Tissue-specific expression of human P-450AROM. The promoter responsible for expression in adipose tissue is different from that utilized in placenta

Maternal recognition of pregnancy in the pig: A servomechanism involving sex steroids, cytokines and prostaglandins

Maternal recognition of pregnancy (MRP) is a term utilized in mammals to describe pathways in which the conceptus alters the endometrial environment to prevent regression of corpora lutea to ensure continued production of progesterone (P4) required for establishment and maintenance of pregnancy. For nearly 40 years after publication of the endocrine/exocrine theory, conceptus estrogen (E2) was considered the primary maternal recognition signal in the pig. Conceptus production of prostaglandin E2 (PGE2) was also considered to be a major factor in preventing luteolysis. An addition to E2 and PGE2, pig conceptuses produce interleukin 1B2 (IL1B2) and interferons (IFN) delta (IFND) and gamma (IFNG). The present review provides brief history of the discovery of E2, PGs and IFNS which led to research investigating the role of these conceptus secreted factors in establishing and maintaining pregnancy in the pig. The recent utilization of gene editing technology allowed a more direct approach to investigate the in vivo roles of IL1B2, E2, PGE2, AND IFNG for establishment of pregnancy. These studies revealed unknown functions for IFNG and ILB2 in addition to PGE2 and E2. Thus, pregnancy recognition signal is via a servomechanism in requiring sequential effects of P4, E2, IL1B2, PGE2 and IFNG. Results indicate that the original established dogma for the role of conceptus E2 and PGs in MRP is a far too simplified model that involves the interplay of numerous mechanisms for inhibiting luteolysis, inducing critical elongation of the conceptuses and resolution of inflammation in pigs.

Nuclear Estrogen Receptors in Prostate Cancer: From Genes to Function

Estrogens are almost ubiquitous steroid hormones that are essential for development, metabolism, and reproduction. They exert both genomic and non-genomic action through two nuclear receptors (ERα and ERβ), which are transcription factors with disregulated functions and/or expression in pathological processes. In the 1990s, the discovery of an additional membrane estrogen G-protein-coupled receptor augmented the complexity of this picture. Increasing evidence elucidating the specific molecular mechanisms of action and opposing effects of ERα and Erβ was reported in the context of prostate cancer treatment, where these issues are increasingly investigated. Although new approaches improved the efficacy of clinical therapies thanks to the development of new molecules targeting specifically estrogen receptors and used in combination with immunotherapy, more efforts are needed to overcome the main drawbacks, and resistance events will be a challenge in the coming years. This review summarizes the state-of-the-art on ERα and ERβ mechanisms of action in prostate cancer and promising future therapies.

Exploration of structural requirements for azole chemicals towards human aromatase CYP19A1 activity: Classification modeling, structure-activity relationships and read-across study

Human aromatase, also called CYP19A1, plays a major role in the conversion of androgens into estrogens. Inhibition of aromatase is an important target for estrogen receptor (ER)-responsive breast cancer therapy. Use of azole compounds as aromatase inhibitors is widespread despite their low selectivity. A toxicological evaluation of commonly used azole-based drugs and agrochemicals with respect to CYP19A1is currently requested by the European Union- Registration, Evaluation, Authorization and Restriction of Chemicals (EU-REACH) regulations due to their potential as endocrine disruptors. In this connection, identification of structural alerts (SAs) is an effective strategy for the toxicological assessment and safe drug design. The present study describes the identification of SAs of azole-based chemicals as guiding experts to predict the aromatase activity. Total 21 SAs associated with aromatase activity were extracted from dataset of 326 azole-based drugs/chemicals obtained from Tox21 library. A cross-validated classification model having high accuracy (error rate 5%) was proposed which can precisely classify azole chemicals into active/inactive toward aromatase. In addition, mechanistic details and toxicological properties (agonism/antagonism) of azoles with respect to aromatase were explored by comparing active and inactive chemicals using structure-activity relationships (SAR). Lastly, few structural alerts were applied to form chemical categories for read-across applications.

Genomic Structure of the Porcine CYP19 Locus and Expression of the CYP19A3 Paralog

Proper, tissue-specific regulation of CYP19, the gene encoding aromatase, the key enzyme of estrogen synthesis, is essential for reproductive processes. Here, we analyzed transcriptional regulation of the porcine CYP19 in female and male gonads and brain by 5'RACE and RT-PCR and comprehensively mapped the pig CYP19 locus by in silico analysis. Our data revealed that the complete locus, including three paralogous copies, CYP19A1, CYP19A2 and CYP19A3, spans approximately 330 kb of the porcine chromosome 1. The locus also harbors the first exon of the Gliomedin gene (GLDN) in reverse orientation. Only transcripts of the CYP19A3 paralog were substantially expressed in gonads and hypothalamus. We identified CYP19A3-associated untranslated exons approximately 160 kb and 50 kb distal from the first codon. The 5´ untranslated regions of transcripts were derived from either a proximal or from one of these distal untranslated exons. Transcripts including only untranslated exons could be amplified from testis, thus suggesting long non-coding transcripts. The data revealed an additional layer of complexity in the regulation of the porcine CYP19 locus. Tissue-specific expression is not only achieved by tissue- and stage-specific expression of the three different CYP19 paralogs, but also by directing the expression of CYP19A3 from different, proximal and distal promoter regions.

History of Estrogen: Its Purification, Structure, Synthesis, Biologic Actions, and Clinical Implications

This mini-review summarizes key points from the Clark Sawin Memorial Lecture on the History of Estrogen delivered at Endo 2018 and focuses on the rationales and motivation leading to various discoveries and their clinical applications. During the classical period of antiquity, incisive clinical observations uncovered important findings; however, extensive anatomical dissections to solidify proof were generally lacking. Initiation of the experimental approach followed later, influenced by Claude Bernard's treatise "An Introduction to the Study of Experimental Medicine." With this approach, investigators began to explore the function of the ovaries and their "internal secretions" and, after intensive investigations for several years, purified various estrogens. Clinical therapies for hot flashes, osteoporosis, and dysmenorrhea were quickly developed and, later, methods of hormonal contraception. Sophisticated biochemical methods revealed the mechanisms of estrogen synthesis through the enzyme aromatase and, after discovery of the estrogen receptors, their specific biologic actions. Molecular techniques facilitated understanding of the specific transcriptional and translational events requiring estrogen. This body of knowledge led to methods to prevent and treat hormone-dependent neoplasms as well as a variety of other estrogen-related conditions. More recently, the role of estrogen in men was uncovered by prismatic examples of estrogen deficiency in male patients and by knockout of the estrogen receptor and aromatase in animals. As studies became more extensive, the effects of estrogen on nearly every organ were described. We conclude that the history of estrogen illustrates the role of intellectual reasoning, motivation, and serendipity in advancing knowledge about this important sex steroid.

Expression and DNA methylation analysis of cyp19a1a in Chinese sea perch Lateolabrax maculatus

Cytochrome P450 aromatase (P450arom), which is encoded by cyp19a1a, can convert androgen to estrogen. Therefore, P450arom is important in gonadal differentiation and maintenance. In this study, we analyzed the expression and DNA methylation of cyp19a from Chinese sea perch Lateolabrax maculatus (sp. cyp19a1a). The sp. cyp19a1a gene consists of 9 exons, but only 3.5 kb, being smaller than the human cyp19a1a, as a result of small introns. The sp. cyp19a1a protein contains 518 amino acid residues and evolutionarily conserved domains and is clustered in the teleost subfamily on the phylogenetic tree. Amino acid alignment indicates that sp. cyp19a1a shares the highest identity (91.6%) to Epinephelus akaara and Lates calcarifer. Endogenous sp. cyp19a1a is detected mainly in stromal cells around the oocytes of stage I ovary, and the gene expression level has no difference after 40 days fresh water culture in both ovary and testis. The sp. Cyp19a1a can catalyze the production of estrogen from androgen in vitro. Seven CpG dinucleotides are found in the proximal promoter. Binding sites of the conserved predicted transcription factors include cAMP response element, steroidogenic factor-1, and SRY-Box. The deletion of this region reduces promoter activity significantly. The methylation level of the seven CpG dinucleotides in cyp19a1a promoter is higher in the testis (44.25 ± 4.04) than in the ovary (24.71 ± 3.05). The induced hypermethylation of the sp. cyp19a1a promoter suppressed promoter transcription function in vitro. These results suggest that DNA methylation may be a mechanism used for natural sex maintenance.

Celebrating 75 years of oestradiol

Oestrogens exert important effects on the reproductive as well as many other organ systems in both men and women. The history of the discovery of oestrogens, the mechanisms of their synthesis, and their therapeutic applications are very important components of the fabric of endocrinology. These aspects provide the rationale for highlighting several key components of this story. Two investigators, Edward Doisy and Alfred Butenandt, purified and crystalized oestrone nearly simultaneously in 1929, and Doisy later discovered oestriol and oestradiol. Butenandt won the Nobel Prize for this work and Doisy's had to await his purification of vitamin K. Early investigators quickly recognized that oestrogens must be synthesized from androgens and later investigators called this process aromatization. The aromatase enzyme was then characterized, its mechanism determined, and its structure identified after successful crystallization. With the development of knock-out methodology, the precise effects of oestrogen in males and females were defined and clinical syndromes of deficiency and excess described. Their discovery ultimately led to the development of oral contraceptives, treatment of menopausal symptoms, therapies for breast cancer, and induction of fertility, among others. The history of the use of oestrogens for postmenopausal women to relieve symptoms has been characterized by cyclic periods of enthusiasm and concern. The individuals involved in these studies, the innovative thinking required, and the detailed understanding made possible by evolving biologic and molecular techniques provide many lessons for current endocrinologists.

Associations between CYP19A1 polymorphisms, Native American ancestry, and breast cancer risk and mortality: the Breast Cancer Health Disparities Study

The cytochrome p450 family 19 gene (CYP19A1) encodes for aromatase, which catalyzes the final step in estrogen biosynthesis and conversion of androgens to estrogens. Genetic variation in CYP19A1 is linked to higher circulating estrogen levels and increased aromatase expression. Using data from the Breast Cancer Health Disparities Study, a consortium of three population-based case-control studies in the United States (n = 3,030 non-Hispanic Whites; n = 2,893 Hispanic/Native Americans (H/NA) and Mexico (n = 1,810), we examined influence of 25 CYP19A1 tagging single-nucleotide polymorphisms (SNPs) on breast cancer risk and mortality, considering NA ancestry. Odds ratios (ORs) and 95 % confidence intervals (CIs) and hazard ratios estimated breast cancer risk and mortality. After multiple comparison adjustment, none of the SNPs were significantly associated with breast cancer risk or mortality. Two SNPs remained significantly associated with increased breast cancer risk in women of moderate to high NA ancestry (≥29 %): rs700518, ORGG 1.36, 95 % CI 1.11-1.67 and rs11856927, ORGG 1.35, 95 % CI 1.05-1.72. A significant interaction was observed for rs2470144 and menopausal status (p adj = 0.03); risk was increased in postmenopausal (ORAA 1.22, 95 % CI 1.05-1.14), but not premenopausal (ORAA 0.78, 95 % CI 0.64-0.95) women. The absence of an overall association with CYP19A1 and breast cancer risk is similar to previous literature. However, this analysis provides support that variation in CYP19A1 may influence breast cancer risk differently in women with moderate to high NA ancestry. Additional research is warranted to investigate the how variation in an estrogen-regulating gene contributes to racial/ethnic disparities in breast cancer.

Molecular characterization and expression of cyp19a gene in Carassius auratus

A cyp19a gene that contains nine exons and eight introns was identified from Carassius auratus and was mainly expressed in the ovary. The cyp19a mRNA level after hatching was initially low, but began to increase from 25 days after hatching. A number of cis-acting elements, such as the oestrogen receptor, steroidogenic factor 1 and SOX-5 recognition sites, were found in the promoter of the cyp19 gene, which possesses a promoter function confirmed by a recombination green fluorescent protein checking system in vitro.

A case of Aromatase deficiency due to a novel CYP19A1 mutation

BACKGROUND

Aromatase deficiency is a rare, autosomal recessive disorder of which there are approximately twenty four case reports. The aromatase enzyme is crucial in the biosynthesis of oestrogens from androgens. The phenotype of aromatase deficiency therefore is the result of androgen excess and oestrogen deficiency in the absence of normal aromatase activity. We report the first case of aromatase deficiency diagnosed in a female adult, at the age of 32 years, due to a novel duplication in the aromatase gene.

CASE PRESENTATION

A 32 year old Indian woman presented with a history of gender assignment difficulties at birth, lack of pubertal development, osteopaenia with fracture and tall stature. She had central obesity, impaired fasting glucose and borderline hypertension. Past examinations had revealed partial fusion of urethra and vagina, hypoplastic uterus and streak ovaries. The ovaries had been excised due to malignant risk after an initial clinical diagnosis of Turner's syndrome with Y mosaicism. Oestrogen replacement commenced shortly after her fracture, in adulthood. After reassessment, aromatase deficiency was diagnosed. Sequencing of the coding exons of the aromatase (CYP19A1; OMIM 109710) gene revealed a novel 27-base duplication in exon 8 (p.Ala306_Ser314dup). This duplication, occurring within the aromatase α-helix, would be likely to disrupt substrate (androgen) and cofactor (protoporphyrin IX) binding, resulting in a lack of oestrogen synthesis.

CONCLUSIONS

We report a female with a phenotype compatible with aromatase deficiency which was unrecognised until adulthood and found she had a novel duplication in CYP19A1. Previous case reports have described polycystic ovarian morphology, especially in childhood and adolescence, but never streak ovaries. This may reflect the few adult cases reported, that aromatase deficiency in females is generally diagnosed at birth and oestrogen treatment commences decades earlier than occurred in our patient. Streak ovaries are consistent with the phenotype of the aromatase knockout mouse followed through adulthood. The observed clinical features of obesity, dysglycaemia and hypertension, are compatible with the observation that lack of a counterbalancing effect of oestrogen on tissue androgens until adulthood may lead to a metabolic syndrome phenotype. This report broadens the spectra of phenotype and genetic mutations underlying this rare disorder.

Association between CYP19A1 genotype and pubertal sagittal jaw growth

INTRODUCTION

Sagittal jaw growth is influenced during puberty by a ratio of androgens and estrogens. The CYP19A1 (formerly CYP19) gene encodes the cytochrome P450 enzyme aromatase (estrogen synthetase), which converts testosterone to estrogen. Genetic variations including single nucleotide polymorphisms might regulate CYP19A1 gene expression or the function of the aromatase protein and thus influence sagittal jaw growth.

METHODS

The annual sagittal jaw growth in 92 pubertal orthodontic patients was determined by using pretreatment and posttreatment cephalometric radiographs. Single nucleotide polymorphisms rs2470144 and rs2445761 were genotyped and haplotypes constructed. Associations between genotypes or haplotypes and the annual sagittal growth were estimated by using JMP (version 9.0; SAS Institute, Cary, NC).

RESULTS

Two single nucleotide polymorphisms were significantly associated with average differences in annual sagittal jaw growth in boys. Haplotype analysis demonstrated that haplotypes T(rs2470144)T(rs2445761) and C(rs2470144)T(rs2445761) had significant effects on annual sagittal maxillary growth and on mandibular growth in boys. No association was found in girls.

CONCLUSIONS

A quantitative trait locus that influences male pubertal sagittal jaw growth might exist in the CYP19A1 gene, and single nucleotide polymorphisms rs2470144 and rs2445761 might be inside this quantitative trait locus or be linked to it.

Evolutionary origins of the estrogen signaling system: insights from amphioxus

Classically, the estrogen signaling system has two core components: cytochrome P450 aromatase (CYP19), the enzyme complex that catalyzes the rate limiting step in estrogen biosynthesis; and estrogen receptors (ERs), ligand activated transcription factors that interact with the regulatory region of target genes to mediate the biological effects of estrogen. While the importance of estrogens for regulation of reproduction, development and physiology has been well-documented in gnathostome vertebrates, the evolutionary origins of estrogen as a hormone are still unclear. As invertebrates within the phylum Chordata, cephalochordates (e.g., the amphioxus of the genus Branchiostoma) are among the closest invertebrate relatives of the vertebrates and can provide critical insight into the evolution of vertebrate-specific molecules and pathways. To address this question, this paper briefly reviews relevant earlier studies that help to illuminate the history of the aromatase and ER genes, with a particular emphasis on insights from amphioxus and other invertebrates. We then present new analyses of amphioxus aromatase and ER sequence and function, including an in silico model of the amphioxus aromatase protein, and CYP19 gene analysis. CYP19 shares a conserved gene structure with vertebrates (9 coding exons) and moderate sequence conservation (40% amino acid identity with human CYP19). Modeling of the amphioxus aromatase substrate binding site and simulated docking of androstenedione in comparison to the human aromatase shows that the substrate binding site is conserved and predicts that androstenedione could be a substrate for amphioxus CYP19. The amphioxus ER is structurally similar to vertebrate ERs, but differs in sequence and key residues of the ligand binding domain. Consistent with results from other laboratories, amphioxus ER did not bind radiolabeled estradiol, nor did it modulate gene expression on an estrogen-responsive element (ERE) in the presence of estradiol, 4-hydroxytamoxifen, diethylstilbestrol, bisphenol A or genistein. Interestingly, it has been shown that a related gene, the amphioxus "steroid receptor" (SR), can be activated by estrogens and that amphioxus ER can repress this activation. CYP19, ER and SR are all primarily expressed in gonadal tissue, suggesting an ancient paracrine/autocrine signaling role, but it is not yet known how their expression is regulated and, if estrogen is actually synthesized in amphioxus, whether it has a role in mediating any biological effects. Functional studies are clearly needed to link emerging bioinformatics and in vitro molecular biology results with organismal physiology to develop an understanding of the evolution of estrogen signaling. This article is part of a Special Issue entitled 'Marine organisms'.

Promoter-specific effects of metformin on aromatase transcript expression

Phase III aromatase inhibitors (AIs) are proving successful in the treatment of hormone-dependent postmenopausal breast cancer. Side-effects associated with total body aromatase inhibition have prompted new research into the development of breast-specific AIs. The identification of tissue- and disease-specific usage of aromatase promoters has made the inhibition of aromatase at the transcriptional level an interesting approach. We have previously demonstrated that AMPK-activating drugs, including metformin, were potent inhibitors of aromatase expression in primary human breast adipose stromal cells (hASCs). This study examines the promoter-specific effects of metformin on inhibiting aromatase expression in hASCs. Tumour-associated promoters PII/PI.3 were activated using forskolin (FSK)/phorbol ester (PMA), whereas normal adipose associated promoter PI.4 was activated using dexamethasone (DEX)/tumour necrosis factor-α (TNFα). Results demonstrate that metformin significantly decreased the FSK/PMA-, but not the DEX/TNFα-mediated expression of total aromatase at concentrations of 10, 20, and 50 μM (P ≤ 0.05). Using PCR to amplify promoter-specific transcripts of aromatase, it appears that the inhibition of the FSK/PMA-mediated expression of aromatase is due to decreases in PII/PI.3-specific transcripts, whereas no effect of metformin is observed on any promoter-specific transcript, including PI.4, in DEX/TNFα-treated hASCs. This report therefore supports the hypothesis that metformin would act as a breast-specific inhibitor of aromatase expression in the context of postmenopausal breast cancer.

Potential utility of natural products as regulators of breast cancer-associated aromatase promoters

Aromatase, the key enzyme in estrogen biosynthesis, converts androstenedione to estrone and testosterone to estradiol. The enzyme is expressed in various tissues such as ovary, placenta, bone, brain, skin, and adipose tissue. Aromatase enzyme is encoded by a single gene CYP 19A1 and its expression is controlled by tissue-specific promoters. Aromatase mRNA is primarily transcribed from promoter I.4 in normal breast tissue and physiological levels of aromatase are found in breast adipose stromal fibroblasts. Under the conditions of breast cancer, as a result of the activation of a distinct set of aromatase promoters (I.3, II, and I.7) aromatase expression is enhanced leading to local overproduction of estrogen that promotes breast cancer. Aromatase is considered as a potential target for endocrine treatment of breast cancer but due to nonspecific reduction of aromatase activity in other tissues, aromatase inhibitors (AIs) are associated with undesirable side effects such as bone loss, and abnormal lipid metabolism. Inhibition of aromatase expression by inactivating breast tumor-specific aromatase promoters can selectively block estrogen production at the tumor site. Although several synthetic chemical compounds and nuclear receptor ligands are known to inhibit the activity of the tumor-specific aromatase promoters, further development of more specific and efficacious drugs without adverse effects is still warranted. Plants are rich in chemopreventive agents that have a great potential to be used in chemotherapy for hormone dependent breast cancer which could serve as a source for natural AIs. In this brief review, we summarize the studies on phytochemicals such as biochanin A, genistein, quercetin, isoliquiritigenin, resveratrol, and grape seed extracts related to their effect on the activation of breast cancer-associated aromatase promoters and discuss their aromatase inhibitory potential to be used as safer chemotherapeutic agents for specific hormone-dependent breast cancer.

Obesity, aromatase and breast cancer

After the menopausal transition, the ovaries cease to make estrogens, yet the incidence of breast cancer increases and the majority of these tumors are estrogen receptor positive. So, where is the estrogen driving this tumor development coming from? Several extragonadal sites, such as bone, brain and adipose tissue, synthesize estrogens from circulating C19 steroids. The largest of these depots is the adipose tissue, and increased BMI is associated with increased breast cancer risk as well as increased circulating estrogen levels. The mechanisms linking obesity to breast cancer risk are not yet completely understood, although it is widely assumed that estrogens produced in the fat play a role. This article aims to provide a comprehensive overview of the regulation of aromatase expression in the breast adipose tissue in response to fat and tumor-derived factors, as well as new evidence suggesting that breast-specific inhibition of aromatase may be possible.

Sex differences in aromatase gene expression in the medaka brain

The brain of teleost fish exhibits a significant degree of sexual plasticity, even in adulthood. This unique feature is almost certainly attributable to a teleost-specific sexual differentiation process of the brain, which remains largely unknown. To dissect the molecular basis of sexual differentiation of the teleost brain, we searched for genes differentially expressed between both sexes in the medaka brain. One gene identified in the screen, cyp19a1b, which encodes the steroidogenic enzyme aromatase, was selected for further analysis. As opposed to the situation in most vertebrates, medaka cyp19a1b is expressed at higher levels in the adult female brain than the male brain. The female-biased expression in the brain is consistent regardless of reproductive or diurnal cycle. Medaka cyp19a1b is expressed throughout the ventricular zones in wide areas of the brain, where, in most regions, females have a greater degree of expression compared to males, with the optic tectum exhibiting the most conspicuous predominance in females. Contrary to what is known in mammals, cyp19a1b expression exhibits neither a transient elevation nor a sex difference in medaka embryos. It is not until just before the onset of puberty that cyp19a1b expression in the medaka brain is sexually differentiated. Finally, cyp19a1b expression in the medaka brain is not under the direct control of sex chromosome genes but relies mostly, if not solely, on oestrogen derived from the gonad. These unique properties of aromatase expression in the brain probably contribute substantially to the less rigid sexual differentiation process, thus ensuring remarkable sexual plasticity in the teleost brain.

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.

The gene for aromatase, a rate-limiting enzyme for local estrogen biosynthesis, is a downstream target gene of Runx2 in skeletal tissues

The essential osteoblast-related transcription factor Runx2 and the female steroid hormone estrogen are known to play pivotal roles in bone homeostasis; however, the functional interaction between Runx2- and estrogen-mediated signaling in skeletal tissues is minimally understood. Here we provide evidence that aromatase (CYP19), a rate-limiting enzyme responsible for estrogen biosynthesis in mammals, is transcriptionally regulated by Runx2. Consistent with the presence of multiple Runx2 binding sites, the binding of Runx2 to the aromatase promoter was demonstrated in vitro and confirmed in vivo by chromatin immunoprecipitation assays. The bone-specific aromatase promoter is activated by Runx2, and endogenous aromatase gene expression is upregulated by Runx2 overexpression, establishing the aromatase gene as a target of Runx2. The biological significance of the Runx2 transcriptional control of the aromatase gene is reflected by the enhanced estrogen biosynthesis in response to Runx2 in cultured cells. Reduced in vivo expression of skeletal aromatase gene and low bone mineral density are evident in Runx2 mutant mice. Collectively, these findings uncover a novel link between Runx2-mediated osteoblastogenic processes and the osteoblast-mediated biosynthesis of estrogen as an osteoprotective steroid hormone.

The multiple roles of estrogens and the enzyme aromatase

Aromatase is the enzyme that catalyzes the last step of estrogen biosynthesis. It is expressed in many tissues such as the gonads, brain and adipose tissue. The regulation of the level and activity of aromatase determines the levels of estrogens that have endocrine, paracrine and autocrine effects on tissues. Estrogens play many roles in the body, regulating reproduction, metabolism and behavior. In the brain, cell survival and the activity of neurons are affected by estrogens and hence aromatase.

Alternative use of multiple exons 1 of aromatase gene in cancerous and normal breast tissues from women over the age of 80 years

INTRODUCTION

Peripherally localized aromatase, which converts circulating androgens into estrogens, is important in the pathogenesis of postmenopausal breast carcinomas. We have previously shown that aromatase mRNA levels are higher in elderly breast carcinomas (EldCa) than breast carcinomas of the control group (ContCa) or normal breast tissues. Aromatase expression has been reported to be regulated through the alternative use of multiple exons 1 (exons 1a-1f and so on); however, the preferential usage of exons 1 in elderly breast tissue has never been systematically examined. In order to properly treat and protect against EldCa, the regulation mechanism of aromatase expression in elderly breast tissues should be elucidated. The aim of the present study is to elucidate whether there are any specific patterns in use of multiple exons 1 in elderly breast tissue.

METHODS

Usage of multiple exons 1 of the aromatase gene and mRNA levels of aromatase were examined by reverse transcription-polymerase chain reaction analysis in breast tissues of 38 elderly patients with breast cancer (age 80-99), and the results were compared with those in 35 patients of the control group (age 37-70). One-factor analysis of variance and the Scheffé test were used for the comparison of aromatase mRNA levels. Patterns of preferential utilization of multiple exons 1 of the aromatase gene were compared by chi2 test for independence or Fisher exact test for independence using a contingency table.

RESULTS

Exon 1d was utilized much more frequently in elderly tissue than in the control group irrespective of cancerous or normal tissue (EldCa, 36/38, 95% versus ContCa, 7/35, 20%, P < 0.0001; normal tissue of the elderly, EldNorm, 30/34, 88% versus normal tissue of controls, ContNorm, 2/29, 7%, P < 0.0001). Twenty EldCa (53%) and 12 EldNorm (35%) used both exons 1c and 1d; however, their dominance was reversed (EldCa, all 1d > 1c; EldNorm, all 1c > 1d).

CONCLUSIONS

Elderly breast tissues exhibited specific patterns in use of multiple exons 1, which at least partly explained the higher aromatase levels in EldCa. The mechanisms of how these specific patterns occur during aging and carcinogenesis should be further examined.

History of aromatase: saga of an important biological mediator and therapeutic target

Aromatase is the enzyme that catalyzes the conversion of androgens to estrogens. Initial studies of its enzymatic activity and function took place in an environment focused on estrogen as a component of the birth control pill. At an early stage, investigators recognized that inhibition of this enzyme could have major practical applications for treatment of hormone-dependent breast cancer, alterations of ovarian and endometrial function, and treatment of benign disorders such as gynecomastia. Two general approaches ultimately led to the development of potent and selective aromatase inhibitors. One targeted the enzyme using analogs of natural steroidal substrates to work out the relationships between structure and function. The other approach initially sought to block adrenal function as a treatment for breast cancer but led to the serendipitous finding that a nonsteroidal P450 steroidogenesis inhibitor, aminoglutethimide, served as a potent but nonselective aromatase inhibitor. Proof of the therapeutic concept of aromatase inhibition involved a variety of studies with aminoglutethimide and the selective steroidal inhibitor, formestane. The requirement for even more potent and selective inhibitors led to intensive molecular studies to identify the structure of aromatase, to development of high-sensitivity estrogen assays, and to "mega" clinical trials of the third-generation aromatase inhibitors, letrozole, anastrozole, and exemestane, which are now in clinical use in breast cancer. During these studies, unexpected findings led investigators to appreciate the important role of estrogens in males as well as in females and in multiple organs, particularly the bone and brain. These studies identified the important regulatory properties of aromatase acting in an autocrine, paracrine, intracrine, neurocrine, and juxtacrine fashion and the organ-specific enhancers and promoters controlling its transcription. The saga of these studies of aromatase and the ultimate utilization of inhibitors as highly effective treatments of breast cancer and for use in reproductive disorders serves as the basis for this first Endocrine Reviews history manuscript.

Sox3: a transcription factor for Cyp19 expression in the frog Rana rugosa

Cyp19 is expressed at a high level in the gonad of the female tadpole of the frog Rana rugosa during sex determination. To identify sequence elements important for expression of Cyp19, we isolated a genomic clone (approximately 40 kbp) carrying R. rugosa Cyp19 and analyzed the nucleotide sequence of the 5'-flanking region to search for potential transcription factor binding sites. Sox (SRY-related HMG box) protein and Sf1 binding sites were found in the ovary-specific promoter region of Cyp19. Because Sox3 is located on the sex chromosome in R. rugosa, we conducted the luciferase reporter assay in Xenopus A6 cells using the promoter region. Sox3 drove the reporter gene in the cells, but Sf1 did not. When sequential deletion of the 2.7 kbp Cyp19-promoter region was undertaken, a fragment spanning nucleotides -191 to +48 was sufficient to drive the transcription of the reporter gene. In site-directed mutagenesis, the binding site at -57 in the region was critical for Sox3 responsiveness. Sox3 lacking the HMG box had no ability to promote Cyp19 transcription. In addition, a chromatin immunoprecipitation (ChIP) assay showed that DNA fragments were enriched 8-fold, as determined by real-time PCR, when chromatin was immunoprecipitated with the anti-His antibody against His-tagged Sox3. The results, taken together, suggest that Sox3 activates Cyp19 transcription by its direct binding to the binding site of the Cyp19 promoter region. Sox3 appears to be a factor that directs indifferent gonads to develop into an ovary in R. rugosa.

Genetic variation in CYP19A1 and risk of breast cancer and fibrocystic breast conditions among women in Shanghai, China

CYP19A1 encodes for aromatase, which irreversibly converts androgens to estrogens; variation in this gene may affect individual susceptibility to breast cancer and other sex hormone-dependent outcomes. In a case-control study nested within a breast self-examination trial conducted in China, we examined whether CYP19A1 polymorphisms (rs1870049, rs1004982, rs28566535, rs936306, rs11636639, rs767199, rs4775936, rs11575899, rs10046, and rs4646) were associated with risk of breast cancer and fibrocystic breast conditions. Cases were diagnosed with breast cancer (n = 614) or fibrocystic breast conditions (n = 465) during 1989 to 2000. Controls were free of breast disease during the same period (n = 879). Presence of proliferative changes within the extratumoral tissue of women with breast cancer and the lesions of women with fibrocystic conditions only was assessed. None of the polymorphisms were associated with overall risk of breast cancer or fibrocystic breast conditions. Differences in breast cancer risk, however, were observed by proliferation status. The risk of breast cancer with (but not without) proliferative fibrocystic conditions was increased among women homozygous for the minor allele of rs1004982 (C), rs28566535 (C), rs936306 (T), and rs4775936 (C) relative to those homozygous for the major allele [age-adjusted odds ratios (95% confidence intervals), 2.19 (1.24-3.85), 2.20 (1.27-3.82), 1.94 (1.13-3.30), and 1.95 (1.07-3.58), respectively]. Also, haplotypes inferred using all polymorphisms were not associated with overall risk of either outcome, although some block-specific haplotypes were associated with an increased risk of breast cancer with concurrent proliferative fibrocystic conditions. Our findings suggest that CYP19A1 variation may enhance breast cancer development in some women, but further confirmation is warranted.

Liver receptor homologue-1 (LRH-1) activates the promoter of brain aromatase (cyp19a2) in a teleost fish, the medaka, Oryzias latipes

The medaka, Oryzias latipes, like other fish, have two distinct aromatase genes, the ovarian (cyp19a1) and brain (cyp19a2) forms. We previously reported that Ad4BP/SF-1, a member of the NR5A subfamily, plays an important role in the regulation of cyp19a1 expression in medaka ovarian follicles during vitellogenesis. In the present study, we investigated whether liver receptor homologue-1 (LRH-1), another NR5A subfamily member, is involved in the regulation of cyp19a2 expression in the medaka brain. In situ hybridization analysis revealed that LRH-1 was expressed in the hypothalamus, where it colocalized with aromatase (cyp19a2). We then showed by transient transfection assays that LRH-1 was able to increase expression of a cyp19a2 reporter gene in various mammalian cell lines, and that mutation of a putative LRH-1 binding site within the cyp19a2 promoter abolished this effect. Taken together, these findings suggest that LRH-1 plays a role in regulating cyp19a2 expression in the medaka brain. This is the first to demonstrate in vitro the activation of brain aromatase by LRH-1 in the vertebrate brain.

A CYP19 (aromatase) polymorphism is associated with increased premenopausal breast cancer risk

Due to the established association between estrogen levels and breast cancer risk, polymorphic variation in genes regulating estrogen levels is thought to be related to breast cancer risk. Aromatase, the protein product of the CYP19 gene, is involved in the production of endogenous estrogens via androgen conversion. We examined whether polymorphic variation in CYP19 associated with increased breast cancer risk in a population based case-control study. We examined two single nucleotide polymorphisms (SNP), rs1008805 (A/G) and rs730154 (C/T), which have been shown to tag SNPs within two different haplotype blocks in CYP19. Among premenopausal women, the presence of at least one G allele at rs1008805 was significantly associated with an increase in the risk of breast cancer (OR = 1.72 [95% CI, 1.20-2.49]), especially with estrogen and progesterone receptor negative breast cancer (OR = 3.89 [1.74-8.70] and OR = 2.52 [1.26-5.05], respectively). No association was observed among postmenopausal women (OR = 1.06 [0.82-1.36]). There was no significant association between rs730154 and breast cancer, regardless of menopausal status. Our results suggest that premenopausal women carrying the G allele at CYP19 rs1008805 have increased risk of breast cancer. The finding supports the potential role of variation in estrogen biosynthesis genes in premenopausal breast cancer risk.

Region-specific expression and sex-steroidal regulation on aromatase and its mRNA in the male rat brain: immunohistochemical and in situ hybridization analyses

The brain has an estrogen-biosynthetic potential resulting from the presence of neuronal aromatase, which controls the intraneural sex-steroidal milieu and is involved in brain sexual differentiation, psychobehavioral regulation, and neuroprotection. In the rat brain, three distinct aromatase-P450-immunoreactive (AromP450-I) neural groups have been categorized in terms of their peak expression time (fetal, fetoneonatal, and young-to-adult groups), suggesting the presence of region-specific regulation on brain AromP450. In the present study, we compared the expressions between AromP450 protein and mRNA by using immunohistochemistry and in situ hybridization with an ovary-derived cRNA probe in serial sections of fetal, fetoneonatal, and adult male rat brains and then performed steroidal manipulations to evaluate the sex-steroidal effects on AromP450 in adult orchiectomized and adrenalectomized (OCX + ADX) male rats. As a result, prominent mRNA signals were detected in the fetal (i.e., the anterior medial preoptic nucleus) and fetoneonatal (i.e., the medial preopticoamygdaloid neuronal arc) groups, although no detectable signal was found in the "young-to-adult" group (i.e., the central amygdaloid nucleus). In addition, the "fetoneonatal" AromP450-I neurons were prominently reduced in number and intensity after OCX + ADX and then were reinstated by the administration of dihydrotestosterone, testosterone, or 17beta-estradiol. In contrast, none of the sex steroids had any significant effects on the young-to-adult group. Several possible explanations were explored for why the young-to-adult group may differ in aromatase expression and regulation, including the possibility that distinct splicing variants or isozymes for aromatase exist in the rat brain.

Polymorphisms of estrogen-biosynthesis genes CYP17 and CYP19 may influence age at menarche: a genetic association study in Caucasian females

Variation in age at menarche (AAM) is known to be substantially influenced by genetic factors, but the true causal genes remain largely unidentified. Because the increased amplitude of estrogen exposure of tissues initiates the onset of menarche, the genes involved in estrogen biosynthesis are natural candidate genes underlying AAM. Our study aimed to identify whether the CYP17 and CYP19, the two key genes involved in the biosynthesis of estrogen, are associated with AAM variation in 1048 females from 354 Caucasian nuclear families. We genotyped 38 SNPs and established the linkage disequilibrium blocks and haplotype structures that covered the full transcript length of those two genes. Family-based and population-based statistical analyses were used to test for associations with all of the single SNPs and haplotypes. Both methods consistently detected significant associations for five SNPs of CYP19 with AAM. Haplotype analyses corroborated our single-SNP results by showing that the haplotypes in block 1 were highly significant to AAM in population-based analyses. However, we could not find any association of CYP17 with AAM. Our study is the first to suggest the important effect of CYP19 on AAM variation in Caucasian females. It will be valuable to replicate and confirm these findings in other independent studies, aiming at eventually finding the hidden genetic mechanisms underlying the variation in AAM.

Aromatase is differentially expressed in peripheral blood leukocytes from children, and adult female and male subjects

OBJECTIVE

Aromatase, the key enzyme involved in estrogen synthesis, is expressed in a variety of cells and tissues including human peripheral blood leukocytes (PBLs). The present study was designed to evaluate PBL aromatase gene expression in male and female subjects of different age groups. In addition, differences in gene expression during the follicular and luteal phase of the menstrual cycle in women, and before and after testosterone administration in men, were estimated.

DESIGN

Aromatase mRNA and protein were measured in PBLs obtained from young (n = 10) and postmenopausal women (n = 10), men (n = 15), and prepubertal children (n = 10). Aromatase mRNA and protein were also measured during the follicular and luteal phases of the menstrual cycle in women, and before and after the intramuscular administration of 250 mg testosterone enanthate in men.

METHODS AND RESULTS

Aromatase mRNA measured by real-time PCR in PBLs from women during the follicular phase was significantly higher than during the luteal phase of the menstrual cycle (P < 0.05). In men, PBL aromatase mRNA values increased significantly following testosterone administration (P < 0.05). PBL mRNA aromatase levels in women during the follicular phase and men after testosterone administration were significantly higher (one-way ANOVA; P < 0.05) than in any other group. Children, postmenopausal women, and women during the luteal phase showed the lowest aromatase mRNA expression. The results of the immunoblot analysis confirmed the data obtained by real-time PCR. A positive correlation between PBL aromatase mRNA values and plasma estradiol and estrone levels during the follicular phase of the menstrual cycle was observed in the group of adult women. No other correlations were found.

CONCLUSIONS

The aromatase gene is differentially expressed in PBLs from women, men, and prepubertal children, indicating a sexual dimorphism in the enzyme expression and an important role of sex steroids in the modulation of aromatase gene expression.

Aromatase expression in the human temporal cortex

The expression of the human cyp19 gene, encoding P450 aromatase, the key enzyme for estrogen biosynthesis, involves alternative splicing of multiple forms of exon I regulated by different promoters. Aromatase expression has been detected in the human cerebral cortex, although the precise cellular distribution and promoter regulation are not fully characterized. We examined the variants of exon I of cyp19 by PCR analysis and the cellular distribution of the enzyme using immunohistochemistry in the human temporal cortex. We detected four different variants of exon I, suggesting a complex regulation of cyp19 in the cerebral cortex. In addition, the enzyme was localized mainly in a large subpopulation of pyramidal neurons and in a subpopulation of astrocytes. However, the majority of GABAergic interneurons identified by their expression of the calcium-binding proteins calbindin, calretinin and parvalbumin, did not display aromatase immunoreactivity. The broad range of potential modulators of the cyp19 gene in the cortex and the widespread expression of the protein in specific neuronal and glial subpopulations suggest that local estrogen formation may play an important role in human cortical function.

Aromatase inhibitors: rationale and use in breast cancer

Considerable data implicate estrogens in breast cancer carcinogenesis and progression. In the postmenopausal woman, estrogens are produced in breast tissues and many other sites throughout the body when androgen precursors are converted into estrogens via the enzyme aromatase. Inhibition of this enzyme with aromatase inhibitors (AIs) has demonstrated reductions in systemic as well as intratumoral estrogens. These drugs have now been utilized in large phase 3 randomized trials and have led to greater improved clinical benefit than the "gold standard," tamoxifen. Questions remain about the long-term side effects and safety profile of AIs. They are associated with increasing incidence of osteoporosis and bone fractures. Nevertheless, AIs add to our armamentarium for therapy and possible prevention of breast cancer.

Localization and expression of aromatase mRNA in adult zebrafish

Estradiol plays a key role in the control of many behavioral and physiological aspects of reproduction therefore the expression of cytochrome P450 aromatase (CYP19), the enzyme responsible for the conversion of androgens to estrogens, is of vital interest. The zebrafish, and many other teleosts, have two aromatase genes (CYP19A1 and CYP19A2) that are expressed predominantly in the ovary and brain, respectively, however, the physiological impact of extra-gonadal aromatase has been poorly described. In this study, in situ hybridizations of whole-mount and paraffin sections of adult zebrafish brains, pituitaries, and ovarian follicles showed that CYP19A2 was strongly expressed in the olfactory bulb (OB), ventral telencephalon (TEL), preoptic area (POA), and ventral/caudal hypothalamic zone (HT) of the brain, and in the anterior and posterior lobes of the pituitary. The regional distribution of the CYP19A2 mRNA did not vary with sex however transcript abundance varied within (male "high expressers" had much higher expression in the OB, TEL, and HT than in "low expressers") and between sexes (higher in OB, TEL, and HT of males than in females). In situ hybridizations of CYP19A1 failed to develop a signal in the brain or pituitary but were detectable by RT-PCR. CYP19A1 was highly expressed in Stage III B follicles (>500 nm) with significantly lower levels in the Stage IV follicles (>680 nm), Stage III A follicles (>350 nm), and Stage I and II follicles (350 microm) which were embedded in connective tissues. The differential expression of the aromatase genes, particularly CYP19A2 in the brain, suggests that the two aromatase genes play different roles in the reproductive behavior and/or physiology of bony fish.

Quantitative determination, by real-time reverse transcription polymerase chain reaction, of aromatase mRNA in invasive ductal carcinoma of the breast

Background

Estrogen is a mitogenic factor that is implicated in the genesis and progression of breast cancer via its binding to estrogen receptor (ER)-α. Synthesis of estrogen in situ is believed to be catalyzed mainly by aromatase. Previous studies comparing the relative contributions from tumor cells and stromal cells to local estrogen synthesis, as assessed by immunohistochemical analysis, were quite controversial and no consistent relationship was found between the presence of aromatase and any clinicopathologic factor. In addition, previous studies into aromatase gene expression and clinicopathologic factors are limited.

Methods

We assessed the level of expression of aromatase mRNA, using quantitative real-time RT-PCR, in 162 cases of invasive ductal carcinoma of the breast. Associations between aromatase expression and different clinicopathologic factors were sought.

Results

It was found that aromatase mRNA was expressed at significantly higher levels in patients older than 50 years, in those without axillary lymph node involvement, in those with tumor size less than 2 cm, and in ER-α positive tumors. However, no relationship was found between aromatase mRNA expression and any other clinicopathologic factor, including histologic grade and progesterone receptor status. Patients with high levels of expression of aromatase mRNA tended to have a better prognosis than did those patients with low expression.

Conclusion

These findings imply that ER-α and aromatase may be coexpressed in endocrine responsive patients. They may also indicate that aromatase expression could be a marker of endocrine responsiveness, and it may have prognostic implications for breast cancer progression.

Analysis of zebrafish cyp19 promoters

Cyp19 encodes P450 aromatase, the key enzyme catalyzing the conversion of androgens into estrogens. Estrogens play a crucial role in the anatomical, functional and behavioral characteristics of sexually dimorphic development. In zebrafish, two cyp19 genes, cyp19a and cyp19b, expressed in ovary and brain, respectively, were found. We have isolated the promoter regions of the zebrafish cyp19 genes from a bacterial artificial chromosome library to search for regulatory sequences that bind to transcription factors. Sequences like arylhydrocarbon receptor (AhR) recognition site, estrogen receptor recognition half sites (1/2ERE) and c-AMP responsive elements were found in the 5'-flanking regions of both cyp19 genes. For ovarian-specific expression, we found binding sites for steroidogenic factor-1 (SF-1), GATA transcription factor 4 (GATA-4) and Wilm tumor 1 (WT1-KTS) on the promoter region of cyp19a but not cyp19b. For brain-specific expression of the cyp19b gene, sequences for recognition of chicken ovalbumin upstream promoter-transcription factor (COUP) and Ptx-1 were detected in the promoter. The importance of these putative control elements in ovary and brain-specific promoter has been assessed by sequence comparison among various species.

Role of CRE-binding protein (CREB) in aromatase expression in breast adipose

Estrogen biosynthesis from C19 steroids is catalyzed by aromatase cytochrome P450. Aromatase is expressed in breast adipose tissue through the use of a distal, cytokine-responsive promoter (promoter I.4). Breast tumors, however, secrete soluble factors that over-stimulate aromatase expression through an alternative proximal cAMP-responsive promoter, promoter II. We have mapped the cAMP-responsive regions of promoter II by transient transfection of 3T3-L1 preadipocytes with aromatase promoter II reporter genes. 5' deletion and mutation analyses identified two cAMP response element (CRE)-like sequences (CRE1 and CRE2) that were essential for cAMP-induced promoter II activity. Electrophoretic mobility shift analysis demonstrated that CRE binding protein (CREB) bound to each element, and that this interaction was enhanced in the presence of cAMP. Quantification of CREB mRNA expression in adipose tissue from normal and tumor bearing breast adipose tissue revealed that CREB expression is approximately five times higher in tumor bearing than in normal breast adipose tissue. Thus, the over expression of aromatase in adipose tissue surrounding breast tumors could arise through increases in both CREB expression and CREB transcriptional activity. Pharmacological inhibition of CREB activity, previously shown to have anti-proliferative effects on cancer cells, might therefore have additional benefits through inhibition of aromatase expression and thus estrogen production in breast adipose.

Molecular characterization and expression of equine testicular cytochrome P450 aromatase

We characterized testicular equine aromatase and its expression. A 2707 bp cDNA was isolated, it encoded a polypeptide of 503 residues with a deduced molecular mass of 57.8 kDa. The sequence features were those of a cytochrome P450 aromatase, with a 78% polypeptide identity with the human counterpart. The gene has a minimal length of 74 kb comprising at least 9 exons and expresses a 2.8 kb mRNA in the testis. Transient cDNA transfections in E293 cells and in vitro translations in a reticulocyte lysate system allowed aromatase protein and activity detections. The activity increased with androstenedione as substrate in a dose-dependent manner. The isolation of testicular aromatase by a new immunoaffinity method demonstrated that the protein could exist either glycosylated or not with a 2 kDa difference. All these results taken together allow new structural studies to progress in the understanding of this cytochrome P450.

Ligands for the peroxisomal proliferator-activated receptor gamma and the retinoid X receptor inhibit aromatase cytochrome P450 (CYP19) expression mediated by promoter II in human breast adipose

Local estrogen biosynthesis in breast adipose tissue, catalyzed by P450 aromatase, contributes to the growth of breast carcinomas. Aromatase expression is regulated by a number of alternative promoters, and in normal adipose tissue it is primarily regulated via the distal promoter I.4. However, in breast adipose containing a tumor, aromatase expression is regulated by the proximal promoter II in response to tumor-derived factors. Previously we have shown that peroxisomal proliferator-activated receptor gamma (PPARgamma) ligands inhibit aromatase expression in normal breast adipose tissue mediated by promoter I.4. In the present study, we investigated the effects of the PPARgamma ligand troglitazone and the retinoid X receptor (RXR) ligand LG101305 on aromatase expression mediated by promoter II. In cultured human breast adipose stromal cells, troglitazone or LG101305 alone inhibited aromatase activity and expression stimulated by inducers of promoter II, in a concentration-dependent manner, and this inhibition was greater in the presence of both ligands. Reporter gene assays showed that troglitazone and LG101305 inhibit transcription from promoter II of the CYP19 gene. However, EMSAs showed that PPARgamma and RXRalpha do not bind to promoter II of the CYP19 gene, indicating that PPARgamma- and RXR-mediated inhibition of aromatase expression via promoter II occurs through an indirect mechanism of action. Because ligands for PPARgamma and RXR inhibit aromatase expression in healthy breast adipose (via promoter I.4), as well as expression induced by tumor-derived factors (via promoter II), such compounds could find utility in the treatment of estrogen-dependent breast cancers.

Liver receptor homologue-1 (LRH-1) regulates expression of aromatase in preadipocytes

Estrogen biosynthesis from C(19) steroids is catalyzed by aromatase cytochrome P450. Aromatase is expressed in breast adipose tissue through the use of a distal, cytokine-responsive promoter (promoter I.4). Breast tumors, however, secrete soluble factors that stimulate aromatase expression through an alternative proximal promoter, promoter II. In other estrogenic tissues such as ovaries, transcription from promoter II requires the presence of the Ftz-F1 homologue steroidogenic factor-1 (SF-1); adipose tissue, however, does not express SF-1. We have explored the hypothesis that in adipose tissue, an alternative Ftz-F1 family member, liver receptor homologue-1 (LRH-1), substitutes for SF-1 in driving transcription from promoter II. In transient transfection assays using 3T3-L1 preadipocytes, promoter II reporter constructs were modestly (2-3-fold) stimulated by either treatment with activators of protein kinases A or C (PKA/C) or by cotransfection with LRH-1. In combination, these treatments synergistically activated promoter II (>30-fold). Induction by LRH-1 (but not by PKA/C) required an AGGTCA motif at -130 base pairs, to which LRH-1 bound in gel shift assays. Activity of GAL4-LRH-1 fusion proteins was not altered by activators of PKA or PKC. Quantitative real-time PCR revealed that LRH-1 (but not SF-1) is expressed in the preadipocyte fraction of human adipose tissue at levels comparable with that of liver. Differentiation of cultured human preadipocytes into mature adipocytes was associated with a time-dependent induction of peroxisome proliferator-activated receptor-gamma (PPARgamma), and rapid loss of LRH-1 and aromatase expression. We conclude that LRH-1 is a preadipocyte-specific nuclear receptor that regulates expression of aromatase in adipose tissue. Alterations in LRH-1 expression and/or activity in adipose tissue could therefore have considerable effects on local estrogen production and breast cancer development.

Aromatase--a brief overview

There is growing awareness that androgens and estrogens have general metabolic roles that are not directly involved in reproductive processes. These include actions on vascular function, lipid and carbohydrate metabolism, as well as bone mineralization and epiphyseal closure in both sexes. In postmenopausal women, as in men, estrogen is no longer solely an endocrine factor but instead is produced in a number of extragonadal sites and acts locally at these sites in a paracrine and intracrine fashion. These sites include breast, bone, vasculature, and brain. Within these sites, aromatase action can generate high levels of estradiol locally without significantly affecting circulating levels. Circulating C19 steroid precursors are essential substrates for extragonadal estrogen synthesis. The levels of these androgenic precursors decline markedly with advancing age in women, possible from the mid-to-late reproductive years. This may be a fundamental reason why women are at increased risk for bone mineral loss and fracture, and possibly decline of cognitive function, compared with men. Aromatase expression in these various sites is under the control of tissue-specific promotors regulated by different cohorts of transcription factors. Thus in principle, it should be possible to develop selective aromatase modulators (SAMs) that block aromatase expression, for example, in breast, but allow unimpaired estrogen synthesis in other tissues such as bone.

Regulation of aromatase promoter activity in human breast tissue by nuclear receptors

Using the yeast one-hybrid approach to screen a human breast tissue hybrid cDNA expression library, we have found that four orphan/nuclear receptors, ERRalpha-1, EAR-2, COUP-TFI (EAR-3), and RARgamma, bind to the silencer (S1) region of the human aromatase gene. S1 down regulates promoters I.3 and II of the human aromatase gene. In this study, the interaction of EAR-2, COUP-TFI, and RARgamma with S1 was confirmed by DNA mobility shift analysis. In contrast to the findings that ERRalpha-1 behaves as a positive regulatory factor, these three nuclear receptors were found, by mammalian cell transfection experiments, to act as negative regulatory factors by binding to S1. Furthermore, the negative action of these three nuclear receptors could override the positive effect of ERRalpha-1. RT-PCR analysis of 11 cell lines and 55 human breast tumor specimens has shown that these nuclear receptors are expressed in human breast tissue. Since EAR-2, COUP-TFI, and RARgamma are expressed at high levels, it is likely that S1 is a negative regulatory element that suppresses aromatase promoters I.3 and II in normal breast tissue. In cancer tissue, S1 may function as a positive element since ERRalpha-1 is expressed, but EAR-2 and RARgamma are only present in a small number of tumor specimens. This hypothesis is sustained by the finding that there is a weak inverse correlation between the expression of COUP-TFI and that of aromatase in breast tumor tissue. Our studies have revealed that estrogen receptor alpha (ERalpha) can also bind to S1, in a ligand-dependent manner. By binding to S1, ERalpha down-regulates the aromatase promoter activity. These results demonstrate that nuclear receptors play important roles in modulating aromatase expression in human breast tissue.

Biosynthesis of neurosteroids and regulation of their synthesis

The brain, like the gonads, adrenal glands, and placenta, is a steroidogenic organ. The steroids synthesized by the brain and by the nervous system, given the name neurosteroids, have a wide variety of diverse functions. In general, they mediate their actions not through classic steroid hormone nuclear receptors but through ion-gated neurotransmitter receptors. This chapter summarizes the biochemistry of the enzymes involved in the biosynthesis of neurosteroids, their localization during development and in adulthood, and the regulation of their expression, highlighting both similarities and differences between expression in the brain and in classic steroidogenic tissues.

The potential role of estrogen in aromatase regulation in the breast

Aromatase is expressed in both normal and malignant breast tissues. Aromatase activity in the breast varies over a wide range. Our previous studies have demonstrated that in situ aromatization contributes to the estrogen content of breast tumors to a major extent. Consequently, alterations of aromatase activity could serve as a major determinant of tissue estradiol content. However, the mechanisms and extent of aromatase regulation in breast tissues have not been fully established. We have observed an inverse correlation between tumor aromatase activity and estrogen content in nude mice bearing xenografts of MCF-7 cells transfected with the aromatase gene. To investigate the potential role of estrogen in aromatase regulation in the breast, studies were carried out in an in vitro model. In this model, MCF-7 cells were cultured long term in estrogen-deprived medium and called by the acronym, LTED cells. We found that long-term estrogen deprivation enhanced aromatase activity by 3-4-fold when compared to the wild-type MCF-7 cells. Re-exposure of LTED cells to estrogen reduced aromatase activity to the levels of the wild-type MCF-7 cells. We also measured aromatase activity in 101 frozen breast carcinoma specimens and compared tumor aromatase activities in pre-menopausal patients versus post-menopausal patients and in post-menopausal patients with or without hormone replacement therapy (HRT). Although statistically not significant, there was a trend paralleling that observed in the in vitro studies. Aromatase activity was higher in breast cancer tissues from the patients with lower circulating estrogen levels. Our data suggest that estrogen may be involved in the regulation of aromatase activity in breast tissues.

Identification of the regulatory regions of the human aromatase P450 (CYP19) gene involved in placenta-specific expression

Expression of the human CYP19 gene in placental syncytiotrophoblast, ovarian granulosa and luteal cells and adipose stromal cells is regulated by tissue-specific promoters which lie upstream of unique untranslated first exons. In placenta, the majority of CYP19 mRNA transcripts contain 5'-sequences encoded by exon I.1 which lies >35 kb upstream of the translation initiation sequence in exon II. Mononuclear cytotrophoblasts isolated from midterm human placenta spontaneously fuse in culture to form multinucleated syncytiotrophoblast. These morphological changes are associated with a marked induction of CYP19 gene expression. To functionally define genomic regions required for placenta-specific expression, fusion genes containing various amounts of exon I.1 5'-flanking sequence linked to the human growth hormone (hGH) structural gene, as reporter, were introduced into human trophoblast cells in primary monolayer culture and into transgenic mice. Our findings using transfected cells and transgenic mice suggest that sequences between -501 and -42 bp upstream of exon I.1 contain a positive enhancer element(s) that mediates the actions of trophoblast-specific transcription factors, as well as a negative element(s) that binds inhibitory transcription factors in other cell types. Our findings from transgenic studies further indicate that mouse placenta contains the necessary transcription factors required to activate the human CYP19 promoter although mouse placenta does not express endogenous aromatase.

Aromatase in atherosclerotic lesions of human aorta

It is well documented that estrogens have atheroprotective effects in humans. Peripheral aromatization of circulating androgens has been demonstrated to exert estrogenic actions in many human tissues, especially in men and post-menopausal women. Recently, production of estrogens mediated by aromatase was detected in cultured smooth muscle cells and aortic endothelial cells and it has been proposed that this in situ produced estrogen may influence the development of atherosclerosis. In this study, we first examined aromatase expression by immunohistochemistry in human aortic tissues obtained from 85 autopsy cases (50 males, 35 females, 49.6 +/- 2.9-year-old) and by mRNA in situ hybridization in 10 cases. We then semi-quantified the level of aromatase mRNA in aortic tissues of 12 men and 12 post-menopausal women by reverse transcriptase-polymerase chain reaction (RT-PCR) to examine whether or not and in which cell types aromatase was expressed. We also studied alternative use of multiple exon 1 of its gene and immunolocalization of 17beta-hydroxysteroid dehydrogenase type I (17beta-HSD I), which converts estrone produced by aromatase to estradiol, a biologically active estrogen. Aromatase immunoreactivity and mRNA hybridization signals and 17beta-HSD I immunoreactivity were all detected in smooth muscle cell (SMC) of the media and thickened intima, especially in SMC adjacent to an atheromatous plaque. The levels of aromatase mRNA were significantly higher in female cases than in male cases (P<0.05). The amount of aromatase mRNA was significantly higher in the specimens with fibroatheroma (P<0.05) than other lesions, and was also significantly higher in the cases utilizing 1c (I.3) or 1d (PII) of exon 1, i.e. gonadal types than those utilizing 1b (I.4), i.e. fibroblasts type as the promoter (P<0.01). These results suggest that estrone and estradiol are produced in SMC of the human aortic wall and that their production is mediated by aromatase and 17beta-HSD I, respectively. Moreover, it was suggested that aromatase overexpression, possibly as a result of alternative splicing, may play some roles in the development of atherosclerosis.

PNRC: a proline-rich nuclear receptor coregulatory protein that modulates transcriptional activation of multiple nuclear receptors including orphan receptors SF1 (steroidogenic factor 1) and ERRalpha1 (estrogen related receptor alpha-1)

PNRC (proline-rich nuclear receptor coregulatory protein) was identified using bovine SF1 (steroidogenic factor 1) as the bait in a yeast two-hybrid screening of a human mammary gland cDNA expression library. PNRC is unique in that it has a molecular mass of 35 kDa, significantly smaller than most of the coregulatory proteins reported so far, and it is proline-rich. PNRC's nuclear localization was demonstrated by immunofluorescence and Western blot analyses. In the yeast two-hybrid assays, PNRC interacted with the orphan receptors SF1 and ERRalpha1 in a ligand-independent manner. PNRC was also found to interact with the ligand-binding domains of all the nuclear receptors tested including estrogen receptor (ER), androgen receptor (AR), glucocorticoid receptor (GR), progesterone receptor (PR), thyroid hormone receptor (TR), retinoic acid receptor (RAR), and retinoid X receptor (RXR) in a ligand-dependent manner. Functional AF2 domain is required for nuclear receptors to bind to PNRC. Furthermore, in vitro glutathione-S-transferase pull-down assay was performed to demonstrate a direct contact between PNRC and nuclear receptors such as SF1. Coimmunoprecipitation experiment using Hela cells that express PNRC and ER was performed to confirm the interaction of PNRC and nuclear receptors in vivo in a ligand-dependent manner. PNRC was found to function as a coactivator to enhance the transcriptional activation mediated by SF1, ERR1 (estrogen related receptor alpha-1), PR, and TR. By examining a series of deletion mutants of PNRC using the yeast two-hybrid assay, a 23-amino acid (aa) sequence in the carboxy-terminal region, aa 278-300, was shown to be critical and sufficient for the interaction with nuclear receptors. This region is proline rich and contains a SH3-binding motif, S-D-P-P-S-P-S. Results from the mutagenesis study demonstrated that the two conserved proline (P) residues in this motif are crucial for PNRC to interact with the nuclear receptors. The exact 23-amino acid sequence was also found in another protein isolated from the same yeast two-hybrid screening study. These two proteins belong to a new family of nuclear receptor coregulatory proteins.