uPAR (84-95)
a potent chemoattractants for basophils

Urokinase induces basophil chemotaxis through a urokinase receptor epitope that is an endogenous ligand for formyl peptide receptor-like 1 and -like 2

Basophils circulate in the blood and are able to migrate into tissues at sites of inflammation. Urokinase plasminogen activator (uPA) binds a specific high affinity surface receptor (uPAR). The uPA-uPAR system is crucial for cell adhesion and migration, and tissue repair. We have investigated the presence and function of the uPA-uPAR system in human basophils. The expression of uPAR was found at both mRNA and protein levels. The receptor was expressed on the cell surface of basophils, in the intact and cleaved forms. Basophils did not express uPA at either the protein or mRNA level. uPA (10(-12)-10(-9) M) and its uPAR-binding N-terminal fragment (ATF) were potent chemoattractants for basophils, but did not induce histamine or cytokine release. Inactivation of uPA enzymatic activity by di-isopropyl fluorophosphate did not affect its chemotactic activity. A polyclonal Ab against uPAR inhibited uPA-dependent basophil chemotaxis. The uPAR-derived peptide 84-95 (uPAR84-95) induced basophil chemotaxis. Basophils expressed mRNA for the formyl peptide receptors formyl peptide receptor (FPR), FPR-like 1 (FPRL1), and FPRL2. The FPR antagonist cyclosporin H prevented chemotaxis induced by FMLP, but not that induced by uPA and uPAR84-95. Incubation of basophils with low and high concentrations of FMLP, which desensitize FPR and FPRL1, respectively, but not FPRL2, slightly reduced the chemotactic response to uPA and uPAR84-95. In contrast, desensitization with WKYMVm, which also binds FPRL2, markedly inhibited the response to both molecules. Thus, uPA is a potent chemoattractant for basophils that seems to act through exposure of the chemotactic uPAR epitope uPAR84-95, which is an endogenous ligand for FPRL2 and FPRL1.

de Paulis A., et al., J Immunol. 2004 Nov 1;173(9):5739-48

Effects of uPAR84–95 and its scrambled peptide on human basophil chemotaxis. Basophils were allowed to migrate with the indicated concentrations of uPAR84–95 and its scrambled peptide for 1 h at 37°C in a humidified (5% CO2) incubator. Values are the mean  SEM from six experiments with different basophil preparations.

Effects of heterologous desensitization between low (5 X 10-7 M) and high (10-4M) concentrations of FMLP, WKYMVm (5 X 10-9M), and uPAR84–95 (10-10M) on basophil chemotaxis. Basophils were incubated in PIPES buffer containing EDTA (4 mM), FMLP (5X 10-7M), FMLP (10-4 M), or WKYMVm (5 X 10-9 M) for 30 min at 37°C. At the end of incubation, cells were washed twice, resuspended in PACGM, and challenged with uPAR84–95 (10-10 M). Basophils were allowed to migrate for 1 h at 37°C in a humidified incubator with 5% CO2. Values are the mean +- SEM from nine experiments. * p < 0.01 compared with cells stimulated with uPAR84–95.