Yan Xiaohui, Xing Juan, Lorin-Nebel Catherine, Estevez Ana Y, Nehrke Keith, Lamitina Todd, Strange Kevin
Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
J Gen Physiol. 2006 Oct;128(4):443-59. doi: 10.1085/jgp.200609611. Epub 2006 Sep 11.
1,4,5-trisphosphate (IP(3))-dependent Ca(2+) signaling regulates gonad function, fertility, and rhythmic posterior body wall muscle contraction (pBoc) required for defecation in Caenorhabditis elegans. Store-operated Ca(2+) entry (SOCE) is activated during endoplasmic reticulum (ER) Ca(2+) store depletion and is believed to be an essential and ubiquitous component of Ca(2+) signaling pathways. SOCE is thought to function to refill Ca(2+) stores and modulate Ca(2+) signals. Recently, stromal interaction molecule 1 (STIM1) was identified as a putative ER Ca(2+) sensor that regulates SOCE. We cloned a full-length C. elegans stim-1 cDNA that encodes a 530-amino acid protein with approximately 21% sequence identity to human STIM1. Green fluorescent protein (GFP)-tagged STIM-1 is expressed in the intestine, gonad sheath cells, and spermatheca. Knockdown of stim-1 expression by RNA interference (RNAi) causes sterility due to loss of sheath cell and spermatheca contractile activity required for ovulation. Transgenic worms expressing a STIM-1 EF-hand mutant that constitutively activates SOCE in Drosophila and mammalian cells are sterile and exhibit severe pBoc arrhythmia. stim-1 RNAi dramatically reduces STIM-1GFP expression, suppresses the EF-hand mutation-induced pBoc arrhythmia, and inhibits intestinal store-operated Ca(2+) (SOC) channels. However, stim-1 RNAi surprisingly has no effect on pBoc rhythm, which is controlled by intestinal oscillatory Ca(2+) signaling, in wild type and IP(3) signaling mutant worms, and has no effect on intestinal Ca(2+) oscillations and waves. Depletion of intestinal Ca(2+) stores by RNAi knockdown of the ER Ca(2+) pump triggers the ER unfolded protein response (UPR). In contrast, stim-1 RNAi fails to induce the UPR. Our studies provide the first detailed characterization of STIM-1 function in an intact animal and suggest that SOCE is not essential for certain oscillatory Ca(2+) signaling processes and for maintenance of store Ca(2+) levels in C. elegans. These findings raise interesting and important questions regarding the function of SOCE and SOC channels under normal and pathophysiological conditions.
1,4,5-三磷酸肌醇（IP(3)）依赖性钙信号调节秀丽隐杆线虫的性腺功能、生育能力以及排便所需的节律性后体壁肌肉收缩（pBoc）。在糙面内质网（ER）钙库耗竭期间，储存性钙内流（SOCE）被激活，并且被认为是钙信号通路中一个必不可少且普遍存在的组成部分。SOCE被认为起到补充钙库和调节钙信号的作用。最近，基质相互作用分子1（STIM1）被鉴定为一种调节SOCE的假定内质网钙传感器。我们克隆了一个全长的秀丽隐杆线虫stim-1 cDNA，它编码一个530个氨基酸的蛋白质，与人类STIM1具有约21%的序列同一性。绿色荧光蛋白（GFP）标记的STIM-1在肠道、性腺鞘细胞和受精囊中表达。通过RNA干扰（RNAi）敲低stim-1表达会导致不育，这是由于排卵所需的鞘细胞和受精囊收缩活性丧失所致。在果蝇和哺乳动物细胞中表达持续激活SOCE的STIM-1 EF手突变体的转基因蠕虫是不育的，并表现出严重的pBoc心律失常。stim-1 RNAi显著降低STIM-1GFP表达，抑制EF手突变诱导的pBoc心律失常，并抑制肠道储存性钙（SOC）通道。然而，令人惊讶的是，stim-1 RNAi对野生型和IP(3)信号突变蠕虫中由肠道振荡性钙信号控制的pBoc节律没有影响，并且对肠道钙振荡和波动也没有影响。通过RNAi敲低内质网钙泵导致肠道钙库耗竭会触发内质网未折叠蛋白反应（UPR）。相比之下，stim-1 RNAi未能诱导UPR。我们的研究首次详细描述了STIM-1在完整动物中的功能，并表明SOCE对于秀丽隐杆线虫中某些振荡性钙信号过程和维持钙库水平并非必不可少。这些发现提出了关于正常和病理生理条件下SOCE和SOC通道功能的有趣且重要的问题。
