DAX-1, as an androgen-target gene,inhibits aromatase expression: a novel mechanism blocking estrogen-dependent breast cancer cell proliferation

Sexual hormones, estrogens and androgens, determine biological response in a tissue- and gender-specific manner and have a pivotal role in endocrine-mediated tumorigenesis. In situ estrogen production by aromatase is a critical determinant for breast cancer growth and progression. On the contrary, clinical and in vitro studies indicate that androgens have a protective role in mammary carcinogenesis. Here, we demonstrated, in hormone-dependent breast cancer cells, the existence of a functional interplay between the androgen receptor (AR), the orphan nuclear receptor DAX-1 and the aromatase enzyme involved in the inhibition of the estrogen-dependent breast cancer cell proliferation exerted by androgen signaling. Indeed, our results revealed, in MCF-7 cells, that ligand-activated AR induces the expression of the orphan nuclear receptor DAX-1 by direct binding to a newly identified androgen-response-element within the DAX-1 proximal promoter. In turn, androgen-induced DAX-1 is recruited, in association with the corepressor N-CoR, within the SF-1/LRH-1 containing region of the aromatase promoter, thereby repressing aromatase expression and activity. In elucidating a novel mechanism by which androgens, through DAX-1, inhibit aromatase expression in breast cancer cell lines, these findings reinforce the theory of androgen- opposing estrogen-action, opening new avenues for therapeutic intervention in estrogen-dependent breast tumors.     

Measurement of Aromatisation by a Urine Technique Suitable for the Evaluation of Aromatase Inhibitors in Vivo

Abstract

By modification of a recently developed method for separation of radio-labelled urinary oestrogens we were able to separate oestrogen metabolites and measure their isotope ratios in urine following injections of [³H]Δ⁴-androstenedione and [¹⁴C]oestrone. This method provides a useful tool for studying in vivo aromatisation of Δ⁴-androstenedione into oestrone in breast cancer patients before and during treatment with aromatase inhibitors.     

Blocking oestradiol synthesis pathways with potent and selective coumarin derivatives

A comprehensive set of 3-phenylcoumarin analogues with polar substituents was synthesised for blocking oestradiol synthesis by 17-β-hydroxysteroid dehydrogenase 1 (HSD1) in the latter part of the sulphatase pathway. Five analogues produced ≥62% HSD1 inhibition at 5?µM and, furthermore, three of them produced ≥68% inhibition at 1?µM. A docking-based structure-activity relationship analysis was done to determine the molecular basis of the inhibition and the cross-reactivity of the analogues was tested against oestrogen receptor, aromatase, cytochrome P450 1A2, and monoamine oxidases. Most of the analogues are only modestly active with 17-β-hydroxysteroid dehydrogenase 2 – a requirement for lowering effective oestradiol levels in vivo. Moreover, the analysis led to the synthesis and discovery of 3-imidazolecoumarin as a potent aromatase inhibitor. In short, coumarin core can be tailored with specific ring and polar moiety substitutions to block either the sulphatase pathway or the aromatase pathway for treating breast cancer and endometriosis.     

Efficacy of exemestane,a new generation of aromatase inhibitor,on sex differentiation in a gonochoristic fish

We report the first use of exemestane (EM), a steroidal aromatase inhibitor (AI) commercially known as aromasin, in studies of sex differentiation in fish. The effectiveness of EM was examined in two different age groups of the gonochoristic fish, Nile tilapia (Oreochromis niloticus). Untreated control fish (all female) showed normal ovarian differentiation through 120 days after hatching (dah), whereas fish treated with EM at 1000 and 2000 µg/g of feed from 9 dah through 35 dah, the critical period for sex differentiation, exhibited complete testicular differentiation; all stages of spermatogenic germ cells were evident and well developed efferent ducts were present. Fish treated with EM at 1000 µg/g of feed from 70 dah through 100 dah significantly suppressed plasma estradiol-17β level and increased level of 11-ketotestosterone. Furthermore, untreated control fish showed strong gonadal expression of the steroidogenic enzymes P450 cholesterol-side chain-cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), and cytochrome P450 aromatase (P450arom). In contrast, EM-treated fish showed immunopositive reactions against P450scc and 3β-HSD but not against P450arom in interstitial Leydig cells. These results indicate that treatment of tilapia juveniles with EM during sex differentiation leads to the development of testes, apparently by a complete suppression of aromatase activity.     

Transdifferentiation,Metaplasia and Tissue Regeneration

Transdifferentiation is defined as the conversion of one cell type to another. It belongs to a wider class of cell type transformations called metaplasias which also includes cases in which stem cells of one tissue type switch to a completely different stem cell. Numerous examples of transdifferentiation exist within the literature. For example, isolated striated muscle of the invertebrate jellyfish (Anthomedusae) has enormous transdifferentiation potential and even functional organs (e.g. tentacles and the feeding organ (manubrium) can be generated in-vitro. In contrast, the potential for transdifferentiation in vertebrates is much reduced, at least under normal (non-pathological) conditions. But despite these limitations, there are some well-documented cases of transdifferentiation occurring in vertebrates. For example, in the newt, the lens of the eye can be formed from the epithelial cells of the iris. Other examples of transdifferentiation include the appearance of hepatic foci in the pancreas, the development of intestinal tissue at the lower end of the oesophagus and the formation of muscle, chondrocytes and neurons from neural precursor cells. Although controversial, recent results also suggest the ability of adult stem cells from different embryological germlayers to produce differentiated cells e.g. mesodermal stem cells forming ecto- or endodermally-derived cell types. This phenomenon may constitute an example of metaplasia. The current review examines in detail some well-documented examples of transdifferentiation, speculates on the potential molecular and cellular mechanisms that underlie the switches in phenotype, together with their significance to organogenesis and regenerative medicine.     

Synthesis of steroid hormones in the porcine oviduct during early pregnancy

Past studies of the oviducts have documented oviductal steroid production during the oestrous cycle in pigs. The present study examined whether the pig oviducts are the source of steroid hormones during early pregnancy. In the ampulla and isthmus, the expression of 3β-hydroxysteroid dehydrogenase (3βHSD) and aromatase cytochrome P450 (CYP19) mRNA by real-time PCR, cellular localization and quantities of the studied proteins by immunofluorescence and Western blot analysis, and concentration of steroid hormones in oviductal flushings by radioimmunoassay, were studied. The expression of 3βHSD in the ampulla and isthmus was correlated (r?=?0.89) and higher on Days 2–3 and 15–16 than on Days 10–11 and 12–13. CYP19 expression was elevated in the ampulla on Days 2–3, 10–11 and 15–16 and in the isthmus on Days 2–3 vs. the other days studied. The studied proteins were localized in oviductal epithelial cells. In the ampulla, the quantity of 3βHSD protein did not change, and was greater in the isthmus on Days 2–3 vs. Days 12–13 of pregnancy. The P450arom protein quantity increased in the ampulla on Days 2–3 vs. Days 10–11 and 15–16 and vs. Days 10–11 and 12–13 in the isthmus. The concentrations of progesterone and androstenedione in oviductal flushings were lowest on Days 12–13 and on Days 2–3 and 15–16, respectively, while oestradiol-17β and oestrone levels did not change. Porcine oviducts are the sources of steroid hormones during early pregnancy. The expression of steroidogenic enzymes primarily increases during the embryos presence in the oviduct, i.e., on Days 2–3 of pregnancy.