Figure 4.

Inhibition of Stat3 by constitutively active MEK1 or overexpression of ERK2. (A) CHO cells were cotransfected with 3 μg of FLAG-Stat3 plasmid and 12 μg of control vector or vector encoding constitutively active MEK1 (CA-MEK). FLAG-Stat3 protein was immunoprecipitated by using FLAG antibodies, and immunoprecipitates were analyzed by using immunoblotting. (B and C) 293T cells were transfected with 15 μg of expression plasmids and 2.5 μg of a β-galactosidase-encoding plasmid that was used to monitor transfection efficiency (>85% of cells). Each transfected dish was split into replicate tissue culture dishes, and after 24 hr, cells were treated with PMA and IL-6 (20 ng/ml) and analyzed by using EMSA. Control, expression vector not containing an insert; ERK2 and JNK1, expression vectors containing an insert encoding, respectively, ERK2 or JNK1.