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

Authors

  • Natalia A. Osna,

    Corresponding author
    1. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska
    • Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, Nebraska
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  • Fawzia Bardag-Gorce,

    1. Department of Pathology, Los Angeles Biomedical Research Institute,Harbor UCLA Medical Center, Torrance, California
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  • Ronda L. White,

    1. Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, Nebraska
    2. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska
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  • Steven A. Weinman,

    1. Department of Internal Medicine, University of Kansas Medical Center, Kansas City, Kansas
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  • Terrence M. Donohue Jr,

    1. Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, Nebraska
    2. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska
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  • Kusum K. Kharbanda

    1. Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, Nebraska
    2. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska
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Reprint requests: Natalia Osna, MD, PhD, Liver Study Unit, Research Service (151), Veterans Affairs Nebraska-Western Iowa Health Care System, 4101 Woolworth Avenue, Omaha, NE 68105; Tel.: 402-995-3735; Fax: 402-449-0604; E-mail: nosna@unmc.edu

Abstract

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.

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