Regulation of expression of 3β-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 3β-hydroxysteroid dehydrogenase/Δ(5→4)isomerase (3βHSD) in primary culture. Agents which increase the intracellular levels of cAMP such as forskolin, dibutyryl cAMP, and LH can positively regulate the expression of 3βHSD in Leydig cells in vitro. The effects of these agents are manifest at several levels and include increases in (1) 3βHSD activity, (2) the cellular levels of immunoreactive 3βHSD, (3) the rate of synthesis of 3βHSD, and (4) the cellular levels of 3βHSD mRNA which can be readily translated into 3βHSD 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 3βHSD. Forskolin can positively regulate the expression of 3βHSD in H540 Leydig tumor cells in which steroidogenesis is responsive to increases in intracellular cAMP, but it has no effect on 3βHSD 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 3βHSD 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 3βHSD.

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