Regulation of the cholesterol ester cycle and progesterone synthesis by juvenile hormone in MA-10 Leydig tumor cells.

We had previously reported that juvenile hormone III (JH III) and the JH analogue 2-(4-phenoxy phenoxy)-ethoxytetrahydropyran exert inhibitory effects on progesterone synthesis by blocking cAMP production in hCG-stimulated MA-10 Leydig tumor cells. In the present study, the effects of JH analogue upon the biosynthetic pathway of progesterone synthesis have been examined. Our results demonstrated that JH analogue inhibited progesterone production even in the presence of 20-hydroxycholesterol or 25-hydroxycholesterol. Furthermore, although JH analogue inhibited pregnenolone production in hCG-stimulated MA-10 cells the activity of the 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) was unaffected. These data suggest that JH analogue might inhibit the steroidogenic pathway in Leydig tumor cells by inhibiting the activity of the cholesterol side chain cleavage (CSCC) enzymatic complex. The JH analogue was also evaluated for inhibitory actions on cholesterol availability. An important effect of this compound was the interference with the cellular process of plasma membrane cholesterol internalization. Moreover, JH analogue inhibited not only the use of cholesterol ester for steroid biosynthesis under Bt2cAMP stimulation, but also the cholesterol ester hydrolase (CEH) activity in MA-10 Leydig tumor cells.

Effects of juvenile hormone on mammalian steroidogenesis.

The effects of juvenile hormone-III (JH-III) and the JH analogue 2-(4-phenoxyphenoxy)-ethoxyte-trahydropiran on testicular steroidogenesis were studied. By using cultured MA-10 Leydig tumor cells as a model, these compounds were found to be potent inhibitors of LH/hCG steroidogenic action in a dose-dependent manner. Scatchard plot analysis of the binding data indicated that the JH analogue did not significantly alter the affinity nor the number of hCG binding sites, as well as GTP binding to plasma membranes. JH analogue inhibited the stimulatory action of both cholera toxin and forskolin on cAMP production and the concomitant steroidogenic response. JH analogue inhibited (Bu)2cAMP-stimulated progesterone synthesis, indicating that a process downstream to the adenylyl cyclase in the steroidogenic pathway is also affected.