51
|
Ferdaoussi M, Dai X, Jensen MV, Wang R, Peterson BS, Huang C, Ilkayeva O, Smith N, Miller N, Hajmrle C, Spigelman AF, Wright RC, Plummer G, Suzuki K, Mackay JP, van de Bunt M, Gloyn AL, Ryan TE, Norquay LD, Brosnan MJ, Trimmer JK, Rolph TP, Kibbey RG, Manning Fox JE, Colmers WF, Shirihai OS, Neufer PD, Yeh ETH, Newgard CB, MacDonald PE. Isocitrate-to-SENP1 signaling amplifies insulin secretion and rescues dysfunctional β cells. J Clin Invest 2015; 125:3847-60. [PMID: 26389676 DOI: 10.1172/jci82498] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 07/24/2015] [Indexed: 01/02/2023] Open
Abstract
Insulin secretion from β cells of the pancreatic islets of Langerhans controls metabolic homeostasis and is impaired in individuals with type 2 diabetes (T2D). Increases in blood glucose trigger insulin release by closing ATP-sensitive K+ channels, depolarizing β cells, and opening voltage-dependent Ca2+ channels to elicit insulin exocytosis. However, one or more additional pathway(s) amplify the secretory response, likely at the distal exocytotic site. The mitochondrial export of isocitrate and engagement with cytosolic isocitrate dehydrogenase (ICDc) may be one key pathway, but the mechanism linking this to insulin secretion and its role in T2D have not been defined. Here, we show that the ICDc-dependent generation of NADPH and subsequent glutathione (GSH) reduction contribute to the amplification of insulin exocytosis via sentrin/SUMO-specific protease-1 (SENP1). In human T2D and an in vitro model of human islet dysfunction, the glucose-dependent amplification of exocytosis was impaired and could be rescued by introduction of signaling intermediates from this pathway. Moreover, islet-specific Senp1 deletion in mice caused impaired glucose tolerance by reducing the amplification of insulin exocytosis. Together, our results identify a pathway that links glucose metabolism to the amplification of insulin secretion and demonstrate that restoration of this axis rescues β cell function in T2D.
Collapse
|
52
|
Martins WC, Tasca CI, Cimarosti H. Battling Alzheimer's Disease: Targeting SUMOylation-Mediated Pathways. Neurochem Res 2015; 41:568-78. [PMID: 26227998 DOI: 10.1007/s11064-015-1681-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2015] [Revised: 06/29/2015] [Accepted: 07/22/2015] [Indexed: 01/10/2023]
Abstract
SUMO (small ubiquitin-like modifier) conjugation is a critically important control process in all eukaryotic cells, because it acts as a biochemical switch and regulates the function of hundreds of proteins in many different pathways. Although the diverse functional consequences and molecular targets of SUMOylation remain largely unknown, SUMOylation is becoming increasingly implicated in the pathophysiology of Alzheimer's disease (AD). Apart from the central SUMO-modified disease-associated proteins, such as amyloid precursor protein, amyloid β, and tau, SUMOylation also regulates several other processes underlying AD. These are involved in inflammation, mitochondrial dynamics, synaptic transmission and plasticity, as well as in protective responses to cell stress. Herein, we review current reports on the involvement of SUMOylation in AD, and present an overview of potential SUMO targets and pathways underlying AD pathogenesis.
Collapse
Affiliation(s)
- Wagner Carbolin Martins
- Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina (UFSC), Campus Trindade, Florianópolis, SC, 88040-900, Brazil
| | - Carla Inês Tasca
- Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina (UFSC), Campus Trindade, Florianópolis, SC, 88040-900, Brazil
| | - Helena Cimarosti
- Departamento de Farmacologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina (UFSC), Campus Trindade, Florianópolis, SC, 88040-900, Brazil.
| |
Collapse
|
53
|
Yang KC, Nerbonne JM. Mechanisms contributing to myocardial potassium channel diversity, regulation and remodeling. Trends Cardiovasc Med 2015; 26:209-18. [PMID: 26391345 DOI: 10.1016/j.tcm.2015.07.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 07/11/2015] [Accepted: 07/12/2015] [Indexed: 01/19/2023]
Abstract
In the mammalian heart, multiple types of K(+) channels contribute to the control of cardiac electrical and mechanical functioning through the regulation of resting membrane potentials, action potential waveforms and refractoriness. There are similarly vast arrays of K(+) channel pore-forming and accessory subunits that contribute to the generation of functional myocardial K(+) channel diversity. Maladaptive remodeling of K(+) channels associated with cardiac and systemic diseases results in impaired repolarization and increased propensity for arrhythmias. Here, we review the diverse transcriptional, post-transcriptional, post-translational, and epigenetic mechanisms contributing to regulating the expression, distribution, and remodeling of cardiac K(+) channels under physiological and pathological conditions.
Collapse
Affiliation(s)
- Kai-Chien Yang
- Department of Pharmacology, National Taiwan University, Taipei, Taiwan; Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
| | - Jeanne M Nerbonne
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO; Internal Medicine, Washington University School of Medicine, St. Louis, MO; Cardiovascular Division, Washington University School of Medicine, St. Louis, MO.
| |
Collapse
|
54
|
SUMO1 Affects Synaptic Function, Spine Density and Memory. Sci Rep 2015; 5:10730. [PMID: 26022678 PMCID: PMC4650663 DOI: 10.1038/srep10730] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Accepted: 04/17/2015] [Indexed: 01/19/2023] Open
Abstract
Small ubiquitin-like modifier-1 (SUMO1) plays a number of roles in cellular events and recent evidence has given momentum for its contributions to neuronal development and function. Here, we have generated a SUMO1 transgenic mouse model with exclusive overexpression in neurons in an effort to identify in vivo conjugation targets and the functional consequences of their SUMOylation. A high-expressing line was examined which displayed elevated levels of mono-SUMO1 and increased high molecular weight conjugates in all brain regions. Immunoprecipitation of SUMOylated proteins from total brain extract and proteomic analysis revealed ~95 candidate proteins from a variety of functional classes, including a number of synaptic and cytoskeletal proteins. SUMO1 modification of synaptotagmin-1 was found to be elevated as compared to non-transgenic mice. This observation was associated with an age-dependent reduction in basal synaptic transmission and impaired presynaptic function as shown by altered paired pulse facilitation, as well as a decrease in spine density. The changes in neuronal function and morphology were also associated with a specific impairment in learning and memory while other behavioral features remained unchanged. These findings point to a significant contribution of SUMO1 modification on neuronal function which may have implications for mechanisms involved in mental retardation and neurodegeneration.
Collapse
|
55
|
McIntyre JC, Joiner AM, Zhang L, Iñiguez-Lluhí J, Martens JR. SUMOylation regulates ciliary localization of olfactory signaling proteins. J Cell Sci 2015; 128:1934-45. [PMID: 25908845 PMCID: PMC4457158 DOI: 10.1242/jcs.164673] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Accepted: 03/24/2015] [Indexed: 11/20/2022] Open
Abstract
Cilia are evolutionarily conserved organelles found on many mammalian cell types, including neuronal populations. Although neuronal cilia, including those on olfactory sensory neurons (OSNs), are often delineated by localization of adenylyl cyclase 3 (AC3, also known as ADCY3), the mechanisms responsible for targeting integral membrane proteins are largely unknown. Post-translational modification by small ubiquitin-like modifier (SUMO) proteins plays an important role in protein localization processes such as nuclear-cytosolic transport. Here, we identified through bioinformatic analysis that adenylyl cyclases harbor conserved SUMOylation motifs, and show that AC3 is a substrate for SUMO modification. Functionally, overexpression of the SUMO protease SENP2 prevented ciliary localization of AC3, without affecting ciliation or cilia maintenance. Furthermore, AC3-SUMO mutants did not localize to cilia. To test whether SUMOylation is sufficient for cilia entry, we compared localization of ANO2, which possesses a SUMO motif, and ANO1, which lacks SUMOylation sites and does not localize to cilia. Introduction of SUMOylation sites into ANO1 was not sufficient for ciliary entry. These data suggest that SUMOylation is necessary but not sufficient for ciliary trafficking of select constituents, further establishing the link between ciliary and nuclear import.
Collapse
Affiliation(s)
- Jeremy C McIntyre
- Department of Pharmacology and Therapeutics, University of Florida, PO Box 100267, Gainesville, FL 32610, USA
| | - Ariell M Joiner
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Lian Zhang
- Department of Pharmacology and Therapeutics, University of Florida, PO Box 100267, Gainesville, FL 32610, USA
| | - Jorge Iñiguez-Lluhí
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Jeffrey R Martens
- Department of Pharmacology and Therapeutics, University of Florida, PO Box 100267, Gainesville, FL 32610, USA
| |
Collapse
|
56
|
King AN, Manning CF, Trimmer JS. A unique ion channel clustering domain on the axon initial segment of mammalian neurons. J Comp Neurol 2015; 522:2594-608. [PMID: 24477962 DOI: 10.1002/cne.23551] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2013] [Revised: 01/21/2014] [Accepted: 01/22/2014] [Indexed: 01/11/2023]
Abstract
The axon initial segment (AIS) plays a key role in initiation of action potentials and neuronal output. The plasma membrane of the AIS contains high densities of voltage-gated ion channels required for these electrical events, and much recent work has focused on defining the mechanisms for generating and maintaining this unique neuronal plasma membrane domain. The Kv2.1 voltage-gated potassium channel is abundantly present in large clusters on the soma and proximal dendrites of mammalian brain neurons. Kv2.1 is also a component of the ion channel repertoire at the AIS. Here we show that Kv2.1 clusters on the AIS of brain neurons across diverse mammalian species including humans define a noncanonical ion channel clustering domain deficient in Ankyrin-G. The sites of Kv2.1 clustering on the AIS are sites where cisternal organelles, specialized intracellular calcium release membranes, come into close apposition with the plasma membrane, and are also sites of clustering of γ-aminobutyric acid (GABA)ergic synapses. Using an antibody specific for a single Kv2.1 phosphorylation site, we find that the phosphorylation state differs between Kv2.1 clusters on the proximal and distal portions of the AIS. Together, these studies show that the sites of Kv2.1 clustering on the AIS represent specialized domains containing components of diverse neuronal signaling pathways that may contribute to local regulation of Kv2.1 function and AIS membrane excitability.
Collapse
Affiliation(s)
- Anna N King
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, California, 95616
| | | | | |
Collapse
|
57
|
Fricke F, Dietz MS, Heilemann M. Single-Molecule Methods to Study Membrane Receptor Oligomerization. Chemphyschem 2014; 16:713-21. [DOI: 10.1002/cphc.201402765] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Indexed: 11/06/2022]
|
58
|
Hyper-SUMOylation of the Kv7 potassium channel diminishes the M-current leading to seizures and sudden death. Neuron 2014; 83:1159-71. [PMID: 25189211 DOI: 10.1016/j.neuron.2014.07.042] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/29/2014] [Indexed: 02/02/2023]
Abstract
Sudden unexplained death in epilepsy (SUDEP) is the most common cause of premature mortality in epilepsy and was linked to mutations in ion channels; however, genes within the channel protein interactome might also represent pathogenic candidates. Here we show that mice with partial deficiency of Sentrin/SUMO-specific protease 2 (SENP2) develop spontaneous seizures and sudden death. SENP2 is highly enriched in the hippocampus, often the focus of epileptic seizures. SENP2 deficiency results in hyper-SUMOylation of multiple potassium channels known to regulate neuronal excitability. We demonstrate that the depolarizing M-current conducted by Kv7 channel is significantly diminished in SENP2-deficient hippocampal CA3 neurons, primarily responsible for neuronal hyperexcitability. Following seizures, SENP2-deficient mice develop atrioventricular conduction blocks and cardiac asystole. Both seizures and cardiac conduction blocks can be prevented by retigabine, a Kv7 channel opener. Thus, we uncover a disease-causing role for hyper-SUMOylation in the nervous system and establish an animal model for SUDEP.
Collapse
|
59
|
Henley JM, Craig TJ, Wilkinson KA. Neuronal SUMOylation: mechanisms, physiology, and roles in neuronal dysfunction. Physiol Rev 2014; 94:1249-85. [PMID: 25287864 PMCID: PMC4187031 DOI: 10.1152/physrev.00008.2014] [Citation(s) in RCA: 135] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Protein SUMOylation is a critically important posttranslational protein modification that participates in nearly all aspects of cellular physiology. In the nearly 20 years since its discovery, SUMOylation has emerged as a major regulator of nuclear function, and more recently, it has become clear that SUMOylation has key roles in the regulation of protein trafficking and function outside of the nucleus. In neurons, SUMOylation participates in cellular processes ranging from neuronal differentiation and control of synapse formation to regulation of synaptic transmission and cell survival. It is a highly dynamic and usually transient modification that enhances or hinders interactions between proteins, and its consequences are extremely diverse. Hundreds of different proteins are SUMO substrates, and dysfunction of protein SUMOylation is implicated in a many different diseases. Here we briefly outline core aspects of the SUMO system and provide a detailed overview of the current understanding of the roles of SUMOylation in healthy and diseased neurons.
Collapse
Affiliation(s)
- Jeremy M Henley
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Tim J Craig
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Kevin A Wilkinson
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| |
Collapse
|
60
|
Abstract
Potassium channels are pore-forming transmembrane proteins that regulate a multitude of biological processes by controlling potassium flow across cell membranes. Aberrant potassium channel functions contribute to diseases such as epilepsy, cardiac arrhythmia, and neuromuscular symptoms collectively known as channelopathies. Increasing evidence suggests that cancer constitutes another category of channelopathies associated with dysregulated channel expression. Indeed, potassium channel–modulating agents have demonstrated antitumor efficacy. Potassium channels regulate cancer cell behaviors such as proliferation and migration through both canonical ion permeation–dependent and noncanonical ion permeation–independent functions. Given their cell surface localization and well-known pharmacology, pharmacological strategies to target potassium channel could prove to be promising cancer therapeutics.
Collapse
Affiliation(s)
- Xi Huang
- Howard Hughes Medical Institute, Department of Physiology, and Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158Howard Hughes Medical Institute, Department of Physiology, and Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158Howard Hughes Medical Institute, Department of Physiology, and Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158
| | - Lily Yeh Jan
- Howard Hughes Medical Institute, Department of Physiology, and Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158Howard Hughes Medical Institute, Department of Physiology, and Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158Howard Hughes Medical Institute, Department of Physiology, and Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158
| |
Collapse
|
61
|
Wasik U, Filipek A. Non-nuclear function of sumoylated proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:2878-2885. [PMID: 25110347 DOI: 10.1016/j.bbamcr.2014.07.018] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Revised: 07/11/2014] [Accepted: 07/30/2014] [Indexed: 12/16/2022]
Abstract
Post-translational modification by the SUMO moiety is now regarded as one of the key regulatory modifications in eukaryotic cells. Up to now, plenty of sumoylated proteins have been found to be involved in nuclear processes such as chromatin organization, transcription and DNA repair as well as in other cellular functions. Since the number of data concerning sumoylated proteins and their function outside the nucleus has grown rapidly, in this review we summarized the results describing the non-nuclear role of SUMO substrates. In particular, we focused on the role of sumoylation in the regulation of channel activity, receptor function, G-protein signaling, activity of enzymes, cytoskeletal organization, exocytosis, autophagy and mitochondrial dynamics.
Collapse
Affiliation(s)
- Urszula Wasik
- Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Anna Filipek
- Nencki Institute of Experimental Biology, Warsaw, Poland.
| |
Collapse
|
62
|
Wang L, Rodriguiz RM, Wetsel WC, Sheng H, Zhao S, Liu X, Paschen W, Yang W. Neuron-specific Sumo1-3 knockdown in mice impairs episodic and fear memories. J Psychiatry Neurosci 2014; 39:259-66. [PMID: 24690371 PMCID: PMC4074237 DOI: 10.1503/jpn.130148] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Growing evidence suggests that small ubiquitin-like modifier (SUMO) conjugation plays a key role in brain plasticity by modulating activity-dependent synaptic transmission. However, these observations are based largely on cell culture experiments. We hypothesized that episodic and fear memories would be affected by silencing SUMO1-3 expression. METHODS To investigate the role of SUMO conjugation in neuronal functioning in vivo, we generated a novel Sumo transgenic mouse model in which a Thy1 promoter drives expression of 3 distinct microRNAs to silence Sumo1-3 expression, specifically in neurons. Wild-type and Sumo1-3 knockdown mice were subjected to a battery of behavioural tests to elucidate whether Sumoylation is involved in episodic and emotional memory. RESULTS Expression of Sumo1-3 microRNAs and the corresponding silencing of Sumo expression were particularly pronounced in hippocampal, amygdala and layer V cerebral cortex neurons. The Sumo knockdown mice displayed anxiety-like responses and were impaired in episodic memory processes, contextual and cued fear conditioning and fear-potentiated startle. LIMITATIONS Since expression of Sumo1-3 was silenced in this mouse model, we need to verify in future studies which of the SUMO paralogues play the pivotal role in episodic and emotional memory. CONCLUSION Our results indicate that a functional SUMO conjugation pathway is essential for emotionality and cognition. This novel Sumo knockdown mouse model and the technology used in generating this mutant may help to reveal novel mechanisms that underlie a variety of neuropsychiatric conditions associated with anxiety and impairment of episodic and emotional memory.
Collapse
Affiliation(s)
| | | | | | | | | | | | - Wulf Paschen
- Correspondence to: W. Paschen or W. Yang, Department of Anesthesiology, Multidisciplinary Neuroprotection Laboratories, Duke University Medical Center, 130 + 152 Sands Building, Research Dr., Durham, NC 27710, USA; or
| | - Wei Yang
- Correspondence to: W. Paschen or W. Yang, Department of Anesthesiology, Multidisciplinary Neuroprotection Laboratories, Duke University Medical Center, 130 + 152 Sands Building, Research Dr., Durham, NC 27710, USA; or
| |
Collapse
|
63
|
Specific de-SUMOylation triggered by acquisition of spatial learning is related to epigenetic changes in the rat hippocampus. Neuroreport 2014; 24:976-81. [PMID: 24089016 DOI: 10.1097/wnr.0000000000000025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Histone acetyltransferase activity by transcriptional cofactors such as CREB-binding protein (CBP) and post-translational modifications by small ubiquitin-like modifier-1 (SUMO-1) have shown to be relevant for synaptic and neuronal activity. Here, we investigate whether SUMOylation of CBP plays a role in spatial learning. We assessed protein levels of CBP/p300, SUMO-1, and CBP SUMOylation in the hippocampi of rats trained on the Morris water maze task. Furthermore, we evaluated the post-translational modifications at Zif268, BDNF, and Arc/Arg3.1 promoters using chromatin immunoprecipitation with anti-Acetyl-Histone H3-Lys14 (H3K14Ac) and SUMO-1. We found that CBP/p300 protein expression is unchanged in animals trained for 7 days. However, H3K14Ac-specific histone acetyltransferase activity showed specific hyperacetylation at promoters of Zif268 and BDNF-pI but not of Arc/Arg3.1 and BDNF-pIV. In naive animals, CBP is selectively SUMOylated and the Arc/Arg3.1 promoter is differentially occupied by SUMO-1, although SUMO-1 levels are unchanged. These results suggest a specific negative regulation by SUMO-1 on CBP function and its effect on epigenetic changes triggered by spatial learning and memory processes.
Collapse
|
64
|
Affiliation(s)
- Geoffrey W Abbott
- 1360 Medical Surge II, Dept. of Pharmacology, School of Medicine, University of California, Irvine, CA 92697, USA.
| | | |
Collapse
|
65
|
Dai XQ, Spigelman AF, Khan S, Braun M, Manning Fox JE, MacDonald PE. SUMO1 enhances cAMP-dependent exocytosis and glucagon secretion from pancreatic α-cells. J Physiol 2014; 592:3715-26. [PMID: 24907310 DOI: 10.1113/jphysiol.2014.274084] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Post-translational modification by the small ubiquitin-like modifier-1 (SUMO1) limits insulin secretion from β-cells by inhibiting insulin exocytosis and glucagon-like peptide-1 (GLP-1) receptor signalling. The secretion of glucagon from α-cells is regulated in a manner opposite to that of insulin; it is inhibited by elevated glucose and GLP-1, and increased by adrenergic signalling. We therefore sought to determine whether SUMO1 modulates mouse and human α-cell function. Action potentials (APs), ion channel function and exocytosis in single α-cells from mice and humans, identified by glucagon immunostaining, and glucagon secretion from intact islets were measured. The effects of SUMO1 on α-cell function and the respective inhibitory and stimulatory effects of exendin 4 and adrenaline were examined. Upregulation of SUMO1 increased α-cell AP duration, frequency and amplitude, in part as a result of increased Ca(2+) channel activity that led to elevated exocytosis. The ability of SUMO1 to enhance α-cell exocytosis was cAMP-dependent and resulted from an increased L-type Ca(2+) current and a shift away from exocytosis dependent on non-L-type channels, an effect that was mimicked by knockdown of the deSUMOylating enzyme sentrin/SUMO-specific protease-1 (SENP1). Finally, although SUMO1 prevented GLP-1 receptor-mediated inhibition of α-cell Na(+) channels and single-cell exocytosis, it failed to prevent the exendin 4-mediated inhibition of glucagon secretion. Consistent with its cAMP dependence, however, SUMO1 enhanced α-cell exocytosis and glucagon secretion stimulated by adrenaline. Thus, by contrast with its inhibitory role in β-cell exocytosis, SUMO1 is a positive regulator of α-cell exocytosis and glucagon secretion under conditions of elevated cAMP.
Collapse
Affiliation(s)
- Xiao-Qing Dai
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Aliya F Spigelman
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Shara Khan
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Matthias Braun
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Jocelyn E Manning Fox
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Patrick E MacDonald
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| |
Collapse
|
66
|
Sesti F, Wu X, Liu S. Oxidation of KCNB1 K(+) channels in central nervous system and beyond. World J Biol Chem 2014; 5:85-92. [PMID: 24921000 PMCID: PMC4050120 DOI: 10.4331/wjbc.v5.i2.85] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 01/26/2014] [Accepted: 03/03/2014] [Indexed: 02/05/2023] Open
Abstract
KCNB1, a voltage-gated potassium (K(+)) channel that conducts a major delayed rectifier current in the brain, pancreas and cardiovascular system is a key player in apoptotic programs associated with oxidative stress. As a result, this protein represents a bona fide drug target for limiting the toxic effects of oxygen radicals. Until recently the consensus view was that reactive oxygen species trigger a pro-apoptotic surge in KCNB1 current via phosphorylation and SNARE-dependent incorporation of KCNB1 channels into the plasma membrane. However, new evidence shows that KCNB1 can be modified by oxidants and that oxidized KCNB1 channels can directly activate pro-apoptotic signaling pathways. Hence, a more articulated picture of the pro-apoptotic role of KCNB1 is emerging in which the protein induces cell's death through distinct molecular mechanisms and activation of multiple pathways. In this review article we discuss the diverse functional, toxic and protective roles that KCNB1 channels play in the major organs where they are expressed.
Collapse
|
67
|
Kv2 channel regulation of action potential repolarization and firing patterns in superior cervical ganglion neurons and hippocampal CA1 pyramidal neurons. J Neurosci 2014; 34:4991-5002. [PMID: 24695716 DOI: 10.1523/jneurosci.1925-13.2014] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Kv2 family "delayed-rectifier" potassium channels are widely expressed in mammalian neurons. Kv2 channels activate relatively slowly and their contribution to action potential repolarization under physiological conditions has been unclear. We explored the function of Kv2 channels using a Kv2-selective blocker, Guangxitoxin-1E (GxTX-1E). Using acutely isolated neurons, mixed voltage-clamp and current-clamp experiments were done at 37°C to study the physiological kinetics of channel gating and action potentials. In both rat superior cervical ganglion (SCG) neurons and mouse hippocampal CA1 pyramidal neurons, 100 nm GxTX-1E produced near-saturating block of a component of current typically constituting ∼60-80% of the total delayed-rectifier current. GxTX-1E also reduced A-type potassium current (IA), but much more weakly. In SCG neurons, 100 nm GxTX-1E broadened spikes and voltage clamp experiments using action potential waveforms showed that Kv2 channels carry ∼55% of the total outward current during action potential repolarization despite activating relatively late in the spike. In CA1 neurons, 100 nm GxTX-1E broadened spikes evoked from -70 mV, but not -80 mV, likely reflecting a greater role of Kv2 when other potassium channels were partially inactivated at -70 mV. In both CA1 and SCG neurons, inhibition of Kv2 channels produced dramatic depolarization of interspike voltages during repetitive firing. In CA1 neurons and some SCG neurons, this was associated with increased initial firing frequency. In all neurons, inhibition of Kv2 channels depressed maintained firing because neurons entered depolarization block more readily. Therefore, Kv2 channels can either decrease or increase neuronal excitability depending on the time scale of excitation.
Collapse
|
68
|
Plant LD, Xiong D, Dai H, Goldstein SAN. Individual IKs channels at the surface of mammalian cells contain two KCNE1 accessory subunits. Proc Natl Acad Sci U S A 2014; 111:E1438-46. [PMID: 24591645 PMCID: PMC3986162 DOI: 10.1073/pnas.1323548111] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
KCNE1 (E1) β-subunits assemble with KCNQ1 (Q1) voltage-gated K(+) channel α-subunits to form IKslow (IKs) channels in the heart and ear. The number of E1 subunits in IKs channels has been an issue of ongoing debate. Here, we use single-molecule spectroscopy to demonstrate that surface IKs channels with human subunits contain two E1 and four Q1 subunits. This stoichiometry does not vary. Thus, IKs channels in cells with elevated levels of E1 carry no more than two E1 subunits. Cells with low levels of E1 produce IKs channels with two E1 subunits and Q1 channels with no E1 subunits--channels with one E1 do not appear to form or are restricted from surface expression. The plethora of models of cardiac function, transgenic animals, and drug screens based on variable E1 stoichiometry do not reflect physiology.
Collapse
Affiliation(s)
| | | | - Hui Dai
- Department of Biochemistry, Brandeis University, Waltham, MA, 02453
| | | |
Collapse
|
69
|
Trimmer JS. Ion channels and pain: important steps towards validating a new therapeutic target for neuropathic pain. Exp Neurol 2014; 254:190-4. [PMID: 24508559 DOI: 10.1016/j.expneurol.2014.01.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 01/24/2014] [Accepted: 01/29/2014] [Indexed: 10/25/2022]
Affiliation(s)
- James S Trimmer
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, CA 95616, USA; Department of Physiology and Membrane Biology, University of California, Davis, CA 95616, USA.
| |
Collapse
|
70
|
Arant RJ, Ulbrich MH. Deciphering the subunit composition of multimeric proteins by counting photobleaching steps. Chemphyschem 2014; 15:600-5. [PMID: 24481650 DOI: 10.1002/cphc.201301092] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Indexed: 12/28/2022]
Abstract
The limit of subdiffraction imaging with fluorescent proteins currently lies at 20 nm, and therefore most protein complexes are too small (2-5 nm) to spatially resolve their individual subunits by optical means. However, the number and stoichiometry of subunits within an immobilized protein complex can be resolved by the observation of photobleaching steps of individual fluorophores or co-localization of single-molecule fluorescence emission in multiple colors. We give an overview of the proteins that have been investigated by this approach and the different techniques that can be used to immobilize and label the proteins. This minireview should serve as a guideline for scientists who want to employ single-molecule subunit counting for their research.
Collapse
Affiliation(s)
- Ryan J Arant
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720 (USA)
| | | |
Collapse
|
71
|
Luo J, Ashikaga E, Rubin PP, Heimann MJ, Hildick KL, Bishop P, Girach F, Josa-Prado F, Tang LTH, Carmichael RE, Henley JM, Wilkinson KA. Receptor trafficking and the regulation of synaptic plasticity by SUMO. Neuromolecular Med 2013; 15:692-706. [PMID: 23934328 DOI: 10.1007/s12017-013-8253-y] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2013] [Accepted: 07/25/2013] [Indexed: 12/18/2022]
Abstract
Timely and efficient information transfer at synapses is fundamental to brain function. Synapses are highly dynamic structures that exhibit long-lasting activity-dependent alterations to their structure and transmission efficiency, a phenomenon termed synaptic plasticity. These changes, which occur through alterations in presynaptic release or in the trafficking of postsynaptic receptor proteins, underpin the formation and stabilisation of neural circuits during brain development, and encode, process and store information essential for learning, memory and cognition. In recent years, it has emerged that the ubiquitin-like posttranslational modification SUMOylation is an important mediator of several aspects of neuronal and synaptic function. Through orchestrating synapse formation, presynaptic release and the trafficking of postsynaptic receptor proteins during forms of synaptic plasticity such as long-term potentiation, long-term depression and homeostatic scaling, SUMOylation is being increasingly appreciated to play a central role in neurotransmission. In this review, we outline key discoveries in this relatively new field, provide an update on recent progress regarding the targets and consequences of protein SUMOylation in synaptic function and plasticity, and highlight key outstanding questions regarding the roles of protein SUMOylation in the brain.
Collapse
Affiliation(s)
- Jia Luo
- School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol, BS8 1TD, UK
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
72
|
Dysfunction of the ubiquitin proteasome and ubiquitin-like systems in schizophrenia. Neuropsychopharmacology 2013; 38:1910-20. [PMID: 23571678 PMCID: PMC3746696 DOI: 10.1038/npp.2013.84] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 04/01/2013] [Accepted: 04/02/2013] [Indexed: 02/06/2023]
Abstract
Protein expression abnormalities have been implicated in the pathophysiology of schizophrenia, but the underlying cause of these changes is not known. We sought to investigate ubiquitin and ubiquitin-like (UBL) systems (SUMOylation, NEDD8ylation, and Ufmylation) as putative mechanisms underlying protein expression abnormalities seen in schizophrenia. For this, we performed western blot analysis of total ubiquitination, free ubiquitin, K48- and K63-linked ubiquitination, and E1 activases, E2 conjugases, and E3 ligases involved in ubiquitination and UBL post-translational modifications in postmortem brain tissue samples from persons with schizophrenia (n=13) and comparison subjects (n=13). We studied the superior temporal gyrus (STG) of subjects from the Mount Sinai Medical Center brain collection that were matched for age, tissue pH, and sex. We found an overall reduction of protein ubiquitination, free ubiquitin, K48-linked ubiquitination, and increased K63 polyubiquitination in schizophrenia. Ubiquitin E1 activase UBA (ubiquitin activating enzyme)-6 and E3 ligase Nedd (neural precursor cell-expressed developmentally downregulated)-4 were decreased in this illness, as were E3 ligases involved in Ufmylation (UFL1) and SUMOylation (protein inhibitor of activated STAT 3, PIAS3). NEDD8ylation was also dysregulated in schizophrenia, with decreased levels of the E1 activase UBA3 and the E3 ligase Rnf7. This study of ubiquitin and UBL systems in schizophrenia found abnormalities of ubiquitination, Ufmylation, SUMOylation, and NEDD8ylation in the STG in this disorder. These results suggest a novel approach to the understanding of schizophrenia pathophysiology, where a disruption in homeostatic adaptation of the cell underlies discreet changes seen at the protein level in this illness.
Collapse
|
73
|
Droescher M, Chaugule VK, Pichler A. SUMO rules: regulatory concepts and their implication in neurologic functions. Neuromolecular Med 2013; 15:639-60. [PMID: 23990202 DOI: 10.1007/s12017-013-8258-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 08/08/2013] [Indexed: 01/17/2023]
Abstract
Posttranslational modification of proteins by the small ubiquitin-like modifier (SUMO) is a potent regulator of various cellular events. Hundreds of substrates have been identified, many of them involved in vital processes like transcriptional regulation, signal transduction, protein degradation, cell cycle regulation, DNA repair, chromatin organization, and nuclear transport. In recent years, protein sumoylation increasingly attracted attention, as it could be linked to heart failure, cancer, and neurodegeneration. However, underlying mechanisms involving how modification by SUMO contributes to disease development are still scarce thus necessitating further research. This review aims to critically discuss currently available concepts of the SUMO pathway, thereby highlighting regulation in the healthy versus diseased organism, focusing on neurologic aspects. Better understanding of differential regulation in health and disease may finally allow to uncover pathogenic mechanisms and contribute to the development of disease-specific therapies.
Collapse
Affiliation(s)
- Mathias Droescher
- Department of Epigenetics, Max Planck Institute of Immunobiology and Epigenetics, Stübeweg 51, 79108, Freiburg, Germany
| | | | | |
Collapse
|
74
|
Shelat PB, Plant LD, Wang JC, Lee E, Marks JD. The membrane-active tri-block copolymer pluronic F-68 profoundly rescues rat hippocampal neurons from oxygen-glucose deprivation-induced death through early inhibition of apoptosis. J Neurosci 2013; 33:12287-99. [PMID: 23884935 PMCID: PMC3721839 DOI: 10.1523/jneurosci.5731-12.2013] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Revised: 06/11/2013] [Accepted: 06/14/2013] [Indexed: 01/01/2023] Open
Abstract
Pluronic F-68, an 80% hydrophilic member of the Pluronic family of polyethylene-polypropylene-polyethylene tri-block copolymers, protects non-neuronal cells from traumatic injuries and rescues hippocampal neurons from excitotoxic and oxidative insults. F-68 interacts directly with lipid membranes and restores membrane function after direct membrane damage. Here, we demonstrate the efficacy of Pluronic F-68 in rescuing rat hippocampal neurons from apoptosis after oxygen-glucose deprivation (OGD). OGD progressively decreased neuronal survival over 48 h in a severity-dependent manner, the majority of cell death occurring after 12 h after OGD. Administration of F-68 for 48 h after OGD rescued neurons from death in a dose-dependent manner. At its optimal concentration (30 μm), F-68 rescued all neurons that would have died after the first hour after OGD. This level of rescue persisted when F-68 administration was delayed 12 h after OGD. F-68 did not alter electrophysiological parameters controlling excitability, NMDA receptor-activated currents, or NMDA-induced increases in cytosolic calcium concentrations. However, F-68 treatment prevented phosphatidylserine externalization, caspase activation, loss of mitochondrial membrane potential, and BAX translocation to mitochondria, indicating that F-68 alters apoptotic mechanisms early in the intrinsic pathway of apoptosis. The profound neuronal rescue provided by F-68 after OGD and the high level of efficacy with delayed administration indicate that Pluronic copolymers may provide a novel, membrane-targeted approach to rescuing neurons after brain ischemia. The ability of membrane-active agents to block apoptosis suggests that membranes or their lipid components play prominent roles in injury-induced apoptosis.
Collapse
Affiliation(s)
- Phullara B. Shelat
- Department of Pediatrics, University of Chicago, Chicago, Illinois 60637
| | - Leigh D. Plant
- Department of Pediatrics, University of Chicago, Chicago, Illinois 60637
| | - Janice C. Wang
- Department of Pediatrics, University of Chicago, Chicago, Illinois 60637
| | - Elizabeth Lee
- Department of Pediatrics, University of Chicago, Chicago, Illinois 60637
| | - Jeremy D. Marks
- Department of Pediatrics, University of Chicago, Chicago, Illinois 60637
| |
Collapse
|
75
|
Silveirinha V, Stephens GJ, Cimarosti H. Molecular targets underlying SUMO-mediated neuroprotection in brain ischemia. J Neurochem 2013; 127:580-91. [PMID: 23786482 DOI: 10.1111/jnc.12347] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Revised: 06/14/2013] [Accepted: 06/17/2013] [Indexed: 01/11/2023]
Abstract
SUMOylation (small ubiquitin-like modifier conjugation) is an important post-translational modification which is becoming increasingly implicated in the altered protein dynamics associated with brain ischemia. The function of SUMOylation in cells undergoing ischemic stress and the identity of small ubiquitin-like modifier (SUMO) targets remain in most cases unknown. However, the emerging consensus is that SUMOylation of certain proteins might be part of an endogenous neuroprotective response. This review brings together the current understanding of the underlying mechanisms and downstream effects of SUMOylation in brain ischemia, including processes such as autophagy, mitophagy and oxidative stress. We focus on recent advances and controversies regarding key central nervous system proteins, including those associated with the nucleus, cytoplasm and plasma membrane, such as glucose transporters (GLUT1, GLUT4), excitatory amino acid transporter 2 glutamate transporters, K+ channels (K2P1, Kv1.5, Kv2.1), GluK2 kainate receptors, mGluR8 glutamate receptors and CB1 cannabinoid receptors, which are reported to be SUMO-modified. A discussion of the roles of these molecular targets for SUMOylation could play following an ischemic event, particularly with respect to their potential neuroprotective impact in brain ischemia, is proposed.
Collapse
Affiliation(s)
- Vasco Silveirinha
- School of Pharmacy, Hopkins Building, University of Reading, Whiteknights, Reading, UK
| | | | | |
Collapse
|
76
|
Dustrude ET, Wilson SM, Ju W, Xiao Y, Khanna R. CRMP2 protein SUMOylation modulates NaV1.7 channel trafficking. J Biol Chem 2013; 288:24316-31. [PMID: 23836888 DOI: 10.1074/jbc.m113.474924] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated sodium channel (NaV) trafficking is incompletely understood. Post-translational modifications of NaVs and/or auxiliary subunits and protein-protein interactions have been posited as NaV-trafficking mechanisms. Here, we tested if modification of the axonal collapsin response mediator protein 2 (CRMP2) by a small ubiquitin-like modifier (SUMO) could affect NaV trafficking; CRMP2 alters the extent of NaV slow inactivation conferred by the anti-epileptic (R)-lacosamide, implying NaV-CRMP2 functional coupling. Expression of a CRMP2 SUMOylation-incompetent mutant (CRMP2-K374A) in neuronal model catecholamine A differentiated (CAD) cells did not alter lacosamide-induced NaV slow inactivation compared with CAD cells expressing wild type CRMP2. Like wild type CRMP2, CRMP2-K374A expressed robustly in CAD cells. Neurite outgrowth, a canonical CRMP2 function, was moderately reduced by the mutation but was still significantly higher than enhanced GFP-transfected cortical neurons. Notably, huwentoxin-IV-sensitive NaV1.7 currents, which predominate in CAD cells, were significantly reduced in CAD cells expressing CRMP2-K374A. Increasing deSUMOylation with sentrin/SUMO-specific protease SENP1 or SENP2 in wild type CRMP2-expressing CAD cells decreased NaV1.7 currents. Consistent with a reduction in current density, biotinylation revealed a significant reduction in surface NaV1.7 levels in CAD cells expressing CRMP2-K374A; surface NaV1.7 expression was also decreased by SENP1 + SENP2 overexpression. Currents in HEK293 cells stably expressing NaV1.7 were reduced by CRMP2-K374A in a manner dependent on the E2-conjugating enzyme Ubc9. No decrement in current density was observed in HEK293 cells co-expressing CRMP2-K374A and NaV1.1 or NaV1.3. Diminution of sodium currents, largely NaV1.7, was recapitulated in sensory neurons expressing CRMP2-K374A. Our study elucidates a novel regulatory mechanism that utilizes CRMP2 SUMOylation to choreograph NaV1.7 trafficking.
Collapse
Affiliation(s)
- Erik T Dustrude
- Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
| | | | | | | | | |
Collapse
|
77
|
Krumova P, Weishaupt JH. Sumoylation in neurodegenerative diseases. Cell Mol Life Sci 2013; 70:2123-38. [PMID: 23007842 PMCID: PMC11113377 DOI: 10.1007/s00018-012-1158-3] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2012] [Revised: 08/30/2012] [Accepted: 09/03/2012] [Indexed: 12/12/2022]
Abstract
The yeast SUMO (small ubiquitin-like modifier) orthologue SMT3 was initially discovered in a genetic suppressors screen for the centromeric protein Mif2 (Meluh and Koshland in Mol Bio Cell 6:793-807, 1). Later, it turned out that the homologous mammalian proteins SUMO1 to SUMO4 are reversible protein modifiers that can form isopeptide bonds with lysine residues of respective target proteins (Mahajan et al. in Cell 88:97-107, 2). This was the discovery of a post-translational modification called sumoylation, which enzymatically resembles ubiquitination. However, very soon it became clear that SUMO attachments served a far more diverse role than ubiquitination. Meanwhile, numerous cellular processes are known to be subject to the impact of SUMO modification, including transcription, protein targeting, protein solubility, apoptosis or activity of various enzymes. In many instances, SUMO proteins create new protein interaction surfaces or block existing interaction domains (Geiss-Friedlander and Melchior in Nat Rev in Mol Cell Biol 8:947-956, 3). For the past few years, sumoylation attracted increasing attention as a versatile regulator of toxic protein properties in neurodegenerative diseases. In this review, we summarize the growing knowledge about the involvement of sumoylation in neurodegeneration, and discuss the underlying molecular principles affected by this multifaceted and intriguing post-translational modification.
Collapse
Affiliation(s)
- Petranka Krumova
- Neuroscience, Novartis Institutes for Biomedical Research, Novartis Pharma AG, 4002, Basel, Switzerland.
| | | |
Collapse
|
78
|
Abstract
The Kv2.1 voltage-gated K(+) channel is found both freely diffusing over the plasma membrane and concentrated in micron-sized clusters localized to the soma, proximal dendrites, and axon initial segment of hippocampal neurons. In transfected HEK cells, Kv2.1 channels within cluster microdomains are nonconducting. Using total internal reflection fluorescence microscopy, the number of GFP-tagged Kv2.1 channels on the HEK cell surface was compared with K(+) channel conductance measured by whole-cell voltage clamp of the same cell. This approach indicated that, as channel density increases, nonclustered channels cease conducting. At the highest density observed, only 4% of all channels were conducting. Mutant Kv2.1 channels that fail to cluster also possessed the nonconducting state with 17% conducting K(+) at higher surface densities. The nonconducting state was specific to Kv2.1 as Kv1.4 was always conducting regardless of the cell-surface expression level. Anti-Kv2.1 immunofluorescence intensity, standardized to Kv2.1 surface density in transfected HEK cells, was used to determine the expression levels of endogenous Kv2.1 in cultured rat hippocampal neurons. Endogenous Kv2.1 levels were compared with the number of conducting channels determined by whole-cell voltage clamp. Only 13 and 27% of the endogenous Kv2.1 was conducting in neurons cultured for 14 and 20 d, respectively. Together, these data indicate that the nonconducting state depends primarily on surface density as opposed to cluster location and that this nonconducting state also exists for native Kv2.1 found in cultured hippocampal neurons. This excess of Kv2.1 protein relative to K(+) conductance further supports a nonconducting role for Kv2.1 in excitable tissues.
Collapse
|
79
|
Ju W, Li Q, Wilson SM, Brittain JM, Meroueh L, Khanna R. SUMOylation alters CRMP2 regulation of calcium influx in sensory neurons. Channels (Austin) 2013; 7:153-9. [PMID: 23510938 DOI: 10.4161/chan.24224] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The axon/dendrite specification collapsin response mediator protein 2 (CRMP2) bidirectionally modulates N-type voltage-gated Ca ( 2+) channels (CaV2.2). Here we demonstrate that small ubiquitin-like modifier (SUMO) protein modifies CRMP2 via the SUMO E2-conjugating enzyme Ubc9 in vivo. Removal of a SUMO conjugation site KMD in CRMP2 (K374A/M375A/D376A; CRMP2AAA) resulted in loss of SUMOylated CRMP2 without compromising neurite branching, a canonical hallmark of CRMP2 function. Increasing SUMOylation levels correlated inversely with calcium influx in sensory neurons. CRMP2 deSUMOylation by SUMO proteases SENP1 and SENP2 normalized calcium influx to those in the CRMP2AAA mutant. Thus, our results identify a novel role for SUMO modification in CRMP2/CaV2.2 signaling pathway.
Collapse
Affiliation(s)
- Weina Ju
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, IN, USA
| | | | | | | | | | | |
Collapse
|
80
|
Plant LD, Zuniga L, Araki D, Marks JD, Goldstein SAN. SUMOylation silences heterodimeric TASK potassium channels containing K2P1 subunits in cerebellar granule neurons. Sci Signal 2012; 5:ra84. [PMID: 23169818 DOI: 10.1126/scisignal.2003431] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The standing outward K(+) current (IKso) governs the response of cerebellar granule neurons to natural and medicinal stimuli including volatile anesthetics. We showed that SUMOylation silenced half of IKso at the surface of cerebellar granule neurons because the underlying channels were heterodimeric assemblies of K2P1, a subunit subject to SUMOylation, and the TASK (two-P domain, acid-sensitive K(+)) channel subunits K2P3 or K2P9. The heterodimeric channels comprised the acid-sensitive portion of IKso and mediated its response to halothane. We anticipate that SUMOylation also influences sensation and homeostatic mechanisms in mammals through TASK channels formed with K2P1.
Collapse
Affiliation(s)
- Leigh D Plant
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | | | | | | | | |
Collapse
|
81
|
Prabakaran S, Lippens G, Steen H, Gunawardena J. Post-translational modification: nature's escape from genetic imprisonment and the basis for dynamic information encoding. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2012; 4:565-83. [PMID: 22899623 DOI: 10.1002/wsbm.1185] [Citation(s) in RCA: 223] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
We discuss protein post-translational modification (PTM) from an information processing perspective. PTM at multiple sites on a protein creates a combinatorial explosion in the number of potential 'mod-forms', or global patterns of modification. Distinct mod-forms can elicit distinct downstream responses, so that the overall response depends partly on the effectiveness of a particular mod-form to elicit a response and partly on the stoichiometry of that mod-form in the molecular population. We introduce the 'mod-form distribution'-the relative stoichiometries of each mod-form-as the most informative measure of a protein's state. Distinct mod-form distributions may summarize information about distinct cellular and physiological conditions and allow downstream processes to interpret this information accordingly. Such information 'encoding' by PTMs may facilitate evolution by weakening the need to directly link upstream conditions to downstream responses. Mod-form distributions provide a quantitative framework in which to interpret ideas of 'PTM codes' that are emerging in several areas of biology, as we show by reviewing examples of ion channels, GPCRs, microtubules, and transcriptional co-regulators. We focus particularly on examples other than the well-known 'histone code', to emphasize the pervasive use of information encoding in molecular biology. Finally, we touch briefly on new methods for measuring mod-form distributions.
Collapse
|
82
|
Menegola M, Clark E, Trimmer JS. The importance of immunohistochemical analyses in evaluating the phenotype of Kv channel knockout mice. Epilepsia 2012; 53 Suppl 1:142-9. [PMID: 22612819 DOI: 10.1111/j.1528-1167.2012.03485.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
To gain insights into the phenotype of voltage-gated potassium (Kv)1.1 and Kv4.2 knockout mice, we used immunohistochemistry to analyze the expression of component principal or α subunits and auxiliary subunits of neuronal Kv channels in knockout mouse brains. Genetic ablation of the Kv1.1 α subunit did not result in compensatory changes in the expression levels or subcellular distribution of related ion channel subunits in hippocampal medial perforant path and mossy fiber nerve terminals, where high levels of Kv1.1 are normally expressed. Genetic ablation of the Kv4.2 α subunit did not result in altered neuronal cytoarchitecture of the hippocampus. Although Kv4.2 knockout mice did not exhibit compensatory changes in the expression levels or subcellular distribution of the related Kv4.3 α subunit, we found dramatic decreases in the cellular and subcellular expression of specific Kv channel interacting proteins (KChIPs) that reflected their degree of association and colocalization with Kv4.2 in wild-type mouse and rat brains. These studies highlight the insights that can be gained by performing detailed immunohistochemical analyses of Kv channel knockout mouse brains.
Collapse
Affiliation(s)
- Milena Menegola
- Departments of Neurobiology, Physiology and Behavior Physiology and Membrane Biology, University of California-Davis, One Shields Avenue, Davis, CA 95616-8519, U.S.A
| | | | | |
Collapse
|
83
|
Craig TJ, Henley JM. Protein SUMOylation in spine structure and function. Curr Opin Neurobiol 2012; 22:480-7. [PMID: 22054923 PMCID: PMC3379963 DOI: 10.1016/j.conb.2011.10.017] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 10/18/2011] [Accepted: 10/18/2011] [Indexed: 11/18/2022]
Abstract
The active regulation of spine structure and function is of fundamental importance for information storage in the brain. Many proteins involved in spine development and activity-dependent remodelling are potential or validated substrates for modification by the Small Ubiquitin-like Modifier (SUMO). The functional consequences of neuronal protein SUMOylation appear diverse and, in many cases, have not yet been determined. However, for several proteins SUMOylation has been shown to be a key regulator, which has a profound impact on spine dynamics and protein trafficking and function. Here we provide an overview of neuronal SUMOylation and discuss how greater understanding of this relatively recently discovered posttranslational modification will provide insight into the complexity of protein interactions that control synaptic activity and dysfunction.
Collapse
Affiliation(s)
- Tim J Craig
- MRC Centre for Synaptic Plasticity, School of Biochemistry Medical Sciences Building, University of Bristol, University Walk, Bristol, BS8 1TD, UK
| | | |
Collapse
|
84
|
DeSUMOylation Controls Insulin Exocytosis in Response to Metabolic Signals. Biomolecules 2012; 2:269-81. [PMID: 24970137 PMCID: PMC4030845 DOI: 10.3390/biom2020269] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 05/14/2012] [Accepted: 05/16/2012] [Indexed: 12/25/2022] Open
Abstract
The secretion of insulin by pancreatic islet β-cells plays a pivotal role in glucose homeostasis and diabetes. Recent work suggests an important role for SUMOylation in the control of insulin secretion from β-cells. In this paper we discuss mechanisms whereby (de)SUMOylation may control insulin release by modulating β-cell function at one or more key points; and particularly through the acute and reversible regulation of the exocytotic machinery. Furthermore, we postulate that the SUMO-specific protease SENP1 is an important mediator of insulin exocytosis in response to NADPH, a metabolic secretory signal and major determinant of β-cell redox state. Dialysis of mouse β-cells with NADPH efficiently amplifies β-cell exocytosis even when extracellular glucose is low; an effect that is lost upon knockdown of SENP1. Conversely, over-expression of SENP1 itself augments β-cell exocytosis in a redox-dependent manner. Taken together, we suggest that (de)SUMOylation represents an important mechanism that acutely regulates insulin secretion and that SENP1 can act as an amplifier of insulin exocytosis.
Collapse
|
85
|
Craig TJ, Jaafari N, Petrovic MM, Jacobs SC, Rubin PP, Mellor JR, Henley JM. Homeostatic synaptic scaling is regulated by protein SUMOylation. J Biol Chem 2012; 287:22781-8. [PMID: 22582390 PMCID: PMC3391081 DOI: 10.1074/jbc.m112.356337] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Homeostatic scaling allows neurons to alter synaptic transmission to compensate for changes in network activity. Here, we show that suppression of network activity with tetrodotoxin, which increases surface expression of AMPA receptors (AMPARs), dramatically reduces levels of the deSUMOylating (where SUMO is small ubiquitin-like modifier) enzyme SENP1, leading to a consequent increase in protein SUMOylation. Overexpression of the catalytic domain of SENP1 prevents this scaling effect, and we identify Arc as a SUMO substrate involved in the tetrodotoxin-induced increase in AMPAR surface expression. Thus, protein SUMOylation plays an important and previously unsuspected role in synaptic trafficking of AMPARs that underlies homeostatic scaling.
Collapse
Affiliation(s)
- Tim J Craig
- Medical Research Council Centre for Synaptic Plasticity, School of Biochemistry, University of Bristol, Bristol BS8 1TD, United Kingdom
| | | | | | | | | | | | | |
Collapse
|
86
|
Baver SB, O'Connell KMS. The C-terminus of neuronal Kv2.1 channels is required for channel localization and targeting but not for NMDA-receptor-mediated regulation of channel function. Neuroscience 2012; 217:56-66. [PMID: 22554782 DOI: 10.1016/j.neuroscience.2012.04.054] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 04/20/2012] [Accepted: 04/21/2012] [Indexed: 11/27/2022]
Abstract
The delayed rectifier voltage-gated potassium channel Kv2.1 underlies a majority of the somatic K(+) current in neurons and is particularly important for regulating intrinsic neuronal excitability. Various stimuli alter Kv2.1 channel gating as well as localization of the channel to cell-surface cluster domains. It has been postulated that specific domains within the C-terminus of Kv2.1 are critical for channel gating and sub-cellular localization; however, the distinct regions that govern these processes remain elusive. Here we show that the soluble C-terminal fragment of the closely related channel Kv2.2 displaces Kv2.1 from clusters in both rat hippocampal neurons and HEK293 cells, however neither steady-state activity nor N-methyl-d-aspartate (NMDA)-dependent modulation is altered in spite of this non-clustered localization. Further, we demonstrate that the C-terminus of Kv2.1 is not necessary for steady-state gating, sensitivity to intracellular phosphatase or NMDA-dependent modulation, though this region is required for localization of Kv2.1 to clusters. Thus, the molecular determinants of Kv2.1 localization and modulation are distinct regions of the channel that function independently.
Collapse
Affiliation(s)
- S B Baver
- Department of Physiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA
| | | |
Collapse
|
87
|
Manning Fox JE, Hajmrle C, Macdonald PE. Novel roles of SUMO in pancreatic β-cells: thinking outside the nucleus. Can J Physiol Pharmacol 2012; 90:765-70. [PMID: 22486776 DOI: 10.1139/y11-134] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The endocrine pancreas is critically important in the regulation of energy metabolism, with defective insulin secretion from pancreatic islet β-cells a major contributing factor to the development of type 2 diabetes. Small ubiquitin-like modifier (SUMO) proteins have been demonstrated to covalently modify a wide range of target proteins, mediating a broad range of cellular processes. While the effects of SUMOylation on β-cell gene transcription have been previously reviewed, recent reports indicate roles for SUMO outside of the nucleus. In this review we shall focus on the reported non-nuclear roles of SUMOylation in the regulation of β-cells, including SUMOylation as a novel signaling pathway in the acute regulation of insulin secretion.
Collapse
Affiliation(s)
- Jocelyn E Manning Fox
- Department of Pharmacology and Alberta Diabetes Institute, Li Ka Shing Centre, University of Alberta, Edmonton, AB T6G 2E1, Canada.
| | | | | |
Collapse
|
88
|
Fesce R, Forti L, Polenghi A, Locarno A, Canella R, Sacchi O, Rossi ML. Can selectivity be functionally modulated in ion channels? ACTA ACUST UNITED AC 2012; 138:367-70. [PMID: 21875981 PMCID: PMC3171083 DOI: 10.1085/jgp.201110690] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Riccardo Fesce
- Neuroscience Research Center, Insubria University, 21052 Busto Arsizio, Italy
- Neuroscience Division, San Raffaele Scientific Institute, 20132 Milano, Italy
| | - Lia Forti
- Neuroscience Research Center, Insubria University, 21052 Busto Arsizio, Italy
| | - Alice Polenghi
- Neuroscience Research Center, Insubria University, 21052 Busto Arsizio, Italy
| | - Albina Locarno
- Neuroscience Research Center, Insubria University, 21052 Busto Arsizio, Italy
| | - Rita Canella
- Department of Biology and Evolution, Physiology and Biophysics Section, Ferrara University, 44121 Ferrara, Italy
| | - Oscar Sacchi
- Department of Biology and Evolution, Physiology and Biophysics Section, Ferrara University, 44121 Ferrara, Italy
| | - Maria Lisa Rossi
- Department of Biology and Evolution, Physiology and Biophysics Section, Ferrara University, 44121 Ferrara, Italy
| |
Collapse
|
89
|
Rajan S, Torres J, Thompson MS, Philipson LH. SUMO downregulates GLP-1-stimulated cAMP generation and insulin secretion. Am J Physiol Endocrinol Metab 2012; 302:E714-23. [PMID: 22234371 PMCID: PMC3311292 DOI: 10.1152/ajpendo.00486.2011] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Glucagon-like peptide-1 (GLP-1)-based incretin therapy is becoming central to the treatment of type 2 diabetes. Activation of incretin hormone receptors results in rapid elevation of cAMP followed by enhanced insulin secretion. However, the incretin effect may be significantly impaired in diabetes. The objective of this study is to investigate downregulation of GLP-1 signaling by small ubiquitin-related modifier protein (SUMO). Mouse islets exposed to high glucose showed increased expression of endogenous SUMO transcripts and its conjugating enzyme Ubc-9. Overexpression of SUMO-1 in mouse insulinoma 6 (MIN6) cells and primary mouse β-cells resulted in reduced static and real-time estimates of intracellular cAMP upon receptor stimulation with exendin-4, a GLP-1 receptor (GLP-1R) agonist. GLP1-R was covalently modified by SUMO. Overexpression of SUMO-1 attenuated cell surface trafficking of GLP-1R, which resulted in significantly reduced insulin secretion when stimulated by exendin-4. Partial knock down of SUMO-conjugating enzyme Ubc-9 resulted in enhanced exendin-4-stimulated insulin secretion in mouse islets exposed to high glucose. Thus, SUMO modification of the GLP-1R could be a contributing factor to reduced incretin responsiveness. Elucidating mechanisms of GLP-1R regulation by sumoylation will help improve our understanding of incretin biology and of GLP-1-based treatment of type 2 diabetes.
Collapse
|
90
|
Plant LD. A Role for K2P Channels in the Operation of Somatosensory Nociceptors. Front Mol Neurosci 2012; 5:21. [PMID: 22403526 PMCID: PMC3293133 DOI: 10.3389/fnmol.2012.00021] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Accepted: 02/09/2012] [Indexed: 12/20/2022] Open
Abstract
The ability to sense mechanical, thermal, and chemical stimuli is critical to normal physiology and the perception of pain. Contact with noxious stimuli triggers a complex series of events that initiate innate protective mechanisms designed to minimize or avoid injury. Extreme temperatures, mechanical stress, and chemical irritants are detected by specific ion channels and receptors clustered on the terminals of nociceptive sensory nerve fibers and transduced into electrical information. Propagation of these signals, from distant sites in the body to the spinal cord and the higher processing centers of the brain, is also orchestrated by distinct groups of ion channels. Since their identification in 1995, evidence has emerged to support roles for K2P channels at each step along this pathway, as receptors for physiological and noxious stimuli, and as determinants of nociceptor excitability and conductivity. In addition, the many subtypes of K2P channels expressed in somatosensory neurons are also implicated in mediating the effects of volatile, general anesthetics on the central and peripheral nervous systems. Here, I offer a critical review of the existing data supporting these attributes of K2P channel function and discuss how diverse regulatory mechanisms that control the activity of K2P channels act to govern the operation of nociceptors.
Collapse
Affiliation(s)
- Leigh D Plant
- Department of Biochemistry, Brandeis University Waltham, MA, USA
| |
Collapse
|
91
|
MacDonald PE. Signal integration at the level of ion channel and exocytotic function in pancreatic β-cells. Am J Physiol Endocrinol Metab 2011; 301:E1065-9. [PMID: 21934040 DOI: 10.1152/ajpendo.00426.2011] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Whole body energy balance is ensured by the exquisite control of insulin secretion, the dysregulation of which has serious consequences. Although a great deal has been learned about the control of insulin secretion from pancreatic β-cells in the past 30 years, there remains much to be understood about the molecular mechanisms and interactions that underlie the precise control of this process. Numerous molecular interactions at the plasma membrane mediate the excitatory and amplifying events involved in insulin secretion; this includes interactions between ion channels, signal transduction machinery, and exocytotic proteins. The present Perspectives article considers evidence that key membrane and membrane-associated proteins essential to insulin secretion are regulated in concert as a functional unit, ensuring an integrated excitatory and exocytotic response to the signals that control insulin secretion.
Collapse
Affiliation(s)
- Patrick E MacDonald
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada.
| |
Collapse
|
92
|
Phosphorylation of the voltage-gated potassium channel Kv2.1 by AMP-activated protein kinase regulates membrane excitability. Proc Natl Acad Sci U S A 2011; 108:18132-7. [PMID: 22006306 DOI: 10.1073/pnas.1106201108] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Firing of action potentials in excitable cells accelerates ATP turnover. The voltage-gated potassium channel Kv2.1 regulates action potential frequency in central neurons, whereas the ubiquitous cellular energy sensor AMP-activated protein kinase (AMPK) is activated by ATP depletion and protects cells by switching off energy-consuming processes. We show that treatment of HEK293 cells expressing Kv2.1 with the AMPK activator A-769662 caused hyperpolarizing shifts in the current-voltage relationship for channel activation and inactivation. We identified two sites (S440 and S537) directly phosphorylated on Kv2.1 by AMPK and, using phosphospecific antibodies and quantitative mass spectrometry, show that phosphorylation of both sites increased in A-769662-treated cells. Effects of A-769662 were abolished in cells expressing Kv2.1 with S440A but not with S537A substitutions, suggesting that phosphorylation of S440 was responsible for these effects. Identical shifts in voltage gating were observed after introducing into cells, via the patch pipette, recombinant AMPK rendered active but phosphatase-resistant by thiophosphorylation. Ionomycin caused changes in Kv2.1 gating very similar to those caused by A-769662 but acted via a different mechanism involving Kv2.1 dephosphorylation. In cultured rat hippocampal neurons, A-769662 caused hyperpolarizing shifts in voltage gating similar to those in HEK293 cells, effects that were abolished by intracellular dialysis with Kv2.1 antibodies. When active thiophosphorylated AMPK was introduced into cultured neurons via the patch pipette, a progressive, time-dependent decrease in the frequency of evoked action potentials was observed. Our results suggest that activation of AMPK in neurons during conditions of metabolic stress exerts a protective role by reducing neuronal excitability and thus conserving energy.
Collapse
|
93
|
Mandikian D, Cerda O, Sack JT, Trimmer JS. A SUMO-Phospho tag team for wrestling with potassium channel gating. ACTA ACUST UNITED AC 2011; 137:435-9. [PMID: 21518832 PMCID: PMC3082924 DOI: 10.1085/jgp.201110648] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Affiliation(s)
- Danielle Mandikian
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, CA 95616, USA
| | | | | | | |
Collapse
|
94
|
Abstract
New evidence reveals that the common electrolyte disorder hypokalemia can induce K2P1 channels that are normally selective for K+ to break the rules and conduct Na+. This defiant behavior leads to paradoxical depolarization of many cells in the heart, increasing the risk for lethal arrhythmia. The new research resolves a mystery uncovered 50 years ago and bestows an array of new riddles. Here, I discuss how K2P1 might achieve this alchemy--through stable residence of the K+ selectivity filter in a Na+-conductive state between its open and C-inactive configurations--and predict that other K+ channels and environmental stimuli will be discovered to produce the same excitatory misconduct.
Collapse
Affiliation(s)
- Steve A N Goldstein
- Department of Pediatrics and Institute for Molecular Pediatric Sciences, University of Chicago, Chicago, IL 60615, USA.
| |
Collapse
|