Glycosyltransferase and sialic acid levels of normal and transformed cells

The glycobiology of brain tumors: disease relevance and therapeutic potential

The oligosaccharides that decorate cell surface glycoconjugates play important roles in intercellular recognition and cell-extracellular matrix interactions, and thus the regulation of cellular migration, metastasis and invasivity. Virtually all tumor cells display aberrant cell-surface glycosylation patterns brought about by alterations in their biosynthetic machinery. This holds true for highly invasive, malignant brain tumors as well as tumor cells that metastasize to the brain. The field of glycobiology is well established with essentially all of the biochemical pathways for oligosaccharide metabolism characterized and all of the 'glycogenes' involved in these pathways cloned. Yet there has been a paucity of progress toward the development of therapeutics. However, recent studies aimed at controlled glycosylation of therapeutic antibodies and mucins with anticancer vaccine potential, the emergence of new and highly sensitive tools for the identification of tumor-associated biomarkers and the manipulation of the expression of glycogenes that inhibit brain tumor invasivity have emerged. The opportunity now exists to answer questions as to how glycogenes are regulated at the genomic and transcriptomic level and how altered glycogene expression patterns lead to altered cell surface glycoconjugates. These studies should lead to the development of ways to directly regulate tumor cell glycogene expression, which should have significant therapeutic potential.

alpha2,3-sialyltransferase mRNA and alpha2,3-linked glycoprotein sialylation are increased in malignant gliomas

CMP-NeuAc: Galbeta1,3(4)GlcNAc alpha2,3-sialyltransferase (alpha2,3-ST) mRNA was expressed in human glioma specimens, human fetal astrocytes, and a panel of brain tumor cell lines. Maackia amurensis agglutinin staining revealed the presence of alpha2,3-linked sialic acids on glioma cell surfaces and extracellular matrices whereas normal human adult astrocytes were negative. Increased expression of alpha2,3-linked glycoprotein sialylation may play a role in glial tumorigenesis.

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.

Significance of serum protein and lipid-bound sialic acid as a marker for genitourinary malignancies

A prospective study was done to evaluate the roles of serum N-acetylneuraminic acid (NANA) and the lipid-bound subfraction of sialic acid (LSA) concentrations in the detection and staging of cancer, and the follow-up of treatment in patients with genitourinary malignancies. Multiple determinations were obtained in 177 subjects: 90 normal volunteers, 38 patients with prostate cancer, 20 patients with bladder cancer, 15 patients with renal cell cancer, and 14 patients with benign urologic diseases. The results showed a low incidence of elevated values in patients with early stages of cancer and a high incidence of false-positive values with serum NANA concentrations in patients with benign urologic diseases, especially prostatitis. Serum NANA and LSA concentrations were highly correlated with the stage and grade in patients with advanced urologic cancer, and may be used as markers of tumor activity during follow-up under treatment; currently, however, they are not useful in the screening of patients for urologic cancer. Their usefulness in prostatic cancer is at least comparable to that of acid phosphatase determinations by the enzymatic and radioimmunoassay methods, which were elevated in a smaller percentage of patients with prostate cancer than were the NANA or LSA concentrations.

Changes in cell-surface sialic acid content during chick embryo development

The amount of cell-surface sialic acid found in the material released by trypsin from chick fibroblasts rose markedly from day 8 to day 16 of embryo development. The rise seemed to result from two processes: increased sialylation of N-linked carbohydrate chains, and enhancement of the amount of O-linked structures. Eight-day cells were more quickly detached from the substrate than 16-day cells, since in 8-day fibroblasts detachment of half the adherent cells only required 10 min, compared to 20 min in 16-day fibroblasts. Re-adhesion to the substrate was also faster for the younger fibroblasts, and 40% of the 8-day trypsin-treated cells re-adhered within 30 min compared to about 3 h for the same proportion of 16-day cells. The age-dependent differences in the amount of cell-surface sialic acid do not account for the differences in the adhesive capacity of embryo cells. The fact that neuraminidase did not affect cell detachment or re-adhesion indicates that cell-surface sialic acid does not play an important part in the adhesive capacity of embryo fibroblasts.

Biochemical evidence for the role of alkyl-lysophospholipids on liver sialyltransferase

Antineoplastic alkyl-lysophospholipids were found to exert a strong inhibitory effect on membranous or solubilized asialomucin-sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity. This inhibitory effect was dependent on the presence of the choline moiety in position 3 of the glycerol molecule, as well as on the presence of long ether-linked aliphatic side chain in position 1 and the absence of any large substituent in position 2. As an example, 1-octadecyl-2-O-methyl-glycero-3-phosphorylcholine acted as a mixed-type inhibitor. Such an inhibitory process on sialyltransferase activity might be an additional factor in the tumor cell destructive effect of alkyl-lysophospholipids.

Synthesis of sialoglycoconjugates during dimethylsulfoxide-induced erythrodifferentiation of friend leukemia cells

We have previously shown that erythroid differentiation of Friend murine leukemia cells by dimethylsulfoxide results in a decrease in sialic acid content and net negative surface charge. The mechanism responsible for the decrease in sialic acid content was examined by measuring the synthesis of sialic acid from N-acetylmannosamine and its catabolic removal from sialoconjugates during the maturation process. A decrease in the incorporation of N-[3H]acetylmannosamine into sialoglycoconjugates occurred as early as 12 h after exposure to dimethylsulfoxide. Radioactivity incorporated into sialoglycoconjugates was relatively stable in untreated and dimethyl-sulfoxide-treated cells, implying that catabolic removal of sialic acid residues was not a factor in the decreased surface sialic acid content of differentiated erythroleukemia cells. In addition, no difference existed between control and treated cells in sialyltransferase activity. Significant decreases occurred, however, in the incorporation of radioactivity from N-[3H]acetylmannosamine into N-acetylneuraminic acid, CMP-N-acetylneuraminic acid and a material tentatively identified as N-acetylmannosamine-6-phosphate, 48 h after the addition of dimethylsulfoxide. The decrease in sialic acid biosynthesis in differentiated erythroleukemia cells was reflected by an 83% decrease in the amount of radioactively-labeled sialic acid released by neuraminidase treatment of cells exposed to dimethylsulfoxide. These findings are consistent with a cellular aging phenomenon triggered by the polar solvent-induced differentiation of the leukemic cells into more mature forms.

Sialyltransferase, sialic acid and sialoglycoconjugates in metastatic tumor and human liver tissue

1. The specific activities of sialytransferase in metastatic tumor sites were 5-37% of those of uninvolved non-cancerous tissue. The non-cancerous host tissues had a slightly lower average sialyltransferase activity than that of non-pathological control livers (986 vs 1194 dpm/min/mg protein). 2. The levels of total and bound sialic acid are increased 1.4 to 7.2-fold in homogenates, supernatants and resuspended pellets of metastatic tumor sites compared to non-cancerous and non-pathological control livers. For all these tissues, 24-29% of the bound sialic acid is found on soluble components (in the 16,300 g supernatant). 3. Soluble sialoglycoconjugates from most metastatic tumor sites give gel filtration profiles different from those of non-cancerous and non-pathological control livers.

Specificity of porcine liver gal beta (1 leads to 3)galnac-r alpha(2 leads to 3) sialyltransferase sialylation of mucin-type acceptors and ganglioside GM1 in vitro

Porcine liver microsomes are capable of transferring sialic acid from CMP-NeuAc to [14C]galactosylated ovine submaxillary asialo-mucin, porcine submaxillary asialo/afuco-mucin and ganglioside GM1. The specificity of the porcine liver sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) towards the first acceptor, [14C]Gal-GalNAc-protein, was investigated by means of methylation studies on the oligosaccharides changes cleft-off from the sialylated product glycoprotein by beta-elimination under reductive conditions. It appeared that sialic acid was transferred solely to position C-3 of galactose residues on Gal beta(1 leads to 3)GalNAc disaccharide units. Transfer to GalNAc residues was completely absent. Competition experiments and heat activation studies suggested that the same enzyme also converts ganglioside GM1 to ganglioside GD1a. Therefore, this porcine liver sialyltransferase can be designated as a Gal beta(1 leads to 3)GalNAc-R alpha(2 leads to 3) sialyltransferase.

Metastatic potential is positively correlated with cell surface sialylation of cultured murine tumor cell lines

The ability of murine tumor cells to metastasize spontaneously from subcutaneous sites is positively correlated with the total sialic acid content of the cells in culture, the degree to which the sialic acid is exposed on the tumor cell surface, and, most strongly, with the degree of sialylation of galactosyl and N-acetylgalactosaminyl residues in cell surface glycoconjugates. These findings suggest that sialic acid on the cell surface may play a role in tumor cell metastasis.

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.

Altered reactivity for A, B, H antigens in transitional cell carcinomas of the urinary bladder. A study of the mechanisms involved

Transitional cell carcinomas (TCCs) of the urinary bladder show variable blood group (BG) antigen reactivity even in the non-invasive stage. A correlation exists between the tumor reactivity and subsequent clinical course: when the expected BG antigen(s) is retained, the clinical course is favorable; absence of the expected antigen(s) denotes an aggressive potential. In the present study we investigated some of the possible mechanisms of altered BG antigen reactivity in TCCs. It was found that the "loss" of A, B, H reactivity is a quantitative phenomenon and the threshold for positive reactions depends on the method of tissue processing and the titer of the antisera. Thus, in the 35 cases studied, paraffin processing resulted in reduced reactivity compared to fresh-frozen tissue sections. The reactivity of tumors that appeared positive when tested with undiluted antisera was found reduced when quantitatively compared to that of normal mucosa from the same individual. Excessive or inappropriate sialylation does not appear to be responsible for the reduced BG antigen reactivity of the tumors. In fact, TCCs (9 cases) had significantly reduced sialic acid content compared to normal bladder mucosae (6 cases) regardless of their A, B, H reactivity and neuraminidase did not change their reactions for BG antigens. In addition, spontaneous unmasking of the Thomsen-Friedenreich (T) antigen was observed in invasive tumors that were negative for the expected BG antigen(s). Tumors from patients of blood group A or B often showed increased reactivity for the H antigen, although their A or B antigen was reduced or absent. In view of the known biosynthetic sequence from H to A and B substances, these observations suggest a specific biochemical defect in the tumors.

Isolation and characterization of the plasma membranes of cultured lymphoblasts from patients with cystic fibrosis and normal individuals

Plasma membranes were isolated from two cystic fibrosis lymphoblastoid cell lines and two age and sex-matched normal cell lines after controlled cell disruption. The preparations were enriched approx. 20-fold in plasma membrane markers and were essentially free of markers for other organelles except the Golgi-localized enzyme, galactosyltransferase. Sodium dodecyl sulphate polyacrylamide gel electrophoresis showed virtually identical polypeptide profiles after staining with Coomassie blue. Membranes from normal cells contained 0.49--0.67 mumol/mg of total phospholipid/mg membrane protein and those from cystic fibrosis cells, 0.53-0.67 mumol. The cholesterol content was 0.35-0.41 ummol/mg protein for normal, and 0.43--0.49 mumol for cystic fibrosis cell membranes. The proportions of individual phospholipid classes and their fatty acid compositions as well as that of the total membrane lipid also did not differ significantly in the two cell types. The bulk lipid fluidity as reflected by the fluorescence polarization of beta-parinaric acid and diphenylhexatriene was also not changed. The carbohydrate composition of cell surface glycopeptides released with papain was not consistently different with the normal and cystic fibrosis cells. The quantity of fucose in intact plasma membranes was also quantitated enzymatically and found to be very similar in both cell types.

Cell surface sialylation of glycoproteins and glycosphingolipids in cultured metastatic variant RNA-virus transformed non-producer BALB/c 3T3 cell lines

The sialic acid composition and the display of cell surface sialyl components of several metastatic variant RNA-virus-transformed non-producer BALB/c 3T3 have been studied in culture. The following observations have been made concerning the sialyl components in these lines: (1) the compositions of whole-cell total, protein-bound and lipid-bound sialic acid were not appreciably different; (2) the surface sialic acid studied using the neuraminidase-galactose oxidase method and metabolic labelling followed by neuraminidase hydrolysis showed a positive correlation with the metastatic properties of these lines; (3) the degree of surface sialylation determined by galactose oxidase--sodium borotritide labelling of neuraminidase-treated and untreated cells revealed that 44--89% of exposed galactose and/or N-acetyl galactosamine residues of total cell-surface saccharides were sialylated in highly and intermediately metastatic lines as compared with 11-30% in the poorly and non-metastatic lines; (4) the cell surface glycoproteins and glycosphingolipids contributed equally well in their degree of sialylation and there was a positive correlation with the metastatic properties of the cells in vivo; (5) the cell surface proteins labelled by the lactoperoxidase-catalyzed iodination technique, followed by gel electrophoresis, showed some minor differences between metastatic variant lines. However, glycoproteins detected by the galactose oxidase labelling of neuraminidase-treated and untreated cells showed major differences in composition between the metastatic variant lines. The study of four highly metastatic lines has shown that the cells of these lines were enriched in several sialyl-glycoproteins, whereas three non tumorigenic lines and two poorly metastatic or non-metastatic lines contained unsialylated glycoproteins. The results indicate an enhancement of the degree of sialylation of surface glycoconjugates accompanying the metastatic process in RNA-virus-transformed mouse lines.

Detection of ectosiallyltransferase activity using whole cells. Correction of misleading results due to the release of intracellular CMP-N-acetylneuraminic acid

An inhibitory effect due to broken cells is observed when sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) is measured with mixture of intact and homogenized lymphocytes. This intracellular inhibitory factor ib purified and characterized as CMP-N-acetylneuraminic acid (CMP-NeuNAc) by its behavior in various chromatographic and electrophoretic systems and by its susceptibility to CMP-NeuNAc hydrolase. This endogenous CMP-NeuNAc leads to an isotopic dilution of the exogenous labelled CMP-NeuNAc explaining the apparently lower activity of homogenate when compared to whole cells. Consequently, the radioactivity bound to acceptors may not be related to a known number of sialyl residues transferred, calling into question the validity of comparing the incorporation of [14C]NeuNAc by homogenate and whole cells in order to assign sialyltransferase activity to ectoenzyme. A new approach is developed to detect ectoglycosyltransferases with whole cells, taking into account that both intracellular enzymes and endogenous precursor may be introduced by the small percentage of broken cells.

Sialyltransferase activities of aging diploid fibroblasts

Sialyltransferase activity and cell-cell adhesion rates of aging WI-38 cells were studied to determine the possible basis for a previously described decrease in membrane bound sialic acid and loss of proliferation of senescent cells. Ectosialyltransferase was demonstrated on the surface of both young and old WI-38 cells. The sialyltransferase assays consist of an enzyme source which is either the surface of intact cells (ectoenzyme) or a Triton X-100 cell homogenate, the nucleotide sialic acid donor (cytidine monophosphate-N-acetylneuraminic acid), and an asialo-acceptor which may be endogenous to the enzyme preparation or may be added exogenously. When sialyltransferase activity is measured in the absence of exogenous acceptors, there is a greater amount of sialic acid transferred by odl cells. However, when exogenous acceptors are provided, the amount of transfer is stimulated to a greater extent in young cells equalizing the amount of sialic acid incorporated into young and old cells. This suggests that there are fewer asialoglycoproteins and that acceptor concentration is a limiting factor in assays of young cell sialyltransferase. The end result of this may be the previously described decreased amount of membrane-bound sialic acid of old cells. A change in the adhesiveness of old cells is described which may be related to the altered cell surface.

Increased resistance to influenza as a possible source of heterozygote advantage in cystic fibrosis

Cystic fibrosis is the most common lethal or semi-lethal genetic disease in Caucasians of Central European origin, among whom it is inherited as an autosomal recessive trait at a frequency approximately 10 times that expected from recurrent mutation alone. A decreased sialic acid content has been observed in cell surface glycoproteins on cystic fibrosis fibroblasts and in numerous soluble glycoprotein preparations from cystic fibrosis homozygotes. Sialic acid residues on cell surface glycoconjugates play an essential role in the binding and infectivity of myxoviruses and paramyxoviruses, including those causing pandemic influenza. It is suggested that increased resistance to these viruses conferred by similar but quantitatively smaller alterations in sialoglycoconjugate structure in cystic fibrosis heterozygotes may have provided a selective advantage to maintain the high frequency of the cystic fibrosis gene in Caucasian populations.

Structure of the disaccharide chain of galactosyl-N-acetylgalactosaminyl-protein synthesized in vitro

In order to obtain a [14C]galactosyl-N-acetylgalactosaminyl-protein which would be useful as an acceptor in studies on the specificity of glycosyltransferases, a porcine submaxillary gland microsomal galactosyltransferase preparation was used for the galactosylation in vitro of N-acetylgalactosaminyl-protein (desialylated ovine submaxillary mucin). The newly formed oligosaccharide unit was obtained as a reduced disaccharide after alkaline borohydride treatment of the [14C]galactosyl-N-acetylgalactosaminyl-protein product and as glycopeptides by proteolytic digestion of the glycoprotein. The reduced disaccharide consisted of equimolar amounts of galactose and N-acetylgalactosaminitol and was characterized by thin-layer chromatography, high-voltage electrophoresis and gas-liquid chromatography. Periodate oxidation studies on the reduced disaccharide revealed that [14C]galactose was linked to position C-3 on the N-acetylgalactosaminyl residue. Digestion of the reduced disaccharide and the glycopeptides with galactosidases gave equivocal results as to the anomeric configuration of the [14C]galactose residue. Nuclear magnetic resonance of the reduced disaccharide, however, definitely indicated that the configuration was beta. The specificity of the porcine submaxillary gland galactosyltransferase thus can be defined as a uridine diphosphogalactose: alpha-D-N-acetylgalactosaminyl-protein beta 1 leads to 3 transferase activity.

Decrease of human serum fucosyltransferase as an indicator of successful tumor therapy

Surgical removal of colon carcinomas leads to a decrease in the rate of incorporation of [14C]fucose into its endogenous acceptor in human serum; normal incorporation rates are attained within 14 days. A similar time course has been determined for alpha2- and alpha3-fucosyltransferase when either desialo- or desialodegalactofetuin are employed as exogenous acceptors. A correlation has also been seen between transferase activity and the therapeutic response of patients with breast cancer. These results indicate that the determination of fucosyltransferase activity can facilitate the diagnosis of neoplasia, and the success of surgery, chemotherapy, or radiation.

Sialyltransferase activity in regenerating rat liver

Liver microsomal fractions catalyse the transfer of sialic acid from CMP-N-acetyl-neuraminic acid to various exogenous acceptors such as desialylated fetuin, desialylated human Tamm-Horsfall glycoprotein and desialylated bovine submaxillary-gland mucin. An increase in the rate of incorporation of sialic acid into desialylated glycoproteins was found after a lag period (7h) in regenerating liver. The increase was maximum 24h after partial hepatectomy for all acceptors tested. At later times after operation the sialyltransferase activity remained high only for desialylated fetuin. No soluble factors from liver or serum of partially hepatectomized animals influenced the activity of the sialyltransferases bound to the microsomal fraction. The sensitivity of sialyltransferases to activation by Triton X-100, added to the incubation medium, was unchanged in the microsomal preparation from animals 24h after sham operation or partial hepatectomy. The full activity of sialyltransferases towards the various desialylated acceptors showed some differences. Human Tamm-Horsfall glycoprotein was a good acceptor of sialic acid only when desialylated by mild acid hydrolysis. After this treatment, but not after enzymic hydrolysis, a decrease in molecular weight of human Tamm-Horsfall glycoprotein was observed. Further, the sialyltransferase activity as a function of incubation temperature gave different curves according to the acceptor used. The relationship between the biosynthesis of glycoproteins by regenerating liver and the sialyltransferase activity of microsomal fraction after partial hepatectomy is discussed.

Comparison of the surface glycoprotein components in the isolated cells of hamster melanotic and amelanotic melanomas

A suspension of melanoma cells isolated non-enzymatically from tumors (melanotic and amelanotic) of transplantable melanoma in Syrian hamster was treated with trypsin to obtain surface material. In the material released from the cell surface contents of protein, aminosugars, fucose, sialic acids and hexoses were determined. Differences in the composition of the surface material derived from two kinds of melanoma were observed. The differences in the surface glycoprotein composition seem to be related to biological properties of both melanomas.

Cell surface and metabolic labelling of the proteins of normal and transformed chicken cells

We have studied the surface proteins of normal and transformed chick cells using four-labelling techniques with different specificities, (a) lactoperoxidase catalysed iodination (b) galactose oxidase/B3H4 (c) pyridoxal phosphate/B3H4 and (d) periodate/B3H4. All methods labelled a large external transformation-sensitive (LETS) protein, in agreement with previous studies. In addition, using galactose oxidase and periodate labelling techniques, we present evidence which suggests that the transformed cell surface glycoproteins are more sialylated. The LETS protein was also labelled with (14C) glucosamine and after trypsinization a small band of identical molecular weight to LETS remained, possibly representing an internal pool of the protein. In contrast LETS protein labelled with (3H) fucose was completely removed by trypsin, suggesting that the internal pool of the protein is incompletely glycosylated. Evidence is also presented to show that although the level of the protein is drastically reduced at the transformed cell surface, it is still synthesised and shed into the medium.

Sindbis virus glycoproteins: effect of the host cell on the oligosaccharides

Sindbis virus was grown in four different host cells and the carbohydrate portions of the glycoproteins were analyzed. Sindbis virus grown in BHK-21 cells has more sialic acid and galactose than Sindbis virus grown in chicken embryo cells. In other respects the carbohydrates from virus grown in these two hosts are very similar. Sindbis virus grown either in chick cells transformed by Rous sarcoma virus or in BHK cells transformed by polyoma virus was also examined. In comparisons of virus from normal and transformed cells, differences in the amount of sialic acid were observed; but otherwise the carbohydrate structures appeared basically similar. The growth conditions used for the host cell also affected the degree of completion of the carbohydrate chains of the viral glycoproteins.

Cholera toxin and cell growth: role of membrane gangliosides

The binding of cholera toxin to three transformed mouse cell lines derived from the same parent strain, and the effects of the toxin on DNA synthesis and adenylate cyclase activity, vary in parallel with the ganglioside composition of the cells. TAL/N cells of early passage, which contain large quantities of gangliosides G(M3), G(M2), G(M1), and G(Dla), as well as the glycosyltransferases necessary for the synthesis of these gangliosides, bind the most cholera toxin and are the most sensitive to its action. TAL/N cells of later passage, which lack chemically detectable G(M1) and G(Dla) and which have no UDP-Gal:G(M2) galactosyltransferase activity, are intermediate in binding and response to the toxin. SVS AL/N cells, which lack G(M2) in addition to G(M1) and G(Dla) and which have little detectable UDP-GalNAc:G(M3)N-acetylgalactosaminyltransferase activity, bind the least amount of toxin. The SVS AL/N cells are the least responsive to inhibition of DNA synthesis and stimulation of adenylate cyclase activity by cholera toxin. Gangliosides (especially G(M1)), which appear to be the natural membrane receptors for cholera toxin, may normally have important roles in the regulation of cell growth and cAMP-mediated responses.

Isolation of a major cell surface glycoprotein from fibroblasts

A cell surface component has been isolated in partially purified form from cultured chick embryo and chick heart fibroblasts. This glycoprotein is similar to a protein recently reported to be present at the surface of normal cells, and missing after neoplastic transformation. It is a major cell surface glycoprotein that is synthesized by cultured fibroblasts, but is not collagen. It is shown to be markedly trypsin-sensitive, and its recovery from the cell surface is dependent on cell density. It is excluded from Sephadex G-200, but is not rapidly sedimented by ultracentrifugation, and has an apparent molecular weight of 220,000. The isolation of this cell surface glycoprotein may now provide a means of determining its function.

Electrophoretic mobility and agglutinability of red blood cells: a "new" polymorphism in mice

A quantitative method has been developed to determine agglutinability of mouse red blood cells. Tests with different inbred strains of mice revealed only two phenotypes. The same inbred strains were tested with the cytopherometer to determine the electrophoretic mobility of the corresponding red cells. Again, two phenotypes were uncovered, and faster mobility was found in the red cells that had higher agglutinability. The genetic control of this character is autosomal and codominant, and segregates independently of H-2 and coat color.