Background：

The Gab family of adaptor proteins function as molecular scaffolds that mediate protein recruit-ment to RTKs. Cytokine/growth factor triggering of protein tyrosine kinase receptors (RTKs) initiates signaling cascades that progress to the nucleus where signals for activation， proliferation and differentiation occur. This scaffolding mechanism represents a critical link in cytokine/growth factor signaling routes. Gab 1-4 contain Pleckstrin homology and potential binding sites for SH2 and SH3 domain-containing proteins. The recruitment of signaling partners to Gab family members is phosphorylation-dependent. Insulin receptor and EGF receptor signaling are among the cascades that rely on Gab family members to elicit a nuclear response to an extracellular stimulus. Gab 4 (GRB2-associated-binding protein 4)， also designated GRB2-associated-binding protein 2-like (Gab 2-like)， is a 574 amino acid protein that shares 62% sequence similarity with Gab 2 and contains one Pleckstrin homology domain.