The role of protein glycosylation inhibitors in the prevention of metastasis and therapy of cancer.

Oligosaccharide moieties of cell-surface glycoproteins are thought to be involved in recognition events during cancer metastasis and invasion. Swainsonine, an inhibitor of the Golgi alpha-mannosidase II, has been shown to block pulmonary colonization by tumor cells and stimulate components of the immune system. Swainsonine also abrogates much of the toxicity of chemotherapeutic agents and stimulates bone marrow hematopoietic progenitor cells, suggesting additional therapeutic applications. We are currently characterizing the ability of swainsonine to modify cell growth in human and murine bone marrow progenitor cells. Furthermore, we are examining crucial steps in metastasis that depend upon cell surface molecules that play a role in cell-matrix interactions. Our work shows that tumor cell adhesion to collagen IV in vitro is rapidly stimulated by cis-polyunsaturated fatty acids and is dependent on protein kinase C activity. We are investigating the hypothesis that integrins are critical components of this adhesion and are examining potential signal transduction pathways that lead to the modulation of cell adhesion.

High resolution and high sensitivity methods for oligosaccharide mapping and characterization by normal phase high performance liquid chromatography following derivatization with highly fluorescent anthranilic acid.

Facile labeling of oligosaccharides (acidic and neutral) in a nonselective manner was achieved with highly fluorescent anthranilic acid (AA, 2-aminobenzoic acid) (more than twice the intensity of 2-aminobenzamide, AB) for specific detection at very high sensitivity. Quantitative labeling in acetate-borate buffered methanol (approximately pH 5.0) at 80 degreesC for 60 min resulted in negligible or no desialylation of the oligosaccharides. A high resolution high performance liquid chromatographic method was developed for quantitative oligosaccharide mapping on a polymeric-NH2bonded (Astec) column operating under normal phase and anion exchange (NP-HPAEC) conditions. For isolation of oligosaccharides from the map by simple evaporation, the chromatographic conditions developed use volatile acetic acid-triethylamine buffer (approximately pH 4.0) systems. The mapping and characterization technology was developed using well characterized standard glycoproteins. The fluorescent oligosaccharide maps were similar to the maps obtained by the high pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), except that the fluorescent maps contained more defined peaks. In the map, the oligosaccharides separated into groups based on charge, size, linkage, and overall structure in a manner similar to HPAEC-PAD with contribution of -COOH function from the label, anthranilic acid. However, selectivity of the column for sialic acid linkages was different. A second dimension normal phase HPLC (NP-HPLC) method was developed on an amide column (TSK Gel amide-80) for separation of the AA labeled neutral complex type and isomeric structures of high mannose type oligosaccharides. The oligosaccharides labeled with AA are compatible with biochemical and biophysical techniques, and use of matrix assisted laser desorption mass spectrometry for rapid determination of oligosaccharide mass map of glycoproteins is demonstrated. High resolution of NP-HPAEC and NP-HPLC methods combined with mass spectrometry (MALDI-TOF) can provide an effective technology for analyzing a wide repertoire of oligosaccharide structures and for determining the action of both transferases and glycosidases.

Sea urchin egg receptor for sperm: the oligosaccharide chains stabilize sperm binding.

Sulfated O-linked oligosaccharides from the sea urchin egg receptor have been shown to bind to acrosome-reacted sperm and to inhibit fertilization in a competitive bioassay. However, the inhibitory activity of these isolated chains was much lower than that of a recombinant protein representing a portion of the extracellular domain of the receptor. Because the isolated oligosaccharides lacked the potential polyvalency that they might have when linked to the polypeptide backbone, in the current study we asked if their inhibitory activity could be increased by chemically coupling them to a protein to form a neoglycoprotein. Using a recombinant fragment of the receptor we could not detect an oligosaccharide dependent increase in inhibitory activity with this neoglycoprotein, probably because of the much higher inhibitory activity of the polypeptide backbone. Therefore, we examined the activity of the oligosaccharides coupled to a protein lacking the ability to inhibit fertilization, namely, bovine serum albumin. A marked increase in the inhibitory activity of the oligosaccharides was observed with this neoglycoprotein. Finally, because inhibition by the oligosaccharides and the polypeptide was measured in an end point assay, namely, inhibition of fertilization, we sought a more direct, kinetically sensitive way to measure their properties. Accordingly, an assay was devised (R.L. Stears and W.J. Lennarz, unpublished observations) involving measurement of sperm binding to beads that was dependent on the presence of the receptor or its components. This assay revealed that sperm binding to beads via the recombinant protein peaked at 10 sec and then declined. In contrast, binding mediated by neoglycosylated recombinant protein reached a plateau. Thus, binding of sperm to the oligosaccharides resulted in a more stable interaction than that observed in binding to the polypeptide backbone.

The involvement of O-linked oligosaccharide chains of the sea urchin egg receptor for sperm in fertilization.

Recent investigations on the sea urchin egg receptor for sperm have led to its sequencing and the demonstration that it is a 350 kDa glycoprotein. In the current study, the N- and O-linked oligosaccharide chains were cleaved from the protein fractionated on concanavalin A-agarose. The putative O-linked oligosaccharide chains that did not bind to the lectin were further fractionated by anion-exchange chromatography. Using a competition bioassay that measured the ability of these oligosaccharide chains to inhibit fertilization, it was found that the N-linked chains were devoid of inhibitory activity. Rather, the inhibitory activity was localized to the O-linked chains, with the most highly charged, sulphated chains showing the highest inhibitory activity. The bioactive oligosaccharides were labelled by reduction and assayed for binding to sperm. The results of the binding assay, coupled with the fertilization bioassay, indicate that the oligosaccharides inhibit fertilization by binding to acrosome-reacted sperm. The bioactive oligosaccharide lacked species specificity in fertilization bioassays, unlike the intact receptor and a recombinant aglyco protein containing only the extracellular domain of the receptor. Since previous work showed that the recombinant protein inhibits fertilization species specifically and binds to acrosome-reacted sperm, a two-step model of sperm-egg interaction is proposed. The first step is postulated to be a low-affinity ionic interaction of the sulphated O-linked oligosaccharide chains of the receptor with sperm that is not species specific. This is followed by a high-affinity, species-specific interaction of the sperm with one or more binding sites on the polypeptide chain of the receptor.

Polylactosamines are not obligate receptors for invasion of Plasmodium falciparum malaria as shown in HEMPAS variant II-gal- erythrocytes.

A HEMPAS (hereditary erythroblastic multinuclearity with positive acidified serum test) erythrocyte, atypical Variant II (referred to herein as Variant II-gal-), lacking long-chain polylactosamine on both glycoproteins (Band 3 and 4.5) and glycosphingolipids, was characterized by the carbohydrate profile of the erythrocyte membrane according to Fukuda et al. (Blood, 73, 1331-1339, 1989). Two laboratories previously reported that polylactosamine isolated from the erythrocyte protein Band 3 inhibited invasion of red blood cells by Plasmodium falciparum in malarial culture, suggesting a role for this carbohydrate in adhesion of the parasite. Therefore, HEMPAS erythrocyte Variant II-gal- presented a unique opportunity to further examine this premise. Freshly drawn blood samples (normal and HEMPAS Variant II-gal-) were separately incubated with P. falciparum from mannitol-synchronized cultures. The parasite was found to invade HEMPAS Variant II-gal- erythrocytes at a 30% lower rate through two life cycles, as shown by microscopic evaluation of invasion and by [3H]hypoxanthine incorporation into parasite. This observation, along with the published fact that glycophorin-deficient MkMk cells are also infectable, but at a lower rate, indicates that neither sialoglycoproteins nor polylactosamines are an obligate adhesive ligand for P. falciparum, although the possibility remains that either may still contribute to adhesive events during infection.

The sea urchin egg receptor for sperm: isolation and characterization of the intact, biologically active receptor.

The species-specific binding of sea urchin sperm to the egg is mediated by an egg cell surface receptor. Although earlier studies have resulted in the cloning and sequencing of the receptor, structure/function studies require knowledge of the structure of the mature cell surface protein. In this study, we report the purification of this glycoprotein to homogeneity from a cell surface complex of Strongylocentrotus purpuratus eggs using lectin and ion exchange chromatography. Based on the yield of receptor it can be calculated that each egg contains approximately 1.25 x 10(6) receptor molecules on its surface. The receptor, which has an apparent M(r) of 350 kD, is a highly glycosylated transmembrane protein composed of approximately 70% carbohydrate. Because earlier studies on the partially purified receptor and on a pure, extracellular fragment of the receptor indicated that the carbohydrate chains were important in sperm binding, we undertook compositional analysis of the carbohydrate in the intact receptor. These analyses and lectin binding studies revealed that the oligosaccharide chains of the receptor are sulfated and that both N- and O-linked chains are present. Functional analyses revealed that the purified receptor retained biological activity; it inhibited fertilization in a species-specific and dose-dependent manner, and polystyrene beads coated with it bound to acrosome-reacted sperm in a species-specific manner. The availability of biochemical quantities of this novel cell recognition molecule opens new avenues to studying the interaction of complementary cell surface ligands in fertilization.