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Sarmiento BE, Santos Menezes LF, Schwartz EF. Insulin Release Mechanism Modulated by Toxins Isolated from Animal Venoms: From Basic Research to Drug Development Prospects. Molecules 2019; 24:E1846. [PMID: 31091684 PMCID: PMC6571724 DOI: 10.3390/molecules24101846] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 04/23/2019] [Accepted: 05/09/2019] [Indexed: 12/12/2022] Open
Abstract
Venom from mammals, amphibians, snakes, arachnids, sea anemones and insects provides diverse sources of peptides with different potential medical applications. Several of these peptides have already been converted into drugs and some are still in the clinical phase. Diabetes type 2 is one of the diseases with the highest mortality rate worldwide, requiring specific attention. Diverse drugs are available (e.g., Sulfonylureas) for effective treatment, but with several adverse secondary effects, most of them related to the low specificity of these compounds to the target. In this context, the search for specific and high-affinity compounds for the management of this metabolic disease is growing. Toxins isolated from animal venom have high specificity and affinity for different molecular targets, of which the most important are ion channels. This review will present an overview about the electrical activity of the ion channels present in pancreatic β cells that are involved in the insulin secretion process, in addition to the diversity of peptides that can interact and modulate the electrical activity of pancreatic β cells. The importance of prospecting bioactive peptides for therapeutic use is also reinforced.
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Affiliation(s)
- Beatriz Elena Sarmiento
- Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF 70910-900, Brazil.
| | - Luis Felipe Santos Menezes
- Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF 70910-900, Brazil.
| | - Elisabeth F Schwartz
- Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF 70910-900, Brazil.
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Plasma membrane insertion of KCa2.3 (SK3) is dependent upon the SNARE proteins, syntaxin-4 and SNAP23. PLoS One 2018; 13:e0196717. [PMID: 29768434 PMCID: PMC5955555 DOI: 10.1371/journal.pone.0196717] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Accepted: 04/18/2018] [Indexed: 02/03/2023] Open
Abstract
We previously demonstrated endocytosis of KCa2.3 is caveolin-1-, dynamin II- and Rab5-dependent. KCa2.3 then enters Rab35/EPI64C- and RME-1-containing recycling endosomes and is returned to the plasma membrane (PM). Herein, we report on the mechanism by which KCa2.3 is inserted into the PM during recycling and following exit from the Golgi. We demonstrate KCa2.3 colocalizes with SNAP-23 and Syntaxin-4 in the PM of HEK and endothelial cells by confocal immunofluorescence microscopy. We further show KCa2.3 can be co-immunoprecipitated with SNAP-23 and Syntaxin-4. Overexpression of either Syntaxin-4 or SNAP-23 increased PM expression of KCa2.3, whereas shRNA-mediated knockdown of these SNARE proteins significantly decreased PM KCa2.3 expression, as assessed by cell surface biotinylation. Whole-cell patch clamp studies confirmed knockdown of SNAP-23 significantly decreased the apamin sensitive, KCa2.3 current. Using standard biotinylation/stripping methods, we demonstrate shRNA mediated knockdown of SNAP-23 inhibits recycling of KCa2.3 following endocytosis, whereas scrambled shRNA had no effect. Finally, using biotin ligase acceptor peptide (BLAP)-tagged KCa2.3, coupled with ER-resident biotin ligase (BirA), channels could be biotinylated in the ER after which we evaluated their rate of insertion into the PM following Golgi exit. We demonstrate knockdown of SNAP-23 significantly slows the rate of Golgi to PM delivery of KCa2.3. The inhibition of both recycling and PM delivery of newly synthesized KCa2.3 channels likely accounts for the decreased PM expression observed following knockdown of these SNARE proteins. In total, our results suggest insertion of KCa2.3 into the PM depends upon the SNARE proteins, Syntaxin-4 and SNAP-23.
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Jezek M, Zörb C, Merkt N, Geilfus CM. Anthocyanin Management in Fruits by Fertilization. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2018; 66:753-764. [PMID: 29297687 DOI: 10.1021/acs.jafc.7b03813] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Anthocyanins are water-soluble vacuolar plant pigments that are mainly synthesized in epidermal layers and the flesh of fruits such as apples, cherries, grapes, and other berries. Because of their attractive red to purple coloration and their health-promoting potential, anthocyanins are significant determinants for the quality and market value of fruits and fruit-derived products. In crops, anthocyanin accumulation in leaves can be caused by nutrient deficiency which is usually ascribed to insufficient nitrogen or phosphorus fertilization. However, it is a little-known fact that the plant's nutrient status also impacts anthocyanin synthesis in fruits. Hence, strategic nutrient supply can be a powerful tool to modify the anthocyanin content and consequently the quality and market value of important agricultural commodities. Here we summarize the current knowledge of the influence of plant nutrients on anthocyanin synthesis in fruits of major global market value and discuss the underlying cellular processes that integrate nutrient signaling with fruit anthocyanin formation. It is highlighted that fertilization that is finely tuned in amount and timing has the potential to positively influence the fruit quality by regulating anthocyanin levels. We outline new approaches to enrich plant based foods with health-promoting anthocyanins.
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Affiliation(s)
- Mareike Jezek
- Laboratory of Plant Physiology and Biophysics, University of Glasgow , Glasgow G12 8QQ, United Kingdom
| | - Christian Zörb
- Institute of Crop Science, Quality of Plant Products, University of Hohenheim , Emil-Wolff-Straße 25, 70599 Stuttgart, Germany
| | - Nikolaus Merkt
- Institute of Crop Science, Quality of Plant Products, University of Hohenheim , Emil-Wolff-Straße 25, 70599 Stuttgart, Germany
| | - Christoph-Martin Geilfus
- Division of Controlled Environment Horticulture, Faculty of Life Sciences, Albrecht Daniel Thaer-Institute of Agricultural and Horticultural Sciences, Humboldt-University of Berlin , Albrecht-Thaer-Weg 1, 14195 Berlin, Germany
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Aslamy A, Thurmond DC. Exocytosis proteins as novel targets for diabetes prevention and/or remediation? Am J Physiol Regul Integr Comp Physiol 2017; 312:R739-R752. [PMID: 28356294 DOI: 10.1152/ajpregu.00002.2017] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 03/24/2017] [Accepted: 03/24/2017] [Indexed: 12/17/2022]
Abstract
Diabetes remains one of the leading causes of morbidity and mortality worldwide, affecting an estimated 422 million adults. In the US, it is predicted that one in every three children born as of 2000 will suffer from diabetes in their lifetime. Type 2 diabetes results from combinatorial defects in pancreatic β-cell glucose-stimulated insulin secretion and in peripheral glucose uptake. Both processes, insulin secretion and glucose uptake, are mediated by exocytosis proteins, SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes, Sec1/Munc18 (SM), and double C2-domain protein B (DOC2B). Increasing evidence links deficiencies in these exocytosis proteins to diabetes in rodents and humans. Given this, emerging studies aimed at restoring and/or enhancing cellular levels of certain exocytosis proteins point to promising outcomes in maintaining functional β-cell mass and enhancing insulin sensitivity. In doing so, new evidence also shows that enhancing exocytosis protein levels may promote health span and longevity and may also harbor anti-cancer and anti-Alzheimer's disease capabilities. Herein, we present a comprehensive review of the described capabilities of certain exocytosis proteins and how these might be targeted for improving metabolic dysregulation.
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Affiliation(s)
- Arianne Aslamy
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana; and
| | - Debbie C Thurmond
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana; and .,Department of Molecular and Cellular Endocrinology, Beckman Research Institute of City of Hope, Duarte, California
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Leech CA, Kopp RF, Nelson HA, Nandi J, Roe MW. Stromal Interaction Molecule 1 (STIM1) Regulates ATP-sensitive Potassium ( KATP) and Store-operated Ca 2+ Channels in MIN6 β-Cells. J Biol Chem 2016; 292:2266-2277. [PMID: 28003364 DOI: 10.1074/jbc.m116.767681] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 12/12/2016] [Indexed: 01/14/2023] Open
Abstract
Stromal interaction molecule 1 (STIM1) regulates store-operated Ca2+ entry (SOCE) and other ion channels either as an endoplasmic reticulum Ca2+-sensing protein or when present in the plasma membrane. However, the role of STIM1 in insulin-secreting β-cells is unresolved. We report that lowering expression of STIM1, the gene that encodes STIM1, in insulin-secreting MIN6 β-cells with RNA interference inhibits SOCE and ATP-sensitive K+ (KATP) channel activation. The effects of STIM1 knockdown were reversed by transduction of MIN6 cells with an adenovirus gene shuttle vector that expressed human STIM1 Immunoprecipitation studies revealed that STIM1 binds to nucleotide binding fold-1 (NBF1) of the sulfonylurea receptor 1 (SUR1) subunit of the KATP channel. Binding of STIM1 to SUR1 was enhanced by poly-lysine. Our data indicate that SOCE and KATP channel activity are regulated by STIM1. This suggests that STIM1 is a multifunctional signaling effector that participates in the control of membrane excitability and Ca2+ signaling events in β-cells.
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Affiliation(s)
| | | | - Heather A Nelson
- the Department of Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, New York 13210
| | | | - Michael W Roe
- From the Department of Medicine and .,the Department of Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, New York 13210
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Velasco M, Díaz-García CM, Larqué C, Hiriart M. Modulation of Ionic Channels and Insulin Secretion by Drugs and Hormones in Pancreatic Beta Cells. Mol Pharmacol 2016; 90:341-57. [PMID: 27436126 DOI: 10.1124/mol.116.103861] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 07/18/2016] [Indexed: 12/11/2022] Open
Abstract
Pancreatic beta cells, unique cells that secrete insulin in response to an increase in glucose levels, play a significant role in glucose homeostasis. Glucose-stimulated insulin secretion (GSIS) in pancreatic beta cells has been extensively explored. In this mechanism, glucose enters the cells and subsequently the metabolic cycle. During this process, the ATP/ADP ratio increases, leading to ATP-sensitive potassium (KATP) channel closure, which initiates depolarization that is also dependent on the activity of TRP nonselective ion channels. Depolarization leads to the opening of voltage-gated Na(+) channels (Nav) and subsequently voltage-dependent Ca(2+) channels (Cav). The increase in intracellular Ca(2+) triggers the exocytosis of insulin-containing vesicles. Thus, electrical activity of pancreatic beta cells plays a central role in GSIS. Moreover, many growth factors, incretins, neurotransmitters, and hormones can modulate GSIS, and the channels that participate in GSIS are highly regulated. In this review, we focus on the principal ionic channels (KATP, Nav, and Cav channels) involved in GSIS and how classic and new proteins, hormones, and drugs regulate it. Moreover, we also discuss advances on how metabolic disorders such as metabolic syndrome and diabetes mellitus change channel activity leading to changes in insulin secretion.
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Affiliation(s)
- Myrian Velasco
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Carlos Manlio Díaz-García
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Carlos Larqué
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Marcia Hiriart
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
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Xie Y, Huang X, Liang Y, Xu L, Pei Y, Cheng Y, Zhang L, Tang W. A new compound heterozygous CFTR mutation in a Chinese family with cystic fibrosis. CLINICAL RESPIRATORY JOURNAL 2015; 11:696-702. [PMID: 26471113 DOI: 10.1111/crj.12401] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2015] [Revised: 09/30/2015] [Accepted: 10/05/2015] [Indexed: 12/23/2022]
Abstract
INTRODUCTION Cystic fibrosis (CF) is the most common autosomal recessive disease among Caucasians but is rarer in the Chinese population, because mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. OBJECTIVES To elucidate the causative role of a novel compound heterozygous mutation of CF. MATERIALS AND METHODS In this study, clinical samples were obtained from two siblings with recurrent airway infections, clubbed fingers, salt-sweat and failure to gain weight in a non-consanguineous Chinese family. Next-generation sequencing was performed on the 27 coding exons of CFTR in both children, with confirmation by Sanger sequencing. RESULTS Next-generation sequencing showed the same compound heterozygous CFTR mutation (c.865A>T p.Arg289X and c.3651_3652insAAAT p.Tyr1219X) in both children. CONCLUSIONS As this mutation is consistent with the clinical manifestations of CF and no other mutations were detected after scanning the gene sequence, we suggest that the CF phenotype is caused by compound heterozygosity for c.865A>T and c.3651_3652insAAAT. As c865A>T is not currently listed in the "Cystic Fibrosis Mutation Database", this information about CF in a Chinese population is of interest.
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Affiliation(s)
- Yingjun Xie
- Department of Prenatal Diagnosis, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Xueqiong Huang
- Department of Pediatrics, Pediatric Intensive Care Unit, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Yujian Liang
- Department of Pediatrics, Pediatric Intensive Care Unit, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Lingling Xu
- Department of Pediatrics, Pediatric Intensive Care Unit, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Yuxin Pei
- Department of Pediatrics, Pediatric Intensive Care Unit, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Yucai Cheng
- Department of Pediatrics, Pediatric Intensive Care Unit, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Lidan Zhang
- Department of Pediatrics, Pediatric Intensive Care Unit, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Wen Tang
- Department of Pediatrics, Pediatric Intensive Care Unit, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
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Renigunta V, Fischer T, Zuzarte M, Kling S, Zou X, Siebert K, Limberg MM, Rinné S, Decher N, Schlichthörl G, Daut J. Cooperative endocytosis of the endosomal SNARE protein syntaxin-8 and the potassium channel TASK-1. Mol Biol Cell 2014; 25:1877-91. [PMID: 24743596 PMCID: PMC4055267 DOI: 10.1091/mbc.e13-10-0592] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
SNARE proteins can have functions unrelated to membrane fusion. The unassembled form of the SNARE protein syntaxin-8 interacts with the K+ channel TASK-1; both proteins are internalized via clathrin-mediated endocytosis in a cooperative manner. This is a novel mechanism for the control of endocytosis by cargo proteins. The endosomal SNARE protein syntaxin-8 interacts with the acid-sensitive potassium channel TASK-1. The functional relevance of this interaction was studied by heterologous expression of these proteins (and mutants thereof) in Xenopus oocytes and in mammalian cell lines. Coexpression of syntaxin-8 caused a fourfold reduction in TASK-1 current, a corresponding reduction in the expression of TASK-1 at the cell surface, and a marked increase in the rate of endocytosis of the channel. TASK-1 and syntaxin-8 colocalized in the early endosomal compartment, as indicated by the endosomal markers 2xFYVE and rab5. The stimulatory effect of the SNARE protein on the endocytosis of the channel was abolished when both an endocytosis signal in TASK-1 and an endocytosis signal in syntaxin-8 were mutated. A syntaxin-8 mutant that cannot assemble with other SNARE proteins had virtually the same effect as wild-type syntaxin-8. Total internal reflection fluorescence microscopy showed formation and endocytosis of vesicles containing fluorescence-tagged clathrin, TASK-1, and/or syntaxin-8. Our results suggest that the unassembled form of syntaxin-8 and the potassium channel TASK-1 are internalized via clathrin-mediated endocytosis in a cooperative manner. This implies that syntaxin-8 regulates the endocytosis of TASK-1. Our study supports the idea that endosomal SNARE proteins can have functions unrelated to membrane fusion.
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Affiliation(s)
- Vijay Renigunta
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Thomas Fischer
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Marylou Zuzarte
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Stefan Kling
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Xinle Zou
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Kai Siebert
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Maren M Limberg
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Susanne Rinné
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Niels Decher
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Günter Schlichthörl
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
| | - Jürgen Daut
- Institute of Physiology and Pathophysiology, Marburg University, 35037 Marburg, Germany
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Liang T, Xie L, Chao C, Kang Y, Lin X, Qin T, Xie H, Feng ZP, Gaisano HY. Phosphatidylinositol 4,5-biphosphate (PIP2) modulates interaction of syntaxin-1A with sulfonylurea receptor 1 to regulate pancreatic β-cell ATP-sensitive potassium channels. J Biol Chem 2014; 289:6028-40. [PMID: 24429282 DOI: 10.1074/jbc.m113.511808] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
In β-cells, syntaxin (Syn)-1A interacts with SUR1 to inhibit ATP-sensitive potassium channels (KATP channels). PIP2 binds the Kir6.2 subunit to open KATP channels. PIP2 also modifies Syn-1A clustering in plasma membrane (PM) that may alter Syn-1A actions on PM proteins like SUR1. Here, we assessed whether the actions of PIP2 on activating KATP channels is contributed by sequestering Syn-1A from binding SUR1. In vitro binding showed that PIP2 dose-dependently disrupted Syn-1A·SUR1 complexes, corroborated by an in vivo Forster resonance energy transfer assay showing disruption of SUR1(-EGFP)/Syn-1A(-mCherry) interaction along with increased Syn-1A cluster formation. Electrophysiological studies of rat β-cells, INS-1, and SUR1/Kir6.2-expressing HEK293 cells showed that PIP2 dose-dependent activation of KATP currents was uniformly reduced by Syn-1A. To unequivocally distinguish between PIP2 actions on Syn-1A and Kir6.2, we employed several strategies. First, we showed that PIP2-insensitive Syn-1A-5RK/A mutant complex with SUR1 could not be disrupted by PIP2, consequently reducing PIP2 activation of KATP channels. Next, Syn-1A·SUR1 complex modulation of KATP channels could be observed at a physiologically low PIP2 concentration that did not disrupt the Syn-1A·SUR1 complex, compared with higher PIP2 concentrations acting directly on Kir6.2. These effects were specific to PIP2 and not observed with physiologic concentrations of other phospholipids. Finally, depleting endogenous PIP2 with polyphosphoinositide phosphatase synaptojanin-1, known to disperse Syn-1A clusters, freed Syn-1A from Syn-1A clusters to bind SUR1, causing inhibition of KATP channels that could no longer be further inhibited by exogenous Syn-1A. These results taken together indicate that PIP2 affects islet β-cell KATP channels not only by its actions on Kir6.2 but also by sequestering Syn-1A to modulate Syn-1A availability and its interactions with SUR1 on PM.
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Affiliation(s)
- Tao Liang
- From the Departments of Medicine and
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Abstract
EPAC (Exchange Proteins Activated by cAMP) regulates glutamate transmitter release in the central neurons, but a role underlying this regulation has yet to be identified. Here we show that EPAC binds directly to the intracellular loop of an ATP-sensitive potassium (KATP) channel type-1 sulfonylurea receptor (SUR1) receptor consisting of amino acids 859-881 (SUR1(859-881)). Ablation of EPAC or expression of SUR1(859-881), which intercepts EPAC-SUR1 binding, increases the open probability of KATP channels consisting of the Kir6.1 subunit and SUR1. Opening of KATP channels inhibits glutamate release and reduces seizure vulnerability in adult mice. Therefore, EPAC interaction with SUR1 controls seizure susceptibility and possibly acts via regulation of glutamate release.
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Xie L, Kang Y, Liang T, Dolai S, Xie H, Parsaud L, Lopez JA, He Y, Chidambaram S, Lam PP, James DE, Sugita S, Gaisano HY. RalA GTPase tethers insulin granules to L- and R-type calcium channels through binding α2 δ-1 subunit. Traffic 2013; 14:428-39. [PMID: 23346930 DOI: 10.1111/tra.12047] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Revised: 01/21/2013] [Accepted: 01/24/2013] [Indexed: 01/05/2023]
Abstract
RalA GTPase has been implicated in the regulated delivery of exocytotic vesicles to the plasma membrane (PM) in mammalian cells. We had reported that RalA regulates biphasic insulin secretion, which we have now determined to be contributed by RalA direct interaction with voltage-gated calcium (Cav ) channels. RalA knockdown (KD) in INS-1 cells and primary rat β-cells resulted in a reduction in Ca(2+) currents arising specifically from L-(Cav 1.2 and Cav 1.3) and R-type (Cav 2.3) Ca(2+) channels. Restoration of RalA expression in RalA KD cells rescued these defects in Ca(2+) currents. RalA co-immunoprecipitated with the Cav α2 δ-1 auxiliary subunit known to bind the three Cav s. Moreover, the functional molecular interactions between Cav α2 δ-1 and RalA on the PM shown by total internal reflection fluorescent microscopy/FRET analysis could be induced by glucose stimulation. KD of RalA inhibited trafficking of α2 δ-1 to insulin granules without affecting the localization of the other Cav subunits. Furthermore, we confirmed that RalA and α2 δ-1 functionally interact since RalA KD-induced inhibition of Cav currents could not be recovered by RalA when α2 δ-1 was simultaneously knocked down. These data provide a mechanism for RalA function in insulin secretion, whereby RalA binds α2 δ-1 on insulin granules to tether these granules to PM Ca(2+) channels. This acts as a chaperoning step prior to and in preparation for sequential assembly of exocyst and excitosome complexes that mediate biphasic insulin secretion.
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Affiliation(s)
- Li Xie
- Department of Physiology and Medicine, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
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Neuroprotective role of ATP-sensitive potassium channels in cerebral ischemia. Acta Pharmacol Sin 2013; 34:24-32. [PMID: 23123646 DOI: 10.1038/aps.2012.138] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are weak, inward rectifiers that couple metabolic status to cell membrane electrical activity, thus modulating many cellular functions. An increase in the ADP/ATP ratio opens K(ATP) channels, leading to membrane hyperpolarization. K(ATP) channels are ubiquitously expressed in neurons located in different regions of the brain, including the hippocampus and cortex. Brief hypoxia triggers membrane hyperpolarization in these central neurons. In vivo animal studies confirmed that knocking out the Kir6.2 subunit of the K(ATP) channels increases ischemic infarction, and overexpression of the Kir6.2 subunit reduces neuronal injury from ischemic insults. These findings provide the basis for a practical strategy whereby activation of endogenous K(ATP) channels reduces cellular damage resulting from cerebral ischemic stroke. K(ATP) channel modulators may prove to be clinically useful as part of a combination therapy for stroke management in the future.
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