May act in negative regulation of cell growth and transformation by interacting with nonreceptor tyrosine kinases ABL1 and/or ABL2. May play a role in regulation of EGF-induced Erk pathway activation. Involved in cytoskeletal reorganization and EGFR signaling. Together with EPS8 participates in transduction of signals from Ras to Rac. In vitro, a trimeric complex of ABI1, EPS8 and SOS1 exhibits Rac specific guanine nucleotide exchange factor (GEF) activity and ABI1 seems to act as an adapter in the complex. Regulates ABL1/c-Abl-mediated phosphorylation of ENAH. Recruits WASF1 to lamellipodia and there seems to regulate WASF1 protein level. In brain, seems to regulate the dendritic outgrowth and branching as well as to determine the shape and number of synaptic contacts of developing neurons. Interacts with ABL1, ENAH, STX1A, SNAP25, VAMP2, EPS8, SOS1, SOS2, GRB2, SPTA1, NCKAP1/NAP1, the first SH3 domain of NCK1 and through its N-terminus with WASF1. Part of a complex consisting of ABI1, STX1A and SNAP25. Part of a complex consisting of ABI1, EPS8 and SOS1. Component of the WAVE2 complex composed of ABI1, CYFIP1/SRA1, NCKAP1/NAP1 (NCKAP1l/HEM1 in hematopoietic cells) and WASF2/WAVE2. Interacts (via SH3 domain) with SHANK2 and SHANK3, but not SHANK1; the interaction is direct. Interacts with the heterodimer MYC:MAX; the interaction may enhance MYC:MAX transcriptional activity. Interacts with FNBP1L (via the SH3 domain), WASF2, and CDC42, but only in the presence of FNBP1L (By similarity). Localized to protruding lamellipodia and filopodia tips. May shuttle from the postsynaptic densities to the nucleus. Widely expressed in brain, high levels detected in cortex, hippocampus and cerebellum (at protein level). Low protein levels at birth that increase progressively at least until 14 days after birth. The t-SNARE coiled-coil homology domain is necessary and sufficient for interaction with STX1A. Phosphorylated on tyrosine residues after serum stimulation or induction by v-Abl. Seems to be phosphorylated at Tyr-53 by ABL1, required for nuclear but not for synaptic localization. Belongs to the ABI family.