Effect of SB on p70S and S6 kinase phosphorylation, and GAPDH, REDD1 expression in myeloid leukemia cells. (A) Western blot analysis of Mpl protein expression in primary leukemia cells (AML, ALL, and CML). (B) Western blot analysis of p70S and S6 kinase phosphorylation in 3 primary AML samples after exposure to rhTpo or SB-559457. Control indicates medium alone; TPO, cells treated with rhTpo (2.86μM) + 0.05% DMSO; SB, cells treated with SB-559457 (5μM). Graphs represent densitometry measurements of phosphorylated proteins: p70S6 and S6. Level of phosphorylation is presented as ratio of phosphorylated to total protein expression. (C) Quantitative RT-PCR comparison analysis of GAPDH (top panel) and REDD1 (bottom panel) mRNA level in primary AML cells stimulated with rhTpo (2.86μM) + 0.05% DMSO, or SB-559457 (5μM) for 6 hours.