Guanine nucleotide exchange factor activating the small GTPase RHOA, which, in turn, induces myosin filament formation. Also activates RHOG. Does not activate RAC1, or to a much lower extent than RHOA and RHOG. Part of a functional unit, involving PLEKHG6, MYH10 and RHOA, at the cleavage furrow to advance furrow ingression during cytokinesis. In epithelial cells, required for the formation of microvilli and membrane ruffles on the apical pole. Along with EZR, required for normal macropinocytosis.