O‐linked mucin‐type glycoproteins in normal and malignant colon mucosa: Lack of T‐antigen expression and accumulation of tn and sialosyl‐Tn antigens in carcinomas

Abstract

The expression of carbohydrate core-structures on O-linked glycoproteins was examined in fetal (n = 6), infantile (n = 2), normal adult (n = 15), and malignant (n = 22) colorectal tissue by means of monoclonal antibodies (MAbs) specific for Tn (GalNAc alpha 1-O-R), sialosyl-Tn (NeuAc alpha 2-6GalNAc alpha 1-O-R), and T (Gal beta 1-3GalNAc alpha 1-O-R) antigens. Immunolabelling of solubilized malignant tissue, separated by SDS-PAGE, showed expression of Tn and sialosyl-Tn antigens on 3 molecules of similar mw (230, 210, and 170 kDa), whereas no T antigens could be detected. Immunohistochemical techniques showed that fetal colon mucosa expressed Tn antigens but no sialosyl-Tn antigens. Infantile colon mucosa, however, expressed Tn as well as sialosyl-Tn antigens, and normal adult colon mucosa cells expressed no Tn antigens but sialosyl-Tn in 2 out of 6 biopsies from cecum, which indicates occurrence post partum of alpha-6-NeuAc-transferase. Endothelium in normal adult mucosa showed expression of both Tn and sialosyl-Tn antigens; 82% of carcinoma tissue sections expressed Tn antigens, and 73% expressed sialosyl-Tn antigens in mucin or cytoplasm, or on luminal cell membranes. T antigens could be detected neither in normal mucosa cells at any stage of development, nor in carcinomas. The possibility exists that this could be due to masking of T antigen. Mucin-type blood-group A antigens which contain an internal T-disaccharide were demonstrated in 4 out of 4 A1 tumors by means of MAb HH5. However, urea-containing SDS-PAGE analysis demonstrated an HH5 binding to molecules different from those binding anti-Tn. In remote morphologically normal and abnormal crypts in colons from carcinoma patients, both Tn and sialosyl-Tn antigens were expressed in secreted mucin in 40% of the cases. The data indicate an expression of O-linked Tn and sialosyl-Tn core structures in fetal and infantile colon and in colorectal carcinomas.

Aberrant O‐glycosylation contributes to tumorigenesis in human colorectal cancer

“…Expression of aberrant forms of O‐glycans such as Tn antigen has been frequently observed in patients with CRC7, 43 and reported to be associated with tumour metastatic potential and poor prognosis 44, 45. However, whether defective O‐glycosylation occurs as a result of tumorigenesis or plays a contributing role in tumour development is unclear.…”

Altered mucin expression in the gastrointestinal tract: a review

“…However, apart from the fact that core 3 structure predominates in structural analyses of human colonic mucin [1,2], PNA is not in fact specific for T antigen, binding also to the backbone disaccharide sequence (Gal∃1→3/4GlcNAc-R) [5,6]. Furthermore, highly specific monoclonal antibodies to the T antigen fail to localize this structure in either normal or malignant tissues of the colorectum [12].…”

Direct demonstration of increased expression of Thomsen-Friedenreich (TF) antigen in colonic adenocarcinoma and ulcerative colitis mucin and its concealment in normal mucin.

“…PNA is not totally specific for TFa (Gal#3I -3GalNAca-, on glycoproteins), possessing a high degree of affinity for both TFf (GallI -3GalNAc/3-, on glycolipids) and some affinity for type 1 (Gal61 -3GlcNAc,61-3)n chains (18,19). This uncertainty has been increased by some studies which have failed to demonstrate TFa in colonic malignant tissue using carbohydrate-specific monoclonal antibodies (20, 21 ). In addition, a rigorous analysis of the oligosaccharides in normal adult colonic mucin failed to detect Gal,61 -3GalNAc as a core structure (22).…”