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.

Simultaneous transfection of COS-1 cells with mitochondrial and microsomal steroid hydroxylases: incorporation of a steroidogenic pathway into nonsteroidogenic cells

Transfected, nonsteroidogenic COS-1 cells derived from monkey kidney are found to be capable of supporting the initial and rate-limiting step common to all steroidogenic pathways, the side-chain cleavage of cholesterol to produce pregnenolone. Endogenous COS-1 kidney cell renodoxin reductase and renodoxin are able to sustain low levels of this activity catalyzed by bovine cholesterol side-chain cleavage cytochrome P450 (P450scc) whose synthesis is directed by a transfected plasmid containing P450scc cDNA. Double transfection with both P450scc and adrenodoxin plasmids leads to greater pregnenolone production and indicates that adrenodoxin plays a role as a substrate for this reaction or that bovine adrenodoxin serves as a better electron donor than the endogenous iron-sulfur protein renodoxin. Also it is found that both the bovine adrenodoxin and P450scc precursor proteins are proteolytically processed upon their uptake by COS-1 cell mitochondria to forms having the same electrophoretic mobility as mature bovine adrenodoxin and P450scc. Following triple transfection of COS-1 cells with P450scc, adrenodoxin, and 17 alpha-hydroxylase cytochrome P450 plasmids, pregnenolone produced in mitochondria by the side-chain cleavage reaction can be further metabolized in the endoplasmic reticulum to 17 alpha-hydroxypregnenolone and dehydroepiandrosterone. Although this functional steroidogenic pathway can be incorporated into this nonsteroidogenic cell type, it is found to be nonresponsive to cAMP, a potent activator of steroid hormone biosynthesis in adrenal cortex, testis, and ovary. Thus the cellular mechanisms necessary to support both microsomal and mitochondrial steroid hydroxylase activities appear not to be tissue specific, whereas the acute cAMP-dependent regulation of steroidogenesis is not present in transformed kidney (COS-1) cells.

The 5'-flanking region of the human P-450(SCC) gene shows responsiveness to cAMP-dependent regulation in a transient gene-expression system of Y-1 adrenal tumor cells

The chronic effect of cAMP-dependent regulation on adrenocortical steroidogenesis is known to be revealed in the stimulation of the biosynthesis of steroidogenic enzymes. P-450(SCC), one of the enzymes, catalyzes the first and the rate-limiting reaction in steroidogenesis from cholesterol and its synthesis is regulated by cAMP. In order to investigate cis-acting DNA elements of this gene in response to cAMP-dependent regulation, we have constructed a fusion gene (pSCC5.4k) by ligating the 5'-flanking and the upstream untranslated region (5.4 kb) of the human P-450(SCC) gene to the structural gene for chloramphenicol acetyltransferase (CAT) and transfected it into various culture cells including Y-1 (mouse adrenal tumor), L929 (mouse fibroblast), HTC (rat hepatoma) and Hepa-1 (mouse hepatoma). Only Y-1 cells transfected with pSCC5.4k were found to express transiently the enhanced CAT activity in response to the cAMP analogue, cyclic dibutyryl-AMP (Bt2cAMP). Primer-extension analysis of RNA prepared from the cells treated with or without Bt2cAMP showed that the enhanced CAT activity was due to an increase in the CAT mRNA and that the transcription start site, determined here with the human P-450 gene in the adrenal cortex, was correctly utilized with the fusion gene in the transient expression system. Forskolin and cholera toxin, activators of adenylate cyclase, also increased the expression of the CAT activity in the Y-1 cells. It has been demonstrated, therefore, that the cAMP-dependent regulation of the P-450(SCC) gene in adrenal cortex is faithfully reflected in the transient expression system using Y-1 cells and the fusion gene and that a cis-acting DNA element(s) in response to cAMP is present within the 5'-flanking sequence (5.4 kb) of the P-450(SCC) gene.

Site-directed mutagenesis of basic amino acid residues in the extension peptide of P-450(SCC) precursor: effects on the import of the precursor into mitochondria

The precursor of cytochrome P-450(SCC) (preP-450(SCC], an inner membrane protein of adrenal cortex mitochondria, has an extension peptide consisting of 39 amino acids which is thought to play an essential role in the import of the precursor into mitochondria. The amino terminal portion of the extension peptide contains three positively charged amino acid residues, Arg(4), Arg(9), and Lys(14). To investigate their role in the import of preP-450(SCC) into mitochondria, they were replaced by other amino acids, Ser or Thr, by site-directed mutagenesis. The import of mutated preP-450(SCC)s with single amino acid substitution was much less efficient than with the original precursor. The mutated preP-450(SCC)s with two or three substitutions were not imported. These results suggest that the positively charged amino acid residues in the amino terminal portion of the extension peptide are essential for the import of preP-450(SCC) into mitochondria.

Hormonal regulation of messenger ribonucleic acids for P450scc (cholesterol side-chain cleavage enzyme) and P450c17 (17 alpha-hydroxylase/17,20-lyase) in cultured human fetal adrenal cells

ACTH has acute and long term effects on adrenal steroidogenesis by week 14 of fetal life. We used human fetal adrenal cells to investigate the long term effect of physiological doses of ACTH on mRNAs for P450scc (the cholesterol side-chain cleavage enzyme) and P450c17 (17 alpha-hydroxylase/17,20-lyase). Monolayer cultures of 18- to 24-week gestation fetal zone adrenal cells were maintained in the presence and absence of 10(-9) or 10(-8) M ACTH for up to 12 days. As assessed by RNA dot blots probed with cloned homologous human cDNAs, ACTH increased P450scc and P450c17 mRNAs 4- and 9-fold, respectively, over control values on day 7 of culture. ACTH-mediated stimulation was slightly less on day 12 of culture. The ACTH-mediated accumulation of those mRNAs were time dependent. When cells were exposed to a single 10(-8)-M dose of ACTH, the amount of P450scc and P450c17 mRNA was increased by 24 h, reaching a maximum at 48 h and diminishing by 72 h. When cells were maintained in 10(-8) M ACTH continuously, mRNA for both enzymes accumulated in a similar pattern, reaching a peak at 48 h but remaining at nearly maximal values thereafter, up to 96 h. Dibutyryl cAMP (10(-3) M) mimicked these stimulatory actions of ACTH, although its effect was greater at 24 h and more stable up to 96 h. Angiotensin II (1-100 ng/mL) and hCG (1-100 ng/mL) had no effect on accumulation of P450scc and P450c17 mRNAs. The production of both dehydroepiandrosterone sulfate and cortisol also was stimulated by ACTH, suggesting that the increased mRNAs were translated into active enzymes. These results indicate that ACTH induces human fetal adrenal cells to accumulate mRNAs for both P450scc and P450c17; this effect of ACTH is probably mediated by cAMP. Chronic 96-h stimulation of human fetal adrenal cells did not diminish their responsiveness to ACTH. Together with our earlier studies of the human fetal adrenal, these data indicate that fetal adrenal tissue does not exhibit the desensitization to trophic hormone stimulation characteristic of adult tissue.

Effects of epidermal growth factor on the synthesis of the cholesterol side-chain cleavage enzyme complex in rat ovarian granulosa cells in primary culture

The effect of epidermal growth factor (EGF) on the synthesis of the components of the cholesterol side-chain cleavage enzyme complex (SCC) was studied in rat ovarian granulosa cells. The cells were cultured for 48 h in the presence or absence of EGF (15 ng/ml) and/or FSH (50 ng/ml) after which proteins were radiolabeled by incubation with [35S]methionine followed by immunoprecipitation of newly synthesized P-450scc or adrenodoxin (ISP) with polyclonal antibodies directed against the corresponding proteins from bovine adrenal cortex. In addition the action of EGF on the level of translatable RNA for P-450scc was evaluated using a cell-free translation system programmed with RNA isolated from treated and untreated cells, followed by immunoisolation of newly synthesized proteins. Immunoisolated proteins were separated by polyacrylamide-gel electrophoresis, visualized by fluorography and quantified by densitometry. EGF stimulated progesterone formation by the cells 3-fold and potentiated the FSH-induced stimulation of progesterone formation, but had no effect on cAMP accumulation. EGF also stimulated the synthesis of P-450scc and ISP, and enhanced the FSH-induced synthesis of P-450scc and ISP in a concentration-dependent fashion with a maximal stimulation attained at concentrations ranging from 1.0 to 100 ng/ml. No appreciable changes in the induction pattern were observed when EGF and dibutyryl cyclic AMP (Bt2cAMP) were added together, as compared to when Bt2cAMP was added alone. Neither treatment affected the synthesis of the constitutive mitochondrial enzyme, F1-ATPase. Immunoisolation of P-450scc from the proteins synthesized in a rabbit reticulocyte in vitro translation system programmed with RNA isolated from EGF- and/or FSH-treated cells, revealed that EGF enhanced the FSH-stimulated synthesis of the precursor form of P-450scc.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol side-chain cleavage P450 messenger ribonucleic acid: evidence for hormonal regulation in rat ovarian follicles and constitutive expression in corpora lutea

Using an affinity-purified antibody against cholesterol side-chain cleavage P450 (P450scc) and a human P450scc cDNA probe, 11 rat P450scc cDNA clones were identified and isolated from our rat granulosa cell lambda gt11 cDNA expression library. Two clones were plaque purified and subcloned into pBR322. One of these P450scc cDNA clones, approximately 1.2 kilobases (kb) in size, was used as a probe for Northern and filter hybridization assays to analyze the tissue distribution and hormonal regulation of P450scc mRNA in rat ovarian follicles and corpora lutea. Northern transfers revealed a single P450scc mRNA species about 2.0 kb in size. Filter hybridization assays showed that P450scc mRNA was low in granulosa cells and thecal cells of small antral follicles, was increased in both tissues of preovulatory follicles, and was rapidly (within 7 h) and maximally increased (30-fold) during hCG-induced luteinization. P450scc enzyme and mRNA were also elevated in corpora lutea isolated from pregnant rats (days 4-22 of gestation) and rats 1 day after parturition (day 23). The elevation of P450scc enzyme and mRNA was maintained despite the marked decline in serum progesterone concentrations between days 19-22, suggesting that once P450scc mRNA is induced in luteal tissue it may be constitutively expressed. Administering hormones to granulosa cells in culture and to hypophysectomized immature rats in vivo demonstrated that the induction of P450scc mRNA by FSH in granulosa cells was time, dose, and estradiol dependent. High doses of FSH acting on estradiol-primed cells gave the greatest response. The increase in P450scc mRNA in cultured granulosa cells was also stimulated by forskolin and was directly associated with increased synthesis of cAMP and progesterone accumulation. Thus, whereas the induction of P450scc mRNA in granulosa cells was dependent on hormones and cAMP, the maintenance of P450scc mRNA and P450scc protein in corpora lutea appears to involve constitutive expression of P450scc mRNA.

Gene structure of human cytochrome P-450(SCC), cholesterol desmolase

Four independent clones containing a part of the P-450(SCC), cholesterol desmolase, gene were isolated from human genomic libraries using bovine P-450(SCC) cDNA as a probe. These clones covered the entire P-450(SCC) gene except for a part of the 1st intron. The gene is at least 20 kb long and is split into 9 exons by 8 introns. The sequence analysis revealed that the nine separated exons code for a primary structure consisting of 521 amino acids which shows 72% homology with that of bovine P-450(SCC). A CATT sequence and a TATAAT sequence, which are possibly a "CAT" box, and a "TATA" box, respectively, are present 129 and 91 bp upstream from the initiation codon. An unusual exon/intron junctional sequence that begins with GC was found in the 6th intron of the gene. A putative extension peptide consisting of 39 amino acids was found in the sequence of human P-450(SCC) by comparison with that of the bovine counterpart. Two conserved regions were found in the extension peptide of these two forms of P-450(SCC), suggesting a functional role of the portions in the mitochondrial localization and processing of P-450(SCC) precursor. The mature form of human P-450(SCC) has only one cysteine residue, which was located in the center of the HR2 region (Gotoh et al. (1983) J. Biochem. 97, 807-817). This observation established beyond doubt that the sole cysteine residue in the HR2 region is the 5th ligand to the heme.

Levels of messenger ribonucleic acid encoding cholesterol side-chain cleavage cytochrome P-450, 17 alpha-hydroxylase cytochrome P-450, adrenodoxin, and low density lipoprotein receptor in bovine follicles and corpora lutea throughout the ovarian cycle

To investigate the molecular basis for the pattern of ovarian steroid production during the bovine estrous cycle, the relative levels of mRNA specific for cholesterol side-chain cleavage cytochrome P-450, 17 alpha-hydroxylase cytochrome P-450, adrenodoxin, and low density lipoprotein receptor were determined in ovarian antral follicles of differing size (less than 3-18 mm) and corpora lutea from the early, early-mid, late-mid, and regressionary stages. Total and poly(A)+ RNA was size-fractionated on agarose-formaldehyde gels, transferred to nylon filters and hybridized to specific 32P-labeled probes. The levels of mRNAs for the rate-limiting enzymes in the conversion of cholesterol into progesterone, namely cholesterol side-chain cleavage cytochrome P-450 and its electron donor, adrenodoxin, were higher in corpora lutea than in follicles. Conversely the levels of mRNA specific for the key regulatory enzyme in the conversion of pregnenolone or progesterone to androgen, namely 17 alpha-hydroxylase cytochrome P-450, were high in all antral follicles examined but were low in young corpora lutea and undetectable in more mature corpora lutea. Low density lipoprotein receptor mRNA was detectable in antral follicles and corpora lutea but the levels were greater in corpora lutea. These results suggest that the pattern of changes in steroid hormone biosynthesis during the bovine estrous cycle and in the ovarian content of steroidogenic enzymes is related to and probably dependent upon the pattern of change in levels of mRNAs for steroidogenic enzymes and related proteins.

Coordinate tropic hormone regulation of mRNAs for insulin-like growth factor II and the cholesterol side-chain-cleavage enzyme, P450scc [corrected], in human steroidogenic tissues

Insulin-like growth factors (IGFs) are single-chain polypeptides important for cell proliferation and growth. IGFs are produced in several tissues, suggesting that they function in a paracrine or autocrine fashion as well as functioning as endocrine hormones. We studied the hormonal regulation of IGF-I and IGF-II mRNA in human steroidogenic tissues. In cultured human ovarian granulosa cells, follicle-stimulating hormone, human chorionic gonadotropin, and dibutyryl cAMP increased IGF-II mRNA, but corticotropin [adrenocorticotropic hormone (ACTH)], chorionic somatomammotropin, growth hormone, prolactin, dexamethasone, estradiol, and progesterone had no effect. In cultured human fetal adrenal cells, ACTH and dibutyryl cAMP increased IGF-II mRNA accumulation, but human chorionic gonadotropin and angiotensin II did not. The same five size species of IGF-II mRNA were detected in transfer blots of RNA from granulosa cells and fetal adrenal cells, and all of these increased after hormonal stimuli. Dibutyryl cAMP also increased IGF-II mRNA accumulation in cultured human placental cells. Accumulation of mRNA for the cholesterol side-chain-cleavage monooxygenase [P450scc [corrected]; cholesterol, reduced-adrenal-ferredoxin:oxygen oxidoreductase (side-chain-cleaving), EC 1.14.15.6] was regulated in parallel with IGF-II mRNA in all these steroidogenic tissues. IGF-I mRNA was not detected in transfer blots of these RNAs, and the minimal amounts detected in dot blots showed no detectable change after any of the hormonal stimuli studied. The data indicate that the IGF-II gene is expressed in human steroidogenic tissues and is regulated by cAMP. These data suggest that IGF-II may act in an autocrine or paracrine fashion to stimulate the adrenal and gonadal growth stimulated by ACTH and gonadotropins, respectively.

Rat cholesterol side-chain cleavage enzyme (P-450scc): use of a cDNA probe to study the hormonal regulation of P-450scc mRNA levels in ovarian granulosa cells

A rat ovarian cDNA library was constructed and screened by differential colony hybridization to detect cDNA clones specific for mRNA induced by follicle-stimulating hormone (FSH). The cDNA clone which demonstrated the greatest degree of induction contained a 766-bp insert which was characterized and sequenced. We conclude that this cDNA is specific for the rat gene coding for cholesterol side-chain cleavage enzyme (P-450scc) by virtue of nucleotide sequence homology to the bovine and human P-450scc cDNA sequences. Southern blotting of rat genomic DNA suggests the presence of a single P-450scc gene. Northern blot analysis indicates that P-450scc mRNA is present in steroidogenic tissues (ovary, adrenal, testis), but not in brain, kidney, liver, lung, or heart. The rat P-450scc mRNA is induced by FSH or pregnant mare's serum gonadotropin in ovaries of estrogen-treated immature rats in vivo. In cultured granulosa cells, estradiol treatment alone did not increase P-450scc mRNA levels, but in combination with FSH or 8-Br-cAMP resulted in three- to four-fold increase in this mRNA.