Dok-3 sequesters Grb2 and inhibits the Ras-Erk pathway downstream of protein-tyrosine kinases
Dok-3 sequesters Grb2 and inhibits the Ras-Erk pathway downstream of protein-tyrosine kinases
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DOI：
10.1111/j.1365-2443.2006.00926.x
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发表时间：
2006-02-01
期刊：
影响因子：
2.1
通讯作者：
Yamanashi, Y
中科院分区：
文献类型：
--
作者：
Honma, M;Higuchi, O;Yamanashi, Y
衔接蛋白在协调募集中是必不可少的，在少数情况下，在细胞信号传导过程中抑制各种效应物。Dok-1、Dok-2和Dok-3组成了一个密切相关的衔接子家族，其负调控蛋白酪氨酸激酶（PTK）下游的促分裂原活化蛋白激酶Erk。Dok-1和Dok-2对p120 rasGAP（一种有效的Ras抑制剂）的募集似乎在Ras-Erk通路的负调控中至关重要。然而，由于Dok-3不结合rasGAP，因此尚不清楚Dok-3如何抑制PTK下游的Erk。在这里，我们确定Grb 2作为Dok-3结合蛋白后，其酪氨酸磷酸化。这种相互作用需要Grb 2 SH 2结构域的完整结合基序，并且在这些基序处具有Tyr/Phe取代的突变体（Dok-3-FF）未能抑制胞质PTK Src下游的Ras和Erk活化。由于Grb 2与Ras的关键激活剂Sos形成稳定的复合物，这些数据表明Dok-3抑制Grb 2并抑制Grb 2-Sos复合物激活Ras的能力。事实上，Dok-3而不是Dok-3-FF的强制表达抑制了Grb 2-Sos复合物向Src下游的Shc的募集，这是Ras-Erk途径活化的必要事件。这些发现表明Dok-3从Shc中隔离Grb 2并抑制PTKs下游的Ras-Erk途径。
Adaptor proteins are essential in coordinating recruitment and, in a few cases, restraint of various effectors during cellular signaling. Dok-1, Dok-2 and Dok-3 comprise a closely related family of adaptor, which negatively regulates mitogen-activated protein kinase Erk downstream of protein-tyrosine kinases (PTKs). Recruitment of p120 rasGAP, a potent inhibitor of Ras, by Dok-1 and Dok-2 appears critical in the negative regulation of the Ras-Erk pathway. However, as Dok-3 does not bind rasGAP, it has been unclear how Dok-3 inhibits Erk downstream of PTKs. Here, we identified Grb2 as a Dok-3-binding protein upon its tyrosine phosphorylation. This interaction required the intact binding motifs of the Grb2 SH2 domain, and a mutant (Dok-3-FF) having a Tyr/Phe substitution at these motifs failed to inhibit Ras and Erk activation downstream of a cytoplasmic PTK Src. Because Grb2 forms a stable complex with Sos, a crucial activator of Ras, these data suggest that Dok-3 restrains Grb2 and inhibits the ability of the Grb2-Sos complex to activate Ras. Indeed, forced expression of Dok-3, but not Dok-3-FF, inhibited the recruitment of the Grb2-Sos complex to Shc downstream of Src, which is an essential event for activation of the Ras-Erk pathway. These findings indicate that Dok-3 sequesters Grb2 from Shc and inhibits the Ras-Erk pathway downstream of PTKs.