Department of Physiology, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea.
Department of Biomedicine & Health Sciences, Graduate School, The Catholic University of Korea, Seoul 06591, Korea.
Cells. 2021 Oct 20;10(11):2821. doi: 10.3390/cells10112821.
Calsequestrin 1 (CASQ1) in skeletal muscle buffers and senses Ca in the sarcoplasmic reticulum (SR). CASQ1 also regulates store-operated Ca entry (SOCE) by binding to stromal interaction molecule 1 (STIM1). Abnormal SOCE and/or abnormal expression or mutations in CASQ1, STIM1, or STIM2 are associated with human skeletal, cardiac, or smooth muscle diseases. However, the functional relevance of CASQ1 along with STIM2 has not been studied in any tissue, including skeletal muscle. First, in the present study, it was found by biochemical approaches that CASQ1 is bound to STIM2 via its 92 N-terminal amino acids (C1 region). Next, to examine the functional relevance of the CASQ1-STIM2 interaction in skeletal muscle, the full-length wild-type CASQ1 or the C1 region was expressed in mouse primary skeletal myotubes, and the myotubes were examined using single-myotube Ca imaging experiments and transmission electron microscopy observations. The CASQ1-STIM2 interaction via the C1 region decreased SOCE, increased intracellular Ca release for skeletal muscle contraction, and changed intracellular Ca distributions (high Ca in the SR and low Ca in the cytosol were observed). Furthermore, the C1 region itself (which lacks Ca-buffering ability but has STIM2-binding ability) decreased the expression of Ca-related proteins (canonical-type transient receptor potential cation channel type 6 and calmodulin 1) and induced mitochondrial shape abnormalities. Therefore, in skeletal muscle, CASQ1 plays active roles in Ca movement and distribution by interacting with STIM2 as well as Ca sensing and buffering.
肌质网（SR）中的钙结合蛋白 1（CASQ1）缓冲和感知 Ca。CASQ1 还通过与基质相互作用分子 1（STIM1）结合来调节储存操作的钙进入（SOCE）。异常的 SOCE 和/或 CASQ1、STIM1 或 STIM2 的异常表达或突变与人类骨骼肌、心脏或平滑肌疾病有关。然而，CASQ1 与 STIM2 之间的功能相关性在包括骨骼肌在内的任何组织中都尚未研究过。首先，在本研究中，通过生化方法发现 CASQ1 通过其 92 个 N 端氨基酸（C1 区）与 STIM2 结合。接下来，为了研究 CASQ1-STIM2 相互作用在骨骼肌中的功能相关性，在小鼠原代骨骼肌肌管中表达全长野生型 CASQ1 或 C1 区，并用单肌管 Ca 成像实验和透射电子显微镜观察来检查肌管。通过 C1 区的 CASQ1-STIM2 相互作用降低了 SOCE，增加了骨骼肌收缩的细胞内 Ca 释放，并改变了细胞内 Ca 分布（观察到 SR 中高 Ca 和细胞质溶胶中低 Ca）。此外，C1 区本身（缺乏 Ca 缓冲能力但具有 STIM2 结合能力）降低了与 Ca 相关的蛋白（经典型瞬时受体电位阳离子通道 6 和钙调蛋白 1）的表达，并诱导了线粒体形态异常。因此，在骨骼肌中，CASQ1 通过与 STIM2 相互作用以及 Ca 感应和缓冲来积极参与 Ca 运动和分布。
