Ethanol metabolism alters interferon gamma signaling in recombinant HepG2 cells

Authors

  • Natalia A. Osna,

    Corresponding author
    1. Liver Study Unit, The Omaha Veterans Affairs (VA) Medical Center, University of Nebraska Medical Center, Omaha, NE
    2. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE
    • Liver Study Unit, Research Service (151), VA Medical Center, 4101 Woolworth Avenue, Omaha, NE 68105
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    • fax: 402-449-0604.

  • Dahn L. Clemens,

    1. Liver Study Unit, The Omaha Veterans Affairs (VA) Medical Center, University of Nebraska Medical Center, Omaha, NE
    2. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE
    3. Department of Pathology/Microbiology, University of Nebraska Medical Center, Omaha, NE
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  • Terrence M. Donohue Jr.

    1. Liver Study Unit, The Omaha Veterans Affairs (VA) Medical Center, University of Nebraska Medical Center, Omaha, NE
    2. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE
    3. Department of Pathology/Microbiology, University of Nebraska Medical Center, Omaha, NE
    4. Department of Biochemistry/Molecular Biology, University of Nebraska Medical Center, Omaha, NE
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  • Potential conflict of interest: Nothing to report.

Abstract

We previously showed that IFNγ signal transduction was suppressed by ethanol in recombinant HepG2 cells (VL-17A cells), which express alcohol dehydrogenase (ADH) and CYP2E1. We examined the mechanisms by which STAT1 phosphorylation is blocked by ethanol treatment in VL-17A cells. Cells were exposed to 0 or 100 mmol/L ethanol for 72 hours. STAT1 phosphorylation was determined by Western blot after 1 hour IFNγ exposure. Reduction of STAT1 phosphorylation by ethanol was prevented in the presence of 4MP, DAS, or uric acid, indicating that the oxidative products from ethanol metabolism were partly responsible for suppression of STAT1 phosphorylation. Ethanol exposure decreased STAT1 tyrosine phosphorylation, whereas serine phosphorylation on the protein was unchanged. These effects of ethanol were mimicked by the peroxynitrite (PN) donor, SIN-1, which also blocked tyrosine, but not serine phosphorylation, on STAT1. When cells expressing either ADH (VA-13 cells) or CYP2E1 (E-47 cells) were exposed to ethanol, both ADH- and CYP2E1-generated products reduced STAT1 phosphorylation. In addition, SOCS1, a negative regulator of IFNγ signaling and which is degraded by the proteasome, was stabilized by ethanol treatment, presumably because of inhibited proteasome activity. Furthermore, SIN-1 treatment elevated SOCS1 levels in VL-17A cells, indicating that PN has a role in SOCS1 elevation. In conclusion, under conditions of ethanol-elicited oxidative stress, PN prevents STAT1 phosphorylation by stabilization of SOCS1, and possibly by nitration of tyrosine residues in STAT1 protein. (HEPATOLOGY 2005;42:1109–1117.)

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