Gobert S, Porteu F, Pallu S, Muller O, Sabbah M, Dusanter-Fourt I, Courtois G, Lacombe C, Gisselbrecht S, Mayeux P
Institut Cochin de Génétique Moléculaire (ICGM), Université René Descartes, Paris, France.
Blood. 1995 Jul 15;86(2):598-606.
The erythropoietin (Epo) receptor belongs to the cytokine receptor superfamily. Although the cytokine receptors do not possess a tyrosine kinase consensus sequence in the intracellular domain, rapid stimulation of a tyrosine kinase activity occurs after activation by the ligand. We and others have shown that Epo induces the tyrosine phosphorylation of its cognate receptor as well as phosphorylation of other proteins. In this report, we examined the role of the receptor tyrosine residues in signal transduction. Eight tyrosine residues are located within the intracellular domain of the murine Epo receptor. A single tyrosine residue is present in the region previously shown to be sufficient for proliferative signal transduction. This tyrosine (Tyr 343) was mutated to phenylalanine. Moreover, mutant receptors were also generated with either a tyrosine residue or a phenylalanine residue at position 343 and with a COOH terminal truncation that removed the 7 other tyrosine residues. Expression vectors carrying these mutated receptors were transfected into the interleukin-3-dependent murine cell line Ba/F3. Epo-induced growth was sustained efficiently by all these receptors, although receptors without any tyrosine residues conferred a significantly reduced mitogenic activity. Moreover, all receptors were able to mediate Epo-dependant accumulation of beta-globin mRNA. The mutated receptors all induced the tyrosine phosphorylation of several cellular proteins after Epo stimulation. However, the truncated receptors induced the phosphorylation of a reduced number of proteins, suggesting that phosphorylated tyrosines of the receptor could have a role in the recruitment either of a tyrosine kinase or of tyrosine kinase substrate proteins. The receptors were all able to mediate Epo-induced activation of phosphatidylinositol 3-kinase, although truncated receptors no longer bound phosphatidylinositol 3-kinase.
促红细胞生成素（Epo）受体属于细胞因子受体超家族。尽管细胞因子受体在细胞内结构域中不具有酪氨酸激酶共有序列，但在配体激活后会迅速刺激酪氨酸激酶活性。我们和其他人已经表明，Epo可诱导其同源受体的酪氨酸磷酸化以及其他蛋白质的磷酸化。在本报告中，我们研究了受体酪氨酸残基在信号转导中的作用。八个酪氨酸残基位于小鼠Epo受体的细胞内结构域内。在先前显示足以进行增殖信号转导的区域中存在单个酪氨酸残基。该酪氨酸（Tyr 343）突变为苯丙氨酸。此外，还产生了突变受体，其在343位带有酪氨酸残基或苯丙氨酸残基，并带有COOH末端截短，去除了其他7个酪氨酸残基。携带这些突变受体的表达载体被转染到依赖白细胞介素-3的小鼠细胞系Ba/F3中。尽管没有任何酪氨酸残基的受体赋予的促有丝分裂活性明显降低，但所有这些受体都能有效地维持Epo诱导的生长。此外，所有受体都能够介导Epo依赖的β-珠蛋白mRNA的积累。突变受体在Epo刺激后均诱导了几种细胞蛋白的酪氨酸磷酸化。然而，截短的受体诱导的蛋白磷酸化数量减少，这表明受体的磷酸化酪氨酸可能在募集酪氨酸激酶或酪氨酸激酶底物蛋白中起作用。所有受体都能够介导Epo诱导的磷脂酰肌醇3-激酶的激活，尽管截短的受体不再结合磷脂酰肌醇3-激酶。
