Reciprocal regulation of PKA and Rac signaling
Reciprocal regulation of PKA and Rac signaling
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DOI：
10.1073/pnas.1215902110
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发表时间：
2013-05-21
影响因子：
11.1
通讯作者：
Stefan, Eduard
中科院分区：
文献类型：
--
作者：
Bachmann, Verena A.;Riml, Anna;Stefan, Eduard
激活的 G 蛋白偶联受体 (GPCR) 和受体酪氨酸激酶通过空间和时间控制的激酶和 GTP 酶实体传递细胞外信号。这些酶由多功能支架蛋白协调，以进行精确的细胞内信号处理。 cAMP 依赖性蛋白激酶 A (PKA) 是不同 GPCR 下游分区信号传输的主要例子。 A-激酶锚定蛋白将 PKA 固定到特定的细胞内位点，以确保 PKA 磷酸化事件的精确性和方向性。在这里，我们证明 Rho-GTPase Rac 包含 A 激酶锚定蛋白特性，并与 PKA 形成动态细胞蛋白复合物。这种瞬时核心复合物的形成取决于与 PKA 亚基、cAMP 水平和细胞 GTP 负载的二元相互作用，从而对 PKA 和 Rac 下游信号传导产生双向影响。我们证明 GTP-Rac 可以稳定无活性的 PKA 全酶。然而，β-肾上腺素能受体介导的 GTP-Rac 结合 PKA 激活会将信号传递至 Raf-Mek-Erk 级联，这与细胞增殖密切相关。我们描述了 cAMP 如何增强核 Erk1/2 信号传导的进一步机制：它源自 p21 激活激酶在其进化保守激酶激活环中通过 GTP-Rac 区室化 PKA 活性进行转磷酸化。 p21 激活激酶的单独转磷酸化不足以激活 Erk1/2。它需要两种激酶与 GTP-Rac1 形成复合物，以释放 cAMP-PKA 增强的 Raf-Mek-Erk 激活。因此，GTP-Rac 作为双激酶调节支架发挥作用，有利于 PKA 全酶并有助于增强 Erk1/2 信号传导。我们的研究结果提供了额外的机制见解，即β-肾上腺素受体控制的 PKA 活性如何增强 GTP-Rac 介导的核 Erk1/2 信号传导激活。
Activated G protein-coupled receptors (GPCRs) and receptor tyrosine kinases relay extracellular signals through spatial and temporal controlled kinase and GTPase entities. These enzymes are coordinated by multifunctional scaffolding proteins for precise intracellular signal processing. The cAMP-dependent protein kinase A (PKA) is the prime example for compartmentalized signal transmission downstream of distinct GPCRs. A-kinase anchoring proteins tether PKA to specific intracellular sites to ensure precision and directionality of PKA phosphorylation events. Here, we show that the Rho-GTPase Rac contains A-kinase anchoring protein properties and forms a dynamic cellular protein complex with PKA. The formation of this transient core complex depends on binary interactions with PKA subunits, cAMP levels and cellular GTP-loading accounting for bidirectional consequences on PKA and Rac downstream signaling. We show that GTP-Rac stabilizes the inactive PKA holoenzyme. However, beta-adrenergic receptor-mediated activation of GTP-Rac-bound PKA routes signals to the Raf-Mek-Erk cascade, which is critically implicated in cell proliferation. We describe a further mechanism of how cAMP enhances nuclear Erk1/2 signaling: It emanates from transphosphorylation of p21-activated kinases in their evolutionary conserved kinase-activation loop through GTP-Rac compartmentalized PKA activities. Sole transphosphorylation of p21-activated kinases is not sufficient to activate Erk1/2. It requires complex formation of both kinases with GTP-Rac1 to unleash cAMP-PKA-boosted activation of Raf-Mek-Erk. Consequently GTP-Rac functions as a dual kinase-tuning scaffold that favors the PKA holoenzyme and contributes to potentiate Erk1/2 signaling. Our findings offer additional mechanistic insights how beta-adrenergic receptor-controlled PKA activities enhance GTP-Rac-mediated activation of nuclear Erk1/2 signaling.