ERK1/2 and CREB activation are inhibited in the presence of PD98059.

After performing SDS-PAGE with lysates from cells stimulated with GM-CSF and treated either with diluent or PD98059, blots were probed with phosphorylated ERK1/2 antibody (1:20 000) (A) and antiphosphorylated CREB (Ser133) antibody (B), as described in “Methods.”