AKT ACTIVATION IN ALCOHOLIC PANCREATITIS

Abstract

Background and Aims: Although alcohol abuse is a major cause of pancreatitis, the mechanisms of ethanol toxicity to pancreas are poorly understood. We and others recently showed that PI3K pathway mediates key pathologic responses of cerulein (CR) pancreatitis. Most of PI3K effects are mediated through downstream Akt/PKB kinase, which is negatively regulated by the phosphatase PTEN. The effects of alcohol on this key signaling pathway in pancreas are not known. In this study, we determined the effects of ethanol feeding and CR pancreatitis on pancreatic PI3K/Akt/PTEN system. Methods: Rats were fed for 6 weeks control and ethanol-containing diet (either intragastrically or as liquid diet). Pancreatitis was induced by 4 hourly i.p. injections of 50 μg/kg CR. In pancreatic tissue, we measured PTEN and Akt phosphorylation by Western blot; PI3K activity with in vitro kinase assay; PTEN oxidation and activity, with electromobility shift and enzymatic assays. Results: We found that ethanol feeding stimulated Akt phosphorylation, the effect being more prominent with intragastric (~9 fold) than liquid diet (~2 fold). Furthermore, CR stimulated Akt phosphorylation in ethanol-fed rats to a greater extent (~16-fold) than in control-fed rats (~8-fold). The increase in Akt phosphorylation was not associated with an increase in PI3K activity. Therefore, we tested whether increased Akt phosphorylation is due to PTEN inhibition. We found that ethanol feeding (liquid diet) inhibited pancreatic PTEN activity by 60%. CR pancreatitis only decreased PTEN activity by ~30%. The treatment with both ethanol and CR inhibited PTEN activity much greater than CR only. Two mechanisms mediate PTEN inactivation, namely, its oxidation and phosphorylation. We found that ethanol feeding inactivated PTEN through its oxidation, whereas CR pancreatitis resulted in pronounced PTEN phosphorylation. Combination of ethanol and CR treatments caused maximal PTEN inhibition mediated by both PTEN oxidation and phosphorylation. Conclusions: The results indicate that ethanol feeding and CR pancreatitis both activate Akt. Ethanol feeding activates Akt through inhibiting PTEN. Persistent Akt activation could be a factor predisposing pancreas to alcoholic pancreatitis.