Altered Golgi Localization of Core 2 β-1,6-N-Acetylglucosaminyltransferase Leads to Decreased Synthesis of Branched O-Glycans

• Published in: The Journal of biological chemistry 1997-09, Vol.272 (36), p.22695-22702
• Main Authors: Skrincosky, David, Kain, Renate, El-Battari, Assou, Exner, Markus, Kerjaschki, Dontscho, Fukuda, Minoru
• Format: Article
• Language: English
• Subjects: Animals; Antibodies - immunology; Carbohydrate Sequence; CHO Cells; COS Cells; Cricetinae; Golgi Apparatus - enzymology; N-Acetylglucosaminyltransferases - immunology; N-Acetylglucosaminyltransferases - metabolism; Polysaccharides - biosynthesis; Subcellular Fractions - enzymology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.36.22695

Mucin type O-glycans with core 2 branches are distinct from nonbranched O-glycans, and the amount of core 2 branched O-glycans changes dramatically during T cell differentiation. This oligosaccharide is synthesized only when core 2 β-1,6-N-acetylglucosaminyltransferase (C2GnT) is present, and the expression of this glycosyltransferase is highly regulated. To understand how O-glycan synthesis is regulated by the orderly appearance of glycosyltransferases that form core 2 branched O-glycans, the subcellular localization of C2GnT was determined by using antibodies generated that are specific to C2GnT. The studies using confocal light microscopy demonstrated that C2GnT was localized mainly in cis tomedial-cisternae of the Golgi. We then converted C2GnT to atrans-Golgi enzyme by replacing its Golgi retention signal with that of α-2,6-sialyltransferase, which resides intrans-Golgi. Chinese hamster ovary cells expressing wild type C2GnT and the chimeric C2GnT were then subjected to oligosaccharide analysis. The results obtained clearly indicate that the conversion of C2GnT into a trans-Golgi enzyme resulted in a substantial decrease of core 2 branched oligosaccharides. These results, taken together, strongly suggest that the predominance of core 2 branched oligosaccharides in those cells expressing C2GnT is due to the fact that C2GnT is located earlier in the Golgi than α-2,3-sialyltransferase that competes with C2GnT for the common substrate. Furthermore, alteration of Golgi localization renders the chimeric C2GnT much less efficient in synthesizing core 2 branched oligosaccharides, indicating the critical role of orderly subcellular localization of glycosyltransferases.