Acetaldehyde Disrupts Interferon Alpha Signaling in Hepatitis C Virus Infected Liver Cells by Up-Regulating USP18

Abstract

Background:

Alcohol consumption exacerbates the pathogenesis of HCV-infection and worsens disease outcomes. The exact reasons are not clear yet, but they might be partially attributed to the ability of alcohol to further suppress innate immunity. Innate immunity is known to be already decreased by HCV in liver cells.

Methods and Results:

In this study, we aimed to explore the mechanisms of how alcohol metabolism dysregulates IFNα signaling (STAT1 phosphorylation) in HCV ⁺ hepatoma cells. To this end, CYP2E1 ⁺ Huh7.5 cells were infected with HCV and exposed to the acetaldehyde generating system (AGS). Continuously produced acetaldehyde suppressed IFNα-induced STAT1 phosphorylation, but increased the level of a protease, USP18 (both measured by Western blot), which interferes with IFNα signaling. Induction of USP18 by acetaldehyde was confirmed in primary human hepatocyte cultures and in livers of ethanol-fed HCV transgenic mice. Silencing of USP18 by specific siRNA attenuated the pSTAT1 suppression by acetaldehyde. The mechanism by which acetaldehyde downregulates pSTAT1 is related to an enhanced interaction between IFNαR2 and USP18 that finally dysregulates the cross-talk between the IFN receptor on the cell surface and STAT1. Furthermore, acetaldehyde decreases ISGylation of STAT1 (protein conjugation of a small ubiquitin-like modifier, ISG15, Western blot), which preserves STAT1 activation. Suppressed ISGylation leads to an increase in STAT1 K48 polyubiquitination which allows pSTAT1 degrading by proteasome. We conclude that acetaldehyde disrupts IFNα-induced STAT1 phosphorylation by the upregulation USP18 to block the innate immunity protection in HCV-infected liver cells, thereby contributing to HCV-alcohol pathogenesis. This, in part, may explain the mechanism of HCV-infection exacerbation/progression in alcohol-abusing patients.