bluuebunny/crossref_metadata_2025 huggingface dataset:
Constitutive expression of IGF-binding protein-3 by mammary epithelial cells alters signaling through Akt and p70S6 kinase
Authors: Grill CJ , Sivaprasad U , Cohick WS
Published: December 2004

IGF-binding protein-3 (IGFBP-3) potentiates IGF-I action in the non-transformed mammary epithelial cell line, MAC-T, via a mechanism that is independent of its ability to bind IGF-I. The goal of the present study was to determine if IGFBP-3 might enhance IGF action by influencing intracellular signaling events downstream of the IGF receptor. IGF-I stimulated a time-dependent activation of Akt in which phosphorylation of Ser(473) was detectable by 1 min and maximal at 15 min. In contrast, no activation of extracellular signal-regulated kinase (ERK)1/2 by IGF-I was observed although basal phosphorylation was readily detectable. In MAC-T cells constitutively expressing IGFBP-3 (+BP3), phosphorylation of Akt following stimulation with IGF-I was enhanced relative to mock-transfected cells (Mock). The enhancement was detectable within 1 min of IGF-I treatment and persisted for up to 10 h. The increased phosphorylation observed by Western blotting corresponded to a 1.7-fold increase in Akt kinase activity. The enhanced Akt response was elicited by factors that activate the IGF receptor but exhibit reduced affinity for IGFBP-3, such as Long R(3)IGF-I, B chain IGF-I and insulin. In contrast, [Leu(60)]IGF-I, which binds IGFBP-3 but has reduced affinity for the IGF receptor, failed to induce comparable activation, suggesting that an association between IGF-I and IGFBP-3 is not required for the effect. The enhanced Akt activation could not be mimicked by addition of exogenous IGFBP-3. Akt phosphorylation was also enhanced by transforming growth factor-alpha in +BP3 cells, indicating that the effect was not specific to IGF-I. Similar to Akt, phosphorylation of p70S6 kinase (p70(S6K)) by IGF-I was also enhanced in +BP3 cells relative to Mock cells at both 15 min and 10 h. However, this was largely an effect of lower basal activation of p70(S6K) in +BP3 cells. These data indicate that endogenous IGFBP-3 potentiates IGF action in MAC-T cells by enhancing signaling via the phosphatidylinositol 3-kinase pathway at a point that is downstream of IGF receptor activation. Further studies will delineate specific mechanisms by which IGFBP-3 may influence intracellular events that regulate growth in mammary epithelial cells.
cAMP-dependent transcription of steroidogenic genes in the human adrenal cortex requires a dual-specificity phosphatase in addition to protein kinase A
Authors: Sewer MB , Waterman MR
Published: December 2004

Steroid hormone biosynthesis in the adrenal cortex is controlled by the peptide hormone adrenocorticotropin (ACTH), which acts to increase intracellular cAMP and results in the activation of cAMP-dependent protein kinase A (PKA) and subsequent increase in steroidogenic gene transcription. Protein phosphorylation by PKA activates transcription of genes encoding steroidogenic enzymes; however the precise proteins which are phosphorylated remain to be determined. We have recently shown that phosphoprotein phosphatase (PP) activity is essential for cAMP-dependent transcription of the human CYP17 (hCYP17) gene in H295R adrenocortical cells. The aim of our current studies was to determine if inhibition of PP activity attenuates cAMP-dependent mRNA expression of other steroidogenic genes in H295R cells. Using various inhibitors of serine/threonine and tyrosine PPs, we examined the role of phosphatase activity on cAMP-dependent transcription of steroidogenic genes in the adrenal cortex. CYP11A, CYP11B1/2, CYP21, and adrenodoxin also require PP activity for cAMP-stimulated gene expression. Inhibition of both serine/threonine and tyrosine PP activities suppresses the cAMP-dependent mRNA expression of several steroidogenic genes, suggesting that a dual-specificity PP is essential for conveying ACTH/cAMP-stimulated transcription. We propose that PKA phosphorylates and activates a dual-specificity phosphatase, which mediates steroidogenic gene transcription in response to ACTH/cAMP.
Human alpha 2A-adrenergic receptor gene expressed in transgenic mouse adipose tissue under the control of its regulatory elements
Authors: Boucher J , Castan-Laurell I , Le Lay S , Grujic D , Sibrac D , Krief S , Lafontan M , Lowell BB , Dugail I , Saulnier-Blache JS , Valet P
Published: December 2004

Catecholamines regulate white adipose tissue function and development by acting through beta- and alpha2-adrenergic receptors (ARs). Human adipocytes express mainly alpha 2A- but few or no beta 3-ARs while the reverse is true for rodent adipocytes. Our aim was to generate a mouse model with a human-like alpha2/beta-adrenergic balance in adipose tissue by creating transgenic mice harbouring the human alpha 2A-AR gene under the control of its own regulatory elements in a combined mouse beta 3-AR-/- and human beta 3-AR+/+ background. Transgenic mice exhibit functional human alpha 2A-ARs only in white fat cells. Interestingly, as in humans, subcutaneous adipocytes expressed higher levels of alpha2-AR than perigonadal fat cells, which are associated with a better antilipolytic response to epinephrine. High-fat-diet-induced obesity was observed in transgenic mice in the absence of fat cell size modifications. In addition, analysis of gene expression related to lipid metabolism in isolated adipocytes suggested reduced lipid mobilization and no changes in lipid storage capacity of transgenic mice fed a high-fat diet. Finally, the development of adipose tissue in these mice was not associated with significant modifications of glucose and insulin blood levels. Thus, these transgenic mice constitute an original model of diet-induced obesity for in vivo physiological and pharmacological studies with respect to the alpha2/beta-AR balance in adipose tissue.
The multiple endocrine neoplasia type 1 gene product, menin, inhibits the human prolactin promoter activity
Authors: Namihira H , Sato M , Murao K , Cao WM , Matsubara S , Imachi H , Niimi M , Dobashi H , Wong NC , Ishida T
Published: December 2004

Menin is a protein encoded by the gene mutated in multiple endocrine neoplasia type 1 (MEN1) characterized by multiple endocrine tumors of the parathyroid glands, pancreatic islets and the anterior pituitary, especially prolactinoma. In this study, we examined the effects of menin on human prolactin (hPRL) expression. In rat pituitary GH3 cells stably expressing menin, both PRL gene expression/secretion and thymidine incorporation into DNA were inhibited as compared with mock-transfected cells. The transcriptional activity of PRL promoter in GH3 cells co-transfected with menin was significantly decreased. A deletion mutation (569 delC), which we identified in a Japanese MEN1 family, was introduced into menin. When GH3 cells were transfected with a mutant menin expression vector, inhibition of hPRL promoter activity was partially reversed. These observations suggest that menin inhibits hPRL promoter activity and cell proliferation, raising the possibility that menin might play an important role in the tumorigenesis of prolactinoma.
11beta-hydroxylase and aldosterone synthase expression in fetal rat hippocampal neurons
Authors: MacKenzie SM , Lai M , Clark CJ , Fraser R , Gomez-Sanchez CE ,   Seckl, Connell JM , Davies E
Published: December 2004

The central nervous system produces many of the enzymes responsible for corticosteroid synthesis. A model system to study the regulation of this local system would be valuable. Previously, we have shown that primary cultures of hippocampal neurons isolated from the fetal rat can perform the biochemical reactions associated with the enzymes 11beta-hydroxylase and aldosterone synthase. Here, we demonstrate directly that these enzymes are present within primary cultures of fetal rat hippocampal neurons.
Comparison of the effect of oestradiol, tamoxifen and raloxifene on nerve growth factor-alpha expression in specific neonatal mouse uterine cell types using laser capture microdissection
Authors: Green AR , Edwards RE , Greaves P , White IN
Published: December 2004

Oral dosing of CD-1 mice on days 2-5 after birth with tamoxifen but not raloxifene disrupts the development of the myometrium, resulting in adult uterine adenomyosis. Using laser capture microdissection and RT-PCR we have investigated nerve growth factor (NGF) and cognate receptor expression in uterine cells of 6-day-old pups that may be important in early developmental changes that give rise to adenomyosis. NGF down-regulation is known to occur during terminal myogenic differentiation. NGF was found exclusively in endometrial luminal epithelium of controls. It was up-regulated 18-fold in the luminal epithelium following dosing with tamoxifen but not raloxifene. Western blotting for NGF protein in the whole uterus showed a 25-fold increase after tamoxifen treatment. Expression of the low affinity p75 neutrophin receptor (p75(NTR)) was twofold higher in the myometrium compared with luminal epithelium or stroma. This was not altered following tamoxifen treatment. There was no detectable expression of high affinity tyrosine kinase receptor (trkA(NGFR)). This study shows luminal epithelial cells of the endometrium primarily form NGF. This suggests that NGF normally regulates the differentiation of the mesenchyme into uterine myocytes through paracrine mechanisms and that an early disturbance of this process plays a key role in the subsequent development of adenomyosis.
1,25-Dihydroxyvitamin D3 inhibits thyroid hormone-induced osteocalcin expression in mouse osteoblast-like cells via a thyroid hormone response element
Authors: Varga F , Spitzer S , Rumpler M , Klaushofer K
Published: December 2004

Thyroid hormones are important regulators of bone development and metabolism. We have demonstrated that tri-iodothyronine (T3) increased and 1,25-dihydroxyvitamin D3 (1,25D3) attenuated the T3-stimulated expression of osteocalcin (OCN) in the osteoblast-like cell line MC3T3-E1. By means of transfection of promoter-reporter gene constructs we investigated the basal and the regulated transcription of this gene by both hormones. We found that a 0.67 kbp and a 1.3 kbp fragment of the mouse OCN OG2 promoter containing two Runx2 binding sites were significantly more active than a smaller fragment containing only one Runx2 binding site. The longer promoter fragments showed a higher reporter gene expression when the transfected cells were treated with 10(-7) M T3. This expression was attenuated by 1,25D3 dose-dependently. These fragments contain a sequence homologue to the recently identified binding site for the 1,25D3 receptor (VDR) in the rat OCN promoter. Deletion of a part of the promoter containing this VDR response element-like sequence (VDRE) resulted in a higher basal expression but abrogated the regulation by T3 and 1,25D3. Electrophoretic mobility shift assays revealed that the deleted sequence was able to bind both in vitro-translated chicken thyroid hormone receptor (TR) and proteins from nuclear extracts that reacted with an antiserum against TR. From these data we conclude that the VDRE-like sequence of the OG2 promoter contains a thyroid hormone response element.
Interleukin-1alpha stimulates steroidogenic acute regulatory protein expression via p38 MAP kinase in immature rat Leydig cells
Authors: Svechnikov K , Stocco DM , Soder O
Published: December 2004

We have investigated the involvement of the steroidogenic acute regulatory (StAR) protein in interleukin-1alpha (IL-1alpha)-induced steroidogenesis in immature (40-day-old) and adult Leydig cells in vitro. Further, IL-1alpha-mediated signaling pathway(s) controlling StAR expression in immature Leydig cells were also studied. IL-1alpha stimulated both androgen production and StAR protein expression in a dose- and time-dependent manner in immature but not adult Leydig cells. These effects of IL-1alpha were prevented by pretreatment of the cells with the specific inhibitors of the p38 MAP kinase, SB203580 and PD169316, suggesting that this kinase is an important part of IL-1alpha signaling in the immature Leydig cell. The present results suggest that IL-1alpha, which is constitutively produced by the rat testis from postnatal day 25, is an important paracrine regulator of postnatal Leydig cell maturation. Regulation of StAR protein expression is one of the possible mechanisms by which IL-1alpha contributes to the differentiation of immature Leydig cells into adult cells.
Cloning and expression of a functional estrogen receptor-alpha from African catfish (Clarias gariepinus) pituitary
Authors: Teves AC , Granneman JC , van Dijk W , Bogerd J
Published: December 2004

An African catfish (Clarias gariepinus) estrogen receptor-alpha (cfERalpha) cDNA fragment was amplified by RT-PCR, in combination with a modified 3'-RACE procedure, on total RNA extracted from pituitary. This cDNA fragment was used to screen an African catfish pituitary cDNA library. A clone was obtained that contained an open-reading frame coding for a 620 amino acid cfERalpha protein with a deduced molecular mass of 68.1 kDa. In addition, a partial African catfish estrogen receptor-beta (cfERbeta) cDNA fragment was amplified by RT-PCR on total RNA extracted from testis. Neighbor-joining analysis was used to infer a phylogenetic classification for cfERalpha and cfERbeta. The tree obtained indicated that there are two major clusters of vertebrate ERs: ERalpha and ERbeta. Within each cluster, teleost and tetrapod ER sister clades could be distinguished. The cfERalpha clustered with other teleost ERalphas, whereas cfERbeta clustered with other teleost ERbetas. The ligand-induced transcriptional activity of cfERalpha was demonstrated in a transient gene expression assay using cells in which an acute estrogenic response was created by co-transfecting cultures with recombinant cfERalpha cDNA expression vector constructs in the presence of an estrogen-dependent reporter plasmid. Real-time, quantitative PCR revealed that cfERalpha transcripts were most abundantly expressed in pituitary, while in all other tIssues tested the relative cfERalpha mRNA levels were less than approximately 5% of the level obtained in pituitary. Moreover, we found that, during pubertal development, the relative cfERalpha mRNA levels gradually increased in African catfish pituitary.
Identification of post-translational modifications resulting from LHbeta polymorphisms by matrix-assisted laser desorption time-of-flight mass spectrometric analysis of pituitary LHbeta core fragment
Authors: Jacoby ES , Kicman AT , Iles RK
Published: December 2004

Metabolism of the human chorionic gonadotrophin (hCG)- and LHbeta-subunits (hCGbeta, LHbeta) terminates with the urinary excretion of core fragment (hCGbetacf, LHbetacf) molecules that retain antigenic shape and constituent N-linked carbohydrate moieties. We have previously demonstrated the resolved mass spectra of hCGbetacf, from which the carbohydrate moieties present at two N-linked glycosylation sites were identified. LHbetacf was subjected to the same mass spectrometric analysis. As LHbeta shares 82% homology with hCGbeta but possesses only one glycosylation consensus site a simpler spectral fingerprint of LHbetacf glycoforms was expected. LHbetacf was reduced with dithiothreitol and analysed by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. Glycoforms were predicted by subtracting the peptide mass from the m/z values of the observed peaks and then sequentially subtracting the masses of the monosaccharide residues of hCGbeta N-linked carbohydrates reported in the literature. The mass spectra of LHbetacf revealed a broad single peak ranging from m/z 8700 to 10 700. Following reduction, this peak was replaced by a set of partially resolved peaks between m/z 4130 and 5205 corresponding to glycosylated forms of the peptide LHbeta6-40. A peak at m/z 4252.2 corresponded to the non-glycosylated peptide LHbeta55-93. Remaining peaks indicated that the pooled sample comprised a wide set of glycoforms, contained LHbetacf with two N-linked carbohydrate moieties and indicated evidence of further glycosylation due to amino acid substitution in polymorphic variants. This is evidence that a single nucleotide polymorphism alters the post-translational modification of a protein and hence its structural phenotype.
Nutritional and hormonal factors control the gene expression of FoxOs, the mammalian homologues of DAF-16
Authors: Imae M , Fu Z , Yoshida A , Noguchi T , Kato H
Published: December 2004

Transcription factors of the FoxO family in mammals are orthologues of the Caenorhabditis elegans forkhead factor DAF-16, which has been characterized as a target of insulin-like signalling. Three members of this family have been identified in rodents: FoxO1, FoxO3 and FoxO4, originally termed FKHR, FKHRL1 and AFX respectively. A number of in vitro studies have revealed that FoxOs are regulated through phosphorylation in response to insulin and related growth factors, resulting in their nuclear exclusion and inactivation. To clarify the mechanisms involved in the regulation of these factors in vivo, we investigated in the present study whether or not, and if so how, their mRNA levels in rat liver respond to the stimuli of several nutritional and hormonal factors. Imposed fasting for 48 h significantly elevated mRNA levels of FoxO1 (1.5-fold), FoxO3 (1.4-fold), and FoxO4 (1.6-fold). Refeeding for 3 h recovered the induced mRNA levels of FoxO1 and FoxO3 to the control levels, but did not affect that of FoxO4. FoxO1 and FoxO4 mRNA levels were proved to be highly reflective of their protein levels measured by Western immunoblotting. Of the three FoxO genes, FoxO4 only showed altered levels of mRNA (a 1.5-fold increase) in response to a protein-free diet. Streptozotocin-induced diabetes for 28 days decreased hepatic mRNA levels of FoxO1 and FoxO3 and increased the level of FoxO4 mRNA, but short-term (7 days) diabetes had fewer effects on the expression of these genes. Insulin replacement partially restored the FoxO1 and FoxO4 mRNA levels, but had no effect on the FoxO3 mRNA level. Daily administration for 1 week of dexamethasone, a synthetic glucocorticoid, increased the mRNA levels of FoxO1 (1.8-fold) and FoxO3 (2.4-fold). These results show that the FoxO genes respond differently to nutritional and hormonal factors, suggesting a new mechanism for the regulation of FoxO-dependent gene expression by these factors. Moreover, changes of FoxO1 and FoxO4 in the nucleus in response to fasting also suggest that the regulation of nucleus/cytoplasm translocation actually functions in vivo.
The renin-angiotensin system and male reproduction: new functions for old hormones
Authors: Leung PS , Sernia C
Published: December 2004

The blood-borne renin-angiotensin system (RAS) is known best for its role in the maintenance of blood pressure and electrolyte and fluid homeostasis. However, numerous tIssues show intrinsic angiotensin-generating systems that cater for specific local needs through actions that add to, or differ from, the circulating RAS. The male reproductive system has several sites of intrinsic RAS activity. Recent focus on the epididymis, by our laboratories and by others, has contributed important details about the local RAS in this tIssue. The RAS components have been localized morphologically and topographically; they have been shown to be responsive to androgens and to hypoxia; and angiotensin has been shown to influence tubular, and consequently, fluid secretion. Components of the RAS have also been found in the testis, vas deferens, prostate and semen. Angiotensin II receptors, type 1 and, to a lesser extent, type 2 are widespread, and angiotensin IV receptors have been localized in the prostate. The roles of the RAS in local processes at these sites are still uncertain and have yet to be fully elucidated, although there is evidence for involvement in tubular contractility, spermatogenesis, sperm maturation, capacitation, acrosomal exocytosis and fertilization. Notwithstanding this evidence for the involvement of the RAS in various important aspects of male reproduction, there has so far been a lack of clinical evidence, demonstrable by changes in fertility, for a crucial role of the RAS in male reproduction. However, it is clear that there are several potential targets for manipulating the activity of the male reproductive system by interfering with the locally generated angiotensin systems.
Expression of estrogen, progesterone and androgen receptors in the oviduct of developing, cycling and pre-implantation rats
Authors: Okada A , Ohta Y , Inoue S , Hiroi H , Muramatsu M , Iguchi T
Published: December 2004

To determine expression and localization of receptors for estrogen (ER), progesterone (PR) and androgen (AR), detailed immunohistochemical evaluations were performed in the Sprague-Dawley rat oviduct during pre- and neonatal development, estrous cycle and pre-implantation period. In addition, real-time RT-PCR studies were conducted to evaluate changes in ERalpha, ERbeta, total PR (PR-A+B), PR-B and AR mRNA expressions. All receptors except for ERbeta were detected in epithelial, and stromal or mesenchymal cells of the fetal and neonatal oviduct, and increased with development. During the estrous cycle and early pregnancy, ERalpha and PR-A+B were expressed in epithelial, stromal and muscle cells throughout the oviduct region, and showed changes in expression predominantly in the isthmus. Only a few epithelial cells in the infundibulum (inf) and ampulla (AMP) showed ERbeta staining. AR was detected in stromal and muscle cells throughout the oviduct region, and in epithelial cells of the inf/AMP. Taken together, ERalpha, PR-A+B and AR were detected in the epithelium of the inf/AMP region, but all of these receptors were expressed in a distinct subset of epithelial cells which were negative for beta-tubulin IV, a ciliated epithelial cell marker. These results contribute to a better understanding of the respective roles of ERs, PRs and AR in the rat oviduct.
Identification of hepatic transcriptional changes in insulin-resistant rats treated with peroxisome proliferator activated receptor-alpha agonists
Authors: Frederiksen KS , Wulf EM , Wassermann K , Sauerberg P , Fleckner J
Published: December 2004

Peroxisome proliferator activated receptor (PPAR)-alpha controls the expression of multiple genes involved in lipid metabolism, and activators of PPAR-alpha, such as fibrates, are commonly used drugs in the treatment of hypertriglyceridemia and other dyslipidemic states. Recent data have also suggested a role for PPAR-alpha in insulin resistance and glucose homeostasis. In the present study, we have assessed the transcriptional and physiological responses to PPAR-alpha activation in a diet-induced rat model of insulin resistance. The two PPAR-alpha activators, fenofibrate and Wy-14643, were dosed at different concentrations in high-fat fed Sprague-Dawley rats, and the transcriptional responses were examined in liver using cDNA microarrays. In these analyses, 98 genes were identified as being regulated by both compounds. From this pool of genes, 27 correlated to the observed effect on plasma insulin, including PPAR-alpha itself and the leukocyte antigen-related protein tyrosine phosphatase (PTP-LAR). PTP-LAR was downregulated by both compounds, and showed upregulation as a result of the high-fat feeding. This regulation was also observed at the protein level. Furthermore, downregulation of PTP-LAR by fenofibric acid was demonstrated in rat FaO hepatoma cells in vitro, indicating that the observed regulation of PTP-LAR by fenofibrate and Wy-14643 in vivo is mediated as a direct effect of the PPAR agonists on the hepatocytes. PTP-LAR is one of the first genes involved in insulin receptor signaling to be shown to be regulated by PPAR-alpha agonists. These data suggest that factors apart from skeletal muscle lipid supply may influence PPAR-alpha-mediated amelioration of insulin resistance.
Transcriptional regulation of the mouse steroidogenic acute regulatory protein gene by the cAMP response-element binding protein and steroidogenic factor 1
Authors: Manna PR , Eubank DW , Lalli E , Sassone-Corsi P , Stocco DM
Published: December 2004

Transcriptional induction by cAMP is mediated through the interaction of the cAMP response-element binding protein (CREB) with a cAMP response element (CRE) in the promoter of target genes. The steroidogenic acute regulatory (StAR) protein gene is regulated by cAMP-mediated signaling in steroidogenic cells even though its promoter lacks a consensus CRE. Previously, we have identified three highly conserved 5'-CRE half-sites within the -96/-67 bp region of the mouse StAR gene, and a member of the CREB family (CREB/CRE modulator (CREM)) was shown to be involved in its expression and regulation. Here we show that CREB and CREMtau (but not CREMalpha and CREMbeta) have qualitatively similar effects on StAR promoter activity in response to (Bu)(2)cAMP. Studies on the effects of the functional integrity of the CRE half-sites on CREB-dependent (Bu)(2)cAMP-mediated StAR gene transcription demonstrated the greater importance of the CRE2 site in comparison with the CRE1 and CRE3 sites. The CRE2 sequence was also found to bind specifically to recombinant CREB protein and nuclear extract from MA-10 mouse Leydig tumor cells. The cAMP and CREB/CREM responsive region (-151/-1 bp) of the mouse StAR promoter also contains three recognition motifs for steroidogenic factor 1 (SF-1). Electrophoretic mobility shift assays and reporter gene analyses demonstrated the involvement of different SF-1 elements in StAR gene expression with the order of importance being SF-1/3>SF-1/1>SF-1/2. Specific mutations that eliminated the binding sites of CRE and SF-1 elements, either alone or in combination, resulted in an attenuation of StAR promoter activity, indicating that CREB and SF-1 can regulate StAR gene transcription in a cooperative fashion. In addition, mammalian two-hybrid assays revealed a high affinity protein-protein interaction between CREB/CREMtau and SF-1 which appeared to be dependent upon CREB protein phosphorylation. These findings further demonstrate CREB's role in StAR gene transcription and also provide evidence that the combined action of CREB/CREMtau and SF-1 results in enhanced activation of the StAR promoter.
Hormonal and developmental regulation of the mouse aldose reductase-like gene akr1b7 expression in Leydig cells
Authors: Baron S , Manin M , Aigueperse C , Berger M , Jean C , Veyssiere G , Morel L
Published: December 2004

The akr1b7 gene encodes an aldose reductase-like protein that is responsible for detoxifying isocaproaldehyde generated by the conversion of cholesterol to pregnenolone. The regulation of gene expression by human chorionic gonadotropin (hCG) was first investigated in the MA-10 Leydig tumor cell line. The akr1b7 gene was constitutively expressed and accumulation of its mRNA was increased in a dose- and time-dependent manner by treatment with hCG. akr1b7 mRNA accumulation was sharply increased in the presence of 0.25 nM hCG and it reached a fivefold increase within 2 h. AKR1B7 protein accumulation was delayed compared with that of the corresponding mRNA. In agreement, hCG significantly increased the levels of mRNA and protein of akr1b7 in primary cultures of adult mouse Leydig cells, thus suggesting that LH potentially regulates akr1b7 gene expression in vivo. Expression of akr1b7 was developmentally regulated in the testis. Unexpectedly, levels of akr1b7 mRNA increased from embryonic day 15 to the day of birth and declined until adulthood while AKR1B7 protein levels followed an inverse pattern, suggesting an important role for translational mechanisms.
Steroids control the aromatase gene expression in purified germ cells from the adult male rat
Authors: Bourguiba S , Lambard S , Carreau S
Published: December 2004

The ability of the testis to convert irreversibly androgens into estrogens is related to the presence of a microsomal enzymatic complex named aromatase. In rodents, germ cell production of estrogens is known, although the regulation of the cytochrome p450 aromatase (p450 arom) gene expression is not completely elucidated. In the present study, we have investigated the putative effects of steroids (testosterone, 5alpha-dihydrotestosterone (DHT) and estradiol) on Cyp19 gene expression in purified adult rat pachytene spermatocytes (PSs) and round spermatids (RSs). Using a highly specific quantitative competitive RT-PCR method we established that testosterone enhances in a dose- and time-related manner aromatase gene expression in PSs and RSs; 5alpha-DHT induces the same effect. Furthermore, testosterone increases the estradiol output in both germ cell populations whereas 5alpha-DHT was inefficient, therefore suggesting that the effect of androgens on p450 arom gene transcription was independent of estrogen formation. In fact estradiol inhibits the Cyp19 gene expression in PSs and RSs. ICI 182780, an estrogen receptor antagonist, has no effect on testosterone-stimulated aromatase expression in PSs and RSs. By contrast, ICI 182780 suppresses the inhibitory effect of estradiol on p450 arom mRNA expression in PSs and RSs. Similarly, nilutamide, a non-steroidal anti-androgen specific for androgen receptors, abolishes the testosterone-stimulated aromatase expression in PSs and RSs. These observations show that androgens up-regulate aromatase gene expression in purified adult rat germ cells whereas estrogens exert an opposite effect, which may suggest the presence of androgen and estrogen responsive elements on the aromatase promoter(s).
Evidence for two distinct functional glucocorticoid receptors in teleost fish
Authors: Bury NR , Sturm A , Le Rouzic P , Lethimonier C , Ducouret B , Guiguen Y , Robinson-Rechavi M , Laudet V , Rafestin-Oblin ME , Prunet P
Published: December 2004

Using RT-PCR with degenerated primers followed by screening of a rainbow trout (Oncorhynchus mykiss) intestinal cDNA library, we have isolated from the rainbow trout a new corticosteroid receptor which shows high sequence homology with other glucocorticoid receptors (GRs), but is clearly different from the previous trout GR (named rtGR1). Phylogenetic analysis of these two sequences and other GRs known in mammals, amphibians and fishes indicate that the GR duplication is probably common to most teleost fish. The open reading frame of this new trout GR (named rtGR2) encodes a protein of 669 amino acids and in vitro translation produces a protein of 80 kDa that appears clearly different from rtGR1 protein (88 kDa). Using rtGR2 cDNA as a probe, a 7.3 kb transcript was observed in various tIssues suggesting that this gene would lead to expression of a steroid receptor. In vitro studies were used to further characterize this new corticosteroid receptor. Binding studies with recombinant rtGR1 and rtGR2 proteins show that the two receptors have a similar affinity for dexamethasone (GR1 K(d)=5.05+/-0.45 nM; GR2 K(d)=3.04+/-0.79 nM). Co-transfection of an rtGR1 or rtGR2 expression vector into CHO-K1 or COS-7 cells, along with a reporter plasmid containing multiple consensus glucocorticoid response elements, shows that both clones are able to induce transcriptional activity in the presence of cortisol and dexamethasone. Moreover, at 10(-)(6 )M 11-deoxycortisol and corticosterone partially induced rtGR2 transactivation activity but were without effect on rtGR1. The other major teleost reproductive hormones, as well as a number of their precursors or breakdown products of these and corticosteroid hormones, were without major effects on either receptor. Interestingly, rtGR2 transactivational activity was induced at far lower concentrations of dexamethasone or cortisol (cortisol EC(50)=0.72+/-0.87 nM) compared with rtGR1 (cortisol EC(50)=46+/-12 nM). Similarly, even though RU486 inhibited transactivation activity in both rtGR1 and rtGR2, rtGR1 was more sensitive to this GR antagonist. Altogether, these results indicate that these two GR sequences encode for two functionally distinct GRs acting as ligand-inducible transcription factors in rainbow trout.
The PTEN tumor suppressor is a negative modulator of androgen receptor transcriptional activity
Authors: Nan B , Snabboon T , Unni E , X-J Yuan , Whang YE , Marcelli M
Published: December 2004

To investigate whether the tumor suppressor gene PTEN affects the activity of the androgen receptor (AR), we monitored the expression of the apoptotic gene HA-Bax (inserted in an adenovirus where it is driven by the AR-responsive promoter ARR(2)PB) in the presence or absence of dihydrotestosterone, in PTEN (+) or (-) prostate cancer cell lines, infected with an adenovirus containing wild-type PTEN (Av-CMV-PTEN) or a control LacZ-expressing construct. Our results showed that AR transcriptional activity was antagonized by PTEN expression. This antagonism was not cell line dependent, as it was observed in both LNCaP and LAPC-4 cells, or promoter dependent, as it was observed for a reporter gene (HA-Bax) driven by an exogenous androgen-responsive promoter (the ARR(2)PB promoter), and for a native gene (prostate-specific antigen; PSA) driven by an endogenous AR-responsive promoter. Additional experiments performed with viruses containing constitutively active (Adeno-myrAkt) or dominant negative (Adeno-dnAkt) forms of Akt demonstrated that Akt, a protein kinase whose activation is known to be inhibited by PTEN, mediated the observed antagonism between PTEN and AR transcriptional activity. Recently, two putative Akt phosphorylation sites have been identified in the AR sequence. Site-directed mutagenesis was utilized to convert these two serine into alanine residues. The resulting construct, named CMV-AR S213A&S791A was transfected in AR (-) and PTEN (-) PC-3 cells in the presence or absence of Av-CMV-PTEN and of two reporter plasmids (GRE(2)E1b-Luc and PSA P/E-luc) containing the luciferase gene driven by well-characterized androgen responsive promoters. These experiments demonstrated that, similarly to the wild-type molecule, AR S213A&S791A was transcriptionally inhibited by PTEN, suggesting that Akt does not have an effect on AR transcription by direct phosphorylation, but probably by affecting the availability of a downstream molecule whose main mechanism of action is that of modulating AR transcription. The data presented here suggest that loss of PTEN function may facilitate activation of AR signaling and progression to androgen independence in prostate cancer.
Quantitation of prolactin receptor mRNA in the maternal rat brain during pregnancy and lactation
Authors: Augustine RA , Kokay IC , Andrews ZB , Ladyman SR , Grattan DR
Published: December 2004

Prolactin receptor (PRL-R) expression in the brain is increased in lactating rats compared with non-pregnant animals. The aim of the present study was to determine the time-course of changes in PRL-R mRNA levels during pregnancy and/or lactation, and to determine relative levels of the two forms (short and/or long form) of receptor mRNA in specific brain regions. Brains were collected from female rats on dioestrus, days 7, 14 or 21 of pregnancy, day 7 of lactation or day 7 post-weaning. Frozen, coronal sections were cut (300 microm) and specific hypothalamic nuclei and the choroid plexus were microdissected using a punch technique. Total RNA was extracted and reverse transcribed, then first strand cDNA was amplified using quantitative real-time PCR. Results showed an up-regulation of long-form PRL-R mRNA in the choroid plexus by day 7 of pregnancy compared with dioestrus, which further increased on days 14 and 21 of pregnancy and day 7 of lactation, and then decreased to dioestrous levels on day 7 post-weaning. Short-form PRL-R mRNA levels increased on day 14 of pregnancy relative to dioestrus, increased further on day 7 of lactation and decreased on day 7 post-weaning. Changes in mRNA were reflected in increased levels of PRL-R immunoreactivity in the choroid plexus during pregnancy and lactation, compared with dioestrus. In the arcuate nucleus, long-form PRL-R mRNA was increased during pregnancy. In contrast to earlier work, no significant changes in short- or long-form PRL-R mRNA expression were detected in several other hypothalamic nuclei, suggesting that changes in hypothalamic mRNA levels may not be as marked as previously thought. The up-regulation of PRL-R mRNA and protein expression in the choroid plexus during pregnancy and lactation suggest a possible mechanism whereby increasing levels of peripheral prolactin during pregnancy may have access to the central nervous system. Together with expression of long-form PRL-R mRNA in specific hypothalamic nuclei, these results support a role for prolactin in regulating neuroendocrine and behavioural adaptations in the maternal brain.
Absence of somatic mutations in natriuretic peptide receptor type A gene in human aldosterone-secreting adenomas
Authors: Sarzani R , Salvi F , Pietrucci F , Buglia L , Candelaresi C , Balducci B , Francioni M , Fazioli F , Letizia C , D'Erasmo E , Dessi-Fulgheri P , Rappelli A
Published: December 2004

Somatic mutations of genes codifying for key regulatory proteins are the cause of different types of hormone-secreting adenomas. Natriuretic peptides (NP) are the strongest inhibitors of aldosterone secretion but aldosterone-secreting adenomas (aldosteronomas) are resistant to this inhibition and have reduced binding sites for NPs. The objective of this study was to sequence the entire coding region of the NP receptor type A (NPRA, codified by the Npr1 gene) to find loss-of-function somatic mutations. Total RNA was extracted from eight aldosteronomas and cDNA was synthesized. NPRA mRNA expression was evaluated by Northern blot analysis and compared with beta-actin mRNA as the housekeeping gene. Twelve primer couples were designed on the basis of the Npr1 gene organization to amplify, by PCR, all 22 coding exons of the gene. The two strands of amplified DNAs were purified and directly sequenced by automated capillary sequencer. NPRA mRNA expression did not differ among aldosteronomas. Npr1 open reading frame sequences obtained from eight aldosteronomas did not contain any mutation. The coding sequences of all 22 exons were identical in all samples and identical to published sequences. In the 3'-untranslated region (3'-UTR) a new length difference 3C/4C polymorphism was found at position 15 129 (three adenomas were 3C/4C and two were 3C/3C). Such a 3C/4C polymorphism was present in genomic DNA from 80 control subjects (25, 4C/4C; 40, 3C/4C; 15, 3C/3C). Mutations in the coding exons of the Npr1 gene do not appear to be a common cause of aldosteronomas. Moreover, the exons of Npr1 encoding for the translated portion of mRNA do not appear to be prone to polymorphisms. The polymorphism identified in the 3'-UTR might affect mRNA stability resulting in lower receptor synthesis, but it is not likely to confer a predisposition to the development of aldosteronomas.
The angiotensin type 2 receptor of angiotensin II and neuronal differentiation: from observations to mechanisms
Authors: Gendron L , Payet MD , Gallo-Payet N
Published: December 2004

The angiotensin II (Ang II) type 2 receptor (AT(2)) is a member of the seven-transmembrane domain, G-protein coupled receptor family. This receptor is ubiquitously distributed in the fetus but, in most tIssues, its expression dramatically falls in the first few hours after birth. Based on this observation, the hypothesis that this receptor could be involved in fetal development was raised and, over the past ten Years, many studies have tried to identify a role for the AT(2) receptor using many different tIssues and cell lines. To date, one of the major roles associated with the Ang II AT(2) receptor concerns its ability to induce neuronal differentiation. Indeed, in cells of neuronal origin, activation of the AT(2) receptor was shown to induce neurite outgrowth and elongation, modulate neuronal excitability, promote cellular migration and, in particular conditions, induce neuronal cell death. Regarding its signaling mechanisms, the AT(2) receptor still represents one of the most controversial G-protein coupled receptors since it does not stimulate the production of any of the classical second messengers. This review summarizes knowledge of the functions and the signaling mechanisms involved in the actions of the AT(2) receptor in neurons and cells of neuronal origin. Based on its altered expression in neurological disorders, a role for the AT(2) receptor in control of neuronal plasticity is proposed.
Isolation and characterization of an alternatively spliced variant of transcription factor Islet-1
Authors: Ando K , Shioda S , Handa H , Kataoka K
Published: December 2004

The LIM homeodomain protein Islet-1 (Isl1), one of the earliest markers for motor neuron differentiation, is also expressed in all classes of islet cells in the pancreas. Isl1 is known to bind and regulate the promoters of the insulin, glucagon and somatostatin genes. In this study, we describe isolation of a novel isl1 cDNA species from the mouse islet beta cell line betaTC6, which arose from the utilization of an alternative splicing acceptor site in the fifth exon. This shorter cDNA encodes an Isl1 isoform (Isl1-beta) lacking the carboxy-terminal 23 amino acids of the previously reported product Isl1-alpha. Although the level of isl1-beta mRNA is much lower than that of isl1-alpha, isl1-beta is preferentially expressed in murine insulinoma cell lines but not in glucagonoma cell line. Upon transient transfection, both Isl1-alpha and Isl1-beta accumulate in the nuclei of murine insulinoma cells. We found that Isl1-beta is a relatively more potent transcriptional activator of the insulin promoter than Isl1-alpha and that the Isl1-alpha isoform undergoes phosphorylation. Therefore, the transcriptional activity of Isl1 is potentially regulated by the alternative splicing of its mRNA and by phosphorylation.
Role of conserved hydrophobic amino acids in androgen receptor AF-1 function
Authors: Betney R , McEwan IJ
Published: December 2004

The intracellular androgen receptor (AR) is a ligand-activated transcription factor. Upon binding the steroids testosterone or dihydrotestosterone, the activated receptor translocates to the nucleus, binds to specific DNA response elements and interacts with the transcription machinery in order to regulate gene transcription. In the present study, we have described a highly conserved region (amino acids 224-258) within the AR AF-1 domain and have investigated the role of conserved bulky hydrophobic residues in gene regulation. Mutating pairs of residues (I229A/L236A; V240A/V242A; L251A/L254A) reduced transactivation activity by 25-40%. Mutating residues M244, L246 and V248 to alanines had a more dramatic affect on receptor activity, disrupting activity by at least 60%. The latter mutations also disrupted binding to the RNA polymerase-associated protein 74 subunit of the general transcription factor TFIIF. The protein conformation and stability of the mutant polypeptide in vitro was not significantly different from the wild type. None of the mutations tested disrupted binding of the AF-1 domain with the coactivator protein steroid receptor coactivator-1a. Thus we have concluded that conserved hydrophobic residues are important for receptor-dependent gene transcription and that M244, L246 and V248 are part of the binding interface for TFIIF.
Similarities and differences in uterine gene expression patterns caused by treatment with physiological and non-physiological estrogens
Authors: Watanabe H , Suzuki A , Kobayashi M , Lubahn DB , Handa H , Iguchi T
Published: December 2004

Administration of physiological and non-physiological estrogens during pregnancy or after birth is known to have adverse effects on the development of the reproductive tract and other organs. Although it is believed that both estrogens have similar effects on gene expression, this view has not been tested systematically. To compare the effects of physiological (estradiol; E2) and non-physiological (diethylstilbestrol; DES) estrogens, we used DNA microarray analysis to examine the uterine gene expression patterns induced by the two estrogens. Although E2 and DES induced many genes to respond in the same way, different groups of genes showed varying levels of maximal activities to each estrogen, resulting in different dose-response patterns. Thus, each estrogen has a distinct effect on uterine gene expression. The genes were classified into clusters according to their dose-responses to the two estrogens. Of the eight clusters, only two correlated well with the uterotropic effect of different doses of E2. One of these clusters contained genes that were upregulated by E2, which included genes encoding several stress proteins and transcription factors. The other cluster contained genes that were downregulated by E2, including genes related to metabolism, transcription and detoxification processes. The expression of these genes in estrogen receptor-deficient mice was not affected by E2 treatment, indicating that these genes are affected by the E2-bound estrogen receptor. Thus, of the many genes that are affected by estrogen, it was suggested that only a small number are directly involved in the uterotropic effects of estrogen treatment.
Determinants of spironolactone binding specificity in the mineralocorticoid receptor
Authors: Rogerson FM , Yao YZ , Smith BJ , Dimopoulos N , Fuller PJ
Published: December 2004

Spironolactone is a mineralocorticoid receptor (MR) antagonist in clinical use. The compound has a very low affinity for the glucocorticoid receptor (GR). Determinants of binding specificity of spironolactone to the MR were investigated using chimeras created between the ligand-binding domains (LBDs) of the MR and the GR. These chimeras had previously been used to investigate aldosterone binding specificity to the MR. Spironolactone was able to compete strongly for [(3)H]-aldosterone and [(3)H]-dexamethasone binding to a chimera containing amino acids 804-874 of the MR, and weakly for [(3)H]-dexamethasone binding to a chimera containing amino acids 672-803 of the MR. Amino acids 804-874 were also critical for aldosterone binding specificity. Models of the MR LBD bound to aldosterone and spironolactone were created based on the crystal structure of the progesterone receptor LBD. The ligand-binding pocket of the MR LBD model consisted of 23 amino acids and was predominantly hydrophobic in nature. Analysis of this model in light of the experimental data suggested that spironolactone binding specificity is not governed by amino acids in the ligand-binding pocket.