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 (PubMed:12651066, PubMed:15023524). Can regulate cell morphology in cooperation with activated RAC1 (By similarity). Involved in immune homeostasis by ensuring proper trafficking and availability of T-cell regulator CTLA-4 at T-cell surface (PubMed:31308374). Plays a role in Th2 (T helper cells) development and/or activation, perhaps by interfering with ZAP70 signaling (By similarity). Interacts with ZAP70 (By similarity). Interacts with IRF4, activated RAC1 and F-actin. Both the phosphorylated and non-phosphorylated forms bind phosphatidylinositol 3,4,5-trisphosphate (PtdInsP3). Interacts with RAB11A (PubMed:31308374). Recruited to the plasma membrane upon binding phosphatidylinositol 3,4,5-trisphosphate (PubMed:15023524). Binds to actin filaments (PubMed:15023524). Broadly expressed in the immune system. Highly expressed in T cells (PubMed:31308374). The PH domain is essential for phosphatidylinositol 3,4,5-trisphosphate binding. Tyrosine-phosphorylated by tyrosine-protein kinase LCK in response to T-cell activation. The disease is caused by variants affecting the gene represented in this entry.