CYP2E1 induced by ethanol causes oxidative stress, proteasome inhibition and cytokeratin aggresome (Mallory body-like) formation

Bardag‐Gorce, Fawzia; French, Barbara A.; Li, Nan; Song, Helen; Nguyen, Sheila Khanh; Yong, Holly; Dede, Jennifer; French, Samuel W.

doi:10.1016/j.yexmp.2006.07.007

Cited by 84 publications

(75 citation statements)

References 43 publications

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“…Thus, structural inactivation of the enzyme apparently damages the protein, resulting in the exposure of additional degrons or targeting of additional residues for post-translational modification that marks the protein for ERAD/UPS. ALD inhibitors also led to a significant stabilization of CYP2E1 at 20 h of treatment, entirely consistent with the previously noted relatively slower turnover involved in the ALD process (32)(33)(34)(35)(36)(37)(38).…”

Section: Discussionsupporting

confidence: 88%

Ubiquitin-dependent Proteasomal Degradation of Human Liver Cytochrome P450 2E1

Wang

Guan²,

Acharya

et al. 2011

Journal of Biological Chemistry

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Human liver CYP2E1 is a monotopic, endoplasmic reticulumanchored cytochrome P450 responsible for the biotransformation of clinically relevant drugs, low molecular weight xenobiotics, carcinogens, and endogenous ketones. CYP2E1 substrate complexation converts it into a stable slow-turnover species degraded largely via autophagic lysosomal degradation. Substrate decomplexation/withdrawal results in a fast turnover CYP2E1 species, putatively generated through its futile oxidative cycling, that incurs endoplasmic reticulum-associated ubiquitin-dependent proteasomal degradation (UPD). CYP2E1 thus exhibits biphasic turnover in the mammalian liver. We now show upon heterologous expression of human CYP2E1 in Saccharomyces cerevisiae that its autophagic lysosomal degradation and UPD pathways are evolutionarily conserved, even though its potential for futile catalytic cycling is low due to its sluggish catalytic activity in yeast. This suggested that other factors (i.e. post-translational modifications or "degrons") contribute to its UPD. Indeed, in cultured human hepatocytes, CYP2E1 is detectably ubiquitinated, and this is enhanced on its mechanismbased inactivation. Studies in Ubc7p and Ubc5p genetically deficient yeast strains versus corresponding isogenic wild types identified these ubiquitin-conjugating E2 enzymes as relevant to CYP2E1 UPD. Consistent with this, in vitro functional reconstitution analyses revealed that mammalian UBC7/gp78 and UbcH5a/CHIP E2-E3 ubiquitin ligases were capable of ubiquitinating CYP2E1, a process enhanced by protein kinase (PK) A and/or PKC inclusion. Inhibition of PKA or PKC blocked intracellular CYP2E1 ubiquitination and turnover. Here, through mass spectrometric analyses, we identify some CYP2E1 phosphorylation/ubiquitination sites in spatially associated clusters. We propose that these CYP2E1 phosphorylation clusters may serve to engage each E2-E3 ubiquitination complex in vitro and intracellularly.Hepatic cytochromes P450 (P450s) 2 are endoplasmic reticulum (ER)-anchored hemoproteins involved in the metabolism of numerous endo-and xenobiotics. These substrates can modulate P450 content, diversity, and/or function (see Refs. 1, 2 and references therein) through induction via either increased synthesis or protein stabilization, i.e. half-life prolongation (3-9). By contrast, "suicide" substrate/inactivators accelerate the degradation of certain P450s and dramatically curtail their halflives (10 -23). Such substrate-mediated P450 induction and/or enhanced turnover can influence the severity and the time course of certain pharmacokinetic/pharmacodynamic drugdrug interactions and is an important therapeutic consideration (24 -27).P450 turnover has been proposed to involve various proteolytic mechanisms (6 -9, 28 -38). However, it is now increasingly evident that in common with other type I monotopic ER proteins, P450s such as CYPs 3A (both native and structurally inactivated) undergo ER-associated degradation (ERAD) involving the ubiquitin (Ub)-dependent 26 S proteasomal system (UPS) (6 ...

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Section: Discussionsupporting

confidence: 88%

Ubiquitin-dependent Proteasomal Degradation of Human Liver Cytochrome P450 2E1

Wang

Guan²,

Acharya

et al. 2011

Journal of Biological Chemistry

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“…To verify the hypothesis that gene expression changes are regulated by nuclear proteasome activity, where inhibition is caused by chronic ethanol feeding [20] , proteasome activity was measured in isolated nuclei from the liver of rats fed ethanol chronically, and from the liver of rats given PS-341. Figure 2 shows that chronic ethanol feeding caused a significant decrease in proteasome chymotrypsin-like activity in isolated liver nuclei.…”

Section: Resultsmentioning

confidence: 99%

Epigenetics of proteasome inhibition in the liver of rats fed ethanol chronically

Oliva¹,

Dedes²,

Li³

et al. 2009

WJG

Self Cite

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AIM:To examine the effects of ethanol-induced proteasome inhibition, and the effects of proteasome inhibition in the regulation of epigenetic mechanisms. METHODS:Rats were fed ethanol for 1 mo using the Tsukamoto-French model and were compared to rats given the proteasome inhibitor PS-341 (Bortezomib, Velcade™) by intraperitoneal injection. Microarray analysis and real time PCR were performed and proteasome activity assays and Western blot analysis were performed using isolated nuclei. RESULTS:Chronic ethanol feeding caused a significant inhibition of the ubiquitin proteasome pathway in the nucleus, which led to changes in the turnover of transcriptional factors, histone-modifying enzymes, and, therefore, affected epigenetic mechanisms. Chronic ethanol feeding was related to an increase in histone acetylation, and it is hypothesized that the proteasome proteolytic activity regulated histone modifications by controlling the stability of histone modifying enzymes, and, therefore, regulated the chromatin structure, allowing easy access to chromatin by RNA polymerase, and, thus, proper gene expression. Proteasome inhibition by PS-341 increased histone acetylation similar to chronic ethanol feeding. In addition, proteasome inhibition caused dramatic changes in hepatic remethylation reactions as there was a significant decrease in the enzymes responsible for the regeneration of S-adenosylmethionine, and, in particular, a significant decrease in the betainehomocysteine methyltransferase enzyme. This suggested that hypomethylation was associated with proteasome inhibition, as indicated by the decrease in histone methylation. CONCLUSION:The role of proteasome inhibition in regulating epigenetic mechanisms, and its link to liver injury in alcoholic liver disease, is thus a promising approach to study liver injury due to chronic ethanol consumption.

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“…acetaldehyde and malondialdehyde-acetaldehyde) [34] derived from ethanol metabolism may impair autophagy, similar to that which occurs with the proteasome [35][36][37] . Some of the current evidence for this is circumstantial, but nevertheless compelling as there is evidence of lysosomal damage, as judged by enhanced lysosomal fragility, which could result from either altered lipid metabolism, oxidative stress or both [15] .…”

Section: Suppression Of Autophagymentioning

confidence: 99%

Autophagy and ethanol-induced liver injury

Donohue¹

2009

WJG

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The majority of ethanol metabolism occurs in the liver. Consequently, this organ sustains the greatest damage from ethanol abuse. Ethanol consumption disturbs the delicate balance of protein homeostasis in the liver, causing intracellular protein accumulation due to a disruption of hepatic protein catabolism. Evidence indicates that ethanol or its metabolism impairs trafficking events in the liver, including the process of macroautophagy, which is the engulfment and degradation of cytoplasmic constituents by the lysosomal system. Autophagy is an essential, ongoing cellular process that is highly regulated by nutrients, endocrine factors and signaling pathways. A great number of the genes and gene products that govern the autophagic response have been characterized and the major metabolic and signaling pathways that activate or suppress autophagy have been identified. This review describes the process of autophagy, its regulation and the possible mechanisms by which ethanol disrupts the process of autophagic degradation. The implications of autophagic suppression are discussed in relation to the pathogenesis of alcohol-induced liver injury.

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CYP2E1 induced by ethanol causes oxidative stress, proteasome inhibition and cytokeratin aggresome (Mallory body-like) formation

Cited by 84 publications

References 43 publications

Ubiquitin-dependent Proteasomal Degradation of Human Liver Cytochrome P450 2E1

Ubiquitin-dependent Proteasomal Degradation of Human Liver Cytochrome P450 2E1

Epigenetics of proteasome inhibition in the liver of rats fed ethanol chronically

Autophagy and ethanol-induced liver injury

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