Differentiation-dependent glycosylation of gp190, an oncofetal crypt cell antigen expressed by Caco-2 cells

gp190 is a glycoprotein expressed on the cell surface of several human colon carcinoma cells in culture, on epithelial cells of fetal colon, but not on the normal mucosa of adult colon; thus it is referred to as an oncofetal crypt cell antigen. We report the characterisation of O[emsp4 ]-linked glycans carried by gp190 synthesised by [³H]glucosamine-labelled Caco-2 cells at the confluence (undifferentiated cells) and at three weeks of postconfluence (differentiated cells). By using a specific monoclonal antibody, gp190 was isolated and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The mobility of gp190 from differentiated cells was found to be lower than that from undifferentiated cells, suggesting a more extensive glycosylation process in the former glycoprotein. The major results of the glycan characterisation have been as follows: (i) gp190 carries mainly, if not exclusively, O-linked glycans with the core-2 structure; (ii) the elongation with N-acetyllactosamine units of the Gal1,4GlcNAc1,6(Gal1,3)GalNAc tetrasaccharide predominates in gp190 synthesised by differentiated cells, whereas the direct 2,3sialylation of the tetrasaccharide is prevalent in gp190 synthesised by undifferentiated cells. The increment in the core-2 1,6GlcNAc-transferase activity under the Caco-2 differentiation process may be relevant in producing the larger occurrence of polylactosaminoglycans in gp190 from differentiated cells. Since no change in the activity of the 2,3sialyltransferases upon cell differentiation was observed, we suggest that the lower 2,3sialylation in gp190 synthesised by polarised cells might be due to a changed transit-rate through the distal Golgi apparatus.     

Oxidatively Damaged Erythrocytes Are Recognized by Membrane Proteins of Macrophages

Human erythrocytes incubated with an iron catalyst ADP-chelated Fe³⁺ undergo oxidative damage of the membrane including lipid peroxidation, protein oxidation, and protein aggregation, and become susceptible to recognition by human macrophages. In order to clarify the membrane components of macrophages responsible for the recogrution of the oxidized erythrocytes, binding of the oxidized cells to dot and Western blots of solubilized membrane of macrophages was investigated. The oxidized erythrocytes but not unoxidized cells bound to the dot blots. The binding was effectively inhibited by saccharide chains of band 3, a major glycoprotein of human erythrocytes, and lowered when the saccharide chains of band 3 were removed from the cell surface by pretreatment of the cells with endo-P-galactosidase which specifically cleaves the polylactosaminyl saccharide chains of band 3. The oxidized erythrocytes bound to the membrane proteins of macrophages with molecular mass of about 50, 80, and 120 kDa on Western blots depending on the saccharide chains of band 3 on their surface. The results suggest that the oxidatively damaged erythrocytes are specifically recognized by these proteins of macrophage membrane having saccharide binding ability.     

The synthesis of linear trilactosamine

TrilactosamineGalβ1-4GlcNAcβ1-3Galβ1-4GlcNAcβ1-3Galβ1-4GlcNAcβ-sp, where sp = O(CH₂)₃NH₂ is a spacer, was synthesized. The tetrasaccharide fragment Galβ1-4GlcNAcβ1-3Galβ1-4GlcNAcβ-sp was obtained by successive glycosylation using elongation by one monosaccharide residue at a time; and the tetrasaccharide was then transformed into a hexasaccharide with a disaccharide glycosyl donor. A 2,2,2-trichloroethoxycarbonyl group was used for the protection of the glucosamine amino group.     

FAB-MS characterization of sialyl Lewis x determinants on polylactosamine chains of human airway mucins secreted by patients suffering from cystic fibrosis or chronic bronchitis

Although a large body of structural data exists for bronchial mucins from cystic fibrosis (CF) and chronic bronchitis (CB) patients, little is known about terminal structures carried on poly-N-acetyllactosamine antennae. Such structures are of interest because they are potential ligands for bacterial adhesins and other lectins. In this study, we have used fast atom bombardment mass spectrometry (FAB-MS) to examine terminal sequences released by endo--galactosidase from O-glycans obtained by reductive elimination of bronchial mucins purified from the sputum of 8 CF and 8 CB patients. Our data show that, although the polylactosamine antennae of CF and CB mucins have several terminal sequences in common, they differ significantly in their sialyl Lewis^x (NeuAc2-3Gal1-4[Fuc1-3]GlcNAc1-) content. Thus all examined mucins from CF patients carry sialyl Lewis^x on their polylactosamine antennae, whereas this type of epitope is present on only three out of the eight CB mucins examined, notably in the airways of one CB patient which were heavily infected by Pseudomonas aeruginosa as are the airways of all the CF patients. This suggests that, in airway mucins, the expression of sialyl Lewis^x on polylactosamine antennae is probably more related to inflammation and infection than to a direct effect of the CF defect.