Pub Date : 2017-03-04DOI: 10.1080/19336950.2016.1247528
E. Korkotian, M. Segal
The possible role of store operated calcium entry (SOCE) through the Orai1 channel in central neurons has attracted growing attention in recent years because of its involvement in regulation of calcium homeostasis in the neuron. One unique neuronal compartment associated with calcium homeostasis is the dendritic spine, the site of excitatory synapses in the majority of neurons in the brain. It has been linked to neuronal plasticity, which is highly regulated by calcium influx during intense synaptic activity. The formation, plasticity and longevity of dendritic spines have been studied extensively, but the rules governing these processes are still not clear and not universal. The cultured hippocampal neuron provides a convenient vehicle to study the role of SOCE channels in dendritic spine formation and plasticity. Indeed, recent studies have detected the presence of Orai1 channels in central neurons, and further studies indicated that STIM2, the sensor for endoplasmic reticulum calcium store depletion, is instrumental in maintenance of mature dendritic spines in cultured hippocampal neurons. We have recently analyzed the role of Orai1 in dendritic spine formation and plasticity. This study follows our interest in the role of calcium stores in spine plasticity, where we found that dendritic spines contain ryanodine receptor-type calcium stores. In the more recent study, we employed plasmids that encode the Orai1 protein, as well as plasmids that encode the dominant negative (DN) Orai1. We also knocked down Orai1, using selective siRNA for this protein. In calcium store-depleted neurons a transient elevation of extracellular calcium concentration ([Ca2C]o) caused a rise in [Ca2C]i that was mediated by activation of the SOCE. The store depletion resulted in an increase in STIM2 association with Orai1 in dendritic spines. The response to the rise in [Ca2C]o was larger in spines endowed with a cluster of Orai1 molecules than in spines devoid of Orai1. Furthermore, topical application of calcium-containing medium, in a calcium-free extracellular environment, could trigger the formation of novel dendritic spines, and their location was highly correlated with the presence of Orai1 cluster (Fig. 1). Transfection of neurons with DN-Orai1 resulted in retarded maturation of dendritic spines, a reduction in synaptic connectivity with afferent neurons and a reduction in ability to undergo morphological changes following induction of chemical LTP. Likewise, siRNA-treated neurons had fewer mature dendritic spines, and lower rates of spontaneous mEPSCs compared to scrambled control siRNA-treated neurons. Thus, our results indicate that Orai1 channels are effective in causing a transient rise in [Ca2C]i in dendritic spines so as to facilitate maturation of dendritic spines and functional synapses in central neurons. It is hypothesized that in the absence of active synapses, either because presynaptic fibers still did not yet arrive, or are prevented from releasin
{"title":"Orai1 regulates calcium entry into dendritic spines","authors":"E. Korkotian, M. Segal","doi":"10.1080/19336950.2016.1247528","DOIUrl":"https://doi.org/10.1080/19336950.2016.1247528","url":null,"abstract":"The possible role of store operated calcium entry (SOCE) through the Orai1 channel in central neurons has attracted growing attention in recent years because of its involvement in regulation of calcium homeostasis in the neuron. One unique neuronal compartment associated with calcium homeostasis is the dendritic spine, the site of excitatory synapses in the majority of neurons in the brain. It has been linked to neuronal plasticity, which is highly regulated by calcium influx during intense synaptic activity. The formation, plasticity and longevity of dendritic spines have been studied extensively, but the rules governing these processes are still not clear and not universal. The cultured hippocampal neuron provides a convenient vehicle to study the role of SOCE channels in dendritic spine formation and plasticity. Indeed, recent studies have detected the presence of Orai1 channels in central neurons, and further studies indicated that STIM2, the sensor for endoplasmic reticulum calcium store depletion, is instrumental in maintenance of mature dendritic spines in cultured hippocampal neurons. We have recently analyzed the role of Orai1 in dendritic spine formation and plasticity. This study follows our interest in the role of calcium stores in spine plasticity, where we found that dendritic spines contain ryanodine receptor-type calcium stores. In the more recent study, we employed plasmids that encode the Orai1 protein, as well as plasmids that encode the dominant negative (DN) Orai1. We also knocked down Orai1, using selective siRNA for this protein. In calcium store-depleted neurons a transient elevation of extracellular calcium concentration ([Ca2C]o) caused a rise in [Ca2C]i that was mediated by activation of the SOCE. The store depletion resulted in an increase in STIM2 association with Orai1 in dendritic spines. The response to the rise in [Ca2C]o was larger in spines endowed with a cluster of Orai1 molecules than in spines devoid of Orai1. Furthermore, topical application of calcium-containing medium, in a calcium-free extracellular environment, could trigger the formation of novel dendritic spines, and their location was highly correlated with the presence of Orai1 cluster (Fig. 1). Transfection of neurons with DN-Orai1 resulted in retarded maturation of dendritic spines, a reduction in synaptic connectivity with afferent neurons and a reduction in ability to undergo morphological changes following induction of chemical LTP. Likewise, siRNA-treated neurons had fewer mature dendritic spines, and lower rates of spontaneous mEPSCs compared to scrambled control siRNA-treated neurons. Thus, our results indicate that Orai1 channels are effective in causing a transient rise in [Ca2C]i in dendritic spines so as to facilitate maturation of dendritic spines and functional synapses in central neurons. It is hypothesized that in the absence of active synapses, either because presynaptic fibers still did not yet arrive, or are prevented from releasin","PeriodicalId":9750,"journal":{"name":"Channels","volume":"144 1","pages":"100 - 99"},"PeriodicalIF":3.3,"publicationDate":"2017-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86197930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
ABSTRACT Large-conductance Ca2+- and voltage-activated potassium (MaxiK or BK) channels are composed of a pore-forming α subunit (Slo) and 4 types of auxiliary β subunits or just a pore-forming α subunit. Although multiple N-linked glycosylation sites in the extracellular loop of β subunits have been identified, very little is known about how glycosylation influences the structure and function of BK channels. Using a combination of site-directed mutagenesis, western blot and patch-clamp recordings, we demonstrated that 3 sites in the extracellular loop of β2 subunit are N-glycosylated (N-X-T/S at N88, N96 and N119). Glycosylation of these sites strongly and differentially regulate gating kinetics, outward rectification, toxin sensitivity and physical association between the α and β2 subunits. We constructed a model and used molecular dynamics (MD) to simulate how the glycosylation facilitates the association of α/β2 subunits and modulates the dimension of the extracellular cavum above the pore of the channel, ultimately to modify biophysical and pharmacological properties of BK channels. Our results suggest that N-glycosylation of β2 subunits plays crucial roles in imparting functional heterogeneity of BK channels, and is potentially involved in the pathological phenotypes of carbohydrate metabolic diseases.
{"title":"The glycosylation of the extracellular loop of β2 subunits diversifies functional phenotypes of BK Channels","authors":"Zhigang Huang, Hao-wen Liu, Zhenzhen Yan, Sheng Wang, Lu-Yang Wang, Jiu-ping Ding","doi":"10.1080/19336950.2016.1243631","DOIUrl":"https://doi.org/10.1080/19336950.2016.1243631","url":null,"abstract":"ABSTRACT Large-conductance Ca2+- and voltage-activated potassium (MaxiK or BK) channels are composed of a pore-forming α subunit (Slo) and 4 types of auxiliary β subunits or just a pore-forming α subunit. Although multiple N-linked glycosylation sites in the extracellular loop of β subunits have been identified, very little is known about how glycosylation influences the structure and function of BK channels. Using a combination of site-directed mutagenesis, western blot and patch-clamp recordings, we demonstrated that 3 sites in the extracellular loop of β2 subunit are N-glycosylated (N-X-T/S at N88, N96 and N119). Glycosylation of these sites strongly and differentially regulate gating kinetics, outward rectification, toxin sensitivity and physical association between the α and β2 subunits. We constructed a model and used molecular dynamics (MD) to simulate how the glycosylation facilitates the association of α/β2 subunits and modulates the dimension of the extracellular cavum above the pore of the channel, ultimately to modify biophysical and pharmacological properties of BK channels. Our results suggest that N-glycosylation of β2 subunits plays crucial roles in imparting functional heterogeneity of BK channels, and is potentially involved in the pathological phenotypes of carbohydrate metabolic diseases.","PeriodicalId":9750,"journal":{"name":"Channels","volume":"599 1","pages":"156 - 166"},"PeriodicalIF":3.3,"publicationDate":"2017-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77336595","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-06DOI: 10.1080/19336950.2017.1291213
A. Anishkin, S. Sukharev
Mechanosensitive channels are the molecules closely matching the definition of “machines” in our macroworld—they convert external mechanical forces into motion of the parts to open or close a water-filled pore, with no chemical energy inputs involved. Bacterial mechanosensitive channel MscL from E. coli is the first known and probably the best understood representative of this group. A minimalistic bundle of 5 pairs of interlocked a-helices in the membrane requires no external protein connections. The barrel responds directly to the lipid bilayer tension by tilting of the helices and iris-like expansion that opens a large (»3 nm) pore. Robustness of MscL makes it a promising template for engineering nano-devices operated by force or chemical modification. Known crystal structures and models enabled molecular simulations which visualized lipid interactions and forces acting on specific channel segments. The experimentally estimated timescale of the opening, is in the order of microsecond, whereas the process of subsequent equilibration within the subset of open states may take up to several seconds. Simulations striving for proper representation of these stochastic events must be at least as long. Atomistic simulations on this time scale are currently unattainable thus calling for radical simplifications. Over the last decade, a helpful approximation for MscL was developed using solid-state mechanical engineering tools that present the channel/membrane system as interacting meshworks of finite elastic elements. Despite the apparent simplicity, MscL is surrounded by solvent and a highly anisotropic bilayer that both change their interactions with the protein during the gating. This poses several challenges for the finiteelement approach. One is the necessity to account for large changes of the solvent-accessible area and associated hydration contribution. In part, it was recently addressed by explicitly introducing terms for the hydration energetics. The second oversimplification of the finite-element approach was that, while effective elasticities of different elements can be derived from atomistic calculations, they were assumed to be constant and it is unclear how they change under varying solvation or sequestration inside the lipid. The paper by Bavi et al. published in the current issue addresses these questions. Their elasticity tests of isolated a-helices of MscL in steered molecular dynamics simulations gave different moduli estimations for different domains. As one can expect, the elastic modulus values changed to some extent upon switching from M. tuberculosis MscL to its modeled E. coli homolog. Most importantly, the a-helices became considerably softer when the helix was hydrated, compared with simulations in vacuo. That finding might be crucial for the mechanics of MscL in continuum-based models because the hydration of the pore-lining helices increases dramatically upon channel opening. Moreover, as the lipid-facing helices tilt in th
{"title":"Channel disassembled: Pick, tweak, and soak parts to soften","authors":"A. Anishkin, S. Sukharev","doi":"10.1080/19336950.2017.1291213","DOIUrl":"https://doi.org/10.1080/19336950.2017.1291213","url":null,"abstract":"Mechanosensitive channels are the molecules closely matching the definition of “machines” in our macroworld—they convert external mechanical forces into motion of the parts to open or close a water-filled pore, with no chemical energy inputs involved. Bacterial mechanosensitive channel MscL from E. coli is the first known and probably the best understood representative of this group. A minimalistic bundle of 5 pairs of interlocked a-helices in the membrane requires no external protein connections. The barrel responds directly to the lipid bilayer tension by tilting of the helices and iris-like expansion that opens a large (»3 nm) pore. Robustness of MscL makes it a promising template for engineering nano-devices operated by force or chemical modification. Known crystal structures and models enabled molecular simulations which visualized lipid interactions and forces acting on specific channel segments. The experimentally estimated timescale of the opening, is in the order of microsecond, whereas the process of subsequent equilibration within the subset of open states may take up to several seconds. Simulations striving for proper representation of these stochastic events must be at least as long. Atomistic simulations on this time scale are currently unattainable thus calling for radical simplifications. Over the last decade, a helpful approximation for MscL was developed using solid-state mechanical engineering tools that present the channel/membrane system as interacting meshworks of finite elastic elements. Despite the apparent simplicity, MscL is surrounded by solvent and a highly anisotropic bilayer that both change their interactions with the protein during the gating. This poses several challenges for the finiteelement approach. One is the necessity to account for large changes of the solvent-accessible area and associated hydration contribution. In part, it was recently addressed by explicitly introducing terms for the hydration energetics. The second oversimplification of the finite-element approach was that, while effective elasticities of different elements can be derived from atomistic calculations, they were assumed to be constant and it is unclear how they change under varying solvation or sequestration inside the lipid. The paper by Bavi et al. published in the current issue addresses these questions. Their elasticity tests of isolated a-helices of MscL in steered molecular dynamics simulations gave different moduli estimations for different domains. As one can expect, the elastic modulus values changed to some extent upon switching from M. tuberculosis MscL to its modeled E. coli homolog. Most importantly, the a-helices became considerably softer when the helix was hydrated, compared with simulations in vacuo. That finding might be crucial for the mechanics of MscL in continuum-based models because the hydration of the pore-lining helices increases dramatically upon channel opening. Moreover, as the lipid-facing helices tilt in th","PeriodicalId":9750,"journal":{"name":"Channels","volume":"44 1","pages":"173 - 175 - 223"},"PeriodicalIF":3.3,"publicationDate":"2017-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74271703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-02DOI: 10.1080/19336950.2016.1249076
M. Yadav, C. Goswami
ABSTRACT TRPV3 is a non-selective cationic channel and is important for several physiological functions. It can be activated by physiological temperature and selective endogenous and exogenous compounds. TRPV3 is one of the key ion channel involved in Ca2+-signaling in keratinocyte and thus involved in skin-related functions. Recently, naturally occurring mutations in TRPV3, namely G573A, G573S, G573C and W692G have been detected which are linked with the development of pathophysiological conditions such as Olmsted Syndrome (OS) and other skin disorders. Our qualitative and quantitative data suggests that these naturally occurring TRPV3 mutants are mainly restricted in the ER. Expression of OS-mutants cause impaired vesicular trafficking resulting reduced surface localization of these mutants and other membrane proteins too. OS-mutants also cause reduced cell adhesion, altered distribution and less number of lysosomes. Our data confirms that TRPV3 is a lysosomal protein suggesting that Olmsted Syndrome is a lysosomal disorder. These findings may have a broad implication in the context of keratinocyte functions, skin-degeneration and in skin-cancer.
{"title":"TRPV3 mutants causing Olmsted Syndrome induce impaired cell adhesion and nonfunctional lysosomes","authors":"M. Yadav, C. Goswami","doi":"10.1080/19336950.2016.1249076","DOIUrl":"https://doi.org/10.1080/19336950.2016.1249076","url":null,"abstract":"ABSTRACT TRPV3 is a non-selective cationic channel and is important for several physiological functions. It can be activated by physiological temperature and selective endogenous and exogenous compounds. TRPV3 is one of the key ion channel involved in Ca2+-signaling in keratinocyte and thus involved in skin-related functions. Recently, naturally occurring mutations in TRPV3, namely G573A, G573S, G573C and W692G have been detected which are linked with the development of pathophysiological conditions such as Olmsted Syndrome (OS) and other skin disorders. Our qualitative and quantitative data suggests that these naturally occurring TRPV3 mutants are mainly restricted in the ER. Expression of OS-mutants cause impaired vesicular trafficking resulting reduced surface localization of these mutants and other membrane proteins too. OS-mutants also cause reduced cell adhesion, altered distribution and less number of lysosomes. Our data confirms that TRPV3 is a lysosomal protein suggesting that Olmsted Syndrome is a lysosomal disorder. These findings may have a broad implication in the context of keratinocyte functions, skin-degeneration and in skin-cancer.","PeriodicalId":9750,"journal":{"name":"Channels","volume":"11 1","pages":"196 - 208"},"PeriodicalIF":3.3,"publicationDate":"2017-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76881066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-01-25DOI: 10.1080/19336950.2017.1284717
A. Gradogna, Héctor Gaitán-Peñas, A. Boccaccio, R. Estévez, M. Pusch
ABSTRACT LRRC8 proteins have been shown to underlie the ubiquitous volume regulated anion channel (VRAC). VRAC channels are composed of the LRRC8A subunit and at least one among the LRRC8B-E subunits. In addition to their role in volume regulation, LRRC8 proteins have been implicated in the uptake of chemotherapeutic agents. We had found that LRRC8 channels can be conveniently expressed in Xenopus oocytes, a system without endogenous VRAC activity. The fusion with fluorescent proteins yielded constitutive activity for A/C, A/D and A/E heteromers. Here we tested the effect of the anticancer drug cisplatin on LRRC8A-VFP/8E-mCherry and LRRC8A-VFP/8D-mCherry co-expressing oocytes. Incubation with cisplatin dramatically activated currents for both subunit combinations, confirming that VRAC channels provide an uptake pathway for cisplatin and that intracellular cisplatin accumulation strongly activates the channels. Thus, specific activators of LRRC8 proteins might be useful tools to counteract chemotherapeutic drug resistance.
{"title":"Cisplatin activates volume sensitive LRRC8 channel mediated currents in Xenopus oocytes","authors":"A. Gradogna, Héctor Gaitán-Peñas, A. Boccaccio, R. Estévez, M. Pusch","doi":"10.1080/19336950.2017.1284717","DOIUrl":"https://doi.org/10.1080/19336950.2017.1284717","url":null,"abstract":"ABSTRACT LRRC8 proteins have been shown to underlie the ubiquitous volume regulated anion channel (VRAC). VRAC channels are composed of the LRRC8A subunit and at least one among the LRRC8B-E subunits. In addition to their role in volume regulation, LRRC8 proteins have been implicated in the uptake of chemotherapeutic agents. We had found that LRRC8 channels can be conveniently expressed in Xenopus oocytes, a system without endogenous VRAC activity. The fusion with fluorescent proteins yielded constitutive activity for A/C, A/D and A/E heteromers. Here we tested the effect of the anticancer drug cisplatin on LRRC8A-VFP/8E-mCherry and LRRC8A-VFP/8D-mCherry co-expressing oocytes. Incubation with cisplatin dramatically activated currents for both subunit combinations, confirming that VRAC channels provide an uptake pathway for cisplatin and that intracellular cisplatin accumulation strongly activates the channels. Thus, specific activators of LRRC8 proteins might be useful tools to counteract chemotherapeutic drug resistance.","PeriodicalId":9750,"journal":{"name":"Channels","volume":"2 1","pages":"1443 - 254 - 260"},"PeriodicalIF":3.3,"publicationDate":"2017-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83258290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-01-24DOI: 10.1080/19336950.2017.1286829
I. Levitan
If Cowper’s contention is accurate, then the family of membrane potassium channels is spicy and flavorful indeed. The genomes of organisms as wide-ranging as nematode worms, fruit flies and humans contain 70 or more genes encoding the pore-forming a subunits of different kinds of potassium channels. Adding to this variety at the level of DNA is the fact that potassium channel a subunit mRNA is subject in some organisms to extensive alternative splicing; because potassium channels are functional tetramers, the protein products of the splice variants may combine in different ways to produce a large number of potassium channels with different functional properties. To give just one example, the dSlo gene in Drosophila, which encodes the a subunit of a large conductance (BK) calciumand voltage-activated potassium channel, can be processed into some 144 splice products, which could in principle combine to give rise to as many as 144 (that is, almost 430,000,000) different tetrameric channels from just a single gene! In brief, the combinatorial possibilities are nothing short of staggering. And if this were not sufficient, additional structural and phenotypic variety is conferred by the fact that most (if not all) ion channels do not consist of a subunits alone. It has been known since the early days of ion channel purification that the pore-forming a subunits are associated with so-called auxiliary subunits (often named b, g and so on) that contribute importantly to channel assembly, membrane targeting and function. Finally, these various subunit combinations can be modulated by post-translational modifications, including phosphorylation and glycosylation, sometimes by enzymes that are intimately associated with the ion channel protein itself. In a paper published in this volume of Channels, Huang et al add to the story of ion channel structural and functional diversity by investigating the role of glycosylation of the b2 auxiliary subunit on the mouse BK channel, mSlo. While, as indicated above, it has been known for some time that b subunit glycosylation can influence channel functional properties, Huang et al take things a step further by asking what the structural basis for this modulation by glycosylation might be. To this end they systematically mutate each of the 3 asparagine (N) residues in the extracellular loop of the b2 subunit that reside within consensus sequences for N-linked glycosylation, and identify the glycosylation of N96 as critical for the interaction of b2 with the mSlo a subunit. An interesting and unusual feature of this paper is that the authors don’t simply stop with the identification of the key modulatory glycosylation site, but they go on to carry out molecular dynamics modeling that predicts structural changes in the a subunit that are dependent on glycosylation of the b subunit. The conclusion from these modeling studies is that b2 subunit glycosylation promotes the association of the b2 subunits into a tetrameric struc
{"title":"Sugar and spice and potassium channel modulation","authors":"I. Levitan","doi":"10.1080/19336950.2017.1286829","DOIUrl":"https://doi.org/10.1080/19336950.2017.1286829","url":null,"abstract":"If Cowper’s contention is accurate, then the family of membrane potassium channels is spicy and flavorful indeed. The genomes of organisms as wide-ranging as nematode worms, fruit flies and humans contain 70 or more genes encoding the pore-forming a subunits of different kinds of potassium channels. Adding to this variety at the level of DNA is the fact that potassium channel a subunit mRNA is subject in some organisms to extensive alternative splicing; because potassium channels are functional tetramers, the protein products of the splice variants may combine in different ways to produce a large number of potassium channels with different functional properties. To give just one example, the dSlo gene in Drosophila, which encodes the a subunit of a large conductance (BK) calciumand voltage-activated potassium channel, can be processed into some 144 splice products, which could in principle combine to give rise to as many as 144 (that is, almost 430,000,000) different tetrameric channels from just a single gene! In brief, the combinatorial possibilities are nothing short of staggering. And if this were not sufficient, additional structural and phenotypic variety is conferred by the fact that most (if not all) ion channels do not consist of a subunits alone. It has been known since the early days of ion channel purification that the pore-forming a subunits are associated with so-called auxiliary subunits (often named b, g and so on) that contribute importantly to channel assembly, membrane targeting and function. Finally, these various subunit combinations can be modulated by post-translational modifications, including phosphorylation and glycosylation, sometimes by enzymes that are intimately associated with the ion channel protein itself. In a paper published in this volume of Channels, Huang et al add to the story of ion channel structural and functional diversity by investigating the role of glycosylation of the b2 auxiliary subunit on the mouse BK channel, mSlo. While, as indicated above, it has been known for some time that b subunit glycosylation can influence channel functional properties, Huang et al take things a step further by asking what the structural basis for this modulation by glycosylation might be. To this end they systematically mutate each of the 3 asparagine (N) residues in the extracellular loop of the b2 subunit that reside within consensus sequences for N-linked glycosylation, and identify the glycosylation of N96 as critical for the interaction of b2 with the mSlo a subunit. An interesting and unusual feature of this paper is that the authors don’t simply stop with the identification of the key modulatory glycosylation site, but they go on to carry out molecular dynamics modeling that predicts structural changes in the a subunit that are dependent on glycosylation of the b subunit. The conclusion from these modeling studies is that b2 subunit glycosylation promotes the association of the b2 subunits into a tetrameric struc","PeriodicalId":9750,"journal":{"name":"Channels","volume":"13 1","pages":"166 - 263 - 264"},"PeriodicalIF":3.3,"publicationDate":"2017-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88756170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-01-19DOI: 10.1080/19336950.2017.1279369
Dan Feng, Haiyan Nan, Wen Wang, Linfeng Yan, Pang Du, Lin Zuo, Kun Zhang, Minggao Zhao, G. Cui
ABSTRACT This study aimed to investigate the expression and function of BKCa channels in the Sphincter of Oddi (SO) in a rabbit model of hypercholesterolemia (HC). New Zealand white rabbits were randomly divided into 2 groups: the control group was fed standard chow (n = 18) whereas the high-cholesterol group was fed cholesterol-enriched chow containing 1.5% cholesterol (n = 18). The serum cholesterol level was significantly greater in the HC groups than in the control group, but there was no significant difference in body weight between the control and HC groups. Although the total protein expression of BKCa α- and β1-subunit was not significantly different between the control and HC groups, the Tyr-phosphorylation of BKCa α-subunit was significantly decreased in the HC group than in the control group. In addition, hypercholesterolemia significantly increased Acetylcholine (ACh)-induced contraction of the SO rings. Pretreatment with 30 μM NS1619, a BKCa channel agonist, significantly reduced ACh-induced contraction of the SO rings in HC rabbits. Moreover, pretreatment with 100 μM Na3OV4, a protein tyrosine phosphatase inhibitor, significantly reduced ACh-induced contraction of the SO rings in HC rabbits, whereas it significantly increased upon pretreating with 10 μM Genistein, a tyrosine kinase inhibitor. Whole-cell patch clamp recordings showed that BKCa current density was significantly lower in SOSMCs from HC group than that from control group. Our findings suggest that hypercholesterolemia-induced downregulation of BKCa channel, and Tyr-phosphorylation of BKCa α-subunit may contribute to the hyperresponsiveness of the SO ring in HC rabbits.
{"title":"Expression and alteration of BKCa channels in the sphincter of Oddi's from rabbits with hypercholesterolemia","authors":"Dan Feng, Haiyan Nan, Wen Wang, Linfeng Yan, Pang Du, Lin Zuo, Kun Zhang, Minggao Zhao, G. Cui","doi":"10.1080/19336950.2017.1279369","DOIUrl":"https://doi.org/10.1080/19336950.2017.1279369","url":null,"abstract":"ABSTRACT This study aimed to investigate the expression and function of BKCa channels in the Sphincter of Oddi (SO) in a rabbit model of hypercholesterolemia (HC). New Zealand white rabbits were randomly divided into 2 groups: the control group was fed standard chow (n = 18) whereas the high-cholesterol group was fed cholesterol-enriched chow containing 1.5% cholesterol (n = 18). The serum cholesterol level was significantly greater in the HC groups than in the control group, but there was no significant difference in body weight between the control and HC groups. Although the total protein expression of BKCa α- and β1-subunit was not significantly different between the control and HC groups, the Tyr-phosphorylation of BKCa α-subunit was significantly decreased in the HC group than in the control group. In addition, hypercholesterolemia significantly increased Acetylcholine (ACh)-induced contraction of the SO rings. Pretreatment with 30 μM NS1619, a BKCa channel agonist, significantly reduced ACh-induced contraction of the SO rings in HC rabbits. Moreover, pretreatment with 100 μM Na3OV4, a protein tyrosine phosphatase inhibitor, significantly reduced ACh-induced contraction of the SO rings in HC rabbits, whereas it significantly increased upon pretreating with 10 μM Genistein, a tyrosine kinase inhibitor. Whole-cell patch clamp recordings showed that BKCa current density was significantly lower in SOSMCs from HC group than that from control group. Our findings suggest that hypercholesterolemia-induced downregulation of BKCa channel, and Tyr-phosphorylation of BKCa α-subunit may contribute to the hyperresponsiveness of the SO ring in HC rabbits.","PeriodicalId":9750,"journal":{"name":"Channels","volume":"12 1","pages":"236 - 244"},"PeriodicalIF":3.3,"publicationDate":"2017-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87423419","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-01-13DOI: 10.1080/19336950.2016.1270150
L. Fliegel
The NaC/HC exchanger isoform 1 (NHE1) is a ubiquitous plasma membrane protein that regulates intracellular pH in isolated cardiomyocytes and in other mammalian cells. The N-terminal domain of approximately 500 amino acids is responsible for removal of one intracellular proton in exchange for one extracellular sodium. The intracellular C-terminal of 315 amino acids regulates the membrane domain and is post translationally modified by protein kinase mediated phosphorylation (Fig. 1). NHE1 is intimately involved in heart disease. It contributes to ischemia reperfusion mediated injury. During ischemia, acid load increases and the resultant increase in NHE1 activity contributes to increased intracellular sodium. This elevated sodium leads to reversal of activity of the NaC/Ca2C exchanger and results in an increase in intracellular calcium, triggering deleterious pathways that lead to cell damage and death. Elevated NHE1 activity also contributes to cardiac hypertrophy and its inhibition can prevent cardiac hypertrophy. NHE1 is regulated by protein kinase mediated phosphorylation through the mitogen-activated protein kinase (MAPK) signaling pathway. This pathway of Ras-Raf-MEK-ERK/MAPK (Fig. 1) is conserved and controls a variety of cellular processes including proliferation and metabolism in different cell types. Raf, has three isoforms A-Raf, b¡Raf and Raf-1. The Ser/Thr kinase b-Raf, has mutations in very high frequency in melanomas and in lower frequencies in other types of cancer. The V600E mutation is the most prominent and found in most patients with a b-Raf mutation. The NHE1 protein shares some of the physiological roles of b-Raf being involved in cellular proliferation and promoting tumourigenesis. This led us to examine the potential role of b-Raf in regulation of NHE1 and intracellular pH in malignant melanoma cells with the b-Raf mutation. We demonstrated that melanoma cells with the b-RafV600E mutation had elevated resting intracellular pH that was dependent on NHE1. Also, inhibition or knock down of b-Raf decreased NHE1 activity. This report confirmed that b-Raf is capable of regulation of NHE1 in malignant melanoma cells, but how does this occur and is it common in other cell types? In that study we also demonstrated that b-Raf binds to the cytosolic regulatory domain. b-Raf immunoprecipitated with NHE1 in both HeLa and HEK (human embryonic kidney) cells. Another observation was that in a screen for protein kinases from the heart that bind to the NHE1 tail, the strongest signal observed was an interaction between the NHE1-C terminus and b-Raf. This suggested to us that there may be a regulatory role for b-Raf in the myocardium. It is notable that b-Raf has also been implicated in cardiac hypertrophy in addition to NHE1. It thus occurred to us that there may be a link between b-Raf and NHE1 that is responsible. Our follow up work therefore examined whether b-Raf can regulate NHE1 in myocardial cells. In isolated cardiomyocytes, inhibitio
{"title":"β-Raf activation of the myocardial Na+/H+ exchanger","authors":"L. Fliegel","doi":"10.1080/19336950.2016.1270150","DOIUrl":"https://doi.org/10.1080/19336950.2016.1270150","url":null,"abstract":"The NaC/HC exchanger isoform 1 (NHE1) is a ubiquitous plasma membrane protein that regulates intracellular pH in isolated cardiomyocytes and in other mammalian cells. The N-terminal domain of approximately 500 amino acids is responsible for removal of one intracellular proton in exchange for one extracellular sodium. The intracellular C-terminal of 315 amino acids regulates the membrane domain and is post translationally modified by protein kinase mediated phosphorylation (Fig. 1). NHE1 is intimately involved in heart disease. It contributes to ischemia reperfusion mediated injury. During ischemia, acid load increases and the resultant increase in NHE1 activity contributes to increased intracellular sodium. This elevated sodium leads to reversal of activity of the NaC/Ca2C exchanger and results in an increase in intracellular calcium, triggering deleterious pathways that lead to cell damage and death. Elevated NHE1 activity also contributes to cardiac hypertrophy and its inhibition can prevent cardiac hypertrophy. NHE1 is regulated by protein kinase mediated phosphorylation through the mitogen-activated protein kinase (MAPK) signaling pathway. This pathway of Ras-Raf-MEK-ERK/MAPK (Fig. 1) is conserved and controls a variety of cellular processes including proliferation and metabolism in different cell types. Raf, has three isoforms A-Raf, b¡Raf and Raf-1. The Ser/Thr kinase b-Raf, has mutations in very high frequency in melanomas and in lower frequencies in other types of cancer. The V600E mutation is the most prominent and found in most patients with a b-Raf mutation. The NHE1 protein shares some of the physiological roles of b-Raf being involved in cellular proliferation and promoting tumourigenesis. This led us to examine the potential role of b-Raf in regulation of NHE1 and intracellular pH in malignant melanoma cells with the b-Raf mutation. We demonstrated that melanoma cells with the b-RafV600E mutation had elevated resting intracellular pH that was dependent on NHE1. Also, inhibition or knock down of b-Raf decreased NHE1 activity. This report confirmed that b-Raf is capable of regulation of NHE1 in malignant melanoma cells, but how does this occur and is it common in other cell types? In that study we also demonstrated that b-Raf binds to the cytosolic regulatory domain. b-Raf immunoprecipitated with NHE1 in both HeLa and HEK (human embryonic kidney) cells. Another observation was that in a screen for protein kinases from the heart that bind to the NHE1 tail, the strongest signal observed was an interaction between the NHE1-C terminus and b-Raf. This suggested to us that there may be a regulatory role for b-Raf in the myocardium. It is notable that b-Raf has also been implicated in cardiac hypertrophy in addition to NHE1. It thus occurred to us that there may be a link between b-Raf and NHE1 that is responsible. Our follow up work therefore examined whether b-Raf can regulate NHE1 in myocardial cells. In isolated cardiomyocytes, inhibitio","PeriodicalId":9750,"journal":{"name":"Channels","volume":"101 1","pages":"181 - 182 - 75"},"PeriodicalIF":3.3,"publicationDate":"2017-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88024117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-01-13DOI: 10.1080/19336950.2017.1279368
N. Andharia, A. Joseph, M. Hayashi, M. Okada, H. Matsuda
ABSTRACT The TREK-1 channel, the TWIK-1-related potassium (K+) channel, is a member of a family of 2-pore-domain K+ (K2P) channels, through which background or leak K+ currents occur. An interesting feature of the TREK-1 channel is the run-up of current: i.e. the current through TREK-1 channels spontaneously increases within several minutes of the formation of the whole-cell configuration. To investigate whether intracellular transport is involved in the run-up, we established 293T cell lines stably expressing the TREK-1c channel (K2P2.1) and examined the effects of inhibitors of membrane protein transport, N-methylmaleimide (NEM), brefeldin-A, and an endocytosis inhibitor, pitstop2, on the run-up. The results showing that NEM and brefeldin-A inhibited and pitstop2 facilitated the run-up suggest the involvement of intracellular protein transport. Correspondingly, in cells stably expressing the mCherry-TREK-1 fusion protein, NEM decreased and pitstop2 increased the cell surface localization of the fusion protein. Furthermore, the run-up was inhibited by the intracellular application of a peptide of the C-terminal fragment TREK335–360, corresponding to the interaction site with microtubule-associated protein 2 (Mtap2). This peptide also inhibited the co-immunoprecipitation of Mtap2 with anti-mCherry antibody. The extracellular application of an ezrin inhibitor (NSC668394) also suppressed the run-up and surface localization of the fusion protein. The co-application of these inhibitors abolished the TREK-1c current, suggesting that the additive effects of ezrin and Mtap2 enhance the surface expression of TREK-1c channels and the run-up. These findings clearly showed the involvement of intracellular transport in TREK-1c current run-up and its mechanism.
{"title":"Involvement of intracellular transport in TREK-1c current run-up in 293T cells","authors":"N. Andharia, A. Joseph, M. Hayashi, M. Okada, H. Matsuda","doi":"10.1080/19336950.2017.1279368","DOIUrl":"https://doi.org/10.1080/19336950.2017.1279368","url":null,"abstract":"ABSTRACT The TREK-1 channel, the TWIK-1-related potassium (K+) channel, is a member of a family of 2-pore-domain K+ (K2P) channels, through which background or leak K+ currents occur. An interesting feature of the TREK-1 channel is the run-up of current: i.e. the current through TREK-1 channels spontaneously increases within several minutes of the formation of the whole-cell configuration. To investigate whether intracellular transport is involved in the run-up, we established 293T cell lines stably expressing the TREK-1c channel (K2P2.1) and examined the effects of inhibitors of membrane protein transport, N-methylmaleimide (NEM), brefeldin-A, and an endocytosis inhibitor, pitstop2, on the run-up. The results showing that NEM and brefeldin-A inhibited and pitstop2 facilitated the run-up suggest the involvement of intracellular protein transport. Correspondingly, in cells stably expressing the mCherry-TREK-1 fusion protein, NEM decreased and pitstop2 increased the cell surface localization of the fusion protein. Furthermore, the run-up was inhibited by the intracellular application of a peptide of the C-terminal fragment TREK335–360, corresponding to the interaction site with microtubule-associated protein 2 (Mtap2). This peptide also inhibited the co-immunoprecipitation of Mtap2 with anti-mCherry antibody. The extracellular application of an ezrin inhibitor (NSC668394) also suppressed the run-up and surface localization of the fusion protein. The co-application of these inhibitors abolished the TREK-1c current, suggesting that the additive effects of ezrin and Mtap2 enhance the surface expression of TREK-1c channels and the run-up. These findings clearly showed the involvement of intracellular transport in TREK-1c current run-up and its mechanism.","PeriodicalId":9750,"journal":{"name":"Channels","volume":"16 1","pages":"224 - 235"},"PeriodicalIF":3.3,"publicationDate":"2017-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81944906","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-01-13DOI: 10.1080/19336950.2017.1279370
C. Alcaino, Kaitlyn R. Knutson, P. Gottlieb, G. Farrugia, A. Beyder
ABSTRACT Enterochromaffin (EC) cells are the primary mechanosensors of the gastrointestinal (GI) epithelium. In response to mechanical stimuliEC cells release serotonin (5-hydroxytryptamine; 5-HT). The molecular details ofEC cell mechanosensitivity are poorly understood. Recently, our group found that human and mouseEC cells express the mechanosensitive ion channel Piezo2. The mechanosensitive currents in a humanEC cell model QGP-1 were blocked by the mechanosensitive channel blocker D-GsMTx4. In the present study we aimed to characterize the effects of the mechanosensitive ion channel inhibitor spider peptide D-GsMTx4 on the mechanically stimulated currents from both QGP-1 and human Piezo2 transfected HEK-293 cells. We found co-localization of 5-HT and Piezo2 in QGP-1 cells by immunohistochemistry. QGP-1 mechanosensitive currents had biophysical properties similar to dose-dependently Piezo2 and were inhibited by D-GsMTx4. In response to direct displacement of cell membranes, human Piezo2 transiently expressed in HEK-293 cells produced robust rapidly activating and inactivating inward currents. D-GsMTx4 reversibly and dose-dependently inhibited both the potency and efficacy of Piezo2 currents in response to mechanical force. Our data demonstrate an effective inhibition of Piezo2 mechanosensitive currents by the spider peptide D-GsMTx4.
{"title":"Mechanosensitive ion channel Piezo2 is inhibited by D-GsMTx4","authors":"C. Alcaino, Kaitlyn R. Knutson, P. Gottlieb, G. Farrugia, A. Beyder","doi":"10.1080/19336950.2017.1279370","DOIUrl":"https://doi.org/10.1080/19336950.2017.1279370","url":null,"abstract":"ABSTRACT Enterochromaffin (EC) cells are the primary mechanosensors of the gastrointestinal (GI) epithelium. In response to mechanical stimuliEC cells release serotonin (5-hydroxytryptamine; 5-HT). The molecular details ofEC cell mechanosensitivity are poorly understood. Recently, our group found that human and mouseEC cells express the mechanosensitive ion channel Piezo2. The mechanosensitive currents in a humanEC cell model QGP-1 were blocked by the mechanosensitive channel blocker D-GsMTx4. In the present study we aimed to characterize the effects of the mechanosensitive ion channel inhibitor spider peptide D-GsMTx4 on the mechanically stimulated currents from both QGP-1 and human Piezo2 transfected HEK-293 cells. We found co-localization of 5-HT and Piezo2 in QGP-1 cells by immunohistochemistry. QGP-1 mechanosensitive currents had biophysical properties similar to dose-dependently Piezo2 and were inhibited by D-GsMTx4. In response to direct displacement of cell membranes, human Piezo2 transiently expressed in HEK-293 cells produced robust rapidly activating and inactivating inward currents. D-GsMTx4 reversibly and dose-dependently inhibited both the potency and efficacy of Piezo2 currents in response to mechanical force. Our data demonstrate an effective inhibition of Piezo2 mechanosensitive currents by the spider peptide D-GsMTx4.","PeriodicalId":9750,"journal":{"name":"Channels","volume":"24 1","pages":"245 - 253 - 91"},"PeriodicalIF":3.3,"publicationDate":"2017-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82984751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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