Positive and negative transcriptional regulation of aromatase expression in human breast cancer tissue

Retinoid X receptor-mediated neuroprotection via CYP19 upregulation and subsequent increases in estradiol synthesis

Increasing evidence has shown that one of the major neurosteroids, estradiol, has potent neuroprotective actions. We have reported that estradiol synthesis was enhanced when retinoic acid was added into rat hippocampal slice culture. In this study, we investigated the effects of a potent retinoid X receptor (RXR) agonist, bexarotene, on estrogen synthesis and neuroprotective action in hippocampal slices. Treatment with bexarotene increased estradiol levels as well as estrogen-synthesizing enzymes and CYP19 expression in hippocampal slice cultures. Bexarotene significantly suppressed neuronal cell death induced by oxygen-glucose deprivation (OGD)/reoxygenation. RXR agonists other than bexarotene, such as CD3254, also suppressed neuronal cell death accompanied by OGD/reoxygenation. The RXR antagonists HX531 and UVI3003 and the CYP19 inhibitor letrozole abolished the neuroprotection elicited by bexarotene, indicating that estradiol produced by RXR stimulation protects neurons from ischemic insult. The human brain-specific CYP19 promoter had 6 RXR half sites, and 2 of 6 half sites were responsible for CYP19 expression induced by bexarotene. Bexarotene increased the expression of catalase and glutathione peroxidase 1 and inhibited lipid peroxidation elicited by OGD/reoxygenation, suggesting that the antioxidative property of estrogen contributes to RXR-mediated neuroprotection. Bexarotene also suppressed neuronal injury induced by lipopolysaccharide in the hippocampal slices. Taken together, RXR stimulation can protect neurons via enhanced synthesis of estradiol with antioxidative mechanisms. The RXR-estrogen axis might be a novel mechanism-based strategy to prevent or ameliorate ischemic and/or inflammatory neuronal disorders.

Aromatase inhibitor treatment for breast cancer: short-term effect on bone health

Aim of this study

Aim of this study was to examine the effects of aromatase inhibitors (AIs), which are used in every phase of breast cancer treatment, on the bone mineral density (BMD) of patients with early-stage breast cancer.

Material and methods

Menopausal female patients who were diagnosed with stages 1–3 breast cancer and who were planned for anastrazole or letrozole as adjuvant therapy were examined. After the patients’ BMD was measured, 45 patients without osteoporosis were included in the study. Six months after AI therapy started, the patients’ BMD was measured again.

Results

In this study, we tried to show that there was a statistical difference in the BMD of 45 patients before and 6 months after treatment. Among all measurements (femur and lumbar T-scores), the femur Z-score (p = 0.52) was the only score that was not statistically significant. Statistical significance (p < 0.01) was detected in comparative analysis of the other measurements. According to this analysis, a significant loss of BMD was seen even in the first six months after AI treatment was introduced.

Conclusions

Female patients with breast cancer are at higher risk for bone loss and fractures than healthy women. In this study, we showed the negative effects on BMD of aromatase inhibitor therapy, one of the main contributions to osteoporosis in women with breast cancer. This study is the first to quantify the short-term effect of AI treatment on BMD in postmenopausal women with breast cancer.

CYP19 genetic polymorphism haplotype AASA is associated with a poor prognosis in premenopausal women with lymph node-negative, hormone receptor-positive breast cancer

Given the critical role of CYP19 in estrogen synthesis, we investigated the influence of CYP19 gene polymorphisms on the clinical outcome of lymph node- (LN-) negative, hormone receptor- (HR-) positive early breast cancers. Genotyping for the CYP19 polymorphisms rs4646 (A/C), rs1065779 (A/C), CYP19 (TTTA)n (short allele/long (S/L) allele using the 7 TTTA repeat polymorphism as the cut-off), and rs1870050 (A/C) was performed on 296 patients with LN-negative, HR-positive breast cancers. All patients received adjuvant hormonal therapy. Associations were examined between these 4 genotypes and 6 common haplotypes of CYP19 and distant disease-free survival (DDFS), disease-free survival (DFS), and overall survival (OS). Patients were divided into the 6 subhaplotypes of CCLA (41.1%), AASA (17.1%), CASA (11.9%), CCLC (8.9%), CCSA (7.5%), AASC (8.9%), and others (4.6%). In premenopausal patients, haplotype AASA was significantly associated with a poor DDFS (adjusted hazard ratio (aHR), 3.3; P = 0.001), DFS (aHR, 2.5; P = 0.0008), and OS (aHR, 2.9; P = 0.0004) after adjusting for age, tumor size, tumor grade, estrogen receptor status, progesterone receptor status, chemotherapy, pathology, adjuvant hormone therapy, menopausal status, and radiotherapy. Furthermore, haplotype AASA remained a negative prognostic factor for premenopausal patients receiving adjuvant chemotherapy in terms of DDFS (aHR, 4.5; P = 0.0005), DFS (HR, 3.2; P = 0.003), and OS (HR, 6.4; P = 0.0009). However, in postmenopausal patients, haplotype AASA was not associated with a poor prognosis, whereas the AASC haplotype was significantly associated with a poor DFS (aHR, 3.1; P = 0.03) and OS (aHR, 4.4; P = 0.01). Our results indicate that, in patients with LN-negative, HR-positive breast cancers, genetic polymorphism haplotype AASA is associated with poor survival of premenopausal women but does not affect survival of postmenopausal women.

Multiple roles of COUP-TFII in cancer initiation and progression

Chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an orphan nuclear receptor that acts as a transcriptional activator or repressor in a cell type-dependent manner. Best characterized for its role in the regulation of angiogenesis during mouse development, COUP-TFII also plays important roles in glucose metabolism and cancer. Expression of COUP-TFII is altered in various endocrine conditions. Cell type-specific functions and the regulation of COUP-TFII expression result in its varying physiological and pathological actions in diverse systems. Evidence will be reviewed for oncogenic and tumor-suppressive functions of COUP-TFII, with roles in angiogenesis, metastasis, steroidogenesis, and endocrine sensitivity of breast cancer described. The applicability of current data to our understanding of the role of COUP-TFII in cancer will be discussed.

Zinc and cancer: implications for LIV-1 in breast cancer

Zinc is a trace mineral which is vital for the functioning of numerous cellular processes, is critical for growth, and may play an important role in cancer etiology and outcome. The intracellular levels of this mineral are regulated through the coordinated expression of zinc transporters, which modulate both zinc influx as well as efflux. LIV-1 (ZIP6) was first described in 1988 as an estrogen regulated gene with later work suggesting a role for this transporter in cancer growth and metastasis. Despite evidence of its potential utility as a target gene for cancer prognosis and treatment, LIV-1 has received relatively little attention, with only three prior reviews being published on this topic. Herein, the physiological effects of zinc are reviewed in light of this mineral’s role in cancer growth with specific attention being given to LIV-1 and the potential importance of this transporter to breast cancer etiology.

Melatonin suppresses aromatase expression and activity in breast cancer associated fibroblasts

The main biological active substance secreted by the pineal gland, melatonin (MLT), counteracts the effects of estrogens in breast cancer via exerting a number of its own oncostatic properties. Recent studies of postmenopausal women have identified that the major metabolite of MLT is statistically significantly associated with a lower risk of developing breast cancer. While MLT production decreases with age, breast cancer risk, however, increases with age and obesity. We hypothesize that MLT inhibits estrogen production in breast adipose fibroblasts (BAFs), the main local source of estrogen in breast tumors of postmenopausal women, by inhibiting transcription of the CYP19A1 gene that encodes the key enzyme aromatase. Normal BAFs were cultured from women undergoing breast reduction surgery, while breast cancer-associated fibroblasts (CAFs) were isolated from three women with estrogen receptor (ER) positive invasive ductal carcinomas. MTNR1A and MTNR1B receptor expression and CYP19A1 mRNA expression following MLT treatments were determined by qRT-PCR. BAFs express the G-protein coupled MLT receptors MTNR1A and MTNR1B with elevated levels of MTNR1A found in CAFs. Treatment of BAFs and CAFs with MLT resulted in significant suppression of CYP19A1 transcription and aromatase activity at pharmacological, physiological and sub-physiological concentrations. MLT suppression occurred through promoter-specific PI.4-, PI.3- and PII-derived CYP19A1 mRNA. Stimulation of CYP19A1 PII-mRNA and aromatase activity by prostaglandin E(2) (PGE(2)) were significantly attenuated by physiological doses of MLT. Lower levels of MLT in aging women may increase the risk of progressing ER-positive breast cancer through a decreased ability to suppress CYP19A1 expression and subsequent local estrogen production in BAFs/CAFs.

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'.

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.

Identification of a preneoplastic gene expression profile in tubal epithelium of BRCA1 mutation carriers

Microinvasive carcinomas and high-grade intraepithelial neoplasms are commonly discovered within the fallopian tube of BRCA1 mutation carriers at the time of risk-reducing salpingo-oophorectomy, suggesting that many BRCA1-mutated ovarian carcinomas originate in tubal epithelium. We hypothesized that changes in gene expression profiles within the histologically normal fallopian tube epithelium of BRCA1 mutation carriers would overlap with the expression profiles in BRCA1-mutated ovarian carcinomas and represent a BRCA1 preneoplastic signature. Laser capture microdissection of frozen sections was used to isolate neoplastic cells or histologically normal fallopian tube epithelium, and expression profiles were generated on Affymetrix U133 Plus 2.0 gene expression arrays. Normal-risk controls were 11 women wild type for BRCA1 and BRCA2 (WT-FT). WT-FT were compared with histologically normal fallopian tube epithelium from seven women with deleterious BRCA1 mutations who had foci of at least intraepithelial neoplasm within their fallopian tube (B1-FTocc). WT-FT samples were also compared with 12 BRCA1 ovarian carcinomas (B1-CA). The comparison of WT-FT versus B1-FTocc resulted in 152 differentially expressed probe sets, and the comparison of WT-FT versus B1-CA resulted in 4079 differentially expressed probe sets. The BRCA1 preneoplastic signature was composed of the overlap between these two lists, which included 41 concordant probe sets. Genes in the BRCA1 preneoplastic signature included several known tumor suppressor genes such as CDKN1C and EFEMP1 and several thought to be important in invasion and metastasis such as E2F3. The expression of a subset of genes was validated with quantitative reverse transcription-polymerase chain reaction and immunohistochemistry.

Aromatase inhibitor-associated bone and musculoskeletal effects: new evidence defining etiology and strategies for management

Aromatase inhibitors are widely used as adjuvant therapy in postmenopausal women with hormone receptor-positive breast cancer. While the agents are associated with slightly improved survival outcomes when compared to tamoxifen alone, bone and musculoskeletal side effects are substantial and often lead to discontinuation of therapy. Ideally, the symptoms should be prevented or adequately treated. This review will focus on bone and musculoskeletal side effects of aromatase inhibitors, including osteoporosis, fractures, and arthralgias. Recent advances have been made in identifying potential mechanisms underlying these effects. Adequate management of symptoms may enhance patient adherence to therapy, thereby improving breast cancer-related outcomes.

Intrauterine growth restriction alters hippocampal expression and chromatin structure of Cyp19a1 variants

We evaluated the impact of uteroplacental insufficiency (UPI), and subsequent intrauterine growth restriction (IUGR), on serum testosterone and hippocampal expression of Cyp19a1 variants and aromatase in rats. Additionally, we determined UPI induced histone modification of the promoter regions of Cyp19a1 variants using chromatin immunoprecipitation. Cyp19a1 is the gene encoding the protein aromatase, that catalyzes the biosynthesis of estrogens from androgens and is necessary for masculinization of the brain. IUGR was induced via bilateral uterine artery. UPI increased serum testosterone in day of life 0 (D(0)) and day of life 21 (D(21)) IUGR males to 224% and 299% of control values, respectively. While there was no significant impact of UPI on testosterone in D(0) females, testosterone in D(21) IUGR females was 187% of controls. Cyp19a1 variant 1.f and variant II are expressed in the rat hippocampus at D(0) and D(21). UPI significantly reduced expression of Cyp19a1 variant 1.f in D(0) males, with no impact in females. Similarly at D(0), UPI reduced expression of aromatase, the protein encoded by Cyp19a1, in males. Dimethylation of H3K4 was increased in the promoter region of variant 1.f (P1.f) and trimethylation of H3K4 was decreased in the promoter region of variant II (PII). At D(21), dimethylation of H3K4 is significantly reduced in PII of IUGR males. We conclude that UPI increases serum testosterone and reduces Cyp19a1 variant 1.f expression in the hippocampus of D(0) IUGR males. Additionally, UPI alters the chromatin structure of CYP19a1 at both D(0) and D(21).

Insulin-like growth factor I enhances the expression of aromatase P450 by inhibiting autophagy

Aromatase, a key enzyme of estrogen biosynthesis, is transcriptionally regulated by many growth factors. IGF-I enhances aromatase activity in a variety of cells, but the mechanism of action has not been determined. We herein report our finding of a novel mechanism of action for IGF-I. IGF-I enhanced the dexamethasone (DEX)-induced aromatase activity by 30% in serum-starved THP-1 cells. The increase was associated with a corresponding increase in the level of aromatase protein but not with any change in the mRNA level. Metabolic labeling experiments revealed that IGF-I inhibited the degradation of aromatase. We identified pepstatin A as the most effective inhibitor of aromatase degradation by in vitro assay. Using a nontoxic concentration of pepstatin A, we examined IGF-I's action on aromatase distribution in microsomes and lysosomes. In the presence of pepstatin A, DEX caused an increase in the amount of aromatase in both microsomes and lysosomes, and IGF-I attenuated the DEX-induced accumulation of aromatase in lysosomes and, conversely, enhanced its accumulation in the microsomes. The addition of serum abolished the IGF-I-induced changes. The transport from microsome to lysosome was fluorescently traced in cells using a recombinant aromatase. IGF-I selectively reduced the aromatase signal in the lysosomes. Finally, we observed that IGF-I enhanced the aromatase activity by 50% as early as 1 h after treatment; furthermore, rapamycin, an enhancer of autophagy, completely negated the effect of IGF-I on the enzyme. These results indicate that IGF-I enhances aromatase by the inhibition of autophagy.

Common variations in estrogen-related genes are associated with severe large-joint osteoarthritis: a multicenter genetic and functional study

OBJECTIVE

Several lines of evidence suggest that estrogens influence the development of osteoarthritis (OA). The aim of this study was to explore the association of two common polymorphisms within the aromatase (CYP19A1) and estrogen receptor (ER) alpha (ESR1) genes with severe OA of the lower limbs.

METHODS

The rs1062033 (CYP19A1) and rs2234693 (ESR1) single nucleotide polymorphisms were genotyped in 5528 individuals (3147 patients with severe hip or knee OA, and 2381 controls) from four centres in Spain and the United Kingdom. Gene expression was measured in femoral bone samples from a group of patients.

RESULTS

In the global analysis, both polymorphisms were associated with OA, but there was a significant sex interaction. The GG genotype at rs1062033 was associated with an increased risk of knee OA in women [odds ratio (OR) 1.23; P=0.04]. The CC genotype at rs2234693 tended to be associated with reduced OA risk in women (OR 0.76, P=0.028, for knee OA; OR=0.84, P=0.076 for hip OA), but with increased risk of hip OA in men (OR 1.28; P=0.029). Women with unfavourable genotypes at both loci had an OR of 1.61 for knee OA (P=0.006). The rs1062033 genotype associated with higher OA risk was also associated with reduced expression of the aromatase gene in bone.

CONCLUSIONS

Common genetic variations of the aromatase and ER genes are associated with the risk of severe OA of the large joints of the lower limb in a sex-specific manner. These results are consistent with the hypothesis that estrogen activity may influence the development of large-joint OA.

Hormonal deprivation therapy-induced osteoporosis in postmenopausal women with breast cancer

Aromatase inhibitor (AI) therapy significantly increases the disease-free survival in postmenopausal patients with hormone receptor-positive breast cancer. AIs are potent inhibitors of oestradiol production. Large adjuvant trials showed that the third-generation AIs (i.e., anastrozole, letrozole and exemestane) are risk factors for an increased bone loss, and are associated with an increase in the risk of fractures in women with bone fragility. A comprehensive assessment of risk of fractures must be performed at the initiation of an AI therapy. Antiresorptive drugs (i.e., bisphosphonates and denosumab) are effective for bone loss prevention and treatment in these patients.

Tissue estradiol is selectively elevated in receptor positive breast cancers while tumour estrone is reduced independent of receptor status

Previous studies have suggested elevated estrogen production in tumour-bearing breast quadrants as well as in breast cancers versus benign tissue. Using highly sensitive assays, we determined breast cancer tissue estrogen concentrations together with plasma and benign tissue estrogen concentrations in each quadrant obtained from mastectomy specimens (34 postmenopausal and 13 premenopausal women). We detected similar concentrations of each of the three major estrogens estradiol (E(2)), estrone (E(1)) and E(1)S in tumour-bearing versus non-tumour-bearing quadrants. Considering malignant tumours, intratumour E(1) levels were reduced in cancer tissue obtained from pre- as well as postmenopausal women independent of tumour ER status (average ratio E(1) cancer: benign tissue of 0.2 and 0.3, respectively; p<0.001 for both groups), suggesting intratumour aromatization to be of minor importance. The most striking finding was a significant (4.1-8.6-fold) increased E(2) concentration in ER positive tumours versus normal tissue (p<0.05 and <0.001 for pre- and postmenopausal patients, respectively), contrasting low E(2) concentrations in ER- tumours (p<0.01 and <0.001 comparing E(2) levels between ER+ and ER- tumours in pre- and postmenopausals, respectively). A possible explanation to our finding is increased ligand receptor binding capacity for E(2) in receptor positive tumours but alternative factors influencing intratumour estrogen disposition cannot be excluded.

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.

The alternative noncoding exons 1 of aromatase (Cyp19) gene modulate gene expression in a posttranscriptional manner

Aromatase (Cyp19) is a key enzyme in estrogen biosynthesis and an important target in endocrine therapy for estrogen receptor (ER)-positive postmenopausal breast cancer. Aromatase transcription is driven by multiple tissue-specific promoters, which result in the production of various mRNA transcripts that contain an alternative noncoding exon 1 followed by a common protein-coding region. Transcriptional activity of these promoters is the only known determinant for aromatase protein abundance in a given tissue or cellular context. To determine whether aromatase expression could be influenced by additional regulatory mechanisms, we used a common heterologous promoter to drive the expression of multiple aromatase cDNA sequences that differ only by the alternative exon 1 sequence. These expression vectors gave rise to vastly different levels of aromatase mRNA and protein in multiple cell lines examined. Furthermore, the relative abundance of several mRNA variants did not correlate with that of the corresponding protein product. The variation in mRNA and protein levels is most likely due to a negative effect of certain alternative exons 1 on RNA stability and protein translation. Deletional analyses indicate that the 5' regions of the adipose tissue-specific exons I.3 and I.4 contain the cis-acting elements responsible for modulation of aromatase levels. Thus, our work uncovers an important role of the alternative exons 1 in posttranscriptional regulation of aromatase gene expression.

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.

Cellular targets of estrogen signaling in regeneration of inner ear sensory epithelia

Estrogen signaling in auditory and vestibular sensory epithelia is a newly emerging focus propelled by the role of estrogen signaling in many other proliferative systems. Understanding the pathways with which estrogen interacts can provide a means to identify how estrogen may modulate proliferative signaling in inner ear sensory epithelia. Reviewed herein are two signaling families, EGF and TGFbeta. Both pathways are involved in regulating proliferation of supporting cells in mature vestibular sensory epithelia and have well characterized interactions with estrogen signaling in other systems. It is becoming increasingly clear that elucidating the complexity of signaling in regeneration will be necessary for development of therapeutics that can initiate regeneration and prevent progression to a pathogenic state.

IKKbeta mediates cell shape-induced aromatase expression and estrogen biosynthesis in adipose stromal cells

Aromatase (Cyp19) is a key enzyme in estrogen biosynthesis and an important target in breast cancer therapy. Within tumor microenvironment, tumor cells stimulate aromatase expression in adipose stromal cells (ASCs), which in turn promotes estrogen-dependent growth of estrogen receptor (ER)-positive tumor cells. However, it is not clear how aromatase transcription and estrogen biosynthesis are regulated in ASCs under a precancerous condition. Here we demonstrate that cell shape change alone is sufficient to induce aromatase expression in primary ASCs from cancer-free individuals. The activation of aromatase transcription is mediated by IkappaB kinase-beta (IKKbeta), a kinase previously known for its cancer-promoting activity in tumor cells. Activation of IKKbeta leads to elevated expression of transcription factor CCAAT/enhancer-binding protein-beta (C/EBPbeta), which binds to and stimulates two breast cancer-associated promoters of the aromatase gene. We also show that shape-induced estrogen production in ASCs can stimulate estrogen-dependent transcription in ER-positive breast tumor cells. We suggest that IKKbeta-dependent aromatase induction due to changes in cellular architecture in adipose tissue may contribute to the breast cancer risks associated with high mammagraphic density and obesity.

Lack of complete cross-resistance between different aromatase inhibitors; a real finding in search for an explanation?

While third-generation aromatase inhibitors (anastrozole, letrozole and exemestane) are successfully implemented as adjuvant and first-line therapy for hormone-sensitive breast cancer in postmenopausal women, important questions remain to be addressed. An issue of particular interest is the question about lack of complete cross-resistance between steroidal and non-steroidal compounds. Although the studies reporting this phenomenon in general contain a small number of patients, the findings across the different reports seem consistent. While several potential mechanisms have been suggested, so far we lack scientific proof what mechanisms may be responsible for this finding. Finally, we do not know whether lack of cross-resistance actually signals an improved efficacy for certain compounds or may be due to alternative mechanisms of action. Neither do we know whether some tumours are more sensitive to particular drugs. This paper summarizes clinical findings up to now with respect to lack of cross-resistance and discuss potential mechanisms involved.

The expression and ovarian steroid regulation of endometrial micro-RNAs

MicroRNAs (miRNAs) which regulate gene expression stability displayed an aberrant expression profile in ectopic endometrium (ECE) as compared to eutopic (EUE) and normal endometrium (NE). We assessed the expression of miR-17-5p, miR-23a, miR-23b and miR-542-3p, their predicted target genes, steroidogenic acute regulatory protein, aromatase and cyclooxygenase-2, and influence of ovarian steroids on their expression in endometrial stromal (ESC) and glandular epithelial cells (GEC). The results indicated a lower expression of miR-23b and miR-542-3p and higher level of miR-17-5p in paired ECE and EUE as compared with NE. These levels were elevated and inversely correlated with the level of expression of their respective target genes in ECE. The expression of these miRNAs and genes was differentially regulated by 17beta- estradiol, medroxyprogesterone acetate, ICI-182780 and RU-486, or their respective combinations in ESC and GEC. We concluded that altered expression of specific miRNAs in ECE, affecting the stability of their target genes expression, has direct implications in pathogenesis of endometriosis.

Aromatase inhibitors in ovarian cancer: is there a role?

Estrogen plays a role in ovarian tumorigenesis. Aromatase is the enzyme required for the synthesis of estrogen via conversion of androgen to estrogen, which is the major source of estrogen in postmenopausal women. Aromatase is present in normal ovaries and other tissues (e.g., fat and muscle) as well as in 33-81% tumor tissues of ovarian cancer. Aromatase inhibitors (AIs) block estrogen synthesis by inhibiting aromatase activity. In patients with recurrent ovarian cancer, single-agent AI therapy has been shown to elicit clinical response rates of up to 35.7% and stable disease rates of 20-42%. Given the limited treatment options for recurrent ovarian cancer and the favorable safety profile and convenient use, AI is a rational option for prolonging platinum-free interval in recurrent ovarian cancer. Further studies are required to determine the efficacy of combination treatment with AIs and biological agents, determine the benefit of AIs for treating special types of ovarian cancer (e.g., endometrioid type), and identify biomarkers for targeted patient selection. This review summarizes the current epidemiologic, preclinical, and clinical data regarding estrogen's role in ovarian cancer, the expression and regulation of aromatase in this disease, the development and characteristics of the three generations of AIs, and the preclinical and clinical studies of AIs in the treatment of ovarian cancer.

EP2 and EP4 receptors regulate aromatase expression in human adipocytes and breast cancer cells. Evidence of a BRCA1 and p300 exchange

Cytochrome P450 aromatase (aromatase), a product of the CYP19 gene, catalyzes the synthesis of estrogens from androgens. Because aromatase-dependent estrogen biosynthesis has been linked to hormone-dependent breast carcinogenesis, it is important to elucidate the mechanisms that regulate CYP19 gene expression. The main objective of this study was to identify the receptors (EP) for prostaglandin E(2) (PGE(2)) that mediate the induction of CYP19 transcription in human adipocytes and breast cancer cells. Treatment with PGE(2) induced aromatase, an effect that was mimicked by either EP(2) or EP(4) agonists. Antagonists of EP(2) or EP(4) or small interference RNA-mediated down-regulation of these receptors suppressed PGE(2)-mediated induction of aromatase. PGE(2) via EP(2) and EP(4) stimulated the cAMP-->protein kinase A pathway resulting in enhanced interaction between P-CREB, p300, and the aromatase promoter I.3/II. Overexpressing a mutant form of p300 that lacks histone acetyltransferase activity suppressed PGE(2)-mediated induction of aromatase promoter activity. PGE(2) via EP(2) and EP(4) also caused a reduction in both the amounts of BRCA1 and the interaction between BRCA1 and the aromatase promoter I.3/II. Activation of the aromatase promoter by PGE(2) was suppressed by overexpressing wild-type BRCA1. Silencing of EP(2) or EP(4) also blocked PGE(2)-mediated induction of the progesterone receptor, a prototypic estrogen-response gene. In a mouse model, overexpressing COX-2 in the mammary gland, a known inducer of PGE(2) synthesis, led to increased aromatase mRNA and activity and reduced amounts of BRCA1; these effects were reversed by knocking out EP(2). Taken together, these results suggest that PGE(2) via EP(2) and EP(4) activates the cAMP-->PKA-->CREB pathway leading to enhanced CYP19 transcription and increased aromatase activity. Reciprocal changes in the interaction between BRCA1, p300, and the aromatase promoter I.3/II contributed to the inductive effects of PGE(2).

Aromatase inhibitors: assessment of biochemical efficacy measured by total body aromatase inhibition and tissue estrogen suppression

The implementation of aromatase inhibitors for treatment of early and metastatic breast cancer has been one of the major improvements in endocrine therapy of breast cancer. Measurement of endocrine effects of aromatase inhibition in vivo has been a major tool in the process of evaluating novel compounds. Biochemical efficacy of aromatase inhibitors in vivo may be determined from their effects on "total body aromatization" as well changes in plasma and tissue estrogen levels. Due to high sensitivity, tracer methods allowing calculation of whole body aromatase inhibition are still considered the gold standard. The method developed by our group in collaboration with the Royal Marsden Hospital and the results of this joint program are summarized and discussed. These studies allowed classification of the different aromatase inhibitors and their optimal dosage, selecting the best compounds for clinical evaluation. In vivo total body aromatase assessment is a work-consuming method, allowing such studies to be conducted in a limited number of patients only. In contrast, plasma estrogen measurement is a cruder but simpler method, allowing screening of larger groups of patients. As plasma estrogens arise through passive diffusion of estrogens synthesized in different body compartments, plasma estrogens, as well as total body aromatase assessment, present a rough estimate of total body tissue estrogen production, and changes associated with treatment with aromatase inhibitors reflect the effects on tissue estrogen production in general. However, plasma estrogen levels do not correlate to breast cancer tissue estrogen levels. This is due to the endocrine autonomy of breast cancer tissue with significant local estrogen production in some tumors. Thus, direct measurement of intratumor estrogens is demanded to evaluate the effects of aromatase inhibitors in malignant target tissues. Our group has developed a highly sensitive HPLC-RIA for the simultaneous measurement of estrone, estradiol, and estrone sulfate in malignant breast tissue samples, and we are currently using this method to assess alterations in intratumor estrogen levels during treatment with different aromatase inhibitors.

Breast cancer prognostication and prediction in the postgenomic era

Expanding knowledge, together with implementation of new techniques, has fuelled the area of translational medical research aiming at improving prognostication as well as prediction in cancer therapy. At the same time, new discoveries have revealed a biological complexity we were unaware of only a decade ago. Thus, we are faced with novel challenges with respect to how we may explore issues such as prognostication and predict drug resistance in vivo. While microarray analysis exploring expression of thousands of genes in concert represents a major methodological advancement, discoveries such as the finding of different mechanisms of epigenetic silencing, intronic mutations, that most gene transcripts in the human genome are subject to alternative splicing and that hypersplicing seems to be a tumour-related phenomenon, exemplifies a complex pathology that may not be explored with use of single analytical methods only. This paper discusses clinical settings for studying drug resistance in vivo together with a discussion of contemporary biology in this field. Notably, each individual parameter which has been found correlated to drug resistance in vivo so far represents either a direct drug target or a factor involved in DNA repair or apoptosis. On the basis of these findings, we suggest drug resistance may be explored on the basis of upfront biological hypotheses.

Human SLUG does not directly bind to CtBP1

SLUG is a transcriptional repressor protein implicated to have major role in the oncogenesis and metastasis of human breast cells. We previously have shown by chromatin immunoprecipitation assay that human SLUG (hSLUG) is co-localized with the co-repressor protein CtBP1 as bound to the BRCA2 gene silencer [M.K. Tripathi, S. Misra, S.V. Khedkar, N. Hamilton, C. Irvin-Wilson,, C. Sharan, L. Sealy, G. Chaudhuri, J. Biol. Chem. 280 (2005) 17163-17171]. hSLUG was predicted to be binding directly to CtBP1 because of an apparent presence of CtBP1 binding site in its amino acid sequences. Here, we provide evidence through yeast two-hybrid and in vitro co-immunoprecipitation analyses that hSLUG does not directly interacts with hCtBP1. This observation will help in the study of the mode of action of hSLUG in human cells.

Aromatase destabilizer: novel action of exemestane, a food and drug administration-approved aromatase inhibitor

Using Western blot as the major technique, we studied the effects of the three Food and Drug Administration (FDA)-approved aromatase inhibitors (AI) on aromatase protein stability in the aromatase-overexpressing breast cancer cell line MCF-7aro. We have found that exemestane treatment significantly reduces aromatase protein level. Exemestane induces aromatase degradation in a dose-responsive manner (25-200 nmol/L), and the effect can be seen in as early as 2 hours. Metabolic labeling with S(35)-methionine was used to determine the half-life (t(1/2)) of aromatase protein. In the presence of 200 nmol/L exemestane, the t(1/2) of aromatase was reduced to 12.5 hours from 28.2 hours in the untreated cells. Furthermore, exemestane-induced aromatase degradation can be completely blocked by 10 micromol/L MG132, indicating that the degradation is mediated by proteasome. We also examined the effect of exemestane on aromatase mRNA level using real-time reverse transcription-PCR. No significant changes in mRNA level were detected after 8 hours of treatment with exemestane (200 nmol/L). This is the first report on the evaluation of three FDA-approved AIs on the stability of the aromatase protein. We have found that exemestane, different from letrozole and anastrozole, can destabilize the aromatase protein.

Novel sulfonanilide analogues suppress aromatase expression and activity in breast cancer cells independent of COX-2 inhibition

Aromatase is a particularly attractive target in the treatment of estrogen receptor positive breast cancer. Aromatase levels in breast cancer cells are enhanced by prostaglandins and reduced by COX inhibitors. The synthesis and biological evaluation of a novel series of sulfonanilide analogues derived from the COX-2 selective inhibitor NS-398 are described. The compounds suppress aromatase enzyme activity in SK-BR-3 breast cancer cells in a dose- and time-dependent manner. The effect of these compounds on COX-2 inhibition is investigated in breast cancer cells as well. Structure-activity analysis does not find a correlation between aromatase suppression and COX-2 inhibition. Microsomal aromatase inhibition studies rule out the possibility of direct enzyme inhibition. Real-time PCR analysis demonstrates that the sulfonanilide analogues decrease aromatase gene transcription in SK-BR-3 cells. These studies suggest that the novel sulfonanilide compounds suppress aromatase activity and transcription in SK-BR-3 breast cancer cells independent of COX-2 inhibition.