REGULATION OF EXPRESSION OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE IS MEDIATED BY CAMP IN RAT LEYDIG-CELLS AND H540-RAT LEYDIG TUMOR-CELLS

Leydig cells isolated from testes of adult rats have a relatively high level of expression of 3beta-hydroxysteroid dehydrogenase/DELTA5-->4isomerase (3betaHSD) in primary culture. Agents which increase the intracellular levels of cAMP such as forskolin, dibutyryl cAMP, and LH can positively regulate the expression of 3betaHSD in Leydig cells in vitro. The effects of these agents are manifest at several levels and include increases in (1) 3beta HSD activity, (2) the cellular levels of immunoreactive 3beta HSD, (3) the rate of synthesis of 3beta HSD, and (4) the cellular levels of 3betaHSD mRNA which can be readily translated into 3betaHSD in vitro. Two rat Leydig tumor cell lines which are steroidogenically active, H540 and R2C cells, also have a relatively high level of expression of 3betaHSD. Forskolin can positively regulate the expression of 3betaHSD in H540 Leydig tumor cells in which steroidogenesis is responsive to increases in intracellular cAMP, but it has no effect on 3betaHSD in R2C Leydig tumor cells in which steroidogenesis is unresponsive to increases in intracellular cAMP. These results clearly support the hypothesis that cAMP mediates transcriptional regulation of 3betaHSD in Leydig cells. The implication of these in vitro studies is that, in vivo, LH is required to maintain optimal levels of expression of the gene encoding testicular 3betaHSD.