Analysis of point mutations in murine c-Ha-ras of skin tumors initiated with dibenz[a,j]anthracene and derivatives.

This study was designed to evaluate the point mutations in the murine c-Ha-ras gene of skin papillomas induced by initiation with dibenz[a,j]anthracene (DB[a,j]A), its bay-region anti-diol epoxide ((+/-)anti-DB[a,j]A-DE), and a 7,14-dimethyl analogue (7,14-diMeDB[a,j]A). Recent studies (Nair RV, et al., Chem Res Toxicol 4:115-122, 1991) in our laboratory have revealed both deoxyguanosine (dGuo) and deoxyadenosine (dAdo) adducts formed from the anti- and syn-diol epoxides of DB[a,j]A in cultured mouse epidermal cells after exposure to this hydrocarbon. Using PCR amplification and direct sequencing, we found specific A182----T transversion mutations (eight of 10 tumors) in codon 61 of c-Ha-ras in papillomas induced by initiation with DB[a,j]A. Analysis of papillomas generated by initiation with the more biologically potent analogue 7,14-diMeDB[a,j]A revealed that five of five tumors exhibited A182----T transversions in codon 61. The nature of the changes in the two DB[a,j]A tumors not showing codon 61 mutations in Ha-ras is currently not known since these tumor DNAs also did not possess c-Ha-ras mutations at codons 12, 13, or 59. Interestingly, papillomas produced by initiation with (+/-)anti-DB[a,j]A-DE also possessed A182----T transversion mutations in codon 61 of c-Ha-ras (five of five tumors). These data suggest that dAdo adducts derived from both parent hydrocarbons may play an important role in their tumor-initiating activity and possibly implicate a specific diol epoxide-dAdo adduct in this process.