Involvement of selective reactive oxygen species upstream of proapoptotic branches of unfolded protein response.
Cadmium triggers apoptosis of LLC-PK1 cells through induction of endoplasmic reticulum (ER) stress. We found that cadmium caused generation of reactive oxygen species (ROS) and that cadmium-induced ER stress was inhibited by antioxidants. In contrast, suppression of ER stress did not attenuate cadmium-triggered oxidative stress, suggesting that ER stress occurs downstream of oxidative stress. Exposure of the cells to either O(2)(*), H(2)O(2), or ONOO(-) caused apoptosis, whereas ER stress was induced only by O(2)(*) or ONOO(-). Transfection with manganese superoxide dismutase significantly attenuated cadmium-induced ER stress and apoptosis, whereas pharmacological inhibition of ONOO(-) was ineffective. Interestingly, transfection with catalase attenuated cadmium-induced apoptosis without affecting the level of ER stress. O(2)(*) caused activation of the activating transcription factor 6-CCAAT/enhancer-binding protein-homologous protein (CHOP) and the inositol-requiring ER-to-nucleus signal kinase 1-X-box-binding protein 1 (XBP1) proapoptotic cascades, and overexpression of manganese superoxide dismutase attenuated cadmium-triggered induction of both pathways. Furthermore, phosphorylation of proapoptotic c-Jun N-terminal kinase by O(2)(*) or cadmium was suppressed by dominant-negative inhibition of XBP1. These data elucidated 1) cadmium caused ER stress via generation of ROS, 2) O(2)(*) was selectively involved in cadmium-triggered, ER stress-mediated apoptosis through activation of the activating transcription factor 6-CHOP and inositol-requiring ER-to-nucleus signal kinase 1-XBP1 pathways, and 3) phosphorylation of JNK was caused by O(2)(*)-triggered activation of XBP1.
Yokouchi
Makiko
M
Department of Molecular Signaling, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Shimokato 1110, Chuo, Yamanashi 409-3898, Japan.
Hiramatsu
Nobuhiko
N
Hayakawa
Kunihiro
K
Okamura
Maro
M
Du
Shuqi
S
Kasai
Ayumi
A
Takano
Yosuke
Y
Shitamura
Akihiro
A
Shimada
Tsuyoshi
T
Yao
Jian
J
Kitamura
Masanori
M
D051702:Activating Transcription Factor 6 / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D017931:DNA Primers; D004721:Endoplasmic Reticulum / Q000378:metabolism; D018374:LLC-PK1 Cells; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013552:Swine; D051742:Transcription Factor CHOP / Q000378:metabolism
D051702:Activating Transcription Factor 6; D017931:DNA Primers; D017382:Reactive Oxygen Species; D051742:Transcription Factor CHOP