title: Mutagenesis by O(6)-[4-oxo-4-(3-pyridyl)butyl]guanine in Escherichia coli and human cells.
abstract: Site-specific mutagenesis by O(6)-[4-oxo-4-(3-pyridyl)butyl]guanine (O(6)-pobGua), a product of DNA pyridyloxobutylation by metabolites of the tobacco-specific nitrosamines N-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), was studied in Escherichia coli strain DH10B and human kidney cells (293) when the modified base was incorporated in either a double-stranded or a gapped shuttle vector. In the repair-competent E. coli strain, less than 3% of the colonies produced by double-stranded vectors harboring the modified base were mutant whereas 96% were mutant when DH10B cells were transformed with modified gapped vectors. By contrast, transformation of DH10B cells with plasmids derived from O(6)-pobGua-containing double-stranded and gapped vectors previously replicated in 293 cells produced 7 and 16% mutant colonies, respectively. These percentages increased to 42 and 82%, respectively, when the 293 cells were pretreated with O(6)-benzylguanine to inactivate the O(6)-alkylguanine-DNA alkyltransferase protein. These findings confirm that the adduct is readily repaired by the human O(6)-alkylguanine-DNA alkyltransferase in both double-stranded and gapped vectors and suggest that it is also highly mutagenic in both human cells and E. coli. In the E. coli strain, the adduct produced exclusively G --> A transition mutations although in human 293 cells it also produced G --> T transversions and more complex mutations in addition to G --> A transitions. These data suggest that O(6)-[4-oxo-4-(3-pyridyl)butyl]guanine can contribute significantly to the mutagenic risk posed by exposure to both NNN and NNK in tobacco smoke.
authors.affiliation: Chemistry of Carcinogenesis Laboratory, National Cancer Institute at Frederick, Frederick, Maryland 21702, USA.
authors.forename: Gary T
authors.initials: GT
authors.lastname: Pauly
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Peterson
authors.forename: Robert C
authors.initials: RC
authors.lastname: Moschel
mesh_terms: D002460:Cell Line; D018736:DNA Adducts / Q000378:metabolism / Q000633:toxicity*; D004260:DNA Repair / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity*; D007668:Kidney / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D016297:Mutagenesis, Site-Directed / Q000187:drug effects; D009153:Mutagens / Q000378:metabolism / Q000633:toxicity*
chemical_list: D018736:DNA Adducts; D009153:Mutagens; C097065:O(6)-benzyl-8-oxoguanine; D006147:Guanine