Dual regulation of hepatocyte apoptosis by reactive oxygen species: Increases in transcriptional expression and decreases in proteasomal degradation of BimEL.
Reactive oxygen species (ROS) have a fundamental role in intracellular signaling transduction. We show here that time-dependent extracellular signal-regulated kinase (ERK) activation due to inactivation of protein tyrosine phosphatases was closely linked to hepatocyte apoptosis under sustained exposure to ROS, which is produced through inhibition of ROS-scavenging enzymes. We found, for the first time, that active ERK transcriptionally increased BimEL expression among seven proteins of the Bcl-2 family. Transfection of Bim siRNA inhibited BimEL expression and hepatocyte apoptosis. Although ERK activation also elicited BimEL phosphorylation and subsequent ubiquitination, exposure to ROS for 9 h decreased proteasome activity. Collectively, the amount of BimEL was elevated by its increased expression and decreased degradation, leading to apoptosis. Exposure to ROS for 6 h caused neither reduction of proteasome activity nor hepatocyte apoptosis. These results indicate that the duration of exposure to ROS determines the fate of cells, that is, survival or death, in addition to the species, amounts, and generation sites of ROS.
Ishihara
Yasuhiro
Y
Laboratory of Pharmacology, Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan.
Takeuchi
Kenji
K
Ito
Fumiaki
F
Shimamoto
Norio
N
D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics* / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D055785:Gene Knockdown Techniques; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D008954:Models, Biological; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*; D054875:Ubiquitination / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C000606778:Bcl2l11 protein, rat; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D017382:Reactive Oxygen Species; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D046988:Proteasome Endopeptidase Complex