To discriminate between your distinct junction morphologies, we will refer to these junctions as focal adherens junctions (FAJs).3,11 Regulation of actin dynamics during endothelial cell-cell junction remodeling Many kinds of dynamic actin-based structures and organizations exist, depending on the proteins that bind to it.28 Endothelial cells use distinct actin-based structures at different stages during the process of cell-cell junction formation, maintenance and remodeling, as was described in detail by Hoelzle and colleagues.29 Initial cell contact formation HG-10-102-01 is driven by protruding lamellipodia of adjacent HG-10-102-01 cells. of blood vessels and controls the exchange of solutes, macromolecules and cells from blood to the underlying tissue. The adherens junction component vascular endothelial cadherin (VE-cadherin) is crucial to preserve endothelial barrier function. VE-cadherin regulates several aspects of endothelial biology, including permeability, leukocyte extravasation and blood vessel morphogenesis.1 The extracellular domain of VE-cadherin forms adhesive contacts between neighboring endothelial cells.2 VE-cadherin-based junctions are strengthened by the actin cytoskeleton, which interacts with cadherins through proteins of the catenin family.3 p120-Catenin binds directly to the membrane-proximal region of the cytoplasmic domain of VE-cadherin. -Catenin and -catenin also associate directly with the cadherin cytoplasmic tail and serve as a scaffold to anchor -catenin, which is a key mediator between cadherin and the actin cytoskeleton.4 Although the cadherin-catenin complex is commonly described as the core VE-cadherin complex, many other proteins can associate, such as scaffolding proteins and cytoskeletal regulators.3,5 Some of these proteins, including vinculin,6-11 epithelial protein lost in neoplasm (EPLIN)12,13 -actinin14 and afadin,15,16 have been found to bind to both -catenin and actin HG-10-102-01 Rabbit polyclonal to ZDHHC5 and are therefore suggested to act as a link between the cadherin-catenin complex and actin. However, biochemical studies showed that a minimal cadherin-catenin complex consisting of E-cadherin, -catenin and E-catenin can directly bind to filamentous actin (F-actin). Strong interaction of this minimal cadherin-catenin complex to actin requires force.17 Interestingly, binding of vinculin to E-catenin has also been demonstrated to be stabilized by tension.18,19 In endothelial cells, force exerted on cell-cell junctions was shown to recruit vinculin, which protected VE-cadherin junctions against opening.11 Together, these data suggest that tension on junctions may promote binding of cadherin/-catenin as well as vinculin to -catenin, resulting in their re-enforcement and growth. Conversely, increased actomyosin generated pulling force is important for opening of endothelial cell-cell junctions in response to permeability-inducing factors.20 By altering the magnitude and direction of the forces that are exerted on cell-cell junctions, actin cytoskeleton rearrangements can change the integrity of VE-cadherin-based cell-cell junctions.21 Thus, a finely balanced regulation of actin network organization, together with myosin-II activity, is needed to produce mechanical forces that drive assembly, maintenance and remodeling of adherens junctions (Fig.?1). Open in a separate window Figure 1. Organization of the actin cytoskeleton at endothelial cell-cell junctions. Left: Focal adherens junctions, or zipper-like junctions, are supported by radial actin bundles that exert tension on junction regions resulting in instable junctions and reduced integrity. Right: Linear junctions show the presence of cortical or so-called circumferential actin bundles that promote junction stability. To achieve complete understanding of the tightly regulated spatial organization of cytoskeletal networks near junctions, we need to understand the dynamic signaling network in which Rho GTPases and their activators, GEFs, take part and how they HG-10-102-01 impinge on actomyosin organization. We recently showed that binding of the GEF Trio to VE-cadherin is a crucial event to stabilize endothelial cell-cell junctions.22 Trio displays 2 GEF domains of distinct specificity, enabling activation of multiple Rho GTPases: Rac1, RhoG and RhoA.23,24 Our findings suggest that by activating Rac1 at junctions, Trio promotes the formation of cortical actin bundles adjacent to the junction, which is concomitant with the stabilization of cell-cell junctions and supports endothelial barrier function. Of note, the role of Rac1 in endothelial cell-cell adhesion seems contradictory in some occasions, as Rac1 has also been described to be involved in regulation of loss of VE-cadherin-based cell-cell contacts.25-27 This highlights the importance of the context-dependent and spatio-temporal regulation of Rac1 activity by GEFs at cell-cell junctions. Here, we will discuss how the local architecture of the actin cytoskeleton in proximity to cell-cell junctions is regulated by different GEFs and Rho GTPases and how this influences endothelial barrier function. Actin at endothelial cell-cell junctions F-actin characteristically concentrates at cadherin adhesion sites and can influence cell-cell junctions in different ways. The appearance of junctional actin differs between quiescent.
To discriminate between your distinct junction morphologies, we will refer to these junctions as focal adherens junctions (FAJs)