Lorin-Nebel Catherine, Xing Juan, Yan Xiaohui, Strange Kevin
Vanderbilt University Medical Center, T-4208 Medical Center North, Nashville, TN 37232-2520, USA.
J Physiol. 2007 Apr 1;580(Pt 1):67-85. doi: 10.1113/jphysiol.2006.124883. Epub 2007 Jan 11.
The Ca(2+) release-activated Ca(2+) (CRAC) channel is a plasma membrane Ca(2+) entry pathway activated by endoplasmic reticulum (ER) Ca(2+) store depletion. STIM1 proteins function as ER Ca(2+) sensors and regulate CRAC channel activation. Recent studies have demonstrated that CRAC channels are encoded by the human Orai1 gene and a homologous Drosophila gene. C. elegans intestinal cells express a store-operated Ca(2+) channel (SOCC) regulated by STIM-1. We cloned a full-length C. elegans cDNA that encodes a 293 amino acid protein, ORAI-1, homologous to human and Drosophila Orai1 proteins. ORAI-1 GFP reporters are co-expressed with STIM-1 in the gonad and intestine. Inositol 1,4,5-trisphosphate (IP(3))-dependent Ca(2+) signalling regulates C. elegans gonad function, fertility and rhythmic posterior body wall muscle contraction (pBoc) required for defecation. RNA interference (RNAi) silencing of orai-1 expression phenocopies stim-1 knockdown and causes sterility and prevents intestinal cell SOCC activation, but has no effect on pBoc or intestinal Ca(2+) signalling. Orai-1 RNAi suppresses pBoc defects induced by intestinal expression of a STIM-1 Ca(2+)-binding mutant, indicating that the proteins function in a common pathway. Co-expression of stim-1 and orai-1 cDNAs in HEK293 cells induces large inwardly rectifying cation currents activated by ER Ca(2+) depletion. The properties of this current recapitulate those of the native SOCC current. We conclude that C. elegans expresses bona fide CRAC channels that require the function of Orai1- and STIM1-related proteins. CRAC channels thus arose very early in animal evolution. In C. elegans, CRAC channels do not play obligate roles in all IP(3)-dependent signalling processes and ER Ca(2+) homeostasis. Instead, we suggest that CRAC channels carry out highly specialized and cell-specific signalling roles and that they may function as a failsafe mechanism to prevent Ca(2+) store depletion under pathophysiological and stress conditions.
钙释放激活钙（CRAC）通道是一种质膜钙内流途径，由内质网（ER）钙库耗竭激活。STIM1蛋白作为内质网钙传感器，调节CRAC通道的激活。最近的研究表明，CRAC通道由人类Orai1基因和一个同源的果蝇基因编码。秀丽隐杆线虫肠道细胞表达一种受STIM-1调节的储存操纵性钙通道（SOCC）。我们克隆了一个全长的秀丽隐杆线虫cDNA，它编码一种293个氨基酸的蛋白质ORAI-1，与人及果蝇的Orai1蛋白同源。ORAI-1绿色荧光蛋白报告基因在性腺和肠道中与STIM-1共表达。肌醇1,4,5-三磷酸（IP(3)）依赖性钙信号调节秀丽隐杆线虫的性腺功能、生育能力和排便所需的有节奏的后体壁肌肉收缩（pBoc）。通过RNA干扰（RNAi）沉默orai-1表达可模拟stim-1基因敲除的表型，导致不育，并阻止肠道细胞SOCC激活，但对pBoc或肠道钙信号无影响。Orai-1 RNAi可抑制由肠道表达STIM-1钙结合突变体诱导的pBoc缺陷，表明这些蛋白在共同途径中发挥作用。stim-1和orai-1 cDNA在HEK293细胞中共表达可诱导由内质网钙耗竭激活的大内向整流阳离子电流。该电流的特性概括了天然SOCC电流的特性。我们得出结论，秀丽隐杆线虫表达真正的CRAC通道，这些通道需要Orai1和STIM1相关蛋白的功能。因此，CRAC通道在动物进化过程中很早就出现了。在秀丽隐杆线虫中，CRAC通道并非在所有IP(3)依赖性信号传导过程和内质网钙稳态中都发挥必需作用。相反，我们认为CRAC通道执行高度专业化和细胞特异性的信号传导作用，并且它们可能作为一种故障安全机制，在病理生理和应激条件下防止钙库耗竭。
