Phosphatidylinositol 3,4,5-trisphosphate-dependent guanine nucleotide exchange factor (GEF) which plays a role in the activation of Rho GTPases RAC1, RhoA and CDC42.Can regulate cell morphology in cooperation with activated RAC1.Involved in immune homeostasis by ensuring proper trafficking and availability of T-cell regulator CTLA-4 at T-cell surface.Plays a role in Th2 (T helper cells) development and/or activation, perhaps by interfering with ZAP70 signaling.