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Shin J, Park J, Jeong J, Lam JH, Qiu X, Wu D, Kim K, Lee JY, Robinson CV, Hyun J, Katritch V, Kim KP, Cho Y. Constitutive activation mechanism of a class C GPCR. Nat Struct Mol Biol 2024; 31:678-687. [PMID: 38332368 DOI: 10.1038/s41594-024-01224-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 01/09/2024] [Indexed: 02/10/2024]
Abstract
Class C G-protein-coupled receptors (GPCRs) are activated through binding of agonists to the large extracellular domain (ECD) followed by rearrangement of the transmembrane domains (TMDs). GPR156, a class C orphan GPCR, is unique because it lacks an ECD and exhibits constitutive activity. Impaired GPR156-Gi signaling contributes to loss of hearing. Here we present the cryo-electron microscopy structures of human GPR156 in the Go-free and Go-coupled states. We found that an endogenous phospholipid molecule is located within each TMD of the GPR156 dimer. Asymmetric binding of Gα to the phospholipid-bound GPR156 dimer restructures the first and second intracellular loops and the carboxy-terminal part of the elongated transmembrane 7 (TM7) without altering dimer conformation. Our findings reveal that GPR156 is a transducer for phospholipid signaling. Constant binding of abundant phospholipid molecules and the G-protein-induced reshaping of the cytoplasmic face provide a basis for the constitutive activation of GPR156.
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Affiliation(s)
- Jinwoo Shin
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Junhyeon Park
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Jieun Jeong
- Department of Applied Chemistry, Global Center for Pharmaceutical Ingredient Materials, Kyung Hee University, Yongin, Republic of Korea
| | - Jordy Homing Lam
- Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, USA
- Bridge Institute and Michelson Center for Convergent Biosciences, University of Southern California, Los Angeles, CA, USA
| | - Xingyu Qiu
- Department of Chemistry, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
| | - Di Wu
- Department of Chemistry, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
| | - Kuglae Kim
- Department of Pharmacy, Yonsei University, Incheon, Republic of Korea
| | - Joo-Youn Lee
- Therapeutics and Biotechnology Division, Korea Research Institute of Chemical Technology, 141 Gajeong-ro, Yuseong-gu, Daejeon, Republic of Korea
| | - Carol V Robinson
- Department of Chemistry, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
| | - Jaekyung Hyun
- School of Pharmacy, Sungkyunkwan University, Suwon, Republic of Korea
| | - Vsevolod Katritch
- Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, USA
- Bridge Institute and Michelson Center for Convergent Biosciences, University of Southern California, Los Angeles, CA, USA
- Center for New Technologies in Drug Discovery and Development, University of Southern California, Los Angeles, CA, USA
- Department of Chemistry, University of Southern California, Los Angeles, CA, USA
| | - Kwang Pyo Kim
- Department of Applied Chemistry, Global Center for Pharmaceutical Ingredient Materials, Kyung Hee University, Yongin, Republic of Korea.
- Department of Biomedical Science and Technology, Kyung Hee Medical Science Research Institute, Kyung Hee University, Seoul, Republic of Korea.
| | - Yunje Cho
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Republic of Korea.
- Department of Medical Science and Engineering, Pohang University of Science and Technology, Pohang, Republic of Korea.
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2
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Scharf MM, Humphrys LJ, Berndt S, Di Pizio A, Lehmann J, Liebscher I, Nicoli A, Niv MY, Peri L, Schihada H, Schulte G. The dark sides of the GPCR tree - research progress on understudied GPCRs. Br J Pharmacol 2024. [PMID: 38339984 DOI: 10.1111/bph.16325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Revised: 11/24/2023] [Accepted: 01/08/2024] [Indexed: 02/12/2024] Open
Abstract
A large portion of the human GPCRome is still in the dark and understudied, consisting even of entire subfamilies of GPCRs such as odorant receptors, class A and C orphans, adhesion GPCRs, Frizzleds and taste receptors. However, it is undeniable that these GPCRs bring an untapped therapeutic potential that should be explored further. Open questions on these GPCRs span diverse topics such as deorphanisation, the development of tool compounds and tools for studying these GPCRs, as well as understanding basic signalling mechanisms. This review gives an overview of the current state of knowledge for each of the diverse subfamilies of understudied receptors regarding their physiological relevance, molecular mechanisms, endogenous ligands and pharmacological tools. Furthermore, it identifies some of the largest knowledge gaps that should be addressed in the foreseeable future and lists some general strategies that might be helpful in this process.
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Affiliation(s)
- Magdalena M Scharf
- Karolinska Institutet, Dept. Physiology & Pharmacology, Sec. Receptor Biology & Signaling, Stockholm, Sweden
| | - Laura J Humphrys
- Institute of Pharmacy, University of Regensburg, Regensburg, Germany
| | - Sandra Berndt
- Rudolf Schönheimer Institute for Biochemistry, Molecular Biochemistry, University of Leipzig, Leipzig, Germany
| | - Antonella Di Pizio
- Leibniz Institute for Food Systems Biology at the Technical University of Munich, Freising, Germany
- Chemoinformatics and Protein Modelling, Department of Molecular Life Science, School of Life Science, Technical University of Munich, Freising, Germany
| | - Juliane Lehmann
- Rudolf Schönheimer Institute for Biochemistry, Molecular Biochemistry, University of Leipzig, Leipzig, Germany
| | - Ines Liebscher
- Rudolf Schönheimer Institute for Biochemistry, Molecular Biochemistry, University of Leipzig, Leipzig, Germany
| | - Alessandro Nicoli
- Leibniz Institute for Food Systems Biology at the Technical University of Munich, Freising, Germany
- Chemoinformatics and Protein Modelling, Department of Molecular Life Science, School of Life Science, Technical University of Munich, Freising, Germany
| | - Masha Y Niv
- The Institute of Biochemistry, Food Science and Nutrition, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Lior Peri
- The Institute of Biochemistry, Food Science and Nutrition, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Hannes Schihada
- Institute of Pharmaceutical Chemistry, Philipps-University Marburg, Marburg, Germany
| | - Gunnar Schulte
- Karolinska Institutet, Dept. Physiology & Pharmacology, Sec. Receptor Biology & Signaling, Stockholm, Sweden
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3
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Ma X, Guo J, Fu Y, Shen C, Jiang P, Zhang Y, Zhang L, Yu Y, Fan J, Chai R. G protein-coupled receptors in cochlea: Potential therapeutic targets for hearing loss. Front Mol Neurosci 2022; 15:1028125. [PMID: 36311029 PMCID: PMC9596917 DOI: 10.3389/fnmol.2022.1028125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Accepted: 09/21/2022] [Indexed: 11/29/2022] Open
Abstract
The prevalence of hearing loss-related diseases caused by different factors is increasing worldwide year by year. Currently, however, the patient’s hearing loss has not been effectively improved. Therefore, there is an urgent need to adopt new treatment measures and treatment techniques to help improve the therapeutic effect of hearing loss. G protein-coupled receptors (GPCRs), as crucial cell surface receptors, can widely participate in different physiological and pathological processes, particularly play an essential role in many disease occurrences and be served as promising therapeutic targets. However, no specific drugs on the market have been found to target the GPCRs of the cochlea. Interestingly, many recent studies have demonstrated that GPCRs can participate in various pathogenic process related to hearing loss in the cochlea including heredity, noise, ototoxic drugs, cochlear structure, and so on. In this review, we comprehensively summarize the functions of 53 GPCRs known in the cochlea and their relationships with hearing loss, and highlight the recent advances of new techniques used in cochlear study including cryo-EM, AI, GPCR drug screening, gene therapy vectors, and CRISPR editing technology, as well as discuss in depth the future direction of novel GPCR-based drug development and gene therapy for cochlear hearing loss. Collectively, this review is to facilitate basic and (pre-) clinical research in this area, and provide beneficial help for emerging GPCR-based cochlear therapies.
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Affiliation(s)
- Xiangyu Ma
- State Key Laboratory of Bioelectronics, Jiangsu Province High-Tech Key Laboratory for Bio-Medical Research, Department of Otolaryngology Head and Neck Surgery, Zhongda Hospital, School of Life Sciences and Technology, Advanced Institute for Life and Health, Southeast University, Nanjing, China
| | - Jiamin Guo
- State Key Laboratory of Bioelectronics, Jiangsu Province High-Tech Key Laboratory for Bio-Medical Research, Department of Otolaryngology Head and Neck Surgery, Zhongda Hospital, School of Life Sciences and Technology, Advanced Institute for Life and Health, Southeast University, Nanjing, China
| | - Yaoyang Fu
- Department of Psychiatry, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Cangsong Shen
- College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Pei Jiang
- State Key Laboratory of Bioelectronics, Jiangsu Province High-Tech Key Laboratory for Bio-Medical Research, Department of Otolaryngology Head and Neck Surgery, Zhongda Hospital, School of Life Sciences and Technology, Advanced Institute for Life and Health, Southeast University, Nanjing, China
| | - Yuan Zhang
- Jiangsu Provincial Key Medical Discipline (Laboratory), Department of Otolaryngology Head and Neck Surgery, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, China
- Research Institute of Otolaryngology, Nanjing, China
| | - Lei Zhang
- Department of Otorhinolaryngology, Head and Neck Surgery, The Second Hospital of Anhui Medical University, Hefei, China
| | - Yafeng Yu
- First Affiliated Hospital of Soochow University, Soochow, China
- *Correspondence: Yafeng Yu,
| | - Jiangang Fan
- Department of Otolaryngology Head and Neck Surgery, Sichuan Provincial People’s Hospital, University of Electronic Science and Technology of China, Chengdu, China
- Jiangang Fan,
| | - Renjie Chai
- State Key Laboratory of Bioelectronics, Jiangsu Province High-Tech Key Laboratory for Bio-Medical Research, Department of Otolaryngology Head and Neck Surgery, Zhongda Hospital, School of Life Sciences and Technology, Advanced Institute for Life and Health, Southeast University, Nanjing, China
- Department of Otolaryngology Head and Neck Surgery, Sichuan Provincial People’s Hospital, University of Electronic Science and Technology of China, Chengdu, China
- Co-Innovation Center of Neuroregeneration, Nantong University, Nantong, China
- Institute for Stem Cell and Regeneration, Chinese Academy of Sciences, Beijing, China
- Beijing Key Laboratory of Neural Regeneration and Repair, Capital Medical University, Beijing, China
- Renjie Chai,
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Davis BH, Beasley TM, Amaral M, Szaflarski JP, Gaston T, Perry Grayson L, Standaert DG, Bebin EM, Limdi NA. Pharmacogenetic Predictors of Cannabidiol Response and Tolerability in Treatment-Resistant Epilepsy. Clin Pharmacol Ther 2021; 110:1368-1380. [PMID: 34464454 PMCID: PMC8530979 DOI: 10.1002/cpt.2408] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 08/15/2021] [Indexed: 12/25/2022]
Abstract
In patients with treatment‐resistant epilepsy (TRE), cannabidiol (CBD) produces variable improvement in seizure control. Patients in the University of Alabama at Birmingham CBD Expanded Access Program (EAP) were enrolled in the genomic study and genotyped using the Affymetrix Drug Metabolizing Enzymes and Transporters plus array. Associations between variants and CBD response (≥50% seizure reduction) and tolerability (diarrhea, sedation, and abnormal liver function) was evaluated under dominant and recessive models. Expression quantitative trait loci (eQTL) influencing potential CBD targets was evaluated in the UK Brain Expression Consortium data set (Braineac), and genetic co‐expression examined. Of 169 EAP patients, 112 (54.5% pediatric and 50.0% female) were included in the genetic analyses. Patients with AOX1 rs6729738 CC (aldehyde oxidase; odds ratio (OR) 6.69, 95% confidence interval (CI) 2.19–20.41, P = 0.001) or ABP1 rs12539 (diamine oxidase; OR 3.96, 95% CI 1.62–9.73, P = 0.002) were more likely to respond. Conversely, patients with SLC15A1 rs1339067 TT had lower odds of response (OR 0.06, 95% CI 0.01–0.56, P = 0.001). ABCC5 rs3749442 was associated with lower likelihood of response and abnormal liver function tests, and higher likelihood of sedation. The eQTL revealed that rs1339067 decreased GPR18 expression (endocannabinoid receptor) in white matter (P = 5.6 × 10−3), and rs3749442 decreased hippocampal HTR3E expression (serotonin 5‐HT3E; P = 8.5 × 10−5). Furthermore, 75% of genes associated with lower likelihood of response were co‐expressed. Pharmacogenetic variation is associated with CBD response and influences expression of CBD targets in TRE. Implicated pathways, including cholesterol metabolism and glutathione conjugation, demonstrate potential interactions between CBD and common medications (e.g., statins and acetaminophen) that may require closer monitoring. These results highlight the role of pharmacogenes in fundamental biologic processes and potential genetic underpinnings of treatment‐resistance.
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Affiliation(s)
- Brittney H Davis
- Department of Neurology, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - T Mark Beasley
- Department of Biostatistics, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Michelle Amaral
- HudsonAlpha Institute for Biotechnology, Huntsville, Alabama, USA
| | - Jerzy P Szaflarski
- Department of Neurology, UAB Epilepsy Center, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Tyler Gaston
- Department of Neurology, UAB Epilepsy Center, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Leslie Perry Grayson
- Department of Neurology, UAB Epilepsy Center, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - David G Standaert
- Department of Neurology, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - E Martina Bebin
- Department of Neurology, UAB Epilepsy Center, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Nita A Limdi
- Department of Neurology, University of Alabama at Birmingham, Birmingham, Alabama, USA
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5
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Kindt KS, Akturk A, Jarysta A, Day M, Beirl A, Flonard M, Tarchini B. EMX2-GPR156-Gαi reverses hair cell orientation in mechanosensory epithelia. Nat Commun 2021; 12:2861. [PMID: 34001891 PMCID: PMC8129141 DOI: 10.1038/s41467-021-22997-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 04/10/2021] [Indexed: 12/21/2022] Open
Abstract
Hair cells detect sound, head position or water movements when their mechanosensory hair bundle is deflected. Each hair bundle has an asymmetric architecture that restricts stimulus detection to a single axis. Coordinated hair cell orientations within sensory epithelia further tune stimulus detection at the organ level. Here, we identify GPR156, an orphan GPCR of unknown function, as a critical regulator of hair cell orientation. We demonstrate that the transcription factor EMX2 polarizes GPR156 distribution, enabling it to signal through Gαi and trigger a 180° reversal in hair cell orientation. GPR156-Gαi mediated reversal is essential to establish hair cells with mirror-image orientations in mouse otolith organs in the vestibular system and in zebrafish lateral line. Remarkably, GPR156-Gαi also instructs hair cell reversal in the auditory epithelium, despite a lack of mirror-image organization. Overall, our work demonstrates that conserved GPR156-Gαi signaling is integral to the framework that builds directional responses into mechanosensory epithelia.
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MESH Headings
- Animals
- Cell Polarity/genetics
- Epithelium/metabolism
- Female
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Hair Cells, Auditory/cytology
- Hair Cells, Auditory/metabolism
- Homeodomain Proteins/genetics
- Homeodomain Proteins/metabolism
- Male
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Microscopy, Confocal/methods
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/metabolism
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Zebrafish/metabolism
- Mice
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Affiliation(s)
- Katie S Kindt
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
| | | | | | | | - Alisha Beirl
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
| | | | - Basile Tarchini
- The Jackson Laboratory, Bar Harbor, ME, USA.
- Department of Medicine, Tufts University, Boston, MA, USA.
- Graduate School of Biomedical Science and Engineering (GSBSE), University of Maine, Orono, ME, USA.
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6
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Watkins LR, Orlandi C. In vitro profiling of orphan G protein coupled receptor (GPCR) constitutive activity. Br J Pharmacol 2021; 178:2963-2975. [PMID: 33784795 DOI: 10.1111/bph.15468] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2021] [Accepted: 03/18/2021] [Indexed: 01/02/2023] Open
Abstract
BACKGROUND AND PURPOSE Members of the GPCR family are targeted by a significant fraction of the available FDA-approved drugs. However, the physiological role and pharmacological properties of many GPCRs remain unknown, representing untapped potential in drug design. Of particular interest are ~100 less-studied GPCRs known as orphans because their endogenous ligands are unknown. Intriguingly, disease-causing mutations identified in patients, together with animal studies, have demonstrated that many orphan receptors play crucial physiological roles and, thus, represent attractive drug targets. EXPERIMENTAL APPROACH The majority of deorphanized GPCRs demonstrate coupling to Gi/o . However, a limited number of techniques allow the detection of intrinsically small constitutive activity associated with Gi/o protein activation, which represents a significant barrier in our ability to study orphan GPCR signalling. Using luciferase reporter assays, we effectively detected constitutive Gs , Gq and G12/13 protein signalling by unliganded receptors and introducing various G protein chimeras, we provide a novel, highly sensitive tool capable of identifying Gi/o coupling in unliganded orphan GPCRs. KEY RESULTS Using this approach, we measured the constitutive activity of the entire class C GPCR family that includes eight orphan receptors and a subset of 20 prototypical class A GPCR members, including 11 orphans. Excitingly, this approach illuminated the G protein coupling profile of eight orphan GPCRs (GPR22, GPR137b, GPR88, GPR156, GPR158, GPR179, GPRC5D and GPRC6A) previously linked to pathophysiological processes. CONCLUSION AND IMPLICATIONS We provide a new platform that could be utilized in ongoing studies in orphan receptor signalling and de-orphanization efforts.
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Affiliation(s)
- Lyndsay R Watkins
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York, USA
| | - Cesare Orlandi
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York, USA
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7
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TERUNUMA M. Diversity of structure and function of GABA B receptors: a complexity of GABA B-mediated signaling. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2018; 94:390-411. [PMID: 30541966 PMCID: PMC6374141 DOI: 10.2183/pjab.94.026] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Accepted: 10/09/2018] [Indexed: 05/24/2023]
Abstract
γ-aminobutyric acid type B (GABAB) receptors are broadly expressed in the nervous system and play an important role in neuronal excitability. GABAB receptors are G protein-coupled receptors that mediate slow and prolonged inhibitory action, via activation of Gαi/o-type proteins. GABAB receptors mediate their inhibitory action through activating inwardly rectifying K+ channels, inactivating voltage-gated Ca2+ channels, and inhibiting adenylate cyclase. Functional GABAB receptors are obligate heterodimers formed by the co-assembly of R1 and R2 subunits. It is well established that GABAB receptors interact not only with G proteins and effectors but also with various proteins. This review summarizes the structure, subunit isoforms, and function of GABAB receptors, and discusses the complexity of GABAB receptors, including how receptors are localized in specific subcellular compartments, the mechanism regulating cell surface expression and mobility of the receptors, and the diversity of receptor signaling through receptor crosstalk and interacting proteins.
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Affiliation(s)
- Miho TERUNUMA
- Division of Oral Biochemistry, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan
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8
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Harpsøe K, Boesgaard MW, Munk C, Bräuner-Osborne H, Gloriam DE. Structural insight to mutation effects uncover a common allosteric site in class C GPCRs. Bioinformatics 2017; 33:1116-1120. [PMID: 28011766 PMCID: PMC5408886 DOI: 10.1093/bioinformatics/btw784] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Accepted: 12/07/2016] [Indexed: 01/08/2023] Open
Abstract
Motivation Class C G protein-coupled receptors (GPCRs) regulate important physiological functions and allosteric modulators binding to the transmembrane domain constitute an attractive and, due to a lack of structural insight, a virtually unexplored potential for therapeutics and the food industry. Combining pharmacological site-directed mutagenesis data with the recent class C GPCR experimental structures will provide a foundation for rational design of new therapeutics. Results We uncover one common site for both positive and negative modulators with different amino acid layouts that can be utilized to obtain selectivity. Additionally, we show a large potential for structure-based modulator design, especially for four orphan receptors with high similarity to the crystal structures. Availability and Implementation All collated mutagenesis data is available in the GPCRdb mutation browser at http://gpcrdb.org/mutations/ and can be analyzed online or downloaded in excel format. Supplementary information Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- Kasper Harpsøe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Michael W Boesgaard
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Christian Munk
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Hans Bräuner-Osborne
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - David E Gloriam
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- To whom correspondence should be addressed.
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9
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Flyktman A, Mänttäri S, Nissilä J, Timonen M, Saarela S. Transcranial light affects plasma monoamine levels and expression of brain encephalopsin in the mouse. ACTA ACUST UNITED AC 2015; 218:1521-6. [PMID: 25805701 DOI: 10.1242/jeb.111864] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 03/09/2015] [Indexed: 11/20/2022]
Abstract
Encephalopsin (OPN3) belongs to the light-sensitive transmembrane receptor family mainly expressed in the brain and retina. It is believed that light affects mammalian circadian rhythmicity only through the retinohypothalamic tract, which transmits light information to the suprachiasmatic nucleus in the hypothalamus. However, it has been shown that light penetrates the skull. Here, we present the effect of transcranial light treatment on OPN3 expression and monoamine concentrations in mouse brain and other tissues. Mice were randomly assigned to control group, morning-light group and evening-light group, and animals were illuminated transcranially five times a week for 8 min for a total of 4 weeks. The concentrations of OPN3 and monoamines were analysed using western blotting and HPLC, respectively. We report that transcranial light treatment affects OPN3 expression in different brain areas and plasma/adrenal gland monoamine concentrations. In addition, when light was administered at a different time of the day, the response varied in different tissues. These results provide new information on the effects of light on transmitters mediating mammalian rhythmicity.
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Affiliation(s)
- Antti Flyktman
- University of Oulu, Department of Biology, P.O. Box 3000, Oulu FIN-90014, Finland
| | - Satu Mänttäri
- Finnish Institute of Occupational Health, Aapistie 1, Oulu FI-90220, Finland
| | - Juuso Nissilä
- University of Oulu, Department of Biology, P.O. Box 3000, Oulu FIN-90014, Finland University of Oulu, Institute of Health Sciences, P.O. Box 5000, Oulu FIN-90014, Finland
| | - Markku Timonen
- University of Oulu, Institute of Health Sciences, P.O. Box 5000, Oulu FIN-90014, Finland
| | - Seppo Saarela
- University of Oulu, Department of Biology, P.O. Box 3000, Oulu FIN-90014, Finland
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10
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Mo D, Raabe CA, Reinhardt R, Brosius J, Rozhdestvensky TS. Alternative processing as evolutionary mechanism for the origin of novel nonprotein coding RNAs. Genome Biol Evol 2014; 5:2061-71. [PMID: 24132753 PMCID: PMC3845636 DOI: 10.1093/gbe/evt155] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The evolution of new genes can ensue through either gene duplication and the neofunctionalization of one of the copies or the formation of a de novo gene from hitherto nonfunctional, neutrally evolving intergenic or intronic genomic sequences. Only very rarely are entire genes created de novo. Mostly, nonfunctional sequences are coopted as novel parts of existing genes, such as in the process of exonization whereby introns become exons through changes in splicing. Here, we report a case in which a novel nonprotein coding RNA evolved by intron-sequence recruitment into its structure. cDNAs derived from rat brain small RNAs, revealed a novel small nucleolar RNA (snoRNA) originating from one of the Snord115 copies in the rat Prader–Willi syndrome locus. We suggest that a single-point substitution in the Snord115 region led to the expression of a longer snoRNA variant, designated as L-Snord115. Cell culture and footprinting experiments confirmed that a single nucleotide substitution at Snord115 position 67 destabilized the kink-turn motif within the canonical snoRNA, while distal intronic sequences provided an alternate D-box region. The exapted sequence displays putative base pairing to 28S rRNA and mRNA targets.
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Affiliation(s)
- Dingding Mo
- Institute of Experimental Pathology, ZMBE, University of Muenster, Muenster, Germany
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11
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Pi M, Wu Y, Lenchik NI, Gerling I, Quarles LD. GPRC6A mediates the effects of L-arginine on insulin secretion in mouse pancreatic islets. Endocrinology 2012; 153:4608-15. [PMID: 22872579 PMCID: PMC3512028 DOI: 10.1210/en.2012-1301] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 07/12/2012] [Indexed: 12/11/2022]
Abstract
L-arginine (l-Arg) is an insulin secretagogue, but the molecular mechanism whereby it stimulates insulin secretion from β-cells is not known. The possibility that l-Arg regulates insulin secretion through a G protein-coupled receptor (GPCR)-mediated mechanism is suggested by the high expression of the nutrient receptor GPCR family C group 6 member A (GPRC6A) in the pancreas and TC-6 β-cells and the finding that Gprc6a(-/]minus]) mice have abnormalities in glucose homeostasis. To test the direct role of GPRC6A in regulating insulin secretion, we evaluated the response of pancreatic islets derived from Gprc6a(-/]minus]) mice to L-Arg. We found that the islet size and insulin content were decreased in pancreatic islets from Gprac6a(-/]minus]) mice. These alterations were selective for β-cells, because there were no abnormalities in serum glucagon levels or glucagon content of islets derived from Gprac6a(-/]minus]) mice. Significant reduction was observed in both the pancreatic ERK response to L-Arg administration to Gprc6a(-/]minus]) mice in vivo and L-Arg-induced insulin secretion and production ex vivo in islets isolated from Gprc6a(-/]minus]) mice. L-Arg stimulation of cAMP accumulation in isolated islets isolated from Gprc6a(-/]minus]) mice was also diminished. These findings suggest that l-Arg stimulation of insulin secretion in β-cells is mediated, at least in part, through GPRC6A activation of cAMP pathways.
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Affiliation(s)
- Min Pi
- Department of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
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12
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Hoyle CH. Evolution of neuronal signalling: Transmitters and receptors. Auton Neurosci 2011; 165:28-53. [DOI: 10.1016/j.autneu.2010.05.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Revised: 05/09/2010] [Accepted: 05/18/2010] [Indexed: 11/16/2022]
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13
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Tian Y, Gunther JR, Liao IH, Liu D, Ander BP, Stamova BS, Lit L, Jickling GC, Xu H, Zhan X, Sharp FR. GABA- and acetylcholine-related gene expression in blood correlate with tic severity and microarray evidence for alternative splicing in Tourette syndrome: a pilot study. Brain Res 2011; 1381:228-36. [PMID: 21241679 DOI: 10.1016/j.brainres.2011.01.026] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2010] [Revised: 12/08/2010] [Accepted: 01/10/2011] [Indexed: 10/18/2022]
Abstract
Tourette syndrome (TS) is a complex childhood neurodevelopmental disorder characterized by motor and vocal tics. Recently, altered numbers of GABAergic-parvalbumin (PV) and cholinergic interneurons were observed in the basal ganglia of individuals with TS. Thus, we postulated that gamma-amino butyric acid (GABA)- and acetylcholine (ACh)-related genes might be associated with the pathophysiology of TS. Total RNA isolated from whole blood of 26 un-medicated TS subjects and 23 healthy controls (HC) was processed on Affymetrix Human Exon 1.0 ST arrays. Data were analyzed to identify genes whose expression correlated with tic severity in TS, and to identify genes differentially spliced in TS compared to HC subjects. Many genes (3627) correlated with tic severity in TS (p < 0.05) among which GABA- (p = 2.1 × 10⁻³) and ACh- (p = 4.25 × 10⁻⁸) related genes were significantly over-represented. Moreover, several GABA and ACh-related genes were predicted to be alternatively spliced in TS compared to HC including GABA receptors GABRA4 and GABRG1, the nicotinic ACh receptor CHRNA4 and cholinergic differentiation factor (CDF). This pilot study suggests that at least some of these GABA- and ACh-related genes observed in blood that correlate with tics or are alternatively spliced are involved in the pathophysiology of TS and tics.
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Affiliation(s)
- Yingfang Tian
- University of California at Davis, M.I.N.D., Institute and Department of Neurology, USA
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14
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Kohlmeier KA, Kristiansen U. GABAergic actions on cholinergic laterodorsal tegmental neurons: implications for control of behavioral state. Neuroscience 2010; 171:812-29. [PMID: 20884335 DOI: 10.1016/j.neuroscience.2010.09.034] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Revised: 09/17/2010] [Accepted: 09/17/2010] [Indexed: 11/30/2022]
Abstract
Cholinergic neurons of the pontine laterodorsal tegmentum (LDT) play a critical role in regulation of behavioral state. Therefore, elucidation of mechanisms that control their activity is vital for understanding of how switching between wakefulness, sleep and anesthetic states is effectuated. In vivo studies suggest that GABAergic mechanisms within the pons play a critical role in behavioral state switching. However, the postsynaptic, electrophysiological actions of GABA on LDT neurons, as well as the identity of GABA receptors present in the LDT mediating these actions is virtually unexplored. Therefore, we studied the actions of GABA agonists and antagonists on cholinergic LDT cells by performing patch clamp recordings in mouse brain slices. Under conditions where detection of Cl(-) -mediated events was optimized, GABA induced gabazine (GZ)-sensitive inward currents in the majority of LDT neurons. Post-synaptic location of GABA(A) receptors was demonstrated by persistence of muscimol-induced inward currents in TTX and low Ca(2+) solutions. THIP, a selective GABA(A) receptor agonist with a preference for δ-subunit containing GABA(A) receptors, induced inward currents, suggesting the existence of extrasynaptic GABA(A) receptors. LDT cells also possess GABA(B) receptors as baclofen-activated a TTX- and low Ca(2+)-resistant outward current that was attenuated by the GABA(B) antagonists CGP 55845 and saclofen. The tertiapin sensitivity of baclofen-induced outward currents suggests that a G(IRK) mediated this effect. Further, outward currents were never additive with those induced by application of carbachol, suggesting that they were mediated by activation of GABA(B) receptors linked to the same G(IRK) activated in these cells by muscarinic receptor stimulation. Activation of GABA(B) receptors inhibited Ca(2+) increases induced by a depolarizing voltage step shown previously to activate VOCCs in cholinergic LDT neurons. Baclofen-mediated reductions in depolarization-induced Ca(2+) were unaltered by prior emptying of intracellular Ca(2+) stores, but were abolished by low extracellular Ca(2+) and pre-application of nifedipine, indicating that activation of GABA(B) receptors inhibits influx of Ca(2+) involving L-type Ca(2+) channels. Presence of GABA(C) receptors is suggested by the induction of inward current by (E)-4- amino-2-butenoic acid (TACA) and its inhibition by 1,2,5,6-tetrahydropyridine-4-ylmethylphosphinic (TPMPA), a relatively selective agonist and antagonist, respectively, of GABA(C) receptors. All of these GABA-mediated actions were found to occur in histochemically-identified cholinergic neurons. Taken together, these data indicate for the first time that cholinergic neurons of the LDT exhibit functional GABA(A, B and C) receptors, including extrasynaptically located GABA(A) receptors, which may be tonically activated by synaptic overflow of GABA. Accordingly, the activity of cholinergic LDT neurons is likely to be significantly affected by GABAergic tone within the nucleus, and so, demonstrated effects of GABA on behavioral state may be mediated, in part, via direct actions on cholinergic neurons in the LDT.
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Affiliation(s)
- K A Kohlmeier
- Department of Pharmacology and Pharmacotherapy, The Pharmaceutical Faculty, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark.
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15
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Direct interaction of GABAB receptors with M2 muscarinic receptors enhances muscarinic signaling. J Neurosci 2010; 29:15796-809. [PMID: 20016095 DOI: 10.1523/jneurosci.4103-09.2009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Downregulation of G-protein-coupled receptors (GPCRs) provides an important mechanism for reducing neurotransmitter signaling during sustained stimulation. Chronic stimulation of M(2) muscarinic receptors (M(2)Rs) causes internalization of M(2)R and G-protein-activated inwardly rectifying potassium (GIRK) channels in neuronal PC12 cells, resulting in loss of function. Here, we show that coexpression of GABA(B) R2 receptors (GBR2s) rescues both surface expression and function of M(2)R, including M(2)R-induced activation of GIRKs and inhibition of cAMP production. GBR2 showed significant association with M(2)R at the plasma membrane but not other GPCRs (M(1)R, mu-opioid receptor), as detected by fluorescence resonance energy transfer measured with total internal reflection fluorescence microscopy. Unique regions of the proximal C-terminal domains of GBR2 and M(2)R mediate specific binding between M(2)R and GBR2. In the brain, GBR2, but not GBR1, biochemically coprecipitates with M(2)R and overlaps with M(2)R expression in cortical neurons. This novel heteromeric association between M(2)R and GBR2 provides a possible mechanism for altering muscarinic signaling in the brain and represents a previously unrecognized role for GBR2.
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16
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Wellendorph P, Bräuner-Osborne H. Molecular basis for amino acid sensing by family C G-protein-coupled receptors. Br J Pharmacol 2009; 156:869-84. [PMID: 19298394 DOI: 10.1111/j.1476-5381.2008.00078.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Family C of human G-protein-coupled receptors (GPCRs) is constituted by eight metabotropic glutamate receptors, two gamma-aminobutyric acid type B (GABA(B1-2)) subunits forming the heterodimeric GABA(B) receptor, the calcium-sensing receptor, three taste1 receptors (T1R1-3), a promiscuous L-alpha;-amino acid receptor G-protein-coupled receptor family C, group 6, subtype A (GPRC6A) and seven orphan receptors. Aside from the orphan receptors, the family C GPCRs are dimeric receptors characterized by a large extracellular Venus flytrap domain which bind the endogenous agonists. Except from the GABA(B1-2) and T1R2-3 receptor, all receptors are either activated or positively modulated by amino acids. In this review, we outline mutational, biophysical and structural studies which have elucidated the interaction of the amino acids with the Venus flytrap domains, molecular mechanisms of receptor selectivity and the initial steps in receptor activation.
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Affiliation(s)
- P Wellendorph
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
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17
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Richer M, David M, Villeneuve LR, Trieu P, Ethier N, Pétrin D, Mamarbachi AM, Hébert TE. GABA-B(1) receptors are coupled to the ERK1/2 MAP kinase pathway in the absence of GABA-B(2) subunits. J Mol Neurosci 2008; 38:67-79. [PMID: 19052921 DOI: 10.1007/s12031-008-9163-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Accepted: 11/06/2008] [Indexed: 01/22/2023]
Abstract
In the current model of gamma-aminobutyric acid (GABA) B receptor function, there is a requirement for GABA-B(1/2) heterodimerisation for targetting to the cell surface. However, different lines of evidence suggest that the GABA-B(1) subunit can form a functional receptor in the absence of GABA-B(2). We observed coupling of endogenous GABA-B(1) receptors in the DI-TNC1 glial cell line to the ERK pathway in response to baclofen even though these cells do not express GABA-B(2). GABA-B(1A) receptors were also able to mediate a rapid, transient, and dose-dependent activation of the ERK1/2 MAP kinase pathway when transfected alone into HEK 293 cells. The response was abolished by G(i/o) and MEK inhibition, potentiated by inhibitors of phospholipase C and protein kinase C and did not involve PI-3-kinase activity. Finally, using bioluminescence resonance energy transfer and co-immunoprecipitation, we show the existence of homodimeric GABA-B(1A) receptors in transfected HEK293 cells. Altogether, our observations show that GABA-B(1A) receptors are able to activate the ERK1/2 pathway despite the absence of surface targetting partner GABA-B(2) in both HEK 293 cells and the DI-TNC1 cell line.
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Affiliation(s)
- Maxime Richer
- Département de biochimie and Groupe de recherche universitaire sur le médicament (GRUM), Université de Montréal, Montréal, Québec, Canada
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18
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Chromosomal map of human brain malformations. Hum Genet 2008; 124:73-80. [PMID: 18563447 DOI: 10.1007/s00439-008-0528-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2008] [Accepted: 06/12/2008] [Indexed: 01/10/2023]
Abstract
The etiology of most central nervous system (CNS) malformations remains unknown. We have utilized the fact that autosomal chromosome aberrations are commonly associated with CNS malformations to identify new causative gene loci. The human cytogenetic database, a computerized catalog of the clinical phenotypes associated with cytogenetically detectable human chromosome aberrations, was used to identify patients with 14 selected brain malformations including 541 with deletions, and 290 carrying duplications. These cases were used to develop an autosomal deletion and duplication map consisting of 67 different deleted malformation associated bands (MABs) in 55 regions and 88 different duplicated MABs in 36 regions; 31 of the deleted and 8 duplicated MABs were highly significantly associated (P < 0.001). All holoprosencephaly MABs found in the database contained a known HPE gene providing some level of validation for the approach. Significantly associated MABs are discussed for each malformation together with the published data about known disease-causing genes and reported malformation-associated loci, as well as the limitations of the proposed approach.
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19
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Lagerström MC, Schiöth HB. Structural diversity of G protein-coupled receptors and significance for drug discovery. Nat Rev Drug Discov 2008; 7:339-57. [PMID: 18382464 DOI: 10.1038/nrd2518] [Citation(s) in RCA: 1043] [Impact Index Per Article: 65.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
G protein-coupled receptors (GPCRs) are the largest family of membrane-bound receptors and also the targets of many drugs. Understanding of the functional significance of the wide structural diversity of GPCRs has been aided considerably in recent years by the sequencing of the human genome and by structural studies, and has important implications for the future therapeutic potential of targeting this receptor family. This article aims to provide a comprehensive overview of the five main human GPCR families--Rhodopsin, Secretin, Adhesion, Glutamate and Frizzled/Taste2--with a focus on gene repertoire, general ligand preference, common and unique structural features, and the potential for future drug discovery.
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Affiliation(s)
- Malin C Lagerström
- Department of Neuroscience, Functional Pharmacology, Uppsala University, BMC, BOX 593, 751 24, Uppsala, Sweden
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20
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Kobayashi MS, Asai S, Ishikawa K, Nishida Y, Nagata T, Takahashi Y. Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain. ACTA ACUST UNITED AC 2008; 58:171-91. [PMID: 18440647 DOI: 10.1016/j.brainresrev.2008.03.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2007] [Revised: 02/08/2008] [Accepted: 03/08/2008] [Indexed: 12/20/2022]
Abstract
Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.
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Affiliation(s)
- Megumi Sugahara Kobayashi
- Division of Genomic Epidemiology and Clinical Trials, Advanced Medical Research Center, Nihon University School of Medicine, Oyaguchi-Kami Machi, Itabashi-ku, Tokyo 173-8610, Japan
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21
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Wellendorph P, Burhenne N, Christiansen B, Walter B, Schmale H, Bräuner-Osborne H. The rat GPRC6A: cloning and characterization. Gene 2007; 396:257-67. [PMID: 17478059 DOI: 10.1016/j.gene.2007.03.008] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Revised: 03/16/2007] [Accepted: 03/16/2007] [Indexed: 11/23/2022]
Abstract
GPRC6A is a novel member of family C of G protein-coupled receptors with so far elusive biological function. GPRC6A has been described in human and mouse as a promiscuous l-alpha-amino acid receptor. We now report the cloning, expression analysis and, functional characterization of the rat orthologue of GPRC6A. Full-length cloning of rat GPRC6A (rGPRC6A) was accomplished using amplification of cDNA from taste tissue, and the identity of rGPRC6A confirmed at both the genomic and the protein level by similarity studies. Using selective primers, reverse transcriptase polymerase chain reaction showed that the mRNA is widely but weakly distributed, except for a high expression in the soft palate, the so-called geschmacksstreifen. On the protein level, rGPRC6A was shown to be glycosylated and most likely oligomeric, and using immunochemistry we observed that rGPRC6A is expressed at the plasma membrane of mammalian cell lines. Utilizing co-expression of rGPRC6A and the promiscuous Galpha(q)(G66D) protein in an engineered cell-based inositol phosphate turnover assay, we were able to study the ligand profile of the receptor. We found that l-ornithine is the most potent and efficacious l-amino acid agonist with an EC(50) value of 264 microM, followed by several other aliphatic, neutral, and basic amino acids. Furthermore, the divalent cation Mg(2+) was found to be a positive modulator of the l-ornithine response. The presented quantitative pharmacological data underlines the evolutionary conservation of GPRC6A to the rat and signifies the physiological importance and emerging pharmacological potential of GPRC6A.
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Affiliation(s)
- Petrine Wellendorph
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
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22
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Lu F, Li J, Jiang Z. Computational identification and analysis of G protein-coupled receptor targets. Drug Dev Res 2007. [DOI: 10.1002/ddr.20148] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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23
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Kornau HC. GABAB receptors and synaptic modulation. Cell Tissue Res 2006; 326:517-33. [PMID: 16932937 DOI: 10.1007/s00441-006-0264-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2006] [Accepted: 05/31/2006] [Indexed: 12/18/2022]
Abstract
GABA(B) receptors modulate transmitter release and postsynaptic membrane potential at various types of central synapses. They function as heterodimers of two related seven-transmembrane domain receptor subunits. Trafficking, activation and signalling of GABA(B) receptors are regulated both by allosteric interactions between the subunits and by the binding of additional proteins. Recent studies have shed light on the roles of GABA(B) receptors in plasticity processes at excitatory synapses. This review summarizes our knowledge of the localization, structure and function of GABA(B) receptors in the central nervous system and their use as drug targets for neurological and psychiatric disorders.
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Affiliation(s)
- Hans-Christian Kornau
- Center for Molecular Neurobiology (ZMNH), University of Hamburg, Falkenried 94, 20251 Hamburg, Germany.
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24
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Villalba RM, Raju DV, Hall RA, Smith Y. GABA(B) receptors in the centromedian/parafascicular thalamic nuclear complex: an ultrastructural analysis of GABA(B)R1 and GABA(B)R2 in the monkey thalamus. J Comp Neurol 2006; 496:269-87. [PMID: 16538684 DOI: 10.1002/cne.20950] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Strong gamma-aminobutyric acid type B (GABA(B)) receptor binding has been shown throughout the thalamus, but the distribution of the two GABA(B) receptor subunits, GABA(B) receptor subunit 1 (GABA(B)R1) and GABA(B) receptor subunit 2 (GABA(B)R2), remains poorly characterized. In primates, the caudal intralaminar nuclei, centromedian and parafascicular (CM/PF), are an integral part of basal ganglia circuits and a main source of inputs to the striatum. In this study, we analyzed the subcellular and subsynaptic distribution of GABA(B) receptor subunits by using light and electron microscopic immunocytochemical techniques. Quantitative immunoperoxidase and immunogold analysis showed that both subunits display a similar pattern of distribution in CM/PF, being expressed largely at extrasynaptic and perisynaptic sites in neuronal cell bodies, dendrites, and axon-like processes and less abundantly in axon terminals. Postsynaptic GABA(B)R1 labeling was found mostly on the plasma membrane (70-80%), whereas GABA(B)R2 was more evenly distributed between the plasma membrane and intracellular compartments of CM/PF neurons. A few axon terminals forming symmetric and asymmetric synapses were also labeled for GABA(B)R1 and GABA(B)R2, but the bulk of presynaptic labeling was expressed in small axon-like processes. About 20% of presynaptic vesicle-containing dendrites of local circuit neurons displayed GABA(B)R1/R2 immunoreactivity. Vesicular glutamate transporters (vGluT1)-containing terminals forming asymmetric synapses expressed GABA(B)R1 and/or displayed postsynaptic GABA(B)R1 at the edges of their asymmetric specialization. Overall, these findings provide evidence for multiple sites where GABA(B) receptors could modulate GABAergic and glutamatergic transmission in the primate CM/PF complex.
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Affiliation(s)
- Rosa M Villalba
- Yerkes National Primate Research Center, Emory University, Atlanta, Georgia 30322, USA.
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25
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Kombian SB, Ananthalakshmi KVV, Parvathy SS, Matowe WC. Cholecystokinin-2 receptors couple to cAMP–protein kinase A to depress excitatory synaptic currents in rat nucleus accumbens in vitro. Can J Physiol Pharmacol 2006; 84:203-11. [PMID: 16900946 DOI: 10.1139/y05-119] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We recently reported that the activation of cholecystokinin-2 receptors depress evoked excitatory postsynaptic currents (EPSCs) in nucleus accumbens (NAc) indirectly through γ-aminobutyric acid (GABA) acting on γ-aminobutyric acid-B (GABAB) receptors. Here, we determined the second messenger system that couples cholecystokinin-2 receptors to the observed synaptic depression. Using in vitro forebrain slices of rats and whole-cell patch recording, we tested the hypothesis that cholecystokinin-2 receptors are coupled to cAMP and protein kinase A signaling pathway. Cholecystokinin-8S induced inward currents and depressed evoked EPSCs. Forskolin, an activator of adenylyl cyclase and rolipram that is an inhibitor of phosphodiesterase type IV, independently increased EPSC amplitude and blocked the inward current and synaptic depression induced by cholecystokinin-8S. Furthermore, the membrane-permeable cAMP analog, 8-bromo-cAMP, blocked the cholecystokinin-8S effects. H89, a protein kinase A inhibitor, also blocked cholecystokinin-8S effects. However, depression of the evoked EPSC by baclofen, a GABABreceptor agonist, was not blocked by H89 or forskolin. These findings indicate that cholecystokinin-2, but not GABAB, receptors are coupled to the adenylyl cyclase – cAMP – protein kinase A signaling pathway in the NAc to induce inward currents and cause synaptic depression.
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Affiliation(s)
- Samuel B Kombian
- Department of Applied Therapeutics, Kuwait University, Box 24923, Safat 13110, Kuwait.
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26
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Neto FL, Ferreira-Gomes J, Castro-Lopes JM. Distribution of GABA Receptors in the Thalamus and Their Involvement in Nociception. GABA 2006; 54:29-51. [PMID: 17175809 DOI: 10.1016/s1054-3589(06)54002-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Fani L Neto
- Institute of Histology and Embryology, Faculty of Medicine of Porto and IBMC, 4200-319 Porto, Portugal
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27
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Bjarnadóttir TK, Fredriksson R, Schiöth HB. The gene repertoire and the common evolutionary history of glutamate, pheromone (V2R), taste(1) and other related G protein-coupled receptors. Gene 2005; 362:70-84. [PMID: 16229975 DOI: 10.1016/j.gene.2005.07.029] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2005] [Revised: 06/21/2005] [Accepted: 07/25/2005] [Indexed: 11/25/2022]
Abstract
Glutamate receptors (also known as clan C) are one of the main groups of GPCRs with many subgroup linked through complex evolutionary relationships. We performed thorough searches for genes coding for proteins belonging to this family in the human, mouse, Fugu, and zebrafish genomes, as well as in four invertebrate species. We assembled over 70 new full-length sequences from protein predictions excluding pseudogenes. This resulted in a total of 22 full-length sequences from the human genome, 79 from the mouse genome, 30 from the Fugu genome, and 32 from the zebrafish genome (pseudogenes are not included in these numbers). We show that the vertebrate Glutamate GPCRs form four main phylogenetic groups with a total of eight subgroups (Group I: V2R, TAS1R, GPRC6A, and CASR, Group II: GRM, Group III: GABA together with previously unpublished GPR158 and GPR158L and Group IV: GPRC5). All eight receptor subgroups are present both in mammals and fish, except for GPRC5 and GPR158. The pheromone (V2R), GPRC6, and sweet taste (TAS1) receptors were not found in invertebrates while GRM, GABA, and CASR were found in both C. elegans and C. intestinalis. The pheromone receptors are found in high numbers in mouse, zebrafish and Fugu but are only found as pseudogenes in the human genome. This report provides a comprehensive overview of the expansion/deletions of the groups within the Glutamate receptor family.
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Affiliation(s)
- Thóra K Bjarnadóttir
- Department of Neuroscience, Uppsala University, BMC, Box 593, 751 24, Uppsala, Sweden
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28
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Vollenweider F, Bendfeldt K, Maetzler W, Otten U, Nitsch C. GABA(B) receptor expression and cellular localization in gerbil hippocampus after transient global ischemia. Neurosci Lett 2005; 395:118-23. [PMID: 16298486 DOI: 10.1016/j.neulet.2005.10.079] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2005] [Revised: 10/06/2005] [Accepted: 10/26/2005] [Indexed: 11/19/2022]
Abstract
Using in situ hybridization, the expression of the GABA receptor subtype B subunit 1 (GABA(B) R1) and subunit 2 (GABA(B) R2) following transient global ischemia in the gerbil hippocampus was investigated. In sham-operated animals, mRNAs of both subunits were mainly detected in hippocampal pyramidal cells and interneurons with lower expression levels of the GABA(B) R2 in the CA1 field. Four days after transient cerebral ischemia, neuronal message decreased in conjunction with neuronal death and both receptor subunits disappeared from the pyramidal cell layer. However, GABA(B) R1 and GABA(B) R2 were still expressed in a few cells. In situ hybridization of the GABA synthesizing enzyme glutamic acid decarboxylase 67 (GAD67) remained unchanged after the ischemic insult. Double-labeling experiments revealed that in the postischemic hippocampus GABA(B) R1 and GABA(B) R2 were not present in GFAP-reactive astrocytes, but that the surviving parvalbumin-containing interneurons possessed GABA(B) R1 and GABA(B) R2 mRNA.
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Affiliation(s)
- F Vollenweider
- Functional Neuroanatomy, Institute of Anatomy, Basel University, Pestalozzistrasse 20, CH-4056 Basel, Switzerland.
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29
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Pi M, Faber P, Ekema G, Jackson PD, Ting A, Wang N, Fontilla-Poole M, Mays RW, Brunden KR, Harrington JJ, Quarles LD. Identification of a novel extracellular cation-sensing G-protein-coupled receptor. J Biol Chem 2005; 280:40201-9. [PMID: 16199532 PMCID: PMC1435382 DOI: 10.1074/jbc.m505186200] [Citation(s) in RCA: 246] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The C family G-protein-coupled receptors contain members that sense amino acid and extracellular cations, of which calcium-sensing receptor (CASR) is the prototypic extracellular calcium-sensing receptor. Some cells, such as osteoblasts in bone, retain responsiveness to extracellular calcium in CASR-deficient mice, consistent with the existence of another calcium-sensing receptor. We examined the calcium-sensing properties of GPRC6A, a newly identified member of this family. Alignment of GPRC6A with CASR revealed conservation of both calcium and calcimimetic binding sites. In addition, calcium, magnesium, strontium, aluminum, gadolinium, and the calcimimetic NPS 568 resulted in a dose-dependent stimulation of GPRC6A overexpressed in human embryonic kidney cells 293 cells. Also, osteocalcin, a calcium-binding protein highly expressed in bone, dose-dependently stimulated GPRC6A activity in the presence of calcium but inhibited the calcium-dependent activation of CASR. Coexpression of beta-arrestins 1 and 2, regulators of G-protein signaling RGS2 or RGS4, the RhoA inhibitor C3 toxin, the dominant negative Galpha(q)-(305-359) minigene, and pretreatment with pertussis toxin inhibited activation of GPRC6A by extracellular cations. Reverse transcription-PCR analyses showed that mouse GPRC6A is widely expressed in mouse tissues, including bone, calvaria, and the osteoblastic cell line MC3T3-E1. These data suggest that in addition to sensing amino acids, GPRC6A is a cation-, calcimimetic-, and osteocalcin-sensing receptor and a candidate for mediating extracellular calcium-sensing responses in osteoblasts and possibly other tissues.
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Affiliation(s)
- Min Pi
- From the Kidney Institute, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, Kansas 66160 and
| | | | | | | | | | | | | | | | | | | | - L. Darryl Quarles
- From the Kidney Institute, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, Kansas 66160 and
- To whom correspondence should be addressed: The Kidney Institute and Division of Nephrology, 3901 Rainbow Boulevard, 6018 Wahl Hall East, Kansas City, KS 66160., Tel.: 913-588-9255; Fax: 913-5889251; E-mail:
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30
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Couve A, Calver AR, Fairfax B, Moss SJ, Pangalos MN. Unravelling the unusual signalling properties of the GABA(B) receptor. Biochem Pharmacol 2005; 68:1527-36. [PMID: 15451395 DOI: 10.1016/j.bcp.2004.06.036] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Accepted: 06/08/2004] [Indexed: 12/13/2022]
Abstract
GABA(B) receptors are the cornerstone receptors in the modulation of inhibitory signalling in the central nervous system and continue to be targets for the amelioration of a number of neuropsychiatric and neurological disorders. Unravelling the molecular identity of this receptor has spurred much research over the past five or so years and generated a renewed interest and excitement in the field. Many questions are being answered and lessons learnt, not only about GABA(B) receptor function but also about general mechanisms of G-protein-coupled receptor signalling. However, as questions are being answered as many new questions are being raised and many GABA(B)-related conundrums continue to remain unanswered. In this report, we review some of the most recent work in the area of GABA(B) receptor research. In particular, we focus our attentions on the emerging mechanisms thought to be important in GABA(B) receptor signalling and the growing complex of associated proteins that we consider to be part of the GABA(B) receptor "signalosome."
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Affiliation(s)
- Andrés Couve
- Department of Biophysics and Molecular Physiology, Centro de Estudios Científicos, Avda. Arturo Prat 514, Casilla 1469, Valdivia, Chile
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31
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Gassmann M, Shaban H, Vigot R, Sansig G, Haller C, Barbieri S, Humeau Y, Schuler V, Müller M, Kinzel B, Klebs K, Schmutz M, Froestl W, Heid J, Kelly PH, Gentry C, Jaton AL, Van der Putten H, Mombereau C, Lecourtier L, Mosbacher J, Cryan JF, Fritschy JM, Lüthi A, Kaupmann K, Bettler B. Redistribution of GABAB(1) protein and atypical GABAB responses in GABAB(2)-deficient mice. J Neurosci 2005; 24:6086-97. [PMID: 15240800 PMCID: PMC6729668 DOI: 10.1523/jneurosci.5635-03.2004] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
GABAB receptors mediate slow synaptic inhibition in the nervous system. In transfected cells, functional GABAB receptors are usually only observed after coexpression of GABAB(1) and GABAB(2) subunits, which established the concept of heteromerization for G-protein-coupled receptors. In the heteromeric receptor, GABAB(1) is responsible for binding of GABA, whereas GABAB(2) is necessary for surface trafficking and G-protein coupling. Consistent with these in vitro observations, the GABAB(1) subunit is also essential for all GABAB signaling in vivo. Mice lacking the GABAB(1) subunit do not exhibit detectable electrophysiological, biochemical, or behavioral responses to GABAB agonists. However, GABAB(1) exhibits a broader cellular expression pattern than GABAB(2), suggesting that GABAB(1) could be functional in the absence of GABAB(2). We now generated GABAB(2)-deficient mice to analyze whether GABAB(1) has the potential to signal without GABAB(2) in neurons. We show that GABAB(2)-/- mice suffer from spontaneous seizures, hyperalgesia, hyperlocomotor activity, and severe memory impairment, analogous to GABAB(1)-/- mice. This clearly demonstrates that the lack of heteromeric GABAB(1,2) receptors underlies these phenotypes. To our surprise and in contrast to GABAB(1)-/- mice, we still detect atypical electrophysiological GABAB responses in hippocampal slices of GABAB(2)-/- mice. Furthermore, in the absence of GABAB(2), the GABAB(1) protein relocates from distal neuronal sites to the soma and proximal dendrites. Our data suggest that association of GABAB(2) with GABAB(1) is essential for receptor localization in distal processes but is not absolutely necessary for signaling. It is therefore possible that functional GABAB receptors exist in neurons that naturally lack GABAB(2) subunits.
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Affiliation(s)
- Martin Gassmann
- Pharmazentrum, Department of Clinical-Biological Sciences, University of Basel, CH-4056 Basel, Switzerland
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32
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Jelitai M, Madarasz E. The role of GABA in the early neuronal development. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2005; 71:27-62. [PMID: 16512345 DOI: 10.1016/s0074-7742(05)71002-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Marta Jelitai
- Laboratory of Neural Cell and Developmental Biology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest
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33
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Wellendorph P, Hansen KB, Balsgaard A, Greenwood JR, Egebjerg J, Bräuner-Osborne H. Deorphanization of GPRC6A: a promiscuous L-alpha-amino acid receptor with preference for basic amino acids. Mol Pharmacol 2004; 67:589-97. [PMID: 15576628 DOI: 10.1124/mol.104.007559] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
One of the most important tasks of molecular pharmacology is the deorphanization of the large number of G-protein-coupled receptors with unidentified endogenous agonists. We recently reported the cloning and analysis of expression of a novel human family C G-protein-coupled receptor, termed hGPRC6A. To identify agonists at this orphan receptor, we faced the challenges of achieving surface expression in mammalian cell lines and establishing an appropriate functional assay. Generating a chimeric receptor construct, h6A/5.24, containing the ligand binding amino-terminal domain (ATD) of hGPRC6A with the signal transducing transmembrane and C terminus of the homologous goldfish 5.24 receptor allowed us to overcome these obstacles. Homology modeling of the hGPRC6A ATD based on the crystal structure of the metabotropic glutamate receptor subtype 1 predicted interaction with alpha-amino acids and was employed to rationally select potential ligands. Measurement of Ca2+-dependent chloride currents in Xenopus laevis oocytes facilitated the deorphanization of h6A/5.24 and identification of L-alpha-amino acids as agonists. The most active agonists were basic L-alpha-amino acids, L-Arg, L-Lys, and L-ornithine, suggesting that these may function as endogenous signaling molecules. Measurement of intracellular calcium in tsA cells expressing h6A/5.24 allowed determination of EC50 values, which confirmed the agonist preferences observed in oocytes. Cloning, cell surface expression and deorphanization of the mouse ortholog further reinforces the assignment of the agonist preferences of hGPRC6A. This study demonstrates the utility of a chimeric receptor approach in combination with molecular modeling, for elucidating agonist interaction with GPRC6A, a novel family C G-protein-coupled receptor.
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Affiliation(s)
- Petrine Wellendorph
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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34
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Thuault SJ, Brown JT, Sheardown SA, Jourdain S, Fairfax B, Spencer JP, Restituito S, Nation JHL, Topps S, Medhurst AD, Randall AD, Couve A, Moss SJ, Collingridge GL, Pangalos MN, Davies CH, Calver AR. The GABAB2 subunit is critical for the trafficking and function of native GABAB receptors. Biochem Pharmacol 2004; 68:1655-66. [PMID: 15451409 DOI: 10.1016/j.bcp.2004.07.032] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Accepted: 07/12/2004] [Indexed: 11/25/2022]
Abstract
Studies in heterologous systems have demonstrated that heterodimerisation of the two GABA(B) receptor subunits appears to be crucial for the trafficking and signalling of the receptor. Gene targeting of the GABA(B1) gene has demonstrated that the expression of GABA(B1) is essential for GABA(B) receptor function in the central nervous system (CNS). However, the contribution of the GABA(B2) subunit in the formation of native GABA(B) receptors is still unclear, in particular whether other proteins can substitute for this subunit. We have created a transgenic mouse in which the endogenous GABA(B2) gene has been mutated in order to express a C-terminally truncated version of the protein. As a result, the GABA(B1) subunit does not reach the cell surface and concomitantly both pre- and post-synaptic GABA(B) receptor functions are abolished. Taken together with previous gene deletion studies for the GABA(B1) subunit, this suggests that classical GABA(B) function in the brain is exclusively mediated by GABA(B1/2) heteromers.
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Affiliation(s)
- Seb J Thuault
- Neurology and GI CEDD, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK
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35
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Wellendorph P, Bräuner-Osborne H. Molecular cloning, expression, and sequence analysis of GPRC6A, a novel family C G-protein-coupled receptor. Gene 2004; 335:37-46. [PMID: 15194188 DOI: 10.1016/j.gene.2004.03.003] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2003] [Revised: 02/05/2004] [Accepted: 03/05/2004] [Indexed: 12/13/2022]
Abstract
By similarity searching of the human genome sequence using known family C G-protein-coupled receptors (GPCRs) as query sequences, we have identified a putative novel human gene product of unknown function (located on chromosome band 6q22.31). The transcript, entitled GPRC6A (isoform 1), was cloned from a human kidney cDNA (DNA complementary to RNA) library and shown to encode a protein of 926 amino acids (aa). Protein sequence analysis revealed the presence of a seven-transmembrane (7TM) domain and an unusually long amino-terminal domain (ATD) of 590 amino acids. These traits, along with a significant homology to the human calcium-sensing receptor (CaR, 34% aa sequence identity), the taste receptor 1 (T1R1, 28%), and the metabotropic glutamate receptor 1 (mGluR1, 24%), places GPRC6A in family C of the GPCRs. Interestingly, GPRC6A bears the highest resemblance with an odorant goldfish 5.24 receptor (45%) which suggests that GPRC6A is the human orthologue of this receptor. GPRC6A is widely expressed in brain and peripheral tissues with highest levels in kidney, skeletal muscle, testis, and leucocytes. All three isoforms are expressed in mammalian cells, but are poorly expressed on the cell surface. In this work, we report the existence of two additional GPRC6A isoforms (2 and 3) carrying in-frame deletions in the ATD. Except for the kidney, where isoforms 1 and 2 appear equally expressed, isoforms 2 and 3 are generally less abundant than isoform 1. Analysis of the intron-exon composition of the GPRC6A gene confirms that isoforms 2 and 3 are naturally occurring splice variants.
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Affiliation(s)
- Petrine Wellendorph
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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36
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Charara A, Galvan A, Kuwajima M, Hall RA, Smith Y. An electron microscope immunocytochemical study of GABA(B) R2 receptors in the monkey basal ganglia: a comparative analysis with GABA(B) R1 receptor distribution. J Comp Neurol 2004; 476:65-79. [PMID: 15236467 DOI: 10.1002/cne.20210] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Functional gamma-aminobutyric acid (GABA)(B) receptors are heterodimers made up of GABA(B) R1 and GABA(B) R2 subunits. The subcellular localization of GABA(B) R2 receptors remains poorly known in the central nervous system. Therefore, we performed an ultrastructural analysis of the localization of GABA(B) R2 receptor immunoreactivity in the monkey basal ganglia. Furthermore, to characterize better the neuronal sites at which GABA(B) R1 and GABA(B) R2 may interact to form functional receptors, we compared the relative distribution of immunoreactivity of the two GABA(B) receptors in various basal ganglia nuclei. Light to moderate GABA(B) R2 immunoreactivity was found in cell bodies and neuropil elements in all basal ganglia nuclei. At the electron microscope level, GABA(B) R2 immunoreactivity was commonly expressed postsynaptically, although immunoreactive preterminal axonal segments were also frequently encountered, particularly in the globus pallidus and substantia nigra, where they accounted for the third of the total number of GABA(B) R2-containing elements. A few labeled terminals that displayed the ultrastructural features of glutamatergic boutons were occasionally found in most basal ganglia nuclei, except for the subthalamic nucleus, which was devoid of GABA(B) R2-immunoreactive boutons. The relative distribution of GABA(B) R2 immunoreactivity in the monkey basal ganglia was largely consistent with that of GABA(B) R1, but some exceptions were found, most noticeably in the globus pallidus and substantia nigra, which contained a significantly larger proportion of presynaptic elements labeled for GABA(B) R1 than GABA(B) R2. These findings suggest the possible coexistence and heterodimerization of GABA(B) R1 and GABA(B) R2 at various pre- and postsynaptic sites, but also raise the possibility that the formation of functional GABA(B) receptors in specific compartments of basal ganglia neurons relies on mechanisms other than GABA(B) R1/R2 heterodimerization.
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Affiliation(s)
- Ali Charara
- Yerkes National Primate Research Center, Emory University, Atlanta, Georgia 30322, USA
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37
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Bettler B, Kaupmann K, Mosbacher J, Gassmann M. Molecular structure and physiological functions of GABA(B) receptors. Physiol Rev 2004; 84:835-67. [PMID: 15269338 DOI: 10.1152/physrev.00036.2003] [Citation(s) in RCA: 632] [Impact Index Per Article: 31.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
GABA(B) receptors are broadly expressed in the nervous system and have been implicated in a wide variety of neurological and psychiatric disorders. The cloning of the first GABA(B) receptor cDNAs in 1997 revived interest in these receptors and their potential as therapeutic targets. With the availability of molecular tools, rapid progress was made in our understanding of the GABA(B) system. This led to the surprising discovery that GABA(B) receptors need to assemble from distinct subunits to function and provided exciting new insights into the structure of G protein-coupled receptors (GPCRs) in general. As a consequence of this discovery, it is now widely accepted that GPCRs can exist as heterodimers. The cloning of GABA(B) receptors allowed some important questions in the field to be answered. It is now clear that molecular studies do not support the existence of pharmacologically distinct GABA(B) receptors, as predicted by work on native receptors. Advances were also made in clarifying the relationship between GABA(B) receptors and the receptors for gamma-hydroxybutyrate, an emerging drug of abuse. There are now the first indications linking GABA(B) receptor polymorphisms to epilepsy. Significantly, the cloning of GABA(B) receptors enabled identification of the first allosteric GABA(B) receptor compounds, which is expected to broaden the spectrum of therapeutic applications. Here we review current concepts on the molecular composition and function of GABA(B) receptors and discuss ongoing drug-discovery efforts.
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Affiliation(s)
- Bernhard Bettler
- Pharmazentrum, Dept. of Clinical-Biological Sciences, Institute of Physiology, Univ. of Basel, Klingelbergstr. 50, CH-4056 Basel, Switzerland.
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38
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Martin SC, Steiger JL, Gravielle MC, Lyons HR, Russek SJ, Farb DH. Differential expression of ?-aminobutyric acid type B receptor subunit mRNAs in the developing nervous system and receptor coupling to adenylyl cyclase in embryonic neurons. J Comp Neurol 2004; 473:16-29. [PMID: 15067715 DOI: 10.1002/cne.20094] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
gamma-Aminobutyric acid type B receptors (GABA(B)Rs) mediate both slow inhibitory synaptic activity in the adult nervous system and motility signals for migrating embryonic cortical cells. Previous papers have described the expression of GABA(B)Rs in the adult brain, but the expression and functional significance of these gene products in the embryo are largely unknown. Here we examine GABA(B)R expression from rat embryonic day 10 (E10) to E18 compared with adult and ask whether embryonic cortical neurons contain functional GABA(B)R. GABA(B)R1 transcript levels greatly exceed GABA(B)R2 levels in the developing neural tube at E11, and olfactory bulb and striatum at E17 but equalize in most regions of adult nervous tissue, except for the glomerular and granule cell layers of the main olfactory bulb and the striatum. Consistent with expression differences, the binding affinity of GABA for GABA(B)Rs is significantly lower in adult striatum compared with cerebellum. Multiple lines of evidence from in situ hybridization, RNase protection, and real-time PCR demonstrate that GABA(B)R1a, GABA(B)R1b, GABA(B)R1h (a subunit subtype, lacking a sushi domain, that we have identified in embryonic rat brain), GABA(B)R2, and GABA(B)L transcript levels are not coordinately regulated. Despite the functional requirement for a heterodimer of GABA(B)R subunits, the expression of each subunit mRNA is under independent control during embryonic development, and, by E18, GABA(B)Rs are negatively coupled to adenylyl cyclase in neocortical neurons. The presence of embryonic GABA(B)R transcripts and protein and functional receptor coupling indicates potentially important roles for GABA(B)Rs in modulation of synaptic transmission in the developing embryonic nervous system.
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Affiliation(s)
- Stella C Martin
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118-2394, USA
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39
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Charles KJ, Calver AR, Jourdain S, Pangalos MN. Distribution of a GABAB-like receptor protein in the rat central nervous system. Brain Res 2003; 989:135-46. [PMID: 14556935 DOI: 10.1016/s0006-8993(03)03163-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Using a homology-based bioinformatics approach we have identified the human and rodent orthologues of a novel putative seven transmembrane G protein coupled receptor, termed GABA(BL). The amino acid sequence homology of these cDNAs compared to GABA(B1) and GABA(B2) led us to postulate that GABA(BL) may be a putative novel GABA(B) receptor subunit. We have developed a rabbit polyclonal antisera specific to the GABA(BL) protein and assessed the distribution of GABA(BL) in the rat CNS by immunohistochemistry. Protein expression was particularly dense in regions previously shown to contain known GABA(B) receptor subunits. Dense immunoreactivity was observed in the cortex, major subfields of the hippocampus and the dentate gyrus. GABA(BL) labelling was very conspicuous in the cerebellum, both in the granule cell layer and in Purkinje cells, and was also observed in the substantia gelatinosa and ventral horn motor neurons of the spinal cord. GABA(BL) immunoreactivity was also noted in a subset of parvalbumin positive hippocampal interneurons. Our data suggest a widespread distribution of GABA(BL) throughout the rat CNS.
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Affiliation(s)
- K J Charles
- Neurology Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park North, Third Avenue, Essex, CM19 5AW, Harlow, UK.
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