Effect of growth factor and serum deprivation or stimulation on BCR-ABL–positive cells. Parental and BCR-ABL–positive cell lines were deprived or stimulated with growth factor and/or serum for 16 hours. Effect on cell-cycle progression (PI staining) as well as p27 and Skp2 expression was analyzed in 3 independent experiments. BCR-ABL–positive cells were also treated with 2.5 μM imatinib. (A) Mo7e and Mo7ep210^BCR-ABL cells. (B) Ba/F3 and Ba/F3p210^BCR-ABL cells. Error bars represent SE. (C) Effect on Skp2 and p27 expression of inhibiting constitutively active tyrosine kinases in leukemia cell lines. Cells were incubated with the indicated concentrations of inhibitors for 24 hours and immunoblot analysis was performed on whole cell lysates. Left panel shows MOLM14 cells expressing a FLT3 internal tandem duplication (ITD) treated with 500 nM MLN518. Middle panel shows HEL cells expressing JAK2 V617F treated with 50, 75, 100 μM of AG490. Right panel shows Ba/F3 cells expressing TEL-PDGFRβ treated with 2.5, 5.0, 10 μM imatinib. Skp2 and p27 expression levels were analyzed after inhibition of tyrosine kinase activity. α-Tubulin was used as a loading control.