Genetic Variation of Aflatoxin B1 Aldehyde Reductase Genes (AFAR) in Human Tumour Cells

AFAR genes play a key role in the detoxification of the carcinogen Aflatoxin B(1) (AFB(1)). In the rat, Afar1 induction can prevent AFB(1)-induced liver cancer. It has been proposed that AFAR enzymes can metabolise endogenous diketones and dialdehydes that may be cytotoxic and/or genotoxic. Furthermore, human AFAR1 catalyses the rate limiting step in the synthesis of the neuromodulator gamma-hydroxybutyrate (GHB) and was found elevated in neurodegenerative diseases such as Alzheimer's and dementia with Lewy bodies (DLB). The human AFAR gene family maps to a genomic region in 1p36 of frequent hemizygous deletions in various human cancers. To investigate, if genetic variation of AFAR1 and AFAR2 exists that may alter protein detoxification capabilities and confer susceptibility to cancer, we have analysed a spectrum of human tumours and tumour cell lines for genetic heterogeneity. From 110 DNA samples, we identified nine different amino acid changes; two were in AFAR1 and seven in AFAR2. In AFAR1, we found genetic variation in the proposed substrate-binding amino acid 113, encoding Ala(113) or Thr(113). An AFAR2 variant had a Glu(55) substituted by Lys(55) at a position that is conserved among many aldo-keto reductases. This polarity change may have an effect on the proposed substrate binding amino acids nearby (Met(47), Tyr(48), Asp(50)). Further population analyses and functional studies of the nine variants detected may show if these variants are disease-related.