Nuclear Retinoic Acid Receptors Research Articles

The regulation of FGF21 gene expression by metabolic factors and nutrients.

Fibroblast growth factor 21 (FGF21) gene expression is altered by a wide array of physiological, metabolic, and environmental factors. Among dietary factors, high dextrose, low protein, methionine restriction, short-chain fatty acids (butyric acid and lipoic acid), and all-trans-retinoic acid were repeatedly shown to induce FGF21 expression and circulating levels. These effects are usually more pronounced in liver or isolated hepatocytes than in adipose tissue or isolated fat cells. Although peroxisome proliferator-activated receptor α (PPARα) is a key mediator of hepatic FGF21 expression and function, including the regulation of gluconeogenesis, ketogenesis, torpor, and growth inhibition, there is increasing evidence of PPARα-independent transactivation of the FGF21 gene by dietary molecules. FGF21 expression is believed to follow the circadian rhythm and be placed under the control of first order clock-controlled transcription factors, retinoic acid receptor-related orphan receptors (RORs) and nuclear receptors subfamily 1 group D (REV-ERBs), with FGF21 rhythm being anti-phase to REV-ERBs. Key metabolic hormones such as glucagon, insulin, and thyroid hormone have presumed or clearly demonstrated roles in regulating FGF21 transcription and secretion. The control of the FGF21 gene by glucagon and insulin appears more complex than first anticipated. Some discrepancies are noted and will need continued studies. The complexity in assessing the significance of FGF21 gene expression resides in the difficulty to ascertain (i) when transcription results in local or systemic increase of FGF21 protein; (ii) if FGF21 is among the first or second order genes upregulated by physiological, metabolic, and environmental stimuli, or merely an epiphenomenon; and (iii) whether FGF21 may have some adverse effects alongside beneficial outcomes.

A Retinoic Acid-Hedgehog Cascade Coordinates Mesoderm-Inducing Signals and Endoderm Competence during Lung Specification

Organogenesis of the trachea and lungs requires a complex series of mesoderm-endoderm interactions mediated by WNT, BMP, retinoic acid (RA), and hedgehog (Hh), but how these pathways interact ina gene regulatory network is less clear. Using Xenopus embryology, mouse genetics, and human ES cell cultures, we identified a conserved signaling cascade that initiates respiratory lineage specification. We show that RA has multiple roles; first RA pre-patterns the lateral plate mesoderm and then itpromotes Hh ligand expression in the foregut endoderm. Hh subsequently signals back to the pre-patterned mesoderm to promote expression of the lung-inducing ligands Wnt2/2b and Bmp4. Finally, RA regulates the competence of the endoderm to activate the Nkx2-1+ respiratory program in response to these mesodermal WNT and BMP signals. These data provide insights into early lung development and a paradigm for how mesenchymal signals are coordinated with epithelial competence during organogenesis.

Radioligand binding assay for accurate determination of nuclear retinoid X receptors: A case of triorganotin endocrine disrupting ligands.

Nuclear 9-cis retinoic acid receptors (retinoid X receptors, RXR) are promiscuous dimerization partners for a number of nuclear receptors. In the present study, we established a novel in vitro method for quantitative determination of the nuclear retinoid X receptors in rat liver. One type of high affinity and limited capacity RXR specific binding sites with the Ka value ranging from 1.011 to 1.727×10(9)l/mol and the Bmax value ranging from 0.346 to 0.567pmol/mg, was demonstrated. Maximal 9-cis retinoic acid (9cRA) specific binding to nuclear retinoid X receptors was achieved at 20°C, and the optimal incubation time for the 9cRA-RXR complex formation was 120min. From a number of endocrine disruptors, tributyltins and triphenyltins are known as RXR ligands. Our data confirmed the property of tributyltin chloride or triphenyltin chloride to bind to a high affinity and limited capacity RXR binding sites. Described optimal conditions for ligand binding to RXR molecules enabled us to calculate maximal binding capacity (Bmax) and affinity (Ka) values. This study provides an original RXR radioligand binding assay that can be employed for investigation of novel RXR ligands that comprise both drugs and endocrine disruptors.

All trans-retinoic acid analogs promote cancer cell apoptosis through non-genomic Crabp1 mediating ERK1/2 phosphorylation.

All trans retinoic acid (atRA) is one of the most potent therapeutic agents, but extensive toxicity caused by nuclear RA receptors (RARs) limits its clinical application in treating cancer. AtRA also exerts non-genomic activities for which the mechanism remains poorly understood. We determine that cellular retinoic acid binding protein 1 (Crabp1) mediates the non-genomic activity of atRA, and identify two compounds as the ligands of Crabp1 to rapidly and RAR-independently activate extracellular signal regulated kinase 1/2 (ERK1/2). Non-canonically activated ERK activates protein phosphatase 2A (PP2A) and lengthens cell cycle duration in embryonic stem cells (ESC). This is abolished in Crabp1-null ESCs. Re-expressing Crabp1 in Crabp1-negative cancer cells also sensitizes their apoptotic induction by atRA. This study reveals a physiological relevance of the non-genomic action of atRA, mediated by Crabp1, in modulating cell cycle progression and apoptosis induction, and provides a new cancer therapeutic strategy whereby compounds specifically targeting Crabp1 can modulate cell cycle and cancer cell apoptosis in a RAR-independent fashion, thereby avoiding atRA’s toxicity caused by its genomic effects.

Cellular Retinoic Acid Binding Protein 2 Is Strikingly Downregulated in Human Esophageal Squamous Cell Carcinoma and Functions as a Tumor Suppressor.

Esophageal squamous cell carcinoma (ESCC) is the predominant pathotype of esophageal carcinoma (EC) in China, especially in Henan province, with poor prognosis and limited 5-year survival rate. Cellular retinoic acid binding protein 2 (CRABP2) is a member of the retinoic acid (RA) and lipocalin/cytosolic fatty-acid binding protein family and plays a completely contrary role in tumorigenesis through the retinoid signaling pathway, depending on the nuclear RA receptors (RAR) and PPARbeta/delta receptors. Presently, the biological role of CRABP2 in the development of ESCC has never been reported. Here, we firstly evaluated the expression of CRABP2 at both mRNA and protein levels and showed that it was remarkably downregulated in clinical ESCC tissues and closely correlated with the occurrence position, pathology, TNM stage, size, infiltration depth and cell differentiation of the tumor. Additionally, the biological function assays demonstrated that CRABP2 acted as a tumor suppressor in esophageal squamous carcinogenesis by significantly inhibiting cell growth, inducing cell apoptosis and blocking cell metastasis both in vitro and in vivo. All in all, our finding simplicate that CRABP2 is possibly an efficient molecular marker for diagnosing and predicting the development of ESCC.

Mitotic Activation of a Novel Histone Deacetylase 3-Linker Histone H1.3 Protein Complex by Protein Kinase CK2

Histone deacetylase 3 (HDAC3) and linker histone H1 are involved in both chromatin compaction and the regulation of mitotic progression. However, the mechanisms by which HDAC3 and H1 regulate mitosis and the factors controlling HDAC3 and H1 activity during mitosis are unclear. Furthermore, as of now, no association between class I, II, or IV (non-sirtuin) HDACs and linker histones has been reported. Here we describe a novel HDAC3-H1.3 complex containing silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) and nuclear receptor corepressor 1 (N-CoR) that accumulated in synchronized HeLa cells in late G2 phase and mitosis. Nonetheless, the deacetylation activity by HDAC3 in the complex was evident only in mitotic complexes. HDAC3 associated with H1.3 was highly phosphorylated on Ser-424 only during mitosis. Isolation of inactive HDAC3-H1.3 complexes from late G2 phase cells, and phosphorylation of HDAC3 in the complexes at serine 424 by protein kinase CK2 (also known as casein kinase 2) activated the HDAC3 in vitro. In vivo, CK2α and CK2α' double knockdown cells demonstrated a significant decrease in HDAC3 Ser-424 phosphorylation during mitosis. HDAC3 and H1.3 co-localized in between the chromosomes, with polar microtubules and spindle poles during metaphase through telophase, and partially co-localized with chromatin during prophase and interphase. H1 has been reported previously to associate with microtubules and, therefore, could potentially function in targeting HDAC3 to the microtubules. We suggest that phosphorylation of HDAC3 in the complex by CK2 during mitosis activates the complex for a dual role: compaction of the mitotic chromatin and regulation of polar microtubules dynamic instability.

Peroxisome Proliferator-Activated Receptor β/δ Stimulation Induces the Differentiation of Human Alveolar Epithelial Progenitor Cell

Pulmonary emphysema is a disease in which alveoli in the lung are irreversibly destroyed, compromising lung function. All-trans-retinoic acid (ATRA) reportedly repairs the alveoli of emphysema model mice. In addition, ATRA can activate two nuclear receptors, nuclear retinoic acid receptor (RAR) and peroxisome proliferator-activated receptor (PPAR) β/δ. Both of these receptors induce differentiation in many different cell types. In this study, PPARβ/δ stimulation is shown to induce differentiation of human alveolar epithelial progenitor cells into alveolar type II epithelial (AT-II) cells. PPARβ/δ activation also stimulates the expression of adipose differentiation-related protein mRNA in human alveolar epithelial progenitor cells. These data suggest that PPARβ/δ selective agonists could differentiate human alveolar epithelial progenitor cells without cytotoxic of ATRA derived from stimulation to RAR.

The combined effects of all-trans-retinoic acid and docosahexaenoic acid on the induction of apoptosis in human breast cancer MCF-7 cells.

Breast cancer is one of the most women's cancers in the worldwide. In vivo and in vitro studies showed that all-trans-retinoic acid (ATRA) and docosahexaenoic acid (DHA) can modulate differentiation and apoptosis in both cancer and immune cells. Nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs) activation in the presence of their ligands, plays a critical role in the proliferation, differentiation, and apoptosis of normal cells. We hypothesized that ATRA and DHA, as ligands of RARs and RXRs respectively, may have synergistic effects on the induction of apoptosis in MCF-7 human mammary carcinoma cell lines. MCF-7 cells were seeded in a 24-well plate at 3 × 105 cells per well. The cells were treated with 5 µM ATRA, 30 DHA, and various combinations of them over a 3-day trial. Apoptosis was measured by Annexin V-FITC kit and flow cytometery. Our results showed that the combination treatment of ATRA and DHA (5 µM and 30 µM and half dose at 2.5 µM and 15 µM, respectively) in a dose-dependent manner induced apoptosis rate in MCF-7 cells significantly more than single treatment of ATRA or DHA, as compared to control group (P < 0.05). We conclude that the combination of ATRA and DHA at the well-balanced proportion may be effective in cancer cell apoptosis. Further studies provide details about the potential synergistically effects of combination treatment of ATRA and DHA in growth inhibition and differentiation of human mammary cancer cells.

Effects of retinoic acid on growth hormone-releasing hormone receptor, growth hormone secretagogue receptor gene expression and growth hormone secretion in rat anterior pituitary cells.

Retinoic acid (RA) is an important signaling molecule in embryonic development and adult tissue. The actions of RA are mediated by the nuclear receptors retinoic acid receptor (RAR) and retinoid X receptor (RXR), which regulate gene expression. RAR and RXR are widely expressed in the anterior pituitary gland. RA was reported to stimulate growth hormone (GH) gene expression in the anterior pituitary cells. However, current evidence is unclear on the role of RA in gene expression of growth hormone-releasing hormone receptor (Ghrh-r), growth hormone secretagogue receptor (Ghs-r) and somatostatin receptors (Sst-rs). Using isolated anterior pituitary cells of rats, we examined the effects of RA on gene expression of these receptors and GH release. Quantitative real-time PCR revealed that treatment with all-trans retinoic acid (ATRA; 10(-6) M) for 24 h increased gene expression levels of Ghrh-r and Ghs-r; however, expressions of Sst-r2 and Sst-r5 were unchanged. Combination treatment with the RAR-agonist Am80 and RXR-agonist PA024 mimicked the effects of ATRA on Ghrh-r and Ghs-r gene expressions. Exposure of isolated pituitary cells to ATRA had no effect on basal GH release. In contrast, ATRA increased growth hormone-releasing hormone (GHRH)- and ghrelin-stimulated GH release from cultured anterior pituitary cells. Our results suggest that expressions of Ghrh-r and Ghs-r are regulated by RA through the RAR-RXR receptor complex and that RA enhances the effects of GHRH and ghrelin on GH release from the anterior pituitary gland.

NLS-RARα Inhibits the Effects of All-trans Retinoic Acid on NB4 Cells by Interacting with P38α MAPK.

Nuclear localization signal retinoic acid receptor alpha(NLS-RARα), which forms from the cleavage of promyelocytic leukemia-retinoic acid receptor alpha(PML-RARα) protein by neutrophil elastase(NE), possesses an important role in the occurrence and development of acute promyelocytic leukemia(APL). However, the potential mechanism underlying the effects of NLS-RARα on APL is still not entirely clear. Here, we investigated the effects of NLS-RARα on APL NB4 cells and its mechanism. We found that all-trans retinoic acid(ATRA) could promote differentiation while inhibit proliferation of APL NB4 cells via upregulating the expression of phosphorylated p38α mitogen-activated protein kinase(p-p38α MAPK). We also found that NLS-RARα could inhibit differentiation while accelerate proliferation of NB4 cells via downregulating the expression of p-p38α protein in the presence of ATRA. Furthermore, immunofluorescence and co-immunoprecipitation assays confirmed NLS-RARα interacted with p38α protein directly. Finally, application of PD169316, an inhibitor of p38α protein, suggested that recruitment p38α-combinded NLS-RARα by ATRA eventually caused activation of p38α protein. In summary, our study demonstrated that ATRA cound promote differentiation while inhibit proliferation of APL NB4 cells via activating p38α protein after recruiting p38α-combinded NLS-RARα, while NLS-RARα could inhibit the effects of ATRA in the process.

Xianfanghuomingyin, a Chinese Compound Medicine, Modulates the Proliferation and Differentiation of T Lymphocyte in a Collagen-Induced Arthritis Mouse Model.

In traditional Chinese medicine (TCM), xianfanghuomingyin (XFHM) is used to treat autoimmune diseases, including rheumatoid arthritis (RA). Here, we studied the mechanisms underlying its treatment effects, especially its anti-inflammatory effects in a collagen-induced arthritis (CIA) mouse model. We found that cartilage destruction and pannus formation were alleviated by treatment with XFHM. The abnormal differentiation of Th1 and Th17 cells was downregulated significantly by XFHM, and Th2 and Treg cells were upregulated. Moreover, the expression levels of specific cytokines and transcription factors related to Th1 cells (interferon γ [IFNγ], T-bet) and Th17 cells (interleukin- [IL-] 17) and the nuclear receptor retinoic acid receptor-related orphan receptor-gamma (RORγ) were downregulated. Serum IL-4 and GATA-3, which contribute to Th2 cells differentiation, increased significantly after XFHM administration. These results indicate that XFHM can restore the balance of T lymphocytes and reestablish the immunological tolerance to inhibit autoinflammatory disorder of RA. Taken together, XFHM can be used as a complementary or alternative traditional medicine to treat RA.

Cellular Retinoic Acid Binding Proteins: Genomic and Non-genomic Functions and their Regulation.

Cellular retinoic acid binding proteins (CRABPs) are high-affinity retinoic acid (RA) binding proteins that mainly reside in the cytoplasm. In mammals, this family has two members, CRABPI and II, both highly conserved during evolution. The two proteins share a very similar structure that is characteristic of a "β-clam" motif built up from10-strands. The proteins are encoded by two different genes that share a very similar genomic structure. CRABPI is widely distributed and CRABPII has restricted expression in only certain tissues. The CrabpI gene is driven by a housekeeping promoter, but can be regulated by numerous factors, including thyroid hormones and RA, which engage a specific chromatin-remodeling complex containing either TRAP220 or RIP140 as coactivator and corepressor, respectively. The chromatin-remodeling complex binds the DR4 element in the CrabpI gene promoter to activate or repress this gene in different cellular backgrounds. The CrabpII gene promoter contains a TATA-box and is rapidly activated by RA through an RA response element. Biochemical and cell culture studies carried out in vitro show the two proteins have distinct biological functions. CRABPII mainly functions to deliver RA to the nuclear RA receptors for gene regulation, although recent studies suggest that CRABPII may also be involved in other cellular events, such as RNA stability. In contrast, biochemical and cell culture studies suggest that CRABPI functions mainly in the cytoplasm to modulate intracellular RA availability/concentration and to engage other signaling components such as ERK activity. However, these functional studies remain inconclusive because knocking out one or both genes in mice does not produce definitive phenotypes. Further studies are needed to unambiguously decipher the exact physiological activities of these two proteins.

Non-classical Transcriptional Activity of Retinoic Acid.

It has long been established that the transcriptional activity of retinoic acid (RA) is mediated by members of the nuclear receptor family of ligand-activated transcription factors termed RA receptors (RARs). More recent observations have established that RA also activates an additional nuclear receptor, PPARβ/δ. Partitioning RA between RARs and PPARβ/δ is governed by different intracellular lipid-binding proteins: cellular RA binding protein 2 (CRABP2) delivers RA to nuclear RARs and a fatty acid binding protein (FABP5) delivers the hormone from the cytosol to nuclear PPARβ/δ. Consequently, RA signals through RARs in CRABP2-expressing cells, but activates PPARβ/δ in cells that express a high level of FABP5. RA elicits different and sometimes opposing responses in cells that express different FABP5/CRABP2 ratios because PPARβ/δ and RARs regulate the expression of distinct sets of genes. An overview of the observations that led to the discovery of this non-classical activity of RA are presented here, along with a discussion of evidence demonstrating the involvement of the dual transcriptional activities of RA in regulating energy homeostasis, insulin responses, and adipocyte and neuron differentiation.

Abstract CN05-03: Cooperation between a rexinoid and EGFR-TKI for lung cancer prevention via Cyclin D1 destabilization

Abstract We previously reported that both nuclear retinoic acid receptor (RAR, retinoid) and retinoid X receptor (RXR, rexinoid) agonists can trigger proteasomal degradation of cyclins. This confers check point arrest and repair of carcinogenic DNA damage in bronchial epithelial cells. Mechanisms responsible for this induced degradation were discovered. These included ubiquitin-dependent as well as ISG15-dependent programs that independently destabilized expression of cyclin D1 and other G1 cyclin proteins. The critical receptor that confers this cyclin destabilization was RARβ. Yet, silencing of RARβ; and specifically of the previously unrecognized isoform that we cloned and designated as RARβ1 likely accounts for clinical resistance to classical retinoids (like 13-cis-retinoic acid and all-trans-retinoic acid) in lung carcinogenesis. We sought to learn whether RXR/RAR heterodimer complex activation with a rexinoid was able to trigger cyclin destabilization. This was found to be the case in in vitro studies. This finding implied that the same pathway would be engaged in the in vivo setting. To establish if this occurs, we engineered transgenic mice independently with human surfactant C-driven wild-type cyclin E or a proteasome-degradation resistant cyclin E species. This mouse model was developed because human pre-malignant and malignant lung lesions frequently deregulate cyclin expression. Intriguingly, these mice recapitulated many features of lung carcinogenesis found in patients. Neoplastic changes were enhanced by transgenic expression of the degradation-resistant cyclin E species. We built on this finding by showing that a rexinoid and an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) each chemoprevented lung cancers in vinyl carbamate-induced lung tumors within strain A/J mice. Notably, the rexinoid was more potent that the EGFR-TKI in conferring this chemoprevention. Both agents also reduced cyclin expression, but did so through distinct mechanisms. We sought to learn if a rexinoid (bexarotene) cooperated with an EGFR-TKI (erlotinib) in exerting anti-tumorigenic effects in lung cancer. Cooperation between these agents was found in both murine and human lung cancer cells and even in those cells that exhibited KRAS/p53 mutations. Over the past decade, we translated this work into the cancer clinic through a series of five clinical trials that moved this work through successive phase 0, phase I, and phase II trials of lung and aerodigestive tract cancers. In window of opportunity trials, pharmacodynamic responses (cyclin repression and induced necrosis and inflammatory responses) were seen when intratumoral levels of these drugs were comparable to those necessary to trigger in vitro effects. A phase II trial in heavily pre-treated stage IV non-small cell lung cancer (NSCLC) cases was performed. EGFR and cyclin expression profiles as well as KRAS mutations were searched for in these NSCLC cases. Findings revealed substantial cyclin repression and reduction of lung cancer growth by combined therapy with a rexinoid (bexarotene) and EGFR-TKI (erlotinib). Cyclins were repressed while necrosis and inflammation were induced in post-treatment versus pre-treatment lung tumor biopsies obtained in this window of opportunity trial. Objective anti-tumor responses occurred whether or not KRAS or activating EGFR mutations were detected. This refractory NSCLC trial had 3 major clinical responses (2 had KRAS or EGFR mutations) with prolonged survival (583, 665, and 1460+ days, respectively). Median survival was 22 weeks (16 weeks for controls). Hypertriglyceridemia or rash significantly increased median overall survival to 24 weeks. Thus, this combination regimen revealed substantial clinical anti-tumor activity against NSCLCs. Taken together, these findings indicate that cooperation between a rexinoid and EGFR-TKI can chemoprevent and treat lung cancers by causing cyclin destabilization. These agents are also useful tools to identify other antineoplastics that repress lung cancers by destabilizing cyclin expression or by inhibiting their associated kinases. Evidence for this will be presented in this session. Citation Format: Konstantin H. Dragnev, Vincent Memoli, Sarah J. Freemantle, Samuel Waxman, Ethan Dmitrovsky. Cooperation between a rexinoid and EGFR-TKI for lung cancer prevention via Cyclin D1 destabilization. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr CN05-03.

Circadian clock-coupled lung cellular and molecular functions in chronic airway diseases.

Airway diseases are associated with abnormal circadian rhythms of lung function, reflected in daily changes of airway caliber, airway resistance, respiratory symptoms, and abnormal immune-inflammatory responses. Circadian rhythms are generated at the cellular level by an autoregulatory feedback loop of interlocked transcription factors collectively referred to as clock genes. The molecular clock is altered by cigarette smoke, LPS, and bacterial and viral infections in mouse and human lungs and in patients with chronic airway diseases. Stress-mediated post-translational modification of molecular clock proteins, brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (BMAL1) and PERIOD 2, is associated with a reduction in the activity/level of the deacetylase sirtuin 1 (SIRT1). Similarly, the levels of the nuclear receptor REV-ERBα and retinoic acid receptor-related orphan receptor α (ROR α), critical regulators of Bmal1 expression, are altered by environmental stresses. Molecular clock dysfunction is implicated in immune and inflammatory responses, DNA damage response, and cellular senescence. The molecular clock in the lung also regulates the timing of glucocorticoid sensitivity and phasic responsiveness to inflammation. Herein, we review our current understanding of clock-controlled cellular and molecular functions in the lungs, the impact of clock dysfunction in chronic airway disease, and the response of the pulmonary clock to different environmental perturbations. Furthermore, we discuss the evidence for candidate signaling pathways, such as the SIRT1-BMAL1-REV-ERBα axis, as novel targets for chronopharmacological management of chronic airway diseases.

Retinoid treatment of skin diseases.

Retinoids (vitamin A and its metabolites) are potent natural regulators of cellular activities, including cell growth and differentiation, and they mediate many essential regulatory functions, especially in the skin. Biologically active retinoids exert their effects by binding to nuclear retinoic acid receptors and retinoid-X-receptors. The group of pharmacologically used retinoids include naturally occurring and chemically synthesised vitamin A derivatives. Due to their influence on keratinocyte proliferation, epidermal differentiation and keratinisation, retinoids are commonly used in the field of dermatopharmacology. For safe administration of retinoids, in-depth information about adverse effects and comprehensive information of the patient are important. This article gives an overview on the effects, use, and side-effects of topical and systemic retinoids in dermatology.

Abstract 1774: The effects of diarylthiourea analogs on triple negative breast cancer cell growth

Abstract Breast cancer is the most common cancer occurring in women and the second leading cause of cancer death in women after lung cancer. Breast cancer is often classified at the molecular level in terms of whether the cancer expresses the estrogen receptor, progesterone receptor and human epidermal growth factor 2 receptor. Hormone receptor positive breast cancer accounts for 75-80% of all breast cancer and the remaining 20-25% accounts for the most aggressive types of cancer which are negative for all three receptors– known as triple negative breast cancer (TNBC). The current treatment used to manage TNBC is chemotherapy. Although chemotherapy has been effective in improving patients’ prognosis, a significant number of patients either relapse or develop resistance to these drugs. There is a significant interest in developing new therapeutic drugs aimed at improving outcomes in TNBC patients. Many studies have shown that flexible heteroarotinoids (Flex-Het) are a promising new class of drugs due to their ability to regulate growth, differentiation and apoptosis in a variety of cancer cells without activating the nuclear retinoic acid receptors. Previous studies have shown ShetA2 as the leading Flex-Het anti-cancer drug with the greatest efficacy in treating various types of cancer cells (Liu et al. 2004, Benbrook et al. 2005, and Liu et al. 2007). Some of the limitations of the ShetA2 are its high lipophilicity, toxic side effects and the low yields associated with the laborious synthesis. Therefore, efforts have been made to develop 2nd generation diarylthiourea compounds that retain anti-cancer activity, but with minimal side effects. The objective of this study was to examine the effects of two 2nd generation drugs SL1-18 and SL1-09 on various TNBC cell lines including MDA-MB-453, MDA-MB-231 and MDA-MB-468. Our preliminary data shows that exposure to micromolar levels of the diarylthiourea compounds effectively inhibited cancer cell growth in all three TNBC cell lines; however additional studies are necessary to understand the molecular mechanism of how SL1-18 and SL1-09 work to block cell growth and whether these anti-cancer drugs are promising therapeutic leads for the treatment of triple negative breast cancer. Citation Format: Deborah Nambi, Maggie C. Louie, Shengquan Liu. The effects of diarylthiourea analogs on triple negative breast cancer cell growth. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1774. doi:10.1158/1538-7445.AM2015-1774

RARβ regulates neuronal cell death and differentiation in the avian ciliary ganglion.

ABSTRACTProgrammed cell death during chicken ciliary ganglion (CG) development is mostly discussed as an extrinsically regulated process, guided either by the establishment of a functional balance between preganglionic and postganglionic activity or the availability of target‐derived neurotrophic factors. We found that the expression of the gene coding for the nuclear retinoic acid receptor β (RARB) is transiently upregulated prior to and during the execution phase of cell death in the CG. Using retroviral vectors, the expression of RARB was knocked down during embryonic development in ovo. The knockdown led to a significant increase in CG neuron number after the cell death phase. BrdU injections and active caspase‐3 staining revealed that this increase in neuron number was due to an inhibition of apoptosis during the normal cell death phase. Furthermore, apoptotic neuron numbers were significantly increased at a stage when cell death is normally completed. While the cholinergic phenotype of the neurons remained unchanged after RARB knockdown, the expression of the proneural gene Cash1 was increased, but somatostatin‐like immunoreactivity, a hallmark of the mature choroid neuron population, was decreased. Taken together, these results point toward a delay in neuronal differentiation as well as cell death. The availability of nuclear retinoic acid receptor β (RARβ) and RARβ‐induced transcription of genes could therefore be a new intrinsic cue for the maturation of CG neurons and their predisposition to undergo cell death. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 75: 1204–1218, 2015

Discovery of imidazo[1,5-a]pyridines and -pyrimidines as potent and selective RORc inverse agonists.

The nuclear receptor (NR) retinoic acid receptor-related orphan receptor gamma (RORγ, RORc, or NR1F3) is a promising target for the treatment of autoimmune diseases. RORc is a critical regulator in the production of the pro-inflammatory cytokine interleukin-17. We discovered a series of potent and selective imidazo[1,5-a]pyridine and -pyrimidine RORc inverse agonists. The most potent compounds displayed >300-fold selectivity for RORc over the other ROR family members, PPARγ, and NRs in our cellular selectivity panel. The favorable potency, selectivity, and physiochemical properties of GNE-0946 (9) and GNE-6468 (28), in addition to their potent suppression of IL-17 production in human primary cells, support their use as chemical biology tools to further explore the role of RORc in human biology.

Vitamin A and cognitive processes

Vitamin A and its derivatives, the retinoids, essential for human health, modulate several physiological processes through their interactions with the nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs). They are involved in the modulation of cerebral plasticity including hippocampal neurogenesis and synaptic plasticity, known to underlie cognitive processes. Interestingly, retinoic acid (RA) hyposignaling, which contributes to the deterioration of hippocampal plasticity and function during aging, can be reversed by vitamin A supplementation or RA treatment. However, it is still not clear how vitamin A status modulates plasticity and memory. It is commonly accepted that RA, by binding to its specific nuclear receptors, regulates gene expression, including the expression of plasticity-related genes. Moreover, recent studies suggest that vitamin A could participate in the maintenance of neurobiological functions indirectly, through the glucocorticoid pathway. Here, we present data supporting the importance of vitamin A status in the maintenance of memory processes, and the contribution of naturally occurring RA hyposignaling during aging to the etiology of cognitive decline. We propose that vitamin A supplementation or RA treatment could be a potent way to prevent age-related cognitive impairments by maintaining normal vitamin A and glucocorticoid (GC) status in seniors.