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Transcriptome Analysis Did Not Show Endogenous Stem Cell Characteristics in Murine Lgr5 + Retinal Cells. Int J Mol Sci 2019; 20:ijms20143547. [PMID: 31331079 PMCID: PMC6678859 DOI: 10.3390/ijms20143547] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Revised: 07/05/2019] [Accepted: 07/15/2019] [Indexed: 12/18/2022] Open
Abstract
Lgr5, an intestinal adult stem cell marker, was recently also found in neuronal tissues. We investigated whether retinal Lgr5+ cells express properties of neural stem cells (NSC) and/or of differentiated interneurons during retinal development. RNA was isolated from Lgr5+ and Lgr5− populations from postnatal day 5 (PN5) and adult retinas of Lgr5EGFP-Ires-CreERT2 knock-in mice sorted by fluorescence-activated cell sorting (FACS). Transcriptome analyses were performed on two RNA samples of each developmental stage (PN5 and adult). The online platform PANTHER (Protein ANalysis THrough Evolutionary Relationships) was used to determine overrepresented gene ontology (GO) terms of biological processes within the set of differentially expressed genes. The detailed evaluation included gene expression in regard to stem cell maintenance/proliferation, cell cycle, and Wnt signaling but also markers of differentiated retinal neurons. None of the enriched GO terms of upregulated genes of Lgr5+ cells showed a positive association to NSC. On the contrary, NSC maintenance and proliferation rather prevail in the Lgr5− cell population. Furthermore, results suggesting that Wnt signaling is not active in the Lgr5+ population. Therefore, our transcriptome analysis of Lgr5+ retinal cells suggest that these cells are differentiated neurons, specifically glycinergic amacrine cells.
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Full-length LGR5-positive cells have chemoresistant characteristics in colorectal cancer. Br J Cancer 2016; 114:1251-60. [PMID: 27140312 PMCID: PMC4891500 DOI: 10.1038/bjc.2016.112] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Revised: 03/28/2016] [Accepted: 03/31/2016] [Indexed: 12/22/2022] Open
Abstract
Background: Leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) is a target of Wnt signalling and considered both a cancer stem cell marker and intestinal stem cell marker. We found first some splice variants of LGR5 in human intestine and elucidated the functional feature of full-length LGR5 (LGR5FL). Methods: Reverse transcript PCR using mRNA extracted from intestine revealed the existence of LGR5 splice variants. We designed an antibody that recognises only LGR5FL and assessed immunohistochemically the distribution of LGR5FL-positive cells and Ki-67-positive cells in clinical samples. Results: Two LGR5 splice variants were expressed in the human intestine crypt cells; one lacked exon 5 and the other lacked exons 5–8. Only LGR5FL appeared during cell cycle arrest, whereas the transcript variants appeared when the cell cycle was proceeding. Immunohistochemistry and in situ hybridisation showed that LGR5FL-positive cells were negative for Ki-67. Comparing prechemotherapy and post-chemotherapy specimens, the population of LGR5FL-positive cells significantly increased with therapy (P<0.01). Conclusions: The function of LGR5FL-positive cells had low cell proliferative ability compared with the cells, which expressed splice variants of LGR5 and remained after chemotherapy. Designing therapeutic strategies that target LGR5FL-positive cells seems to be important in colorectal cancer.
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White-Gilbertson S, Davis M, Voelkel-Johnson C, Kasman LM. Sex differences in the MB49 syngeneic, murine model of bladder cancer. Bladder (San Franc) 2016; 3. [PMID: 26998503 PMCID: PMC4795170 DOI: 10.14440/bladder.2016.73] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
OBJECTIVE The MB49 syngeneic, murine model of bladder cancer has been widely used for more than 35 years. In humans, bladder cancer is one third as prevalent in women as in men, with a trend toward lower prevalence in parous compared to nulliparous women. Our objective was to determine if the MB49 bladder cancer model reproduces the sex differences observed in humans, and to determine its sensitivity to testosterone and the pregnancy hormone, human chorionic gonadotropin (hCG). METHODS Male and female C57BL/6 mice were implanted with MB49 murine bladder cancer cells, and observed for tumor growth. MB49 dose responses to hCG and dihydrotestosterone were determined in vitro. RESULTS MB49 tumor growth was significantly greater in male mice than female mice. Pregnancy did not affect MB49 tumor growth in female mice. MB49 cells did not proliferate in response to hCG in vitro and the functional receptor for gonadotropins was absent. Dihydrotestosterone strongly stimulated growth of MB49 cells in vitro. CONCLUSIONS The MB49 murine model of bladder cancer reproduced some aspects of the sex differences observed in humans. Our results suggest that testosterone may stimulate MB49 cell proliferation, which may explain the more rapid MB49 tumor growth observed in male mice.
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Affiliation(s)
- Shai White-Gilbertson
- Department of Microbiology and Immunology, Medical University of South Carolina, 173 Ashley Ave., MSC 504, Charleston, SC 29425, USA
| | - Megan Davis
- Department of Microbiology and Immunology, Medical University of South Carolina, 173 Ashley Ave., MSC 504, Charleston, SC 29425, USA
| | - Christina Voelkel-Johnson
- Department of Microbiology and Immunology, Medical University of South Carolina, 173 Ashley Ave., MSC 504, Charleston, SC 29425, USA
| | - Laura M Kasman
- Department of Microbiology and Immunology, Medical University of South Carolina, 173 Ashley Ave., MSC 504, Charleston, SC 29425, USA
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Mattila SO, Tuusa JT, Petäjä-Repo UE. The Parkinson's-disease-associated receptor GPR37 undergoes metalloproteinase-mediated N-terminal cleavage and ectodomain shedding. J Cell Sci 2016; 129:1366-77. [PMID: 26869225 DOI: 10.1242/jcs.176115] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 02/08/2016] [Indexed: 12/20/2022] Open
Abstract
The G-protein-coupled receptor 37 ( GPR37) has been implicated in the juvenile form of Parkinson's disease, in dopamine signalling and in the survival of dopaminergic cells in animal models. The structure and function of the receptor, however, have remained enigmatic. Here, we demonstrate that although GPR37 matures and is exported from the endoplasmic reticulum in a normal manner upon heterologous expression in HEK293 and SH-SY5Y cells, its long extracellular N-terminus is subject to metalloproteinase-mediated limited proteolysis between E167 and Q168. The proteolytic processing is a rapid and efficient process that occurs constitutively. Moreover, the GPR37 ectodomain is released from cells by shedding, a phenomenon rarely described for GPCRs. Immunofluorescence microscopy further established that although full-length receptors are present in the secretory pathway until the trans-Golgi network, GPR37 is expressed at the cell surface predominantly in the N-terminally truncated form. This notion was verified by flow cytometry and cell surface biotinylation assays. These new findings on the GPR37 N-terminal limited proteolysis may help us to understand the role of this GPCR in the pathophysiology of Parkinson's disease and in neuronal function in general.
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Affiliation(s)
- S Orvokki Mattila
- Medical Research Center Oulu, and Cancer and Translational Medicine Research Unit, University of Oulu, Oulu FI-90014, Finland
| | - Jussi T Tuusa
- Medical Research Center Oulu, and Cancer and Translational Medicine Research Unit, University of Oulu, Oulu FI-90014, Finland
| | - Ulla E Petäjä-Repo
- Medical Research Center Oulu, and Cancer and Translational Medicine Research Unit, University of Oulu, Oulu FI-90014, Finland
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Profiling of urinary proteins in Karan Fries cows reveals more than 1550 proteins. J Proteomics 2015; 127:193-201. [PMID: 26021477 DOI: 10.1016/j.jprot.2015.05.026] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Revised: 05/18/2015] [Accepted: 05/21/2015] [Indexed: 12/15/2022]
Abstract
Urine is a non-invasive source of biological fluid, which reflects the physiological status of the mammals. We have profiled the cow urinary proteome and analyzed its functional significance. The urine collected from three healthy cows was concentrated by diafiltration (DF) followed by protein extraction using three methods, namely methanol, acetone, and ammonium sulphate (AS) precipitation and Proteo Spin urine concentration kit (PS). The quality of the protein was assessed by two-dimensional gel electrophoresis (2DE). In-gel digestion method revealed more proteins (1191) in comparison to in-solution digestion method (541). Collectively, 938, 606 and 444 proteins were identified in LC-MS/MS after in-gel and in-solution tryptic digestion of proteins prepared by AS, PS and DF methods, respectively resulting in identification of a total of 1564 proteins. Gene ontology (GO) using Panther7.0 grouped the majority of the proteins into cytoplasmic (location), catalytic activity (function), and metabolism (biological processes), while Cytoscape grouped proteins into complement and coagulation cascades; protease inhibitor activity and wound healing. Functional significance of few selected proteins seems to play important role in their physiology. Comparative analysis with human urine revealed 315 overlapping proteins. This study reports for the first time evidence of more than 1550 proteins in urine of healthy cow donors. This article is part of a Special Issue entitled: Proteomics in India.
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Lackman JJ, Markkanen PMH, Hogue M, Bouvier M, Petäjä-Repo UE. N-Glycan-dependent and -independent quality control of human δ opioid receptor N-terminal variants. J Biol Chem 2014; 289:17830-42. [PMID: 24798333 DOI: 10.1074/jbc.m114.566273] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Quality control (QC) in the endoplasmic reticulum (ER) scrutinizes newly synthesized proteins and directs them either to ER export or ER-associated degradation (ERAD). Here, we demonstrate that the human δ-opioid receptor (hδOR) is subjected to ERQC in both N-glycan-dependent and -independent manners. This was shown by investigating the biosynthesis and trafficking of wild-type and non-N-glycosylated F27C variants in metabolic pulse-chase assays coupled with flow cytometry and cell surface biotinylation. Both QC mechanisms distinguished the minute one-amino acid difference between the variants, targeting a large fraction of hδOR-Cys(27) to ERAD. However, the N-glycan-independent QC was unable to compensate the N-glycan-dependent pathway, and some incompletely folded non-N-glycosylated hδOR-Cys(27) reached the cell surface in conformation incompatible with ligand binding. The turnover of receptors associating with the molecular chaperone calnexin (CNX) was significantly slower for the hδOR-Cys(27), pointing to an important role of CNX in the hδOR N-glycan-dependent QC. This was further supported by the fact that inhibiting the co-translational interaction of hδOR-Cys(27) precursors with CNX led to their ERAD. Opioid receptor pharmacological chaperones released the CNX-bound receptors to ER export and, furthermore, were able to rescue the Cys(27) variant from polyubiquitination and retrotranslocation to the cytosol whether carrying N-glycans or not. Taken together, the hδOR appears to rely primarily on the CNX-mediated N-glycan-dependent QC that has the capacity to assist in folding, whereas the N-glycan-independent mechanism constitutes an alternative, although less accurate, system for directing misfolded/incompletely folded receptors to ERAD, possibly in altered cellular conditions.
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Affiliation(s)
- Jarkko J Lackman
- From the Department of Anatomy and Cell Biology and the Medical Research Center Oulu, Institute of Biomedicine, University of Oulu, FI-90014 Oulu, Finland and
| | - Piia M H Markkanen
- From the Department of Anatomy and Cell Biology and the Medical Research Center Oulu, Institute of Biomedicine, University of Oulu, FI-90014 Oulu, Finland and
| | - Mireille Hogue
- the Department of Biochemistry, Institute for Research in Immunology and Cancer and Groupe de Recherche Universitaire sur le Médicament, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Michel Bouvier
- the Department of Biochemistry, Institute for Research in Immunology and Cancer and Groupe de Recherche Universitaire sur le Médicament, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Ulla E Petäjä-Repo
- From the Department of Anatomy and Cell Biology and the Medical Research Center Oulu, Institute of Biomedicine, University of Oulu, FI-90014 Oulu, Finland and
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Karakaya C, Guzeloglu-Kayisli O, Hobbs RJ, Gerasimova T, Uyar A, Erdem M, Oktem M, Erdem A, Gumuslu S, Ercan D, Sakkas D, Comizzoli P, Seli E, Lalioti MD. Follicle-stimulating hormone receptor (FSHR) alternative skipping of exon 2 or 3 affects ovarian response to FSH. Mol Hum Reprod 2014; 20:630-43. [PMID: 24670307 DOI: 10.1093/molehr/gau024] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Genes critical for fertility are highly conserved in mammals. Interspecies DNA sequence variation, resulting in amino acid substitutions and post-transcriptional modifications, including alternative splicing, are a result of evolution and speciation. The mammalian follicle-stimulating hormone receptor (FSHR) gene encodes distinct species-specific forms by alternative splicing. Skipping of exon 2 of the human FSHR was reported in women of North American origin and correlated with low response to ovarian stimulation with exogenous follicle-stimulating hormone (FSH). To determine whether this variant correlated with low response in women of different genetic backgrounds, we performed a blinded retrospective observational study in a Turkish cohort. Ovarian response was determined as low, intermediate or high according to retrieved oocyte numbers after classifying patients in four age groups (<35, 35-37, 38-40, >40). Cumulus cells collected from 96 women undergoing IVF/ICSI following controlled ovarian hyperstimulation revealed four alternatively spliced FSHR products in seven patients (8%): exon 2 deletion in four patients; exon 3 and exons 2 + 3 deletion in one patient each, and a retention of an intron 1 fragment in one patient. In all others (92%) splicing was intact. Alternative skipping of exons 2, 3 or 2 + 3 were exclusive to low responders and was independent of the use of agonist or antagonist. Interestingly, skipping of exon 3 occurs naturally in the ovaries of domestic cats--a good comparative model for human fertility. We tested the signaling potential of human and cat variants after transfection in HEK293 cells and FSH stimulation. None of the splicing variants initiated cAMP signaling despite high FSH doses, unlike full-length proteins. These data substantiate the occurrence of FSHR exon skipping in a subgroup of low responders and suggest that species-specific regulation of FSHR splicing plays diverse roles in mammalian ovarian function.
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Affiliation(s)
- Cengiz Karakaya
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT 06510, USA Division of Reproductive Endocrinology and Infertility, IVF Center, Department of Obstetrics and Gynecology, Gazi University Medical School, Ankara 06500 Turkey
| | - Ozlem Guzeloglu-Kayisli
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT 06510, USA Present address: Department of Obstetrics and Gynecology, Ohio State University College of Medicine, Columbus, OH 43210, USA
| | - Rebecca J Hobbs
- Smithsonian Conservation Biology Institute, National Zoological Park, Washington, DC 20008, USA Present address: Taronga Conservation Society Australia, Taronga Western Plains Zoo, Duboo, NSW 2830, Australia
| | - Tsilya Gerasimova
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT 06510, USA
| | - Asli Uyar
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT 06510, USA
| | - Mehmet Erdem
- Division of Reproductive Endocrinology and Infertility, IVF Center, Department of Obstetrics and Gynecology, Gazi University Medical School, Ankara 06500 Turkey
| | - Mesut Oktem
- Division of Reproductive Endocrinology and Infertility, IVF Center, Department of Obstetrics and Gynecology, Gazi University Medical School, Ankara 06500 Turkey
| | - Ahmet Erdem
- Division of Reproductive Endocrinology and Infertility, IVF Center, Department of Obstetrics and Gynecology, Gazi University Medical School, Ankara 06500 Turkey
| | - Seyhan Gumuslu
- Division of Reproductive Endocrinology and Infertility, IVF Center, Department of Obstetrics and Gynecology, Gazi University Medical School, Ankara 06500 Turkey
| | - Deniz Ercan
- Division of Reproductive Endocrinology and Infertility, IVF Center, Department of Obstetrics and Gynecology, Gazi University Medical School, Ankara 06500 Turkey
| | - Denny Sakkas
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT 06510, USA Present address: Boston IVF, Waltham, MA 02451, USA
| | - Pierre Comizzoli
- Smithsonian Conservation Biology Institute, National Zoological Park, Washington, DC 20008, USA
| | - Emre Seli
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT 06510, USA
| | - Maria D Lalioti
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT 06510, USA
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Conn PM, Smithson DC, Hodder PS, Stewart MD, Behringer RR, Smith E, Ulloa-Aguirre A, Janovick JA. Transitioning pharmacoperones to therapeutic use: in vivo proof-of-principle and design of high throughput screens. Pharmacol Res 2013; 83:38-51. [PMID: 24373832 DOI: 10.1016/j.phrs.2013.12.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 12/16/2013] [Accepted: 12/16/2013] [Indexed: 12/26/2022]
Abstract
A pharmacoperone (from "pharmacological chaperone") is a small molecule that enters cells and serves as molecular scaffolding in order to cause otherwise-misfolded mutant proteins to fold and route correctly within the cell. Pharmacoperones have broad therapeutic applicability since a large number of diseases have their genesis in the misfolding of proteins and resultant misrouting within the cell. Misrouting may result in loss-of-function and, potentially, the accumulation of defective mutants in cellular compartments. Most known pharmacoperones were initially derived from receptor antagonist screens and, for this reason, present a complex pharmacology, although these are highly target specific. In this summary, we describe efforts to produce high throughput screens that identify these molecules from chemical libraries as well as a mouse model which provides proof-of-principle for in vivo protein rescue using existing pharmacoperones.
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Affiliation(s)
- P Michael Conn
- Department of Internal Medicine, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States; Department of Cell Biology, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States.
| | - David C Smithson
- Oregon Translational Research and Drug Development Institute (OTRADI), Portland, OR 97201, United States
| | - Peter S Hodder
- Translational Research Institute, Scripps Research Institute, Jupiter, FL 33458, United States
| | - M David Stewart
- Department of Genetics, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, United States; Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, United States
| | - Richard R Behringer
- Department of Genetics, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, United States
| | - Emery Smith
- Translational Research Institute, Scripps Research Institute, Jupiter, FL 33458, United States
| | - Alfredo Ulloa-Aguirre
- Research Support Network, Instituto Nacional de Ciencias Medicas y Nutricion, S-Z Universidad Autonoma de Mexico, Mexico, D.F., Mexico
| | - Jo Ann Janovick
- Department of Internal Medicine, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States; Department of Cell Biology, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States
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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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Endo T, Kobayashi T. Immunization of mice with a newly identified thyroid-stimulating hormone receptor splice variant induces Graves'-like disease. J Autoimmun 2013; 43:18-25. [DOI: 10.1016/j.jaut.2013.02.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Revised: 01/31/2013] [Accepted: 02/20/2013] [Indexed: 10/27/2022]
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12
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Troppmann B, Kleinau G, Krause G, Gromoll J. Structural and functional plasticity of the luteinizing hormone/choriogonadotrophin receptor. Hum Reprod Update 2013; 19:583-602. [DOI: 10.1093/humupd/dmt023] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Alonso V, Friedman PA. Minireview: ubiquitination-regulated G protein-coupled receptor signaling and trafficking. Mol Endocrinol 2013; 27:558-72. [PMID: 23471539 DOI: 10.1210/me.2012-1404] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are the largest and most diverse superfamily of membrane proteins and mediate most cellular responses to hormones and neurotransmitters. Posttranslational modifications are considered the main regulators of all GPCRs. In addition to phosphorylation, glycosylation, and palmitoylation, increasing evidence as reviewed here reveals that ubiquitination also regulates the magnitude and temporospatial aspects of GPCR signaling. Posttranslational protein modification by ubiquitin is a key molecular mechanism governing proteins degradation. Ubiquitination mediates the covalent conjugation of ubiquitin, a highly conserved polypeptide of 76 amino acids, to protein substrates. This process is catalyzed by 3 enzymes acting in tandem: an E1, ubiquitin-activating enzyme; an E2, ubiquitin-carrying enzyme; and an E3, ubiquitin ligase. Ubiquitination is counteracted by deubiquitinating enzymes that deconjugate ubiquitin-modified proteins and rescue the substrate from proteasomal degradation. Although ubiquitination is known to target many GPCRs for lysosomal or proteasomal degradation, emerging findings define novel roles for the basal status of ubiquitination and for rapid deubiquitination and transubiquitination controlling cell surface expression and cellular responsiveness of some GPCRs. In this review, we highlight the classical and novel roles of ubiquitin in the regulation of GPCR function, signaling, and trafficking.
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Affiliation(s)
- Verónica Alonso
- Institute of Applied Molecular Medicine, San Pablo-CEU University School of Medicine, Madrid, 28668, Spain
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Kelemen O, Convertini P, Zhang Z, Wen Y, Shen M, Falaleeva M, Stamm S. Function of alternative splicing. Gene 2013; 514:1-30. [PMID: 22909801 PMCID: PMC5632952 DOI: 10.1016/j.gene.2012.07.083] [Citation(s) in RCA: 509] [Impact Index Per Article: 46.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 07/21/2012] [Accepted: 07/30/2012] [Indexed: 12/15/2022]
Abstract
Almost all polymerase II transcripts undergo alternative pre-mRNA splicing. Here, we review the functions of alternative splicing events that have been experimentally determined. The overall function of alternative splicing is to increase the diversity of mRNAs expressed from the genome. Alternative splicing changes proteins encoded by mRNAs, which has profound functional effects. Experimental analysis of these protein isoforms showed that alternative splicing regulates binding between proteins, between proteins and nucleic acids as well as between proteins and membranes. Alternative splicing regulates the localization of proteins, their enzymatic properties and their interaction with ligands. In most cases, changes caused by individual splicing isoforms are small. However, cells typically coordinate numerous changes in 'splicing programs', which can have strong effects on cell proliferation, cell survival and properties of the nervous system. Due to its widespread usage and molecular versatility, alternative splicing emerges as a central element in gene regulation that interferes with almost every biological function analyzed.
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Affiliation(s)
- Olga Kelemen
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Paolo Convertini
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Zhaiyi Zhang
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Yuan Wen
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Manli Shen
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Marina Falaleeva
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Stefan Stamm
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
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Bernardini L, Moretti-Rojas I, Brush M, Rojas FJ, Balmaceda JP. Failure of hCG/LH receptors to stimulate the transmembrane effector adenylyl cyclase in human endometrium. ACTA ACUST UNITED AC 2013. [DOI: 10.4236/abb.2013.410126] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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16
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Onuma TA, Duan C. Duplicated Kiss1 receptor genes in zebrafish: distinct gene expression patterns, different ligand selectivity, and a novel nuclear isoform with transactivating activity. FASEB J 2012; 26:2941-50. [DOI: 10.1096/fj.11-201095] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Takeshi A. Onuma
- Department of Molecular, Cellular, and Developmental Biology University of Michigan Ann Arbor Michigan USA
| | - Cunming Duan
- Department of Molecular, Cellular, and Developmental Biology University of Michigan Ann Arbor Michigan USA
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Leskelä TT, Lackman JJ, Vierimaa MM, Kobayashi H, Bouvier M, Petäjä-Repo UE. Cys-27 variant of human δ-opioid receptor modulates maturation and cell surface delivery of Phe-27 variant via heteromerization. J Biol Chem 2011; 287:5008-20. [PMID: 22184124 DOI: 10.1074/jbc.m111.305656] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The important role of G protein-coupled receptor homo/heteromerization in receptor folding, maturation, trafficking, and cell surface expression has become increasingly evident. Here we investigated whether the human δ-opioid receptor (hδOR) Cys-27 variant that shows inherent compromised maturation has an effect on the behavior of the more common Phe-27 variant in the early secretory pathway. We demonstrate that hδOR-Cys-27 acts in a dominant negative manner and impairs cell surface delivery of the co-expressed hδOR-Phe-27 and impairs conversion of precursors to the mature form. This was demonstrated by metabolic labeling, Western blotting, flow cytometry, and confocal microscopy in HEK293 and human SH-SY5Y neuroblastoma cells using differentially epitope-tagged variants. The hδOR-Phe-27 precursors that were redirected to the endoplasmic reticulum-associated degradation were, however, rescued by a pharmacological chaperone, the opioid antagonist naltrexone. Co-immunoprecipitation of metabolically labeled variants revealed that both endoplasmic reticulum-localized precursors and mature receptors exist as homo/heteromers. The existence of homo/heteromers was confirmed in living cells by bioluminescence resonance energy transfer measurements, showing that the variants have a similar propensity to form homo/heteromers. By forming both homomers and heteromers, the hδOR-Cys-27 variant may thus regulate the levels of receptors at the cell surface, possibly leading to altered responsiveness to opioid ligands in individuals carrying the Cys-27 variant.
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Affiliation(s)
- Tarja T Leskelä
- Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, FI-90014 Oulu, Finland
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18
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Han B, Wang ZQ, Xue LQ, Ma JH, Liu W, Liu BL, Wu JJ, Pan CM, Chen X, Zhao SX, Lu YL, Wu WL, Qiao J, Song HD. Functional study of an aberrant splicing variant of the human luteinizing hormone (LH) receptor. Mol Hum Reprod 2011; 18:129-35. [PMID: 22002533 DOI: 10.1093/molehr/gar065] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The luteinizing hormone receptor (LHR) is a member of a subfamily of G protein-coupled receptors that is characterized by its alternative splicing. In a previous study, we identified a splice site mutation of intron 6 (IVS6-3C>A) in a patient suffering from Leydig cell hypoplasia, which leads to aberrant splicing of LHR mRNA. In vitro expression analysis confirmed that this mutation results in the skipping of exon 7 in the mature mRNA of the LHR gene. In this study, we determined the impact of IVS6-3C>A on the RNA secondary structure and function of LHR-Del7. The three-dimensional structure of the leucine-rich repeats in LHR was predicted by molecular modeling. Radioactive ligand-binding assays verified that LHR-Del7 has no binding affinity for hCG. Furthermore, we detected negligible cAMP production in cells transfected with LHR-Del7. Cells co-expressing LHR-WT and LHR-Del7 were able to generate cAMP in response to hCG, but there was no significant difference between cells transfected with LHR-WT/vector and LHR-WT/LHR-Del7, although the variant was able to localize to cell surface, similar to wild-type receptor. These results indicated that LHR-Del7 does not have a dominant negative effect on LHR-WT cell surface expression, and although the pathological splicing variant LHR-Del7 was able to localize to cell membranes it failed to bind hCG and had no effect on wild-type LHR.
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Affiliation(s)
- Bing Han
- State Key Laboratory of Medical Genomics, Molecular Medical Center, Shanghai Institute of Endocrinology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, People's Republic of China
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19
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Chambers AE, Stanley PF, Randeva H, Banerjee S. Microvesicle-mediated release of soluble LH/hCG receptor (LHCGR) from transfected cells and placenta explants. Reprod Biol Endocrinol 2011; 9:64. [PMID: 21575145 PMCID: PMC3112408 DOI: 10.1186/1477-7827-9-64] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Accepted: 05/15/2011] [Indexed: 12/24/2022] Open
Abstract
Placental hCG and pitutary LH transduce signals in target tissues through a common receptor (LHCGR). We demonstrate that recombinant LHCGR proteins which include the hormone-binding domain are secreted from transfected cells and that natural LHCGR is also secreted from human placental explants. LHCGR recombinant proteins representing varying lengths of the N-terminal extracellular domain were expressed in Chinese Hamster Ovary cells in suspension culture. Secretion was minimal up to 72h but by 96h 24-37% of the LHCGR had been released into the culture medium. The secreted proteins were folded and sensitive to glycosidases suggesting N-linked glycosylation. Secretion was independent of recombinant size and was mediated via structurally defined membrane vesicles (50-150nm). Similarly cultured human early pregnancy placental explants also released LHCGR via microvesicles. These studies provide the first experimental evidence of the possible mechanistic basis of the secretion of LHCGR.
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Affiliation(s)
- Anne E Chambers
- Department of Clinical Biochemistry, Laboratory Medicine, Birmingham Heartlands Hospital, Bordesley Green East, Birmingham B9 5SS, UK
| | - Paul F Stanley
- Centre for Electron Microscopy Metallurgy and Materials Building, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Harpal Randeva
- Clinical Sciences Research Institute, Medical School Building, Gibbet Hill Campus, University of Warwick, Coventry, UK
| | - Subhasis Banerjee
- Department of Clinical Biochemistry, Laboratory Medicine, Birmingham Heartlands Hospital, Bordesley Green East, Birmingham B9 5SS, UK
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20
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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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21
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Cysteine 27 variant of the delta-opioid receptor affects amyloid precursor protein processing through altered endocytic trafficking. Mol Cell Biol 2011; 31:2326-40. [PMID: 21464208 DOI: 10.1128/mcb.05015-11] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Agonist-induced activation of the δ-opioid receptor (δOR) was recently shown to augment β- and γ-secretase activities, which increased the production of β-amyloid peptide (Aβ), known to accumulate in the brain tissues of Alzheimer's disease (AD) patients. Previously, the δOR variant with a phenylalanine at position 27 (δOR-Phe27) exhibited more efficient receptor maturation and higher stability at the cell surface than did the less common cysteine (δOR-Cys27) variant. For this study, we expressed these variants in human SH-SY5Y and HEK293 cells expressing exogenous or endogenous amyloid precursor protein (APP) and assessed the effects on APP processing. Expression of δOR-Cys27, but not δOR-Phe27, resulted in a robust accumulation of the APP C83 C-terminal fragment and the APP intracellular domain, while the total soluble APP and, particularly, the β-amyloid 40 levels were decreased. These changes upon δOR-Cys27 expression coincided with decreased localization of APP C-terminal fragments in late endosomes and lysosomes. Importantly, a long-term treatment with a subset of δOR-specific ligands or a c-Src tyrosine kinase inhibitor suppressed the δOR-Cys27-induced APP phenotype. These data suggest that an increased constitutive internalization and/or concurrent signaling of the δOR-Cys27 variant affects APP processing through altered endocytic trafficking of APP.
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Abstract
The lutropin receptor (LHR) is a G protein-coupled receptor (GPCR) that mediates the actions of pituitary LH in males and females and that of placental hCG in pregnant women and, therefore, plays an essential role in reproductive physiology. Mutations of the lhcgr gene that result in constitutive activation of the LHR have been shown to be causative of gonadotropin-independent precocious puberty in young boys. Studies on constitutively active mutants (CAMs) of the LHR have been extremely informative in elucidating the roles of the LHR in reproductive physiology as well as in understanding the molecular basis underlying activation of this GPCR. The constitutive activities of hLHR CAMs can be attenuated by introducing mutations into the CAMs that stabilize the resting state of the hLHR or by coexpressing the hLHR CAMs with an hLHR mutant that is stabilized in the resting state, allowing the two forms of the hLHR to heterodimerize. This chapter describes the experimental methods and strategies underlying studies of hLHR CAMs.
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Moriyama K, Sitkovsky MV. Adenosine A2A receptor is involved in cell surface expression of A2B receptor. J Biol Chem 2010; 285:39271-88. [PMID: 20926384 PMCID: PMC2998132 DOI: 10.1074/jbc.m109.098293] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 10/05/2010] [Indexed: 11/06/2022] Open
Abstract
The A2A and A2B adenosine receptors (A2AR and A2BR) are implicated in many physiological processes. However, the mechanisms of their intracellular maturation and trafficking are poorly understood. In comparative studies of A2AR versus A2BR expression in transfected cells, we noticed that the levels of cell surface expression of A2BR were significantly lower than those of A2AR. A large portion of the A2BR was degraded by the proteasome. Studies of cell surface expression of A2BR chimeric molecules in transfectants suggested that A2BR does not have the dominant forward transport signal for export from the endoplasmic reticulum to the cell surface. A2BR surface expression was increased in A2BR chimeras where the A2BR carboxyl terminus (CT) was replaced or fused with the A2AR CT. Co-transfection of A2AR with A2BR enhanced surface expression of A2BR though the F(X)(6)LL motif in the A2AR CT. The requirements of A2AR expression for better A2BR cell surface expression was not only established in transfectants but also confirmed by observations of much lower levels of A2BR-induced intracellular cAMP accumulation in response to A2BR-activating ligand in splenocytes from A2AR(-/-) mice than in wild type mice. The results of mechanistic studies suggested that poor A2BR expression at the cell surface might be accounted for mainly by the lack of a dominant forward transport signal from the endoplasmic reticulum to the plasma membrane; it is likely that A2BR forms a hetero-oligomer complex for better function.
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Affiliation(s)
- Kengo Moriyama
- From the New England Inflammation and Tissue Protection Institute, Departments of Pharmaceutical Science and Biology, Northeastern University, Boston, Massachusetts 02115
| | - Michail V. Sitkovsky
- From the New England Inflammation and Tissue Protection Institute, Departments of Pharmaceutical Science and Biology, Northeastern University, Boston, Massachusetts 02115
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24
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Abstract
A temperature-sensitive chimeric transmembrane protein reveals a mechanism for disposing misfolded proteins that make it to the plasma membrane. Cellular protein homeostasis profoundly depends on the disposal of terminally damaged polypeptides. To demonstrate the operation and elucidate the molecular basis of quality control of conformationally impaired plasma membrane (PM) proteins, we constructed CD4 chimeras containing the wild type or a temperature-sensitive bacteriophage λ domain in their cytoplasmic region. Using proteomic, biochemical, and genetic approaches, we showed that thermal unfolding of the λ domain at the PM provoked the recruitment of Hsp40/Hsc70/Hsp90 chaperones and the E2–E3 complex. Mixed-chain polyubiquitination, monitored by bioluminescence resonance energy transfer and immunoblotting, is responsible for the nonnative chimera–accelerated internalization, impaired recycling, and endosomal sorting complex required for transport–dependent lysosomal degradation. A similar paradigm prevails for mutant dopamine D4.4 and vasopressin V2 receptor removal from the PM. These results outline a peripheral proteostatic mechanism in higher eukaryotes and its potential contribution to the pathogenesis of a subset of conformational diseases.
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Affiliation(s)
- Pirjo M Apaja
- Department of Physiology, McGill University, Montréal, Quebec, Canada
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25
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Hakalahti AE, Vierimaa MM, Lilja MK, Kumpula EP, Tuusa JT, Petäjä-Repo UE. Human beta1-adrenergic receptor is subject to constitutive and regulated N-terminal cleavage. J Biol Chem 2010; 285:28850-61. [PMID: 20587416 DOI: 10.1074/jbc.m110.149989] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The beta(1)-adrenergic receptor (beta(1)AR) is the predominant betaAR in the heart, mediating the catecholamine-stimulated increase in cardiac rate and force of contraction. Regulation of this important G protein-coupled receptor is nevertheless poorly understood. We describe here the biosynthetic profile of the human beta(1)AR and reveal novel features relevant to its regulation using an inducible heterologous expression system in HEK293(i) cells. Metabolic pulse-chase labeling and cell surface biotinylation assays showed that the synthesized receptors are efficiently and rapidly transported to the cell surface. The N terminus of the mature receptor is extensively modified by sialylated mucin-type O-glycosylation in addition to one N-glycan attached to Asn(15). Furthermore, the N terminus was found to be subject to limited proteolysis, resulting in two membrane-bound C-terminal fragments. N-terminal sequencing of the fragments identified two cleavage sites between Arg(31) and Leu(32) and Pro(52) and Leu(53), which were confirmed by cleavage site and truncation mutants. Metalloproteinase inhibitors were able to inhibit the cleavage, suggesting that it is mediated by a matrix metalloproteinase or a disintegrin and metalloproteinase (ADAM) family member. Most importantly, the N-terminal cleavage was found to occur not only in vitro but also in vivo. Receptor activation mediated by the betaAR agonist isoproterenol enhanced the cleavage in a concentration- and time-dependent manner, and it was also enhanced by direct stimulation of protein kinase C and adenylyl cyclase. Mutation of the Arg(31)-Leu(32) cleavage site stabilized the mature receptor. We hypothesize that the N-terminal cleavage represents a novel regulatory mechanism of cell surface beta(1)ARs.
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Affiliation(s)
- Anna E Hakalahti
- Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, FI-90014 Oulu, Finland
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26
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Tuusa JT, Leskelä TT, Petäjä-Repo UE. Human delta opioid receptor biogenesis is regulated via interactions with SERCA2b and calnexin. FEBS J 2010; 277:2815-29. [PMID: 20528919 DOI: 10.1111/j.1742-4658.2010.07699.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Sarco(endo)plasmic reticulum calcium ATPase (SERCA)2b maintains the cellular Ca(2+) homeostasis by transferring Ca(2+) from the cytosol to the lumen of the endoplasmic reticulum (ER). Recently, SERCA2b has also been shown to be involved in the biosynthesis of secreted and membrane proteins via direct protein-protein interactions, involving components of the ER folding and quality-control machinery, as well as newly synthesized G protein-coupled receptors. Here we demonstrate that the human delta opioid receptor (hdeltaOR) exists in a ternary complex with SERCA2b and the ER molecular chaperone calnexin. The interaction between SERCA2b and hdeltaOR in vivo did not require calnexin as it was independent of the C-terminal calnexin-interacting domain of SERCA2b. However, the receptor was able to mediate co-immunoprecipitation of calnexin with the C-terminally truncated SERCA2b. The association of SERCA2b with hdeltaOR was regulated in vitro by Ca(2+) and ATP in a manner that was opposite to the calnexin-hdeltaOR interaction. Importantly, co-expression of the catalytically inactive SERCA2b(D351A) or calnexin binding-compromised SERCA2bDeltaC mutants with the receptor decreased the expression of mature receptors in a manner that did not directly relate to changes in the ER Ca(2+) concentration. We conclude that dynamic interactions among SERCA2b, calnexin and the hdeltaOR precursor orchestrate receptor biogenesis and are regulated by Ca(2+) and ATP. We further hypothesize that the primary role of SERCA2b in this process is to act as a Ca(2+) sensor in the vicinity of active translocons, integrating protein folding with local fluctuations of ER Ca(2+) levels.
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Affiliation(s)
- Jussi T Tuusa
- Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, Oulu, Finland
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27
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Gerasimova T, Thanasoula MN, Zattas D, Seli E, Sakkas D, Lalioti MD. Identification and in vitro characterization of follicle stimulating hormone (FSH) receptor variants associated with abnormal ovarian response to FSH. J Clin Endocrinol Metab 2010; 95:529-36. [PMID: 20061434 PMCID: PMC2840851 DOI: 10.1210/jc.2009-1304] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
CONTEXT FSH mediates cyclic follicle growth and development and is widely used for controlled ovarian stimulation in women undergoing infertility treatment. The ovarian response of women to FSH is variable, ranging from poor response to ovarian hyperstimulation. OBJECTIVE We investigated whether genetic alterations of the FSH receptor (FSHR) contribute to this variability. DESIGN AND PATIENTS Our approach was to study women undergoing treatment with in vitro fertilization falling into the edges of the normal distribution of ovarian response to FSH, with respect to age. SETTING We conducted the study at the Yale Fertility Clinic. METHODS We extracted RNA from cumulus cells surrounding the oocytes of women undergoing in vitro fertilization and analyzed the FSHR mRNA by RT-PCR and sequencing. RESULTS We identified four abnormal FSHR splicing products (three exon deletions and one intron insertion) in the FSHR mRNA in 37% (13 of 35) of women tested. All alterations affected the extracellular ligand-binding portion of the receptor without causing a frameshift. When transfected in HEK293T cells, all four splicing variants showed markedly decreased cAMP activation compared to controls. Untransfected cells showed no response to FSH, whereas all the cell lines showed normal cAMP activation when treated with forskolin, a nonreceptor-mediated cAMP stimulant. None of the normal or mutant forms showed any response to LH or TSH. CONCLUSIONS Our findings strongly indicate FSHR variants as being an intrinsic genetic cause of some forms of infertility and identify a need for functional characterization of these variants and the investigation of more individualized ovarian stimulation protocols.
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Affiliation(s)
- Tsilya Gerasimova
- Department of Obstetrics, Gynecology and Reproductive Sciences, Yale University School of Medicine, 333 Cedar Street, Room FMB 329J, New Haven, Connecticut 06520, USA.
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28
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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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29
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Martikkala E, Lehmusto M, Lilja M, Rozwandowicz-Jansen A, Lunden J, Tomohiro T, Hänninen P, Petäjä-Repo U, Härmä H. Cell-based β2-adrenergic receptor–ligand binding assay using synthesized europium-labeled ligands and time-resolved fluorescence. Anal Biochem 2009; 392:103-9. [DOI: 10.1016/j.ab.2009.05.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2008] [Revised: 05/06/2009] [Accepted: 05/09/2009] [Indexed: 11/25/2022]
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30
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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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31
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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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Kern A, Bryant-Greenwood GD. Mechanisms of relaxin receptor (LGR7/RXFP1) expression and function. Ann N Y Acad Sci 2009; 1160:60-6. [PMID: 19416160 DOI: 10.1111/j.1749-6632.2008.03826.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The LGR7/RXFP1 and LGR8/RXFP2 receptors are unique receptors among the G-protein-coupled receptors (GPCRs) in having a low-density lipoprotein class A (LDL-A) module. Their complex gene organization, among the intron-richest of the GPCRs, suggests that alternative splicing is a common occurrence. We have therefore investigated the role of the LDL-A module and shown the identity, expression, and functions of three LGR7 splice variants in the human decidua. Point mutations of conserved residues or complete deletion of the LDL-A module resulted in loss of the cAMP response to relaxin. Its glycosylation also impacted LGR7 cell surface delivery and therefore receptor activation. The wild-type (WT) LGR7 was expressed as both precursor and mature forms, but deletion of the LDL-A module resulted in expression of only the mature form. Three new alternatively spliced variants of LGR7 were identified, all containing a truncated extracellular region. Their functional characterization showed them exerting dominant negative effects on the WT LGR7 by preventing its homodimerization, maturation, and subsequent trafficking to the cell surface, resulting in loss of function. In summary, different mechanisms have been identified for controlling the cell surface expression and function of the LGR7 protein which are likely to be significant for the role of relaxin in human parturition.
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Affiliation(s)
- András Kern
- The Pacific Biosciences Research Center, University of Hawaii, Honolulu, Hawaii 96822, USA.
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33
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Duvernay MT, Dong C, Zhang X, Zhou F, Nichols CD, Wu G. Anterograde trafficking of G protein-coupled receptors: function of the C-terminal F(X)6LL motif in export from the endoplasmic reticulum. Mol Pharmacol 2008; 75:751-61. [PMID: 19118123 DOI: 10.1124/mol.108.051623] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
We have reported previously that the F(X)(6)LL motif in the C termini is essential for export of alpha(2B)-adrenergic (alpha(2B)-AR) and angiotensin II type 1 receptors (AT1Rs) from the endoplasmic reticulum (ER). Here, we further demonstrate that mutation of the F(X)(6)LL motif similarly abolished the cell-surface expression of alpha(2B)-AR, AT1R, alpha(1B)-AR, and beta(2)-AR, suggesting that the F(X)(6)LL motif plays a general role in ER export of G protein-coupled receptors (GPCRs). Mutation of Phe to Val, Leu, Trp, and Tyr, and mutation of LL to FF and VV, markedly inhibited alpha(2B)-AR transport, indicating that the F(X)(6)LL function cannot be fully substituted by other hydrophobic residues. The structural analysis revealed that the Phe residue in the F(X)(6)LL motif is buried in the transmembrane domains and possibly interacts with Ile58 in beta(2)-AR and Val42 in alpha(2B)-AR, whereas the LL motif is exposed to the cytosolic space. Indeed, mutation of Ile58 in beta(2)-AR and Val42 in alpha(2B)-AR markedly disrupted cell surface transport of the receptors. It is noteworthy that the Val and Ile residues are highly conserved among the GPCRs carrying the F(X)(6)LL motif. Furthermore, the Phe mutant exhibited a stronger interaction with ER chaperones and was more potently rescued by physical and chemical treatments than the LL mutant. These data suggest that the Phe residue is probably involved in folding of alpha(2B)-AR and beta(2)-AR, possibly through interaction with other hydrophobic residues in neighboring domains. These data also provide the first evidence implying crucial roles of the C termini possibly through modulating multiple events in anterograde trafficking of GPCRs.
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Affiliation(s)
- Matthew T Duvernay
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA
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Leskelä TT, Markkanen PMH, Alahuhta IA, Tuusa JT, Petäjä-Repo UE. Phe27Cys Polymorphism Alters the Maturation and Subcellular Localization of the Human δ Opioid Receptor. Traffic 2008; 10:116-29. [DOI: 10.1111/j.1600-0854.2008.00846.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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Markkanen PMH, Petäjä-Repo UE. N-glycan-mediated quality control in the endoplasmic reticulum is required for the expression of correctly folded delta-opioid receptors at the cell surface. J Biol Chem 2008; 283:29086-98. [PMID: 18703511 DOI: 10.1074/jbc.m801880200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A great majority of G protein-coupled receptors are modified by N-glycosylation, but the functional significance of this modification for receptor folding and intracellular transport has remained elusive. Here we studied these phenomena by mutating the two N-terminal N-glycosylation sites (Asn(18) and Asn(33)) of the human delta-opioid receptor, and expressing the mutants from the same chromosomal integration site in stably transfected inducible HEK293 cells. Both N-glycosylation sites were used, and their abolishment decreased the steady-state level of receptors at the cell surface. However, pulse-chase labeling, cell surface biotinylation, and immunofluorescence microscopy revealed that this was not because of intracellular accumulation. Instead, the non-N-glycosylated receptors were exported from the endoplasmic reticulum with enhanced kinetics. The results also revealed differences in the significance of the individual N-glycans, as the one attached to Asn(33) was found to be more important for endoplasmic reticulum retention of the receptor. The non-N-glycosylated receptors did not show gross functional impairment, but flow cytometry revealed that a fraction of them was incapable of ligand binding at the cell surface. In addition, the receptors that were devoid of N-glycans showed accelerated turnover and internalization and were targeted for lysosomal degradation. The results accentuate the importance of protein conformation-based screening before export from the endoplasmic reticulum, and demonstrate how the system is compromised when N-glycosylation is disrupted. We conclude that N-glycosylation of the delta-opioid receptor is needed to maintain the expression of fully functional and stable receptor molecules at the cell surface.
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Affiliation(s)
- Piia M H Markkanen
- Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, FI-90014, Oulu, Finland
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Christis C, Lubsen NH, Braakman I. Protein folding includes oligomerization - examples from the endoplasmic reticulum and cytosol. FEBS J 2008; 275:4700-27. [DOI: 10.1111/j.1742-4658.2008.06590.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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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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Leskelä TT, Markkanen PMH, Pietilä EM, Tuusa JT, Petäjä-Repo UE. Opioid receptor pharmacological chaperones act by binding and stabilizing newly synthesized receptors in the endoplasmic reticulum. J Biol Chem 2007; 282:23171-83. [PMID: 17550902 DOI: 10.1074/jbc.m610896200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Accumulating evidence has indicated that membrane-permeable G protein-coupled receptor ligands can enhance cell surface targeting of their cognate wild-type and mutant receptors. This pharmacological chaperoning was thought to result from ligand-mediated stabilization of immature receptors in the endoplasmic reticulum (ER). In the present study, we directly tested this hypothesis using wild-type and mutant forms of the human delta-opioid receptor as models. ER-localized receptors were isolated by expressing the receptors in HEK293 cells under tightly controlled tetracycline induction and blocking their ER export with brefeldin A. The ER-retained delta-opioid receptor precursors were able to bind [(3)H]diprenorphine with high affinity, and treatment of cells with an opioid antagonist naltrexone led to a 2-fold increase in the number of binding sites. After removing the transport block, the antagonist-mediated increase in the number of receptors was detectable at the cell surface by flow cytometry and cell surface biotinylation assay. Importantly, opioid ligands, both antagonists and agonists, were found to stabilize the ER-retained receptor precursors in an in vitro heat inactivation assay and the treatment enhanced dissociation of receptor precursors from the molecular chaperone calnexin. Thus, we conclude that pharmacological chaperones facilitate plasma membrane targeting of delta-opioid receptors by binding and stabilizing receptor precursors, thereby promoting their release from the stringent ER quality control.
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Affiliation(s)
- Tarja T Leskelä
- Biocenter Oulu and Department of Anatomy and Cell Biology, University of Oulu, FI-90014 Oulu, Finland
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Abstract
Regulation of protein function by posttranslational modification plays an important role in many biological pathways. The most well known among such modifications is protein phosphorylation performed by highly specific protein kinases. In the past decade, however, covalent linkage of the low-molecular-weight protein ubiquitin to substrate proteins (protein ubiquitination) has proven to be yet another widely used mechanism of protein regulation playing a crucial role in virtually all aspects of cellular functions. This review highlights some of the recently discovered and provocative roles for ubiquitination in the regulation of the life cycle and signal transduction properties of 7-transmembrane receptors that serve to integrate many biological functions and play fundamental roles in cardiovascular homeostasis.
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Affiliation(s)
- Sudha K Shenoy
- Duke University Medical Center, Departments of Medicine and Cell Biology, Durham, NC 27710, USA.
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Tuusa JT, Markkanen PMH, Apaja PM, Hakalahti AE, Petäjä-Repo UE. The endoplasmic reticulum Ca2+-pump SERCA2b interacts with G protein-coupled receptors and enhances their expression at the cell surface. J Mol Biol 2007; 371:622-38. [PMID: 17588601 DOI: 10.1016/j.jmb.2007.02.108] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2007] [Revised: 02/22/2007] [Accepted: 02/26/2007] [Indexed: 11/28/2022]
Abstract
Calcium (Ca(2+)) plays a pivotal role in both cellular signaling and protein synthesis. However, it is not well understood how calcium metabolism and synthesis of secreted and membrane-bound proteins are related. Here we demonstrate that the sarco(endo)plasmic reticulum Ca(2+) ATPase 2b (SERCA2b), which maintains high Ca(2+) concentration in the lumen of the endoplasmic reticulum, interacts specifically with the human delta opioid receptor during early steps of receptor biogenesis in human embryonic kidney 293 cells. The interaction involves newly synthesized incompletely folded receptor precursors, because the association between the delta opioid receptor and SERCA2b (i) was short-lived and took place soon after receptor translation, (ii) was not affected by misfolding of the receptor, and (iii) decreased if receptor folding was enhanced by opioid receptor pharmacological chaperone. The physical association with SERCA2b was found to be a universal feature among G protein-coupled receptors within family A and was shown to occur also between the endogenously expressed luteinizing hormone receptor and SERCA2b in rat ovaries. Importantly, active SERCA2b rather than undisturbed Ca(2+) homeostasis was found to be essential for delta opioid receptor biogenesis, as inhibition of its Ca(2+) pumping activity by thapsigargin reduced the interaction and impaired the efficiency of receptor maturation, two phenomena that were not affected by a Ca(2+) ionophore A23187. Nevertheless, inhibition of SERCA2b did not compromise the functionality of receptors that were able to mature. Thus, we propose that the association with SERCA2b is required for efficient folding and/or membrane integration of G protein-coupled receptors.
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Affiliation(s)
- Jussi T Tuusa
- Biocenter Oulu and Department of Anatomy and Cell Biology, University of Oulu, P.O.Box 5000, FI-90014, Oulu, Finland
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Dong C, Filipeanu CM, Duvernay MT, Wu G. Regulation of G protein-coupled receptor export trafficking. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1768:853-70. [PMID: 17074298 PMCID: PMC1885203 DOI: 10.1016/j.bbamem.2006.09.008] [Citation(s) in RCA: 204] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Revised: 09/14/2006] [Accepted: 09/18/2006] [Indexed: 12/26/2022]
Abstract
G protein-coupled receptors (GPCRs) constitute a superfamily of cell-surface receptors which share a common topology of seven transmembrane domains and modulate a variety of cell functions through coupling to heterotrimeric G proteins by responding to a vast array of stimuli. The magnitude of cellular response elicited by a given signal is dictated by the level of GPCR expression at the plasma membrane, which is the balance of elaborately regulated endocytic and exocytic trafficking. This review will cover recent advances in understanding the molecular mechanism underlying anterograde transport of the newly synthesized GPCRs from the endoplasmic reticulum (ER) through the Golgi to the plasma membrane. We will focus on recently identified motifs involved in GPCR exit from the ER and the Golgi, GPCR folding in the ER and the rescue of misfolded receptors from within, GPCR-interacting proteins that modulate receptor cell-surface targeting, pathways that mediate GPCR traffic, and the functional role of export in controlling GPCR signaling.
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Affiliation(s)
| | | | | | - Guangyu Wu
- * Corresponding author. Tel: +1 504 568 2236; Fax: +1 504 568 2361. E-mail address: (G. Wu)
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Petäjä-Repo UE, Hogue M, Leskelä TT, Markkanen PMH, Tuusa JT, Bouvier M. Distinct subcellular localization for constitutive and agonist-modulated palmitoylation of the human delta opioid receptor. J Biol Chem 2006; 281:15780-9. [PMID: 16595649 DOI: 10.1074/jbc.m602267200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein palmitoylation is a reversible lipid modification that plays important roles for many proteins involved in signal transduction, but relatively little is known about the regulation of this modification and the cellular location where it occurs. We demonstrate that the human delta opioid receptor is palmitoylated at two distinct cellular locations in human embryonic kidney 293 cells and undergoes dynamic regulation at one of these sites. Although palmitoylation could be readily observed for the mature receptor (Mr 55,000), [3H]palmitate incorporation into the receptor precursor (Mr 45,000) could be detected only following transport blockade with brefeldin A, nocodazole, and monensin, indicating that the modification occurs initially during or shortly after export from the endoplasmic reticulum. Blocking of palmitoylation with 2-bromopalmitate inhibited receptor cell surface expression, indicating that it is needed for efficient intracellular transport. However, cell surface biotinylation experiments showed that receptors can also be palmitoylated once they have reached the plasma membrane. At this location, palmitoylation is regulated in a receptor activation-dependent manner, as was indicated by the opioid agonist-promoted increase in the turnover of receptor-bound palmitate. This agonist-mediated effect did not require receptor-G protein coupling and occurred at the cell surface without the need for internalization or recycling. The activation-dependent modulation of receptor palmitoylation may thus contribute to the regulation of receptor function at the plasma membrane.
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Affiliation(s)
- Ulla E Petäjä-Repo
- Biocenter Oulu and Department of Anatomy and Cell Biology, University of Oulu, FI-90014, Oulu, Finland.
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