Neuronal growth factor signaling via cAMP

在神经元中，普遍存在的第二信使环磷酸腺苷(CAMP)参与了许多 生长因子信号通路。例如，神经营养因子，如神经生长因子(NGF)， 通过cAMP与神经元分化、神经发生和轴突再生联系在一起。然而，它已经 目前仍不清楚如何将生长因子或其受体与cAMP变化联系起来。轴突引导 信号，如netrin-1，也通过cAMP发出信号，它们与第二代信使的联系也是相似的 不清楚。此前，cAMP的唯一已知来源是受调控的G蛋白家族， 跨膜腺苷酸环化酶(Tmacs)介导cAMP的变化 通过G蛋白偶联作用的神经递质，七个跨膜横跨受体。但所有的 将tmac与神经元生长因子信号或轴突引导信号联系起来的尝试失败了，或者充其量是失败了。 事实证明，这是有争议的。 我们的实验室鉴定了哺乳动物细胞中cAMP的一种独特来源--‘可溶性’腺酰环化酶(SAC)。 与tmacs不同，SAC不受异源三聚体G蛋白的调节，而是受 小苏打和钙离子。在此应用程序的初步结果中，我们演示了SAC是 负责在神经营养因子NGF和轴突引导信号的反应中产生cAMP Netrin-1。 我们已经确定了一些与先前克隆的SAC亚型不同的大脑SAC亚型，以及 在这项拨款申请中，我们建议对这些新的脑部SAC蛋白进行表征。我们还提议 NGF和Netrin-1激活SAC机制的实验研究 确定此信号级联是否被其他神经营养因子和其他神经元所利用 回应。 在这项拨款申请中测试的假设将揭示增长信号和指导信号如何传递它们的 信息转化为神经元活动。这些研究对大脑发育具有重要意义， 退化性疾病与学习和记忆。

In neurons, the ubiquitous second messenger cyclic AMP (cAMP) has been implicated in a number of growth factor signaling pathways. For example, neurotrophins, such as Nerve Growth Factor (NGF), are linked via cAMP to neuronal differentiation, neuritogenesis, and axonal regeneration. However, it has remained unclear how to link the growth factors, or their receptors, to cAMP changes. Axonal guidance cues, such as netrin-1, also signal via cAMP, and their link to second messenger generation is similarly unclear. Previously, the only known source of cAMP had been the family of G protein regulated, transmembrane adenylyl cyclases (tmACs); tmACs mediate the cAMP changes in response to neurotransmitters which act via G protein coupled, seven transmembrane spanning receptors. But all attempts to link tmACs to neuronal growth factor signals or axonal guidance cues have failed, or at best proven controversial. Our laboratory characterized a distinct source of cAMP in mammalian cells, 'soluble' adenylyl cyclase (sAC). In contrast to tmACs, sAC is not modulated by heterotrimeric G proteins but is, instead, regulated by bicarbonate and calcium ions. In preliminary results for this application, we demonstrate that sAC is responsible for cAMP generation in response to both the neurotrophin NGF and the axonal guidance cue netrin-1. We have identified a number of brain isoforms of sAC which differ from the previously cloned isoforms, and in this grant application, we propose to characterize these novel brain sAC proteins. We also propose experiments to elucidate the mechanism of sAC activation in response to NGF and netrin-1 and to determine whether this signaling cascade is utilized by other neurotrophins and in other neuronal responses. The hypotheses tested in this grant application will reveal how growth signals and guidance cues relay their information into neuronal activity. These studies have important implications for brain development, degenerative diseases and learning and memory.