Up-regulates the activity of the Rho guanine nucleotide exchange factor ARHGEF18. Involved in the regulation of the circumferential actomyosin belt in epithelial cells. Promotes cellular adhesion, migration and motility in vitro and may play a role in wound healing. May have a role in mediating cytoskeletal changes associated with steroid-induced cell differentiation. Interacts (via FERM domain) with ARHGEF18 (via C-terminus); the interaction activates ARHGEF18. Accumulates along apical cell-cell boundaries and is also detected in the cytoplasm in a punctate manner. May be negatively regulated by phosphorylation.