Identification of ectopic anionic trypsinâI in rat lungs potentiating pneumotropic virus infectivity and increased enzyme level after virus infection

Towatari, Takae; Ide, Mikiko; Ohba, Kumiko; Chiba, Yuusuke; Murakami, Meiko; Shiota, Mayumi; Kawachi, Miki; Yamada, Hiroshi; Kido, Hiroshi

Identification of ectopic anionic trypsinâI in rat lungs potentiating pneumotropic virus infectivity and increased enzyme level after virus infection

2002

Extracellular cleavage of virus envelope fusion glycoproteins by host cellular proteases is a prerequisite for the infectivity of mammalian and nonpathogenic avian influenza viruses, and Sendai virus. In search of such target processing proteases in the airway, we recently found a new candidate trypsinâlike processing protease in rat lungs, which was induced by Sendai virus infection, and identified as ectopic rat anionic trypsinâI. On SDS/PAGE under reducing and nonreducing conditions, the purified enzyme gave protein bands corresponding to 29 and 22âkDa, respectively, i.e. at the same positions as rat pancreatic anionic trypsinâI. It exhibited an apparent molecular mass of 31âkDa on molecular sieve chromatography and its isoelectric point was pHâ4.7. The aminoâacid sequences of the Nâterminus and proteolytic digest peptides of the purified enzyme were consistent with those of rat pancreatic anionic trypsinâI. Its substrate specificities and inhibitor sensitivities were the same as those of the pancreatic enzyme. The purified enzyme efficiently processed the fusion glycoprotein precursor of Sendai virus and hemagglutinin of human influenzaâA virus, and potentiated the infectivity of Sendai virus in the same doseâdependent manner as the pancreatic one. Immunohistochemical studies revealed that this protease is located in the stromal cells in periâbronchiolar regions. These results suggest that ectopic anionic trypsinâI in rat lungs induced by virus infection may trigger virus spread in rat lungs.

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