title: The host protease TMPRSS2 plays a major role in in vivo replication of emerging H7N9 and seasonal influenza viruses.
abstract: Proteolytic cleavage of the hemagglutinin (HA) protein is essential for influenza A virus (IAV) to acquire infectivity. This process is mediated by a host cell protease(s) in vivo. The type II transmembrane serine protease TMPRSS2 is expressed in the respiratory tract and is capable of activating a variety of respiratory viruses, including low-pathogenic (LP) IAVs possessing a single arginine residue at the cleavage site. Here we show that TMPRSS2 plays an essential role in the proteolytic activation of LP IAVs, including a recently emerged H7N9 subtype, in vivo. We generated TMPRSS2 knockout (KO) mice. The TMPRSS2 KO mice showed normal reproduction, development, and growth phenotypes. In TMPRSS2 KO mice infected with LP IAVs, cleavage of HA was severely impaired, and consequently, the majority of LP IAV progeny particles failed to gain infectivity, while the viruses were fully activated proteolytically in TMPRSS2+/+ wild-type (WT) mice. Accordingly, in contrast to WT mice, TMPRSS2 KO mice were highly tolerant of challenge infection by LP IAVs (H1N1, H3N2, and H7N9) with ≥1,000 50% lethal doses (LD50) for WT mice. On the other hand, a high-pathogenic H5N1 subtype IAV possessing a multibasic cleavage site was successfully activated in the lungs of TMPRSS2 KO mice and killed these mice, as observed for WT mice. Our results demonstrate that recently emerged H7N9 as well as seasonal IAVs mainly use the specific protease TMPRSS2 for HA cleavage in vivo and, thus, that TMPRSS2 expression is essential for IAV replication in vivo.
  
  
  OBJECTIVE
  Influenza A virus (IAV) is a leading pathogen that infects and kills many humans every year. We clarified that the infectivity and pathogenicity of IAVs, including a recently emerged H7N9 subtype, are determined primarily by a host protease, TMPRSS2. Our data showed that TMPRSS2 is the key host protease that activates IAVs in vivo through proteolytic cleavage of their HA proteins. Hence, TMPRSS2 is a good target for the development of anti-IAV drugs. Such drugs could also be effective for many other respiratory viruses, including the recently emerged Middle East respiratory syndrome (MERS) coronavirus, because they are also activated by TMPRSS2 in vitro. Consequently, the present paper could have a large impact on the battle against respiratory virus infections and contribute greatly to human health.
authors.affiliation: Department of Virology 3, National Institute of Infectious Diseases, Tokyo, Japan.
authors.forename: Kouji
authors.initials: K
authors.lastname: Sakai
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ami
authors.forename: Maino
authors.initials: M
authors.lastname: Tahara
authors.forename: Toru
authors.initials: T
authors.lastname: Kubota
authors.forename: Masaki
authors.initials: M
authors.lastname: Anraku
authors.forename: Masako
authors.initials: M
authors.lastname: Abe
authors.forename: Noriko
authors.initials: N
authors.lastname: Nakajima
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Sekizuka
authors.forename: Kazuya
authors.initials: K
authors.lastname: Shirato
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Suzaki
authors.forename: Akira
authors.initials: A
authors.lastname: Ainai
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Nakatsu
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Kanou
authors.forename: Kazuya
authors.initials: K
authors.lastname: Nakamura
authors.forename: Tadaki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Komase
authors.forename: Eri
authors.initials: E
authors.lastname: Nobusawa
authors.forename: Katsumi
authors.initials: K
authors.lastname: Maenaka
authors.forename: Makoto
authors.initials: M
authors.lastname: Kuroda
authors.forename: Hideki
authors.initials: H
authors.lastname: Hasegawa
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kawaoka
authors.forename: Masato
authors.initials: M
authors.lastname: Tashiro
authors.forename: Makoto
authors.initials: M
authors.lastname: Takeda
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000378:metabolism; D054884:Host-Pathogen Interactions; D053118:Influenza A Virus, H1N1 Subtype / Q000502:physiology; D053122:Influenza A Virus, H3N2 Subtype / Q000502:physiology; D053124:Influenza A Virus, H5N1 Subtype / Q000502:physiology; D064766:Influenza A Virus, H7N9 Subtype / Q000502:physiology*; D007928:Lethal Dose 50; D008168:Lung / Q000821:virology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009976:Orthomyxoviridae Infections / Q000473:pathology / Q000821:virology; D012697:Serine Endopeptidases / Q000172:deficiency / Q000378:metabolism*; D016019:Survival Analysis; D014779:Virus Replication
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D012697:Serine Endopeptidases; C000588699:TMPRSS2 protein, mouse