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. Interacts with MYH10. Interacts with ELMO1 and EZR (in an open conformation). Interacts with CSPP1. During mitosis, localizes to the spindle pole, central spindle and cleavage furrow (PubMed:16721066). In epithelial cells, recruited to the apical membrane by EZR where it participates in macropinocytosis (PubMed:17881735). Highest expression in the placenta. Low levels in small intestine, lung, liver, kidney, thymus and heart.