Association of Ang-2 with Integrin β2 Controls Ang-2/PDGF-BB-Dependent Upregulation of Human Peripheral Blood Monocyte Fibrinolysis

Angiopoietin-2 (Ang-2), an angiogenic factor that is generally considered an autocrine factor for endothelial cells was shown in a previous study to upregulate peripheral blood monocyte fibrinolysis in concert with platelet-derived growth factor-BB (PDGF-BB). This upregulation of fibrinolysis was demonstrated to be due to upregulation of elements of the matrix metalloproteinase and serine protease fibrinolytic pathways. The manner in which Ang-2 interacts with monocytes was not elucidated though no expression of the angiopoietin receptor tyrosine kinase Tie-2 was found for monocytes. In this study Ang-2 was found to bind to integrin β₂, and functional inhibition of integrin β₂ eliminated Ang-2/PDGF-BB-mediated upregulation of monocyte fibrin invasion. Additionally, integrin β₂ blockade significantly inhibited the Ang-2/PDGF-BB based increase in matrix metalloproteinase-9 (MMP-9) and membrane type-1-MMP (MT1-MMP). Furthermore, Ang-2/PDGF-BB-upregulated urokinase plasminogen-activator receptor (uPAR) was shown to be associated in complexes with integrin β₂. In addition, Ang-2 was shown to upregulate PDGFR-β expression in monocytes. Therefore several components of the mechanism via which the novel interaction of Ang-2 and PDGF-BB with monocytes occurs have been identified.