Phagocytosis stimulates alternative glycosylation of macrosialin (mouse CD68), a macrophage-specific endosomal protein

Macrosialin (mouse CD68), a macrophage-specific member of the lysosomal-ass ociated membrane protein family, displays N-linked glycosylation and a heav ily sialylated, mucin-like domain. We show that phagocytosis of zymosan by inflammatory peritoneal macrophages potently alters glycan processing of ma crosialin in vitro. The phagocytic glycoform is not induced by other forms of endocytosis and depends on particle internalization. Zymosan uptake does not influence macrosialin protein synthesis, but increases the specific in corporation of D-[2-H-3]mannose, D-[6-H-3]galactose, N-acetyl-D-[1-H-3]gluc osamine and L-[5,6-H-3]fucose by 2-15-fold. The phagocytic glycoform displa ys increased binding of agglutinins from peanut, Amaranthus caudatus and Ga lanthus nivalis, whereas binding of the sialic-acid-specific Maakia amurens is agglutinin is slightly reduced. Digestion by N-Glycanase abolishes the i ncorporation of [H-3]mannose label and Galanthus nivalis agglutinin binding activity, but preserves the incorporation of galactose and N-acetylglucosa mine and specific lectin binding. We also show that phagocytosis increases the complexity and length of O-linked chains. The data presented highlight the importance of differential glycosylation in the biology of macrosialin, phagosomes and macrophages in general.