Missense mutation serine106—-proline causes 17 alpha-hydroxylase deficiency

DHEA: a neglected biological signal that may affect fetal and child development

BACKGROUND

The stress-sensitive maternal hypothalamic-pituitary-adrenal (HPA) axis through the end-product cortisol, represents a primary pathway through which maternal experience shapes fetal development with long-term consequences for child neurodevelopment. However, there is another HPA axis end-product that has been widely ignored in the study of human pregnancy. The synthesis and release of dehydroepiandosterone (DHEA) is similar to cortisol, so it is a plausible, but neglected, biological signal that may influence fetal neurodevelopment. DHEA also may interact with cortisol to determine developmental outcomes. Surprisingly, there is virtually nothing known about human fetal exposure to prenatal maternal DHEA and offspring neurodevelopment. The current study examined, for the first time, the joint impact of fetal exposure to prenatal maternal DHEA and cortisol on infant emotional reactivity.

METHODS

Participants were 124 mother-infant dyads. DHEA and cortisol were measured from maternal hair at 15 weeks (early gestation) and 35 weeks (late gestation). Observational assessments of positive and negative emotional reactivity were obtained in the laboratory when the infants were 6 months old. Pearson correlations were used to examine the associations between prenatal maternal cortisol, prenatal maternal DHEA, and infant positive and negative emotional reactivity. Moderation analyses were conducted to investigate whether DHEA might modify the association between cortisol and emotional reactivity.

RESULTS

Higher levels of both early and late gestation maternal DHEA were linked to greater infant positive emotional reactivity. Elevated late gestation maternal cortisol was associated with greater negative emotional reactivity. Finally, the association between fetal cortisol exposure and infant emotional reactivity was only observed when DHEA was low.

CONCLUSIONS

These new observations indicate that DHEA is a potential maternal biological signal involved in prenatal programming. It appears to act both independently and jointly with cortisol to determine a child's emotional reactivity. Its role as a primary end-product of the HPA axis, coupled with the newly documented associations with prenatal development shown here, strongly calls for the inclusion of DHEA in future investigations of fetal programming.

Genotypic Sex and Severity of the Disease Determine the Time of Clinical Presentation in Steroid 17α-Hydroxylase/17,20-Lyase Deficiency

CONTEXT

Steroid 17α-hydroxylase/17,20-lyase deficiency (17OHD) is characterized by decreased sex steroids and cortisol, and excessive mineralocorticoid action. The clinical symptoms of hypocortisolemia are subtle.

AIM

The clinical, biochemical, and molecular characteristics of patients with 17OHD were evaluated to determine the factors influencing the time of diagnosis and the management.

PATIENTS AND METHODS

Clinical data, steroid profiles by liquid chromatography-tandem mass spectrometry, and Sanger sequencing of the CYP17A1 gene was evaluated in 12 patients with 17OHD diagnosed between 2004 and 2020.

RESULTS

Median age of diagnosis was 13.9 (range: 0.04-29.5) years. Ten of 12 patients had 46,XY karyotype. Except for one boy with partial 17OHD, all patients had female external genitalia hence raised as females. The clinical presentation of 17OHD was earlier (median age: 7 years) in patients, who presented with severe hypertension, atypical genitalia, or positive family history (n = 6, 50%) than those without (median age: 15.3 years; p = 0.0005). The latter group presented with amenorrhea (n = 6, 50%). Steroid profile of patients uniformly showed a typical pattern of 17OHD regardless of the age at diagnosis. Serum gonadotropin concentrations were elevated in patients >12 years (n = 7), normal in pre-adolescents (n = 4), and low in a patient, who had a digenic inheritance of homozygous CYP17A1 and KISS1R mutations.

CONCLUSIONS

Early clinical presentation and diagnosis in 17OHD are associated with symptomatic hypertension in both 46,XX and 46,XY patients or inadequate virilization of external genitalia in 46,XY partial 17OHD. In the absence of these, the clinical presentation is at late pubertal ages at which time amenorrhea and elevated gonadotropins are the hints for diagnosis.

Diagnosis of female 17α-hydroxylase deficiency after gonadectomy: a case report

Background

17α-Hydroxylase deficiency is a recessively inherited autosomal disease caused by mutations in the CYP17A1 gene. It is a rare disease and accounts for approximately 1% of congenital adrenal cortex hyperplasias. Inhibition of 17α-hydroxylase causes low levels of cortisol and high levels of adrenocorticotropic hormone in the blood as well as excessive levels of mineralocorticoids that lead to hypertension and hypokalemia. Usually, the female patients are diagnosed with abnormality of the genitalia or extra genitalia, primary amenorrhea, or hypertension in puberty. We report a case of a 29-year-old woman who had undergone gonadectomy in her childhood due to complete androgen insensitivity syndrome and was diagnosed with 17α-hydroxylase deficiency in adulthood.

Case presentation

Our patient was a Japanese female diagnosed with androgen insensitivity syndrome, and both gonadectomy and episioplasty were performed at the age of 11 years at the University of Tsukuba Hospital. Thereafter, she was transferred to our hospital at the age of 21 years for vaginoplasty. At the age of 25 years, she presented with hypertension followed by complicated hypokalemia at the age of 28 years. The captopril loading test and adrenocorticotropic hormone loading test of her adrenal steroidogenesis revealed primary aldosteronism. After sufficient genetic counseling, a genetic test was performed that identified her as having CYP17A1 gene mutation.

Conclusions

The differential diagnosis of disorders of sex development can be difficult at a young age without complete expression of the phenotype. However, diagnosis at a later age would change the treatment and prognosis of the disease; therefore, a genetic examination should be considered.

The post-translational regulation of 17,20 lyase activity

A single enzyme, microsomal P450c17, catalyzes the 17α-hydroxylase activity needed to make cortisol and the subsequent 17,20 lyase activity needed to produce the 19-carbon precursors of sex steroids. The biochemical decision concerning whether P450c17 stops after 17α-hydroxylation or proceeds to 17,20 lyase activity is largely dependent on three post-translational factors. First, 17,20 lyase activity is especially sensitive to the molar abundance of the electron-transfer protein P450 oxidoreductase (POR). Second, cytochrome b5 strongly promotes 17,20 lyase activity, principally by acting as an allosteric factor promoting the interaction of P450c17 with POR, although a minor role as an alternative electron-transfer protein has not been wholly excluded. Third, the serine/threonine phosphorylation of P450c17 itself promotes 17,20 lyase activity, again apparently by promoting the interaction of P450c17 with POR. The principal kinase that phosphorylates P450c17 to confer 17,20 lyase activity appears to be p38α (MAPK14), which increases the maximum velocity of the 17,20 lyase reaction, while having no effect on the Michaelis constant for 17,20 lyase or any detectable effect on the 17α-hydroxylase reaction. Other kinases can also phosphorylate P450c17, but only p38α has been shown to affect its enzymology. Understanding the mechanisms regulating 17,20 lyase activity is essential for the understanding of hyperandrogenic disorders such as premature, exaggerated adrenarche and the polycystic ovary syndrome, and also for the design of selective 17,20 lyase inhibitors for use in hyperandrogenic states and in sex-steroid dependent cancers.

New, recurrent, and prevalent mutations: Clinical and molecular characterization of 26 Chinese patients with 17alpha-hydroxylase/17,20-lyase deficiency

BACKGROUND

Combined 17alpha-hydroxylase/17,20-lyase deficiency (17OHD), caused by mutations in the CYP17A1 gene, is a rare autosomal recessive form of congenital adrenal hyperplasia and characterized by hyporeninemic hypokalemic hypertension, primary amenorrhea and absence of secondary sexual characteristics.

SUBJECTS AND METHODS

Twenty six 17OHD subjects from 23 Chinese families were recruited. The CYP17A1 gene was sequenced and 17alpha-hydroxylase/17,20-lyase enzymatic activities were assessed in vitro.

RESULTS

Eight CYP17A1 mutations were identified in 23 patients. Of eight mutations, c.985_987delinsAA/p.Y329Kfs and c.1460_1469del/p.D487_F489del mutations accounted for 60.8% (28/46) and 21.7% (10/46) of the mutant alleles, respectively. The enzymatic activities for both mutations were completely abolished. We also identified three novel mutations c.971_972insG/p.K325Afx, c.1464_1466delT/p.F489Sfx and c.1386G>T/p.R462S. The enzymatic activities for c.971_972insG/p.K325Afx and c.1464_1466delT/p.F489Sfx mutations were almost completely abolished, whereas the mutation c.1386G>T/p.R462S only resulted in partial reduction of 17alpha-hydroxylase (34.6%) and 17,20 lyase activities (27.0%), which is correlated with the partial 17OHD phenotype in this patient.

CONCLUSION

The c.985_987delinsAA/p.Y329Kfs and c.1460_1469del/p.D487_F489del mutations are prevalent in Chinese 17OHD patients. The genetic defects are well correlated with the phenotypes in both complete and partial forms of 17OHD.

A review of the literature on common CYP17A1 mutations in adults with 17-hydroxylase/17,20-lyase deficiency, a case series of such mutations among Koreans and functional characteristics of a novel mutation

OBJECTIVE

17α-hydroxylase/17,20-lyase deficiency is a rare form of congenital adrenal hyperplasia, characterized by hypertension and sexual infantilism and caused by loss-of-function mutations in CYP17A1. This study investigated the clinical and molecular characteristics of six adults with 17α-hydroxylase/17,20-lyase deficiency and the functional consequences of a novel CYP17A1 mutation.

MATERIALS AND METHODS

Six phenotypic females, three with 46,XY and three with 46,XX karyotypes, presented with primary amenorrhea and hypertension. All had elevated levels of plasma adrenocorticotropic hormone, serum gonadotropin, progesterone, and 11-deoxycorticosterone, and reduced testosterone and dehydroepiandrosterone sulfate (DHEA-S). All coding exons and flanking intronic sequences of CYP17A1 were directly sequenced using genomic DNA. Wild-type and mutant CYP17A1 cDNAs were inserted into the pcDNA3.1/V5-His-P450c17 vector, and transiently expressed in COS-7 cells. This was followed by an assessment of 17α-hydroxylase and 17,20-lyase activities by measuring the conversions of progesterone to 17-hydroxyprogesterone and 17-hydroxypregnenolone to DHEA.

RESULTS

The mutation analysis identified one patient with compound heterozygosity for p.H373L and p.W406L, one with compound heterozygosity for p.H373L and p.A174E, three with compound heterozygosity for p.Y329fs and p.H373L, and one with homozygosity for p.H373L. An in vitro functional analysis of the novel p.W406L mutation revealed a complete loss of 17α-hydroxylase/17, 20-lyase activities.

CONCLUSIONS

p.H373L was the most common mutation among these Korean patients, consistent with the high allele frequency of p.H373L in Chinese and Japanese populations, suggesting possible founder effects in Asian countries. The novel p.W406L mutation caused a complete loss of both catalytic activities, indicating that this amino acid is critical for P450c17 function.

Phosphorylation of human cytochrome P450c17 by p38α selectively increases 17,20 lyase activity and androgen biosynthesis

Cytochrome P450c17, a steroidogenic enzyme encoded by the CYP17A1 gene, catalyzes the steroid 17α-hydroxylation needed for glucocorticoid synthesis, which may or may not be followed by 17,20 lyase activity needed for sex steroid synthesis. Whether or not P450c17 catalyzes 17,20 lyase activity is determined by three post-translational mechanisms influencing availability of reducing equivalents donated by P450 oxidoreductase (POR). These are increased amounts of POR, the allosteric action of cytochrome b5 to promote POR-P450c17 interaction, and Ser/Thr phosphorylation of P450c17, which also appears to promote POR-P450c17 interaction. The kinase(s) that phosphorylates P450c17 is unknown. In a series of kinase inhibition experiments, the pyridinyl imidazole drugs SB202190 and SB203580 inhibited 17,20 lyase but not 17α-hydroxylase activity in human adrenocortical HCI-H295A cells, suggesting an action on p38α or p38β. Co-transfection of non-steroidogenic COS-1 cells with P450c17 and p38 expression vectors showed that p38α, but not p38β, conferred 17,20 lyase activity on P450c17. Antiserum to P450c17 co-immunoprecipitated P450c17 and both p38 isoforms; however, knockdown of p38α, but not knockdown of p38β, inhibited 17,20 lyase activity in NCI-H295A cells. Bacterially expressed human P450c17 was phosphorylated by p38α in vitro at a non-canonical site, conferring increased 17,20 lyase activity. This phosphorylation increased the maximum velocity, but not the Michaelis constant, of the 17,20 lyase reaction. p38α phosphorylates P450c17 in a fashion that confers increased 17,20 lyase activity, implying that the production of adrenal androgens (adrenarche) is a regulated event.

Blood pressure and human genetic variation in the general population

PURPOSE OF REVIEW

Hypertension is a complex trait with multiple environmental and genetic contributors. Until recently, linkage studies of rare Mendelian disorders of hypertension and hypotension have produced the most notable progress toward understanding the heritable basis of blood pressure (BP). Association studies to identify common variants have been limited in the past by small sample sizes and most findings have lacked replication.

RECENT FINDINGS

Recently, well powered, targeted candidate gene and genome-wide association studies have reported reproducible associations between rare and common genetic variants and BP and hypertension at the population level.

SUMMARY

Identification of novel genes will lead to an improved understanding of BP regulation and the potential for novel therapies.

Deletion of P399_E401 in NADPH cytochrome P450 oxidoreductase results in partial mixed oxidase deficiency

P450 oxidoreductase (POR) is the electron donor for all microsomal P450s including steroidogenic enzymes CYP17A1, CYP19A1 and CYP21A2. We found a novel POR mutation P399_E401del in two unrelated Turkish patients with 46,XX disorder of sexual development. Recombinant POR proteins were produced in yeast and tested for their ability to support steroid metabolizing P450 activities. In comparison to wild-type POR, the P399_E401del protein was found to decrease catalytic efficiency of 21-hydroxylation of progesterone by 68%, 17α-hydroxylation of progesterone by 76%, 17,20-lyase action on 17OH-pregnenolone by 69%, aromatization of androstenedione by 85% and cytochrome c reduction activity by 80%. Protein structure analysis of the three amino acid deletion P399_E401 revealed reduced stability and flexibility of the mutant. In conclusion, P399_E401del is a novel mutation in POR that provides valuable genotype-phenotype and structure-function correlation for mutations in a different region of POR compared to previous studies. Characterization of P399_E401del provides further insight into specificity of different P450s for interaction with POR as well as nature of metabolic disruptions caused by more pronounced effect on specific P450s like CYP17A1 and aromatase.

Clinical evidence for predominance of delta-5 steroid production in women with polycystic ovary syndrome

CONTEXT

In women with polycystic ovary syndrome (PCOS), the basis for ovarian androgen overproduction involves an overall increase of steroidogenesis, notably in the delta-4 pathway. However, in vitro studies have suggested that excessive androgen production occurs predominantly through the delta-5 pathway.

OBJECTIVE

This study was performed to assess androgen dose-responses after human chorionic gonadotropin (hCG) stimulation in PCOS and normal women.

DESIGN

We conducted a prospective study to compare androgen production after iv hCG in PCOS and normal women.

SETTING

The study was conducted in a General Clinical Research Center in an academic medical center.

PARTICIPANTS

Women with PCOS (age, 18-37 yr; n = 10) and normal ovulatory controls (age, 18-37 yr; n = 11) were recruited.

INTERVENTIONS

For dose-response studies, blood samples were obtained before and at 0.5, 24, and 48 h after iv recombinant hCG (1, 10, 25, 100, and 250 μg). A subset of subjects underwent frequent blood sampling over 24 h after iv injection of 25 μg of recombinant hCG.

MAIN OUTCOME MEASURE(S)

We measured basal and stimulated serum 17-hydroxyprogesterone (17-OHP), androstenedione (A), testosterone (T), dehydroepiandrosterone, estradiol, and progesterone responses after hCG administration.

RESULTS

In PCOS women, maximal A and T production was observed at the lowest doses of hCG, whereas responses were minimal in normal women. Incremental responses of 17-OHP, estradiol, and progesterone were greater in PCOS compared to normal women.

CONCLUSION

In PCOS women, maximal A and T responses to hCG relative to those of 17-OHP are consistent with ovarian androgen overproduction via the delta-5 pathway.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

At the crossroads of steroid hormone biosynthesis: the role, substrate specificity and evolutionary development of CYP17

Cytochrome P450s play critical roles in the metabolism of various bioactive compounds. One of the crucial functions of cytochrome P450s in Chordata is in the biosynthesis of steroid hormones. Steroid 17alpha-hydroxylase/17,20-lyase (CYP17) is localized in endoplasmic reticulum membranes of steroidogenic cells. CYP17 catalyzes the 17alpha-hydroxylation reaction of delta4-C₂₁ steroids (progesterone derivatives) and delta5-C₂₁ steroids (pregnenolone derivatives) as well as the 17,20-lyase reaction producing C₁₉-steroids, a key branch point in steroid hormone biosynthesis. Depending on CYP17 activity, the steroid hormone biosynthesis pathway is directed to either the formation of mineralocorticoids and glucocorticoids or sex hormones. In the present review, the current information on CYP17 is analyzed and discussed.

Molecular modeling on inhibitor complexes and active-site dynamics of cytochrome P450 C17, a target for prostate cancer therapy

A molecular model for the P450 enzyme cytochrome P450 C17 (CYP17) is presented based on sequence alignments of multiple template structures and homology modeling. This enzyme plays a central role in the biosynthesis of testosterone and is emerging as a major target in prostate cancer, with the recently developed inhibitor abiraterone currently in advanced clinical trials. The model is described in detail, together with its validation, by providing structural explanations to available site-directed mutagenesis data. The CYP17 molecule in this model is in the form of a triangular prism, with an edge of approximately 55 A and a thickness of approximately 37 A. It is predominantly helical, comprising 13 alpha helices interspersed by six 3(10) helices and 11 beta-sheets. Multinanosecond molecular dynamics simulations in explicit solvent have been carried out, and principal components analysis has been used to reveal the details of dynamics around the active site. Coarse-grained methods have also been used to verify low-frequency motions, which have been correlated with active-site gating. The work also describes the results of docking synthetic inhibitors, including the drug abiraterone and the natural substrate pregnenolone, in the CYP17 active site together with molecular dynamics simulations on the complexes.

Human cytochrome p450c17: single step purification and phosphorylation of serine 258 by protein kinase a

Cytochrome P450c17 (P450c17) is the single microsomal enzyme that catalyzes steroid 17alpha-hydroxylase and 17,20 lyase activities. The ratio of lyase to hydroxylase activity of human P450c17 determines whether steroidogenesis leads to the synthesis of cortisol or sex steroids. This ratio is regulated posttranslationally by factors that influence the efficiency of electron transfer from P450 oxidoreductase to P450c17. One factor favoring more efficient electron transfer and 17,20 lyase activity is cAMP-dependent serine/threonine phosphorylation of P450c17. Identifying the responsible kinase(s) and the P450c17 residues that undergo phosphorylation has been challenging, partly because of difficulties in preparing biochemically useful amounts of pure, catalytically active P450c17. We describe a modified strategy for preparing P450c17 in which the traditional carboxy-terminal 4xHis tag is replaced by 3xGly6xHis. This construct permits more rotational freedom of the protein when bound to the nickel affinity column, reducing steric associations between the protein and the column, and permitting a single-step chromatographic purification to apparent homogeneity. Using this vector, we explored P450c17 phosphorylation by mutagenesis of Ser and/or Thr residues to Asp or Glu to mimic the approximate size and charge of phospho-Ser or phospho-Thr. This strategy did not identify Ser and/or Thr site(s) that increase the ratio of lyase to hydroxylase activity, suggesting that the regulatory phosphorylation strategy of human P450c17 is very complicated. Although previous work has excluded protein kinase A (PKA) as the responsible kinase, the cAMP-inducible nature of the phosphorylation-associated increase in lyase activity suggests that PKA may play a role, possibly as a priming kinase. Using our novel vector and a series of mutations, we identified the P450c17 site phosphorylated by PKA as Ser258.

A single amino acid residue, Ala 105, confers 16alpha-hydroxylase activity to human cytochrome P450 17alpha-hydroxylase/17,20 lyase

In adrenal steroidogenesis, CYP17 catalyses the 17alpha-hydroxylation of pregnenolone and progesterone and the subsequent 17,20-lyase reaction, yielding adrenal androgens. The enzyme exhibits distinctly different selectivities towards these substrates in various species. CYP17 has also been shown to exhibit 16alpha-hydroxylase activity towards progesterone in some species, with only human and chimp CYP17 catalysing the biosynthesis of substantial amounts of 16-OHprogesterone. The 16alpha-hydroxylase activity was investigated by introducing an Ala105Leu substitution into human CYP17. The converse mutation, Leu105Ala was introduced into the baboon, goat and pig enzymes. Wt human CYP17 converted approximately 30% progesterone to 16-OHprogesterone while the Ala105Leu mutant converted negligible amounts to 16-OHprogesterone ( approximately 9%), comparable to wt CYP17 of the other three species when expressed in COS-1 cells. The ratio of 17-hydroxylated products to 16-OHprogesterone of human CYP17 was 2.7 and that of the mutant human construct 10.5. Similar ratios were observed for human and goat CYP17 with the corresponding Ala or Leu residues. Although the Leu105Ala mutation of both baboon and pig CYP17 exhibited the same trend regarding the ratios, the rate of progesterone conversion was reduced. Coexpression with cytochrome b(5) significantly decreased the ratio of 17-hydroxylated products to 16-OHprogesterone in the Leu105 constructs, while effects were negligible with Ala at this position. Homology models show that Ala105 faces towards the active pocket in the predicted B'-C domain of CYP17. The smaller residue allows more flexibility of movement in the active pocket than Leu, presenting both the C16 and C17 of progesterone to the iron-oxy complex.

Steroid 17alpha-hydroxylase deficiency: functional characterization of four mutations (A174E, V178D, R440C, L465P) in the CYP17A1 gene

CONTEXT

Steroid 17alpha-hydroxylase (CYP17A1, alias P450c17) deficiency (17OHD) is a rare form of congenital adrenal hyperplasia. The CYP17A1 enzyme catalyzes two distinct reactions, 17alpha-hydroxylase and 17,20-lyase activities.

OBJECTIVE

The aim of the study was to analyze the structural and functional consequences of three novel (A174E, V178D, and L465P) and one previously reported (R440C) CYP17A1 mutation found in three patients clinically and biochemically presenting with 17OHD.

PATIENTS AND METHODS

Two patients suffering from 46,XY disordered sex development presented at ages 5.5 and 8.8 yr, respectively, with tall stature and hypertension. Mutation analysis revealed compound heterozygous CYP17A1 mutations (A174E/K388X; V178D/R440C). The third patient (46,XX) presented with primary amenorrhea and hypertension at age 15 yr. She was homozygous for the novel L465P mutation. Functional studies employing a yeast microsomal expression system compared wild-type and mutant CYP17A1 both with regard to 17alpha-hydroxylase and 17,20-lyase activity. Mutants were examined in a computational three-dimensional model of the CYP17A1 protein.

RESULTS

The activity assays showed that all three mutants retain only 0-7% of both 17alpha-hydroxylase and 17,20-lyase activity relative to CYP17A1 wild-type activity, corresponding to the in vivo situation. Enzyme kinetic studies proved the impairment of both reactions, respectively. Computer-based three-dimensional model analysis of CYP17A1 using CYP2B4 as template showed that three of the mutations had no direct effect on the active center, whereas one affects the heme coordination.

CONCLUSION

The functional studies revealed that the described missense mutations result in severe 17OHD. Our data are important to predict the phenotypic expressions and provide important information for patient management and genetic counseling.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Androgen synthesis in adrenarche

The enzymes and pathways of steroidogenesis are central to an understanding of adrenarche. The quantitative regulation of steroidogenesis occurs at the first step, the conversion of cholesterol to pregnenolone. Chronic quantitative regulation is principally at the level of transcription of the CYP11A1 gene encoding P450scc, which is the enzymatically rate-limiting step. Acute regulation is mediated by the steroidogenic acute regulatory protein (StAR), which facilitates the rapid influx of cholesterol into mitochondria, where P450scc resides. Qualitative regulation, which determines the type of steroid produced in a cell, is principally at the level of P450c17 (CYP17). In the absence of P450c17 in the zona glomerulosa, C21 deoxy steroids are produced, leading to the mineralocorticoid, aldosterone. In the presence of the 17alpha-hydroxylase but not the 17,20 lyase activity of P450c17 in the zona fasciculata, C21, 17-hydroxy steroids are produced, leading to the glucocorticoid, cortisol. When both the 17alpha-hydroxylase and 17,20 lyase activities of P450c17 are present in the zona reticularis, the androgen precursor DHEA is produced. The discrimination between 17alpha-hydroxylase and 17,20 lyase activities is regulated by two post-translational events, the serine phosphorylation of P450c17 and the allosteric action of cytochrome b5, both of which act to optimize the interaction of P450c17 with its obligatory electron donor, P450 oxidoreductase. In the adrenal zona reticularis, the abundant expression of P450 oxidoreductase and cytochrome b5, and the low expression of 3beta-hydroxysteroid dehydrogenase (HSD3B2) result in the production of the large amounts of DHEA that characterize adrenarche.

Pathways leading to phosphorylation of p450c17 and to the posttranslational regulation of androgen biosynthesis

Cytochrome P450c17 (P450c17) is the single enzyme that catalyzes steroid 17alpha-hydroxylase and 17,20 lyase activities and hence is the crucial decision-making step that determines the class of steroid made in a steroidogenic cell. Although both activities are catalyzed on a single active site, the ratio of these activities is regulated by posttranslational events. Serine phosphorylation of P450c17 increases 17,20 lyase activity by increasing the enzyme's affinity for its redox partner, P450 oxidoreductase. We searched for the relevant kinase(s) that phosphorylates P450c17 by microarray studies and by testing of kinase inhibitors. Microarrays show that 145 of the 278 known serine/threonine kinases are expressed in human adrenal NCI-H295A cells, only six of which were induced more than 2-fold by treatment with 8-Br-cAMP. Key components of the ERK1/2 and MAPK/ERK kinase (MEK)1/2 pathways, which have been implicated in the insulin resistance of PCOS, were not found in NCI-H295A cells, implying that these pathways do not participate in P450c17 phosphorylation. Treatment with various kinase inhibitors that probe the protein kinase A/phosphatidylinositol 3-kinase/Akt pathway and the calcium/calmodulin/MAPK kinase pathway had no effect on the ratio of 17,20 lyase activity to 17alpha-hydroxylase activity, appearing to eliminate these pathways as candidates leading to the phosphorylation of P450c17. Two inhibitors that target the Rho-associated, coiled-coil containing protein kinase (ROCK)/Rho pathway suppressed 17,20 lyase activity and P450c17 phosphorylation, both in NCI-H295A cells and in COS-1 cells transfected with a P450c17 expression vector. ROCK1 phosphorylated P450c17 in vitro, but that phosphorylation did not affect 17,20 lyase activity. We conclude that members of the ROCK/Rho pathway act upstream from the kinase that phosphorylates P450c17 in a fashion that augments 17,20 lyase activity, possibly acting to catalyze a priming phosphorylation.

Androgen biosynthetic pathways in the human prostate

It is well recognized that there are two androgens, namely testosterone (T) and dihydrotestosterone (DHT); T plays an important role in the testis and muscle, and DHT is crucial for the development, function and pathology of the prostate. It is generally thought that DHT is produced from the 5alpha-reduction of circulating T before being inactivated by 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) that converts DHT into 5alpha-androstane-3alpha,17beta-diol (3alpha-diol). However, the presence of various steroidogenic enzymes in the prostate as well as the availability at high levels of various steroid precursors such as dehydroepiandrosterone sulphate (DHEAS), dehydroepiandrosterone (DHEA) and 4-androstenedione (4-dione) strongly suggest the existence of additional pathways involved in the biosynthesis and metabolism of DHT. Because steroidogenesis could be different in different species, data from the literature obtained from various human, dog, rat and mouse prostate tissues, as well as primary cells and prostatic cancer cell lines, provide a somewhat confusing picture. In the present chapter, we review the data in order to provide a clearer picture of the pathways involved in DHT biosynthesis and metabolism in the human prostate.

Genetics of P450 oxidoreductase: sequence variation in 842 individuals of four ethnicities and activities of 15 missense mutations

P450 oxidoreductase (POR) is an electron-donating flavoprotein required for the activity of all microsomal cytochrome P450 enzymes. We sequenced 5,655 bp of the POR gene in a representative population of 842 healthy unrelated individuals in four ethnic groups: 218 African Americans, 260 Caucasian Americans, 179 Chinese Americans, and 185 Mexican Americans. One hundred forty SNPs were detected, of which 43 were found in >/=1% of alleles. Twelve SNPs were in the POR promoter region. Fifteen of 32 exonic variations altered the POR amino acid sequence; 13 of these 15 are previously undescribed missense variations. We found eight indels, only one of which was in the coding region. A previously described variant, A503V, was found on 27.9% of all alleles with some ethnic predilection (19.1% in African Americans, 26.4% in Caucasian Americans, 36.7% Chinese Americans, and 31.0% in Mexican Americans). We built cDNA expression vectors for the 13 previously undescribed missense variants, expressed each protein lacking 27 N-terminal residues in Escherichia coli, and assayed the apparent K(m) and V(max) of each in four assays: reduction of cytochrome c, oxidation of NADPH, 17alpha-hydroxylase activity of P450c17, and 17,20 lyase activity of P450c17. The catalytic activities of several missense mutants differed substantially in these assays, indicating that each POR mutant must be assayed separately with each potential target P450 enzyme. The activity of A503V was reduced to a modest but statistically significant degree in all four assays, suggesting that it may play an important role in interindividual variation in drug response.

Transcription factor GATA-6 in the human adrenocortex: association with adrenal development and aging

Transcription factor GATA-6 has been demonstrated to be expressed in the human fetal and adult adrenal cortex and has been postulated to play an important role in adrenal steroid biosynthesis. However, the status for GATA-6 expression has not been examined in detail especially in relation to adrenal development and aging. Therefore, in this study, we analyzed GATA-6 expression in 11 human fetal adrenals and 19 adrenal glands after birth using immunohistochemistry. In the fetal adrenals, the status of GATA-6 immunoreactivity in the definitive zone was significantly and directly correlated with ages of development (P<0.05) but in the fetal zone was significantly and inversely correlated with ages of development (P<0.05). After birth, GATA-6 was more abundant in the zona fasciculata compared to other zones (P<0.05) but was not related to aging of the subject. These results suggest that GATA-6 expression is involved in the regulation of corticosteroid production in both the human fetal and adult adrenals, and the changes of intra-adrenal GATA-6 expression in the human fetal adrenal plays important roles in developmental changes of both the definitive and fetal zones.

Genotyping of five chinese patients with 17alpha-hydroxylase deficiency diagnosed through high-performance liquid chromatography serum adrenal profile: identification of two novel CYP17 mutations

CONTEXT

17alpha-Hydroxylase deficiency is a rare form of congenital adrenal hyperplasia caused by CYP17 gene mutations.

OBJECTIVE

Five Chinese patients with 17alpha-hydroxylase deficiency were genotyped.

PATIENTS

The five patients derived from four families living in Shandong Province, China. The diagnosis of 17alpha-hydroxylase deficiency was initially established through HPLC serum adrenal profiles in Qilu Hospital, China, from 1983-1993.

RESULTS

Three CYP17 gene mutations were identified from these patients. Among them, V311fs and Y329fs are two novel frame-shifting mutations. V311fs is an 8-bp nucleotide (TTAAATGG) deletion in exon 5. Y329fs is a deletion-insertion combined mutation (TAC-->AA) at codon 329 in exon 6. Two homozygotes for Y329fs and one compound heterozygote for Y329fs and V311fs were identified from three different families. Two homozygous sisters for the D487_S488_F489 deletion were identified.

CONCLUSION

The results confirmed the diagnostic value of the HPLC serum adrenal profile for 17alpha-hydroxylase deficiency. The D487_S488_F489 deletion had been identified in two previously genotyped Chinese families. In our present study, a third Chinese family with this mutation was identified, suggesting that this mutation is a prevalent CYP17 mutation in the Chinese population. The identification of Y329fs mutation in addition to three previously identified mutations at codon 329 suggests that codon 329 is an unstable point of the CYP17 gene. The mutations identified from our five patients appear to be random, but the recurrence of the Y329fs mutation may be attributed to a founder effect. Our studies suggest that 17alpha-hydroxylase deficiency may not be rare in the Chinese population.

Steroidogenic alterations and adrenal androgen excess in PCOS

BACKGROUND

This cross-sectional study was undertaken to improve our understanding of the steroidogenic alterations leading to adrenal hyperandrogenism in polycystic ovarian syndrome (PCOS).

METHODS

Two-hundred and thirty-four women with clinical and biochemical features suggestive of PCOS underwent metabolic and hormonal evaluation. We used the androstenedione/DHEAS ratio as a surrogate for the level of ovarian 3betaHSD activity. We then selected the 90th percentile for the ratio in those with elevated DHEAS (>9 micromol/l) as the cut-off level beyond which excess DHEAS production will be minimized by excess ovarian 3betaHSD activity. This cut-off level was at a ratio of 1.5 and all PCOS women were then divided into two groups, the higher (>1.5) being the group with excess ovarian 3betaHSD activity. We hypothesized that women with a high ratio would be unlikely to have DHEAS excess due to the rapid conversion of DHEA to androstenedione. Those with a low ratio (concordant ovarian and adrenal steroidogenesis) could then either have high DHEAS or normal DHEAS, depending on whether CYP17 activity was higher or lower respectively.

RESULTS

Insulin resistance was found to be associated with decreased CYP17 activity while irregular cycles and neuroendocrine dysfunction were determined to be associated with higher ovarian 3betaHSD activity.

CONCLUSION

Adrenal androgen excess in PCOS seems to be related to insulin sensitivity as well as decreased activity of 3betaHSD, the latter being preferentially present in those women with regular cycles or without neuroendocrine dysfunction.

Seventeen alpha-hydroxylase deficiency

Seventeen alpha-hydroxylase deficiency (17OHD) is a rare form of congenital adrenal hyperplasia in which defects in the biosynthesis of cortisol and sex steroid result in mineralocorticoid excess, hypokalemic hypertension and sexual abnormalities such as pseudohermaphroditism in males, and sexual infantilism in females. The disease is inherited in an autosomal recessive pattern, and is caused by mutations in the gene encoding cytochrome P450c17 (CYP17), which is the single polypeptide that mediates both 17alpha-hydroxylase and 17,20-lyase activities. We report the case of a 15-year-old patient with 17OHD who had a female phenotype but male karyotype (46,XY). The diagnosis was made based on classical clinical features, biochemical data and molecular genetic study. Two mutations were identified by polymerase chain reaction amplification and sequencing, including a S106P point mutation in exon 2 and a 9-bp (GACTCTTTC) deletion from nucleotide position 1519 in exon 8 of CYP17. The first of these mutations was found in the father and the second in the mother, and both have been previously reported in Asia. The patient's hypertension and hypokalemia resolved after glucocorticoid replacement and treatment with potassium-sparing diuretics. Sex hormone replacement was prescribed for induction of sexual development and reduction of the final height. Prophylactic gonadectomy was scheduled. In summary, 17OHD should be suspected in patients with hypokalemic hypertension and lack of secondary sexual development so that appropriate therapy can be implemented.

Diversity and function of mutations in p450 oxidoreductase in patients with Antley-Bixler syndrome and disordered steroidogenesis

P450 oxidoreductase (POR) is the obligatory flavoprotein intermediate that transfers electrons from reduced nicotinamide adenine dinucleotide phosphate (NADPH) to all microsomal cytochrome P450 enzymes. Although mouse Por gene ablation causes embryonic lethality, POR missense mutations cause disordered steroidogenesis, ambiguous genitalia, and Antley-Bixler syndrome (ABS), which has also been attributed to fibroblast growth factor receptor 2 (FGFR2) mutations. We sequenced the POR gene and FGFR2 exons 8 and 10 in 32 individuals with ABS and/or hormonal findings that suggested POR deficiency. POR and FGFR2 mutations segregated completely. Fifteen patients carried POR mutations on both alleles, 4 carried mutations on only one allele, 10 carried FGFR2 or FGFR3 mutations, and 3 patients carried no mutations. The 34 affected POR alleles included 10 with A287P (all from whites) and 7 with R457H (four Japanese, one African, two whites); 17 of the 34 alleles carried 16 "private" mutations, including 9 missense and 7 frameshift mutations. These 11 missense mutations, plus 10 others found in databases or reported elsewhere, were recreated by site-directed mutagenesis and were assessed by four assays: reduction of cytochrome c, oxidation of NADPH, support of 17alpha-hydroxylase activity, and support of 17,20 lyase using human P450c17. Assays that were based on cytochrome c, which is not a physiologic substrate for POR, correlated poorly with clinical phenotype, but assays that were based on POR's support of catalysis by P450c17--the enzyme most closely associated with the hormonal phenotype--provided an excellent genotype/phenotype correlation. Our large survey of patients with ABS shows that individuals with an ABS-like phenotype and normal steroidogenesis have FGFR mutations, whereas those with ambiguous genitalia and disordered steroidogenesis should be recognized as having a distinct new disease: POR deficiency.

Regulation of cytochrome b5 gene transcription by Sp3, GATA-6, and steroidogenic factor 1 in human adrenal NCI-H295A cells

Sex steroid synthesis requires the 17,20 lyase activity of P450c17, which is enhanced by cytochrome b5, acting as an allosteric factor to promote association of P450c17 with its electron donor, P450 oxidoreductase. Cytochrome b5 is preferentially expressed in the fetal adrenal and postadrenarchal adrenal zona reticularis; the basis of this tissue-specific, developmentally regulated transcription of the b5 gene is unknown. We found b5 expression in all cell lines tested, including human adrenal NCI-H295A cells, where its mRNA is reduced by cAMP and phorbol ester. Multiple sites, between -83 and -122 bp upstream from the first ATG, initiate transcription. Deletional mutagenesis localized all detectable promoter activity within -327/+15, and deoxyribonuclease I footprinting identified protein binding at -72/-107 and -157/-197. DNA segments -65/-40, -114/-70 and -270/-245 fused to TK32/Luc yielded significant activity, and mutations in their Sp sites abolished that activity; electrophoretic mobility shift assay (EMSA) showed that Sp3, but not Sp1, binds to these Sp sites. Nuclear factor 1 (NF-1) and GATA-6, but not GATA-4 bind to the NF-1 and GATA sites in -157/-197. In Drosophila S2 cells, Sp3 increased -327/Luc activity 58-fold, but Sp1 and NF-1 isoforms were inactive. Mutating the three Sp sites ablated activity without or with cotransfection of Sp1/Sp3. In NCI-H295A cells, mutating the three Sp sites reduced activity to 39%; mutating the Sp, GATA, and NF-1 sites abolished activity. In JEG-3 cells, GATA-4 was inactive, GATA-6 augmented -327/Luc activity to 231% over the control, and steroidogenic factor 1 augmented activity to 655% over the control; these activities required the Sp and NF-1 sites. Transcription of cytochrome b5 shares many features with the regulation of P450c17, whose activity it enhances.

17alpha-hydroxylase/17,20-Lyase deficiency due to novel compound heterozygote mutations: treatment for tall stature in a female with male pseudohermaphroditism and spontaneous puberty in her affected sister

We report on two German sisters with deficiency in the 17alpha-hydroxylase/17,20-lyase enzyme corresponding to typical hormone profile. A paternal nonsense mutation R388X in exon 7 and a maternal missense mutation P428L in exon 8 of the CYP17 gene have been identified in both girls. Residual in vitro 17alpha-hydroxylase activity for the conversion of [3H]-Preg to [3H]-17OH-Preg has been detected in transfected 293-cells expressing P428L mutant enzyme; however, no 17,20-lyase activity was observed converting [3H]-17OH-Preg into [3H]-DHEA. The 46,XX-sister spontaneously entered puberty. The 46,XY-sister with a predicted adult height of 203 cm was treated with a high dose of conjugated estrogens and resulted with a final height of 186.9 cm. The present data suggest that compound heterozygous 46,XX females bearing a P428L allele may develop spontaneous onset of puberty. Furthermore, in 46,XY females with tall stature, treatment with conjugated estrogens may lead to a significant reduction of their predicted adult height.

Regulation of 17,20 lyase activity by cytochrome b5 and by serine phosphorylation of P450c17

Cytochrome P450c17 catalyzes the 17alpha-hydroxylase activity required for glucocorticoid synthesis and the 17,20 lyase activity required for sex steroid synthesis. Most P450 enzymes have fixed ratios of their various activities, but the ratio of these two activities of P450c17 is regulated post-translationally. We have shown that serine phosphorylation of P450c17 and the allosteric action of cytochrome b5 increase 17,20 lyase activity, but it has not been apparent whether these two post-translational mechanisms interact. Using purified enzyme systems, we now show that the actions of cytochrome b5 are independent of the state of P450c17 phosphorylation. Suppressing cytochrome b5 expression in human adrenal NCI-H295A cells by >85% with RNA interference had no effect on 17alpha-hydroxylase activity but reduced 17,20 lyase activity by 30%. Increasing P450c17 phosphorylation could compensate for this reduced activity. When expressed in bacteria, human P450c17 required either cytochrome b5 or phosphorylation for 17,20 lyase activity. The combination of cytochrome b5 and phosphorylation was not additive. Cytochrome b5 and phosphorylation enhance 17,20 lyase activity independently of each other, probably by increasing the interaction between P450c17 and NADPH-cytochrome P450 oxidoreductase.

Disorders of androgen synthesis--from cholesterol to dehydroepiandrosterone

Androgens and estrogens are primarily made from dehydroepiandrosterone (DHEA), which is made from cholesterol via four steps. First, cholesterol enters the mitochondria with the assistance of the steroidogenic acute regulatory protein (StAR). Mutations in the StAR gene cause congenital lipoid adrenal hyperplasia (lipoid CAH), a potentially lethal disease in which virtually no steroids are made. Lipoid CAH is common among Palestinian Arabs and people from eastern Arabia, and among Korean and Japanese people. Second, within the mitochondria, cholesterol is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc; disorder of this enzyme is very rare, probably due to embryonic lethality. Third, pregnenolone undergoes 17alpha-hydroxylation by microsomal P450c17. 17alpha-Hydroxylase deficiency, manifesting as female sexual infantilism and hypertension, is rare except in Brazil. Finally, 17-OH pregnenolone is converted to DHEA by the 17,20 lyase activity of P450c17. The ratio of the 17,20 lyase to 17alpha-hydroxylase activity of P450c17 determines the ratio of C21 to C19 steroids produced. This ratio is regulated posttranslationally by at least three factors: the abundance of the electron-donating protein P450 oxidoreductase (POR), the presence of cytochrome b5 and the serine phosphorylation of P450c17. Mutations of POR are a new, recently described disorder manifesting as the Antley-Bixler skeletal dysplasia syndrome, and a form of polycystic ovary syndrome.

Functional characterization of mutant CYP17 genes isolated from a 17 alpha-hydroxylase/17,20-lyase-deficient patient

CYP17 has a dual enzymatic activity that is necessary for steroid hormone biosynthesis. It catalyzes the 17 alpha-hydroxylation of progesterone or pregnenolone and also removes an acetyl moiety of hydroxy-progesterone or hydroxypregnenolone by its 17,20-lyase activity to produce androstenedione or dehydroepiandrosterone (DHEA), respectively. We previously isolated a compound heterozygous mutant of CYP17 from a Korean female patient: 1-base deletion and 1-base transversion mutation at 1 allele and 3-base deletion mutation at the other allele. Here we tested the functional activities of these 2 mutant CYP17 alleles using a transfection analysis in COS-1 cells with radiolabeled substrates and thin layer chromatography. Both mutant CYP17 genes lost not only 17 alpha-hydroxylation activity, but also 17,20-lyase activity in this assay system. This nonfunctional nature of 2 mutant CYP17 genes explains the clinical manifestation of a patient who had 17 alpha-hydroxylase deficiency.

P450 oxidoreductase deficiency: a new disorder of steroidogenesis affecting all microsomal P450 enzymes

Combined partial deficiency of 17alpha-hydroxylase and 21-hydroxylase activities was first described in 1985; however the genes for P450c17 and P450c21 in these patients lack mutations. In 1986 we postulated that this disorder might be due to mutations in P450 oxidoreductase (POR), the flavoprotein that donates electron to these and all other microsomal P450 enzymes, but this hypothesis was not tested until the POR gene sequence became available through the genome database. We found five POR missense mutations in our first four patients. In vitro assays of the activities of these mutations showed that the standard assay of POR activity, reduction of cytochrome c, correlated poorly with the patients' phenotypes, but that assays of POR-supported 17alpha-hydroxylase and 17,20 lyase activities correlated well. POR deficiency is a new disorder of adrenal and gonadal steroidogenesis that affects all microsomal cytochrome P450 enzymes, hence may have important implications for genetic differences in drug metabolism.

Colocalization of P450c17 and cytochrome b5 in androgen-synthesizing tissues of the human

Androgens are an integral part of human physiology. The de novo production of androgens is generally limited to the adrenal cortex and the gonads. Androgen synthesis by these steroidogenic tissues requires the bifunctional enzyme cytochrome P450c17, which catalyzes both 17 hydroxylase and 17,20 lyase activities. 17,20-lyase activity is relevant to the regulation of androgen production, and is allosterically modulated through the action of an accessory protein, cytochrome b5 (CytB5). Our objective was to determine the cellular localization of P450c17 and CytB5 in androgen-synthesizing tissues of the human. Immunohistochemical analyses of P450c17 and CytB5 were performed on fetal and adult human adrenals, ovaries, and testes. In the fetal adrenal, CytB5 and P450c17 were both found in the cells of the fetal zone, but not in the neocortex. In the adult adrenal, the zona fasciculata was immunoreactive for P450c17 only, whereas the zona reticularis was immunopositive for both P450c17 and CytB5. In the adult gonads, P450c17 and CytB5 were colocalized in the Leydig cells of the testis, theca interna cells of the follicle, theca lutein cells, and isolated cell clusters in the ovarian stroma. Whereas P450c17 and CytB5 were colocalized in the Leydig cells of the fetal testes, there was no immunostaining for either in the midgestational fetal ovary. Our findings of colocalization of CytB5 and P450c17 are strongly supportive of the view that CytB5 plays an important role in the regulation of the androgen biosynthetic pathway in the fetal and adult human.

Analysis of neurological disease in four dimensions: insight from ALS-PDC epidemiology and animal models

The causal factor(s) responsible for sporadic neurological diseases are unknown and the stages of disease progression remain undefined and poorly understood. We have developed an animal model of amyotrophic lateral sclerosis-parkinsonism dementia complex which mimics all the essential features of the disease with the initial neurological insult arising from neurotoxins contained in washed cycad seeds. Animals fed washed cycad develop deficits in motor, cognitive, and sensory behaviors that correlate with the loss of neurons in specific regions of the central nervous system. The ability to recreate the disease by exposure to cycad allows us to extend the model in multiple dimensions by analyzing behavioral, cellular, and biochemical changes over time. In addition, the ability to induce toxin-based neurodegeneration allows us to probe the interactions between genetic and epigenetic factors. Our results show that the impact of both genetic causal and susceptibility factors with the cycad neurotoxins are complex. The article describes the features of the model and suggests ways that our understanding of cycad-induced neurodegeneration can be used to decipher and identify the early events in various human neurological diseases.

P450c17 deficiency in Brazilian patients: biochemical diagnosis through progesterone levels confirmed by CYP17 genotyping

P450c17 deficiency is an autosomal recessive disorder and a rare cause of congenital adrenal hyperplasia characterized by hypertension, hypokalemia, and impaired production of sex hormones. We performed a clinical, hormonal, and molecular study of 11 patients from 6 Brazilian families with the combined 17alpha-hydroxylase/17,20-lyase deficiency phenotype. All patients had elevated basal serum levels of progesterone (1.8-38 ng/ml; 0.57-12 pmol/liter) and suppressed plasma renin activity. CYP17 genotyping identified 5 missense mutations. The compound heterozygous mutation R362C/W406R was found in 1 family, whereas the homozygous mutations R96W, Y329D, and P428L were seen in the other 5 families. The R96W mutation has been described as the cause of p450c17 deficiency in Caucasian patients. The other mutations were not found in 50 normal subjects screened by allele-specific oligonucleotide hybridization (Y329D, R362C, and W406R) or digestion with HphI (P428L) and were recently found in other Brazilian patients. Therefore, we elucidated the genotype of 11 individuals with p450c17 deficiency and concluded that basal progesterone measurement is a useful marker of p450c17 deficiency and that its use should reduce the misdiagnosis of this deficiency in patients presenting with male pseudohermaphroditism, primary or secondary amenorrhea, and mineralocorticoid excess syndrome.

A novel compound heterozygous mutation in the CYP17 (P450 17alpha-hydroxylase) gene leading to 17alpha-hydroxylase/17,20-lyase deficiency

Mutations in the CYP17 gene impair steroid biosynthesis in the adrenals and gonads and often cause 17alpha-hydroxylase/17,20-lyase deficiency, leading to amenorrhea, sexual infantilism, and hypokalemic low aldosterone hypertension. Several CYP17 mutations resulting in 17alpha-hydroxylase/17,20-lyase deficiency have been reported previously. In the present study, we found a novel CYP17 mutation from the molecular analysis of a Korean patient with primary amenorrhea with a 46,XX karyotype, and hypokalemic hypertension. We sequenced all 8 exons of the CYP17 gene that were amplified from patient's genomic DNA using polymerase chain reaction (PCR) and found a compound heterozygous mutation in the CYP17 structural gene; a 1-base deletion and a 1-base transversion (TAC-->AA) at codon 329, leading to the production of a truncated protein (1-417 amino acids), and a 3-base deletion (TCC, either 350-351 or 351-352 codon) in the other allele. Restriction enzyme digestion analysis of patient's and parental DNA showed that the 1-base deletion and the 3-base deletion are inherited from mother and father, respectively. Here we conclude that these novel compound heterozygous mutations might account for the patient's clinical manifestations of 17alpha-hydroxylase/17,20-lyase deficiency.

Xenopus laevis ovarian CYP17 is a highly potent enzyme expressed exclusively in oocytes. Evidence that oocytes play a critical role in Xenopus ovarian androgen production

Progesterone has long been considered the primary mediator of Xenopus oocyte maturation. We have recently shown, however, that androgens, which are equal or more potent promoters of maturation and are present at higher levels in ovulating frogs, may also be playing an important physiologic role in mediating maturation. Here, we examined the role of CYP17, a key enzyme mediating sex steroid synthesis, in Xenopus ovarian androgen production. We found that the 17,20-lyase activities of Xenopus CYP17 exceeded the 17alpha-hydroxylase activities in both the Delta4 and Delta5 pathways; thus, Xenopus CYP17 rapidly converted pregnenolone and progesterone to dehydroepiandrosterone (DHEA) and androstenedione, respectively. This remarkably robust activity exceeds that of CYP17 from most higher vertebrates, and likely explains why virtually no progesterone is detected in ovulating frogs. Additionally, ovarian CYP17 activity was present exclusively in oocytes, although all other enzymes involved in sex steroid production were expressed almost entirely in surrounding follicular cells. This compartmentalization suggests a "two-cell" model whereby Xenopus ovarian androgen production requires both follicular cells and oocytes themselves. The requirement of oocytes for ovarian androgen production further introduces the unusual paradigm whereby germ cells may be responsible for producing important steroids used to mediate their own maturation.

Molecular dynamics of substrate complexes with hamster cytochrome P450c17 (CYP17): mechanistic approach to understanding substrate binding and activities

The cytochrome P450c17 isoforms from various animal species have different substrate selectivity, especially for 17,20-lyase activity. In particular, the human P450c17 selectively produces dehydroepiandrosterone with little androstenedione (AD). Hamster P450c17, on the other hand, produces both of these steroids at comparable rates. We thus investigated if computational analysis could explain the difference in activity profiles. Therefore, we inserted the four P450c17 substrates-pregnenolone, progesterone, and their 17alpha-hydroxylated forms-inside our hamster P450c17 model, which we derived from our human P450c17 model based on the crystal structure of P450BMP. We performed molecular dynamics (MD) simulations on the complexes and analyzed the resultant trajectories to identify amino acids that interact with substrates. Starting with substrates in two different orientations, we obtained two sets of binding trajectories in each case. The first set of trajectories reveal structural rearrangements that occur during binding, whereas the second set of trajectories reflects substrate orientations during catalysis. Our modeling suggests that three distinct steps are required for substrate selectivity and binding to the hamster P450c17: (1) recognition of the substrate at the putative substrate entrance, characterized by a pocket at the surface of the hamster P450c17 containing charged residues R96 and D116; (2) entry of the substrate into the active site, in an intermediate position directed by possible hydrogen bonding of the substrates with the heme D-ring propionate group, R96, R440, and T306; followed by (3) 90 degrees counterclockwise rotation of the substrates, positioning them in optimal position for reactivity, a process that may be directed by hydrogen bonding to the 110-112 region of the hamster P450c17. With some substrates, we obtained trajectories which suggest that major distortions in the I-helix and opening of the H-I loop occur during substrate binding. In conclusion, these modeling exercises provide insight to possible structural reorganizations that occur during substrate binding and suggest that amino acids that participate in three distinct steps of this process may all contribute to substrate binding and activity.

Protein phosphatase 2A and phosphoprotein SET regulate androgen production by P450c17

Cytochrome P450c17 catalyzes 17 alpha-hydroxylation needed for cortisol synthesis and 17,20 lyase activity needed to produce sex steroids. Serine phosphorylation of P450c17 specifically increases 17,20 lyase activity, but the physiological factors regulating this effect remain unknown. Treating human adrenal NCI-H295A cells with the phosphatase inhibitors okadaic acid, fostriecin, and cantharidin increased 17,20 lyase activity, suggesting involvement of protein phosphatase 2A (PP2A) or 4 (PP4). PP2A but not PP4 inhibited 17,20 lyase activity in microsomes from cultured cells, but neither affected 17 alpha-hydroxylation. Inhibition of 17,20 lyase activity by PP2A was concentration-dependent, could be inhibited by okadaic acid, and was restored by endogenous protein kinases. PP2A but not PP4 coimmunoprecipitated with P450c17, and suppression of PP2A by small interfering RNA increased 17,20 lyase activity. Phosphoprotein SET found in adrenals inhibited PP2A, but not PP4, and fostered 17,20 lyase activity. The identification of PP2A and SET as post-translational regulators of androgen biosynthesis suggests potential additional mechanisms contributing to adrenarche and hyperandrogenic disorders such as polycystic ovary syndrome.

Androgen biosynthesis from cholesterol to DHEA

Androgens and estrogens are made from dehydroepiandrosterone (DHEA), which is made from cholesterol via four steps. First, cholesterol enters the mitochondria with the assistance of the steroidogenic acute regulatory protein (StAR). Mutations in the StAR gene cause congenital lipoid adrenal hyperplasia. Second, within the mitochondria, cholesterol is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc. Third, pregnenolone undergoes 17alpha-hydroxylation by microsomal P450c17. Finally, 17-OH pregnenolone is converted to DHEA by the 17,20 lyase activity of P450c17. The ratio of the 17,20 lyase to 17alpha-hydroxylase activity of P450c17 determines the ratio of C21 to C19 steroids produced. This ratio is regulated post-translationally by at least three factors: the abundance of the electron-donating protein P450 oxidoreductase, the presence of cytochrome b(5), and the serine phosphorylation of P450c17. Study of these and related factors may yield important information about the pathophysiology of adrenarche and the polycystic ovary syndrome (PCOS).

Molecular evolution of adrenarche: structural and functional analysis of p450c17 from four primate species

Adrenarche is the prepubertal onset of increased adrenal secretion of 19-carbon steroids, especially dehydroepiandrosterone (DHEA). However, while human beings and chimpanzees exhibit adrenarche, other primates such as the baboon and rhesus monkey do not, and the adrenals of most other mammals produce little or no DHEA. Thus, the acquisition of adrenarche is a very recent evolutionary event. DHEA is produced from pregnenolone by the successive 17alpha-hydroxylase and 17,20 lyase activities of a single enzyme, P450c17. To ascertain whether sequence differences in P450c17 contribute to adrenarche, we cloned the rhesus monkey cDNA from adrenal tissue and cloned the chimpanzee and baboon cDNAs from genomic DNA using an exon-trapping strategy. Using microsomes from yeast transformed with rhesus, baboon, chimp, or human P450c17, we measured the Michaelis constant and maximum velocity for the 17alpha-hydroxylase and 17,20 lyase activities. The human and chimp enzymes differ at only two amino acids and baboon and rhesus P450c17 only at a single residue; the human/chimp enzyme differed from the baboon/rhesus enzyme by 25-27 residues (95% identity). Surprisingly, the greatest difference in enzymatic activities was a marked increase in 17alpha-hydroxylase activity of P450c17 in the baboon, which differs from rhesus only at residue 255 [arginine (Arg) in baboon, histine (His) in rhesus]. Residue 255 is also Arg in human and chimp. Wild-type human P450c17 and its Arg255His mutant had similar 17alpha-hydroxylase activities, but the Arg255Ala mutant had decreased 17alpha-hydroxylase activity. These data establish that Arg255 is important for 17alpha-hydroxylase activity and show that the evolution of adrenarche in higher primates is not determined by variations in the sequence of P450c17.

Genetic analysis of the cytochrome P-450c17alpha (CYP17) and aldosterone synthase (CYP11B2) in Japanese patients with 17alpha-hydroxylase deficiency

OBJECTIVE

To determine the clinical and molecular genetic characterization of two Japanese patients with 17alpha-hydroxylase deficiency, we analysed the 17alpha-hydroxylase/17,20-lyase gene (CYP17). Next, to clarify the mechanism of hypoaldosteronism in 17alpha-hydroxylase deficiency, we analysed the expression of aldosterone synthase (CYP11B2) messenger RNA and sequenced CYP11B2 in these patients.

PATIENTS

Patient 1 (46 XY), phenotypically female, sought medical attention for hypertension, amenorrhea and infantile genitalia. Patient 2 (46 XX), phenotypically female, presented for hypertension and amenorrhea. Hormonal data in both patients showed decreased levels of sex steroids, cortisol, aldosterone and plasma renin activity and extreme elevation of deoxycortisol.

DESIGN

Direct sequencing of CYP17 and CYP11B2 was performed using genomic DNA from the patients. An expression studies of mutated forms of CYP17 was performed using COS-1 cells. The expression of CYP11B2 messenger RNA in mononuclear leucocytes (MNLs) of these patients and normal subjects was measured using the competitive polymerase chain reaction

METHOD

The effect of renin secretion stimulation on the levels of CYP11B2 messenger RNA in MNLs of normal subjects was also studied.

RESULTS

We detected two novel genetic defects in 17alpha-hydroxylase. Sequence analysis revealed one base pair deletion (T) at codon 243 in exon 4 in patient 1. CYP17 in patient 2 contained a point mutation (C to T) at position 415 in exon 8. Transfected cells of mutant from patient 1 had no 17alpha-hydroxylase or 17,20-lyase activity. The R415C mutant protein showed very weak activity of 17alpha-hydroxylase or 17,20-lyase activity. In the renin secretion stimulating test, the increase in CYP11B2 messenger RNA levels in MNLs was parallel with that of plasma aldosterone concentration. The expression of CYP11B2 mRNA in NMLs of these patients was lower compared to controls. No mutations in CYP11B2, including the 5' flanking region, were found.

CONCLUSIONS

These results indicate that the novel mutations of the CYP17 gene found in these patients inactivate cytochrome P450c17 function, and that hypoaldosteronism in these patients may be partly explained by a decreased activity of aldosterone synthase, which is regulated at the transcriptional level.

Thiazolidinediones but not metformin directly inhibit the steroidogenic enzymes P450c17 and 3beta -hydroxysteroid dehydrogenase

Androgen biosynthesis requires 3beta-hydroxysteroid dehydrogenase type II (3betaHSDII) and the 17alpha-hydroxylase and 17,20-lyase activities of cytochrome P450c17. Thiazolidinedione and biguanide drugs, which are used to increase insulin sensitivity in type 2 diabetes, lower serum androgen concentrations in women with polycystic ovary syndrome. However, it is unclear whether this is secondary to increased insulin sensitivity or to direct effects on steroidogenesis. To investigate potential actions of these drugs on P450c17 and 3betaHSDII, we used "humanized yeast" that express these steroidogenic enzymes in microsomal environments. The biguanide metformin had no effect on either enzyme, whereas the thiazolidinedione troglitazone inhibited 3betaHSDII (K(I) = 25.4 +/- 5.1 microm) and both activities of P450c17 (K(I) for 17alpha-hydroxylase, 8.4 +/- 0.6 microm; K(I) for 17,20-lyase, 5.3 +/- 0.7 microm). The action of troglitazone on P450c17 was competitive, but it was mainly a noncompetitive inhibitor of 3betaHSDII. The thiazolidinediones rosiglitazone and pioglitazone exerted direct but weaker inhibitory effects on both P450c17 and 3betaHSDII. These differential effects of the thiazolidinediones do not correlate with their effects on insulin sensitivity, suggesting that distinct regions of the thiazolidinedione molecule mediate these two actions. Thus, thiazolidinediones inhibit two key enzymes in human androgen synthesis contributing to their androgen-lowering effects, whereas metformin affects androgen synthesis indirectly, probably by lowering circulating insulin concentrations.

A-6G variant of the angiotensinogen gene and essential hypertension in Han, Tibetan, and Yi populations

To investigate the relationship between the A-6G variant in the promoter of the angiotensinogen gene and essential hypertension in Han, Tibetan, and Yi populations. All patients with essential hypertension were selected by WHO criteria. And the polymorphism of the A-6G variant was determined by PCR/RFLP. The data were analyzed by t test and chi2 test. There was no significant difference in the genotype or allele frequencies between normotensives and hypertensives in the Han, Tibetan, and Yi populations, respectively. However, when the subjects were divided into male and female subgroups, the genotype distributions among hypertensives and normotensives of the Tibetan female group were as follows: AA, 37% vs. 48%; AG, 52% vs. 48%; GG, 11% vs. 4%, respectively and the frequency of the G allele was significantly higher in hypertensives than in normotensives in the Tibetan female group (0.37 vs. 0.28, chi2=4.25, p<0.05). In addition, we observed that there was a significant difference between the Han and Tibetan normotensive groups in the distributions of the allele and genotype frequencies of the A-6G variant. The frequency of the G allele was 0.29 and 0.17 in the Tibetan normotensive and Han groups, respectively (p<0.001). The G allele of the A-6G variant was associated with hypertension in the Tibetan females, but not in the Yi or Han females. And we confirmed that there was a significant difference in the prevalence of the allele frequencies of the A-6G variant between the Han and Tibetan normotensive groups.

The genetics, pathophysiology, and management of human deficiencies of P450c17

P450c17 commands a central role in human steroidogenesis as the qualitative regulator of steroid hormone flux. Consequently, the study of P450c17 deficiencies in human beings serves to illustrate many aspects of the physiology of steroid biosynthesis and to demonstrate salient features of the genetics and biochemistry of P450c17 itself. Furthermore, classic 17-hydroxylase deficiency was first described in patients with sexual infantilism and hypertension, but it is now recognized that partial and selective forms of P450c17 deficiencies also exist. These patients demonstrate a range of phenotypes, illustrating the multiple roles of P450c17 in human biology. This article reviews the genetics and biochemistry of P450c17 as a prelude for understanding the pathophysiology of these diseases and approaches to their diagnosis and management.

Probing structural and functional domains of human P450c17

Human P450c17 performs at least six chemical transformations, but this spectrum of activity is differentially regulated by structural changes and by redox partner proteins. Furthermore, P450c17 isoforms from different species with approximately 90% amino acid identity exhibit markedly different relative rates for these transformations. Although this phenomenology has been recognized for nearly 20 years, the underlying chemistry and structural basis for these effects are poorly understood. We have constructed a structural model of human P450c17 using computational chemistry to understand informative, naturally occurring human mutations and to provide a rational basis for designing alterations in P450c17 that probe functional domains of the protein. We have mapped with considerable confidence key residues involved in the interaction with redox partner proteins, including K89, R347, and R358, which form positive charges on the "proximal" surface of P450c17. Neutralization of these charges selectively impairs 17, 20-lyase activity without large reductions in 17alpha-hydroxylase activity or 17alpha-hydroxypregnenolone binding. We are now directing our efforts to the identification of key residues in the active site that mediate the substrate specificity and catalytic selectivity of human P450c17.

Conversion of pregnenolone to DHEA by human 17alpha-hydroxylase/17, 20-lyase (P450c17). Evidence that DHEA is produced from the released intermediate, 17alpha-hydroxypregnenolone

Most previous studies using reconstituted systems and fast kinetics suggest that the conversion of pregnenolone to dehydroepiandrosterone (DHEA; the precursor of androgen and estrogen biosynthesis) by P450c17 does not require the release of the intermediate 17alpha-OHPreg (a precursor of cortisol biosynthesis). With such a mechanism, it is difficult to conceive how high amounts of DHEA may be produced in some cells or tissues, such as the testis and cells from the adrenal reticularis, while in other tissues such as the fasciculata zone, high levels of 17alpha-OHPreg are synthesized. In this report, we address this matter using intact transfected cells, which better reflect the actual cellular conditions. Furthermore, by using transfected cells, we can conveniently analyze human enzymes, as we are not restricted by the availability of human tissues as in the case of methods using purified or partially purified enzymes. Using intact HEK-293 cells transfected with human P450c17 in culture, we showed, in a time course study of the transformation of pregnenolone, that there is an accumulation of 17alpha-OHPreg, and that, subsequently, the accumulated 17alpha-OHPreg decreases with a concomitant increase in DHEA production. The DHEA/17alpha-OHPreg ratio changes from 0.1 :1 after 1 h incubation to 50 : 1 after 20 h. This result strongly suggests that the transformation of Preg to DHEA proceeds through two steps in which DHEA is produced from the released intermediate 17alpha-OHPreg. We also show that high levels of substrate vs. enzyme concentration will lead to high hydroxylase activity whereas the reverse will increase the lyase activity. The result is in good agreement with recent observations suggesting that surrounding enzymes and steroids could modulate the lyase activity. Cotransfection of vectors expressing cytochrome b5 and NADPH cytochrome P450 reductase indicates that both are required for an optimum production of DHEA.

Compound heterozygous mutations (PHE53/54DEL and HIS373LEU) of the P450c17 gene result in a 17alpha-hydroxylase/17,20-lyase deficient male pseudohermaphrodite with unambiguous external genitalia

The autosomal recessive disease 17alpha-hydroxylase/17,20-lyase deficiency is characterized by mutation of the P450c17 enzyme, which catalyzes 17alpha-hydroxylation and 17,20-lysis in the steroidogenic pathways. Although 17 mutations of this enzyme have been reported, only a few of them resulted in a completely unambiguous phenotype of female external genitalia in 46, XY individuals. We report here a Japanese patient with a 46,XY karyotype, who showed such a unambiguous female external genitalia. Nucleotide sequencing of the P450c17 gene revealed the patient to be a compound heterozygote carrying two different mutations (PHE53/54DEL in exon 1 and HIS373LEU in exon 6). As these mutations have been previously detected in unrelated Japanese patients, it is confirmed that these mutations accumulate regionally. Since these mutations could be screened by a multiple genotyping method, the method is applicable when 17alpha-hydroxylase/17, 20-lyase deficiency is suspected in Japanese patients.