Global Snapshot of the Influence of Endocytosis upon EGF Receptor Signaling Output

Trafficking of activated receptors may dictate the signaling output through the exposure to a changing palette of substrates and effectors. Here, we have used the acute application of a chemical inhibitor of dynamin activity, Dynasore, to inhibit internalization of activated EGF receptors together with quantitative mass spectrometry. This has generated a global snapshot of phosphorylation associated changes, which are contingent upon the endosomal trafficking of the activated EGF receptor. Using a SILAC approach, we have been able to quantitate >500 proteins in pTyr immunoprecipitation experiments and close to 800 individual phosphopeptides through affinity based enrichment strategies. This study provides >2 orders of magnitude increase in the coverage of potential EGF effectors than hitherto assessed in the context of endocytosis. There is a strong positive correlation between EGF responsiveness and sensitivity to Dynasore, with ∼40% of EGF responses being significantly changed by endocytic inhibition. Proteins which are functionally linked to endosomal sorting are strongly influenced by receptor entry, suggesting that the activated receptor can govern its fate by influencing endosomal dynamics. However, the majority of EGF-responsive enzymes which we quantify, do not exhibit this property. Hence, our results provide many examples of key signaling proteins that are impervious to EGFR receptor endocytosis but nevertheless confirm the broad principle of endocytosis influence upon the network response.