A urokinase receptor-associated protein with specific collagen binding properties

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• The plasminogen activation system is crucial for extracellular proteolysis and tissue remodeling.
• Urokinase and its receptor (uPAR) are key regulators of this system.
• Understanding interactions at the cell surface is vital for comprehending tissue remodeling processes.

Purpose of the Study:

• To identify novel molecular interaction partners of urokinase and its receptor on the cell surface.
• To characterize the function of newly identified proteins involved in the plasminogen activation cascade.

Main Methods:

• Covalent protein cross-linking combined with mass spectrometry.
• Peptide mapping and primary structure analysis of protein conjugates.
• Nanoelectrospray tandem mass spectrometric sequencing for protein identification.
• cDNA cloning and sequencing.

Main Results:

• A specific tri-molecular complex involving urokinase receptor, pro-urokinase, and a novel protein was identified.
• The novel protein, uPARAP, was identified as the human homologue of a murine membrane-bound lectin.
• uPARAP belongs to the macrophage mannose receptor protein family and contains collagen-binding domains.
• uPARAP strongly binds collagen V at the site of plasminogen activation.

Conclusions:

• uPARAP is a novel urokinase receptor-associated protein involved in extracellular proteolysis.
• Its collagen V binding suggests roles in cell adhesion and matrix degradation.
• uPARAP may modulate tissue remodeling through its interaction with the plasminogen activation system.