Shedding of human neuroblastoma gangliosides

Gangliosides shed by tumor cells are implicated in modulating tumor formation. For example, rapid progression of human neuroblastoma tumors is associated with high circulating levels of shed GD2 ganglioside. To elucidate the kinetic and qualitative characteristics of tumor cell ganglioside shedding, which is difficult to accomplish in vivo, we examined this process in LAN-5 human neuroblastoma cells in vitro. Three major gangliosides, GD2, GM2 and GT1b, comprise 82% of the mean total of 38 nmol LBSA/10(8) cells. These molecules are shed very rapidly (1-3 pmol/10(6) cells per h, or approx. 0.5% of the total cell gangliosides per h). Quantitative and qualitative characteristics of ganglioside shedding are remarkably constant over a 40-fold range of cell density. Not only GD2, but every major carbohydrate species is shed, in proportion to its concentration in the cell, with slightly greater shedding of ceramide subspecies containing shorter chain fatty acids. These findings were confirmed in three other neuroblastoma cell lines, LAN-1, IMR and KCNR. We suggest that the high expression and rapid generalized shedding of human neuroblastoma tumor gangliosides results in significant in vivo accumulation of these biologically active molecules during tumor growth.