Effect of pharmacologic inhibitors on DNR-induced ERK1 stimulation.

U937 cells were either untreated or preincubated in the absence or presence of various pharmacologic inhibitors: 25 mM N-Ac for 2 hours, 10 μg/mL D609 for 1 hour, 25 nmol/L wortmannin for 30 minutes, 250 μM 8-bromo-cAMP for 30 minutes, or 50 μM PD98059 for 30 minutes. ERK1 kinase activity was evaluated, following a further incubation of 15 minutes with 1 μM DNR, as described in “ Materials and methods.” Results are mean ± SEM of 4 independent determinations. *P < .05; **P < .01 compared with cells treated with DNR alone.