101
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López Sanjurjo CI, Tovey SC, Taylor CW. Rapid recycling of Ca2+ between IP3-sensitive stores and lysosomes. PLoS One 2014; 9:e111275. [PMID: 25337829 PMCID: PMC4206489 DOI: 10.1371/journal.pone.0111275] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Accepted: 09/28/2014] [Indexed: 11/26/2022] Open
Abstract
Inositol 1,4,5-trisphosphate (IP3) evokes release of Ca2+ from the endoplasmic reticulum (ER), but the resulting Ca2+ signals are shaped by interactions with additional intracellular organelles. Bafilomycin A1, which prevents lysosomal Ca2+ uptake by inhibiting H+ pumping into lysosomes, increased the amplitude of the initial Ca2+ signals evoked by carbachol in human embryonic kidney (HEK) cells. Carbachol alone and carbachol in combination with parathyroid hormone (PTH) evoke Ca2+ release from distinct IP3-sensitive Ca2+ stores in HEK cells stably expressing human type 1 PTH receptors. Bafilomycin A1 similarly exaggerated the Ca2+ signals evoked by carbachol or carbachol with PTH, indicating that Ca2+ released from distinct IP3-sensitive Ca2+ stores is sequestered by lysosomes. The Ca2+ signals resulting from store-operated Ca2+ entry, whether evoked by thapsigargin or carbachol, were unaffected by bafilomycin A1. Using Gd3+ (1 mM) to inhibit both Ca2+ entry and Ca2+ extrusion, HEK cells were repetitively stimulated with carbachol to assess the effectiveness of Ca2+ recycling to the ER after IP3-evoked Ca2+ release. Blocking lysosomal Ca2+ uptake with bafilomycin A1 increased the amplitude of each carbachol-evoked Ca2+ signal without affecting the rate of Ca2+ recycling to the ER. This suggests that Ca2+ accumulated by lysosomes is rapidly returned to the ER. We conclude that lysosomes rapidly, reversibly and selectively accumulate the Ca2+ released by IP3 receptors residing within distinct Ca2+ stores, but not the Ca2+ entering cells via receptor-regulated, store-operated Ca2+ entry pathways.
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Affiliation(s)
| | - Stephen C. Tovey
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
| | - Colin W. Taylor
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
- * E-mail:
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102
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Galione A. A primer of NAADP-mediated Ca(2+) signalling: From sea urchin eggs to mammalian cells. Cell Calcium 2014; 58:27-47. [PMID: 25449298 DOI: 10.1016/j.ceca.2014.09.010] [Citation(s) in RCA: 98] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Revised: 09/28/2014] [Accepted: 09/29/2014] [Indexed: 02/04/2023]
Abstract
Since the discovery of the Ca(2+) mobilizing effects of the pyridine nucleotide metabolite, nicotinic acid adenine dinucleotide phosphate (NAADP), this molecule has been demonstrated to function as a Ca(2+) mobilizing intracellular messenger in a wide range of cell types. In this review, I will briefly summarize the distinct principles behind NAADP-mediated Ca(2+) signalling before going on to outline the role of this messenger in the physiology of specific cell types. Central to the discussion here is the finding that NAADP principally mobilizes Ca(2+) from acidic organelles such as lysosomes and it is this property that allows NAADP to play a unique role in intracellular Ca(2+) signalling. Lysosomes and related organelles are small Ca(2+) stores but importantly may also initiate a two-way dialogue with other Ca(2+) storage organelles to amplify Ca(2+) release, and may be strategically localized to influence localized Ca(2+) signalling microdomains. The study of NAADP signalling has created a new and fruitful focus on the lysosome and endolysosomal system as major players in calcium signalling and pathophysiology.
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Affiliation(s)
- Antony Galione
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.
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103
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Abstract
In the 30 years since IP3 (inositol 1,4,5-trisphosphate) was first shown to release Ca2+ from intracellular stores, the importance of spatially organized interactions within IP3-regulated signalling pathways has been universally recognized. Recent evidence that addresses three different levels of the structural determinants of IP3-evoked Ca2+ signalling is described in the present review. High-resolution structures of the N-terminal region of the IP3R (IP3 receptor) have established that the two essential phosphate groups of IP3 bind to opposite sides of the IP3-binding site, pulling its two domains together. This conformational change is proposed to disrupt an interaction between adjacent subunits within the tetrameric IP3R that normally holds the channel in a closed state. Similar structural changes are thought to allow gating of ryanodine receptors. cAMP increases the sensitivity of IP3Rs and thereby potentiates the Ca2+ signals evoked by receptors that stimulate IP3 formation. We speculate that both IP3 and cAMP are delivered to IP3Rs within signalling junctions, wherein the associated IP3Rs are exposed to a saturating concentration of either messenger. The concentration-dependent effects of extracellular stimuli come from recruitment of junctions rather than from a graded increase in the activity of individual junctions. IP3Rs within 'IP3 junctions' respond directly to receptors that stimulate phospholipase C, whereas extra-junctional IP3Rs are exposed to suboptimal concentrations of IP3 and open only when they are sensitized by cAMP. These results highlight the importance of selective delivery of diffusible messengers to IP3Rs. The spatial organization of IP3Rs also allows them to direct Ca2+ to specific intracellular targets that include other IP3Rs, mitochondria and Ca2+-regulated channels and enzymes. IP3Rs also interact functionally with lysosomes because Ca2+ released by IP3Rs, but not that entering cells via store-operated Ca2+ entry pathways, is selectively accumulated by lysosomes. This Ca2+ uptake shapes the Ca2+ signals evoked by IP3 and it may regulate lysosomal behaviour.
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104
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105
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Guerrero-Hernandez A, Gallegos-Gomez ML, Sanchez-Vazquez VH, Lopez-Mendez MC. Acidic intracellular Ca(2+) stores and caveolae in Ca(2+) signaling and diabetes. Cell Calcium 2014; 56:323-31. [PMID: 25182518 DOI: 10.1016/j.ceca.2014.08.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Accepted: 08/07/2014] [Indexed: 12/19/2022]
Abstract
Acidic Ca(2+) stores, particularly lysosomes, are newly discovered players in the well-orchestrated arena of Ca(2+) signaling and we are at the verge of understanding how lysosomes accumulate Ca(2+) and how they release it in response to different chemical, such as NAADP, and physical signals. Additionally, it is now clear that lysosomes play a key role in autophagy, a process that allows cells to recycle components or to eliminate damaged structures to ensure cellular well-being. Moreover, lysosomes are being unraveled as hubs that coordinate both anabolism via insulin signaling and catabolism via AMPK. These acidic vesicles have close contact with the ER and there is a bidirectional movement of information between these two organelles that exquisitely regulates cell survival. Lysosomes also connect with plasma membrane where caveolae are located as specialized regions involved in Ca(2+) and insulin signaling. Alterations of all these signaling pathways are at the core of insulin resistance and diabetes.
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106
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Penny CJ, Kilpatrick BS, Han JM, Sneyd J, Patel S. A computational model of lysosome-ER Ca2+ microdomains. J Cell Sci 2014; 127:2934-43. [PMID: 24706947 DOI: 10.1242/jcs.149047] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Acidic organelles form an important intracellular Ca(2+) pool that can drive global Ca(2+) signals through coupling with endoplasmic reticulum (ER) Ca(2+) stores. Recently identified lysosome-ER membrane contact sites might allow formation of Ca(2+) microdomains, although their size renders observation of Ca(2+) dynamics impractical. Here, we generated a computational model of lysosome-ER coupling that incorporated a previous model of the inositol trisphosphate (IP3) receptor as the ER Ca(2+) 'amplifier' and lysosomal leaks as the Ca(2+) 'trigger'. The model qualitatively described global Ca(2+) responses to the lysosomotropic agent GPN, which caused a controlled but substantial depletion of small solutes from the lysosome. Adapting this model to physiological lysosomal leaks induced by the Ca(2+) mobilising messenger NAADP demonstrated that lysosome-ER microdomains are capable of driving global Ca(2+) oscillations. Interestingly, our simulations suggest that the microdomain [Ca(2+)] need not be higher than that in the cytosol for responses to occur, thus matching the relatively high affinity of IP3 receptors for Ca(2+). The relative distribution and overall density of the lysosomal leaks dictated whether microdomains triggered or modulated global signals. Our data provide a computational framework for probing lysosome-ER Ca(2+) dynamics.
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Affiliation(s)
- Christopher J Penny
- Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK
| | - Bethan S Kilpatrick
- Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK
| | - Jung Min Han
- Department of Mathematics, University of Auckland, Auckland 1142, New Zealand
| | - James Sneyd
- Department of Mathematics, University of Auckland, Auckland 1142, New Zealand
| | - Sandip Patel
- Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK
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107
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van der Kant R, Neefjes J. Small regulators, major consequences - Ca²⁺ and cholesterol at the endosome-ER interface. J Cell Sci 2014; 127:929-38. [PMID: 24554437 DOI: 10.1242/jcs.137539] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The ER is the largest cellular compartment and a major storage site for lipids and ions. In recent years, much attention has focused on contacts between the ER and other organelles, and one particularly intimate relationship is that between the ER and the endosomal system. ER-endosome contacts intensify when endosomes mature, and the ER participates in endosomal processes, such as the termination of surface receptor signaling, multi-vesicular body formation, and transport and fusion events. Cholesterol and Ca(2+) are transferred between the ER and endosomes, possibly acting as messengers for ER-endosome crosstalk. Here, we summarize different types of ER-endosomal communication and discuss membrane contact sites that might facilitate this crosstalk. We review the protein pairs that interact at the ER-endosome interface and find that many of these have a role in cholesterol exchange. We also summarize Ca(2+) exchange between the ER and endosomes, and hypothesize that ER-endosome contacts integrate several cellular functions to guide endosomal maturation. We post the hypothesis that failure in ER-endosome contacts is an unrecognized but important contributor to diseases, such as Niemann-Pick type C disease, Alzheimer's disease and amyotrophic lateral sclerosis.
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Affiliation(s)
- Rik van der Kant
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA
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108
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Lam AK, Galione A. The endoplasmic reticulum and junctional membrane communication during calcium signaling. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2542-59. [DOI: 10.1016/j.bbamcr.2013.06.004] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 06/03/2013] [Accepted: 06/03/2013] [Indexed: 12/13/2022]
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109
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Li X, Garrity AG, Xu H. Regulation of membrane trafficking by signalling on endosomal and lysosomal membranes. J Physiol 2013; 591:4389-401. [PMID: 23878375 DOI: 10.1113/jphysiol.2013.258301] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Endosomal and lysosomal membrane trafficking requires the coordination of multiple signalling events to control cargo sorting and processing, and endosome maturation. The initiation and termination of signalling events in endosomes and lysosomes is not well understood, but several key regulators have been identified, which include small GTPases, phosphoinositides, and Ca2+. Small GTPases act as master regulators and molecular switches in a GTP-dependent manner, initiating signalling cascades to regulate the direction and specificity of endosomal trafficking. Phosphoinositides are membrane-bound lipids that indicate vesicular identities for recruiting specific cytoplasmic proteins to endosomal membranes, thus allowing specificity of membrane fusion, fission, and cargo sorting to occur within and between specific vesicle compartments. In addition, phosphoinositides regulate the function of membrane proteins such as ion channels and transporters in a compartment-specific manner to mediate transport and signalling. Finally, Ca2+, a locally acting second messenger released from intracellular ion channels, may provide precise spatiotemporal regulation of endosomal signalling and trafficking events. Small GTPase signalling can regulate phosphoinositide conversion during endosome maturation, and electrophysiological studies on isolated endosomes have shown that endosomal and lysosomal Ca2+ channels are directly modulated by endosomal lipids. Thus trafficking and maturation of endosomes and lysosomes can be precisely regulated by dynamic changes in GTPases and membrane lipids, as well as Ca2+ signalling. Importantly, impaired phosphoinositide and Ca2+ signalling can cause endosomal and lysosomal trafficking defects at the cellular level, and a spectrum of lysosome storage diseases.
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Affiliation(s)
- Xinran Li
- H. Xu: University of Michigan, MCDB, 3089 Natural Science Building (Kraus), 830 North University, Ann Arbor, MI 48109, USA.
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110
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Decuypere JP, Paudel RC, Parys J, Bultynck G. Intracellular Ca(2+) signaling: A novel player in the canonical mTOR-controlled autophagy pathway. Commun Integr Biol 2013; 6:e25429. [PMID: 24265855 PMCID: PMC3829968 DOI: 10.4161/cib.25429] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 06/17/2013] [Indexed: 01/08/2023] Open
Abstract
Functional intracellular Ca(2+) signaling is essential for the upregulation of the canonical mTOR-controlled autophagy pathway triggered by rapamycin or by nutrient deprivation. Moreover, modifications in the Ca(2+)-signaling machinery coincide with autophagy stimulation. This results in enhanced intracellular Ca(2+) signaling essential for driving the autophagy process. Yet, the mechanisms upstream (the players causing the changes in Ca(2+) signaling) and downstream (the targets of the altered Ca(2+) signals) of this Ca(2+)-dependent autophagy pathway remain elusive. Here, we speculate about these mechanisms based on our current knowledge.
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Affiliation(s)
- Jean-Paul Decuypere
- Laboratory of Molecular and Cellular Signaling; Department of Cellular and Molecular Medicine; KU Leuven; Leuven, Belgium ; Current affiliation: Laboratory of Abdominal Transplant Surgery; Department of Microbiology and Immunology; University Hospitals Leuven; KU Leuven; Leuven, Belgium
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111
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Abstract
NAADP is a potent Ca2+ mobilizing messenger [1-3]. Since its discovery in 1995 [4] a considerable volume of literature has shown that NAADP couples cell stimulation to endolysosomal Ca2+ release and thereby the regulation of many cellular functions [5]. However definition of its molecular mechanism of action has proved far from easy. Since 2009, a consensus emerged as several independent groups coalesced upon the two-pore channel (TPC) family as NAADP-activated channels essential for Ca2+ release from endolysosomal Ca2+ stores [6-8]. However this view has been recently challenged by data clearly showing that TPCs function as Na+-selective channels apparently insensitive to NAADP [9;10]. Given the two fundamental characteristics defining an ion channel comprise the opening stimulus and the nature of the permeant ions, scrutiny of these seeming irreconcilable viewpoints is essential. The purpose of this commentary is to distil the remaining consensus while interrogating these divergent viewpoints. From this analysis, critical experimental needs are identified.
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Affiliation(s)
- Jonathan S Marchant
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
| | - Sandip Patel
- Department of Cell and Developmental Biology, University College London, London, UK
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112
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Jiang YL, Lin AHY, Xia Y, Lee S, Paudel O, Sun H, Yang XR, Ran P, Sham JSK. Nicotinic acid adenine dinucleotide phosphate (NAADP) activates global and heterogeneous local Ca2+ signals from NAADP- and ryanodine receptor-gated Ca2+ stores in pulmonary arterial myocytes. J Biol Chem 2013; 288:10381-94. [PMID: 23443655 PMCID: PMC3624421 DOI: 10.1074/jbc.m112.423053] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Revised: 02/08/2013] [Indexed: 11/06/2022] Open
Abstract
Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent Ca(2+)-mobilizing messenger that releases Ca(2+) from endolysosomal organelles. Recent studies showed that NAADP-induced Ca(2+) release is mediated by the two-pore channels (TPCs) TPC1 and TPC2. However, the expression of TPCs and the NAADP-induced local Ca(2+) signals have not been examined in vascular smooth muscle. Here, we found that both TPC1 and TPC2 are expressed in rat pulmonary arterial smooth muscle cells (PASMCs), with TPC1 being the major subtype. Application of membrane-permeant NAADP acetoxymethyl ester to PASMCs elicited a biphasic increase in global [Ca(2+)]i, which was independent of extracellular Ca(2+) and blocked by the NAADP antagonist Ned-19 or the vacuolar H(+)-ATPase inhibitor bafilomycin A1, indicating Ca(2+) release from acidic endolysosomal Ca(2+) stores. The Ca(2+) response was unaffected by xestospongin C but was partially blocked by ryanodine or thapsigargin. NAADP triggered heterogeneous local Ca(2+) signals, including a diffuse increase in cytosolic [Ca(2+)], Ca(2+) sparks, Ca(2+) bursts, and regenerative Ca(2+) release. The diffuse Ca(2+) increase and Ca(2+) bursts were ryanodine-insensitive, presumably arising from different endolysosomal sources. Ca(2+) sparks and regenerative Ca(2+) release were inhibited by ryanodine, consistent with cross-activation of loosely coupled ryanodine receptors. Moreover, Ca(2+) release stimulated by endothelin-1 was inhibited by Ned-19, ryanodine, or xestospongin C, suggesting that NAADP-mediated Ca(2+) signals interact with both ryanodine and inositol 1,4,5-trisphosphate receptors during agonist stimulation. Our results show that NAADP mediates complex global and local Ca(2+) signals. Depending on the physiological stimuli, these diverse Ca(2+) signals may serve to regulate different cellular functions in PASMCs.
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Affiliation(s)
- Yong-Liang Jiang
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
- the State Key Laboratory of Respiratory Diseases, The First Affiliated Hospital, Guangzhou Medical University, 510120 Guangzhou, China
| | - Amanda H. Y. Lin
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
| | - Yang Xia
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
| | - Suengwon Lee
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
| | - Omkar Paudel
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
| | - Hui Sun
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
| | - Xiao-Ru Yang
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
| | - Pixin Ran
- the State Key Laboratory of Respiratory Diseases, The First Affiliated Hospital, Guangzhou Medical University, 510120 Guangzhou, China
| | - James S. K. Sham
- From the Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 and
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113
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Tovey SC, Taylor CW. Cyclic AMP directs inositol (1,4,5)-trisphosphate-evoked Ca2+ signalling to different intracellular Ca2+ stores. J Cell Sci 2013; 126:2305-13. [PMID: 23525004 DOI: 10.1242/jcs.126144] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Cholesterol depletion reversibly abolishes carbachol-evoked Ca(2+) release from inositol (1,4,5)-trisphosphate (IP3)-sensitive stores, without affecting the distribution of IP3 receptors (IP3R) or endoplasmic reticulum, IP3 formation or responses to photolysis of caged IP3. Receptors that stimulate cAMP formation do not alone evoke Ca(2+) signals, but they potentiate those evoked by carbachol. We show that these potentiated signals are entirely unaffected by cholesterol depletion and that, within individual cells, different IP3-sensitive Ca(2+) stores are released by carbachol alone and by carbachol combined with receptors that stimulate cAMP formation. We suggest that muscarinic acetylcholine receptors in lipid rafts deliver IP3 at high concentration to associated IP3R, stimulating them to release Ca(2+). Muscarinic receptors outside rafts are less closely associated with IP3R and provide insufficient local IP3 to activate IP3R directly. These IP3R, probably type 2 IP3R within a discrete Ca(2+) store, are activated only when their sensitivity is increased by cAMP. Sensitization of IP3R by cAMP extends the effective range of signalling by phospholipase C, allowing muscarinic receptors that are otherwise ineffective to recruit additional IP3-sensitive Ca(2+) stores.
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Affiliation(s)
- Stephen C Tovey
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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114
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Morgan AJ, Davis LC, Wagner SKTY, Lewis AM, Parrington J, Churchill GC, Galione A. Bidirectional Ca²⁺ signaling occurs between the endoplasmic reticulum and acidic organelles. ACTA ACUST UNITED AC 2013; 200:789-805. [PMID: 23479744 PMCID: PMC3601362 DOI: 10.1083/jcb.201204078] [Citation(s) in RCA: 125] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
After acidic organelles induce signaling to activate ER calcium ion release, local microdomains of high calcium at ER–acidic organelle junctions feed back to activate further acidic organelle calcium release. The endoplasmic reticulum (ER) and acidic organelles (endo-lysosomes) act as separate Ca2+ stores that release Ca2+ in response to the second messengers IP3 and cADPR (ER) or NAADP (acidic organelles). Typically, trigger Ca2+ released from acidic organelles by NAADP subsequently recruits IP3 or ryanodine receptors on the ER, an anterograde signal important for amplification and Ca2+ oscillations/waves. We therefore investigated whether the ER can signal back to acidic organelles, using organelle pH as a reporter of NAADP action. We show that Ca2+ released from the ER can activate the NAADP pathway in two ways: first, by stimulating Ca2+-dependent NAADP synthesis; second, by activating NAADP-regulated channels. Moreover, the differential effects of EGTA and BAPTA (slow and fast Ca2+ chelators, respectively) suggest that the acidic organelles are preferentially activated by local microdomains of high Ca2+ at junctions between the ER and acidic organelles. Bidirectional organelle communication may have wider implications for endo-lysosomal function as well as the generation of Ca2+ oscillations and waves.
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Affiliation(s)
- Anthony J Morgan
- Department of Pharmacology, University of Oxford, Oxford OX1 3QT, England, UK.
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