Cross-talk between fMLP and vitronectin receptors triggered by urokinase receptor-derived SRSRY peptide

The urokinase receptor (uPAR) sustains cell migration through its capacity to promote pericellular proteolysis, to regulate integrin function and to mediate chemotactic signaling in response to urokinase. We have characterized the early signaling events triggered by the Ser-Arg-Ser-Arg-Tyr (SRSRY) chemotactic uPAR sequence. Cell exposure to SRSRY peptide promotes directional migration on vitronectin-coated filters, regardless of uPAR expression, in a specific and dose-dependent manner, with maximal effect at a concentration level as low as 10 nM. A similar concentration profile is observed in a quantitative analysis of SRSRY-dependent cytoskeletal rearrangements, mostly consisting of filamentous structures localized in a single cell region. SRSRY analogues with alanine substitutions fail to drive F-actin formation and cell migration, indicating a critical role for each amino acidic residue. Just like with ligand-dependent uPAR signaling, SRSRY stimulates PKC activity and results in ERK1/2 phosphorylation. The involvement of the high affinity fMLP receptor (FPR) in this process is indicated by the finding that 100 nM fMLP inhibits binding of D2D3 to the cell surface, as well as SRSRY-stimulated cell migration and F-actin polarization. Moreover, cell exposure to SRSRY promotes FPR-dependent vitronectin release and increased uPAR/ƒÑvƒÒ5 vitronectin receptor physical association, indicating that ƒÑvƒÒ5 activity is regulated by the SRSRY uPAR sequence via FPR. Finally, we provide evidence that ƒÑvƒÒ5 is required for SRSRY-dependent ERK1/2 phosphorylation, whereas it is not required for PKC activation. The data indicate that the ability of uPAR to stimulate cell migration and cytoskeletal rearrangements is retained by the SRSRY peptide alone, and that it is supported by cross-talk between FPR and alphaVbeta5.