Glycosaminoglycans and other carbohydrate groups bound to proteins of control and transformed 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.

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.

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.

Increased sialylation of complex glycopeptides during differentiation of mouse embryonal carcinoma cells

High-molecular-weight, asparagine-linked glycopeptides--the lactosaminoglycans--are the major class of protein-bound carbohydrates synthesized by F9 cells; these cells synthesize only minor amounts of smaller glycopeptides. In contrast, F9ACC19, an endodermal cell line derived from F9 cells, synthesizes only minor amounts of lactosaminoglycans and a high proportion of smaller glycopeptides. Biochemical analysis of the small glycopeptides from F9ACC19 cells revealed that they are larger, bind less efficiently to concanavalin-A Sepharose and contain more sialic acid than their counterparts from F9 cells. Both cell types contain a small proportion of high-mannose glycopeptides. When synthesized by F9ACC19 cells, the glycopeptides of vesicular stomatitis virus show a high level of sialylation as compared to those synthesized by F9 cells, where few or no sialic-acid residues are present; this shows that the differences observed in total glycopeptides reflect differences in the glycosylation machinery of the cells. Consistent with this observation, sialyltransferase activity in vitro using a variety of acceptors was found to be markedly higher in F9ACC19 than in F9 cells, while galactosyltransferase activity was reduced several fold in F9ACC19 cells. These data support the hypothesis that the increased sialyltransferase activity in endodermal differentiated F9ACC19 cells may block the terminal galactose residue of glycopeptides, thereby inhibiting the synthesis of lactosaminoglycans in these cells.

Identification of exposed surface glycoproteins of four human bladder carcinoma cell lines

Three cell surface protein-specific methods were used to radiolabel the major glycoproteins of four human bladder carcinoma cell lines: The well-differentiated lines RT112 and TR4 and more anaplastic lines T24 and EJ. Five acidic glycoproteins iodinated in all lines by the lactoperoxidase/125I method were designated CP-175/5.8-6.0 (apparent molecular weight X 10(-3)/pl of iodoprotein), GP-155/5.0-5.3, GP-145/4.9-5.2, GP-130/4.8-5.5 and GP-110/4.9-5.3. Another iodinated glycoprotein, GP-200/5.5-6.0, was prominently labelled in RT112 and RT4 but was not detected in T24 or EJ. GP-200 as well as GP-175, GP-155 and GP-145 were not detected by the galactose oxidase/NaB(3H)4 method and were poorly labelled by the neuraminidase-galactose oxidase/NaB(3H)4 and NaIO4/NaB(3H)4 labelling methods. The major sialogalactoproteins identified in the four lines by the neuraminidase-galactose oxidase/NaB(3H)4 and NaIO4/NaB(3H)4 methods were GP-130, and a duplet of GP-90 and GP-80 which were poorly iodinated by lactoperoxidase/125I. The galactose oxidase/NaB(3H)4 reaction was increased by between 4- and 10-fold and many additional glycoproteins were labelled after neuraminidase treatment, indicating that the cell surface galactose and N-acetylgalactosamine residues of glycoproteins are highly sialylated. In cell lines RT112 and RT4 there was prominent labelling of very high molecular weight sialogalactoconjugates that was not present in extracts of T24 and EJ.

Lentil lectin-bound glycoproteins of cultured rheumatoid synovial cells

Synovial cell lines were cultured from 5 rheumatoid arthritis (RA) patients, from 4 patients with other synovial inflammation and from 4 non-inflammatory controls. Protein synthesis was studied by [35S]methionine labelling. Glycoproteins containing D-glucose or D-mannose were separated by affinity chromatography with immobilized lentil lectin and analysed by SDS-electrophoresis in polyacrylamide gradient gels (SDS-gradient PAGE). About 12% of labelled protein was bound to the lectin column (range 7.9-20.0%). Proteins of RA cells showed no differences in binding compared with proteins of the reference cells. At least 40 glycoproteins were separated by SDS-gradient PAGE. No new or missing bands were observed in RA cells, but several quantitative changes and microheterogeneity of some polypeptide molecular weights were noted.

Similarity in the bound carbohydrate groups of glycoproteins from cells of several vertebrate classes

The carbohydrate groups of the glycoproteins of human, hamster, chick, reptile and fish cells growing in culture have been fractionated in succession according to size (Sephadex G-50), affinity for concanavalin A, charge (DEAE-Sephadex) and by thin-layer chromatography. It was found that despite the complexity of the array of separable glycopeptides in each type of cell, most of these structures seemed to be common to all of the cells. This suggests that they have existed in a relatively stable state for several hundreds of millions of years throughout the evolution of the vertebrates.

Variation of the carbohydrates of glycoproteins of cells growing on different surfaces

The carbohydrate components of some glycoproteins of hamster cells differ as a function of their growth on various substrates; glass, plastic, or plastic coated with collagen. This observation is interpreted as an effect of the environment on cellular structure at the molecular level. The basis of the change and its possible significance are discussed.

Isolation and partial characterization of a mucin-type glycoprotein from plasma membranes of human melanoma cells

Plasma membranes were isolated from HM7 melanoma cells grown in the presence of [3H]glucosamine and Na2(35)SO4 or [3H]mannose and [14C]glucosamine. The labeled glycoconjugates were solubilized with 0.6 M lithium diiodosalicylate/0.5% Triton X-100. Fractionation of glycoconjugates by repeated chromatography on columns of Sepharose CL-6B and DEAE-Sepharose and by affinity chromatography on WGA-Sepharose yielded three radiochemically homogeneous glycoproteins. One of these having an apparent molecular weight of 100,000 was found to contain clusters of (AcNeu)1 or 2 leads to [Gal leads to GalNAc] linked O-glycosidically to the protein. One other glycoprotein contained both O-glycosidically and N-glycosidically-linked oligosaccharides, and the third contained only N-glycosidically-linked carbohydrates. Preliminary results indicate that the 100,000 molecular weight mucin-type glycoprotein is present in significantly reduced quantitites in cultured human fetal uveal melanocytes. Further, the bulk of the glycoproteins from the melanocytes were of lower molecular size compared to those from the melanoma cells.

The membrane glycoproteins of the malignant cell

Experiments are described and reviewed demonstrating that the bound carbohydrates of glycoproteins of many forms of malignant cells differ from their normal counterpart. The difference involves many oligosaccharide groups and is essentially quantitative. The characteristics of the difference are discussed. Despite the consistency of the finding its significance is unknown because the function of bound carbohydrates is largely unknown. Some properties of protein-bound carbohydrates that may be of special relevance to malignancy and other pathological processes are considered. The array of structures found in the cell is highly complex but seems to be similar in man, hamster, mouse, chick and fish. On the other hand, the biosynthesis of these structures can be influenced and altered by the environment and by drugs; the cell is tolerant of variation in its bound carbohydrate; microheterogeneity of the carbohydrates is probably the rule rather than the exception; experiments to test the function of bound carbohydrate show only small effects. A role for the bound carbohydrates in evolution is proposed that is consistent with these characteristics. It is also postulated that altered, bound carbohydrates of most glycoprotein does not endanger the life of the cell but may be responsible for involvement and change of many processes some of which permit the malignant cell to divide persistently and to prosper.