1
|
López-Serrano AL, Zamora-Cárdenas R, Aréchiga-Figueroa IA, Salazar-Fajardo PD, Ferrer T, Alamilla J, Sánchez-Chapula JA, Navarro-Polanco RA, Moreno-Galindo EG. Differential voltage-dependent modulation of the ACh-gated K+ current by adenosine and acetylcholine. PLoS One 2022; 17:e0261960. [PMID: 35030226 PMCID: PMC8759768 DOI: 10.1371/journal.pone.0261960] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 12/14/2021] [Indexed: 11/18/2022] Open
Abstract
Inhibitory regulation of the heart is determined by both cholinergic M2 receptors (M2R) and adenosine A1 receptors (A1R) that activate the same signaling pathway, the ACh-gated inward rectifier K+ (KACh) channels via Gi/o proteins. Previously, we have shown that the agonist-specific voltage sensitivity of M2R underlies several voltage-dependent features of IKACh, including the ‘relaxation’ property, which is characterized by a gradual increase or decrease of the current when cardiomyocytes are stepped to hyperpolarized or depolarized voltages, respectively. However, it is unknown whether membrane potential also affects A1R and how this could impact IKACh. Upon recording whole-cell currents of guinea-pig cardiomyocytes, we found that stimulation of the A1R-Gi/o-IKACh pathway with adenosine only caused a very slight voltage dependence in concentration-response relationships (~1.2-fold EC50 increase with depolarization) that was not manifested in the relative affinity, as estimated by the current deactivation kinetics (τ = 4074 ± 214 ms at -100 mV and τ = 4331 ± 341 ms at +30 mV; P = 0.31). Moreover, IKACh did not exhibit relaxation. Contrarily, activation of the M2R-Gi/o-IKACh pathway with acetylcholine induced the typical relaxation of the current, which correlated with the clear voltage-dependent effect observed in the concentration-response curves (~2.8-fold EC50 increase with depolarization) and in the IKACh deactivation kinetics (τ = 1762 ± 119 ms at -100 mV and τ = 1503 ± 160 ms at +30 mV; P = 0.01). Our findings further substantiate the hypothesis of the agonist-specific voltage dependence of GPCRs and that the IKACh relaxation is consequence of this property.
Collapse
Affiliation(s)
- Ana Laura López-Serrano
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico
| | - Rodrigo Zamora-Cárdenas
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico
| | - Iván A. Aréchiga-Figueroa
- CONACYT, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, S.L.P., Mexico
| | | | - Tania Ferrer
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico
| | - Javier Alamilla
- CONACYT, Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico
| | - José A. Sánchez-Chapula
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico
| | | | - Eloy G. Moreno-Galindo
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico
- * E-mail:
| |
Collapse
|
2
|
Evans F, Hernández JA, Chifflet S. Signaling pathways in cytoskeletal responses to plasma membrane depolarization in corneal endothelial cells. J Cell Physiol 2019; 235:2947-2962. [PMID: 31535377 DOI: 10.1002/jcp.29200] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Accepted: 08/26/2019] [Indexed: 01/01/2023]
Abstract
In previous work, we reported that plasma membrane potential depolarization (PMPD) provokes cortical F-actin remodeling in bovine corneal endothelial (BCE) cells in culture, which eventually leads to the appearance of intercellular gaps. In kidney epithelial cells it has been shown that PMPD determines an extracellular-signal-regulated kinase (ERK)/Rho-dependent increase in diphosphorylated myosin light chain (ppMLC). The present study investigated the signaling pathways involved in the response of BCE cells to PMPD. Differently to renal epithelial cells, we observed that PMPD leads to a decrease in monophosphorylated MLC (pMLC) without affecting diphosphorylated MLC. Also, that the pMLC reduction is a consequence of cyclic adenosine 3',5'-monophosphate (cAMP)/protein kinase A (PKA) activation. In addition, we found evidence that the cAMP increase mostly depends on soluble adenylyl cyclase activity. Inhibition of this enzyme reduces the effect of PMPD on the cAMP rise, F-actin remodeling, and pMLC decrease. No changes in phosho-ERK were observed, although we could determine that RhoA undergoes activation. Our results suggested that active RhoA is not involved in the intercellular gap formation. Overall, the findings of this study support the view that, differently to renal epithelial cells, in BCE cells PMPD determines cytoskeletal reorganization via activation of the cAMP/PKA pathway.
Collapse
Affiliation(s)
- Frances Evans
- Departamento de Histología y Embriología, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay
| | - Julio A Hernández
- Sección Biofísica, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Silvia Chifflet
- Departamento de Bioquímica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay
| |
Collapse
|
3
|
Salazar-Fajardo PD, Aréchiga-Figueroa IA, López-Serrano AL, Rodriguez-Elias JC, Alamilla J, Sánchez-Chapula JA, Tristani-Firouzi M, Navarro-Polanco RA, Moreno-Galindo EG. The voltage-sensitive cardiac M 2 muscarinic receptor modulates the inward rectification of the G protein-coupled, ACh-gated K + current. Pflugers Arch 2018; 470:1765-1776. [PMID: 30155776 DOI: 10.1007/s00424-018-2196-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 07/28/2018] [Accepted: 08/13/2018] [Indexed: 11/25/2022]
Abstract
The acetylcholine (ACh)-gated inwardly rectifying K+ current (IKACh) plays a vital role in cardiac excitability by regulating heart rate variability and vulnerability to atrial arrhythmias. These crucial physiological contributions are determined principally by the inwardly rectifying nature of IKACh. Here, we investigated the relative contribution of two distinct mechanisms of IKACh inward rectification measured in atrial myocytes: a rapid component due to KACh channel block by intracellular Mg2+ and polyamines; and a time- and concentration-dependent mechanism. The time- and ACh concentration-dependent inward rectification component was eliminated when IKACh was activated by GTPγS, a compound that bypasses the muscarinic-2 receptor (M2R) and directly stimulates trimeric G proteins to open KACh channels. Moreover, the time-dependent component of IKACh inward rectification was also eliminated at ACh concentrations that saturate the receptor. These observations indicate that the time- and concentration-dependent rectification mechanism is an intrinsic property of the receptor, M2R; consistent with our previous work demonstrating that voltage-dependent conformational changes in the M2R alter the receptor affinity for ACh. Our analysis of the initial and time-dependent components of IKACh indicate that rapid Mg2+-polyamine block accounts for 60-70% of inward rectification, with M2R voltage sensitivity contributing 30-40% at sub-saturating ACh concentrations. Thus, while both inward rectification mechanisms are extrinsic to the KACh channel, to our knowledge, this is the first description of extrinsic inward rectification of ionic current attributable to an intrinsic voltage-sensitive property of a G protein-coupled receptor.
Collapse
Affiliation(s)
- Pedro D Salazar-Fajardo
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de Julio 965, Colonia Villa San Sebastián, C.P, 28045, Colima, COL, Mexico
| | - Iván A Aréchiga-Figueroa
- CONACyT, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, SLP, Mexico
| | - Ana Laura López-Serrano
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de Julio 965, Colonia Villa San Sebastián, C.P, 28045, Colima, COL, Mexico
| | - Julio C Rodriguez-Elias
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de Julio 965, Colonia Villa San Sebastián, C.P, 28045, Colima, COL, Mexico
| | - Javier Alamilla
- CONACyT, Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, COL, Mexico
| | - José A Sánchez-Chapula
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de Julio 965, Colonia Villa San Sebastián, C.P, 28045, Colima, COL, Mexico
| | - Martin Tristani-Firouzi
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT, 84112, USA.
| | - Ricardo A Navarro-Polanco
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de Julio 965, Colonia Villa San Sebastián, C.P, 28045, Colima, COL, Mexico.
| | - Eloy G Moreno-Galindo
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de Julio 965, Colonia Villa San Sebastián, C.P, 28045, Colima, COL, Mexico.
| |
Collapse
|
4
|
Chen IS, Furutani K, Kurachi Y. Structural determinants at the M2 muscarinic receptor modulate the RGS4-GIRK response to pilocarpine by impairment of the receptor voltage sensitivity. Sci Rep 2017; 7:6110. [PMID: 28733581 PMCID: PMC5522400 DOI: 10.1038/s41598-017-05128-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 05/24/2017] [Indexed: 12/23/2022] Open
Abstract
Membrane potential controls the response of the M2 muscarinic receptor to its ligands. Membrane hyperpolarization increases response to the full agonist acetylcholine (ACh) while decreasing response to the partial agonist pilocarpine. We previously have demonstrated that the regulator of G-protein signaling (RGS) 4 protein discriminates between the voltage-dependent responses of ACh and pilocarpine; however, the underlying mechanism remains unclear. Here we show that RGS4 is involved in the voltage-dependent behavior of the M2 muscarinic receptor-mediated signaling in response to pilocarpine. Additionally we revealed structural determinants on the M2 muscarinic receptor underlying the voltage-dependent response. By electrophysiological recording in Xenopus oocytes expressing M2 muscarinic receptor and G-protein-gated inwardly rectifying K+ channels, we quantified voltage-dependent desensitization of pilocarpine-induced current in the presence or absence of RGS4. Hyperpolarization-induced desensitization of the current required for RGS4, also depended on pilocarpine concentration. Mutations of charged residues in the aspartic acid-arginine-tyrosine motif of the M2 muscarinic receptor, but not intracellular loop 3, significantly impaired the voltage-dependence of RGS4 function. Thus, our results demonstrated that voltage-dependence of RGS4 modulation is derived from the M2 muscarinic receptor. These results provide novel insights into how membrane potential impacts G-protein signaling by modulating GPCR communication with downstream effectors.
Collapse
Affiliation(s)
- I-Shan Chen
- Department of Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka, 565-0871, Japan
| | - Kazuharu Furutani
- Department of Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka, 565-0871, Japan. .,Global Center for Medical Engineering and Informatics, Osaka University, Suita, Osaka, 565-0871, Japan.
| | - Yoshihisa Kurachi
- Department of Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka, 565-0871, Japan. .,Global Center for Medical Engineering and Informatics, Osaka University, Suita, Osaka, 565-0871, Japan.
| |
Collapse
|
5
|
Moreno-Galindo EG, Sanchez-Chapula JA, Tristani-Firouzi M, Navarro-Polanco RA. Pharmacological Conversion of a Cardiac Inward Rectifier into an Outward Rectifier Potassium Channel. Mol Pharmacol 2016; 90:334-40. [PMID: 27247338 DOI: 10.1124/mol.116.104950] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 05/27/2016] [Indexed: 01/20/2023] Open
Abstract
Potassium (K(+)) channels are crucial for determining the shape, duration, and frequency of action-potential firing in excitable cells. Broadly speaking, K(+) channels can be classified based on whether their macroscopic current outwardly or inwardly rectifies, whereby rectification refers to a change in conductance with voltage. Outwardly rectifying K(+) channels conduct greater current at depolarized membrane potentials, whereas inward rectifier channels conduct greater current at hyperpolarized membrane potentials. Under most circumstances, outward currents through inwardly rectifying K(+) channels are reduced at more depolarized potentials. However, the acetylcholine-gated K(+) channel (KACh) conducts current that inwardly rectifies when activated by some ligands (such as acetylcholine), and yet conducts current that outwardly rectifies when activated by other ligands (for example, pilocarpine and choline). The perplexing and paradoxical behavior of KACh channels is due to the intrinsic voltage sensitivity of the receptor that activates KACh channels, the M2 muscarinic receptor (M2R). Emerging evidence reveals that the affinity of M2R for distinct ligands varies in a voltage-dependent and ligand-specific manner. These intrinsic receptor properties determine whether current conducted by KACh channels inwardly or outwardly rectifies. This review summarizes the most recent concepts regarding the intrinsic voltage sensitivity of muscarinic receptors and the consequences of this intriguing behavior on cardiac physiology and pharmacology of KACh channels.
Collapse
Affiliation(s)
- Eloy G Moreno-Galindo
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Colima, México (E.G.M.-G., J.A.S.-C., R.A.N.-P.); Nora Eccles Harrison Cardiovascular Research and Training Institute, and Division of Pediatric Cardiology, University of Utah, Salt Lake City, Utah (M.T.-F.)
| | - Jose A Sanchez-Chapula
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Colima, México (E.G.M.-G., J.A.S.-C., R.A.N.-P.); Nora Eccles Harrison Cardiovascular Research and Training Institute, and Division of Pediatric Cardiology, University of Utah, Salt Lake City, Utah (M.T.-F.)
| | - Martin Tristani-Firouzi
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Colima, México (E.G.M.-G., J.A.S.-C., R.A.N.-P.); Nora Eccles Harrison Cardiovascular Research and Training Institute, and Division of Pediatric Cardiology, University of Utah, Salt Lake City, Utah (M.T.-F.)
| | - Ricardo A Navarro-Polanco
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Colima, México (E.G.M.-G., J.A.S.-C., R.A.N.-P.); Nora Eccles Harrison Cardiovascular Research and Training Institute, and Division of Pediatric Cardiology, University of Utah, Salt Lake City, Utah (M.T.-F.)
| |
Collapse
|
6
|
Short-term desensitization of muscarinic K+ current in the heart. Biophys J 2014; 105:1515-25. [PMID: 24048003 DOI: 10.1016/j.bpj.2013.08.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Revised: 08/06/2013] [Accepted: 08/09/2013] [Indexed: 01/10/2023] Open
Abstract
Acetylcholine (ACh) rapidly increases cardiac K(+) currents (IKACh) by activating muscarinic K(+) (KACh) channels followed by a gradual amplitude decrease within seconds. This phenomenon is called short-term desensitization and its precise mechanism and physiological role are still unclear. We constructed a mathematical model for IKACh to examine the conditions required to reconstitute short-term desensitization. Two conditions were crucial: two distinct muscarinic receptors (m2Rs) with different affinities for ACh, which conferred an IKACh response over a wide range of ACh concentrations, and two distinct KACh channels with different affinities for the G-protein βγ subunits, which contributed to reconstitution of the temporal behavior of IKACh. Under these conditions, the model quantitatively reproduced several unique properties of short-term desensitization observed in myocytes: 1), the peak and quasi-steady states with 0.01-100 μM [ACh]; 2), effects of ACh preperfusion; and 3), recovery from short-term desensitization. In the presence of 10 μM ACh, the IKACh model conferred recurring spontaneous firing after asystole of 8.9 s and 10.7 s for the Demir and Kurata sinoatrial node models, respectively. Therefore, two different populations of KACh channels and m2Rs may participate in short-term desensitization of IKACh in native myocytes, and may be responsible for vagal escape at nodal cells.
Collapse
|
7
|
Chen IS, Furutani K, Inanobe A, Kurachi Y. RGS4 regulates partial agonism of the M2 muscarinic receptor-activated K+ currents. J Physiol 2014; 592:1237-48. [PMID: 24421355 PMCID: PMC3961084 DOI: 10.1113/jphysiol.2013.269803] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 01/07/2014] [Indexed: 12/20/2022] Open
Abstract
Partial agonists are used clinically to avoid overstimulation of receptor-mediated signalling, as they produce a submaximal response even at 100% receptor occupancy. The submaximal efficacy of partial agonists is due to conformational change of the agonist-receptor complex, which reduces effector activation. In addition to signalling activators, several regulators help control intracellular signal transductions. However, it remains unclear whether these signalling regulators contribute to partial agonism. Here we show that regulator of G-protein signalling (RGS) 4 is a determinant for partial agonism of the M2 muscarinic receptor (M2R). In rat atrial myocytes, pilocarpine evoked smaller G-protein-gated K(+) inwardly rectifying (KG) currents than those evoked by ACh. In a Xenopus oocyte expression system, pilocarpine acted as a partial agonist in the presence of RGS4 as it did in atrial myocytes, while it acted like a full agonist in the absence of RGS4. Functional couplings within the agonist-receptor complex/G-protein/RGS4 system controlled the efficacy of pilocarpine relative to ACh. The pilocarpine-M2R complex suppressed G-protein-mediated activation of KG currents via RGS4. Our results demonstrate that partial agonism of M2R is regulated by the RGS4-mediated inhibition of G-protein signalling. This finding helps us to understand the molecular components and mechanism underlying the partial agonism of M2R-mediated physiological responses.
Collapse
Affiliation(s)
- I-Shan Chen
- Department of Pharmacology, Graduate School of MedicineJapan
| | - Kazuharu Furutani
- Department of Pharmacology, Graduate School of MedicineJapan
- Center for Advanced Medical Engineering and Informatics, Osaka UniversityJapan
| | - Atsushi Inanobe
- Department of Pharmacology, Graduate School of MedicineJapan
- Center for Advanced Medical Engineering and Informatics, Osaka UniversityJapan
| | - Yoshihisa Kurachi
- Department of Pharmacology, Graduate School of MedicineJapan
- Center for Advanced Medical Engineering and Informatics, Osaka UniversityJapan
| |
Collapse
|
8
|
Navarro-Polanco RA, Aréchiga-Figueroa IA, Salazar-Fajardo PD, Benavides-Haro DE, Rodríguez-Elías JC, Sachse FB, Tristani-Firouzi M, Sánchez-Chapula JA, Moreno-Galindo EG. Voltage sensitivity of M2 muscarinic receptors underlies the delayed rectifier-like activation of ACh-gated K(+) current by choline in feline atrial myocytes. J Physiol 2013; 591:4273-86. [PMID: 23652593 DOI: 10.1113/jphysiol.2013.255166] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Choline (Ch) is a precursor and metabolite of the neurotransmitter acetylcholine (ACh). In canine and guinea pig atrial myocytes, Ch was shown to activate an outward K(+) current in a delayed rectifier fashion. This current has been suggested to modulate cardiac electrical activity and to play a role in atrial fibrillation pathophysiology. However, the exact nature and identity of this current has not been convincingly established. We recently described the unique ligand- and voltage-dependent properties of muscarinic activation of ACh-activated K(+) current (IKACh) and showed that, in contrast to ACh, pilocarpine induces a current with delayed rectifier-like properties with membrane depolarization. Here, we tested the hypothesis that Ch activates IKACh in feline atrial myocytes in a voltage-dependent manner similar to pilocarpine. Single-channel recordings, biophysical profiles, specific pharmacological inhibition and computational data indicate that the current activated by Ch is IKACh. Moreover, we show that membrane depolarization increases the potency and efficacy of IKACh activation by Ch and thus gives the appearance of a delayed rectifier activating K(+) current at depolarized potentials. Our findings support the emerging concept that IKACh modulation is both voltage- and ligand-specific and reinforce the importance of these properties in understanding cardiac physiology.
Collapse
Affiliation(s)
- Ricardo A Navarro-Polanco
- E. G. Moreno-Galindo: C.U.I.B., Universidad de Colima, Av. 25 de Julio 965, Colonia Villa San Sebastián, C.P. 28045 Colima, Col., México.
| | | | | | | | | | | | | | | | | |
Collapse
|
9
|
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.
Collapse
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
| | | |
Collapse
|
10
|
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.
Collapse
Affiliation(s)
- Adele Stewart
- Department of Pharmacology, Carver College of Medicine, University of Iowa Iowa City, IA, USA
| | | | | |
Collapse
|
11
|
The plasma membrane potential and the organization of the actin cytoskeleton of epithelial cells. Int J Cell Biol 2012; 2012:121424. [PMID: 22315611 PMCID: PMC3272338 DOI: 10.1155/2012/121424] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2011] [Accepted: 10/08/2011] [Indexed: 12/22/2022] Open
Abstract
The establishment and maintenance of the polarized epithelial phenotype require a characteristic organization of the cytoskeletal components. There are many cellular effectors involved in the regulation of the cytoskeleton of epithelial cells. Recently, modifications in the plasma membrane potential (PMP) have been suggested to participate in the modulation of the cytoskeletal organization of epithelia. Here, we review evidence showing that changes in the PMP of diverse epithelial cells promote characteristic modifications in the cytoskeletal organization, with a focus on the actin cytoskeleton. The molecular paths mediating these effects may include voltage-sensitive integral membrane proteins and/or peripheral proteins sensitive to surface potentials. The voltage dependence of the cytoskeletal organization seems to have implications in several physiological processes, including epithelial wound healing and apoptosis.
Collapse
|
12
|
Sahlholm K. The role of RGS protein in agonist-dependent relaxation of GIRK currents in Xenopus oocytes. Biochem Biophys Res Commun 2011; 415:509-14. [PMID: 22068057 DOI: 10.1016/j.bbrc.2011.10.106] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Accepted: 10/22/2011] [Indexed: 01/28/2023]
Abstract
G protein coupled inward rectifier K(+) channels (GIRK) are activated by the G(βγ) subunits of G proteins upon activation of G protein coupled receptors (GPCRs). Receptor-stimulated GIRK currents are known to possess a curious property, termed "agonist-dependent relaxation," denoting a slow current increase upon stepping the membrane voltage from positive to negative potentials. Regulators of G protein signaling (RGS) proteins have earlier been implicated in this phenomenon since RGS coexpression was required for relaxation to be observed in heterologous expression systems. However, a recent study presented contrasting evidence that GIRK current relaxation reflects voltage sensitive agonist binding to the GPCR. The present study re-examined the role of RGS protein in agonist-dependent relaxation and found that RGS coexpression is not necessary for the relaxation phenomenon. However, RGS4 speeds up relaxation kinetics, allowing the phenomenon to be observed using shorter voltage steps. These findings resolve the controversy regarding the role of RGS protein vs. GPCR voltage sensitivity in mediating agonist-dependent relaxation of GIRK currents.
Collapse
Affiliation(s)
- Kristoffer Sahlholm
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
| |
Collapse
|
13
|
Affiliation(s)
- Riccardo Olcese
- Department of Anaesthesiology-Division of Molecular Medicine, Cardiovascular Research Laboratories and Brain Research Institute, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA 90075, USA.
| |
Collapse
|
14
|
Kimple AJ, Bosch DE, Giguère PM, Siderovski DP. Regulators of G-protein signaling and their Gα substrates: promises and challenges in their use as drug discovery targets. Pharmacol Rev 2011; 63:728-49. [PMID: 21737532 DOI: 10.1124/pr.110.003038] [Citation(s) in RCA: 184] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Because G-protein coupled receptors (GPCRs) continue to represent excellent targets for the discovery and development of small-molecule therapeutics, it is posited that additional protein components of the signal transduction pathways emanating from activated GPCRs themselves are attractive as drug discovery targets. This review considers the drug discovery potential of two such components: members of the "regulators of G-protein signaling" (RGS protein) superfamily, as well as their substrates, the heterotrimeric G-protein α subunits. Highlighted are recent advances, stemming from mouse knockout studies and the use of "RGS-insensitivity" and fast-hydrolysis mutations to Gα, in our understanding of how RGS proteins selectively act in (patho)physiologic conditions controlled by GPCR signaling and how they act on the nucleotide cycling of heterotrimeric G-proteins in shaping the kinetics and sensitivity of GPCR signaling. Progress is documented regarding recent activities along the path to devising screening assays and chemical probes for the RGS protein target, not only in pursuits of inhibitors of RGS domain-mediated acceleration of Gα GTP hydrolysis but also to embrace the potential of finding allosteric activators of this RGS protein action. The review concludes in considering the Gα subunit itself as a drug target, as brought to focus by recent reports of activating mutations to GNAQ and GNA11 in ocular (uveal) melanoma. We consider the likelihood of several strategies for antagonizing the function of these oncogene alleles and their gene products, including the use of RGS proteins with Gα(q) selectivity.
Collapse
Affiliation(s)
- Adam J Kimple
- Department of Pharmacology, UNC Neuroscience Center, UNC School of Medicine, University of North Carolina at Chapel Hill, 120 Mason Farm Road, Suite 4010, Chapel Hill, NC 27599-7365, USA
| | | | | | | |
Collapse
|
15
|
Moreno-Galindo EG, Sánchez-Chapula JA, Sachse FB, Rodríguez-Paredes JA, Tristani-Firouzi M, Navarro-Polanco RA. Relaxation gating of the acetylcholine-activated inward rectifier K+ current is mediated by intrinsic voltage sensitivity of the muscarinic receptor. J Physiol 2011; 589:1755-67. [PMID: 21282289 DOI: 10.1113/jphysiol.2010.204115] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Normal heart rate variability is critically dependent upon the G-protein-coupled, acetylcholine (ACh)-activated inward rectifier K+ current, I(KACh). A unique feature of I(KACh) is the so-called ‘relaxation' gating property that contributes to increased current at hyperpolarized membrane potentials. I(KACh) relaxation refers to a slow decrease or increase in current magnitude with depolarization or hyperpolarization, respectively. The molecular mechanism underlying this perplexing gating behaviour remains unclear. Here, we consider a novel explanation for I(KACh) relaxation based upon the recent finding that G-protein-coupled receptors (GPCRs) are intrinsically voltage sensitive and that the muscarinic agonists acetylcholine (ACh) and pilocarpine (Pilo) manifest opposite voltage-dependent I(KACh) modulation. We show that Pilo activation of I(KACh) displays relaxation characteristics opposite to that of ACh. We explain the opposite effects of ACh and Pilo using Markov models of I(KACh) that incorporate ligand-specific, voltage-dependent parameters. Based on experimental and computational findings, we propose a novel molecular mechanism to describe the enigmatic relaxation gating process: I(KACh) relaxation represents a voltage-dependent change in agonist affinity as a consequence of a voltage-dependent conformational change in the muscarinic receptor.
Collapse
|
16
|
Sjögren B, Neubig RR. Thinking outside of the "RGS box": new approaches to therapeutic targeting of regulators of G protein signaling. Mol Pharmacol 2010; 78:550-7. [PMID: 20664002 PMCID: PMC2981398 DOI: 10.1124/mol.110.065219] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Accepted: 07/22/2010] [Indexed: 11/22/2022] Open
Abstract
Regulators of G protein signaling (RGS) proteins are emerging as potentially important drug targets. The mammalian RGS protein family has more than 20 members and they share a common ∼120-residue RGS homology domain or "RGS box." RGS proteins regulate signaling via G protein-coupled receptors by accelerating GTPase activity at active α subunits of G proteins of the G(q) and G(i/o) families. Most studies searching for modulators of RGS protein function have been focused on inhibiting the GTPase accelerating protein activity. However, many RGS proteins contain additional domains that serve other functions, such as interactions with proteins or subcellular targeting. Here, we discuss a rationale for therapeutic targeting of RGS proteins by regulation of expression or allosteric modulation to permit either increases or decreases in RGS function. Several RGS proteins have reduced expression or function in pathophysiological states, so strategies to increase RGS function would be useful. Because several RGS proteins are rapidly degraded by the N-end rule pathway, finding ways to stabilize them may prove to be an effective way to enhance RGS protein function.
Collapse
Affiliation(s)
- Benita Sjögren
- Department of Pharmacology, University of Michigan, 1150 W Medical Center Dr, MSRB III, Ann Arbor, MI 48109, USA
| | | |
Collapse
|
17
|
Murakami S, Suzuki S, Ishii M, Inanobe A, Kurachi Y. Cellular modelling: experiments and simulation to develop a physiological model of G-protein control of muscarinic K+ channels in mammalian atrial cells. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2010; 368:2983-3000. [PMID: 20478917 DOI: 10.1098/rsta.2010.0093] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The first model of G-protein-K(ACh) channel interaction was developed 14 years ago and then expanded to include both the receptor-G-protein cycle and G-protein-K(ACh) channel interaction. The G-protein-K(ACh) channel interaction used the Monod-Wyman-Changeux allosteric model with the idea that one K(ACh) channel is composed of four subunits, each of which binds one active G-protein subunit (G(betagamma)). The receptor-G-protein cycle used a previous model to account for the steady-state relationship between K(ACh) current and intracellular guanosine-5-triphosphate at various extracellular concentrations of acetylcholine (ACh). However, simulations of the activation and deactivation of K(ACh) current upon ACh application or removal were much slower than experimental results. This clearly indicates some essential elements were absent from the model. We recently found that regulators of G-protein signalling are involved in the control of K(ACh) channel activity. They are responsible for the voltage-dependent relaxation behaviour of K(ACh) channels. Based on this finding, we have improved the receptor-G-protein cycle model to reproduce the relaxation behaviour. With this modification, the activation and deactivation of K(ACh) current in the model are much faster and now fall within physiological ranges.
Collapse
Affiliation(s)
- Shingo Murakami
- Division of Molecular and Cellular Pharmacology, Department of Pharmacology, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
| | | | | | | | | |
Collapse
|
18
|
Hibino H, Inanobe A, Furutani K, Murakami S, Findlay I, Kurachi Y. Inwardly rectifying potassium channels: their structure, function, and physiological roles. Physiol Rev 2010; 90:291-366. [PMID: 20086079 DOI: 10.1152/physrev.00021.2009] [Citation(s) in RCA: 1055] [Impact Index Per Article: 75.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Inwardly rectifying K(+) (Kir) channels allow K(+) to move more easily into rather than out of the cell. They have diverse physiological functions depending on their type and their location. There are seven Kir channel subfamilies that can be classified into four functional groups: classical Kir channels (Kir2.x) are constitutively active, G protein-gated Kir channels (Kir3.x) are regulated by G protein-coupled receptors, ATP-sensitive K(+) channels (Kir6.x) are tightly linked to cellular metabolism, and K(+) transport channels (Kir1.x, Kir4.x, Kir5.x, and Kir7.x). Inward rectification results from pore block by intracellular substances such as Mg(2+) and polyamines. Kir channel activity can be modulated by ions, phospholipids, and binding proteins. The basic building block of a Kir channel is made up of two transmembrane helices with cytoplasmic NH(2) and COOH termini and an extracellular loop which folds back to form the pore-lining ion selectivity filter. In vivo, functional Kir channels are composed of four such subunits which are either homo- or heterotetramers. Gene targeting and genetic analysis have linked Kir channel dysfunction to diverse pathologies. The crystal structure of different Kir channels is opening the way to understanding the structure-function relationships of this simple but diverse ion channel family.
Collapse
Affiliation(s)
- Hiroshi Hibino
- Department of Pharmacology, Graduate School of Medicine and The Center for Advanced Medical Engineering and Informatics, Osaka University, Osaka 565-0871, Japan
| | | | | | | | | | | |
Collapse
|
19
|
4-Hydroxy-2-nonenal induces calcium overload via the generation of reactive oxygen species in isolated rat cardiac myocytes. J Card Fail 2009; 15:709-16. [PMID: 19786260 DOI: 10.1016/j.cardfail.2009.04.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2008] [Revised: 04/14/2009] [Accepted: 04/23/2009] [Indexed: 11/21/2022]
Abstract
BACKGROUND It has been reported that that the amount of 4-hydroxy-2-nonenal (HNE), which is a major lipid peroxidation product and a cytotoxic aldehyde, is increased in the human failing myocardium. This study was designed to determine whether HNE has a pro-oxidant effect in cardiac myocytes and whether HNE causes Ca(2+) overload. METHODS AND RESULTS Exposure to HNE for 10 minutes in the presence of ferric nitrilotriacetate induced the production of hydroxyl radical (.OH) in the rat myocardium as assessed by electron spin resonance spectroscopy, and HNE induced the generation of reactive oxygen species (ROS) in a dose-dependent manner as assessed by 2', 7'-dichlorofluorescein diacetate fluorescence. HNE increased intracellular Ca(2+) concentration ([Ca(2+)](i)) as assessed by fura-2 ratio in a dose- and time-dependent manner. After 20 minutes of HNE (400 micromol/L) exposure, hypercontracture was induced in 67% of the cells. Catalase, an antioxidative enzyme that can decompose hydrogen peroxide (H(2)O(2)), significantly attenuated the increase in [Ca(2+)](i) and completely inhibited hypercontracture. Carvedilol, a beta-blocker with potent antioxidant activity, also significantly attenuated the increase in [Ca(2+)](i) and completely inhibited hypercontracture, but propranolol had no effect on either [Ca(2+)](i) increase or hypercontracture. CONCLUSIONS HNE induces the formation of ROS, especially H(2)O(2) and .OH, in cardiomyocytes and subsequently ROS cause intracellular Ca(2+) overload. HNE formation may play an important role as a mediator of oxidative stress in heart failure.
Collapse
|
20
|
Iankova I, Chavey C, Clapé C, Colomer C, Guérineau NC, Grillet N, Brunet JF, Annicotte JS, Fajas L. Regulator of G protein signaling-4 controls fatty acid and glucose homeostasis. Endocrinology 2008; 149:5706-12. [PMID: 18635652 PMCID: PMC2605582 DOI: 10.1210/en.2008-0717] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Circulating free fatty acids are a reflection of the balance between lipogenesis and lipolysis that takes place mainly in adipose tissue. We found that mice deficient for regulator of G protein signaling (RGS)-4 have increased circulating catecholamines, and increased free fatty acids. Consequently, RGS4-/- mice have increased concentration of circulating free fatty acids; abnormally accumulate fatty acids in liver, resulting in liver steatosis; and show a higher degree of glucose intolerance and decreased insulin secretion in pancreas. We show in this study that RGS4 controls adipose tissue lipolysis through regulation of the secretion of catecholamines by adrenal glands. RGS4 controls the balance between adipose tissue lipolysis and lipogenesis, secondary to its role in the regulation of catecholamine secretion by adrenal glands. RGS4 therefore could be a good target for the treatment of metabolic diseases.
Collapse
Affiliation(s)
- Irena Iankova
- Métabolisme et cancer
INSERM : U834Université Montpellier ICentre de recherche Inserm
60, rue de navacelles
34090 MONTPELLIER,FR
- IRCM, Institut de recherche en cancérologie de Montpellier
INSERM : U896Université Montpellier IFR
| | - Carine Chavey
- Métabolisme et cancer
INSERM : U834Université Montpellier ICentre de recherche Inserm
60, rue de navacelles
34090 MONTPELLIER,FR
- IRCM, Institut de recherche en cancérologie de Montpellier
INSERM : U896Université Montpellier IFR
| | - Cyrielle Clapé
- Métabolisme et cancer
INSERM : U834Université Montpellier ICentre de recherche Inserm
60, rue de navacelles
34090 MONTPELLIER,FR
- IRCM, Institut de recherche en cancérologie de Montpellier
INSERM : U896Université Montpellier IFR
| | - Claude Colomer
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Nathalie C. Guérineau
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Nicolas Grillet
- DESN, Développement et évolution du système nerveux
CNRS : UMR8542Ecole Normale Supérieure de Paris46 Rue d'Ulm
75230 PARIS CEDEX 05,FR
- TSRI, The Scripps Research institute
The Scripps Research Institute10550 N Torrey Pines Rd
La Jolla, CA 92037,US
| | - Jean-François Brunet
- DESN, Développement et évolution du système nerveux
CNRS : UMR8542Ecole Normale Supérieure de Paris46 Rue d'Ulm
75230 PARIS CEDEX 05,FR
| | - Jean-Sébastien Annicotte
- Métabolisme et cancer
INSERM : U834Université Montpellier ICentre de recherche Inserm
60, rue de navacelles
34090 MONTPELLIER,FR
- IRCM, Institut de recherche en cancérologie de Montpellier
INSERM : U896Université Montpellier IFR
| | - Lluis Fajas
- Métabolisme et cancer
INSERM : U834Université Montpellier ICentre de recherche Inserm
60, rue de navacelles
34090 MONTPELLIER,FR
- IRCM, Institut de recherche en cancérologie de Montpellier
INSERM : U896Université Montpellier IFR
- CHU Arnaud de Villeneuve
CHRU MontpellierHôpital Arnaud de Villeneuve, F-34295 Montpellier,FR
- * Correspondence should be adressed to: Lluis Fajas
| |
Collapse
|
21
|
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.
Collapse
Affiliation(s)
- Rebecca A Roof
- Department of Pharmacology, 1150 W. Medical Center Dr, University of Michigan, Ann Arbor, MI 48109, USA
| | | | | | | | | | | | | |
Collapse
|
22
|
Ishii M, Ikushima M, Kurachi Y. In vivo interaction between RGS4 and calmodulin visualized with FRET techniques: possible involvement of lipid raft. Biochem Biophys Res Commun 2005; 338:839-46. [PMID: 16246308 DOI: 10.1016/j.bbrc.2005.10.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2005] [Accepted: 10/05/2005] [Indexed: 10/25/2022]
Abstract
Regulators of G-protein signaling (RGS) are a family of proteins which accelerate intrinsic GTP-hydrolysis on heterotrimeric G-protein-alpha-subunits. Although it has been suggested that the function of RGS4 is reciprocally regulated by competitive binding of the membrane phospholipid, phosphatidylinositol-3,4,5,-trisphosphate(PtdIns(3,4,5)P(3)), and Ca(2+)/calmodulin (CaM), it remains to be shown that these interactions occur in vivo. Here, using fluorescence resonance energy transfer (FRET) techniques, we show that an elevation of intracellular Ca(2+) concentration by ionomycin increased the FRET efficiency from ECFP (a variant of cyan fluorescent protein)-labeled calmodulin to Venus (a variant of yellow fluorescent protein)-labeled RGS4. The increase in FRET efficiency was greatly attenuated by pre-treating the cells with methyl-beta-cyclodextrin, which depletes membrane cholesterol and thus disrupts lipid rafts. These results provide the first demonstration of a Ca(2+)-dependent interaction between RGS4 and CaM in vivo and show that association in lipid rafts of the plasma membrane might be involved in this physiological regulation of RGS proteins.
Collapse
Affiliation(s)
- Masaru Ishii
- Department of Pharmacology, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
| | | | | |
Collapse
|
23
|
Ishii M, Kurachi Y. [System biology]. Nihon Yakurigaku Zasshi 2005; 126:117-20. [PMID: 16205014 DOI: 10.1254/fpj.126.117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
|
24
|
Ishii M, Fujita S, Yamada M, Hosaka Y, Kurachi Y. Phosphatidylinositol 3,4,5-trisphosphate and Ca2+/calmodulin competitively bind to the regulators of G-protein-signalling (RGS) domain of RGS4 and reciprocally regulate its action. Biochem J 2005; 385:65-73. [PMID: 15324308 PMCID: PMC1134674 DOI: 10.1042/bj20040404] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2004] [Revised: 07/26/2004] [Accepted: 08/23/2004] [Indexed: 11/17/2022]
Abstract
RGS (regulators of G-protein signalling) are a diverse group of proteins, which accelerate intrinsic GTP hydrolysis on heterotrimeric G-protein a subunits. They are involved in the control of a physiological behaviour known as 'relaxation' of G-protein-gated K+ channels in cardiac myocytes. The GTPase-accelerating activity of cardiac RGS proteins, such as RGS4, is inhibited by PtdIns(3,4,5)P3 (phosphatidylinositol 3,4,5-trisphosphate) and this inhibition is cancelled by Ca2+/calmodulin (CaM) formed during membrane depolarization. G-protein-gated K+ channel activity decreases on depolarization owing to the facilitation of GTPase-activating protein activity by RGS proteins and vice versa on hyperpolarization. The molecular mechanism responsible for this reciprocal control of RGS action by PtdIns(3,4,5)P3 and Ca2+/CaM, however, has not been fully elucidated. Using lipid-protein co-sedimentation assay and surface plasmon resonance measurements, we show in the present study that the control of the GTPase-accelerating activity of the RGS4 protein is achieved through the competitive binding of PtdIns(3,4,5)P3 and Ca2+/CaM within its RGS domain. Competitive binding occurs exclusively within the RGS domain and involves a cluster of positively charged residues located on the surface opposite to the Ga interaction site. In the RGS proteins conserving these residues, the reciprocal regulation by PtdIns(3,4,5)P3 and Ca2+/CaM may be important for their physiological regulation of G-protein signalling.
Collapse
Key Words
- calmodulin
- g-protein
- phosphoinositide
- reciprocal regulation
- regulators of g-protein signalling (rgs)
- ach, acetylcholine
- cbb, coomassie brilliant blue
- cam, calmodulin
- dic16, dihexadecanoyl
- gap, gtpase-activating protein
- gst, glutathione s-transferase
- kg, g-protein-gated k+
- kir, inward rectifier k+
- pc, l-α-phosphaphatidylcholine
- pe, l-α-phosphatidylethanolamine
- ptdins(4,5)p2, phosphatidylinositol 4,5-bisphosphate
- ptdins(3,4,5)p3, phosphatidylinositol 3,4,5-trisphosphate
- ptdins(5)p, phosphatidylinositol 5-phosphate
- rgs, regulators of g-protein signalling
- ru, resonance unit
- spr, surface plasmon resonance for brevity, the single-letter system for amino acids has been used, e.g. k99 means lys99
Collapse
Affiliation(s)
- Masaru Ishii
- Department of Pharmacology, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Satoru Fujita
- Department of Pharmacology, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Mitsuhiko Yamada
- Department of Pharmacology, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Yukio Hosaka
- Department of Pharmacology, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Yoshihisa Kurachi
- Department of Pharmacology, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| |
Collapse
|
25
|
Abstract
The present paper demonstrates a remarkable pervasiveness of underlying Ca(2+) signaling motifs among the available biochemical findings in schizophrenic patients and among the major molecular hypotheses of this disease. In addition, the paper reviews the findings suggesting that Ca(2+) is capable of inducing structural and cognitive deficits seen in schizophrenia. The evidence of the ability of antipsychotic drugs to affect Ca(2+) signaling is also presented. Based on these data, it is proposed that altered Ca(2+) signaling may constitute the central unifying molecular pathology in schizophrenia. According to this hypothesis schizophrenia can result from alterations in multiple proteins and other molecules as long as these alterations lead to abnormalities in certain key aspects of intracellular Ca(2+) signaling cascades.
Collapse
Affiliation(s)
- Michael S Lidow
- Department of Biomedical Sciences and Program of Neuroscience, University of Maryland, Room 5-A-12, HHH, 666 W. Baltimore Street, Baltimore, MD 21201, USA.
| |
Collapse
|
26
|
Kurachi Y, Ishii M. Cell signal control of the G protein-gated potassium channel and its subcellular localization. J Physiol 2004; 554:285-94. [PMID: 12923211 PMCID: PMC1664760 DOI: 10.1113/jphysiol.2003.048439] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
G protein-gated inward rectifier K(+) (K(G)) channels are directly activated by the betagamma subunits released from pertussis toxin-sensitive G proteins, and contribute to neurotransmitter-induced deceleration of heart beat, formation of slow inhibitory postsynaptic potentials in neurones and inhibition of hormone release in endocrine cells. The physiological roles of K(G) channels are critically determined by mechanisms which regulate their activity and their subcellular localization. K(G) channels are tetramers of inward rectifier K(+) (Kir) channel subunits, Kir3.x. The combination of Kir3.x subunits in each K(G) channel varies among tissues and cell types. Each subunit of the channel possesses one Gbetagamma binding site. The binding of Gbetagamma increases the number of functional K(G) channels via a mechanism that can be described by the Monod-Wyman-Changeux allosteric model. During voltage pulses K(G) channel current alters time dependently. The K(G) current exhibits inward rectification due to blockade of outward-going current by intracellular Mg(2+) and polyamines. Upon repolarization, this blockade is relieved practically instantaneously and then the current slowly increases further. This slow current alteration is called 'relaxation'. Relaxation is caused by the voltage-dependent behaviour of regulators of G protein signalling (RGS proteins), which accelerate intrinsic GTP hydrolysis mediated by the Galpha subunit. Thus, the relaxation behaviour of K(G) channels reflects the time course with which the G protein cycle is altered by RGS protein activity at each membrane potential. Subcellular localization of K(G) channels is controlled by several distinct mechanisms, some of which have been recently clarified. The neuronal K(G) channel, which contains Kir3.2c, is localized in the postsynaptic density (PSD) of various neurones including dopaminergic neurones in substantia nigra. Its localization at PSD may be controlled by PDZ domain-containing anchoring proteins. The K(G) channel in thyrotrophs is localized exclusively on secretary vesicles, which upon stimulation are rapidly inserted into the plasma membrane and causes hyperpolarization of the cell. This mechanism indicates a novel negative feedback regulation of exocytosis. In conclusion, K(G) channels are under the control of a variety of signalling molecules which regulate channel activity, subcellular localization and thus their physiological roles in myocytes, neurones and endocrine cells.
Collapse
Affiliation(s)
- Yoshihisa Kurachi
- Department of Pharmacology II, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
| | | |
Collapse
|
27
|
Abstract
Regulators of G-protein signaling (RGS) proteins are a family of proteins, which accelerate GTPase-activity intrinsic to the alpha subunits of heterotrimeric G-proteins and play crucial roles in the physiological control of G-protein signaling. If RGS proteins were active unrestrictedly, they would completely suppress various G-protein-mediated cell signaling as has been shown in the over-expression experiments of various RGS proteins. Thus, physiologically the modes of RGS-action should be under some regulation. The regulation can be achieved through the control of either the protein function and/or the subcellular localization. Examples for the former are as follows: (i) Phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) inhibits RGS-action, which can be recovered by Ca(2+)/calmodulin. This underlies a voltage-dependent "relaxation" behavior of G-protein-gated K(+) channels. (ii) A modulatory protein, 14-3-3, binds to the RGS proteins phosphorylated by PKA and inhibits their actions. For the latter mechanism, additional regulatory modules, such as PDZ, PX, and G-protein gamma subunit-like (GGL) domains, identified in several RGS proteins may be responsible: (i) PDZ domain of RGS12 interacts with a G-protein-coupled chemokine receptor, CXCR2, and thus facilitates its GAP action on CXCR2-mediated G-protein signals. (ii) RGS9 forms a complex with a type of G-protein beta-subunit (Gbeta5) via its GGL domain, which facilitates the GAP function of RGS9. Both types of regulations synergistically control the mode of action of RGS proteins in the physiological conditions, which contributes to fine tunings of G-protein signalings.
Collapse
Affiliation(s)
- Masaru Ishii
- Department of Pharmacology, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, 565-0871, Osaka, Japan
| | | |
Collapse
|
28
|
Abstract
Regulator of G-protein signaling (RGS) proteins are a family of proteins that accelerate intrinsic GTP hydrolysis on alpha subunits of trimeric G proteins. They play crucial roles in the physiological regulation of G-protein-mediated cell signaling. If RGS proteins were active unrestrictedly, they would completely suppress G-protein-mediated signaling. Therefore, it is important to understand how the actions of RGS proteins are regulated under different physiological conditions. We have discovered a physiological mode of regulation of a RGS protein in cardiac myocytes. The voltage-dependent formation of Ca2+/calmodulin (CaM) facilitated the GTPase activity of RGS proteins by removing intrinsic inhibition mediated by the phospholipid phosphatidylinositol-3,4,5-trisphosphate. This modulation of RGS protein action underlies the characteristic "relaxation" behavior of G-protein-gated K+ channels in native cardiac myocytes. This article describes briefly the discovery of this novel mode of RGS protein modulation in native cardiac myocytes and then gives details of the biochemical and electrophysiological assays used for the functional investigation of this modulation. These assays would be useful for dissecting the physiological modes of action of RGS proteins in controlling G-protein-mediated signaling machinery.
Collapse
Affiliation(s)
- Masaru Ishii
- Department of Pharmacology, Osaka University Graduate School of Medicine, Osaka, Japan
| | | |
Collapse
|
29
|
Werry TD, Wilkinson GF, Willars GB. Mechanisms of cross-talk between G-protein-coupled receptors resulting in enhanced release of intracellular Ca2+. Biochem J 2003; 374:281-96. [PMID: 12790797 PMCID: PMC1223610 DOI: 10.1042/bj20030312] [Citation(s) in RCA: 145] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2003] [Revised: 06/03/2003] [Accepted: 06/05/2003] [Indexed: 12/21/2022]
Abstract
Alteration in [Ca(2+)](i) (the intracellular concentration of Ca(2+)) is a key regulator of many cellular processes. To allow precise regulation of [Ca(2+)](i) and a diversity of signalling by this ion, cells possess many mechanisms by which they are able to control [Ca(2+)](i) both globally and at the subcellular level. Among these are many members of the superfamily of GPCRs (G-protein-coupled receptors), which are characterized by the presence of seven transmembrane domains. Typically, those receptors able to activate PLC (phospholipase C) enzymes cause release of Ca(2+) from intracellular stores and influence Ca(2+) entry across the plasma membrane. It has been well documented that Ca(2+) signalling by one type of GPCR can be influenced by stimulation of a different type of GPCR. Indeed, many studies have demonstrated heterologous desensitization between two different PLC-coupled GPCRs. This is not surprising, given our current understanding of negative-feedback regulation and the likely shared components of the signalling pathway. However, there are also many documented examples of interactions between GPCRs, often coupling preferentially to different signalling pathways, which result in a potentiation of Ca(2+) signalling. Such interactions have important implications for both the control of cell function and the interpretation of in vitro cell-based assays. However, there is currently no single mechanism that adequately accounts for all examples of this type of cross-talk. Indeed, many studies either have not addressed this issue or have been unable to determine the mechanism(s) involved. This review seeks to explore a range of possible mechanisms to convey their potential diversity and to provide a basis for further experimental investigation.
Collapse
Affiliation(s)
- Tim D Werry
- Department of Cell Physiology and Pharmacology, Medical Sciences Building, University of Leicester, UK
| | | | | |
Collapse
|
30
|
Bösche LI, Wellner-Kienitz MC, Bender K, Pott L. G protein-independent inhibition of GIRK current by adenosine in rat atrial myocytes overexpressing A1 receptors after adenovirus-mediated gene transfer. J Physiol 2003; 550:707-17. [PMID: 12815176 PMCID: PMC2343091 DOI: 10.1113/jphysiol.2003.041962] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
G protein-activated inwardly rectifying K+ (GIRK) channels, important regulators of membrane excitability in the heart and central nervous system, are activated by interaction with betagamma subunits from heterotrimeric G proteins upon receptor stimulation. In atrial myocytes various endogenous receptors couple to GIRK channels, including the canonical muscarinic M2 receptor (M2AChR) and the A1 adenosine receptor (A1AdoR). Saturating stimulation of A1AdoR in atrial myocytes activates only a fraction of the GIRK current that is activated via M2AChR, which reflects a lower density of A1AdoR. In the present study A1AdoR were overexpressed by means of adenovirus-mediated gene transfer using green fluorescent protein (GFP) as the reporter. Confirmatory to a previous study, this resulted in an increased sensitivity of macroscopic GIRK current (ACh-activated K+ current (IK(ACh))) to stimulation by Ado. However, in the majority of GFP-positive myocytes, exposure to Ado at concentrations > or =1 microM resulted in activation of IK(ACh) followed by a rapid inhibition. In those cells a rebound activation of current was recorded upon washout of Ado. The inhibitory component could be recorded in isolation when IK(ACh) was activated by M2AChR-stimulation and brief pulses of Ado were superimposed. In myocytes loaded with GTP-gamma-S, IK(ACh), irreversibly activated by brief exposure to agonist, was still reversibly inhibited by Ado, suggesting that inhibition is independent of G protein cycling. In myocytes co-transfected with adenoviral vectors encoding A1AdoR and GIRK4 subunit, no inhibition of GIRK current by Ado was observed. As acute desensitization of atrial GIRK current, which is reminiscent of the inhibition described here, has been shown to be absent in myocytes overexpressing GIRK4, this suggests that acute desensitization and the novel inhibition might share a common pathway whose target is the GIRK channel complex or its GIRK1 subunit.
Collapse
Affiliation(s)
- Leif I Bösche
- Department of Physiology, Ruhr-University Bochum, D-4480 Bochum, Germany
| | | | | | | |
Collapse
|
31
|
Tosetti P, Pathak N, Jacob MH, Dunlap K. RGS3 mediates a calcium-dependent termination of G protein signaling in sensory neurons. Proc Natl Acad Sci U S A 2003; 100:7337-42. [PMID: 12771384 PMCID: PMC165876 DOI: 10.1073/pnas.1231837100] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
G proteins modulate synaptic transmission. Regulators of G protein signaling (RGS) proteins accelerate the intrinsic GTPase activity of Galpha subunits, and thus terminate G protein activation. Whether RGS proteins themselves are under cellular control is not well defined, particularly in native cells. In dorsal root ganglion neurons overexpressing RGS3, we find that G protein signaling is rapidly terminated (or "desensitized") by calcium influx through voltage-gated channels. This rapid desensitization is most likely mediated by direct binding of calcium to RGS3, as deletion of an EF-hand domain in RGS3 abolishes both the desensitization (observed physiologically) and a calcium-RGS3 interaction (observed in a gel-shift assay). A naturally occurring variant of RGS3 that lacks the EF hand neither binds calcium nor produces rapid desensitization, giving rise instead to a slower calcium-dependent desensitization that is attenuated by a calmodulin antagonist. Thus, activity-evoked calcium entry in sensory neurons may provide differential control of G protein signaling, depending on the isoform of RGS3 expressed in the cells. In complex neural circuits subjected to abundant synaptic inhibition by G proteins (as occurs in dorsal spinal cord), rapid termination of inhibition by electrical activity by EF hand-containing RGS3 may ensure the faithful transmission of information from the most active sensory inputs.
Collapse
Affiliation(s)
- Patrizia Tosetti
- Department of Neuroscience, Tufts University School of Medicine and Molecular Cardiology Research Institute, New England Medical Center, Boston, MA 02111, USA
| | | | | | | |
Collapse
|
32
|
Wieland T, Mittmann C. Regulators of G-protein signalling: multifunctional proteins with impact on signalling in the cardiovascular system. Pharmacol Ther 2003; 97:95-115. [PMID: 12559385 DOI: 10.1016/s0163-7258(02)00326-1] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Regulator of G-protein signalling (RGS) proteins form a superfamily of at least 25 proteins, which are highly diverse in structure, expression patterns, and function. They share a 120 amino acid homology domain (RGS domain), which exhibits GTPase accelerating activity for alpha-subunits of heterotrimeric G-proteins, and thus, are negative regulators of G-protein-mediated signalling. Based on the organisation of the Rgs genes, structural similarities, and differences in functions, they can be divided into at least six subfamilies of RGS proteins and three more families of RGS-like proteins. Many of these proteins regulate signalling processes within cells, not only via interaction with G-protein alpha-subunits, but are G-protein-regulated effectors, Gbetagamma scavenger, or scaffolding proteins in signal transduction complexes as well. The expression of at least 16 different RGS proteins in the mammalian or human myocardium have been described. A subgroup of at least eight was detected in a single atrial myocyte. The exact functions of these proteins remain mostly elusive, but RGS proteins such as RGS4 are involved in the regulation of G(i)-protein betagamma-subunit-gated K(+) channels. An up-regulation of RGS4 expression has been consistently found in human heart failure and some animal models. Evidence is increasing that the enhanced RGS4 expression counter-regulates the G(q/11)-induced signalling caused by hypertrophic stimuli. In the vascular system, RGS5 seems to be an important signalling regulator. It is expressed in vascular endothelial cells, but not in cultured smooth muscle cells. Its down-regulation, both in a model of capillary morphogenesis and in an animal model of stroke, render it a candidate gene, which may be involved in the regulation of capillary growth, angiogenesis, and in the pathophysiology of stroke.
Collapse
Affiliation(s)
- Thomas Wieland
- Institut für Pharmakologie und Toxikologie, Fakultät für Klinische Medizin Mannheim der Universität Heidelberg, Maybachstrasse 14-16, D-68169 Mannheim, Germany.
| | | |
Collapse
|
33
|
Bender K, Wellner-Kienitz MC, Pott L. Transfection of a phosphatidyl-4-phosphate 5-kinase gene into rat atrial myocytes removes inhibition of GIRK current by endothelin and alpha-adrenergic agonists. FEBS Lett 2002; 529:356-60. [PMID: 12372628 DOI: 10.1016/s0014-5793(02)03426-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
GIRK (G protein-activated inward-rectifying K(+) channel) channels, important regulators of membrane excitability in the heart and in the central nervous, are activated by interaction with betagamma subunits from heterotrimeric G proteins upon receptor stimulation. For activation interaction of the channel with phosphatidylinositol 4,5-bisphosphate (PtIns(4,5)P(2)) is conditional. Previous studies have provided evidence that in myocytes PtIns(4,5)P(2) levels relevant to GIRK channel regulation are under regulatory control of receptors activating phospholipase C. In the present study a phosphatidyl-4-phosphate 5-kinase was expressed in atrial myocytes by transient transfection. This did not affect basal properties of GIRK current activated by acetylcholine via M(2) receptors but completely abolished inhibition of guanosine triphosphate-gamma-S activated current by endothelin-1 or alpha-adrenergic agonists. We conclude that though PtIns(4,5)P(2) is conditional for channel gating, its normal level in the membrane is not limiting basal function of GIRK channels. Moreover, our data provide further evidence for a regulation of GIRK channels by alpha(1A) receptors and endothelin-A receptors, endogenously expressed in atrial myocytes, via depletion of PtIns(4,5)P(2).
Collapse
Affiliation(s)
- Kirsten Bender
- Department of Physiology, Ruhr-University Bochum, D-4480 Bochum, Germany
| | | | | |
Collapse
|
34
|
Ishii M, Inanobe A, Kurachi Y. PIP3 inhibition of RGS protein and its reversal by Ca2+/calmodulin mediate voltage-dependent control of the G protein cycle in a cardiac K+ channel. Proc Natl Acad Sci U S A 2002; 99:4325-30. [PMID: 11904384 PMCID: PMC123647 DOI: 10.1073/pnas.072073399] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2002] [Accepted: 02/06/2002] [Indexed: 01/10/2023] Open
Abstract
Regulators of G protein signaling (RGS) accelerate intrinsic GTP hydrolysis on alpha subunits of trimeric G proteins and play crucial roles in the physiological regulation of G protein-mediated cell signaling. The control mechanisms of the action of RGS proteins per se are poorly clarified, however. We recently showed a physiological mode of action of a RGS protein in cardiac myocytes. The voltage-dependent formation of Ca2+/calmodulin facilitated the GTPase activity of RGS by an unidentified mechanism, which underlay the "relaxation" behavior of G protein-gated K+ (K(G)) channels. Here we report the mechanism which is the reversal by Ca2+/calmodulin of phosphatidylinositol-3,4,5,-trisphosphate (PIP3)-mediated inhibition of RGS. Purified RGS4 protein alone inhibited GTP-induced K(G) channel activity in inside-out patches from atrial myocytes. The inhibitory effect of RGS4 was reduced by PIP3 and restored by addition of Ca2+/calmodulin. The intracellular application of anti-PIP3 antibody abolished the RGS-dependent relaxation behavior of K(G) current in atrial myocytes. This study, therefore, reveals a general physiological control mechanism of RGS proteins by lipid-protein interaction.
Collapse
Affiliation(s)
- Masaru Ishii
- Department of Pharmacology II, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | | | | |
Collapse
|
35
|
Neubig RR, Siderovski DP. Regulators of G-protein signalling as new central nervous system drug targets. Nat Rev Drug Discov 2002; 1:187-97. [PMID: 12120503 DOI: 10.1038/nrd747] [Citation(s) in RCA: 327] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
G-protein-coupled receptors (GPCRs) are major targets for drug discovery. The regulator of G-protein signalling (RGS)-protein family has important roles in GPCR signal transduction. RGS proteins contain a conserved RGS-box, which is often accompanied by other signalling regulatory elements. RGS proteins accelerate the deactivation of G proteins to reduce GPCR signalling; however, some also have an effector function and transmit signals. Combining GPCR agonists with RGS inhibitors should potentiate responses, and could markedly increase the agonist's regional specificity. The diversity of RGS proteins with highly localized and dynamically regulated distributions in brain makes them attractive targets for pharmacotherapy of central nervous system disorders.
Collapse
Affiliation(s)
- Richard R Neubig
- Departments of Pharmacology and Internal Medicine (Hypertension Division), University of Michigan, Ann Arbor, Massachusetts 48109-0632, USA.
| | | |
Collapse
|