Surface glycoproteins and concanavalin-A-mediated agglutinability of clonal variants and tumour cells derived from SV40-virus-transformed mouse 3T3 cells

Structural differences between complex-type Asn-linked glycan chains of glycoproteins in rat hepatocytes and Zajdela hepatoma cells

Using serial lectin-affinity chromatography, glycosidase digestion, and NMR and methylation analysis, the structures of complex N-linked glycan chains (M(r) range 2000-3500) of rat hepatocytes and poorly differentiated chemically transformed Zajdela ascites hepatoma cells were determined and compared. The results revealed considerable differences between the two cell types: (i) hepatoma cells only expressed tri- and/or tetra-antennary complex N-linked glycan chains, whereas hepatocytes displayed large amounts of bi-antennary N-linked structures and smaller amounts of tri-/tetra-antennary structures; (ii) 20% of the glycan chains in hepatoma cells contained a bisecting GlcNAc residue which was beta (1,4)-linked to the beta-mannosyl residue of the core and was not detected in the hepatocytes; (iii) hepatoma cells expressed a high proportion of the fucosylated or not GlNAc beta (1,6) Man alpha 1-->branch, whereas hepatocytes only contained a little of this branch; (iv) hepatoma cells, but not hepatocytes, exhibited a repeating (Gal beta(1,4) GlcNAc beta (1,3)) sequence characteristic of poly-N-acetyllactosaminoglycans. These glycans were capped by both alpha-galactosyl and sialyl residues; (v) The alpha (2,3)/alpha (2,6)-linkage ratio of sialic acid was significantly higher in hepatoma cells (4/1 vs. 2/1 in hepatocytes); (vi) Only hepatocytes expressed an unusual structure in which a sialyl residue was alpha (2,6)-linked to a GlcNAc residue located within a NeuAc alpha (2,3) Gal beta (1,3) GlcNAc branch which was beta (1,4)-linked to Man alpha 1,3-->. The differences between these complex N-linked glycan chains in hepatocytes and hepatoma cells seem to be both quantitative and qualitative, since some glycan structures were only present in one cell type.

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.

Structural changes induced in the sugar chains of glycoproteins by malignant transformation of producing cells and their clinical application

Altered glycosylation is widely observed in glycoproteins produced by tumors. One of the most consistently observed alterations is the increase of larger asparagine-linked sugar chains in the plasma membrane glycoproteins. This phenomenon is brought about by the increase of N-acetylglucosaminyltransferase V, which is responsible for the formation of the GlcNAc beta 1----6Man alpha-1----6 group. The enrichment of the complex-type sugar chains containing the -GlcNAc beta 1----6(-GlcNAc beta 1----2)Man alpha 1----6 group is correlated with tumorigenicity and metastasic potential of tumor cells. Comparative study of the sugar chains of human chorionic gonadotropin isolated from the urine of pregnant women and of patients with trophoblastic diseases including choriocarcinoma revealed that many new oligosaccharides are included in the tumor hCG. The altered glycosylation of hCG is brought about by the ectopic expression of N-acetylglucosaminyltransferase IV. With use of this altered glycosylation, a novel method useful for the diagnosis of choriocarcinoma was established.

Changes in surface glycopeptides after malignant transformation of rat liver cells and during the regression of hepatoma cells

Normal liver cells, Zajdela's hepatoma cells, and regressing hepatoma cells were metabolically labeled with either radioactive glucosamine or mannose. Glycopeptides obtained by exhaustive pronase digestion of these cells were compared after fractionation by gel filtration on Bio-Gel P-6. Chemical analysis, affinity chromatography on immobilized lectins, alkaline treatment, and susceptibility toward endo-beta-N-acetylglucosaminidase and tunicamycin revealed dramatic changes in the glycopeptide patterns of transformed cells during the recovery of normal phenotype. The most prominent feature was the presence on the surface of hepatoma cells of a large glycopeptide, which was absent from normal liver cells and disappeared almost completely during the regression of hepatoma cells. This large glycopeptide had a Mr of 70,000, contained essentially O-glycosidically linked glycan chains, and did not result from a hypersialylation. N-glycosidically linked glycopeptides, high-mannose, and complex-type oligosaccharides were present in distinct proportions according to the differentiation state. Transformation of liver cells led to a reduction of high-mannose type oligosaccharides and an increase in the degree of branching of complex-type oligosaccharides. In addition, "bisected" glycopeptides were present only on hepatoma cells. The pattern of N-linked glycopeptides of normal liver cells was recovered during the regression of hepatoma cells. The origin of glycopeptide differences between normal and transformed cells and the evidence of a relation between carbohydrate changes, in particular the appearance of a large glycopeptide, and tumorigenicity are discussed.

Transfection by human oncogenes: concomitant induction of tumorigenicity and tumor-associated membrane alterations

NIH 3T3 cells were transfected with DNA derived from human bladder carcinoma, colon carcinoma and HL60 promyelocytic leukemia cells. The transfectants were examined for the presence of human oncogenes in relation to tumorigenic potential and composition of surface-located fucosyl glycopeptides by gel filtration, Concanavalin-A-binding and high-performance liquid chromatography. All transfectants, harboring 3 different human cellular ras genes, appeared to be tumorigenic in nude mice and displayed characteristically altered glycopeptides. The surface glycopeptides were consistently changed to higher apparent molecular weight due to enrichment in higher-branched sialic-acid-containing glycopeptides. Similar alterations have been found previously in virally- and chemically-transformed cells in vitro and tumors raised in vivo, and were designated as cancer-related or tumor-associated glycopeptides. Revertants derived from HL60-DNA-induced transfectants, which had lost the transfected human N-ras oncogene, simultaneously lost their tumorigenic potential and expression of cancer-related membrane glycopeptides. In addition, spontaneous transformants, exhibiting morphology and growth patterns indistinguishable from those of tumor-DNA-induced transfectants, neither contained transferred human DNA sequences nor expressed cancer-related glycopeptides. Nevertheless these cells were capable, after prolonged latency periods, of inducing tumors in nude mice. Cells derived from such tumors constantly displayed cancer-related glycopeptides on their surface, suggesting selection of tumorigenic cells from spontaneous transformants during passage in nude mice. In one of these tumors at least, an endogenous mouse ras-gene appeared to be activated. The results indicate a close correlation between the presence of activated ras-oncogenes in the genome of the transfected cells, the tumorigenic potential of these cells and the expression of surface-located cancer-related glycopeptides. The data suggest that functions provided by human ras-oncogenes contribute to the alteration of membrane glycopeptides on tumor cells.

Cytoplasmic 3H-arginine polypeptides of Ehrlich ascites tumour cells

Low molecular weight ninhydrin positive peptide fractions of the Ehrlich tumour cell cytoplasm were isolated and characterized. After preliminary gel filtration of the cytoplasm on Sephadex G-25 column, the peptide mixture was fractionated on cationic exchanger SP-Sephadex C-25 column and eluted with increasing pH gradient. Five peaks were obtained. Only the first peak contained sugar component. All five peptides were studied with respect to molecular weight, isoelectric point and electrophoretic homogeneity. The cytoplasm of Ehrlich tumour cells contains one peptide of acidic (pI-5.0), two slightly basic (pI-7.7 and pI-7.7) and two strongly basic nature (pI-8.7 and pI-8.9). Molecular weights varied from 8 500 to 18 500 daltons. The origin of these peptides is briefly discussed.

Appearance of altered cell-surface fucosyl glycopeptides in concomitance with chromosomal alterations in the gross virus-infected pre-leukemic thymus of the rat

The appearance of a class of fast-eluting cell-surface glycopeptides that are encountered almost exclusively in malignant and certain pre-malignant cells was monitored in the course of leukemogenesis in the thymus of rats injected at birth with Gross leukemia virus. The altered glycopeptides appeared as early as 15 days after virus injection, when the animals were still clinically healthy and no histological signs of the disease were present in the thymus. Their amount was further increased at 30 days, and reached a maximum in the fully developed lymphoma. The development of this early phenotypic marker of malignancy appeared to be concomitant with that of chromosomal anomalies in the thymus. Since these anomalies are non-random, the existence of a causal relationship between the glycopeptide change and the loss of specific chromosomes might be hypothesized.

Transformation-specific cell killing by a cancer-associated galactosyltransferase acceptor and cellular binding

Cancer-associated galactosyltransferase acceptor (CAGA glycoprotein), a small glycoprotein purified from human malignant effusion that selectively kills transformed cells, was tritiated by reductive methylation in the presence of NaB(3)H(4). CAGA-glycoprotein-sensitive cells (baby-hamster kidney cells transformed by polyoma virus and chick-embryo fibroblasts infected with Ts68 temperature-sensitive mutant of Rous sarcoma virus grown at 37 degrees C, the permissive temperature) bound 3-5-fold more (3)H-labelled CAGA glycoprotein than did their CAGA-glycoprotein-resistant non-transformed counterparts. The Rous-sarcoma-virus-infected chick-embryo fibroblasts grown at non-permissive temperature (41 degrees C) bound an intermediate amount of (3)H-labelled CAGA glycoprotein; however, this intermediate amount appeared to be sufficient to induce inhibition of cell growth when the infected chick-embryo fibroblasts treated at 41 degrees C were switched to 37 degrees C. Binding of (3)H-labelled CAGA glycoprotein was time- and temperature-dependent and was not inhibited by monosaccharide. Binding was completely inhibited by the oligosaccharide liberated by endoglucosaminidase H treatment or by exhaustive Pronase digestion of intact CAGA glycoprotein. However, the isolated oligosaccharide failed to demonstrate the growth-inhibition characteristics of the intact glycopeptide. Binding of (3)H-labelled CAGA glycoprotein was unaffected by co-incubation with the peptide core released by endoglucosaminidase H treatment. (3)H-labelled CAGA glycoprotein bound to intact cells could be removed by trypsin treatment up to 4h after addition of the glycoprotein but not thereafter. This time course paralleled the decreasing reversibility of growth inhibition. However, all (3)H-labelled CAGA glycoprotein was found in the supernatant when cells were first disrupted by sonication followed by trypsin treatment for up to 12h. (3)H-labelled CAGA glycoprotein linked to Sepharose 4B failed to cause growth inhibition in CAGA-glycoprotein-sensitive cells. These findings suggest that binding of CAGA glycoprotein occurs via its oligosaccharide moiety. Binding appears to be a necessary but not sufficient condition to induce cell killing. Growth inhibition appears to depend on internalization of the glycoprotein and the presence of a transformation-specific cell process.

Products of cultured neuroglial cells. III. Release of an 85,000 molecular weight glycoprotein by C6 glioma cells in vitro

With [3H]fucose as a marker, C6 glioma cells in culture released an 85,000 molecular weight molecule into the medium as the major extracellular glycoprotein. The quantity and extracellular/cytoplasmic ratio of this glycoprotein suggest that its cellular processing is different from that of five other released glycoproteins of molecular weights 55,000, 115,000, 130,000, 150,000, and 170,000. Nearly 40% of newly synthesized glycoproteins in the cells was released into the culture medium. Major glycoproteins retained by the cells migrated electrophoretically to molecular weight positions of 82,000, 110,000, 120,000, 140,000, and 160,000, and approximately one-third of these returned glycoproteins were labile to trypsinization. Both synthesis and release of these macromolecules were inhibited more than 95% with cycloheximide treatment, demonstrating that nearly all fucosylation was linked to protein synthesis. Since 40% of all glycoproteins was released under conditions of more than 99% cellular viability, it is likely that these extracellular glycoproteins are physiological products of membrane turnover and secretion, but not of cell lysis. The results provide a basis for the further study of glial differentiation and of shed glioma antigens.

Transformation-dependent quantitative changes in glycopeptide binding to concanavalin A-sepharose

Differentially L-fucose-labelled glycopeptides from the surface of a Syrian golden hamster (SGH) fetal lung control cell line were compared with those from chemically-transformed and tumour cell lines derived from the control line by cochromatography on Concanavalin A-Sepharose (Con A-Sepharose) and Sephadex G-50. Quantitative differences were found both in the unbound and specifically-bound fractions between control and transformed cells upon Con A-Sepharose chromatography. In the glycopeptides from transformed and tumour cells, the unretarded fraction was concomitantly decreased compared to the controls. When the ratio of unbound to specifically-bound fractions was used, a statistically significant difference could be calculated between the values of control versus transformed or tumour cells. In all transformed and tumour cell lines investigated, the quantitative change in Concanavalin A binding, expressed as an increase of the ratio of unretarded to specifically-bound glycopeptides, was paralleled by a shift of transformed or tumour glycopeptides to higher apparent molecular weight compared to the control in gel chromatography.

Early changes in the glycopeptides of human B-lymphocytes after Epstein-Barr virus infection in vitro

Human B lymphocytes obtained from healthy donors were infected with Epstein-Barr virus in vitro. From the initiation of infection to the final establishment of a permanent lymphoblastoid cell line, fucosyl glycopeptides of the cell surface were investigated. In order of appearance the following events took place: expression of Epstein-Barr virus-determined nuclear antigen, mitotic activity of the cells and specific glycopeptide alterations on the cell surface. This specific alteration in glycopeptides, as determined by gel filtration, is manifested by the appearance of fast-eluting glycopeptides and was similar to that found on Burkitt lymphoma cells. Neither pokeweed-mitogen-stimulated B lymphocytes nor exponentially growing normal T lymphocytes exposed fast-eluting glycopeptides on their surfaces. Therefore, it is concluded that the appearance of these fast-eluting glycopeptides on the surface of lymphoblastoid cells after EBV infection is not the result of culture conditions or conditions of growth as such. The similarity with glycopeptides derived from Burkitt lymphoma cells, and the observation that a considerable proportion of the B cells becomes immortalized, are discussed.

Cell surface glycoprotein changes in Epstein-Barr virus-positive and -negative human hematopoietic cell lines

It has previously been shown that differential fucose labelling of many normal and homologous tumor cells, followed by proteolytic release and degradation, yields glycopeptides which upon gel filtration shown an increase in fast-eluting glycopeptides for the tumor cells. This technique has now been applied to cell-surface glycoproteins of different human hematopoietic cell lines. These lines included Epstein-Barr virus (EBV)-carrying lymphoblastoid cell lines of presumed non-neoplastic origin, and malignant EBV-genome-positive Burkitt lymphoma and EBV-negative non-Burkitt lymphoma, leukemia and myeloma lines. As compared with normal peripheral lymphocytes, both the lymphoblastoid type of cell lines and the different types of lines of proven malignant ancestry contained the fast-eluting glycopeptides on their cell surface with very few exceptions. It is therefore concluded that (I) malignant conversion of human lymphoid cell in vivo is commonly, but not obligatorily, associated with a specific change in the composition of the fucosyl glycopeptides, and (2) EBV infection of B lymphocytes does not lead only to the well-documented immortalization in vitro but also, as a rule, to the same type of alteration in fucosyl glycopeptides as was demonstrated for the neoplastic cell lines. It proved possible to distinguish several categories of hematopoietic cell lines due to the effect that pretreatment of the glycopeptides with neuraminidase or mild acid exerted on their subsequent chromatographic behavior.

Membrane glycoprotein changes in primary mammary tumors associated with autonomous growth

Primary and transplanted mammary tumors of the GR mouse were explanted in tissue culture and grown in the presence of radioactive fucose. Labelled membrane glycopeptides were isolated and compared by cochromatography with differentially labelled glycopeptides from normal mammary gland tissue. Differences with controls in the glycopeptide elution profiles were observed in autonomous, hormone-independent tumors but were absent in histologically similar tumors which required a continuous hormonal stimulus for growth. The results suggest that alterations in membrane glycopeptides are associated with the capacity of autonomous, hormone-independent growth of murine adenocarcinoma cells.

Chemical and immunological studies of cell surfaces from normal and transformed cells

Immunological and chemical studies of cell surfaces from normal and transformed BALB/c fibroblasts have shown alterations associated with transformation. The cells studied include normal lines which do not cause tumors when injected into BALB/c mice, viral transformants, and spontaneous transformants which cause tumors that either regress or grow progressively, killing the host. The spontaneously transformed progressors include cell lines which are immunogenic and nonimmunogenic as determined by the ability of tumor excision to protect an animal from subsequent rechallenge by tumor cells. Tumor-bearing mice produce lymphocytes which are nonspecifically cytotoxic for all the normal and transformed lines. Some of the cell lines induce specific antibody formation in BALB/hosts. Antisera have been prepared in rabbits which are specific for the transformed cell lines. These antisera can be used to determine specific surface changes on the transformed cells. Chemical studies have shown glycolipid alterations between the normal cells and some, but not all, of the transformants. Glycoproteins labeled by lactoperoxidase-125I or [3H] glucosamine were compared by SDS gel electrophoresis. Results from these studies do not show changes associated with malignancy. Individual glycoprotein regions from gels were treated with pronase, and the glycopeptides compared by Sephadex G50 chromatography. Alterations in glycopeptides from several cellular glycoproteins are the only changes which appear to be associated with malignancy.