GEMIN4 functions as a coregulator of the mineralocorticoid receptor

Molecular pharmacology of mineralocorticoid receptor antagonists: The role of co-regulators

Mineralocorticoid receptor (MR) antagonists have shown remarkable benefits in the treatment of cardiovascular disease. However, their underutilization in clinical practice may be attributed to concerns regarding the risk of hyperkalemia. An ideal selective MR modulator would inhibit the detrimental effects of MR in non-epithelial cells of the cardiovascular system while sparing its physiological function in kidney epithelial cells, thereby reducing the risk of adverse events. To address this issue, a new generation of non-steroidal MR antagonists, including esaxereneone, balcinrenone, ocedurenone, and finerenone, has been developed with distinct molecular structures and pharmacology. They share a mechanism of action that is different from the previously developed steroidal MR antagonists, leading to altered co-regulator interaction, potentially involving conformational changes of the receptor. Interfering with MR co-regulator interaction or the co-regulator itself may enable selective targeting of downstream signaling cascades and - in the long term - lead to more personalized medicine. In this review article, we summarize what is currently known about the mechanisms of action of the different MR antagonists with a focus on MR co-factor interaction and what may be inferred from this for future developments.

Crosstalk between Aldosterone and Glycation through Rac-1 Induces Diabetic Nephropathy

Background: Advanced glycation end products (AGEs) interaction with its receptor (RAGE) and aldosterone (Aldo) through the mineralocorticoid receptor (MR) activates Rac-1 and NF-κB independently in diabetic nephropathy (DN). However, the crosstalk of Aldo with AGEs-RAGE is still unresolved. Our study examined the impact of the AGEs-Aldo complex on renal cells and its effect on the RAGE-MR interaction. Methods and results: Glycation of human serum albumin (HSA) (40 mg/mL) with methylglyoxal (10 mM) in the presence of Aldo (100 nM) and aminoguanidine (AG) (100 nM) was performed. Glycation markers such as fructosamine and carbonyl groups and fluorescence of AGEs, pentosidine, and tryptophan followed by protein modification were measured. Renal (HEK-293T) cells were treated with the glycated HSA-Aldo (200 μg/mL) along with FPS-ZM1 and spironolactone antagonists for RAGE and Aldo, respectively, for 24 h. Glycation markers and esRAGE levels were measured. Protein and mRNA levels of RAGE, MR, Rac-1, and NF-κB were estimated. Glycation markers were enhanced with Aldo when albumin was only 14-16% glycated. AGEs-Aldo complex upregulated RAGE, MR, Rac-1 and NF-κB expressions. However, FPS-ZM1 action might have activated the RAGE-independent pathway, further elevating MR, Rac-1, and NF-κB levels. Conclusion: Our study concluded that the presence of Aldo has a significant impact on glycation. In the presence of AGEs-Aldo, RAGE-MR crosstalk exerts inflammatory responses through Rac-1 in DN. Insights into this molecular interplay are crucial for developing novel therapeutic strategies to alleviate DN in the future.

Advances in understanding and treating diabetic kidney disease: focus on tubulointerstitial inflammation mechanisms

Diabetic kidney disease (DKD) is a serious complication of diabetes that can lead to end-stage kidney disease. Despite its significant impact, most research has concentrated on the glomerulus, with little attention paid to the tubulointerstitial region, which accounts for the majority of the kidney volume. DKD's tubulointerstitial lesions are characterized by inflammation, fibrosis, and loss of kidney function, and recent studies indicate that these lesions may occur earlier than glomerular lesions. Evidence has shown that inflammatory mechanisms in the tubulointerstitium play a critical role in the development and progression of these lesions. Apart from the renin-angiotensin-aldosterone blockade, Sodium-Glucose Linked Transporter-2(SGLT-2) inhibitors and new types of mineralocorticoid receptor antagonists have emerged as effective ways to treat DKD. Moreover, researchers have proposed potential targeted therapies, such as inhibiting pro-inflammatory cytokines and modulating T cells and macrophages, among others. These therapies have demonstrated promising results in preclinical studies and clinical trials, suggesting their potential to treat DKD-induced tubulointerstitial lesions effectively. Understanding the immune-inflammatory mechanisms underlying DKD-induced tubulointerstitial lesions and developing targeted therapies could significantly improve the treatment and management of DKD. This review summarizes the latest advances in this field, highlighting the importance of focusing on tubulointerstitial inflammation mechanisms to improve DKD outcomes.

Structure-function relationships of the aldosterone receptor

The cellular response to the adrenal steroid aldosterone is mediated by the mineralocorticoid receptor (MR), a member of the nuclear receptor superfamily of ligand-dependent transcription factors. The MR binds more than one physiological ligand with binding at the MR determined by pre-receptor metabolism of glucocorticoid ligands by 11β hydroxysteroid dehydrogenase type 2. The MR has a wide tissue distribution with multiple roles beyond the classical role in electrolyte homeostasis including cardiovascular function, immune cell signaling, neuronal fate and adipocyte differentiation. The MR has three principal functional domains, an N-terminal ligand domain, a central DNA binding domain and a C-terminal, ligand binding domain, with structures having been determined for the latter two domains but not for the whole receptor. MR signal-transduction can be best viewed as a series of interactions which are determined by the conformation conferred on the receptor by ligand binding. This conformation then determines subsequent intra- and inter-molecular interactions. These interactions include chromatin, coregulators and other transcription factors, and additional less well characterized cytoplasmic non-genomic effects via crosstalk with other signaling pathways. This chapter will provide a review of MR structure and function, and an analysis of the critical interactions involved in MR-mediated signal transduction, which contribute to ligand- and tissue-specificity. Understanding the relevant mechanisms for selective MR signaling in terms of these interactions opens the possibility of novel therapeutic approaches for the treatment of MR-mediated diseases.

Association of polymorphic variants in GEMIN genes with the risk of depression in a Polish population

Background

The role of miRNA in depression is widely described by many researchers. miRNA is a final product of many genes involved in its formation (maturation). One of the final steps in the formation of miRNAs is the formation of the RISC complex, called the RNA-induced silencing complex, which includes, among others, GEMIN proteins. Single-nucleotide polymorphisms (SNPs) may lead to disturbance of miRNA biogenesis and function. The objective of our research was to assess the relationship between the appearance of depression and single nucleotide polymorphisms in the GEMIN3 (rs197388) and GEMIN4 (rs7813; rs3744741) genes. Our research provides new knowledge on the genetic factors that influence the risk of depression. They can be used as an element of diagnostics helpful in identifying people at increased risk, as well as indicating people not at risk of depression.

Methods

A total of 218 participants were examined, including individuals with depressive disorders (n = 102; study group) and healthy people (n = 116, control group). All the patients in the study group and the people in the control group were non-related native Caucasian Poles from central Poland. Blood was collected from study and control groups in order to assess the SNPs of GEMIN genes.

Results

An analysis of the results obtained showed that in patient population, the risk of depression is almost doubled by polymorphic variants of the genes: rs197388/GEMIN3 genotype A/A in the recessive model and rs3744741/GEMIN4 genotype T/T, codominant and recessive model. The dual role of rs7813/GEMIN4 is noteworthy, where the G/A genotype in the codominant and over dominant model protects against depression.

Importance of Micromilieu for Pathophysiologic Mineralocorticoid Receptor Activity—When the Mineralocorticoid Receptor Resides in the Wrong Neighborhood

The mineralocorticoid receptor (MR) is a member of the steroid receptor family and acts as a ligand-dependent transcription factor. In addition to its classical effects on water and electrolyte balance, its involvement in the pathogenesis of cardiovascular and renal diseases has been the subject of research for several years. The molecular basis of the latter has not been fully elucidated, but an isolated increase in the concentration of the MR ligand aldosterone or MR expression does not suffice to explain long-term pathologic actions of the receptor. Several studies suggest that MR activity and signal transduction are modulated by the surrounding microenvironment, which therefore plays an important role in MR pathophysiological effects. Local changes in micromilieu, including hypoxia, ischemia/reperfusion, inflammation, radical stress, and aberrant salt or glucose concentrations affect MR activation and therefore may influence the probability of unphysiological MR actions. The surrounding micromilieu may modulate genomic MR activity either by causing changes in MR expression or MR activity; for example, by inducing posttranslational modifications of the MR or novel interaction with coregulators, DNA-binding sites, or non-classical pathways. This should be considered when developing treatment options and strategies for prevention of MR-associated diseases.

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.

Mineralocorticoid receptor actions in cardiovascular development and disease

Mineralocorticoid receptors (MRs) are transcriptional regulators that mediate the diverse physiological and pathophysiological actions of corticosteroid hormones across many tissues. In the kidney aldosterone control of sodium/water resorption via DNA-binding actions of the MR is established. MRs also regulate tissues not involved in electrolyte homeostasis such as the heart, adipose tissue, brain, and inflammatory cells where the MRs can respond to both aldosterone and cortisol. The pathology of inappropriate MR activation in non-epithelial tissues are well-described, and steroidal antagonists of the MR have been clinically beneficial in the management of heart failure and blood pressure for decades. However, the role of cortisol-dependent MR activation in the physiological setting is less well defined. Like other steroid hormone receptors, the MR also regulates non-DNA-binding pathways including MAPK pathways and G protein coupled receptors to provide diversity to MR signaling. Whether nonDNA binding pathways are more relevant for MR activation in non-epithelial, versus epithelial, tissues remain unclear. This review will focus on molecular regulation of ligand-dependent MR activation and the physiology and pathophysiology of MR actions in the heart with a focus on the cardiomyocyte and provide a discussion of relevant genomic and non-genomic MR pathways and potential new transcriptional partners for the MR and their relevance for health and disease. Understanding MR actions in the heart will provide new insights into cell-selective mechanisms that underpin the therapeutic benefits of MRAs, and are a critical step towards developing next-generation tissue selective MR modulators with improved safety profiles.

Micro-RNA Biogenesis Genes (AGO1 and GEMIN4) Single Nucleotide Variants of Bad Prognosis and Poor Therapeutic Response in Egyptian Chronic Myeloid Leukemia Patients: Case–control Study

BACKGROUND: Chronic myeloid leukemia (CML) is one of the most common hematological tumors. Gene candidate studies cleared the association of single genetic variants (SNVs) to the risk and progression in CML. MicroRNA biogenesis genes disruption contributes a fundamental role in carcinogenesis. AIM: We aimed to determine the association between rs636832 and rs2740348 SNVs of AGO1 gene and GEMIN4 gene, respectively, and the risk and prognosis in CML Egyptian patients with 5 years survival estimation. METHODS: The study was conducted on 110 newly diagnosed CML patients and 110 age and sex healthy matched controls. Real-time polymerase chain reaction utilizing TaqMan probes was operated to demonstrate genetic modalities of rs636832 and rs2740348. RESULTS: No significance difference was observed between the cases and controls regarding the genotypic and allelic frequencies for both variants. On the other hand, the rs636832 GG genotype was more evident at a younger age of diagnosis and associated with the poor grades of the Sokal and Eutos scores. As well, rs2740348 CC genotype was encountered in high Eutos score levels. Regarding the response therapy, rs636832 GG genotype was overrepresented in the resistance to Imatinib while rs2740348 CC genotype was prevalent in the resistance to both Imatinib and Nilotinib. Overall survival was of no statistical significance for both variants. CONCLUSION: Our study revealed that the major homozygous genotypes of both variants were associated with bad prognostic clinical scores and poor response to therapy but with no role in CML risk.

Structural determinants of activation of the mineralocorticoid receptor: an evolutionary perspective

The mineralocorticoid receptor (MR) plays a central role in sodium homoeostasis by transducing the response to aldosterone in the distal nephron and other sodium transporting epithelia. The MR is a member of the nuclear receptor family of ligand-dependent transcription factors; it is unusual in being the receptor for two steroid hormones aldosterone and cortisol (which also binds to the closely related glucocorticoid receptor). Less well recognised is that progesterone also binds to the MR with high affinity. The conformation of the ligand-bound receptor is determined by the ligand including whether the conformation is agonist or antagonist. An agonist MR conformation then enables interactions with DNA, other MR (homodimerization) and coregulatory molecules to regulate gene expression. Insights into the structural determinants of an agonist response to ligand come from studies of the evolution of the MR. Progesterone is an agonist in the fish MR, but antagonist in the MR of terrestrial vertebrates; this switch results from the loss of a critical leucine that mediates a leucine:leucine interaction between helix 1 and helix 8 which enables the agonist response to progesterone. The insights into the intramolecular dynamics of activation suggest novel ways in which MR antagonism may be achieved beyond the current, progesterone-based antagonists in clinical use.

Identification of two independent SUMO-interacting motifs in Fas-associated factor 1 (FAF1): Implications for mineralocorticoid receptor (MR)-mediated transcriptional regulation

Fas-associated factor 1 (FAF1) was originally isolated as a Fas-associated factor and was subsequently found to interact with numerous other proteins that are involved in various cellular events including Fas-mediated apoptosis, nuclear factor (NF)-κB, Wnt/β-catenin, and transforming growth factor (TGF)-β signaling pathways, mineralocorticoid receptor (MR)-mediated transactivation, and ubiquitin-dependent processes. Herein, we defined two small ubiquitin-like modifier (SUMO)-interacting motifs (SIMs) within FAF1 and demonstrated to be crucial for transcriptional modulation of the MR. Our study demonstrated that the SIMs of FAF1 do not play a significant role in regulating its subcellular localization, Fas-mediated apoptosis, or NF-κB or Wnt/β-catenin pathways. Remarkably, FAF1 interacts with the sumoylated MR and represses aldosterone-activated MR transactivation in a SIM-dependent manner. Moreover, silencing of endogenous FAF1 in cells resulted in an increase in the induction of MR target genes by aldosterone, indicating that FAF1 functions as an MR co-repressor. We further provide evidence to suggest that the mechanisms of FAF1/SIM-mediated MR transrepression involve inhibition of MR N/C interactions and promotion of MR polyubiquitination and degradation. Sumoylation has been linked to impacting of repressive properties on several transcription factors and cofactors. Our findings therefore provide mechanistic insights underlying SUMO-dependent transcriptional repression of the MR.

Composition of the Survival Motor Neuron (SMN) Complex in Drosophila melanogaster

Spinal Muscular Atrophy (SMA) is caused by homozygous mutations in the human survival motor neuron 1 (SMN1) gene. SMN protein has a well-characterized role in the biogenesis of small nuclear ribonucleoproteins (snRNPs), core components of the spliceosome. SMN is part of an oligomeric complex with core binding partners, collectively called Gemins. Biochemical and cell biological studies demonstrate that certain Gemins are required for proper snRNP assembly and transport. However, the precise functions of most Gemins are unknown. To gain a deeper understanding of the SMN complex in the context of metazoan evolution, we investigated its composition in Drosophila melanogaster Using transgenic flies that exclusively express Flag-tagged SMN from its native promoter, we previously found that Gemin2, Gemin3, Gemin5, and all nine classical Sm proteins, including Lsm10 and Lsm11, co-purify with SMN. Here, we show that CG2941 is also highly enriched in the pulldown. Reciprocal co-immunoprecipitation reveals that epitope-tagged CG2941 interacts with endogenous SMN in Schneider2 cells. Bioinformatic comparisons show that CG2941 shares sequence and structural similarity with metazoan Gemin4. Additional analysis shows that three other genes (CG14164, CG31950 and CG2371) are not orthologous to Gemins 6-7-8, respectively, as previously suggested. In D.melanogaster, CG2941 is located within an evolutionarily recent genomic triplication with two other nearly identical paralogous genes (CG32783 and CG32786). RNAi-mediated knockdown of CG2941 and its two close paralogs reveals that Gemin4 is essential for organismal viability.

Interaction of the Mineralocorticoid Receptor With RACK1 and Its Role in Aldosterone Signaling

The mineralocorticoid receptor (MR) is a member of the steroid-thyroid hormone receptor superfamily of ligand-dependent transcription factors with diverse functions including the biological actions of aldosterone. Identification of the various transcriptional coregulators of MR is essential for understanding the complexity of MR signaling pathways under physiological and pathological conditions. We used a yeast two-hybrid system to find proteins that interact with a full-length MR and found, among other proteins, that MR interacted specifically with receptor for activated C kinase 1 (RACK1), a scaffolding protein. Overexpression of RACK1 using a tetracycline-inducible lentivirus in mouse cortical collecting duct M1 cells stably expressing the rat MR and a Gaussia luciferase gene reporter under a hormone-response element promoter resulted in enhanced agonist-dependent MR transactivation. Knockdown of RACK1 protein expression by short hairpin RNAs led to a significant reduction in MR activation of the reporter gene and the endogenous genes Ctla2α and Psca. We also demonstrated that RACK1 regulation of MR action is mediated through phosphorylation by the PKC-β signaling pathway. MR and RACK1 were coimmunoprecipitated using an MR antibody in male Sprague-Dawley brain tissue and M1-rMR cells, and colocalization in M1-rMR cells and male rat brains was confirmed by immunofluorescence and immunohistochemistry. The scaffolding protein RACK1 is associated with MR under basal and agonist-stimulated conditions and facilitates agonist-stimulated MR actions through PKC-β. These findings indicate that RACK1 is a newly described coactivator of MR.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Coregulators as mediators of mineralocorticoid receptor signalling diversity

The cloning of the mineralocorticoid receptor (MR) 30 years ago was the start of a new era of research into the regulatory processes of MR signalling at target genes in the distal nephron, and subsequently in many other tissues. Nuclear receptor (NR) signalling is modified by interactions with coregulatory proteins that serve to enhance or inhibit the gene transcriptional responses. Over 400 coregulatory proteins have been described for the NR super family, many with functional roles in signalling, cellular function, physiology and pathophysiology. Relatively few coregulators have however been described for the MR although recent studies have demonstrated both ligand and/or tissue selectivity for MR-coregulator interactions. A full understanding of the cell, ligand and promoter-specific requirements for MR-coregulator signalling is an essential first step towards the design of small molecular inhibitors of these protein-protein interactions. Tissue-selective steroidal or non-steroidal modulators of the MR are also a desired therapeutic goal. Selectivity, as for other steroid hormone receptors, will probably depend on differential expression and recruitment of coregulatory proteins.

Future drug discovery in renin-angiotensin-aldosterone system intervention

INTRODUCTION

Renin-angiotensin-aldosterone system inhibitors (RAASIs), including angiotensin-converting enzyme inhibitors, angiotensin AT1 receptor blockers and mineralocorticoid receptor antagonists (MRAs), are the cornerstone for the treatment of cardiovascular and renal diseases. Areas covered: The authors searched MEDLINE, PubMed and ClinicalTrials.gov to identify eligible full-text English language papers. Herein, the authors discuss AT2-receptor agonists and ACE2/angiotensin-(1-7)/Mas-receptor axis modulators, direct renin inhibitors, brain aminopeptidase A inhibitors, biased AT1R blockers, chymase inhibitors, multitargeted drugs, vaccines and aldosterone receptor antagonists as well as aldosterone synthase inhibitors. Expert opinion: Preclinical studies have demonstrated that activation of the protective axis of the RAAS represents a novel therapeutic strategy for treating cardiovascular and renal diseases, but there are no clinical trials supporting our expectations. Non-steroidal MRAs might become the third-generation of MRAs for the treatment of heart failure, diabetes mellitus and chronic kidney disease. The main challenge for these new drugs is that conventional RAASIs are safe, effective and cheap generics. Thus, the future of new RAASIs will be directed by economical/strategic reasons.

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.