Department of Biological Sciences, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, Korea.
Department of Biological Sciences, Center for Genomic Integrity (CGI), Institute for Basic Science (IBS), Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, Korea.
Exp Mol Med. 2020 Jun;52(6):940-950. doi: 10.1038/s12276-020-0448-3. Epub 2020 Jun 5.
The endoplasmic reticulum (ER) stress response is an adaptive mechanism that is activated upon disruption of ER homeostasis and protects the cells against certain harmful environmental stimuli. However, critical and prolonged cell stress triggers cell death. In this study, we demonstrate that Flightless-1 (FliI) regulates ER stress-induced apoptosis in colon cancer cells by modulating Ca homeostasis. FliI was highly expressed in both colon cell lines and colorectal cancer mouse models. In a mouse xenograft model using CT26 mouse colorectal cancer cells, tumor formation was slowed due to elevated levels of apoptosis in FliI-knockdown (FliI-KD) cells. FliI-KD cells treated with ER stress inducers, thapsigargin (TG), and tunicamycin exhibited activation of the unfolded protein response (UPR) and induction of UPR-related gene expression, which eventually triggered apoptosis. FliI-KD increased the intracellular Ca concentration, and this upregulation was caused by accelerated ER-to-cytosolic efflux of Ca. The increase in intracellular Ca concentration was significantly blocked by dantrolene and tetracaine, inhibitors of ryanodine receptors (RyRs). Dantrolene inhibited TG-induced ER stress and decreased the rate of apoptosis in FliI-KD CT26 cells. Finally, we found that knockdown of FliI decreased the levels of sorcin and ER Ca and that TG-induced ER stress was recovered by overexpression of sorcin in FliI-KD cells. Taken together, these results suggest that FliI regulates sorcin expression, which modulates Ca homeostasis in the ER through RyRs. Our findings reveal a novel mechanism by which FliI influences Ca homeostasis and cell survival during ER stress.
内质网（ER）应激反应是一种适应性机制，当 ER 稳态受到破坏时会被激活，从而保护细胞免受某些有害环境刺激的影响。然而，严重和长期的细胞应激会引发细胞死亡。在这项研究中，我们证明 Flightless-1（FliI）通过调节钙稳态来调节 ER 应激诱导的结肠癌细胞凋亡。FliI 在结肠细胞系和结直肠癌小鼠模型中均高度表达。在使用 CT26 结肠癌细胞的小鼠异种移植模型中，由于 FliI 敲低（FliI-KD）细胞中凋亡水平升高，肿瘤形成速度减慢。用 ER 应激诱导剂 thapsigargin（TG）和衣霉素处理的 FliI-KD 细胞表现出未折叠蛋白反应（UPR）的激活和 UPR 相关基因表达的诱导，最终引发细胞凋亡。FliI-KD 增加了细胞内 Ca 浓度，这种上调是由于 Ca 从内质网到细胞质的快速流出引起的。细胞内 Ca 浓度的增加被肌醇 1,4,5-三磷酸受体（RyRs）抑制剂 dantrolene 和 tetracaine 显著阻断。Dantrolene 抑制 TG 诱导的 ER 应激并降低 FliI-KD CT26 细胞中的凋亡率。最后，我们发现 FliI 敲低降低了 sorcin 和 ER Ca 的水平，并且 TG 诱导的 ER 应激通过在 FliI-KD 细胞中转染 sorcin 得到恢复。总之，这些结果表明 FliI 调节 sorcin 的表达，通过 RyRs 调节 ER 中的钙稳态。我们的研究结果揭示了一种新的机制，即 FliI 在 ER 应激期间通过调节钙稳态影响细胞存活。
