Ecdysteroid Effects on the Cell Cycle of Drosophila melanogaster Cells

Ecdysteroids are polyhydroxylated steroids possessing a 5α hydrogen and a conjugated 7-ene-6-one function in the B ring. Their most impressive biological effects are seen in insects, in which they regulate the timing of the larval, pupal, and adult molts. For the past several years a number of laboratories (Courgeon 1972; Savakis et al. 1981; Stevens et al. 1981; Berger 1978) have been examining the mode of action of two ecdysteroids, 20-OH-ecdysone and its more potent analog, ponasterone A, on the Kc cell line established from embryos of Drosophila melanogaster by Echalier and Ohanessian (1970). The results of these studies reveal ecdysteroids to be very similar in their mode of action to vetebrate steroid hormones. Thus shortly after the administration of 20-OH-ecdysone to cultured cells there is apparently a marked increase in the synthesis of several specific proteins (Savakis et al. 1980). Following longer exposure to hormone the Kc cells respond with increased enzyme activity (Cherbas et al. 1977; Best-Bel pomme et al. 1978), alteration of both cell shape (Cherbas et al. 1980; Cougeon 1972; O’Connor and Chang 1981) and cellular agglutinability (Rosset 1978), and modifications of cell surfaces (Metakovski et al. 1975). The existence of high-affinity binding sites for ecdysteroids in cultured cells (Maroy et al. 1978) is consistent with the preceding events being receptor mediated, as suggested by the current steroid paradigm (Yamamoto and Alberts 1976).