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Morad H, Luqman S, Tan CH, Swann V, McNaughton PA. TRPM2 ion channels steer neutrophils towards a source of hydrogen peroxide. Sci Rep 2021; 11:9339. [PMID: 33927223 PMCID: PMC8085234 DOI: 10.1038/s41598-021-88224-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Accepted: 03/31/2021] [Indexed: 01/16/2023] Open
Abstract
Neutrophils must navigate accurately towards pathogens in order to destroy invaders and thus defend our bodies against infection. Here we show that hydrogen peroxide, a potent neutrophil chemoattractant, guides chemotaxis by activating calcium-permeable TRPM2 ion channels and generating an intracellular leading-edge calcium "pulse". The thermal sensitivity of TRPM2 activation means that chemotaxis towards hydrogen peroxide is strongly promoted by small temperature elevations, suggesting that an important function of fever may be to enhance neutrophil chemotaxis by facilitating calcium influx through TRPM2. Chemotaxis towards conventional chemoattractants such as LPS, CXCL2 and C5a does not depend on TRPM2 but is driven in a similar way by leading-edge calcium pulses. Other proposed initiators of neutrophil movement, such as PI3K, Rac and lyn, influence chemotaxis by modulating the amplitude of calcium pulses. We propose that intracellular leading-edge calcium pulses are universal drivers of the motile machinery involved in neutrophil chemotaxis.
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Affiliation(s)
- Hassan Morad
- Wolfson Centre for Age-Related Diseases, King's College London, Guy's Campus, London Bridge, London, SE1 1UL, UK
| | - Suaib Luqman
- Wolfson Centre for Age-Related Diseases, King's College London, Guy's Campus, London Bridge, London, SE1 1UL, UK
- CSIR-Central Institute of Medicinal and Aromatic Plants, Uttar Pradesh, Lucknow, 226015, India
| | - Chun-Hsiang Tan
- Wolfson Centre for Age-Related Diseases, King's College London, Guy's Campus, London Bridge, London, SE1 1UL, UK
- Department of Neurology, Kaohsiung Medical University Hospital, and Graduate Institute of Clinical Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan
| | - Victoria Swann
- Wolfson Centre for Age-Related Diseases, King's College London, Guy's Campus, London Bridge, London, SE1 1UL, UK
- School of Cellular and Molecular Medicine, University of Bristol, Bristol, UK
| | - Peter A McNaughton
- Wolfson Centre for Age-Related Diseases, King's College London, Guy's Campus, London Bridge, London, SE1 1UL, UK.
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Al-Jumaa M, Hallett MB, Dewitt S. Cell surface topography controls phagocytosis and cell spreading: The membrane reservoir in neutrophils. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1867:118832. [PMID: 32860836 DOI: 10.1016/j.bbamcr.2020.118832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 08/13/2020] [Accepted: 08/19/2020] [Indexed: 10/23/2022]
Abstract
Neutrophils exhibit rapid cell spreading and phagocytosis, both requiring a large apparent increase in the cell surface area. The wrinkled surface topography of these cells may provide the membrane reservoir for this. Here, the effects of manipulation of the neutrophil cell surface topography on phagocytosis and cell spreading were established. Chemical expansion of the plasma membrane or osmotic swelling had no effects. However, osmotic shrinking of neutrophils inhibited both cell spreading and phagocytosis. Triggering a Ca2+ signal in osmotically shrunk cells (by IP3 uncaging) evoked tubular blebs instead of full cell spreading. Phagocytosis was halted at the phagocytic cup stage by osmotic shrinking induced after the phagocytic Ca2+ signalling. Restoration of isotonicity was able to restore complete phagocytosis. These data thus provide evidence that the wrinkled neutrophil surface topography provides the membrane reservoir to increase the available cell surface area for phagocytosis and spreading by neutrophils.
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Affiliation(s)
- Maha Al-Jumaa
- Neutrophil Signalling Group, Cardiff University School of Medicine, Cardiff CF14 4XN, UK
| | - Maurice B Hallett
- Neutrophil Signalling Group, Cardiff University School of Medicine, Cardiff CF14 4XN, UK
| | - Sharon Dewitt
- Matrix Biology & Tissue Repair Research Unit, College of Biomedical and Life Sciences, School of Dentistry, Cardiff University, Cardiff CF14 4XY, UK.
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3
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Cuesta Torres LF, Zhu W, Öhrling G, Larsson R, Patel M, Wiese CB, Rye KA, Vickers KC, Tabet F. High-density lipoproteins induce miR-223-3p biogenesis and export from myeloid cells: Role of scavenger receptor BI-mediated lipid transfer. Atherosclerosis 2019; 286:20-29. [PMID: 31096070 DOI: 10.1016/j.atherosclerosis.2019.04.227] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 04/17/2019] [Accepted: 04/30/2019] [Indexed: 12/22/2022]
Abstract
BACKGROUND AND AIMS We recently showed that miR-223-3p on high-density lipoproteins (HDL) is exported to endothelial cells, where it inhibits inflammation. However, the origin of miR-223-3p on HDL is unknown. We hypothesize that HDL-associated miR-223-3p originates in myeloid cells and is exported to HDL in a scavenger receptor BI (SR-BI)-dependent manner. METHODS Polymorphonuclear neutrophils (PMNs) and human monocyte derived macrophages (HMDMs) were incubated with native HDL (nHDL) or discoidal reconstituted HDL (rHDL). Total RNA was isolated before and after incubation. Mature and primary miR-223-3p (pri-mir-223-3p) levels were quantified by real-time PCR. RESULTS Incubation with nHDL and rHDL increased miR-223-3p export from PMNs and HMDMs. In PMNs, nHDL but not rHDL, increased mature and pri-mir-223-3p. Incubation with HDL also increased Dicer mRNA, a critical regulator of miRNA biogenesis. Incubation of HMDMs with nHDL did not increase cellular levels of mature miR-223-3p, but significantly increased pri-mir-223 levels. Incubation with rHDL had no effect on either mature or pri-mir-223-3p levels. Activated PMNs increased miR-223-3p export to HDL and the production of reactive oxygen species and activated protein kinase C. Blocking HDL binding to SR-BI increased miR-223-3p export to HDL in both PMNs and HMDMs, but did not affect mature and primary miR-223-3p levels. Chemical inhibition of cholesterol flux by Block Lipid Transport (BLT)-1 inhibited HDL-induced pri-mir-223 expression in PMNs. CONCLUSIONS HDL-associated miR-223-3p originates in PMNs and macrophages. HDL stimulates miR-223-3p biogenesis in PMNs in a process that is regulated by SR-BI-mediated lipid flux.
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Affiliation(s)
| | - Wanying Zhu
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Gustav Öhrling
- School of Medical Sciences, University of New South Wales Sydney, NSW, Australia
| | - Rasmus Larsson
- School of Medical Sciences, University of New South Wales Sydney, NSW, Australia
| | - Mili Patel
- School of Medical Sciences, University of New South Wales Sydney, NSW, Australia
| | - Carrie B Wiese
- Department of Molecular Physiology & Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Kerry-Anne Rye
- School of Medical Sciences, University of New South Wales Sydney, NSW, Australia
| | - Kasey C Vickers
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Molecular Physiology & Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Fatiha Tabet
- School of Medical Sciences, University of New South Wales Sydney, NSW, Australia.
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4
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Ishak R, Hallett MB. Defective rapid cell shape and transendothelial migration by calpain-1 null neutrophils. Biochem Biophys Res Commun 2018; 506:1065-1070. [DOI: 10.1016/j.bbrc.2018.10.174] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Accepted: 10/28/2018] [Indexed: 12/26/2022]
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5
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Francis EA, Heinrich V. Extension of chemotactic pseudopods by nonadherent human neutrophils does not require or cause calcium bursts. Sci Signal 2018. [PMID: 29535263 DOI: 10.1126/scisignal.aal4289] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Global bursts in free intracellular calcium (Ca2+) are among the most conspicuous signaling events in immune cells. To test the common view that Ca2+ bursts mediate rearrangement of the actin cytoskeleton in response to the activation of G protein-coupled receptors, we combined single-cell manipulation with fluorescence imaging and monitored the Ca2+ concentration in individual human neutrophils during complement-mediated chemotaxis. By decoupling purely chemotactic pseudopod formation from cell-substrate adhesion, we showed that physiological concentrations of anaphylatoxins, such as C5a, induced nonadherent human neutrophils to form chemotactic pseudopods but did not elicit Ca2+ bursts. By contrast, pathological or supraphysiological concentrations of C5a often triggered Ca2+ bursts, but pseudopod protrusion stalled or reversed in such cases, effectively halting chemotaxis, similar to sepsis-associated neutrophil paralysis. The maximum increase in cell surface area during pseudopod extension in pure chemotaxis was much smaller-by a factor of 8-than the known capacity of adherent human neutrophils to expand their surface. Because the measured rise in cortical tension was not sufficient to account for this difference, we attribute the limited deformability to a reduced ability of the cytoskeleton to generate protrusive force in the absence of cell adhesion. Thus, we hypothesize that Ca2+ bursts in neutrophils control a mechanistic switch between two distinct modes of cytoskeletal organization and dynamics. A key element of this switch appears to be the expedient coordination of adhesion-dependent lock or release events of cytoskeletal membrane anchors.
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Affiliation(s)
- Emmet A Francis
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, USA
| | - Volkmar Heinrich
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, USA.
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6
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Direct In Vivo Manipulation and Imaging of Calcium Transients in Neutrophils Identify a Critical Role for Leading-Edge Calcium Flux. Cell Rep 2015; 13:2107-17. [PMID: 26673320 DOI: 10.1016/j.celrep.2015.11.010] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2015] [Revised: 09/21/2015] [Accepted: 10/30/2015] [Indexed: 10/22/2022] Open
Abstract
Calcium signaling has long been associated with key events of immunity, including chemotaxis, phagocytosis, and activation. However, imaging and manipulation of calcium flux in motile immune cells in live animals remain challenging. Using light-sheet microscopy for in vivo calcium imaging in zebrafish, we observe characteristic patterns of calcium flux triggered by distinct events, including phagocytosis of pathogenic bacteria and migration of neutrophils toward inflammatory stimuli. In contrast to findings from ex vivo studies, we observe enriched calcium influx at the leading edge of migrating neutrophils. To directly manipulate calcium dynamics in vivo, we have developed transgenic lines with cell-specific expression of the mammalian TRPV1 channel, enabling ligand-gated, reversible, and spatiotemporal control of calcium influx. We find that controlled calcium influx can function to help define the neutrophil's leading edge. Cell-specific TRPV1 expression may have broad utility for precise control of calcium dynamics in other immune cell types and organisms.
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Hübner K, Surovtsova I, Yserentant K, Hänsch M, Kummer U. Ca2+ dynamics correlates with phenotype and function in primary human neutrophils. Biophys Chem 2013; 184:116-25. [PMID: 24262430 DOI: 10.1016/j.bpc.2013.09.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Revised: 09/19/2013] [Accepted: 09/23/2013] [Indexed: 12/11/2022]
Abstract
Central to the immune defense function of neutrophils is to sense, to move and to kill. Neutrophils acquire distinct cellular states necessary to fulfill these functions each associated with a particular phenotype. The cells constituting the neutrophil population are presumably not synchronized with respect to their actual state, e.g. due to maturity or preactivation. It is also likely that they exhibit a different degree of phenotypic plasticity (that is, the ability to switch to a particular state). Calcium is known to play a crucial role in neutrophils such as for cell motility. The present study focuses on characterizing the cell-to-cell variability at the morphological as well as at the level of calcium dynamics by studying single primary human neutrophils. We apply long-term multivariate live cell imaging to (i) characterize neutrophil phenotypes of different functional states, (ii) analyze the distribution of cells being in these states and, (iii) study the individual intracellular calcium response simultaneously with shape changes. We are able to differentiate the five distinct subpopulations of neutrophils based on quantitative parameters of cell morphology and motility. As a major result, we demonstrate that the calcium dynamics of individual cells correlates with their respective functional state. Finally, we see a number of cells that undergo spontaneous phenotypic changes from one cellular state to another. These events are preceded either by exhibiting the calcium dynamics of the future state or by switching to the respective calcium dynamics in parallel to switching the morphology. Based on our results we conclude that specific calcium dynamics carries crucial information for the function and phenotype of neutrophils.
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Affiliation(s)
- Katrin Hübner
- Modeling of Biological Processes, BioQuant, COS Heidelberg, University of Heidelberg, Heidelberg, Germany
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8
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Gahl RF, Tekle E, Tjandra N. Single color FRET based measurements of conformational changes of proteins resulting from translocation inside cells. Methods 2013; 66:180-7. [PMID: 23872323 DOI: 10.1016/j.ymeth.2013.07.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2013] [Revised: 06/14/2013] [Accepted: 07/08/2013] [Indexed: 10/26/2022] Open
Abstract
Translocation of proteins to different parts of the cell is necessary for many cellular mechanisms as a means for regulation and a variety of other functions. Identifying how these proteins undergo conformational changes or interact with various partners during these events is critical to understanding how these mechanisms are executed. A protocol is presented that identifies conformational changes in a protein that occur during translocation while overcoming challenges in extracting distance information in very different environments of a living cell. Only two samples are required to be prepared and are observed with one optical setup. Live-cell FRET imaging has been applied to identify conformational changes between two native cysteines in Bax, a member of the Bcl-2 family of proteins that regulates apoptosis. Bax exists in the cytosol and translocates to the mitochondria outer membrane upon apoptosis induction. The distance, r, between the two native cysteines in the cytosolic structure of Bax necessitates the use of a FRET donor-accepter pair with R0~r as the most sensitive probe for identifying structural changes at these positions. Alexa Fluor 546 and Dabcyl, a dark acceptor, were used as FRET pairs - resulting in single color intensity variations of Alexa-546 as a measure of FRET efficiency. An internal reference, conjugated to Bax, was employed to normalize changes in fluorescence intensity of Alexa Fluor 546 due to inherent inhomogeneities in the living cell. This correction allowed the true FRET effects to be measured with increased precision during translocation. Normalization of intensities to the internal reference identified a FRET efficiency of 0.45±0.14 in the cytosol and 0.11±0.20 in the mitochondria. The procedure for the conjugation of the internal reference and FRET probes as well as the data analysis is presented.
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Affiliation(s)
- Robert F Gahl
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart Lung and Blood Institute - National Institutes of Health, Bethesda, MD 20892, United States
| | - Ephrem Tekle
- Laboratory of Biochemistry, Biochemistry and Biophysics Center, National Heart Lung and Blood Institute - National Institutes of Health, Bethesda, MD 20892, United States
| | - Nico Tjandra
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart Lung and Blood Institute - National Institutes of Health, Bethesda, MD 20892, United States.
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9
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Hallett MB, Dewitt S. A trick of the light: the optical properties of living cytoplasm which can mislead. Integr Biol (Camb) 2011; 3:180-4. [DOI: 10.1039/c0ib00039f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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10
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Integrins and ion channels in cell migration: implications for neuronal development, wound healing and metastatic spread. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 674:107-23. [PMID: 20549944 DOI: 10.1007/978-1-4419-6066-5_10] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cells migration is necessary for proper embryonic development and adult tissue remodeling. Its mechanisms determine the physiopathology of processes such as neuronal targeting, inflammation, wound healing and metastatic spread. Crawling of cells onto solid surfaces requires a controlled sequence of cell protrusions and retractions that mainly depends on sophisticated regulation of the actin cytoskeleton, although the contribution of microtubules should not be neglected. This process is triggered and modulated by a combination of diffusible and fixed environmental signals. External cues are sensed and integrated by membrane receptors, including integrins, which transduce these signals into cellular signaling pathways, often centered on the small GTPase proteins belonging to the Rho family. These pathways regulate the coordinated cytoskeletal rearrangements necessary for proper timing of adhesion, contraction and detachement at the front and rear side of cells finding their way through the extracellular spaces. The overall process involves continuous modulation of cell motility, shape and volume, in which ion channels play major roles. In particular, Ca2+ signals have both global and local regulatory effects on cell motility, because they target the contractile proteins as well as many regulatory proteins. After reviewing the fundamental mechanisms of eukaryotic cell migration onto solid substrates, we briefly describe how integrin receptors and ion channels are involved in cell movement. We next examine a few processes in which these mechanisms have been studied in depth. We thus illustrate how integrins and K+ channels control cell volume and migration, how intracellular Ca2+ homeostasis affects the motility of neuronal growth cones and what is known about the ion channel roles in epithelial cell migration. These mechanisms are implicated in a variety of pathological processes, such as the disruption of neural circuits and wound healing. Finally, we describe the interaction between neoplastic cells and their local environment and how derangement of adhesion can lead to metastatic spread. It is likely that the cellular mechanisms controlled by integrin receptors, ion channels or both participate in the entire metastatic process. Until now, however, evidence is limited to a few steps of the metastatic cascade, such as brain tumor invasiveness.
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11
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Abstract
The use of fluorescent probes is one of the most powerful techniques for gaining spatial and temporal knowledge of dynamic events within living cells. Localized increases in the signal from cytosolic fluorescent protein constructs, for example, are frequently used as evidence for translocation of proteins to specific sites within the cell. However, differences in optical and geometrical properties of cytoplasm can influence the recorded intensity of the probe signal. Pseudopodia are especially problematic because their cytoplasmic properties can cause abrupt increases in fluorescent signal of both GFP and fluorescein. Investigators should therefore be cautious when interpreting fluorescence changes within a cell, as these can result from either translocation of the probe or changes in the optical properties of the milieu surrounding the probe.
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Affiliation(s)
- Sharon Dewitt
- Neutrophil Signalling Group and Department of Haematology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, Wales, UK
| | - Richard L. Darley
- Neutrophil Signalling Group and Department of Haematology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, Wales, UK
| | - Maurice B. Hallett
- Neutrophil Signalling Group and Department of Haematology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, Wales, UK
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12
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Wall IB, Moseley R, Baird DM, Kipling D, Giles P, Laffafian I, Price PE, Thomas DW, Stephens P. Fibroblast dysfunction is a key factor in the non-healing of chronic venous leg ulcers. J Invest Dermatol 2008; 128:2526-40. [PMID: 18449211 DOI: 10.1038/jid.2008.114] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Chronic age-related degenerative disorders, including the formation of chronic leg wounds, may occur due to aging of the stromal tissues and ensuing dysfunctional cellular responses. This study investigated the impact of environmental-driven cellular aging on wound healing by conducting a comprehensive analysis of chronic wound fibroblast (CWF) behavior in comparison with patient-matched healthy skin normal fibroblasts (NF). The dysfunctional wound healing abilities of CWF correlated with a significantly reduced proliferative life span and early onset of senescence compared with NF. However, pair-wise comparisons of telomere dynamics between NF and CWF indicated that the induction of senescence in CWF was telomere-independent. Microarray and functional analysis suggested that CWFs have a decreased ability to withstand oxidative stress, which may explain why these cells prematurely senescence. Microarray analysis revealed lower expression levels of several CXC chemokine genes (CXCL-1, -2, -3, -5, -6, -12) in CWF compared with NF (confirmed by ELISA). Functionally, this was related to impaired neutrophil chemotaxis in response to CWF-conditioned medium. Although the persistence of non-healing wounds is, in part, due to prolonged chronic inflammation and bacterial infection, our investigations show that premature fibroblast aging and an inability to correctly express a stromal address code are also implicated in the disease chronicity.
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Affiliation(s)
- Ivan B Wall
- Wound Biology Group, Cardiff Institute of Tissue Engineering and Repair, Cardiff University, Cardiff, UK
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13
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Maroto R, Hamill OP. MscCa Regulation of Tumor Cell Migration and Metastasis. CURRENT TOPICS IN MEMBRANES 2007; 59:485-509. [PMID: 25168147 DOI: 10.1016/s1063-5823(06)59019-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The acquisition of cell motility is a required step in order for a cancer cell to migrate from the primary tumor and spread to secondary sites (metastasize). For this reason, blocking tumor cell migration is considered a promising approach for preventing the spread of cancer. However, cancer cells just as normal cells can migrate by several different modes referred to as "amoeboid," "mesenchymal," and "collective cell." Under appropriate conditions, a single cell can switch between modes. A consequence of this plasticity is that a tumor cell may be able to avoid the effects of an agent that targets only one mode by switching modes. Therefore, a preferred strategy would be to target mechanisms that are shared by all modes. This chapter reviews the evidence that Ca(2+) influx via the mechanosensitive Ca(2+)-permeable channel (MscCa) is a critical regulator of all modes of cell migration and therefore represents a very good therapeutic target to block metastasis.
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Affiliation(s)
- Rosario Maroto
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas 77555
| | - Owen P Hamill
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas 77555
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14
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Abstract
Neuronal motility is a fundamental feature that underlies the development, regeneration, and plasticity of the nervous system. Two major developmental events--directed migration of neuronal precursor cells to the proper positions and guided elongation of axons to their target cells--depend on large-scale neuronal motility. At a finer scale, motility is also manifested in many aspects of neuronal structures and functions, ranging from differentiation and refinement of axonal and dendritic morphology during development to synapse remodeling associated with learning and memory in the adult brain. As a primary second messenger that conveys the cytoplasmic actions of electrical activity and many neuroactive ligands, Ca(2+) plays a central role in the regulation of neuronal motility. Recent studies have revealed common Ca(2+)-dependent signaling pathways that are deployed for regulating cytoskeletal dynamics associated with neuronal migration, axon and dendrite development and regeneration, and synaptic plasticity.
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Affiliation(s)
- James Q Zheng
- Department of Neuroscience and Cell Biology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
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15
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Panaro MA, Acquafredda A, Sisto M, Lisi S, Maffione AB, Mitolo V. Biological role of the N-formyl peptide receptors. Immunopharmacol Immunotoxicol 2006; 28:103-27. [PMID: 16684671 DOI: 10.1080/08923970600625975] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Ligation of N-formyl-methionyl-leucyl-phenylalanine (fMLP) to its specific cell surface receptors triggers different cascades of biochemical events, eventually leading to cellular activation. The formyl peptide receptors (FPRs) are members of the seven-transmembrane, G-protein coupled receptors superfamily, expressed at high levels on polymorphonuclear and mononuclear phagocytes. The main responses elicited upon ligation of formylated peptides, referred to as cellular activation, are those of morphological polarization, locomotion, production of reactive-oxygen species and release of proteolytic enzymes. FPRs have in recent years been shown to be expressed also in several non myelocytic populations, suggesting other unidentified functions for this receptor family, independent of the inflammatory response. Finally, a number of ligands acting as exogenous or host-derived agonists for FPRs, as well as ligands acting as FPRs antagonists, have been described, indicating that these receptors may be differentially modulated by distinct molecules.
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Affiliation(s)
- M A Panaro
- Department of Human Anatomy and Histology, University of Bari, Italy.
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16
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Rada BK, Geiszt M, Hably C, Ligeti E. Consequences of the electrogenic function of the phagocytic NADPH oxidase. Philos Trans R Soc Lond B Biol Sci 2006; 360:2293-300. [PMID: 16321799 PMCID: PMC1569590 DOI: 10.1098/rstb.2005.1768] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
NADPH oxidase of phagocytic cells transfers a single electron from intracellular NADPH to extracellular O2, producing superoxide (O.-2), the precursor to several other reactive oxygen species. The finding that a genetic defect of the enzyme causes chronic granulomatous disease (CGD), characterized by recurrent severe bacterial infections, linked O.-2 generation to destruction of potentially pathogenic micro-organisms. In this review, we focus on the consequences of the electrogenic functioning of NADPH oxidase. We show that enzyme activity depends on the possibilities for compensating charge movements. In resting neutrophils K+ conductance dominates, but upon activation the plasma membrane rapidly depolarizes beyond the opening threshold of voltage-gated H+ channels and H+ efflux becomes the major charge compensating factor. K+ release is likely to contribute to the killing of certain bacteria but complete elimination only occurs if O.-2 production can proceed at full capacity. Finally, the reversed membrane potential of activated neutrophils inhibits Ca2+ entry, thereby preventing overloading the cells with Ca2+. Absence of this limiting mechanism in CGD cells may contribute to the pathogenesis of the disease.
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17
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Selvatici R, Falzarano S, Mollica A, Spisani S. Signal transduction pathways triggered by selective formylpeptide analogues in human neutrophils. Eur J Pharmacol 2006; 534:1-11. [PMID: 16516193 DOI: 10.1016/j.ejphar.2006.01.034] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Revised: 01/03/2006] [Accepted: 01/20/2006] [Indexed: 01/01/2023]
Abstract
Human neutrophils are highly specialised for their primary function, i.e. phagocytosis and destruction of microorganisms. Leukocyte recruitment to sites of inflammation and infection is dependent upon the presence of a gradient of locally produced chemotactic factors. The bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) was one of the first of these to be identified and is a highly potent leukocyte chemoattractant. It interacts with its receptor on the neutrophil membrane, activating these cells through a G-protein-coupled pathway. Two functional fMLP receptors have thus far been cloned and characterized, namely FPR (formyl peptide receptor) and FPRL1 (FPR like-1), with high and low affinities for fMLP, respectively. FMLP is known to activate phospholipase C (PLC), PLD, PLA2 and phosphatidylinositol-3-kinase (PI3K), and it also activates tyrosine phosphorylation. The second messengers resulting from the fMLP receptor interaction act on various intracellular kinases, including protein kinase C (PKC) and mitogen-activated protein kinases (MAPKs). The activation of these signal transduction pathways is known to be responsible for various biochemical responses which contribute to physiological defence against bacterial infection and cell disruption. This review will consider the ability of selective analogues (ligands able to discriminate between different biological responses) to activate a single spectrum of signal transduction pathways capable of producing a unique set of cellular responses, hypothesising that a distinctive imprint of signal protein activation may exist. Through more complete understanding of intracellular signaling, new drugs could be developed for the selective inflammatory blockade.
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Affiliation(s)
- Rita Selvatici
- Dipartimento di Medicina Sperimentale e Diagnostica, Sezione Genetica Medica, Via Fossato di Mortara 74, Università degli Studi di Ferrara, 44100 Ferrara, Italy
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18
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Cavicchioni G, Fraulini A, Turchetti M, Varani K, Falzarano S, Pavan B, Spisani S. Biological activity of for-Met-Leu-Phe-OMe analogs: Relevant substitutions specifically trigger killing mechanisms in human neutrophils. Eur J Pharmacol 2005; 512:1-8. [PMID: 15814083 DOI: 10.1016/j.ejphar.2005.02.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 02/08/2005] [Accepted: 02/10/2005] [Indexed: 10/25/2022]
Abstract
Two analogs of the prototypical peptide for-Met-Leu-Phe-OMe (fMLP-OMe), for-Gln-Tyr-Phe-OMe (1) and for-Gln-Tyr-Tyr-OMe (2), carrying unusual hydrophilic residues, were synthesized in order to investigate whether they provoked specific biological responses, as well as intracellular calcium mobilization, in human neutrophils. Whereas neither compound stimulates chemotaxis, both are able to elicit lysosomal enzyme production. However compound 1 is able to trigger copious superoxide anion production while compound 2 only elicits minor superoxide anion production. In binding experiments on formylpeptide receptors, the newly synthesized compounds for-Gln-Tyr-Phe-OMe (1) and for-Gln-Tyr-Tyr-OMe (2) showed affinity values in the micromolar range. These derivatives demonstrate inability to find a positive contribute from single substitutions. A very important result of this research is the evidence of the ability of the formyl group alone to trigger the primary target of the human neutrophil activity, i.e. killing mechanisms, by activating the specific receptor conformation.
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Affiliation(s)
- Giorgio Cavicchioni
- Department of Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17/19, 44100 Ferrara, Italy.
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Tian W, Dewitt S, Laffafian I, Hallett MB. Ca(2+), calpain and 3-phosphorylated phosphatidyl inositides; decision-making signals in neutrophils as potential targets for therapeutics. ACTA ACUST UNITED AC 2004; 56:565-71. [PMID: 15142332 DOI: 10.1211/0022357023466] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The chemical signals within neutrophils that control their behaviour are complex and these signals control the complex activity of neutrophils with precision. Failure of neutrophils to reform their antibacterial activity would lead to infection, while over-activity of neutrophils may lead to tissue damage and inflammatory disease. The identity of some of the intracellular signals is becoming clear and insights into the potential for interplay between them are being sought. Although it is well established that cytosolic free Ca(2+) plays a role, it is only recently that the importance of intracellular protease, calpain, and the 3-position phosphorylated phosphatidyl inositides is becoming recognised. In this review these three key signals are discussed as potential therapeutic targets for the modulation of neutrophil activity.
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Affiliation(s)
- Wei Tian
- Department of Surgery, University of Wales College of Medicine, Heath Park, Cardiff, CF14 4XN, UK
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Tian W, Laffafian I, Dewitt S, Hallett MB. Exclusion of exogenous phosphatidylinositol-3,4,5-trisphosphate from neutrophil-polarizing pseudopodia: stabilization of the uropod and cell polarity. EMBO Rep 2004; 4:982-8. [PMID: 14528267 PMCID: PMC1326405 DOI: 10.1038/sj.embor.embor947] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2002] [Revised: 06/11/2003] [Accepted: 08/21/2003] [Indexed: 12/17/2022] Open
Abstract
Although there is accumulating evidence that the generation and localization of phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) have important functions in neutrophil polarization and chemotaxis, the mechanism of this linkage has yet to be established. Here, using exogenous fluorescent PtdIns(3,4,5)P(3) introduced into the inner leaflet of the neutrophil plasma membrane by a cationic carrier, we show that: first, PtdIns(3,4,5)P(3) uniformly delivered to the neutrophil plasma membrane is excluded from newly forming pseudopodia; second, PtdIns(3,4,5)P(3) translocates to and is immobilized at the pole opposite a stable polarizing pseudopod; third, asymmetric delivery of PtdIns(3,4,5)P(3) to the neutrophil triggers the generation of polarizing pseudopodia at the opposite pole; and finally, PtdIns(3,4,5)P(3) triggers repetitive Ca(2+) signals, the onset of which precedes morphological polarization. These data suggest that translocation and immobilization of PtdIns(3,4,5)P(3) or a 3,x-phosphorylated metabolite in the uropod functions as an important polarization cue that defines neutrophil polarity and stabilizes the generation of pseudopodia at the opposite pole.
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Affiliation(s)
- Wei Tian
- Neutrophil Signalling Group, University
Department of Surgery, University of Wales College of Medicine, Heath
Park, Cardiff CF14 4XN, UK
| | - Iraj Laffafian
- Neutrophil Signalling Group, University
Department of Surgery, University of Wales College of Medicine, Heath
Park, Cardiff CF14 4XN, UK
| | - Sharon Dewitt
- Neutrophil Signalling Group, University
Department of Surgery, University of Wales College of Medicine, Heath
Park, Cardiff CF14 4XN, UK
| | - Maurice B. Hallett
- Neutrophil Signalling Group, University
Department of Surgery, University of Wales College of Medicine, Heath
Park, Cardiff CF14 4XN, UK
- Tel: +44 29 20 742748; Fax: +44 29 20 761623;
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Dewitt S, Hallett MB. Cytosolic free Ca(2+) changes and calpain activation are required for beta integrin-accelerated phagocytosis by human neutrophils. J Cell Biol 2002; 159:181-9. [PMID: 12379807 PMCID: PMC2173489 DOI: 10.1083/jcb.200206089] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phagocytosis of microbes coated with opsonins such as the complement component C3bi is the key activity of neutrophils. However, the mechanism by which opsonins enhance the rate of phagocytosis by these cells is unknown and has been difficult to study, partly because of the problem of observing and quantifying the events associated with phagocytosis. In this study, C3bi-opsonized particles were presented to neutrophils with a micromanipulator, so that the events of binding, pseudopod cup formation, engulfment, and completion of phagocytosis were clearly defined and distinguished from those involved with chemotaxis. Using this approach in combination with simultaneous phase contrast and Ca(2+) imaging, the temporal relationship between changes in cytosolic free Ca(2+) concentration and phagocytosis were correlated. Here we show that whereas small, localized Ca(2+) changes occur at the site of particle attachment and cup formation as a result of store release, rapid engulfment of the particle required a global change in cytosolic free Ca(2+) which resulted from Ca(2+) influx. This latter rise in cytosolic free Ca(2+) concentration also liberated a fraction of beta2 integrin receptors which were initially immobile on the neutrophil surface, as demonstrable by both fluorescence recovery after laser bleaching and by visualization of localized beta2 integrin labelling. Inhibitors of calpain activation prevented both the Ca(2+)-induced liberation of beta2 integrin and the rapid stage of phagocytosis, despite the persistence of the global Ca(2+) signal. Therefore, we propose that Ca(2+) activation of calpain causes beta2 integrin liberation, and that this signal plays a key role in the acceleration of beta2 integrin-mediated phagocytosis.
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Affiliation(s)
- Sharon Dewitt
- Neutrophil Signalling Group, University Department of Surgery, University of Wales College of Medicine, Cardiff CF14 4XN, United Kingdom
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Dewitt S, Laffafian I, Hallett MB. Does neutrophil CD38 have a role in Ca++ signaling triggered by beta2 integrin? Nat Med 2002; 8:307; author reply 307-8. [PMID: 11927913 DOI: 10.1038/nm0402-307a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Lund FE, Randall TD, Partida-Sánchez S. Reply to 'Does neutrophil CD38 have a role in Ca++ signaling triggered by β2 integrin?'. Nat Med 2002. [DOI: 10.1038/nm0402-307b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Morris MR, Doull IJ, Hallett MB. Osmotically induced cytosolic free Ca(2+) changes in human neutrophils. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1538:20-7. [PMID: 11341979 DOI: 10.1016/s0167-4889(00)00133-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cytosolic free Ca(2+) concentration in neutrophils was measured by ratiometric fluorometry of intracellular fura2. Increasing the extracellular osmolarity, by either NaCl (300-600 mM) or sucrose (600-1200 mM), caused a rise in cytosolic free Ca(2+) (Delta(max) approximately equal to 600 nM). This was not due to cell lysis as the cytosolic free Ca(2+) concentration was reversed by restoration of isotonicity and a second rise in cytosolic free Ca(2+) could be provoked by repeating the change in extracellular osmolarity. Furthermore, the rise in cytosolic free Ca(2+) concentration occurred in the absence of extracellular Ca(2+), demonstrating that release of intracellular fura2 into the external medium did not occur. The osmotically-induced rise in cytosolic free Ca(2+) was not inhibited by either the phospholipase C-inhibitor U73122, or the microfilament inhibitor cytochalasin B, suggesting that neither signalling via inositol tris-phosphate or the cytoskeletal system were involved. However, the rise in cytosolic free Ca(2+) may have resulted from a reduction in neutrophil water volume in hyperosmotic conditions. As these rises in cytosolic Ca(2+) (Delta(max) approximately equal to 600 nM) were large enough to provoke changes in neutrophil activity, we propose that conditions which removes cell water may similarly elevate cytosolic free Ca(2+) to physiologically important levels.
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Affiliation(s)
- M R Morris
- Molecular Signalling Group, Department of Surgery, University of Wales College of Medicine, Cardiff, UK
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Preobrazhensky AA, Dragan S, Kawano T, Gavrilin MA, Gulina IV, Chakravarty L, Kolattukudy PE. Monocyte chemotactic protein-1 receptor CCR2B is a glycoprotein that has tyrosine sulfation in a conserved extracellular N-terminal region. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 165:5295-303. [PMID: 11046064 DOI: 10.4049/jimmunol.165.9.5295] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Monocyte chemotactic protein-1 (MCP-1) binding to its receptor, CCR2B, plays an important role in a variety of diseases involving infection, inflammation, and/or injury. In our effort to understand the molecular basis of this interaction and its biological consequences, we recognized a conserved hexad of amino acids at the N-terminal extracellular domain of several chemokine receptors, including CCR2B. Human embryonic kidney 293 cells expressing Flag-tagged CCR2B containing site-directed mutations in this region, 21-26, including a consensus tyrosine sulfation site were used to determine MCP-1 binding and its biological consequences. The results showed that several of these amino acids are important for MCP-1 binding and consequent lamellipodium formation, chemotaxis, and signal transduction involving adenylate cyclase inhibition and Ca(2+) influx into cytoplasm. Mutations that prevented adenylate cyclase inhibition and Ca(2+) influx did not significantly inhibit lamellipodium formation and chemotaxis, suggesting that these signaling events are not involved in chemotaxis. CCR2B was found to be sulfated at Tyr(26); this sulfation was abolished by the substitution of Tyr with Ala and severely reduced by substitution of Asp(25), a part of the consensus sulfation site. The expressed CCR2B was found to be N:-glycosylated, as N:-glycosidase F treatment of the receptor or growth of the cells in tunicamycin reduced the receptor size to the same level, from 50 to 45 kDa. Thus, CCR2B is the first member of the CC chemokine receptor family shown to be a glycoprotein that is sulfated at the N-terminal Tyr. These post-translational modifications probably have significant biological functions.
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Affiliation(s)
- A A Preobrazhensky
- Neurobiotechnology Center and Departments of Biochemistry and Molecular and Cellular Biochemistry, Ohio State University, Columbus, OH 43210, USA
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Pettit EJ, Hallett MB. Release of ‘caged’ cytosolic Ca2+ triggers rapid spreading of human neutrophils adherent via integrin engagement. J Cell Sci 1998; 111 ( Pt 15):2209-15. [PMID: 9664042 DOI: 10.1242/jcs.111.15.2209] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The role of the transient rise in cytosolic free Ca2+ which occurs during neutrophil adhesion and cell spreading is unclear. In order to establish whether such a Ca2+ signal triggers neutrophil shape change, neutrophils co-loaded with fluo3 and Nitr5 (‘caged’ Ca2+) were used with rapid-time confocal laser scanning microscopy. Here we show that the photolytic generation of a Ca2+ rise in neutrophils which were adherent to an integrin-engaging surface, triggered a rapid change in cell morphology, with increases in cell diameter of approximately 175% occurring within 90 seconds of the Ca2+ signal. In non-adhered neutrophils or neutrophils on plain glass, no acceleration of the rate of spreading occurring in response to the release of ‘caged Ca2+’ could be demonstrated. It was concluded that although a rise in cytosolic free Ca2+ was not the sole trigger for neutrophil shape change, with other signals generated by integrin engagement, a rise in cytosolic free Ca2+ accelerated the rate of neutrophil spreading.
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Affiliation(s)
- E J Pettit
- Molecular Signalling Group, Department of Surgery, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN, UK
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Fabbri E, Spisani S, Biondi C, Barbin L, Colamussi ML, Cariani A, Traniello S, Torrini I, Ferretti ME. Two for-Met-Leu-Phe-OMe analogues trigger selective neutrophil responses. A differential effect on cytosolic free Ca2+. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1359:233-40. [PMID: 9434129 DOI: 10.1016/s0167-4889(97)00101-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
For-Thp-Leu-Ain-OMe and for-Met-delta(z)Leu-Phe-OMe are two conformationally restricted fMLP-OMe analogues able to discriminate between different biological responses of human neutrophils. In this paper, we demonstrate that the former peptide, which evokes only chemotaxis, does not alter human neutrophil Ca2+ levels. In contrast, for-Met-delta(z)Leu-Phe-OMe, which induces superoxide anion release and degranulation but not chemotaxis, significantly increases the cation concentration. The chelation of Ca2+ in both extracellular and intracellular media abolishes O2- production triggered by for-Met-delta(z)Leu-Phe-OMe, while the same procedure does not affect neutrophil chemotaxis towards for-Thp-Leu-Ain-OMe. We therefore suggest that chemotaxis, unlike superoxide anion release, is independent of Ca2+ enhancement in human neutrophils.
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Affiliation(s)
- E Fabbri
- Dipartimento di Biologia, Università degli Studi, Ferrara, Italy
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29
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Galkin AA, Tumanov EA, Timin EN, Karelin AA. Effect of activators on neutrophil mobility. Bull Exp Biol Med 1997. [DOI: 10.1007/bf02446839] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Abstract
Our defence against microbes depends largely on the ability of neutrophils to migrate from the blood stream to sites of infection. Although the ability of animal cells to move may be primitive, and also fundamental for a number of phenomena in biology, the cellular mechanism by which neutrophils are able to move rapidly towards the infection remains an enigma. Even though the structures of the receptors involved have been sequenced and many of the molecules involved in neutrophil adherence and traction identified, the essential mechanisms that control and regulate the neutrophil motor remain obscure. Here, an outline of the fundamental inadequacies in our current understanding is given, along with some recent developments that promise to produce some significant advances.
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Affiliation(s)
- M B Hallett
- Molecular Signalling Group, University Department of Surgery, University of Wales College of Medicine, Heath Park, Cardiff, UK
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Yumura S, Furuya K, Takeuchi I. Intracellular free calcium responses during chemotaxis of Dictyostelium cells. J Cell Sci 1996; 109 ( Pt 11):2673-8. [PMID: 8937985 DOI: 10.1242/jcs.109.11.2673] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A calcium ion indicator, fura-2 bovine serum albumin, was introduced into Dictyostelium discoideum cells by electroporation. The concentration of intracellular calcium ions ([Ca2+]i) increased transiently in vegetative cells upon stimulation with submicromolar concentrations of folic acid, a chemoattractant for this organism at the vegetative stage. Similar [Ca2+]i responses were also observed in aggregation-competent cells upon stimulation with subnanomolar concentrations of cAMP, a chemoattractant at the aggregation stage. The [Ca2+]i response caused by cAMP was 2.1 times higher than that caused by folic acid. The magnitude of these responses depended on the concentration of Ca2+ in the external buffer. The presence of magnesium ions inhibited the [Ca2+]i responses in a dose-dependent manner. [Ca2+]i was higher in the rear region than in the anterior region of cells freely migrating on the surface, although such a gradient was not always maintained. When aggregation competent cells were locally stimulated by the application of a microcapillary containing cAMP, the cells extended pseudopods toward the microcapillary. In these cases, an increase in [Ca2+]i was transiently observed in the region opposite to the tip of the capillary. At the slug stage, [Ca2+]i was higher in prestalk cells than in prespore cells of slugs. The possibility that the [Ca2+]i is spatially regulated within a cell was discussed.
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Affiliation(s)
- S Yumura
- Department of Biology, Faculty of Science, Yamaguchi University, Japan.
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Affiliation(s)
- D A Lauffenburger
- Center for Biomedical Engineering, Massachusetts Institute of Technology Cambridge 02139, USA
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