Ethanol induces apoptosis in hepatocytes by a pathway involving novel protein kinase C isoforms

Area of Science:

• Hepatology
• Molecular Biology
• Cellular Biology

Background:

• Ethanol abuse is a primary cause of cirrhosis.
• Ethanol induces hepatocyte apoptosis through oxidative stress, MAPKs, and tyrosine kinases.
• The interplay between these pathways, particularly novel protein kinase C (nPKC) isoforms, in ethanol-induced apoptosis is not well understood.

Purpose of the Study:

• To elucidate the role of nPKC isoforms (PKCdelta and PKCepsilon) in ethanol-induced apoptosis in hepatocytes.
• To investigate the interplay between nPKC, MAPK signaling, oxidative stress, and caspase-3 in this process.

Main Methods:

• Primary rat hepatocytes were treated with ethanol.
• Western blotting and nuclear translocation assays were used to assess protein activation and localization.
• Inhibitors of nPKC, oxidative stress, tyrosine kinase, and caspase-3 were employed.

Main Results:

• Ethanol induced membrane translocation of PKCdelta and PKCepsilon, leading to MAPK activation and nuclear translocation of NF-kappaB and AP-1, ultimately increasing hepatocyte apoptosis.
• Inhibition of PKCdelta and PKCepsilon reduced MAPK activation, NF-kappaB/AP-1 translocation, and apoptosis.
• Ethanol-induced tyrosine phosphorylation of PKCdelta, its cleavage by caspase-3, and nuclear translocation were observed.
• Inhibition of oxidative stress, tyrosine kinase, or caspase-3 attenuated these effects and reduced apoptosis.

Conclusions:

• Ethanol induces hepatocyte apoptosis through a novel mechanism involving the activation of nPKC isoforms (PKCdelta and PKCepsilon).
• This pathway involves oxidative stress, tyrosine kinase activation, caspase-3 cleavage, and subsequent nuclear translocation of PKCdelta fragments.
• Targeting these nPKC isoforms and associated signaling molecules may offer therapeutic strategies for alcoholic liver disease.