ELAM-1 mediates cell adhesion by recognition of a carbohydrate ligand, sialyl-Lex

Isolation and characterization of microvessel endothelial cells from human mammary adipose tissue

A method for the isolation and long-term culture of human microvessel endothelial cells from mammary adipose tissue (HuMMEC) obtained at breast reduction surgery has been developed. Pure cultures of HuMMEC were isolated by sequential digestion of the fat with collagenase and trypsin followed by specific selection of microvessel fragments with Ulex europaeus agglutinin-1 coated magnetic beads (Dynabeads). The resulting cells formed contact-inhibited monolayers on gelatin and fibronectin substrates and capillary-like "tubes" on Matrigel; they also expressed von Willebrand factor, angiotensin-converting enzyme, and accumulated acetylated low density lipoprotein. Further immunofluorescence characterization revealed the presence of antigens for the endothelial cell specific monoclonal antibodies EN4 and H4-7/33. In addition, the origin of these cells was confirmed by the demonstration of the cell adhesion molecules, platelet endothelial cell adhesion molecule-1 (CD31), and endothelial leukocyte adhesion molecule-1 (ELAM-1/E-selectin) upon stimulation with tumor necrosis factor (TNF) alpha. HuMMEC were found to express-1 ELAM-1 at lower levels of TNF alpha (< 10 ng/ml) than required by human umbilical vein endothelial cells. These cells should provide a useful in vitro model for studying various aspects of microvascular biology and pathology.

P- and E-selectin use common sites for carbohydrate ligand recognition and cell adhesion

The selectins are a family of three calcium-dependent lectins that mediate adhesive interactions between leukocytes and the endothelium during normal and abnormal inflammatory episodes. Previous work has implicated the carbohydrate sialyl Lewis(x) (sLe(x); sialic acid alpha 2-3 galactose beta 1-4 [Fucose alpha 1-3] N-acetyl glucosamine) as a component of the ligand recognized by E- and P-selectin. In the case of P-selectin, other components of the cell surface, including 2'6-linked sialic acid and sulfatide (galactose-4-sulfate ceramide), have also been proposed for adhesion mediated by this selectin. We have recently defined a region of the E-selectin lectin domain that appears to be directly involved with carbohydrate recognition and cell adhesion (Erbe, D. V., B. A. Wolitzky, L. G. Presta, C. R. Norton, R. J. Ramos, D. K. Burns, R. M. Rumberger, B. N. N. Rao, C. Foxall, B. K. Brandley, and L. A. Lasky. 1992. J. Cell Biol. 119:215-227). Here we describe a similar analysis of the P-selectin lectin domain which demonstrates that a homologous region of this glycoprotein's lectin motif is involved with carbohydrate recognition and cell binding. In addition, we present evidence that is inconsistent with a biological role for either 2'6-linked sialic acid or sulfatide in P-selectin-mediated adhesion. These results suggest that a common region of the E- and P-selectin lectin domains appears to mediate carbohydrate recognition and cell adhesion.

Higher-affinity oligosaccharide ligands for E-selectin

A series of synthetic oligosaccharides based on sialyl Lewis x (sLex; Neu5Ac alpha 2-3Gal beta 1-4[Fuc alpha 1-3]GlcNAc) and sialyl Lewis a (sLea; Neu5Ac alpha 2-3Gal beta 1-3[Fuc alpha 1-4]GlcNAc) was used to study the binding interactions of selectins. E-selectin-immunoglobulin fusion protein (E-selectin-Ig) bound to immobilized bovine serum albumin (BSA)-neoglycoproteins containing sLex or sLea in a Ca(2+)-dependent manner. Solution-phase sLex tetrasaccharide blocked this interaction by 50% at a concentration of 750 +/- 20 microM (IC50). sLea was more effective (IC50 = 220 +/- 20 microM), while nonsialylated, nonfucosylated derivatives showed little or no activity at concentrations up to 1 mM. Attachment of an 8-methoxycarbonyloctyl aglycone in a beta linkage to the anomeric carbon of the GlcNAc of sLex or sLea increased their blocking activity nearly twofold. Finally, replacement of the 2-N-acetyl substituent of the GlcNAc by an azido or amino group resulted in substantial increases in activity, with the most potent inhibitor being amino substituted sLea, which was 36-fold more active (IC50 = 21 +/- 3 microM) than the reducing tetrasaccharide sLex. In contrast to results obtained with E-selectin-Ig, P-selectin-Ig binding to immobilized BSA-sLea was blocked modestly by most oligosaccharides at 1 mM, with no substantial differences among them. IC50 values of soluble oligosaccharides determined in competitive binding studies accurately predicted blocking of leukocyte adhesion to recombinant E-selectin-Ig and to cytokine-activated endothelium.

Expression of the developmental I antigen by a cloned human cDNA encoding a member of a beta-1,6-N-acetylglucosaminyltransferase gene family

The blood group i/I antigens were the first identified alloantigens that display a dramatic change during human development. The i and I antigens are determined by linear and branched poly-N-acetyllactosaminoglycans, respectively. In human erythrocytes during embryonic development, the fetal (i) antigen is replaced by the adult (I) antigen as a result of the appearance of a beta-1,6-N-acetylglucosaminyltransferase, the I-branching enzyme. Here, we report the cDNA cloning and expression of this branching enzyme that converts linear into branched poly-N-acetyllactosaminoglycans, thus introducing the I antigen in transfected cells. The cDNA sequence predicts a protein with type II membrane topology as has been found for all other mammalian glycosyltransferases cloned to date. The Chinese hamster ovary cells that stably express the isolated cDNA acquire I-branched structures as evidenced by the structural analysis of glycopeptides from these cells. Comparison of the amino acid sequence with those of other glycosyltransferases revealed that this I-branching enzyme and another beta-1,6-N-acetylglucosaminyltransferase that forms a branch in O-glycans are strongly homologous in the center of their putative catalytic domains. Moreover, the genes encoding these two beta-1,6-N-acetylglucosaminyltransferases were found to be located at the same locus on chromosome 9, band q21. These results indicate that the I-branching enzyme represents a member of a beta-1,6-N-acetylglucosaminyltransferase gene family of which expression is controlled by developmental programs.

The HNK-1 reactive sulfoglucuronyl glycolipids are ligands for L-selectin and P-selectin but not E-selectin

E-selectin, L-selectin, and P-selectin are related cell adhesion molecules that bind via their lectin domains to sialyl Lewis x and related carbohydrate determinants. Reports have indicated that sulfated glycolipids and polysaccharides also bind selectins. To extend these findings, we compared binding of selectin-IgG chimeras to immobilized sulfated and sialylated glycosphingolipids. E-, L-, and P-selectin chimeras all bound to surfaces absorbed with 2,3-sialyl Lewis x glycolipid or sulfatide (galactosylceramide I3-sulfate) but not to surfaces adsorbed with control sulfated lipids (octadecyl sulfate, sphingosine sulfate). Notably, the L- and P-selectin chimeras but not E-selectin chimera bound to surfaces adsorbed with sulfoglucuronyl glycosphingolipids (SGNL lipids; e.g., IV3 glucuronylneolactotetraosylceramide V3-sulfate). These unusual lipids have been reported as antigenic determinants for monoclonal IgM antibodies produced in patients with neuropathy associated with paraproteinemia and react with the mouse monoclonal antibody HNK-1. Binding of L- and P-selectin chimeras to SGNL lipids was specifically inhibited by appropriate anti-selectin antibodies. While binding of all three selectin chimeras to sialyl Lewis x was blocked by removal of calcium, binding to SGNL lipid was only modestly reduced by EDTA. Chemically desulfated SGNL lipid retained binding activity for L- and P-selectin chimeras, while methyl esterification of the glucuronic acid eliminated binding. We conclude that SGNL lipids, unlike sialyl Lewis x and sulfatides, selectively support L- and P-selectin but not E-selectin chimera binding. The presence of SGNL lipids on brain microvascular endothelium (and other endothelia) may implicate these molecules in leukocyte trafficking to the nervous system and elsewhere.

Sulphation requirement for GlyCAM-1, an endothelial ligand for L-selectin

L-selectin participates in the initial attachment of leukocytes to the vascular endothelium. On lymphocytes, it mediates binding to high endothelial venules of lymph nodes. As a selectin it functions as a calcium-dependent lectin recognizing carbohydrate-bearing ligands on endothelial cells. Two lymph node ligands for L-selectin have been identified as sulphated glycoproteins of M(r) approximately 50K and approximately 90K, called Sgp50 and Sgp90 (ref. 10). The recently cloned Sgp50 (ref. 12), now designated GlyCAM-1, is a high endothelial venule-associated, mucin-like glycoprotein containing predominantly O-linked carbohydrate chains. Sialylation of GlyCAM-1 is necessary for its ligand activity and a role for fucosylation is suspected. We have used chlorate as a metabolic inhibitor of sulphation, and report here that GlyCAM-1 has an additional requirement for sulphate.

Synthesis of chemically modified sialic acid-containing sialyl-LeX ganglioside analogues recognized by the selectin family

Sialyl Lewis X ganglioside analogues containing 5-acetamido-3,5-dideoxy-L-arabino-2-heptulopyranosylonic acid (C7-Neu5Ac), 5-acetamido-3,5-dideoxy-D-galacto-2-octulopyranosylonic acid (C8-Neu5Ac), and 5-acetamido-3,5-dideoxy-L-glycero-D-galacto-1-2-nonulopyranosylonic++ + acid (8-epi-Neu5Ac) in place of N-acetylneuraminic acid (Neu5Ac) have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl 6-O-benzoyl-beta-D-galactopyranoside with the phenyl or methyl 2-thioglycoside derivatives of the respective sialic acids, using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid as a promoter in acetonitrile, gave the three required 2-(trimethylsilyl)ethyl (2S)-sialyl-(2-->3)-beta-galactopyranosides. These were converted via O-benzoylation, selective transformation of the 2-(trimethylsilyl)ethyl group to acetyl, and introduction of the methylthio group with methylthiotrimethylsilane into the corresponding glycosyl donors. Glycosylation of 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-(1-->3)-O-(2-acetamido-6-O- benzyl- 2-deoxy-beta-D-glucopyranosyl)-(1-->3)-2,4,6-tri-O-benzyl-beta-D- galactopyranoside with these donors in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) afforded the expected beta-glycosides, which were converted into the corresponding alpha-trichloroacetimidates, and these, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol, gave the required beta-glycosides. Finally, these were transformed via selective reduction of the azide group, condensation with octadecanoic acid, O-deacylation, and de-esterification into the target compounds in good yields.

Selectins

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New perspectives on basic mechanisms in lung disease. 2. Neutrophil traffic in the lungs: role of haemodynamics, cell adhesion, and deformability

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A cancer-reactive human monoclonal antibody derived from a colonic cancer patient treated with local immunotherapy

A human monoclonal antibody, YJ-37 (IgM) was generated through the fusion of human B lymphoblastoid cell line HO-323 with the regional lymph node lymphocytes from a colonic cancer patient who was treated with a local immunotherapy. This antibody was purified and conjugated with biotin, after which direct immunohistochemical staining was performed. The results revealed that YJ-37 selectively reacted with colonic cancer (7/19), gastric cancer (3/6), endometrial cancer (1/2) and colonic adenoma (7/13), but not with normal epithelia. Membrane immunofluorescence and FACS analysis also showed that YJ-37 bound to tumor cell surfaces. Furthermore, the chemical structure of the antigen defined by YJ-37 was analyzed by means of thin-layer chromatography immunostaining and ELISA. The results indicated that YJ-37 reacted with sialylated lacto-series carbohydrate chains, which have been reported to accumulate in cancer cells.

Phosphorylation of surface E-selectin and the effect of soluble ligand (sialyl Lewisx) on the half-life of E-selectin

E-selectin (ELAM-1) is an adhesion molecule for leukocytes that is transiently expressed on endothelial cells. Following cell surface expression of E-selectin on human umbilical vein endothelial cells (HUVEC) stimulated with tumor necrosis factor, the induced E-selectin molecules are rapidly degraded. The kinetics of turnover of surface disposed E-selectin were investigated. The rapid disappearance of surface E-selectin is temperature dependent and sensitive to the lysosomotropic agent chloroquine. The half-life of E-selectin is not affected by inclusion of soluble sialyl Lewis x (sLex) ligands in the medium. Surface E-selectin is phosphorylated on one or more serine residues, but this modification is not obviously related to internalization.

Role of laminin carbohydrates on cellular interactions

Laminins, a family of large multidomain glycoproteins of the basal lamina, have been implicated in the development and maintenance of cellular and tissue organization. Considerable interest has arisen concerning the ways in which laminin carries out its biological functions. Previously these biologic responses have been primarily attributed to the peptide sequences of laminin, however, newer studies suggest that laminin carbohydrates may also participate in such cellular activities. Recently, a subpopulation of laminin molecules purified from EHS sarcoma by lectin affinity chromatography has been shown to contain about 25 to 30% carbohydrate. Most of the carbohydrates present are complex-type asparagine-linked oligosaccharides encompassing many different structures, some of which are unique to laminin. To date, the biological function of the carbohydrates of laminin remains somewhat unclear. They do not appear to be needed for heparin binding or to enhance proteinase stability, however, current evidence suggests they are important in cellular spreading and neurite outgrowth. It is our hypothesis that in the covalently-linked carbohydrate moieties of laminin will ultimately prove to be involved in information transfer to responsive cells. It is the purpose of this review to delineate current concepts of the structure and function of this unique glycoprotein's sugar chains.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Mechanisms of monocyte recruitment and accumulation

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Multi-recognition capability of E-selectin in a dynamic flow system, as evidenced by differential effects of sialidases and anti-carbohydrate antibodies on selectin-mediated cell adhesion at low vs. high wall shear stress: a preliminary note

E-selectin has a "multi-recognition" capability in terms of epitope binding specificity, depending on adhesion conditions (static vs. low- or high-shear stress dynamic systems). Specifically, (i) adhesion based on expression of alpha 2-->3 sialylated Le(x) (SLe(x)) is prominent under static or low shear stress dynamic conditions; (ii) adhesion under high shear stress dynamic conditions does not depend on the known SLe(x) species, but rather on Lex with an adjacent unidentified sialosyl substitution, which shows different susceptibility to sialidases and antibodies compared to known SLe(x).

Stimulation of neutrophil adhesion by antibodies recognizing CD15 (Le(X)) and CD15-expressing carcinoembryonic antigen-related glycoprotein NCA-160

The carbohydrate antigen, CD15 (Le(X)), and its sialylated derivative have recently been shown to be involved in the binding of neutrophils to the endothelial lectins, E-selectin and P-selectin. Neutrophil NCA-160, a carcinoembryonic antigen (CEA)-related glycoprotein, is the major carrier of CD15, which is also expressed on the common beta 2 chain of leucocyte integrins. Rabbit IgG antibodies directed against CEA, which cross-react with neutrophil NCAs, increase the adhesion of neutrophils to plastic. This effect is also observed with F(ab')2 and Fab antibody fragments and a monoclonal antibody (mAb) recognizing the same antigen. Anti-CD15 mAbs inhibit adhesion at higher concentrations, but augment adhesion at lower concentrations. Anti-CEA and anti-CD15 antibodies cause the homotypic adhesion of neutrophils demonstrable by light microscopy and flow cytometry. Anti-(integrin beta 2 chain) mAbs inhibit both adhesion to plastic and homotypic adhesion. These results suggest that binding of ligand to NCA-160 is able to trigger neutrophil adhesion events which have been shown to be integrin mediated. Anti-CD15 mAbs do not, however, induce a respiratory burst from neutrophils.

In vitro biosynthesis of GbOse4Cer (globoside) and GM2 ganglioside by the (1-->3) and (1-->4)-N-acetyl beta-D-galactosaminyltransferases from embryonic chicken brain. Solubilization, purification, and characterization of the transferases

(1-->4)-N-Acetyl-beta-D-galactosaminyltransferase (GalNAcT-1) and (1-->3)-N-acetyl-beta-D-galactosaminyltransferase (GalNAcT-2), which are involved in the in vitro biosynthesis of GM2 and GbOse4Cer glycosphingolipids, respectively, have been solubilized and separated by differential detergent extraction from a membrane preparation of 19-day-old embryonic chicken brain. The separated GalNAcT-1 activity had a pH optima of 7.8-8.0, and the separated GalNAcT-2 activity a single pH optimum of 7.2. Furthermore, the partially purified GalNAcT-2 preparation catalyzed the transfer of N-acetylgalactosamine from UDP-D-[3H]GalNAc to only GbOse3Cer and nLcOse5Cer. Both GalNAcT-1 and GalNAcT-2 activities were purified to approximately 316- and 428-fold, respectively, by use of UDP-hexanolamine-Sepharose 4B affinity-column chromatography. However, the partially purified GalNAcT-1 preparation appeared to be active only with GM3, lactosylceramide, and lactotriaosylceramide. The proposed linkage of the N-acetylgalactosamine unit incorporated into GM3 is beta-D-GalpNAc-(1-->4)-GM3 from the isolation of [3H]threitol after hydrolysis of the desialylated, lead tetraacetate-treated, enzymic product, beta-D-GalpNAc-(1-->4)-beta-D-[6-3H]Galp-(1-->4)-beta-D-Glcp-(1-->1)-Cer . In addition, beta-D-GalpNAc-(1-->3)-GbOse3Cer was produced, as shown by the identification of 2,4,6-tri-O-methyl-galactose after permethylation and hydrolysis of the GalNAcT-2 enzymic product, GalpNAc-[6-3H]Galp--->Gal-->Glc-->Cer.

Leukotriene B4-induced hyperadhesiveness of endothelial cells for neutrophils: relation to CD54

Leukotriene B4 (LTB4) induced an in vitro transient state of hyperadhesiveness in cultured human umbilical vein endothelial cells (HUVEC), leading to a 2.2-fold increase in the binding of neutrophil granulocytes (PMN), which was less than that conferred by platelet activating factor (PAF) though more than thrombin did (3.4- or 2.0-fold increases, respectively). This study concerns the role of the adhesive molecules CD18 and CD54 for the LTB4- (as well as thrombin- and PAF-) induced endothelial hyperadhesiveness. The MoAbs 60.3 (to the CD18 molecule on PMN) and 84H10 (to one epitope of CD54 on the HUVEC) blocked the adherence of PMN to LTB4-treated HUVEC, whereas MoAb LB-2 (directed at another CD54 epitope) failed to do so. MoAb 84H10 blocked 43% of the thrombin-induced hyperadhesiveness, whereas the PAF response was unaffected. Thus, LTB4-induced HUVEC hyperadhesiveness may therefore be related to a specific domain on the CD54 (or on an antigenically related molecule) as well as being dependent on CD18, whereas the involvement of CD54 was much less or non-existent for the thrombin and PAF responses, respectively.

Human epidermal keratinocyte expression of sialyl-Lewis X

Cell-surface oligosaccharides can function as ligands for intercellular adhesion receptors, matrix proteins, and growth factors. We report that human neonatal and adult epidermal keratinocytes (KC) express sialyl Lewis X [s-Le(x); SA alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3R], a ligand for endothelial and platelet selectins. Freshly isolated or cultured KC bind FH6 monoclonal antibody (MoAb), which is specific for s-Le(x)-containing oligosaccharides. The relevant epitope is bona fide s-Le(x), because sialidase treatment of KC suspensions abrogates FH6 binding while generating de novo KC reactivity with anti-Le(x). KC stained in ice-cold suspension display a knobby membrane distribution of s-Le(x) detectable by immunofluorescence microscopy. As others have reported, FH6 appeared not to bind KC in perpendicular skin sections. However, basal KC in intact epidermal sheets exhibited obvious "honeycomb" reactivity with FH6 when stained and viewed en face, suggesting that s-Le(x) in intact epidermis may occur in bands that parallel the major tissue axis. FH6 specifically immunoprecipitated proteins of Mr 34 kd, 44 kd, and 56 kd from [35S]-labeled KC, and anti-Le(x) precipitated similar proteins from sialidase-treated KC. The enzymatic basis for KC s-Le(x) expression was studied by analyzing acceptor specificities and other properties of KC fucosyltransferases. Results indicate that KC express both Lewis- and myeloid-type alpha 1-3fucosyltransferases. KC s-Le(x) could be an important element of the epithelial milieu, because both epithelial cells and immune cells that home to epithelia express s-Le(x) and related structures, and because KC s-Le(x) is well positioned for selectin-mediated platelet binding after trans-cutaneous wounding. The apparent distributions of s-Le(x) in epidermis and on isolated KC are compatible with a functional role for s-Le(x) in these intercellular interactions.

The ELAM-1 ligand sialosyl-Le(X) is present on Langerhans cells isolated from stratified epithelium

In this study we show the expression of the newly identified carbohydrate ligand, sialosyl-Le(X) on Langerhans cells. The receptor for sialosyl-Le(X) is the endothelial leukocyte adhesion molecule-1 (ELAM-1) present on activated endothelial cells. Using flow cytometry, Langerhans cells were selected due to positivity for an antibody against CD1a and low orthogonal light scatter. The CD1a antigen stained by the OKT6 antibody is considered a maturational marker of Langerhans cells in agreement with the specific labeling of dendritic cells in the epithelium only. Double immunostaining (OKT6/anti-sialosyl-Le(X)) using flow cytometry and immunohistochemistry demonstrated that almost all OKT6-positive cells in normal stratified epithelium expressed sialosyl-Le(X). Conversely, by immunohistochemistry of oral epithelium with acute inflammation, additional dendritic cells negative for OKT6 were found to express sialosyl-Le(X). In addition, sialosyl-Le(X)-positive but not OKT6-positive dendritic cells were found in the submucosa. These findings indicate that the carbohydrate antigen sialosyl-Le(X) is expressed earlier than the CD1a antigen in the maturation of the Langerhans cell lineage. Future studies should aim at investigating the importance of adhesion between sialosyl Le(X) and ELAM-1 in epithelial recruitment of Langerhans cells.

Ganglioside binding proteins of calf brain with ubiquitin-like N-terminals

Two ganglioside-associated protein components I and II have been isolated from crude ganglioside preparations of calf brain by DEAE-Sephadex ion-exchange chromatography. Both components exhibited binding capacity in aqueous media for gangliosides of the 'ganglio' series but not for neutral glycosphingolipids (polyglycosylceramides) and only a low capacity for sialosylparagloboside. Each protein bound individual gangliosides with different efficiency. Upon prolonged incubation of component I with gangliosides, complexes with high (30:1) and low (6:1) glycolipid/protein molar ratios were formed. The latter but not the former complex was able to penetrate Sephadex G-200 beads. Both components inhibited plating efficiency of cultured mouse N2a neuroblastoma cells. The molecular masses of components I and II were determined by SDS/PAGE to be 11-12 kDa and 28 kDa, respectively. Carbohydrates (fucose, mannose, galactose, N-acetylglucosamine, N-acetylgalactosamine, and some sialic acid) were found only in component II. When examined by reverse-phase HPLC each component separated into two major closely migrating peaks which were subsequently examined by Edman degradation. Amino acid sequences of the N-terminal portions of three of these peaks (one peak from component I and both peaks from component II) showed, as far as the sequences were established, identity with the sequence of ubiquitin. It is hypothesized that the proteins may be instrumental in intracellular trafficking of gangliosides.

Use of large-scale hydrazinolysis in the preparation of N-linked oligosaccharide libraries: application to brain tissue

In this report, we describe the preparation of a library of N-linked glycans from whole murine brain obtained by the large-scale hydrazinolysis of an acetone powder of the tissue followed by chromatographic procedures. 84% of the characterized oligosaccharides were found to be anionic, the remainder neutral. The anionic species were successively neutralized by neuraminidase (29%), aq. hydrofluoric acid (30%), and methanolysis (26%), indicating that approximately equal portions were sensitive to desialylation, dephosphorylation and desulfation, respectively. The presence of the sulfated fraction was confirmed by direct 35SO4 metabolic labelling. A residual partially characterized fraction was found to be anionic through possession of carboxylic acid groups, unrelated to sialic acid. The purified oligosaccharides, in the absence of their original protein conjugates, were shown to retain those immunological characteristics essential for recognition by a specific monoclonal antibody, LS (412), that is known to recognize a carbohydrate epitope present on a number of neural adhesion molecules and functional in neural cell adhesion. These properties confirm the viability of scaling up the size of the hydrazinolysis procedure and adapting it to whole tissue for the production of glycan libraries and for the probing of structures of interest.

The selectin family of carbohydrate-binding proteins: structure and importance of carbohydrate ligands for cell adhesion

Protein-carbohydrate interactions have been found to be important in many steps in lymphocyte recirculation and inflammatory responses. A family of carbohydrate-binding proteins or lectins, termed selectins, has been discovered and shown to be involved directly in these processes. The three known selectins, termed L-, E- and P-selectins, have domains homologous to other Ca(2+)-dependent (C-type) lectins. L-selectin is expressed constitutively on lymphocytes, E-selectin is expressed by activated endothelial cells, and P-selectin is expressed by activated platelets and endothelial cells. Here, we review the nature of the carbohydrate determinants in tissues recognized by these selectins. The expression of specific sialylated, fucosylated and sulfated carbohydrates in activated endothelium and high endothelial venules promotes interactions with L-selectin on leukocyte surfaces. In contrast, E- and P-selectins recognize specific carbohydrate determinants related to sialyl Le(x) antigen on neutrophil and monocyte surfaces. The discovery of the selectins has generated excitement among glycoconjugate researchers that other carbohydrate-binding proteins and their cognate ligands will be found to function in regulating many types of cellular interactions.

Selectins: interpreters of cell-specific carbohydrate information during inflammation

Although a bewildering array of cell surface carbohydrate structures have been described, the physiological relevance of any of these complex molecules has often eluded biologists. A family of cell surface glycoproteins, the "selectins," has a characteristic ability to use some of these carbohydrate structures in adhesive mechanisms that help localize leukocytes to regions of inflammation. This article will review the biology of these carbohydrate-binding adhesive proteins and discuss the potential for developing anti-inflammatory antagonists that could inhibit binding events that are selectin-mediated.

A metastasis-associated antigen is present on a 60 kDa glycoprotein in transitional cell carcinoma of the human urinary bladder

We have previously shown that the degree of expression of Lex-related carbohydrate epitopes, namely, Lotus tetragonolobus agglutinin (LTA) receptors, SSEA-1 and FH6, correlates with the metastatic potential of transitional cell carcinoma of the human urinary bladder. In an effort to obtain a better reagent with which to detect a metastasis-associated epitope, monoclonal antibodies were produced against LTA receptors from BOY bladder carcinoma cells. One antigen defined by such a monoclonal antibody, MM4, indeed showed better correlation with the metastatic potential of the tumour than did other carbohydrate markers. In the LTA receptors, MM4 antigen was located only on a 60 kDa glycoprotein. In extracts from primary carcinomas and lymph node metastases, the 60 kDa glycoprotein was the principal carrier of MM4 antigen. LTA receptors from these sources were composed of arrays of glycoproteins, while the 60 kDa one was invariably present. Metastasis-associated carbohydrate epitopes on the 60 kDa glycoprotein may promote metastasis by interaction with carbohydrate-recognizing proteins such as selectins on host cells.

Lex and related structures as adhesion molecules

Le(x) (alpha 1-->3 fucosylated type 2 chain) functions as an adhesion molecule capable of Ca(2+)-mediated homotypic binding. Cells with high surface expression of Le(x) therefore exhibit strong self-aggregation (based on Le(x)-Le(x) interaction) in the presence of Ca2+. In this review, I have summarized several lines of supporting data for this concept, and the role of Le(x)-Le(x) interaction in the process of embryo compaction and autoaggregation of F9 teratocarcinoma cells. In general, cell adhesion events based on Le(x)-Le(x) interaction may be followed and reinforced by integrin- or Ig receptor-based adhesion systems. SLe(x), the 2-->3 sialosyl derivative of Le(x), and its positional isomer SLe(a), have been identified as the target molecules for selectin-dependent cell adhesion. Adhesion of leukocytes or tumour cells to ECs or platelets, which express E-selectin and P-selectin respectively, is initiated by this process. The target epitopes SLe(x) and SLe(a) are presented mainly on transmembrane glycoproteins having many clusters of O-linked carbohydrate chains. Therefore, inhibition of O-glycosylation may be effective for blocking selectin-mediated cell adhesion. The abundant presence of Le(x) epitope in the central nervous system, and the physiological changes of Le(x) expression as described in this monograph, reflect the adhesive properties of this molecule and its sialyosylated and/or fucosylated derivatives.

Expression of CD15 (FAL) on myeloid cells and chromosomal localization of the gene

Different CD15 murine monoclonal antibodies were studied. These antibodies appeared to react specifically with the human myeloid-lineage-derived cell types in both peripheral blood and bone marrow. The antigens recognized by these antibodies were immunoprecipitated from lysates of 125I-labelled neutrophilic PMNs of healthy donors and subsequently analysed by electrophoresis on SDS-polyacrylamide gel and autoradiography. All antibodies precipitated the same membrane polypeptides from the membrane-iodinated PMN lysates: 105 and 150-kDa as most prominent, together with 260-, 230-, 67- and 52-kDa polypeptides. Absorption studies were performed with synthesized carbohydrate molecules. Antibody B4.3 appears to be directed against 3-alpha-fucosyl-N-acetyl-lactosamine (FAL). Competition experiments with 125I-labelled B4.3 demonstrated complete inhibition of binding by B4.3 and three other CD15 antibodies (VIM D5, UJ308, MI/N1), and partial inhibition by three additional antibodies (FMC10, FMC12, FMC13), indicating binding to the same antigenic structure. None of the antibodies reacted with monocytes using the immunofluorescence technique, but after neuraminidase digestion of these cells, positive reactions were obtained with all antibodies. Immunoprecipitation with lysates of both native and neuraminidase-digested monocytes showed no polypeptide bands. Monocytic differentiation of the myeloid cell line HL60 by 12-O-tetradecanoylphorbol-13-acetate (TPA) was accompanied by a decrease in reactivity with the antibodies, which could be reversed by neuraminidase digestion. This indicates that 3-alpha-fucosyl-N-acetyl-lactosamine is masked for the detection with antibodies upon monocytic differentiation by sialylation. Human x mouse myeloid cell hybrids were obtained after fusion of human myeloid cells and the HPRT-deficient murine myeloid cell line WEHI-TG.(ABSTRACT TRUNCATED AT 250 WORDS)

The blood group antigen-related glycoepitopes: key structural determinants in immunogenesis and AIDS pathogenesis

This overview will focus on the functional and pathophysiological aspects of blood group antigen (BGA)-related glycodeterminants with regard to immunogenesis and AIDS pathogenesis. It has been postulated that in a broad range of histogenetically different tissues and organs, BGA-related glycoepitopes are expressed on the cell surface at definite stages of cell differentiation. These glycoepitopes are expressed during embryogenesis, organogenesis, tissue repair, regeneration, remodelling and maturation when 'sorting-out' of one homotypic cell population from a heterotypic assemblage of cells occurs (1). In this event, the BGA-related glycoepitopes, if being expressed on the cell surface, play roles of key structural determinants in cell-cell recognition, association and aggregation. This mechanism will be discussed in relation to immunogenesis with regard to antigen presentation, self-non-self discrimination, and positive and negative selection during thymic education. It is postulated that the appearance of BGA-related glycoepitopes on the cell membrane is a consequence of the association of major histocompatibility complex antigens (MHC) and peptides, with the subsequent elimination of cells carrying a high density of BGA-related glycoepitopes on their surface. After human immunodeficiency virus (HIV) glycoproteins are glycosylated by host cell glycosyltransferases, the virus may use the BGA-related glycodeterminants as ligands and/or receptors for expansion to a spectrum of target cells during AIDS development and generalization of the infection throughout the body. We will review the experimental evidence that supports the concept that HIV uses an alternative to the gp120/CD4 ligand/receptor system, and that the alternative mechanism is probably carbohydrate-mediated in nature.

Platelets and cancer metastasis: a causal relationship?

Cancer metastasis is a highly coordinated and dynamic multistep process in which cancer cells undergo extensive interactions with various host cells before they establish a secondary metastatic colony. Ample morphological studies have documented the close association of circulating tumor cells with host platelets. Several lines of evidence provide strong support for the concept that tumor cell-platelet interactions (i.e., TCIPA) significantly contribute to hematogenous metastasis. Clinically, cancer patients with advanced diseases are characterized by a variety of thromboembolic disorders including thrombocytosis. Pharmacologically, various anti-platelet agents/anticoagulants have demonstrated potent inhibitory effects on tumor cell-platelet interactions as well as spontaneous or experimental metastasis. Experimentally, interference with many of the intermediate steps of tumor cell-platelet interactions has resulted in diminished platelet aggregation induced by tumor cells and blocked cancer metastasis. Platelet interaction with tumor cells is a sequential process which involves two general types of mediators, i.e., membrane-bound molecules (adhesion molecules) and soluble release products. alpha IIb beta 3 integrin receptors present on both platelets as well as on tumor cells and 12(S)-HETE, a 12-lipoxygenase metabolite of arachidonic acid, are prototypical examples of each category. Mechanistically, platelets may contribute to metastasis by: (1) stabilizing tumor cell arrest in the vasculature, (2) stimulating tumor cell proliferation, (3) promoting tumor cells extravasation by potentiating tumor cell-induced endothelial cell retraction, and (4) enhancing tumor cell interaction with the extracellular matrix.