Hata A, Sabe H, Kurosaki T, Takata M, Hanafusa H
Laboratory of Molecular Oncology, Rockefeller University, New York, New York 10021, USA.
Mol Cell Biol. 1994 Nov;14(11):7306-13. doi: 10.1128/mcb.14.11.7306-7313.1994.
In B cells, two classes of protein tyrosine kinases (PTKs), the Src family of PTKs (Lyn, Fyn, Lck, and Blk) and non-Src family of PTKs (Syk), are known to be involved in signal transduction induced by the stimulation of the B-cell antigen receptor (BCR). Previous studies using Lyn-negative chicken B-cell clones revealed that Lyn is necessary for transduction of signals through the BCR. The kinase activity of the Src family of PTKs is negatively regulated by phosphorylation at the C-terminal tyrosine residue, and the PTK Csk has been demonstrated to phosphorylate this C-terminal residue of the Src family of PTKs. To investigate the role of Csk in BCR signaling, Csk-negative chicken B-cell clones were generated. In these Csk-negative cells, Lyn became constitutively active and highly phosphorylated at the autophosphorylation site, indicating that Csk is necessary to sustain Lyn in an inactive state. Since the C-terminal tyrosine phosphorylation of Lyn is barely detectable in the unstimulated, wild-type B cells, our data suggest that the activities of Csk and a certain protein tyrosine phosphatase(s) are balanced to maintain Lyn at a hypophosphorylated and inactive state. Moreover, we show that the kinase activity of Syk was also constitutively activated in Csk-negative cells. The degree of activation of both the Lyn and Syk kinases in Csk-negative cells was comparable to that observed in wild-type cells after BCR stimulation. However, BCR stimulation was still necessary in Csk-negative cells to elicit tyrosine phosphorylation of cellular proteins, as well as calcium mobilization and inositol 1,4,5-trisphosphate generation. These results suggest that not only activation of the Lyn and Syk kinases but also additional signals induced by the cross-linking of the BCR are required for full transduction of BCR signaling.
在B细胞中，已知两类蛋白酪氨酸激酶（PTK），即PTK的Src家族（Lyn、Fyn、Lck和Blk）和非Src家族的PTK（Syk），参与B细胞抗原受体（BCR）刺激诱导的信号转导。先前使用Lyn阴性鸡B细胞克隆的研究表明，Lyn对于通过BCR转导信号是必需的。PTK的Src家族的激酶活性通过C末端酪氨酸残基的磷酸化而受到负调控，并且已证明PTK Csk可使Src家族的PTK的该C末端残基磷酸化。为了研究Csk在BCR信号传导中的作用，生成了Csk阴性鸡B细胞克隆。在这些Csk阴性细胞中，Lyn变得组成性激活并在自身磷酸化位点高度磷酸化，表明Csk对于维持Lyn处于非活性状态是必需的。由于在未刺激的野生型B细胞中几乎检测不到Lyn的C末端酪氨酸磷酸化，我们的数据表明Csk和某种蛋白酪氨酸磷酸酶的活性是平衡的，以维持Lyn处于低磷酸化和非活性状态。此外，我们表明Syk的激酶活性在Csk阴性细胞中也被组成性激活。Csk阴性细胞中Lyn和Syk激酶的激活程度与BCR刺激后野生型细胞中观察到的程度相当。然而，在Csk阴性细胞中，BCR刺激对于引发细胞蛋白的酪氨酸磷酸化以及钙动员和肌醇1,4,5-三磷酸的产生仍然是必需的。这些结果表明，不仅Lyn和Syk激酶的激活，而且BCR交联诱导的其他信号对于BCR信号的完全转导也是必需的。
