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Bellezza I, Minelli A. Adenosine in sperm physiology. Mol Aspects Med 2017; 55:102-109. [DOI: 10.1016/j.mam.2016.11.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Revised: 11/23/2016] [Accepted: 11/23/2016] [Indexed: 10/20/2022]
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Tobo A, Tobo M, Nakakura T, Ebara M, Tomura H, Mogi C, Im DS, Murata N, Kuwabara A, Ito S, Fukuda H, Arisawa M, Shuto S, Nakaya M, Kurose H, Sato K, Okajima F. Characterization of Imidazopyridine Compounds as Negative Allosteric Modulators of Proton-Sensing GPR4 in Extracellular Acidification-Induced Responses. PLoS One 2015; 10:e0129334. [PMID: 26070068 PMCID: PMC4466532 DOI: 10.1371/journal.pone.0129334] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Accepted: 05/07/2015] [Indexed: 02/02/2023] Open
Abstract
G protein-coupled receptor 4 (GPR4), previously proposed as the receptor for sphingosylphosphorylcholine, has recently been identified as the proton-sensing G protein-coupled receptor (GPCR) coupling to multiple intracellular signaling pathways, including the Gs protein/cAMP and G13 protein/Rho. In the present study, we characterized some imidazopyridine compounds as GPR4 modulators that modify GPR4 receptor function. In the cells that express proton-sensing GPCRs, including GPR4, OGR1, TDAG8, and G2A, extracellular acidification stimulates serum responsive element (SRE)-driven transcriptional activity, which has been shown to reflect Rho activity, with different proton sensitivities. Imidazopyridine compounds inhibited the moderately acidic pH-induced SRE activity only in GPR4-expressing cells. Acidic pH-stimulated cAMP accumulation, mRNA expression of inflammatory genes, and GPR4 internalization within GPR4-expressing cells were all inhibited by the GPR4 modulator. We further compared the inhibition property of the imidazopyridine compound with psychosine, which has been shown to selectively inhibit actions induced by proton-sensing GPCRs, including GPR4. In the GPR4 mutant, in which certain histidine residues were mutated to phenylalanine, proton sensitivity was significantly shifted to the right, and psychosine failed to further inhibit acidic pH-induced SRE activation. On the other hand, the imidazopyridine compound almost completely inhibited acidic pH-induced action in mutant GPR4. We conclude that some imidazopyridine compounds show specificity to GPR4 as negative allosteric modulators with a different action mode from psychosine, an antagonist susceptible to histidine residues, and are useful for characterizing GPR4-mediated acidic pH-induced biological actions.
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Affiliation(s)
- Ayaka Tobo
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Masayuki Tobo
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Takashi Nakakura
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Masashi Ebara
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Hideaki Tomura
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Chihiro Mogi
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Dong-Soon Im
- Laboratory of Pharmacology, College of Pharmacy, Pusan National University, Busan, Republic of Korea
| | - Naoya Murata
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Atsushi Kuwabara
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Saki Ito
- Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan
| | - Hayato Fukuda
- Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan
| | - Mitsuhiro Arisawa
- Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan
| | - Satoshi Shuto
- Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan
- Center for Research and Education on Drug Discovery, Hokkaido University, Sapporo, Japan
| | - Michio Nakaya
- Department of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan
| | - Hitoshi Kurose
- Department of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan
| | - Koichi Sato
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
- * E-mail: (FO); (KS)
| | - Fumikazu Okajima
- Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
- * E-mail: (FO); (KS)
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Abstract
Adenosine-5'-triphosphate is released by neuroendocrine, endocrine, and other cell types and acts as an extracellular agonist for ligand-gated P2X cationic channels and G protein-coupled P2Y receptors in numerous organs and tissues, including the endocrine system. The breakdown of ATP by ectonucleotidases not only terminates its extracellular messenger functions, but also provides a pathway for the generation of two additional agonists: adenosine 5'-diphosphate, acting via some P2Y receptors, and adenosine, a native agonist for G protein-coupled adenosine receptors, also expressed in the endocrine system. This article provides a review of purinergic signaling pathways in the hypothalamic magnocellular neurosecretory cells and neurohypophysis, hypothalamic parvocellular neuroendocrine system, adenohypophysis, and effector glands organized in five axes: hypothalamic-pituitary-gonadal, hypothalamic-pituitary-thyroid, hypothalamic-pituitary-adrenal, hypothalamic-pituitary-growth hormone, and hypothalamic-pituitary-prolactin. We attempted to summarize current knowledge of purinergic receptor subtypes expressed in the endocrine system, including their roles in intracellular signaling, hormone secretion, and other cell functions. We also briefly review the release mechanism for adenosine-5'-triphosphate by neuroendocrine, endocrine and surrounding cells, the enzymes involved in adenosine-5'-triphosphate hydrolysis to adenosine-5'-diphosphate and adenosine, and the relevance of this pathway for sequential activation of receptors and termination of signaling.
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Lundius EG, Vukojevic V, Hertz E, Stroth N, Cederlund A, Hiraiwa M, Terenius L, Svenningsson P. GPR37 protein trafficking to the plasma membrane regulated by prosaposin and GM1 gangliosides promotes cell viability. J Biol Chem 2013; 289:4660-73. [PMID: 24371137 DOI: 10.1074/jbc.m113.510883] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The subcellular distribution of the G protein-coupled receptor GPR37 affects cell viability and is implicated in the pathogenesis of parkinsonism. Intracellular accumulation and aggregation of GPR37 cause cell death, whereas GPR37 located in the plasma membrane provides cell protection. We define here a pathway through which the recently identified natural ligand, prosaposin, promotes plasma membrane association of GPR37. Immunoabsorption of extracellular prosaposin reduced GPR37(tGFP) surface density and decreased cell viability in catecholaminergic N2a cells. We found that GPR37(tGFP) partitioned in GM1 ganglioside-containing lipid rafts in the plasma membrane of live cells. This partitioning required extracellular prosaposin and was disrupted by lipid raft perturbation using methyl-β-cyclodextrin or cholesterol oxidase. Moreover, complex formation between GPR37(tGFP) and the GM1 marker cholera toxin was observed in the plasma membrane. These data show functional association between GPR37, prosaposin, and GM1 in the plasma membrane. These results thus tie together the three previously defined components of the cellular response to insult. Our findings identify a mechanism through which the receptor's natural ligand and GM1 may protect against toxic intracellular GPR37 aggregates observed in parkinsonism.
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Verzijl D, IJzerman AP. Functional selectivity of adenosine receptor ligands. Purinergic Signal 2011; 7:171-92. [PMID: 21544511 PMCID: PMC3146648 DOI: 10.1007/s11302-011-9232-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Accepted: 04/05/2011] [Indexed: 12/11/2022] Open
Abstract
Adenosine receptors are plasma membrane proteins that transduce an extracellular signal into the interior of the cell. Basically every mammalian cell expresses at least one of the four adenosine receptor subtypes. Recent insight in signal transduction cascades teaches us that the current classification of receptor ligands into agonists, antagonists, and inverse agonists relies very much on the experimental setup that was used. Upon activation of the receptors by the ubiquitous endogenous ligand adenosine they engage classical G protein-mediated pathways, resulting in production of second messengers and activation of kinases. Besides this well-described G protein-mediated signaling pathway, adenosine receptors activate scaffold proteins such as β-arrestins. Using innovative and sensitive experimental tools, it has been possible to detect ligands that preferentially stimulate the β-arrestin pathway over the G protein-mediated signal transduction route, or vice versa. This phenomenon is referred to as functional selectivity or biased signaling and implies that an antagonist for one pathway may be a full agonist for the other signaling route. Functional selectivity makes it necessary to redefine the functional properties of currently used adenosine receptor ligands and opens possibilities for new and more selective ligands. This review focuses on the current knowledge of functionally selective adenosine receptor ligands and on G protein-independent signaling of adenosine receptors through scaffold proteins.
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Affiliation(s)
- Dennis Verzijl
- Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands
| | - Ad P. IJzerman
- Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands
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Yang A, Mucsi AD, Desrosiers MD, Chen JF, Schnermann JB, Blackburn MR, Shi Y. Adenosine mediated desensitization of cAMP signaling enhances T-cell responses. Eur J Immunol 2010; 40:449-59. [PMID: 19950175 PMCID: PMC3468332 DOI: 10.1002/eji.200939586] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Adenosine has long been regarded as a crucial anti-inflammatory agent that protects the host from excessive damage. It has been reported to play an important role in suppressing immune activation, particularly that of T cells. However, it is a general observation that induction of T-cell activation is an efficient event despite the high adenosine levels that are often present in the affected host due to injury or stress. We report here that prior to antigenic stimulation via TCR/CD3, exposure of T cells to adenosine desensitizes adenosine receptors, so as to create a window of time where the T cells are insensitive to this ubiquitous suppressor. T cells from mice that were pre-exposed to this manipulation showed stronger responses to antigenic stimulation; therefore, the P1 adenosine receptor desensitization demonstrated an adjuvant-like effect. Our results suggest that adenosine receptor desensitization may be a mechanism for T cells to escape the general suppression during early points of T-cell activation and may emerge as a potential alternative for vaccine adjuvants.
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Affiliation(s)
- Ailian Yang
- Immunology Research Group and Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alta., Canada
| | - Ashley D. Mucsi
- Immunology Research Group and Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alta., Canada
| | - Melanie D. Desrosiers
- Immunology Research Group and Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alta., Canada
| | - Jiang-Fan Chen
- Molecular Neuropharmacology Laboratory, Department of Neurology, Boston University School of Medicine, Boston, MA, USA
| | - Jürgen B. Schnermann
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, MA, USA
| | - Michael R. Blackburn
- Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Medical School, Houston, TX, USA
| | - Yan Shi
- Immunology Research Group and Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alta., Canada
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Scavone JL, Van Bockstaele EJ. Mu-opioid receptor redistribution in the locus coeruleus upon precipitation of withdrawal in opiate-dependent rats. Anat Rec (Hoboken) 2009; 292:401-11. [PMID: 19248160 DOI: 10.1002/ar.20860] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Administration of mu-opioid receptor (MOR) agonists is known to produce adaptive changes within noradrenergic neurons of the rat locus coeruleus (LC). Alterations in the subcellular distribution of MOR have been shown to occur in the LC in response to full agonists and endogenous peptides; however, there is considerable debate in the literature whether trafficking of MOR occurs after chronic exposure to the partial-agonist morphine. In the present study, we examined adaptations in MOR after chronic opioid exposure using immunofluorescence and electron microscopy (EM), using receptor internalization as a functional endpoint. MOR trafficking in LC neurons was characterized in morphine-dependent rats that were given naltrexone at a dose known to precipitate withdrawal. After chronic morphine exposure, a subtle redistribution of MOR immunoreactivity from the membrane to the cytosol was detected within dendrites of LC neurons. Interestingly, an acute injection of naltrexone in rats exposed to chronic morphine produced a robust internalization of MOR, whereas administration of naltrexone failed to do so in naïve animals. These findings provide anatomical evidence for modified regulation of MOR trafficking after chronic morphine treatment in brain noradrenergic neurons. Adaptations in the MOR signaling pathways that regulate internalization may occur as a consequence of chronic treatment and precipitation of withdrawal. Mechanisms underlying this effect might include differential MOR regulation in the LC, or downstream effects of withdrawal-induced enkephalin (ENK) release from afferents to the LC.
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Affiliation(s)
- Jillian L Scavone
- Department of Neurosurgery, Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, Pennsylania, USA
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Nakav S, Chaimovitz C, Sufaro Y, Lewis EC, Shaked G, Czeiger D, Zlotnik M, Douvdevani A. Anti-inflammatory preconditioning by agonists of adenosine A1 receptor. PLoS One 2008; 3:e2107. [PMID: 18461129 PMCID: PMC2329854 DOI: 10.1371/journal.pone.0002107] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Accepted: 03/23/2008] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Adenosine levels rise during inflammation and modulate inflammatory responses by engaging with four different G protein-coupled receptors. It is suggested that adenosine exhibits pro-inflammatory effects through its A(1) receptor (A(1)R), and anti-inflammatory effects through A(2A) receptor (A(2A)R). Therefore, understanding of the mechanisms that govern adenosine receptor regulation may advance treatment of various inflammatory disorders. We previously reported that peak A(1)R expression during leukocyte recruitment, is followed by a peak in A(2A)R during inflammation resolution. PRINCIPAL FINDINGS Here, we examined whether A(1)R activation sequentially induces A(2A)R expression and by this reverses inflammation. The effect of adenosine on A(1)R mediated A(2A)R expression was examined in peritoneal macrophages (PMPhi) and primary peritoneal mesothelial cells (PMC) in vitro. Induction of A(2A)R was inhibited by pertussis toxin (PTX) and partly dependent on A(2A)R stimulation. Administration of A(1)R agonists to healthy mice reduced A(1)R expression and induced A(2A)R production in PMC. Mice that were preconditioned with A(1)R agonists 24 hours before E. coli inoculation exhibited decreased TNFalpha and IL-6 sera levels and reduced leukocytes recruitment. Preconditioning was blocked by pretreatment with A(1)R antagonist, as well as, or by late treatment with A(2A)R antagonist, and was absent in A(2A)R(-/-) mice. CONCLUSIONS Our data suggest that preconditioning by an A(1)R-agonist promotes the resolution of inflammation by inducing the production of A(2A)R. Future implications may include early treatment during inflammatory disorders or pretreatment before anticipated high risk inflammatory events, such as invasive surgery and organ transplantation.
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Affiliation(s)
- Sigal Nakav
- Department of Clinical Biochemistry, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Cidio Chaimovitz
- Department of Nephrology, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Yuval Sufaro
- Department of Clinical Biochemistry, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Eli C. Lewis
- Department of Clinical Biochemistry, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Gad Shaked
- Department of General Surgery, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - David Czeiger
- Department of General Surgery, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Moshe Zlotnik
- Department of Nephrology, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Amos Douvdevani
- Department of Clinical Biochemistry, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Department of Nephrology, Soroka Medical University Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
- * E-mail:
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Morello S, Ito K, Yamamura S, Lee KY, Jazrawi E, Desouza P, Barnes P, Cicala C, Adcock IM. IL-1 beta and TNF-alpha regulation of the adenosine receptor (A2A) expression: differential requirement for NF-kappa B binding to the proximal promoter. THE JOURNAL OF IMMUNOLOGY 2007; 177:7173-83. [PMID: 17082635 DOI: 10.4049/jimmunol.177.10.7173] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Adenosine is a potent endogenous regulator of airway inflammation that acts through specific receptor subtypes that can either cause constriction (A1R, A2BR, and A3R) or relaxation (A2AR) of the airways. We therefore examined the effects of key inflammatory mediators on the expression of the A2AR in a lung epithelial cell line (A549). IL-1beta and TNF-alpha increased the expression of the A2AR gene at the mRNA and protein levels. In contrast, LPS had no effect on A2AR gene expression. IL-1beta and TNF-alpha rapidly activated p50 and p65, but not C-Rel, RelB, or p52, and both IL-1beta- and TNF-alpha-stimulated A2AR expression was inhibited by the IkappaB kinase 2 inhibitor AS602868 in a concentration-dependent manner. Using chromatin immunoprecipitation assays, we demonstrate that IL-1beta can enhance p65 association with putative kappaB binding sites in the A2AR promoter in a temporal manner. In contrast, TNF-alpha failed to enhance p65 binding to these putative sites. Functionally, the two most 5' kappaB sites were important for IL-1beta-, but not TNF-alpha-, induced A2AR promoter reporter gene activity. Finally, neither TNF-alpha nor Il-1beta had any effect on A2AR mRNA transcript degradation. These results directly implicate a major role for NF-kappaB in the regulation of A2AR gene transcription by IL-1beta and TNF-alpha but suggest that the effects of TNF-alpha on A2AR gene transcription are not mediated through the proximal promoter.
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Affiliation(s)
- Silvana Morello
- Airways Disease Section, NHLI Imperial College London, London, United Kingdom
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Fukunaga S, Setoguchi S, Hirasawa A, Tsujimoto G. Monitoring ligand-mediated internalization of G protein-coupled receptor as a novel pharmacological approach. Life Sci 2006; 80:17-23. [PMID: 16978657 DOI: 10.1016/j.lfs.2006.08.022] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Revised: 07/12/2006] [Accepted: 08/16/2006] [Indexed: 11/17/2022]
Abstract
Agonist activation of a G protein-coupled receptor (GPCR) results in the redistribution of the receptor protein away from the cell surface into internal cellular compartments through a process of endocytosis known as internalization. Visualization of receptor internalization has become experimentally practicable by using fluorescent reagents such as green fluorescent protein (GFP). In this study, we examined whether the ligand-mediated internalization of a GPCR can be exploited for pharmacological evaluations. We acquired fluorescent images of cells expressing GFP-labeled GPCRs and evaluated the ligand-mediated internalization quantitatively by image processing. Using beta2-adrenoceptor and vasopressin V1a receptor as model GPCRs that couple to Gs and Gq, respectively, we first examined whether these GFP-tagged GPCRs exhibited appropriate pharmacology. The rank order of receptor internalization potency for a variety of agonists and antagonists specific to each receptor corresponded well with that previously observed in ligand binding studies. In addition to chemical ligand-induced internalization, this cell-based fluorescence imaging system successfully monitored the internalization of the proton-sensing GPCR TDAG8, and that of the free fatty acid-sensitive GPCR GPR120. The results show that monitoring receptor internalization can be a useful approach for pharmacological characterization of GPCRs and in fishing for ligands of orphan GPCRs.
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Affiliation(s)
- Shin'ichi Fukunaga
- Department of Genomic Drug Discovery Science, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida-shimo-adachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
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Abstract
This study aimed to investigate the potential for flavonoid action at A(1) adenosine receptors in vitro. In a radioligand binding assay for A(1) adenosine receptor occupancy in particulate preparations from guinea-pig cerebral cortex, flavonoids competed in concentration-dependent manners with Hill slopes typically not different from unity. Of the flavonoids tested, quercetin showed highest affinity (pKi value of 5.33). At a concentration of 28 mm, quercetin evoked a rightward shift in the N(6)-cyclopentyladenosine-induced inhibition of electrically evoked contractions of the guinea-pig isolated ileum, allowing the calculation of a pK(i) value of 4.71. These data suggest, therefore, that flavonoids represent an additional dietary source of A(1) adenosine receptor antagonists (beyond the methylxanthines, caffeine and theophylline).
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Affiliation(s)
- Stephen P H Alexander
- Institute of Neuroscience and School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK.
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Klaasse EC, van den Hout G, Roerink SF, de Grip WJ, Ijzerman AP, Beukers MW. Allosteric modulators affect the internalization of human adenosine A1 receptors. Eur J Pharmacol 2005; 522:1-8. [PMID: 16214128 DOI: 10.1016/j.ejphar.2005.08.052] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2005] [Accepted: 08/10/2005] [Indexed: 10/25/2022]
Abstract
To study the effect of allosteric modulators on the internalization of human adenosine A(1) receptors, the receptor was equipped with a C-terminal yellow fluorescent protein tag. The introduction of this tag did not affect the radioligand binding properties of the receptor. CHO cells stably expressing this receptor were subjected during 16 h to varying concentrations of the agonist N(6)-cyclopentyladenosine (CPA) in the absence or presence of 10 microM of the allosteric enhancer PD 81,723 ((2-amino-4,5-dimethyl-3-thienyl)-[3-(trifluoromethyl)phenyl]methanone) or the allosteric inhibitor SCH-202676 (N-(2,3-diphenyl-1,2,4-thiadiazol-5(2H)-ylidene)methanamine). CPA itself was able to internalize 25% and 40% of the receptors at a concentration of 400 nM or 4 muM, respectively. Addition of either PD 81,723 or SCH-202676 alone had no effect on internalization. However, with PD 81,723 a slight amount of internalization was obtained already at 40 nM of CPA and at 400 nM CPA 59% of the receptors internalized. SCH-202676 on the other hand effectively prevented CPA-induced internalization of the receptor.
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Affiliation(s)
- Elisabeth C Klaasse
- Department of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, The Netherlands
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Capecchi PL, Camurri A, Pompella G, Mazzola A, Maccherini M, Diciolla F, Lazzerini PE, Abbracchio MP, Laghi-Pasini F. Upregulation of A2A adenosine receptor expression by TNF-alpha in PBMC of patients with CHF: a regulatory mechanism of inflammation. J Card Fail 2005; 11:67-73. [PMID: 15704067 DOI: 10.1016/j.cardfail.2004.04.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
BACKGROUND Tumor necrosis factor (TNF)-alpha plays a role in congestive heart failure (CHF). A2A adenosine receptor (A(2A)R) activation on immune cells putatively reduces the release of cytokines contributing to CHF progression. The study is aimed at determining the role of the A(2A)R in the modulation of TNF-alpha production, and the ex vivo effect of TNF-alpha on A(2A)R in peripheral blood mononuclear cells (PBMC) from CHF patients. METHODS AND RESULTS Plasma levels of TNF-alpha and TNF-alpha production from lipopolysaccharide (LPS)-stimulated PBMC were evaluated in 26 CHF patients in comparison to controls. The effects of the A(2A)R agonist CGS-21680 and antagonist ZM-241385 on TNF-alpha production from PBMC were also evaluated. Finally, reverse transcriptase-polymerase chain reaction and Western blot analyses of A(2A)R in PBMC were performed in TNF-alpha-treated and untreated cells. TNF-alpha production from LPS-stimulated PBMC was enhanced in CHF patients with respect to controls. CGS-21680 blunted TNF-alpha production in both groups; ZM-241385 reverted this effect. A(2A)R expression in PBMC was higher in CHF patients than in controls. TNF-alpha addition produced an increase in A(2A)R in PBMC from controls but not in PBMC from CHF patients. CONCLUSIONS PBMC from CHF patients show an upregulation of A(2A)R-mediated inhibition of TNF-alpha, which may represents a mechanism of protection against inappropriate cytokine production.
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Affiliation(s)
- Pier Leopoldo Capecchi
- Department of Clinical Medicine and Immunological Sciences, Section of Clinical Immunology, University of Siena, Siena, Italy
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Schlag BD, Lou Z, Fennell M, Dunlop J. Ligand Dependency of 5-Hydroxytryptamine 2C Receptor Internalization. J Pharmacol Exp Ther 2004; 310:865-70. [PMID: 15113845 DOI: 10.1124/jpet.104.067306] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Agonist-induced internalization of G protein-coupled receptors (GPCRs) is a well characterized phenomenon believed to contribute to receptor desensitization. The 5-hydroxytryptamine (5-HT)2C subtype of serotonin receptor is a GPCR that we have shown to internalize upon agonist incubation. In this study, we have examined the effects of 5-HT2C receptor agonists serotonin, Ro 60-0175 [(S)-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine], and WAY-161503 [(4aR)-8,9-dichloro-2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a]quinoxalin-5(6H)-one]; partial agonists mCPP [1-(m-chlorophenyl)piperazine] and DOI [(+)-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane]; inverse agonists SB-206553 [N-3-pyridinyl-3,5-dihydro-5-methylbenzo(1,2-b:4,5-b')dipyrrole-1(2H)carboxamide] and mianserin; and neutral antagonists SB-242084 [6-chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-indoline] and 5-methoxygramine on the internalization of a C-terminal green fluorescent protein (GFP)-tagged 5-HT2C receptor (VSV isoform) expressed in transiently transfected human embryonic kidney cells. We detected internalization with an automated, cell-based fluorescence-imaging system (Arrayscan) and monitored function with intracellular Ca2+ measurements (flourometric imaging plate reader). The 5-HT2C-GFP construct exhibited appropriate pharmacology, and we observed that although all three agonists resulted in similar magnitudes of dose-dependent internalization, the partial agonists resulted in approximately 50% less internalization, and the inverse agonists and neutral antagonists failed to induce internalization. These results were confirmed by confocal microscopy. They demonstrate that the 5-HT2C receptor is internalized by incubation with agonists and partial agonists but not with inverse agonists or neutral antagonists.
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Affiliation(s)
- Brian D Schlag
- Neuroscience Discovery Research, Wyeth Research, CN 8000, Princeton, NJ 08543, USA
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Nguyen DK, Montesinos MC, Williams AJ, Kelly M, Cronstein BN. Th1 Cytokines Regulate Adenosine Receptors and Their Downstream Signaling Elements in Human Microvascular Endothelial Cells. THE JOURNAL OF IMMUNOLOGY 2003; 171:3991-8. [PMID: 14530318 DOI: 10.4049/jimmunol.171.8.3991] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We and others have shown that adenosine, acting at its receptors, is a potent modulator of inflammation and angiogenesis. To better understand the regulation of adenosine receptors during these processes we studied the effects of IL-1, TNF-alpha, and IFN-gamma on expression and function of adenosine receptors and select members of their coupling G proteins in human dermal microvascular endothelial cells (HMVEC). HMVEC expressed message and protein for A(2A) and A(2B), but not A(1) or A(3) receptors. IL-1 and TNF-alpha treatment increased message and protein expression of A(2A) and A(2B) receptor. IFN-gamma treatment also increased the expression of A(2B) receptors, but decreased expression of A(2A) receptors. Resting HMVEC and IFN-gamma-treated cells showed minimal cAMP response to the selective A(2A) receptor agonist 2-[2-(4-chlorophenyl)ethoxy]adenosine (MRE0094). In contrast, MRE0094 stimulated a dose-dependent increase in cAMP levels in TNF-alpha-treated cells that was almost completely blocked by the A(2A) receptor antagonist ZM-241385 (4-[2-[7-amino-2-(2-furyl)[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl]phenol). The nonselective adenosine receptor agonist 5'-(N-ethylcarboxamido)adenosine increased cAMP levels in both TNF-alpha- and IFN-gamma-treated cells, but not control cells, and its effect was only partially reversed by ZM-241385 in TNF-alpha-treated cells and not affected in IFN-gamma-treated cells. HMVEC expressed a higher level of G protein beta1 isoform than beta4 isoform. Although none of the cytokines tested affected G(beta1) expression, both IL-1 and TNF-alpha significantly up-regulated G(beta4) expression. These findings indicate that inflammatory cytokines modulate adenosine receptor expression and function on HMVECs and suggest that the interaction between proinflammatory cytokines and adenosine receptors may affect therapeutic responses to anti-inflammatory drugs that act via adenosine-dependent mechanisms.
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MESH Headings
- 3' Flanking Region/physiology
- Adenosine/analogs & derivatives
- Adenosine/pharmacology
- Cell Line
- Cytokines/pharmacology
- Cytokines/physiology
- Endothelium, Vascular/cytology
- Endothelium, Vascular/immunology
- Endothelium, Vascular/metabolism
- GTP-Binding Protein beta Subunits/biosynthesis
- Humans
- Inflammation Mediators/pharmacology
- Interferon-gamma/pharmacology
- Interleukin-1/pharmacology
- Microcirculation/cytology
- Microcirculation/immunology
- Microcirculation/metabolism
- Phenethylamines/pharmacology
- Protein Isoforms/biosynthesis
- Protein Subunits/biosynthesis
- RNA, Messenger/biosynthesis
- Receptor, Adenosine A2A/biosynthesis
- Receptor, Adenosine A2A/metabolism
- Receptor, Adenosine A2B/biosynthesis
- Receptor, Adenosine A2B/metabolism
- Receptors, Purinergic P1/biosynthesis
- Receptors, Purinergic P1/metabolism
- Receptors, Purinergic P1/physiology
- Signal Transduction/immunology
- Th1 Cells/immunology
- Th1 Cells/metabolism
- Tumor Necrosis Factor-alpha/pharmacology
- Up-Regulation/immunology
- Vascular Endothelial Growth Factor A/biosynthesis
- Vascular Endothelial Growth Factor A/genetics
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Affiliation(s)
- D Khoa Nguyen
- Division of Clinical Pharmacology, Department of Medicine, New York University School of Medicine, New York, NY 10016, USA
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16
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Abstract
The purine nucleoside adenosine acts via four distinct adenosine receptor subtypes: the adenosine A(1), A(2A), A(2B), and A(3) receptor. They are all G protein-coupled receptors (GPCR) coupling to classical second messenger pathways such as modulation of cAMP production or the phospholipase C (PLC) pathway. In addition, they couple to mitogen-activated protein kinases (MAPK), which could give them a role in cell growth, survival, death and differentiation. Although each of the adenosine receptors can activate one or more of the MAPKs, the mechanisms appear to differ substantially, both between receptor subtypes in the same cell type and between the same receptor in different cell types.
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Affiliation(s)
- Gunnar Schulte
- Department of Physiology and Pharmacology, Karolinska Institutet, S-171 77, Stockholm, Sweden.
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17
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Van Oekelen D, Luyten WHML, Leysen JE. 5-HT2A and 5-HT2C receptors and their atypical regulation properties. Life Sci 2003; 72:2429-49. [PMID: 12650852 DOI: 10.1016/s0024-3205(03)00141-3] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The 5-HT(2A) and 5-HT(2C) receptors belong to the G-protein-coupled receptor (GPCR) superfamily. GPCRs transduce extracellular signals to the interior of cells through their interaction with G-proteins. The 5-HT(2A) and 5-HT(2C) receptors mediate effects of a large variety of compounds affecting depression, schizophrenia, anxiety, hallucinations, dysthymia, sleep patterns, feeding behaviour and neuro-endocrine functions. Binding of such compounds to either 5-HT(2) receptor subtype induces processes that regulate receptor sensitivity. In contrast to most other receptors, chronic blockade of 5-HT(2A) and 5-HT(2C) receptors leads not to an up- but to a (paradoxical) down-regulation. This review deals with published data involving such non-classical regulation of 5-HT(2A) and 5-HT(2C) receptors obtained from in vivo and in vitro studies. The underlying regulatory processes of the agonist-induced regulation of 5-HT(2A) and 5-HT(2C) receptors, commonly thought to be desensitisation and resensitisation, are discussed. The atypical down-regulation of both 5-HT(2) receptor subtypes by antidepressants, antipsychotics and 5-HT(2) antagonists is reviewed. The possible mechanisms of this paradoxical down-regulation are discussed, and a new hypothesis on possible heterologous regulation of 5-HT(2A) receptors is proposed.
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Affiliation(s)
- Dirk Van Oekelen
- Johnson and Johnson Pharmaceutical, p/a Janssen Pharmaceutica, Turnhoutseweg 30, B-2340 Beerse, Belgium
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18
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Trincavelli ML, Costa B, Tuscano D, Lucacchini A, Martini C. Up-regulation of A(2A) adenosine receptors by proinflammatory cytokines in rat PC12 cells. Biochem Pharmacol 2002; 64:625-31. [PMID: 12167481 DOI: 10.1016/s0006-2952(02)01222-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The purpose of this study was to examine the regulation of A(2A) adenosine receptor (A(2A) AR) gene expression induced by proinflammatory cytokines in PC12 cells. The A(2A) AR mRNA levels were substantially increased following 3-48 hr PC12 cell treatment with interleukin 1 beta (500 unit/mL) or tumor necrosis factor alpha (1000 unit/mL), as revealed by RT-PCR analysis. In parallel, cell cytokine treatment induced an up-regulation of A(2A) receptor protein. Equilibrium radioligand binding studies on treated-cells showed a significant increase in maximum density of [3H] 2-(carboxyethylphenylethylamino) adenosine-5'-carboxamide binding sites, with no significant changes in the affinity constant value. The increase in A(2A) receptor density was also demonstrated by Western blot analysis. Interleukin 1 beta and tumor necrosis factor alpha effects on A(2A) AR mRNA and protein levels were detectable after 3 hr cytokine treatment and reached a maximum within 24 and 48 hr, respectively. These results demonstrated the existence of heterologous regulation of A(2A) ARs by proinflammatory cytokines. The biological significance of this regulation might be associated with modulating cellular activity in response to tissue damage associated with inflammatory mediator production.
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Affiliation(s)
- Maria L Trincavelli
- Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, Italy
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19
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León D, Albasanz JL, Ruíz MA, Fernández M, Martín M. Adenosine A1 receptor down-regulation in mothers and fetal brain after caffeine and theophylline treatments to pregnant rats. J Neurochem 2002; 82:625-34. [PMID: 12153486 DOI: 10.1046/j.1471-4159.2002.01008.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Pregnant rats were treated daily with 1 g/L of caffeine or theophylline in their drinking water during pregnancy and the effect of these methylxanthines on adenosine A1 receptor was assayed using binding and reverse transcription polymerase chain reaction (RT-PCR) assays in brains from both mothers and full-term fetuses. In plasma membranes from pregnant rat brain, caffeine and theophylline caused a significant decrease in total receptor numbers, of the same order in both cases (30%), with no significant changes on receptor affinity. The effect of these adenosine receptor antagonists on plasma membranes from fetal brains was more marked, being detected at approximately 50% of the total receptors detected in control conditions. However, in this tissue, a significant increase in the receptor affinity, of the same order in both cases, was also detected after antagonist administration. No significant variation on the potency of caffeine and theophylline as antagonists was detected after treatments in mothers; however, higher affinities were detected in fetuses. A decrease in the total receptor numbers in fetal brain was associated with an increase in the mRNA coding A1 receptor, as determined by RT-PCR assays, not having detected any mRNA difference in maternal brain. No variation in the levels of mRNA coding A2A receptor was detected in any case. These results suggest that maternal caffeine or theophylline intake modulates adenosine A1 receptor, causing a down-regulation of adenosine A1 receptor in brain in both mothers and fetuses.
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Affiliation(s)
- David León
- Area de Bioquímica, Facultad de Químicas, Centro Regional de Investigaciones Biomédicas, Universidad de Castilla-La Mancha,Ciudad Real, Spain
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20
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Rees DA, Lewis MD, Lewis BM, Smith PJ, Scanlon MF, Ham J. Adenosine-regulated cell proliferation in pituitary folliculostellate and endocrine cells: differential roles for the A(1) and A(2B) adenosine receptors. Endocrinology 2002; 143:2427-36. [PMID: 12021208 DOI: 10.1210/endo.143.6.8837] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A(1) and A(2) adenosine receptors have been identified in the pituitary gland, but the cell type(s) on which they are located and their effects on pituitary cell growth are not known. Therefore, we analyzed the expression of A(1) and A(2) receptors in primary rat anterior pituitary cells, two pituitary folliculostellate (TtT/GF and Tpit/F1) and two pituitary endocrine (GH(3) and AtT20) cell lines, and compared their effects on cell proliferation. In anterior pituitary and folliculostellate cells, adenosine and adenosine receptor agonists (5'-N-ethylcarboxamidoadenosine, a universal agonist, and CGS 21680, an A(2A) receptor agonist) stimulated cAMP levels with a rank order of potency that indicates the presence of functional A(2B) receptors. This stimulation, however, was not observed in either GH(3) or AtT20 cells, where adenosine and the A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine inhibited VIP/forskolin-stimulated cAMP production. Expression of A(2B) and A(1) receptors in the folliculostellate cells and that of the A(1) receptor in the endocrine cells were confirmed by RT-PCR, immunocytochemistry, and ligand binding. Adenosine and 5'-N-ethylcarboxamidoadenosine dose-dependently (10 nM to 10 microM) stimulated growth in the folliculostellate, but not in the endocrine, cells, whereas in the latter, 100 microM adenosine and 2-chloro-N(6)-cyclopentyladenosine inhibited cell proliferation by slowing cell cycle progression. These data highlight the differential expression of A(1) and A(2B) adenosine receptors in pituitary cells and provide evidence for opposing effects of adenosine on pituitary folliculostellate and endocrine cell growth.
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Affiliation(s)
- D A Rees
- Department of Medicine, University of Wales College of Medicine, Cardiff, United Kingdom CF14 4XN.
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21
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Gray JA, Roth BL. Paradoxical trafficking and regulation of 5-HT(2A) receptors by agonists and antagonists. Brain Res Bull 2001; 56:441-51. [PMID: 11750789 DOI: 10.1016/s0361-9230(01)00623-2] [Citation(s) in RCA: 210] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
5-Hydroxytryptamine(2A) (serotonin(2A), 5-HT(2A)) receptors are important for many physiologic processes including platelet aggregation, smooth muscle contraction, and the modulation of mood and perception. A large number of pharmaceutical agents mediate their actions, at least in part, by modulating the number and/or activity of 5-HT(2A) receptors. Drugs with action at 5-HT(2A) receptors are used in the treatment of many disorders, including schizophrenia, depression, and anxiety disorders. This review summarizes over two decades of research on the regulation of 5-HT(2A) receptors and provides a comprehensive review of numerous in vivo studies describing the paradoxical phenomenon of 5-HT(2A) receptor down-regulation by chronic treatment with antidepressants and antipsychotics. In addition, studies reporting antagonist-induced internalization of 5-HT(2A) receptors and other G protein-coupled receptors will be highlighted as a possible mechanism to explain this paradoxical down-regulation. Finally, a review of the cellular and molecular mechanisms that may be responsible for agonist-mediated desensitization and internalization of 5-HT(2A) receptors will be presented.
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Affiliation(s)
- J A Gray
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4935, USA
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22
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Khoa ND, Montesinos MC, Reiss AB, Delano D, Awadallah N, Cronstein BN. Inflammatory cytokines regulate function and expression of adenosine A(2A) receptors in human monocytic THP-1 cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 167:4026-32. [PMID: 11564822 DOI: 10.4049/jimmunol.167.7.4026] [Citation(s) in RCA: 193] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Adenosine, acting at its receptors, particularly A(2A) receptors, is a potent endogenous anti-inflammatory agent that modulates the functions and differentiation of inflammatory and immune cells. Because the inflammatory milieu abounds in proinflammatory cytokines, we investigated the effects of Th1-inflammatory cytokines on function and expression of adenosine A(2A) receptors in the human monocytic cell line THP-1. We found that, consistent with previous reports, adenosine and 2-[p-(2-carnonylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine (CGS-21680), a selective A(2A) receptor agonist, suppress IL-12 production but increase IL-10 production in LPS-activated THP-1 cells. These effects were blocked by the A(2A) receptor antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385). More importantly, the suppressive effect of adenosine and CGS-21680 on IL-12 production was significantly enhanced in cells pretreated with either IL-1 (10 U/ml) or TNF-alpha (100 U/ml) but markedly attenuated in cells pretreated with IFN-gamma (100 U/ml). Similarly, IL-1 and TNF-alpha treatment potentiated the stimulatory effect of adenosine and CGS-21680 on IL-10 production, whereas IFN-gamma treatment almost completely abolished this effect. CGS-21680 stimulated an increase in intracellular cAMP in a time- and dose-dependent manner in IL-1- and TNF-alpha-treated cells but not in control or IFN-gamma-treated cells. Both IL-1 and TNF-alpha increased A(2A) receptor mRNA and protein. In parallel with its effect on A(2A) receptor function, IFN-gamma down-regulated A(2A) receptor message and protein. Because adenosine mediates many of the antiinflammatory effects of drugs such as methotrexate, these observations suggest that local changes in the cytokine milieu may influence the therapeutic response to those drugs by altering the expression and function of adenosine receptors on inflammatory cells.
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Affiliation(s)
- N D Khoa
- Division of Clinical Pharmacology, Department of Medicine, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA
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23
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Abstract
In addition to hypothalamic and feedback inputs, the secretory cells of the anterior pituitary are influenced by the activity of factors secreted within the gland. The list of putative intrapituitary factors has been expanding steadily over the past decade, although until recently much of the work was limited to descriptions of potential interactions. This took the form of evidence of production within the pituitary of factors already known to influence activity of secretory cells, or further descriptions of actions on pituitary cells by such factors when added exogenously. A new phase of discovery has been entered, with extensive efforts being made to delineate the control of the synthesis and secretion of the pituitary factors within the gland, regulation of the receptors and response mechanisms for the factors in pituitary cells, and measurements of the endogenous actions of the factors through the use of specific immunoneutralization, receptor blockade, tissue from transgenic animals, and other means. Taken together, these findings are producing blueprints of the intrapituitary interactions that influence each of the individual types of secretory cells, leading toward an understanding of the physiological significance of the interactions. The purpose of this article is to review the recent literature on many of the factors acting as intrapituitary signals and to present such finding in the context of the physiology of the secretory cells.
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Affiliation(s)
- J Schwartz
- Department of Physiology, University of Adelaide, SA, Australia.
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24
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Minelli A, Allegrucci C, Piomboni P, Mannucci R, Lluis C, Franco R. Immunolocalization of A1 adenosine receptors in mammalian spermatozoa. J Histochem Cytochem 2000; 48:1163-71. [PMID: 10950874 DOI: 10.1177/002215540004800901] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The presence of A1 adenosine receptors (A1AR) in mammalian spermatozoa was previously demonstrated by radiochemical and immunochemical detection. This study was performed to investigate the cellular location of the A1AR to determine whether these receptors were somehow connected with ecto-adenosine deaminase and to evaluate their function in calcium uptake. By immunofluorescence staining we showed that in mammalian spermatozoa A1AR were constantly localized in the acrosomal region. This finding was confirmed by immunogold detection. Confocal analyses with anti-A1 and anti-ADA antibodies showed a high degree of co-localization. Calcium loading assay showed that this association was functional and affected calcium accumulation in mammalian spermatozoa. Therefore, we concluded that the acrosomal localization of A1AR was a constant feature in mammalian sperm. Moreover, these A1 receptors were functionally coupled to ecto-ADA and were able to modulate calcium uptake into an IP3-gated store.(J Histochem Cytochem 48:1163-1171, 2000)
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Affiliation(s)
- A Minelli
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Sezione Biochimica Cellulare, Università di Perugia, Perugia, Italia.
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25
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Brooke SM, Sapolsky RM. A cautionary note: the actions of adenosine agonists and antagonists may be reversed under certain conditions in primary cultures. Brain Res Bull 2000; 51:307-12. [PMID: 10704780 DOI: 10.1016/s0361-9230(99)00238-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
It is now generally accepted that adenosine has a neuroprotective role in the central nervous system. Agonists of adenosine such as 2-chloroadenosine (2-ClA) have been shown to be neuroprotective, while antagonists such as 8-phenyltheophylline (8-PT) increase neurotoxicity. However, paradoxical results have been reported with adenosine analogues, especially with respect to length of time of administration. We observe similarly contradictory findings with respect to 2-ClA and 8-PT actions in primary hippocampal cultures exposed to glutamate or kainic acid. We found 8-PT and 2-ClA had antagonist and agonist actions, respectively, only with acute (1 h) treatment; with chronic treatment (24 h), 2-ClA had no effects, while 8-PT had significant agonist actions. We also show that with variations in the type of culturing system, concentration, and pH that 8-PT's neurotoxic antagonist actions could be dramatically changed. We, therefore, present this paper as a cautionary note in experimenting with adenosine analogues.
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Affiliation(s)
- S M Brooke
- Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA.
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