Wilson B S, Kapp N, Lee R J, Pfeiffer J R, Martinez A M, Platt Y, Letourneur F, Oliver J M
Department of Pathology, University of New Mexico School of Medicine, Albuquerque 87131.
J Biol Chem. 1995 Feb 24;270(8):4013-22. doi: 10.1074/jbc.270.8.4013.
In RBL-2H3 rat tumor mast cells, cross-linking the high affinity IgE receptor, Fc epsilon R1, activates the protein-tyrosine kinases Lyn and Syk and initiates a series of responses including protein-tyrosine phosphorylation, inositol 1,4,5-trisphosphate synthesis, Ca2+ mobilization, secretion, membrane ruffling, and actin plaque assembly. The development of chimeric receptors containing cytoplasmic domains of individual subunits of the heterotrimeric (alpha beta gamma 2) Fc epsilon R1 has simplified analyses of early signaling events in RBL-2H3 cells. Here, RBL-2H3 cells were transfected with cDNAs encoding the extracellular and transmembrane domains of the interleukin-2 receptor alpha subunit (the Tac antigen) joined to the C-terminal cytoplasmic domains of the Fc epsilon R1 gamma and beta subunits (TT gamma and TT beta). Both sequences contain tyrosine activation motifs implicated in antigen receptor signal transduction. TT gamma and TT beta are expressed independently of the native Fc epsilon R1, as demonstrated by the ability of Tac cross-linking agents to trigger the clustering and internalization through coated pits of both chimeric receptors without co-clustering the Fc epsilon R1. A full range of signaling activities is induced by TT gamma cross-linking; the TT gamma-induced responses are slower and, except for Lyn activation, smaller than the Fc epsilon R1-induced responses. In striking contrast, TT beta cross-linking elicits no tyrosine phosphorylation or signaling responses, it impairs basal activities measured in secretion and anti-PY (anti-phosphotyrosine antibody) immune complex kinase assays, and it antagonizes Fc epsilon R1-induced Lyn and Syk activation, protein-tyrosine phosphorylation, and signaling responses. We hypothesize that the isolated beta subunit binds a specific kinase or coupling protein(s) required for signaling activity, sequestering it from the signal-transducing gamma subunit. Binding the same kinase or coupling protein to the beta subunit of the intact Fc epsilon R1 may serve instead to present it to the adjacent gamma subunit, resulting in enhanced kinase activation and signaling responses.
在RBL - 2H3大鼠肿瘤肥大细胞中，高亲和力IgE受体FcεR1的交联可激活蛋白酪氨酸激酶Lyn和Syk，并引发一系列反应，包括蛋白酪氨酸磷酸化、肌醇1,4,5 - 三磷酸合成、Ca2 + 动员、分泌、膜皱襞形成和肌动蛋白斑组装。含有异源三聚体（αβγ2）FcεR1单个亚基细胞质结构域的嵌合受体的开发简化了对RBL - 2H3细胞早期信号事件的分析。在此，用编码白细胞介素 - 2受体α亚基（Tac抗原）的细胞外和跨膜结构域与FcεR1γ和β亚基（TTγ和TTβ）的C末端细胞质结构域连接的cDNA转染RBL - 2H3细胞。这两个序列都含有与抗原受体信号转导相关的酪氨酸激活基序。如Tac交联剂能够触发两种嵌合受体通过包被小窝的聚集和内化而不使FcεR1共聚集所证明的，TTγ和TTβ独立于天然FcεR1表达。TTγ交联可诱导一系列完整的信号活性；TTγ诱导的反应较慢，除了Lyn激活外，比FcεR1诱导的反应小。与之形成鲜明对比的是，TTβ交联不会引发酪氨酸磷酸化或信号反应，它会损害在分泌和抗PY（抗磷酸酪氨酸抗体）免疫复合物激酶测定中测得的基础活性，并且它会拮抗FcεR1诱导的Lyn和Syk激活、蛋白酪氨酸磷酸化和信号反应。我们推测，分离的β亚基结合信号活性所需的特定激酶或偶联蛋白，使其与信号转导γ亚基分离。将相同的激酶或偶联蛋白与完整FcεR1的β亚基结合，可能反而会将其呈递给相邻的γ亚基，从而导致激酶激活和信号反应增强。
