Mutagenesis of codon 248 of the human p53 tumor suppressor gene by N-ethyl-N-nitrosourea.

Base pair mutations in the p53 tumor suppressor gene are among the most frequently observed genetic changes in human malignancies. Several mutational hotspots have been identified and tumor- and tissue-specific differences have been observed. We studied the mutability of hotspot codon 248, CGG, in human fibroblasts in response to the alkylating agent N-ethyl-N-nitrosourea (ENU) by MspI RFLP/PCR analysis. Alkylating agents are implicated as etiological agents in carcinogenesis in the gut and other tissues in the human. ENU induced preferentially G to A transitions in the non-transcribed strand. The predominant mutation involving the G-residue of the CpG dinucleotide was observed with an absolute frequency of 4 x 10(-7). The corresponding C to T transition in the first position of codon 248 was observed at several fold lower frequency suggesting more efficient excision repair of the transcribed strand. The G to A transition in the third position of codon 248 occurred at low frequency. Our results are compatible with a role for aliphatic alkylating agents in human tumors with codon 248 mutations since almost all mutations reported in this codon are transitions in the CpG-dinucleotide.