Figure 1.

Trametinib primes B-ALL cells to apoptosis through BIM dephosphorylation. (a and b) Western blottings showing phospho-MEK (ppMEK), total MEK (MEK1/2), phospho-ERK (ppERK), total ERK (ERK1/2), and α-tubulin (loading control) in five BCR-ABL1⁺ B-ALL cell lines (a) and six BCR-ABL1⁻ cell lines (b). The dotted line indicates where discontinuous sections of blots were joined. (c) Western blottings showing ppERK and ERK1/2 (loading control) in B-ALL cells treated with trametinib (40 nM) at the indicated times. (d) Dose–response curves for trametinib (72 h) treatment of 697, BV173R, and SUP-B15 B-ALL cells. Cell viability (%) is relative to dimethyl sulfoxide (DMSO) control and A375 (BRAF^V600E melanoma) cells provide a positive control for sensitive cells. (e) Graphs represent apoptotic cells (%) after treatment with DMSO (control) or trametinib (40nM) at the indicated times. (f) Western blottings showing phospho-S69-BIM (pBIM) and total BIM (BIM_EL) in BIM immunoprecipitates from 697, BV173R, and SUP-B15 cells treated with trametinib (40 nM) for the times indicated. (g) Western blottings showing BIM, BCL-2, BCL-XL, MCL-1, and α-tubulin (loading control) in cell lysates and BIM co-IPs from 697, BV173R, and SUP-B15 cells treated with DMSO (control; D) or trametinib (40 nM; T) for 24 h. (h) Graphs represent normalized quantification of BIM co-IPs from triplicate experiments for samples shown in panel (g). Error bars in panels (d, e, and h): S.E.M. *P<0.05; **P<0.01