Ligand-independent oligomerization of cell-surface erythropoietin receptor is mediated by the transmembrane domain
Ligand-independent oligomerization of cell-surface erythropoietin receptor is mediated by the transmembrane domain
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DOI：
10.1073/pnas.081069198
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发表时间：
2001-04-10
影响因子：
11.1
通讯作者：
Lodish, HF
中科院分区：
文献类型：
--
作者：
Constantinescu, SN;Keren, T;Lodish, HF
促红细胞生成素 (Epo) 与 Epo 受体 (EpoR) 的结合对于成熟红细胞的产生至关重要。尽管已明确Epo结合的EpoR是二聚体，但尚不清楚在没有配体的情况下，完整的EpoR是单体还是寡聚体。使用活细胞表面表位标记受体的抗体介导的免疫荧光共补（寡聚化），我们在此表明全长鼠EpoR的主要部分以预先形成的二聚体/寡聚体存在于BOSC细胞中，BOSC细胞是人胚胎肾293T衍生的细胞。这种观察到的寡聚化是特异性的，因为在相同条件下，表位标记的 EpoR 不会与其他几种标记的受体（血小板生成素受体、转化生长因子 β 受体 II 型或催乳素受体）寡聚化，引人注目的是，EpoR 跨膜 (TM) 结构域而不是细胞外或细胞内结构域使催乳素受体能够与 EpoR 共配。 EpoR 寡聚物不具有组成型活性，需要 Epo 结合来诱导信号传导。与酪氨酸激酶受体（例如胰岛素受体）相比，当其 TM 结构域被糖蛋白 A 的强二聚化 TM 结构域取代时，酪氨酸激酶受体（例如胰岛素受体）无法发出信号，而 EpoR 可以耐受其 TM 结构域被糖蛋白 A 的 TM 结构域取代并保留信号传导。我们提出了一个模型，其中 TM 结构域诱导的二聚化将未配体的 EpoR 维持在非活性状态，可以通过 Epo 的生理水平轻松切换到活性状态。
Binding of erythropoietin (Epo) to the Epo receptor (EpoR) is crucial for production of mature red cells. Although it is well established that the Epo-bound EpoR is a dimer, it is not clear whether, in the absence of ligand, the intact EpoR is a monomer or oligomer. Using antibody-mediated immunofluorescence copatching (oligomerizing) of epitope-tagged receptors at the surface of live cells, we show herein that a major fraction of the full-length murine EpoR exists as preformed dimers/oligomers in BOSC cells, which are human embryo kidney 293T-derived cells. This observed oligomerization is specific because, under the same conditions, epitope-tagged EpoR did not oligomerize with several other tagged receptors (thrombopoietin receptor, transforming growth factor beta receptor type II, or prolactin receptor), Strikingly, the EpoR transmembrane (TM) domain but not the extracellular or intracellular domains enabled the prolactin receptor to copatch with EpoR, Preformed EpoR oligomers are not constitutively active and Epo binding was required to induce signaling. In contrast to tyrosine kinase receptors (e.g,, insulin receptor), which cannot signal when their TM domain is replaced by the strongly dimerizing TM domain of glycophorin A, the EpoR could tolerate the replacement of its TM domain with that of glycophorin A and retained signaling. We propose a model in which TM domain-induced dimerization maintains unliganded EpoR in an inactive state that can readily be switched to an active state by physiologic levels of Epo.