Ethanol rapidly inhibits IL-6-activated STAT3 and C/EBP mRNA expression in freshly isolated rat hepatocytes.
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.
Chen
J
J
Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
Kunos
G
G
Gao
B
B
D000818:Animals; D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000494:pharmacology*; D015850:Interleukin-6 / Q000378:metabolism*; D053613:Janus Kinase 1; D053614:Janus Kinase 2; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D053634:TYK2 Kinase; D013997:Time Factors; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D009687:Nuclear Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; C494088:Stat3 protein, rat; D015534:Trans-Activators; D000431:Ethanol; D014443:Tyrosine; D012694:Serine; D011505:Protein-Tyrosine Kinases; C507906:Jak1 protein, rat; C507927:Jak2 protein, rat; D053613:Janus Kinase 1; D053614:Janus Kinase 2; D053634:TYK2 Kinase; C499357:Tyk2 protein, rat