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

Abstract

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.

Proteasome inhibitor treatment reduced fatty acid, triacylglycerol and cholesterol synthesis

“…A KEGG functional pathway analysis showed that proteasome inhibitor drug treatment significantly down regulated fatty acid metabolism, biosynthesis, and fatty acid elongation [Oliva et al, 2009]. Data mining of this microarray analysis showed that proteasome inhibitor treatment down regulated the gene expression of sterol regulatory element binding protein 1 (SREBP-1c) and that of the downstream lipogenic enzyme (Table 2).…”

Nuclear effects of ethanol-induced proteasome inhibition in liver cells

“…However, the linkage of ethanol-induced proteasome inhibition to the changes in the expression of these genes still needs to be determined. Data mining of microarray analysis of proteasome inhibition has shown that, similar to ethanol-treated rat liver, several genes are changed, which indicates an epigenetic phenomenon c proteasome inhibition [17,50] .…”

“…Indeed, analyses performed on the livers of rats given PS-341 (bortezomib, Velcade®), a dipeptide boronic acid used to inhibit proteasome activity, and used today as an anticancer agent in human myeloma [51] , have shown down-regulation of gene expression for methionine metabolizing enzymes. Proteasome inhibition causes a decrease in methionine adenosyltransferase (MAT1a), in S-adenosylhomocysteine hydrolase gene expression, and a marked decrease in gene expression of betaine-homocysteine methyltransferase [50,52] and Cbs [53] , which affects cellular methylation. Rats fed ethanol chronically also exhibit a relatively low level of MAT1a, which is associated with low levels of SAMe and faster growth [54] .…”

Increased activity of the complement system in the liver of patients with alcoholic hepatitis

“…Apoptosis of hepatocytes is a major characteristic of ALD (Higuchi et al, 1996; Oliva et al, 2009). Our current study shows increased C1q immunoreactivity and gene expression in patients with AH.…”