Kato Y, Hori S, Fujita N, Tsuruo T
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
Biochem Biophys Res Commun. 1998 Jan 14;242(2):250-5. doi: 10.1006/bbrc.1997.7917.
Platelets are nonproliferative and terminally differentiated cells. Platelets offer an attractive model system to study the various biochemical events leading to structural and functional alterations in activated cells. When platelets are exposed to stimuli, they are activated, undergo a dramatic shape change, adhere to each other, and aggregate. Several monoclonal antibodies (mAbs) that recognize CD9, GPIIb/IIIa (alpha IIb beta 3 intergrins), or GPIV are known to stimulate human platelet aggregation. However, no mAbs able to induce aggregation of mouse platelets have been reported. We have established an anti-mouse platelet mAb (AIP21) that can promote mouse platelet aggregation by itself. Because mouse platelets did not express the Fc receptor (FcR, CD32) on their surfaces and because AIP21 is an IgM subclass, AIP21 might promote platelet aggregation through an FcR-independent mechanism. We could not identify the antigen recognized by AIP21, but flow cytometric analysis revealed that it was not identical to CD9, GPIV, or integrins (i.e., alpha IIb, alpha v, alpha 5, alpha 6, beta 1, and beta 3 integrins). During the aggregation of mouse platelets mediated by AIP21, several 50-68-kDa proteins are rapidly phosphorylated at tyrosine residues. This phosphorylation by AIP21 was dose-dependent and did not require plasma components. We identified the 52-kDa phosphorylated protein as Shc. These results indicate that AIP21 could be useful for investigating the mechanisms of mouse platelet aggregation.
血小板是无增殖能力的终末分化细胞。血小板为研究导致活化细胞结构和功能改变的各种生化事件提供了一个有吸引力的模型系统。当血小板受到刺激时，它们会被激活，发生显著的形状变化，相互黏附并聚集。已知几种识别CD9、糖蛋白IIb/IIIa（αIIbβ3整合素）或糖蛋白IV的单克隆抗体（mAb）可刺激人血小板聚集。然而，尚未有能诱导小鼠血小板聚集的单克隆抗体的报道。我们已经制备了一种抗小鼠血小板单克隆抗体（AIP21），它自身就能促进小鼠血小板聚集。由于小鼠血小板表面不表达Fc受体（FcR，CD32），且AIP21是IgM亚类，AIP21可能通过一种不依赖FcR的机制促进血小板聚集。我们无法鉴定出AIP21识别的抗原，但流式细胞术分析表明它与CD9、糖蛋白IV或整合素（即αIIb、αv、α5、α6、β1和β3整合素）不同。在AIP21介导的小鼠血小板聚集中，几种5⁰⁻⁶⁸ kDa的蛋白质在酪氨酸残基处迅速磷酸化。AIP21引起的这种磷酸化是剂量依赖性的，且不需要血浆成分。我们鉴定出52 kDa的磷酸化蛋白为Shc。这些结果表明AIP21可能有助于研究小鼠血小板聚集的机制。
