KPT-330 treatment alters the subcellular localization of tumor suppressors and negative regulators of PP2A. (A) Single-channel and merged confocal micrographs of 32D-BCR/ABL cells treated with vehicle or KPT-330 (1 µM, 12 hours) and stained with anti-SET, anti-PP2Ac, anti-hnRNP A1, anti-CIP2A, anti-IkBα, or anti-FoxO3a antibody (left panels; green or red), 4,6 diamidino-2-phenylindole (middle; blue), and merged (right). SET and hnRNP A1 (B), and p21 and p53 (C) protein levels in nuclear and cytoplasmic subcellular fractionated extracts from vehicle- and KPT-330–treated (1 µM, 12 hours) 32D-BCR/ABL cells. Histone H1 and Grb2 levels were used as a control for purity of nuclear and cytoplasmic fractions, respectively. (D) KPT-330–mediated XPO1 inhibition abrogates leukemogenesis by altering nuclear/cytoplasmic shuttling. In Ph⁺ acute leukemia progenitors, XPO1 expression is increased at least in part through a BCR-ABL1 kinase-dependent mechanism, and is responsible for nuclear export of the SET oncogene and CIP2A, and for the nucleocytoplasmic shuttling activity of hnRNP A1, a regulator of SET mRNA metabolism. SET and CIP2A are BCR-ABL1/Jak2- and BCR-ABL1-regulated inhibitors of the PP2A tumor suppressor, respectively. In these cells, XPO1 activity also controls the subcellular localization of important regulators of cell survival as p53, p21, IκBα, and FoxO3a. Bottom panel: On inhibition of XPO1 activity with the SINE KPT-330, the SET and CIP2A proteins are sequestered in the nucleus, which leads to activation of PP2A that, in turn, triggers inhibition/degradation of BCR-ABL1 contributing to cell death. Cytoplasmic accumulation of hnRNP A1 also contributes to the decreased SET levels. In addition, nuclear accumulation of p53, p21, IκBα, and FoxO3a also likely contribute to impair leukemogenesis of Ph⁺ acute leukemia progenitors.