Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Mol Cell. 2012 Oct 26;48(2):298-312. doi: 10.1016/j.molcel.2012.08.011. Epub 2012 Sep 13.
In T cells, the adaptor Bam32 is coupled to Erk activation downstream of the TCR by an unknown mechanism. We characterized in Jurkat cells and primary T lymphocytes a pathway dependent on Bam32-PLC-γ1-Pak1 complexes, in which Pak1 kinase activates Raf-1 and Mek-1, both upstream of Erk. In the Bam32-PLC-γ1-Pak1 complex, catalytically inactive PLC-γ1 is used as a scaffold linking Bam32 to Pak1. PLC-γ1(C-SH2) directly binds S141 of Bam32, preventing LAT-mediated activation of Ras by PLC-γ1. The Bam32-PLC-γ1 interaction enhances the binding of the SH3 domain of the phospholipase with Pak1. The PLC-γ1(SH3)-Pak1 interaction activates Pak1 independently of the small GTPases Rac1/Cdc42, previously described as being the only activators of Pak1 in T cells. Direct binding of the SH3 domain of PLC-γ1 to Pak1 dissociates inactive Pak1 homodimers, a mechanism required for Pak1 activation. We have thus uncovered a LAT/Ras-independent, Bam32-nucleated pathway that activates Erk signaling in T cells.
在 T 细胞中，衔接蛋白 Bam32 通过一种未知的机制与 TCR 下游的 Erk 激活偶联。我们在 Jurkat 细胞和原代 T 淋巴细胞中鉴定了一条依赖于 Bam32-PLC-γ1-Pak1 复合物的途径，在该途径中，Pak1 激酶激活 Raf-1 和 Mek-1，它们均在上游激活 Erk。在 Bam32-PLC-γ1-Pak1 复合物中，无催化活性的 PLC-γ1 用作支架，将 Bam32 与 Pak1 连接起来。PLC-γ1(C-SH2)直接结合 Bam32 的 S141，从而阻止 PLC-γ1 通过 LAT 介导的 Ras 激活。Bam32-PLC-γ1 相互作用增强了磷脂酶的 SH3 结构域与 Pak1 的结合。PLC-γ1(SH3)-Pak1 相互作用独立于 Rac1/Cdc42 等小 GTP 酶激活 Pak1，Rac1/Cdc42 先前被描述为 T 细胞中唯一激活 Pak1 的因子。PLC-γ1 的 SH3 结构域与 Pak1 的直接结合使无活性的 Pak1 同源二聚体解离，这是 Pak1 激活所必需的机制。因此，我们揭示了一种 LAT/Ras 非依赖性、由 Bam32 引发的途径，该途径可激活 T 细胞中的 Erk 信号转导。
