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Abstract
The urokinase-type plasminogen activator receptor (uPAR) is a glycosylphosphatidyl inositol–anchored protein that mediates cell adhesion to the extracellular matrix protein vitronectin (VN). We demonstrate here that this cell adhesion process is accompanied by the formation of an adhesion patch characterized by an accumulation of uPAR into areas of direct contact between the cell and the matrix. The adhesion patch requires the glycolipid anchor and develops only on a VN-coated substrate, but not on fibronectin. It consists of detergent-insoluble microdomains that accumulate F-actin and tyrosine-phosphorylated proteins, but not β1 integrins. Lack of inhibition of adhesion in the presence of integrin-blocking reagents and adhesion on a VN fragment without the RGD sequence indicated that the adhesion of uPAR-bearing cells on VN could occur independently of integrins. Hence, uPAR-mediated cell adhesion on VN relies on the formation of a unique cellular structure that we have termed “detergent-insoluble adhesion patch” (DIAP).