Gab 1 (GRB2-associated binder 1), one such member of the IRS family, plays an important role in cellular growth response, transformation and apoptosis. Gab 1 is a multi-substrate docking protein that functions downstream in the signaling pathways of different receptor kinases, including EGFR. Gab1 is tyrosine phosphorylated normally in response to insulin and consequently enhances phosphatidylinositol 3- kinase (PI3K) binding. In response to osmotic shock, tyrosine-phosphorylated Gab 1 (p-Gab 1) also binds and activates phosphatidylinositol 3-kinase, suggesting that Gab 1 is the major site for PI3K recruitment following osmotic shock stimulation.