Adapter protein that provides a link between the endocytic membrane traffic and the actin assembly machinery. Acts as guanine nucleotide exchange factor (GEF) for CDC42, and thereby stimulates actin nucleation mediated by WASL and the ARP2/3 complex (By similarity). Plays a role in the assembly and maturation of clathrin-coated vesicles (PubMed:20448150). Recruits FCHSD2 to clathrin-coated pits (By similarity). Involved in endocytosis of activated EGFR, and probably also other growth factor receptors (By similarity). Involved in endocytosis of integrin beta-1 (ITGB1) and transferrin receptor (TFR); internalization of ITGB1 as DAB2-dependent cargo but not TFR may involve association with DAB2 (By similarity). Promotes ubiquitination and subsequent degradation of EGFR, and thereby contributes to the down-regulation of EGFR-dependent signaling pathways. In chromaffin cells, required for normal exocytosis of catecholamines (By similarity). Required for rapid replenishment of release-ready synaptic vesicles at presynaptic active zones (PubMed:23633571). Inhibits ARHGAP31 activity toward RAC1 (By similarity). Plays a role in synaptic vesicle endocytosis in brain neurons. Interacts (via DH domain) with CDC42. Interacts (via SH3 domain 1) with WASL (By similarity). Interacts with dynamin, SNAP25 and SNAP23 (PubMed:10373452). Interacts with clathrin-associated proteins and other components of the endocytic machinery, such as SPIN90, EPS15, EPN1, EPN2, STON2, FCHO1, FCHO2 and DAB2 (PubMed:20448150). Interacts (via SH3 domains) with REPS1 and SGIP1. Interacts with ARHGAP31. Interacts with ADAM15 (By similarity). Interacts with PRRT2 (PubMed:26797119). Interacts (via SH3 domain 4) with FCHSD2 (via SH3 domain 2). Interacts (via SH3 domain 1) with DENND2B (By similarity). Interacts (via SH3 domains) with CBL (By similarity). Isoform 2: Interacts with CBL and DNM1. Isoform 2: Interacts with LMNA. Isoform 2: Interacts with importin subunit KPNA1; this is likely to mediate its import into the nucleus (By similarity). Colocalizes with SGIP1 at the plasma membrane in structures corresponding most probably to clathrin-coated pits. Colocalizes with RAB13 on cytoplasmic vesicles that are most likely recycling endosomes. Shuttles between the cytoplasm and nucleus in an XPO1/CRM1-dependent manner. Detected in brain, spleen, lung, liver and heart (at protein level). Ubiquitous. Detected in brain, spleen, lung, liver, skeletal muscle and kidney. SH3-1 and SH3-4 bind to ARHGAP31 (By similarity). SH3-3, SH3-4 and SH3-5, but not SH3-1 and SH3-2 domains, bind to dynamin. The KLERQ domain binds to SNAP-25 and SNAP-23. In an autoinhibited form the SH3 domain 5 may bind intramolecularly to the DH domain, thus blocking the CDC42-binding site.