Studies on the Glycosphingolipids of Normal and Virally Transformed 3T3 Mouse Fibroblasts

Qualitative and quantitative cellular glycomics of glycosphingolipids based on rhodococcal endoglycosylceramidase-assisted glycan cleavage, glycoblotting-assisted sample preparation, and matrix-assisted laser desorption ionization tandem time-of-flight mass spectrometry analysis

Glycosphingolipids (GSLs) are crucially important components of the cellular membrane, where they comprise microdomains with many critical biological functions. Despite this fact, qualitative and quantitative techniques for the analysis of GSLs still lag behind the needs of researchers. In this study, a reliable procedure for the elucidation of cellular GSL-glycomes was established based on (a) enzymatic glycan cleavage by endoglycosylceramidases derived from Rhodococcus sp. in combination with (b) glycoblotting-assisted sample preparation. The mixture of endoglycosylceramidase I and II was employed to maximize the release of glycan moieties from the major classes of GSLs (i.e. ganglio-, (neo)lacto- and globo-series GSLs). The glycoblotting technique enabled the quantitative detection of GSL-glycans using as few as 2 × 10(5) cells. Thirty-seven different kinds of cellular GSL glycans were successfully observed in 11 kinds of cells, including Chinese hamster ovary cells and their lectin-resistant mutants as well as murine and human embryonic carcinoma cells. Furthermore, in-depth structural clarification in terms of discrimination of isomers was achieved by MALDI-TOF/TOF mass spectrometry analysis and/or linkage-specific glycosidase digestion. These novel analytical techniques were shown to be capable of delineating cell-specific GSL-glycomes. Thus, they are anticipated to have a broad range of applications for the characterization, description, and comparison of various cellular/tissue samples in the fields of drug discovery and regenerative medicine.

Altered ganglioside composition in virally transformed rat embryo fibroblasts

The composition of gangliosides was examined in a normal rat embryo fibroblast cell line (REF52) and in two viral transformants: a polyoma transformant (REF52-PyMLV) and a simian viral 40 transformant (REF52-SV40). The distribution of gangliosides in the cell lines was determined using gas-liquid chromatography and high-performance thin-layer chromatography. N-acetylneuraminic acid was the predominant sialic acid species detected in the three cell lines. The total ganglioside concentration (microgram/100 mg dry weight of cells) in the normal, PyMLV, and SV40 lines was 144.7 +/- 10.4, 153.8 +/- 9.2, and 86.1 +/- 6.8, respectively. Gangliosides GM3, GM2, GM1, and GD1a were the major species in the normal and transformed lines. The distribution of these gangliosides, however, differed markedly between the normal and the transformed lines and also between the transformed lines themselves. The transformed cells also differed from the normal cells in growth rate, morphology, and social behavior. The cell line with highest GM3 content (PyMLV) formed islands, whereas the normal and SV40 cell lines, which had lower GM3 levels, grew as monolayers. The findings suggest that PyMLV and SV40 transformation can have multiple and different effects on cellular ganglioside distribution and growth behavior.

The bimodal growth response of Swiss 3T3 cells to the B subunit of cholera toxin is independent of the density of its receptor, ganglioside GM1

The B subunit of cholera toxin, a protein which binds specifically to cell surface ganglioside GM1, has been shown to have a bimodal effect on DNA synthesis in Swiss 3T3 fibroblasts. The B subunit induced cellular proliferation of confluent and quiescent cells while it inhibited the growth of the same cells when they were sparse and rapidly dividing. The amount of cell surface GM1 increased when the cells reached confluency. To examine the hypothesis that the variation in levels of GM1 was responsible for the bimodal effect, we increased GM1 levels in rapidly dividing cells by insertion of exogenous GM1 or by treatment of the cells with neuraminidase to convert polysialogangliosides to GM1. Even after the level of GM1 was increased to levels similar to those found in confluent cells, the B subunit still inhibited, rather than stimulated, their growth. Therefore, this result indicates that the bimodal response to the B subunit is not solely a function of the concentration of cell surface GM1; rather it is the growth stage that determines the fate of the signal transduced by the interaction of the B subunit and ganglioside GM1.

Ganglioside variations in human liver cirrhosis and hepatocellular carcinoma as shown by two-dimensional thin-layer chromatography

Gangliosides isolated from 5 cases of normal liver tissues, 11 cases of liver cirrhosis and 5 cases of hepatocellular carcinoma were compared in their concentrations and compositions. Quantitative analysis revealed no significant change of ganglioside levels between normal and cirrhotic liver tissues or hepatocellular carcinoma. There was also no significant difference (p greater than 0.05) between cirrhotic liver tissues and hepatocellular carcinoma. Two dimensional thin-layer chromatography of the total ganglioside preparations of liver tissues from both liver cirrhosis and hepatocellular carcinoma showed proliferation of GM2, GD3, GD1 and at least two unidentified components, named provisionally spots Nos. 1 and 2 in the present report, and loss of GM3. Sialidase treatment and thin-layer chromatography showed the components of these spots to be sialidase-labile monosialogangliosides and distinctly different from GD3 which was described elsewhere.

Gangliosides in neuroblastomas

Neuroblastomas from children presenting with tumors at various ages and different primary sites (abdominal, adrenals, pelvic, and thoracic) were studied. Analysis of the ganglioside patterns of 53 tumors indicated that patients who were either disease positive 2 yr following surgery or dead of disease, had significantly (p less than 0.005) less GT1b plus GD1b than tumors from patients that were disease free 2 yr post surgery. The presence of GD2 in 45 of the tumors correlates well with the suggestion that it can be used as a marker in neuroblastoma diagnosis. Children with thoracic neuroblastomas have a significantly better prognosis than children with tumors in other anatomic sites. Analysis of the ganglioside composition of these tumors only, indicated that they had a significantly higher (p less than 0.005) concentration of GT1b and GD1b and a significantly lower concentration (p less than 0.025) of monosialogangliosides than those patients who were dead of disease or had persistent disease. These results suggest that low levels of GT1b and GD1b correlate with a poor prognosis. The thoracic neuroblastomas may be comprised of more "differentiated" neuroblastoma cells (ganglioside patterns more similar to the CNS), and this may contribute to the fact that about 85% of children with thoracic neuroblastoma recover. To understand why the ganglioside pattern may serve as a prognostic indicator for neuroblastoma, it is necessary to know whether gangliosides have specific roles in neuronal differentiation. Our approach to this question is to compare the effect(s) of added ganglioside or the corresponding oligosaccharide on neuroblastoma cells. Results obtained suggest that the oligosaccharide from GM1 is able to enhance neuritogenesis by S20Y murine neuroblastoma cells to the same extent that GM1 does.

Asymmetric distribution of gangliosides in rat renal brush-border and basolateral membranes

Highly enriched brush-border and basolateral membranes isolated from rat renal cortex were used to study the distribution of endogenous gangliosides in the two distinct plasma membrane domains of epithelial cells. These two membrane domains differed in their glycolipid composition. The basolateral membranes contained more of both neutral and acidic glycolipids, expressed on a protein basis. In both membranes, the neutral glycolipids corresponding to mono-, di-, tri- and tetraglycosylceramides were present. The basolateral membranes contained more diglycosylceramide than the brush-border membranes. The major gangliosides found were GM4, GM3, and GD3 with minor amounts of GM1 and GD1a. The latter were identified and quantified by sensitive iodinated cholera toxin binding assays. When the distribution of individual gangliosides was calculated as a percent of total gangliosides, the brush-border membranes were enriched with GM3, GM1 and GD1a compared to the basolateral membranes, which were enriched with GD3 and GM4. The observation of a distinct distribution of glycolipids between brush-border and basolateral membranes of the same epithelial cell suggests that there may be a specific sorting and insertion process for epithelial plasma membrane glycolipids. In turn, asymmetric glycolipid biogenesis may reflect differences in glycolipid function between the two domains of the epithelial plasma membrane.

Subcellular distribution and biosynthesis of rat liver gangliosides

Gangliosides have generally been assumed to be localized primarily in the plasma membrane. Analysis of gangliosides from isolated subcellular membrane fractions of rat liver indicated that 76% of the total ganglioside sialic acid was present in the plasma membrane. Mitochondria and endoplasmic reticulum fractions, while containing only low levels of gangliosides on a protein basis, each contained approx. 10% of total ganglioside sialic acid. Gangliosides also were present in the Golgi apparatus and nuclear membrane fractions, and soluble gangliosides were in the supernatant. Individual gangliosides were non-homogeneously distributed and each membrane fraction was characterized by a unique ganglioside composition. Plasma membrane contained only 14 and 28% of the total GD1a and GD3, respectively, but 80-90% of the GM1, GD1b, GT1b and GQ1b. Endoplasmic reticulum, when corrected for plasma membrane contamination, contained only trace amounts of GM1, GD1b, GT1b and GQ1b, but 11 and 5% of the total GD1a and GD3, respectively. The ganglioside composition of highly purified endoplasmic reticulum was similar. Ganglioside biosynthetic enzymes were concentrated in the Golgi apparatus. However, low levels of these enzymes were present in the highly purified endoplasmic reticulum fractions. Pulse-chase experiments with [3H]galactose revealed that total gangliosides were labeled first in the Golgi apparatus, mitochondria and supernatant within 10 min. Labeled gangliosides were next observed at 30 min in the endoplasmic reticulum, plasma membrane and nuclear membrane fractions. Analysis of the individual gangliosides also revealed that GM3, GM1, GD1a and GD1b were labeled first in the Golgi apparatus at 10 min. These studies indicate that gangliosides synthesized in the Golgi apparatus may be transported not only to the plasma membrane, but to the endoplasmic reticulum and to other internal endomembranes as well.

Carbohydrate structure in tumor immunity

Researchers have endeavored to define surface alterations associated with neoplasia for at least 25 years. In comparisons of normal tissues with animal and human tumors, cultured cells before and after transformation with oncogenic agents, tumorigenic and nontumorigenic transformed cells, metastatic and nonmetastatic tumor cells, high- and low-metastatic variants, and tumor cells before and after induction of differentiation to a less malignant phenotype, a consistent finding has been some form of alteration in surface carbohydrate structures. These changes in glycolipids, glycoproteins and glycosaminoglycans are reviewed, and their structures are illustrated. Both nucleotide sugar biosynthesis and glycosyltransferase changes have been associated with these alterations. In some cases, alterations in transformed cells were related to growth, rather than transformation. In others, the altered glycoconjugates are truly tumor-associated. There is evidence that cell surface glycoconjugates may function in growth control. Altered carbohydrate structures could also serve as receptors for growth promoting factors and be directly responsible for altered growth control. Recent studies with monoclonal antibodies indicate that the vast majority of antibodies recognizing tumor-associated antigens are detecting altered carbohydrate structures. Mechanisms by which the immune system can recognize these carbohydrate structures are considered, and immune recognition of tumor-associated carbohydrate structural alterations is explored. A number of these hypotheses relating to alterations in glycosylation, growth control, and tumor immunity deserve further investigation.

Biochemical properties of acteylcholine receptor subunits from Torpedo californica

Four polypeptide chains composing acetylcholine receptors from the electric organ of Torpedo californica were purified by preparative electrophoresis in sodium dodecyl sulfate. Their apparent mole ratio alpha/beta/gamma/delta is 2:1:1:1. These chains are not readily distinguished by amino acid or carbohydrate composition but are distinguished by apparent molecular weight and polypeptide maps. By peptide maps, no extensive homology is evident between these chains or between any of these chains and higher molecular weight chains found in receptor-enriched membrane fragments.

Ganglioside patterns of metastatic and non-metastatic transplantable hepatocellular carcinomas of the rat

In previous investigations, we correlated levels of sialic acid, gangliosides, and ganglioside glycosyltransferases with tumorigenesis over a 24-week continuum of growth of hepatocellular neoplasms of the rat induced by the carcinogen N-2-fluorenylacetamide. However, metastatic tumors developed only rarely and were not analyzed. To investigate surface changes associated with metastasis, well-differentiated and poorly differentiated hepatocellular carcinomas were transplanted to syngeneic recipient rats. From those, several metastatic and nonmetastatic isolates were obtained and compared. Both total and ganglioside sialic acid amounts in transplantable hepatomas were elevated above control liver values but were significantly lower for metastatic lines than for nonmetastatic lines. The nonmetastatic lines were characterized by ganglioside patterns depleted in the precursor ganglioside GM3 (sialic acid-galactose-glucose-ceramide) and elevated in the products of the monosialoganglioside pathway. In contrast, metastatic isolates exhibited a restoration of GM3 and nearer normal amounts of other gangliosides. The findings point to differences in sialic acid-containing glycolipids, comparing metastatic and nonmetastatic hepatocellular carcinomas, and further extend the concept that ganglioside alterations do not cause tumorigenesis but are the end result of a cascade of events which apparently continue beyond the onset of metastasis.

Gangliosides of cultured cells of a rat mammary carcinoma cell line

Ganglioside content of rat mammary carcinoma-derived cells grown in layers in vitro was nearly as high as that of apical membrane-derived milk fat globule membrane and nearly four time higher than the content of normal, lactating mammary tissue on a protein basis. The major ganglioside of these carcinoma-derived cells was identified as GDla (sialic acid-Gal-GalNAc-sialic acid)-Gal-Glc-Cer. Relative to carcinoma-derived cells, rat mammary tissue and milk fat globule membrane had more complex ganglioside patterns but appeared to lack substantial quantities of GDla.

Glycolipids as indicators of tumorigenesis

Hyperplastic liver nodules and hepatocellular carcinomas were induced in rats by oral administration of the carcinogen N-2-fluorenylacetamide. Neoplastic tissue was compared with control, fetal, neonatal, and precancerous liver tissues. The development of the tumors was slow, such that temporal changes in the biochemical and morphologic development of carcinogenesis could be identified. Ganglioside sialic acid levels were elevated in all but the most poorly differentiated tumors. Experiments to monitor individual enzymes suggested that the alterations in glycolipid composition were a direct effect of alterations in biosynthetic activities. The pattern during tumorigenesis was the inverse of that during normal development. Also, ganglioside patterns showed a progressive simplification from hyperplastic nodules to well-differentiated hepatomas and through two grades of poorly differentiated hepatomas. An increase in the activity of the branchpoint enzyme of ganglioside biosynthesis preceded both a decrease in the branchpoint enzyme of the disialoganglioside pathway and a marked increase in the galactosyltranferase of GM1 formation. The results indicate that ganglioside deletions are the end result of a cascade of events in the tumorigenic transformation. The onset of ganglioside deletions but not of the cascade per se may correlate with the onset of malignancy. Glycolipid levels are elevated early in certain surrounding tissues especially in the blood. In rats bearing transplantable hepatomas, serum levels of lipid-bound sialic acid were elevated 2.5-fold. Similar results were obtained with sera of mice bearing transplantable mammary carcinomas and of cancer patients. These findings provide new emphasis for gangliosides in both cancer detection and as regulatory signals for growth and multiplication of cells.

Liver homing in the rat of 111Indium labelled beef and neuraminidase-treated rat erythrocytes (studies with a gamma camera)

The rate of liver homing of 111In-labelled erythrocytes has been measured under a Gamma Camera. Homing of neuraminidase-treated or xenogeneic erythrocytes is delayed by preinjection of glycolipids or glycopeptides.

Gangliosides of active and inactive neuroblastoma clones

It is possible to divide neuroblastoma cells into clones able to synthesize neurotransmitters (active clones) or not (inactive clones). The analysis of gangliosides of active and inactive clones shows that their total lipid sialic acids is markedly lower than that of neuron-enriched fractions prepared from brain. The ganglioside pattern of the cultured cells also differs notably from those obtained with neuronal fractions from brain. The absence of tri- and tetrasialogangliosides and the presence of appreciable amounts of the simplest monosialogangliosides are particularly noticeable in the neuroblastoma. Morphological differentiation obtained by serum deprivation, dibutyryl cyclic AMP or bromodeoxyuridine does not restore a true neuronal pattern. Gangliosides could not therefore be used as a marker of neuronal differentiation in this type of cell. No correlations can be found between the ganglioside pattern and the ability of cells to synthesize neurotransmitters.

Biosynthesis and function of gangliosides

Gangliosides are unique acidic glycolipids that are selectively concentrated in the plasma membrane of cells. Surface labeling studies have demonstrated that at least a portion of the oligosaccharde chain of gangliosides extends beyond the hydrophe) is imbedded in the membrane bilayer. It is becoming increasingly apparent that gangliosides participate in the internalization of environmental signals elicited by cholera toxin and glycoprotein hormones such as thyrotropic hormone and chorionic gonadotropin as well as other substances such as interferon and possibly serotonin. The mechanism by which cholera toxin binds to a specific ganglioside receptor on the celraction of trophic agents with gangliosides. We would predict that analyogous phenomena involving gangliosides will be discovered in brain. The biosynthesis of gangliosides proceeds by the ordered sequential addition of sugars to the lipid moiety. These reactions are catalyzed by a cluster of membrane-bound glycosyltransferases. Any alteration in the activity or specificity of one of these enzymes will result in a dramatic change in the ganglioside pattern of an afflicted cell or organ. The drastic consequences that accompany abnormalities of ganglioside synthesis have been documented in a heritable metabolic disorder in vivo and in tumorigenic transformation of cells in vitro. In this article, we have attempted to unify these observations and to provide a reasonable interpretation of the role of gangliosides in mediating cell surface phenomena.

A comparative study of the glycolipids of human, bird and fish testes and of human sperm

The glycolipids of human testis and sperm have been compared. Both adult testis and the sperm exhibited remarkably complex, but generally similar, patterns of glycolipids. In particular, both contained appreciable amounts of the sulfogalactosylmonoalkylmonoacylglycerol, recently shown to be the principal glycolipid of the testis and sperm of a number of animals. In contrast, immature (prebuteral) human testis did not contain this compound. To extend knowledge on the possible distribution of sulfogalactosylmonoalkylmonoacylglycerol in the testes of other chordates, we have also analysed the glycolipids of the testes of a number of birds and fish. None of the testes from these species contained the above compound. Instead, sulfogalactosylceramide was found to be a major glycolipid of the testis of mature fowl, duck and skate-fish and sulfogalactosylglucosylceramide of the testis of mature salmon and trout. Immature duck testis contained only a trace of sulfogalactosylceramide. These studies reveal intriguing differences between the sulfatides of various chordates, lend support to the concept that sulfatides increase markedly in testis at a specific stage of spermatogenesis and suggest an important role for sulfatides in testicular and spermatozoal function.

The effect of SV40 transformation on the chromosomal proteins of 3T3 mouse embryo fibroblasts

The composition and metabolism of chromosomal proteins-histones and nonhistones chromosomal proteins-were examined in normal and SV40 transformed 3T3 mouse cells. Variations were observed, many of which were similar to those previously reported for normal and SV40 transformed W138 human diploid fibroblasts. The possible implications of these viral induced changes in the protein component of the genome for the phenotypic modifications which occur in transformed cells are discussed.

Studies on the glycolipids of sheep thymus and of normal and concanavalin A-stimulated sheep peripheral lymphocytes

The neutral glycolipids and gangliosides of sheep thymus and of sheep peripheral lymphocytes were compared. The patterns of both of these major classes of glycolipids were more complex in thymus than in the lymphocytes. The incorporation of radioactivity from D-[1-14C]galactose into the individual glycolipids of control and concanavalin A-stimulated sheep peripheral lymphocytes was also studied. A marked enhancement of incorporation into trihexosylceramide and an alteration of the pattern of incorporation into gangliosides were noted in the mitogen-treated cells. The results suggest that significant alterations of glycolipid composition and metabolism may occur during at least certain stages of lymphocyte differentiation.

Biosynthesis of plasma membrane components by SV40-virus-transformed 3T3 mouse cells temperature sensitive for expression of some transformed cell properties

We have studied the plasma membranes of an SV40-transformed 3T3 cell line temperature sensitive for the transformed growth phenotype (ts H6-15 cells), and have found that they vary little as a function of temperature of cultivation. Analysis by polyacrylamide gel electrophoresis was performed on plasma membranes prepared from ts H6-15 cells cultured at the permissive (32 degrees C) and non-permissive (39 degrees C) temperatures and radioactively-labelled in several ways. No significant differences were seen when the electrophoretic patterns of polypeptides of the plasma membranes of ts H6-15 cells, grown through 3-4 generations in medium containing radioactive leucine (32 degrees C and 39 degrees C temperatures) were compared. Plasma membranes derived from cells similarly grown in medium with radioactive glucosamine indicated that extensive alterations in the intrinsic glycopeptides occurred in association with alteration in growth phenotype. A shift towards decreased synthesis of large molecular weight (congruent to 100 000-160 000) glycopeptides occurred in cells grown at the temperature of non-transformed growth (39 degrees C). A decrease in amount of a 120 000 molecular weight glycopeptide at 39 degrees C was the most prominent of these alterations. We have studied the surface exposure of polypeptides and glycopeptides of intact cells grown at 32 and 39 degrees C, using lactoperoxidase-catalyzed iodination, NaBH4 reduction of galactose oxidase-treated cells, and metabolic-labelling with glucosamine of trypsin-sensitive molecules. We found no major qualitative differences between whole cell extracts or between plasma membrane preparations of cells cultivated at the permissive and non-permissive temperatures. Of special interest was the observation that the formation and surface exposure of a trypsin-sensitive, 240 000 molecular weight polypeptide appeared not to be ts in ts H6-15 cells. The significance of these observations will be discussed.

A consideration of the role of cell surface macromolecules in the process of viral transformation

There is extensive physiological evidence implicating the cell surface as the key organelle which mediates the cell:cell interactions which underlie both normal and neoplastic growth. This information has now been supplemented with biochemical and biophysical data which indicates that surface macromolecules, in particular the heteroglycans of transformed cells, differ from those which lie at the periphery of normal cells. In the case of cells neoplastically transformed by most tumour viruses it is clear that the small virus genome (2-5 x 10(6) daltons) cannot carry the total genetic information to accomodate these various biochemical modifications, if indeed they are encoded in separate genes (1). To examine the part played in transformation by cellular genes coding for surface heteroglycan formation, we have turned to a study of SV-3T3 cells (ts H6-15) which are temperature-sensitive for expression of the transformed cell phenotype (2). The data show that cells grown under conditions permissive and non-permissive for such expression exhibit the same pattern of formation of glycolipids, and the majority of the polypeptides of the plasma membrane. There are, however, significant differences in the synthesis of some glycopeptides. A large molecular weight, trypsin-labile glycopeptide, present at the surface of untransformed fibroblasts but barely measurable in some of their virus-transformed derivatives (3), was detected, essentially at the same level, at the surface of ts H6-15 cells grown at the permissive and non-permissive temperatures. The signficance of these observations is discussed.

Fibroblast surface antigen (SF): molecular properties, distribution in vitro and in vivo, and altered expression in transformed cells

We have recently described a cell type-specific surface (SF) antigen that is deleted in chick fibroblasts transformed by Rous sarcoma virus, SF antigen is a major surface component and makes up about 0.5% of the total protein on normal cultured fibroblasts. The antigen is shed from normal cells and is present in circulation (serum, plasma), and in vivo, also, in tissue boundary membranes. The molecular equivalents of both cellular and serum SF antigen are distinct, large polypeptides, one of which (SF210, MW 210,000) is glycosylated and, on the cell surface, highly susceptible to proteases and accessible to surface iodination. Immunofluorescence and scanning electron microscopy have indicated that the antigen is located in fibrillar structures of the cell surface, membrane ridges, and processes. Human SF antigen is present in human fibroblasts and in human serum. We have recently shown that human SF antigen is identical to what has been known as the "cold-insoluble globulin" and that it shows affinity toward fibrin and fibrinogen. Our results also indicate that loss of the transformation-sensitive surface proteins is due not to loss of synthesis but to lack of insertion of the protein in the neoplastic cell surface. Both normal and transformed cells produce the SF antigen, but the latter do not retain it in the cell surface. The loss of SF antigen, a major cell surface component, from malignant cells creates an impressive difference between the surface properties of normal and malignant cells. The possible significance of SF antigen to the integrity of the normal membrane and its interaction to surrounding structures is discussed.

Mass spectrometric analysis of permethylated glycosphingolipids I. Sequence analysis of two blood-group B active glycosphingolipids from human B erythrocyte membranes

Two blood group B active glycosphingolipids (B-I and B-II) formerly isolated and purified from human B erythrocytes (16) were investigated by mass spectrometry after permethylation. B-I yielded fragments up to m/e 1266 and B-II up to m/e 1495, showing the sequence of six and seven carbohydrate residues respectively. In combination with additional experimental evidence (18) the glycosphingolipids are demonstrated to be a gal-[ fuc ]-gal-glcNAc-gal-glc-ceramide (B-I) and a gal-[ fuc ]-gal-glcNAc-gal-glcNAc-gal-glc-ceramide (B-II). Mass spectrometric evidence for the ceramide residues are also obtained indicating besides spingosine C24-,C24:1-, and C22-fatty acids as main constituents.

Gangliosides of chemically and virally transformed rat embryo cells

The gangliosides of control rat embryo cells, 3-methylcholanthrene, Rauscher leukemia virus, and combined 3-methylcholanthrene-Rauscher leukemia virus transformants were examined using [14 C]glucosamine as a tracer. All four cell lines exhibited a complex pattern of gangliosides. While N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosyl-glucosyl-ceramide was the major ganglioside in the control cell line, N-acetylneuraminyl-galactosyl-glucosyl-ceramide was the major ganglioside in the three transformants. The 3-methylcholanthrene transformant possessed a ganglioside pattern different from that of the Rauscher leukemia virus transformant. Hydrolysis of the gangliosides indicated that galactosamine, N-acetyl-and N-glycolylneuraminic acid were the labeled components in all cell lines.