CCAAT/enhancer binding protein delta up-regulates aromatase promoters I.3/II in breast cancer epithelial cells

Basic biology and roles of CEBPD in cardiovascular disease

CCAAT/enhancer-binding protein delta (CEBPD), as an evolutionarily conserved protein in mammals, belongs to the CEBP transcription factor family, which modulates many biological processes. The diversity of CEBPD functions partly depends on the cell type and cellular context. Aberrant CEBPD expression and activity are associated with multiple organ diseases, including cardiovascular diseases. In this review, we describe the basic molecular biology of CEBPD to understand its expression regulation, modifications, and functions. Here, we summarize the recent advances in genetically modified animals with CEBPD. Finally, we discuss the contribution of CEBPD to cardiovascular diseases and highlight the strategies for developing novel therapies targeting CEBPD.

19-hydroxy Steroids in the Aromatase Reaction: Review on Expression and Potential Functions

Scientific evidence related to the aromatase reaction in various biological processes spanning from mid-1960 to today is abundant; however, as our analytical sensitivity increases, a new look at the old chemical reaction is necessary. Here, we review an irreversible aromatase reaction from the substrate androstenedione. It proceeds in 3 consecutive steps. In the first 2 steps, 19-hydroxy steroids are produced. In the third step, estrone is produced. They can dissociate from the enzyme complex and either accumulate in tissues or enter the blood.

In this review, we want to highlight the potential importance of these 19-hydroxy steroids in various physiological and pathological conditions. We focus primarily on 19-hydroxy steroids, and in particular on the 19-hydroxyandrostenedione produced by the incomplete aromatase reaction. Using a PubMed database and the search term “aromatase reaction,” 19-hydroxylation of androgens and steroid measurements, we detail the chemistry of the aromatase reaction and list previous and current methods used to measure 19-hydroxy steroids.

We present evidence of the existence of 19-hydroxy steroids in brain tissue, ovaries, testes, adrenal glands, prostate cancer, as well as during pregnancy and parturition and in Cushing’s disease. Based on the available literature, a potential involvement of 19-hydroxy steroids in the brain differentiation process, sperm motility, ovarian function, and hypertension is suggested and warrants future research.

We hope that with the advancement of highly specific and sensitive analytical methods, future research into 19-hydroxy steroids will be encouraged, as much remains to be learned and discovered.

Regulation of aromatase expression: Potential therapeutic insight into breast cancer treatment

Estrogen signaling has been implicated in hormone-dependent breast cancer which constitutes >75% of breast cancer diagnosis and other malignancies. Aromatase, the key enzyme involved in the synthesis of estrogen, is often dysregulated in breast cancers. This has led to the administration of aromatase-inhibitors (AIs), commonly used for hormone-dependent breast cancers. Unfortunately, the increasing development of acquired resistance to the current AIs and modulators of estrogen receptors, following initial disease steadiness, has posed a serious clinical challenge in breast cancer treatment. In this review we highlight historical and recent advances on the transcriptional and post-translational regulation of aromatase in both physiological and pathological contexts. We also discuss the different drug combinations targeting various tumor promoting cell signaling pathways currently being developed and tested both in laboratory settings and in the clinic.

Let-7g inhibits synthesis of estradiol by downregulating activity of aromatase in JEG3 cells

BACKGROUND

Increased production of estrogen in human placenta during pregnancy closely associates with parturition. Aromatase, encoded by CYP19A1 gene, is an enzyme critical for biosynthesis of estrogen. Despite numerous efforts in the past few decades ascribed to characterizing the mechanisms of transcriptional control of aromatase, the posttranscriptional control of CYP19A1 remains poorly understood.

OBJECTIVE

In this study, we sought to investigate the role of microRNA, let-7g, in posttranscriptional regulation of aromatase in human trophoblast choriocarcinoma cell line, JEG3.

METHODS AND RESULTS

We show that the expression of let-7g was downregulated in JEG3 cell line, but upregulated in primary term trophoblast; conversely, aromatase was upregulated in JEG3 but downregulated in primary trophoblast. We further show that let-7g antagomirs and mimics increased and decreased aromatase expression, respectively; and let-7g directly targeted 3'-untranslated region of CYP19A1 mRNA by using dual luciferase assay. Using ELISA, we also demonstrate that let-7g antagomirs and mimics robustly increased and decreased production of estradiol, respectively.

DISCUSSION

Our results suggest that aromatase expression is regulated at multiple molecular layers in the placenta. These results further suggest that JEG3 cell line is a valuable tool to study additional mechanisms associated with human birth.

Peroxisome proliferator-activated receptor gamma, coactivator 1α enhances local estrogen biosynthesis by stimulating aromatase activity in endometriosis

CONTEXT

Endometriosis is an estrogen-dependent disease, and estrogen is overproduced by abnormally elevated aromatase in endometriotic tissues. Peroxisome proliferator-activated receptor gamma, coactivator 1α (PGC-1α) is a transcriptional coactivator-modulating steroid hormone.

OBJECTIVE

To investigate the effect of PGC-1α on aromatase activity in endometriosis.

DESIGN

Specimens from ovarian endometrioma (OE), endometrium with endometriosis (EE), and normal endometrium (NE) were analyzed for PGC-1α and aromatase expression. PGC-1α-dependent changes in aromatase expression in primary cultured stromal cells (SCs) were identified using luciferase and enzymatic assays, exon I-specific RT-PCR, and real-time PCR. Environmental stimulus-induced changes in PGC-1α were also examined.

RESULTS

PGC-1α was more highly expressed in OE than in EE and NE (P < .01). In OE, PGC-1α was coexpressed with aromatase, and their mRNA expressions were also correlated (r = 0.56, P = .02). PGC-1α was recruited to the nuclear receptor half-site between PI.3 and PII in the aromatase promoter. PGC-1α overexpression enhanced aromatase promoter activity (P < .01), mRNA expression (P < .05), and enzymatic activity (P < .01) in SCs from OE, but not in SCs from EE or NE. The levels of PI.3, PII, and exon II mRNA increased and transcriptional enhancement was abolished by mutation of the PGC-1α-interacting site. PGC-1α expression was enhanced in SCs from OE by tumor necrosis factor (TNF)-α (P < .05) but not by hypoxia or 17β-estradiol.

CONCLUSIONS

PGC-1α stimulated by TNF-α regulates aromatase expression and activity to promote local estrogen biosynthesis in OE, suggesting that PGC-1α is a promising candidate for novel targeted therapies in endometriosis treatment.

CYP19 expression is induced by 2,3,7,8-tetrachloro-dibenzo-para-dioxin in human glioma cells

Dioxins are the most concerned environmental pollutants. Recent studies have shown that these compounds could disrupt the proper functioning of our endocrine system. Estrogen is synthesized in glial cells of the brain. The hormone has been linked to the maintenance of normal brain operation, ranging from neurotransmission to synapse formation. Aromatase or CYP19 is the enzyme responsible for estrogen synthesis. In the present study, we demonstrated that 2,3,7,8-tetrachloro-dibenzo-para-dioxin (TCDD) stimulated the enzyme activity in human brain cells as low as 1pM. Increased brain-specific CYP19 mRNA species was also observed in these cells. Since the brain-specific promoter I.f of CYP19 contains two binding motifs for CCAAT/enhancer binding protein, electrophoretic mobility shift assay was performed to validate the activation. We further traced the triggering signal and found that the mitogen-activated protein kinases ERK-1/2 were activated. In summary, TCDD could induce CYP19 transcription in brain cells. Exposure to the pollutant might perturb the hormonal balance in the brain.

Methylseleninic acid is a novel suppressor of aromatase expression

Elevated circulating estrogen levels, as a result of increased peripheral aromatization of androgens by aromatase, have been indicated to underlie the association between obesity and a higher risk of breast cancer in postmenopausal women. Although aromatase inhibitors have been used as a first-line therapy for estrogen receptor-positive breast cancer in postmenopausal women, their potential as breast cancer chemopreventive agents has been limited due to toxicities and high costs. It is therefore imperative to develop new aromatase-inhibiting/suppressing agents with lower toxicities and lower costs for breast cancer chemoprevention, especially in obese postmenopausal women. The expression of the aromatase gene, CYP19, is controlled in a tissue-specific manner by the alternate use of different promoters. In obese postmenopausal women, increased peripheral aromatase is primarily attributed to the activity of the glucocorticoid-stimulated promoter, PI.4, and the cAMP-stimulated promoter, PII. In the present study, we show that methylseleninic acid (MSA), a second-generation selenium compound, can effectively suppress aromatase activation by dexamethasone, a synthetic glucocorticoid, and forskolin, a specific activator of adenylate cyclase. Unlike the action of aromatase inhibitors, MSA suppression of aromatase activation is not mediated via direct inhibition of aromatase enzymatic activity. Rather, it is attributable to a marked downregulation of promoters PI.4- and PII-specific aromatase mRNA expression, and thereby a reduction of aromatase protein. Considering the low-cost and low-toxicity nature of MSA, our findings provide a strong rationale for the further development of MSA as a breast cancer chemopreventive agent for obese postmenopausal women.

Dietary flavones and flavonones display differential effects on aromatase (CYP19) transcription in the breast cancer cells MCF-7

Aromatase or cytochrome P450 (CYP19) enzyme catalyzes the rate-determining reaction in estrogen synthesis. Inhibiting aromatase is a major strategy in treating breast cancer patients. However, suppression on the transcriptional activity may be equally important in controlling aromatase. Dietary flavones and flavonones have been previously demonstrated to be the most potent aromatase-inhibitory flavonoids. In the present study we examined their effects on the transcription regulation of CYP19 in MCF-7 cells. Real-time PCR results indicated that luteolin suppressed CYP19 mRNA expression while hesperetin increased it. Reporter gene assays were employed to look into the transactivity of CYP19 driven by promoters I.3 and II, and the result was consistent with the observation in mRNA expression. Further investigation using truncation reporter gene and electrophoretic mobility shift assays suggested that luteolin and hesperetin differentially influenced AP-1- and C/EBP-binding on the CYP19 promoter. Western blot analysis indicated that signaling transduction pathways involving JNK and ERK could be the underlying mechanisms for their actions. The present study showed that dietary flavones and flavonones might differentially regulate aromatase transcription in breast cells in addition to the inhibition at the enzyme level.

Epigenetic mechanisms regulating CYP19 transcription in human breast adipose fibroblasts

Cytochrome aromatase p450, encoded by the gene CYP19, catalyzes the synthesis of estrogens from androgens. In post-menopausal women, adipose becomes the major site for estrogen production, where basal CYP19 transcription is driven by distal promoter I.4. In breast adipose fibroblasts (BAFs), CYP19 expression is elevated in the presence of tumour-derived factors through use of promoters I.3 and II. We show for the first time that DNA methylation contributes to CYP19 regulation in BAFs and breast cell lines. Promoter I.4 and I.3/II-derived mRNA were not dependent on the CpG methylation status within respective promoters. However, inhibition of DNA methylation with 5-aza-2'-deoxycytidine resulted in a significant approximately 40-fold induction in CYP19 mRNA expression in BAFs and breast cell lines. These studies uncover a new layer of complexity in the regulation of aromatase where CYP19 appears to be inhibited by DNA methylation and evokes the possibility that disruption to this epigenetic regulation may give rise to an increase in aromatase levels in the breast.

The HDAC inhibitor LBH589 (panobinostat) is an inhibitory modulator of aromatase gene expression

Aromatase converts androgens to estrogens. Although third-generation aromatase inhibitors (AIs) are important drugs in hormonal therapy for breast cancer in postmenopausal women, there are concerns about the side effects associated with the estrogen deprivation achieved with AIs. Expression of aromatase in breast cancer tissue is driven by different promoters than those in noncancer tissues; thus, suppression of aromatase expression in cancer tissues through the down-regulation of breast tumor-specific promoters would reduce the side effects associated with whole-body suppression of estrogen biosynthesis by AIs. We report that histone deacetylase inhibitor LBH589 (panobinostat) is a potent inhibitor of aromatase expression (with an IC(50) value < 25 nM). LBH589 selectively suppresses human aromatase gene promoters I.3/II, which are preferentially used in breast cancer tissue. Furthermore, using the H295R cell culture model, we found that achieving the same degree of inhibition of aromatase activity required only one-fifth as much letrozole (an AI) in the presence of 25 nM LBH589 as in the absence of LBH589. We also used an H295R/MCF7 coculture model to demonstrate the synergistic interaction of LBH589 + letrozole in suppressing the proliferation of hormone-responsive breast cancer cells. Finally, our results also indicate that LBH589 down-regulates the activity of promoters I.3/II in an epigenetic fashion. LBH589 reduces the levels of C/EBPdelta, decreases the binding of C/EBPdelta, and increases the levels and binding of acetyl-histones to the promoters I.3/II. These findings provide an important basis for future clinical evaluations of LBH589 in hormone-dependent breast cancer.

Aromatase expression is increased in BRCA1 mutation carriers

BACKGROUND

Until recently, the molecular mechanisms explaining increased incidence of ovarian and breast cancers in carriers of BRCA1 gene mutations had not been clearly understood. Of significance is the finding that BRCA1 negatively regulates aromatase expression in vitro. Our objective was to characterise aromatase gene (CYP19A1) and its promoter expression in breast adipose and ovarian tissue in BRCA1 mutation carriers and unaffected controls.

METHODS

We measured aromatase transcripts, total and promoter-specific (PII, PI.3, PI.4) in prophylactic oophorectomy or mastectomy, therapeutic mastectomy, ovarian and breast tissue from unaffected women.

RESULTS

We demonstrate that the lack of functional BRCA1 protein correlates to higher aromatase levels in 85% of BRCA1 mutation carriers. This increase is mediated by aberrant transcriptional regulation of aromatase; in breast adipose by increases in promoter II/I.3 and I.4-specific transcripts; and in the ovary with elevation in promoter I.3 and II-specific transcripts.

CONCLUSION

Understanding the link between BRCA1 and aromatase is significant in terms of understanding why carcinogenesis is restricted to estrogen-producing tissues in BRCA1 mutation carriers.

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.

Dietary administration of the licorice flavonoid isoliquiritigenin deters the growth of MCF-7 cells overexpressing aromatase

Licorice is the sweet-tasting rhizomes of a bean plant and is quite commonly used in Western countries for culinary purposes, while it is a medicinal herb in China. Many flavonoids have been isolated from licorice, and their pharmacological properties may be applicable in preventive medicine. Overexposure to estrogen has been implicated in the etiology of breast cancer, and cytochrome P450 (CYP) 19 enzyme, or aromatase, catalyzes the rate-limiting reaction. Phytocompounds that are able to inhibit this enzyme may potentially suppress breast cancer development. In the present study the licorice flavonoid isoliquiritigenin (ILN) was shown to be an aromatase inhibitor in recombinant protein and MCF-7 cells stably transfected with CYP19 (MCF-7aro). ILN displayed a K(i) value of around 3 muM, and it also blocked the MCF-7aro cell growth pertaining to the enzyme activity in vitro. Subsequently, the compound administered in diet was given to ovariectomized athymic mice transplanted with MCF-7aro cells. This mouse model is widely accepted for studying postmenopausal breast cancer. The phytochemical significantly deterred the xenograft growth without affecting the body weight. Subsequently, the flavonoid's effect on CYP19 transcriptional control in vitro was also investigated. At the mRNA level, ILN could also suppress the expression in wild-type MCF-7 cells. Reporter gene assay and real-time PCR verified that the transactivity of CYP19 driven by promoters I.3 and II was suppressed in these cells. Deactivation of C/EBP could be the underlying molecular mechanism. Our study demonstrated that ILN was an inhibitor of aromatase and a potential chemopreventive agent against breast cancer.