GTPase-activating protein for ADP ribosylation factor family members, including ARF1. Multidomain scaffold protein that interacts with numerous proteins and therefore participates in many cellular functions, including receptor internalization, focal adhesion remodeling, and signaling by both G protein-coupled receptors and tyrosine kinase receptors (By similarity). Through PAK1 activation, positively regulates microtubule nucleation during interphase (PubMed:27012601). Plays a role in the regulation of cytokinesis; for this function, may act in a pathway also involving ENTR1 and PTPN13 (PubMed:23108400). May promote cell motility both by regulating focal complex dynamics and by local activation of RAC1 (PubMed:10938112, PubMed:11896197). May act as scaffold for MAPK1/3 signal transduction in focal adhesions. Recruits MAPK1/3/ERK1/2 to focal adhesions after EGF stimulation via a Src-dependent pathway, hence stimulating cell migration (PubMed:15923189). Plays a role in brain development and function. Involved in the regulation of spine density and synaptic plasticity that is required for processes involved in learning (By similarity). Plays an important role in dendritic spine morphogenesis and synapse formation (PubMed:12695502, PubMed:15800193). In hippocampal neurons, recruits guanine nucleotide exchange factors (GEFs), such as ARHGEF7/beta-PIX, to the synaptic membrane. These in turn locally activate RAC1, which is an essential step for spine morphogenesis and synapse formation (PubMed:12695502). May contribute to the organization of presynaptic active zones through oligomerization and formation of a Piccolo/PCLO-based protein network, which includes ARHGEF7/beta-PIX and FAK1 (By similarity). In neurons, through its interaction with liprin-alpha family members, may be required for AMPA receptor (GRIA2/3) proper targeting to the cell membrane (By similarity). In complex with GABA(A) receptors and ARHGEF7, plays a crucial role in regulating GABA(A) receptor synaptic stability, maintaining GPHN/gephyrin scaffolds and hence GABAergic inhibitory synaptic transmission, by locally coordinating RAC1 and PAK1 downstream effector activity, leading to F-actin stabilization (PubMed:25284783). May also be important for RAC1 downstream signaling pathway through PAK3 and regulation of neuronal inhibitory transmission at presynaptic input (By similarity). Required for successful bone regeneration during fracture healing (By similarity). The function in intramembranous ossification may, at least partly, exerted by macrophages in which GIT1 is a key negative regulator of redox homeostasis, IL1B production, and glycolysis, acting through the ERK1/2/NRF2/NFE2L2 axis (By similarity). May play a role in angiogenesis during fracture healing (By similarity). In this process, may regulate activation of the canonical NF-kappa-B signal in bone mesenchymal stem cells by enhancing the interaction between NEMO and 'Lys-63'-ubiquitinated RIPK1/RIP1, eventually leading to enhanced production of VEGFA and others angiogenic factors (PubMed:31502302). Essential for VEGF signaling through the activation of phospholipase C-gamma and ERK1/2, hence may control endothelial cell proliferation and angiogenesis (PubMed:19273721). Forms homodimers and possibly oligomers (By similarity). May forms heterooligomers with GIT2 (By similarity). Interacts with G protein-coupled receptor kinases, including GRK2, GRK3, GRK5 and GRK6 (By similarity). Interacts with PPFIA1, PPFIA2 and PPFIA4 (By similarity). Interacts with GRIP1 and forms a ternary complex with PPFIA1 and GRIP1 (By similarity). Directly interacts with ARHGEF7/beta-PIX, forming in vitro a heptameric complex made of a GIT1 dimer and an ARHGEF7 trimer (PubMed:10896954, PubMed:27012601). Directly interacts with PXN/paxillin; this interaction is enhanced in the presence of ARHGEF7 (PubMed:10896954, PubMed:10938112, PubMed:27012601). Directly interacts (via C-terminus) with TGFB1I1/Hic-5 (via LD motif 3) (PubMed:12153727). Directly interacts with PTK2/FAK1 (By similarity). May interact with PTK2B/PYK2; this interaction may be indirect (By similarity). Interacts with AMPA receptors GRIA2/3 (By similarity). Directly interacts with protein Piccolo/PCLO (By similarity). Forms a complex with Ephrin-B1/EFNB1 and NCK2/GRB4 (via SH2); this interaction is important for spine morphogenesis and synapse formation. Interaction with NCK2 is transient and depends upon GIT1 phosphorylation at Tyr-383 (By similarity). Interacts with GRIN3A/GluN3A (via C-terminus); this interaction competes with GIT1 interaction with ARHGEF7 and limits synaptic localization of GIT1 (By similarity). Interacts with IKBKG/NEMO in resting bone mesenchymal stem cells, as well as in TNF-stimulated cells; this interaction may increase IKBKG affinity for 'Lys-63'-linked polyubiquitin chains (PubMed:31502302). Interacts with GABA(A) receptors, including GABRB3 and GABRG2 (By similarity). Interacts with SCRIB (PubMed:15182672, PubMed:19041750). Interacts (via N- and C-terminus) with ENTR1/SDCCAG3 (via N-terminus); this interaction is direct (PubMed:23108400). May form a tripartite complex with ENTR1 and PTPN13 (PubMed:23108400). Interacts with YWHAZ (By similarity). Interacts with PAK1 (PubMed:27012601). Interacts with PAK3 (PubMed:10896954). Directly interacts (via N-terminus) with gamma-tubulin (PubMed:27012601). Interacts with MAPK1 and MAPK3; this interaction is required for MAPK1/3 recruitment to focal adhesions (By similarity). Cycles between at least 3 distinct intracellular compartments, including focal adhesions, cytosolic complexes, containing at least PXN/paxillin, ARHGEF7 and PAK1, and membrane protrusions. During cell migration, moves from the disassembling adhesions into the cytosol and towards the leading edge. In adherent cells, localizes to adhesions. Recruitment to adhesions may be mediated by RAC and active tyrosine-phosphorylated PXN (PubMed:11896197). May be present in both excitatory and inhibitory synapses. In hippocampal neurons, recruitment of GIT1 to synapses is regulated by ephrinB activation and ephrinB downstream effector GRB4/NCK2. In hippocampal neurons, partially colocalizes with PCLO (By similarity). Interaction with GRIN3A limits GIT1 synaptic localization (By similarity). Localization to the centrosome does not depend upon the presence of gamma-tubulin (PubMed:27012601). Up-regulated at the transcriptional level by MYC. The coiled coil region mediates dimerization. Phosphorylated by PAK1 (PubMed:27012601). Phosphorylation on tyrosine residues may be catalyzed by PTK2/FAK1 and SRC in growing fibroblasts. Phosphorylation at Tyr-383 is induced by activation of Ephrin-B1/EFNB1 and catalyzed by SRC family kinases. It is required for the interaction with NCK2 and for GIT1 recruitment to synapses in hippocampal neurons (By similarity). Extended N-terminus.