Constitutive activation of Stat3 in wild-type WT1-infected 32D cells. IL-3–deprived 32D cells were stimulated with IL-3 (100 U/mL) or G-CSF (20 ng/mL). Cell lysates were prepared at the indicated time and subjected to Western blot analysis, using antibodies directed against phosphorylated Stat3 protein (top panel) or Stat3 protein (middle panel), or using a mixture of antibodies directed against ERK1 or ERK2 (bottom panel). Arrows indicate activated ERK2.