Elliott S, Lorenzini T, Yanagihara D, Chang D, Elliott G
Amgen, Amgen Center, Thousand Oaks, California 91320, USA.
J Biol Chem. 1996 Oct 4;271(40):24691-7. doi: 10.1074/jbc.271.40.24691.
Oligomerization of cytokine receptors including the erythropoietin (EPO) receptor has been advanced as a model for activation. If homodimerization of the EPO receptor activates it, then bivalent antibodies raised to the extracellular domain of the EPO receptor should also homodimerize and activate. Mouse monoclonal antibodies (IgG) raised to the soluble, extracellular domain of the human EPO receptor (EPOR) were found that would stimulate thymidine uptake of an human EPO-dependent cell line, UT-7/EPO. Dose response curves showed bell shapes where activity was low at low and high concentrations. Monovalent (Fab) fragments bound to the receptor but did not stimulate thymidine uptake, which indicates that two antibody binding sites are required for activation. The anti-EPOR antibodies stimulated the formation of burst forming unit erythroid colonies from human CD34(+) cells purified from peripheral blood. This indicates that homodimerization of the EPO receptor by anti-EPOR antibodies is sufficient for both proliferation and differentiation of erythroid progenitor cells and that the constraints on dimerization necessary for activation are rather loose.
包括促红细胞生成素（EPO）受体在内的细胞因子受体的寡聚化已被提出作为一种激活模型。如果EPO受体的同型二聚化使其激活，那么针对EPO受体胞外域产生的二价抗体也应能同型二聚化并激活。研究发现，针对人EPO受体（EPOR）可溶性胞外域产生的小鼠单克隆抗体（IgG）能刺激人EPO依赖细胞系UT-7/EPO摄取胸苷。剂量反应曲线呈钟形，在低浓度和高浓度时活性较低。单价（Fab）片段与受体结合但不刺激胸苷摄取，这表明激活需要两个抗体结合位点。抗EPOR抗体刺激从外周血纯化的人CD34(+)细胞形成红系爆式集落形成单位。这表明抗EPOR抗体使EPO受体同型二聚化足以促进红系祖细胞的增殖和分化，并且激活所需的二聚化限制相当宽松。
