ABSTRACT Replication of influenza A virus (IAV) is highly reliant on host cell function, and to identify the key host factor required in the influenza A virus life cycle, a genome-wide CRISPR/Cas9 knockout (KO) screen was conducted in A549 cells infected by H1N1 influenza virus. The results showed that glucosamine (UDP-N-acetyl)-2-epimerase/N-acetylmannosamine kinase (GNE) plays a crucial role in the replication of influenza A virus, and knockout of the GNE significantly reduced the replication of multiple subtype influenza A viruses in A549 cells, and restoration of the GNE expression in the GNE-knockout cells partially recovered IAV infection. Additionally, overexpression of the GNE in wild-type (WT) cells promoted IAV infection to a certain extent. Further study showed that the GNE is involved in α-2,3- and α-2,6-linked sialic acid (Sia) synthesis, which is the major receptor of the influenza A virus, and the GNE knockout downregulated the α-2,3- and α-2,6-linked sialic acid expression. In summary, the knockout of the GNE inhibits adsorption and endocytosis of IAV. This study provides a new approach to elucidate the replication mechanism of IAV and identifies GNE as a potential target for anti-influenza drug development. IMPORTANCE Influenza A virus infection requires the assistance of the host proteins. Glucosamine (UDP-N-acetyl)-2-epimerase/N-acetylmannosamine kinase (GNE) was identified as an important host factor in influenza A virus infection by genome-wide CRISPR screening. GNE knockout (KO) extensively inhibited the replication of multiple subtype influenza A viruses. It indirectly participated in IAV adsorption and endocytosis by regulating the expression of sialic acid (Sia), the main receptor of IAV. This finding provides novel insights into the replication mechanism of IAV.
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