Influenza A Viruses Enter Host Cells via Extracellular Ca²⁺ Influx-Involved Clathrin-Mediated Endocytosis

Influenza A virus (IAV) is internalized into its host cells by endocytosis, which involves many cellular proteins and molecules. In this study, we focus on the function of calcium ion (Ca²⁺) in IAV endocytosis. We have found that IAV infection is accompanied by the increase in concentration of cytosolic Ca²⁺, which is mainly attributed to the influx of extracellular Ca²⁺. When Ca²⁺ influx is abolished, IAV internalization will be markedly suppressed, but the virus attachment to its host cells will be unaffected. Extracellular Ca²⁺ influx is essential to the clathrin-mediated endocytosis (CME) of IAVs but dispensable to the clathrin-independent endocytosis of the virus and is dispensable to the CME of transferrin or low-density lipoprotein as a control. Ca²⁺ influx might participate in the dynamin-promoted membrane fission in the CME of IAVs. Our study highlights that IAVs enter host cells via extracellular Ca²⁺ influx-involved clathrin- and dynamin-dependent endocytosis, which will facilitate better understanding of IAV infection and development of anti-influenza drugs.