TPC2 is a novel NAADP-sensitive Ca2+ release channel, operating as a dual sensor of luminal pH and Ca2+.
TPC2 is a novel NAADP-sensitive Ca2+ release channel, operating as a dual sensor of luminal pH and Ca2+.
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DOI：
10.1074/jbc.m110.156927
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发表时间：
2010-11-05
期刊：
影响因子：
--
通讯作者：
Sitsapesan R
中科院分区：
文献类型：
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作者：
Pitt SJ;Funnell TM;Sitsapesan M;Venturi E;Rietdorf K;Ruas M;Ganesan A;Gosain R;Churchill GC;Zhu MX;Parrington J;Galione A;Sitsapesan R
烟酸腺嘌呤二核苷酸磷酸(NAADP)是一种能够启动许多基本细胞过程所需的细胞内钙离子释放的分子。最近的证据表明，双孔通道(TPC)与NAADP诱导的溶酶体样酸性细胞器的钙释放有关；然而，还没有直接的证据表明TPC可以作为NAADP敏感的钙释放通道。有争议的证据也表明兰尼定受体是NAADP的主要靶点。我们证明TPC2，溶酶体的主要靶向异构体，是一种对钙离子具有选择性的阳离子通道，这将使它在细胞环境中扮演钙释放通道的角色。NAADP以浓度依赖的方式开放TPC2通道，与高亲和力激活和低亲和力抑制部位结合。这一过程的核心是渠道的发光环境。TPC2对NAADP的敏感性强烈依赖于允许极低水平的NAADP打开通道的管腔[Ca~(2+)]。同时，流明pH通过将TPC2在低pH时的可逆激活转换为中性pH下的不可逆激活来控制NAADP与TPC2的亲和力。进一步的证据表明TPC可能是NAADP诱导的细胞内钙释放的途径，这是通过使用NAADP诱导的细胞内钙释放的选择性阻断剂Ned-19获得的。NED-19在1μm时以非竞争性方式拮抗TPC2的NAADP激活，但在纳摩尔浓度时增强NAADP的激活。这一单通道研究为NAADP信号的特殊机制特征提供了期待已久的分子基础，并为理解NAADP如何调节关键的生理事件提供了一个框架。
Nicotinic acid adenine dinucleotide phosphate (NAADP) is a molecule capable of initiating the release of intracellular Ca2+ required for many essential cellular processes. Recent evidence links two-pore channels (TPCs) with NAADP-induced release of Ca2+ from lysosome-like acidic organelles; however, there has been no direct demonstration that TPCs can act as NAADP-sensitive Ca2+ release channels. Controversial evidence also proposes ryanodine receptors as the primary target of NAADP. We show that TPC2, the major lysosomal targeted isoform, is a cation channel with selectivity for Ca2+ that will enable it to act as a Ca2+ release channel in the cellular environment. NAADP opens TPC2 channels in a concentration-dependent manner, binding to high affinity activation and low affinity inhibition sites. At the core of this process is the luminal environment of the channel. The sensitivity of TPC2 to NAADP is steeply dependent on the luminal [Ca2+] allowing extremely low levels of NAADP to open the channel. In parallel, luminal pH controls NAADP affinity for TPC2 by switching from reversible activation of TPC2 at low pH to irreversible activation at neutral pH. Further evidence earmarking TPCs as the likely pathway for NAADP-induced intracellular Ca2+ release is obtained from the use of Ned-19, the selective blocker of cellular NAADP-induced Ca2+ release. Ned-19 antagonizes NAADP-activation of TPC2 in a non-competitive manner at 1 μm but potentiates NAADP activation at nanomolar concentrations. This single-channel study provides a long awaited molecular basis for the peculiar mechanistic features of NAADP signaling and a framework for understanding how NAADP can mediate key physiological events.