Regulation of 3 beta-hydroxysteroid dehydrogenase/delta 5----4-isomerase expression by adrenocorticotropin in bovine adrenocortical cells

CCAAT/enhancer-binding protein β is involved in the breed-dependent transcriptional regulation of 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase in adrenal gland of preweaning piglets

The enzyme 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase (3β-HSD) catalyzes the biosynthesis of all steroid hormones. The molecular mechanisms regulating porcine adrenal 3β-HSD expression in different breeds are still poorly understood. In this study, we aimed to compare the expression of 3β-HSD between preweaning purebred Large White (LW) and Erhualian (EHL) piglets and to explore the potential factors regulating 3β-HSD transcription. EHL had significantly higher serum levels of cortisol (P<0.01) and testosterone (P<0.01), which were associated with significantly higher expression of 3β-HSD mRNA (P<0.01) and protein (P<0.05) in the adrenal gland, compared with LW piglets. The 5' flanking region of the porcine 3β-HSD gene showed significant sequence variations between breeds, and the sequence of EHL demonstrated an elevated promoter activity (P<0.05) in luciferase reporter gene assay. Higher adrenal expression of 3β-HSD in EHL was accompanied with higher CCAAT/enhancer binding protein β (C/EBPβ) expression (P<0.05), enriched histone H3 acetylation (P<0.05) and C/EBPβ binding to 3β-HSD promoter (P<0.05). In addition, higher androgen receptor (AR) (P=0.06) and lower glucocorticoid receptor (GR) (P<0.05) were detected in EHL. Co-immunoprecipitation analysis revealed interactions of C/EBPβ with both AR and GR. These results indicate that the C/EBPβ binding to 3β-HSD promoter is responsible, at least in part, for the breed-dependent 3β-HSD expression in adrenal gland of piglets. The sequence variations of 3β-HSD promoter and the interactions of AR and/or GR with C/EBPβ may also participate in the regulation.

Variation in 3β-hydroxysteroid dehydrogenase activity and in pregnenolone supply rate can paradoxically alter androstenedione synthesis

The 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3β-HSD) and 17α-hydroxylase/17,20-lyase cytochrome P450 (P450c17) enzymes are important in determining the balance of the synthesis of different steroids such as progesterone (P4), glucocorticoids, androgens, and estrogens. How this is achieved is not a simple matter because each of the two enzymes utilizes more than one substrate and some substrates are shared in common between the two enzymes. The two synthetic pathways, Δ(4) and Δ(5), are interlinked such that it is difficult to predict how the synthesis of each steroid changes when any of the enzyme activities is varied. In addition, the P450c17 enzyme exhibits different substrate specificities among species, particularly with respect to the 17,20-lyase activity. The mathematical model developed in this study simulates the network of reactions catalyzed by 3β-HSD and P450c17 that characterizes steroid synthesis in human, non-human primate, ovine, and bovine species. In these species, P450c17 has negligible 17,20-lyase activity with the Δ(4)-steroid 17α-hydroxy-progesterone (17OH-P4); therefore androstenedione (A4) is synthesized efficiently only from dehydroepiandrosterone (DHEA) through the Δ(5) pathway. The model helps to understand the interplay between fluxes through the Δ(4) and Δ(5) pathways in this network, and how this determines the response of steroid synthesis to the variation in 3β-HSD activity or in the supply of the precursor substrate, pregnenolone (P5). The model simulations show that A4 synthesis can change paradoxically when 3β-HSD activity is varied. A decrease in 3β-HSD activity to a certain point can increase A4 synthesis by favouring metabolism through the Δ(5) pathway, though further decrease in 3β-HSD activity beyond that point eventually limits A4 synthesis. The model also showed that due to the competitive inhibition of the enzymes' activities by substrates and products, increasing the rate of P5 supply above a certain point can suppress the synthesis of A4, DHEA, and 17OH-P4, and consequently drive more P5 towards P4 synthesis.

Molecular biology of the 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase gene family

The 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3beta-HSD) isoenzymes are responsible for the oxidation and isomerization of Delta(5)-3beta-hydroxysteroid precursors into Delta(4)-ketosteroids, thus catalyzing an essential step in the formation of all classes of active steroid hormones. In humans, expression of the type I isoenzyme accounts for the 3beta-HSD activity found in placenta and peripheral tissues, whereas the type II 3beta-HSD isoenzyme is predominantly expressed in the adrenal gland, ovary, and testis, and its deficiency is responsible for a rare form of congenital adrenal hyperplasia. Phylogeny analyses of the 3beta-HSD gene family strongly suggest that the need for different 3beta-HSD genes occurred very late in mammals, with subsequent evolution in a similar manner in other lineages. Therefore, to a large extent, the 3beta-HSD gene family should have evolved to facilitate differential patterns of tissue- and cell-specific expression and regulation involving multiple signal transduction pathways, which are activated by several growth factors, steroids, and cytokines. Recent studies indicate that HSD3B2 gene regulation involves the orphan nuclear receptors steroidogenic factor-1 and dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome gene 1 (DAX-1). Other findings suggest a potential regulatory role for STAT5 and STAT6 in transcriptional activation of HSD3B2 promoter. It was shown that epidermal growth factor (EGF) requires intact STAT5; on the other hand IL-4 induces HSD3B1 gene expression, along with IL-13, through STAT 6 activation. However, evidence suggests that multiple signal transduction pathways are involved in IL-4 mediated HSD3B1 gene expression. Indeed, a better understanding of the transcriptional factors responsible for the fine control of 3beta-HSD gene expression may provide insight into mechanisms involved in the functional cooperation between STATs and nuclear receptors as well as their potential interaction with other signaling transduction pathways such as GATA proteins. Finally, the elucidation of the molecular basis of 3beta-HSD deficiency has highlighted the fact that mutations in the HSD3B2 gene can result in a wide spectrum of molecular repercussions, which are associated with the different phenotypic manifestations of classical 3beta-HSD deficiency and also provide valuable information concerning the structure-function relationships of the 3beta-HSD superfamily. Furthermore, several recent studies using type I and type II purified enzymes have elegantly further characterized structure-function relationships responsible for kinetic differences and coenzyme specificity.

The human 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase type 2 promoter is a novel target for the immediate early orphan nuclear receptor Nur77 in steroidogenic cells

The human (h) 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase type 2 (3beta-HSD2) enzyme, encoded by the hHSD3B2 gene, is mainly found in gonads and adrenals. This enzyme catalyzes an essential early step in the biosynthesis of all classes of steroid hormones. The critical nature of the enzyme is supported by the occurrence of human syndromes that are associated with insufficient 3beta-HSD2 expression and/or activity. Although the need for a functional 3beta-HSD2 enzyme is indisputable, the molecular mechanisms that regulate HSD3B2 expression (both basal and hormone-induced) in steroidogenic cells remain poorly understood. A role for the Nur77 family of immediate-early orphan nuclear receptors in steroidogenesis has received recent interest. For example, Nur77 is present in gonads and adrenals, where its expression is robustly and rapidly induced by hormones that stimulate steroidogenic gene expression. Moreover, the expression patterns of Nur77 and at least one key steroidogenic gene (hHSD3B2) closely parallel one another. We now report that the hHSD3B2 promoter is indeed a novel target for Nur77 in both testicular Leydig cells and adrenal cells. We have mapped a novel response element located at -130 bp specific for Nur77 and not other orphan nuclear receptors (steroidogenic factor-1 and liver receptor homolog-1) previously shown to regulate hHSD3B2 promoter activity. This Nur77 element is essential and sufficient to confer Nur77 responsiveness to the hHSD3B2 promoter, and its mutation blunts basal and hormone-induced hHSD3B2 promoter activity in steroidogenic cells. We also show that Nur77 synergizes with all members of the steroid receptor coactivator family of coactivators on the hHSD3B2 promoter. Taken together, our identification of Nur77 as an important regulator of HSD3B2 promoter activity helps us to better define the tissue-specific and hormonal regulation of the HSD3B2 gene in steroidogenic cells.

Ontogeny of 3beta-hydroxysteroid dehydrogenase expression in the rat adrenal gland as studied by immunohistochemistry

The enzyme 3beta-hydroxysteroid dehydrogenase plays a crucial role in the steroidogenic process in the adrenal gland. In the present study we tried to characterize its localization and developmental changes in the rat adrenal cortex during the postnatal period, using immunohistochemical methods. The development of the different zones evidenced specific particularities: the zona glomerulosa almost lacked 3beta-HSD in the first days after birth; then, 3beta-HSD increased, attaining a maximum around day 20 and afterwards it decreased again and remained less intense than the neighbouring zona fasciculata up until adulthood (65 days of age). The zona fasciculata was already intensely stained at birth and the expression of 3beta-HSD increased rapidly reaching a maximum after 2 weeks of life and that level was maintained from then on. The inner part of the zona fasciculata and the zona reticularis both of which develop postnatally were faintly immunostained before day 20. The expression of 3beta-HSD increased after that age to become approximately as intense as in the outer zona fasciculata and so remaining until day 90. The development of the zona glomerulosa was parallel to the secretion of aldosterone. The same did not occur with the zona fasciculata as the intensity of staining during the first 14 postnatal days was accompanied by very low levels of corticosterone.

The regulation of 3 beta-hydroxysteroid dehydrogenase expression

3 beta-Hydroxysteroid dehydrogenasel delta 5-->4-isomerase (3 beta-HSD) catalyzes the formation of delta 4-3-ketosteroids from delta 5-3 beta-hydroxysteroids, an obligate step in the biosynthesis not only of androgens and estrogens but also of mineralocorticoids and glucocorticoids. The enzyme is expressed in the adrenal cortex and in steroidogenic cells of the gonads, consistent with this role. However, 3 beta-HSD is also expressed in many other tissues, such as the liver and kidney, where its function is not entirely clear. It is established that a family of closely related genes encode for 3 beta-HSD. The various 3 beta-HSD isoforms are expressed in a tissue-specific manner involving separate mechanisms of regulation. The human type I 3 beta-HSD is expressed at high levels in syncytial trophoblast and in sebaceous glands, and the type II isoform is almost exclusively expressed in the adrenal cortex and gonads. An important feature in liver and kidney (at least of hamster, mouse, rabbit, and rat) is the sexual dimorphic nature of 3 beta-HSD expression. We briefly review studies on the regulation of the human 3 beta-HSD I and II genes in human trophoblast and adrenal cortex and extend this to discuss the rat 3 beta-HSD I gene expressed in adrenals and gonads. The complexity of 3 beta-HSD expression through multiple signaling pathways acting on a multigene family of enzymes may contribute importantly to the diverse patterns and locations of steroid hormone biosynthesis.

Altering culture conditions reveals strain-related differences in activity and immunoreactive isoforms of 3 beta-hydroxysteroid dehydrogenase-isomerase in mouse Leydig cells

We previously reported that 3 beta-hydroxysteroid dehydrogenase-isomerase (3 beta HSD) activity is higher in Leydig cells from C57BL/6J mice than those from C3H/HeJ mice. This study examines whether the differences in 3 beta HSD activity in Leydig cells from the two strains of mice are due to the expression of different 3 beta HSD isoforms and if a specific isoform corresponds with the amount of 3 beta HSD activity under various culture conditions. Leydig cells were plated in Waymouth's +15% horse serum (HS) medium. Some cultures were terminated 24 h later after plating (day 1) and assayed for 3 beta HSD activity or immunoreactivity. The remaining cultures were maintained in HS or changed to serum-free medium. We demonstrate for the first time that two 3 beta HSD immunoreactive isoforms are expressed in freshly isolated Leydig cells and those cultured for 1 day. The same two 3 beta HSD isoforms are detectable in both strains. Thus, the previously reported strain-related differences in 3 beta HSD activity are not due to the expression of different isoforms. When cultured for 8 days, the higher molecular weight 3 beta HSD immunoreactive band is no longer detectable in Leydig cells from either strain. When maintained in HS, 3 beta HSD activity in C57BL/6J Leydig cells decreases significantly by day 8, while 3 beta HSD activity in C3H/HeJ Leydig cells does not change through day 8. When Leydig cells were cultured in serum-free medium, 3 beta HSD activity is maintained in cultured Leydig cells from C57BL/6J and significantly increases in C3H/HeJ 3 beta HSD by day 8. These data suggest that HS has a strain-specific inhibitory effect on 3 beta HSD activity, causing a significant decrease in C57BL/6J 3 beta HSD activity and preventing an increase in C3H/HeJ. Densitometric analysis reveals a correspondence between changes in 3 beta HSD activity and the lower molecular weight isoform but not the higher molecular weight isoform. Treatment with cAMP induces the immunoreactive mass of the lower molecular isoform but not the higher molecular isoform of 3 beta HSD. Currently, it is unclear what the function of the higher molecular weight 3 beta HSD isoform is in mouse Leydig cells.

Regulation of primary response and specific genes in adrenal cells by peptide hormones and growth factors

Using cultured bovine adrenal fasciculata cells (BAC), we investigated the effects of two hormones, corticotropin (ACTH) and angiotensin II (Ang-II) and two growth factors, insulin-like growth factors I (IGF-I) and transforming growth factor beta 1 (TGF beta 1), on the mRNA levels of nuclear proto-oncogenes of the Fos and Jun families and on the mRNA levels of genes expressed in BAC coding for ACTH and AT1 receptors, cytochrome P450scc and P450 17 alpha and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD). ACTH and IGF-1 increased c-fos and jun-B mRNA levels early with later increases in the levels of mRNA for the ACTH receptor and the three steroidogenic enzymes, and enhanced steroidogenic responses to both ACTH and Ang-II. In contrast, Ang-II increased mRNA coding for the three proto-oncogenes (cfos, c-jun, and jun-B), decreased those for P450 17 alpha and 3 beta-HSD, and caused marked homologous and heterologous steroidogenic desensitization. TGF beta 1 increased only jun-B mRNA and markedly reduced BAC-differentiated functions and steroidogenic responsiveness to both ACTH and Ang-II. The long-term effects of ACTH on human adrenal fasciculata cells were comparable with those observed in BAC, whereas the long term effects of Ang-II and TGF beta 1 were different from those observed in BAC. Whether these species-specific differences are related to a different effect of these factors on proto-oncogene expression is not yet known.

The effect of transforming growth factor-beta on steroidogenesis and expression of key steroidogenic enzymes with a human ovarian thecal-like tumor cell model

OBJECTIVE

Our purpose was to determine the effects of transforming growth factor-beta on steroidogenesis and regulation of steroidogenic enzyme expression by use of a human ovarian thecal-like tumor cell culture system.

STUDY DESIGN

Human ovarian thecal-like tumor cells were treated in serum-free medium in the presence or absence of forskolin and transforming growth factor-beta 1. The accumulation of progesterone and androstenedione in the culture medium was evaluated by radioimmunoassay. The effects of forskolin with or without transforming growth factor-beta 1 on the enzymatic activity of P450c17 and 3 beta HSD, the expression of immunodetectable P450c17 protein, and the expression of messenger ribonucleic acid for P450scc, P450c17, and 3 beta HSD were determined.

RESULTS

Basal steroid secretion, steroidogenic enzyme activity, enzyme protein, and messenger ribonucleic acid expression were not affected by transforming growth factor-beta 1 alone. Forskolin treatment significantly stimulated steroid production and the enzymatic activity of P450c17 and 3 beta HSD up to 10-fold above basal levels. However, transforming growth factor-beta 1 inhibited forskolin-stimulated androstenedione production to near basal levels and increased progesterone 1.4- to 2-fold while suppressing P450c17 enzyme activity to near basal levels, but it did not affect 3 beta HSD activity. Forskolin-stimulated immunodetectable P450c17 alpha protein was markedly inhibited by transforming growth factor-beta 1. In addition, transforming growth factor-beta 1 markedly inhibited the forskolin-stimulation of P450c17 messenger ribonucleic acid, while not significantly altering P450scc or 3 beta HSD messenger ribonucleic acid expression.

CONCLUSION

Forskolin stimulated human ovarian thecal-like tumor cell steroidogenesis, P450c17 and 3 beta HSD activity, immunodetectable P450c17, and messenger ribonucleic acid content for P450scc, P450c17, and 3 beta HSD. Transforming growth factor-beta 1 inhibited forskolin stimulation of androstenedione production through the inhibition of P450c17 expression.

Ontogeny of immunoreactive and bioactive microsomal steroidogenic enzymes during adrenocortical development in rats

The functional development of the neonatal rat adrenal cortex is characterized by a triphasic response to adrenocorticotropic hormone (ACTH), with a nadir in responsiveness around neonatal day 10 (d10). In this study, the hypothesis was tested that hyporesponsiveness to ACTH partly results from deficiencies in steroidogenic enzyme content. Immunoreactive (ir) levels of mitochondrial cytochrome P450 enzymes (side chain cleavage (P450scc) and 11 beta-hydroxylase (P450c11)) did not change during neonatal development. Immunoreactive levels of microsomal 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD), however, were significantly and comparably lower in both day 1 (d1) and d10 neonates compared to adult rats. Activity of 3 beta-HSD did not parallel changes in ir 3 beta-HSD content. Enzyme activity was low on d1 (approximately 39% of adult activity), but by d10 was statistically equivalent to that of microsomes from adult adrenal glands. Immunoreactive levels of microsomal cytochrome P450 21 alpha-hydroxylase (P450c21) were significantly lower in d1 glands than in adult glands (by approximately 50%), but by d10 were statistically indistinguishable from adults. On the other hand, P450c21 activity was equivalent on d1 and d10 and both were significantly lower compared to adults (approximately 62% of adult activity). ACTH injections from d3-d10 facilitated the adrenocortical steroidogenic response to ACTH on d10. This treatment increased levels of ir 3 beta-HSD, but not ir P450c21. The results suggest that rat adrenocortical 3 beta-HSD and P450c21 are developmentally and differentially regulated, and that ir levels of the proteins are not correlated with enzyme activity during the neonatal period. One possible explanation for these observations is that multiple isoforms of the two enzymes, with different antigenic and enzymatic properties, may be expressed during development at different times. In addition, the combined decreased activities of these two enzymes can almost entirely account for the decreased steroidogenic output of rat adrenocortical cells on d1, but not during the later neonatal period.

Glucocorticoids enhance the cholesterol side-chain cleavage activity of ovine adrenocortical mitochondria

We have shown previously that a chronic treatment with glucocorticoids enhances cAMP- or ACTH-induced steroidogenesis of cultured ovine adrenocortical cells. This effect appears to involve a greater amount of cholesterol in mitochondria. Hence, the present study aimed to define the role of glucocorticoids in cholesterol metabolism by these cells. 2-day-old cultures were exposed to different hormones or inhibitors (10(-6) M ACTH, 10(-5) M metyrapone) for 28-48 h. At the end of the treatment period, the cells were stimulated for 2 h with 10(-3) M 8Br-cAMP, in the presence of 10(-3) M aminoglutethimide (in order to load mitochondria with cholesterol). Mitochondria were then isolated and incubated without or with 100 microM cholesterol either in the presence or absence of 10(-3) M CaCl2, or with 25 microM 22R-hydroxycholesterol. Mitochondria isolated from dexamethasone-treated cells produced consistently more pregnenolone than mitochondria from control cells, suggesting that at least part of the additional cholesterol present in these mitochondria was available for steroidogenesis. However, similar differences were obtained when mitochondria were incubated in the presence of exogenous cholesterol, both with or without calcium, or in the presence of 22R-hydroxycholesterol. Pregnenolone production under these latter conditions was much higher than when endogenous cholesterol was the only substrate. Conversely, metyrapone treatment of the cells resulted in lower production of pregnenolone from 22R-hydroxycholesterol by their mitochondria. Likewise ACTH treatment enhanced pregnenolone production by isolated mitochondria irrespective of the incubation conditions. These effects of dexamethasone and ACTH were not related to higher amounts of adrenodoxin, adrenodoxin reductase or cytochrome P450scc. These results indicate that exposure of ovine adrenocortical cells to glucocorticoids or ACTH enhances their steroidogenic potency not only by increasing the amount of cholesterol available for steroidogenesis but also by enhancing some step(s) involved in the transformation of cholesterol into pregnenolone.

Type beta 1 transforming growth factor is an inhibitor of 3 beta-hydroxysteroid dehydrogenase isomerase in mouse adrenal tumor cell line Y1

In the Y1 mouse adrenal tumor cell line, the 3 beta-hydroxysteroid dehydrogenase isomerase enzyme (3 beta-HSD) which catalyzes the transformation of 3 beta-hydroxy-5-ene steroids to 3-keto-4-ene steroids is active. The effect of type beta 1 transforming growth factor (TGF beta 1), a potent modulator of adrenocortical differentiated functions, on the 3 beta-HSD enzyme was studied. Four isoforms of 3 beta-HSD yielding proteins of different mobility on SDS-PAGE were previously detected in the mouse; whereas only one form was present in the mouse adrenal, we detected two isoforms in the Y1 cells. An inhibition of the basal enzymatic activity was observed after TGF beta 1 treatment which was correlated with a decrease in 3 beta-HSD protein (both isoforms) and mRNA levels.

Peptide hormone and growth factor regulation of nuclear proto-oncogenes and specific functions in adrenal cells

Among the large number of immediate early genes, nuclear proto-oncogenes of the Fos and Jun families, have been postulated to be involved in the long-term effects of several growth factors on cell differentiation and/or multiplication. Since adrenal cell differentiated functions appear to be regulated by specific hormones and growth factors, the effects of these factors on proto-oncogene mRNA levels were analysed in bovine adrenal fasciculata cells (BAC) in culture. Corticotropin (ACTH) and insulin-like growth factor I increased c-fos and jun-B mRNA, but had no effect on c-jun mRNA and these early changes were associated with a later increase in BAC specific function [ACTH receptors, cytochrome P450 17 alpha) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD)] and an enhanced steroidogenic responsiveness to both ACTH and angiotensin-II (A-II). On the other hand, A-II increased the three proto-oncogene (c-fos, c-jun and jun-B) mRNAs, induced a decrease of P450 17 alpha and 3 beta-HSD and caused a marked homologous and heterologous (ACTH) densitization. Transforming growth factor beta 1 which only increased jun-B mRNA, markedly reduced BAC differentiated functions and the steroidogenic responsiveness to both ACTH and A-II. Thus, it is postulated that the proto-oncoproteins encoded by the immediate early genes may play a role in the long-term effects of peptide hormones and growth factors on BAC differentiated functions.

Regulation of bovine adrenal cell corticotropin receptor mRNA levels by corticotropin (ACTH) and angiotensin-II (A-II)

Bovine adrenal fasciculata-reticularis cells (BAC) expressed at least four ACTH receptor (ACTH-R) mRNA transcripts, one major of 3.6 kb and three minor of 4.2, 1.8 and 1.3 kb. ACTH and A-II increased ACTH-R mRNA levels in a time- and dose-dependent manner. At maximal concentrations, ACTH caused a 2.7-fold increase in the level of the major transcript of 3.6 kb with an ED50 = 10(-11) M and A-II produced a 2.4-fold increase with an ED50 = 5 x 10(-8) M. Under our experimental conditions, the stimulatory effects of both hormones appeared to be due to post-transcriptional changes rather than to transcriptional regulation since the hormonal effects were also observed in actinomycin-treated cells. The results indicate that regulation of ACTH-R mRNA levels may be one mechanism by which ACTH and A-II regulate adrenocortical functions.

Cloning of ACTH-regulated genes in the adrenal cortex

To search for genes that are induced by ACTH in adrenocortical cells, we screened adrenal cortex cDNA libraries by a differential hybridization method using cDNA probes representing mRNAs from cells with or without ACTH stimulation. Forty clones were identified as ACTH induced (yielding a frequency of about 1/2500 plaques screened), and two clones as ACTH repressed. The cDNAs isolated and sequenced include nuclear genes for microsomal steroidogenic enzymes and novel proteins of yet unidentified functions, and mitochondrial genes encoding subunits of oxidative phosphorylation enzymes. Northern blot analysis of RNA from cells stimulated with ACTH confirmed the induction of these genes by ACTH, yet revealed important differences in the relative responses of the respective mRNAs. The time courses showed the major increase in the initial 6 h; and a decline after 24-36 h. The enhancement of the levels of the mRNAs could be ascribed to transcriptional activation. Since the mitochondrial genome is transcribed as a single polycistronic unit, to account for the > 20-fold differences in the levels of the mitochondrial mRNAs it is necessary to invoke differential stabilities of these mRNAs. The synchronous increase in the expression of both the steroidogenic enzymes and the mitochondrial oxidative phosphorylation system subunits, provides evidence for coregulation of steroidogenic and energy producing capacities of adrenal cells to meet the metabolic needs of steroid hormone production. Suppression of beta-actin gene expression may be related to changes in actin polymerization during ACTH-dependent cytoskeletal reorganization.

Structure, regulation and role of 3 beta-hydroxysteroid dehydrogenase, 17 beta-hydroxysteroid dehydrogenase and aromatase enzymes in the formation of sex steroids in classical and peripheral intracrine tissues

In addition to the classical steroidogenic tissues, namely the ovaries, testes, adrenals and placenta, a large series of human peripheral tissues possess all the enzymatic systems required for the formation of active androgens and oestrogens from a relatively large supply of precursor steroids provided by the adrenals. This chapter describes the structure, function, tissue-specific expression and regulation of the 3 beta-HSD and 17 beta-HSD gene families as well as some information about the aromatase gene. While, so far, most therapeutic approaches have been aimed and limited at controlling steroid formation by the classical steroidogenic tissues, it is clear that major efforts should now be turned towards intracrinology in order to understand better the physiological mechanisms controlling local steroid formation in peripheral target tissues and thus be in a position to develop novel therapeutic approaches that take into account the high proportion of steroids that are made locally and are responsible for the growth and function of normal as well as cancerous tissue.

Regulation of expression of the 3 beta-hydroxysteroid dehydrogenases of human placenta and fetal adrenal

The appropriate expression of 3 beta-hydroxysteroid dehydrogenase/delta 5-->4-isomerase (3 beta-HSD) is vital for mammalian reproduction, fetal growth and life maintenance. Several isoforms of 3 beta-HSD, the products of separate genes, have been identified in various species including man. Current investigations are targeted toward defining the processes that regulate the levels of specific isoforms in various steroidogenic tissues of man. High levels of expression of 3 beta-HSD were observed in placental tissues. It has been generally considered that the multinucleated syncytiotrophoblastic cells are the principal sites of 3 beta-HSD expression and, moreover, that 3 beta-HSD expression is intimately associated with cyclic AMP-promoted formation of syncytia. Herein we report the presence of 3 beta-HSD immunoreactive and mRNA species in uninucleate cytotrophoblasts in the chorion laeve, similar to that in syncytia but not cytotrophoblast placenta. In vitro, 3 beta-HSD levels in chorion laeve cytotrophoblasts were not increased with time nor after treatment with adenylate cyclase activators, whereas villous cytotrophoblasts spontaneously demonstrated progressive, increased 3 beta-HSD expression. Moreover, 3 beta-HSD synthesis appeared to precede morphologic syncytial formation. Thus high steroidogenic enzyme expression in placenta is not necessarily closely linked to formation of syncytia. Both Western immunoblot and enzymic activity analyses also indicated that the 3 beta-HSD expressed in these cytotrophoblastic populations was the 3 beta-HSD type I gene product (M(r), 45K) and not 3 beta-HSD type II (M(r), 44K) expressed in fetal testis. In cultures of fetal zone and definitive zone cell of human fetal adrenal, 3 beta-HSD expression was not detected until ACTH was added. ACTH, likely acting in a cyclic AMP-dependent process, induced 3 beta-HSD type II activity and mRNA expression. The higher level of 3 beta-HSD mRNA in definitive zone compared with fetal zone cells was associated with parallel increases in cortisol secretion relative to dehydroepiandrosterone sulfate formation.

Separate induction of the two isozymes of cytochrome P-450(11) beta in rat adrenal zona glomerulosa cells

In the rat adrenal cortex, two isozymes of cytochrome P-450(11) beta (CYP11B1 and CYP11B2) have been identified. They are encoded by two different genes with a homology much higher in their coding than in their 5'-flanking regions. CYP11B1 is found in all the zones of the gland and catalyzes a single hydroxylation of deoxycorticosterone (DOC) in the 11 beta- or the 18-position. CYP11B2 is produced exclusively in the zona glomerulosa and catalyzes all three reactions involved in the conversion of DOC to aldosterone. In vivo and in vitro, the expression of the genes encoding CYP11B1 and CYP11B2 is regulated by two separate control systems which appear to operate both independently and interdependently. In vivo zona glomerulosa expression of CYP11B1 was enhanced by ACTH treatment or potassium depletion and was lowered by potassium repletion. CYP11B2 expression disappeared upon potassium depletion or ACTH treatment, but reappeared during potassium repletion. In vitro, only CYP11B1 activity was detectable and responsive to ACTH treatment in zona glomerulosa cells cultured at a potassium concentration of 6.4 mmol/l. Aldosterone biosynthetic activity and mRNA encoding CYP11B2 could be detected only after at least 1 day of exposure to a high extracellular potassium concentration (> or = 12 mmol/l).

Human endometrial 3 beta-hydroxysteroid dehydrogenase/isomerase can locally reduce intrinsic estrogenic/progestagenic activity ratios of a steroidal drug (Org OD 14)

In vitro conversion in human endometrial tissue of Org OD 14 [17 alpha-hydroxy-7 alpha-methyl-19-norpregn-5(10)-en-20-yn-3-one, a 3-keto-delta 5-10-19-nortestosterone derivative structurally related to norethynodrel] to its 4-ene isomer was demonstrated and measured spectrophotometrically and by chromatographic separation of the labeled metabolite from the tritiated precursor. The endometrial isomerase catalyzing this conversion is the 3 beta-hydroxy-steroid dehydrogenase/isomerase (3 beta HSD/isomerase), detected by Western blotting as a 42 kDa band, as confirmed by the inhibition of Org OD 14 isomerization with an antibody against this enzyme. The endometrial isomerase activity was found to be higher in secretory than in proliferative tissue and to be influenced by progestins, as suggested by the small but significant increase in activity resulting from exposure of proliferative endometrium to medroxyprogesterone acetate under organotypic culture conditions. In addition to the expected physiologic importance of endometrial 3 beta HSD/isomerase in the local metabolism of circulating steroids of adrenal origin, its presence in the endometrium is likely to have pharmacologic relevance, as illustrated by the local conversion of Org OD 14 to the 4-ene isomer, a metabolite with higher progestagenic and lower estrogenic potencies than those of its precursor. The local, tissue-specific, modification of the precursor would yield intracellular concentration ratios of Org OD 14 to 4-ene isomer in the endometrium significantly lower than those in blood. As a result, the estrogenic effects of Org OD 14 or of its 3-hydroxy metabolites on endometrial cell proliferation are minimized by the local formation of the progestagenic 4-ene isomer. This is a favorable feature of Org OD 14 since it selectively prevents undesirable proliferative stimulation of the endometrium in postmenopausal users while preserving its beneficial effects on other tissues, including bone.

Angiotensin-II-directed glomerulosa cell function in fetal adrenal cells

These studies were undertaken to examine the role of angiotensin II (A-II) in the regulation of adrenal glomerulosa cell differentiation. We were interested particularly in the ability of A-II to support aldosterone production in fetal adrenal cells. Many in vitro studies on acute A-II stimulation of aldosterone synthesis in adrenocortical cells have been documented. However, it is the long-term modification of steroid-metabolizing enzyme expression that leads to the formation and release of specific adrenal steroids. Herein, we used primary cultures of fetal bovine adrenal (FBA) cells to examine the effects of A-II on aldosterone production and the expression of aldosterone synthase cytochrome P450 (P450c18). A-II treatment caused the primary cultures to maintain glomerulosa cell functions. Cells treated for 3 days with A-II increased aldosterone production by 10-fold. A-II stimulation of aldosterone production occurred rapidly (within 30 min) and in a dose-dependent manner. In addition, A-II enhanced the activity of P450c18, the enzyme responsible for conversion of corticosterone to aldosterone. A-II also suppressed ACTH-promoted cortisol production, while increasing ACTH-stimulated release of aldosterone. It appears that these effects of chronic treatment with A-II were mediated through an A-II type 1 (AT(1)) receptor since the AT(1) receptor antagonist, Dup753, blocked aldosterone production and the increased P450c18 activity. Receptor binding studies suggest that FBA cells possess approx. 110,000 AT(1) binding sites/cell with K(d) = 1.8 × 10(-9) M. Via AT(1) receptors, A-II was able to stimulate both inositol phosphates and cAMP production. The stimulation of cAMP production, however, was much less than seen following ACTH treatment. These data give support to the hypothesis that A-II is involved in the differentiation of fetal adrenal cells into glomerulosa cells. This process appears to be mediated through regulation of steroid-metabolizing enzyme expression and the activation of steroid production.