GAB1 is a member of the IRS1-like multisubstrate docking protein family and is a direct substrate of the epidermal growth factor receptor and the insulin receptor. GAB1 is tyrosine phosphorylated upon stimulation of cells with various cytokines, growth factors, and antigen receptor. Tyrosine phosphorylation of GAB1 mediates interaction with several proteins that contain SH2 domains such as SHP2 and phosphatidylinositol 3-kinase. GAB1 is an important mediator of branching tubulogenesis and plays a central role in cellular growth response, transformation and apoptosis.