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Ethanol rapidly inhibits IL-6-activated STAT3 and C/EBP mRNA expression in freshly isolated rat hepatocytes
1Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
Abstract:
The ability of ethanol to inhibit regenerative processes in the liver is thought to play a key role in the development of alcoholic liver disease. To understand the underlying mechanisms, we investigated the effects of ethanol on the Janus kinasesignal transducer and activator transcription factor (JAK-STAT) signaling pathways in hepatocytes. Treatment of freshly isolated adult rat hepatocytes with 10-100 mM ethanol rapidly (< 3 min) inhibits interleukin-6 (IL-6)-induced STAT3 activation, tyrosine and serine phosphorylation and IL-6-induced CCAAT enhancer binding protein (C/EBP) alpha and beta mRNA expression. Western analyses, in vitro kinase assays and in vivo cell labelling assays indicate that this inhibitory effect is not due to blocking the upstream-located JAK1, JAK2 or Tyk2 activation. On the contrary, acute ethanol exposure significantly potentiates IL-6-induced JAK1 autophosphorylation in vitro and in vivo. Pretreatment with sodium vanadate, a non-selective tyrosine phosphatase inhibitor, or with MG132 and lactacystin, proteasome inhibitors, does not abolish the ethanol inhibition of IL-6-induced STAT3 activation, suggesting that activation of protein tyrosine phosphatases or the ubiquitin-proteasome pathway is not involved. In view of the critical role of IL-6 signaling in liver regeneration, these findings suggest that the ability of biologically relevant concentrations of ethanol to markedly inhibit IL-6-induced STAT3 phosphorylation is one of the cellular mechanisms involved in the pathogenesis and progression of alcoholic liver diseases.
Insights
Ethanol inhibits liver regeneration by blocking interleukin-6 (IL-6)-induced STAT3 activation in hepatocytes. This disruption of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is key to alcoholic liver disease progression.
Area of Science:
- Hepatology and molecular biology
- Alcoholic liver disease pathogenesis
- Cellular signaling pathways
Background:
- Ethanol's inhibition of liver regeneration is crucial in alcoholic liver disease (ALD).
- The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is vital for liver regeneration.
- Understanding ethanol's impact on JAK-STAT signaling in hepatocytes is essential for ALD research.
Purpose of the Study:
- To investigate the effects of ethanol on JAK-STAT signaling pathways in hepatocytes.
- To elucidate the cellular mechanisms by which ethanol contributes to ALD.
- To determine if ethanol affects IL-6-induced STAT3 activation.
Main Methods:
- Primary adult rat hepatocytes were treated with varying ethanol concentrations (10-100 mM).
- Interleukin-6 (IL-6) stimulation was used to assess STAT3 activation and downstream gene expression.
- Western blot analysis, in vitro kinase assays, and cell labeling assays were performed.
- Involvement of tyrosine phosphatases and proteasome degradation pathways was examined using specific inhibitors.
Main Results:
- Ethanol rapidly (< 3 min) inhibited IL-6-induced STAT3 activation, phosphorylation, and CCAAT enhancer binding protein (C/EBP) alpha and beta mRNA expression.
- Ethanol did not inhibit upstream JAK1, JAK2, or Tyk2 activation but potentiated IL-6-induced JAK1 autophosphorylation.
- Inhibition of STAT3 activation by ethanol was not affected by tyrosine phosphatase or proteasome inhibitors.
Conclusions:
- Biologically relevant ethanol concentrations markedly inhibit IL-6-induced STAT3 phosphorylation in hepatocytes.
- This inhibition of IL-6/STAT3 signaling is a significant cellular mechanism in the pathogenesis and progression of alcoholic liver diseases.
- Ethanol's disruption of liver regenerative signaling contributes to ALD development.