Apoptosis signal-regulating kinase 1 is crucial for oxidative stress-induced but not for osmotic stress-induced hepatocyte cell death.
OBJECTIVE
In this study, we investigated the involvement of apoptosis signal-regulating kinase 1 (ASK1) in oxidative stress and osmotic stress-induced hepatocyte death.


METHODS
Activation of ASK1-JNK/p38 cascade and resulting cell death induced by oxidative and osmotic stress was investigated by Western immunoblot analysis and cell toxicity assay using human hepatoma cell lines, Huh7 expressing high level of ASK1 and HepG2 cells expressing low level of ASK1. Gene knock-down of ASK1 using shRNA against ASK1 was conducted using mouse hepatocyte cell line, AML12.


RESULTS
Activation of ASK1-JNK/p38 cascade and cell death in Huh7 expressing high level of ASK1 was markedly induced by the oxidative stress. HepG2 expressing low level of ASK1 was resistant to oxidative stress while cell death induced by osmotic stress was comparable between Huh7 and HepG2 cells. Although the phosphorylation of ASK1 was not observed by osmotic stress, the phosphorylation of p38 and JNK and resulting cell death was induced in both cell lines. The phosphorylation of ASK1 and p38/JNK in the mouse primary hepatocyte were also increased by oxidative stress. Knock-down of ASK1 mRNA in AML12 in vitro significantly reduced oxidative stress-induced cell death, however, knock-down of ASK1 in cells did not affect the osmotic stress-induced cell death.


CONCLUSIONS
This study revealed that ASK1 regulates oxidative stress- but not osmotic stress-induced hepatocyte death, suggesting ASK1 plays a critical role in oxidative-stress induced hepatocyte death. These results raise the possibility that an ASK1 may be a promising therapeutic target for liver diseases caused by oxidative stress.
Taki
Kenji
K
Discovery Biology-3, Nagoya Laboratories, Pfizer Global Research and Development, Pfizer Japan Inc., 5-2 Taketoyo, Aichi, 470-2393, Japan.
Shimozono
Rieko
R
Kusano
Hajime
H
Suzuki
Nobutaka
N
Shinjo
Katsuhiro
K
Eda
Hiroyuki
H
D000818:Animals; D015153:Blotting, Western; D016923:Cell Death; D045744:Cell Line, Tumor; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D048848:MAP Kinase Kinase Kinase 5 / Q000096:biosynthesis / Q000502:physiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009997:Osmotic Pressure; D018384:Oxidative Stress; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction
D048848:MAP Kinase Kinase Kinase 5