lnterferon-γ Inhibits Steroidogenesis and Accumulation of mRNA of the Steroidogenic Enzymes P450scc and P450c17 in Cultured Porcine Leydig Cells

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Abstract
The inhibitory effects of recombinant porcine interferon-.gamma. (IFN.gamma.) on human CG (hCG)-stimulated testosterone production, and on mRNA concentrations of cholesterol side-chain cleavage (P450scc) and 17.alpha.-hydroxylase/C17-20lyase (P450c17) were investigated using porcine primary Leydig cell culture as a model. After preincubation of Leydig cells for 24 h with 1000 pm IFN.gamma., hCG-stimulated (10 ng/ml, 2 h) testosterone production was inhibited by 50%, whereas no significant changes were seen in hCG-stimulated cAMP production. Incubation with 10 .mu.M 5-cholestene-3.beta.,22(R)-diol or 10 .mu.M 5-cholestene-3.beta.,20.alpha.-diol together with hCG (10 ng/ml, 2 h) reversed most of the inhibitory effect of IFN.gamma., suggesting that IFN.gamma. inhibits P450scc activity, possibly by inhibiting the substrate (cholesterol) availability for P450scc. Incubation with IFN.gamma. also decreased basal concentrations of P450scc (45%) and P450c17 (35%) mRNA, although these changes probably did not contribute to the decreased testosterone production. Long-term treatment with hCG (100 ng/ml, 24 h) increased P450scc mRNA (3- to 4-fold) and P450c17 mRNA (4- to 5-fold) concentrations. Simultaneous treatment with IFN.gamma. attenuated these hCG-induced increases in P450scc mRNA (50%) and P450c17 mRNA (40-100%) concentrations, as well as in testosterone production (77%). This inhibition of testosterone production could only be partly reversed by the hydroxylated cholesterol derivatives. This suggests that in addition to possible suppression of cholesterol availability, decreased P450scc and/or P450c17 activities (through decreased mRNA concentrations) were also involved in the IFN.gamma. suppressed steroidogenic capacity of porcine Leydig cells during long-term hCG stimulation.
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