MECHANISM OF CALCIUM MOBILIZATION

细胞拥有不同的机制来传递来自细胞的信息 外部环境对细胞内反应的影响。与配体的结合 表面受体可导致体内产生第二信使 这个细胞和第一个被发现的这样的信使是cAMP。受体 由于体内钙离子的动员，激活也可以提高钙离子浓度 商店。三磷酸肌醇(IP3)作为信号转导蛋白的发现 这一过程在信号转导过程中具有集中的钙离子动员作用。我们的 研究证实，除了IP3外，体内的钙离子还储存 可以由两个新的信使通过完全独立的方式动员 小路。环腺苷二磷酸核糖(CADPR)和烟酸腺嘌呤 发现了磷酸二核苷酸(NAADP)及其结构 在我的实验室里确定的。CADPR是一种来源于 NAD，但与cAMP不同，它的主要信号功能是通过直接 Ca~(2+)诱导的Ca~(2+)释放(CICR)的调控机制 钙离子在IP3途径旁的动员。植物中的各种细胞 对哺乳动物物种表现出对cADPR的反应，这表明 信号通路的概括性。类似于cADPR、NAADP、a 代谢物NADP，也能调动钙储藏，但释放 机制及其作用于的存储不同于cADPR。这两个 然而，钙激动剂是密切相关的，因为相同的 在适当的条件下，代谢酶可以合成 其一，建议建立一个统一的机制来监管这两条途径。 CADPR和NAADP介导的信号转导途径的阐明 可能会对我们对信号的理解产生重要影响 转导机制。目标I是开发和使用RIA用于 测定cADPR的细胞含量。目标2是净化和 鉴定一种依赖cGMP的ADP-核糖环化酶。目标3是 表征环化酶依赖于cGMP的激活。这三个人 本研究的目的是明确刺激因素和激活机制。 CADPR途径。结果将提供必要的证据 建立cadpr作为第二信使。目标4是确定 CADPR在钙波传播中的作用。它一般都是 认为CICR机制在钙波的传播中起着至关重要的作用。 我们的发现cADPR可以调节CICR对钙的敏感性 有必要调查其在这一进程中的作用。目标5是为了 研究NAADP介导的钙信号转导机制。我们会 探索NAADP的结构-功能关系，探索NAADP的结构和功能 其合成的调控机制及其可能的作用 参与细胞内钙离子振荡的调节。

Cells possess various mechanisms for transducing information from the external environment to intracellular responses. Binding of ligands to surface receptors can lead to production of second messengers inside the cell and the first such messenger identified is cAMP. Receptor activation can also elevate Ca2+ due to mobilization of internal Ca2+ stores. The discovery of inositol trisphosphate (IP3) as a messenger for this process has centralized Ca2+ mobilization in signaling. Our research establishes that, in addition to IP3, the internal Ca2+ stores can be mobilized by two new messengers via totally independent pathways. Cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) were discovered and their structures determined in my lab. CADPR is a new cyclic nucleotide derived from NAD, but unlike cAMP, its main signaling function is through direct modulation of Ca2+-induced CA2+ release (CICR), a major mechanism of Ca2+ mobilization beside the IP3-pathway. A variety of cells from plant to mammalian species are shown to be responsive to cADPR, indicating the generality of the signaling pathway. Similar to cADPR, NAADP, a metabolite of NADP, can also mobilize Ca2+ stores, but the release mechanism and the stores it acts on are distinct from cADPR. These two Ca2+ agonists are, nevertheless, intimately related, since the same metabolic enzymes can, under appropriate conditions, synthesize either one, suggesting a unified mechanism may regulate both pathways. Elucidation of the signaling pathways mediated by cADPR and NAADP is likely to have an important impact on our understanding of signal transduction mechanisms. Aim I is to develop and use a RIA for measuring cellular content of cADPR. Aim 2 is to purify and characterize a cGMP-dependent ADP-ribosyl cyclase. Aim 3 is to characterize the cGMP-dependent activation of the cyclase. These three Aims focus on identifying the stimuli and the activation mechanism of the cADPR-pathway. Results will provide the necessary evidence for establishing cADPR as a second messenger. Aim 4 is to determine the role of cADPR in the propagation of Ca2+ waves. It is generally believed that the CICR mechanism is crucial in propagating Ca2+ waves. Our finding that cADPR can modulate the Ca2+ sensitivity of CICR makes it relevant to investigate its role in the process. Aim 5 is to characterize the Ca2+ signaling mechanism mediated by NAADP. We will probe the structure-function relationship of NAADP, explore the regulatory mechanisms of its synthesis and investigate its possible role in mediating Ca2+ oscillations in cells.