Inhibition of ERK and JNK MAPKs, but not PI3Ks, partially reverses the inhibitory effect of expression of TEL/PDGFβR on IL-3–induced proliferation. XTT bioreduction metabolic assays were set up as described in “Materials and methods” using 1000 (A,C-E) or 3000 (F) cells/well. (A) BaF/3 tTA cells were cultured in 1 ng/mL rmIL-3 and doses of inhibitors indicated and an XTT was performed. (B) Tyrosine phosphorylation of cellular proteins and TEL/PDGFβR (upper panels) were assessed in cells incubated for 1 hour with DMSO alone (C), 10 μM U0126 (UO), or 5 μM SP600125 (SP). Blots were reprobed with anti-PDGFβR antibodies (lower panels); note SP lane is underloaded. (C-E) BaF/3 clone TP2 was used. ▪ represents cells incubated in the presence of 2 μg/mL Tet; ▴, cells incubated in the presence of 2 μg/mL Tet and either (C) 5 μM LY294002, (D) 5 μM U0126, or (E) 5 μM SP600125. □ indicates cells incubated in the absence of Tet; ○, cells incubated in the absence of Tet and either (C) 5 μM LY294002, (D) 5 μM U0126, or (E) 5 μM SP600125. In all cases readings obtained in the absence of IL-3 were on average 0.19 to 0.32 absorbance units. (F) cTP14FI cells were incubated with 500 pg/mL IL-3 alone (♦) or with different doses of U0126 (▪). The mean values with SDs are plotted for each point.