SummaryThe urokinase receptor is a multifunctional receptor modulating both proteolytic dependent and independent processes. It binds the extracellular proteolytic enzyme urokinase and engages lateral interactions with several transmembrane receptors, including integrins and the EGFR. Both, by initiating a proteolytic cascade acting on the extracellular matrix components, and by regulating the activity of important signal transducers, uPAR participates not only in the modulation of cell-cell and cell-extracellular matrix interactions, but also in the control of extracellular signals determining the proliferative state of a cell. Alteration of such a complex and finely modulated mechanism results in unregulated cell proliferation and altered tissue organization, typically associated with tumor progression.