A Specific Metabolic Activity on the Surface Membrane in Malignant Cell-Transformation

Abstract

The carbohydrate-binding protein, Concanavalin A (Con A), binds to glucose-or mannose-like sites on the cell-surface membrane. Unless the cells are treated with trypsin, this protein agglutinates malignantly transformed cells, but not normal cells. The transformed cells were agglutinated at 240C but not at 40C. Transformed and normal cells treated with trypsin were agglutinated at both 240C and 4VC with high concentrations of Con A (500 jug/ml), but only at 240C with low concentrations (5 ug/ml). The same number of Con A molecules were bound to normal and transformed cells at both temperatures. The results indicate that the site for Con A on the surface membrane contains two activities, a component that binds Con A molecules (B) and a component that determines agglutination (A). B is not temperature sensitive and is active in normal and transformed cells, whereas A, which is temperature sensitive, is in an active form only in transformed cells. A can be activated by trypsin, and the increased activity per cell allows agglutination at 4VC with a high, but not with a low, concentration of Con A. Agglutination of transformed cells by wheatgerm agglutinin, which binds to N-acetyl-D-glucosaminelike sites, and by soybean agglutinin, which binds to Nacetyl-D-galactosamine-like sites, was not temperature sensitive. Thus, the temperature-sensitive component A is specific for Con A, and malignant transformation of normal cells, which results in agglutinability by Con A, is associated with the activation of a specific temperaturesensitive activity on the surface membrane.Studies with the carbohydrate-binding protein Concanavalin A (Con A) (1), which binds to glucose-or mannose-like sites on the surface membrane, have shown a difference in the structural organization of the surface membrane of normal and malignantly-transformed cells. Transformed cells can be agglutinated by Con A, but this protein only agglutinates normal cells after they have been treated with trypsin (2). Measurements of the binding of labeled Con A molecules to the cell surface show that the change in the structure of the surface membrane in cell transformation can be explained by three types of changes in the structural organization of binding sites for Con A. There can be an exposure of cryptic sites, a concentration of exposed sites by a decrease in cell size, or a rearrangement of exposed sites without a decrease in cell size that results in a clustering of sites (3, 4). The change in the structure of the surface membrane in cell transformation is also reflected by a difference in the location of sites for aminoacid and carbohydrate transport (5), and by a differential toxic effect of Con A on normal and transformed cells (6). The present experiments were undertaken to determine (a) whether agglutination of transformed cells by Con A is due only to the binding of Con A molecules to the surface membrane or whether it also requires specific metabolic activities, (b) whether agglutination of normal cells after treatment with trypsin is due to t...

Differences in the Binding of Fluorescent Concanavalin A to the Surface Membrane of Normal and Transformed Cells

“…This agglutination is temperature sensitive (3). Measurements of the binding of radioactively labeled Con A to cells cultured under different conditions have shown that the change in structure of the surface membrane in cell transformation can be explained by three types of changes in binding sites.…”

Galactosyltransferase and Concanavalin A Agglutination of Cells

“…Others have explained Con A agglutinability by suggesting the presence of masked and unmasked sites; only the latter would permit agglutination (14). Still others have proposed an enzymatic involvement in the Con A agglutination process (15). shown by macro-Ouchterlony immunodiffusion, as well as the ability to purify the rabbit erythrocyte galactosyltransferase on Con A-Sepharose.…”

Changes in concanavalin A-mediated agglutination of hormone-dependent mouse mammary tumour cells during serial transplantation

“…Concanavalin A (Con A) is widely used in comparative studies of normal and tumour cells. In many cases, Con A agglutinates tutmoutr cells more easily than noninmitotic normal cells (Inbar & Sachs,1 969; Burger, 1969;Inbar et al, 1971). Con A is often used in experiments where a causal relation is sought between agglutinability and (lifferences in growth control (Burger, 1970;Inbar et al, 1972 (Sluyser & Van Nie, 1974).…”