Kashiwagi Hirokazu, Shiraga Masamichi, Kato Hisashi, Kamae Tsuyoshi, Yamamoto Naoko, Tadokoro Seiji, Kurata Yoshiyuki, Tomiyama Yoshiaki, Kanakura Yuzuru
Department of Hematology and Oncology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Blood. 2005 Aug 1;106(3):913-21. doi: 10.1182/blood-2004-10-4092. Epub 2005 Apr 14.
Semaphorin 3A (Sema3A) is a secreted disulfide-bound homodimeric molecule that induces growth cone collapse and repulsion of axon growth in the nervous system. Recently, it has been demonstrated that Sema3A is produced by endothelial cells and inhibits integrin function in an autocrine fashion. In this study, we investigated the effects of Sema3A on platelet function by using 2 distinct human Sema3A chimera proteins. We detected expression of functional Sema3A receptors in platelets and dose-dependent and saturable binding of Sema3A to platelets. Sema3A dose-dependently inhibited activation of integrin alphaIIbbeta3 by all agonists examined including adenosine diphosphate (ADP), thrombin, convulxin, phorbol 12-myristate 13-acetate, and A23187. Sema3A inhibited not only platelet aggregation induced by thrombin or collagen but also platelet adhesion and spreading on immobilized fibrinogen. Moreover, Sema3A impaired alphaIIbbeta3-independent spreading on glass coverslips and aggregation-independent granular secretion. Sema3A inhibited agonist-induced elevation of filamentous action (F-actin) contents, phosphorylation of cofilin, and Rac1 activation. In contrast, Sema3A did not affect the levels of cyclic nucleotides or agonist-induced increase of intracellular Ca2+ concentrations. Thus, the extensive inhibition of platelet function by Sema3A appears to be mediated, at least in part, through impairment of agonist-induced Rac1-dependent actin rearrangement.
信号素3A（Sema3A）是一种分泌型的、通过二硫键结合的同二聚体分子，它可诱导生长锥塌陷并在神经系统中排斥轴突生长。最近，有研究表明Sema3A由内皮细胞产生，并以自分泌方式抑制整合素功能。在本研究中，我们使用两种不同的人Sema3A嵌合蛋白来研究Sema3A对血小板功能的影响。我们检测了血小板中功能性Sema3A受体的表达以及Sema3A与血小板的剂量依赖性和饱和性结合。Sema3A对包括二磷酸腺苷（ADP）、凝血酶、convulxin、佛波醇12 -肉豆蔻酸酯13 -乙酸酯和A23187在内的所有检测激动剂诱导的整合素αIIbβ3活化均具有剂量依赖性抑制作用。Sema3A不仅抑制凝血酶或胶原诱导的血小板聚集，还抑制血小板在固定化纤维蛋白原上的黏附和铺展。此外，Sema3A损害了在玻璃盖玻片上不依赖αIIbβ3的铺展以及不依赖聚集的颗粒分泌。Sema3A抑制激动剂诱导的丝状肌动蛋白（F -肌动蛋白）含量升高以及丝切蛋白的磷酸化和Rac1活化。相比之下，Sema3A不影响环核苷酸水平或激动剂诱导的细胞内Ca2 +浓度升高。因此，Sema3A对血小板功能的广泛抑制似乎至少部分是通过损害激动剂诱导的Rac1依赖性肌动蛋白重排介导的。
