Expression of αvβ3 integrin promotes tumor cell migration and invasion. Migration and Matrigel invasion assays were performed in Transwell migration chambers (8 μm pore size). (a) Haptotactic migration in response to collagen IV, osteopontin and vitronectin and the effect of neutralizing β3 antibodies. (b) Effect of the matrix metalloproteinase inhibitor AG3340 (10 μM) on the haptotactic migration of 4T1.2 and 66cl4beta3 cells. (c) Chemotactic migration of 66cl4pBabe and 66cl4beta3 cells towards a monolayer of bone stromal cells seeded in the lower chamber. (d) Invasion of cells through Matrigel in response to a serum chemotactic gradient. All assays were performed in duplicate wells and the cells counted from three fields of view/membrane at 40× magnification (a, b and d) or 20× magnification (c). The experiments were repeated at least twice and the data represent the mean number of migrated cells ± standard deviation of six fields of view/condition from a representative experiment performed in duplicate wells. *P < 0.01, **P < 0.001.