Molecular biology of mineralocorticoid metabolism

Mineralocorticoids are adrenal steroid hormones that regulate the retention of sodium by the kidney and, hence, are crucial in the regulation of sodium balance, intravascular volume, and blood pressure. The molecular biology of mineralocorticoid biosynthesis and action has only recently been elucidated. The genes encoding the various enzymes that convert cholesterol to mineralocorticoids have now been cloned. This has revealed the molecular basis of several inherited forms of mineralocorticoid excess, which cause hypertension, and several forms of mineralocorticoid deficiency, which cause salt loss. The cloning of the mineralocorticoid receptor revealed a paradox. Both the mineralocorticoid and the glucocorticoid receptor are activated equally by cortisol, even though cortisol has very modest mineralocorticoid activity. This is explained by the cloning of two genes for the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta HSD). Type-II 11 beta HSD, found primarily in the kidney, irreversibly converts cortisol to cortisone, which does not activate the mineralocorticoid receptor. Type-II 11 beta HSD thus defends the mineralocorticoid receptor from being activated by the very high concentrations of cortisol in the blood. Recent studies in genetically hypertensive rats suggest that other enzymes or factors that regulate salt balance may remain undiscovered. Thus the study of mineralocorticoid biosynthesis and action remains one of the most promising approaches to understanding hypertension.

Gonadotropin-releasing hormone-stimulated calcium mobilization is altered in pituitary cultures from anestrous ewes

GnRH transiently increases intracellular calcium ([Ca2+]i) in pituitary gonadotrophs in culture. This effect is observed within 10 sec of GnRH treatment, lasts 1-5 min, and is thought to be an important intracellular signal leading to the secretion of LH. Recent studies with ovine pituitary cultures uncovered seasonal differences in this transient calcium response to GnRH. This finding led to the hypothesis that anestrus alters the pituitary response to GnRH and prompted this study on seasonal effects on LH secretion and [Ca2+]i mobilization. Inhibin was used to enhance pituitary sensitivity to GnRH. Results showed that pituitary cultures from 16 cycling ewes secreted an average of 9% +/- 2% of stored LH after treatment with 10 nM GnRH (stored LH = 470 +/- 66 ng/million cells); 9% +/- 1% of pituitary cells increased the concentration of [Ca2+]i from 75-150 nM up to 400-1400 nM. When cultures were pretreated with inhibin, GnRH released an average of 15% +/- 3% of stored LH (stored LH = same as above), and 38% +/- 4% of cells transiently increased [Ca2+]i above 400 nM. Results also showed that pituitary cultures from 11 acycling ewes secreted similar percentages of LH although the cells contained less LH to begin with (stored LH = 190 +/- 24 ng/million cells), but absolutely none of these cells (500 counted) increased [Ca2+]i after GnRH treatment, with or without inhibin present. Levels of GnRH receptor mRNA were unchanged by season. These data show that LH secretion and the rapid, transient increase in [Ca2+]i caused by GnRH are uncoupled in the unique situation of anestrus. It is possible, in fact, that these two parameters are not necessarily coupled during estrous conditions and that the transient change in [Ca2+]i is connected with LH synthesis or some other gonadotroph function. The data also show that inhibin can increase GnRH-responding cells up to 38%, a fact suggesting that inhibin may be a differentiation factor capable of transforming multipotent pituitary cells into gonadotrophs in sheep.

Gene conversion in the CYP11B2 gene encoding P450c11AS is associated with, but does not cause, the syndrome of corticosterone methyloxidase II deficiency

Cytochrome P450c11AS (aldosterone synthase) has 11 beta-hydroxylase, 18-hydroxylase, and 18-oxidase activities and is expressed solely in the adrenal zona glomerulosa. Corticosterone methyloxidase II (CMOII) deficiency denotes a rare disorder of adrenal steroidogenesis in which only the 18-oxidase activity of P450c11AS is disrupted, while the 11 beta-hydroxylase and 18-hydroxylase activities persist. Such patients have elevated serum concentrations of corticosterone and 18-hydroxycorticosterone and very low or unmeasurable concentrations of aldosterone, often resulting in a clinical salt-losing crisis in infancy. One pair of point mutations, Arg181-->Trp and Val386-->Ala, has been previously characterized to cause this disorder in an inbred Iranian Jewish population. We have sought mutations causing CMOII deficiency in outbred populations. In three of four unrelated P450c11AS alleles from two unrelated patients with CMOII deficiency, we found a gene conversion event in which exons 3 and 4 of the CYP11B2 gene encoding P450c11AS were changed to the sequence of the nearby CYP11B1 gene, which encodes the related enzyme P450c11 beta. This conversion resulted in a mutant P450c11AS protein carrying three changes: Asp141-->Glu, Lys151-->Asn, and Ile246-->Thr. We built seven vectors expressing P450c11AS carrying each mutation singly, each of the three possible pairs of mutations, and the triple mutation as found in the proband. The activities of both the normal P450c11AS and the various mutants in transfected nonsteroidogenic COS-1 cells were very low, but their activities in steroidogenic MA-10 and JEG-3 cells were 10- to 20-fold higher. In these systems all of the mutants retained normal 18-oxidase activity, indicating that the detected gene conversion event is associated with but does not cause CMOII deficiency. None of the four CYP11B2 alleles in these two patients bore other identifiable mutations. These patients might have mutations in the promoters or other noncoding regions, or mutations in genes other than CYP11B2 may cause the syndrome of CMOII deficiency.

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.

Isolation of nine different biologically and immunologically active molecular variants of bovine follicular inhibin

A combination of immunoaffinity chromatography, SDS-PAGE, and electroelution was used to simultaneously isolate 0.36-4.65 mg of nine different molecular forms of inhibin (pro alpha C-29 kDa; fully processed 34 kDa; and large inhibin forms 49, 53, 58, 77, 88, 110, and > 160 kDa) from 0.675 L of bovine follicular fluid (bFF). Each inhibin form, except pro alpha C, cross-reacted with inhibin alpha C 1-26-and beta A 82-114-subunit-directed antibodies during immunoblot analysis. Pro alpha C cross-reacted only with alpha-subunit antibodies. The inhibin forms consisted of 22-, 29-, 49-, or 58-kDa alpha subunits and 17- or 58-kDa beta subunits. During cultures of ovine pituitary cells, a 5-ng/ml dose of each inhibin form (except pro alpha C) suppressed basal accumulation of FSH 30% to 50% but increased GnRH-induced LH release 40% to 248%. The various inhibin forms cross-reacted in parallel fashion with standard curves generated during homologous and heterologous RIAs but with markedly different relative immunopotencies. In the RIAs, pro alpha cross-reacted 3- to 18-fold more than the fully processed inhibin form. The fully processed and the seven different large forms of inhibin cross-reacted with different relative immunopotencies in a two-site dimer-specific ELISA. We concluded that 1) a combination of immunoaffinity extraction, SDS-PAGE, and electroelution simultaneously isolated relatively large amounts of highly enriched preparations of nine different molecular forms of immunologically and biologically active inhibin from bFF; 2) eight different dimeric forms of bovine inhibin may regulate both basal FSH and GnRH-induced LH secretion by the pituitary gland, and 3) eight or nine different molecular forms of inhibin cross-react with different relative immunopotencies in the two-site dimer-specific assay or RIAs.

T-->A transversion 11 bp from a splice acceptor site in the human gene for steroidogenic acute regulatory protein causes congenital lipoid adrenal hyperplasia

Congenial lipoid adrenal hyperplasia (lipoid CAH) is the most severe form of CAH. Affected individuals can make no adrenal or gonadal steroids. All affected individuals are phenotypic females irrespective of gonadal sex, and frequently die in infancy if mineralocorticoid and glucocorticoid replacements are not instituted. Recent data implicate the steroidogenic acute regulatory (StAR) protein in this disorder. We now describe a 46,XY patient of Vietnamese ancestry with lipoid CAH who had a somewhat milder form of the disease. Diagnosis was at 10 weeks of age, and low levels of plasma progesterone, corticosterone, 180H-corticosterone and androstenedione were detectable. Testicular RNA for StAR was reverse transcribed, amplified, cloned and sequenced, revealing a 185 bp deletion corresponding to all of exon 5. The corresponding mRNA did not encode active protein in transfected cells. Cloned genomic DNA from the patient revealed only a T-->A transversion in intron 4,11 bp from the splice acceptor site of exon 5. This transversion destroys an NcoI site; digestion of PCR-amplified genomic DNA from the patient and both parents confirmed that the patient was homozygous and the parents were heterozygous. Expression vectors for StAR minigenes were constructed containing all StAR exons plus introns 4, 5 and 6 either with or without the T-->A mutation in intron 4. RNase protection assays showed that expression of the vector with normal intron 4 yielded correctly spliced StAR mRNA in transfected COS-1 cells, while most, but not all StAR mRNA from the vector with the T-->A transversion in intron 4 was abnormally spliced. RNase protection of the patient's testicular RNA confirmed that most, but not all StAR mRNA was similarly spliced abnormally. Splicing errors appear to be a rare cause of genetic diseases, but subtle intronic mutations may be missed when genomic DNA is the only material available for study. The low level of normal StAR mRNA produced may account for the later clinical presentation and low levels of steroid hormones detected in this patient.

Hybridization of the complementary mRNAs for P450c21 (steroid 21-hydroxylase) and tenascin-X is prevented by sequence-specific binding of nuclear proteins

The CYP21 gene that encodes the steroid 21-hydroxylase, P450c21, is overlapped on the opposite strand of DNA by the TX-X gene encoding the extracellular matrix protein, tenascin-X. These transcripts contain perfectly complementary segments of 299 bases at their 3'-ends. As these genes are tandemly duplicated and are transcribed in the adrenal cortex, we investigated whether these self-complementary transcripts formed RNA-RNA hybrids in vivo. Formation of heterogeneous nuclear ribonucleoprotein complexes between nascent RNA transcripts and nuclear proteins might modulate such potential RNA-RNA interactions. Using a double RNase protection assay, we found that these RNAs form very small amounts of double-stranded RNA-RNA hybrids in adrenal cells in vivo. To understand why these mRNAs fail to hybridize in vivo, we studied the actions of nuclear proteins on the binding and annealing of their complementary regions in vitro. The nucleation of interstrand annealing was kinetically favored over binding and was efficiently promoted by nuclear extracts. However, RNA-RNA strand zippering was inhibited, suggesting that protein binding and/or stable RNA secondary structures contribute to discontiguous base pairing. Increasing concentrations of nuclear proteins increased the relative proportion of these RNAs in perfect RNase-resistant duplexes but reached only about 20% of the total available RNA strands at saturating concentrations of nuclear proteins. Preincubation of either of the two single-stranded RNAs with nuclear proteins strongly inhibited the nucleation step of annealing, whereas preincubation of both strands abolished the annealing. RNase footprinting of the wild type and mutagenized overlapping transcripts suggested that sequence-specific binding of nuclear proteins is limited to the 5'-half of each RNA strand. These results indicate that the transcription of complementary, opposite-strand RNAs is not a mechanism for the regulation of the abundance of adrenal P450c21 mRNA and suggest that nuclear proteins strongly interfere with interstrand RNA base pairing in vitro as well as in vivo.

Serine phosphorylation of human P450c17 increases 17,20-lyase activity: implications for adrenarche and the polycystic ovary syndrome

Microsomal cytochrome P450c17 catalyzes both steroid 17 alpha-hydroxylase activity and scission of the C17-C20 steroid bond (17,20-lyase) on the same active site. Adrenal 17 alpha-hydroxylase activity is needed to produce cortisol throughout life, but 17,20-lyase activity appears to be controlled independently in a complex, age-dependent pattern. We show that human P450c17 is phosphorylated on serine and threonine residues by a cAMP-dependent protein kinase. Phosphorylation of P450c17 increases 17,20-lyase activity, while dephosphorylation virtually eliminates this activity. Hormonally regulated serine phosphorylation of human P450c17 suggests a possible mechanism for human adrenarche and may be a unifying etiologic link between the hyperandrogenism and insulin resistance that characterize the polycystic ovary syndrome.

A promoter within intron 35 of the human C4A gene initiates abundant adrenal-specific transcription of a 1 kb RNA: location of a cryptic CYP21 promoter element?

Complement component C4 is encoded by two nearly identical genes, C4A and C4B, that encode a C4 precursor that is proteolytically cleaved into the alpha, beta and gamma subunits of the mature protein. C4 is expressed primarily in liver and to a much lesser extent in immune cells. We have identified a unique 1 kb RNA transcript, termed Z, that arises from a cryptic promoter lying in the intron between exons 35 and 36 of the C4 gene. Primer extension, RNase protection, and 5' RACE experiments locate the cap site in intron 35, 55 bases upstream from exon 36. Northern blotting and RNase protection assays show that expression of this 1 kb Z RNA transcript is confined to the adrenal gland. Z RNA contains the same open reading frame as C4 which predicts a protein of 131 amino acids, but antisera to C4 do not interact with epitopes on this protein when it is synthesized by cell-free translation, hence the presence or absence of a Z protein in vivo could not be determined. Transfection of Z promoter/reporter constructs into human adrenal NCI-H295 cells shows that most if not all of the sequences required for high-level adrenal expression lie within 235 bases upstream from the cap site, but that this region is inactive when transfected into COS-1, JEG-3 and Hep-G2 cells, suggesting it contains an adrenal-specific element. The 222 bases upstream from the cap site are 75% identical in the human C4A and mouse Slp genes, and contain a potential binding site for steroidogenic factor 1 (SF-1), an orphan zinc-finger nuclear receptor. We propose that this region, like a nearby region in the mouse genome, functions as an upstream element of the P450c21 promoter, and may be a component of an adrenal-specific locus-control region.

Mutation T318M in the CYP11B2 gene encoding P450c11AS (aldosterone synthase) causes corticosterone methyl oxidase II deficiency

Corticosterone methyl oxidase (CMO) deficiency refers to disorders of aldosterone synthesis due to mutations in the CYP11B2 gene encoding cytochrome P450c11AS, which is the adrenal aldosterone synthase. Type I CMO deficiency is associated with low concentrations of 18OH-corticosterone and aldosterone, due to severe mutations in P450c11AS; while type II CMO deficiency is associated with high concentrations of 18OH-corticosterone and low concentrations of aldosterone, due to less severe mutations of P450c11AS. A single type of mutation, compound homozygosity for R181W and V386A, has been reported as the cause of CMOII deficiency in an inbred population. We now report a patient with a typical clinical and hormonal picture of CMOII deficiency. Direct sequencing of patient and parent DNAs showed that the mother's allele contributed R181W and the deletion/frameshift mutation delta C372, while the father's allele contributed T318M and V386A. These mutants were recreated in cDNA expression vectors singly and in the parental pairs, showing that neither allele contributed any measurable activity. This would suggest the patient should have CMOI deficiency. These studies suggest that other factors besides P450c11AS are involved in the genesis of the distinctive CMOI and CMOII phenotypes.

Structure of the human steroidogenic acute regulatory protein (StAR) gene: StAR stimulates mitochondrial cholesterol 27-hydroxylase activity

Steroidogenic acute regulatory protein (StAR) plays a key role in steroid hormone synthesis by enhancing the metabolism of cholesterol into pregnenolone. We determined the organization of the StAR structural gene, mapped to 8p11.2. The gene spans 8 kb and consists of seven exons interrupted by six introns. The 1.3 kb of DNA upstream from the transcription start site directed expression of a luciferase reporter gene in mouse Y-1 adrenal cortical tumor cells but not in BeWo choriocarcinoma cells. Reporter gene expression in the Y-1 cells was increased more than 2-fold by 8-Br-cAMP, indicating that the 1.3 kb DNA fragment contains sequences that confer tissue-specific expression and cAMP regulation. The sequence of a related StAR pseudogene, mapped to chromosome 13, lacks introns and has an insertion, numerous substitutions, and deletions. Expression of StAR in COS-1 cells cotransfected with cholesterol 27-hydroxylase (P450c27) and adrenodoxin resulted in a 6-fold increase in formation of 3 beta-hydroxy-5-cholestenoic acid, demonstrating that StAR's actions are not specific to steroidogenesis but extend to other mitochondrial cholesterol-metabolizing enzymes.

Chronic venous insufficiency

The consequences of chronic deep venous insufficiency are a major medical concern and result in significant loss of human productivity in addition to a significant compromise of lifestyles. The postphlebitic syndrome of chronic venous stasis and ulceration is a result of chronic venous hypertension and reflects a sequela of events occurring secondary to venous valvular insufficiency and reflux. Diagnostic techniques have advanced considerably; however, the prevention and management of this entity continue to be inadequate. Many new areas are being explored, both from a medical and a surgical perspective, and it is hoped that as clinical investigation proceeds, new conceptual approaches and techniques will arise to combat this difficult medical problem. The literature reviewed in this article reflects a spectrum of research attempting to understand the basic underlying hemodynamic as well as cellular and tissue changes that contribute to the development of postphlebitic signs and symptoms. More investigation is needed to enable us to proceed from the descriptive understanding of this entity to the mechanisms that result in this disease state. Preventive and curative management needs to succeed the current palliative approach to therapy.

Reading and evaluating qualitative research studies

Qualitative research is now published across the family practice and medical literature. This article is designed to help busy family physicians decide which qualitative studies are worth reading and to provide them with the tools to appreciate and evaluate research design and analysis. By using clinical analogies, the qualitative research process can be better understood.

Sequences promoting the transcription of the human XA gene overlapping P450c21A correctly predict the presence of a novel, adrenal-specific, truncated form of tenascin-X

A compact region in the human class III major histocompatibility locus contains the human genes for the fourth component of human complement (C4) and steroid 21-hydroxylase (P450c21) in one transcriptional orientation, while the gene for the extracellular matrix protein tenascin-X (TN-X) overlaps the last exon of P450c21 on the opposite strand of DNA in the opposite transcriptional orientation. This complex locus is duplicated into A and B loci, so that the organization is 5'-C4A-21A-XA-C4B-21B-XB-3'. Although this duplication event truncated the 65-kb X(B) gene to a 4.5-kb XA gene, the XA gene is transcriptionally active in the adrenal cortex. To examine the basis of the tissue-specific expression of XA and C4B, we cloned the 1763-bp region that lies between the cap sites for XA and C4B and analyzed its promoter activity in both the XA and the C4 orientations. Powerful, liver-specific sequences lie within the first 75 to 138 bp from the C4B cap site, and weaker elements lie within 128 bp of the XA cap site that function in both liver and adrenal cells. Because these 128 bp upstream from the XA cap site are perfectly preserved in the XB gene encoding TN-X, we sought to determine whether a transcript similar to XA arises within the XB gene. RNase protection assays, cDNA cloning, and RT/PCR show that adrenal cells contain a novel transcript, termed short XB (XB-S), which has the same open reading frame as TN-X.(ABSTRACT TRUNCATED AT 250 WORDS)

Human steroidogenic acute regulatory protein: functional activity in COS-1 cells, tissue-specific expression, and mapping of the structural gene to 8p11.2 and a pseudogene to chromosome 13

Steroidogenic acute regulatory protein (StAR) appears to mediate the rapid increase in pregnenolone synthesis stimulated by tropic hormones. cDNAs encoding StAR were isolated from a human adrenal cortex library. Human StAR, coexpressed in COS-1 cells with cytochrome P450scc and adrenodoxin, increased pregnenolone synthesis > 4-fold. A major StAR transcript of 1.6 kb and less abundant transcripts of 4.4 and 7.5 kb were detected in ovary and testis. Kidney had a lower amount of the 1.6-kb message. StAR mRNA was not detected in other tissues including placenta. Treatment of granulosa cells with 8-bromo-adenosine 3',5'-cyclic monophosphate for 24 hr increased StAR mRNA 3-fold or more. The structural gene encoding StAR was mapped using somatic cell hybrid mapping panels to chromosome 8p. Fluorescence in situ hybridization placed the StAR locus in the region 8p11.2. A StAR pseudogene was mapped to chromosome 13. We conclude that StAR expression is restricted to tissues that carry out mitochondrial sterol oxidations subject to acute regulation by cAMP and that StAR mRNA levels are regulated by cAMP.

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.

Expression and characterization of truncated human heme oxygenase (hHO-1) and a fusion protein of hHO-1 with human cytochrome P450 reductase

A human heme oxygenase (hHO-1) gene without the sequence coding for the last 23 amino acids has been expressed in Escherichia coli behind the pho A promoter. The truncated enzyme is obtained in high yields as a soluble, catalytically-active protein, making it available for the first time for detailed mechanistic studies. The purified, truncated hHO-1/heme complex is spectroscopically indistinguishable from that of the rat enzyme and converts heme to biliverdin when reconstituted with rat liver cytochrome P450 reductase. A self-sufficient heme oxygenase system has been obtained by fusing the truncated hHO-1 gene to the gene for human cytochrome P450 reductase without the sequence coding for the 20 amino acid membrane binding domain. Expression of the fusion protein in pCWori+ yields a protein that only requires NADPH for catalytic turnover. The failure of exogenous cytochrome P450 reductase to stimulate turnover and the insensitivity of the catalytic rate toward changes in ionic strength establish that electrons are transferred intramolecularly between the reductase and heme oxygenase domains of the fusion protein. The Vmax for the fusion protein is 2.5 times higher than that for the reconstituted system. Therefore, either the covalent tether does not interfere with normal docking and electron transfer between the flavin and heme domains or alternative but equally efficient electron transfer pathways are available that do not require specific docking.

Role of steroidogenic acute regulatory protein in adrenal and gonadal steroidogenesis

Congenital lipoid adrenal hyperplasia is an autosomal recessive disorder that is characterized by impaired synthesis of all adrenal and gonadal steroid hormones. In three unrelated individuals with this disorder, steroidogenic acute regulatory protein, which enhances the mitochondrial conversion of cholesterol into pregnenolone, was mutated and nonfunctional, providing genetic evidence that this protein is indispensable normal adrenal and gonadal steroidogenesis.

The 5'-flanking region of the ovine follicle-stimulating hormone-beta gene contains six progesterone response elements: three proximal elements are sufficient to increase transcription in the presence of progesterone

Progesterone (P4) can alter the synthesis and secretion of FSH from pituitary gonadotropes of sheep. In this study, the 5'-flanking region (4.7 kilobases) of the ovine FSH beta gene was tested for binding by human progesterone receptors (hPR), using an immunoprecipitation technique. Three fragments were bound by hPR. Competition experiments using homologous and heterologous DNA fragments revealed this binding to be specific and of high affinity (Kd = 1.2-47 nM). The fragment sequences were screened for potential P4 response elements (PREs). Six PRE-like elements were found among the three immunoprecipitated fragments. Band shift experiments discerned that each of these PRE-like sequences could be bound by hPR. In functional studies, each of the PRE-like elements could enhance the expression of a reporter gene driven by a heterologous promoter in a hormone-dependent manner. The 5'-flanking region of the ovine FSH beta gene was tested for P4 responsiveness using a luciferase reporter. In the presence of P4, there was a 2- to 3-fold increase in luciferase activity when the entire 4.7 kilobases of the 5'-flanking sequence were present, whereas no increase was seen in a construct that contained only 84 basepairs 5' to the transcription start site. This effect on transcription was dose dependent for P4. Deletion studies revealed that the three PRE-like elements closest to the transcription start site (-250 to -137) were sufficient to create the hormone-dependent enhancement. These results indicate that the 5'-flanking sequence of the ovine FSH beta gene contains sequences capable of being bound by hPR and may be responsible for the effects of P4 on FSH beta synthesis and secretion. This study is the first to show binding and function of PR for a gonadotropin gene.

Artificial mutations in P450c11AS (aldosterone synthase) can increase enzymatic activity: a model for low-renin hypertension?

The conversion of 11-deoxycorticosterone (DOC) to aldosterone is catalyzed by a single enzyme, termed P450c11AS, which has 11 beta-hydroxylase, 18-hydroxylase and 18-oxidase activities. The normotensive Dahl salt-resistant (R) rat has two mutation in P450c11AS that increase its aldosterone synthase activity. If such a mutation were to occur in human patients the predicted phenotype would be low-renin hypertension with elevated ratios of plasma aldosterone to plasma renin activity. Before searching for P450c11AS mutations in such patients we sought to determine if mutations in human P450c11AS could increase enzymatic activity in a fashion analogous to the Dahl R rat. We used site-directed mutagenesis of the human P450c11AS cDNA to create the mutants Glu 136-->Asp, Lys 251-->Arg and the combination of the two; these mutations correspond to those seen in the Dahl R rat. Cells transfected with these mutant human P450c11AS sequences could convert [14C]DOC to corticosterone, 18OH-corticosterone, and aldosterone. In particular the Lys 251-->Arg mutant produced 4 times as much 18OH-corticosterone and 50-80% more aldosterone than the wild type. These data show that mutations of human P450c11AS can increase enzymatic activity, suggesting that such mutations could, in theory, be the basis of some forms of human low-renin hypertension.

Prenatal diagnosis of congenital lipoid adrenal hyperplasia

Congenital lipoid adrenal hyperplasia (lipoid CAH) is a rare genetic disorder of adrenal and gonadal steroidogenesis of unknown cause in which cholesterol cannot be converted to pregnenolone. As a result, affected individuals can make no steroid hormones, so that all affected newborns are phenotypic females, irrespective of karyotype. We studied two pregnancies in a family with two previously affected children by examining fetal karyotype, genital ultrasonography, and amniotic fluid steroid concentrations and by performing ACTH tests on family members. Prenatal diagnosis correctly identified both an unaffected XX fetus and an affected XY fetus. In the affected pregnancy, amniotic fluid concentrations of progesterone and pregnenolone were 30% and 50% of normal, respectively, but concentrations of 17 alpha-hydroxypregnenolone, 17 alpha-hydroxyprogesterone, cortisol, dehydroepiandrosterone, androstenedione, and estriol were either extremely low or undetectable, suggesting that these detected steroids were donated by maternal steroidogenesis. Fetal cord blood obtained at the termination of pregnancy showed very low concentrations of estrogens donated by the mother's circulation. Absent fetal steroidogenesis was confirmed by gas chromatography and mass spectrometry of both fetal and maternal serum. The responses of 10 different steroids to adrenal stimulation with ACTH in the obligately heterozygous parents were normal. Thus, unlike the case with other forms of CAH, heterozygosity cannot be determined by hormonal responses to provocative testing with ACTH. Immunocytochemistry and Western blotting showed that the affected placental tissue contained P450scc protein, confirming that P450scc is intact in these patients.

Qualitative analysis: how to begin making sense

The clinical process used to make sense of patient concerns closely parallels the analysis process of qualitative research. This partly explains why qualitative research methods are appropriate for many family practice research questions. Unfortunately, the language used by qualitative researchers, especially with regards to analysis, is often obscure. This impedes family physicians from implementing qualitative research. This paper overviews qualitative analysis and introduces a language and means by which family physicians can begin to make sense of qualitative data. The concepts, "reflexivity," "iteration," "data saturation," and "text," are defined. Three core steps of qualitative analysis are identified and compared to the diagnostic process. They consist of choosing an organizing system, reducing the data, and making connections. Four idealized ways for conducting these steps, editing, template, quasistatistical, and immersion/crystallization, are presented and compared to four ways of approaching patient concerns. Finally, the process of creating an appropriate qualitative analysis strategy is described for a hypothetical research study and some pitfalls and principles of qualitative analysis are reviewed.