Abstract
The non-steroidal ecdysone agonist, RH-5992, induces a precocious incomplete molt in lepidopteran insects but is refractory to insects of other orders. We used two lepidopteran cell lines, FPMI-CF-203 (CF-203) and IPRI-MD-66 (MD-66) and two dipteran cell lines, DM-2 and K c, to investigate the lepidopteran specificity of RH-5992. The mRNAs for hormone receptor 3 homologues cloned from Drosophila (DHR3) and Choristoneura (CHR3) are directly induced by 20-hydroxyecdysone (20E) and serve as suitable markers for studying ecdysone action. Dose response experiments showed that 10 −7 M 20E induced CHR3 mRNA in CF-203 cells and DHR3 mRNA in DM-2 cells. Concentrations of RH-5992 as low as 10 −10 M induced CHR3 mRNA in CF-203 cells, whereas concentrations as high as 10 −6 M induced only very low levels of DHR3 mRNA in DM-2 cells. Studies using 14C- RH-5992 revealed that lepidopteran cell lines (CF-203 and MD-66) retained more of this compound within the cells than the dipteran cell lines (DM-2 and K c). The clearance of RH-5992 from DM-2 cells was temperature dependent and was blocked by 10 −5 M ouabain, an inhibitor of Na +, K +-ATPase suggesting that the efflux was due to active transport.
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