Proteolysis of the urokinase-type plasminogen activator receptor by metalloproteinase-12: implication for angiogenesis in fibrin matrices

Abstract

IntroductionThe urokinase-type plasminogen activator (u-PA) and its cellular receptor (u-PAR, CD87) are involved in cell migration such as occurs during tumor invasion and angiogenesis. 1 The u-PAR regulates the u-PA activity on the cell surface not only by mediating the localization of u-PA and the internalization of u-PA/inhibitor complexes but also by an increase in the efficiency of plasminogen activation by u-PAR-bound u-PA. 2 Pro-u-PA bound to the receptor can be converted into the protease u-PA and subsequently be inhibited by plasminogen activator inhibitor type 1 (PAI-1). The u-PA:PAI-1 complex is subsequently internalized and degraded in the lysosomes, while the u-PAR is recycled to the cell surface. Besides a role in controlling u-PA activity, u-PAR is involved in activating cell signaling pathways, including diacylglycerol formation, activation of a serine kinase, focal adhesion kinase, tyrosine kinase(s), and the activation of the Janus kinase/signal transducer and activator of transcription pathway. Furthermore, u-PAR enforces cellular interaction with the extracellular matrix, in particular by binding to the matrix protein vitronectin and to integrins. Recently, u-PAR has been shown to possess chemokine-like activity mediating chemotaxis of monocytes, neutrophils, and smooth muscle cells. 3,4 The u-PAR is a glycosyl phosphatidylinositol (GPI)-anchored receptor that contains 3 homologous domains. The amino-terminal domain (D1) is involved in both the binding of u-PA 5,6 and the interaction with vitronectin, 7,8 but the other 2 domains of u-PAR are also indispensable for high-affinity interactions. 9,10 The GPI anchor of u-PAR can be cleaved by GPI-specific phospholipases, resulting in a soluble form of u-PAR (su-PAR). Recently, Wilhelm et al showed that a cellular phospholipase D might be involved in the release of su-PAR. 11 In addition to the shedding of the full-size u-PAR, the finding of truncated D2D3 fragments of u-PAR on the cell membrane implies that D1 domains can also be cleaved directly from u-PAR. Cleavage of u-PAR between domains D1 and D2 can be mediated by proteolytic activity of u-PA, directly or indirectly via the plasminogen activation/plasmin 12,13 or by other proteases such as chymotrypsin and elastase. 5,14 A similar region has not been observed between domains D2 and D3. 15 The soluble form of u-PAR has been found in vitro in culture supernatants of tumor cell lines, 12,16 in vivo in plasma and serum, [17][18][19][20] in uterine tissue cultures from women with endometriosis, 21 and in ascitic and cystic fluid from ovarian cancer patients. 22,23 Recently, Chavakis et al 24 reported that normal human vascular cells (smooth muscle cells and endothelial cells) also release su-PAR in the medium, especially after stimulation with phorbol myristate acetate (PMA).Numerous studies have shown the involvement of u-PAR in the migration and tissue infiltration of cells. The u-PAR undoubtedly plays an important role in the migration and invasion of monocytes, 25 34 Previously we have provid...

Gelatinase-mediated migration and invasion of cancer cells

“…Furthermore, MMP-9 could cleave the uPA-binding domain from uPAR in vitro. uPAR cleavage has also been observed on the cell surface, and this cleavage can be inhibited with a broad-spectrum MMP inhibitor BB-94 (Koolwijk et al, 2001). We found that a gelatinase-selective smallmolecule inhibitor and the CTT peptide inhibited the cellular cleavage of uPAR.…”

“…This suggests that uPA and MMPs are activated prior to integrin activation and remain associated to the integrins. Furthermore, uPAR can be cleaved by uPA (Hoyer-Hansen et al, 1992) or MMPs in vitro (Andolfo et al, 2002;Koolwijk et al, 2001) and the cleaved uPAR form is also found in invasive tumor xenografts (Solberg et al, 1994). The cleavage occurs between domains 1 and 2 impairs uPA and integrin binding (Montuori et al, 2002) and exposes a chemotactic epitope (Fazioli et al, 1997) suggesting that this cleavage is one of the cell migration regulating events on the cell surface.…”

Metalloproteinases and their inhibitors in tumor angiogenesis

“…This report suggests that EC-derived MMP-12 may be involved in negative regulation of angiogenesis via uPAR shedding, perhaps providing a negative feedback mechanism to limit neovascularization. 123 However, another group has reported that treatment of mice with BB94 increased the levels of MMP-9 and MMP-2 in their livers. 124 In light of this report, the effects of BB94 on endothelial expression of MMPs will need to be tested, as it is possible that the proangiogenic effects of BB94 seen in the previous report 123 are due to increased MMP-9 and MMP-2 production (leading to enhanced activity when levels exceed that of the inhibitor) and not a result of MMP inhibition.…”

Matrix Metalloproteinases and Cancer - Roles in Threat and Therapy

“…MMPs inhibit the process of angiogenesis by the following mechanism: i) By cleavage of plasminogen which releases angiostatin (Cornelius et al, 1998); ii) By cleaving collagen XVIII which produces endostatin (Ferreras, 2000); iii) By shedding of cell surface bound urokinase type plasminogen activator receptors which are required for the endothelial cell invasion in to fibrin (Koolwijk et al, 2001). …”