Involvement of Integrin α(v)β(3) and Cell Adhesion Molecule L1 in Transendothelial Migration of Melanoma Cells

Tumor metastasis involves many stage-specific adhesive interactions. The expression of several cell adhesion molecules, notably the integrin α(v)β(3), has been associated with the metastatic potential of tumor cells. In this study, we used a novel in vitro assay to examine the role of α(v)β(3) in the transmigration of melanoma cells through a monolayer of human lung microvascular endothelial cells. Confocal microscopy revealed the presence of the integrin α(v)β(3) on melanoma membrane protrusions and pseudopods penetrating the endothelial junction. α(v)β(3) was also enriched in heterotypic contacts between endothelial cells and melanoma cells. Transendothelial migration of melanoma cells was inhibited by either a cyclic Arg-Gly-Asp peptide or the anti-α(v)β(3) monoclonal antibody LM609. Although both platelet endothelial cell adhesion molecule-1 and L1 are known to bind integrin α(v)β(3), only L1 serves as a potential ligand for α(v)β(3) during melanoma transendothelial migration. Also, polyclonal antibodies against L1 partially inhibited the transendothelial migration of melanoma cells. However, addition of both L1 and α(v)β(3) antibodies did not show additive effects, suggesting that they are components of the same adhesion system. Together, the data suggest that interactions between the integrin α(v)β(3) on melanoma cells and L1 on endothelial cells play an important role in the transendothelial migration of melanoma cells.