Alon R, Feigelson SW, Manevich E et al.Alpha4beta1-dependent adhesion strengthening under mechanical strain is regulated by paxillin association with the alpha4-cytoplasmic domain. J Cell Biol 171:1073-1084

Department of Immunology, The Weizmann Institute of Science, Rehovot 76100, Israel.
The Journal of Cell Biology (Impact Factor: 9.83). 01/2006; 171(6):1073-84. DOI: 10.1083/jcb.200503155
Source: PubMed


The capacity of integrins to mediate adhesiveness is modulated by their cytoplasmic associations. In this study, we describe a novel mechanism by which alpha4-integrin adhesiveness is regulated by the cytoskeletal adaptor paxillin. A mutation of the alpha4 tail that disrupts paxillin binding, alpha4(Y991A), reduced talin association to the alpha4beta1 heterodimer, impaired integrin anchorage to the cytoskeleton, and suppressed alpha4beta1-dependent capture and adhesion strengthening of Jurkat T cells to VCAM-1 under shear stress. The mutant retained intrinsic avidity to soluble or bead-immobilized VCAM-1, supported normal cell spreading at short-lived contacts, had normal alpha4-microvillar distribution, and responded to inside-out signals. This is the first demonstration that cytoskeletal anchorage of an integrin enhances the mechanical stability of its adhesive bonds under strain and, thereby, promotes its ability to mediate leukocyte adhesion under physiological shear stress conditions.

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    • "AKT1/2 and GSK3β. However, a number of focal adhesion proteins that have been previously implicated in mechanotransduction4243 had many more antibodies that did not change as a function of time and/or material than AKT and GSK3β, e.g. paxillin (Fig. S2A, yellow data; Fig. S2B). "
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    ABSTRACT: Cells secrete and assemble extracellular matrix throughout development, giving rise to time-dependent, tissue-specific stiffness. Mimicking myocardial matrix stiffening, i.e. ~10-fold increase over 1 week, with a hydrogel system enhances myofibrillar organization of embryonic cardiomyocytes compared to static hydrogels, and thus we sought to identify specific mechanosensitive proteins involved. Expression and/or phosphorylation state of 309 unique protein kinases were examined in embryonic cardiomyocytes plated on either dynamically stiffening or static mature myocardial stiffness hydrogels. Gene ontology analysis of these kinases identified cardiogenic pathways that exhibited time-dependent up-regulation on dynamic versus static matrices, including PI3K/AKT and p38 MAPK, while GSK3β, a known antagonist of cardiomyocyte maturation, was down-regulated. Additionally, inhibiting GSK3β on static matrices improved spontaneous contraction and myofibril organization, while inhibiting agonist AKT on dynamic matrices reduced myofibril organization and spontaneous contraction, confirming its role in mechanically-driven maturation. Together, these data indicate that mechanically-driven maturation is at least partially achieved via active mechanosensing at focal adhesions, affecting expression and phosphorylation of a variety of protein kinases important to cardiomyogenesis.
    Full-text · Article · Sep 2014 · Scientific Reports
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    • "One mechanism for stabilization is integrin clustering upon ligand binding and intracellular signaling (outside-in signaling) through adapter proteins (Alon and Dustin, 2007). Linkage of VLA-4 to the actin cytoskeleton through the adapter protein paxillin is critical for stabilization of leukocyte adhesion when exposed to fluid flow and transmission of mechanical force (Alon et al., 2005). Despite this, the actin cytoskeleton in leukocytes has generally been viewed as a relatively static structure that tethers integrins in the cell membrane and restricts their lateral diffusion (Kucik et al., 1996; van Kooyk et al., 1999). "
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    ABSTRACT: Leukocytes arrested on inflamed endothelium via integrins are subjected to force imparted by flowing blood. How leukocytes respond to this force and resist detachment is poorly understood. Live-cell imaging with Lifeact-transfected U937 cells revealed that force triggers actin polymerization at upstream α4β1 integrin adhesion sites and the adjacent cortical cytoskeleton. Scanning electron microscopy revealed that this culminates in the formation of structures that anchor monocyte adhesion. Inhibition of actin polymerization resulted in cell deformation, displacement, and detachment. Transfection of dominant-negative constructs and inhibition of function or expression revealed key signaling steps required for upstream actin polymerization and adhesion stabilization. These included activation of Rap1, phosphoinositide 3-kinase γ isoform, and Rac but not Cdc42. Thus, rapid signaling and structural adaptations enable leukocytes to stabilize adhesion and resist detachment forces.
    Preview · Article · Apr 2012 · The Journal of Cell Biology
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    • "The mechanosensitivity of integrin adhesions, in a variety of cell types, has attracted much attention in recent years [44], [45], [46], [47], [48], [49], [50], [51], [52] Studies of focal adhesions and the associated contractile actomyosin stress fibers, indicated that the integrity of the adhesion sites depends on the contractile forces applied to them, either by the endogenous cytoskeleton contractility [53], [54], or by external mechanical perturbations [55]. Thus, relaxation of actomyosin contraction, using myosin II inhibitors or Rho kinase inhibitors, leads to deterioration of focal adhesions and the associated stress fibers [56], [57]. "
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