DNR triggered activation of Raf-1 in U937 cells.

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, or 25 nM wortmannin for 30 minutes. U937 cells were further incubated for 15 minutes with 1 μM DNR, and Raf-1 kinase activity was measured as described in “Materials and methods.” Results are mean ± SEM of 3 independent determinations. *P < .01 compared with cells treated with DNR alone.