Prosurvival kinase PIM2 is a therapeutic target for eradication of chronic myeloid leukemia stem cells.
Leyuan Ma, Magnolia L Pak, Jianhong Ou, Jun Yu, Pamela St Louis, Yi Shan, Lloyd Hutchinson, Shaoguang Li, Michael A Brehm, Lihua Julie Zhu, Michael R Green
Author Information
Leyuan Ma: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605.
Magnolia L Pak: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605.
Jianhong Ou: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605.
Jun Yu: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605.
Pamela St Louis: Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605.
Yi Shan: Division of Hematology/Oncology, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605.
Lloyd Hutchinson: Department of Pathology, University of Massachusetts Medical School, Worcester, MA 01605.
Shaoguang Li: Division of Hematology/Oncology, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605.
Michael A Brehm: Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605.
Lihua Julie Zhu: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605.
Michael R Green: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605; Michael.Green@umassmed.edu. ORCID
A major obstacle to curing chronic myeloid leukemia (CML) is the intrinsic resistance of CML stem cells (CMLSCs) to the drug imatinib mesylate (IM). Prosurvival genes that are preferentially expressed in CMLSCs compared with normal hematopoietic stem cells (HSCs) represent potential therapeutic targets for selectively eradicating CMLSCs. However, the discovery of such preferentially expressed genes has been hampered by the inability to completely separate CMLSCs from HSCs, which display a very similar set of surface markers. To overcome this challenge, and to minimize confounding effects of individual differences in gene expression profiles, we performed single-cell RNA-seq on CMLSCs and HSCs that were isolated from the same patient and distinguished based on the presence or absence of BCR-ABL. Among genes preferentially expressed in CMLSCs is , which encodes a prosurvival serine-threonine kinase that phosphorylates and inhibits the proapoptotic protein BAD. We show that IM resistance of CMLSCs is due, at least in part, to maintenance of BAD phosphorylation by PIM2. We find that in CMLSCs, expression is promoted by both a BCR-ABL-dependent (IM-sensitive) STAT5-mediated pathway and a BCR-ABL-independent (IM-resistant) STAT4-mediated pathway. Combined treatment with IM and a PIM inhibitor synergistically increases apoptosis of CMLSCs, suppresses colony formation, and significantly prolongs survival in a mouse CML model, with a negligible effect on HSCs. Our results reveal a therapeutically targetable mechanism of IM resistance in CMLSCs. The experimental approach that we describe can be generally applied to other malignancies that harbor oncogenic fusion proteins or other characteristic genetic markers.
