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 mos t frequently observed genetic changes in human malignancies. Several m utational 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 age nt N-ethyl-N-nitrosourea (ENU) by MspI RFLP/PCR analysis. Alkylating a gents are implicated as etiological agents in carcinogenesis in the gu t and other tissues in the human. ENU induced preferentially G to A tr ansitions in the non-transcribed strand. The predominant mutation invo lving the G-residue of the CpG dinudeotide was observed with an absolu te 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 freque ncy suggesting more efficient excision repair of the transcribed stran d. The G to A transition in the third position of codon 248 occurred a t low frequency. Our results are compatible with a role for aliphatic alkylating agents in human tumors with codon 248 mutations since almos t all mutations reported in this codon are transitions in the CpG-dinu cleotide.