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Conformational surveillance of Orai1 by a rhomboid intramembrane protease prevents inappropriate CRAC channel activation. Mol Cell 2021; 81:4784-4798.e7. [PMID: 34800360 PMCID: PMC8657799 DOI: 10.1016/j.molcel.2021.10.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/14/2021] [Accepted: 10/26/2021] [Indexed: 12/19/2022]
Abstract
Calcium influx through plasma membrane calcium release-activated calcium (CRAC) channels, which are formed of hexamers of Orai1, is a potent trigger for many important biological processes, most notably in T cell-mediated immunity. Through a bioinformatics-led cell biological screen, we have identified Orai1 as a substrate for the rhomboid intramembrane protease RHBDL2. We show that RHBDL2 prevents stochastic calcium signaling in unstimulated cells through conformational surveillance and cleavage of inappropriately activated Orai1. A conserved disease-linked proline residue is responsible for RHBDL2’s recognizing the active conformation of Orai1, which is required to sharpen switch-like signaling triggered by store-operated calcium entry. Loss of RHBDL2 control of CRAC channel activity causes severe dysregulation of downstream CRAC channel effectors, including transcription factor activation, inflammatory cytokine expression, and T cell activation. We propose that this surveillance function may represent an ancient activity of rhomboid proteases in degrading unwanted signaling proteins. A screen for transmembrane substrates of the rhomboid intramembrane protease RHBDL2 RHBDL2 cleaves the CRAC channel protein Orai1 when it is inappropriately activated Conformational change in these calcium channels is recognized by RHBDL2 An Orai1 mutant that cannot be cleaved by RHBDL2 causes a human disease syndrome
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2
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Tiffner A, Derler I. Isoform-Specific Properties of Orai Homologues in Activation, Downstream Signaling, Physiology and Pathophysiology. Int J Mol Sci 2021; 22:8020. [PMID: 34360783 PMCID: PMC8347056 DOI: 10.3390/ijms22158020] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 07/21/2021] [Accepted: 07/23/2021] [Indexed: 11/21/2022] Open
Abstract
Ca2+ ion channels are critical in a variety of physiological events, including cell growth, differentiation, gene transcription and apoptosis. One such essential entry pathway for calcium into the cell is the Ca2+ release-activated Ca2+ (CRAC) channel. It consists of the Ca2+ sensing protein, stromal interaction molecule 1 (STIM1) located in the endoplasmic reticulum (ER) and a Ca2+ ion channel Orai in the plasma membrane. The Orai channel family includes three homologues Orai1, Orai2 and Orai3. While Orai1 is the "classical" Ca2+ ion channel within the CRAC channel complex and plays a universal role in the human body, there is increasing evidence that Orai2 and Orai3 are important in specific physiological and pathophysiological processes. This makes them an attractive target in drug discovery, but requires a detailed understanding of the three Orai channels and, in particular, their differences. Orai channel activation is initiated via Ca2+ store depletion, which is sensed by STIM1 proteins, and induces their conformational change and oligomerization. Upon STIM1 coupling, Orai channels activate to allow Ca2+ permeation into the cell. While this activation mechanism is comparable among the isoforms, they differ by a number of functional and structural properties due to non-conserved regions in their sequences. In this review, we summarize the knowledge as well as open questions in our current understanding of the three isoforms in terms of their structure/function relationship, downstream signaling and physiology as well as pathophysiology.
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Affiliation(s)
| | - Isabella Derler
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, A-4020 Linz, Austria;
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3
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Wendimu MY, Alqinyah M, Vella S, Dean P, Almutairi F, Davila-Rivera R, Rayatpisheh S, Wohlschlegel J, Moreno S, Hooks SB. RGS10 physically and functionally interacts with STIM2 and requires store-operated calcium entry to regulate pro-inflammatory gene expression in microglia. Cell Signal 2021; 83:109974. [PMID: 33705894 DOI: 10.1016/j.cellsig.2021.109974] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 02/19/2021] [Accepted: 03/04/2021] [Indexed: 01/14/2023]
Abstract
Chronic activation of microglia is a driving factor in the progression of neuroinflammatory diseases, and mechanisms that regulate microglial inflammatory signaling are potential targets for novel therapeutics. Regulator of G protein Signaling 10 is the most abundant RGS protein in microglia, where it suppresses inflammatory gene expression and reduces microglia-mediated neurotoxicity. In particular, microglial RGS10 downregulates the expression of pro-inflammatory mediators including cyclooxygenase 2 (COX-2) following stimulation with lipopolysaccharide (LPS). However, the mechanism by which RGS10 affects inflammatory signaling is unknown and is independent of its canonical G protein targeted mechanism. Here, we sought to identify non-canonical RGS10 interacting partners that mediate its anti-inflammatory mechanism. Through RGS10 co-immunoprecipitation coupled with mass spectrometry, we identified STIM2, an endoplasmic reticulum (ER) localized calcium sensor and a component of the store-operated calcium entry (SOCE) machinery, as a novel RGS10 interacting protein in microglia. Direct immunoprecipitation experiments confirmed RGS10-STIM2 interaction in multiple microglia and macrophage cell lines, as well as in primary cells, with no interaction observed with the homologue STIM1. We further determined that STIM2, Orai channels, and the calcium-dependent phosphatase calcineurin are essential for LPS-induced COX-2 production in microglia, and this pathway is required for the inhibitory effect of RGS10 on COX-2. Additionally, our data demonstrated that RGS10 suppresses SOCE triggered by ER calcium depletion and that ER calcium depletion, which induces SOCE, amplifies pro-inflammatory genes. In addition to COX-2, we also show that RGS10 suppresses the expression of pro-inflammatory cytokines in microglia in response to thrombin and LPS stimulation, and all of these effects require SOCE. Collectively, the physical and functional links between RGS10 and STIM2 suggest a complex regulatory network connecting RGS10, SOCE, and pro-inflammatory gene expression in microglia, with broad implications in the pathogenesis and treatment of chronic neuroinflammation.
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Affiliation(s)
- Menbere Y Wendimu
- From the Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, United States of America
| | - Mohammed Alqinyah
- From the Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, United States of America
| | - Stephen Vella
- Department of Cellular Biology, University of Georgia, Athens, GA 30602, United States of America
| | - Phillip Dean
- From the Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, United States of America
| | - Faris Almutairi
- From the Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, United States of America
| | - Roseanne Davila-Rivera
- From the Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, United States of America
| | - Shima Rayatpisheh
- Department of Biological Chemistry, University of California, Los Angeles 90095, United States of America
| | - James Wohlschlegel
- Department of Biological Chemistry, University of California, Los Angeles 90095, United States of America
| | - Silvia Moreno
- Department of Cellular Biology, University of Georgia, Athens, GA 30602, United States of America
| | - Shelley B Hooks
- From the Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, United States of America.
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4
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Alansary D, Peckys DB, Niemeyer BA, de Jonge N. Detecting single ORAI1 proteins within the plasma membrane reveals higher-order channel complexes. J Cell Sci 2020; 133:jcs.240358. [PMID: 31822631 DOI: 10.1242/jcs.240358] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Accepted: 12/02/2019] [Indexed: 12/22/2022] Open
Abstract
ORAI1 proteins form highly selective Ca2+ channels in the plasma membrane. Crystallographic data point towards a hexameric stoichiometry of ORAI1 channels, whereas optical methods postulated ORAI1 channels to reside as dimers at rest, and other data suggests that they have a tetrameric configuration. Here, liquid-phase scanning transmission electron microscopy (STEM) and quantum dot (QD) labeling was utilized to study the conformation of ORAI1 proteins at rest. To address the question of whether ORAI1 was present as a dimer, experiments were designed using single ORAI1 monomers and covalently linked ORAI1 dimers with either one or two label-binding positions. The microscopic data was statistically analyzed via the pair correlation function. Label pairs were found in all cases, even for concatenated dimers with one label-binding position, which is only possible if a significant fraction of ORAI1 was assembled in larger order oligomers than dimers, binding at least two QDs. This interpretation of the data was consistent with Blue Native PAGE analysis showing that ORAI1 is mainly present as a complex of an apparent molecular mass larger than that calculated for a dimer.
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Affiliation(s)
- Dalia Alansary
- Molecular Biophysics, University of Saarland, Center for Integrative Physiology and Molecular Medicine, 66421 Homburg/Saar, Germany
| | - Diana B Peckys
- Molecular Biophysics, University of Saarland, Center for Integrative Physiology and Molecular Medicine, 66421 Homburg/Saar, Germany
| | - Barbara A Niemeyer
- Molecular Biophysics, University of Saarland, Center for Integrative Physiology and Molecular Medicine, 66421 Homburg/Saar, Germany
| | - Niels de Jonge
- INM - Leibniz Institute for New Materials, 66123 Saarbrücken, Germany .,Department of Physics, University of Saarland, 66123 Saarbrücken, Germany
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5
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Cai X, Nwokonko RM, Loktionova NA, Abdulqadir R, Baraniak JH, Wang Y, Trebak M, Zhou Y, Gill DL. Pore properties of Orai1 calcium channel dimers and their activation by the STIM1 ER calcium sensor. J Biol Chem 2018; 293:12962-12974. [PMID: 29954946 PMCID: PMC6102135 DOI: 10.1074/jbc.ra118.003424] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Revised: 05/31/2018] [Indexed: 11/06/2022] Open
Abstract
Store-operated Ca2+ entry signals are mediated by plasma membrane Orai channels activated through intermembrane coupling with Ca2+-sensing STIM proteins in the endoplasmic reticulum (ER). The nature of this elaborate Orai-gating mechanism has remained enigmatic. Based on the Drosophila Orai structure, mammalian Orai1 channels are hexamers comprising three dimeric subunit pairs. We utilized concatenated Orai1 dimers to probe the function of key domains within the channel pore and gating regions. The Orai1-E106Q selectivity-filter mutant, widely considered a dominant pore blocker, was surprisingly nondominant within concatenated heterodimers with Orai1-WT. The Orai1-E106Q/WT heterodimer formed STIM1-activated nonselective cation channels with significantly enlarged apparent pore diameter. Other Glu-106 substitutions entirely blocked the function of heterodimers with Orai1-WT. The hydrophobic pore-lining mutation V102C, which constitutively opens channels, was suppressed by Orai1-WT in the heterodimer. In contrast, the naturally occurring R91W pore-lining mutation associated with human immunodeficiency was completely dominant-negative over Orai-WT in heterodimers. Heterodimers containing the inhibitory K85E mutation extending outward from the pore helix gave an interesting partial effect on both channel activation and STIM1 binding, indicating an important allosteric link between the cytosolic Orai1 domains. The Orai1 C-terminal STIM1-binding domain mutation L273D powerfully blocked STIM1-induced channel activation. The Orai1-L273D/WT heterodimer had drastically impaired STIM1-induced channel gating but, unexpectedly, retained full STIM1 binding. This reveals the critical role of Leu-273 in transducing the STIM1-binding signal into the allosteric conformational change that initiates channel gating. Overall, our results provide important new insights into the role of key functional domains that mediate STIM1-induced gating of the Orai1 channel.
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Affiliation(s)
- Xiangyu Cai
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Robert M Nwokonko
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Natalia A Loktionova
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Raz Abdulqadir
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - James H Baraniak
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Youjun Wang
- Beijing Key Laboratory of Gene Resources and Molecular Development College of Life Sciences, Beijing Normal University, Beijing 100875, China
| | - Mohamed Trebak
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Yandong Zhou
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
| | - Donald L Gill
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
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Kang N, Kang JY, Park S, Shin DM. Increased store-operated Ca 2+ entry mediated by GNB5 and STIM1. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2018; 22:343-348. [PMID: 29719456 PMCID: PMC5928347 DOI: 10.4196/kjpp.2018.22.3.343] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 02/14/2018] [Accepted: 02/19/2018] [Indexed: 01/27/2023]
Abstract
Recent human genetic studies have shown that Gβ5 is related to various clinical symptoms, such as sinus bradycardia, cognitive disability, and attention deficit hyperactivity disorder. Although the calcium signaling cascade is closely associated with a heterotrimeric G-protein, the function of Gβ5 in calcium signaling and its relevance to clinical symptoms remain unknown. In this study, we investigated the in vitro changes of store-operated calcium entry (SOCE) with exogenous expression of Gβ5. The cells expressing Gβ5 had enhanced SOCE after depletion of calcium ion inside the endoplasmic reticulum. Gβ5 also augmented Stim1- and Orai1-dependent SOCE. An ORAI1 loss-of-function mutant did not show inhibition of Gβ5-induced SOCE, and a STIM1-ERM truncation mutant showed no enhancement of SOCE. These results suggested a novel role of GNB5 and Stim1, and provided insight into the regulatory mechanism of SOCE.
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Affiliation(s)
- Namju Kang
- Department of Oral Biology, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul 03722, Korea
| | - Jung Yun Kang
- Department of Oral Biology, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul 03722, Korea
| | - Soonhong Park
- Department of Oral Biology, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul 03722, Korea
| | - Dong Min Shin
- Department of Oral Biology, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul 03722, Korea
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Ohba T, Watanabe H, Murakami M, Iino K, Adachi T, Baba Y, Kurosaki T, Ono K, Ito H. Stromal interaction molecule 1 haploinsufficiency causes maladaptive response to pressure overload. PLoS One 2017; 12:e0187950. [PMID: 29145451 PMCID: PMC5690472 DOI: 10.1371/journal.pone.0187950] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Accepted: 10/14/2017] [Indexed: 11/18/2022] Open
Abstract
Stromal interaction molecule 1 (STIM1), an endo/sarcoplasmic reticulum Ca2+ sensor, has been shown to control a Ca2+-dependent signal that promotes cardiac hypertrophy. However, whether STIM1 has adaptive role that helps to protect against cardiac overload stress remains unknown. We hypothesized that STIM1 deficiency causes a maladaptive response to pressure overload stress. We investigated STIM1 heterozygous KO (STIM1+/–) mice hearts, in which STIM1 protein levels decreased to 27% of wild-type (WT) with no compensatory increase in STIM2. Under stress-free conditions, no significant differences were observed in electrocardiographic and echocardiographic parameters or blood pressure between STIM1+/–and WT mice. However, when STIM1+/–mice were subjected to transverse aortic constriction (TAC), STIM1+/–mice had a higher mortality rate than WT mice. The TAC-induced increase in the heart weight to body weight ratio (mean mg/g ± standard error of the mean) was significantly inhibited in STIM1+/–mice (WT sham, 4.12 ± 0.14; WT TAC, 6.23 ± 0.40; STIM1+/–sham, 4.53 ± 0.16; STIM1+/–TAC, 4.63 ± 0.08). Reverse transcription-polymerase chain reaction analysis of the left ventricles of TAC-treated STIM1+/–mice showed inhibited induction of cardiac fetal genes, including those encoding brain and atrial natriuretic proteins. Western blot analysis showed upregulated expression of transient receptor potential channel 1 (TRPC1) in TAC-treated WT mice, but suppressed expression in TAC-treated STIM1+/–mice. Taken together, the hearts of STIM1 haploinsufficient mice had a superficial resemblance to the WT phenotype under stress-free conditions; however, STIM1 haploinsufficient mice showed a maladaptive response to cardiac pressure overload.
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Affiliation(s)
- Takayoshi Ohba
- Department of Cell Physiology, Akita University Graduate School of Medicine, Akita, Japan
| | - Hiroyuki Watanabe
- Department of Cardiovascular and Respiratory Medicine, Akita University Graduate School of Medicine, Akita, Japan
- * E-mail:
| | - Manabu Murakami
- Department of Pharmacology, Hirosaki University, Graduate School of Medicine, Aomori, Japan
| | - Kenji Iino
- Department of Cardiovascular and Respiratory Medicine, Akita University Graduate School of Medicine, Akita, Japan
| | - Takeshi Adachi
- Department of Cell Physiology, Akita University Graduate School of Medicine, Akita, Japan
| | - Yoshihiro Baba
- Laboratory for Lymphocyte Differentiation, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Tomohiro Kurosaki
- Laboratory for Lymphocyte Differentiation, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Kyoichi Ono
- Department of Cell Physiology, Akita University Graduate School of Medicine, Akita, Japan
| | - Hiroshi Ito
- Department of Cardiovascular and Respiratory Medicine, Akita University Graduate School of Medicine, Akita, Japan
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Altered mitochondrial function, capacitative calcium entry and contractions in the aorta of hypertensive rats. J Hypertens 2017; 35:1594-1608. [PMID: 28403042 DOI: 10.1097/hjh.0000000000001360] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
OBJECTIVE It has been suggested that Ca entry through store-operated Ca channels (SOCs) is regulated by a dynamic interplay between the endoplasmic reticulum Ca stores and the mitochondria. These relationships drive the activation and inactivation of SOCs, yet it remains unclear whether this regulation of SOCs by mitochondria is altered in the aorta of spontaneously hypertensive rats (SHRs). METHODS We performed a thorough study of the mitochondrial membrane potential, the ability of mitochondria to deal with cytosolic Ca, capacitative Ca entry (CCE), and stromal interaction molecule 1 (STIM1) and calcium release-activated calcium modulator 1 (orai1) protein expression, as well as the contractile capacity of aortic rings, in normotensive Wistar Kyoto rats (WKYs) and SHRs. RESULTS Changes were observed in aortic tissue and cultured vascular smooth muscle cells isolated from SHRs relative to WKYs, including more depolarized mitochondria, stronger CCE upon the addition of Ca, larger cytosolic Ca transients (cytosolic Ca concentration) or aortic ring contraction elicited by endoplasmic reticulum depletion and a significant increase in STIM1 protein expression but not of orai1. CONCLUSION These results suggest that the impaired Ca buffering capacity of partially depolarized mitochondria dysregulates CCE, leading to overfilling of the endoplasmic reticulum Ca store through enhanced STIM1/orai1 interactions and an increase in aorta contractions in SHRs. Thus, understanding the implications of the alterations to STIM1/orai1, and their relationship to mitochondria, may aid drug development and therapeutic strategies to treat hypertension, as well as its long-term sequelae in poorly controlled patients.
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Pathophysiological Significance of Store-Operated Calcium Entry in Megakaryocyte Function: Opening New Paths for Understanding the Role of Calcium in Thrombopoiesis. Int J Mol Sci 2016; 17:ijms17122055. [PMID: 27941645 PMCID: PMC5187855 DOI: 10.3390/ijms17122055] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 11/28/2016] [Accepted: 11/28/2016] [Indexed: 12/16/2022] Open
Abstract
Store-Operated Calcium Entry (SOCE) is a universal calcium (Ca2+) influx mechanism expressed by several different cell types. It is now known that Stromal Interaction Molecule (STIM), the Ca2+ sensor of the intracellular compartments, together with Orai and Transient Receptor Potential Canonical (TRPC), the subunits of Ca2+ permeable channels on the plasma membrane, cooperate in regulating multiple cellular functions as diverse as proliferation, differentiation, migration, gene expression, and many others, depending on the cell type. In particular, a growing body of evidences suggests that a tight control of SOCE expression and function is achieved by megakaryocytes along their route from hematopoietic stem cells to platelet production. This review attempts to provide an overview about the SOCE dynamics in megakaryocyte development, with a focus on most recent findings related to its involvement in physiological and pathological thrombopoiesis.
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10
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The STIM1-binding site nexus remotely controls Orai1 channel gating. Nat Commun 2016; 7:13725. [PMID: 27929067 PMCID: PMC5155162 DOI: 10.1038/ncomms13725] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 10/26/2016] [Indexed: 01/17/2023] Open
Abstract
The ubiquitously expressed Orai Ca2+ channels are gated through a unique process of intermembrane coupling with the Ca2+-sensing STIM proteins. Despite the significance of Orai1-mediated Ca2+ signals, how gating of Orai1 is triggered by STIM1 remains unknown. A widely held gating model invokes STIM1 binding directly to Orai1 pore-forming helix. Here we report that an Orai1 C-terminal STIM1-binding site, situated far from the N-terminal pore helix, alone provides the trigger that is necessary and sufficient for channel gating. We identify a critical ‘nexus' within Orai1 connecting the peripheral C-terminal STIM1-binding site to the Orai1 core helices. Mutation of the nexus transforms Orai1 into a persistently open state exactly mimicking the action of STIM1. We suggest that the Orai1 nexus transduces the STIM1-binding signal through a conformational change in the inner core helices, and that STIM1 remotely gates the Orai1 channel without the necessity for direct STIM1 contact with the pore-forming helix.
How plasma membrane Orai Ca2+ channels are activated by STIM proteins to activate Ca2+ signals is still not fully known. Here the authors show that a nexus region located at the Orai1 C-terminus allows channel gating without a direct interaction of STIM1 with the channel pore.
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11
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Cai X, Zhou Y, Nwokonko RM, Loktionova NA, Wang X, Xin P, Trebak M, Wang Y, Gill DL. The Orai1 Store-operated Calcium Channel Functions as a Hexamer. J Biol Chem 2016; 291:25764-25775. [PMID: 27780862 DOI: 10.1074/jbc.m116.758813] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 10/17/2016] [Indexed: 12/17/2022] Open
Abstract
Orai channels mediate store-operated Ca2+ signals crucial in regulating transcription in many cell types, and implicated in numerous immunological and inflammatory disorders. Despite their central importance, controversy surrounds the basic subunit structure of Orai channels, with several biochemical and biophysical studies suggesting a tetrameric structure yet crystallographic evidence indicating a hexamer. We systematically investigated the subunit configuration of the functional Orai1 channel, generating a series of tdTomato-tagged concatenated Orai1 channel constructs (dimers to hexamers) expressed in CRISPR-derived ORAI1 knock-out HEK cells, stably expressing STIM1-YFP. Surface biotinylation demonstrated that the full-length concatemers were surface membrane-expressed. Unexpectedly, Orai1 dimers, trimers, tetramers, pentamers, and hexamers all mediated similar and substantial store-operated Ca2+ entry. Moreover, each Orai1 concatemer mediated Ca2+ currents with inward rectification and reversal potentials almost identical to those observed with expressed Orai1 monomer. In Orai1 tetramers, subunit-specific replacement with Orai1 E106A "pore-inactive" subunits revealed that functional channels utilize only the N-terminal dimer from the tetramer. In contrast, Orai1 E106A replacement in Orai1 hexamers established that all the subunits can contribute to channel formation, indicating a hexameric channel configuration. The critical Ca2+ selectivity filter-forming Glu-106 residue may mediate Orai1 channel assembly around a central Ca2+ ion within the pore. Thus, multiple E106A substitutions in the Orai1 hexamer may promote an alternative "trimer-of-dimers" channel configuration in which the C-terminal E106A subunits are excluded from the hexameric core. Our results argue strongly against a tetrameric configuration for Orai1 channels and indicate that the Orai1 channel functions as a hexamer.
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Affiliation(s)
- Xiangyu Cai
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Yandong Zhou
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Robert M Nwokonko
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Natalia A Loktionova
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Xianming Wang
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Ping Xin
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Mohamed Trebak
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Youjun Wang
- the Beijing Key Laboratory of Gene Resources and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, China
| | - Donald L Gill
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
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12
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Shaikh S, Troncoso R, Criollo A, Bravo-Sagua R, García L, Morselli E, Cifuentes M, Quest AFG, Hill JA, Lavandero S. Regulation of cardiomyocyte autophagy by calcium. Am J Physiol Endocrinol Metab 2016; 310:E587-E596. [PMID: 26884385 PMCID: PMC4835942 DOI: 10.1152/ajpendo.00374.2015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Accepted: 02/10/2016] [Indexed: 11/22/2022]
Abstract
Calcium signaling plays a crucial role in a multitude of events within the cardiomyocyte, including cell cycle control, growth, apoptosis, and autophagy. With respect to calcium-dependent regulation of autophagy, ion channels and exchangers, receptors, and intracellular mediators play fundamental roles. In this review, we discuss calcium-dependent regulation of cardiomyocyte autophagy, a lysosomal mechanism that is often cytoprotective, serving to defend against disease-related stress and nutrient insufficiency. We also highlight the importance of the subcellular distribution of calcium and related proteins, interorganelle communication, and other key signaling events that govern cardiomyocyte autophagy.
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Affiliation(s)
- Soni Shaikh
- Advanced Center for Chronic Disease and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas and Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Rodrigo Troncoso
- Advanced Center for Chronic Disease and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas and Facultad de Medicina, Universidad de Chile, Santiago, Chile
- Instituto de Nutrición y Tecnología de los Alimentos, Universidad de Chile, Santiago, Chile
| | - Alfredo Criollo
- Advanced Center for Chronic Disease and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas and Facultad de Medicina, Universidad de Chile, Santiago, Chile
- Instituto de Investigación en Ciencias Odontológicas, Facultad de Odontología, Universidad de Chile, Santiago, Chile
| | - Roberto Bravo-Sagua
- Advanced Center for Chronic Disease and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas and Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Lorena García
- Advanced Center for Chronic Disease and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas and Facultad de Medicina, Universidad de Chile, Santiago, Chile
- Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias Quimicas y Farmaceuticas, Universidad de Chile, Santiago, Chile
| | - Eugenia Morselli
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Mariana Cifuentes
- Instituto de Nutrición y Tecnología de los Alimentos, Universidad de Chile, Santiago, Chile
| | - Andrew F G Quest
- Advanced Center for Chronic Disease and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas and Facultad de Medicina, Universidad de Chile, Santiago, Chile
- Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile; and
| | - Joseph A Hill
- Departments of Internal Medicine (Cardiology Division) and
- Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Sergio Lavandero
- Advanced Center for Chronic Disease and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas and Facultad de Medicina, Universidad de Chile, Santiago, Chile;
- Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias Quimicas y Farmaceuticas, Universidad de Chile, Santiago, Chile
- Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile; and
- Departments of Internal Medicine (Cardiology Division) and
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Saul S, Stanisz H, Backes CS, Schwarz EC, Hoth M. How ORAI and TRP channels interfere with each other: interaction models and examples from the immune system and the skin. Eur J Pharmacol 2013; 739:49-59. [PMID: 24291108 DOI: 10.1016/j.ejphar.2013.10.071] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 10/08/2013] [Accepted: 10/17/2013] [Indexed: 11/16/2022]
Abstract
Four types of Ca(2+) selective ion channels are known, ten voltage gated Ca(2+) (CaV) channels, four CatSper channels, three store operated CRAC channels (ORAI channels) and at least two members of the TRPV subfamily (TRPV5, TRPV6). Some of the other TRP channels also show some Ca(2+) selectivity like certain splice variants of TRPM3. In addition to Ca(2+) selective channels, various cation channels play an important role for Ca(2+) entry and furthermore, they may also regulate Ca(2+) entry through other channels by modulating the membrane potential or other means as outlined in this review. Of the different types of cation channels, TRP channels form one of the most prominent families of non-selective cation channels with functional relevance in electrically non-excitable and electrically excitable cell types. Among these, the seven channels of the TRPC subfamily are rather non-selective with very modest Ca(2+) selectivity, whereas in the other subfamilies, cation selectivity ranges from monovalent selectivity (i.e. TRPM4, TRPM5) to divalent selectivity (i.e. TRPM6, TRPM7) or Ca(2+) selectivity (i.e. TRPV5, TRPV6). Rather than discussing the heavily reviewed individual functions of ORAI or TRP channels, we summarize data and present models how TRP and ORAI may functionally interact to guide cellular functions. We focus on T lymphocytes representing a more ORAI-dominated tissue and skin as model system in which both ORAI and TRP channel have been reported to control relevant functions. We present several interaction models how ORAI and TRP may interfere with each other's function.
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Affiliation(s)
- Stephanie Saul
- Department of Biophysics, School of Medicine, Saarland University, Homburg, Germany
| | - Hedwig Stanisz
- Department of Dermatology, School of Medicine, Saarland University, Homburg, Germany
| | - Christian S Backes
- Department of Biophysics, School of Medicine, Saarland University, Homburg, Germany
| | - Eva C Schwarz
- Department of Biophysics, School of Medicine, Saarland University, Homburg, Germany
| | - Markus Hoth
- Department of Biophysics, School of Medicine, Saarland University, Homburg, Germany.
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