INTEGRIN-ALPHA-V-BETA-3 AND INTEGRIN-ALPHA-V-BETA-5 CONTRIBUTE TO CELL ATTACHMENT TO VITRONECTIN BUT DIFFERENTIALLY DISTRIBUTE ON THE CELL-SURFACE

We investigated the role of the integrins alpha-v-beta-3 and alpha-v-beta-5 in mediating vitronectin adhesion of three phenotypically distinct cell types. M21 human melanoma cells and H2981 lung carcinoma cells use both alpha-v-containing integrins in adhering to vitronectin while UCLA-P3 lung carcinoma cells adhere exclusively with alpha-v-beta-5. Specifically, monoclonal antibodies directed to functional epitopes on both receptors were required to block adhesion of M21 or H2981 cells while adhesion of UCLA-P3 cells to vitronectin could be blocked with a monoclonal antibody to alpha-v-beta-5. Although both receptors are involved in M21 and H2981 cell adhesion to vitronectin, only alpha-v-beta-3 can be detected in focal contacts, colocalizing with vinculin, talin, and the ends of actin filaments, while alpha-v-beta-5 shows a distinct, nonfocal contact, distribution on the cell surface. These results provide the first evidence that two homologous integrins that recognize the same ligand distribute differentially on the cell surface.