Domain 1 of the urokinase-type plasminogen activator receptor is required for its morphologic and functional, beta2 integrin-mediated connection with actin cytoskeleton in human microvascular endothelial cells: failure of association in systemic sclerosis endothelial cells

Arthritis Rheum. 2006 Dec;54(12):3926-38. doi: 10.1002/art.22263.


Objective: In systemic sclerosis (SSc) microvascular endothelial cells (MVECs), angiogenesis is blocked by matrix metalloproteinase 12-dependent cleavage of domain 1 of the urokinase-type plasminogen activator receptor (uPAR). Since integrins are associated with the invasive activity of uPAR in angiogenesis, this study was undertaken to show whether full-size and truncated uPAR are differentially associated with integrins and with motor components of the cytoskeleton.

Methods: SSc and normal MVECs were isolated from human skin biopsy specimens and studied by confocal laser scanning microscopy and immunoprecipitation to assess the mechanisms of association of truncated and full-size uPAR with integrins and the actin cytoskeleton. The integrin composition of the MVECs was studied by reverse transcription-polymerasechain reaction. Cell migration and capillary morphogenesis were studied on fibrinogen substrates. Involvement of Rac and Cdc42 was evaluated by Western blotting.

Results: Only full-size uPAR showed a connection with the actin cytoskeleton in ECs. This connection was mediated by the uPAR-associated alphaMu- and alphaX-subunits of beta2 integrin, and was absent from SSc MVECs. The cleaved uPAR was not associated with beta2 integrins or with actin. beta3 integrins were associated with both the full-size and cleaved uPAR at focal contacts. The uncoupling of uPAR from beta2 integrins in SSc MVECs impaired the activation of Rac and Cdc42 (thus inhibiting their mediation of uPAR-dependent cytoskeletal rearrangements and cell motility) and blocked the integrin-engagement-delivered signals to the actin cytoskeleton. Invasion and capillary morphogenesis on fibrinogen-coated substrates indicated that ligation of uPAR by uPA empowers the beta2/beta3 integrin-dependent invasion of fibrinogen, and that this system is impaired in SSc MVECs.

Conclusion: The reduced angiogenic properties of SSc MVECs can be explained by the effects of uPAR truncation and the subsequent loss of the beta2 integrin-mediated connection of uPAR with the actin cytoskeleton in these ECs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism*
  • CD18 Antigens / genetics
  • CD18 Antigens / metabolism*
  • Cell Movement / drug effects
  • Cells, Cultured
  • Chemotaxis / drug effects
  • Cytoskeleton / metabolism*
  • Cytoskeleton / ultrastructure
  • Down-Regulation
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / drug effects
  • Endothelium, Vascular / metabolism*
  • GTPase-Activating Proteins / metabolism
  • Gene Expression
  • Humans
  • Mannose-Binding Lectins / chemistry
  • Mannose-Binding Lectins / metabolism*
  • Membrane Glycoproteins / chemistry
  • Membrane Glycoproteins / metabolism*
  • Microcirculation / cytology
  • Microcirculation / drug effects
  • Neovascularization, Pathologic / metabolism
  • Neovascularization, Pathologic / pathology
  • Neovascularization, Pathologic / physiopathology
  • Protein Structure, Tertiary
  • RNA, Messenger / metabolism
  • Receptors, Cell Surface / chemistry
  • Receptors, Cell Surface / metabolism*
  • Scleroderma, Systemic / metabolism*
  • Scleroderma, Systemic / physiopathology
  • Skin / blood supply
  • Urokinase-Type Plasminogen Activator / pharmacology
  • cdc42 GTP-Binding Protein / metabolism


  • ARHGAP32 protein, human
  • Actins
  • CD18 Antigens
  • GTPase-Activating Proteins
  • MRC2 protein, human
  • Mannose-Binding Lectins
  • Membrane Glycoproteins
  • RNA, Messenger
  • Receptors, Cell Surface
  • Urokinase-Type Plasminogen Activator
  • cdc42 GTP-Binding Protein