Tumor gangliosides enhance α2β1 integrin-dependent platelet activation

Abstract

Gamgliosides, sialic acid-containing glycosphingolipids, enhance platelet adhesion to collagen and consequent platelet activation. For example, gangliosides shed by neuroblastoma tumor cells (NBTG) added to a subthreshold (non-activating) concentration (1 μg/ml) of collagen, cause platelet aggregation (59 ± 10%) and ATP release (2.3 ± 0.2 nmol) equivalent to that caused by 10 μg/ml collagen alone. Here we report further studies to characterize this effect. Platelet aggregation and ATP release were not induced by NBTG in combination with subthreshold concentrations of adenosine diphosphate, epinephrine, thrombin or arachidonic acid, suggesting that NBTG specifically influences collagen-mediated platelet activation. Maximal platelet aggregation and ATP release required extracellular magnesium and only a short (1 min) preincubation with NBTG, suggesting a collagen receptor-mediated mechanism of this ganglioside activity. Since gangliosides interact with several integrin receptors, we determined whether NBTG influences α 2 β 1, a major integrin collagen receptor on platelets. Incubation of platelets with a monoclonal antibody directed against the α 2 chain (5E8) blocked the increase in platelet aggregation (9 ± 3% vs. 80 ± 2%) and ATP release (< 0.2 vs. 2.5 ± 0.1 nmol) induced by NBTG and 1 μg/ml collagen. Incubation with an antibody to the non-integrin collagen receptor, CD36, or with an isotype control antibody did not abrogate the effect of NBTG. Finally, NBTG and its major component, G D2, enhanced α 2 β 1-mediated platelet adhesion to immobilized collagen in an antibody 5E8-inhibitable manner. These findings implicate the α 2 β 1-collagen interaction as a target of the effect of tumor-derived gangliosides.