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Force‐Induced α4 Integrin‐Dependent Monocyte Adhesion Strengthening and F‐Actin Remodeling Requires Actomyosin Contractility and Talin‐1
Author(s) -
Ibrahim Hisham M,
Hyduk Sharon J,
Cybulsky Myron I
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.55.8
Subject(s) - microbiology and biotechnology , integrin , actin cytoskeleton , myosin light chain kinase , vinculin , adhesion , cell adhesion , myosin , actin , chemistry , cytoskeleton , actin remodeling , focal adhesion , cell adhesion molecule , biophysics , biology , cell , signal transduction , biochemistry , organic chemistry
During inflammation, monocytes roll and arrest on inflamed endothelium, at which point they are subjected to increased hydrodynamic forces imparted by the flowing blood. We showed previously that stabilization of α4 integrin‐mediated monocyte adhesion and resistance to detachment involves rapid actin polymerization and accumulation of filamentous actin (F‐actin) at upstream adhesion sites and in the adjacent cortical actin cytoskeleton (J Cell Biol 2012; 197:115–129). Using parallel plate flow chamber assays with a VCAM‐1‐coated adhesion surface, U937 monocyte‐like cell line and confocal imaging we further investigated mechanisms of adhesion strengthening and actin cytoskeleton dynamics in cells undergoing α4 integrin‐mediated adhesion. Myosin ATPase, calcium/calmodulin, myosin light chain kinase and Rho kinase signaling were required for α4 integrin‐mediated adhesion strengthening in the presence of hydrodynamic force. Upon introduction of fluid flow (2 dynes/cm 2 ), adherent U937 cells flattened and the cell contact area with the adhesion surface increased both parallel and perpendicular to the direction of fluid flow. In addition, F‐actin at the adhesion surface redistributed towards the periphery of the adhesion surface contact area. Increased cell adhesion surface contact area and F‐actin redistribution were highly reproducible responses observed in >90% of adherent cells. Unlike F‐actin, α4 integrins remained localized throughout the adhesion contact area, and formed clusters in response to flow. Inhibition of myosin ATPase prevented force‐induced lateral spreading of U937 cells and F‐actin redistribution at the adhesion surface. siRNA knockdown of talin‐1, an adaptor molecule that binds to the integrin β‐chain cytoplasmic tail and mediates outside‐in‐signaling as well as interaction with the actin cytoskeleton, also inhibited α4 integrin‐dependent adhesion stabilization, lateral spreading and redistribution of F‐actin. These data suggest that integrin‐dependent adhesion stabilization and cytoskeletal remodeling induced by hydrodynamic force require both actomyosin contraction and talin‐1. When U937 cells were adhered to poly‐L‐lysine, we observed that hydrodynamic force induced a similar increase in the cell adhesion surface contact area and F‐actin redistribution; however, in this setting neither myosin ATPase nor talin‐1 were required. This suggests that adherent cells can respond to hydrodynamic force in an integrin‐independent manner, but adhesion mediated by α4 integrins inhibits the force‐induced, integrin‐independent response. Support or Funding Information Funded by CIHR