Cytosporone B is an agonist for nuclear orphan receptor Nur77

NR4A1 Acts as a Novel Regulator of Platelet Activation and Thrombus Formation

BACKGROUND

Mounting evidence indicates that nuclear receptors play a critical regulatory role in platelet pathophysiology and thrombotic disorders. Although NR4A (the nuclear receptor subfamily 4 group A) plays an important role in cardiovascular pathophysiology, the expression profile and biological function of NR4A member 1 (NR4A1) in platelets have never been reported.

METHODS

We evaluated the functions and the underlying mechanisms of NR4A1 in platelet activation and thrombus formation using platelet-specific NR4A1-deficient mice and NR4A1-specific agonists. Using a hyperlipidemic mouse model and platelets from patients with hypercholesterolemia, we explored the influence of hypercholesterolemia on NR4A1 expression and the effects of NR4A1-specific agonists on platelet hyperreactivity induced by hypercholesterolemia.

RESULTS

NR4A1 was expressed in both human and mouse platelets. Platelet-specific NR4A1 deletion accelerated FeCl3-induced carotid arterial occlusive thrombus formation, enhanced collagen/epinephrine-induced pulmonary thromboembolism, and exacerbated microvascular microthrombi obstruction and infarct expansion in an acute myocardial infarction model. NR4A1-deficient platelets exhibited enhanced agonist-induced aggregation responses, integrin αIIbβ3 activation, dense granule release, α-granule release, platelet spreading, and clot retraction. Consistently, pharmacological activation of NR4A1 by specific agonists decreased platelet activation in both mouse and human platelets. Mechanistically, CAP1 (adenylyl cyclase-associated protein 1) was identified as the direct downstream interacting protein of NR4A1. NR4A1 deletion decreased cAMP levels and phosphorylation of VASP (vasodilator-stimulated phosphoprotein), while NR4A1-specific agonists increased cAMP levels and phosphorylation of VASP in platelets. Importantly, NR4A1 expression in platelets was upregulated in the setting of hypercholesterolemia, which was derived from its upregulation in megakaryocytes in a reactive oxygen species-dependent manner. Platelets from hypercholesterolemic patients and mice exhibited hyperreactivity. However, NR4A1-specific agonists significantly inhibited the activation of hypercholesterolemic platelets to the levels of healthy control platelets.

CONCLUSIONS

We provide the first evidence that nuclear receptor NR4A1 negatively regulates platelet activation and thrombus formation. NR4A1 may serve as a novel therapeutic target for managing thrombosis-based cardiovascular diseases, especially with hypercholesterolemia.

NR4A1 suppresses breast cancer growth by repressing c-Fos-mediated lipid and redox dyshomeostasis

The specific function of NR4A1 as a transcriptional regulator in cancer remains unclear. Here we report the biological effect of NR4A1 in suppressing breast cancer (BC) growth. We found that NR4A1 deficiency was correlated with BC progression in the clinic. Genetic deletion of NR4A1 in BC cells significantly promoted cellular proliferation and tumor growth. Moreover, global metabolome screening indicated that the deletion of NR4A1 resulted in tumor lipid remodeling and phospholipid accumulation, which was accompanied by increases in fatty acid and lipid uptake. In addition, NR4A1 knockout induced oxidative stress that aggravated redox balance disruption. Mechanistically, transcriptomic and epigenomic analyses revealed that NR4A1 restrained BC cell proliferation by directly interacting with c-Fos and competitively inhibiting c-Fos binding to the promoter of the target gene PRDX6, which is involved in lipid and redox homeostasis. Notably, we confirmed that the treatment of BC cells with the selective NR4A1 agonist cytosporone B significantly activated the expression of NR4A1, followed by increased interaction between NR4A1 and c-Fos, thereby interfering with c-Fos-mediated transcriptional regulation of BC cell growth. Thus, NR4A1 plays a vital role in reducing the c-Fos-induced activation of downstream signaling cascades in BC, suggesting that agents that activate NR4A1 may be potential therapeutic strategies.

Clemastine fumarate alleviates endoplasmic reticulum stress through the Nur77/GFPT2/CHOP pathway after ischemia/reperfusion in rat hearts

BACKGROUND AND PURPOSE

Clemastine fumarate (CLE) is an H1 receptor (H1R) antagonist that is used clinically to treat various allergic disorders. It blocks histamine release from mast cells and inhibits H1R. Preliminary studies have shown that CLE can reduce myocardial ischemia/reperfusion (I/R) injury. In this study, we confirmed the efficacy of CLE against myocardial I/R injury using in vivo and in vitro examinations.

EXPERIMENTAL APPROACH

To test the efficacy of CLE against myocardial I/R injury, we established a rat model of myocardial hypoxia/reperfusion injury. A series of assessments were conducted to determine cardiac function, measure areas of myocardial infarction, and analyze the histopathological changes. Additionally, we developed a rat model of cardiomyocyte hypoxia/reoxygenation (H/R); in both models, we quantified the expression levels of key markers and cardiac injury-specific proteins to assess the biochemical milieu influenced by CLE treatment.

KEY RESULTS

Our findings demonstrated that CLE reduced the expression of nerve growth factor-induced gene B (Nur77), glutamine-fructose-6-phosphate transaminase 2 (GFPT2), and C/EBP homologous protein (CHOP) and decreased the area of myocardial infarction and the degree of endoplasmic reticulum stress. CLE pretreatment ameliorated abnormal fibers and myocardial edema and reduced the inflammatory cell infiltration caused by I/R injury. While Nur77 overexpression aggravated cardiac function, these effects were ameliorated by the downregulation of Nur77.

CONCLUSION AND IMPLICATIONS

We anticipate that these results validate the hypothesis that CLE mitigates apoptosis and reduces endogenous stress within myocardial cells by modulating Nur77, GFPT2, and CHOP expression. These findings elucidate the therapeutic mechanisms by which CLE alleviates myocardial I/R injury. In addition, they will serve as a new theoretical foundation for developing future treatment strategies and enhancing clinical applications in cardiac care.

The endocannabinoid anandamide mediates anti-inflammatory effects through activation of NR4A nuclear receptors

BACKGROUND AND PURPOSE

Endocannabinoids are lipid mediators, which elicit complex biological effects that extend beyond the central nervous system. Tissue concentrations of endocannabinoids increase in atherosclerosis, and for the endocannabinoid N-arachidonoyl-ethanolamine (anandamide, AEA), this has been linked to an anti-inflammatory function. In this study, we set out to determine the anti-inflammatory mechanism of action of AEA, specifically focusing on vascular smooth muscle cells.

EXPERIMENTAL APPROACH

RNA-sequencing, RT-qPCR, LC-MS/MS, NanoBit, ChIP, microscale thermophoresis, NMR structural footprinting, Gal4 reporter gene assays and loss of function approaches in cell and ex vivo organ culture were used.

KEY RESULTS

AEA pretreatment attenuated the cytokine-mediated induction of inflammatory gene expression such as CCL2. This effect was also observed in preparations obtained from cannabinoid receptor knockout mice and after pertussis toxin treatment. The anti-inflammatory effect of AEA required preincubation, suggesting an effect through gene induction. AEA increased the expression of the nuclear receptors NR4A1 and NR4A2. Knockdown and knockout of these receptors blocked the AEA-mediated anti-inflammatory effect in cell culture and aortic organ culture, respectively. Conversely, NR4A agonists (CsnB, C-DIM12) attenuated inflammatory gene expression. AEA binds to NR4A, and mutations in NR4A attenuated this effect. The interaction of AEA with NR4A caused recruitment of the nuclear corepressor NCoR1 to the CCL2 promoter, resulting in gene suppression.

CONCLUSION AND IMPLICATIONS

By binding to NR4A, AEA elicits an anti-inflammatory response in vascular smooth muscle cells. NR4A-binding by AEA analogues may represent novel anti-inflammatory agents.

The endocannabinoid anandamide prevents TH17 programming of activated T lymphocytes while preserving TH1 responses

Introduction

Anandamide (AEA) is an endocannabinoid that has recently been recognized as a regulator of various inflammatory diseases as well as cancer. While AEA was thought to predominantly engage cannabinoid (CB) receptors, recent findings suggest that, given its protective anti-inflammatory role in pathological conditions, anandamide may engage not only CB receptors.

Methods

In this study, we studied the role of exogenous AEA in a mouse AirPouch model of acute inflammation by examining immune cell infiltrates by flow cytometry. Human primary immune cells were used to validate findings towards immune cell activation and migration by flow cytometry and bead-based ELISA.

Results

We found that AEA decreases the acute infiltration of myeloid cells including granulocytes and monocytes into the inflamed area, but unexpectedly increases the number of T cells at the site of inflammation. This was related to AEA signaling through nuclear receptor subfamily 4A (NR4A) transcription factors rather than CB receptors. Exploring regulatory mechanisms in the human system, we found that AEA broadly inhibits the migratory capacity of immune cells, arguing for blocked emigration of T cells from the inflamed tissue. Taking a closer look at the impact of AEA on T cells revealed that AEA profoundly alters the activation and exhaustion status of CD4+ T and CD8+ T cells, thereby strongly inhibiting TH17 responses, while not altering TH1 differentiation.

Discussion

These data suggest that AEA has the potential to block chronic inflammation without influencing crucial anti-viral and anti-microbial immune defense mechanisms, and may therefore be an attractive molecule to interfere with the establishment of chronic inflammation.

The orphan nuclear receptor Nr4a1 contributes to interstitial cardiac fibrosis via modulation of cardiac fibroblast and macrophage phenotype

The orphan nuclear receptor Nr4a1 has complex biological functions and has been implicated in numerous diseases, including cardiovascular disease. While protective in atherosclerosis and myocardial ischemia, Nr4a1 has been shown to cause cardiac fibrosis in non-ischemic adverse remodeling of the heart. However, mechanisms underlying these actions are still poorly understood. Accordingly, we sought to: (1) understand the contribution of Nr4a1 to the inflammatory environment including macrophage phenotype; and (2) determine the contribution of Nr4a1 to cardiac fibroblast phenotype in the fibrotic heart. Wild type and Nr4a1-/- mice were infused with angiotensin II (1500 ng/kg/min) to induce cardiac fibrosis and diastolic dysfunction. Nr4a1 deletion prevented cardiac fibrosis and maintained normal diastolic function. We determined that macrophages lacking Nr4a1 had distinctly different phenotypes to wild type macrophages, with Nr4a1 deletion preventing the induction of a pro-inflammatory macrophage phenotype, instead promoting an anti-inflammatory phenotype. This had functional consequences in that macrophages lacking Nr4a1 showed a reduced ability to induce cardiac fibroblast migration. Interestingly, deletion of Nr4a1 in isolated cardiac fibroblasts also had profound effects on their phenotype and function, with these cells not able to produce excess extracellular matrix proteins, convert to a myofibroblast phenotype, or respond to macrophage stimuli. Nr4a1 causes cardiac fibrosis and subsequent diastolic dysfunction by inducing a pro-inflammatory phenotype in macrophages and by pushing cardiac fibroblasts towards a pro-fibrotic phenotype in response to pro-fibrotic stimuli. Nr4a1 is also critical for macrophage/fibroblast interactions.

Discovery of a novel exceptionally potent and orally active Nur77 ligand NB1 with a distinct binding mode for cancer therapy

The orphan nuclear receptor Nur77 is emerging as an attractive target for cancer therapy, and activating Nur77's non-genotypic anticancer function has demonstrated strong therapeutic potential. However, few Nur77 site B ligands have been identified as excellent anticancer compounds. There are no co-crystal structures of effective anticancer agents at Nur77 site B, which greatly limits the development of novel Nur77 site B ligands. Moreover, the lack of pharmaceutical ligands restricts Nur77's therapeutic proof of concept. Herein, we developed a first-in-class Nur77 site B ligand (NB1) that significantly inhibited cancer cells by mediating the Nur77/Bcl-2-related apoptotic effect at mitochondria. The X-ray crystallography suggests that NB1 is bound to the Nur77 site B with a distinct binding mode. Importantly, NB1 showed favorable pharmacokinetic profiles and safety, as evidenced by its good oral bioavailability in rats and lack of mortality, bodyweight loss, and pathological damage at the 512.0 mg/kg dose in mice. Furthermore, oral administration of NB1 demonstrated remarkable in vivo anticancer efficacy in an MDA-MB-231 xenograft model. Together, our work discovers NB1 as a new generation Nur77 ligand that activates the Nur77/Bcl-2 apoptotic pathway with a safe and effective cancer therapeutic potency.

Inhibition of colorectal cancer aggressiveness by Oleanolic acid through Nur77 degradation

BACKGROUND

Colorectal cancer (CRC) is the second primary malignancy in China with tough treatment challenge. Although Oleanolic acid (OA) protects against various cancers, its mechanisms in CRC are not well defined. Our previously study showed that Nur77 has CRC promoting effect. Thus, we investigated the roles of OA as Nur77 ligand and the regulatory effects on Nur77 degradation in CRC progression.

METHODS

The proliferative and metastatic phenotypes of OA was examined by CCK-8, EdU, organoid culture, would healing and transwell assays, respectively. Epithelial-mesenchymal transition (EMT) properties were assessed by Western blotting (WB). The interaction between OA and Nur77 was monitored by molecular docking and Molecular Dynamics stimulation (MD). Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene set enrichment analysis (GSEA) were employed to screen the downstream regulatory pathways. The half-time and proteasome degradation of Nur77 were treated with cycloheximide (CHX) and MG132. Co-immunoprecipitation (Co-IP) and ubiquitination assays were employed to detect direct association between Nur77 and PPARγ. Rescued experiments were performed by Nur77 agonist Cytosporone B (Csn-B) treatment. The findings were verified in xenograft and in situ models.

RESULTS

For the first time, we found the effect of OA on ubiquitination degradation. OA inhibited CRC cell survival and EMT phenotypes by suppressing Nur77. Mechanistically, OA directly bind to Nur77 and facilitated the ubiquitin degradation of Nur77. During this process, PPARγ acted as the ubiquitination activator via interacting with Nur77. Rescued experiments revealed that OA-induced inhibition was recovered by replenishing Nur77. In both subcutaneous and orthotopic CRC models, OA exhibited significant anti-tumor effect together with Nur77 inhibition.

CONCLUSION

We revealed a new regulatory effect of OA in CRC tumorigenesis via PPARγ-mediated Nur77 ubiquitin degradation.

Comprehensive characterization of a novel small-molecule activator for the nuclear receptor Nur77: Chemical, molecular, and biological insights

The nuclear receptor Nur77 is a transcription factor belonging to the NR4A subfamily. Upon activation, it regulates a wide array of biological and pathophysiological processes by modulating the expression of its target genes. Previous findings have classified Nur77 as an orphan receptor because of the discovery of a structurally atypical ligand-binding domain and the lack of identification of an endogenous ligand. Nevertheless, recent studies have uncovered several endogenous, natural, and small synthetic molecules that can bind to and activate Nur77. However, developing selective and potent Nur77 activators remains a significant challenge. The discovery of novel and potential small synthetic molecules that modulate Nur77 activity will facilitate therapeutic interventions of Nur77 against several human diseases. In this study, we have reported the development of a novel and effective Nur77 ligand. Our data show that (1E,4E)-1,5-di(pyrazin-2-yl)penta-1,4-dien-3-one (PB) induces Nur77 transcriptional activity by interacting with a putative Nur77 ligand binding site by forming solid hydrogen bonding. Calculated chemical parameters denote that PB has sophisticated chemical features that will enhance its interaction with the Nur77 ligand-binding domain. Molecular docking simulations showed that PB fits in the Nur77 putative ligand binding site with solid hydrogen bonding, and molecular dynamics simulations indicate that PB binding would stabilize the Nur77 ligand binding domain. Further, in vitro studies revealed that PB increases Nur77 nuclear expression and activity, inhibits cigarette smoke-induced inflammatory phenotype of airway epithelial cells, and protects against apoptosis. These findings provide insights into developing an effective Nur77 small-molecule activator which could be developed into a therapeutic agent against inflammatory diseases.

Cytosporones Y and Z, new antifungal polyketides produced by the fungal strain Trichoderma sp. FKI-6626

Two new antifungal polyketides, named cytosporones Y (1) and Z (2), were discovered from the cultured broth of Trichoderma sp. FKI-6626. Their structures were elucidated by MS and NMR analysis. Both compounds exhibited antifungal activity against five Aspergillus species, the causative agents of aspergillosis.

New opportunities to overcome T cell dysfunction: the role of transcription factors and how to target them

Immune checkpoint blockade (ICB) therapies, which block inhibitory receptors on T cells, can be efficacious in reinvigorating dysfunctional T cell responses. However, most cancers do not respond to these therapies and even in those that respond, tumors can acquire resistance. New strategies are needed to rescue and recruit T cell responses across patient populations and disease states. In this review, we define mechanisms of T cell dysfunction, focusing on key transcription factor (TF) networks. We discuss the complex and sometimes contradictory roles of core TFs in both T cell function and dysfunction. Finally, we review strategies to target TFs using small molecule modulators, which represent a challenging but highly promising opportunity to tune the T cell response toward sustained immunity.

Nur77 protects the bladder urothelium from intracellular bacterial infection

Intracellular infections by Gram-negative bacteria are a significant global health threat. The nuclear receptor Nur77 (also called TR3, NGFI-B, or NR4A1) was recently shown to sense cytosolic bacterial lipopolysaccharide (LPS). However, the potential role for Nur77 in controlling intracellular bacterial infection has not been examined. Here we show that Nur77 protects against intracellular infection in the bladder by uropathogenic Escherichia coli (UPEC), the leading cause of urinary tract infections (UTI). Nur77 deficiency in mice promotes the formation of UPEC intracellular bacterial communities (IBCs) in the cells lining the bladder lumen, leading to persistent infection in bladder tissue. Conversely, treatment with a small-molecule Nur77 agonist, cytosporone B, inhibits invasion and enhances the expulsion of UPEC from human urothelial cells in vitro, and significantly reduces UPEC IBC formation and bladder infection in mice. Our findings reveal a new role for Nur77 in control of bacterial infection and suggest that pharmacologic agonism of Nur77 function may represent a promising antibiotic-sparing therapeutic approach for UTI.

Targeting KPNB1 with genkwadaphnin suppresses gastric cancer progression through the Nur77-mediated signaling pathway

Gastric cancer (GC) remains a global challenge due to the lack of early detection and precision therapies. Genkwadaphnin (DD1), a natural diterpene isolated from the bud of Flos GenkWa (Thymelaeaceae), serves as a Karyopherin β1 (KPNB1) inhibitor. In this study, we investigated the anti-tumor effect of DD1 in both cell culture and animal models. Our findings reveal that KPNB1, a protein involved in nuclear import, was highly expressed in GC tissues and associated with a poor prognosis in patients. We demonstrated that DD1, alongside the established KPNB1 inhibitor importazole (IPZ), inhibited GC cell proliferation and tumor growth by enhancing both genomic and non-genomic activity of Nur77. DD1 and IPZ reduced the interaction between KPNB1 and Nur77, resulting in Nur77 cytoplasmic accumulation and triggering mitochondrial apoptosis. The inhibitors also increased the expression of the Nur77 target apoptotic genes ATF3, RB1CC1 and PMAIP1, inducing apoptosis in GC cell. More importantly, loss of Nur77 effectively rescued the inhibitory effect of DD1 and IPZ on GC cells in both in vitro and in vivo experiments. In this study, we for the first time explored the relationship between KPNB1 and Nur77, and found KPNB1 inhibition could significantly increase the expression of Nur77. Moreover, we investigated the function of KPNB1 in GC for the first time, and the results suggested that KPNB1 could be a potential target for cancer therapy, and DD1 might be a prospective therapeutic candidate.

Nur77 as a novel regulator of Paneth cell differentiation and function

Serving as a part of intestinal innate immunity, Paneth cells play an important role in intestinal homeostasis maintenance via their multiple functions. However, the regulation of Paneth cells has been proven to be complex and diverse. Here, we identified nuclear receptor Nur77 as a novel regulator of Paneth cell differentiation and function. Nur77 deficiency led to the loss of Paneth cells in murine ileal crypts. Intestinal tissues or organoids with Nur77 deficiency exhibited the impaired intestinal stem cell niche and failed to enhance antimicrobial peptide expression after Paneth cell degranulation. The defects in Paneth cells and antimicrobial peptides in Nur7-/- mice led to intestinal microbiota disorders. Nur77 deficiency rendered postnatal mice susceptible to necrotizing enterocolitis. Mechanistically, Nur77 transcriptionally inhibited Dact1 expression to activate Wnt signaling activity, thus promoting Paneth cell differentiation and function. Taken together, our data suggest the regulatory role of Nur77 in Paneth cell differentiation and function and reveal a novel Dact1-mediated Wnt inhibition mechanism in Paneth cell development.

Surface Chemistry of Cytosporone-B Incorporated in Models for Microbial Biomembranes as Langmuir Monolayers

Cytosporone-B, a polyketide renowned for its antimicrobial properties, was integrated into Langmuir monolayers composed of dipalmitoylphosphoethanolamine (DPPE) and dioleoylphosphoethanolamine (DOPE) lipids, effectively emulating microbial cytoplasmic membranes. This compound exhibited an expansive influence on DPPE monolayers while inducing condensation in DOPE monolayers. This led to a notable reduction in the compressibility modulus for both lipids, with a more pronounced effect observed for DPPE. The heightened destabilization observed in DOPE monolayers subjected to biologically relevant pressures was particularly noteworthy, as evidenced by surface pressure-time curves at constant area. In-depth analysis using infrared spectroscopy at the air-water interface unveiled alterations in the alkyl chains of the lipids induced by cytosporone-B. This was further corroborated by surface potential measurements, indicating a heightened tilt in the acyl chains upon drug incorporation. Notably, these observed effects did not indicate an aggregating process induced by the drug. Overall, the distinctive impact of cytosporone-B on each lipid underscores the importance of understanding the nuanced effects of microbial drugs on membranes, whether in condensed or fluid states.

Semaglutide ameliorates cardiac remodeling in male mice by optimizing energy substrate utilization through the Creb5/NR4a1 axis

Semaglutide, a glucagon-like peptide-1 receptor agonist, is clinically used as a glucose-lowering and weight loss medication due to its effects on energy metabolism. In heart failure, energy production is impaired due to altered mitochondrial function and increased glycolysis. However, the impact of semaglutide on cardiomyocyte metabolism under pressure overload remains unclear. Here we demonstrate that semaglutide improves cardiac function and reduces hypertrophy and fibrosis in a mouse model of pressure overload-induced heart failure. Semaglutide preserves mitochondrial structure and function under chronic stress. Metabolomics reveals that semaglutide reduces mitochondrial damage, lipid accumulation, and ATP deficiency by promoting pyruvate entry into the tricarboxylic acid cycle and increasing fatty acid oxidation. Transcriptional analysis shows that semaglutide regulates myocardial energy metabolism through the Creb5/NR4a1 axis in the PI3K/AKT pathway, reducing NR4a1 expression and its translocation to mitochondria. NR4a1 knockdown ameliorates mitochondrial dysfunction and abnormal glucose and lipid metabolism in the heart. These findings suggest that semaglutide may be a therapeutic agent for improving cardiac remodeling by modulating energy metabolism.

Exploring the impact of the PNPLA3 I148M variant on primary human hepatic stellate cells using 3D extracellular matrix models

BACKGROUND & AIMS

The PNPLA3 rs738409 C>G (encoding for I148M) variant is a risk locus for the fibrogenic progression of chronic liver diseases, a process driven by hepatic stellate cells (HSCs). We investigated how the PNPLA3 I148M variant affects HSC biology using transcriptomic data and validated findings in 3D-culture models.

METHODS

RNA sequencing was performed on 2D-cultured primary human HSCs and liver biopsies of individuals with obesity, genotyped for the PNPLA3 I148M variant. Data were validated in wild-type (WT) or PNPLA3 I148M variant-carrying HSCs cultured on 3D extracellular matrix (ECM) scaffolds from human healthy and cirrhotic livers, with/without TGFB1 or cytosporone B (Csn-B) treatment.

RESULTS

Transcriptomic analyses of liver biopsies and HSCs highlighted shared PNPLA3 I148M-driven dysregulated pathways related to mitochondrial function, antioxidant response, ECM remodelling and TGFB1 signalling. Analogous pathways were dysregulated in WT/PNPLA3-I148M HSCs cultured in 3D liver scaffolds. Mitochondrial dysfunction in PNPLA3-I148M cells was linked to respiratory chain complex IV insufficiency. Antioxidant capacity was lower in PNPLA3-I148M HSCs, while reactive oxygen species secretion was increased in PNPLA3-I148M HSCs and higher in bioengineered cirrhotic vs. healthy scaffolds. TGFB1 signalling followed the same trend. In PNPLA3-I148M cells, expression and activation of the endogenous TGFB1 inhibitor NR4A1 were decreased: treatment with the Csn-B agonist increased total NR4A1 in HSCs cultured in healthy but not in cirrhotic 3D scaffolds. NR4A1 regulation by TGFB1/Csn-B was linked to Akt signalling in PNPLA3-WT HSCs and to Erk signalling in PNPLA3-I148M HSCs.

CONCLUSION

HSCs carrying the PNPLA3 I148M variant have impaired mitochondrial function, antioxidant responses, and increased TGFB1 signalling, which dampens antifibrotic NR4A1 activity. These features are exacerbated by cirrhotic ECM, highlighting the dual impact of the PNPLA3 I148M variant and the fibrotic microenvironment in progressive chronic liver diseases.

IMPACT AND IMPLICATIONS

Hepatic stellate cells (HSCs) play a key role in the fibrogenic process associated with chronic liver disease. The PNPLA3 genetic mutation has been linked with increased risk of fibrogenesis, but its role in HSCs requires further investigation. Here, by using comparative transcriptomics and a novel 3D in vitro model, we demonstrate the impact of the PNPLA3 genetic mutation on primary human HSCs' behaviour, and we show that it affects the cell's mitochondrial function and antioxidant response, as well as the antifibrotic gene NR4A1. Our publicly available transcriptomic data, 3D platform and our findings on NR4A1 could facilitate the discovery of targets to develop more effective treatments for chronic liver diseases.

Nur77-IRF1 axis inhibits esophageal squamous cell carcinoma growth and improves anti-PD-1 treatment efficacy

The nuclear receptor Nur77 plays paradoxical roles in numerous cancers. However, whether Nur77 inhibits esophageal squamous cell carcinoma (ESCC) growth and affects immunological responses against ESCC has not been determined. The functional role of Nur77 in ESCC was investigated in this study using human ESCC cell lines, quantitative real-time polymerase chain reaction (PCR), cell proliferation and colony formation assays, flow cytometry analysis, western blotting and animal models. The target gene controlled by Nur77 was verified using dual-luciferase reporter assays, chromatin immunoprecipitation analysis and functional rescue experiments. To examine the clinical importance of Nur77, 72 human primary ESCC tissues were subjected to immunohistochemistry. Taken together, these findings showed that, both in vitro and in vivo, Nur77 dramatically reduced ESCC cell growth and triggered apoptosis. Nur77 directly interacts with the interferon regulatory factor 1 (IRF1) promoter to inhibit its activity in ESCC. Pharmacological induction of Nur77 using cytosporone B (CsnB) inhibited ESCC cell proliferation and promoted apoptosis both in vitro and in vivo. Furthermore, CsnB increased CD8+ T-cell infiltration and cytotoxicity to inhibit the formation of ESCC tumors in an immunocompetent mouse model. In ESCC tissues, Nur77 expression was downregulated, and IRF1 expression was increased; moreover, their expression levels were negatively related. IRF1 and Nur77 were strongly correlated with overall survival. These findings suggested that Nur77 targets and regulates the IRF1/PD-L1 axis to serve as a tumor suppressor in ESCC. Graphical abstract of the regulatory mechanism of Nur77 overexpression downregulates IRF1 in the inhibition of ESCC progression and enhance anti-PD-1 therapy efficacy.

Nr4a1 enhances Wnt4 transcription to promote mesenchymal stem cell osteogenesis and alleviates inflammation-inhibited bone regeneration

Intense inflammatory response impairs bone marrow mesenchymal stem cell (BMSC)-mediated bone regeneration, with transforming growth factor (TGF)-β1 being the most highly expressed cytokine. However, how to find effective and safe means to improve bone formation impaired by excessive TGF-β1 remains unclear. In this study, we found that the expression of orphan nuclear receptor Nr4a1, an endogenous repressor of TGF-β1, was suppressed directly by TGF-β1-induced Smad3 and indirectly by Hdac4, respectively. Importantly, Nr4a1 overexpression promoted BMSC osteogenesis and reversed TGF-β1-mediated osteogenic inhibition and pro-fibrotic effects. Transcriptomic and histologic analyses confirmed that upregulation of Nr4a1 increased the transcription of Wnt family member 4 (Wnt4) and activated Wnt pathway. Mechanistically, Nr4a1 bound to the promoter of Wnt4 and regulated its expression, thereby enhancing the osteogenic capacity of BMSCs. Moreover, treatment with Nr4a1 gene therapy or Nr4a1 agonist Csn-B could promote ectopic bone formation, defect repair, and fracture healing. Finally, we demonstrated the correlation of NR4A1 with osteogenesis and the activation of the WNT4/β-catenin pathway in human BMSCs and fracture samples. Taken together, these findings uncover the critical role of Nr4a1 in bone formation and alleviation of inflammation-induced bone regeneration disorders, and suggest that Nr4a1 has the potential to be a therapeutic target for accelerating bone healing.

Nur77 increases mitophagy and decreases aggregation of α-synuclein by modulating the p-c-Abl/p-PHB2 Y121 in α-synuclein PFF SH-SY5Y cells and mice

Parkinson's disease (PD) is characterized by the progressive death of dopamine (DA) neurons and the pathological accumulation of α-synuclein (α-syn) fibrils. In our previous study, simulated PHB2 phosphorylation was utilized to clarify the regulatory role of c-Abl in PHB2-mediated mitophagy in PD models. In this investigation, we employed an independently patented PHB2Y121 phosphorylated antibody in the PD model to further verify that the c-Abl inhibitor STI571 can impede PHB2Y121 phosphorylation, decrease the formation of α-Syn polymers, and improve autophagic levels. The specific involvement of Nur77 in PD pathology has remained elusive. We also investigate the contribution of Nur77, a nuclear transcription factor, to α-syn and mitophagy in PD. Our findings demonstrate that under α-syn, Nur77 translocates from the cytoplasm to the mitochondria, improving PHB-mediated mitophagy by regulating c-Abl phosphorylation. Moreover, Nur77 overexpression alleviates the expression level of pS129-α-syn and the loss of DA neurons in α-syn PFF mice, potentially associated with the p-c-Abl/p-PHB2 Y121 axis. This study provides initial in vivo and in vitro evidence that Nur77 protects PD DA neurons by modulating the p-c-Abl/p-PHB2 Y121 axis, and STI571 holds promise as a treatment for PD.

Biosynthesis of Cytosporones in Leotiomycetous Filamentous Fungi

Polyketides with the isochroman-3-one pharmacophore are rare among fungal natural products as their biosynthesis requires an unorthodox S-type aromatic ring cyclization. Genome mining uncovered a conserved gene cluster in select leotiomycetous fungi that encodes the biosynthesis of cytosporones, including isochroman-3-one congeners. Combinatorial biosynthesis in total biosynthetic and biocatalytic formats in Saccharomyces cerevisiae and in vitro reconstitution of key reactions with purified enzymes revealed how cytosporone structural and bioactivity diversity is generated. The S-type acyl dihydroxyphenylacetic acid (ADA) core of cytosporones is assembled by a collaborating polyketide synthase pair. Thioesterase domain-catalyzed transesterification releases ADA esters, some of which are known Nur77 modulators. Alternatively, hydrolytic release allows C6 hydroxylation by a flavin-dependent monooxygenase, yielding a trihydroxybenzene moiety. Reduction of the C9 carbonyl by a short chain dehydrogenase/reductase initiates isochroman-3-one formation, affording cytosporones with cytotoxic and antimicrobial activity. Enoyl di- or trihydroxyphenylacetic acids are generated as shunt products, while isocroman-3,4-diones are formed by autoxidation. The cytosporone pathway offers novel polyketide biosynthetic enzymes for combinatorial synthetic biology to advance the production of "unnatural" natural products for drug discovery.

The dopamine transporter antagonist vanoxerine inhibits G9a and suppresses cancer stem cell functions in colon tumors

Cancer stem cells (CSCs), functionally characterized by self-renewal and tumor-initiating activity, contribute to decreased tumor immunogenicity, while fostering tumor growth and metastasis. Targeting G9a histone methyltransferase (HMTase) effectively blocks CSC functions in colorectal tumors by altering pluripotent-like molecular networks; however, existing molecules directly targeting G9a HMTase activity failed to reach clinical stages due to safety concerns. Using a stem cell-based phenotypic drug-screening pipeline, we identified the dopamine transporter (DAT) antagonist vanoxerine, a compound with previously demonstrated clinical safety, as a cancer-specific downregulator of G9a expression. Here we show that gene silencing and chemical antagonism of DAT impede colorectal CSC functions by repressing G9a expression. Antagonizing DAT also enhanced tumor lymphocytic infiltration by activating endogenous transposable elements and type-I interferon response. Our study unveils the direct implication of the DAT-G9a axis in the maintenance of CSC populations and an approach to improve antitumor immune response in colon tumors.

Regulation of the Nur77-P2X7r Signaling Pathway by Nodakenin: A Potential Protective Function against Alcoholic Liver Disease

Alcoholic liver disease (ALD) is the main factor that induces liver-related death worldwide and represents a common chronic hepatopathy resulting from binge or chronic alcohol consumption. This work focused on revealing the role and molecular mechanism of nodakenin (NK) in ALD associated with hepatic inflammation and lipid metabolism through the regulation of Nur77-P2X7r signaling. In this study, an ALD model was constructed through chronic feeding of Lieber-DeCarli control solution with or without NK treatment. Ethanol (EtOH) or NK was administered to AML-12 cells, after which Nur77 was silenced. HepG2 cells were exposed to ethanol (EtOH) and subsequently treated with recombinant Nur77 (rNur77). Mouse peritoneal macrophages (MPMs) were treated with lipopolysaccharide/adenosine triphosphate (LPS/ATP) and NK, resulting in the generation of conditioned media. In vivo, histopathological alterations were markedly alleviated by NK, accompanied by reductions in serum triglyceride (TG), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels and the modulation of Lipin-1, SREBP1, and Nur77 levels in comparison to the EtOH-exposed group (p < 0.001). Additionally, NK reduced the production of P2X7r and NLRP3. NK markedly upregulated Nur77, inhibited P2X7r and Lipin-1, and promoted the function of Cytosporone B, a Nur77 agonist (p < 0.001). Moreover, Nur77 deficiency weakened the regulatory effect of NK on P2X7r and Lipin-1 inhibition (p < 0.001). In NK-exposed MPMs, cleaved caspase-1 and mature IL-1β expression decreased following LPS/ATP treatment (p < 0.001). NK also decreased inflammatory-factor production in primary hepatocytes stimulated with MPM supernatant. NK ameliorated ETOH-induced ALD through a reduction in inflammation and lipogenesis factors, which was likely related to Nur77 activation. Hence, NK is a potential therapeutic approach to ALD.

Lactic acid induces transcriptional repression of macrophage inflammatory response via histone acetylation

Lactic acid has emerged as an important modulator of immune cell function. It can be produced by both gut microbiota and the host metabolism at homeostasis and during disease states. The production of lactic acid in the gut microenvironment is vital for tissue homeostasis. In the present study, we examined how lactic acid integrates cellular metabolism to shape the epigenome of macrophages during pro-inflammatory response. We found that lactic acid serves as a primary fuel source to promote histone H3K27 acetylation, which allows the expression of immunosuppressive gene program including Nr4a1. Consequently, macrophage pro-inflammatory function was transcriptionally repressed. Furthermore, the histone acetylation induced by lactic acid promotes a form of long-term immunosuppression ("trained immunosuppression"). Pre-exposure to lactic acid induces lipopolysaccharide tolerance. These findings thus indicate that lactic acid sensing and its effect on chromatin remodeling in macrophages represent a key homeostatic mechanism that can provide a tolerogenic tissue microenvironment.

Bis-Indole Derivatives as Dual Nuclear Receptor 4A1 (NR4A1) and NR4A2 Ligands

Bis-indole derived compounds such as 1,1-bis(3'-indolyl)-1-(3,5-disubstitutedphenyl) methane (DIM-3,5) and the corresponding 4-hydroxyl analogs (DIM8-3,5) are NR4A1 ligands that act as inverse NR4A1 agonists and are potent inhibitors of tumor growth. The high potency of several DIM-3,5 analogs (IC50 < 1 mg/kg/day), coupled with the >60% similarity of the ligand-binding domains (LBDs) of NR4A1 and NR4A2 and the pro-oncogenic activities of both receptors lead us to hypothesize that these compounds may act as dual NR4A1 and NR4A2 ligands. Using a fluorescence binding assay, it was shown that 22 synthetic DIM8-3,5 and DIM-3,5 analogs bound the LBD of NR4A1 and NR4A2 with most KD values in the low µM range. Moreover, the DIM-3,5 and DIM8-3,5 analogs also decreased NR4A1- and NR4A2-dependent transactivation in U87G glioblastoma cells transfected with GAL4-NR4A1 or GAL4-NR4A2 chimeras and a UAS-luciferase reporter gene construct. The DIM-3,5 and DIM8-3,5 analogs were cytotoxic to U87 glioblastoma and RKO colon cancer cells and the DIM-3,5 compounds were more cytotoxic than the DIM8-3,5 compounds. These studies show that both DIM-3,5 and DIM8-3,5 compounds previously identified as NR4A1 ligands bind both NR4A1 and NR4A2 and are dual NR4A1/2 ligands.

Chemotherapeutic Mechanism of Action of the Synthetic Resorcinolic Methyl 3,5-dimethoxy-2-octanoylbenzoate

Resorcinolic lipids are described as potential examples of selective chemotherapeutic adjuvants that can enhance the effects of cyclophosphamide (CYC) while promoting cell death without causing DNA damage. Therefore, the current study attempted to describe how the resorcinolic lipid methyl 3,5-dimethoxy-2-octanoylbenzoate (AMS35BB) interacted with DNA (DNA docking) and how this compound affected genetic toxicology models and other biological characteristics when combined with CYC. We observed that AMS35BB, used alone (7.5 and 10 mg/kg), increases the frequency of genomic damage (comet assay) but not chromosomal damage (micronuclei assay), lowers phagocytosis, and promotes cell death in Swiss male mice. When used in association with CYC, AMS35BB can reduce the risk of genomic damage by up to 33.8% as well as chromosomal damage, splenic phagocytosis, cell death, and lymphocyte frequency. Molecular docking showed that AMS35BB had a higher affinity than the active metabolite of CYC for binding to the DNA double helix major groove. As a result, AMS35BB has the potential to be both an adjuvant when used in association with CYC and a therapeutic candidate for the development of a selective chemotherapeutic drug.

Resveratrol-derived inhibitors of the E3 ubiquitin ligase PELI1 inhibit the metastasis of triple-negative breast cancer

Triple-negative breast cancer (TNBC), as the most challenging subtype of breast cancer, exerts highly invasive ability and metastatic nature to the lymph nodes, which is correlated with poor survival rates among patients. Pellino-1 (PELI1) is an E3 ubiquitin ligase involved in tumor invasion and metastasis, and has the potential to be developed as a novel therapeutic target for TNBC. In this study, we identified a potent inhibitor of PELI1, namely compound 3d, on the basis of natural stilbene framework through medicinal chemistry approaches. This novel PELI1 inhibitor 3d showed potent binding affinity to PELI1 (Kd 8.2 μM) in fluorescence quenching assay, and markedly interrupted the interaction of PELI1 and SNAIL/SLUG confirmed by co-immunoprecipitation. Moreover, 3d exhibited potent antitumor activity in inhibiting tumor cell migration in scratch wound healing assay without affecting cell proliferation in vitro, and down-regulated the downstream EMT-effectors of PELI1 as assessed by western blotting. In the experimental lung metastasis model, 3d showed anti-TNBC metastasis efficacy without observable toxicity in vivo.

Unsaturation of serine lipids modulating the interaction of a cytosporone with models of the external leaflet of tumorigenic cell membranes

Cytosporone-B was isolated from fungi and incorporated in models of tumorigenic cell membranes using palmitoyloleoylglycerophosphoserine (POPS) and dipalmitoyl glycerophosphoserine (DPPS) lipids. While for DPPS, the compound condensed the monolayer and decreased the surface compressional modulus, it expanded and kept the compressional modulus for POPS. Hysteresis for compression-expansion cycles was more sensitive for POPS than for DPPS, while a high degree of destabilization was observed for POPS. As observed with infrared spectroscopy and Brewster angle microscopy, specific changes were selective regarding molecular organization and morphology. Atomic force microscopy for transferred monolayers as Langmuir-Blodgett films also confirmed such specificities. We believe these data can help understand the mechanism of action of bioactive drugs in lipid interfaces at the molecular level.

Discovery of 5-(Pyrimidin-2-ylamino)-1H-indole-2-carboxamide Derivatives as Nur77 Modulators with Selective and Potent Activity Against Triple-Negative Breast Cancer

The orphan nuclear receptor Nur77 has been validated as a potential drug target for treating breast cancer. Therefore, focusing on the SAR study of the lead 8b (KDSPR(Nur77) = 354 nM), we found the active compound ja which exhibited improved Nur77-binding capability (KDSPR(Nur77) = 91 nM) and excellent antiproliferative activities against breast cancer cell lines. Interestingly, ja acted as a potent and selective Nur77 antagonist, displaying good potency against triple-negative breast cancer (TNBC) cell lines but did not inhibit human normal breast cancer cell line MCF-10A (SI > 20). Exceptionally, ja Nur77-dependently caused mitochondria dysfunction and induced the caspase-dependent apoptosis by mediating the TP53 phosphorylation pathway. Moreover, ja significantly suppressed MDA-MB-231 xenograft tumor growth but had no apparent side effects in mice and zebrafish. Overall, ja demonstrated to be the first Nur77 modulator mediating the TP53 phosphorylation pathway that has the potential as a novel anticancer agent for TNBC.

Exploring Fatty Acid Mimetics as NR4A Ligands

The ligand-activated transcription factors Nur77, Nurr1, and NOR-1 forming the NR4A family of nuclear receptors are considered as potential targets in various pathologies, including neurodegeneration and cancer. However, chemical tools for pharmacological NR4A modulation as a prerequisite for target validation are rare. Recent findings suggest that NR4As bind fatty acid metabolites and fatty acid mimetic (FAM) drugs, opening new opportunities for NR4A modulator development. We have explored the chemical space of FAM NR4A ligands by using fragment screening, in silico analysis, and systematic structure-activity relationship evaluation. From a chemically diverse library of 92 fragments, we identified 11 new FAM NR4A agonist and inverse agonist scaffolds. Structural optimization of the most active FAM fragment yielded NR4A agonists with submicromolar potency and binding affinity, demonstrating remarkable potential of FAM as NR4A-modulating tools and drugs.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

NR4A1 Aggravates Myocardial Ischaemia-Reperfusion Injury by Inhibiting OPA1-Mediated Mitochondrial Fusion

Mitochondrial fusion is an important process that protects the myocardium. However, mitochondrial fusion is often inhibited in myocardial ischaemia-reperfusion injury (IR). The upstream mechanism of this effect is unclear. Nuclear receptor subfamily 4 group A member 1 (NR4A1) can aggravate myocardial IR and increase the level of oxidative stress, thereby affecting mitochondrial function and morphology. Inhibiting NR4A1 can improve oxidative stress levels and mitochondrial function and morphology, thereby reducing IR. Downregulating NR4A1 increases the expression level of the mitochondrial fusion-related protein optic atrophy 1 (OPA1), which is associated with these benefits. Inhibiting OPA1 expression with MYLS22 abrogates the effects of NR4A1 downregulation on IR. Furthermore, NR4A1 disrupts mitochondrial dynamics and activates the STING and NF-κB pathways. Insufficient mitochondrial fusion and increased apoptosis and inflammatory reactions worsen irreversible damage to cardiomyocytes. In conclusion, NR4A1 can exacerbate IR by inhibiting OPA1, causing mitochondrial damage.

Orphan nuclear receptor nr4a1 regulates winter depression-like behavior in medaka

About 10% of the population suffers from depression in winter at high latitude. Although it has become a serious public health issue, its underlying mechanism remains unknown and new treatments and therapies are required. As an adaptive strategy, many animals also exhibit depression-like behavior in winter. Previously, it has been reported that celastrol, a traditional Chinese medicine, can rescue winter depression-like behavior in medaka, an excellent model of winter depression. Nuclear receptor subfamily 4 group A member 1 (nr4a1, also known as nur77) is a known target of celastrol, and the signaling pathway of nr4a1 was suggested to be inactive in medaka brain during winter, implying the association of nr4a1 and winter depression-like behavior. However, the direct evidence for its involvement in winter depression-like behavior remains unclear. The present study found that nr4a1 was suppressed in the medaka brain under winter conditions. Cytosporone B, nr4a1 chemical activator, reversed winter depression-like behavior under winter conditions. Additionally, nr4a1 mutant fish generated by CRISPR/Cas9 system showed decreased sociability under summer conditions. Therefore, our results demonstrate that the seasonal regulation of nr4a1 regulates winter depression-like behavior and offers potential therapeutic target.

Natural compounds targeting nuclear receptors for effective cancer therapy

Human nuclear receptors (NRs) are a family of forty-eight transcription factors that modulate gene expression both spatially and temporally. Numerous biochemical, physiological, and pathological processes including cell survival, proliferation, differentiation, metabolism, immune modulation, development, reproduction, and aging are extensively orchestrated by different NRs. The involvement of dysregulated NRs and NR-mediated signaling pathways in driving cancer cell hallmarks has been thoroughly investigated. Targeting NRs has been one of the major focuses of drug development strategies for cancer interventions. Interestingly, rapid progress in molecular biology and drug screening reveals that the naturally occurring compounds are promising modern oncology drugs which are free of potentially inevitable repercussions that are associated with synthetic compounds. Therefore, the purpose of this review is to draw our attention to the potential therapeutic effects of various classes of natural compounds that target NRs such as phytochemicals, dietary components, venom constituents, royal jelly-derived compounds, and microbial derivatives in the establishment of novel and safe medications for cancer treatment. This review also emphasizes molecular mechanisms and signaling pathways that are leveraged to promote the anti-cancer effects of these natural compounds. We have also critically reviewed and assessed the advantages and limitations of current preclinical and clinical studies on this subject for cancer prophylaxis. This might subsequently pave the way for new paradigms in the discovery of drugs that target specific cancer types.

An optimized Nurr1 agonist provides disease-modifying effects in Parkinson's disease models

The nuclear receptor, Nurr1, is critical for both the development and maintenance of midbrain dopamine neurons, representing a promising molecular target for Parkinson's disease (PD). We previously identified three Nurr1 agonists (amodiaquine, chloroquine and glafenine) that share an identical chemical scaffold, 4-amino-7-chloroquinoline (4A7C), suggesting a structure-activity relationship. Herein we report a systematic medicinal chemistry search in which over 570 4A7C-derivatives were generated and characterized. Multiple compounds enhance Nurr1's transcriptional activity, leading to identification of an optimized, brain-penetrant agonist, 4A7C-301, that exhibits robust neuroprotective effects in vitro. In addition, 4A7C-301 protects midbrain dopamine neurons in the MPTP-induced male mouse model of PD and improves both motor and non-motor olfactory deficits without dyskinesia-like behaviors. Furthermore, 4A7C-301 significantly ameliorates neuropathological abnormalities and improves motor and olfactory dysfunctions in AAV2-mediated α-synuclein-overexpressing male mouse models. These disease-modifying properties of 4A7C-301 may warrant clinical evaluation of this or analogous compounds for the treatment of patients with PD.

Noncanonical contribution of microglial transcription factor NR4A1 to post-stroke recovery through TNF mRNA destabilization

Microglia-mediated neuroinflammation is involved in various neurological diseases, including ischemic stroke, but the endogenous mechanisms preventing unstrained inflammation is still unclear. The anti-inflammatory role of transcription factor nuclear receptor subfamily 4 group A member 1 (NR4A1) in macrophages and microglia has previously been identified. However, the endogenous mechanisms that how NR4A1 restricts unstrained inflammation remain elusive. Here, we observed that NR4A1 is up-regulated in the cytoplasm of activated microglia and localizes to processing bodies (P-bodies). In addition, we found that cytoplasmic NR4A1 functions as an RNA-binding protein (RBP) that directly binds and destabilizes Tnf mRNA in an N6-methyladenosine (m6A)-dependent manner. Remarkably, conditional microglial deletion of Nr4a1 elevates Tnf expression and worsens outcomes in a mouse model of ischemic stroke, in which case NR4A1 expression is significantly induced in the cytoplasm of microglia. Thus, our study illustrates a novel mechanism that NR4A1 posttranscriptionally regulates Tnf expression in microglia and determines stroke outcomes.

Nr4a1 promotes renal interstitial fibrosis by regulating the p38 MAPK phosphorylation

BACKGROUND

Renal interstitial fibrosis (RIF) is a common pathway to end-stage renal disease regardless of the initial etiology. Currently, the molecular mechanisms for RIF remains not fully elucidated. Nuclear receptor subfamily 4 group A member 1(Nr4a1), a member of the NR4A subfamily of nuclear receptors, is a ligand-activated transcription factor. The role of Nr4a1 in RIF remains largely unknown.

METHODS

In this study, we determined the role and action mechanism of Nr4a1 in RIF. We used unilateral ureteral obstruction (UUO) mice and transforming growth factor (TGF)-β1-treated human renal proximal tubular epithelial cells (HK-2 cells) as in vivo and in vitro models of RIF. A specific Nr4a1 agonist Cytosporone B (Csn-B) was applied to activate Nr4a1 both in vivo and in vitro, and Nr4a1 small interfering RNA was applied in vitro. Renal pathological changes were evaluated by hematoxylin and eosin and Masson staining, and the expression of fibrotic proteins including fibronectin (Fn) and collagen-I (Col-I), and phosphorylated p38 MAPK was measure by immunohistochemical staining and western blot analysis.

RESULTS

The results showed that Nr4a1 was upregulated in UUO mouse kidneys, and was positively correlated with the degree of interstitial kidney injury and the levels of fibrotic proteins. Csn-B treatment aggravated UUO-induced renal interstitial fibrosis, and induced p38 MAPK phosphorylation. In vitro, TGF-β induced Nr4a1 expression, and Nr4a1 downregulation prevented TGF-β1-induced expression of Fn and Col-I and the activation of p38 MAPK. Csn-B induced fibrotic proteins expression and p38 MAPK phosphorylation, and moreover Csn-B induced fibrotic proteins expression was abrogated by treatment with p38 MAPK inhibitor SB203580. We provided further evidence that Csn-B treatment promoted cytoplasmic accumulation of Nr4a1.

CONCLUSION

The findings in the present study indicate that Nr4a1 promotes renal fibrosis potentially through activating p38 MAPK kinase.

Nr4a nuclear receptors: markers and modulators of antigen receptor signaling

Nr4a1-3 encode a small family of orphan nuclear hormone receptors with transcriptional activity. Their expression reflects both acute and chronic antigen-receptor signaling in T and B-cells, and they have been implicated in critical aspects of lymphocyte development, tolerance, and function. These include roles in regulatory T-cell (Treg), thymic-negative selection, humoral responses, anergy, and exhaustion. Here, we review recent advances in this field such as functional roles in B-cells, transcriptional targets, and mechanism of action. We highlight recurrent themes, including integration of antigen-receptor signaling with costimulatory input, as well as unanswered questions and translational applications of this work.

The nuclear receptor subfamily 4 group A1 in human disease

Nuclear receptor 4A1 (NR4A1), a member of the NR4A subfamily, acts as a gene regulator in a wide range of signaling pathways and responses to human diseases. Here, we provide a brief overview of the current functions of NR4A1 in human diseases and the factors involved in its function. A deeper understanding of these mechanisms can potentially improve drug development and disease therapy.

Nur77 Serves as a Potential Prognostic Biomarker That Correlates with Immune Infiltration and May Act as a Good Target for Prostate adenocarcinoma

Prostate adenocarcinoma (PRAD) is the most frequent malignancy, and is the second leading cause of death due to cancer in men. Thus, new prognostic biomarkers and drug targets for PRAD are urgently needed. As we know, nuclear receptor Nur77 is important in cancer development and changes in the tumor microenvironment; whereas, the function of Nur77 in PRAD remains to be elucidated. The TCGA database was used to explore the Nur77 expression and its role in the prognosis of PRAD. It was shown that Nur77 was down regulated in PRAD, and low Nur77 expression was correlated with advanced clinical pathologic characteristics (high grade, histological type, age) and poor prognosis. Furthermore, key genes screening was examined by univariate Cox analysis and Kaplan-Meier survival. Additionally, Nur77 was closely related to immune infiltration and some anti-tumor immune functions. The differentially expressed genes (DEGs) were presented by protein-protein interaction (PPI) network analysis. Therefore, the expression level of Nur77 might help predict the survival of PRAD cases, which presents a new insight and a new target for the treatment of PRAD. In vitro experiments verified that natural product malayoside targeting Nur77 exhibited significant therapeutic effects on PRAD and largely induced cell apoptosis by up-regulating the expression of Nur77 and its mitochondrial localization. Taken together, Nur77 is a prognostic biomarker for patients with PRAD, which may refresh the profound understanding of PRAD individualized treatment.

3-Heptylidene-4,6-Dimethoxy-3H-Isobenzofuran-1-One Is Genotoxic, Increases the Frequency of Cell Death, and Potentiates the Effects of Cyclophosphamide and Cisplatin

3-heptylidene-4,6-dimethoxy-3H-isobenzofuran-1-one (Phthalide 1) is the precursor of three resorcinol lipids that have been described as potential chemotherapeutic agents and capable of potentiating the effects of cyclophosphamide. In this study, we evaluated the genotoxic potential, cell-killing potential, and interactions with cyclophosphamide and cisplatin of phthalide 1. Twelve groups were created from 120 mice: Negative Control, cyclophosphamide (100 mg/kg), cisplatin (6 mg/kg), Phthalide 1 (5, 10 and 20 mg/kg), and associations of 1 with cyclophosphamide and 1 with cisplatin. The results demonstrate that 1 increases (p < 0.05) the frequency of chromosomal damage, liver and kidney cell death, and splenic phagocytosis. The association of 1 with cyclophosphamide and cisplatin demonstrated a chemopreventive effect and, therefore, a reduction (p < 0.05) in the frequency of chromosomal damage. However, cell death and splenic phagocytosis did not suffer significant variations. As a result of the above, 1 has potential chemotherapeutic application and may be a candidate for developing a new generation of chemotherapeutics. In addition, it has characteristics to be used as a chemotherapy adjuvant in association with cyclophosphamide and cisplatin since it increases the frequency of cell death induced by chemotherapy. We also reported that the chemopreventive effect of 1, in association with cyclophosphamide and cisplatin, can prevent adverse effects (induction of DNA damage in non-tumor cells) without interfering with the mode of action of chemotherapy drugs and, therefore, without reducing the induction of cell death.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

The overuse of antibiotics has led to severe bacterial drug resistance. Blocking pathogen virulence devices is a highly effective approach to combating bacterial resistance worldwide. Type three secretion systems (T3SSs) are significant virulence factors in Gram-negative pathogens. Inhibition of these systems can effectively weaken infection whilst having no significant effect on bacterial growth. Therefore, T3SS inhibitors may be a powerful weapon against resistance in Gram-negative bacteria, and there has been increasing interest in the research and development of T3SS inhibitors. This review outlines several reported small-molecule inhibitors of the T3SS, covering those of synthetic and natural origin, including their sources, structures, and mechanisms of action.

Multifunctions of CRIF1 in cancers and mitochondrial dysfunction

Sustaining proliferative signaling and enabling replicative immortality are two important hallmarks of cancer. The complex of cyclin-dependent kinase (CDK) and its cyclin plays a decisive role in the transformation of the cell cycle and is also critical in the initiation and progression of cancer. CRIF1, a multifunctional factor, plays a pivotal role in a series of cell biological progresses such as cell cycle, cell proliferation, and energy metabolism. CRIF1 is best known as a negative regulator of the cell cycle, on account of directly binding to Gadd45 family proteins or CDK2. In addition, CRIF1 acts as a regulator of several transcription factors such as Nur77 and STAT3 and partly determines the proliferation of cancer cells. Many studies showed that the expression of CRIF1 is significantly altered in cancers and potentially regarded as a tumor suppressor. This suggests that targeting CRIF1 would enhance the selectivity and sensitivity of cancer treatment. Moreover, CRIF1 might be an indispensable part of mitoribosome and is involved in the regulation of OXPHOS capacity. Further, CRIF1 is thought to be a novel target for the underlying mechanism of diseases with mitochondrial dysfunctions. In summary, this review would conclude the latest aspects of studies about CRIF1 in cancers and mitochondria-related diseases, shed new light on targeted therapy, and provide a more comprehensive holistic view.

HK1 from hepatic stellate cell-derived extracellular vesicles promotes progression of hepatocellular carcinoma

Extracellular vesicles play crucial roles in intercellular communication in the tumor microenvironment. Here we demonstrate that in hepatic fibrosis, TGF-β stimulates the palmitoylation of hexokinase 1 (HK1) in hepatic stellate cells (HSCs), which facilitates the secretion of HK1 via large extracellular vesicles in a TSG101-dependent manner. The large extracellular vesicle HK1 is hijacked by hepatocellular carcinoma (HCC) cells, leading to accelerated glycolysis and HCC progression. In HSCs, the nuclear receptor Nur77 transcriptionally activates the expression of depalmitoylase ABHD17B to inhibit HK1 palmitoylation, consequently attenuating HK1 release. However, TGF-β-activated Akt functionally represses Nur77 by inducing Nur77 phosphorylation and degradation. We identify the small molecule PDNPA that binds Nur77 to generate steric hindrance to block Akt targeting, thereby disrupting Akt-mediated Nur77 degradation and preserving Nur77 inhibition of HK1 release. Together, this study demonstrates an overlooked function of HK1 in HCC upon its release from HSCs and highlights PDNPA as a candidate compound for inhibiting HCC progression.

Dereplication of Cytochalasans and Octaketides in Cytotoxic Extracts of Endophytic Fungi from Casearia arborea (Salicaceae)

Endophytes have been shown to be a source of novel drug prototypes. The Casearia genus is known for presenting cytotoxic clerodane diterpenes; however, there are few reports on secondary metabolites produced by its fungal microbiota. Thus, in the present study endophytic fungi obtained from the fresh leaves of C. arborea were grown in potato dextrose broth and rice to perform a secondary metabolite prospection study. The cytotoxic profile of the crude extracts at 10 µg/mL was determined by a colorimetric assay on tumor cell lines. The endophytes producing cytotoxic extracts were identified through phylogenetic analysis and belong to Diaporthe and Colletotrichum species. Metabolites present in these extracts were organized in molecular networking format based on HRMS-MS, and a dereplication process was performed to target compounds for chromatographic purification. Metabolic classes, such as lipids, peptides, alkaloids, and polyketides were annotated, and octaketide and cytochalasin derivatives were investigated. Cytochalasin H was purified from the cytotoxic Diaporthe sp. CarGL8 extract and its cytotoxic activity was determined on human cancer cell lines A549, MCF-7, and HepG2. The data collected in the present study showed that molecular networking is useful to understand the chemical profile of complex matrices to target compounds, minimizing the cost and time spent in purification processes.

Fragment-based discovery of orphan nuclear receptor Nur77/NGFI-B ligands

The transcription factor nerve growth factor-induced clone B (NGFI-B, Nur77, NR4A1) is an orphan nuclear receptor playing a role in cell survival and apoptosis regulation. Pharmacological Nur77 modulation holds promise for cancer and (neuro-)inflammatory disease treatment. The available Nur77 ligand scaffolds based on highly lipophilic natural products cytosporone B, celastrol and isoalantolactone are inadequate for the development of potent Nur77 modulators with favorable properties as chemical tools and future drugs. By fragment library screening and subsequent modeling for fragment extension, we have obtained a set of new Nur77 ligands offering alternative chemotypes for the development of Nur77 agonists and inverse agonists. Computer-aided fragment extension in a second stage screening yielded a Nur77 agonist with significant activation efficacy and preference over the related NR4A receptors.