Cell-specific, promoter-dependent mineralocorticoid agonist activity of spironolactone

D-Pinitol mitigates post-traumatic stress disorder-like behaviors induced by single prolonged stress in mice through mineralocorticoid receptor antagonism

Post-traumatic stress disorder (PTSD) is a mental illness that can occur in individuals who have experienced trauma. Current treatments for PTSD, typically serotonin reuptake inhibitors, have limited effectiveness for patients and often cause serious adverse effects. Therefore, a novel class of treatment with better pharmacological profile is necessary. D-Pinitol has been reported to be effective for depression and anxiety disorders, but there are no reports associated with PTSD. In the present study, we investigated the effects of D-pinitol in a mouse model of PTSD induced by a single prolonged stress (SPS) protocol. We examined the therapeutic effects of D-pinitol on emotional and cognitive impairments in the SPS mouse model. We also investigated the effects of D-pinitol on fear memory formation. Mineralocorticoid receptor transactivation assay, Western blot, and quantitative PCR were employed to investigate how D-pinitol exerts its pharmacological activities. D-Pinitol ameliorated PTSD-like behaviors in a SPS mouse model. D-Pinitol also normalized the increased mRNA expression levels and protein levels of the mineralocorticoid receptor in the amygdala. A mineralocorticoid receptor agonist reversed the effects of D-pinitol on fear extinction and recall, and the antagonistic property of D-pinitol against the mineralocorticoid receptor was confirmed in vitro. Our findings suggest that D-pinitol could serve as a potential therapeutic agent for PTSD due to its antagonistic effect on the mineralocorticoid receptor.

Renoprotective Effects of Mineralocorticoid Receptor Antagonists Against Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a growing epidemic worldwide and a leading cause of end-stage kidney disease. Mineralocorticoid receptor (MR) blockade using Finerenone is a recently approved therapeutic approach to slow down the progression of DKD in patients with type 2 diabetes in addition to other therapies such as angiotensin-II converting enzyme inhibitors (ACEIs), angiotensin II receptor blockers (ARBs), sodium-glucose co-transporter 2 (SGLT2) inhibitors, and glucagon-like peptide 1 (GLP-1) analogs. This review elaborates on the pathophysiologic pathways activated by aldosterone (the human mineralocorticoid) in DKD, the pharmacology of three different generations of mineralocorticoid receptor antagonists (MRAs), specifically, spironolactone, eplerenone, and finerenone, and the mechanisms by which these MRAs elicit their protective effects on the kidney under diabetic settings.

The infralimbic mineralocorticoid blockage prevents the stress-induced impairment of aversive memory extinction in rats

Individuals deal with adversity and return to a normal lifestyle when adversity ends. Nevertheless, in specific cases, traumas may be preceded by memory distortions in stress-related malaises, and memory extinction impairment is strictly associated with the symptoms of post-traumatic stress disorder. Glucocorticoids (GCs), the central stress mediator, target mineralocorticoid (MR) and glucocorticoid (GR) receptors and coordinate stress responses. Despite MRs being present in brain regions essential to cognition, emotions, and initial stress processing, such as the medial prefrontal cortex (mPFC), most studies attempt to elucidate the stress-induced deleterious actions of GCs via GR. Therefore, it is necessary to understand the relationship between stress, infralimbic mPFC (IL), and memory and how MR-mediated intracellular signaling influences this relationship and modulates memory extinction. We observed that acutely restraint-stressed male Wistar rats showed high corticosterone (CORT) levels, and previous intra-IL-spironolactone administration (a selective MR antagonist) decreased it 60 min after the stress started. Intra-IL-CORT118335, a novel mixed MR/GR selective modulator, increased CORT throughout stress exposure. Ten days after stress, all rats increased freezing in the memory retrieval test and acquired the aversive contextual memory. During the extinction test, intra-IL injection of spironolactone, but not CORT118335, prevented the stress-impaired memory extinction, suggesting that the IL-MR activity controls CORT concentration, and it is crucial to the establishment of late extinction impairment. Also, the concomitant GR full activation overrode MR blockage. It increased CORT levels leading to the stress-induced extinction memory impairment, reinforcing that the MR/GR balance is crucial to predicting stress-induced behavioral outcomes.

Effects of spironolactone on extrasystoles and heart rate variability in haemodialysis patients: a randomised crossover trial

BACKGROUND

Spironolactone treatment reduces mortality in haemodialysis (HD) patients. The objective of this study was to evaluate if spironolactone affects cardiac electric activity in this population.

METHODS

Participants were randomised to start with spironolactone 50 mg daily or observation (12 weeks) with subsequent washout (6 weeks) and crossover to the other intervention (12 weeks). Long-term electrocardiograms were recorded and assessed with blinding to treatment. The primary outcome was premature ventricular complexes (PVC), and secondary outcomes were atrial premature contractions (APC) and heart rate variability (HRV).

RESULTS

Thirty participants were recruited, and data for 16 participants were included in the analysis. Treatment was associated with an increase in PVCs by 9.7 [95% confidence interval (CI): 1.5 to 18] h^-1. HRV time-domain variables increased during treatment, the standard deviation of all beat-to-beat intervals by 18 (95% CI: 3.3 to 32) milliseconds (ms) and the standard deviation of the averages of beat-to-beat intervals in all 5-min segments of the entire recording by 16 (95% CI: 1.5 to 30) ms. There were no significant differences in other variables.

CONCLUSION

Spironolactone treatment increases PVCs in HD, indicating a possible proarrhythmic effect. However, improved cardiac autonomic function, as indicated by an increased HRV, may contribute to the survival benefit from spironolactone treatment in HD patients.

Nonsteroidal antagonists of the mineralocorticoid receptor

PURPOSE OF REVIEW

The broad clinical use of steroidal mineralocorticoid receptor antagonists (MRAs) is limited by the potential risk of inducing hyperkalemia when given on top of renin-angiotensin system blockade. Drug discovery campaigns have been launched aiming for the identification of nonsteroidal MRAs with an improved safety profile. This review analyses the evidence for the potential of improved safety profiles of nonsteroidal MRAs and the current landscape of clinical trials with nonsteroidal MRAs.

RECENT FINDINGS

At least three novel nonsteroidal MRAs have reportedly demonstrated an improved therapeutic index (i.e. less risk for hyperkalemia) in comparison to steroidal antagonists in preclinical models. Five pharmaceutical companies have nonsteroidal MRAs in clinical development with a clear focus on the treatment of chronic kidney diseases. No clinical data have been published so far for MT-3995 (Mitsubishi), SC-3150 (Daiichi-Sankyo), LY2623091 (Eli Lilly) and PF-03882845 (Pfizer). In contrast, data from two clinical phase II trials are available for finerenone (Bayer) which demonstrated safety and efficacy in patients with heart failure and additional chronic kidney diseases, and significantly reduced albuminuria in patients with diabetic nephropathy. Neither hyperkalemia nor reductions in kidney function were limiting factors to its use.

SUMMARY

Novel, nonsteroidal MRAs are currently tested in clinical trials. Based on preclinical and first clinical data, these nonsteroidal MRAs might overcome the limitations of today's steroidal antagonists.

Mineralocorticoid receptor antagonists-pharmacodynamics and pharmacokinetic differences

Mineralocorticoid receptor antagonists (MRAs) are best known as potassium-sparing diuretics due to their blockade of aldosterone action in renal epithelial tissues. They are also beneficial for the treatment of heart failure, primarily due to effects in non-epithelial tissues. Currently there are only two steroidal MRAs that have been approved for use; spironolactone (and its active metabolite canrenone) and eplerenone. However, the search is on for novel generations of MRAs with increased potency and tissue selectivity. A number of novel non-steroidal compounds are in preclinical and early development, with one agent moving to phase III trials. The development of these agents and the mechanisms for their pharmacologic superiority compared to earlier generations of MRAs will be discussed in this review.

A Mixed Glucocorticoid/Mineralocorticoid Selective Modulator With Dominant Antagonism in the Male Rat Brain

Adrenal glucocorticoid hormones are potent modulators of brain function in the context of acute and chronic stress. Both mineralocorticoid (MRs) and glucocorticoid receptors (GRs) can mediate these effects. We studied the brain effects of a novel ligand, C118335, with high affinity for GRs and modest affinity for MRs. In vitro profiling of receptor-coregulator interactions suggested that the compound is a "selective modulator" type compound for GRs that can have both agonistic and antagonistic effects. Its molecular profile for MRs was highly similar to those of the full antagonists spironolactone and eplerenone. C118335 showed predominantly antagonistic effects on hippocampal mRNA regulation of known glucocorticoid target genes. Likewise, systemic administration of C118335 blocked the GR-mediated posttraining corticosterone-induced enhancement of memory consolidation in an inhibitory avoidance task. Posttraining administration of C118335, however, gave a strong and dose-dependent impairment of memory consolidation that, surprisingly, reflected involvement of MRs and not GRs. Finally, C118335 treatment acutely suppressed the hypothalamus-pituitary-adrenal axis as measured by plasma corticosterone levels. Mixed GR/MR ligands, such as C118335, can be used to unravel the mechanisms of glucocorticoid signaling. The compound is also a prototype of mixed GR/MR ligands that might alleviate the harmful effects of chronic overexposure to endogenous glucocorticoids.

Mineralocorticoid receptor signaling reduces numbers of circulating human naïve T cells and increases their CD62L, CCR7, and CXCR4 expression

The role of mineralocorticoid receptors (MRs) in human T-cell migration is not yet understood. We have recently shown that the MR antagonist spironolactone selectively increases the numbers of circulating naïve and central memory T cells during early sleep, which is the time period in the 24 h cycle hallmarked by predominant MR activation. To investigate whether this effect is specific to spironolactone's blockade of MRs and to study the underlying molecular mechanisms, healthy humans were given the selective MR-agonist fludrocortisone or placebo and numbers of eight T-cell subsets and their CD62L and CXCR4 expression were analyzed. Fludrocortisone selectively reduced counts of naïve CD4(+) , central memory CD4(+), and naïve CD8(+) T cells and increased CXCR4 expression on the naïve subsets. In complementing in vitro studies, fludrocortisone enhanced CXCR4 and CD62L expression, which was counteracted by spironolactone. Incubation of naïve T cells with spironolactone alone reduced CD62L and CCR7 expression. Our results indicate a regulatory influence of MR signaling on human T-cell migration and suggest a role for endogenous aldosterone in the redistribution of T-cell subsets to lymph nodes, involving CD62L, CCR7, and CXCR4. Facilitation of T-cell homing following sleep-dependent aldosterone release might thus essentially contribute to sleep's well-known role in supporting adaptive immunity.

The diuretic torasemide does not prevent aldosterone-mediated mineralocorticoid receptor activation in cardiomyocytes

Aldosterone binds to the mineralocorticoid receptor (MR) and exerts pleiotropic effects beyond enhancing renal sodium reabsorption. Excessive mineralocorticoid signaling is deleterious during the evolution of cardiac failure, as evidenced by the benefits provided by adding MR antagonists (MRA) to standard care in humans. In animal models of cardiovascular diseases, MRA reduce cardiac fibrosis. Interestingly diuretics such as torasemide also appear efficient to improve cardiovascular morbidity and mortality, through several mechanisms. Among them, it has been suggested that torasemide could block aldosterone binding to the MR. To evaluate whether torasemide acts as a MRA in cardiomyocytes, we compared its effects with a classic MRA such as spironolactone. We monitored ligand-induced nuclear translocation of MR-GFP and MR transactivation activity in the cardiac-like cell line H9C2 using a reporter gene assay and known endogenous aldosterone-regulated cardiac genes. Torasemide did not modify MR nuclear translocation. Aldosterone-induced MR transactivation activity was reduced by the MRA spironolactone, not by torasemide. Spironolactone blocked the induction by aldosterone of endogenous MR-responsive genes (Sgk-1, PAI-1, Orosomucoid-1, Rgs-2, Serpina-3, Tenascin-X), while torasemide was ineffective. These results show that torasemide is not an MR antagonist; its association with MRA in heart failure may however be beneficial, through actions on complementary pathways.

Mechanisms of ligand specificity of the mineralocorticoid receptor

The mineralocorticoid receptor (MR) differs from the other steroid receptors in that it responds to two physiological ligands, aldosterone and cortisol. In epithelial tissues, aldosterone selectivity is determined by the activity of 11β-hydroxysteroid dehydrogenase type 2, while in other tissues, including the heart and regions of the central nervous system, cortisol is the primary ligand for the MR where it may act as an antagonist. Clinical trials have demonstrated the potential of MR antagonists in the treatment of cardiovascular disease, though their use has been limited by concurrent hyperkalaemia. In order to better target the MR, an understanding of the structural determinants of tissue- and ligand-specific MR activation is needed. Interactions of the MR have been identified, which exhibit ligand discrimination and/or specificity. These interactions include those of the ligand-binding domain with ligand, with the N-terminal domain and with putative co-regulatory molecules. Agonist and antagonist binding have been characterised using chimeras between the human MR and the glucocorticoid receptor or the zebra fish MR together with molecular modelling. The interaction between the N-terminus and the C-terminus is aldosterone dependent but is unexpectedly antagonised by cortisol and deoxycorticosterone in the human MR. Nuclear receptor-mediated transactivation is critically dependent on, and modulated by, co-regulatory molecules. Proteins that interact with the MR in the presence of either aldosterone or cortisol, but not both, have been identified. The successful identification of ligand-specific interactions of the MR may provide the basis for the development of novel MR ligands with tissue specificity.

Characterization of the zebrafish (Danio rerio) mineralocorticoid receptor

Comparison between evolutionarily distant receptors can provide critical insights into both structure and function. Sequence comparison between the mineralocorticoid receptors (MR) of the zebrafish (zMR) and human (hMR) reveals a high degree of sequence conservation in the major functional domains. We isolated a zMR cDNA to contrast the transcriptional response to a range of ligands and to establish whether a teleost MR exhibits the amino/carboxyl-terminal interaction (N/C-interaction) previously reported for the hMR. Aldosterone, deoxycorticosterone (DOC) and cortisol induced zMR transcriptional activity with similar efficacy to that observed with the hMR. The hMR antagonist, spironolactone, acted as an agonist with the zMR. The zMR exhibited an N/C-interaction in response to aldosterone but, in contrast to the hMR, cortisol and DOC predominantly stimulated the interaction in the zMR. Conservation of the N/C-interaction between evolutionarily distant MR provides evidence of functional significance.

Glucocorticoids Activate Cardiac Mineralocorticoid Receptors During Experimental Myocardial Infarction

Myocardial ischemia-reperfusion leads to significant changes in redox state, decreased postischemic functional recovery, and cardiomyocyte apoptosis, with development and progression of heart failure. Ischemia-reperfusion in the isolated perfused rat heart has been used as a model of heart failure. Clinically, mineralocorticoid receptor blockade in heart failure decreases morbidity and mortality versus standard care alone. The effects of corticosteroids on infarct area and apoptosis were determined in rat hearts subjected to 30 minutes of ischemia and 2.5 hours of reperfusion. Both aldosterone and cortisol increased infarct area and apoptotic index, an effect half-maximal between 1 and 10 nM and reversed by spironolactone. Dexamethasone and mifepristone aggravated infarct area and apoptotic index, similarly reversed by spironolactone. Spironolactone alone reduced infarct area and apoptotic index below ischemia-reperfusion alone, in hearts from both intact and adrenalectomized rats. The present study shows that cardiac damage is aggravated by activation of mineralocorticoid receptors by aldosterone or cortisol or of glucocorticoid receptors by dexamethasone. Mifepristone unexpectedly acted as a glucocorticoid receptor agonist, for which there are several precedents. Spironolactone protected cardiomyocytes via inverse agonist activity at mineralocorticoid receptors, an effect near maximal at a relatively low dose (10 nM). Spironolactone acts not merely by excluding corticosteroids from mineralocorticoid receptors but as a protective inverse agonist at low concentration. Mineralocorticoid receptor antagonists may, thus, provide an additional therapeutic advantage in unstable angina and acute myocardial infarction.

Protective effect of spironolactone on endothelial cell apoptosis

Human umbilical vein endothelial cells (HUVECs) undergo apoptosis in response to serum deprivation. We show that the nonspecific mineralocorticoid receptor antagonist, spironolactone, protects from caspase-3 activation induced by serum deprivation in contrast to the selective mineralocorticoid receptor antagonist, eplerenone, that is nonprotective. We also demonstrate that progesterone, hydrocortisone, and dexamethasone all protect HUVECs from serum-deprivation-induced caspase-3 activation, whereas aldosterone and dihydrotestosterone have no effect. Spironolactone has been demonstrated to display agonist activity only to the progesterone receptor (PR), and we additionally show that spironolactone and progesterone, but not eplerenone, inhibit mitochondrial cytochrome c release and cleavage of nuclear poly (ADP-ribose) polymerase (PARP) and increase cell viability. Additionally, the PR antagonist mifepristone (RU486) partially blocked the inhibitory effect of both spironolactone and progesterone on caspase-3 activation, cytochrome c release, and nuclear PARP cleavage. Nitric oxide (NO) protects HUVECs from apoptosis in response to various stimuli including serum-deprivation; however, the NO synthase inhibitor N-monomethyl-l-arginine, did not abolish inhibition of caspase-3 activation or PARP cleavage by spironolactone. Thus, we demonstrate that spironolactone protects HUVECs from serum-deprivation-induced apoptosis by inhibition of caspase-3 activity, cytochrome c release and PARP cleavage by a NO-independent mechanism; further, this effect is likely mediated by the agonist properties of spironolactone toward the PR.

Biochemical mechanisms of drug action: what does it take for success?

Drug discovery is extremely difficult. There are many unanticipated scientific, medical and business challenges to every drug discovery programme. It is important to increase our understanding of the fundamental properties of effective drugs so that we can anticipate potential problems in developing new agents. This article addresses potential drug discovery and development risks associated with the biochemical mechanism of drug action, and proposes simple rules to minimize these risks.

Opposite regulation of the rat and human cytosolic aspartate aminotransferase genes by fibrates

Fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARalpha) activator, increases the expression of the cytosolic aspartate aminotransferase (cAspAT) gene in human liver cells, which may partially explain the increase of this enzyme in the serum of individuals undergoing fenofibrate treatment. Conversely, in rodents, fenofibrate represses the expression of the cAspAT gene. We compared the mechanisms of fenofibrate action in human and rat hepatoma cells. Transfection assays of the wild-type and mutated rat promoters in Fao and H4IIEC3 cells established a critical role for sequences similar to nuclear receptor responsive elements in the -404/-366 bp region. Nuclear proteins bound to these sequences and the amounts of protein bound were decreased by fenofibrate treatment, probably accounting for the decreased gene expression. Pharmacological studies confirmed the involvement of PPARalpha. However, this receptor did not bind directly to these sequences. The human promoter was cloned and the regulatory region localized between -2663/-706 bp. Co-transfection assays suggested that, in humans, the PPARalpha was also involved in the increase in expression of the cAspAT gene due to fibrates, without the presence of a canonical PPAR responsive element.

Aldosterone impairs insulin responsiveness in U-937 human promonocytic cells via the downregulation of its own receptor

In an earlier study, we have reported an inhibition of insulin receptor (IR) mRNA levels and insulin binding by aldosterone in U-937 human promonocytic cells. In the present extension of our studies, we demonstrate that this inhibition by aldosterone had no effects on basal glucose transport or on basal thymidine incorporation into DNA, while the cell responsiveness reflected by the maximal response to insulin was decreased by 23% for glucose transport and by 31% for DNA synthesis after the aldosterone treatment. We also prove that this inhibition of the insulin response by aldosterone is mediated by a downregulation of the levels of mineralocorticoid receptors (MRs) (50% decrease) and their mRNA (50% decrease). In addition, the mineralocorticoid antagonist spironolactone reversed the decrease in MR mRNA levels elicited by aldosterone, which suggests the involvement of this receptor in the process.

Spironolactone increases integrin beta3 gene expression in kidney and heart muscle cells

In clinical trials of heart failure, spironolactone, an antagonist of the mineralocorticoid receptor (MR), reduced mortality rates by unknown mechanisms. We hypothesized that spironolactone functions by upregulating expression of certain cardiovascular genes. An RNA differential display technique was used to identify genes whose expression was increased by spironolactone in an Xenopus kidney epithelial cell line (A6), a known target of aldosterone. We found that integrin beta3 gene expression was increased by spironolactone, and reversed by aldosterone or dexamethasone in a dose dependent manner. Competition binding studies and RT-PCR indicate the presence of MR in A6 cells, suggesting that regulation of expression occurred primarily through MR. Spironolactone also increased integrin beta3 expression in rat neonatal cardiomyocytes. In summary, spironolactone increases integrin beta3 gene expression in kidney epithelial cells and cardiomyocytes. The findings suggest new mechanisms for spironolactone actions with possible relevance to treatment of heart disease.

Modification of an essential amino group in the mineralocorticoid receptor evidences a differential conformational change of the receptor protein upon binding of antagonists, natural agonists and the synthetic agonist 11,19-oxidoprogesterone

The alkylation of amino groups of the mineralocorticoid receptor (MR) with pyridoxal 5'-phosphate or 2,4,6-trinitrobenzenesulphonate (TNBS) under controlled conditions modifies only one lysyl residue, which accounts for a 70% inhibition of steroid binding capacity. The Kd of aldosterone for MR is not affected by the treatment, but the total number of binding sites is greatly decreased. The modified receptor is capable of dynamically conserving its association with the hsp90-based heterocomplex. Importantly, the binding of natural agonists protects the hormone binding capacity of the MR from the inactivating action of alkylating agents. In contrast, antagonistic steroids are totally incapable of providing such protection. Like the antagonistic ligands, and despite its potent mineralocorticoid biological effect, the sole MR specific synthetic agonist known to date, 11,19-oxidoprogesterone (11-OP), shows no protective effect upon treatment of the MR with pyridoxal 5'-phosphate or TNBS. Limited digestion of the MR with alpha-chymotrypsin generates a 34 kDa fragment, which becomes totally resistant to digestion upon binding of natural agonists, but not upon binding of antagonists. Interestingly, the synthetic 21-deoxypregnanesteroid 11-OP exhibits an intermediate pattern of proteolytic degradation, suggesting that the conformational change generated in the MR is not equivalent to that induced by antagonists or natural agonists. We conclude that in the first steps of activation, the MR changes its conformation upon binding of the ligand. However, the nature of this conformational change depends on the nature of the ligand. The experimental evidence shown in this work suggests that a single lysyl group can determine the hormone specificity of the MR.

Expression of the 11beta-hydroxysteroid dehydrogenase type II enzyme in breast tumors and modulation of activity and cell growth in PMC42 cells

Manipulating the metabolism of glucocorticoids may serve as a useful adjunct in the treatment of breast cancer. The 11beta-hydroxysteroid dehydrogenase type 2 enzyme (11betaHSD2) potently inactivates glucocorticoids thereby protecting the non-selective mineralocorticoid receptor (MR) in fluid transporting tissues. In the present study, Western blot analysis showed the presence of 11betaHSD2 in 66% of the breast tumor samples. The 11betaHSD2 and MR are also present in the breast tumor cell line PMC42. Glycyrrhetinic acid abolished glucocorticoid metabolism and inhibited cell growth by 40%, the latter at concentrations consistent with glucocorticoid receptor (GR) and MR binding studies. Metabolism was increased by glucocorticoids, the anti-glucocorticoid RU 38486 and anti-mineralocorticoid spironolactone, while aldosterone had no effect. Neither cortisol nor aldosterone affected cell proliferation, but both RU 38486 and spironolactone caused a significant decrease in cell number. The effects of RU 38486 were only observed at micromolar concentrations and are inconsistent with an action via GR or progesterone receptor (PR). This study shows that 11betaHSD2 activity and cell proliferation of PMC42 cells can be modulated via steroid receptors.

Induction of secreted type IIA phospholipase A2 gene transcription by interleukin-1beta. Role of C/EBP factors

Secreted type IIA phospholipase A(2), which is involved in arachidonic acid release, is abundantly produced by chondrocytes and secreted in the synovial fluids of patients affected by rheumatoid arthritis. Transfection experiments showed that interleukin-1beta stimulates the phospholipase A(2) [-1614; +20] promoter activity by 6-7-fold and that the [-210; -176] fragment is critical for this stimulation. CAAT enhancer-binding protein (C/EBP) beta and C/EBPdelta transcription factors bind to this element as shown by bandshift experiments. Interleukin-1beta increased the levels of C/EBPdelta mRNA as soon as 2 h and up to 24 h without affecting those of C/EBPbeta. Higher amounts of C/EBPdelta proteins correlate with the stimulation of C/EBPdelta mRNA. Mutations or 5' deletions in the upstream [-247; -210] region reduced by 2-fold the basal and interleukin-1beta-stimulated transcription activities. Two types of factors bind to overlapping sequences on this fragment: NF1-like proteins and the glucocorticoid receptor. The glucocorticoid receptor is responsible for a moderate stimulation of the promoter activity by dexamethasone and may interact with C/EBP factors to achieve a full transcription activity in basal conditions and in the presence of interleukin-1beta. A [-114; -85] proximal regulatory element forms three complexes in bandshift experiments, the slowest mobility one involving the Sp1 zinc finger factor. Mutation of this sequence reduced to 2-fold the stimulation of the promoter activity by interleukin-1beta or the C/EBP factors. Induction of the transcription of secreted type IIA phospholipase A(2) gene by interleukin-1beta in chondrocytes absolutely requires C/EBPbeta and C/EBPdelta factors but does not involve NF-kappaB.

Mineralocorticoid action

The physiology of mineralocorticoid action, particularly with respect to epithelial sodium transport, is well defined. A full understanding of the molecular basis of mineralocorticoid action has however proven to be more elusive. In the last decade insights into structural and functional aspects of the mineralocorticoid receptor combined with emerging details of the components of the mediators of the sodium flux has resulted in a clearer picture. This review focuses on two aspects of these new developments; the mineralocorticoid receptor and putative aldosterone induced proteins.

Inhibition by aldosterone of insulin receptor mRNA levels and insulin binding in U-937 human promonocytic cells

The effect of aldosterone on insulin receptor (IR) expression was investigated in U-937 human promonocytic cells. The putative involvement of the mineralocorticoid receptor (MR) was also analysed. Aldosterone binding assays indicated the presence of MRs with high affinity and limited capacity in these cells. RNA blot assays showed that aldosterone treatment decreased the levels of the two major IR mRNAs (11 and 8.5 kb) present in these cells in a dose- and time-dependent manner. The partial reversal of such a decrease by the mineralocorticoid antagonist spironolactone suggested that MR was involved in the process. Experiments with the RNA synthesis inhibitor actinomycin D indicated that the decrease in IR mRNA content in aldosterone-treated cells was not the result of transcript destabilisation. The inhibitory action of aldosterone was not prevented by the simultaneous presence of the protein synthesis inhibitor cycloheximide, suggesting that the reduction of IR gene expression occurs as a direct response to the action of aldosterone. Furthermore, insulin binding assays showed that aldosterone decreased IR capacity but did not alter receptor affinity. In addition, the IR turnover resulted unaltered. These results provide the first evidence for an in vitro modulation of human IR expression by aldosterone.

Down-regulation of cytochrome P450 1A1 gene promoter by oxidative stress. Critical contribution of nuclear factor 1

Oxidative stress interferes with several cellular functions, in particular transcriptional regulation. We show here that the human cytochrome P450 1A1 (CYP1A1) is down-regulated at the transcriptional level by oxidative stress. Basal as well as 2,3,7, 8-tetrachloro-p-dioxin-induced promoter activities are strongly impaired by H2O2 treatment or glutathione depletion with L-buthionine-(S,R)-sulfoximine. Tumor necrosis factor alpha inhibits CYP1A1 expression, and this inhibition is prevented by the antioxidant pyrrolidine dithiocarbamate. We show that these regulations depend on the integrity of the nuclear factor 1 (NFI) site located in the proximal promoter. We therefore examined the redox regulation of this transcription factor. Treatment of human HepG2 or rat H4 hepatoma cells with H2O2 or L-buthionine-(S, R)-sulfoximine inactivates the binding of the NFI transcription factor to its DNA consensus sequence. Furthermore, H2O2 treatment leads to a dose-dependent decrease of reporter gene expressions driven by promoters containing NFI binding sites. Glutathione depletion and catalase inhibition also repress a NFI-driven promoter. Under the same conditions, the CP-1 transcription factor activity is not affected by oxidative stress. Thus, NFI seems particularly sensitive to oxidative stress. This accounts, at least partially, for the regulation of cyp1A1 gene expression.