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Abstract: Paracrine interactions between adipose fibroblasts and malignant epithelial cells are essential for structural and hormonal support of breast tumors. Factors derived from malignant epithelial cells inhibit adipogenic differentiation of fibroblasts and upregulate expression of aromatase, which stimulates estrogen synthesis and creates a localized, growth-stimulatory environment. Here, we characterized the gene expression profile of breast adipose fibroblasts in an in vitro model of malignancy to identify other paracrine interactions that support tumor growth. Primary breast adipose fibroblasts from cancer-free women were treated with conditioned media from malignant breast epithelial cells or normal breast epithelial cells, and differences in gene expression were identified by microarray. A total of 79 differentially regulated genes encoding cytokines, enzymes, angiogenic factors, cytoskeletal proteins, extra-cellular matrix remodeling proteins, signal transduction proteins and cell surface receptors were identified, and 6 of these were verified by real-time PCR. Among these, the expression of aldo-keto reductase family 1, member C3 (AKR1C3) was upregulated. AKR1C3 has multiple enzymatic properties, including conversion of estrone to estradiol and androstenedione to testosterone. Immunoreactive AKR1C3 was detected in epithelial and stromal components of benign lesions and ductal carcinomas in situ, and in 59.8% of epithelial and 69.6% of stromal cells in invasive breast carcinomas. AKR1C3 expression was significantly higher in myoepithelial cells surrounding the neoplastic epithelium of ductal carcinoma in situ compared with those surrounding benign epithelial lesions. Importantly, AKR1C3 and aromatase mRNA levels correlated positively in 61 malignant breast tumors (R =0.3967, p =0.00156). Malignant epithelial cell-conditioned medium significantly increased formation of testosterone and estradiol from androstenedione in breast adipose fibroblasts. In conclusion, malignant epithelial cell-derived factors significantly upregulate the enzymes AKR1C3 and aromatase that catalyze a series of complementary reactions to convert the circulating precursor androstenedione to biologically active estradiol in vitro in the stromal fibroblasts, and in vivo, in stromal component of breast tumors. [Copyright &y& Elsevier]

The aromatase gene encodes the key enzyme for estrogen formation. Aromatase enzyme inhibitors eliminate total body estrogen production and are highly effective therapeutics for postmenopausal breast cancer. A distal promoter (I.4) regulates low levels of aromatase expression in tumor-free breast adipose tissue. Two proximal promoters (I.3/II) strikingly induce in vivo aromatase expression in breast fibroblasts surrounding malignant cells. Treatment of breast fibroblasts with medium conditioned with malignant breast epithelial cells (MCM) or a surrogate hormonal mixture (dibutyryl (Bt2)cAMP plus phorbol diacetate (PDA)) induces promoters I.3/II. The mechanism of promoter-selective expression, however, is not clear. Here we reported that sodium butyrate profoundly decreased MCM- or Bt2cAMP + PDA-induced promoter I.3/II-specific aromatase mRNA. MCM, Bt2cAMP + PDA, or sodium butyrate regulated aromatase mRNA or activity only via promoters I.3/II but not promoters I.1 or I.4 in breast, ovarian, placental, and hepatic cells. Mechanistically, recruitment of phosphorylated ATF-2 by a CRE (-211/-199, promoter I.3/II) conferred inductions by MCM or Bt2cAMP + PDA. Chromatin immunoprecipitation-PCR and immunoprecipitation-immunoblotting assays indicated that MCM or Bt2cAMP + PDA stabilized a complex composed of phosphorylated ATF-2, C/EBPβ, and cAMP-response element-binding protein (CREB)-binding protein in the common regulatory region of promoters I.3/II. Overall, histone acetylation patterns of promoters 1.3/II did not correlate with sodium butyrate-dependent silencing of promoters I.3/II. Sodium butyrate, however, consistently disrupted the activating complex composed of phosphorylated ATF-2, C/EBPβ, and CREB-binding protein. This was mediated, in part, by decreased ATF-2 phosphorylation. Together, these findings represent a novel mechanism of sodium butyrate action and provide evidence that aromatase activity can be ablated in a signaling pathway- and cell-specific fashion. [ABSTRACT FROM AUTHOR]

Abstract: Pathogenesis and growth of three common women''s cancers (breast, endometrium and ovary) are linked to estrogen. A single gene encodes the key enzyme for estrogen biosynthesis named aromatase, inhibition of which effectively eliminates estrogen production in the entire body. Aromatase inhibitors successfully treat breast cancer, whereas their roles in endometrial and ovarian cancers are less clear. Ovary, testis, adipose tissue, skin, hypothalamus and placenta express aromatase normally, whereas breast, endometrial and ovarian cancers overexpress aromatase and produce local estrogen exerting paracrine and intracrine effects. Tissue-specific promoters distributed over a 93-kb regulatory region upstream of a common coding region alternatively control aromatase expression. A distinct set of transcription factors regulates each promoter in a signaling pathway- and tissue-specific manner. In cancers of breast, endometrium and ovary, aromatase expression is primarly regulated by increased activity of the proximally located promoter I.3/II region. Promoters I.3 and II lie 215bp from each other and are coordinately stimulated by PGE2 via a cAMP-PKA-dependent pathway. In breast adipose fibroblasts exposed to PGE2 secreted by malignant epithelial cells, PKC is also activated, and this potentiates cAMP-PKA-dependent induction of aromatase. Thus, inflammatory substances such as PGE2 may play important roles in inducing local production of estrogen that promotes tumor growth. [Copyright &y& Elsevier]

Estrogen is produced in a number of human tissues including the ovary, placenta and extraglandular sites such as adipose tissue, skin and the brain. Aromatase is the key enzyme that regulates estrogen formation in these tissues. Aromatase activity is not detectable in normal endometrium. In contrast, aromatase is expressed aberrantly in endometriosis and is stimulated by PGE2. This results in local production of estrogen, which induces PGE2 formation and establishes a positive feedback cycle. Another abnormality in endometriosis, i.e. deficient 17β-hydroxysteroid dehydrogenase (17β-HSD) type 2 expression, impairs the inactivation of estradiol to estrone. These molecular aberrations collectively favor accumulation of increasing quantities of estradiol and PGE2 in endometriosis. The clinical relevance of these findings was exemplified by the successful treatment of an unusually aggressive case of postmenopausal endometriosis using an aromatase inhibitor. [Copyright &y& Elsevier]