Wei, Y. et al. Regulation of α5β1 integrin conformation and function by urokinase receptor binding. J. Cell Biol. 168, 501-511

Department of Medicine and Pulmonary and Critical Care Division, University of California, San Francisco, San Francisco, CA 94143, USA.
The Journal of Cell Biology (Impact Factor: 9.83). 02/2005; 168(3):501-11. DOI: 10.1083/jcb.200404112
Source: PubMed


Urokinase-type plasminogen activator receptors (uPARs), up-regulated during tumor progression, associate with beta1 integrins, localizing urokinase to sites of cell attachment. Binding of uPAR to the beta-propeller of alpha3beta1 empowers vitronectin adhesion by this integrin. How uPAR modifies other beta1 integrins remains unknown. Using recombinant proteins, we found uPAR directly binds alpha5beta1 and rather than blocking, renders fibronectin (Fn) binding by alpha5beta1 Arg-Gly-Asp (RGD) resistant. This resulted from RGD-independent binding of alpha5beta1-uPAR to Fn type III repeats 12-15 in addition to type III repeats 9-11 bound by alpha5beta1. Suppression of endogenous uPAR by small interfering RNA in tumor cells promoted weaker, RGD-sensitive Fn adhesion and altered overall alpha5beta1 conformation. A beta1 peptide (res 224NLDSPEGGF232) that models near the known alpha-chain uPAR-binding region, or a beta1-chain Ser227Ala point mutation, abrogated effects of uPAR on alpha5beta1. Direct binding and regulation of alpha5beta1 by uPAR implies a modified "bent" integrin conformation can function in an alternative activation state with this and possibly other cis-acting membrane ligands.

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    • "The biological activity of SuPAR is not fully known, so it may be either an active molecule or simply the result of an increased release of uPAR on the cell surface. Nonetheless, uPAR interacts with both uPA and vitronectin, and the latter interacts with integrins in order to regulate cell motility [19, 20]. "
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    ABSTRACT: Focal segmental glomerulosclerosis (FSGS) is a glomerulopathy associated with nephrotic syndrome and podocyte injury. FSGS occurs both in children and adults and it is considered the main idiopathic nephrotic syndrome nowadays. It is extremely difficult to establish a morphological diagnosis, since some biopsies lack a considerable quantifiable number of sclerotic glomeruli, given their focal aspect and the fact that FSGS occurs in less than half of the glomeruli. Therefore, many biological molecules have been evaluated as potential markers that would enhance the diagnosis of FSGS. Some of these molecules and receptors are associated with the pathogenesis of FSGS and have potential use in diagnosis.
    Disease markers 02/2014; 2014:192836. DOI:10.1155/2014/192836 · 1.56 Impact Factor
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    • "These results suggest that α5β1 integrins at the cell surface were reversibly inactivated by uPA/inhibitor treatment. These findings are very similar to previous results showing that αV-integrins (Czekay et al, 2003) and α5β1 integrins (Wei et al, 2005) show reduced activity in the presence of uPA and PAI-1. "
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    ABSTRACT: Binding of type-1 plasminogen activator inhibitor (PAI-1) to cell surface urokinase (uPA) promotes inactivation and internalization of adhesion receptors (e.g., urokinase receptor (uPAR), integrins) and leads to cell detachment from a variety of extracellular matrices. In this report, we begin to examine the mechanism of this process. We show that neither specific antibodies to uPA, nor active site inhibitors of uPA, can detach the cells. Thus, cell detachment is not simply the result of the binding of macromolecules to uPA and/or of the inactivation of uPA. We further demonstrate that another uPA inhibitor, protease nexin-1 (PN-1), also stimulates cell detachment in a uPA/uPAR-dependent manner. The binding of both inhibitors to uPA leads to the specific inactivation of the matrix-engaged integrins and the subsequent detachment of these integrins from the underlying extracellular matrix (ECM). This inhibitor-mediated inactivation of integrins requires direct interaction between uPAR and those integrins since cells attached to the ECM through integrins incapable of binding uPAR do not respond to the presence of either PAI-1 of PN-1. Although both inhibitors initiate the clearance of uPAR, only PAI-1 triggers the internalization of integrins. However, cell detachment by PAI-1 or PN-1 does not depend on the endocytosis of these integrins since cell detachment was also observed when clearance of these integrins was blocked. Thus, PAI-1 and PN-1 induce cell detachment through two slightly different mechanisms that affect integrin metabolism. These differences may be important for distinct cellular processes that require controlled changes in the subcellular localization of these receptors.
    Journal of Cellular Physiology 09/2009; 220(3):655-63. DOI:10.1002/jcp.21806 · 3.84 Impact Factor
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    • "Identified receptors in the C-terminal part of fibronectin include α4β1 [66], [67], syndecan proteoglycans 68, 69, and RGD-independent α5β1 interaction induced by the urokinase plasminogen activator receptor (uPAR) [70], [71]. We could not find evidence that integrin α4β1 is an adhesion receptor in the fibronectin-null cells used in the present experiments, i.e., the cells did not adhere to a coating of vascular cell adhesion molecule (VCAM) (results not shown). "
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    ABSTRACT: Fibronectin-null cells assemble soluble fibronectin shortly after adherence to a substrate coated with intact fibronectin but not when adherent to the cell-binding domain of fibronectin (modules (7)F3-(10)F3). Interactions of adherent cells with regions of adsorbed fibronectin other than modules (7)F3-(10)F3, therefore, are required for early display of the cell surface sites that initiate and direct fibronectin assembly. To identify these regions, coatings of proteolytically derived or recombinant pieces of fibronectin containing modules in addition to (7)F3-(10)F3 were tested for effects on fibronectin assembly by adherent fibronectin-null fibroblasts. Pieces as large as one comprising modules (2)F3-(14)F3, which include the heparin-binding and cell adhesion domains, were not effective in supporting fibronectin assembly. Addition of module (1)F3 or the C-terminal modules to modules (2)F3-(14)F3 resulted in some activity, and addition of both (1)F3 and the C-terminal modules resulted in a construct, (1)F3-C, that best mimicked the activity of a coating of intact fibronectin. Constructs (1)F3-C V0, (1)F3-C V64, and (1)F3-C Delta(V(15)F3(10)F1) were all able to support fibronectin assembly, suggesting that (1)F3 through (11)F1 and/or (12)F1 were important for activity. Coatings in which the active parts of (1)F3-C were present in different proteins were much less active than intact (1)F3-C. These results suggest that (1)F3 acts together with C-terminal modules to induce display of fibronectin assembly sites on adherent cells.
    PLoS ONE 02/2009; 4(1):e4113. DOI:10.1371/journal.pone.0004113 · 3.23 Impact Factor
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