Dehydroepiandrosterone-enhanced dual specificity protein phosphatase (DDSP) prevents diet-induced and genetic obesity.

Dehydroepiandrosterone (DHEA) exerts a wide variety of therapeutic effects against medical disorders, such as diabetes and obesity. However, the molecular basis of DHEA action remains to be clarified. Previously, we reported that DHEA-enhanced dual specificity protein phosphatase, designated DDSP, is one of the target molecules of DHEA. To examine the role of DDSP in DHEA signaling, we generated mice that carry a DDSP transgene in which expression is driven by the CAG promoter (DDSP-Tg). DDSP-Tg mice weighed significantly less than wild-type (WT) control mice when a high fat diet was supplied (p < 0.01). No difference in food-intake or locomotor activity was found between DDSP-Tg and WT mice. Oxygen consumption of DDSP-Tg mice was higher than that of WT mice (p < 0.01), which suggested an increase in basal metabolism in DDSP-Tg mice. To further investigate the role of DDSP in genetic obese mice, DDSP-Tg mice with a db/db background were generated (DDSP-Tg db/db). We observed cancellation of obesity by the db/db mutation and development of a cachexic phenotype in DDSP-Tg db/db mice. In conclusion, our study shows that expression of DDSP leads to prevention of diet-induced and genetic (db/db) obesity. Anti-obese effects of DHEA might be mediated through DDSP, which might be a therapeutic target for intervention of obesity.

Modification of glucocorticoid sensitivity by MAP kinase signaling pathways in glucocorticoid-induced T-cell apoptosis.

OBJECTIVE: Glucocorticoid is widely used for the treatment of diseases such as hematological malignancies. Glucocorticoid sensitivity is different from person to person and the mechanism of the regulation of glucocorticoid sensitivity is not well known. Glucocorticoid resistance is a major clinical problem. METHODS AND RESULTS: Here, using glucocorticoid-induced T-cell apoptosis, a model system for the analysis of the mechanism of glucocorticoid action, we clarified that mitogen-activated protein kinases (MAPKs) modify glucocorticoid sensitivity, namely that the activation of extracellular signal-regulated protein kinase (ERK) and p38 MAP kinase reduce and enhance glucocorticoid sensitivity, respectively. CONCLUSION: These findings might provide new tools for overcoming glucocorticoid-resistance.

Dehydroepiandrosterone negatively regulates the p38 mitogen-activated protein kinase pathway by a novel mitogen-activated protein kinase phosphatase.

Dehydroepiandrosterone-sulfate, the sulfated form of dehydroepiandrosterone, is the most abundant steroid in young adults, but gradually declines with aging. In humans, the clinical application of dehydroepiandrosterone targeting some collagen diseases, such as systemic lupus erythematosus, as an adjunctive treatment has been applied in clinical trial. Here, we report that dehydroepiandrosterone may negatively regulate the mitogen-activated protein kinase pathway in humans via a novel dual specificity protein phosphatase, DDSP (dehydroepiandrosterone-enhanced dual specificity protein phosphatase). DDSP is highly homologous to LCPTP/HePTP, a tissue-specific protein tyrosine phosphatase (PTP) which negatively regulates both ERK and p38-mitogen-activated protein kinase, and is transcribed from the PTPN7 locus by alternative splicing. Although previous reports have shown that the mRNA expression of the LCPTP/HePTP gene was inducible by extracellular signals such as T-cell antigen receptor stimulation, reverse transcribed (RT)-PCR experiments using specific sets of primers suggested that the expression of LCPTP/HePTP was constitutive while the actual inducible sequence was that of DDSP. Furthermore DDSP was widely distributed among different types of human tissues and specifically interacted with p38-mitogen-activated protein kinase. This inducible negative regulation of the p38-mitogen-activated protein kinase-dependent pathway may help to clarify the broad range of dehydroepiandrosterone actions, thereby aiding the development of new preventive or adjunctive applications for human diseases.

Androgen receptor null male mice develop late-onset obesity caused by decreased energy expenditure and lipolytic activity but show normal insulin sensitivity with high adiponectin secretion.

Androgen receptor (AR) null male mice (AR(L-/Y)) revealed late-onset obesity, which was confirmed by computed tomography-based body composition analysis. AR(L-/Y) mice were euphagic compared with the wild-type male (AR(X/Y)) controls, but they were also less dynamic and consumed less oxygen. Transcript profiling indicated that AR(L-/Y) mice had lower transcripts for the thermogenetic uncoupling protein 1, which was subsequently found to be ligand-dependently activated by AR. We also found enhanced secretion of adiponectin, which is insulin sensitizing, from adipose tissue and a relatively lower expression of peroxisome proliferator-activated receptor-gamma in white adipose tissue in comparison to AR(X/Y) mice. Both factors might explain why the overall insulin sensitivity of AR(L-/Y) mice remained intact, despite their apparent obesity. The results revealed that AR plays important roles in male metabolism by affecting the energy balance, and it is negative to both adiposity and insulin sensitivity.

[Adrenal androgen and bone metabolism].

Dehydroepiandrosterone-sulfate (DHEA-S), the sulfated form of dehydroepiandrosterone, is the most abundant steroids in human, although its biological activities are seemingly weak. Recently, basic and clinical observations suggest dehydroepiandrosterone (DHEA) increase bone mineral densities in the elderly. Large-scale double-blinded clinical trials are necessary.

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 presence of both the amino- and carboxyl-terminal domains in the AR is essential for the completion of a transcriptionally active form with coactivators and intranuclear compartmentalization common to the steroid hormone receptors: a three-dimensional imaging study.

To clarify the physiological significance of the intranuclear speckled distribution, or foci formation, of liganded steroid receptors, the subnuclear distribution of green (GFP), yellow (YFP), and cyan (CFP) fluorescent protein-tagged receptors and coactivators was investigated. The foci formation of 5 alpha-dihydrotestosterone (DHT)-bound AR-GFP in COS7 cells was abolished by the cotransfection of a CBP Delta (118-2393) fragment eliciting a dominant negative effect on the transactivation capacity of the AR. The N-terminal AR fragment (AR-AF-1-YFP), which has a strong constitutive transactivation function, formed foci without DHT, whereas the C-terminal AR fragment (AR-AF-2-CFP), which has a quite low transactivation function, was distributed homogeneously even in the presence of DHT. The reporter gene assay showed a synergism between the transactivation functions of AR-AF-1 and AR-AF-2. This synergism was not reflected by the above two-dimensional imaging. In contrast, a three-dimensional imaging method clearly showed a difference in the intranuclear spatial distribution. The DHT-bound wild-type AR-GFP alone or AR-AF-1-YFP plus DHT-bound AR-AF-2-CFP was distributed as approximately 300 discrete spots in one nucleus, whereas AR-AF-1-YFP alone was distributed as one volume in a reticular pattern. Furthermore, not only AR but also the glucocorticoid receptor-YFP, ER alpha -GFP, and YFP-tagged SRC-1, TIF2, and CBP were found to be accumulated in identical spots in the presence of ligand. All of the above results indicate that CBP is one of the factors essential for foci formation of the AR, and may propose the hypothesis that transcriptionally activated steroid receptors, regardless of the type of receptor, are transferred to common compartments (foci) and form a complex with coactivators, and this process is essential to full transactivation.

Protein kinase A potentiates adrenal 4 binding protein/steroidogenic factor 1 transactivation by reintegrating the subcellular dynamic interactions of the nuclear receptor with its cofactors, general control nonderepressed-5/transformation/transcription domain-associated protein, and suppressor, dosage-sensitive sex reversal-1: a laser confocal imaging study in living KGN cells.

The mechanism through which protein kinase A (PKA) potentiates the transactivation ability of adrenal 4 binding protein/steroidogenic factor 1 (Ad4BP/SF-1) is currently unclear. In the present study, we investigated the mechanism by applying laser confocal microscopy and fluorescence recovery after photobleaching technique. In KGN cells, forskolin (a PKA stimulator) could reorganize wild-type Ad4BP/SF-1, but not mutant Ad4BP/SF-1 (G35E), from a diffuse distribution pattern to foci formation in the nucleus. The subcellular distributions of GCN5 (general control nonderepressed) and TRRAP (transformation/transcription domain-associated protein), both of which were recently proved to be working in the same complex as the third class of nuclear receptor coactivators, were unexpectedly diffuse inside and outside the nucleus, respectively, when they were separately transfected. However TRRAP was translocated into the nucleus in the presence of GCN5, and together with GCN5 colocalized with Ad4BP/SF-1 in the same foci when PKA was activated. A luciferase assay also indicated that these two cofactors enhanced Ad4BP/SF-1 transactivation.Dosage-sensitive sex reversal (DAX-1) interacts with and thus inhibits Ad4BP/SF-1 transactivation. The coexistence of the two proteins dramatically altered their respective subnuclear distributions. They colocalized extensively, suggestive of binding, and Ad4BP/SF-1 was sharply immobilized when DAX-1 was coexpressed, whereas PKA could maintain mobility, as evidenced by Fluorescence Recovery After Photobleaching showing that Ad4BP/SF-1 mobility recovered after forskolin treatment.Therefore, the PKA signal pathway may modify the interaction between Ad4BP/SF-1 and its activators and repressor (GCN5 and TRRAP are integrated, whereas DAX-1 is disassociated), and thus stimulate the Ad4BP/SF-1 transactivation.

A benzimidazole fungicide, benomyl, and its metabolite, carbendazim, induce aromatase activity in a human ovarian granulose-like tumor cell line (KGN).

Endocrine disruptor chemicals are known to cause a range of abnormalities in sexual differentiation and reproduction. One mechanism underlying such effects may be via alteration of aromatase activity, which is responsible for estrogen production. A good screening system for identifying endocrine disruptors has long been desired. We have recently established a human ovarian granulosa-like tumor cell line, KGN, which possesses a relatively high level of aromatase expression and is considered a useful mammalian model for investigating the in vitro effects of various chemicals on aromatase activity. In this study we screened 55 different candidate chemicals for endocrine disruptors by assaying aromatase activity. Only benomyl, known as both a benzimidazole fungicide and a microtubule-interfering agent, was found to induce aromatase activity in association with increased levels of aromatase mRNA in KGN cells. The effect of benomyl was presumed to be mediated by its metabolite carbendazim, because it produced an effect equivalent to that of benomyl. The mechanism underlying the benomyl-induced increase in aromatase activity appears independent of the cAMP-protein kinase A pathway. Treatment with taxol, another class of microtubule-interfering agents, also caused induction of aromatase in KGN cells. Both benomyl and taxol changed KGN cell morphology, including the development of cell roundness and a disorganized network of microtubules. These results indicate that benomyl is a potential endocrine disruptor that provides a novel estrogenicity and operates through a microtubule-interfering mechanism.

Activin signaling through type IB activin receptor stimulates aromatase activity in the ovarian granulosa cell-like human granulosa (KGN) cells.

In addition to a stimulatory effect on FSH production by the pituitary gland, activin is thought to have a paracrine or autocrine role in follicular development in the ovary, where it is produced. Recently, we established a human ovarian granulosa tumor cell line, KGN, which possesses in vivo characteristics of granulosa cells, namely the expression of functional FSH receptors and cytochrome P-450 aromatase. Here, we have demonstrated the activin signaling pathway and its role in KGN cells. A series of transient transfection experiments revealed that activin type IB receptor (ActRIB) is an essential component of the activin signaling pathway in KGN cells. Smad2 was found to act downstream of ActRIB as an intracellular signal transmitter. Smad7, but not Smad6, was an inhibitory Smad in the pathway. Finally, we show that FSH receptor expression and cytochrome P-450 (P-450) aromatase activity was up-regulated by activin stimulation through ActRIB in KGN cells. These results show that we have clarified the signaling mechanisms and the roles of activin in the human granulosa cell line, KGN. Activin signaling mediated by ActRIB-Smad2 system in the ovary may thus be essential for the regulation of follicular differentiation.

Mechanism of action of anti-aging DHEA-S and the replacement of DHEA-S.

The plasma ACTH and cortisol levels do not change during aging. On the other hand, the plasma dehydroepiandrosterone sulfate (DHEA-S) changes remarkably during aging. Before puberty, the plasma DHEA-S level both in males and females is very low, however, it rapidly increases at puberty, and thereafter significantly decreases both linearly and age-dependently. Cytochrome P450c17 has two enzyme activities, 17-alpha-hydroxylase and 17,20-lyase. Cortisol is synthesized by 17-alpha-hydroxylase, and DHEA is synthesized by 17,20-lyase. The mechanism of dissociation of cortisol and DHEA synthesis in aging depends on another regulator of 17,20-lyase of cytochrome P450c17 such as cytochrome P450 reductase. We demonstrated significant decrease in cytochrome P450 reductase activity in bovine aged adrenal glands. We clarified the beneficial effects of DHEA as an anti-aging steroid based on both in vitro and in vivo experiments, such as the stimulatory effect of immune system, anti-diabetes mellitus, anti-atherosclerosis, anti-dementia (neurosteroid), anti-obesity and anti-osteoporosis. It is very important to identify the mechanism of action of DHEA. We clarified the conversion of DHEA to estrone by cytochrome P450 aromatase in primary cultured human osteoblasts. We indentified high affinity of DHEA binding with K(d)=6.6 nM in antigen and DHEA stimulated human T lymphocytes. We searched for the target genes that are specifically induced in activated T lymphocytes in the presence of DHEA by subtractive hybridization screening for differentially expressed transcripts. The double blind, randomized human replacement therapies utilizing DHEA are also reviewed.

Dehydroepiandrosterone (DHEA) as a possible source for estrogen formation in bone cells: correlation between bone mineral density and serum DHEA-sulfate concentration in postmenopausal women, and the presence of aromatase to be enhanced by 1,25-dihydroxyvitamin D3 in human osteoblasts.

A significant positive correlation between bone mineral density (BMD) and serum dehydroepiandrosterone sulfate (DHEA-S) was found in 120 postmenopausal women (51-99 years old) but no correlation was seen between BMD and serum estradiol. In subset analysis, strong positive correlation of serum DHEA-S and estrone with BMD was observed in postmenopausal women aged less than 69 years old. To study a possible role of DHEA-S in preventing osteoporosis, we characterized aromatase activity converting androgens to estrogens in human osteoblasts, because postmenopausal women maintain considerable levels of adrenal androgens. Glucocorticoids at 10(-9) to 10(-7) M induced transiently the expression of and the enzymatic activity of aromatase cytochrome P450 (P450AROM) in primary cultured osteoblasts. 1,25-Dihydroxyvitamin D3 (1,25-(OH)(2)D(3)) alone did not induce the aromatase activity, but enhanced and maintained the glucocorticoid-induced P450AROM gene expression. Analysis of the activity of P450AROM gene 1b (I.4) promoter, which is used dominantly in human osteoblasts, indicated that the region from -888 bp to -500 bp, which does not contain a typical vitamin D responsive element, is responsible for the enhancing effect of 1,25-(OH)(2)D(3). These results may suggest that adrenal androgen, DHEA, is converted to estrone in osteoblast by P450AROM, which is positively regulated by glucocorticoid and 1,25-(OH)(2)D(3), and is important in maintaining BMD in the sixth to the seventh decade, after menopause.

Aromatase in bone: roles of Vitamin D3 and androgens.

We have mainly focused on the regulatory mechanism of cytochrome P450 aromatize in bone cells. Our previous study demonstrated a strong positive correlation of serum dehydroepiandrosterone sulfate (DHEA-S) and estrone (E1) with BMD in postmenopausal women but no correlation between serum estradiol (E2) and BMD in the same group. In addition, administration of DHEA to ovariectomized rat significantly increased BMD. These in vivo findings strongly suggested that circulating adrenal androgen may be converted to estrogen in osteoblast and may contribute to BMD maintenance. Actually, in cultured human osteoblast cells, DHEA was found to convert to androstenedione by 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity and then androstenedione to estrone through the apparent aromatase activity. The aromatase activity in cultured human osteoblast cells was significantly increased by dexamethasone (DEX). Interestingly, DEX and 1alpha,25-dihydroxyvitamin D3 (VD3) synergistically enhanced aromatase activity as well as P450arom mRNA expression. A little stronger induction of aromatase activity by DEX and VD3 was observed in cultured human fibroblasts. The increase of the aromatase activity by DEX and VD3 was accompanied with the increase of luciferase activity of fibroblast cells transfected with Exon 1b-promoter-luciferase construct, but not of osteoblasts transfected with the same construct, suggesting a different regulatory mechanism of aromatase by DEX and 1alpha,25-dihydroxyvitamin D3 (VD3) between these two cells despite the same promotor usage. In human bone cells, intracrine mechanism through aromatase activity, together with a positive regulation of aromatase activity by glucocorticoid and VD3, may contribute to the local production of estrogens, thus leading to protective effect against osteoporosis especially after menopause. The effect of sex steroids (estrogen versus testosterone) in bone remodeling was also briefly reviewed based on several recent findings in this field.

Activation function-1 domain of androgen receptor contributes to the interaction between two distinct subnuclear compartments.

The nucleus contains different sets of functional compartments often called "speckles". The splicing factor compartment (SFC) has been speculated to consist of SFs and transcription factors, which thus make transcription-splicing coupling possible at the periphery of SFC. Androgen receptor (AR), as well as glucocorticoid receptor (GR), is unique since most, if not all, of its activities are mediated via the constitutive activity of the activation function-1 (AF-1) function. Transcriptionally active AR produces 250-400 subnuclear fine speckles11 shared with GR or estrogen receptor (ER), which colocalize with chiefly activation function-2 (AF-2)-interacting p160 family- or CBP-related speckles. We herein report the isolation of ANT-1 (AR N-terminal domain (NTD) transactivating protein-1) enhancing autonomous AF-1 transactivation function of AR or GR, but not of estrogen receptor alpha (ERalpha). The ANT-1 was identical to a binding protein of human splicing factor U5 snRNP (U5 snRNP-associated protein). ANT-1 was compartmentalized into 15-20 coarse SFC speckles which were spatially distinct from but surrounded by the AR compartments. Our results suggest that ANT-1 may play a key role in the molecular interaction between two spatially distinct subnuclear compartments in a receptor-specific fashion, and thereby induce the strong autonomous transactivation functions either of AR- or GR-AF-1.

Coregulator-related diseases.

Coregulators are a group of proteins, which modulate the nuclear receptor transactivation function. In this study, a new "coregulator disease" concept was proposed from observations of a case of androgen insensitivity syndrome (AIS) and cases involving Rubinstein-Taybi syndrome and X-linked dementia and hypothyroidism syndrome. In addition, coregulators are thought to be closely associated with the pathogenesis of several diseases such as hormone-dependent cancers and leukemia. Based on these observations, the clinical disorders associated with some coregulator abnormalities were reviewed.

[DHEA and bone metabolism].

A strong positive correlation of serum dehydroepiandrosterone sulfate (DHEA-S) and estrone (E1) with bone mineral density (BMD) in postmenopausal women but no correlation between serum estradiol (E2) and BMD in the same group suggest that circulating adrenal androgen may be converted to estrogen in peripheral tissues including osteoblast and may contribute to BMD maintenance. Actually, in cultured human osteoblast cells, DHEA can be converted to androstenedione and then androstenedione to estrone through the apparent aromatase activity. In human bone cells, intracrine mechanism through aromatase activity may contribute to the local production of estrogens, thus leading to protective effect against osteoporosis especially after menopause.

Identification of endocrine disrupting chemicals activating SXR-mediated transactivation of CYP3A and CYP7A1.

Endocrine disrupting chemicals (EDCs) have emerged as a major public health issue because of their potentially disruptive effects on physiological hormonal actions. SXR (steroid xenobiotic receptor), also known as NR1I2, regulates CYP3A expression in response to exogenous chemicals, such as EDCs, after binding to SXRE (SXR response element). In our study, luciferase assay showed that 14 out of 55 EDCs could enhance SXR-mediated rat or human CYP3A gene transcription nearly evenly, and could also activate rat CYP7A1 gene transcription by cross-interaction of SXR and LXRE (LXRα response element). SXR diffused in the nucleus without ligand, whereas intranuclear foci of liganded SXR were produced. Furthermore, endogenous mRNA expression of CYP3A4 gene was enhanced by the 14 positive EDCs. Our results suggested a probable mechanism of EDCs disrupting the steroid or xenobiotic metabolism homeostasis via SXR.