Background & aims: Alcohol-induced progression of hepatitis C virus (HCV) infection is related to dysfunction of innate immunity in hepatocytes. Endogenously produced interferon (IFN)α induces activation of interferon-stimulated genes (ISGs) via triggering of the Janus kinase-signal transducer and activator of transcription 1 (STAT1) pathway. This activation requires protein methyltransferase 1-regulated arginine methylation of STAT1. Here, we aimed to study whether STAT1 methylation also depended on the levels of demethylase jumonji domain-containing 6 protein (JMJD6) and whether ethanol and HCV affect JMJD6 expression in hepatocytes.
Methods: Huh7.5-CYP (RLW) cells and hepatocytes were exposed to acetaldehyde-generating system (AGS) and 50 mmol/L ethanol, respectively. JMJD6 messenger RNA and protein expression were measured by real-time polymerase chain reaction and Western blot. IFNα-activated cells either overexpressing JMJD6 or with knocked-down JMJD6 expression were tested for STAT1 methylation, ISG activation, and HCV RNA. In vivo studies have been performed on C57Bl/6 mice (expressing HCV structural proteins or not) or chimeric mice with humanized livers fed control or ethanol diets.
Results: AGS exposure to cells up-regulated JMJD6 expression in RLW cells. These results were corroborated by ethanol treatment of primary hepatocytes. The promethylating agent betaine reversed the effects of AGS/ethanol. Similar results were obtained in vivo, when mice were fed control/ethanol with and without betaine supplementation. Overexpression of JMJD6 suppressed STAT1 methylation, IFNα-induced ISG activation, and increased HCV-RNA levels. In contrast, JMJD6 silencing enhanced STAT1 methylation, ISG stimulation by IFNα, and attenuated HCV-RNA expression in Huh7.5 cells.
Conclusions: We conclude that arginine methylation of STAT1 is suppressed by JMJD6. Both HCV and acetaldehyde increase JMJD6 levels, thereby impairing STAT1 methylation and innate immunity protection in hepatocytes exposed to the virus and/or alcohol.
Keywords: 4-MP, 4-methylpirazole; ADH, alcohol dehydrogenase; AGS, acetaldehyde-generating system; AMI-1, protein arginine N-methyltransferase inhibitor; Ach, acetaldehyde; Alcohol; BHMT, betaine-homocysteine-S-methyltransferase; CYP2E1, cytochrome P450 2E1; HCV; HCV, hepatitis C virus; IFN, interferon; ISG, interferon-stimulated gene; JAK-STAT, Janus kinase–STAT, signal transducer and activator of transcription; JMJD6; JMJD6, jumonji domain-containing 6 protein; OA, okadaic acid; OAS-1, 2’-5’-oligoadenylate synthetase-1; OASL, 2’-5’-oligoadenylate synthetase-like protein; PCR, polymerase chain reaction; PP2A, protein phosphatase 2A; PRMT1, protein methyl transferase 1; RT, reverse-transcription; SAM, S-adenosylmethionine; STAT1; TK-NOG, thymidine kinase transgene-NOD/Shi-scid/IL-2Rγnull mice; cDNA, complementary DNA; mRNA, messenger RNA; siRNA, short interfering RNA.