Effects of methoprene, its metabolites, and breakdown products on retinoid-activated pathways in transfected cell lines

Methoprene (isopropyl (2E,4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate) is an insect juvenile hormone agonist that blocks metamorphosis in some insects. Recent evidence suggests that a metabolite, methoprene acid, activates vertebrate retinoid X receptors (RXRs), and may interfere with retinoic acid-regulated developmental processes. Methoprene, methoxy-methoprene acid, and two major breakdown products were tested for their ability to interfere with retinoid-regulated pathways when using transfected cells. The CV-1 cells were transiently transfected with genes encoding RXRs and response elements attached to luciferase reporters, and retinoic acid-sensitive F9 cells were stably transfected with retinoic acid receptor (RAR)/RXR response elements attached a lacZ reporter (Sil-REM/β-gal-NEO). Experiments confirmed that methoxy-methoprene acid acted as a ligand for RXRs and was capable of activating transcription through RAR/RXR response elements. However, neither methoprene nor the breakdown products, 7-methoxycitronellal and 7-methoxycitronellic acid, activated transcription in transfected CV-1 or F9 cells. Methoprene and methoxy-methoprene acid may interfere with the conversion of all-trans-retinol and all-trans-retinaldehyde to all-trans-retinoic acid in the F9-derived cell line. Methoprene was as effective as the retinol dehydrogenase inhibitor citral in blocking the retinol-induced transcription of RAR/RXR-regulated reporter genes, whereas methoxy-methoprene acid blocked transcription stimulated by retinaldehyde.