Regulation of the cholesterol side-chain cleavage cytochrome P-450 and adrenodoxin mRNAs in cultured choriocarcinoma cells

Abstract

Cytochrome P-450 scc ( p450 scc) catalyzes the cholesterol side-chain cleavage reaction, a rate-limiting enzymatic step for progesterone synthesis in trophoblastic and other steroidogenic cells. Adrenodoxin is the iron/sulfur protein donating electrons to P-450 scc during this reaction. We examined the effects of cholera toxin (CT), an activator of adenylate cyclase, and 12- O-tetradecanoylphorbol acetate (TPA), a phorbol ester protein kinase C activator, on the levels of mRNAs encoding P-450 scc and adrenodoxin in JEG-3 choriocarcinoma cells. CT induced in a concentration- and time-dependent manner P-450 scc and adrenodoxin mRNA levels to 8-fold and 1.5-fold above that of control, respectively. TPA also increased P-450 scc and adrenodoxin mRNA levels about 3-fold and 1.5-fold above that of control, respectively. Epidermal growth factor (EGF) was found to weakly induce P-450 scc mRNA accumulation with a maximal 20% stimulation above basal levels. The effects of CT and TPA were apparently additive on both mRNAs. The protein synthesis inhibitor cycloheximide diminished basal, CT-, TPA-, and EGF-stimulated P-450 scc mRNA accumulation whereas the opposite was observed for the adrenodoxin mRNA. Insulin-like growth factor I (IGF-1) appeared to have no effect on either mRNA. These data indicate that: (1) the accumulation of P-450 scc and adrenodoxin mRNAs is mainly controlled by the cyclic adenosine 3′, 5′-monophosphate (cAMP)-dependent pathway but their stimulation by TPA- and EGF-induced signals may also play a weaker synergistic role; (2) the protein synthesis inhibitor cycloheximide inhibits basal, CT-, TPA- and EGF-stimulated P-450 scc mRNA levels while it increases the expression of adrenodoxin mRNA suggesting that in the malignant trophoblasts these two enzyme mRNAs are differentially controlled.