Pathways of mucin O-glycosylation in normal and malignant rat colonic epithelial cells reveal a mechanism for cancer-associated Sialyl-Tn antigen expression.
The Sialyl-Tn antigen (Sialyl alpha-Ser/Thr) is expressed as a cancer-associated antigen on the surface of cancer cells. Its presence is associated with a poor prognosis in patients with colorectal and other cancers. We previously reported that Sialyl-Tn expression in LSC human colon cancer cells could be explained by a specific lack of the activity of core 1 beta3-Gal-transferase (Brockhausen et al., Glycoconjugate J. 15, 595-603, 1998) and an inability to synthesize the common O-glycan core structures. To support this mechanism, or find other mechanisms to explain Sialyl-Tn antigen expression, we investigated the O-glycosylation pathways in clonal rat colon cancer cell lines that were selected for positive or negative expression of Sialyl-Tn antigen, and compared these pathways to those in normal rat colonic mucosa. Normal rat colonic mucosa had very active glycosyltransferases synthesizing O-glycan core structures 1 to 4. Several sialyl-, sulfo- and fucosyltransferases were also active. An M type core 2 beta6-GlcNAc-transferase was found to be present in rat colon mucosa and all of the rat colon cancer cells. O-glycosylation pathways in rat colon cancer cells were significantly different from normal rat colonic mucosa; for example, rat colon cancer cells lost the ability to synthesize O-glycan core 3. All rat colon cancer cell lines, regardless of the Sialyl-Tn phenotype, expressed glycosyltransferases assembling complex O-glycans of core 1 and core 2 structures (unlike human LSC colon cancer cells which lack core 1 beta3-Gal-transferase activity). It was the activity of CMP-sialic acid:GalNAc-mucin alpha6-sialyltransferase that coincided with Sialyl-Tn expression. Sialyl-Tn negative cells had a several fold higher activity of core 2 beta6-GlcNAc-transferase which synthesizes complex O-glycans that may mask adjacent Sialyl-Tn epitopes. The results suggest a new mechanism controlling Sialyl-Tn expression in cancer cells.
Brockhausen
I
I
Department of Medicine, Queen's University, Kingston, Ontario, Canada.
Yang
J
J
Lehotay
M
M
Ogata
S
S
Itzkowitz
S
S
D000595:Amino Acid Sequence; D000818:Animals; D015295:Antigens, Tumor-Associated, Carbohydrate / Q000235:genetics / Q000378:metabolism*; D002240:Carbohydrate Sequence; D002455:Cell Division / Q000235:genetics; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D005753:Gastric Mucosa / Q000166:cytology / Q000378:metabolism; D006031:Glycosylation; D008969:Molecular Sequence Data; D009077:Mucins / Q000737:chemistry / Q000378:metabolism*; D017351:N-Acetylglucosaminyltransferases / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D012016:Reference Values; D012799:Sialyltransferases / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
D015295:Antigens, Tumor-Associated, Carbohydrate; D009077:Mucins; D011134:Polysaccharides; C040286:Tn antigen; D017351:N-Acetylglucosaminyltransferases; C053024:beta-1,3-galactosyl-O-glycosyl-glycoprotein beta-1,6-acetylglucosaminyl transferase; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase