| Background |
The Grb-associated binder (Gab) family is a family of adaptor proteins recruited by a wide variety of receptor tyrosine kinases (RTKs) such as EGFR, HGFR, insulin receptor, cytokine receptor and B cell antigen receptors. Upon stimulation of RTKs by their cognate ligand, Gab is recruited to the plasma membrane where it is phosphorylated and functions as a scaffold Multiple tyrosine phosphorylation sites of Gab1 protein have been identified Phosphorylation of Tyr472 regulates its binding to p85 PI3 kinase Phosphorylation of Gab1 at Tyr307, Tyr373 and Tyr407 modulates its association to PLCγ Phosphorylation of Tyr627 and Tyr659 is required for Gab1 binding to and activation of the protein tyrosine phosphatase SHP2Gab2 is also phosphorylated by tyrosine kinases. Tyr452 is a potential binding site of p85, the regulatory subunit of PI3 kinase. Tyr614 is essential for SHP2 association. Furthermore, Akt phosphorylates Gab2 at Ser159 and inhibits Gab2 tyrosine phosphorylation, suggesting that Akt is engaged in negative feedback regulation of Gab2 signaling.
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