Endothelial cell invasion is a key step in angiogenic blood vessel formation. Sphingosine-1-phosphate (S1P) has been previously reported to play a role in endothelial cell proliferation, survival, migration, and angiogenesis. Here, we examine the ability of S1P to regulate human endothelial cell invasion into three-dimensional collagen or fibrin matrices. We show that S1P potently stimulated human endothelial cell invasion, lumen formation, and branching morphogenesis in collagen, and fibrin matrices, (5- and 15-fold increases in invasion were observed, respectively). The S1P-induced invasion response was pertussis-toxin sensitive and completely dependent on integrins. Addition of integrin blocking reagents revealed that the alpha2beta1 integrin regulated invasion in collagen matrices, while a combination of alphavbeta3 and alpha5beta1 integrins regulated invasion in fibrin. Additionally, the S1P-induced invasion response was dependent on matrix metalloproteinases (MMPs). Tissue inhibitor of metalloproteinase-3 (TIMP-3) was the only physiologic inhibitor of metalloproteinases that completely inhibited the potent stimulation of invasion induced by S1P. In contrast, TIMP-I had no blocking effect on invasion or morphogenesis, while TIMP-2 and TIMP-4 partially reduced invasion but completely blocked lumen formation events. Collectively, these data reveal a marked ability of S I P to induce metalloproteinase- and integrin-dependent human endothelial cell invasion and morphogenesis in both collagen and fibrin three-dimensional matrices, the two most physiologically relevant matrices for angiogenesis. (C) 2003 Elsevier Inc. All rights reserved.