Horikawa Y, Matsumura I, Hashimoto K, Shiraga M, Kosugi S, Tadokoro S, Kato T, Miyazaki H, Tomiyama Y, Kurata Y, Matsuzawa Y, Kanakura Y
Department of Internal Medicine II, Osaka University Medical School, Osaka, Japan.
Blood. 1997 Nov 15;90(10):4031-8.
Thrombopoietin (TPO) is implicated as a primary regulator of megakaryopoiesis and thrombopoiesis through binding to the cytokine receptor c-Mpl (the product of the c-mpl proto-oncogene). In an effort to determine the pathophysiological role of TPO-c-Mpl system in essential thrombocythemia (ET), we have examined the levels of serum TPO and the expression and function of platelet c-Mpl in 17 patients with ET. In spite of extreme thrombocytosis, serum TPO levels were slightly elevated or within normal range in most, if not all, patients with ET (mean +/- SD, 1.31 +/- 1.64 fmol/mL), as compared with normal subjects (0.76 +/- 0.21 fmol/mL). Flow cytometric and Western blot analyses revealed that the expression of platelet c-Mpl was strikingly reduced in all patients with ET. Furthermore, the expression of platelet c-mpl mRNA was found to be significantly decreased in the ET patients tested. In contrast, almost identical levels of GPIIb/IIIa protein and mRNA were expressed in platelets from ET patients and normal controls. In addition to expression level, activation state of platelet c-Mpl was investigated in ET patients. Immunoblotting with anti-phosphotyrosine antibody showed that no aberrant protein-tyrosine phosphorylation was observed in platelets of ET patients before treatment with TPO, and the levels of TPO-induced protein-tyrosine phosphorylation, including c-Mpl-tyrosyl phosphorylation, roughly paralleled those of c-Mpl expression, suggesting that c-Mpl-mediated signaling pathway was not constitutively activated in platelets of ET patients. These results suggested that the TPO-c-Mpl system may not be directly linked to pathogenesis of ET, and that gene(s) mutated in ET may be important in regulating the levels of c-mpl gene expression in addition to the growth and differentiation of multipotential hematopoietic stem cells.
血小板生成素（TPO）通过与细胞因子受体c-Mpl（c-mpl原癌基因的产物）结合，被认为是巨核细胞生成和血小板生成的主要调节因子。为了确定TPO-c-Mpl系统在原发性血小板增多症（ET）中的病理生理作用，我们检测了17例ET患者的血清TPO水平以及血小板c-Mpl的表达和功能。与正常受试者（0.76±0.21 fmol/mL）相比，尽管ET患者存在极度血小板增多症，但大多数（即使不是全部）患者的血清TPO水平仅略有升高或在正常范围内（平均值±标准差，1.３1±1.64 fmol/mL）。流式细胞术和蛋白质印迹分析显示，所有ET患者血小板c-Mpl的表达均显著降低。此外，在检测的ET患者中发现血小板c-mpl mRNA的表达也显著下降。相比之下，ET患者和正常对照者血小板中GPIIb/IIIa蛋白和mRNA的表达水平几乎相同。除了表达水平外，我们还研究了ET患者血小板c-Mpl的激活状态。用抗磷酸酪氨酸抗体进行免疫印迹分析表明，在TPO治疗前，ET患者血小板中未观察到异常的蛋白酪氨酸磷酸化，TPO诱导的蛋白酪氨酸磷酸化水平，包括c-Mpl酪氨酸磷酸化，大致与c-Mpl表达水平平行，这表明ET患者血小板中c-Mpl介导的信号通路未被组成性激活。这些结果表明，TPO-c-Mpl系统可能与ET的发病机制没有直接联系，并且ET中发生突变的基因除了在多能造血干细胞的生长和分化中起重要作用外，可能在调节c-mpl基因表达水平方面也很重要。
