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Adhesion/growth-regulatory galectins (gals) exert their functionality by the cis/trans-cross-linking of distinct glycans after initial one-point binding. In order to define the specificity of ensuing association events leading to cross-linking, we recently established a cell-based assay using fluorescent glycoconjugates as flow cytometry probes and tested it on two human gals (gal-1 and -3). Here we present a systematic study of tandem-repeat-type gal-4, -8 and -9 loaded on Raji cells resulting in the following key insights: (i) all three gals bound to oligolactosamines; (ii) binding to ligands with Galβ1-3GlcNAc or Galβ1-3GalNAc as basic motifs was commonly better than that to canonical Galβ1-4GlcNAc; (iii) all three gals bound to 3'-O-sulfated and 3'-sialylated disaccharides mentioned above better than that to parental neutral forms and (iv) histo-blood group ABH antigens were the highest affinity ligands in both the cell and the solid-phase assay. Fine specificity differences were revealed as follows: (i) gal-8 and -9, but not gal-4, bound to disaccharide Galβ1-3GlcNAc; (ii) increase in binding due to negatively charged substituents was marked only in the case of gal-4 and (iii) gal-4 and -8 bound preferably to histo-blood group A glycans, whereas gal-9 targeted B-type glycans. Experiments with single carbohydrate recognition domains (CRDs) of gal-4 showed that the C-CRD preferably bound to ABH glycans, whereas the N-CRD associated with oligolactosamines. In summary, the comparative analysis disclosed the characteristic profiles of glycan reactivity for the accessible CRD of cell-bound gals. These results indicate the distinct sets of functionality for these three members of the same subgroup of human gals.

Galectins are a family of beta-galactoside binding lectins, homological by a sequence of the carbohydrate-binding site. In this review literature data about structure and carbohydrate specificity of galectins are discussed. The role of galectins in the regulation of cell adhesion in immune response, inflammation, and cancer progression is considered.

Comparisons of carbohydrate profiles between control and apoptotic colon carcinoma cells were performed by flow cytometry using a set of lectins and anti-carbohydrate antibodies. The six cell lines analyzed presented distinct carbohydrate profiles before induction of apoptosis. PHA-L and MAA binding decreased after induction of apoptosis by UV-treatment. In contrast an increase of PNA binding was observed after induction of apoptosis, except on SW-48 cells for which a decrease occurred. A decrease of SNA binding was observed after induction of apoptosis from strongly positive control cell lines, whereas it increased on weakly positive ones. All the blood group related antigens A, H, Lewis a, Lewis x, Lewis b, and Lewis y, had their expression strongly diminished on apoptotic cells. These changes occurred irrespective of the mode of apoptosis induction since similar results were obtained after UV, TNFalpha, or anti-Fas treatment. Fucosyltransferases activities were also decreased after apoptosis induction, except for alpha1,3fucosyltransferase in anti-Fas treated HT-29 cells, where it was strongly augmented. This could be attributed to the IFNgamma preteatment required to induce Fas expression on these cells. Fucosidase activity decreased after induction of apoptosis suggesting that it was not responsible for the loss of fucosylated structures. In the rat PRO cell line, H blood group antigens are mainly carried by a high molecular weight variant of CD44. It could be shown that the loss of H antigen after induction of apoptosis correlated with a loss of the carrier glycoprotein.

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