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

The adiponectin paralog C1q/TNF-related protein 3 (CTRP3) stimulates testosterone production through the cAMP/PKA signaling pathway

CTRP3, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. It is expressed at high levels in adipose tissue and has recently emerged as a novel adipokine. In the present study, we provide the first evidence for a physiological role of the new adipokine, CTRP3, in the reproductive system. CTRP3 was specifically expressed in interstitial Leydig cells, where testosterone is produced, in the adult mouse testis. CTRP3 increased testosterone production by TM3 mouse Leydig cells in a dose-dependent manner. The increased testosterone production was linked to upregulation of steroidogenic proteins expression, such as steroidogenic acute regulatory (StAR) protein and cholesterol side-chain cleavage cytochrome P450 (P450scc). Moreover, increases in intracellular cyclic AMP (cAMP) concentrations and the phosphorylation of cAMP-response element binding protein (CREB) in CTRP3-stimulated TM3 Leydig cells were observed. Inhibition of this signaling pathway by a specific protein kinase A (PKA) inhibitor, H89, blocked testosterone production in CTRP3-stimulated Leydig cells, suggesting that the stimulatory effect of CTRP3 on testosterone production is associated with activation of the cAMP/PKA signaling pathway. Thus, our results demonstrate a physiological role for CTRP3 in testicular steroidogenesis and provide novel insights in the intracellular mechanisms activated by this protein.

HumanCYP11A1 promoter drives Cre recombinase expression in the brain in addition to adrenals and gonads

The first step of steroid biosynthesis is catalyzed by cytochrome P450scc, encoded by CYP11A1. To achieve steroidogenic tissue-specific inactivation of genes in vivo by the Cre-loxP approach, we used the 4.4-kb regulatory region of the human CYP11A1 gene to drive Cre recombinase expression in the tissues that produce steroids. The resulting SCC-Cre mice express high levels of Cre in the adrenal cortex and gonads at the same sites as that for the endogenous CYP11A1 expression. In addition, Cre activity was found in the diencephalon and midbrain. In the developing brain, the Cre activity was first detected in the embryonic day 10.5. Our study is the first to show that the 4.4-kb CYP11A1 promoter is transcriptionally active in the brain in vivo.

Salt-inducible kinase in steroidogenesis and adipogenesis

The salt-inducible kinases (SIKs) are a family of related serine-threonine kinases. In cultured adrenocortical cells, SIK1 is rapidly but transiently induced by adrenocorticotropin (ACTH) treatment, suggesting that it contributes to ACTH-mediated induction of steroidogenic enzymes. However, ACTH treatment of Y1 mouse adrenocortical cells stimulates a rapid translocation of SIK1 from the nucleus to the cytoplasm, and SIK1 represses the transcription of a steroidogenic enzyme by inhibiting the action of cAMP-responsive elements in the promoter. These studies suggest that SIK1 has a role in the fine tuning of steroidogenic enzyme production during the initial phase of steroidogenesis. SIK2 is found in adipocytes and phosphorylates a specific serine residue in insulin receptor substrate-1. This finding, along with the fact that its expression is raised in the white adipose tissue of mice with type 2 diabetes mellitus, suggests that SIK2 might be involved in metabolic regulation in adipose tissue. Thus, members of the SIK family are emerging as important modulators of key processes such as steroid hormone biosynthesis by the adrenal cortex and insulin signaling in adipocytes.

Salt-inducible kinase represses cAMP-dependent protein kinase-mediated activation of human cholesterol side chain cleavage cytochrome P450 promoter through the CREB basic leucine zipper domain

Salt-inducible kinase (SIK), one of the serine/threonine protein kinases, was transiently expressed in Y1 cells during the early phase of the ACTH/cAMP-dependent protein kinase (PKA)-mediated signal transduction. The overexpression of SIK(N), the SIK's N-terminal kinase domain, repressed the expression of the side chain cleavage cytochrome P450 (CYP11A) gene. To elucidate the mechanism of the repression by SIK, several CYP11A promoter constructs were tested for the promoter activities in the presence of PKA and/or SIK(N). A cAMP-response element (CRE)-like sequence present in the promoter was shown to be responsible not only for the PKA-mediated promoter activation but also for the SIK(N)-mediated repression. When the Gal4 DNA binding domain-linked full-length CRE-binding protein (CREB) construct was cotransfected with Gal4 reporter gene, SIK(N) repressed the PKA-induced reporter gene expression. However, SIK(N) could not repress the PKA-induced reporter activity conferred by Gal4 DNA binding domain-linked basic leucine zipper (bZIP)-less CREB or bZIP-disrupted CREB. On the other hand, SIK(N) could repress the kinase-inducible domain-disrupted CREB-dependent reporter gene expression in the presence of PKA. The in vitro kinase reaction studies showed that SIK(N) could not phosphorylate CREB, and PKA failed to phosphorylate SIK(N). Taken together, these results suggest that SIK(N), cooperating with PKA, may act on the CREB's bZIP domain and repress the CREB-mediated transcriptional activation of the CYP11A gene.

A novel zinc finger protein TReP-132 interacts with CBP/p300 to regulate human CYP11A1 gene expression

The human CYP11A1 gene is expressed specifically in steroidogenic tissues and encodes cytochrome P450scc, which catalyzes the first step in steroid synthesis. A region of the 5'-flanking DNA of the gene from nucleotides -155 to -131 (-155/-131) is shown to activate transcription in steroidogenic human placental JEG-3 (1) and adrenal NCI-H295 cells. Using this region of the gene as probe, a cDNA clone of 4.4 kilobase pairs was isolated by screening JEG-3 cell and human placental cDNA expression libraries. The open reading frame encodes three zinc fingers of the C(2)H(2) subtype, and separate regions rich in glutamate, proline, and glutamine, which are indicative of a DNA-binding protein involved in gene transcription. Expression of the cDNA in vitro and in HeLa cells yields a protein of 132 kDa, which concurs with the predicted size. Northern blot analysis demonstrate expression of two TReP-132 transcripts of 4.4 and 7.5 kilobase pairs in the thymus, adrenal cortex, and testis; and expression is also found in the steroidogenic JEG-3, NCI-H295, and MCF-7 cell lines. Immunocytochemistry analysis demonstrates localization of the HA-tagged TReP-132 protein in the nucleus. The expression of exogenous TReP-132 in HeLa cells was demonstrated to interact with the -155/-131 region in bandshift analysis. Transfection of the cDNA in placental JEG-3 and adrenal NCI-H295 cells increases expression of a reporter construct controlled by the P450scc gene 5'-flanking region from nucleotides -1676 to +49. Moreover, a chimeric protein generated by fusion of TReP-132 with the Gal4 DNA-binding domain was able to significantly increase promoter activity of a reporter construct via Gal4-binding sites upstream of the E1b minimal promoter. Coexpression of CREB-binding protein (CBP)/p300 with TReP-132 has an additive effect on promoter activity, and the proteins were demonstrated to interact physically. Thus, these results together indicate the isolation of a novel zinc-finger transcriptional regulating protein of 132 kDa (TReP-132) involved in the regulation of P450scc gene expression.

Functions of the upstream and proximal steroidogenic factor 1 (SF-1)-binding sites in the CYP11A1 promoter in basal transcription and hormonal response

The CYP11A1 gene encodes P450scc (cholesterol side-chain cleavage enzyme), which catalyzes the first step for the synthesis of steroids. Expression of CYP11A1 is controlled by transcription factor SF-1 (steroidogenic factor 1). Two functional SF-1-binding sites, P and U, located at -40 and -1,600 regions of the CYP11A1 gene, have been identified, but their exact functions with respect to basal activation vs. cAMP response have not been dissected. We have addressed this question by examining the ability of the mutated human CYP11A1 promoter to drive LacZ reporter gene expression in transgenic mouse lines. The activity of the mtP mutant promoter was greatly reduced, indicating the importance of the P site. Mutation of the upstream U site also resulted in reduced reporter gene expression, but some residual activity remained. This residual reporter gene activity was detected in the adrenal and gonad in a tissue-specific manner. ACTH and hCG can stimulate LacZ gene expression in the adrenals and testes of transgenic mice driven by the wild-type but not the mtU promoter. These results indicate that the upstream SF-1-binding site is required for hormonal stimulation. Our experiments demonstrate the participation of both the proximal and the upstream SF-1-binding sites in hormone-responsive transcription.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

Activator protein-2 mediates transcriptional activation of the CYP11A1 gene by interaction with Sp1 rather than binding to DNA

The ovine P45 side chain cleavage (CYP11A1) enzyme gene, which catalyzes the initial enzymatic step in steroid hormone biosynthesis is transcriptionally regulated in cultured steroidogenic human trophoblastic JEG-3 cells. The ovine CYP11A1 promoter contains two GC-rich footprinted regions referred to as ovine footprints 5 (OF5) and OF3, which are well conserved among the CYP11A1 promoters of different species. These GC-rich sequences resemble activator protein-2 (AP-2)/Sp1 binding sites and were previously implicated in basal and cAMP-regulated activity of the bovine and ovine CYP11A1 promoters. In the current studies, AP-2 induced the ovine CYP11A1 promoter 4.5-fold in JEG-3 cells with full induction requiring the previously defined cAMP-responsive elements. Point mutation of OF3 abolished induction by AP-2, and OF3 was sufficient for induction by AP-2 when linked to a heterologous promoter. AP-2 induction of the CYP11A1 promoter required the basic region (N165-N278) and the carboxy terminus of AP-2 (N413-N437). In the course of investigating the mechanisms by which OF5 and OF3 regulated CYP11A1 transcription, we found that OF5 and OF3 bound Sp1 and Sp3 in JEG-3 cells. AP-2 did not bind OF5 or OF3 directly but rather formed a multiprotein complex with Sp1 in JEG-3 cells. AP-2 associated directly with Sp1 in vitro requiring the AP-2 basic region and the Sp1 carboxy terminus. AP-2 induced Sp1/Sp3 activity independently of AP-2 binding to DNA using a GAL4 paradigm. The Sp1 and Sp3 transactivation domains were linked to the DNA-binding domain of GAL4, and their activity was assessed using a luciferase reporter gene containing only the GAL4 DNA-binding sites linked to the minimal TATA site. AP-2 induced Sp1/ Sp3-GAL4 activity 3- to 4-fold, requiring both the amino and extreme carboxy terminus of AP-2. We conclude that AP-2 can bind to and stimulate Sp1 activity and induces the ovine CYP11A1 promoter through conserved Sp1/Sp3-binding sites in JEG-3 cells. The induction of Sp1 activity by AP-2 may contribute to the induction of other genes that bind Sp1.

Circadian expression of the maize catalase Cat3 gene is highly conserved among diverse maize genotypes with structurally different promoters

The Cat3 gene of maize exhibits a transcriptionally regulated circadian rhythm. In the present study we examined the following: (1) the extent of the circadian Cat3 expression between maize genotypes of diverse origin; (2) the functional significance of a Tourist transposable element located in the Cat3 promoter of the inbred line W64A, which harbors putative regulatory elements (GATA repeat, CCAAT boxes) shown to be involved in the light induction and circadian regulation of the Arabidopsis CAB2, as well as other plant genes; and (3) aspects of the physiological role of CAT-3 in maize metabolism. Results confirm that the circadian Cat3 expression is a general phenomenon in maize. Regulation of Cat3 gene expression is not dependent on the presence of the Tourist element in the promoter of the gene nor on the presence of motifs similar to those found significant in the circadian expression of the Arabidopsis CAB2 gene. Structural diversity was revealed in the Cat3 promoters of maize genotypes of diverse origins. However, highly conserved regions with putative regulatory motifs were identified. Relevance of the conserved regions to the circadian regulation of the gene is discussed. Possible physiological roles of CAT-3 are suggested.

Regulation of the human P450scc gene by steroidogenic factor 1 is mediated by CBP/p300

Regulation of the human CYP11A gene encoding cytochrome P450scc, which catalyzes the first step of steroid synthesis, is regulated by many trans-acting transcription factors including steroidogenic factor 1 (SF-1). Transfection experiments in human adrenal NCI-H295 cells demonstrate regulation of the P450scc gene promoter region that contains several putative SF-1 binding sites. Cotransfection of SF-1 with a luciferase reporter construct containing the P450scc gene 5'-flanking region from nucleotides -1676 to +49 increased promoter activity, and deletion of the nucleotide sequence from position -1676 to -1620, which removes a putative cAMP response element (CRE), did not affect the stimulatory response to SF-1. As well, further deletion of the promoter region to nucleotide -110, which contains only one SF-1 binding site, still retained the ability to respond to exogenous SF-1. However, mutation of the remaining site which abolished SF-1 protein/DNA interaction also abrogated any functional response to the factor. All the P450scc reporter constructs which responded to SF-1 were further stimulated by exogenous p300 and CREB-binding protein (CBP), suggesting interaction between SF-1 and p300/CBP. As well, mutation of the binding site that abrogated the response to SF-1 also abolished the response to p300 and CBP. Cotransfection of the adenovirus E1A oncoprotein, which has been shown to interact with p300/CBP and interfere with its function, decreased the stimulatory effect of SF-1 and p300/CBP. Cotransfection of a mutated E1A protein, RG2, which does not interact with p300/CBP, did not alter the stimulatory effect of SF-1 and p300/CBP on the P450scc promoter. Deletion of the region from amino acid residues 2-67 in E1A, which has been postulated to interact with p300/CBP, also abolished the inhibitory effect of E1A, whereas deletion of the region from residues 120 to 140 had no effect. Two regions of CBP from amino acids 1 to 451 and from 1460 to 1891 were demonstrated to interact with SF-1 in vitro. Coexpression of fragments of the p300 protein fused to the VP16 protein in the presence of SF-1 and the -110 P450scc reporter construct indicated in vivo the interaction of two regions of p300 with SF-1, thus confirming the in vitro results. Taken together these results indicate that regulation of the human P450scc gene by SF-1 is mediated by p300/CBP. Due to the many putative roles of SF-1 to regulate many genes, its interaction with p300/CBP is potentially a key component effecting important physiological processes.

The testis and the adrenal are (transcriptionally) the same

We have been studying the transcriptional regulation of the rat P450c17 gene in both adrenocortical and Leydig cells, to assess which DNA sequences are required for its basal and hormonally stimulated transcription. Comparing the transcriptional regulation in both of these cell types enables us to demonstrate whether specific nuclear factors required for transcriptional regulation of the rat P450c17 gene are tissue-specifically expressed, and whether the same cis-acting DNA elements in the gene are required for transcriptional regulation in both of these two different steroidogenic tissues. Using such an approach, we previously demonstrated that the transcriptional regulation of the rat P450scc gene uses different cis-acting DNA sequences in steroidogenic versus neural tissues, and requires the expression of tissue-specific nuclear factors that are unique to neural tissue. However, in studying the transcriptional regulation of the rat P450c17 gene in cultured mouse adrenocortical Y-1 and mouse Leydig MA-10 cells, we have shown that identical DNA sequences necessary for basal and cAMP-stimulated transcriptional regulation in these two cell types, and that identical nuclear factors from Y-1 and from MA-10 cells bind to these sequences. We have identified four transcriptionally active regions within 500 bp of the transcription initiation start site that are important for basal and/or cAMP-stimulated transcriptional regulation of this gene in Y-1 and MA-10 cells. This paper will discuss two of these regions in greater detail. By studying the regulation of the rat P450c17 gene, we have identified two new members of the orphan nuclear receptor gene family and have discovered new alternative mechanisms by which orphan nuclear receptors activate gene transcription in both mouse adrenocortical Y-1 and Leydig MA-10 cells.

Transcriptional regulation of the CYP11A1 and ferredoxin genes

The first step in the synthesis of all steroids is the cleavage of cholesterol side chain, catalyzed by an electron transport system located in mitochondria consisting of ferredoxin reductase, ferredoxin, and cytochrome P450scc. These proteins are present in adrenal, gonad, placenta, and some parts of the brain. In addition, ferredoxin and ferredoxin reductase are also found in the kidney and liver. Whereas ferredoxin reductase levels remain constant in the cell, ferredoxin and P450scc levels are stimulated by trophic hormones using cAMP as an intracellular messenger. The ferredoxin promoter is relatively simple, consisting of a TATA box and two Sp1-binding sites. This simple module is enough to direct cAMP-dependent transcription in a steroidogenic cell-specific fashion. The regulatory region for the P450scc gene is more complex, containing many protein binding sites for different regulation purposes. Its TATA box directs cAMP-dependent transcription in a cell-type-specific manner. A transcription factor, steroidogenic factor 1 (SF1), activates P450scc gene expression. The tissue-specific expression of the P450scc gene is probably accomplished through the interaction of SF1 with other protein factors located further upstream of the control region. SF1 may also be involved in the cAMP response. An upstream region binding to cAMP-Responsive Element Binding Protein CREB and AP1 can respond to cAMP for gene activation. These analyses of regulatory elements provide the structural architecture for transcriptional regulation of the ferredoxin and the CYP11A11 gene.

Mitochondrial specificity of the early steps in steroidogenesis

Studies in human beings, animals, and cell systems show that the rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone. In the adrenals and gonads, this step is subject to both acute and chronic regulation. Chronic regulation is primarily, but not exclusively at the level of gene transcription, leading to the production of more steroidogenic machinery and thus increasing the cellular capacity for steroidogenesis. Chronic regulation can be inhibited by inhibiting protein synthesis with cycloheximide, but this response varies among various cell types and species. Although the P450scc enzyme system that converts cholesterol to pregnenolone is inherently very slow, the principal site of acute regulation is at the delivery of free cholesterol to mitochondria, rather than at the delivery of reducing equivalents to P450scc. Even when the Vmax of the P450scc system is increased 6-fold by genetic engineering, delivery of cholesterol to the enzyme remains rate-limiting. Targeting of a genetically engineered fusion of the P450scc system to either mitochondria or to the endoplasmic reticulum of non-steroidogenic cells demonstrates that the mitochondrial environment is absolutely required for the conversion of cholesterol to pregnenolone, and that this absolute requirement is not based on either the nature of the available electron donors for P450scc or the availability of substrate. Various factors have been proposed as the essential mediator for the transport of cholesterol into mitochondria to initiate steroidogenesis. A recently identified protein termed Steroidogenic Acute Regulatory protein (StAR) has the necessary properties of enhancing steroidogenesis, rapid cAMP inducibility and rapid cycloheximide sensitivity that characterize the long-sought acute regulator of steroidogenesis. StAR is expressed in steroidogenic tissues exhibiting an acute response but not in steroidogenesis. StAR is expressed in steroidogenic tissues exhibiting an acute response but not in steroidogenic tissues (placenta, brain) that do not exhibit this response. Mutations in StAR are now shown to cause Congenital Lipoid Adrenal Hyperplasia, the last unsolved form of CAH. The actions of StAR can be circumvented by the use of hydroxycholesterols that can freely diffuse into mitochondria, proving that StAR functions as an acute regulator of cholesterol access to mitochondria.

Regulation of cholesterol side-chain cleavage cytochrome P450 in mouse testis Leydig cell line I-10

We have characterized regulation of steroidogenesis in a mouse testis Leydig cell line, I-10. Progesterone secretion was increased in a time- and dose-dependent fashion by 8-Br-cAMP treatment. The amount of cholesterol side-chain cleavage enzyme (P450scc), the first and rate-limiting enzyme for the synthesis of steroids, as detected by immunoblotting, was also increased. The calcium ionophore A23187 decreased the amount of P450scc, but it did not interfere with cAMP stimulation of the accumulation of P450scc. This regulation of P450scc expression by cAMP and A23187 is at the post-transcriptional level because the amount of P450scc mRNA was not affected by either treatment. This result was further confirmed by direct measurement of transcription in the presence or absence of forskolin treatment. I-10, however, supported cAMP-dependent transcriptional activation of the exogenous gene, as shown by the increased expression of a reporter gene under the control of the -600 to -2,500 fragment of the P450scc gene. The ability for transcriptional activation of the exogenous but not endogenous P450scc gene makes I-10 a unique steroidogenic cell line.

Epidermal growth factor and c-Jun act via a common DNA regulatory element to stimulate transcription of the ovine P-450 cholesterol side chain cleavage (CYP11A1) promoter

The P-450 side chain cleavage (CYP11A1) gene encodes the enzyme that catalyzes the initial step in steroid biosynthesis, resulting in the conversion of cholesterol to pregnenolone. Expression of the CYP11A1 gene is increased by hormones, such as adrenocorticotropin and luteinizing hormone, as well as by a number of growth factors, suggesting that its promoter may contain regulatory elements that respond to multiple signal transduction pathways. Using transient expression assays of the ovine CYP11A1 promoter in JEG-3 placental cells, distinct regulatory elements were found to mediate transcriptional stimulation by cAMP and epidermal growth factor (EGF). The cAMP response was mediated through a GC-rich sequence localized between -117 and -92. In contrast, EGF induced CYP11A1 transcription through an adjacent but distinct sequence (-92 to -77 base pairs) that was shown previously to bind nuclear proteins in DNase I footprinting reactions. This EGF-responsive element (EGF-RE) resembles an activator protein-1 (AP-1) site and was also required for transactivation by co-transfected c-Jun. A point mutation within the EGF-RE impaired stimulation by both EGF and c-Jun, suggesting that these pathways converge on a common regulatory element. Transfer of single or multiple copies of the EGF-RE upstream of an heterologous promotor conferrd EGF and c-Jun responses, providing further evidence that this element is sufficient for both responses. Transfection studies employing mutant c-Jun proteins confirmed a requirement for its DNA binding, leucine zipper and amino-terminal domains, each of which are required for activation of a classical AP-1 reporter. Gel shift studies demonstrated that protein binding to the CYP11A1 EGF-RE was competed specifically by a canonical AP-1 site, and the addition of an anti-JUN antibody confirmed the presence of AP-1 proteins. Consistent with the possibility that EGF may act in part via c-Jun, EGF stimulated the activity of a chimeric GAL4 c-Jun protein, indicating that JUN can serve as a potential target of EGF in JEG-3 cells. EGF also induced mitogen-activated protein kinase activity, and a dominant negative mutant of mitogen-activated protein kinase partially blocked EGF stimulation of GAL4 c-Jun activity. We conclude that EGF stimulates the CYP11A1 promoter through an AP-1 like element and that c-Jun is one of the targets of EGF action.

Characterization of placental transcriptional activation of the human gene for P450scc

Steroid hormones, which are ubiquitous regulators of physiologic processes, are produced primarily in the adrenals, gonads, and placenta. Each steroidogenic cell type produces different steroids due to cell-specific expression of various steroidogenic enzymes, but all steroidogenesis is initiated by P450scc, the mitochondrial enzyme that converts cholesterol to pregnenolone. We previously showed the unique segments of the P450scc promoter that are responsible for basal and cAMP-induced expression of this gene in the placenta are not employed for expression in the adrenal (C.C.D. Moore, D.W. Hum, and W.L. Miller, Mol. Endocrinol. 6, 2045-2058, 1992). We now show that sequences between -142 and -153 exhibit placental-specific activator activity. Sequences between -131 and -155 can confer activator activity to a 32-bp promoter from the thymidine kinase gene of herpes simplex virus in an orientation-independent fashion. Two protein complexes, termed IV and VII, interact specifically with DNA from -131 to -155. Mutating bases -142 to -151 abolishes formation of complex VII and partially inhibits complex IV, suggesting that the proteins forming these complexes bind neighboring segments of DNA. Mutating only two cytosines at bases 141 and 142 also eliminates the formation of complex VII and reduces the transcriptional activity of the activator by about 75-80%, indicating that complex VII is important for placental expression of P450scc. The sequence from -140 to -149 on the antisense strand resembles an NF-kappa B binding site. Antibodies to NF-kappa B subunit p50, but not to p52, p65, or c-Rel, will supershift some but not all of complex IV, whereas none of these antibodies interact with complex VII. A consensus NF-kappa B oligonucleotide does not form complex IV, suggesting that p50 interacts with the protein component, but not the DNA component of complex IV. Photoaffinity UV cross-linking yielded single bands of cross-linked DNA-protein complexes at approximately 85 kD for complex IV and approximately 70 kD for complex VII, indicating that separate proteins form complexes IV and VII. Southwestern blotting identified a single protein of 55 kD forming complex VII but did not identify the protein forming complex IV. Bandshifts and Southwestern blots with nuclear extracts from steroidogenic human placental JEG-3 cells and human adrenal NCI-H295 cells show that this 55-kD protein is found in placental but not adrenal cells. This 55-kD nuclear protein appears to be a trans-acting factor necessary for placental but not adrenal expression of P450scc.

Regulatory mechanisms of cAMP-dependent and cell-specific expression of human steroidogenic cytochrome P450scc (CYP11A1) gene

Cytochrome P450scc (CYP11A1) is the enzyme that catalyzes the side-chain cleavage reaction of cholesterol, the first and rate-limiting reaction in the biosynthesis of steroid hormones in the adrenal cortex. DNase-I-footprinting analysis using nuclear extracts from the bovine adrenal cortex and the 5' upstream regulatory region (nucleotides -1697 to -1523) of the CYP11A1 gene, which is mainly required for response to cAMP [Inoue, H., Watanabe, N., Higashi, Y. & Fujii-Kuriyama, Y. (1991) Eur. J. Biochem. 195, 563-569], revealed that some protein factors bound to that region. One of the sequences protected by the binding factors is a cAMP-responsive-element (CRE)-like sequence, which is known to be recognized by CRE-binding protein (CREB) or its related proteins, and another is a sequence designated Ad4 which is bound by a tissue-specific factor, Ad4-binding protein (Ad4BP). The region containing the two closely arranged DNA sequences showed a high level of cAMP responsive and cell-specific expression when it was fused to the basal promoters. Introduction of point mutations in these sequences demonstrated that the CREB/ATF factors and Ad4BP bound to the sequences showed synergistic enhancer effects on cAMP-responsive and cell-specific expression of the CYP11A1 gene.

Neurosteroid biosynthesis: genes for adrenal steroidogenic enzymes are expressed in the brain

To determine if neurosteroids (steroids synthesized in the brain) are produced by enzymes found in steroidogenic tissues, we determined if mRNA for five steroidogenic enzymes could be detected in brain tissues or cultured cells. We detected mRNAs for adrenodoxin, P450scc (cholesterol side-chain cleavage enzyme) and P450c11 beta (11 beta-hydroxylase) but not for P450c17 (17 alpha-hydroxylase/17,20 lyase) or P450c11AS (aldosterone synthase) in rat brains and cultures of rat glial cells. P450scc mRNA abundance in brain or primary glial cultures was approximately 0.01% of that found in the adrenal, but more P450scc mRNA was detected in C6 glial cells. Both P450scc and P450c11 beta mRNAs were most abundant in the cortex, but there were region-specific differences for both mRNAs, and sex-specific differences for P450c11 beta mRNA. P450scc mRNA was equally abundant in mixed glial cultures containing both astrocytes and oligodendrocytes as in astrocyte-enriched cultures, and P450scc immunoreactivity co-localized with GFAP immunoreactivity in cultured astrocytes. P450c11 beta mRNA was not detected in the mixed primary glial cultures for the C6 glioma cell line that synthesize P450scc mRNA, suggesting that glial cells do not synthesize P450c11 beta mRNA. Thus some of the same enzymes involved in steroidogenesis in classic endocrine tissues are found in a cell-specific and region-specific fashion in the brain. Neurosteroids may be derivatives of known classic steroids, and/or may function through non-classic steroid hormone receptors, such as GABAA, N-methyl-D-aspartate, and corticosterone receptors.

Differential regulation of the CYP11A1 (P450scc) and ferredoxin genes in adrenal and placental cells

The regulation of the genes encoding cholesterol side-chain cleavage enzyme (P450scc) and ferredoxin, two components in the first step of steroid synthetic pathways, was studied by RNA analyses of endogenous and transfected genes. cAMP rather than calcium was the major secondary messenger that stimulated expression of both P450scc and ferredoxin genes in human placental JEG-3 cells. The effect of cAMP on P450scc expression was abolished by cycloheximide in JEG-3 cells, but it was superinduced in mouse adrenal Y1 cells. For ferredoxin expression, both reagents have synergistic effect in Y1 and JEG-3 cells. To test the mechanism of regulation, DNA segments containing regulatory elements of the P450scc and ferredoxin genes were connected to reporter genes and analyzed in cotransfection experiments. The results showed that the proximal cAMP-responsive sequences of both P450scc and ferredoxin genes were stimulated by cAMP early in both Y1 and JEG-3 cells, requiring no new protein synthesis. This indicates a common mechanism for the regulated expression of both genes. P450scc possessed an additional upstream cAMP-responsive sequence that also responded to cAMP induction in a different manner from the proximal element. The presence of additional upstream regulatory elements makes it possible for the P450scc gene to be further regulated.

Effect of insulin-like growth factor-I on cholesterol side-chain cleavage cytochrome P450 messenger ribonucleic acid expression in ovarian theca-interstitial cells stimulated to differentiate in vitro

Currently available evidence supports the hypothesis that insulin-like growth factor-I (IGF-I) may play a role in stimulating ovarian theca-interstitial cell (TIC) differentiation in preantral follicles. The purpose of the present studies was to examine the potential role of IGF-I in TIC differentiation by determining the effects of IGF-I on cholesterol side-chain cleavage cytochrome P450 (P450SCC) mRNA expression in TIC stimulated to differentiate in vitro. TIC were isolated from the ovaries of hypophysectomized immature rats by Percoll gradient centrifugation and cultured in the presence and absence of LH and IGF-I up to 6 days. At various times cytoplasmic RNA was extracted from the TIC and P450SCC mRNA was measured by specific assay using reverse transcription followed by the polymerase chain reaction. Increasing concentrations of LH (0-1 microgram/ml) stimulated a dose-related increase in P450SCC mRNA (ED50 = 36.2 +/- 5.5 ng/ml) which reached maximal levels at 100 ng/ml of LH. Addition of IGF-I (30 ng/ml) caused a small increase in P450SCC mRNA over TIC treated with LH alone but did not alter the ED50 for LH stimulation. IGF-I alone also stimulated an increase in P450SCC mRNA which reached approximately 3-fold over unstimulated levels at 100 ng/ml. In the presence of LH, IGF-I stimulated a dose-related increase in P450SCC mRNA (ED50 = 1.2 +/- 0.05 ng/ml). Time-course studies revealed that expression of P450SCC mRNA was greatest at 2 days in TIC treated with IGF-I alone, LH alone or LH plus IGF-I and then declined at 4 and 6 days.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel cAMP-dependent regulatory region including a sequence like the cAMP-responsive element, far upstream of the human CYP21A2 gene

Deletion mutants in the 5' upstream sequence of the human CYP21A2 gene demonstrated a novel regulatory DNA element responsible for cAMP-dependent expression of the gene in the transient expression system using Y-1 cells (mouse adrenocortical tumor cell line). This regulatory element (-2574 to -2489 bp) was also found to exhibit a strong enhancer activity through heterologous promoters in response to cAMP and to contain a sequence like the cAMP-responsive element (CRE) and a CAAT-like sequence. The CRE-like sequence has a five-base motif (5'-TGACG-3') of the palindromic CRE consensus (TGACGTCA). Competitive gel mobility shift assays using nuclear extracts of bovine adrenal cortex with sequences typical of the binding sites for the binding proteins of CRE and the CAAT-like sequence revealed that these binding proteins, or related factors, bound to their cognate DNA binding sites in the upstream enhancer region of the CYP21A2 gene. These two enhancer elements and their cognate binding factors cooperate with previously identified tissue-specific enhancers (adrenal-specific protein factor and Ad4-like sequences) and their binding factors to express a high level of cAMP-responsive expression of the CYP21A2 gene.

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

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

cDNA cloning and transcriptional properties of a novel GC box-binding protein, BTEB2

We have cloned a cDNA for a novel GC box-binding protein designated BTEB2 from a human placenta cDNA library using rat BTEB cDNA (Imataka et al. (1992). EMBO J. 11,3663-3671. as a hybridization probe. BTEB2 consists of 219 amino acids and contains three contiguous zinc finger motifs at its C-terminus. The zinc finger domains showed 59% and 64% sequence similarity to those of Sp1 and BTEB, respectively. Adjacent to the N-terminal of the zinc finger motifs, a short sequence rich in basic amino acids is conserved between BTEB2 and Sp1. Furthermore, This basic sequence concurs with the N-terminal half of the consensus sequence for basic domains of the proteins containing both helix-loop-helix and leucine zipper motifs. The other region of BTEB2 is notably rich in proline, serine, threonine, and alanine residues. BTEB2 expressed in Escherichia coli showed DNA-binding activity whose specificity was closely similar to that of Sp1. Cotransfection experiments using Hepa-1 cells (a mouse hepatoma cell line) with a BTEB2 expression plasmid and GC box-containing reporter plasmids revealed that BTEB2 apparently activated the expression of the CAT activity. Moreover, when BTEB2 was fused to GAL4 DNA-binding domain, the chimeric protein could enhance the transcription through promoters containing GAL4-binding sites. Analysis of the BTEB2 mRNA by RNA blot analysis demonstrated that the mRNA was expressed specifically in testis and placenta with different sizes, 20S and 28S, respectively, among various organs examined.

Rainbow trout ovarian cholesterol side-chain cleavage cytochrome P450 (P450scc). cDNA cloning and mRNA expression during oogenesis

A cDNA clone encoding cholesterol side-chain cleavage cytochrome P450 (P450scc) was isolated from a rainbow trout ovarian follicle cDNA library. The cDNA contains an open reading frame of 1,542 nucleotides encoding a protein of 514 amino acids. The predicted amino acid sequence of trout P450scc shows 48% homology with that of human, and 46% homology with that of rat, bovine and pig. P450scc activity was confirmed by transfected COS-1 monkey kidney tumour cells with an expression vector for trout P450scc cDNA and subsequent detection of conversion from 25-hydroxycholesterol to pregnenolone by radioimmunoassay. The cDNA only hybridized to a single 1.8 kb RNA transcript. The transcript was not found in early vitellogenic follicles, barely detected in postvitellogenic follicles, and abundant in postovulatory follicles.

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature

We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.

In vivo regulation of gene expression of enzymes controlling aldosterone synthesis in rat adrenal

We studied the effect of alterations in the intake of sodium and potassium as well as changes in circulating adrenocorticotropin (ACTH) on the expression of the two rate-limiting systems of aldosterone formation in the rat. Low sodium and high potassium intake promoted time-dependent increases in the zona glomerulosa cytochrome P450scc (P450scc) and cytochrome P450c11 (P450c11) protein and mRNA levels, but no changes were found in the zona fasciculata-reticularis. In addition, these responses were associated with markedly elevated transcriptional activities. To further define the contribution of P450c11 and P450c18 (aldosterone synthase) in response to these differing intakes, we evaluated their mRNA levels using gene-specific oligonucleotide probes. P450c18 mRNA was restricted to the zona glomerulosa, whereas P450c11 mRNA was detected in both zona glomerulosa and zona fasciculata-reticularis. Furthermore, only P450c18 mRNA was induced by both low sodium or high potassium intake, as P450c11 mRNA levels remained unchanged. Captopril, an inhibitor of angiotensin-I converting enzyme, abolished the enhancing effects of the low sodium regimen on P450scc and P450c18 mRNA levels. Captopril also suppressed the augmentation of P450c18 mRNA observed with potassium supplementation but had no effect on P450scc mRNA levels. When the hypocholesterolemic drug 4-aminopyrazolopyrimidine (4-APP) was administered to rats for 3 consecurive days, both the level of plasma ACTH and the adrenal content of mRNA encoding P450scc increased 24 h post final injection. The coadministration of dexamethasone with 4-APP prevented these increases. In contrast, the mRNA content of P450c11 remained at control levels. In conclusion, this work demonstrates that variations in the intake of sodium and potassium act on the expression of the CYP11B2 gene, but not on that of the CYP11B1 gene. Moreover angiotensin-II (A-II) is an important factor in this mechanism of action. Both ions also enhance the expression of the CYP11A1 gene. A-II appears to participate in the mechanism of action of the low sodium intake at this level. Another mechanism is postulated for the action of potassium supplementation since captopril did not prevent the increased expression of the CYP11A1 gene. In addition, the fact that 4-APP enhanced the mRNA level of P450scc but not that of P450c, also demonstrates different regulation of the P450s involved at the early and final steps of aldosteroone formation in the rat adrenal zona glomerulosa in vivo.

P450scc regulation in pig granulosa cells: investigation into the mechanism of induction

P450scc catalyses the first and rate-limiting reaction in steroidogenesis and is hormonally regulated. By Northern analysis, using a bovine cDNA probe, we have studied the regulation of P450scc mRNA in pig granulosa cells cultivated in vitro. Using transcription and translation inhibitors, we show that the gonadotropin-induced accumulation of P450scc mRNA mainly results from increased transcription, and that this stimulation, at least in part, is protein synthesis-dependent. Although transcriptional regulation of P450scc gene expression is found in other steroidogenic cells, cycloheximide-sensitivity of this regulation is not widespread. Pig granulosa cells thus would constitute a useful model to study this mechanism of regulation.

Characterization of a cis-acting regulatory element involved in human-aromatase P-450 gene expression

The characteristics of a cis-acting regulatory region involved in the human-aromatase P-450 gene have been examined by transient expression analysis. The region spans from -242 - -166 relative to the cap site of the gene. A fragment containing the region excised from the gene enhances heterologous promoter activity as well as its own promoter activity in a position-independent and orientation-independent manner. The fragment exerts its enhancer activity in human BeWo choriocarcinoma cells in which the aromatase P-450 gene is expressed, but not in other cell lines tested. Deletion of 38 bp from the 3' end of the fragment results in a complete loss of enhancer activity. A gel-retardation assay with nuclear extracts from BeWo cells suggests the existence of a nuclear factor(s) which interacts with the fragment. These results suggest that the regulatory element in the fragment is involved in efficient transcription of the human-aromatase P-450 gene.

Regulation of the cholesterol side-chain cleavage cytochrome P-450 and adrenodoxin mRNAs in cultured choriocarcinoma cells

Cytochrome P-450scc (P-450scc) catalyzes the cholesterol side-chain cleavage reaction, a rate-limiting enzymatic step for progesterone synthesis in trophoblastic and other steroidogenic cells. Adrenodoxin is the iron/sulfur protein donating electrons to P-450scc during this reaction. We examined the effects of cholera toxin (CT), an activator of adenylate cyclase, and 12-O-tetradecanoylphorbol acetate (TPA), a phorbol ester protein kinase C activator, on the levels of mRNAs encoding P-450scc and adrenodoxin in JEG-3 choriocarcinoma cells. CT induced in a concentration- and time-dependent manner P-450scc and adrenodoxin mRNA levels to 8-fold and 1.5-fold above that of control, respectively. TPA also increased P-450scc and adrenodoxin mRNA levels about 3-fold and 1.5-fold above that of control, respectively. Epidermal growth factor (EGF) was found to weakly induce P-450scc mRNA accumulation with a maximal 20% stimulation above basal levels. The effects of CT and TPA were apparently additive on both mRNAs. The protein synthesis inhibitor cycloheximide diminished basal, CT-, TPA-, and EGF-stimulated P-450scc mRNA accumulation whereas the opposite was observed for the adrenodoxin mRNA. Insulin-like growth factor I (IGF-I) appeared to have no effect on either mRNA. These data indicate that: (1) the accumulation of P-450scc and adrenodoxin mRNAs is mainly controlled by the cyclic adenosine 3',5'-monophosphate (cAMP)-dependent pathway but their stimulation by TPA- and EGF-induced signals may also play a weaker synergistic role; (2) the protein synthesis inhibitor cycloheximide inhibits basal, CT-, TPA- and EGF-stimulated P-450scc mRNA levels while it increases the expression of adrenodoxin mRNA suggesting that in the malignant trophoblasts these two enzyme mRNAs are differentially controlled.