Role of Sumoylation in Alcohol Dehydrogenase 1 (ADH1) Stability and Activity in Alcoholic Liver Disease

Abstract

BackgroundAlcohol abuse is a leading factor in mortality from liver disease and increases the risk for a wide range of adverse health effects. The liver, as the primary site of alcohol metabolism, is a major target of injury. The spectrum of Alcoholic Liver Diseases (ALD) includes simple steatosis, alcoholic hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Alcohol dehydrogenase 1 (ADH1) is an enzyme, member of the oxidoreductase family and it is a dimeric protein in the cytosol of cells. ADH1 plays a pivotal role in contributing to the increase in rate of ethanol elimination from the blood. As the first enzyme of the major oxidative pathway of alcohol metabolism, it converts ethanol into acetaldehyde. 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. SUMOylation is a post‐translational modification that modulates multiple cellular processes such as signal transduction, stress responses, cellular trafficking, protein‐protein interactions, protein‐DNA interactions, and transcriptional activity. Sumoylation is oxidative stress inducible. There are four distinct types of SUMO, small ubiquitin‐like modifier, proteins in humans (SUMO‐1, −2, 3‐ and −4). SUMOylation is often increased under oxidative stress. We recently reported that ubiquitin conjugating enzyme 9 (Ubc9), the sole E2 enzyme of SUMOylation, is induced in intragastric ethanol‐infusion (EI) treated mice. Our aim was to examine whether the dysregulated sumoylation could influence the ethanol‐induced ADH1 function in both ALD and HCC elucidating the molecular mechanism(s).MethodsMass Spectrometry by SUMO binding columns was performed to purify sumoylated proteins form total livers of Binge ethanol fed mouse model. Primary mouse hepatocytes and HepG2 cells (HCC cell line) were used to perform in vitro experiments. Protein and mRNA levels were measured using Western Blotting and RT‐PCR, respectively. Tryglicerides production was examined by Nile red staining.ResultsWe found that ADH1 is sumoylated in binge mice livers analyzing the peptide‐sequencing data from sample purified by SUMO immunoaffinity columns. In vitro experiments showed ethanol treatment increased ADH1 protein and mRNA levels in primary mouse hepatocytes and HepG2 cells. Sumoylation controls ADH1 expression and protein stability in ethanol treatment cellular model providing a protein stability in co‐treatment with ethanol. In addition, we found Ubc9 is required for ethanol‐induced triglycerides accumulation.ConclusionsWe report for the first time that ethanol‐mediated sumoylation increased ADH1 protein level in livers of binge mice and that ethanol feeding modulates the sumoylation status of the key proteins in alcoholic liver disease.. Sumoylation could play an important role in modulating ADH1 enzymatic activity by its expression and protein stability control. This novel finding thereby opens a new area of investigation examining the importance of ADH1 sumoylation in alcoholic liver disease and in HCC maybe suggesting its potential role in the therapeutic approch.Support or Funding InformationSupported by NIH grant 5 K01 AA022372‐04(Maria Lauda Tomasi)