Integrin Mediates Chemotactic and Haptotactic Motility in Human Melanoma Cells through Different Signaling Pathways

Abstract Distinctions between chemotaxis and haptotaxis of cells to extracellular matrix proteins have not been defined in terms of mechanisms or signaling pathways. Migration of A2058 human melanoma cells to soluble (chemotaxis) and substratum-bound (haptotaxis) vitronectin, mediated by αβ, provided a system with which to address these questions. Both chemotaxis and haptotaxis were completely inhibited by treatment with RGD-containing peptides. Chemotaxis was abolished by a blocking antibody to αβ (LM609), whereas haptotaxis was inhibited only by approximately 50%, suggesting involvement of multiple receptors and/or signaling pathways. However, blocking antibodies to αβ, also present on A2058 cells, did not inhibit. Pertussis toxin treatment of cells inhibited chemotaxis by >80%, but did not inhibit haptotaxis. Adhesion and spreading over vitronectin induced the phosphorylation of paxillin on tyrosine. In cells migrating over substratum-bound vitronectin, tyrosine phosphorylation of paxillin increased 5-fold between 45 min and 5 h. Dilutions of anti-αβ that inhibited haptotaxis also inhibited phosphorylation of paxillin (by 50%) and modestly reduced cell spreading. In contrast, soluble vitronectin (50-100 μg/ml) did not induce tyrosine phosphorylation of paxillin. The data suggest that soluble vitronectin stimulates chemotaxis predominantly through a G protein-mediated pathway that is functionally linked to αβ. Haptotaxis is analogous to directional cell spreading and requires αβ-mediated tyrosine phosphorylation of paxillin.