Yokouchi M, Hiramatsu N, Hayakawa K, Kasai A, Takano Y, Yao J, Kitamura M
Department of Molecular Signaling, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi 409-3898, Japan.
Cell Death Differ. 2007 Aug;14(8):1467-74. doi: 10.1038/sj.cdd.4402154. Epub 2007 Apr 27.
Cadmium is a widely distributed nephrotoxic metal that causes renal tubular injury. In this report, we investigated involvement of endoplasmic reticulum (ER) stress and individual unfolded protein responses in cadmium-initiated apoptosis of tubular epithelial cells. Cadmium chloride (CdCl(2)) induced expression of endogenous ER stress markers, GRP78, GRP94 and CHOP in vitro and in vivo, and subsequently caused cytological changes typical of apoptosis. Attenuation of ER stress by transfection with ER chaperone GRP78 or ORP150 suppressed CdCl(2)-triggered apoptosis. In response to CdCl(2), phosphorylation of RNA-dependent protein kinase-like ER kinase (PERK) and eukaryotic translation initiation factor 2alpha (eIF2alpha) was observed. Enhanced phosphorylation of eIF2alpha attenuated, whereas inhibition of eIF2alpha exacerbated CdCl(2)-induced apoptosis. Activating transcription factor 6 (ATF6) was also activated by CdCl(2) and blockade of this process suppressed induction of CHOP and thereby improved cell survival. CdCl(2) also triggered activation of the inositol-requiring ER-to-nucleus signal kinase 1 (IRE1)-X-box-binding protein 1 (XBP1) pathway and inhibition of XBP1 attenuated apoptosis independent of GRP78 and CHOP. c-Jun N-terminal kinase (JNK), another molecule downstream of IRE1, was also phosphorylated by CdCl(2) and its inhibition attenuated apoptosis. These results evidenced bidirectional regulation of apoptosis in cadmium-exposed cells. The ATF6 and IRE1 pathways cooperatively caused apoptosis via induction of CHOP, activation of XBP1 and phosphorylation of JNK, and the PERK-eIF2alpha pathway counteracted the proapoptotic processes.
镉是一种广泛分布的具有肾毒性的金属，可导致肾小管损伤。在本报告中，我们研究了内质网（ER）应激和个体未折叠蛋白反应在镉引发的肾小管上皮细胞凋亡中的作用。氯化镉（CdCl₂）在体外和体内诱导内源性ER应激标志物GRP78、GRP94和CHOP的表达，随后引起典型的凋亡细胞学变化。通过转染ER伴侣蛋白GRP78或ORP150减轻ER应激可抑制CdCl₂触发的凋亡。在CdCl₂作用下，观察到RNA依赖性蛋白激酶样内质网激酶（PERK）和真核翻译起始因子2α（eIF2α）的磷酸化。eIF2α磷酸化增强可减轻凋亡，而抑制eIF2α则会加剧CdCl₂诱导的凋亡。活化转录因子6（ATF6）也被CdCl₂激活，阻断这一过程可抑制CHOP的诱导，从而提高细胞存活率。CdCl₂还触发了肌醇需求性内质网到细胞核信号激酶1（IRE1）-X盒结合蛋白1（XBP1）途径的激活，抑制XBP1可减轻凋亡，且与GRP78和CHOP无关。IRE1下游的另一个分子c-Jun氨基末端激酶（JNK）也被CdCl₂磷酸化，抑制其活性可减轻凋亡。这些结果证明了镉暴露细胞中凋亡的双向调节。ATF6和IRE1途径通过诱导CHOP、激活XBP1和JNK磷酸化协同导致凋亡，而PERK-eIF2α途径则对抗促凋亡过程。
