Adapter protein which acts downstream of several membrane receptors including cytokine, antigen, hormone, cell matrix and growth factor receptors to regulate multiple signaling pathways. Regulates osteoclast differentiation mediating the TNFRSF11A/RANK signaling. In allergic response, it plays a role in mast cells activation and degranulation through PI-3-kinase regulation. Also involved in the regulation of cell proliferation and hematopoiesis. Interacts with HCK (By similarity). Interacts with SHC1; may mediate interaction with receptors. Interacts with SYK. Interacts with PI-3 kinase. Interacts with GRB2 (via SH3 2 domain). Interacts (phosphorylated) with PTPN11. Interacts with TNFRSF11A (via cytoplasmic domain). Interacts (phosphorylated) with 14-3-3 family proteins SFN, YWHAB, YWHAE, YWHAG, YWHAH, YWHAQ and YWHAZ; prevents interaction with GRB2 and attenuates GAB2 signaling. Ubiquitously expressed. The SH3-binding motifs mediate interaction with SHC1 and GRB2. The PH domain mediates phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3,4-bisphosphate binding. Phosphorylated upon EGF stimulation. Phosphorylated on tyrosine residues by HCK upon IL6 signaling (By similarity). Phosphorylated on tyrosine residue(s) by the thrombopoietin receptor (TPOR), stem cell factor receptor (SCFR), and T-cell and B-cell antigen receptors, gp130, IL-2R and IL-3R. Phosphorylated upon stimulation of TNFRSF11A/RANK by TNFSF11/RANKL. Dephosphorylated by PTPN11. Mice are viable and healthy for up to 15 months. However, they have reduced number of mast cells and develop osteopetrosis. Belongs to the GAB family.