Binding of Gab2 to tyrosine phosphorylated Shc promotes the phosphorylation of Gab2 by an unknown kinase. Gab2 becomes tyrosine phosphorylated in response to IL-2 (Brockdorff et al. 2001) and IL-3 (Gu et al. 1998). Chimeric receptors were used to demonstrate that Shc is sufficient for Gab2 tyrosine phosphorylation. In response to IL-3, Grb2 was also required, reflecting that Gab2 is recruited to the activated cytokine receptor complex as a complex of Gab2:Grb2 (Gu et al. 2000).