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Cao Z, Yan L, Shen Z, Chen Y, Shi Y, He X, Zhou N. A novel splice variant of Gαq-coupled Bombyx CAPA-PVK receptor 1 functions as a specific Gαi/o-linked receptor for CAPA-PK. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1867:118718. [PMID: 32289337 DOI: 10.1016/j.bbamcr.2020.118718] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 04/05/2020] [Accepted: 04/07/2020] [Indexed: 01/04/2023]
Abstract
Alternative splicing enables G protein-coupled receptor (GPCR) genes to greatly increase the number of structurally and functionally distinct receptor isoforms. However, the functional role and relevance of the individual GPCR splice variants in regulating physiological processes are still to be assessed. A naturally occurring alternative splice variant of Bombyx CAPA-PVK receptor, BomCAPA-PVK-R1-Δ341, has been shown to act as a dominant-negative protein to regulate cell surface expression and function of the canonical CAPA-PVK receptor. Herein, using functional assays, we identify the splice variant Δ341 as a specific receptor for neuropeptide CAPA-PK, and upon activation, Δ341 signals to ERK1/2 pathway. Further characterization demonstrates that Δ341 couples to Gαi/o, distinct from the Gαq-coupled canonical CAPA-PVK receptor, triggering ERK1/2 phosphorylation through Gβγ-PI3K-PKCζ signaling cascade. Moreover, our ELISA data show that the ligand-dependent internalization of the splice variant Δ341 is significantly impaired due to lack of GRKs-mediated phosphorylation sites. Our findings highlight the potential of this knowledge for molecular, pharmacological and physiological studies on GPCR splice variants in the future.
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Affiliation(s)
- Zheng Cao
- Institute of Biochemistry, College of Life Sciences, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Lili Yan
- Institute of Biochemistry, College of Life Sciences, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Zhangfei Shen
- Department of Economic Zoology, College of Animal Sciences, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Yu Chen
- Institute of Biochemistry, College of Life Sciences, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Ying Shi
- Institute of Biochemistry, College of Life Sciences, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Xiaobai He
- College of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu 212018, China
| | - Naiming Zhou
- Institute of Biochemistry, College of Life Sciences, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, China.
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2
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Zhou J, Zhao S, Dunker AK. Intrinsically Disordered Proteins Link Alternative Splicing and Post-translational Modifications to Complex Cell Signaling and Regulation. J Mol Biol 2018; 430:2342-2359. [DOI: 10.1016/j.jmb.2018.03.028] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Revised: 03/25/2018] [Accepted: 03/27/2018] [Indexed: 10/24/2022]
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Schober DA, Croy CH, Ruble CL, Tao R, Felder CC. Identification, expression and functional characterization of M4L, a muscarinic acetylcholine M4 receptor splice variant. PLoS One 2017; 12:e0188330. [PMID: 29211764 PMCID: PMC5718406 DOI: 10.1371/journal.pone.0188330] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/03/2017] [Indexed: 11/24/2022] Open
Abstract
Rodent genomic alignment sequences support a 2-exon model for muscarinic M4 receptor. Using this model a novel N-terminal extension was discovered in the human muscarinic acetylcholine M4 receptor. An open reading frame was discovered in the human, mouse and rat with a common ATG (methionine start codon) that extended the N-terminus of the muscarinic acetylcholine M4 receptor subtype by 155 amino acids resulting in a longer variant. Transcriptional evidence for this splice variant was confirmed by RNA-Seq and RT-PCR experiments performed from human donor brain prefrontal cortices. We detected a human upstream exon indicating the translation of the mature longer M4 receptor transcript. The predicted size for the longer two-exon M4 receptor splice variant with the additional 155 amino acid N-terminal extension, designated M4L is 69.7 kDa compared to the 53 kDa canonical single exon M4 receptor (M4S). Western blot analysis from a mammalian overexpression system, and saturation radioligand binding with [3H]-NMS (N-methyl-scopolamine) demonstrated the expression of this new splice variant. Comparative pharmacological characterization between the M4L and M4S receptors revealed that both the orthosteric and allosteric binding sites for both receptors were very similar despite the addition of an N-terminal extension.
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Affiliation(s)
- Douglas A. Schober
- Neuroscience, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, Indiana, United States of America
| | - Carrie H. Croy
- Neuroscience, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, Indiana, United States of America
| | - Cara L. Ruble
- Neuroscience, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, Indiana, United States of America
| | - Ran Tao
- Lieber Institute for Brain Development, Baltimore, Maryland, United States of America
| | - Christian C. Felder
- Neuroscience, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, Indiana, United States of America
- * E-mail:
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Salazar K, Cerda G, Martínez F, Sarmiento JM, González C, Rodríguez F, García-Robles M, Tapia JC, Cifuentes M, Nualart F. SVCT2 transporter expression is post-natally induced in cortical neurons and its function is regulated by its short isoform. J Neurochem 2014; 130:693-706. [DOI: 10.1111/jnc.12793] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 05/28/2014] [Accepted: 05/29/2014] [Indexed: 02/06/2023]
Affiliation(s)
- Katterine Salazar
- Laboratorio de Neurobiología y Células Madres; Facultad de Ciencias Biológicas; Centro de Microscopía Avanzada CMA-BIOBIO; Universidad de Concepción; Concepción Chile
| | - Gustavo Cerda
- Laboratorio de Neurobiología y Células Madres; Facultad de Ciencias Biológicas; Centro de Microscopía Avanzada CMA-BIOBIO; Universidad de Concepción; Concepción Chile
| | - Fernando Martínez
- Laboratorio de Neurobiología y Células Madres; Facultad de Ciencias Biológicas; Centro de Microscopía Avanzada CMA-BIOBIO; Universidad de Concepción; Concepción Chile
| | - José M. Sarmiento
- Departamento de Fisiología; Facultad de Medicina; Universidad Austral de Chile; Valdivia Chile
| | - Carlos González
- Departamento de Fisiología; Facultad de Medicina; Universidad Austral de Chile; Valdivia Chile
| | - Federico Rodríguez
- Laboratorio de Neurobiología y Células Madres; Facultad de Ciencias Biológicas; Centro de Microscopía Avanzada CMA-BIOBIO; Universidad de Concepción; Concepción Chile
| | - María García-Robles
- Laboratorio de Neurobiología y Células Madres; Facultad de Ciencias Biológicas; Centro de Microscopía Avanzada CMA-BIOBIO; Universidad de Concepción; Concepción Chile
| | - Juan Carlos Tapia
- Department of Neuroscience; Columbia University; New York city New York USA
| | - Manuel Cifuentes
- Departamento de Biología Celular, Genética y Fisiología; Facultad de Ciencias; Centro de Investigaciones Biomédicas en Red de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN); Instituto de Investigación Biomédica de Málaga (IBIMA); Campus Universitario de Teatinos s/n; Universidad de Málaga; Málaga España
| | - Francisco Nualart
- Laboratorio de Neurobiología y Células Madres; Facultad de Ciencias Biológicas; Centro de Microscopía Avanzada CMA-BIOBIO; Universidad de Concepción; Concepción Chile
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5
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De Bellis M, Pisani F, Mola MG, Basco D, Catalano F, Nicchia GP, Svelto M, Frigeri A. A novel human aquaporin-4 splice variant exhibits a dominant-negative activity: a new mechanism to regulate water permeability. Mol Biol Cell 2013; 25:470-80. [PMID: 24356448 PMCID: PMC3923639 DOI: 10.1091/mbc.e13-06-0331] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
An alternatively spliced transcript of human AQP4 that lacks exon 4 is identified. In transfected cells, AQP4-Δ4 shows no water transport properties, is retained in the ER, and has a dominant-negative effect on full-length AQP4. In skeletal muscles, AQP4-Δ4 mRNA expression inversely correlates with the level of AQP4 protein in different muscles. Two major isoforms of aquaporin-4 (AQP4) have been described in human tissue. Here we report the identification and functional analysis of an alternatively spliced transcript of human AQP4, AQP4-Δ4, that lacks exon 4. In transfected cells AQP4-Δ4 is mainly retained in the endoplasmic reticulum and shows no water transport properties. When AQP4-Δ4 is transfected into cells stably expressing functional AQP4, the surface expression of the full-length protein is reduced. Furthermore, the water transport activity of the cotransfectants is diminished in comparison to transfectants expressing only AQP4. The observed down-regulation of both the expression and water channel activity of AQP4 is likely to originate from a dominant-negative effect caused by heterodimerization between AQP4 and AQP4-Δ4, which was detected in coimmunoprecipitation studies. In skeletal muscles, AQP4-Δ4 mRNA expression inversely correlates with the level of AQP4 protein and is physiologically associated with different types of skeletal muscles. The expression of AQP4-Δ4 may represent a new regulatory mechanism through which the cell-surface expression and therefore the activity of AQP4 can be physiologically modulated.
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Affiliation(s)
- Manuela De Bellis
- Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari, Italy Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland M. Sarcone Hospital, 70038 Terlizzi, Bari, Italy
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Zhou J, Huang Y, Li L, Zhu L, Zhang D, Zhang S, Chen Y. Identification of two novel, alternatively spliced mRNA transcripts of the human follicle-stimulating hormone receptor. Mol Reprod Dev 2013; 80:916-23. [PMID: 24009160 DOI: 10.1002/mrd.22227] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Accepted: 08/04/2013] [Indexed: 11/08/2022]
Abstract
Glycoprotein hormone receptors contain large extracellular domains encoded by multiple exons that can be alternatively spliced. Using human ovarian surface epithelium, we cloned two new splice variants of the human follicle-stimulating hormone receptor (FSH-R) gene, hFSH-R2 and hFSH-R3. The hFSH-R2 splice variant differed from the full-length FSH-R mRNA by the deletion of exon 10 and inclusion of two small exons after exon 9 whereas the hFSH-R3 splice variant retained only exons 1-6 of the full-length transcript. Both variants were expressed at low levels, but were detected in cells from follicular fluid derived from 30 different subjects. Transfection of these two variants individually into KGN cells, an ovarian cancer cell line that expresses wild-type FSH-R, reduced FSH-mediated phosphorylation of ERK(1/2), Akt, and p38/MAPK. Furthermore, in vitro co-expression of either hFSH-R2 or hFSH-R3 and full-length FSH-R in HEK293T cells reduced signal transduction through full-length FSH-R. Further studies are needed to fully elucidate the functions of these receptor isoforms.
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Affiliation(s)
- Jun Zhou
- Department of Surgery, The Women's Hospital, School of Medicine, Zhejiang University, Zhejiang Province, China
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7
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Rodríguez FS, Salazar KA, Jara NA, García-Robles MA, Pérez F, Ferrada LE, Martínez F, Nualart FJ. Retracted: Superoxide-dependent uptake of vitamin C in human glioma cells. J Neurochem 2013; 127:793-804. [DOI: 10.1111/jnc.12365] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 06/25/2013] [Accepted: 07/08/2013] [Indexed: 11/30/2022]
Affiliation(s)
- Federico S. Rodríguez
- Laboratory of Neurobiology and Stem Cells; Center for Advanced Microscopy CMA BIOBIO; University of Concepcion; Concepcion Chile
| | - Katterine A. Salazar
- Laboratory of Neurobiology and Stem Cells; Center for Advanced Microscopy CMA BIOBIO; University of Concepcion; Concepcion Chile
| | - Nery A. Jara
- Laboratory of Neurobiology and Stem Cells; Center for Advanced Microscopy CMA BIOBIO; University of Concepcion; Concepcion Chile
| | | | | | - Luciano E. Ferrada
- Laboratory of Neurobiology and Stem Cells; Center for Advanced Microscopy CMA BIOBIO; University of Concepcion; Concepcion Chile
| | - Fernando Martínez
- Laboratory of Neurobiology and Stem Cells; Center for Advanced Microscopy CMA BIOBIO; University of Concepcion; Concepcion Chile
- Laboratory of Cellular Biology; University of Concepcion; Concepcion Chile
| | - Francisco J. Nualart
- Laboratory of Neurobiology and Stem Cells; Center for Advanced Microscopy CMA BIOBIO; University of Concepcion; Concepcion Chile
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Hasunuma I, Toyoda F, Okada R, Yamamoto K, Kadono Y, Kikuyama S. Roles of arginine vasotocin receptors in the brain and pituitary of submammalian vertebrates. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 304:191-225. [PMID: 23809437 DOI: 10.1016/b978-0-12-407696-9.00004-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
This chapter reviews the functions of arginine vasotocin (AVT) and its receptors in the central nervous system (CNS) of primarily submammalian vertebrates. The V1a-type receptor, which is widely distributed in the CNS of birds, amphibians, and fish, is one of the most important receptors involved in the expression of social and reproductive behaviors. In mammals, the V1b receptor of arginine vasopressin, an AVT ortholog, is assumed to be involved in aggression, social memory, and stress responses. The distribution of the V1b-type receptor in the brain of submammalian vertebrates has only been reported in an amphibian species, and its putative functions are discussed in this review. The functions of V2-type receptor in the CNS are still unclear. Recent phylogenetical and pharmacological analyses have revealed that the avian VT1 receptor can be categorized as a V2b-type receptor. The distribution of this newly categorized VT1 receptor in the brain of avian species should contribute to our knowledge of the possible roles of the V2b-type receptor in the CNS of other nonmammalian vertebrates. The functions of AVT in the amphibian and avian pituitaries are also discussed, focusing on the V1b- and V1a-type receptors.
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Affiliation(s)
- Itaru Hasunuma
- Department of Biology, Faculty of Science, Toho University, Chiba, Japan.
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9
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Bouley R, Nunes P, Andriopoulos B, McLaughlin M, Webber MJ, Lin HY, Babitt JL, Gardella TJ, Ausiello DA, Brown D. Heterologous downregulation of vasopressin type 2 receptor is induced by transferrin. Am J Physiol Renal Physiol 2012; 304:F553-64. [PMID: 23235478 DOI: 10.1152/ajprenal.00438.2011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Vasopressin (VP) binds to the vasopressin type 2 receptor (V2R) to trigger physiological effects including body fluid homeostasis and blood pressure regulation. Signaling is terminated by receptor downregulation involving clathrin-mediated endocytosis and V2R degradation. We report here that both native and epitope-tagged V2R are internalized from the plasma membrane of LLC-PK1 kidney epithelial cells in the presence of another ligand, transferrin (Tf). The presence of iron-saturated Tf (holo-Tf; 4 h) reduced V2R binding sites at the cell surface by up to 33% while iron-free (apo-Tf) had no effect. However, no change in green fluorescent protein-tagged V2R distribution was observed in the presence of bovine serum albumin, atrial natriuretic peptide, or ANG II. Conversely, holo-Tf did not induce the internalization of another G protein-coupled receptor, the parathyroid hormone receptor. In contrast to the effect of VP, Tf did not increase intracellular cAMP or modify aquaporin-2 distribution in these cells, although addition of VP and Tf together augmented VP-induced V2R internalization. Tf receptor coimmunoprecipitated with V2R, suggesting that they interact closely, which may explain the additive effect of VP and Tf on V2R endocytosis. Furthermore, Tf-induced V2R internalization was abolished in cells expressing a dominant negative dynamin (K44A) mutant, indicating the involvement of clathrin-coated pits. We conclude that Tf can induce heterologous downregulation of the V2R and this might desensitize VP target cells without activating downstream V2R signaling events. It also provides new insights into urine-concentrating defects observed in rat models of hemochromatosis.
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Affiliation(s)
- Richard Bouley
- 1Nephrology Division, MGH Center for Systems Biology, Program in Membrane Biology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA.
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10
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Congenital nephrogenic diabetes insipidus: the current state of affairs. Pediatr Nephrol 2012; 27:2183-204. [PMID: 22427315 DOI: 10.1007/s00467-012-2118-8] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 01/14/2012] [Accepted: 01/17/2012] [Indexed: 01/02/2023]
Abstract
The anti-diuretic hormone arginine vasopressin (AVP) is released from the pituitary upon hypovolemia or hypernatremia, and regulates water reabsorption in the renal collecting duct principal cells. Binding of AVP to the arginine vasopressin receptor type 2 (AVPR2) in the basolateral membrane leads to translocation of aquaporin 2 (AQP2) water channels to the apical membrane of the collecting duct principal cells, inducing water permeability of the membrane. This results in water reabsorption from the pro-urine into the medullary interstitium following an osmotic gradient. Congenital nephrogenic diabetes insipidus (NDI) is a disorder associated with mutations in either the AVPR2 or AQP2 gene, causing the inability of patients to concentrate their pro-urine, which leads to a high risk of dehydration. This review focuses on the current knowledge regarding the cell biological aspects of congenital X-linked, autosomal-recessive and autosomal-dominant NDI while specifically addressing the latest developments in the field. Based on deepened mechanistic understanding, new therapeutic strategies are currently being explored, which we also discuss here.
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Gonzalez A, Borquez M, Trigo CA, Brenet M, Sarmiento JM, Figueroa CD, Navarro J, Gonzalez CB. The splice variant of the V2 vasopressin receptor adopts alternative topologies. Biochemistry 2011; 50:4981-6. [PMID: 21534618 DOI: 10.1021/bi2001278] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The V2 receptor gene encodes two receptor variants by alternative splicing, the canonical V2 receptor (V2a receptor) and V2b. The V2b variant has an amino acid sequence identical to that of the V2a receptor up to the sixth transmembrane domain, but the V2b sequences corresponding to the putative seventh transmembrane domain and the carboxyl terminus are different from those of the V2a receptor. Here we investigate the topology and subcellular distribution of the V2b variant. We found that, in contrast to the V2a receptor, the V2b adopted two topologies: one with six transmembrane segments with the C-terminus on the extracellular side of the membrane and another with seven transmembrane segments with the C-terminus on the intracellular side, similar to typical G-protein-coupled receptors. Furthermore, we observed that both topological isoforms oligomerized with the V2a canonical receptor. Unlike the V2a receptor, V2b did not move to the plasma membrane, but it is retained in the ER--Golgi compartments. These findings indicate that the C-terminal sequence beyond the sixth transmembrane of the V2a is required for the stabilization of the seven-transmembrane topology of the receptor and is also essential for the trafficking of the receptor to the plasma membrane.
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Affiliation(s)
- Alexis Gonzalez
- Department of Physiology, Universidad Austral de Chile, Valdivia, Chile
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12
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Markovic D, Challiss RAJ. Alternative splicing of G protein-coupled receptors: physiology and pathophysiology. Cell Mol Life Sci 2009; 66:3337-52. [PMID: 19629391 PMCID: PMC11115665 DOI: 10.1007/s00018-009-0093-4] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2009] [Revised: 06/30/2009] [Accepted: 07/03/2009] [Indexed: 12/16/2022]
Abstract
The G protein-coupled receptors (GPCRs) are a superfamily of transmembrane receptors that have a broad distribution and can collectively recognise a diverse array of ligands. Activation or inhibition of GPCR signalling can affect many (patho)physiological processes, and consequently they are a major target for existing and emerging drug therapies. A common observation has been that the pharmacological, signalling and regulatory properties of GPCRs can differ in a cell- and tissue-specific manner. Such "phenotypic" diversity might be attributable to post-translational modifications and/or association of GPCRs with accessory proteins, however, post-transcriptional mechanisms are also likely to contribute. Although approximately 50% of GPCR genes are intronless, those that possess introns can undergo alternative splicing, generating GPCR subtype isoforms that may differ in their pharmacological, signalling and regulatory properties. In this review we shall highlight recent research into GPCR splice variation and discuss the potential consequences this might have for GPCR function in health and disease.
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Affiliation(s)
- Danijela Markovic
- Department of Cell Physiology and Pharmacology, University of Leicester, Henry Wellcome Building, Leicester, UK.
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Evans RT, Seasholtz AF. Soluble corticotropin-releasing hormone receptor 2alpha splice variant is efficiently translated but not trafficked for secretion. Endocrinology 2009; 150:4191-202. [PMID: 19520785 PMCID: PMC2736082 DOI: 10.1210/en.2009-0285] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
CRH directs the physiological and behavioral responses to stress. Its activity is mediated by CRH receptors (CRH-R) 1 and 2 and modulated by the CRH-binding protein. Aberrant regulation of this system has been associated with anxiety disorders and major depression, demonstrating the importance of understanding the regulation of CRH activity. An mRNA splice variant of CRH-R2alpha (sCRH-R2alpha) was recently identified that encodes the receptor's ligand-binding extracellular domain but terminates before the transmembrane domains. It was therefore predicted to serve as a secreted decoy receptor, mimicking the ability of CRH-binding protein to sequester free CRH. Although the splice variant contains a premature termination codon, predicting its degradation by nonsense-mediated RNA decay, cycloheximide experiments and polysome profiles demonstrated that sCRH-R2alpha mRNA escaped this regulation and was efficiently translated. However, the resulting protein was unable to serve as a decoy receptor because it failed to traffic for secretion because of an ineffective signal peptide and was ultimately subjected to proteosomal degradation. Several other truncated splice variants of G protein-coupled transmembrane receptors regulate the amount of full-length receptor expression through dimerization and misrouting; however, receptor binding assays and immunofluorescence of cells cotransfected with sCRH-R2alpha and CRH-R2alpha or CRH-R1 indicated that sCRH-R2alpha protein does not alter trafficking or binding of full-length CRH-R. Although sCRH-R2alpha protein does not appear to function as an intracellular or extracellular decoy receptor, the regulated unproductive splicing of CRH-R2alpha pre-mRNA to sCRH-R2alpha may selectively alter the cellular levels of full-length CRH-R2alpha mRNA and hence functional CRH-R2alpha receptor levels.
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Affiliation(s)
- Ryan T Evans
- Department of Biological Chemistry, Molecular and Behavioral Neuroscience Institute, The University ofMichigan, Ann Arbor, Michigan 48109-2200, USA
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Dickinson RE, Stewart AJ, Myers M, Millar RP, Duncan WC. Differential expression and functional characterization of luteinizing hormone receptor splice variants in human luteal cells: implications for luteolysis. Endocrinology 2009; 150:2873-81. [PMID: 19246536 DOI: 10.1210/en.2008-1382] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The human LH receptor (LHR) plays a key role in luteal function and the establishment of pregnancy through its interaction with the gonadotropins LH and human chorionic gonadotropin. We previously identified four splice variants of the LHR in human luteinized granulosa cells (LGCs) and corpora lutea (CL). Real-time quantitative PCR revealed that expression of the full-length LHR (LHRa) and the most truncated form (LHRd) changed significantly in CL harvested at different stages of the ovarian cycle (P < 0.01, ANOVA). LHRa expression was reduced in the late luteal CL (P < 0.05). Conversely, an increase in LHRd expression was observed in the late luteal CL (P < 0.01). Chronic manipulation of human chorionic gonadotropin in LGC primary cultures supported the in vivo findings. LHRd encodes a protein lacking the transmembrane and carboxyl terminal domains. COS-7 cells expressing LHRd were unable to produce cAMP in response to LH stimulation. COS-7 cells coexpressing LHRd and LHRa also failed to generate cAMP in response to LH, suggesting that this truncated form has a negative effect on the signaling of LHRa. Immunofluorescence staining of LGC and COS-7 cells implied that there is a reduction in cell surface expression of LHRa when LHRd is present. Overall, these results imply expression of LHR splice variants is regulated in the human CL. Furthermore, during functional luteolysis a truncated variant could modulate the cell surface expression and activity of full-length LHR.
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Affiliation(s)
- Rachel E Dickinson
- Department of Reproductive and DevelopmentalSciences, Division of Obstetrics and Gynaecology, Centre for Reproductive Biology,The Queen's Medical Research Institute, Edinburgh, United Kingdom.
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Böselt I, Römpler H, Hermsdorf T, Thor D, Busch W, Schulz A, Schöneberg T. Involvement of the V2 vasopressin receptor in adaptation to limited water supply. PLoS One 2009; 4:e5573. [PMID: 19440390 PMCID: PMC2680020 DOI: 10.1371/journal.pone.0005573] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Accepted: 04/06/2009] [Indexed: 01/11/2023] Open
Abstract
Mammals adapted to a great variety of habitats with different accessibility to water. In addition to changes in kidney morphology, e.g. the length of the loops of Henle, several hormone systems are involved in adaptation to limited water supply, among them the renal-neurohypophysial vasopressin/vasopressin receptor system. Comparison of over 80 mammalian V2 vasopressin receptor (V2R) orthologs revealed high structural and functional conservation of this key component involved in renal water reabsorption. Although many mammalian species have unlimited access to water there is no evidence for complete loss of V2R function indicating an essential role of V2R activity for survival even of those species. In contrast, several marsupial V2R orthologs show a significant increase in basal receptor activity. An increased vasopressin-independent V2R activity can be interpreted as a shift in the set point of the renal-neurohypophysial hormone circuit to realize sufficient water reabsorption already at low hormone levels. As found in other desert mammals arid-adapted marsupials show high urine osmolalities. The gain of basal V2R function in several marsupials may contribute to the increased urine concentration abilities and, therefore, provide an advantage to maintain water and electrolyte homeostasis under limited water supply conditions.
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Affiliation(s)
- Iris Böselt
- Institute of Biochemistry, Molecular Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Holger Römpler
- Rudolf-Böhm-Institute of Pharmacology and Toxicology, Medical Faculty, University of Leipzig, Leipzig, Germany
- Department of Organismic and Evolutionary Biology and the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, United States of America
| | - Thomas Hermsdorf
- Institute of Biochemistry, Molecular Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Doreen Thor
- Institute of Biochemistry, Molecular Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Wibke Busch
- Institute of Biochemistry, Molecular Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Angela Schulz
- Institute of Biochemistry, Molecular Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Torsten Schöneberg
- Institute of Biochemistry, Molecular Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
- * E-mail:
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16
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Vargas KJ, Sarmiento JM, Ehrenfeld P, Añazco CC, Villanueva CI, Carmona PL, Brenet M, Navarro J, Müller-Esterl W, González CB. Postnatal expression of V2 vasopressin receptor splice variants in the rat cerebellum. Differentiation 2009; 77:377-85. [PMID: 19281786 DOI: 10.1016/j.diff.2008.11.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2008] [Revised: 10/29/2008] [Accepted: 11/30/2008] [Indexed: 11/30/2022]
Abstract
The V(2) vasopressin receptor gene contains an alternative splice site in exon-3, which leads to the generation of two splice variants (V(2a) and V(2b)) first identified in the kidney. The open reading frame of the alternatively spliced V(2b) transcript encodes a truncated receptor, showing the same amino acid sequence as the canonical V(2a) receptor up to the sixth transmembrane segment, but displaying a distinct sequence to the corresponding seventh transmembrane segment and C-terminal domain relative to the V(2a) receptor. Here, we demonstrate the postnatal expression of V(2a) and V(2b) variants in the rat cerebellum. Most importantly, we showed by in situ hybridization and immunocytochemistry that both V(2) splice variants were preferentially expressed in Purkinje cells, from early to late postnatal development. In addition, both variants were transiently expressed in the neuroblastic external granule cells and Bergmann fibers. These results indicate that the cellular distributions of both splice variants are developmentally regulated, and suggest that the transient expression of the V(2) receptor is involved in the mechanisms of cerebellar cytodifferentiation by AVP. Finally, transfected CHO-K1 expressing similar amounts of both V(2) splice variants, as that found in the cerebellum, showed a significant reduction in the surface expression of V(2a) receptors, suggesting that the differential expression of the V(2) splice variants regulates the vasopressin signaling in the cerebellum.
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Affiliation(s)
- Karina J Vargas
- Department of Physiology, Universidad Austral de Chile, Valdivia 509-9200, Chile
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17
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Biswas S, Russell RJ, Jackson CJ, Vidovic M, Ganeshina O, Oakeshott JG, Claudianos C. Bridging the synaptic gap: neuroligins and neurexin I in Apis mellifera. PLoS One 2008; 3:e3542. [PMID: 18974885 PMCID: PMC2570956 DOI: 10.1371/journal.pone.0003542] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2008] [Accepted: 09/16/2008] [Indexed: 01/07/2023] Open
Abstract
Vertebrate studies show neuroligins and neurexins are binding partners in a trans-synaptic cell adhesion complex, implicated in human autism and mental retardation disorders. Here we report a genetic analysis of homologous proteins in the honey bee. As in humans, the honeybee has five large (31–246 kb, up to 12 exons each) neuroligin genes, three of which are tightly clustered. RNA analysis of the neuroligin-3 gene reveals five alternatively spliced transcripts, generated through alternative use of exons encoding the cholinesterase-like domain. Whereas vertebrates have three neurexins the bee has just one gene named neurexin I (400 kb, 28 exons). However alternative isoforms of bee neurexin I are generated by differential use of 12 splice sites, mostly located in regions encoding LNS subdomains. Some of the splice variants of bee neurexin I resemble the vertebrate α- and β-neurexins, albeit in vertebrates these forms are generated by alternative promoters. Novel splicing variations in the 3′ region generate transcripts encoding alternative trans-membrane and PDZ domains. Another 3′ splicing variation predicts soluble neurexin I isoforms. Neurexin I and neuroligin expression was found in brain tissue, with expression present throughout development, and in most cases significantly up-regulated in adults. Transcripts of neurexin I and one neuroligin tested were abundant in mushroom bodies, a higher order processing centre in the bee brain. We show neuroligins and neurexins comprise a highly conserved molecular system with likely similar functional roles in insects as vertebrates, and with scope in the honeybee to generate substantial functional diversity through alternative splicing. Our study provides important prerequisite data for using the bee as a model for vertebrate synaptic development.
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Affiliation(s)
- Sunita Biswas
- University of Queensland, Queensland Brain Institute, Brisbane, Queensland, Australia
- Australian National University, Research School of Biological Sciences, Canberra, Australian Capital Territory, Australia
- CSIRO Entomology, Black Mountain, Canberra, Australian Capital Territory, Australia
| | - Robyn J. Russell
- CSIRO Entomology, Black Mountain, Canberra, Australian Capital Territory, Australia
| | - Colin J. Jackson
- CSIRO Entomology, Black Mountain, Canberra, Australian Capital Territory, Australia
| | - Maria Vidovic
- Australian National University, Research School of Biological Sciences, Canberra, Australian Capital Territory, Australia
| | - Olga Ganeshina
- University of Queensland, Queensland Brain Institute, Brisbane, Queensland, Australia
| | - John G. Oakeshott
- CSIRO Entomology, Black Mountain, Canberra, Australian Capital Territory, Australia
| | - Charles Claudianos
- University of Queensland, Queensland Brain Institute, Brisbane, Queensland, Australia
- CSIRO Entomology, Black Mountain, Canberra, Australian Capital Territory, Australia
- * E-mail:
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18
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Cloning and characterization of dominant negative splice variants of the human histamine H4 receptor. Biochem J 2008; 414:121-31. [DOI: 10.1042/bj20071583] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The H4R (histamine H4 receptor) is the latest identified member of the histamine receptor subfamily of GPCRs (G-protein-coupled receptors) with potential functional implications in inflammatory diseases and cancer. The H4R is primarily expressed in eosinophils and mast cells and has the highest homology with the H3R. The occurrence of at least twenty different hH3R (human H3R) isoforms led us to investigate the possible existence of H4R splice variants. In the present paper, we report on the cloning of the first two alternatively spliced H4R isoforms from CD34+ cord blood-cell-derived eosinophils and mast cells. These H4R splice variants are localized predominantly intracellularly when expressed recombinantly in mammalian cells. We failed to detect any ligand binding, H4R–ligand induced signalling or constitutive activity for these H4R splice variants. However, when co-expressed with full-length H4R [H4R(390) (H4R isoform of 390 amino acids)], the H4R splice variants have a dominant negative effect on the surface expression of H4R(390). We detected H4R(390)–H4R splice varianthetero-oligomers by employing both biochemical (immunoprecipitation and cell-surface labelling) and biophysical [time-resolved FRET (fluorescence resonance energy transfer)] techniques. mRNAs encoding the H4R splice variants were detected in various cell types and expressed at similar levels to the full-length H4R(390) mRNA in, for example, pre-monocytes. We conclude that the H4R splice variants described here have a dominant negative effect on H4R(390) functionality, as they are able to retain H4R(390) intracellularly and inactivate a population of H4R(390), presumably via hetero-oligomerization.
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Kern A, Hubbard D, Amano A, Bryant-Greenwood GD. Cloning, expression, and functional characterization of relaxin receptor (leucine-rich repeat-containing g protein-coupled receptor 7) splice variants from human fetal membranes. Endocrinology 2008; 149:1277-94. [PMID: 18079195 PMCID: PMC2275365 DOI: 10.1210/en.2007-1348] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The relaxin receptor [leucine-rich repeat-containing G protein-coupled receptor 7 (LGR7)] belongs to the leucine-rich repeat containing G protein-coupled receptors subgroup C. Three new LGR7 splice variants have been cloned from the human fetal membranes and shown to be truncated versions of the full-length receptor, encoded by different lengths of the extracellular domain. The expression of their mRNAs has been confirmed by both qualitative and quantitative PCR and shown to be higher in the chorion and decidua before, compared with after, spontaneous labor. When HEK293 cells were transfected with each LGR7 splice variant, their proteins were retained within the endoplasmic reticulum. However, the protein for the shortest variant was also secreted into the medium. We have characterized the intracellular functions and effects of these LGR7 variants on the function of the wild-type (WT)-LGR7. In coexpression studies, each splice variant interacted directly with the WT-LGR7 and exerted a dominant-negative effect on cAMP accumulation by the WT-LGR7 after relaxin treatment. This interaction resulted in the sequestration of the WT-LGR7 inside the cells by down-regulation of its maturation and cell surface delivery. The constitutive homodimerization of WT-LGR7 has been shown here to take place in the endoplasmic reticulum, and the presence of any one of the splice variants decreased this by the formation of heterodimers with the WT-LGR7, supporting the view that homodimerization is a prerequisite for receptor trafficking to the cell surface. These data suggest that the dominant-negative effects of the LGR7 splice variants expressed in the chorion and decidua could be functionally significant in the peripartal period by inhibiting the function of WT-LGR7 and dampening the responsiveness of these tissues to endogenous relaxin.
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Affiliation(s)
- András Kern
- The Pacific Biosciences Research Center, University of Hawaii, Honolulu, Hawaii 96822, USA.
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20
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Long SH, Berna MJ, Thill M, Pace A, Pradhan TK, Hoffmann KM, Serrano J, Jensen RT. Secretin-receptor and secretin-receptor-variant expression in gastrinomas: correlation with clinical and tumoral features and secretin and calcium provocative test results. J Clin Endocrinol Metab 2007; 92:4394-402. [PMID: 17711922 PMCID: PMC2464459 DOI: 10.1210/jc.2007-0986] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
CONTEXT/OBJECTIVES The diagnosis of Zollinger-Ellison syndrome requires secretin testing in 60% of patients. Even with secretin, the diagnosis may be difficult because variable responses occur, and 6-30% have negative testing. The basis for variability or negative responses is unclear. It is unknown whether the tumor density of secretin receptors or the presence of a secretin-receptor-variant, which can act as a dominant negative, is important. The aim of this study was to investigate these possibilities. PATIENTS/METHODS Secretin-receptor and variant mRNA expression was determined in gastrinomas using real-time PCR from 54 Zollinger-Ellison syndrome patients. Results were correlated with Western blotting, secretin-receptor immunohistochemistry, with gastrin-provocative test results and tumoral/clinical/laboratory features. RESULTS Secretin-receptor mRNA was detectible in all gastrinomas but varied 132-fold with a mean of 0.89 +/- 0.12 molecules per beta-actin. Secretin-receptor PCR results correlated closely with Western blotting (r = 0.95; P < 0.0001) and receptor immunohistochemistry (P = 0.0015; r = 0.71). The variant was detected in all gastrinomas, but levels varied 102-fold and were 72-fold lower than the total. Secretin-receptor levels correlated with variant levels, Deltasecretin, but not Deltacalcium and with tumor location, but not growth, extent, or clinical responses. Variant levels did not correlate with the Deltasecretin. Detailed analysis provides no evidence that variant expression modified the secretin-receptor response or accounted for negative tests. CONCLUSIONS Secretin-receptor and secretin-receptor-variant expressions occur in all gastrinomas. Because the expression of the total, but not variant, correlated with the secretin results and no evidence for dominant negative activity of the variant was found, our results suggest that the total secretin-receptor density is an important determinant of the secretin test response.
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Affiliation(s)
- Scott H Long
- Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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21
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Conn PM, Ulloa-Aguirre A, Ito J, Janovick JA. G Protein-Coupled Receptor Trafficking in Health and Disease: Lessons Learned to Prepare for Therapeutic Mutant Rescue in Vivo. Pharmacol Rev 2007; 59:225-50. [PMID: 17878512 DOI: 10.1124/pr.59.3.2] [Citation(s) in RCA: 200] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
G protein-coupled receptors (GPCR) comprise the largest family of drug targets. This is not surprising as many signaling systems rely on this class of receptor to convert external and internal stimuli to intracellular responses. As is the case with other membrane proteins, GPCRs are subjected to a stringent quality control mechanism at the endoplasmic reticulum, which ensures that only correctly folded proteins enter the secretory pathway. Because of this quality control system, point mutations resulting in protein sequence variations may result in the production of misfolded and disease-causing proteins that are unable to reach their functional destinations in the cell. There is now a wealth of information demonstrating the functional rescue of misfolded mutant receptors by small nonpeptide molecules originally designed to serve as receptor antagonists; these small molecules ("pharmacoperones") serve as molecular templates, promoting correct folding and allowing the mutants to pass the scrutiny of the cellular quality control system and be expressed at the cell surface membrane. Two of these systems are especially well characterized: the gonadotropin-releasing hormone and the vasopressin type 2 receptors, which play important roles in regulating reproduction and water homeostasis, respectively. Mutations in these receptors can lead to well defined diseases that are recognized as being caused by receptor misfolding that may potentially be amenable to treatment with pharmacoperones. This review is focused on protein misfolding and misrouting related to various disease states, with special emphasis on these two receptors, which have proved to be of value for development of drugs potentially useful in regulating GPCR trafficking in healthy and disease states.
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Affiliation(s)
- P Michael Conn
- Divisions of Neuroscience and Reproductive Biology, ONPRC/OHSU, Beaverton, OR 97006, USA.
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22
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Davies JQ, Chang GW, Yona S, Gordon S, Stacey M, Lin HH. The Role of Receptor Oligomerization in Modulating the Expression and Function of Leukocyte Adhesion-G Protein-coupled Receptors. J Biol Chem 2007; 282:27343-27353. [PMID: 17620333 DOI: 10.1074/jbc.m704096200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The human leukocyte adhesion-G protein-coupled receptors (GPCRs), the epidermal growth factor (EGF)-TM7 proteins, are shown here to function as homo- and hetero-oligomers. Using cell surface cross-linking, co-immunoprecipitation, and fluorescence resonance energy transfer analysis of EMR2, an EGF-TM7 receptor predominantly expressed in myeloid cells, we demonstrate that it forms dimers in a reaction mediated exclusively by the TM7 moiety. We have also identified a naturally occurring but structurally unstable EMR2 splice variant that acts as a dominant negative modulator by dimerizing with the wild type receptor and down-regulating its expression. Additionally, heterodimerization between closely related EGF-TM7 members is shown to result in the modulation of expression and ligand binding properties of the receptors. These findings suggest that receptor homo- and hetero-oligomerization play a regulatory role in modulating the expression and function of leukocyte adhesion-GPCRs.
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Affiliation(s)
- John Q Davies
- Sir William Dunn School of Pathology, University of Oxford, South Parks Rd., Oxford, OX1 3RE, United Kingdom and the
| | - Gin-Wen Chang
- Sir William Dunn School of Pathology, University of Oxford, South Parks Rd., Oxford, OX1 3RE, United Kingdom and the
| | - Simon Yona
- Sir William Dunn School of Pathology, University of Oxford, South Parks Rd., Oxford, OX1 3RE, United Kingdom and the
| | - Siamon Gordon
- Sir William Dunn School of Pathology, University of Oxford, South Parks Rd., Oxford, OX1 3RE, United Kingdom and the
| | - Martin Stacey
- Sir William Dunn School of Pathology, University of Oxford, South Parks Rd., Oxford, OX1 3RE, United Kingdom and the.
| | - Hsi-Hsien Lin
- Department of Microbiology and Immunology, College of Medicine, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-San, Tao-Yuan, Taiwan.
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23
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Talebizadeh Z, Lam DY, Theodoro MF, Bittel DC, Lushington GH, Butler MG. Novel splice isoforms for NLGN3 and NLGN4 with possible implications in autism. J Med Genet 2006; 43:e21. [PMID: 16648374 PMCID: PMC2564526 DOI: 10.1136/jmg.2005.036897] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 09/16/2005] [Accepted: 09/25/2005] [Indexed: 11/04/2022]
Abstract
OBJECTIVE To screen cDNA for NLGN3 and NLGN4 from lymphoblastoid cells from autistic subjects. METHODS AND RESULTS 10 young autistic females and 30 non-autistic subjects were studied for alterations in two X linked genes, NLGN3 and NLGN4. A novel NLGN4 isoform lacking exon 4, which occurred de novo on the paternal allele, was identified in one of the autistic females. Monoallelic expression of NLGN4 was seen in this subject and in 11 of 14 informative autistic and non-autistic females using a single nucleotide polymorphism found at 3' UTR. Additionally, the NLGN3 transcript was present in two isoforms (with and without exon 7) in nine of 10 autistic females and in 30 non-autistic subjects, including parents of the autistic female having only the complete transcript with exon 7, and from the whole brain of a control. The novel truncated NLGN3 product may have a regulatory role, as reported in other proteins (for example, vasopressin receptor) by attenuating the function of the full length isoform, resulting in a reduction of the mature protein. Three dimensional protein structures were characterised using comparative modelling, and significant changes were suggested in the protein cores for these two neuroligin isoforms. CONCLUSIONS Splice variants may lead to potentially abnormal neuroligins in the causation of autism spectrum disorders.
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24
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Apaja PM, Tuusa JT, Pietilä EM, Rajaniemi HJ, Petäjä-Repo UE. Luteinizing hormone receptor ectodomain splice variant misroutes the full-length receptor into a subcompartment of the endoplasmic reticulum. Mol Biol Cell 2006; 17:2243-55. [PMID: 16495341 PMCID: PMC1446094 DOI: 10.1091/mbc.e05-09-0875] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2005] [Revised: 02/06/2006] [Accepted: 02/13/2006] [Indexed: 11/11/2022] Open
Abstract
The luteinizing hormone receptor (LHR) is a G protein-coupled receptor that is expressed in multiple RNA messenger forms. The common rat ectodomain splice variant is expressed concomitantly with the full-length LHR in tissues and is a truncated transcript corresponding to the partial ectodomain with a unique C-terminal end. Here we demonstrate that the variant alters the behavior of the full-length receptor by misrouting it away from the normal secretory pathway in human embryonic kidney 293 cells. The variant was expressed as two soluble forms of M(r) 52,000 and M(r) 54,000, but although the protein contains a cleavable signal sequence, no secretion to the medium was observed. Only a very small fraction of the protein was able to gain hormone-binding ability, suggesting that it is retained in the endoplasmic reticulum (ER) by its quality control due to misfolding. This was supported by the finding that the variant was found to interact with calnexin and calreticulin and accumulated together with these ER chaperones in a specialized juxtanuclear subcompartment of the ER. Only proteasomal blockade with lactacystin led to accumulation of the variant in the cytosol. Importantly, coexpression of the variant with the full-length LHR resulted in reduction in the number of receptors that were capable of hormone binding and were expressed at the cell surface and in targeting of immature receptors to the juxtanuclear ER subcompartment. Thus, the variant mediated misrouting of the newly synthesized full-length LHRs may provide a way to regulate the number of cell surface receptors.
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Affiliation(s)
- Pirjo M Apaja
- Biocenter Oulu, University of Oulu, FI-90014 Oulu, Finland
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25
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Sasaki M, Miyosawa K, Ohkubo S, Nakahata N. Physiological Significance of Thromboxane A2 Receptor Dimerization. J Pharmacol Sci 2006; 100:263-70. [PMID: 16565578 DOI: 10.1254/jphs.fp0050839] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
The thromboxane A(2) receptor (TP), one of the G protein-coupled receptors (GPCRs), consists of two splicing variants, TPalpha and TPbeta, which differ in their C-terminal regions. In the present study, we investigated whether TPalpha and TPbeta formed homo- or hetero-dimers and whether the dimerization changed the function of TP. The immunofluorescent analysis using human embryonic kidney (HEK) 293 cells expressing either FLAG-tagged TPalpha or TPbeta showed that TPalpha is mainly distributed on plasma membranes and TPbeta existed on plasma membranes and within the cells. Co-immunoprecipitation analysis using HEK293 cells expressing both TPalpha and TPbeta showed that TPalpha and TPbeta formed homo- and hetero-dimers. U46619, a TP agonist, caused phosphoinositide hydrolysis and elevation of [Ca(2+)](i) in a concentration-dependent manner in Chinese hamster ovary (CHO) cells expressing TPalpha or TPbeta. The responses were observed to a greater extent in the cells expressing TPalpha than TPbeta. In the cells expressing both TPalpha and TPbeta, U46619-induced responses were observed to a lesser extent than in the cells expressing TPalpha alone. Furthermore, [(3)H]SQ29548 binding showed that the level of the cell surface expression of TP was the following order: the cells expressing TPalpha > TPalpha and TPbeta > TPbeta. These results indicate that TPalpha and TPbeta formed homo- and hetero-dimers, and TP-mediated signaling may be regulated by the hetero-dimer.
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MESH Headings
- 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology
- Alternative Splicing
- Animals
- Bridged Bicyclo Compounds, Heterocyclic
- CHO Cells
- Cell Membrane/metabolism
- Cricetinae
- Cricetulus
- Dimerization
- Dose-Response Relationship, Drug
- Fatty Acids, Unsaturated
- Green Fluorescent Proteins
- Humans
- Hydrazines/metabolism
- Microscopy, Confocal
- Oligopeptides
- Peptides
- Protein Isoforms/drug effects
- Protein Isoforms/genetics
- Protein Isoforms/metabolism
- Receptors, Thromboxane A2, Prostaglandin H2/drug effects
- Receptors, Thromboxane A2, Prostaglandin H2/genetics
- Receptors, Thromboxane A2, Prostaglandin H2/metabolism
- Recombinant Fusion Proteins
- Signal Transduction
- Transfection
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Affiliation(s)
- Masako Sasaki
- Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University, Japan
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26
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Evans PD, Maqueira B. Insect octopamine receptors: a new classification scheme based on studies of cloned Drosophila G-protein coupled receptors. INVERTEBRATE NEUROSCIENCE 2005; 5:111-8. [PMID: 16211376 DOI: 10.1007/s10158-005-0001-z] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2005] [Accepted: 07/20/2005] [Indexed: 11/29/2022]
Abstract
Insect octopamine receptors are G-protein coupled receptors. They can be coupled to second messenger pathways to mediate either increases or decreases in intracellular cyclic AMP levels or the generation of intracellular calcium signals. Insect octopamine receptors were originally classified on the basis of second messenger changes induced in a variety of intact tissue preparations. Such a classification system is problematic if more than one receptor subtype is present in the same tissue preparation. Recent progress on the cloning and characterization in heterologous cell systems of octopamine receptors from Drosophila and other insects is reviewed. A new classification system for insect octopamine receptors into "alpha-adrenergic-like octopamine receptors (OctalphaRs)", "beta-adrenergic-like octopamine receptors (OctbetaRs)" and "octopamine/tyramine (or tyraminergic) receptors" is proposed based on their similarities in structure and in signalling properties with vertebrate adrenergic receptors. In future studies on the molecular basis of octopamine signalling in individual tissues it will be essential to identify the relative expression levels of the different classes of octopamine receptor present. In addition, it will be essential to identify if co-expression of such receptors in the same cells results in the formation of oligomeric receptors with specific emergent pharmacological and signalling properties.
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Affiliation(s)
- Peter D Evans
- The Inositide Laboratory, The Babraham Institute, Cambridge, CB2 4AT, UK.
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27
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Maqueira B, Chatwin H, Evans PD. Identification and characterization of a novel family of Drosophila beta-adrenergic-like octopamine G-protein coupled receptors. J Neurochem 2005; 94:547-60. [PMID: 15998303 DOI: 10.1111/j.1471-4159.2005.03251.x] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Insect octopamine receptors carry out many functional roles traditionally associated with vertebrate adrenergic receptors. These include control of carbohydrate metabolism, modulation of muscular tension, modulation of sensory inputs and modulation of memory and learning. The activation of octopamine receptors mediating many of these actions leads to increases in the levels of cyclic AMP. However, to date none of the insect octopamine receptors that have been cloned have been convincingly shown to be capable of directly mediating selective and significant increases in cyclic AMP levels. Here we report on the identification and characterization of a novel, neuronally expressed family of three Drosophila G-protein coupled receptors that are selectively coupled to increases in intracellular cyclic AMP levels by octopamine. This group of receptors, DmOct beta1R (CG6919), DmOct beta2R (CG6989) and DmOct beta3R (CG7078) shows homology to vertebrate beta-adrenergic receptors. When expressed in Chinese hamster ovary cells all three receptors show a strong preference for octopamine over tyramine for the accumulation of cyclic AMP but show unique pharmacological profiles when tested with a range of synthetic agonists and antagonists. Thus, the pharmacological profile of individual insect tissue responses to octopamine might vary with the combination and the degree of expression of the individual octopamine receptors present.
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Sarmiento JM, Ehrenfeld P, Añazco CC, Reyes CE, Troncoso S, Figueroa CD, Müller-Esterl W, González CB. Differential distribution of the vasopressin V2 receptor along the rat nephron during renal ontogeny and maturation. Kidney Int 2005; 68:487-96. [PMID: 16014025 DOI: 10.1111/j.1523-1755.2005.00426.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Ontogeny and cellular distribution of vasopressin receptors in the kidney are key factors determining the role of vasopressin in renal physiology. Expression of vasopressin V(2) receptor (V(2)R) mRNA and the immunoreactive protein in rat kidney were investigated. METHODS An antiserum directed to epitope TLD25 of the rat V(2)R sequence was characterized by Western blotting. Expression of V(2)R mRNA was assessed by reverse transcription-polymerase chain reaction (RT-PCR), and on protein level by immunohistochemistry. RESULTS Specificity of the antiserum was documented by Western blots from cells expressing a fusion protein of V(2)R and GFP. Using lysates of rat kidney and of native cell lines expressing V(2)R but not V(1)R, our antiserum to peptide TLD25 revealed a major band of 55 kD corresponding to the monomeric form of V(2)R, and a band of 110 kD most likely representing the homodimeric form of the receptor. This highly specific antiserum allowed us to localize the V(2)R in thick ascending limbs, distal convoluted and connecting tubules, and in collecting ducts. During ontogeny, immunoreactivity was first observed at the luminal membrane on prenatal day 20, emerging at the basolateral side from postnatal day 5 on. RT-PCR demonstrated V(2)R transcripts from prenatal day 18 to gradually increasing thereafter. CONCLUSION Expression of V(2)R is first detectable in the late embryonic stage of rat ontogeny starting from day E18 and gradually increasing with kidney maturation. In the adult kidney, V(2)R is differentially distributed in the various nephron segments.
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MESH Headings
- Age Factors
- Animals
- Antibody Specificity
- Cell Membrane/metabolism
- Female
- Gene Expression Regulation, Developmental
- Gestational Age
- Immunohistochemistry
- Kidney Tubules, Collecting/embryology
- Kidney Tubules, Collecting/physiology
- Kidney Tubules, Distal/embryology
- Kidney Tubules, Distal/physiology
- Loop of Henle/embryology
- Loop of Henle/physiology
- Male
- Nephrons/embryology
- Nephrons/physiology
- Pregnancy
- RNA, Messenger/analysis
- Rats
- Rats, Sprague-Dawley
- Receptors, Vasopressin/genetics
- Receptors, Vasopressin/immunology
- Receptors, Vasopressin/metabolism
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Affiliation(s)
- José M Sarmiento
- Institutos de Fisiología and Histología y Patología, Facultad de Medicina, Universidad Austral de Chile, Valdivia, Chile
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