Temporal regulation of EGF signalling networks by the scaffold protein Shc1

Cell-surface receptors frequently use scaffold proteins to recruit cytoplasmic targets, but the rationale for this is uncertain. Activated receptor tyrosine kinases, for example, engage scaffolds such as Shc1 that contain phosphotyrosine (pTyr)-binding (PTB) domains. Using quantitative mass spectrometry, here we show that mammalian Shc1 responds to epidermal growth factor (EGF) stimulation through multiple waves of distinct phosphorylation events and protein interactions. After stimulation, Shc1 rapidly binds a group of proteins that activate pro-mitogenic or survival pathways dependent on recruitment of the Grb2 adaptor to Shc1 pTyr sites. Akt-mediated feedback phosphorylation of Shc1 Ser 29 then recruits the Ptpn12 tyrosine phosphatase. This is followed by a sub-network of proteins involved in cytoskeletal reorganization, trafficking and signal termination that binds Shc1 with delayed kinetics, largely through the SgK269 pseudokinase/adaptor protein. Ptpn12 acts as a switch to convert Shc1 from pTyr/Grb2-based signalling to SgK269-mediated pathways that regulate cell invasion and morphogenesis. The Shc1 scaffold therefore directs the temporal flow of signalling information after EGF stimulation. The Shc1 scaffold mediates a switch in the signaling output of the epidermal growth factor receptor tyrosine kinase over time through recruitment of successive waves of proteins with distinct biological functions. More than a support role for scaffold proteins Receptor-associated scaffolds are generally thought of as relatively static components of signalling pathways that link an activated receptor to downstream targets and expand the receptor's range and potency. An example is the scaffold protein Shc1, which binds to the activated EGF receptor tyrosine kinase. Here, Tony Pawson and colleagues use a quantitative proteomics approach to demonstrate that Shc1 is more than just a simple adaptor; it recruits successive waves of proteins with distinct functions and thereby switches the signalling output of the EGF receptor over time.