Figure 5.

Staurosporine-induced aggregation is blocked by protein tyrosine kinase inhibitors. (a) U937 cells were pretreated for 1.5 h with various concentrations of genistein and herbimycin A as indicated, before addition of staurosporine (100 nM, 4 h) or PMA (80 nM, 12 h). The concentrations of inhibitor used with PMA were 50 and 1.2 μM for genistein and herbimycin, respectively. Aggregation is expressed as a % of the aggregation obtained in the absence of inhibitor. Mean±s.e.m. of three experiments and values that differ significantly from control (i.e. no inhibitor) (ANOVA with post hoc Dunnett's, P<0.05) are indicated by an asterisk. Aggregation in the medium alone was less than 10%. (b) U937 cells (5 × 10⁶) were incubated in the presence of staurosporine (100 nM) for various time periods indicated. Cells were lysed and analyzed for phospho-tyrosine proteins as described in Methods. Mean±s.e.m. of three experiments.