Lin J, Tao J, Dyer R B, Herzog N K, Justement L B
Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston 77555, USA.
J Immunol. 1997 Nov 15;159(10):4823-33.
Signal transduction mediated by the B cell Ag receptor involves the activation of multiple protein tyrosine kinases that are members of the Src family (i.e., Fyn, Lyn, Blk, Lck). To determine whether members of the Src family possess common physical and/or enzymatic properties that enable them to potentiate signal transduction via the B cell Ag receptor, we expressed the protein tyrosine kinase Src in the B lymphoma cell line K46-17 mu m lambda. Based on coprecipitation analysis and two-color immunofluorescence, this heterologous Src family kinase was observed to physically associate with the B cell Ag receptor. Additional experiments demonstrated that B cell Ag receptor cross-linking results in increased tyrosine phosphorylation and activation of Src. Several parameters of B cell activation, including tyrosine phosphorylation of intracellular substrates, calcium mobilization, and transcription factor activation, were potentiated in cells that expressed Src when compared with control cells. To determine whether potentiation of Ag receptor-mediated signaling by Src was dependent on its catalytic activity, a kinase-deficient form of Src was expressed in K46-17 mu m lambda cells. Transfectants expressing kinase-deficient Src exhibited an enhanced responsiveness to stimulation through the B cell Ag receptor that was comparable with transfectants expressing wild-type Src. Additionally, kinase-deficient Src was observed to associate with the endogenous kinase Lyn in an activation-dependent manner. These findings indicate that members of the Src family may potentiate Ag receptor-mediated signaling via a kinase-independent mechanism(s) that involves amplification of kinase recruitment to the Ag receptor activation complex.
由B细胞抗原受体介导的信号转导涉及多种蛋白酪氨酸激酶的激活，这些激酶是Src家族的成员（即Fyn、Lyn、Blk、Lck）。为了确定Src家族成员是否具有共同的物理和/或酶学特性，使其能够增强通过B细胞抗原受体的信号转导，我们在B淋巴瘤细胞系K46-17μmλ中表达了蛋白酪氨酸激酶Src。基于共沉淀分析和双色免疫荧光，观察到这种异源Src家族激酶与B细胞抗原受体发生物理结合。进一步的实验表明，B细胞抗原受体交联导致Src的酪氨酸磷酸化增加和激活。与对照细胞相比，在表达Src的细胞中，B细胞激活的几个参数，包括细胞内底物的酪氨酸磷酸化、钙动员和转录因子激活，均得到增强。为了确定Src对抗原受体介导信号的增强作用是否依赖于其催化活性，在K46-17μmλ细胞中表达了一种激酶缺陷型的Src。表达激酶缺陷型Src的转染子对通过B细胞抗原受体的刺激表现出增强的反应性，这与表达野生型Src的转染子相当。此外，观察到激酶缺陷型Src以激活依赖的方式与内源性激酶Lyn结合。这些发现表明，Src家族成员可能通过一种不依赖激酶的机制增强抗原受体介导的信号转导，该机制涉及激酶募集到抗原受体激活复合物的扩增。
