Constitutive activation of the Nrf2/Keap1 pathway in insecticide-resistant strains of Drosophila

Abstract

Pesticide resistance poses a major challenge for the control of vector-borne human diseases and agricultural crop protection. Although a number of studies have defined how mutations in specific target proteins can lead to insecticide resistance, much less is known about the mechanisms by which constitutive overexpression of detoxifying enzymes contribute to metabolic pesticide resistance. Here we show that the Nrf2/Keap1 pathway is constitutively active in two laboratory-selected DDT-resistant strains of Drosophila, 91R and RDDTR, leading to the overexpression of multiple detoxifying genes. Disruption of the Drosophila Nrf2 ortholog, CncC, or overexpression of Keap1, is sufficient to block this transcriptional response. In addition, a CncC-responsive reporter is highly active in both DDT-resistant strains and this response is dependent on the presence of an intact CncC binding site in the promoter. Microarray analysis revealed that ~20% of the genes differentially expressed in the 91R strain are known CncC target genes. Finally, we show that CncC is partially active in these strains, consistent with the fitness cost associated with constitutive activation of the pathway. This study demonstrates that the Nrf2/Keap1 pathway contributes to the widespread overexpression of detoxification genes in insecticide-resistant strains and raises the possibility that inhibitors of this pathway could provide effective synergists for insect population control.

Metabolomic profiling of permethrin-treated Drosophila melanogaster identifies a role for tryptophan catabolism in insecticide survival

“…1, glycine is likely being metabolised via threonine using sarcosine and allothreonine as sinks. The conversion of glycine to sarcosine occurs via the putative glycine methyltransferase, encoded by CG6188, a gene known to be upregulated in DDT resistant Drosophila strains (Misra et al, 2013). This would stimulate the consumption of methionine for cysteine synthesis though the production of Sadenosylhomocysteine.…”

p62/Sequestosome-1, Autophagy-related Gene 8, and Autophagy in Drosophila Are Regulated by Nuclear Factor Erythroid 2-related Factor 2 (NRF2), Independent of Transcription Factor TFEB

“…Loss of DmKeap1 resulted in high mRNA levels of gstD1, a CncC target gene, and this correlates with enhanced oxidative stress response and extended life span in Drosophila (17,19,20). Recently, overexpression of detoxifying enzymes has also been reported in two insecticide-resistant strains of Drosophila due to constitutive activation of CncC (21).…”

Understanding the Mechanisms Involved in the Regulation of Cytochrome P450 Gene Expression in Drosophila melanogaster (Diptera: Drosophilidae)

“…Drosophila melanogaster has been used broadly as a model system to understand the molecular mechanisms underlying insecticide resistance [25]. Further studies also addressed the mechanisms that underlie this regulation, mapping critical promoter elements that are required for P450 gene induction in response to pesticides or the wellstudied xenobiotic phenobarbital (PB) [39][40][41][42][43][44][45].…”

“…The Drosophila dKeap1 contains Kelch repeats homologous to those that mediate Keap1 interaction with Nrf2 as well as a sequence motif that is required for mammalian Keap1 export from the nucleus [18]. Overexpression of CncC and depletion of dKeap1 in Drosophila melanogaster activates the transcription of many genes including Cyp6g1 and Cyp6a2 that protect cells from xenobiotic compounds, whereas dKeap1 overexpression represses their transcription, indicating that the functions of these protein families in the xenobiotic response are conserved between mammals and Drosophila (Figure 2A-2C) [18,25].…”

“…Interestingly, AhR/ ARNT and Nrf2/Keap 1 display a multilevel crosstalk where the latter is also a target of the former [22][23][24]. Previous studies also revealed the orthologs to Aryl hydrocarbon receptor/(AhR) Aryl hydrocarbon nuclear receptor (ARNT) and Nuclear factor erythroid factor 2 (Nrf2)/ Kelch-like associated protein 1(Keap 1) in Drosophila melanogaster to be Spineless (Ss)/Tango (Tgo) and Cap 'n' collar isoform C (CnCC)/ Drosophila Kelch-like ECH-associated protein 1 (dKeap 1) respectively [25][26][27][28]. Therefore, to understand the mechanism by which these P450s are regulated in Drosophila melanogaster (an insect model) the basics underpinning this regulation are described below:…”