Ethanol induces apoptosis in hepatocytes by a pathway involving novel protein kinase C isoforms.
Ethanol abuse is one of the major etiologies of cirrhosis. Ethanol has been shown to induce apoptosis via activation of oxidative stress, mitogen-activated protein kinases (MAPK), and tyrosine kinases. However, there is a paucity of data that examine the interplay among these molecules. In the present study we have systematically elucidated the role of novel protein kinase C isoforms (nPKC; PKCdelta and PKCepsilon) in ethanol-induced apoptosis in hepatocytes. Ethanol enhanced membrane translocation of PKCdelta and PKCepsilon, which was associated with the phosphorylation of p38MAPK, p42/44MAPK and JNK1/2, and the nuclear translocation of NF-kappaB and AP-1. This resulted in increased apoptosis in primary rat hepatocytes. Inhibition of both PKCdelta and PKCepsilon resulted in a decreased MAPK activation, decreased nuclear translocation of NF-kappaB and AP-1, and inhibition of apoptosis. In addition, ethanol activated the tyrosine phosphorylation of PKCdelta via tyrosine kinase in hepatocytes. The tyrosine phosphorylated PKCdelta was cleaved by caspase-3 and these fragments were translocated to the nucleus. Inhibition of ethanol-induced oxidative stress blocked the membrane translocation of PKCdelta and PKCepsilon, and the tyrosine phosphorylation of PKCdelta in hepatocytes. Inhibition of oxidative stress, tyrosine kinase or caspase-3 activity caused a decreased nuclear translocation of PKCdelta in response to ethanol, and was associated with less apoptosis.


CONCLUSIONS
These results provide a newly-described mechanism by which ethanol induces apoptosis via activation of nPKC isoforms in hepatocytes.
Zhang
Yanhong
Y
Department of Internal Medicine, Transplant Research Program, University of California, Davis Medical Center, Sacramento, CA 95817, USA.
Venugopal
Senthil K
SK
He
Songqing
S
Liu
Pingguo
P
Wu
Jian
J
Zern
Mark A
MA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D000431:Ethanol / Q000494:pharmacology*; D005452:Fluoresceins / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D008665:Metalloporphyrins / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011092:Polyethylene Glycols / Q000494:pharmacology; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051744:Protein Kinase C-epsilon / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000494:pharmacology
D005452:Fluoresceins; D007527:Isoenzymes; D008665:Metalloporphyrins; D047428:Protein Kinase Inhibitors; D017382:Reactive Oxygen Species; C097284:manganese(III)-tetrakis(4-benzoic acid)porphyrin; C029569:diacetyldichlorofluorescein; D000431:Ethanol; D011092:Polyethylene Glycols; D013482:Superoxide Dismutase; C063471:polyethylene glycol-superoxide dismutase; D051745:Protein Kinase C-delta; D051744:Protein Kinase C-epsilon; D020928:Mitogen-Activated Protein Kinases; D053148:Caspase 3