Desmosome-anchored intermediate filaments facilitate tension-sensitive RhoA signaling for epithelial homeostasis
Epithelia are subject to diverse forms of mechanical stress during development and post-embryonic life. They possess multiple mechanisms to preserve tissue integrity against tensile forces, which characteristically involve specialized cell-cell adhesion junctions coupled to the cytoskeleton. Desmosomes connect to intermediate filaments (IF) via desmoplakin (DP) 1,2, while the E-cadherin complex links to the actomyosin cytoskeleton in adherens junctions (AJ) 3. These distinct adhesion-cytoskeleton systems support different strategies to preserve epithelial integrity, especially against tensile stress. IFs coupled to desmosomes can passively respond to tension by strain-stiffening 4-10, whereas for AJs a variety of mechanotransduction mechanisms associated with the E-cadherin apparatus itself 11,12, or proximate to the junctions 13, can modulate the activity of its associated actomyosin cytoskeleton by cell signaling. We now report a pathway where these systems collaborate for active tension-sensing and epithelial homeostasis. We found that DP was necessary for epithelia to activate RhoA at AJ on tensile stimulation, an effect that required its capacity to couple IF to desmosomes. DP exerted this effect by facilitating the association of Myosin VI with E-cadherin, the mechanosensor for the tension-sensitive RhoA pathway at AJ 12. This connection between the DP-IF system and AJ-based tension-sensing promoted epithelial resilience when contractile tension was increased. It further facilitated epithelial homeostasis by allowing apoptotic cells to be eliminated by apical extrusion. Thus, active responses to tensile stress in epithelial monolayers reflect an integrated response of the IF- and actomyosin-based cell-cell adhesion systems.