Role of Sumoylation in Aldehyde Dehydrogenase 2 (ALDH) function during Alcoholic Liver Disease

Background Chronic alcohol abuse causes liver disease that progress from steatosis through stages of steatohepatitis, fibrosis, cirrhosis and eventually hepatic failure. Acetaldehyde, a major toxic ethanol metabolite, is mutagenic and carcinogenic, playing an important role in the pathogenesis of alcoholic liver disease (ALD) inducing production of reactive oxygen species (ROS) and apoptosis. ALDH2 is the major enzyme that metabolizes acetaldehyde produced from alcohol metabolism. Sumoylation is a posttranslational modification able to modify the activity, localization, and expression of the target protein by a covalent bind where small ubiquitin modifier (SUMO) is a tag. Increased ROS production enhances the global protein SUMO conjugation profile. We previously demonstrated that the level of Ubiquitin‐conjugation enzyme 9 (Ubc9), a sole E2‐conjugating enzyme essential for sumoylation, is induced in the livers of intragastric ethanol‐infusion (EI) treated mice. Our aim was to examine whether the dysregulated sumoylation could regulate the ethanol‐induced ALDH2 function in ALD and elucidate the molecular mechanism(s). Methods Studies were done using in vivo binge ethanol‐fed mice and primary mouse hepatocytes. Sumoylation protein profiling and expression were measured by Mass Spectrometry and Western blot analyses, respectively. ALDH2 activity was analyzed using commercial kit. Results We found that ALDH2 is sumoylated in binge mice livers analyzing the peptide‐sequencing data from sample purified by SUMO immunoaffinity columns. In addition, we found that both Ubc9 and ALDH2 mRNA and protein levels are increased in the livers of binge mice and ethanol‐treated hepatocytes. Interestingly, Ubc9 silencing prevented ethanol‐mediated induction in ALDH2 protein level. ALDH2 activity assay showed that Ubc9 is required for ALDH2 to be enzymatically active in primary mouse hepatocytes. Finally, we confirmed the peptide‐sequencing data of sumoylated ALDH2 using in vivo binge mice livers finding increased level of SUMO1/2/3‐ALDH2 complex formation following ethanol treatment. Conclusions We report for the first time that ethanol‐mediated sumoylation increased ALDH2 protein level and enzymatic activity in livers of binge mice and primary hepatocytes. This novel finding thereby opens a new area of investigation examining the importance of ALDH2 sumoylation in alcoholic liver disease. Support or Funding Information NIAAA Grant: 5 K01 AA022372‐04