Aberrant O-glycosylation inhibits stable expression of dysadherin, a carcinoma-associated antigen, and facilitates cell–cell adhesion

• Published in: Glycobiology (Oxford) 2003-07, Vol.13 (7), p.521-527
• Main Authors: Tsuiji, Hitomi, Takasaki, Seiichi, Sakamoto, Michiie, Irimura, Tatsuro, Hirohashi, Setsuo
• Format: Article
• Language: English
• Subjects: Acetylgalactosamine - analogs & derivatives; Acetylgalactosamine - pharmacology; Benzyl Compounds - pharmacology; benzyl-α-GalNAc; Blotting, Western; bovine serum albumin; BSA; Cadherins - metabolism; Calcium - pharmacology; Cell Adhesion - drug effects; Cell Line, Tumor; Cell Size - drug effects; cell–cell adhesion; dysadherin; E-cadherin; Gene Expression Regulation - drug effects; Glycosylation - drug effects; HEPES; high-pH anion-exchange chromatography with pulsed amperometric detection; HPAEC-PAD; Humans; Immunohistochemistry; Membrane Glycoproteins - biosynthesis; Membrane Glycoproteins - metabolism; N-2-hydroxy-ethylpiperazine-N′-2-ethanesulfonic acid; Neoplasm Proteins - biosynthesis; Neoplasm Proteins - metabolism; Neuraminidase - metabolism; O-glycosylation; PBS; phosphate buffered saline; SDS–PAGE; sialomucin complex; SMC; sodium dodecyl sulfate–polyacrylamide gel electrophoresis
• ISSN: 0959-6658; 1460-2423
• DOI: 10.1093/glycob/cwg065

Recently, we identified dysadherin, a novel carcinoma-associated glycoprotein, and showed that overexpression of dysadherin in human hepatocarcinoma PLC/PRF/5 cells could suppress E-cadherin-mediated cell–cell adhesion and promote tumor metastasis. The present study shows evidence that dysadherin is actually O-glycosylated. This was based on a direct carbohydrate composition analysis of a chimera protein of an extracellular domain of dysadherin fused to an Fc fragment of immunoglobulin. To assess the importance of O-glycosylation in dysadherin function, dysadherin-transfected hepatocarcinoma cells were cultured in a medium containing benzyl-α-GalNAc, a modulator of O-glycosylation. This treatment facilitated homotypic cell adhesion among dysadherin transfectants accompanied with morphological changes, indicating that the anti-adhesive effect of dysadherin was weakened. Modification of O-glycan synthesis also resulted in down-regulation of dysadherin expression and up-regulation of E-cadherin expression in dysadherin transfectants but did not affect E-cadherin expression in mock transfectants. Structural analysis of O-glycans released from the dysadherin chimera proteins indicated that a series of O-glycans with core 1 and 2 structures are attached to dysadherin, and their sialylation is remarkably inhibited by benzyl-α-GalNAc treatment. However, sialidase treatment of the cells did not affect calcium-dependent cell aggregation, which excluded the possibility that sialic acid itself is directly involved in cell–cell adhesion. We suggest that aberrant O-glycosylation in carcinoma cells inhibits stable expression of dysadherin and leads to the up-regulation of E-cadherin expression by an unknown mechanism, resulting in increased cell–cell adhesion. The carbohydrate-directed approach to the regulation of dysadherin expression might be a new strategy for cancer therapy.