The hamster androgen receptor promoter: a molecular analysis

The Harderian gland: Endocrine function and hormonal control

The Harderian gland (HG) is an exocrine gland located within the eye socket in a variety of tetrapods. During the 1980s and 1990s the HG elicited great interest in the scientific community due to its morphological and functional complexity, and from a phylogenetic point of view. A comparative approach has contributed to a better understanding of its physiology. Whereas the chemical nature of its secretions (mucous, serous or lipids) varies between different groups of tetrapods, the lipids represent the more common component among different species. Indeed, besides being an accessory to lubricate the nictitating membrane, the lipids may have a pheromonal function. Porphyrins and melatonin secretion is a feature of the rodent HG. The porphyrins, being phototransducers, could modulate HG melatonin production. The melatonin synthesis suggests an involvement of the HG in the retinal-pineal axis. Finally, StAR protein and steroidogenic enzyme activities in the rat HG suggests that the gland contributes to steroid hormone synthesis. Over the past twenty years, much has become known on the hamster (Mesocricetus auratus) HG, unique among rodents in displaying a remarkable sexual dimorphism concerning the contents of porphyrins and melatonin. Mainly for this reason, the hamster HG has been used as a model to compare, under normal conditions, the physiological oxidative stress between females (strong) and males (moderate). Androgens are responsible for the sexual dimorphism in hamster and they are known to control the HG secretory activity in different species. Furthermore, HG is a target of pituitary, pineal and thyroid hormones. This review offers a comparative panorama of the endocrine activity of the HG as well as the hormonal control of its secretory activity, with a particular emphasis on the sex dimorphic aspects of the hamster HG.

Hormonal regulation and characterization of MHG30 gene, a desaturase-like gene of hamster harderian gland

The harderian gland (HG) is an orbital gland of the vast majority of land vertebrates. In the Syrian hamster these glands display a marked sexual dimorphism. Here we present data on a male specific clone named MHG30. The MHG30 cDNA (1470 bp) has significant sequence homologies with human #15μ10#Δ6-desaturase enzymes. The expression of MHG30 has been found in male HG and in the liver of both sexes, no other tissue showing the presence of MHG30 mRNA. Castration brings the MHG30 levels below detectable level in about 7 days. In in vitro cultures of male hamster HG cells, androgens (A) determine an enhancement of MHG30 expression in a time-dependent manner. Conversely, a continuous decrement has been observed in control cells and in cells treated with A plus flutamide (F) or with A and cycloheximide (Cy). Incubation of cells in cultures supplemented with desamethason (Dex) or thyroid hormone (T3) also increases MHG30 expression while 17β-estradiol prevents the stimulatory effect exerted by A, Dex and T3. Findings strongly suggest that the MHG30 gene could be involved in supporting the sexual dimorphism and its expression is likely triggered by a series of hormonal interactions.

Thyroid hormones in male reproductive development: evidence for direct crosstalk between the androgen and thyroid hormone axes

Thyroid hormones (THs) exert a broad range of effects on development in vertebrate species, demonstrating connections in nearly every biological endocrine system. In particular, studies have shown that THs play a role in sexual differentiation and gonadal development in mammalian and non-mammalian species. There is considerable evidence that the effects of THs on reproductive development are mediated through the female hormonal axis; however, recent findings suggest a more direct crosstalk between THs and the androgen axis. These findings demonstrate that THs have considerable influence in the sexual ontogeny of male vertebrates, through direct interactions with select sex-determining-genes and regulation of gonadotropin production in the hypothalamus-pituitary-gonad axis. THs also regulate androgen biosynthesis and signaling through direct and indirect regulation of steroidogenic enzyme expression and activity. Novel promoter analysis presented in this work demonstrates the potential for direct and vertebrate wide crosstalk at the transcriptional level in mice (Mus musculus), Western clawed frogs (Silurana tropicalis) and medaka (Oryzias latipes). Cumulative evidence from previous studies; coupled with novel promoter analysis suggests mechanisms for a more direct crosstalk between the TH and male reproductive axes across vertebrate species.

Mechanisms and significance of nuclear receptor auto- and cross-regulation

The number of functional hormone receptors expressed by a cell in large part determines its responsiveness to the hormonal signal. The regulation of hormone receptor gene expression is therefore a central component of hormone action. Vertebrate steroid and thyroid hormones act by binding to nuclear receptors (NR) that function as ligand-activated transcription factors. Nuclear receptor genes are regulated by diverse and interacting intracellular signaling pathways. Nuclear receptor ligands can regulate the expression of the gene for the NR that mediates the hormone's action (autoregulation), thus influencing how a cell responds to the hormone. Autoregulation can be either positive or negative, the hormone increasing or decreasing, respectively, the expression of its own NR. Positive autoregulation (autoinduction) is often observed during postembryonic development, and during the ovarian cycle, where it enhances cellular sensitivity to the hormonal signal to drive the developmental process. By contrast, negative autoregulation (autorepression) may become important in the juvenile and adult for homeostatic negative feedback responses. In addition to autoregulation, a NR can influence the expression other types of NRs (cross-regulation), thus modifying how a cell responds to a different hormone. Cross-regulation by NRs is an important means to temporally coordinate cell responses to a subsequent (different) hormonal signal, or to allow for crosstalk between hormone signaling pathways.

Androgens and the male reproductive tract: an overview of classical roles and current perspectives

Androgens are steroid hormones that play key roles in the development and maintenance of male phenotype and reproductive function. These hormones also affect the function of several non-reproductive organs, such as bone and skeletal muscle. Endogenous androgens exert most of their effects by genomic mechanisms, which involve hormone binding to the androgen receptor (AR), a ligand-activated transcription factor, resulting in the modulation of gene expression. AR-induced non-genomic mechanisms have also been reported. A large number of steroidal and non-steroidal AR-ligands have been developed for therapeutic use, including the treatment of male hypogonadism (AR agonists) and prostate diseases (AR antagonists), among other pathological conditions. Here, the AR gene and protein structure, mechanism of action and AR gene homologous regulation were reviewed. The AR expression pattern, its in vivo regulation and physiological relevance in the developing and adult testis and epididymis, which are sites of sperm production and maturation, respectively, were also presented.

Prognostic relevance of androgen receptor detection in operable breast cancer

BACKGROUND AND OBJECTIVES

Androgen receptor (AR) is relevant for prognostication in breast cancer. Different determination methods and cut-off levels hamper interpretation and comparisons of studies. Long-term prognostic evaluation of different AR assays in patients comprising operable breast cancers is scarce.

METHODS

AR was evaluated in 120 primary tumors using the dextran-coated charcoal method (charc-AR), and quantitative immunohistochemistry (IHC) on whole sections (WS) and tissue microarrays (TMA). Nuclear and cytoplasmic-AR localization was determined, and the prognostic importance of AR assays was assessed. Comparisons and correlations with the mitotic activity index (MAI), estrogen receptor (ERalpha), progesterone receptor (PR), HER-2, and histological grade (WHO I-III) were made.

RESULTS

Nuclear-AR in WS, but not charc-AR, strongly correlated with MAI (P = 0.001). However, prognostic information appeared in univariate survival analyses only. Nuclear-AR in TMA was not prognostic. Charc-AR was independent prognostic in node positives both for relapse free survival (RFS) and breast cancer specific survival (BCSS). Both charc-AR and IHC cytoplasmic-AR provided independent prognostic survival information for BCSS in women <55 years.

CONCLUSION

Methods that can detect AR localized in the cytoplasm yield important prognostic information, and further studies in patients with operable breast cancer are warranted.

Hormonal regulation and characterisation of the aldehyde oxidase-like gene of hamster Harderian gland

The HG is a compound tubulo-alveolar gland located in the orbital cavity of the majority of vertebrates. In the golden hamster it shows a clear cut sexual dimorphism in both morphological and biochemical parameters such as cell types, protein pattern, lipid metabolism, porphyrin content, steroid hormone receptor expression. In a previous study we found that in primary culture of male hamster Harderian gland (HG), androgens (A) increase the MHG07 (male Harderian gland) expression and this effect is abrogated by both flutamide and cycloheximide. The present study represents a deeper analysis on MHG07 regulation by other members of steroid/thyroid hormone superfamily. Estrogens (E) impair the stimulatory effect of A and after the addition of a pure anti-estrogen, ICI 164,384, the negative effect of E is abrogated. Dexamethasone (Dex), used alone or in combination with A negatively affect the MHG07 expression. Also T(3) increases the expression of MHG07 mRNA. Progesterone (P) does not affect the expression of MHG07 mRNA. The use of cycloheximide abrogates the effect of steroids, suggesting that the latter act through their own receptors. Dose-response experiments show that low steroid concentrations (10(-12)M) are sufficient to affect the MHG07 expression. It is argued that the expression of MHG07 is under a highly coordinate relationship between androgen, estrogen, glucocorticoid, retinoic acid and thyroid hormones.

Sequence analysis of retinoic acid receptor alpha, beta and gamma isoforms in the lizard, Podarcis sicula

Vitamin A and its principal biologically active derivative, retinoic acid (RA), play a fundamental role in diverse processes, such as proliferation, differentiation, morphogenesis, metabolism and apoptosis of many types of cells. In addition, RA has been shown to be involved in the regulation of testicular function. These effects are mediated by interaction with two families of nuclear receptors, retinoic acid receptor (RAR) and retinoid X receptor (RXR), each with three subtypes alpha, beta and gamma. The physiological involvement of retinoids in testicular function has been conducted mainly in mammals. Recently, we found that exogenous all-trans-retinoic acid impairs spermatogenesis and enhance testicular germ cell apoptosis in the lizard, Podarcis sicula, a seasonal breeder. To further investigate the role of retinoic acid in lizard, we focus this work principally on the characterization of lizard retinoic acid receptors (alpha, beta and gamma isoforms). RARalpha is 2720 bp long with a putative ORF between 699 and 2133. A Kozac sequence is present at 696 and a putative poly-adenilation site is present in position 2612. The RARalpha sequence shares 87% homology with mouse RARalpha mRNA while it has 76 and 80% homology with lizard RARbeta and gamma mRNAs. RARbeta is 2478 bp long showing a putative ORF between 196 and 1543. A canonical Kozac sequence is present at 193 and a putative poly-adenilation site is present at 2294. RARbeta shares 91% homology with mouse RARbeta mRNA and has 76% homology with both RARalpha and gamma. RARgamma is 2416bp long. With a putative ORF between 444 and 1818. A Kozac sequence is present at 441 and a putative poly-adenilation site is present at 2288. RARgamma shares 86% homology with mouse RARbeta mRNA and has 80 and 76% homology with both RARalpha and beta respectively. It is worth to note that, as in mouse, the 5'UTR of all isoforms is TATA and CAAT less. Both Northern blot and PCR analyses indicate that lizard testis expresses only RARalpha and RARbeta mRNAs, while RARgamma mRNA transcript was not found. In the period analysed, RARbeta was expressed during the gonadal full activity (May) and RARalpha was present in the post-reproductive period (August). During the autumnal recrudescence (October) RARalpha and RARbeta are co-expressed and, as indicated by quantitative PCR analysis, RARbeta mRNA levels are lower than RARalpha ones. Thus, the appearance and abundance of each receptor correspond to a specific phase of lizard reproductive cycle, allow us to hypothesize that each RAR subtype could play a specific role in the regulation of spermatogenetic activity. The results of the present study show, for the first time, the characterization of RAR mRNAs in the testis of lizard P. sicula, whose expression is related to the different phase of reproductive cycle. Moreover, the gamma form, is principally expressed in the skin during the March-July period, having probably a role in regulating skin homeostasis and colour livery, which are important factor in mating during the reproductive cycle.

17beta-estradiol induces apoptosis in the developing rodent prostate independently of ERalpha or ERbeta

Estrogens induce both proliferative and antiproliferative responses in the prostate gland. To date, antiproliferative effects of estrogens are generally considered to be due to systemic antiandrogenic actions. However, estrogen action mediated through estrogen receptor (ER) beta was recently suggested as another mechanism of induction of apoptosis in the prostate. This study aimed to explore the hypothesis that the antiproliferative effects of estrogen are directly mediated through ERbeta using a prostate organ culture system. We previously reported effects of 17beta-estradiol (E2) using rat ventral prostate (VP) tissues, and adapted the system for culturing mouse tissues. In both rat and mouse models, estrogen-induced apoptosis was detected that was spatially and regionally localized to the epithelium of the distal tips. Using organ cultures of alphaER knockout (alphaERKO) and betaERKO prostates, we failed to demonstrate that apoptosis induced by E2 was mediated through either receptor subtype. Activation of ER-selective ligands (ERalpha, propyl pyrazole triol, ERbeta, diaryl-proprionitrile, and 5alpha-androstane-3beta,17beta-diol) in organ culture experiments failed to induce apoptosis, as did the membrane impermeable conjugate E2:BSA, discounting the possibility of nongenomic effects. Consequently, E2 regulation of androgen receptor (AR) expression was examined and, in the presence of nanomolar testosterone levels, E2 caused a specific reduction in AR protein expression in wild-type, alphaERKO, and betaERKO mice, particularly in the distal region where apoptosis was detected. This down-regulation of AR protein provides a possible mechanism for the proapoptotic action of E2 that is independent of ERs or nongenomic effects.