Interferons activate the p42/44 mitogen-activated protein kinase and JAK-STAT (Janus kinase-signal transducer and activator transcription factor) signalling pathways in hepatocytes: differential regulation by acute ethanol via a protein kinase C-dependent mechanism.
Interferons (IFNs) have been used in the treatment of viral hepatitis. However, their effectiveness is much reduced (<10%) in alcoholics. The mechanism underlying this resistance remains unknown. Here, we report that IFN-alpha/beta and IFN-gamma rapidly activate the JAK-STAT1 (Janus kinase-signal transducer and activator transcription factor 1) and p42/44 mitogen-activated protein kinase (p42/44 MAPK) in freshly isolated rat hepatocytes. Treatment of hepatocytes with 25-100 mM ethanol for 30 min inhibited IFN-beta- or IFN-gamma-induced STAT1 activation and tyrosine phosphorylation. The inhibitory effect of ethanol was not reversed by pretreatment with either sodium vanadate, a non-selective tyrosine phosphatase inhibitor, or with MG132, a specific proteasome inhibitor. This suggests that protein tyrosine phosphatases or the ubiquitin-proteasome pathway are not involved in the inhibitory action of ethanol. In contrast with the JAK-STAT signalling pathway, acute ethanol exposure significantly potentiated IFN-beta or IFN-gamma-induced activation of p42/44 MAPK, and caused marked activation of protein kinase C (PKC). Inhibition of PKC partially antagonized ethanol attenuation of IFN-induced STAT1 activation, suggesting that PKC may be involved. Taken together, these findings suggest that the ability of biologically relevant concentrations of ethanol (less than 100 mM) to markedly inhibit IFN-activated STAT1 is one of the cellular mechanisms responsible for the observed resistance of IFN therapy in alcoholics.
Nguyen
V A
VA
Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA.
Chen
J
J
Hong
F
F
Ishac
E J
EJ
Gao
B
B
D000818:Animals; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004347:Drug Interactions; D004357:Drug Synergism; D004789:Enzyme Activation; D000431:Ethanol / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D016898:Interferon-alpha / Q000494:pharmacology; D016899:Interferon-beta / Q000494:pharmacology; D007371:Interferon-gamma / Q000494:pharmacology; D007372:Interferons / Q000494:pharmacology*; D048031:JNK Mitogen-Activated Protein Kinases; D053613:Janus Kinase 1; D048670:MAP Kinase Kinase 4; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D050794:STAT1 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D014452:Ubiquitins / Q000378:metabolism
D004268:DNA-Binding Proteins; D016898:Interferon-alpha; D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; C494081:Stat1 protein, rat; D015534:Trans-Activators; D014452:Ubiquitins; D000431:Ethanol; D014443:Tyrosine; D016899:Interferon-beta; D007371:Interferon-gamma; D007372:Interferons; D011505:Protein-Tyrosine Kinases; C507906:Jak1 protein, rat; D053613:Janus Kinase 1; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D017027:Protein Tyrosine Phosphatases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex