Vassbotn F S, Havnen O K, Heldin C H, Holmsen H
Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
J Biol Chem. 1994 May 13;269(19):13874-9.
Human platelets contain platelet-derived growth factor (PDGF) in their alpha-granules which is released during platelet exocytosis. We show by immunoprecipitation and 125I-PDGF binding experiments that human platelets have functionally active PDGF alpha-receptors, but not beta-receptors. The PDGF alpha-receptor (PDGFR-alpha) was identified as a 170-kDa glycosylated protein-tyrosine kinase as found in other cell types. Stimulation of platelets with 0.1 unit/ml thrombin resulted in a significant increase (2-5-fold) of the tyrosine phosphorylation of the PDGFR-alpha, as determined by immunoprecipitation with phosphotyrosine antiserum as well as with PDGFR-alpha antiserum. The observed thrombin-induced autophosphorylation of the PDGFR-alpha was inhibited by the addition of a neutralizing monoclonal PDGF antibody. Thus, our results suggest that the platelet PDGFR-alpha is stimulated in an autocrine manner by PDGF secreted during platelet activation. Preincubation of platelets with PDGF inhibited thrombin-induced platelet aggregation and secretion of ATP + ADP and beta-hexosaminidase. Thrombin-induced platelet aggregation was also reversed when PDGF was added 30 s after thrombin stimulation. Inhibition of the autocrine PDGF pathway during platelet activation by the PDGF antibody led to a potentiation of thrombin-induced beta-hexosaminidase secretion. Thus, the PDGFR-alpha takes part in a negative feedback regulation during platelet activation. Our demonstration of PDGF alpha-receptors on human platelets and its inhibitory function during platelet activation identifies a new possible role of PDGF in the regulation of thrombosis.
人血小板的α-颗粒中含有血小板衍生生长因子（PDGF），该因子在血小板胞吐过程中释放。我们通过免疫沉淀和¹²⁵I-PDGF结合实验表明，人血小板具有功能活性的PDGFα受体，但没有β受体。PDGFα受体（PDGFR-α）被鉴定为一种170 kDa的糖基化蛋白酪氨酸激酶，与其他细胞类型中发现的相同。用0.1单位/毫升凝血酶刺激血小板后，通过用抗磷酸酪氨酸抗血清以及PDGFR-α抗血清进行免疫沉淀测定，发现PDGFR-α的酪氨酸磷酸化显著增加（2 - 5倍）。添加中和性单克隆PDGF抗体可抑制观察到的凝血酶诱导的PDGFR-α自磷酸化。因此，我们的结果表明，血小板活化过程中分泌的PDGF以自分泌方式刺激血小板PDGFR-α。血小板与PDGF预孵育可抑制凝血酶诱导的血小板聚集以及ATP + ADP和β-己糖胺酶的分泌。在凝血酶刺激30秒后添加PDGF，也可逆转凝血酶诱导的血小板聚集。PDGF抗体在血小板活化过程中抑制自分泌PDGF途径，导致凝血酶诱导的β-己糖胺酶分泌增强。因此，PDGFR-α在血小板活化过程中参与负反馈调节。我们在人血小板上证明了PDGFα受体及其在血小板活化过程中的抑制功能，确定了PDGF在血栓形成调节中的一个新的可能作用。
