Identification of Endosomal Epidermal Growth Factor Receptor Signaling Targets by

Epidermal growth factor (EGF) receptor (EGFR) signal transduction is organized by scaffold and adaptor pro-teins, which have specific subcellular distribution. On a way from the plasma membrane to the lysosome EGFRs are still in their active state and can signal from distinct subcellular locations. To identify organelle-specific tar-gets of EGF receptor signaling on endosomes a combi-nation of subcellular fractionation, two-dimensional DIGE, fluorescence labeling of phosphoproteins, and MALDI-TOF/TOF mass spectrometry was applied. All together 23 EGF-regulated (phospho)proteins were identified as being differentially associated with endosomal fractions by functional organelle proteomics; among them were pro-teins known to be involved in endosomal trafficking and cytoskeleton rearrangement (Alix, myosin-9, myosin reg