Redox-dependent Gating of G Protein-coupled Inwardly Rectifying K+ Channels

Zeidner, Gil; Sadja, Rona; Reuveny, Eitan

doi:10.1074/jbc.m105189200

Cited by 38 publications

(37 citation statements)

References 57 publications

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“…Osmotically driven guard cell inflation is thereby inhibited and guard cell deflation is promoted, resulting in inhibition of stomatal opening, promotion of stomatal closure, and reduced plant water loss. Guard-cell K in currents share with GIRK channels the properties of inward rectification, activation by ATP, activation by PtdInsP 2 , and regulation by cellular redox status (9,10,(20)(21)(22)(23). We previously showed that genetic depletion of GPA1 relieves ABA inhibition of guard-cell K in currents (24,25).…”

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confidence: 99%

Abscisic acid regulation of guard-cell K ⁺ and anion channels in Gβ- and RGS-deficient Arabidopsis lines

Fan

Zhang

Chen³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

108

141

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In mammals, basal currents through G protein-coupled inwardly rectifying K ؉ (GIRK) channels are repressed by G␣i/oGDP, and the channels are activated by direct binding of free G␤␥ subunits released upon stimulation of G␣ i/o-coupled receptors. However, essentially all information on G protein regulation of GIRK electrophysiology has been gained on the basis of coexpression studies in heterologous systems. A major advantage of the model organism, Arabidopsis thaliana, is the ease with which knockout mutants can be obtained. We evaluated plants harboring mutations in the sole Arabidopsis G␣ (AtGPA1), G␤ (AGB1), and Regulator of G protein Signaling (AtRGS1) genes for impacts on ion channel regulation. In guard cells, where K ؉ fluxes are integral to cellular regulation of stomatal apertures, inhibition of inward K ؉ (Kin) currents and stomatal opening by the phytohormone abscisic acid (ABA) was equally impaired in Atgpa1 and agb1 single mutants and the Atgpa1 agb1 double mutant. AGB1 overexpressing lines maintained a wild-type phenotype. The Atrgs1 mutation did not affect K in current magnitude or ABA sensitivity, but Kin voltage-activation kinetics were altered. Thus, Arabidopsis cells differ from mammalian cells in that they uniquely use the G␣ subunit or regulation of the heterotrimer to mediate K in channel modulation after ligand perception. In contrast, outwardly rectifying (K out) currents were unaltered in the mutants, and ABA activation of slow anion currents was conditionally disrupted in conjunction with cytosolic pH clamp. Our studies highlight unique aspects of ion channel regulation by heterotrimeric G proteins and relate these aspects to stomatal aperture control, a key determinant of plant biomass acquisition and drought tolerance.G protein-coupled inwardly rectifying potassium or ''GIRK'' channels (also known as Kir3 channels) comprise important targets of heterotrimeric G protein regulation in mammals (1, 2). GIRK channels mediate signals from muscarinic, adrenergic, opioid, dopaminergic, and GABA B receptors (3). Basal activity of GIRK channels is repressed by their direct binding of G␣ i/o GDP (4, 5) within a macromolecular complex that includes G␤␥ (4-7). Upon activation of G i/o -coupled G protein-coupled receptors (GPCRs), formation of the GTP-bound form of G␣ i/o both alleviates G␣-mediated repression and releases ␤␥ dimers that independently interact with the channel (7,8). G␤ 1-4 ␥ binding strengthens GIRK interaction with phosphatidylinositol 4,5-bisphosphate (PtdInsP 2 ), thereby promoting conformational changes that increase channel open time (3, 9-11). Conversely, G␣ q -based activation of phospholipase C opposes GIRK activity via both depletion of PtdInsP 2 and activation of PKC-based phosphorylation events (12).Numerous studies analyzing GIRK activity in Xenopus oocytes and cultured mammalian cells have led to the beautifully intricate model described above. However, studies analyzing GIRK activity in the appropriate native cell context upon genetic depletion of G␤ subunits are lack...

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confidence: 99%

Abscisic acid regulation of guard-cell K ⁺ and anion channels in Gβ- and RGS-deficient Arabidopsis lines

Fan

Zhang

Chen³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

108

141

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“…Thiol/disulfide exchange reactions at the level of cysteine residues in proteins depend on the ϪSH group of GSH and have been suggested to regulate the progression of apoptosis (68,94), Thiol-exchange reactions might also be involved in the regulation of ion channels and changes in the ionic homeostasis of the cell. In fact, previous reports demonstrate that sulfhydryl groups within cytosolic cysteine domains of ion channels directly modulate channel activity (95)(96)(97).…”

Section: Discussionmentioning

confidence: 99%

Glutathione Depletion and Disruption of Intracellular Ionic Homeostasis Regulate Lymphoid Cell Apoptosis

Franco

DeHaven

Sifre

et al. 2008

Journal of Biological Chemistry

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Intracellular glutathione (GSH) depletion is an important hallmark of apoptosis. We have recently shown that GSH depletion by its extrusion regulates apoptosis independently of excessive reactive oxygen species accumulation. However, the mechanisms by which GSH depletion regulates apoptosis are still unclear. Because disruption of intracellular ionic homeostasis, associated with apoptotic volume decrease (AVD), is necessary for the progression of apoptotic cell death, we sought to evaluate the relationship between GSH transport and ionic homeostasis during Fas ligand (FasL)-induced apoptosis in Jurkat cells. GSH depletion in response to FasL was paralleled by distinct degrees of AVD identified by differences in cellular forward scatter and electronic impedance analysis. Inhibition of GSH efflux prevented AVD, K ؉ loss, and the activation of two distinct ionic conductances, mediated by Kv1.3 and outward rectifying Cl Apoptosis or programmed cell death is a ubiquitous energydependent, evolutionary conserved process. Under physiological conditions it is important not only in the constant turnover of cells in all tissues, but also during the normal development and senescence of the organism. Moreover, its deregulation has been observed to occur as either a cause or consequence of distinct pathologies (1, 2). A clear example is apoptosis mediated by Fas ligand (FasL) 2 receptor (Fas/CD95/Apo-1) activation, which is necessary for immune system homeostasis because of its role in the rapid clearance of immunoreactive T cells maintaining the immune balance and reducing the risk of autoimmune diseases (3). Apoptosis is a highly ordered process characterized by the progressive activation of precise pathways leading to specific biochemical and morphological alterations. Initial stages of apoptosis are characterized by activation of initiator caspases, changes in the cellular redox potential, intracellular ionic homeostasis, cell shrinkage or apoptotic volume decrease (AVD), loss of membrane lipid asymmetry, and chromatin condensation. Later stages associated with the execution phase of apoptosis are characterized by execution caspase and endonuclease activation, apoptotic body formation, and cell fragmentation (4, 5). Reduced glutathione (GSH) is the most abundant low molecular weight thiol in animal cells and is the major determinant in the redox potential of the cell. It is involved in many cellular processes, including antioxidant defense, drug detoxification, signaling, and proliferation (6 -10). Glutathione loss is an early hallmark in the progression of cell death in response to different apoptotic stimuli (11)(12)(13)(14)(15)(16)(17)(18)(19). Death receptor (including Fas)-induced GSH depletion has been clearly associated with the activation of a plasma membrane transport mechanism and not to its oxidation by reactive oxygen species (ROS) (20 -23). Several studies have shown a correlation between GSH efflux and the progression of apoptosis, and inhibition of GSH loss is able to rescue cells from cell death progress...

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“…Similar to Cys-49 in Kir1.1, the accessibility of Cys-42 in Kir6.2 is reduced in the open state. In GIRK1/ GIRK4 heteromeric channels, the N-terminal cysteines were shown to mediate the redox modulation of channel currents (29). Zeidner et al (29) proposed that the neighboring lysines stabilize the oxidation of these cysteines, and as a result, mixed disulfides are formed by interaction with reduced glutathione, which inhibits channel activity.…”

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confidence: 99%

“…In GIRK1/ GIRK4 heteromeric channels, the N-terminal cysteines were shown to mediate the redox modulation of channel currents (29). Zeidner et al (29) proposed that the neighboring lysines stabilize the oxidation of these cysteines, and as a result, mixed disulfides are formed by interaction with reduced glutathione, which inhibits channel activity. The GIRK subunits also have a cysteine within the middle C terminus that is at the homologous position as Cys-308 in Kir1.1.…”

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confidence: 99%

A Role for the Middle C Terminus of G-protein-activated Inward Rectifier Potassium Channels in Regulating Gating

Guo¹,

Waldron

Murrell‐Lagnado

2002

Journal of Biological Chemistry

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We have used sulfhydryl-modifying reagents to investigate the regulation of G-protein-activated inward rectifier potassium (GIRK) channels via their cytoplasmic domains. Modification of either the conserved N-terminal cysteines (GIRK1C53 and GIRK2C65) or the middle C-terminal cysteines (GIRK1C310 and GIRK2C321) independently inhibited GIRK1/GIRK2 heteromeric channels. With the exception of GIRK2C65, these cysteines were relatively inaccessible to large modifying reagents. The accessibility was further reduced by a mutation at the end of the second transmembrane domain that stabilized the open state of the channel. Thus it is unlikely that these cysteines line the permeation pathway of the open pore. Cysteines introduced 3 and 6 amino acids upstream of GIRK2C321 (G318C and E315C) were considerably more accessible. The effect of modification was dependent on the charge of the reagent. Modification of E315C in GIRK2 and E304C in GIRK1 by sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES(؊)) increased the current by ϳ17-fold, whereas modification by 2-aminoethyl methanethiosulfonate hydrochloride (MTSEA(؉)), abolished the current. There was no effect on single-channel conductance. Members of the Kir family of potassium channels are regulated by many different intracellular ligands. For the GIRK 1 channels, it has been shown that G ␤␥ subunits (1-3), phosphoinositides (4 -6), and Na ϩ (7-9) all directly interact with the channel to increase activity. In contrast, polyamines and Mg 2ϩ interact with the channel to inhibit currents by a mechanism of pore blockade (10 -12). The majority of regulators of Kir channels bind to regions within the cytoplasmic N-and C-terminal tails of the Kir subunits. Kir subunits contain two transmembrane (TM) segments with a short N terminus and a long C terminus of between 200 and 300 amino acids. Little is known of the structure of the cytoplasmic regions or of the conformational changes that occur during the process of regulation.Kir subunits assemble as tetramers, and the second TM helices line the pore and form a gate that controls ion flux (13-17). For different members of the Kir family, the region of high sequence similarity extends ϳ30 amino acids from TM1 into the N terminus and ϳ170 amino acids from TM2 into the C terminus. The cytoplasmic regions adjacent to TM1 and TM2 have been proposed to form an intracellular vestibule of the pore (18). Modification of cysteines introduced into these regions of Kir2.1 inhibit channel currents, and at the E224C position the extent of inhibition was shown to be proportional to the size of the modifying reagent, suggesting that the mechanism was one of pore blockade. The Glu-224 residue in Kir2.1 and a histidine at a similar position in Kir6.2 (His-216) were also shown to affect polyamine block by electrostatic interactions, suggesting that they face the permeation pathway (19 -21). Positively charged residues within the proximal C terminus are also known to be important for binding phosphoinositides, and an aspartate within this region of...

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Redox-dependent Gating of G Protein-coupled Inwardly Rectifying K+ Channels

Cited by 38 publications

References 57 publications

Abscisic acid regulation of guard-cell K ⁺ and anion channels in Gβ- and RGS-deficient Arabidopsis lines

Abscisic acid regulation of guard-cell K ⁺ and anion channels in Gβ- and RGS-deficient Arabidopsis lines

Glutathione Depletion and Disruption of Intracellular Ionic Homeostasis Regulate Lymphoid Cell Apoptosis

A Role for the Middle C Terminus of G-protein-activated Inward Rectifier Potassium Channels in Regulating Gating

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Redox-dependent Gating of G Protein-coupled Inwardly Rectifying K+ Channels

Cited by 38 publications

References 57 publications

Abscisic acid regulation of guard-cell K + and anion channels in Gβ- and RGS-deficient Arabidopsis lines

Abscisic acid regulation of guard-cell K + and anion channels in Gβ- and RGS-deficient Arabidopsis lines

Glutathione Depletion and Disruption of Intracellular Ionic Homeostasis Regulate Lymphoid Cell Apoptosis

A Role for the Middle C Terminus of G-protein-activated Inward Rectifier Potassium Channels in Regulating Gating

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Abscisic acid regulation of guard-cell K ⁺ and anion channels in Gβ- and RGS-deficient Arabidopsis lines

Abscisic acid regulation of guard-cell K ⁺ and anion channels in Gβ- and RGS-deficient Arabidopsis lines