Effect of gangliosides on binding, internalization and cytotoxic activity of ricin

The only gangliosides in Burkitts' lymphoma EB-3 cells is GM3. Treatment of Burkitts' lymphoma EB-3 cells with ganglosides GM1 or GM3 results in their binding to and partial incorporation into the cell membrane. About 25% of cell-associated ganglioside GM 1 can interact with the ricin. However, such an increase in the number of binding sites does not enhance but rather decreases the cytotoxic effect of ricin. A similar protective effect was observed when the cells were pretreated with ganglioside GM3. In contrast, the increase in ricin binding sites caused by pretreatment of the cells with neuraminidase was accompanied by increase in ricin cytotoxicity. These differences may be related to observed differences in the rate of ricin-endocytosis by native and ganglioside-treated cells.