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Liu Y, Ding M, Liu YP, Zhang XC, Xing JX, Xuan JF, Xia X, Yao J, Wang BJ. Functional analysis of haplotypes and promoter activity at the 5' region of the human GABRB3 gene and associations with schizophrenia. Mol Genet Genomic Med 2019; 7:e652. [PMID: 30908890 PMCID: PMC6503024 DOI: 10.1002/mgg3.652] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Revised: 02/21/2019] [Accepted: 02/26/2019] [Indexed: 12/18/2022] Open
Abstract
Background This study investigated the effects of haplotypes T‐G and C‐A derived from NG_012836.1:g.4160T>C and NG_012836.1:g.4326G>A on protein expression levels in vitro and identified the functional sequence in the regulatory region of the GABRB3 gene linked to possible associations with schizophrenia. Methods Recombinant plasmids with haplotypes T‐G and C‐A and 10 recombinant vectors containing deletion fragments from the GABRB3 gene 5′ regulatory region were transfected into HEK‐293, SK‐N‐SH, and SH‐SY5Y cells. The relative fluorescence intensity of the two haplotypes and different sequences was compared using a dual luciferase reporter assay system. Results The relative fluorescence intensity of haplotype C‐A was significantly lower than that of T‐G. We shortened the core promoter sequence of the GABRB3 gene 5′ regulation region from −177 bp to −18 bp (ATG+1). We also found an expression suppression region from −1,735 bp to −1,638 bp and an enhanced regulatory region from −1,638 bp to −1,335 bp. Multiple inhibitory functional elements were identified in the region from −680 bp to −177 bp. Conclusion We demonstrated that haplotype C‐A might increase the risk of schizophrenia and found multiple regulatory regions that had an effect on GABRB3 receptor expression.
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Affiliation(s)
- Yi Liu
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Mei Ding
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Yong-Ping Liu
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Xi-Cen Zhang
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Jia-Xin Xing
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Jin-Feng Xuan
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Xi Xia
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Jun Yao
- School of Forensic Medicine, China Medical University, Shenyang, China
| | - Bao-Jie Wang
- School of Forensic Medicine, China Medical University, Shenyang, China
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Delahanty RJ, Zhang Y, Bichell TJ, Shen W, Verdier K, Macdonald RL, Xu L, Boyd K, Williams J, Kang JQ. Beyond Epilepsy and Autism: Disruption of GABRB3 Causes Ocular Hypopigmentation. Cell Rep 2017; 17:3115-3124. [PMID: 28009282 DOI: 10.1016/j.celrep.2016.11.067] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 09/26/2016] [Accepted: 11/21/2016] [Indexed: 01/12/2023] Open
Abstract
Reduced ocular pigmentation is common in Angelman syndrome (AS) and Prader-Willi syndrome (PWS) and is long thought to be caused by OCA2 deletion. GABRB3 is located in the 15q11-13 region flanked by UBE3A, GABRA5, GABRG3, and OCA2. Mutations in GABRB3 have frequently been associated with epilepsy and autism, consistent with its role in neurodevelopment. We report here a robust phenotype in the mouse in which deletion of Gabrb3 alone causes nearly complete loss of retinal pigmentation due to atrophied melanosomes, as evidenced by electron microscopy. Using exome and RNA sequencing, we confirmed that only the Gabrb3 gene was disrupted while the Oca2 gene was intact. However, mRNA abundance of Oca2 and other genes adjacent to Gabrb3 is substantially reduced in Gabrb3-/- mice, suggesting complex transcriptional regulation in this region. These results suggest that impairment in GABRB3 downregulates OCA2 and indirectly causes ocular hypopigmentation and visual defects in AS and PWS.
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Affiliation(s)
- Ryan J Delahanty
- Division of Epidemiology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37212, USA; Department of Human Genetics, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Yanfeng Zhang
- Division of Epidemiology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Terry Jo Bichell
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Wangzhen Shen
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Kelienne Verdier
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Robert L Macdonald
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA; Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37212, USA; Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37212, USA; Vanderbilt Brain Institute, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Lili Xu
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Kelli Boyd
- Pathology Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Janice Williams
- Vanderbilt Electron Microscopy Core, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Jing-Qiong Kang
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA; Vanderbilt Brain Institute, Vanderbilt University Medical Center, Nashville, TN 37212, USA.
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Abstract
OBJECTIVE Copy number variations encompassing the chromosome 15q11-q13 region have been implicated in the pathogenesis of several neurodevelopmental disorders including schizophrenia. The study aimed to investigate whether the GABRB3 gene mapped to 15q12 was associated with schizophrenia. MATERIALS AND METHODS We resequenced the promoter and all the exonic regions of the GABRB3 gene in 349 patients with schizophrenia and 386 control participants from Taiwan using the Sanger sequencing method. We also used a reporter gene assay to assess the functional impact of variants identified from the promoter region. RESULTS We identified a total of six common single nucleotide polymorphisms and eight rare variants in this sample. No genetic association of these common single nucleotide polymorphisms with schizophrenia was detected. A missense mutation Y402H at exon 9 was detected in two patients and two controls. Polyphen-2 predicted that the impact of this variant was benign. In addition, we identified two patient-specific variants at the promoter of GABRB3 that showed significantly increased promoter activity in a reporter gene assay. CONCLUSION The identification of two private patient-only variants at the promoter region with enhanced promoter activity supports the rare allele hypothesis of schizophrenia and suggests that increased GABRB3 expression may confer an increased risk of schizophrenia.
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Abstract
The γ-aminobutyric acid receptor type A (GABAA receptor) is a ligand-gated chloride channel that mediates major inhibitory functions in the central nervous system. GABAA receptors function mainly as pentamers containing α, β, and either γ or δ subunits. A number of antiepileptic drugs have agonistic effects on GABAA receptors. Hence, dysfunctions of GABAA receptors have been postulated to play important roles in the etiology of epilepsy. In fact, mutations or genetic variations of the genes encoding the α1, α6, β2, β3, γ2, or δ subunits (GABRA1, GABRA6, GABRB2, GABRB3, GABRG2, and GABRD, respectively) have been associated with human epilepsy, both with and without febrile seizures. Epilepsy resulting from mutations is commonly one of following, genetic (idiopathic) generalized epilepsy (e.g., juvenile myoclonic epilepsy), childhood absence epilepsy, genetic epilepsy with febrile seizures, or Dravet syndrome. Recently, mutations of GABRA1, GABRB2, and GABRB3 were associated with infantile spasms and Lennox-Gastaut syndrome. These mutations compromise hyperpolarization through GABAA receptors, which is believed to cause seizures. Interestingly, most of the insufficiencies are not caused by receptor gating abnormalities, but by complex mechanisms, including endoplasmic reticulum (ER)-associated degradation, nonsense-mediated mRNA decay, intracellular trafficking defects, and ER stress. Thus, GABAA receptor subunit mutations are now thought to participate in the pathomechanisms of epilepsy, and an improved understanding of these mutations should facilitate our understanding of epilepsy and the development of new therapies.
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Bazyan AS, van Luijtelaar G. Neurochemical and behavioral features in genetic absence epilepsy and in acutely induced absence seizures. ISRN NEUROLOGY 2013; 2013:875834. [PMID: 23738145 PMCID: PMC3664506 DOI: 10.1155/2013/875834] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 02/06/2013] [Indexed: 02/08/2023]
Abstract
The absence epilepsy typical electroencephalographic pattern of sharp spikes and slow waves (SWDs) is considered to be due to an interaction of an initiation site in the cortex and a resonant circuit in the thalamus. The hyperpolarization-activated cyclic nucleotide-gated cationic I h pacemaker channels (HCN) play an important role in the enhanced cortical excitability. The role of thalamic HCN in SWD occurrence is less clear. Absence epilepsy in the WAG/Rij strain is accompanied by deficiency of the activity of dopaminergic system, which weakens the formation of an emotional positive state, causes depression-like symptoms, and counteracts learning and memory processes. It also enhances GABAA receptor activity in the striatum, globus pallidus, and reticular thalamic nucleus, causing a rise of SWD activity in the cortico-thalamo-cortical networks. One of the reasons for the occurrence of absences is that several genes coding of GABAA receptors are mutated. The question arises: what the role of DA receptors is. Two mechanisms that cause an infringement of the function of DA receptors in this genetic absence epilepsy model are proposed.
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Affiliation(s)
- A. S. Bazyan
- Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Science, Russian Federation, 5A Butlerov Street, Moscow 117485, Russia
| | - G. van Luijtelaar
- Biological Psychology, Donders Centre for Cognition, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen, P.O. Box 9104, 6500 HE Nijmegen, The Netherlands
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Machuca-Parra AI, Miledi R, Martínez-Torres A. Identification of the minimal promoter for specific expression of the GABAρ1 receptor in retinal bipolar cells. J Neurochem 2013; 124:175-88. [PMID: 23106649 DOI: 10.1111/jnc.12067] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Revised: 09/26/2012] [Accepted: 10/23/2012] [Indexed: 11/29/2022]
Abstract
γ-aminobutyric acid (GABA)ρ receptors regulate rapid synaptic ion currents in the axon end of retinal ON bipolar neurons, acting as a point of control along the visual pathway. In the GABAρ1 subunit knock out mouse, inhibition mediated by this receptor is totally eliminated, showing its role in neural transmission in retina. GABAρ1 mRNA is expressed in mouse retina after post-natal day 7, but little is known about its transcriptional regulation. To identify the GABAρ1 promoter, in silico analyses were performed and indicated that a 0.290-kb fragment, flanking the 5'-end of the GABAρ1 gene, includes putative transcription factor-binding sites, two Inr elements, and lacks a TATA-box. A rapid amplification of cDNA ends (RACE) assay showed three transcription start sites (TSS) clustered in the first exon. Luciferase reporter assays indicated that a 0.232-kb fragment upstream from the ATG is the minimal promoter in transfected cell lines and in vitro electroporated retinae. The second Inr and AP1 site are important to activate transcription in secretin tumor cells (STC-1) and retina. Finally, the 0.232-kb fragment drives green fluorescent protein (GFP) expression to the inner nuclear layer, where bipolar cells are present. This first work paves the way for further studies of molecular elements that control GABAρ1 transcription and regulate its expression during retinal development.
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Affiliation(s)
- Arturo Israel Machuca-Parra
- Departamento de Neurobiología Celular y Molecular, Universidad Nacional Autónoma de México, Instituto de Neurobiología, Querétaro, Mexico
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Tanaka M, Bailey JN, Bai D, Ishikawa-Brush Y, Delgado-Escueta AV, Olsen RW. Effects on promoter activity of common SNPs in 5' region of GABRB3 exon 1A. Epilepsia 2012; 53:1450-6. [PMID: 22765836 DOI: 10.1111/j.1528-1167.2012.03572.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE The β3 subunit of the γ-aminobutyric acid type A receptors (GABA(A) -Rs) is an essential component of GABA(A) -Rs in fetal, perinatal, and adult mammalian brain. Various transcripts of the β3 subunit gene (GABRB3) produce various proteins with different N-termini. Rare variants in this N-terminus (exon 1A and exon 2) of GABRB3 protein segregate in affected family members of two multigeneration-multiplex families with remitting childhood absence epilepsy (rCAE), suggesting GABRB3 is a major Mendelian epilepsy gene for rare families with CAE. Therefore, the N-terminus of GABRB3 could be important for GABRB3 regulation in development, and its alteration could produce rCAE. Herein we determine if single nucleotide polymorphisms (SNPs) within the 1,148-bp region upstream from exon 1A influence the expression of GABRB3. METHODS We studied luciferase reporter expression for promoter activity, 1,148-bp upstream from exon 1A, using human embryonic kidney 293 cells. We generated constructs of the promoter region and compared different SNP haplotypes in 48 patients with rCAE. Next, we compared frequencies of rs20317, located in the core promoter region, and rs4906902, located in the enhancer region between 48 patients with rCAE and >500 healthy controls matched for ethnicity and ancestral origin. KEY FINDINGS Highest luciferase expression occurred 230-bp upstream of exon 1A. The construct that excluded this region lost luciferase activity. Therefore, this region contains the core promoter of exon 1A. Allele C but not allele G (rs20317) significantly increased luciferase expression activity. Allele C creates binding motifs for cMYB and EGR-3. Longer constructs overlapping this region have a binding motif for REST (RE1-silencing transcription factor), a critical epigenetic modulator for neuronal genes. REST represses expression of neuronal genes in nonneuronal tissues, resulting in reduced luciferase expression activity. Even in the suppressed condition, the longer construct enhanced luciferase expression activity of the shorter construct, which excluded the distal end containing rs4906902. However, allele frequencies of rs20317 and rs4906902 were not significantly associated with 48 rCAE patients in comparison to >500 controls matched for ethnicity and ancestral origin. SIGNIFICANCE Common SNPs in the promoter region increase luciferase expression activity. An epigenetic modulator, REST, specifically alters expression of GABRB3 exon 1A transcripts, suggesting epigenetic regulation by REST dominantly controls the expression of GABRB3 variant 2 transcript in early life GABA(A) signaling. Abnormal epigenetic regulation could be involved in absence seizures.
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Affiliation(s)
- Miyabi Tanaka
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California 90095-1735, USA
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Delahanty RJ, Kang J, Brune CW, Kistner EO, Courchesne E, Cox NJ, Cook EH, Macdonald RL, Sutcliffe JS. Maternal transmission of a rare GABRB3 signal peptide variant is associated with autism. Mol Psychiatry 2011; 16:86-96. [PMID: 19935738 PMCID: PMC3428055 DOI: 10.1038/mp.2009.118] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Maternal 15q11-q13 duplication is the most common copy number variant in autism, accounting for ∼1-3% of cases. The 15q11-q13 region is subject to epigenetic regulation, and genomic copy number losses and gains cause genomic disorders in a parent-of-origin-specific manner. One 15q11-q13 locus encodes the GABA(A) receptor β3 subunit gene (GABRB3), which has been implicated by several studies in both autism and absence epilepsy, and the co-morbidity of epilepsy in autism is well established. We report that maternal transmission of a GABRB3 signal peptide variant (P11S), previously implicated in childhood absence epilepsy, is associated with autism. An analysis of wild-type and mutant β3 subunit-containing α1β3γ2 or α3β3γ2 GABA(A) receptors shows reduced whole-cell current and decreased β3 subunit protein on the cell surface due to impaired intracellular β3 subunit processing. We thus provide the first evidence of an association between a specific GABA(A) receptor defect and autism, direct evidence that this defect causes synaptic dysfunction that is autism relevant and the first maternal risk effect in the 15q11-q13 autism duplication region that is linked to a coding variant.
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Affiliation(s)
- Ryan J. Delahanty
- Department of Molecular Physiology & Biophysics, Vanderbilt University, Nashville, TN
| | - Jingqiong Kang
- Department of Neurology, Vanderbilt University, Nashville, TN
| | - Camille W. Brune
- Department of Psychiatry, Institute for Juvenile Research, University of Illinois at Chicago, Chicago, IL
| | - Emily O. Kistner
- Department of Health Studies, The University of Chicago, Chicago, IL
| | - Eric Courchesne
- Department of Neurosciences, University of California San Diego, La Jolla, CA
| | - Nancy J. Cox
- Department of Medicine, The University of Chicago, Chicago, IL
| | - Edwin H. Cook
- Department of Psychiatry, Institute for Juvenile Research, University of Illinois at Chicago, Chicago, IL
| | | | - James S. Sutcliffe
- Department of Molecular Physiology & Biophysics, Vanderbilt University, Nashville, TN,Department of Psychiatry, Vanderbilt University, Nashville, TN
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Pignataro L, Varodayan FP, Tannenholz LE, Harrison NL. The regulation of neuronal gene expression by alcohol. Pharmacol Ther 2009; 124:324-35. [PMID: 19781570 DOI: 10.1016/j.pharmthera.2009.09.002] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2009] [Accepted: 09/02/2009] [Indexed: 10/20/2022]
Abstract
In recent years there has been an explosion of interest in how genes regulate alcohol drinking and contribute to alcoholism. This work has been stimulated by the completion of the human and mouse genome projects and the resulting availability of gene microarrays. Most of this work has been performed in drinking animals, and has utilized the extensive genetic variation among different mouse strains. At the same time, a much smaller amount of effort has gone into the in vitro study of the mechanisms underlying the regulation of individual genes by alcohol. These studies at the cellular and sub-cellular level are beginning to reveal the ways in which alcohol can interact with the transcriptional, translational and post-translational events inside the cell. Detailed studies of the promoter regions within several individual alcohol-responsive genes (ARGs) have been performed and this work has uncovered intricate signaling pathways that may be generalized to larger groups of ARGs. In the last few years several distinct ARGs have been identified from 35,000 mouse genes, by both the "top-down" approach (ex vivo gene arrays) and the "bottom-up" methods (in vitro promoter analysis). These divergent methodologies have converged on a surprisingly small number of genes encoding ion channels, receptors, transcription factors and proteins involved in synaptic function and remodeling. In this review we will describe some of the most interesting cellular and microarray work in the field, and will outline specific examples of genes for which the mechanisms of regulation by alcohol are now somewhat understood.
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Affiliation(s)
- Leonardo Pignataro
- Department of Anesthesiology and Department of Pharmacology, The College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032, USA.
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Kang I, Lindquist DG, Kinane TB, Ercolani L, Pritchard GA, Miller LG. Rapid Communication Isolation and Characterization of the Promoter of the Human GABAA Receptor α1 Subunit Gene. J Neurochem 2008. [DOI: 10.1046/j.1471-4159.1994.62041643.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Tanaka M, Olsen RW, Medina MT, Schwartz E, Alonso ME, Duron RM, Castro-Ortega R, Martinez-Juarez IE, Pascual-Castroviejo I, Machado-Salas J, Silva R, Bailey JN, Bai D, Ochoa A, Jara-Prado A, Pineda G, Macdonald RL, Delgado-Escueta AV. Hyperglycosylation and reduced GABA currents of mutated GABRB3 polypeptide in remitting childhood absence epilepsy. Am J Hum Genet 2008; 82:1249-61. [PMID: 18514161 DOI: 10.1016/j.ajhg.2008.04.020] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2007] [Revised: 04/09/2008] [Accepted: 04/24/2008] [Indexed: 12/24/2022] Open
Abstract
Childhood absence epilepsy (CAE) accounts for 10% to 12% of epilepsy in children under 16 years of age. We screened for mutations in the GABA(A) receptor (GABAR) beta 3 subunit gene (GABRB3) in 48 probands and families with remitting CAE. We found that four out of 48 families (8%) had mutations in GABRB3. One heterozygous missense mutation (P11S) in exon 1a segregated with four CAE-affected persons in one multiplex, two-generation Mexican family. P11S was also found in a singleton from Mexico. Another heterozygous missense mutation (S15F) was present in a singleton from Honduras. An exon 2 heterozygous missense mutation (G32R) was present in two CAE-affected persons and two persons affected with EEG-recorded spike and/or sharp wave in a two-generation Honduran family. All mutations were absent in 630 controls. We studied functions and possible pathogenicity by expressing mutations in HeLa cells with the use of Western blots and an in vitro translation and translocation system. Expression levels did not differ from those of controls, but all mutations showed hyperglycosylation in the in vitro translation and translocation system with canine microsomes. Functional analysis of human GABA(A) receptors (alpha 1 beta 3-v2 gamma 2S, alpha 1 beta 3-v2[P11S]gamma 2S, alpha 1 beta 3-v2[S15F]gamma 2S, and alpha 1 beta 3-v2[G32R]gamma 2S) transiently expressed in HEK293T cells with the use of rapid agonist application showed that each amino acid transversion in the beta 3-v2 subunit (P11S, S15F, and G32R) reduced GABA-evoked current density from whole cells. Mutated beta 3 subunit protein could thus cause absence seizures through a gain in glycosylation of mutated exon 1a and exon 2, affecting maturation and trafficking of GABAR from endoplasmic reticulum to cell surface and resulting in reduced GABA-evoked currents.
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Affiliation(s)
- Miyabi Tanaka
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine, University of California Los Angeles, CA 90095, USA
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Inoue H, Kayano S, Aoki Y, Kure S, Yamada A, Hata A, Matsubara Y, Suzuki Y. Association of the GABRB3 Gene with Nonsyndromic Oral Clefts. Cleft Palate Craniofac J 2008; 45:261-6. [DOI: 10.1597/06-142] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Objective:Nonsyndromic oral clefts are common craniofacial anomalies classified into two subgroups: cleft lip with or without cleft palate and isolated cleft palate. Nonsyndromic oral clefts are multifactorial diseases, with both genetic and environmental factors involved in their pathogenesis. The inhibitory neurotransmitter, γ-aminobutyric acid plays a role in normal embryonic, and particularly facial, development and γ-aminobutyric acid receptor type A β-3 subunit (GABRB3) knockout mice have been shown to have cleft palate. The GABRB3 gene is therefore a strong candidate gene for nonsyndromic oral clefts. We investigated here whether genetic variations of the GABRB3 gene affect the risk for nonsyndromic oral clefts.Method:In this case-control study, a total of 178 Japanese patients with cleft lip with or without cleft palate and 374 unrelated controls were recruited and were genotyped for six single nucleotide polymorphisms and a dinucleotide repeat marker of the GABRB3 gene.Results:None of the single nucleotide polymorphisms showed complete linkage disequilibrium with other single nucleotide polymorphisms. In a case-control association study with the six-locus haplotype of the gene, TGTGCT haplotype frequency in patients with cleft lip with or without cleft palate was significantly higher than in the controls (corrected p value = .029). None of the alleles of the dinucleotide repeat marker showed significant association with cleft lip with or without cleft palate.Conclusions:Our data suggest that the GABRB3 gene is involved in the pathogenesis of cleft lip with or without cleft palate in the Japanese population.
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Affiliation(s)
- Hiroki Inoue
- Department of Public Health, Chiba University Graduate School of Medicine, Chiba, Japan
| | - Shuji Kayano
- Department of Plastic Surgery, Tohoku University School of Medicine, Sendai, Japan
| | - Yoko Aoki
- Department of Medical Genetics, Tohoku University School of Medicine, Sendai, Japan
| | - Shigeo Kure
- Department of Medical Genetics, Tohoku University School of Medicine, Sendai, Japan
| | - Atsushi Yamada
- Department of Plastic Surgery, Tohoku University School of Medicine, Sendai, Japan
| | - Akira Hata
- Department of Public Health, Chiba University Graduate School of Medicine, Chiba, Japan
| | - Yoichi Matsubara
- Department of Medical Genetics, Tohoku University School of Medicine, Sendai, Japan
| | - Yoichi Suzuki
- Department of Public Health, Chiba University Graduate School of Medicine, Chiba, Japan
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Reddy TE, Shakhnovich BE, Roberts DS, Russek SJ, DeLisi C. Positional clustering improves computational binding site detection and identifies novel cis-regulatory sites in mammalian GABAA receptor subunit genes. Nucleic Acids Res 2007; 35:e20. [PMID: 17204484 PMCID: PMC1807961 DOI: 10.1093/nar/gkl1062] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2006] [Revised: 10/18/2006] [Accepted: 11/20/2006] [Indexed: 11/12/2022] Open
Abstract
Understanding transcription factor (TF) mediated control of gene expression remains a major challenge at the interface of computational and experimental biology. Computational techniques predicting TF-binding site specificity are frequently unreliable. On the other hand, comprehensive experimental validation is difficult and time consuming. We introduce a simple strategy that dramatically improves robustness and accuracy of computational binding site prediction. First, we evaluate the rate of recurrence of computational TFBS predictions by commonly used sampling procedures. We find that the vast majority of results are biologically meaningless. However clustering results based on nucleotide position improves predictive power. Additionally, we find that positional clustering increases robustness to long or imperfectly selected input sequences. Positional clustering can also be used as a mechanism to integrate results from multiple sampling approaches for improvements in accuracy over each one alone. Finally, we predict and validate regulatory sequences partially responsible for transcriptional control of the mammalian type A gamma-aminobutyric acid receptor (GABA(A)R) subunit genes. Positional clustering is useful for improving computational binding site predictions, with potential application to improving our understanding of mammalian gene expression. In particular, predicted regulatory mechanisms in the mammalian GABA(A)R subunit gene family may open new avenues of research towards understanding this pharmacologically important neurotransmitter receptor system.
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Affiliation(s)
- Timothy E. Reddy
- Bioinformatics Program, Boston University24 Cummington Street, Boston, MA 02215, USA
| | - Boris E. Shakhnovich
- Bioinformatics Program, Boston University24 Cummington Street, Boston, MA 02215, USA
| | - Daniel S. Roberts
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine715 Albany St., Boston, MA 02118, USA
- Program in BioMedical Neuroscience, Boston University44 Cummington Street, Boston, MA 02215, USA
| | - Shelley J. Russek
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine715 Albany St., Boston, MA 02118, USA
| | - Charles DeLisi
- Bioinformatics Program, Boston University24 Cummington Street, Boston, MA 02215, USA
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine715 Albany St., Boston, MA 02118, USA
- Biomedical Engineering, Boston University44 Cummington Street, Boston, MA 02215, USA
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Lagrange AH, Botzolakis EJ, Macdonald RL. Enhanced macroscopic desensitization shapes the response of alpha4 subtype-containing GABAA receptors to synaptic and extrasynaptic GABA. J Physiol 2006; 578:655-76. [PMID: 17124266 PMCID: PMC2151343 DOI: 10.1113/jphysiol.2006.122135] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Up-regulation of the GABAA receptor alpha4 subunit subtype has been consistently shown in multiple animal models of chronic epilepsy. This isoform is expressed in both thalamus and hippocampus and is likely to play a significant role in regulating corticothalamic and hippocampal rhythms. However, little is known about its physiological properties, thus limiting understanding of the role of alpha4 subtype-containing GABAA receptors in normal and abnormal physiology. We used rapid GABA application to recombinant GABAA receptors expressed in HEK293T cells to compare the macroscopic kinetic properties of alpha4beta3gamma2L receptors to those of the more widely distributed alpha1beta3gamma2L receptors. These receptor currents had similar peak current amplitudes and GABA EC50 values. However, alpha4beta3gamma2L currents activated more slowly when exposed to submaximal GABA concentrations, had more fast desensitization (tau = 15-100 ms), and had less residual current during long GABA applications. In addition, alpha4beta3gamma2L currents deactivated more slowly than alpha1beta3gamma2L currents. Peak currents evoked by repetitive, brief GABA applications were more strongly attenuated for alpha4beta3gamma2L currents than alpha1beta3gamma2L currents. Moreover, the time required to recover from desensitization was prolonged in alpha4beta3gamma2L currents compared to alpha1beta3gamma2L currents. We also found that exposure to prolonged low levels of GABA, similar to those that might be present in the extrasynaptic space, greatly suppressed the response of alpha4beta3gamma2L currents to higher concentrations of GABA, while alpha1beta3gamma2L currents were less affected by exposure to low levels of GABA. Taken together, these data suggest that alpha4beta3gamma2L receptors have unique kinetic properties that limit the range of GABA applications to which they can respond maximally. While similar to alpha1beta3gamma2L receptors in their ability to respond to brief and low frequency synaptic inputs, alpha4beta3gamma2L receptors are less efficacious when exposed to prolonged tonic GABA or during repetitive stimulation, as may occur during learning and seizures.
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Affiliation(s)
- Andre H Lagrange
- Department of Neurology, Vanderbilt University Medical Centre, 6140 Medical Research Building III, 465 21st Ave, South, Nashville, TN 37232-8552, USA.
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Yamashita M, Marszalec W, Yeh JZ, Narahashi T. Effects of ethanol on tonic GABA currents in cerebellar granule cells and mammalian cells recombinantly expressing GABA(A) receptors. J Pharmacol Exp Ther 2006; 319:431-8. [PMID: 16844844 DOI: 10.1124/jpet.106.106260] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The effects of ethanol on the GABA(A) receptors, which are regarded as one of the most important target sites of ethanol, are very controversial, ranging from potentiation to no effect. The delta subunit-containing GABA(A) receptors expressed in Xenopus oocytes were recently reported to be potently augmented by ethanol. We performed patch-clamp experiments using the cerebellar granule cells and mammalian cells expressing recombinant GABA(A) receptors. In granule cells, the sensitivity to GABA increased from 7 to 11 days in vitro. Furosemide, an antagonist of alpha6-containing GABA(A) receptors, inhibited GABA-induced currents more potently at 11 to 14 days than at 7 days. Ethanol at 30 mM had either no effect or an inhibitory effect on currents induced by low concentrations of GABA in granule cells. On alpha4beta2delta, alpha6beta2delta, or alpha6beta3deltaGABA(A) receptors expressed in Chinese hamster ovary cells, ethanol at 10, 30, and 100 mM had either no effect or an inhibitory effect on GABA currents. Ethanol inhibition of GABA(A) receptor was observed in all of the subunit combinations examined. In contrast, the perforated patch-clamp method to record the GABA currents revealed ethanol effects on the alpha6beta2delta subunits ranging from slight potentiation to slight inhibition. Ethanol seems to exert a dual action on the GABA(A) receptors and the potentiating action may depend on intracellular milieu. Thus, the differences between the GABA(A) receptors expressed in mammalian host cells and those in Xenopus oocytes in the response to ethanol might be due to changes in intracellular components under patch-clamp conditions.
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Affiliation(s)
- Megumi Yamashita
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, 303 E. Chicago Ave., Chicago, IL 60611-3008, USA
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17
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Urak L, Feucht M, Fathi N, Hornik K, Fuchs K. A GABRB3 promoter haplotype associated with childhood absence epilepsy impairs transcriptional activity. Hum Mol Genet 2006; 15:2533-41. [PMID: 16835263 DOI: 10.1093/hmg/ddl174] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Childhood absence epilepsy (CAE) is considered to exhibit a complex non-Mendelian pattern of inheritance. So far, only few CAE susceptibility genes have been identified. In a previous study of our group, an association between the GABA(A) receptor beta3 subunit (GABRB3) gene and CAE was shown. To further investigate this association, we screened 45 CAE patients of the first study for mutations in the 10 exons, the exon-intron boundaries and the regulatory sequences of GABRB3. Although we found no functionally relevant mutation, we did identify 13 single nucleotide polymorphisms (SNPs) in the GABRB3 gene region from the exon 1a promoter to the beginning of intron 3. Using these SNPs we defined four haplotypes for the respective GABRB3 gene region. A transmission disequilibrium test in the same 45 CAE patients and their parents indicated a significant association of this region and CAE (P=0.007075). Reporter gene assays in NT2 cells using exon 1a promoter constructs indicated that the disease-associated haplotype 2 promoter causes a significantly lower transcriptional activity than the haplotype 1 promoter that is over-represented in the controls. In silico analysis suggested that an exchange from T (haplotype 1) to C (haplotype 2) within this promoter impairs binding of the neuron-specific transcriptional activator N-Oct-3. Electrophoretic mobility shift assays demonstrated that the respective polymorphism reduces the nuclear protein binding affinity, thus explaining the results of the reporter gene assays. Reduced expression of the GABRB3 gene could therefore be one potential cause for the development of CAE, pathogenetically relevant in our patient group.
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Affiliation(s)
- Lydia Urak
- Division of Biochemistry and Molecular Biology, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria
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Downing SS, Lee YT, Farb DH, Gibbs TT. Benzodiazepine modulation of partial agonist efficacy and spontaneously active GABA(A) receptors supports an allosteric model of modulation. Br J Pharmacol 2006; 145:894-906. [PMID: 15912137 PMCID: PMC1576208 DOI: 10.1038/sj.bjp.0706251] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Benzodiazepines (BZDs) have been used extensively for more than 40 years because of their high therapeutic index and low toxicity. Although BZDs are understood to act primarily as allosteric modulators of GABA(A) receptors, the mechanism of modulation is not well understood. The applicability of an allosteric model with two binding sites for gamma-aminobutyric acid (GABA) and one for a BZD-like modulator was investigated. This model predicts that BZDs should enhance the efficacy of partial agonists. Consistent with this prediction, diazepam increased the efficacy of the GABA(A) receptor partial agonist kojic amine in chick spinal cord neurons. To further test the validity of the model, the effects of diazepam, flurazepam, and zolpidem were examined using wild-type and spontaneously active mutant alpha1(L263S)beta3gamma2 GABA(A) receptors expressed in HEK-293 cells. In agreement with the predictions of the allosteric model, all three modulators acted as direct agonists for the spontaneously active receptors. The results indicate that BZD-like modulators enhance the amplitude of the GABA response by stabilizing the open channel active state relative to the inactive state by less than 1 kcal, which is similar to the energy of stabilization conferred by a single hydrogen bond.
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Affiliation(s)
- Scott S Downing
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, 715 Albany St, Boston, MA 02118, U.S.A
| | - Yan T Lee
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, 715 Albany St, Boston, MA 02118, U.S.A
| | - David H Farb
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, 715 Albany St, Boston, MA 02118, U.S.A
| | - Terrell T Gibbs
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, 715 Albany St, Boston, MA 02118, U.S.A
- Author for correspondence:
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Tian H, Chen HJ, Cross TH, Edenberg HJ. Alternative splicing and promoter use in the human GABRA2 gene. ACTA ACUST UNITED AC 2005; 137:174-83. [PMID: 15950776 DOI: 10.1016/j.molbrainres.2005.03.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Revised: 02/24/2005] [Accepted: 03/03/2005] [Indexed: 11/25/2022]
Abstract
GABA(A) receptors mediate the majority of the fast synaptic inhibition in the mammalian brain. They are the targets of several important drugs, including benzodiazepines, which are used as anxiolytics, sedatives, anti-convulsants, and in the treatment of alcohol withdrawal symptoms. Non-coding variations in GABRA2, the gene encoding the alpha2 subunit, are associated with the risk for alcoholism, suggesting that regulatory differences are important. GABRA2 mRNAs from whole human brain and from three brain regions were examined for evidence of alternative splicing using reverse transcription-PCR and DNA sequencing. A complex pattern of alternative splicing and alternative promoter use of the human GABRA2 mRNA was demonstrated. There are four major isoforms consisting of combinations of two alternative 5' and 3' exons, as well as minor isoforms lacking exon 4 or exon 8. The alternative 5' exons each lie downstream of a functional promoter sequence, as shown by transient transfection assays. The promoter activities of naturally occurring haplotypes differed, indicating genetic differences in gene expression.
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Affiliation(s)
- Huijun Tian
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, 635 Barnhill Drive, Room 4063E, Indianapolis, IN 46202-5122, USA
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20
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McCauley JL, Olson LM, Delahanty R, Amin T, Nurmi EL, Organ EL, Jacobs MM, Folstein SE, Haines JL, Sutcliffe JS. A linkage disequilibrium map of the 1-Mb 15q12 GABA(A) receptor subunit cluster and association to autism. Am J Med Genet B Neuropsychiatr Genet 2004; 131B:51-9. [PMID: 15389768 DOI: 10.1002/ajmg.b.30038] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Autism is a complex genetic neuropsychiatric condition characterized by deficits in social interaction and language and patterns of repetitive or stereotyped behaviors and restricted interests. Chromosome 15q11.2-q13 is a candidate region for autism susceptibility based on observations of chromosomal duplications in a small percentage of affected individuals and findings of linkage and association. We performed linkage disequilibrium (LD) mapping across a 1-Mb interval containing a cluster of GABA(A) receptor subunit genes (GABRB3, GABRA5, and GABRG3) which are good positional and functional candidates. Intermarker LD was measured for 59 single nucleotide polymorphism (SNP) markers spanning this region, corresponding to an average marker spacing of 17.7 kb(-1). We identified haplotype blocks, and characterized these blocks for common (>5%) haplotypes present in the study population. At this marker resolution, haplotype blocks comprise <50% of the DNA in this region, consistent with a high local recombination rate. Identification of haplotype tag SNPs reduces the overall number of markers necessary to detect all common alleles by only 12%. Individual SNPs and multi-SNP haplotypes were examined for evidence of allelic association to autism, using a dataset of 123 multiplex autism families. Six markers individually, across GABRB3 and GABRA5, and several haplotypes inclusive of those markers, demonstrated nominally significant association. These results are positively correlated with the position of observed linkage. These studies support the existence of one or more autism risk alleles in the GABA(A) receptor subunit cluster on 15q12 and have implications for analysis of LD and association in regions with high local recombination.
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Affiliation(s)
- Jacob L McCauley
- Department of Molecular Physiology and Biophysics, Center for Human Genetics Research, Nashville, TN 37232, USA
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21
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Simon J, Wakimoto H, Fujita N, Lalande M, Barnard EA. Analysis of the Set of GABAA Receptor Genes in the Human Genome. J Biol Chem 2004; 279:41422-35. [PMID: 15258161 DOI: 10.1074/jbc.m401354200] [Citation(s) in RCA: 192] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The genes of the ionotropic gamma-aminobutyric acid receptor (GABR) subunits have shown an unusual chromosomal clustering, but only now can this be fully specified by analyses of the human genome. We have characterized the genes encoding the 18 known human GABR subunits, plus one now located here, for their precise locations, sizes, and exon/intron structures. Clusters of 17 of the 19, distributed between five chromosomes, are specified in detail, and their possible significance is considered. By applying search algorithms designed to recognize sequences of all known GABR-type subunits in species from man down to nematodes, we found no new GABR subunit is detectable in the human genome. However, the sequence of the human orthologue of the rat GABR rho3 receptor subunit was uncovered by these algorithms, and its gene could be analyzed. Consistent with those search results, orthologues of the beta4 and gamma4 subunits from the chicken, not cloned from mammals, were not detectable in the human genome by specific searches for them. The relationships are consistent with the mammalian subunit being derived from the beta line and epsilon from the gamma line, with mammalian loss of beta4 and gamma4. In their structures the human GABR genes show a basic pattern of nine coding exons, with six different genomic mechanisms for the alternative splicing found in various subunits. Additional noncoding exons occur for certain subunits, which can be regulatory. A dicysteine loop and its exon show remarkable constancy between all GABR subunits and species, of deduced functional significance.
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Affiliation(s)
- Joseph Simon
- Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
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22
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Steiger JL, Russek SJ. GABAA receptors: building the bridge between subunit mRNAs, their promoters, and cognate transcription factors. Pharmacol Ther 2004; 101:259-81. [PMID: 15031002 DOI: 10.1016/j.pharmthera.2003.12.002] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The type A gamma-aminobutyric acid (GABA(A)) receptors mediate the majority of fast inhibitory neurotransmission in the CNS, and alterations in GABA(A) receptor function is believed to be involved in the pathology of several neurological and psychiatric illnesses, such as epilepsy, anxiety, Alzheimer's disease, and schizophrenia. GABA(A) receptors can be assembled from eight distinct subunit families defined by sequence similarity: alpha(1-6), beta(1-3), gamma(1-3), delta, pi, theta, and rho(1-3). The regulation of GABA(A) receptor function in the brain is a highly compensating system, influencing both the number and the composition of receptors at the cell surface. While transcriptional and translational points of control operate in parallel, it is becoming increasingly evident that many functional changes in GABA(A) receptors reflect the differential gene regulation of its subunits. The fact that certain GABA(A) receptor subunit genes are transcribed in distinct cell types during specific periods of development strongly suggests that genetic control plays a major role in the choice of subunit variants available for receptor assembly. This review focuses on the physiological conditions that alter subunit mRNA levels, the promoters that may control such levels, and the use of a conceptual framework created by bioinformatics to study coordinate and independent GABA(A) receptor subunit gene regulation. As this exciting field moves closer to identifying the language hidden inside the chromatin of GABA(A) receptor subunit gene clusters, future experiments will be aimed at testing models generated by computational analysis with biologically relevant in vivo and in vitro assays. It is hoped that through this functional genomic approach there will be the identification of new targets for therapeutic intervention.
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Affiliation(s)
- Janine L Steiger
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, MA 02118, USA
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23
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Henderson LP, Jorge JC. Steroid modulation of GABAA receptors:from molecular mechanisms to CNS roles in reproduction, dysfunction and drug abuse. MOLECULAR INSIGHTS INTO ION CHANNEL BIOLOGY IN HEALTH AND DISEASE 2004. [DOI: 10.1016/s1569-2558(03)32010-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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Fuchs K, Celepirovic N. The 5'-flanking region of the rat GABA(A) receptor alpha2-subunit gene (Gabra2). J Neurochem 2002; 82:1512-23. [PMID: 12354299 DOI: 10.1046/j.1471-4159.2002.01098.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The GABA(A) receptor alpha2-subunit gene (Gabra2) has a specific spatial and temporal pattern of expression in rat brain. As a first step towards understanding the molecular mechanism underlying this regulation, we have investigated the structural properties of the 5'- flanking region of the rat Gabra2 gene. We identified six alpha2 transcript isoforms, each of which differs only in the 5'-untranslated region (UTR). Alignment of cDNA and genomic DNA sequences revealed that six 5'-UTRs are generated from three alternative first exons by alternative splicing using internal and terminal 5'-splice donor sites present in these exons. Promoter regions containing multiple transcription initiation sites were identified in the 5' proximity of each first exon. Two of these promoters lack TATA and CCAAT sequences. Finally, we have shown that differential activation of alternative promoters is used for the expression of the alpha2 mRNA isoforms during brain development, and that the diversity at the 5'-end of these transcripts affects GABA(A) receptor expression. Taken together, these results suggest that the expression of the Gabra2 gene can be influenced at both the transcriptional and post-transcriptional levels.
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Affiliation(s)
- Karoline Fuchs
- Division of Biochemistry and Molecular Biology, Brain Research Institute, University of Vienna, Austria.
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25
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Jentsch TJ, Stein V, Weinreich F, Zdebik AA. Molecular structure and physiological function of chloride channels. Physiol Rev 2002; 82:503-68. [PMID: 11917096 DOI: 10.1152/physrev.00029.2001] [Citation(s) in RCA: 934] [Impact Index Per Article: 42.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cl- channels reside both in the plasma membrane and in intracellular organelles. Their functions range from ion homeostasis to cell volume regulation, transepithelial transport, and regulation of electrical excitability. Their physiological roles are impressively illustrated by various inherited diseases and knock-out mouse models. Thus the loss of distinct Cl- channels leads to an impairment of transepithelial transport in cystic fibrosis and Bartter's syndrome, to increased muscle excitability in myotonia congenita, to reduced endosomal acidification and impaired endocytosis in Dent's disease, and to impaired extracellular acidification by osteoclasts and osteopetrosis. The disruption of several Cl- channels in mice results in blindness. Several classes of Cl- channels have not yet been identified at the molecular level. Three molecularly distinct Cl- channel families (CLC, CFTR, and ligand-gated GABA and glycine receptors) are well established. Mutagenesis and functional studies have yielded considerable insights into their structure and function. Recently, the detailed structure of bacterial CLC proteins was determined by X-ray analysis of three-dimensional crystals. Nonetheless, they are less well understood than cation channels and show remarkably different biophysical and structural properties. Other gene families (CLIC or CLCA) were also reported to encode Cl- channels but are less well characterized. This review focuses on molecularly identified Cl- channels and their physiological roles.
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Affiliation(s)
- Thomas J Jentsch
- Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, Hamburg, Germany.
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26
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Nurmi EL, Bradford Y, Chen Y, Hall J, Arnone B, Gardiner MB, Hutcheson HB, Gilbert JR, Pericak-Vance MA, Copeland-Yates SA, Michaelis RC, Wassink TH, Santangelo SL, Sheffield VC, Piven J, Folstein SE, Haines JL, Sutcliffe JS. Linkage disequilibrium at the Angelman syndrome gene UBE3A in autism families. Genomics 2001; 77:105-13. [PMID: 11543639 DOI: 10.1006/geno.2001.6617] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Autistic disorder is a neurodevelopmental disorder with a complex genetic etiology. Observations of maternal duplications affecting chromosome 15q11-q13 in patients with autism and evidence for linkage and linkage disequilibrium to markers in this region in chromosomally normal autism families indicate the existence of a susceptibility locus. We have screened the families of the Collaborative Linkage Study of Autism for several markers spanning a candidate region covering approximately 2 Mb and including the Angelman syndrome gene (UBE3A) and a cluster of gamma-aminobutyric acid (GABA(A)) receptor subunit genes (GABRB3, GABRA5, and GABRG3). We found significant evidence for linkage disequilibrium at marker D15S122, located at the 5' end of UBE3A. This is the first report, to our knowledge, of linkage disequilibrium at UBE3A in autism families. Characterization of null alleles detected at D15S822 in the course of genetic studies of this region showed a small (approximately 5-kb) genomic deletion, which was present at somewhat higher frequencies in autism families than in controls.
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Affiliation(s)
- E L Nurmi
- Program in Human Genetics, Department of Molecular Physiology & Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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27
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Erlitzki R, Gong Y, Zhang M, Minuk G. Identification of gamma-aminobutyric acid receptor subunit types in human and rat liver. Am J Physiol Gastrointest Liver Physiol 2000; 279:G733-9. [PMID: 11005760 DOI: 10.1152/ajpgi.2000.279.4.g733] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
GABA is a potent inhibitory neurotransmitter that binds to heterooligomeric receptors in the mammalian brain. In a previous study, we documented specific GABA binding to isolated rat hepatocytes that resulted in inhibition of hepatocyte proliferation. The purpose of the present study was to define the nature of hepatic GABA(A) receptors and to document their expression during rapid liver growth (after partial hepatectomy). PCRs with gene-specific primers derived from published sequences were performed with Marathon-ready human and rat liver cDNA. Two GABA(A) receptor subunit types (beta3 and epsilon) were expressed in human liver and one subunit type (beta3) in rat liver. PCR amplification of the human GABA(A) receptorbeta3-subunit produced a single product (molecular mass 53-59 kDa). In the case of the epsilon-subunit, two PCR products were identified. After partial hepatectomy, GABA(A) receptorbeta3-subunit expression inversely correlated with regenerative activity (r = -0.527, P = 0.006). In conclusion, these results indicate that in the human liver GABA(A) receptors consist of the beta3- and epsilon-subunit types, whereas in the rat liver only the beta3-subunit type is expressed. The results also support the hypothesis that GABAergic activity serves to maintain hepatocytes in a quiescent state.
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Affiliation(s)
- R Erlitzki
- Department of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada R3E 3P5
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28
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Kramer PR, Krishnamurthy R, Mitchell PJ, Wray S. Transcription factor activator protein-2 is required for continued luteinizing hormone-releasing hormone expression in the forebrain of developing mice. Endocrinology 2000; 141:1823-38. [PMID: 10803593 DOI: 10.1210/endo.141.5.7452] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
LHRH is the neuropeptide responsible for reproductive function. Prenatally, LHRH expression begins when neurons are in the olfactory pit and continues as these cells migrate into the brain. Thus, LHRH neurons maintain neuropeptide expression through very distinct environments. The regulatory interactions that control onset and continued expression of the LHRH phenotype are unknown. To begin to address this question primary LHRH neurons were removed from nasal explants at different ages. A complementary DNA (cDNA) subtraction screen was performed comparing a 3.5-days in vitro LHRH neuron [approximately embryonic day 15 (E15) in vivo] to two 10.5-days in vitro LHRH neurons (approximately postnatal day 1 in vivo). The transcription factor activator protein-2 (AP-2alpha) was differentially expressed and was present in the developmentally younger LHRH neuron. In vivo analysis revealed that LHRH neurons expressed AP-2 as they migrated across the cribriform plate and into the forebrain beginning on E13.5, but that coexpression of LHRH and AP-2 was no longer detected in postnatal day 1 animals. This suggested a regulatory role for AP-2 in LHRH neurons. Analysis of animals lacking AP-2alpha revealed a dramatic decrease in forebrain LHRH neurons between E13.5 and E14.5, correlating with normal onset of AP-2 expression in LHRH neurons as they entered the central nervous system. Nasal cells robustly expressing LHRH were still present on E 14.5. The continued presence of forebrain LHRH cells is proposed based on a second marker, galanin, and lack of increased apoptotic/necrotic cells in this region. A decrease in LHRH messenger RNA in forebrain neurons indicates regulation of LHRH occurred at the transcriptional or posttranscriptional level in mutant animals. These results indicate a developmentally restricted involvement of the transcription factor AP-2 in LHRH expression once the LHRH neurons have migrated into the forebrain, but before establishment of an adult-like distribution.
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Affiliation(s)
- P R Kramer
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4156, USA
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29
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McLean PJ, Shpektor D, Bandyopadhyay S, Russek SJ, Farb DH. A minimal promoter for the GABA(A) receptor alpha6-subunit gene controls tissue specificity. J Neurochem 2000; 74:1858-69. [PMID: 10800928 DOI: 10.1046/j.1471-4159.2000.0741858.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ability of nerve cells to regulate the expression of specific neurotransmitter receptors is of central importance to nervous system function, but little is known about the DNA elements that mediate neuron specific gene expression. The type A gamma-aminobutyric acid (GABA(A)) receptor alpha6-subunit gene, which is expressed exclusively in cerebellar granule cells, presents a unique opportunity to study the cis elements involved in restricting gene expression to a distinct neuronal population. In an effort to identify the regulatory elements that govern cerebellar granule cell-specific gene expression, the proximal 5' flanking regions for the human, rat, and mouse alpha6 genes were cloned and sequenced, and a major transcriptional initiation site was identified in the rodent genes. Functional analysis of rat alpha6 gene-reporter constructs in primary neuronal cultures reveals that a 155-bp TATA-less promoter region (-130 to +25 bp) constitutes a minimal promoter that can drive cerebellar granule cell-specific expression. Internal deletion and decoy competition studies demonstrate that the minimal promoter contains a 60-bp region (-130 to -70 bp) that is critical for enhanced promoter activity in cerebellar granule cells. Activity of the compromised promoter containing the deletion cannot be rescued by placing the 60-bp region downstream of the reporter gene, demonstrating that it is not a classical enhancer but rather a positionally dependent regulator. An additional cerebellar-specific activating sequence is located between -324 and -130 bp, and a downstream negative regulatory region (+158 to +294) has been shown to be active in fibroblasts but inactive in cerebellar granule cells. Taken together, the results suggest a possible mechanism for the control of cerebellar granule cell-specific expression of the GABA(A) receptor alpha6 subunit gene.
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Affiliation(s)
- P J McLean
- Department of Pharmacology, Boston University School of Medicine, Massachusetts 02118, USA
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30
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Abstract
A cDNA encoding an ionotropic gamma-aminobutyric acid (GABA) receptor subunit was isolated from a lobster (Homarus americanus) cDNA library. A longer version of this cDNA, containing a 108-bp insert, was also detected. The two cDNAs are predicted to encode alternatively spliced proteins of 485 and 521 amino acids, respectively. The sequences were most similar to the Drosophila RDL (resistance to dieldrin) GABA subunit with 54% identity, and 30-35% identity with vertebrate ionotropic GABA receptor subunits. Only the shorter clone formed functional ion channels when transfected into human embryonic kidney (HEK) 293 cells. GABA caused a Cl(-)-selective current in the presence of GABA that was blocked by picrotoxin. The GABA-induced current was weakly sensitive to the GABA(A) antagonist, bicuculline, but was enhanced by pentobarbital. Expression of the GABA receptor mRNA was highest in brain and the olfactory organ, but was not detected in leg muscle. These data suggest that the isolated cDNAs are likely to encode proteins that comprise subunits of native GABA receptors expressed in olfactory receptor neurons and projection neurons of the olfactory deutocerebrum.
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Affiliation(s)
- B Hollins
- Department of Physiology, University of Kentucky, Lexington 40536-0298, USA.
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31
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Davies PA, Hoffmann EB, Carlisle HJ, Tyndale RF, Hales TG. The influence of an endogenous beta3 subunit on recombinant GABA(A) receptor assembly and pharmacology in WSS-1 cells and transiently transfected HEK293 cells. Neuropharmacology 2000; 39:611-20. [PMID: 10728882 DOI: 10.1016/s0028-3908(99)00163-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Cell lines are commonly used for studying recombinant heterooligomeric ion channels with defined subunit composition. Such studies often ignore the contribution of endogenous proteins in the assembly of mature channels. We examined whether an endogenous subunit was required for the functional expression of gamma-aminobutyric acid type A (GABA(A)) receptors in WSS-1 cells, HEK293 cells stably expressing recombinant alpha1 and gamma2 subunits. Our pharmacological and RT-PCR analyses of GABA(A) receptors and their mRNAs in WSS-1 cells confirm the presence of alpha1 and gamma2 subunits and suggest the existence of an endogenous beta3 subunit. Whole-cell GABA-evoked currents recorded from untransfected WSS-1 cells were blocked by bicuculline methiodide and enhanced by anesthetics and anticonvulsants including the subunit-selective compounds diazepam and loreclezole. These data suggest that, in addition to the gamma2 subunit, WSS-1 cell receptors also contain beta2/3 subunits. RT-PCR revealed that WSS-1 cells and parental HEK293 cells contain beta3 mRNA. We examined the contribution of the beta3 subunit in the function of receptors formed by expression of alpha1 and gamma2S subunits. Untransfected HEK293 cells were unresponsive to GABA. Cells transfected with alpha1 and gamma2S cDNAs displayed small diazepam and loreclezole responsive GABA-activated currents. By contrast, the expression of alpha1 and gamma2S cDNAs in the neuroblastoma NB41A3 cell line, that lacks beta subunit mRNAs, failed to produce functional receptors. These data reaffirm that alpha1 and gamma2S subunits alone do not form functional GABA(A) receptors and that receptors of WSS-1 cells contain alpha1, beta3 and gamma2S subunits.
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Affiliation(s)
- P A Davies
- Department of Pharmacology, The George Washington University, Washington, DC 20037, USA
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32
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Mu W, Burt DR. The mouse GABA(A) receptor alpha3 subunit gene and promoter. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1999; 73:172-80. [PMID: 10581410 DOI: 10.1016/s0169-328x(99)00258-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Gamma-aminobutyric acid (GABA) type A receptors are multisubunit ligand-gated ion channels which mediate inhibition in the brain. The GABA(A) receptor alpha3 subunit gene exhibits extensive variation in its developmental and regional expression, but the detailed mechanisms governing the expression patterns of this gene remain unknown. We have cloned and begun to characterize the murine alpha3 subunit gene Gabra3. All but one of the 10 exons and the intron-exon boundaries have been sequenced; the first intron is in the 5' untranslated region (5'UTR) of the alpha3 mRNA. Rapid amplification of the cDNA 5'-end (5'-RACE) and RNase protection indicated many transcription start sites, with the major site (=+1) corresponding to a 5'UTR of 178 bases. Most sites were in or just downstream of a region of 55 (mouse) and 25 (human) GA repeats in the proximal promoter, as revealed by genome walking of Gabra3 and the human gene GABRA3. No canonical TATA or CAAT boxes or initiator (Inr) sites were found in either promoter, but both contained conserved consensus sites for several transcription factors. Progressive deletion of the mouse promoter produced positive or negative effects on expression of reporter (luciferase) constructs, with the highest observed activity in several types of transiently transfected cells for a construct containing bases -320 to +35. The GA repeats and a much shorter nearby series of four GC repeats, the first three of which are part of a consensus E2F site, appear to contribute significantly to mouse promoter activity. Upstream GA repeats enhanced activity of the SV40 promoter, and the GA repeat sequence bound nuclear proteins from several tissues.
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Affiliation(s)
- W Mu
- Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 655 W. Baltimore St., Baltimore, MD 21201-1559, USA
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33
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Mu W, Burt DR. Transcriptional regulation of GABAA receptor gamma2 subunit gene. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1999; 67:137-47. [PMID: 10101240 DOI: 10.1016/s0169-328x(99)00049-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have cloned the promoter regions of the genes for the mouse and human gamma2 subunits of the type A receptors for gamma-aminobutyric acid (GABA). For the mouse, the two major transcription start sites were at +1 (by definition) and +43, as established by rapid amplification of cDNA ends (RACE) and primer extension. This numbering places the start methionine at +297. There was no TATA or CCAAT box. Both mouse and human sequences have a candidate neuron-restrictive silencer element (NRSE) site in the first intron (+956 in mouse). We made assorted mouse-based promoter/reporter (luciferase) constructs starting from a core extending from -331 to +136, varying sizes at both ends, and including and excluding the putative NRSE and more proximal sequences. These were tested by transient transfection in several neuron-like and non-neuronal cell lines. Both proximal and distal downstream elements appeared to help direct expression to neuron-like cells, the NRSE in the intron, by repression in non-neurons, and a 24-bp portion of the 5' untranslated region starting at +113 (named GPE1) by preferentially promoting expression in neuron-like cells. Cotransfected human NRSF (transcription factor for NRSE) reduced reporter expression in neuron-like cells for constructs containing the NRSE in two locations. In gel mobility shift assays, the mouse gamma2 NRSE and a consensus NRSE both bound in vitro translated NRSF very similarly, and the NRSF gave the same major shifted band with the mouse gamma2 NRSE as was observed with nuclear extracts.
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Affiliation(s)
- W Mu
- Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 655 W. Baltimore St., Baltimore, MD 21201-1559, USA
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34
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Abstract
Recent advances in molecular biology and complementary information derived from neuropharmacology, biochemistry and behavior have dramatically increased our understanding of various aspects of GABAA receptors. These studies have revealed that the GABAA receptor is derived from various subunits such as alpha1-alpha6, beta1-beta3, gamma1-gamma3, delta, epsilon, pi, and rho1-3. Furthermore, two additional subunits (beta4, gamma4) of GABAA receptors in chick brain, and five isoforms of the rho-subunit in the retina of white perch (Roccus americana) have been identified. Various techniques such as mutation, gene knockout and inhibition of GABAA receptor subunits by antisense oligodeoxynucleotides have been used to establish the physiological/pharmacological significance of the GABAA receptor subunits and their native receptor assemblies in vivo. Radioligand binding to the immunoprecipitated receptors, co-localization studies using immunoaffinity chromatography and immunocytochemistry techniques have been utilized to establish the composition and pharmacology of native GABAA receptor assemblies. Partial agonists of GABAA receptors are being developed as anxiolytics which have fewer and less severe side effects as compared to conventional benzodiazepines because of their lower efficacy and better selectivity for the GABAA receptor subtypes. The subunit requirement of various drugs such as anxiolytics, anticonvulsants, general anesthetics, barbiturates, ethanol and neurosteroids, which are known to elicit at least some of their pharmacological effects via the GABAA receptors, have been investigated during the last few years so as to understand their exact mechanism of action. Furthermore, the molecular determinants of clinically important drug-targets have been investigated. These aspects of GABAA receptors have been discussed in detail in this review article.
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Affiliation(s)
- A K Mehta
- Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78284-7764, USA
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35
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Noble EP, Zhang X, Ritchie T, Lawford BR, Grosser SC, Young RM, Sparkes RS. D2 dopamine receptor and GABA(A) receptor beta3 subunit genes and alcoholism. Psychiatry Res 1998; 81:133-47. [PMID: 9858031 DOI: 10.1016/s0165-1781(98)00084-5] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
As the dopaminergic and GABAergic systems have been implicated in alcohol-related behaviors, variants of the D2 dopamine receptor (DRD2) and GABA(A) receptor beta3 subunit (GABRB3) genes were determined in a population-based association study of Caucasian non-alcoholic and alcoholic subjects. In severe alcoholics, compared to non-alcoholics, a significant increase was found in the prevalence (P = 1.7 x 10(-5)) and frequency (P = 1.6 x 10(-5)) of the DRD2 minor (A1) allele. Moreover, a significant progressive increase was observed in A1 allelic prevalence (P = 3.1 x 10(-6)) and frequency (P = 2.7 x 10(-6)) in the order of non-alcoholics, less severe and severe alcoholics. In severe alcoholics, compared to non-alcoholics, a significant decrease was found in the prevalence (P = 4.5 x 10(-3)) and frequency (P = 2.7 x 10(-2)) of the GABRB3 major (G1) allele. Furthermore, a significant progressive decrease was noted in G1 allelic prevalence (P = 2.4 x 10(-3)) and frequency (P = 1.9 x 10(-2)) in non-alcoholics, less severe and severe alcoholics, respectively. In sum, in the same population of non-alcoholics and alcoholics studied, variants of both the DRD2 and GABRB3 genes independently contribute to the risk for alcoholism, with the DRD2 variants revealing a stronger effect than the GABRB3 variants. However, when the DRD2 and the GABRB3 variants are combined, the risk for alcoholism is more robust than when these variants are considered separately.
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Affiliation(s)
- E P Noble
- Alcohol Research Center and Department of Psychiatry and Biobehavioral Sciences, UCLA, Neuropsychiatric Institute, Los Angeles, CA 90024-1759, USA.
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36
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Liu SC, Parent L, Harvey RJ, Darlison MG, Barnes EM. Chicken GABA(A) receptor beta4 subunits form robust homomeric GABA-gated channels in Xenopus oocytes. Eur J Pharmacol 1998; 354:253-9. [PMID: 9754927 DOI: 10.1016/s0014-2999(98)00453-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Chicken GABA(A) receptor beta4L and beta4S subunits were expressed in Xenopus oocytes by cRNA injection. Oocytes expressing either beta4 subunit alone or in combination with the chicken alpha1 subunit were studied using the two-electrode voltage-clamp technique. Both the beta4L and beta4S subunits form homomeric GABA-gated Cl- channels with similar efficiencies. In comparison, oocytes expressing either the chicken alpha1 or beta2S polypeptide show no or barely detectable GABA responses, as reported by others for most single-subunit vertebrate GABA(A) receptors. The GABA-gated currents due to the beta4L-subunit homomer were not affected by the presence of actinomycin D during cRNA expression, indicating that nascent oocyte polypeptides are not required for channel formation. The homomeric beta4L-subunit receptors show high affinity for GABA with an EC50 value of 4.3 +/- 0.4 microM and a Hill coefficient of 1.1 +/- 0.1 (n = 6). In response to GABA application at the EC25 value, currents elicited from the beta4L-subunit receptor are enhanced by 50 microM pentobarbital (110 +/- 10%, n = 3) and 10 microM loreclezole (60 +/- 3%, n = 3), inhibited by 10 microM picrotoxinin (93 +/- 3%, n = 3), but not affected by 1 microM diazepam. These properties are similar to those found for oocytes expressing heteromeric chicken alpha1beta4L and alpha1beta2S receptors. Since the beta subunits of GABA(A) receptors provide essential determinants for receptor assembly and subcellular localization, homomeric beta4-subunit receptors are a useful model system for further study of the structure and function of GABA(A) receptors.
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Affiliation(s)
- S C Liu
- Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030, USA
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37
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Hevers W, Lüddens H. The diversity of GABAA receptors. Pharmacological and electrophysiological properties of GABAA channel subtypes. Mol Neurobiol 1998; 18:35-86. [PMID: 9824848 DOI: 10.1007/bf02741459] [Citation(s) in RCA: 351] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The amino acid gamma-aminobutyric-acid (GABA) prevails in the CNS as an inhibitory neurotransmitter that mediates most of its effects through fast GABA-gated Cl(-)-channels (GABAAR). Molecular biology uncovered the complex subunit architecture of this receptor channel, in which a pentameric assembly derived from five of at least 17 mammalian subunits, grouped in the six classes alpha, beta, gamma, delta, sigma and epsilon, permits a vast number of putative receptor isoforms. The subunit composition of a particular receptor determines the specific effects of allosterical modulators of the GABAARs like benzodiazepines (BZs), barbiturates, steroids, some convulsants, polyvalent cations, and ethanol. To understand the physiology and diversity of GABAARs, the native isoforms have to be identified by their localization in the brain and by their pharmacology. In heterologous expression systems, channels require the presence of alpha, beta, and gamma subunits in order to mimic the full repertoire of native receptor responses to drugs, with the BZ pharmacology being determined by the particular alpha and gamma subunit variants. Little is known about the functional properties of the beta, delta, and epsilon subunit classes and only a few receptor subtype-specific substances like loreclezole and furosemide are known that enable the identification of defined receptor subtypes. We will summarize the pharmacology of putative receptor isoforms and emphasize the characteristics of functional channels. Knowledge of the complex pharmacology of GABAARs might eventually enable site-directed drug design to further our understanding of GABA-related disorders and of the complex interaction of excitatory and inhibitory mechanisms in neuronal processing.
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Affiliation(s)
- W Hevers
- Department of Psychiatry, University of Mainz, Germany
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38
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Cook EH, Courchesne RY, Cox NJ, Lord C, Gonen D, Guter SJ, Lincoln A, Nix K, Haas R, Leventhal BL, Courchesne E. Linkage-disequilibrium mapping of autistic disorder, with 15q11-13 markers. Am J Hum Genet 1998; 62:1077-83. [PMID: 9545402 PMCID: PMC1377089 DOI: 10.1086/301832] [Citation(s) in RCA: 274] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
Autistic disorder is a complex genetic disease. Because of previous reports of individuals with autistic disorder with duplications of the Prader-Willi/Angelman syndrome critical region, we screened several markers across the 15q11-13 region, for linkage disequilibrium. One hundred forty families, consisting predominantly of a child with autistic disorder and both parents, were studied. Genotyping was performed by use of multiplex PCR and capillary electrophoresis. Two children were identified who had interstitial chromosome 15 duplications and were excluded from further linkage-disequilibrium analysis. Use of the multiallelic transmission-disequilibrium test (MTDT), for nine loci on 15q11-13, revealed linkage disequilibrium between autistic disorder and a marker in the gamma-aminobutyric acidA receptor subunit gene, GABRB3 155CA-2 (MTDT 28.63, 10 df, P=.0014). No evidence was found for parent-of-origin effects on allelic transmission. The convergence of GABRB3 as a positional and functional candidate along with the linkage-disequilibrium data suggests the need for further investigation of the role of GABRB3 or adjacent genes in autistic disorder.
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Affiliation(s)
- E H Cook
- Department of Psychiatry, University of Chicago, Chicago, IL 60637, USA.
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39
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Sands SA, de Blas AL, Chronwall BM. Dopamine D2 receptor effects on GABA(A) receptor expression may modify melanotrope peptide release. Peptides 1998; 19:397-401. [PMID: 9493875 DOI: 10.1016/s0196-9781(97)00381-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Stimulation of melanotrope dopamine D2 receptors decreases mitotic rate, calcium channel activity, and the biosynthesis of several proteins. This study demonstrates that D2 receptor activation also affects GABA(A) receptor beta2/beta3 subunit immunoreactivity. Following chronic treatment with haloperidol, a D2 receptor antagonist, GABA(A) receptor immunoreactivity increased, whereas it decreased after chronic treatment with bromocriptine, a dopamine D2 receptor agonist. Thus, these data indicate that D2 function regulates GABA(A) receptor expression in melanotropes, a mechanism by which peptide release may be modified.
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Affiliation(s)
- S A Sands
- School of Biological Sciences, University of Missouri-Kansas City, 64110, USA
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40
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Lüscher B, Häuselmann R, Leitgeb S, Rülicke T, Fritschy JM. Neuronal subtype-specific expression directed by the GABA(A) receptor delta subunit gene promoter/upstream region in transgenic mice and in cultured cells. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1997; 51:197-211. [PMID: 9427522 DOI: 10.1016/s0169-328x(97)00242-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The promoter of the GABA(A) receptor delta subunit gene was analyzed in transgenic mice and in cultured cells to study sequences involved in neuronal subtype-specific gene expression. A 6.4-kb genomic fragment faithfully directed neuron-specific transcription of a lacZ reporter gene in the central nervous system. The transgene expression pattern in the cerebral cortex, hippocampal formation, thalamus, and brainstem was consistent with the regional and neuronal subtype-specific expression of the endogenous delta subunit protein in both developing and mature brain. In the cerebellum, however, the transgene was ectopically expressed in Purkinje cells and silent in granule cells, where the endogenous delta subunit is abundantly expressed. These mice provide a useful tool for investigating activity-dependent regulation of GABA(A) receptor expression under physiological and pathological conditions. Transfection studies using primary cortical neurons and astroglial cells revealed that the delta subunit gene promoter was selectively active in neurons even when truncated to a 267-bp core fragment. In conclusion, the delta subunit gene promoter/upstream region contains the information for neuronal subtype-specific expression in the entire brain except in the cerebellum and is selectively active in primary cortical neurons in vitro.
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Affiliation(s)
- B Lüscher
- Institute of Pharmacology, ETH and University of Zürich, Switzerland.
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41
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Wilke K, Gaul R, Klauck SM, Poustka A. A gene in human chromosome band Xq28 (GABRE) defines a putative new subunit class of the GABAA neurotransmitter receptor. Genomics 1997; 45:1-10. [PMID: 9339354 DOI: 10.1006/geno.1997.4885] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We have isolated and sequenced a novel human gene (GABRE) of the GABAA neurotransmitter receptor family. A cDNA sequence of the gene coding for a 506 amino acid protein was identified, representing a member of a putative new class (epsilon) of the GABAA receptor. The gene is transcribed at least at low level in several different tissues, with the highest levels being detected in adult heart and placenta. Alternative splicing of GABRE transcripts isolated from different tissues was observed at multiple positions of the gene, yielding an unusually complex variety of cDNA variants. The structure of the 5' region of most cDNAs is compatible with expression of protein sequence epsilon only in adult brain, whereas in other tissues, the majority of transcripts code for truncated protein sequences. The GABRE gene extends over 14 kb and is clustered together with the alpha 3 and the putative beta 4 GABAA receptor subunit genes in an approximately 0.8-Mb interval in chromosome band Xq28, located in the candidate regions of two different neurologic diseases. Based on features of conservation of protein sequences, gene structure, and genomic organization of GABAA receptor gene clusters, we propose that the epsilon and gamma subunit genes have a common ancestor and that GABAA receptor gene clusters in the human genome have diverged by multiple duplication events of an ancestral gene cluster containing one each alpha, beta, and gamma/epsilon precursor gene.
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Affiliation(s)
- K Wilke
- Deutsches Krebsforschungszentrum, Abteilung Molekulare Genomanalyse, Heidelberg, Germany
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42
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Kim Y, Glatt H, Xie W, Sinnett D, Lalande M. Human gamma-aminobutyric acid-type A receptor alpha5 subunit gene (GABRA5): characterization and structural organization of the 5' flanking region. Genomics 1997; 42:378-87. [PMID: 9205108 DOI: 10.1006/geno.1997.4770] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The gamma-aminobutyric acid-type A receptor alpha5 subunit gene (GABRA5) is widely expressed in brain and localized to the imprinted human chromosome 15q11-q13. A combination of cDNA library screening and 5' RACE analysis led to identification of three distinct mRNA isoforms of GABRA5 in human adult and fetal brain tissues, each of which differs only in the noncoding 5' UTR sequence. Alignment of the genomic and cDNA sequences of GABRA5 revealed that the mRNA isoforms resulted from three alternative first exons 1A, 1B, and 1C. Northern blot analysis showed that the expression of GABRA5 was not only tissue specific but region specific in brain. CAT reporter assays revealed promoter elements in the 5' proximity of each first exon. The GABRA5 promoter regions lacked TATA and CCAAT boxes but contained several other consensus transcriptional factor recognition sequences. These findings suggest that the differential exon 1 usage of GABRA5 arises as a consequence of alternative promoter activation.
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Affiliation(s)
- Y Kim
- Children's Hospital, Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115, USA
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43
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Hedblom E, Kirkness EF. A novel class of GABAA receptor subunit in tissues of the reproductive system. J Biol Chem 1997; 272:15346-50. [PMID: 9182563 DOI: 10.1074/jbc.272.24.15346] [Citation(s) in RCA: 180] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
A novel subunit of the gamma-aminobutyrate, type A (GABAA) receptor family has been identified in human and rat tissues. The subunit displays 30-40% amino acid identity with known family members and represents a distinct subunit class (termed pi). Transcripts of the pi subunit were detected in several human tissues and were particularly abundant in the uterus. The pi subunit protein can assemble with known GABAA receptor subunits and confer unique ligand binding properties to the recombinant receptors in which it combines. Most notably, the presence of the pi subunit alters the sensitivity of recombinant receptors to the endogenous steroid, pregnanolone. Identification of the pi subunit indicates a new target for pharmacological manipulation of GABAA receptors that are located outside of the central nervous system.
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Affiliation(s)
- E Hedblom
- The Institute for Genomic Research, Rockville, Maryland 20850, USA
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44
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Abstract
The genes encoding the gamma-aminobutyric acid (GABA) type-A receptor subunits beta 3 (GABRB3), alpha 5 (GABRA5), and gamma 3 (GABRG3) map to chromosome 15q11-q13. The three genes are contained within roughly 800 kb of the distal part of the imprinted Prader-Willi and Angelman syndrome region. A 570-kb contig encompassing GABRB3 and GABRA5 has been constructed in P1, lambda phage, and PAC clones. GABRB3 spans 250 kb of DNA and is organized into 9 exons that range from 68 to 504 bp, while GABRA5 is encoded by 11 exons (65 to 924 bp in length) within 86 kb. The exon/intron borders for both genes have been characterized and, primers have been designed to amplify each of the individual exons. Two reference STR markers have been positioned in the contig. The reference STR for GABRB3 is in fact located at least 60 kb beyond the 3' terminus of GABRB3, while D15S97 is contained within intron 4 of GABRB3. The detailed physical map of this GABAA receptor subunit gene cluster should not only be useful in genetic studies of the 15q11-q13 region, but will also be important for investigating the evolution and expression of the GABAA receptor gene superfamily.
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Affiliation(s)
- K Glatt
- Genetics Division, Children's Hospital, Boston, Massachusetts 02115, USA
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45
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Davies PA, Kirkness EF, Hales TG. Modulation by general anaesthetics of rat GABAA receptors comprised of alpha 1 beta 3 and beta 3 subunits expressed in human embryonic kidney 293 cells. Br J Pharmacol 1997; 120:899-909. [PMID: 9138697 PMCID: PMC1564547 DOI: 10.1038/sj.bjp.0700987] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. Radioligand binding and patch-clamp techniques were used to study the actions of gamma-aminobutyric acid (GABA) and the general anaesthetics propofol (2,6-diisopropylphenol), pentobarbitone and 5 alpha-pregnan-3 alpha-ol-20-one on rat alpha 1 and beta 3 GABAA receptor subunits, expressed either alone or in combination. 2. Membranes from HEK293 cells after transfection with alpha 1 cDNA did not bind significant levels of [35S]-tert-butyl bicyclophosphorothionate ([35S]-TBPS) (< 0.03 pmol mg-1 protein). GABA (100 microM) applied to whole-cells transfected with alpha 1 cDNA and clamped at -60 mV, also failed to activate discernible currents. 3. The membranes of cells expressing beta 3 cDNAs bound [35S]-TBPS (approximately 1 pmol mg-1 protein). However, the binding was not influenced by GABA (10 nM-100 microM). Neither GABA (100 microM) nor picrotoxin (10 microM) affected currents recorded from cells expressing beta 3 cDNA, suggesting that beta 3 subunits do not form functional GABAA receptors or spontaneously active ion channels. 4. GABA (10 nM-100 microM) modulated [35S]-TBPS binding to the membranes of cells transfected with both alpha 1 and beta 3 cDNAs. GABA (0.1 microM-1 mM) also dose-dependently activated inward currents with an EC50 of 9 microM recorded from cells transfected with alpha 1 and beta 3 cDNAs, clamped at -60 mV. 5. Propofol (10 nM-100 microM), pentobarbitone (10 nM-100 microM) and 5 alpha-pregnan-3 alpha-ol-20-one (1 nM-30 microM) modulated [35S]-TBPS binding to the membranes of cells expressing either alpha 1 beta 3 or beta 3 receptors. Propofol (100 microM), pentobarbitone (1 mM) and 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) also activated currents recorded from cells expressing alpha 1 beta 3 receptors. 6. Propofol (1 microM-1 mM) and pentobarbitone (1 mM) both activated currents recorded from cells expressing beta 3 homomers. In contrast, application of 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) failed to activate detectable currents. 7. Propofol (100 microM)-activated currents recorded from cells expressing either alpha 1 beta 3 or beta 3 receptors reversed at the Cl- equilibrium potential and were inhibited to 34 +/- 13% and 39 +/- 10% of control, respectively, by picrotoxin (10 microM). 5 alpha-Pregnan-3 alpha-ol-20-one (100 nM) enhanced propofol (100 microM)-evoked currents mediated by alpha 1 beta 3 receptors to 1101 +/- 299% of control. In contrast, even at high concentration 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) caused only a modest facilitation (to 128 +/- 12% of control) of propofol (100 microM)-evoked currents mediated by beta 3 homomers. 8. Propofol (3-100 microM) activated alpha 1 beta 3 and beta 3 receptors in a concentration-dependent manner. For both receptor combinations, higher concentrations of propofol (300 microM and 1 mM) caused a decline in current amplitude. This inhibition of receptor function reversed rapidly during washout resulting in a "surge' current on cessation of propofol (300 microM and 1 mM) application. Surge currents were also evident following pentobarbitone (1 mM) application to cells expressing either receptor combination. By contrast, this phenomenon was not apparent following applications of 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) to cells expressing alpha 1 beta 3 receptors. 9. These observations demonstrate that rat beta 3 subunits form homomeric receptors that are not spontaneously active, are insensitive to GABA and can be activated by some general anaesthetics. Taken together, these data also suggest similar sites on GABAA receptors for propofol and barbiturates, and a separate site for the anaesthetic steroids.
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Affiliation(s)
- P A Davies
- Department of Anesthesiology, UCLA Medical Center 90095, USA
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Nadler LS, Raetzman LT, Dunkle KL, Mueller N, Siegel RE. GABAA receptor subunit expression and assembly in cultured rat cerebellar granule neurons. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1996; 97:216-25. [PMID: 8997506 DOI: 10.1016/s0165-3806(96)00143-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The assembly of multisubunit GABAA receptors in specific neuronal populations is a complex process which is poorly understood. To begin to examine receptor assembly, alpha 1, beta 2/3, and gamma 2 subunit polypeptide expression and association, as well as receptor binding, were examined in cultured rat cerebellar granule neurons. Western blots revealed two alpha 1-immunoreactive proteins. A 39 kDa species was maximal at 2 days in culture and subsequently declined. In contrast, a 51 kDa polypeptide, the anticipated size of the mature alpha 1 subunit, was first detected at 4 days and increased throughout the culture period. Additional studies demonstrated that the beta 2/3 and gamma 2 subunits were detectable at 2 days and attained maximal levels by 6 days. The level of [3H]Ro15-1788 binding, a measure of assembled receptors, rose in parallel with the increases in the 51 kDa alpha 1, beta 2/3 and gamma 2 subunits. Moreover, the 51 kDa alpha 1, beta 2/3, and gamma 2 subunits were associated in receptor complexes. However, immunohistochemical studies demonstrated the presence of substantial intracellular subunit staining. This finding suggest that only some of the subunits expressed in granule neurons contribute to functional GABAA receptors on the cell surface.
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Affiliation(s)
- L S Nadler
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4965, USA
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Szabó G, Katarova Z, Körtvély E, Greenspan RJ, Urbán Z. Structure and the promoter region of the mouse gene encoding the 67-kD form of glutamic acid decarboxylase. DNA Cell Biol 1996; 15:1081-91. [PMID: 8985122 DOI: 10.1089/dna.1996.15.1081] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have cloned and determined the complete structure of the murine gene encoding the 67-kD form of glutamic acid decarboxylase (GAD67), the gamma-aminobutyric acid synthetic enzyme. Its coding region comprises 18 exons spanning 42 kb of genomic DNA. Exon 1 together with 64 bp of exon 2 defines the 5' untranslated region of GAD67 mRNA. Exon 18 specifies the protein's carboxyl terminal and the entire 3' untranslated region. Exons 7/A and 7/B are solely contained in the coding regions of two alternatively spliced bicistronic embryonic mRNAs, which code for the truncated embryonic GAD forms. The promoter region (P1) corresponding to the main group of transcription initiation sites is devoid of TATA and CAAT boxes but has putative binding sites for the transcription factor SP1 and is embedded in a large G + C-rich domain of a CpG island, features shared by the promoters of constitutively expressed housekeeping genes. Primer extension data suggests the existence of additional transcription start sites at 130 bp and 295 bp upstream from the major initiation site that are utilized less frequently in adult brain. The tentative distal promoters (P2 and P3) that correspond to the minor start sites resemble tissue-specific promoters with TATA and CAAT-like boxes. In 1.3 kb of the 5'-upstream region, we identified several putative transcription factor binding sites such as AP2, Hox, E-box, egr-1, and NF-kappaB and putative neuronal-specific regulatory elements, including the neuronal-restrictive silencer element, which may have functional significance in the developmental and tissue-specific expression of the GAD67 gene.
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MESH Headings
- Animals
- Base Sequence
- Binding Sites
- Cloning, Molecular
- CpG Islands/genetics
- Exons/genetics
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Enzymologic
- Genes/genetics
- Glutamate Decarboxylase/genetics
- Mice
- Mice, Inbred BALB C
- Molecular Sequence Data
- Promoter Regions, Genetic/genetics
- RNA Splicing
- RNA, Messenger/analysis
- RNA, Messenger/genetics
- Restriction Mapping
- Sequence Analysis, DNA
- Sequence Homology, Nucleic Acid
- Transcription Factors/metabolism
- Transcription, Genetic/genetics
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Affiliation(s)
- G Szabó
- Institute of Biochemistry, Biological Research Center, Szeged, Hungary
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Cibelli G, Schoch S, Pajunk H, Brand IA, Thiel G. A (G+C)-rich motif in the aldolase C promoter functions as a constitutive transcriptional enhancer element. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 237:311-7. [PMID: 8620889 DOI: 10.1111/j.1432-1033.1996.0311n.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The enzyme fructose-1,6-bisphosphate aldolase consists of three isozymes that are expressed in a tissue-specific manner. Using antibodies against aldolase B and C, it is shown that aldolase C is expressed in virtually all neuronal cell lines derived from the central and peripheral nervous system. Recently, experiments with transgenic mice indicated that a (G+C)-rich region of the aldolase C promoter might function as a neuron-specific control element of the rat aldolase C gene [Thomas, M., Makeh, I., Briand, P., Kahn, A. & Skala, H. (1993) Eur. J. Biochem. 218, 143-151). To functionally analyse this element, a plasmid consisting of four copies of this (G+C)-rich sequence, a TATA box, and the rabbit beta-globin gene as reporter was constructed. This plasmid was transfected into neuronal and nonneuronal cell lines and transcription was monitored by RNase protection mapping of the beta-globin mRNA. It is shown that the (G+C)-rich element of the aldolase C promoter directs transcription in neuronal as well as in nonneuronal cells. In contrast, the synapsin I promoter, used as a control for neuron-specific gene expression, directed transcription only in neuronal cells. In gel-retardation assays, two major DNA-protein complexes were detected with the (G+C)-rich element of the aldolase C promoter used as a DNA probe and nuclear extracts from brain and liver as a source for DNA-binding proteins. These DNA-proteins interactions could be impaired by a DNA probe that contained an Sp1-binding site, indicating that Sp1 or an Sp1-related factor binds to the aldolase C promoter (G+C)-rich element. This was confirmed by supershift analysis with antibodies specific for Sp1. The zinc finger transcription factor zif268/egr-1, also known to recognize a (G+C)-rich consensus site, did not, however, bind to the (G+C)-rich motif of the aldolase C promoter, nor could it stimulate transcription in transactivation assays from this control region. From these data, we conclude that the (G+C)-rich element of the aldolase C promoter functions as a constitutive transcriptional response element mediated by Sp1 and Sp1-related transcription factors.
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Affiliation(s)
- G Cibelli
- Institute for Genetics, University of Cologne, Germany
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Lambert JJ, Belelli D, Hill-Venning C, Callachan H, Peters JA. Neurosteroid modulation of native and recombinant GABAA receptors. Cell Mol Neurobiol 1996; 16:155-74. [PMID: 8743967 DOI: 10.1007/bf02088174] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
1. The pioneering work of Hans Selye over 50 years ago demonstrated that certain steroid metabolites can produce a rapid depression of central nervous system activity. 2. Research during the last 10 years has established that such effects are mediated by a nongenomic and specific interaction of these steroids with the brain's major inhibitory receptor, the GABAA receptor. 3. Here we describe the molecular mechanism of action of such steroids and review attempts to define the steroid binding site on the receptor protein. The therapeutic potential of such neurosteroids is discussed.
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Affiliation(s)
- J J Lambert
- Department of Pharmacology & Clinical Pharmacology, University of Dundee, Ninewells Hospital and Medical School, Scotland
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Mathews GC, Bolos-Sy AM, Covey DF, Rothman SM, Ferrendelli JA. Physiological comparison of alpha-ethyl-alpha-methyl-gamma-thiobutyrolactone with benzodiazepine and barbiturate modulators of GABAA receptors. Neuropharmacology 1996; 35:123-36. [PMID: 8734480 DOI: 10.1016/0028-3908(95)00180-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The GABAA receptor/chloride ionophore (GABAR) is allosterically modulated by several classes of anticonvulsant agents, including benzodiazepines and barbiturates, and some alkyl-substituted butyrolactones. To test the hypothesis that the anticonvulsant butyrolactones act at a distinct positive-modulatory site on the GABAR, we examined the physiological effects of a butyrolactone, a benzodiazepine and a barbiturate on GABA-mediated currents in voltage-clamped neurons and cells transfected with various subunit combinations. The butyrolactone, alpha-ethyl-alpha-methyl-gamma-thiobutyrolactone (alpha EMTBL), altered the EC50 for GABA and changed the apparent cooperativity of GABA responses. In contrast, the benzodiazepine chlordiazepoxide altered the EC50 for GABA with no effect on apparent cooperativity. The barbiturate phenobarbital altered both the EC50 and the amplitude of the maximal GABA response without altering apparent cooperativity. The GABA-mediated effect of the barbiturate, but not the benzodiazepine, added to the maximal effect of the butyrolactone, supporting the hypothesis that butyrolactones do not exert their effect at the barbiturate effector site. Both alpha EMTBL and phenobarbital potentiated GABA currents in transfected cells containing the alpha 1 beta 2 and alpha 1 gamma 2 subunit combinations, as well as alpha 1 subunits alone. Chlordiazepoxide had the minimum requirement of an alpha subunit and a gamma subunit. Specific GABARs lacking benzodiazepine or barbiturate modulation were tested for modulation by alpha EMTBL. The alpha 6 beta 2 gamma 2 combination was modulated by the butyrolactone but not chlordiazepoxide. However, GABARs comprising rho1 subunits were sensitive to both phenobarbital and alpha EMTBL. Although the molecular determinants for alpha EMTBL action appear similar to the barbiturates, our data support the conclusion that alpha EMTBL interacts with GABARs in a distinct manner from barbiturates and benzodiazepines.
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Affiliation(s)
- G C Mathews
- Department of Molecular Biology, Washington University School of Medicine, St Louis, MO 63110, USA
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