Remodeling of cell surface oligosaccharides by introduction of glycogenes and its application

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N-Acetylglucosaminyltransferase-III (GnT-III) catalyzes the formation of bisecting N-acetylglucosamine (GlcNAc) in the biosynthesis of N-linked oligosaccharides. To examine the effect of biosecting GlcNAc on the natural killer (NK) cytotoxicity, the GnT-III gene was introduced into NK-sensitive K562 cells that have no detectable GnTIII activity. Introduction of the gene resulted in complete blockage of the NK cytotoxicity against the transfected cells and also in a decrease of the binding of the effector cells to the target cells. After s.c. injection into nude mice, GnT-III-transfectants produced spleen colonization, although no spleen lesions were formed by control cells. In nude mice depleted of NK cells by anti-asialo GM1 antibody, both transfectants and controls yielded spleen colonization equally. These results indicate that K562 cells expressing GnT-III are resistant to NK cytotoxicity, resulting in spleen colonization in nude mice.The functional consequence of the sugar chain remodeling was examined in rat pheochromocytoma (PC12) cells by transfection of GnT-III gene. Nerve growth factor (NGF) stimulates neurite outgrowth for differentiation in PC12 cells, and the stimulation is mediated by a glycoprotein receptor for NGF,Trk. Transfection of GnT-III gene lead to loss of changes in morphology and growth rate upon NGF treatment. The detailed studies revealed that the altered structure of sugar chain in Trk impaired dimerization and phosphorylation of the receptor. These suggest that the function of glycoprotein receptor such as Trk is modified by alteration of N-glycan structure.