FilGAP, a Rho-ROCK-regulated GAP for Rac, controls adherens junctions in MDCK cells

Rho family small GTPases are essential for the formation of adherens junctions in epithelial cells. Here, we found that FilGAP (also known as ARHGAP24), a Rac-specific Rho GTPase-activating protein, promoted the formation of adherens junctions in Madin-Darby canine kidney (MDCK) cells. Knockdown of FilGAP by siRNA stimulated the disassembly and migration of MDCK cells induced by hepatocyte growth factor (HGF). By contrast, forced expression of FilGAP induced accumulation of E-cadherin at adherens junctions. Endogenous FilGAP colocalized with E-cadherin at adherens junctions, and depletion of FilGAP reduced the amount of E-cadherin expressed at the surface. The Rac GAP domain of FilGAP was necessary for the suppression of cell scattering induced by HGF. In agreement with this, siRNA-mediated knockdown of both Rac1 and FilGAP suppressed cell scattering induced by HGF. Forced expression of Rho kinase (ROCK, of which there are two isoforms ROCK1 and ROCK2) induced the accumulation of E-cadherin at the adherens junction, and depletion of FilGAP prevented the accumulation of E-cadherin. Moreover, wild-type FilGAP but not a non-phosphorylatable FilGAP mutant rescued the accumulation of E-cadherin at adherens junctions. These results suggest that FilGAP might regulate cell-cell adhesion through inactivation of Rac downstream of Rho-ROCK-signaling in MDCK cells.