TMPRSS2 activates hemagglutinin-esterase glycoprotein of influenza C virus.

Sato, Ko; Hayashi, Hideki; Shimotai, Yoshitaka; Yamaya, Mutsuo; Hongo, Seiji; Kawakami, Kazuyoshi; Matsuzaki, Yoko; Nishimura, Hidekazu

Influenza C virus (ICV) has only one kind of spike protein, the hemagglutinin-esterase (HE) glycoprotein. HE functions similarly to hemagglutinin (HA) and neuraminidase of the influenza A and B viruses (IAV/IBV). It has a monobasic site, which is cleaved by some host enzyme(s). The cleavage is essential to activating the virus, but the enzyme(s) in the respiratory tract has not been identified. This study investigated whether the host serine proteases, transmembrane protease serine S1, members 2 (TMPRSS2), and human airway trypsin-like protease (HAT), which reportedly cleave HA of IAV/IBV, are involved in HE cleavage. We established TMPRSS2- and HAT-expressing MDCK (MDCK-TMPRSS2, MDCK-HAT) cells. ICV showed multicycle replication with HE cleavage without trypsin in MDCK-TMPRSS2 cells as well as IAV did. The HE cleavage and multicycle replication did not appear in MDCK-HAT cells infected with ICV without trypsin, while HA cleavage and multi-step growth of IAV appeared in the cells. Amino acid sequences of the HE cleavage site in 352 ICV strains were completely preserved. Camostat and nafamostat suppressed the growth of ICV and IAV in human nasal surface epithelial (HNE) cells. Therefore, this study revealed that, at least, TMPRSS2 is involved in HE cleavage and suggested that nafamostat could be a candidate for therapeutic drugs of ICV infection. Importance Influenza C virus (ICV) is a pathogen that causes acute respiratory illness, mostly in children, but there are no anti-ICV drugs. ICV has only one kind of spike protein, the hemagglutinin-esterase (HE) glycoprotein on the virion surface, that possesses receptor binding, receptor destroying, and membrane fusion activities. The HE cleavage is essential for the virus to be activated, but the enzyme(s) in the respiratory tract has not been identified. This study revealed that transmembrane protease serine S1, members 2 (TMPRSS2), and not human airway trypsin-like protease (HAT), is involved in HE cleavage. This is a novel study on the host enzymes involved in HE cleavage, and the result suggests that the host enzymes, such as TMPRSS2, may be a target for therapeutic drugs of the ICV infection.