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Ježek P, Holendová B, Jabůrek M, Dlasková A, Plecitá-Hlavatá L. Contribution of Mitochondria to Insulin Secretion by Various Secretagogues. Antioxid Redox Signal 2022; 36:920-952. [PMID: 34180254 PMCID: PMC9125579 DOI: 10.1089/ars.2021.0113] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca2+ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca2+ influx was found to enhance GSIS, reflecting cytosolic Ca2+ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca2+ and K+ channels) or the superimposed Ca2+ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca2+ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub β-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.
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Affiliation(s)
- Petr Ježek
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Blanka Holendová
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Martin Jabůrek
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Andrea Dlasková
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Lydie Plecitá-Hlavatá
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
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Li M, Gong S, Han X, Zhang S, Ren Q, Cai X, Luo Y, Zhou L, Zhang R, Liu W, Zhu Y, Zhou X, Sun Y, Li Y, Ma Y, Ji L. Genetic variants of ABCC8 and phenotypic features in Chinese early onset diabetes. J Diabetes 2021; 13:542-553. [PMID: 33300273 DOI: 10.1111/1753-0407.13144] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2020] [Revised: 11/21/2020] [Accepted: 12/06/2020] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND ABCC8 variants cause neonatal diabetes, maturity onset diabetes of the young (MODY), and hyperinsulinemic hypoglycemia because of activating or inactivating variants. In this study we used targeted exon sequencing to investigate genetic variants of ABCC8 and phenotypic features in Chinese patients with early onset diabetes (EOD). METHODS A cross-sectional study of 543 Chinese patients with EOD was recruited and the exons of them were conducted targeted sequencing. The pathogenicity of ABCC8 variants was defined according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guideline. The phenotypes of patients owing to ABCC8 variants (ABCC8-MODY) were characterized. RESULTS Among the 543 participants, eight (1.5%) patients with ABCC8-MODY were identified. They harbored eight missense ABCC8 variants (p.R306C, p.E1326K, and p.R1379H, previously reported; p.R298C, p.F1176C, p.R1221W, p.K1358R, and p.I1404V) classified as likely pathogenic. Two family members with ABCC8-MODY were also confirmed. The average diagnosed age of the 10 patients was 26.8 ± 12.9 years. The majority of them had unsatisfactory glucose control, 80% of them had diabetic kidney disease, and neurological features were not observed. CONCLUSION Using targeted exon sequencing followed by pathogenicity analysis, we could be able to make genetic diagnoses for eight (1.5%) patients with ABCC8-MODY. The phenotype was variable with higher risk of diabetic microvascular complications. Genetic diagnosis is conducive for facilitating the personalized treatment of ABCC8-MODY.
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Affiliation(s)
- Meng Li
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Siqian Gong
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Xueyao Han
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Simin Zhang
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Qian Ren
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Xiaoling Cai
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Yingying Luo
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Lingli Zhou
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Rui Zhang
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Wei Liu
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Yu Zhu
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Xianghai Zhou
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Yanfang Sun
- Department of Internal Medicine, Hebei Province Sanhe Hospital, Langfang, China
| | - Yufeng Li
- Department of Endocrinology and Metabolism, Capital Medical University Pinggu Hospital, Beijing, China
| | - Yumin Ma
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
| | - Linong Ji
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China
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Li M, Han X, Ji L. Clinical and Genetic Characteristics of ABCC8 Nonneonatal Diabetes Mellitus: A Systematic Review. J Diabetes Res 2021; 2021:9479268. [PMID: 34631896 PMCID: PMC8497126 DOI: 10.1155/2021/9479268] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Revised: 08/11/2021] [Accepted: 08/16/2021] [Indexed: 02/06/2023] Open
Abstract
OBJECTIVES Diabetes mellitus (DM) is a major chronic metabolic disease in the world, and the prevalence has been increasing rapidly in recent years. The channel of KATP plays an important role in the regulation of insulin secretion. The variants in ABCC8 gene encoding the SUR1 subunit of KATP could cause a variety of phenotypes, including neonatal diabetes mellitus (ABCC8-NDM) and ABCC8-induced nonneonatal diabetes mellitus (ABCC8-NNDM). Since the features of ABCC8-NNDM have not been elucidated, this study is aimed at concluding the genetic features and clinical characteristics. METHODS We comprehensively reviewed the literature associated with ABCC8-NNDM in the following databases: MEDLINE, PubMed, and Web of Science to investigate the features of ABCC8-NNDM. RESULTS Based on a comprehensive literature search, we found that 87 probands with ABCC8-NNDM carried 71 ABCC8 genetic variant alleles, 24% of whom carried inactivating variants, 24% carried activating variants, and the remaining 52% carried activating or inactivating variants. Nine of these variants were confirmed to be activating or inactivating through functional studies, while four variants (p.R370S, p.E1506K, p.R1418H, and p.R1420H) were confirmed to be inactivating. The phenotypes of ABCC8-NNDM were variable and could also present with early hyperinsulinemia followed by reduced insulin secretion, progressing to diabetes later. They had a relatively high risk of microvascular complications and low prevalence of nervous disease, which is different from ABCC8-NDM. CONCLUSIONS Genetic testing is essential for proper diagnosis and appropriate treatment for patients with ABCC8-NNDM. And further studies are required to determine the complex mechanism of the variants of ABCC8-NNDM.
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Affiliation(s)
- Meng Li
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China 100044
| | - Xueyao Han
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China 100044
| | - Linong Ji
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Peking University Diabetes Center, Beijing, China 100044
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Jacobson DA, Shyng SL. Ion Channels of the Islets in Type 2 Diabetes. J Mol Biol 2019; 432:1326-1346. [PMID: 31473158 DOI: 10.1016/j.jmb.2019.08.014] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 08/19/2019] [Accepted: 08/21/2019] [Indexed: 02/06/2023]
Abstract
Ca2+ is an essential signal for pancreatic β-cell function. Ca2+ plays critical roles in numerous β-cell pathways such as insulin secretion, transcription, metabolism, endoplasmic reticulum function, and the stress response. Therefore, β-cell Ca2+ handling is tightly controlled. At the plasma membrane, Ca2+ entry primarily occurs through voltage-dependent Ca2+ channels. Voltage-dependent Ca2+ channel activity is dependent on orchestrated fluctuations in the plasma membrane potential or voltage, which are mediated via the activity of many ion channels. During the pathogenesis of type 2 diabetes the β-cell is exposed to stressful conditions, which result in alterations of Ca2+ handling. Some of the changes in β-cell Ca2+ handling that occur under stress result from perturbations in ion channel activity, expression or localization. Defective Ca2+ signaling in the diabetic β-cell alters function, limits insulin secretion and exacerbates hyperglycemia. In this review, we focus on the β-cell ion channels that control Ca2+ handling and how they impact β-cell dysfunction in type 2 diabetes.
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Affiliation(s)
- David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, 7415 MRB4 (Langford), 2213 Garland Avenue, Nashville, TN 37232, USA.
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, L224, MRB 624, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
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Balamurugan K, Kavitha B, Yang Z, Mohan V, Radha V, Shyng SL. Functional characterization of activating mutations in the sulfonylurea receptor 1 (ABCC8) causing neonatal diabetes mellitus in Asian Indian children. Pediatr Diabetes 2019; 20:397-407. [PMID: 30861254 DOI: 10.1111/pedi.12843] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2018] [Revised: 01/28/2019] [Accepted: 02/24/2019] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND Gain-of-function of ATP-sensitive K+ (KATP ) channels because of mutations in the genes encoding SUR1 (ABCC8) or Kir6.2 (KCNJ11) is a major cause of neonatal diabetes mellitus (NDM). Our aim is to determine molecular defects in KATP channels caused by ABCC8 mutations in Asian Indian children with NDM by in vitro functional studies. METHODS Wild-type (WT; NM_000352.4) or mutant sulfonylurea receptor 1 (SUR1) and Kir6.2 were co-expressed in COSm6 cells. Biogenesis efficiency and surface expression of mutant channels were assessed by immunoblotting and immunostaining. The response of mutant channels to cytoplasmic ATP and ADP was assessed by inside-out patch-clamp recordings. The response of mutant channels to known KATP inhibitors in intact cells were determined by 86 Rb efflux assays. RESULTS Five SUR1 missense mutations, D212Y, P254S, R653Q, R992C, and Q1224H, were studied and showed increased activity in MgATP/MgADP. Two of the mutants, D212Y and P254S, also showed reduced response to ATP4- inhibition, as well as markedly reduced surface expression. Moreover, all five mutants were inhibited by the KATP channel inhibitors glibenclamide and carbamazepine. CONCLUSIONS The study shows the mechanisms by which five SUR1 mutations identified in Asian Indian NDM patients affect KATP channel function to cause the disease. The reduced ATP4- sensitivity caused by the D212Y and P254S mutations in the L0 of SUR1 provides novel insight into the role of L0 in channel inhibition by ATP. The results also explain why sulfonylurea therapy is effective in two patients and inform how it should be effective for the other three patients.
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Affiliation(s)
- Kandasamy Balamurugan
- Department of Molecular Genetics, Madras Diabetes Research Foundation, ICMR Advanced Centre for Genomics of Type 2 Diabetes and Dr. Mohan's Diabetes Specialties Centre, WHO Collaborating Centre for Non-Communicable Diseases Prevention & Control, IDF Centre of Education, Chennai, India.,Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon
| | - Babu Kavitha
- Department of Molecular Genetics, Madras Diabetes Research Foundation, ICMR Advanced Centre for Genomics of Type 2 Diabetes and Dr. Mohan's Diabetes Specialties Centre, WHO Collaborating Centre for Non-Communicable Diseases Prevention & Control, IDF Centre of Education, Chennai, India
| | - Zhongying Yang
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon
| | - Viswanathan Mohan
- Department of Molecular Genetics, Madras Diabetes Research Foundation, ICMR Advanced Centre for Genomics of Type 2 Diabetes and Dr. Mohan's Diabetes Specialties Centre, WHO Collaborating Centre for Non-Communicable Diseases Prevention & Control, IDF Centre of Education, Chennai, India
| | - Venkatesan Radha
- Department of Molecular Genetics, Madras Diabetes Research Foundation, ICMR Advanced Centre for Genomics of Type 2 Diabetes and Dr. Mohan's Diabetes Specialties Centre, WHO Collaborating Centre for Non-Communicable Diseases Prevention & Control, IDF Centre of Education, Chennai, India
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon
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Sikimic J, McMillen TS, Bleile C, Dastvan F, Quast U, Krippeit-Drews P, Drews G, Bryan J. ATP binding without hydrolysis switches sulfonylurea receptor 1 (SUR1) to outward-facing conformations that activate K ATP channels. J Biol Chem 2018; 294:3707-3719. [PMID: 30587573 DOI: 10.1074/jbc.ra118.005236] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Revised: 12/19/2018] [Indexed: 11/06/2022] Open
Abstract
Neuroendocrine-type ATP-sensitive K+ (KATP) channels are metabolite sensors coupling membrane potential with metabolism, thereby linking insulin secretion to plasma glucose levels. They are octameric complexes, (SUR1/Kir6.2)4, comprising sulfonylurea receptor 1 (SUR1 or ABCC8) and a K+-selective inward rectifier (Kir6.2 or KCNJ11). Interactions between nucleotide-, agonist-, and antagonist-binding sites affect channel activity allosterically. Although it is hypothesized that opening these channels requires SUR1-mediated MgATP hydrolysis, we show here that ATP binding to SUR1, without hydrolysis, opens channels when nucleotide antagonism on Kir6.2 is minimized and SUR1 mutants with increased ATP affinities are used. We found that ATP binding is sufficient to switch SUR1 alone between inward- or outward-facing conformations with low or high dissociation constant, KD , values for the conformation-sensitive channel antagonist [3H]glibenclamide ([3H]GBM), indicating that ATP can act as a pure agonist. Assembly with Kir6.2 reduced SUR1's KD for [3H]GBM. This reduction required the Kir N terminus (KNtp), consistent with KNtp occupying a "transport cavity," thus positioning it to link ATP-induced SUR1 conformational changes to channel gating. Moreover, ATP/GBM site coupling was constrained in WT SUR1/WT Kir6.2 channels; ATP-bound channels had a lower KD for [3H]GBM than ATP-bound SUR1. This constraint was largely eliminated by the Q1179R neonatal diabetes-associated mutation in helix 15, suggesting that a "swapped" helix pair, 15 and 16, is part of a structural pathway connecting the ATP/GBM sites. Our results suggest that ATP binding to SUR1 biases KATP channels toward open states, consistent with SUR1 variants with lower KD values causing neonatal diabetes, whereas increased KD values cause congenital hyperinsulinism.
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Affiliation(s)
- Jelena Sikimic
- From the Institute of Pharmacy, Department of Pharmacology, University of Tübingen, D-72076 Tübingen, Germany and
| | - Timothy S McMillen
- Pacific Northwest Diabetes Research Institute, Seattle, Washington 98122, and
| | - Cita Bleile
- From the Institute of Pharmacy, Department of Pharmacology, University of Tübingen, D-72076 Tübingen, Germany and
| | - Frank Dastvan
- Pacific Northwest Diabetes Research Institute, Seattle, Washington 98122, and
| | - Ulrich Quast
- Department of Experimental and Clinical Pharmacology and Toxicology, Eberhard Karls University Hospitals and Clinics, D-72074 Tübingen, Germany
| | - Peter Krippeit-Drews
- From the Institute of Pharmacy, Department of Pharmacology, University of Tübingen, D-72076 Tübingen, Germany and
| | - Gisela Drews
- From the Institute of Pharmacy, Department of Pharmacology, University of Tübingen, D-72076 Tübingen, Germany and
| | - Joseph Bryan
- Pacific Northwest Diabetes Research Institute, Seattle, Washington 98122, and
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Martin GM, Kandasamy B, DiMaio F, Yoshioka C, Shyng SL. Anti-diabetic drug binding site in a mammalian K ATP channel revealed by Cryo-EM. eLife 2017; 6:31054. [PMID: 29035201 PMCID: PMC5655142 DOI: 10.7554/elife.31054] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2017] [Accepted: 10/11/2017] [Indexed: 12/25/2022] Open
Abstract
Sulfonylureas are anti-diabetic medications that act by inhibiting pancreatic KATP channels composed of SUR1 and Kir6.2. The mechanism by which these drugs interact with and inhibit the channel has been extensively investigated, yet it remains unclear where the drug binding pocket resides. Here, we present a cryo-EM structure of a hamster SUR1/rat Kir6.2 channel bound to a high-affinity sulfonylurea drug glibenclamide and ATP at 3.63 Å resolution, which reveals unprecedented details of the ATP and glibenclamide binding sites. Importantly, the structure shows for the first time that glibenclamide is lodged in the transmembrane bundle of the SUR1-ABC core connected to the first nucleotide binding domain near the inner leaflet of the lipid bilayer. Mutation of residues predicted to interact with glibenclamide in our model led to reduced sensitivity to glibenclamide. Our structure provides novel mechanistic insights of how sulfonylureas and ATP interact with the KATP channel complex to inhibit channel activity.
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
| | - Balamurugan Kandasamy
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
| | - Frank DiMaio
- Department of Biochemistry, University of Washington, Seattle, United States
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, United States
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
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Abstract
Since the discovery of the KATP channel in 1983, numerous studies have revealed its physiological functions. The KATP channel is expressed in various organs, including the pancreas, brain and skeletal muscles. It functions as a "metabolic sensor" that converts the metabolic status to electrical activity. In pancreatic beta-cells, the KATP channel regulates the secretion of insulin by sensing a change in the blood glucose level and thus maintains glucose homeostasis. In 2004, heterozygous gain-of-function mutations in the KCNJ11 gene, which encodes the Kir6.2 subunit of the KATP channel, were found to cause neonatal diabetes. In some mutations, diabetes is accompanied by severe neurological symptoms [developmental delay, epilepsy, neonatal diabetes (DEND) syndrome]. This review focuses on mutations of Kir6.2, the pore-forming subunit and sulfonylurea receptor (SUR) 1, the regulatory subunit of the KATP channel, which cause neonatal diabetes/DEND syndrome and also discusses the findings of the pathological mechanisms that are associated with neonatal diabetes, and its neurological features.
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Affiliation(s)
- Kenju Shimomura
- Department of Medical Electrophysiology, Fukushima Medical University School of Medicine, Japan
| | - Yuko Maejima
- Department of Medical Electrophysiology, Fukushima Medical University School of Medicine, Japan
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Ashcroft FM, Puljung MC, Vedovato N. Neonatal Diabetes and the K ATP Channel: From Mutation to Therapy. Trends Endocrinol Metab 2017; 28:377-387. [PMID: 28262438 PMCID: PMC5582192 DOI: 10.1016/j.tem.2017.02.003] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 01/30/2017] [Accepted: 02/01/2017] [Indexed: 12/25/2022]
Abstract
Activating mutations in one of the two subunits of the ATP-sensitive potassium (KATP) channel cause neonatal diabetes (ND). This may be either transient or permanent and, in approximately 20% of patients, is associated with neurodevelopmental delay. In most patients, switching from insulin to oral sulfonylurea therapy improves glycemic control and ameliorates some of the neurological disabilities. Here, we review how KATP channel mutations lead to the varied clinical phenotype, how sulfonylureas exert their therapeutic effects, and why their efficacy varies with individual mutations.
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Affiliation(s)
- Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, OX1 3PT, UK.
| | - Michael C Puljung
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, OX1 3PT, UK
| | - Natascia Vedovato
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, OX1 3PT, UK
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Martin GM, Yoshioka C, Rex EA, Fay JF, Xie Q, Whorton MR, Chen JZ, Shyng SL. Cryo-EM structure of the ATP-sensitive potassium channel illuminates mechanisms of assembly and gating. eLife 2017; 6. [PMID: 28092267 PMCID: PMC5344670 DOI: 10.7554/elife.24149] [Citation(s) in RCA: 128] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 01/11/2017] [Indexed: 12/18/2022] Open
Abstract
KATP channels are metabolic sensors that couple cell energetics to membrane excitability. In pancreatic β-cells, channels formed by SUR1 and Kir6.2 regulate insulin secretion and are the targets of antidiabetic sulfonylureas. Here, we used cryo-EM to elucidate structural basis of channel assembly and gating. The structure, determined in the presence of ATP and the sulfonylurea glibenclamide, at ~6 Å resolution reveals a closed Kir6.2 tetrameric core with four peripheral SUR1s each anchored to a Kir6.2 by its N-terminal transmembrane domain (TMD0). Intricate interactions between TMD0, the loop following TMD0, and Kir6.2 near the proposed PIP2 binding site, and where ATP density is observed, suggest SUR1 may contribute to ATP and PIP2 binding to enhance Kir6.2 sensitivity to both. The SUR1-ABC core is found in an unusual inward-facing conformation whereby the two nucleotide binding domains are misaligned along a two-fold symmetry axis, revealing a possible mechanism by which glibenclamide inhibits channel activity. DOI:http://dx.doi.org/10.7554/eLife.24149.001 The hormone insulin reduces blood sugar levels by encouraging fat, muscle and other body cells to take up sugar. When blood sugar levels rise following a meal, cells within the pancreas known as beta cells should release insulin. In people with diabetes, the beta cells fail to release insulin, meaning that the high blood sugar levels are not corrected. When blood sugar levels are high, beta cells generate more energy in the form of ATP molecules. The increased level of ATP causes channels called ATP-sensitive potassium (KATP) channels in the membrane of the cell to close. This triggers a cascade of events that leads to the release of insulin. Some treatments for diabetes alter how the KATP channels work. For example, a widely prescribed medication called glibenclamide (also known as glyburide in the United States) stimulates the release of insulin by preventing the flow of potassium through KATP channels. It remains unknown exactly how ATP and glibenclamide interact with the channel’s molecular structure to stop the flow of potassium ions. KATP channels are made up of two proteins called SUR1 and Kir6.2. To investigate the structure of the KATP channel, Martin et al. purified channels made of the hamster form of the SUR1 protein and the mouse form of Kir6.2, which each closely resemble their human counterparts. The channels were purified in the presence of ATP and glibenclamide and were then rapidly frozen to preserve their structure, which allowed them to be visualized individually using electron microscopy. By analyzing the images taken from many channels, Martin et al. constructed a highly detailed, three-dimensional map of the KATP channel. The structure revealed by this map shows how SUR1 and Kir6.2 work together and provides insight into how ATP and glibenclamide interact with the channel to block the flow of potassium, and hence stimulate the release of insulin. An important next step will be to improve the structure to more clearly identify where ATP and glibenclamide bind to the KATP channel. It will also be important to study the structures of channels that are bound to other regulatory molecules. This will help researchers to fully understand how KATP channels located throughout the body operate under healthy and diseased conditions. This knowledge will aid in the design of more effective drugs to treat several devastating diseases caused by defective KATP channels. DOI:http://dx.doi.org/10.7554/eLife.24149.002
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, Oregon, United States
| | - Emily A Rex
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Jonathan F Fay
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Qing Xie
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Matthew R Whorton
- Vollum Institute, Oregon Health and Science University, Portland, Oregon, United States
| | - James Z Chen
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
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Vedovato N, Ashcroft FM, Puljung MC. The Nucleotide-Binding Sites of SUR1: A Mechanistic Model. Biophys J 2016; 109:2452-2460. [PMID: 26682803 PMCID: PMC4699857 DOI: 10.1016/j.bpj.2015.10.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 10/22/2015] [Accepted: 10/22/2015] [Indexed: 12/19/2022] Open
Abstract
ATP-sensitive potassium (KATP) channels comprise four pore-forming Kir6.2 subunits and four modulatory sulfonylurea receptor (SUR) subunits. The latter belong to the ATP-binding cassette family of transporters. KATP channels are inhibited by ATP (or ADP) binding to Kir6.2 and activated by Mg-nucleotide interactions with SUR. This dual regulation enables the KATP channel to couple the metabolic state of a cell to its electrical excitability and is crucial for the KATP channel’s role in regulating insulin secretion, cardiac and neuronal excitability, and vascular tone. Here, we review the regulation of the KATP channel by adenine nucleotides and present an equilibrium allosteric model for nucleotide activation and inhibition. The model can account for many experimental observations in the literature and provides testable predictions for future experiments.
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Affiliation(s)
- Natascia Vedovato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Michael C Puljung
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
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Molecular action of sulphonylureas on KATP channels: a real partnership between drugs and nucleotides. Biochem Soc Trans 2016; 43:901-7. [PMID: 26517901 PMCID: PMC4613533 DOI: 10.1042/bst20150096] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Sulphonylureas stimulate insulin secretion from pancreatic β-cells primarily by closing ATP-sensitive K+ channels in the β-cell plasma membrane. The mechanism of channel inhibition by these drugs is unusually complex. As direct inhibitors of channel activity, sulphonylureas act only as partial antagonists at therapeutic concentrations. However, they also exert an additional indirect inhibitory effect via modulation of nucleotide-dependent channel gating. In this review, we summarize current knowledge and recent advances in our understanding of the molecular mechanism of action of these drugs.
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Proks P, de Wet H, Ashcroft FM. Sulfonylureas suppress the stimulatory action of Mg-nucleotides on Kir6.2/SUR1 but not Kir6.2/SUR2A KATP channels: a mechanistic study. ACTA ACUST UNITED AC 2015; 144:469-86. [PMID: 25348414 PMCID: PMC4210431 DOI: 10.1085/jgp.201411222] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Sulfonylureas suppress the stimulatory effect of Mg-nucleotides on recombinant β-cell (Kir6.2/SUR1) but not cardiac (Kir6.2/SUR2A) KATP channels. Sulfonylureas, which stimulate insulin secretion from pancreatic β-cells, are widely used to treat both type 2 diabetes and neonatal diabetes. These drugs mediate their effects by binding to the sulfonylurea receptor subunit (SUR) of the ATP-sensitive K+ (KATP) channel and inducing channel closure. The mechanism of channel inhibition is unusually complex. First, sulfonylureas act as partial antagonists of channel activity, and second, their effect is modulated by MgADP. We analyzed the molecular basis of the interactions between the sulfonylurea gliclazide and Mg-nucleotides on β-cell and cardiac types of KATP channel (Kir6.2/SUR1 and Kir6.2/SUR2A, respectively) heterologously expressed in Xenopus laevis oocytes. The SUR2A-Y1206S mutation was used to confer gliclazide sensitivity on SUR2A. We found that both MgATP and MgADP increased gliclazide inhibition of Kir6.2/SUR1 channels and reduced inhibition of Kir6.2/SUR2A-Y1206S. The latter effect can be attributed to stabilization of the cardiac channel open state by Mg-nucleotides. Using a Kir6.2 mutation that renders the KATP channel insensitive to nucleotide inhibition (Kir6.2-G334D), we showed that gliclazide abolishes the stimulatory effects of MgADP and MgATP on β-cell KATP channels. Detailed analysis suggests that the drug both reduces nucleotide binding to SUR1 and impairs the efficacy with which nucleotide binding is translated into pore opening. Mutation of one (or both) of the Walker A lysines in the catalytic site of the nucleotide-binding domains of SUR1 may have a similar effect to gliclazide on MgADP binding and transduction, but it does not appear to impair MgATP binding. Our results have implications for the therapeutic use of sulfonylureas.
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Affiliation(s)
- Peter Proks
- Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK
| | - Heidi de Wet
- Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK
| | - Frances M Ashcroft
- Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK
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Zhou Q, Chen PC, Devaraneni PK, Martin GM, Olson EM, Shyng SL. Carbamazepine inhibits ATP-sensitive potassium channel activity by disrupting channel response to MgADP. Channels (Austin) 2015; 8:376-82. [PMID: 24849284 DOI: 10.4161/chan.29117] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In pancreatic β-cells, K(ATP) channels consisting of Kir6.2 and SUR1 couple cell metabolism to membrane excitability and regulate insulin secretion. Sulfonylureas, insulin secretagogues used to treat type II diabetes, inhibit K(ATP) channel activity primarily by abolishing the stimulatory effect of MgADP endowed by SUR1. In addition, sulfonylureas have been shown to function as pharmacological chaperones to correct channel biogenesis and trafficking defects. Recently, we reported that carbamazepine, an anticonvulsant known to inhibit voltage-gated sodium channels, has profound effects on K(ATP) channels. Like sulfonylureas, carbamazepine corrects trafficking defects in channels bearing mutations in the first transmembrane domain of SUR1. Moreover, carbamazepine inhibits the activity of K(ATP) channels such that rescued mutant channels are unable to open when the intracellular ATP/ADP ratio is lowered by metabolic inhibition. Here, we investigated the mechanism by which carbamazepine inhibits K(ATP) channel activity. We show that carbamazepine specifically blocks channel response to MgADP. This gating effect resembles that of sulfonylureas. Our results reveal striking similarities between carbamazepine and sulfonylureas in their effects on K(ATP) channel biogenesis and gating and suggest that the 2 classes of drugs may act via a converging mechanism.
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Ortiz D, Bryan J. Neonatal Diabetes and Congenital Hyperinsulinism Caused by Mutations in ABCC8/SUR1 are Associated with Altered and Opposite Affinities for ATP and ADP. Front Endocrinol (Lausanne) 2015; 6:48. [PMID: 25926814 PMCID: PMC4397924 DOI: 10.3389/fendo.2015.00048] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Accepted: 03/21/2015] [Indexed: 12/28/2022] Open
Abstract
ATP-sensitive K(+) (KATP) channels composed of potassium inward-rectifier type 6.2 and sulfonylurea receptor type 1 subunits (Kir6.2/SUR1)4 are expressed in various cells in the brain and endocrine pancreas where they couple metabolic status to membrane potential. In β-cells, increases in cytosolic [ATP/ADP]c inhibit KATP channel activity, leading to membrane depolarization and exocytosis of insulin granules. Mutations in ABCC8 (SUR1) or KCNJ11 (Kir6.2) can result in gain or loss of channel activity and cause neonatal diabetes (ND) or congenital hyperinsulinism (CHI), respectively. SUR1 is reported to be a Mg(2+)-dependent ATPase. A prevailing model posits that ATP hydrolysis at SUR1 is required to stimulate openings of the pore. However, recent work shows nucleotide binding, without hydrolysis, is sufficient to switch SUR1 to stimulatory conformations. The actions of nucleotides, ATP and ADP, on ND (SUR1E1506D) and CHI (SUR1E1506K) mutants, without Kir6.2, were compared to assess both models. Both substitutions significantly impair hydrolysis in SUR1 homologs. SUR1E1506D has greater affinity for MgATP than wildtype; SUR1E1506K has reduced affinity. Without Mg(2+), SUR1E1506K has a greater affinity for ATP(4-) consistent with electrostatic attraction between ATP(4-), unshielded by Mg(2+), and the basic lysine. Further analysis of ND and CHI ABCC8 mutants in the second transmembrane and nucleotide-binding domains (TMD2 and NBD2) found a relation between their affinities for ATP (±Mg(2+)) and their clinical phenotype. Increased affinity for ATP is associated with ND; decreased affinity with CHI. In contrast, MgADP showed a weaker relationship. Diazoxide, known to reduce insulin release in some CHI cases, potentiates switching of CHI mutants from non-stimulatory to stimulatory states consistent with diazoxide stabilizing a nucleotide-bound conformation. The results emphasize the greater importance of nucleotide binding vs. hydrolysis in the regulation of KATP channels in vivo.
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Affiliation(s)
- David Ortiz
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
| | - Joseph Bryan
- Pacific Northwest Diabetes Research Institute, Seattle, WA, USA
- *Correspondence: Joseph Bryan, Pacific Northwest Diabetes Research Institute, 720 Broadway, Seattle, WA 98122, USA e-mail:
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Martin GM, Chen PC, Devaraneni P, Shyng SL. Pharmacological rescue of trafficking-impaired ATP-sensitive potassium channels. Front Physiol 2013; 4:386. [PMID: 24399968 PMCID: PMC3870925 DOI: 10.3389/fphys.2013.00386] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Accepted: 12/09/2013] [Indexed: 12/25/2022] Open
Abstract
ATP-sensitive potassium (KATP) channels link cell metabolism to membrane excitability and are involved in a wide range of physiological processes including hormone secretion, control of vascular tone, and protection of cardiac and neuronal cells against ischemic injuries. In pancreatic β-cells, KATP channels play a key role in glucose-stimulated insulin secretion, and gain or loss of channel function results in neonatal diabetes or congenital hyperinsulinism, respectively. The β-cell KATP channel is formed by co-assembly of four Kir6.2 inwardly rectifying potassium channel subunits encoded by KCNJ11 and four sulfonylurea receptor 1 subunits encoded by ABCC8. Many mutations in ABCC8 or KCNJ11 cause loss of channel function, thus, congenital hyperinsulinism by hampering channel biogenesis and hence trafficking to the cell surface. The trafficking defects caused by a subset of these mutations can be corrected by sulfonylureas, KATP channel antagonists that have long been used to treat type 2 diabetes. More recently, carbamazepine, an anticonvulsant that is thought to target primarily voltage-gated sodium channels has been shown to correct KATP channel trafficking defects. This article reviews studies to date aimed at understanding the mechanisms by which mutations impair channel biogenesis and trafficking and the mechanisms by which pharmacological ligands overcome channel trafficking defects. Insight into channel structure-function relationships and therapeutic implications from these studies are discussed.
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University Portland, OR, USA
| | - Pei-Chun Chen
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University Portland, OR, USA
| | - Prasanna Devaraneni
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University Portland, OR, USA
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University Portland, OR, USA
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Proks P, de Wet H, Ashcroft FM. Molecular mechanism of sulphonylurea block of K(ATP) channels carrying mutations that impair ATP inhibition and cause neonatal diabetes. Diabetes 2013; 62:3909-19. [PMID: 23835339 PMCID: PMC3806600 DOI: 10.2337/db13-0531] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Sulphonylurea drugs are the therapy of choice for treating neonatal diabetes (ND) caused by mutations in the ATP-sensitive K(+) channel (KATP channel). We investigated the interactions between MgATP, MgADP, and the sulphonylurea gliclazide with KATP channels expressed in Xenopus oocytes. In the absence of MgATP, gliclazide block was similar for wild-type channels and those carrying the Kir6.2 ND mutations R210C, G334D, I296L, and V59M. Gliclazide abolished the stimulatory effect of MgATP on all channels. Conversely, high MgATP concentrations reduced the gliclazide concentration, producing a half-maximal block of G334D and R201C channels and suggesting a mutual antagonism between nucleotide and gliclazide binding. The maximal extent of high-affinity gliclazide block of wild-type channels was increased by MgATP, but this effect was smaller for ND channels; channels that were least sensitive to ATP inhibition showed the smallest increase in sulphonylurea block. Consequently, G334D and I296L channels were not fully blocked, even at physiological MgATP concentrations (1 mmol/L). Glibenclamide block was also reduced in β-cells expressing Kir6.2-V59M channels. These data help to explain why patients with some mutations (e.g., G334D, I296L) are insensitive to sulphonylurea therapy, why higher drug concentrations are needed to treat ND than type 2 diabetes, and why patients with severe ND mutations are less prone to drug-induced hypoglycemia.
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Abstract
Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in pancreatic β-cells play a crucial role in insulin secretion and glucose homeostasis. These channels are composed of two subunits: a pore-forming subunit (Kir6.2) and a regulatory subunit (sulphonylurea receptor-1). Recent studies identified large number of gain of function mutations in the regulatory subunit of the channel which cause neonatal diabetes. Majority of mutations cause neonatal diabetes alone, however some lead to a severe form of neonatal diabetes with associated neurological complications. This review focuses on the functional effects of these mutations as well as the implications for treatment.
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Affiliation(s)
- Peter Proks
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
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Ortiz D, Gossack L, Quast U, Bryan J. Reinterpreting the action of ATP analogs on K(ATP) channels. J Biol Chem 2013; 288:18894-902. [PMID: 23665564 DOI: 10.1074/jbc.m113.476887] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Neuroendocrine-type K(ATP) channels, (SUR1/Kir6.2)4, couple the transmembrane flux of K(+), and thus membrane potential, with cellular metabolism in various cell types including insulin-secreting β-cells. Mutant channels with reduced activity are a cause of congenital hyperinsulinism, whereas hyperactive channels are a cause of neonatal diabetes. A current regulatory model proposes that ATP hydrolysis is required to switch SUR1 into post-hydrolytic conformations able to antagonize the inhibitory action of nucleotide binding at the Kir6.2 pore, thus coupling enzymatic and channel activities. Alterations in SUR1 ATPase activity are proposed to contribute to neonatal diabetes and type 2 diabetes risk. The regulatory model is partly based on the reduced ability of ATP analogs such as adenosine 5'-(β,γ-imino)triphosphate (AMP-PNP) and adenosine 5'-O-(thiotriphosphate) (ATPγS) to stimulate channel activity, presumably by reducing hydrolysis. This study uses a substitution at the catalytic glutamate, SUR(1E1507Q), with a significantly increased affinity for ATP, to probe the action of these ATP analogs on conformational switching. ATPγS, a slowly hydrolyzable analog, switches SUR1 conformations, albeit with reduced affinity. Nonhydrolyzable AMP-PNP and adenosine 5'-(β,γ-methylenetriphosphate) (AMP-PCP) alone fail to switch SUR1, but do reverse ATP-induced switching. AMP-PCP displaces 8-azido-[(32)P]ATP from the noncanonical NBD1 of SUR1. This is consistent with structural data on an asymmetric bacterial ABC protein that shows that AMP-PNP binds selectively to the noncanonical NBD to prevent conformational switching. The results imply that MgAMP-PNP and MgAMP-PCP (AMP-PxP) fail to activate K(ATP) channels because they do not support NBD dimerization and conformational switching, rather than by limiting enzymatic activity.
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Affiliation(s)
- David Ortiz
- Pacific Northwest Diabetes Research Institute, Seattle, Washington 98122, USA
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Current world literature. Curr Opin Organ Transplant 2013; 18:111-30. [PMID: 23299306 DOI: 10.1097/mot.0b013e32835daf68] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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