ALDH2(E487K) mutation increases protein turnover and promotes murine hepatocarcinogenesis

Abstract

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) in the liver removes toxic aldehydes including acetaldehyde, an intermediate of ethanol metabolism. Nearly 40% of East Asians inherit an inactive ALDH2*2 variant, which has a lysine-for-glutamate substitution at position 487 (E487K), and show a characteristic alcohol flush reaction after drinking and a higher risk for gastrointestinal cancers. Here we report the characterization of knockin mice in which the ALDH2(E487K) mutation is inserted into the endogenous murine Aldh2 locus. These mutants recapitulate essentially all human phenotypes including impaired clearance of acetaldehyde, increased sensitivity to acute or chronic alcohol-induced toxicity, and reduced ALDH2 expression due to a dominant-negative effect of the mutation. When treated with a chemical carcinogen, these mutants exhibit increased DNA damage response in hepatocytes, pronounced liver injury, and accelerated development of hepatocellular carcinoma (HCC). Importantly, ALDH2 protein levels are also significantly lower in patient HCC than in peritumor or normal liver tissues. Our results reveal that ALDH2 functions as a tumor suppressor by maintaining genomic stability in the liver, and the common human ALDH2 variant would present a significant risk factor for hepatocarcinogenesis. Our study suggests that the ALDH2*2 allele-alcohol interaction may be an even greater human public health hazard than previously appreciated. ALDH2*2 polymorphism | Asian flush | alcohol metabolism | mouse model | liver cancer M itochondrial aldehyde dehydrogenase 2 (ALDH2) is essential for alcohol detoxification. It is the second enzyme in the major oxidative pathway of alcohol metabolism, removing acetaldehyde (ACE), a toxic intermediate product from ethanol metabolism (1). More than 500 million people worldwide, mostly in East Asia, have a G-to-A point mutation in their ALDH2 gene (2, 3). This mutation results in a glutamic acid-to-lysine substitution at residue 487 (E487K) of the human ALDH2 protein (designated ALDH2*2). ALDH2*2 has significantly reduced ability to metabolize ACE (4, 5). Importantly, its activity is partially dominant-negative over that of the wild-type ALDH2*1, due to the structural alterations introduced by the mutation to the ALDH2 homotetramer complex (6). As a result, individuals with a heterozygous ALDH2*2/2*1 genotype have less than half the wild-type activity, and ALDH2*2/2*2 homozygotes have very low residual activity (7). Accumulated ACE can cause an alcohol flush reaction, commonly found in Asians with this variant after alcohol consumption (also called "Asian glow").ACE binds to cellular proteins and DNA, leading to DNA damage and organ injury (8). Specifically, endogenous aldehydes are detrimental to hematopoietic stem cells that are defective in Fanconi anemia DNA repair (9, 10). As a result, Fanconi anemia patients with the ALDH2*2 allele exhibit accelerated disease progression (11). ALDH2*2 can also increase the risk for gastrointestinal cancers, such as gastric carcinoma (12), esophagea...

Emerging Associations of the ALDH2*2 Polymorphism with Disease Susceptibility

“…Others hypothesize that the ALDH2*2 subunits destabilize NAD + in the ALDH2*1 cofactor binding site [5]. Finally, additional data demonstrate a decrease in protein stability of the ALDH2*2 enzyme in comparison to ALDH2*1 [36].…”

“…The dominant negative low enzyme activity associated with expression of the ALDH2*2 allele leads to undesirable physiological reactions that challenge a healthy liver following the consumption of alcohol [36]. In an ALDH2*1 homozygous individual, consumption of 0.5 g/kg of ethanol (equivalent to 3-4 drinks in an average weight male) led to a mean blood acetaldehyde concentration of 1.8 μM.…”

Overexpression of the androgen receptor in human hepatoma cells and its effect on fatty acid metabolism

“…A previous study in phosphatase and tensin homolog null nonalcoholic steatohepatitis liver tissue isolated from mice revealed that ACSL1 expression is decreased, and is almost non-existent in tumors isolated from these livers (21). A recent study (22) demonstrated that the presence of a specific mutation in ALDH2 (E487 K) led to increased protein turnover and promoted murine hepatocarcinogenesis. The presence of the DnaJ heat shock protein family (Hsp40) member B1-PRKACA chimeric transcript in fibrolamellar HCC suggests that this genetic alteration contributes to tumor pathogenesis (23).…”

Sorafenib-Resistant Hepatocellular Carcinoma Stratified by Phosphorylated ERK Activates PD-1 Immune Checkpoint

“…First, two mouse hepatoma models were identified to represent homogeneous pERK + and pERK -tumors. DEN, a chemical carcinogen, can induce hepatoma in mice after injected to 14-day old pups [19], and the tumors found in mice aged over 8 months were all pERK , in which tumorigenesis is driven by continuous hepatocyte turnover and progenitor cell activation [20,21], express no pERK (Figure 2A and 2B). After tumors were visually confirmed and photographed after median laparotomy (Supplementary Figure 2A and 2B), both groups of mice were treated with sorafenib or PBS daily for three weeks after complete recovery from surgery.…”

“…F/F ; Alb-Cre +/− , for liver tumor in mice were generated as described previously [19,20]. Sorafenib (30 mpk) or PBS was administered by oral gavage daily for 21 consecutive days.…”