Aflatoxin B 1-induced TP53 mutational pattern in normal human cells using the FASAY ( Functional Analysis of Separated Alleles in Yeast)

Abstract

Mutations in the TP53 gene are the most common alterations in human tumours. In hepatocellular carcinoma (HCC) related to exposure to aflatoxin B 1, a specific G > T transversion in codon 249 is classically described as a hot spot. However, AFB 1 is suspected to be a potent carcinogen in tissues other than the liver. By using the FASAY functional assay in yeast, the present study aimed at depicting the mutational pattern of TP53 in normal human fibroblasts after in vitro exposure to AFB 1. Molecular analysis of mutants revealed that codon 245 was the main hot spot, whereas no mutations were found in codon 249. The locations of mutations within GG and GC/CG sequences are well in accordance with AFB 1-adduct location data. In our assay with normal human fibroblasts, AFB 1 mainly induced G > A transitions, followed by G > T and A > G mutations. This suggests that G > T transversions at codon 249 were likely the result of a selection bias in human HCC rather than a true fingerprint of AFB 1 adducts. Indeed, a comparison of the mutation pattern with that found in human HCC excluding codon 249 reveals that the two spectra are quite similar. Furthermore, the similarity between our in vitro spectrum with that identified in AFB 1-induced lung tumours in mice suggests that AFB 1 may be a potent lung carcinogen in humans.