Frog cytochrome P-450 (11 beta,aldo), a single enzyme involved in the final steps of glucocorticoid and mineralocorticoid biosynthesis

Elaboration of the Corticosteroid Synthesis Pathway in Primates through a Multistep Enzyme

Metabolic networks are complex cellular systems dependent on the interactions among, and regulation of, the enzymes in the network. Although there is great diversity of types of enzymes that make up metabolic networks, the models meant to understand the possible evolutionary outcomes following duplication neglect specifics about the enzyme, pathway context, and cellular constraints. To illuminate the mechanisms that shape the evolution of biochemical pathways, I functionally characterize the consequences of gene duplication of an enzyme family that performs multiple subsequent enzymatic reactions (a multistep enzyme) in the corticosteroid pathway in primates. The products of the corticosteroid pathway (aldosterone and cortisol) are steroid hormones that regulate metabolism and stress response in tetrapods. These steroid hormones are synthesized by a multistep enzyme Cytochrome P450 11B (CYP11B) that performs subsequent steps on different carbon atoms of the steroid derivatives. Through ancestral state reconstruction and in vitro characterization, I find that the primate ancestor of the CYP11B1 and CYP11B2 paralogs had moderate ability to synthesize both cortisol and aldosterone. Following duplication in Old World primates, the CYP11B1 homolog specialized on the production of cortisol, whereas its paralog, CYP11B2, maintained its ability to perform multiple subsequent steps as in the ancestral pathway. Unlike CYP11B1, CYP11B2 could not specialize on the production of aldosterone because it is constrained to perform earlier steps in the corticosteroid synthesis pathway to achieve the final product aldosterone. These results suggest that enzyme function, pathway context, along with tissue-specific regulation, both play a role in shaping potential outcomes of metabolic network elaboration.

The SARS-CoV-2 receptor and other key components of the Renin-Angiotensin-Aldosterone System related to COVID-19 are expressed in enterocytes in larval zebrafish

People with underlying conditions, including hypertension, obesity, and diabetes, are especially susceptible to negative outcomes after infection with coronavirus SARS-CoV-2, which causes COVID-19. Hypertension and respiratory inflammation are exacerbated by the Renin-Angiotensin-Aldosterone System (RAAS), which normally protects from rapidly dropping blood pressure via Angiotensin II (Ang II) produced by the enzyme Ace. The Ace paralog Ace2 degrades Ang II, counteracting its chronic effects, and serves as the SARS-CoV-2 receptor. Ace, the coronavirus, and COVID-19 comorbidities all regulate Ace2, but we do not yet understand how. To exploit zebrafish (Danio rerio) to help understand the relationship of the RAAS to COVID-19, we must identify zebrafish orthologs and co-orthologs of human RAAS genes and understand their expression patterns. To achieve these goals, we conducted genomic and phylogenetic analyses and investigated single cell transcriptomes. Results showed that most human RAAS genes have one or more zebrafish orthologs or co-orthologs. Results identified a specific type of enterocyte as the specific site of expression of zebrafish orthologs of key RAAS components, including Ace, Ace2, Slc6a19 (SARS-CoV-2 co-receptor), and the Angiotensin-related peptide cleaving enzymes Anpep (receptor for the common cold coronavirus HCoV-229E), and Dpp4 (receptor for the Middle East Respiratory Syndrome virus, MERS-CoV). Results identified specific vascular cell subtypes expressing Ang II receptors, apelin, and apelin receptor genes. These results identify genes and cell types to exploit zebrafish as a disease model for understanding mechanisms of COVID-19.

An intestinal cell type in zebrafish is the nexus for the SARS-CoV-2 receptor and the Renin-Angiotensin-Aldosterone System that contributes to COVID-19 comorbidities

People with underlying conditions, including hypertension, obesity, and diabetes, are especially susceptible to negative outcomes after infection with the coronavirus SARS-CoV-2. These COVID-19 comorbidities are exacerbated by the Renin-Angiotensin-Aldosterone System (RAAS), which normally protects from rapidly dropping blood pressure or dehydration via the peptide Angiotensin II (Ang II) produced by the enzyme Ace. The Ace paralog Ace2 degrades Ang II, thus counteracting its chronic effects. Ace2 is also the SARS-CoV-2 receptor. Ace , the coronavirus, and COVID-19 comorbidities all regulate Ace2 , but we don't yet understand how. To exploit zebrafish ( Danio rerio ) as a disease model to understand mechanisms regulating the RAAS and its relationship to COVID-19 comorbidities, we must first identify zebrafish orthologs and co-orthologs of human RAAS genes, and second, understand where and when these genes are expressed in specific cells in zebrafish development. To achieve these goals, we conducted genomic analyses and investigated single cell transcriptomes. Results showed that most human RAAS genes have an ortholog in zebrafish and some have two or more co-orthologs. Results further identified a specific intestinal cell type in zebrafish larvae as the site of expression for key RAAS components, including Ace, Ace2, the coronavirus co-receptor Slc6a19, and the Angiotensin-related peptide cleaving enzymes Anpep and Enpep. Results also identified specific vascular cell subtypes as expressing Ang II receptors, apelin , and apelin receptor genes. These results identify specific genes and cell types to exploit zebrafish as a disease model for understanding the mechanisms leading to COVID-19 comorbidities.

SUMMARY STATEMENT

Genomic analyses identify zebrafish orthologs of the Renin-Angiotensin-Aldosterone System that contribute to COVID-19 comorbidities and single-cell transcriptomics show that they act in a specialized intestinal cell type.

New Insights in the Functional Zonation of the Canine Adrenal Cortex

BACKGROUND

Current understanding of adrenal steroidogenesis is that the production of aldosterone or cortisol depends on the expression of aldosterone synthase (CYP11B2) and 11β-hydroxylase cytochrome P450 (CYP11B1), respectively. However, this has never been studied in dogs, and in some species, a single CYP11B catalyzes both cortisol and aldosterone formation. Analysis of the canine genome provides data of a single CYP11B gene which is called CYP11B2, and a large sequence gap exists near the so-called CYP11B2 gene.

OBJECTIVES

To investigate the zonal expression of steroidogenic enzymes in the canine adrenal cortex and to determine whether dogs have 1 or multiple CYP11B genes.

ANIMALS

Normal adrenal glands from 10 healthy dogs.

METHODS

Zona fasciculata (zF) and zona glomerulosa (zG) tissue was isolated by laser microdissection. The mRNA expression of steroidogenic enzymes and their major regulators was studied with RT-qPCR. Southern blot was performed to determine whether the sequence gap contains a CYP11B gene copy. Immunohistochemistry (IHC) was performed for 17α-hydroxylase/17,20-lyase (CYP17).

RESULTS

Equal expression (P = .62) of the so-called CYP11B2 gene was found in the zG and zF. Southern blot revealed a single gene. CYP17 expression (P = .05) was significantly higher in the zF compared with the zG, which was confirmed with IHC.

CONCLUSIONS AND CLINICAL IMPORTANCE

We conclude that there is only 1 CYP11B gene in canine adrenals. The zone-specific production of aldosterone and cortisol is probably due to zone-specific CYP17 expression, which makes it an attractive target for selective inhibition of cortisol synthesis without affecting mineralocorticoid production in the zG.

The CYP11B subfamily

The biosynthesis of steroid hormones is dependent on P450-catalyzed reactions. In mammals, cholesterol is the common precursor of all steroid hormones, and its conversion to pregnenolone is the initial and rate-limiting step in hormone biosynthesis in steroidogenic tissues such as gonads and adrenal glands. The production of glucocorticoids and mineralocorticoids takes place in the adrenal gland and the final steps are catalyzed by 2 mitochondrial cytochromes P450, CYP11B1 (11β-hydroxylase or P45011β) and CYP11B2 (aldosterone synthase or P450aldo). The occurrence and development of these 2 enzymes in different species, their contribution to the biosynthesis of steroid hormones as well as their regulation at different levels (gene expression, cellular regulation, regulation on the level of proteins) is the topic of this chapter.

Origin of the response to adrenal and sex steroids: Roles of promiscuity and co-evolution of enzymes and steroid receptors

Many responses to adrenal and sex steroids are mediated by receptors that belong to the nuclear receptor family of transcription factors. We investigated the co-evolution of these vertebrate steroid receptors and the enzymes that synthesize adrenal and sex steroids through data mining of genomes from cephalochordates [amphioxus], cyclostomes [lampreys, hagfish], chondrichthyes [sharks, rays, skates], actinopterygii [ray-finned fish], sarcopterygii [coelacanths, lungfishes and terrestrial vertebrates]. An ancestor of the estrogen receptor and 3-ketosteroid receptors evolved in amphioxus. A corticoid receptor and a progesterone receptor evolved in cyclostomes, and an androgen receptor evolved in gnathostomes. Amphioxus contains CYP11, CYP17, CYP19, 3β/Δ5-4-HSD and 17β-HSD14, which suffice for the synthesis of estradiol and Δ5-androstenediol. Amphioxus also contains CYP27, which catalyzes the synthesis of 27-hydroxy-cholesterol, another estrogen. Lamprey contains, in addition, CYP21, which catalyzes the synthesis of 11-deoxycortisol. Chondrichthyes contain, in addition, CYP11A, CYP11C, CYP17A1, CYP17A2. Coelacanth also contains CYP11C1, the current descendent from a common ancestor with modern land vertebrate CYP11B genes, which catalyze the synthesis of cortisol, corticosterone and aldosterone. Interestingly, CYP11B2, aldosterone synthase, evolved from separate gene duplications in at least old world monkeys and two suborders of rodents. Sciurognathi (including mice and rats) and Hystricomorpha (including guinea pigs). Thus, steroid receptors and steroidogenic enzymes co-evolved at key transitions in the evolution of vertebrates. Together, this suite of receptors and enzymes through their roles in transcriptional regulation of reproduction, development, homeostasis and the response to stress contributed to the evolutionary diversification of vertebrates. This article is part of a Special Issue entitled 'Steroid/Sterol signaling'.

Sunitinib Inhibits Cell Proliferation and Alters Steroidogenesis by Down-Regulation of HSD3B2 in Adrenocortical Carcinoma Cells

The multi-tyrosine kinase inhibitor sunitinib is used in the treatment of several solid tumors. Animal experiments pointed to an adrenotoxic effect of sunitinib. Therefore, we evaluated the expression of key targets of sunitinib in human adrenocortical carcinoma (ACC) tumor samples and investigated its in vitro effects in ACC cell lines. We carried out immunohistochemistry for vascular endothelial growth factor (VEGF) and its receptor (VEGF-R2) in 157 ACC samples and nine normal adrenal glands. VEGF and VEGF-R2 protein were expressed in 72 and 99% of ACC samples, respectively. Using NCI-H295 and SW13 ACC cell lines, we investigated the effects of sunitinib on cell proliferation. Sunitinib reduced dose-dependently cell viability of both NCI-H295 and SW13 cells (SW13: 0.1 μM 96 ± 7%, 1 μM 90 ± 9%*, 5 μM 62 ± 6%*, controls 100 ± 9%; *p < 0.05). To determine sunitinib effects on steroidogenesis, we measured steroid hormones in cell culture supernatant by gas chromatography-mass spectrometry. We observed a pronounced decrease of cortisol secretion (1 μM 90.1 ± 1.5%*, 5 μM 57.2 ± 0.3%*, controls 100 ± 2.4%) and a concomitant increase in the DHEA/4-androstenedione and 17-hydroxypregnenolone/17-hydroxyprogesterone ratios, indicating specific inhibition of 3β-hydroxysteroid dehydrogenase (HSD3B2). In yeast microsomes transformed with HSD3B2, no direct inhibition of HSD3B2 by sunitinib was detected. Sunitinib induced down-regulation of HSD3B2 mRNA and protein in ACC cell lines (mRNA: 1 μM 44 ± 16%*; 5 μM 22 ± 2%*; 10 μM 19 ± 4%*; protein: 1 μM 82 ± 8%; 5 μM 63 ± 8%*; 10 μM 55 ± 9%*). CYP11B1 was down-regulated at mRNA but not at protein level and CYP11A1 remained unchanged. In conclusion, target molecules of sunitinib are expressed in the vast majority of ACC samples. Sunitinib exhibits anti-proliferative effects in vitro, and appears to specifically block adrenal steroidogenesis by down-regulation of HSD3B2, rendering it a promising option for treatment of ACC.

Molecular cloning of two isoforms of 11beta-hydroxylase and their expressions in the Nile tilapia, Oreochromis niloticus

P450 11beta-hydroxylase, encoded by P450(11beta) gene, is a key mitochondrial enzyme to produce 11beta-hydroxy testosterone, substrate for the production of 11-ketotestosterone (11-KT), which has been shown to be potent androgen in several fish species. In the present work, two alternative splicing isoforms i.e. P450(11beta)-1 and P450(11beta)-2 cDNAs were cloned from the Nile tilapia, Oreochromis niloticus. They were 1614 and 1227bp in length with open reading frames encoding proteins of 537 and 408 amino acids, respectively. In contrast to P450(11beta)-1, which derived from 9 exons of the P450(11beta) gene, the 7th and 8th exons were absent in P450(11beta)-2. Tilapia P450(11beta)-1 shares the highest homology with that of medaka, Oryzias latipes. Expressions of P450(11beta)-1 and -2 were detected in the kidney and head kidney of both sexes, and in the testis but not in the ovary, with P450(11beta)-2 lower than P450(11beta)-1. Ontogenic expressions of both isoforms were detected in testis from 50dah onwards. P450(11beta)-1 and -2 were strongly expressed in sex reversed XX testis after fadrozole and tamoxifen treatment, but completely inhibited in 17beta-estradiol induced XY ovary. The existence of two alternatively spliced isoforms and the sexual dimorphic expression of P450(11beta)s were further confirmed by Northern blot. Strong expression signals in Leydig cells and weak signals in spermatogonia were detected by in situ hybridization and immunohistochemistry. Taken together, our data suggest a role for P450(11beta) in the spermatogenesis of tilapia through the production of 11-KT in testis, in addition to cortisol production in head kidney.

Construction of 3D models of the CYP11B family as a tool to predict ligand binding characteristics

Aldosterone is synthesised by aldosterone synthase (CYP11B2). CYP11B2 has a highly homologous isoform, steroid 11beta-hydroxylase (CYP11B1), which is responsible for the biosynthesis of aldosterone precursors and glucocorticoids. To investigate aldosterone biosynthesis and facilitate the search for selective CYP11B2 inhibitors, we constructed three-dimensional models for CYP11B1 and CYP11B2 for both human and rat. The models were constructed based on the crystal structure of Pseudomonas Putida CYP101 and Oryctolagus Cuniculus CYP2C5. Small steric active site differences between the isoforms were found to be the most important determinants for the regioselective steroid synthesis. A possible explanation for these steric differences for the selective synthesis of aldosterone by CYP11B2 is presented. The activities of the known CYP11B inhibitors metyrapone, R-etomidate, R-fadrazole and S-fadrazole were determined using assays of V79MZ cells that express human CYP11B1 and CYP11B2, respectively. By investigating the inhibitors in the human CYP11B models using molecular docking and molecular dynamics simulations we were able to predict a similar trend in potency for the inhibitors as found in the in vitro assays. Importantly, based on the docking and dynamics simulations it is possible to understand the enantioselectivity of the human enzymes for the inhibitor fadrazole, the R-enantiomer being selective for CYP11B2 and the S-enantiomer being selective for CYP11B1.

A cDNA for European sea bass (Dicentrachus labrax) 11beta-hydroxylase: gene expression during the thermosensitive period and gonadogenesis

Steroid P450 11beta-hydroxylase, encoded by the CYP11B gene, is a key mitochondrial enzyme for the production of 11-oxygenated androgens, which have been shown to be potent masculinising steroids in several fish species. In this study we have isolated a CYP11B cDNA of 1903 base pairs from the testis of European sea bass (Dicentrarchus labrax) encoding a predicted protein of 552 amino acids. The amino acid identities to other vertebrate 11beta-hydroxylase proteins ranged from 66% to 72% to other fish; 45% to amphibian and 35-39% to mammalian. Southern blot indicated that a single CYP11B gene is present. Northern blot analysis detected two transcripts in testis and head kidney, one of the same size of the isolated clone and the other of 3.9 kb. Reverse transcriptase-polymerase chain reaction showed abundant mRNA expression only in testis and head kidney, being residual in a range of other tissues. Expression of CYP11B and CYP19A (which encodes for ovarian aromatase) was detected from at least 4 days post-hatching and did not appear to be affected by rearing temperature (15 and 20 degrees C) during the first 60 days, a period in which high temperatures promote masculinisation in European sea bass. Throughout, gonadogenesis (60-300 dph), a highly dimorphic pattern of CYP11B expression was consistent with a role of this gene in testicular development.

Evolution of hormone-receptor complexity by molecular exploitation

According to Darwinian theory, complexity evolves by a stepwise process of elaboration and optimization under natural selection. Biological systems composed of tightly integrated parts seem to challenge this view, because it is not obvious how any element's function can be selected for unless the partners with which it interacts are already present. Here we demonstrate how an integrated molecular system-the specific functional interaction between the steroid hormone aldosterone and its partner the mineralocorticoid receptor-evolved by a stepwise Darwinian process. Using ancestral gene resurrection, we show that, long before the hormone evolved, the receptor's affinity for aldosterone was present as a structural by-product of its partnership with chemically similar, more ancient ligands. Introducing two amino acid changes into the ancestral sequence recapitulates the evolution of present-day receptor specificity. Our results indicate that tight interactions can evolve by molecular exploitation-recruitment of an older molecule, previously constrained for a different role, into a new functional complex.

CYP17- and CYP11B-dependent steroid hydroxylases as drug development targets

Steroid hormone biosynthesis is catalyzed by the action of a series of cytochrome P450 enzymes as well as reductases. Defects in steroid hydroxylating P450s are the cause of several severe defects such as the adrenogenital syndrome (AGS), corticosterone methyl oxidase (CMO) I or II deficiencies, or pseudohermaphroditism. In contrast, overproduction of steroid hormones can be involved in breast or prostate cancer, in hypertension, and heart fibrosis. Besides inhibiting the action of the steroid hormones on the level of steroid hormone receptors by using antihormones, which often is connected with severe side effects, more recently the steroid hydroxylases themselves turned out to be promising new targets for drug development. Since the 3-dimensional structures of steroid hydroxylases are not yet available, computer models of the corresponding CYPs may help to develop new inhibitors of these enzymes. During the past years, the necessary test systems have been developed and new compounds have been synthesized, which displayed selective and specific inhibition of CYP17, CYP11B2, and CYP11B1. With some of these potential new drugs, clinical trials are under way. It can be expected that in the near future some of these compounds will contribute to our arsenal of new and selective drugs.

Molecular identity and gene expression of aldosterone synthase cytochrome P450

11Beta-hydroxylase (CYP11B1) of bovine adrenal cortex produced corticosterone as well as aldosterone from 11-deoxycorticosterone in the presence of the mitochondrial P450 electron transport system. CYP11B1s of pig, sheep, and bullfrog, when expressed in COS-7 cells, also performed corticosterone and aldosterone production. Since these CYP11B1s are present in the zonae fasciculata and reticularis as well as in the zona glomerulosa, the zonal differentiation of steroid production may occur by the action of still-unidentified factor(s) on the enzyme-catalyzed successive oxygenations at C11- and C18-positions of steroid. In contrast, two cDNAs, one encoding 11beta-hydroxylase and the other encoding aldosterone synthase (CYP11B2), were isolated from rat, mouse, hamster, guinea pig, and human adrenals. The expression of CYP11B1 gene was regulated by cyclic AMP (cAMP)-dependent signaling, whereas that of CYP11B2 gene by calcium ion-signaling as well as cAMP-signaling. Salt-inducible protein kinase, a cAMP-induced novel protein kinase, was one of the regulators of CYP11B2 gene expression.

Steroid 11-Beta-Hydroxylase Deficiency Caused by Compound Heterozygosity for a Novel Mutation, p.G314R, in One CYP11B1 Allele, and a Chimeric CYP11B2/CYP11B1 in the Other Allele

AIMS

Steroid 11beta-hydroxylase deficiency (11beta-OHD) is the second most common (5-8%) cause of congenital adrenal hyperplasia (CAH), and results from homozygous or compound heterozygous mutations or deletions of the responsible gene CYP11B1. In order to better understand the molecular basis causing 11beta-OHD, we performed detailed studies of CYP11B1 in a newly described patient diagnosed with the classical signs of 11beta-OHD.

METHODS

CYP11B1 of the patient was investigated by polymerase chain reaction (PCR), sequencing, restriction fragment length polymorphism (RFLP) analysis, Southern blotting, and transient cell expression.

RESULTS

We identified two new mutated alleles in CYP11B1. In one allele CYP11B1 has a g.940G-->C (p.G314R) missense mutation. On the other allele we found a chimeric gene that consists of part of the aldosterone synthase gene (CYP11B2) at exons 1-3 and part of the 11beta-hydroxylase gene (CYP11B1) at exons 4-9. Inin vitro studies, the g.940G-->C (p.G314R) mutation abolished all hydroxylase activity in comparison with the wild-type 11beta-hydroxylase. The chimeric CYP11B2/CYP11B1 protein retained 11beta-hydroxylase enzymatic activity in vitro.

CONCLUSION

This case is caused by compound heterozygosity for a nonfunctional missense mutation and a chimeric CYP11B2/CYP11B1 gene with hydroxylase activity that is controlled by the CYP11B2 promoter. The most likely explanation is that the CYP11B2 promoter does not function in the zona fasciculata/reticularis where cortisol is exclusively synthesized.

Congenital adrenal hyperplasia secondary to 11beta-hydroxylase deficiency in a domestic cat

A calico-colored domestic shorthair cat was examined because of possible cryptorchidism. The cat had a fully formed penis, prepuce, and scrotum, but no descended testes, and exploratory laparotomy revealed a grossly normal female internal genital tract (ie, 2 ovaries, 2 uterine horns, and uterine body). Chromosomal analysis revealed a normal female (38,XX) karyotype. Four months later, the cat was examined because of polyuria, polydipsia, and inappropriate urination. Serum cortisol and aldosterone concentrations were low, and results of an ACTH stimulation test were suggestive of decreased adrenal gland function. Serum ACTH, testosterone, androstenedione, progesterone, 17-hydroxyprogesterone, 11-deoxycortisol, and deoxycorticosterone concentrations were high, and a diagnosis of congenital adrenal hyperplasia secondary to 11beta-hydroxylase deficiency was made. Treatment with prednisone diminished clinical signs but had a variable effect on corticosteroids hormone concentrations. To the author's knowledge, this is the first report of congenital adrenal hyperplasia in a cat.

Modulation of aldosterone and cortisol synthesis on the molecular level

CYP11B1 and the closely related CYP11B2 are involved in the production of adrenal steroid hormones. Although in human their primary structure is 93% identical they are involved in the biosynthesis of functionally diverse products, such as glucocorticoids and mineralocorticoids, respectively. In contrast, bovine CYP11B1 combines both activities in one single enzyme. The CYP11B family belongs to class I cytochromes P450 that have been described in bacteria and mitochondria and receive their electrons from a low molecular weight iron sulphur protein which is reduced by a NADPH-dependent FAD-containing reductase. In this review, we summarise the current knowledge on the modulation of aldosterone and cortisol synthesis by transcriptional regulation, on the molecular level as consequence of mutations found in patients suffering from steroid hormone-related diseases as well as introduced by site-directed mutagenesis and as consequence of protein-protein interaction with both CYP11A1 and the natural redox partner adrenodoxin.

The human steroid hydroxylases CYP1B1 and CYP11B2

Major advances have been made during the last decade in our understanding of adrenal steroid hormone biosynthesis. Two key players in these pathways are the human mitochondrial cytochrome P450 enzymes CYP11B1 and CYP11B2, which catalyze the final steps in the biosynthesis of cortisol and aldosterone. Using data from mutations found in patients suffering from steroid hormone-related diseases, from mutagenesis studies and from the construction of three-dimensional models of these enzymes, structural information could be deduced that provide a clue to the stereo- and regiospecific steroid hydroxylation reactions carried out by these enzymes. In this review, we summarize the current knowledge on the physiological function and the biochemistry of these enzymes. Furthermore, the pharmacological and toxicological importance of these steroid hydroxylases, the means for the identification of their potential inhibitors and possible biotechnological applications are discussed.

Expression and localization of cytochrome P450(11beta,aldo) mRNA in the frog brain

The present study is focused on biosynthesis of adrenal steroids in the frog brain. Employing RT-PCR method using total RNA from the adult Rana nigromaculata brain, we isolated a 419-bp fragment of cDNA encoding cytochrome P450(11beta,aldo), which catalyzes the final step of biosynthesis of the frog adrenal steroids, corticosterone and aldosterone. The deduced amino acid sequence of R. nigromaculata brain cytochrome P450(11beta,aldo) shared a high homology (88.8%) with that of R. catesbeiana adrenal cytochrome P450(11beta,aldo). Southern blot analysis of the RT-PCR product confirmed the P450(11beta,aldo) transcription in the frog brain without a clear-cut sex difference. Then, we analyzed the P450(11beta,aldo) mRNA expression in different brain regions of the adult frog by RT-PCR method. The P450(11beta,aldo) gene was transcribed in the telencephalon, diencephalon, midbrain, and cerebellum. The transcript level of the frog beta-actin gene was relatively constant in all the frog samples examined. In situ hybridization analysis showed that the P450(11beta,aldo) gene was transcribed abundantly in the cells throughout the frog brain, such as the pallium mediale in the telencephalon, the nucleus preopticus in the diencephalon, the stratum griseum superficiale tecti in the midbrain, and Purkinje cells in the cerebellum. These results taken together suggest that the frog brain synthesizes adrenal steroids, such as corticosterone and aldosterone.

Analyses of the CYP11B gene family in the guinea pig suggest the existence of a primordial CYP11B gene with aldosterone synthase activity

In this study we describe the isolation of three genes of the CYP11B family of the guinea pig. CYP11B1 codes for the previously described 11beta-hydroxylase [Bülow, H.E.,Möbius, K., Bähr, V. & Bernhardt, R. (1996) Biochem. Biophys. Res. Commun. 221, 304-312] while CYP11B2 represents the aldosterone synthase gene. As no expression for CYP11B3 was detected this gene might represent a pseudogene. Transient transfection assays show higher substrate specificity for its proper substrate for CYP11B1 as compared to CYP11B2, which could account for the zone-specific synthesis of mineralocorticoids and glucocorticoids, respectively. Thus, CYP11B2 displayed a fourfold higher ability to perform 11beta-hydroxylation of androstenedione than CYP11B1, while this difference is diminished with the size of the C17 substituent of the substrate. Furthermore, analyses with the electron transfer protein adrenodoxin indicate differential sensitivity of CYP11B1 and CYP11B2 as well as the three hydroxylation steps catalysed by CYP11B2 to the availability of reducing equivalents. Together, both mechanisms point to novel protein intrinsic modalities to achieve tissue-specific production of mineralocorticoids and glucocorticoids in the guinea pig. In addition, we conducted phylogenetic analyses. These experiments suggest that a common CYP11B ancestor gene that possessed both 11beta-hydroxylase and aldosterone synthase activity underwent a gene duplication event before or shortly after the mammalian radiation with subsequent independent evolution of the system in different lines. Thus, a differential mineralocorticoid and glucocorticoid synthesis might be an exclusive achievement of mammals.

Molecular cloning and expression during spermatogenesis of a cDNA encoding testicular 11beta-hydroxylase (P45011beta) in rainbow trout (Oncorhynchus mykiss)

Cytochrome P450 1beta-hydroxylase (P450(11beta)) is an important steroidogenic enzyme for glucocorticoid and mineralocorticoid production in vertebrates. In teleosts, P450(11beta) also plays a role in the production of 11-ketotestosterone (11-KT), the predominant androgen in male fish. In this study, we cloned a cDNA encoding rainbow trout (Oncorhynchus mykiss) testicular P450(11beta). The cDNA contains 1,740 nucleotides that encode a protein of 551 amino acids which shares 65.2% homology with testicular P450(11beta) from Japanese eel, and 33-45% homology with adrenal P450(11beta) from rat, human, and frog. HEK293 cells transfected with an expression vector containing the rainbow trout P450(11beta) cDNA open reading frame showed 11beta-hydroxylating activity in the presence of exogenous testosterone. Analysis of tissue distribution by RT-PCR showed great abundance of P450(11beta) mRNA in testis and head kidney. In order to clarify the sites of P450(11beta) gene expression, cRNA in situ hybridization analysis was performed. Hybridization signals were detected in Leydig cells and head kidney inter-renal cells. The results of Northern blot analysis indicated a single 1.8-kb transcript encoding P450(11beta) in testis and in head kidney, suggesting that the testicular form of P450(11beta) may also be involved in cortisol production by inter-renal cells. Seasonal changes in total P450(11beta) mRNA levels in testes during spermatogenesis showed a pattern similar to that of plasma androgens. These results suggest that androgen production in male rainbow trout is partially regulated by changes in abundance of P450(11beta) mRNA.

The effect of amino-acid substitutions I112P, D147E and K152N in CYP11B2 on the catalytic activities of the enzyme

By replacing specific amino acids at positions 112, 147 and 152 of the human aldosterone synthase (CYP11B2) with the corresponding residues from human, mouse or rat 11beta-hydroxylase (CYP11B1), we have been able to investigate whether these residues belong to structural determinants of individual enzymatic activities. When incubated with 11-deoxycorticosterone (DOC), the 11beta-hydroxylation activity of the mutants was most effectively increased by combining D147E and I112P (sixfold increase). The two substitutions displayed an additive effect. The same tendency can be observed when using 11-deoxycortisol as a substrate, although the effect is less pronounced. The second step of the CYP11B2-dependent DOC conversion, the 18-hydroxylation activity, was not as strongly increased as the 11beta-hydroxylation potential. Activity was unaffected by D147E, whereas the single mutant I112P displayed the most pronounced activation (70% enhancement), thus causing different increasing effects on the first two enzymatic reaction steps. A slightly enhanced aldosterone synthesis from DOC could be measured due to increased levels of the intermediates. However, the 18-oxidation activity of all the mutants, except for I112S and D147E, was slightly reduced. The strongly enhanced 18-hydroxycorticosterone and aldosterone formation observed in the mutants provides important information on a possible role of such amino-acid replacements in the development of essential hypertension. Furthermore, the results indicate the possibility of a differential as well as independent modification of CYP11B2 reaction steps. The combination of functional data and computer modelling of CYP11B2 suggests an indirect involvement of residue 147 in the regulation of CYP11B isoform specific substrate conversion due to its location on the protein surface. In addition, the results indicate the functional significance of amino-acid 112 in the putative substrate access channel of human CYP11B2. Thus, we present the first example of substrate recognition and conversion being attributed to the N-terminal part of human CYP11B2.

Baboon cytochrome P450c11 is encoded by more than one gene

Two P450c11 genes, sharing 99% homology, were cloned from Cape baboon adrenal tissue using RT-PCR. The cDNAs showed 96% and 94.6% sequence identity to human P450c11 and aldosterone synthase, respectively. One of the gene sequences contained a termination codon in exon one. The cloned cDNAs were expressed in COS 1 cells and the metabolism of deoxycorticosterone to corticosterone investigated. The expressed enzyme exhibited 1 beta hydroxylase activity, but no aldosterone synthase activity.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Modulation of aldosterone biosynthesis by adrenodoxin mutants with different electron transport efficiencies

Aldosterone biosynthesis is highly regulated on different levels by hormones, potassium, lipid composition of the membrane and the molecular structure of its gene. Here, the influence of the electron transport efficiency from adrenodoxin (Adx) to CYP11B1 on the activities of bovine CYP11B1 has been investigated using a liposomal reconstitution system with truncated mutants of Adx. It could be clearly demonstrated that Adx mutants Adx 4-114 and Adx 4-108, possessing enhanced electron transfer abilities, produce increases in corticosterone and aldosterone biosynthesis. Based on the Vmax values of corticosterone and aldosterone formation, Adx 4-108 and Adx 4-114 enhance corticosterone synthesis 1.3-fold and aldosterone formation threefold and twofold, respectively. The production of 18-hydroxycorticosterone was changed only slightly in these Adx mutants. The effect of Adx 1-108 on the product patterns of bovine CYP11B1, human CYP11B1 and human CYP11B2 was confirmed in COS-1 cells by cotransfection of CYP11B- and Adx-containing expression vectors. It could be shown that Adx 1-108 enhances the formation of aldosterone by bovine CYP11B1 and by human CYP11B2, and stimulates the production of corticosterone by bovine CYP11B1 and human CYP11B1 and CYP11B2 also.

Interaction of CYP11B1 (cytochrome P-45011 beta) with CYP11A1 (cytochrome P-450scc) in COS-1 cells

The interactions of CYP11B1 (cytochrome P-45011beta), CYP11B2 (cytochrome P-450aldo) and CYP11A1 (cytochrome P-450scc) were investigated by cotransfection of their cDNA into COS-1 cells. The effect of CYP11A1 on CYP11B isozymes was examined by studying the conversion of 11-deoxycorticosterone to corticosterone, 18-hydroxycorticosterone and aldosterone. It was shown that when human or bovine CYP11B1 and CYP11A1 were cotransfected they competed for the reducing equivalents from the limiting source contained in COS-1 cells; this resulted in a decrease of the CYP11B activities without changes in the product formation patterns. The competition of human CYP11A1 with human CYP11B1 and CYP11B2 could be diminished with excess expression of bovine adrenodoxin. However, the coexpression of bovine CYP11B1 and CYP11A1 in the presence of adrenodoxin resulted in a stimulation of 11beta-hydroxylation activity of CYP11B1 and in a decrease of the 18-hydroxycorticosterone and aldosterone formation. These results suggest that the interactions of CYP11A1 with CYP11B1 and CYP11B2 do not have an identical regulatory function in human and in bovine adrenal tissue.

Adrenal zonation: clues from 11beta-hydroxylase and aldosterone synthase

Aldosterone and cortisol are the major mineralocorticoid and glucocorticoid produced by the human adrenal. Circulating levels of angiotensin II and potassium control the adrenal production of aldosterone, while the production of cortisol is controlled mainly by adrenocorticotropin. The capacity of the adrenal cortex to differentially produce aldosterone and cortisol relies to a large degree on the expression of aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1). CYP11B2 catalyzes the final steps in the biosynthesis of aldosterone and is expressed solely in the glomerulosa of the adrenal cortex, while CYP11B1 catalyzes the final steps in the biosynthesis of cortisol and is expressed in the fasciculata/reticularis. The zonal expression of these two isozymes appears to result from transcriptional regulation of the two genes. Herein, the recent progress in defining the cellular mechanisms that regulate transcription of these two isozymes and thus the capacity of the adrenal gland to differentially produce aldosterone and cortisol is discussed.

Molecular approaches to evaluate pollutants

Many organisms are in use to test pollutants and their extensive variability clearly emerges from reviews since researchers in the world are involved in continuous effort to set up new assays and to improve those already in use. In the present paper we focus the attention on the mixed function oxidase system and the DNA adduct formation which are two biomarkers widely used and extensively studied in mammals and fish by different Authors. We compare their results with the ones we obtained in amphibians, which result to be a good model. Moreover we present some significative results obtained by the use of cultured cell lines to test the herbicide MCPA. The results obtained demonstrate that the amphibian Xenopus is a suitable indicator for induction of cytochrome P-450 by B[a]P as well as for production of DNA adducts. Cultured cells evidenced that cytoskeletal array and thiol proteins are molecular targets of the herbicide used, demonstrating that risk assessment can be properly analysed in in vitro systems.

Eel (Anguilla japonica) testis 11beta-hydroxylase gene is expressed in interrenal tissue and its product lacks aldosterone synthesizing activity

A recombinant expression vector containing Japanese eel (Anguilla japonica) testis cytochrome P450(11 beta) (11beta-hydroxylase) cDNA was introduced into COS-1 cells. Enzymatic activity of the expressed P450(11 beta) for corticosteroid synthesis was analysed by incubating transfected cells with 14C-labelled 11-deoxycorticosterone or 3H-labelled deoxycortisol as substrates. Thin layer chromatography of incubation medium revealed that a high percentage of 11-deoxycorticosterone was converted into corticosterone and 11-dehydrocorticosterone but no aldosterone was detected. Similarly, deoxycortisol was converted into cortisol and cortisone. These results show that eel P450(11beta) does not possess significant aldosterone synthesizing activity. Northern blot analysis detected a 1.8 kb transcript of P450(11beta) using RNA extracted from interrenals of untreated Japanese eel but no hybridization signal was apparent using RNA extracted from brain, spleen, heart, muscle or testis. Immunohistochemistry using an antiserum against P450(11beta) also revealed strong immunostaining in interrenal cells.

Late steps of aldosterone biosynthesis: sheep are not rats

1. The last three steps of aldosterone biosynthesis have been demonstrated to be catalysed by a single enzyme, referred to as CYP11B (or P450(11) beta) in cow, pig, sheep and bullfrog and as CYP11B2 (or P450aldo) in rat, human, mouse and hamster. 2. The related enzyme CYP11B1 (also referred to as P450(11) beta) in rat, human, mouse and hamster does not have aldosterone synthesis activity, but no such enzyme has been reported in the cow, pig or sheep to date. 3. Exclusive aldosterone secretion in the zona glomerulosa (ZG) of the adrenal cortex in species such as rat, human, mouse and hamster could be ascribed to the restricted distribution of CYP11B2 to the same region in the adrenal cortex. 4. In other species, such as cow, pig and sheep, the CYP11B enzyme is expressed throughout the adrenal cortex and, thus, the exclusive aldosterone biosynthesis in the ZG could not be explained simply by the distribution of the enzyme. 5. We have shown in the sheep that potassium loading and acute sodium depletion stimulate the CYP11B transcript levels, which are not further increased by chronic sodium depletion. 6. The predominant CYP11B in the sheep adrenal cortex catalyses the synthesis of aldosterone from deoxycorticosterone (DOC) in vitro, is expressed throughout the adrenal cortex and the corresponding transcript levels are increased by K+ loading or sodium depletion. In short, as far as the last step of aldosterone biosynthesis is concerned, sheep are different from rats. In the rat, the CYP11B2 transcript or protein is elevated by K+ loading or sodium depletion, but not the CYP11B1 transcript or protein. 7. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to one preferentially involving 18-OH-DOC and not corticosterone.

The microsomal mixed function oxidase system of amphibians and reptiles: components, activities and induction

This article reviews current research in amphibian and reptilian cytochromes P450, important to the overall understanding of xenobiotic metabolism in the ecosystem and the evolution of P450s. Amphibians and reptilians contain the normal mixed function oxidase system (MFO). In general the MFO content and activities are less than those found in mammals, but only a few of the known activities have been examined in these vertebrate classes. Research to date has focused on two families of cytochromes P450, CYP1 and 2. The isoforms examined catalyze the classic activities but there have been notable absences. The total number of isoforms present and the breadth of substrates metabolized are yet unknown. Induction by foreign compounds (xenobiotics) is lengthier and yields lower levels of induced activity than is typically found in mammals. When these animals are pretreated with 3-methylcholanthrene (3MC) and beta-naphthaflavone (BNF), which are known to induce the same isoform in mammals, multiple isoforms are induced with different activities. Phenobarbital-pretreatment in turtles and alligators induces cytochromes P450 and suggestive data indicates induction in the lizard Agama lizard and the newt Pleurodeles waltl. In amphibians and reptiles a CYP2B protein does appear to be present along with constitutive activities associated with the 2 family of cytochromes P450. The markedly different response to classic inducers combined with lower or absent activities alters the view of how amphibians and reptilians respond to xenobiotic challenges.

Cloning of a membrane-spanning protein with epidermal growth factor-like repeat motifs from adrenal glomerulosa cells

The three zones of adrenal cortex are thought to arise from a single multipotential stem cell, but the mechanisms underlying the zonal differentiation during embryonic development of adrenal cortex are poorly understood. Employing subtraction cloning strategy, we isolated three distinct clones that were specifically expressed in the rat glomerulosa zone. One clone, named zona glomerulosa specific clone, encoded a membrane-spanning protein with a signal peptide at the N-terminus, six epidermal growth factor-like repeat motifs, and a transmembrane domain near the C-terminus. It was identified as a rat homolog of preadipocyte factor-1 (Pref-1), a factor involved in maintaining the undifferentiated status of preadipocyte. Immunohistochemical studies confirmed the presence of Pref-1 protein in the glomerulosa zone. Detailed examination revealed that the zone is divided into two layers; the first is a few-cells-thick layer present underneath the capsule (expressing both Pref-1 protein and aldosterone synthase cytochrome P450), and the second layer is beneath the first (containing Pref-1 protein but not aldosterone synthase). Moreover, another cell layer was found beneath the second layer and above the fasciculata zone, whose cells contained no Pref-1 protein, aldosterone synthase, or 11beta-hydroxylase. These findings suggest that a recently reported aldosterone synthase- and 11beta-hydroxylase-less cell layer between the two zones is composed of two kinds of cell: Pref-1 protein-positive and -negative cells. The level of Pref-1 message in the adrenal glands of animals having various pituitary-adrenal axis activities, as well as various plasma salt concentrations, correlated with the total number of glomerulosa cells. However, the specific content of Pref-1 message in a cell was fairly constant. When the adrenal gland was surgically enucleated and the remaining capsule regenerated, the level of Pref-1 transcript was significantly suppressed at the early phase. At this phase, only a minor population of the cortical cells expressed Pref-1 protein, most of these cells already expressing a fasciculata/reticularis-specific marker, inner zone antigen. These findings suggest that the capsular cells, mostly composed of the glomerulosa cells, may have potential for differentiating into other zones' cells, and the down-regulation of Pref-1 expression may be an important step in the adrenal zonal differentiation.

Hypothesis: aldosterone is synthesized by an alternative pathway during severe sodium depletion. 'A new wine in an old bottle'

1. The last three steps of aldosterone biosynthesis, 11 beta-hydroxylation, 18-hydroxylation and 18-oxidation, have been demonstrated to be catalysed by one enzyme, which is the cytochrome P450(11 beta) (CYP11B) in cow, pig, sheep and bullfrog or cytochrome P450aldo (CYP11B2) in rat, human, mouse and hamster. 2. The related enzyme P450(11 beta) (CYP11B1) from rat, human, mouse and hamster adrenals displays 11 beta-hydroxylation and 18-hydroxylation activities, but not 18-oxidation activity in vitro. No such enzyme has been reported in the cow, pig or sheep to date. 3. Data showing the dissociation of aldosterone secretion from plasma angiotensin II (AngII) levels indicate the presence of other factor(s) that regulate aldosterone biosynthesis in response to changes in body sodium status. Thus, we propose the existence of a 'sodium status factor' that regulates aldosterone biosynthesis in addition to AngII, K+, adrenocorticotropic hormone and atrial natriuretic peptide. 4. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to a pathway using 18-hydroxy-deoxycorticosterone (18-OH-DOC) rather than corticosterone as an intermediate. This switch may be mediated via the putative 'sodium status factor'. 5. Two models of the hypothesis will be discussed in this paper: (i) a 'one-enzyme' model; and (ii) a 'two-enzyme' model. 6. The one-enzyme model proposes that P450aldo (P450(11 beta) as in the case of the cow, sheep and pig) changes its enzymatic activity during severe sodium deficiency (i.e. switching to the alternative aldosterone biosynthesis pathway). 7. The two-enzyme model proposes that, under normal circumstances, P450aldo synthesizes aldosterone from deoxycorticosterone, while during severe sodium deficiency the P450(11 beta) provides the substrate (i.e. 18-OH-DOC) for the P450aldo.

Identification of functional domains of rat intestinal phospholipase B/lipase. Its cDNA cloning, expression, and tissue distribution

A cDNA encoding a rat intestinal Ca(2+)-independent phospholipase B/lipase (PLB/LIP) was cloned from an ileac mucosa cDNA library using a probe amplified by polymerase chain reaction based on the purified enzyme's sequence. PLB/LIP consists of an NH2-terminal signal peptide, four tandem repeats of about 350 amino acids each, and a hydrophobic domain near the COOH terminus. The enzyme purified previously was found to be derived from the second repeat part. To examine the function of each domain, the full-length PLB/LIP, individual repeats, and a protein lacking the COOH-terminal hydrophobic stretch were expressed in COS-7 cells. The results showed that the second repeat, but not the other repeats, had all the activities (phospholipase A2, lysophospholipase, and lipase) found in the purified natural and expressed full-length enzymes, suggesting repeat 2 is a catalytic domain. The full-length enzyme was mainly present in membrane fractions and efficiently solubilized by treatment with 1% Triton X-100, but not with phosphatidylinositol-specific phospholipase C. Deletion of the COOH-terminal hydrophobic stretch caused the secretion of > 90% of synthesized PLB/LIP into culture media. These results suggest the hydrophobic domain is not replaced by a glycosylphosphatidylinositol anchor but serves as a membrane anchor directly. A message of the full-length PLB/LIP was abundantly expressed in the ileum and also, in a smaller, but significant amount, in the esophagus and testis. Immunohistochemistry showed that PLB/LIP is localized in brush border membranes of the absorptive cells, Paneth cells, and acrosomes of spermatid, suggesting its roles related and unrelated to intestinal digestion.

Polyadenylation-mediated translational regulation of maternal P450(11beta) mRNA in frog oocytes

Northern blot analysis of bullfrog tissues using a cDNA probe of cytochrome P450(11beta) showed that a large amount of message was present in the ovary as well as in the adrenal tissue. Two kinds of mRNA of different sizes were found in the ovary. Sequence determination of the two cDNAs and analysis by reverse-transcription polymerase chain reaction indicated that the protein encoded by the larger mRNA was identical to the adrenal enzyme, while the protein encoded by the smaller had a truncated sequence lacking an extension peptide necessary for the protein transport to the mitochondria. The mRNAs were present in the oocytes but not in the follicular cells, and their content in an oocyte varied little during its maturation. Immunoblot analyses of the mitochondrial fraction of oocytes failed to demonstrate the presence of P450(11beta) protein. In contrast the eggs were found to contain a large amount of enzymatically active protein. Interestingly the mRNA has a cis-element called cytoplasmic polyadenylation element at its 3' untranslated region. When poly(A) tails of the message prepared from eggs and oocytes were examined by RNase H digestion or reverse-transcription polymerase chain reaction, those of eggs were about 150 nucleotides longer than those of oocytes. These results suggest that translation of the message is stimulated during the oocyte maturation as a result of enhanced polyadenylation at its 3'-end. Finally a finding is presented that progesterone was converted to 11beta-hydroxyprogesterone by the frog P450(11beta), implying that the enzyme expressed in eggs may control a level of progesterone which is needed to initiate the oocyte maturation.

Functional and expression analysis of ovine steroid 11 beta-hydroxylase (cytochrome P450 11 beta)

In this study, the ovine steroid 11 beta-hydroxylase (P450(11 beta) or CYP11B) cDNA previously reported by us (1) was transfected into COS-7 cells. Using 3H-11-deoxycorticosterone (3H-DOC) as the substrate, and paper partition chromatography for separation of steroid products, the expressed enzyme was shown to catalyse the conversion of DOC to corticosterone (B), 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), 18-hydroxy-corticosterone (18-OH-B), and aldosterone (ALDO). These results suggest that the expressed ovine cDNA exhibited 11 beta-hydroxylase, 18-hydroxylase and aldosterone synthesis activities. The enzymatic activity of the enzyme was further analysed by adding unlabelled steroids to compete with 3H-DOC. The conversion of 3H-DOC to 3H-ALDO was inhibited by the addition of excess DOC, B and 18-OH-DOC, indicating that all these steroids were potential substrates of the enzyme. The results also demonstrated that 18-hydroxylation could occur before 11 beta-hydroxylation with this enzyme. However, the addition of excess cold 18-OH-B had no significant effect on the level of 3H-ALDO that was synthesised. This result could imply that 18-OH-B is not an intermediate involved in the conversion of DOC to aldosterone, or, more likely, the enzyme substrate site is not accessible readily. Our results also indicated that DOC was preferred to 18-OH-DOC as a substrate for the enzyme. We have demonstrated by hybridisation histochemistry using specific oligonucleotide probes that the corresponding P450(11 beta) RNA transcript was present in all zones in the sheep adrenal cortex. In summary, we have shown that the enzyme encoded by the predominant P450(11 beta) cDNA isolated from the sheep adrenocortical cDNA library has all the enzymatic activities to biosynthesise ALDO from DOC. The corresponding transcript of this ovine P450(11 beta) cDNA was located throughout the adrenal cortex and thus the inability of the zonae fasciculata-reticularis to secrete ALDO remains to be understood.

Purification and characterization of a cytochrome P450 from liver microsomes of Xenopus laevis

A new cytochrome P450 (P450) has been purified to near homogeneity from Xenopus laevis liver microsomes. Two steps of column chromatographies (n-octylamino Sepharose 4B and Mono Q) and fast protein liquid chromatofocusing were performed consecutively, and the final preparation containing 19 nmol P450/mg protein gave a single band of 52 kDa on SDS-PAGE at an isoelectric point of 6.7. This enzyme had a common feature of microsomal P450s in NH2-terminal region, and some of the internal sequences were similar to the corresponding sequences of reported P450s. The purified Xenopus P450 cross-reacted with antibodies against CYP2B1, rat CYP2E1, and CYP2C13, but not with rat CYP1A1, CYP3A2, or CYP4A1. Upon reconstitution with rat NADPH-cytochrome P450 reductase and phospholipid, the Xenopus P450 catalyzed aniline hydroxylation and N-nitrosodimethylamine N-demethylation. Cytochrome b5 enhanced these reactions. This P450 did not catalyze the hydroxylation of either hexobarbital or testosterone. Thus, the catalytic activities of this P450 were comparable with those of mammalian CYP2E1. Expression of this P450 was observed in liver, kidney, lung, and testis, and the level was highest in kidney. Tissue specificity of expression was the same in both male and female frogs.

The amino acid substitutions Ser288Gly and Val320Ala convert the cortisol producing enzyme, CYP11B1, into an aldosterone producing enzyme

Transfection studies with cDNAs encoding hybrids between the highly similar cytochrome P450 enzymes, CYP11B1 (steroid 11 beta-hydroxylase) and CYP11B2 (aldosterone synthase) have identified which amino acids determine the different activities of the enzymes.

Fish testicular 11beta-hydroxylase: cDNA cloning and mRNA expression during spermatogenesis

We isolated and characterized a cDNA encoding testicular 11beta-hydroxylase, cytochrome P450(11beta) from the Japanese eel (Anguilla japonica) testis. The cDNA contains an open reading frame that encodes a protein of 511 amino acids. The predicted amino acid sequence shares 38-48% homology with those of adrenal P450(11beta) from mammals and frog. Transient expression in COS 1 cells confirmed that the protein encoded by this cDNA had P450(11beta) activity. Northern blotting revealed a single 1.8 kb long transcript of P450(11beta). This transcript was not found in immature eel testes prior to an injection with human chorionic gonadotropin (hCG), but it was present in eel testes after hCG injection.

Cytochrome P450(11 beta): ectopic expression in oocyte and its physiological implication

Cytochrome P450(11 beta) (steroid 11 beta-hydroxylase) catalyzes an essential step for biosynthesis of glucocorticoid as well as mineralocorticoid, and therefore is believed to exist specifically in the adrenocortical mitochondria. We previously isolated a complementary DNA clone encoding this enzyme from bullfrog (Rana catesbeiana) adrenal tissues and characterized the enzyme expressed in COS cells. To explore the tissue distribution of the enzyme we performed Northern blot analysis. Unexpectedly we found that a large amount of the mRNA exists in the ovary as well as the adrenal gland. It was present in oocytes, but not in follicular cells. The P450 protein was not found during early stages of oocyte development, and at the final stage of maturation the message appeared to be translated. Evidence was obtained that the stage-dependent translation of the mRNA was due to the regulated polyadenylation at its 3'-end. In oocytes of various organisms several maternal mRNAs are known to add poly(A) tails in the cytoplasm during the progesterone-induced maturation.

Functional expression of the guinea pig 11b-hydroxylase in COS-1 cells

We expressed a guinea pig 11 beta-hydroxylase cDNA (1) in COS-1 cells. In order to find the optimal expression system we compared three expression plasmids, each driven by a different promoter. Although promoters exhibited different transcriptional activities this did not result in different enzymatic activities. Upon cotransfection with bovine adrenodoxin a 5-fold increase of enzyme activity was achieved. A comparison with the bovine 11 beta-hydroxylase clearly demonstrated that the guinea pig enzyme was not able to produce significant amounts of 18-hydroxylated and 18-oxidized products from deoxycorticosterone under the experimental conditions used.

11 beta-hydroxylase activity in recombinant yeast mitochondria. In vivo conversion of 11-deoxycortisol to hydrocortisone

In mammals, the final 11 beta-hydroxylation step of the hydrocortisone biosynthesis pathway is performed by a mitochondrial enzyme, namely cytochrome P-450(11 beta), together with the electron carriers adrenodoxin and NADPH adrenodoxin oxidoreductase. Successful production of a functional steroid 11 beta-hydroxylase activity was obtained in recombinant yeast in vivo. This conversion was achieved by coexpression of a mitochondrially targeted adrenodoxin and a modified bovine P-450(11 beta) whose natural presequence was replaced by a yeast presequence, together with an unexpected yeast endogenous NADPH-adrenodoxin-reductase-like activity. Adrenodoxin and P-450(11 beta) behave as a mitochondrial matrix and membrane protein, respectively. Saccharomyces cerevisiae apparently produces a mitochondrial protein which is capable of transferring electrons to bovine adrenodoxin, which in turn transfers the electrons to P-450(11 beta). The endogenous adrenodoxin oxidoreductase gains electrons specifically from NADPH. The notion that a yeast microsomal NADPH P-450 oxidoreductase can transfer electrons to mammalian microsomal P-450s can be extended to mitochondria, where an NADPH adrenodoxin oxidoreductase protein transfers electrons to adrenodoxin and renders a mitochondrial mammalian P-450 functional in vivo. The physiological function of this yeast NADPH adrenodoxin oxidoreductase activity is not known.

Engineering a mineralocorticoid- to a glucocorticoid-synthesizing cytochrome P450

Site-directed mutagenesis of a domain (amino acids 299-338) aligning to the I-helix region of P450cam, P450BM3 and P450terp was used to investigate the different regioselectivities displayed in the hydroxylation reactions performed by human aldosterone synthase (P450aldo) and 11beta-hydroxylase (P45011beta). The two enzymes are 93% identical and are essential for the synthesis of mineralocorticoids and glucocorticoids in the human adrenal gland. Single replacement of P450aldo residues for P45011 beta-specific residues at positions 296, 301, 302, 320, and 335 only gave rise to slightly increased 11beta-hydroxylase activities. However, a L301P/A320V double substitution increased 11beta-hydroxylase activity to 60% as compared with that of P45011 beta. Additionally substituting Ala-320 for Val-320 of P45011 beta further enhanced this activity to 85%. The aldosterone synthase activities of the mutant P450aldo proteins were suppressed to a varying degree, with triple replacement mutant L301P/E302D/A320V retaining only 10% and double replacement mutant L301P/A320V retaining only 13% of the P450aldo wild type activity. These results demonstrate a switch in regio- and stereoselectivities of the engineered P450aldo enzyme due to manipulation of residues at three critical positions, and we attribute the determination of these features in P450aldo to the structure of a region analogous to the I-helix in P450cam.