Cell Density Regulates Antibody Accessibility and Metabolic Turnover of Gangliosides in Human Glioma Cells

The effects of cell density on the gangliosides of 4 human glioma cell lines were studied. The cell lines used were KG-1C (GM3-dominant) , A172 and H4 (GM2-dominant), and Hs683 (GM3, GM2-co-dominant) cells. All these cell lines showed higher immunofluorescence with anti-ganglioside antibodies in FACS analysis at sparse density than at confluent density. Steric hindrance from cell surface proteins had been removed by the pretreatment of the cells with trypsin. The chemical content of gangliosides was consistent throughout the time of cell growth. The mechanisms of crypticity of gangliosides at confluent culture were under investigation. We first evaluated the metabolic turnover rate of gang-liosides at different cell densities. The results clearly showed a more rapid turn-over of gangliosides at sparse density from approximately 2 to 4 fold in terms of radioactivities of incorporated tritium into gangliosides. The profiles of labeled gangliosides were also different between the sparse and confluent cultures. We speculate that better accessibilities of antibodies toward gangliosides should be facilitated by the same mechanism which should, in turn, provide easier access of carbohydrate-hydrolysis enzymes to gangliosides at sparse cell density in order to keep an enhanced turnover rate.