Differential transcription of cytochrome P450s and glutathione S transferases in DDT-susceptible and -resistant Drosophila melanogaster strains in response to DDT and oxidative stress

Metabolic DDT resistance in Drosophila melanogaster has previously been associated with constitutive over-transcription of cytochrome P450s. Increased P450 activity has also been associated with increased oxidative stress. In contrast, over-transcription of glutathione S transferases (GSTs) has been associated with resistance to oxidative stress. However, little is known in regards to the impact of xenobiotics on induction of P450s and GSTs and if there exist differences in inducibility between the pesticide susceptible and resistant strains. Thus, we investigated the transcriptional expression of GSTs and P450s in DDT resistant (Wisconsin) and susceptible (Canton-S) Drosophila strains in response to exposure to DDT and the oxidative stressor H₂O₂. Wisconsin constitutively over-transcribed P450s, constitutively under-transcribed 27% of its total GSTs, and was more susceptible to H₂O₂ than Canton-S. DDT exposure induced GST expression only in the Wisconsin strain and not in the Canton-S strain. These results suggest that there are potentially more differences between pesticide susceptible and resistant strains than just constitutive expression of P450s; there may also exist, at least in some strains, differences in their patterns of inducibility of P450s and GSTs. Within the context of the Wisconsin strain, these differences may be contributing to the fly lines increased susceptibility to oxidative stress.