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Raut P, Weller SR, Obeng B, Soos BL, West BE, Potts CM, Sangroula S, Kinney MS, Burnell JE, King BL, Gosse JA, Hess ST. Cetylpyridinium chloride (CPC) reduces zebrafish mortality from influenza infection: Super-resolution microscopy reveals CPC interference with multiple protein interactions with phosphatidylinositol 4,5-bisphosphate in immune function. Toxicol Appl Pharmacol 2022; 440:115913. [PMID: 35149080 PMCID: PMC8824711 DOI: 10.1016/j.taap.2022.115913] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 01/04/2022] [Accepted: 02/04/2022] [Indexed: 01/12/2023]
Abstract
The COVID-19 pandemic raises significance for a potential influenza therapeutic compound, cetylpyridinium chloride (CPC), which has been extensively used in personal care products as a positively-charged quaternary ammonium antibacterial agent. CPC is currently in clinical trials to assess its effects on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) morbidity. Two published studies have provided mouse and human data indicating that CPC may alleviate influenza infection, and here we show that CPC (0.1 μM, 1 h) reduces zebrafish mortality and viral load following influenza infection. However, CPC mechanisms of action upon viral-host cell interaction are currently unknown. We have utilized super-resolution fluorescence photoactivation localization microscopy to probe the mode of CPC action. Reduction in density of influenza viral protein hemagglutinin (HA) clusters is known to reduce influenza infectivity: here, we show that CPC (at non-cytotoxic doses, 5-10 μM) reduces HA density and number of HA molecules per cluster within the plasma membrane of NIH-3T3 mouse fibroblasts. HA is known to colocalize with the negatively-charged mammalian lipid phosphatidylinositol 4,5-bisphosphate (PIP2); here, we show that nanoscale co-localization of HA with the PIP2-binding Pleckstrin homology (PH) reporter in the plasma membrane is diminished by CPC. CPC also dramatically displaces the PIP2-binding protein myristoylated alanine-rich C-kinase substrate (MARCKS) from the plasma membrane of rat RBL-2H3 mast cells; this disruption of PIP2 is correlated with inhibition of mast cell degranulation. Together, these findings offer a PIP2-focused mechanism underlying CPC disruption of influenza and suggest potential pharmacological use of this drug as an influenza therapeutic to reduce global deaths from viral disease.
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Affiliation(s)
- Prakash Raut
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
| | - Sasha R Weller
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Bright Obeng
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Brandy L Soos
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Bailey E West
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Christian M Potts
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Suraj Sangroula
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Marissa S Kinney
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - John E Burnell
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Benjamin L King
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA
| | - Julie A Gosse
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME, USA.
| | - Samuel T Hess
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA.
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Klein O, Azouz NP, Sagi-Eisenberg R. Measurement of Exocytosis in Genetically Manipulated Mast Cells. Methods Mol Biol 2021; 2233:181-192. [PMID: 33222135 DOI: 10.1007/978-1-0716-1044-2_12] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The hallmark of mast cell activation is secretion of immune mediators by regulated exocytosis. Measurements of mediator secretion from mast cells that are genetically manipulated by transient transfections provide a powerful tool for deciphering the underlying mechanisms of mast cell exocytosis. However, common methods to study regulated exocytosis in bulk culture of mast cells suffer from the drawback of high signal-to-noise ratio because of their failure to distinguish between the different mast cell populations, that is, genetically modified mast cells versus their non-transfected counterparts. In particular, the low transfection efficiency of mast cells poses a significant limitation on the use of conventional methodologies. To overcome this hurdle, we developed a method, which discriminates and allows detection of regulated exocytosis of transfected cells based on the secretion of a fluorescent secretory reporter. We used a plasmid encoding for Neuropeptide Y (NPY) fused to a monomeric red fluorescent protein (NPY-mRFP), yielding a fluorescent secretory granule-targeted reporter that is co-transfected with a plasmid encoding a gene of interest. Upon cell trigger, NPY-mRFP is released from the cells by regulated exocytosis, alongside the endogenous mediators. Therefore, using NPY-mRFP as a reporter for mast cell exocytosis allows either quantitative, via a fluorimeter assay, or qualitative analysis, via confocal microscopy, of the genetically manipulated mast cells. Moreover, this method may be easily modified to accommodate studies of regulated exocytosis in any other type of cell.
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Affiliation(s)
- Ofir Klein
- Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Nurit P Azouz
- Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
- Department of Pediatrics, Cincinnati Children Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - Ronit Sagi-Eisenberg
- Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
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3
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Baksheeva VE, Nemashkalova EL, Firsov AM, Zalevsky AO, Vladimirov VI, Tikhomirova NK, Philippov PP, Zamyatnin AA, Zinchenko DV, Antonenko YN, Permyakov SE, Zernii EY. Membrane Binding of Neuronal Calcium Sensor-1: Highly Specific Interaction with Phosphatidylinositol-3-Phosphate. Biomolecules 2020; 10:biom10020164. [PMID: 31973069 PMCID: PMC7072451 DOI: 10.3390/biom10020164] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 01/15/2020] [Accepted: 01/17/2020] [Indexed: 12/20/2022] Open
Abstract
Neuronal calcium sensors are a family of N-terminally myristoylated membrane-binding proteins possessing a different intracellular localization and thereby targeting unique signaling partner(s). Apart from the myristoyl group, the membrane attachment of these proteins may be modulated by their N-terminal positively charged residues responsible for specific recognition of the membrane components. Here, we examined the interaction of neuronal calcium sensor-1 (NCS-1) with natural membranes of different lipid composition as well as individual phospholipids in form of multilamellar liposomes or immobilized monolayers and characterized the role of myristoyl group and N-terminal lysine residues in membrane binding and phospholipid preference of the protein. NCS-1 binds to photoreceptor and hippocampal membranes in a Ca2+-independent manner and the binding is attenuated in the absence of myristoyl group. Meanwhile, the interaction with photoreceptor membranes is less dependent on myristoylation and more sensitive to replacement of K3, K7, and/or K9 of NCS-1 by glutamic acid, reflecting affinity of the protein to negatively charged phospholipids. Consistently, among the major phospholipids, NCS-1 preferentially interacts with phosphatidylserine and phosphatidylinositol with micromolar affinity and the interaction with the former is inhibited upon mutating of N-terminal lysines of the protein. Remarkably, NCS-1 demonstrates pronounced specific binding to phosphoinositides with high preference for phosphatidylinositol-3-phosphate. The binding does not depend on myristoylation and, unexpectedly, is not sensitive to the charge inversion mutations. Instead, phosphatidylinositol-3-phosphate can be recognized by a specific site located in the N-terminal region of the protein. These data provide important novel insights into the general mechanism of membrane binding of NCS-1 and its targeting to specific phospholipids ensuring involvement of the protein in phosphoinositide-regulated signaling pathways.
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Affiliation(s)
- Viktoriia E. Baksheeva
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; (V.E.B.); (A.M.F.); (N.K.T.); (P.P.P.); (Y.N.A.)
| | - Ekaterina L. Nemashkalova
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, 142290 Moscow Region, Russia; (E.L.N.); (S.E.P.)
| | - Alexander M. Firsov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; (V.E.B.); (A.M.F.); (N.K.T.); (P.P.P.); (Y.N.A.)
| | - Arthur O. Zalevsky
- Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, 119992 Moscow, Russia;
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences, 117997 Moscow, Russia
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, 119991 Moscow, Russia
| | - Vasily I. Vladimirov
- Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences in Pushchino, Pushchino, 142290 Moscow Region, Russia; (V.I.V.); (D.V.Z.)
| | - Natalia K. Tikhomirova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; (V.E.B.); (A.M.F.); (N.K.T.); (P.P.P.); (Y.N.A.)
| | - Pavel P. Philippov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; (V.E.B.); (A.M.F.); (N.K.T.); (P.P.P.); (Y.N.A.)
| | - Andrey A. Zamyatnin
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; (V.E.B.); (A.M.F.); (N.K.T.); (P.P.P.); (Y.N.A.)
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, 119991 Moscow, Russia
| | - Dmitry V. Zinchenko
- Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences in Pushchino, Pushchino, 142290 Moscow Region, Russia; (V.I.V.); (D.V.Z.)
| | - Yuri N. Antonenko
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; (V.E.B.); (A.M.F.); (N.K.T.); (P.P.P.); (Y.N.A.)
| | - Sergey E. Permyakov
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, 142290 Moscow Region, Russia; (E.L.N.); (S.E.P.)
| | - Evgeni Yu. Zernii
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; (V.E.B.); (A.M.F.); (N.K.T.); (P.P.P.); (Y.N.A.)
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, 119991 Moscow, Russia
- Correspondence: ; Tel.: +7-495-939-2344
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Sheats MK, Yin Q, Fang S, Park J, Crews AL, Parikh I, Dickson B, Adler KB. MARCKS and Lung Disease. Am J Respir Cell Mol Biol 2019; 60:16-27. [PMID: 30339463 DOI: 10.1165/rcmb.2018-0285tr] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
MARCKS (myristoylated alanine-rich C kinase substrate) is a prominent PKC substrate expressed in all eukaryotic cells. It is known to bind to and cross-link actin filaments, to serve as a bridge between Ca2+/calmodulin and PKC signaling, and to sequester the signaling molecule phosphatidylinositol 4,5-bisphosphate in the plasma membrane. Since the mid-1980s, this evolutionarily conserved and ubiquitously expressed protein has been associated with regulating cellular events that require dynamic actin reorganization, including cellular adhesion, migration, and exocytosis. More recently, translational studies have implicated MARCKS in the pathophysiology of a number of airway diseases, including chronic obstructive pulmonary disease, asthma, lung cancer, and acute lung injury/acute respiratory distress syndrome. This article summarizes the structure and cellular function of MARCKS (also including MARCKS family proteins and MARCKSL1 [MARCKS-like protein 1]). Evidence for MARCKS's role in several lung diseases is discussed, as are the technological innovations that took MARCKS-targeting strategies from theoretical to therapeutic. Descriptions and updates derived from ongoing clinical trials that are investigating inhalation of a MARCKS-targeting peptide as therapy for patients with chronic bronchitis, lung cancer, and ARDS are provided.
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Affiliation(s)
| | - Qi Yin
- 2 Department of Molecular Biomedical Sciences, North Carolina State University College of Veterinary Medicine, Raleigh, North Carolina; and
| | - Shijing Fang
- 2 Department of Molecular Biomedical Sciences, North Carolina State University College of Veterinary Medicine, Raleigh, North Carolina; and
| | - Joungjoa Park
- 2 Department of Molecular Biomedical Sciences, North Carolina State University College of Veterinary Medicine, Raleigh, North Carolina; and
| | - Anne L Crews
- 2 Department of Molecular Biomedical Sciences, North Carolina State University College of Veterinary Medicine, Raleigh, North Carolina; and
| | - Indu Parikh
- 3 BioMarck Pharmaceuticals, Durham, North Carolina
| | | | - Kenneth B Adler
- 2 Department of Molecular Biomedical Sciences, North Carolina State University College of Veterinary Medicine, Raleigh, North Carolina; and
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Tuna KM, Liu BC, Yue Q, Ghazi ZM, Ma HP, Eaton DC, Alli AA. Mal protein stabilizes luminal membrane PLC-β3 and negatively regulates ENaC in mouse cortical collecting duct cells. Am J Physiol Renal Physiol 2019; 317:F986-F995. [PMID: 31364376 PMCID: PMC6843038 DOI: 10.1152/ajprenal.00446.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2018] [Revised: 07/18/2019] [Accepted: 07/18/2019] [Indexed: 01/15/2023] Open
Abstract
Abnormally high epithelial Na+ channel (ENaC) activity in the aldosterone-sensitive distal nephron and collecting duct leads to hypertension. Myelin and lymphocyte (Mal) is a lipid raft-associated protein that has been previously shown to regulate Na+-K-2Cl- cotransporter and aquaporin-2 in the kidney, but it is not known whether it regulates renal ENaC. ENaC activity is positively regulated by the anionic phospholipid phosphate phosphatidylinositol 4,5-bisphosphate (PIP2). Members of the myristoylated alanine-rich C-kinase substrate (MARCKS) family increase PIP2 concentrations at the plasma membrane, whereas hydrolysis of PIP2 by phospholipase C (PLC) reduces PIP2 abundance. Our hypothesis was that Mal protein negatively regulates renal ENaC activity by stabilizing PLC protein expression at the luminal plasma membrane. We investigated the association between Mal, MARCKS-like protein, and ENaC. We showed Mal colocalizes with PLC-β3 in lipid rafts and positively regulates its protein expression, thereby reducing PIP2 availability at the plasma membrane. Kidneys of 129Sv mice injected with MAL shRNA lentivirus resulted in increased ENaC open probability in split-open renal tubules. Overexpression of Mal protein in mouse cortical collecting duct (mpkCCD) cells resulted in an increase in PLC-β3 protein expression at the plasma membrane. siRNA-mediated knockdown of MAL in mpkCCD cells resulted in a decrease in PLC-β3 protein expression and an increase in PIP2 abundance. Moreover, kidneys from salt-loaded mice showed less Mal membrane protein expression compared with non-salt-loaded mice. Taken together, Mal protein may play an essential role in the negative feedback of ENaC gating in principal cells of the collecting duct.
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Affiliation(s)
- Kubra M Tuna
- Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida
| | - Bing-Chen Liu
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Qiang Yue
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Zinah M Ghazi
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - He-Ping Ma
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Douglas C Eaton
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Abdel A Alli
- Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida
- Department of Medicine, Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
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6
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Shim JK, Caron MA, Weatherly LM, Gerchman LB, Sangroula S, Hattab S, Baez AY, Briana TJ, Gosse JA. Antimicrobial agent triclosan suppresses mast cell signaling via phospholipase D inhibition. J Appl Toxicol 2019; 39:1672-1690. [PMID: 31429102 DOI: 10.1002/jat.3884] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 07/02/2019] [Accepted: 07/03/2019] [Indexed: 12/27/2022]
Abstract
Humans are exposed to the antimicrobial agent triclosan (TCS) through use of TCS-containing products. Exposed tissues contain mast cells, which are involved in numerous biological functions and diseases by secreting various chemical mediators through a process termed degranulation. We previously demonstrated that TCS inhibits both Ca2+ influx into antigen-stimulated mast cells and subsequent degranulation. To determine the mechanism linking the TCS cytosolic Ca2+ depression to inhibited degranulation, we investigated the effects of TCS on crucial signaling enzymes activated downstream of the Ca2+ rise: protein kinase C (PKC; activated by Ca2+ and reactive oxygen species [ROS]) and phospholipase D (PLD). We found that TCS strongly inhibits PLD activity within 15 minutes post-antigen, a key mechanism of TCS mast cell inhibition. In addition, experiments using fluorescent constructs and confocal microscopy indicate that TCS delays antigen-induced translocations of PKCβII, PKCδ and PKC substrate myristoylated alanine-rich C-kinase. Surprisingly, TCS does not inhibit PKC activity or overall ability to translocate, and TCS actually increases PKC activity by 45 minutes post-antigen; these results are explained by the timing of both TCS inhibition of cytosolic Ca2+ (~15+ minutes post-antigen) and TCS stimulation of ROS (~45 minutes post-antigen). These findings demonstrate that it is incorrect to assume that all Ca2+ -dependent processes will be synchronously inhibited when cytosolic Ca2+ is inhibited by a toxicant or drug. The results offer molecular predictions of the effects of TCS on other mammalian cell types, which share these crucial signal transduction elements and provide biochemical information that may underlie recent epidemiological findings implicating TCS in human health problems.
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Affiliation(s)
- Juyoung K Shim
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine
| | - Molly A Caron
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine
| | - Lisa M Weatherly
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine.,Graduate School of Biomedical Science and Engineering, University of Maine, Orono, Maine
| | - Logan B Gerchman
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine
| | - Suraj Sangroula
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine
| | - Siham Hattab
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine
| | - Alan Y Baez
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine
| | - Talya J Briana
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine
| | - Julie A Gosse
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, Maine.,Graduate School of Biomedical Science and Engineering, University of Maine, Orono, Maine
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7
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The membrane environment of cadherin adhesion receptors: a working hypothesis. Biochem Soc Trans 2019; 47:985-995. [DOI: 10.1042/bst20180012] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Revised: 06/09/2019] [Accepted: 06/11/2019] [Indexed: 11/17/2022]
Abstract
Abstract
Classical cadherin cell adhesion receptors are integral membrane proteins that mediate cell–cell interactions, tissue integrity and morphogenesis. Cadherins are best understood to function as membrane-spanning molecular composites that couple adhesion to the cytoskeleton. On the other hand, the membrane lipid environment of the cadherins is an under-investigated aspect of their cell biology. In this review, we discuss two lines of research that show how the membrane can directly or indirectly contribute to cadherin function. Firstly, we consider how modification of its local lipid environment can potentially influence cadherin signalling, adhesion and dynamics, focusing on a role for phosphoinositide-4,5-bisphosphate. Secondly, we discuss how caveolae may indirectly regulate cadherins by modifying either the lipid composition and/or mechanical tension of the plasma membrane. Thus, we suggest that the membrane is a frontier of cadherin biology that is ripe for re-exploration.
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Zhang Q, Chao TC, Patil VS, Qin Y, Tiwari SK, Chiou J, Dobin A, Tsai CM, Li Z, Dang J, Gupta S, Urdahl K, Nizet V, Gingeras TR, Gaulton KJ, Rana TM. The long noncoding RNA ROCKI regulates inflammatory gene expression. EMBO J 2019; 38:e100041. [PMID: 30918008 PMCID: PMC6463213 DOI: 10.15252/embj.2018100041] [Citation(s) in RCA: 65] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 02/12/2019] [Accepted: 02/14/2019] [Indexed: 12/15/2022] Open
Abstract
Long noncoding RNAs (lncRNAs) can regulate target gene expression by acting in cis (locally) or in trans (non-locally). Here, we performed genome-wide expression analysis of Toll-like receptor (TLR)-stimulated human macrophages to identify pairs of cis-acting lncRNAs and protein-coding genes involved in innate immunity. A total of 229 gene pairs were identified, many of which were commonly regulated by signaling through multiple TLRs and were involved in the cytokine responses to infection by group B Streptococcus We focused on elucidating the function of one lncRNA, named lnc-MARCKS or ROCKI (Regulator of Cytokines and Inflammation), which was induced by multiple TLR stimuli and acted as a master regulator of inflammatory responses. ROCKI interacted with APEX1 (apurinic/apyrimidinic endodeoxyribonuclease 1) to form a ribonucleoprotein complex at the MARCKS promoter. In turn, ROCKI-APEX1 recruited the histone deacetylase HDAC1, which removed the H3K27ac modification from the promoter, thus reducing MARCKS transcription and subsequent Ca2+ signaling and inflammatory gene expression. Finally, genetic variants affecting ROCKI expression were linked to a reduced risk of certain inflammatory and infectious disease in humans, including inflammatory bowel disease and tuberculosis. Collectively, these data highlight the importance of cis-acting lncRNAs in TLR signaling, innate immunity, and pathophysiological inflammation.
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Affiliation(s)
- Qiong Zhang
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Ti-Chun Chao
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Veena S Patil
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Yue Qin
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Shashi Kant Tiwari
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Joshua Chiou
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | | | - Chih-Ming Tsai
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Zhonghan Li
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Jason Dang
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Shagun Gupta
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Kevin Urdahl
- Center for Infectious Disease Research (CIDR), Seattle, WA, USA
- Department of Immunology, University of Washington School of Medicine, Seattle, WA, USA
| | - Victor Nizet
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego School of Medicine, La Jolla, CA, USA
| | | | - Kyle J Gaulton
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Tariq M Rana
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, CA, USA
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9
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Xu C, Fang Y, Yang Z, Jing Y, Zhang Y, Liu C, Liu W. MARCKS regulates tonic and chronic active B cell receptor signaling. Leukemia 2019; 33:710-729. [PMID: 30209404 DOI: 10.1038/s41375-018-0244-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Revised: 06/12/2018] [Accepted: 07/30/2018] [Indexed: 01/16/2023]
Abstract
Tonic or chronic active B-cell receptor (BCR) signaling is essential for the survival of normal or some malignant B cells, respectively. However, the molecular mechanism regulating the strength of these two types of BCR signaling remains unknown. Here, using high-speed high-resolution single-molecule tracking in live cells, we identified that PKCβ, STIM1, and IP3R1/2/3 molecules affected the lateral Brownian mobile behavior of BCRs on the plasma membrane of quiescent B cells, which was correlated to the strength of BCR signaling. Further mechanistic studies revealed that these three molecules influenced BCR mobility by regulating the membrane tethering of MARCKS to the inner leaflet of the plasma membrane. Indeed, membrane-untethered or deficiency of MARCKS significantly decreased, while membrane-tethered or overexpression of MARCKS drastically increased the lateral mobility of BCRs. Functional experiments indicated that the membrane-tethered MARCKS suppressed the survival and/or proliferation in both B-cell tumor cells and mouse primary splenic B cells in vitro and in vivo. Mechanistically, we found that membrane-tethered MARCKS increased BCR lateral mobility, and thus decreased BCR nanoclustering by disturbing the interaction between cortical F-actin and the inner leaflet of the plasma membrane, resulting in the suppression of the strength of both tonic and chronic active BCR signaling. Conclusively, MARCKS is a newly identified molecule regulating the strength of BCR signaling by modulating cytoskeleton and plasma membrane interactions, both in the physiological and pathological conditions, suggesting that MARCKS is a putative target for drug design.
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Affiliation(s)
- Chenguang Xu
- MOE Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, School of Life Sciences, Institute for Immunology, Tsinghua University, Beijing, 100084, China
| | - Yan Fang
- MOE Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, School of Life Sciences, Institute for Immunology, Tsinghua University, Beijing, 100084, China
| | - Zhiyong Yang
- Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA, 94143, USA
| | - Yukai Jing
- Department of Pathogen Biology, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, 430030, China
| | - Yonghui Zhang
- School of Pharmaceutical Sciences, Collaborative Innovation Center for Biotherapy, Tsinghua University, Beijing, 100084, China
| | - Chaohong Liu
- Department of Pathogen Biology, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, 430030, China.
| | - Wanli Liu
- MOE Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, School of Life Sciences, Institute for Immunology, Tsinghua University, Beijing, 100084, China.
- Beijing Key Lab for Immunological Research on Chronic Diseases, Beijing, 100084, China.
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10
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A PKC-MARCKS-PI3K regulatory module links Ca2+ and PIP3 signals at the leading edge of polarized macrophages. PLoS One 2018; 13:e0196678. [PMID: 29715315 PMCID: PMC5929533 DOI: 10.1371/journal.pone.0196678] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Accepted: 04/17/2018] [Indexed: 12/21/2022] Open
Abstract
The leukocyte chemosensory pathway detects attractant gradients and directs cell migration to sites of inflammation, infection, tissue damage, and carcinogenesis. Previous studies have revealed that local Ca2+ and PIP3 signals at the leading edge of polarized leukocytes play central roles in positive feedback loop essential to cell polarization and chemotaxis. These prior studies showed that stimulation of the leading edge Ca2+ signal can strongly activate PI3K, thereby triggering a larger PIP3 signal, but did not elucidate the mechanistic link between Ca2+ and PIP3 signaling. A hypothesis explaining this link emerged, postulating that Ca2+-activated PKC displaces the MARCKS protein from plasma membrane PIP2, thereby releasing sequestered PIP2 to serve as the target and substrate lipid of PI3K in PIP3 production. In vitro single molecule studies of the reconstituted pathway on lipid bilayers demonstrated the feasibility of this PKC-MARCKS-PI3K regulatory module linking Ca2+ and PIP3 signals in the reconstituted system. The present study tests the model predictions in live macrophages by quantifying the effects of: (a) two pathway activators—PDGF and ATP that stimulate chemoreceptors and Ca2+ influx, respectively; and (b) three pathway inhibitors—wortmannin, EGTA, and Go6976 that inhibit PI3K, Ca2+ influx, and PKC, respectively; on (c) four leading edge activity sensors—AKT-PH-mRFP, CKAR, MARCKSp-mRFP, and leading edge area that report on PIP3 density, PKC activity, MARCKS membrane binding, and leading edge expansion/contraction, respectively. The results provide additional evidence that PKC and PI3K are both essential elements of the leading edge positive feedback loop, and strongly support the existence of a PKC-MARCKS-PI3K regulatory module linking the leading edge Ca2+ and PIP3 signals. As predicted, activators stimulate leading edge PKC activity, displacement of MARCKS from the leading edge membrane and increased leading edge PIP3 levels, while inhibitors trigger the opposite effects. Comparison of the findings for the ameboid chemotaxis of leukocytes with recently published findings for the mesenchymal chemotaxis of fibroblasts suggests that some features of the emerging leukocyte leading edge core pathway (PLC-DAG-Ca2+-PKC-MARCKS-PIP2-PI3K-PIP3) may well be shared by all chemotaxing eukaryotic cells, while other elements of the leukocyte pathway may be specialized features of these highly optimized, professional gradient-seeking cells. More broadly, the findings suggest a molecular mechanism for the strong links between phospho-MARCKS and many human cancers.
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11
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Franke NE, Kaspers GL, Assaraf YG, van Meerloo J, Niewerth D, Kessler FL, Poddighe PJ, Kole J, Smeets SJ, Ylstra B, Bi C, Chng WJ, Horton TM, Menezes RX, Musters RJP, Zweegman S, Jansen G, Cloos J. Exocytosis of polyubiquitinated proteins in bortezomib-resistant leukemia cells: a role for MARCKS in acquired resistance to proteasome inhibitors. Oncotarget 2018; 7:74779-74796. [PMID: 27542283 PMCID: PMC5342701 DOI: 10.18632/oncotarget.11340] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Accepted: 07/26/2016] [Indexed: 12/11/2022] Open
Abstract
PSMB5 mutations and upregulation of the β5 subunit of the proteasome represent key determinants of acquired resistance to the proteasome inhibitor bortezomib (BTZ) in leukemic cells in vitro. We here undertook a multi-modality (DNA, mRNA, miRNA) array-based analysis of human CCRF-CEM leukemia cells and BTZ-resistant subclones to determine whether or not complementary mechanisms contribute to BTZ resistance. These studies revealed signatures of markedly reduced expression of proteolytic stress related genes in drug resistant cells over a broad range of BTZ concentrations along with a high upregulation of myristoylated alanine-rich C-kinase substrate (MARCKS) gene expression. MARCKS upregulation was confirmed on protein level and also observed in other BTZ-resistant tumor cell lines as well as in leukemia cells with acquired resistance to other proteasome inhibitors. Moreover, when MARCKS protein expression was demonstrated in specimens derived from therapy-refractory pediatric leukemia patients (n = 44), higher MARCKS protein expression trended (p = 0.073) towards a dismal response to BTZ-containing chemotherapy. Mechanistically, we show a BTZ concentration-dependent association of MARCKS protein levels with the emergence of ubiquitin-containing vesicles in BTZ-resistant CEM cells. These vesicles were found to be extruded and taken up in co-cultures with proteasome-proficient acceptor cells. Consistent with these observations, MARCKS protein associated with ubiquitin-containing vesicles was also more prominent in clinical leukemic specimen with ex vivo BTZ resistance compared to BTZ-sensitive leukemia cells. Collectively, we propose a role for MARCKS in a novel mechanism of BTZ resistance via exocytosis of ubiquitinated proteins in BTZ-resistant cells leading to quenching of proteolytic stress.
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Affiliation(s)
- Niels E Franke
- Department of Pediatric Oncology/Hematology, VU University Medical Center, Amsterdam, The Netherlands
| | - Gertjan L Kaspers
- Department of Pediatric Oncology/Hematology, VU University Medical Center, Amsterdam, The Netherlands
| | - Yehuda G Assaraf
- The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel
| | - Johan van Meerloo
- Department of Pediatric Oncology/Hematology, VU University Medical Center, Amsterdam, The Netherlands.,Department of Hematology, VU University Medical Center, Amsterdam, The Netherlands
| | - Denise Niewerth
- Department of Pediatric Oncology/Hematology, VU University Medical Center, Amsterdam, The Netherlands
| | - Floortje L Kessler
- Department of Hematology, VU University Medical Center, Amsterdam, The Netherlands
| | - Pino J Poddighe
- Department of Clinical Genetics, VU University Medical Center, Amsterdam, The Netherlands
| | - Jeroen Kole
- Department of Physiology, VU University, Amsterdam, The Netherlands
| | - Serge J Smeets
- Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands
| | - Bauke Ylstra
- Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands
| | - Chonglei Bi
- Department of Experimental Therapeutics, Cancer Science Institute of Singapore, National University of Singapore, Singapore.,Current address: BGI-Shenzhen, Shenzhen, China
| | - Wee Joo Chng
- Department of Experimental Therapeutics, Cancer Science Institute of Singapore, National University of Singapore, Singapore
| | - Terzah M Horton
- Texas Children's Cancer Center, Baylor College of Medicine, Houston, TX, USA
| | - Rene X Menezes
- Department of Epidemiology and Biostatistics, VU University Medical Center, Amsterdam, The Netherlands
| | | | - Sonja Zweegman
- Department of Hematology, VU University Medical Center, Amsterdam, The Netherlands
| | - Gerrit Jansen
- Department of Rheumatology, Amsterdam Rheumatology and immunology Center, VU University Medical Center, Amsterdam, The Netherlands
| | - Jacqueline Cloos
- Department of Pediatric Oncology/Hematology, VU University Medical Center, Amsterdam, The Netherlands.,Department of Hematology, VU University Medical Center, Amsterdam, The Netherlands
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12
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Prognostic value of a 25-gene assay in patients with gastric cancer after curative resection. Sci Rep 2017; 7:7515. [PMID: 28790411 PMCID: PMC5548732 DOI: 10.1038/s41598-017-07604-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Accepted: 06/28/2017] [Indexed: 12/26/2022] Open
Abstract
This study aimed to develop and validate a practical, reliable assay for prognosis and chemotherapy benefit prediction compared with conventional staging in Gastric cancer (GC). Twenty-three candidate genes with significant correlation between quantitative hybridization and microarray results plus 2 reference genes were selected to form a 25-gene prognostic classifier, which can classify patients into 3 distinct groups of different risk of mortality obtained by analyzing microarray data from 78 frozen tumor specimens. The 25-gene assay was associated with overall survival in both training (P = 0.017) and testing cohort (P = 0.005) (462 formalin-fixed paraffin-embedded samples). The risk prediction in stages I + II is significantly better than that in stages III. Analysis demonstrated that this 25-gene signature is an independent prognostic predictor and show higher prognostic accuracy than conventional TNM staging in early stage patients. Moreover, only high-risk patients in stage I + II were found benefit from adjuvant chemotherapy (P = 0.043), while low-risk patients in stage III were not found benefit from adjuvant chemotherapy. In conclusion, our results suggest that this 25-gene assay can reliably identify patients with different risk for mortality after surgery, especially for stage I + II patients, and might be able to predict patients who benefit from chemotherapy.
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13
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McLeish KR, Merchant ML, Creed TM, Tandon S, Barati MT, Uriarte SM, Ward RA. Frontline Science: Tumor necrosis factor-α stimulation and priming of human neutrophil granule exocytosis. J Leukoc Biol 2017; 102:19-29. [PMID: 28096297 DOI: 10.1189/jlb.3hi0716-293rr] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2016] [Revised: 12/19/2016] [Accepted: 12/20/2016] [Indexed: 12/24/2022] Open
Abstract
Neutrophil granule exocytosis plays an important role in innate and adaptive immune responses. The present study examined TNF-α stimulation or priming of exocytosis of the 4 neutrophil granule subsets. TNF-α stimulated exocytosis of secretory vesicles and gelatinase granules and primed specific and azurophilic granule exocytosis to fMLF stimulation. Both stimulation and priming of exocytosis by TNF-α were dependent on p38 MAPK activity. Bioinformatic analysis of 1115 neutrophil proteins identified by mass spectrometry as being phosphorylated by TNF-α exposure found that actin cytoskeleton regulation was a major biologic function. A role for p38 MAPK regulation of the actin cytoskeleton was confirmed experimentally. Thirteen phosphoproteins regulated secretory vesicle quantity, formation, or release, 4 of which-Raf1, myristoylated alanine-rich protein kinase C (PKC) substrate (MARCKS), Abelson murine leukemia interactor 1 (ABI1), and myosin VI-were targets of the p38 MAPK pathway. Pharmacologic inhibition of Raf1 reduced stimulated exocytosis of gelatinase granules and priming of specific granule exocytosis. We conclude that differential regulation of exocytosis by TNF-α involves the actin cytoskeleton and is a necessary component for priming of the 2 major neutrophil antimicrobial defense mechanisms: oxygen radical generation and release of toxic granule contents.
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Affiliation(s)
- Kenneth R McLeish
- Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky, USA; and .,Robley Rex Veterans Affairs Medical Center, Louisville, Kentucky, USA
| | - Michael L Merchant
- Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky, USA; and
| | - T Michael Creed
- Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky, USA; and
| | - Shweta Tandon
- Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky, USA; and
| | - Michelle T Barati
- Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky, USA; and
| | - Silvia M Uriarte
- Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky, USA; and
| | - Richard A Ward
- Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky, USA; and
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Roles for lipid heterogeneity in immunoreceptor signaling. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:830-836. [PMID: 26995463 DOI: 10.1016/j.bbalip.2016.03.019] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 03/12/2016] [Accepted: 03/14/2016] [Indexed: 11/22/2022]
Abstract
Immune receptors that specifically recognize foreign antigens to activate leukocytes in adaptive immune responses belong to a family of multichain cell surface proteins. All of these contain immunoreceptor tyrosine-based activation motifs in one or more subunits that initiate signaling cascades following stimulated tyrosine phosphorylation by Src-family kinases. As highlighted in this review, lipids participate in this initial activation step, as well as in more downstream signaling steps. We summarize evidence for cholesterol-dependent ordered lipids serving to regulate the store-operated Ca(2+) channel, Orai1, and we describe the sensitivity of Orai1 coupling to the ER Ca(2+) sensor, STIM1, to inhibition by polyunsaturated fatty acids. Phosphoinositides play key roles in regulating STIM1-Orai1 coupling, as well as in the stimulated Ca(2+) oscillations that are a consequence of IgE receptor signaling in mast cells. They also participate in the coupling between the plasma membrane and the actin cytoskeleton, which regulates immune receptor responses in T cells, B cells, and mast cells, both positively and negatively, depending on the cellular context. Recent studies show that other phospholipids with mostly saturated acylation also participate in coupling between receptors and the actin cytoskeleton. Lipid heterogeneity is a central feature of the intimate relationship between the plasma membrane and the actin cytoskeleton. The detailed nature of these interactions and how they are dynamically regulated to initiate and propagate receptor-mediated cell signaling are challenging questions for further investigation. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.
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15
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Phosphatidylinositol phosphate kinase PIPKIγ and phosphatase INPP5E coordinate initiation of ciliogenesis. Nat Commun 2016; 7:10777. [PMID: 26916822 PMCID: PMC4773430 DOI: 10.1038/ncomms10777] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Accepted: 01/19/2016] [Indexed: 02/08/2023] Open
Abstract
Defective primary cilia are causative to a wide spectrum of human genetic disorders, termed ciliopathies. Although the regulation of ciliogenesis is intensively studied, how it is initiated remains unclear. Here we show that type Iγ phosphatidylinositol 4-phosphate (PtdIns(4)P) 5-kinase (PIPKIγ) and inositol polyphosphate-5-phosphatase E (INPP5E), a Joubert syndrome protein, localize to the centrosome and coordinate the initiation of ciliogenesis. PIPKIγ counteracts INPP5E in regulating tau-tubulin kinase-2 (TTBK2) recruitment to the basal body, which promotes the removal of microtubule capping protein CP110 and the subsequent axoneme elongation. Interestingly, INPP5E and its product—PtdIns(4)P—accumulate at the centrosome/basal body in non-ciliated, but not ciliated, cells. PtdIns(4)P binding to TTBK2 and the distal appendage protein CEP164 compromises the TTBK2-CEP164 interaction and inhibits the recruitment of TTBK2. Our results reveal that PtdIns(4)P homoeostasis, coordinated by PIPKIγ and INPP5E at the centrosome/ciliary base, is vital for ciliogenesis by regulating the CEP164-dependent recruitment of TTBK2. The primary cilium is essential for embryonic development and tissue pattern formation. Here the authors show that PIPKIγ localizes to the basal body of the primary cilium and cooperates with the Joubert Syndrome associated protein INPP5E to regulate the initiation of ciliogenesis.
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In Vitro Neutrophil Migration Requires Protein Kinase C-Delta (δ-PKC)-Mediated Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) Phosphorylation. Inflammation 2016; 38:1126-41. [PMID: 25515270 DOI: 10.1007/s10753-014-0078-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Dysregulated release of neutrophil reactive oxygen species and proteolytic enzymes contributes to both acute and chronic inflammatory diseases. Therefore, molecular regulators of these processes are potential targets for new anti-inflammatory therapies. We have shown previously that myristoylated alanine-rich C-kinase substrate (MARCKS), a well-known actin binding protein and protein kinase C (PKC) substrate, is a key regulator of neutrophil functions. In the current study, we investigate the role of PKC-mediated MARCKS phosphorylation in neutrophil migration and adhesion in vitro. We report that treatment of human neutrophils with the δ-PKC inhibitor rottlerin significantly attenuates f-Met-Leu-Phe (fMLF)-induced MARCKS phosphorylation (IC50=5.709 μM), adhesion (IC50=8.4 μM), and migration (IC50=6.7 μM), while α-, β-, and ζ-PKC inhibitors had no significant effect. We conclude that δ-PKC-mediated MARCKS phosphorylation is essential for human neutrophil migration and adhesion in vitro. These results implicate δ-PKC-mediated MARCKS phosphorylation as a key step in the inflammatory response of neutrophils.
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17
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Abstract
Our long-term efforts to elucidate receptor-mediated signalling in immune cells, particularly transmembrane signalling initiated by FcɛRI, the receptor for IgE in mast cells, led us unavoidably to contemplate the role of the heterogeneous plasma membrane. Our early investigations with fluorescence microscopy revealed co-redistribution of certain lipids and signalling components with antigen-cross-linked IgE-FcɛRI and pointed to participation of ordered membrane domains in the signalling process. With a focus on this function, we have worked along with others to develop diverse and increasingly sophisticated tools to analyse the complexity of membrane structure that facilitates regulation and targeting of signalling events. The present chapter describes how initial membrane interactions of clustered IgE-FcɛRI lead to downstream cellular responses and how biochemical information integrated with nanoscale resolution spectroscopy and imaging is providing mechanistic insights at the level of molecular complexes.
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Affiliation(s)
- David Holowka
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, U.S.A
| | - Barbara Baird
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, U.S.A
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18
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Abstract
Mast cells play a key role in allergy and inflammation processes as part of the immune response. The activation of mast cells via antigen binding and cross-linking of IgE receptors initiates the onset of dramatic calcium (Ca(2+)) mobilization dynamics that promote the release of mediators of inflammation and allergy. Ca(2+) signaling in mast cells has been studied extensively using a variety of research tools and techniques. In these studies, a large number of proteins have been identified to participate in various stages of these processes. Here we describe single-cell imaging as an important approach for examining Ca(2+) signaling and exocytosis in mast cells. Single-cell imaging tools have advanced significantly over the last 10 years, in part due to improvements in microscope technology and in part due to the development of a new generation of Ca(2+) indicators and genetically encoded Ca(2+) sensors. The single-cell imaging techniques described here provide the spatial and temporal resolution required to decipher the signaling events that are critical for mast cell functions.
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19
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Shelby SA, Holowka D, Baird B, Veatch SL. Distinct stages of stimulated FcεRI receptor clustering and immobilization are identified through superresolution imaging. Biophys J 2014; 105:2343-54. [PMID: 24268146 DOI: 10.1016/j.bpj.2013.09.049] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 09/05/2013] [Accepted: 09/09/2013] [Indexed: 12/25/2022] Open
Abstract
Recent advances in fluorescence localization microscopy have made it possible to image chemically fixed and living cells at 20 nm lateral resolution. We apply this methodology to simultaneously record receptor organization and dynamics on the ventral surface of live RBL-2H3 mast cells undergoing antigen-mediated signaling. Cross-linking of IgE bound to FcεRI by multivalent antigen initiates mast cell activation, which leads to inflammatory responses physiologically. We quantify receptor organization and dynamics as cells are stimulated at room temperature (22°C). Within 2 min of antigen addition, receptor diffusion coefficients decrease by an order of magnitude, and single-particle trajectories are confined. Within 5 min of antigen addition, receptors organize into clusters containing ∼100 receptors with average radii of ∼70 nm. By comparing simultaneous measurements of clustering and mobility, we determine that there are two distinct stages of receptor clustering. In the first stage, which precedes stimulated Ca(2+) mobilization, receptors slow dramatically but are not tightly clustered. In the second stage, receptors are tightly packed and confined. We find that stimulation-dependent changes in both receptor clustering and mobility can be reversed by displacing multivalent antigen with monovalent ligands, and that these changes can be modulated through enrichment or reduction in cellular cholesterol levels.
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Affiliation(s)
- Sarah A Shelby
- Department of Chemistry and Chemical Biology, and Field of Biophysics, Cornell University, Ithaca, NY
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Baier A, Ndoh VNE, Lacy P, Eitzen G. Rac1 and Rac2 control distinct events during antigen-stimulated mast cell exocytosis. J Leukoc Biol 2014; 95:763-774. [PMID: 24399839 DOI: 10.1189/jlb.0513281] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 12/18/2013] [Accepted: 12/18/2013] [Indexed: 02/02/2023] Open
Abstract
The release of preformed mediators from immune cells is through a process described as exocytosis. In mast cells, exocytosis is regulated by several coordinated intracellular signaling pathways. Here, we investigated the role of the hematopoietic-specific Rho GTPase, Rac2, and the ubiquitously expressed Rac1, in controlling mast cell exocytosis. These two isoforms showed equivalent levels of expression in mouse BMMCs. Although Rac1 and Rac2 share 92% sequence identity, they were not functionally redundant, as Rac2-/- BMMCs were defective in exocytosis, even though Rac1 levels were unaffected. Antigen-stimulated WT mast cells underwent a series of morphological transitions: initial flattening, followed by actin-mediated peripheral membrane ruffling and calcium influx, which preceded exocytosis. Whereas membrane ruffling was unaffected in Rac2-/- BMMCs, calcium influx was decreased significantly. Calcium influx was studied further by examining SOCE. In Rac2-/- BMMCs, the activation of PLCγ1 and calcium release from intracellular stores occurred normally; however, activation of plasma membrane calcium channels was defective, shown by the lack of extracellular calcium influx and a reduction of YFP-STIM1 puncta at the plasma membrane. Additionally, we used the small molecule Rac inhibitor, EHT 1864, to target Rac signaling acutely in WT BMMCs. EHT 1864 blocked exocytosis and membrane ruffling completely in conjunction with exocytosis. Our findings suggest that antigen-stimulated membrane ruffling in mast cells is a Rac1-mediated process, as this persisted in the absence of Rac2. Therefore, we define distinct modes of Rac-regulated mast cell exocytosis: Rac2-mediated calcium influx and Rac1-mediated membrane ruffling.
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Affiliation(s)
| | - Vivian N E Ndoh
- Department of Cell Biology and
- Department of Medicine, University of Örebro, Örebro, Sweden
| | - Paige Lacy
- The Pulmonary Research Group, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada; and
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21
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Chen P, Deng Z, Wang T, Chen L, Li J, Feng Y, Zhang S, Nin Y, Liu D, Chen Y, Ou X, Wen F. The potential interaction of MARCKS-related peptide and diltiazem on acrolein-induced airway mucus hypersecretion in rats. Int Immunopharmacol 2013; 17:625-32. [PMID: 24012931 DOI: 10.1016/j.intimp.2013.08.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 07/24/2013] [Accepted: 08/06/2013] [Indexed: 02/05/2023]
Abstract
UNLABELLED Airway mucus hypersecretion is recognized as a pathophysiological feature of airway inflammation. Ca2+ entry and myristoylated alanine-rich C kinase substrate translocation are considered as important factors in such process. To investigate the potential interaction of myristoylated alanine-rich C kinase substrate (MARCKS)-related peptide and diltiazem on acrolein-induced airway mucus hypersecretion in rats, rat model of airway mucus hypersecretion was established by inhalation of acrolein on 12 consecutive days. MARCKS-related peptide, diltiazem, saline or the combination (MARCKS-related peptide+diltiazem) was intratracheally administered respectively. The rats were received pilocarpine to stimulate mucus release before sacrifices. The expression of Mucin5ac in bronchoalveolar lavage fluid (BALF) was measured by ELISA. Intracellular Muc5ac level was detected by immunohistochemical staining and western-blot. Muc5ac mRNA in lung was analyzed by RT-PCR. RESULTS Instillation of MARCKS-related peptide attenuated the release of Muc5ac in BALF induced by acrolein(p<0.05). Diltiazem alone had no effect on mucus hypersecretion induced by acrolein. However, the release of Muc5ac in BALF was further reduced when challenged with simultaneous instillation with MARCKS-related peptide and diltiazem, compared with MARCKS-related peptide alone (p<0.05). The intracellular level of Muc5ac in lung was increased when treated with MARCKS-related peptide alone or MARCKS-related peptide plus diltiazem (p<0.05). Nevertheless, diltiazem alone did not take effect as above. CONCLUSIONS In the model of airway mucus hypersecretion induced by acrolein, MARCKS-related peptide attenuated mucus secretion and the inhibitory effect was enhanced by diltiazem, which may be due to a further diminution of the intracellular free calcium concentration and retention of mucin within epithelial goblet cells.
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Affiliation(s)
- Peng Chen
- Department of Respiratory Medicine, The Third People's Hospital of Chengdu, Chengdu, Sichuan 610031, China; Division of Pulmonary Diseases, State Key Laboratory of Biotherapy of China, Department of Respiratory Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
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Smith NL, Abi Abdallah DS, Butcher BA, Denkers EY, Baird B, Holowka D. Toxoplasma gondii inhibits mast cell degranulation by suppressing phospholipase Cγ-mediated Ca(2+) mobilization. Front Microbiol 2013; 4:179. [PMID: 23847603 PMCID: PMC3701878 DOI: 10.3389/fmicb.2013.00179] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Accepted: 06/14/2013] [Indexed: 12/21/2022] Open
Abstract
Toxoplasma gondii is well-known to subvert normal immune responses, however, mechanisms are incompletely understood. In particular, its capacity to alter receptor-activated Ca2+-mediated signaling processes has not been well-characterized. In initial experiments, we found evidence that T. gondii infection inhibits Ca2+ responses to fMetLeuPhe in murine macrophages. To further characterize the mechanism of inhibition of Ca2+ mobilization by T. gondii, we used the well-studied RBL mast cell model to probe the capacity of T. gondii to modulate IgE receptor-activated signaling within the first hour of infection. Ca2+ mobilization that occurs via IgE/FcεRI signaling leads to granule exocytosis in mast cells. We found that T. gondii inhibits antigen-stimulated degranulation in infected cells in a strain-independent manner. Under these conditions, we found that cytoplasmic Ca2+ mobilization, particularly antigen-mediated Ca2+ release from intracellular stores, is significantly reduced. Furthermore, stimulation-dependent activation of Syk kinase leading to tyrosine phosphorylation and activation of phospholipase Cγ is inhibited by infection. Therefore, we conclude that inhibitory effects of infection are likely due to parasite-mediated inhibition of the tyrosine kinase signaling cascade that results in reduced hydrolysis of phosphatidylinositol 4,5-bisphosphate. Interestingly, inhibition of IgE/FcεRI signaling persists when tachyzoite invasion is arrested via cytochalasin D treatment, suggesting inhibition is mediated by a parasite-derived factor secreted into the cells during the invasion process. Our study provides direct evidence that immune subversion by T. gondii is initiated concurrently with invasion.
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Affiliation(s)
- Norah L Smith
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University Ithaca, NY, USA
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Abstract
PKC (protein kinase C) has been in the limelight since the discovery three decades ago that it acts as a major receptor for the tumour-promoting phorbol esters. Phorbol esters, with their potent ability to activate two of the three classes of PKC isoenzymes, have remained the best pharmacological tool for directly modulating PKC activity. However, with the discovery of other phorbol ester-responsive proteins, the advent of various small-molecule and peptide modulators, and the need to distinguish isoenzyme-specific activity, the pharmacology of PKC has become increasingly complex. Not surprisingly, many of the compounds originally touted as direct modulators of PKC have subsequently been shown to hit many other cellular targets and, in some cases, not even directly modulate PKC. The complexities and reversals in PKC pharmacology have led to widespread confusion about the current status of the pharmacological tools available to control PKC activity. In the present review, we aim to clarify the cacophony in the literature regarding the current state of bona fide and discredited cellular PKC modulators, including activators, small-molecule inhibitors and peptides, and also address the use of genetically encoded reporters and of PKC mutants to measure the effects of these drugs on the spatiotemporal dynamics of signalling by specific isoenzymes.
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Affiliation(s)
- Alyssa X. Wu-Zhang
- Department of Pharmacology, University of California San Diego, La Jolla, CA 92093-0721, (858) 534-4527, Fax: (858) 822-5888
| | - Alexandra C. Newton
- Department of Pharmacology, University of California San Diego, La Jolla, CA 92093-0721, (858) 534-4527, Fax: (858) 822-5888
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MARCKS protein is phosphorylated and regulates calcium mobilization during human acrosomal exocytosis. PLoS One 2013; 8:e64551. [PMID: 23704996 PMCID: PMC3660367 DOI: 10.1371/journal.pone.0064551] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Accepted: 04/17/2013] [Indexed: 12/01/2022] Open
Abstract
Acrosomal exocytosis is a calcium-regulated exocytosis that can be triggered by PKC activators. The involvement of PKC in acrosomal exocytosis has not been fully elucidated, and it is unknown if MARCKS, the major substrate for PKC, participates in this exocytosis. Here, we report that MARCKS is expressed in human spermatozoa and localizes to the sperm head and the tail. Calcium- and phorbol ester-triggered acrosomal exocytosis in permeabilized sperm was abrogated by different anti-MARCKS antibodies raised against two different domains, indicating that the protein participates in acrosomal exocytosis. Interestingly, an anti-phosphorylated MARCKS antibody was not able to inhibit secretion. Similar results were obtained using recombinant proteins and phospho-mutants of MARCKS effector domain (ED), indicating that phosphorylation regulates MARCKS function in acrosomal exocytosis. It is known that unphosphorylated MARCKS sequesters PIP2. This phospholipid is the precursor for IP3, which in turn triggers release of calcium from the acrosome during acrosomal exocytosis. We found that PIP2 and adenophostin, a potent IP3-receptor agonist, rescued MARCKS inhibition in permeabilized sperm, suggesting that MARCKS inhibits acrosomal exocytosis by sequestering PIP2 and, indirectly, MARCKS regulates the intracellular calcium mobilization. In non-permeabilized sperm, a permeable peptide of MARCKS ED also inhibited acrosomal exocytosis when stimulated by a natural agonist such as progesterone, and pharmacological inducers such as calcium ionophore and phorbol ester. The preincubation of human sperm with the permeable MARCKS ED abolished the increase in calcium levels caused by progesterone, demonstrating that MARCKS regulates calcium mobilization. In addition, the phosphorylation of MARCKS increased during acrosomal exocytosis stimulated by the same activators. Altogether, these results show that MARCKS is a negative modulator of the acrosomal exocytosis, probably by sequestering PIP2, and that it is phosphorylated during acrosomal exocytosis.
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Santos MDS, Naal RMZG, Baird B, Holowka D. Inhibitors of PI(4,5)P2 synthesis reveal dynamic regulation of IgE receptor signaling by phosphoinositides in RBL mast cells. Mol Pharmacol 2013; 83:793-804. [PMID: 23313938 DOI: 10.1124/mol.112.082834] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is a versatile phospholipid that participates in many membrane-associated signaling processes. PI(4,5)P2 production at the plasma membrane (PM) depends on levels of its precursor, phosphatidylinositol 4-phosphate (PI4P), synthesized principally by two intracellular enzymes, PI4-kinases IIIα and IIIb; the former is preferentially inhibited by phenylarsine oxide (PAO). We found that PAO and quercetin, another lipid kinase inhibitor, rapidly inhibit Ca(2+) responses to antigen in IgE-sensitized rat basophilic leukemia mast cells. Quercetin also rapidly inhibits store-operated Ca(2+) influx stimulated by thapsigargin. In addition, quercetin and PAO effectively inhibit antigen-stimulated ruffling and spreading in these cells, and they inhibit endocytosis of crosslinked IgE receptor complexes, evidently by inhibiting pinching off of endocytic vesicles containing the clustered IgE receptors. A minimal model to account for these diverse effects is inhibition of PI(4,5)P2 synthesis by PAO and quercetin. To characterize the direct effects of these agents on PI(4,5)P2 synthesis, we monitored the reappearance of the PI(4,5)P2-specific PH domain PH-phospholipase C δ-EGFP at the PM after Ca(2+) ionophore (A23187)-induced PI(4,5)P2 hydrolysis, followed by Ca(2+) chelation with excess EGTA. Resynthesized PI(4,5)P2 initially appears as micron-sized patches near the PM. Addition of quercetin subsequent to A23187-induced PI(4,5)P2 hydrolysis reduces PI(4,5)P2 resynthesis in PM-associated patches, and PAO reduces PI(4,5)P2 at the PM while enhancing PI(4,5)P2 accumulation at the Golgi complex. Taken together, these results provide evidence that PI4P generated by PI4-kinase IIIα is dynamically coupled to PI(4,5)P2 pools at the PM that are important for downstream signaling processes activated by IgE receptors.
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Affiliation(s)
- Marcela de Souza Santos
- Departamento de Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, SãoPaulo, Brazil
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Signal transduction pathways involving phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate: Convergences and divergences among eukaryotic kingdoms. Prog Lipid Res 2013; 52:1-14. [DOI: 10.1016/j.plipres.2012.08.003] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 08/22/2012] [Accepted: 08/23/2012] [Indexed: 11/18/2022]
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Multiple roles for the actin cytoskeleton during regulated exocytosis. Cell Mol Life Sci 2012; 70:2099-121. [PMID: 22986507 DOI: 10.1007/s00018-012-1156-5] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Revised: 08/28/2012] [Accepted: 08/30/2012] [Indexed: 01/01/2023]
Abstract
Regulated exocytosis is the main mechanism utilized by specialized secretory cells to deliver molecules to the cell surface by virtue of membranous containers (i.e., secretory vesicles). The process involves a series of highly coordinated and sequential steps, which include the biogenesis of the vesicles, their delivery to the cell periphery, their fusion with the plasma membrane, and the release of their content into the extracellular space. Each of these steps is regulated by the actin cytoskeleton. In this review, we summarize the current knowledge regarding the involvement of actin and its associated molecules during each of the exocytic steps in vertebrates, and suggest that the overall role of the actin cytoskeleton during regulated exocytosis is linked to the architecture and the physiology of the secretory cells under examination. Specifically, in neurons, neuroendocrine, endocrine, and hematopoietic cells, which contain small secretory vesicles that undergo rapid exocytosis (on the order of milliseconds), the actin cytoskeleton plays a role in pre-fusion events, where it acts primarily as a functional barrier and facilitates docking. In exocrine and other secretory cells, which contain large secretory vesicles that undergo slow exocytosis (seconds to minutes), the actin cytoskeleton plays a role in post-fusion events, where it regulates the dynamics of the fusion pore, facilitates the integration of the vesicles into the plasma membrane, provides structural support, and promotes the expulsion of large cargo molecules.
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Kalwa H, Sartoretto JL, Sartoretto SM, Michel T. Angiotensin-II and MARCKS: a hydrogen peroxide- and RAC1-dependent signaling pathway in vascular endothelium. J Biol Chem 2012; 287:29147-58. [PMID: 22773836 DOI: 10.1074/jbc.m112.381517] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MARCKS is an actin-binding protein that modulates vascular endothelial cell migration and cytoskeleton signaling (Kalwa, H., and Michel, T. (2011) J. Biol. Chem. 286, 2320-2330). Angiotensin-II is a vasoactive peptide implicated in vascular physiology as well as pathophysiology; the pathways connecting angiotensin-II and cytoskeletal remodeling are incompletely understood. Here we show that MARCKS is expressed in intact arterial preparations, with prominent staining of the endothelium. In endothelial cells, angiotensin-II-promoted MARCKS phosphorylation is abrogated by PEG-catalase, implicating endogenous H(2)O(2) in the angiotensin-II response. Studies using the H(2)O(2) biosensor HyPer2 reveal that angiotensin-II promotes increases in intracellular H(2)O(2). We used a Rac1 FRET biosensor to show that angiotensin-II promotes Rac1 activation that is attenuated by PEG-catalase. siRNA-mediated Rac1 knockdown blocks angiotensin-II-stimulated MARCKS phosphorylation. Cell imaging studies using a phosphoinositide 4,5-bisphosphate (PIP(2)) biosensor revealed that angiotensin-II PIP(2) regulation depends on MARCKS and H(2)O(2). siRNA-mediated knockdown of MARCKS or Rac1 attenuates receptor-mediated activation of the tyrosine kinase c-Abl and disrupts actin fiber formation. These studies establish a critical role for H(2)O(2) in angiotensin-II signaling to the endothelial cytoskeleton in a novel pathway that is critically dependent on MARCKS, Rac1, and c-Abl.
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Affiliation(s)
- Hermann Kalwa
- Cardiovascular Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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Holowka D, Calloway N, Cohen R, Gadi D, Lee J, Smith NL, Baird B. Roles for ca(2+) mobilization and its regulation in mast cell functions. Front Immunol 2012; 3:104. [PMID: 22586429 PMCID: PMC3346949 DOI: 10.3389/fimmu.2012.00104] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Accepted: 04/16/2012] [Indexed: 01/08/2023] Open
Abstract
Mobilization of Ca2+ in response to IgE receptor-mediated signaling is a key process in many aspects of mast cell function. Here we summarize our current understanding of the molecular bases for this process and the roles that it plays in physiologically relevant mast cell biology. Activation of IgE receptor signaling by antigen that crosslinks these complexes initiates Ca2+ mobilization as a fast wave that is frequently followed by a series of Ca2+ oscillations which are dependent on Ca2+ influx-mediated by coupling of the endoplasmic reticulum luminal Ca2+ sensor STIM1 to the calcium release activated calcium channel protein Orai1. Granule exocytosis depends on this process, together with the activation of protein kinase C isoforms, and specific roles for these signaling steps are beginning to be understood. Ca2+ mobilization also plays important roles in stimulated exocytosis of recycling endosomes and newly synthesized cytokines, as well as in antigen-mediated chemotaxis of rat mucosal mast cells. Phosphoinositide metabolism plays key roles in all of these processes, and we highlight these roles in several cases.
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Affiliation(s)
- David Holowka
- Department of Chemistry and Chemical Biology, Cornell University Ithaca, NY, USA
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Johnson JL, Erickson JW, Cerione RA. C-terminal di-arginine motif of Cdc42 protein is essential for binding to phosphatidylinositol 4,5-bisphosphate-containing membranes and inducing cellular transformation. J Biol Chem 2012; 287:5764-74. [PMID: 22215673 DOI: 10.1074/jbc.m111.336487] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rho GTPases regulate a diverse range of processes that are dependent on their proper cellular localization. The membrane localization of these GTPases is due in large part to their carboxyl-terminal geranylgeranyl moiety. In addition, most of the Rho family members contain a cluster of positively charged residues (i.e. a "polybasic domain"), directly preceding their geranylgeranyl moiety, and it has been suggested that this domain serves to fine-tune their localization among different cellular membrane sites. Here, we have taken a closer look at the role of the polybasic domain of Cdc42 in its ability to bind to membranes and induce the transformation of fibroblasts. A FRET assay for the binding of Cdc42 to liposomes of defined composition showed that Cdc42 associates more strongly with liposomes containing phosphatidylinositol 4,5-bisphosphate (PIP(2)) when compared either with uncharged control membranes or with liposomes containing a charge-equivalent amount of phosphatidylserine. The carboxyl-terminal di-arginine motif (Arg-186 and Arg-187) was shown to play an essential role in the binding of Cdc42 to PIP(2)-containing membranes. We further showed that substitutions for the di-arginine motif, when introduced within a constitutively active ("fast cycling") Cdc42(F28L) background, had little effect on the ability of the activated Cdc42 mutant to induce microspikes/filopodia in NIH 3T3 cells, whereas they eliminated its ability to transform fibroblasts. Taken together, these findings suggest that the di-arginine motif within the carboxyl terminus of Cdc42 is necessary for this GTPase to bind at membrane sites containing PIP(2), where it can initiate signaling activities that are essential for the oncogenic transformation of cells.
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Affiliation(s)
- Jared L Johnson
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
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