Apical Golgi localization of N,N′-diacetyllactosediamine synthase, β4GalNAc-T3, is responsible for LacdiNAc expression on gastric mucosa

beta 1,4-N-acetylgalactosan nyltransferase III (beta 4GaINAc-T3), which was recently cloned and identified, exhibits GaINAc transferase activity toward a GlcNAcP residue with beta 1,4-linkage, forming the N,N'-diacetyllactosediamine, GatNAc beta 1,4GIcNAc (LacdiNAc or LDN). Though LacdiNAc has not been found in the gastric mucosa, a large amount of transcript was detected in our previous study. To increase our knowledge of beta 4GaINAc-T3 expression and its product LacdiNAc, we examined the exact localization of beta 4GaINAc-T3 in human gastric mucosa using a newly developed antibody, monoclonal antibody (mAb) K1356. This antibody specifically detected the enzyme that transfected the beta 4GaINAc-T3 gene into MKN45 cells, and the terminal beta GaINAc epitope yielded on the cell surface was recognized by a lectin, Wisteria floribunda agglutinin (WFA). beta 4GaINAc-T3 was localized in the supra-miclear region of surface mucous cells in gastric mucosa, and WFA positively stained the mucins secreted by the cells. In contrast, in the cells of the glandular compartment in the fundic glands and a few cells in the pyloric glands, beta 4GaINAc-T3 was observed in the basolateral position of the nucleus, where no WFA reactivity was detected. The anti-Tn (GaINAc alpha-O-Ser/Thr) antibody staining did not overlap with the WFA staining. By measuring the binding activity of WFA using automated frontal affinity chromatography (FAC), we found WFA to bind most strongly LacdiNAc among the sugar chains examined. Neither beta 4GaINAc-T3 nor WFA-positive staining was detected in intestinal metaplastic cells. These results suggest that the supra-miclear expression of beta 4GaINAc-T3 is essential for the formation of LacdiNAc on the surface mucous cells and that LacdiNAc and beta 4GaINAc-T3 are novel differentiation markers of surface mucous cells in the gastric mucosa.