Abstract
Several cell-damaging effects of ethanol are due to its major metabolite acetaldehyde but its mechanisms are not known. We have studied the effect of acetaldehyde on p42/44 mitogen-activated protein kinase (MAPK) and p46/p54 c-Jun N-terminal kinase (JNK 1/2) in rat hepatocytes. Acetaldehyde caused peak activation of p42/44 MAPK at 10 min followed by JNK activation at 1 h. These responses were acetaldehyde dose-dependent (0.2–5 mM). There was a consistently higher activation of p46 JNK than p54 JNK. Ethanol also activated both p42/44 MAPK and p46/p54 JNK. The activation of JNK by ethanol, however, was not significantly affected by treatment of hepatocytes with 4-methylpyrazole, an alcohol dehydrogenase inhibitor. Cells treated with 200 mM ethanol for 1 h accumulated 0.35 ± 0.02 mM acetaldehyde, but the magnitude of JNK activation was greater than that expected with 0.35 mM acetaldehyde. Thus, ethanol-activated JNK may be both acetaldehyde-dependent and -independent. The activation of JNK by ethanol or acetaldehyde was insensitive to the treatment of hepatocytes with genistein (tyrosine kinase inhibitor) and 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide (GF109203X) (protein kinase C inhibitor). Remarkably, in contrast to the above-mentioned effects on normal hepatocytes, acetaldehyde was unable to increase JNK activity in hepatocytes isolated from rats chronically fed ethanol for 6 weeks and indicated a loss of this acetaldehyde response. Thus, temporal activation of the p42/44 MAPK and p46/p54 JNK, the greater activation of p46 JNK than p54 JNK, and loss of JNK activation after chronic ethanol exposure indicate that these kinases are differentially affected by ethanol metabolite acetaldehyde.
Footnotes
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This work was supported by a Grant AA11962 from National Institute on Alcohol Abuse and Alcoholism and was presented at the 2001 American Society for Pharmacology and Experimental Therapeutics meeting (FASEB J15:A571).
- Abbreviations:
- MAPK
- mitogen-activated protein kinase
- JNK
- c-Jun N-terminal kinase
- MBP
- myelin basic protein
- FBS
- fetal bovine serum
- 4-MP
- 4-methylpyrazole
- PKC
- protein kinase C
- ADH
- alcohol dehydrogenase
- GF109203X
- 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide
- Received December 11, 2001.
- Accepted February 13, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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