Effects of human brain cell culture conditions on [14C]glucosamine radioactivity incorporation into gangliosides

Human glioma cells (12-18) and fetal neural cells (CH II) in culture were exposed for 20 hr to [14C]glucosamine to determine the level and distribution of radiolabel incorporated into gangliosides. Cells of identical passage levels at two stages of growth, preconfluent and confluent, were preincubated for 0 to 60 hr in serum-free medium (SFM). Both higher cell densities and longer incubations in SFM caused a change in the amounts and patterns of radiolabeled gangliosides. Preincubation for 60 hr in SFM caused an increase (P less than 0.05) in the percent of total recovered ganglioside radiolabel in GM1 of CH II cells, from 10.5 to 16.7% in preconfluent cells and from 14.1 to 31.9% in confluent cells. Conversely, the proportion of radiolabel in GM3 and GM2 decreased with longer preincubations in SFM. A similar preincubation of glioma cells caused an increase in the proportion of label into GD1a of both preconfluent and confluent cells (P less than 0.02) from 4 to 11% of the total ganglioside radioactivity. Higher cell densities also resulted in consistently higher percent (of total ganglioside) incorporation into GD1a of 12-18 cells (P less than 0.05) and GM1 of CH II (P less than 0.01). These results show that there is a shift in the incorporation of precursor label into more complex gangliosides under conditions associated with the arrest of cell division. These phenomena may represent a regulatory response of the ganglioside biosynthetic apparatus to changes in extracellular environment and cell contact.