Binding of monosialoganglioside by murine thymus cells in vitro.

Abstract

Abstract Binding of tritium-labeled monosialoganglioside (G m1 ) by intact thymocytes of young AKR/J mice was studied in vitro . The binding was dependent on time, temperature, concentration of cells, and ganglioside, suggesting that the cells possess a finite number of G m1 -binding sites. Binding, which could be observed as early as 15 sec, was very rapid, reaching a plateau in about 5 min, followed by a slow and steady increment up to 4 hr of incubation. Cellular binding of G m1 appeared to be tight with very little exchange with exogenous gangliosides. G m1 was almost entirely recovered intact 30 min after it was bound by thymus cells. The structural components of G m1 (galactose, glucose, N -acetylneuraminic acid, mixed ceramides, and lactosylceramide) did not compete with G m1 for cellular binding. The relative specificity of the G m1 -binding site was revealed by the lack of competition by lactosylceramide and very weak competition by disialoganglioside and trisialoganglioside that appeared to be due to a G m1 contamination in these preparations. Further characterization of the G m1 -thymocyte interaction indicated that it was a Ca 2+ -dependent process, since chelating agents ethyleneglycolbis(β-aminoethyl ether)- N,N′ -tetraacetic acid and ethylenediaminetetraacetic acid inhibited the binding up to 75 to 80%, and the inhibition by ethyleneglycolbis(β-aminoethyl ether)- N,N′ -tetraacetic acid was reversed by the addition of excess of Ca 2+ . Also, there appeared to be no overlap of the G m1 -binding site with the binding site for concanavalin A. Finally, a comparison of the amount of G m1 bound by leukemic and nonleukemic thymus cells revealed that the tumor cells have a higher capacity to bind G m1 molecules than do normal thymus cells on a per cell basis under several experimental conditions.