Interaction of PAHs and PCBs with ecdysone-dependent gene expression and cell proliferation

This study was done to determine whether PAHs and PCBs can interact with th e arthropod steroid hormone system, Ecdysteroid molting hormones control gr owth, molting, and reproduction in arthropods. A spike in 20-OH ecdysone (2 0 HE) triggers the molt cycle in crustaceans, and earlier studies have show n that PAHs can affect this molt cycle in several crab species. However, th e mechanism of this molt cycle interaction is unknown. Both PAHs and PCBs i nteract with other nuclear receptors; however, nothing is known about their ability to interact with the invertebrate ecdysone receptor (EcR). Four PA Hs, benzo[a]pyrene, benzo[b] fluoranthene, pyrene, and chrysene, and the co mmercial PCB mixture, Aroclor 1254, were used to determine the ability of t hese classes of compounds to induce ecdysone-dependent reporter gene expres sion and to modify the proliferation and differentiation response of the ec dysteroid-responsive C1.8+ cell line. The four PAHs were each able to enhan ce the ecdysteroid response in both the reporter gene and the cell prolifer ation assays only when given in conjunction with ecdysteroids. Aroclor 1254 had no effect in either system, either alone or in conjunction with ecdyst eroids. These studies show that although the PAHs alone do not activate ecd ysteroid-dependent gene expression or cell differentiation, they are able t o enhance the effect of ecdysteroids, presumably through a non-receptor-med iated process. This mechanism may explain the effects on molting which have been reported after low-level crude oil exposures in crustaceans. (C) 1999 Academic Press.