The regulation of plasmin generation on cell surfaces is of critical importance in the control of vascular homeostasis. Cellderived microparticles participate in the dissemination of biological activities. However, their capacity to promote plasmin generation has not been documented. In this study, we show that endothelial microparticles (EMPs) from tumor necrosis factor ␣ (TNF␣) - IntroductionMicroparticles (MPs) are vesicles resulting from the blebbing of the cellular membrane of most activated or apoptotic cells. 1 These microvesicles have been described in various cellular models and in different pathological conditions as reliable hallmarks of cell damage. 2 Because they convey various bioactive effectors originating from the parent cells, MPs may exhibit a spectrum of biological activities: they regulate endothelial or blood cell functions, participate in inflammatory responses or angiogenesis, and propagate biological responses involved in hemostatic balance. 3 We previously reported the capacity of endothelial cells to release microparticles after inflammatory stimulation and the presence of increased levels of circulating endothelial microparticles (EMPs) in patients with thrombotic disorders. 4 Since this initial report, elevated levels of EMPs have been documented in various pathological conditions including coronary syndromes, 5 renal failure, 6 diabetes, 7 antiphospholipid syndrome, 8 thrombotic thrombocytopenic purpura, 9 and sickle cell disease, 10 in which they reflect endothelial dysfunction and are associated with a poor clinical outcome.EMPs provide procoagulant phospholipid surfaces for the assembly and activation of coagulation factors, mainly through phosphatidylserine translocation to the exoplasmic leaflet as a result of membrane remodeling. Their involvement in thrombin generation also results from their capacity to harbor, deliver, or induce tissue factor activity. 11-13 However, a more complex contribution to the hemostatic balance is suggested by their expression of thrombomodulin, tissue factor pathway inhibitor, and endothelial protein C receptor, thus providing a possible antithrombotic counterbalance. 14,15 Another key regulator of the vascular homeostasis is the plasminogen activation system. Plasminogen activation is mediated by 2 serine proteases: tissue-type plasminogen activator (tPA), which is mainly implicated in fibrinolysis, and urokinase-type plasminogen activator (uPA), which is critically involved in pericellular proteolysis due to its high affinity cell-surface receptor uPAR. 16 Plasmin generation induced by uPA and subsequent activation of matrix metalloproteinases (MMPs) promote cell migration through interstitial matrix and participate in processes such as tissue remodeling, cancer invasion, and angiogenesis. [17][18][19] Importantly, we have shown that uncontrolled plasminogen activation can have deleterious consequences by inducing cell detachment and apoptosis. 20,21 The regulation of plasmin generation at the endothelial surface is therefore of critical importa...

Endothelial progenitor cells (EPC) display a unique ability to repair vascular injury and promote neovascularization although the underlying molecular mechanisms remain poorly understood. Urokinase-type plasminogen activator (uPA) and its receptor (uPAR) play a critical role in cell migration and angiogenesis by facilitating proteolysis of extracellular matrix. The aim of the present study was to characterize the uPA/uPAR-dependent proteolytic potential of EPC outgrown from human umbilical cord blood and to analyze its contribution to their angiogenic properties in vitro. Cells derived from EPC (EPDC), presenting typical features of late outgrowth endothelial cells, were compared to mature endothelial cells, represented by human umbilical vein endothelial cells (HUVEC). Using quantitative flow cytometry, enzyme-linked immunosorbent assays and zymography, we demonstrated that EPDC displayed higher levels of uPA and uPAR. In conditioned culture media, uPA-dependent proteolytic activity was also found to be significantly increased in EPDC. This activity was paralleled by a higher secretion of pro-metalloproteinase-2 (pro-MMP-2). Inhibition of EPDC-associated uPA by monoclonal antibodies that block either uPA activity or receptor binding, significantly reduced proliferation, migration and capillary like tube formation. Moreover, tumor necrosis factor-alpha and vascular endothelial growth factor, known to be locally secreted in ischemic areas, further increased the proteolytic potential of EPDC by up-regulating uPA and uPAR expression respectively. The EPDC response to these factors was found to be more pronounced than that of HUVEC. In conclusion, these findings indicated that EPDC are characterized by high intrinsic uPA/uPAR-dependent proteolytic potential that could contribute to their invasive and angiogenic behaviour.

Recently, independent studies have shown that the expression of two integrin chains, β4 and α2, plus the epithelial cadherin are related to tumour progression in human bladder carcinomas. For the first time, we compare the expression of these three cell adhesion molecules using immunohistochemical analysis of consecutive cryosections from a series of 50 bladder tumours. E‐cadherin, β4, and α2 were strongly expressed in normal urothelium. A majority of non‐invasive bladder cancers stained positively for E‐cadherin (62%), whereas only 29% expressed normal positivity for α2, and only 35% for β4. However, most invasive tumours presented an aberrant expression of α2 (81%), β4 (100%), and E‐cadherin (75%). We studied the correlation of immunoreactivity with histological grade and stage. The α2 pattern was not correlated with stage and grade. In contrast, loss of normal β4 expression was significantly related to increasing tumour grade and deep invasion with a higher correlation for grade. Finally, E‐cadherin expression was highly correlated with stage, but not with grade. Thus our results indicate that, although many invasive bladder tumours presented a disorder in expression of the two integrins α2 and β4, E‐cadherin appeared to be a better marker of invasiveness in bladder carcinomas.