Ms. Kang et al., ACCUMULATION OF PENTAMANNOSE OLIGOSACCHARIDES IN HUMAN MONONUCLEAR LEUKOCYTES BY ACTION OF SWAINSONINE, AN INHIBITOR OF GLYCOPROTEIN PROCESSING, Carbohydrate research, 248, 1993, pp. 327-337
Swainsonine, a known inhibitor of the alpha-mannosidase II involved in
processing of asparagine-linked glycoproteins, causes accumulation of
hybrid-type oligosaccharide-containing glycoproteins in mammalian cel
ls. Swainsonine augments lymphokine-activated, killer-cell induction a
t suboptimal doses of interlekin-2; the amount needed to increase LAY,
activity is 100-1000 fold higher than required to completely inhibit
mannosidase II. Human mononuclear lymphocytes, when treated with these
relatively high (58 muM) concentrations of swainsonine showed a 3-4 f
old increase in D-[H-3]mannose incorporation into the glycan as compar
ed to glycans of untreated cells. Analysis indicated accumulation of h
igh-mannose type, free oligosaccharides in the soluble fractions of th
e cell. Chromatographic analysis of glycan obtained by D-[2-H-3]mannos
e labeling of human mononuclear lymphocytes showed synthesis of a new
oligosaccharide, at 58 muM of swainsonine, that contained 36% of the t
otal radioactivity incorporated into the glycan (oligosaccharide pool)
. This oligosaccharide fraction was resistant to hydrolysis by endogly
cosidase H, endoglycosidase F, O and N-glycanase, but was susceptible
to cleavage by Jack bean a-mannosidase and was bound > 90% to concanav
alin A-Sepharose. A similar chromatographic elution profile was obtain
ed from glycans labeled with D-[2-H-3]mannose from mouse B16F10 melano
ma and baby hamster kidney cells subsequent to swainsonine treatment.
Methylation analysis of free oligosaccharides obtained from MNL reveal
ed the presence of a pentamannose. These results indicate the accumula
tion of a free high-mannose oligosaccharide rather than expected hybri
d-type structure on treatment of cells with relatively high concentrat
ions of swainsonine.