Approach to the Involvement of Influenza B Neuraminidase in the Cleavage of HA by Host Cell Protease Using Low pH‐Induced Cell Fusion Reaction

Abstract

ts7, a temperature-sensitive mutant defective in neuraminidase (NA) of influenza B/ Kanagawa/73, lacks NA enzymatic activity at the nonpermissive temperature (37.5 C). When MDCK cells were infected with the mutant at the permissive temperature (32 C) and exposed to pH 5.2 medium, extensive cell fusion occurred. In contrast, at the nonpermissive temperature cells did not show cell fusion at all unless they were pretreated with trypsin, suggesting that at 37.5 C the hemagglutinin (HA) of ts7 is expressed at the cell surface in an uncleaved form. It was also found that the replacement of RNA segment 6 of ts7 with that of wild-type B/Lee resulted in the emergence of low pH-induced fusion activity as well as NA enzymatic activity at the incubation temperature of 37.5 C and that the addition of bacterial NA to the cultures infected with ts7 at 37.5 C early in infection brought about low pH-induced cell fusion. We suggest that the removal of neuraminic acid from the carbohydrate moiety of HA by NA is essential for the cleavage of HA by cellular protease.

Influenza Hemagglutinin and Neuraminidase: Yin–Yang Proteins Coevolving to Thwart Immunity

“…NA plays an essential role in completing the infectious cycle by enabling virion release and preventing HA-mediated aggregation of virions by desialylating HA (and other NA molecules) [54,55,56,57] and possibly virion glycolipids as well. For some strains, HA desialylation is required for HA cleavage by proteases to activate fusion activity [58,59].…”

Development of Lentiviral Vectors Pseudotyped With Influenza B Hemagglutinins: Application in Vaccine Immunogenicity, mAb Potency, and Sero-Surveillance Studies

“…For influenza B, HA activation has been observed in embryonated chicken eggs ( 64 ), and in both a trypsin−dependent and independent manner in MDCK cells ( 65 , 66 ). Additionally, experiments have shown that neuraminidase could also have a role in HA activation by removing glucidic residues on the HA surface ( 67 , 68 ). Furthermore, it was shown that influenza B HA can be cleaved by porcine pancreatic elastase when the cleavage-linked arginine is substituted with an alanine or a valine ( 61 ).…”

Development and use of Lentiviral Vectors Pseudotyped with Influenza B Haemagglutinins: application to vaccine immunogenicity, mAb potency and sero-surveillance studies

“…For influenza B, HA activation has been observed in embryonated chicken eggs (Zhirnov et al 1994), and in a trypsin-dependent and independent manner in MDCK cells (Noma et al 1998;Lugovtsev et al 2013). Additionally, experiments have shown that the NA could also have a role in HA activation by removing glucidic residues on the HA surface (Yamamoto-Goshima & Maeno 1994;Shibata et al 1993). Furthermore, it was shown that influenza B HA can be cleaved by porcine pancreatic elastase when the cleavage-linked arginine is substituted with an alanine or a valine (Stech et al 2011).…”