Ecdysone signaling and transcript signature in Drosophila cells resistant against methoxyfenozide

. [Display omitted] ▶ Here we report on the selection of Drosophila melanogaster Schneider S2 cells for a ∼1000-fold resistance over 4 months against methoxyfenozide, a non-steroidal ecdysteroid agonist with a dibenzoylhydrazine structure, representing a group of novel biorational insecticides. ▶ When resistant cells were relaxed from pressure in methoxyfenozide-free medium, induction of the reporter construct was observed. In parallel, EcR/USP functionality was also restored when resistant cells were rescued by a Drosophila EcR plasmid. ▶ With use of Drosophila oligo 14kv1 microarrays, a selection of 324 differentially expressed genes in resistant versus susceptible cells was assigned covering diverse functions as transport, enzyme activity, cytoskeleton organization, cell cycle machinery, transcription/translation and ecdysteroid signaling. ▶ Besides the identification of (primary and secondary) target genes of the EcR/USP signaling pathway, the microarray analysis also allows to gain insights into the mechanism of methoxyfenozide resistance and on the crosstalk between ecdysteroid signaling and cell proliferation-linked processes. Methoxyfenozide (RH-2485) is a non-steroidal ecdysteroid agonist with a dibenzoylhydrazine structure, representing a group used as novel biorational insecticides in the control of insect pests. Here we report on the selection of Drosophila melanogaster S2 cells for resistance to inhibition of cell proliferation by methoxyfenozide by ∼1000-fold over 4 months. Cells were exposed to gradually increasing concentrations of methoxyfenozide and selected out based on the ecdysteroid-sensitive response for cell proliferation. In the resistant cells, the ecdysteroid receptor (EcR/USP) complex was no longer active in the presence of methoxyfenozide. But when resistant cells were relaxed from pressure in methoxyfenozide-free medium, induction of the reporter construct was observed. In parallel, EcR/USP functionality was also restored when resistant cells were rescued by a Drosophila EcR plasmid. However, it was striking that in the resistant cells the ecdysteroid-sensitive response for cell proliferation was not restored upon methoxyfenozide withdrawal, indicating permanent changes in the physiology of the cells during selection. To investigate changes in gene expression caused by inactivation of the EcR/USP complex in resistant cells, Drosophila oligo 14kv1 microarrays were used and probed with cDNAs from resistant cells in the presence