Figure 2.

Inhibition of Stat3 by ionomycin and GM-CSF is reversed by the MEK inhibitor PD98059. MM6 cells were treated with ionomycin (1 μg/ml) or GM-CSF (100 ng/ml), followed by a 12-min stimulation with IL-6 (20 ng/ml). (A) Cell extracts were assayed for binding to the hSIE oligonucleotide, and the same extracts were analyzed by immunoblotting with specific Stat3 antiserum. (B) Cell extracts were immunoprecipitated with ERK2 antibodies. Seventy-five percent of each immunoprecipitate was used in a kinase assay, and 25% was analyzed by immunoblotting.