Antagonism in the human mineralocorticoid receptor

Ancient and modern mechanisms compete in progesterone receptor activation

The progesterone receptor (PR) belongs to the steroid receptor family of ligand-regulated transcription factors, controlling genes important for development, metabolism, and reproduction. Understanding how diverse ligands bind and modulate PR activity will illuminate the design of ligands that control PR-driven signaling pathways. Here, we use molecular dynamics simulations to investigate how PR dynamics are altered by functionally diverse ligands. Using a library of 33 steroidal ligands that range from inactive to EC50 < 0.1 nM, we reveal an unexpected evolutionary basis for the wide gamut of activation. While other oxosteroid receptors employ an evolutionarily conserved mechanism dependent on a hydrogen bond between the receptor and ligand, extant PR has evolved a preference for activation that is not reliant on this polar interaction. We demonstrate that potent ligands utilize the modern PR mechanism while weaker ligands coopt the defunct ancestral mechanism by forming hydrogen bonds with Asn719. Based on their structures and dynamic signatures, ligands partition into four classes (inactive, weak, moderate and high potency) that interact distinctly with the PR binding pocket. Further, we use luciferase reporter assays and PR mutants to probe the roles of pocket residues in mediating distinct PR mechanisms. This combination of MD simulations and in vitro studies provide insight into how the evolutionary history of PR shapes its response to diverse ligands.

Priority list of potential endocrine-disrupting chemicals in food chemical contaminants: a docking study and in vitro/epidemiological evidence integration

Diet is an important exposure route of endocrine-disrupting chemicals (EDCs), but many unfiltered potential EDCs remain in food. The in silico prediction of EDCs is a popular method for preliminary screening. Potential EDCs in food were screened using Endocrine Disruptome, an open-source platform for inverse docking, to predict the binding probabilities of 587 food chemical contaminants with 18 human nuclear hormone receptor (NHR) conformations. In total, 25 contaminants were bound to multiple NHRs such as oestrogen receptor α/β and androgen receptor. These 25 compounds mainly include pesticides and per- and polyfluoroalkyl substances (PFASs). The prediction results were validated with the in vitro data. The structural features and the crucial amino acid residues of the four NHRs were also validated based on previous literature. The findings indicate that the screening has good prediction efficiency. In addition, the epidemic evidence about endocrine interference of PFASs in food on children was further validated through this screening. This study provides preliminary screening results for EDCs in food and a priority list for in vitro and in vivo research.

Novel 1,4-Dihydropyridine Derivatives as Mineralocorticoid Receptor Antagonists

The mineralocorticoid receptor (MR) belongs to the steroid receptor subfamily of nuclear receptors. MR is a transcription factor key in regulating blood pressure and mineral homeostasis. In addition, it plays an important role in a broad range of biological and pathological conditions, greatly expanding its interest as a pharmacological target. Non-steroidal MR antagonists (MRAs) are of particular interest to avoid side effects and achieve tissue-specific modulation of the receptor. The 1,4-dihydropyridine (1,4-DHP) ring has been identified as an appropriate scaffold to develop non-steroidal MRAs. We report the identification of a novel series of 1,4-DHP that has been guided by structure-based drug design, focusing on the less explored DHP position 2. Interestingly, substituents at this position might interfere with MR helix H12 disposition, which is essential for the recruitment of co-regulators. Several of the newly synthesized 1,4-DHPs show interesting properties as MRAs and have a good selectivity profile. These 1,4-DHPs promote MR nuclear translocation with less efficiency than the natural agonist aldosterone, which explains, at least in part, its antagonist character. Molecular dynamic studies are suggestive of several derivatives interfering with the disposition of H12 in the agonist-associated conformation, and thus, they might stabilize an MR conformation unable to recruit co-activators.

Cardiovascular and Renal Outcomes with Finerenone, a Selective Mineralocorticoid Receptor Antagonist

Overactivation of the renin-angiotensin-aldosterone system (RAAS) has been shown to be pathologic in heart failure and albuminuric chronic kidney disease (CKD), triggering pro-inflammatory and pro-fibrotic cellular pathways. The standard of care in these disease states includes treatment with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers. Mineralocorticoid receptor antagonists (MRAs) are also a mainstay in the treatment of heart failure with reduced ejection fraction; however, therapy is often limited by treatment-related hyperkalemia. In albuminuric CKD, the risk of hyperkalemia, acute kidney injury (AKI), and hypotension also remains significant. Finerenone is a novel non-steroidal MRA that may obviate some of these concerns and have therapeutic potential in additional patient populations. Finerenone was developed using the chemical structure of a dihydropyridine channel blocker but optimized to create a bulky MRA without any activity at the L-type calcium channel. It has several novel cellular mechanisms that may account for its ability to reduce cardiac hypertrophy and proteinuria more efficiently than an equinatriuretic dose of a steroidal MRA, while retaining anti-inflammatory and anti-fibrotic properties. Finerenone also has a lower rate of treatment-related hyperkalemia and AKI than steroidal MRAs with a smaller effect on systolic blood pressure, greatly expanding its therapeutic utility. The recently published FIGARO-DKD and FIDELIO-DKD trials demonstrate that treatment with finerenone in patients with type II diabetes and albuminuric CKD results in improved cardiovascular outcomes and a lower risk of CKD progression. Patients enrolled in these studies were already on maximally tolerated ACE inhibitor or angiotensin receptor blocker therapy. Trials investigating finerenone's therapeutic effect in patients with heart failure with preserved ejection fraction (HFpEF) and non-diabetic CKD, as well sodium-glucose cotransporter 2 (SGLT2) and finerenone combination therapy in patients with diabetic nephropathy, are ongoing.

Prediction of the endocrine-disrupting ability of 49 per- and polyfluoroalkyl substances: In silico and epidemiological evidence

The toxic effects of per- and polyfluoroalkyl substances (PFASs) on humans are mediated by nuclear hormone receptors (NHRs). However, data on the interaction of PFASs and NHRs is limited. Endocrine Disruptome, an inverse docking tool, was used in this study to simulate the docking of 49 common PFASs with 14 different types of human NHRs. According to the findings, 25 PFASs have a high or moderately high probability of binding to more than five NHRs, with androgen receptor (AR) and mineralocorticoid receptor (MR) being the most likely target NHRs. Molecular docking analyses revealed that the binding modes of PFASs with the two NHRs were similar to those of their corresponding co-crystallized ligands. PFASs, in particular, may disrupt the endocrine system by binding to MR. This finding is consistent with epidemiological research that has linked PFASs to MR-related diseases. Our findings may contribute to a better understanding of the health risks posed by PFASs.

Structural and molecular determinants of mineralocorticoid receptor signalling

During the past decades, the mineralocorticoid receptor (MR) has evolved from a much-overlooked member of the steroid hormone receptor family to an important player, not only in volume and electrolyte homeostasis but also in pathological changes occurring in an increasing number of tissues, especially the renal and cardiovascular systems. Simultaneously, a wealth of information about the structure, interaction partners and chromatin requirements for genomic signalling of steroid hormone receptors became available. However, much of the information for the MR has been deduced from studies of other family members and there is still a lack of knowledge about MR-specific features in ligand binding, chromatin remodelling, co-factor interactions and general MR specificity-conferring mechanisms that can completely explain the differences in pathophysiological function between MR and its closest relative, the glucocorticoid receptor. This review aims to give an overview of the current knowledge of MR structure, signalling and co-factors modulating its activity.

Effect of Water Molecules on the Activating S810L Mutation of the Mineralocorticoid Receptor

The mineralocorticoid receptor (MR) is a nuclear receptor whose endogenous ligands are mineralocorticoids, a type of steroid hormone. The activating S810L mutation is known to cause severe early-onset and pregnancy-related hypertension. Progesterone binds to the wild-type (WT) MR as a passive antagonist with fast dissociation; however, it binds to the S810L mutant as a full agonist with slow dissociation. The switch in the biological activity of progesterone is considered to be one of the causes of the disease. First, we used steered molecular dynamics simulations to analyze the dissociation process of progesterone for the WT and the S810L mutant. Progesterone in the WT dissociated from the ligand-binding pocket with a weak force in comparison with progesterone in the S810L mutant due to the large inflow of water molecules into the pocket. Therefore, we used conventional molecular dynamics simulations for the ligand-free structures of the WT and the S810L mutant to investigate the effect of the mutation on the inflow of water. In the WT, water molecules enter the ligand-binding pocket in two ways: in the vicinity of (i) Arg817 and (ii) Ser810. In contrast, few water molecules enter the pocket in the S810L mutant because of the large size and hydrophobic nature of the Leu810 side chain. Fast dissociation is a common feature among passive antagonists of MR; therefore, we inferred that the water inflow could be responsible for the dissociation kinetics of progesterone in the WT and the S810L mutant.

Roles of Nuclear Receptors in Vascular Calcification

Vascular calcification is defined as an inappropriate accumulation of calcium depots occurring in soft tissues, including the vascular wall. Growing evidence suggests that vascular calcification is an actively regulated process, sharing similar mechanisms with bone formation, implicating both inhibitory and inducible factors, mediated by osteoclast-like and osteoblast-like cells, respectively. This process, which occurs in nearly all the arterial beds and in both the medial and intimal layers, mainly involves vascular smooth muscle cells. In the vascular wall, calcification can have different clinical consequences, depending on the pattern, localization and nature of calcium deposition. Nuclear receptors are transcription factors widely expressed, activated by specific ligands that control the expression of target genes involved in a multitude of pathophysiological processes, including metabolism, cancer, inflammation and cell differentiation. Some of them act as drug targets. In this review we describe and discuss the role of different nuclear receptors in the control of vascular calcification.

Blockade of mineralocorticoid receptor ameliorates oral contraceptive-induced insulin resistance by suppressing elevated uric acid and glycogen synthase kinase-3 instead of circulating mineralocorticoid

Context: Estrogen-progestin combined oral contraceptive (COC) has been connected to mineralocorticoid receptor (MR) activation and adverse cardiometabolic events. We consequently hypothesised that insulin resistance (IR), hyperuricemia, and elevated circulating GSK-3 induced by COC is through activation of MR via mineralocorticoid and glucocorticoid pathways.Methods: Female Wistar rats aged 12 weeks received (po) vehicle and COC (1.0 μg ethinylestradiol plus 5.0 μg levonorgestrel) with or without MR blocker (0.25 mg/kg spironolactone; Spl), daily for eight weeks.Results: Data showed that COC treatment led to increased IR, 1-hour postload glucose level, insulinemia, triglyceride/HDL-cholesterol ratio, total cholesterol/HDL-cholesterol ratio, uric acid, GSK-3, aldosterone, corticosterone values, impaired glucose tolerance and pancreatic β-cell function. However, MR blockade by Spl ameliorated all these alterations except that of aldosterone.Conclusion: The results demonstrate that COC induces IR, hyperuricemia and high GSK-3 levels through activation of MR via glucocorticoid dependent pathway.

Interaction between accumulated 21-deoxysteroids and mineralocorticoid signaling in 21-hydroxylase deficiency

21-Hydroxylase deficiency (21OHD) is a rare genetic disorder in which salt-wasting syndrome occurs in 75% of cases, due to inability to synthesize cortisol and aldosterone. Recent mass spectrometry progress allowed identification of 21-deoxysteroids, i.e., 17-hydroxyprogesterone (17OHP), 21-deoxycortisol (21DF), and 21-deoxycorticosterone (21DB). We hypothesized that they may interfere with mineralocorticoid signaling and fludrocortisone therapy in patients with congenital adrenal hyperplasia (CAH) without effective glucocorticoid replacement and ACTH suppression. Our goal was to quantify circulating 21-deoxysteroids in a pediatric cohort with CAH related to 21OHD and to examine their impact on mineralocorticoid receptor (MR) activation. Twenty-nine patients with salt-wasting phenotype were classified in two groups according to their therapeutic control. During routine follow-up, 17OHP, 21DF, 21DB, and cortisol levels were quantified by liquid chromatography with tandem mass spectrometry before hydrocortisone intake and 1 and 2.5 h following treatment administration. Luciferase reporter gene assays were performed on transfected HEK293T cells while in silico modeling examined structural interactions between these steroids within ligand-binding domain of MR. Plasma 17OHP, 21DF, and 21DB accumulate in uncontrolled patients reaching micromolar concentrations even after hydrocortisone intake. 21DF and 21DB act as partial MR agonists with antagonist features similar to 17OHP, consistent with altered anchoring to Asn⁷⁷⁰ and unfavorable contact with Ala⁷⁷³ in ligand-binding pocket of MR. Our results demonstrate a complex interaction between all accumulating 21-deoxysteroids in uncontrolled 21OHD patients and mineralocorticoid signaling and suggest that appropriate steroid profiling should optimize management and follow-up of such patients, as keeping those steroids to low plasma levels should attest therapeutic efficacy and prevent interference with MR signaling.

Corticosteroid receptors adopt distinct cyclical transcriptional signatures

Mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) are two closely related hormone-activated transcription factors that regulate major pathophysiologic functions. High homology between these receptors accounts for the crossbinding of their corresponding ligands, MR being activated by both aldosterone and cortisol and GR essentially activated by cortisol. Their coexpression and ability to bind similar DNA motifs highlight the need to investigate their respective contributions to overall corticosteroid signaling. Here, we decipher the transcriptional regulatory mechanisms that underlie selective effects of MRs and GRs on shared genomic targets in a human renal cellular model. Kinetic, serial, and sequential chromatin immunoprecipitation approaches were performed on the period circadian protein 1 ( PER1) target gene, providing evidence that both receptors dynamically and cyclically interact at the same target promoter in a specific and distinct transcriptional signature. During this process, both receptors regulate PER1 gene by binding as homo- or heterodimers to the same promoter region. Our results suggest a novel level of MR-GR target gene regulation, which should be considered for a better and integrated understanding of corticosteroid-related pathophysiology.-Le Billan, F., Amazit, L., Bleakley, K., Xue, Q.-Y., Pussard, E., Lhadj, C., Kolkhof, P., Viengchareun, S., Fagart, J., Lombès, M. Corticosteroid receptors adopt distinct cyclical transcriptional signatures.

Interleukin 6-Mediated Endothelial Barrier Disturbances Can Be Attenuated by Blockade of the IL6 Receptor Expressed in Brain Microvascular Endothelial Cells

Compromised blood-brain barrier (BBB) by dysregulation of cellular junctions is a hallmark of many cerebrovascular disorders due to the pro-inflammatory cytokines action. Interleukin 6 (IL6) is implicated in inflammatory processes and in secondary brain injury after subarachnoid hemorrhage (SAH) but its role in the maintenance of cerebral endothelium still requires a precise elucidation. Although IL6 has been shown to exert pro-inflammatory action on brain microvascular endothelial cells (ECs), the expression of one of the IL6 receptors, the IL6R is controversially discussed. In attempt to reach more clarity in this issue, we present here an evident baseline expression of the IL6R in BBB endothelium in vivo and in an in vitro model of the BBB, the cEND cell line. A significantly increased expression of IL6R and its ligand was observed in BBB capillaries 2 days after experimental SAH in mice. In vitro, we saw IL6 administration resulting in an intracellular and extracellular elevation of IL6 protein, which was accompanied by a reduced expression of tight and adherens junctions, claudin-5, occludin, and vascular-endothelial (VE-) cadherin. By functional assays, we could demonstrate IL6-incubated brain ECs to lose their endothelial integrity that can be attenuated by inhibiting the IL6R. Blockade of the IL6R by a neutralizing antibody has reconstituted the intercellular junction expression to the control level and caused a restoration of the transendothelial electrical resistance of the cEND cell monolayer. Our findings add depth to the current understanding of the involvement of the endothelial IL6R in the loss of EC integrity implicating potential therapy options.

11β-HSD2 SUMOylation Modulates Cortisol-Induced Mineralocorticoid Receptor Nuclear Translocation Independently of Effects on Transactivation

The enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) has an essential role in aldosterone target tissues, conferring aldosterone selectivity for the mineralocorticoid receptor (MR) by converting 11β-hydroxyglucocorticoids to inactive 11-ketosteroids. Congenital deficiency of 11β-HSD2 causes a form of salt-sensitive hypertension known as the syndrome of apparent mineralocorticoid excess. The disease phenotype, which ranges from mild to severe, correlates well with reduction in enzyme activity. Furthermore, polymorphisms in the 11β-HSD2 coding gene (HSD11B2) have been linked to high blood pressure and salt sensitivity, major cardiovascular risk factors. 11β-HSD2 expression is controlled by different factors such as cytokines, sex steroids, or vasopressin, but posttranslational modulation of its activity has not been explored. Analysis of 11β-HSD2 sequence revealed a consensus site for conjugation of small ubiquitin-related modifier (SUMO) peptide, a major posttranslational regulatory event in several cellular processes. Our results demonstrate that 11β-HSD2 is SUMOylated at lysine 266. Non-SUMOylatable mutant K266R showed slightly higher substrate affinity and decreased Vmax, but no effects on protein stability or subcellular localization. Despite mild changes in enzyme activity, mutant K266R was unable to prevent cortisol-dependent MR nuclear translocation. The same effect was achieved by coexpression of wild-type 11β-HSD2 with sentrin-specific protease 1, a protease that catalyzes SUMO deconjugation. In the presence of 11β-HSD2-K266R, increased nuclear MR localization did not correlate with increased response to cortisol or increased recruitment of transcriptional coregulators. Taken together, our data suggests that SUMOylation of 11β-HSD2 at residue K266 modulates cortisol-mediated MR nuclear translocation independently of effects on transactivation.

Histone deacetylase inhibition, but not a mineralocorticoid receptor antagonist spironolactone, attenuates atypical transcription by an activating mutant MR (MRS 810L )

A mutation in the mineralocorticoid receptor (MRS 810L ) leads to early-onset hypertension, which is markedly exacerbated during pregnancy. The mutation causes progesterone and even the MR antagonist spironolactone to become potent agonists. Thus, it is hard to control hypertension in patients harbouring this mutation. We hypothesized that histone deacetylase inhibition (HDACi), but not the MR antagonist spironolactone, attenuates atypical transcriptional activity of activating mutant MR (MRS 810L ). We established HEK293T cells overexpressing wild-type MR (MRWT ) or MRS 810L and determined their transcriptional activities by luciferase assay. Expression of MR target genes was measured by quantitative real-time PCR (qRT-PCR). Treatment with aldosterone increased the expression of MR target genes as well as the transcriptional activities in HEK293T cells transfected either with MRWT or MRS 810L . Treatment with either spironolactone or progesterone also increased the expression of MR target genes as well as transcriptional activity, but only in HEK293T cells transfected with MRS 810L . Spironolactone abolished the promoter activity stimulated by aldosterone in HEK293T cells transfected with MRWT . Treatment with HDAC inhibitors attenuated the transcriptional activity as well as the expression of MR target genes induced by aldosterone, spironolactone, or progesterone whether HEK293T cells were transfected with either MRWT or MRS 810L . These results indicate that HDACi, but not an MR antagonist spironolactone, attenuates atypical transcriptional activity of an activating mutant MR (MRS 810L ).

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Evolution of the mineralocorticoid receptor: sequence, structure and function

The mineralocorticoid receptor (MR) is descended from a corticoid receptor (CR), which has descendants in lamprey and hagfish, cyclostomes (jawless fish), a taxon that evolved at the base of the vertebrate line. A distinct MR and GR first appear in cartilaginous fishes (Chondrichthyes), such as sharks, skates, rays and chimeras. Skate MR has a strong response to corticosteroids that are mineralocorticoids and glucocorticoids in humans. The half-maximal responses (EC50s) for skate MR for the mineralocorticoids aldosterone and 11-deoxycorticosterone are 0.07 nM and 0.03 nM, respectively. EC50s for the glucocorticoids cortisol and corticosterone are 1 nM and 0.09 nM, respectively. The physiological mineralocorticoid in ray-finned fish, which do not synthesize aldosterone, is not fully understood because several 3-ketosteroids, including cortisol, 11-deoxycortisol, corticosterone, 11-deoxycorticosterone and progesterone are transcriptional activators of fish MR. Further divergence of the MR and GR in terrestrial vertebrates, which synthesize aldosterone, led to emergence of aldosterone as a selective ligand for the MR. Here, we combine sequence analysis of the CR and vertebrate MRs and GRs, analysis of crystal structures of human MR and GR and data on transcriptional activation by 3-ketosteroids of wild-type and mutant MRs and GRs to investigate the evolution of selectivity for 3-ketosteroids by the MR in terrestrial vertebrates and ray-finned fish, as well as the basis for binding of some glucocorticoids by human MR and other vertebrate MRs.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Mineralocorticoid receptor mutations

Aldosterone and the mineralocorticoid receptor (MR) are key elements for maintaining fluid and electrolyte homeostasis as well as regulation of blood pressure. Loss-of-function mutations of the MR are responsible for renal pseudohypoaldosteronism type 1 (PHA1), a rare disease of mineralocorticoid resistance presenting in the newborn with weight loss, failure to thrive, vomiting and dehydration, associated with hyperkalemia and metabolic acidosis, despite extremely elevated levels of plasma renin and aldosterone. In contrast, a MR gain-of-function mutation has been associated with a familial form of inherited mineralocorticoid hypertension exacerbated by pregnancy. In addition to rare variants, frequent functional single nucleotide polymorphisms of the MR are associated with salt sensitivity, blood pressure, stress response and depression in the general population. This review will summarize our knowledge on MR mutations in PHA1, reporting our experience on the genetic diagnosis in a large number of patients performed in the last 10 years at a national reference center for the disease. We will also discuss the influence of rare MR variants on blood pressure and salt sensitivity as well as on stress and cognitive functions in the general population.

Familial Multiplicity of Estrogen Insensitivity Associated With a Loss-of-Function ESR1 Mutation

CONTEXT

Estrogens influence many physiological processes in mammals, including reproduction. Estrogen peripheral actions are mainly mediated through estrogen receptors (ERs) α and β, encoded by ESR1 and ESR2 genes, respectively.

OBJECTIVE

The study's aim was to describe a family in which 3 members presented with estrogen insensitivity.

DESIGN AND SETTING

Clinical evaluation and genetic and mutational analysis were performed in an academic medical center.

PATIENTS AND INTERVENTIONS

An ESR1 mutation was identified in 2 sisters and 1 brother, originating from a consanguineous Algerian family, who did not enter puberty and presented with delayed bone maturation consistent with estrogen insensitivity. The 2 sisters had enlarged multicystic ovaries. Hormonal evaluation as well as genetic and mutational analysis were performed.

RESULTS

Hormonal evaluation revealed extremely high plasma 17β-estradiol (>50-fold normal range) associated with elevated gonadotropin levels (greater than threefold normal range), highly suggestive of estrogen resistance. The 3 affected patients carried a homozygous mutation of a highly conserved arginine 394 for which histidine was substituted through an autosomal recessive mode of transmission. Structural and functional analysis of the mutant ERα revealed strongly reduced transcriptional activity and the inability to securely anchor the activating hormone, estradiol, compared with wild-type ERα. A group of other potential ER activating ligands were tested, but none overcame the estrogen insensitivity in these patients.

CONCLUSION

Description and analysis of this family of patients with mutant ERα provide additional clinical findings toward identification and characterization of what was previously thought to be a highly rare clinical condition.

Corticosteroid and progesterone transactivation of mineralocorticoid receptors from Amur sturgeon and tropical gar

The response to a panel of steroids by the mineralocorticoid receptor (MR) from Amur sturgeon and tropical gar, two basal ray-finned fish, expressed in HEK293 cells was investigated. Half-maximal responses (EC50s) for transcriptional activation of sturgeon MR by 11-deoxycorticosterone, corticosterone, 11-deoxycortisol, cortisol and aldosterone, and progesterone (Prog) were between 13 and 150 pM. For gar MR, EC50s were between 8 and 55 pM. Such low EC50s support physiological regulation by these steroids of the MR in sturgeon and gar. Companion studies with human and zebrafish MRs found higher EC50s compared with EC50s for sturgeon and gar MRs, with EC50s for zebrafish MR closer to gar and sturgeon MRs than was human MR. For zebrafish MR, EC50s were between 75 and 740 pM; for human MR, EC50s were between 65 pM and 2 nM. In addition to Prog, spironolactone (spiron) and 19nor-progesterone (19norP) were agonists for all three fish MRs, in contrast with their antagonist activity for human MR, which is hypothesized to involve serine-810 in human MR because all three steroids are agonists for a mutant human Ser810Leu-MR. Paradoxically, sturgeon, gar, and zebrafish MRs contain a serine corresponding to serine-810 in human MR. Our data suggest alternative mechanism(s) for Prog, spiron, and 19norP as MR agonists in these three ray-finned fishes and the need for caution in applying data for Prog signaling in zebrafish to human physiology.

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.

Combined oral contraceptive synergistically activates mineralocorticoid receptor through histone code modifications

Clinical studies have shown that the use of combined oral contraceptive in pre-menopausal women is associated with fluid retention. However, the molecular mechanism is still elusive. We hypothesized that combined oral contraceptive (COC) ethinyl estradiol (EE) and norgestrel (N) synergistically activates mineralocorticoid receptor (MR) through histone code modifications. Twelve-week-old female Sprague-Dawley rats were treated with olive oil (control), a combination of 0.1µg EE and 1.0µg N (low COC) or 1.0µg EE and 10.0µg N (high COC) as well as 0.1 or 1.0µg EE and 1.0 or 10.0µg N daily for 6 weeks. Expression of MR target genes in kidney cortex was determined by quantitative real-time polymerase chain reaction. MR was quantified by western blot. Recruitment of MR and RNA polymerase II (Pol II) on promoters of target genes as well as histone code modifications was analyzed by chromatin immunoprecipitation assay. Treatment with COC increased renal cortical expression of MR target genes such as serum and glucocorticoid-regulated kinase 1 (Sgk-1), glucocorticoid-induced leucine zipper (Gilz), epithelial Na(+)channel (Enac) and Na(+)-K(+)-ATPase subunit α1 (Atp1a1). Although COC increased neither serum aldosterone nor MR expression in kidney cortex, it increased recruitment of MR and Pol II in parallel with increased H3Ac and H3K4me3 on the promoter regions of MR target genes. However, treatment with EE or N alone did not affect renal cortical expression of Sgk-1, Gilz, Enac or Atp1a1. These results indicate that COC synergistically activates MR through histone code modifications.

Finerenone Impedes Aldosterone-dependent Nuclear Import of the Mineralocorticoid Receptor and Prevents Genomic Recruitment of Steroid Receptor Coactivator-1

Aldosterone regulates sodium homeostasis by activating the mineralocorticoid receptor (MR), a member of the nuclear receptor superfamily. Hyperaldosteronism leads todeleterious effects on the kidney, blood vessels, and heart. Although steroidal antagonists such as spironolactone and eplerenone are clinically useful for the treatment of cardiovascular diseases, they are associated with several side effects. Finerenone, a novel nonsteroidal MR antagonist, is presently being evaluated in two clinical phase IIb trials. Here, we characterized the molecular mechanisms of action of finerenone and spironolactone at several key steps of the MR signaling pathway. Molecular modeling and mutagenesis approaches allowed identification of Ser-810 and Ala-773 as key residues for the high MR selectivity of finerenone. Moreover, we showed that, in contrast to spironolactone, which activates the S810L mutant MR responsible for a severe form of early onset hypertension, finerenone displays strict antagonistic properties. Aldosterone-dependent phosphorylation and degradation of MR are inhibited by both finerenone and spironolactone. However, automated quantification of MR subcellular distribution demonstrated that finerenone delays aldosterone-induced nuclear accumulation of MR more efficiently than spironolactone. Finally, chromatin immunoprecipitation assays revealed that, as opposed to spironolactone, finerenone inhibits MR, steroid receptor coactivator-1, and RNA polymerase II binding at the regulatory sequence of the SCNN1A gene and also remarkably reduces basal MR and steroid receptor coactivator-1 recruitment, unraveling a specific and unrecognized inactivating mechanism on MR signaling. Overall, our data demonstrate that the highly potent and selective MR antagonist finerenone specifically impairs several critical steps of the MR signaling pathway and therefore represents a promising new generation MR antagonist.

Molecular determinants of the recognition of ulipristal acetate by oxo-steroid receptors

The human progesterone receptor (PR) plays a key role in reproductive function in women. PR antagonists have numerous applications in female health care including regular and emergency contraception, and treatment of hormone-related pathological conditions such as breast cancer, endometriosis, and leiomyoma. The main factor limiting their long-term administration is the fact that they cross-bind to other oxo-steroid receptors. Ulipristal acetate (UPA), a highly potent PR antagonist, has recently come onto the market and is much more selective for PR than the other oxo-steroid receptors (androgen, AR, glucocorticoid, GR, and mineralocorticoid, MR receptors) and, remarkably, it displays lower GR-inactivating potency than RU486. We adopted a structural approach to characterizing the binding of UPA to the oxo-steroid receptors at the molecular level. We solved the X-ray crystal structure of the ligand-binding domain (LBD) of the human PR complexed with UPA and a peptide from the transcriptional corepressor SMRT. We used the X-ray crystal structure of the GR in its antagonist conformation to dock UPA within its ligand-binding cavity. Finally, we generated three-dimensional models of the LBD of androgen and mineralocorticoid receptors (AR and MR) in an antagonist conformation and docked UPA within them. Comparing the structures revealed that the network of stabilizing contacts between the UPA C11 aryl group and the LBD is responsible for its high PR antagonist potency. It also showed that it is the inability of UPA to contact Gln642 in GR that explains why it has lower potency in inactivating GR than RU486. Finally, we found that the binding pockets of AR and MR are too small to accommodate UPA, and allowed us to propose that the extremely low sensitivity of MR to UPA is due to inappropriate interactions with the C11 substituent. All these findings open new avenues for designing new PR antagonist compounds displaying greater selectivity.

Local motifs involved in the canonical structure of the ligand-binding domain in the nuclear receptor superfamily

Structural and sequence alignment analyses have revealed the existence of class-dependent and -independent local motifs involved in the overall fold of the ligand-binding domain (LBD) in the nuclear receptor (NR) superfamily. Of these local motifs, three local motifs, i.e., AF-2 fixed motifs, were involved in the agonist conformation of the activation function-2 (AF-2) region of the LBD. Receptor-agonist interactions increased the stability of these AF-2 fixed motifs in the agonist conformation. In contrast, perturbation of the AF-2 fixed motifs by a ligand or another protein molecule led the AF-2 architecture to adopt an antagonist conformation. Knowledge of this process should provide us with novel insights into the 'agonism' and 'antagonism' of NRs.

A new strategy for selective targeting of progesterone receptor with passive antagonists

Currently available progesterone (P4) receptor (PR) antagonists, such as mifepristone (RU486), lack specificity and display partial agonist properties, leading to potential drawbacks in their clinical use. Recent x-ray crystallographic studies have identified key contacts involved in the binding of agonists and antagonists with PR opening the way for a new rational strategy for inactivating PR. We report here the synthesis and characterization of a novel class of PR antagonists (APRn) designed from such studies. The lead molecule, the homosteroid APR19, displays in vivo endometrial anti-P4 activity. APR19 inhibits P4-induced PR recruitment and transactivation from synthetic and endogenous gene promoters. Importantly, it exhibits high PR selectivity with respect to other steroid hormone receptors and is devoid of any partial agonist activity on PR target gene transcription. Two-hybrid and immunostaining experiments reveal that APR19-bound PR is unable to interact with either steroid receptor coactivators 1 and 2 (SRC1 and SCR2) or nuclear receptor corepressor (NcoR) and silencing mediator of retinoid acid and thyroid hormone receptor (SMRT), in contrast to RU486-PR complexes. APR19 also inhibits agonist-induced phosphorylation of serine 294 regulating PR transcriptional activity and turnover kinetics. In silico docking studies based on the crystal structure of the PR ligand-binding domain show that, in contrast to P4, APR19 does not establish stabilizing hydrogen bonds with the ligand-binding cavity, resulting in an unstable ligand-receptor complex. Altogether, these properties highly distinguish APR19 from RU486 and likely its derivatives, suggesting that it belongs to a new class of pure antiprogestins that inactivate PR by a passive mechanism. These specific PR antagonists open new perspectives for long-term hormonal therapy.

The decrease of mineralcorticoid receptor drives angiogenic pathways in colorectal cancer

Angiogenesis plays a crucial role in tumor growth and progression. Low expression of mineralocorticoid receptor (MR) in several malignant tumors correlates with disease recurrence and overall survival. Previous studies have shown that MR expression is decreased in colorectal cancer (CRC). Here we hypothesize that decreased MR expression can contribute to angiogenesis and poor patient survival in colorectal malignancies. In a cohort of CRC patients, we analyzed tumor MR expression, its correlation with tumor microvascular density and its impact on survival. Subsequently, we interrogated the role of MR in angiogenesis in an in vitro model, based on the colon cancer cell line HCT116, ingenierized to re-express a physiologically controlled MR. In CRC, decreased MR expression was associated with increased microvascular density and poor patient survival. In pchMR transfected HCT116, aldosterone or natural serum steroids largely inhibited mRNA expression levels of both VEGFA and its receptor 2/KDR. In CRC, MR activation may significantly decrease angiogenesis by directly inhibiting dysregulated VEGFA and hypoxia-induced VEGFA mRNA expression. In addition, MR activation attenuates the expression of the VEGF receptor 2/KDR, possibly dampening the activation of a VEGFA/KDR dependent signaling pathway important for the survival of tumor cells under hypoxic conditions.

Aldosterone resistance: structural and functional considerations and new perspectives

Aldosterone plays an essential role in the maintenance of fluid and electrolyte homeostasis in the distal nephron. Loss-of-function mutations in two key components of the aldosterone response, the mineralocorticoid receptor and the epithelial sodium channel ENaC, lead to type 1 pseudohypoaldosteronism (PHA1), a rare genetic disease of aldosterone resistance characterized by salt wasting, dehydration, failure to thrive, hyperkalemia and metabolic acidosis. This review describes the clinical, biological and genetic characteristics of the different forms of PHA1 and highlights recent advances in the understanding of the pathogenesis of the disease. We will also discuss genotype-phenotype correlations and new clinical and genetic entities that may prove relevant for patient's care in neonates with renal salt losing syndromes and/or failure to thrive.

Structural determinants of ligand binding to the mineralocorticoid receptor

The first and critical step in the mechanism of aldosterone action is its binding to the mineralocorticoid receptor (MR), a member of the nuclear receptor superfamily. Over the last 40 years, numerous studies have attempted to determine the structural determinants of ligand-binding to MR. An initial set of data showed that hsp90 is bound to the receptor via specific regions and maintains it in a ligand-binding competent state. Site-directed mutagenesis and functional studies guided by a 3D model of the MR ligand-binding domain (LBD) made it possible to identify the residues responsible for the high affinity and selectivity for aldosterone, and to characterize the mechanisms of MR activation and inactivation. The recent determination of the X-ray crystal structures of the LBD of the wild-type MR and MR(S810L), which is responsible for a familial form of hypertension, has made it possible to elucidate the peculiar mechanism of activation of MR(S810L) and established a clear structure/activity relationship for steroidal and non-steroidal MR antagonists.

Mineralocorticoid receptor mutations and a severe recessive pseudohypoaldosteronism type 1

Pseudohypoaldosteronism type 1 (PHA1) is a rare genetic disease of mineralocorticoid resistance characterized by salt wasting and failure to thrive in infancy. Here we describe the first case of a newborn with severe recessive PHA1 caused by two heterozygous mutations in NR3C2, gene coding for the mineralocorticoid receptor (MR). Independent segregation of the mutations occurred in the family, with p.Ser166X being transmitted from the affected father and p.Trp806X from the asymptomatic mother Whereas the truncated MR(166X) protein was degraded, MR(806X) was expressed both at the mRNA and protein level. Functional studies demonstrated that despite its inability to bind aldosterone, MR(806X) had partial ligand-independent transcriptional activity. Partial nuclear localization of MR(806X) in the absence of hormone was identified as a prerequisite to initiate transcription. This exceptional case broadens the spectrum of clinical phenotypes of PHA1 and demonstrates that minimal residual activity of MR is compatible with life. It also suggests that rare hypomorphic NR3C2 alleles may be more common than expected from the prevalence of detected PHA1 cases. This might prove relevant for patient's care in neonatal salt losing disorders and may affect renal salt handling and blood pressure in the general population.

Two panels of steroid receptor luciferase reporter cell lines for compound profiling

Steroid hormone receptors represent a major target in drug discovery. As ligand inducible transcription factors, their activity can be modulated by small lipophilic molecules. Here we describe two panels of potent and selective luciferase reporter cell lines based on cells with low endogenous steroid receptor activity (U2OS). The panels contain reporter cell lines for estrogen receptors α and β, androgen, glucocorticoid, mineralocorticoid, and progesterone receptors. In the first panel, the activation of either synthetic, steroid response elements containing promoter or viral promoter is mediated by full-length steroid receptors. The second panel is based on the expression of the chimeric receptor, which was created by the replacement of the N-terminal part of the molecule by Gal4 DBD and that binds to multiple UAS sites in the reporter promoter. Both panels were extensively characterized by profiling 28 ligands in dose response manner in agonist and antagonist mode. We have analyzed and compared the responses to tested ligands from both panels and concluded that in general both systems generated similar qualitative response in terms of potency, efficacy, partial agonism/antagonism, mixed agonistic/antagonistic profiles and the rank of potencies was well conserved between both panels. However, we have also identified some artifacts introduced by the Gal4/LBD reporter assays in contrast to their full-length receptor reporter counterparts. Keeping in mind the advantages and drawbacks of each reporter format, these cell lines represent powerful and selective tools for profiling large compound libraries (HTS) and for detailed study of mechanisms by which compounds exert their biological effects.

Insights from the structure of estrogen receptor into the evolution of estrogens: implications for endocrine disruption

In the last decade, there has been important progress in understanding the origins and evolution of receptors for adrenal steroids (aldosterone, cortisol) and sex steroids (estradiol, progesterone, testosterone) due to the sequencing of genomes from animals that are at key sites in vertebrate evolution. Although the estrogen receptor [ER] appears to be the ancestral vertebrate steroid receptor and estradiol [E2] is the physiological ligand for vertebrate ERs, the identity of the ancestral ligand(s) for the ER remains unknown. Here, using an analysis of crystal structures of human ERα with E2 and other chemicals and 3D models of human ERα with 27-hydroxycholesterol and 5-androsten-3β,17β-diol, I propose that one or more Δ5 steroids were the ancestral ligands for the ER, with E2 evolving later as the canonical estrogen. The evidence that chemicals with a β-hydroxy at C3 in a saturated A ring can act as estrogens and the conformational flexibility of the vertebrate ER can explain the diversity of synthetic chemicals that disrupt estrogen responses by binding to vertebrate ERs.

Gender and the renin-angiotensin-aldosterone system

Premenopausal women are protected to some extent from cardiovascular and kidney diseases. Because this protection weakens after menopause, sex hormones are believed to play an important role in the pathogenesis of cardiovascular and kidney diseases. The cardiovascular system and the kidneys are regulated by the renin-angiotensin-aldosterone system (RAAS), which in turn, appears to be regulated by sex hormones. In general, oestrogen increases angiotensinogen levels and decreases renin levels, angiotensin-converting enzyme (ACE) activity, AT(1) receptor density, and aldosterone production. Oestrogen also activates counterparts of the RAAS such as natriuretic peptides, AT(2) receptor density, and angiotensinogen (1-7). Progesterone competes with aldosterone for mineralocorticoid receptor. Less is known about androgens, but testosterone seems to increase renin levels and ACE activity. These effects of sex hormones on the RAAS can explain at least some of the gender differences in cardiovascular and kidney diseases.

Conformation of the mineralocorticoid receptor N-terminal domain: evidence for induced and stable structure

The mineralocorticoid receptor (MR) binds the steroid hormones aldosterone and cortisol and has an important physiological role in the control of salt homeostasis. Regions of the protein important for gene regulation have been mapped to the amino-terminal domain (NTD) and termed activation function (AF)1a, AF1b, and middle domain (MD). In the present study, we used a combination of biophysical and biochemical techniques to investigate the folding and function of the MR-NTD transactivation functions. We demonstrate that MR-AF1a and MR-MD have relatively little stable secondary structure but have the propensity to form α-helical conformation. Induced folding of the MR-MD enhanced protein-protein binding with a number of coregulatory proteins, including the coactivator cAMP response element-binding protein-binding protein and the corepressors SMRT and RIP140. By contrast, the MR-AF1b domain appeared to have a more stable conformation consisting predominantly of β-secondary structure. Furthermore, MR-AF1b specifically interacted with the TATA-binding protein, via an LxxLL-like motif, in the absence of induced folding. Together, these data suggest that the MR-NTD contains a complex transactivation system made up of distinct structural and functional domains. The results are discussed in the context of the induced folding paradigm for steroid receptor NTDs.

A new mode of mineralocorticoid receptor antagonism by a potent and selective nonsteroidal molecule

Limitations of current steroidal mineralocorticoid receptor (MR) antagonists have stimulated the search for a new generation of molecules. We screened for novel nonsteroidal compounds and identified MR antagonists derived from the chemical class of dihydropyridines. Chemical optimization resulted in BR-4628, which displays high in vitro and in vivo MR potency as well as selectivity with respect to the other steroid hormone receptors and the L-type calcium channel. Biochemical studies demonstrated that BR-4628 forms complexes with MR that do not promote the recruitment of transcriptional co-regulators. Docking experiments, using the crystal structure of the MR ligand-binding domain in an agonist conformation, revealed that BR-4628 accommodates in the MR ligand-binding cavity differently in comparison with the classical steroidal MR antagonists. An alanine scanning mutagenesis approach, based on BR-4628 docking, allowed identifying its anchoring mode within the ligand-binding cavity. Altogether, we propose that BR-4628 is a bulky antagonist that inactivates MR through a passive mechanism. It represents the prototype of a new class of MR antagonists.

The L-, N-, and T-type triple calcium channel blocker benidipine acts as an antagonist of mineralocorticoid receptor, a member of nuclear receptor family

Aldosterone-induced activation of mineralocorticoid receptor, a member of the nuclear receptor family, results in increased tissue damage such as vascular inflammation and cardiac and perivascular fibrosis. Benidipine, a long-lasting dihydropyridine calcium channel blocker, is used for hypertension and angina. Benidipine exhibits pleiotropic pharmacological features such as renoprotective and cardioprotective effects through triple blockade of L-, N-, and T-type calcium channels. However, the mechanism of additional beneficial effects on end-organ damage is poorly understood. Here, we examined the effects of benidipine and other calcium channel blockers on aldosterone-induced mineralocorticoid receptor activation using luciferase reporter assay system. Benidipine showed more potent activity than efonidipine, amlodipine, or azelnidipine. Benidipine depressed the response to higher concentrations of aldosterone, whereas pretreatment of eplerenone, a steroidal mineralocorticoid receptor antagonist, did not. Binding studies using [(3)H] aldosterone indicated that benidipine and other calcium channel blockers competed for binding to mineralocorticoid receptor. Benidipine and other calcium channel blockers showed antagonistic activity on Ser810 to Leu mutant mineralocorticoid receptor, which is identified in patients with early-onset hypertension. On the other hand, eplerenone partially activated the mutant. Results of analysis using optical isomers of benidipine indicated that inhibitory effect of aldosterone-induced mineralocorticoid receptor activation was independent of its primary blockade of calcium channels. These results suggested that benidipine directly inhibits aldosterone-induced mineralocorticoid receptor activation, and the antagonistic activity might contribute to the drug's pleiotropic pharmacological features.

Structural and functional relationships of the steroid hormone receptors' N-terminal transactivation domain

Steroid hormone receptors are members of a family of ligand inducible transcription factors, and regulate the transcriptional activation of target genes by recruiting coregulatory proteins to the pre-initiation machinery. The binding of these coregulatory proteins to the steroid hormone receptors is often mediated through their two activation functional domains, AF1, which resides in the N-terminal domain, and the ligand-dependent AF2, which is localized in the C-terminal ligand-binding domain. Compared to other important functional domains of the steroid hormone receptors, our understanding of the mechanisms of action of the AF1 are incomplete, in part, due to the fact that, in solution, AF1 is intrinsically disordered (ID). However, recent studies have shown that AF1 must adopt a functionally active and folded conformation for its optimal activity under physiological conditions. In this review, we summarize and discuss current knowledge regarding the molecular mechanisms of AF1-mediated gene activation, focusing on AF1 conformation and coactivator binding. We further propose models for the binding/folding of the AF1 domains of the steroid hormone receptors and their protein:protein interactions. The population of ID AF1 can be visualized as a collection of many different conformations, some of which may be assuming the proper functional folding for other critical target binding partners that result in the ultimate assembly of AF1:coactivator complexes and subsequent gene regulation. Knowledge of the mechanisms involved therein will significantly help in understanding how signals from a steroid to a specific target gene are conveyed.

Regulation of activities of steroid hormone receptors by tibolone and its primary metabolites

This work was undertaken (i) to study deeply the estrogen, androgen and progestative activities of tibolone and its metabolites (ii) to determine whether tibolone and its metabolites present glucocorticoid or mineralocorticoid activity. For this purpose, we used human cell lines bearing a luciferase gene with a responsive element under the control of human estrogen receptor alpha (ERalpha) or estrogen receptor beta (ERbeta) or androgen receptor (AR) or chimeric Gal4 fusion with progesterone receptor (PR), glucocorticoid receptor (GR) or mineralocorticoid receptor (MR). The major tibolone metabolites, the two hydroxymetabolites, bind and activate ER with a preference for ERalpha. Tibolone and the Delta(4)-tibolone are agonists for AR and PR and surprisingly 3alpha- and 3beta-OH-tibolone are antagonists for them. Moreover we showed for the first time that tibolone and its primary metabolites are GR and MR antagonists with a stronger affinity for MR than for GR. In conclusion, tibolone by these actions on different receptors and by this capacity to transform in different metabolites, has more complex effects than initially supposed.

Glucocorticoids regulate the human occludin gene through a single imperfect palindromic glucocorticoid response element

The 65kDa protein occludin is an essential element of the blood-brain barrier. This integral membrane protein represents an important part of the tight junctions, which seal and protect the blood brain barrier against paracellular diffusion of solutes to the brain parenchyme and are therefore responsible for the high resistance and low permeability between cerebral capillary endothelial cells. However, the molecular basis for the regulation of occludin gene expression is only incompletely understood. In former projects we showed that treatment of a brain microvascular cell line, cEND, with glucocorticoids resulted in increased occludin expression in cell-cell-contacts [Förster, C., Silwedel, C., Golenhofen, N., Burek, M., Kietz, S., Mankertz, J., Drenckhahn, D., 2005. Occludin as direct target for glucocorticoid-induced improvement of blood-brain barrier properties in a murine in vitro system. J. Physiol. 565, Pt 2, 475-486]. Induction of occludin expression by glucocorticoids was shown to be dependent on the glucocorticoid receptor. This study aims to identify the underlying molecular mechanism of gene expression and to identify potential glucocorticoid receptor binding sites within the occludin promoter, the glucocorticoid response elements. We identified one candidate glucocorticoid response element within the distal part of the occludin promoter that differs from the consensus glucocorticoid response element by the presence of a 4-basepair instead of a 3-basepair spacer between two highly degenerate halfsites (5'-ACATGTGTTTACAAAT-3'). Chromatin immunoprecipitation assay and site-directed mutagenesis confirmed binding of the glucocorticoid receptor to this site. The need for glucocorticoid receptor dimerization to induce gene expression was further confirmed by transfection studies using wild type and glucocorticoid receptor dimerization-deficient expression vectors, indicating that transactivation of occludin occurs through the glucocorticoid response element (GRE).

Glucocorticoids increase VE-cadherin expression and cause cytoskeletal rearrangements in murine brain endothelial cEND cells

Recent studies have shown the influence of glucocorticoids on the expression of the tight junction protein occludin in the brain capillary endothelial cell line cEND, contributing to improvement in endothelial barrier functions. In this study, we investigated glucocorticoid effects on the expression of the adherens junction proteins VE- (vascular-endothelial) cadherin, alpha-catenin and beta-catenin as well as that of ZO-1, the plaque protein shared by both adherens and tight junctions on stimulation with dexamethasone. We were able to show a positive influence of dexamethasone administration on VE-cadherin protein levels as well as a rearrangement of VE-cadherin protein to the cytoskeleton after dexamethasone treatment. Investigation of transcriptional activation of the VE-cadherin promoter by dexamethasone, however, did not point to direct glucocorticoid-mediated VE-cadherin gene induction but rather suggested indirect steroid effects leading to increased VE-cadherin protein synthesis. Dexamethasone was further shown to induce cellular differentiation into a cobblestone cellular morphology and reinforcement of adherens junctions concomitant with the increased anchorage of VE-cadherin to the actin cytoskeleton. We thus propose that glucocorticoid effects on VE-cadherin protein synthesis and organization are important for the formation of both adherens and tight junction, and for improved barrier properties in microvascular brain endothelial cells.

Helix 3-helix 5 interactions in steroid hormone receptor function

Steroid hormones working through their receptors regulate a wide variety of physiologic processes necessary for normal homeostasis. Recent years have witnessed great advances in our understanding of how these hormones interact with their receptors, and have brought us closer to the era of directed drug design. We previously described a novel intramolecular interaction between helix 3 and helix 5 which is responsible for a Mendelian form of human hypertension. Further studies revealed that this interaction is highly conserved throughout the steroid hormone receptor family and functions as a key regulator of steroid hormone receptor sensitivity and specificity. Here, we review the contribution of helix 3-helix 5 interaction to steroid hormone receptor activity, with an eye towards how this knowledge may aid in the creation of novel therapeutic agonists and antagonists.

Superior nuclear receptor selectivity and therapeutic index of methylprednisolone aceponate versus mometasone furoate

Although introduced more than 50 years ago, topical glucocorticoids are still the first line therapy for many inflammatory skin disorders such as atopic eczema, contact dermatitis and many others. Recently, significant improvements have been made to optimize the ratio of desired to unwanted effects. While with early compounds such as triamcinolone, topical side effects such as skin atrophy and telangiectasias can be observed rather frequently, newer drugs such as methylprednisolone aceponate or mometasone furoate have a significantly improved therapeutic index. The present study compared these two modern topical glucocorticoids, which possess the highest therapeutic index currently found, in terms of nuclear receptor selectivity in vitro and induction of the most important local side effects (skin atrophy and telangiectasias) in a relevant rodent model in vivo. We demonstrate that methylprednisolone aceponate displays higher specificity in nuclear receptor binding compared with mometasone furoate. Methylprednisolone aceponate was also markedly superior in terms of minimizing induction of skin atrophy or telangiectasias when compared with mometasone furoate. Based on these observations, methylprednisolone aceponate is expected to have a greater therapeutic index as compared with mometasone furoate, at least in the test systems used here. The degree to which this observation may translate into a clinical setting requires confirmation.

Evolution of the corticosteroid receptor signalling pathway in fish

The corticosteroid receptors (CR) control a vast array of physiological processes acting primarily as ligand-dependent transcription factors. The origins of the gnathostomata CRs can be traced back to an ancestral steroid receptor present in a primitive agnathan vertebrate. A genome duplication event in the early gnathostomes is believed to have produced a set of two CRs still present today in Sarcopterygii (lobe-finned fish and tetrapods), i.e. a glucocorticoid (GR) and mineralocorticoid receptor (MR), with divergent function and different ligands, cortisol and aldosterone, respectively. A further genome duplication occurred in the early evolutionary history of the teleosts, and the teleost CR system seems to have diversified, consisting now of 2 GRs and a MR. Teleosts lack aldosterone and the main corticosteroid is believed to be cortisol. However, the mineralocorticoid, 11-deoxycorticosterone (DOC), has been identified as an agonist for the rainbow trout MR, suggesting it may be the ancestral ligand for the MR. The retention of two GRs in teleosts suggests neofunctionalisation of one of the duplicated genes, but this hypothesis requires further work. In rainbow trout, transactivation and transrepression activities of the two GRs show marked differences in their sensitivity to glucocorticoids, suggesting a mechanism that may allow the two GRs to control different physiological pathways. Whether a similar mechanism is seen throughout the actinopterygii or whether this is specific to the salmonid lineage remains to be verified.