Control of IP3R-Mediated Calcium Release

 描述(申请人提供)：细胞内钙信号控制许多生理现象。这些信号通常是通过开放内质网(ER)膜上的Ryanodine受体(RyR)或三磷酸肌醇受体(IP3R)钙释放通道而产生的。在其中一个通道占主导地位的组织中，经常会出现与另一个通道之间的功能性串扰。这种钙释放通道之间的串扰已经在平滑肌、心肌和最近的骨骼肌中被记录下来。换句话说，每一项的功能都对两者都有影响。这里，我们的重点是1型IP3R的局部钙调控。IP3R介导的Ca~(2+)释放受局部IP3和Ca~(2+)协同作用的控制。IP3-控制信号(来源、大小、动力学)定义得相当清楚。相反，由于钙离子调控信号的多模式性质，人们对其知之甚少。钙调控信号模式包括胞内钙激活、胞质内钙失活、内质网内钙调节(管腔调节)、自体钙调节(Feed Throughing)和胞间钙调节。每一种都是单独探索的，但从来没有被定义为一个整体。IP3R的局部多模式钙调控是一个重要的障碍，它限制了我们对IP3R分级钙信号(通道到喷到波)和“量子”钙释放的理解。对钙离子调控知之甚少的方式有自体FT、FT间和内质网内钙调节。通常，它们的存在(更不用说重要性了)因为缺乏明确的信息而受到质疑(因为重叠的信号和反馈循环排除了对变量的单独测试)。这一障碍在这里被克服，并首次将多模式IP3R局部钙调控定义为一个整体。这一点意义重大，因为IP3R控制着几乎所有细胞中的钙信号，其异常功能可能会产生致命的后果。这意味着IP3R局部调控机制既是潜在的病理失败点，也是治疗干预的合理靶点，因此了解其分子基础对人类健康具有重要意义。在这里，三个拥有独特互补资源和专业知识的实验室联合起来解决这一假设：多模式IP3R局部钙控制(激活、失活和馈送)包括一个管腔内孔内钙-镁敏感部位，该部位调控通道的IP3敏感性，后一种新发现的机制解释了IP3R介导的细胞内量子钙释放。这项提议采用了一种多学科(分子到细胞)精心设计的方法来检验这一假设。其具体目的是1)明确1型IP3R功能的多模式局部钙调控；2)确定1型IP3R量子钙释放的分子基础。这项工作将建立单个IP3R1功能的多模式局部钙调控的生物物理基础，并可能确定一种新的(也是长期寻找的)单IP3R分子机制来解释量子释放。这将代表着我们对IP3R1本地控制的理解的重大进步。

 DESCRIPTION (provided by applicant): Intracellular Ca2+ signals govern numerous physiological phenomena. Often these signals are generated by opening of ryanodine receptor (RyR) or inositol trisphosphate receptor (IP3R) Ca2+ release channels on the endoplasmic reticulum (ER) membrane. In tissues where one of these channels dominates, functional cross talk with the other is often present. Such cross talk between Ca2+ release channels has been documented in smooth, cardiac and recently skeletal muscle. In other words, function of each has ramifications on both. Here, our focus is the local Ca2+ control of the type-1 IP3R. IP3R-mediated Ca2+ release is controlled by the concerted actions of local IP3 and Ca2+. The IP3-control signal (source, size, kinetics) is fairly well defined. In contrast, the Ca2+-control signa is poorly understood because of its multi-modal nature. The Ca2+ control signal modes include cytosolic Ca2+ activation, cytosolic Ca2+ inactivation, intra-ER Ca2+ regulation (luminal regulation), auto-FT (Feed Through) and inter-FT Ca2+ regulation. Each has been explored separately but never have all been defined as a whole. The ill-defined local multi-modal Ca2+ control of the IP3R is a significant obstacle that has limited our understanding of both IP3R hierarchical Ca2+ signaling (channel to puff to wave) and "quantal" Ca2+ release. The least understood Ca2+ control modes are auto-FT, inter-FT and intra-ER Ca2+ regulation. Often, their existence (let alone significance) has been questioned due to the lack of definitive information (as the overlapping signals and feedback-loops have precluded separate testing of variables). This obstacle is overcome here and multi- modal IP3R local Ca2+ control defined as a whole for the first time. This is significant because IP3R governs Ca2+ signaling in nearly all cells and its abnormal function can have lethal ramifications. This means IP3R local control mechanisms are both potential points of pathological failure and logical targets for therapeutic intervention, making knowledge of their molecular basis highly significant to human health. Here, 3 laboratories with unique complementary resources and expertise combine to address the hypothesis: Multi-modal IP3R local Ca2+ control (activation, inactivation & feed through) includes a luminal intra-pore Ca2+-Mg2+ sensing site that governs the channel's IP3 sensitivity, the latter newly discovered mechanism explains IP3R-mediated quantal Ca2+ release in cells. This proposal applies a multidisciplinary (molecular to cellular) carefully crafted approach to tes this hypothesis. The specific aims are to 1) define multi-modal local Ca2+ control of type-1 IP3R function and 2) identify the molecular basis of quantal type-1 IP3R Ca2+ release. This work will establish the biophysical basis of multi-modal local Ca2+ control of single IP3R1 function and likely will identify a novel (and long sought) single IP3R molecular mechanism that explains quantal release. This will represent a significant advancement in our understanding of IP3R1 local control.