Discovery of Orally Available Retinoic Acid Receptor-Related Orphan Receptor γ-t/Dihydroorotate Dehydrogenase Dual Inhibitors for the Treatment of Refractory Inflammatory Bowel Disease.

Inflammatory bowel disease (IBD) is a multifactorial autoimmune disease, representing a major clinical challenge. Herein, a strategy of dual-targeting approach employing retinoic acid receptor-related orphan receptor γ-t (RORγt) and dihydroorotate dehydrogenase (DHODH) was proposed for the treatment of IBD. Dual RORγt/DHODH inhibitors are expected not only to reduce RORγt-driven Th17 cell differentiation but also to mitigate the expansion and activation of T cells, which may enhance anti-inflammatory effects. Starting from 2-aminobenzothiazole hit 1, a series of 2-aminotetrahydrobenzothiazoles were discovered as potent dual RORγt/DHODH inhibitors. Compound 14d stands out with IC50 values of 0.110 µM for RORγt and of 0.297 µM for DHODH. With acceptable mouse pharmacokinetic profiles, 14d exhibited remarkable in vivo anti-inflammatory activity and dose-dependently alleviated the severity of dextran sulfate sodium (DSS)-induced acute colitis in mice. Taken together, the present study provides a novel framework for the development of therapeutic agents for the treatment of IBD.

Appraisal of the human health related toxicological information available on dicyclopentadiene (DCPD) in view of assessing the substance's potential to cause endocrine disruption.

Dicyclopentadiene (DCPD) is an olefinic hydrocarbon which is manufactured and imported into the European Union (EU) at greater than 1000 tons per year. Concerns related to fetotoxic effects observed in reproductive toxicity studies at high doses led the REACH registrants to self-classify DCPD as a Category 2 reproductive toxicant under the EU CLP Regulation. DCPD was also reviewed in the European Union in the frame of an ongoing European Chemical Agency (ECHA) Community Rolling Action Plan (CoRAP) procedure and under the French National Strategy on Endocrine Disruptors (SNPE). To elucidate whether the developmental effects may be triggered by an endocrine mode of action, the Lower Olefins Sector Group (LOSG) of the European Chemical Industry Council (CEFIC) formed an ad hoc expert team to review the available scientific information pertaining to the potential endocrine activity and adversity of DCPD. Existing experimental data was complemented with structure activity modelling using ECHA-recommended (Q)SAR tools. Overall, considering the available information from (Q)SAR, mechanistic in vitro and in vivo studies, no indication of endocrine-mediated adversity was found. Hence, the available evidence supports the conclusion that DCPD does not cause developmental toxicity via an endocrine mode of action. Further work is ongoing to support this conclusion.

Natural products as modulators of retinoic acid receptor-related orphan receptors (RORs).

Covering: 1994 to 2020 Retinoic acid receptor-related orphan receptors (RORs) belong to a subfamily of the nuclear receptor superfamily and possess prominent roles in circadian rhythm, metabolism, inflammation, and cancer. They have been subject of research for over two decades and represent attractive but challenging drug targets. Natural products were among the first identified ligands of RORs and continue to be of interest to this day. This review focuses on ligands and indirect modulators of RORs from natural sources and explores their roles in a therapeutic context.

Retinoic acid receptor-targeted drugs in neurodegenerative disease.

INTRODUCTION: Neurodegenerative diseases including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and Parkinson's disease (PD) are characterized by progressive neuronal loss and currently lack effective treatments that block the degenerative process. It has been suggested that retinoids, a class of vitamin A-derived compounds, may hold potential as future therapeutics for these disorders. AREAS COVERED: In this review, we explore the role of retinoids in modulating various signaling pathways in the brain which influence pathologically relevant processes such as cellular differentiation, immune and antioxidant response, neurite outgrowth and neurite regeneration. These actions are predominantly mediated by the retinoic acid receptors and we discuss the developmental history of ligands for these receptors, assessing how refinements in receptor binding specificity and improved pharmacokinetic properties may influence the management of off-target effects. EXPERT OPINION: New approaches to understanding retinoid's mechanisms of action, including non-genomic pathways, and how these mechanisms interact may prove vital in the development of future retinoid-based neurodegenerative disease treatments.

CRABP2 and FABP5 expression levels in diseased and normal pancreas.

Recently, stromal targeting, by agents such as All trans retinoic acid (ATRA), has been regarded as a promising avenue for the treatment of pancreatic ductal adenocarcinoma (PDAC). The intra-cellular transportation of ATRA to the nuclear receptors is performed by either: fatty acid binding protein 5 (FABP5) or cellular retinoic acid binding protein 2 (CRABP2), dictating the transcription of downstream genes and, thus, eventual cell phenotype. Here, we explored the levels of each protein, in pancreatic tissues of patients presenting with a range of pancreatic diseases (pancreatic ductal adenocarcinoma (PDAC), chronic pancreatitis (CP), cholangiocarcinoma (CC)). We demonstrate that there is a significantly lower CRABP2 and FABP5 expression in activated fibroblasts or pancreatic stellate cells (PSC) in PDAC, as well as other diseased pancreas as in CC and CP, versus quiescent fibroblasts. The quiescent fibroblasts consistently show a pattern of high FABP5:CRABP2 ratio, whereas PSC in all non-PDAC tissues showed a low FABP5:CRABP2 ratio. PSC in PDAC patients had a range of FABP5:CRABP2 ratios (high, even and low). There was a lower CRABP2 expression in cancerous epithelial cells (PDAC) versus normal epithelial cells. This is also present in other disease states (CP, CC). Contrasting to the patterns seen for fibroblasts, the FABP5 expression in PDAC epithelial cells matched that of the normal epithelial cells. However, the normal epithelial cells had a high FABP5:CRABP2 ratio, compared to the PDAC epithelial cells. These ratios may have correlation with tumor progression, and overall survival. These findings could be confirmed in in vitro cell lysates. CRABP2 and FABP5 levels and ratios could serve as valuable biomarkers.

Retinoic acid receptor γ activation promotes differentiation of human induced pluripotent stem cells into esophageal epithelium.

BACKGROUND: The esophagus is known to be derived from the foregut. However, the mechanisms regulating this process remain unclear. In particular, the details of the human esophagus itself have been poorly researched. In this decade, studies using human induced pluripotent stem cells (hiPSCs) have proven powerful tools for clarifying the developmental biology of various human organs. Several studies using hiPSCs have demonstrated that retinoic acid (RA) signaling promotes the differentiation of foregut into tissues such as lung and pancreas. However, the effect of RA signaling on the differentiation of foregut into esophagus remains unclear. METHODS: We established a novel stepwise protocol with transwell culture and an air-liquid interface system for esophageal epithelial cell (EEC) differentiation from hiPSCs. We then evaluated the effect of all-trans retinoic acid (ATRA), which is a retinoic acid receptor (RAR)α, RARß and RARγ agonist, on the differentiation from the hiPSC-derived foregut. Finally, to identify which RAR subtype was involved in the differentiation, we used synthetic agonists and antagonists of RARα and RARγ, which are known to be expressed in esophagus. RESULTS: We successfully generated stratified layers of cells expressing EEC marker genes that were positive for lugol staining. The enhancing effect of ATRA on EEC differentiation was clearly demonstrated with quantitative reverse transcription polymerase chain reaction, immunohistology, lugol-staining and RNA sequencing analyses. RARγ agonist and antagonist enhanced and suppressed EEC differentiation, respectively. RARα agonist had no effect on the differentiation. CONCLUSION: We revealed that RARγ activation promotes the differentiation of hiPSCs-derived foregut into EECs.

LncRNA-H19 induces hepatic stellate cell activation via upregulating alcohol dehydrogenase III-mediated retinoic acid signals.

Activation of hepatic stellate cells (HSCs) is a pivotal event in liver fibrosis, characterized by enhanced retinoic acid signals. Although up-regulated retinoic acid signal responds further to maintain HSC activation, the underlying molecular mechanisms are largely unknown. In this study, we sought to investigate the role of lncRNA-H19 in regulation of retinoic acid signals, and to further examine the underlying mechanism in this molecular context. We found that lncRNA-H19 upregulation could enhance retinoic acid signals to induce HSC activation, whereas lncRNA-H19 knockdown completely disturbed retinoic acid signals. Moreover, the activation of retinoic acid signals impaired the lncRNA-H19 knockdown mediated HSC inactivation. Interestingly, we also found that enhanced retinoic acid signals by lncRNA-H19 was associated with a coordinate increase in retinol metabolism during HSC activation. Increased retinol metabolism contributed to obvious lipid droplet consumption. Importantly, we identified that alcohol dehydrogenase III (ADH3) was essential for lncRNA-H19 to enhance retinoic acid signals. The inhibition of ADH3 completely abrogated the lncRNA-H19 mediated retinoic acid signals and HSC activation. Of note, we identified dihydroartemisinin (DHA) as a natural inhibitor for lncRNA-H19. Treatment with DHA significantly decreased the expression of lncRNA-H19, reduced the expression of ADH3, blocked retinoic acid signals, and in turn, inhibited HSC activation. Overall, these results provided novel implications to reveal the molecular mechanism of increased retinoic acid signals during HSC activation, and identify lncRNA-H19/ADH3 pathway as a potential target for the treatment of liver fibrosis.

In vitro bone-like nodules generated from patient-derived iPSCs recapitulate pathological bone phenotypes.

The recapitulation of bone formation via the in vitro generation of bone-like nodules is frequently used to understand bone development. However, current bone-induction techniques are slow and difficult to reproduce. Here, we report the formation of bone-like nodules within ten days, via the use of retinoic acid (RA) to induce the osteogenic differentiation of human induced pluripotent stem cells (hiPSCs) into osteoblast-like and osteocyte-like cells that create human bone tissue when implanted in calvarial defects in mice. We also show that the induction of bone formation depends on cell signalling through the RA receptors RARα and RARß, which simultaneously activate the BMP (bone morphogenetic protein) and Wnt signalling pathways. Moreover, by using patient-derived hiPSCs, the bone-like nodules recapitulated the osteogenesis-imperfecta phenotype, which was rescued via the correction of disease-causing mutations and partially by an mTOR (mechanistic target of rapamycin) inhibitor. The method of inducing bone nodules may serve as a fast and reproducible model for the study of the formation of both healthy and pathological bone.

Inhibition of Cell Proliferation in an NRAS Mutant Melanoma Cell Line by Combining Sorafenib and α-Mangostin.

α-Mangostin is a natural product commonly used in Asia for cosmetic and medicinal applications including topical treatment of acne and skin cancer. Towards finding new pharmacological strategies that overcome NRAS mutant melanoma, we performed a cell proliferation-based combination screen using a collection of well-characterized small molecule kinase inhibitors and α-Mangostin. We found that α-Mangostin significantly enhances Sorafenib pharmacological efficacy against an NRAS mutant melanoma cell line. The synergistic effects of α-Mangostin and Sorafenib were associated with enhanced inhibition of activated AKT and ERK, induced ER stress, and reduced autophagy, eventually leading to apoptosis. The structure of α-Mangostin resembles several inhibitors of the Retinoid X receptor (RXR). MITF expression, which is regulated by RXR, was modulated by α-Mangostin. Molecular docking revealed that α-Mangostin can be accommodated by the ligand binding pocket of RXR and may thereby compete with RXR-mediated control of MITF expression. In summary, these data demonstrate an unanticipated synergy between α-Mangostin and sorafenib, with mechanistic actions that convert a known safe natural product to a candidate combinatorial therapeutic agent.

Synthesis and characterization of a new retinoic acid ECPIRM as potential chemotherapeutic agent for human cutaneous squamous carcinoma.

Cutaneous squamous cell carcinoma (CSCC) is one of the most common cancers worldwide, requiring effective therapeutic interventions. Retinoids are important chemopreventive and therapeutic agents for a variety of human cancers including CSCC. In this study we synthesized a novel retinoic derivative N-(4-ethoxycarbonylphenyl) isoretinamide (ECPIRM) and evaluated its biological activities and possible mechanisms in human cutaneous squamous cell lines. ECPIRM had better inhibitory effect on the proliferation of squamous carcinoma cells SCL-1 and colo-16, compared with All-trans retinoic acid and 13-cis retinoic acid. ECPIRM had less toxicity to normal keratinocyte cell line HaCaT. Mechanistically, ECPIRM induced G1 cell cycle arrest in SCL-1 cells, via the downregulation of CDK2, CDK4, cycling D1 and cyclin E expression and upregulation of p21. In addition, these effects were at least partially due to the inhibition of JNK/ ERK-AP-1 signaling pathway by ECPIRM. Importantly, these effects of ECPIRM are independent of the classical retinoid receptor pathway, suggesting that the novel compound will have less side-effects in chemotherapy. These findings demonstrate that ECPIRM is a potential inhibitor of MPAK-AP-1 pathway, and is a potential therapeutic agent against CSCC.

MicroRNA networks regulated by all-trans retinoic acid and Lapatinib control the growth, survival and motility of breast cancer cells.

SKBR3-cells, characterized by ERBB2/RARA co-amplification, represent a subgroup of HER2+ breast-cancers sensitive to all-trans retinoic acid (ATRA) and Lapatinib. In this model, the two agents alone or in combination modulate the expression of 174 microRNAs (miRs). These miRs and predicted target-transcripts are organized in four interconnected modules (Module-1 to -4). Module-1 and Module-3 consist of ATRA/Lapatinib up-regulated and potentially anti-oncogenic miRs, while Module-2 contains ATRA/Lapatinib down-regulated and potentially pro-oncogenic miRs. Consistent with this, the expression levels of Module-1/-3 and Module-2 miRs are higher and lower, respectively, in normal mammary tissues relative to ductal-carcinoma-in-situ, invasive-ductal-carcinoma and metastases. This indicates associations between tumor-progression and the expression profiles of Module-1 to -3 miRs. Similar associations are observed with tumor proliferation-scores, staging, size and overall-survival using TCGA (The Cancer Genome Atlas) data. Forced expression of Module-1 miRs, (miR-29a-3p; miR-874-3p) inhibit SKBR3-cell growth and Module-3 miRs (miR-575; miR-1225-5p) reduce growth and motility. Module-2 miRs (miR-125a; miR-193; miR-210) increase SKBR3 cell growth, survival and motility. Some of these effects are of general significance, being replicated in other breast cancer cell lines representing the heterogeneity of this disease. Finally, our study demonstrates that HIPK2-kinase and the PLCXD1-phospholipase-C are novel targets of miR-193a-5p/miR-210-3p and miR-575/miR-1225-5p, respectively.

4-Amino-2-trifluoromethyl-phenyl retinate inhibits the migration of BGC-823 human gastric cancer cells by downregulating the phosphorylation level of MLC II.

4-Amino-2-trifluoromethyl-phenyl retinate (ATPR) is a novel all-trans retinoic acid (ATRA) derivative which was reported to have a superior antitumor effect in breast cancer cells. However, little is known about its antitumor effects on human gastric cancer cells and the mechanisms have not been fully elucidated. The results of the present study suggest that in the human gastric carcinoma cell line BGC-823, ATPR plays a more effective role than ATRA at the same dose in inhibiting proliferation, migration and inducing differentiation after the same treatment time. Furthermore, we investigated the preliminary mechanism of ATPR's anti­migration effect. Immunofluorescence assay demonstrated that claudin-18 positioned from cytoplasm to cell surface following ATPR stimuli. Real-time quantitative RT-PCR and western blot analyses showed that ATPR had significant effects on downregulation of the phosphorylation level of myosin light chain II (MLC II) by suppressing myosin light chain kinase (MLCK) and Rho-associated coiled-coil containing kinase (ROCK), as well as its regulation in the protein expression of RARα and RARß. Moreover, ATPR increased the activity of myosin phosphatase by inhibiting ROCK. Consequently, ATPR showed more promising antitumor effects than ATRA in BGC-823 in vitro, and it may conduct its anti-migration effects by decreasing the phosphorylation level of MLC II, as well as by regulating MLCK and ROCK as downstream target genes.

MicroRNA-302b-inhibited E2F3 transcription factor is related to all trans retinoic acid-induced glioma cell apoptosis.

All-trans retinoic acid (ATRA), a derivative of retinoid, is involved in the onset of differentiation and apoptosis in a wide variety of normal and cancer cells. MicroRNAs (miRNAs) are small non-coding RNAs that control gene expression. Several miRNAs were identified to participate in ATRA-mediated cell differentiation. However, no studies have demonstrated whether miRNA can enhance ATRA cytotoxicity, thereby resulting in cell apoptosis. This study investigated the effects of ATRA-mediated miRNA expression in activating apoptotic pathways in glioblastoma. First, we found that high-dose ATRA treatment significantly reduced cell viability, caspase-dependent apoptosis, endoplasmic reticular (ER) stress activation, and intracellular reactive oxygen species accumulation. From microarray data, miR-302b was analyzed as a putative downstream regulator upon ATRA treatment. Furthermore, we found that ATRA up-regulated miR-302b expression in a dose- and time-dependent manner through retinoic acid receptor α-mediated pathway. Overexpression and knockdown of miR-302b significantly influenced ATRA-mediated cytotoxicity. E2F3, an important transcriptional regulator of glioma proliferation, was validated to be a direct target gene of miR-302b. The miR-302b-reduced E2F3 levels were also identified to be associated with ATRA-mediated glioma cell death. These results emphasize that an ATRA-mediated miR-302b network may provide novel therapeutic strategies for glioblastoma therapy. We propose that high-dose all-trans retinoic acid (ATRA) treatment, a derivative of retinoid, significantly induces glioblastoma cell apoptosis via caspase-dependent apoptosis, endoplasmic reticular (ER) stress, and intracellular reactive oxygen species (ROS) accumulation. The miR-302b overexpression enhanced by ATRA-mediated retinoic acid receptor (RAR)α pathway was also identified. The E2F3 repression, a novel target gene of miR-302b, was involved in ATRA-induced glioblastoma cell cytotoxicity.

A potential target of Tanshinone IIA for acute promyelocytic leukemia revealed by inverse docking and drug repurposing.

Tanshinone IIA is a pharmacologically active ingredient extracted from Danshen, a Chinese traditional medicine. Its molecular mechanisms are still unclear. The present study utilized computational approaches to uncover the potential targets of this compound. In this research, PharmMapper server was used as the inverse docking tool and the results were verified by Autodock vina in PyRx 0.8, and by DRAR-CPI, a server for drug repositioning via the chemical-protein interactome. Results showed that the retinoic acid receptor alpha (RARα), a target protein in acute promyelocytic leukemia (APL), was in the top rank, with a pharmacophore model matching well the molecular features of Tanshinone IIA. Moreover, molecular docking and drug repurposing results showed that the complex was also matched in terms of structure and chemical-protein interactions. These results indicated that RARα may be a potential target of Tanshinone IIA for APL. The study can provide useful information for further biological and biochemical research on natural compounds.

Activation of a retinoic acid receptor pathway by thiazolidinediones induces production of vascular endothelial growth factor/vascular permeability factor in OP9 adipocytes.

Thiazolidinediones, ligands of peroxisome proliferator-activated receptorγ (PPARγ), are used in the management of type 2 diabetes mellitus. However, they can cause edema, which often leads to a discontinuation of treatment. The mechanism by which thiazolidinediones induce edema is poorly understood. We have confirmed that troglitazone (TGZ), a thiazolidinedione, induced the differentiation of a preadipocyte cell line, OP9, into adipocytes. The differentiated OP9 cells produced vascular permeability factors and the activity was completely neutralized by an antibody against vascular endothelial growth factor (VEGF). TGZ induced the expression of VEGF but not interleukin-6 and monocyte chemoattractant protein-1. 2-chloro-5-nitrobenzanilide (GW9662) blocked both the differentiation and the production of VEGF induced by TGZ. 15-deoxy-Δ(12,14)-Prostaglandin J2, a natural ligand of PPARγ, and another PPARγ agonist, ginkgolic acid, also induced an increase in the expression of VEGE as well as the differentiation of OP9 cells. Indomethacin, a nonsteroidal anti-inflammatory drug (NSAID) with PPARγ activity, up-regulated VEGF expression, but acetylsalicylic acid, a NSAID without PPARγ activity, did not. Although VEGF expression was enhanced under hypoxic conditions, the expression of hypoxia inducible factor and Ets-1 was down-regulated during the TGZ-induced differentiation. On the other hand, retinoic acid enhanced the expression of VEGF despite inhibiting the TGZ-induced differentiation. Moreover, retinoic acid receptor (RAR) ß expression was increased by TGZ and retinoic acid. These findings suggested that the major adipocyte-derived vascular permeability factor produced in response to TGZ was VEGF, and a RAR pathway was involved in the production.

Adapalene suppresses sebum accumulation via the inhibition of triacylglycerol biosynthesis and perilipin expression in differentiated hamster sebocytes in vitro.

BACKGROUND: Acne is a chronic inflammatory disease in sebaceous glands and pilosebaceous units where excess sebum production and follicular hyperkeratinization are observed. Adapalene, which exerts comedolytic and anti-inflammatory effects, is used for the topical treatment of mild to moderate acne. OBJECTIVE: We examined the effect of adapalene on sebum production and accumulation in sebaceous gland cells (sebocytes). METHODS: The regulation of sebum production was examined by oil red O and nile red staining and the measurement of triacylglycerols (TGs) in differentiated hamster sebocytes. The gene expression and production of diacylglycerol acyltransferase-1 (DGAT-1) and perilipin 1 (PLIN1) were analyzed using real-time PCR and Western blotting, respectively. RESULTS: Adapalene suppressed sebum accumulation as lipid droplets in spontaneously and insulin-differentiated hamster sebocytes. The TG production, and the gene expression and production of DGAT-1, a rate-limiting enzyme of TG biosynthesis, were dose-dependently inhibited by adapalene in insulin-, 5α-dihydrotestosterone- or a peroxisome proliferator activating receptor γ agonist, troglitazone-differentiated hamster sebocytes. In addition, the inhibition of TG production by adapalene interfered with antagonists against nuclear retinoic acid and retinoid X receptors (CD2665 and UVI3006, respectively) in the differentiated sebocytes. Furthermore, the production of PLIN1, a lipid storage droplet protein, was transcriptionally inhibited by adapalene in the differentiated sebocytes. CONCLUSIONS: These results suggest that adapalene exerts an inhibitory action for sebum accumulation due to the suppression of TG and PLIN1 production in differentiated hamster sebocytes. Furthermore, these findings may contribute to a novel understanding of the molecular mechanisms of adapalene for acne treatment and prevention.

Screening for potential effects of endocrine-disrupting chemicals in peri-urban creeks and rivers in Melbourne, Australia using mosquitofish and recombinant receptor-reporter gene assays.

Sexually mature male mosquitofish (Gambusia holbrooki) were collected from various sites around Melbourne in 2009 to evaluate the performance of gonopodial indices as a biomarker for endocrine disruption in Melbourne's waterways. The mosquitofish indices assessed were body length (BL), gonopodial length (GL)/BL ratio, ray 4:6 ratio and the absence or presence of hooks and serrae, and these varied between sites. The study was complemented by measurements of estrogenic, retinoid, thyroid and aryl hydrocarbon (AhR) receptor activities of the water. Male mosquitofish were 16.3-21.5 mm in length, and although there was a statistically significant positive relationship showing that bigger fish had longer gonopodia than small fish (r2 = 0.52, p < 0.001), there were few significant differences in GL/BL ratio of fish between sites. Measured estrogenic activity was mostly in the range 0.1-1.7 ng/L EEQ, with one site having much higher levels (~12 ng/L EEQ). Aryl hydrocarbon (AhR) receptor activity was observed in all water samples (7-180 ng/L ßNF EQ), although there was no consistent pattern in the level of AhR activity observed, i.e., 'clean' sites were as likely to return a high AhR activity response as urban or wastewater treatment plant (WWTP)-impacted sites. There was no correlation between measurements of receptor actvity and gonopodial length (GL):BL ratio and BL. We conclude that the mosquitofish gonopodia only fulfills part of the criteria for biomarker selection for screening. The mosquitofish indices assessed were cheap and easy-to-perform procedures; however, there is no baseline data from the selected sites to evaluate whether differences in the morpholical indices observed at a site were a result of natural selection in the population or due to estrogenic exposure.

Relaxant effect of all-trans-retinoic acid via NO-sGC-cGMP pathway and calcium-activated potassium channels in rat mesenteric artery.

Intraperitoneal injection of all-trans-retinoic acid (ATRA) results in a reduction of blood pressure in spontaneously hypertensive rats. However, the mechanisms involved in this effect are not clear. We hypothesized that ATRA may relax resistance arteries. In this study, we found that ATRA relaxed phenylephrine-preconstricted mesenteric arterial rings, which were abrogated by the removal of the endothelium. Pretreatment of endothelium-intact arterial rings with an inhibitor of endothelial nitric oxide (NO) synthase, N(G)-nitro-l-arginine methyl ester (l-NAME), or soluble guanylyl cyclase, 1H-[1,2,4]-oxadiazole-[4,3-α]-quinoxaline-1-one, reduced the vasorelaxant effect of ATRA. Incubation of mesenteric arterial rings with ATRA increased the production of NO and cGMP, which were blocked by N(G)-nitro-l-arginine methyl ester. The vasorelaxant effect of ATRA was markedly attenuated in the presence of an inhibitor of big conductance calcium-activated potassium channels (charybdotoxin), but not with an inhibitor of voltage-dependent potassium channel (4-aminopyridine) or ATP-sensitive potassium channel (glibenclamide). Activation of retinoic acid receptors (RARs) with CH55 or retinoic X receptors (RXRs) with LGD1069 induced the vasorelaxation of phenylephrine-preconstricted mesenteric arterial rings. The RAR (BMS493) and RXR (UVI3003) antagonists blocked the ATRA-induced vasorelaxation. The vasorelaxant effect ATRA is physiologically relevant because the intravenous infusion of ATRA decreased blood pressure in normotensive rats. We conclude that ATRA relaxes resistance vessels via both RARs and RXRs receptors that are mediated by the endothelium-dependent NO-cGMP pathway, which may participate in the control of blood pressure.

Poly (ADP-ribose) glycohydrolase regulates retinoic acid receptor-mediated gene expression.

Poly-(ADP-ribose) glycohydrolase (PARG) is a catabolic enzyme that cleaves ADP-ribose polymers synthesized by poly-(ADP-ribose) polymerases. Here, transcriptome profiling and differentiation assay revealed a requirement of PARG for retinoic acid receptor (RAR)-mediated transcription. Mechanistically, PARG accumulates early at promoters of RAR-responsive genes upon retinoic acid treatment to promote the formation of an appropriate chromatin environment suitable for transcription. Silencing of PARG or knockout of its enzymatic activity maintains the H3K9me2 mark at the promoter of the RAR-dependent genes, leading to the absence of preinitiation complex formation. In the absence of PARG, we found that the H3K9 demethylase KDM4D/JMJD2D became PARsylated. Mutation of two glutamic acids located in the Jumonji N domain of KDM4D inhibited PARsylation. PARG becomes dispensable for ligand-dependent transcription when either a PARP inhibitor or a non-PARsylable KDM4D/JMJD2D mutant is used. Our results define PARG as a coactivator regulating chromatin remodeling during RA-dependent gene expression.

The p85α regulatory subunit of PI3K mediates cAMP-PKA and retinoic acid biological effects on MCF7 cell growth and migration.

Phosphoinositide-3-OH kinase (PI3K) signalling regulates various cellular processes, including cell survival, growth, proliferation and motility, and is among the most frequently mutated pathways in cancer. Although the involvement of p85αPI3K SH2 domain in signal transduction has been extensively studied, the function of the SH3 domain at the N-terminus remains elusive. A serine (at codon 83) adjacent to the N-terminal SH3 domain in the PI3K regulatory subunit p85αPI3K that is phosphorylated by protein kinase A (PKA) in vivo and in vitro has been identified. Virtually all receptors binding p85αPI3K can cooperate with cAMP-PKA signals via phosphorylation of p85αPI3KSer83. To analyse the role of p85αPI3KSer83 in retinoic acid (RA) and cAMP signalling, in MCF7 cells, we used p85αPI3K mutated forms, in which Ser83 has been substituted with alanine (p85A) to prevent phosphorylation or with aspartic acid (p85D) to mimic the phosphorylated residue. We demonstrated that p85αPI3KSer83 is crucial for the synergistic enhancement of RARα/p85αPI3K binding induced by cAMP/RA co-treatment in MCF7 cells. Growth curves, colorimetric MTT assay and cell cycle analysis demonstrated that phosphorylation of p85αPI3KSer83 plays an important role in the control of MCF7 cell proliferation and in RA-induced inhibition of proliferation. Wound healing and transwell experiments demonstrated that p85αPI3KSer83 was also essential both for the control of migratory behaviour and for the reduction of motility induced by RA. This study points to p85αPI3KSer83 as the physical link between different pathways (cAMP-PKA, RA and FAK), and as an important regulator of MCF7 cell proliferation and migration.