Immunohistochemical demonstration of α1,4-N-acetylglucosaminyltransferase that forms GlcNAcα 1,4Galβ residues in human gastrointestinal mucosa

Abstract

α1,4-N-acetylglucosaminyltransferase (α4GnT) is a glycosyltransferase that mediates transfer of GlcNAc to βGal residues with α1,4-1inkage, forming GlcNAcα1→ 4Galβ→R structures. In normal human tissues, glycoproteins having GlcNAccα1→4Galβ→R structures at non-reducing terminals are exclusively limited to the mucins secreted from glandular mucous cells of gastric mucosa, Brunner's gland of duodenum, and accessory gland of pancreaticobiliary tract. Recently, we have isolated a cDNA encoding human α4GnT by expression cloning. Although α4GnT plays a key role in producing this unique glycan in vitro, the actual localization of α4GnT was not determined. In this study we examined the localization of α4GnT in various human tissues, including gastrointestinal mucosa, using a newly developed antibody against human α4GnT. The specificity of the antibody was confirmed by analyses of human gastric adenocarcinoma AGS cells transfected by α4GnT cDNA. Expression of α4GnT was largely associated with the Golgi region of mucous cells that produce the mucous glycoproteins having GlcNAcα1→4Galβ→R, such as the glandular mucous cells of stomach and Brunner's gland. An immunoprecipitation experiment disclosed that two distinct mucin proteins, MUC5AC and MUC6 present in gastric mucin, carried the GlcNAcα1→4Galβ→R structures. These results indicate that α4GnT is critical to form the mucous glycoproteins having GlcNAcα1→4Galβ→R on MUC6 and MUC5AC in vivo.