Effect of pharmacological inhibitors of ERK, PKCδ, and actin polymerization on cell-cell aggregation or cell-fibronectin adhesion induced by ligation of surface adhesion molecules with aggregation-activating antibodies or immobilized fibronectin.
(A left panel) U937 cells were incubated with pro-aggregative (activating) antibodies (1 µg/ml each as IgG1) to CD98 (AHN-18, 1 µg/ml), CD29 (MEM101A, 1 µg/ml), CD147 (M6-1D4, 10 µg/ml), and CD43 (161-46, 1 µg/ml) in the presence of chemical inhibitors to ERK (U0126, 25 µM), PKCδ (rottlerin, 10 µM), and actin polymerization (Cyto B: cytochalasin B, 10 µM) for 3 h. Aggregation of cells in the absence of stimuli (normal conditions) was less than 4%. Percentage of aggregation was quantitatively determined by cell-cell adhesion assays. (A right panel) Images of the aggregated cells in culture were obtained using an inverted phase-contrast microscope attached to a video camera, and captured using NIH image software. (B) U937 cells pretreated with 10 µg/ml of function blocking antibody to CD29 (P5D2) or inhibitors [U0126 (20 µM) and cytochalasin B (10 µM)] were seeded on fibronectin (50 µg/ml)-immobilized plates and further incubated for 3 h. Attached cells were determined by crystal violet assay, as described in Materials and Methods. (C) Cytotoxic activity of U0126, rottlerin, and CytoB was confirmed by a conventional MTT assay. Results (aggregation relative to control culture in the presence of stimuli or % of cytotoxicity) are expressed as mean±SEM from three independent experiments performed in triplicate. **p<0.01 compared to the control group.
