Down-regulation of MCL-1 sensitizes prednisone-resistant MLL-rearranged ALL cells. (A) RNA interference experiments delivering short hairpin RNA(shRNA) molecules directed against human MCL-1 into prednisolone-resistant SEMK2 (MLL-rearranged ALL) or MV4-11 (MLL-rearranged AML) cells by viral infections, show severe suppression in MCL-1 protein expression compared with control cells (infected with empty vectors). The indicated ratios are normalized against β-tubulin and represent MCL-1 intensities relative to SEMK2 control cells (first lane) The effects of MCL-1 down-regulation on the in vitro prednisolone response on (B) SEMK2 or (C) MV4-11 cells were assessed by 2-day MTT cytotoxicity assays, performed in triplicate. The graphs show the mean prednisolone response curves in cells infected with either empty vectors (C indicates controls) or vectors encoding shRNAs against human MCL-1 (KD, knock-down), derived from 2 independent RNA interference experiments.