginine 203 of PB1 as a critical residue for its interaction with NAMPT. The mutation (arginine 203 to proline, R203P) of PB1 hindered the association of PB1 with NAMPT, PA, and PB2, thereby impairing the RdRp activity and limiting IAV transcription and replication. Collectively, these findings uncover a critical role of NAMPT in regulating IAV replication and characterize the antiviral property of the NAMPT inhibitor FK866 against IAVs, providing insights for the development of novel anti-influenza strategies. IMPORTANCE Influenza A virus (IAV) causes acute respiratory diseases in humans and animals and poses a great threat to public health, highlighting the urgent need for more effective antiviral treatments. Here, we found that the nicotinamide phosphoribosyltransferase (NAMPT) inhibitor FK866 significantly suppressed the replication of IAV in vitro and in vivo . Of note, FK866 markedly attenuated the replication of different IAV subtypes, including H1N1, H3N2, and H9N2, suggesting FK866 as a potential broad-spectrum antiviral against IAVs. Mechanistically, NAMPT interacted with viral polymerase basic protein 1 (PB1) and enhanced the association of PB1 with PA and PB2. FK866 could interfere with the viral polymerase activity, thereby limiting the synthesis of IAV viral RNA, complementary RNA, and messenger RNA. These findings reveal that the NAMPT inhibitor FK866 restricts IAV replication by perturbing viral polymerase activity and provide insights into the development of potential antivirals against IAV infection.