Dual Roles of Gastric Gland Mucin-specific O-glycans in Prevention of Gastric Cancer

Abstract

Gastric gland mucin is secreted from gland mucous cells, including pyloric gland cells and mucous neck cells located in the lower layer of the gastric mucosa. These mucins typically contain O-glycans carrying terminal α1,4-linked N-acetylglucosamine residues (αGlcNAc) attached to the scaffold protein MUC6, and biosynthesis of the O-glycans is catalyzed by the glycosyltransferase, α1,4-N-acetylglucosaminyltransferase (α4GnT). We previously used expression cloning to isolate cDNA encoding α4GnT, and then demonstrated that αGlcNAc functions as natural antibiotic against Helicobacter pylori, a microbe causing various gastric diseases including gastric cancer. More recently, it was shown that αGlcNAc serves as a tumor suppressor for differentiated-type adenocarcinoma. This review summarizes these findings and identifies dual roles for αGlcNAc in gastric cancer.

Keywords: expression cloning; glycosyltransferase, H. pylori; knockout mouse; mucin histochemistry.

Fig. 1

Histochemical demonstration of the surface mucin- and gland mucin-specifc glycans in human stomach, as revealed by GOCTS-PCS staining. Glycans in the surface mucin are detected by the GOCTS reaction as a blue color, while glycans in gland mucin appear brown following PCS staining. HE, Hematoxylin & Eosin. Bars=200 µm.

Fig. 2

Comparison of αGlcNAc and class III mucin in human gastrointestinal tract. Expression of αGlcNAc in the gastrointestinal tract mirrors that of class III mucin. αGlcNAc panels: immunohistochemistry with HIK1083 antibody. Class III mucin panels: paradoxical Concanavalin A staining. Bar=200 µm, and bar in inset indicates 20 µm. (from Nakayama et al. 1999; Copyright 1999 National Academy of Sciences, USA)

Fig. 3

αGlcNAc biosynthesis. αGlcNAc is synthesized by a concerted reaction of various glycosyltransferases. α4GnT, which transfers GlcNAc from UDP-GlcNAc to βGal residues attached to serine/threonine residues present in O-glycans with an α1,4-linkage, plays a key role to form αGlcNAc. UDP, uridine diphosphate. ppGalNAcT, polypeptide N-acetylgalactosaminyltransferase. β3GalT, β1,3-galactosyltransferase. C2GnT, core 2 β1,6-N-acetylglucosaminyltransferase. β4GalT, β1,4-galactosyltransferase. α4GnT, α1,4-N-acetylglucosaminyltransferase.

Fig. 4

Expression cloning strategy used to obtain α4GnT cDNA. See text for detail.

Fig. 5

Expression of αGlcNAc and α4GnT in human gastric mucosa. (A) αGlcNAc is expressed in gland mucin secreted from the pyloric gland. (B) α4GnT is detected in the supranuclear region, which corresponds to the Golgi apparatus of the pyloric gland cells. (C) αGlcNAc is expressed in the medial Golgi of mucous neck cells of the fundic gland. A: Immunohistochemistry with HIK1083 antibody. B and C: Immunohistochemistry with anti-α4GnT antibody. Bars=200 µm (B) and 50 µm (B, inset), respectively. Bar=500 nm (C). (C is from Zhang et al. 2001; doi: 10.1177/002215540104900505 on SAGE Journals)

Fig. 6

Expression of class III mucin on gastric adenocarcinoma AGS cells stably transfected with α4GnT cDNA. AGS-α4GnT cells express αGlcNAc and are positive for class III mucin. AGS-mock cells, transfected by vector alone, are negative for both αGlcNAc and class III mucin. αGlcNAc is detected by immunocytochemistry with HIK1083 antibody, and class III mucin is detected by paradoxical Concanavalin A staining. Bar=50 µm. (from Nakayama et al. 1999; Copyright 1999 National Academy of Sciences, USA)

Fig. 7

Antimicrobial activity of αGlcNAc against H. pylori infection. (A) Chronic active gastritis of human gastric mucosa caused by H. pylori infection. The microbe is rarely found in the gland mucin expressing αGlcNAc. Left panel shows Hematoxylin & Eosin staining, and right panel shows immunofluorecent staining using anti-H. pylori antibody (as a green color) and HIK1083 antibody for αGlcNAc (as a red color). Bar=100 µm. (B) Growth curves of H. pylori cultured in the presence of sCD43 carrying αGlcNAc (αGlcNAc (+)) or sCD43 lacking αGlcNAc (αGlcNAc (–)). One milliunit of αGlcNAc (+) corresponds to 1 µg of GlcNAcα-pNP. A600: absorbance at 600 nm. (C) Scanning electron micrographs showing H. pylori incubated with 31.2 mU/ml of sCD43 carrying αGlcNAc (αGlcNAc (+)) or the same protein concentration of sCD43 lacking αGlcNAc (αGlcNAc (–)) for 3 days. Bar=1 µm. (Panels B and C from Kawakubo et al. 2004; Copyright 2004 American Association for the Advancement of Science)

Fig. 8

Loss of αGlcNAc in A4gnt-deficient mice. αGlcNAc is completely absent in gland mucous cells of the gastric mucosa and in Brunner’s glands of the duodenal mucosa of A4gnt-deficient mouse (A4gnt^–/–). Shown is immunohistochemistry of one-week-old mice with αGlcNAc-specific HIK1083 antibody. Bar=100 µm.

Fig. 9

Gastric pathology of A4gnt-deficient mice. Representative histopathology analysis showing hyperplasia at 5 weeks (upper right), high-grade dysplasia at 20 weeks (lower left), and differentiated type adenocarcinoma at 50 weeks (lower right) in the pyloric mucosa of A4gnt-deficient mice. For comparison (upper left), pyloric mucosa from a 5-week-old wild-type mouse is shown. Bar=100 µm.

Fig. 10

Human early gastric differentiated-type adenocarcinoma. No expression of αGlcNAc is seen in MUC6-positive adenocarcinoma cells. Normal pyloric glands (*) adjacent to the carcinoma cells are positive for both αGlcNAc and MUC6. HE, Hematoxylin & Eosin. αGlcNAc and MUC6 are detected by immunocytochemistry with HIK1083 and anti-MUC6 (clone CLH5) antibodies, respectively. Bar=100 µm.