Tension-Sensitive Actin Assembly Supports Contractility at the Epithelial Zonula Adherens

Abstract

Summary Background Actomyosin-based contractility acts on cadherin junctions to support tissue integrity and morphogenesis. The actomyosin apparatus of the epithelial zonula adherens (ZA) is built by coordinating junctional actin assembly with Myosin II activation. However, the physical interaction between Myosin and actin filaments that is necessary for contractility can induce actin filament turnover, potentially compromising the contractile apparatus itself. Results We now identify tension-sensitive actin assembly as one cellular solution to this design paradox. We show that junctional actin assembly is maintained by contractility in established junctions and increases when contractility is stimulated. The underlying mechanism entails the tension-sensitive recruitment of vinculin to the ZA. Vinculin, in turn, directly recruits Mena/VASP proteins to support junctional actin assembly. By combining strategies that uncouple Mena/VASP from vinculin or ectopically target Mena/VASP to junctions, we show that tension-sensitive actin assembly is necessary for junctional integrity and effective contractility at the ZA. Conclusions We conclude that tension-sensitive regulation of actin assembly represents a mechanism for epithelial cells to resolve potential design contradictions that are inherent in the way that the junctional actomyosin system is assembled. This emphasizes that maintenance and regulation of the actin scaffolds themselves influence how cells generate contractile tension.

Spatial integration of E-cadherin adhesion, signalling and the epithelial cytoskeleton

“…Global contractility levels are known to influence actin turnover at junctions [20,48,49]. These data are in line with the paramount influence that a unique architecture of F-actin structures has on the properties of specific cytoskeletal proteins, from regulation of contraction to disassembly [50,51].…”

“…In spite of extensive progress in the identification of cytoskeletal proteins found at junctions [18,19], the precise F-actin organization and the specific actin remodelling functions at cadherin contacts lack in-depth understanding. A pool of G-actin at junctions [20] has unknown functions, but may provide a local pool of monomers for filament remodelling. F-actin accumulation at junctions may be a net result of actin polymerization, depolymerisation, stabilization and recruitment of short filaments.…”

Coronin 1B supports RhoA signaling at cell-cell junctions through Myosin II

“…The phosphomimetic form of the myosin regulatory light chain (MRLC-DD) has been previously shown to restore NMII contractility to cells when its upstream activators are inhibited. 27,28 Indeed, expression of MRLC-DD in Coronin 1B K D MCF-7 cells restored junctional RhoA localization. (Fig.…”

E-cadherin-mediated force transduction signals regulate global cell mechanics

“…α-Catenin is a crucial mechanical link between homophilic intercellular E-cadherin bonds and the actin cytoskeleton (Barry et al, 2014;Buckley et al, 2014;Cavey et al, 2008;Desai et al, 2013;Nagafuchi et al, 1991). Experimental evidence supports a mechanism in which the force-dependent exposure of a cryptic binding site in α-catenin recruits vinculin, and enables localized actin polymerization through the Mena-VASP complex associated with vinculin (Barry et al, 2014;Buckley et al, 2014;le Duc et al, 2010;Leerberg et al, 2014;Thomas et al, 2013;Yao et al, 2014;Yonemura et al, 2010). This mechanism is consistent with measured force-activated changes in the viscoelasticity of Ecadherin adhesions (le Duc et al, 2010), but the stiffening response could also reflect additional force-transduction mechanism(s).…”