Mechanosensitive calcium signaling promotes epithelial tight junction remodeling by activating RhoA

Epithelia maintain an effective barrier by actively remodeling cell-cell junctions in response to mechanical stimuli. Cells often respond to mechanical stress through activation of RhoA and dynamic remodeling of actomyosin. Previously, we found that local leaks in the epithelial tight junction barrier are rapidly repaired by localized, transient activation of RhoA, a process we termed "Rho flares", but how Rho flares are initiated remains unknown. Here, we discovered that intracellular calcium flashes occur in Xenopus laevis embryonic epithelial cells undergoing rapid remodeling of tight junctions via activation of Rho flares. Calcium flashes originate at the site of leaks and propagate into the cell. Depletion of intracellular calcium or inhibition of mechanosensitive calcium channels (MSC) reduced the amplitude of calcium flashes and diminished the activation of Rho flares. Furthermore, MSC-dependent calcium influx was necessary to maintain global barrier function by regulating repair of local tight junction proteins through efficient contraction of junctions. Collectively, we propose that MSC-dependent calcium flashes are an important mechanism allowing epithelial cells to sense and respond to local leaks induced by mechanical stimuli.