We investigated the effects of cadmium (Cd2+) on transcription of the cytochrome p450 side chain cleavage (p450scc) gene and on progesterone synthesis in stable granulosa cells. We used the stable porcine granulosa cell line, JC-410, genetically modified to express a luciferase genomic construct carrying 2320 base pairs (bp) of the p450scc gene promoter (p450scc-2320-LUC). A construct containing only the luciferase gene, pOLUC, was used as a promoterless control. At 1 microM, cadmium chloride (CdCl2) increased transient expression of p450scc-2320-LUC in JC-410 cells by 2.6-fold after 24-h incubation. A similar pattern of stimulation by CdCl2 was observed in cells transiently transfected with a luciferase genomic construct carrying 100 bp of the p450scc gene promoter p450scc-100-LUC, whereas no stimulation by CdCl2 was observed in cells transfected with pOLUC. At 0.6, 1, and 2 microM, CdCl2 stimulated the activity of the p450scc-2320-LUC promoter in a dose-related fashion by 1.58-, 3.19-, and 2.67-fold, respectively, after 24-h incubation. Northern blot analysis showed that CdCl2 at 0.1, 1, 2, and 3 microM increased p450scc mRNA levels by 3.13-, 1.38-, 1.61-, and 1.57-fold, respectively, after 24-h incubation. After 48-h incubation, CdCl2 at 0.6, 1, and 2 microM further increased p450scc mRNA levels by 3.43-, 2.08-, and 2.4-fold, respectively. At 1, 2, and 3 microM, CdCl2 inhibited progesterone synthesis to 0.48-, 0.38-, and 0.29-fold, respectively. After 48-h incubation, CdCl2 at 0.1 microM stimulated progesterone synthesis by 1.6-fold. We conclude that Cd2+ has a dual action in stable porcine granulosa cells: Low concentrations activate, whereas high concentrations inhibit, expression of the p450scc gene and progesterone synthesis. The stimulatory effect of Cd2+ appears to be mediated via a cis-acting element located 100 bp upstream of the p450scc gene transcription start site.
The purpose of the present study was to examine the effects of progestins on progesterone synthesis and expression of the cytochrome P450 cholesterol side-chain cleavage gene (P450(scc)) in a stable porcine granulosa cell line, the JC-410. Cells were incubated for 48 h with the synthetic progestogen-levornorgestrel with or without RU486 (progesterone and glucocorticoid receptor antagonist) or RWJ26819 (progesterone agonist without affinity to glucocorticoid receptors). Both levonorgestrel and RU486 enhanced progesterone accumulation in a dose-dependent manner. RU486 did not antagonize the effects of levonorgestrel, and RWJ26819 had no effect on progesterone production in cultured JC-410 cells. Progesterone and levonorgestrel increased steady state P450(scc) mRNA levels after 3-6 h of treatment. Progesterone and RU486 at 0.1, 1, and 10 microM increased the transcription rate of P450(scc) transiently expressed in JC-410 cells after 18 h of incubation; 30 microM had no effect, and 100 microM suppressed transcription. Levonorgestrel did not affect transcription of the P450(scc) gene, and RWJ26819 reduced its transcription. Progesterone and RU486 significantly decreased the number of cells and total protein content after 72 and 24 h of incubation, respectively. Levonorgestrel had no effect, whereas RWJ26819 increased (24 h) but subsequently reduced (72 h) cell number and protein content. The present results indicate that progestins are capable of directly modulating progesterone biosynthesis in porcine JC-410 granulosa cells. These effects may be exerted in part through the regulation of P450(scc) gene expression. Ostensible differences exist between progesterone and its synthetic analogues in the control of progesterone secretion in the stable porcine granulosa cell line in vitro.
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