OXY-RADICAL INDUCED MUTAGENESIS OF HOTSPOT CODON-248 AND CODON-249 OFTHE HUMAN P53 GENE

Oxidants are suspected to represent important human carcinogens. They are mutagenic and may participate in the activation of proto-oncogenes and the inactivation of tumor suppressor genes. We have studied the c apacity of hydrogen peroxide plus ferric chloride (FeCl3) to induce ba se pair changes in the hotspot codons 248 and 249 of the p53 tumor sup pressor gene in human fibroblasts. In codon 248 (CGG) H2O2/FeCl3 only induced the transversion of G to C in the second position and the tran sition of G to A in the third position. No evidence was obtained for s pontaneous or oxidant-induced deamination of 5-methylcytosine in the C pG dinucleotide of codon 248 since neither C to T transitions in the f irst position nor G to A transitions in the middle position were obser ved. H2O2/FeCl3, efficiently induced G to T transversions at both G-re sidues of codon 249 (AGG) and C to A transversions at the first positi on of codon 250 (CCC). It is evident that H2O2/FeCI3 possesses essenti ally the same mutagenic specificity for codons 249 and 250 of p53 as b ulky carcinogens such as aflatoxin B1, benzo(a)pyrene or heterocyclic amines. In particular, it is not possible to eliminate oxidants from t he list of candidate carcinogens which may be responsible for the high incidence of p53 codon 249 AGT mutations in hepatocellular carcinoma from certain areas of the world.