REGULATION BY RETINOIDS OF LUTEINIZING-HORMONE CHORIONIC-GONADOTROPIN RECEPTOR, CHOLESTEROL SIDE-CHAIN CLEAVAGE CYTOCHROME-P-450, 3-BETA-HYDROXYSTEROID DEHYDROGENASE DELTA(5-4)-ISOMERASE AND 17-ALPHA-HYDROXYLASE C-17-20 LYASE CYTOCHROME-P-450 MESSENGER-RIBONUCLEIC-ACID LEVELS IN THE K9 MOUSE LEYDIG-CELL LINE

Vitamin A is a potent regulator of testicular function. We have reported that retinol (R) and retinoic acid (RA) induced a down regulation of luteinizing hormone/human chorionic gonadotropin (LH/CG) binding sites in K9 Leydig cells. In the present study we evaluated the effect of R and RA on LH/CG receptors, cholesterol side-chain cleavage cytochrome P-450 (P-450 scc), 17 alpha-hydroxylase/C-17-20 lyase (P-450 17 alpha) and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) mRNA levels in K9 mouse Leydig cells. To validate K9 cells as a model for studying Leydig cell steroidogenesis at the molecular level, we first investigated the effect of hCG on mRNA levels of the steroidogenic enzymes. P-450 scc, 3 beta HSD and P-450 17 alpha were expressed constitutively. The addition of 10 ng/ml hCG enhanced mRNA levels for the three genes within 2 h. Maximal accumulation of P-450 scc, P-450 17 alpha and 3 beta HSD mRNA in treated cells represents a 2,5-, 8.5- and 4-fold increase over control values, respectively. P-450 17 alpha expression reached a maximum by 4 h and then declined rapidly to return to control value by 24 h, The pattern of LH/CG receptor mRNAs in K9 cells was very similar to that of MA10 Leydig cells and showed six transcripts of 1.1, 1.6, 1.9, 2.6, 4.2 and 7.0 kb. Treatment of cells with R or RA resulted in a time- and dose-dependent decrease in air six species. Comparing the time course of the reduction in mRNA levels and in binding activity, we postulate that retinoids down regulate LH/CG receptors primarily by reducing their mRNAs. Addition of R or RA greatly enhanced P-450 17 alpha mRNA levels in a time- and dose-dependent manner with maximal induction at 12 h (about a 5 fold increase) using 10(-6) M R or RA. The level of P-450 17 alpha mRNA remained high throughout the treatment. Under the same conditions, 3 beta HSD mRNA levels were repressed but the effect was long term (70% decrease after 8 days with 10(-6) M R or RA). On the contrary, P-450 sec expression was not affected.