J Biol Chem, Vol. 273, Issue 28, 17399-17405, July 10, 1998

Biosynthesis of Branched Polylactosaminoglycans
EMBRYONAL CARCINOMA CELLS EXPRESS MIDCHAIN 1,6-N-ACETYLGLUCOSAMINYLTRANSFERASE ACTIVITY THAT GENERATES BRANCHES TO PREFORMED LINEAR BACKBONES

Anne Leppänen, Ying Zhu, Hannu Maaheimo, Jari Helin, Eero Lehtonen^§, and Ossi Renkonen

From the  Institute of Biotechnology and Department of Biosciences, University of Helsinki, P. O. Box 56, FIN-00014 Helsinki and ^§ Division of Pathology, Haartman Institute, University of Helsinki, P. O. Box 21, FIN-00014 Helsinki, Finland

Two types of 1,6-GlcNAc transferases (IGnT6) are involved in in vitro branching of polylactosamines: dIGnT6 (distally acting), transferring to the penultimate galactose residue in acceptors like GlcNAc1-3Gal1-4GlcNAc1-R, and cIGnT6 (centrally acting), transferring to the midchain galactoses in acceptors of the type (GlcNAc1-3)Gal1-4GlcNAc1-3Gal1-4GlcNAc1-R. The roles of the two transferases in the biosynthesis of branched polylactosamine backbones have not been clearly elucidated. We report here that cIGnT6 activity is expressed in human (PA1) and murine (PC13) embryonal carcinoma (EC) cells, both of which contain branched polylactosamines in large amounts. In the presence of exogenous UDP-GlcNAc, lysates from both EC cells catalyzed the formation of the branched pentasaccharide Gal1-4GlcNAc1-3(GlcNAc1-6)Gal1-4GlcNAc from the linear tetrasaccharide Gal1-4GlcNAc1-3Gal1-4GlcNAc. The PA1 cell lysates were shown to also catalyze the formation of the branched heptasaccharides Gal1-4GlcNAc1-3Gal1-4GlcNAc1-3(GlcNAc1-6)Gal1-4GlcNAc and Gal1-4GlcNAc1-3(GlcNAc1-6)Gal1-4GlcNAc1-3Gal1-4GlcNAc from the linear hexasaccharide Gal1-4GlcNAc1-3Gal1-4GlcNAc1-3Gal1-4GlcNAc in reactions characteristic to cIGnT6. By contrast, dIGnT6 activity was not detected in the lysates of the two EC cells that were incubated with UDP-GlcNAc and the acceptor trisaccharide GlcNAc1-3Gal1-4GlcNAc. Hence, it appears likely that cIGnT6, rather than dIGnT6 is responsible for the synthesis of the branched polylactosamine chains in these cells.