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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    • "The biological activity of suPAR is not entirely known and it is not verified whether the molecule is active or just a result of increased cell surface release of uPAR. However, uPAR interacts with both uPA and vitronectin, the latter a structure that also interacts with integrins to regulate cellular motility [29] [30] and based on the SRS- RY motif in the linker region of suPAR, a chemotactic activity of the D2-D3 segment is likely to be assumed [31] [32] [33]. Recent studies have suggested an association between increased suPAR levels and risk for developing type 2 diabetes and CVD in patients above 40 years of age [34]. "
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    ABSTRACT: ABSTRACT We have studied the presence of novel inflammatory markers as soluble urokinase plasminogen activator receptor (suPAR) and natural IgM antibodies directed against phosphorylcholine (αPC-IgM) in Swedish diabetic patients (n = 164) and in healthy control subjects (n = 41). SuPAR is expressed by several types of immune cells and has been shown to be a marker of disease severity and predict mortality during infections. It has also been associated with low-grade inflammation. High levels of αPC-IgM have been shown to negatively associate with the risk of cardiovascular disease and vascular inflammation. This has been suggested to be more common among diabetic patients than in the background population. The patients were 15-34 years of age and were included in the diabetes incidence study in Sweden (DISS). They were all clinically diagnosed to have either T1D (n = 82) or T2D (n = 82). All subjects were matched in gender and age. Commercially available ELISA was used to detect suPAR and αPC-IgM. We found that suPAR levels were higher in diabetic patients (n = 164, Q2 = 4.5 mg/L) compared to in healthy control subjects (n = 41, Q2 = 2.7 mg/L; p < 0.0001), and in patients classified with T2D (n = 82; Q2 = 4.9) compared to in patients classified with T1D (n = 82; p=0.0002). The difference between T2D and T1D was even more obvious when LADA (n = 17) was extracted from the T2D group. SuPAR levels did also correlate with BMI (rs = 0.50; p < 0.0001), C-peptide levels (rs = 0.23; p < 0.0001) and CRP (rs = 0.58; p < 0.0001). Titers of αPC-IgM did not significantly differ between patients and controls. This is the first study to show the difference in suPAR levels between T1D and T2D patients. The high levels of suPAR in T2D patients indicate a strong activation of the immune system and its relation to disease progression needs to be further investigated. However, our data do not support a role for αPC-IgM in the development of diabetes.
    Full-text · Article · Jan 2011 · Journal of Diabetes Mellitus
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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.
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