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Yadav N, Thelma BK. Deletion induced splicing in RIC3 drives nicotinic acetylcholine receptor regulation with implications for endoplasmic reticulum stress in human astrocytes. Glia 2023; 71:1217-1232. [PMID: 36602087 DOI: 10.1002/glia.24333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Revised: 11/25/2022] [Accepted: 12/22/2022] [Indexed: 01/06/2023]
Abstract
Nicotinic acetylcholine receptor (nAChR) dysregulation in astrocytes is reported in neurodegenerative disorders. Modulation of nAChRs through agonists confers protection to astrocytes from stress but regulation of chaperones involved in proteostasis with pathological implications is unclear. Resistance to inhibitors of cholinesterase 3 (RIC3), a potential chaperone of nAChRs is poorly studied in humans. We characterized RIC3 in astrocytes derived from an isogenic wild-type and Cas9 edited "del" human iPSC line harboring a 25 bp homozygous deletion in exon2. Altered RIC3 transcript ratio due to deletion induced splicing and an unexpected gain of α7nAChR expression were observed in "del" astrocytes. Transcriptome analysis showed higher expression of neurotransmitter/G-protein coupled receptors mediated by cAMP and calcium/calmodulin-dependent kinase signaling with increased cytokines/glutamate secretion. Functional implications examined using tunicamycin induced ER stress in wild-type astrocyte stress model showed cell cycle arrest, RIC3 upregulation, reduction in α7nAChR membrane levels but increased α4nAChR membrane expression. Conversely, tunicamycin-treated "del" astrocytes showed a comparatively higher α4nAChR membrane expression and upsurged cAMP signaling. Furthermore, reduced expression of stress markers CHOP, phospho-PERK and lowered XBP1 splicing in western blot and qPCR, validated by proteome-based pathway analysis indicated lowered disease severity. Findings indicate (i) a complex RNA regulatory mechanism via exonic deletion induced splicing; (ii) RIC-3 as a disordered protein having contrasting effects on co-expressed nAChR subtypes under basal/stress conditions; and (iii) RIC3 as a potential drug target against ER stress in astrocytes for neurodegenerative/nicotine-related brain disorders. Cellular rescue mechanism through deletion induced exon skipping may encourage ASO-based therapies for tauopathies.
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Affiliation(s)
- Navneesh Yadav
- Department of Genetics, University of Delhi South Campus, New Delhi, India
| | - B K Thelma
- Department of Genetics, University of Delhi South Campus, New Delhi, India
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2
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Brunello L, Ménard C, Rousset M, Vignes M, Charnet P, Cens T. Different efficiency of auxiliary/chaperone proteins to promote the functional reconstitution of honeybee glutamate and acetylcholine receptors in Xenopus laevis oocytes. INSECT MOLECULAR BIOLOGY 2022; 31:620-633. [PMID: 35587772 PMCID: PMC9546428 DOI: 10.1111/imb.12791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 05/12/2022] [Indexed: 06/15/2023]
Abstract
Heterologous expression systems (e.g., Xenopus laevis oocytes) are useful to study the biophysical properties and pharmacology of ionotropic receptors such as ionotropic glutamate (iGLuRs) and nicotinic acetylcholine (nAChRs) receptors. However, insect receptors often require the co-expression of chaperone proteins to be functional. Only few iGluRs and nAChRs have been successfully expressed in such systems. Here, we compared the efficiency of chaperone proteins to promote the functional expression of one Apis mellifera iGluR and several nAChR subunit combinations (α1α8β1, α7, α2α8β1 and α2α7α8β1) in Xenopus oocytes. To this end, we cloned a new iGluR (GluR-1) and potential chaperone proteins (e.g., SOL-1, Neto, NACHO) and tested more than 40 combinations of human, nematode and honeybee proteins. We obtained robust expression of GluR-1 and α1α8β1 when co-expressed with honeybee chaperone proteins and found that nAChR expression critically depended on the α1 subunit N-terminal sequence. We recorded small ACh-gated currents in few oocytes when the α7 subunit was co-expressed with Caenorhabditis elegans RIC-3, but none of the chaperone proteins allowed efficient expression of α2α8β1 or α2α7α8β1. Our results show that only some protein combinations can reconstitute functional receptors in Xenopus oocytes and that protein combination efficient in one species is not always efficient in another species.
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Affiliation(s)
- Lorène Brunello
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Claudine Ménard
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Matthieu Rousset
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Michel Vignes
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Pierre Charnet
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Thierry Cens
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
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3
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Speculation on How RIC-3 and Other Chaperones Facilitate α7 Nicotinic Receptor Folding and Assembly. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27144527. [PMID: 35889400 PMCID: PMC9318448 DOI: 10.3390/molecules27144527] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 07/07/2022] [Accepted: 07/09/2022] [Indexed: 11/17/2022]
Abstract
The process of how multimeric transmembrane proteins fold and assemble in the endoplasmic reticulum is not well understood. The alpha7 nicotinic receptor (α7 nAChR) is a good model for multimeric protein assembly since it has at least two independent and specialized chaperones: Resistance to Inhibitors of Cholinesterase 3 (RIC-3) and Nicotinic Acetylcholine Receptor Regulator (NACHO). Recent cryo-EM and NMR data revealed structural features of α7 nAChRs. A ser-ala-pro (SAP) motif precedes a structurally important but unique "latch" helix in α7 nAChRs. A sampling of α7 sequences suggests the SAP motif is conserved from C. elegans to humans, but the latch sequence is only conserved in vertebrates. How RIC-3 and NACHO facilitate receptor subunits folding into their final pentameric configuration is not known. The artificial intelligence program AlphaFold2 recently predicted structures for NACHO and RIC-3. NACHO is highly conserved in sequence and structure across species, but RIC-3 is not. This review ponders how different intrinsically disordered RIC-3 isoforms from C. elegans to humans interact with α7 nAChR subunits despite having little sequence homology across RIC-3 species. Two models from the literature about how RIC-3 assists α7 nAChR assembly are evaluated considering recent structural information about the receptor and its chaperones.
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Why Does Knocking Out NACHO, But Not RIC3, Completely Block Expression of α7 Nicotinic Receptors in Mouse Brain? Biomolecules 2020; 10:biom10030470. [PMID: 32204458 PMCID: PMC7175337 DOI: 10.3390/biom10030470] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 03/11/2020] [Accepted: 03/17/2020] [Indexed: 12/19/2022] Open
Abstract
Alpha7 nicotinic acetylcholine receptors (α7nAChRs) are interesting not only because of their physiological effects, but because this receptor requires chaperones to traffic to cell surfaces (measured by alpha-bungarotoxin [αBGT] binding). While knockout (KO) animals and antibodies that react across species exist for tmem35a encoding the protein chaperone NACHO, commercially available antibodies against the chaperone RIC3 that allow Western blots across species have not been generally available. Further, no effects of deleting RIC3 function (ric3 KO) on α7nAChR expression are reported. Finally, antibodies against α7nAChRs have shown various deficiencies. We find mouse macrophages bind αBGT but lack NACHO. We also report on a new α7nAChR antibody and testing commercially available anti-RIC3 antibodies that react across species allowing Western blot analysis of in vitro cultures. These antibodies also react to specific RIC3 splice variants and single-nucleotide polymorphisms. Preliminary autoradiographic analysis reveals that ric3 KOs show subtle αBGT binding changes across different mouse brain regions, while tmem35a KOs show a complete loss of αBGT binding. These findings are inconsistent with effects observed in vitro, as RIC3 promotes αBGT binding to α7nAChRs expressed in HEK cells, even in the absence of NACHO. Collectively, additional regulatory factors are likely involved in the in vivo expression of α7nAChRs.
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Koperniak TM, Garg BK, Boltax J, Loring RH. Cell-specific effects on surface α7 nicotinic receptor expression revealed by over-expression and knockdown of rat RIC3 protein. J Neurochem 2013; 124:300-9. [PMID: 23157401 DOI: 10.1111/jnc.12095] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2012] [Revised: 09/14/2012] [Accepted: 10/02/2012] [Indexed: 12/01/2022]
Abstract
We tested whether surface α7 nicotinic acetylcholine receptor expression is dependent on an endogenous chaperone named Resistance to Inhibitors of Cholinesterase 3 (RIC3) by comparing RIC3 protein in rat GH4C1 and human SH-EP1 cells, which express strikingly different surface receptor levels following α7 transfection. Cloned rat RIC3 exists in at least two isoforms because of an ambiguous splice site between exons 4 and 5. Both rat isoforms permit surface α7 expression in SH-EP1 and human embryonic kidney (HEK) cells measured by α-bungarotoxin binding. Contrary to expectations, endogenous RIC3 protein expression determined by immunoblots did not differ between untransfected GH4C1 or SH-EP1 cells. siRNA against rat RIC3 exon 4 and shRNA against exons 2, 5 and 6 knocked down transfected rat RIC3 expression in SH-EP1 cells and simultaneously blocked toxin binding. However, no RNAi construct blocked binding when co-transfected with α7 into GH4C1 cells. shRNA against rat exons 2 and 5 knocked down rat RIC3 protein transfected into GH4C1 cells with a time course suggesting a protein half-life of a few days. These results suggest GH4C1 cells may possess unknown chaperone(s) allowing high surface α7 expression in the absence of known RIC3 splice variants.
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Affiliation(s)
- Thomas M Koperniak
- Department of Pharmaceutical Science, Northeastern University, Boston, MA 02115, USA
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Bennett HM, Lees K, Harper KM, Jones AK, Sattelle DB, Wonnacott S, Wolstenholme AJ. Xenopus laevis RIC-3 enhances the functional expression of the C. elegans homomeric nicotinic receptor, ACR-16, in Xenopus oocytes. J Neurochem 2012; 123:911-8. [PMID: 22970690 PMCID: PMC3549563 DOI: 10.1111/jnc.12013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Revised: 08/23/2012] [Accepted: 09/10/2012] [Indexed: 01/25/2023]
Abstract
RIC-3 enhances the functional expression of certain nicotinic acetylcholine receptors (nAChRs) in vertebrates and invertebrates and increases the availability of functional receptors in cultured cells and Xenopus laevis oocytes. Maximal activity of RIC-3 may be cell-type dependent, so neither mammalian nor invertebrate proteins is optimal in amphibian oocytes. We cloned the X. laevis ric-3 cDNA and tested the frog protein in oocyte expression studies. X. laevis RIC-3 shares 52% amino acid identity with human RIC-3 and only 17% with that of Caenorhabditis elegans. We used the C. elegans nicotinic receptor, ACR-16, to compare the ability of RIC-3 from three species to enhance receptor expression. In the absence of RIC-3, the proportion of oocytes expressing detectable nAChRs was greatly reduced. Varying the ratio of acr-16 to X. laevis ric-3 cRNAs injected into oocytes had little impact on the total cell current. When X. laevis, human or C. elegans ric-3 cRNAs were co-injected with acr-16 cRNA (1 : 1 ratio), 100 μM acetylcholine induced larger currents in oocytes expressing X. laevis RIC-3 compared with its orthologues. This provides further evidence for a species-specific component of RIC-3 activity, and suggests that X. laevis RIC-3 is useful for enhancing the expression of invertebrate nAChRs in X. laevis oocytes.
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Affiliation(s)
- Hayley M Bennett
- Department of Infectious Diseases and Center for Tropical & Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA
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Chaperoning α7 neuronal nicotinic acetylcholine receptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:718-29. [PMID: 22040696 DOI: 10.1016/j.bbamem.2011.10.012] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2011] [Revised: 09/25/2011] [Accepted: 10/17/2011] [Indexed: 11/22/2022]
Abstract
The α7 subtype of nicotinic acetylcholine receptors (AChRs) is one of the most abundant members of the Cys-loop family of receptors present in the central nervous system. It participates in various physiological processes and has received much attention as a potential therapeutic target for a variety of pathologies. The importance of understanding the mechanisms controlling AChR assembly and cell-surface delivery lies in the fact that these two processes are key to determining the functional pool of receptors actively engaged in synaptic transmission. Here we review recent studies showing that RIC-3, a protein originally identified in the worm Caenorhabditis elegans, modulates the expression of α7 AChRs in a subtype-specific manner. Potentiation of AChR expression by post-transcriptional events is also critically assessed.
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Walstab J, Hammer C, Lasitschka F, Möller D, Connolly CN, Rappold G, Brüss M, Bönisch H, Niesler B. RIC-3 exclusively enhances the surface expression of human homomeric 5-hydroxytryptamine type 3A (5-HT3A) receptors despite direct interactions with 5-HT3A, -C, -D, and -E subunits. J Biol Chem 2010; 285:26956-26965. [PMID: 20522555 PMCID: PMC2930695 DOI: 10.1074/jbc.m110.122838] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although five 5-hydroxytryptamine type 3 (5-HT3) subunits (A-E) have been cloned, knowledge on the regulation of their assembly is limited. RIC-3 has been identified as a chaperone specific for the pentameric ligand-gated nicotinic acetylcholine and 5-HT(3) receptors. Therefore, we examined the impact of RIC-3 on differently composed 5-HT(3) receptors with the focus on 5-HT3C, -D, and -E subunits. The influence of RIC-3 on these receptor subtypes is supported by the presence of RIC3 mRNA in tissues expressing at least one of the subunits 5-HT3C, -D, and -E. Furthermore, immunocytochemical studies on transfected mammalian cells revealed co-localization in the endoplasmic reticulum and direct interaction of RIC-3 with 5-HT3A, -C, -D, and -E. Functional and pharmacological characterization was performed using HEK293 cells expressing 5-HT3A or 5-HT3A + 5-HT3B (or -C, -D, or -E) in the presence or absence of RIC-3. Ca(2+) influx analyses revealed that RIC-3 does not influence the 5-HT concentration-response relationship on 5-HT(3)A receptors but leads to differential increases of 5-HT-induced maximum response (E(max)) on cells expressing different subunits. Increases of E(max) were due to analogously enhanced B(max) values for binding of the 5-HT(3) receptor antagonist [(3)H]GR65630. The observed enhanced cell surface expression of the tested 5-HT3 subunit combinations correlated with the increased surface expression of 5-HT3A as determined by flow cytometry. In conclusion, we showed that RIC-3 can interact with 5-HT3A, -C, -D, and -E subunits and predominantly enhances the surface expression of homomeric 5-HT(3)A receptors in HEK293 cells. These data implicate a possible role of RIC-3 in determining 5-HT(3) receptor composition in vivo.
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Affiliation(s)
- Jutta Walstab
- Department of Human Molecular Genetics, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany; Institute of Pharmacology and Toxicology, University of Bonn, Reuterstrasse 2b, 53113 Bonn, Germany
| | - Christian Hammer
- Department of Human Molecular Genetics, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany
| | - Felix Lasitschka
- Institute of Pathology, University of Heidelberg, Im Neuenheimer Feld 220/221, 69120 Heidelberg, Germany
| | - Dorothee Möller
- Department of Human Molecular Genetics, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany
| | - Christopher N Connolly
- Centre for Neuroscience, Division of Medical Sciences, Ninewells Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - Gudrun Rappold
- Department of Human Molecular Genetics, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany
| | - Michael Brüss
- Institute of Pharmacology and Toxicology, University of Bonn, Reuterstrasse 2b, 53113 Bonn, Germany
| | - Heinz Bönisch
- Institute of Pharmacology and Toxicology, University of Bonn, Reuterstrasse 2b, 53113 Bonn, Germany
| | - Beate Niesler
- Department of Human Molecular Genetics, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany.
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Biala Y, Liewald JF, Ben-Ami HC, Gottschalk A, Treinin M. The conserved RIC-3 coiled-coil domain mediates receptor-specific interactions with nicotinic acetylcholine receptors. Mol Biol Cell 2009; 20:1419-27. [PMID: 19116311 PMCID: PMC2649256 DOI: 10.1091/mbc.e08-08-0851] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 11/25/2008] [Accepted: 12/22/2008] [Indexed: 01/23/2023] Open
Abstract
RIC-3 belongs to a conserved family of proteins influencing nicotinic acetylcholine receptor (nAChR) maturation. RIC-3 proteins are integral membrane proteins residing in the endoplasmic reticulum (ER), and containing a C-terminal coiled-coil domain (CC-I). Conservation of CC-I in all RIC-3 family members indicates its importance; however, previous studies could not show its function. To examine the role of CC-I, we studied effects of its deletion on Caenorhabditis elegans nAChRs in vivo. Presence of CC-I promoted maturation of particular nAChRs expressed in body-wall muscle, whereas it was not required for other nAChR subtypes expressed in neurons or pharyngeal muscles. This effect is receptor-specific, because it could be reproduced after heterologous expression. Consistently, coimmunoprecipitation analysis showed that CC-I enhances the interaction of RIC-3 with a nAChR that requires CC-I in vivo; thus CC-I appears to enhance affinity of RIC-3 to specific nAChRs. However, we found that this function of CC-I is redundant with functions of sequences downstream to CC-I, potentially a second coiled-coil. Alternative splicing in both vertebrates and invertebrates generates RIC-3 transcripts that lack the entire C-terminus, or only CC-I. Thus, our results suggest that RIC-3 alternative splicing enables subtype specific regulation of nAChR maturation.
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Affiliation(s)
- Yoav Biala
- *Department of Physiology, Hebrew University, Hadassah Medical School, Jerusalem, 91120, Israel; and
| | - Jana F. Liewald
- Department of Biochemistry, Chemistry and Pharmacy, Institute of Biochemistry, Biocenter N210/220 and
| | - Hagit Cohen Ben-Ami
- *Department of Physiology, Hebrew University, Hadassah Medical School, Jerusalem, 91120, Israel; and
| | - Alexander Gottschalk
- Department of Biochemistry, Chemistry and Pharmacy, Institute of Biochemistry, Biocenter N210/220 and
- Cluster of Excellence Frankfurt-Macromolecular Complexes (CEF-MC), Johann Wolfgang Goethe-University Frankfurt, D-60438 Frankfurt, Germany
| | - Millet Treinin
- *Department of Physiology, Hebrew University, Hadassah Medical School, Jerusalem, 91120, Israel; and
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Treinin M. RIC-3 and nicotinic acetylcholine receptors: Biogenesis, properties, and diversity. Biotechnol J 2008; 3:1539-47. [DOI: 10.1002/biot.200800179] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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