Cleavage of?influenza?virus hemagglutinin (HA) by host?proteases?is essential for virus infectivity. HA of most?influenza?A and?B?(IAV/IBV)?viruses?is cleaved at a monobasic motif by trypsin-like?proteases. Previous studies have reported that transmembrane serine?protease?2 (TMPRSS2) is essential for activation of H7N9 and H1N1pdm IAV in mice, but that?H3N2?IAV and IBV activation is independent of TMPRSS2 and carried out by as-yet-undetermined?protease(s). Here, to?identify?additional H3 IAV- and IBV-activating?proteases, we used RNA-Seq to investigate the?protease?repertoire of?murine?lower?airway?tissues, primary type II alveolar epithelial cells (AECII), and the mouse lung cell line ... More
Cleavage of?influenza?virus hemagglutinin (HA) by host?proteases?is essential for virus infectivity. HA of most?influenza?A and?B?(IAV/IBV)?viruses?is cleaved at a monobasic motif by trypsin-like?proteases. Previous studies have reported that transmembrane serine?protease?2 (TMPRSS2) is essential for activation of H7N9 and H1N1pdm IAV in mice, but that?H3N2?IAV and IBV activation is independent of TMPRSS2 and carried out by as-yet-undetermined?protease(s). Here, to?identify?additional H3 IAV- and IBV-activating?proteases, we used RNA-Seq to investigate the?protease?repertoire of?murine?lower?airway?tissues, primary type II alveolar epithelial cells (AECII), and the mouse lung cell line MLE-15. Among 13 candidates identified, TMPRSS4, TMPRSS13, hepsin, and prostasin activated H3 and IBV HA in vitro. IBV activation and replication was reduced in AECII from Tmprss2/Tmprss4-deficient mice compared with wild-type or Tmprss2-deficient mice, indicating that?murine?TMPRSS4 is involved in IBV activation. Multicycle replication of?H3N2?IAV and IBV in AECII of Tmprss2/Tmprss4-deficient mice varied in sensitivity to?protease?inhibitors, indicating that different, but overlapping, sets of?murine?proteases?facilitate H3 and IBV HA cleavages. Interestingly, human hepsin and prostasin orthologs did not?activate?H3, but did?activate?IBV HA in vitro. Our results indicate that TMPRSS4 is an IBV-activating?protease?in?murine?AECII and suggest that TMPRSS13, hepsin, and prostasin cleave H3 and IBV HA in mice. They further show that hepsin and prostasin orthologs might contribute to the differences observed in TMPRSS2-independent activation of H3 in?murine?and human airways.
