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Blondelle J, Biju A, Lange S. The Role of Cullin-RING Ligases in Striated Muscle Development, Function, and Disease. Int J Mol Sci 2020; 21:E7936. [PMID: 33114658 PMCID: PMC7672578 DOI: 10.3390/ijms21217936] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 10/11/2020] [Accepted: 10/13/2020] [Indexed: 02/07/2023] Open
Abstract
The well-orchestrated turnover of proteins in cross-striated muscles is one of the fundamental processes required for muscle cell function and survival. Dysfunction of the intricate protein degradation machinery is often associated with development of cardiac and skeletal muscle myopathies. Most muscle proteins are degraded by the ubiquitin-proteasome system (UPS). The UPS involves a number of enzymes, including E3-ligases, which tightly control which protein substrates are marked for degradation by the proteasome. Recent data reveal that E3-ligases of the cullin family play more diverse and crucial roles in cross striated muscles than previously anticipated. This review highlights some of the findings on the multifaceted functions of cullin-RING E3-ligases, their substrate adapters, muscle protein substrates, and regulatory proteins, such as the Cop9 signalosome, for the development of cross striated muscles, and their roles in the etiology of myopathies.
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Affiliation(s)
- Jordan Blondelle
- Department of Medicine, University of California, La Jolla, CA 92093, USA
| | - Andrea Biju
- Department of Medicine, University of California, La Jolla, CA 92093, USA
| | - Stephan Lange
- Department of Medicine, University of California, La Jolla, CA 92093, USA
- Department of Molecular and Clinical Medicine, University of Gothenburg, 41345 Gothenburg, Sweden
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2
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Almutairi F, Lee JK, Rada B. Regulator of G protein signaling 10: Structure, expression and functions in cellular physiology and diseases. Cell Signal 2020; 75:109765. [PMID: 32882407 PMCID: PMC7579743 DOI: 10.1016/j.cellsig.2020.109765] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 08/26/2020] [Accepted: 08/27/2020] [Indexed: 01/22/2023]
Abstract
Regulator of G protein signaling 10 (RGS10) belongs to the superfamily of RGS proteins, defined by the presence of a conserved RGS domain that canonically binds and deactivates heterotrimeric G-proteins. RGS proteins act as GTPase activating proteins (GAPs), which accelerate GTP hydrolysis on the G-protein α subunits and result in termination of signaling pathways downstream of G protein-coupled receptors. RGS10 is the smallest protein of the D/R12 subfamily and selectively interacts with Gαi proteins. It is widely expressed in many cells and tissues, with the highest expression found in the brain and immune cells. RGS10 expression is transcriptionally regulated via epigenetic mechanisms. Although RGS10 lacks multiple of the defined regulatory domains found in other RGS proteins, RGS10 contains post-translational modification sites regulating its expression, localization, and function. Additionally, RGS10 is a critical protein in the regulation of physiological processes in multiple cells, where dysregulation of its expression has been implicated in various diseases including Parkinson's disease, multiple sclerosis, osteopetrosis, chemoresistant ovarian cancer and cardiac hypertrophy. This review summarizes RGS10 features and its regulatory mechanisms, and discusses the known functions of RGS10 in cellular physiology and pathogenesis of several diseases.
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Affiliation(s)
- Faris Almutairi
- Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, University of Georgia, Athens, GA, USA; Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, USA
| | - Jae-Kyung Lee
- Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, GA, USA
| | - Balázs Rada
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, USA.
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3
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Kirschner Peretz N, Segal S, Yaniv Y. May the Force Not Be With You During Culture: Eliminating Mechano-Associated Feedback During Culture Preserves Cultured Atrial and Pacemaker Cell Functions. Front Physiol 2020; 11:163. [PMID: 32265724 PMCID: PMC7100534 DOI: 10.3389/fphys.2020.00163] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Accepted: 02/12/2020] [Indexed: 01/24/2023] Open
Abstract
Cultured cardiomyocytes have been shown to possess significant potential as a model for characterization of mechano-Ca2+, mechano-electric, and mechano-metabolic feedbacks in the heart. However, the majority of cultured cardiomyocytes exhibit impaired electrical, mechanical, biochemical, and metabolic functions. More specifically, the cells do not beat spontaneously (pacemaker cells) or beat at a rate far lower than their physiological counterparts and self-oscillate (atrial and ventricular cells) in culture. Thus, efforts are being invested in ensuring that cultured cardiomyocytes maintain the shape and function of freshly isolated cells. Elimination of contraction during culture has been shown to preserve the mechano-Ca2+, mechano-electric, and mechano-metabolic feedback loops of cultured cells. This review focuses on pacemaker cells, which reside in the sinoatrial node (SAN) and generate regular heartbeat through the initiation of the heart’s electrical, metabolic, and biochemical activities. In parallel, it places emphasis on atrial cells, which are responsible for bridging the electrical conductance from the SAN to the ventricle. The review provides a summary of the main mechanisms responsible for mechano-electrical, Ca2+, and metabolic feedback in pacemaker and atrial cells and of culture methods existing for both cell types. The work concludes with an explanation of how the elimination of mechano-electrical, mechano-Ca2+, and mechano-metabolic feedbacks during culture results in sustained cultured cell function.
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Affiliation(s)
- Noa Kirschner Peretz
- Biomedical Engineering Faculty, Technion Israel Institute of Technology, Haifa, Israel
| | - Sofia Segal
- Biomedical Engineering Faculty, Technion Israel Institute of Technology, Haifa, Israel
| | - Yael Yaniv
- Biomedical Engineering Faculty, Technion Israel Institute of Technology, Haifa, Israel
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Squires KE, Montañez-Miranda C, Pandya RR, Torres MP, Hepler JR. Genetic Analysis of Rare Human Variants of Regulators of G Protein Signaling Proteins and Their Role in Human Physiology and Disease. Pharmacol Rev 2018; 70:446-474. [PMID: 29871944 DOI: 10.1124/pr.117.015354] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Regulators of G protein signaling (RGS) proteins modulate the physiologic actions of many neurotransmitters, hormones, and other signaling molecules. Human RGS proteins comprise a family of 20 canonical proteins that bind directly to G protein-coupled receptors/G protein complexes to limit the lifetime of their signaling events, which regulate all aspects of cell and organ physiology. Genetic variations account for diverse human traits and individual predispositions to disease. RGS proteins contribute to many complex polygenic human traits and pathologies such as hypertension, atherosclerosis, schizophrenia, depression, addiction, cancers, and many others. Recent analysis indicates that most human diseases are due to extremely rare genetic variants. In this study, we summarize physiologic roles for RGS proteins and links to human diseases/traits and report rare variants found within each human RGS protein exome sequence derived from global population studies. Each RGS sequence is analyzed using recently described bioinformatics and proteomic tools for measures of missense tolerance ratio paired with combined annotation-dependent depletion scores, and protein post-translational modification (PTM) alignment cluster analysis. We highlight selected variants within the well-studied RGS domain that likely disrupt RGS protein functions and provide comprehensive variant and PTM data for each RGS protein for future study. We propose that rare variants in functionally sensitive regions of RGS proteins confer profound change-of-function phenotypes that may contribute, in newly appreciated ways, to complex human diseases and/or traits. This information provides investigators with a valuable database to explore variation in RGS protein function, and for targeting RGS proteins as future therapeutic targets.
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Affiliation(s)
- Katherine E Squires
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia (K.E.S., C.M.-M., J.R.H.); and School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia (R.R.P., M.P.T.)
| | - Carolina Montañez-Miranda
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia (K.E.S., C.M.-M., J.R.H.); and School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia (R.R.P., M.P.T.)
| | - Rushika R Pandya
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia (K.E.S., C.M.-M., J.R.H.); and School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia (R.R.P., M.P.T.)
| | - Matthew P Torres
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia (K.E.S., C.M.-M., J.R.H.); and School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia (R.R.P., M.P.T.)
| | - John R Hepler
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia (K.E.S., C.M.-M., J.R.H.); and School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia (R.R.P., M.P.T.)
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Role of hippocampal 5-HT1A receptors in the antidepressant-like phenotype of mice expressing RGS-insensitive Gαi2 protein. Neuropharmacology 2018; 141:296-304. [PMID: 30189184 DOI: 10.1016/j.neuropharm.2018.09.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 08/31/2018] [Accepted: 09/02/2018] [Indexed: 12/11/2022]
Abstract
A single base mutation in the Gαi2 protein (G184S) renders this Gα subunit insensitive to the negative modulatory effects of Regulator of G-protein Signaling (RGS) proteins. Mice expressing this RGS insensitive (RGSi) variant of Gαi2 (RGSi Gαi2) display a spontaneous antidepressant-like phenotype that is reversible by treatment with the 5-HT1A receptor (5-HT1AR) antagonist WAY100635. Here we test the hypothesis that increased activity of 5-HT1ARs in the hippocampus of RGSi Gαi2 knock-in mice is responsible for the expression of the observed antidepressant-like behavior. We administered the 5-HT1AR antagonist WAY100635 or the agonist 8-OH-DPAT via bilateral intra-hippocampal infusion cannulae and evaluated antidepressant-like behavior using the tail suspension test (TST). WAY100635 reversed the antidepressant-like phenotype of the RGSi Gαi2 knock-in mice and 8-OH-DPAT produced an antidepressant-like response in wild type mice that was blocked by systemic WAY100635. Furthermore, intra-hippocampal infusion of the RGS19/4 inhibitor CCG-203769 produced an antidepressant-like effect in female mice. Ex-vivo slice recording confirmed the 5-HT1AR-mediated decrease in hippocampal CA1 pyramidal neuron excitability was enhanced in the RGSi Gαi2 knock-in mice. There was no change in hippocampal 5-HT1AR expression as measured by ligand binding but there was a compensatory reduction in Gαi proteins. The findings demonstrate that RGS protein control of hippocampal 5-HT1AR signaling is necessary and sufficient to account for the antidepressant-like phenotype in the RGSi Gαi2 knock-in mice and that RGS proteins highly expressed in the hippocampus should be investigated as targets for novel antidepressant therapies.
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Lee KN, Lu X, Nguyen C, Feng Q, Chidiac P. Cardiomyocyte specific overexpression of a 37 amino acid domain of regulator of G protein signalling 2 inhibits cardiac hypertrophy and improves function in response to pressure overload in mice. J Mol Cell Cardiol 2017. [PMID: 28641980 DOI: 10.1016/j.yjmcc.2017.06.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Regulator of G protein signalling 2 (RGS2) is known to play a protective role in maladaptive cardiac hypertrophy and heart failure via its ability to inhibit Gq- and Gs- mediated GPCR signalling. We previously demonstrated that RGS2 can also inhibit protein translation and can thereby attenuate cell growth. This G protein-independent inhibitory effect has been mapped to a 37 amino acid domain (RGS2eb) within RGS2 that binds to eukaryotic initiation factor 2B (eIF2B). When expressed in neonatal rat cardiomyocytes, RGS2eb attenuates both protein synthesis and hypertrophy induced by Gq- and Gs- activating agents. In the current study, we investigated the potential cardioprotective role of RGS2eb by determining whether RGS2eb transgenic (RGS2eb TG) mice with cardiomyocyte specific overexpression of RGS2eb show resistance to the development of hypertrophy in comparison to wild-type (WT) controls. Using transverse aortic constriction (TAC) in a pressure-overload hypertrophy model, we demonstrated that cardiac hypertrophy was inhibited in RGS2eb TG mice compared to WT controls following four weeks of TAC. Expression of the hypertrophic markers atrial natriuretic peptide (ANP) and β-myosin heavy chain (MHC-β) was also reduced in RGS2eb TG compared to WT TAC animals. Furthermore, cardiac function in RGS2eb TG TAC mice was significantly improved compared to WT TAC mice. Notably, cardiomyocyte cell size was significantly decreased in TG compared to WT TAC mice. These results suggest that RGS2 may limit pathological cardiac hypertrophy at least in part via the function of its eIF2B-binding domain.
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Affiliation(s)
- Katherine N Lee
- Department of Physiology and Pharmacology, University of Western Ontario, London, ON, N6A5C1, Canada
| | - Xiangru Lu
- Department of Physiology and Pharmacology, University of Western Ontario, London, ON, N6A5C1, Canada
| | - Chau Nguyen
- School of Pharmacy, D'Youville College, Buffalo, New York 14201, USA
| | - Qingping Feng
- Department of Physiology and Pharmacology, University of Western Ontario, London, ON, N6A5C1, Canada
| | - Peter Chidiac
- Department of Physiology and Pharmacology, University of Western Ontario, London, ON, N6A5C1, Canada.
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Li L, Luo HS. G-Protein Signaling Protein-17 (RGS17) Is Upregulated and Promotes Tumor Growth and Migration in Human Colorectal Carcinoma. Oncol Res 2017; 26:27-35. [PMID: 28337960 PMCID: PMC7844555 DOI: 10.3727/096504017x14900515946914] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Colorectal carcinoma is one of the leading causes of cancer-related deaths and has a high tendency for metastasis, which makes it a priority to find novel methods to diagnose and treat colorectal carcinoma at a very early stage. We studied the role of the regulator of G-protein signaling (RGS) family of proteins RGS17 in colorectal carcinoma growth and metastasis. We found that RGS17 was upregulated in both clinical colorectal carcinoma tissues and cultured colorectal carcinoma cells. Knockdown of RGS17 by specific siRNA decreased the cell proliferation rate, whereas overexpression of RGS17 with expression plasmid increased the rate in cultured cells. Consistently, a mouse model for colorectal carcinoma also showed that depletion of RGS17 significantly inhibited tumor growth in vivo. Moreover, a Transwell assay showed that RGS17 promoted the ability of colorectal carcinoma cells to migrate and invade. These data suggest that RGS17 is overexpressed in colorectal carcinoma and promotes cell proliferation, migration, and invasion.
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Affiliation(s)
- Ling Li
- Department of Gastroenterology, Renmin Hospital of Wuhan University, Wuhan, P.R. China
| | - He-Sheng Luo
- Department of Gastroenterology, Renmin Hospital of Wuhan University, Wuhan, P.R. China
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8
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Regulator of G protein signalling 14 attenuates cardiac remodelling through the MEK-ERK1/2 signalling pathway. Basic Res Cardiol 2016; 111:47. [PMID: 27298141 PMCID: PMC4906057 DOI: 10.1007/s00395-016-0566-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 06/01/2016] [Indexed: 12/02/2022]
Abstract
In the past 10 years, several publications have highlighted the role of the regulator of G protein signalling (RGS) family in multiple diseases, including cardiovascular diseases. As one of the multifunctional family members, RGS14 is involved in various biological processes, such as synaptic plasticity, cell division, and phagocytosis. However, the role of RGS14 in cardiovascular diseases remains unclear. In the present study, we used a genetic approach to examine the role of RGS14 in pathological cardiac remodelling in vivo and in vitro. We observed that RGS14 was down-regulated in human failing hearts, murine hypertrophic hearts, and isolated hypertrophic cardiomyocytes. Moreover, the extent of aortic banding-induced cardiac hypertrophy and fibrosis was exacerbated in RGS14 knockout mice, whereas RGS14 transgenic mice exhibited a significantly alleviated response to pressure overload. Furthermore, research of the underlying mechanism revealed that the RGS14-dependent rescue of cardiac remodelling was attributed to the abrogation of mitogen-activated protein kinase (MEK)–extracellular signal-regulated protein kinase (ERK) 1/2 signalling. The results showed that constitutive activation of MEK1 nullified the cardiac protection in RGS14 transgenic mice, and inhibition of MEK–ERK1/2 by U0126 reversed RGS14 deletion-related hypertrophic aggravation. These results demonstrated that RGS14 attenuated the development of cardiac remodelling through MEK–ERK1/2 signalling. RGS14 exhibited great potential as a target for the treatment of pathological cardiac remodelling.
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Sjögren B, Parra S, Atkins KB, Karaj B, Neubig RR. Digoxin-Mediated Upregulation of RGS2 Protein Protects against Cardiac Injury. J Pharmacol Exp Ther 2016; 357:311-9. [PMID: 26941169 PMCID: PMC4851323 DOI: 10.1124/jpet.115.231571] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2015] [Accepted: 03/01/2016] [Indexed: 12/31/2022] Open
Abstract
Regulator of G protein signaling (RGS) proteins have emerged as novel drug targets since their discovery almost two decades ago. RGS2 has received particular interest in cardiovascular research due to its role in regulating Gqsignaling in the heart and vascular smooth muscle. RGS2(-/-)mice are hypertensive, prone to heart failure, and display accelerated kidney fibrosis. RGS2 is rapidly degraded through the proteasome, and human mutations leading to accelerated RGS2 protein degradation correlate with hypertension. Hence, stabilizing RGS2 protein expression could be a novel route in treating cardiovascular disease. We previously identified cardiotonic steroids, including digoxin, as selective stabilizers of RGS2 protein in vitro. In the current study we investigated the functional effects of digoxin-mediated RGS2 protein stabilization in vivo. Using freshly isolated myocytes from wild-type and RGS2(-/-)mice treated with vehicle or low-dose digoxin (2µg/kg/day for 7 days) we demonstrated that agonist-induced cAMP levels and cardiomyocyte contractility was inhibited by digoxin in wild-type but not in RGS2(-/-)mice. This inhibition was accompanied by an increase in RGS2 protein levels in cardiomyocytes as well as in whole heart tissue. Furthermore, digoxin had protective effects in a model of cardiac injury in wild-type mice and this protection was lost in RGS2(-/-)mice. Digoxin is the oldest known therapy for heart failure; however, beyond its activity at the Na(+)/K(+)-ATPase, the exact mechanism of action is not known. The current study adds a novel mechanism, whereby through stabilizing RGS2 protein levels digoxin could exert its protective effects in the failing heart.
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Affiliation(s)
- Benita Sjögren
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (B.S., B.K., R.R.N.); and Department of Pharmacology (S.P.) and Department of Internal Medicine (K.B.A.), University of Michigan, Ann Arbor, Michigan
| | - Sergio Parra
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (B.S., B.K., R.R.N.); and Department of Pharmacology (S.P.) and Department of Internal Medicine (K.B.A.), University of Michigan, Ann Arbor, Michigan
| | - Kevin B Atkins
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (B.S., B.K., R.R.N.); and Department of Pharmacology (S.P.) and Department of Internal Medicine (K.B.A.), University of Michigan, Ann Arbor, Michigan
| | - Behirda Karaj
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (B.S., B.K., R.R.N.); and Department of Pharmacology (S.P.) and Department of Internal Medicine (K.B.A.), University of Michigan, Ann Arbor, Michigan
| | - Richard R Neubig
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (B.S., B.K., R.R.N.); and Department of Pharmacology (S.P.) and Department of Internal Medicine (K.B.A.), University of Michigan, Ann Arbor, Michigan
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Tinker A, Finlay M, Nobles M, Opel A. The contribution of pathways initiated via the Gq\11 G-protein family to atrial fibrillation. Pharmacol Res 2016; 105:54-61. [DOI: 10.1016/j.phrs.2015.11.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 11/19/2015] [Indexed: 01/28/2023]
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Hayes MP, Roman DL. Regulator of G Protein Signaling 17 as a Negative Modulator of GPCR Signaling in Multiple Human Cancers. AAPS JOURNAL 2016; 18:550-9. [PMID: 26928451 DOI: 10.1208/s12248-016-9894-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Accepted: 02/15/2016] [Indexed: 02/08/2023]
Abstract
Regulators of G protein signaling (RGS) proteins modulate G protein-coupled receptor (GPCR) signaling networks by terminating signals produced by active Gα subunits. RGS17, a member of the RZ subfamily of RGS proteins, is typically only expressed in appreciable amounts in the human central nervous system, but previous works have shown that RGS17 expression is selectively upregulated in a number of malignancies, including lung, breast, prostate, and hepatocellular carcinoma. In addition, this upregulation of RGS17 is associated with a more aggressive cancer phenotype, as increased proliferation, migration, and invasion are observed. Conversely, decreased RGS17 expression diminishes the response of ovarian cancer cells to agents commonly used during chemotherapy. These somewhat contradictory roles of RGS17 in cancer highlight the need for selective, high-affinity inhibitors of RGS17 to use as chemical probes to further the understanding of RGS17 biology. Based on current evidence, these compounds could potentially have clinical utility as novel chemotherapeutics in the treatment of lung, prostate, breast, and liver cancers. Recent advances in screening technologies to identify potential inhibitors coupled with increasing knowledge of the structural requirements of RGS-Gα protein-protein interaction inhibitors make the future of drug discovery efforts targeting RGS17 promising. This review highlights recent findings related to RGS17 as both a canonical and atypical RGS protein, its role in various human disease states, and offers insights on small molecule inhibition of RGS17.
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Affiliation(s)
- Michael P Hayes
- Department of Pharmaceutical Sciences and Experimental Therapeutics, University of Iowa, Iowa City, Iowa, USA
| | - David L Roman
- Department of Pharmaceutical Sciences and Experimental Therapeutics, University of Iowa, Iowa City, Iowa, USA. .,Cancer Signaling and Experimental Therapeutics Program, Holden Comprehensive Cancer Center, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA. .,, 115 S. Grand Avenue, S327 PHAR, Iowa City, Iowa, 52242, USA.
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Song D, Nishiyama M, Kimura S. Potent inhibition of angiotensin AT1 receptor signaling by RGS8: importance of the C-terminal third exon part of its RGS domain. J Recept Signal Transduct Res 2016; 36:478-87. [PMID: 26754208 DOI: 10.3109/10799893.2015.1130056] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
R4/B subfamily RGS (regulator of G protein signaling) proteins play roles in regulation of many GPCR-mediated responses. Multiple RGS proteins are usually expressed in a cell, and it is difficult to point out which RGS protein species are functionally important in the cell. To evaluate intrinsic potency of these RGS proteins, we compared inhibitory effects of RGS1, RGS2, RGS3, RGS4, RGS5, RGS8 and RGS16 on AT1 receptor signaling. Intracellular Ca(2+) responses to angiotensin II were markedly attenuated by transiently expressed RGS2, RGS3 and RGS8, compared to weak inhibition by RGS1, RGS4, RGS5 and RGS16. N-terminally deleted RGS2 (RGS2 domain) lost this potent inhibitory effect, whereas RGS domains of RGS3 and RGS8 showed strong inhibition similar to those of the full-length proteins. To investigate key determinants that specify the differences in potency, we constructed chimeric domains by replacing one or two of three exon parts of RGS8 domain with the corresponding part of RGS5. The chimeric RGS8 domains containing the first or the second exon part of RGS5 showed strong inhibitory effects similar to that of wild type RGS8, but the chimeric domain with the third exon part of RGS5 lost its activity. On the contrary, replacement of the third exon part of RGS5 with the corresponding residues of RGS8 increased the inhibitory effect. The role of the third exon part of RGS8 domain was further confirmed with the chimeric RGS8/RGS4 domains. These results indicate the potent inhibitory activity of RGS8 among R4/B subfamily proteins and importance of the third exon.
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Affiliation(s)
- Dan Song
- a Department of Biochemistry and Molecular Pharmacology , Graduate School of Medicine, Chiba University , Chuo-Ku , Chiba , Japan
| | - Mariko Nishiyama
- a Department of Biochemistry and Molecular Pharmacology , Graduate School of Medicine, Chiba University , Chuo-Ku , Chiba , Japan
| | - Sadao Kimura
- a Department of Biochemistry and Molecular Pharmacology , Graduate School of Medicine, Chiba University , Chuo-Ku , Chiba , Japan
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Opel A, Nobles M, Montaigne D, Finlay M, Anderson N, Breckenridge R, Tinker A. Absence of the Regulator of G-protein Signaling, RGS4, Predisposes to Atrial Fibrillation and Is Associated with Abnormal Calcium Handling. J Biol Chem 2015; 290:19233-44. [PMID: 26088132 PMCID: PMC4521044 DOI: 10.1074/jbc.m115.666719] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 06/15/2015] [Indexed: 01/11/2023] Open
Abstract
The description of potential molecular substrates for predisposition to atrial fibrillation (AF) is incomplete, and it is unknown what role regulators of G-protein signaling might play. We address whether the attenuation of RGS4 function may promote AF and the mechanism through which this occurs. For this purpose, we studied a mouse with global genetic deletion of RGS4 (RGS4(-/-)) and the normal littermate controls (RGS4(+/+)). In vivo electrophysiology using atrial burst pacing revealed that mice with global RGS4 deletion developed AF more frequently than control littermates. Isolated atrial cells from RGS4(-/-) mice show an increase in Ca(2+) spark frequency under basal conditions and after the addition of endothelin-1 and abnormal spontaneous Ca(2+) release events after field stimulation. Isolated left atria studied on a multielectrode array revealed modest changes in path length for re-entry but abnormal electrical events after a pacing train in RGS4(-/-) mice. RGS4 deletion results in a predisposition to atrial fibrillation from enhanced activity in the Gαq/11-IP3 pathway, resulting in abnormal Ca(2+) release and corresponding electrical events.
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Affiliation(s)
- Aaisha Opel
- From the British Heart Foundation Laboratories, Department of Medicine, University College London, Rayne Institute, London WC1E 6JJ, United Kingdom and the William Harvey Heart Centre, Barts & The London School of Medicine & Dentistry, London EC1M 6BQ, United Kingdom
| | - Muriel Nobles
- the William Harvey Heart Centre, Barts & The London School of Medicine & Dentistry, London EC1M 6BQ, United Kingdom
| | - David Montaigne
- the William Harvey Heart Centre, Barts & The London School of Medicine & Dentistry, London EC1M 6BQ, United Kingdom
| | - Malcolm Finlay
- the William Harvey Heart Centre, Barts & The London School of Medicine & Dentistry, London EC1M 6BQ, United Kingdom
| | - Naomi Anderson
- the William Harvey Heart Centre, Barts & The London School of Medicine & Dentistry, London EC1M 6BQ, United Kingdom
| | - Ross Breckenridge
- From the British Heart Foundation Laboratories, Department of Medicine, University College London, Rayne Institute, London WC1E 6JJ, United Kingdom and
| | - Andrew Tinker
- From the British Heart Foundation Laboratories, Department of Medicine, University College London, Rayne Institute, London WC1E 6JJ, United Kingdom and the William Harvey Heart Centre, Barts & The London School of Medicine & Dentistry, London EC1M 6BQ, United Kingdom
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Doupnik CA. RGS Redundancy and Implications in GPCR-GIRK Signaling. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2015; 123:87-116. [PMID: 26422983 DOI: 10.1016/bs.irn.2015.05.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Regulators of G protein signaling (RGS proteins) are key components of GPCR complexes, interacting directly with G protein α-subunits to enhance their intrinsic GTPase activity. The functional consequence is an accelerated termination of G protein effectors including certain ion channels. RGS proteins have a profound impact on the membrane-delimited gating behavior of G-protein-activated inwardly rectifying K(+) (GIRK) channels as demonstrated in reconstitution assays and recent RGS knockout mice studies. Akin to GPCRs and G protein αβγ subunits, multiple RGS isoforms are expressed within single GIRK-expressing neurons, suggesting functional redundancy and/or specificity in GPCR-GIRK channel signaling. The extent and impact of RGS redundancy in neuronal GPCR-GIRK channel signaling is currently not fully appreciated; however, recent studies from RGS knockout mice are providing important new clues on the impact of individual endogenous RGS proteins and the extent of RGS functional redundancy. Incorporating "tools" such as engineered RGS-resistant Gαi/o subunits provide an important assessment method for determining the impact of all endogenous RGS proteins on a given GPCR response and an accounting benchmark to assess the impact of individual RGS knockouts on overall RGS redundancy within a given neuron. Elucidating the degree of regulation attributable to specific RGS proteins in GIRK channel function will aid in the assessment of individual RGS proteins as viable therapeutic targets in epilepsy, ataxia's, memory disorders, and a growing list of neurological disorders.
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Affiliation(s)
- Craig A Doupnik
- Department of Molecular Pharmacology & Physiology, University of South Florida College of Medicine, Tampa, Florida, USA.
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15
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Sjögren B, Swaney S, Neubig RR. FBXO44-Mediated Degradation of RGS2 Protein Uniquely Depends on a Cullin 4B/DDB1 Complex. PLoS One 2015; 10:e0123581. [PMID: 25970626 PMCID: PMC4430315 DOI: 10.1371/journal.pone.0123581] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 03/05/2015] [Indexed: 12/30/2022] Open
Abstract
The ubiquitin-proteasome system for protein degradation plays a major role in regulating cell function and many signaling proteins are tightly controlled by this mechanism. Among these, Regulator of G Protein Signaling 2 (RGS2) is a target for rapid proteasomal degradation, however, the specific enzymes involved are not known. Using a genomic siRNA screening approach, we identified a novel E3 ligase complex containing cullin 4B (CUL4B), DNA damage binding protein 1 (DDB1) and F-box protein 44 (FBXO44) that mediates RGS2 protein degradation. While the more typical F-box partners CUL1 and Skp1 can bind FBXO44, that E3 ligase complex does not bind RGS2 and is not involved in RGS2 degradation. These observations define an unexpected DDB1/CUL4B-containing FBXO44 E3 ligase complex. Pharmacological targeting of this mechanism provides a novel therapeutic approach to hypertension, anxiety, and other diseases associated with RGS2 dysregulation.
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Affiliation(s)
- Benita Sjögren
- Department of Pharmacology & Toxicology, Michigan State University, 1355 Bogue Street, East Lansing, MI 48824, United States of America
| | - Steven Swaney
- Center for Chemical Genomics, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, MI 48109, United States of America
| | - Richard R Neubig
- Department of Pharmacology & Toxicology, Michigan State University, 1355 Bogue Street, East Lansing, MI 48824, United States of America
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Woodard GE, Jardín I, Berna-Erro A, Salido GM, Rosado JA. Regulators of G-protein-signaling proteins: negative modulators of G-protein-coupled receptor signaling. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 317:97-183. [PMID: 26008785 DOI: 10.1016/bs.ircmb.2015.02.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Regulators of G-protein-signaling (RGS) proteins are a category of intracellular proteins that have an inhibitory effect on the intracellular signaling produced by G-protein-coupled receptors (GPCRs). RGS along with RGS-like proteins switch on through direct contact G-alpha subunits providing a variety of intracellular functions through intracellular signaling. RGS proteins have a common RGS domain that binds to G alpha. RGS proteins accelerate GTPase and thus enhance guanosine triphosphate hydrolysis through the alpha subunit of heterotrimeric G proteins. As a result, they inactivate the G protein and quickly turn off GPCR signaling thus terminating the resulting downstream signals. Activity and subcellular localization of RGS proteins can be changed through covalent molecular changes to the enzyme, differential gene splicing, and processing of the protein. Other roles of RGS proteins have shown them to not be solely committed to being inhibitors but behave more as modulators and integrators of signaling. RGS proteins modulate the duration and kinetics of slow calcium oscillations and rapid phototransduction and ion signaling events. In other cases, RGS proteins integrate G proteins with signaling pathways linked to such diverse cellular responses as cell growth and differentiation, cell motility, and intracellular trafficking. Human and animal studies have revealed that RGS proteins play a vital role in physiology and can be ideal targets for diseases such as those related to addiction where receptor signaling seems continuously switched on.
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Affiliation(s)
- Geoffrey E Woodard
- Department of Surgery, Uniformed Services University of the Health Sciences, Bethesda, MD, USA; Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, Bethesda, MD, USA
| | - Isaac Jardín
- Department of Physiology, University of Extremadura, Caceres, Spain
| | - A Berna-Erro
- Department of Physiology, University of Extremadura, Caceres, Spain
| | - Gines M Salido
- Department of Physiology, University of Extremadura, Caceres, Spain
| | - Juan A Rosado
- Department of Physiology, University of Extremadura, Caceres, Spain
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17
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Chidiac P, Sobiesiak AJ, Lee KN, Gros R, Nguyen CH. The eIF2B-interacting domain of RGS2 protects against GPCR agonist-induced hypertrophy in neonatal rat cardiomyocytes. Cell Signal 2014; 26:1226-34. [PMID: 24576550 DOI: 10.1016/j.cellsig.2014.02.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Revised: 02/05/2014] [Accepted: 02/11/2014] [Indexed: 11/29/2022]
Abstract
The protective effect of Regulator of G protein Signaling 2 (RGS2) in cardiac hypertrophy is thought to occur through its ability to inhibit the chronic GPCR signaling that promotes pathogenic growth both in vivo and in cultured cardiomyocytes. However, RGS2 is known to have additional functions beyond its activity as a GTPase accelerating protein, such as the ability to bind to eukaryotic initiation factor, eIF2B, and inhibit protein synthesis. The RGS2 eIF2B-interacting domain (RGS2(eb)) was examined for its ability to regulate hypertrophy in neonatal ventricular myocytes. Both full-length RGS2 and RGS2(eb) were able to inhibit agonist-induced cardiomyocyte hypertrophy, but RGS2(eb) had no effect on receptor-mediated inositol phosphate production, cAMP production, or ERK 1/2 activation. These results suggest that the protective effects of RGS2 in cardiac hypertrophy may derive at least in part from its ability to govern protein synthesis.
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Affiliation(s)
- Peter Chidiac
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON N6A 5C1, Canada
| | - Alina J Sobiesiak
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON N6A 5C1, Canada
| | - Katherine N Lee
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON N6A 5C1, Canada
| | - Robert Gros
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON N6A 5C1, Canada
| | - Chau H Nguyen
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON N6A 5C1, Canada; School of Pharmacy, D'Youville College, Buffalo, NY 14201, USA.
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18
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Keinan D, Yang S, Cohen RE, Yuan X, Liu T, Li YP. Role of regulator of G protein signaling proteins in bone. Front Biosci (Landmark Ed) 2014; 19:634-48. [PMID: 24389209 DOI: 10.2741/4232] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Regulators of G protein signaling (RGS) proteins are a family with more than 30 proteins that all contain an RGS domain. In the past decade, increasing evidence has indicated that RGS proteins play crucial roles in the regulation of G protein coupling receptors (GPCR), G proteins, and calcium signaling during cell proliferation, migration, and differentiation in a variety of tissues. In bone, those proteins modulate bone development and remodeling by influencing various signaling pathways such as GPCR-G protein signaling, Wnt, calcium oscillations and PTH. This review summarizes the recent advances in the understanding of the regulation of RGS gene expression, as well as the functions and mechanisms of RGS proteins, especially in regulating GPCR-G protein signaling, Wnt signaling, calcium oscillations signaling and PTH signaling during bone development and remodeling. This review also highlights the regulation of different RGS proteins in osteoblasts, chondrocytes and osteoclasts. The knowledge from the recent advances of RGS study summarized in the review would provide the insights into new therapies for bone diseases.
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Affiliation(s)
- David Keinan
- Department of Oral Biology, School of Dental Medicine, University at Buffalo, The State University of New York, 3435 Main Street, Buffalo, NY 14214
| | - Shuying Yang
- Department of Oral Biology, School of Dental Medicine, University at Buffalo, The State University of New York, 3435 Main Street, Buffalo, NY 14214
| | - Robert E Cohen
- Department of Periodontics and Endodontics, School of Dental Medicine, University at Buffalo, The State University of New York, 3435 Main Street, Buffalo, NY, 14214, USA
| | - Xue Yuan
- Department of Oral Biology School of Dental Medicine, University at Buffalo, The State University of New York, B36 Foster Hall, Buffalo, NY 14214
| | - Tongjun Liu
- Department of Oral Biology School of Dental Medicine, University at Buffalo, The State University of New York, B36 Foster Hall, Buffalo, NY 14214
| | - Yi-Ping Li
- Department of Pathology, University of Alabama at Birmingham (UAB), 1825 University Blvd, Birmingham AL 35294, USA
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Bodle CR, Mackie DI, Roman DL. RGS17: an emerging therapeutic target for lung and prostate cancers. Future Med Chem 2013; 5:995-1007. [PMID: 23734683 PMCID: PMC3865709 DOI: 10.4155/fmc.13.91] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Ligands for G-protein-coupled receptors (GPCRs) represent approximately 50% of currently marketed drugs. RGS proteins modulate heterotrimeric G proteins and, thus, GPCR signaling, by accelerating the intrinsic GTPase activity of the Gα subunit. Given the prevalence of GPCR targeted therapeutics and the role RGS proteins play in G protein signaling, some RGS proteins are emerging as targets in their own right. One such RGS protein is RGS17. Increased RGS17 expression in some prostate and lung cancers has been demonstrated to support cancer progression, while reduced expression of RGS17 can lead to development of chemotherapeutic resistance in ovarian cancer. High-throughput screening is a powerful tool for lead compound identification, and utilization of high-throughput technologies has led to the discovery of several RGS inhibitors, thus far. As screening technologies advance, the identification of novel lead compounds the subsequent development of targeted therapeutics appears promising.
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Affiliation(s)
- Christopher R Bodle
- The Department of Pharmaceutical Sciences & Experimental Therapeutics, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Division of Medicinal & Natural Products Chemistry, University of Iowa, College of Pharmacy, Iowa City, IA, USA
| | - Duncan I Mackie
- The Department of Pharmaceutical Sciences & Experimental Therapeutics, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Division of Medicinal & Natural Products Chemistry, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Cancer Signaling and Experimental Therapeutics Program, The Holden Comprehensive Cancer Center, University of Iowa Hospitals & Clinics, Iowa City, IA, USA
| | - David L Roman
- The Department of Pharmaceutical Sciences & Experimental Therapeutics, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Division of Medicinal & Natural Products Chemistry, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Cancer Signaling and Experimental Therapeutics Program, The Holden Comprehensive Cancer Center, University of Iowa Hospitals & Clinics, Iowa City, IA, USA
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Jones DL, Tuomi JM, Chidiac P. Role of Cholinergic Innervation and RGS2 in Atrial Arrhythmia. Front Physiol 2012; 3:239. [PMID: 22754542 PMCID: PMC3386567 DOI: 10.3389/fphys.2012.00239] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2011] [Accepted: 06/12/2012] [Indexed: 01/25/2023] Open
Abstract
The heart receives sympathetic and parasympathetic efferent innervation as well as the ability to process information internally via an intrinsic cardiac autonomic nervous system (ICANS). For over a century, the role of the parasympathetics via vagal acetylcholine release was related to controlling primarily heart rate. Although in the late 1800s shown to play a role in atrial arrhythmia, the myocardium took precedence from the mid-1950s until in the last decade a resurgence of interest in the autonomics along with signaling cascades, regulators, and ion channels. Originally ignored as being benign and thus untreated, recent emphasis has focused on atrial arrhythmia as atrial fibrillation (AF) is the most common arrhythmia seen by the general practitioner. It is now recognized to have significant mortality and morbidity due to resultant stroke and heart failure. With the aging population, there will be an unprecedented increased burden on health care resources. Although it has been known for more than half a century that cholinergic stimulation can initiate AF, the classical concept focused on the M2 receptor and its signaling cascade including RGS4, as these had been shown to have predominant effects on nodal function (heart rate and conduction block) as well as contractility. However, recent evidence suggests that the M3 receptor may also playa role in initiation and perpetuation of AF and thus RGS2, a putative regulator of the M3 receptor, may be a target for therapeutic intervention. Mice lacking RGS2 (RGS2−/−), were found to have significantly altered electrophysiological atrial responses and were more susceptible to electrically induced AF. Vagally induced or programmed stimulation-induced AF could be blocked by the selective M3R antagonist, darifenacin. These results suggest a potential surgical target (ICANS) and pharmacological targets (M3R, RGS2) for the management of AF.
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Affiliation(s)
- Douglas L Jones
- Department of Physiology and Pharmacology, The University of Western Ontario London, ON, Canada
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21
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Mighiu AS, Heximer SP. Controlling Parasympathetic Regulation of Heart Rate: A Gatekeeper Role for RGS Proteins in the Sinoatrial Node. Front Physiol 2012; 3:204. [PMID: 22707940 PMCID: PMC3374348 DOI: 10.3389/fphys.2012.00204] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Accepted: 05/23/2012] [Indexed: 11/13/2022] Open
Abstract
Neurotransmitters released from sympathetic and parasympathetic nerve terminals in the sinoatrial node (SAN) exert their effects via G-protein-coupled receptors. Integration of these different G-protein signals within pacemaker cells of the SAN is critical for proper regulation of heart rate and function. For example, excessive parasympathetic signaling can be associated with sinus node dysfunction (SND) and supraventricular arrhythmias. Our previous work has shown that one member of the regulator of G-protein signaling (RGS) protein family, RGS4, is highly and selectively expressed in pacemaker cells of the SAN. Consistent with its role as an inhibitor of parasympathetic signaling, RGS4-knockout mice have reduced basal heart rates and enhanced negative chronotropic responses to parasympathetic agonists. Moreover, RGS4 appears to be an important part of SA nodal myocyte signaling pathways that mediate G-protein-coupled inwardly rectifying potassium channel (GIRK) channel activation/deactivation and desensitization. Since RGS4 acts immediately downstream of M2 muscarinic receptors, it is tempting to speculate that RGS4 functions as a master regulator of parasympathetic signaling upstream of GIRKs, HCNs, and L-type Ca2+ channels in the SAN. Thus, loss of RGS4 function may lead to increased susceptibility to conditions associated with increased parasympathetic signaling, including bradyarrhythmia, SND, and atrial fibrillation.
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Affiliation(s)
- Alexandra S Mighiu
- Department of Physiology, Heart and Stroke/Richard Lewar Centre of Excellence in Cardiovascular Research, University of Toronto Toronto, ON, Canada
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22
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Sjögren B, Parra S, Heath LJ, Atkins KB, Xie ZJ, Neubig RR. Cardiotonic steroids stabilize regulator of G protein signaling 2 protein levels. Mol Pharmacol 2012; 82:500-9. [PMID: 22695717 DOI: 10.1124/mol.112.079293] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Regulator of G protein signaling 2 (RGS2), a G(q)-specific GTPase-activating protein, is strongly implicated in cardiovascular function. RGS2(-/-) mice are hypertensive and prone to heart failure, and several rare human mutations that accelerate RGS2 degradation have been identified among patients with hypertension. Therefore, pharmacological up-regulation of RGS2 protein levels might be beneficial. We used a β-galactosidase complementation method to screen several thousand compounds with known pharmacological functions for those that increased RGS2 protein levels. Several cardiotonic steroids (CTSs), including ouabain and digoxin, increased RGS2 but not RGS4 protein levels. CTSs increased RGS2 protein levels through a post-transcriptional mechanism, by slowing protein degradation. RGS2 mRNA levels in primary vascular smooth muscle cells were unaffected by CTS treatment, whereas protein levels were increased 2- to 3-fold. Na(+)/K(+)-ATPase was required for the increase in RGS2 protein levels, because the effect was lost in Na(+)/K(+)-ATPase-knockdown cells. Furthermore, we demonstrated that CTS-induced increases in RGS2 levels were functional and reduced receptor-stimulated, G(q)-dependent, extracellular signal-regulated kinase phosphorylation. Finally, we showed that in vivo treatment with digoxin led to increased RGS2 protein levels in heart and kidney. CTS-induced increases in RGS2 protein levels and function might modify several deleterious mechanisms in hypertension and heart failure. This novel CTS mechanism might contribute to the beneficial actions of low-dose digoxin treatment in heart failure. Our results support the concept of small-molecule modulation of RGS2 protein levels as a new strategy for cardiovascular therapy.
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Affiliation(s)
- Benita Sjögren
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109, USA
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Kach J, Sethakorn N, Dulin NO. A finer tuning of G-protein signaling through regulated control of RGS proteins. Am J Physiol Heart Circ Physiol 2012; 303:H19-35. [PMID: 22542620 DOI: 10.1152/ajpheart.00764.2011] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Regulators of G-protein signaling (RGS) proteins are GTPase-activating proteins (GAP) for various Gα subunits of heterotrimeric G proteins. Through this mechanism, RGS proteins regulate the magnitude and duration of G-protein-coupled receptor signaling and are often referred to as fine tuners of G-protein signaling. Increasing evidence suggests that RGS proteins themselves are regulated through multiple mechanisms, which may provide an even finer tuning of G-protein signaling and crosstalk between G-protein-coupled receptors and other signaling pathways. This review summarizes the current data on the control of RGS function through regulated expression, intracellular localization, and covalent modification of RGS proteins, as related to cell function and the pathogenesis of diseases.
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Affiliation(s)
- Jacob Kach
- Department of Medicine, University of Chicago, Illinois, 60637, USA
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Ang R, Opel A, Tinker A. The Role of Inhibitory G Proteins and Regulators of G Protein Signaling in the in vivo Control of Heart Rate and Predisposition to Cardiac Arrhythmias. Front Physiol 2012; 3:96. [PMID: 22783193 PMCID: PMC3390690 DOI: 10.3389/fphys.2012.00096] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 03/27/2012] [Indexed: 12/17/2022] Open
Abstract
Inhibitory heterotrimeric G proteins and the control of heart rate. The activation of cell signaling pathways involving inhibitory heterotrimeric G proteins acts to slow the heart rate via modulation of ion channels. A large number of Regulators of G protein signalings (RGSs) can act as GTPase accelerating proteins to inhibitory G proteins and thus it is important to understand the network of RGS\G-protein interaction. We will review our recent findings on in vivo heart rate control in mice with global genetic deletion of various inhibitory G protein alpha subunits. We will discuss potential central and peripheral contributions to the phenotype and the controversies in the literature.
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Affiliation(s)
- Richard Ang
- Centre for Clinical Pharmacology, Division of Medicine, University College LondonLondon, UK
| | - Aaisha Opel
- Centre for Clinical Pharmacology, Division of Medicine, University College LondonLondon, UK
| | - Andrew Tinker
- William Harvey Heart Centre, Barts and The London School of Medicine and DentistryLondon, UK
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Stewart A, Huang J, Fisher RA. RGS Proteins in Heart: Brakes on the Vagus. Front Physiol 2012; 3:95. [PMID: 22685433 PMCID: PMC3368389 DOI: 10.3389/fphys.2012.00095] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Accepted: 03/27/2012] [Indexed: 12/14/2022] Open
Abstract
It has been nearly a century since Otto Loewi discovered that acetylcholine (ACh) release from the vagus produces bradycardia and reduced cardiac contractility. It is now known that parasympathetic control of the heart is mediated by ACh stimulation of G(i/o)-coupled muscarinic M2 receptors, which directly activate G protein-coupled inwardly rectifying potassium (GIRK) channels via Gβγ resulting in membrane hyperpolarization and inhibition of action potential (AP) firing. However, expression of M2R-GIRK signaling components in heterologous systems failed to recapitulate native channel gating kinetics. The missing link was identified with the discovery of regulator of G protein signaling (RGS) proteins, which act as GTPase-activating proteins to accelerate the intrinsic GTPase activity of Gα resulting in termination of Gα- and Gβγ-mediated signaling to downstream effectors. Studies in mice expressing an RGS-insensitive Gα(i2) mutant (G184S) implicated endogenous RGS proteins as key regulators of parasympathetic signaling in heart. Recently, two RGS proteins have been identified as critical regulators of M2R signaling in heart. RGS6 exhibits a uniquely robust expression in heart, especially in sinoatrial (SAN) and atrioventricular nodal regions. Mice lacking RGS6 exhibit increased bradycardia and inhibition of SAN AP firing in response to CCh as well as a loss of rapid activation and deactivation kinetics and current desensitization for ACh-induced GIRK current (I(KACh)). Similar findings were observed in mice lacking RGS4. Thus, dysregulation in RGS protein expression or function may contribute to pathologies involving aberrant electrical activity in cardiac pacemaker cells. Moreover, RGS6 expression was found to be up-regulated in heart under certain pathological conditions, including doxorubicin treatment, which is known to cause life-threatening cardiotoxicity and atrial fibrillation in cancer patients. On the other hand, increased vagal tone may be cardioprotective in heart failure where acetylcholinesterase inhibitors and vagal stimulation have been proposed as potential therapeutics. Together, these studies identify RGS proteins, especially RGS6, as new therapeutic targets for diseases such as sick sinus syndrome or other maladies involving abnormal autonomic control of the heart.
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Affiliation(s)
- Adele Stewart
- Department of Pharmacology, Carver College of Medicine, University of Iowa Iowa City, IA, USA
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Zhang H, Gu S, Al-Sabeq B, Wang S, He J, Tam A, Cifelli C, Mathalone N, Tirgari S, Boyd S, Heximer SP. Origin-specific epigenetic program correlates with vascular bed-specific differences in Rgs5 expression. FASEB J 2011; 26:181-91. [PMID: 21965603 DOI: 10.1096/fj.11-185454] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Cells from multiple origins contribute to vascular smooth muscle cell (VSMC) development. Phenotypic heterogeneity of VSMCs is associated with their point of developmental origin; however, the mechanisms driving such differences are unknown. We here examined the mechanisms controlling vascular bed-specific differences in Rgs5 expression during development. Rgs5 levels were similar across different regions of the vasculature in neonatal animals but were >15-fold higher in descending aortas compared with carotid arteries of adult mice. Thus, vessel bed-specific changes in regulation of Rgs5 expression occurred during vessel maturation. Examination of adult Rgs5-LacZ reporter mice revealed lower Rgs5 expression in VSMCs originating from the third (carotid artery) branchial arch compared with those originating in the fourth and sixth (aortic B segment, right subclavian, and ductus arteriosus) branchial arches. Indeed, a mosaic Rgs5 expression pattern, with discreet LacZ boundaries between VSMCs derived from different developmental origins, was observed. Furthermore, Rgs5-LacZ expression was correlated with the site of VSMC origin (splanchic mesoderm ≈ local mesenchyme > somites > proepicardium > mesothelium). Surprisingly, Rgs5 reporter activity in cultured carotid artery- and descending aorta-derived cells did not recapitulate the differences observed in vivo. Consistent with a developmental origin-specific epigenetic mechanism driving the observed expression differences in vivo, the Rgs5 promoter showed increased methylation on CpG dinucleotides in carotid arteries compared with that in descending aortas in adult but not in neonatal mice. In vitro methylation of the Rgs5 promoter confirmed that its activity is sensitive to transcriptional down-regulation by CpG methylation. These data suggest that an origin-dependent epigenetic program regulates vascular bed- and maturation state-dependent regulation of VSMC-specific gene transcription.
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Affiliation(s)
- Hangjun Zhang
- Department of Physiology, Heart, and Stroke, University of Toronto, Toronto, ON Canada
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27
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Abstract
Signal transduction through G-protein-coupled receptors (GPCRs) is central for the regulation of virtually all cellular functions and has been widely implicated in human disease. Regulators of G-protein signaling (RGS proteins) belong to a diverse protein family that was originally discovered for their ability to accelerate signal termination in response to GPCR stimulation, thereby reducing the amplitude and duration of GPCR effects. All RGS proteins share a common RGS domain that interacts with G protein α subunits and mediates their biological regulation of GPCR signaling. However, RGS proteins differ widely in size and the organization of their sequences flanking the RGS domain, which contain several additional functional domains that facilitate protein-protein (or protein-lipid) interactions. RGS proteins are subject to posttranslational modifications, and, in addition, their expression, activity, and subcellular localization can be dynamically regulated. Thus, there exists a wide array of mechanisms that facilitate their proper function as modulators and integrators of G-protein signaling. Several RGS proteins have been implicated in the cardiac remodeling response and heart rate regulation, and changes in RGS protein expression and/or function are believed to participate in the pathophysiology of cardiac hypertrophy, failure and arrhythmias as well as hypertension. This review is based on recent advances in our understanding of the expression pattern, regulation, and functional role of canonical RGS proteins, with a special focus on the healthy heart and the diseased heart. In addition, we discuss their potential and promise as therapeutic targets as well as strategies to modulate their expression and function.
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Affiliation(s)
- Peng Zhang
- Cardiovascular Research Center, Rhode Island Hospital and Alpert Medical School of Brown University, 1 Hoppin St, Providence, RI 02903, USA
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Sibbel SP, Talbert ME, Bowden DW, Haffner SM, Taylor KD, Chen YDI, Wagenknecht LE, Langefeld CD, Norris JM. RGS6 variants are associated with dietary fat intake in Hispanics: the IRAS Family Study. Obesity (Silver Spring) 2011; 19:1433-8. [PMID: 21233807 PMCID: PMC3683650 DOI: 10.1038/oby.2010.333] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Recently, a genome-wide association scan was completed in the IRAS (Insulin Resistance Atherosclerosis Study) Family Study (IRASFS) Hispanic-American cohort. Multiple single-nucleotide polymorphisms (SNPs) in the G-protein signaling 6 (RGS6) gene were found to be associated with adiposity phenotypes. RGS6 has shown downstream antagonistic interplay with opioid receptors, targets of fatty/sugary food agonists. The possibility that RGS6 promotes tolerance and tachyphylaxis among the opioid receptor is a plausible pathway for overconsuming fat/sugar-laden food. Therefore, we hypothesized that RGS6 variants are associated with intake of fatty/sugary foods. In 932 Hispanics from San Antonio and San Luis Valley, CO, the following dietary intake variables were assessed using the Block Brief 2000 food frequency questionnaire: total calories, total fat, % calories from fat, % calories from saturated fat, protein, % calories from protein, carbohydrates, % calories from carbohydrates, and daily frequency of servings of fats/oils/sweets. We tested for association between 23 SNPs in RGS6 and dietary intake using a variance components measured genotype approach. All models were adjusted for gender, recruitment site, admixture, BMI, and age. Using an additive genetic model, rs1402064 was associated with higher intake of fats/oils/sweets, total calories, total fat and saturated fat (P = 0.0007, 0.026, 0.023, and 0.024). SNPs rs847330 and rs847354 were associated with higher intake of fats/oils/sweets (P = 0.002 and 0.018), total fat (P = 0.040 and 0.048) and saturated fat (P = 0.044 and 0.041). Finally, rs769148 was associated with higher intake of fats/oils/sweets (P = 0.002). RGS6 is a new candidate gene for adiposity traits that may be associated with a behavioral tendency toward fat-laden food intake.
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Affiliation(s)
- Scott P. Sibbel
- Department of Epidemiology, Colorado School of Public Health, University of Colorado Denver, Aurora, Colorado, USA
| | - Matthew E. Talbert
- Department of Biochemistry, Wake Forest University, Winston-Salem, North Carolina, USA
| | - Donald W. Bowden
- Department of Biochemistry, Wake Forest University, Winston-Salem, North Carolina, USA
| | - Steve M. Haffner
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - Kent D. Taylor
- Medical Genetics Institute, Burns and Allen Cedars-Sinai Research Institute, Los Angeles, California, USA
| | - Yii-Der I. Chen
- Medical Genetics Institute, Burns and Allen Cedars-Sinai Research Institute, Los Angeles, California, USA
| | - Lynne E. Wagenknecht
- Department of Epidemiology, Division of Public Health Sciences, Wake Forest University, Winston-Salem, North Carolina, USA
| | - Carl D. Langefeld
- Department of Biostatistical Sciences, Division of Public Health Sciences, Wake Forest University, Winston-Salem, North Carolina, USA.
| | - Jill M. Norris
- Department of Epidemiology, Colorado School of Public Health, University of Colorado Denver, Aurora, Colorado, USA
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Zhang P, Su J, King ME, Maldonado AE, Park C, Mende U. Regulator of G protein signaling 2 is a functionally important negative regulator of angiotensin II-induced cardiac fibroblast responses. Am J Physiol Heart Circ Physiol 2011; 301:H147-56. [PMID: 21498776 DOI: 10.1152/ajpheart.00026.2011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cardiac fibroblasts play a key role in fibrosis development in response to stress and injury. Angiotensin II (ANG II) is a major profibrotic activator whose downstream effects (such as phospholipase Cβ activation, cell proliferation, and extracellular matrix secretion) are mainly mediated via G(q)-coupled AT(1) receptors. Regulators of G protein signaling (RGS), which accelerate termination of G protein signaling, are expressed in the myocardium. Among them, RGS2 has emerged as an important player in modulating G(q)-mediated hypertrophic remodeling in cardiac myocytes. To date, no information is available on RGS in cardiac fibroblasts. We tested the hypothesis that RGS2 is an important regulator of ANG II-induced signaling and function in ventricular fibroblasts. Using an in vitro model of fibroblast activation, we have demonstrated expression of several RGS isoforms, among which only RGS2 was transiently upregulated after short-term ANG II stimulation. Similar results were obtained in fibroblasts isolated from rat hearts after in vivo ANG II infusion via minipumps for 1 day. In contrast, prolonged ANG II stimulation (3-14 days) markedly downregulated RGS2 in vivo. To delineate the functional effects of RGS expression changes, we used gain- and loss-of-function approaches. Adenovirally infected RGS2 had a negative regulatory effect on ANG II-induced phospholipase Cβ activity, cell proliferation, and total collagen production, whereas RNA interference of endogenous RGS2 had opposite effects, despite the presence of several other RGS. Together, these data suggest that RGS2 is a functionally important negative regulator of ANG II-induced cardiac fibroblast responses that may play a role in ANG II-induced fibrosis development.
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Affiliation(s)
- Peng Zhang
- Cardiovascular Research Center, Rhode Island Hospital and Alpert Medical School of Brown Univ., 1 Hoppin St., Providence, RI 02903, USA.
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Matsuzaki N, Nishiyama M, Song D, Moroi K, Kimura S. Potent and selective inhibition of angiotensin AT1 receptor signaling by RGS2: roles of its N-terminal domain. Cell Signal 2011; 23:1041-9. [PMID: 21291998 DOI: 10.1016/j.cellsig.2011.01.023] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Revised: 01/05/2011] [Accepted: 01/24/2011] [Indexed: 11/24/2022]
Abstract
Emerging evidence indicates that R4/B subfamily RGS (regulator of G protein signaling) proteins play roles in functional regulation in the cardiovascular system. In this study, we compared effects of three R4/B subfamily proteins, RGS2, RGS4 and RGS5 on angiotensin AT1 receptor signaling, and investigated roles of the N-terminus of RGS2. In HEK293T cells expressing AT1 receptor stably, intracellular Ca(2+) responses induced by angiotensin II were much more strongly attenuated by RGS2 than by RGS4 and RGS5. N-terminally deleted RGS2 proteins lost this potent inhibitory effect. Replacement of the N-terminal residues 1-71 of RGS2 with the corresponding residues (1-51) of RGS5 decreased significantly the inhibitory effect. On the other hand, replacement of the residues 1-51 of RGS5 with the residues 1-71 of RGS2 increased the inhibitory effect dramatically. Furthermore, we investigated functional contribution of N-terminal subdomains of RGS2, namely, an N-terminal region (residues 16-55) with an amphipathic α helix domain (the subdomain N1), a probable non-specific membrane-targeting subdomain, and another region (residues 56-71) between the α helix and the RGS box (the subdomain N2), a probable GPCR-recognizing subdomain. RGS2 chimera proteins with the residues 1-33 or 34-52 of RGS5 showed weak inhibitory activity, and either of RGS5 chimera proteins with residues 1-55 or 56-71 of RGS2 showed strong inhibitory effects on AT1 receptor signaling. The present study indicates the essential roles of both N-terminal subdomains for the potent inhibitory activity of RGS2 on AT1 receptor signaling.
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Affiliation(s)
- Naoko Matsuzaki
- Department of Biochemistry and Molecular Pharmacology, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan
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Kaur K, Kehrl JM, Charbeneau RA, Neubig RR. RGS-insensitive Gα subunits: probes of Gα subtype-selective signaling and physiological functions of RGS proteins. Methods Mol Biol 2011; 756:75-98. [PMID: 21870221 DOI: 10.1007/978-1-61779-160-4_4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The Regulator of G protein Signaling (RGS) proteins were identified as a family in 1996 and humans have more than 30 such proteins. Their best known function is to suppress G Protein-Coupled Receptors (GPCR) signaling by increasing the rate of Gα turnoff through stimulation of GTPase activity (i.e., GTPase acceleration protein or GAP activity). The GAP activity of RGS proteins on the Gαi and Gαq family of G proteins can terminate signals initiated by both α and βγ subunits. RGS proteins also serve as scaffolds, assembling signal-regulating modules. Understanding the physiological roles of RGS proteins is of great importance, as GPCRs are major targets for drug development. The traditional method of using RGS knockout mice has provided some information about the role of RGS proteins but in many cases effects are modest, perhaps because of redundancy in RGS protein function. As an alternative approach, we have utilized a glycine-to-serine mutation in the switch 1 region of Gα subunits that prevents RGS binding. The mutation has no known effects on Gα binding to receptor, Gβγ, or effectors. Alterations in function resulting from the G>S mutation imply a role for both the specific mutated Gα subunit and its regulation by RGS protein activity. Mutant rodents expressing these G>S mutant Gα subunits have strong phenotypes and provide important information about specific physiological functions of Gαi2 and Gαo and their control by RGS. The conceptual framework behind this approach and a summary of recent results is presented in this chapter.
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Affiliation(s)
- Kuljeet Kaur
- Department of Pharmacology, The University of Michigan Medical School, Ann Arbor, MI, USA
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Posokhova E, Wydeven N, Allen KL, Wickman K, Martemyanov KA. RGS6/Gβ5 complex accelerates IKACh gating kinetics in atrial myocytes and modulates parasympathetic regulation of heart rate. Circ Res 2010; 107:1350-4. [PMID: 20884879 DOI: 10.1161/circresaha.110.224212] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
RATIONALE The parasympathetic reduction in heart rate involves the sequential activation of m2 muscarinic cholinergic receptors (m(2)Rs), pertussis toxin-sensitive (Gi/o) heterotrimeric G proteins, and the atrial potassium channel I(KACh). Molecular mechanisms regulating this critical signal transduction pathway are not fully understood. OBJECTIVE To determine whether the G protein signaling regulator Rgs6/Gβ5 modulates m(2)R-I(KACh) signaling and cardiac physiology. METHODS AND RESULTS Cardiac expression of Rgs6, and its interaction with Gβ5, was demonstrated by immunoblotting and immunoprecipitation. Rgs6(-/-) mice were generated by gene targeting, and the cardiac effects of Rgs6 ablation were analyzed by whole-cell recordings in isolated cardiomyocytes and ECG telemetry. Loss of Rgs6 yielded profound delays in m(2)R-I(KACh) deactivation kinetics in both neonatal atrial myocytes and adult sinoatrial nodal cells. Rgs6(-/-) mice exhibited mild resting bradycardia and altered heart rate responses to pharmacological manipulations that were consistent with enhanced m(2)R-I(KACh) signaling. CONCLUSIONS The cardiac Rgs6/Gβ5 complex modulates the timing of parasympathetic influence on atrial myocytes and heart rate in mice.
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Affiliation(s)
- Ekaterina Posokhova
- Department of Pharmacology, University of Minnesota, Minneapolis, MN 55455, USA
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Yang J, Huang J, Maity B, Gao Z, Lorca RA, Gudmundsson H, Li J, Stewart A, Swaminathan PD, Ibeawuchi SR, Shepherd A, Chen CK, Kutschke W, Mohler PJ, Mohapatra DP, Anderson ME, Fisher RA. RGS6, a modulator of parasympathetic activation in heart. Circ Res 2010; 107:1345-9. [PMID: 20864673 DOI: 10.1161/circresaha.110.224220] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Parasympathetic regulation of heart rate is mediated by acetylcholine binding to G protein-coupled muscarinic M2 receptors, which activate heterotrimeric G(i/o) proteins to promote G protein-coupled inwardly rectifying K(+) (GIRK) channel activation. Regulator of G protein signaling (RGS) proteins, which function to inactivate G proteins, are indispensable for normal parasympathetic control of the heart. However, it is unclear which of the more than 20 known RGS proteins function to negatively regulate and thereby ensure normal parasympathetic control of the heart. OBJECTIVE To examine the specific contribution of RGS6 as an essential regulator of parasympathetic signaling in heart. METHODS AND RESULTS We developed RGS6 knockout mice to determine the functional impact of loss of RGS6 on parasympathetic regulation of cardiac automaticity. RGS6 exhibited a uniquely robust expression in the heart, particularly in sinoatrial and atrioventricular nodal regions. Loss of RGS6 provoked dramatically exaggerated bradycardia in response to carbachol in mice and isolated perfused hearts and significantly enhanced the effect of carbachol on inhibition of spontaneous action potential firing in sinoatrial node cells. Consistent with a role of RGS6 in G protein inactivation, RGS6-deficient atrial myocytes exhibited a significant reduction in the time course of acetylcholine-activated potassium current (I(K)(ACh)) activation and deactivation, as well as the extent of I(K)(ACh) desensitization. CONCLUSIONS RGS6 is a previously unrecognized, but essential, regulator of parasympathetic activation in heart, functioning to prevent parasympathetic override and severe bradycardia. These effects likely result from actions of RGS6 as a negative regulator of G protein activation of GIRK channels.
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Affiliation(s)
- Jianqi Yang
- Department of Pharmacology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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Tuomi JM, Chidiac P, Jones DL. Evidence for enhanced M3 muscarinic receptor function and sensitivity to atrial arrhythmia in the RGS2-deficient mouse. Am J Physiol Heart Circ Physiol 2009; 298:H554-61. [PMID: 19966055 DOI: 10.1152/ajpheart.00779.2009] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Atrial fibrillation (AF) is the most common arrhythmia seen in general practice. Muscarinic ACh receptors (M2R, M3R) are involved in vagally induced AF. M2R and M3R activate the heterotrimeric G proteins, G(i) and G(q), respectively, by promoting GTP binding, and these in turn activate distinct K(+) channels. Signaling is terminated by GTP hydrolysis, a process accelerated by regulator of G protein signaling (RGS) proteins. RGS2 is selective for G(q) and thus may regulate atrial M3R signaling. We hypothesized that knockout of RGS2 (RGS2(-/-)) would render the atria more susceptible to electrically induced AF. One-month-old male RGS2(-/-) and C57BL/6 wild-type (WT) mice were instrumented for intracardiac electrophysiology. Atrial effective refractory periods (AERPs) were also determined in the absence and presence of carbachol, atropine, and/or the selective M3R antagonist darifenacin. Susceptibility to electrically induced AF used burst pacing and programmed electrical stimulation with one extrastimulus. Real-time RT-PCR measured atrial and ventricular content of RGS2, RGS4, M2R, M3R, and M4R mRNA. AERP was lower in RGS2(-/-) compared with WT mice in both the high right atrium (HRA) (30 +/- 1 vs. 34 +/- 1 ms, P < 0.05) and mid right atrium (MRA) (21 +/- 1 vs. 24 +/- 1 ms, P < 0.05). Darifenacin eliminated this difference (HRA: 37 +/- 2 vs. 39 +/- 2 ms, and MRA: 30 +/- 2 vs. 30 +/- 1, P > 0.4). RGS2(-/-) were more susceptible than WT mice to atrial tachycardia/fibrillation (AT/F) induction (11/22 vs. 1/25, respectively, P < 0.05). Muscarinic receptor expression did not differ between strains, whereas M2R expression was 70-fold higher than M3R (P < 0.01). These results suggest that RGS2 is an important cholinergic regulator in the atrium and that RGS2(-/-) mice have enhanced susceptibility to AT/F via enhanced M3 muscarinic receptor activity.
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Affiliation(s)
- Jari M Tuomi
- Department of Physiology and Pharmacology, University of Western Ontario, London Health Science Center, London, Ontario, Canada
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Slepak VZ. Structure, function, and localization of Gβ5-RGS complexes. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2009; 86:157-203. [PMID: 20374716 DOI: 10.1016/s1877-1173(09)86006-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Members of the R7 subfamily of regulator of G protein signaling (RGS) proteins (RGS6, 7, 9, and 11) exist as heterodimers with the G protein beta subunit Gβ5. These protein complexes are only found in neurons and are defined by the presence of three domains: DEP/DHEX, Gβ5/GGL, and RGS. This article summarizes published work in the following areas: (1) the functional significance of structural organization of Gβ5-R7 complexes, (2) regional distribution of Gβ5-R7 in the nervous system and regulation of R7 family expression, (3) subcellular localization of Gβ5-R7 complexes, and (4) novel binding partners of Gβ5-R7 proteins. The review points out some contradictions between observations made by different research groups and highlights the importance of using alternative experimental approaches to obtain conclusive information about Gβ5-R7 function in vivo.
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Affiliation(s)
- Vladlen Z Slepak
- Department of Molecular and Cellular Pharmacology and the Neuroscience Program, University of Miami School of Medicine, Miami, Florida 33136, USA
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McGrath MF, de Bold AJ. Transcriptional analysis of the mammalian heart with special reference to its endocrine function. BMC Genomics 2009; 10:254. [PMID: 19486520 PMCID: PMC2694839 DOI: 10.1186/1471-2164-10-254] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2008] [Accepted: 06/01/2009] [Indexed: 12/19/2022] Open
Abstract
Background Pharmacological and gene ablation studies have demonstrated the crucial role of the endocrine function of the heart as mediated by the polypeptide hormones ANF and BNP in the maintenance of cardiovascular homeostasis. The importance of these studies lies on the fact that hypertension and chronic congestive heart failure are clinical entities that may be regarded as states of relative deficiency of ANF and BNP. These hormones are produced by the atrial muscle cells (cardiocytes), which display a dual secretory/muscle phenotype. In contrast, ventricular cardiocytes display mainly a muscle phenotype. Comparatively little information is available regarding the genetic background for this important phenotypic difference with particular reference to the endocrine function of the heart. We postulated that comparison of gene expression profiles between atrial and ventricular muscles would help identify gene transcripts that underlie the phenotypic differences associated with the endocrine function of the heart. Results Comparison of gene expression profiles in the rat heart revealed a total of 1415 differentially expressed genes between the atria and ventricles based on a 1.8 fold cut-off. The identification of numerous chamber specific transcripts, such as ANF for the atria and Irx4 for the ventricles among several others, support the soundness of the GeneChip data and demonstrates that the differences in gene expression profiles observed between the atrial and ventricular tissues were not spurious in nature. Pathway analysis revealed unique expression profiles in the atria for G protein signaling that included Gαo1, Gγ2 and Gγ3, AGS1, RGS2, and RGS6 and the related K+ channels GIRK1 and GIRK4. Transcripts involved in vesicle trafficking, hormone secretion as well as mechanosensors (e.g. the potassium channel TREK-1) were identified in relationship to the synthesis, storage and secretion of hormones. Conclusion The data developed in this investigation describes for the first time data on gene expression particularly centred on the secretory function of the heart. This provides for a rational approach in the investigation of determinants of the endocrine of the heart in health and disease.
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Affiliation(s)
- Monica Forero McGrath
- Department of Cellular Molecular Medicine, Faculty of Medicine, Cardiovascular Endocrinology Laboratory, University of Ottawa Heart Institute, Ottawa, Canada.
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RGS proteins: identifying new GAPs in the understanding of blood pressure regulation and cardiovascular function. Clin Sci (Lond) 2009; 116:391-9. [PMID: 19175357 DOI: 10.1042/cs20080272] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Understanding the mechanisms that underlie BP (blood pressure) variation in humans and animal models may provide important clues for reducing the burden of uncontrolled hypertension in industrialized societies. High BP is often associated with increased signalling via G-protein-coupled receptors. Three members of the RGS (regulator of G-protein signalling) superfamily RGS2, RGS4 and RGS5 have been implicated in the attenuation of G-protein signalling pathways in vascular and cardiac myocytes, as well as cells of the kidney and autonomic nervous system. In the present review, we discuss the current state of knowledge regarding their differential expression and function in cardiovascular tissues, and the likelihood that one or more of these alleles are candidate hypertension genes. Together, findings from the studies described herein suggest that development of methods to modulate the expression and function of RGS proteins may be a possible strategy for the treatment and prevention of hypertension and cardiovascular disease.
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Small molecule protein-protein interaction inhibitors as CNS therapeutic agents: current progress and future hurdles. Neuropsychopharmacology 2009; 34:126-41. [PMID: 18800065 DOI: 10.1038/npp.2008.151] [Citation(s) in RCA: 131] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Protein-protein interactions are a crucial element in cellular function. The wealth of information currently available on intracellular-signaling pathways has led many to appreciate the untapped pool of potential drug targets that reside downstream of the commonly targeted receptors. Over the last two decades, there has been significant interest in developing therapeutics and chemical probes that inhibit specific protein-protein interactions. Although it has been a challenge to develop small molecules that are capable of occluding the large, often relatively featureless protein-protein interaction interface, there are increasing numbers of examples of small molecules that function in this manner with reasonable potency. This article will highlight the current progress in the development of small molecule protein-protein interaction inhibitors that have applications in the treatment or study of central nervous system function and disease. In particular, we will focus upon recent work towards developing small molecule inhibitors of amyloid-beta and alpha-synuclein aggregation, inhibitors of critical components of G-protein-signaling pathways, and PDZ domain inhibitors.
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Stuart Gibbons A, Scarr E, McOmish CE, Hannan AJ, Thomas EA, Dean B. Regulator of G-protein signalling 4 expression is not altered in the prefrontal cortex in schizophrenia. Aust N Z J Psychiatry 2008; 42:740-5. [PMID: 18622782 DOI: 10.1080/00048670802206338] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
OBJECTIVES Regulator of G-protein signalling 4 (RGS4) modulates signal transduction through several neurotransmitter receptor systems associated with the pathology of schizophrenia. A reported decrease in RGS4 expression in the prefrontal cortex of schizophrenia patients followed by supporting evidence from association studies implicated RGS4 as a susceptibility gene for schizophrenia. Subsequent efforts to extend these findings in post-mortem brain tissue have produced conflicting results. The aim of the present study was to reconcile these discrepancies by examining RGS4 expression in the dorsolateral prefrontal and parietal cortices from subjects with schizophrenia. METHODS RGS4 mRNA and protein levels were measured in post-mortem Brodmann area (BA)9 and BA40 tissue from 19 schizophrenia patients subjects and 19 pair-matched controls using in situ hybridization and western blotting. RESULTS Levels of RGS4 mRNA (F(1,73)=1.845; p >0.05) or protein (F(1,72)=3.336 x 10(-4), p >0.05) did not vary significantly with diagnosis in BA9 or BA40 from subjects with schizophrenia. CONCLUSIONS Altered RGS4 expression is not universally present throughout the cortex of people with schizophrenia.
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Affiliation(s)
- Andrew Stuart Gibbons
- Rebecca L. Cooper Research Laboratories, Mental Health Research Institute of Victoria, Parkville, Vic., Australia.
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Cifelli C, Rose RA, Zhang H, Voigtlaender-Bolz J, Bolz SS, Backx PH, Heximer SP. RGS4 regulates parasympathetic signaling and heart rate control in the sinoatrial node. Circ Res 2008; 103:527-35. [PMID: 18658048 DOI: 10.1161/circresaha.108.180984] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Heart rate is controlled by the opposing activities of sympathetic and parasympathetic inputs to pacemaker myocytes in the sinoatrial node (SAN). Parasympathetic activity on nodal myocytes is mediated by acetylcholine-dependent stimulation of M(2) muscarinic receptors and activation of Galpha(i/o) signaling. Although regulators of G protein signaling (RGS) proteins are potent inhibitors of Galpha(i/o) signaling in many tissues, the RGS protein(s) that regulate parasympathetic tone in the SAN are unknown. Our results demonstrate that RGS4 mRNA levels are higher in the SAN compared to right atrium. Conscious freely moving RGS4-null mice showed increased bradycardic responses to parasympathetic agonists compared to wild-type animals. Moreover, anesthetized RGS4-null mice had lower baseline heart rates and greater heart rate increases following atropine administration. Retrograde-perfused hearts from RGS4-null mice showed enhanced negative chronotropic responses to carbachol, whereas SAN myocytes showed greater sensitivity to carbachol-mediated reduction in the action potential firing rate. Finally, RGS4-null SAN cells showed decreased levels of G protein-coupled inward rectifying potassium (GIRK) channel desensitization and altered modulation of acetylcholine-sensitive potassium current (I(KACh)) kinetics following carbachol stimulation. Taken together, our studies establish that RGS4 plays an important role in regulating sinus rhythm by inhibiting parasympathetic signaling and I(KACh) activity.
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Affiliation(s)
- Carlo Cifelli
- Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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Hendriks-Balk MC, Peters SLM, Michel MC, Alewijnse AE. Regulation of G protein-coupled receptor signalling: focus on the cardiovascular system and regulator of G protein signalling proteins. Eur J Pharmacol 2008; 585:278-91. [PMID: 18410914 DOI: 10.1016/j.ejphar.2008.02.088] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2008] [Revised: 01/18/2008] [Accepted: 02/06/2008] [Indexed: 11/17/2022]
Abstract
G protein-coupled receptors (GPCRs) are involved in many biological processes. Therefore, GPCR function is tightly controlled both at receptor level and at the level of signalling components. Well-known mechanisms by which GPCR function can be regulated comprise desensitization/resensitization processes and GPCR up- and downregulation. GPCR function can also be regulated by several proteins that directly interact with the receptor and thereby modulate receptor activity. An additional mechanism by which receptor signalling is regulated involves an emerging class of proteins, the so-called regulators of G protein signalling (RGS). In this review we will describe some of these control mechanisms in more detail with some specific examples in the cardiovascular system. In addition, we will provide an overview on RGS proteins and the involvement of RGS proteins in cardiovascular function.
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Affiliation(s)
- Mariëlle C Hendriks-Balk
- Department Pharmacology and Pharmacotherapy, Academic Medical Center, Amsterdam, The Netherlands
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Bender K, Nasrollahzadeh P, Timpert M, Liu B, Pott L, Kienitz MC. A role for RGS10 in beta-adrenergic modulation of G-protein-activated K+ (GIRK) channel current in rat atrial myocytes. J Physiol 2008; 586:2049-60. [PMID: 18276732 DOI: 10.1113/jphysiol.2007.148346] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The effect of beta-adrenergic stimulation on endogenous G-protein-activated K(+) (GIRK) current has been investigated in atrial myocytes from hearts of adult rats. Beta-adrenergic stimulation (10 microm isoprenaline, Iso) had no effect on activation kinetics, peak current or steady-state current but resulted in slowing of deactivation upon washout of acetylcholine (ACh), the time constant (tau(d)) being increased by a factor of about 2.5. The effect of Iso could be mimicked by inclusion of cAMP (500 microm) in the filling solution of the patch clamp pipette. The Iso-induced increase in tau(d) was blocked by the selective beta(1) receptor antagonist CGP-20112A (2 microm) and by the PKA inhibitor H9 (100 microm included in the pipette solution). A candidate for mediating these effects is RGS10, one of the regulators of G-protein signalling (RGS) species expressed in cardiac myocytes. Overexpression of RGS10 by adenoviral gene transfer resulted in a reduction in tau(d) of 60%. Sensitivity of tau(d) to Iso remained in cells overexpressing RGS10. Overexpression of RGS4 caused a comparable reduction in tau(d), which became insensitive to Iso. Expression of an RGS10 carrying a mutation (RGS10-S168A), which deletes a PKA phosphorylation site, caused a decrease in tau(d) comparable to overexpression of wild-type RGS10. Sensitivity of tau(d) to Iso was lost in RGS10-S168A-expressing myocytes. Silencing of RGS10 by means of adenovirus-mediated transcription of a short hairpin RNA did not affect basal tau(d) but removed sensitivity to Iso. These data suggest that endogenous RGS10 has GTPase-activating protein (GAP) activity on the G-protein species that mediates activation of atrial GIRK channels. Moreover, RGS10, via PKA-dependent phosphorylation, enables a crosstalk between beta-adrenergic and muscarinic cholinergic signalling.
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Affiliation(s)
- Kirsten Bender
- Institute of Physiology, Ruhr-University Bochum, D-44780 Bochum, Germany
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Iwai K, Koike M, Ohshima S, Miyatake K, Uchiyama Y, Saeki Y, Ishii M. RGS18 acts as a negative regulator of osteoclastogenesis by modulating the acid-sensing OGR1/NFAT signaling pathway. J Bone Miner Res 2007; 22:1612-20. [PMID: 17576169 DOI: 10.1359/jbmr.070612] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
UNLABELLED We showed that RGS18, a myeloid lineage-specific RGS protein that is inhibited after activation of the RANK/RANKL system, is a negative regulator of osteoclastogenesis. RGS18 acts through an external acidosis-sensing osteoclastogenic mechanism through the OGR1/NFAT pathway. INTRODUCTION Osteoclasts are bone-resorbing multinuclear giant cells that are differentiated from mononuclear macrophage/monocyte lineage precursors stimulated by the RANK/RANKL system. The regulators of G-protein signaling (RGS) family is a diverse group of proteins that accelerate intrinsic GTP hydrolysis on heterotrimeric G-protein alpha subunits and play crucial roles in physiological regulation of G-protein-mediated cell signaling in various tissues and organs. We examined the expression and function of RGS18, a myeloid lineage-specific RGS protein, during osteoclastogenesis. MATERIALS AND METHODS A macrophage/monocyte lineage cell line, RAW264.7, and primary osteoclast precursor monocytes derived from mouse bone marrow cultured with macrophage-colony stimulating factor (M-CSF) (bone marrow-derived monocytes [BMMs]) were used in this study. Both cell types differentiate into osteoclast-like cells on activation by RANKL. Expression of different RGS proteins, including RGS18, was assessed by gene-specific RT-PCR. The subcellular distribution of RGS18 on native osteoclasts in bone tissues, as well as in RAW264.7 cells, was examined by immunohistochemistry using a specific polyclonal antibody. Short interfering RNA against RGS18 was used to inhibit the function endogenous RGS18 in these cell types. Activation of NFATc1, an osteoclastogenic transcription factor, on external acidosis was assessed by visualizing the nuclear localization of NFATc1 visualized with anti-NFATc1 antibody. RESULTS RAW264.7 and BMM cells both expressed mRNA for 10 different mammalian RGS proteins, including RGS18. Expression of RGS18 is significantly inhibited by RANKL both cell types, and inhibition of RGS18 function using RNA interference prominently enhanced osteoclastogenesis on stimulation with RANKL. The effect of RGS18 inhibition was reversed by blocking of proton-sensing OGR1 signaling, and overexpression of exogenous RGS18 inhibited extracellular acidosis-mediated NFATc1 activation. Immunohistochemical studies of mouse bone tissues revealed expression of RGS18 in osteoclasts in vivo. CONCLUSIONS RGS18 acts as a negative regulator of the acidosis-induced osteoclastogenic OGR1/NFAT signaling pathway, and RANKL stimulates osteoclastogenesis by inhibiting expression of RGS18. Therefore, the results suggest a novel control mechanism of osteoclastogenesis by RGS proteins.
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Affiliation(s)
- Kaori Iwai
- Department of Clinical Research, National Hospital Organization, Osaka, Japan
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Fu Y, Huang X, Piao L, Lopatin AN, Neubig RR. Endogenous RGS proteins modulate SA and AV nodal functions in isolated heart: implications for sick sinus syndrome and AV block. Am J Physiol Heart Circ Physiol 2007; 292:H2532-9. [PMID: 17277016 DOI: 10.1152/ajpheart.01391.2006] [Citation(s) in RCA: 40] [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
G protein-coupled receptors play a pivotal role in regulating cardiac automaticity. Their function is controlled by regulator of G protein signaling (RGS) proteins acting as GTPase-activating proteins for Galpha subunits to suppress Galpha(i) and Galpha(q) signaling. Using knock-in mice in which Galpha(i2)-RGS binding and negative regulation are disrupted by a genomic Galpha(i2)G184S (GS) point mutation, we recently (Fu Y, Huang X, Zhong H, Mortensen RM, D'Alecy LG, Neubig RR. Circ Res 98: 659-666, 2006) showed that endogenous RGS proteins suppress muscarinic receptor-mediated bradycardia. To determine whether this was due to direct regulation of cardiac pacemakers or to alterations in the central nervous system or vascular responses, we examined isolated, perfused hearts. Isoproterenol-stimulated beating rates of heterozygote (+/GS) and homozygote (GS/GS) hearts were significantly more sensitive to inhibition by carbachol than were those of wild type (+/+). Even greater effects were seen in the absence of isoproterenol; the potency of muscarinic-mediated bradycardia was enhanced fivefold in GS/GS and twofold in +/GS hearts compared with +/+. A(1)-adenosine receptor-mediated bradycardia was unaffected. In addition to effects on the sinoatrial node, +/GS and GS/GS hearts show significantly increased carbachol-induced third-degree atrioventricular (AV) block. Atrial pacing studies demonstrated an increased PR interval and AV effective refractory period in GS/GS hearts compared with +/+. Thus loss of the inhibitory action of endogenous RGS proteins on Galpha(i2) potentiates muscarinic inhibition of cardiac automaticity and conduction. The severe carbachol-induced sinus bradycardia in Galpha(i2)G184S mice suggests a possible role for alterations of Galpha(i2) or RGS proteins in sick sinus syndrome and pathological AV block.
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Affiliation(s)
- Ying Fu
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109-0632, USA
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Tian L, Kammermeier PJ. G protein coupling profile of mGluR6 and expression of Gα proteins in retinal ON bipolar cells. Vis Neurosci 2007; 23:909-16. [PMID: 17266783 DOI: 10.1017/s0952523806230268] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2006] [Accepted: 09/10/2006] [Indexed: 12/25/2022]
Abstract
Metabotropic glutamate receptor 6 (mGluR6) is a group III, pertussis toxin (PTX)-sensitive G protein coupled mGluR that plays a specialized role in the retina. Retinal ON bipolar cells, which receive direct glutamatergic input from photoreceptor cells, express mGluR6 as their primary postsynaptic glutamate receptor. Activation of mGluR6 in these cells initiates an intracellular signaling cascade ultimately leading to inhibition of a cation channel and cell hyperpolarization. The primary mediator of this pathwayin vivois Gαo, but the potential roles of other G proteins from the Gαi/ofamily in the regulation of this or other signaling pathways in ON bipolar cells are unclear. To determine which specific G proteins from the Gαi/ofamily are able to couple to mGluR6, a Gα reconstitution system was employed using PTX-insensitive Gα mutants expressed with mGluR6 in PTX-treated sympathetic neurons from the rat superior cervical ganglion (SCG). The efficiency of coupling to mGluR6 was Goa> Gob, Gi1> Gi2, Gi3, whereas no coupling was observed with Gαz, nor with the retinal Gα proteins, rod (GNAT2) or cone (GNAT1) transducin (GαTr-R, GαTr-C). Finally, the expression of Gα proteins determined to couple with mGluR6 was examined in rat ON bipolar cells using single cell RT-PCR. Co-expression of mGluR6 message was used to distinguish ON from OFF bipolar cells. Expression of Gαowas detected in every ON bipolar cell examined. Message for Gαi1, which coupled moderately to mGluR6, was not detected in ON bipolar cells, nor was Gαi3, which coupled to mGluR6 in only a few cells but on average did not exhibit statistically significant coupling. Finally, though Gαi2was detectable in ON bipolar cells, its coupling to mGluR6 in the SCG system was not significant. Together, these data indicate that signaling through mGluR6 in mammalian ON bipolar cells is highly focused, apparently acting through a single Gα protein subtype.
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Affiliation(s)
- Liantian Tian
- Department of Biomedical Sciences, Kent State University, Rootstown, Ohio, USA
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Jaén C, Doupnik CA. RGS3 and RGS4 Differentially Associate with G Protein-coupled Receptor-Kir3 Channel Signaling Complexes Revealing Two Modes of RGS Modulation. J Biol Chem 2006; 281:34549-60. [PMID: 16973624 DOI: 10.1074/jbc.m603177200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
RGS3 and RGS4 are GTPase-activating proteins expressed in the brain and heart that accelerate the termination of G(i/o)- and G(q)-mediated signaling. We report here the determinants mediating selective association of RGS4 with several G protein-coupled receptors (GPCRs) that form macromolecular complexes with neuronal G protein-gated inwardly rectifying potassium (Kir3 or GIRK) channels. Kir3 channels are instrumental in regulating neuronal firing in the central and peripheral nervous system and pacemaker activity in the heart. By using an epitope-tagged degradation-resistant RGS4 mutant, RGS4(C2V), immunoprecipitation of several hemagglutinin-tagged G(i/o)-coupled and G(q)-coupled receptors expressed in Chinese hamster ovary (CHO-K1) cells readily co-precipitated both Kir3.1/Kir3.2a channels and RGS4(C2V). In contrast to RGS4(C2V), the closely related and functionally active RGS3 "short" isoform (RGS3s) did not interact with any of the GPCR-Kir3 channel complexes examined. Deletion and chimeric RGS constructs indicate both the N-terminal domain and the RGS domain of RGS4(C2V) are necessary for association with m2 receptor-Kir3.1/Kir3.2a channel complexes, where the GPCR was found to be the major target for RGS4(C2V) interaction. The functional impact of RGS4(C2V) "precoupling" to the GPCR-Kir3 channel complex versus RGS3s "collision coupling" was a 100-fold greater potency in the acceleration of G protein-dependent Kir3 channel-gating kinetics with no attenuation in current amplitude. These findings demonstrate that RGS4, a highly regulated modulator and susceptibility gene for schizophrenia, can directly associate with multiple GPCR-Kir3 channel complexes and may affect a wide range of neurotransmitter-mediated inhibitory and excitatory events in the nervous and cardiovascular systems.
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MESH Headings
- Amino Acid Sequence
- Animals
- CHO Cells
- Cells, Cultured
- Cricetinae
- Electrophoretic Mobility Shift Assay
- G Protein-Coupled Inwardly-Rectifying Potassium Channels/genetics
- G Protein-Coupled Inwardly-Rectifying Potassium Channels/metabolism
- GTP-Binding Protein alpha Subunit, Gi2/genetics
- GTP-Binding Protein alpha Subunit, Gi2/metabolism
- GTP-Binding Proteins/genetics
- GTP-Binding Proteins/metabolism
- GTPase-Activating Proteins/genetics
- GTPase-Activating Proteins/metabolism
- Gene Expression Regulation
- Hemagglutinins/genetics
- Hemagglutinins/metabolism
- Humans
- Immunoblotting
- Immunoprecipitation
- Ion Channel Gating
- Kinetics
- Mice
- Molecular Sequence Data
- Oocytes/metabolism
- RGS Proteins/genetics
- RGS Proteins/metabolism
- Receptor, Muscarinic M2/genetics
- Receptor, Muscarinic M2/metabolism
- Receptor, Serotonin, 5-HT1A/genetics
- Receptor, Serotonin, 5-HT1A/metabolism
- Receptors, Lysophosphatidic Acid/genetics
- Receptors, Lysophosphatidic Acid/metabolism
- Sequence Deletion
- Sequence Homology, Amino Acid
- Serotonin/pharmacology
- Signal Transduction
- Transfection
- Xenopus laevis/metabolism
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Affiliation(s)
- Cristina Jaén
- Department of Molecular Pharmacology and Physiology, University of South Florida College of Medicine, Tampa, Florida 33612, USA
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Roof RA, Jin Y, Roman DL, Sunahara RK, Ishii M, Mosberg HI, Neubig RR. Mechanism of action and structural requirements of constrained peptide inhibitors of RGS proteins. Chem Biol Drug Des 2006; 67:266-74. [PMID: 16629824 DOI: 10.1111/j.1747-0285.2006.00373.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Regulators of G-protein signaling (RGS) accelerate guanine triphosphate hydrolysis by Galpha-subunits and profoundly inhibit signaling by G protein-coupled receptors. The distinct expression patterns and pathophysiologic regulation of RGS proteins suggest that inhibitors may have therapeutic potential. We previously reported the design of a constrained peptide inhibitor of RGS4 (1: Ac-Val-Lys-[Cys-Thr-Gly-Ile-Cys]-Glu-NH2, S-S) based on the structure of the Galphai switch 1 region but its mechanism of action was not established. In the present study, we show that 1 inhibits RGS4 by mimicking and competing for binding with the switch 1 region of Galphai and that peptide 1 shows selectivity for RGS4 and RGS8 versus RGS7. Structure-activity relationships of analogs related to 1 are described that illustrate key features for RGS inhibition. Finally, we demonstrate activity of the methylene dithioether-bridged peptide inhibitor, 2, to modulate muscarinic receptor-regulated potassium currents in atrial myocytes. These data support the proposed mechanism of action of peptide RGS inhibitors, demonstrate their action in native cells, and provide a starting point for the design of RGS inhibitor drugs.
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Affiliation(s)
- Rebecca A Roof
- Department of Pharmacology, 1150 W. Medical Center Dr, University of Michigan, Ann Arbor, MI 48109, USA
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Abstract
There is accumulating evidence that regulators of G-protein signalling (RGS) can have roles in signal transduction that are not related to GAP activity. Furthermore, RGSs have much more selective effects in vivo than might be anticipated from their behaviour in in vitro assays. I discuss the molecular mechanisms by which these phenomena might be explained including specific interactions between the RGS and G-protein coupled receptor, G-protein and effector.
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Affiliation(s)
- Andrew Tinker
- BHF Laboratories and Department of Medicine, University College London, 5 University Street, London WC1E 6JJ, UK.
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