(366g) Intracellular Time and Length Scales in Receptor-Mediated Cell Signaling

In response to upstream stimuli including the activation of receptor tyrosine kinases, protein complexes are formed that are involved in the process of cellular signal transduction.  In many cases, the linkages between proteins in these complexes are formed by reversible binding interactions between phosphorylated tyrosines and cognate Src homology 2 (SH2) domains.  Given that phosphotyrosines on receptors and intracellular signaling proteins are under constant regulation by protein tyrosine phosphatases (PTPs), it seems likely that PTPs could exert substantial control over the persistence of signaling complexes in time and space, but this has not been previously explored.  Here, through implementation of a combined experimental and computational approach, we demonstrate the validity of this hypothesis.  Specifically, we show that linear, chain-like protein complexes nucleated by the activation of the epidermal growth factor receptor (EGFR) and held together by phosphotyrosine-SH2 interactions are highly transient species that fall apart and reform many times during the overall time scale of signal transduction, with the linkages in the chain regulated by PTPs.  We use our model to quantitatively identify the time and length scales over which signaling complexes can remain in complex in response to EGFR activation, and identify the activity of PTPs as the most important determinant of these time and length scales through sensitivity analysis.  This new view of protein complex formation and regulation by PTPs has important implications for our fundamental understanding of signal transduction dynamics under normal conditions and for our understanding of how signaling may be perturbed in diseases characterized by oncogenic kinase mutations or perturbations to PTP expression or activity.