RGD-dependent vacuolation and lumen formation observed during endothelial cell morphogenesis in three-dimensional fibrin matrices involves the alpha(v)beta(3) and alpha(5)beta(1) integrins.

Recent data have revealed the involvement of the alpha(v)beta(3) integrin in angiogenesis. However, few studies to date have provided a convincing role for this receptor in in vitro assays of endothelial cell morphogenesis where defined steps can be examined. Here, we present data showing that two integrins, alpha(v)beta(3) and alpha(5)beta(1), regulate human endothelial cell vacuolation and lumen formation in three-dimensional fibrin matrices. Cells resuspended in fibrin formed intracellular vacuoles that coalesced into lumenal structures. These morphogenic events were completely inhibited by the simultaneous addition of anti-alpha(v)beta(3) and anti-alpha(5) integrin antibodies. Complete blockade was also accomplished with a combination of the cyclic Arg-Gly-Asp (cRGD) peptide and anti-alpha(5) integrin antibodies. No blockade was observed with the control Arg-Gly-Glu (RGE) peptide alone or in combination with control antibodies. Finally, we were able to demonstrate regression of vacuoles and lumens several hours after the addition of cRGD peptides combined with anti-alpha(5) integrin antibodies. These effects were not observed with control peptides alone or in combination with control antibodies. We report here the novel involvement of both the alpha(v)beta(3) and alpha(5)beta(1) integrins in vacuolation and lumen formation in a fibrin matrix, implicating a role for multiple integrins in endothelial cell morphogenesis.