Article

Regulation of α5β1 integrin conformation and function by urokinase receptor binding

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: 9.69). 02/2005; 168(3):501-11. DOI: 10.1083/jcb.200404112
Source: PubMed

ABSTRACT 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.

0 Bookmarks
 · 
118 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The urokinase receptor (uPAR) is a glycosylphosphatidylinositol (GPI)-linked membrane protein with no cytosolic domain that localizes to lipid raft microdomains. Our laboratory and others have documented that lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) exhibit a hypermotile phenotype. This study was undertaken to elucidate the molecular mechanism whereby uPAR ligation with its cognate ligand, urokinase, induces a motile phenotype in human lung fibroblasts. We found that uPAR ligation with urokinase's receptor binding domain (amino terminal fragment, ATF) leads to enhanced migration of fibroblasts on fibronectin in a protease-independent, lipid raft-dependent manner. Ligation of uPAR with ATF recruited α5β1 integrin and the acylated form of the Src family kinase, Fyn, to lipid rafts. The biological consequences of this translocation were an increase in fibroblast motility, and a switch of the integrin-initiated signal pathway for migration away from the lipid raft-independent focal adhesion kinase pathway, and towards a lipid raft-dependent caveolin-Fyn-Shc pathway. Furthermore, the ability of an integrin homologous peptide as well as an antibody that competes with β1 for uPAR binding block this effect. In addition, its relative insensitivity to cholesterol depletion suggests that the interactions of α5β1 integrin and uPAR drive the translocation of α5β1 integrin/acylated Fyn signaling complexes into lipid rafts upon uPAR ligation through protein-protein interactions. This signal switch is a novel pathway leading to the hypermotile phenotype of IPF patient-derived fibroblasts, seen with uPAR ligation. This uPAR dependent, fibrotic matrix selective, and pro-fibrotic fibroblast phenotype may be amenable to targeted therapeutics designed to ameliorate IPF.
    Journal of Biological Chemistry 03/2014; 289(18). DOI:10.1074/jbc.M113.498576 · 4.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mucin 1 (MUC1) is overexpressed in various human malignant tumors and its expression is correlated with a poor prognosis. MUC1 engages in signal transduction by interacting with receptors for growth and differentiation factors, which contributes to the growth and survival of cancer cells. However, the mechanism by which MUC1 promotes cancer cell invasion remains unclear. Microarray analysis revealed that expression of urokinase-type plasminogen activator (uPA) was elevated in MUC1-overexpressing cells. Furthermore, up- and down-modulation of MUC1 expression was clearly correlated with the change of uPA expression. An immunochemical study showed that the distribution of uPA coincided with that of MUC1 in various human cancer tissues. The MUC1 C-terminal domain (MUC1-CD) was associated with nuclear factor-κB (NF-κB) p65 in MUC1-expressing cells. Chromatin immunoprecipitation (ChIP) assays demonstrated that MUC1-CD existed with NF-κB p65 on the uPA promoter. Luciferase assays indicated that the uPA transcriptional activity was correlated with the level of MUC1 expression and that this MUC1-enhancing effect on the uPA transcription was abolished by introduction of mutations into the NF-κB binding sites on the uPA promoter. These results indicate that formation of the MUC1-CD and NF-κB p65 complex enhanced nuclear translocation of NF-κB p65 and subsequent occupancy of NF-κB binding region on the uPA promoter, leading to elevated transcription of uPA. We also demonstrated that uPA induced by MUC1 enhanced the matrix metalloproteinase (MMP)-2 and -9 activities, and consequently promoted cancer cell invasion. Thus, a MUC1 co-operating NF-κB signaling pathway plays a critical role in cancer cell invasion in MUC1-expressing cells.
    Journal of Biological Chemistry 11/2014; DOI:10.1074/jbc.M114.586461 · 4.60 Impact Factor
  • [Show abstract] [Hide abstract]
    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 · 2.17 Impact Factor
    This article is viewable in ResearchGate's enriched format

Preview (3 Sources)

Download
1 Download
Available from