Testi R, Pulcinelli F M, Cifone M G, Botti D, Del Grosso E, Riondino S, Frati L, Gazzaniga P P, Santoni A
Department of Experimental Medicine, University of Rome La Sapienza, Italy.
J Immunol. 1992 May 1;148(9):2867-71.
CD69 is a signal transducing disulfide-linked homodimer functionally expressed on platelets, CD3bright thymocytes, and activated lymphocytes. In an attempt to investigate early molecular events in CD69-mediated cell activation we studied the relative contribution of phospholipase A2 (PLA2) and phosphatidylinositol-specific phospholipase C-dependent pathways during platelet activation induced by CD69 stimulation. Thromboxane A2 (TXA2) synthetase inhibitor and TXA2R inhibitor R68070 were able to inhibit platelet aggregation induced by CD69 stimulation, indicating that TXA2 was the main mediator of the response. CD69-induced arachidonic acid release and TXA2 production were essentially PLA2 dependent because they could be blocked by the PLA2 inhibitor quinacrine. Inositol 1,3,4-trisphosphate generation was clearly detectable after CD69 cross-linking, but it was completely abrogated by quinacrine and R68070 and therefore secondary to TXA2 release and TXA2R engagement. Finally, direct measurement of enzymatic activity in vitro using radiolabeled phospholipid vesicles showed that CD69 cross-linking resulted in PLA2-dependent arachidonic acid and lysophosphatidylcholine generation from phosphatidylcholine, which was sensitive to quinacrine but not to R68070. By contrast, CD69-induced 1,2-diacylglycerol release from phosphatidylinositol 4,5-bisphosphate was blocked by both inhibitors. These results indicate a preferential involvement of PLA2 in CD69-dependent signal transduction in platelets and provide evidence for the unique role of PLA2-mediated activation pathways in transmembrane receptor signaling.
CD69是一种通过二硫键连接的信号转导同型二聚体，在血小板、CD3bright胸腺细胞和活化淋巴细胞上功能性表达。为了研究CD69介导的细胞活化早期分子事件，我们研究了磷脂酶A2（PLA2）和磷脂酰肌醇特异性磷脂酶C依赖性途径在CD69刺激诱导的血小板活化过程中的相对作用。血栓素A2（TXA2）合成酶抑制剂和TXA2R抑制剂R68070能够抑制CD69刺激诱导的血小板聚集，表明TXA2是该反应的主要介质。CD69诱导的花生四烯酸释放和TXA2产生基本上依赖于PLA2，因为它们可被PLA2抑制剂奎纳克林阻断。CD69交联后可明显检测到肌醇1,3,4-三磷酸的生成，但它被奎纳克林和R68070完全消除，因此是TXA2释放和TXA2R结合的继发结果。最后，使用放射性标记的磷脂囊泡在体外直接测量酶活性表明，CD69交联导致PLA2依赖性花生四烯酸和溶血磷脂酰胆碱从磷脂酰胆碱生成，这对奎纳克林敏感但对R68070不敏感。相比之下，CD69诱导的磷脂酰肌醇4,5-二磷酸释放1,2-二酰基甘油被两种抑制剂阻断。这些结果表明PLA2优先参与血小板中CD69依赖性信号转导，并为PLA2介导的活化途径在跨膜受体信号传导中的独特作用提供了证据。
