Shedding of gangliosides from tumor cells depends on cell density

Abstract

The ganglioside composition of mouse ascites hepatoma (MAH) cells, the ascites fluid and cell-conditioned media were determined and found to be qualitatively identical, but quantitatively different. The ganglioside content of the ascites fluid and the medium conditioned by MAH-cells at the native cell concentration (108 cells/ml) comprised, respectively, 74.9 and 23% of the cell-associated gangliosides. When incubated at lower cell-density (106 cells/ml) the cells were released at about 3 times higher the amount of ganglioside per cell than during incubation at the native concentration. Centrifugation of the dense-cell-conditioned medium revealed the major part of the released gangliosides to be associated with a 150,000 .times. g pellet that probably contains shed plasma membrane fragments. In the 150,000 .times. g pellet of the extracellular fluids the relative content of the most polar cell ganglioside corresponding chromatographically to GT1b was about 10-times higher than in the cells. The possibility is raised that the more intense shedding of gangliosides from less crowded MAH cells may play a role in the self protection of the tumor from host immune rejection during initial stages of growth.