Abstract
Carboxylesterase-mediated metabolism is one of major mechanisms involved in insecticide resistance. Our previous study has identified multiple carboxylesterase genes with their expression levels were significantly upregulated in pyrethroid resistant house flies. To further explore their metabolic functions, we used insect Spodoptera frugiperda (Sf9) cells to express these carboxylesterases in vitro and measure their hydrolytic activities toward esterase substrates. Our results indicated that these carboxylesterases can efficiently hydrolyze α-naphthyl acetate rather than β- naphthyl acetate. A cell based MTT cytotoxicity assay indicated that carboxylesterase-expressing cells show enhanced tolerance to permethrin, suggesting important roles of these carboxylesterases in metabolizing permethrin and thereby protecting cells from permethrin treatments. The metabolic functions of carboxylesterases were further verified by conducting in vitro metabolism studies toward permethrin and its potential metabolites 3-phenoxybenzyl alcohol and 3-phenoxybenzaldehyde, which not only suggested the potential metabolic pathway of permethrin in insects, but also important roles of these candidate carboxylesterases in metabolizing permethrin and conferring resistance in house flies. Homology modeling and docking were finally conducted to reflect interactions between permethrin ligand and carboxylesterase proteins, visually confirming the metabolic functions of carboxylesterases to insecticides in house flies.
Highlights
House flies, Musca domestica, are ubiquitous agricultural and sanitary pests that can mechanically transmit more than 100 human and animal disease pathogens, including bacterial, protozoan, helminthic, and viral pathogens (Sasaki et al, 2000; Barin et al, 2010; Gordon Hewitt, 2011; Abbas et al, 2014; Scott et al, 2014)
Our results indicated that carboxylesterase proteins obtained from insect Sf 9 cells were capable of hydrolyzing α-naphthyl acetate (α-NA) to produce α-naphthol at different efficiencies, with a hydrolytic activity ranging from 6083.5 to 13810.1 pmol · min−1 · mg−1, which were 1.8–4.0 fold higher than that measured in either the parental Sf 9 cells or the pENTRTM CAT (plasmid producing baculovirus expressing chloramphenicol acetyltransferase (CAT) protein [Invitrogen]) infected cells served as controls (Table 1), indicating the strong hydrolytic capabilities of carboxylesterases in metabolizing esterase substrate α-NA
Overexpressed carboxylesterases lead to increased activities, which further results in the enhanced metabolism of xenobiotics or endogenous compounds (Bass and Field, 2011; Zhang et al, 2013; Grigoraki et al, 2015)
Summary
Musca domestica, are ubiquitous agricultural and sanitary pests that can mechanically transmit more than 100 human and animal disease pathogens, including bacterial, protozoan, helminthic, and viral pathogens (Sasaki et al, 2000; Barin et al, 2010; Gordon Hewitt, 2011; Abbas et al, 2014; Scott et al, 2014). Multiple carboxylesterase genes have shown to be transcriptionally up-regulated in various resistant insects, including house flies (Cao et al, 2008; Bao et al, 2010; Zhang et al, 2010; Adelman et al, 2011; Bass and Field, 2011; Fuentes-Contreras et al, 2013; Demkovich et al, 2015) These overexpressed carboxylesterases are thought to sequester the insecticides and hydrolyze them into less harmful substances, facilitating excretion outside the insect bodies (Field and Blackman, 2003; Wheelock et al, 2005). In both Aedes aegypti and Anopheles gambiae mosquitoes, pyrethroids can be metabolized by carboxylesterases to form PBOH (phenoxybenzoic alcohol) and PBCHO (phenoxybenzaldehyde), which can be further metabolized by cytochrome P450 monooxygenases to PBCOOH (phenoxybenzoic acid) (Somwang et al, 2011; Chandor-Proust et al, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
