Control of O-glycan branch formation - Molecular cloning of human cDNA encoding a novel beta 1,6-N-acetylglucosaminyltransferase forming core 2 and core 4

A novel human UDP-GlcNAc: Gal/GlcNAc beta 1-3GalNAc alpha beta 1,6GlcNAc-tr ansferase, designated C2/4GnT, was identified by BLAST analysis of expresse d sequence tags. The sequence of C2/4GnT encoded a putative type II transme mbrane protein with significant sequence similarity to human C2GnT and IGnT , Expression of the secreted form of C2/4GnT in insect cells showed that th e gene product had UDP-N-acetyl-alpha-D-glucosamine: acceptor beta 1,6-N-ac etylglucosaminyltransferase (beta 1,6GlcNAc-transferase) activity. Analysis of substrate specificity revealed that the enzyme catalyzed O-glycan branc h formation of the core 2 and core 4 type. NMR analyses of the product form ed with core 3-para-nitrophenyl confirmed the product core 4-para-nitrophen yl, The coding region of C2/4GnT was contained in a single exon and located to chromosome 15q21.3. Northern analysis revealed a restricted expression pattern of C2/4GnT mainly in colon, kidney, pancreas, and small intestine. No expression of C2/4GnT was detected in brain, heart, liver, ovary, placen ta, spleen, thymus, and peripheral blood leukocytes, The expression of core 2 O-glycans has been correlated with cell differentiation processes and ca ncer. The results confirm the predicted existence of a beta 1,6GlcNAc-trans ferase that functions in both core 2 and core 4 O-glycan branch formation. The redundancy in beta 1,6Glc-NAc-transferases capable of forming core 2 O- glycans is important for understanding the mechanisms leading to specific c hanges in core 2 branching during cell development and malignant transforma tion.