Acts as a negative regulator of SRC by activating CSK which inhibits SRC activity and downstream signaling, leading to impaired cell spreading and migration. Regulates dendritic spine morphology. Involved in calcium-dependent exocytosis. May play a role in neurotransmitter release or synapse maintenance. Interacts with BCAR1/p130Cas through its C-terminal domain and with CSK, CTTN and SRC (By similarity). Also interacts with MAPRE3/EB3, SORBS3/vinexin and the N-terminal coiled-coil region of SNAP25. Localized to the perinuclear region, lamellopodia, cortical actin and actin stress fibers but not to focal adhesions. Strongly expressed in axons and dendrites of the CA1 and CA3 hippocampal regions and of the dentate gyrus. Detected in both presynapses and postsynapses and enriched in postsynaptic density fractions. Expressed exclusively in brain. Abundant in telencephalon and expressed moderately in cerebellum, hypothalamus, thalamus, superior and inferior colliculi, and olfactory bulb. No expression detected in medulla oblongata, spinal cord or pituitary gland. Enriched in the neuropil rather than soma in the thalamus, corpus striatum and cerebral cortex. Detected in astrocytes. In the embryo, expression increases dramatically between E14.5 and E18.5 (at protein level). Tyrosine-phosphorylated in response to EGF and to cell adhesion to integrin ligands. Belongs to the SRCIN1 family.