Enzymatic Basis for the Structural Changes of Asparagine-linked Sugar Chains of Membrane Glycoproteins of Baby Hamster Kidney Cells Induced by Polyoma Transformation

Previous studies indicated that enrichment of the GlcNAc beta 1----6Man alpha 1---- group with concomitant decrease of the GlcNAc beta 1----4Man alpha 1---- group occurs in the complex-type asparagine-linked sugar chains of the membrane glycoproteins of baby hamster kidney cells transformed by polyoma virus. The enzymatic basis of the chemical change is reported in this paper. By using oligosaccharides isolated from the urine of patients with a variety of exoglycosidase deficiencies, beta-N-acetylglucosaminyltransferases in the cell homogenate were successfully assayed separately. Both baby hamster kidney cells and their polyoma transformants contain beta-N-acetylglucosaminyltransferases I, II, IV, V, and VI, but not beta-N-acetylglucosaminyltransferase III. The beta-N-acetylglucosamine residue added by each beta-N-acetylglucosaminyltransferase (GnT) is shown below. (formula see text) Comparative studies of the specific activities of the five beta-N-acetylglucosaminyltransferases in the two cell lines revealed that the value of beta-N-acetylglucosaminyltransferase V in the polyoma transformant was twice of that in the normal cells, while those of the other four transferases in the two cell lines were not significantly different. Therefore the increase in beta-N-acetylglucosaminyltransferase V may be the direct cause of the changes found in the sugar chains of surface glycoproteins in baby hamster kidney cells transformed by polyoma virus.