Muto A, Watanabe S, Miyajima A, Yokota T, Arai K
Department of Molecular and Developmental Biology, Institute of Medical Science, University of Tokyo, Japan.
J Exp Med. 1996 Apr 1;183(4):1911-6. doi: 10.1084/jem.183.4.1911.
Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) receptor (hGMR) consists of alpha and beta subunits, and the precise stoichiometry of these subunits has remained to be determined. In this work, oligomerization of the beta subunit was studied using a chemical cross-linker. In Ba/F3, a mouse interleukin-3-dependent cell line expressing both subunits of hGMR (Ba/F3-alpha,beta), a protein with a molecular mass corresponding to that of a homodimer of the beta subunit (beta homodimer) was detected only when cells were treated with the cross-linker. Dimerization of the beta subunit was confirmed by coimmunoprecipitation of a tagged beta subunit with the wild type beta subunit COS7 cells. The beta homodimer had already formed in the absence of hGM-CSF, whereas stimulation with the ligand brought both alpha and beta subunits into a complex, the result being tyrosine phosphorylation of the beta homodimer. Tyrosine phosphorylation of the subunit was impaired by deletion of the cytoplasmic domain of the alpha subunit without interfering with the association of both subunits. These results indicate that the beta homodimer, which alone is insufficient for signaling, forms the functional hGMR with the alpha subunit in response to hGM-CSF.
人粒细胞巨噬细胞集落刺激因子（hGM-CSF）受体（hGMR）由α和β亚基组成，这些亚基的确切化学计量比仍有待确定。在这项研究中，使用化学交联剂对β亚基的寡聚化进行了研究。在Ba/F3（一种表达hGMR两个亚基的小鼠白细胞介素-3依赖性细胞系，Ba/F3-α,β）中，只有在用交联剂处理细胞时，才能检测到一种分子量与β亚基同型二聚体（β同型二聚体）相对应的蛋白质。通过在COS7细胞中对带有标签的β亚基与野生型β亚基进行共免疫沉淀，证实了β亚基的二聚化。β同型二聚体在没有hGM-CSF的情况下已经形成，而配体刺激使α和β亚基形成复合物，结果是β同型二聚体发生酪氨酸磷酸化。α亚基胞质结构域的缺失会损害亚基的酪氨酸磷酸化，但不影响两个亚基的结合。这些结果表明，单独不足以进行信号传导的β同型二聚体在hGM-CSF的作用下与α亚基形成功能性hGMR。
