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Ramezani M, Wagenknecht-Wiesner A, Wang T, Holowka DA, Eliezer D, Baird BA. Alpha synuclein modulates mitochondrial Ca 2+ uptake from ER during cell stimulation and under stress conditions. NPJ Parkinsons Dis 2023; 9:137. [PMID: 37741841 PMCID: PMC10518018 DOI: 10.1038/s41531-023-00578-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 09/08/2023] [Indexed: 09/25/2023] Open
Abstract
Alpha synuclein (a-syn) is an intrinsically disordered protein prevalent in neurons, and aggregated forms are associated with synucleinopathies including Parkinson's disease (PD). Despite the biomedical importance and extensive studies, the physiological role of a-syn and its participation in etiology of PD remain uncertain. We showed previously in model RBL cells that a-syn colocalizes with mitochondrial membranes, depending on formation of N-terminal helices and increasing with mitochondrial stress1. We have now characterized this colocalization and functional correlates in RBL, HEK293, and N2a cells. We find that expression of a-syn enhances stimulated mitochondrial uptake of Ca2+ from the ER, depending on formation of its N-terminal helices but not on its disordered C-terminal tail. Our results are consistent with a-syn acting as a tether between mitochondria and ER, and we show increased contacts between these two organelles using structured illumination microscopy. We tested mitochondrial stress caused by toxins related to PD, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP/MPP+) and carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and found that a-syn prevents recovery of stimulated mitochondrial Ca2+ uptake. The C-terminal tail, and not N-terminal helices, is involved in this inhibitory activity, which is abrogated when phosphorylation site serine-129 is mutated (S129A). Correspondingly, we find that MPTP/MPP+ and CCCP stress is accompanied by both phosphorylation (pS129) and aggregation of a-syn. Overall, our results indicate that a-syn can participate as a tethering protein to modulate Ca2+ flux between ER and mitochondria, with potential physiological significance. A-syn can also prevent cellular recovery from toxin-induced mitochondrial dysfunction, which may represent a pathological role of a-syn in the etiology of PD.
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Affiliation(s)
- Meraj Ramezani
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853, USA
| | | | - Tong Wang
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853, USA
| | - David A Holowka
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853, USA
| | - David Eliezer
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, 10065, USA.
| | - Barbara A Baird
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853, USA.
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2
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Lam CKC, Truong K. Engineering a synthesis-friendly serum responsive promoter for antibiotic selection of genomic integration in cell-based therapy. Biotechnol Lett 2022; 44:605-611. [PMID: 35294696 DOI: 10.1007/s10529-022-03244-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Accepted: 03/04/2022] [Indexed: 11/24/2022]
Abstract
For clinical cell-based therapies (e.g. CAR-T cells), the genomic integration of therapeutic genes into cells are selected using inefficient resistance genes of host origin to avoid potential immune response from using more efficient resistance genes of foreign origin. In principle, a serum-responsive promoter could express efficient resistance genes during the cell manufacturing stage that could then diminish during in vivo administration. To avoid genomic instability, we designed a synthesis-friendly serum-responsive promoter (SFSp) with no extreme GC ratios or repeats greater than 9 base pairs. SFSp was used to express a fluorescent reporter, whose expression was diminished after serum starvation. Furthermore, SFSp could be used in replacement of weak promoters (e.g. SV40p) for expressing efficient resistance genes (e.g. blasticidin resistance) from genomic integration via lentiviral infection. Thus, the regulation of resistance genes using SFSp could be a valuable tool in cell-based therapeutics to increase selection efficiency and reduce immunogenicity.
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Affiliation(s)
- Chee Ka Candice Lam
- Institute of Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON, M5S 3G9, Canada
| | - Kevin Truong
- Edward S. Rogers, Sr. Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Circle, Toronto, ON, M5S 3G4, Canada. .,Institute of Biomedical Engineering, University of Toronto, 164 College Street Room 407, Rosebrugh Building, Toronto, ON, M5S 3G9, Canada.
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3
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Milici A, Sanchez A, Talavera K. Silica Nanoparticles Inhibit Responses to ATP in Human Airway Epithelial 16HBE Cells. Int J Mol Sci 2021; 22:10173. [PMID: 34576336 PMCID: PMC8467126 DOI: 10.3390/ijms221810173] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 09/16/2021] [Indexed: 11/16/2022] Open
Abstract
Because of their low cost and easy production, silica nanoparticles (SiNPs) are widely used in multiple manufacturing applications as anti-caking, densifying and hydrophobic agents. However, this has increased the exposure levels of the general population and has raised concerns about the toxicity of this nanomaterial. SiNPs affect the function of the airway epithelium, but the biochemical pathways targeted by these particles remain largely unknown. Here we investigated the effects of SiNPs on the responses of 16HBE14o- cultured human bronchial epithelial (16HBE) cells to the damage-associated molecular pattern ATP, using fluorometric measurements of intracellular Ca2+ concentration. Upon stimulation with extracellular ATP, these cells displayed a concentration-dependent increase in intracellular Ca2+, which was mediated by release from intracellular stores. SiNPs inhibited the Ca2+ responses to ATP within minutes of application and at low micromolar concentrations, which are significantly faster and more potent than those previously reported for the induction of cellular toxicity and pro-inflammatory responses. SiNPs-induced inhibition is independent from the increase in intracellular Ca2+ they produce, is largely irreversible and occurs via a non-competitive mechanism. These findings suggest that SiNPs reduce the ability of airway epithelial cells to mount ATP-dependent protective responses.
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Affiliation(s)
| | | | - Karel Talavera
- Laboratory of Ion Channel Research, Department of Cellular and Molecular Medicine, VIB Center for Brain & Disease Research, Herestraat 49, 3000 Leuven, Belgium; (A.M.); (A.S.)
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4
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Stavsky A, Stoler O, Kostic M, Katoshevsky T, Assali EA, Savic I, Amitai Y, Prokisch H, Leiz S, Daumer-Haas C, Fleidervish I, Perocchi F, Gitler D, Sekler I. Aberrant activity of mitochondrial NCLX is linked to impaired synaptic transmission and is associated with mental retardation. Commun Biol 2021; 4:666. [PMID: 34079053 PMCID: PMC8172942 DOI: 10.1038/s42003-021-02114-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Accepted: 03/22/2021] [Indexed: 02/04/2023] Open
Abstract
Calcium dynamics control synaptic transmission. Calcium triggers synaptic vesicle fusion, determines release probability, modulates vesicle recycling, participates in long-term plasticity and regulates cellular metabolism. Mitochondria, the main source of cellular energy, serve as calcium signaling hubs. Mitochondrial calcium transients are primarily determined by the balance between calcium influx, mediated by the mitochondrial calcium uniporter (MCU), and calcium efflux through the sodium/lithium/calcium exchanger (NCLX). We identified a human recessive missense SLC8B1 variant that impairs NCLX activity and is associated with severe mental retardation. On this basis, we examined the effect of deleting NCLX in mice on mitochondrial and synaptic calcium homeostasis, synaptic activity, and plasticity. Neuronal mitochondria exhibited basal calcium overload, membrane depolarization, and a reduction in the amplitude and rate of calcium influx and efflux. We observed smaller cytoplasmic calcium transients in the presynaptic terminals of NCLX-KO neurons, leading to a lower probability of release and weaker transmission. In agreement, synaptic facilitation in NCLX-KO hippocampal slices was enhanced. Importantly, deletion of NCLX abolished long term potentiation of Schaffer collateral synapses. Our results show that NCLX controls presynaptic calcium transients that are crucial for defining synaptic strength as well as short- and long-term plasticity, key elements of learning and memory processes.
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Affiliation(s)
- Alexandra Stavsky
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Ohad Stoler
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Marko Kostic
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Tomer Katoshevsky
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Essam A Assali
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Ivana Savic
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Yael Amitai
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Holger Prokisch
- Institute of Human Genetics, School of Medicine, Technische Universität München, Munich, Germany
- Institute of Neurogenomics, Helmholtz Zentrum München, Munich, Germany
| | - Steffen Leiz
- Department of Pediatrics, Klinikum Dritter Orden, Munich, Germany
| | | | - Ilya Fleidervish
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Fabiana Perocchi
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center (HDC), Helmholtz Zentrum München, Munich, Germany
- Munich Cluster for Systems Neurology, Munich, Germany
| | - Daniel Gitler
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
| | - Israel Sekler
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
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5
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Lam CKC, Truong K. Engineering a Synthesis-Friendly Constitutive Promoter for Mammalian Cell Expression. ACS Synth Biol 2020; 9:2625-2631. [PMID: 32927951 DOI: 10.1021/acssynbio.0c00310] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Since cell-based therapies require the constitutive and stable expression of therapeutic transgenes, lentiviral infection is commonly used to integrate gene material regulated by standard constitutive promoters. Unfortunately, none of the standard or synthetic constitutive promoters can be easily synthesized at low cost due to the presence of repeated subsequences. Thus, in this paper, we designed a synthetic constitutive promoter (named SFCp) that can drive the expression of fluorescent proteins that subsequently trafficked to intended subcellular localizations and the expression of synthetic proteins that rewired the cellular response of Ca2+ to cell morphology changes. Furthermore, SFCp can be used to avoid sequence homology that can theoretically result in loss of genetic material by homologous recombination in tandem constructs. As gene synthesis becomes an indispensable tool in the arsenal of synthetic biology, it is essential to develop a toolbox of gene synthesis friendly components for cell engineering such as constitutive promoters.
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Affiliation(s)
- Chee Ka Candice Lam
- Institute of Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada
| | - Kevin Truong
- Institute of Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada
- Edward S. Rogers, Sr. Department of Electrical and Computer Engineering, University of Toronto, 10 King’s College Circle, Toronto, Ontario M5S 3G4, Canada
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6
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Sharma S, Thibodeau S, Lytton J. Signal pathway analysis of selected obesity-associated melanocortin-4 receptor class V mutants. Biochim Biophys Acta Mol Basis Dis 2020; 1866:165835. [PMID: 32423884 DOI: 10.1016/j.bbadis.2020.165835] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 04/18/2020] [Accepted: 05/06/2020] [Indexed: 01/30/2023]
Abstract
Mutations in the melanocortin-4 receptor (MC4R) in humans are the single most common cause of rare monogenic 1severe obesity, and polymorphisms in this gene are also associated with obesity in the general population. The MC4R is a G-protein coupled receptor, and in vitro analysis suggests that MC4R can signal through several different G-protein subtypes. In vivo studies show complex outcomes, with different G-proteins in different cells responsible for different physiological responses linked to obesity. There is an emerging consensus that Gαq-linked signals in the paraventricular nucleus of the hypothalamus are essential for normal satiety and the control of feeding behavior. Many MC4R mutations have been analyzed for the molecular defect underlying their association with obesity, which has revealed a group - referred to as class V mutants - with no measurable change in receptor function. However, Gαq-linked signaling leading to Ca2+ release has only been examined for a few MC4R mutations. In this study, we have examined seven MC4R class V mutants, as well as two other well-characterized signal-defective mutants as controls, with respect to G-protein signaling coupled to cAMP production, mitogen-activated protein kinase (MAPK) activation, and Ca2+ release. These data confirm, with one exception (E308K), the expected pattern of cAMP and MAPK signaling for wild type and mutant MC4R. Our results also demonstrate normal MSH-induced Ca2+ signals for wild type as well as all the class V mutants, but not the signal-defective controls. Thus, the means by which class V MC4R mutations lead to obesity remains an open question.
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Affiliation(s)
- Sunita Sharma
- Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Stephanie Thibodeau
- Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Jonathan Lytton
- Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Canada.
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7
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Extracellular ATP activates store-operated Ca 2+ entry in white adipocytes: functional evidence for STIM1 and ORAI1. Biochem J 2018; 475:691-704. [PMID: 29335300 PMCID: PMC5813502 DOI: 10.1042/bcj20170484] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Revised: 01/05/2018] [Accepted: 01/13/2018] [Indexed: 12/26/2022]
Abstract
In the present study, we have applied ratiometric measurements of intracellular Ca2+ concentrations ([Ca2+]i) to show that extracellularly applied ATP (adenosine triphosphate) (100 µM) stimulates store-operated Ca2+ entry (SOCE) in 3T3-L1 adipocytes. ATP produced a rapid increase in [Ca2+]i consisting of an initial transient elevation followed by a sustained elevated phase that could be observed only in the presence of extracellular Ca2+. Gene expression data and [Ca2+]i recordings with uridine-5′-triphosphate or with the phospholipase C (PLC) inhibitor U73122 demonstrated the involvement of purinergic P2Y2 receptors and the PLC/inositol trisphosphate pathway. The [Ca2+]i elevation produced by reintroduction of a Ca2+-containing intracellular solution to adipocytes exposed to ATP in the absence of Ca2+ was diminished by known SOCE antagonists. The chief molecular components of SOCE, the stromal interaction molecule 1 (STIM1) and the calcium release-activated calcium channel protein 1 (ORAI1), were detected at the mRNA and protein level. Moreover, SOCE was largely diminished in cells where STIM1 and/or ORAI1 had been silenced by small interfering (si)RNA. We conclude that extracellular ATP activates SOCE in white adipocytes, an effect predominantly mediated by STIM1 and ORAI1.
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8
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Ta CM, Acheson KE, Rorsman NJG, Jongkind RC, Tammaro P. Contrasting effects of phosphatidylinositol 4,5-bisphosphate on cloned TMEM16A and TMEM16B channels. Br J Pharmacol 2017; 174:2984-2999. [PMID: 28616863 PMCID: PMC5573538 DOI: 10.1111/bph.13913] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 06/09/2017] [Accepted: 06/10/2017] [Indexed: 12/19/2022] Open
Abstract
Background and Purpose Ca2+‐activated Cl− channels (CaCCs) are gated open by a rise in intracellular Ca2+ concentration ([Ca2+]i), typically provoked by activation of Gq‐protein coupled receptors (GqPCR). GqPCR activation initiates depletion of plasmalemmal phosphatidylinositol 4,5‐bisphosphate (PIP2). Here, we determined whether PIP2 acts as a signalling lipid for CaCCs coded by the TMEM16A and TMEM16B genes. Experimental Approach Patch‐clamp electrophysiology, in conjunction with genetically encoded systems to control cellular PIP2 content, was used to define the mechanism of action of PIP2 on TMEM16A and TMEM16B channels. Key Results A water‐soluble PIP2 analogue (diC8‐PIP2) activated TMEM16A channels by up to fivefold and inhibited TMEM16B by ~0.2‐fold. The effects of diC8‐PIP2 on TMEM16A currents were especially pronounced at low [Ca2+]i. In contrast, diC8‐PIP2 modulation of TMEM16B channels did not vary over a broad [Ca2+]i range but was only detectable at highly depolarized membrane potentials. Modulation of TMEM16A and TMEM16B currents was due to changes in channel gating, while single channel conductance was unaltered. Co‐expression of TMEM16A or TMEM16B with a Danio rerio voltage‐sensitive phosphatase (DrVSP), which degrades PIP2, led to reduction and enhancement of TMEM16A and TMEM16B currents respectively. These effects were abolished by an inactivating mutation in DrVSP and antagonized by simultaneous co‐expression of a phosphatidylinositol‐4‐phosphate 5‐kinase that catalyses PIP2 formation. Conclusions and Implications PIP2 acts as a modifier of TMEM16A and TMEM16B channel gating. Drugs interacting with PIP2 signalling may affect TMEM16A and TMEM16B channel gating and have potential uses in basic science and implications for therapy.
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Affiliation(s)
- Chau M Ta
- Department of Pharmacology, University of Oxford, Oxford, UK
| | | | - Nils J G Rorsman
- Department of Pharmacology, University of Oxford, Oxford, UK.,OXION Wellcome Trust Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
| | | | - Paolo Tammaro
- Department of Pharmacology, University of Oxford, Oxford, UK.,OXION Wellcome Trust Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
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9
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Qudrat A, Kim JI, Truong K. The spatiotemporal relationship between local Ca(2+) signaling and P2X2R-activated membrane blebbing. Cell Calcium 2016; 59:164-71. [PMID: 26846906 DOI: 10.1016/j.ceca.2016.01.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2015] [Revised: 01/12/2016] [Accepted: 01/12/2016] [Indexed: 12/24/2022]
Abstract
Mammalian P2X receptors (P2XRs), a family of seven ionotropic purinergic receptors, function as ion channels modulating diverse cellular processes such as secretion, apoptosis and proliferation in response to extracellular ATP. Previously, it was shown that upon ATP stimulus, the P2X7 receptor (a member of P2XR family) triggers plasma membrane (PM) blebbing in HEK293 cells. In this study, we demonstrate that this phenomenon extends to another member of the P2XR family-P2X2 receptor (P2X2R). Similar to P2X7 receptor, P2X2R blebbing is dependent on Ca(2+)-calmodulin and ROCK-I. To elucidate the spatiotemporal relationship between Ca(2+) signaling and blebbing, protein biosensors and switches were used to image and generate Ca(2+) signals, respectively, while observing PM blebbing in cells. Blebbing cannot be initiated by Ca(2+) influx from the endoplasmic reticulum or by Ca(2+) transport across the PM by other Ca(2+) channels. To trigger blebbing, it is necessary for Ca(2+) to enter specifically through the P2X2R. Lastly, a local Ca(2+) signal near a fragment that encodes the intracellular P2X2R C-terminus tail is sufficient to trigger blebbing.
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Affiliation(s)
- Anam Qudrat
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON, Canada M5S 3G9
| | - Jae Ik Kim
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON, Canada M5S 3G9
| | - Kevin Truong
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON, Canada M5S 3G9; Edward S. Rogers, Sr. Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Circle, Toronto, ON, Canada M5S 3G4.
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10
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Lindenburg LH, Vinkenborg JL, Oortwijn J, Aper SJA, Merkx M. MagFRET: the first genetically encoded fluorescent Mg2+ sensor. PLoS One 2013; 8:e82009. [PMID: 24312622 PMCID: PMC3846734 DOI: 10.1371/journal.pone.0082009] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Accepted: 10/29/2013] [Indexed: 01/14/2023] Open
Abstract
Magnesium has important structural, catalytic and signaling roles in cells, yet few tools exist to image this metal ion in real time and at subcellular resolution. Here we report the first genetically encoded sensor for Mg2+, MagFRET-1. This sensor is based on the high-affinity Mg2+ binding domain of human centrin 3 (HsCen3), which undergoes a transition from a molten-globular apo form to a compactly-folded Mg2+-bound state. Fusion of Cerulean and Citrine fluorescent domains to the ends of HsCen3, yielded MagFRET-1, which combines a physiologically relevant Mg2+ affinity (Kd = 148 µM) with a 50% increase in emission ratio upon Mg2+ binding due to a change in FRET efficiency between Cerulean and Citrine. Mutations in the metal binding sites yielded MagFRET variants whose Mg2+ affinities were attenuated 2- to 100-fold relative to MagFRET-1, thus covering a broad range of Mg2+ concentrations. In situ experiments in HEK293 cells showed that MagFRET-1 can be targeted to the cytosol and the nucleus. Clear responses to changes in extracellular Mg2+ concentration were observed for MagFRET-1-expressing HEK293 cells when they were permeabilized with digitonin, whereas similar changes were not observed for intact cells. Although MagFRET-1 is also sensitive to Ca2+, this affinity is sufficiently attenuated (Kd of 10 µM) to make the sensor insensitive to known Ca2+ stimuli in HEK293 cells. While the potential and limitations of the MagFRET sensors for intracellular Mg2+ imaging need to be further established, we expect that these genetically encoded and ratiometric fluorescent Mg2+ sensors could prove very useful in understanding intracellular Mg2+ homeostasis and signaling.
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Affiliation(s)
- Laurens H. Lindenburg
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Jan L. Vinkenborg
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Jorn Oortwijn
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Stijn J. A. Aper
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Maarten Merkx
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- * E-mail:
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11
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Mueller MH, Xue B, Glatzle J, Hahn J, Grundy D, Kreis ME. Extrinsic afferent nerve sensitivity and enteric neurotransmission in murine jejunum in vitro. Am J Physiol Gastrointest Liver Physiol 2009; 297:G655-62. [PMID: 19679823 DOI: 10.1152/ajpgi.00128.2009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Enteric and extrinsic sensory neurons respond to similar stimuli. Thus they may be activated in series or in parallel. Because signal transmission via synapses or mediator release would depend on calcium, we investigated its role for extrinsic afferent sensitivity to chemical and mechanical stimulation. Extracellular multiunit afferent recordings were made in vitro from paravascular nerve bundles supplying the mouse jejunum. Intraluminal pressure and afferent nerve responses were recorded under control conditions and under four conditions designed to interfere with enteric neurotransmission. We found that phasic intestinal contractions ceased after switching perfusion to Ca(2+)-free buffer with or without a purinergic P2 receptor antagonist, pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid) (PPADS) or cadmium (blocking all Ca(2+)-channels) but not following omega-conotoxin GVIA (N-type Ca(2+)-channel blocker). Luminal HCl (pH 2) and 5-HT (500 microM) evoked peak firing of 17 +/- 4 impulses per second (imp/s) (n = 10) and 21 +/- 4 imp/s (n = 13) under control conditions. These responses were reduced to 4 +/- 2 imp/s and 5 +/- 2 imp/s by cadmium (n = 7, P < 0.05), to 7 +/- 2 imp/s and 6 +/- 1 imp/s by Ca(2+)-free perfusion (n = 6, P < 0.05), and to 3 +/- 1 imp/s and 4 +/- 1 imp/s by Ca(2+)-free perfusion with PPADS (n = 6, P < 0.05). Responses were unchanged by omega-conotoxin GVIA. Mechanical ramp distension of the intestinal segment to 60 cmH(2)O was not altered by any of the experimental conditions. We concluded that HCl and 5-HT activate extrinsic afferents via a calcium-dependent mechanism, which is unlikely to involve enteric neurons carrying N-type calcium channels. Extrinsic mechanosensitivity is independent of enteric neurotransmission. It appears that cross talk from the enteric to the extrinsic nervous system does not mediate extrinsic afferent sensitivity.
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Affiliation(s)
- Mario H Mueller
- Department of Surgery and 2Walter-Brendel Institute of Surgical Research, Ludwig-Maximilian's University, Munich, Germany
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12
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Abstract
Nitric oxide production is stimulated by an increase of the concentration of cytosolic Ca(2+) in vascular endothelial cells. Recent evidence suggests that nitric oxide and cGMP might attenuate Ca(2+) influx and, at the same time, initiate a Ca(2+) removal mechanism, thereby decreasing the intracellular concentration of endothelial Ca(2+) in a negative feedback fashion. Such a negative feedback mechanism could serve to protect the endothelial cells from the detrimental effects of excessive nitric oxide and Ca(2+).
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Affiliation(s)
- Xiaoqiang Yao
- Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.
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13
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De Luisi A, Hofer AM. Evidence that Ca(2+) cycling by the plasma membrane Ca(2+)-ATPase increases the 'excitability' of the extracellular Ca(2+)-sensing receptor. J Cell Sci 2003; 116:1527-38. [PMID: 12640037 DOI: 10.1242/jcs.00368] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The extracellular Ca(2+)-sensing receptor (CaR) is a widely expressed G-protein-coupled receptor that translates information about [Ca(2+)] in the extracellular milieu to the interior of the cell, usually via intracellular Ca(2+) signaling pathways. Using fura-2 imaging of cytoplasmic [Ca(2+)], we observed that HEK293 cells expressing CaR oscillated readily under conditions permissive for CaR activation. Spiking was also triggered in the absence of external Ca(2+) by the CaR agonist spermine (1 mM). Oscillating cells were typically located in clusters of closely apposed cells, but Ca(2+) spiking was insensitive to the gap junction inhibitor 18alpha-glycyrrhetinic acid. We hypothesized that Ca(2+) signals might be amplified, in part, through a positive feedback loop in which Ca(2+) extrusion via the plasma membrane Ca(2+)-ATPase (PMCA) activates CaRs on the same cell or adjacent cells through local increases in [Ca(2+)](out). In support of this idea, addition of exogenous Ca(2+) buffers (keeping free [Ca(2+)](out) constant) attenuated or eliminated Ca(2+) signals (manifested as oscillations), as did PMCA inhibitors (HgCl(2), orthovanadate and Caloxin 2A1). Measurement of extracellular [Ca(2+)] using the near membrane probe fura-C(18) revealed that external [Ca(2+)] rose following receptor activation, sometimes displaying an oscillatory pattern. Our data suggest that PMCA-mediated cycling of Ca(2+) across the plasma membrane leads to localized increases in [Ca(2+)](out) that increase the excitability of CaR.
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Affiliation(s)
- Annunziata De Luisi
- Dipartimento di Fisiologia Generale ed Ambientale, Universitá di Bari, Via Amendola 165/A, I-70126 Bari, Italy
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Smart ML, Gu B, Panchal RG, Wiley J, Cromer B, Williams DA, Petrou S. P2X7 receptor cell surface expression and cytolytic pore formation are regulated by a distal C-terminal region. J Biol Chem 2003; 278:8853-60. [PMID: 12496266 DOI: 10.1074/jbc.m211094200] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The importance of the cytosolic C-terminal region of the P2X7 receptor (P2X7R) is unquestioned, yet little is known about the functional domains of this region and how they may contribute to the numerous properties ascribed to this receptor. A structure-function analysis of truncated and single-residue-mutated P2X7 receptors was performed in HEK-293 cells and Xenopus oocytes. Cells expressing receptors truncated at residue 581 (of 595) have negligible ethidium ion uptake, whereas those expressing the P2X7R truncated at position 582 give wild type ethidium ion uptake suggesting that pore formation requires over 95% of the C-terminal tail. Channel function was evident even in receptors that were truncated at position 380 indicating that only a small portion of the cytosolic region is required for channel activity. Surprisingly, truncations in the region between residues 551 and 581 resulted in non-functional receptors with no detectable cell surface expression in HEK-293 cells. A more detailed analysis revealed that mutations of single residues within this region could also abolish receptor function and cell surface expression, suggesting that this region may participate in regulating the surface expression of the pore-forming P2X7R.
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Affiliation(s)
- Megan L Smart
- Department of Physiology, the University of Melbourne, Victoria 3010, Australia
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15
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Aguiari G, Campanella M, Manzati E, Pinton P, Banzi M, Moretti S, Piva R, Rizzuto R, del Senno L. Expression of polycystin-1 C-terminal fragment enhances the ATP-induced Ca2+ release in human kidney cells. Biochem Biophys Res Commun 2003; 301:657-64. [PMID: 12565830 DOI: 10.1016/s0006-291x(02)03011-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Polycystin-1 (PC1) is a membrane protein expressed in tubular epithelia of developing kidneys and in other ductal structures. Recent studies indicate this protein to be putatively important in regulating intracellular Ca(2+) levels in various cell types, but little evidence exists for kidney epithelial cells. Here we examined the role of the PC1 cytoplasmic tail on the activity of store operated Ca(2+) channels in human kidney epithelial HEK-293 cell line. Cells were transiently transfected with chimeric proteins containing 1-226 or 26-226 aa of the PC1 cytoplasmic tail fused to the transmembrane domain of the human Trk-A receptor: TrkPC1 wild-type and control Trk truncated peptides were expressed at comparable levels and localized at the plasma membrane. Ca(2+) measurements were performed in cells co-transfected with PC1 chimeras and the cytoplasmic Ca(2+)-sensitive photoprotein aequorin, upon activation of the phosphoinositide pathway by ATP, that, via purinoceptors, is coupled to the release of Ca(2+) from intracellular stores. The expression of TrkPC1 peptide, but not of its truncated form, enhanced the ATP-evoked cytosolic Ca(2+) concentrations. When Ca(2+) assays were performed in HeLa cells characterized by Ca(2+) stores greater than those of HEK-293 cells, the histamine-evoked cytosolic Ca(2+) increase was enhanced by TrkPC1 expression, even in absence of external Ca(2+). These observations indicate that the C-terminal tail of PC1 in kidney and other epithelial cells upregulates a Ca(2+) channel activity also involved in the release of intracellular stores.
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Affiliation(s)
- Gianluca Aguiari
- Department of Biochemistry and Molecular Biology, Section of General Pathology, University of Ferrara, Italy
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16
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Cetinkaya I, Ciarimboli G, Yalçinkaya G, Mehrens T, Velic A, Hirsch JR, Gorboulev V, Koepsell H, Schlatter E. Regulation of human organic cation transporter hOCT2 by PKA, PI3K, and calmodulin-dependent kinases. Am J Physiol Renal Physiol 2003; 284:F293-302. [PMID: 12388397 DOI: 10.1152/ajprenal.00251.2002] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Properties and regulation of the human organic cation (OC) transporter type 2 (hOCT2) expressed in HEK-293 cells were extensively characterized using the fluorescent OC 4-[4-(dimethylamino)styryl]-N-methylpyridinium (ASP(+)). ASP(+) uptake was electrogenic and inhibited by TPA(+) (EC(50) = 2.7 microM), tetraethylammonium (EC(50) = 35 microM), cimetidine (EC(50) = 36 microM), or quinine (EC(50) = 6.7 microM). Stimulation with carbachol or ATP decreased initial uptake by 44 +/- 3 (n = 14) and 34 +/- 4% (n = 21), respectively, independently of PKC but dependent on phosphatidylinositol 3-kinase (PI3K). PKA stimulation decreased uptake by 18 +/- 4% (n = 40). Inhibition of calmodulin (CaM), Ca(2+)/CaM-dependent kinase II, or myosin light chain kinase decreased uptake by 63 +/- 2 (n = 15), 40 +/- 4 (n = 30), and 31 +/- 4% (n = 16), respectively. Inhibition of CaM resulted in a significant change in the EC(50) value for the inhibition of ASP(+) uptake by tetraethylammonium. In conclusion, we demonstrate that the hOCT2 is inhibited by PI3K and PKA and activated by a CaM-dependent signaling pathway, probably via a change in substrate affinity.
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Affiliation(s)
- Ibrahim Cetinkaya
- Medizinische Klinik und Poliklinik D, Experimentelle Nephrologie, and Klinik und Poliklinik für Kinderheilkunde, Universitätsklinikum Münster, D-48149 Münster, Germany
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