Stable interaction between α5β1 integrin and Tie2 tyrosine kinase receptor regulates endothelial cell response to Ang-1

During angiogenic remodeling, Ang-1, the ligand of Tie2 tyrosine kinase, is involved in vessel sprouting and stabilization through unclear effects on nascent capillaries and mural cells. In our study, we hypothesized that the Ang-1/Tie2 system could crosstalk with integrins, and be influenced by the dynamic interactions between extracellular matrix and endothelial cells (ECs). Here, we show that alpha(5)beta(1) specifically sensitizes and modulates Tie2 receptor activation and signaling, allowing EC survival at low concentrations of Ang-1 and inducing persistent EC motility. Tie2 and alpha(5)beta(1) interact constitutively; alpha(5)beta(1) binding to fibronectin increases this association, whereas Ang-1 stimulation recruits p85 and FAK to this complex. Furthermore, we demonstrate that Ang-1 is able to mediate selectively alpha(5)beta(1) outside-in FAK phosphorylation. Thus, Ang-1 triggers signaling pathways through Tie2 and alpha(5)beta(1) receptors that could crosstalk when Tie2/alpha(5)beta(1) interaction occurs in ECs plated on fibronectin. By using blocking antibodies, we consistently found that alpha(5)beta(1), but not alpha v beta 3 activation, is essential to Ang-1-dependent angiogenesis in vivo.