Correlative fine specificity of several Thomsen-Friedenreich disaccharide-binding proteins with an effect on tumor cell proliferation

Epithelial cancer cells show increased cell surface expression of mucin ant igens with aberrant O-glycosylation, notably type I core (Gal beta1-3GalNAc alpha), termed Thomsen-Friedenreich disaccharide (TFD), a chemically well- defined carbohydrate antigen with a proven link to malignancy. Several TFD- binding proteins influence the proliferation of cells to which they bind. W e studied the fine specificity of TFD-binding proteins and its relationship with epithelial tumor cell proliferation. Competitive binding assays again st asialoglycophorin showed that Agaricus bisporus lectin (ABL) and human a nti-TFD monoclonal antibody (mAb) TF1 were inhibited only by TFD and its or -derivatives. Peanut agglutinin (PNA), mAb TF2, and mAb TF5 were also inhib ited by other carbohydrates such as lacto-N-biose (Gal beta1-3GlcNAc), lact ose, and (Me alpha or beta) Gal, indicating lower recognition of the axial C-4 hydroxyl group position of GalNAc from TFD, and the major relevance of the terminal Gal on interaction of these three TFD-binding proteins. In the direct glycolipid-binding assay, ABL bound mostly to alpha -anomeric TFD-b earing glycolipids, whereas PNA interacted mainly with beta -linked TFD. Of the three anti-TFD mAbs analyzed, all bound N5b (terminal beta -TFD), but only TF2 interacted with N6 (terminal alpha -TFD), These findings indicate that TFD-binding proteins that stimulate the proliferation of epithelial tu mor cell lines recognize mainly a terminal beta -Gal region of beta -linked TFD, whereas ABL, which inhibits the proliferation of these tumor cells, b inds mainly to subterminal GalNAc of alpha -anomeric TFD.