Spassova Maria A, Soboloff Jonathan, He Li-Ping, Xu Wen, Dziadek Marie A, Gill Donald L
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Proc Natl Acad Sci U S A. 2006 Mar 14;103(11):4040-5. doi: 10.1073/pnas.0510050103. Epub 2006 Mar 6.
Receptor-induced Ca(2+) signals are key to the function of all cells and involve release of Ca(2+) from endoplasmic reticulum (ER) stores, triggering Ca(2+) entry through plasma membrane (PM) "store-operated channels" (SOCs). The identity of SOCs and their coupling to store depletion remain molecular and mechanistic mysteries. The single transmembrane-spanning Ca(2+)-binding protein, STIM1, is necessary in this coupling process and is proposed to function as an ER Ca(2+) sensor to provide the trigger for SOC activation. Here we reveal that, in addition to being an ER Ca(2+) sensor, STIM1 functions within the PM to control operation of the Ca(2+) entry channel itself. Increased expression levels of STIM1 correlate with a gain in function of Ca(2+) release-activated Ca(2+) (CRAC) channel activity. Point mutation of the N-terminal EF hand transforms the CRAC channel current (I(CRAC)) into a constitutively active, Ca(2+) store-independent mode. Mutants in the EF hand and cytoplasmic C terminus of STIM1 alter operational parameters of CRAC channels, including pharmacological profile and inactivation properties. Last, Ab externally applied to the STIM1 N-terminal EF hand blocks both I(CRAC) in hematopoietic cells and SOC-mediated Ca(2+) entry in HEK293 cells, revealing that STIM1 has an important functional presence within the PM. The results reveal that, in addition to being an ER Ca(2+) sensor, STIM1 functions within the PM to exert control over the operation of SOCs. As a cell surface signaling protein, STIM1 represents a key pharmacological target to control fundamental Ca(2+)-regulated processes including secretion, contraction, metabolism, cell division, and apoptosis.
受体诱导的Ca(2+)信号是所有细胞功能的关键，涉及内质网（ER）储存库中Ca(2+)的释放，通过质膜（PM）“储存-操纵通道”（SOCs）触发Ca(2+)内流。SOCs的身份及其与储存耗竭的偶联仍然是分子和机制上的谜团。单跨膜Ca(2+)结合蛋白STIM1在这一偶联过程中是必需的，被认为作为内质网Ca(2+)传感器发挥作用，为SOC激活提供触发信号。在此我们揭示，除了作为内质网Ca(2+)传感器外，STIM1还在质膜内发挥作用，控制Ca(2+)内流通道本身的运作。STIM1表达水平的增加与Ca(2+)释放激活的Ca(2+)（CRAC）通道活性的功能增强相关。N端EF手的点突变将CRAC通道电流（I(CRAC)）转变为组成性激活的、不依赖Ca(2+)储存的模式。STIM1的EF手和细胞质C端的突变改变了CRAC通道的运作参数，包括药理学特征和失活特性。最后，外部应用于STIM1 N端EF手的抗体阻断了造血细胞中的I(CRAC)以及HEK293细胞中SOC介导的Ca(2+)内流，揭示STIM1在质膜内具有重要的功能存在。结果表明，除了作为内质网Ca(2+)传感器外，STIM1还在质膜内发挥作用，对SOCs的运作进行控制。作为一种细胞表面信号蛋白，STIM1代表了一个关键的药理学靶点，可用于控制包括分泌、收缩、代谢、细胞分裂和凋亡在内的基本Ca(2+)调节过程。
