Regulation of 3 beta-hydroxysteroid dehydrogenase expression in human adrenocortical H295R cells

Previous studies of the effects of angiotensin II (All), alone or in combination with activators of the protein kinase. A signalling pathway, have yielded inconsistent findings on the expression of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD and 17 alpha-hydroxylase cytochrome P450 (P450c17) as well as the corresponding responses on steroid secretory products in human adrenocortical cells. We have used the human adrenocortical carcinoma H295R cell further to evaluate this question, as well as to determine the role of protein kinase C in each of these responses to All. Treatment with All alone resulted in a marked increase in aldosterone secretion and a significant increase in cortisol secretion (1-8-fold). The increased formation of 17-hydroxysteroids was accompanied by an increased level of P450c17 mRNA and activity. Increases in 3 beta-HSD expression were also seen at the level of mRNA and to a lesser extent, at the level of activity. Because of the comparatively low basal 17 alpha-hydroxylase and high basal 3 beta-HSD activities of H295R cells, however, the overall effect of All treatment was actually a rise in the 17 alpha-hydroxylase/3 beta-HSD activity ratio, so resulting in increased formation of 17 alpha-hydroxysteroids such as cortisol. While treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) reproduced the effect of All on 3 beta-HSD expression, TPA failed to reproduce the effects of All on P450c17 because it caused a marked decrease in P450c17 expression. Thus the stimulatory effect of All on P450c17 expression, unlike that on 3 beta-HSD expression, was not mediated by protein kinase C but, like the action of K, was probably mediated via the Ca2+ signalling pathway. Treatment with forskolin resulted in a dramatic increase in both cortisol and dehydroepiandrosterone (DHEA) secretion together with increases in expression of 3 beta-HSD and P450c17 as measured at the level of mRNA and activity. Consistent with the increase in 17 alpha-hydroxysteroid formation, the effect on P450c17 expression was greater than that on 3 beta-HSD at the level of activity, so a larger 17 alpha-hydroxylase/3 beta-HSD activity ratio was achieved. Cotreatment with forskolin and All, however, resulted in a dose-dependent reduction in cortisol and DHEA secretion concomitant with a marked attenuation of 3 beta-HSD and P450c17 expression. While forskolin-induced expression of 3 beta-HSD was not further increased at the level of mRNA by cotreatment with All, additivity was observed as the level of activity changed. Thus All cotreatment resulted in a marked reduction in the forskolin-induced increase in the 17 alpha-hydroxylase/3 beta-HSD activity ratio, and so 17 alpha-hydroxysteroid synthesis was attenuated. The effect of All cotreatment on changes in forskolin-induced 3 beta-HSD activity was blocked by the All type 1 (AT1) antagonist DuP753 (Losartan), confirming the involvement of the AT1 receptor-linked phospholipase C in activating protein kinase C.

Intraovarian immunolocalization of steroidogenic enzymes in a Hokkaido brown bear, Ursus arctos yesoensis during the mating season

Immunolocalization for four steroidogenic enzymes was performed on an ovary taken from a Hokkaido brown bear during the mating season. This specimen is considered to be in the follicular phase because of the presence of large follicles. In large follicles, cholesterol side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) were immunolocalized in theca interna cells and granulosa cells. 17 alpha-hydroxylase/C17-C20 lyase cytochrome P450 (P450c 17) was immunolocalized in theca interna cells but not in granulosa cells. Aromatase cytochrome P450 (P450arom) was immunolocalized only in granulosa cells. In medium follicles, however, P450scc and 3 beta HSD were immunolocalized only in theca interna cells, and the immunoreactivity of P450arom was detected in neither theca interna cells nor granulosa cells. Immunoreactivities of P450scc, 3 beta HSD and P450c 17 but not P450arom were detected in interstitial cells. This study suggests that estrogen biosynthesis takes place through interrelation between theca cells and granulosa cells and is explained by the so-called two-cell mechanism. Furthermore, the granulosa cells in large follicles have the capability for pregnenolone and progesterone biosynthesis, and the interstitial cell in the bear ovary is also a steroidogenic site.

Differential control of 17 alpha-hydroxylase and 3 beta-hydroxysteroid dehydrogenase expression in human adrenocortical H295R cells

Previous studies of human adrenocortical cells have given inconsistent findings concerning the effects of angiotensin II (AII) alone or in combination with activators of the protein kinase A-signaling pathway on expression of cholesterol side-chain cleavage cytochrome P450 (P450scc), 17 alpha-hydroxylase cytochrome P450 (P450c17), and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), as well as the corresponding effects on adrenocortical cell steroid secretory products. We have used the human adrenocortical carcinoma H295R cell to evaluate further this question and determine the role of protein kinase C in each of these responses to AII. Treatment with AII alone (10 nmol/L, 48 h) resulted in a significant increase in cortisol production (1.8-fold), as well as a much greater effect on aldosterone production. This increased formation of 17 alpha-hydroxysteroids was accompanied by increased expression of P450c17 as determined at the level of messenger RNA (mRNA) and enzyme activity. Similar increases in expression of P450scc were observed at the level of mRNA. Increases in 3 beta-HSD expression were also seen at the level of mRNA and, to a lesser extent, at the level of enzyme activity. Because of the comparatively low basal 17 alpha-hydroxylase and high basal 3 beta-HSD activity of H295R cells, however, the overall effect of AII treatment was actually a rise in the 17 alpha-hydroxylase/3 beta-HSD activity ratio, resulting in increased formation of 17 alpha-hydroxysteroids such as cortisol. Whereas treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) reproduced the effect of AII on 3 beta-HSD expression, TPA failed to reproduce the effects of AII on P450c17 and P450scc and even resulted in a marked decrease in expression of P450c17. Thus, the stimulatory effect of AII alone on P450c17 expression was not mediated via protein kinase C but, like the action of K+, was probably mediated via the Ca(2+)-signaling pathway. Treatment with forskolin (10 mumol/L, 48 h) resulted in a dramatic increase in both cortisol and dehydroepiandrosterone production together with increases in expression of P450c17, P450scc, and 3 beta-HSD as measured at the level of mRNA and activity. Consistent with the increase in 17 alpha-hydroxysteroid formation, the effect on 17 alpha-hydroxylase expression was greater than that on 3 beta-HSD at the level of enzyme activity, so a larger 17 alpha-hydroxylase/3 beta-HSD activity ratio was achieved. Cotreatment with forskolin and AII, however, resulted in a dose-dependent reduction in cortisol and DHEA production concomitant with a marked attenuation of P450scc and P450c17 expression. Although forskolin-induced expression of 3 beta-HSD was not further increased at the level of mRNA by cotreatment with AII, additivity was observed at the level of changes in enzyme activity. Thus, AII cotreatment resulted in a marked reduction of the forskolin-induced increase in 17 alpha-hydroxylase/3 beta-HSD activity ratio, and so, 17 alpha-hydroxysteroid synthesis was attenuated. These effects of AII cotreatment on expression of P450c17 and P450scc were reproduced by cotreatment with TPA (10 nmol/L), suggesting the involvement of protein kinase C in these attenuative responses. Furthermore, the effect of AII cotreatment on changes in forskolin-induced 17 alpha-hydroxylase and 3 beta-HSD activities were blocked by the AII Type 1 (AT1) receptor antagonist DuP753 (Losartan), confirming the involvement of an AT1 receptor-linked phospholipase C in activating protein kinase C.

Regulation of 11 beta-hydroxysteroid dehydrogenase type 2 activity and mRNA in human choriocarcinoma cells

The type 2 isoform of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD2), which catalyzes the conversion of cortisol to hormonally inactive cortisone in man, is principally expressed in the placenta and mineralocorticoid target tissues, kidney and colon. To date, few studies have addressed the regulation of this novel 11 beta-HSD2 isoform. We have characterized the nature and regulation of the 11 beta-HSD activity expressed in a human cytotrophoblastic cell line, the JEG-3 choriocarcinoma cell. The 11 beta-HSD activity in JEG-3 cell homogenates required NAD+ as cofactor with NADP+ ineffective and demonstrated a high affinity for cortisol (apparent Km 31 nM). Incubation of JEG-3 cells with forskolin and dibutyryl cyclic AMP increased 11 beta-HSD2 activity several-fold in a time-dependent manner, while treatment with phorbol ester had little, if any, effect on 11 beta-HSD2 activity. Northern blot analysis of RNA isolated from JEG-3 cells after these treatments demonstrated a marked increase in a 1.9 kb 11 beta-HSD2 mRNA species in cells treated with forskolin for 24 h. We conclude that 11 beta-HSD2 is regulated by activation of the protein kinase A pathway, but not the protein kinase C pathway in human choriocarcinoma cells, and that this regulation occurs at a pretranslational level. JEG-3 cells provide an excellent model for further studies on the regulation of 11 beta-HSD2 gene expression in human trophoblast tissue.

The hamster adrenal cytochrome P450C11 has equipotent 11beta-hydroxylase and 19-hydroxylase activities, but no aldosterone synthase activity

We have isolated a hamster adrenal P45OC11 cDNA which shared 90 and 84% homology, respectively, with the nucleotide sequence and the amino acid sequence of the hamster adrenal P450aldo. Both P450C11 and P450aldo cDNA coding sequences were inserted in the plasmid pBluescript SK, transcribed and then translated using a rabbit reticulocyte system in the presence of [35S]methionine. The reaction products were immunoprecipitated with an anti-bovine P450C11 antibody for P450C11 and with an anti-hamster P450aldo for P450aldo. Immunoprecipitated proteins were analyzed by polyacrylamide gel electrophoresis. A single 35S-labeled protein band was detected for P450C11 and for P450aldo, respectively. P450C11 and P450aldo cDNAs were then both inserted into the expression vector pCMV5 containing a viral sequence specific for the attachment of ribosomes to mRNA. These constructions were transfected in COS-1 cells. 24 h after transfection, the presence of P450C11 and P450aldo mRNAs was determined by Northern blot analysis. In a time study experiment we found that P450C11 transformed the labeled-steroid into [14C]corticosterone, [14C]19-OH-deoxycorticosterone and [14C]18-OH-deoxycorticosterone in ratios of 1:1.11:0.07, after 2 h of incubation; no [14C]aldosterone could be detected. Cells transfected with plasmids harboring the P450aldo cDNA transformed [14C]deoxycorticosterone to [14C]corticosterone, [14C]aldosterone, [14C]18-OH-corticosterone, [14C]18-OH-deoxycorticosterone, [14C]19-OH-deoxycorticosterone and [14C]11-dehydrocorticosterone in ratios of 1:0.25:0.45:0.04:0.04:0.04 after 12 h of incubation. These results indicate that one P450 catalyzes the ultimate step of glucocorticoid formation and a separate P450 is involved in the final steps of aldosterone formation in hamster adrenals. The capacity of the hamster adrenal P450C11 to hydroxylate at positions 11beta and 19 in nearly equal ratio makes this animal an excellent model to study the mechanism of synthesis and inhibition of 19-OH-deoxycorticosterone, the precursor of 19-nor-deoxycorticosterone, a very potent mineralocorticoid involved in the development of essential hypertension.

Adrenal androgen biosynthesis with special attention to P450c17

In vitro studies of human adrenal androgen synthesis are limited because of the difficulties in obtaining adrenals. We describe the use of the human adrenocortical tumor H295 cell line as a model to evaluate mechanisms controlling C19-steroid production. The cells were characterized with regard to responsiveness to a variety of agents as measured by steroid secretion and induction of 17 alpha-hydroxylase cytochrome P450 (P450c17) expression, a key enzyme in C19-steroid production. Forskolin and dibutyryl cAMP, which were more effective than ACTH, enhanced the production of DHEA and androstenedione over a 48-hour treatment period. Agents that act by increasing intracellular calcium (angiotensin II and K+ ions) as well as protein kinase A pathway activators (ACTH, forskolin, and dibutyryl cAMP) individually increased the mRNA levels and activity of P450c17. In addition, angiotensin II but not K+ ions attenuated the increased expression promoted by the kinase A agonists. Thus, the complexity of human adrenal P450c17 expression through multiple signaling pathways may contribute importantly to the diverse patterns of human adrenocortical steroidogenesis.

Ca(2+)-regulated expression of steroid hydroxylases in H295R human adrenocortical cells

Although changes in the expression of key steroidogenic enzymes such as cytochrome P450 cholesterol side-chain cleavage, 17 alpha-hydroxylase (P450c17), aldosterone synthase, and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in the human adrenal cortex are known to be controlled by factors activating the protein kinase A or protein kinase C signaling pathways, little is known concerning the effects of increased intracellular Ca2+. In this study we describe the effects of K+, an agent known to increase intracellular Ca2+ through the opening of voltage-sensitive Ca2+ channels, on steroidogenesis in H295R human adrenocortical cells and corresponding changes in expression of these vital steroidogenic enzymes. Treatment of cells for 48 h with K+ (14 mM) resulted in an increase in aldosterone (3.5-fold) as well as the 17 alpha-hydroxylated steroids cortisol (2.9-fold) and dehydroepiandrosterone (DHEA; 3.7-fold). This action of K+ was accompanied by a dose-dependent (P < 0.05 at 6 mM K+ or above) and time-dependent (P < 0.05 at 24 h and beyond) increase in expression of P450c17 and, to a lesser extent, cytochrome P450 cholesterol side-chain cleavage messenger RNA (mRNA). Treatment with K+ also caused a time-dependent increase in aldosterone synthase mRNA levels, which were detectable by 12 h. Treatment with K+, however, was without effect on 3 beta HSD expression. These effects contrast with those of (Bu)2cAMP, which stimulated a greater increase in cortisol and DHEA secretion as well as P450c17 expression. The effects of K+ treatment also differ from those of AII, which promoted a greater aldosterone secretory response (5.7-fold), but a lesser effect on DHEA secretion (2.2-fold) and P450c17 expression. Although AII and TPA (known activators of protein kinase C) as well as forskolin and (Bu)2cAMP (known activators of protein kinase A) increased the expression of 3 beta HSD mRNA, K+ treatment was without effect, suggesting that elevation of [Ca2+]i in response to K+ did not activate the protein kinase C or protein kinase A signaling pathways. Furthermore, the effects of K+ on steroid secretion and 17 alpha-hydroxylase activity were reproduced by the voltage-sensitive Ca2+ channel activator BAYK 8644, and increases in P450c17 mRNA in response to K+ were reversed by the Ca2+ channel antagonist, nifedipine. We conclude that K+ can modulate the expression of key steroidogenic enzymes in H295R cells through the Ca2+ signaling pathway without involvement of the protein kinase A or protein kinase C pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Type 2 11 beta-hydroxysteroid dehydrogenase in foetal and adult life

Two isoforms of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) catalyse the interconversion of active cortisol to inactive cortisone; 11 beta-HSD1 is a low affinity, NADP(H)-dependent dehydrogenase/oxo-reductase, and 11 beta-HSD2 a high affinity, NAD-dependent dehydrogenase. Because of the importance of 11 beta-HSD in regulating corticosteroid hormone action, we have analysed the distribution of the 11 beta-HSD isoforms in human adult and foetal tissues (including placenta), and, in addition have performed a series of substrate specificity studies on the novel, kidney 11 beta-HSD2 isoform. Using an RT-PCR approach, we failed to detect 11 beta-HSD1 mRNA in any human mid-gestational foetal tissues. In contrast 11 beta-HSD2 mRNA was present in foetal lung, adrenal, colon and kidney. In adult tissues 11 beta-HSD2 gene expression was confined to the mineralocorticoid target tissues, kidney and colon, whilst 11 beta-HSD1 was expressed predominantly in glucocorticoid target tissues, liver, lung, pituitary and cerebellum. In human kidney homogenates, 11-hydroxylated progesterone derivatives, glycyrrhetinic acid, corticosterone and the "end products" cortisone and 11-dehydrocorticosterone were potent inhibitors of the NAD-dependent conversion of cortisol to cortisone. Finally high levels of 11 beta-HSD2 mRNA and activity were observed in term placentae, which correlated positively with foetal weight. The tissue-specific distribution of the 11 beta-HSD isoforms is in keeping with their differential roles, 11 beta-HSD1 regulating glucocorticoid hormone action and 11 beta-HSD2 mineralocorticoid hormone action. The correlation of 11 beta-HSD2 activity in the placenta with foetal weight suggests, in addition, a crucial role for this enzyme in foetal development, possibly in mediating ontogeny of the foetal hypothalamo-pituitary-adrenal axis.

Expression and characterization of isoforms of 3 beta-hydroxysteroid dehydrogenase/delta 5-->4-isomerase in the hamster

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-->4-isomerase (3 beta-HSD) is essential for the production of all classes of steroid hormones. Multiple isozymes of this enzyme have been demonstrated in the kidney and liver of both the rat and the mouse, although the function of the enzyme in these tissues is unknown. We have characterized three isozymes of 3 beta-HSD expressed in various tissues of the hamster. Both western and northern blot analyses demonstrated very high levels of 3 beta-HSD in the adrenal, kidney and male liver. Conversely, there were extremely low levels of enzyme expression in the female liver. cDNA libraries prepared from RNA isolated from hamster adrenal, kidney and liver were screened with a full-length cDNA encoding human type 1 3 beta-HSD. Separate cDNAs encoding three isoforms of 3 beta-HSD were isolated from these libraries. To examine the properties of the isoforms, the cDNAs were ligated into expression vectors for over-expression in 293 human fetal kidney cells. The type 1 isoform, isolated from an adrenal cDNA library, was identified as a high-affinity 3 beta-hydroxysteroid dehydrogenase. A separate isoform, designated type 2, was isolated from the kidney, and this was also a high-affinity dehydrogenase/isomerase. Two cDNAs were isolated from the liver, one identical in sequence to type 2 of the kidney, and a distinct cDNA encoding an isoform designated type 3. The type 3 3 beta-HSD possessed no steroid dehydrogenase activity but was found to function as a 3-ketosteroid reductase. Thus male hamster liver expresses a high-affinity 3 beta-HSD (type 2) and a 3-ketosteroid reductase (type 3), whereas the kidney of both sexes express the type 2 3 beta-HSD isoform. These differ from the type 1 3 beta-HSD expressed in the adrenal cortex.

Potassium negatively regulates angiotensin II type 1 receptor expression in human adrenocortical H295R cells

We have previously shown that the human adrenocortical H295R cell line expresses the type 1 angiotensin II receptor (AT1-R) and that expression of this receptor is downregulated at the level of mRNA by forskolin or dibutyryl-cAMP as well as by angiotensin II (Ang II). In this study we examine the effects of K+ on both AT1-R mRNA and receptors, as monitored through 125I-Ang II binding in the presence of PD 123319. After treatment with a maximal stimulatory steroidogenic dose of K+ (14 mmol/L), H295R cells showed an increase in cytosolic free Ca2+ from 113 to 212 nmol/L. Unlike the effects of Ang II, this increase could be abolished by pretreatment with the Ca2+ channel antagonist nifedipine (1 mumol/L). AT1-R mRNA levels also fell in response to elevated extracellular K+ in a dose-dependent (Kd, 9 mmol/L; maximal fall in message at 12 mmol/L) and time-dependent (maximum 50% at 12 hours) manner. The change in AT1-R mRNA level was less rapid than that in response to activation of phosphoinositidase C by Ang II or adenylyl cyclase by forskolin or by dibutyryl-cAMP. Unlike the action of Ang II but similar to the action of forskolin or dibutyryl-cAMP, the action of K+ was sustained. Changes in mRNA level in response to treatment with K+, Ang II, or dibutyryl-cAMP were also paralleled by changes in 125I-Ang II binding in each case.(ABSTRACT TRUNCATED AT 250 WORDS)

Absence of molecular defect in the type II 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) gene in premature pubarche children and hirsute female patients with moderately decreased adrenal 3 beta-HSD activity

To date the molecular basis and hormonal criteria for inherited mild late-onset 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) deficiency congenital adrenal hyperplasia (CAH) have not been defined. We have thus investigated the presence or absence of mutation in the type II 3 beta-HSD gene encoding adrenal/gonadal 3 beta-HSD in each of five premature pubarche children and hirsute female patients manifesting moderately decreased adrenal 3 beta-HSD activity. ACTH-stimulated hormonal levels in all patients compared with mean levels in pubertal stage-matched normal subjects were between 2.5 and 6.5 SD for 17-hydroxypregnenolone levels, and between 2.5 and 7 SD for dehydroepiandrosterone levels in all except one patient. 17-Hydroxypregnenolone to cortisol ratios were between 2.5 and 4.3 SD, and dehydroepiandrosterone to androstenedione ratios were between 3 and 8.6 SD. The type II 3 beta-HSD gene regions of a putative promoter, exons I, II, III, and IV, and exon-intron boundaries in all subjects were amplified by polymerase chain reaction and then sequenced. All patients had normal sequences of the type II 3 beta-HSD gene in both alleles. Three female patients heterozygotic for severe 3 beta-HSD deficiency CAH with one allele mutation of the gene demonstrated normal ACTH-stimulated hormone profiles. These data indicate that moderately decreased adrenal 3 beta-HSD activity resulting in modestly increased delta 5 precursor steroid levels and delta 5 to delta 4 steroid ratios in premature pubarche and hirsute patients is not caused by a mutation in the type II 3 beta-HSD gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of human 11 beta-hydroxysteroid dehydrogenase isoforms using reverse-transcriptase-polymerase chain reaction and localization of the type 2 isoform to renal collecting ducts

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD), responsible for the interconversion of hormonally active cortisol to inactive cortisone, dictates specificity for the mineralocorticoid receptor (MR) in the distal nephron and colon. Two isoforms of human 11 beta-HSD have been cloned, an NADP(H)-dependent (type 1) dehydrogenase/oxo-reductase enzyme, and a high-affinity NAD-dependent (type 2) unidirectional dehydrogenase. Using the reverse-transcriptase polymerase chain reaction (RT-PCR) amplification of RNA extracted from human adult tissues, type 1 11 beta-HSD mRNA was found in decidua, placenta, liver, lung, spleen, kidney medulla, cerebellum and pituitary, but was absent in kidney cortex, sigmoid and rectal colon, salivary gland and thyroid. In contrast, type 2 11 beta-HSD mRNA was found only in placenta and in the classical mineralocorticoid target tissues, kidney cortex, kidney medulla, sigmoid and rectal colon, salivary gland, and colonic epithelial cell lines (AAC1 and RGC28). In situ hybridization studies of renal cortex, cortico-medullary junction and medulla using a 35S-labeled antisense cRNA probe for type 2 human 11 beta-HSD, revealed specific localization of type 2 11 beta-HSD mRNA expression exclusively to renal cortical and medullary collecting ducts. Type 1 and type 2 isoforms of human 11 beta-HSD are expressed in a distinct tissue-specific fashion, in keeping with the proposed differences in their physiological roles. Type 2 11 beta-HSD is found predominantly in mineralocorticoid target tissues where it serves to protect the MR in an autocrine fashion.

Type 2 11 beta-hydroxysteroid dehydrogenase messenger ribonucleic acid and activity in human placenta and fetal membranes: its relationship to birth weight and putative role in fetal adrenal steroidogenesis

Two isoforms of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) have been described which catalyze the interconversion of cortisol (F) to cortisone (E). 11 beta HSD activity has previously been reported in placenta and fetal membranes, where its role may be to protect the developing fetus from glucocorticoid excess. Furthermore, in the rat, an association between placental 11 beta HSD activity and the subsequent development of hypertension in the offspring has been reported. We have characterized the isoforms of 11 beta HSD in human fetal membranes and dissected placental tissue at term and investigated the relationship between placental 11 beta HSD activity and fetal and placental weights. 11 beta HSD activity studies in the presence of 0.1 mumol/L F and NAD (indicative of type 2 isoform activity) revealed high levels of activity in trophoblast dissected free of vessels (561 +/- 87 pmol E/h.mg protein; n = 4) > undissected placenta > cotyledenous vessels dissected away from trophoblast > placental and reflected amnion. In contrast, in the presence of 2.5 mumol/L F and NADP (indicative of type 1 isoform activity), only decidua and chorion demonstrated significant levels of 11 beta HSD activity. Type 1 11 beta HSD activity in chorion was probably due to decidual contamination, in that it was absent in decidua-free fused chorion obtained from a twin pregnancy. In keeping with these data, type 1 11 beta HSD messenger ribonucleic acid (1.5 kilobases) was detected in decidua, but in no other tissue, and high levels of type 2 11 beta HSD messenger ribonucleic acid (1.9 kilobases) were found in undissected placenta and trophoblast. In 27 term placentas, 11 beta HSD activity varied from 194-448 pmol E/h.mg protein. There was a weak, but significant, positive correlation between term placental 11 beta HSD activity and fetal weight (r = 0.408; P = 0.034), but no correlation with placental weight. Thus, in man, the reported association of a small fetus and a large placenta predisposing to adult hypertension cannot be explained on the basis of defective 11 beta HSD activity. However, the placenta offers an immense reservoir for F clearance (1.73-7.95 mumol/min.placenta) and may be a principal factor driving fetal ACTH secretion and, hence, fetal adrenal steroidogenesis.

Immunohistochemical evaluation of the cellular localization and ontogeny of 3 beta-hydroxysteroid dehydrogenase/delta 5-4 isomerase in the human fetal adrenal gland

The enzyme, 3 beta-hydroxysteroid dehydrogenase/delta 5-4 isomerase (3 beta-HSD) is an essential element in the biosynthetic pathway for potent adrenal steroid hormones that appear to regulate maturation of many tissues in utero and are critical for homeostasis after birth. The results of prior studies are suggestive that 3 beta-HSD activity in the human fetal adrenal (HFA) is very low and restricted to the outer zone of cortical cells, the neocortex (NC), during mid-gestation. Near the time of birth, however, there must be enhanced expression of this enzyme to allow for adaptation to extrauterine life. In the present study, we sought to characterize, by use of immunohistochemical methods, the cellular localization and developmental changes of 3 beta-HSD in the HFA during the interval of 11-41 wks gestation. Early in gestation, 11-15 wks, we noted considerable 3 beta-HSD in NC and in occasional fetal zone (FZ) cells as well. Thereafter until 24-25 wks, 3 beta-HSD was very low in NC cells and virtually absent from the FZ. Throughout the third trimester, the outer 1/2-2/3 of the NC was increasingly immunostained and clusters of immunoreactive cells also appeared near the central medullary vein of the adrenal. The NC cells and those located in the cortical cuff region that expressed 3 beta-HSD resembled zona glomerulosa cells. Among many other fetal tissues studied, only testicular Leydig cells (18,19 wks) and hilar cells of the ovary (26 wks) were found to contain 3 beta-HSD in quantities sufficient to be detected by immunohistochemistry. These results are suggestive of a heretofore undocumented stimulus to 3 beta-HSD in the HFA in early gestation followed by a suppression of the adrenal concentration of this enzyme during mid-gestation. High levels of 3 beta-HSD in early development may facilitate cortisol production, which is believed to play a role in differentiation of the medullary precursors during this developmental period. The control of adrenal 3 beta-HSD during human fetal development may be more complex than initially envisioned and requires further study.

Hormonal regulation of angiotensin II type 1 receptor expression and AT1-R mRNA levels in human adrenocortical cells

Human adrenocortical H295R cells express AII receptors which are predominantly of the AT1 but not AT2 subclass. These receptors are functionally coupled to phosphoinositidase C in a manner similar to that seen in fetal human, sheep and bovine adrenocortical cells. Treatment of H295R cells with forskolin or dbcAMP to activate the protein kinase A pathway caused a rapid (maximal by 3 h) and sustained decrease in AT1-R mRNA levels which in turn preceded a time-dependent (maximal by 12 h) and dose-dependent loss of [125I]AII binding and phosphoinositidase C activation on subsequent AII challenge. Thus, both decreased AT1-R mRNA levels and functional receptor expression appear to parallel each other in response to activation of protein kinase A. Activation of the Ca2+/protein kinase C pathways by treatment with AII also caused a rapid (maximal by 3 h) and dose-dependent loss in AT1-R mRNA, but mRNA levels subsequently rose again, approaching control levels by 36 h. Treatment with AII for 48 h had little effect on either [125I]AII binding or the subsequent phosphoinositidase C response. The effect of AII, but not forskolin, was blocked by the presence of cycloheximide. The action of AII on AT1-R mRNA was probably mediated through both protein kinase C and Ca(2+)-sensitive protein kinases as the effect at 4 h was not completely reproduced by phorbol ester alone, but was fully reproduced by a combination of phorbol ester and Ca2+ ionophore. However, increased Ca2+ influx alone, due to treatment with BAYK8644 or elevated extracellular K+, also resulted in a decrease in AT1-R mRNA levels. Thus in the H295R cell, control of AT1-R expression appears to be complex, being achieved at least in part through control of the level of AT1-R mRNA by multiple independent signaling pathways including protein kinase A, protein kinase C and Ca2+.

Variation in the expression of human 3 beta-hydroxysteroid dehydrogenase

Polymorphic genetic variation shows that the genes for human 3 beta-hydroxysteroid dehydrogenases (3 beta-HSD) types I and II are closely linked. The type II mutations A82T, S100N and L173R are associated with male pseudohermaphroditism and A82T is associated, with variable penetrance, with female premature puberty. When expressed in vitro A82T showed less than 5% of normal activity and L173R showed a 30-50% reduction in activity. PCR experiments and direct genomic cloning show that there is a larger family of 3 beta-HSD sequences which require to be tested for expression. The phenomenon of epitopic heterogeneity of 3 beta-HSD is discussed and is now shown to apply to testicular Leydig cells as well as extrauterine trophoblast. RT-PCR analyses indicate that the phenomenon is most likely to be due to post-translational modification affecting the carboxytermini 3 beta-HSD types I and II. This phenomenon may reflect a further level at which enzyme activity is regulated.

Cortisol to cortisone: glucocorticoid to mineralocorticoid

11 beta-hydroxysteroid dehydrogenase (11 beta-HSD), by converting cortisol and corticosterone to hormonally inactive cortisone and 11-dehydrocorticosterone, respectively, is an important pre-receptor signaling pathway for the renal mineralocorticoid receptor (MR). This receptor has an equal affinity for the glucocorticoids, cortisol and corticosterone, and for the mineralocorticoid, aldosterone. In states of 11 beta-HSD deficiency such as the syndrome of apparent mineralocorticoid excess (AME) and licorice ingestion, cortisol acts as a potent mineralocorticoid. In addition to the established and cloned type I 11 beta-HSD, a second 11 beta-HSD isoform has been reported in rabbit kidney and human placenta. We have analyzed the kinetics of 11 beta-HSD activity in human kidney and compared it with the expressed human type I 11 beta-HSD cDNA. Microsomes were prepared from mid-gestational human fetal kidneys and incubated with various concentrations of cortisol (0.0125-10 microM) and NAD or NADP. Kinetic analysis revealed a high affinity (apparent Km 60 nM) isoform, the activity of which was exclusively NAD-dependent. No convincing NADP-dependent activity was seen. Similarly with cortisone as a substrate no 11-oxoreductase activity was evident. In contrast, when type I human 11 beta-HSD was ligated into the expression vector pcDNAI and transiently transfected into COS-I cells, low affinity (apparent Km 2.1 microM) NADP-dependent activity was seen. 11-Oxoreductase activity was also observed. The cloned type I human 11 beta-HSD encodes an enzyme with both low-affinity, NADP-dependent, dehydrogenase and 11-oxoreductase activities, but this activity is absent in human fetal kidney (and probably adult kidney).(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence of a steroidogenic enzyme gene dose effect on adrenal gene expression in hereditary rabbit congenital adrenal hyperplasia

We previously reported the gene deletion encoding cytochrome P-450 cholesterol side-chain cleavage enzyme (P-450SCC, resulting in complete elimination of the adrenal gene expression and causing congenital adrenal hyperplasia in the rabbit. Using the rabbit congenital adrenal hyperplasia model, we investigated the wild type (wt) P-450SCC gene dose effect on gene expression in three P-450SCC genotype animals [wt/wt, wt/mutant (mt), mt/mt] identified by Southern blot analysis. Northern blots using a rabbit P-450SCC cDNA probe revealed no detectable P-450SCC mRNA in individual adrenals of animals with congenital adrenal hyperplasia (mt/mt) and approximately half or slightly less than half the levels of the mRNA in the pooled adrenals of five heterozygous (wt/mt) newborn animals compared with the mRNA levels in the pooled adrenals of five homozygous normal (wt/wt) newborn animals. Identical P-450SCC mRNA levels were found individual adrenals of adult animals with regard to the P-450SCC genotype, although at a higher expression level than in the newborn animals of the same genotype. Control Northern blots using human CPY21-B cDNA and cytoplasmic actin cDNA probes confirmed the accuracy and integrity of RNA. Western immunoblotting using anti-ovine P-450SCC antibody revealed decreased P-450SCC protein in the adrenals of wt/mt animals at approximately half the level of the P-450SCC protein in the adrenals of the wt/wt animals. Baseline and ACTH-stimulated serum corticosterone (B) levels in vivo were similar between the age-matched wt/mt and wt/wt animals, whereas ACTH-stimulated B levels in adult animals were higher than those in the newborn animals irrespective of P-450SCC genotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Over-expression of human type I (placental) 3 beta-hydroxy-5-ene-steroid dehydrogenase/isomerase in insect cells infected with recombinant baculovirus

Human type I placental 3 beta-hydroxy-5-ene-steroid dehydrogenase/steroid 5-->4-ene-isomerase (3 beta-HSD/isomerase) synthesizes androstenedione from fetal dehydroepiandrosterone and progesterone from pregnenolone. The full length cDNA that encodes type I 3 beta-HSD/isomerase was inserted into the baculovirus, Autographa californica multiple nucleocapsid polyhedrosis virus, and expressed in Spodoptera fungiperda (Sf-9) insect cells. Western blots showed that the baculovirus-infected Sf-9 cells produced an immunoreactive protein that co-migrated with purified placental 3 beta-HSD/isomerase. Ultracentrifugation localized the expressed enzyme activities in all the membrane-associated organelles of the Sf-9 cell (nuclear, mitochondrial and microsomal). Kinetic studies showed that the expressed enzyme has 3 beta-HSD and isomerase activities. The Michaelis-Menton constant is very similar for the 3 beta-HSD substrate, 5 alpha-androstan-3 beta- ol-17-one, in the Sf-9 cell homogenate (Km = 17.9 microM) and placental microsomes (Km = 16.7 microM). The 3 beta-HSD activity (Vmax = 14.5 nmol/min/mg) is 1.6-fold higher in the Sf-9 cell homogenate compared to placental microsomes (Vmax = 9.1 nmol/min/mg). The Km values are almost identical for the isomerase substrate, 5-androstene-3,17-dione, in the Sf-9 cell homogenate (Km = 14.7 microM) and placental microsomes (Km = 14.4 microM). The specific isomerase activity is 1.5-fold higher in the Sf-9 cells (Vmax = 25.7 nmol/min/mg) relative to placenta (Vmax = 17.2 nmol/min/mg). These studies show that our recombinant baculovirus system over-expresses fully active enzyme that is kinetically identical to native 3 beta-HSD/isomerase in human placenta.

Ovarian 3 beta-hydroxysteroid dehydrogenase/delta 5-4-isomerase of rainbow trout: its cDNA cloning and properties of the enzyme expressed in a mammalian cell

A cDNA clone encoding 3 beta-hydroxysteroid dehydrogenase delta 5-4-isomerase (3 beta-HSD) was isolated from a cDNA library of rainbow trout ovarian thecal cells. Southern hybridization analysis of trout genomic DNA with the cDNA suggested the presence of a single gene encoding 3 beta-HSD in the rainbow trout showing a total genomic size of less than 4 kilobases (kb). The cDNA hybridized to a species of mRNA isolated from rainbow trout ovaries; the 1.4 kb transcripts were most abundant in trout ovaries during the later stages of oogenesis. The trout 3 beta-HSD expressed in non-steroidogenic monkey kidney tumor (COS-1) cells showed a unique enzymatic 3 beta-HSD activity. Dehydroepiandrosterone was a more favoral substrate of the trout 3 beta-HSD than 1- alpha-hydroxypregnenolone. Interestingly, the trout 3 beta-HSD expressed in COS-1 cells exhibited minimal ability to convert pregnenolone to progesterone.

Immunolocalization of steroidogenic enzymes P450scc, 3 beta HSD, P450c17 and P450arom in the corpus luteum of the Hokkaido brown bear (Ursus arctos yesoensis) in relation to delayed implantation

The objective was the immunocytochemical localization of steroidogenic enzymes in the corpus luteum of Hokkaido brown bears during the period of delayed implantation. Cholesterol side-chain cleavage cytochrome P450 (P450scc), 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), 17 alpha-hydroxylase cytochrome P450 (P450c17) and aromatase cytochrome P450 (P450arom) were localized as biosynthetic sites of pregnenolone, progesterone, androgens, and oestrogens, respectively. Ovaries containing corpora lutea were obtained from three mature bears during the expected delayed implantation period and ovarian sections were immunostained by the avidin-biotin-peroxidase complex method using polyclonal antibodies generated against steroidogenic enzymes of mammalian origin. P450scc and 3 beta HSD were localized in all luteal cells, whereas P450c17 (0.4-5.1% of 1000 cells) and P450arom (7.1-11.2% of 1000 cells) were localized in only a few luteal cells. These data suggest that luteal cells contain steroidogenic enzymes required for progesterone synthesis but also have a minimum capability for synthesizing androgen and oestrogen during the delayed implantation period in Hokkaido brown bears.

Human kidney 11 beta-hydroxysteroid dehydrogenase is a high affinity nicotinamide adenine dinucleotide-dependent enzyme and differs from the cloned type I isoform

11 beta-Hydroxysteroid dehydrogenase (11 beta HSD) catalyzes the conversion of cortisol to cortisone and plays an important role in the mammalian kidney in regulating cortisol access to the mineralocorticoid receptor. 11 beta HSD-deficient states, such as the syndrome of apparent mineralocorticoid excess (AME), and licorice ingestion result in hypertension in which cortisol acts as a mineralocorticoid. A gene and complementary DNA sequence encoding type I human 11 beta HSD have been described, but this gene is normal in patients with AME. Separate 11 beta HSD isoforms have been described in rat and rabbit kidney, but 11 beta HSD has not been characterized in human kidney. Kinetic analysis of 11 beta HSD activity in human fetal kidney microsomes revealed only a high affinity isoform (apparent Km, 60 nmol/L for cortisol, 13 nmol/L for corticosterone), the activity of which was exclusively nicotinamide adenine dinucleotide (NAD) dependent. No 11-oxo-reductase activity was seen in either renal homogenates or microsomes. 11 beta-Dehydrogenase activity was inhibited by glycyrrhetinic acid (the active ingredient in licorice) in a competitive fashion, with a Ki of 8.7 nmol/L. This 11 beta HSD isoform was clearly distinct from the type I h11 beta HSD enzyme, in that COS-1 cells transfected with type I h11 beta HSD complementary DNA expressed a low affinity (apparent Km, 2.13 mumol/L) isoform, the activity of which was NAD phosphate dependent. 11-Oxo-reductase activity was present in intact transfected cells (apparent Km for cortisone, 0.36 mumol/L), but not in cell lysates. In contrast to the cloned, low affinity, type I h11 beta HSD enzyme, human kidney contains a high affinity NAD-dependent 11 beta HSD isoform. It seems probable that this isoform is responsible for protecting the renal mineralocorticoid receptor from glucocorticoid excess, and a defect in its activity may explain AME.

Regulation of type 1 angiotensin II receptor messenger ribonucleic acid expression in human adrenocortical carcinoma H295 cells

We have studied the hormonal regulation of type 1 angiotensin-II receptor (AT1-R) mRNA expression and [125I]angiotensin-II ([125I]AII) binding in human adrenocortical carcinoma H295 cells, which exhibit predominantly AT1-subtype receptors. Activation of the cAMP signaling pathway with forskolin or (Bu)2cAMP caused a rapid decrease in AT1-R mRNA levels (decreased 65% within 3 h). This preceded a time-dependent (maximal, 70% within 12 h) and dose-dependent (IC50, 2 microM forskolin) loss of [125I]AII binding together with decreased phosphoinositidase-C activation (72% decrease) on subsequent AII challenge. Thus, the decreases in AT1-R mRNA levels and functional receptor expression parallel each other in response to activation of protein kinase-A. AII treatment also caused a rapid loss in AT1-R mRNA (maximal, 80% decrease within 3 h), but 48-h treatment caused both [125I]AII binding and the subsequent phosphoinositidase-C response to decrease by only 6% (P < 0.05) and 22% (P < 0.05), respectively. The effect of AII on AT1-R mRNA levels was fully reproduced by the combination of calcium ionophore (A23187) and phorbol ester (12-O-tetradecanoylphorbol 13-acetate), suggesting that AII action was through protein kinase-C and possibly other Ca(2+)-sensitive protein kinases. The effect of AII, but not forskolin, was reversed by treatment in the presence of cycloheximide. In conclusion, control of AT1-R expression is differentially regulated by adenylate cyclase and phosphoinositidase-C signaling pathways, which act at multiple levels in human adrenocortical cells.

The presence of two cytochrome P450 aldosterone synthase mRNAs in the hamster adrenal

We isolated a cDNA from a hamster adrenal cDNA library which was similar in sequence to those of the mouse and rat P450c18 cDNAs. The hamster P450c18 cDNA, however, was shorter than the rat and mouse P450c18 cDNAs at its 5'-end and the peptide leader sequence was absent. From a hamster genomic library we isolated and sequenced the first seven exons and a 5'-flanking region of the first P450c18 gene exon. With this information we were able to generate a P450c18 cDNA containing the peptide leader sequence using the polymerase chain reaction. Northern analyses were performed on adrenals from hamsters maintained on a low sodium diet for 0, 4, 7 and 10 days using a 32P-labeled sequence specific to P450c18; two mRNA bands were found at 2 and 3.4 kb. The intensity of both bands was increased about 3- to 5-fold under sodium restriction compared to controls. A distinct mRNA band of 2.3 kb hybridized with an oligonucleotide specific to P450(11) beta and its intensity did not change following low sodium intake. Immunoblotting analyses were performed using an antibovine adrenal P450(11) beta antibody that does not discriminate between P450(11) beta and P450c18 proteins. Three bands were detected at 52, 48 and 45 kDa in homogenate preparations of entire glands. Furthermore, the 45 kDa protein band was present in homogenates of the zona glomerulosa and absent in homogenates of the zone fasciculata-reticularis. In conclusion, these results show that the hamster adrenals express P450c18 as do mouse, rat and human adrenal glands. Furthermore, two P450c18 mRNAs, which are inducible by a low sodium intake, are present in the hamster adrenal vs one for the rat. The physiological role of these two hamster adrenal mRNA species remains to be elucidated.