Contribution of alpha-D-galactopyranosyl end groups to attachment of highly and low metastatic murine fibrosarcoma cells to various substrates

Cell surface laminin-like substances and laminin-related carbohydrates of rat ascites hepatoma AH7974 and its variants with different lung-colonizing potential

Rat ascites hepatoma AH7974 cells strongly expressed antilaminin antibody-reactive substances (laminin-like substances) and Griffonia simplicifolia isolectin B4 (GS)-reactive carbohydrate (alpha-D-galactose; alpha-Gal) on their cell surface. The alpha-Gal expression was not apparently influenced by the pretreatment of cells with methanol. The cell membrane laminin-like substances has approximate molecular weights of 150, 62 and 56 kDa in denaturating reducing conditions, of which the 62 and 56 kDa bands were stained with GS. The cell membrane molecules bearing alpha-Gal were 62 and 56 kDa and were stained with antilaminin antibody. Therefore, the major molecules bearing alpha-Gal residues of AH7974 cell membrane are considered to be laminin-like substances. To determine the role of the substances in metastasis, we selected four cell lines (74AD, 74AD-f, 74FL, 74FL-a) from AH7974 in culture. 74AD and 74FL-a are adherent lines and 74AD-f and 74FL are floating lines. All of these cell lines strongly expressed laminin-like substances, but a marked difference was found in expression of alpha-Gal, which was most strongly expressed by 74FL, followed by 74AD, and rarely by 74AD-f and 74FL-a; the staining intensity was positively correlated with their experimental lung-colonizing potential. Cell membrane laminin-like substances were 200, 97, 62, 56 and 46 kDa and among them 62 and 56 kDa molecules were glycosylated with alpha-Gal. The pretreatment of 74FL cells with antilaminin antibody or with human type A serum (containing natural antibody to alpha-Gal epitope) depressed remarkably the lung-colonizing potential of the cells. These results suggest that the expression of 62 and 56 kDa laminin-like substances with alpha-Gal residues on tumor cell surfaces is one of the determinants associated with lung-colonizing potential of these cells.

alpha-D-galactose-bearing glycoproteins on the surface of stimulated murine peritoneal macrophages. Biochemical and immunochemical characterization of purified glycoproteins

Two glycoproteins were isolated from lysates of thioglycollate-stimulated, murine peritoneal macrophages by affinity chromatography on immobilized Griffonia simplicifolia I lectin and by preparative SDS/PAGE. The glycoproteins were readily labeled on the surface of intact macrophages with 3H and 125I. The labeled glycoproteins migrated as broad bands of molecular mass 92-109 kDa and 115-125 kDa. The mobility of the glycoproteins decreased only slightly after reduction with dithiothreitol, indicating the absence of intersubunit disulfide bridges. The 92-kDa and 115-kDa glycoproteins had pI 5.2-5.4 and pI less than or equal to 4, respectively. Digestion of both glycoproteins with alpha-galactosidase released 23% of their 3H content and abolished their ability to bind to the G. simplicifolia I lectin, showing that they contain terminal alpha-D-galactosyl groups. After reduction with 2-mercaptoethanol, each glycoprotein fraction was sensitive to N-glycanase; the 115-kDa glycoproteins produced a smear with the front at approximately 67 kDa, whereas the 92-kDa glycoprotein gave two bands of 61 kDa and 75 kDa. Unreduced glycoproteins were insensitive to N-glycanase, suggesting the presence of intramolecular disulfide bonds. Although each glycoprotein fraction was sensitive to endoglycosidase H, this enzyme produced only slight changes in molecular mass when compared with N-glycanase. From these results as well as from the specificity of the enzymes involved, it is concluded that each glycoprotein fraction contains complex-type oligosaccharides and a small amount of high-mannose and/or hybrid-type oligosaccharides. While each glycoprotein fraction was bound to Datura stramonium lectin, they failed to react with anti-[i-(Den)] serum and their digestion with endo-beta-galactosidase did not cause a band shift in SDS/PAGE. Taken together, these results suggest the presence of N-acetyllactosamine units which are not arrayed in linear form but occur as single units, bound either to C2 and C6, or to C2 and C4, or both, of outer mannosyl residues on complex-type oligosaccharides. The glycoprotein(s) fraction precipitated with anti-[I (Step)] serum, suggesting the presence of branched lactosaminoglycans. Digestion of both glycoprotein fractions with a mixture of sialidase and O-glycanase did not alter their mobility in SDS/PAGE, suggesting a lack or low content of O-linked trisaccharides and tetrasaccharides. Each glycoprotein fraction was bound specifically to Sambucus nigra and Maackia amurensis immobilized lectins, indicating the presence of sialic acid linked alpha 2,6 to subterminal D-galactose or N-acetylgalactosamine residues, and alpha 2,3 to N-acetyllactosamine residues, respectively.

The blood group antigens (BGA)-related glycoepitopes. A key structural determinant in immunogenesis and cancer pathogenesis

This overview has been focused on the functional and pathophysiological aspects of blood group antigens (BGA)-related glycodeterminants. 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 during embryogenesis, organogenesis, tissue repair, regeneration, remodeling and maturation when 'sorting-out' behaviour of one homotypic cell population from heterotypic assemblage of cells occurs. In this event the BGA-related glycoepitopes, if being expressed on the cell surface, play a role of key structural determinants in cell-cell recognition, association and aggregation. This mechanisms has been discussed in relation to immunogenesis regarding of antigen presentation, self-non-self discrimination, positive and negative selection during thymic education. It is postulated that the appearance of the BGA-related glycoepitopes on the cell membrane is a consequence of the association of MHC and peptides, with subsequent elimination of cells carring high density of BGA-related glycoepitopes on their surface. In cancer it has been considered as a key mechanism of phenotypic divergence of tumor cells, immunoselection, tumor progression and metastasis.

Differential expression of glycoproteins containing alpha-D-galactosyl groups on normal human breast epithelial cells and MCF-7 human breast carcinoma cells

Cell surface glycoproteins were isolated from the lysates of 125I-labeled normal human mammary epithelial cells (NHMEC) and from the human breast carcinoma cell line MCF-7, of blood-group O phenotype, by affinity chromatography on Griffonia simplicifolia I lectin-Sepharose. Specific elution of glycoproteins from the column with methyl alpha-D-galactoside suggests the presence of alpha-D-galactosyl groups on these moieties. SDS-PAGE analysis of isolated glycoproteins revealed both quantitative and qualitative differences between glycoproteins from normal and malignant cells. Three major glycoproteins of Mr 180 kDa, 85 kDa and the 44 kDa were obtained from MCF-7 cells. The 180-kDa glycoprotein was absent in NHMEC and the 44-kDa glycoprotein was very weakly expressed in these cells. The only glycoprotein which was found in almost equal amount in the lysate from both normal and malignant cells was the 85-kDa glycoprotein. These results indicate differences between normal human mammary epithelial cells and one kind of malignant human mammary epithelial cells, in the expression of glycoproteins containing alpha-D-galactosyl groups, irrespective of blood-group phenotype; they also demonstrate that alpha-D-galactosyl group are expressed in a very restrictive manner on the surface of this tumor cell line.

Attachment of tumor cells to endothelial monolayers: detection of surface molecules involved in cell-cell binding

Trypsinization of P815 mastocytoma cells interferes with their ability to bind to endothelial monolayers in vitro, suggesting the involvement of proteins in cell-cell binding. Binding is also dependent upon divalent cations. Incubation of tumor cells with tunicamycin, which blocks protein glycosylation, or the monosaccharide N-acetyl-D-glucosamine could also inhibit binding. In addition, antibodies prepared against whole P815 cells had the ability to interfere with tumor cell binding. The protein fragments released from P815 cells by trypsin interfered with the binding of fresh P815 cells to endothelium. Moreover, those fragments as well as CHAPS extracts of tumor cell membranes were able to neutralize the inhibitory effect of an anti-P815 antibody on tumor cell-endothelial cell binding. These observations, taken together, strongly suggest the presence of adhesion molecules on the tumor cell. The anti-P815 antibody preparation could also inhibit endothelial binding of an unrelated tumor. Ehrlich ascites (EA). In addition, membrane preparations of EA could neutralize the antibody's effect on intact P815, and membrane preparations of P815 could neutralize the antibody's effect on EA. These observations suggest that there are common epitopes on these tumor cells and raise the possibility that a variety of tumors may share common mechanisms for attachment to endothelium. This, in turn, raises the possibility that monospecific antibodies against such epitopes might be useful agents for interfering with metastasis in vivo.

Influence of the carbohydrate moiety on the growth inhibitory activity and adhesiveness of 3T3 cell plasma membranes

Treatment of 3T3 cell plasma membranes with glycosidase enzymes decreased their ability to inhibit cell growth and also decreased their binding to 3T3 cells. This suggests that carbohydrate is required for complete function of inhibitory activity and that inhibition is associated with membrane adhesion.

Malignant cell glycoproteins and glycolipids

The cell surface is involved in cell growth and division, cell-cell interaction, communication, differentiation and migration, and other processes likely to be involved in malignant transformation and/or the metastatic spread of cancer. Although there are many alterations of glycoproteins and glycolipids on the malignant cell surface, it is unclear whether these alterations are epiphenomena or an integral part of the malignancy process. This article reviews the recent literature and some earlier studies relevant for understanding emerging concepts and trends with respect to malignant cell glycoconjugates. Emphasis is on structural alterations of the carbohydrate portions of malignant cell glycoproteins and glycolipids and on the enzymes (glycosyltransferases and glycosidases) involved in their metabolism. Practical applications derived from malignant cell glycoconjugate studies are discussed briefly with respect to the diagnosis, staging, monitoring, and treatment of malignant disease. The review concludes by indicating which research areas on malignant cell glycoconjugates are likely to be fruitful in increasing our basic understanding of, and ability to deal effectively with, malignant disease.

Marker polypeptide differences between spontaneous strongly and weakly metastatic cancer cells identified by 2-dimensional gel electrophoresis

A recent 2-dimensional gel electrophoresis study revealed several polypeptide differences between a strongly metastatic and a weakly metastatic clone from a single chemically induced murine fibrosarcoma (Jellum et al., 1984). To exclude the possibility that this was merely coincidental, the study is extended here to 2 other fibrosarcomas recently and similarly induced in mice of the same inbred strain. Metastatic potential was defined by the number of lung metastases spontaneously formed from a transplanted primary footpad tumor. One strongly (or moderately) metastatic cell line and I weakly metastatic line from each of the 3 fibrosarcomas were examined in the same experiments. In confirmation of our previous results, the same polypeptides consistently occurred in considerably greater amounts in the weakly metastatic than in the strongly metastatic cells. One of these marker polypeptides was absent from the strongly metastatic cell lines. In comparison with 2 of the 3 most metastatic lines, the third line was only moderately metastatic, and differed least strongly from the 3 weakly metastatic cell lines with regard to expression of th marker polypeptides. Marker polypeptide expression showed no consistent correlation with tumorigenicity. No other consistent polypeptide differences between strongly metastatic and weakly metastatic cells could be identified among the approximately 2,000 cellular polypeptides separated on the gels.

Glycoprotein modifications of sarcoma L-1 tumor cells by tunicamycin, swainsonine, bromoconduritol or 1-desoxynojirimycin treatment inhibits their metastatic lung colonization in Balb/c-mice

Synthesis and expression of cell surface carbohydrates appear to be involved in recognition events associated with tumor invasion and metastasis. Thus, the potential of murine sarcoma L-1 cells to form experimental lung metastases after i.v. injection was assessed after inhibiting tumor cell protein glycosylation with tunicamycin, swainsonine, bromoconduritol, or 1-desoxynojirimycin. Incubation of sarcoma L-1 cells with 0.5 microgram (or above) of these substances/ml medium for 20-24 h significantly inhibited lung colonization. Cytotoxic side effects or additional organ manifestations could not be found. Gas liquid chromatographic examinations of carbohydrates from treated L-1 cells indicated that sugar synthesis was evidently inhibited. These results suggest that specific glycan structures on tumor cells are required for expression of the metastatic phenotype.

Thromboplastin release, but not content, correlates with spontaneous metastasis of cancer cells

No previous studies on the possible contribution of cancer-cell procoagulants to metastasis have fulfilled all the criteria for attaining biologically relevant and readily interpretable data (Grimstad et al., 1986), viz: (1) Spontaneous metastasis from primary tumors should be assessed in syngeneic animals; (2) cloned cell lines should be used to correlate cell properties, because heterogeneity within the cell lines employed is a source of serious error; (3) enough clones, derived from the same original tumor, should be used to identify only nonrandom correlations. Observing these criteria, we examined the procoagulant activities of 19 murine fibrosarcoma cell clones and 4 uncloned cell lines with high to moderate or low potential for lung metastases formation. The procoagulant activity found was exclusively of the thromboplastin (tissue factor, factor III) type. It occurred in all cell homogenates, but the quantities did not correlate with metastatic potential. In contrast, all highly to moderately metastatic cell clones and lines from 2 different fibrosarcomas shed thromboplastin activity into the culture medium, whereas no weakly metastatic cells did. Histological examination further supported these indications that release of thromboplastin from cancer cells can promote metastasis by initiating blood clotting and thereby facilitating arrest of the cancer cells in target organ vessels. Examination of a third fibrosarcoma showed that release of thromboplastin activity is not necessary for metastasis in all tumors.

Molecular identification of lectin binding sites differentiating related low and high metastatic murine lymphomas

We have previously shown that differences in cell surface carbohydrates can be detected in related murine tumor lines of varying metastatic capacity using plant lectins such as soybean agglutinin (SBA) or Vicia villosa (VV) but not concanavalin A (ConA). Here we show that weakly metastatic Eb cells bind SBA via four glycoproteins and one GL2-like glycolipid. The major high-affinity SBA binding component of weakly metastatic ESb-MP cells was a glycoprotein of 210-220 kd. Highly metastatic ESb cells also expressed this protein but the oligosaccharide side chains were altered in such a way that SBA-binding was completely lost while ConA and peanut agglutinin (PNA) binding remained similar. Quantitative binding studies using iodinated lectins indicated that SBA binding of ESb cells could only be detected at lectin concentrations greater than 75 micrograms/ml. The role of altered carbohydrates in metastasis is discussed.

The application of lectins to the characterization and isolation of mammalian cell populations

Mammalian cells invariably contain a vast array of glycosylated moieties, both inside the cell and on the cell surface. There is an increasing awareness of the utility of these carbohydrates in delineating the phenotype or function of many populations of cells. To this end lectins are extremely useful reagents. Lectins are carbohydrate-binding proteins and glycoproteins of non-immune origin derived from numerous plants and animals. A wide variety of lectins with many distinct carbohydrate specificities have been isolated. Historically the most common laboratory techniques utilizing lectins have been agglutination, mitogen stimulation, and fluorescence techniques. Recent advances in the development and conjugation procedure for labels and matrices have led to the creation of numerous novel lectin-based assays. Lectins are currently used not only to identify cells with specified carbohydrate groups, but also to quantitate the carbohydrate groups or to isolate the carbohydrate-bearing cells or structures.

Structural basis for altered soybean agglutinin lectin binding between a murine metastatic lymphoma and an adhesive low malignant variant

By selection for plastic adhesiveness we have previously established a variant tumor line (ESb-MP) from the metastatic murine lymphoma ESb. In contrast to the parental line, the adhesion variant is significantly decreased in malignancy and is altered in the capacity to bind soybean agglutinin (SBA) lectin. Here we show biochemically that the major SBA-binding cell-surface component of ESb-MP cells is the T200 glycoprotein. In ESb cells, T200 antigens bind SBA only after sialidase treatment. Enzymatic studies suggested that glycans detected by the lectin with or without sialidase treatment are different. Inhibition of N-glycosylation by tunicamycin and biosynthetic labeling revealed two T200 chains for ESb-MP cells that were larger in size than the single chain detected in ESb cells. Studies on the biosynthesis revealed that ESb-MP cells expressed two precursor chains for T200 whereas ESb cells displayed only one. There was no size difference detectable in the mature T200 molecules of ESb and ESb-MP cells. Our data suggest that the molecules differ in expression of O-linked glycans that can be recognized by SBA. Additional O-linked sugars on ESb-MP T200 molecules seem to be expressed in particular after trimming of the second T200 precursor chain.

Endogenous galactoside-binding lectins: a new class of functional tumor cell surface molecules related to metastasis

The formation of secondary tumors by circulating cancer cells (blood-borne metastasis) correlates with an increased tendency of the cells to form emboli by aggregation with other tumor cells or with host cells. Although it is evident that cell-cell recognition and adhesion are mediated by cell surface components, the identity of these molecules is only now being unraveled. Over the last decade an increasing number of studies have demonstrated the presence of endogenous carbohydrate-binding proteins on the surface of various normal cells, and it has been proposed that such lectin-like molecules might be involved in intercellular adhesion. We have shown that various tumor cell lines contain endogenous galactose-specific lectins. Lectin activity was detected at the cell surface by the binding of asialofetuin. This glycoprotein also enhanced the aggregation of the tumor cells. After purification by affinity chromatography on immobilized asialofetuin the lectin activity was associated with two proteins of Mr 14,500 and 34,000. By using polyclonal and monoclonal antilectin antibodies in conjunction with various immunologic techniques we have demonstrated that the endogenous lectins are present on the surface of different tumor cells. Quantitation of cell surface lectins by flow cytometric analyses of antilectin antibody binding revealed that among related tumor cells those exhibiting a higher metastatic potential expressed more lectin on their surface. The binding of monoclonal antilectin antibodies to metastatic cells decreased asialofetuin-induced homotypic aggregation in vitro and suppressed the ability of the cells to form lung metastases after intravenous injection in the tail vein of syngeneic mice. These results strongly implicate the tumor cell surface lectins in cell adhesion and metastasis. We propose that such lectins can increase the ability of tumor cells that enter the blood stream to form aggregates with other tumor cells, or to adhere to host cells or the extracellular matrix and thereby increase their metastatic potential. Other contributing components to tumor cell-host cell interactions are cell surface carbohydrate-binding proteins that have been detected on lymphocytes, platelets, macrophages, hepatocytes, and endothelial cells. These lectin-like molecules might recognize and bind carbohydrates expressed on the surface of tumor cells and enhance emboli formation and organ colonization.

Cell-surface laminin-like molecules and alpha-D-galactopyranosyl end-groups of cloned strongly and weakly metastatic murine fibrosarcoma cells

Indications from previous work that cancer cell-surface laminin-like molecules and alpha-D-galactopyranosyl end-groups may contribute to spontaneous metastasis were further investigated. Both moieties are known to mediate cell attachment to various foreign surfaces. Five strongly metastatic and 5 weakly metastatic cell clones from a murine fibrosarcoma were examined for the occurrence of both cell-surface moieties by immunofluorescence flow cytometry and microscopy. None of these clones was rich in laminin-like molecules, which were least strongly expressed by the highly metastatic clones. The alpha-D-galactopyranosyl end-groups were strongly expressed by all strongly metastatic clones and by 2 weakly metastatic clones, but were only weakly expressed by the other weakly metastatic clones. These results indicate that the laminin-like cell-surface molecules are not necessary for spontaneous metastasis formation. However, the alpha-D-galactopyranosyl end-groups may be necessary, but are not sufficient for the cancer cells to form metastases. These carbohydrates are known to occur on the laminin-like molecules. The present results show that they must also exist on other cell-surface molecules.

The role of tumor-cell surface carbohydrate in experimental metastasis

Quantitative studies on the binding of concanavalin A (Con A) and wheat-germ agglutinin (WGA) to a series of rat hepatocarcinoma metastatic variants revealed a positive correlation between the amount of cell-surface-bound lectin and lung colonization potential. Scatchard analysis of Con A and WGA binding to 10 individual clones isolated from a subcutaneous (s.c.) tumor transplant and to tumor-cell isolates from 10 individual spontaneous lung metastases from the same animal showed diverse binding characteristics for these cell populations. Nevertheless, the expression of Con A receptor sites accurately predicted the lung colonization potential of 3 isolates from the lung metastases. Higher lectin binding curves were observed for the clones from the subcutaneous tumor than for the isolates from lung metastases. These data suggest that a high Con-A binding potential is indicative of a high lung colonization potential for these hepatocarcinoma cells, but that this phenotype may be rapidly lost during tumor outgrowth in the lungs. The binding of tumor cells to vascular endothelial cell monolayers was inhibited in the presence of Con A; however, no inhibition was observed with 2 other lectins. Attachment of tumor cells to endothelial cell monolayers was also inhibited by the monosaccharides methyl alpha-D-mannopyranoside and N-acetyl-D-galactosamine. Other monosaccharides tested did not alter the attachment of tumor cells to endothelial cell monolayers.

Oligosaccharide modification by swainsonine treatment inhibits pulmonary colonization by B16-F10 murine melanoma cells

Oligosaccharide moieties of cell-surface glycoconjugates are thought to be involved in recognition events associated with tumor metastasis and invasion. Using swainsonine (SW), an inhibitor of Golgi alpha-mannosidase II that results in the formation of hybrid-type oligosaccharides on N-linked glycoproteins, we have tested the hypothesis that specific glycan structures are required for pulmonary colonization by tumor cells. B16-F10 murine melanoma cells were treated with SW in growth medium and then injected intravenously into syngeneic C57BL/6 mice. This treatment resulted in dramatic inhibition of colonization, but it had no effect on B16-F10 viability or on cellular tumorigenicity after subcutaneous implantation. SW-treated radiolabeled B16-F10 cells were cleared from the lungs at a greater rate than control cells, suggesting that one effect of treatment is to alter tumor cell retention in the target organ. Our results implicate specific glycan structures in pulmonary colonization and offer a potential approach for identification of specific macromolecules involved in tumor cell-organ recognition during metastasis.