Regulation of estrogen biosynthesis in human adipose stromal cells. Effects of dibutyryl cyclic AMP, epidermal growth factor, and phorbol esters on the synthesis of aromatase cytochrome P-450

Updates on Mechanisms of Cytochrome P450 Catalysis of Complex Steroid Oxidations

Cytochrome P450 (P450) enzymes dominate steroid metabolism. In general, the simple C-hydroxylation reactions are mechanistically straightforward and are generally agreed to involve a perferryl oxygen species (formally FeO3+). Several of the steroid transformations are more complex and involve C-C bond scission. We initiated mechanistic studies with several of these (i.e., 11A1, 17A1, 19A1, and 51A1) and have now established that the dominant modes of catalysis for P450s 19A1 and 51A1 involve a ferric peroxide anion (i.e., Fe3+O2¯) instead of a perferryl ion complex (FeO3+), as demonstrated with 18O incorporation studies. P450 17A1 is less clear. The indicated P450 reactions all involve sequential oxidations, and we have explored the processivity of these multi-step reactions. P450 19A1 is distributive, i.e., intermediate products dissociate and reassociate, but P450s 11A1 and 51A1 are highly processive. P450 17A1 shows intermediate processivity, as expected from the release of 17-hydroxysteroids for the biosynthesis of key molecules, and P450 19A1 is very distributive. P450 11B2 catalyzes a processive multi-step oxidation process with the complexity of a chemical closure of an intermediate to a locked lactol form.

Adipose tissue engineering with cells in engineered matrices

Tissue engineering has shown promise for the development of constructs to facilitate large volume soft tissue augmentation in reconstructive and cosmetic plastic surgery. This article reviews the key progress to date in the field of adipose tissue engineering. In order to effectively design a soft tissue substitute, it is critical to understand the native tissue environment and function. As such, the basic physiology of adipose tissue is described and the process of adipogenesis is discussed. In this article, we have focused on tissue engineering using a cell-seeded scaffold approach, where engineered extracellular matrix substitutes are seeded with exogenous cells that may contribute to the regenerative response. The strengths and limitations of each of the possible cell sources for adipose tissue engineering, including adipose-derived stem cells, are detailed. We briefly highlight some of the results from the major studies to date, involving a range of synthetic and naturally derived scaffolds. While these studies have shown that adipose tissue regeneration is possible, more research is required to develop optimized constructs that will facilitate safe, predictable and long-term augmentation in clinical applications.

Mechanical phenotype is important for stromal aromatase expression

Evidence that aromatase expression in tumor-associated breast stroma is elevated, provides a rationale for use of aromatase inhibitors (AIs) in breast cancer treatment. However, regulation of local aromatase expression in cancer-free breast stroma is poorly understood. Recent clinical work indicates that stromal cells in dense breast tissue tend to express higher levels of aromatase than their counterpart from non-dense tissue. Consistent with the clinical observation, our cell culture-based study indicated that cell density, cell shape, and extracellular matrix (ECM) significantly induced stromal aromatase expression via a distinct signal transduction pathway. In addition, we identified a number of cell surface markers that are commonly associated with aromatase-expressing stromal cells. As mammographic density is one of the strongest and most prevalent risk factors for breast cancer, these findings provide a potential mechanistic link between alterations in tissue composition of dense breast tissue and increased stromal aromatase expression. Further exploration of the in vitro model system may advance understanding of an important problem in breast cancer biology.

Estrogen receptor-related receptor alpha mediates up-regulation of aromatase expression by prostaglandin E2 in prostate stromal cells

Estrogen receptor-related receptor alpha (ERRalpha) is an orphan member of the nuclear receptor superfamily of transcription factors. ERRalpha is highly expressed in the prostate, especially in prostate stromal cells. However, little is known about the regulation and function of ERRalpha, which may contribute to the progression of prostatic diseases. We previously found that prostaglandin E2 (PGE2) up-regulated the expression of aromatase in prostate stromal cells. Here we show that PGE2 also up-regulates the expression of ERRalpha, which, as a transcription factor, further mediates the regulatory effects of PGE2 on the expression of aromatase. ERRalpha expression was up-regulated by PGE2 in prostate stromal cell line WPMY-1, which was mediated mainly through the protein kinase A signaling pathway by PGE2 receptor EP2. Suppression of ERRalpha activity by chlordane (an antagonist of ERRalpha) or small interfering RNA knockdown of ERRalpha blocked the increase of expression and promoter activity of aromatase induced by PGE2. Overexpression of ERRalpha significantly increased aromatase expression and promoter activity, which were further augmented by PGE2. Chromatin immunoprecipitation assay demonstrated that ERRalpha directly bound to the aromatase promoter in vivo, and PGE2 enhanced the recruitment of ERRalpha and promoted transcriptional regulatory effects on aromatase expression in WPMY-1. 17Beta-estradiol concentration in WPMY-1 medium was up-regulated by ERRalpha expression, and that was further increased by PGE2. Our results provided evidence that ERRalpha contributed to local estrogen production by up-regulating aromatase expression in response to PGE2 and provided further insights into the potential role of ERRalpha in estrogen-related prostatic diseases.

Regulation of breast cancer-associated aromatase promoters

By converting androstenedione to estrone, or testosterone to estradiol, aromatase is a key enzyme in estrogen biosynthesis. Encoded by a single gene CYP19, aromatase is expressed in various tissues, including ovary, placenta, bone, brain, skin, and adipose tissue, via partially tissue-specific promoters, and is essential for normal estrogen-dependent physiological functions. In disease-free breast tissue, aromatase mRNA is primarily transcribed from the weak promoter I.4 and maintained at low levels in breast adipose stromal fibroblasts. In breast cancer a distinct set of aromatase promoters, i.e. I.3, II, and I.7, is activated, leading to a marked increase in aromatase expression in breast tumors and breast adipose tissue adjacent to a breast tumor, and a consequent local overproduction of estrogen that promotes growth and progression of breast cancer. In addition, the total amount of promoter I.4-specific aromatase transcript in breast adipose fibroblasts may also be increased due to both cytokine-induced desmoplastic reaction and cytokine-stimulated promoter I.4 activity in breast cancer. Targeting aromatase has proven beneficial in treating breast cancer, since aromatase inhibitors are the most effective endocrine treatment of breast cancer to date. However, aromatase inhibitors cause major side effects such as bone loss and abnormal lipid metabolism, due to indiscriminate reduction of aromatase activity in all expression sites of the body. Therefore, inhibition of aromatase expression via breast cancer-associated aromatase promoters is a useful strategy to selectively block local aromatase production, and hence estrogen synthesis, in breast cancer. This review will summarize the significant findings on regulation of the breast cancer-associated aromatase promoters, and highlight the discovery of chemical compounds and nuclear receptor ligands that specifically inhibit activation of these aromatase promoters. Clinical side effects of these agents require development of new drugs with better specificity and efficacy, and epigenetic therapies with breast cancer tissue-selective aromatase siRNA-conjugated nanoparticles.

Prostaglandin E(2) induces breast cancer related aromatase promoters via activation of p38 and c-Jun NH(2)-terminal kinase in adipose fibroblasts

Aromatase is the key enzyme for estrogen biosynthesis. A distal promoter, PI.4, maintains baseline levels of aromatase in normal breast adipose tissue. In contrast, malignant breast epithelial cells secrete prostaglandin E(2) (PGE(2)), which stimulates aromatase expression via proximal promoters PI.3/PII in a cyclic AMP (cAMP)- and protein kinase C (PKC)-dependent manner in adjacent breast adipose fibroblasts (BAF), leading to increased local concentrations of estrogen. Although an effective treatment for breast cancer, aromatase inhibitors indiscriminately abolish estrogen synthesis in all tissues, causing major side effects. To identify drug targets to selectively block aromatase and estrogen production in breast cancer, we investigated PGE(2)-stimulated signaling pathways essential for aromatase induction downstream of cAMP and PKC in human BAFs. Here, we show that PGE(2) or its surrogate hormonal mixture dibutyryl cAMP (Bt(2)cAMP) + phorbol diacetate (PDA) stimulated the p38, c-jun NH(2)-terminal kinase (JNK)-1, and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase pathways. Inhibition or small interfering RNA-mediated knockdown of p38 or JNK1, but not ERK, inhibited PGE(2)- or Bt(2)cAMP + PDA-induced aromatase activity and expression via PI.3/PII. Conversely, overexpression of wild-type p38alpha or JNK1 enhanced PGE(2)-stimulated aromatase expression via PII. PGE(2) or Bt(2)cAMP + PDA stimulated c-Jun and activating transcription factor-2 (ATF2) phosphorylation and binding to the PI.3/PII region. Specific activation of protein kinase A (PKA) or EPAC with cAMP analogues stimulated p38 and JNK1; however, only PKA-activating cAMP analogues induced aromatase expression. The PKC activator PDA effectively stimulated p38 and JNK1 phosphorylation but not aromatase expression. Taken together, PGE(2) activation of p38 and JNK1 via PKA and PKC is necessary for aromatase induction in BAFs, and p38 and JNK1 are potential new drug targets for tissue-specific ablation of aromatase expression in breast cancer.

Role of the progesterone receptor (PR) in the regulation of inflammatory response pathways and aromatase in the breast

There is convincing evidence to suggest that estrogen and inflammatory mediators play important roles in growth and progression of breast cancer. Moreover, local conversion of androgens to estrogens by aromatase (product of CYP19 gene) occurs in 70% of all breast cancers. The actions of aromatase in both the breast tumor and in surrounding adipose stromal and endothelial cells can result in high local levels of estrogen production that stimulate tumor growth. The efficacy of current endocrine therapies is predicted only if the tumor contains significant amounts of ER. Presence of PR in the tumor also is an important predictor of tumor aggressiveness and responsiveness to endocrine therapy. Immunoreactivity for aromatase in human breast tumors is highly correlated with that for cyclooxygenase 2 (COX-2), the rate-determining enzyme in prostanoid biosynthesis. COX-2 expression also is correlated with expression of HER-2/neu, an oncogene expressed in >30% of breast tumors. In this manuscript, we will review findings to suggest that induction of COX-2 by inflammatory cytokines acting through NF-kappaB contributes to the increase in CYP19 expression and breast cancer progression, and that PR plays a dominant protective role in breast cancer cells by antagonizing NF-kappaB activation of COX-2.

CYP19A1 genetic polymorphisms may be associated with obesity-related phenotypes in Chinese women

OBJECTIVE

To examine the relationship between genetic polymorphisms of the CYP19A1 gene and obesity-related phenotypes, body mass index (BMI) and waist-to-hip ratio (WHR).

SUBJECTS

In total, 1241 Chinese women, who were recruited as community controls for a population-based case-control study of breast cancer.

METHODS

Nineteen haplotype tagging single nucleotide polymorphisms (htSNPs) in four haplotype blocks were genotyped.

RESULTS

Significant associations were observed for WHR at three SNPs that are located in haplotype block 1, including rs2445765, rs1004984 and rs1902584 (P=0.05, 0.04 and 0.01, respectively). Women, particularly premenopausal women, who carried the minor allele at any of these SNPs, had higher WHR than those without it. Of these three SNPs, the strongest association was observed at rs1902584, which is the closest to Promoter I.4, the major promoter for adipose tissue. Haplotype analyses indicated an association between the haplotype TCCAT in block 1 and WHR with a P-value of 0.02.

CONCLUSION

These results suggested that CYP19A1 genetic polymorphisms may be associated with the risk of obesity among Chinese women, especially among premenopausal women. The CYP19A1 protein (aromatase) plays a critical role in estrogen biosynthesis and thus affects body fat distribution and regulation.

Paracrine-stimulated gene expression profile favors estradiol production in breast tumors

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.

Activation of peroxisome proliferator-activated receptor-gamma and retinoid X receptor inhibits aromatase transcription via nuclear factor-kappaB

Our previous studies demonstrated that a peroxisome proliferator-activated receptor (PPAR)-gamma ligand, troglitazone (TGZ),and/or a retinoid X receptor (RXR) ligand, LG100268 (LG), decreased the aromatase activity in both cultured human ovarian granulosa cells and human granulosa-like tumor KGN cells. In the present study, we further found that a combined treatment of TGZ+LG decreased aromatase promoter II (ArPII) activity in both ovarian KGN cells and fibroblast NIH-3T3 cells in a PPARgamma-dependent manner. Furthermore, the inhibition of both aromatase activity and the transcription of ArPII by TGZ+LG was completely eliminated when nuclear factor-kappaB (NF-kappaB) signaling was blocked by specific inhibitors, suggesting NF-kappaB, which is endogenously expressed in both fibroblast and granulosa cells, might be a mediator of this inhibition. Interestingly, activation of NF-kappaB by either forced expression of the p65 subunit or NF-kappaB-inducing kinase up-regulated ArPII activity. Positive regulation of aromatase by endogenous NF-kappaB was also suggested by the fact that NF-kappaB-specific inhibitors suppress basal activity of the aromatase gene. A concomitant formation of high-order complex between NF-kappaB p65 and ArPII was also observed by chromatin immunoprecipitation assay. Although activation of PPARgamma and RXR affected endogenous expression levels of neither inhibitory kappaBalpha nor p65, it impaired the interaction between NF-kappaB and ArPII and the p65 based transcription as well. Altogether, these results indicate that activation of a nuclear receptor system, constituted by PPARgamma and RXR, down-regulates aromatase expression through the suppression of NF-kappaB-dependent aromatase activation and thus provide a new insight in the mechanism of regulation of the aromatase gene.

The effect of CYP19 and COMT polymorphisms on exercise-induced fat loss in postmenopausal women

OBJECTIVE

To examine whether genetic polymorphisms in CYP19 [intron 4 (TTTA)n; n = 7 to 13 and a 3-base pair deletion, which is in strong linkage disequilibrium with the seven repeat] and COMT (Val108/158Met) modified the change in BMI, total and percentage body fat, or subcutaneous and intra-abdominal fat during a year-long exercise intervention trial. These genes metabolize estrogens and androgens, which are important in body fat regulation.

RESEARCH METHODS AND PROCEDURES

A randomized intervention trial was used, with an intervention goal of 225 min/wk of moderate-intensity exercise for one year. Participants (n = 173) were postmenopausal, 50 to 75 years old, sedentary, overweight or obese, and not taking hormone therapy at baseline.

RESULTS

Exercisers with two vs. no CYP19 11-repeat alleles had a larger decrease in total fat (-3.1 kg vs. -0.5 kg, respectively, p = 0.01) and percentage body fat (-2.4% vs. -0.6%, respectively, p = 0.001). Exercisers with the COMT Met/Met vs. Val/Val genotype had a smaller decrease in percentage fat (-0.7% vs. -1.9%, respectively, p = 0.05). Among exercisers, women with the COMT Val/Val genotype and at least one copy of the CYP19 11-repeat allele vs. those with neither genotype/allele had a significantly larger decrease in BMI (-1.0 vs. +0.1 kg/m2, respectively, p = 0.009), total fat (-2.9 vs. -0.5 kg, respectively, p = 0.004), and percentage body fat (-2.6% vs. -0.4%, respectively, p < 0.001).

DISCUSSION

Genetic polymorphisms in CYP19 and COMT may be important for body fat regulation and possibly modify the effect of exercise on fat loss in postmenopausal women.

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.

Real-time reverse transcription PCR assay of CYP19 expression: application to a well-defined series of post-menopausal breast carcinomas

Aromatase, the product of the CYP19 gene, plays a key role in androgenic steroids transformation into estrogens from various hormonal sensitive tissues. Thus, in situ expression of CYP19 has been suggested to be involved in breast tumor growth especially in post-menopausal patients.We developed a real-time quantitative RT-PCR assay based on fluorescent TaqMan methodology to quantify total CYP19 gene expression at the mRNA level in breast tumors. This method, based on nucleic acid quantification in homogeneous solutions, has the potential to become a standard in terms of its sensitivity, wide dynamic range and high-throughput capacity. In a well-defined series of 107 post-menopausal breast tumor samples, relative CYP19 mRNA levels ranged from 1 to 131. Among the four major CYP19 exon I-spliced transcripts, designated I.a, I.b, I.c and I.d, mRNA levels of the latter three correlated positively with total CYP19 mRNA levels. In ER alpha-positive breast tumors, CYP19 and ER alpha mRNA levels correlated negatively with each other (P=0.0078, r=-0.266), while CYP19 and ER beta mRNA levels correlated positively (P=0.00012, r=+0.388). Patients with high CYP19 mRNA levels did not relapse more frequently or have shorter relapse-free survival than other patients. Finally, mRNA levels of IL6, a major CYP19 regulatory factor, were significantly higher in tumors strongly expressing CYP19 than in tumors weakly expressing CYP19 (P=0.018). In conclusion, CYP19 expression did not influence the outcome of post-menopausal patients with breast cancer.

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.

Effect of tibolone (Org OD14) and its metabolites on aromatase and estrone sulfatase activity in human breast adipose stromal cells and in MCF-7 and T47D breast cancer cells

Tibolone (Org OD14) is a synthetic steroid used for post-menopausal hormone replacement therapy (HRT). Since HRT might increase breast cancer risk, it is important to determine the possible effects of tibolone on breast tissues. Tibolone and its metabolites Org 4094, Org 30126 and Org OM38 have been reported to inhibit estrone sulfatase activity in MCF-7 and T47D breast cancer cell lines, which suggest beneficial effects on hormone dependent breast cancer by reducing local production of free estrogens. Breast adipose stromal cells (ASCs) contain aromatase activity-an obligatory step in the biosynthesis of estrogens-and possibly contain sulfatase activity. We investigated the effects of tibolone, its metabolites and the pure progestin Org 2058 on PGE(2)-stimulated aromatase activity and on sulfatase activity in human ASC primary cultures and on sulfatase activity in MCF-7 and T47D cell lines. In MCF-7, tibolone and metabolites, but not Org 2058, were found to inhibit sulfatase activity. In T47D, tibolone inhibited sulfatase only at 10(-6)M, although weakly. ASC had high sulfatase activity, which was inhibited by 10(-6)M of tibolone, Org 4094 and Org 30126, but not by Org OM38 or Org 2058. Surprisingly, aromatase activity in ASC was increased by both tibolone and Org 2058 at 10(-6)M. As ligand binding assay results and immunohistochemistry indicated the absence of progesterone and estrogen receptors in ASC, these effects on aromatase and sulfatase activity in ASC likely take place by other routes. Because tibolone and its metabolites inhibit sulfatase activity, and because tibolone only increases aromatase activity at a high concentration, we conclude that effects of tibolone on the breast are probably safe.

Influence of cytokines and growth factors on distinct steroidogenic enzymes in vitro: a short tabular data collection

Cytokines (IL-1, IL-6, IL-8, IL-11, TNF, IFN-gamma, and TGF-beta) and growth factors (EGF, bFGF, aFGF, and KGF) play an important role in modulation of hormone secretion by directly influencing specific enzyme steps of steroidogenesis in various endocrine cell types. For this tabular data collection, the following enzyme steps were considered: steroidogenic acute regulatory protein (StAR), side chain cleavage enzyme (P450scc), 3 beta-hydroxysteroid dehydrogenase, 17-alpha-hydroxylase/17,20-lyase (P450c17), 17-beta-hydroxysteroid-dehydrogenase, aromatase complex, 5-alpha-reductase, P450c21, DHEAS sulfatase, and DHEA sulfotransferase. This collection summarizes the current information on how the mentioned cytokines and growth factors influence particular enzyme steps.

Demonstration of aromatase activity and its regulation in breast tumor and benign breast fibroblasts

Breast tumors from post-menopausal women contain higher amounts of estradiol than would be predicted from levels circulating in plasma. This observation raised the hypothesis that tumors may synthesize estradiol in situ and increase their tissue estradiol levels via this mechanism. The key enzyme involved in tissue estrogen synthesis, aromatase, is present in breast tumors but, according to some investigators, not in sufficient concentration to be biologically meaningful. We postulated that foci of cells in breast tumors might contain high amounts of aromatase and this locally produced estrogen might act in a paracrine or autocrine fashion. To test this hypothesis, we utilized immunohistochemistry to localize the aromatase enzyme, an histological scoring system to quantitate it, and culture of isolated breast cells to demonstrate its potential regulation. In 26 archival breast tumors, 16 (62%) contained aromatase by radiometric assay. With the immunohistochemical method, we detected areas with staining in the stroma as well as tumor epithelial cells. Staining ranged from the intensity approaching that seen in placenta to levels just distinguishable from background. We adopted an histological scoring system (H-score) from that used to quantitate progesterone receptor levels in tissue and used it to quantitate aromatase activity. A higher histologic score was found in stromal spindle cells (13) than in tumor epithelial cells (4.8). The biochemical aromatase results correlated with the H-score of stromal but not epithelial cells. To further study stromal cells from tumors, we isolated stromal cells from breast tumors and the benign areas of breast distal to the tumor and grew them in culture. Addition of dexamethasone, phorbol esters, and cyclic AMP analogues stimulated aromatase enzyme and messenger RNA levels substantially. Use of aromatase enzyme inhibitors such as letrozole blocked estrogen production but did not alter aromatase message levels. Epithelial cells, whether nonmalignant or cancer derived, exhibited no regulation by dexamethasone, phorbol esters, or cAMP analogues. These data, taken together, suggest that stromal cells may be more important than epithelial cancer cells for estrogen production in breast tumors. The ability to stimulate aromatase activity substantially with various enhancers of aromatase provides further credence for an important biologic role of estrogen production in tumor tissue.

Transcriptional regulation of CYP19 gene (aromatase) expression in adipose stromal cells in primary culture

Estrogen biosynthesis in adipose tissue increases with age and obesity, and has been implicated in the development of endometrial cancer and breast cancer. In normal human adipose tissue, expression of the CYP19 gene which encodes aromatase P450, the enzyme responsible for estrogen biosynthesis, is regulated by a distal promoter, namely promoter I.4. Stimulation of expression in adipose stromal cells by members of the type 1 cytokine family, i.e. interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF) and oncostatin M (OSM), is mediated via a Jak-STAT3 signaling pathway and a GAS element upstream of promoter I.4. In contrast, aromatase expression in breast adipose tissue proximal to tumor is increased three- to four-fold to the utilization of another promoter, namely promoter II, proximal to the translation initiation site. In the present report, we show that prostaglandin (PG) E2 is the most potent factor which stimulates aromatase expression via cyclic AMP and promoter II. PGE2 acts via EP1 and EP2 receptor subtypes to stimulate both the PKC and PKA pathways. The combined stimulation of both of these pathways results in the maximal expression of promoter II-specific CYP19 transcripts. Because PGE2 is a major secretory product both of breast tumor epithelial cells and fibroblasts, as well as of macrophages infiltrating the tumor site, then this could be the mechanism whereby estrogen biosynthesis is stimulated in breast sites adjacent to a tumor, leading in turn to increased growth and development of the tumor itself.

11 beta-Hydroxysteroid dehydrogenase 1 activity and gene expression in human adipose stromal cells: effect on aromatase activity

The biological activity of glucocorticoids in target tissues can be influenced by locally produced 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD), the enzyme responsible for the interconversion of cortisol and its inactive metabolite cortisone. In human adipose stromal cells, glucocorticoids are potent stimulators of the conversion of androgens to estrogens (aromatase activity). The present study was designed to determine whether 11 beta-HSD activity was present in human adipose stromal cells, and if changes in the activity of this enzyme could influence aromatase activity. 11 beta-HSD activity was determined by a radiometric conversion assay in breast adipose tissue from six patients. It was found that both dehydrogenase (cortisol to cortisone) and reductase (cortisone to cortisol) activities were present in all six subjects, and the reductase activity was always predominant. Carbenoxolone (CBX), a potent inhibitor of 11 beta-HSD, added to the culture medium at 50 and 200 microM, resulted in 39 +/- 4% and 85 +/- 1% inhibition, respectively, of both reductase and dehydrogenase activity of 11 beta-HSD. To determine whether alterations in 11 beta-HSD could influence aromatase activity, the effect of CBX (200 microM) on cortisol- and cortisone-induced changes in the conversion of androstenedione to estrone was examined. CBX prevented the stimulatory effect of cortisone and minimally potentiated the stimulatory effect of cortisol on aromatase activity, reflecting an inhibition of the local activation of cortisone and the local metabolism of cortisol, respectively. In order to determine whether the product of the 11 beta-HSD 1 gene was responsible for the observed 11 beta-HSD activity, total RNA extracts from these cells were subjected to Northern blot analysis using human 11 beta-HSD 1 cDNA as the probe. A single 1.8 11 beta-HSD 1 transcript was detected, and its abundance was reduced by CBX. No 11 beta-HSD 2 mRNA was detected. The present results demonstrate that the 11 beta-HSD 1 gene is expressed and functional in human breast adipose stromal cells and that changes in 11 beta-HSD 1 activity result in alterations in aromatase activity.

[In vitro gene expression of aromatase in rat testicular cells]

The ability of the male gonad to convert androgens into estrogens is well known; the microsomal enzymatic complex involved in this transformation is named aromatase and is composed of a specific cytochrome P450 aromatase (P450arom) and a ubiquitous reductase. Using a highly specific RT-PCR method we have measured the amount of P450arom mRNA in purified Leydig and Sertoli cells prepared from 20, 40 and 70-80 day-old rats. The amount of P450arom mRNA in the Leydig cells is independent of age (40 x 10(-3) attomoles/micrograms of total RNA); in contrast, in the immature rat Sertoli cells, after 5 days of culture the amount of P450arom mRNA is 20-fold lower when compared to that of 20-day-old rat Sertoli cells (71 x 10(-3) attomoles/micrograms of total RNA). Nevertheless, irrespective of the age, the addition of either FSH or dbcAMP for 6 h increases the level of P450arom mRNA in the rat Sertoli cell preparations. Therefore, we evidenced that during testicular maturation not only the Leydig cells but also the Sertoli cells of the rat have the capacity to express the gene for cytochrome P450 aromatase.

RU486 is a potent inhibitor of aromatase induction in human breast adipose tissue stromal cells

Aromatization of circulating androgens in adipose tissue is a major source of estrogens in postmenopausal women. As part of our efforts to elucidate the mechanism of aromatase induction in human breast adipose tissue, we tested the effects of the antiglucocorticoid and antiprogestin, RU486, on aromatase induction in primary cultures of adipose tissue stromal cells in a serum-free system devoid of phenol-red. Under these conditions 1 microM cortisol alone induces low levels of aromatase activity within one day, whereas platelet-derived growth factor BB (PDGF) potentiates this effect two- to three-fold. The well-known strong inductive effect of dibutyryl-cAMP (db-cAMP) is also augmented by cortisol, but is inhibited by PDGF in the absence of cortisol. RU486 completely prevented aromatase induction by cortisol and PDGF. Induction by db-cAMP in the presence and absence of cortisol was significantly inhibited by RU486. Even lower activities were measured when RU486 was added to cells stimulated with PDGF and db-cAMP in the absence or presence of cortisol. Similar results were obtained after prolonged incubation. The inhibitory effects of RU486 are dose dependent, less than 1 microM completely blocking the effects of cortisol, whereas 10 microM are needed to block db-cAMP induction. RU486 does not affect cell number, cellular protein, viability or house-keeping enzymes such as lactate dehydrogenase (LDH), and therefore seems to act specifically. The time course of RU486 action on the db-cAMP induction of aromatase indicates that it acts via a newly synthetized mediator or target in stromal cells. These results suggest that all known inducers of aromatase in adipose tissue depend upon the action of signalling molecules (probably members of the nuclear receptor superfamily) which can be blocked by RU486. The inhibitory action of PDGF seems to be independent of steroid hormone action, as seems some basal activity induced by db-cAMP. In conclusion, this in vitro study suggests that RU486 might be a useful tool for the therapy of estrogen-dependent tumours through its inhibition of aromatase induction.

Three-component model of oestrogen formation and regulation of intratumoural oestrogen pool in breast neoplasms

Although a two-component model system (i.e. epithelial and stromal spindle-shaped cells) may explain the regulation of aromatase activity and the location of possible intratumoural sources of oestrogen production in mammary neoplasms, a third component, consisting of lymphocytes and macrophages, may also be considered. Examples are presented, suggesting the importance of a three-component model for a more complete understanding of the regulation of oestrogen production in breast-tumour tissue.

Regulation of placenta-specific expression of the aromatase cytochrome P-450 gene. Involvement of the trophoblast-specific element binding protein

The aromatase (cytochrome P-450AROM) gene contains multiple untranslated exons I that are differentially transcribed in a tissue-specific manner. DNA sequences within the initial -301 upstream of placenta-specific exon I (exon Ia) are sufficient for placenta-specific expression of aromatase. In gel mobility shift assay, three separate domains in this region form specific binding complexes with proteins extracted from choriocarcinoma JEG-3 nuclei. A fragment containing these domains activates transcription driven by a heterologous promoter in a cell type-specific manner. Two of the binding domains that form major complexes in gel shift assay compete with each other and with a DNA fragment containing the trophoblast-specific element (TSE), which is derived from the enhancer region of the human chorionic gonadotropin alpha-subunit gene and is believed to confer placenta-specific expression of the gene. The core sequence RNCCTNNRG is sufficient for recognition of the TSE-binding protein, which is detected only in nuclear extracts prepared from placenta and choriocarcinoma. A mutation introduced in the distal TSE core in aromatase promoter resulted in marked reduction of transcriptional activity, although TSE region by itself did not show enhancer activity as that in human chorionic gonadotropin alpha-subunit gene.

Human fetal adrenal hydroxysteroid sulphotransferase: cDNA cloning, stable expression in V79 cells and functional characterisation of the expressed enzyme

Dehydroepiandrosterone sulphate (DHEAS) is a major adrenal secretory product, particularly in the fetus where it serves as a substrate for oestrogen biosynthesis by the placenta. The enzyme in the adrenal responsible for synthesising DHEAS, hydroxysteroid sulphotransferase (HST), is therefore essential for human development. We have isolated a full-length cDNA clone, encoding human fetal adrenal HST, and constructed a stable cell line expressing it by transfection into V79 Chinese hamster lung fibroblast cells. This cDNA was essentially identical to that isolated from adult human liver, where the role of HST is less well understood. This recombinant cell line allowed determination of the substrate specificity and kinetic properties of this enzyme towards various steroid hormones, and by comparison of these activities with human liver cytosol we have shown that HST is the major sulphotransferase responsible for the sulphation of DHEA, androsterone and pregnenolone in man and that, functionally, the hepatic and adrenal enzymes are very similar. The expressed HST was also active with testosterone, cortisol (although at low levels) and the xenobiotic 17 alpha-ethinyloestradiol, but not with oestrone or 1-naphthol. We have therefore created a valuable resource for the study of this important enzyme.

Transcriptional regulation of the human aromatase cytochrome P450 gene expression in human placental cells

The human aromatase cytochrome P450 gene, CYP 19, spans more than 75 kb in the human genome. Recently, it is proposed that the expression of the CYP 19 gene is regulated in part by tissue-specific promoters through the use of mechanisms involving alternative splicing of a number of untranslated exons. In this study, we have characterized cis-acting elements involved in the transcriptional regulation of the gene in human placental cells, where the majority of the transcripts contain the 5'-untranslated sequence encoded by exon I.1. By transient expression analyses in human BeWo choriocarcinoma cells using the bacterial chloramphenicol acetyltransferase gene as a reporter gene, we localized an enhancer element in the region between -242 and -166 relative to the major cap site of the gene. Furthermore, we demonstrate that the element between -2141 and -2115 participates in the 12-O-tetradecanoylphorbol 13-acetate (TPA)-mediated enhancement of gene expression. By screening a human placental cDNA expression library, we have isolated a cDNA clone (lambda 1-2) encoding a peptide which binds specifically to the element between -2141 and -2115. Sequence analysis of the clone revealed that the insert of lambda 1-2 encodes a part of the amino acid sequence of NF-IL6 (also termed as LAP and C/EBP beta). Northern blot analysis reveals expression of the NF-IL6 gene in BeWo cells and human placenta. These results indicate that NF-IL6 is one of the nuclear factors which participate in TPA-mediated transcriptional enhancement of CYP 19 gene expression.

Aromatase gene expression in adipose tissue: relationship to breast cancer

Recent studies have established that concentration gradients of aromatase expression occur within the breast, with the highest levels of expression occurring in sites proximal to a tumor. These variations in aromatase expression correlate with regional differences in the relative proportions of the histologic components of breast adipose tissue, in particular adipocytes and stromal cells, since regions containing the highest numbers of stromal cells are the sites of elevated aromatase transcript levels. Although the initiating events are unknown, it is proposed that, once neoplastic cells start to replicate, tumor growth will be promoted by locally increased estrogen levels. In turn, growth factors produced by the tumor in response to locally increased estrogen levels may further increase aromatase expression in the surrounding adipose tissue. Thus a positive feed-back loop is established in which locally-produced estrogens and tumor-derived growth factors act by paracrine and autocrine mechanisms to sustain the growth and development of the tumor. Further support for this concept is obtained from the observation that aromatase expression in breast adipose is regulated by enhancer elements that appear to respond positively to growth factors, in contrast to expression in granulosa cells, which is inhibited by growth factors.

Induction of aromatase gene expression in human placental choriocarcinoma (JAR) cells by phorbol esters

The expression of aromatase in JAR cells, human placental choriocarcinoma cells, was found to be induced by the treatment of phorbol 12,13-diacetate (PDA), phorbol 12,13-didecanoate (PDD), or phorbol 12-myristate 13-acetate (TPA), but not 4 alpha-phorbol, 12,13-didecanoate (4 alpha PDD). At 1 microM or higher concentrations, these phorbol esters increased the level of aromatase mRNA and aromatase activity in a dose- and time-dependent fashion. Since the rates of the decrease of aromatase mRNA in phorbol ester treated and untreated cells were not significantly different in the presence of actinomycin D, the induction was not due to an increase in the stability of aromatase mRNA, but rather due to an increase in the synthesis of aromatase mRNA. The stimulation was not inhibited by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). It is thought that the induction either follows a protein kinase C-independent manner or results from a down-regulation of protein kinase C pathway. Studies from several laboratories have revealed that the regulation of the expression of aromatase in estrogen-producing cells involves very complex processes. The apparent induction of aromatase expression in JAR cells by phorbol esters represent a mechanism modulating estrogen production in human placental choriocarcinoma cells, that may or may not be utilized in other estrogen-producing cells.

Breast cancer and expression of aromatase in breast adipose tissue

Extraglandular conversion of C19 steroids to estrogens takes place primarily in the stromal cell component of adipose tissue and is catalyzed by an enzyme complex comprising aromatase cytochrome P450 (P450arom; the product of the CYP19 gene) together with the flavoprotein NADPH-cytochrome P450 reductase. It has been proposed that increased local aromatase activity in breast adipose tissue may influence the growth o f breast carcinomas. Using competitive polymerase chain reaction following reverse transcription (RT-PCR), we quantified P450arom transcripts in breast adipose tissue from mastectomy specimens. In 10 of 15 patients, the highest transcript levels were found in the quadrant where the tumor was located. We also found the highest proportions of adipose stromal cells versus adipocytes in these quadrants. These findings suggest that regional differences in the relative proportions o f these histologic components give rise to local elevated concentrations of estrogens. Although the initiating events are not known, once a neoplastic change has occurred, tumor growth may be promoted by these locally increased estrogen levels. Our data regarding hormonally regulated use of tissue-specific promoters for CYP19 gene transcription suggest preferential utilization of certain upstream regulatory regions of the gene in breast adipose tissue, resulting in increased expression of aromatase.

Regulation of aromatase expression in human tissues

Extraglandular conversion of C19 steroids to estrogens takes place primarily in the stromal cell compartments of adipose tissue and is catalyzed by aromatase cytochrome P450 (P450arom, the product of the CYP19 gene). CYP19 gene expression and aromatase activity in breast adipose stromal cells in culture are subject to complex hormonal regulation, which was recently found to be mediated in part by alternative use of tissue-specific promoters of the CYP19 gene. It has been proposed that increased local aromatase activity in breast adipose tissue may influence the growth of breast carcinomas. Using competitive RT-PCR, we quantified P450arom transcripts in breast adipose tissue from mastectomy specimens. In 10 out of 15 patients, the highest transcript levels were found in the quadrant where the tumor was located. We also found the highest proportions of adipose stromal cells vs. adipocytes in these quadrants. These findings suggest that regional differences in the relative proportions of the histologic components give rise to local elevated concentrations of estrogens. Although the initiating events are not known, once a neoplastic change has occurred, tumor growth may be promoted by these locally increased estrogen levels. We are currently investigating alternative promoter use for CYP19 gene transcription to explain this association. Our results underscore the importance of aromatase inhibitors as effective agents in treatment of hormone-responsive breast cancer, since aromatase inhibitors reduce local aromatase activity as well as blood estradiol levels.

Exon-specific northern analysis and rapid amplification of cDNA ends (RACE) reveal that the proximal promoter II (PII) is responsible for aromatase cytochrome P450 (CYP19) expression in human ovary

Estrogens are synthesized from C19 steroids by a unique form of cytochrome P450, aromatase cytochrome P-450 (P-450AROM; the product of the CYP19 gene). We have shown that tissue-specific expression of human P-450AROM is determined, in part, by the use of alternative promoters. Previous methods of analysis for determining the specific 5'-termini of the different transcripts included S1 nuclease protection, primer extension, and Northern analysis. In the present study we have used the RACE procedure (rapid amplification of cDNA ends) to amplify and clone the 5' termini of P-450AROM transcripts expressed in human corpus luteum (CL). Sequencing of the resulting clones supports the results of the previously performed studies. Specifically, the proximal promoter, PII, is the predominant promoter utilized in CL, such that the start of transcription occurs 26 bp downstream of the putative TATA sequence. A minority of the clones possess an alternative 5'-end, namely I.3. Exon-specific Northern analysis confirms that the majority of the P-450AROM transcripts in CL tissue contain sequence specific for promoter II. Similarly, exon-specific Northern analysis indicates that transcripts in human follicles, as well as granulosa cells in culture, contain primarily sequence specific for promoter II.

Metabolism of dehydroepiandrosterone by cultured human adipose stromal cells: identification of 7 alpha-hydroxydehydroepiandrosterone as a major metabolite using high performance liquid chromatography and mass spectrometry

Studies of the metabolism of dehydroepiandrosterone (DHA) by cultured human adipose stromal cells revealed that the most abundant metabolite detected by HPLC was a polar compound accounting for up to 45% of total radioactivity. This metabolite was isolated by chromatography on Lipidex 5000 from the culture medium of breast adipose stromal cells cultured with unlabelled DHA (5 microM) and identified by combined capillary gas chromatography and mass spectrometry as 7 alpha-hydroxydehydroepiandrosterone (7 alpha-OHDHA). In breast adipose stromal cells, the conversion of DHA to 7 alpha-OHDHA was linear from a substrate concentration of 10 nM to 1 microM. At 1 microM substrate concentration, the formation of 7 alpha-OHDHA in four patients ranged from 6.1 to 22.5 ng/10(5) cells/24 h. Incubations carried out in primary culture and up to the fifth subculture revealed continued formation of 7 alpha-OHDHA. Adipose stromal cells from abdomen, flank and perinephric fat also produced 7 alpha-OHDHA from DHA. These studies have shown that 7 alpha-OHDHA is a major metabolite of DHA in human adipose stromal cells. The variability from patient to patient and the magnitude of this conversion suggests that this pathway may play an important role in the peripheral metabolism of DHA.

Molecular cloning of a cDNA showing alternative splicing of the 5'-untranslated sequence of mRNA for human aromatase P-450

A new type of full-length cDNA clone encoding human aromatase P-450 was isolated from a human placental cDNA library. The clone, designated as pES-4, has a 3130-bp insert. The nucleotide sequences of the translated region and the 3'-untranslated region of the insert of pES-4 are exactly identical with those of the cDNA clone characterized previously. However, the sequence of the 5'-untranslated region of the insert has characteristic feature, i.e. an extra sequence of 109 bp is present at a junction between exon 1 and exon 2 on the processed human aromatase mRNA. Analysis of the genomic clones containing the region between exon 1 and exon 2 of the human aromatase P-450 gene reveals that the 109-bp genomic segment, encoding the same sequence as the extra sequence observed in pES-4, is located approximately 10-kbp downstream of exon 1 and that the nucleotide sequences of the 5'-flanking and the 3'-flanking regions of the segment conform to the GT-AG rule for RNA splicing. By means of reverse transcription and polymerase chain reaction, relative amounts of the pES-4-type mRNA are estimated to be approximately 4.8% and 2.3% of the processed aromatase P-450 mRNA in human placenta and human BeWo choriocarcinoma cells, respectively. These results indicate that the segment of 109 bp between exon 1 and exon 2 is a new exon hitherto unidentified and that heterogeneity observed in the 5'-untranslated sequence of human aromatase P-450 mRNA is, at least in part, caused by alternative splicing of this new exon.

Growth suppression of MCF-7 human breast cancer cells by aromatase inhibitors: a new system for aromatase inhibitor screening

In our previous study we found that MCF-7 cells possess aromatase activity and stimulate estrogen receptor-mediated growth. The pathways through which androgens are converted to estrogens by aromatase and estrogens interact with estrogen receptors contribute significantly to growth stimulation. The administration of aromatase inhibitor results in suppression of growth stimulation by androgens. This system enabled us to assess directly the biological activities of aromatase inhibitors. Aromatase activity was inhibited in a dose-dependent manner by the addition of aminoglutethimide and CGS 16949A, competitive inhibitors, and of 14 alpha-hydroxy-4-androstene-3,6,17-trione and 4-hydroxy-androstenedione, mechanism-based inhibitors. After preincubation with mechanism-based inhibitors, aromatase activity was significantly suppressed, whereas after preincubation with competitive inhibitors, it was adversely increased. These effects were concentration- and time-dependent. Preincubation with competitive inhibitors resulted in augmentation of subsequent androgen stimulation of thymidine incorporation, while preincubation with mechanism-based inhibitors resulted in diminished stimulation by subsequent androgen administration. These results suggest that in MCF-7 cells competitive inhibitors adversely induce aromatase and accelerate the subsequent androgen stimulation of DNA synthesis. Suicide inhibitors are more effective than competitive inhibitors. This system will be useful for aromatase inhibitor screening.

A unique aromatase (P-450AROM) mRNA formed by alternative use of tissue-specific exons 1 in human skin fibroblasts

Aromatase mRNA in human skin fibroblasts was greatly increased in the presence of dexamethasone. Aromatase cDNA was prepared depending on mRNA of dexamethasone-treated fibroblasts by the PCR method including the rapid amplification of cDNA ends (RACE) protocol. The isolated cDNA had the same sequence as placental aromatase cDNA in the region encoded by exons 2-10. However, all 5'-fragments obtained from fibroblast aromatase cDNA contained a unique sequence in the region encoded by exon 1. A unique sequence was also deduced for the region between exons 1 and 2 of the placental aromatase gene from its cDNA, indicating that this region is used as an exon 1 by alternative splicing in skin fibroblasts. Tissue-specific use of multiple exons 1 in the splicing of aromatase transcripts was demonstrated by the mRNAs obtained from various tissues.

Immunohistochemical distribution of aromatase and 3B-hydroxysteroid dehydrogenase in human hair follicle and sebaceous gland

Human hair follicles (HF) and sebaceous glands (SG) were assessed for the presence and distribution of the cytochrome P-450-aromatase (AR) and 3B-hydroxysteroid dehydrogenase (3B-HSD) enzymes. Immunohistochemical methods were used to examine both enzymes in male and female human skin specimens at various ages and different body sites. AR was found in the external root sheath of anagen, terminal HF, and in SG, whereas the 3B-HSD was found only in the SG. AR was rarely found in telogen HF. The expression of both enzymes, AR and 3B-HSD, did not vary with body site or sex. Localizing AR in the external root sheath of anagen HF suggests that AR may have a function in the HF cycle. We hypothesize that AR may be one of many enzymes or factors that play a role in the HF cycle by regulating the level of androgens formed locally, whereas 3B-HSD is localized in SG, converting weak androgen precursors to potent androgens, stimulating lipogenesis.

De novo expression of aromatase in gastric carcinoma. Light and electron microscopic immunohistochemical and immunoblot study

We have performed immunohistochemical and immunochemical studies of steroidogenic enzymes involved in estrogen biosynthesis in 30 cases of gastric carcinoma in order to investigate possible in situ production of estradiol (E 2) in carcinoma cells. Positive incidence of immunoreactivity for E 2, testosterone (T), cholesterol side-chain cleavage enzyme (P-450 scc) and aromatase (P-450 arom) were 17/30 (56.7%), 11/30 (36.7%), 3/30 (10.0%) and 23/30 (76.7%), respectively on light microscopy. Estrogen receptor (ER) immunoreactivity was not observed in any of the 30 cases examined. Normal gastric mucosa was negative for P-450 arom and P-450 scc. Examination of serial sections revealed that immunoreactivity of E 2 and P-450 arom were located in the same cells of carcinomatous glands. Immunoelectron microscopy demonstrated that E 2 and P-450 arom were located along the membrane and cisternae of smooth endoplasmic reticulum (sER). Western blot analysis showed one major band of 55 kDa of P-450 arom in the gastric carcinoma tissues examined. Retrospective analysis of immunohistochemistry of E 2 in 108 cases of gastric carcinoma revealed that E 2 positive carcinoma cases were likely to demonstrate better survival rate than negative cases. These results above strongly suggest that E 2 is produced by de novo expressed aromatase in gastric carcinoma cells and is possibly involved in the biology of gastric carcinoma cells.

Steroid chemistry and hormone controls during the hair follicle cycle

Human hair follicles contain several steroid enzymes capable of transforming weak androgens, such as dehydroepiandrosterone, into more potent target tissue androgens, such as testosterone and dihydrotestosterone. Kinetic constants have been evaluated for the 3-alpha, 3-beta, and 17-beta hydroxysteroid dehydrogenase enzymes, 5a-reductase, and the aromatase enzyme in isolated human HF from scalp of men and women with androgenetic alopecia. The apparent Km values did not differ for each enzyme whether present in bald, receded HF or thick, anagen HF of men or women. However, levels of specific activity varied greatly in the frontal versus occipital HF analyzed. The androgen receptor content and activation factors also differ between men and women. The steroid mechanisms influencing AGA in men and women may be similar, but differences in the specific activity/amounts of enzymes, receptors, and activation factors differ between men and women. These findings may explain the varied clinical presentations of men and women with AGA, and may shape treatment options for the future.

Isolation of a full-length cDNA encoding mouse aromatase P450

A full-length cDNA clone for aromatase P450 has been isolated from a pregnant mouse ovarian cDNA library. The insert of this clone (2394 bp) contains a 1509-bp open reading frame encoding 503 amino acid residues together with a 46-bp 5'-untranslated stretch and an 839-bp 3'-untranslated region to which a poly(A) tract is attached. Northern blot analysis of ovarian RNA from pregnant mice reveals a major mRNA band of 2.5 kb with a minor band of 2.1 kb. Comparison of mouse aromatase P450 with that of rat, human, and chicken shows 91, 81, and 69% identity in the nucleotide sequence and 92, 79, and 69% identity in the deduced amino acid sequence, respectively. The membrane-spanning domain of mouse aromatase P450 is estimated to be an extremely hydrophobic segment located within the N-terminal region of the molecule. Furthermore, a highly conserved heme-binding domain is noticed.

Structural and functional characterization of human aromatase P-450 gene

The gene encoding aromatase P-450 (CYP XIX) has been isolated from two types of human genomic DNA libraries. It spans at least 70 kb and consists of 10 exons. The translational initiation site and the termination site are located in exon 2 and exon 10, respectively. The promoter region of the gene contains a TATA box, a CAAT box and two putative AP-1 binding sites beginning at -28, -83, -55 and -68 bp, respectively, from the transcriptional initiation site. In addition, a palindromic nucleotide sequence is observed between -209 and -196 and two types of repetitious hexanucleotide (consensus: AATGAA and CCATAAGG) are also present within the regions between -485 and -433 and between -358 and -331. Transient expression studies of chloramphenicol acetyltransferase constructs bearing various lengths of 5'-flanking region of the gene show that the region between -500 and -243 contains negative cis-acting element(s), whereas the region between -242 and -183 is required for efficient transcriptional activity. Northern blot analysis demonstrates that the expression of aromatose P-450 gene is remarkably stimulated by treatment of cells with 12-O-tetradecanoyl-phorbol 13-acetate. By chloramphenicol acetyltransferase assay the region up to nucleotide position -242 relative to the transcriptional initiation site is shown to participate in the transcriptional responsiveness to this phorbol ester.

Expression of estrogen synthetase (P-450 aromatase) during adipose differentiation of 3T3-L1 cells

The expression of estrogen synthetase (aromatase), catalyzing a rate limiting reaction in estrogen formation, was examined in 3T3-L1 cells during adipose differentiation. The expression of another P-450 enzyme, cholesterol side-chain cleavage enzyme (P-450scc) by the cells was also studied for comparison. The level of specific mRNA for aromatase increased 17-fold during adipogenic conversion and the elevated level was maintained in fully differentiated adipocytes. The level of specific mRNA for P-450scc increased about 5-fold, mainly due to net increase of cellular RNA. Various reagents, such as dexamethasone, testosterone and 1-methyl-3-isobutylxanthine, affected the expression of specific mRNA for aromatase markedly in adipocytes but had scarcely any effect on its level in fibroblasts. In contrast, these reagents caused similar increases in the level of mRNA for P-450scc in the two types of cells. Thus the 3T3-L1 cell line during adipogenic differentiation may be a useful system for studies on the mechanism regulating aromatase gene expression.

Differential effects of 12-O-tetradecanoylphorbol 13-acetate on cytochrome P-450-dependent monooxygenase activities in rat hepatoma cells: induction of P-450I and suppression of P-450II

We have studied the effects of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) on cytochrome P-450-dependent monooxygenase activities in several differentiated and dedifferentiated Reuber rat hepatoma cell lines using aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH), ethoxyresorufin O-deethylase (EROD), and aldrin epoxidase (AE) as test systems. The following results were obtained: (1) Exposure of cultures to 400 nM TPA for 18-24 h increased AHH activities in the differentiated lines 2sFou, H41IEC3/G- and Fao as well as in the dedifferentiated line 5L, 1.5-2.5-fold. The phorbol ester did not affect AHH activity in the dedifferentiated line H5. (2) EROD, a marker for P-450I, was induced by the phorbol ester to a similar degree as AHH. (3) A monoclonal antibody directed against P-450I strongly inhibited the AHH activity induced by TPA. (4) The onset of AHH or EROD induction by TPA was much later than that elicited by benz[a]anthracene. (6) In contrast to the induction of AHH and EROD, TPA decreased AE activity, a marker for P-450II, by about 50% in all the cell lines containing this monooxygenase activity. (7) The half-maximum-effect concentration of TPA for inducing or suppressing AHH and AE, respectively, was approximately 20 nM. (8) TPA did not interfere with AHH induction by benz[a]anthracene. However, the phorbol ester moderately decreased AHH induction and markedly suppressed AE induction by dexamethasone. The results indicate that TPA simultaneously induces P-450I and suppresses P-450II forms in rat hepatoma cells. P-450I induction by TPA in these cells did not appear to depend on their status of differentiation. Furthermore, the results suggest that the mechanism of P-450I induction by TPA differs from that elicited by polycyclic aromatic hydrocarbons or glucocorticoids.