An A/G polymorphism in the promoter of mitochondrial aldehyde dehydrogenase (ALDH2): Effects of the sequence variant on transcription factor binding and promoter strength

Introduction: The strong protective effect of the ALDH2*2 mutation on risk of alcoholism suggests that other mutations that reduce mitochondrial aldeh yde dehydrogenase (ALDH) activity in the liver might also deter drinking. T his study describes a polymorphic locus found in the promoter of the ALDH2 gene that affects expression of reporter constructs. Methods: Polymerase chain reaction (PCR)-based sequencing was used to searc h for polymorphisms. The ability of the promoter Variants to bind transcrip tion factors apolipoprotein A regulatory protein 1 (ARP-1) and chicken oval bumin upstream promoter-transcription factor (COUP-TF) was tested in gel re tardation assays using in vitro synthesized transcription factors. The vari ant promoters were tested for transcriptional activity using a heterologous promoter system and transient transfection assays. Results: A common polymorphism (A or G) in the human ALDH2 promoter region was found at -361 base pair (bp) from the translation start site. This poly morphism was found at different frequencies in African Americans, Caucasian s, and Asians. The polymorphism occurs adjacent to the core binding motif f or the transcription factors COUP-TF and ARP-1. Competition and binding aff inity determinations did not show differences in the ability of these two s equences to bind the factors. Reporter genes containing these elements upst ream of a basal thymidine kinase promoter had similar activity when transfe cted into a fibroblast (CV-1) cell line. However, the reporter containing t he G allele was more active than that containing the A allele in hepatoma ( H4IIEC3) cells. Conclusions: The -361 bp A/G polymorphism is common in all racial groups te sted. The G allele was more active than the A allele in a transfection assa y. The basis for this difference is not known. If the differences in activi ty of the promoter constructs were paralleled by differences in ALDH2 enzym e activity in the liver, this polymorphism could affect risk of alcoholism.