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 alphav beta3, 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 alphavbeta3 (LM609), whereas haptotaxis was inhibited only by approximately 50%, suggesting involvement of multiple receptors and/or signaling pathways. However,
blocking antibodies to alphavbeta5, 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- alphavbeta3 that inhibited haptotaxis also inhibited phosphorylation of
paxillin (by approximately 50%) and modestly reduced cell spreading. In contrast, soluble
vitronectin (50-100 microg/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 alphavbeta3. Haptotaxis is analogous to directional cell spreading and requires alphavbeta3-mediated
tyrosine phosphorylation of
paxillin.