title: Entry from the cell surface of severe acute respiratory syndrome coronavirus with cleaved S protein as revealed by pseudotype virus bearing cleaved S protein.
abstract: Severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) is known to take an endosomal pathway for cell entry; however, it is thought to enter directly from the cell surface when a receptor-bound virion spike (S) protein is affected by trypsin, which induces cleavage of the S protein and activates its fusion potential. This suggests that SARS-CoV bearing a cleaved form of the S protein can enter cells directly from the cell surface without trypsin treatment. To explore this possibility, we introduced a furin-like cleavage sequence in the S protein at amino acids 798 to 801 and found that the mutated S protein was cleaved and induced cell fusion without trypsin treatment when expressed on the cell surface. Furthermore, a pseudotype virus bearing a cleaved S protein was revealed to infect cells in the presence of a lysosomotropic agent as well as a protease inhibitor, both of which are known to block SARS-CoV infection via an endosome, whereas the infection of pseudotypes with an uncleaved, wild-type S protein was blocked by these agents. A heptad repeat peptide, derived from a SARS-CoV S protein that is known to efficiently block infections from the cell surface, blocked the infection by a pseudotype with a cleaved S protein but not that with an uncleaved S protein. Those results indicate that SARS-CoV with a cleaved S protein is able to enter cells directly from the cell surface and agree with the previous observation of the protease-mediated cell surface entry of SARS-CoV.
authors.affiliation: Department of Virology III, National Institute of Infectious Diseases, Murayama Branch, 4-7-1 Gakuen, Mushai-Murayama, Tokyo 208-0011, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Watanabe
authors.forename: Shutoku
authors.initials: S
authors.lastname: Matsuyama
authors.forename: Kazuya
authors.initials: K
authors.lastname: Shirato
authors.forename: Masami
authors.initials: M
authors.lastname: Maejima
authors.forename: Shuetsu
authors.initials: S
authors.lastname: Fukushi
authors.forename: Shigeru
authors.initials: S
authors.lastname: Morikawa
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Taguchi
mesh_terms: D002459:Cell Fusion; D011992:Endosomes / Q000821:virology; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000502:physiology*; D010196:Pancreatic Elastase / Q000502:physiology; D045473:Severe acute respiratory syndrome-related coronavirus / Q000502:physiology*; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins / Q000502:physiology*
chemical_list: D008562:Membrane Glycoproteins; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus; D010196:Pancreatic Elastase
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