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Phosphorylation of RXRα mediates the effect of JNK to suppress hepatic FGF21 expression and promote metabolic syndrome. Proc Natl Acad Sci U S A 2022; 119:e2210434119. [PMID: 36282921 PMCID: PMC9636906 DOI: 10.1073/pnas.2210434119] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The cJun NH2-terminal kinase (JNK) signaling pathway in the liver promotes systemic changes in metabolism by regulating peroxisome proliferator-activated receptor α (PPARα)-dependent expression of the hepatokine fibroblast growth factor 21 (FGF21). Hepatocyte-specific gene ablation studies demonstrated that the Mapk9 gene (encoding JNK2) plays a key mechanistic role. Mutually exclusive inclusion of exons 7a and 7b yields expression of the isoforms JNK2α and JNK2β. Here we demonstrate that Fgf21 gene expression and metabolic regulation are primarily regulated by the JNK2α isoform. To identify relevant substrates of JNK2α, we performed a quantitative phosphoproteomic study of livers isolated from control mice, mice with JNK deficiency in hepatocytes, and mice that express only JNK2α or JNK2β in hepatocytes. We identified the JNK substrate retinoid X receptor α (RXRα) as a protein that exhibited JNK2α-promoted phosphorylation in vivo. RXRα functions as a heterodimeric partner of PPARα and may therefore mediate the effects of JNK2α signaling on Fgf21 expression. To test this hypothesis, we established mice with hepatocyte-specific expression of wild-type or mutated RXRα proteins. We found that the RXRα phosphorylation site Ser260 was required for suppression of Fgf21 gene expression. Collectively, these data establish a JNK-mediated signaling pathway that regulates hepatic Fgf21 expression.
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2
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RXR – centralny regulator wielu ścieżek sygnałowych w organizmie. POSTEP HIG MED DOSW 2021. [DOI: 10.2478/ahem-2021-0005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Abstrakt
Receptory jądrowe (NRs) tworzą największą nadrodzinę czynników transkrypcyjnych, które odgrywają ważną rolę w regulacji wielu procesów biologicznych. Receptor kwasu 9-cis-retinowego (RXR) wydaje się odgrywać szczególną rolę wśród tej grupy białek, a to ma związek z jego zdolnością do tworzenia dimerów z innymi NRs. Ze względu na kontrolę ekspresji wielu genów, RXR stanowi bardzo dobry cel licznych terapii. Nieprawidłowości w szlakach modulowanych przez RXR są powiązane m.in. z chorobami neurodegeneracyjnymi, otyłością, cukrzycą, a także nowotworami. Istnieje wiele związków mogących regulować aktywność transkrypcyjną RXR. Jednak obecnie dopuszczonych do użytku klinicznego jest tylko kilka z nich. Retinoidy normalizują wzrost i różnicowanie komórek skóry i błon śluzowych, ponadto działają immunomodulująco oraz przeciwzapalnie. Stąd są stosowane przede wszystkim w chorobach skóry i w terapii niektórych chorób nowotworowych. W artykule przedstawiono ogólne wiadomości na temat RXR, jego budowy, ligandów i mechanizmu działania oraz potencjalnej roli w terapii nowotworów i zespołu metabolicznego.
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Shao M, Lu L, Wang Q, Ma L, Tian X, Li C, Li C, Guo D, Wang Q, Wang W, Wang Y. The multi-faceted role of retinoid X receptor in cardiovascular diseases. Biomed Pharmacother 2021; 137:111264. [PMID: 33761589 DOI: 10.1016/j.biopha.2021.111264] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 01/04/2021] [Accepted: 01/07/2021] [Indexed: 01/14/2023] Open
Abstract
Retinoid X receptors (RXRs) are members of ligand-dependent transcription factors whose effects on a diversity of cellular processes, including cellular proliferation, the immune response, and lipid and glucose metabolism. Knock out of RXRα causes a hypoplasia of the myocardium which is lethal during fetal life. In addition, the heart maintains a well-orchestrated balances in utilizing fatty acids (FAs) and other substrates to meet the high energy requirements. As the master transcriptional regulators of lipid metabolism, RXRs become particularly important for the energy needs of the heart. Accumulating evidence suggested that RXRs may exert direct beneficial effects in the heart both through heterodimerization with other nuclear receptors (NRs) and homodimerization, thus standing as suitable targets for treating in cardiovascular diseases. Although compounds that target RXRs are promising drugs, their use is limited by toxicity. A better understanding of the structural biology of RXRs in cardiovascular disease should enable the rational design of more selective nuclear receptor modulators to overcome these problems. Here, this review summarizes a brief overview of RXRs structure and versatility of RXR action in the control of cardiovascular diseases. And we also discussed the therapeutic potential of RXR ligand.
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Affiliation(s)
- Mingyan Shao
- School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Linghui Lu
- College of Traditional Chinese Medicine, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Qian Wang
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing, 100191, China
| | - Lin Ma
- School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Xue Tian
- School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Changxiang Li
- College of Traditional Chinese Medicine, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Chun Li
- Modern Research Center of Traditional Chinese Medicine, School of Traditional Chinese Material Medica, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Dongqing Guo
- School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Qiyan Wang
- School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, China
| | - Wei Wang
- School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, China.
| | - Yong Wang
- School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, China; College of Traditional Chinese Medicine, Beijing University of Chinese Medicine, Beijing, 100029, China.
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Sołtys K, Ożyhar A. Ordered structure-forming properties of the intrinsically disordered AB region of hRXRγ and its ability to promote liquid-liquid phase separation. J Steroid Biochem Mol Biol 2020; 198:105571. [PMID: 31881311 DOI: 10.1016/j.jsbmb.2019.105571] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 12/19/2019] [Accepted: 12/23/2019] [Indexed: 12/31/2022]
Abstract
The retinoid X receptor (RXR) is a member of the nuclear receptor (NR) superfamily that occupies the central position among other NRs by forming both homodimers and heterodimers with other representatives of the family. RXR shares similar structural domains with other members of NRs. The major differences in the subtypes and isoforms of RXR are in the AB region. To date, there have been no data concerning the molecular properties of the AB region of hRXRγ (AB_hRXG). Here, we describe the biochemical and biophysical properties of the recombinant AB_hRXG. The results indicate that AB_hRXG shows the structural and functional characteristics of the pre-molten globule-like (PMG-like) group of intrinsically disordered proteins (IDPs) and also has a significant propensity for folding. We also present the first experimental evidence showing that the AB region of NRs promotes the formation of liquid-liquid phase separation (LLPS).
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Affiliation(s)
- Katarzyna Sołtys
- Department of Biochemistry, Faculty of Chemistry, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wroclaw, Poland.
| | - Andrzej Ożyhar
- Department of Biochemistry, Faculty of Chemistry, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wroclaw, Poland
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5
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Xu A, Zhang N, Cao J, Zhu H, Yang B, He Q, Shao X, Ying M. Post-translational modification of retinoic acid receptor alpha and its roles in tumor cell differentiation. Biochem Pharmacol 2020; 171:113696. [DOI: 10.1016/j.bcp.2019.113696] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Accepted: 11/05/2019] [Indexed: 12/22/2022]
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6
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Chen L, Wu L, Zhu L, Zhao Y. Overview of the structure-based non-genomic effects of the nuclear receptor RXRα. Cell Mol Biol Lett 2018; 23:36. [PMID: 30093910 PMCID: PMC6080560 DOI: 10.1186/s11658-018-0103-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 07/27/2018] [Indexed: 12/12/2022] Open
Abstract
The nuclear receptor RXRα (retinoid X receptor-α) is a transcription factor that regulates the expression of multiple genes. Its non-genomic function is largely related to its structure, polymeric forms and modification. Previous research revealed that some non-genomic activity of RXRα occurs via formation of heterodimers with Nur77. RXRα-Nur77 heterodimers translocate from the nucleus to the mitochondria in response to certain apoptotic stimuli and this activity correlates with cell apoptosis. More recent studies revealed a significant role for truncated RXRα (tRXRα), which interacts with the p85α subunit of the PI3K/AKT signaling pathway, leading to enhanced activation of AKT and promoting cell growth in vitro and in animals. We recently reported on a series of NSAID sulindac analogs that can bind to tRXRα through a unique binding mechanism. We also identified one analog, K-80003, which can inhibit cancer cell growth by inducing tRXRα to form a tetramer, thus disrupting p85α-tRXRα interaction. This review analyzes the non-genomic effects of RXRα in normal and tumor cells, and discusses the functional differences based on RXRα protein structure (structure source: the RCSB Protein Data Bank).
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Affiliation(s)
- Liqun Chen
- College of Biological Science and Engineering, Fuzhou University, Fuzhou, 350108 China
| | - Lingjuan Wu
- College of Biological Science and Engineering, Fuzhou University, Fuzhou, 350108 China
| | - Linyan Zhu
- College of Biological Science and Engineering, Fuzhou University, Fuzhou, 350108 China
| | - Yiyi Zhao
- College of Biological Science and Engineering, Fuzhou University, Fuzhou, 350108 China
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7
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Becares N, Gage MC, Pineda-Torra I. Posttranslational Modifications of Lipid-Activated Nuclear Receptors: Focus on Metabolism. Endocrinology 2017; 158:213-225. [PMID: 27925773 PMCID: PMC5413085 DOI: 10.1210/en.2016-1577] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 12/02/2016] [Indexed: 12/18/2022]
Abstract
Posttranslational modifications (PTMs) occur to nearly all proteins, are catalyzed by specific enzymes, and are subjected to tight regulation. They have been shown to be a powerful means by which the function of proteins can be modified, resulting in diverse effects. Technological advances such as the increased sensitivity of mass spectrometry-based techniques and availability of mutant animal models have enhanced our understanding of the complexities of their regulation and the effect they have on protein function. However, the role that PTMs have in a pathological context still remains unknown for the most part. PTMs enable the modulation of nuclear receptor function in a rapid and reversible manner in response to varied stimuli, thereby dramatically altering their activity in some cases. This review focuses on acetylation, phosphorylation, SUMOylation, and O-GlcNAcylation, which are the 4 most studied PTMs affecting lipid-regulated nuclear receptor biology, as well as on the implications of such modifications on metabolic pathways under homeostatic and pathological situations. Moreover, we review recent studies on the modulation of PTMs as therapeutic targets for metabolic diseases.
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Affiliation(s)
- Natalia Becares
- Centre for Clinical Pharmacology, Division of Medicine, University College of London, London, United Kingdom
| | - Matthew C Gage
- Centre for Clinical Pharmacology, Division of Medicine, University College of London, London, United Kingdom
| | - Inés Pineda-Torra
- Centre for Clinical Pharmacology, Division of Medicine, University College of London, London, United Kingdom
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8
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Jusu S, Presley JF, Kremer R. Phosphorylation of Human Retinoid X Receptor α at Serine 260 Impairs Its Subcellular Localization, Receptor Interaction, Nuclear Mobility, and 1α,25-Dihydroxyvitamin D3-dependent DNA Binding in Ras-transformed Keratinocytes. J Biol Chem 2017; 292:1490-1509. [PMID: 27852823 PMCID: PMC5270490 DOI: 10.1074/jbc.m116.758185] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 10/14/2016] [Indexed: 11/06/2022] Open
Abstract
Human retinoid X receptor α (hRXRα) plays a critical role in DNA binding and transcriptional activity through heterodimeric association with several members of the nuclear receptor superfamily, including the human vitamin D receptor (hVDR). We previously showed that hRXRα phosphorylation at serine 260 through the Ras-Raf-MAPK ERK1/2 activation is responsible for resistance to the growth inhibitory effects of 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3), the biologically active metabolite of vitamin D3 To further investigate the mechanism of this resistance, we studied intranuclear dynamics of hVDR and hRXRα-tagged constructs in living cells together with endogenous and tagged protein in fixed cells. We find that hVDR-, hRXRα-, and hVDR-hRXRα complex accumulate in the nucleus in 1α,25(OH)2D3-treated HPK1A cells but to a lesser extent in HPK1ARas-treated cells. Also, by using fluorescence resonance energy transfer (FRET), we demonstrate increased interaction of the hVDR-hRXRα complex in 1α,25(OH)2D3-treated HPK1A but not HPK1ARas cells. In HPK1ARas cells, 1α,25(OH)2D3-induced nuclear localization and interaction of hRXRα are restored when cells are treated with the MEK1/2 inhibitor UO126 or following transfection of the non-phosphorylatable hRXRα Ala-260 mutant. Finally, we demonstrate using fluorescence loss in photobleaching and quantitative co-localization with chromatin that RXR immobilization and co-localization with chromatin are significantly increased in 1α,25(OH)2D3-treated HPK1ARas cells transfected with the non-phosphorylatable hRXRα Ala-260 mutant. This suggests that hRXRα phosphorylation significantly disrupts its nuclear localization, interaction with VDR, intra-nuclear trafficking, and binding to chromatin of the hVDR-hRXR complex.
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Affiliation(s)
- Sylvester Jusu
- From the Department of Medicine, Calcium Research Laboratory, Royal Victoria Hospital, McGill University, Montreal, Quebec H4A 3J1
- the Department of Medicine, Experimental Therapeutics and Metabolism Program, McGill University Health Center, Montreal, Quebec H4A 3J1, Canada
| | - John F Presley
- the Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 0C7, and
| | - Richard Kremer
- From the Department of Medicine, Calcium Research Laboratory, Royal Victoria Hospital, McGill University, Montreal, Quebec H4A 3J1,
- the Department of Medicine, Experimental Therapeutics and Metabolism Program, McGill University Health Center, Montreal, Quebec H4A 3J1, Canada
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9
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Synergic stress in striped catfish (Pangasianodon hypophthalmus, S.) exposed to chronic salinity and bacterial infection: Effects on kidney protein expression profile. J Proteomics 2016; 142:91-101. [DOI: 10.1016/j.jprot.2016.04.046] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Revised: 04/28/2016] [Accepted: 04/28/2016] [Indexed: 12/14/2022]
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10
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Zhang X, Zhou H, Su Y. Targeting truncated RXRα for cancer therapy. Acta Biochim Biophys Sin (Shanghai) 2016; 48:49-59. [PMID: 26494413 DOI: 10.1093/abbs/gmv104] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 08/24/2015] [Indexed: 01/08/2023] Open
Abstract
Retinoid X receptor-alpha (RXRα), a unique member of the nuclear receptor superfamily, is a well-established drug target, representing one of the most important targets for pharmacologic interventions and therapeutic applications for cancer. However, how RXRα regulates cancer cell growth and how RXRα modulators suppress tumorigenesis are poorly understood. Altered expression and aberrant function of RXRα are implicated in the development of cancer. Previously, several studies had demonstrated the presence of N-terminally truncated RXRα (tRXRα) proteins resulted from limited proteolysis of RXRα in tumor cells. Recently, we discovered that overexpression of tRXRα can promote tumor growth by interacting with tumor necrosis factor-alpha-induced phosphoinositide 3-kinase and NF-κB signal transduction pathways. We also identified nonsteroidal anti-inflammatory drug Sulindac and analogs as effective inhibitors of tRXRα activities via a unique binding mechanism. This review discusses the emerging roles of tRXRα and modulators in the regulation of cancer cell survival and death as well as inflammation and our recent understanding of tRXRα regulation by targeting the alternate binding sites on its surface.
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Affiliation(s)
- Xiaokun Zhang
- School of Pharmaceutical Sciences, Xiamen University, Xiamen 361102, China Sanford Burnham Prebys Medical Discovery Institute, Cancer Center, La Jolla, CA 92037, USA
| | - Hu Zhou
- School of Pharmaceutical Sciences, Xiamen University, Xiamen 361102, China
| | - Ying Su
- School of Pharmaceutical Sciences, Xiamen University, Xiamen 361102, China Sanford Burnham Prebys Medical Discovery Institute, Cancer Center, La Jolla, CA 92037, USA
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11
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Kovalevich J, Yen W, Ozdemir A, Langford D. Cocaine induces nuclear export and degradation of neuronal retinoid X receptor-γ via a TNF-α/JNK- mediated mechanism. J Neuroimmune Pharmacol 2015; 10:55-73. [PMID: 25586717 PMCID: PMC4336643 DOI: 10.1007/s11481-014-9573-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Accepted: 11/26/2014] [Indexed: 12/14/2022]
Abstract
Cocaine abuse represents an immense societal health and economic burden for which no effective treatment currently exists. Among the numerous intracellular signaling cascades impacted by exposure to cocaine, increased and aberrant production of pro-inflammatory cytokines in the CNS has been observed. Additionally, we have previously reported a decrease in retinoid-X-receptor-gamma (RXR-γ) in brains of mice chronically exposed to cocaine. Through obligate heterodimerization with a number of nuclear receptors, RXRs serve as master regulatory transcription factors, which can potentiate or suppress expression of a wide spectrum of genes. Little is known about the regulation of RXR levels, but previous studies indicate cellular stressors such as cytokines negatively regulate levels of RXRs in vitro. To evaluate the mechanism underlying the cocaine-induced decreases in RXR-γ levels observed in vivo, we exposed neurons to cocaine in vitro and examined pathways which may contribute to disruption in RXR signaling, including activation of stress pathways by cytokine induction. In these studies, we provide the first evidence that cocaine exposure disrupts neuronal RXR-γ signaling in vitro by promoting its nuclear export and degradation. Furthermore, we demonstrate this effect may be mediated, at least in part, by cocaine-induced production of TNF-α and its downstream effector c-Jun-NH-terminal kinase (JNK). Findings from this study are therefore applicable to both cocaine abuse and to pathological conditions characterized by neuroinflammatory factors, such as neurodegenerative disease.
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Affiliation(s)
- Jane Kovalevich
- Department of Neuroscience, Temple University School of Medicine, Medical Education Research Building, 3500 North Broad Street, Philadelphia, PA, 19140, USA
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12
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Smith KP, Gifford KM, Waitzman JS, Rice SE. Survey of phosphorylation near drug binding sites in the Protein Data Bank (PDB) and their effects. Proteins 2015; 83:25-36. [PMID: 24833420 PMCID: PMC4233198 DOI: 10.1002/prot.24605] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Revised: 04/28/2014] [Accepted: 05/09/2014] [Indexed: 12/21/2022]
Abstract
While it is currently estimated that 40 to 50% of eukaryotic proteins are phosphorylated, little is known about the frequency and local effects of phosphorylation near pharmaceutical inhibitor binding sites. In this study, we investigated how frequently phosphorylation may affect the binding of drug inhibitors to target proteins. We examined the 453 non-redundant structures of soluble mammalian drug target proteins bound to inhibitors currently available in the Protein Data Bank (PDB). We cross-referenced these structures with phosphorylation data available from the PhosphoSitePlus database. Three hundred twenty-two of 453 (71%) of drug targets have evidence of phosphorylation that has been validated by multiple methods or labs. For 132 of 453 (29%) of those, the phosphorylation site is within 12 Å of the small molecule-binding site, where it would likely alter small molecule binding affinity. We propose a framework for distinguishing between drug-phosphorylation site interactions that are likely to alter the efficacy of drugs versus those that are not. In addition we highlight examples of well-established drug targets, such as estrogen receptor alpha, for which phosphorylation may affect drug affinity and clinical efficacy. Our data suggest that phosphorylation may affect drug binding and efficacy for a significant fraction of drug target proteins.
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Affiliation(s)
- Kyle P Smith
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, 60611
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13
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A Role for Acyclic Retinoid in the Chemoprevention of Hepatocellular Carcinoma: Therapeutic Strategy Targeting Phosphorylated Retinoid X Receptor-α. Diseases 2014. [DOI: 10.3390/diseases2030226] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
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14
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Pan J, Guleria RS, Zhu S, Baker KM. Molecular Mechanisms of Retinoid Receptors in Diabetes-Induced Cardiac Remodeling. J Clin Med 2014; 3:566-94. [PMID: 26237391 PMCID: PMC4449696 DOI: 10.3390/jcm3020566] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Revised: 03/17/2014] [Accepted: 03/25/2014] [Indexed: 02/07/2023] Open
Abstract
Diabetic cardiomyopathy (DCM), a significant contributor to morbidity and mortality in diabetic patients, is characterized by ventricular dysfunction, in the absence of coronary atherosclerosis and hypertension. There is no specific therapeutic strategy to effectively treat patients with DCM, due to a lack of a mechanistic understanding of the disease process. Retinoic acid, the active metabolite of vitamin A, is involved in a wide range of biological processes, through binding and activation of nuclear receptors: retinoic acid receptors (RAR) and retinoid X receptors (RXR). RAR/RXR-mediated signaling has been implicated in the regulation of glucose and lipid metabolism. Recently, it has been reported that activation of RAR/RXR has an important role in preventing the development of diabetic cardiomyopathy, through improving cardiac insulin resistance, inhibition of intracellular oxidative stress, NF-κB-mediated inflammatory responses and the renin-angiotensin system. Moreover, downregulated RAR/RXR signaling has been demonstrated in diabetic myocardium, suggesting that impaired RAR/RXR signaling may be a trigger to accelerate diabetes-induced development of DCM. Understanding the molecular mechanisms of retinoid receptors in the regulation of cardiac metabolism and remodeling under diabetic conditions is important in providing the impetus for generating novel therapeutic approaches for the prevention and treatment of diabetes-induced cardiac complications and heart failure.
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Affiliation(s)
- Jing Pan
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
| | - Rakeshwar S Guleria
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
| | - Sen Zhu
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
| | - Kenneth M Baker
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
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Abstract
The discovery of retinoic acid receptors arose from research into how vitamins are essential for life. Early studies indicated that Vitamin A was metabolized into an active factor, retinoic acid (RA), which regulates RNA and protein expression in cells. Each step forward in our understanding of retinoic acid in human health was accomplished by the development and application of new technologies. Development cDNA cloning techniques and discovery of nuclear receptors for steroid hormones provided the basis for identification of two classes of retinoic acid receptors, RARs and RXRs, each of which has three isoforms, α, β and ɣ. DNA manipulation and crystallographic studies revealed that the receptors contain discrete functional domains responsible for binding to DNA, ligands and cofactors. Ligand binding was shown to induce conformational changes in the receptors that cause release of corepressors and recruitment of coactivators to create functional complexes that are bound to consensus promoter DNA sequences called retinoic acid response elements (RAREs) and that cause opening of chromatin and transcription of adjacent genes. Homologous recombination technology allowed the development of mice lacking expression of retinoic acid receptors, individually or in various combinations, which demonstrated that the receptors exhibit vital, but redundant, functions in fetal development and in vision, reproduction, and other functions required for maintenance of adult life. More recent advancements in sequencing and proteomic technologies reveal the complexity of retinoic acid receptor involvement in cellular function through regulation of gene expression and kinase activity. Future directions will require systems biology approaches to decipher how these integrated networks affect human stem cells, health, and disease.
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16
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Piskunov A, Al Tanoury Z, Rochette-Egly C. Nuclear and extra-nuclear effects of retinoid acid receptors: how they are interconnected. Subcell Biochem 2014; 70:103-127. [PMID: 24962883 DOI: 10.1007/978-94-017-9050-5_6] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The nuclear retinoic acid receptors (RAR α, β and γ) and their isoforms are ligand-dependent regulators of transcription Transcription , which mediate the effects of all-trans retinoic acid (RA), the active endogenous metabolite of Vitamin A. They heterodimerize with Retinoid X Receptors (RXRs α, β and γ), and regulate the expression of a battery of target genes Target genes involved in cell growth and differentiation Differentiation . During the two last decades, the description of the crystallographic structures of RARs, the characterization of the polymorphic response elements of their target genes Target genes , and the identification of the multiprotein complexes involved in their transcriptional activity have provided a wealth of information on their pleiotropic effects. However, the regulatory scenario became even more complicated once it was discovered that RARs are phosphoproteins and that RA can activate kinase signaling cascades via a pool of RARs present in membrane lipid rafts. Now it is known that these RA-activated kinases Kinases translocate to the nucleus where they phosphorylate RARs and other retinoid signaling factors. The phosphorylation Phosphorylation state of the RARs dictates whether the transcriptional programs which are known to be induced by RA are facilitated and/or switched on. Thus, kinase signaling pathways appear to be crucial for fine-tuning the appropriate physiological activity of RARs.
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Affiliation(s)
- Aleksandr Piskunov
- IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), INSERM, U964, CNRS, UMR7104, Université de Strasbourg, 1 rue Laurent Fries, BP 10142, 67404, Illkirch Cedex, France,
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17
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Protein tyrosine phosphatase inhibition down-regulates ligand-induced ABCA1 expression. Atherosclerosis 2013; 228:362-9. [DOI: 10.1016/j.atherosclerosis.2013.03.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Revised: 02/05/2013] [Accepted: 03/09/2013] [Indexed: 11/22/2022]
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18
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Moskalev A, Plyusnina E, Shaposhnikov M, Shilova L, Kazachenok A, Zhavoronkov A. The role of D-GADD45 in oxidative, thermal and genotoxic stress resistance. Cell Cycle 2012; 11:4222-41. [PMID: 23095639 PMCID: PMC3524218 DOI: 10.4161/cc.22545] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
There is a relationship between various cellular stress factors and aging. In earlier studies, we demonstrated that overexpression of the D-GADD45 gene increases the life span of Drosophila melanogaster. In this study, we investigate the relationship between D-GADD45 activity and resistance to oxidative, genotoxic and thermal stresses as well as starvation. In most cases, flies with constitutive and conditional D-GADD45 overexpression in the nervous system were more stress-resistant than ones without overexpression. At the same time, most of the studied stress factors increased D-GADD45 expression in the wild-type strain. The lifespan-extending effect of D-GADD45 overexpression was also retained after exposure to chronic and acute gamma-irradiation, with doses of 40 сGy and 30 Gy, respectively. However, knocking out D-GADD45 resulted in a significant reduction in lifespan, lack of radiation hormesis and radioadaptive response. A dramatic decrease in the spontaneous level of D-GADD45 expression was observed in the nervous system as age progressed, which may be one of the causes of the age-related deterioration of organismal stress resistance. Thus, D-GADD45 expression is activated by most of the studied stress factors, and D-GADD45 overexpression resulted in an increase of stress resistance.
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Affiliation(s)
- Alexey Moskalev
- Laboratory of Molecular Radiobiology and Gerontology, Institute of Biology, Komi Science Center of Russian Academy of Sciences, Syktyvkar, Russia.
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19
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Zassadowski F, Rochette-Egly C, Chomienne C, Cassinat B. Regulation of the transcriptional activity of nuclear receptors by the MEK/ERK1/2 pathway. Cell Signal 2012; 24:2369-77. [PMID: 22906493 DOI: 10.1016/j.cellsig.2012.08.003] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Accepted: 08/09/2012] [Indexed: 01/08/2023]
Abstract
Cells undergo continuous and simultaneous external influences regulating their behavior. As an example, during differentiation, they go through different stages of maturation and gene expression is regulated by several simultaneous signaling pathways. We often tend at separating the nuclear pathways from the signaling ones initiated at membrane receptors. However, it is essential to keep in mind that all these pathways are interconnected to achieve a fine regulation of cell functions. The regulation of transcription by nuclear receptors has been thoroughly studied, but it now appears that a critical level of this regulation involves the action of several kinases that target the nuclear receptors themselves as well as their partners. The purpose of this review is to highlight the importance of one family of the mitogen-activated protein kinase (MAPK) superfamily, the MEK/ERK1/2 pathway, in the transcriptional activity of nuclear receptors.
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20
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Singh AB, Guleria RS, Nizamutdinova IT, Baker KM, Pan J. High glucose-induced repression of RAR/RXR in cardiomyocytes is mediated through oxidative stress/JNK signaling. J Cell Physiol 2012; 227:2632-44. [PMID: 21882190 DOI: 10.1002/jcp.23005] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The biological actions of retinoids are mediated by nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs). We have recently reported that decreased expression of RARα and RXRα has an important role in high glucose (HG)-induced cardiomyocyte apoptosis. However, the regulatory mechanisms of HG effects on RARα and RXRα remain unclear. Using neonatal cardiomyocytes, we found that ligand-induced promoter activity of RAR and RXR was significantly suppressed by HG. HG promoted protein destabilization and serine-phosphorylation of RARα and RXRα. Proteasome inhibitor MG132 blocked the inhibitory effect of HG on RARα and RXRα. Inhibition of intracellular reactive oxidative species (ROS) abolished the HG effect. In contrast, H(2)O(2) stimulation suppressed the expression and ligand-induced promoter activity of RARα and RXRα. HG promoted phosphorylation of ERK1/2, JNK and p38 MAP kinases, which was abrogated by an ROS inhibitor. Inhibition of JNK, but not ERK and p38 activity, reversed HG effects on RARα and RXRα. Activation of JNK by over expressing MKK7 and MEKK1, resulted in significant downregulation of RARα and RXRα. Ligand-induced promoter activity of RARα and RXRα was also suppressed by overexpression of MEKK1. HG-induced cardiomyocyte apoptosis was potentiated by activation of JNK, and prevented by all-trans retinoic acid and inhibition of JNK. Silencing the expression of RARα and RXRα activated the JNK pathway. In conclusion, HG-induced oxidative stress and activation of the JNK pathway negatively regulated expression/activation of RAR and RXR. The impaired RAR/RXR signaling and oxidative stress/JNK pathway forms a vicious circle, which significantly contributes to hyperglycemia induced cardiomyocyte apoptosis.
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Affiliation(s)
- Amar B Singh
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A&M Health Science Center, Central Texas Veterans Health Care System, Temple, Texas 76504, USA
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21
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Map2k4 functions as a tumor suppressor in lung adenocarcinoma and inhibits tumor cell invasion by decreasing peroxisome proliferator-activated receptor γ2 expression. Mol Cell Biol 2011; 31:4270-85. [PMID: 21896780 DOI: 10.1128/mcb.05562-11] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
MAP2K4 encodes a dual-specificity kinase (mitogen-activated protein kinase kinase 4, or MKK4) that is mutated in a variety of human malignancies, but the biochemical properties of the mutant kinases and their roles in tumorigenesis have not been fully elucidated. Here we showed that 8 out of 11 cancer-associated MAP2K4 mutations reduce MKK4 protein stability or impair its kinase activity. On the basis of findings from bioinformatic studies on human cancer cell lines with homozygous MAP2K4 loss, we posited that MKK4 functions as a tumor suppressor in lung adenocarcinomas that develop in mice owing to expression of mutant Kras and Tp53. Conditional Map2k4 inactivation in the bronchial epithelium of mice had no discernible effect alone but increased the multiplicity and accelerated the growth of incipient lung neoplasias induced by oncogenic Kras. MKK4 suppressed the invasion and metastasis of Kras-Tp53-mutant lung adenocarcinoma cells. MKK4 deficiency increased peroxisomal proliferator-activated receptor γ2 (PPARγ2) expression through noncanonical MKK4 substrates, and PPARγ2 enhanced tumor cell invasion. We conclude that Map2k4 functions as a tumor suppressor in lung adenocarcinoma and inhibits tumor cell invasion by decreasing PPARγ2 levels.
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22
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Zhang Z, Kovalenko P, Cui M, Desmet M, Clinton SK, Fleet JC. Constitutive activation of the mitogen-activated protein kinase pathway impairs vitamin D signaling in human prostate epithelial cells. J Cell Physiol 2010; 224:433-42. [PMID: 20432439 DOI: 10.1002/jcp.22139] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We studied the effect of prolonged activation of mitogen-activated protein kinase (MAPK) signaling on 1,25 dihydroxyvitamin D (1,25(OH)(2)D(3)) action in the immortalized human prostate epithelial cell line RWPE1 and its Ki-Ras transformed clone RWPE2. 1,25(OH)(2)D(3)-treatment caused growth arrest and induced gene expression in both cell lines but the response was blunted in RWPE2 cells. Vitamin D receptor (VDR) levels were lower in RWPE2 cells but VDR over-expression did not increase vitamin-D-mediated gene transcription in either cell line. In contrast, MAPK inhibition restored normal vitamin D transcriptional responses in RWPE2 cells and MAPK activation with constitutively active MEK1R4F reduced vitamin-D-regulated transcription in RWPE1 cells. 1,25(OH)(2)D(3)-mediated transcription depends upon the VDR and its heterodimeric partner the retinoid X receptor (RXR) so we studied whether changes in the VDR-RXR transcription complex occur in response to MAPK activation. Mutation of putative phosphorylation sites in the activation function 1 (AF-1) domain (S32A, T82A) of RXRalpha restored 1,25(OH)(2)D(3)-mediated transactivation in RWPE2 cells. Mammalian two-hybrid and co-immunoprecipitation assays revealed a vitamin-D-independent interaction between steroid receptor co-activator-1 (SRC-1) and RXRalpha that was reduced by MAPK activation and was restored in RWPE2 cells by mutating S32 and T82 in the RXRalpha AF-1 domain. Our data show that a common contributor to cancer development, prolonged activation of MAPK signaling, impairs 1,25(OH)(2)D(3)-mediated transcription in prostate epithelial cells. This is due in part to the phosphorylation of critical amino acids in the RXRalpha AF-1 domain and impaired co-activator recruitment.
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Affiliation(s)
- Zhentao Zhang
- Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana 47907-2059, USA
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23
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Kosters A, White DD, Sun H, Thevananther S, Karpen SJ. Redundant roles for cJun-N-terminal kinase 1 and 2 in interleukin-1beta-mediated reduction and modification of murine hepatic nuclear retinoid X receptor alpha. J Hepatol 2009; 51:898-908. [PMID: 19767119 PMCID: PMC2818213 DOI: 10.1016/j.jhep.2009.06.029] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 05/29/2009] [Accepted: 06/23/2009] [Indexed: 01/28/2023]
Abstract
BACKGROUND/AIMS Retinoid X receptor alpha (RXRalpha), the heterodimeric partner for multiple nuclear receptors (NRs), was shown to be an essential target for inflammation-induced cJun-N-terminal kinase (JNK) signaling in vitro. This study aimed to explore the role of hepatic JNK signaling and its effects on nuclear RXRalpha levels downstream of interleukin-1beta (IL-1beta) in vivo. METHODS Effects of IL-1beta on hepatic NR-dependent gene expression, nuclear RXRalpha levels, and roles for individual JNK isoforms were studied in wild-type, Jnk1(-/-), and Jnk2(-/-) mice and in primary hepatocytes of each genotype. RESULTS IL-1beta administration showed a time-dependent reduction in expression of the hepatic NR-dependent genes Ntcp, Cyp7a1, Cyp8b1, Abcg5, Mrp2, and Mrp3. IL-1beta treatment for 1h activated JNK and resulted in both post-translational modification and reduction of nuclear RXRalpha. In wild-type primary hepatocytes, IL-1beta modified and reduced nuclear RXRalpha levels time dependently, which was prevented by chemical inhibition of JNK as well as by inhibition of proteasomal degradation. Individual absence of either JNK1 or JNK2 did not significantly influence the reduction or modification of hepatic nuclear RXRalpha by IL-1beta both in vivo and in primary hepatocytes. CONCLUSIONS Functional redundancy exists for JNK1 and JNK2 in IL-1beta-mediated alterations of hepatic nuclear RXRalpha levels, stressing the importance of this pathway in mediating the hepatic response to inflammation.
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Affiliation(s)
- Astrid Kosters
- Texas Children's Liver Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
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24
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Jivan A, Earnest S, Juang YC, Cobb MH. Radial spoke protein 3 is a mammalian protein kinase A-anchoring protein that binds ERK1/2. J Biol Chem 2009; 284:29437-45. [PMID: 19684019 DOI: 10.1074/jbc.m109.048181] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Initially identified in Chlamydomonas, RSP3 (radial spoke protein 3) is 1 of more than 20 identified radial spoke structural components of motile cilia and is required for axonemal sliding and flagellar motility. The mammalian orthologs for this and other radial spoke proteins, however, remain to be characterized. We found mammalian RSP3 to bind to the MAPK ERK2 through a yeast two-hybrid screen designed to identify interacting proteins that have a higher affinity for the phosphorylated, active form of the protein kinase. Consistent with the screening result, the human homolog, RSPH3, interacts with and is a substrate for ERK1/2. Moreover, RSPH3 is a protein kinase A-anchoring protein (AKAP) that scaffolds the cAMP-dependent protein kinase holoenzyme. The binding of RSPH3 to the regulatory subunits of cAMP-dependent protein kinase, RIIalpha and RIIbeta, is regulated by ERK1/2 activity and phosphorylation. Here we describe an ERK1/2-interacting AKAP and suggest a mechanism by which cAMP-dependent protein kinase-AKAP binding can be modulated by the activity of other enzymes.
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Affiliation(s)
- Arif Jivan
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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25
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Shimizu M, Takai K, Moriwaki H. Strategy and mechanism for the prevention of hepatocellular carcinoma: phosphorylated retinoid X receptor alpha is a critical target for hepatocellular carcinoma chemoprevention. Cancer Sci 2009; 100:369-74. [PMID: 19068086 PMCID: PMC11159360 DOI: 10.1111/j.1349-7006.2008.01045.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Hepatocellular carcinoma (HCC) is a major health care problem worldwide. The prognosis of patients with HCC is poor because even in the early stages when surgical treatment might be expected to be curative, the incidence of recurrence in patients with underlying cirrhosis is very high due to multicentric carcinogenesis. Therefore, strategies to prevent recurrence and second primary HCC are required to improve the prognosis. One of the most practical approaches to prevent the multicentric development of HCC is 'clonal deletion' therapy, which is defined as the removal of latent (i.e. invisible) (pre)malignant clones from the liver in a hypercarcinogenic state. Retinoids, a group of structural and functional analogs of vitamin A, exert their biological function primarily through two distinct nuclear receptors, retinoic acid receptors and retinoid X receptors (RXR), and abnormalities in the expression and function of these receptors are highly associated with the development of various cancers, including HCC. In particular, a malfunction of RXRalpha due to phosphorylation by the Ras-mitogen-activated protein kinase signaling pathway is profoundly associated with the development of HCC and thus may be a critical target for HCC chemoprevention. Acyclic retinoid, which has been clinically shown to reduce the incidence of a post-therapeutic recurrence of HCC, can inhibit Ras activity and phosphorylation of the extracellular signal-regulated kinase and RXRalpha proteins. In conclusion, the inhibition of RXRalpha phosphorylation and the restoration of its physiological function as a master regulator for nuclear receptors may be a potentially effective strategy for HCC chemoprevention and clonal deletion. Acyclic retinoid, which targets phosphorylated RXRalpha, may thus play a critical role in preventing the development of multicentric HCC.
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Affiliation(s)
- Masahito Shimizu
- Department of Medicine, Gifu University Graduate School of Medicine, Gifu, Japan.
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26
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Cui M, Zhao Y, Hance KW, Shao A, Wood RJ, Fleet JC. Effects of MAPK signaling on 1,25-dihydroxyvitamin D-mediated CYP24 gene expression in the enterocyte-like cell line, Caco-2. J Cell Physiol 2009; 219:132-42. [PMID: 19097033 DOI: 10.1002/jcp.21657] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We examined the role of the extracellular signal regulated kinases (ERK) in 1,25-dihydroxyvitamin D (1,25(OH)(2)D(3))-induced gene expression in the differentiated Caco-2 cells. 1,25(OH)(2)D(3)-regulated expression of the 25-hydroxyvitamin D, 24-hydroxylase (CYP24) gene (both natural gene and promoter construct) was strongly modulated by altering ERK activity (i.e., reduced by MEK inhibitors and dominant negative (dn) ERK1 and ERK2, activated by epidermal growth factor) but ERK inhibition had no effect on 1,25(OH)(2)D(3)-regulated expression of the transient receptor potential cation channel, subfamily V, member 6 (TRPV6). ERK5-mediated phosphorylation of the transcription factor Ets-1 enhanced 1,25(OH)(2)D(3)-mediated CYP24 gene transcription in proliferating but not differentiated Caco-2 cells due to reduced levels of ERK5 and Ets-1 (total and phosphoprotein levels) in differentiated cells. MEK inhibition reduced 1,25(OH)(2)D(3)-induced 3X-VDRE promoter activity but had no impact on the association of vitamin D receptor (VDR) with chromatin suggesting a role for co-activator recruitment in ERK-modulation of vitamin D-regulated CYP24 gene activation. Chromatin immunoprecipitation assays revealed that the ERK1/2 target, mediator 1 (MED1), is recruited to the CYP24, but not the TRPV6, promoter following 1,25(OH)(2)D(3) treatment. MED1 phosphorylation was sensitive to activators and inhibitors of the ERK1/2 signaling and MED1 siRNA reduced 1,25(OH)(2)D(3)-regulated human CYP24 promoter activity. This suggests ERK1/2 signaling enhances 1,25(OH)(2)D(3) effects on the CYP24 promoter by MED1-mediated events. Our data show that there are both promoter-specific and cell stage-specific roles for the ERK signaling pathway on 1,25(OH)(2)D(3)-mediated gene induction in enterocyte-like Caco-2 cells.
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Affiliation(s)
- Min Cui
- Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana 47906-2059, USA
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27
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Hepatocellular transport in acquired cholestasis: new insights into functional, regulatory and therapeutic aspects. Clin Sci (Lond) 2008; 114:567-88. [PMID: 18377365 DOI: 10.1042/cs20070227] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The recent overwhelming advances in molecular and cell biology have added enormously to our understanding of the physiological processes involved in bile formation and, by extension, to our comprehension of the consequences of their alteration in cholestatic hepatopathies. The present review addresses in detail this new information by summarizing a number of recent experimental findings on the structural, functional and regulatory aspects of hepatocellular transporter function in acquired cholestasis. This comprises (i) a short overview of the physiological mechanisms of bile secretion, including the nature of the transporters involved and their role in bile formation; (ii) the changes induced by nuclear receptors and hepatocyte-enriched transcription factors in the constitutive expression of hepatocellular transporters in cholestasis, either explaining the primary biliary failure or resulting from a secondary adaptive response; (iii) the post-transcriptional changes in transporter function and localization in cholestasis, including a description of the subcellular structures putatively engaged in the endocytic internalization of canalicular transporters and the involvement of signalling cascades in this effect; and (iv) a discussion on how this new information has contributed to the understanding of the mechanism by which anticholestatic agents exert their beneficial effects, or the manner in which it has helped the design of new successful therapeutic approaches to cholestatic liver diseases.
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28
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Kacevska M, Robertson GR, Clarke SJ, Liddle C. Inflammation and CYP3A4-mediated drug metabolism in advanced cancer: impact and implications for chemotherapeutic drug dosing. Expert Opin Drug Metab Toxicol 2008; 4:137-49. [PMID: 18248309 DOI: 10.1517/17425255.4.2.137] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
BACKGROUND The inability to accurately predict treatment outcomes for cancer patients in terms of tumour response and anticancer drug toxicity is a severe limitation inherent in current approaches to chemotherapy. Many anticancer drugs are metabolically cleared by cytochrome P450 3A4 (CYP3A4), the predominant CYP expressed in liver. CYP3A4 expression exhibits marked interindividual variation and is repressed in acute inflammatory states. OBJECTIVES (1) To review the relevance of CYP3A4 variability to drug metabolism in the setting of cancer and to understand how inflammation associated with malignancy contributes to both this variability and to adverse treatment outcomes. (2) To examine the relationship between tumour-induced inflammation and repression of CYP3A4 and to explore methods of dosing of anticancer drugs in the setting of advanced cancer. METHODS Review of relevant literature covering both human and animal studies as well as in vitro mechanistic studies. RESULTS/CONCLUSIONS Interindividual variability in CYP3A4 expression is a major confounding factor for effective cancer treatment and methods to predict CYP3A4-mediated drug clearance may have clinical utility in this setting. Although acute inflammation has long been recognised to repress drug metabolism, it is now becoming apparent that cancer patients exhibiting clinical and laboratory features of an inflammatory response have reduced expression of CYP3A4 and possibly other genes relevant to anticancer drug disposition.
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Affiliation(s)
- Marina Kacevska
- University of Sydney, Storr Liver Unit, Westmead Millennium Institute, Westmead Hospital, Westmead, NSW, Australia
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29
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Staudinger JL, Lichti K. Cell signaling and nuclear receptors: new opportunities for molecular pharmaceuticals in liver disease. Mol Pharm 2008; 5:17-34. [PMID: 18159925 PMCID: PMC2387130 DOI: 10.1021/mp700098c] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Liver-enriched nuclear receptors (NRs) collectively function as metabolic and toxicological "sensors" that mediate liver-specific gene-activation in mammals. NR-mediated gene-environment interaction regulates important steps in the hepatic uptake, metabolism, and excretion of glucose, fatty acids, lipoproteins, cholesterol, bile acids, and xenobiotics. Hence, liver-enriched NRs play pivotal roles in the overall control of energy homeostasis in mammals. While it is well-recognized that ligand-binding is the primary mechanism behind activation of NRs, recent research reveals that multiple signal transduction pathways modulate NR-function in liver. The interface between specific signal transduction pathways and NRs helps to determine their overall responsiveness to various environmental and physiological stimuli. In general, phosphorylation of hepatic NRs regulates multiple biological parameters including their transactivation capacity, DNA binding, subcellular location, capacity to interact with protein-cofactors, and protein stability. Certain pathological conditions including inflammation, morbid obesity, hyperlipidemia, atherosclerosis, insulin resistance, and type-2 diabetes are known to modulate selected signal transduction pathways in liver. This review will focus upon recent insights regarding the molecular mechanisms that comprise the interface between disease-mediated activation of hepatic signal transduction pathways and liver-enriched NRs. This review will also highlight the exciting opportunities presented by this new knowledge to develop novel molecular and pharmaceutical strategies for combating these increasingly prevalent human diseases.
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Affiliation(s)
- Jeff L Staudinger
- University of Kansas, Department of Pharmacology and Toxicology, 1251 Wescoe Hall Dr, 5038 Malott Hall, Lawrence, Kansas 66045, USA.
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30
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Shimizu M, Moriwaki H. Synergistic Effects of PPARgamma Ligands and Retinoids in Cancer Treatment. PPAR Res 2008; 2008:181047. [PMID: 18528526 PMCID: PMC2408709 DOI: 10.1155/2008/181047] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 04/21/2008] [Accepted: 05/01/2008] [Indexed: 01/04/2023] Open
Abstract
Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily. The activation of PPARs by their specific ligands is regarded as one of the promising strategies to inhibit cancer cell growth. However, recent clinical trials targeting several common cancers showed no beneficial effect when PPAR ligands are used as a monotherapy. Retinoid X receptors (RXRs), which play a critical role in normal cell proliferation as a master regulator for nuclear receptors, preferentially form heterodimers with PPARs. A malfunction of RXRalpha due to phosphorylation by the Ras/MAPK signaling pathway is associated with the development of certain types of human malignancies. The activation of PPARgamma/RXR heterodimer by their respective ligands synergistically inhibits cell growth, while inducing apoptosis in human colon cancer cells when the phosphorylation of RXRalpha was inhibited. We herein review the synergistic antitumor effects produced by the combination of the PPAR, especially PPARgamma, ligands plus other agents, especially retinoids, in a variety of human cancers. We also focus on the phosphorylation of RXRalpha because the inhibition of RXRalpha phosphorylation and the restoration of its physiological function may activate PPAR/RXR heterodimer and, therefore, be a potentially effective and critical strategy for the inhibition of cancer cell growth.
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Affiliation(s)
- Masahito Shimizu
- Department of Medicine, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan
| | - Hisataka Moriwaki
- Department of Medicine, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan
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31
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Yoshimura K, Muto Y, Shimizu M, Matsushima-Nishiwaki R, Okuno M, Takano Y, Tsurumi H, Kojima S, Okano Y, Moriwaki H. Phosphorylated retinoid X receptor alpha loses its heterodimeric activity with retinoic acid receptor beta. Cancer Sci 2007; 98:1868-74. [PMID: 17900311 PMCID: PMC11159768 DOI: 10.1111/j.1349-7006.2007.00621.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2007] [Revised: 07/30/2007] [Accepted: 08/16/2007] [Indexed: 11/29/2022] Open
Abstract
A malfunction in retinoid X receptor (RXR) alpha due to phosphorylation is associated with the development of hepatocellular carcinoma. However, the precise mechanisms by which phosphorylated RXRalpha loses its physiological function remain unclear. In the present study we examined whether phosphorylation of RXRalpha affects its dimeric activity. Fluorescence resonance energy transfer studies and immunoprecipitation assays showed that the physical interaction between RXRalpha and retinoic acid receptor beta was impaired when 293T cells were transfected with phosphomimic mutant RXRalpha (T82D/S260D), whereas this interaction was activated at a level similar to wild-type RXRalpha-transfected cells when the cells were transfected with an unphosphorylated mutant RXRalpha (T82A/S260A). Treating the T82A/S260A-transfected cells with retinoid resulted in a significant increase in the transcriptional activities of the retinoic acid receptor responsive element and RXR responsive element promoters, whereas these transcriptional activities did not increase in the T82D/S260D-transfected cells. Transfection with T82A/S260A enhanced both the inhibition of cell growth and the induction of apoptosis caused by retinoid, although the T82D/S260D-transfected cells lost their responsiveness to retinoid. Moreover, transfection with T82A/S260A caused an inhibition of cell growth and a reduction of colony-forming ability in soft agar in HuH7 human hepatocellular carcinoma cells. These findings suggest that phosphorylation of RXRalpha abolishes its ability to form homodimers and heterodimers with RXR and retinoic acid receptor beta, thus resulting in the loss of cell growth control and the acceleration of cancer development. In conclusion, the inhibition of RXRalpha phosphorylation and the restoration of its original function as a master regulator of nuclear receptors might therefore be an effective strategy for controlling cancer cell growth.
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Affiliation(s)
- Kotaro Yoshimura
- Department of Medicine, Gifu University Graduate School of Medicine, Gifu, 501-1194, Japan
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32
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Abstract
Mitogen-activated protein (MAP) kinase kinase 4 (MKK4) is a component of stress activated MAP kinase signaling modules. It directly phosphorylates and activates the c-Jun N-terminal kinase (JNK) and p38 families of MAP kinases in response to environmental stress, pro-inflammatory cytokines and developmental cues. MKK4 is ubiquitously expressed and the targeted deletion of the Mkk4 gene in mice results in early embryonic lethality. Further studies in mice have indicated a role for MKK4 in liver formation, the immune system and cardiac hypertrophy. In humans, it is reported that loss of function mutations in the MKK4 gene are found in approximately 5% of tumors from a variety of tissues, suggesting it may have a tumor suppression function. Furthermore, MKK4 has been identified as a suppressor of metastasis of prostate and ovarian cancers. However, the role of MKK4 in cancer development appears complex as other studies support a pro-oncogenic role for MKK4 and JNK. Here we review the biochemical and functional properties of MKK4 and discuss the likely mechanisms by which it may regulate the steps leading to the formation of cancers.
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Affiliation(s)
- A J Whitmarsh
- Faculty of Life Sciences, University of Manchester, Manchester, UK
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33
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Sun K, Montana V, Chellappa K, Brelivet Y, Moras D, Maeda Y, Parpura V, Paschal BM, Sladek FM. Phosphorylation of a conserved serine in the deoxyribonucleic acid binding domain of nuclear receptors alters intracellular localization. Mol Endocrinol 2007; 21:1297-311. [PMID: 17389749 DOI: 10.1210/me.2006-0300] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Nuclear receptors (NRs) are a superfamily of transcription factors whose genomic functions are known to be activated by lipophilic ligands, but little is known about how to deactivate them or how to turn on their nongenomic functions. One obvious mechanism is to alter the nuclear localization of the receptors. Here, we show that protein kinase C (PKC) phosphorylates a highly conserved serine (Ser) between the two zinc fingers of the DNA binding domain of orphan receptor hepatocyte nuclear factor 4alpha (HNF4alpha). This Ser (S78) is adjacent to several positively charged residues (Arg or Lys), which we show here are involved in nuclear localization of HNF4alpha and are conserved in nearly all other NRs, along with the Ser/threonine (Thr). A phosphomimetic mutant of HNF4alpha (S78D) reduced DNA binding, transactivation ability, and protein stability. It also impaired nuclear localization, an effect that was greatly enhanced in the MODY1 mutant Q268X. Treatment of the hepatocellular carcinoma cell line HepG2 with PKC activator phorbol 12-myristate 13-acetate also resulted in increased cytoplasmic localization of HNF4alpha as well as decreased endogenous HNF4alpha protein levels in a proteasome-dependent fashion. We also show that PKC phosphorylates the DNA binding domain of other NRs (retinoic acid receptor alpha, retinoid X receptor alpha, and thyroid hormone receptor beta) and that phosphomimetic mutants of the same Ser/Thr result in cytoplasmic localization of retinoid X receptor alpha and peroxisome proliferator-activated receptor alpha. Thus, phosphorylation of this conserved Ser between the two zinc fingers may be a common mechanism for regulating the function of NRs.
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Affiliation(s)
- Kai Sun
- Environmental Toxicology Graduate Program, University of California, Riverside, California 92521, USA
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McGrane MM. Vitamin A regulation of gene expression: molecular mechanism of a prototype gene. J Nutr Biochem 2007; 18:497-508. [PMID: 17320364 DOI: 10.1016/j.jnutbio.2006.10.006] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2006] [Revised: 09/23/2006] [Accepted: 10/16/2006] [Indexed: 10/23/2022]
Abstract
Vitamin A regulation of gene expression is a well-characterized example of direct nutrient regulation of gene expression. The downstream metabolites of retinol, all-trans and 9-cis retinoic acids are the bioactive components that bind and activate their cognate nuclear receptors to regulate target genes. There are multiple retinoid receptor subtypes that are encoded by separate genes and each subtype has different isoforms. These receptors are Class II members of the thyroid/retinoid/vitamin D superfamily of nuclear receptors. The characterization of the retinoid receptors and the DNA response elements of target genes that bind these receptors have vastly expanded our knowledge of the mechanism of retinoid regulation of target genes. The basic regulatory mechanism of retinoids interacting with their cognate receptors is further complicated by the interaction of coactivators and corepressors, nuclear proteins that are involved in activation or repression of transcription, respectively. Most of these coregulators are involved in modifying chromatin and nucleosome structure such that chromatin is relaxed or condensed, and in bridging between the upstream enhancer domains and the transcription preinitiation complex. Retinoid regulation of the rate of transcription of target genes and the duration of the retinoid response is further complicated by covalent modification of the retinoid receptors by phosphorylation involved in coactivator association and ubiquitinylation involved in the degradation of retinoid receptors. This review presents a prototype retinoid responsive gene that encodes the phosphoenolpyruate carboxykinase (PEPCK) gene as an example of a specific mechanism of retinoid regulation of a metabolic gene. The retinoid response elements and overall mechanism of retinoid regulation of the PEPCK gene have been well documented by both in vitro and in vivo methods. We provide detailed information on the specific nuclear receptors, coactivators and chromatin modification events that occur when vitamin A is deficient and, therefore, retinoids are not available to activate the nuclear retinoid-signaling cascade.
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Affiliation(s)
- Mary M McGrane
- Department of Nutritional Sciences, The University of Connecticut, Storrs, CT 06269, USA.
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Bogoyevitch MA, Kobe B. Uses for JNK: the many and varied substrates of the c-Jun N-terminal kinases. Microbiol Mol Biol Rev 2006; 70:1061-95. [PMID: 17158707 PMCID: PMC1698509 DOI: 10.1128/mmbr.00025-06] [Citation(s) in RCA: 439] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The c-Jun N-terminal kinases (JNKs) are members of a larger group of serine/threonine (Ser/Thr) protein kinases from the mitogen-activated protein kinase family. JNKs were originally identified as stress-activated protein kinases in the livers of cycloheximide-challenged rats. Their subsequent purification, cloning, and naming as JNKs have emphasized their ability to phosphorylate and activate the transcription factor c-Jun. Studies of c-Jun and related transcription factor substrates have provided clues about both the preferred substrate phosphorylation sequences and additional docking domains recognized by JNK. There are now more than 50 proteins shown to be substrates for JNK. These include a range of nuclear substrates, including transcription factors and nuclear hormone receptors, heterogeneous nuclear ribonucleoprotein K, and the Pol I-specific transcription factor TIF-IA, which regulates ribosome synthesis. Many nonnuclear substrates have also been characterized, and these are involved in protein degradation (e.g., the E3 ligase Itch), signal transduction (e.g., adaptor and scaffold proteins and protein kinases), apoptotic cell death (e.g., mitochondrial Bcl2 family members), and cell movement (e.g., paxillin, DCX, microtubule-associated proteins, the stathmin family member SCG10, and the intermediate filament protein keratin 8). The range of JNK actions in the cell is therefore likely to be complex. Further characterization of the substrates of JNK should provide clearer explanations of the intracellular actions of the JNKs and may allow new avenues for targeting the JNK pathways with therapeutic agents downstream of JNK itself.
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Affiliation(s)
- Marie A Bogoyevitch
- Cell Signalling Laboratory, Biochemistry and Molecular Biology (M310), School of Biomedical, Biomolecular and Chemical Sciences, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
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Li QP, Qi X, Pramanik R, Pohl NM, Loesch M, Chen G. Stress-induced c-Jun-dependent Vitamin D receptor (VDR) activation dissects the non-classical VDR pathway from the classical VDR activity. J Biol Chem 2006; 282:1544-51. [PMID: 17121851 DOI: 10.1074/jbc.m604052200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Vitamin D receptor (VDR) is a ligand-dependent transcription factor that mediates vitamin D(3)-induced gene expression. Our previous work has established that stress MAPK signaling stimulates VDR expression (Qi, X., Pramank, R., Wang, J., Schultz, R. M., Maitra, R. K., Han, J., DeLuca, H. F., and Chen, G. (2002) J. Biol. Chem. 277, 25884-25892) and VDR inhibits cell death in response to p38 MAPK activation (Qi, X., Tang, J., Pramanik, R., Schultz, R. M., Shirasawa, S., Sasazuki, T., Han, J., and Chen, G. (2004) J. Biol. Chem. 279, 22138-22144). Here we show that c-Jun is essential for VDR expression and VDR in turn inhibits c-Jun-dependent cell death by non-classical mechanisms. In response to stress c-Jun is recruited to the Vdr promoter before VDR protein expression is induced. The necessary and sufficient role of c-Jun in VDR expression was established by the fact that c-Jun knock-out decreases VDR expression, whereas c-Jun restoration recovers its activity. Existence of the non-classical VDR pathway was suggested by a requirement of both c-Jun and VDR in stress-induced VDR activity and further demonstrated by VDR inhibiting c-Jun-dependent cell death independent of its classical transcriptional activity and independent of vitamin D(3). c-Jun is also required for vitamin D(3)-induced classical VDR transcriptional activity by a mechanism likely involving physical interactions between c-Jun and VDR proteins. These results together reveal a non-classical mechanism by which VDR acts as a c-Jun/AP-1 target gene to modify c-Jun activity in stress response through increased protein expression independent of classical transcriptional regulations.
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Affiliation(s)
- Qing-Ping Li
- Department of Pharmacology and Toxicology, Medical College of Wisconsin, USA
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Geier A, Wagner M, Dietrich CG, Trauner M. Principles of hepatic organic anion transporter regulation during cholestasis, inflammation and liver regeneration. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1773:283-308. [PMID: 17291602 DOI: 10.1016/j.bbamcr.2006.04.014] [Citation(s) in RCA: 221] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Revised: 04/21/2006] [Accepted: 04/24/2006] [Indexed: 12/16/2022]
Abstract
Hepatic uptake and biliary excretion of organic anions (e.g., bile acids and bilirubin) is mediated by hepatobiliary transport systems. Defects in transporter expression and function can cause or maintain cholestasis and jaundice. Recruitment of alternative export transporters in coordination with phase I and II detoxifying pathways provides alternative pathways to counteract accumulation of potentially toxic biliary constituents in cholestasis. The genes encoding for organic anion uptake (NTCP, OATPs), canalicular export (BSEP, MRP2) and alternative basolateral export (MRP3, MRP4) in liver are regulated by a complex interacting network of hepatocyte nuclear factors (HNF1, 3, 4) and nuclear (orphan) receptors (e.g., FXR, PXR, CAR, RAR, LRH-1, SHP, GR). Bile acids, proinflammatory cytokines, hormones and drugs mediate causative and adaptive transporter changes at a transcriptional level by interacting with these nuclear factors and receptors. Unraveling the underlying regulatory mechanisms may therefore not only allow a better understanding of the molecular pathophysiology of cholestatic liver diseases but should also identify potential pharmacological strategies targeting these regulatory networks. This review is focused on general principles of transcriptional basolateral and canalicular transporter regulation in inflammation-induced cholestasis, ethinylestradiol- and pregnancy-associated cholestasis, obstructive cholestasis and liver regeneration. Moreover, the potential therapeutic role of nuclear receptor agonists for the management of liver diseases is highlighted.
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Affiliation(s)
- Andreas Geier
- Department of Internal Medicine III, Aachen University (RWTH), Aachen, Germany.
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Zimmerman TL, Thevananther S, Ghose R, Burns AR, Karpen SJ. Nuclear export of retinoid X receptor alpha in response to interleukin-1beta-mediated cell signaling: roles for JNK and SER260. J Biol Chem 2006; 281:15434-40. [PMID: 16551633 DOI: 10.1074/jbc.m508277200] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
As the obligate heterodimer partner to class II nuclear receptors, the retinoid X receptor alpha (RXRalpha) plays a vital physiological role in the regulation of multiple hepatic functions, including bile formation, intermediary metabolism, and endobiotic/xenobiotic detoxification. Many RXRalpha-regulated genes are themselves suppressed in inflamed liver via unknown mechanisms, which constitute a substantial component of the negative hepatic acute phase response. In this study we show that RXRalpha, generally considered a stable nuclear resident protein, undergoes rapid nuclear export in response to signals initiated by the pro-inflammatory cytokine interleukin-1beta (IL-1beta), a central activator of the acute phase response. Within 30 min of exposure to IL-1beta, nuclear levels of RXRalpha are markedly suppressed in human liver-derived HepG2 cells, temporally coinciding with its appearance in the cytoplasm. The nuclear residence of RXRalpha is maintained by inhibiting c-jun N-terminal kinase (JNK, curcumin or SP600125) or CRM-1-mediated nuclear export (Leptomycin B). Pretreatment with the proteasome inhibitor MG132 blocks IL-1beta-mediated reductions in nuclear RXRalpha levels while increasing accumulation in the cytoplasm. Mutational studies identify one residue, serine 260, a JNK phosphoacceptor site whose phosphorylation status had an unknown role in RXRalpha function, as critical for IL-1beta-mediated nuclear export of transfected human RXRalpha-green fluorescent fusion constructs. These findings indicate that inflammation-mediated cell signaling leads to rapid and profound reductions in nuclear RXRalpha levels, via a multistep, JNK-dependent mechanism involving Ser260, nuclear export, and proteasomal degradation. Thus, inflammation-meditated cell signaling targets RXRalpha for nuclear export and degradation; a potential mechanism that explains the broad suppression of RXRalpha-dependent gene expression in the inflamed liver.
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Affiliation(s)
- Tracy L Zimmerman
- Texas Children's Liver Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA
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39
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Bour G, Taneja R, Rochette‐Egly C. Mouse embryocarcinoma F9 cells and retinoic acid: A model to study the molecular mechanisms of endodermal differentiation. NUCLEAR RECEPTORS IN DEVELOPMENT 2006. [DOI: 10.1016/s1574-3349(06)16007-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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40
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Bruck N, Bastien J, Bour G, Tarrade A, Plassat JL, Bauer A, Adam-Stitah S, Rochette-Egly C. Phosphorylation of the retinoid x receptor at the omega loop, modulates the expression of retinoic-acid-target genes with a promoter context specificity. Cell Signal 2005; 17:1229-39. [PMID: 16038797 DOI: 10.1016/j.cellsig.2004.12.006] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Accepted: 12/21/2004] [Indexed: 11/26/2022]
Abstract
The retinoid response is mediated by two classes of nuclear receptors, the retinoic acid receptors (RARalpha, beta, and gamma) and the retinoid X receptors (RXRalpha, beta, and gamma) which act as ligand-dependent heterodimeric RAR/RXR transcription activators. Like most transcription factors, RARs and RXRs are regulated by phosphorylation processes. Here, we report that stress agents induce RXRalpha phosphorylation, subsequently to the activation of the stress-activated protein kinases cascade (JNKs). This phosphorylation process concerns three residues located in the N-terminal AF-1 domain of RXRalpha and one located in the omega loop of the Ligand Binding Domain. To decipher how stress-induced RXRalpha phosphorylation influences the transcription of RA-target genes, we used a ribotoxic stress agent, anisomycin, which activates signaling kinases without promoting DNA or protein damages, at subinhibitory concentrations. Taking advantage of vectors expressing recombinant RXRalpha mutated at its phosphorylation sites and of F9 cell lines re-expressing the same RXRalpha mutants in an RXRalpha null background, we provide evidence that stress signaling modulates RAR/RXRalpha-mediated transcription, through the phosphorylation of RXRalpha at the residue located in the Omega loop, in a promoter context-dependent manner.
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Affiliation(s)
- Nathalie Bruck
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM /ULP, BP 10142, 67404 Illkirch Cedex, France
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41
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Mann KK, Padovani AMS, Guo Q, Colosimo AL, Lee HY, Kurie JM, Miller WH. Arsenic trioxide inhibits nuclear receptor function via SEK1/JNK-mediated RXRalpha phosphorylation. J Clin Invest 2005; 115:2924-33. [PMID: 16184197 PMCID: PMC1224295 DOI: 10.1172/jci23628] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2004] [Accepted: 07/19/2005] [Indexed: 01/01/2023] Open
Abstract
We have previously published that 2 proven treatments for acute promyelocytic leukemia, As2O3 and retinoic acid, can be antagonistic in vitro. We now report that As2O3 inhibits ligand-induced transcription of the retinoic acid receptor, as well as other nuclear receptors that heterodimerize with the retinoid X receptor alpha (RXRalpha). As2O3 did not inhibit transactivation of the estrogen receptor or the glucocorticoid receptor, which do not heterodimerize with RXRalpha. We further show that As2O3 inhibits expression of several target genes of RXRalpha partners. Phosphorylation of RXRalpha has been reported to inhibit nuclear receptor signaling, and we show by in vivo labeling and phosphoamino acid detection that As2O3 phosphorylated RXRalpha in the N-terminal ABC region exclusively on serine residues. Consistent with our previous data implying a role for JNK in As2O3-induced apoptosis, we show that pharmacologic or genetic inhibition of JNK activation decreased As2O3-induced RXRalpha phosphorylation and blocked the effects of As2O3 on RXRalpha-mediated transcription. A mutational analysis indicated that phosphorylation of a specific serine residue, S32, was primarily responsible for inhibition of RXRalpha-mediated transcription. These data may provide some insight into the rational development of chemotherapeutic combinations involving As2O3 as well as into molecular mechanisms of arsenic-induced carcinogenesis resulting from environmental exposure.
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Affiliation(s)
- Koren K Mann
- Montréal Centre for Experimental Therapeutics in Cancer, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, McGill University, Montréal, Québec, Canada
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Piu F, Gauthier NK, Wang F. β-arrestin 2 modulates the activity of nuclear receptor RAR β2 through activation of ERK2 kinase. Oncogene 2005; 25:218-29. [PMID: 16170358 DOI: 10.1038/sj.onc.1209024] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The activity of retinoid receptors activity can be regulated by various extracellular stimuli. In an effort to understand the molecular basis for this phenomenon, the role of beta-arrestins was investigated. Beta-Arrestins constitute a class of proteins involved in the internalization of agonist-activated receptors. They have also been linked to MAPK activation suggesting a direct involvement in signaling cascades. Here, we report that beta-arrestin 2 stimulates the transcriptional activation of the retinoid RAR and RXR receptors. Of all the retinoid receptors, the RAR beta2 subtype showed the strongest sensitivity to beta-arrestin 2 action. Interestingly, this event requires the presence of the MAP kinase ERK2, but not that of JNK or P38. Site-directed mutagenesis showed that Ser 22 and Leu 217 are critical residues of the RAR beta2 receptor through which beta-arrestin 2 effects are mediated. More importantly, we demonstrate that the induction of PC12 growth inhibition by Nerve Growth Factor is indeed dependent upon RAR beta2 transcriptional activation in a beta-arrestin 2- and ERK2-dependent manner.
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Affiliation(s)
- F Piu
- ACADIA Pharmaceuticals Inc., San Diego, CA 92121, USA.
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43
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Tarrade A, Bastien J, Bruck N, Bauer A, Gianni M, Rochette-Egly C. Retinoic acid and arsenic trioxide cooperate for apoptosis through phosphorylated RXR alpha. Oncogene 2005; 24:2277-88. [PMID: 15688020 DOI: 10.1038/sj.onc.1208402] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Arsenite trioxide (As2O3) induces apoptosis in several cell lines by disturbing key signal transduction pathways through its oxidative properties. Here, we report that As2O3 also induces the phosphorylation of the retinoid receptor RXRalpha, subsequent to oxidative damages and the activation of the stress-activated protein kinases cascade (JNKs). We also report that RA amplifies both As2O3-induced phosphorylation of RXRalpha and apoptosis. Taking advantage of 'rescue' F9 cell lines expressing RXRalpha mutated at its phosphorylation sites, in an RXRalpha null background, we provide evidence that RXRalpha is a key element involved in that potentiating effect. Finally, we demonstrate that As2O3 also abrogates the transactivation of RA-target genes.
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Affiliation(s)
- Anne Tarrade
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 10142, 67404 Illkirch Cedex, France
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44
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45
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Jahan A, Chiang JYL. Cytokine regulation of human sterol 12alpha-hydroxylase (CYP8B1) gene. Am J Physiol Gastrointest Liver Physiol 2005; 288:G685-95. [PMID: 15550563 DOI: 10.1152/ajpgi.00207.2004] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Sterol 12alpha-hydroxylase (CYP8B1) catalyzes cholic acid synthesis in the liver and is feedback inhibited by bile acids. In addition to activating farnesoid X receptor (nuclear receptor subfamily 1H4), bile acids also induce inflammatory cytokines in hepatocytes. The objective of this study was to investigate the mechanism by which inflammatory cytokines inhibit human CYP8B1 gene transcription. Real-time PCR assays revealed that both chenodeoxycholic acid (CDCA) and interleukin-1beta (IL-1beta) markedly reduced CYP8B1, cholesterol 7alpha-hydroxylase CYP7A1 and hepatic nuclear factor 4alpha (HNF4alpha) mRNA expression levels in human primary hepatocytes. However, CDCA induced, but IL-1beta reduced, small heterodimer partner (SHP) mRNA expression. IL-1beta inhibited human CYP8B1 reporter activity only in liver cells, and a c-Jun NH(2)-terminal kinase (JNK)-specific inhibitor-blocked IL-1beta inhibition. Activated JNK1 or c-Jun inhibited, whereas their dominant negative forms blocked, IL-1beta inhibition of CYP8B1 transcription. Mutagenesis analyses mapped an IL-1beta response element to a previously identified bile acid response element, which contains an HNF4alpha binding site. A dominant negative HNF4alpha inhibited CYP8B1 gene transcription and ectopically expressed HNF4alpha blocked IL-1beta inhibition. Furthermore, IL-1beta inhibited HNF4alpha gene transcription, protein expression, and binding to the CYP8B1 gene. JNK1 phosphorylated HNF4alpha and a JNK-specific inhibitor blocked the IL-1beta inhibition of HNF4alpha expression. These results suggest that IL-1beta inhibits CYP8B1 gene transcription via a mitogen-activated protein kinase/JNK pathway that inhibits HNF4alpha gene expression and its DNA-binding ability. This mechanism may play an important role in the adaptive response to inflammatory cytokines and in the protection of the liver during cholestasis.
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Affiliation(s)
- Asmeen Jahan
- Dept. of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, P. O Box 95, Rootstown, OH 44272, USA
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Srinivas H, Juroske DM, Kalyankrishna S, Cody DD, Price RE, Xu XC, Narayanan R, Weigel NL, Kurie JM. c-Jun N-terminal kinase contributes to aberrant retinoid signaling in lung cancer cells by phosphorylating and inducing proteasomal degradation of retinoic acid receptor alpha. Mol Cell Biol 2005; 25:1054-69. [PMID: 15657432 PMCID: PMC543999 DOI: 10.1128/mcb.25.3.1054-1069.2005] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Retinoic acid (RA) is the ligand for nuclear RA receptors (RARs and RXRs) and is crucial for normal epithelial cell growth and differentiation. During malignant transformation, human bronchial epithelial cells acquire a block in retinoid signaling caused in part by a transcriptional defect in RARs. Here, we show that activation of c-Jun N-terminal kinase (JNK) contributes to RAR dysfunction by phosphorylating RARalpha and inducing degradation through the ubiquitin-proteasomal pathway. Analysis of RARalpha mutants and phosphopeptide mapping revealed that RARalpha residues Thr181, Ser445, and Ser461 are phosphorylated by JNK. Mutation of these residues to alanines prevented efficient ubiquitination of RARalpha and increased the stability of the protein. We investigated the importance of RARalpha phosphorylation by JNK as a mediator of retinoid resistance in lung cancer. Mice that develop lung cancer from activation of a latent K-ras oncogene had high intratumoral JNK activity and low RARalpha levels and were resistant to treatment with an RAR ligand. JNK inhibition in a human lung cancer cell line enhanced RARalpha levels, ligand-induced activity of RXR-RAR dimers, and growth inhibition by RA. These findings point to JNK as a key mediator of aberrant retinoid signaling in lung cancer cells.
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Affiliation(s)
- Harish Srinivas
- Department of Thoracic/Head and Neck Oncology-Unit 432, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA
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Pettersson F, Couture MC, Hanna N, Miller WH. Enhanced retinoid-induced apoptosis of MDA-MB-231 breast cancer cells by PKC inhibitors involves activation of ERK. Oncogene 2004; 23:7053-66. [PMID: 15273718 DOI: 10.1038/sj.onc.1207956] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Retinoids are vitamin A derivatives, which cause growth inhibition, differentiation and/or apoptosis in various cell types, including some breast cancer cells. In general, estrogen receptor (ER)-positive cells are retinoic acid (RA) sensitive, whereas ER-negative cells are resistant. In this report, we show that ER-negative MDA-MB-231 cells are strongly growth inhibited by retinoids in combination with a PKC inhibitor. While neither RA nor GF109203X (GF) has a significant growth inhibitory effect in these cells, RA+GF potently suppress proliferation. We found that RA+GF induce apoptosis, as shown by an increase in fragmented DNA, Annexin-V-positive cells and caspase-3 activation. Apoptosis was also induced by GF in combination with two synthetic retinoids. Expression of phosphorylated as well as total PKC was decreased by GF and this was potentiated by RA. In addition, treatment with GF caused a strong and sustained activation of ERK1/2 and p38-MAPK, as well as a weaker activation of JNK. Importantly, inhibition of ERK but not p38 or JNK suppressed apoptosis induced by RA+GF, indicating that activation of ERK is specifically required. In support of this novel finding, the ability of other PKC inhibitors to cause apoptosis in combination with RA correlates with ability to cause sustained activation of ERK.
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Affiliation(s)
- Filippa Pettersson
- Lady Davis Institute for Medical Research, McGill University, 3755 Cote-Ste-Catherine Rd, Montreal, Quebec, Canada H3T 1E2
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Gimeno A, Zaragozá R, Viña JR, Miralles VJ. Vitamin E activates CRABP-II gene expression in cultured human fibroblasts, role of protein kinase C. FEBS Lett 2004; 569:240-4. [PMID: 15225641 DOI: 10.1016/j.febslet.2004.05.073] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2004] [Revised: 05/17/2004] [Accepted: 05/27/2004] [Indexed: 10/26/2022]
Abstract
The treatment of human fibroblasts with different tocopherols in the presence of retinol caused an increase in cytoplasmic retinoic acid binding protein II (CRABP-II) mRNA and protein. The possibility of an involvement of protein kinase C (PKC) in the response to tocopherols was supported by the results obtained with the PKC-specific inhibitors, calphostin C and bisindolylmaleimide I. The effect of alpha-tocopherol was prevented by okadaic acid, suggesting that a protein phosphatase is responsible for PKC dephosphorylation produced by the presence of tocopherols. The results shown support the hypothesis that phosphorylation/dephosphorylation of RXRalpha via PKC may be involved in the regulation of CRABP-II gene expression.
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Affiliation(s)
- Amparo Gimeno
- Departamento de Bioquímica y Biología Molecular, Facultades de Farmacia y Medicina, Avda. Vicent Andrés Estellés s/n, Universidad de Valencia, Valencia, Spain
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Narayanan R, Sepulveda VAT, Falzon M, Weigel NL. The functional consequences of cross-talk between the vitamin D receptor and ERK signaling pathways are cell-specific. J Biol Chem 2004; 279:47298-310. [PMID: 15331595 DOI: 10.1074/jbc.m404101200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The actions of the active metabolite of 1,25-(OH)2D3 (1,25-D) are mediated primarily by the vitamin D receptor (VDR), a member of the nuclear receptor family of ligand-activated transcription factors. Although their ligands cause transcriptional activation, many of the ligands also rapidly activate cellular signaling pathways through mechanisms that have not been fully elucidated. We find that 1,25-D causes a rapid, but sustained activation of ERK (extracellular signal-regulated kinase) in bone cell lines. However, the effect of ERK activation on VDR transcriptional activity was cell line-specific. Inhibition of ERK activation by the MEK inhibitor, U0126, stimulated VDR activity in MC3T3-E1 cells, but inhibited the activity in MG-63 cells as well as in HeLa cells. VDR is not a known target of ERK. We found that the ERK target responsible for reduced VDR activity in MC3T3-E1 cells is RXRalpha. MC3T3-E1 cells express lower levels of RXRbeta and RXRgamma than either HeLa or MG-63 cells. Although overexpression of RXRalpha in MC3T3-E1 cells increased VDR activity, U0126 further enhanced the activity. In contrast, overexpression of RXRgamma stimulated VDR activity but abrogated the stimulation by U0126. Thus, although 1,25-D treatment activates ERK in many cell types, subsequently inducing changes independent of VDR, the effects of treatment with 1,25-D on the transcriptional activity of VDR are RXR isoform-specific. In cells in which RXRalpha is the VDR partner, the transcriptional activation of VDR by 1,25-D is attenuated by the concomitant activation of ERK. In cells utilizing RXRgamma, ERK activation enhances VDR transcriptional activity.
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Affiliation(s)
- Ramesh Narayanan
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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Ghose R, Zimmerman TL, Thevananther S, Karpen SJ. Endotoxin leads to rapid subcellular re-localization of hepatic RXRalpha: A novel mechanism for reduced hepatic gene expression in inflammation. NUCLEAR RECEPTOR 2004; 2:4. [PMID: 15312234 PMCID: PMC514570 DOI: 10.1186/1478-1336-2-4] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/02/2004] [Accepted: 08/16/2004] [Indexed: 11/10/2022]
Abstract
BACKGROUND: Lipopolysaccharide (LPS) treatment of animals down-regulates the expression of hepatic genes involved in a broad variety of physiological processes, collectively known as the negative hepatic acute phase response (APR). Retinoid X receptor alpha (RXRalpha), the most highly expressed RXR isoform in liver, plays a central role in regulating bile acid, cholesterol, fatty acid, steroid and xenobiotic metabolism and homeostasis. Many of the genes regulated by RXRalpha are repressed during the negative hepatic APR, although the underlying mechanism is not known. We hypothesized that inflammation-induced alteration of the subcellular location of RXRalpha was a common mechanism underlying the negative hepatic APR. RESULTS: Nuclear RXRalpha protein levels were significantly reduced (~50%) within 1-2 hours after low-dose LPS treatment and remained so for at least 16 hours. RXRalpha was never detected in cytosolic extracts from saline-treated mice, yet was rapidly and profoundly detectable in the cytosol from 1 hour, to at least 4 hours, after LPS administration. These effects were specific, since the subcellular localization of the RXRalpha partner, the retinoic acid receptor (RARalpha), was unaffected by LPS. A potential cell-signaling modulator of RXRalpha activity, c-Jun-N-terminal kinase (JNK) was maximally activated at 1-2 hours, coincident with maximal levels of cytoplasmic RXRalpha. RNA levels of RXRalpha were unchanged, while expression of 6 sentinel hepatic genes regulated by RXRalpha were all markedly repressed after LPS treatment. This is likely due to reduced nuclear binding activities of regulatory RXRalpha-containing heterodimer pairs. CONCLUSION: The subcellular localization of native RXRalpha rapidly changes in response to LPS administration, correlating with induction of cell signaling pathways. This provides a novel and broad-ranging molecular mechanism for the suppression of RXRalpha-regulated genes in inflammation.
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Affiliation(s)
- Romi Ghose
- Texas Children's Liver Center, Department of Pediatrics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Tracy L Zimmerman
- Texas Children's Liver Center, Department of Pediatrics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Sundararajah Thevananther
- Texas Children's Liver Center, Department of Pediatrics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Saul J Karpen
- Texas Children's Liver Center, Department of Pediatrics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
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