CrkL increases adhesion of 32D cells to fibronectin by activating VLA-4 and VLA-5. (A) Antibodies against VLA-4 and VLA-5 inhibit adhesion of CrkL-overexpressing 32D cells to fibronectin. 32DE/Tet-CrkL cells were cultured for 24 hours in the absence of tetracycline and allowed to attach to wells coated with 10 μg/mL fibronectin in the absence (Control) or in the presence of indicated anti-integrin MoAbs or irrelevant MoAb (IgG), as indicated. The extent of cell adhesion was quantitated as described in Materials and Methods. (B) Analysis of VLA-4 and VLA-5 expression in 32DE/Tet-CrkL cells by flow cytometry. 32DE/Tet-CrkL cells were cultured in the presence (upper panels) or absence (lower panels) of tetracycline for 24 hours and stained with indicated anti-integrin MoAbs or left unstained as control (Control), as indicated. Cells were further stained with fluorescein-labeled secondary antibody and subjected to flow cytometry.