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.