The Effect of Ethanol-Induced Cytochrome p4502E1 on the Inhibition of Proteasome Activity by Alcohol

doi:10.1006/bbrc.2000.3889

Biochemical and Biophysical Research Communications

Volume 279, Issue 1, 9 December 2000, Pages 23-29

https://doi.org/10.1006/bbrc.2000.3889 Get rights and content

Abstract

The present investigation was undertaken to determine the effect of CYP2E1 induction by ethanol on the inhibition of proteasomal activity in wild-type and CYP2E1 knockout C57 black mice. The proteasomal chymotrypsin-like activity decreased significantly in ethanol-fed wild-type mice liver, but was not reduced in ethanol-fed knockout mice liver. The 26S proteasomal activity was decreased more by ethanol feeding than was the 20S proteasomal fraction. Individual hepatocytes lost immunostaining of the proteasomes in the centrilobular zone in the livers of ethanol-fed wild-type mice and the knockout mouse liver. There was increased product of protein oxidation in the liver in the wild type but not in the knockout mice given ethanol. Taken together, these results suggest that CYP2E1 induction was responsible for the decrease in proteasome activity seen in the wild-type mice which head to the accumulation of oxidized proteins which were increased as the result of free radicals generated by CYP2E1 metabolism of ethanol.

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Citation Excerpt :
Therefore, it is more likely that the elevated levels of HIF-1α in alcohol-exposed mice (Fig. 2) and human specimens (Fig. 5) could result from CYP2E1-related increased oxidative stress, which can oxidatively modify one of the enzymes in the 26S proteasomal multiprotein complex involved in the ubiquitin-dependent degradation of HIF-1α. For instance, various subunits of the 26S proteasomal complex can be covalently modified through (1) adduct formation with 4-hydroxynonenal [43], (2) phosphorylation [44], and (3) oxidative modification of Cys residues [45] in a CYP2E1-dependent manner, because proteasomal activities were not significantly decreased in alcohol-exposed Cyp2e1-null mice [46]. In addition to the suppression by chronic alcohol administration, proteasomal activities can also be suppressed by acute binge alcohol exposure [47].
Binge drinking, a common pattern of alcohol ingestion, is known to potentiate liver injury caused by chronic alcohol abuse. This study was aimed at investigating the effects of acute binge alcohol on hypoxia-inducible factor-1α (HIF-1α)-mediated liver injury and the roles of alcohol-metabolizing enzymes in alcohol-induced hypoxia and hepatotoxicity. Mice and human specimens assigned to binge or nonbinge groups were analyzed for blood alcohol concentration (BAC), alcohol-metabolizing enzymes, HIF-1α-related protein nitration, and apoptosis. Binge alcohol promoted acute liver injury in mice with elevated levels of ethanol-inducible cytochrome P450 2E1 (CYP2E1) and hypoxia, both of which were colocalized in the centrilobular areas. We observed positive correlations among elevated BAC, CYP2E1, and HIF-1α in mice and humans exposed to binge alcohol. The CYP2E1 protein levels (r = 0.629, p = 0.001) and activity (r = 0.641, p = 0.001) showed a significantly positive correlation with BAC in human livers. HIF-1α levels were also positively correlated with BAC (r = 0.745, p < 0.001) or CYP2E1 activity (r = 0.792, p < 0.001) in humans. Binge alcohol promoted protein nitration and apoptosis with significant correlations observed between inducible nitric oxide synthase and BAC, CYP2E1, or HIF-1α in human specimens. Binge-alcohol-induced HIF-1α activation and subsequent protein nitration or apoptosis seen in wild type were significantly alleviated in the corresponding Cyp2e1-null mice, whereas pretreatment with an HIF-1α inhibitor, PX-478, prevented HIF-1α elevation with a trend of decreased levels of 3-nitrotyrosine and apoptosis, supporting the roles of CYP2E1 and HIF-1α in binge-alcohol-mediated protein nitration and hepatotoxicity. Thus binge alcohol promotes acute liver injury in mice and humans at least partly through a CYP2E1–HIF-1α-dependent apoptosis pathway.

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Regular ArticleThe Effect of Ethanol-Induced Cytochrome p4502E1 on the Inhibition of Proteasome Activity by Alcohol

Abstract

Hepatology

J. Nutr.

Hepatology

J. Nutr.

Hepatology

J. Biol. Chem.

Anal. Biochem.

Method Enzymol.

Method Enzymol.

J. Biol. Chem.

Alcohol

Hepatology

Arch. Biochem. Biophys.

Regular Article
The Effect of Ethanol-Induced Cytochrome p4502E1 on the Inhibition of Proteasome Activity by Alcohol