Inhibitory effect of ethanol on AMPK phosphorylation is mediated in part through elevated ceramide levels

Suthat Liangpunsakul, Margaret S. Sozio, Eric Shin, Zhenwen Zhao, Yan Xu, Ruth A. Ross, Yan Zeng, David Crabb

Research output: Contribution to journalArticle

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Abstract

Ethanol treatment of cultured hepatoma cells and of mice inhibited the activity of AMP-activated protein kinase (AMPK). This study shows that the inhibitory effect of ethanol on AMPK phosphorylation is exerted through the inhibition of the phosphorylation of upstream kinases and the activation of protein phosphatase 2A (PP2A). Inhibition of AMPK phosphorylation by palmitate was attributed to ceramide-dependent PP2A activation. We hypothesized that the inhibitory effect of ethanol on AMPK phosphorylation was mediated partly through the generation of ceramide. The effect of ethanol and inhibitors of ceramide synthesis on AMPK phosphorylation, ceramide levels, and PP2A activity were assessed in rat hepatoma cells (H4IIEC3). The effect of ethanol on hepatic ceramide levels was also studied in C57BL/6J mice fed the Lieber-DeCarli diet. In H4IIEC3 cells, ceramide reduced AMPK phosphorylation when they were treated for between 4 and 12 h. The basal level of AMPK phosphorylation in hepatoma cells was increased with the treatment of ceramide synthase inhibitor, fumonisin B1. Ethanol treatment significantly increased cellular ceramide content and PP2A activity by ∼18-23%, when the cells were treated with ethanol for between 4 and 12 h. These changes in intracellular ceramide concentrations and PP2A activity correlated with the time course over which ethanol inhibited AMPK phosphorylation. The activation of PP2A and inhibition of AMPK phosphorylation caused by ethanol was attenuated by fumonisin B1 and imipramine, an acid sphingomyelinase (SMase) inhibitor. There was a significant increase in the levels of ceramide and acid SMase mRNA in the livers of ethanol-fed mice compared with controls. We concluded that the effect of ethanol on AMPK appears to be mediated in part through increased cellular levels of ceramide and activation of PP2A.

Original languageEnglish
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume298
Issue number6
DOIs
StatePublished - Jun 2010

Fingerprint

AMP-Activated Protein Kinases
Ceramides
Protein Phosphatase 2
Ethanol
Phosphorylation
Sphingomyelin Phosphodiesterase
Hepatocellular Carcinoma
Acids
Imipramine
Palmitates
Liver
Inbred C57BL Mouse
Cultured Cells
Phosphotransferases
Diet

Keywords

  • Protein phosphatase 2A

ASJC Scopus subject areas

  • Gastroenterology
  • Physiology (medical)
  • Physiology
  • Hepatology

Cite this

Inhibitory effect of ethanol on AMPK phosphorylation is mediated in part through elevated ceramide levels. / Liangpunsakul, Suthat; Sozio, Margaret S.; Shin, Eric; Zhao, Zhenwen; Xu, Yan; Ross, Ruth A.; Zeng, Yan; Crabb, David.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 298, No. 6, 06.2010.

Research output: Contribution to journalArticle

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abstract = "Ethanol treatment of cultured hepatoma cells and of mice inhibited the activity of AMP-activated protein kinase (AMPK). This study shows that the inhibitory effect of ethanol on AMPK phosphorylation is exerted through the inhibition of the phosphorylation of upstream kinases and the activation of protein phosphatase 2A (PP2A). Inhibition of AMPK phosphorylation by palmitate was attributed to ceramide-dependent PP2A activation. We hypothesized that the inhibitory effect of ethanol on AMPK phosphorylation was mediated partly through the generation of ceramide. The effect of ethanol and inhibitors of ceramide synthesis on AMPK phosphorylation, ceramide levels, and PP2A activity were assessed in rat hepatoma cells (H4IIEC3). The effect of ethanol on hepatic ceramide levels was also studied in C57BL/6J mice fed the Lieber-DeCarli diet. In H4IIEC3 cells, ceramide reduced AMPK phosphorylation when they were treated for between 4 and 12 h. The basal level of AMPK phosphorylation in hepatoma cells was increased with the treatment of ceramide synthase inhibitor, fumonisin B1. Ethanol treatment significantly increased cellular ceramide content and PP2A activity by ∼18-23{\%}, when the cells were treated with ethanol for between 4 and 12 h. These changes in intracellular ceramide concentrations and PP2A activity correlated with the time course over which ethanol inhibited AMPK phosphorylation. The activation of PP2A and inhibition of AMPK phosphorylation caused by ethanol was attenuated by fumonisin B1 and imipramine, an acid sphingomyelinase (SMase) inhibitor. There was a significant increase in the levels of ceramide and acid SMase mRNA in the livers of ethanol-fed mice compared with controls. We concluded that the effect of ethanol on AMPK appears to be mediated in part through increased cellular levels of ceramide and activation of PP2A.",
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