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Dudem S, Boon PX, Mullins N, McClafferty H, Shipston MJ, Wilkinson RDA, Lobb I, Sergeant GP, Thornbury KD, Tikhonova IG, Hollywood MA. Oxidation modulates LINGO2-induced inactivation of large conductance, Ca 2+-activated potassium channels. J Biol Chem 2023; 299:102975. [PMID: 36738787 PMCID: PMC10020666 DOI: 10.1016/j.jbc.2023.102975] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 01/27/2023] [Accepted: 01/29/2023] [Indexed: 02/05/2023] Open
Abstract
Ca2+ and voltage-activated K+ (BK) channels are ubiquitous ion channels that can be modulated by accessory proteins, including β, γ, and LINGO1 BK subunits. In this study, we utilized a combination of site-directed mutagenesis, patch clamp electrophysiology, and molecular modeling to investigate if the biophysical properties of BK currents were affected by coexpression of LINGO2 and to examine how they are regulated by oxidation. We demonstrate that LINGO2 is a regulator of BK channels, since its coexpression with BK channels yields rapid inactivating currents, the activation of which is shifted ∼-30 mV compared to that of BKα currents. Furthermore, we show the oxidation of BK:LINGO2 currents (by exposure to epifluorescence illumination or chloramine-T) abolished inactivation. The effect of illumination depended on the presence of GFP, suggesting that it released free radicals which oxidized cysteine or methionine residues. In addition, the oxidation effects were resistant to treatment with the cysteine-specific reducing agent DTT, suggesting that methionine rather than cysteine residues may be involved. Our data with synthetic LINGO2 tail peptides further demonstrate that the rate of inactivation was slowed when residues M603 or M605 were oxidized, and practically abolished when both were oxidized. Taken together, these data demonstrate that both methionine residues in the LINGO2 tail mediate the effect of oxidation on BK:LINGO2 channels. Our molecular modeling suggests that methionine oxidation reduces the lipophilicity of the tail, thus preventing it from occluding the pore of the BK channel.
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Affiliation(s)
- Srikanth Dudem
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Louth, Ireland
| | - Pei Xin Boon
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Louth, Ireland
| | - Nicholas Mullins
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Louth, Ireland
| | - Heather McClafferty
- Centre for Discovery Brain Sciences, University of Edinburgh, Scotland, United Kingdom
| | - Michael J Shipston
- Centre for Discovery Brain Sciences, University of Edinburgh, Scotland, United Kingdom
| | | | - Ian Lobb
- Almac Discovery Ltd, Health Sciences Building, Belfast, NIR, United Kingdom
| | - Gerard P Sergeant
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Louth, Ireland
| | - Keith D Thornbury
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Louth, Ireland
| | - Irina G Tikhonova
- School of Pharmacy, Queen's University of Belfast, NIR, United Kingdom
| | - Mark A Hollywood
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Louth, Ireland.
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2
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Moral-Sanz J, Lewis SA, MacMillan S, Meloni M, McClafferty H, Viollet B, Foretz M, Del-Pozo J, Mark Evans A. AMPK deficiency in smooth muscles causes persistent pulmonary hypertension of the new-born and premature death. Nat Commun 2022; 13:5034. [PMID: 36028487 PMCID: PMC9418192 DOI: 10.1038/s41467-022-32568-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 08/05/2022] [Indexed: 11/10/2022] Open
Abstract
AMPK has been reported to facilitate hypoxic pulmonary vasoconstriction but, paradoxically, its deficiency precipitates pulmonary hypertension. Here we show that AMPK-α1/α2 deficiency in smooth muscles promotes persistent pulmonary hypertension of the new-born. Accordingly, dual AMPK-α1/α2 deletion in smooth muscles causes premature death of mice after birth, associated with increased muscularisation and remodeling throughout the pulmonary arterial tree, reduced alveolar numbers and alveolar membrane thickening, but with no oedema. Spectral Doppler ultrasound indicates pulmonary hypertension and attenuated hypoxic pulmonary vasoconstriction. Age-dependent right ventricular pressure elevation, dilation and reduced cardiac output was also evident. KV1.5 potassium currents of pulmonary arterial myocytes were markedly smaller under normoxia, which is known to facilitate pulmonary hypertension. Mitochondrial fragmentation and reactive oxygen species accumulation was also evident. Importantly, there was no evidence of systemic vasculopathy or hypertension in these mice. Moreover, hypoxic pulmonary vasoconstriction was attenuated by AMPK-α1 or AMPK-α2 deletion without triggering pulmonary hypertension.
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Affiliation(s)
- Javier Moral-Sanz
- Centre for Discovery Brain Sciences and Cardiovascular Science, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh, EH8 9XD, UK
| | - Sophronia A Lewis
- Centre for Discovery Brain Sciences and Cardiovascular Science, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh, EH8 9XD, UK
| | - Sandy MacMillan
- Centre for Discovery Brain Sciences and Cardiovascular Science, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh, EH8 9XD, UK
| | - Marco Meloni
- Centre for Cardiovascular Science, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, EH16 4TJ, UK
| | - Heather McClafferty
- Centre for Discovery Brain Sciences and Cardiovascular Science, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh, EH8 9XD, UK
| | - Benoit Viollet
- Université Paris Cité, CNRS, INSERM, Institut Cochin, F-75014, Paris, France
| | - Marc Foretz
- Université Paris Cité, CNRS, INSERM, Institut Cochin, F-75014, Paris, France
| | - Jorge Del-Pozo
- R(D)SVS, University of Edinburgh Easter Bush Campus, EH25 9RG, Roslin, Edinburgh, UK
| | - A Mark Evans
- Centre for Discovery Brain Sciences and Cardiovascular Science, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh, EH8 9XD, UK.
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3
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Duncan PJ, McClafferty H, Nolan O, Ding Q, Homer NZM, Le Tissier P, Walker BR, Shipston MJ, Romanò N, Chambers TJG. Corticotroph isolation from Pomc-eGFP mice reveals sustained transcriptional dysregulation characterising a mouse model of glucocorticoid-induced suppression of the hypothalamus-pituitary-adrenal axis. J Neuroendocrinol 2022; 34:e13165. [PMID: 35833423 PMCID: PMC9539609 DOI: 10.1111/jne.13165] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 04/16/2022] [Accepted: 04/18/2022] [Indexed: 11/27/2022]
Abstract
Glucocorticoids (GC) are prescribed for periods > 3 months to 1%-3% of the UK population; 10%-50% of these patients develop hypothalamus-pituitary-adrenal (HPA) axis suppression, which may last over 6 months and is associated with morbidity and mortality. Recovery of the pituitary and hypothalamus is necessary for recovery of adrenal function. We developed a mouse model of dexamethasone (DEX)-induced HPA axis dysfunction aiming to further explore recovery in the pituitary. Adult male wild-type C57BL6/J or Pomc-eGFP transgenic mice were randomly assigned to receive DEX (approximately 0.4 mg kg-1 bodyweight day-1 ) or vehicle via drinking water for 4 weeks following which treatment was withdrawn and tissues were harvested after another 0, 1, and 4 weeks. Corticotrophs were isolated from Pomc-eGFP pituitaries using fluorescence-activated cell sorting, and RNA extracted for RNA-sequencing. DEX treatment suppressed corticosterone production, which remained partially suppressed at least 1 week following DEX withdrawal. In the adrenal, Hsd3b2, Cyp11a1, and Mc2r mRNA levels were significantly reduced at time 0, with Mc2r and Cyp11a1 remaining reduced 1 week following DEX withdrawal. The corticotroph transcriptome was modified by DEX treatment, with some differences between groups persisting 4 weeks following withdrawal. No genes supressed by DEX exhibited ongoing attenuation 1 and 4 weeks following withdrawal, whereas only two genes were upregulated and remained so following withdrawal. A pattern of rebound at 1 and 4 weeks was observed in 14 genes that increased following suppression, and in six genes that were reduced by DEX and then increased. Chronic GC treatment may induce persistent changes in the pituitary that may influence future response to GC treatment or stress.
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Affiliation(s)
- Peter J. Duncan
- Centre for Discovery Brain SciencesUniversity of EdinburghEdinburghUK
| | | | - Oscar Nolan
- Centre for Discovery Brain SciencesUniversity of EdinburghEdinburghUK
| | - Qinghui Ding
- Centre for Discovery Brain SciencesUniversity of EdinburghEdinburghUK
| | - Natalie Z. M. Homer
- Centre for Cardiovascular ScienceUniversity of Edinburgh, Queen's Medical Research InstituteEdinburghUK
| | - Paul Le Tissier
- Centre for Discovery Brain SciencesUniversity of EdinburghEdinburghUK
| | - Brian R. Walker
- Centre for Cardiovascular ScienceUniversity of Edinburgh, Queen's Medical Research InstituteEdinburghUK
- Translational & Clinical Research InstituteNewcastle UniversityNewcastle upon TyneUK
| | | | - Nicola Romanò
- Centre for Discovery Brain SciencesUniversity of EdinburghEdinburghUK
| | - Thomas J. G. Chambers
- Centre for Discovery Brain SciencesUniversity of EdinburghEdinburghUK
- Edinburgh Centre for Endocrinology and DiabetesNHS Lothian, Metabolic Unit, Western General HospitalEdinburghUK
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4
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McClafferty H, Runciman H, Shipston MJ. Site-specific deacylation by ABHD17a controls BK channel splice variant activity. J Biol Chem 2020; 295:16487-16496. [PMID: 32913120 PMCID: PMC7864050 DOI: 10.1074/jbc.ra120.015349] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 08/26/2020] [Indexed: 12/15/2022] Open
Abstract
S-Acylation, the reversible post-translational lipid modification of proteins, is an important mechanism to control the properties and function of ion channels and other polytopic transmembrane proteins. However, although increasing evidence reveals the role of diverse acyl protein transferases (zDHHC) in controlling ion channel S-acylation, the acyl protein thioesterases that control ion channel deacylation are very poorly defined. Here we show that ABHD17a (α/β-hydrolase domain-containing protein 17a) deacylates the stress-regulated exon domain of large conductance voltage- and calcium-activated potassium (BK) channels inhibiting channel activity independently of effects on channel surface expression. Importantly, ABHD17a deacylates BK channels in a site-specific manner because it has no effect on the S-acylated S0-S1 domain conserved in all BK channels that controls membrane trafficking and is deacylated by the acyl protein thioesterase Lypla1. Thus, distinct S-acylated domains in the same polytopic transmembrane protein can be regulated by different acyl protein thioesterases revealing mechanisms for generating both specificity and diversity for these important enzymes to control the properties and functions of ion channels.
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Affiliation(s)
- Heather McClafferty
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Hamish Runciman
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Michael J Shipston
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, United Kingdom.
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5
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Abstract
The lack of specific pharmacological tools to interrogate the functional role of palmitoyl acyltransferases (zDHHCs) in mammalian cells has significantly hampered the understanding of this important gene family. Gene silencing by RNA interference (RNAi) is a process in eukaryotes that allows specific knockdown of the expression of proteins by targeting their coding mRNA. RNAi can thus be used as a proteomic tool to study the functional role of specific zDHHCs in cells by analyzing the effects of endogenous zDHHC knockdown on their protein targets or pathways. Here we describe the application of short interfering RNA (siRNA), a class of short (20-25 base pairs) double-stranded RNAs, to knockdown endogenous zDHHC enzymes expressed in human embryonic kidney (HEK293) cells and subsequent validation of knockdown efficiency using RT-qPCR to quantify zDHHC mRNA levels.
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Affiliation(s)
- Heather McClafferty
- Centre for Discovery Brain Sciences, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, UK
| | - Michael J Shipston
- Centre for Discovery Brain Sciences, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, UK.
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6
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Duncan PJ, Bi D, McClafferty H, Chen L, Tian L, Shipston MJ. S-Acylation controls functional coupling of BK channel pore-forming α-subunits and β1-subunits. J Biol Chem 2019; 294:12066-12076. [PMID: 31213527 PMCID: PMC6690687 DOI: 10.1074/jbc.ra119.009065] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 06/17/2019] [Indexed: 12/11/2022] Open
Abstract
The properties and physiological function of pore-forming α-subunits of large conductance calcium- and voltage-activated potassium (BK) channels are potently modified by their functional coupling with regulatory subunits in many tissues. However, mechanisms that might control functional coupling are very poorly understood. Here we show that S-acylation, a dynamic post-translational lipid modification of proteins, of the intracellular S0–S1 loop of the BK channel pore-forming α-subunit controls functional coupling to regulatory β1-subunits. In HEK293 cells, α-subunits that cannot be S-acylated show attenuated cell surface expression, but expression was restored by co-expression with the β1-subunit. However, we also found that nonacylation of the S0–S1 loop reduces functional coupling between α- and β1-subunits by attenuating the β1-subunit-induced left shift in the voltage for half-maximal activation. In mouse vascular smooth muscle cells expressing both α- and β1-subunits, BK channel α-subunits were endogenously S-acylated. We further noted that S-acylation is significantly reduced in mice with a genetic deletion of the palmitoyl acyltransferase (Zdhhc23) that controls S-acylation of the S0–S1 loop. Genetic deletion of Zdhhc23 or broad-spectrum pharmacological inhibition of S-acylation attenuated endogenous BK channel currents independently of changes in cell surface expression of the α-subunit. We conclude that functional effects of S-acylation on BK channels depend on the presence of β1-subunits. In the absence of β1-subunits, S-acylation promotes cell surface expression, whereas in its presence, S-acylation controls functional coupling. S-Acylation thus provides a mechanism that dynamically regulates the functional coupling with β1-subunits, enabling an additional level of conditional, cell-specific control of ion-channel physiology.
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Affiliation(s)
- Peter J Duncan
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Danlei Bi
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Heather McClafferty
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Lie Chen
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Lijun Tian
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Michael J Shipston
- Centre for Discovery Brain Sciences, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom.
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7
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Romanò N, McClafferty H, Walker JJ, Le Tissier P, Shipston MJ. Heterogeneity of Calcium Responses to Secretagogues in Corticotrophs From Male Rats. Endocrinology 2017; 158:1849-1858. [PMID: 28323954 PMCID: PMC5460926 DOI: 10.1210/en.2017-00107] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 03/10/2017] [Indexed: 11/30/2022]
Abstract
Heterogeneity in homotypic cellular responses is an important feature of many biological systems, and it has been shown to be prominent in most anterior pituitary hormonal cell types. In this study, we analyze heterogeneity in the responses to hypothalamic secretagogues in the corticotroph cell population of adult male rats. Using the genetically encoded calcium indicator GCaMP6s, we determined the intracellular calcium responses of these cells to corticotropin-releasing hormone and arginine-vasopressin. Our experiments revealed marked population heterogeneity in the response to these peptides, in terms of amplitude and dynamics of the responses, as well as the sensitivity to different concentrations and duration of stimuli. However, repeated stimuli to the same cell produced remarkably consistent responses, indicating that these are deterministic on a cell-by-cell level. We also describe similar heterogeneity in the sensitivity of cells to inhibition by corticosterone. In summary, our results highlight a large degree of heterogeneity in the cellular mechanisms that govern corticotroph responses to their physiological stimuli; this could provide a mechanism to extend the dynamic range of the responses at the population level to allow adaptation to different physiological challenges.
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Affiliation(s)
- Nicola Romanò
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Heather McClafferty
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Jamie J. Walker
- 2Centre for Biomedical Modelling and Analysis, University of Exeter, Exeter EX2 5DW, United Kingdom
- Engineering and Physical Sciences Research Council Centre for Predictive Modelling in Healthcare, University of Exeter, Exeter EX4 4QJ, United Kingdom
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, United Kingdom
- Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Bristol BS1 3NY, United Kingdom
| | - Paul Le Tissier
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Michael J. Shipston
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
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8
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Chen L, Bi D, Lu ZH, McClafferty H, Shipston MJ. Distinct domains of the β1-subunit cytosolic N terminus control surface expression and functional properties of large-conductance calcium-activated potassium (BK) channels. J Biol Chem 2017; 292:8694-8704. [PMID: 28373283 PMCID: PMC5448097 DOI: 10.1074/jbc.m116.769505] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 03/17/2017] [Indexed: 11/06/2022] Open
Abstract
The properties and function of large-conductance calcium- and voltage-activated potassium (BK) channels are modified by the tissue-specific expression of regulatory β1-subunits. Although the short cytosolic N-terminal domain of the β1-subunit is important for controlling both BK channel trafficking and function, whether the same, or different, regions of the N terminus control these distinct processes remains unknown. Here we demonstrate that the first six N-terminal residues including Lys-3, Lys-4, and Leu-5 are critical for controlling functional regulation, but not trafficking, of BK channels. This membrane-distal region has features of an amphipathic helix that is predicted to control the orientation of the first transmembrane-spanning domain (TM1) of the β1-subunit. In contrast, a membrane-proximal leucine residue (Leu-17) controls trafficking without affecting functional coupling, an effect that is in part dependent on controlling efficient endoplasmic reticulum exit of the pore-forming α-subunit. Thus cell surface trafficking and functional coupling with BK channels are controlled by distinct domains of the β1-subunit N terminus.
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Affiliation(s)
- Lie Chen
- From the Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom.,PAPRSB Institute of Health Sciences, Universiti Brunei Darussalam, Jalan Tungku Link BE1410, Brunei Darussalam
| | - Danlei Bi
- From the Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom.,Neurodegenerative Disease Research Center, School of Life Sciences, University of Science and Technology of China, Hefei 230026, China,and
| | - Zen Huat Lu
- PAPRSB Institute of Health Sciences, Universiti Brunei Darussalam, Jalan Tungku Link BE1410, Brunei Darussalam.,Division of Genetics and Genomics, The Roslin Institute, University of Edinburgh, Edinburgh EH25 9RG, Scotland, United Kingdom
| | - Heather McClafferty
- From the Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Michael J Shipston
- From the Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom,
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9
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Illison J, Tian L, McClafferty H, Werno M, Chamberlain LH, Leiss V, Sassmann A, Offermanns S, Ruth P, Shipston MJ, Lukowski R. Obesogenic and Diabetogenic Effects of High-Calorie Nutrition Require Adipocyte BK Channels. Diabetes 2016; 65:3621-3635. [PMID: 27605626 DOI: 10.2337/db16-0245] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 08/16/2016] [Indexed: 11/13/2022]
Abstract
Elevated adipose tissue expression of the Ca2+- and voltage-activated K+ (BK) channel was identified in morbidly obese men carrying a BK gene variant, supporting the hypothesis that K+ channels affect the metabolic responses of fat cells to nutrients. To establish the role of endogenous BKs in fat cell maturation, storage of excess dietary fat, and body weight (BW) gain, we studied a gene-targeted mouse model with global ablation of the BK channel (BKL1/L1) and adipocyte-specific BK-deficient (adipoqBKL1/L2) mice. Global BK deficiency afforded protection from BW gain and excessive fat accumulation induced by a high-fat diet (HFD). Expansion of white adipose tissue-derived epididymal BKL1/L1 preadipocytes and their differentiation to lipid-filled mature adipocytes in vitro, however, were improved. Moreover, BW gain and total fat masses of usually superobese ob/ob mice were significantly attenuated in the absence of BK, together supporting a central or peripheral role for BKs in the regulatory system that controls adipose tissue and weight. Accordingly, HFD-fed adipoqBKL1/L2 mutant mice presented with a reduced total BW and overall body fat mass, smaller adipocytes, and reduced leptin levels. Protection from pathological weight gain in the absence of adipocyte BKs was beneficial for glucose handling and related to an increase in body core temperature as a result of higher levels of uncoupling protein 1 and a low abundance of the proinflammatory interleukin-6, a common risk factor for diabetes and metabolic abnormalities. This suggests that adipocyte BK activity is at least partially responsible for excessive BW gain under high-calorie conditions, suggesting that BK channels are promising drug targets for pharmacotherapy of metabolic disorders and obesity.
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Affiliation(s)
- Julia Illison
- Pharmakologie, Toxikologie und Klinische Pharmazie, Institut für Pharmazie, Tübingen, Germany
| | - Lijun Tian
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, U.K
| | - Heather McClafferty
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, U.K
| | - Martin Werno
- Strathclyde Institute of Pharmacy and Biomedical Sciences, Strathclyde University, Glasgow, U.K
| | - Luke H Chamberlain
- Strathclyde Institute of Pharmacy and Biomedical Sciences, Strathclyde University, Glasgow, U.K
| | - Veronika Leiss
- Department of Pharmacology and Experimental Therapy, Institute of Experimental and Clinical Pharmacology and Toxicology, University Hospital Tübingen, Tübingen, Germany
| | - Antonia Sassmann
- Department of Pharmacology, Max-Planck-Institute for Heart and Lung Research, Bad Nauheim, Germany
| | - Stefan Offermanns
- Department of Pharmacology, Max-Planck-Institute for Heart and Lung Research, Bad Nauheim, Germany
| | - Peter Ruth
- Pharmakologie, Toxikologie und Klinische Pharmazie, Institut für Pharmazie, Tübingen, Germany
| | - Michael J Shipston
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, U.K
| | - Robert Lukowski
- Pharmakologie, Toxikologie und Klinische Pharmazie, Institut für Pharmazie, Tübingen, Germany
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10
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Bi D, Chen L, McClafferty H, Tian L, Shipston M. Palmitoylation of large conductance calcium‐ and voltage activated potassium (BK) channel β‐subunits. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.913.26] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Danlei Bi
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
| | - Lie Chen
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
| | | | - Lijun Tian
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
| | - Mike Shipston
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
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11
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Chen L, Bi D, McClafferty H, Steeb F, Tian L, Shipston M. β4‐subunit palmitoylation controls cell surface expression of large conductance calcium‐ and voltage‐ dependent potassium (BK) channels. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.913.25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Lie Chen
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
| | - Danlei Bi
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
| | | | - Franziska Steeb
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
| | - Lijun Tian
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
| | - Mike Shipston
- School of Biomedical ScienceUniversity of EdinburghEdinburghUnited Kingdom
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12
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Chen L, Bi D, Tian L, McClafferty H, Steeb F, Ruth P, Knaus HG, Shipston MJ. Palmitoylation of the β4-subunit regulates surface expression of large conductance calcium-activated potassium channel splice variants. J Biol Chem 2013; 288:13136-44. [PMID: 23504458 PMCID: PMC3642354 DOI: 10.1074/jbc.m113.461830] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Regulatory β-subunits of large conductance calcium- and voltage-activated potassium (BK) channels play an important role in generating functional diversity and control of cell surface expression of the pore forming α-subunits. However, in contrast to α-subunits, the role of reversible post-translational modification of intracellular residues on β-subunit function is largely unknown. Here we demonstrate that the human β4-subunit is S-acylated (palmitoylated) on a juxtamembrane cysteine residue (Cys-193) in the intracellular C terminus of the regulatory β-subunit. β4-Subunit palmitoylation is important for cell surface expression and endoplasmic reticulum (ER) exit of the β4-subunit alone. Importantly, palmitoylated β4-subunits promote the ER exit and surface expression of the pore-forming α-subunit, whereas β4-subunits that cannot be palmitoylated do not increase ER exit or surface expression of α-subunits. Strikingly, however, this palmitoylation- and β4-dependent enhancement of α-subunit surface expression was only observed in α-subunits that contain a putative trafficking motif (… REVEDEC) at the very C terminus of the α-subunit. Engineering this trafficking motif to other C-terminal α-subunit splice variants results in α-subunits with reduced surface expression that can be rescued by palmitoylated, but not depalmitoylated, β4-subunits. Our data reveal a novel mechanism by which palmitoylated β4-subunit controls surface expression of BK channels through masking of a trafficking motif in the C terminus of the α-subunit. As palmitoylation is dynamic, this mechanism would allow precise control of specific splice variants to the cell surface. Our data provide new insights into how complex interplay between the repertoire of post-transcriptional and post-translational mechanisms controls cell surface expression of BK channels.
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Affiliation(s)
- Lie Chen
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
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Zhou X, Wulfsen I, Korth M, McClafferty H, Lukowski R, Shipston MJ, Ruth P, Dobrev D, Wieland T. Palmitoylation and membrane association of the stress axis regulated insert (STREX) controls BK channel regulation by protein kinase C. J Biol Chem 2012; 287:32161-71. [PMID: 22843729 DOI: 10.1074/jbc.m112.386359] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Large-conductance, calcium- and voltage-gated potassium (BK) channels play an important role in cellular excitability by controlling membrane potential and calcium influx. The stress axis regulated exon (STREX) at splice site 2 inverts BK channel regulation by protein kinase A (PKA) from stimulatory to inhibitory. Here we show that palmitoylation of STREX controls BK channel regulation also by protein kinase C (PKC). In contrast to the 50% decrease of maximal channel activity by PKC in the insertless (ZERO) splice variant, STREX channels were completely resistant to PKC. STREX channel mutants in which Ser(700), located between the two regulatory domains of K(+) conductance (RCK) immediately downstream of the STREX insert, was replaced by the phosphomimetic amino acid glutamate (S700E) showed a ∼50% decrease in maximal channel activity, whereas the S700A mutant retained its normal activity. BK channel inhibition by PKC, however, was effectively established when the palmitoylation-mediated membrane-anchor of the STREX insert was removed by either pharmacological inhibition of palmitoyl transferases or site-directed mutagenesis. These findings suggest that STREX confers a conformation on BK channels where PKC fails to phosphorylate and to inhibit channel activity. Importantly, PKA which inhibits channel activity by disassembling the STREX insert from the plasma membrane, allows PKC to further suppress the channel gating independent from voltage and calcium. Our results present an important example for the cross-talk between ion channel palmitoylation and phosphorylation in regulation of cellular excitability.
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Affiliation(s)
- Xiaobo Zhou
- Division of Experimental Cardiology, Mannheim Medical Faculty, Heidelberg University, D-68167 Mannheim, Germany.
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Tian L, McClafferty H, Knaus HG, Ruth P, Shipston MJ. Distinct acyl protein transferases and thioesterases control surface expression of calcium-activated potassium channels. J Biol Chem 2012; 287:14718-25. [PMID: 22399288 PMCID: PMC3340283 DOI: 10.1074/jbc.m111.335547] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein palmitoylation is rapidly emerging as an important determinant in the regulation of ion channels, including large conductance calcium-activated potassium (BK) channels. However, the enzymes that control channel palmitoylation are largely unknown. Indeed, although palmitoylation is the only reversible lipid modification of proteins, acyl thioesterases that control ion channel depalmitoylation have not been identified. Here, we demonstrate that palmitoylation of the intracellular S0-S1 loop of BK channels is controlled by two of the 23 mammalian palmitoyl-transferases, zDHHC22 and zDHHC23. Palmitoylation by these acyl transferases is essential for efficient cell surface expression of BK channels. In contrast, depalmitoylation is controlled by the cytosolic thioesterase APT1 (LYPLA1), but not APT2 (LYPLA2). In addition, we identify a splice variant of LYPLAL1, a homolog with ∼30% identity to APT1, that also controls BK channel depalmitoylation. Thus, both palmitoyl acyltransferases and acyl thioesterases display discrete substrate specificity for BK channels. Because depalmitoylated BK channels are retarded in the trans-Golgi network, reversible protein palmitoylation provides a critical checkpoint to regulate exit from the trans-Golgi network and thus control BK channel cell surface expression.
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Affiliation(s)
- Lijun Tian
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, EH8 9XD, Scotland
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15
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Jeffries O, Tian L, McClafferty H, Shipston MJ. An electrostatic switch controls palmitoylation of the large conductance voltage- and calcium-activated potassium (BK) channel. J Biol Chem 2011; 287:1468-77. [PMID: 22084244 PMCID: PMC3256903 DOI: 10.1074/jbc.m111.224840] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Protein palmitoylation is a major dynamic posttranslational regulator of protein function. However, mechanisms that control palmitoylation are poorly understood. In many proteins, palmitoylation occurs at cysteine residues juxtaposed to membrane-anchoring domains such as transmembrane helices, sites of irreversible lipid modification, or hydrophobic and/or polybasic domains. In particular, polybasic domains represent an attractive mechanism to dynamically control protein palmitoylation, as the function of these domains can be dramatically influenced by protein phosphorylation. Here we demonstrate that a polybasic domain immediately upstream of palmitoylated cysteine residues within an alternatively spliced insert in the C terminus of the large conductance calcium- and voltage-activated potassium channel is an important determinant of channel palmitoylation and function. Mutation of basic amino acids to acidic residues within the polybasic domain results in inhibition of channel palmitoylation and a significant right-shift in channel half maximal voltage for activation. Importantly, protein kinase A-dependent phosphorylation of a single serine residue within the core of the polybasic domain, which results in channel inhibition, also reduces channel palmitoylation. These data demonstrate the key role of the polybasic domain in controlling stress-regulated exon palmitoylation and suggests that phosphorylation controls the domain by acting as an electrostatic switch.
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Affiliation(s)
- Owen Jeffries
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
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Liang Z, Chen L, McClafferty H, Lukowski R, MacGregor D, King JT, Rizzi S, Sausbier M, McCobb DP, Knaus HG, Ruth P, Shipston MJ. Control of hypothalamic-pituitary-adrenal stress axis activity by the intermediate conductance calcium-activated potassium channel, SK4. J Physiol 2011; 589:5965-86. [PMID: 22041182 PMCID: PMC3286679 DOI: 10.1113/jphysiol.2011.219378] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Non-technical summary Our ability to respond to stress is critically dependent upon the release of the stress hormone adrenocorticotrophic hormone (ACTH) from corticotroph cells of the anterior pituitary gland. ACTH release is controlled by the electrical properties of corticotrophs that are determined by the movement of ions through channel pores in the plasma membrane. We show that a calcium-activated potassium ion channel called SK4 is expressed in corticotrophs and regulates ACTH release. We provide evidence of how SK4 channels control corticotroph function, which is essential for understanding homeostasis and for treating stress-related disorders. Abstract The anterior pituitary corticotroph is a major control point for the regulation of the hypothalamic–pituitary–adrenal (HPA) axis and the neuroendocrine response to stress. Although corticotrophs are known to be electrically excitable, ion channels controlling the electrical properties of corticotrophs are poorly understood. Here, we exploited a lentiviral transduction system to allow the unequivocal identification of live murine corticotrophs in culture. We demonstrate that corticotrophs display highly heterogeneous spontaneous action-potential firing patterns and their resting membrane potential is modulated by a background sodium conductance. Physiological concentrations of corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) cause a depolarization of corticotrophs, leading to a sustained increase in action potential firing. A major component of the outward potassium conductance was mediated via intermediate conductance calcium-activated (SK4) potassium channels. Inhibition of SK4 channels with TRAM-34 resulted in an increase in corticotroph excitability and exaggerated CRH/AVP-stimulated ACTH secretion in vitro. In accordance with a physiological role for SK4 channels in vivo, restraint stress-induced plasma ACTH and corticosterone concentrations were significantly enhanced in gene-targeted mice lacking SK4 channels (Kcnn4−/−). In addition, Kcnn4−/− mutant mice displayed enhanced hypothalamic c-fos and nur77 mRNA expression following restraint, suggesting increased neuronal activation. Thus, stress hyperresponsiveness observed in Kcnn4−/− mice results from enhanced secretagogue-induced ACTH output from anterior pituitary corticotrophs and may also involve increased hypothalamic drive, thereby suggesting an important role for SK4 channels in HPA axis function.
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Affiliation(s)
- Zhi Liang
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH89XD, Scotland, UK
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Düfer M, Neye Y, Hörth K, Krippeit-Drews P, Hennige A, Widmer H, McClafferty H, Shipston MJ, Häring HU, Ruth P, Drews G. BK channels affect glucose homeostasis and cell viability of murine pancreatic beta cells. Diabetologia 2011; 54:423-32. [PMID: 20981405 PMCID: PMC4005923 DOI: 10.1007/s00125-010-1936-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Accepted: 09/08/2010] [Indexed: 01/04/2023]
Abstract
AIMS/HYPOTHESIS Evidence is accumulating that Ca(2+)-regulated K(+) (K(Ca)) channels are important for beta cell function. We used BK channel knockout (BK-KO) mice to examine the role of these K(Ca) channels for glucose homeostasis, beta cell function and viability. METHODS Glucose and insulin tolerance were tested with male wild-type and BK-KO mice. BK channels were detected by single-cell RT-PCR, cytosolic Ca(2+) concentration ([Ca(2+)](c)) by fura-2 fluorescence, and insulin secretion by radioimmunoassay. Electrophysiology was performed with the patch-clamp technique. Apoptosis was detected via caspase 3 or TUNEL assay. RESULTS BK channels were expressed in murine pancreatic beta cells. BK-KO mice were normoglycaemic but displayed markedly impaired glucose tolerance. Genetic or pharmacological deletion of the BK channel reduced glucose-induced insulin secretion from isolated islets. BK-KO and BK channel inhibition (with iberiotoxin, 100 nmol/l) broadened action potentials and abolished the after-hyperpolarisation in glucose-stimulated beta cells. However, BK-KO did not affect action potential frequency, the plateau potential at which action potentials start or glucose-induced elevation of [Ca(2+)](c). BK-KO had no direct influence on exocytosis. Importantly, in BK-KO islet cells the fraction of apoptotic cells and the rate of cell death induced by oxidative stress (H(2)O(2), 10-100 μmol/l) were significantly increased compared with wild-type controls. Similar effects were obtained with iberiotoxin. Determination of H(2)O(2)-induced K(+) currents revealed that BK channels contribute to the hyperpolarising K(+) current activated under conditions of oxidative stress. CONCLUSIONS/INTERPRETATION Ablation or inhibition of BK channels impairs glucose homeostasis and insulin secretion by interfering with beta cell stimulus-secretion coupling. In addition, BK channels are part of a defence mechanism against apoptosis and oxidative stress.
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Affiliation(s)
- M Düfer
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany
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Ross FA, Rafferty JN, Dallas ML, Ogunbayo O, Ikematsu N, McClafferty H, Tian L, Widmer H, Rowe ICM, Wyatt CN, Shipston MJ, Peers C, Hardie DG, Evans AM. Selective expression in carotid body type I cells of a single splice variant of the large conductance calcium- and voltage-activated potassium channel confers regulation by AMP-activated protein kinase. J Biol Chem 2011; 286:11929-36. [PMID: 21209098 PMCID: PMC3069395 DOI: 10.1074/jbc.m110.189779] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Inhibition of large conductance calcium-activated potassium (BKCa) channels mediates, in part, oxygen sensing by carotid body type I cells. However, BKCa channels remain active in cells that do not serve to monitor oxygen supply. Using a novel, bacterially derived AMP-activated protein kinase (AMPK), we show that AMPK phosphorylates and inhibits BKCa channels in a splice variant-specific manner. Inclusion of the stress-regulated exon within BKCa channel α subunits increased the stoichiometry of phosphorylation by AMPK when compared with channels lacking this exon. Surprisingly, however, the increased phosphorylation conferred by the stress-regulated exon abolished BKCa channel inhibition by AMPK. Point mutation of a single serine (Ser-657) within this exon reduced channel phosphorylation and restored channel inhibition by AMPK. Significantly, RT-PCR showed that rat carotid body type I cells express only the variant of BKCa that lacks the stress-regulated exon, and intracellular dialysis of bacterially expressed AMPK markedly attenuated BKCa currents in these cells. Conditional regulation of BKCa channel splice variants by AMPK may therefore determine the response of carotid body type I cells to hypoxia.
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Affiliation(s)
- Fiona A Ross
- College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, United Kingdom
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Jeffries O, Geiger N, Rowe ICM, Tian L, McClafferty H, Chen L, Bi D, Knaus HG, Ruth P, Shipston MJ. Palmitoylation of the S0-S1 linker regulates cell surface expression of voltage- and calcium-activated potassium (BK) channels. J Biol Chem 2010; 285:33307-33314. [PMID: 20693285 PMCID: PMC2963414 DOI: 10.1074/jbc.m110.153940] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
S-Palmitoylation is rapidly emerging as an important post-translational mechanism to regulate ion channels. We have previously demonstrated that large conductance calcium- and voltage-activated potassium (BK) channels are palmitoylated within an alternatively spliced (STREX) insert. However, these studies also revealed that additional site(s) for palmitoylation must exist outside of the STREX insert, although the identity or the functional significance of these palmitoylated cysteine residues are unknown. Here, we demonstrate that BK channels are palmitoylated at a cluster of evolutionary conserved cysteine residues (Cys-53, Cys-54, and Cys-56) within the intracellular linker between the S0 and S1 transmembrane domains. Mutation of Cys-53, Cys-54, and Cys-56 completely abolished palmitoylation of BK channels lacking the STREX insert (ZERO variant). Palmitoylation allows the S0-S1 linker to associate with the plasma membrane but has no effect on single channel conductance or the calcium/voltage sensitivity. Rather, S0-S1 linker palmitoylation is a critical determinant of cell surface expression of BK channels, as steady state surface expression levels are reduced by ∼55% in the C53:54:56A mutant. STREX variant channels that could not be palmitoylated in the S0-S1 linker also displayed significantly reduced cell surface expression even though STREX insert palmitoylation was unaffected. Thus our work reveals the functional independence of two distinct palmitoylation-dependent membrane interaction domains within the same channel protein and demonstrates the critical role of S0-S1 linker palmitoylation in the control of BK channel cell surface expression.
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Affiliation(s)
- Owen Jeffries
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Nina Geiger
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom; Pharmacology and Toxicology, Institute of Pharmacy, University Tuebingen, 72076 Tuebingen, Germany
| | - Iain C M Rowe
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Lijun Tian
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Heather McClafferty
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Lie Chen
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Danlei Bi
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
| | - Hans Guenther Knaus
- Division for Molecular and Cellular Pharmacology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Medical University Innsbruck, Peter-Mayr Strasse 1, 6020 Innsbruck, Austria
| | - Peter Ruth
- Pharmacology and Toxicology, Institute of Pharmacy, University Tuebingen, 72076 Tuebingen, Germany
| | - Michael J Shipston
- From the Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom.
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Tian L, McClafferty H, Jeffries O, Shipston MJ. Multiple palmitoyltransferases are required for palmitoylation-dependent regulation of large conductance calcium- and voltage-activated potassium channels. J Biol Chem 2010; 285:23954-62. [PMID: 20507996 PMCID: PMC2911306 DOI: 10.1074/jbc.m110.137802] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Palmitoylation is emerging as an important and dynamic regulator of ion channel function; however, the specificity with which the large family of acyl palmitoyltransferases (zinc finger Asp-His-His-Cys type-containing acyl palmitoyltransferase (DHHCs)) control channel palmitoylation is poorly understood. We have previously demonstrated that the alternatively spliced stress-regulated exon (STREX) variant of the intracellular C-terminal domain of the large conductance calcium- and voltage-activated potassium (BK) channels is palmitoylated and targets the STREX domain to the plasma membrane. Using a combined imaging, biochemical, and functional approach coupled with loss-of-function (small interfering RNA knockdown of endogenous DHHCs) and gain-of-function (overexpression of recombinant DHHCs) assays, we demonstrate that multiple DHHCs control palmitoylation of the C terminus of STREX channels, the association of the STREX domain with the plasma membrane, and functional channel regulation. Cysteine residues 12 and 13 within the STREX insert were the only endogenously palmitoylated residues in the entire C terminus of the STREX channel. Palmitoylation of this dicysteine motif was controlled by DHHCs 3, 5, 7, 9, and 17, although DHHC17 showed the greatest specificity for this site upon overexpression of the cognate DHHC. DHHCs that palmitoylated the channel also co-assembled with the channel in co-immunoprecipitation experiments, and knockdown of any of these DHHCs blocked regulation of the channel by protein kinase A-dependent phosphorylation. Taken together our data reveal that a subset of DHHCs controls STREX palmitoylation and function and suggest that DHHC17 may preferentially target cysteine-rich domains. Finally, our approach may prove useful in elucidating the specificity of DHHC palmitoylation of intracellular domains of other ion channels and transmembrane proteins.
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Affiliation(s)
- Lijun Tian
- Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh EH89XD, Scotland, United Kingdom
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Tian L, McClafferty H, Chen L, Shipston MJ. Reversible Tyrosine Protein Phosphorylation Regulates Large Conductance Voltage- and Calcium-activated Potassium Channels via Cortactin. J Biol Chem 2008; 283:3067-3076. [DOI: 10.1074/jbc.m706826200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
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Tian L, Chen L, McClafferty H, Sailer CA, Ruth P, Knaus HG, Shipston MJ. A noncanonical SH3 domain binding motif links BK channels to the actin cytoskeleton via the SH3 adapter cortactin. FASEB J 2006; 20:2588-90. [PMID: 17065230 DOI: 10.1096/fj.06-6152fje] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Calcium-activated potassium (BK) channels play a central role in regulating multiple physiological processes, from the control of blood flow to neuronal excitability. Coordinated regulation of BK channel activity by changes in actin cytoskeleton dynamics has been implicated in several of these processes and related disease states such as epilepsy and stroke. However, how BK channels interact with the actin cytoskeleton is essentially unknown. Here we demonstrate noncanonical Src homology domain 3 (SH3) binding site motifs in the intracellular C terminus of the BK channel pore-forming alpha-subunit that are conserved from fish to humans. These noncanonical motifs target multiple SH3 domain cellular signaling proteins to BK channels, including the SH3 adapter protein cortactin (EMS1). We demonstrate that cortactin provides a molecular bridge between BK channels and the cortical actin cytoskeleton in cells. Disruption of the SH3-mediated interaction prevents the regulation of BK channel activity controlled by changes in actin cytoskeletal dynamics. Targeting of cortactin to BK channels via a novel, noncanonical SH3 domain binding motif has important implications for the coordination of BK channel function in normal physiology and disease.
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Affiliation(s)
- Lijun Tian
- Centre for Integrative Physiology, School of Biomedical Science, University of Edinburgh, Edinburgh EH8 9XD, Scotland, UK
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McCartney CE, McClafferty H, Huibant JM, Rowan EG, Shipston MJ, Rowe ICM. A cysteine-rich motif confers hypoxia sensitivity to mammalian large conductance voltage- and Ca-activated K (BK) channel alpha-subunits. Proc Natl Acad Sci U S A 2005; 102:17870-6. [PMID: 16306267 PMCID: PMC1308893 DOI: 10.1073/pnas.0505270102] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Cellular responses to hypoxia are tissue-specific and dynamic. However, the mechanisms that underlie this differential sensitivity to hypoxia are unknown. Large conductance voltage- and Ca-activated K (BK) channels are important mediators of hypoxia responses in many systems. Although BK channels are ubiquitously expressed, alternative pre-mRNA splicing of the single gene encoding their pore-forming alpha-subunits provides a powerful mechanism for generating functional diversity. Here, we demonstrate that the hypoxia sensitivity of BK channel alpha-subunits is splice-variant-specific. Sensitivity to hypoxia is conferred by a highly conserved motif within an alternatively spliced cysteine-rich insert, the stress-regulated exon (STREX), within the intracellular C terminus of the channel. Hypoxic inhibition of the STREX variant is Ca-sensitive and reversible, and it rapidly follows the change in oxygen tension by means of a mechanism that is independent of redox or CO regulation. Hypoxia sensitivity was abolished by mutation of the serine (S24) residue within the STREX insert. Because STREX splice-variant expression is tissue-specific and dynamically controlled, alternative splicing of BK channels provides a mechanism to control the plasticity of cellular responses to hypoxia.
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Affiliation(s)
- Claire E McCartney
- Department of Physiology and Pharmacology, Strathclyde Institute for Biomedical Sciences, University of Strathclyde, 27 Taylor Street, Glasgow G4 0NR, United Kingdom
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Chen L, Tian L, MacDonald SHF, McClafferty H, Hammond MSL, Huibant JM, Ruth P, Knaus HG, Shipston MJ. Functionally Diverse Complement of Large Conductance Calcium- and Voltage-activated Potassium Channel (BK) α-Subunits Generated from a Single Site of Splicing. J Biol Chem 2005; 280:33599-609. [PMID: 16081418 DOI: 10.1074/jbc.m505383200] [Citation(s) in RCA: 136] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The pore-forming alpha-subunits of large conductance calcium- and voltage-activated potassium (BK) channels are encoded by a single gene that undergoes extensive alternative pre-mRNA splicing. However, the extent to which differential exon usage at a single site of splicing may confer functionally distinct properties on BK channels is largely unknown. Here we demonstrated that alternative splicing at site of splicing C2 in the mouse BK channel C terminus generates five distinct splice variants: ZERO, e20, e21(STREX), e22, and a novel variant deltae23. Splice variants display distinct patterns of tissue distribution with e21(STREX) expressed at the highest levels in adult endocrine tissues and e22 at embryonic stages of mouse development. deltae23 is not functionally expressed at the cell surface and acts as a dominant negative of cell surface expression by trapping other BK channel splice variant alpha-subunits in the endoplasmic reticulum and perinuclear compartments. Splice variants display a range of biophysical properties. e21(STREX) and e22 variants display a significant left shift (>20 mV at 1 microM [Ca2+]i) in half-maximal voltage of activation compared with ZERO and e20 as well as considerably slower rates of deactivation. Splice variants are differentially sensitive to phosphorylation by endogenous cAMP-dependent protein kinase; ZERO, e20, and e22 variants are all activated, whereas e21 (STREX) is the only variant that is inhibited. Thus alternative pre-mRNA splicing from a single site of splicing provides a mechanism to generate a physiologically diverse complement of BK channel alpha-subunits that differ dramatically in their tissue distribution, trafficking, and regulation.
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Affiliation(s)
- Lie Chen
- Centre for Integrative Physiology, Membrane Biology Group, University of Edinburgh, Hugh Robson Building, Edinburgh EH8 9XD, Scotland, United Kingdom
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Findlay HE, McClafferty H, Ashley RH. Surface expression, single-channel analysis and membrane topology of recombinant Chlamydia trachomatis Major Outer Membrane Protein. BMC Microbiol 2005; 5:5. [PMID: 15673471 PMCID: PMC549562 DOI: 10.1186/1471-2180-5-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Accepted: 01/26/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Chlamydial bacteria are obligate intracellular pathogens containing a cysteine-rich porin (Major Outer Membrane Protein, MOMP) with important structural and, in many species, immunity-related roles. MOMP forms extensive disulphide bonds with other chlamydial proteins, and is difficult to purify. Leaderless, recombinant MOMPs expressed in E. coli have yet to be refolded from inclusion bodies, and although leadered MOMP can be expressed in E. coli cells, it often misfolds and aggregates. We aimed to improve the surface expression of correctly folded MOMP to investigate the membrane topology of the protein, and provide a system to display native and modified MOMP epitopes. RESULTS C. trachomatis MOMP was expressed on the surface of E. coli cells (including "porin knockout" cells) after optimizing leader sequence, temperature and medium composition, and the protein was functionally reconstituted at the single-channel level to confirm it was folded correctly. Recombinant MOMP formed oligomers even in the absence of its 9 cysteine residues, and the unmodified protein also formed inter- and intra-subunit disulphide bonds. Its topology was modeled as a (16-stranded) beta-barrel, and specific structural predictions were tested by removing each of the four putative surface-exposed loops corresponding to highly immunogenic variable sequence (VS) domains, and one or two of the putative transmembrane strands. The deletion of predicted external loops did not prevent folding and incorporation of MOMP into the E. coli outer membrane, in contrast to the removal of predicted transmembrane strands. CONCLUSIONS C. trachomatis MOMP was functionally expressed on the surface of E. coli cells under newly optimized conditions. Tests of its predicted membrane topology were consistent with beta-barrel oligomers in which major immunogenic regions are displayed on surface-exposed loops. Functional surface expression, coupled with improved understanding of MOMP's topology, could provide modified antigens for immunological studies and vaccination, including live subunit vaccines, and might be useful to co-express MOMP with other chlamydial membrane proteins.
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Affiliation(s)
- Heather E Findlay
- Division of Biomedical Sciences, University of Edinburgh Medical School, George Square, Edinburgh EH8 9XD, UK
- Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
| | - Heather McClafferty
- Division of Biomedical Sciences, University of Edinburgh Medical School, George Square, Edinburgh EH8 9XD, UK
| | - Richard H Ashley
- Division of Biomedical Sciences, University of Edinburgh Medical School, George Square, Edinburgh EH8 9XD, UK
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Tian L, Coghill LS, McClafferty H, MacDonald SHF, Antoni FA, Ruth P, Knaus HG, Shipston MJ. Distinct stoichiometry of BKCa channel tetramer phosphorylation specifies channel activation and inhibition by cAMP-dependent protein kinase. Proc Natl Acad Sci U S A 2004; 101:11897-902. [PMID: 15280542 PMCID: PMC511071 DOI: 10.1073/pnas.0402590101] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2004] [Accepted: 06/21/2004] [Indexed: 02/06/2023] Open
Abstract
Large conductance voltage- and calcium-activated potassium (BK(Ca)) channels are important signaling molecules that are regulated by multiple protein kinases and protein phosphatases at multiple sites. The pore-forming alpha-subunits, derived from a single gene that undergoes extensive alternative pre-mRNA splicing, assemble as tetramers. Although consensus phosphorylation sites have been identified within the C-terminal domain of alpha-subunits, it is not known whether phosphorylation of all or single alpha-subunits within the tetramer is required for functional regulation of the channel. Here, we have exploited a strategy to study single-ion channels in which both the alpha-subunit splice-variant composition is defined and the number of consensus phosphorylation sites available within each tetramer is known. We have used this approach to demonstrate that cAMP-dependent protein kinase (PKA) phosphorylation of the conserved C-terminal PKA consensus site (S899) in all four alpha-subunits is required for channel activation. In contrast, inhibition of BK(Ca) channel activity requires phosphorylation of only a single alpha-subunit at a splice insert (STREX)-specific PKA consensus site (S4(STREX)). Thus, distinct modes of BK(Ca) channel regulation by PKA phosphorylation exist: an "all-or-nothing" rule for activation and a "single-subunit" rule for inhibition. This essentially digital regulation has important implications for the combinatorial and conditional regulation of BK(Ca) channels by reversible protein phosphorylation.
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Affiliation(s)
- Lijun Tian
- Membrane Biology Group, Division of Biomedical Science, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
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