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从肌浆网（SR）或内质网（ER）中隔离的细胞内储存中释放Ca。为了使肌肉细胞中的兴奋-收缩耦合或非肌肉细胞中的兴奋-分泌耦合有效运行，反离子穿过 SR 或 ER 膜的运动必须伴随 Ca 的快速流出，以中和 Ca 释放过程中产生的瞬时负电位。尽管已报道 SR 或 ER 膜中存在单价阳离子选择性通道，但尚未鉴定出编码 SR 或 ER 局部阳离子选择性通道的基因。我们最近发现了一种编码三聚体细胞内阳离子选择性通道（TRIC）的新基因，该通道在羧基末端含有细胞内膜保留序列，在氨基末端含有保守的亮氨酸拉链基序。纯化的 TRIC 蛋白可以在脂质双层膜中形成阳离子选择性通道，这为 TRIC 在 Ca 释放的急性期提供某些方面的反离子运动机制提供了可能性。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。该项目的重点是定义 TRIC 的细胞和分子功能，作为调节 SR 膜对单价阳离子渗透性的反离子通道和/或作为 Ca 跨 SR 膜转运的调节剂。我们将首先使用脂质双层重建系统建立 TRIC 的单通道特性。通过生化和分子检测，我们将确定 TRIC 的相互作用伙伴，这些伙伴可能参与调节 TRIC 通道活性，或调节骨骼肌中 TRIC 和 SERCA 之间的功能相互作用。通过野生型对照和缺乏 TRIC 的突变体肌纤维之间的比较研究，我们将确定 TRIC 在介导 SR 急性期 Ca 释放和 SR 主动 Ca 摄取中的生理作用。由于 TRIC 代表了一类针对细胞内细胞器的新型阳离子通道，了解这种蛋白质在肌肉生理学中的作用将为我们提供有关肌肉相关疾病中 Ca 信号传导调节的宝贵见解，以及其他 Ca 调节功能失调导致病理学的疾病（如神经退行性疾病）的见解。

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.