MOLECULAR CHARACTERIZATION OF HPRT MUTATIONS FROM CHINESE-HAMSTER OVARY CELLS TREATED WITH 1-NITROSOBENZO[A]PYRENE, 3-NITROSOBENZO[A]PYRENE, AND 6-NITROSOBENZO[A]PYRENE

1-, 3-, and 6-Nitrobenzo[a] pyrene (nitro-BaP) are environmental conta minants that can be metabolized to genotoxic derivatives by either nit roreduction or ring-oxidation. In this study, we examined the types of mutations produced by the primary nitroreduced metabolites, 1-, 3-, a nd 6-nitroso-BaP (NO-BaP) in the hprt gene of Chinese hamster ovary ce lls. RNA from 6-thioguanine-resistant mutants was reverse-transcribed to cDNA and the hprt coding sequence was amplified and sequenced. The mutational patterns produced by the three compounds exhibited extensiv e similarities: 1) bose pair substitutions accounted for 67% (28/42) o f 1-NO-BaP, 51% (26/51) of 3-NO-BaP, and 50% (11/22) of 6-NO-BaP mutat ions; 19-36% of the mutations were exon deletions and 14-18% were fram eshifts; 2) most (64-84%) of the simple base pair substitutions occurr ed at G:C, mainly G:C --> T:A and G:C --> C:G transversions; 3) 98% (4 6/47) of the simple base pair substitutions at G:C had the mutated dG on the non-transcribed strand and 81% (38/47) were located with the mu tated dG flanked 3' by at least one purine; and 4) most simple base pa ir substitutions (48/62, 77%) occurred in exons 2, 3, and 8 of the hpr t gene. Although there were no significant differences among the mutat ion profiles of the NO-BaPs, a significant difference did exist betwee n the mutation pattern produced by 3-NO-BaP and the mutation pattern p reviously determined for the ring-oxidized product of 3-nitro-BaP meta bolism, nti-9,10-epoxy-7,8,9,10-tetrahydro-3-nitrobenzo[a] pyrene. Thi s observation indicates that differences in the structures of closely related adducts con be important enough to have an effect on mutation profiles. (C) 1998 Wiley-Liss, Inc.