Metabolic activities in human skin fibroblasts preloaded with labeled GM2-ganglioside

Density-dependent expression of ganglioside GM3 by human skin fibroblasts in an all-or-none fashion, as a possible modulator of cell growth in vitro

The expression of GM3 in human skin fibroblasts (cell type MF II) was investigated biochemically and immunochemically by means of the monoclonal antibody M2590. A cell density-related increase in total gangliosides (about threefold) and especially in GM3 (about sixfold) was found upon attainment of confluency. Immunostaining with mAb M2590 revealed that in preconfluent cultures GM3 is expressed by only a few cells in an all-or-none fashion. The portion of GM3-expressing cells increases in parallel with cell density. In confluent cultures, which are growth-arrested by contact inhibition, all cells are intensely stained by mAb M2590, indicating a high content of GM3 in the plasma membrane. These data suggest that increased cellular M2590 binding is due to an increased GM3 content rather than to an altered conformation or arrangement in the cell membrane. GM3-expressing cells usually show a broad, flat morphology, like that of cells in the resting state (G1/G0-phase) of the cell cycle. The M2590 staining on these cells appear as clusters, orientated along straight lines and indicating an ordered distribution of GM3 in the plasma membrane. A dose-dependent inhibition of cell growth by addition of exogenous gangliosides supports the possible involvement of these glycosphingolipids in the regulation of cell growth.