Yi T, Zhang J, Miura O, Ihle J N
Department of Cancer Biology, Cleveland Clinic Foundation Research Institute, OH.
Blood. 1995 Jan 1;85(1):87-95.
Erythropoietin (Epo) binding to its receptor (EpoR) induces tyrosine phosphorylation in responsive cells and this ability is required for a mitogenic response. One of the substrates of tyrosine phosphorylation is the Epo receptor (EpoR). The carboxyl region of EpoR cytoplasmic domain is required for EpoR phosphorylation and has been shown to negatively affect the response to Epo both in vivo and in cell lines. Hematopoietic cell phosphatase (HCP) has also been hypothesized to negatively regulate erythropoiesis, based on the hypersensitivity to Epo of erythroid lineage cells in moth-eaten mice that genetically lack HCP. In the studies presented here, we show that HCP binds the tyrosine phosphorylated Epo receptor through the amino-terminal src-homology 2 (SH2) domain of HCP. Using a series of phosphotyrosine-containing peptides, potential HCP binding sites in the cytoplasmic domain of the EpoR are identified. The results support the concept that, after Epo stimulation, phosphorylation of EpoR provides a docking site for HCP in the receptor complex. Recruitment of HCP to the complex and its subsequent dephosphorylation of substrates and/or associated kinases may be important to mitigate the ligand-induced mitogenic response.
促红细胞生成素（Epo）与其受体（EpoR）结合可诱导反应性细胞中的酪氨酸磷酸化，而这种能力是有丝分裂反应所必需的。酪氨酸磷酸化的底物之一是促红细胞生成素受体（EpoR）。EpoR细胞质结构域的羧基区域是EpoR磷酸化所必需的，并且已证明在体内和细胞系中均会对Epo反应产生负面影响。基于基因缺失造血细胞磷酸酶（HCP）的噬齿小鼠中红系谱系细胞对Epo的超敏反应，也有人推测HCP对红细胞生成具有负调控作用。在本文所展示的研究中，我们发现HCP通过其氨基末端的src同源2（SH2）结构域与酪氨酸磷酸化的Epo受体结合。利用一系列含磷酸酪氨酸的肽段，我们鉴定出了EpoR细胞质结构域中潜在的HCP结合位点。这些结果支持了这样一种概念，即Epo刺激后，EpoR的磷酸化在受体复合物中为HCP提供了一个停靠位点。HCP募集到复合物中以及随后对底物和/或相关激酶的去磷酸化作用，对于减轻配体诱导的有丝分裂反应可能很重要。
