Ganesan Murali, Poluektova Larisa Y, Tuma Dean J, Kharbanda Kusum K, Osna Natalia A
Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, Nebraska.
Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska.
Alcohol Clin Exp Res. 2016 Nov;40(11):2329-2338. doi: 10.1111/acer.13226. Epub 2016 Sep 26.
Alcohol consumption exacerbates the pathogenesis of hepatitis C virus (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 the innate immunity. Innate immunity is known to be already decreased by HCV in liver cells.
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 (Ach) generating system (AGS).
Continuously produced Ach 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 Ach 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 Ach. The mechanism by which Ach down-regulates 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, Ach 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 Ach disrupts IFNα-induced STAT1 phosphorylation by the up-regulation of 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.
饮酒会加剧丙型肝炎病毒（HCV）感染的发病机制并恶化疾病预后。确切原因尚不清楚，但可能部分归因于酒精进一步抑制先天免疫的能力。已知HCV会使肝细胞中的先天免疫降低。
在本研究中，我们旨在探究酒精代谢如何失调HCV肝癌细胞中IFNα信号传导（STAT1磷酸化）的机制。为此，用HCV感染CYP2E1 Huh7.5细胞，并使其暴露于乙醛（Ach）生成系统（AGS）。
持续产生的Ach抑制IFNα诱导的STAT1磷酸化，但增加了一种蛋白酶USP18的水平（均通过蛋白质印迹法测定），该蛋白酶会干扰IFNα信号传导。在原代人肝细胞培养物和乙醇喂养的HCV转基因小鼠肝脏中证实了Ach对USP18的诱导作用。用特异性siRNA沉默USP18可减弱Ach对pSTAT1的抑制作用。Ach下调pSTAT1的机制与IFNαR2和USP18之间增强的相互作用有关，最终失调细胞表面IFN受体与STAT1之间的相互作用。此外，Ach降低了STAT1的ISGylation（一种小泛素样修饰物ISG15的蛋白质缀合，蛋白质印迹法），这会保留STAT1的激活。ISGylation受到抑制会导致STAT1 K48多聚泛素化增加，从而使pSTAT1通过蛋白酶体降解。
我们得出结论，Ach通过上调USP18破坏IFNα诱导的STAT1磷酸化，从而阻断HCV感染的肝细胞中的先天免疫保护，进而导致HCV-酒精发病机制。这在一定程度上可能解释了酗酒患者中HCV感染加剧/进展的机制。
