Effects of tunicamycin on B16 metastatic melanoma cell surface glycoproteins and blood-borne arrest and survival properties

The role of cell surface glycoproteins in determining in vivo blood-borne arrest and survival characteristics of murine melanoma sublines of low (B16-F1) or high (B16-F10) potential to form experimental lung metastases after injection i.v. was assessed after inhibiting tumor cell protein glycosylation with tunicamycin. Incubation of B16-F1 or B16-F10 cells with 0.5 micrograms (or above) tunicamycin per ml for 12 to 36 hr inhibited significantly lung tumor colony formation. Examination of B16 cells in the presence of 0.5 micrograms drug per ml indicated that complex oligosaccharide synthesis was inhibited greater than 90%, while protein synthesis remained at about 50% of the control levels. Tunicamycin induced morphological changes in B16-F1 and B16-F10 cells such as cellular rounding. Cell growth was also inhibited by tunicamycin. These effects were reversible, and B16 cells recovered their normal morphologies and growth rates within 24 hr after removal of the drug. Exposed cell surface protein analyzed by lactoperoxidase-catalyzed 125I iodination-sodium dodecyl sulfate-polyacrylamide gel electrophoresis-autoradiography showed few changes after tunicamycin treatment; however, sialogalactoproteins (detected by the binding of 125I-labeled R. communis agglutinin I to polyacrylamide gels containing desialized B16 cell surface components) were reduced dramatically by the drug. The adhesive properties of untreated and tunicamycin-treated B16 cells were assessed by the binding of 51Cr-labeled B16 cells to endothelial cell monolayers. Tunicamycin-treated B16-F1 and B16-F10 cells adhered at lower rates to endothelial cells such that after 24 to 36 hr of drug (0.5 micrograms/ml) treatment adhesion was almost completely blocked, suggesting that tunicamycin-induced cell surface glycoprotein changes in B16 melanoma cells may interfere with tumor cell-host cell interactions that lead to arrest and survival of blood-borne malignant cells.

Structure of carbohydrate unit A or porcine thyroglobulin

The unit A-type glycopeptides were purified from porcine thyroglobulin by Pronase digestion followed by chromatography on a DEAE-Sephadex A-25 column. These glycopeptides were separated into five fractions (UA-I, -II, -IV and -V) by Dowex 50W (X2) column chromatography. Fractions UA-I, -II, -III, -IV and -V were found to have the compositions (Man)9(GlcNAc)2-Asn, (Man)8(GlcNAc)2-Asn, (Man)7(GlcNAc)2-Asn, (Man)6(GlcNAc)2-Asn and (Man)5(GlcNAc)2-Asn respectively. The structures of these five fractions were investigated by the combination of exo- and endo-glycosidase digestions, methylation analysis. Smith periodate degradation and acetolysis. The results showed that fraction UA-V had the simplest structure: see formula in text. The larger glycopeptides (fractions UA-I, -II, -III and -IV) contained additional mannose residues alpha (1 leads to 2)-linked to the terminal mannose residues in the above core structure. These unit A-type glycopeptides appear to be biosynthetic intermediates that are to be processed to form complex-type glycopeptides (unit B-type sugar chains).

The structure of carbohydrate unit B of porcine thyroglobulin

The oligosaccharide fraction was obtained from porcine thyroglobulin by hydrazinolysis. Four fractions of unit B-type oligosaccharides were purified by successive chromatographies on columns of DEAE-cellulose and concanavalin A-Sepharose, and their structures were investigated by the combination of endo- and exo-glycosidase digestions, methylation analysis and Smith degradation. From the results of these studies, the structures of the unit B oligosaccharides were proposed to be as follows: see formula in text. Thus the glycoprotein was found to have triantennary and biantennary complex-type oligosaccharides as acidic sugar chains. Concerning the triantennary oligosaccharides, the following structural features were shown: (1) the sialic acid residues were not localized on certain specific branches but distributed on all three branches; (2) however, alpha (2 leads to 3)-linked sialic acid residues were exclusively located on the terminal of the branch arising from C-4 of the branching alpha-mannose residue, whereas alpha (2 leads to 6)-linked sialic acid residues occupied terminals of the other branches; (3) the outer branching alpha-mannose residue was attached to C-3 or C-6 of an inner branching beta-linked mannose residue, and both types were observed to exist.

Structure of a complex-type sugar chain of human glycophorin A

Tryptic glycopeptide T1 of human glycophorin A [Tomita, M., & Marchesi, V. T. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 2964-2968] was subjected to hydrazinolysis. After N-acetylation, the complex-type oligosaccharides were isolated by gel filtration. The major neutral oligosaccharide (2000 molecular weight) was purified by a combination of ion-exchange and gel-permeation chromatography. Treatments with endo- and exo-glycosidases, periodate oxidation, and methylation analysis indicated that the major neutral oligosaccharide has the following structure: Gal beta 1 leads to -4GlcNAc beta 1 leads to 2Man alpha 1 leads to 6(GlcNAc beta 1 leads to 4)(Gal beta 1 leads to -4GlcNAc beta 1 leads to 2Man alpha 1 leads to 3)Man beta 1 leads to 4GlcNAc beta 1 leads to 4-(Fuc alpha 1 leads to 6)GlcNAc. This oligosaccharide was retained by Ricinus communis agglutinin-Sepharose and retarded by Sepharose 4B coupled with erythroagglutinating E4 isolectin from Phaseolus vulgaris. Retention by concanavalin A-Sepharose was observed only after treatment of the oligosaccharide with beta-galactosidase.

Mechanism of the concanavalin A-induced change of membrane fluidity of chicken erythrocytes

When chicken erythrocytes labeled with a stearic acid derivative spin label was treated with concanavalin A (Con A), ESR spectra showed a change in the peaks due to the labels in membrane lipids, indicating an increase of membrane lipid fluidity. Addition of Con A increased the fluidity rapidly. This change was reversible only up to 30 min after adding Con A, and thereafter it gradually became irreversible. However, if the erythrocytes were treated with cytochalasin B and methyl alpha-D-mannoside, a complete return of fluidity to the normal level could be observed at any stage after the binding of Con A. The observation of freeze-fracture replicas of erythrocyte membranes by transmission electron microscopy also showed that the redistribution of intramembranous particles gradually became irreversible after exposure to Con A. These results suggest that the microfilament-like system, which modulates the distribution of cell surface receptors for Con A, participates in the modulation of membrane fluidity. Phospholipid methylation of chicken erythrocyte membrane was stimulated immediately after the binding of Con A. A methyltransferase inhibitor, 5'-deoxy-5'-S-isobutyl adenosine, abolished the increase of membrane fluidity within the first 10 min and also that occurring later than 60 min after adding Con A, but it was without effect on the elevated fluidity found between 20 and 60 min. Removal of extracellular Ca2+ had an inhibitory effect on the lasting increase of fluidity. These results suggest that the first increase of membrane fluidity by Con A may be caused by phospholipid methylation, while the second increase may depend on the rearrangement of Con A receptor glycoproteins through cross-linking wit Con A. The irreversible part of the membrane fluidity increase probably depends on Ca2+ influx, phospholipid methylation, and peripheral membrane proteins which constitute the microfilament-like system at the membrane inner surface.

The role of glycoconjugates in metastatic melanoma blood-borne arrest and cell surface properties

The role of glycoconjugates in cell surface and blood-borne implantation properties of murine metastatic melanoma sublines of low (B16-F1) or high (B16-F10) potential to colonize lungs was investigated by treating melanoma cells with the antibiotic tunicamycin. This drug prevents glycosylation of glycoproteins by inhibiting the formation of lipid-linked oligosaccharide precursors. The degree of tunicamycin-mediated modifications in glycoproteins was assessed by monitoring the decrease in cell surface sialogalactoproteins by binding of 125I-labeled Ricinus communis agglutinin I. Scanning electron microscopy of tunicamycin-treated B16-F1 and B16-F10 cells showed morphologic changes such as cell rounding and formation of numerous surface blebs. Tunicamycin-treated B16-F1 and B16-F10 cells lost their lung colonization abilities when injected intravenously into C57BL/6 mice, concomitant with lowered rates of adhesion to endothelial cell monolayers, endothelial extracellular matrix (basal lamina), and polyvinyl-immobilized fibronectin in vitro, suggesting that this drug inhibits experimental metastasis by modifying the surface glycoproteins involved in determining the adhesive properties of malignant cells.

The carbohydrate moiety of band-3 glycoprotein of human erythrocyte membranes

Band-3 glycoprotein was purified from human blood-group-A erythrocyte membranes by selective solubilization and gel chromatography on Sepharose 6B in the presence of sodium dodecyl sulphate. The purified glycoprotein was subjected to hydrazinolysis in order to release the carbohydrate moiety. The released oligosaccharides were N-acetylated and applied to a column of DEAE-cellulose. Most of the band-3 oligosaccharides obtained were found to be free of sialic acids. When this neutral fraction was subjected to gel chromatography on a column of Sephadex G-50, two broad peaks were observed indicating that the band-3 glycoprotein was heterogeneous in the size of the oligosaccharide moieties. All fractions from gel chromatography were found to contain galactose, mannose, N-acetylglucosamine and fucose. The higher-molecular-weight (mol.wt. 3000-8000) peak consisted of fucose, mannose, galactose, N-acetylglucosamine and N-acetylgalactosamine in a molar proportion of 1.6:3.0:8.4:10.5:0.2. Most of these oligosaccharides were digested with a mixture of beta-galactosidase and beta-N-acetylhexosaminidase after alpha-L-fucosidase treatment to give a small oligosaccharide with the structure alpha Man2-beta Man-beta GlcNAc-GlcNAc. Methylation studies and limited degradation by nitrous acid deamination showed that the oligosaccharides contained the repeating disaccharide Gal beta 1----4GlcNAc beta 1----3, with branching points at C-6 of some of the galactose residues. These results indicate that a major portion of the band-3 oligosaccharide has a common core structure, with heterogeneity in the numbers of the repeating disaccharides, and contains fucose residues both in the peripheral portion and in the core portion. Haemagglutination tests were also carried out to determine the blood-group specificities of the glycoprotein and the results demonstrated the presence of both blood-group-H and I antigenic activities.

Concanavalin A-induced increase in the membrane fluidity of chicken erythrocytes

To determine the fluidity of the membrane lipid phase, chicken erythrocytes were labeled with a stearic acid derivative spin label. When chicken erythrocytes were treated with concanavalin A (Con A), ESR spectra showed a change in the peaks of the labels in membrane lipids, indicating an increase of membrane fluidity. The degree of the increase in fluidity of the membrane lipid phase depended on the valency of the lectin used. Tetravalent Con A induced an increase of membrane fluidity at a concentration as low as 30 micrograms/ml, while a monovalent derivative of Con A did not affect membrane fluidity. This increase in membrane fluidity was observed within 10 min after the addition of Con A. If bound Con A was removed with methyl alpha-D-mannoside later than 60 min after its addition, a complete return of the fluidity to the normal level could not be observed. However, no change was found in the composition of phospholipids or in the fatty acid compositions of phosphatidylcholine and phosphatidylethanolamine of chicken erythrocytes after the addition of Con A, indicating that this increase in membrane fluidity is not caused by a change of lipid composition. The clustering of membrane receptors of chicken erythrocytes for Con A was demonstrated when the two-dimensional distribution of ferritin-conjugated Con A on the membranes was assayed by transmission electron microscopy. Furthermore, it was shown that major receptors for Con A of chicken erythrocytes were transmembrane glycoproteins having apparent molecular weights of 100K, 45, and 33K.

The association between major sialoglycoprotein and spectrin of human erythrocyte membranes as detected by fluorescence resonance energy transfer

The interactions among the major sialoglycoprotein and peripheral proteins of human erythrocyte membranes were investigated by the long range resonance energy transfer between different fluorescent moieties separately conjugated to proteins. Consequently, direct association between the major sialoglycoprotein and spectrin was observed and divalent cations were required for their association.

Distribution of ferritin-conjugated lectins on sialidase-treated membranes of human erythrocytes

The labeling of sialidase-treated, human erythrocyte membranes with ferritin-conjugates of four plant lectins, concanavalin A, Ricinus communis hemagglutinin, Bauhinia purpurea hemagglutinin and Arachis hypogoea hemagglutinin, is reported. Among these ferritin-conjugated lectins, ferritin-conjugated concanavalin A and ferritin-conjugated R. communis hemagglutinin were found in clusters on the sialidase-treated membranes, whereas ferritin-conjugated B. purpurea hemagglutinin and ferritin-conjugated A. hypogoea hemagglutinin were found in a random distribution on the membranes. Furthermore, when the membranes were labeled with a mixutre of concanavalin A and ferritin-conjugated B. purpurea hemagglutinin, ferritin particles were found in clusters, indicating that the membrane receptors for B. purpurea hemagglutinin were forced to more together with those for concanavalin A. A method for the quantitative estimation of the clustering of ferritin particles on the membranes was also devised and applied to the labeling of sialidase-treated, human erythrocyte membranes with the above four ferritin-conjugated lectins.

Purification and characterization of a hemagglutinin from Arachis hypogeae

A. hypogaea hemagglutinin was purified by ammonium sulfate fractionation and Sepharose 6 B column chromatography. The homogeneity of the purified hemagglutinin was ascertained by ultracentrifugal analysis and polyacrylamide gel electrophoresis. It has a molecular weight of 106.500 and is a tetramer of a subunit with a molecular weight of 27.000. The purified hemagglutinin agglutinated neuraminidase-treated human erythrocytes regardless of their ABO group type, but did not agglutinate intact erythrocytes. In hapten inhibition assays with simple sugars, the so-called Mäkelä's group 2 sugars, which bear the same configuration of hydroxy groups at C-3 and C-4 as D-galactopyranose, were inhibitors for this hemagglutinin. It does not contain any carbohydrate, in contrast to most phytohemagglutinins except concanavalin A and wheat germ agglutinin.

Immunochemical and chemical investigations of the structure of glycoprotein fragments obtained from epiglycanin, a glycoprotein at the surface of the TA3-Ha cancer cell

The structures of the carbohydrate chains present in fragments of a large-molecular-weight glycoprotein, epiglycanin, cleaved from the surface of viable TA3-Ha murine mammary carcinoma ascites cells and purified by gel filtration, were studied by immunochemical and chemical methods. Inhibitory activities for neuraminidase-treated and untreated glycoprotein material in the hemagglutination of NN-specific human erythrocytes by eight purified lectins were determined. Excellent inhibition was obtained in the Bauhinia purpurea, Arachis hypogaea, Iberis amara, and Wistaria floribunda systems, and weak inhibition against the Ricinus communis and Glycine max lectins. No activity against hemagglutination by the Phaseolus vulgaris and Phaseolus limensis lectins was observed. These results, when compared with those obtained by periodate oxidation, alkaline borohydride reduction, and partial methylation, suggest the possible presence of six different carbohydrate chains of 1 to 5 components in length, having as terminal groups N-acetylneuraminic acid, galactose, and 2-acetamido-2-deoxygalactose. All chains are attached to a single polypeptide chain by O-glycosyl bonds involving a 2-acetamido-2-deoxygalactose residue and a serine or threonine residue. It is suggested that the native molecule of epiglycanin of molecular weight 500,000 contains more than 500 carbohydrate chains attached to a single polypeptide chain of similar to 1,300 amino acid units.

Carbohydrate-binding specificity of the so-called galactose-specific phytohemagglutinins

The carbohydrate-binding specificities of various so-called galactose-specific phytohemagglutinins were investigated by means of hemagglutination-inhibition assays. As hapten inhibitors, glycopeptides prepared by pronase-digestion of various glycoproteins (porcine submaxillary mucin, bovine submaxillary mucin, and porcine thyroglobulin), and several glycosides of D-galactose and 2-acetamido-2-deoxy-D-galactose were employed. The results indicate that these galactose-specific phytohemagglutinins may recognize the sugar residue penultimate to D-galactose or 2-acetamido-2-deoxy-D-galactose residues of the sugar chain with which they interact, and that they can be classified into three groups based on the type of sugar sequence which they primarily recognize.