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MiR-148a inhibits the proliferation and migration of glioblastoma by targeting ITGA9. Hum Cell 2019; 32:548-556. [DOI: 10.1007/s13577-019-00279-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2019] [Accepted: 08/28/2019] [Indexed: 02/04/2023]
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Directional Transport of a Bead Bound to Lamellipodial Surface Is Driven by Actin Polymerization. BIOMED RESEARCH INTERNATIONAL 2017; 2017:7804251. [PMID: 28246604 PMCID: PMC5299216 DOI: 10.1155/2017/7804251] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/27/2016] [Revised: 10/31/2016] [Accepted: 11/30/2016] [Indexed: 01/02/2023]
Abstract
The force driving the retrograde flow of actin cytoskeleton is important in the cellular activities involving cell movement (e.g., growth cone motility in axon guidance, wound healing, or cancer metastasis). However, relative importance of the forces generated by actin polymerization and myosin II in this process remains elusive. We have investigated the retrograde movement of the poly-d-lysine-coated bead attached with the optical trap to the edge of lamellipodium of Swiss 3T3 fibroblasts. The velocity of the attached bead drastically decreased by submicromolar concentration of cytochalasin D, latrunculin A, or jasplakinolide, indicating the involvement of actin turnover. On the other hand, the velocity decreased only slightly in the presence of 50 μM (-)-blebbistatin and Y-27632. Comparative fluorescence microscopy of the distribution of actin filaments and that of myosin II revealed that the inhibition of actin turnover by cytochalasin D, latrunculin A, or jasplakinolide greatly diminished the actin filament network. On the other hand, inhibition of myosin II activity by (-)-blebbistatin or Y-27632 little affected the actin network but diminished stress fibers. Based on these results, we conclude that the actin polymerization/depolymerization plays the major role in the retrograde movement, while the myosin II activity is involved in the maintenance of the dynamic turnover of actin in lamellipodium.
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Hong Z, Reeves KJ, Sun Z, Li Z, Brown NJ, Meininger GA. Vascular smooth muscle cell stiffness and adhesion to collagen I modified by vasoactive agonists. PLoS One 2015; 10:e0119533. [PMID: 25745858 PMCID: PMC4351978 DOI: 10.1371/journal.pone.0119533] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 01/22/2015] [Indexed: 11/25/2022] Open
Abstract
In vascular smooth muscle cells (VSMCs) integrin-mediated adhesion to extracellular matrix (ECM) proteins play important roles in sustaining vascular tone and resistance. The main goal of this study was to determine whether VSMCs adhesion to type I collagen (COL-I) was altered in parallel with the changes in the VSMCs contractile state induced by vasoconstrictors and vasodilators. VSMCs were isolated from rat cremaster skeletal muscle arterioles and maintained in primary culture without passage. Cell adhesion and cell E-modulus were assessed using atomic force microscopy (AFM) by repetitive nano-indentation of the AFM probe on the cell surface at 0.1 Hz sampling frequency and 3200 nm Z-piezo travelling distance (approach and retraction). AFM probes were tipped with a 5 μm diameter microbead functionalized with COL-I (1mg\ml). Results showed that the vasoconstrictor angiotensin II (ANG-II; 10−6) significantly increased (p<0.05) VSMC E-modulus and adhesion probability to COL-I by approximately 35% and 33%, respectively. In contrast, the vasodilator adenosine (ADO; 10−4) significantly decreased (p<0.05) VSMC E-modulus and adhesion probability by approximately −33% and −17%, respectively. Similarly, the NO donor (PANOate, 10−6 M), a potent vasodilator, also significantly decreased (p<0.05) the VSMC E-modulus and COL-I adhesion probability by −38% and −35%, respectively. These observations support the hypothesis that integrin-mediated VSMC adhesion to the ECM protein COL-I is dynamically regulated in parallel with VSMC contractile activation. These data suggest that the signal transduction pathways modulating VSMC contractile activation and relaxation, in addition to ECM adhesion, interact during regulation of contractile state.
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Affiliation(s)
- Zhongkui Hong
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States of America
- Department of Pharmacology and Physiology, University of Missouri, Columbia, Missouri, United States of America
| | - Kimberley J. Reeves
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States of America
| | - Zhe Sun
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States of America
- Department of Pharmacology and Physiology, University of Missouri, Columbia, Missouri, United States of America
| | - Zhaohui Li
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States of America
| | - Nicola J. Brown
- Department of Oncology, University of Sheffield, Sheffield, United Kingdom
| | - Gerald A. Meininger
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States of America
- Department of Pharmacology and Physiology, University of Missouri, Columbia, Missouri, United States of America
- * E-mail:
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Ostuni MA, Guellec J, Hermand P, Durand P, Combadière C, Pincet F, Deterre P. CX3CL1, a chemokine finely tuned to adhesion: critical roles of the stalk glycosylation and the membrane domain. Biol Open 2014; 3:1173-82. [PMID: 25395671 PMCID: PMC4265755 DOI: 10.1242/bio.20149845] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The multi-domain CX3CL1 transmembrane chemokine triggers leukocyte adherence without rolling and migration by presenting its chemokine domain (CD) to its receptor CX3CR1. Through the combination of functional adhesion assays with structural analysis using FRAP, we investigated the functional role of the other domains of CX3CL1, i.e., its mucin stalk, transmembrane domain, and cytosolic domain. Our results indicate that the CX3CL1 molecular structure is finely adapted to capture CX3CR1 in circulating cells and that each domain has a specific purpose: the mucin stalk is stiffened by its high glycosylation to present the CD away from the membrane, the transmembrane domain generates the permanent aggregation of an adequate amount of monomers to guarantee adhesion and prevent rolling, and the cytosolic domain ensures adhesive robustness by interacting with the cytoskeleton. We propose a model in which quasi-immobile CX3CL1 bundles are organized to quickly generate adhesive patches with sufficiently high strength to capture CX3CR1+ leukocytes but with sufficiently low strength to allow their patrolling behavior.
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Affiliation(s)
- Mariano A Ostuni
- INSERM, U 1135, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France Sorbonne Universités, UPMC Université Paris 06, UMRS CR7, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France CNRS, ERL 8255, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France Present address: INSERM, U 1134, Biologie Intégrée du Globule Rouge; Université Paris Diderot; Institut National de la Transfusion Sanguine, 6 rue Alexandre Cabanel, 75015, Paris, France
| | - Julie Guellec
- INSERM, U 1135, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France Sorbonne Universités, UPMC Université Paris 06, UMRS CR7, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France CNRS, ERL 8255, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France
| | - Patricia Hermand
- INSERM, U 1135, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France Sorbonne Universités, UPMC Université Paris 06, UMRS CR7, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France CNRS, ERL 8255, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France
| | - Pauline Durand
- Sorbonne Universités, UPMC Université Paris 06, UMR 94550 ENS Laboratoire de Physique Statistique, F-75005, Paris, France
| | - Christophe Combadière
- INSERM, U 1135, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France Sorbonne Universités, UPMC Université Paris 06, UMRS CR7, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France CNRS, ERL 8255, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France
| | - Frédéric Pincet
- Sorbonne Universités, UPMC Université Paris 06, UMR 94550 ENS Laboratoire de Physique Statistique, F-75005, Paris, France
| | - Philippe Deterre
- INSERM, U 1135, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France Sorbonne Universités, UPMC Université Paris 06, UMRS CR7, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France CNRS, ERL 8255, Centre d'Immunologie et des Maladies Infectieuses, F-75013, Paris, France
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The effect of ligand affinity on integrins’ lateral diffusion in cultured cells. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2012; 42:281-90. [DOI: 10.1007/s00249-012-0873-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 10/26/2012] [Accepted: 11/16/2012] [Indexed: 01/16/2023]
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Hong Z, Sun Z, Li Z, Mesquitta WT, Trzeciakowski JP, Meininger GA. Coordination of fibronectin adhesion with contraction and relaxation in microvascular smooth muscle. Cardiovasc Res 2012; 96:73-80. [PMID: 22802110 DOI: 10.1093/cvr/cvs239] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
AIMS The regulation of vascular diameter by vasoconstrictors and vasodilators requires that vascular smooth muscle cells (VSMCs) be physically coupled to extracellular matrix (ECM) and neighbouring cells in order for a vessel to mechanically function and transfer force. The hypothesis was tested that integrin-mediated adhesion to the ECM is dynamically up-regulated in VSMCs during contractile activation in response to a vasoconstrictor and likewise down-regulated during relaxation in response to a vasodilator. METHODS AND RESULTS VSMCs were isolated from the Sprague-Dawley rat cremaster muscles. Atomic force microscopy (AFM) with fibronectin (FN)-functionalized probes was employed to investigate the biomechanical responses and adhesion of VSMCs. Responses to angiotensin II (Ang II; 10(-6) M) and adenosine (Ado; 10(-4) M) were recorded by measurements of cell cortical elasticity and cell adhesion. The results showed that Ang II caused an immediate increase in adhesion (+27%) between the probe and cell. Cell stiffness increased (+70%) in parallel with the adhesion change. Ado decreased adhesion (-15%) to FN and reduced (-30%) stiffness. CONCLUSION Changes in the receptor-mediated activation of the contractile apparatus cause parallel alterations in cell adhesion and cell cortical elasticity. These studies support the hypothesis that the regulation of cell adhesion is coordinated with contraction and demonstrate the dynamic nature of cell adhesion to the ECM. It is proposed that coordination of adhesion and VSMC contraction is an important mechanism that allows for an efficient transfer of force between the contractile apparatus of the cell and the extracellular environment.
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Affiliation(s)
- Zhongkui Hong
- Dalton Cardiovascular Research Center, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA
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Yamodo IH, Blystone SD. Calcium Integrin Binding Protein Associates with Integrins α Vβ 3 and α IIbβ 3 Independent of β 3 Activation Motifs. ACTA ACUST UNITED AC 2012; 1:30-37. [PMID: 24163826 DOI: 10.4236/cellbio.2012.12004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Calcium Integrin Binding protein (CIB) has been identified as interacting specifically with the cytoplasmic tail of the integrin αIIb domain to induce receptor activation and integrin αIIbβ3 mediated cell adhesion to extracellular proteins. In K562 cells stably expressing mutated integrin αVβ3, or chimeric αVβ3 carrying αIIb cytoplasmic tail, we report that the interaction of CIB with β3 integrins is not αIIbβ3 specific but binds αIIb as well as αV cytoplasmic tail domains. A double mutation of two proline residues to alanine residues in the αIIb cytoplasmic domain, previously shown to disturb its conformation, inhibits chimeric αV/αIIbβ3-CIB interaction. This demonstrates that αIIb cytoplasmic domain loop-like conformation is required for interaction with CIB. Moreover, mutations of β3 cytoplasmic domain residues Tyr-747 and/or Tyr-759 to phenylalanine residues (Y747F, Y759F, and Y747,759F) as well as residues Ser-752 to proline or alanine (S752P and S752A), do not affect the αIIbβ3 or αVβ3 interaction with CIB. Since tyrosine residues Tyr-747 and/or Tyr-759 are the sites of tyrosine phosphorylation of β3 subunit, these results suggest that the β3 integrin-CIB interaction occurs through a β3-phosphorylation independent mechanism. Likewise, ablation of conformation-dependent affinity change in β3 Ser752Pro mutation had no affect on CIB-β3 interaction. In summary, our results demonstrate that the αIIb-subunit integrin and CIB interaction is non-exclusive and requires the loop-like αIIb-cytoplasmic domain conformation. An interaction of CIB with αV-containing integrins provides an additional role for this molecule in keeping with its expression outside of platelets.
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Affiliation(s)
- Innocent H Yamodo
- Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, USA
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Mundhekar AN, Bullard DC, Kucik DF. Intracellular heterogeneity in adhesiveness of endothelium affects early steps in leukocyte adhesion. Am J Physiol Cell Physiol 2006; 291:C130-7. [PMID: 16769816 DOI: 10.1152/ajpcell.00261.2005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Endothelial cell junctions are thought to be preferential sites for transmigration. However, the factors that determine the site of transmigration are not well defined. Our data show that the preferential role of endothelial cell junctions is not limited to transmigration but extends to earlier steps of leukocyte recruitment, such as rolling and arrest. We used primary mouse neutrophils and mouse aortic endothelium in a flow chamber system to compare adhesive interactions near endothelial cell junctions to interactions over endothelial cell centers. We found differences in both rolling velocity and arrest frequency for neutrophils at endothelial cell junctions vs. more central areas of endothelial cells. Differences were governed by adhesion molecule interactions, not local topography. Interestingly, the role of particular adhesion molecules depended on their location on the endothelial cell surface. Although ICAM-1 stabilized and slowed rolling over central areas of the cell, it did not influence rolling velocity over endothelial cell junctions. P-selectin and VCAM-1 were more important for rolling near endothelial cell junctions than E-selectin. This demonstrates that adhesive properties of endothelial cell junctions influence early events in the adhesion cascade, which may help explain how leukocytes are localized to sites of eventual transmigration.
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Affiliation(s)
- Ameya N Mundhekar
- Department of Biomedical Engineering, University of Alabama at Birmingham, 35294, USA
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Titushkin I, Cho M. Distinct membrane mechanical properties of human mesenchymal stem cells determined using laser optical tweezers. Biophys J 2006; 90:2582-91. [PMID: 16399828 PMCID: PMC1403190 DOI: 10.1529/biophysj.105.073775] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The therapeutic efficacy of mesenchymal stem cells (MSCs) in tissue engineering and regenerative medicine is determined by their unique biological, mechanical, and physicochemical characteristics, which are yet to be fully explored. Cell membrane mechanics, for example, has been shown to critically influence MSC differentiation. In this study, we used laser optical tweezers to measure the membrane mechanics of human MSCs and terminally differentiated fibroblasts by extracting tethers from the outer cell membrane. The average tether lengths were 10.6+/-1.1 microm (hMSC) and 3.0+/-0.5 microm (fibroblasts). The tether extraction force did not increase during tether formation, which suggests existence of a membrane reservoir intended to buffer membrane tension fluctuations. Cytoskeleton disruption resulted in a fourfold tether length increase in fibroblasts but had no effect in hMSCs, indicating weak association between the cell membrane and hMSC actin cytoskeleton. Cholesterol depletion, known to decrease lipid bilayer stiffness, caused an increase in the tether length both in fibroblasts and hMSCs, as does the treatment of cells with DMSO. We postulate that whereas fibroblasts use both the membrane rigidity and membrane-cytoskeleton association to regulate their membrane reservoir, hMSC cytoskeleton has only a minor impact on stem cell membrane mechanics.
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Affiliation(s)
- Igor Titushkin
- Department of Bioengineering, University of Illinois, Chicago, Illinois 60607, USA
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Hirata H, Ohki K, Miyata H. Mobility of integrin alpha5beta1 measured on the isolated ventral membranes of human skin fibroblasts. Biochim Biophys Acta Gen Subj 2005; 1723:100-5. [PMID: 15777736 DOI: 10.1016/j.bbagen.2005.01.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Revised: 01/26/2005] [Accepted: 01/26/2005] [Indexed: 10/25/2022]
Abstract
We have measured the lateral mobility of individual alpha5 integrin molecules in ventral plasma membranes of fibroblasts, which were prepared by removal of apical surfaces and nuclei followed by elimination of actin filaments with gelsolin, an actin-severing protein. The cytoplasmic domain of individual integrin molecules was tagged with 100 nm fluorescent polystyrene bead, and motion of the bead was observed and video-recorded. Position of the bead in each frame was determined from the centroid of the fluorescence image, from which plots of the mean-square displacement against time intervals were derived. Within short intervals of time (<100 ms) the mean-square displacement was proportional to the time interval, and the averaged translational diffusion coefficient of (5.3+/-4.4) x 10(-10) cm2/s was obtained with a broad distribution of (1.3-20) x 10(-10) cm2/s. The broad distribution might reflect the oligomerized state of integrin. The largest diffusion coefficient was comparable to that of lipid molecules previously measured in cells and probably represented the diffusion of a single integrin molecule in the presence of little interference of actin cytoskeleton or extracellular matrix. In longer time intervals (>100 ms) the motion of the bead was confined in an area, the average diameter of which was 410+/-160 nm. This was similar to the values described in previous reports, in which the motion of other membrane receptors labeled on their extracellular domain was measured in living cells.
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Affiliation(s)
- Hiroaki Hirata
- Physics department, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai Miyagi 980-8578, Japan
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11
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Blystone SD. Integrating an integrin: a direct route to actin. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1692:47-54. [PMID: 15246678 DOI: 10.1016/j.bbamcr.2004.04.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2003] [Accepted: 04/08/2004] [Indexed: 01/13/2023]
Abstract
Integrins were so named for their ability to link the extracellular and intracellular skeletons. Now almost 20 years into integrin research, numerous questions remain as to how this interaction is accomplished and how it is modified to achieve a desired phenotype. As the cell adhesion and actin assembly fields are merging in combined approaches, novel actin assembly mechanisms are being uncovered. Some of the earliest identified cytoplasmic linker molecules, believed to mediate integrin-actin binding, are once again the subject of scrutiny as potential dynamic mediators of cell anchorage. It seems plausible that each unique cellular morphology occurs as the result of activation of distinct actin assembly systems that are either stabilized by unique bundling and linker proteins or modified for progression to a new phenotype. While this research initiative is likely to continue rapidly in a forward fashion, it remains to be clarified how integrins assemble the most stable and basic cytoskeletal phenotype, the adherent cell with prominent stress fibers. Recent investigations point towards a shift in the current model of anchoring at the cell periphery by providing both mechanisms and evidence for de novo actin assembly orchestrated by the adhesion site. Lacking a complete pathway from integrin ligation to an integrated extracellular-intracellular skeleton in any single system, this review proposes a simple model of integrin-mediated stress fiber integration by drawing from work in multiple systems.
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Affiliation(s)
- Scott D Blystone
- Department of Cell and Developmental Biology, SUNY Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA.
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Chen H, Mocsai A, Zhang H, Ding RX, Morisaki JH, White M, Rothfork JM, Heiser P, Colucci-Guyon E, Lowell CA, Gresham HD, Allen PM, Brown EJ. Role for plastin in host defense distinguishes integrin signaling from cell adhesion and spreading. Immunity 2003; 19:95-104. [PMID: 12871642 DOI: 10.1016/s1074-7613(03)00172-9] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Integrin ligation activates both cell adhesion and signal transduction, in part through reorganization of the actin cytoskeleton. Plastins (also known as fimbrins) are actin-crosslinking proteins of the cortical cytoskeleton present in all cells and conserved from yeast to mammals. Here we show that plastin-deficient polymorphonuclear neutrophils (PMN) are deficient in killing the bacterial pathogen Staphylococcus aureus in vivo and in vitro, despite normal phagocytosis. Like integrin beta2-deficient PMN, plastin-deficient PMN cannot generate an adhesion-dependent respiratory burst, because of markedly diminished integrin-dependent syk activation. Unlike beta2(-/-) PMN, plastin-deficient PMN adhere and spread normally. Deficiency of plastin thus separates the classical integrin receptor functions of adhesion and spreading from intracellular signal transduction.
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Affiliation(s)
- Hua Chen
- Program in Microbial Pathogenesis and Host Defense and University of California, San Francisco, San Francisco, CA 94143, USA
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Abstract
Leukocyte adhesion must be tightly controlled in order for leukocytes to patrol the body as nonadherent cells, yet stop and emigrate from the blood into tissues at sites of infection or inflammation. A key element in this process is activation of beta2 integrins. While beta2 integrin activation involves conformational changes that increase affinity for ligand, evidence is accumulating that rearrangement of integrins, resulting in increases in avidity, is at least as important in regulating binding capacity. Recent work has established the importance of diffusion and rearrangement of integrins to activation of leukocyte adhesion, and has begun to unravel the molecular basis of its regulation.
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Affiliation(s)
- Dennis F Kucik
- Research Service, Birmingham VA Medical Center and University of Alabama at Birmingham, USA.
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Bertoni A, Tadokoro S, Eto K, Pampori N, Parise LV, White GC, Shattil SJ. Relationships between Rap1b, affinity modulation of integrin alpha IIbbeta 3, and the actin cytoskeleton. J Biol Chem 2002; 277:25715-21. [PMID: 11994301 DOI: 10.1074/jbc.m202791200] [Citation(s) in RCA: 148] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The affinity of integrin alpha(IIb)beta(3) for fibrinogen is controlled by inside-out signals that are triggered by agonists like thrombin. Agonist treatment of platelets also activates Rap1b, a small GTPase known to promote integrin-dependent adhesion of other cells. Therefore, we investigated the role of Rap1b in alpha(IIb)beta(3) function by viral transduction of GFP-Rap1 chimeras into murine megakaryocytes, which exhibit inside-out signaling similar to platelets. Expression of constitutively active GFP-Rap1b (V12) had no effect on unstimulated megakaryocytes, but it greatly augmented fibrinogen binding to alpha(IIb)beta(3) induced by a PAR4 thrombin receptor agonist (p < 0.01). The Rap1b effect was cell-autonomous and was prevented by pre-treating cells with cytochalasin D or latrunculin A to inhibit actin polymerization. Rap1b-dependent fibrinogen binding to megakaryocytes was blocked by POW-2, a novel monovalent antibody Fab fragment specific for high affinity murine alpha(IIb)beta(3). In contrast to GFP-Rap1b (V12), expression of GFP-Rap1GAP, which deactivates endogenous Rap1, inhibited agonist-induced fibrinogen binding (p < 0.01), as did dominant-negative GFP-Rap1b (N17) (p < 0.05). None of these treatments affected surface expression of alpha(IIb)beta(3). These studies establish that Rap1b can augment agonist-induced ligand binding to alpha(IIb)beta(3) through effects on integrin affinity, possibly by modulating alpha(IIb)beta(3) interactions with the actin cytoskeleton.
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Affiliation(s)
- Alessandra Bertoni
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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