Aberrant O-glycosylation inhibits stable expression of dysadherin, a carcinoma-associated antigen, and facilitates cell-cell adhesion.
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-alpha-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-alpha-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.
Tsuiji
Hitomi
H
Pathology Division, National Cancer Center Research Institute, Chuo-ku, Tokyo 104-0045, Japan.
Takasaki
Seiichi
S
Sakamoto
Michiie
M
Irimura
Tatsuro
T
Hirohashi
Setsuo
S
D000116:Acetylgalactosamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001593:Benzyl Compounds / Q000494:pharmacology; D015153:Blotting, Western; D015820:Cadherins / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects; D045744:Cell Line, Tumor; D048429:Cell Size / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects*; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D007473:Ion Channels; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D008840:Microfilament Proteins; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000378:metabolism*; D009439:Neuraminidase / Q000378:metabolism
D001593:Benzyl Compounds; D015820:Cadherins; C451410:FXYD5 protein, human; D007473:Ion Channels; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D009363:Neoplasm Proteins; C080739:benzyl-alpha-N-acetylgalactosamine; D009439:Neuraminidase; D000116:Acetylgalactosamine; D002118:Calcium