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

Demonstration of the existence, and partial characterization, of a cell-surface beta-hexosaminidase from rat splenocytes

Rat splenocytes are shown to exhibit cell-surface located beta-N-acetylglucosaminidase and beta-galactosidase activities. Preincubation experiments, solubilization experiments and chemical cross-linking experiments show that these enzymatic activities are indeed cell-surface localized. The solubilization and partial purification of the beta-N-acetylglucosaminidase activity is reported. Kinetic studies of the partially purified material with a variety of competitive inhibitors at several pH values suggest that at physiological pH the cell surface beta-N-acetylglucosaminidase may function as a carbohydrate binding protein rather than as a glycosidase.

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.

An analysis of concanavalin A-mediated agglutination in two Chinese hamster ovary subclones whose surface phenotypes respond to maintenance in medium supplemented with dibutyryl cyclic AMP. V. Biochemical composition of the plasma membrane

We have used two Chinese hamster ovary subclones whose surface phenotype has been extensively investigated with regard concanavalin A-mediated cell-cell agglutination and concanavalin A-induced receptor site clustering to investigate what changes in membrane composition, if any, can be correlated with the concanavalin A-detected changes in surface phenotype. These cell clones are uniquely disposed for this purpose since maintenance of the cells under different growth conditions produces changes in agglutinability and receptor site mobility in one cell clone (H-7W) but not the other (K-1). After extensive characterization of the surface membranes of these two subclones we have been unable to identify any change in the membrane peptides, glycopeptide, cholesterol, or fatty acid composition which can be directly correlated with the concanavalin A-detected surface phenotypes. It is of particular interest to note that we have been unable to correlate the presence or absence of the large external transformation-sensitive glycoprotein with the relative mobility of the lectin receptors or with the degree of concanavalin A-mediated cell agglutination. Furthermore we have been unable, in this system, to corroborate earlier data suggesting a role for cholesterol in determining the relative mobility of the lectin receptors. Thus using a cell system consisting of genetically matched cell clones, we have been unable to identify any changes in the biochemical composition of the plasma membrane which might be associated with the surface phenotypes detected by concanavalin A.