REGULATION BY RETINOIDS OF LUTEINIZING-HORMONE CHORIONIC-GONADOTROPINRECEPTOR, 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 INTHE K9 MOUSE LEYDIG-CELL LINE

Vitamin A is a potent regulator of testicular function. We have report ed that retinol (R) and retinoic acid (RA) induced a down regulation o f luteinizing hormone/human chorionic gonadotropin (LH/CG) binding sit es in K9 Leydig cells. In the present study we evaluated the effect of R and RA on LH/CG receptors, cholesterol side-chain cleavage cytochro me P-450 (P-450 scc), 17 alpha-hydroxylase/C-17-20 lyase (P-450 17 alp ha) and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) mRNA levels i n K9 mouse Leydig cells. To validate K9 cells as a model for studying Leydig cell steroidogenesis at the molecular level, we first investiga ted the effect of hCG on mRNA levels of the steroidogenic enzymes. P-4 50 scc, 3 beta HSD and P-450 17 alpha were expressed constitutively. T he addition of 10 ng/ml hCG enhanced mRNA levels for the three genes w ithin 2 h. Maximal accumulation of P-450 scc, P-450 17 alpha and 3 bet a HSD mRNA in treated cells represents a 2,5-, 8.5- and 4-fold increas e 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 sim ilar 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 activit y, we postulate that retinoids down regulate LH/CG receptors primarily by reducing their mRNAs. Addition of R or RA greatly enhanced P-450 1 7 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. Th e 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.