title: Protease-mediated entry via the endosome of human coronavirus 229E.
abstract: Human coronavirus 229E, classified as a group I coronavirus, utilizes human aminopeptidase N (APN) as a receptor; however, its entry mechanism has not yet been fully elucidated. We found that HeLa cells infected with 229E via APN formed syncytia when treated with trypsin or other proteases but not in a low-pH environment, a finding consistent with syncytium formation by severe acute respiratory syndrome coronavirus (SARS-CoV). In addition, trypsin induced cleavage of the 229E S protein. By using infectious viruses and pseudotyped viruses bearing the 229E S protein, we found that its infection was profoundly blocked by lysosomotropic agents as well as by protease inhibitors that also prevented infection with SARS-CoV but not that caused by murine coronavirus mouse hepatitis virus strain JHMV, which enters cells directly from the cell surface. We found that cathepsin L (CPL) inhibitors blocked 229E infection the most remarkably among a variety of protease inhibitors tested. Furthermore, 229E infection was inhibited in CPL knockdown cells by small interfering RNA, compared with what was seen for a normal counterpart producing CPL. However, its inhibition was not so remarkable as that found with SARS-CoV infection, which seems to indicate that while CPL is involved in the fusogenic activation of 229E S protein in endosomal infection, not-yet-identified proteases could also play a part in that activity. We also found 229E virion S protein to be cleaved by CPL. Furthermore, as with SARS-CoV, 229E entered cells directly from the cell surface when cell-attached viruses were treated with trypsin. These findings suggest that 229E takes an endosomal pathway for cell entry and that proteases like CPL are involved in this mode of entry.
authors.affiliation: Department of Virology III, Laboratory of Viral Respiratory Infections, National Institute of Infectious Diseases, Musashi-Murayama, Tokyo, Japan.
authors.forename: Miyuki
authors.initials: M
authors.lastname: Kawase
authors.forename: Kazuya
authors.initials: K
authors.lastname: Shirato
authors.forename: Shutoku
authors.initials: S
authors.lastname: Matsuyama
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Taguchi
mesh_terms: D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism; D028941:Coronavirus 229E, Human / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D011992:Endosomes / Q000821:virology*; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008562:Membrane Glycoproteins / Q000378:metabolism; D006517:Murine hepatitis virus / Q000502:physiology; D010447:Peptide Hydrolases / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D045473:Severe acute respiratory syndrome-related coronavirus / Q000502:physiology; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins / Q000378:metabolism; D010948:Viral Plaque Assay; D053586:Virus Internalization
chemical_list: D008562:Membrane Glycoproteins; D034741:RNA, Small Interfering; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus; D002403:Cathepsins; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; C534281:CTSL protein, human; D056668:Cathepsin L; C534278:Ctsl protein, mouse