title: In vitro recapitulating of TP53 mutagenesis in hepatocellular carcinoma associated with dietary aflatoxin B1 exposure.
abstract: OBJECTIVE
  Dietary exposure to aflatoxin B(1) (AFB(1)), in addition to other known factors, increases risk for human hepatocellular carcinoma (HCC). HCCs from AFB(1)-exposed individuals frequently have distinct TP53 mutations, such as G to T transversions in the second guanine of codon 249 (AGG to AGT), and a characteristic mutational spectrum predominated by G:C to T:A mutations.
  
  
  METHODS
  To recapitulate the distinctive features of TP53 mutations in AFB(1)-associated HCC, we investigated AFB(1)-induced DNA adduction in relation to mutagenesis in transgenic mouse fibroblasts exposed to AFB(1) in vitro.
  
  
  RESULTS
  Immunodotblot determination of DNA adducts in the overall genome of AFB(1)-exposed cells revealed the dose-dependant formation of persistent imidazole ring-opened AFB(1)-DNA adducts. DNA footprinting analysis of the cII transgene in AFB(1)-exposed cells verified the dose-dependent and sequence-specific formation of DNA adducts. The preferential formation of AFB(1)-induced DNA adducts along the cII transgene was almost exclusively localized to guanine-containing sequences encompassing CpG dinucleotides. Mutation analysis of the cII transgene in AFB(1)-exposed cells revealed a dose-dependent induction of cII mutant frequency (P < .001) and a unique induced mutational spectrum characterized by predominant induction of G:C to T:A transversions that occurred within CpG sequence contexts. Notably, codons 42 and 45 of the cII transgene, which have identical sequence contexts to that of codon 249 of human TP53, constituted 2 frequently mutated sites in AFB(1)-exposed cells that contained the G to T transversion signature mutation at their third base positions.
  
  
  CONCLUSIONS
  In this model system, AFB(1)-induced DNA adduction and mutagenesis recapitulate the unique mutational features of TP53 in AFB(1)-associated human HCC.
authors.affiliation: Department of Cancer Biology, Beckman Research Institute of the City of Hope National Medical Center, Duarte, California 91010, USA. ania@coh.org
authors.forename: Ahmad
authors.initials: A
authors.lastname: Besaratinia
authors.forename: Sang-In
authors.initials: SI
authors.lastname: Kim
authors.forename: Pierre
authors.initials: P
authors.lastname: Hainaut
authors.forename: Gerd P
authors.initials: GP
authors.lastname: Pfeifer
mesh_terms: D016604:Aflatoxin B1 / Q000633:toxicity*; D000818:Animals; D002273:Carcinogens / Q000633:toxicity*; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000235:genetics*; D002478:Cells, Cultured; D018736:DNA Adducts / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000187:drug effects; D016158:Genes, p53 / Q000235:genetics*; D008113:Liver Neoplasms / Q000139:chemically induced / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D009152:Mutagenicity Tests; D009154:Mutation / Q000187:drug effects*
chemical_list: D002273:Carcinogens; D018736:DNA Adducts; D016604:Aflatoxin B1