Urokinase receptor cleavage and shedding: occurrence and consequences.

Sidenius, Nicolai (2000). Urokinase receptor cleavage and shedding: occurrence and consequences. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f95b

Abstract

The urokinase-type plasminogen activator receptor (uPAR), is a multifunctional protein with an impressive range of distinct, but overlapping functions in the process of tissue remodelling and cell migration: 1) uPAR regulates extracellular proteolysis by promoting plasminogen activation; 2) uPAR regulates cell adhesion as an adhesion receptor for vitronectin and by its capacity to modulate integrin function; 3) uPAR regulates cell migration as a signal transduction molecule and by its intrinsic chemotactic activity. In this thesis I have analysed the consequences, and occurrence, of uPAR cleavage and shedding.
In chapter 3 I analyse the structural requirements for uPAR to promote cellular adhesion to vitronectin. I demonstrate that cell surface expression of intact uPAR is necessary and sufficient to promote binding of the myeloid cell line 32D to vitronectin. In this cell system the uPAR mediated cell binding does not lead to cell spreading and does not require integrin activation. In chapter 4 I demonstrate that the chemotactic activity of uPAR maps to the linker region which connects the first and second domain of uPAR. This chemotactic epitope (the SRSRY motif) is required and sufficient for the chemotactic activity of soluble uPAR fragments and appears to induce signalling similar to that induced by uPAR ligands such as uPA. In chapter 5 I show that uPAR and the uPAR fragments Dl and D2D3 are indeed generated on the cell surface and released to the surroundings by several different cell types. In chapter 6 I describe and characterise the presence of soluble uPAR and uPAR fragments in vivo. I demonstrate that suPAR as well as the suPAR fragments Dl and D2D3 are present in human urine. Using mice xenografted with human model tumours I demonstrate that the tumour tissue is a source of urinary suPAR antigen and that the suPAR fragment pattern in urine correlates with uPAR cleavage in the tumour tissue.