Ectopic expression of RanGAP confers resistance to imatinib. (A-B) K562^S cells were nucleofected with the pDsRed1-N1 RanGAP plasmid for expression of RanGAP or control vector, followed by culture in graded concentrations of imatinib. RanGAP expression was confirmed by qRT-PCR (A). At 120 hours, the viable cells were quantified by flow cytometric analyses (B).