The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ronen Alon - One of the best experts on this subject based on the ideXlab platform.
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talin 1 and paxillin facilitate distinct steps in rapid vla 4 mediated adhesion strengthening to vascular cell adhesion molecule 1
Journal of Biological Chemistry, 2007Co-Authors: Eugenia Manevich, Valentin Grabovsky, Sara W Feigelson, Ronen AlonAbstract:VLA-4 (alpha4beta1) is a key integrin in lymphocytes, interacting with endothelial vascular cell adhesion molecule 1 (VCAM-1) on blood vessels and stroma. To dissect the contribution of the two cytoskeletal VLA-4 adaptor partners paxillin and talin to VLA-4 adhesiveness, we transiently knocked them down in Jurkat T cells and primary resting human T cells by small interfering RNA silencing. Paxillin was required for VLA-4 adhesiveness to low density VCAM-1 under shear stress conditions and was found to control mechanical stability of bonds mediated by the alpha4 subunit but did not affect the integrin affinity or avidity to VCAM-1 in shear-free conditions. Talin 1 maintained VLA-4 in a high affinity conformation, thereby promoting rapid VLA-4 adhesion strengthening to VCAM-1 under both shear stress and shear-free conditions. Talin 1, but not paxillin, was required for VLA-4 to undergo optimal stimulation by the prototypic chemokine, CXCL12, under shear stress conditions. Interestingly, talin 1 and paxillin played the same distinct roles in VLA-4 adhesions of primary T lymphocytes, although VLA-4 affinity to VCAM-1 was at least 200-fold lower in these cells than in Jurkat cells. Collectively, our results suggest that whereas paxillin is a mechanical regulator of VLA-4 bonds generated in the absence of chemokine signals and low VCAM-1 occupancy, talin 1 is a versatile VLA-4 affinity regulator implicated in both spontaneous and chemokine-triggered rapid adhesions to VCAM-1.
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the cd81 tetraspanin facilitates instantaneous leukocyte vla 4 adhesion strengthening to vascular cell adhesion molecule 1 vcam 1 under shear flow
Journal of Biological Chemistry, 2003Co-Authors: Sara W Feigelson, Valentin Grabovsky, Revital Shamri, Shoshana Levy, Ronen AlonAbstract:Abstract Leukocyte integrins must rapidly strengthen their binding to target endothelial sites to arrest rolling adhesions under physiological shear flow. We demonstrate that the integrin-associated tetraspanin, CD81, regulates VLA-4 and VLA-5 adhesion strengthening in monocytes and primary murine B cells. CD81 strengthens multivalent VLA-4 contacts within subsecond integrin occupancy without altering intrinsic adhesive properties to low density ligand. CD81 facilitates both VLA-4-mediated leukocyte rolling and arrest on VCAM-1 under shear flow as well as VLA-5-dependent adhesion to fibronectin during short stationary contacts. CD81 also augments VLA-4 avidity enhancement induced by either chemokine-stimulated Gi proteins or by protein kinase C activation, although it is not required for Gi protein or protein kinase C signaling activities. In contrast to other proadhesive integrin-associated proteins, CD81-promoted integrin adhesiveness does not require its own ligand occupancy or ligation. These results provide the first demonstration of an integrin-associated transmembranal protein that facilitates instantaneous multivalent integrin occupancy events that promote leukocyte adhesion to an endothelial ligand under shear flow.
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the chemokine sdf 1 activates the integrins lfa 1 vla 4 and vla 5 on immature human cd34 cells role in transendothelial stromal migration and engraftment of nod scid mice
Blood, 2000Co-Authors: Amnon Peled, Valentin Grabovsky, Orit Kollet, Tanya Ponomaryov, Isabelle Petit, Suzanna Franitza, Michal Magid Slav, Arnon Nagler, Ofer Lider, Ronen AlonAbstract:Hematopoietic stem cell homing and engraftment require several adhesion interactions, which are not fully understood. Engraftment of nonobese/severe combined immunodeficiency (NOD/SCID) mice by human stem cells is dependent on the major integrins very late activation antigen–4 (VLA-4); VLA-5; and to a lesser degree, lymphocyte function associated antigen–1 (LFA-1). Treatment of human CD34+cells with antibodies to either VLA-4 or VLA-5 prevented engraftment, and treatment with anti–LFA-1 antibodies significantly reduced the levels of engraftment. Activation of CD34+ cells, which bear the chemokine receptor CXCR4, with stromal derived factor 1 (SDF-1) led to firm adhesion and transendothelial migration, which was dependent on LFA-1/ICAM-1 (intracellular adhesion molecule–1) and VLA-4/VCAM-1 (vascular adhesion molecule–1). Furthermore, SDF-1–induced polarization and extravasation of CD34+/CXCR4+ cells through the extracellular matrix underlining the endothelium was dependent on both VLA-4 and VLA-5. Our results demonstrate that repopulating human stem cells functionally express LFA-1, VLA-4, and VLA-5. Furthermore, this study implies a novel approach to further advance clinical transplantation.
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high affinity very late antigen 4 subsets expressed on t cells are mandatory for spontaneous adhesion strengthening but not for rolling on vcam 1 in shear flow
Journal of Immunology, 1999Co-Authors: Chun Chen, Roy R Lobb, James L Mobley, Oren Dwir, Frida Shimron, Valentin Grabovsky, Yoji Shimizu, Ronen AlonAbstract:The very late Ag-4 (VLA-4) integrin supports both rolling and firm adhesion of leukocytes on VCAM-1 under shear flow. The molecular basis for the unique ability of a single adhesion molecule to mediate these versatile adhesive processes was investigated. VLA-4 occurs in multiple activation states, with different affinities to ligand. In this study we tested how these states regulate VLA-4 adhesiveness under shear flow in Jurkat T cells and PBL. VLA-4 on nonstimulated Jurkat cells supported rolling and spontaneous arrest on VCAM-1, whereas a Jurkat activation mutant with reduced VLA-4 affinity failed to spontaneously arrest after tethering to or during rolling on VCAM-1. The contribution of VLA-4 affinity for ligand to rolling and spontaneous arrests on immobilized VCAM-1 was dissected using soluble VLA-4 ligands, which selectively block high affinity states. VLA-4 saturation with ligand completely blocked spontaneous adhesion strengthening post-tethering to VCAM-1, but did not impair rolling on the endothelial ligand. High affinity VLA-4 was found to comprise a small subset of VLA-4 on resting Jurkat cells and PBL. This subset is essential for firm adhesion but not for tethering or rolling adhesions on VCAM-1. Interestingly, low and high affinity VLA-4 states were found to mediate similar initial tethering to ligand. High affinity VLA-4, constitutively expressed on circulating T cells, may control their early adhesion strengthening on VCAM-1-expressing endothelium before exposure to vascular chemokines and activation of additional integrins.
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sequential regulation of alpha 4 beta 1 and alpha 5 beta 1 integrin avidity by cc chemokines in monocytes implications for transendothelial chemotaxis
Journal of Cell Biology, 1996Co-Authors: Christian Weber, Ronen Alon, Bernhard Moser, Timothy A SpringerAbstract:Leukocyte emigration possibly requires dynamic regulation of integrin adhesiveness for endothelial and extracellular matrix ligands. Adhesion assays on purified vascular cell adhension molecule (VCAM)-1, fibronectin, and fibronectin fragments revealed distinct kinetic patterns for the regulation of very late antigen (VLA)-4 (alpha 4 beta 1) and VLA-5 (alpha 5 beta 1) avidity by the CC chemokines monocyte inflammatory protein (MIP)-1 alpha, RANTES (regulated on activation, normal T expressed and secreted), or monocyte chemoattractant protein (MCP)-1 in monocytes. CC chemokines induced early activation and subsequent deactivation of VLA-4, whereas upregulation of VLA-5 avidity occurred later and persisted. Controlled detachment assays in shear flow suggested that adhesive strength of VLA-4 for VCAM-1 or the 40-kD fragment of fibronectin (FN40) is more rapidly increased and subsequently reduced by MCP-1 than by MIP-1 alpha, and confirmed late and sustained activation of the adhesive strength of VLA-5 for the 120-kD fragment of fibronectin (FN120). Mn2+ or the stimulating beta 1 mAb TS2/16 strongly and stably enhanced monocyte binding to VCAM-1 or fibronectin, and locked beta 1 integrins in a high avidity state, which was not further modulated by CC chemokines. Mn2+ and mAb TS2/16 inhibited CC chemokine-induced transendothelial migration, particularly chemotaxis across stimulated endothelium that involved VLA-4 and VCAM-1. VLA-4 on Jurkat cells is of constitutively high avidity and interfered with migration across barriers expressing VCAM-1. Low but not high site densities of VCAM-1 or FN40 promoted, while FN120 impaired, beta 1 integrin-dependent monocyte chemotaxis to MCP-1 across filters coated with these substrates. Thus, we show that CC chemokines can differentially and selectively regulate avidity of integrins sharing common beta subunits. Transient activation and deactivation of VLA-4 may serve to facilitate transendothelial diapedesis, whereas late and prolonged activation of VLA-5 may mediate subsequent interactions with the basement membrane and extracellular matrix.
R Gold - One of the best experts on this subject based on the ideXlab platform.
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blockade of signaling via the very late antigen vla 4 and its counterligand vascular cell adhesion molecule 1 vcam 1 causes increased t cell apoptosis in experimental autoimmune neuritis
Acta Neuropathologica, 2002Co-Authors: V I Leussink, R R Lobb, R B Pepinsky, K V Toyka, Uwe K Zettl, Sebastian Jander, Guido Stoll, R GoldAbstract:We characterized the early effects of anti-very late antigen (VLA-4) and its counterligand vascular cell adhesion molecule-1 (VCAM-1) antibody therapy on T cell infiltration and apoptosis in adoptive transfer experimental autoimmune neuritis of female Lewis rats. At the peak of disease, animals were treated with anti-VCAM-1 monoclonal antibody (mAb), anti-VLA-4 mAb, or the respective isotype mAb controls 18, 12, or 6 h before perfusion. Anti-VCAM-1 led to a rapid, significant increase of apoptotic T cells in the sciatic nerve with a maximum after 6 h, preceding the significant decrease of T cell infiltration seen after 18 h. This was accompanied by a significant reduction in mRNA levels for IFN-γ and inducible nitric oxide synthase. The results for anti-VLA-4 treatment showed a similar trend. The early increase of T cell apoptosis following disruption of VLA-4/VCAM-1 interaction may reflect a novel signaling component of proapoptotic pathways.
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the role of the very late antigen 4 and its counterligand vascular cell adhesion molecule 1 in the pathogenesis of experimental autoimmune neuritis of the lewis rat
Brain, 1998Co-Authors: U Enders, R R Lobb, R B Pepinsky, H P Hartung, K V Toyka, R GoldAbstract:We have investigated the functional role of very late antigen-4 [VLA-4 (alpha4/beta1) integrin] and vascular cell adhesion molecule-1 (VCAM-1) in experimental autoimmune neuritis (EAN), an animal model of the Guillain-Barre syndrome, using neutralizing monoclonal antibodies (mAbs) as probes. Disease was induced by intravenous adoptive transfer of P2 specific T cells (AT-EAN), or by immunization with bovine myelin (active EAN). Preventive treatment with 500 microg anti-VLA-4 mAb (TA-2) or with an isotype control antibody was given in AT-EAN 4 h before cell transfer and at day 3. Intravenous injection of 500 microg anti-VCAM-1 mAb (5F10) or a corresponding isotype control was given in AT-EAN 4 h before disease induction, and at days 2, 4 and 6. Preventive treatment of active EAN with mAb to VLA-4 or VCAM-1 was performed at days 5, 9 and 13. On immunohistochemical examination, VCAM-1 in sciatic nerve was found to be upregulated at early stages of EAN (days 3-5 after T-cell transfer), whilst no expression was noted in healthy controls. In both EAN models, blockade of VLA-4 markedly attenuated disease severity. Blockade of VCAM-1 also significantly ameliorated the disease course and diminished T-cell infiltration in sciatic nerve, but to a lesser degree. These experiments demonstrate the critical role of VLA-4 in the pathogenesis of EAN and show that upregulation of VCAM-1 expression contributes, at least in part, to the progression of the disease in the early stages. Future studies are needed to assess the potential contribution of other VLA-4 ligands.
Valentin Grabovsky - One of the best experts on this subject based on the ideXlab platform.
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talin 1 and paxillin facilitate distinct steps in rapid vla 4 mediated adhesion strengthening to vascular cell adhesion molecule 1
Journal of Biological Chemistry, 2007Co-Authors: Eugenia Manevich, Valentin Grabovsky, Sara W Feigelson, Ronen AlonAbstract:VLA-4 (alpha4beta1) is a key integrin in lymphocytes, interacting with endothelial vascular cell adhesion molecule 1 (VCAM-1) on blood vessels and stroma. To dissect the contribution of the two cytoskeletal VLA-4 adaptor partners paxillin and talin to VLA-4 adhesiveness, we transiently knocked them down in Jurkat T cells and primary resting human T cells by small interfering RNA silencing. Paxillin was required for VLA-4 adhesiveness to low density VCAM-1 under shear stress conditions and was found to control mechanical stability of bonds mediated by the alpha4 subunit but did not affect the integrin affinity or avidity to VCAM-1 in shear-free conditions. Talin 1 maintained VLA-4 in a high affinity conformation, thereby promoting rapid VLA-4 adhesion strengthening to VCAM-1 under both shear stress and shear-free conditions. Talin 1, but not paxillin, was required for VLA-4 to undergo optimal stimulation by the prototypic chemokine, CXCL12, under shear stress conditions. Interestingly, talin 1 and paxillin played the same distinct roles in VLA-4 adhesions of primary T lymphocytes, although VLA-4 affinity to VCAM-1 was at least 200-fold lower in these cells than in Jurkat cells. Collectively, our results suggest that whereas paxillin is a mechanical regulator of VLA-4 bonds generated in the absence of chemokine signals and low VCAM-1 occupancy, talin 1 is a versatile VLA-4 affinity regulator implicated in both spontaneous and chemokine-triggered rapid adhesions to VCAM-1.
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the cd81 tetraspanin facilitates instantaneous leukocyte vla 4 adhesion strengthening to vascular cell adhesion molecule 1 vcam 1 under shear flow
Journal of Biological Chemistry, 2003Co-Authors: Sara W Feigelson, Valentin Grabovsky, Revital Shamri, Shoshana Levy, Ronen AlonAbstract:Abstract Leukocyte integrins must rapidly strengthen their binding to target endothelial sites to arrest rolling adhesions under physiological shear flow. We demonstrate that the integrin-associated tetraspanin, CD81, regulates VLA-4 and VLA-5 adhesion strengthening in monocytes and primary murine B cells. CD81 strengthens multivalent VLA-4 contacts within subsecond integrin occupancy without altering intrinsic adhesive properties to low density ligand. CD81 facilitates both VLA-4-mediated leukocyte rolling and arrest on VCAM-1 under shear flow as well as VLA-5-dependent adhesion to fibronectin during short stationary contacts. CD81 also augments VLA-4 avidity enhancement induced by either chemokine-stimulated Gi proteins or by protein kinase C activation, although it is not required for Gi protein or protein kinase C signaling activities. In contrast to other proadhesive integrin-associated proteins, CD81-promoted integrin adhesiveness does not require its own ligand occupancy or ligation. These results provide the first demonstration of an integrin-associated transmembranal protein that facilitates instantaneous multivalent integrin occupancy events that promote leukocyte adhesion to an endothelial ligand under shear flow.
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subsecond induction of α4 integrin clustering by immobilized chemokines stimulates leukocyte tethering and rolling on endothelial vascular cell adhesion molecule 1 under flow conditions
Journal of Experimental Medicine, 2000Co-Authors: Valentin Grabovsky, Chun Chen, Sara W Feigelson, Amnon Peled, Diederik A Bleijs, Guy Cinamon, Francoise Baleux, Frenando Arenzanaseisdedos, Tsvee Lapidot, Yvette Van KooykAbstract:Leukocyte recruitment to target tissue is initiated by weak rolling attachments to vessel wall ligands followed by firm integrin-dependent arrest triggered by endothelial chemokines. We show here that immobilized chemokines can augment not only arrest but also earlier integrin-mediated capture (tethering) of lymphocytes on inflamed endothelium. Furthermore, when presented in juxtaposition to vascular cell adhesion molecule 1 (VCAM-1), the endothelial ligand for the integrin very late antigen 4 (VLA-4, α4β1), chemokines rapidly augment reversible lymphocyte tethering and rolling adhesions on VCAM-1. Chemokines potentiate VLA-4 tethering within <0.1 s of contact through Gi protein signaling, the fastest inside-out integrin signaling events reported to date. Although VLA-4 affinity is not altered upon chemokine signaling, subsecond VLA-4 clustering at the leukocyte-substrate contact zone results in enhanced leukocyte avidity to VCAM-1. Endothelial chemokines thus regulate all steps in adhesive cascades that control leukocyte recruitment at specific vascular beds.
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the chemokine sdf 1 activates the integrins lfa 1 vla 4 and vla 5 on immature human cd34 cells role in transendothelial stromal migration and engraftment of nod scid mice
Blood, 2000Co-Authors: Amnon Peled, Valentin Grabovsky, Orit Kollet, Tanya Ponomaryov, Isabelle Petit, Suzanna Franitza, Michal Magid Slav, Arnon Nagler, Ofer Lider, Ronen AlonAbstract:Hematopoietic stem cell homing and engraftment require several adhesion interactions, which are not fully understood. Engraftment of nonobese/severe combined immunodeficiency (NOD/SCID) mice by human stem cells is dependent on the major integrins very late activation antigen–4 (VLA-4); VLA-5; and to a lesser degree, lymphocyte function associated antigen–1 (LFA-1). Treatment of human CD34+cells with antibodies to either VLA-4 or VLA-5 prevented engraftment, and treatment with anti–LFA-1 antibodies significantly reduced the levels of engraftment. Activation of CD34+ cells, which bear the chemokine receptor CXCR4, with stromal derived factor 1 (SDF-1) led to firm adhesion and transendothelial migration, which was dependent on LFA-1/ICAM-1 (intracellular adhesion molecule–1) and VLA-4/VCAM-1 (vascular adhesion molecule–1). Furthermore, SDF-1–induced polarization and extravasation of CD34+/CXCR4+ cells through the extracellular matrix underlining the endothelium was dependent on both VLA-4 and VLA-5. Our results demonstrate that repopulating human stem cells functionally express LFA-1, VLA-4, and VLA-5. Furthermore, this study implies a novel approach to further advance clinical transplantation.
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high affinity very late antigen 4 subsets expressed on t cells are mandatory for spontaneous adhesion strengthening but not for rolling on vcam 1 in shear flow
Journal of Immunology, 1999Co-Authors: Chun Chen, Roy R Lobb, James L Mobley, Oren Dwir, Frida Shimron, Valentin Grabovsky, Yoji Shimizu, Ronen AlonAbstract:The very late Ag-4 (VLA-4) integrin supports both rolling and firm adhesion of leukocytes on VCAM-1 under shear flow. The molecular basis for the unique ability of a single adhesion molecule to mediate these versatile adhesive processes was investigated. VLA-4 occurs in multiple activation states, with different affinities to ligand. In this study we tested how these states regulate VLA-4 adhesiveness under shear flow in Jurkat T cells and PBL. VLA-4 on nonstimulated Jurkat cells supported rolling and spontaneous arrest on VCAM-1, whereas a Jurkat activation mutant with reduced VLA-4 affinity failed to spontaneously arrest after tethering to or during rolling on VCAM-1. The contribution of VLA-4 affinity for ligand to rolling and spontaneous arrests on immobilized VCAM-1 was dissected using soluble VLA-4 ligands, which selectively block high affinity states. VLA-4 saturation with ligand completely blocked spontaneous adhesion strengthening post-tethering to VCAM-1, but did not impair rolling on the endothelial ligand. High affinity VLA-4 was found to comprise a small subset of VLA-4 on resting Jurkat cells and PBL. This subset is essential for firm adhesion but not for tethering or rolling adhesions on VCAM-1. Interestingly, low and high affinity VLA-4 states were found to mediate similar initial tethering to ligand. High affinity VLA-4, constitutively expressed on circulating T cells, may control their early adhesion strengthening on VCAM-1-expressing endothelium before exposure to vascular chemokines and activation of additional integrins.
Martin E Hemler - One of the best experts on this subject based on the ideXlab platform.
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multiple activation states of vla 4 mechanistic differences between adhesion to cs1 fibronectin and to vascular cell adhesion molecule 1
Journal of Biological Chemistry, 1993Co-Authors: Akihide Masumoto, Martin E HemlerAbstract:Abstract We examined the effects of a stimulatory anti-beta 1 mAb (TS2/16) and different divalent cations on VLA-4-mediated cell adhesion to vascular cell adhesion molecule-1 (VCAM-1), to the fibronectin-derived CS1 peptide, and to larger fibronectin fragments. Using optimal binding conditions (in the presence of mAb TS2/16 and 1.0 mM Mn2+), the levels of VLA-4-mediated adhesion to VCAM-1 and to CS1 peptide were virtually indistinguishable, and half-maximal inhibition of adhesion to both ligands was achieved using similar levels of an anti-alpha 4 antibody. However, using suboptimal adhesion conditions, two critical differences between adhesion to CS1 peptide (or larger fibronectin fragments) and VCAM-1 were consistently observed. First, stimulation by added mAb TS2/16 had a substantially greater effect on adhesion to CS1 than to VCAM-1 and second, Ca2+ was much less able to support adhesion to CS1 than to VCAM-1. These two differences between adhesion to CS1 peptide and to VCAM-1 were most obvious among cell lines which synthesized inactive or partly active VLA-4 but were not obvious for fully active VLA-4. Together, these results not only reveal crucial differences in the mechanisms of VLA-4 binding to its two ligands, but also lead to increased understanding of the variable activation states of VLA-4. The differential ability to utilize Ca2+ displayed by VLA-4 in different states of activation and the activation of inactive or partly active VLA-4 by the addition of Mn2+ both point to divalent cation sites playing an essential role in determining VLA-4 regulation and ligand specificity.
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functional and structural analysis of vla 4 integrin alpha 4 subunit cleavage
Journal of Biological Chemistry, 1992Co-Authors: Joaquin Teixido, Christina M Parker, Paul D Kassner, Martin E HemlerAbstract:Abstract The cell surface heterodimer VLA-4 (alpha 4 beta 1), a member of the integrin family of adhesion receptors, is involved in both cell-extracellular matrix and cell-cell adhesion. Unlike any other integrin alpha subunit, the intact (150 kDa) alpha 4 subunit of VLA-4 can sometimes be cleaved into two noncovalently associated fragments (80 and 70 kDa). Using biosynthetic and mixing experiments, we found that human alpha 4 cleavage is a regulated, compartmentalized event, occurring soon after maturation of the beta 1-associated alpha 4 subunit. Cleavage of alpha 4, which is increased following T cell activation, has been suggested to correlate with altered VLA-4 functions. To address directly the functional importance of alpha 4 cleavage, we have studied VLA-4-mediated adhesion functions in cells expressing intact alpha 4 in comparison with cells expressing cleaved alpha 4. For this purpose, we first sequenced the N terminus of the endogenously produced 70-kDa alpha 4 fragment and identified the alpha 4 cleavage site between Lys557-Arg558 and Ser559. To abolish cleavage, we converted Arg558 to Leu or Lys557 to Gln by site-directed mutagenesis of the alpha 4 cDNA and then transfected both mutant and wild type alpha 4 cDNAs into VLA-4-negative K562 cells. Whereas transfection with wild type alpha 4 cDNA yielded predominantly cleaved alpha 4 subunit, the Leu558-alpha 4 yielded only intact alpha 4 subunit, and Gln557-alpha 4 yielded mostly intact alpha 4 subunit. Transfectants with the intact or the cleaved alpha 4 were equally capable of engaging in VLA-4-dependent adhesion to vascular cell adhesion molecule-1 and to the Hep II fragment of fibronectin (40 kDa) and aggregated equally well in response to anti-alpha 4 antibodies. Thus, cleavage of the alpha 4 subunit in these transfectants did not alter any of the known VLA-4-mediated adhesion functions.
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t cell receptor dependent antigen specific stimulation of a murine t cell clone induces a transient vla protein mediated binding to extracellular matrix
Journal of Immunology, 1991Co-Authors: Bosco M C Chan, J G P Wong, Martin E HemlerAbstract:Upon Ag stimulation, an arsonate-specific murine T cell clone exhibited a rapid but transient increase in cell adhesion to collagen, fibronectin, and laminin. This increase in cell adhesion was not observed when a mutant T cell clone lacking TCR expression was utilized. However, upon stimulation by phorbol esters, both parent and mutant T cell clones exhibited a similar transient increase in adhesion to the three matrix proteins. The observed cell adhesion was extensively inhibited by antibodies to the integrin beta 1 subunit, indicating the involvement of VLA proteins. Despite changes in the adhesive properties, there was essentially no difference in the expression of VLA-1, -3, -4, -5, and -6 between resting and stimulated T cells. Together these results suggest that Ag stimulation transmits signals via the TCR complex resulting in a rapid, but transient, up-regulation of matrix protein binding by VLA proteins already present at the cell surface. Because the appropriate reagents that recognize individual mouse VLA proteins were not available, we used the human T cell line Jurkat to demonstrate that T cell binding to collagen, laminin, and fibronectin is mediated largely by VLA-2, VLA-6, and a combination of VLA-5 and VLA-4, respectively.
Carl G Figdor - One of the best experts on this subject based on the ideXlab platform.
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the small gtpase rap1 is required for mn2 and antibody induced lfa 1 and vla 4 mediated cell adhesion
Journal of Biological Chemistry, 2002Co-Authors: Kim M T De Bruyn, Savithri Rangarajan, Kris A Reedquist, Carl G FigdorAbstract:Abstract In T-lymphocytes the Ras-like small GTPase Rap1 plays an essential role in stimulus-induced inside-out activation of integrin LFA-1 (αLβ2) and VLA-4 (α4β1). Here we show that Rap1 is also involved in the direct activation of these integrins by divalent cations or activating antibodies. Inhibition of Rap1 either by Rap GTPase-activating protein (RapGAP) or the Rap1 binding domain of RalGDS abolished both Mn2+- and KIM185 (anti-LFA-1)-induced LFA-1-mediated cell adhesion to intercellular adhesion molecule 1. Mn2+- and TS2/16 (anti-VLA-4)-induced VLA-4-mediated adhesion were inhibited as well. Interestingly, both Mn2+, KIM185 and TS2/16 failed to induce elevated levels of Rap1GTP. These findings indicate that available levels of GTP-bound Rap1 are required for the direct activation of LFA-1 and VLA-4. Pharmacological inhibition studies demonstrated that both Mn2+- and KIM185-induced adhesion as well as Rap1-induced adhesion require intracellular calcium but not signaling activity of the MEK-ERK pathway. Moreover, functional calmodulin signaling was shown to be a prerequisite for Rap1-induced adhesion. From these results we conclude that in addition to stimulus-induced inside-out activation of integrins, active Rap1 is required for cell adhesion induced by direct activation of integrins LFA-1 and VLA-4. We suggest that Rap1 determines the functional availability of integrins for productive binding to integrin ligands.
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the small gtpase rap1 is required for mn2 and antibody induced lfa 1 and vla 4 mediated cell adhesion
Journal of Biological Chemistry, 2002Co-Authors: Kim M T De Bruyn, Savithri Rangarajan, Kris A Reedquist, Carl G Figdor, Johannes L BosAbstract:In T-lymphocytes the Ras-like small GTPase Rap1 plays an essential role in stimulus-induced inside-out activation of integrin LFA-1 (alpha(L)beta(2)) and VLA-4 (alpha(4)beta(1)). Here we show that Rap1 is also involved in the direct activation of these integrins by divalent cations or activating antibodies. Inhibition of Rap1 either by Rap GTPase-activating protein (RapGAP) or the Rap1 binding domain of RalGDS abolished both Mn(2+)- and KIM185 (anti-LFA-1)-induced LFA-1-mediated cell adhesion to intercellular adhesion molecule 1. Mn(2+)- and TS2/16 (anti-VLA-4)-induced VLA-4-mediated adhesion were inhibited as well. Interestingly, both Mn(2+), KIM185 and TS2/16 failed to induce elevated levels of Rap1GTP. These findings indicate that available levels of GTP-bound Rap1 are required for the direct activation of LFA-1 and VLA-4. Pharmacological inhibition studies demonstrated that both Mn(2+)- and KIM185-induced adhesion as well as Rap1-induced adhesion require intracellular calcium but not signaling activity of the MEK-ERK pathway. Moreover, functional calmodulin signaling was shown to be a prerequisite for Rap1-induced adhesion. From these results we conclude that in addition to stimulus-induced inside-out activation of integrins, active Rap1 is required for cell adhesion induced by direct activation of integrins LFA-1 and VLA-4. We suggest that Rap1 determines the functional availability of integrins for productive binding to integrin ligands.
