Department of Hygiene and Public Health I, Tokyo Women's Medical University, Japan.
Arch Toxicol. 2012 Jan;86(1):37-44. doi: 10.1007/s00204-011-0742-x. Epub 2011 Aug 2.
Cadmium exposure is known to cause endoplasmic reticulum (ER) stress. In our current study, we examined the effects of salubrinal, a selective inhibitor of eukaryotic translation initiation factor 2 subunit α (eIF2α) dephosphorylation, on apoptotic cell death and ER stress-signaling events in HK-2 human renal proximal tubular cells exposed to cadmium chloride (CdCl(2)). Using phase-contrast microscopy and a cell viability assay, we observed that salubrinal suppressed CdCl(2)-induced cellular damage and cell death. Treatment with salubrinal reduced the number of TUNEL-positive cells and the cleavages of caspase-3 and poly(ADP-ribose) polymerase, but not the cleavage of light chain 3B, indicating protection from CdCl(2)-induced apoptosis but not autophagy. Although eIF2α remained phosphorylated after CdCl(2) exposure to salubrinal-treated HK-2 cells, the expression of activating transcription factor 4 (ATF4) and the 78 kDa glucose-regulated protein (GRP78) was not increased. On the other hand, CdCl(2)-induced expression of C/EBP homologous protein (CHOP) was reduced by salubrinal treatment. Expression of ATF4, an upstream regulator of GRP78 and CHOP, appeared to be a prerequisite for full protection by salubrinal against cadmium cytotoxicity, because CdCl(2)-induced cellular damage was not fully suppressed in ATF4-deficient cells. Phosphorylated forms of mitogen-activated protein kinases (MAPKs), including c-Jun NH(2)-terminal kinase (JNK), p38, and extracellular signal-regulated protein kinase (ERK), increased after CdCl(2) exposure, whereas salubrinal suppressed the phosphorylation of JNK and p38 but not ERK. These results suggest that salubrinal protects CdCl(2)-exposed HK-2 cells from apoptosis by suppressing cell death signal transduction pathways.
镉暴露已知会引起内质网（ER）应激。在我们目前的研究中，我们研究了选择性的真核翻译起始因子 2 亚单位α（eIF2α）去磷酸化抑制剂 salubrinal 对氯化镉（CdCl2）暴露的 HK-2 人肾近端肾小管细胞中细胞凋亡和 ER 应激信号事件的影响。通过相差显微镜和细胞活力测定，我们观察到 salubrinal 抑制了 CdCl2 诱导的细胞损伤和细胞死亡。salubrinal 处理减少了 TUNEL 阳性细胞的数量和 caspase-3 和多聚（ADP-核糖）聚合酶的裂解，但不减少轻链 3B 的裂解，表明其对 CdCl2 诱导的细胞凋亡而非自噬有保护作用。尽管 eIF2α在 salubrinal 处理的 HK-2 细胞暴露于 CdCl2 后仍保持磷酸化，但激活转录因子 4（ATF4）和 78 kDa 葡萄糖调节蛋白（GRP78）的表达并未增加。另一方面，salubrinal 处理降低了 CdCl2 诱导的 C/EBP 同源蛋白（CHOP）的表达。ATF4 是 GRP78 和 CHOP 的上游调节因子，其表达似乎是 salubrinal 完全抵抗镉细胞毒性的前提，因为 ATF4 缺陷细胞中 CdCl2 诱导的细胞损伤未完全被抑制。MAPK （包括 c-Jun NH2-末端激酶（JNK），p38 和细胞外信号调节蛋白激酶（ERK））的磷酸化形式在 CdCl2 暴露后增加，而 salubrinal 抑制了 JNK 和 p38 的磷酸化，但不抑制 ERK。这些结果表明 salubrinal 通过抑制细胞死亡信号转导途径来保护 CdCl2 暴露的 HK-2 细胞免于凋亡。
