title: Proteolytic activation of the 1918 influenza virus hemagglutinin.
abstract: Proteolytic activation of the hemagglutinin (HA) protein is indispensable for influenza virus infectivity, and the tissue expression of the responsible cellular proteases impacts viral tropism and pathogenicity. The HA protein critically contributes to the exceptionally high pathogenicity of the 1918 influenza virus, but the mechanisms underlying cleavage activation of the 1918 HA have not been characterized. The neuraminidase (NA) protein of the 1918 influenza virus allows trypsin-independent growth in canine kidney cells (MDCK). However, it is at present unknown if the 1918 NA, like the NA of the closely related strain A/WSN/33, facilitates HA cleavage activation by recruiting the proprotease plasminogen. Moreover, it is not known which pulmonary proteases activate the 1918 HA. We provide evidence that NA-dependent, trypsin-independent cleavage activation of the 1918 HA is cell line dependent and most likely plasminogen independent since the 1918 NA failed to recruit plasminogen and neither exogenous plasminogen nor the presence of the A/WSN/33 NA promoted efficient cleavage of the 1918 HA. The transmembrane serine protease TMPRSS4 was found to be expressed in lung tissue and was shown to cleave the 1918 HA. Accordingly, coexpression of the 1918 HA with TMPRSS4 or the previously identified HA-processing protease TMPRSS2 allowed trypsin-independent infection by pseudotypes bearing the 1918 HA, indicating that these proteases might support 1918 influenza virus spread in the lung. In summary, we show that the previously reported 1918 NA-dependent spread of the 1918 influenza virus is a cell line-dependent phenomenon and is not due to plasminogen recruitment by the 1918 NA. Moreover, we provide evidence that TMPRSS2 and TMPRSS4 activate the 1918 HA by cleavage and therefore may promote viral spread in lung tissue.
authors.affiliation: Nikolaus Fiebiger Center for Molecular Medicine, University Hospital Erlangen, 91054 Erlangen, Germany.
authors.forename: Chawaree
authors.initials: C
authors.lastname: Chaipan
authors.forename: Darwyn
authors.initials: D
authors.lastname: Kobasa
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bertram
authors.forename: Ilona
authors.initials: I
authors.lastname: Glowacka
authors.forename: Imke
authors.initials: I
authors.lastname: Steffen
authors.forename: Theodros Solomon
authors.initials: TS
authors.lastname: Tsegaye
authors.forename: Makoto
authors.initials: M
authors.lastname: Takeda
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Bugge
authors.forename: Semi
authors.initials: S
authors.lastname: Kim
authors.forename: Youngwoo
authors.initials: Y
authors.lastname: Park
authors.forename: Andrea
authors.initials: A
authors.lastname: Marzi
authors.forename: Stefan
authors.initials: S
authors.lastname: Pöhlmann
mesh_terms: D002460:Cell Line; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000378:metabolism*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D009439:Neuraminidase / Q000378:metabolism; D010958:Plasminogen / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D008565:Membrane Proteins; C483468:hemagglutinin, human influenza A virus; D010958:Plasminogen; D009439:Neuraminidase; D012697:Serine Endopeptidases; C421305:TMPRSS2 protein, human; C528837:TMPRSS4 protein, human