Abstract
SummaryTight-junction-regulated actomyosin activity determines epithelial and endothelial tension on adherens junctions and drives morphogenetic processes; however, whether or not tight junctions themselves are under tensile stress is not clear. Here, we use a tension sensor based on ZO-1, a scaffolding protein that links the junctional membrane to the cytoskeleton, to determine if tight junctions carry a mechanical load. Our data indicate that ZO-1 is under mechanical tension and that forces acting on ZO-1 are regulated by extracellular matrix (ECM) stiffness and the junctional adhesion molecule JAM-A. JAM-A depletion stimulates junctional recruitment of p114RhoGEF/ARHGEF18, mechanical tension on ZO-1, and traction forces at focal adhesions. p114RhoGEF is required for activation of junctional actomyosin activity and tight junction integrity on stiff but not soft ECM. Thus, junctional ZO-1 bears a mechanical load, and junction assembly is regulated by interplay between the physical properties of the ECM and adhesion-regulated signaling at tight junctions.
Highlights
Intercellular junctions integrate mechanical forces during cell and tissue morphogenesis
ZO-1 Is under Tensile Stress Tensile forces acting on proteins can be measured by incorporating elastic modules into proteins that consist of fluorescent proteins functioning as FRET pairs that are linked by an elastic peptide (Grashoff et al, 2010)
To test if ZO-1 is under tensile stress, we constructed a ZO-1-based sensor in which an elastic FRET module was inserted between the N-terminal motifs that interact with junctional partners and the C-terminal domain (CTD) containing the actin-binding region (ABR) (Figure 1A)
Summary
Intercellular junctions integrate mechanical forces during cell and tissue morphogenesis. Tight junctions form paracellular diffusion barriers and function as signaling hubs that regulate epithelial and endothelial cell and tissue morphogenesis (Balda and Matter, 2016). They are formed by transmembrane adhesion, adaptor, and signaling proteins (Zihni et al, 2016). They regulate actomyosin activity and, thereby, cytoskeletal tension acting on adherens junctions (Cartagena-Rivera et al, 2017; Hatte et al, 2018; Tornavaca et al, 2015). Such regulatory processes are important for morphogenetic processes and epithelial and endothelial barrier properties
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