Valentino L A, Ladisch S
Department of Padiatrics, Rush Children's Hospital, Chicago, IL 60612-3833, USA.
Biochim Biophys Acta. 1996 May 24;1316(1):19-28. doi: 10.1016/0925-4439(95)00092-5.
Gangliosides, 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 microgram/ml) of collagen, cause platelet aggregation (59 +/- 10%) and ATP release (2.3 +/- 0.2 nmol) equivalent to that caused by 10 micrograms/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 alpha 2 beta 1, a major integrin collagen receptor on platelets. Incubation of platelets with a monoclonal antibody directed against the alpha 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 microgram/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, GD2, enhanced alpha 2 beta 1-mediated platelet adhesion to immobilized collagen in an antibody 5E8-inhibitable manner. These findings implicate the alpha 2 beta 1-collagen interaction as a target of the effect of tumor-derived gangliosides.
神经节苷脂是含唾液酸的糖鞘脂，可增强血小板与胶原蛋白的黏附以及随后的血小板激活。例如，将神经母细胞瘤肿瘤细胞（NBTG）释放的神经节苷脂添加到亚阈值（非激活）浓度（1微克/毫升）的胶原蛋白中，会导致血小板聚集（59±10%）和ATP释放（2.3±0.2纳摩尔），这与单独使用10微克/毫升胶原蛋白所引起的情况相当。在此，我们报告进一步的研究以表征这种效应。NBTG与亚阈值浓度的二磷酸腺苷、肾上腺素、凝血酶或花生四烯酸联合使用时，不会诱导血小板聚集和ATP释放，这表明NBTG特异性地影响胶原蛋白介导的血小板激活。最大程度的血小板聚集和ATP释放需要细胞外镁，并且仅需与NBTG进行短时间（1分钟）的预孵育，这表明这种神经节苷脂活性是由胶原蛋白受体介导的机制。由于神经节苷脂与几种整合素受体相互作用，我们确定NBTG是否影响α2β1，这是血小板上主要的整合素胶原蛋白受体。用针对α2链的单克隆抗体（5E8）孵育血小板，可阻断由NBTG和1微克/毫升胶原蛋白诱导的血小板聚集增加（9±3%对80±2%）以及ATP释放（<0.2对2.5±0.1纳摩尔）。用针对非整合素胶原蛋白受体CD36的抗体或同型对照抗体孵育，不会消除NBTG的作用。最后，NBTG及其主要成分GD2，以抗体5E8可抑制的方式增强了α2β1介导的血小板与固定化胶原蛋白的黏附。这些发现表明α2β1-胶原蛋白相互作用是肿瘤衍生神经节苷脂作用的靶点。
