Clathrin and LRP-1-independent constitutive endocytosis and recycling of uPAR

Research output: Contribution to journalArticle


BACKGROUND: The urokinase receptor (uPAR/CD87) is highly expressed in malignant tumours. uPAR, as a GPI anchored protein, is preferentially located at the cell surface, where it interacts with its ligands urokinase (uPA) and the extracellular matrix protein vitronectin, thus promoting plasmin generation, cell-matrix interactions and intracellular signalling events. Interaction with a complex formed by uPA and its inhibitor PAI-1 induces cell surface down regulation and recycling of the receptor via the clathrin-coated pathway, a process dependent on the association to LRP-1.

METHODOLOGY/PRINCIPAL FINDINGS: In this study, we have found that along with the ligand-induced down-regulation, uPAR also internalizes and recycles constitutively through a second pathway that is independent of LRP-1 and clathrin but shares some properties with macropinocytosis. The ligand-independent route is amiloride-sensitive, does not require uPAR partitioning into lipid rafts, is independent of the activity of small GTPases RhoA, Rac1 and Cdc42, and does not require PI3K activity. Constitutively endocytosed uPAR is found in EEA1 positive early/recycling endosomes but does not reach lysosomes in the absence of ligands. Electron microscopy analysis reveals the presence of uPAR in ruffling domains at the cell surface, in macropinosome-like vesicles and in endosomal compartments.

CONCLUSIONS/SIGNIFICANCE: These results indicate that, in addition to the ligand-induced endocytosis of uPAR, efficient surface expression and membrane trafficking might also be driven by an uncommon macropinocytic mechanism coupled with rapid recycling to the cell surface.


  • Katia Cortese
  • Macarena Sahores
  • Chris D Madsen
  • Carlo Tacchetti
  • Francesco Blasi
External organisations
  • Vita-Salute San Raffaele University
Research areas and keywords


  • Amiloride, Cell Compartmentation, Cell Line, Clathrin, Dose-Response Relationship, Drug, Endocytosis, Endosomes, Humans, Ligands, Low Density Lipoprotein Receptor-Related Protein-1, Lysosomes, Membrane Microdomains, Monomeric GTP-Binding Proteins, Phosphatidylinositol 3-Kinases, Plasminogen Activator Inhibitor 1, Plasminogen Activators, Receptors, Urokinase Plasminogen Activator, Journal Article, Research Support, Non-U.S. Gov't
Original languageEnglish
Article numbere3730
JournalPLoS ONE
Issue number11
Publication statusPublished - 2008
Publication categoryResearch
Externally publishedYes