101
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Bhatnagar A, Willins DL, Gray JA, Woods J, Benovic JL, Roth BL. The dynamin-dependent, arrestin-independent internalization of 5-hydroxytryptamine 2A (5-HT2A) serotonin receptors reveals differential sorting of arrestins and 5-HT2A receptors during endocytosis. J Biol Chem 2001; 276:8269-77. [PMID: 11069907 DOI: 10.1074/jbc.m006968200] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
5-Hydroxytryptamine 2A (5-HT2A) receptors, a major site of action of clozapine and other atypical antipsychotic medications, are, paradoxically, internalized in vitro and in vivo by antagonists and agonists. The mechanisms responsible for this paradoxical regulation of 5-HT2A receptors are unknown. In this study, the arrestin and dynamin dependences of agonist- and antagonist-mediated internalization were investigated in live cells using green fluorescent protein (GFP)-tagged 5-HT2A receptors (SR2-GFP). Preliminary experiments indicated that GFP tagging of 5-HT2A receptors had no effect on either the binding affinities of several ligands or agonist efficacy. Likewise, both the native receptor and SR2-GFP were internalized via endosomes in vitro. Experiments with a dynamin dominant-negative mutant (dynamin K44A) demonstrated that both agonist- and antagonist-induced internalization were dynamin-dependent. By contrast, both the agonist- and antagonist-induced internalization of SR2-GFP were insensitive to three different arrestin (Arr) dominant-negative mutants (Arr-2 V53D, Arr-2-(319-418), and Arr-3-(284-409)). Interestingly, 5-HT2A receptor activation by agonists, but not antagonists, induced greater Arr-3 than Arr-2 translocation to the plasma membrane. Importantly, the agonist-induced internalization of 5-HT2A receptors was accompanied by differential sorting of Arr-2, Arr-3, and 5-HT2A receptors into distinct plasma membrane and intracellular compartments. The agonist-induced redistribution of Arr-2 and Arr-3 into intracellular vesicles and plasma membrane compartments distinct from those involved in 5-HT2A receptor internalization implies novel roles for Arr-2 and Arr-3 independent of 5-HT2A receptor internalization and desensitization.
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Affiliation(s)
- A Bhatnagar
- Department of Biochemistry, Case Western Reserve University Medical School, Cleveland, Ohio 44106, USA
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102
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Lin JW, Ju W, Foster K, Lee SH, Ahmadian G, Wyszynski M, Wang YT, Sheng M. Distinct molecular mechanisms and divergent endocytotic pathways of AMPA receptor internalization. Nat Neurosci 2000; 3:1282-90. [PMID: 11100149 DOI: 10.1038/81814] [Citation(s) in RCA: 470] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Internalization of postsynaptic AMPA receptors depresses excitatory transmission, but the underlying dynamics and mechanisms of this process are unclear. Using immunofluorescence and surface biotinylation, we characterized and quantified basal and regulated AMPA receptor endocytosis in cultured hippocampal neurons, in response to synaptic activity, AMPA and insulin. AMPA-induced AMPA receptor internalization is mediated in part by secondary activation of voltage-dependent calcium channels, and in part by ligand binding independent of receptor activation. Although both require dynamin, insulin- and AMPA-induced AMPA receptor internalization are differentially dependent on protein phosphatases and sequence determinants within the cytoplasmic tails of GluR1 and GluR2 subunits. AMPA receptors internalized in response to AMPA stimulation enter a recycling endosome system, whereas those internalized in response to insulin diverge into a distinct compartment. Thus, the molecular mechanisms and intracellular sorting of AMPA receptors are diverse, and depend on the internalizing stimulus.
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Affiliation(s)
- J W Lin
- Howard Hughes Medical Institute, Massachusetts General Hospital (Wellman 423), 50 Blossom Street, Boston, Massachusetts 02114, USA
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103
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Anji A, Kumari M, Sullivan Hanley NR, Bryan GL, Hensler JG. Regulation of 5-HT(2A) receptor mRNA levels and binding sites in rat frontal cortex by the agonist DOI and the antagonist mianserin. Neuropharmacology 2000; 39:1996-2005. [PMID: 10963743 DOI: 10.1016/s0028-3908(00)00026-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the present study we have characterized the time course of effect of administration of the serotonin(2) (5-HT(2)) receptor antagonist mianserin, or the 5-HT(2) receptor agonist (+/-)-2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI), on 5-HT(2A) receptor binding sites and mRNA levels in rat frontal cortex. Radioligand binding and ribonuclease protection assays were performed with separate hemispheres of frontal cortex from each animal to examine concomitant changes in 5-HT(2A) receptor sites and mRNA levels. The decrease in cortical 5-HT(2A) receptor sites in response to chronic DOI administration was not accompanied by changes in 5-HT(2A) receptor mRNA. A single injection of DOI produced a transient decrease in 5-HT(2A) receptor mRNA levels detected 1 h post-injection. The density of 5-HT(2A) receptor sites, however, was not significantly reduced following a single injection of DOI. The down-regulation of cortical 5-HT(2A) receptor sites in response to a single injection of mianserin was accompanied by reductions in 5-HT(2A) receptor mRNA levels. Following 4 days of mianserin administration, however, we did not observe a change in 5-HT(2A) receptor mRNA levels, although 5-HT(2A) receptor density was decreased. Thus, changes in receptor mRNA may initially contribute to the down-regulation of 5-HT(2A) receptors in response to acute mianserin administration. Sustained changes in 5-HT(2A) receptor mRNA, however, appear not to be involved in maintaining the down-regulation of 5-HT(2A) receptor number with chronic mianserin administration. Mechanisms other than the regulation of receptor mRNA levels appear to underlie the down-regulation of 5-HT(2A) receptor sites in response to chronic administration of the agonist DOI.
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Affiliation(s)
- A Anji
- Department of Pharmacology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78284-7764, USA
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104
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Zhukovskaya NL, Neumaier JF. Clozapine downregulates 5-hydroxytryptamine6 (5-HT6) and upregulates 5-HT7 receptors in HeLa cells. Neurosci Lett 2000; 288:236-40. [PMID: 10889351 DOI: 10.1016/s0304-3940(00)01225-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Clozapine is an atypical antipsychotic with high affinity for several serotonin receptors. This drug causes paradoxical downregulation of 5-hydroxytryptamine(2A) (5-HT)(2A) receptors, but its modulation of other serotonin receptors has not been studied. We examined the effects of clozapine and several other drugs on the regulation of rat 5-HT(6) and 5-HT(7) receptors individually expressed in transfected HeLa cells. Both 5-HT(6) and 5-HT(7) receptor densities (B(max)) were reduced by 5-carboxamidotryptamine, an agonist, and methiothepin, an inverse agonist. Clozapine reduced 5-HT(6) B(max). This suggests that 5-HT(6) receptors are also paradoxically downregulated by the antagonist clozapine. 5-Hydroxytryptamine(7) receptor B(max), on the other hand, was increased by clozapine. Clozapine's modulation of the 5-HT(6) and 5-HT(7) receptor levels may be important in the action of this atypical antipsychotic.
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Affiliation(s)
- N L Zhukovskaya
- Department of Psychiatry and Behavioral Sciences, Harborview Medical Center, University of Washington, Box 359911, 325 Ninth Avenue, Seattle, WA 98195, USA
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105
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Abi-Dargham A, Krystal J. Serotonin Receptors as Targets of Antipsychotic Medications. NEUROTRANSMITTER RECEPTORS IN ACTIONS OF ANTIPSYCHOTIC MEDICATIONS 2000. [DOI: 10.1201/9781420041774.ch6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/14/2023]
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106
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Oliver KR, Kinsey AM, Wainwright A, Sirinathsinghji DJ. Localization of 5-ht(5A) receptor-like immunoreactivity in the rat brain. Brain Res 2000; 867:131-42. [PMID: 10837806 DOI: 10.1016/s0006-8993(00)02273-3] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
5-Hydroxytryptamine exerts modulatory physiological effects on both the central and peripheral nervous systems by activation of discrete receptor families. 5-ht(5A) is among the recently cloned, novel 5-HT receptors and currently under investigation to identify its pharmacological characteristics and potential physiological function(s). In this study, antibodies raised to a 5-ht(5A)-specific peptide were characterized using dot blot, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunohistochemistry, and the distribution of 5-ht(5A)-like immunoreactive material determined in rat brain. A major band of 41 kDa was observed following SDS-PAGE, corresponding to the predicted size of this receptor. 5-ht(5A)-like immunoreactivity was detected in areas known to have significant serotonergic input, such as hypothalamic and amygdaloid nuclei. Interestingly, 5-ht(5A)-like immunoreactivity showed a predilection for the suprachiasmatic nucleus, suggesting its possible role in the regulation of circadian rhythms, a function previously ascribed to 5-HT(1A) and 5-HT(7) receptors.
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Affiliation(s)
- K R Oliver
- Merck, Sharp and Dohme Research Laboratories, Neuroscience Research Centre, Essex CM20 2QR, Harlow, UK.
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107
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Chang M, Zhang L, Tam JP, Sanders-Bush E. Dissecting G protein-coupled receptor signaling pathways with membrane-permeable blocking peptides. Endogenous 5-HT(2C) receptors in choroid plexus epithelial cells. J Biol Chem 2000; 275:7021-9. [PMID: 10702266 DOI: 10.1074/jbc.275.10.7021] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To determine the intracellular signaling mechanism of the 5-HT(2C) receptor endogenously expressed in choroid plexus epithelial cells, we implemented a strategy of targeted disruption of protein-protein interactions. This strategy entails the delivery of conjugated membrane-permeable peptides that disrupt domain interaction at specific steps in the signaling cascade. As proof of concept, two peptides targeted against receptor-G protein interaction domains were examined. Only G(q)CT, which targets the receptor-G(q) protein interacting domain, disrupted 5-HT(2C) receptor-mediated phosphatidylinositide hydrolysis. G(s)CT, targeting the receptor-G(s) protein, disrupted beta2 adrenergic receptor-mediated activation of cAMP but not 5-HT(2C) receptor-mediated phosphatidylinositide hydrolysis. The peptide MPS-PLCbeta1M, mimicking the domain of phospholipase Cbeta1 (PLCbeta1) interacting with active Galpha(q), also blocked 5-HT(2C) receptor activation. In contrast, peptides PLCbeta2M and Phos that bind to and sequester free Gbetagamma subunits were ineffective at blocking 5-HT(2C) receptor-mediated phosphoinositol turnover. However, both peptides disrupted Gbetagamma-mediated alpha(2A) adrenergic receptor activation of mitogen-activated protein kinase. These results provide the first direct demonstration that active Galpha(q) subunits mediate endogenous 5-HT(2C) receptor activation of PLCbeta and that Gbetagamma subunits released from Galpha(q) heterotrimeric proteins are not involved. Comparable results were obtained with metabotropic glutamate receptor 5 expressed in astrocytes. Thus, conjugated, membrane-permeable peptides are effective tools for the dissection of intracellular signals.
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Affiliation(s)
- M Chang
- Department of Pharmacology and Center for Molecular Neuroscience, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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108
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Vergé D, Calas A. Serotoninergic neurons and serotonin receptors: gains from cytochemical approaches. J Chem Neuroanat 2000; 18:41-56. [PMID: 10708918 DOI: 10.1016/s0891-0618(99)00050-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Serotonergic systems, their phylogeny and ontogeny have been thoroughly described up to the ultrastructural level, thanks to the multiplicity of methodological approaches. They have often been referred to as a 'Rosetta stone', as several features first described for serotonin neurons or paraneurons have been then extended to other neurotransmitter systems: coexistence with neuropeptides or even a canonical neurotransmitter (GABA), volume transmission, regrowth after lesioning, and characterization of multiple receptor subtypes. This review deals with the contributions of neuroanatomical approaches for studying serotoninergic systems, and focuses on recent advances concerning the topological relationships between serotonergic innervation, receptors and target cells. This aspect is particularly important with regard to the possibility for serotonin to act through classical synaptic transmission and/or non-junctional transmission. Serotonin then can selectively regulate different neuronal systems through the activation of distinct receptor subtypes, which in turn can be linked to different transduction pathways. Neurocytochemical approaches constitute unique tools to analyse both anatomical and functional characteristics of complex neuronal systems.
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Affiliation(s)
- D Vergé
- Laboratoire de Neurobiologie des Signaux Intercellulaires, Institut des Neurosciences, Université Pierre et Marie Curie, CNRS UMR 7624, 7 Quai Saint-Bernard, 75005, Paris, France.
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109
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Rodríguez JJ, Garcia DR, Pickel VM. Subcellular distribution of 5-hydroxytryptamine2A and N-methyl-D-aspartate receptors within single neurons in rat motor and limbic striatum. J Comp Neurol 1999; 413:219-31. [PMID: 10524335 DOI: 10.1002/(sici)1096-9861(19991018)413:2<219::aid-cne4>3.0.co;2-f] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The dorsolateral caudate-putamen nucleus (CPN) and the nucleus accumbens (NAc) shell, respectively, are involved in many motor and limbic functions that are affected by activation of the 5-hydroxytryptamine2A receptor (5HT2AR) and the N-methyl-D-aspartate subtype of glutamate receptor (NMDAR). We examined the functional sites for 5HT2AR activation and potential interactions involving the NMDAR subunit NR1 (NMDAR1) within these striatal regions. For this examination, sequence-specific antipeptide antisera against these receptors were localized by electron microscopic dual-labeling immunocytochemistry in the rat brain. In the dorsolateral CPN and the NAc shell, the 5HT2AR-labeled profiles were mainly dendrites, but somata and axons were also immunoreactive. The neuronal somata contained round unindented nuclei that are typical of spiny striatal neurons, although few dendritic spines were 5HT2AR immunolabeled. In all neuronal profiles, the 5HT2AR labeling was primarily associated with cytoplasmic organelles and more rarely was localized to synaptic or nonsynaptic plasma membranes. Colocalization of 5HT2AR and NMDAR1 was seen primarily in somata and dendrites. Significantly greter numbers of 5HT2AR- or 5HT2AR- and NMDAR1-containing dendrites were seen in the dorsolateral CPN than in the NAc shell. As compared with 5HT2AR, NMDAR1 labeling was more often observed in dendritic spines, and these were also more numerous in the CPN. These results indicate that 5HT2A and NMDA receptors are coexpressed but differentially targeted in single spiny striatal neurons and are likely to play a major role in control of motor functions involving the dorsolateral CPN.
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Affiliation(s)
- J J Rodríguez
- Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA
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110
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MESH Headings
- Analgesics, Opioid/pharmacology
- Animals
- Endocytosis/drug effects
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
- Enkephalins/pharmacology
- Humans
- Morphine/pharmacology
- Nerve Tissue Proteins/drug effects
- Receptors, Cell Surface/drug effects
- Receptors, G-Protein-Coupled
- Receptors, Opioid, delta/drug effects
- Receptors, Opioid, delta/genetics
- Receptors, Opioid, mu/drug effects
- Receptors, Opioid, mu/genetics
- Signal Transduction/drug effects
- Signal Transduction/physiology
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Affiliation(s)
- B L Roth
- Department of Psychiatry, Case Western Reserve University Medical School, Cleveland, Ohio 44106, USA
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111
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Gelber EI, Kroeze WK, Willins DL, Gray JA, Sinar CA, Hyde EG, Gurevich V, Benovic J, Roth BL. Structure and function of the third intracellular loop of the 5-hydroxytryptamine2A receptor: the third intracellular loop is alpha-helical and binds purified arrestins. J Neurochem 1999; 72:2206-14. [PMID: 10217304 DOI: 10.1046/j.1471-4159.1999.0722206.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Understanding the precise structure and function of the intracellular domains of G protein-coupled receptors is essential for understanding how receptors are regulated, and how they transduce their signals from the extracellular milieu to intracellular sites. To understand better the structure and function of the intracellular domain of the 5-hydroxytryptamine2A (5-HT2A) receptor, a model G(alpha)q-coupled receptor, we overexpressed and purified to homogeneity the entire third intracellular loop (i3) of the 5-HT2A receptor, a region previously implicated in G-protein coupling. Circular dichroism spectroscopy of the purified i3 protein was consistent with alpha-helical and beta-loop, -turn, and -sheet structure. Using random peptide phage libraries, we identified several arrestin-like sequences as i3-interacting peptides. We subsequently found that all three known arrestins (beta-arrestin, arrestin-3, and visual arrestin) bound specifically to fusion proteins encoding the i3 loop of the 5-HT(2A) receptor. Competition binding studies with synthetic and recombinant peptides showed that the middle portion of the i3 loop, and not the extreme N and C termini, was likely to be involved in i3-arrestin interactions. Dual-label immunofluorescence confocal microscopic studies of rat cortex indicated that many cortical pyramidal neurons coexpressed arrestins (beta-arrestin or arrestin-3) and 5-HT2A receptors, particularly in intracellular vesicles. Our results demonstrate (a) that the i3 loop of the 5-HT2A receptor represents a structurally ordered domain composed of alpha-helical and beta-loop, -turn, and -sheet regions, (b) that this loop interacts with arrestins in vitro, and is hence active, and (c) that arrestins are colocalized with 5-HT2A receptors in vivo.
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Affiliation(s)
- E I Gelber
- Department of Biochemistry, Case Western Reserve University Medical School, Cleveland, Ohio 44106-4935, USA
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