Figure 1.

Staurosporine induces rapid homotypic aggregation of U937 cells, which is blocked by protein kinase inhibitors. (a) U937 cells were incubated with medium alone (1), staurosporine (100 nM, 4 h) (2), PMA (80 nM, 24 h) and (3) anti-CD29 (MEM101A) (0.5 μg ml⁻¹ 4 h) (panel 4), as described in Methods. Images of cells in culture at this time point were obtained using an inverted phase contrast microscope, attached to a video camera, and captured using NIH image software. (b) Concentration response and kinetics of U937 aggregation in response to staurosporine or PMA. U937 cells were incubated in the presence or absence of staurosporine or PMA, at a range of concentrations for various times as indicated. Mean±s.e.m. of three experiments. (c) Selectivity of U937 aggregation response to staurosporine and other protein kinase inhibitors. U937 cells were incubated in the presence of inhibitors (staurosporine (100 nM), KT5720 (500 nM), K-252b (500 nM), GF109203X (1 μM), H-89 (50 μM) and H-7 (50 μM)) for 3 h. Aggregation was measured as described in Methods. Mean±s.e.m. of three experiments. (d) Lack of response to GF109203X at a range of concentrations and time points (as for panel b).