Figure 4

Growth factor receptors are internalized into clathrin-coated vesicles (CCVs) following ligand binding and receptor activation (1–5). These CCVs are uncoated (6) and mature into early endosomes (EE) (7) that may serve as transport endosomes [48]. The concentration of growth factor in transport endosomes is high enough to guarantee effectively 100% receptor occupancy. Hence, if the endosome-associated receptor encounters a phosphatase, the phosphorylation signal is rapidly regenerated.