BACTERIAL AND MAMMALIAN DNA ALKYLTRANSFERASES SENSITIZE ESCHERICHIA-COLI TO THE LETHAL AND MUTAGENIC EFFECTS OF DIBROMOALKANES

Here we confirm and extend our previous studies demonstrating that the mutagenic potency of 1,2-dibromoethane (DBE) and dibromomethane (DBM) is markedly enhanced (not prevented) in bacteria expressing the O-6-a lkylguanine-DNA alkyltransferase (ATase) encoded by the Escherichia co li ogt gene, We demonstrate that, in close parallel with mutagenesis, the Ogt ATase sensitizes the bacteria to the lethal effects of these c arcinogens, suggesting that one or more of the potentially mutagenic l esions induced by DBE and DBM in the presence of Ogt has additional le thal capacity, We further demonstrate that the sensitization to both l ethality and mutagenesis by DBE and DBM is a property shared by other DNA alkyltransferases. This objective was accomplished by quantifying the induction of mutations and lethal events in ogt(-) ada(-) E. coli expressing an exogenous bacterial or mammalian ATase from a multicopy plasmid, Mammalian recombinant ATases enhanced the lethal and mutageni c actions of DBE and suppressed the lack of sensitivity of the vector- transformed bacteria to DBM. In most cases the order of effectiveness of the ATases ranked: murine > human > Ogt > rat, Further comparisons included the full-length Ada ATase from E. coli and a truncated Ada ve rsion (T-ada) that retains the O-6-methylguanine binding domain of the protein, The full-length Ada ATase was effective in enhancing the let hality but not the mutagenicity induced by DBE and DBM, The T-ada ATas e provided less sensitization than Ada to lethality by DBE, but of the three bacterial ATases T-ada yielded the highest sensitization to mut agenesis by this compound, T-ada and Ada ATases were in general less e ffective than the mammalian versions, with the exception of the rat re combinant ATase, The effectiveness of the different mammalian and bact erial ATases in promoting the deleterious actions of dibromoalkanes wa s compared with the effectiveness of these proteins in suppressing the lethal and mutagenic effects induced by N-nitroso-N-methylurea. The a bility to sensitize E. coli to the lethal and mutagenic effects of DBE and DBM seems restricted to DNA alkyltransferase, since overexpressio n of thioredoxin (Trx) or glutaredoxin (Grx1) in ogt(-) ada(-) cells s howed no effect, in spite of the reported potential of bioactive dihal oethane-derived species to alkylate Trx.