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Impaired methylation as a novel mechanism for proteasome suppression in liver cells

Natalia A Osna1, Ronda L White, Terrence M Donohue

  • 1Liver Study Unit, The Omaha Veterans Affairs (VA) Medical Center, Omaha, NE 68105, USA. nosna@UNMC.edu

Biochemical and Biophysical Research Communications
|December 23, 2009
PubMed

Insights

Ethanol exposure impairs liver cell proteasome activity through reduced protein methylation, not just oxidative stress. This novel mechanism highlights methylation

Area of Science:

  • Biochemistry
  • Cell Biology
  • Molecular Biology

Background:

  • The proteasome, a protein degradation enzyme, is regulated by ethanol-induced oxidative stress via CYP2E1 metabolites.
  • Emerging evidence suggests additional mechanisms beyond oxidative stress influence proteasome regulation.

Purpose of the Study:

  • To investigate if impaired protein methylation during ethanol exposure contributes to proteasome activity suppression in liver cells.
  • To elucidate the role of protein methylation in ethanol-induced proteasome dysfunction.

Main Methods:

  • Measured chymotrypsin-like proteasome activity in liver cells, cytosols, nuclear extracts, and purified 20S proteasome.
  • Assessed the impact of ethanol, tubercidin, and S-adenosylmethionine (SAM) on proteasome activity.
  • Utilized methyl lysine-specific antibodies to detect methylation on proteasome subunits.

Main Results:

  • Ethanol and tubercidin reduced proteasome activity, an effect reversed by S-adenosylmethionine (SAM).
  • Proteasome activity decline occurred in both nuclear and cytosolic fractions.
  • Low SAM:S-adenosylhomocysteine (SAH) ratios suppressed proteasome function in vitro, and a 25kDa subunit showed methyl lysine reactivity.

Conclusions:

  • Impaired methylation of proteasome subunits suppresses proteasome activity in liver cells.
  • This represents a novel mechanism of proteasome regulation by ethanol, independent of oxidative stress.

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