The urokinase-type plasminogen activator (uPA) is able to cleave its cell surface receptor (uPAR) anchored to the cell membrane through a glycophosphatidylinositol tail. The cleavage leads to the formation of cell surface truncated forms, devoid of the N-terminal domain 1 (D1) and unmasks or disrupts, depending on the cleavage site, a sequence in the D1-D2 linker region (residues 88 -92), which in the soluble form is a potent chemoattractant for monocyte-like cells. To investigate the possible role(s) of the cleaved forms of cell surface glycophosphatidylinositol-anchored uPAR, uPAR-negative human embrional kidney 293 cells were transfected with the cDNA of intact uPAR (uPAR-293) or with cDNAs corresponding to the truncated forms of uPAR exposing (D2D3-293) or lacking (D2D3wc-293) the peptide 88 -92 (P88 -92). Cell adhesion assays and co-immunoprecipitation experiments indicated that the removal of D1, independently of the presence of P88 -92, abolished the lateral interaction of uPAR with integrins and its capability to regulate integrin adhesive functions. The expression of intact uPAR induced also a moderate increase in 293 cell proliferation, which was accompanied by the activation of ERK. Also this effect was abolished by D1 removal, independently of the presence of P88 -92. The expression of intact and truncated uPARs regulated cell directional migration toward uPA, the specific uPAR ligand, and toward fMLP, a bacterial chemotactic peptide. In fact, the uPA-dependent cell migration required the expression of intact uPAR, including D1, whereas the fMLP-dependent cell migration required the expression of a P88 -92 containing uPAR and was independent of the presence of D1. Together these observations indicate that uPA-mediated uPAR cleavage and D1 removal, occurring on the cell surface of several cell types, can play a fundamental role in the regulation of multiple uPAR functions.

Angiogenesis is a multistep complex phenomenon critical for several inflammatory and neoplastic disorders. Basophils, normally confined to peripheral blood, can infiltrate the sites of chronic inflammation. In an attempt to obtain insights into the mechanism(s) underlying human basophil chemotaxis and its role in inflammation, we have characterized the expression and function of vascular endothelial growth factors (VEGFs) and their receptors in these cells. Basophils express mRNA for three isoforms of VEGF-A (121, 165, and 189) and two isoforms of VEGF-B (167 and 186). Peripheral blood and basophils in nasal polyps contain VEGF-A localized in secretory granules. The concentration of VEGF-A in basophils was 144.4 ± 10.8 pg/106 cells. Immunologic activation of basophils induced the release of VEGF-A. VEGF-A (10–500 ng/ml) induced basophil chemotaxis. Supernatants of activated basophils induced an angiogenic response in the chick embryo chorioallantoic membrane that was inhibited by an anti-VEGF-A Ab. The tyrosine kinase VEGFR-2 (VEGFR-2/KDR) mRNA was expressed in basophils. These cells also expressed mRNA for the soluble form of VEGFR-1 and neuropilin (NRP)1 and NRP2. Flow cytometric analysis indicated that basophils express epitopes recognized by mAbs against the extracellular domains of VEGFR-2, NRP1, and NRP2. Our data suggest that basophils could play a role in angiogenesis and inflammation through the expression of several forms of VEGF and their receptors.

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The urokinase-mediated plasminogen activation (PA) system is involved in many physiological and pathological events that include cell migration and tissue remodelling, such as embryogenesis, ovulation, inflammation, wound healing, angiogenesis, and tumor invasion and metastasis. The urokinase receptor (uPAR) is a key molecule of this system and can bind extracellular and cell membrane molecules such as urokinase (uPA), vitronectin (VN), integrins and chemotaxis receptors. These multiple interactions can be modulated by the shedding or the cleavage of the cell membrane receptor. Indeed, cleaved forms of uPAR, lacking the N-terminal D1 domain, have been detected on the surface of cells and in tissues, while soluble forms have been found in biological fluids. Cleaved and soluble forms could represent the intermediary products of the uPAR metabolism or active molecules with precise and distinct functional roles. Here, we review the data concerning the in vitro and in vivo identification of these uPAR forms, their origin and functions, and the role that uPAR shedding and cleavage could play in biological processes.

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.

The urokinase-type plasminogen activator receptor (uPAR) is a GPI-anchored cell-surface receptor involved in many physiological and pathological events that include cell migration and tissue invasion. uPAR traditional role was considered the focusing of uPA proteolytic activity on the cell surface; however, different uPAR activities have been demonstrated in the last years. In fact, cell surface uPAR functionally interacts with integrins, fMLP-receptors (fMLP-Rs) and growth factor receptors, thus regulating cell adhesion, migration and proliferation. uPAR also exists in a soluble form (suPAR) that has been detected in human body fluids. Both cell surface and suPAR can be proteolytically cleaved, thus generating truncated forms lacking the N-terminal domain and exposing the specific sequence able to interact with the fMLP-Rs. The cleaved form of suPAR binds and activates the fMLP-Rs and regulates the activity of MCP-1, RANTES and SDF1 receptors. Here, we review the role that shedding and cleavage could play in regulating uPAR structural/functional interaction with other cell-surface receptors and in uPAR-mediated biological and pathological processes.

Helicobacter pylori-derived peptide RpL1 aa 2–20 (Hp(2–20)) in addition to its antimicrobial action exerts several immunomodulatory effects in eukaryotic cells by interacting with formyl peptide receptors (FPRs). It has recently been shown that activation of FPRs facilitates intestinal epithelial cell restitution. We investigated whether Hp(2–20) induces healing of injured gastric mucosa and assessed the mechanisms underlying any such effect. We investigated the expression of FPRs in two gastric epithelial cell lines (MKN-28 and AGS) at mRNA and protein level. To determine whether FPRs were functional we performed chemotaxis experiments and proliferation assays and studied the Hp(2–20)-activated downstream signaling pathway. The effect of Hp(2–20) on mucosal healing was evaluated in rats after indomethacin-induced injury. Here we show that: (1) FPRs were expressed in both cell lines; (2) Hp(2–20) stimulated migration and proliferation of gastric epithelial cells; (3) this effect was specifically mediated by formyl peptide receptor-like 1 (FPRL1) and FPRL2 and was associated with activation of FPR-related downstream signaling pathways; (4) Hp(2–20) up-regulated the expression and secretion of vascular endothelial growth factor; and (5) Hp(2–20) accelerated healing of rat gastric mucosa after injury brought about by indomethacin at both the macroscopic and microscopic levels. In conclusion, by interacting with FRPL1 and FPRL2, H. pylori-derived Hp(2–20) induces cell migration and proliferation, as well as the expression of vascular endothelial growth factor, thereby promoting gastric mucosal healing. This study provides further evidence of the complexity of the relationship between H. pylori and human gastric mucosa, and it suggests that a bacterial product may be used to heal gastric mucosal injury.

Cell division cycle 25 (Cdc25) proteins are highly conserved dual specificity phosphatases that regulate cyclin-dependent kinases and represent attractive drug targets for anticancer therapies. To discover more potent and diverse inhibitors of Cdc25 biological activity, virtual screening was performed by docking 2.1 million compounds into the Cdc25B active site. An initial subset of top-ranked compounds was selected and assayed, and 15 were found to have enzyme inhibition activity at micromolar concentration. Among these, four structurally diverse inhibitors with a different inhibition profile were found to inhibit human MCF-7, PC-3, and K562 cancer cell proliferation and significantly affect the cell cycle progression. A subsequent hierarchical similarity search with the most active reversible Cdc25B inhibitor found led to the identification of an additional set of 19 ligands, three of which were confirmed as Cdc25B inhibitors with IC(50) values of 7.9, 4.2, and 9.9 μM, respectively.