Anthracycline-triggered activation of ERK1 in U937 cells.

ERK1 kinase activity was evaluated in U937 cells treated for 5 to 30 minutes with 0.1 μM (A) or 1 μM DNR (B) by MBP phosphorylation as described in “Materials and methods.” Results are mean ± SEM of 3 independent determinations. *P < .01. (C) ERK activation was assayed in U937 cells treated with either 0.1 μM or 1 μM DNR with anti-P–MAPK as described in “ Materials and methods.” Results are representative of 3 independent experiments. (D) ERK activation was also determined in 1 μM doxorubicin (DOX)–treated cells.