INTEGRIN ALPHA(V)BETA(3), MEDIATES CHEMOTACTIC AND HAPTOTACTIC MOTILITY IN HUMAN-MELANOMA CELLS THROUGH DIFFERENT SIGNALING PATHWAYS

Distinctions between chemotaxis and haptotaxis of cells to extracellul ar matrix proteins have not been defined in terms of mechanisms or sig naling pathways. Migration of A2058 human melanoma cells to soluble (c hemotaxis) and substratum-bound (haptotaxis) vitronectin, mediated by alpha(v) beta(3) provided a system with which to address these questio ns. Both chemotaxis and haptotaxis were completely inhibited by treatm ent with RGD-containing peptides. Chemotaxis was abolished by a blocki ng antibody to alpha(v) beta(3) (LM609), whereas haptotaxis was inhibi ted only by approximately 50%, suggesting involvement of multiple rece ptors and/or signaling pathways. However, blocking antibodies to alpha (v) beta(3) also present on A2058 cells, did not inhibit. Pertussis to xin treatment of cells inhibited chemotaxis by > 80%, but did not inhi bit haptotaxis. Adhesion and spreading over vitronectin induced the ph osphorylation of paxillin on tyrosine. In cells migrating over substra tum-bound vitronectin, tyrosine phosphorylation of paxillin increased 5-fold between 45 min and 5 h. Dilutions of anti-alpha(v) beta(3) that inhibited haptotaxis also inhibited phosphorylation of paxillin (by a lpha 50%) and modestly reduced cell spreading. In contrast, soluble vi tronectin (50-100 mu g/ ml) did not induce tyrosine phosphorylation of paxillin. The data suggest that soluble vitronectin stimulates chemot axis predominantly through a G protein-mediated pathway that is functi onally linked to alpha(v) beta(3). Haptotaxis is analogous to directio nal cell spreading and requires alpha v beta 3-mediated tyrosine phosp horylation of paxillin.