A shared promoter element regulates the expression of three steroidogenic enzymes

The adrenal cortex of the mouse coordinately expresses three cytochrome P450 enzymes that are required for the biosynthesis of corticosteroids: cholesterol side-chain cleavage enzyme (SCC), steroid 21-hydroxylase (21-OHase), and steroid 11 beta-hydroxylase (11 beta-OHase). Within their 5'-flanking regions, we previously identified six elements containing variations of an AGGTC motif that regulated expression in mouse Y1 adrenocortical cells: 21-OHase elements at -210, -140, and -65; SCC elements at -70 and -40; and an 11 beta-OHase element at -310. We demonstrate here that all six elements interact with the same, or closely related, DNA-binding protein(s). First, these elements all formed complexes of similar mobility in gel shift assays, suggesting that they interacted with protein(s) of similar size. Additional larger complexes were seen with those probes containing exact AGGTCA sequences. Second, competition experiments confirmed that the factor(s) interacting with different elements had closely related or identical recognition specificities. Finally, indistinguishable profiles of shift activities were seen upon fractionation of nuclear proteins over sequential chromatographic columns. Collectively, these results suggest that related elements interact with a shared protein to regulate three essential steroidogenic enzymes. An AGGTCA sequence motif comprises the response element for several members of the nuclear hormone receptor family. Oligonucleotide competitions and specific effects of antisera in gel shift assays implicated chicken ovalbumin upstream promoter-transcription factor in the formation of the larger complexes seen with the elements containing exact AGGTCA sequences. Therefore, this member of the nuclear hormone receptor family also may regulate the expression of the adrenal steroidogenic enzymes.

Multiple mechanisms for regulation of 3 beta-hydroxysteroid dehydrogenase/delta 5----delta 4-isomerase, 17 alpha-hydroxylase/C17-20 lyase cytochrome P450, and cholesterol side-chain cleavage cytochrome P450 messenger ribonucleic acid levels in primary cultures of mouse Leydig cells

The regulation of mRNA levels for delta 5-3 beta-hydroxysteroid dehydrogenase/delta 5----delta 4-isomerase (3 beta HSD), 17 alpha-hydroxylase/C17-20 lyase cytochrome P450 (P450(17 alpha] and cholesterol side-chain cleavage cytochrome P450 (P450scc) was studied in primary cultures of mouse Leydig cells. Treatment of Leydig cells with 8-bromo-cAMP (cAMP) was essential for expression of P450(17 alpha) mRNA, but not for 3 beta HSD. Treatment with cAMP caused a decrease in basal levels of 3 beta HSD mRNA. The addition of aminoglutethimide (AG), an inhibitor of cholesterol metabolism, to the cAMP-treated cultures resulted in increased expression of both 3 beta HSD and P450(17 alpha) mRNA levels. The addition of testosterone or the androgen agonist mibolerone to cAMP- plus AG-treated cultures reduced 3 beta HSD and P450(17 alpha) mRNA to levels comparable to those observed when cells were treated with cAMP only. The glucocorticoid dexamethasone reduced both basal and cAMP- plus AG-induced increases in 3 beta HSD mRNA, but not in P450(17 alpha) mRNA. Estradiol at a concentration of 1 microM had no effect on cAMP- plus AG-induced 3 beta HSD or P450(17 alpha) mRNA levels. The role of protein synthesis in mediating the cAMP induction of 3 beta HSD, P450(17 alpha), and P450scc was investigated. The addition of cycloheximide (10 micrograms/ml) to cAMP-treated cultures for 24 h completely suppressed both constitutive and cAMP-induced 3 beta HSD mRNA levels. Cycloheximide also repressed cAMP-induced levels of P450(17 alpha) to 12% of levels observed in the absence of cycloheximide. In sharp contrast, 24-h treatment with cycloheximide did not suppress cAMP induction of P450scc mRNA, but reduced basal levels by approximately 50%. A time course of induction by cAMP (50 microM) of P450(17 alpha) and P450scc mRNA showed very similar rates of increase in P450(17 alpha) and P450scc mRNA, with the greatest increase occurring between 12 and 24 h of treatment. The results of the study demonstrate that in normal mouse Leydig cells steady state levels of mRNA for 3 beta HSD, P450(17 alpha), and P450scc are differentially regulated. cAMP is required for maximal levels of all three mRNAs. There is high constitutive expression of 3 beta HSD and P450scc mRNA, while expression of P450(17 alpha) mRNA is absolutely dependent on cAMP stimulation. Endogenously produced testosterone negatively regulates the expression of cAMP-induced P450(17 alpha) and 3 beta HSD, while the glucocorticoid dexamethasone negatively regulates 3 beta HSD and P450scc.(ABSTRACT TRUNCATED AT 400 WORDS)

Interleukin-1 inhibits cholesterol side-chain cleavage cytochrome P450 expression in primary cultures of Leydig cells

Interleukin-1 (IL-1) is a potent inhibitor of Leydig cell function. We have reported that IL-1 inhibited hCG-induced cAMP and testosterone formation. In the present study we evaluated the effect of IL-1 on Leydig cell cholesterol side-chain cleavage cytochrome P450 (P450scc) mRNA levels. P450scc is the rate-limiting enzyme for Leydig cell steroidogenesis. Highly purified Leydig cells were prepared from adult Sprague-Dawley male rats (55-65 day-old) using the combination of elutriation and Percoll gradient. Purified Leydig cells were then cultured with or without IL-1 beta (1-100 ng/ml) and recombinant human monocyte-derived IL-1 receptor antagonist (250 ng/ml) for 24 h. hCG (10 ng/ml), 8-bromo-cAMP (0.1 mM), or 4 beta-phorbol 12 beta-myristate 13 alpha-acetate was then added, and cultures were continued for an additional 6 h. P450scc mRNA levels of Leydig cells were very low to undetectable after 24 h in culture and could be stimulated by the addition of either hCG (10 ng/ml) or 8-bromo-cAMP (0.1 mM), but the addition of 4 beta-phorbol 12 beta-myristate 13 alpha-acetate had no effect. P450scc mRNA levels increased as early as 2 h after the addition of hCG. Furthermore, cycloheximide (1 microgram/ml) markedly blocked hCG-induced P450scc mRNA expression. This indicates that synthesis of a labile new protein(s) is required for the induction of P450scc mRNA by hCG. IL-1 beta inhibited hCG-stimulated testosterone formation and P450scc mRNA expression in a dose-dependent manner. The inhibitory effects of IL-1 beta could be reversed by the concomitant addition of IL-1 receptor antagonist. Our results suggest that P450scc mRNA levels of Leydig cells are modulated by IL-1. This may be one mechanism that could explain the inhibitory effects of IL-1 on Leydig cell steroidogenesis.

Ovarian actions of tumor necrosis factor-alpha (TNF alpha): pleiotropic effects of TNF alpha on differentiated functions of untransformed swine granulosa cells

We have examined interactions between tumor necrosis factor-alpha (TNF alpha), a product of the immune system, and ovarian cells using serum-free monolayer cultures of untransformed swine granulosa cells. Recombinant human TNF alpha, a potent cytoactive product of activated macrophages, bound specifically and with high affinity to intact granulosa cells. Binding sites had an apparent Kd of 0.17 nM (95% confidence interval, 0.065-0.31), and a binding capacity of 80 nmol/micrograms DNA (95% confidence interval, 52-110). The binding capacity of granulosa cells for TNF alpha (but not the binding affinity) was increased approximately 2-fold by treatment with FSH and insulin. The biological effects of TNF alpha on pig granulosa cells were expressed after 48 and 96 h in culture. At the latter time, TNF alpha significantly suppressed insulin- and insulin- plus FSH-stimulated progesterone accumulation, with respective ID50 values of 0.08 +/- 0.008 and 0.06 +/- 0.014 nM, but did not affect basal progesterone accumulation or DNA content. TNF alpha also significantly attenuated the stimulatory effect of combined treatment with FSH and insulin on cAMP generation during 48-96 h of culture. TNF alpha inhibited the stimulatory effects of forskolin, cholera toxin, and the cAMP analog 8-bromo-cAMP on progesterone accumulation, indicating multiple sites of action of this immune modulator. Inhibition of progestin biosynthesis was observed even in the presence of 25-hydroxycholesterol, a soluble oxygenated sterol substrate for the cholesterol side-chain cleavage reaction, and was accompanied by decreased concentrations of specific cellular mRNA encoding cholesterol side-chain cleavage enzyme. There were no changes in the amounts of a constitutively expressed enzyme, phosphoglyceraldehyde dehydrogenase. Inhibitory actions of TNF alpha were specific to de novo steroid hormone biosynthesis, since nanomolar concentrations of this cytokine stimulated accumulation of prostaglandin E2 and prostaglandin F2 alpha basally and during treatment with FSH, cholera toxin, or 8-bromo-cAMP. In contrast, prostaglandin accumulation was not enhanced by interferon-gamma or interleukin-2. In summary, untransformed porcine granulosa cells exhibit specific, high affinity, low capacity saturable binding sites for TNF alpha, and the number of such binding sites can be regulated by combined treatment with insulin and FSH. Granulosa cells are susceptible to the inhibitory actions of TNF alpha on FSH- and insulin-supported progesterone biosynthesis and cAMP accumulation. One important locus of TNF alpha action is blockade of hormonally stimulated increases in specific mRNA encoding the cholesterol side-chain cleavage cytochrome P450 enzyme.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of CYP11A (P450SCC) and CYP17 (P450(17) alpha) gene expression in bovine luteal cells in primary culture

Cholesterol side chain cleavage cytochrome P450 (P450SCC) and 17 alpha-hydroxylase cytochrome P450 (P450(17) alpha) are key enzymes involved in steroid hormone biosynthesis. The 5'-flanking regions of the corresponding bovine genes have recently been characterized in the adrenal-derived Y1 cell line and specific DNA sequences, required for basal and cAMP-dependent gene expression, were identified. In order to investigate the molecular mechanisms controlling P450SCC and P450(17) alpha gene expression throughout the ovarian cycle, we devised an electroporation protocol to transfect bovine luteal cells in primary culture with specific chimeric DNA constructs. Transfection of such cells with reporter gene constructs containing 186 base pairs (bp) or more of the CYP11A (P450SCC) 5'-regulatory region resulted in cAMP-responsive reporter gene expression. Reporter gene constructs containing 101 bp or less of this regulatory region were expressed neither in the presence nor in the absence of forskolin. Thus, expression of the CYP11A gene in bovine luteal cells in primary culture appears to be controlled by a cis-acting element located between -186 to -101 bp. Transfection of bovine luteal cells in primary culture with reporter gene constructs containing increasing deletions of the bovine CYP17 (P450(17) alpha) 5'-regulatory region clearly demonstrated that none of the sequences were capable of promoting significant reporter gene expression, neither in the presence nor absence of forskolin. Since no 17 alpha-hydroxylase activity and no specific mRNA encoding P450(17) alpha have been detected in the bovine corpus luteum, the failure of expression of the P450(17) alpha reporter gene constructs mimics that of the endogenous gene. These results demonstrate that the regulation of CYP11A gene expression in bovine luteal cells is carried out by the same cis-acting element (-183/-101) which serves this role in the adrenal Y1 cell line. On the other hand, expression of the CYP17 gene in bovine luteal cells appears to be completely repressed, due to the absence of specific positive transcription factor(s) or the presence of negative regulatory factor(s). Thus, transfection experiments using bovine luteal cells in primary culture represent a first step towards the elucidation of molecular mechanisms underlying the regulation of cytochrome P450 gene expression throughout the ovarian cycle.

Regional mapping of genes encoding human steroidogenic enzymes: P450scc to 15q23-q24, adrenodoxin to 11q22; adrenodoxin reductase to 17q24-q25; and P450c17 to 10q24-q25

Steroid hormones are synthesized by a complex array of 10 enzymes. The genes for each of these have now been cloned, and previous work has determined the regional chromosomal assignments of six of these. We used in situ hybridization to determine the regional chromosomal assignments of the four remaining enzymes. The CYP11A1 gene encodes mitochondrial P450scc, which converts cholesterol to pregnenolone, and is located on 15q23-q24. The gene for adrenodoxin, which receives electrons from adrenodoxin reductase and transfers them to P450scc, is on 11q22 while its pseudogenes are on 20q11-q12. The gene for adrenodoxin reductase is on 17q24-q25. The CYP17 gene encodes P450c17, which has both 17 alpha-hydroxylase and 17,20-lyase activities, and is located on 10q24-q25. None of the 10 genes involved in human steroidogenesis is closely linked to another gene for a steroidogenic enzyme.

Expression and regulation of adrenodoxin and P450scc mRNA in rodent tissues

The rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone. This reaction occurs in steroidogenic tissue in the inner mitochondrial membrane, and is mediated by the cholesterol side-chain cleavage enzyme. This enzyme system transfers electrons from NADPH to cholesterol through its three protein components: adrenodoxin reductase, adrenodoxin, and the terminal oxidase, P450scc. We have previously shown that P450scc mRNA is regulated by tropic hormones and cAMP by a cycloheximide-independent mechanism in mouse Leydig tumor MA-10 cells. We now show that the mRNA for adrenodoxin, another component of the cholesterol side-chain cleavage enzyme system, is regulated by tropic hormones and cAMP in MA-10 cells. We cloned rat adrenodoxin cDNA to analyze adrenodoxin mRNA in various rat tissues and in MA-10 cells by RNase protection assays. Adrenodoxin mRNA is found in virtually all rat tissues examined, although it is most abundant in adrenals, ovaries, and testes. MA-10 cells synthesize two species of adrenodoxin mRNA, one of 1.2 kb and the other of 0.8 kb. Both of these adrenodoxin mRNAs are increased approximately six-fold by 1 mM 8-Br-cAMP, five-fold by 10 microM forskolin, and three-fold by both 25 ng/ml hCG and by 100 ng/ml LH. Maximal adrenodoxin mRNA accumulation occurs by 4 h of hormonal stimulation. The cAMP-mediated increase in adrenodoxin mRNA accumulation is independent of protein synthesis, since treatment with cycloheximide or puromycin in the absence or presence of cAMP does not inhibit, and even increases, adrenodoxin mRNA accumulation.

Follicle-stimulating hormone increases concentrations of messenger ribonucleic acid encoding cytochrome P450 cholesterol side-chain cleavage enzyme in primary cultures of porcine granulosa cells

FSH is the primary hormonal inducer of ovarian follicle maturation and a critically important regulator of steroidogenesis in granulosa cells. We examined possible molecular mechanisms subserving FSH action by assessing concentrations of cytochrome P450 cholesterol side-chain cleavage (P450scc) mRNA in porcine granulosa cells maintained in serum-free culture. Cellular concentrations of specific P450scc mRNA were measured by Northern blot hybridization using a 32P-labeled 1-kilobase porcine cDNA clone. Specificity was tested by estimating the granulosa cell mRNA content of the constitutively expressed enzyme, glyceraldehyde-3-phosphate dehydrogenase. Steroidogenesis was evaluated by measuring concomitant progesterone accumulation in the culture medium. Treatment with ovine FSH (100 ng/ml) increased P450scc mRNA concentrations in a time-dependent fashion, with significant effects on both P450scc mRNA concentrations and progesterone accumulation by 4 h and a maximal increase (8- to 10-fold) at 48 h. FSH dose-response studies at 48 h revealed a significant stimulatory effect of 30 ng/ml FSH on P450scc mRNA accumulation and progesterone production, with a maximal effect at 100 ng/ml FSH. To examine the role of cAMP in mediating granulosa cell P450scc mRNA accumulation, granulosa cells were treated with forskolin, cholera toxin, 8-bromo-cAMP, 8-bromo-cGMP, 5'AMP, or cAMP analogs that differentially stimulate the two isoenzymes of protein kinase-A. Increased specific P450scc mRNA accumulation and progesterone production occurred in response to each agent except 5'AMP and 8-bromo-cGMP. No effects of these agents were observed on glyceraldehyde-3-phosphate dehydrogenase mRNA. To assess possible feedback effects of steroid or sterol on FSH-stimulated P450scc mRNA concentrations, granulosa cells were treated with aminoglutethimide to block or with low density lipoprotein to stimulate steroid production. Inhibition of sterol utilization by the cholesterol side-chain cleavage enzyme had no effect on basal or FSH-stimulated concentrations of P450scc mRNA, but markedly suppressed progesterone production. Low density lipoprotein, which increases intracellular sterol, also did not alter basal or FSH-stimulated P450scc mRNA accumulation, suggesting that neither the utilization nor the availability of sterol regulates specific P450scc mRNA levels. Estradiol alone did not increase P450scc mRNA accumulation, but did augment progesterone production. Treatment of granulosa cells with estradiol and FSH produced a synergistic increase in progesterone concentrations, but did not affect FSH-stimulated P450scc mRNA accumulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of testicular P-450 cholesterol side-chain cleavage and P-450 C17-20 lyase/C17 hydroxylase enzymes in the neonatal and adult rat

Adult Leydig cells respond to LH or hCG with an initial stimulation of testosterone secretion followed by LH receptor down-regulation and blockade of androgen biosynthesis. In contrast, fetal Leydig cells respond with increased LH receptor number and enhanced steroidogenesis. In this study, the molecular mechanisms of high-dose hCG treatment on steroidogenesis in adult and neonatal testes (containing predominantly the fetal generation of Leydig cells) were examined using two recombinant DNA clones specific for enzymes of the rat steroidogenic pathway (P-450 cholesterol side-chain cleavage enzyme, P-450scc and P-450 17 alpha-hydroxylase/C17-20 lyase, P-450c17). We treated adult (60 days of age) and neonatal (2 days of age) rats with a single high dose of hCG (600 IU/kg), sc. The high dose of hCG caused neonatal testicular P450scc and P450c17 mRNA levels to increase, and stimulated adult testicular P450scc mRNA levels, but caused a decrease in adult P450c17 mRNA levels. These studies suggest that high doses of hCG regulate testosterone production differently in adult and fetal Leydig cells at a pretranslational level of the P450c17 enzyme, while mRNA for P450scc is stimulated in both the adult and fetal Leydig cell.

Expression of mRNA species encoding steroidogenic enzymes in the rat ovary

We have examined the levels of expression of mRNA species encoding cholesterol side-chain cleavage cytochrome P-450 (P-450scc), 17 alpha-hydroxylase cytochrome P-450 (P-450(17 alpha), aromatase cytochrome P-450 (P-450AROM) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) in rat ovaries throughout the oestrous cycle, during pregnancy and in immature animals treated with pregnant mare serum gonadotrophin (PMSG). Total or poly(A)(+)-enriched RNA was prepared from adult rat ovaries throughout the oestrous cycle, from immature rat ovaries 24 and 48 h after treatment and from adult rat ovaries on days 10, 14, 17 and 21 of gestation. Expression of the mRNA species was examined by Northern analysis using specific [32P]cDNA probes. During the oestrous cycle P-450scc mRNA of approximately 1.9 kb was detected at low levels, while 3 beta-HSD mRNA of 1.7 kb was in relatively high abundance throughout the oestrous cycle. While P-450(17) alpha mRNA of 1.9 kb and P-450AROM of 2.7, 2.2 and 1.7 kb were highly abundant during dioestrus, pro-oestrus and oestrus, the levels of these mRNA species decreased markedly to be nearly undetectable during metoestrus. During pregnancy there was considerably more variation in the expression of the mRNA species examined. Expression of P-450scc mRNA was at low, but detectable, levels until day 14, thereafter expression increased to high levels (day 14-21 of gestation). Levels of P-450(17) alpha mRNA on day 10 of gestation were lower than at pro-oestrus during the oestrous cycle and decreased further on days 14 and 17. Expression of 3 beta-HSD was decreased on day 10, but on days 14, 17 and 21 of gestation high mRNA levels were detectable. Ovarian expression of the three P-450AROM species was dramatically increased between days 14 and 17 of pregnancy, but declined by day 21. In immature rats, P-450scc mRNA was detected at low levels in unstimulated animals and increased markedly after treatment with PMSG, while subsequent treatment with human chorionic gonadotrophin (hCG) had a minimal effect on expression. Expression of P-450(17) alpha mRNA was high in unstimulated immature and PMSG-treated rats, but diminished after treatment with hCG. All three P-450AROM mRNA species were undetectable in ovaries from unstimulated immature animals; however, induction of all three was observed in PMSG-treated rats, but this expression decreased to undetectable levels upon subsequent administration of hCG.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Expression of messenger ribonucleic acids that encode for 3 beta-hydroxysteroid dehydrogenase and cholesterol side-chain cleavage enzyme throughout the luteal phase of the macaque menstrual cycle

To study further the control of the primate corpus luteum, we obtained corpora lutea from cynomolgus macaques at defined stages of the luteal phase and examined steady state mRNA levels in these corpora lutea by Northern analysis for the two major enzymes involved in progesterone biosynthesis, cytochrome P450 cholesterol side-chain cleavage (P450SCC) and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD). mRNAs for both P450SCC and 3 beta HSD were maximal or near maximal shortly after ovulation and luteinization (days 3-5 of the luteal phase). mRNA for P450SCC exhibited a slight, but nonsignificant (P greater than 0.05) decline throughout the remainder of the luteal phase and was undetectable upon luteal regression. Steady state levels of 3 beta HSD mRNA were significantly lower (P less than 0.05) from corpora lutea removed during the midluteal phase (days 7-8 of the luteal phase) than those in newly formed corpora lutea and declined to 10% of early luteal phase values by days 13-15 of the luteal phase. 3 beta HSD mRNA levels fell to nondetectable values upon luteal regression. These results reveal a paradoxical relationship between the steroidogenic activity of the primate corpus luteum in vivo and the steady state levels of the mRNAs that encode for the major enzymes involved in progesterone biosynthesis. Unlike serum progesterone concentrations, which are very low immediately after ovulation and then rise during the midluteal phase, the steady stale levels of P450SCC mRNA and 3 beta HSD appeared to be maximal or near maximal shortly after ovulation and declined throughout the remainder of the luteal phase. These findings are consistent with the notion that luteal lifespan is set at the time of ovulation and luteinization, and the decline in luteal function may be due in part to decay of specialized luteal cell mRNAs with finite half-lives.

Structures of regulatory regions in the human cytochrome P-450scc (desmolase) gene

The mechanism of regulatory expression of human cytochrome P-450scc gene by cAMP was investigated in a transient expression system using Y-1 cells (mouse adrenal tumor cell line) and a chimeric DNA composed of the structural gene for bacterial chloramphenicol acetyltransferase and the 5' flanking upstream sequence of the cytochrome P-450scc (cholesterol desmolase) gene which was revealed to contain a DNA element(s) responsive to cAMP [Inoue, H. et al. (1988) Eur. J. Biochem. 171, 435-440]. Introduction of deletions and point mutations in the upstream regulatory sequence demonstrated that three regions were mainly required for response to cAMP. These regions contained a short similar sequence. All of them have a 5-bp motif GTCAT (or ATGAC) in common, and have at least two motifs which conserve four out of five base pairs of the consensus sequence of the cAMP-responsive element (CRE), CGTCA (or TGACG). They are all apparently necessary for regulation by cAMP. Gel mobility shift assays suggested that a binding factor(s) to these regions was present in the nuclear extracts of Y-1 cells and adrenal cortex tissues and appeared to be different from the somatostatin CRE-binding protein. Deletion analysis also suggested that the region around -44 was essential to the basal transcriptional activity. This region shows some similarity to the CTF NF-1 binding site [Johnson and McKnight (1989) Annu. Rev. Biochem. 58, 799-839].

Tumor necrosis factor as a potent inhibitor of adrenocorticotropin-induced cortisol production and steroidogenic P450 enzyme gene expression in cultured human fetal adrenal cells

We have previously demonstrated that tumor necrosis factor alpha (TNF-alpha), a multifunctional cytokine mainly produced by activated monocytes, inhibits the ACTH-induced production of cortisol in cultures of human fetal adrenals. To clarify the molecular basis of this suppression, we investigated the effect of recombinant TNF-alpha (rTNF-alpha) on the messenger RNAs (mRNAs) for adrenal cytochrome P450 oxidases, P450scc (cholesterol side-chain cleavage enzyme/20.22-desmolase), P450c11 (11 beta-hydroxylase/18-hydroxylase/18-methyl oxidase), P450c17 (17 alpha-hydroxylase/17,20-lyase), and P450c21 (21-hydroxylase). Northern and dot blot experiments showed that 36 h incubation of primary cultures of human fetal adrenals with ACTH (200 ng/ml) increased the levels of all P450 enzymes severalfold. Preincubation of the cultures with rTNF-alpha at concentrations ranging from 0.1-100 ng/ml produced a dose-dependent inhibition of the ACTH-induced accumulation of all P450 mRNAs. The decrease in the expression of genes for steroidogenic enzymes was accompanied by a similar decrease in the production of cortisol but not in that of dehydroepiandrosterone sulphate nor androstenedione. Neither the basal expression of P450 enzymes nor the basal secretion of the steroids was significantly altered by 10 ng/ml of rTNF-alpha. rTNF-alpha did not affect the level of actin mRNA, the cell viability, nor the cell number. All the effects brought about by rTNF-alpha could be neutralized by addition of monoclonal anti-TNF-alpha antibody. These results show that TNF-alpha suppresses the synthesis of cortisol and shifts the steroid secretory pattern towards androgen production at least partly by suppressing the accumulation of mRNAs for adrenal cytochrome P450 oxidases.

Human proopiomelanocortin-(79-96), a proposed androgen stimulatory hormone, does not affect steroidogenesis in cultured human fetal adrenal cells

Whether the production of human adrenal androgens is stimulated by a hormone other than ACTH or angiotensin-II has long been controversial. A candidate for such a cortical androgen stimulatory hormone (CASH) is the proximal 18-amino acid hinge region of proopiomelanocortin (POMC). This region of POMC lies to the amino-terminal side of the ACTH region, displays considerable amino acid sequence variation among mammals, and has been reported to stimulate the secretion of dehydroepiandrosterone (DHEA) from cultured adult adrenal cells. We cultured human fetal adrenal cells with 10(-8) M CASH-18, 10(-13) M ACTH, 10(-8) M CASH-18 plus 10(-13) M ACTH, 10(-8) M ACTH, or vehicle alone. Culture media were assayed for cortisol, DHEA, and DHEA sulfate, and cellular RNA was assayed for P450scc and P450c17 mRNAs. ACTH (10(-8 M) increased steroid secretion and the mRNAs for P450scc and P450c17, but the other treatments were indistinguishable from the control. Thus, CASH-18 does not affect steroidogenesis in primary cultures of human fetal adrenal cells. These data could be consistent with a model in which adrenarche, the onset of adrenal androgen synthesis at 8-10 yr of age, is mediated by developmentally programmed synthesis of a receptor for CASH. Alternatively, they are also consistent with this region of POMC having no CASH activity.

Regulation of expression of the genes encoding steroidogenic enzymes

In recent years it has become apparent that tropic hormones involved in steroidogenesis act to regulate the expression of the enzymes involved in the various steroidogenic pathways. This is particularly evident in the ovary where the episodic secretion of steroids throughout the ovarian cycle is regulated largely by changes in the levels of the particular enzymes involved in each step of the steroid biosynthetic pathways. Recently, the genes for the various cytochrome P450 species involved in ovarian steroidogenesis, namely cholesterol side-chain cleavage P450 (P450SCC), 17 alpha-hydroxylase P450 (P450(17 alpha], and aromatase cytochrome P450 (P450AROM) have been isolated and characterized, making it possible to study the regulation of expression at the molecular level. To this end, a series of chimeric constructs have been prepared in which fragments of the 5'-untranslated region of bovine P450(17 alpha) and P450SCC have been inserted upstream of the chloramphenicol acetyl transferase (CAT) and beta-globin reporter genes. These constructs have been used to transfect primary cultures of bovine luteal and thecal cells. The results indicate that cAMP responsiveness lies within defined regions of genes which do not contain a classical CRE, similar to previous results utilizing adrenal cells in culture. Furthermore, although constructs containing both the P450(17 alpha) and P450SCC 5'-upstream regions are expressed in both luteal and thecal cell cultures, only those containing the P450SCC sequences are expressed in luteal cells. Studies on the expression of P450AROM indicate that the promoter which is responsible for its expression in human placenta is not operative in the corpus luteum. Thus estrogen biosynthesis may be regulated by the differential use of tissue specific promoters, thus accounting for the complexity and multifactorial nature of the expression of this activity.

Rat cholesterol side-chain cleavage cytochrome P-450 (P-450scc) gene. Structure and regulation by cAMP in vitro

The entire rat P-450scc gene has been cloned, positions/sequences of the exon-intron boundaries (I-IX) are described and 940 base pairs (bp) of 5'-flanking DNA have been sequenced, compared to mouse, bovine and human genes, and analyzed by functional assays. Primer extension analysis mapped the transcription start site 32 bp upstream of the initiator methionine codon. The rat P-450scc promoter was ligated to the human growth hormone (GH) gene yielding p-940RsccGH. This rat P-450scc fusion gene and a mouse gene (p-1500MsccGH) were transiently transfected into primary cultures of rat granulosa cells and Y1 adrenal cells. In the Y1 cells primer extension analysis showed that the rat P-450sccGH gene was expressed at lower basal levels than that of the mouse gene but showed greater stimulation (4-8-fold) in response to 8-bromo-cyclic AMP than the mouse (3-4-fold). Similar results were obtained when the fusion genes were transfected into primary cultures of rat granulosa cells and production of GH was measured in the media of the cells stimulated with forskolin. Furthermore, we document that gonadotropins (follicle-stimulating hormone/luteinizing hormone) can induce luteinization of granulosa cells in vitro, that this process is associated with constitutive maintenance of P-450scc mRNA in the absence of hormones/cAMP, that these events associated with luteinization are differentiation-stage specific and occur only in granulosa cells of preovulatory follicles but not in small antral follicles, that the process can be inhibited by cycloheximide if the protein synthesis inhibitor is present during the first 6 h of exposure to luteinizing hormone but not if added for short durations (3-5 h) later, and that once luteinization is induced P-450scc mRNA expression and progesterone biosynthesis are not strictly dependent on cAMP. Thus, the P-450scc gene is regulated by both cAMP-dependent and cAMP-independent mechanisms, each of which are associated with a specific stage of granulosa cell differentiation. The DNA domains involved in regulating these two diverse processes remain to be determined. Although there was remarkable sequence homology among rat, mouse, bovine, and human genes within 70 bp of the transcriptional start site, no other sequence similarities revealed conserved functional domains among the four genes. Although some cAMP-responsive element-like sequences are present in the rat gene, these were not conserved in the other species; including the mouse which showed high sequence homology with the rat throughout 900 bp of 5'-flanking DNA. Thus, the cAMP domains specific to this and other steroidogenic genes remain to be clearly identified.

2-hydroxyestradiol enhanced progesterone production by porcine granulosa cells: dependence on de novo cholesterol synthesis and stimulation of cholesterol side-chain cleavage activity and cytochrome P450scc messenger ribonucleic acid levels

2-Hydroxyestradiol (2-OH-E2) stimulates progestin secretion by granulosa cells, but the intracellular locus of the stimulatory effect has not been clarified. The objectives of the present studies were to 1) determine the role of de novo sterol synthesis in the effect of 2-OH-E2 on progestin biosynthesis, and 2) examine the effects of 2-OH-E2 on cholesterol side-chain cleavage (SCC) activity and the level of messenger RNA (mRNA) for P450scc. Inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase with lovastatin (5 micrograms/ml) or mevinolin (5 micrograms/ml) reduced FSH- and 2-OH-E2-stimulated (but not E2-stimulated) progesterone production. Mevalonate (20 mM) enhanced basal progesterone production and reversed the inhibitory effect of lovastatin but did not affect progesterone biosynthesis in the presence of 2-OH-E2. As an index of the activity of cholesterol SCC enzyme, granulosa cells were exposed to 25-hydroxycholesterol (10 micrograms/ml) for 24 h and progesterone secretion monitored. Conversion of 25-hydroxycholesterol into progesterone was stimulated 2- to 3-fold by maximally effective concentrations of 2-OH-E2, E2, and FSH. 2-OH-E2 and/or E2 further enhanced 25-hydroxycholesterol conversion in the presence of FSH, LH, and epinephrine. Aminoglutethimide, an inhibitor of SCC, reduced 2-OH-E2- and 2-OH-E2 plus FSH-stimulated progesterone production by 97% and 95%, respectively. 2-OH-E2 also increased basal (by 2 to 3-fold) and FSH-stimulated (to 3.5-fold of FSH-treated controls) levels of mRNA for cytochrome P450scc. Collectively, our studies support the hypothesis that 2-OH-E2-enhanced progesterone biosynthesis by porcine granulosa cells is dependent on de novo cholesterol synthesis and is associated with increased levels of the mRNA encoding cytochrome P-450scc, which leads to increases in basal and gonadotropin-induced SCC activity.

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements

Long-term regulation of mammalian steroid hormone synthesis occurs principally by transcriptional regulation of the gene for the rate-limiting cholesterol side-chain cleavage enzyme P450scc. Adrenal steroidogenesis is regulated primarily by two hormones: adrenocorticotropin, which works via cyclic AMP (cAMP) and protein kinase A, and angiotensin II, which works via Ca2+ and protein kinase C. Forskolin and 8-bromo-cAMP stimulated, while prolonged treatment with a phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) and a calcium ionophore (A23187) additively suppressed accumulation of endogenous P450scc mRNA in transformed murine adrenal Y1 cells. In Y1 cells transfected with 2,327 base pairs of the human P450scc promoter fused to the bacterial gene for chloramphenicol acetyltransferase (CAT), forskolin increased CAT activity 900% while combined TPA plus A23187 reduced CAT activity to 15% of the control level. Forskolin induced the P450scc promoter as rapidly as a promoter containing two cAMP-responsive elements fused to a simian virus 40 promoter, a system known to respond directly to cAMP. Basal expression was increased by sequences between -89 and -152 and was increased further by sequences between -605 and -2327. This upstream region also conferred inducibility by cAMP. TPA plus A23187 transiently increased CAT activity before repressing it, reflecting the complex actions of angiotensin II in vivo. Repression by prolonged treatment with TPA plus A23187 was mediated by multiple elements between -89 and -343. Induction of CAT activity by forskolin was not diminished by treatment with TPA plus A23187, nor were the regions of the promoter responsible for regulation by the two pathways coisolated. Thus, the human gene for P450scc is repressed by TPA plus A23187 by mechanisms and sequences independent of those that mediate induction by cAMP.

Differential response of luteinizing hormone receptor and steroidogenic enzyme gene expression to human chorionic gonadotropin stimulation in the neonatal and adult rat testis

To study further the functional differences of the fetal-neonatal and adult growth phases of Leydig cells, neonatal (5-day-old) and adult (60-day-old) male rats were challenged with a 600 IU/kg injection of human CG (hCG). Certain Leydig cell responses were monitored 1, 2, and 3 days after the hCG injection. The down-regulation of LH receptors and blockage of the 17-hydroxylase/C17-20 lyase step in adult testis, and the absence of these responses in neonatal testis were confirmed. Novel data were obtained on concomitant responses of LH receptor and steroidogenic enzyme messenger RNAs (mRNAs). The LH receptor mRNA was increased 4-5-fold by 2 days after hCG injection in the neonatal testis (P less than 0.05), but in the adult was decreased during all 3 days by 50% (P less than 0.05). The mRNA level of the cytochrome P450 for cholesterol side chain cleavage responded similarly at both ages, with a 180-260% increase during 2 and 3 days (P less than 0.05-0.01). In contrast, the 17-hydroxylase/17,20-lyase cytochrome P450 mRNAs displayed opposite responses, increasing 4.5-fold in 2 days (P less than 0.01) in the neonates, but decreasing by 80% in 1 day in the adults (P less than 0.01). No response of the aromatase cytochrome P450 mRNA to hCG stimulation was found at either age studied. These results demonstrate that the functional differences of the neonatal and adult Leydig cells to high gonadotropic stimulation occur at the level of expression of specific genes, including those of the LH receptor and the 17-hydroxylase/17,20-lyase cytochrome P450. Although aromatization of testicular androgens has been suggested to mediate the blockade of the 17-hydroxylase/C17-20 lyase step in adult testes, altered steady state levels of aromatase mRNA are not involved in this response. LH receptor mRNA decreases in adult rat testis in response to treatment with high levels of hCG. Thus, this phenomenon of down-regulation of membrane receptors includes a decreased LH receptor mRNA as well as cellular internalization of the existing receptors.

Follicle-stimulating hormone regulation of cytochrome P-450 side-chain cleavage messenger ribonucleic acid accumulation by porcine granulosa cells isolated from small and medium follicles

The experiments described here were conducted to examine regulation of cytochrome P-450 side-chain cleavage (SCC) mRNA accumulation in porcine granulosa cells isolated from small (1-4-mm) and medium (5-6-mm) follicles. Granulosa cells were cultured under the following conditions: 1) for 48 h or 96 h with 0, 50, or 200 ng/ml porcine FSH; 2) for 96 h with 200 ng/ml FSH and aminoglutethimide (100 microM); and 3) for 96 h with forskolin (100 microM). Total RNA was extracted and examined by Northern and dot-blot hybridization analysis, and culture media were assayed for progesterone concentration. Northern blot analysis revealed a single band approximately 2.1 kb in size. Accumulation of SCC mRNA by granulosa cells was both FSH dose- and culture time-dependent (p less than 0.05) with maximal increases approximately 4.5 times control levels. Aminoglutethimide reduced progesterone production by about 80% while having no effect on granulosa cell accumulation of SCC mRNA compared to cells stimulated with 200 ng/ml of FSH. Forskolin-treated cells produced significantly more progesterone than did cells treated with FSH, but accumulation of SCC mRNA was similar. In response to FSH, concentration of SCC mRNA did not vary with follicle size, but granulosa cells from small follicles produced significantly more progesterone than did those from medium follicles. These results demonstrate that concentration of SCC mRNA in cultured porcine granulosa cells is FSH dose-dependent, does not vary significantly in cells from small- and medium-sized follicles, and is correlated with progesterone production, but may not parallel progesterone secretion. This last observation indicates that control at sites other than SCC mRNA can affect progesterone production.

Insulin-like growth factor type I increases concentrations of messenger ribonucleic acid encoding cytochrome P450 cholesterol side-chain cleavage enzyme in primary cultures of porcine granulosa cells

Insulin-like growth factor type I (IGF-I) is an important intraovarian peptide that stimulates granulosa cell steroidogenesis during follicular development. The cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc) that converts cholesterol to pregnenolone is the rate-limiting step in progesterone biosynthesis. Since treatment of primary cultures of immature porcine granulosa cells with IGF-I will increase progesterone production as well as the synthesis of immunoprecipitable P450scc enzyme, we examined possible molecular mechanisms subserving these inductive effects of IGF-I. To this end, cultures of porcine granulosa cells were maintained in serum-free medium with or without IGF-I under various treatment paradigms. Cellular concentrations of specific P450scc mRNA were measured by Northern blot hybridization using a 32P-labeled 1-kilobase porcine cDNA clone. Northern blot autoradiogram densitometry data were normalized with a constitutively expressed 1.2-kilobase chicken glyceraldehyde-3-phosphate dehydrogenase cDNA clone. Steroidogenesis was monitored by measuring concomitant progesterone accumulation in the culture medium. Treatment with pure recombinant human IGF-I (100 ng/ml) significantly increased P450scc mRNA concentrations after 18 h, and maximal stimulation (10- to 20-fold) occurred by 48 h for both P450scc mRNA and progesterone accumulation. The IGF-I dose-response curve studied at 48 h showed a significant increase in P450scc mRNA levels at a minimal IGF-I concentration of 1 ng/ml (although progesterone production was not increased). Treatment with equimolar concentrations of epidermal growth factor, IGF-I, or insulin significantly increased P450scc mRNA concentrations, whereas fibroblast growth factor did not. To examine possible mechanisms underlying stimulation of P450scc by IGF-I, immature granulosa cells were treated with aminoglutethimide (a P450scc enzyme inhibitor), low density lipoprotein (to increase cholesterol delivery to granulosa cells), or estradiol in the presence or absence of IGF-I. Aminoglutethimide had no effect, alone or with IGF-I, on P450scc mRNA concentrations, but suppressed progesterone production. Low density lipoprotein alone also did not stimulate P450scc mRNA levels and only slightly increased progesterone accumulation, but acted synergistically with IGF-I to augment P450scc mRNA concentrations and progesterone accumulation. Estradiol alone did not stimulate P450scc mRNA concentrations, but did significantly increase progesterone production. Estradiol cotreatment with IGF-I synergistically enhanced progesterone production, but did not alter IGF-I-stimulated P450scc mRNA concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropin increases expression of c-fos and beta-actin genes in the rat adrenals

It is widely accepted that expression of protooncogenes is coupled with cellular proliferation and differentiation. Since ACTH stimulates not only steroidogenesis but also cellular proliferation, we investigated whether ACTH affects the expression of c-fos, c-myc, and beta-actin genes. The effect of ACTH on adrenal glands was studied in hypophysectomized rats. Changes in the mRNA levels were studied by Northern and dot blot analyses. It was demonstrated that ACTH induces increases in mRNAs encoding c-fos and beta-actin in adrenal glands of hypophysectomized rats. When stimulated by ACTH (5 IU/100 g BW), the mRNA levels of both genes increase rapidly; the maximum levels are observed at 30 min for c-fos and 6 h for beta-actin. Both mRNAs declined to near-control levels by 6-24 h. The levels of mRNAs encoding cholesterol side-chain cleavage cytochrome P-450 and 21-hydroxylase cytochrome P-450 began to increase 3 and 12 h after ACTH administration, respectively. This increase continued for 24 h after ACTH treatment. Increases in total adrenal RNA and adrenal weight occurred slowly after ACTH treatment. On the other hand, the levels of c-myc mRNA were very low and were not increased by ACTH administration. These results suggest that increased expression of c-fos and beta-actin genes by ACTH may have important roles in mediating its action on adrenals.

Sertoli cells are the primary site of prodynorphin gene expression in rat testis: regulation of mRNA and secreted peptide levels by cyclic adenosine 3' ,5'-monophosphate analogs in cultured cells

Prodynorphin is one of three endogenous opioid peptide genes expressed in testis. Through the use of cell fractionation procedures and Northern blot analysis, Sertoli cells were found to be the primary site of prodynorphin mRNA synthesis in rat testis. In situ hybridization of a prodynorphin cRNA probe to fixed adult tissue confirmed this result. Treatment of primary cultures of rat Sertoli cells with a cAMP analog, 8-(4-chlorophenylthio)cAMP, resulted in a transient 5.6-fold increase in steady state prodynorphin mRNA levels relative to those in control cells. This increase was maximal at 48 h of treatment, after which mRNA levels gradually declined. Treatment of Sertoli cells with cAMP analogs resulted in concurrent 2.6-fold decreases in sulfated glycoprotein-2 mRNA levels. Culture medium from Sertoli cells showed a 3.1-fold increase in secreted dynorphin immunoreactivity after treatment with 8-(4-chlorophenylthio)cAMP. Chromatographic analysis indicates that the majority of the immunoreactive dynorphin peptide synthesized in Sertoli cells is present as high mol wt species, with some processing to bioactive peptides.

Deduced amino acid sequence of heme binding region of chicken cholesterol side chain cleavage cytochrome P450

The primary structure of the carboxy terminal 296 amino acids of chicken cholesterol side chain cleavage cytochrome P450 (P450scc) was deduced from a partial cDNA clone isolated from a chicken ovarian cDNA library. The sequence contained putative steroid binding and heme binding regions. Comparison of this sequence with the corresponding sequences of three mammalian forms of P450scc shows greater than 50% homology. The heme binding region of the avian P450scc shows 76% homology with the heme binding regions of rat and human P450scc and 81% homology with that of bovine P450scc.

Steroid hydroxylase gene expression in the ovine fetal adrenal gland following ACTH infusion

Between 90 and 120 days of gestation (term = 147 +/- 5), when plasma cortisol concentrations in the fetus are at a minimum, levels of mRNA encoding the steroidogenic enzymes 17 alpha-hydroxylase (P-450(17 alpha] and cholesterol side-chain cleavage (P-450scc) are also very low. Over the following 30 days, P-450(17 alpha) and P-450scc gene expression increases concurrent with increasing fetal cortisol concentration. The hypothesis tested in this study was that cortisol biosynthesis is minimal in the period 90-120 days because of insufficient ACTH. Fetuses were cannulated between 98-102 days of gestation. Following recovery, 7 fetuses received 24-h ACTH infusions (12 micrograms/24 h) and 5 fetuses received 24-h vehicle infusions; 4 ACTH-infused and 4-vehicle-infused fetuses were then sacrificed immediately after cessation of the infusion. The other fetuses were left in utero for 3 days prior to sacrifice. Fetal blood samples were analysed for ACTH and cortisol and the adrenals processed for hybridization histochemistry and Northern blot analysis. ACTH, but not vehicle, induced significant increases in the width of the adrenal cortex and in the levels of P-450(17 alpha) and P-450scc mRNA. Concurrently, fetal plasma ACTH and cortisol concentrations also increased significantly. In adrenals from fetuses left in utero for 3 days after cessation of the ACTH infusion, P-450(17 alpha) and P-450scc mRNA levels returned to control levels. Plasma ACTH and cortisol levels also approximated basal values. P-450c21 mRNA levels did not vary significantly at any time with the treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the promoter region of the gene encoding mouse cholesterol side-chain cleavage enzyme

The cholesterol side-chain cleavage enzyme (SCC) catalyzes the initial and rate-limiting step in the synthesis of steroid hormones. The mouse gene encoding SCC was cloned and the nucleotide sequence of its 5'-flanking region determined. This sequence includes an AP-1 motif at -319 and two motifs, AGGTCA at -70 and AGCCTTG at -40, that match elements proposed to be important in the expression of steroid 21-hydroxylase. When transfected into mouse Y1 adrenocortical tumor cells, 1.5 kilobase pairs of 5'-flanking region of the SCC gene directed high levels of expression of a growth hormone reporter gene; treatment of the transfected Y1 cells with 8-bromo-cAMP increased this expression by 5-fold. In contrast, transfected mouse MA-10 Leydig cells showed appreciably lower expression, suggesting that SCC expression in Leydig cells requires additional elements not contained in the 5'-flanking region of the SCC gene used in these experiments. Deletion experiments showed that 424 base pairs of 5'-flanking sequences were sufficient for regulated expression in Y1 cells and mapped two regulatory regions: one from -424 to -327 and a second from -219 to -77. DNase I footprinting and gel mobility shift analyses of these 424 base pairs defined several interactions between nuclear proteins and the SCC promoter, including footprints centered over the AP-1 motif, over a sequence at -120, and over the sequences (-70 and -40) that resemble 21-hydroxylase promoter elements. Finally, site-selected mutagenesis of the potential elements at -40, -70, or -120 decreased SCC promoter activity in transfected Y1 adrenocortical cells, thus establishing their importance in SCC expression.

Mechanism for control of hydroxymethylglutaryl-coenzyme A reductase and cytochrome P-450 side chain cleavage message and enzyme in the corpus luteum

The present study was undertaken to investigate the mechanism for control of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase and cytochrome P-450 side chain cleavage (P-450scc), enzymes involved in the synthesis and processing of cholesterol in the corpus luteum of pregnant rats. The role of sterol and estradiol were investigated by administering 4-aminopyrazolo-[3,4d]pyrimidine (4-APP), aminoglutethimide and/or estradiol to day 12 hypophysectomized-hysterectomized pregnant rats. Estradiol treatment markedly increased mRNA levels of HMG-CoA reductase in the corpus luteum. This stimulatory effect of estradiol was specific for the reductase since the mRNA for luteal P-450scc did not increase following estradiol treatment. To determine whether estradiol's action on HMG-CoA reductase mRNA was mediated by changes in cellular free cholesterol, the separate and combined action of estradiol and either 4-APP or aminoglutethimide on both sterol content and HMG-CoA reductase expression was examined. The estradiol induced rise in HMG-CoA reductase was not accompanied by a decrease in luteal cholesterol. 4-APP treatment depleted cholesterol in the corpus luteum and induced a greater increase in HMG-CoA reductase mRNA than estradiol. Combined treatment with estradiol and 4-APP resulted in a synergistic increase in HMG-CoA reductase mRNA despite the fact that estradiol did not further reduce the 4-APP induced decrease in luteal sterol content. This indicates that luteal cells possess an estradiol-mediated mechanism for up-regulation of HMG-CoA reductase gene expression which is distinct from the cholesterol negative feedback regulation. However, estradiol stimulation of HMG-CoA reductase was totally inhibited when sterol content was elevated by aminoglutethimide, suggesting that estradiol stimulation of HMG-CoA reductase expression is not sufficient to overcome the negative regulatory effect of cholesterol. In contrast to HMG-CoA reductase mRNA which appears to be controlled by sterol and estradiol, P-450scc mRNA levels remained constant in corpora lutea despite wide changes in sterol and steroid content induced by either 4-APP, aminoglutethimide or estradiol treatment. However, interestingly, aminoglutethimide increased substantially the content of P-450scc protein. This increase in P-450scc enzyme was not due to a greater amount of translatable message since similar levels of immunoprecipitable 35S-P-450scc were translated in vitro from luteal mRNA of rats treated with or without aminoglutethimide. In summary, results of this investigation have revealed that the expression of HMG-CoA reductase and cytochrome P-450scc are controlled by totally different mechanisms in the rat corpus luteum.(ABSTRACT TRUNCATED AT 400 WORDS)

Alteration in the expression of genes for cholesterol side-chain cleavage enzyme and 21-hydroxylase by hypophysectomy and ACTH administration in the rat adrenal

The changes in steady-state levels of mRNA for cholesterol side-chain cleavage cytochrome P-450 (P-450scc) and steroid 21-hydroxylase cytochrome P-450 (P-450c21) caused by hypophysectomy and ACTH treatment were determined in rat adrenals. Hypophysectomy caused marked decreases in adrenal weight and total RNA per gland. Administration of ACTH resulted in increases in adrenal weight and total RNA. A significant correlation between the amount of RNA and adrenal weight was observed. Both P-450scc and P-450c21 mRNAs were decreased by hypophysectomy and increased by ACTH treatment. P-450scc mRNA decreased to 20% and P-450c21 mRNA to 76% of control values 1 day after hypophysectomy. ACTH caused a significant increase in P-450scc mRNA after 3 h. However, a significant increase in P-450c21 mRNA was observed 12 h after administration of ACTH. These results are concordant with previous studies in vitro utilizing cultured adrenocortical cells. Moreover, the induction of steady-state levels of P-450scc mRNA was faster than that observed by other investigators in studies in vitro. These results may indicate that integrity of the adrenal gland in vivo is important for the action of ACTH.

Glucocorticoid and cyclic adenosine 3'5'-monophosphate-mediated induction of cholesterol side-chain cleavage cytochrome P450 (P450scc) in MA-10 tumor Leydig cells. Increases in mRNA are cycloheximide sensitive

The regulation of cholesterol side-chain cleavage enzyme (P450scc) was investigated in MA-10 tumor Leydig cells. We recently demonstrated that the constitutive and cAMP-stimulated expression of P450scc in normal mouse Leydig cells is negatively regulated by glucocorticoids. We now report that glucocorticoids have the opposite effect in MA-10 cells causing a 1.7-fold increase in the rate of P450scc synthesis and a 2.1-fold increase in the amount of P450scc mRNA. Treatment of MA-10 cells with 10 microM 8-bromo-cAMP (8-Br-cAMP) (cAMP) resulted in a 1.7-fold increase in P450scc synthesis and a 3-fold increase in P450scc mRNA. Combined treatment with dexamethasone and cAMP resulted in additive increases in synthesis (2.8-fold) and mRNA (5.3-fold). Increases in de novo synthesis and mRNA levels were reflected by modest increases in the amount of immunoreactive P450scc enzyme protein. Dexamethasone-mediated stimulation in synthesis and accumulation of P450scc mRNA were blocked by the antiglucocorticoid RU-486. Cycloheximide blocked both cAMP- and dexamethasone-induced increases but had no effect on constitutive levels of P450scc mRNA. Treatment of MA-10 cells with 10 microM 8-Br-cAMP had no effect on cell morphology and stimulated progesterone accumulation to a minor degree. Treatment of MA-10 cells with 1 mM 8-Br-cAMP resulted in cell rounding and loss of cells from culture dishes. The results of this study demonstrate that: 1) dexamethasone increases P450scc de novo synthesis and mRNA levels in MA-10 tumor Leydig cells, opposite to the effect in normal Leydig cells; 2) dexamethasone- and cAMP-stimulated increases occur via distinct mechanisms; 3) and synthesis of protein factor(s) is required to mediate the action of both dexamethasone and cAMP.

Expression of messenger ribonucleic acid species encoding steroidogenic enzymes in human follicles and corpora lutea throughout the menstrual cycle

The levels of expression of mRNA species encoding cholesterol side-chain cleavage cytochrome P-450 (P450scc), 17 alpha-hydroxylase cytochrome P450 (P450(17 alpha], aromatase cytochrome P-450 (P-450AROM), and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) were examined in human follicles and corpora lutea (CL) throughout the menstrual cycle. Tissues were obtained from women undergoing hysterectomy and oophorectomy. The largest follicle or the CL was dissected from the ovary depending on whether the surgery was performed in the follicular or luteal phase. The day of the cycle was determined by onset of last menstrual period and was confirmed by endometrial histology. Total RNA was examined by Northern blot analysis, using as probes specific 32P-labeled cDNA inserts encoding each human enzyme. Early follicles demonstrated detectable mRNA for both P450scc and P450(17 alpha), but not for P450AROM or 3 beta HSD. P450AROM was detectable late in the follicular phase and appeared markedly induced in the CL. 3 beta HSD was detectable only in the CL. Levels of P450(17 alpha) mRNA remained relatively unchanged throughout the cycle, whereas P450scc mRNA levels were greatly increased in the CL. The presence of P450(17 alpha) mRNA in the human CL is of interest, since it is absent from the bovine CL, and this is consistent with the ability of the human, but not the bovine, CL to synthesize 17 alpha-hydroxyprogesterone and estrogens. The fact that P450AROM expression is highest in CL is surprising, since plasma estrogen levels are highest during the late follicular phase of the cycle, and may suggest that CL estrogen biosynthesis is limited by 17 alpha-hydroxylase or 17,20-lyase activities.

Insulin-like growth factor-I selectively stimulates cholesterol side-chain cleavage expression in ovarian theca-interstitial cells

Evidence accumulating in the literature supports the concept that insulin-like growth factor I (IGF-I) may be an important local regulator of ovarian function. Recent studies have demonstrated that IGF-I synergistically augments LH stimulation of theca-interstitial cell (TIC) androgen biosynthesis. The purpose of the present studies was to begin to elucidate the molecular mechanisms of the interaction between IGF-I and LH. TIC were purified from ovaries of hypophysectomized immature rats by Percoll gradient centrifugation. When isolated TIC (5 x 10(6) viable cells per dish) were cultured (4 days) in serum-free medium, low amounts (less than 10 ng/ml) of androsterone were produced. Basal androsterone production was not changed by incubation with IGF-I (30 ng/ml). Treatment with LH (50 ng/ml) caused an 85-fold stimulation of androsterone synthesis that was further increased 2.1-fold by concomitant treatment with IGF-I. Immunoblot analysis demonstrated that untreated TIC contained low levels of 17 alpha-hydroxylase/C17-20 lyase enzyme (P450(17 alpha] that were unchanged by incubation with IGF-I alone. LH treatment increased P450(17 alpha) content 5.5-fold and coincubation with LH plus IGF-I increased P450(17 alpha) content 16-fold above control levels. Cholesterol side chain cleavage enzyme (P450scc) was readily detected in immunoblots from untreated TIC. P450scc content was increased 2.6-fold by LH treatment and 4.2-fold by LH plus IGF-I. Interestingly, IGF-I alone induced a 2-fold increase in P450scc. To determine if the increases in P450scc content were associated with increased enzyme activity, progesterone production was measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional expression of microsomal and mitochondrial cytochrome P-450 (d and SCC) in COS-7 cells from cloned cDNA

Using full length cDNA introduced into COS-7 cells, two species of P-450 with entirely different physiological functions have been expressed in enzymatically active form. One is P-450d, which is known to reside in the microsomes of rat hepatocytes where it acts as a drug-metabolizing enzyme; the other is P-450(SCC), which catalyzes the conversion of cholesterol to pregnenolone in the rate-limiting reaction of steroidogenesis in mitochondria of adrenal cortex cells. Northern blot and immunoblot analyses revealed that the mRNA and protein of these P-450 species were efficiently produced in COS-7 cells. The protein contents amounted to nearly 0.1% of the total cell protein as estimated from immunoblotting and low temperature CO difference spectra. The subcellular localization of the products indicated that they were correctly sorted to the microsomes and mitochondria, respectively. We have succeeded in eliciting most of the activity of the expressed microsomal P-450d by reconstruction with NADPH-cytochrome P-450 reductase, while the optimal conditions for the mitochondrial enzyme in the COS cells remain to be studied. These results show the applicability of the COS-7 expression system to investigations of the functions of members of the P-450 superfamily whose cDNA has been newly isolated.

Angiotensin II inhibits luteinizing hormone-stimulated cholesterol side chain cleavage expression and stimulates basic fibroblast growth factor expression in bovine luteal cells in primary culture

Angiotensin II has been identified immunohistochemically in the ovaries of both rats and humans. Here we present evidence that angiotensin II (an extremely vasoactive agent in a wide range of tissues) may be involved in the regulation of the major steroidogenic enzyme in the ovary, cholesterol side chain cleavage cytochrome P-450 (P-450scc), as well as of basic fibroblast growth factor (bFGF), which has been implicated as an angiogenic factor in the bovine corpus luteum. We have used primary cultures of bovine luteal cells to examine the effect of angiotensin II and its receptor antagonist, saralasin, on expression of mRNA encoding bFGF as well as on progesterone production and the expression of mRNA encoding cholesterol side chain cleavage cytochrome P-450 (P-450scc). Neither angiotensin II nor saralasin when added alone to the culture medium had any effect on basal progesterone production. Luteinizing hormone (LH) caused a 15-fold increase in progesterone accumulation after 24 h of exposure which was reduced to 5-fold in the presence of angiotensin II. This appeared to be receptor-mediated in that although saralasin alone had no effect on LH-stimulated progesterone accumulation, it significantly reversed the inhibition by angiotensin II. This pattern was mirrored by the levels of mRNA encoding P-450scc, i.c., LH induced the highest levels of expression of this message, these levels were reduced by angiotensin II, and saralasin partially overcame this reduction. Levels of mRNA encoding bFGF were elevated by both LH and angiotensin II. Treatment with saralasin, however, resulted in complete inhibition of bFGF mRNA expression in the presence of both LH and angiotensin II. These results suggest a role for angiotensin II to mediate the action of LH as a regulator of bFGF expression and hence, potentially, angiogenesis. Local production of angiotensin II might also contribute to the refractoriness of luteal progesterone secretion to LH at the time of luteal regression.

Cyclic AMP-dependent and -independent regulation of cholesterol side chain cleavage cytochrome P-450 (P-450scc) in rat ovarian granulosa cells and corpora lutea. cDNA and deduced amino acid sequence of rat P-450scc

We report the isolating and sequencing of three cDNA clones encoding rat P-450scc, the nucleotide and protein sequences of which are highly homologous to those of bovine and human P-450scc, especially in the putative heme and steroid binding domains. We document that different molecular mechanisms regulate P-450scc in granulosa cells of preovulatory (PO) follicles prior to and after luteinization. Luteinizing hormone/human chorionic gonadotropin (LH/hCG) and cAMP are obligatory to induce P-450scc mRNA in PO granulosa cells in vivo and in vitro. Once P-450scc mRNA is induced as a consequence of the LH/hCG surge it is constitutively maintained by luteinized cells in vivo (0-4 days) and in vitro (0-9 days) in the absence of gonadotropins, is susceptible to modulation by prolactin and is no longer regulated by cAMP. Exposure to elevated concentrations of hCG in vivo for 5-7 h was required for PO granulosa cells to undergo a functional transition establishing the stable luteal cell phenotype. Transient exposure of PO + hCG (7 h) follicles in vitro to the RNA synthesis inhibitor actinomycin D (1 microgram/ml) or the protein synthesis inhibitor cycloheximide (10 micrograms/ml), for 1-5 h prior to culturing the granulosa cells failed to disrupt the induction of P-450scc mRNA, progesterone biosynthesis, and appearance of the luteal cell morphology. Inhibitors of protein kinase A (Rp-cAMPS; 1-500 microM and N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H8); 1-200 microM) added directly to the luteinized cell cultures also failed to alter P-450scc mRNA in these cells, although the cells contain in vivo amounts of mRNA for RII beta, RI alpha, and C alpha, the primary subunits of protein kinase A found in the rat ovary. These data suggest that expression of the P-450scc gene in rat ovarian follicular cells is regulated in a sequential manner by cAMP-dependent and cAMP-independent mechanisms associated with granulosa cells and luteal cells, respectively.

Characterization of two genes encoding human steroid 11 beta-hydroxylase (P-450(11) beta)

Steroid 11 beta-hydroxylase (P-450(11) beta) is a mitochondrial cytochrome P-450 enzyme necessary for cortisol biosynthesis. Deficiency of 11 beta-hydroxylase causes a hypertensive form of congenital adrenal hyperplasia. A partial cDNA clone encoding this enzyme has been previously isolated and the corresponding gene, CYP11B1, mapped to human chromosome 8q. This gene has now been isolated along with a second linked homologous gene, CYP11B2. Each gene contains nine exons. The eight introns are identical in location to the introns of the CYP11A gene encoding another mitochondrial P-450 enzyme, cholesterol desmolase, confirming that 11 beta-hydroxylase and cholesterol desmolase are in the same gene family within the P-450 superfamily. The nucleotide sequences of CYP11B1 and B2 are 95% identical in coding regions and about 90% identical in introns. The putative proteins encoded by CYP11B1 and B2 each contain 503 amino acids including a 24-residue signal peptide and have sequences that are 93% identical to each other and 75% identical to the predicted sequence of bovine P-450(11) beta. There are no obviously deleterious mutations in coding sequences of CYP11B2. However, the 5'-flanking regions of CYP11B1 and B2 have diverged considerably, and B2 transcripts were not detected in human adrenal mRNA or among cDNA clones.

The structural genes encoding P450scc and P450arom are closely linked on mouse chromosome 9

The chromosomal location of the two genes that encode the cytochrome P450 enzymes, P450SCC (cholesterol side-chain cleavage) and P450arom (aromatase), was identified in the mouse. Genomic DNA from several progenitor strains of recombinant inbred (RI) strains of mice was tested with various restriction endonucleases for restriction fragment length variations. Variation in Bam HI fragment length was detected between A/J and C57BL/6J. Genomic DNA from 43 RI strains derived from A/J and C57BL/6J was analyzed in a similar manner. Complete concordance of the strain distribution pattern for P450SCC and that of P450arom was observed for 43 RI strains. The lack of recombination indicates that the structural genes encoding P450SCC and P450arom are closely linked. The strain distribution patterns of the P450SCC and P450arom genes were compared with other markers previously mapped in these RI lines. The results demonstrate that both P450SCC and P450arom are found on mouse chromosome 9. Of the other loci on mouse chromosome 9, P450SCC and P450arom are most closely linked to the gene encoding P1450. Among 31 RI strains for which the three loci were analyzed, only one example of discordance was found. Human P450SCC, P450arom and P1450 have been mapped to human chromosome 15. However, the distance between the human P450SCC gene and other loci has not been determined. The information presented in this report, along with other studies, indicate conservation between homologous human and mouse chromosomal regions and suggest that human P450SCC will be found to be closely linked with human P450arom.

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.

Estradiol regulation of sterol carrier protein-2 independent of cytochrome P450 side-chain cleavage expression in the rat corpus luteum

A major action of estradiol in the corpus luteum of the pregnant rat is to increase the supply of cholesterol substrate for progesterone production by stimulating both cholesterol synthesis and uptake. To determine whether this steroid also affects cholesterol metabolism and transport, estradiol's action on the expression of cytochrome P450 side-chain cleavage enzyme (P450scc) and the cholesterol transport protein, sterol carrier protein-2 (SCP2), was examined. Mitochondria isolated from corpora lutea of estradiol-treated rats secreted significantly more progestagen than mitochondria of control corpora lutea. Several findings indicate that estradiol enhances cholesterol transport and availability to the P450scc rather than affects the expression of this enzyme: 1) the difference in mitochondrial progestagen synthesis induced by estradiol was obliterated by the presence of 25-hydroxycholesterol; 2) immunoblotting of P450scc indicated no stimulatory effect of estradiol on the amount of enzyme; and 3) levels of P450scc mRNA were not increased by estradiol. Whereas estradiol had no stimulatory effect on P450scc it caused a mark (3-fold) increase in the mitochondrial content of SCP2. Thus, the increase in luteal progestagen synthesis stimulated by estradiol appears to be associated with an increase in mitochondrial SCP2 and is independent of luteal P450 content or message.

Aromatase cytochrome P450 and cholesterol side-chain cleavage cytochrome P450 in corpora lutea of pregnant rats: diverse regulation by peptide and steroid hormones

In previous studies we have shown that aromatase cytochrome P450 (P450arom) mRNA and protein increase markedly in luteal tissue between days 10-19 of gestation, whereas cholesterol side-chain cleavage cytochrome P450 (P450scc) appears to be constitutively maintained regardless of hormonal changes occurring during pregnancy. To identify pituitary and placental hormones that regulate these two P450 enzymes in the rat corpus luteum, serum LH activity and pituitary PRL release were selectively inhibited by administration of LH antiserum (LH-Ab) or CB-154, respectively. Placental hormones were removed by hysterectomy. Hormonal activities were replaced by the administration of hCG, PRL, testosterone (T), or estradiol (E), given individually or in combination. Induction of aromatase mRNA transcripts (3.3, 2.6, and 1.9 kilobases) and protein (54,000 mol wt) between days 10-15 of gestation was blocked by either surgical hysterectomy or LH-Ab treatment. Hysterectomy on day 10 combined with CB-154 abolished not only aromatase mRNA, but also markedly reduced P450scc mRNA (2.0 kilobases) by day 12. Induction of aromatase was partially restored in the day 10-15 hysterectomized rats by treatment with PRL plus E (most effective), PRL plus T, or PRL alone, but not by either T or E alone. Similar results were observed 2 days after hysterectomy (day 12), except that hysterectomy alone caused a transient 3.5-fold increase in P450arom mRNA and protein, most likely due to a transient release of pituitary LH. Aromatase mRNA and protein were also increased in intact pregnant rats treated with hCG between days 10-12. However, no effect of hCG was observed before (days 8-10) or after (days 13-19) midgestation. Likewise, LH-Ab had no effect if given after day 13. Despite hormone-specific regulation of the content of aromatase protein, E biosynthesis in vitro was not strictly related to aromatase enzyme content. We conclude that aromatase mRNA and protein are maintained by PRL at a low level of expression in the first half of pregnancy, can be modulated by LH at midgestation, and are subsequently induced to high levels in the second half of gestation by placental factors (rat placental lactogen-1 and T) and the conversion of T to E in the corpus luteum. P450scc appears to be constitutively maintained. Thus, two P450 genes known to be regulated by LH/cAMP in the rat follicle are controlled by diverse peptide and steroid signal transduction mechanisms in the corpus luteum.

The roles of cAMP and cAMP-dependent protein kinase in the expression of cholesterol side chain cleavage and steroid 11 beta-hydroxylase genes in mouse adrenocortical tumor cells

The expression of the genes encoding cholesterol side chain cleavage enzyme (SCC) and steroid 11 beta-hydroxylase (11 beta-OHase) was examined in Y1 mouse adrenocortical tumor cells and in derivative cell lines defective in cAMP-dependent protein kinase activity. Y1 cells expressed both genes constitutively, and treatment with 8-bromo-cAMP (8-Br-cAMP) increased expression 5-10-fold. In three independent protein kinase mutants, expression of SCC and 11 beta-OHase was impaired to degrees dependent upon the severity of defect in cAMP-dependent protein kinase activity. In Kin-2, the least impaired mutant clone, basal expression of SCC was the same as in Y1 cells. Treatment of Kin-2 with 8-Br-cAMP increased SCC RNA to the levels seen in stimulated Y1 cells. In contrast, clone Kin-8, the most severe mutant, expressed markedly diminished basal and 8-Br-cAMP-stimulated levels of SCC mRNA. Kin-7 had basal and 8-Br-cAMP-stimulated levels of SCC mRNA which were intermediate to Kin-2 and Kin-8. None of the Kin mutants constitutively expressed detectable levels of 11 beta-OHase transcripts, and only Kin-2 responded to treatment with 8-Br-cAMP with increased expression of 11 beta-OHase; however, the time course of induction in Kin-2 was significantly delayed. The disparate patterns of expression of SCC and 11 beta-OHase in the Kin mutants suggest that these genes differ in their absolute requirement for cAMP-dependent protein kinase activity. Experiments also were performed in which Kin-7 and Kin-8 mutants were restored to cAMP-responsive states by transfection with genes encoding normal sub-units of cAMP-dependent protein kinase. These phenotypic revertants recovered 8-Br-cAMP-inducible expression of SCC and 11 beta-OHase. These results strongly support the hypothesis that impaired expression of steroidogenic enzymes in the Kin mutants results directly from defects in cAMP-dependent protein kinase activity.

Cytochromes P-45011 beta, P-450scc and adrenodoxin gene expression during adrenocortical regeneration in the rat

Circulating levels of 11-deoxycorticosterone are increased during the development of adrenal-regeneration hypertension. The present studies were undertaken to examine the mechanisms involved in this increase. Plasmids containing cDNA inserts coding for cytochrome P-45011 beta, cytochrome P-450scc and adrenodoxin were used to determine, by Northern blot analysis, mRNA levels at 1, 2 and 3 weeks of adrenal regeneration. There was a striking decrease in mRNA transcripts for all three enzymes during the first week of regeneration when compared with intact adrenal tissue. Over the next 2 weeks the mRNA levels increased to 64% for P-45011 beta, to 80% for P-450scc and to 82% for adrenodoxin. Actin mRNA levels were 70% of control levels in the first week but were back to control levels by the second week. The present findings suggest that decreased expression of steroid 11 beta-hydroxylase could contribute to the increased secretion of 11-deoxycorticosterone during the early stages of adrenal regeneration.

Effect of ACTH on the stability of mRNAs encoding bovine adrenocortical P-450scc, P-45011 beta, P-45017 alpha, P-450C21 and adrenodoxin

ACTH treatment of bovine adrenocortical cells in primary culture causes increased accumulation of mRNAs encoding cytochromes P-450SCC, P-450(11)beta, P-450(17) alpha, P-450C21 and adrenodoxin as well as increased transcriptional activity of their respective genes. In this study we have shown that ACTH does not greatly affect the half-life of mRNAs encoding P-450(11)beta, P-450(17)alpha, P-450C21 and adrenodoxin. However, in the case of P-450SCC mRNA, ACTH causes a five-fold increase in the half-life leading to a significant stabilization of P-450SCC mRNA. Thus it appears that the levels of mRNAs encoding P-450(11)beta, P-450(17)alpha, P-450C21 and adrenodoxin are regulated by ACTH primarily at the transcriptional level, while that for P-450SCC is regulated at both the transcriptional and post-transcriptional levels.

The 5'-region of the P450XIA1 (P450scc) gene contains a basal promoter and an adrenal-specific activating domain

The first step to the synthesis of all steroids is catalyzed by P450scc. We constructed nine deletion mutants of the 5'-region of the P450scc gene and connected them to a CAT reporter gene to assay transcriptional activity of the P450scc promoter. A short 145 bp fragment stimulated transcription by two fold. This DNA was active in all cells tested irrespective of their tissue origin and steroidogenic activity. DNA at -145/-573 of the upstream region did not increase transcription any further. DNA including 2500 bp of the upstream region stimulated transcription by 10 fold only in adrenal Y-1 cells. Hence in the -145 region contains a low level P450scc promoter and the 2500 bp DNA possesses an adrenal specific enhancing element.

Tissue distribution and levels of gene expression of three steroid hydroxylases in ovine fetal adrenal glands

Northern blotting and hybridization histochemistry were used to evaluate the ontogeny and cellular distribution of the mRNAs of the cytochrome P-450 enzymes: cholesterol side-chain cleavage (P-450scc), 17 alpha-hydroxylase (P-450(17 alpha] and 21-hydroxylase (P-450c21) in 40 ovine fetal adrenals from 42 days of gestation until term (151 days). The genes for P-450(17 alpha) and P-450scc were expressed strongly in tissue from young (40-60 days) and old fetuses (120 days to term), but to a very minor degree in 90-120 day fetuses. P-450c21 showed a steady increase throughout gestation. In the morphologically immature an unzoned adrenal of the 40-50 day fetus there was some differentiation in gene expression, all cells containing P-450scc and P-450c21 but a few lacking P-450(17 alpha). Once morphological zonation had occurred (80 days), P-450(17 alpha) was confined to the fasciculata. After 120 days there was a radial maturation pattern of the fasciculata cells morphologically, adult-type cells first appearing at the medullary border. However, P-450(17 alpha) and P-450scc mRNAs were equally well expressed in all sections of the fasciculata. The conclusions were: 1) the previously demonstrated triphasic cortisol biosynthetic capacity of ovine fetal adrenals was correlated with the presence, absence, and reappearance of mRNAs P-450(17 alpha) and P-450scc; 2) morphological appearance of fetal adrenocortical cells and expression of three major steroidogenic enzyme genes were not correlated.

Cellular senescence involves stochastic processes causing loss of expression of differentiated function genes: transfection with SV40 as a means for dissociating effects of senescence on growth and on differentiated function gene expression

In the accompanying work we demonstrated that the decline in expression of steroid 17 alpha-hydroxylase in mass cultures and clones of adrenocortical cells is the result of a stochastic switching process which yields mixtures of expressing and nonexpressing cells. There is an apparent positive correlation between the replicative potential of adrenocortical cell cultures and the number of cells in the culture that can express 17 alpha-hydroxylase. We investigated this by extending the cells' replicative potential by transfecting them with cloned SV40 virus. Cells from a senescent subclone, with very limited remaining replicative potential, were transfected. The cell population showed a progressive increase in growth rate and gave rise to a line of cells that expressed T antigen and which was apparently immortalized. Induction of mRNA for 17 alpha-hydroxylase by cyclic AMP was absent in this line of cells, as it was in the senescent cells prior to transfection. The cells remained responsive to gene induction by cyclic AMP as evidenced by increases in mRNA and activity for cholesterol side-chain cleavage. The absence of 17 alpha-hydroxylase expression in this line was not the result of interference by SV40 T antigen. When early passage cells were transfected with pSV3neo, which contains the early region of SV40 and neo, and were selected with G418, SV40 T antigen-expressing lines were derived which showed high levels of expression of 17 alpha-hydroxylase after induction with cyclic AMP. These cells maintained high levels of expression of 17 alpha-hydroxylase through four successive recloning events, over a period of replication much longer than that achievable by nontransfected cells. Thus, transfection by SV40 can be used to dissociate effects of senescence on growth and differentiated gene expression. T antigen expression selectively affects growth, but preserves the state of expression of a differentiated function gene as it was prior to transfection.

Effects of dietary sodium restriction and potassium intake on cholesterol side-chain cleavage cytochrome P-450 and adrenodoxin mRNA levels

We studied the effect of dietary sodium restriction (3 weeks) and high potassium intake (7 days) on transcriptional regulation of cytochrome P-450 cholesterol side chain cleavage (P-450 scc) and adrenodoxin (Adx) in rat adrenal glands. Northern blotting analysis demonstrated that both treatments markedly increased P-450scc and Adx mRNA levels in the zona glomerulosa (Z-G) and the zona fasciculata-reticularis (Z-F-R) compared with controls. The Z-G appears to be more sensitive to variations in electrolytes than does the Z-F-R. The low sodium diet provoked a 2.9-fold increase in P-450scc mRNA level in the Z-G compared to 2.1-fold in the Z-F-R, whereas Adx mRNA levels were enhanced 2.2- and 1.7-fold respectively in these two zones. Restriction of sodium intake provoked significant increases in plasma ACTH, aldosterone and corticosteroids compared with controls. In the Z-G of KCl-loaded rats, we found a 1.6-fold increase in P-450scc and a 2.1-fold increase in Adx mRNA levels, and in the Z-F-R there was a 1.7- and 1.8-fold enhancement. There were no changes in beta-actin mRNA levels upon dietary treatments. These results thus indicate that both sodium depletion and high potassium intake in rats could act at the transcriptional level of P-450scc and Adx, two components of a rate-limiting step in steroidogenesis leading to aldosterone production. In addition, the elevation in plasma ACTH level in response to Na+ restriction suggests a possible involvement of ACTH in the response of the adrenal glands to sodium depletion.

Human adrenodoxin: cloning of three cDNAs and cycloheximide enhancement in JEG-3 cells

Adrenodoxin is an iron-sulfur protein serving as an electron transport intermediate for two mitochondrial steroidogenic cytochromes P450. We have cloned and sequenced three human adrenal adrenodoxin cDNAs. The longest 5'-untranslated region was 131 bases long, and the coding sequences, identical in all three clones, predict a preprotein of 180 amino acids. The 3'-untranslated regions were 235, 596, and 776 bases long due to the presence of alternate polyadenylation sites. RNA transfer blots showed multiple size species of adrenodoxin mRNA consistent with finding multiple polyadenylation sites. Similar sized cross-hybridizing RNA species are found abundantly in the adrenal and testis and to a lesser degree in RNA from human fetal brain, spleen, placenta, kidney, liver, and intestine, as well as in cultured fibroblasts, suggesting the same or a very similar iron-sulfur protein is found in mitochondria of nonsteroidogenic tissues. JEG-3 cells, a transformed progesterone-producing line of trophoblastic origin, accumulate mRNAs for cytochrome P450scc (the mitochondrial cholesterol side-chain cleavage enzyme), adrenodoxin, and the fos oncogene when stimulated with 8-bromo-cyclic AMP. Addition of actinomycin D to such cultures blocked cAMP-induced accumulation of mRNAs for cytochrome P450scc and adrenodoxin. Addition of cycloheximide or puromycin to such cultures substantially reduced basal levels and markedly attenuated the cAMP-induced accumulation of cytochrome P450scc mRNA, but augmented the accumulation of adrenodoxin and fos mRNAs in additive and multiplicative fashions, respectively. These data indicate that the cAMP-induced synthesis of the steroidogenic machinery is not wholly dependent on cycloheximide-sensitive protein mediators.