The cross-talk between the urokinase receptor and fMLP receptors regulates the activity of the CXCR4 chemokine receptor.

The receptor (CXCR4) for the stromal-derived factor-1 (SDF1) and the urokinase-receptor (uPAR) are up-regulated in various tumors. We show that CXCR4-transfected cells migrate toward SDF1 on collagen (CG) and do not on vitronectin (VN). Co-expression of cell-surface uPAR, which is a VN receptor, impairs SDF1-induced migration on CG and allows migration on VN. Blocking fMLP receptors (fMLP-R), alpha-v integrins or the uPAR region capable to interact with fMLP-Rs, impairs migration of uPAR/CXCR4-transfected cells on VN and restores their migration on CG. uPAR co-expression also reduces the adherence of CXCR4-expressing cells to various components of the extracellular matrix (ECM) and influences the partitioning of beta1 and alpha-v integrins to membrane lipid-rafts, affecting ECM-dependent signaling. uPAR interference in CXCR4 activity has been confirmed in cells from prostate carcinoma. Our results demonstrate that uPAR expression regulates the adhesive and migratory ability of CXCR4-expressing cells through a mechanism involving fMLP receptors and alpha-v integrins.