Ethanol and Hepatitis C Virus Suppress Peptide-MHC Class I Presentation in Hepatocytes by Altering Proteasome Function

Background: Previously, we reported that exposure of hepatitis C virus (HCV) core-expressing ethanol (EtOH)-metabolizing cells to EtOH significantly suppresses proteasome activity which exists as 26S (20S and 19S) and as an unassociated 20S particle. The replacement of the constitutive proteasomal subunits with immunoproteasome (IPR) favors antigen processing. Here, we examined the effects of EtOH consumption by HCV core transgenic mice on proteasome activity in hepatocytic lysates and in partially purified 26S proteasome and the impact of these changes on antigen presentation. Methods: HCV ^- and HCV ⁺ core transgenic mice were fed chow diet with or without 20% (v/v) EtOH in water for 4 weeks. Following the feeding regimen, hepatocytes were isolated and examined for chymotrypsin-like proteasome activity, oxidative stress, and the presentation of SIINFEKL-H2Kb complex. Additionally, the constitutive proteasome and IPR were purified for further analysis and identification of proteasome-interacting proteins (PIPs). Results: EtOH significantly decreased proteasome activity in hepatocytes of HCV ⁺ mice, and this finding correlated with oxidative stress and dysregulated methylation reactions. In isolated 26S proteasome, EtOH suppressed proteasome activity equally in HCV ⁺ and HCV ^- mice. EtOH feeding caused proteasome instability and lowered the content of both constitutive and IPR subunits in the 20S proteasome. In addition, the level of other PIPs, PA28 and UCHL5, were also suppressed after EtOH exposure. Furthermore, in EtOH-fed mice and, especially, in HCV ⁺ mice, the presentation of SIINFEKL-H2Kb complex in hepatocytes was also decreased. Conclusions: Proteasomal dysfunction induced by EtOH feeding and exacerbated by the presence of HCV structural proteins led to suppression of SIINFEKL-H2Kb presentation in hepatocytes.