The activity and biosynthesis of cholesterol side-chain cleavage enzyme in cultured immature pig testis cells

Effects of ACTH and expression of the melanocortin-2 receptor in the neonatal mouse testis

ACTH has been shown to stimulate androgen production by the fetal/neonatal mouse testis through the melanocortin type 2 receptor (MC2R). This study was designed to localize the expression of MC2R in the neonatal mouse testis and characterize the effects of ACTH on testicular androgen production. Using immunohistochemistry, MC2R was localized to the fetal-type Leydig cell population of the neonatal testis. ACTH caused a time-dependent increase in cyclic AMP (cAMP) and testosterone production by isolated cells with an increase in cAMP apparent in < 3 min. There was no additive effect of maximally stimulating doses of ACTH and human chorionic gonadotropin (hCG). Androgen production in response to ACTH and hCG was reduced by UO126 and dexamethasone, which are the inhibitors of ERK1/2 and phospholipase A2 respectively. Expression of mRNA encoding StAR was increased fourfold by both ACTH and hCG, although expression of mRNA encoding for steroidogenic enzymes was not markedly affected. The potency of N-terminal fragments of ACTH to stimulate androgen production was similar to that seen previously in the adrenal. Data indicate that both LH and ACTH, acting through their respective receptors, stimulate steroidogenesis by fetal-type Leydig cells via arachidonic acid, protein kinase A, and ERK1/2 activation of StAR.

Regulation of steroid hydroxylase gene expression: importance to physiology and disease

Steroid hydroxylase gene expression is multifactorial in nature, being regulated by tissue-specific, developmental, constitutive and signal transduction systems. The biochemistry of this complex pattern of regulation is not yet clearly elucidated, but studies in several laboratories have led to an understanding of specific aspects of regulation, particularly that involving signal transduction. The complexity of regulation appears to be necessary for normal human physiology because of the wide variety of steroid hormones produced by these enzymes. Genetic diseases associated with the steroid hydroxylases provide examples of how aberrant physiology can result from alterations in the multifactorial regulation of steroid hydroxylase gene expression.

Luteinizing hormone induction of the cholesterol side-chain cleavage enzyme in cultured immature rat Leydig cells: no role of insulin-like growth factor-I?

Long-term inductive effects of luteinizing hormone (LH) on cholesterol side-chain cleavage (CSCC) enzyme activity were studied, using cultured Leydig cells isolated from 21-day-old rats. Particular reference was given to the role of insulin-like growth factor-I (IGF-I) as an autocrine or paracrine modulator or as an essential extracellular mediator of LH action. The CSCC enzyme activity was measured using an excess of 22(R)-hydroxycholesterol as substrate to saturate the enzyme, and inhibitors of pregnenolone metabolism to concentrate all the products of the enzyme reaction in pregnenolone. The rate of sterol conversion into pregnenolone (CSCC enzyme activity) reflected the amount of cytochrome P-450scc (P-450scc), as was shown by Western blotting. In cells cultured without LH, the CSCC enzyme activity decreased to 10% on day 7 of the culture period. In the presence of various doses of LH ranging from 0.01 to 100 ng/ml, the CSCC enzyme activity also diminished during the first 3 days of culture, but during the following days, the amount of CSCC enzyme was stimulated by LH. In contrast to the absence of any LH effect on the activity of the CSCC enzyme during the first days of the culture, the endogenous steroid production (no added 22(R)-hydroxycholesterol) could be stimulated at least 10-fold by high doses of LH. When LH (1 ng/ml) was added to cells which had been cultured for 7 days without hormones, CSCC enzyme activity was elevated 8-fold after 4 days of exposure of LH. These effects of LH could be mimicked by dbcAMP (0.5 mM). No evidence could be provided that IGF-I plays any role in the LH induction of the CSCC enzyme; neither the addition of exogenous IGF-I or analogs that do not bind to IGF-I binding proteins (IGFBPs) nor the inactivation of endogenous IGF-I action (through binding to IGFBP and antibodies to IGF-I or via masking of IGF-I receptor by antibodies) could influence the LH induced CSCC enzyme activity. The present data raise the question under which conditions IGF-I is capable of modulating Leydig cell steroidogenesis.

Regulated expression of cytochrome P-450scc (cholesterol-side-chain cleavage enzyme) in cultured cell lines detected by antibody against bacterially expressed human protein

The first step in the synthesis of steroids is catalysed by cytochrome P-450ssc (cholesterol-side-chain cleavage enzyme). We have investigated the synthesis of this enzyme in three cultured cell lines at the protein and hormone secretion levels. Hormone levels were measured by an enzyme immunoassay using a monoclonal antibody against progesterone. The protein level was detected using polyclonal antibodies directed against a P-450scc fusion protein overproduced in Escherichia coli. Utilizing a bacteriophage T7 promoter expression system, a large amount of human P-450scc fusion protein was produced and easily purified. P-450scc was synthesized in the mouse adrenal tumour cell line Y1 and human choriocarcinoma cell line JEG-3, but not in monkey kidney cell line COS-1. The production of P-450scc in Y1 and JEG-3 cells was stimulated by 8-bromo cyclic AMP, the effect of which was not observed until 6 h after induction and was more pronounced at 24 h. Y1 and JEG-3 cells exhibited a difference in progesterone secretion after induction.

cAMP regulates P450scc gene expression by a cycloheximide-insensitive mechanism in cultured mouse Leydig MA-10 cells

Mouse MA-10 Leydig tumor cells synthesize and secrete progesterone in response to human chorionic gonadotropin, luteinizing hormone, and cAMP but may not synthesize androgens. Maximal doses of human chorionic gonadotropin, ovine luteinizing hormone, forskolin, or 8-bromoadenosine 3',5'-cyclic monophosphate, stimulated cytochrome P450scc mRNA accumulation 1.5- to 3-fold and progesterone secretion 10- to 100-fold in MA-10 cells. P450scc mRNA increased by 2 hr and was maximal by 8 hr; polymerase run-on experiments showed this was due to increased P450scc gene transcription. MA-10 cells are a hormonally homogeneous population, as all cells expressed P450scc mRNA and responded to cAMP equally. cAMP-stimulated accumulation of P450scc mRNA continued in the presence of cycloheximide. Gonadotropins stimulated testicular steroidogenesis by coordinate cAMP-induced increases in P450scc gene transcription, mRNA accumulation, and P450scc activity. We cloned rat P450c17 cDNA and showed it detected no P450c17 mRNA in control or cAMP-stimulated MA-10 cells by RNA transfer blots or RNase protection assays. Similarly, HPLC detected no 17 alpha-hydroxyprogesterone or testosterone synthesis in MA-10 cells. Thus MA-10 cells, unlike untransformed Leydig cells, do not express detectable amounts of P450c17 mRNA or P450c17 activity.

Regulation of steroid hydroxylase gene expression is multifactorial in nature

In summary, regulation of steroid hydroxylase gene expression is complex and multifactorial, involving cAMP-dependent and -independent mechanisms required for maintenance of optimal steroidogenic capacity, tissue-specific mechanisms which lead to different steroidogenic pathways in different tissues, and developmental mechanisms which lead to fetal imprinting of steroid hydroxylase expression and which probably overlap with both maintenance and tissue-specific mechanisms. Future studies will involve identification of the trans-acting factors associated with each of these aspects of the multifactorial regulation and characterization of the cis-regulatory elements to which they bind. Such studies will inevitably lead to the identification of genes encoding these trans-acting factors and investigation of their regulation. In this way, it will be possible to work outward from the steroid hydroxylase genes toward the cell surface receptors in order to elucidate the series of events which lead to cAMP-dependent and -independent regulation of steroid hydroxylase gene expression.

Regulation of cholesterol side-chain cleavage cytochrome P-450 gene expression in adrenal cells in monolayer culture

Utilizing a cDNA probe specific for bovine cytochrome P-450scc and primary monolayer cultures of bovine adrenocortical cells and human fetal adrenal cells, it has been shown that the chronic action of ACTH on the adrenal cortex includes regulation of P-450scc gene expression at the transcriptional level. The bovine P-450scc cDNA hybridizes strongly to human, pig and rat RNA. Advantage was taken of the cross-reactivity of the bovine P-450scc cDNA with human P-450scc RNA to examine the regulation of P-450scc gene expression by ACTH in human fetal adrenal cells. This process is mediated by cyclic AMP and is inhibited by cycloheximide, in a fashion similar to bovine adrenocortical cells, suggestive that a protein factor(s) activates the response in both species. Hence, the actions of ACTH to regulate P-450scc gene expression in bovine adult adrenocortical cells and human fetal adrenal cells appear to proceed by similar mechanisms.