Role of the PC-PLC–derived DAG pathway 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. (A) Phosphatidylcholine levels were evaluated, following a further incubation of 5 minutes with 1 μM DNR, as described in “Materials and methods.” (B) ERK1 kinase activity was evaluated as described in “Materials and methods” following a further incubation of 5 minutes with 25 μM DiC8. Results are mean ± SEM of 3 independent experiments. *P < .01 compared with cells treated with DNR alone.