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ABSTRACT. 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.-KEY WORDS: glucosidase inhibitor, glycoprotein, glycosylation, influenza.I n f l u e n z a A v i r u s h a s t w o m e m b r a n e -b o u n d gl y c o pr ot e i ns , t h e he m a g g l ut i n i n ( H A ) a nd t he neuraminidase (NA) [14]. The HA is the type I glycoprotein, binding to a sialic acid-containing receptor on the host cell surface. It also mediates the fusion process of the virus particle with the endosomal membrane. The NA is the type II glycoprotein, serving as a receptor-destroying enzyme. It catalyzes cleavage of the α-ketosidic linkage between a terminal sialic acid residue and the adjacent sugar residue.N-linked oligosaccharides on glycoproteins undergo the sequential trimming process during the transport pathway t o t h e i r f i na l de s t i n a t i o n [ 9] . T he c o r e u n i t of oligosaccharide is transferred to the asparagine side chain at the glycosylation consensus sequence (Asn-X-Ser/Thr) from a dolichol pyrophosphate precursor. It is then subjected to the first step of trimming in the endoplasmic reticulum (ER) by glucosidase I. It removes the α-1,2-linked glucose from the three terminal glucose residues. Following this, glucosidase II catalyses the removal of the two remaining α-1,3-linked glucoses. After α-1,2-mannosidase removes two external mannose residues from the core, the glycoprotein is transported to the Golgi apparatus for further trimming.Recent evidence suggests that trimming of N-linked oligosaccharides in the ER plays an important role in glycoprotein maturation [5,7,12,15,22]. Maturation of glycoproteins often depends upon the extent of trimming of N-linked oligosaccharide side chains, for inhibitors of glucosidases I and II such as castanospermine (CST), 1-deoxynojirimycin (dNM) and bromoconduritol (BCT) impair the folding of some glycoproteins. The ER molecular chaperone calnexin is suggeste...

The LiBASys clinical analyzer made possible measurement of the complementary tumor markers, HCC, total AFP, AFP-L3 and DCP.

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