Instituto de Biología y Genética Molecular (IBGM), Universidad de Valladolid y Consejo Superior de Investigaciones Científicas (CSIC), C/ Sanz y Forés, 3, 47003-Valladolid, Spain.
Biochem J. 2011 Aug 1;437(3):469-75. doi: 10.1042/BJ20110479.
CALHM1 (calcium homoeostasis modulator 1), a membrane protein with similarity to NMDA (N-methyl-D-aspartate) receptor channels that localizes in the plasma membrane and the ER (endoplasmic reticulum) of neurons, has been shown to generate a plasma-membrane Ca(2+) conductance and has been proposed to influence Alzheimer's disease risk. In the present study we have investigated the effects of CALHM1 on intracellular Ca(2+) handling in HEK-293T [HEK (human embryonic kidney)-293 cells expressing the large T-antigen of SV40 (simian virus 40)] cells by using targeted aequorins for selective monitorization of Ca(2+) transport by organelles. We find that CALHM1 increases Ca(2+) leak from the ER and, more importantly, reduces ER Ca(2+) uptake by decreasing both the transport capacity and the Ca(2+) affinity of SERCA (sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase). As a result, the Ca(2+) content of the ER is drastically decreased. This reduction in the Ca(2+) content of the ER triggered the UPR (unfolded protein response) with induction of several ER stress markers, such as CHOP [C/EBP (CCAAT/enhancer-binding protein)-homologous protein], ERdj4, GRP78 (glucose-regulated protein of 78 kDa) and XBP1 (X-box-binding protein 1). Thus CALHM1 might provide a relevant link between Ca(2+) homoeostasis disruption, ER stress and cell damage in the pathogenesis of neurodegenerative diseases.
CALHM1（钙稳态调节剂 1）是一种与 NMDA（N-甲基-D-天冬氨酸）受体通道具有相似性的膜蛋白，位于神经元的质膜和内质网（ER）中，已被证明能产生质膜 Ca2+电导，并被提议影响阿尔茨海默病的风险。在本研究中，我们通过使用靶向的水母发光蛋白来选择性监测细胞器的 Ca2+转运，研究了 CALHM1 对 HEK-293T[HEK（人胚肾）-293 细胞表达 SV40（猿猴病毒 40）的大 T 抗原]细胞内 Ca2+处理的影响。我们发现，CALHM1 增加了 ER 中的 Ca2+泄漏，更重要的是，通过降低 SERCA（肌浆/内质网 Ca2+-ATP 酶）的转运能力和 Ca2+亲和力，减少了 ER Ca2+摄取，从而大大降低了 ER 的 Ca2+含量。这种 ER 中 Ca2+含量的减少触发了 UPR（未折叠蛋白反应），诱导了几种 ER 应激标志物的表达，如 CHOP[CCAAT/增强子结合蛋白（C/EBP）同源蛋白]、ERdj4、GRP78（葡萄糖调节蛋白 78 kDa）和 XBP1（X-盒结合蛋白 1）。因此，CALHM1 可能为钙稳态破坏、ER 应激和神经退行性疾病发病机制中的细胞损伤之间提供了一个相关的联系。
