Lex glycosphingolipids-mediated cell aggregation

Membrane adhesion via homophilic saccharide-saccharide interactions investigated by neutron scattering

Solid-supported membrane multilayers doped with membrane-anchored oligosaccharides bearing the LewisX motif (Le(X) lipid) were utilized as a model system of membrane adhesion mediated via homophilic carbohydrate-carbohydrate interactions. Specular and off-specular neutron scattering in bulk aqueous electrolytes allowed us to study multilayer structure and membrane mechanics at full hydration at various Ca(2+) concentrations, indicating that membrane-anchored Le(X) cross-links the adjacent membranes. To estimate forces and energies required for cross-linking, we theoretically modeled the interactions between phospholipid membranes and compared this model with our experimental results on membranes doped with Le(X) lipids. We demonstrated that the bending rigidity, extracted from the off-specular scattering signals, is not significantly influenced by the molar fraction of Le(X) lipids, while the vertical compression modulus (and thus the intermembrane confinement) increases with the molar fraction of Le(X) lipids.

Weak calcium-mediated interactions between Lewis X-related trisaccharides studied by NMR measurements of residual dipolar couplings

The Lewis X (LeX) determinant, a trisaccharide with the carbohydrate sequence Galbeta(1-->4)[Fucalpha(1-->3)]GlcNAcbeta, is believed to be responsible for Ca2+-mediated cell-cell interactions. In partly oriented phases composed of mixtures of penta(ethyleneglycol)monododecyl ether HO(CH2CH2O)5C12H25 and n-hexanol in the presence of Ca2+ ions, the variation of the residual dipolar couplings 1DCH of various CiHi vectors in LeX as a function of the concentration of the trisaccharide demonstrates the existence of very weak LeX-Ca2+-LeX complexes in solution. Synthetic 3-, 4-, and 6-deoxy-LeX variants were also shown to form complexes in the presence of calcium ions, despite the replacement of one of their hydroxyl groups by hydrogen atoms. This is the first direct observation in solution of a calcium-mediated interaction between LeX molecules.

Apoptosis of human breast carcinoma cells in the presence of cis-platin and L-/D-PPMP: IV. Modulation of replication complexes and glycolipid: Glycosyltransferases

Apoptosis of human breast carcinoma cells (SKBR-3, MCF-7, and MDA-468) has been observed after treatment of these cells with anti-cancer drug cis-platin and glycosphingolipid biosynthesis inhibitor L- and D-PPMP, respectively. These drugs initiated apoptosis in a dose-dependent manner as measured by phenotypic morphological changes, by binding of a fluorescent phophatidyl serine-specific dye (PSS-380) onto the outer leaflet of the cell membranes, and by activation of caspases, -3, -8, and -9. It was observed that in two hours very little apoptotic process had started but predominant biochemical changes occurred after 6 h. DNA degradation started after 24 hours of drug treatment. However, very little is known about the stability of the ';Replication Complexes'' during the apoptotic process. DNA helicases are motor proteins that catalyze the melting of genomic DNA during its replication, repair, and recombination processes. Previously, DNA helicase-III was characterized as a component of the replication complexes isolated from embryonic chicken brains as well as breast and colon carcinoma cells. Helicase activities were measured by a novel method (ROME assay), and DNA polymerase-alpha activities were determined by regular chain extension of the nicked ACT-DNA, by determining values obtained from +/- aphidicolin-treated incubation mixtures. In all three breast carcinoma cell lines, a common trend was observed: a decrease of activities of DNA polymerase-alpha and Helicase III. A sharp decrease of activities of the glycolipid sialyltransferases: SAT-2 (CMP-NeuAc; GD3 alpha2-8 sialyltransferase) and SAT-4 (CMP-NeuAc: GM1a alpha2-3 sialyltransferase) was observed in the apoptotic carcinoma cells treated with L-PPMP compared with cis-platin.

Convenient and rapid analysis of linkage isomers of fucose-containing oligosaccharides by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry (MALDI-QIT-TOF MS) was used to analyze three pyridylamino (PA)-fucosyloligosaccharides isolated from human milk: lacto-N-fucopentaose (LNFP) I [Fucalpha1-2Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glc-PA], LNFP II [Galbeta1-3(Fucalpha1-4)GlcNAcbeta1-3Galbeta1-4Glc-PA], and LNFP III [Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-3Galbeta1-4Glc-PA]. These oligosaccharides are linkage isomers. MALDI-QIT-TOF MS provides MS(n) spectra, which we used to characterize these PA-oligosaccharides. MS/MS/MS analysis of the non-reducing end tri-saccharide ions generated by MS/MS was able to distinguish these oligosaccharide isomers. The MALDI-QIT-TOF MS is a very convenient and rapid method, therefore, it would be useful for high throughput structural analyses of various types of pyridylaminated oligosaccharide isomers.

Specific and non specific interactions involving Le( X ) determinant quantified by lipid vesicle micromanipulation

Carbohydrate-carbohydrate recognition is emerging today as an important type of interaction in cell adhesion. One Ca(2+)mediated homotypic interaction between two Lewis( X ) determinants (Le( X )) has been proposed to drive cell adhesion in murine embryogenesis. Here, the adhesion energies of lipid vesicles functionalized with glycolipids bearing monomeric or dimeric Le( X ) determinants were measured in NaCl or CaCl(2) media with the micropipette aspiration technique. These experiments on Le( X ) with an environment akin to that provided by biological membrane confirmed the existence of this specific calcium dependent interaction of monomeric Le( X ). In contrast, dimeric Le( X ) produced a repulsive contribution. By using a simple model involving the various contributions to the adhesion free energy, specific and non specific interactions could be separated and quantified. The involvement of calcium ions has been discussed in the monomeric and dimeric Le( X ) lipids.

Role of the Lewis(x) glycan determinant in corneal epithelial cell adhesion and differentiation

In this study we demonstrate that in corneal epithelium there is cell-cell contact-regulated expression of a 145-kDa glycoprotein (GP) bearing the glycan determinant Lewis(x) (Le(x)) (Galbeta(1,4)[Fucalpha(1,3)]GlcNAc). This glycoprotein (Le(x)-GP) was expressed in confluent/contact-inhibited cultures but not in sparse cultures of corneal epithelium. In contrast, a 135-kDa glycoprotein bearing precursor, unfucosylated, lactosamine-containing glycans (Galbeta1-4GlcNAcbeta1-R) was expressed in sparse cultures. Immunofluorescence staining and confocal microscopy of confluent cultures revealed that in corneal epithelium, Le(x) antigen is located in high density at sites of cell-cell adhesion. In in vitro cell-cell adhesion assays, anti-Le(x), but not anti-sialyl-Le(x) monoclonal antibodies, inhibited the formation of corneal epithelial cell-cell adhesion. Also, when added to confluent cultures, antibodies to Le(x) disrupted the monolayer and caused tightly packed polygonal cells to round up. Analysis of the expression of Fut genes that encode alpha-1,3-fucosyltransferases, the enzymes that generate the Le(x) determinant, revealed that confluent/contact-inhibited cultures of rabbit corneal epithelium contain markedly elevated levels of Fut4 and Fut3/5/6 gene transcripts compared with sparse cultures. These data suggest that the Fut4 and Fut3/5/6 genes are targets of cell-cell contact-regulated signals and that Fut gene products direct cell-cell contact-associated expression of Le(x) on the Le(x)-GP in corneal epithelium. Immunohistochemical analysis revealed that the expression of Le(x) antigen in the epithelium of adult and developing corneas is related to the stage of differentiation of the cells. Although early differentiated cells robustly expressed Le(x), relatively undifferentiated cells did not, and the expression level was relatively low in terminally differentiated cells. Overall, these data provide evidence that a Le(x)-bearing glycoprotein plays a role through the Le(x) determinant in corneal epithelial cell-cell adhesion, and these data suggest that Le(x)-mediated cell-cell interactions contribute to mechanisms that mediate corneal epithelial cell differentiation.

Ultraweak sugar-sugar interactions for transient cell adhesion

Carbohydrate-carbohydrate interactions are rarely considered in biologically relevant situations such as cell recognition and adhesion. One Ca(2+)-mediated homotypic interaction between two Lewis(x) determinants (Le(x)) has been proposed to drive cell adhesion in murine embryogenesis. Here, we confirm the existence of this specific interaction by reporting the first direct quantitative measurements in an environment akin to that provided by membranes. The adhesion between giant vesicles functionalized with Le(x) was obtained by micropipette aspiration and contact angle measurements. This interaction is below the thermal energy, and cell-cell adhesion will require a large number of molecules, as illustrated by the Le(x) concentration peak observed at the cell membranes during the morula stage of the embryo. This adhesion is ultralow and therefore difficult to measure. Such small interactions explain why the concept of specific interactions between carbohydrates is often neglected.

ABH and Lewis histo-blood group antigens in cancer

Antigens of the ABH and Lewis histo-blood group family can be found on many normal cells, mainly of epithelial type. In carcinomas, altered expression of the various carbohydrate epitopes of this family occur, and are often strongly associated with either a good or bad prognosis. A review of the available data on these tumor-associated markers, their biosynthesis and their prognostic value is proposed here. For a long time it has been unclear whether their presence could affect the behavior of carcinoma cells. Recent data, however, indicate that they play biological roles in the course of tumor progression. The presence of sialyl-Le(a) or sialyl-Le(x), which are ligands for selectins, promotes the metastatic process by facilitating interaction with the endothelium of distant organs. The loss of A and B antigens increases cellular motility, while the presence of H epitopes increases resistance to apoptosis by mechanisms that remain to be defined. The Le(y) antigen has procoagulant and angiogenic activities. All these observations are used to present a model that may account for the described associations between the presence or loss of these markers and the outcome of disease. Finally, their potential clinical applications as tumor-associated markers or as targets of immunotherapy are reviewed.

Human alpha (1,3)-fucosyltransferase IV (FUTIV) gene expression is regulated by elk-1 in the U937 cell line

The alpha1,3-fucosyltransferase IV (FucTIV) encoded by its gene (FUTIV) is responsible for synthesis of Le(x) (Galbeta4[Fucalpha3]GlcNAcbeta3Galbeta1,R), which causes compaction in the morula stage of the preimplantation mouse embryo, as well as alpha1,3-fucosylation at multiple internal GlcNAc of unbranched poly-N-acetyllactosamine, termed "myeloglycan," the physiological epitope of E-selectin. Since myeloglycan-type structure is also expressed in various types of human cancer and may mediate E-selectin-dependent metastasis, expression of FUTIV is oncodevelopmentally regulated. The mechanisms controlling FUTIV expression remain to be clarified. In this report, we further characterize FUTIV gene structure and define a non-TATA box-dependent transcriptional start region just upstream from the translational start. FUTIV promoter/reporter fusion constructs defined a "full-length" promoter and highly active fragments in the macrophage-derived U937 and myeloid HL60 cell lines. One highly active fragment contains a consensus binding site for the Ets-1 transcription factor (Withers, D. A., and Hakomori, S. (1997) Glycoconj. J. 14, 764). Gel shift analysis shows specific binding to this site in nuclear extracts from U937 cells. Mutation of the Ets consensus site significantly reduces FUTIV promoter activity in both cell lines. Gel supershift and dominant negative cotransfection experiments identified the Ets family member Elk-1 as one component binding and regulating the FUTIV promoter in U937 cells. The significance of FUTIV regulation by Elk-1 is discussed.

The acceptor and site specificity of alpha 3-fucosyltransferase V. High reactivity of the proximal and low of the distal galbeta 1-4GlcNAc unit in i-type polylactosamines

We report here on in vitro acceptor and site specificity of recombinant alpha3-fucosyltransferase V (Fuc-TV) with 40 oligosaccharide acceptors. Galbeta1-4GlcNAc (LN) and GalNAcbeta1-4GlcNAc (LDN) reacted rapidly; Galbeta1-3GlcNAc (LNB) reacted moderately, and GlcNAcbeta1-4GlcNAc (N, N'-diacetyl-chitobiose) reacted slowly yet distinctly. In neutral and terminally alpha3-sialylated polylactosamines of i-type, the reducing end LN unit reacted rapidly and the distal (sialyl)LN group very slowly; the midchain LNs revealed intermediate reactivities. The data suggest that a distal LN neighbor enhances but a proximal LN neighbor reduces the reactivity of the midchain LNs. This implies that Fuc-TV may bind preferably the tetrasaccharide sequence Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAc for transfer at the underlined monosaccharide. Terminal alpha3-sialylation of i-type polylactosamines almost doubled the reactivities of the LN units at all positions of the chains. We conclude that, in comparison with human Fuc-TIV and Fuc-TIX, Fuc-TV reacted with a highly distinct site specificity with i-type polylactosamines. The Fuc-TV reactivity of free LNB resembled that of LNBbeta1-3'R of a polylactosamine, contrasting strongly with the dissimilarity of the reactivities of the analogous pair of LN and LNbeta1-3'R. This observation supports the notion that LN and LNB may be functionally bound at distinct sites on Fuc-TV surface. Our data show that Fuc-TV worked well with a very wide range of LN-glycans, showing weak reactivity only with distal (sialyl)LN units of i-type polylactosamines, biantennary N-glycans, and I branches of polylactosamines.