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Basmisanil, a highly selective GABA A-α5 negative allosteric modulator: preclinical pharmacology and demonstration of functional target engagement in man. Sci Rep 2021; 11:7700. [PMID: 33833333 PMCID: PMC8032764 DOI: 10.1038/s41598-021-87307-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 03/26/2021] [Indexed: 12/21/2022] Open
Abstract
GABAA-α5 subunit-containing receptors have been shown to play a key modulatory role in cognition and represent a promising drug target for cognitive dysfunction, as well as other disorders. Here we report on the preclinical and early clinical profile of a novel GABAA-α5 selective negative allosteric modulator (NAM), basmisanil, which progressed into Phase II trials for intellectual disability in Down syndrome and cognitive impairment associated with schizophrenia. Preclinical pharmacology studies showed that basmisanil is the most selective GABAA-α5 receptor NAM described so far. Basmisanil bound to recombinant human GABAA-α5 receptors with 5 nM affinity and more than 90-fold selectivity versus α1, α2, and α3 subunit-containing receptors. Moreover, basmisanil inhibited GABA-induced currents at GABAA-α5 yet had little or no effect at the other receptor subtypes. An in vivo occupancy study in rats showed dose-dependent target engagement and was utilized to establish the plasma exposure to receptor occupancy relationship. At estimated receptor occupancies between 30 and 65% basmisanil attenuated diazepam-induced spatial learning impairment in rats (Morris water maze), improved executive function in non-human primates (object retrieval), without showing anxiogenic or proconvulsant effects in rats. During the Phase I open-label studies, basmisanil showed good safety and tolerability in healthy volunteers at maximum GABAA-α5 receptor occupancy as confirmed by PET analysis with the tracer [11C]-Ro 15-4513. An exploratory EEG study provided evidence for functional activity of basmisanil in human brain. Therefore, these preclinical and early clinical studies show that basmisanil has an ideal profile to investigate potential clinical benefits of GABAA-α5 receptor negative modulation.
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Ye J, Zou G, Zhu R, Kong C, Miao C, Zhang M, Li J, Xiong W, Wang C. Structural basis of GABARAP-mediated GABA A receptor trafficking and functions on GABAergic synaptic transmission. Nat Commun 2021; 12:297. [PMID: 33436612 PMCID: PMC7803741 DOI: 10.1038/s41467-020-20624-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 12/04/2020] [Indexed: 01/07/2023] Open
Abstract
GABAA receptors (GABAARs) are the primary fast inhibitory ion channels in the central nervous system. Dysfunction of trafficking and localization of GABAARs to cell membranes is clinically associated with severe psychiatric disorders in humans. The GABARAP protein is known to support the stability of GABAARs in synapses, but the underlying molecular mechanisms remain to be elucidated. Here, we show that GABARAP/GABARAPL1 directly binds to a previously unappreciated region in the γ2 subunit of GABAAR. We demonstrate that GABARAP functions to stabilize GABAARs via promoting its trafficking pathway instead of blocking receptor endocytosis. The GABARAPL1-γ2-GABAAR crystal structure reveals the mechanisms underlying the complex formation. We provide evidence showing that phosphorylation of γ2-GABAAR differentially modulate the receptor's binding to GABARAP and the clathrin adaptor protein AP2. Finally, we demonstrate that GABAergic synaptic currents are reduced upon specific blockage of the GABARAP-GABAAR complex formation. Collectively, our results reveal that GABARAP/GABARAPL1, but not other members of the Atg8 family proteins, specifically regulates synaptic localization of GABAARs via modulating the trafficking of the receptor.
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Affiliation(s)
- Jin Ye
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Guichang Zou
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Ruichi Zhu
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
- Center of Systems Biology and Human Health, Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
| | - Chao Kong
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Chenjian Miao
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Mingjie Zhang
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
- Center of Systems Biology and Human Health, Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
| | - Jianchao Li
- Division of Cell, Developmental and Integrative Biology, School of Medicine, South China University of Technology, 510006, Guangzhou, P.R. China.
| | - Wei Xiong
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China.
- Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, 200031, Shanghai, P.R. China.
| | - Chao Wang
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China.
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Nuwer JL, Fleck MW. Anterograde trafficking signals in GABA A subunits are required for functional expression. Channels (Austin) 2019; 13:440-454. [PMID: 31610743 PMCID: PMC6802930 DOI: 10.1080/19336950.2019.1676368] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/30/2022] Open
Abstract
Pentameric GABAA receptors are composed from 19 possible subunits. The GABAA β subunit is unique because the β1 and β3 subunits can assemble and traffic to the cell surface as homomers, whereas most of the other subunits, including β2, are heteromers. The intracellular domain (ICD) of the GABAA subunits has been implicated in targeting and clustering GABAA receptors at the plasma membrane. Here, we sought to test whether and how the ICD is involved in functional expression of the β3 subunit. Since θ is the most homologous to β but does not form homomers, we created two reciprocal chimeric subunits, swapping the ICD between the β3 and θ subunits, and expressed them in HEK293 cells. Surface expression was detected with immunofluorescence and functional expression was quantified using whole-cell patch-clamp recording with fast perfusion. Results indicate that, unlike β3, neither the β3/θIC nor the θ/β3IC chimera can traffic to the plasma membrane when expressed alone; however, when expressed in combination with either wild-type α3 or β3, the β3/θIC chimera was functionally expressed. This suggests that the ICD of α3 and β3 each contain essential anterograde trafficking signals that are required to overcome ER retention of assembled GABAA homo- or heteropentamers.
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Affiliation(s)
- Jessica L Nuwer
- Neuroscience & Experimental Therapeutics, Albany Medical College , Albany , NY , USA
| | - Mark W Fleck
- Neuroscience & Experimental Therapeutics, Albany Medical College , Albany , NY , USA
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Fan J, Li D, Chen HS, Huang JG, Xu JF, Zhu WW, Chen JG, Wang F. Metformin produces anxiolytic-like effects in rats by facilitating GABA A receptor trafficking to membrane. Br J Pharmacol 2018; 176:297-316. [PMID: 30318707 DOI: 10.1111/bph.14519] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2018] [Revised: 09/15/2018] [Accepted: 09/19/2018] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND AND PURPOSE Altered function or expression of GABAA receptors contributes to anxiety disorders. Benzodiazepines are widely prescribed for the treatment of anxiety. However, the long-term use of benzodiazepines increases the risk of developing drug dependence and tolerance. Thus, it is urgent to explore new therapeutic approaches. Metformin is widely used to treat Type 2 diabetes and other metabolic syndromes. However, the role of metformin in psychiatric disorders, especially anxiety, remains largely unknown. EXPERIMENTAL APPROACH We examined the effects of metformin on anxiety-like behaviour of rats in open field test and elevated plus maze test. We also observed the effect of metformin (10 μM, in vitro; 100 mg·kg-1 , in vivo) on the trafficking of GABAA receptors, as mechanisms underlying the anxiolytic effects of metformin. KEY RESULTS Metformin (100 mg·kg-1 , i.p. 30 min) displayed a robust and rapid anxiolytic effect, without tolerance. Metformin up-regulated the surface expression of GABAA receptors and increased miniature inhibitory postsynaptic currents (mIPSCs). AMP-activated protein kinase (AMPK) activated by metformin-induced stimulation of forkhead box O3a (FoxO3a) transcriptional activity, followed by increased expression of GABAA receptor-associated protein (GABARAP) and its binding to GABAA receptors finally resulted in the membrane insertion of GABAA receptors. CONCLUSIONS AND IMPLICATIONS Metformin increased mIPSCs by up-regulating the membrane insertion of GABAA receptors, via a pathway involving AMPK, FoxO3a, and the GABAA receptor-associated protein. Thus metformin has a potential new use in the treatment of anxiety disorders.
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Affiliation(s)
- Jun Fan
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Di Li
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Hong-Sheng Chen
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Jian-Geng Huang
- Department of Pharmaceutics, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Jun-Feng Xu
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Wen-Wen Zhu
- Department of Pharmaceutics, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Jian-Guo Chen
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.,The Key Laboratory of Neurological Diseases (HUST), Ministry of Education of China, Wuhan, China.,Hubei Key Laboratory of Drug Target Research and Pharmacodynamic Evaluation (HUST), Wuhan, China.,Laboratory of Neuropsychiatric Diseases, The Institute of Brain Research, Huazhong University of Science and Technology, Wuhan, China.,The Collaborative-Innovation Center for Brain Science, Wuhan, China
| | - Fang Wang
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.,The Key Laboratory of Neurological Diseases (HUST), Ministry of Education of China, Wuhan, China.,Hubei Key Laboratory of Drug Target Research and Pharmacodynamic Evaluation (HUST), Wuhan, China.,Laboratory of Neuropsychiatric Diseases, The Institute of Brain Research, Huazhong University of Science and Technology, Wuhan, China.,The Collaborative-Innovation Center for Brain Science, Wuhan, China
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Chen Y, Sun HQ, Eichorst JP, Albanesi JP, Yin H, Mueller JD. Comobility of GABARAP and Phosphatidylinositol 4-Kinase 2A on Cytoplasmic Vesicles. Biochemistry 2018; 57:3556-3559. [PMID: 29792687 DOI: 10.1021/acs.biochem.8b00224] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
We previously reported that recruitment of the type IIA phosphatidylinositol 4-kinase (PI4K2A) to autophagosomes by GABARAP, a member of the Atg8 family of autophagy-related proteins, is important for autophagosome-lysosome fusion. Because both PI4K2A and GABARAP have also been implicated in the intracellular trafficking of plasma membrane receptors in the secretory/endocytic pathway, we characterized their interaction in cells under nonautophagic conditions. Fluorescence fluctuation spectroscopy measurements revealed that GABARAP exists predominantly as a cytosolic monomer in live cells, but is recruited to small cytoplasmic vesicles upon overexpression of PI4K2A. C-Terminal lipidation of GABARAP, which is essential for its autophagic activities, is not necessary for its recruitment to these PI4K2A-containing transport vesicles. However, a GABARAP truncation mutant lacking C-terminal residues 103-117 fails to bind to PI4K2A, is not recruited to cytoplasmic vesicles, and does not codistribute with PI4K2A on subcellular organelles. These observations suggest that the PI4K2A-GABARAP interaction plays a role in membrane trafficking both under autophagic and nonautophagic conditions.
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Affiliation(s)
- Yan Chen
- School of Physics and Astronomy , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | | | - John P Eichorst
- School of Physics and Astronomy , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | | | | | - Joachim D Mueller
- School of Physics and Astronomy , University of Minnesota , Minneapolis , Minnesota 55455 , United States
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Mathew S, Faheem M, Al-Malki AL, Kumosani TA, Qadri I. In silico inhibition of GABARAP activity using antiepileptic medicinal derived compounds. Bioinformation 2015; 11:189-95. [PMID: 26124559 PMCID: PMC4479051 DOI: 10.6026/97320630011189] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2015] [Accepted: 03/14/2015] [Indexed: 01/25/2023] Open
Abstract
Epilepsy is a neurological disorder affecting more than 50 million people worldwide. It can be controlled by antiepileptic drugs (AEDs) but more than 30% patients are still resistant to AEDs. To overcome this problem, researchers are trying to develop novel approaches to treat epilepsy including the use of herbal medicines. The γ-amino butyric acid type-A receptor associated protein (GABARAP) is ubiquitin-like modifier implicated in the intracellular trafficking of GABAAR. An in silico mutation was created at 116 amino acid position G116A, and an in silico study was carried out to identify the potential binding inhibitors (with antiepileptic properties) against the active sites of GABARAP. Five different plant derived compounds namely (a) Aconitine (b) Berberine (c) Montanine (d) Raubasine (e) Safranal were selected, and their quantitative structure-activity relationships (QSAR) have been conducted to search the inhibitory activity of the selected compounds. The results have shown maximum number of hydrogen bond (H-bond) interactions of Raubasine with highest interaction energy among all of the five compounds. So, Raubasine could be the best fit ligand of GABARAP but in vitro, and in vivo studies are necessary for further confirmation.
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Affiliation(s)
- Shilu Mathew
- Center of Excellence in Genomic Medicine Research, King Abdulaziz University, Jeddah, KSA
- Authors contributed equally
| | - Muhammad Faheem
- Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah, KSA
- Authors contributed equally
| | | | - Taha A Kumosani
- Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah, KSA
- Experimental Biochemistry Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, KSA
| | - Ishtiaq Qadri
- Medical Biotechnology and Translational Medicine Research, King Fahd Medical Research Center, King Abdul Aziz University, PO Box 80216 Jeddah 21589, Saudi Arabia
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Asano S, Nemoto T, Kitayama T, Harada K, Zhang J, Harada K, Tanida I, Hirata M, Kanematsu T. Phospholipase C-related catalytically inactive protein (PRIP) controls KIF5B-mediated insulin secretion. Biol Open 2014; 3:463-74. [PMID: 24812354 PMCID: PMC4058080 DOI: 10.1242/bio.20147591] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We previously reported that phospholipase C-related catalytically inactive protein (PRIP)-knockout mice exhibited hyperinsulinemia. Here, we investigated the role of PRIP in insulin granule exocytosis using Prip-knockdown mouse insulinoma (MIN6) cells. Insulin release from Prip-knockdown MIN6 cells was higher than that from control cells, and Prip knockdown facilitated movement of GFP-phogrin-labeled insulin secretory vesicles. Double-immunofluorescent staining and density step-gradient analyses showed that the KIF5B motor protein co-localized with insulin vesicles in Prip-knockdown MIN6 cells. Knockdown of GABAA-receptor-associated protein (GABARAP), a microtubule-associated PRIP-binding partner, by Gabarap silencing in MIN6 cells reduced the co-localization of insulin vesicles with KIF5B and the movement of vesicles, resulting in decreased insulin secretion. However, the co-localization of KIF5B with microtubules was not altered in Prip- and Gabarap-knockdown cells. The presence of unbound GABARAP, freed either by an interference peptide or by Prip silencing, in MIN6 cells enhanced the co-localization of insulin vesicles with microtubules and promoted vesicle mobility. Taken together, these data demonstrate that PRIP and GABARAP function in a complex to regulate KIF5B-mediated insulin secretion, providing new insights into insulin exocytic mechanisms.
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Affiliation(s)
- Satoshi Asano
- Department of Cellular and Molecular Pharmacology, Division of Basic Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan
| | - Tomomi Nemoto
- Laboratory of Molecular and Cellular Biophysics, Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan
| | - Tomoya Kitayama
- Department of Cellular and Molecular Pharmacology, Division of Basic Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan
| | - Kae Harada
- Department of Cellular and Molecular Pharmacology, Division of Basic Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan
| | - Jun Zhang
- Department of Cellular and Molecular Pharmacology, Division of Basic Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan
| | - Kana Harada
- Department of Cellular and Molecular Pharmacology, Division of Basic Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan
| | - Isei Tanida
- Laboratory of Biomembranes, Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, Tokyo 162-8640, Japan
| | - Masato Hirata
- Laboratory of Molecular and Cellular Biochemistry, Faculty of Dental Science, Kyushu University, Fukuoka 812-8582, Japan
| | - Takashi Kanematsu
- Department of Cellular and Molecular Pharmacology, Division of Basic Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan
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Li C, Chen S, Yu Y, Zhou C, Wang Y, Le K, Li D, Shao W, Lu L, You Y, Peng J, Huang H, Liu P, Shen X. BIG1, a brefeldin A-inhibited guanine nucleotide-exchange factor, is required for GABA-gated Cl⁻ influx through regulation of GABAA receptor trafficking. Mol Neurobiol 2013; 49:808-19. [PMID: 24198228 DOI: 10.1007/s12035-013-8558-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2013] [Accepted: 09/22/2013] [Indexed: 10/26/2022]
Abstract
GABAA receptors (GABAARs) mediate the majority of fast synaptic inhibition. Trafficking regulation and protein-protein interactions that maintain the appropriate number of GABAARs at the cell surface are considered to be important mechanisms for controlling the strength of synaptic inhibition. Here, we report that BIG1, a brefeldin A (BFA)-inhibited guanine nucleotide-exchange factor (GEF) which has a known role in vesicle trafficking, is a new binding partner of GABAARs. Treatment of neurons with BFA, an uncompetitive inhibitor of BIG1 GEF activity, or depletion of BIG1 by small RNA interference (siRNA) significantly decreased GABAARs at the neuronal surface and suppressed GABA-gated influx of chloride ions. Over-expression of HA-tagged BIG1-E793K, a dominant-negative mutant, also significantly decreased GABAARs at the neuronal surface, but had no effect on the total amount of GABAARs. Inhibition of GABAAR endocytosis by muscimol increased both GABAARs and BIG1 at the neuronal surface in a time-dependent fashion, and this increase could be abolished by bicuculline. Finally, depletion of BIG1 by siRNA inhibited the muscimol-stimulated increase of GABAARs. Those data suggest an important function of BIG1 in trafficking of GABAARs to the cell surface through its GEF activity. Thus, we identify an important role of BIG1 in modulating GABA-gated Cl(-) influx through the regulation of cell surface expression of GABAARs.
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Affiliation(s)
- Cuixian Li
- Laboratory of Pharmacology and Toxicology, School of Pharmaceutical Sciences, Sun Yat-sen University, No. 132, Waihuan East Road, Higher Education Mega Center, Guangzhou, 510006, People's Republic of China
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Perkins DI, Trudell JR, Asatryan L, Davies DL, Alkana RL. Charge and geometry of residues in the loop 2 β hairpin differentially affect agonist and ethanol sensitivity in glycine receptors. J Pharmacol Exp Ther 2012; 341:543-51. [PMID: 22357974 DOI: 10.1124/jpet.111.190942] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Recent studies highlighted the importance of loop 2 of α1 glycine receptors (GlyRs) in the propagation of ligand-binding energy to the channel gate. Mutations that changed polarity at position 52 in the β hairpin of loop 2 significantly affected sensitivity to ethanol. The present study extends the investigation to charged residues. We found that substituting alanine with the negative glutamate at position 52 (A52E) significantly left-shifted the glycine concentration response curve and increased sensitivity to ethanol, whereas the negative aspartate substitution (A52D) significantly right-shifted the glycine EC₅₀ but did not affect ethanol sensitivity. It is noteworthy that the uncharged glutamine at position 52 (A52Q) caused only a small right shift of the glycine EC₅₀ while increasing ethanol sensitivity as much as A52E. In contrast, the shorter uncharged asparagine (A52N) caused the greatest right shift of glycine EC₅₀ and reduced ethanol sensitivity to half of wild type. Collectively, these findings suggest that charge interactions determined by the specific geometry of the amino acid at position 52 (e.g., the 1-Å chain length difference between aspartate and glutamate) play differential roles in receptor sensitivity to agonist and ethanol. We interpret these results in terms of a new homology model of GlyR based on a prokaryotic ion channel and propose that these mutations form salt bridges to residues across the β hairpin (A52E-R59 and A52N-D57). We hypothesize that these electrostatic interactions distort loop 2, thereby changing agonist activation and ethanol modulation. This knowledge will help to define the key physical-chemical parameters that cause the actions of ethanol in GlyRs.
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Affiliation(s)
- Daya I Perkins
- Alcohol and Brain Research Laboratories, Departments of Pharmacology and Pharmaceutical Sciences, University of Southern California, Los Angeles, CA, USA
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Vithlani M, Terunuma M, Moss SJ. The dynamic modulation of GABA(A) receptor trafficking and its role in regulating the plasticity of inhibitory synapses. Physiol Rev 2011; 91:1009-22. [PMID: 21742794 DOI: 10.1152/physrev.00015.2010] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inhibition in the adult mammalian central nervous system (CNS) is mediated by γ-aminobutyric acid (GABA). The fast inhibitory actions of GABA are mediated by GABA type A receptors (GABA(A)Rs); they mediate both phasic and tonic inhibition in the brain and are the principle sites of action for anticonvulsant, anxiolytic, and sedative-hypnotic agents that include benzodiazepines, barbiturates, neurosteroids, and some general anesthetics. GABA(A)Rs are heteropentameric ligand-gated ion channels that are found concentrated at inhibitory postsynaptic sites where they mediate phasic inhibition and at extrasynaptic sites where they mediate tonic inhibition. The efficacy of inhibition and thus neuronal excitability is critically dependent on the accumulation of specific GABA(A)R subtypes at inhibitory synapses. Here we evaluate how neurons control the number of GABA(A)Rs on the neuronal plasma membrane together with their selective stabilization at synaptic sites. We then go on to examine the impact that these processes have on the strength of synaptic inhibition and behavior.
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Affiliation(s)
- Mansi Vithlani
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts, USA
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11
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Smith KR, Oliver PL, Lumb MJ, Arancibia-Carcamo IL, Revilla-Sanchez R, Brandon NJ, Moss SJ, Kittler JT. Identification and characterisation of a Maf1/Macoco protein complex that interacts with GABAA receptors in neurons. Mol Cell Neurosci 2010; 44:330-41. [PMID: 20417281 DOI: 10.1016/j.mcn.2010.04.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2009] [Revised: 03/09/2010] [Accepted: 04/09/2010] [Indexed: 01/16/2023] Open
Abstract
The majority of fast inhibitory synaptic transmission in the mammalian nervous system is mediated by GABA(A) receptors (GABA(A)Rs). Here we report a novel interaction between the protein Maf1 and GABA(A)R beta-subunit intracellular domains. We find Maf1 to be highly expressed in brain and enriched in the hippocampus and cortex. In heterologous cells and neurons we show Maf1 co-localises with GABA(A)Rs in intracellular compartments and at the cell surface. In neurons, Maf1 is found localised in the cytoplasm in dendrites, partially overlapping with GABA(A)Rs and inhibitory synapses and in addition is enriched in the neuronal nucleus. We also report that Maf1 interacts with a novel coiled-coil domain containing protein that we have called Macoco (for Maf1 interacting coiled-coil protein). Like Maf1, Macoco can also be found localised to inhibitory synapses and directly interacts with GABA(A)Rs. Expressing Macoco in neurons increases surface GABA(A)R levels. Our results suggest that Maf1 and Macoco are novel GABA(A)R interacting proteins important for regulating GABA(A)R surface expression and GABA(A)R signalling in the brain.
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Affiliation(s)
- Katharine R Smith
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
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Tabakoff B, Saba L, Printz M, Flodman P, Hodgkinson C, Goldman D, Koob G, Richardson HN, Kechris K, Bell RL, Hübner N, Heinig M, Pravenec M, Mangion J, Legault L, Dongier M, Conigrave KM, Whitfield JB, Saunders J, Grant B, Hoffman PL. Genetical genomic determinants of alcohol consumption in rats and humans. BMC Biol 2009; 7:70. [PMID: 19874574 PMCID: PMC2777866 DOI: 10.1186/1741-7007-7-70] [Citation(s) in RCA: 130] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Accepted: 10/27/2009] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND We have used a genetical genomic approach, in conjunction with phenotypic analysis of alcohol consumption, to identify candidate genes that predispose to varying levels of alcohol intake by HXB/BXH recombinant inbred rat strains. In addition, in two populations of humans, we assessed genetic polymorphisms associated with alcohol consumption using a custom genotyping array for 1,350 single nucleotide polymorphisms (SNPs). Our goal was to ascertain whether our approach, which relies on statistical and informatics techniques, and non-human animal models of alcohol drinking behavior, could inform interpretation of genetic association studies with human populations. RESULTS In the HXB/BXH recombinant inbred (RI) rats, correlation analysis of brain gene expression levels with alcohol consumption in a two-bottle choice paradigm, and filtering based on behavioral and gene expression quantitative trait locus (QTL) analyses, generated a list of candidate genes. A literature-based, functional analysis of the interactions of the products of these candidate genes defined pathways linked to presynaptic GABA release, activation of dopamine neurons, and postsynaptic GABA receptor trafficking, in brain regions including the hypothalamus, ventral tegmentum and amygdala. The analysis also implicated energy metabolism and caloric intake control as potential influences on alcohol consumption by the recombinant inbred rats. In the human populations, polymorphisms in genes associated with GABA synthesis and GABA receptors, as well as genes related to dopaminergic transmission, were associated with alcohol consumption. CONCLUSION Our results emphasize the importance of the signaling pathways identified using the non-human animal models, rather than single gene products, in identifying factors responsible for complex traits such as alcohol consumption. The results suggest cross-species similarities in pathways that influence predisposition to consume alcohol by rats and humans. The importance of a well-defined phenotype is also illustrated. Our results also suggest that different genetic factors predispose alcohol dependence versus the phenotype of alcohol consumption.
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Affiliation(s)
- Boris Tabakoff
- Department of Pharmacology, University of Colorado, Denver, Aurora, CO, USA
| | - Laura Saba
- Department of Pharmacology, University of Colorado, Denver, Aurora, CO, USA
| | - Morton Printz
- Department of Pharmacology, University of California San Diego, La Jolla, CA, USA
| | - Pam Flodman
- Department of Pediatrics, University of California Irvine, Irvine, CA, USA
| | - Colin Hodgkinson
- Laboratory of Neurogenetics, National Institute on Alcohol Abuse and Alcoholism, Bethesda, MD, USA
| | - David Goldman
- Laboratory of Neurogenetics, National Institute on Alcohol Abuse and Alcoholism, Bethesda, MD, USA
| | - George Koob
- Committee on the Neurobiology of Addictive Disorders, The Scripps Research Institute, La Jolla, CA, USA
| | - Heather N Richardson
- Committee on the Neurobiology of Addictive Disorders, The Scripps Research Institute, La Jolla, CA, USA
- Department Psychology-Neuroscience, University of Massachusetts Amherst, Amherst, MA, USA
| | - Katerina Kechris
- Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado Denver, Aurora, CO, USA
| | - Richard L Bell
- Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Norbert Hübner
- Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | | | - Michal Pravenec
- Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic
| | - Jonathan Mangion
- MRC Clinical Sciences Centre, London, UK
- Applied Biosystems, Lingley House, 120 Birchwood Blvd., Warrington, Cheshire, WA3 7QH, UK
| | - Lucie Legault
- Department of Psychiatry, McGill University, Montreal, Quebec, Canada
| | - Maurice Dongier
- Department of Psychiatry, McGill University, Montreal, Quebec, Canada
| | - Katherine M Conigrave
- Drug Health Services, Royal Prince Alfred Hospital, Sydney Medical School, University of Sydney, New South Wales, Australia
| | | | - John Saunders
- School of Medicine, University of Queensland, Brisbane, Queensland, Australia
| | - Bridget Grant
- Division of Epidemiology, National Institute on Alcohol Abuse and Alcoholism, Rockville, MD, USA
| | - Paula L Hoffman
- Department of Pharmacology, University of Colorado, Denver, Aurora, CO, USA
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13
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Perkins DI, Trudell JR, Crawford DK, Asatryan L, Alkana RL, Davies DL. Loop 2 structure in glycine and GABA(A) receptors plays a key role in determining ethanol sensitivity. J Biol Chem 2009; 284:27304-14. [PMID: 19656948 DOI: 10.1074/jbc.m109.023598] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The present study tests the hypothesis that the structure of extracellular domain Loop 2 can markedly affect ethanol sensitivity in glycine receptors (GlyRs) and gamma-aminobutyric acid type A receptors (GABA(A)Rs). To test this, we mutated Loop 2 in the alpha1 subunit of GlyRs and in the gamma subunit of alpha1beta2gamma2GABA(A)Rs and measured the sensitivity of wild type and mutant receptors expressed in Xenopus oocytes to agonist, ethanol, and other agents using two-electrode voltage clamp. Replacing Loop 2 of alpha1GlyR subunits with Loop 2 from the deltaGABA(A)R (deltaL2), but not the gammaGABA(A)R subunit, reduced ethanol threshold and increased the degree of ethanol potentiation without altering general receptor function. Similarly, replacing Loop 2 of the gamma subunit of GABA(A)Rs with deltaL2 shifted the ethanol threshold from 50 mm in WT to 1 mm in the GABA(A) gamma-deltaL2 mutant. These findings indicate that the structure of Loop 2 can profoundly affect ethanol sensitivity in GlyRs and GABA(A)Rs. The deltaL2 mutations did not affect GlyR or GABA(A)R sensitivity, respectively, to Zn(2+) or diazepam, which suggests that these deltaL2-induced changes in ethanol sensitivity do not extend to all allosteric modulators and may be specific for ethanol or ethanol-like agents. To explore molecular mechanisms underlying these results, we threaded the WT and deltaL2 GlyR sequences onto the x-ray structure of the bacterial Gloeobacter violaceus pentameric ligand-gated ion channel homologue (GLIC). In addition to being the first GlyR model threaded on GLIC, the juxtaposition of the two structures led to a possible mechanistic explanation for the effects of ethanol on GlyR-based on changes in Loop 2 structure.
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Affiliation(s)
- Daya I Perkins
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California 90089, USA
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14
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Crawford DK, Perkins DI, Trudell JR, Bertaccini EJ, Davies DL, Alkana RL. Roles for loop 2 residues of alpha1 glycine receptors in agonist activation. J Biol Chem 2008; 283:27698-27706. [PMID: 18658152 PMCID: PMC2562068 DOI: 10.1074/jbc.m802384200] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Revised: 06/20/2008] [Indexed: 11/06/2022] Open
Abstract
The present study tested the hypothesis that several residues in Loop 2 of alpha1 glycine receptors (GlyRs) play important roles in mediating the transduction of agonist activation to channel gating. This was accomplished by investigating the effect of cysteine point mutations at positions 50-60 on glycine responses in alpha1GlyRs using two-electrode voltage clamp of Xenopus oocytes. Cysteine substitutions produced position-specific changes in glycine sensitivity that were consistent with a beta-turn structure of Loop 2, with odd-numbered residues in the beta-turn interacting with other agonist-activation elements at the interface between extracellular and transmembrane domains. We also tested the hypothesis that the charge at position 53 is important for agonist activation by measuring the glycine response of wild type (WT) and E53C GlyRs exposed to methanethiosulfonate reagents. As earlier, E53C GlyRs have a significantly higher EC(50) than WT GlyRs. Exposing E53C GlyRs to the negatively charged 2-sulfonatoethyl methanethiosulfonate, but not neutral 2-hydroxyethyl methanethiosulfonate, positively charged 2-aminoethyl methanethiosulfonate, or 2-trimethylammonioethyl methanethiosulfonate, decreased the glycine EC(50) to resemble WT GlyR responses. Exposure to these reagents did not significantly alter the glycine EC(50) for WT GlyRs. The latter findings suggest that the negative charge at position 53 is important for activation of GlyRs through its interaction with positive charge(s) in other neighboring agonist activation elements. Collectively, the findings provide the basis for a refined molecular model of alpha1GlyRs based on the recent x-ray structure of a prokaryotic pentameric ligand-gated ion channel and offer insight into the structure-function relationships in GlyRs and possibly other ligand-gated ion channels.
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Affiliation(s)
- Daniel K Crawford
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California 90089; Neuroscience Graduate Program, University of Southern California, Los Angeles, California 90089
| | - Daya I Perkins
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California 90089
| | - James R Trudell
- Department of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California 94305
| | - Edward J Bertaccini
- Department of Anesthesia and Beckman Program for Molecular and Genetic Medicine, Stanford School of Medicine, Stanford, California 94305; Department of Anesthesia, Palo Alto Veterans Affairs Health Care System, Palo Alto, California 94304
| | - Daryl L Davies
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California 90089.
| | - Ronald L Alkana
- Alcohol and Brain Research Laboratory, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California 90089; Neuroscience Graduate Program, University of Southern California, Los Angeles, California 90089
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15
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Tretter V, Moss SJ. GABA(A) Receptor Dynamics and Constructing GABAergic Synapses. Front Mol Neurosci 2008; 1:7. [PMID: 18946540 PMCID: PMC2526003 DOI: 10.3389/neuro.02.007.2008] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2008] [Accepted: 05/16/2008] [Indexed: 12/04/2022] Open
Abstract
GABAA receptors are located on the majority of neurons in the central and peripheral nervous system, where they mediate important actions of the neurotransmitter gamma-aminobutyric acid. Early in development the trophic properties of GABA allow a healthy development of the nervous system. Most neurons have a high intracellular Cl-concentration early in life due to the late functional expression of the Cl-pump KCC2, therefore GABA has excitatory effects at this stage. Upon higher expression and activation of KCC2 GABA takes on its inhibitory effects while glutamate functions as the major excitatory neurotransmitter. Like all multisubunit membrane proteins the GABAA receptor is assembled in the ER and travels through the Golgi and remaining secretory pathway to the cell surface, where it mediates GABA actions either directly at the synapses or at extrasynaptic sites responding to ambient GABA to provide a basal tonic inhibitory state. In order to adapt to changing needs and information states, the GABAergic system is highly dynamic. That includes subtype specific trafficking to different locations in the cell, regulation of mobility by interaction with scaffold molecules, posttranslational modifications, that either directly affect channel function or the interaction with other proteins and finally the dynamic exchange between surface and intracellular receptor pools, that either prepare receptors for recycling to the surface or degradation. Here we give an overview of the current understanding of GABAA receptor functional and molecular dynamics that play a major part in maintaining the balance between excitation and inhibition and in changes in network activity.
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Affiliation(s)
- Verena Tretter
- Department of Neuroscience, University of Pennsylvania Philadelphia, PA, USA
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16
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Cook JL, Re RN, deHaro DL, Abadie JM, Peters M, Alam J. The trafficking protein GABARAP binds to and enhances plasma membrane expression and function of the angiotensin II type 1 receptor. Circ Res 2008; 102:1539-47. [PMID: 18497328 DOI: 10.1161/circresaha.108.176594] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Proteins that bind to the intracellular expanses, particularly cytoplasmic tail regions, of heptahelical integral membrane receptors are of particular interest in that they can mediate or modulate trafficking or intracellular signaling. In an effort to distinguish new proteins that might promote angiotensin II type 1 (AT(1)) receptor intracellular events, we screened a yeast 2-hybrid mouse brain library with the rat AT(1A) receptor (AT(1)R) carboxyl terminus and identified GABARAP, a protein involved in intracellular trafficking of the GABA(A) receptor, as a binding partner for the AT(1)R. Interaction of GABARAP with the AT(1)R carboxyl terminus was further substantiated using GST pull-down assays, and binding of the full-length tagged AT(1)R to GABARAP was verified using coimmunoprecipitation. Bioluminescence resonance energy transfer assays further confirmed specific interaction of GABARAP with AT(1)R. Moreover, GABARAP clearly increased the steady-state level of plasma membrane-associated AT(1)R in PC-12 cells. Cotransfection of GABARAP with an AT(1)R fluorescent fusion protein increased PC-12 cell surface expression of the AT(1)R more than 6-fold when standardized to the level of intracellular expression. Furthermore, GABARAP overexpression in CHO-K1 cells engineered to express AT(1)R increased angiotensin II binding sites 3.7-fold and angiotensin II-induced phospho-extracellular signal-regulated kinase 1/2 and cellular proliferation significantly over levels obtained with AT(1)R overexpression alone. In addition, small interfering RNA-mediated knockdown of GABARAP reduced the steady-state levels of the AT(1)R fluorescent fusion protein by 43% and its cell surface expression by 84%. Immunoblot analyses confirmed the quantitative image data. We conclude that GABARAP binds to and promotes trafficking of the AT(1)R to the plasma membrane.
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Affiliation(s)
- Julia L Cook
- Division of Research, Ochsner Clinic Foundation, Ochsner Health System, 1514 Jefferson Hwy, New Orleans, LA 70121, USA.
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17
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Jacob TC, Moss SJ, Jurd R. GABA(A) receptor trafficking and its role in the dynamic modulation of neuronal inhibition. Nat Rev Neurosci 2008; 9:331-43. [PMID: 18382465 PMCID: PMC2709246 DOI: 10.1038/nrn2370] [Citation(s) in RCA: 465] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
GABA (gamma-aminobutyric acid) type A receptors (GABA(A)Rs) mediate most fast synaptic inhibition in the mammalian brain, controlling activity at both the network and the cellular levels. The diverse functions of GABA in the CNS are matched not just by the heterogeneity of GABA(A)Rs, but also by the complex trafficking mechanisms and protein-protein interactions that generate and maintain an appropriate receptor cell-surface localization. In this Review, we discuss recent progress in our understanding of the dynamic regulation of GABA(A)R composition, trafficking to and from the neuronal surface, and lateral movement of receptors between synaptic and extrasynaptic locations. Finally, we highlight a number of neurological disorders, including epilepsy and schizophrenia, in which alterations in GABA(A)R trafficking occur.
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Affiliation(s)
- Tija C. Jacob
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA
| | - Stephen J. Moss
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA
- Department of Pharmacology, University College London, WC1E 6BT, UK
| | - Rachel Jurd
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA
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18
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Marsden KC, Beattie JB, Friedenthal J, Carroll RC. NMDA receptor activation potentiates inhibitory transmission through GABA receptor-associated protein-dependent exocytosis of GABA(A) receptors. J Neurosci 2007; 27:14326-37. [PMID: 18160640 PMCID: PMC6673443 DOI: 10.1523/jneurosci.4433-07.2007] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Revised: 11/02/2007] [Accepted: 11/10/2007] [Indexed: 11/21/2022] Open
Abstract
The trafficking of postsynaptic AMPA receptors (AMPARs) is a powerful mechanism for regulating the strength of excitatory synapses. It has become clear that the surface levels of inhibitory GABA(A) receptors (GABA(A)Rs) are also subject to regulation and that GABA(A)R trafficking may contribute to inhibitory plasticity, although the underlying mechanisms are not fully understood. Here, we report that NMDA receptor activation, which has been shown to drive excitatory long-term depression through AMPAR endocytosis, simultaneously increases expression of GABA(A)Rs at the dendritic surface of hippocampal neurons. This NMDA stimulus increases miniature IPSC amplitudes and requires the activity of Ca2+ calmodulin-dependent kinase II and the trafficking proteins N-ethylmaleimide-sensitive factor, GABA receptor-associated protein (GABARAP), and glutamate receptor interacting protein (GRIP). These data demonstrate for the first time that endogenous GABARAP and GRIP contribute to the regulated trafficking of GABA(A)Rs. In addition, they reveal that the bidirectional trafficking of AMPA and GABA(A) receptors can be driven by a single glutamatergic stimulus, providing a potent postsynaptic mechanism for modulating neuronal excitability.
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Affiliation(s)
- Kurt C. Marsden
- Dominick P. Purpura Department of Neuroscience, Rose Kennedy Center for Mental Retardation, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, and
| | - Jennifer B. Beattie
- Dominick P. Purpura Department of Neuroscience, Rose Kennedy Center for Mental Retardation, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, and
| | - Jenna Friedenthal
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520
| | - Reed C. Carroll
- Dominick P. Purpura Department of Neuroscience, Rose Kennedy Center for Mental Retardation, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, and
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19
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Sun H, Hu XQ, Emerit MB, Schoenebeck JC, Kimmel CE, Peoples RW, Miko A, Zhang L. Modulation of 5-HT3 receptor desensitization by the light chain of microtubule-associated protein 1B expressed in HEK 293 cells. J Physiol 2007; 586:751-62. [PMID: 18063656 DOI: 10.1113/jphysiol.2007.136440] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Regulation of ligand-gated ion channel (LGIC) function and trafficking by cytoskeleton proteins has been the topic of recent research. Here, we report that the light chain (LC1) of microtubule-associated protein 1B (MAP1B) specifically interacted with the 5-HT(3A) receptor, a predominant serotonin-gated ion channel in the brain. LC1 and 5-HT(3A) receptors were colocalized in central neurons and in HEK 293 cells expressing 5-HT(3A) receptors. LC1 reduced the steady-state density of 5-HT(3A) receptors at the membrane surface of HEK 293 cells and significantly accelerated receptor desensitization time constants from 3.8 +/- 0.3 s to 0.8 +/- 0.1 s. However, LC1 did not significantly alter agonist binding affinity and single-channel conductance of 5-HT(3A) receptors. On the other hand, application of specific LC1 antisense oligonucleotides and nocodazole, a microtubule disruptor, significantly prolonged the desensitization time of the recombinant and native neuronal 5-HT(3) receptors by 3- to 6-fold. This kinetic change induced by nocodazole was completely rescued by addition of LC1 but not GABA(A) receptor-associated protein (GABARAP), suggesting that LC1 can specifically interact with 5-HT(3A) receptors. These observations suggest that the LC1-5-HT(3A) receptor interaction contributes to a mechanism that regulates receptor desensitization kinetics. Such dynamic regulation may play a role in reshaping the efficacy of 5-HT(3) receptor-mediated synaptic transmission.
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Affiliation(s)
- Hui Sun
- Laboratory for Integrative Neuroscience, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, 5625 Fishers Lane, TS24, Bethesda, MD 20892, USA
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20
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Kawaguchi SY, Hirano T. Sustained structural change of GABA(A) receptor-associated protein underlies long-term potentiation at inhibitory synapses on a cerebellar Purkinje neuron. J Neurosci 2007; 27:6788-99. [PMID: 17581966 PMCID: PMC6672699 DOI: 10.1523/jneurosci.1981-07.2007] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Fast inhibitory synaptic transmission is predominantly mediated by GABA(A) receptor (GABA(A)R) in the CNS. Although several types of neuronal activity-dependent plasticity at GABAergic synapses have been reported, the detailed mechanism is elusive. Here we show that binding of structurally altered GABA(A)R-associated protein (GABARAP) to GABA(A)R gamma2 subunit and to tubulin is critical for long-term potentiation [called rebound potentiation (RP)] at inhibitory synapses on a cerebellar Purkinje neuron (PN). Either inhibition of GABARAP association with GABA(A)Rgamma2 or deletion of tubulin binding region of GABARAP impaired RP. Inhibition of tubulin polymerization also suppressed RP. Thus, precise regulation of GABA(A)Rgamma2-GABARAP-microtubule interaction is critical for RP. Furthermore, competitive inhibition of GABARAP binding to GABA(A)Rgamma2 after the RP establishment attenuated the potentiated response, suggesting that GABARAP is critical not only for the induction but also for the maintenance of RP. Fluorescence resonance energy transfer analysis revealed that GABARAP underwent sustained structural alteration after brief depolarization of a PN depending on the activity of Ca2+/calmodulin-dependent protein kinase II (CaMKII), which is required for the RP induction. The susceptibility of GABARAP to undergo structural alteration was abolished by an amino acid replacement in GABARAP. Furthermore, RP was impaired by expression of the mutant GABARAP with the replacement. Together, we conclude that GABA(A)R association with structurally altered GABARAP downstream of CaMKII activation is essential for RP.
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Affiliation(s)
- Shin-ya Kawaguchi
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan, and
- Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
| | - Tomoo Hirano
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan, and
- Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
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21
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Chen ZW, Chang CSS, Leil TA, Olsen RW. C-terminal modification is required for GABARAP-mediated GABA(A) receptor trafficking. J Neurosci 2007; 27:6655-63. [PMID: 17581952 PMCID: PMC6672693 DOI: 10.1523/jneurosci.0919-07.2007] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We investigated the ubiquitin-like modification of GABA(A) receptor-associated protein (GABARAP) and its function. A fusion protein of GABARAP with v5 in the N terminus and myc in the C terminus was expressed in rat cultured hippocampal neurons and PC12 cells. Western blotting with antibodies to v5 and myc revealed that the C terminus of GABARAP was cleaved off. Cleavage was blocked by mutating the C-terminal Gly116 to Ala, suggesting that G116 is required for the processing. Unlike ubiquitin, GABARAP was not incorporated covalently into higher-molecular-weight protein complexes. Nor was GABARAP degraded by ubiquitinylation through the proteasome, although GABARAP formed noncovalent dimers. Immunofluorescent confocal microscopy demonstrated that recombinantly expressed GABARAP was diffusely localized in PC12 cells. However, prevention of C-terminal processing in the mutant GABARAP(G116A) resulted in redistribution to the Golgi. In neurons, punctate cytoplasmic staining of GABARAP was seen in soma and processes, whereas GABARAP(G116A) was limited to soma. Compared with wild-type GABARAP, the colocalization and interaction of GABARAP(G116A) with GABA(A) receptors were significantly reduced, resulting in a reduction in expression of receptors in the plasma membrane. When alpha1beta2gamma2S-containing GABA(A) receptors were expressed in oocytes, the increased surface expression of GABA(A) receptors, as shown by increased GABA currents and surface-accessible GABA(A) receptor subunit polypeptides resulting from GABARAP coexpression, was prevented by mutation G116A. In addition, the distribution of NSF (N-ethylmaleimide-sensitive factor) was affected in GABARAP(G116A)-expressing neurons. These results suggest that glycine 116 is required for C-terminal processing of GABARAP and that processing is essential for the localization of GABARAP and its functions as a trafficking protein.
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Affiliation(s)
- Zi-Wei Chen
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1735
| | - Chang-Sheng S. Chang
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1735
| | - Tarek A. Leil
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1735
| | - Richard W. Olsen
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1735
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22
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Mizokami A, Kanematsu T, Ishibashi H, Yamaguchi T, Tanida I, Takenaka K, Nakayama KI, Fukami K, Takenawa T, Kominami E, Moss SJ, Yamamoto T, Nabekura J, Hirata M. Phospholipase C-related inactive protein is involved in trafficking of gamma2 subunit-containing GABA(A) receptors to the cell surface. J Neurosci 2007; 27:1692-701. [PMID: 17301177 PMCID: PMC6673751 DOI: 10.1523/jneurosci.3155-06.2007] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The subunit composition of GABA(A) receptors is known to be associated with distinct physiological and pharmacological properties. Previous studies that used phospholipase C-related inactive protein type 1 knock-out (PRIP-1 KO) mice revealed that PRIP-1 is involved in the assembly and/or the trafficking of gamma2 subunit-containing GABA(A) receptors. There are two PRIP genes in mammals; thus the roles of PRIP-1 might be compensated partly by those of PRIP-2 in PRIP-1 KO mice. Here we used PRIP-1 and PRIP-2 double knock-out (PRIP-DKO) mice and examined the roles for PRIP in regulating the trafficking of GABA(A) receptors. Consistent with previous results, sensitivity to diazepam was reduced in electrophysiological and behavioral analyses of PRIP-DKO mice, suggesting an alteration of gamma2 subunit-containing GABA(A) receptors. The surface numbers of diazepam binding sites (alpha/gamma2 subunits) assessed by [3H]flumazenil binding were reduced in the PRIP-DKO mice as compared with those of wild-type mice, whereas the cell surface GABA binding sites (alpha/beta subunits, assessed by [3H]muscimol binding) were increased in PRIP-DKO mice. The association between GABA(A) receptors and GABA(A) receptor-associated protein (GABARAP) was reduced significantly in PRIP-DKO neurons. Disruption of the direct interaction between PRIP and GABA(A) receptor beta subunits via the use of a peptide corresponding to the PRIP-1 binding site reduced the cell surface expression of gamma2 subunit-containing GABA(A) receptors in cultured cell lines and neurons. These results suggest that PRIP is implicated in the trafficking of gamma2 subunit-containing GABA(A) receptors to the cell surface, probably by acting as a bridging molecule between GABARAP and the receptors.
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Affiliation(s)
- Akiko Mizokami
- Laboratory of Molecular and Cellular Biochemistry, Faculty of Dental Science, and Station for Collaborative Research
| | - Takashi Kanematsu
- Laboratory of Molecular and Cellular Biochemistry, Faculty of Dental Science, and Station for Collaborative Research
| | - Hitoshi Ishibashi
- Department of Cellular and System Physiology, Faculty of Medical Science, and
| | - Taku Yamaguchi
- Department of Neuropharmacology, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan
| | - Isei Tanida
- Department of Biochemistry, Juntendo University School of Medicine, Tokyo 113-8421, Japan
| | - Kei Takenaka
- Department of Biochemistry, Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Keiichi I. Nakayama
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan
| | - Kiyoko Fukami
- Laboratory of Genome and Biosignal, Tokyo University of Pharmacy and Life Science, Tokyo 192-0392, Japan
| | - Tadaomi Takenawa
- Department of Biochemistry, Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Eiki Kominami
- Department of Biochemistry, Juntendo University School of Medicine, Tokyo 113-8421, Japan
| | - Stephen J. Moss
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
| | - Tsuneyuki Yamamoto
- Department of Pharmacology, Faculty of Pharmaceutical Science, Nagasaki International University, Nagasaki 859-3298, Japan, and
| | - Junichi Nabekura
- Department of Developmental Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan
| | - Masato Hirata
- Laboratory of Molecular and Cellular Biochemistry, Faculty of Dental Science, and Station for Collaborative Research
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Potential therapeutic implications of intracrine angiogenesis. Med Hypotheses 2007; 69:414-21. [PMID: 17320306 DOI: 10.1016/j.mehy.2006.10.065] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2006] [Accepted: 10/23/2006] [Indexed: 01/19/2023]
Abstract
Angiogenesis, in most cases, is a requirement for tumor growth beyond a diameter of a few millimeters and is, therefore, a major target for cancer therapy. The intracellular actions of certain extracellular signaling proteins (intracrines) have been reported, and it is clear that intracrines such as vascular endothelial growth factor, basic fibroblast growth factor, angiogenin, angiotensin, and endothelin, among others, are involved in angiogenesis. We have proposed that intracrine networks play an important role in angiogenesis, and have suggested that very similar intracrine networks exist in some tumor cells. These notions have implications for the development of anti-angiogenesis therapies because they suggest that the inhibition of intracellular intracrine trafficking pathways may be an effective therapeutic target. Here the participation and regulation of intracrines in angiogenesis is explored, as are the actions of various anti-angiogenic factors.
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Abstract
The fidelity of synaptic function is dependent on the expression of the appropriate neurotransmitter receptor subtype, the targeting and trafficking of receptors to synapses as well as the regulation of the actual number of receptors at synapses. GABAA (γ-aminobutyric acid type A) receptors and NMDA (N-methyl-D-aspartate) receptors are both examples of ligand-gated, heteromeric neurotransmitter receptors whose cell-surface expression is dynamic and tightly regulated. NMDA receptors are localized at excitatory synapses. These synapses are highly structured but dynamic, with the interplay between NMDA receptors and NMDA receptor-associated scaffolding proteins regulating the expression of functional cell-surface synaptic and extrasynaptic receptors. Based on current information, inhibitory synapses seem to be less ordered, and a GABAA receptor equivalent of PSD-95 (postsynaptic density-95), the scaffolding molecule pivotal to the organization of NMDA receptor complexes at synapses, is yet to be validated. In the present paper, processes regulating the trafficking, assembly and molecular organization of both NMDA receptors and GABAA receptors will be discussed.
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Affiliation(s)
- F A Stephenson
- School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, UK.
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Bogdanov Y, Michels G, Armstrong-Gold C, Haydon PG, Lindstrom J, Pangalos M, Moss SJ. Synaptic GABAA receptors are directly recruited from their extrasynaptic counterparts. EMBO J 2006; 25:4381-9. [PMID: 16946701 PMCID: PMC1570424 DOI: 10.1038/sj.emboj.7601309] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2006] [Accepted: 08/03/2006] [Indexed: 11/08/2022] Open
Abstract
GABAA receptors mediate the majority of fast synaptic inhibition in the brain. The accumulation of these ligand-gated ion channels at synaptic sites is a prerequisite for neuronal inhibition, but the molecular mechanisms underlying this phenomenon remain obscure. To further understand these processes, we have examined the cellular origins of synaptic GABAA receptors. To do so, we have created fluorescent GABAA receptors that are capable of binding -bungarotoxin (Bgt), facilitating the visualization of receptor endocytosis, exocytosis and delivery to synaptic sites. Imaging with Bgt in hippocampal neurons revealed that GABAA receptor endocytosis occurred exclusively at extrasynaptic sites, consistent with the preferential colocalization of extrasynaptic receptors with the AP2 adaptin. Receptor insertion into the plasma membrane was also predominantly extrasynaptic, and pulse-chase analysis revealed that these newly inserted receptors were then able to access directly synaptic sites. Therefore, our results demonstrate that synaptic GABAA receptors are directly recruited from their extrasynaptic counterparts. Moreover, they illustrate a dynamic mechanism for neurons to modulate GABAA receptor number at inhibitory synapses by controlling the stability of extrasynaptic receptors.
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Affiliation(s)
- Yury Bogdanov
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, USA
- Department of Pharmacology, University College, London, UK
| | - Guido Michels
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, USA
- Department of Pharmacology, University College, London, UK
- Department of Internal Medicine III, University of Cologne, Cologne, Germany
| | | | - Philip G Haydon
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, USA
| | - Jon Lindstrom
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, USA
| | | | - Stephen J Moss
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, USA
- Department of Pharmacology, University College, London, UK
- Department of Neuroscience, University of Pennsylvania, 145 Johnson Pavilion, Hamilton Walk, Philadelphia, PA 19104, USA. Tel.: +1 215 898 1998; Fax: +1 215 898 1347; E-mail:
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26
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Kumar S, Khisti RT, Morrow AL. Regulation of native GABAA receptors by PKC and protein phosphatase activity. Psychopharmacology (Berl) 2005; 183:241-7. [PMID: 16220337 DOI: 10.1007/s00213-005-0161-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Accepted: 07/29/2005] [Indexed: 10/25/2022]
Abstract
RATIONALE AND OBJECTIVE Protein kinase C (PKC) modulation of ionotropic receptors is a common mechanism for regulation of channel function. The effects of PKC and phosphatase activation on native gamma-aminobutyric acid (GABA(A)) receptors in adult brain are unknown. Previous studies of recombinant GABA(A) receptors have provided evidence that PKC activation inhibits receptor function, whereas other studies suggest that PKC either increases or does not alter GABA(A) receptor function. The present study explored (a) the effects of PKC and phosphatase activity on GABA-mediated (36)Cl(-) uptake in cerebral cortical synaptoneurosomes and (b) the effect of PKC activity on muscimol-induced loss of righting reflex (LORR) in adult rats. METHODS GABA(A) receptor function in vitro was measured by muscimol-induced (36)Cl(-) uptake into cerebral cortical synaptoneurosomes. The in vivo effect of PKC on GABA(A)-mediated function was measured by intracerebroventricular (i.c.v.) injection of 4-beta-phorbol-12,13-dibutyrate (PDBu) or calphostin C followed by determination of muscimol-induced LORR. RESULTS Adenosine triphosphate (ATP) and PDBu produced a concentration-dependent and specific reduction in muscimol-stimulated (36)Cl(-) uptake that was blocked by the PKC inhibitor calphostin C. Both adenosine diphosphate and 4alphaPDBu were ineffective. Phosphatase inhibition produced similar inhibition of muscimol responses. Furthermore, i.c.v. administration of PDBu and calphostin C produced opposing effects on both the onset and the duration of muscimol-induced LORR in rats. CONCLUSIONS The present study provides evidence that PKC activation reduces GABA(A) receptor function in native receptors both in vitro and in vivo. Phosphatase inhibitors decrease muscimol-mediated Cl(-) uptake in GABA(A) receptors demonstrating coordinated regulation of native receptors by PKC and phosphatases.
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Affiliation(s)
- Sandeep Kumar
- Department of Psychiatry, Bowles Center for Alcohol Studies, UNC School of Medicine, Chapel Hill, NC 27599, USA
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