TRIC, a Novel Modulator of Intracellular Ca Homeostasis

描述(申请人提供)：细胞信号的一个基本方面是从肌浆网(SR)或内质网(ER)中隔离的细胞内存储中释放钙。对于肌肉细胞的兴奋-收缩偶联或非肌肉细胞的兴奋-分泌偶联的有效操作，反离子跨SR或ER膜的运动必须伴随着钙的快速外流，以中和钙释放过程中产生的瞬时负电位。尽管在SR或ER膜上发现了对单价阳离子具有选择性的通道，但尚未发现编码SR或ER定位阳离子选择性通道的基因。我们最近发现了一个编码三聚体细胞内阳离子选择通道(TIC)的新基因，它在羧基末端含有细胞膜保留序列，在氨基末端含有保守的亮氨酸拉链基序。纯化的TIRE蛋白可以在脂质双层膜上形成一个阳离子选择性通道，为钙释放急性期的反离子运动机制提供了一定的可能性。生化研究发现TRIC和SERCA之间存在功能上的相互作用，这可能会影响SR内的钙稳态。本项目的重点是确定TRIC的细胞和分子功能，它是调节SR膜对单价阳离子的通透性的反离子通道，和/或作为SR膜上钙转运的调节器。我们将首先使用脂质双层重建系统来建立TIC的单通道特性。通过生化和分子分析，我们将确定TIC的相互作用伙伴，这些伙伴可能参与调节TIC的通道活性，或者参与调节TIC和SERCA在骨骼肌中的功能相互作用。通过对野生型对照和缺乏TERE的突变型肌肉纤维的比较研究，我们将确定TERE在调节SR释放钙的急性期和主动摄取钙到SR中的生理作用。由于TIC代表了一类针对细胞内细胞器的新型阳离子通道，了解该蛋白在肌肉生理学中的作用将为我们提供有价值的见解，使我们了解钙信号在肌肉相关疾病中的调节，以及在钙调节功能障碍导致病理变化的其他疾病中，如神经退行性疾病。

DESCRIPTION (provided by applicant): A fundamental aspect of cellular signaling is the release of Ca from sequestered intracellular stores in the sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER). For efficient operation of excitation-contraction coupling in muscle cells, or excitation-secretion coupling in non-muscle cells, counter ion movement across the SR or ER membrane must accompany the rapid efflux of Ca to neutralize the transient negative potential produced during Ca release. Although channels selective for monovalent cations have been reported in SR or ER membranes, no gene has been identified that encodes a SR or ER localized cation selective channel. We have recently discovered a novel gene encoding a trimeric intracellular cation-selective channel (TRIC) that contains an intracellular membrane-retention sequence at the carboxyl-terminus and a conserved leucine-zipper motif at the amino-terminus. Purified TRIC protein can form a cation-selective channel in lipid bilayer membrane, providing the possibility that TRIC may provide certain aspects of the counter-ion movement mechanism during the acute phase of Ca release. Biochemical studies identify a functional interaction between TRIC and SERCA, which may influence Ca homeostasis inside the SR. The focus of this project is to define the cellular and molecular functions of TRIC as a counter-ion channel in regulating the permeability of SR membrane to monovalent cations and/or as a modulator of Ca transport across the SR membrane. We will first establish the single channel properties of TRIC using the lipid bilayer reconstitution system. Through biochemical and molecular assays, we will identify the interacting partners for TRIC that may participate in regulating the channel activity of TRIC, or in modulating the functional interaction between TRIC and SERCA in skeletal muscle. Through comparative studies between wild type control and mutant muscle fibers lacking TRIC, we will define the physiological role of TRIC in mediating both the acute phase of Ca release from the SR and active Ca uptake into the SR. As TRIC represents a novel class of cation channels targeted to an intracellular organelle, knowledge of the role of this protein in muscle physiology will provide us valuable insights into the regulation of Ca signaling in muscle-related diseases, and in other diseases where dysfunctional Ca regulation results in pathology, such as neurodegenerative disorders.