Galpha and Gbeta gamma require distinct Src-dependent pathways to activate Rap1 and Ras.
Galpha and Gbeta gamma require distinct Src-dependent pathways to activate Rap1 and Ras.
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发表时间：
2002
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通讯作者：
J. Schmitt;P. Stork
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作者：
J. Schmitt;P. Stork
Src酪氨酸激酶是β -肾上腺素能受体激动剂异丙肾上腺素激活细胞外信号调节激酶（ERKs）所必需的。在这项研究中，我们研究了Src在刺激两种小G蛋白Ras和Rap1中的作用，这两种小G蛋白与异丙肾上腺素向ERKs的信号传导有关。我们证明了Rap1和Ras的异丙肾上腺素的激活都需要Src。在HEK293细胞中，异丙肾上腺素激活Rap1，刺激Rap1与B-Raf的结合，并激活ERKs，这些都是通过PKA实现的。相反，异丙肾上腺素激活Ras需要gbetagama亚基，不依赖于PKA，导致磷酸化肌醇3激酶依赖性激活AKT。有趣的是，β -肾上腺素能刺激Rap1和ERKs，而不是Ras和AKT，可以被Src突变体（SrcS17A）阻断，该突变体不能被PKA磷酸化和激活。此外，Src突变体（SrcS17D）模仿PKA丝氨酸17的磷酸化，刺激Rap1激活、Rap1/B-Raf关联和ERK激活，但不刺激Ras或AKT。这些数据表明，Rap1的激活，而不是Ras的激活，是通过PKA直接磷酸化Src介导的。我们提出β(2)-肾上腺素能受体通过两种独立的机制激活Src，介导不同的信号通路，一种是通过Galpha(s)到Rap1和ERKs，另一种是通过β - γ到Ras和AKT。
The Src tyrosine kinase is necessary for activation of extracellular signal-regulated kinases (ERKs) by the beta-adrenergic receptor agonist, isoproterenol. In this study, we examined the role of Src in the stimulation of two small G proteins, Ras and Rap1, that have been implicated in isoproterenol's signaling to ERKs. We demonstrate that the activation of isoproterenol of both Rap1 and Ras requires Src. In HEK293 cells, isoproterenol activates Rap1, stimulates Rap1 association with B-Raf, and activates ERKs, all via PKA. In contrast, the activation by isoproterenol of Ras requires Gbetagamma subunits, is independent of PKA, and results in the phosphoinositol 3-kinase-dependent activation of AKT. Interestingly, beta-adrenergic stimulation of both Rap1 and ERKs, but not Ras and AKT, can be blocked by a Src mutant (SrcS17A) that is incapable of being phosphorylated and activated by PKA. Furthermore, a Src mutant (SrcS17D), which mimics PKA phosphorylation at serine 17, stimulates Rap1 activation, Rap1/B-Raf association, and ERK activation but does not stimulate Ras or AKT. These data suggest that Rap1 activation, but not that of Ras, is mediated through the direct phosphorylation of Src by PKA. We propose that the beta(2)-adrenergic receptor activates Src via two independent mechanisms to mediate distinct signaling pathways, one through Galpha(s) to Rap1 and ERKs and the other through Gbetagamma to Ras and AKT.