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Luo H, Marron Fernandez de Velasco E, Wickman K. Neuronal G protein-gated K + channels. Am J Physiol Cell Physiol 2022; 323:C439-C460. [PMID: 35704701 PMCID: PMC9362898 DOI: 10.1152/ajpcell.00102.2022] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels exert a critical inhibitory influence on neurons. Neuronal GIRK channels mediate the G protein-dependent, direct/postsynaptic inhibitory effect of many neurotransmitters including γ-aminobutyric acid (GABA), serotonin, dopamine, adenosine, somatostatin, and enkephalin. In addition to their complex regulation by G proteins, neuronal GIRK channel activity is sensitive to PIP2, phosphorylation, regulator of G protein signaling (RGS) proteins, intracellular Na+ and Ca2+, and cholesterol. The application of genetic and viral manipulations in rodent models, together with recent progress in the development of GIRK channel modulators, has increased our understanding of the physiological and behavioral impact of neuronal GIRK channels. Work in rodent models has also revealed that neuronal GIRK channel activity is modified, transiently or persistently, by various stimuli including exposure drugs of abuse, changes in neuronal activity patterns, and aversive experience. A growing body of preclinical and clinical evidence suggests that dysregulation of GIRK channel activity contributes to neurological diseases and disorders. The primary goals of this review are to highlight fundamental principles of neuronal GIRK channel biology, mechanisms of GIRK channel regulation and plasticity, the nascent landscape of GIRK channel pharmacology, and the potential relevance of GIRK channels to the pathophysiology and treatment of neurological diseases and disorders.
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Affiliation(s)
- Haichang Luo
- Department of Pharmacology, University of Minnesota, Minneapolis, MN, United States
| | | | - Kevin Wickman
- Department of Pharmacology, University of Minnesota, Minneapolis, MN, United States
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2
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Feng H, Yuan Y, Williams MR, Roy AJ, Leipprandt JR, Neubig RR. MICE WITH GNAO1-ASSOCIATED MOVEMENT DISORDER EXHIBIT REDUCED INHIBITORY SYNAPTIC INPUT TO CEREBELLAR PURKINJE CELLS. J Neurophysiol 2022; 127:607-622. [PMID: 35080448 DOI: 10.1152/jn.00720.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
GNAO1 encodes Gαo, a heterotrimeric G protein alpha subunit in the Gi/o family. In this report, we used a Gnao1 mouse model "G203R" previously described as a "gain-of-function" Gnao1 mutant with movement abnormalities and enhanced seizure susceptibility. Here, we report an unexpected second mutation resulting in a loss-of-function Gαo protein and describe alterations in central synaptic transmission. Whole cell patch clamp recordings from Purkinje cells (PCs) in acute cerebellar slices from Gnao1 mutant mice showed significantly lower frequencies of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) compared to WT mice. There was no significant change in sEPSCs or mEPSCs. Whereas mIPSC frequency was reduced, mIPSC amplitudes were not affected, suggesting a presynaptic mechanism of action. A modest decrease in the number of molecular layer interneurons was insufficient to explain the magnitude of IPSC suppression. Paradoxically, Gi/o inhibitors (pertussis toxin), enhanced the mutant-suppressed mIPSC frequency and eliminated the difference between WT and Gnao1 mice. While GABAB receptor regulates mIPSCs, neither agonists nor antagonists of this receptor altered function in the mutant mouse PCs. This study is the first electrophysiological investigation of the role of Gi/o proteinin cerebellar synaptic transmission using an animal model with a loss-of-function Gi/o protein.
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Affiliation(s)
- Huijie Feng
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, United States
| | - Yukun Yuan
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, United States
| | - Michael R Williams
- Department of Pediatrics and Human Development, Michigan State University, Grand Rapids, MI, United States
| | - Alex J Roy
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, United States
| | - Jeffrey R Leipprandt
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, United States
| | - Richard R Neubig
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, United States
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3
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Ahn D, Chung KY. The Conformational Dynamics of Heterotrimeric G Proteins During GPCR-Mediated Activation. Subcell Biochem 2022; 99:271-284. [PMID: 36151379 DOI: 10.1007/978-3-031-00793-4_8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Heterotrimeric G proteins (G proteins) are essential cellular signaling proteins that mediate extracellular signals to achieve various cellular functions. G-protein-coupled receptors (GPCRs) are the major guanine nucleotide exchange factors (GEFs) that induce G proteins to release guanosine diphosphate and rapidly bind to guanosine triphosphate, resulting in G protein activation. G proteins undergo dynamic conformational changes during the activation/inactivation process, and the precise structural mechanism of GPCR-mediated G protein activation is of great interest. Over the last decade, a number of GPCR-G protein complex structures have been identified, yet an understanding of the mechanisms underlying allosteric conformational changes during receptor-mediated G protein activation and GPCR-G protein coupling selectivity is only now emerging. This review discusses recent studies on the dynamic conformational changes of G proteins and provides insight into the structural mechanism of GPCR-mediated G protein activation.
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Affiliation(s)
- Donghoon Ahn
- School of Pharmacy, Sungkyunkwan University, Suwon, Republic of Korea
| | - Ka Young Chung
- School of Pharmacy, Sungkyunkwan University, Suwon, Republic of Korea.
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4
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Heblinski M, Bladen C, Connor M. Regulation of heterologously expressed 5-HT 1B receptors coupling to potassium channels in AtT-20 cells. Br J Pharmacol 2018; 176:451-465. [PMID: 30447001 DOI: 10.1111/bph.14547] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2018] [Revised: 10/08/2018] [Accepted: 10/17/2018] [Indexed: 01/14/2023] Open
Abstract
BACKGROUND AND PURPOSE 5-HT1B receptors are widely expressed GPCRs and a target of triptans, the most commonly prescribed anti-migraine drugs. There is very limited information about the acute, agonist-induced regulation of 5-HT1B receptor signalling and so we sought to characterize this in a neuron-like system. EXPERIMENTAL APPROACH Epitope-tagged human 5-HT1B receptors were expressed in mouse AtT20 cells. 5-HT1B receptor signalling was assessed using whole-cell patch-clamp recordings of endogenous G protein-gated inwardly rectified potassium (GIRK) channels, and receptor localization measured using immunofluorescence. KEY RESULTS 5-HT (EC50 65 nM) and sumatriptan (EC50 165 nM) activated GIRK channels in AtT20 cells expressing 5-HT1B receptors. Continuous application of both 5-HT (EC50 120 nM) and sumatriptan (EC50 280 nM) produced profound desensitization of 5-HT1B receptor signalling within a few minutes. Complete recovery from desensitization was observed after 10 min. Both 5-HT and sumatriptan induced significant heterologous desensitization of SRIF (somatostatin)-activated GIRK currents, with the 5-HT-induced heterologous desensitization being blocked by the protein kinase inhibitor staurosporine. Both agonists induced modest 5-HT1B receptor internalization, with a time course much slower than receptor desensitization. CONCLUSIONS AND IMPLICATIONS In AtT-20 cells, 5-HT1B receptors undergo rapid and reversible desensitization at concentrations of agonist similar to those required to activate the receptor. Desensitization is incomplete, and the continued signalling of the receptor in the presence of the agonist may lead to cellular adaptations. Finally, 5-HT1B receptor activation causes significant heterologous desensitization, which may lead to a reduced effectiveness of unrelated drugs in vivo.
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Affiliation(s)
- Marika Heblinski
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Christopher Bladen
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Mark Connor
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
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5
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Brink T, Leiss V, Siegert P, Jehle D, Ebner JK, Schwan C, Shymanets A, Wiese S, Nürnberg B, Hensel M, Aktories K, Orth JHC. Salmonella Typhimurium effector SseI inhibits chemotaxis and increases host cell survival by deamidation of heterotrimeric Gi proteins. PLoS Pathog 2018; 14:e1007248. [PMID: 30102745 PMCID: PMC6107295 DOI: 10.1371/journal.ppat.1007248] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Revised: 08/23/2018] [Accepted: 07/27/2018] [Indexed: 12/20/2022] Open
Abstract
Salmonella enterica serotype Typhimurium (S. Typhimurium) is one of the most frequent causes of food-borne illness in humans and usually associated with acute self-limiting gastroenteritis. However, in immunocompromised patients, the pathogen can disseminate and lead to severe systemic diseases. S. Typhimurium are facultative intracellular bacteria. For uptake and intracellular life, Salmonella translocate numerous effector proteins into host cells using two type-III secretion systems (T3SS), which are encoded within Salmonella pathogenicity islands 1 (SPI-1) and 2 (SPI-2). While SPI-1 effectors mainly promote initial invasion, SPI-2 effectors control intracellular survival and proliferation. Here, we elucidate the mode of action of Salmonella SPI-2 effector SseI, which is involved in control of systemic dissemination of S. Typhimurium. SseI deamidates a specific glutamine residue of heterotrimeric G proteins of the Gαi family, resulting in persistent activation of the G protein. Gi activation inhibits cAMP production and stimulates PI3-kinase γ by Gαi-released Gβγ subunits, resulting in activation of survival pathways by phosphorylation of Akt and mTOR. Moreover, SseI-induced deamidation leads to non-polarized activation of Gαi and, thereby, to loss of directed migration of dendritic cells. Salmonella Typhimurium is one of the most common causes of gastroenteritis in humans. In immunocompromised patients, the pathogen can cause systemic infections. Crucial virulence factors are encoded on two Salmonella pathogenicity islands SPI-1 and SPI-2. While SPI-1 encodes virulence factors essential for host cell invasion, intracellular proliferation of the pathogen depends mainly on SPI-2 effectors. Here, we elucidate the mode of action of Salmonella SPI-2 effector SseI. SseI activates heterotrimeric G proteins of the Gαi family by deamidation of a specific glutamine residue. Deamidation blocks GTP hydrolysis by Gαi, resulting in a persistently active G protein. Gi activation inhibits cAMP production and stimulates PI3Kγ by Gαi-released Gβγ subunits, resulting in activation of survival pathways by phosphorylation of Akt and mTOR. Moreover, deamidation of Gαi leads to a loss of directed migration in dendritic cells. The data offers a new perspective in the understanding of the actions of SseI.
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Affiliation(s)
- Thorsten Brink
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Veronika Leiss
- Abteilung für Pharmakologie und Experimentelle Therapie, Medizinische Fakultät und ICePhA, Eberhard-Karls-Universität Tübingen, Germany
| | - Peter Siegert
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Doris Jehle
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Julia K. Ebner
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- Spemann Graduate School of Biology and Medicine (SGBM), Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- Fakultät für Biologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Carsten Schwan
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Aliaksei Shymanets
- Abteilung für Pharmakologie und Experimentelle Therapie, Medizinische Fakultät und ICePhA, Eberhard-Karls-Universität Tübingen, Germany
| | - Sebastian Wiese
- Zentrum für Biosystemanalyse, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Bernd Nürnberg
- Abteilung für Pharmakologie und Experimentelle Therapie, Medizinische Fakultät und ICePhA, Eberhard-Karls-Universität Tübingen, Germany
| | - Michael Hensel
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany
| | - Klaus Aktories
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- * E-mail:
| | - Joachim H. C. Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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Dascal N, Kahanovitch U. The Roles of Gβγ and Gα in Gating and Regulation of GIRK Channels. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2015; 123:27-85. [DOI: 10.1016/bs.irn.2015.06.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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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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8
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Jones JC, Duffy JW, Machius M, Temple BRS, Dohlman HG, Jones AM. The crystal structure of a self-activating G protein alpha subunit reveals its distinct mechanism of signal initiation. Sci Signal 2011; 4:ra8. [PMID: 21304159 PMCID: PMC3551277 DOI: 10.1126/scisignal.2001446] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In animals, heterotrimeric guanine nucleotide-binding protein (G protein) signaling is initiated by G protein-coupled receptors (GPCRs), which activate G protein α subunits; however, the plant Arabidopsis thaliana lacks canonical GPCRs, and its G protein α subunit (AtGPA1) is self-activating. To investigate how AtGPA1 becomes activated, we determined its crystal structure. AtGPA1 is structurally similar to animal G protein α subunits, but our crystallographic and biophysical studies revealed that it had distinct properties. Notably, the helical domain of AtGPA1 displayed pronounced intrinsic disorder and a tendency to disengage from the Ras domain of the protein. Domain substitution experiments showed that the helical domain of AtGPA1 was necessary for self-activation and sufficient to confer self-activation to an animal G protein α subunit. These findings reveal the structural basis for a mechanism for G protein activation in Arabidopsis that is distinct from the well-established mechanism found in animals.
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Affiliation(s)
- Janice C. Jones
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Jeffrey W. Duffy
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Mischa Machius
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599, USA
- Center for Structural Biology, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Brenda R. S. Temple
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
- R. L. Juliano Structural Bio-informatics Core Facility, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Henrik G. Dohlman
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Alan M. Jones
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599, USA
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA
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9
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Olijslagers JE, Werkman TR, McCreary AC, Kruse CG, Wadman WJ. Modulation of midbrain dopamine neurotransmission by serotonin, a versatile interaction between neurotransmitters and significance for antipsychotic drug action. Curr Neuropharmacol 2010; 4:59-68. [PMID: 18615139 DOI: 10.2174/157015906775203020] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2005] [Revised: 08/23/2005] [Accepted: 09/17/2005] [Indexed: 11/22/2022] Open
Abstract
Schizophrenia has been associated with a dysfunction of brain dopamine (DA). This, so called, DA hypothesis has been refined as new insights into the pathophysiology of schizophrenia have emerged. Currently, dysfunction of prefrontocortical glutamatergic and GABAergic projections and dysfunction of serotonin (5-HT) systems are also thought to play a role in the pathophysiology of schizophrenia. Refinements of the DA hypothesis have lead to the emergence of new pharmacological targets for antipsychotic drug development. It was shown that effective antipsychotic drugs with a low liability for inducing extra-pyramidal side-effects have affinities for a range of neurotransmitter receptors in addition to DA receptors, suggesting that a combination of neurotransmitter receptor affinities may be favorable for treatment outcome.This review focuses on the interaction between DA and 5-HT, as most antipsychotics display affinity for 5-HT receptors. We will discuss DA/5-HT interactions at the level of receptors and G protein-coupled potassium channels and consequences for induction of depolarization blockade with specific attention to DA neurons in the ventral tegmental area (VTA) and the substantia nigra zona compacta (SN), neurons implicated in treatment efficacy and the side-effects of schizophrenia, respectively. Moreover, it has been reported that electrophysiological interactions between DA and 5-HT show subtle, but important, differences between the SN and the VTA which could explain (in part) the effectiveness and lower propensity to induce side-effects of the newer atypical antipsychotic drugs. In that respect the functional implications of DA/5-HT interactions for schizophrenia will be discussed.
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Affiliation(s)
- J E Olijslagers
- Center for NeuroScience-Swammerdam Institute for Life Sciences, University of Amsterdam, Kruislaan 320, 1098 SM Amsterdam, The Netherlands.
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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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11
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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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12
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Endogenous RGS proteins attenuate Galpha(i)-mediated lysophosphatidic acid signaling pathways in ovarian cancer cells. Cell Signal 2007; 20:381-9. [PMID: 18083345 DOI: 10.1016/j.cellsig.2007.10.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2007] [Accepted: 10/30/2007] [Indexed: 01/06/2023]
Abstract
Lysophosphatidic acid is a bioactive phospholipid that is produced by and stimulates ovarian cancer cells, promoting proliferation, migration, invasion, and survival. Effects of LPA are mediated by cell surface G-protein coupled receptors (GPCRs) that activate multiple heterotrimeric G-proteins. G-proteins are deactivated by Regulator of G-protein Signaling (RGS) proteins. This led us to hypothesize that RGS proteins may regulate G-protein signaling pathways initiated by LPA in ovarian cancer cells. To determine the effect of endogenous RGS proteins on LPA signaling in ovarian cancer cells, we compared LPA activity in SKOV-3 ovarian cancer cells expressing G(i) subunit constructs that are either insensitive to RGS protein regulation (RGSi) or their RGS wild-type (RGSwt) counterparts. Both forms of the G-protein contained a point mutation rendering them insensitive to inhibition with pertussis toxin, and cells were treated with pertussis toxin prior to experiments to eliminate endogenous G(i/o) signaling. The potency and efficacy of LPA-mediated inhibition of forskolin-stimulated adenylyl cyclase activity was enhanced in cells expressing RGSi G(i) proteins as compared to RGSwt G(i). We further showed that LPA signaling that is subject to RGS regulation terminates much faster than signaling thru RGS insensitive G-proteins. Finally, LPA-stimulated SKOV-3 cell migration, as measured in a wound-induced migration assay, was enhanced in cells expressing Galpha(i2) RGSi as compared to cells expressing Galpha(i2) RGSwt, suggesting that endogenous RGS proteins in ovarian cancer cells normally attenuate this LPA effect. These data establish RGS proteins as novel regulators of LPA signaling in ovarian cancer cells.
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13
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Rosenhouse-Dantsker A, Logothetis DE. New roles for a key glycine and its neighboring residue in potassium channel gating. Biophys J 2006; 91:2860-73. [PMID: 16877518 PMCID: PMC1578466 DOI: 10.1529/biophysj.105.080242] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2005] [Accepted: 06/12/2006] [Indexed: 11/18/2022] Open
Abstract
Potassium channel activation regulates cellular excitability in cells such as neurons and heart. Ion channel activity relies on a switching mechanism between two conformations, the open and closed states, known as gating. It has been suggested that potassium channels are gated via a pivoted mechanism of the pore-lining helix. Our analysis suggests that hinging occurs at the residue immediately preceding the central glycine of the inner helix. Furthermore, we show that the highly conserved central glycine is necessary to prevent constraining interactions with critical residues in its vicinity, including those located in the selectivity filter. We show that such interactions can impair channel function, and that upon their removal channel activity can be restored.
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Affiliation(s)
- Avia Rosenhouse-Dantsker
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, New York, USA
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14
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Clancy SM, Fowler CE, Finley M, Suen KF, Arrabit C, Berton F, Kosaza T, Casey PJ, Slesinger PA. Pertussis-toxin-sensitive Galpha subunits selectively bind to C-terminal domain of neuronal GIRK channels: evidence for a heterotrimeric G-protein-channel complex. Mol Cell Neurosci 2005; 28:375-89. [PMID: 15691717 DOI: 10.1016/j.mcn.2004.10.009] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2004] [Accepted: 10/25/2004] [Indexed: 11/19/2022] Open
Abstract
Neuronal G-protein-gated inwardly rectifying potassium (Kir3; GIRK) channels are activated by G-protein-coupled receptors that selectively interact with PTX-sensitive (Galphai/o) G proteins. Although the Gbetagamma dimer is known to activate GIRK channels, the role of the Galphai/o subunit remains unclear. Here, we established that Galphao subunits co-immunoprecipitate with neuronal GIRK channels. In vitro binding studies led to the identification of six amino acids in the GIRK2 C-terminal domain essential for Galphao binding. Further studies suggested that the Galphai/obetagamma heterotrimer binds to the GIRK2 C-terminal domain via Galpha and not Gbetagamma. Galphai/o binding-impaired GIRK2 channels exhibited reduced receptor-activated currents, but retained normal ethanol- and Gbetagamma-activated currents. Finally, PTX-insensitive Galphaq or Galphas subunits did not bind to the GIRK2 C-terminus. Together, these results suggest that the interaction of PTX-sensitive Galphai/o subunit with the GIRK2 C-terminal domain regulates G-protein receptor coupling, and may be important for establishing specific Galphai/o signaling pathways.
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Affiliation(s)
- Sinead M Clancy
- Peptide Biology Laboratory, The Salk Institute for Biological Studies, 10010 N. Torrey Pines Road, La Jolla, CA 92037, USA
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Abstract
Discovery of "regulators of G-protein signaling" (RGS) as GTPase-activating proteins for heterotrimeric G proteins has provided a highly sought "missing link," reconciling past discrepancies between the in vitro GTPase activity of purified G proteins and the kinetics of physiological responses mediated by G-protein signaling in vivo. With the number of RGS genes in the mammalian genome at more than 30, associating specific RGS proteins to specific G-protein-coupled receptor (GPCR) signaling events has become a focus of RGS investigators. The ubiquitous expression of multiple RGS proteins has complicated this effort, yet the outlook has been encouraged with the identification of RGS9 as the determinant mediating rapid recovery of the transducin-dependent photoresponse. G-protein-gated inwardly rectifying potassium (GIRK) channels that mediate inhibitory synaptic transmission via GPCR activation of pertussis toxin-sensitive G proteins are similarly accelerated by RGS proteins when reconstituted in heterologous cell expression systems and fully reproduce the gating properties of native GIRK channels in neurons and cardiomyocytes. The endogenous neuronal and cardiac RGS protein(s) that accelerate GPCR-->GIRK channel-gating kinetics are currently not known. This article describes methods used to measure the receptor-dependent GIRK channel-gating parameters reconstituted in Chinese hamster ovary (CHO-K1) cells and Xenopus oocytes, as well as rat atrial myocytes and rat cerebellar granule neurons as model cells with native GPCR-->GIRK channel signaling. Applications of these methods for structure-function-based studies of RGS proteins, G proteins, and GPCRs are discussed. We also describe single cell reverse transcriptase polymerase chain reaction methods developed to profile atrial myocyte and neuronal RGS expression to identify specific RGS proteins for targeted knockdown or knockout.
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Affiliation(s)
- Craig A Doupnik
- Department of Physiology and Biophysics, University of South Florida College of Medicine, Tampa 33612, USA
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