cAMP activates transcription of the human glucocorticoid receptor gene promoter

Hormone-controlled cooperative binding of transcription factors drives synergistic induction of fasting-regulated genes

During fasting, hepatocytes produce glucose in response to hormonal signals. Glucagon and glucocorticoids are principal fasting hormones that cooperate in regulating glucose production via gluconeogenesis. However, how these hormone signals are integrated and interpreted to a biological output is unknown. Here, we use genome-wide profiling of gene expression, enhancer dynamics and transcription factor (TF) binding in primary mouse hepatocytes to uncover the mode of cooperation between glucagon and glucocorticoids. We found that compared to a single treatment with each hormone, a dual treatment directs hepatocytes to a pro-gluconeogenic gene program by synergistically inducing gluconeogenic genes. The cooperative mechanism driving synergistic gene expression is based on ‘assisted loading’ whereby a glucagon-activated TF (cAMP responsive element binding protein; CREB) leads to enhancer activation which facilitates binding of the glucocorticoid receptor (GR) upon glucocorticoid stimulation. Glucagon does not only activate single enhancers but also activates enhancer clusters, thereby assisting the loading of GR also across enhancer units within the cluster. In summary, we show that cells integrate extracellular signals by an enhancer-specific mechanism: one hormone-activated TF activates enhancers, thereby assisting the loading of a TF stimulated by a second hormone, leading to synergistic gene induction and a tailored transcriptional response to fasting.

The Phosphodiesterase Inhibitor Ensifentrine Reduces Production of Proinflammatory Mediators in Well Differentiated Bronchial Epithelial Cells by Inhibiting PDE4

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel that impair airway salt and fluid secretion. Excessive release of proinflammatory cytokines and chemokines by CF bronchial epithelium during airway infection leads to chronic inflammation and a slow decline in lung function; thus, there is much interest in finding safe and effective treatments that reduce inflammation in CF. We showed previously that the cyclic nucleotide phosphodiesterase (PDE) inhibitor ensifentrine (RPL554; Verona Pharma) stimulates the channel function of CFTR mutants with abnormal gating and also those with defective trafficking that are partially rescued using a clinically approved corrector drug. PDE inhibitors also have known anti-inflammatory effects; therefore, we examined whether ensifentrine alters the production of proinflammatory cytokines in CF bronchial epithelial cells. Ensifentrine reduced the production of monocyte chemoattractant protein-1 and granulocyte monocyte colony-stimulating factor (GM-CSF) during challenge with interleukin-1β Comparing the effect of ensifentrine with milrinone and roflumilast, selective PDE3 and PDE4 inhibitors, respectively, demonstrated that the anti-inflammatory effect of ensifentrine was mainly due to inhibition of PDE4. Beneficial modulation of GM-CSF was further enhanced when ensifentrine was combined with low concentrations of the β ₂-adrenergic agonist isoproterenol or the corticosteroid dexamethasone. The results indicate that ensifentrine may have beneficial anti-inflammatory effects in CF airways particularly when used in combination with β ₂-adrenergic agonists or corticosteroids. SIGNIFICANCE STATEMENT: Airway inflammation that is disproportionate to the burden of chronic airway infection causes much of the pathology in the cystic fibrosis (CF) lung. We show here that ensifentrine beneficially modulates the release of proinflammatory factors in well differentiated CF bronchial epithelial cells that is further enhanced when combined with β₂-adrenergic agonists or low-concentration corticosteroids. The results encourage further clinical testing of ensifentrine, alone and in combination with β₂-adrenergic agonists or low-concentration corticosteroids, as a novel anti-inflammatory therapy for CF.

Nuclear translocation of the unliganded glucocorticoid receptor is influenced by membrane fluidity, but not A2AR agonism

Epidemiological evidence suggests that chronic consumption of caffeine, a non-selective antagonist of adenosine A_2AR receptors (A_2AR), can be neuroprotective in a number of age-related neurodegenerative disorders including Alzheimer's disease. A growing body of work shows that this neuroprotection may act via a synergistic interaction with the glucocorticoid receptor (GR) and its associated genetic response elements. Therefore, we hypothesized that A_2AR signaling may directly stimulate glucocorticoid receptor translocation via downstream signaling elements within the cell. Surprisingly, we found no effect of A_2AR agonism on GR translocation in the absence of steroid. As expected, membrane-bound dexamethasone was capable of stimulating full GR translocation, albeit at a slower rate. This non-liganded translocation was unaffected by A_2AR ligands, providing strong evidence that GR translocation occurs independently of activation of A_2ARs. To identify other potential mechanisms of translocation, membrane fluidity was increased significantly by benzyl alcohol, which also induced full nuclear translocation of the GR, but unlike the membrane-bound dexamethasone, benzyl alcohol did result in transcriptional upregulation of GR-dependent genes. Taken together, our data shows that the unliganded GR is sensitive to changes in membrane state and can be transcriptionally active.

Glucocorticoid Receptor α Mediates Roflumilast's Ability to Restore Dexamethasone Sensitivity in COPD

Background

Glucocorticoids are commonly prescribed to treat inflammation of the respiratory system; however, they are mostly ineffective for controlling chronic obstructive pulmonary disease (COPD)-associated inflammation. This study aimed to elucidate the molecular mechanisms responsible for such glucocorticoid inefficacy in COPD, which may be instrumental to providing better patient outcomes. Roflumilast is a selective phosphodiesterase-4 (PDE4) inhibitor with anti-inflammatory properties in severe COPD patients who have a history of exacerbations. Roflumilast has a suggested ability to mitigate glucocorticoid resistance, but the mechanism is unknown.

Methods

To understand the mechanism that mediates roflumilast-induced restoration of glucocorticoid sensitivity in COPD, we tested the role of glucocorticoid receptor α (GRα). Roflumilast's effects on GRα expression and transcriptional activity were assessed in bronchial epithelial cells from COPD patients.

Results

We found that both GRα expression and activity are downregulated in bronchial epithelial cells from COPD patients and that roflumilast stimulates both GRα mRNA synthesis and GRα's transcriptional activity in COPD bronchial epithelial cells. We also demonstrate that roflumilast enhances dexamethasone's ability to suppress pro-inflammatory mediator production, in a GRα-dependent manner.

Discussion

Our findings highlight the significance of roflumilast-induced GRα upregulation for COPD therapeutic strategies by revealing that roflumilast restores glucocorticoid sensitivity by sustaining GRα expression.

Can the anti-inflammatory activities of β2-agonists be harnessed in the clinical setting?

Beta2-adrenoreceptor agonists (β2-agonists) are primarily bronchodilators, targeting airway smooth muscle and providing critical symptomatic relief in conditions such as bronchial asthma and chronic obstructive pulmonary disease. These agents also possess broad-spectrum, secondary, anti-inflammatory properties. These are mediated largely, though not exclusively, via interactions with adenylyl cyclase-coupled β2-adrenoreceptors on a range of immune and inflammatory cells involved in the immunopathogenesis of acute and chronic inflammatory disorders of the airways. The clinical relevance of the anti-inflammatory actions of β2-agonists, although often effective in the experimental setting, remains contentious. The primary objectives of the current review are: firstly, to assess the mechanisms, both molecular and cell-associated, that may limit the anti-inflammatory efficacy of β2-agonists; secondly, to evaluate pharmacological strategies, several of which are recent and innovative, that may overcome these limitations. These are preceded by a consideration of the various types of β2-agonists, their clinical applications, and spectrum of anti-inflammatory activities, particularly those involving adenosine 3',5'-cyclic adenosine monophosphate-activated protein kinase-mediated clearance of cytosolic calcium, and altered gene expression in immune and inflammatory cells.

Breed-dependent transcriptional regulation of 5'-untranslated GR (NR3C1) exon 1 mRNA variants in the liver of newborn piglets

Glucocorticoids are vital for life and regulate an array of physiological functions by binding to the ubiquitously expressed glucocorticoid receptor (GR, also known as NR3C1). Previous studies demonstrate striking breed differences in plasma cortisol levels in pigs. However, investigation into the breed-dependent GR transcriptional regulation is hampered by lacking porcine GR promoter information. In this study, we sequenced 5.3 kb upstream of the translation start codon of the porcine GR gene, and identified seven alternative 5′-untranslated exons 1–4, 1–5, 1–6, 1–7, 1–8, 1–9,10 and 1–11. Among all these mRNA variants, exons 1–4 and 1–5, as well as the total GR were expressed significantly (P<0.05) higher in the liver of newborn piglets of Large White (LW) compared with Erhualian, a Chinese indigenous breed. Overall level of CpG methylation in the region flanking exons 1–4 and 1–5 did not show breed difference. However, nuclear content of Sp1, p-CREB and GR in the liver was significantly (P<0.05) higher in LW piglets, associated with enhanced binding of p-CREB, and higher level of histone H3 acetylation in 1–4 and 1–5 promoters. In contrast, GR binding to promoters of exons 1–4 and 1–5 was significantly diminished in LW piglets, implicating the presence of negative GREs. These results indicate that the difference in the hepatic expression of GR transcript variants between two breeds of pigs is determined, at least partly, by the disparity in the binding of transcription factors and the enrichment of histone H3 acetylation to the promoters.

Psychoneuroimmunology meets neuropsychopharmacology: translational implications of the impact of inflammation on behavior

The potential contribution of chronic inflammation to the development of neuropsychiatric disorders such as major depression has received increasing attention. Elevated biomarkers of inflammation, including inflammatory cytokines and acute-phase proteins, have been found in depressed patients, and administration of inflammatory stimuli has been associated with the development of depressive symptoms. Data also have demonstrated that inflammatory cytokines can interact with multiple pathways known to be involved in the development of depression, including monoamine metabolism, neuroendocrine function, synaptic plasticity, and neurocircuits relevant to mood regulation. Further understanding of mechanisms by which cytokines alter behavior have revealed a host of pharmacologic targets that may be unique to the impact of inflammation on behavior and may be especially relevant to the treatment and prevention of depression in patients with evidence of increased inflammation. Such targets include the inflammatory signaling pathways cyclooxygenase, p38 mitogen-activated protein kinase, and nuclear factor-κB, as well as the metabolic enzyme, indoleamine-2,3-dioxygenase, which breaks down tryptophan into kynurenine. Other targets include the cytokines themselves in addition to chemokines, which attract inflammatory cells from the periphery to the brain. Psychosocial stress, diet, obesity, a leaky gut, and an imbalance between regulatory and pro-inflammatory T cells also contribute to inflammation and may serve as a focus for preventative strategies relevant to both the development of depression and its recurrence. Taken together, identification of mechanisms by which cytokines influence behavior may reveal a panoply of personalized treatment options that target the unique contributions of the immune system to depression.

Activation of cAMP-protein kinase A abrogates STAT5-mediated inhibition of glucocorticoid receptor signaling by interferon-alpha

IFN-alpha has been found to inhibit glucocorticoid receptor (GR) function by activating janus kinase-signal transducer and activator of transcription (JAK-STAT) inflammatory signaling pathways. In contrast, through stimulation of protein kinase A (PKA), cAMP has been shown to enhance GR function and can inhibit inflammatory signaling. We therefore examined whether increased cAMP-PKA pathway activation could reverse IFN-alpha-induced inhibition of GR function and whether decreased cAMP-PKA activity might exacerbate IFN-alpha effects on the GR. Activation of cAMP by forskolin (10 μM) reversed the inhibitory effects of mIFN-alpha (1000 U/ml) on dexamethasone (DEX)-induced MMTV-luciferase activity in hippocampal HT22 cells. Forskolin treatment also blocked both IFN-alpha-induced activation of phosphorylated STAT5 (pSTAT5) and inhibitory protein-protein interactions between pSTAT5 and GR in the nucleus of HT22 cells treated with IFN-alpha and DEX. These effects of forskolin were reversed by co-administration of the PKA inhibitor, H89. Conversely, the combination of IFN-alpha and treatment with either H89 or siRNA directed against the alpha and beta catalytic subunit isoforms of PKA led to an additive inhibitory effect on DEX-induced GR activity in HT22 cells. Taken together, these findings suggest that inhibition of GR signaling by mIFN-alpha and STAT5 can be reversed by activation of cAMP-PKA pathways, whereas decreased PKA activity increases the inhibitory effect of IFN-alpha on GR function. Given decreased PKA activity found in patients with major depression, these data suggest that depressed patients may be vulnerable to cytokine effects on GR, and cAMP-PKA agonists may serve to reverse glucocorticoid resistance in patients with depression and increased inflammation.

Eating ourselves to death (and despair): the contribution of adiposity and inflammation to depression

Obesity and related metabolic conditions are of epidemic proportions in most of the world, affecting both adults and children. The accumulation of lipids in the body in the form of white adipose tissue in the abdomen is now known to activate innate immune mechanisms. Lipid accumulation causes adipocytes to directly secrete the cytokines interleukin (IL) 6 and tumor necrosis factor alpha (TNFalpha), but also monocyte chemoattractant protein 1 (MCP-1), which results in the accumulation of leukocytes in fat tissue. This sets up a chronic inflammatory state which is known to mediate the association between obesity and conditions such as cardiovascular disease, type 2 diabetes, and cancer. There is also a substantial literature linking inflammation with risk for depression. This includes the observations that: (1) people with inflammatory diseases such as multiple sclerosis, cardiovascular disease, and psoriasis have elevated rates of depression; (2) many people administered inflammatory cytokines such as interferon alpha develop depression that is indistinguishable from depression in non-medically ill populations; (3) a significant proportion of depressed persons show upregulation of inflammatory factors such as IL-6, C-reactive protein, and TNFalpha; (4) inflammatory cytokines can interact with virtually every pathophysiologic domain relevant to depression, including neurotransmitter metabolism, neuroendocrine function, and synaptic plasticity. While many factors may contribute to the association between inflammatory mediators and depression, we hypothesize that increased adiposity may be one causal pathway. Mediational analysis suggests a bi-directional association between adiposity and depression, with inflammation possibly playing an intermediary role.

Antidepressants, but not antipsychotics, modulate GR function in human whole blood: an insight into molecular mechanisms

Clinical studies have demonstrated an impairment of glucocorticoid receptor (GR)-mediated negative feedback on the hypothalamic-pituitary-adrenal (HPA) axis in patients with major depression (GR resistance), and its resolution by antidepressant treatment. Recently, we showed that this impairment is indeed due to a dysfunction of GR in depressed patients (Carvalho et al., 2009), and that the ability of the antidepressant clomipramine to decrease GR function in peripheral blood cells is impaired in patients with major depression who are clinically resistant to treatment (Carvalho et al. 2008). To further investigate the effect of antidepressants on GR function in humans, we have compared the effect of the antidepressants clomipramine, amytriptiline, sertraline, paroxetine and venlafaxine, and of the antipsychotics, haloperidol and risperidone, on GR function in peripheral blood cells from healthy volunteers (n=33). GR function was measured by glucocorticoid inhibition of lypopolysaccharide (LPS)-stimulated interleukin-6 (IL-6) levels. Compared to vehicle-treated cells, all antidepressants inhibited dexamethasone (DEX, 10-100nM) inhibition of LPS-stimulated IL-6 levels (p values ranging from 0.007 to 0.1). This effect was specific to antidepressants, as antipsychotics had no effect on DEX-inhibition of LPS-stimulated IL-6 levels. The phosphodiesterase (PDE) type 4 inhibitor, rolipram, potentiated the effect of antidepressants on GR function, while the GR antagonist, RU-486, inhibited the effect of antidepressants on GR function. These findings indicate that the effect of antidepressants on GR function are specific for this class of psychotropic drugs, and involve second messenger pathways relevant to GR function and inflammation. Furthermore, it also points towards a possible mechanism by which one maybe able to overcome treatment-resistant depression. Research in this field will lead to new insights into the pathophysiology and treatment of affective disorders.

Cytokines and glucocorticoid receptor signaling. Relevance to major depression

Data suggest that the activation of immune responses and the release of inflammatory cytokines may play a role in the pathophysiology of major depression. One mechanism by which cytokines may contribute to depression is through their effects on the glucocorticoid receptor (GR). Altered GR function in depression has been demonstrated by neuroendocrine challenge tests that reliably reveal reduced GR sensitivity as manifested by nonsuppression of cortisol following dexamethasone administration in vivo and lack of immune suppression following administration of glucocorticoids in vitro. Relevant to the GR, cytokines have been shown to decrease GR expression, block translocation of the GR from cytoplasm to nucleus, and disrupt GR-DNA binding through nuclear protein-protein interactions. In addition, cytokines have been shown to increase the expression of the relatively inert GR beta isoform. Specific cytokine signaling molecules that have been shown to be involved in the disruption of GR activity include p38 mitogen-activated protein kinase, which is associated with reduced GR translocation, and signal transducer and activator of transcription (STAT)5, which binds to GR in the nucleus. Nuclear factor-kappaB (NF-kappaB) also has been shown to lead to GR suppression through mutually inhibitory GR-NF-kappaB nuclear interactions. Interestingly, several antidepressants have been shown to enhance GR function, as has activation of protein kinase A (PKA). Antidepressants and PKA activation have also been found to inhibit inflammatory cytokines and their signaling pathways, suggesting that drugs that target both inflammatory responses and the GR may have special efficacy in the treatment of depression.

Activation of TR4 orphan nuclear receptor gene promoter by cAMP/PKA and C/EBP signaling

In earlier studies, we had suggested that the fasting signal induces TR4 orphan nuclear receptor expression in vivo. The detailed mechanism(s), however, remain unclear. In this study, we found that cAMP/PKA, the mediator of fasting and glucagon signals, could induce TR4 gene expression that in turn modulates gluconeogenesis. Mechanistic dissection by in vitro studies in hepatocytes demonstrated that cAMP/PKA might trigger C/EBP alpha and beta binding to the selective cAMP response element, which is located at the TR4 promoter, thus inducing TR4 transcription. We also demonstrated that the binding activity of C/EBPs to the TR4 promoter is increased in response to cAMP treatment. Together, our data identified a new signaling pathway from the fasting signal --> cAMP/PKA --> C/EBP alpha and beta --> TR4 --> gluconeogenesis in hepatocytes; and suggested that TR4 could be an important regulator to control glucose homeostasis. The identification of activator(s)/inhibitor(s) or ligand(s) of TR4 may provide us an alternative way to control gluconeogenesis.

Phosphodiesterase 4 inhibitors augment levels of glucocorticoid receptor in B cell chronic lymphocytic leukemia but not in normal circulating hematopoietic cells

Type 4 cyclic AMP (cAMP) phosphodiesterase (PDE4) inhibitors, a class of compounds in clinical development that activate cAMP-mediated signaling by inhibiting cAMP catabolism, offer a feasible means by which to potentiate glucocorticoid-mediated apoptosis in lymphoid malignancies such as B-cell chronic lymphocytic leukemia (B-CLL). In this study, we show that PDE4 inhibitors up-regulate glucocorticoid receptor (GRalpha) transcript levels in B-CLL cells but not T-CLL cells or Sezary cells or normal circulating T cells, B cells, monocytes, or neutrophils. Because GRalpha transcript half-life does not vary in CLL cells treated with the prototypic PDE4 inhibitor rolipram, the 4-fold increase in GRalpha mRNA levels observed within 4 h of rolipram treatment seems to result from an increase in GRalpha transcription. Rolipram treatment increases levels of transcripts derived from the 1A3 promoter to a greater extent than the 1B promoter. Treatment of B-CLL cells with two other PDE4 inhibitors currently in clinical development also augments GR transcript levels and glucocorticoid-mediated apoptosis. Washout studies show that simultaneous treatment with both drug classes irreversibly augments apoptosis over the same time frame that GR up-regulation occurs. Although treatment of B-CLL cells with glucocorticoids reduces basal GRalpha transcript levels in a dose-related manner, cotreatment with rolipram maintained GRalpha transcript levels above baseline. Our results suggest that as a result of their unusual sensitivity to PDE4 inhibitor-mediated up-regulation of GRalpha expression, treatment of B-CLL patients with combined PDE4 inhibitor/glucocorticoid therapy may be of therapeutic benefit in this disease.

Aromatase expression in a human osteoblastic cell line increases in response to prostaglandin E(2) in a dexamethasone-dependent fashion

Recent progress supports the importance of local estrogen secretion in human bone tissue to increase and maintain bone-mineral density. In a previous report, we found that forskolin (FSK) synergistically induces aromatase (CYP19: a rate-limiting enzyme for estrogen synthesis) expression in dexamethasone (Dex) dependent manner in a human osteoblastic cell line, SV-HFO [Watanabe M, Ohno S, Nakajin S. Forskolin and dexamethasone synergistically induce aromatase (CYP19) expression in the human osteoblastic cell line SV-HFO. Eur J Endocrinol 2005;152:619-24]. In this report, we investigated whether prostaglandin (PG) E(2) induces estrogen production, in other words, if PGE(2) exerts the same effect as FSK because PGE(2) is the major prostanoid in the bone and is one of the key molecules in the osteoblast. We found PGE(2) up-regulates aromatase activity synergistically, but this up-regulation depends on Dex. CYP19 gene expression was also increased synergistically by Dex and PGE(2). Promoter I.4 was activated synergistically by PGE(2) and Dex. PGE(2) receptor, EP(1), EP(2) and EP(4) were involved in the up-regulation of aromatase activity in response to PGE(2) in a Dex-dependent manner. The cAMP-PKA pathway and Ca(2+) signaling pathway were involved in the up-regulation of aromatase activity in response to PGE(2). Furthermore, glucocorticoid response element on promoter I.4 sequence was an essential minimum requirement for its activity and synergism of PGE(2) and Dex. These findings are the first report on osteoblastic cell line which uses predominantly promoter I.4 to drive aromatase expression. These findings also suggest that endogenous PGE(2) produced in bone mainly may synergistically support local estrogen production in osteoblastic cells in the presence of glucocorticoid.

Involvement of the hypothalamic-pituitary-adrenal axis in the antidepressant-like effects of mild hypoxic preconditioning in rats

The preconditioning (PC) by using mild intermittent hypobaric hypoxia (PC) increases a resistance of the brain to severe hypoxia/ischemia and various stresses. Recently, potent antidepressant-like effects of PC have been described in animal models of depression. In the present study, the impact of PC on the activity and feedback regulation of the hypothalamic-pituitary-adrenal axis (HPA) impaired in depression has been studied in the model of shock-induced depression in rats. PC completely prevented depressive-like behavior (54% reduction in ambulance, 59% reduction in rearing in the open field, 654% increase of the anxiety level in the elevated plus maze), the HPA hyperactivity and the impairment of HPA feedback regulation that appeared in response to the inescapable footshock. Not affecting basal HPA activity, PC remarkably enhanced the HPA reactivity to stresses and substantially up-regulated the expression of glucocorticoid receptors in the ventral hippocampus following footshock that apparently contributes to the mechanisms responsible for the antidepressant-like action of PC.

Cytokine-effects on glucocorticoid receptor function: relevance to glucocorticoid resistance and the pathophysiology and treatment of major depression

Glucocorticoids play an essential role in the response to environmental stressors, serving initially to mobilize bodily responses to challenge and ultimately serving to restrain neuroendocrine and immune reactions. A number of diseases including autoimmune, infectious and inflammatory disorders as well as certain neuropsychiatric disorders such as major depression have been associated with decreased responsiveness to glucocorticoids (glucocorticoid resistance), which is believed to be related in part to impaired functioning of the glucocorticoid receptor (GR). Glucocorticoid resistance, in turn, may contribute to excessive inflammation as well as hyperactivity of corticotropin releasing hormone and sympathetic nervous system pathways, which are known to contribute to a variety of diseases as well as behavioral alterations. Recent data indicate that glucocorticoid resistance may be a result of impaired GR function secondary to chronic exposure to inflammatory cytokines as may occur during chronic medical illness or chronic stress. Indeed, inflammatory cytokines and their signaling pathways including mitogen-activated protein kinases, nuclear factor-kappaB, signal transducers and activators of transcription, and cyclooxygenase have been found to inhibit GR function. Mechanisms include disruption of GR translocation and/or GR-DNA binding through protein-protein interactions of inflammatory mediators with the GR itself or relevant steroid receptor cofactors as well as alterations in GR phosphorylation status. Interestingly, cAMP signal transduction pathways can enhance GR function and inhibit cytokine signaling. Certain antidepressants have similar effects. Thus, further understanding the effects of cytokines on GR signaling and the mechanisms involved may reveal novel therapeutic targets for reversal of glucocorticoid resistance and restoration of glucocorticoid-mediated inhibition of relevant bodily/immune responses during stress and immune challenge.

Increases in preproenkephalin mRNA levels in the Syrian hamster: The influence of glucocorticoids is dependent on age and tissue

In adult hamsters, basal proenkephalin (Penk) gene expression in adrenals is independent of glucocorticoids and glucocorticoid receptor blockade, by RU 486, increases striatal preproenkephalin (PPenk) mRNA levels. However, glucocorticoids maintain both basal and induced Penk gene expression in rat adrenal (medulla) and striatum. This suggests species and tissue-specific differences in Penk gene regulation. Since studies show temporal coordination in Penk gene expression in developing hamster adrenal and striatum, we tested the hypothesis that increasing PPenk mRNA levels are dependent, while basal levels are independent of glucocorticoids in developing hamsters. To facilitate this study, we examined the influence of glucocorticoids on the temporal increases in developing hamster PPenk mRNA observed in adrenals between postnatal days 0 and 4 and in striatum between postnatal days 12 and 48. PPenk mRNA levels were determined in hamster pups after treatment with increasing doses of metyrapone (an 11beta hydroxylase inhibitor) or with the glucocorticoid receptor antagonist RU 486 +/- metyrapone between postnatal days 2 and 4. Levels were also determined 36 days after hypophysectomy at age 16-17 days. Although plasma glucocorticoid levels and/or the influence from glucocorticoids were reduced, only developmental increases in PPenk mRNA are influenced by glucocorticoids in hamster adrenals, while basal adrenal mRNA levels are unchanged. However, pituitary influence on striatal PPenk mRNA levels appears complex and may involve steroid and/or non-steroid factors. These results suggest that glucocorticoids regulate hamster Penk gene expression via a mechanism that varies with age and tissue and functions during the induction of the Penk gene and not to maintain basal gene expression. Possible mechanisms and species variation are discussed.

Forskolin and dexamethasone synergistically induce aromatase (CYP19) expression in the human osteoblastic cell line SV-HFO

OBJECTIVE

Recent progress supports the importance of local estrogen secretion in human bone tissues to increase and maintain bone mineral density. In a previous study, we reported that the expression of aromatase (CYP19) is dexamethasone (Dex)-dependent and oncostatin M (OSM) increases the expression synergistically with Dex. In the present study, we examined the effects of forskolin (FSK) as another potential synergistic factor.

RESULTS

Co-administration of 100 nM Dex and 10 microM FSK increased aromatase activity 4-fold compared with Dex alone. The results of reverse transcriptase (RT)-PCR suggest that the amount of CYP19 gene transcript was also up-regulated by FSK synergistically with Dex, and that promoter I.4, which is not activated by FSK alone, is activated by FSK synergistically with Dex. The results of RT-PCR also suggest that promoter II, which responds to FSK, was not activated even in the presence of FSK in SV-HFO. The promoter I.4 sequence that was transfected into SV-HFO was activated by FSK synergistically with Dex.

CONCLUSIONS

Synergistic up-regulation of aromatase activity, CYP19 gene transcript, and promoter I.4 activity were Dex-dependent and not up-regulated by FSK alone. The results of this work may form the basis of bone-specific estrogen-replacement therapy that increases the estrogen concentration in bone tissue only.

Pharmacotherapy and airway remodelling in asthma?

Over the last few decades attention has largely focused on airway inflammation in asthma, but more recently it has been appreciated that there are important structural airway changes which have been grouped together under the term "airway remodelling". It is only now that questions have been asked about the impact of treatment on these structural changes. This review examines the nature of these structural airway changes, the mechanisms of their generation, their potential consequences, and what is known about the ability of anti-asthma treatments to modulate these changes.

Trout GH promoter analysis reveals a modular pattern of regulation consistent with the diversification of GH gene control and function in vertebrates

In vertebrates, growth hormone (GH) gene expression requires the pituitary-specific transcription factor Pit-1/GHF1 but is differently regulated by a variety of factors in different vertebrate species. Here, we have studied the transcriptional activity of the trout GH (tGH) promoter, which is synergistically stimulated by cAMP and glucocorticoid. Gel shift assays indicated that Pit-1 binds as a dimer to three high affinity sites in the -226/+24 tGH region, and that recombinant cAMP response element (CRE)-binding protein (CREB) binds to a CRE situated between the two distal Pit-1 sites. Deletional and mutational transfection experiments, performed in pituitary Pit-1-expressing GC cells, showed that the different Pit-1 sites play distinct roles and are obligatory elements in the mechanisms mediating cAMP and glucocorticoid responses. Remarkably, the results suggest a hierarchical modular model of regulation of the tGH promoter, according to which a critical module, triggered by Pit-1 bound to the proximal Pit-1 site, is necessary and sufficient to turn on and drive basal levels of transcription. The latter may be stimulated synergistically by two Pit-1-dependent reciprocally non-cooperative auxiliary modules, activated by cAMP and glucocorticoid, respectively. Such modularity explains, in evolutionary terms, the crucial role played by Pit-1 in transcriptional activation and the emergence of the wide variety of mechanisms regulating transcriptional levels of GH, prolactin and other Pit-1-target genes in vertebrates.