Enzymatic synthesis of alpha3'sialylated and multiply alpha3fucosylated biantennary polylactosamines. A bivalent [sialyl diLex]-saccharide inhibited lymphocyte-endothelium adhesion organ-selectively

Sialyl Lewisx-P-selectin cascade mediates tumor-mesothelial adhesion in ascitic fluid shear flow

Organ-specific colonization suggests that specific cell–cell recognition is essential. Yet, very little is known about this particular interaction. Moreover, tumor cell lodgement requires binding under shear stress, but not static, conditions. Here, we successfully isolate the metastatic populations of cancer stem/tumor-initiating cells (M-CSCs). We show that the M-CSCs tether more and roll slower than the non-metastatic (NM)-CSCs, thus resulting in the preferential binding to the peritoneal mesothelium under ascitic fluid shear stress. Mechanistically, this interaction is mediated by P-selectin expressed by the peritoneal mesothelium. Insulin-like growth factor receptor-1 carrying an uncommon non-sulfated sialyl-Lewis^x (sLe^x) epitope serves as a distinct P-selectin binding determinant. Several glycosyltransferases, particularly α1,3-fucosyltransferase with rate-limiting activity for sLe^x synthesis, are highly expressed in M-CSCs. Tumor xenografts and clinical samples corroborate the relevance of these findings. These data advance our understanding on the molecular regulation of peritoneal metastasis and support the therapeutic potential of targeting the sLe^x-P-selectin cascade.

Tumor cell in the peritoneum are often exposed to shear forces generated by ascitic flow during metastasis. Here, the authors show that metastatic cancer stem cells tether more and roll slower than the non-metastatic counterparts, and that sialyl-Lewis^x -P-selectin axis mediates peritoneal metastasis.

Site-specific fucosylation of sialylated polylactosamines by alpha1,3/4-fucosyltransferases-V and -VI Is defined by amino acids near the N terminus of the catalytic domain

Fucose transfer from GDP-fucose to GlcNAc residues of the sialylated polylactosamine acceptor NeuAcalpha2-3Galbeta1-4Glc-NAcbeta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glcbeta1-ceramide leads to two isomeric monofucosyl antigens, VIM2 and sialyl-Le(x). Human alpha1,3/4-fucosyltransferase (FucT)-V catalyzes primarily the synthesis of VIM2, whereas human FucT-VI catalyzes primarily the synthesis of sialyl-Le(x). Thus, these two enzymes have distinct "site-specific fucosylation" properties. Amino acid sequence alignment of these enzymes showed that there are 24 amino acid differences in their catalytic domains. Studies were conducted to determine which of the amino acid differences are responsible for the site-specific fucosylation properties of each enzyme. Domain swapping (replacing a portion of the catalytic domain from one enzyme with an analogous portion from the other enzyme) demonstrated that site-specific fucosylation was defined within a 40-amino acid segment containing 8 amino acid differences between the two enzymes. Site-directed mutagenesis studies demonstrated that the site-specific fucosylation properties of these enzymes could be reversed by substituting 4 amino acids from one sequence with the other. These results were observed in both in vitro enzyme assays and flow cytometric analyses of Chinese hamster ovary cells transfected with plasmids containing the various enzyme constructs. Modeling studies of human FucT using a structure of a bacterial fucosyltransferase as a template demonstrated that the amino acids responsible for site-specific fucosylation map near the GDP-fucose-binding site. Additional enzyme studies demonstrated that FucT-VI has approximately 12-fold higher activity compared with FucT-V and that the Trp(124)/Arg(110) site in these enzymes is responsible primarily for this activity difference.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

Controlled release of saccharides from matrix tablets

The aim of this study was to design site specific, controlled release tablets of N-acetyl-d-glucosamine (NAG), maltose monohydrate and maltopentaose by using hydrophobic matrix formers starch acetate (SA) and ethyl cellulose (EC). The optimized matrices, which had either low porosity and high drug load or high porosity and low drug load, released the saccharides within the desired 2-4 h. In general, it was possible to control the release rate of saccharides by altering the relative amount of hydrophobic matrix former in the tablet and tablet porosity. The release type of saccharides from these formulations varied from immediate release to sustained release. In the case of sustained release formulations, it was found that the release of maltose monohydrate and maltopentaose was biphasic and slower than the release rate of NAG from similar tablets. NAG release kinetics followed square root of time kinetics, while in the case of maltose monohydrate and maltopentaose, the release kinetics were zero order in both phases. The biphasic dissolution profile was proposed to be caused by water mediated recrystallisation of the disordered material formed during the dissolution. Both SA and EC matrices were found to represent suitable controlled oral delivery vehicles for saccharides.

Glycosulfopeptides with O-glycans containing sialylated and polyfucosylated polylactosamine bind with low affinity to P-selectin

P-selectin glycoprotein ligand-1 (PSGL-1), a dimeric mucin on leukocytes, is the best characterized ligand for selectins. P-selectin binds stereospecifically to the extreme N terminus of PSGL-1, which contains three clustered tyrosine sulfates (TyrSO3-) adjacent to a Thr residue with a core 2-based O-glycan expressing sialyl Lewis x (C2-O-sLe(x)). GSP-6, a synthetic glycosulfopeptide modeled after the N terminus of PSGL-1, containing three TyrSO3- residues and a short, monofucosylated C2-O-sLe(x) bound to P-selectin with high affinity (K(d) approximately 650 nm). However, PSGL-1 from human HL-60 cells contains higher levels of O-glycans that are sialylated and polyfucosylated polylactosamines (PFPL). Furthermore, studies with fucosyltransferase-deficient mice suggest that sialylated PFPL structures contribute to binding to P-selectin. To resolve whether sialylated PFPL O-glycans participate in binding of PSGL-1 to human P-selectin, we synthesized glycosulfopeptides, designated GSP-6' and GSP-6", with three TyrSO3- residues and either difucosylated polylactosamine (C2-O-Le(x)-sLe(x)) or trifucosylated polylactosamine (C2-O-Le(x)-Le(x)-sLe(x)). Binding of the GSPs to P-selectin was measured by affinity chromatography, fluorescence solid-phase assays, and equilibrium gel filtration. Unexpectedly, both GSP-6' and GSP-6" bound to P-selectin with low affinity (K(d) approximately 37 microm for GSP-6' and K(d) approximately 50 microm for GSP-6"). Binding of GSP-6' and GSP-6" to P-selectin required fucosylation and, to a lesser extent, sialylation as well as the sulfated peptide backbone of GSP-6' and GSP-6". These results demonstrate that contrary to expectations, a core 2 O-glycan containing sialylated PFPL does not promote high affinity binding of PSGL-1 to P-selectin.

Glycosylation might provide endothelial zip codes for organ-specific leukocyte traffic into inflammatory sites

Inflammatory diseases are characterized by the leukocyte infiltration into tissues. L-selectin on lymphocytes and its endothelial glycosylated ligands are instrumental in the initiation of lymphocyte extravasation. Immunohistochemical stainings with monoclonal antibodies against functionally active glycan-decorated L-selectin ligands, ie, sialyl-Lewis x (sLex, 2F3, and HECA-452) or sulfated extended core 1 lactosamine (MECA-79), were performed on more than 400 specimen representatives for thyroiditis, myocarditis, psoriasis, vasculitis, ulcerative colitis, and their corresponding noninflamed tissues. The endothelial expression of sLex or sulfo sLex glycans in postcapillary venules was either absent or low in control tissues. The de novo induction of endothelial expression of sLex or sulfo sLex glycans was detected in all inflamed tissues. Furthermore, each organ carried its own modification of sLex or sulfo sLex glycans, ie, zip code. Our results suggest that these zip code glycans may provide means for organ selective leukocyte traffic that could be used in selective leukocyte traffic inhibition.

A peptide mimic of selectin ligands abolishes in vivo inflammation but has no effect on the rat heart allograft survival1

Acute heart allograft rejection is characterized by leukocyte infiltration and myocyte damage, key elements in the histological grading of rejection. The induction of selectins and their ligands on the graft postcapillary venular endothelium increases leukocyte tethering to, rolling on, and extravasation through the endothelium into graft parenchyma. We have characterized peptide mimicking selectin ligands by screening phage peptide libraries using anti-Lewis A antibodies and E-selectin as target molecules. The effect of this selectin- binding peptide, IELLQAR, on the prevention of inflammation and tissue damage and on the prolongation of graft survival in inbred DA (RT1a) rat heart allografts transplanted to WF (RT1v) recipients was tested. Bovine serum albumin (0.1%, solvent), VTSIAQA (control peptide), or IELLQAR were either continuously infused into the peritoneum via osmotic mini pumps or injected twice daily IV. Treatment with bovine serum albumin and VTSIAQA did not alter the number of graft infiltrating leukocytes or the histological grade of acute rejection, all scored as grade 4. On the contrary, the selectin binding peptide, IELLQAR, dose-dependently reduced inflammation and at the highest dose (6.0 mg/kg per day) eliminated the majority of graft infiltrating leukocytes, reduced the histological grade from 4 to 1B, but had no effect on graft survival. These data indicate that the intensity of inflammation related to the allograft rejection does not correlate to the graft survival.

O-glycans on human high endothelial CD34 putatively participating in L-selectin recognition

Leukocyte traffic into lymph nodes and sites of inflammation is guided by L-selectin. Experiments performed in vitro and with gene-deleted mice suggest that CD34 recognizes L-selectin if decorated by 6-sulfo sialyl Lewis x (sLex) saccharides and the MECA-79 epitope. However, very little is known about glycosylation of human L-selectin ligands. We report here on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) profiles of N- and O-linked oligosaccharide fractions from human tonsillar endothelial CD34. All detected O-glycans were sialylated; some were also monosulfated or monosulfated and monofucosylated. If a given CD34-glycan may carry all requirements for L-selectin recognition, that is, both 6-sulfo-sLex and MECA-79 epitopes, only one O-glycan fraction, O-9, SA(2)Hex(3)HexNAc(3)- Fuc(1)(SO(3))(1), meets the criteria. A candidate structure is SAalpha2-3Galbeta1-4(Fucalpha1-3)(6-sulfo)GlcNAcbeta1-3Galbeta1-3(SAalpha2-3Galbeta1-4GlcNAcbeta1-6)GalNAc. However, if sulfo sLex glycans are supplemented with separate sulfated, nonfucosylated O-glycans, saccharides in O-6, O-8, or O-9, putatively carrying MECA-79 epitopes, could form multiglycan binding epitopes for L-selectin.

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.

Synthetic multivalent ligands in the exploration of cell-surface interactions

Processes such as cell-cell recognition and the initiation of signal transduction often depend on the formation of multiple receptor-ligand complexes at the cell surface. Synthetic multivalent ligands are unique probes of these complex cell-surface-binding events. Multivalent ligands can be used as inhibitors of receptor-ligand interactions or as activators of signal transduction pathways. Emerging from these complementary applications is insight into how cells exploit multivalent interactions to bind with increased avidity and specificity and how cell-surface receptor organization influences signaling and the cellular responses that result.

De novo induction of endothelial L-selectin ligands during kidney allograft rejection

Acute kidney allograft rejection is characterized by a lymphocyte infiltration. L-selectin on lymphocytes and its endothelial glycosylated ligands are instrumental in the initiation of lymphocyte extravasation to sites of inflammation. From more than 500 core biopsy specimens taken from kidneys after transplantation, 250 biopsies were graded to have signs of acute rejection. Of these, 52 biopsies with various grades of histologic signs of acute rejection were selected for the study. Controls were 15 biopsies taken within 30 min after revascularization and 10 specimens from well-functioning allografts showing no clinical or histologic evidence of rejection. Immunochemical stainings with monoclonal antibodies against functionally active decorated L-selectin ligands. i.e., sialyl-Lewis x (sLex, 2F3 and HECA-452) or sulfated lactosamine (MECA-79) were performed. Although no endothelial 2F3 and MECA-79 epitopes were detected in nonrejecting control specimens, the expression was induced at the onset and during acute allograft rejections. The level of expression (in semi-quantitative score) of 2F3 reactivity correlated with the severity of rejection (P<0.0001, grade I versus grade IIB), and the level of expression decreased as the rejection resolved. Kidney biopsies taken shortly after revascularization and thus undergoing reperfusion injury showed endothelial staining with another anti sLex antibody, HECA-452. This staining disappeared from well-functioning grafts and reappeared at the onset of an acute allograft rejection. These results suggest that expression of functionally active, properly glycosylated L-selectin ligands might have a role in reperfusion injury and in the initiation of acute rejections after human kidney allograft transplantation.

Two time-resolved fluorometric high-throughput assays for quantitation of GDP-L-fucose

Two rapid and simple procedures for the quantitative analysis of GDP-l-fucose (GDP-Fuc) are described. The methods are based on time-resolved fluorescence and microplate assay technology. The first assay relies on measuring the enzyme activity of alpha1, 3-fucosyltransferase. In this assay, transfer of fucose from GDP-Fuc converts sialyllactosamine to sialyl Lewis x tetrasaccharide, which is detected and quantified by relevant antibodies on a microplate. The formation of the reaction product is directly dependent on the presence of GDP-Fuc in the concentration range of 10-10,000 nM. In the second method GDP-Fuc inhibits the binding of fucose-specific Aleuria aurantia lectin to fucosylated glycan on a microwell. The lectin-based assay is less sensitive than the enzyme assay, but it is cheaper and faster. We used these assays in monitoring the amount of GDP-Fuc in crude lysates of transgenic yeast, which expresses the enzymes producing GDP-Fuc. The newly developed assays are versatile and applicable to measure also other nucleotide sugars or glycosyltransferase activities in a high-throughput manner.

Biosynthesis of sialylated and fucosylated selectin ligands of HL-60 cells in vitro. Midchain alpha3-fucose units inhibit terminal alpha6-sialylation but not alpha3-sialylation of polylactosamines

Polylactosamines Neu5Ac alpha2-3'Lex beta1-3'Lex beta1-3'Lex and Neu5Ac alpha2-3'LNbeta1-3'Lex beta1-3'Lex [Lex, Gal beta1-4(Fuc alpha1-3)GlcNAc; LN, Gal beta1-4GlcNAc] decorate selectin counterreceptors in human HL-60 cells. Here, we show that HL-60 cell lysates catalyze distal alpha3-sialylation of LNbeta1-3'LNbeta1-3'LN and LNbeta1-3'Lex beta1-3'Lex efficiently, outlining two potential sets of biosynthetic pathways leading to the selectin ligands. In one set, alpha3-sialylation precedes internal fucosylation of the polylactosamine backbone, whereas in the other one, internal fucosylation is initiated before alpha3-sialylation. In contrast to alpha3-sialylation, LNbeta1-3'Lex beta1-3'Lex was alpha6-sialylated much less efficiently than LNbeta1-3'LNbeta1-3'LN by HL-60 cell lysates. Hence, internal fucosylation may regulate the extent of alpha6-sialylation of polylactosamines in these cells.