Acts as guanine nucleotide exchange factor (GEF) for RhoA GTPases. May play a role in actin cytoskeleton reorganization in different tissues since its activation induces formation of actin stress fibers. Also acts as a GEF for RAC1, inducing production of reactive oxygen species (ROS). Does not act as a GEF for CDC42. The G protein beta-gamma (Gbetagamma) subunits of heterotrimeric G proteins act as activators, explaining the integrated effects of LPA and other G-protein coupled receptor agonists on actin stress fiber formation, cell shape change and ROS production. Required for EPB41L4B-mediated regulation of the circumferential actomyosin belt in epithelial cells. Interacts with SEPT9; interaction may inhibit GEF activity. Interacts with Gbetagamma subunits GNB1 and GNG2 (By similarity). Interacts with EPB41L4B. Interacts with PATJ (via C-terminus). In unactivated eosinophils, distributed around the cell periphery in the perimembranous region (By similarity). In activated eosinophils, relocates to the tip of the nucleopod, a membrane structure formed during activation when the nucleus moves to one end of the cell, and is also concentrated in membrane protrusions at the opposite end of the cell (By similarity). Localizes to the apical cell membrane in epithelial cells (By similarity).