Effect of glycosylation and glucose trimming inhibitors on the influenza A virus glycoproteins

N-glycosylation and glucose trimming of the influenza virus hemagglutinin (HA) and neuraminidase (NA) were studied by using glycosylation inhibitor (tunicamycin; TM) and glucosidase inhibitors. TM treatment of MDCK cells infected with a reassortant virus NWS-N8 resulted in reduced transport of the viral glycoproteins to the cell surface. The degree of the effects differed between the HA and the NA (80% reduction for the HA and 97% reduction for the NA), indicating a difference in dependency on N-glycosylation between these glycoproteins. Differential dependency on glucose trimming was clearly demonstrated when the surface transport of the glycoproteins was compared after treatment of the virus-infected cells with glucosidase inhibitors. Fluorescence-activated cell sorting (FACS) analysis revealed that the surface transport of the NA reduced to 50% after castanospermine (CST) treatment but not did that of the HA. An anti-viral effect of a glucosidase inhibitor on the NWS-N8 strain was also demonstrated. The correlation between the expression of the NA on the cell surface and virus yield suggests that CST may interfere with virus release through its effect on the NA.