MEK inhibitors block ERK phosphorylation.

U937 cells were pretreated with the indicated inhibitors, as described previously, before incubation with BRY (10 nM; 30 minutes). (Top) Western blot illustrating the levels of phosphorylated ERK using the phosphorylated p44/p42 MAPK-specific antibody. (Bottom) Western blot with MAPK antibody confirming equal loading and transfer of proteins.