TRIC, a Novel Modulator of Intracellular Ca Homeostasis

描述（由申请人提供）：细胞信号传导的一个基本方面是钙从肌浆网（SR）或内质网（ER）中隔离的细胞内储存的释放。为了使肌肉细胞的兴奋-收缩耦合或非肌肉细胞的兴奋-分泌耦合有效地运行，反离子穿过SR或ER膜必须伴随着钙的快速流出，以中和钙释放过程中产生的瞬态负电位。虽然有报道称SR或ER膜中存在选择性一价阳离子的通道，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（TRIC）的新基因，该基因在羧基端包含胞内膜保留序列，在氨基端包含保守的亮氨酸拉链基序。纯化后的TRIC蛋白可以在脂质双层膜中形成阳离子选择通道，这为TRIC在钙释放急性期提供反离子运动机制的某些方面提供了可能性。生化研究确定了TRIC和SERCA之间的功能相互作用，这可能会影响SR内的Ca稳态。本项目的重点是定义TRIC的细胞和分子功能，作为调节SR膜对单价阳离子的渗透性的反离子通道和/或作为Ca在SR膜上运输的调节剂。我们将首先利用脂质双分子层重构系统建立TRIC的单通道性质。通过生化和分子分析，我们将确定TRIC的相互作用伙伴，这些伙伴可能参与调节TRIC的通道活性，或调节骨骼肌中TRIC和SERCA之间的功能相互作用。通过对野生型对照和缺乏TRIC的突变肌纤维的比较研究，我们将确定TRIC在介导钙从SR释放的急性期和钙进入SR的活性摄取中的生理作用。由于TRIC代表了一类针对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，以调节钙信号在肌肉相关疾病中的作用。以及其他钙调节功能失调导致病理的疾病，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.